Loss of mitochondrial membrane potential is not essential to hepatocyte killing by allyl alcohol

Modulating carbonyl cytotoxicity in intact rat hepatocytes by inhibiting carbonyl-metabolizing enzymes. I. Aliphatic alkenals

The cytotoxicity of alkenals towards hepatocytes was related to their electrophilicity not their hydrophobicity as cytotoxicity decreased as the chain length increased from acrolein to hexenal and then cytotoxicity increased from hexenal to nonenal. The sequence of events found was rapid glutathione depletion, lipid peroxidation, and inhibition of respiration before cell lysis occurred. Cytotoxicity markedly increased if glutathione was depleted beforehand. Although acrolein-induced cytotoxicity was only delayed by antioxidants or glycolytic substrates (e.g. fructose), it was prevented by NADH generators (e.g. xylitol and sorbitol) due to increased metabolism by ADH1. Cytotoxicity induced by trans,trans-2,4-decadienal (decadienal), on the other hand, was prevented by antioxidants and/or glycolytic substrates but was not prevented by NADH generators. Decadienal-induced cytotoxicity was also more increased by mitochondrial ALDH2 inhibitors than acrolein and was more increased by decreasing mitochondrial NAD+ with rotenone or decreased by increasing mitochondrial NAD+ with oxaloacetate. This suggests that the high electrophilicity of acrolein makes acrolein a more promiscuous inhibitor than decadienal. This results in the inactivation of more enzymes required for cell viability including the cytosolic and mitochondrial ALDHs as well as other enzymes (e.g. mitochondrial) making the reductive detoxication of acrolein by ADH1 more important than the oxidative detoxification by ALDHs. Decadienal is detoxified by all cytosolic and mitochondrial ALDHs and is less dependent on ADH1 for detoxication. There was also marked cytotoxic synergism between acrolein and decadienal presumably because of ALDH inactivation by acrolein.

Oxidation of pyridine nucleotides is an early event in the lethality of allyl alcohol

The involvement of altered pyridine nucleotide concentrations in the cytolethality of allyl alcohol was studied in isolated rat hepatocytes. NAD+, NADH, NADP+, NADPH and viability loss (leakage of lactate dehydrogenase into the medium) were measured in cells incubated with 0.5 mM allyl alcohol with or without the addition of 2 mM dithiothreitol at 30 min. Exposure to allyl alcohol increased NADH levels in the first 15 min of incubation. A sharp drop in NADH and NADPH with an accumulation of NADP+ occurred between 30 and 60 min of incubation with allyl alcohol, indicating an oxidation and interconversion of pyridine nucleotides. Dithiothreitol prevented the oxidation of pyridine nucleotides, but not their reduction or interconversion, and protected against cell killing by allyl alcohol. The results suggest that pyridine nucleotide oxidation might be important for allyl alcohol-induced cytotoxicity; however, a causal relationship between pyridine nucleotide oxidation and cell killing is yet to be demonstrated.