International Journal of Pharmaceutical Research | October-December 2013 | Volume 5 | Issue 4 | 21 Research Article In vivo Antioxidant Potential of Thespesia populnea L., Bark Extract against Mercury Induced Oxidative Stress GOVINDARAJ PRASANNARAJ, RICHARD L. JAYARAJ, JOHN RAVINDAR D., NAMASIVAYAM ELANGOVAN  Department of Biotechnology, Periyar University, Periyar Palkalai Nagar, Salem-636011 Tamil Nadu, India. ABSTRACT The toxicity of mercury in humans and animals are well established and this depends greatly on the mercuric compounds. In this study Thespesia populnea has been investigated for its possible protective role in mercury induced cellular damage using Swiss albino mice. The liver marker enzymes SGPT and SGOT exhibited higher activity and the antioxidant enzymes CAT, GPx and GST in mercuric chloride [HgCl2] treated animals were lower. Liver histopathology showed that Thespesia populnea bark extract inhibited these amendments, had reduced fat cyst formation and developed binucleated cells induced by HgCl2 intoxication. From these results we conclude that enhanced levels of antioxidant enzymes and reduced amount of serum amino transaminase are responsible for the major protecting mechanisms of T. populnea bark extract in mercury induced oxidative stress in liver. Key words: Thespesia populnea, oxidative stress, mercury, antioxidant enzymes  Address for correspondence Namasivayam Elangovan, Department of Biotechnology, Periyar University, Periyar Palkalai Nagar, Salem- 636011, Tamil Nadu, India. E-mail address: elangovannn@gmail.com, Phone: +91-9789097142 Received: 25/07/2013, Revised: 15/08/2013, Accepted: 25/08/2013 INTRODUCTION Heavy metals are persistent environmental contami- nants, since they cannot be degraded or destroyed. They are chemical elements capable of spreading in the environmental compartments and circulating between them. Indeed, heavy metals emitted to the atmosphere with the composition of fine particles or in the gaseous form are transported by atmospheric fluxes to consider- able distances and enter ecosystems of remote regions. Many heavy metals are necessary for functioning of human bodies and other living organisms in small amounts but increased exposure causes a lot of health defects [1]. The sources of heavy metal pollution in the environment can be natural and anthropogenic. The natural sources include mother rocks and minerals of the metals. The main anthropogenic sources are agri- culture, black and colored metallurgy, transportation and mining related operations [2-5]. WHO reported that main threats to human health from heavy metals are associated with exposure to lead, cadmium, mercury and arsenic [6]. Mercury a highly toxic metal, causes a variety of ad- verse health effects including neurological, renal, res- piratory, immune, dermatologic, reproductive and de- velopmental sequelle, due to wide use of mercury in agriculture, industrial, medical and its exposure cannot be avoided [7]. The toxicity of mercury greatly depends on the forms of mercury compounds (elemental, inor- ganic and organic). Inorganic mercury present in the environment is a well-established toxicant to human health [8]. Exposure to mercury promotes the reactive oxygen species (ROS) formation such as hydrogen per- oxides and these ROS enhances the subsequent iron and copper induced production of lipid peroxides and highly reactive hydroxyl radicals [9-10]. Detrimental effects caused by free radicals occur when there is an imbalance between free radical production and radical scavenging capacity of antioxidant system in favour of former [11]. Free radicals and intermediate products of peroxidation are capable of damaging the integrity and altering the function of biomembranes, which can lead to the devel-