S.35.04 - Immune factors as biomarkers for stress-related psychiatric and pain disorders

Abstract

Evidence for a role of immune system in hyperalgesic pain states is increasing. Recent work in neuroimmunology suggests that the immune system does more than simply perform its well known functions of recognizing and removing invading pathogens and tumors. Interest in neuroinflammation and neuroimmune activation has grown rapidly in recent years with the recognition of the role of central nervous system inflammatiom and immune responses in the aetiology of pain states. Among various theories, the role of inflammatory responses of the injured nerve has recently received attention. Cytokines are heterogenous group of polypeptides that activate the immune system and mediate inflammatory responses, acting on a variety of tissue, including the peripheral and central nervous system. Interleukin-6 (IL-6) a pro-inflammatory cytokine, is potentially important in pain aetiology, have pronociceptive actions. Neuropathic pain may be due to a primary insult to the peripheral or central nervous system. Substances released during inflammation from immune cells play an important role in the development and maintenance of chronic pain. Nimesulide, a highly selective cox-2 inhibitor, effectively reduces hyperalgesia due to peripherally administration of inflammatory agents like formalin. The safety of nimesulide was reported for some conditions in which other NSAIDs are contraindicated. Here we have determined the effect of nimesulide on pain behaviour and serum IL-6 level in chronic constriction injury (CCI) model of neuropathic pain.Experiments were carried out on male Wistar rats, (weight 150–200 g, n = 8). Rats were divided into 3 different groups: 1- CCI + saline 0.9% 2- Sham + saline 0.9% (control) 3- CCI + drug. Nimesulide (1.25, 2.5, 5 mg/kg, i.p.) was injected 1h before surgery and continued daily to day 14 post-ligation. 42 °C water for thermal hyperalgesia, von Frey filaments for mechanical allodynia, acetone test for cool allodynia and 10 °C water for cold hyperalgesia were respectively used as pain behavioural tests. Behavioural tests were recorded before surgery and on postoperative days 1, 3, 5, 7, 10, 14 and the serum concentration of IL-6 was determined at the day 14.The results of this study showed a decrease in hyperalgesia and allodynia following nimesulide administration.It appears that nimesulide was able to reduce pain behaviour due to nerve inflammation and a parallel decrease in the serum IL-6 concentration was observed.The immune system is an important mediator in the cascade of events that ultimately results in hyperalgesia. Cytokines contribute to the patheogenesis of neuropathic pain, therefore drugs that inhibit cytokine release from immune cells may reduce inflammatory pain states.