Interaction of antimony tartrate with the tripeptide glutathione implication for its mode of action

The tripeptide glutathione (gamma-L-Glu-L-Cys-Gly, GSH) is thought to play an important role in the biological processing of antimony drugs. We have studied the complexation of the antileishmanial drug potassium antimony(III) tartrate to GSH in both aqueous solution and intact red blood cells by NMR spectroscopy and electrospray ionization mass spectrometry. The deprotonated thiol group of the cysteine residue is shown to be the only binding site for Sb(III), and a complex with the stoichiometry [Sb(GS)3] is formed. The stability constant for [Sb(GS)3] was determined to be log K 25 (I = 0.1 M, 298 K) based on a competition reaction between tartrate and GSH at different pH* values. In spite of being highly thermodynamically stable, the complex is kinetically labile. The rate of exchange of GSH between its free and Sb-bound form is pH-dependent, ranging from slow exchange on the 1H-NMR timescale at low pH (2 s-1 at pH 3.2) to relatively rapid exchange at biological pH (> 440 s-1). Such facile exchange may be important in the transport of Sb(III) in various biofluids and tissues in vivo. Our spin-echo 1H-NMR data show that Sb(III) rapidly entered red blood cell walls and was complexed by intracellular glutathione.

Comparative toxicity and tissue distribution of antimony potassium tartrate in rats and mice dosed by drinking water or intraperitoneal injection

Antimony potassium tartrate (APT) is a complex salt that until recently was used worldwide as an antischistosomal drug. Treatment was efficacious only if APT was administered intravenously to humans at a near lethal total dose of 36 mg/kg. Because unconfirmed epidemiologic studies suggested there might be an association between APT treatment and bladder cancer, we initiated prechronic toxicity studies with the drug to select a route of administration and doses in the event that chronic studies of APT were needed. The toxicity and concentration of tissue antimony levels were compared in 14-d studies with F344 rats and B6C3F1 mice administered APT in the drinking water or by ip injection to determine the most appropriate route for longer term studies. Drinking water doses estimated by water consumption were 0, 16, 28, 59, 94 and 168 mg/kg in rats and 0, 59, 98, 174, 273, and 407 mg/kg in mice. APT was poorly absorbed and relatively nontoxic orally, whereas ip administration of the drug caused mortality, body weight decrements, and lesions in the liver and kidney at doses about one order of magnitude below those in drinking water. Because of these data and the dose-related accumulation of antimony in the target organs, an ip dose regimen was selected for subsequent studies. Both sexes of F344 rats and B6C3F1 mice were given 0, 1.5, 3, 6, 12, and 24 mg/kg doses of APT every other day for 90 d by ip injection. There were no clinical signs of toxicity nor gross or microscopic lesions in mice that could be attributed to toxicity of APT, although elevated concentrations of antimony were detected in the liver and spleen of mice. Rats were more sensitive than mice to the toxic effects of APT, exhibiting dose-related mortality, body weight decrements, and hepatotoxicity. The concentrations of antimony measured in liver, blood, kidney, spleen, and heart of rats were proportional to dose, but there were no biochemical changes indicative of toxicity except in the liver. Hepatocellular degeneration and necrosis occurred in association with dose-related elevations in activities of the liver-specific serum enzymes sorbitol dehydrogenase and alanine aminotransferase. By alternating the site of abdominal injection and the days of treatment, mesenteric inflammation at the site of administration was minimized in the rats and mice, indicating that the ip route would be suitable for chronic studies.(ABSTRACT TRUNCATED AT 400 WORDS)