Molecular and Cellular Biochemistry 87: 79-84, 1989. © 1989 Kluwer Academic Publishers - Printed in the Netherlands. Original Article Involvement of cytochrome bs in the cytotoxic response to Escherichia coli Lipopolysaccharide M. Teresa Portol6s, In6s Diaz-Laviada, M. Jestls Ainaga, Raffaella Pagani and Angel M. Municio Department of Biochemistry and Molecular Biology I, Faculty of Chemistry, Universidad Complutense, 28040-Madrid, Spain Received11 May 1988;accepted19 December1988 Key words: endotoxins, cytochrome bs, cytochrome P450, hepatocyte cultures, detoxification Abstract Cytotoxic lesions, induced by Gram-negative lipopolysaccharides (LPS), occur mainly in liver where the microsomal compartment of hepatocytes is involved in the detoxification mechanisms as well as in the biosynthesis of different active metabolites. The alterations induced by LPS from E. coli 0111 : B4 on cytochrome b5 and its correlation with cyto- chrome P450, have been studied using an in vivo reversible endotoxic shock model and 24 h non-replicative hepatocyte monolayers. Results show that cytochrome b5 is directly affected by LPS that induces also a membrane damage with an active release of lactate dehydrogenase (LDH). The increase of cytochrome b5 levels may enhance the efficiency of the electron transport, thus facilitating the cytochrome P450-associate oxidations and reactions involved in the repair mechanisms of membranes. Introduction Endotoxic shock comprises a cascade of metabolic, hemodynamic, and clinical changes resulting from the release of lipopolysaccharides (LPS) into the bloodstream that cause severe cytotoxic lesions [1]. Functional and metabolic disturbances occur in liv- er [2, 3] which exerts a LPS clearance function with the participation of both parenchymal and Kupffer cells [4-6]. Binding of endotoxic E. coli 0111:B4 LPS to freshly isolated [7] and cultured hepatocytes [8] was previously studied showing that LPS binds to particular ingredients of the membrane bilayer al- tering its microviscosity properties [9] and metabo- lic pathways which involves altered hormone-re- ceptor binding, gluconeogenic response and sec- ond messengers production [10]. These effects in- creased the interest of the hepatocyte microsomal compartment which is recognized as the major size of detoxification metabolism, in which cytochrome P450-dependent monooxygenases play a key role. We have previously shown, in primary cultures of adult rat hepatocytes, that LPS depresses the cyto- chrome P450 levels by a direct action on cells [11]. Recently, much attention has been focused on the role of cytochrome b5 in the microsomal mixed function oxidase system and the synergistic effect of NADH or NADPH-supported reactions [12, 13]. Also the involvement of cytochrome b5 in the transfer of electrons is required for both the mono- oxygenase reactions [14, 15] and the membrane remodelation through fatty acid desaturation [16] and elongation [17]. In order to know the direct action of LPS on parenchymal liver cells, cytochrome b5 levels and