Antinociceptive activity of filenadol on inflammatory pain

Life Sciences, Vol. 57, No. 14, pp. PL 181-186, 1995 Copyright 8 1995 Ekevier Science Inc. Printed in the USA. All rights reserved O&24-3205/95 $9.50 + .oO

Pergamon

0024-3205(95)020984

PHARMACOLOGY LElTERS Accelerated Communication ANTINOCICEPTIVE

ACTIVITY

OF FILENADOL ON INFLAMMATORY

PAIN

G. Bustos, M.L. Ferrandiz, M.J. Sanz, M. Paya and M. J. Alcaraz Department

of Pharmacology, University of Valencia, Spain.

(SubmittedJune 7, 1995; accepted June 16, 1995; received in final form July 20, 1995) The novel analgesic filenadol (d,l -erythro-I-(3’,4’-methylenedioxyphenyl)-lAbstract. morpholinopropan-2-01) inhibited phenyl-p-benzoquinone-induced writhing in mice with ID60 values of 68.8 (p.o.1, 1.67 (i.v.1 and 0.48 (i.c.v.1 mg/kg. Hyperalgesia induced by arachidonic acid, PGE2 or LTB4 in this test was also decreased by filenadol (ID50= 24.4, 3.7 and 50.1 mgikg p.o., respectively). This compound was effective on PGE2, LTB4, bradykinin, PAF or IL-18-induced decrease in pain threshold in the rat paw pressure model and almost totally suppressed the writhing induced by zymosan in mice, while peritoneal % and only at 100 mg/kg significant production of 6-ketoPGF1 o was inhibited by 48.5-62 inhibition of LTC4 was achieved. The late phase of formalin-induced pain response in mice was prevented by filenadol, without affecting the oedema. Filenadol is an antinociceptive agent that reduces the hyperalgesic effects of inflammatory mediators besides inhibiting partially the synthesis of eicosanoids. Key Word: filenadol, analgesic, eiunanoids, phenyl-p-benzquinone, zymosan Introduction A major objective in pain therapy is to develop analgesics possessing the necessary efficacy in a variety of clinical situations but devoid of adverse side effects which can limit their utility. Filenadol therapeutic (d,l -erythro-I-(3’,4’-methylenedioxyphenyl)-lmorpholinopropan-2-01) is a novel analgesic drug able to inhibit the nociceptive responses induced by chemical, mechanical and thermal stimuli in rodents, with different potency (1,2). This compound also exerts weak anti-pyretic and anti-inflammatory actions in different experimental models and its analgesic activity has also been confirmed in clinical trials suggesting a favorable side-effect profile (2-4). To obtain information about the mode of antinociceptive action of filenadol on inflammatory pain we have studied its influence on the writhing response to intraperitoneal administration of chemicals and inflammatory mediators as well as on the pain induced by subplantar injection of formalin and the hyperalgesic response to pressure after injection of different inflammatory agents. In the present study we have also characterized the differential activity of filenadol on arachidonic acid metabolism and eicosanoid-induced hyperalgesia.

Corresponding Author: Prof. M.J. Alcaraz. Department of Pharmacology, Pharmacy. Avda. And&s Vicent Estelles s/n, 46100 Burjassot, Valencia, Spain.

Faculty

of

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An~inociceptive Activity of Filenadol

Materials

Vol. 57, No. 14, 1995

and Methods

Phenyl-p-benzoquinone-induced writhing. Animals were maintained under standard environmental conditions (room temperature: 20-22°C; relative humidity: 55-60 %, lightdark rhythm: 12/l 2 h) with free access to standard pellet food and drinking water but 16 hours before the experiments they were deprived of food. Groups of 6 female, 24-29 g, albino Swiss CD-l mice were injected intraperitoneally with 0.2 ml of a 0.02 % w/v solution of phenyl-p-benzoquinone in ethanol/distilled water: 5/95 v/v. The irritant induced a series of abdominal constrictions and hind limb extensions which were counted for a 20 minutes period commencing immediately after irritant injection. Vehicle or drugs were administered orally 1 hour prior to phenyl-p-benzoquinone in a volume of 0.5 ml. In other sets of experiments i.v. (0.2 ml) and i.c.v. (5~1) administrations were made followed 5 minutes later by injection of phenyl-p-benzoquinone. Hyperalgesia experiments in mice: 30 minutes after vehicle or drugs administration, 100 ng/kg PGE2, 10 ng/kg arachidonic acid or 100 nglkg LTB4 was injected intraperitoneally in a volume of 0.2 ml and 30 minutes later 0.2 ml of 0.01 % phenyl-p-benzoquinone was injected by the same route. The pain response was assessed as above. Rat paw pressure hyperalgesia. Male Sprague Dawley rats weighing 125-l 50 g were starved for 16 h with free access to water. Test compounds or vehicle were administered orally (1 ml) and 1 hour later hyperalgesia was induced by injection into the hind paw of ILlp (0.1 I.U.), PGE2 (100 ng), LTB4 (20 ng), bradykinin (20 ng) or PAF (20 ng), in a volume of 10 ~1. At specified time intervals later (20 minutes for bradykinin and PAF, 1 hour for PGE2 and LTB4 and 3 hours for IL-lp), the pressure was applied to the dorsum of the paw linearly with time using an Analgesy-meter (Ugo Basile, Milan, Italy) until the animal presented a squeak reaction. Results were expressed as the percentage decrease in the nociceptive threshold from the baseline value (before treatment). Zymosan peritonitis. The effect of filenadol on eicosanoid generation was evaluated in the mouse zymosan peritonitis test described by Doherty et al. (5). Test compounds or vehicle were administered orally 1 hour before i.p. injection of zymosan. Radioimmunoassays for 6keto-PGF1, and LTC4 were performed in peritoneal fluid. Formalin-induced pain. The procedure was that described by Hunskaar and Hole (6). Male, 25 to 30 g, Swiss albino CD-l mice were injected subplantar in one hindpaw with formalin (2.5 % v/v in phosphate buffered saline pH 7.3, 20 /.~l) and the duration of paw licking monitored in the periods O-5 minutes (early phase) and 15-30 minutes (late phase). At the end of each phase paw volumes were measured using a plethysmometer (Ugo Basile, Milan, Italy). Test compounds were administered i.p. 30 minutes before formalin injection. Chemicals. Filenadol hydrochloride was synthesized in Ferrer lnternacional (Barcelona, Spain) laboratories. Other materials were purchased from Sigma Chemical Co. (St. Louis, MO, USA). Radioimmunoassay kits for 6-keto-PGFI a. and LTC4 were from ITISA, DuPont, Madrid, Spain. Data analysis. Results were expressed as means+S.E.M. Percentages of inhibition were calculated with respect to the control group (vehicle). Antinociceptive potency was assessed in terms of the dose inhibiting the pain response by 50% (ID501 with its 95% confidence intervals (Cl) as determined by linear regression analysis using the computer program Inplot4. Treatment groups were compared with controls by analysis of variance followed by Dunnett’s test.

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Antinociceptive Activity of Filenadol

Vol. 57, No. 14, 1995

Effects of filenadol, indomethacin

Table I and codeine on phenyl-p-benzoquinone-induced

writhing.

Drug

PBQ(0.02%) ID50 95% Cl (mg/kg)

PBQ(O.01 O/6)+ PGE2 PBQ(O.01 %I + LTB4 PBCXO.01 %I + AA ID50 95% Cl ID50 95% Cl IDa 95% Cl (mg/kg) (mglkg) (mgkg)

F I C

68.8154.2-95.7) 0.1710.05-0.29~ 2.3(1.1-5.2)

3.7(2.5-4.8) 0.25(0.18-0.32) >5

F = Filenadol, acid.

= Indomethacin,

C=

50.1(42.9-56.2) 0.22(0.17-0.25) >5 PBQ

24.4(12.6-32.8) 0.05(0.01-0.10) >5

phenyl-p-benzoquinone;

AA =arachidonic

Results Administration of phenyl-p-benzoquinone to mice in the control group resulted in 20.5 + 1.8 (n = 18) writhes at a concentration of irritant of 0.02%. The effect of filenadol and reference compounds on oral administration against phenyl-p-benzoquinone-induced writhing is shown in table I. In this model filenadol displayed dose-related inhibitory effects, its potency being lower than that of indomethacin or codeine. After i.v. or i.c.v. administration filenadol showed ID50 values of 1.67 (0.19-5.0) and 0.48 (0.29-l .36) mg/kg, respectively. At the concentration of 0.01% phenyl-p-benzoquinone induced 8.1 f 1.6 (n = 18) writhes in the control group. This concentration was chosen for the experiments intended to assess the effects of filenadol on the hyperalgesia caused by inflammatory mediators. In the experimental models used for hyperalgesic studies inflammatory mediators did not induced pain to a significant extent when administered alone. Pretreatment with PGE2, LTB4 or arachidonic acid determined a number of writhes after i.p. injection of 0.01% phenyl-p-benzoquinone of 17.1 f 2.7 (n = 121, 17.8 + 2.2 (n = 12) and 18.1 + 2.5 (n = 121, respectively. Against PGE2-induced hyperalgesia in filenadol mice, exhibited potent antinociceptive effects and with a lower potency, it also inhibited arachidonic acid- and LTB4-induced hyperalgesia. In contrast, indomethacin showed a high potency on arachidonic acid-induced hyperalgesia while doses necessary to inhibit writhing in PGE2 or LTB4-induced hyperalgesia were similar to those active against phenyl-p-benzoquinone alone. Codeine up to 5 mglkg (the highest dose used in phenyl-p-benzoquinone-induced writhing) failed to significantly inhibit the pain response in these hyperalgesic experiments. In the rat paw pressure hyperalgesia, responses of animals treated with indomethacin (5 mg/kg) did not differ from those of vehicle-treated animals (control group) in PGE2, IL-16, LTB4, or PAF-induced hyperalgesia, but significantly inhibited bradykinininduced hyperalgesia (figure 1). Filenadol administered orally at 80 mg/kg exhibited significant antihyperalgesic effects for all the inflammatory mediators used.

response, higher generation suppressed

the mouse peritonitis model significantly a smaller on the of 6-keto-PGFI, (100 mg/kg, filenadol was to achieve (40.0+%, P
inhibited writhing 2). Only the inhibition of mglkg, p.0.)

PL-184

Vol. 57, No. 14,1995

Antinociceptive Activity of Filenadol

LTB4

PGE2

IL-q3

BK

PAF

Fig.1 Effect of filenadol and indomethacin on hyperalgesia induced by different mediators in the rat paw pressure test. Control: solid colums, Filenadol (80 mglkg, p.0.): open columns and lndomethacin (5mglkg. p.o.1: hatched columns. Results show means + S.E.M. from 6-l 2 animals. * PCO.05, ** PCO.01. Formalin induces a nociceptive response in the mouse paw involving an early phase lasting the first 5 minutes and a late phase lasting from 20 to 30 minutes after the injection (6). Treatment with codeine (5 mg/kg i.p.1 reduced the duration of licking of the hind paw during both the early and late phase reponses following injection of formalin (table II), whereas indomethacin (5 mg/kg i.p.) only inhibited the late phase besides the inhibition of oedema. Filenadol dose-dependently inhibited the late phase of the nociceptive response to formalin in mice (table II) but did not have any effect on oedema (data not shown).

Antinociceptive

Table II effects of filenadol and reference compounds in the formalin test EARLY Dose fmglkg)

CONTROL FILENADOL

CODEINE INDOMETHACIN

30 10 5 5 5

Results show means+S.E.M.

Licking (s) 56.8k4.9 40.2+8.4 41.3k8.4 48.7k4.5 28.2+5.1** 41 .Of4.7 from 6 animals.

PHASE Inhibition (%I ---30 27 14 50 28 * P ~0.05,

LATE PHASE Licking (s) 118.3k13.1 28.8+5.2** 49.2f16.0** 102.2+19.9 53.6+11.5* 57.8f13.7** ** P ~0.01.

Inhibition (%I ---76 58 13 55 51

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Antinociceptive Activity of Pilenadol

Vol. 57, No. 14, 1995

Discussion Eicosanoids sensitize nociceptors to other stimuli present in inflammatory lesions, (7). lntraperitoneal administration of PGE2 thus leading to peripheral hyperalgesia potentiates phenyl-p-benzoquinone-induced writhing, a hyperalgesic response which is not controlled by non-steroid anti-inflammatory drugs (8).

b)

a) I

6.25

12.5

25

601

-

50

Filenadoi (rnglkg)

Effect of filenadol on zymosan-induced peritoneal fluid. Results show means*

Fifenadol (rnglkg)

Fig. 2 peritonitis. a) Writhing and b) 6-Keto-PGFI, level in S.E.M. from 6-22 animals. * P
In our study, indomethacin was more effective on arachidonic acid-induced hyperalgesia than on PGE2-induced hyperalgesia in mice and without effect on PGE2induced hyperalgesia in the rat paw pressure test, indicating a preferential effect on prostaglandin synthesis. Nevertheless, filenadol inhibited PGE2-induced hyperalgesia in mice and rats. Inhibitors of cycle-oxygenase activity like indomethacin are inactive on LTB4 hyperalgesia (9), which has been confirmed in our study. Corroboration of the effect of filenadol on the hyperalgesia induced by eicosanoids in mice was accomplished by injecting these mediators into the paw of filenadol-treated rats to measure pain threshold to pressure. In the zymosan-induced writhing test cycle-oxygenase inhibitors exert their analgesic action by inhibiting PG12 formation (5). Nevertheless the data presented here are consistent with the suggestion that inhibition by filenadol of arachidonate metabolism is responsible for only a part of its antinociceptive activity in this experimental model since it was more effective on writhing than on arachidonic acid metabolism. On the other hand, the lower ability of filenadol to inhibit prostaglandin synthesis, as compared with non-steroid antiinflammatory drugs could result in a reduced potential of damaging effects at gastrointestinal level. In fact, previous studies in rats have demonstrated the lack of irritant gastrointestinal effects by filenadol at 140-470 mg/kg p.o. (2).

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Antinociceptive Activity of Filenadol

Vol. 57, No. 14, 1995

Filenadol has weak anti-pyretic and anti-inflammatory activities (2). In fact, it was unable to inhibit formalin-induced oedema at doses that exerted analgesic effects on the late phase, suggesting that the antinociception is not likely due to an anti-inflammatory action of filenadol. This compound was active in antinociception tests sensitive to nonsteroid anti-inflammatory drugs and reduced partially the synthesis of eicosanoids. In addition, filenadol inhibited the nociceptive action of eicosanoids and other mediators like bradykinin, PAF or IL-18 and it is interesting to note that the effective doses used in our study are within the range of therapeutic doses used in man (3,4). Acknowledaements G. Bustos thanks

Ferrer International,

Barcelona,

Spain, for financial

support.

References 1. E. FORNE, R. FOGUET, A. SACRISTAN AND J.A. ORTli!, Spanish patent 502470 (1982). 2. Anonymous, Drugs of the Future 11 1037-l 038 (1986). 3. F. ATERO, B. MARTI’NEZ, C. PASCUAL, J.M. PARAMO, R. RODRIGUEZ, M. BATURONE, J. TORRES, R. MONFORT AND M. MARQUEZ, Proceedings of the “XIII Reunidn National de la Sociedad Espairola de Farmacologia” Murcia, Spain C-101 (1988). 4. R. LLOMBART, J.L. LLOMBART, R. COLOMINA, J. CASAFONT AND J. VERGES, Proceedings of the “XIII Reunion National de la Sociedad Espafiola de Farmacologia” Murcia, Spain C-l 02 (I 988). 5. N.S. DOHERTY, T.H. BEAVER, K.Y. CHAN, J.E. COUTANT AND G.L. WESTRICH, Br. J. Pharmacol. 91 39-47 (I 987). 6. S. HUNSKAAR AND K. HOLE, Pain 30 103-l 14 (I 987). 7. H.P. RANG, S. BEVAN AND A. DRAY, Br. Med. Bull. 47 534-548 (1991). 8. G.W.L. JAMES AND M.K. CHURCH, Arzneim. -Forsch. 28(1) 804-807 (1978). 9. J.D. LEVINE, W. LAU, G. KWIAT AND E.J. GOETZL, Science 225 743-745 (1984).