Persistent Link:
http://hdl.handle.net/10150/282228
Title:
Photooxidation and beta-carotene: Effects in membrane models
Author:
Stratton, Steven Paul, 1968-
Issue Date:
1996
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:
Intake and serum levels of β-carotene have inverse associations with cancer risk. Previous research indicates chemopreventive actions may be due to antioxidant properties. Photooxidation reactions are an important source of reactive oxygen species. Photosensitizers can damage tissue by catalyzing the formation of oxyradicals and singlet oxygen (¹O₂). β-Carotene efficiently quenches ¹O₂ catalytically via a physical reaction. However, concomitant chemical reactions during photosensitized oxidations consume β-carotene. This dissertation is a study of β-carotene antioxidant mechanisms in solution and phospholipid membrane models of photooxidation. Photosensitized oxidation of β-carotene in solution yielded products analyzed by reverse-phase HPLC, UV-vis spectrophotometry, and mass spectrometry. These products were identified as β-ionone, β-apo-14'-carotenal, β-apo-10'-carotenal, β-apo-8'-carotenal, and the novel product β-carotene-5,8-endoperoxide, which was determined to be a specific marker for ¹O₂ oxidation of β-carotene. To study the effect of β-carotene and other agents on photooxidation, an isotope dilution GC-MS assay was developed which quantitatively distinguishes ¹O₂-mediated and radical-mediated lipid peroxidation products resulting from photosensitized oxidation of dilinoleoylphosphatidylcholine liposomes. This unique assay utilizes quantitative standards of 9- and 10-hydroxyoctadecadienoate and was used to generate "photooxidation profiles" of the photosensitizers methylene blue, Rose Bengal, and tetraphenylporphine. These profiles indicate a shift from Type II to Type I photooxidation mechanisms in later stages. In the liposome system, β-carotene successfully inhibited both ¹O₂-mediated and radical-mediated lipid peroxidation at early stages but was less effective at later stages. Production of radical-mediated products increased faster than ¹O₂-mediated products at later stages even though 40% of the initial β-carotene was present after 4 h. β-Carotene-5,8-endoperoxide was not detected in this system. Equimolar α-tocopherol was ineffective in inhibiting lipid peroxidation, however, a 10-fold increase in α-tocopherol concentration inhibited almost all radical-mediated lipid peroxidation as well as early-stage ¹O₂-mediated lipid peroxidation. Cumene hydroperoxide stimulated radical-mediated lipid peroxidation. Type II photooxidation products may enhance Type I mechanisms. β-Carotene was shown quantitatively to suppress photooxidation by inhibiting Type II mechanisms alone. Since β-Carotene may prevent tissue damage due to photooxidation, an understanding of the mechanisms involved will be important in maximizing its protective effects.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Health Sciences, Toxicology.; Chemistry, Biochemistry.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Pharmacology and Toxicology
Degree Grantor:
University of Arizona
Advisor:
Liebler, Daniel C.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titlePhotooxidation and beta-carotene: Effects in membrane modelsen_US
dc.creatorStratton, Steven Paul, 1968-en_US
dc.contributor.authorStratton, Steven Paul, 1968-en_US
dc.date.issued1996en_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.abstractIntake and serum levels of β-carotene have inverse associations with cancer risk. Previous research indicates chemopreventive actions may be due to antioxidant properties. Photooxidation reactions are an important source of reactive oxygen species. Photosensitizers can damage tissue by catalyzing the formation of oxyradicals and singlet oxygen (¹O₂). β-Carotene efficiently quenches ¹O₂ catalytically via a physical reaction. However, concomitant chemical reactions during photosensitized oxidations consume β-carotene. This dissertation is a study of β-carotene antioxidant mechanisms in solution and phospholipid membrane models of photooxidation. Photosensitized oxidation of β-carotene in solution yielded products analyzed by reverse-phase HPLC, UV-vis spectrophotometry, and mass spectrometry. These products were identified as β-ionone, β-apo-14'-carotenal, β-apo-10'-carotenal, β-apo-8'-carotenal, and the novel product β-carotene-5,8-endoperoxide, which was determined to be a specific marker for ¹O₂ oxidation of β-carotene. To study the effect of β-carotene and other agents on photooxidation, an isotope dilution GC-MS assay was developed which quantitatively distinguishes ¹O₂-mediated and radical-mediated lipid peroxidation products resulting from photosensitized oxidation of dilinoleoylphosphatidylcholine liposomes. This unique assay utilizes quantitative standards of 9- and 10-hydroxyoctadecadienoate and was used to generate "photooxidation profiles" of the photosensitizers methylene blue, Rose Bengal, and tetraphenylporphine. These profiles indicate a shift from Type II to Type I photooxidation mechanisms in later stages. In the liposome system, β-carotene successfully inhibited both ¹O₂-mediated and radical-mediated lipid peroxidation at early stages but was less effective at later stages. Production of radical-mediated products increased faster than ¹O₂-mediated products at later stages even though 40% of the initial β-carotene was present after 4 h. β-Carotene-5,8-endoperoxide was not detected in this system. Equimolar α-tocopherol was ineffective in inhibiting lipid peroxidation, however, a 10-fold increase in α-tocopherol concentration inhibited almost all radical-mediated lipid peroxidation as well as early-stage ¹O₂-mediated lipid peroxidation. Cumene hydroperoxide stimulated radical-mediated lipid peroxidation. Type II photooxidation products may enhance Type I mechanisms. β-Carotene was shown quantitatively to suppress photooxidation by inhibiting Type II mechanisms alone. Since β-Carotene may prevent tissue damage due to photooxidation, an understanding of the mechanisms involved will be important in maximizing its protective effects.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectHealth Sciences, Toxicology.en_US
dc.subjectChemistry, Biochemistry.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplinePharmacology and Toxicologyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorLiebler, Daniel C.en_US
dc.identifier.proquest9720609en_US
dc.identifier.bibrecord.b34537077en_US
All Items in UA Campus Repository are protected by copyright, with all rights reserved, unless otherwise indicated.