J BIOCHEM MOLECULAR TOXICOLOGY Volume 15, Number 6, 2001 Beneficial Effect of Nitric Oxide Synthase Inhibitor on Hepatotoxicity Induced by Allyl Alcohol Khurshid Alam, 1 Mahmoud N. Nagi, 2 Othman A. Al-Shabanah, 2 and Abdullah M. Al-Bekairi 2 1 Department of Biochemistry, Faculty of Medicine, Aligarh Muslim University, Aligarh, India; E-mail: kalam786@rediffmail.com 2 Department of Pharmacology, College of Pharmacy, King Saud University, P.O. Box 2457, Riyadh 11451, Saudi Arabia Received 5 May 2001; revised 24 August 2001; accepted 1 September 2001 ABSTRACT: The effect of aminoguanidine (a selective inhibitor of inducible nitric oxide synthase) on allyl alcohol-induced liver injury was assessed by the mea- surement of serum ALT and AST activities and histo- pathological examination. When aminoguanidine (50– 300 mg/kg, i.p.) was administered to mice 30 min before a toxic dose of allyl alcohol (75 L/kg, i.p.), significant changes related to liver injury were observed. In the presence of aminoguanidine the level of ALT and AST enzymes were significantly decreased. All symptoms of liver necrosis produced by allyl alcohol toxicity al- most completely disappeared when animals were pre- treated with aminoguanidine at 300 mg/kg. Depletion of hepatic glutathione as a consequence of allyl alco- hol metabolism was minimal in mice pretreated with aminoguanidine at 300 mg/kg. It was found that the inhibition of toxicity was not due to alteration in al- lyl alcohol metabolism since aminoguanidine did not effect alcohol dehydrogenase activity both in vivo and in vitro. C  2001 John Wiley & Sons, Inc. J Biochem Mol Toxicol 15:317–321, 2001 KEY WORDS: Allyl Alcohol; Hepatotoxicity; Amino- guanidine; Nitric Oxide; Mice INTRODUCTION Allyl alcohol has long been known to produce necrosis in the livers of rats and mice. Allyl alco- hol is metabolized by cytosolic alcohol dehydroge- nase to acrolein, an unsaturated aldehyde belonging to the class of 2-alkenals [1,2]. Acrolein is a power- ful electrophile and reacts with nucleophiles, such as sulfhydryl groups. Glutathione is primarily involved in the reaction that results in dramatic depletion [3,4]. The reaction is markedly accelerated by the activity of cytosolic glutathione S-transferase [5]. Correspondence to: Khurshid Alam. c  2001 John Wiley & Sons, Inc. DOI 10.1002/jbt.10008 It has been suggested that the alkylation of nucleo- philic groups of cellular macromolecules affected by acrolein after glutathione depletion is the event actu- ally leading to cell injury [6]. However, other reports have suggested that a major role in the production of al- lyl alcohol-induced hepatotoxicity might be played by lipid peroxidation [7,8]. Acrolein depletes glutathione content of the hepatocytes thereby sensitizing the cells to the constitutive flux of activated oxygen species [9] and in activated hepatic macrophages glutathione has no major impact on nitric oxide (NO) production [10]. Very recently, it has been demonstrated that a single dose of aminoguanidine (AG), a relatively selective in- hibitor of an inducible form of nitric oxide synthase (iNOS) [11], protected against acetaminophen-induced hepatotoxicity [12], as well as thioacetamide-induced hepatotoxicity [13], two glutathione depleting agents. These reports demonstrated that NO is an important mediator of hepatotoxicity and changes in its genera- tion or actions contribute to pathologic states. Another study concluded that NOS plays an important role in liver cirrhosis following carbon tetrachloride (CCl 4 ) in- toxication to rats [14]. The above report was based on the findings that plasma levels of nitrates/nitrites, evi- dence of NO production, were significantly increased in cirrhotic animals and decreased in the presence of AG to levels not significantly different from the control. The present work was carried out to determine the protec- tive action of AG, an iNOS synthase inhibitor, against allyl alcohol-induced hepatotoxicity vis-a-vis the role of NO in hepatotoxicity. MATERIALS AND METHODS Chemicals Aminoguanidine (AG) and allyl alcohol (>98%) were obtained from BDH Chemicals Ltd. (Poole, England). Ethanol (96% v/v) was purchased from 317