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The clastogenic activity of phenolic oxidation products Hanham, Ann Frances


Several epidemiological studies .have demonstrated the importance of diet in the development of gastro-intestinal carcinomas in man. This study examines the role of plant phenolics, major components of the human diet. Employing a CHO cell test system, it was observed that phenolics with at least two hydroxyl groups in the ortho position, relative to each other were particularly clastogenic. This activity was abolished by the addition of S9, a rat liver microsomal preparation. The clastogenic activity of these compounds was found to increase with time, alkaline pH, and the presence of transition metals. It was therefore deduced that the source of activity might be an oxidative by-product. High' pressure liquid chromatography was used to separate out these oxidative products. No activity was found to reside in any of the separated components or combinations of components. Further study therefore centred on oxidative products not retained by chromatography and on those labile to this.process. Under oxidative conditions, the presence of hydrogen peroxide was detected. Levels measured were sufficient to explain the clastogenic activity of completely oxidized solutions of phenolic acids. Addition of the enzyme, catalase, appeared to abolish all activity of completely oxidized solutions. Hydrogen peroxide could not, however, account for the genotoxic effects measured in freshly prepared solutions. The presence of superoxide was detected in actively oxidizing solutions of plant phenolics. Its production appeared to be pH-dependent. Addition of superoxide dismutase increased the clastogenic activity of compounds tested, presumably by converting superoxide to peroxide, a more stable oxidative by-product. Addition of tyrosinase, a monophenol oxidase, also increased the clastogenic activity of freshly prepared solutions. Since this enzyme catalyzes the oxidation of several phenolics without subsequent generation of peroxide, it was deduced that phenolic free radicals must also be present which could be at least partially responsible for the enhanced biological activity. Electron spin resonance proved this was the case. Using electron spin resonance, the primary oxidative products were characterized both at high pH and by enzymatic activation. The results obtained agree with those published in the literature. Several reports in the literature have suggested that phenolics may also act as free radical scavengers. The importance of plant phenolics in diet may therefore depend on the oxidative conditions of the system to be tested. Under oxidative conditions, free radicals appear to be generated, which are capable of causing mutations and chromosomal rearrangements. Phenolic oxidation products may therefore play a role as initiators and promotors of carcinogenesis. However, under alternate conditions, phenolics may also act to scavenge free radicals, and could therefore be classed as inhibitors of carcinogenesis.

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