Role of glutathione in the biliary excretion of the arsenical drugs trimelarsan and melarsoprol

doi:10.1016/S0006-2952(00)00263-X

Biochemical Pharmacology

Volume 59, Issue 11, 1 June 2000, Pages 1375-1385

https://doi.org/10.1016/S0006-2952(00)00263-X Get rights and content

Abstract

After administration of the inorganic sodium arsenite or arsenate to rats, the biliary excretion of arsenic is rapid, is accompanied by the biliary output of large amounts of GSH, and is completely arrested by the GSH depletor diethyl maleate (DEM). We studied the biliary excretion of trimelarsan (TMA) and melarsoprol (MAP) in rats in order to determine whether biliary excretion is also significant in the disposition of these trivalent organic arsenicals that are used as therapeutic agents and whether GSH is also involved in their hepatobiliary transport. After injection of either drug (100 μmol/kg, i.v.), arsenic was rapidly excreted in bile (up to 1 μmol/kg · min, ∼55% of dose/100 min). Concurrently, TMA and MAP increased the biliary output of GSH 3- and 6 fold, and lowered the hepatic GSH content by 24% and 27%, respectively. In TMA-injected rats, pretreatment with DEM or buthionine sulfoximine decreased the initial biliary excretion of arsenic by 75% and 40%, respectively, whereas in MAP-injected rats these GSH depletors diminished arsenic output by 45% and 20%. Both arsenicals reacted with GSH in vitro, giving rise to the same product, which was also shown by HPLC analysis to be a major biliary metabolite of both TMA and MAP. This metabolite was sensitive to γ-glutamyltranspeptidase in vitro and its biliary excretion was virtually prevented by the GSH depletors, confirming that it is a GSH conjugate (purportedly melarsen–diglutathione). Some TMA was excreted in the bile unchanged, whereas a significant amount of MAP also appeared there as two glucuronides. The biliary excretion of unchanged TMA and MAP glucuronides was increased by experimental depletion of GSH. These studies indicate that the biliary excretion of TMA and MAP (1) is very significant in their disposition, (2) is partially dependent on the hepatic availability of GSH, as these arsenicals are excreted in part as a GSH conjugate, and (3) is concomitant with the increased appearance of GSH in bile, probably originating from dissociation of the unstable GSH conjugate of these arsenicals. Thus, conjugation with GSH is important in the elimination of both TMA and MAP, although glucuronidation is also involved in the fate of MAP.

Section snippets

Chemicals

TMA, melarsen, and melarsen oxide were provided by Rhone-Poulenc Rorer, whereas Arsobal™ in an injection containing 180 mg MAP in 5 mL propylene glycol was a gift from Specia. BSO, 5,5′-dithiobis(2-nitrobenzoic acid), GGT (type II from bovine liver), and glutathione reductase (type III) were purchased from Sigma Chemical Co. and reduced glutathione, NADPH, and phosphoric acid from Reanal. Acetonitrile for gradient HPLC was obtained from Spektrum-3D, DEM from Koch-Light Laboratories, d-glucaric

Biliary excretion of arsenic and glutathione after administration of TMA or MAP

As arsenic in control rat bile was not detected, arsenic in bile after administration of TMA and MAP originates entirely from the injected arsenicals. Therefore, biliary excretion of arsenic following administration of TMA or MAP reflects excretion of these arsenicals and/or their arsenic-containing metabolites into bile. As indicated in Fig. 1 (top), the biliary excretion of arsenic increased dramatically immediately after injection of TMA or MAP (100 μmol/kg, i.v.), reaching maximal rates of

Discussion

This study has revealed both similarities and differences in the biliary excretion of arsenite, an inorganic trivalent arsenical studied earlier 9, 10, and the two trivalent organic arsenical drugs, TMA and MAP. In rats, biliary excretion is significant for both arsenite and the melarsophenylarsine-type drugs. Nevertheless, both the extent and the maximal rate of biliary excretion of arsenic in rats injected with TMA or MAP exceed those in rats exposed to arsenite. Following injection of

Acknowledgements

This paper is based on a study supported by the Hungarian National Scientific Research Fund, the Hungarian Ministry of Social Welfare, and the Hungarian Academy of Sciences. The authors thank István Schweibert for technical assistance as well as Mrs. Katalin Gyulai for typing the manuscript.

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The study investigated whether dietary reduced glutathione (GSH) could be useful in alleviating arsenic-induced female gonadal injury in Wistar rats. Ingestion of sodium arsenite contaminated water (0.4 ppm) to Wister rats for seven estrous cycles (28 days) significantly diminished ovarian key steroidogenic enzymes activities and gonadotrophins and estradiol signaling along with disrupted ovarian and uterine growth. Oxidative stress as well as histological distortion of ovarian and uterine tissue was prominent along with prolonged diestrus in arsenic-exposed rats. Decreased levels of dopamine (DA) and norepinephrine (NE) and elevated level of 5-hydroxytryptamine (5-HT) in midbrain and diencephalons were also evident following arsenic exposure. All these deleterious effects of arsenic ingestion were mitigated by administration of GSH (8.0 mg/100 g body weight/day). Only tissue deposition of arsenic appeared to be unaffected by dietary GSH. The study highlighted that co-administration of GSH could ameliorate arsenic-mediated injuries of female reproductive organs.
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Pharmacokinetics and tissue distribution of the antileukaemic organoarsenicals arsthinol and melarsoprol in mice
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Melarsoprol and arsthinol have been shown to be effective on various leukaemia cell lines. Nevertheless, the tissue distribution of these compounds remains a key point since the bone marrow is considered as the site of action and the central nervous system as the site of the main toxicity. In this study, we have determined the exposure of each organ (blood, liver, bone marrow and brain) to arsenic, irrespectively of the exact nature of arsenic species contained by the organ.
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Arsenate (AsV), the environmentally prevalent form of arsenic, is converted sequentially in the body to arsenite (AsIII), monomethylarsonic acid (MMAsV), monomethylarsonous acid (MMAsIII), and dimethylarsinic acid (DMAsV) and some trimethylated metabolites. Although the biliary excretion of arsenic in rats is known to be glutathione (GSH)-dependent, involving transport of arsenic-GSH conjugates, the role of GSH in the reduction of AsV to the more toxic AsIII in vivo has not been defined. Therefore, we studied how the fate of AsV is influenced by buthionine sulfoximine (BSO), which depletes GSH in tissues. Control and BSO-treated rats were given AsV (50 μmol/kg, i.v.) and arsenic metabolites in bile, urine, blood and tissues were analysed by HPLC-HG-AFS. BSO increased retention of AsV in blood and tissues and decreased appearance of AsIII in blood, bile (by 96%) and urine (by 63%). The biliary excretion of MMAsIII was also nearly abolished, the appearance of MMAsIII and MMAsV in the blood was delayed and the renal concentrations of these monomethylated arsenicals were decreased by BSO. Interestingly, appearance of DMAsV in blood and urine remained unchanged and the concentrations of this metabolite in the kidneys and muscle were even increased in response to BSO. To test the role of γ-glutamyltranspeptidase (GGT) in arsenic disposition, the effect of the of the GGT inhibitor acivicin was investigated in rats injected with AsIII (50 μmol/kg, i.v.). Acivicin lowered the hepatic and renal GGT activities and increased the biliary as well as urinary excretion of GSH, but failed to alter the disposition (i.e. blood and tissue concentrations, biliary and urinary excretion) of AsIII and its metabolites. In conclusion, shortage of GSH decreases not only the hepatobiliary transport of arsenic, but also reduction of AsV and the formation of monomethylated arsenic, while not hindering the production of dimethylated arsenic. While GSH plays an important role in the disposition and toxicity of arsenic, GGT, which hydrolyses GSH and GSH conjugates, apparently does not influence the fate of the GSH-reactive trivalent arsenicals in rats.

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Chemotherapy and Metabolic InhibitorsRole of glutathione in the biliary excretion of the arsenical drugs trimelarsan and melarsoprol

Abstract

Section snippets

Chemicals

Biliary excretion of arsenic and glutathione after administration of TMA or MAP

Discussion

Acknowledgements

Blood

Trans R Soc Trop Med Hyg

Blood

Toxicol Appl Pharmacol

Biochem Pharmacol

Biochem Pharmacol

Biochem Pharmacol

Methods Enzymol

Anal Biochem

J Chromatography B Biomed Appl

Mol Biochem Parasitol

Anal Biochem

Toxicol Appl Pharmacol

Chem Biol Interact

J Chromatogr Biomed Appl B

Chemotherapy and Metabolic Inhibitors
Role of glutathione in the biliary excretion of the arsenical drugs trimelarsan and melarsoprol