No abstract

Palmitoylethanolamide (PEA) is an endogenous lipid that is thought to be involved in endogenous protective mechanisms activated as a result of stimulation of inflammatory response. In spite of the well demonstrated anti-inflammatory properties of PEA, its involvement in controlling pain pathways still remains poorly characterized. On this basis, we tested the efficacy of PEA in vivo against a peculiar persistent pain, such as neuropathic one. PEA was administered i.p. to mice with chronic constriction injury of sciatic nerve (CCI) once a day for one week starting the day after the lesion. This therapeutic regimen evoked a relief of both thermal hyperalgesia and mechanical allodynia in neuropathic mice. Various selective receptor antagonists were used in order to clarify the relative contribution of cannabinoid, vanilloid and peroxisome proliferator-activated receptor to PEA-induced effects. The results indicated that CB(1), PPARgamma and TRPV1 receptors mediated the antinociception induced by PEA, suggesting that the most likely mechanism might be the so-called "entourage effect" due to the PEA-induced inhibition of the enzyme catalyzing the endocannabinoid anandamide (AEA) degradation that leads to an enhancement of its tissue levels thus increasing its analgesic action. In addition, the hypothesis that PEA might act through the modulation of local mast cells degranulation is sustained by our findings showing that PEA significantly reduced the production of many mediators such as TNFalpha and neurotrophic factors, like NGF. The findings presented here, in addition to prove the beneficial effects of PEA in chronic pain, identify new potential targets for analgesic medicine.

Cannabidiol (CBD), a nonpsychoactive marijuana constituent, was recently shown as an oral antihyperalgesic compound in a rat model of acute inflammation. We examined whether the CBD antihyperalgesic effect could be mediated by cannabinoid receptor type 1 (CB1) or cannabinoid receptor type 2 (CB2) and/or by transient receptor potential vanilloid type 1 (TRPV1). Rats received CBD (10 mg kg À1) and the selective antagonists:-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)pyrazole-3 carboxamide) for CB2 and capsazepine (CPZ) for TRPV1 receptors. The intraplantar injection of carrageenan in rats induced a time-dependent thermal hyperalgesia, which peaked at 3 h and decreased at the following times. CBD, administered 2 h after carrageenan, abolished the hyperalgesia to the thermal stimulus evaluated by plantar test. Neither SR141716 (0.5 mg kg À1) nor SR144528 (3 and 10 mg kg À1) modified the CBD-induced antihyperalgesia; CPZ partially at the lowest dose (2 mg kg À1) and fully at the highest dose (10 mg kg À1) reversed this effect. These results demonstrate that TRPV1 receptor could be a molecular target of the CBD antihyperalgesic action.

Cannabidiol, the major non-psychoactive component of marijuana, has various pharmacological actions of clinical interest. It is reportedly effective as an anti-inflammatory and anti-arthritic in murine collagen-induced arthritis. The present study examined the anti-inflammatory and anti-hyperalgesic effects of cannabidiol, administered orally (5-40 mg/kg) once a day for 3 days after the onset of acute inflammation induced by intraplantar injection of 0.1 ml carrageenan (1% w/v in saline) in the rat. At the end of the treatment prostaglandin E2 (PGE2) was assayed in the plasma, and cyclooxygenase (COX) activity, production of nitric oxide (NO; nitrite/nitrate content), and of other oxygen-derived free radicals (malondialdehyde) in inflamed paw tissues. All these markers were significantly increased following carrageenan. Thermal hyperalgesia, induced by carrageenan and assessed by the plantar test, lasted 7 h. Cannabidiol had a time- and dose-dependent anti-hyperalgesic effect after a single injection. Edema following carrageenan peaked at 3 h and lasted 72 h; a single dose of cannabidiol reduced edema in a dose-dependent fashion and subsequent daily doses caused further time- and dose-related reductions. There were decreases in PGE2 plasma levels, tissue COX activity, production of oxygen-derived free radicals, and NO after three doses of cannabidiol. The effect on NO seemed to depend on a lower expression of the endothelial isoform of NO synthase. In conclusion, oral cannabidiol has a beneficial action on two symptoms of established inflammation: edema and hyperalgesia.

Neuropathic pain consequent to peripheral injury is associated with local inflammation and overexpression of nitric oxide synthases (NOS) and inflammatory cytokines in locally recruited macrophages, Schwann and glial cells. We investigated the time course and localization of nitric oxide synthases (NOS) and cytokines in the central (spinal cord and thalamus) and peripheral nervous system (nerve and dorsal root ganglia), in a mouse model of mononeuropathy induced by sciatic nerve chronic constriction injury. ATP is recognized as an endogenous pain mediator. Therefore we also evaluated the role of purinergic signalling in pain hypersensitivity employing the P2 receptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), on pain behaviour, NOS and cytokines. The PPADS daily administration starting on day 3 after injury dose- and time-dependently decreased both tactile allodynia and thermal hyperalgesia. PPADS (25mg/kg) completely reversed nociceptive hypersensitivity and simultaneously reduced the increased NO/NOS system and IL-1beta in both peripheral (injured sciatic nerve and L4-L6 ipsilateral dorsal root ganglia) and central steps of nervous system (L4-L6 spinal cord and thalamus) involved in pain signalling. IL-6 was overexpressed only in the peripheral nervous system and PPADS prolonged administration reduced it in sciatic nerve. In conclusion, we hypothesize that NO/NOS and IL-1beta have a pronociceptive role in this neuropathy model, and that purinergic antagonism reduces pain hypersensitivity by inhibiting their overactivity.

1 The antiin¯ammatory activity of synthetic cannabinoid nabilone in the rat model of carrageenaninduced acute hindpaw in¯ammation was compared with that of the endocannabinoid palmitoylethanolamide and the nonsteroidal antiin¯ammatory drug indomethacin. 2 Preliminary experiments in rats used a tetrad of behavioural tests, speci®c for tetrahydrocannabinol-type activity in the CNS. These showed that the oral dose of nabilone 2.5 mg kg 71 had no cannabinoid psychoactivity. 3 Intraplantar injection of carrageenan (1% w v 71 ) elicited a time-dependent increase in paw volume and thermal hyperalgesia. 4 Nabilone (0.75, 1.5, 2.5 mg kg 71 , p.o.), given 1 h before carrageenan, reduced the development of oedema and the associated hyperalgesia in a dose-related manner. Nabilone 2.5 mg kg 71 , palmitoylethanolamide 10 mg kg 71 and indomethacin 5 mg kg 71 , given p.o. 1 h before carrageenan, also reduced the in¯ammatory parameters in a time-dependent manner. 5 The selective CB 2 cannabinoid receptor antagonist {N-[(1S)-endo-1,3,3-trimethyl bicyclo [2.2.1]heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)pyrazole-3 carboxamide} (SR 144528), 3 mg kg 71 p.o. 1 h before nabilone and palmitoylethanolamide, prevented the anti-oedema and antihyperalgesic e ects of the two cannabinoid agonists 3 h after carrageenan. 6 Our ®ndings show the antiin¯ammatory e ect of nabilone and con®rm that of palmitoylethanolamide indicating that these actions are mediated by an uncharacterized CB 2 -like cannabinoid receptor.

No abstract

1 An attractive alternative to the use of direct agonists at the cannabinoid receptor type 1 (CB1) in the control of neuropathic pain may be to potentiate the actions of endogenous cannabinoids. Thus, the effects of AM404, an inhibitor of anandamide uptake, were assessed in an experimental model of neuropathic pain in rats. 2 Daily treatment with AM404 prevented, time-and dose-dependently, the development of thermal hyperalgesia and mechanical allodynia in neuropathic rats. Antagonists at cannabinoid CB1 or CB2 receptors, or at the transient receptor potential vanilloid type 1 receptor, each partially reversed effects induced by AM404. A complete reversal was obtained when the three antagonists were given together, suggesting that all three receptors are involved. 3 AM404 treatment affected two pathways involved in the generation and maintenance of neuropathic pain, one mediated by nitric oxide (NO) and the other by cytokines. AM404 completely prevented the overproduction of NO and the overexpression of nNOS, inhibited the increase in tumour necrosis factor a (TNFa) and enhanced the production of interleukin-10. Both NO and TNFa are known to contribute to the apoptotic process, which plays an important role in the establishment of chronic pain states. AM404 treatment prevented the increase in the ratio between pro-and antiapoptotic gene bax/bcl-2 expression observed in the spinal cord of neuropathic rats. 4 Taken together, these findings suggest that inhibition of endocannabinoid uptake, by blocking the putative anandamide carrier, results in the relief of neuropathic pain and may represent a novel strategy for treating chronic pain.