Detection of potential chemopreventive agents in plants
Abstract
In efforts to prevent cancer growing attention has been paid to the identification of chemical compounds for use as chemopreventive agents. In order to screen and rapidly fractionate plant extracts to isolate potential chemopreventive agents, an assay measuring their effects on the metabolism of benzo(a)pyrene (B(a)P) to water-soluble derivatives in hamster embryo cell cultures was utilized. Activity-directed fractionation of an extract of Trifolium pratense led to the isolation of biochanin A, an isoflavone. Biochanin A was found to inhibit two pathways of metabolism of B(a)P in hamster embryo cells: the cytochrome P-450 system and conjugation of B(a)P-phenols to glucuronides. Biochanin A treatment of hamster embryo cell cultures resulted in a decrease in the binding of B(a)P to DNA, especially through the carcinogenic (+)-anti-B(a)P-7,8-diol-9,10-epoxide. Biochanin A was not mutagenic and was an effective inhibitor of B(a)P-induced mutagenesis in the hamster embryo cell-mediated V79 cell mutation assay. To determine which flavonoids would have the greatest ability to inhibit B(a)P metabolism, a series of isoflavonoids and flavonoids were tested in the hamster embryo cell culture B(a)P metabolism assay. Analysis of structure-activity relationships indicated the importance of the 5- and 7-hydroxyl groups and a 2,3-double bond for activity and that flavonoids were more active than the corresponding isoflavonoids. Studies on the metabolism of B(a)P by hepatic microsomes from rats induced with various classes of cytochrome P-450 inducers demonstrated that those flavonoids active in inhibiting the metabolic activation of B(a)P in cells were potent inhibitors of $\beta$-naphthoflavone-induced cytochrome P-450. No correlation was found with effects on noninduced or phenobarbital-induced cytochrome P-450. Studies with a series of glucosinolates demonstrated that specific glucosinolates can increase the activation of B(a)P in hamster embryo cell cultures, illustrating the importance of caution in considering their effects on various classes of carcinogens in the selection of compounds as potential chemopreventive agents. The above studies demonstrate the ability of the B(a)P metabolism in hamster embryo cell culture assay to allow the isolation and characterization of potential chemopreventive agents from plants. These results indicate that based upon inhibition of B(a)P activation and relatively low toxicity, the flavonoids acacetin and kaempferide are promising candidates for testing as chemopreventive agents.
Degree
Ph.D.
Advisors
Baird, Purdue University.
Subject Area
Pharmacology|Pharmaceuticals|Oncology
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