- Email: [email protected]
TRPV1 mediates the anticonvulsant effects of acetaminophen in mice
Epilepsy Research 145 (2018) 153–159
Contents lists available at ScienceDirect
Epilepsy Research journal homepage: www.elsevier.com/locate/epilepsyres
TRPV1 mediates the anticonvulsant effects of acetaminophen in mice ⁎
T
Katsuya Suemaru, Misato Yoshikawa , Hiroaki Aso, Masahiko Watanabe School of Pharmacy, Shujitsu University, 1-6-1 Nishigawara, Naka-ku, Okayama, 703-8516, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: Acetaminophen Anticonvulsant effect Epileptogenesis TRPV1 receptors Cannabinoid receptors
Objective: Acetaminophen is one of the most commonly used analgesic and antipyretic drugs. It has been reported that acetaminophen has anticonvulsant effects in several animal models of seizure. An active metabolite of acetaminophen, AM404, inhibits the uptake of the endocannabinoid anandamide. However, the mechanism of the anticonvulsant effect of acetaminophen is unknown. Methods: This study was performed to examine whether or not acetaminophen can protect against pentylenetetrazol-induced kindling in mice and to investigate the precise mechanisms of the anticonvulsant effect of acetaminophen using the fully kindled mouse models. Results: Repeated administration of acetaminophen significantly delayed the progression of seizure severity induced by pentylenetetrazol. Additionally, acetaminophen showed a dose-dependent anticonvulsant activity against fully pentylenetetrazol-kindled seizures. AM404 also exhibited a dose-dependent anticonvulsant activity in fully kindled animals. The anticonvulsant activity of acetaminophen was antagonized by capsazepine and AMG9810, two transient receptor potential vanilloid-1 (TRPV1) antagonists. However, the transient receptor potential ankyrin 1 (TRPA1) antagonist HC030031 and CB1 receptor antagonist AM251 had no effect. Conclusion: These findings suggest that acetaminophen has an anticonvulsant effect in pentylenetetrazol-kindled mouse models and TRPV1 mediates the anticonvulsant action.
1. Introduction Acetaminophen is one of the most popular and widely used drugs for the treatment of pain and fever. Several mechanisms of acetaminophen action have been described that involve modulation of the endogenous cannabinoid system. Endocannabinoids are lipid mediators that act as endogenous agonists for type-1 and type-2 cannabinoid (CB1 and CB2, respectively) receptors, and anandamide and 2-arachidonoylglycerol (2-AG) are the main endogenous agonists. Additionally, anandamide is a potent activator of transient receptor potential vanilloid 1 (TRPV1), a member of the family of transient receptor potential (TRP) channels (De Petrocellis et al., 2000). Previous studies have shown that the cerebrospinal fluid levels of anandamide are reduced in patients with untreated newly diagnosed temporal lobe epilepsy (Romigi et al., 2010), and mRNA levels of the CB1 receptor are decreased in the hippocampal tissue of patients with intractable temporal lobe epilepsy (Ludányi et al., 2008). Recent clinical trials for drug-resistant seizures showed that cannabidiol, the main nonpsychotomimetic compound from Cannabis sativa, reduced seizures
(Devinsky et al., 2017). These findings suggest that the endocannabinoid system plays a role in the inhibition of seizures in humans with epilepsy. Recent studies have revealed that active metabolites of acetaminophen are important for its mechanism of action. N-acetyl-p-benzoquinoneimine (NAPQI) is a toxic metabolite of acetaminophen formed in the spinal cord, liver and kidneys. NAPQI activates the potent transient receptor potential ankyrin 1 (TRPA1), and mediates the antinociceptive and hypothermic actions of acetaminophen (Andersson et al., 2011; Gentry et al., 2015). Acetaminophen can also be metabolized by fatty acid amide hydrolase (FAAH) to an arachidonic acidconjugated metabolite of acetaminophen (AM404) in the brain and spinal cord (Högestätt et al., 2005). AM404 is known to inhibit the uptake of endocannabinoid anandamide into presynaptic neurons and activate cannabinoid and TRPV1 receptors (Beltramo et al., 1997; De Petrocellis et al., 2000). Accordingly, acetaminophen is considered to bring about its pharmacological actions by activation of cannabinoid receptors and/or the TRP channel system in the central nervous system. The major cannabinoid receptors in the central nervous system are
Abbreviations: AM404, N-(4-hydroxyphenyl-5Z,8Z,11Z,14Z-eicosatetraenamide); GABA, γ-aminobutyric acid; PG, prostaglandin; TRPV1, transient receptor potential vanilloid-1; TRPA1, transient receptor potential ankyrin 1 ⁎ Corresponding author. E-mail addresses: [email protected] (K. Suemaru), [email protected] (M. Yoshikawa), [email protected] (H. Aso), [email protected] (M. Watanabe). https://doi.org/10.1016/j.eplepsyres.2018.06.016 Received 23 January 2018; Received in revised form 19 June 2018; Accepted 30 June 2018 Available online 03 July 2018 0920-1211/ © 2018 Elsevier B.V. All rights reserved.
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
tonic seizures were monitored by an observer who was blind to the treatment.
CB1 receptors, and their activation reduces seizure severity in pentylenetetrazol-kindled mouse models (Bahremand et al., 2009). Endocannabinoid anandamide was reported to induce significant anticonvulsant effects in several seizure animal models (Wallace et al., 2002; Manna and Umathe, 2012; Bhaskaran and Smith, 2010). We recently found that acetaminophen has a significant anticonvulsant effect against fully pentylenetetrazol-kindled seizures (Suemaru et al., 2018). However, the relationship between acetaminophen and epileptogenesis remains unknown. In this study, we examined the repeat administration of acetaminophen on the development of pentylenetetrazol kindling in mice. Moreover, we investigated the mechanisms of acetaminophen action using fully pentylenetetrazol-kindled mouse models and compared them with that of the typical antiepileptic drug, sodium valproate.
2.4. Pentylenetetrazol kindling Kindling is a phenomenon in which repeated application of initially subconvulsive stimulation leads to seizures and increased seizure susceptibility persists over long periods of time. Mice at 5 weeks of age weighing 25–28 g were used for the pentylenetetrazol kindling. Kindling was induced by daily i.p. administration of 40 mg/kg of pentylenetetrazol, 5 days per week for 12 days. The seizure score was determined using the Racine scale (stages 1–5). The seizure intensity was scored as follows: stage 0, no response; stage 1, ear and facial twitching; stage 2, myoclonic body jerks; stage 3, forelimb clonus, rearing; stage 4, clonic seizures, turn onto the side; and stage 5, generalized clonic seizures, turn onto the back (Racine, 1972). For the evaluation of epileptogenesis activity, acetaminophen at doses that negligibly affects acute pentylenetetrazol seizures (100 and 300 mg/kg, i.p.) was repeatedly administered to the animals 30 min before pentylenetetrazol injection for 12 days. We also determined the anticonvulsive actions of acetaminophen, AM404 and WIN55212-2 (non-selective CB1 and CB2 receptor agonists) using fully pentylenetetrazol-kindled mice (8–10 weeks of age). Fully kindled was defined as the occurrence of three consecutive stage 4 or 5 seizures after administration of pentylenetetrazol (40 mg/kg) for 12 days. The kindled mice were injected intraperitoneally with acetaminophen, AM404, WIN55212-2 or valproate 30 min before the pentylenetetrazol (40 mg/kg, i.p.) test. Control groups received vehicle in the same manner. All behavioral seizures were observed for 20 min after injection of the test compound and recorded by an observer who was blind to the treatment. To investigate the mechanism of the anticonvulsive action of acetaminophen, the effects of AM251 (CB1 antagonist/inverse agonist), capsazepine and AMG9810 (TRPV1 receptor antagonists) and HC030031 (TRPA1 receptor antagonist) were determined using fully pentylenetetrazol-kindled mice (Fig. 1). These drugs were injected 45 min before the test. HC030031 was orally administered and the other drugs were intraperitoneally administered. Acetaminophen or valproate was injected 30 min before the test.
2. Methods and methods 2.1. Animals All animal care and experimental procedures were in accordance with the Guiding Principles for the Care and Use of Laboratory Animals adopted by the Japanese Pharmacological Society and approved by the Ethical Committee for Animal Experimentation committee of Shujitsu University (approval code 025-002). Male ICR mice were purchased from Shimizu Laboratory Supplies Co., Ltd. (Kyoto, Japan). Animals were maintained in an air-conditioned room with controlled temperature (22 ± 2 °C) under a 12/12 h light/dark cycle with lights on at 08:00 h. Mice were housed from 4 weeks of age in standard size plastic cages (32 × 18 × 24 cm) with paper bedding (4–5 mice per cage). The mice were allowed free access to food and water except during experiments. 2.2. Drugs Acetaminophen (Sigma-Aldrich, St. Louis, MO, USA), AM404 (Sigma-Aldrich), and AM251 (Sigma-Aldrich) were dissolved in polyoxyethylene castor oil (cremophor®) vehicle (18:1:1, saline: cremophor®: ethanol). WIN55212-2 (Sigma-Aldrich), capsazepine (SigmaAldrich) and AMG9810 (Tocris Bioscience, Bristol, UK) were emulsified in 1% Tween 80. HC030031 (Tocris Bioscience) was emulsified in 0.5% methylcellulose. Pentylenetetrazol (Sigma-Aldrich) and sodium valproate (Research Chemicals Inc., Toronto, Ontario, Canada) were dissolved in saline. Drugs were administered at a volume of 0.1–0.2 mL/10 g of body weight.
2.5. Statistical analysis All data contributing to seizure severity scores are expressed as the mean ± standard error of the mean (SEM). Development of pentylenetetrazol kindling was analyzed by repeated measures two-way ANOVA with treatment as a between-subjects factor and with day as a within-subject factor. Data of fully pentylenetetrazol-kindled seizures were analyzed by the Mann-Whitney test or Kruskal-Wallis test followed by Steel’s test. The chi-square test was used to compare the incidence of seizures. P-values < 0.05 were considered significant.
2.3. Acute pentylenetetrazol seizures To set the test dose of acetaminophen for pentylenetetrazol kindling, we first determined the anticonvulsive action against maximal pentylenetetrazol seizures using naive mice (8 weeks of age, weight 32–37 g). Pentylenetetrazol at a dose of 80 mg/kg was injected intraperitoneally (i.p.) 30 min after the administration of acetaminophen. The animals were observed for 20 min after injection, and clonic and
Fig. 1. Scheme of the experimental protocol for the fully pentylenetetrazol-kindled seizures test. 154
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
3.3. Effect on fully pentylenetetrazol-kindled seizures In the pentylenetetrazol-kindled mouse, the seizure severity scores were dose dependently decreased by valproate (30–300 mg/kg, i.p.), which served as a positive control. Acetaminophen (30–450 mg/kg, i.p.) showed a dose-dependent anticonvulsant activity. An active metabolite of acetaminophen, AM404 (10 and 30 mg/kg, i.p.), also exhibited slight anticonvulsant activity and there was a significant difference at a dose of 30 mg/kg (Fig. 4). Win 55212-2 (1 and 3 mg/kg, i.p.), a non-selective CB1 and CB2 receptor agonist, showed dose-dependent anticonvulsant activity against fully pentylenetetrazol-kindled seizures. Fig. 5 shows that the effect of AM251, a CB1 antagonist/inverse agonist, against the anticonvulsant action of acetaminophen or valproate. AM251 (1 and 3 mg/kg, i.p.) had no effect against fully pentylenetetrazol-kindled seizures. Moreover, AM251 had no effect against the anticonvulsant activities of acetaminophen (300 mg/kg, i.p.) and valproate (300 mg/kg, i.p.). HC030031 (30–300 mg/kg, p.o.), a TRPA1 receptor antagonist, had no effect against fully pentylenetetrazol-kindled seizures (Fig. 6). It also had no effect against the anticonvulsant activities of acetaminophen (300 mg/kg, i.p.) or valproate (300 mg/kg, i.p.), indicating that these compounds did not act through the TRPA1 receptor. TRPV1 receptor antagonists, capsazepine (1 and 3 mg/kg, i.p.) and AMG9810 (1–10 mg/kg, i.p.), showed a dose-dependent anticonvulsant activity against fully pentylenetetrazol-kindled seizures (Fig. 7). The anticonvulsant activity of acetaminophen (300 mg/kg, i.p.) was antagonized by capsazepine (1 and 3 mg/kg, i.p.) and AMG9810 (1 and 3 mg/kg, i.p.). However, both TRPV1 receptor antagonists had no effect on the anticonvulsant activity of valproate (300 mg/kg, i.p.).
Fig. 2. Effect of acetaminophen against acute pentylenetetrazol-induced seizures in mice. Pentylenetetrazol (80 mg/kg, i.p.) was injected 30 min after the intraperitoneal administration of acetaminophen (n = 10/group). Each value is expressed as the percentage of animals exhibiting clonic seizures (n = 10). * P < 0.05, versus the vehicle-treated control group (Chi-square test).
3. Results 3.1. Effect of acetaminophen on acute pentylenetetrazol seizures In the acute pentylenetetrazol-induced seizure test, pentylenetetrazol (80 mg/kg) induced clonic seizures in all mice treated with vehicle. Acetaminophen treatment (300 mg/kg, i.p.) showed no significant anticonvulsant effect (Fig. 2). However, acetaminophen at a dose of 450 mg/kg significantly (P < 0.05) suppressed the clonic seizures.
3.2. Effect of acetaminophen on pentylenetetrazol kindling 4. Discussion Repeated administration of sub-convulsive pentylenetetrazol (40 mg/kg, i.p.) induced kindling in mice as revealed by the progressive increase in seizure score (Fig. 3). Daily treatment with acetaminophen (100 mg/kg, i.p.) before pentylenetetrazol slightly delayed the progression of seizure severity induced by pentylenetetrazol. However, repeated measures two-way ANOVA revealed no significant effect of acetaminophen treatment (F 1, 319 = 3.95, p = 0.056) and no significant treatment × day interaction (F 11, 319 = 1.41, p = 0.165). Acetaminophen (300 mg/kg, i.p.) pre-treatment significantly reduced the seizure score throughout the 12 days of the study period. Repeated measures two-way ANOVA revealed a significant effect of acetaminophen treatment (F 1, 319 = 35.28, p < 0.001) and a significant treatment × day interaction (F 11, 319 = 5.41, p < 0.001).
We recently reported that acetaminophen showed no significant anticonvulsant effects in acute-seizure models induced by maximum electroshock whereas acetaminophen exhibited significant anticonvulsant effects in animal models of chronic epilepsy induced by corneal electroshock or pentylenetetrazol kindling (Suemaru et al., 2018). In this study, we confirmed that acetaminophen at doses of 30–450 mg/kg (i.p.) showed dose-dependent anticonvulsant activity against fully pentylenetetrazol-kindled seizures. By comparison, previous rodent studies have shown that acetaminophen exerts antinociceptive effects at doses of 100–400 mg/kg (Mallet et al., 2010; Pini et al., 1996, 1997) or antipyretic effects at doses of 100–300 mg/kg (Ayoub et al., 2004; Gentry et al., 2015). These results suggest that acetaminophen exhibits its antinociceptive and anticonvulsant actions in rodents over a similar dose range. However, high doses of acetaminophen (300–700 mg/kg) were reported to cause hepatotoxicity in rodents (Yamaura et al., 2012; Kawakami et al., 2017). Therefore, it is unclear whether or not a typical 15 mg/kg therapeutic dose of acetaminophen would have an anticonvulsant effect in humans. Acetaminophen is metabolized to AM404 which in turn, inhibits the uptake of endocannabinoid anandamide into neurons and activates CB1 and TRPV1 receptors (De Petrocellis et al., 2000). Anandamide was reported to induce significant anticonvulsant effects in several mouse models of seizure, such as a maximal electroshock model (Wallace et al., 2002), an acute pentylenetetrazol-induced seizure (Manna and Umathe, 2012), and a pilocarpine-induced status epilepticus mouse model (Bhaskaran and Smith, 2010). Moreover, CB1 receptor antagonists have been reported to abolish the anticonvulsant effect of anandamide in the maximal electroshock model and acute pentylenetetrazol-induced seizures (Vilela et al., 2013; Naderi et al., 2011). These findings indicate the anticonvulsant action of anandamide is mediated through activation of central CB1 receptors. It has also been reported that TRPV1 receptors modulate seizure activity in animal models of seizures and epilepsy (Nazıroğlu, 2015). Manna and Umathe (2012)
Fig. 3. Effect of acetaminophen on the development of pentylenetetrazol kindling in mice. Pentylenetetrazol (40 mg/kg, i.p.) was injected 30 min after the intraperitoneal administration of acetaminophen (100 and 300 mg/kg, i.p.) for 12 days (n = 11–20 /group). Each value represents the mean seizure score ± SEM. The pentylenetetrazol kindling data were analyzed by repeated measures two-way ANOVA. 155
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
Fig. 4. Effects of valproate, Win 55212-2, acetaminophen, and AM404 in pentylenetetrazol-kindled mice. Valproate, Win 55212-2, acetaminophen, and AM404 were intraperitoneally injected 30 min before the administration of pentylenetetrazol (40 mg/kg, i.p.). Each value represents the mean seizure score ± SEM (n = 10/group). * P < 0.05, ** P < 0.01, versus the vehicle-treated control group (Steel’s test).
Fig. 5. Effects of the CB1 antagonist/inverse agonist AM251 on the anticonvulsant action of acetaminophen and valproate in pentylenetetrazol-kindled mice. Acetaminophen, valproate, and vehicle were intraperitoneally injected 30 min before the administration of pentylenetetrazol (40 mg/kg, i.p.). AM251 was intraperitoneally injected 45 min before the pentylenetetrazol administration. Each value represents the mean seizure score ± SEM (n = 10/group). ** P < 0.01, versus the vehicle-treated control group (Mann-Whitney test or Steel’s test). NS (no significance).
suggest that TRPV1 mediates the anticonvulsant action of acetaminophen. However, taking into consideration the observation that the TRPV1 antagonists capsazepine and AMG9810 exhibited anticonvulsant activities, TRPV1 receptors, which are located throughout different areas of the brain, may be involved in the anticonvulsant action of acetaminophen. Recently, it has been reported that TRPV1 knockout mice exhibited exacerbation of hyperthermic seizures (Barrett et al., 2016) and pentylenetetrazol-induced seizures (Jia et al., 2015). To confirm the precise role of TRPV1 in the anticonvulsant activities of acetaminophen, further experimental work is needed using TRPV1
reported that the TRPV1 agonist capsaicin exhibited pro-convulsant activity and intracerebroventricular administration of capsazepine, a TRPV1 antagonist, suppressed acute pentylenetetrazol-induced seizures in mice (Manna and Umathe, 2012). In the present study, treatment with capsazepine and AMG9810, both TRPV1 antagonists, resulted in slight but significant anticonvulsant activity against fully pentylenetetrazol-kindled seizures. Interestingly, the anticonvulsant activity of acetaminophen was reduced by pretreatment with the TRPV1 antagonists. Additionally, the CB1 antagonist/inverse agonist AM251 had no effect on the anticonvulsant activities of acetaminophen. These results 156
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
Fig. 6. Effects of the TRPA1 antagonist HC030031 on the anticonvulsant action of acetaminophen and valproate in pentylenetetrazol-kindled mice. Acetaminophen, valproate, and vehicle were intraperitoneally injected 30 min before the administration of pentylenetetrazol (40 mg/kg, i.p.). HC030031 was orally administered 45 min before the pentylenetetrazol administration. Each value represents the mean seizure score ± SEM (n = 10/group). ** P < 0.01, versus the vehicle-treated control group (Mann-Whitney test). NS (no significance).
55212-2 exhibits its anticonvulsant activity via the CB1 and TRPV1 receptors. It is well known that inflammation, fever and stress reduce the seizure threshold. Although high doses of a TRPV1 agonist resulted in persistent desensitization of TRPV1 (Caterina et al., 1997), its anxiolytic-like action has been shown in a mouse elevated plus-maze test at low doses of 100–200 mg/kg (Zaitone et al., 2012). Therefore, the
knockout mice. In the present study, the non-selective CB1 and CB2 receptor agonist Win 55212-2 showed a dose-dependent anticonvulsant activity against fully pentylenetetrazol-kindled seizures. WIN 55212-2 was also reported to inhibit TRPV1 functional activities (Patwardhan et al., 2006) and modulate TRPV1 activation by altering receptor phosphorylation (Jeske et al., 2006). Therefore, these findings suggested that WIN
Fig. 7. Effects of the TRPV1 antagonists capsazepine and AMG9810 on the anticonvulsant action of acetaminophen or valproate in pentylenetetrazol-kindled mice. Acetaminophen, valproate, and vehicle were intraperitoneally injected 30 min before the administration of pentylenetetrazol (40 mg/kg, i.p.). Capsazepine and AMG9810 were intraperitoneally injected 45 min before the pentylenetetrazol administration. Each value represents the mean seizure score ± SEM (n = 10/group). * P < 0.05, ** P < 0.01, versus the vehicle-treated control group (Mann-Whitney test or Steel’s test). NS (no significance). 157
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
However, the brain concentration of AM404 after peripheral administration is unknown. Thus, it will be important to define the concentration of AM404 in the brain to obtain a better understanding of its pharmacological actions and those of acetaminophen. TRPV1, a non-selective cation channel, is expressed in the neuronal and glial cells of various brain regions. TRPV1 modulates synaptic transmission by a presynaptic and/or postsynaptic mechanism (Köfalvi et al., 2007; Shoudai et al., 2010; Fawley et al., 2014). Moreover, TRPV1 receptors are thought to be functionally localized intracellularly (Brailoiu et al., 2011; Fowler, 2013). Recently, it has been reported that stimulation of microglial TRPV1 receptors controls microglia activation and indirectly enhances glutamatergic transmission in neurons (Marrone et al., 2017). It is well known that glutamate is the major excitatory neurotransmitter in the central nervous system and plays important roles in seizure and epilepsy. Therefore, it has been proposed that the anticonvulsant action of TRPV1 receptor antagonists is mediated through the modulation of glutaminergic systems. However, further studies into the precise mechanism underlying the anticonvulsant effect of acetaminophen are needed.
anxiolytic effects of acetaminophen may partly contribute to its anticonvulsant activity. The kindling model of epilepsy has been used to investigate the process of epileptogenesis and discover new antiepileptic drugs (Löscher, 2011). Antiepileptic drugs show different profiles of therapeutic effectiveness in blocking the different stages of seizure evolution in the kindling model. For example, phenytoin, carbamazepine and lamotrigine do not block the development of kindling acquisition but are highly effective against fully kindled seizures in the amygdalakindling model. In contrast, valproate is effective at preventing kindling development and blocking the fully kindled seizures (Post, 2004). However, it was reported that valproate at sub-anticonvulsive doses failed to prevent the development of pentylenetetrazol kindling (Ohno et al., 2010). In the present study, acetaminophen at doses of 100–300 mg/kg (i.p.) had no effect against the acute pentylenetetrazol seizures. However, acetaminophen at a dose of 300 mg/kg (i.p.) abolished the kindling acquisition in a pentylenetetrazol kindling model. These findings suggest the possibility that acetaminophen affects the process of epileptogenesis. However, in this study, acetaminophen at a dose of 300 mg/kg (i.p.) showed significant anticonvulsant activity against fully pentylenetetrazol-kindled seizures. In the kindling model of epilepsy, electrical or chemical kindling are epileptogenic models used for understanding the epileptogenic process. Therefore, further studies are needed to evaluate epileptogenesis using an electrical kindling model of epilepsy. Shirazi et al. reported that N-oleoyldopamine, a TRPV1 receptor agonist, accelerated the pentylenetetrazol kindling in rats, and AMG9810, a TRPV1 receptor antagonist, delayed the development of amygdala kindling in rats (Shirazi et al., 2014). Thus, it is important to clarify the involvement of TRPV1 receptors in the inhibitory process of kindling by acetaminophen. Recent studies have revealed that active metabolites of acetaminophen play important roles in its mechanism of action. NAPQI, a metabolite of acetaminophen, activates TRPA1 receptors, and it has been reported that TRPA1 receptors mediate the antinociceptive and hypothermic actions of acetaminophen (Andersson et al., 2011; Gentry et al., 2015). In this study, HC030031, a TRPA1 receptor antagonist, did not affect the anticonvulsant effect of acetaminophen in pentylenetetrazol-kindled mice. in vitro studies have reported that anandamide is an endogenous agonist of CB1 and also activates TRPV1, and that AM404 is a weak agonist of CB1 receptors and a potent activator of TRPV1 receptors (Zygmunt et al., 2000; De Petrocellis et al., 2000). It has been reported that acute intracerebroventricular administration of low doses of anandamide or AM404 produced anticonvulsant effects, while those at higher doses exhibited a pro-convulsant effect in acute pentylenetetrazol-induced seizures in mice (Manna and Umathe, 2012). These findings indicated the biphasic effects of anandamide and AM404 on the regulation of neuronal activity during seizures (Umathe et al., 2012). An active metabolite of acetaminophen, AM404, inhibits the uptake of anandamide and activates CB1 and TRPV1 receptors (De Petrocellis et al., 2000). In the present study, the anticonvulsant activity of acetaminophen was antagonized by the TRPV1 antagonists capsazepine and AMG9810. However, CB1 antagonist/inverse agonist AM251 had no effect. Taken together, these results suggest that the TRPV1 receptors stimulated by both AM404 and anandamide may be involved in the anticonvulsant action of acetaminophen. Previous rodent studies have shown that acetaminophen exhibits antinociceptive effects (100–400 mg/kg, i.p.) (Mallet et al., 2010; Pini et al., 1996, 1997), and AM404 (1–10 mg/kg, i.p.) elicits a dose-dependent antinociceptive effect (La Rana et al., 2006). In this study, AM404 (30 mg/kg, i.p.) exhibited slight anticonvulsant activity compared with acetaminophen (30–450 mg/kg, i.p.) in pentylenetetrazolkindled mouse models. Acetaminophen is metabolized by FAAH to AM404 in the brain and spinal cord (Högestätt et al., 2005) and it is reported that the concentration of AM404 in rat brain following acetaminophen (300 mg/kg, i.p.) is 10.3 pmol/g (Högestätt, et al., 2005).
5. Conclusion The present study revealed that acetaminophen has apparent anticonvulsant effects in pentylenetetrazol-kindled mouse models and TRPV1 mediates the anticonvulsant action of acetaminophen. Conflict of interest The authors declare no conflict of interest. Acknowledgements We are grateful to Yohei Tanemoto, Norihiko Osawa, and Takahiro Haji for their technical assistance. We thank Renee Mosi, PhD, from Edanz Group (www.edanzediting.com/ac) for editing a draft of this manuscript. References Andersson, D.A., Gentry, C., Alenmyr, L., Killander, D., Lewis, S.E., Andersson, A., Bucher, B., Galzi, J.-L., Sterner, O., Bevan, S., Högestätt, E.D., Zygmunt, P.M., 2011. TRPA1 mediates spinal antinociception induced by acetaminophen and the cannabinoid Δ9tetrahydrocannabiorcol. Nat. Commun. 2, 551. Ayoub, S.S., Botting, R.M., Goorha, S., Colville-Nash, P.R., Willoughby, D.A., Ballou, L.R., 2004. Acetaminophen-induced hypothermia in mice is mediated by a prostaglandin endoperoxide synthase 1 gene-derived protein. Proc. Natl. Acad. Sci. U. S. A. 101, 11165–11169. Bahremand, A., Nasrabady, S.E., Shafaroodi, H., Ghasemi, M., Dehpour, A.R., 2009. Involvement of nitrergic system in the anticonvulsant effect of the cannabinoid CB1 agonist ACEA in the pentylenetetrazole-induced seizure in mice. Epilepsy Res. 84, 110–119. Barrett, K.T., Wilson, R.J.A., Scantlebury, M.H., 2016. TRPV1 deletion exacerbates hyperthermic seizures in an age-dependent manner in mice. Epilepsy Res. 128, 27–34. Beltramo, M., Stella, N., Calignano, A., Lin, S.Y., Makriyannis, A., Piomelli, D., 1997. Functional role of high-affinity anandamide transport, as revealed by selective inhibition. Science 277, 1094–1097. Bhaskaran, M.D., Smith, B.N., 2010. Cannabinoid-mediated inhibition of recurrent excitatory circuitry in the dentate gyrus in a mouse model of temporal lobe epilepsy. PLoS One 5, e10683. Brailoiu, G.C., Oprea, T.I., Zhao, P., Abood, M.E., Brailoiu, E., 2011. Intracellular cannabinoid type 1 (CB1) receptors are activated by anandamide. J. Biol. Chem. 286, 29166–29174. Caterina, M.J., Schumacher, M.A., Tominaga, M., Rosen, T.A., Levine, J.D., Julius, D., 1997. The capsaicin receptor: a heat-activated ion channel in the pain pathway. Nature 389, 816–824. De Petrocellis, L., Bisogno, T., Davis, J.B., Pertwee, R.G., Di Marzo, V., 2000. Overlap between the ligand recognition properties of the anandamide transporter and the VR1 vanilloid receptor: inhibitors of anandamide uptake with negligible capsaicinlike activity. FEBS Lett. 483, 52–56. Devinsky, O., Cross, J.H., Laux, L., Marsh, E., Miller, I., Nabbout, R., Scheffer, I.E., Thiele, E.A., Wright, S., Cannabidiol in Dravet Syndrome Study Group, 2017. Trial of cannabidiol for drug-resistant seizures in the dravet syndrome. N. Engl. J. Med. 376, 2011–2020. Fawley, J.A., Hofmann, M.E., Andresen, M.C., 2014. Cannabinoid 1 and transient receptor
158
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
potential vanilloid 1 receptors discretely modulate evoked glutamate separately from spontaneous glutamate transmission. J. Neurosci. 34, 8324–8332. Fowler, C.J., 2013. Transport of endocannabinoids across the plasma membrane and within the cell. FEBS J. 280, 1895–1904. Gentry, C., Andersson, D.A., Bevan, S., 2015. TRPA1 mediates the hypothermic action of acetaminophen. Sci. Rep. 5, 12771. Högestätt, E.D., Jönsson, B.A.G., Ermund, A., Andersson, D.A., Björk, H., Alexander, J.P., Cravatt, B.F., Basbaum, A.I., Zygmunt, P.M., 2005. Conversion of acetaminophen to the bioactive N-acylphenolamine AM404 via fatty acid amide hydrolase-dependent arachidonic acid conjugation in the nervous system. J. Biol. Chem. 280, 31405–31412. Jeske, N.A., Patwardhan, A.M., Gamper, N., Price, T.J., Akopian, A.N., Hargreaves, K.M., 2006. Cannabinoid WIN 55,212-2 regulates TRPV1 phosphorylation in sensory neurons. J. Biol. Chem. 281, 32879–32890. Jia, Y.-F., Li, Y.-C., Tang, Y.-P., Cao, J., Wang, L.-P., Yang, Y.-X., Xu, L., Mao, R.-R., 2015. Interference of TRPV1 function altered the susceptibility of PTZ-induced seizures. Front. Cell. Neurosci. 9, 20. Kawakami, K., Moritani, C., Uraji, M., Fujita, A., Kawakami, K., Hatanaka, T., Suzaki, E., Tsuboi, S., 2017. Hepatoprotective effects of rice-derived peptides against acetaminophen-induced damage in mice. J. Clin. Biochem. Nutr. 60, 115–120. Köfalvi, A., Pereira, M.F., Rebola, N., Rodrigues, R.J., Oliveira, C.R., Cunha, R.A., 2007. Anandamide and NADA bi-directionally modulate presynaptic Ca2+ levels and transmitter release in the hippocampus. Br. J. Pharmacol. 151, 551–563. La Rana, G., Russo, R., Campolongo, P., Bortolato, M., Mangieri, R.A., Cuomo, V., Iacono, A., Raso, G.M., Meli, R., Piomelli, D., Calignano, A., 2006. Modulation of neuropathic and inflammatory pain by the endocannabinoid transport inhibitor AM404 [N-(4hydroxyphenyl)-eicosa-5,8,11,14-tetraenamide]. J. Pharmacol. Exp. Ther. 317, 1365–1371. Löscher, W., 2011. Critical review of current animal models of seizures and epilepsy used in the discovery and development of new antiepileptic drugs. Seizure 20, 359–368. Ludányi, A., Eross, L., Czirják, S., Vajda, J., Halász, P., Watanabe, M., Palkovits, M., Maglóczky, Z., Freund, T.F., Katona, I., 2008. Downregulation of the CB1 cannabinoid receptor and related molecular elements of the endocannabinoid system in epileptic human hippocampus. J. Neurosci. 28, 2976–2990. Mallet, C., Barrière, D.A., Ermund, A., Jönsson, B.A.G., Eschalier, A., Zygmunt, P.M., Högestätt, E.D., 2010. TRPV1 in brain is involved in acetaminophen-induced antinociception. PLoS One 5, e12748. Manna, S.S.S., Umathe, S.N., 2012. Involvement of transient receptor potential vanilloid type 1 channels in the pro-convulsant effect of anandamide in pentylenetetrazoleinduced seizures. Epilepsy Res. 100, 113–124. Marrone, M.C., Morabito, A., Giustizieri, M., Chiurchiù, V., Leuti, A., Mattioli, M., Marinelli, S., Riganti, L., Lombardi, M., Murana, E., Totaro, A., Piomelli, D., Ragozzino, D., Oddi, S., Maccarrone, M., Verderio, C., Marinelli, S., 2017. TRPV1 channels are critical brain inflammation detectors and neuropathic pain biomarkers in mice. Nat. Commun. 8, 15292. Naderi, N., Ahmad-Molaei, L., Aziz Ahari, F., Motamedi, F., 2011. Modulation of anticonvulsant effects of cannabinoid compounds by GABA-A receptor agonist in acute pentylenetetrazole model of seizure in rat. Neurochem. Res. 36, 1520–1525. Nazıroğlu, M., 2015. TRPV1 channel: a potential drug target for treating epilepsy. Curr.
Neuropharmacol. 13, 239–247. Ohno, Y., Ishihara, S., Terada, R., Serikawa, T., Sasa, M., 2010. Antiepileptogenic and anticonvulsive actions of levetiracetam in a pentylenetetrazole kindling model. Epilepsy Res. 89, 360–364. Patwardhan, A.M., Jeske, N.A., Price, T.J., Gamper, N., Akopian, A.N., Hargreaves, K.M., 2006. The cannabinoid WIN 55,212-2 inhibits transient receptor potential vanilloid 1 (TRPV1) and evokes peripheral antihyperalgesia via calcineurin. Proc. Natl. Acad. Sci. U. S. A. 103, 11393–11398. Pini, L.A., Sandrini, M., Vitale, G., 1996. The antinociceptive action of paracetamol is associated with changes in the serotonergic system in the rat brain. Eur. J. Pharmacol. 308, 31–40. Pini, L.A., Vitale, G., Ottani, A., Sandrini, M., 1997. Naloxone-reversible antinociception by paracetamol in the rat. J. Pharmacol. Exp. Ther. 280, 934–940. Post, R.M., 2004. Neurobiology of seizures and behavioral abnormalities. Epilepsia 45 (Suppl. (2)), 5–14. Racine, R.J., 1972. Modification of seizure activity by electrical stimulation. II. Motor seizure. Electroencephalogr. Clin. Neurophysiol. 32, 281–294. Romigi, A., Bari, M., Placidi, F., Marciani, M.G., Malaponti, M., Torelli, F., Izzi, F., Prosperetti, C., Zannino, S., Corte, F., Chiaramonte, C., Maccarrone, M., 2010. Cerebrospinal fluid levels of the endocannabinoid anandamide are reduced in patients with untreated newly diagnosed temporal lobe epilepsy. Epilepsia 51, 768–772. Shirazi, M., Izadi, M., Amin, M., Rezvani, M.E., Roohbakhsh, A., Shamsizadeh, A., 2014. Involvement of central TRPV1 receptors in pentylenetetrazole and amygdala-induced kindling in male rats. Neurol. Sci. 35, 1235–1241. Shoudai, K., Peters, J.H., McDougall, S.J., Fawley, J.A., Andresen, M.C., 2010. Thermally active TRPV1 tonically drives central spontaneous glutamate release. J. Neurosci. 30, 14470–14475. Suemaru, K., Yoshikawa, M., Tanaka, A., Araki, H., Aso, H., Watanabe, M., 2018. Anticonvulsant effects of acetaminophen in mice: comparison with the effects of nonsteroidal anti-inflammatory drugs. Epilepsy Res. 140, 22–28. Umathe, S.N., Manna, S.S.S., Jain, N.S., 2012. Endocannabinoid analogues exacerbate marble-burying behavior in mice via TRPV1 receptor. Neuropharmacology 62, 2024–2033. Vilela, L.R., Medeiros, D.C., Rezende, G.H.S., de Oliveira, A.C.P., Moraes, M.F.D., Moreira, F.A., 2013. Effects of cannabinoids and endocannabinoid hydrolysis inhibition on pentylenetetrazole-induced seizure and electroencephalographic activity in rats. Epilepsy Res. 104, 195–202. Wallace, M.J., Martin, B.R., DeLorenzo, R.J., 2002. Evidence for a physiological role of endocannabinoids in the modulation of seizure threshold and severity. Eur. J. Pharmacol. 452, 295–301. Yamaura, K., Nakayama, N., Shimada, M., Ueno, K., 2012. Protective effects of natsumikan (Citrus natsudaidai) extract on acetaminophen-induced lethal hepatotoxicity in mice. Pharmacogn. Res. 4, 234–236. Zaitone, S.A., El-Wakeil, A.F., Abou-El-Ela, S.H., 2012. Inhibition of fatty acid amide hydrolase by URB597 attenuates the anxiolytic-like effect of acetaminophen in the mouse elevated plus-maze test. Behav. Pharmacol. 23, 417–425. Zygmunt, P.M., Chuang, H., Movahed, P., Julius, D., Högestätt, E.D., 2000. The anandamide transport inhibitor AM404 activates vanilloid receptors. Eur. J. Pharmacol. 396, 39–42.
159
Contents lists available at ScienceDirect
Epilepsy Research journal homepage: www.elsevier.com/locate/epilepsyres
TRPV1 mediates the anticonvulsant effects of acetaminophen in mice ⁎
T
Katsuya Suemaru, Misato Yoshikawa , Hiroaki Aso, Masahiko Watanabe School of Pharmacy, Shujitsu University, 1-6-1 Nishigawara, Naka-ku, Okayama, 703-8516, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: Acetaminophen Anticonvulsant effect Epileptogenesis TRPV1 receptors Cannabinoid receptors
Objective: Acetaminophen is one of the most commonly used analgesic and antipyretic drugs. It has been reported that acetaminophen has anticonvulsant effects in several animal models of seizure. An active metabolite of acetaminophen, AM404, inhibits the uptake of the endocannabinoid anandamide. However, the mechanism of the anticonvulsant effect of acetaminophen is unknown. Methods: This study was performed to examine whether or not acetaminophen can protect against pentylenetetrazol-induced kindling in mice and to investigate the precise mechanisms of the anticonvulsant effect of acetaminophen using the fully kindled mouse models. Results: Repeated administration of acetaminophen significantly delayed the progression of seizure severity induced by pentylenetetrazol. Additionally, acetaminophen showed a dose-dependent anticonvulsant activity against fully pentylenetetrazol-kindled seizures. AM404 also exhibited a dose-dependent anticonvulsant activity in fully kindled animals. The anticonvulsant activity of acetaminophen was antagonized by capsazepine and AMG9810, two transient receptor potential vanilloid-1 (TRPV1) antagonists. However, the transient receptor potential ankyrin 1 (TRPA1) antagonist HC030031 and CB1 receptor antagonist AM251 had no effect. Conclusion: These findings suggest that acetaminophen has an anticonvulsant effect in pentylenetetrazol-kindled mouse models and TRPV1 mediates the anticonvulsant action.
1. Introduction Acetaminophen is one of the most popular and widely used drugs for the treatment of pain and fever. Several mechanisms of acetaminophen action have been described that involve modulation of the endogenous cannabinoid system. Endocannabinoids are lipid mediators that act as endogenous agonists for type-1 and type-2 cannabinoid (CB1 and CB2, respectively) receptors, and anandamide and 2-arachidonoylglycerol (2-AG) are the main endogenous agonists. Additionally, anandamide is a potent activator of transient receptor potential vanilloid 1 (TRPV1), a member of the family of transient receptor potential (TRP) channels (De Petrocellis et al., 2000). Previous studies have shown that the cerebrospinal fluid levels of anandamide are reduced in patients with untreated newly diagnosed temporal lobe epilepsy (Romigi et al., 2010), and mRNA levels of the CB1 receptor are decreased in the hippocampal tissue of patients with intractable temporal lobe epilepsy (Ludányi et al., 2008). Recent clinical trials for drug-resistant seizures showed that cannabidiol, the main nonpsychotomimetic compound from Cannabis sativa, reduced seizures
(Devinsky et al., 2017). These findings suggest that the endocannabinoid system plays a role in the inhibition of seizures in humans with epilepsy. Recent studies have revealed that active metabolites of acetaminophen are important for its mechanism of action. N-acetyl-p-benzoquinoneimine (NAPQI) is a toxic metabolite of acetaminophen formed in the spinal cord, liver and kidneys. NAPQI activates the potent transient receptor potential ankyrin 1 (TRPA1), and mediates the antinociceptive and hypothermic actions of acetaminophen (Andersson et al., 2011; Gentry et al., 2015). Acetaminophen can also be metabolized by fatty acid amide hydrolase (FAAH) to an arachidonic acidconjugated metabolite of acetaminophen (AM404) in the brain and spinal cord (Högestätt et al., 2005). AM404 is known to inhibit the uptake of endocannabinoid anandamide into presynaptic neurons and activate cannabinoid and TRPV1 receptors (Beltramo et al., 1997; De Petrocellis et al., 2000). Accordingly, acetaminophen is considered to bring about its pharmacological actions by activation of cannabinoid receptors and/or the TRP channel system in the central nervous system. The major cannabinoid receptors in the central nervous system are
Abbreviations: AM404, N-(4-hydroxyphenyl-5Z,8Z,11Z,14Z-eicosatetraenamide); GABA, γ-aminobutyric acid; PG, prostaglandin; TRPV1, transient receptor potential vanilloid-1; TRPA1, transient receptor potential ankyrin 1 ⁎ Corresponding author. E-mail addresses: [email protected] (K. Suemaru), [email protected] (M. Yoshikawa), [email protected] (H. Aso), [email protected] (M. Watanabe). https://doi.org/10.1016/j.eplepsyres.2018.06.016 Received 23 January 2018; Received in revised form 19 June 2018; Accepted 30 June 2018 Available online 03 July 2018 0920-1211/ © 2018 Elsevier B.V. All rights reserved.
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
tonic seizures were monitored by an observer who was blind to the treatment.
CB1 receptors, and their activation reduces seizure severity in pentylenetetrazol-kindled mouse models (Bahremand et al., 2009). Endocannabinoid anandamide was reported to induce significant anticonvulsant effects in several seizure animal models (Wallace et al., 2002; Manna and Umathe, 2012; Bhaskaran and Smith, 2010). We recently found that acetaminophen has a significant anticonvulsant effect against fully pentylenetetrazol-kindled seizures (Suemaru et al., 2018). However, the relationship between acetaminophen and epileptogenesis remains unknown. In this study, we examined the repeat administration of acetaminophen on the development of pentylenetetrazol kindling in mice. Moreover, we investigated the mechanisms of acetaminophen action using fully pentylenetetrazol-kindled mouse models and compared them with that of the typical antiepileptic drug, sodium valproate.
2.4. Pentylenetetrazol kindling Kindling is a phenomenon in which repeated application of initially subconvulsive stimulation leads to seizures and increased seizure susceptibility persists over long periods of time. Mice at 5 weeks of age weighing 25–28 g were used for the pentylenetetrazol kindling. Kindling was induced by daily i.p. administration of 40 mg/kg of pentylenetetrazol, 5 days per week for 12 days. The seizure score was determined using the Racine scale (stages 1–5). The seizure intensity was scored as follows: stage 0, no response; stage 1, ear and facial twitching; stage 2, myoclonic body jerks; stage 3, forelimb clonus, rearing; stage 4, clonic seizures, turn onto the side; and stage 5, generalized clonic seizures, turn onto the back (Racine, 1972). For the evaluation of epileptogenesis activity, acetaminophen at doses that negligibly affects acute pentylenetetrazol seizures (100 and 300 mg/kg, i.p.) was repeatedly administered to the animals 30 min before pentylenetetrazol injection for 12 days. We also determined the anticonvulsive actions of acetaminophen, AM404 and WIN55212-2 (non-selective CB1 and CB2 receptor agonists) using fully pentylenetetrazol-kindled mice (8–10 weeks of age). Fully kindled was defined as the occurrence of three consecutive stage 4 or 5 seizures after administration of pentylenetetrazol (40 mg/kg) for 12 days. The kindled mice were injected intraperitoneally with acetaminophen, AM404, WIN55212-2 or valproate 30 min before the pentylenetetrazol (40 mg/kg, i.p.) test. Control groups received vehicle in the same manner. All behavioral seizures were observed for 20 min after injection of the test compound and recorded by an observer who was blind to the treatment. To investigate the mechanism of the anticonvulsive action of acetaminophen, the effects of AM251 (CB1 antagonist/inverse agonist), capsazepine and AMG9810 (TRPV1 receptor antagonists) and HC030031 (TRPA1 receptor antagonist) were determined using fully pentylenetetrazol-kindled mice (Fig. 1). These drugs were injected 45 min before the test. HC030031 was orally administered and the other drugs were intraperitoneally administered. Acetaminophen or valproate was injected 30 min before the test.
2. Methods and methods 2.1. Animals All animal care and experimental procedures were in accordance with the Guiding Principles for the Care and Use of Laboratory Animals adopted by the Japanese Pharmacological Society and approved by the Ethical Committee for Animal Experimentation committee of Shujitsu University (approval code 025-002). Male ICR mice were purchased from Shimizu Laboratory Supplies Co., Ltd. (Kyoto, Japan). Animals were maintained in an air-conditioned room with controlled temperature (22 ± 2 °C) under a 12/12 h light/dark cycle with lights on at 08:00 h. Mice were housed from 4 weeks of age in standard size plastic cages (32 × 18 × 24 cm) with paper bedding (4–5 mice per cage). The mice were allowed free access to food and water except during experiments. 2.2. Drugs Acetaminophen (Sigma-Aldrich, St. Louis, MO, USA), AM404 (Sigma-Aldrich), and AM251 (Sigma-Aldrich) were dissolved in polyoxyethylene castor oil (cremophor®) vehicle (18:1:1, saline: cremophor®: ethanol). WIN55212-2 (Sigma-Aldrich), capsazepine (SigmaAldrich) and AMG9810 (Tocris Bioscience, Bristol, UK) were emulsified in 1% Tween 80. HC030031 (Tocris Bioscience) was emulsified in 0.5% methylcellulose. Pentylenetetrazol (Sigma-Aldrich) and sodium valproate (Research Chemicals Inc., Toronto, Ontario, Canada) were dissolved in saline. Drugs were administered at a volume of 0.1–0.2 mL/10 g of body weight.
2.5. Statistical analysis All data contributing to seizure severity scores are expressed as the mean ± standard error of the mean (SEM). Development of pentylenetetrazol kindling was analyzed by repeated measures two-way ANOVA with treatment as a between-subjects factor and with day as a within-subject factor. Data of fully pentylenetetrazol-kindled seizures were analyzed by the Mann-Whitney test or Kruskal-Wallis test followed by Steel’s test. The chi-square test was used to compare the incidence of seizures. P-values < 0.05 were considered significant.
2.3. Acute pentylenetetrazol seizures To set the test dose of acetaminophen for pentylenetetrazol kindling, we first determined the anticonvulsive action against maximal pentylenetetrazol seizures using naive mice (8 weeks of age, weight 32–37 g). Pentylenetetrazol at a dose of 80 mg/kg was injected intraperitoneally (i.p.) 30 min after the administration of acetaminophen. The animals were observed for 20 min after injection, and clonic and
Fig. 1. Scheme of the experimental protocol for the fully pentylenetetrazol-kindled seizures test. 154
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
3.3. Effect on fully pentylenetetrazol-kindled seizures In the pentylenetetrazol-kindled mouse, the seizure severity scores were dose dependently decreased by valproate (30–300 mg/kg, i.p.), which served as a positive control. Acetaminophen (30–450 mg/kg, i.p.) showed a dose-dependent anticonvulsant activity. An active metabolite of acetaminophen, AM404 (10 and 30 mg/kg, i.p.), also exhibited slight anticonvulsant activity and there was a significant difference at a dose of 30 mg/kg (Fig. 4). Win 55212-2 (1 and 3 mg/kg, i.p.), a non-selective CB1 and CB2 receptor agonist, showed dose-dependent anticonvulsant activity against fully pentylenetetrazol-kindled seizures. Fig. 5 shows that the effect of AM251, a CB1 antagonist/inverse agonist, against the anticonvulsant action of acetaminophen or valproate. AM251 (1 and 3 mg/kg, i.p.) had no effect against fully pentylenetetrazol-kindled seizures. Moreover, AM251 had no effect against the anticonvulsant activities of acetaminophen (300 mg/kg, i.p.) and valproate (300 mg/kg, i.p.). HC030031 (30–300 mg/kg, p.o.), a TRPA1 receptor antagonist, had no effect against fully pentylenetetrazol-kindled seizures (Fig. 6). It also had no effect against the anticonvulsant activities of acetaminophen (300 mg/kg, i.p.) or valproate (300 mg/kg, i.p.), indicating that these compounds did not act through the TRPA1 receptor. TRPV1 receptor antagonists, capsazepine (1 and 3 mg/kg, i.p.) and AMG9810 (1–10 mg/kg, i.p.), showed a dose-dependent anticonvulsant activity against fully pentylenetetrazol-kindled seizures (Fig. 7). The anticonvulsant activity of acetaminophen (300 mg/kg, i.p.) was antagonized by capsazepine (1 and 3 mg/kg, i.p.) and AMG9810 (1 and 3 mg/kg, i.p.). However, both TRPV1 receptor antagonists had no effect on the anticonvulsant activity of valproate (300 mg/kg, i.p.).
Fig. 2. Effect of acetaminophen against acute pentylenetetrazol-induced seizures in mice. Pentylenetetrazol (80 mg/kg, i.p.) was injected 30 min after the intraperitoneal administration of acetaminophen (n = 10/group). Each value is expressed as the percentage of animals exhibiting clonic seizures (n = 10). * P < 0.05, versus the vehicle-treated control group (Chi-square test).
3. Results 3.1. Effect of acetaminophen on acute pentylenetetrazol seizures In the acute pentylenetetrazol-induced seizure test, pentylenetetrazol (80 mg/kg) induced clonic seizures in all mice treated with vehicle. Acetaminophen treatment (300 mg/kg, i.p.) showed no significant anticonvulsant effect (Fig. 2). However, acetaminophen at a dose of 450 mg/kg significantly (P < 0.05) suppressed the clonic seizures.
3.2. Effect of acetaminophen on pentylenetetrazol kindling 4. Discussion Repeated administration of sub-convulsive pentylenetetrazol (40 mg/kg, i.p.) induced kindling in mice as revealed by the progressive increase in seizure score (Fig. 3). Daily treatment with acetaminophen (100 mg/kg, i.p.) before pentylenetetrazol slightly delayed the progression of seizure severity induced by pentylenetetrazol. However, repeated measures two-way ANOVA revealed no significant effect of acetaminophen treatment (F 1, 319 = 3.95, p = 0.056) and no significant treatment × day interaction (F 11, 319 = 1.41, p = 0.165). Acetaminophen (300 mg/kg, i.p.) pre-treatment significantly reduced the seizure score throughout the 12 days of the study period. Repeated measures two-way ANOVA revealed a significant effect of acetaminophen treatment (F 1, 319 = 35.28, p < 0.001) and a significant treatment × day interaction (F 11, 319 = 5.41, p < 0.001).
We recently reported that acetaminophen showed no significant anticonvulsant effects in acute-seizure models induced by maximum electroshock whereas acetaminophen exhibited significant anticonvulsant effects in animal models of chronic epilepsy induced by corneal electroshock or pentylenetetrazol kindling (Suemaru et al., 2018). In this study, we confirmed that acetaminophen at doses of 30–450 mg/kg (i.p.) showed dose-dependent anticonvulsant activity against fully pentylenetetrazol-kindled seizures. By comparison, previous rodent studies have shown that acetaminophen exerts antinociceptive effects at doses of 100–400 mg/kg (Mallet et al., 2010; Pini et al., 1996, 1997) or antipyretic effects at doses of 100–300 mg/kg (Ayoub et al., 2004; Gentry et al., 2015). These results suggest that acetaminophen exhibits its antinociceptive and anticonvulsant actions in rodents over a similar dose range. However, high doses of acetaminophen (300–700 mg/kg) were reported to cause hepatotoxicity in rodents (Yamaura et al., 2012; Kawakami et al., 2017). Therefore, it is unclear whether or not a typical 15 mg/kg therapeutic dose of acetaminophen would have an anticonvulsant effect in humans. Acetaminophen is metabolized to AM404 which in turn, inhibits the uptake of endocannabinoid anandamide into neurons and activates CB1 and TRPV1 receptors (De Petrocellis et al., 2000). Anandamide was reported to induce significant anticonvulsant effects in several mouse models of seizure, such as a maximal electroshock model (Wallace et al., 2002), an acute pentylenetetrazol-induced seizure (Manna and Umathe, 2012), and a pilocarpine-induced status epilepticus mouse model (Bhaskaran and Smith, 2010). Moreover, CB1 receptor antagonists have been reported to abolish the anticonvulsant effect of anandamide in the maximal electroshock model and acute pentylenetetrazol-induced seizures (Vilela et al., 2013; Naderi et al., 2011). These findings indicate the anticonvulsant action of anandamide is mediated through activation of central CB1 receptors. It has also been reported that TRPV1 receptors modulate seizure activity in animal models of seizures and epilepsy (Nazıroğlu, 2015). Manna and Umathe (2012)
Fig. 3. Effect of acetaminophen on the development of pentylenetetrazol kindling in mice. Pentylenetetrazol (40 mg/kg, i.p.) was injected 30 min after the intraperitoneal administration of acetaminophen (100 and 300 mg/kg, i.p.) for 12 days (n = 11–20 /group). Each value represents the mean seizure score ± SEM. The pentylenetetrazol kindling data were analyzed by repeated measures two-way ANOVA. 155
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
Fig. 4. Effects of valproate, Win 55212-2, acetaminophen, and AM404 in pentylenetetrazol-kindled mice. Valproate, Win 55212-2, acetaminophen, and AM404 were intraperitoneally injected 30 min before the administration of pentylenetetrazol (40 mg/kg, i.p.). Each value represents the mean seizure score ± SEM (n = 10/group). * P < 0.05, ** P < 0.01, versus the vehicle-treated control group (Steel’s test).
Fig. 5. Effects of the CB1 antagonist/inverse agonist AM251 on the anticonvulsant action of acetaminophen and valproate in pentylenetetrazol-kindled mice. Acetaminophen, valproate, and vehicle were intraperitoneally injected 30 min before the administration of pentylenetetrazol (40 mg/kg, i.p.). AM251 was intraperitoneally injected 45 min before the pentylenetetrazol administration. Each value represents the mean seizure score ± SEM (n = 10/group). ** P < 0.01, versus the vehicle-treated control group (Mann-Whitney test or Steel’s test). NS (no significance).
suggest that TRPV1 mediates the anticonvulsant action of acetaminophen. However, taking into consideration the observation that the TRPV1 antagonists capsazepine and AMG9810 exhibited anticonvulsant activities, TRPV1 receptors, which are located throughout different areas of the brain, may be involved in the anticonvulsant action of acetaminophen. Recently, it has been reported that TRPV1 knockout mice exhibited exacerbation of hyperthermic seizures (Barrett et al., 2016) and pentylenetetrazol-induced seizures (Jia et al., 2015). To confirm the precise role of TRPV1 in the anticonvulsant activities of acetaminophen, further experimental work is needed using TRPV1
reported that the TRPV1 agonist capsaicin exhibited pro-convulsant activity and intracerebroventricular administration of capsazepine, a TRPV1 antagonist, suppressed acute pentylenetetrazol-induced seizures in mice (Manna and Umathe, 2012). In the present study, treatment with capsazepine and AMG9810, both TRPV1 antagonists, resulted in slight but significant anticonvulsant activity against fully pentylenetetrazol-kindled seizures. Interestingly, the anticonvulsant activity of acetaminophen was reduced by pretreatment with the TRPV1 antagonists. Additionally, the CB1 antagonist/inverse agonist AM251 had no effect on the anticonvulsant activities of acetaminophen. These results 156
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
Fig. 6. Effects of the TRPA1 antagonist HC030031 on the anticonvulsant action of acetaminophen and valproate in pentylenetetrazol-kindled mice. Acetaminophen, valproate, and vehicle were intraperitoneally injected 30 min before the administration of pentylenetetrazol (40 mg/kg, i.p.). HC030031 was orally administered 45 min before the pentylenetetrazol administration. Each value represents the mean seizure score ± SEM (n = 10/group). ** P < 0.01, versus the vehicle-treated control group (Mann-Whitney test). NS (no significance).
55212-2 exhibits its anticonvulsant activity via the CB1 and TRPV1 receptors. It is well known that inflammation, fever and stress reduce the seizure threshold. Although high doses of a TRPV1 agonist resulted in persistent desensitization of TRPV1 (Caterina et al., 1997), its anxiolytic-like action has been shown in a mouse elevated plus-maze test at low doses of 100–200 mg/kg (Zaitone et al., 2012). Therefore, the
knockout mice. In the present study, the non-selective CB1 and CB2 receptor agonist Win 55212-2 showed a dose-dependent anticonvulsant activity against fully pentylenetetrazol-kindled seizures. WIN 55212-2 was also reported to inhibit TRPV1 functional activities (Patwardhan et al., 2006) and modulate TRPV1 activation by altering receptor phosphorylation (Jeske et al., 2006). Therefore, these findings suggested that WIN
Fig. 7. Effects of the TRPV1 antagonists capsazepine and AMG9810 on the anticonvulsant action of acetaminophen or valproate in pentylenetetrazol-kindled mice. Acetaminophen, valproate, and vehicle were intraperitoneally injected 30 min before the administration of pentylenetetrazol (40 mg/kg, i.p.). Capsazepine and AMG9810 were intraperitoneally injected 45 min before the pentylenetetrazol administration. Each value represents the mean seizure score ± SEM (n = 10/group). * P < 0.05, ** P < 0.01, versus the vehicle-treated control group (Mann-Whitney test or Steel’s test). NS (no significance). 157
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
However, the brain concentration of AM404 after peripheral administration is unknown. Thus, it will be important to define the concentration of AM404 in the brain to obtain a better understanding of its pharmacological actions and those of acetaminophen. TRPV1, a non-selective cation channel, is expressed in the neuronal and glial cells of various brain regions. TRPV1 modulates synaptic transmission by a presynaptic and/or postsynaptic mechanism (Köfalvi et al., 2007; Shoudai et al., 2010; Fawley et al., 2014). Moreover, TRPV1 receptors are thought to be functionally localized intracellularly (Brailoiu et al., 2011; Fowler, 2013). Recently, it has been reported that stimulation of microglial TRPV1 receptors controls microglia activation and indirectly enhances glutamatergic transmission in neurons (Marrone et al., 2017). It is well known that glutamate is the major excitatory neurotransmitter in the central nervous system and plays important roles in seizure and epilepsy. Therefore, it has been proposed that the anticonvulsant action of TRPV1 receptor antagonists is mediated through the modulation of glutaminergic systems. However, further studies into the precise mechanism underlying the anticonvulsant effect of acetaminophen are needed.
anxiolytic effects of acetaminophen may partly contribute to its anticonvulsant activity. The kindling model of epilepsy has been used to investigate the process of epileptogenesis and discover new antiepileptic drugs (Löscher, 2011). Antiepileptic drugs show different profiles of therapeutic effectiveness in blocking the different stages of seizure evolution in the kindling model. For example, phenytoin, carbamazepine and lamotrigine do not block the development of kindling acquisition but are highly effective against fully kindled seizures in the amygdalakindling model. In contrast, valproate is effective at preventing kindling development and blocking the fully kindled seizures (Post, 2004). However, it was reported that valproate at sub-anticonvulsive doses failed to prevent the development of pentylenetetrazol kindling (Ohno et al., 2010). In the present study, acetaminophen at doses of 100–300 mg/kg (i.p.) had no effect against the acute pentylenetetrazol seizures. However, acetaminophen at a dose of 300 mg/kg (i.p.) abolished the kindling acquisition in a pentylenetetrazol kindling model. These findings suggest the possibility that acetaminophen affects the process of epileptogenesis. However, in this study, acetaminophen at a dose of 300 mg/kg (i.p.) showed significant anticonvulsant activity against fully pentylenetetrazol-kindled seizures. In the kindling model of epilepsy, electrical or chemical kindling are epileptogenic models used for understanding the epileptogenic process. Therefore, further studies are needed to evaluate epileptogenesis using an electrical kindling model of epilepsy. Shirazi et al. reported that N-oleoyldopamine, a TRPV1 receptor agonist, accelerated the pentylenetetrazol kindling in rats, and AMG9810, a TRPV1 receptor antagonist, delayed the development of amygdala kindling in rats (Shirazi et al., 2014). Thus, it is important to clarify the involvement of TRPV1 receptors in the inhibitory process of kindling by acetaminophen. Recent studies have revealed that active metabolites of acetaminophen play important roles in its mechanism of action. NAPQI, a metabolite of acetaminophen, activates TRPA1 receptors, and it has been reported that TRPA1 receptors mediate the antinociceptive and hypothermic actions of acetaminophen (Andersson et al., 2011; Gentry et al., 2015). In this study, HC030031, a TRPA1 receptor antagonist, did not affect the anticonvulsant effect of acetaminophen in pentylenetetrazol-kindled mice. in vitro studies have reported that anandamide is an endogenous agonist of CB1 and also activates TRPV1, and that AM404 is a weak agonist of CB1 receptors and a potent activator of TRPV1 receptors (Zygmunt et al., 2000; De Petrocellis et al., 2000). It has been reported that acute intracerebroventricular administration of low doses of anandamide or AM404 produced anticonvulsant effects, while those at higher doses exhibited a pro-convulsant effect in acute pentylenetetrazol-induced seizures in mice (Manna and Umathe, 2012). These findings indicated the biphasic effects of anandamide and AM404 on the regulation of neuronal activity during seizures (Umathe et al., 2012). An active metabolite of acetaminophen, AM404, inhibits the uptake of anandamide and activates CB1 and TRPV1 receptors (De Petrocellis et al., 2000). In the present study, the anticonvulsant activity of acetaminophen was antagonized by the TRPV1 antagonists capsazepine and AMG9810. However, CB1 antagonist/inverse agonist AM251 had no effect. Taken together, these results suggest that the TRPV1 receptors stimulated by both AM404 and anandamide may be involved in the anticonvulsant action of acetaminophen. Previous rodent studies have shown that acetaminophen exhibits antinociceptive effects (100–400 mg/kg, i.p.) (Mallet et al., 2010; Pini et al., 1996, 1997), and AM404 (1–10 mg/kg, i.p.) elicits a dose-dependent antinociceptive effect (La Rana et al., 2006). In this study, AM404 (30 mg/kg, i.p.) exhibited slight anticonvulsant activity compared with acetaminophen (30–450 mg/kg, i.p.) in pentylenetetrazolkindled mouse models. Acetaminophen is metabolized by FAAH to AM404 in the brain and spinal cord (Högestätt et al., 2005) and it is reported that the concentration of AM404 in rat brain following acetaminophen (300 mg/kg, i.p.) is 10.3 pmol/g (Högestätt, et al., 2005).
5. Conclusion The present study revealed that acetaminophen has apparent anticonvulsant effects in pentylenetetrazol-kindled mouse models and TRPV1 mediates the anticonvulsant action of acetaminophen. Conflict of interest The authors declare no conflict of interest. Acknowledgements We are grateful to Yohei Tanemoto, Norihiko Osawa, and Takahiro Haji for their technical assistance. We thank Renee Mosi, PhD, from Edanz Group (www.edanzediting.com/ac) for editing a draft of this manuscript. References Andersson, D.A., Gentry, C., Alenmyr, L., Killander, D., Lewis, S.E., Andersson, A., Bucher, B., Galzi, J.-L., Sterner, O., Bevan, S., Högestätt, E.D., Zygmunt, P.M., 2011. TRPA1 mediates spinal antinociception induced by acetaminophen and the cannabinoid Δ9tetrahydrocannabiorcol. Nat. Commun. 2, 551. Ayoub, S.S., Botting, R.M., Goorha, S., Colville-Nash, P.R., Willoughby, D.A., Ballou, L.R., 2004. Acetaminophen-induced hypothermia in mice is mediated by a prostaglandin endoperoxide synthase 1 gene-derived protein. Proc. Natl. Acad. Sci. U. S. A. 101, 11165–11169. Bahremand, A., Nasrabady, S.E., Shafaroodi, H., Ghasemi, M., Dehpour, A.R., 2009. Involvement of nitrergic system in the anticonvulsant effect of the cannabinoid CB1 agonist ACEA in the pentylenetetrazole-induced seizure in mice. Epilepsy Res. 84, 110–119. Barrett, K.T., Wilson, R.J.A., Scantlebury, M.H., 2016. TRPV1 deletion exacerbates hyperthermic seizures in an age-dependent manner in mice. Epilepsy Res. 128, 27–34. Beltramo, M., Stella, N., Calignano, A., Lin, S.Y., Makriyannis, A., Piomelli, D., 1997. Functional role of high-affinity anandamide transport, as revealed by selective inhibition. Science 277, 1094–1097. Bhaskaran, M.D., Smith, B.N., 2010. Cannabinoid-mediated inhibition of recurrent excitatory circuitry in the dentate gyrus in a mouse model of temporal lobe epilepsy. PLoS One 5, e10683. Brailoiu, G.C., Oprea, T.I., Zhao, P., Abood, M.E., Brailoiu, E., 2011. Intracellular cannabinoid type 1 (CB1) receptors are activated by anandamide. J. Biol. Chem. 286, 29166–29174. Caterina, M.J., Schumacher, M.A., Tominaga, M., Rosen, T.A., Levine, J.D., Julius, D., 1997. The capsaicin receptor: a heat-activated ion channel in the pain pathway. Nature 389, 816–824. De Petrocellis, L., Bisogno, T., Davis, J.B., Pertwee, R.G., Di Marzo, V., 2000. Overlap between the ligand recognition properties of the anandamide transporter and the VR1 vanilloid receptor: inhibitors of anandamide uptake with negligible capsaicinlike activity. FEBS Lett. 483, 52–56. Devinsky, O., Cross, J.H., Laux, L., Marsh, E., Miller, I., Nabbout, R., Scheffer, I.E., Thiele, E.A., Wright, S., Cannabidiol in Dravet Syndrome Study Group, 2017. Trial of cannabidiol for drug-resistant seizures in the dravet syndrome. N. Engl. J. Med. 376, 2011–2020. Fawley, J.A., Hofmann, M.E., Andresen, M.C., 2014. Cannabinoid 1 and transient receptor
158
Epilepsy Research 145 (2018) 153–159
K. Suemaru et al.
potential vanilloid 1 receptors discretely modulate evoked glutamate separately from spontaneous glutamate transmission. J. Neurosci. 34, 8324–8332. Fowler, C.J., 2013. Transport of endocannabinoids across the plasma membrane and within the cell. FEBS J. 280, 1895–1904. Gentry, C., Andersson, D.A., Bevan, S., 2015. TRPA1 mediates the hypothermic action of acetaminophen. Sci. Rep. 5, 12771. Högestätt, E.D., Jönsson, B.A.G., Ermund, A., Andersson, D.A., Björk, H., Alexander, J.P., Cravatt, B.F., Basbaum, A.I., Zygmunt, P.M., 2005. Conversion of acetaminophen to the bioactive N-acylphenolamine AM404 via fatty acid amide hydrolase-dependent arachidonic acid conjugation in the nervous system. J. Biol. Chem. 280, 31405–31412. Jeske, N.A., Patwardhan, A.M., Gamper, N., Price, T.J., Akopian, A.N., Hargreaves, K.M., 2006. Cannabinoid WIN 55,212-2 regulates TRPV1 phosphorylation in sensory neurons. J. Biol. Chem. 281, 32879–32890. Jia, Y.-F., Li, Y.-C., Tang, Y.-P., Cao, J., Wang, L.-P., Yang, Y.-X., Xu, L., Mao, R.-R., 2015. Interference of TRPV1 function altered the susceptibility of PTZ-induced seizures. Front. Cell. Neurosci. 9, 20. Kawakami, K., Moritani, C., Uraji, M., Fujita, A., Kawakami, K., Hatanaka, T., Suzaki, E., Tsuboi, S., 2017. Hepatoprotective effects of rice-derived peptides against acetaminophen-induced damage in mice. J. Clin. Biochem. Nutr. 60, 115–120. Köfalvi, A., Pereira, M.F., Rebola, N., Rodrigues, R.J., Oliveira, C.R., Cunha, R.A., 2007. Anandamide and NADA bi-directionally modulate presynaptic Ca2+ levels and transmitter release in the hippocampus. Br. J. Pharmacol. 151, 551–563. La Rana, G., Russo, R., Campolongo, P., Bortolato, M., Mangieri, R.A., Cuomo, V., Iacono, A., Raso, G.M., Meli, R., Piomelli, D., Calignano, A., 2006. Modulation of neuropathic and inflammatory pain by the endocannabinoid transport inhibitor AM404 [N-(4hydroxyphenyl)-eicosa-5,8,11,14-tetraenamide]. J. Pharmacol. Exp. Ther. 317, 1365–1371. Löscher, W., 2011. Critical review of current animal models of seizures and epilepsy used in the discovery and development of new antiepileptic drugs. Seizure 20, 359–368. Ludányi, A., Eross, L., Czirják, S., Vajda, J., Halász, P., Watanabe, M., Palkovits, M., Maglóczky, Z., Freund, T.F., Katona, I., 2008. Downregulation of the CB1 cannabinoid receptor and related molecular elements of the endocannabinoid system in epileptic human hippocampus. J. Neurosci. 28, 2976–2990. Mallet, C., Barrière, D.A., Ermund, A., Jönsson, B.A.G., Eschalier, A., Zygmunt, P.M., Högestätt, E.D., 2010. TRPV1 in brain is involved in acetaminophen-induced antinociception. PLoS One 5, e12748. Manna, S.S.S., Umathe, S.N., 2012. Involvement of transient receptor potential vanilloid type 1 channels in the pro-convulsant effect of anandamide in pentylenetetrazoleinduced seizures. Epilepsy Res. 100, 113–124. Marrone, M.C., Morabito, A., Giustizieri, M., Chiurchiù, V., Leuti, A., Mattioli, M., Marinelli, S., Riganti, L., Lombardi, M., Murana, E., Totaro, A., Piomelli, D., Ragozzino, D., Oddi, S., Maccarrone, M., Verderio, C., Marinelli, S., 2017. TRPV1 channels are critical brain inflammation detectors and neuropathic pain biomarkers in mice. Nat. Commun. 8, 15292. Naderi, N., Ahmad-Molaei, L., Aziz Ahari, F., Motamedi, F., 2011. Modulation of anticonvulsant effects of cannabinoid compounds by GABA-A receptor agonist in acute pentylenetetrazole model of seizure in rat. Neurochem. Res. 36, 1520–1525. Nazıroğlu, M., 2015. TRPV1 channel: a potential drug target for treating epilepsy. Curr.
Neuropharmacol. 13, 239–247. Ohno, Y., Ishihara, S., Terada, R., Serikawa, T., Sasa, M., 2010. Antiepileptogenic and anticonvulsive actions of levetiracetam in a pentylenetetrazole kindling model. Epilepsy Res. 89, 360–364. Patwardhan, A.M., Jeske, N.A., Price, T.J., Gamper, N., Akopian, A.N., Hargreaves, K.M., 2006. The cannabinoid WIN 55,212-2 inhibits transient receptor potential vanilloid 1 (TRPV1) and evokes peripheral antihyperalgesia via calcineurin. Proc. Natl. Acad. Sci. U. S. A. 103, 11393–11398. Pini, L.A., Sandrini, M., Vitale, G., 1996. The antinociceptive action of paracetamol is associated with changes in the serotonergic system in the rat brain. Eur. J. Pharmacol. 308, 31–40. Pini, L.A., Vitale, G., Ottani, A., Sandrini, M., 1997. Naloxone-reversible antinociception by paracetamol in the rat. J. Pharmacol. Exp. Ther. 280, 934–940. Post, R.M., 2004. Neurobiology of seizures and behavioral abnormalities. Epilepsia 45 (Suppl. (2)), 5–14. Racine, R.J., 1972. Modification of seizure activity by electrical stimulation. II. Motor seizure. Electroencephalogr. Clin. Neurophysiol. 32, 281–294. Romigi, A., Bari, M., Placidi, F., Marciani, M.G., Malaponti, M., Torelli, F., Izzi, F., Prosperetti, C., Zannino, S., Corte, F., Chiaramonte, C., Maccarrone, M., 2010. Cerebrospinal fluid levels of the endocannabinoid anandamide are reduced in patients with untreated newly diagnosed temporal lobe epilepsy. Epilepsia 51, 768–772. Shirazi, M., Izadi, M., Amin, M., Rezvani, M.E., Roohbakhsh, A., Shamsizadeh, A., 2014. Involvement of central TRPV1 receptors in pentylenetetrazole and amygdala-induced kindling in male rats. Neurol. Sci. 35, 1235–1241. Shoudai, K., Peters, J.H., McDougall, S.J., Fawley, J.A., Andresen, M.C., 2010. Thermally active TRPV1 tonically drives central spontaneous glutamate release. J. Neurosci. 30, 14470–14475. Suemaru, K., Yoshikawa, M., Tanaka, A., Araki, H., Aso, H., Watanabe, M., 2018. Anticonvulsant effects of acetaminophen in mice: comparison with the effects of nonsteroidal anti-inflammatory drugs. Epilepsy Res. 140, 22–28. Umathe, S.N., Manna, S.S.S., Jain, N.S., 2012. Endocannabinoid analogues exacerbate marble-burying behavior in mice via TRPV1 receptor. Neuropharmacology 62, 2024–2033. Vilela, L.R., Medeiros, D.C., Rezende, G.H.S., de Oliveira, A.C.P., Moraes, M.F.D., Moreira, F.A., 2013. Effects of cannabinoids and endocannabinoid hydrolysis inhibition on pentylenetetrazole-induced seizure and electroencephalographic activity in rats. Epilepsy Res. 104, 195–202. Wallace, M.J., Martin, B.R., DeLorenzo, R.J., 2002. Evidence for a physiological role of endocannabinoids in the modulation of seizure threshold and severity. Eur. J. Pharmacol. 452, 295–301. Yamaura, K., Nakayama, N., Shimada, M., Ueno, K., 2012. Protective effects of natsumikan (Citrus natsudaidai) extract on acetaminophen-induced lethal hepatotoxicity in mice. Pharmacogn. Res. 4, 234–236. Zaitone, S.A., El-Wakeil, A.F., Abou-El-Ela, S.H., 2012. Inhibition of fatty acid amide hydrolase by URB597 attenuates the anxiolytic-like effect of acetaminophen in the mouse elevated plus-maze test. Behav. Pharmacol. 23, 417–425. Zygmunt, P.M., Chuang, H., Movahed, P., Julius, D., Högestätt, E.D., 2000. The anandamide transport inhibitor AM404 activates vanilloid receptors. Eur. J. Pharmacol. 396, 39–42.
159