Di-(2-propylheptyl) phthalate (DPHP) and its metabolites in blood of rats upon single oral administration of DPHP.

Di-(2-propylheptyl) phthalate (DPHP) does not act as a reproductive toxicant or endocrine disruptor in contrast to other phthalates. Considering adverse effects of phthalates to be linked to their metabolism, it was the aim of the present study to investigate in the rat the blood burden of DPHP and its metabolites as a basis for understanding the toxicological behavior of DPHP. Rats were administered single oral doses of DPHP of 0.7 and 100mg/kg body weight. Concentration-time courses of DPHP and metabolites were monitored in blood. The areas under the concentration-time curves in blood (AUCs), normalized for the dose of DPHP, showed the following order: DPHP

Dissolution of copper-rich granules in hepatic lysosomes by D-penicillamine prevents the development of fulminant hepatitis in Long-Evans cinnamon rats.

BACKGROUND/AIM: The Long-Evans cinnamon rat has a mutation homologous to the human Wilson disease gene, leading to gross copper accumulation and the development of hepatitis. D-penicillamine, a copper-chelating drug widely and efficiently used in treating Wilson disease, has also been shown to prevent hepatitis in Long-Evans cinnamon rats. The objectives of this study were: i) to investigate the effectiveness of D-penicillamine when administered to the already affected animals, and ii) to elucidate the mechanism of action of the drug. METHODS: Long-Evans cinnamon rats were divided into groups according to age and treatment with D-penicillamine. The drug was administered orally before and after the onset of hepatitis. Livers were examined by light and electron microscopy. The effect of D-penicillamine on the subcellular distribution and binding of copper was investigated in more detail. Finally, the interaction between D-penicillamine and specific hepatic copper-binding proteins was studied in vitro. RESULTS: D-penicillamine when given to either healthy or diseased animals prevented or reversed hepatitis, respectively. The drug particularly inhibited the disease-specific accumulation of copper in lysosomes of hepatocytes, tissue macrophages and Kupffer cells. When administered to diseased animals, the drug sequestered copper particularly from insoluble lysosomal particles. According to results obtained in vitro, the mobilization of this copper is likely to proceed through the solubilization of these particles. In contrast and as supported by the in vitro data, D-penicillamine had only a minor effect on copper bound to metallothionein in the cytosol. CONCLUSION: Our findings on the Long-Evans cinnamon rat provide some conclusions on the mechanism of action of D-penicillamine in Wilson disease therapy. The drug prevents the formation or promotes the solubilization of copper-rich particles which occur in lysosomes of hepatocytes and Kupffer cells in the livers of patients with Wilson disease. Once chelated with D-penicillamine copper might then be excreted into urine. However, the mobilization of copper by D-penicillamine seems to be limited due to the binding of the metal to metallothionein in liver cytosol. This copper, even at relatively high concentrations, apparently may be well tolerated.

Association of copper to metallothionein in hepatic lysosomes of Long-Evans cinnamon (LEC) rats during the development of hepatitis [se e comments].

BACKGROUND: The Long-Evans cinnamon (LEC) rat has a mutation homologous to the human Wilson's disease gene, leading to copper-induced hepatotoxicity. The mechanism of how excess copper damages the liver or what chemical form of copper is toxic is still unclear. RESULTS: In liver cytosol, copper levels were highest just before the onset of hepatitis and declined thereafter. In cytosol, total copper was bound to metallothionein (MT). Considerable amounts of both copper and iron accumulated in lysosomes with increasing age and development of liver damage. Lysosomal levels of presumably reactive non-MT-bound copper were increased. In severely affected livers, large amounts of copper were associated with insoluble material of high density which, upon ultrastructural information, was found to be derived from the lysosomes of Kupffer cells. This copper-rich material is considered to consist of polymeric degradation products of copper-MT. CONCLUSION: We suggest that chronic copper toxicity in LEC rats involves the uptake of copper-loaded MT into lysosomes, where it is incompletely degraded and polymerizes to an insoluble material containing reactive copper. This copper, together with iron, initiates lysosomal lipid peroxidation, leading to hepatocyte necrosis. Subsequent to phagocytosis by Kupffer cells, the reactive copper may amplify liver damage either directly or through stimulation of these cells.

2-Chloroacetophenone is an effective glutathione depletor in isolated rat hepatocytes.

The glutathione (GSH) depleting effect of 2-chloroacetophenone (CN) was studied in freshly isolated rat hepatocytes. CN proved to be more effective in depleting GSH than diethylmaleate, phorone or styrene oxide. The reaction between GSH and CN followed a 1:1 stoichiometry, allowing adjustment of cellular GSH concentrations at distinct levels. After incubating cells (8 mg protein/ml) with 200 mumol CN/l for 5 min, GSH depletion was almost complete without signs of cytotoxicity. At 300 mumol/l CN, GSH depletion persisted, and cytotoxicity occurred after 30 min. Activities of cytochrome P450 dependent enzymes, even at concentrations up to 500 mumol CN/l, were only marginally affected. Therefore, CN is of particular value for in vitro studies at decreased availability of GSH.

2-Nitropropane induces DNA repair synthesis in rat hepatocytes in vitro and in vivo.

The genotoxicity of 2-nitropropane (2-NP) and 1-nitropropane (1-NP) was investigated by measuring the induction of DNA repair synthesis in rat liver cells in vitro and in vivo. 2-NP strongly induced DNA repair synthesis in both cases. When applied in vivo, 2-NP was considerably more effective in hepatocytes from males than in those from females. 1-NP was not active in vitro or in vivo. 2-NP and 1-NP did not induce repair in cell lines of extrahepatic origin derived from rat, mouse, hamster and man. The results are consistent with the reported carcinogenicity of 2-NP in rat liver and suggest that the formation of hepatocarcinomas by 2-NP is due to the generation of a genotoxic metabolite from 2-NP by liver-specific metabolism.