Metabolism of pyridine nucleotides in cultured rat hepatocytes intoxicated with tert-butyl hydroperoxide

Abstract

The alterations in the metabolism of pyridine nucleotides, as well as the role such changes play in the genesis of lethal cell injury, were explored in cultured rat hepatocytes intoxicated with tert-butyl hydroperoxide (TBHP). The loss of NADPH, NADH, and NAD equalled the increase in NADP, with little if any change in the total content of pyridine nucleotides. Identical alterations occurred in the presence of N,N'-diphenyl-p-phenylenediamine, an antioxidant that prevented the death of the cells. Inhibition of glutathione reductase by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) reduced the extent of the increase in NADP and the decrease in NADPH. At the same time, BCNU increased the cell killing. Depletion of ATP with oligomycin reduced the loss of NAD and the accumulation of NADP. Treatment of the hepatocytes with the poly(ADP-ribose) polymerase inhibitor 3-aminobenzamide had no effect on the depletion of NAD. Thus, all of the alterations in pyridine nucleotides that accompany the exposure of cultured hepatocytes to TBHP can be dissociated from the development of lethal cell injury. The changes do suggest, however, a rapid interconversion of the respective species. The initial response reflects activation of glutathione reductase with the consequent oxidation of NADPH to NADP. The conversion of NADH to NAD and then NAD to NADP, the latter by nicotinamide adenine dinucleotide kinase, can account for the increase in NADP over the resulting from the oxidation of NADPH by glutathione reductase. Finally, there was no evidence in cultured hepatocytes treated with TBHP for changes in NAD that reflect the activation of poly(ADP-ribose) polymerase.