Hepatotoxic effects of SH-reagents in human and rat hepatocyte cultures and in situ perfused rat livers.

Effects organic mercurials (PCMBS, PCMB, mersalyl) an alkylating reagent (NEM), disulphide reagents (DTP, CPDS) and the dithiocarbamate agent DSF (disulfiram) were studied in hepatocyte culture. Cytotoxicity, was on a high level (organic mercurials), moderate (NEM, DTP), or none (DSF, CPDS). The organic mercurials and NEM induced glutathione depletion. Disulphide compounds were detoxified by metallothionein binding. Organic mercurials inhibited the cellular glucose uptake. The most prominent effect of NEM, DTP and DSF was an inhibition of the TCA-cycle. The hepatocellular BSP metabolism was delayed by all tested compounds. Albumin synthesis was stimulated by pyruvate and blocked by PCMB and PCMBS, by inhibiting the hepatocellular amino acid uptake. Phase I and II biotransformation reactions were inhibited by PCMBS and PCMB by direct binding to Cyt. P450 cysteinyl-residues and active sites of UDP-glucuronyltransferases. DSF probably reacts by diminishing the availability of the cofactor NADPH. Isolated ALDH (EC 1, 2, 1.3) was inhibited by all studied compounds. In cellular systems, DSF and the organomercurials inhibited ALDH, thereby reducing the cell's capacity of ethanol catabolism. All tested compounds showed, in low doses, the anabolic ability of insulin mimicking, as demonstrated in a balanced endocrine in vitro testsystem. Morphology, Exposure to NEM, DTP, CPDS, DSF did not result in any morphological alterations in the cell cultures. However, an exposure to PCMBS and PCMB, resulted in extensive bleb-formation, as a result of SH group blocking at the cell's outer membrane. It can be concluded, that cultured hepatocytes from human or rat origin, resist an exposure to alkylating and disulphide SH-reagents up to relatively high dose (1.0 mM). However, organic mercury compounds triggered an extensive bleb formation, as a result of SH-blocking, thereby disturbing the osmotic balance by blocking Na+/K+ carriers. Of all tested reagents, organic mercury compounds arose as the most toxic reagents.

Nature of inhibition of renal aspartate reabsorption in experimental Fanconi syndrome.

Administration of heavy metals or maleic acid induces a condition resembling the Fanconi syndrome. In the case of metals, an apparently uncompetitive inhibition of reabsorption of amino acids was observed 2 days or longer after injection into rabbits (E. C. Foulkes and S. Blanck, Toxicol. Appl. Pharmacol. 64, 103-107, 1982). Transport of aspartate is now shown to be similarly inhibited by maleic acid and cephaloridin. Because maleic acid, as well as p-chloromercuribenzoate (PCMB) and Cd (in presence of mercaptoethanol), exerts an apparent uncompetitive effect within minutes of injection, the inhibition cannot simply reflect characteristics of regenerating epithelium. At low doses, PCMB inhibits aspartate reabsorption without altering transport of certain neutral amino acids, calcium, or p-aminohippurate. The apparent uncompetitive inhibition of aspartate reabsorption therefore does not connote general cytotoxicity. Metals cause relatively specific effects, manifested by functional lesions at the brush border. The mechanism of the aminoaciduric action of maleic acid remains unclear but cannot, under present conditions, involve back leakage of amino acids into tubular urine.