Relationship between glutathione concentration and metabolism of the pyrrolizidine alkaloid, monocrotaline, in the isolated, perfused liver.
The influence of GSH concentration on metabolism of monocrotaline was examined in the isolated, perfused rat liver. Chloroethanol (0.37 mmol/kg), diethyl maleate (5.6 mmol/kg), and buthionine sulfoximine (72.9 mmol/kg) given in vivo reduced hepatic GSH from 3.7 mumol/g wet weight to 1.5, 0.6 and 0.9 mumol/g, respectively. Livers were then perfused in vitro for 1 hr with monocrotaline (0.5 mM). GSH depletion had no effect on the total release of pyrrolic metabolites of monocrotaline. Depletion, however, markedly affected the pattern of pyrrole release. Biliary release of 7-glutathionyl-6,7-dihydro-1-hydroxy-methyl-5H-pyrrolizine (GSDHP) was reduced by up to 72%. Pretreatment with diethyl maleate or buthionine sulfoximine increased the level of protein-bound pyrroles in the liver by 107 and 84%, respectively. Such pyrroles are probably responsible for liver toxicity. GSH depletion also led to a doubling of dehydromonocrotaline release into the perfusate. This metabolite is probably responsible for the extrahepatic toxicity of monocrotaline. Release into perfusate of the relatively nontoxic metabolite, 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP) was correspondingly decreased. Hepatic GSH content was increased to 4.4 mumol/g by pretreatment with oxo-4-thiazolidine carboxylate (4.76 mmol/kg). This agent increased total pyrrolic metabolites by 54%. Biliary release of GSDHP and perfusate release of dehydromonocrotaline and DHP were all increased. Thus, hepatic GSH levels regulate the metabolism of monocrotaline and dehydromonocrotaline and, consequently, the hepatic and extrahepatic toxicity of monocrotaline. GSH depletion leads to a switch from the biliary release of the midly toxic GSDHP to the perfusate release of the highly toxic dehydromonocrotaline. GSH depletion also permits more dehydromonocrotaline in the liver to become available for macromolecular alkylation. These findings suggest that nutritional intake of sulfur-containing amino acids can influence the severity of pyrrolizidine poisoning.
Department of Pharmacology, College of Medicine, University of Arizona, Tucson 85724.
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Yan
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Huxtable
D000704:Analysis of Variance; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000633:toxicity; D001646:Bile / Q000378:metabolism; D019328:Buthionine Sulfoximine; D005023:Ethylene Chlorohydrin / Q000494:pharmacology; D005978:Glutathione / Q000031:analogs & derivatives / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008298:Maleates / Q000494:pharmacology; D008717:Methionine Sulfoximine / Q000031:analogs & derivatives / Q000494:pharmacology; D016686:Monocrotaline / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000378:metabolism* / Q000633:toxicity; D010477:Perfusion; D011758:Pyrroles / Q000378:metabolism; D011761:Pyrrolidonecarboxylic Acid; D051381:Rats; D017207:Rats, Sprague-Dawley; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines
C091658:7-glutathionyl-6,7-dihydro-1-hydroxymethyl-5H-pyrrolizine; D000964:Antimetabolites, Antineoplastic; D008298:Maleates; D011758:Pyrroles; D013844:Thiazoles; D053778:Thiazolidines; D008717:Methionine Sulfoximine; C014114:monocrotaline pyrrole; D019328:Buthionine Sulfoximine; D016686:Monocrotaline; D005023:Ethylene Chlorohydrin; C014476:diethyl maleate; D005978:Glutathione; D011761:Pyrrolidonecarboxylic Acid; C029536:2-oxothiazolidine-4-carboxylic acid