Cephalosporin-induced alteration in hepatic glutathione redox state: A potential mechanism for inhibition of hepatic reduction of vitamin K₁;2,3-epoxide in the rat

Hypoprothrombinemia is a serious adverse effect of antimicrobial therapy that occurs after administration of some second- and third-generation cephalosporins which contain the methyltetrazole-thiol (MTT) group. Previous studies have shown that in vitro MTT directly inhibits microsomal γ-carboxylation of a synthetic pentapeptide. Since MTT is a thiocarbamide, a type of compound that can increase oxidation of glutathione, the present studies were carried out to determine whether alterations in hepatic glutathione redox state might interfere with vitamin K metabolism. Dose-related increases in biliary efflux and hepatic concentration of oxidized glutathione (GSSG) occurred after intravenous administration of MTT or MTT-containing antibiotics to rats. This finding suggested that these compounds could alter the hepatic glutathione redox state in vivo. Microsomal reduction of vitamin K epoxide occurred in the presence of 100 μM dithiothreitol (DTT), but was inhibited by preincubation with GSSG at concentrations as low as 10 μM. At higher concentrations of DTT (1.0 mM) inhibition by GSSG persisted, but higher concentrations were required, suggesting that the thiol/disulfide ratio, rather than the absolute concentration of GSSG was important. By contrast, GSSG did not effect microsomal γ-carboxylation of a pentapeptide, using either vitamin K₁ or its hydroquinone as a cofactor. These findings suggest a novel mechanism for the hypoprothrombinemia occurring after administration of MTT-containing antibiotics.