Effect of Zinc on Lipid Peroxidation in Liver Microsomes and Mitochondria 1

While studying the role of certain metals and chelating agents in controlling tissue injury, we found that zinc salts stabilize lysosomal membranes in vitro (1, 2): the rupture of these particles with the resulting release of their enzymes was decreased roughly 50% by low (millimolar) concentrations of zinc. The lysis of cells or subcellular structures is frequently attributed to peroxidation of the lipid components of their membranes (3-5). Thus, one possible explanation of this effect of zinc is that it interferes in some way with peroxidation of unsaturated fatty acids in the lysosomal membrane. This hypothesis was evaluated in in vivo and in vitro experiments using carbon tetrachloride to induce lipid peroxidation.

The toxic effects of CCl₄ in vivo are due to the metabolism of this agent by the liver microsomal drug oxidizing system to the trichloromethyl radical CCl₃ (6). This free radical attacks unsaturated lipids in intracellular membranes, oxidizing them and causing membrane distortion. This process terminates in cell necrosis (7). Lipid peroxidation can also be induced in vitro by incubating isolated liver microsomes with CCl₄ in the presence of NADPH or a NADPH-generating system (8). We have found that zinc prevents or significantly reduces the CCl₄-induced formation of lipid peroxides both in vivo and in vitro.

Methods. Male rats (Simonson, 200 ± 15 g) fed standard Purina lab chow diet were injected sc twice weekly with CCl₄ at the dose 0.1 ml/100 g. Zinc acetate (5 mg/100 g) was administered daily by intragastric gavage. Control rats were gavaged accordingly with saline. Rats were sacrificed by decapitation after 20 and 34 days. The livers were perfused in situ with 20 ml of ice cold saline and homogenized by hand with all-glass homogenizers in three volumes of Tris-KCl buffer (0.05 M, pH 7.4).