Distribution and regulation of cyclooxygenase-2 in carrageenan-induced inflammation

1 We characterized the regulation of cyclooxygenase-2 (COX-2) at the mRNA, protein and mediator level in two rat models of acute inflammation, carrageenan-induced paw oedema and mechanical hyperalgesia. 2 Carrageenan was injected in the hind paw of rat at low (paw oedema) and high doses (hyperalgesia). COX-2 and prostaglandin E2 (PGE2) levels were measured by RT-PCR and immunological assays. We also determined the distribution of COX-2 by immunohistochemistry. 3 The injection of carrageenan produced a significant and parallel induction of both COX-2 and PGE2. This induction was significantly higher in hyperalgesia than in paw oedema. This was probably due to the 9 fold higher concentration of carrageenan used to provoke hyperalgesia. 4 Immunohistochemical examination showed COX-2 immunoreactivity in the epidermis, skeletal muscle and inflammatory cells of rats experiencing hyperalgesia. In paw oedema however, only the epidermis showed positive COX-2 immunoreactivity. 5 Pretreatment with indomethacin completely abolished the induction of COX-2 in paw oedema but not in hyperalgesia. 6 These results suggest that multiple mechanisms regulate COX-2 induction especially in the more severe model. In carrageenan-induced paw oedema, prostanoid production have been linked through the expression of the COX-2 gene which suggest the presence of a positive feedback loop mechanism.     

Carrageenan-induced mouse paw oedema is biphasic, age-weight dependent and displays differential nitric oxide cyclooxygenase-2 expression

Injection of carrageenan 1% (50 microl) in the mouse paw causes a biphasic response: an early inflammatory response that lasts 6 h and a second late response that peaks at 72 h, declining at 96 h. Only mice 7- or 8-week old, weighing 32-34 g, displayed a consistent response in both phases. In 8-week-old mice, myeloperoxidase (MPO) levels are significantly elevated in the early phase at 6 h and reach their maximum at 24 h to decline to basal value at 48 h. Nitrate+nitrite (NO(x)) levels in the paw are maximal after 2 h and slowly decline thereafter in contrast to prostaglandin E(2) levels that peak in the second phase at the 72 h point. Western blot analysis showed that inducible nitric oxide synthase (iNOS) is detectable at 6 h and cyclooxygenase 2 (COX-2) at 24 h point, respectively. Analysis of endothelial nitric oxide synthase (eNOS), iNOS and COX-2 expression at 6 and 24 h in 3-8-week-old mice demonstrated that both eNOS and iNOS expressions are dependent upon the age-weight of mice, as opposite to COX-2 that is present only in the second phase of the oedema and is not linked to mouse age-weight. Subplantar injection of carrageenan to C57BL/6J causes a biphasic oedema that is significantly reduced by about 20% when compared to CD1 mice. Interestingly, in these mice, iNOS expression is absent up to 6 h, as opposite to CD1, and becomes detectable at the 24 h point. Cyclooxygenase (COX-1) expression is upregulated between 4 and 24 h after carrageenan injection, whereas in CD1 mice COX-1 remains unchanged after irritant agent injection. MPO levels are maximal at the 24 h point and they are significantly lower, at 6 h point, than MPO levels detected in CD1 mice. In conclusion, mouse paw oedema is biphasic and age-weight dependent. The present results are the first report on the differential expressions of eNOS, iNOS, COX-1 and COX-2 in response to carrageenan injection in the two phases of the mouse paw oedema.     

Studies on the anti-inflammatory and anti-nociceptive effects of melatonin in the rat.

The present study aimed to evaluate the anti-inflammatory and anti-nociceptive effects of melatonin in the rat. Acute inflammation was induced by sub-plantar injection of carrageenan (1%) in the rat hind paw. The rats received vehicle or drug 30 min before carrageenan administration and were evaluated for paw oedema at 1, 2, 3, and 4 h post-carrageenan. The induced inflammation and the formation of oedema were determined by measurement of the paw thickness. Nociception was tested by determining vocalization following electrical stimulation of the tail. Given intraperitoneally (i.p.) 30 min before carrageenan, melatonin caused significant and a dose-dependent reduction of hind paw swelling induced by carrageenan. At doses of 0.5 and 1 mg kg(-1), melatonin inhibited the carrageenan-induced oedema by 20.5 and 29.6% versus control values at 4 h post-carrageenan, respectively. Melatonin (0.5 and 1 mg kg(-1), i.p.) 30 min beforehand displayed anti-nociceptive effect in the electric stimulation of the rat tail test, increasing nociceptive thresholds to electrically-induced pain at 4 h post-treatment by 29.6 and 39.5%, respectively. Melatonin given simultaneously with the non-selective COX-1 and COX-2 inhibitor indomethacin (5 mg kg(-1), i.p.) 30 min prior to carrageenan, enhanced the anti-inflammatory effect of the latter in the carrageenan-induced paw oedema model by 23%. Melatonin (0.5 mg kg(-1), i.p.) increased the anti-nociceptive effect of indomethacin (5 mg kg(-1), i.p.). Meanwhile, the anti-inflammatory and anti-nociceptive effect of the highly selective COX-2 inhibitor rofecoxib (2.25 mg kg(-1), i.p.) was only slightly increased by melatonin administration at 0.5 mg kg(-1). Melatonin enhanced the anti-inflammatory effect of cysteamine (300 mg kg(-1), s.c.) in the carrageenan-induced paw oedema. Melatonin (20 and 40 microg per paw) given prior to carrageenan into the rat hind paw was devoid of anti-inflammatory effect. These results indicate that melatonin possesses anti-inflammatory and anti-nociceptive properties in the rat and enhance those of indomethacin. This effect is likely to be centrally mediated.     

Inducible nitric oxide synthase and cyclooxygenase-2 participate in anti-inflammatory and analgesic effects of the natural marine compound lemnalol from Formosan soft coral Lemnalia cervicorni

Lemnalol (8-isopropyl-5-methyl-4-methylene-decahydro-1,5-cyclo-naphthalen-3-ol) is a natural compound isolated from the marine soft coral Lemnalia cervicorni. In the present study, the anti-inflammatory and anti-nociceptive properties of lemnalol were investigated in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells and carrageenan-injected rats, respectively. Our results demonstrate that lemnalol significantly inhibited the expression of the pro-inflammatory proteins, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), in LPS-stimulated RAW 264.7 cells. An in vivo inflammation model was induced by intraplantar injection of carrageenan into rat hind paws. An intramuscular injection of lemnalol (15 mg/kg) 10 min before carrageenan injection resulted in significant inhibition of carrageenan-induced rat paw edema and thermal hyperalgesia behavior. Western blot experiments revealed that the carrageenan-induced expression of iNOS and COX-2 in paw tissue was significantly down-regulated by lemnalol. Moreover, post-intrathecal injection of lemnalol produced a dose-dependent anti-nociceptive effect in carrageenan-injected rats (1 and 5 microg). The present results indicate that the marine-derived compound lemnalol had anti-inflammatory and analgesic effects in LPS-stimulated RAW 264.7 cells and carrageenan-injected rats, respectively. In addition, inhibition of elevated iNOS and COX-2 protein expression as well as neurophil infiltration of carrageenan-injected paws may be involved in the beneficial effects of lemnalol.     

Effects of valeryl salicylate, a COX-1 inhibitor, on models of acute inflammation in mice.

The effect of valeryl salicylate (VS), an inhibitor of cyclooxygenase-1 (COX-1), was evaluated in arachidonic acid or croton oil-induced ear oedema and carrageenan-induced paw oedema in mice. Ear oedema was induced by topical administration of arachidonic acid (2mg per ear; 20 microliters) or croton oil (1mg per ear; 20 microliters) to the inner surface of the left ear and the change in the ear's thickness was measured with a precision micrometer (Fisher, USA). VS significantly inhibited the arachidonic acid ear oedema after lh at doses of 1.5-45 micrograms per ear; however, only at the dose of 45 micrograms per ear was it able to significantly reduce the croton oil-induced oedema at 6h. Paw oedema was induced by the injection of 25 microliters of 1% carrageenan into the plantar aponeurosis of the right hind paw. The oedema was evaluated at 0.5, 1, 2, 4, 24, 48 and 72h. Previously in our experiments, we observed two peaks in paw oedema formation: one at 2h, in the early phase (0-4h), and the other, occurring at 48h after carrageenan injection, in the late phase (24-72h). The pre-treatment with VS significantly reduced the paw oedema at 2h, the same effect observed with celecoxib and indomethacin treatments. At 24h, VS did not inhibit oedema but significantly increased it mainly at 48h after carrageenan injection. These results showed that VS was pharmacologically active in these models and suggest that COX-1 may participate in the early and late phases of inflammation in the models studied.     

Nitric oxide: a key mediator in the early and late phase of carrageenan-induced rat paw inflammation.

1 The role of nitric oxide (NO) derived from constitutive and inducible nitric oxide synthase (cNOS and iNOS) and its relationship to oxygen-derived free radicals and prostaglandins (PG) was investigated in a carrageenan-induced model of acute hindpaw inflammation. 2 The intraplantar injection of carrageenan elicited an inflammatory response that was characterized by a time-dependent increase in paw oedema, neutrophil infiltration, and increased levels of nitrite/nitrate (NO2-/NO3-) and prostaglandin E2(PGE2) in the paw exudate. 3 Paw oedema was maximal by 6 h and remained elevated for 10 h following carrageenan administration. The non-selective cNOS/iNOS inhibitors, NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine methyl ester (L-NAME) given intravenously (30-300 mg kg-1) 1 h before or after carrageenan administration, inhibited paw oedema at all time points. 4 The selective iNOS inhibitors, N-iminoethyl-L-lysine (L-NIL) or aminoguanidine (AG), failed to inhibit carrageenan-induced paw oedema during the first 4 h following carrageenan administration, but inhibited paw oedema at subsequent time points (from 5-10 h). iNOS mRNA was detected between 3 to 10 h following carrageenan administration using ribonuclease protection assays. iNOS protein was first detected 6 h and was maximal 10 h following carrageenan administration as shown by Western blot analysis. Administration of the iNOS inhibitors 5 h after carrageenan (a time point where iNOS was expressed) inhibited paw oedema at all subsequent time points. Infiltrating neutrophils were not the source of iNOS since pretreatment with colchicine (2 mg kg-1) suppressed neutrophil infiltration, but did not inhibit the iNOS mRNA expression or the elevated NO2-/NO3- levels in the paw exudate. 5 Inhibition of paw oedema by the NOS inhibitors was associated with attenuation of both the NO2-/NO3- and PGE2 levels in the paw exudate. These inhibitors also reduced the neutrophil infiltration at the site of inflammation. 6 Recombinant human Cu/Zn superoxide dismutase coupled to polyethyleneglycol (PEGrhSOD; 12 x 10(3) u kg-1), administered intravenously either 30 min prior to or 1 h after carrageenan injection, inhibited paw oedema and neutrophil infiltration, but had no effect on NO2-/NO3- or PGE2 production in the paw exudate. The administration of catalase (40 x 10(3) u kg-1), given intraperitoneally 30 min before carrageenan administration, had no effect on paw oedema. Treatment with desferrioxamine (300 mg kg-1), given subcutaneously 1 h before carrageenan, inhibited paw oedema during the first 2 h after carrageenan administration, but not at later times. 7 These results suggest that the NO produced by cNOS is involved in the development of inflammation at early time points following carrageenan administration and that NO produced by iNOS is involved in the maintenance of the inflammatory response at later time points. The potential interactions of NO with superoxide anion and PG is discussed.     

The anti-inflammatory effects of the phosphodiesterase inhibitor pentoxifylline in the rat.

The present study aimed to evaluate the anti-inflammatory effects of pentoxifylline (PTX), a non-specific phosphodiesterase inhibitor in the rat. Acute inflammation was induced by subplantar injection of carrageenan (1%) in the rat hind paw. Results showed that intraperitoneal (i.p.) administration of PTX (36 or 72 mg kg(-1)) 30 min prior to carrageenan reduced the paw oedema response in dose-dependent manner with a maximal effect of 18.9 and 40.1%, respectively, at 2h post-carrageenan (P<0.001 and <0.001 at respective doses). Theophylline given at equimolar doses (29.9 or 45.8 mg kg(-1), i.p.) did not reduce the oedema response. With higher doses of PTX (144-300 mg kg(-1), i.p.) the anti-oedema effect of the drug was more pronounced, but mainly confined to the first 2h following carrageenan injection and decreasing rapidly thereafter. PTX (72 mg kg(-1), i.p.) given 30 min after carrageenan challenge reduced the oedema response by 24.7 and 26.2% at 1 and 2h after dosing (P<0.05 and <0.05, respectively). PTX (36 or 72 mg kg(-1), i.p.) co-administered with indomethacin (5 mg kg(-1), i.p.) 30 min before carrageenan had little modulatory effect on the anti-oedema effect of indomethacin, but the higher dose of PTX (144 mg kg(-1), i.p.) reduced the anti-inflammatory effect of indomethacin by 24% at 4h post-carrageenan. PTX (72 mg kg(-1), i.p.) enhanced the anti-oedema effect of the selective COX-2 inhibitor celecoxib (33 mg kg(-1), i.p.) by 55.1% at 4h post-carrageenan. In contrast, the higher dose of PTX (144 mg kg(-1), i.p.) reduced the anti-oedema effect of celecoxib by 46.8% at 4h post-carrageenan. PTX (36 or 72 mg kg(-1)) enhanced the anti-oedema effect of dexamethasone (0.1 mg kg(-1)) with maximal effect of 76 and 104.8% at 2h post-carrageenan (P<0.01 and <0.01 for respective doses). PTX (0.6 mg per paw) given with carrageenan into the rat hind paw reduced the oedema response with a maximal effect of 33.4% at 1h following carrageenan. PTX (0.6 mg per paw) given in the contralateral hind paw reduced the carrageenan-induced paw oedema for 1h by 32.2%. Thus, PTX, when given at doses comparable to those used in man for treatment of circulatory disorders displayed anti-inflammatory in vivo and enhanced the anti-inflammatory effect of a selective COX-2 inhibitor or dexamethasone. PTX may have therapeutic potential as anti-inflammatory agent either alone or in combination with non-steroidal anti-inflammatory drugs or with steroids. There is also an intriguing possibility for the use of topical preparations for the management of local inflammatory conditions.     

外周疼痛模型大鼠脊髓背角环氧化酶表达时程的研究

目的 探讨环氧化酶参与疼痛过程的特点,从而为揭示疼痛的中枢机制提供线索.方法 选取雄性Sprague-Dawley大鼠50只,20只大鼠右侧后肢足掌皮下注射生理盐水100μl作为对照组.30只大鼠右侧后肢足掌皮下注射5%(体积分数)福尔马林液100μl作为实验组,注射后2、6 h和1、3、7、14天作为测试时间点,每个时间点随机选取5只大鼠,断头后取大鼠脊髓腰膨大部位1 cm(L4～5)组织并分离出背角部分,以免疫印迹法检测不司时间点环氧化酶1和环氧化酶2蛋白的表达.结果 福尔马林注射后大鼠脊髓环氧化酶1表达在注射后1 d开始增多,达到对照组的(2.44±0.43)倍,持续到14 d表达仍明显增多,达对照组的(3.30±0.39)倍.环氧化酶2的表达仪在注射后2 h表达明显增多,达对照组的(1.87±0.34)倍,注射后6 h即恢复到正常,观察到第14天仍然没有变化.结论 环氧化酶1和2可能都参与疼痛的中枢机制,环氧化酶2在疼痛的早期或发生中起作用,而环氧化酶1可能参与疼痛的维持.

Abstract：

Objective To compare the expression of two cyclooxygenase (COX) isoforms (COX-1 and COX-2) in the spinal cord of rats with inflammatory pain following peripheral formalin injection. Methods Experiments were performed on adult male Sprague-Dawley rats. 100μl of 5% formalin were injected subcutaneously into plantar hind paw of 30 rats to induce pain. The changes of COX-1 and COX-2 expression were evaluated by western blot in 30 rats, respectively at 2 hours, 6 hours, 1 day, 3 days, 7 days and 14 days after injection. The control group rats were injected with 100 μl of 0.9% saline instead of formalin in 20 rats. Results The expression of COX-1 significantly increased at 1day, 3 days, 7 days and 14 days, but the expression of COX-2 only transiently increased at 2 hours. Conclusions COX-1 and COX-2 are increasingly expressed in the spinal cord, furthermore,spinal COX-2 expression is induced early and transiently increased. COX-1 is up-regulated later and remains elevated for long time, which may explain the long-term hyperalgesia evoked by formalin injection.     

Effect of pre-existing inflammation on carrageenan-induced paw oedema in rats

Twenty-four hours after injection of carrageenan into one hind paw, injection of the same amount into the contralateral paw produced a significantly attenuated inflammatory response. However, when the second injection was given 7 days later, the inflammation induced in the contralateral paw was comparable with the initial response to carrageenan. A time-course study of carrageenan-induced inflammation in rats showed that significant oedema persisted 24 h after carrageenan administration and complete recovery was achieved in 7 days. The attenuated inflammatory response in the contralateral paw after 24 h was antagonized by bilateral adrenalectomy and chemical sympathectomy induced by 6-hydroxydopamine. Carrageenan-induced paw oedema was also significantly less in rats with subacute inflammation induced by the croton oil granuloma pouch technique. This attenuated response was antagonized by pretreatment of the rats with metyrapone, an inhibitor of adrenocorticoid synthesis, and by 6-hydroxydopamine. It is likely that the pre-existing acute or subacute inflammation attenuates the inflammatory response of carrageenan, by acting as a stressor, inducing activation of the sympatho-adrenal system.     

Novel phenanthridine (PHE-4i) derivative inhibits carrageenan-induced rat hind paw oedema through suppression of hydrogen sulfide

This study was conducted to assess the anti-inflammatory effect of a novel synthesized phenanthridine alkaloid (PHE-4i) and to examine the possible involvement of hydrogen sulfide (H₂S) in anti-inflammatory mechanism. The synthesized phenanthridine derivative PHE-4i (2, 5, and 10 mg/kg) was administered intraperitoneally to rats. One hour following treatment, inflammation was induced by intraplantar injection of carrageenan (1 %), in the hind paw. Paw volume as the index of inflammation was measured before and after carrageenan injection. Neutrophil sequestration into the hind paw was quantified by measuring tissue myeloperoxidase (MPO) activity and was compared for the inhibition of H₂S production. Pretreatment with PHE-4i significantly reduced carrageenan-induced hind paw weight, MPO activity, leukocyte infiltration, and H₂S production in a dose-dependent manner (p < 0.001). These results indicate that the anti-inflammatory effect of PHE-4i on carrageenan-induced rat paw oedema could be via the inhibition of the gaseous mediator H₂S.     

Anti-inflammatory action of interleukin 1 through the pituitary-adrenal axis in rats

The influence of lipopolysaccharide (LPS) and the endogenous pyrogens, recombinant human interleukin 1 (rHu-IL 1) and tumor necrosis factor (rHu-TNF), on acute inflammation was investigated in rats. LPS (0.3-3 micrograms/kg i.v.), rHu-IL 1 alpha (3-30 micrograms/kg), rHu-IL 1 beta (0.3-3 micrograms/kg) and rHu-TNF (3-30 micrograms/kg) inhibited the hind paw edema induced by carrageenan in a dose-related manner. The potency of rHu-IL 1 beta was 10 times or more than of rHu-IL 1 alpha. rHu-IL 1 alpha and rHu-TNF also inhibited the dextran-induced hind paw edema. Both types of rHu-IL 1 (0.001-10 ng/paw) neither inhibited nor enhanced the edema when given directly into the inflamed paw. rHu-IL 1 alpha did not show any significant anti-edema activity in adrenalectomized rats. The 3 cytokines tested caused a significant increase in the plasma levels of ACTH and corticosterone after i.v. administration; the potency of rHu-IL 1 beta was about 10 times that of rHu-IL 1 alpha. These results suggest that both rHu-IL 1 and rHu-TNF inhibit paw edema at least in part through pituitary-adrenal axis stimulation, and that rHu-IL 1 has no pro-inflammatory action in the paw edema induced by carrageenan in rats.     

Selective inhibitors of cyclo-oxygenase-2 (COX-2) induce hypoalgesia in a rat paw model of inflammation

1. It is well-established that inhibitors of cyclo-oxygenase (COX) and hence of prostaglandin (PG) biosynthesis reverse inflammatory hyperalgesia and oedema in both human and animal models of inflammatory pain. 2. Paw oedema and hyperalgesia in rats were induced by injecting carrageenan (250 micro g paw(-1)) into a hindpaw. Both inflammatory responses were followed for 24 h after the injection, measuring hyperalgesia by decreased pain threshold in the paws and oedema by plethysmography. 3. Three selective inhibitors of cyclo-oxygenase-2 (COX-2), celecoxib, rofecoxib and SC 236, given systemically in a range of doses, before the inflammatory stimulus, abolished carrageenan-induced hyperalgesia with little reduction of oedema. These inhibitors also induced hypoalgesia, increasing nociceptive thresholds in the inflamed paw above normal, non-inflamed levels. This hypoalgesia was lost at the higher doses of the selective inhibitors, although hyperalgesia was still prevented. 4. In paws injected with saline only, celecoxib, given at the dose inducing the maximum hypoalgesia after carrageenan, did not alter the nociceptive thresholds. 5. Two non-selective inhibitors of COX-2, indomethacin and piroxicam, abolished hyperalgesia and reduced oedema but did not induce hypoalgesia. 6. Celecoxib given locally into the paw also abolished inflammatory hyperalgesia and induced hypoalgesia without reducing oedema. 7. We conclude that hypoalgesia is expressed only over a critical range of COX-2 inhibition and that concomitant inhibition of COX-1 prevents expression of hypoalgesia, although hyperalgesia is still prevented. 8 Our results suggest a novel anti-nociceptive pathway mediating hypoalgesia, involving COX-2 selectively and having a clear peripheral component. This peripheral component can be further explored for therapeutic purposes.     

Different mechanisms underlie the analgesic actions of paracetamol and dipyrone in a rat model of inflammatory pain

BACKGROUND AND PURPOSE: The analgesics, paracetamol and dipyrone are weak inhibitors of the cyclooxygenase isoforms 1 or 2 (COX-1, COX-2) but more potent on COX-3. Both are also weak anti-inflammatory agents, relative to their analgesic and antipyretic activities. In a model of inflammatory pain mediated by prostaglandins, both compounds were analgesic. We have analysed this shared effect further in order to elucidate the underlying mechanisms.EXPERIMENTAL APPROACH: Inflammation was induced in one hind paw of rats by intraplantar injection of 250 microg lambda-carrageenan (CG) and the contralateral paw injected with saline. Nociceptive thresholds to mechanical stimulation were measured immediately before and for 6 h after, injection of CG. The analgesics were s.c. or locally (intraplantar) injected either 30 min before or 2 h after CG. In some groups, naltrexone was injected (s.c. or intraplantar), 1 h before CG. KEY RESULTS: Pretreatment with paracetamol or dipyrone (60-360 mg kg(-1)) reversed hyperalgesia induced by CG and increased nociceptive threshold in the inflamed paw above the basal level (hypoalgesia). Paracetamol, but not dipyrone, also raised nociceptive thresholds in the non-inflamed paw. Subcutaneous, but not local, administration of naltrexone, a specific opioid antagonist, reversed the hypoalgesia induced by paracetamol, but similar naltrexone treatment had no effect on dipyrone-induced analgesia.CONCLUSIONS AND IMPLICATIONS: Although both paracetamol and dipyrone are inhibitors of COX isoforms and thus of prostaglandin biosynthesis and were analgesic in our model, their analgesic actions were functionally and mechanistically different. Satisfactory mechanisms of action for these analgesics still remain to be established.     

Spinal cord SP release and hyperalgesia in monoarthritic rats: involvement of the GABAB receptor system.

1. Monoarthritis was induced in Lewis rats by interdermal injection in the left hind paw of a suspension of Mycobacterium tubercolusis in mineral oil (500 micrograms 100 microliters-1). Controls were injected with 100 microliters mineral oil. 2. Withdrawal latencies to thermal stimuli of the inflamed paw, the contralateral and both paws of control rats were measured at daily intervals after injection by the plantar test. 3. After detection of the pain threshold, rat spinal cords were removed and horizontal dorsal slices were mounted in a 3-compartment bath to measure electrically-evoked release of substance P-like immunoreactivity (SP-LI). 4. The inflamed paw of monoarthritic rats exhibited a lower pain threshold to thermal stimuli than the contralateral paw of the same animals and both paws of control rats. Inflamed paw hyperalgesia was maximal two days after injection, and declined gradually between 7 to 21 days with no evidence of excitability of withdrawal reflexes after 28 days. 5. During the 28 days study, monoarthritic rats gained less weight than control rats. 6. Electrical stimulation of the dorsal roots attached to rat isolated spinal cord slices induced a significant increase (174 +/- 18% of basal outflow which was 30.3 fmol 8 ml-1, n = 5) in SP-LI release. 7. One-week after induction of inflammation no differences in the amount of SP-LI released from the spinal cord of incomplete Freund's adjuvant-treated rats (IFA) and Freund's adjuvant-treated rats (CFA) were detected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of inflammatory paw oedema by cysteamine in the rat.

Cysteamine, a potent somatostatin depletor, was used in the present study to investigate the role of endogenous somatostatin in acute peripheral inflammation. The acute inflammation was induced by intraplantar injection of carrageenan (1%), histamine (5 micromol), or formalin (2.5%) in the rat hind paw. The induced inflammation and the formation of oedema were determined by measurement of the paw thickness. Given subcutaneously (s.c.) 1 h before carrageenan, cysteamine caused significant, dose-dependent and long-lasting inhibition of rat paw oedema induced by carrageenan. At doses of 12.5, 25, 50 or 100 mg kg (-1), cysteamine significantly inhibited the carrageenan-induced paw oedema at 4 h by 52.3, 40, 40.7 or 26.3%. Cysteamine given at 300 mg kg (-1), a dose well known to deplete tissue somatostatin, reduced oedema by only 16.2% vs control values. Significant inhibition of the carrageenan-induced rat paw oedema was still evident 24 h post-injection at cysteamine doses of 12.5, 25, 50 or 100 mg kg (-1). Given s.c. at 300 mg kg (-1), 4 h prior to carrageenan, cysteamine decreased rat paw oedema at 4 h by 14.9%. Cysteamine (300 mg kg (-1)), 4 h beforehand, had little modulatory effect on the oedema induced by formalin (2.5%) but reduced that caused by intraplantar histamine (5 micromol). The anti-oedematogenic effect of indomethacin, but not that of the selective COX-2 inhibitor celecoxib, was less marked in rats pre-treated with cysteamine at 300 mg kg (-1). Cysteamine (0.3 microg- 0.3 mg paw (-1)) co-administered with carrageenan was devoid of anti-inflammatory effect and even promoted inflammation at low concentrations. Cysteamine given locally alone induced slight paw oedema. These data indicate that systemic cysteamine possesses potent and long-lasting anti-inflammatory effects and modulates the anti-inflammatory effect of cyclooxygenase inhibitors in a model of peripheral inflammation in the rat. The effect of cysteamine is likely to be mediated via central action.     

Depression of drug metabolism in the mouse by a combination of Mycobacterium butyricum and anaesthetics.

1 Subcutaneous injection of Mycobacterium butyricum suspended in mineral oil into the mouse hind paw caused an oedematous local inflammation. Hind paw swelling was maximum 5 days after injection and was still apparent at day 30. 2 Drug metabolism in vivo (as monitored by ketamine- or pentobarbitone-induced sleeping times) was not affected by the inflammatory disease. However, administration of ketamine or pentobarbitone at day 1 led to significantly elevated sleeping times when the mice showing local inflammation were retested at day 5 with the anaesthetics. 3 Indomethacin inhibited hind paw oedema in the mouse but did not affect ketamine-Mycobacterium butyricum-induced depression of drug metabolism. 4 Prolongation of ketamine-induced anaesthesia by combination with Mycobacterium butyricum at day 5 correlated with the degree of hind paw inflammation at this time. 5 The data suggest that anaesthetics (i.e., ketamine and pentobarbitone) may sensitize hepatic membranes to the effect of Mycobacterium butyricum or some toxic compound elaborated during the active phase of inflammation.     

The α7 nicotinic ACh receptor agonist compound B and positive allosteric modulator PNU-120596 both alleviate inflammatory hyperalgesia and cytokine release in the rat

BACKGROUND AND PURPOSE

Agonists selective for the α7 nicotinic acetylcholine (nACh) receptor produce anti-hyperalgesic effects in rodent models of inflammatory pain, via direct actions on spinal pain circuits and possibly via attenuated release of peripheral pro-inflammatory mediators. Increasingly, allosteric modulation of ligand-gated receptors is recognized as a potential strategy to obtain desired efficacy in the absence of the putative adverse effects associated with agonist activation.

EXPERIMENTAL APPROACH

We compared the anti-hyperalgesic and anti-inflammatory effects of the α7 nACh receptor agonist compound B with the positive allosteric modulator (PAM) PNU-120596 and the standard non-steroidal anti-inflammatory drug (NSAID), diclofenac, in rats with hind paw inflammation induced by either formalin, carrageenan or complete Freund''s adjuvant (CFA).

KEY RESULTS

When administered before carrageenan, both diclofenac (30 mg·kg⁻¹) and PNU-120596 (30 mg·kg⁻¹) significantly reduced mechanical hyperalgesia and weight-bearing deficits for up to 4 h. Compound B (30 mg·kg⁻¹) also attenuated both measures of pain-like behaviour, albeit less robustly. Whereas compound B and PNU-120596 attenuated the carrageenan-induced increase in levels of TNF-α and IL-6 within the hind paw oedema, diclofenac only attenuated IL-6 levels. Established mechanical hyperalgesia induced by carrageenan or CFA was also partially reversed by compound B and PNU-120596. However, diclofenac was considerably more efficacious. Formalin-induced nocifensive behaviours were only reversed by compound B, albeit at doses which disrupted motor performance.

CONCLUSIONS AND IMPLICATIONS

α7 nACh receptor PAMs could prove to be useful in the treatment of inflammatory pain conditions, which respond poorly to NSAIDs or in situations where NSAIDs are contra-indicated.     

Involvement of peripheral cyclooxygenase-1 and cyclooxygenase-2 in inflammatory pain

Pain-induced functional impairment in the rat (PIFIR) is a model of inflammatory and arthritic pain similar to that of clinical gout. Nociception is induced by the intra-articular injection of uric acid into the right hind limb, inducing its dysfunction. Animals then receive analgesic drugs and the recovery of functionality over time is assessed as an expression of antinociception. We have examined the role of peripheral prostaglandins synthesized by cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) in inflammatory pain using the PIFIR model. Rofecoxib (a selective COX-2 inhibitor) and SC-560 (a selective COX-1 inhibitor) both produced dose-dependent effects. When the inhibitors were administered before uric acid, they showed similar potency, but the antinociceptive efficacy of SC-560 was lower than rofecoxib; the best antinociceptive effects were obtained with the dose of 100 microg/articulation of each inhibitor (pre-treatment). In post-treatment (inhibitors administered after the uric acid), rofecoxib showed the least antinociceptive effect and SC-560 was more potent than rofecoxib. The inhibition of both COX-1 and COX-2 produced a more profound analgesic effect than the inhibition of either COX-1 or COX-2 alone. The present data support the idea that both COX isoforms contribute to the development and maintenance of local inflammatory nociception. Thus, it could be expected that inhibition of both COX-1 and COX-2 is required for non-steroidal anti-inflammatory drugs (NSAID)-induced antinociception in the rat. These findings suggest that the therapeutic effects of NSAIDs may involve, at least in part, inhibition of COX-1 and COX-2.     

The depression of hepatic drug-metabolizing enzyme activity in rats with carrageenan-induced inflammation. II. The effect on the status of plasma antipyrine concentration in rats]

The variation of hepatic drug-metabolism was investigated in male Wistar rats bearing hind paw edema induced by carrageenan (1%, 0.1 ml, s.c.). The content of cytochrome P-450 and the biotransformation of aminopyrine in the hepatic 9000 x g supernatant (S-9) decreased after the subcutaneous injection of carrageenan to rat hind paw. In carrageenan-treated rats the plasma concentration of antipyrine after the administration of antipyrine (20 mg/kg, i.v.) was higher than that of control rats. In comparison with the control groups, the pharmacokinetic parameters of antipyrine in carrageenan-treated rats was altered. AUC0-200 and t 1/2 significantly increased and CLtot and ke significantly decreased. On the other hand, no change of the volume of distribution (Vd) was observed. The results indicate that the hepatic drug metabolism under the carrageenan-induced inflammation is inhibited both in vitro and in vivo.