Allyl alcohol cytotoxicity in isolated rat hepatocytes: effects of azide, fasting, and fructose

Relationship between mitochondrial dysfunction and toxicity of propyl gallate in isolated rat hepatocytes

The relationship between cytotoxicity and mitochondrial dysfunction caused by propyl gallate (PG) has been studied in hepatocytes freshly prepared from fasted rats. Hepatocytes isolated from fasted (18 h) rats were significantly more susceptible to the toxicity of PG than hepatocytes from fed rats. The addition of fructose (15 mM), an alternative carbohydrate source, to hepatocyte suspensions resulted in the prevention of PG (1 mM)-induced cell killing accompanied by decrease in intracellular ATP loss during a 3 h-incubation period. Despite this, fructose did not completely prevent an abrupt loss of intracellular glutathione caused by PG, but effectively inhibited the loss of protein thiol levels. Fructose elicited a concentration (0.5-20mM)-dependent protection against the cytotoxicity of 1.5 mM PG. The incubation of hepatocytes with sodium azide (4 mM), an inhibitor of oxidative phosphorylation, enhanced the toxicity induced by PG (1 mM), but coincubation with fructose delayed the onset of toxicity. Neither azide alone nor fructose plus azide did affect the cell viability during the incubation period. Furthermore, the addition of 2 mM salicylamide, nontoxic to hepatocytes during the incubation period, enhanced PG (1 mM)-induced cytotoxicity and decreased the loss of free PG. These results indicate that the onset of cytotoxicity caused by PG may depend on the intracellular energy status and that mitochondria are critical target for the compound. In addition, the toxicity caused by the inhibition of mitochondrial ATP synthesis is related to the concentration of PG remaining in cell suspensions.

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.

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

Allyl alcohol-induced LDH leakage from isolated rat hepatocytes was preceded by a decrease in rhodmine 123 retention, signifying a loss of mitochondrial membrane potential. Addition of dithiothreitol (DTT) prevented the drop in membrane potential and completely prevented cell killing by allyl alcohol. In contrast, cyclosporin A and trifluoperazine delayed the loss of membrane potential without affecting cytolethality. The results indicate that a drop in mitochondrial membrane potential is not essential for allyl alcohol lethality. The mitochondrial dysfunction produced by allyl alcohol appears to be the consequence of an earlier event in the toxicity that is reversible by DTT.