Effects of the anti-AIDS drug dideoxyinosine on hepatic glycolysis in the perfused rat liver: role of intracellular calcium stores

A comparative 90-day toxicity study of allyl acetate, allyl alcohol and acrolein

Allyl acetate (AAC), allyl alcohol (AAL), and acrolein (ACR) are used in the manufacture of detergents, plastics, pharmaceuticals, and chemicals and as agricultural agents. A metabolic relationship exists between these chemicals in which allyl acetate is metabolized to allyl alcohol and subsequently to the highly reactive, alpha,beta-unsaturated aldehyde, acrolein. Due to the weaker reactivity of the protoxicants, allyl acetate and allyl alcohol, relative to acrolien we hypothesized the protoxicants would attain greater systemic exposure and therefore deliver higher doses of acrolein to the internal organs. By extension, the higher systemic exposure to acrolein we hypothesized should lead to more internal organ toxicity in the allyl acetate and allyl alcohol treated animals relative to those treated with acrolein. To address our hypothesis we compared the range of toxicities produced by all three chemicals in male and female Fischer 344/N rats and B6C3F1 mice exposed 5 days a week for 3 months by gavage in 0.5% methylcellulose. Rats (10/group) were dosed with 0-100mg/kg allyl acetate, 0-25mg/kg allyl alcohol, or 0-10mg/kg acrolein. Mice (10/group) were dosed with 0-125mg/kg allyl acetate, 0-50mg/kg allyl alcohol, or 0-20mg/kg acrolein. The highest dose of allyl acetate and acrolein decreased survival in both mice and rats. The primary target organ for the toxicity of all three chemicals in both species and sexes was the forestomach; squamous epithelial hyperplasia was observed following exposure to each chemical. In both species the highest allyl acetate dose group exhibited forestomach epithelium necrosis and hemorrhage and the highest dose of acrolein led to glandular stomach hemorrhage. Liver histopathology was the most apparent with allyl acetate, was also observed with allyl alcohol, but was not observed with acrolein. All chemicals had effects on the hematopoietic system with allyl acetate having the most pronounced effect. When dosed at quantities limited by toxicity, allyl acetate and allyl alcohol produce higher levels of urinary mercapturic acids than the minimally toxic dose of acrolein. This observation is likely due to biotransformation of allyl acetate and ally alcohol to acrolein that occurs after absorption and suggests that these chemicals are protoxicants that increase systemic exposure of acrolein. Increased systemic exposure to acrolein is likely responsible for the differences in hepatic toxicological profile observed with these chemicals.

Hepatic purine and pyrimidine metabolism: implications for antiviral chemotherapy of viral hepatitis

The use of nucleoside analogues as antiviral agents is expanding. For most nucleoside analogues, intracellular phosphorylation is the major prerequisite for activity. Antiviral activity may be limited by poor uptake, absence of appropriate activating enzymes, catabolism, and competition from endogenous nucleotides. Appreciation of these factors, which are species-, tissue- and cell-specific is important in the understanding of the pharmacology and toxicology of nucleoside analogues. The use of nucleoside analogues against the agents of viral hepatitis is inherently problematic for many reasons including active hepatic nucleoside catabolism, probable absence of virus-specific activating enzymes, competition from endogenous nucleotides synthesised de novo or derived from RNA turnover, and factors related to mitochondrial toxicity. Despite these drawbacks, some nucleoside analogues have been found efficacious against hepatitis B virus and it is likely that as knowledge of their mechanism of action accumulates, their efficacy can be improved both by rational drug design and by use in combination with other drugs, including interferon.

Fulminant hepatitis with severe lactate acidosis in HIV-infected patients on didanosine therapy

We report two cases of fulminant hepatic failure in HIV-1-infected patients treated with didanosine (ddI). Clinical manifestations including vomiting, diarrhoea and dyspnoea were identical in both cases. Biological data mainly revealed hepatic failure and lactic acidosis. Histological examination of liver biopsies showed diffuse microvesicular steatosis. The outcome was fatal in both patients. The only comparable case previously reported (Lai et al., 1991) showed close similarities in the clinical, biological and histological manifestations with microvesicular steatosis. This prompted us to suspect that ddI might be responsible for fulminant hepatitis in all three AIDS patients. This toxic effect may be added to the list of potential adverse events occurring during ddI therapy.

Disruption of mitochondrial energetics and DNA synthesis by the anti-AIDS drug dideoxyinosine

The purpose of this study was to clarify the role of the mitochondria as a site for the reported hepatotoxic effects of the anti-AIDS drug dideoxyinosine (ddI). Data show that ddI interfered with the mitochondrial redox state in perfused livers leading to more oxidized mitochondria. This effect was reflected by a significant decrease in the mitochondrial NADH/NAD+ ratios from basal values of 0.40 +/- 0.04 to 0.28 +/- 0.02 within 10 min following the infusion of ddI. In suspensions of isolated mitochondria utilizing succinate as a substrate, ddI diminished state 3 and stimulated state 4 respiration significantly, suggesting an uncoupling effect by ddI. Incubation of mitochondria with ddI resulted in a significant decrease in the mitochondrial respiratory control ratios (state 3/state 4 respiration) to 0.8 +/- 0.02 from corresponding control values of 6.0 +/- 0.40 Data also show that ddI inhibited mitochondrial DNA synthesis as evidenced by the decrease in [3H]thymidine incorporation into mitochondrial DNA. This study confirms the need for a close monitoring of patients receiving the dideoxyinosine anti-AIDS drugs and for prompt discontinuation of these drugs before potential irreversible liver damage occurs.