Detection of a reactive pyrrole in the hepatic metabolism of the pyrrolizidine alkaloid, monocrotaline.
Pyrrolizidine alkaloids such as monocrotaline are bioactivated in the liver, resulting in veno-occlusive disease of the liver, pulmonary arterial hypertension, and right ventricular hypertrophy. We have searched for the formation of a reactive, alkylating pyrrole intermediate in the metabolism of monocrotaline by isolated rat liver microsomes, using the sulfhydryl-containing resin, thiopropyl sepharose 6B, as a trapping agent. Control experiments show that a toxic, chemically reactive, alkylating pyrrole such as dehydromonocrotaline binds covalently to the resin via a thioether bond, but that a less toxic, poorly alkylating pyrrole, such as dehydroretronecine, does not. Isolated hepatic microsomes metabolize monocrotaline to produce a pyrrole that binds to the resin, and that can be detected by means of the Ehrlich color reagent (p-dimethylaminobenzaldehyde). The pyrrole is releasable by silver nitrate treatment, thereby establishing it to be bound via a thioether linkage. In buffered ethanolic silver nitrate the major product is 7-ethoxy-1-hydroxymethyl-6,7-dihydro-5H-pyrrolizine (O7-ethyldehydroretronecine). This establishes that the thioether linkage is at the 7-position. The same product is obtained on release of the resin-bound pyrrole formed from the reaction of dehydromonocrotaline with the resin, thereby establishing the intermediacy of dehydromonocrotaline in the metabolism of monocrotaline.
Glowaz
S L
SL
Department of Pharmacology, College of Medicine, University of Arizona, Tucson 85724.
Michnika
M
M
Huxtable
R J
RJ
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D066298:In Vitro Techniques; D008297:Male; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism*; D016686:Monocrotaline / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism*; D011758:Pyrroles / Q000032:analysis; D051381:Rats
D011758:Pyrroles; C014114:monocrotaline pyrrole; D016686:Monocrotaline