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The monosodium iodoacetate model of osteoarthritis: a model of chronic nociceptive pain in rats?
Neuroscience Letters 370 (2004) 236–240
The monosodium iodoacetate model of osteoarthritis: a model of chronic nociceptive pain in rats? Rachel Combe∗ , Steve Bramwell, Mark J. Field Pain Therapeutics, Pfizer Global Research and Development, Ramsgate Road, Sandwich, Kent CT139NJ, UK Received 22 July 2004; received in revised form 13 August 2004; accepted 13 August 2004
Abstract Osteoarthritis (OA) is a widespread condition affecting the elderly population. One of the most prominent features but least studied symptoms is chronic pain associated with OA. The study objective was to determine pain endpoints in rats with monosodium iodoacetate (MIA) induced OA, and to investigate the efficacy of common nociceptive agents. Sprague–Dawley rats received an intraarticular injection of either 25 l 80 mg/ml MIA or 25 l 0.9% sterile saline into the right knee joint. Changes in von Frey thresholds and latencies to stroking with a cotton bud (punctate and dynamic allodynia, respectively) were measured pre- and for up to 10 weeks post-intraarticular injection. Changes in hind paw weight distribution were also determined. Both punctate allodynia and a weight bearing deficit were observed in MIA-treated rats for up to 10 weeks. Interestingly, dynamic allodynia was not detected at any time point tested. Morphine (0.3–3 mg/kg, s.c.) and tramadol (3–100 mg/kg, p.o.) dose-dependently inhibited punctate allodynia and partially reversed weight bearing deficit. In conclusion, the MIA model of OA is reproducible and mimics OA pain in humans. Analgesic drug studies indicate this model may be useful for investigating chronic nociceptive pain. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Osteoarthritis; Punctate allodynia; Dynamic allodynia; Weight bearing; Nociceptive pain
Osteoarthritis (OA) is a chronic condition widespread in the elderly population. The majority of patients will experience chronic pain, which impacts significantly on their quality of life. Patients with OA have pain that typically worsens with weight bearing and activity, and also joint stiffness in the morning or after rest. The causes of OA have not been fully determined, however, biomechanical forces affecting the articular cartilage and subchondral bone, biochemical changes in the articular cartilage and synovial membrane, and genetic factors are thought to be of importance [16,18,12]. Currently, no disease-modifying drugs are available so the objective of pharmacological treatment has been aimed at reducing pain, maintaining and/or improving joint mobility and reducing functional impairment. Animal models have provided useful tools for investigating pain arising from other conditions,
∗
Corresponding author. Tel.: +44 1304 645535; fax: +44 1304 651817. E-mail address: [email protected] (R. Combe).
0304-3940/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2004.08.023
such as peripheral neuropathies. Examples include nerve ligation approaches in rats that model some aspects of neuropathic pain [1,8]. Interestingly, although animal models of osteoarthritis are widely used, they have been used mainly to study the pathophysiology and progression of joint damage with little characterisation of the associated pain [9,10,13]. One such model is the monosodium iodoacetate (MIA) induced arthritis model first described by Kalbhen some 20 years ago [14]. The structural integrity of articular cartilage relies on the normal functioning of chondrocytes. Local injection of MIA, an inhibitor of glycolysis, disrupts chondrocyte metabolism and produces cartilage degeneration. The histopathology of the degenerating joint is similar to that seen in the human condition [13]. Moreover, at the later stages of joint damage in the MIA model, exposed subchondral bone and damaged synovium is present and is associated with joint pain, as seen in humans [10]. Following intraarticular injection of MIA there is an initial inflammatory response [2]. This inflammation was characterised by Bove and
R. Combe et al. / Neuroscience Letters 370 (2004) 236–240
colleagues histologically as expansion of the synovial membrane by proteinaceous oedema fluid and fibrin with infiltrating macrophages, neutrophils, plasma cells and lymphocytes. By day 7, inflammation within the synovium and surrounding tissue has largely resolved and is not expected to play a role in mediating pain. However, the potential of this model to predict efficacy of antinociceptive agents in OA and its value as a general model of chronic nociceptive pain has yet to be determined. The objectives of this study were to establish measurable pain endpoints in rats with MIA-induced OA, and to assess the efficacy of morphine and tramadol, both of which are used to treat chronic nociceptive pain and have demonstrated clinical efficacy in this condition [5]. All experiments conformed to the ethical guidelines for investigation of experimental pain in conscious animals [21] and in full compliance with the UK Animals (Scientific Procedures) Act, 1986. Male Sprague–Dawley rats (125–175 g; Charles River, Kent, UK) were housed in groups of four under a 12 h light/dark cycle (lights on at 07:00 a.m.) with food and water ad libitum. Rats were anaesthetised with a 2% isofluorane O2 mixture and given a single intraarticular injection of monosodium iodoacetate (Sigma, Poole, UK) through the infrapatella ligament of the right knee [7]. MIA was dissolved in 0.9% sterile saline and administered in a volume of 25 l using a 26 gauge, 0.5 in. needle. Control animals were given a single intraarticular injection into the right knee of 25 l 0.9% sterile saline. Assessment of punctate and dynamic allodynia was performed as previously described by Field et al. [8]. Briefly, punctate allodynia was evaluated by application of von Frey hairs in ascending order of force to the plantar surface of the hind paws. Dynamic allodynia was assessed by lightly stroking the plantar surface of the hind paw with a cotton bud. Paw withdrawal thresholds (PWT) to von Frey hairs and withdrawal latencies to cotton bud stimulus were assessed in the same group of animals on various days post-intraarticular injection. The effect of joint damage on the weight distribution through the right (arthritic) and left (untreated) knee was assessed using an incapacitance tester (Linton Instrumentation, Norfolk, UK) [2]. Briefly, an incapacitance tester measures weight distribution on the two hind paws. The force exerted by each hind limb is measured in grams. The inhibitory effects of morphine and tramadol on punctate allodynia and weight bearing deficit were investigated. Compounds were administered 14 days post-intraarticular injection having established stable baseline PWT and weight bearing deficits prior to drug administration. Animals were administered (on separate test days) with either vehicle, morphine (0.3–3 mg/kg, s.c.) or tramadol (3–100 mg/kg, p.o.) and changes from baseline were assessed for up to 3 h. All experiments were performed by an observer blind to drug treatment. Morphine sulphate was obtained from Sigma and was administered s.c. in 0.9% saline. Tramadol hydrochloride was
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Fig. 1. Development of punctate (A) and dynamic (B) allodynia, and weight bearing deficit (C) following intraarticular injection of MIA or saline. Rats were injected with either 2 mg of MIA () or saline () in the right knee. (A) Baseline (BL) paw withdrawal thresholds (PWT) were determined in both hind paws for all animals prior to injection. PWT to von Frey hairs were assessed on various days post-injection. Results are expressed as median force (g) required to induce a paw withdrawal in 10 animals per group (vertical bars represent first and third quartiles). ∗ P < 0.05, ∗∗ P < 0.01, ∗∗∗ P < 0.001 significantly different (Mann–Whitney U test) from saline-treated group at each time point. (B) Baseline (BL) paw withdrawal latencies (PWL) to cotton bud stimulus were determined for both hind paws for all animals prior to injection. Results are expressed as mean PWL (s) in 10 animals per group (vertical bars represent ±S.E.M.). ∗ P < 0.05, ∗∗ P < 0.01, ∗∗∗ P < 0.001 significantly different (one-way ANOVA followed by Dunnett’s t test) from saline-treated group. (C) Baseline (BL) hind paw weight distribution was determined for all animals prior to injection. Changes in hind paw weight distribution were assessed on various days post-injection. Results are expressed as mean change in weight distribution (contralateral–ipsilateral) (g) in 10 animals per group (vertical bars represent ±S.E.M.). ∗ P < 0.05, ∗∗ P < 0.01, ∗∗∗ P < 0.001 significantly different (one-way ANOVA followed by Dunnett’s t test) from saline-treated group.
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Fig. 2. Effects of morphine (A, C) and tramadol (B, D) on punctate allodynia and change in hind paw weight distribution following intraarticular injection MIA. Morphine was subcutaneously administered and tramadol was orally administered 30 min prior to the measurement of pain parameters on separate test days Rats were injected with 2 mg of MIA into the right knee 2 weeks previously. Baseline (BL) paw withdrawal thresholds (PWT) or hind paw weight distribution was determined for all animals prior to administration of drug. Punctate allodynia data expressed as median force (g) required to induce a paw withdrawal in 10 animals per group (vertical bars represent first and third quartiles) and ∗ P < 0.05, ∗∗ P < 0.01, ∗∗∗ P < 0.001 significantly different (Mann–Whitney U test) from vehicle-treated group at each time point. The dotted line represents the contralateral PWT. Changes in hind paw weight distribution are expressed as mean change in weight distribution (ipsilateral–contralateral) (g) in 10 animals per group (vertical bars represent ±S.E.M.) and ∗ P < 0.05, ∗∗ P < 0.01, ∗∗∗ P < 0.001 significantly different (one-way ANOVA followed by Dunnett’s t test) from vehicle-treated group. The dashed line represents weight distribution for rats treated with intraarticular saline.
obtained from Sigma and was administered p.o. in Millipore filtered water. Drug administration was in a volume of 1 ml/kg. Punctate allodynia was detected in all MIA-treated rats from day 7 (first test day) until day 70, with all animals demonstrating a PWT to the previously innocuous 4.0 g force or below (Fig. 1A) as compared to the normal PWT of 8.0 g. Dynamic allodynia was not detected in rats in either group from day 7 until day 70, and did not change from baseline values (Fig. 1B). Neither the contralateral paw of MIA-treated rats or the control group animals showed changes from baseline at any time point. A weight bearing deficit was detected in all MIA-treated rats at the time points tested, ranging from an approximate 50 g deficit at day 7 post-intraarticular injection to a maximum of approximately 100 g deficit on days 14 to 42 postintraarticular injection (Fig. 1C). The change in hind paw weight distribution over time closely follows that of punctate allodynia.
All animals showed a baseline weight bearing deficit of approximately 85 g. Morphine (0.3–3 mg/kg) produced a dose-dependent attenuation of the punctate allodynia in the MIA-treated rats with a minimum effective dose (MED) of 1 mg/kg (Fig. 2A). Tramadol dose-dependently (3–100 mg/kg) attenuated punctate allodynia with a MED of 10 mg/kg (Fig. 2B). Neither morphine nor tramadol increased PWT above baseline values in the contralateral paw (data not shown). Morphine 3 mg/kg reduced weight bearing deficit by 25 g (31% inhibition), 0.5 h post-administration (Fig. 2C). Tramadol 100 mg/kg reduced weight bearing deficit by 37 g (41% inhibition), 1 h post-administration (Fig. 2D). Rats treated with vehicle in each of the drug studies showed no change in PWT values or weight bearing deficit. The present study demonstrates pain endpoints are measurable in a chemically induced model of osteoarthritis. Punctate allodynia in the ipsilateral paw was detected in all MIA-treated rats throughout the study period, with the maximum effect seen between days 14 and 42 post-treatment.
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Dynamic allodynia was not observed in MIA-treated rats at any time point tested. Punctate and dynamic allodynia are transmitted by different sensory neurones, with punctate allodynia signalled by A␦ primary sensory neurones, and dynamic allodynia by A primary sensory neurones [8]. In humans, the origin of OA-associated joint pain is thought to be due to the stimulation of C-fibres and A␦ nerve endings in the synovium and surrounding joint structures, such as ligaments and muscles [3,4]. Thus, it may not be surprising we could not detect pain from a dynamic A-driven stimulus. Studies using thermal hyperalgesia as the behavioural endpoint may elucidate whether C-fibres play a role in the MIA model. Change in hind paw weight distribution closely followed the changes seen in punctate allodynia. Change in weight distribution in the MIA model has been reported previously [2] and was found to be a reliable and robust endpoint measure, a finding in agreement with the present study. However, to our knowledge there have been no studies published investigating punctate and dynamic allodynia in this model. Measurement of punctate allodynia is used routinely, for example, in neuropathic pain models [8] as it is rapid and technically straightforward. Indeed, von Frey filaments have been used clinically to assess mechanical sensation and pain thresholds in patients with chronic arthropathies [11]. This study measures allodynia in the skin overlying the knee and in the present study allodynia is measured in the foot after injection of MIA into the knee. However, referred pain in OA patients has also been reported [15]. In the Hendiani study [11], increased thresholds for innocuous mechanical sensation and decreased pain thresholds to mechanical von Frey stimulation in patients with OA were detected. Central sensitisation was suggested as an underlying mechanism to explain the development of allodynia. The introduction of MIA to the knee joint results in an acute inflammation [2] leading to the release of substance P, bradykinin, prostaglandins [19], etc. into the local area. The inflammatory response following intraarticular injection of MIA has largely resolved by day 7 and is not expected to play a role in mediating pain [2]. However, this inflammatory response can induce a sensitisation of peripheral receptors with changes in the response characteristics of primary afferent fibres [17] and lead to a C-fibre mediated decrease in response threshold [20] and an increased input to the spinal cord [6]. Extended activation of nociceptive pathways leading to moderate or severe pain can develop into chronic pain states. This phenomenon is termed chronic nociceptive pain. Hence, our studies with analgesics have been focussed on elucidating whether this model is useful as a model of chronic nociceptive pain. Nociceptive pain will often respond well to weak (e.g. codeine) or strong opioids, which are still the mainstay in the treatment of the more severe forms of chronic pain [17]. Morphine is a mu () opioid agonist and tramadol, a newer analgesic option for moderate to moderately severe pain, is a centrally acting agent with weak agonist activity at opioid receptors and an indirect action on monoaminergic systems. Both morphine and tramadol are clinically effective against
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nociceptive pain and in this study attenuated the punctate allodynia and the weight bearing deficit. Interestingly, both compounds fully reversed punctate allodynia, but weight bearing deficit was inhibited by a maximum of 40%. This may be an endpoint measure that allows the development of new treatments with improved efficacy but further studies are required to elucidate this. The MIA-induced model of OA is reproducible and mimics features associated with OA pain in humans. Both punctate allodynia and a weight bearing deficit are present in this model and these endpoint measures may be of use to differentiate between analgesic compounds. Additionally, analgesic drug studies indicate that this model may be useful for the investigation of chronic nociceptive pain. References [1] G.J. Bennett, Y.K. Xie, A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man, Pain 33 (1988) 87–107. [2] S.E. Bove, S.L. Calcaterra, R.M. Brooker, C.M. Huber, R.E. Guzman, P.L. Juneau, D.J. Schrier, K.S. Kilgore, Weight bearing as a measure of disease progression and efficacy of anti-inflammatory compounds in a model of monosodium iodoacetate-induced osteoarthritis, Osteoarthritis Cartilage 11 (2003) 821–830. [3] W.W. Buchanan, W.F. Kean, Osteoarthritis. I. Epidemiological risk factors and historical considerations, Inflammopharmacology 10 (2002) 5–21. [4] W.W. Buchanan, W.F. Kean, Osteoarthritis. II. Pathology and pathogenesis, Inflammopharmacology 10 (2002) 19–48. [5] P. Dalgin, The TPS-OA Study Group, Comparison of tramadol and ibuprofen for the chronic pain of osteoarthritis (abstract), Arthritis Rheum. 40 (1997) S86. [6] R. Dubner, Neuronal plasticity and pain following peripheral tissue inflammation or nerve injury, in: M. Bond, E. Charlton, C.J. Woolf (Eds.), Proceedings of the VIth World Congress on Pain, 1995, pp. 263–276. [7] J. Dunham, S. Hoedt-Schmidt, D.A. Kalbhen, Prolonged effect of iodoacetate on articular cartilage and its modification by an antirheumatic drug, Int. J. Exp. Pathol. 74 (1993) 283–289. [8] M.J. Field, S. Bramwell, J. Hughes, L. Singh, Detection of static and dynamic components of mechanical allodynia in rat models of neuropathic pain: are they signalled by distinct primary sensory neurones? Pain 83 (1999) 303–311. [9] B.E. Gencosmanoglu, M. Eryavuz, S. Dervisoglu, Effects of some nonsteroidal anti-inflammatory drugs on articular cartilage of rats in an experimental model of osteoarthritis, Res. Exp. Med. (Berl.) 200 (2001) 215–226. [10] C. Guingamp, P. Gegout-Pottie, L. Philippe, B. Terlain, P. Netter, P. Gillet, Mono-iodoacetate-induced experimental osteoarthritis: a dose–response study of loss of mobility, morphology, and biochemistry, Arthritis Rheum. 40 (1997) 1670–1679. [11] J.A. Hendiani, K.N. Westlund, N. Lawand, N. Goel, J. Lisse, T. McNearney, Mechanical sensation and pain thresholds in patients with chronic arthropathies, J. Pain 4 (2003) 203–211. [12] D. Holderbaum, T.M. Haqqi, R.W. Moskowitz, Genetics and osteoarthritis: exposing the iceberg, Arthritis Rheum. 42 (1999) 397–405. [13] M.J. Janusz, E.B. Hookfin, S.A. Heitmeyer, J.F. Woessner, A.J. Freemont, J.A. Hoyland, K.K. Brown, L.C. Hsieh, N.G. Almstead, B. De, M.G. Natchus, S. Pikul, Y.O. Taiwo, Moderation of iodoacetateinduced experimental osteoarthritis in rats by matrix metalloproteinase inhibitors, Osteoarthritis Cartilage 9 (2001) 751–760.
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[14] D.A. Kalbhen, Chemical model of osteoarthritis—a pharmacological evaluation, J. Rheumatol. 14 (1987) 130–131 (Spec No.). [15] W.F. Kean, R. Kean, W.W. Buchanan, Osteoarthritis: symptoms, signs and source of pain, Inflammopharmacology 12 (2004) 3–31. [16] V.C. Mow, L.A. Setton, F. Fuilak, A. Ratcliffe, Mechanical factors in articular cartilage and their role in osteoarthritis, in: K.E. Keuttner, V.M. Goldberg (Eds.), Osteoarthritic Disorders, American Academy of Orthopaedic Surgeons, Rosemont, IL, 1995, pp. 147–172. [17] S. Petersen-Felix, M. Curatolo, Neuroplasticity—an important factor in acute and chronic pain, Swiss Med Wkly. 132 (2002) 273–278.
[18] A.R. Poole, Imbalances of anabolism and catabolism of cartilage matrix components in osteoarthritis, in: K.E. Keuttner, V.M. Goldberg (Eds.), Osteoarthritic Disorders, American Academy of Orthopaedic Surgeons, Rosemont, IL, 1995, pp. 147–172. [19] H.P. Rang, S. Bevan, A. Dray, Chemical activation of nociceptive peripheral neurones, Br. Med. Bull. 47 (1991) 534–548. [20] C.J. Woolf, M.W. Salter, Neuronal plasticity: increasing the gain in pain, Science 288 (2000) 1765–1769. [21] M. Zimmerman, Ethical guidelines for investigations of experimental pain in conscious animals, Pain 16 (1983) 109–110.
The monosodium iodoacetate model of osteoarthritis: a model of chronic nociceptive pain in rats? Rachel Combe∗ , Steve Bramwell, Mark J. Field Pain Therapeutics, Pfizer Global Research and Development, Ramsgate Road, Sandwich, Kent CT139NJ, UK Received 22 July 2004; received in revised form 13 August 2004; accepted 13 August 2004
Abstract Osteoarthritis (OA) is a widespread condition affecting the elderly population. One of the most prominent features but least studied symptoms is chronic pain associated with OA. The study objective was to determine pain endpoints in rats with monosodium iodoacetate (MIA) induced OA, and to investigate the efficacy of common nociceptive agents. Sprague–Dawley rats received an intraarticular injection of either 25 l 80 mg/ml MIA or 25 l 0.9% sterile saline into the right knee joint. Changes in von Frey thresholds and latencies to stroking with a cotton bud (punctate and dynamic allodynia, respectively) were measured pre- and for up to 10 weeks post-intraarticular injection. Changes in hind paw weight distribution were also determined. Both punctate allodynia and a weight bearing deficit were observed in MIA-treated rats for up to 10 weeks. Interestingly, dynamic allodynia was not detected at any time point tested. Morphine (0.3–3 mg/kg, s.c.) and tramadol (3–100 mg/kg, p.o.) dose-dependently inhibited punctate allodynia and partially reversed weight bearing deficit. In conclusion, the MIA model of OA is reproducible and mimics OA pain in humans. Analgesic drug studies indicate this model may be useful for investigating chronic nociceptive pain. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Osteoarthritis; Punctate allodynia; Dynamic allodynia; Weight bearing; Nociceptive pain
Osteoarthritis (OA) is a chronic condition widespread in the elderly population. The majority of patients will experience chronic pain, which impacts significantly on their quality of life. Patients with OA have pain that typically worsens with weight bearing and activity, and also joint stiffness in the morning or after rest. The causes of OA have not been fully determined, however, biomechanical forces affecting the articular cartilage and subchondral bone, biochemical changes in the articular cartilage and synovial membrane, and genetic factors are thought to be of importance [16,18,12]. Currently, no disease-modifying drugs are available so the objective of pharmacological treatment has been aimed at reducing pain, maintaining and/or improving joint mobility and reducing functional impairment. Animal models have provided useful tools for investigating pain arising from other conditions,
∗
Corresponding author. Tel.: +44 1304 645535; fax: +44 1304 651817. E-mail address: [email protected] (R. Combe).
0304-3940/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2004.08.023
such as peripheral neuropathies. Examples include nerve ligation approaches in rats that model some aspects of neuropathic pain [1,8]. Interestingly, although animal models of osteoarthritis are widely used, they have been used mainly to study the pathophysiology and progression of joint damage with little characterisation of the associated pain [9,10,13]. One such model is the monosodium iodoacetate (MIA) induced arthritis model first described by Kalbhen some 20 years ago [14]. The structural integrity of articular cartilage relies on the normal functioning of chondrocytes. Local injection of MIA, an inhibitor of glycolysis, disrupts chondrocyte metabolism and produces cartilage degeneration. The histopathology of the degenerating joint is similar to that seen in the human condition [13]. Moreover, at the later stages of joint damage in the MIA model, exposed subchondral bone and damaged synovium is present and is associated with joint pain, as seen in humans [10]. Following intraarticular injection of MIA there is an initial inflammatory response [2]. This inflammation was characterised by Bove and
R. Combe et al. / Neuroscience Letters 370 (2004) 236–240
colleagues histologically as expansion of the synovial membrane by proteinaceous oedema fluid and fibrin with infiltrating macrophages, neutrophils, plasma cells and lymphocytes. By day 7, inflammation within the synovium and surrounding tissue has largely resolved and is not expected to play a role in mediating pain. However, the potential of this model to predict efficacy of antinociceptive agents in OA and its value as a general model of chronic nociceptive pain has yet to be determined. The objectives of this study were to establish measurable pain endpoints in rats with MIA-induced OA, and to assess the efficacy of morphine and tramadol, both of which are used to treat chronic nociceptive pain and have demonstrated clinical efficacy in this condition [5]. All experiments conformed to the ethical guidelines for investigation of experimental pain in conscious animals [21] and in full compliance with the UK Animals (Scientific Procedures) Act, 1986. Male Sprague–Dawley rats (125–175 g; Charles River, Kent, UK) were housed in groups of four under a 12 h light/dark cycle (lights on at 07:00 a.m.) with food and water ad libitum. Rats were anaesthetised with a 2% isofluorane O2 mixture and given a single intraarticular injection of monosodium iodoacetate (Sigma, Poole, UK) through the infrapatella ligament of the right knee [7]. MIA was dissolved in 0.9% sterile saline and administered in a volume of 25 l using a 26 gauge, 0.5 in. needle. Control animals were given a single intraarticular injection into the right knee of 25 l 0.9% sterile saline. Assessment of punctate and dynamic allodynia was performed as previously described by Field et al. [8]. Briefly, punctate allodynia was evaluated by application of von Frey hairs in ascending order of force to the plantar surface of the hind paws. Dynamic allodynia was assessed by lightly stroking the plantar surface of the hind paw with a cotton bud. Paw withdrawal thresholds (PWT) to von Frey hairs and withdrawal latencies to cotton bud stimulus were assessed in the same group of animals on various days post-intraarticular injection. The effect of joint damage on the weight distribution through the right (arthritic) and left (untreated) knee was assessed using an incapacitance tester (Linton Instrumentation, Norfolk, UK) [2]. Briefly, an incapacitance tester measures weight distribution on the two hind paws. The force exerted by each hind limb is measured in grams. The inhibitory effects of morphine and tramadol on punctate allodynia and weight bearing deficit were investigated. Compounds were administered 14 days post-intraarticular injection having established stable baseline PWT and weight bearing deficits prior to drug administration. Animals were administered (on separate test days) with either vehicle, morphine (0.3–3 mg/kg, s.c.) or tramadol (3–100 mg/kg, p.o.) and changes from baseline were assessed for up to 3 h. All experiments were performed by an observer blind to drug treatment. Morphine sulphate was obtained from Sigma and was administered s.c. in 0.9% saline. Tramadol hydrochloride was
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Fig. 1. Development of punctate (A) and dynamic (B) allodynia, and weight bearing deficit (C) following intraarticular injection of MIA or saline. Rats were injected with either 2 mg of MIA () or saline () in the right knee. (A) Baseline (BL) paw withdrawal thresholds (PWT) were determined in both hind paws for all animals prior to injection. PWT to von Frey hairs were assessed on various days post-injection. Results are expressed as median force (g) required to induce a paw withdrawal in 10 animals per group (vertical bars represent first and third quartiles). ∗ P < 0.05, ∗∗ P < 0.01, ∗∗∗ P < 0.001 significantly different (Mann–Whitney U test) from saline-treated group at each time point. (B) Baseline (BL) paw withdrawal latencies (PWL) to cotton bud stimulus were determined for both hind paws for all animals prior to injection. Results are expressed as mean PWL (s) in 10 animals per group (vertical bars represent ±S.E.M.). ∗ P < 0.05, ∗∗ P < 0.01, ∗∗∗ P < 0.001 significantly different (one-way ANOVA followed by Dunnett’s t test) from saline-treated group. (C) Baseline (BL) hind paw weight distribution was determined for all animals prior to injection. Changes in hind paw weight distribution were assessed on various days post-injection. Results are expressed as mean change in weight distribution (contralateral–ipsilateral) (g) in 10 animals per group (vertical bars represent ±S.E.M.). ∗ P < 0.05, ∗∗ P < 0.01, ∗∗∗ P < 0.001 significantly different (one-way ANOVA followed by Dunnett’s t test) from saline-treated group.
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Fig. 2. Effects of morphine (A, C) and tramadol (B, D) on punctate allodynia and change in hind paw weight distribution following intraarticular injection MIA. Morphine was subcutaneously administered and tramadol was orally administered 30 min prior to the measurement of pain parameters on separate test days Rats were injected with 2 mg of MIA into the right knee 2 weeks previously. Baseline (BL) paw withdrawal thresholds (PWT) or hind paw weight distribution was determined for all animals prior to administration of drug. Punctate allodynia data expressed as median force (g) required to induce a paw withdrawal in 10 animals per group (vertical bars represent first and third quartiles) and ∗ P < 0.05, ∗∗ P < 0.01, ∗∗∗ P < 0.001 significantly different (Mann–Whitney U test) from vehicle-treated group at each time point. The dotted line represents the contralateral PWT. Changes in hind paw weight distribution are expressed as mean change in weight distribution (ipsilateral–contralateral) (g) in 10 animals per group (vertical bars represent ±S.E.M.) and ∗ P < 0.05, ∗∗ P < 0.01, ∗∗∗ P < 0.001 significantly different (one-way ANOVA followed by Dunnett’s t test) from vehicle-treated group. The dashed line represents weight distribution for rats treated with intraarticular saline.
obtained from Sigma and was administered p.o. in Millipore filtered water. Drug administration was in a volume of 1 ml/kg. Punctate allodynia was detected in all MIA-treated rats from day 7 (first test day) until day 70, with all animals demonstrating a PWT to the previously innocuous 4.0 g force or below (Fig. 1A) as compared to the normal PWT of 8.0 g. Dynamic allodynia was not detected in rats in either group from day 7 until day 70, and did not change from baseline values (Fig. 1B). Neither the contralateral paw of MIA-treated rats or the control group animals showed changes from baseline at any time point. A weight bearing deficit was detected in all MIA-treated rats at the time points tested, ranging from an approximate 50 g deficit at day 7 post-intraarticular injection to a maximum of approximately 100 g deficit on days 14 to 42 postintraarticular injection (Fig. 1C). The change in hind paw weight distribution over time closely follows that of punctate allodynia.
All animals showed a baseline weight bearing deficit of approximately 85 g. Morphine (0.3–3 mg/kg) produced a dose-dependent attenuation of the punctate allodynia in the MIA-treated rats with a minimum effective dose (MED) of 1 mg/kg (Fig. 2A). Tramadol dose-dependently (3–100 mg/kg) attenuated punctate allodynia with a MED of 10 mg/kg (Fig. 2B). Neither morphine nor tramadol increased PWT above baseline values in the contralateral paw (data not shown). Morphine 3 mg/kg reduced weight bearing deficit by 25 g (31% inhibition), 0.5 h post-administration (Fig. 2C). Tramadol 100 mg/kg reduced weight bearing deficit by 37 g (41% inhibition), 1 h post-administration (Fig. 2D). Rats treated with vehicle in each of the drug studies showed no change in PWT values or weight bearing deficit. The present study demonstrates pain endpoints are measurable in a chemically induced model of osteoarthritis. Punctate allodynia in the ipsilateral paw was detected in all MIA-treated rats throughout the study period, with the maximum effect seen between days 14 and 42 post-treatment.
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Dynamic allodynia was not observed in MIA-treated rats at any time point tested. Punctate and dynamic allodynia are transmitted by different sensory neurones, with punctate allodynia signalled by A␦ primary sensory neurones, and dynamic allodynia by A primary sensory neurones [8]. In humans, the origin of OA-associated joint pain is thought to be due to the stimulation of C-fibres and A␦ nerve endings in the synovium and surrounding joint structures, such as ligaments and muscles [3,4]. Thus, it may not be surprising we could not detect pain from a dynamic A-driven stimulus. Studies using thermal hyperalgesia as the behavioural endpoint may elucidate whether C-fibres play a role in the MIA model. Change in hind paw weight distribution closely followed the changes seen in punctate allodynia. Change in weight distribution in the MIA model has been reported previously [2] and was found to be a reliable and robust endpoint measure, a finding in agreement with the present study. However, to our knowledge there have been no studies published investigating punctate and dynamic allodynia in this model. Measurement of punctate allodynia is used routinely, for example, in neuropathic pain models [8] as it is rapid and technically straightforward. Indeed, von Frey filaments have been used clinically to assess mechanical sensation and pain thresholds in patients with chronic arthropathies [11]. This study measures allodynia in the skin overlying the knee and in the present study allodynia is measured in the foot after injection of MIA into the knee. However, referred pain in OA patients has also been reported [15]. In the Hendiani study [11], increased thresholds for innocuous mechanical sensation and decreased pain thresholds to mechanical von Frey stimulation in patients with OA were detected. Central sensitisation was suggested as an underlying mechanism to explain the development of allodynia. The introduction of MIA to the knee joint results in an acute inflammation [2] leading to the release of substance P, bradykinin, prostaglandins [19], etc. into the local area. The inflammatory response following intraarticular injection of MIA has largely resolved by day 7 and is not expected to play a role in mediating pain [2]. However, this inflammatory response can induce a sensitisation of peripheral receptors with changes in the response characteristics of primary afferent fibres [17] and lead to a C-fibre mediated decrease in response threshold [20] and an increased input to the spinal cord [6]. Extended activation of nociceptive pathways leading to moderate or severe pain can develop into chronic pain states. This phenomenon is termed chronic nociceptive pain. Hence, our studies with analgesics have been focussed on elucidating whether this model is useful as a model of chronic nociceptive pain. Nociceptive pain will often respond well to weak (e.g. codeine) or strong opioids, which are still the mainstay in the treatment of the more severe forms of chronic pain [17]. Morphine is a mu () opioid agonist and tramadol, a newer analgesic option for moderate to moderately severe pain, is a centrally acting agent with weak agonist activity at opioid receptors and an indirect action on monoaminergic systems. Both morphine and tramadol are clinically effective against
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nociceptive pain and in this study attenuated the punctate allodynia and the weight bearing deficit. Interestingly, both compounds fully reversed punctate allodynia, but weight bearing deficit was inhibited by a maximum of 40%. This may be an endpoint measure that allows the development of new treatments with improved efficacy but further studies are required to elucidate this. The MIA-induced model of OA is reproducible and mimics features associated with OA pain in humans. Both punctate allodynia and a weight bearing deficit are present in this model and these endpoint measures may be of use to differentiate between analgesic compounds. Additionally, analgesic drug studies indicate that this model may be useful for the investigation of chronic nociceptive pain. References [1] G.J. Bennett, Y.K. Xie, A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man, Pain 33 (1988) 87–107. [2] S.E. Bove, S.L. Calcaterra, R.M. Brooker, C.M. Huber, R.E. Guzman, P.L. Juneau, D.J. Schrier, K.S. Kilgore, Weight bearing as a measure of disease progression and efficacy of anti-inflammatory compounds in a model of monosodium iodoacetate-induced osteoarthritis, Osteoarthritis Cartilage 11 (2003) 821–830. [3] W.W. Buchanan, W.F. Kean, Osteoarthritis. I. Epidemiological risk factors and historical considerations, Inflammopharmacology 10 (2002) 5–21. [4] W.W. Buchanan, W.F. Kean, Osteoarthritis. II. Pathology and pathogenesis, Inflammopharmacology 10 (2002) 19–48. [5] P. Dalgin, The TPS-OA Study Group, Comparison of tramadol and ibuprofen for the chronic pain of osteoarthritis (abstract), Arthritis Rheum. 40 (1997) S86. [6] R. Dubner, Neuronal plasticity and pain following peripheral tissue inflammation or nerve injury, in: M. Bond, E. Charlton, C.J. Woolf (Eds.), Proceedings of the VIth World Congress on Pain, 1995, pp. 263–276. [7] J. Dunham, S. Hoedt-Schmidt, D.A. Kalbhen, Prolonged effect of iodoacetate on articular cartilage and its modification by an antirheumatic drug, Int. J. Exp. Pathol. 74 (1993) 283–289. [8] M.J. Field, S. Bramwell, J. Hughes, L. Singh, Detection of static and dynamic components of mechanical allodynia in rat models of neuropathic pain: are they signalled by distinct primary sensory neurones? Pain 83 (1999) 303–311. [9] B.E. Gencosmanoglu, M. Eryavuz, S. Dervisoglu, Effects of some nonsteroidal anti-inflammatory drugs on articular cartilage of rats in an experimental model of osteoarthritis, Res. Exp. Med. (Berl.) 200 (2001) 215–226. [10] C. Guingamp, P. Gegout-Pottie, L. Philippe, B. Terlain, P. Netter, P. Gillet, Mono-iodoacetate-induced experimental osteoarthritis: a dose–response study of loss of mobility, morphology, and biochemistry, Arthritis Rheum. 40 (1997) 1670–1679. [11] J.A. Hendiani, K.N. Westlund, N. Lawand, N. Goel, J. Lisse, T. McNearney, Mechanical sensation and pain thresholds in patients with chronic arthropathies, J. Pain 4 (2003) 203–211. [12] D. Holderbaum, T.M. Haqqi, R.W. Moskowitz, Genetics and osteoarthritis: exposing the iceberg, Arthritis Rheum. 42 (1999) 397–405. [13] M.J. Janusz, E.B. Hookfin, S.A. Heitmeyer, J.F. Woessner, A.J. Freemont, J.A. Hoyland, K.K. Brown, L.C. Hsieh, N.G. Almstead, B. De, M.G. Natchus, S. Pikul, Y.O. Taiwo, Moderation of iodoacetateinduced experimental osteoarthritis in rats by matrix metalloproteinase inhibitors, Osteoarthritis Cartilage 9 (2001) 751–760.
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