Mechanisms Of Chemically Induced Photosensitivity

当光与皮肤和眼睛内的内源性或外源性化学物质相互作用时，会产生光敏。这一过程可能产生不良的临床后果，如光毒性（过度晒伤）、光过敏、光致癌性和/或光致突变性；或者在肿瘤光动力治疗（PDT）和煤焦油、蒽醌或补骨脂素（PUVA）治疗牛皮癣中有有益的效果。本研究项目的目的是阐明光敏剂发挥其毒性或治疗作用的光化学机制，并设计适当的体外或体内试验来检测光敏剂。氟喹诺酮类（FLQ）是一类相对较新的抗菌药物，可用于治疗革兰氏阴性和革兰氏阳性细菌感染。当用于人类时，FLQs经常引起光毒性。最近的研究表明，洛美沙星（LOME）和氟罗沙星（FLER）可引起HR/J小鼠的鳞状细胞癌，这些小鼠注射了这些药物并接受UV-A （315-400nm）照射。然而，我们无法证明UVA/LOME在TgAC转基因小鼠暴露12周后的光致癌性，即使这些小鼠皮肤中LOME的水平（~2ug/g）与HR/J动物相同或更高。我们用8-甲氧基补骨脂素/UVA重复了这个实验，发现虽然TgAC小鼠确实发生了乳头状瘤，但它的发展速度比HR/J小鼠慢。金毛是一种草药，广泛用于许多医疗应用，包括眼洗剂和护肤液，目前正在接受国家毒理学计划的测试。本文研究了黄芪中最丰富的两种生物碱小檗碱和水合碱以及少量的生物碱加拿大碱、棕榈碱和水合碱的光化学和光生物学特性。小檗碱/UVA和水合碱/UVA损伤角质细胞DNA，通过彗星测定。加那丁和巴马汀效果较差。在水溶液中，小檗碱和水合碱都不能使单线态氧光敏，但在二氯甲烷中，小檗碱产生单线态氧的量子产率为0.34。这表明疏水环境是光敏化所必需的。我们的数据表明，虽然小檗碱在水中是一种弱单线态氧光敏剂，但在疏水环境中能够产生活性氧。因此，小檗碱对DNA或膜的损伤可能涉及光动力学机制。核桃酮（5-羟基-1,4-萘醌）存在于黑核桃中，是膳食补充剂、染发剂和核桃油剂的一种成分。压碎的黑核桃壳有时用于皮肤治疗真菌、细菌或病毒感染。目前，国家毒理学计划正在对Juglone进行研究。我们发现核桃酮对角质形成细胞是有毒的，角质形成细胞将其代谢为半醌自由基。后者与氧反应生成超氧化物和羟基自由基。这些反应在紫外线照射下都没有增强。防晒剂2-苯基苯并咪唑-5-磺酸（PBSA）及其母体2-苯基苯并咪唑（PBI）在UVB照射下可通过I型和II型机制引起DNA光损伤。在紫外照射下，PBSA好氧溶液产生超氧自由基和羟基自由基，并被5,5-二甲基-1-吡咯啉n -氧化物（DMPO）捕获。在中性水溶液（pH 7.4）中，当存在半胱氨酸、谷胱甘肽和叠氮化物时，PBSA表现出较强的氧化性能，利用自旋阱DMPO检测了s -半胱氨酸、谷胱甘肽和叠氮基自由基。在MeCN中，PBI和PBSA生成的单线态氧的量子产率分别为0.07和0.04。我们的研究表明，紫外照射PBSA和PBI会产生多种自由基和活性氧，这些自由基和活性氧可能参与了DNA的光损伤。

Summary of Work: Photosensitization can result when light interacts with endogenous or exogenous chemical agents in the skin and eyes. This process can produce undesirable clinical consequences, such as phototoxicity (exaggerated sunburn), photoallergy, photocarcinogenicity and/or photomutagenicity ; or it can have beneficial effects as in tumor photodynamic therapy (PDT) and coal tar, anthralin or psoralen (PUVA) therapy for psoriasis. The objective of this research project is to elucidate the photochemical mechanisms whereby photosensitizers exert their toxic or therapeutic effects and to design appropriate in vitro or in vivo tests to detect photosensitizers. Fluoroquinolones (FLQ) are a relatively new class of antibacterials that are useful in the treatment of gram-negative and gram-positive bacterial infections. When used in humans FLQs often cause phototoxicity. Recent studies by others have shown that lomefloxacin (LOME) and fleroxacin (FLER) cause squamous cell carcinomas in HR/J mice injected with these drugs and irradiated with UV-A (315-400nm). However, we have been unable to demonstrate the photocarcinogenicity of UVA/LOME in the TgAC transgenic mouse after 12 weeks of exposure, even though the skin levels of LOME in these mice (~2ug/g) were the same or higher than those obtained in the HR/J animals. We have repeated this experiment with 8-methoxypsoralen/UVA and found that, while the TgAC mouse does develop papillomas, it does so more slowly than the HR/J mouse. Goldenseal is a herb, widely used for numerous medical applications including eyewashes and skin lotions, which is currently undergoing testing by the National Toxicology Program. We have studied the photochemistry and photobiology of berberine and hydrastine, the two most abundant Goldenseal alkaloids and minor alkaloids canadine, palmatine and hydrastinine. Berberine/UVA and hydrastine/UVA damage keratinocyte DNA as measured by the Comet assay. Canadine and palmatine were less effective. Neither berberine nor hydrastine photosensitizes singlet oxygen in aqueous solutions, but singlet oxygen is produced by berberine with a quantum yield 0.34 in methylene chloride. This suggests that a hydrophobic environment is required for photosensitization. Our data show that, although a weak singlet oxygen photosensitizer in water, berberine is able to produce reactive oxygen species in a hydrophobic environment. Thus DNA or membrane damage by berberine may involve a photodynamic mechanism. Juglone (5-hydroxy-1,4-naphthoquinone) is present in black walnuts and is a component of dietary supplements, hair dyes and walnut oil stains. Crushed black walnut hulls are sometimes applied to the skin to treat fungal, bacterial or viral infections. Juglone is currently undergoing study by the National Toxicology Program. We have found that juglone is toxic to keratinocytes which metabolize it to a semiquinone free radical. Reaction of the latter with oxygen generates superoxide and the hydroxyl radical. None of these reactions was enhaced by UV radiation. The sunscreen agent, 2-phenylbenzimidazole-5-sulfonic acid (PBSA), and its parent 2-phenylbenzimidazole (PBI) cause DNA photodamage via both Type I and Type II mechanisms when UVB irradiated. During UV irradiation of an aerobic solution of PBSA, superoxide and hydroxyl radicals were generated and trapped by 5,5-dimethyl-1-pyrroline N-oxide (DMPO). PBSA showed strong oxidizing properties when UV irradiated in neutral aqueous solution (pH 7.4) in the presence of cysteine, glutathione and azide, as evidenced by the detection of S-cysteinyl, glutathiyl and azidyl radicals with the aid of the spin trap DMPO. PBI and PBSA generated singlet oxygen with quantum yields 0.07 and 0.04 respectively in MeCN. Our studies demonstrate that UV irradiation of PBSA and PBI generates a variety of free radicals and active oxygen species that may be involved in the photodamage of DNA.