Tocotrienol ameliorates behavioral and biochemical alterations in the rat model of alcoholic neuropathy Vinod Tiwari, Anurag Kuhad, Kanwaljit Chopra * Pharmacology Research Laboratory, University Institute of Pharmaceutical Sciences, UGC Center of Advanced Study, Panjab University, Chandigarh-160 014, India article info Article history: Received 29 March 2009 Received in revised form 27 May 2009 Accepted 28 May 2009 Keywords: Alcoholic neuropathy Hyperalgesia Allodynia Oxidative stress Vitamin E Tocotrienol abstract Chronic alcohol consumption produces a painful peripheral neuropathy for which there is no reliable suc- cessful therapy, which is mainly due to lack of understanding of its pathobiology. Alcoholic neuropathy is characterized by spontaneous burning pain, hyperalgesia (an exaggerated pain in response to painful stimuli) and allodynia (a pain evoked by normally innocuous stimuli). Chronic alcohol intake is known to decrease the nociceptive threshold with increased oxidative–nitrosative stress and release of proin- flammatory cytokines coupled with activation of protein kinase C. The aim of the present study is to investigate the effect of both isoforms of vitamin E, a-tocopherol (100 mg/kg; oral gavage) and tocotri- enol (50, 100 and 200 mg/kg; oral gavage) against alcohol-induced neuropathic pain in rats. Male Wistar rats, were administered 35% v/v ethanol (10 g/kg; oral gavage) for 10 weeks, and were treated with a-tocopherol and tocotrienol for the same duration. Ethanol-treated animals showed a significant decrease in nociceptive threshold as evident from decreased tail flick latency (thermal hyperalgesia) and decreased paw-withdrawal threshold in Randall–Sellito test (mechanical hyperalgesia) and von-Frey hair test (mechanical allodynia) along with the reduction in nerve glutathione and superoxide dismutase levels. TNF-a and IL-1b levels were also significantly increased in both serum and sciatic nerve of ethanol- treated rats. Treatment with a-tocopherol and tocotrienol for 10 weeks significantly improved all the above-stated functional and biochemical deficits in a dose-dependent manner with more potent effects observed with tocotrienol. The study demonstrates the effectiveness of tocotrienol in attenuation of alco- holic neuropathy. Ó 2009 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. 1. Introduction The peripheral neuropathy is a potentially incapacitating com- plication of chronic consumption of ethanol, characterized by pain and dysesthesias, primarily in the lower extremities, and is poorly relieved by available therapies [28,29]. Depending on the criteria and patient selection, incidence of peripheral neuropathy ranging from 10% to 50% has been reported [28]. Primarily it is an axonal neuropathy characterized by wallerian degeneration of the axons and a reduction in the myelination of neural fibers [47]. Contro- versy surrounds the pathogenic role of alcohol in the development of this neuropathy. Studies on rat models have indicated that alco- hol does have a direct neurotoxic effect on spinal cord and neuro- nal organelles [6,30]. Acetaldehyde, one of the most toxic metabolites of ethanol, has a direct neurotoxic effect [17,16]. Oxidative stress is known to play a very important role in the experimental animal models of neuropathic pain. Lee et al., [20] suggested that reactive oxygen species are importantly involved in the development and maintenance of capsaicin-induced pain, particularly in the process of central sensitization in the rats’ spinal cord. Padi et al. [31] demonstrated that chronic administration of minocycline when started early before peripheral nerve injury could attenuate the development of neuropathic pain by inhibiting proinflammatory cytokines release and oxidative and nitrosative stress in mononeuropathic rats. A significant decrease in the activ- ity of antioxidant enzymes (superoxide dismutase and catalase) and an increase in lipid peroxidation were observed in the sciatic nerves of diabetic rats with established neuropathic pain [40]. Dina et al. [9] demonstrated that hyperalgesia is present in an established model of chronic alcoholism in the rat and that PKC signaling plays a critical role in the enhanced nociception produced by chronic alcohol. Ethanol is oxidized to acetaldehyde by cyto- chrome P450, which increases reactive oxygen species, with con- comitant changes in redox balance [24]. Rats given chronic ethanol show enhanced production of oxidative markers, such as thiobarbituric acid-reactive substances, hydrogen peroxide, and OH À like species [8]. Studies have suggested that chronic ethanol increases oxidative damage to proteins, lipids, and DNA [23,26]. Vitamin E is one of the essential fat-soluble nutrients that func- tion as an antioxidant in the human body. Burton and Ingold [3] presented the first comprehensive review article discussing that 0304-3959/$36.00 Ó 2009 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.pain.2009.05.028 * Corresponding author. Tel.: +91 172 2534105; fax: +91 172 2541142. E-mail address: dr_chopra_k@yahoo.com (K. Chopra). PAIN Ò 145 (2009) 129–135 www.elsevier.com/locate/pain