Vol 8, Issue 4, 2015 ISSN - 0974-2441 MELATONIN AMELIORATES FLUORIDE INDUCED NEUROTOXICITY IN YOUNG RATS: AN IN VIVO EVIDENCE AYUSHI JAIN 1,3 , VINOD KUMAR MEHTA 2 , REENA CHITTORA 3 , ABBAS ALI MAHDI 1 , MAHEEP BHATNAGAR 3* 1 Department of Biochemistry, King George Medical University, Lucknow, Uttar Pradesh, India. 2 Department of Neurology, King George Medical University, Lucknow, Uttar Pradesh, India. 3 Department of Zoology, Mohanlal Sukhadia University, Udaipur, Rajasthan, India. Email: mbhatnagar@yahoo.com Received: 17 April 2015, Revised and Accepted: 09 May 2015 ABSTRACT Objective: Developing brain is highly vulnerable to environmental toxins. Recently, fluoride was declared as a developmental neurotoxin and heralded search for natural neuroprotectant. In this study, we have evaluated the neuroprotective and anti-inflammatory efficacy of melatonin in fluoride- induced neurotoxicity. Methods: Animals were divided into following groups; the first group was used as a control. Groups 2, 3, and 4 were treated with melatonin (10 mg/kg body weight [BW]), sodium fluoride (NaF 4 mg/kg BW) and NaF (4 mg/kg BW) plus melatonin (10 mg/kg BW), respectively. Young rats were orally administered their respective doses daily for 60 days. Biochemical and behavioral analysis were performed. The level of proinflammatory cytokine, tumor necrosis factor alpha (TNF-a) was also determined. Results: Data obtained showed that NaF significantly (p<0.001) increased thiobarbituric acid reactive substances (TBARS), reactive oxygen species (ROS) concentration and decreased the activities of glutathione (GSH) and GSH peroxidase. On the other hand, melatonin plus NaF treated group showed a significant decrease in the levels of TBARS and ROS while it increased the activities of antioxidant enzymes and GSH content. In addition, melatonin significantly attenuated the fluoride-induced increase in the TNF-α level of the brain. Melatonin also prevented the cognitive deficit as shown by the increased retention latency in the passive avoidance task (p<0.001). Conclusion: This study suggests that melatonin has therapeutic potential since it suppresses fluoride-induced inflammation, cognitive impairment, and oxidative stress in the brain. Keywords: Oxidative stress, Inflammation, Melatonin, Tumor necrosis factor alpha, Fluoride. INTRODUCTION Developmental neurotoxins can cause multiple effects on the brain and learning-memory disabilities. Recently, fluoride was classified as a developmental neurotoxin by medical authorities [1]. Fluoride availability in drinking water beyond the safe limits has been a global problem [2]. Enhanced oxidative stress, decreased antioxidant pool, and neurodegeneration have been established by a number of studies in fluorosis [3-5]. Varied neurological manifestations are also observed in advance stages of fluorosis [6]. Fluoride exerts powerful effects on various enzymes, oxidant/antioxidant systems and cellular functions [4]. The underlying mechanism is however not clear. In spite of the severe health hazards associated with the slow toxin fluoride, there are only limited reports on the development of suitable neuroprotectant against it. Thus, our aim was to search for a potent neuroprotectant against fluoride neurotoxicity for a mitigating effect. In this regard, the pineal hormone melatonin is an important biomolecule, which is a potent neuroprotectant. Melatonin (nacetyl-5-methoxytryptamine) is synthesized mainly in the pineal gland and has powerful antioxidant properties as proven by several in vivo and in vitro studies [7-10]. Studies have reported relationship between fluoride and oxidative stress, but none of these reports illustrate blended interactions of fluoride, oxidative stress, inflammation and behavioral alterations which could be an added advantage in understanding the mechanism of cognitive alterations in fluoride neurotoxicity. Hence, this study is aimed to quantify the biochemical, behavioral, and inflammatory parameters and to correlate their interactions with supplementation of a biomolecule, which may help further in understanding the mechanism of fluoride perturbation in central nervous system. METHODS Animals Young Wistar rats, weighing 50-60 g (18 days old) were used in this study. The rats were housed in a temperature-controlled room 22-24°C with a 12:12 light: Dark cycle. Water and food were given ad libitum. All protocols described were reviewed and approved by the Local Institutional Committee for the Ethical Use of Animals and the laboratory was approved by Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA), Government of India. (Approval no. #973/ac/06/CPCSEA). The animals were randomly divided into the following groups, Group I - Control, Group II - melatonin, Group III - NaF, Group IV - NaF + melatonin. The rats in the NaF treated, Group III and Group IV, had access to drinking water with a 3 mg L −1 NaF solution for 60 days. Melatonin was administered between 6 and 7 p.m. administered by gastric gavages (0.1 ml 10 g −1 body weight [BW]) at a dose of 10 mg kg −1 bw −1 . Biochemical tests At the end of the treatment period, the animals were sacrificed by decapitation. Brain were dissected out, weighed, rinsed in ice-cold saline and used immediately or stored frozen at −70°C until analysis. Brain tissue samples were thawed and homogenized in 10% (w v −1 ) ice-cold 0.1 M phosphate buffer (pH 7.4) and centrifuged for 10 minutes at the temperature of 4°C at 10,000 g. The supernatants were collected, and aliquots (stored at −20°C) were prepared to determine various parameters. Total protein content was estimated by the method of Lowry et al., 1951 [11]. Then the hemolysate was used for the estimation of oxidative stress parameters. Research Article