Impaired mitochondrial energy metabolism and kinetic properties of cytochrome oxidase following acute aluminium phosphide exposure in rat liver Raina Dua, Aditya Sunkaria, Vijay Kumar, Kiran Dip Gill * Department of Biochemistry, Postgraduate Institute of Medical Education and Research, Chandigarh 160012, India article info Article history: Received 9 August 2009 Accepted 11 September 2009 Keywords: Aluminium phosphide Cytochrome oxidase Lipid peroxidation Oxidative phosphorylation abstract The present study was designed with an aim to analyze the effect of acute aluminium phosphide (ALP) exposure (10 mg/kg b.wt, intragastrically) on the kinetic characteristics of cytochrome oxidase and energy metabolism in male Wistar rat liver mitochondria. Liver mitochondrial preparations from ALP- treated rats exhibited significant decrease (66%) in the activity of cytochrome oxidase suggesting that there was a decrease in the catalytic efficiency of the active oxidase molecules on ALP treatment. The decreased activity of cytochrome oxidase with altered NADH and succinic dehydrogenase activities might have contributed towards a significant decline in state 3 and state 4 respiration as observed. These alter- ations in the electron transport chain complexes in turn adversely affected the ATP synthesis rate as well as ATP levels in the mitochondria isolated from treated rats. The alterations in the respiratory chain, was followed by enhanced lipid peroxidation in rat liver mitochondria which might have further contributed to change in the fluidity of membrane as depicted by decreased fatty acid content of liver mitochondria. However, no significant change was observed in cholesterol and phospholipids content in our study. The present study thus highlights the significance of altered mitochondrial respiratory chain functions and membrane integrity after acute ALP exposure. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Aluminium phosphide (ALP), is one of the most extensively used metal phosphides for the protection of stored products and crops because of its efficacy, lack of persistence and harmless decomposition products (WHO, 1988) but has also been shown to be severely toxic to both humans and animals (Bogle et al., 2006). The clinical signs and symptoms associated with acute ALP exposure are attributed to a highly poisonous gas, phosphine, librated from the phosphide when it comes in contact with mois- ture present in air and leads to multisystem involvement resulting in serious consequences (Stewart et al., 2003). Exposure to ALP is a widespread cause of poisoning from industrial and agricultural chemical exposure (Gupta et al., 2003; Abder-Rahman et al., 2000; Saleh-Al, 1994) and is accompanied with nausea, vomiting, severe shock, acute respiratory distress, altered sensorium and coma. Hypotension, tachycardia and marked bradycardia are other symptoms associated with ALP poisoning (Sudakin, 2005). Acute hypoxic encephalopathy due to ALP exposure has also been re- ported (Dua and Gill, 2004) which may lead to death as a result of complete depression of central nervous system and paralysis of the respiratory centers of the brain (WHO, 1988). In vitro and in vivo studies have implicated phosphine in exert- ing its toxic effects primarily through inhibition of cytochrome oxi- dase, the terminal enzyme of mitochondrial electron transport chain (Price and Dance, 1983; Dua and Gill, 2004). Experimental and observational studies have subsequently demonstrated that the inhibition of cytochrome c oxidase and other enzymes leads to the generation of superoxide radicals and cellular peroxides, and subsequent cellular injury through lipid peroxidation and other oxidant mechanisms (Bolter and Chefurka, 1990; Chugh et al., 1996). This may facilitate peroxidation of polyunsaturated fatty acids with loss of membrane integrity. The free radical med- iated peroxidation of polyunsaturated fatty acids with loss of membrane integrity is recognized as a mechanism for genesis of injury to the tissues (Tappel, 1973). Aluminium phosphide is also known to exert its toxic actions primarily by interference with mitochondrial energy production (Chefurka et al., 1976). Mitochondria are the cellular sites of aero- bic respiration and produce majority of cellular ATP via oxidative phosphorylation. In this process electrons are transported along the mitochondrial respiratory chain in a series of transfer reactions that use redox energy harvested from metabolism to establish a proton gradient which is used to drive the phosphorylation of ADP by the F O F 1 -ATPase. Cytochrome c oxidase (complex IV) deliv- ers the electrons to the final electron acceptor, molecular oxygen, which is reduced to water. It has been reported that cytochrome 0278-6915/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.fct.2009.09.014 * Corresponding author. Tel.: +91 0172 2745177; fax: +91 0172 2744401. E-mail address: kdgill2002@yahoo.co.in (K.D. Gill). Food and Chemical Toxicology 48 (2010) 53–60 Contents lists available at ScienceDirect Food and Chemical Toxicology journal homepage: www.elsevier.com/locate/foodchemtox