Menadione-induced cytotoxicity effects on human erythrocyte membranes studied by electron paramagnetic resonance.

Menadione (2-methyl-1,4-naphthoquinone) is cytotoxic to hepatocytes. In order to begin to investigate the changes in the physical state of membranes induced by this cytotoxic substance, electron paramagnetic resonance (EPR) spin-labeling techniques were used in conjunction with spin labels specific for cytoskeletal proteins, bilayer lipids, or cell-surface sialic acid or galactose to investigate erythrocyte membranes. We studied the molecular effects of oxidation of 200 microM menadione on the different membrane domains. The major findings are: (1) menadione increases protein-protein interactions (P < 0.001) of cytoskeletal proteins, (2) there is a slightly significant increase in the rotational motion of spin-labeled sialic acid (P < 0.05), while (3) the physical state of galactose residues was unaffected by menadione. Since glycophorin is coupled to the major cytoskeletal protein, spectrin, by protein 4.1, we suggest that menadione-induced oxidation could alter the conformation of protein 4.1. As a consequence, single or multiple sites of weakness could be induced leading to the alteration of the interactions of the cytoskeletal network and its anchoring domains in the membrane. These results are discussed with reference to possible mechanisms involved in the cytotoxic action of menadione.