Pyrrolizidine alkaloids: Hepatic metabolism and extrahepatic toxicity.

Persistent Link:
http://hdl.handle.net/10150/186599
Title:
Pyrrolizidine alkaloids: Hepatic metabolism and extrahepatic toxicity.
Author:
Wild, Stacie Lynn.
Issue Date:
1994
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Pyrrolizidine alkaloids are proposed to be metabolized in the liver to reactive pyrrole species, or dehydroalkaloids. These reactive pyrroles are hypothesized to be responsible for pyrrolizidine alkaloid toxicity. This dissertation research has established that dehydroalkaloids are, in fact, metabolites of pyrrolizidine alkaloids. It was first determined that dehydromonocrotaline is produced during hepatic microsomal metabolism of monocrotaline and that it has the ability to bind in vitro with a synthetic thiol-containing resin, Thiopropyl Sepharose 6B. Similarly, synthetic dehydromonocrotaline binds to this resin. Dehydromonocrotaline was identified as a pyrrolizidine alkaloid metabolite based upon its resin cleavage products. When resin-bound pyrrole, synthetic or microsomally generated, was cleaved in a buffered, ethanolic silver nitrate solution, O⁷-ethyl dehydroretronecine was the major product, supporting the suggestion that the pyrrole generated by hepatic microsomes is dehydromonocrotaline. This system was then used to determine the formation of dehydroalkaloids from other pyrrolizidine alkaloids. These other alkaloids--trichodesmine, retrorsine, senecionine and heliotrine--cause toxicity to the liver as well as to extrahepatic organs. Their metabolism in this system reveals that alkaloids which produce extrahepatic toxicity have an increased percentage of reactive metabolites formed by phenobarbital-induced hepatic microsomes. Therefore, this system in vitro can be a good predictor of alkaloids which may produce extrahepatic toxicity in vivo. Trichodesmine is a pyrrolizidine alkaloid that is unique in its neurotoxicity. It is structurally similar to monocrotaline, yet it varies widely in its toxicity. It was determined that trichodesmine is more toxic in the rat than monocrotaline as indexed by LD₅₀ values. The distribution of pyrrolic metabolites reveals that trichodesmine treatment results in brain pyrrole levels 4 times higher than monocrotaline, retrorsine, or control. Histopathologic investigation of trichodesmine-treated animals reveals severe neuronal death in the cerebral cortex. These results suggest that neurotoxicity observed with trichodesmine is a result of pyrrole metabolites reaching the brain, thus providing further evidence for the involvement of pyrrole metabolites in pyrrolizidine alkaloid-induced extrahepatic toxicity.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Dissertations, Academic.; Toxicology.; Pharmacology.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Pharmacology and Toxicology; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Huxtable, Ryan J.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titlePyrrolizidine alkaloids: Hepatic metabolism and extrahepatic toxicity.en_US
dc.creatorWild, Stacie Lynn.en_US
dc.contributor.authorWild, Stacie Lynn.en_US
dc.date.issued1994en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractPyrrolizidine alkaloids are proposed to be metabolized in the liver to reactive pyrrole species, or dehydroalkaloids. These reactive pyrroles are hypothesized to be responsible for pyrrolizidine alkaloid toxicity. This dissertation research has established that dehydroalkaloids are, in fact, metabolites of pyrrolizidine alkaloids. It was first determined that dehydromonocrotaline is produced during hepatic microsomal metabolism of monocrotaline and that it has the ability to bind in vitro with a synthetic thiol-containing resin, Thiopropyl Sepharose 6B. Similarly, synthetic dehydromonocrotaline binds to this resin. Dehydromonocrotaline was identified as a pyrrolizidine alkaloid metabolite based upon its resin cleavage products. When resin-bound pyrrole, synthetic or microsomally generated, was cleaved in a buffered, ethanolic silver nitrate solution, O⁷-ethyl dehydroretronecine was the major product, supporting the suggestion that the pyrrole generated by hepatic microsomes is dehydromonocrotaline. This system was then used to determine the formation of dehydroalkaloids from other pyrrolizidine alkaloids. These other alkaloids--trichodesmine, retrorsine, senecionine and heliotrine--cause toxicity to the liver as well as to extrahepatic organs. Their metabolism in this system reveals that alkaloids which produce extrahepatic toxicity have an increased percentage of reactive metabolites formed by phenobarbital-induced hepatic microsomes. Therefore, this system in vitro can be a good predictor of alkaloids which may produce extrahepatic toxicity in vivo. Trichodesmine is a pyrrolizidine alkaloid that is unique in its neurotoxicity. It is structurally similar to monocrotaline, yet it varies widely in its toxicity. It was determined that trichodesmine is more toxic in the rat than monocrotaline as indexed by LD₅₀ values. The distribution of pyrrolic metabolites reveals that trichodesmine treatment results in brain pyrrole levels 4 times higher than monocrotaline, retrorsine, or control. Histopathologic investigation of trichodesmine-treated animals reveals severe neuronal death in the cerebral cortex. These results suggest that neurotoxicity observed with trichodesmine is a result of pyrrole metabolites reaching the brain, thus providing further evidence for the involvement of pyrrole metabolites in pyrrolizidine alkaloid-induced extrahepatic toxicity.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectDissertations, Academic.en_US
dc.subjectToxicology.en_US
dc.subjectPharmacology.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplinePharmacology and Toxicologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairHuxtable, Ryan J.en_US
dc.contributor.committeememberBrendel, Klausen_US
dc.contributor.committeememberGandolfi, A. Jayen_US
dc.contributor.committeememberHalpert, James R.en_US
dc.contributor.committeememberLaird, Hugh E.en_US
dc.identifier.proquest9424933en_US
dc.identifier.oclc722384683en_US
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