title: Metabolic activation of pyrrolizidine alkaloids leading to phototoxicity and photogenotoxicity in human HaCaT keratinocytes.
abstract: Pyrrolizidine alkaloids, produced by a large number of poisonous plants with wide global distribution, are associated with genotoxicity, tumorigenicity, and hepatotoxicity in animals and humans. Mammalian metabolism converts pyrrolizidine alkaloids to reactive pyrrolic metabolites (dehydropyrrolizidine alkaloids) that form covalent protein and DNA adducts. Although a mechanistic understanding is currently unclear, pyrrolizidine alkaloids can cause secondary (hepatogenous) photosensitization and induce skin cancer. In this study, the phototoxicity of monocrotaline, riddelliine, dehydromonocrotaline, dehydroriddelliine, and dehydroretronecine (DHR) in human HaCaT keratinocytes under ultraviolet A (UVA) irradiation was determined. UVA irradiation of HaCaT cells treated with dehydromonocrotaline, dehydroriddelline, and DHR resulted in increased release of lactate dehydrogenase and enhanced photocytotoxicity proportional to the UVA doses. UVA-induced photochemical DNA damage also increased proportionally with dehydromonocrotaline and dehydroriddelline. UVA treatment potentiated the formation of 8-hydroxy-2'-deoxyguanosine DNA adducts induced by dehydromonocrotaline in HaCaT skin keratinocytes. Using electron spin resistance trapping, we found that UVA irradiation of dehydromonocrotaline and dehydroriddelliine generates reactive oxygen species (ROS), including hydroxyl radical, singlet oxygen, and superoxide, and electron transfer reactions, indicating that cytotoxicity and genotoxicity of these compounds could be mediated by ROS. Our results suggest that dehydropyrrolizidine alkaloids formed or delivered to the skin cause pyrrolizidine alkaloid-induced secondary photosensitization and possible skin cancer.
authors.affiliation: a National Center for Toxicological Research , US Food and Drug Administration , Jefferson , Arkansas , USA.
authors.forename: Chia-Chi
authors.initials: CC
authors.lastname: Wang
authors.forename: Qingsu
authors.initials: Q
authors.lastname: Xia
authors.forename: Meng
authors.initials: M
authors.lastname: Li
authors.forename: Shuguang
authors.initials: S
authors.lastname: Wang
authors.forename: Yuewei
authors.initials: Y
authors.lastname: Zhao
authors.forename: William H
authors.initials: WH
authors.lastname: Tolleson
authors.forename: Jun-Jie
authors.initials: JJ
authors.lastname: Yin
authors.forename: Peter P
authors.initials: PP
authors.lastname: Fu
mesh_terms: D002461:Cell Line, Transformed; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage; D017484:Dermatitis, Phototoxic / Q000209:etiology*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D015227:Lipid Peroxidation / Q000187:drug effects / Q000528:radiation effects; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000528:radiation effects; D015394:Molecular Structure; D011763:Pyrrolizidine Alkaloids / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity*; D017382:Reactive Oxygen Species / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D011763:Pyrrolizidine Alkaloids; D017382:Reactive Oxygen Species
keywords: UVA light; dehydropyrrolizidine alkaloids; human HaCaT keratinocytes; lipid peroxidation; photoirradiation; reactive oxygen species