María Eugenia Maciel

Inhibition of the Rat Breast Cytosolic Bioactivation of Ethanol to Acetaldehyde by Some Plant Polyphenols and Folic Acid

Abstract: There is a well-established association between alcohol consumption and breast cancer risk. About 4% of the breast cancers in developed countries are estimated to be attributable to drinking alcohol. The mechanism of tumor promotion by alcohol remains unknown. Recent studies from our laboratory and others showed the ability of mammary tissue to bioactivate ethanol to mutagenic/carcinogenic acetaldehyde and free radicals. Xanthine oxidoreductase (XOR) is an enzyme involved in those biotransformation processes. In the present study, we provide evidence of the ability of different natural polyphenols and of folic acid derivatives to inhibit the biotransformation of alcohol to acetaldehyde by rat breast cytosolic XOR. Folic acid and dihydrofolic acid, at concentrations of 10 μM, inhibited 100% and 84%, respectively, of the cytosolic acetaldehyde formation. Thirty-five polyphenols were tested in these initial experiments: ellagic acid, myricetin, quercetin, luteolin, and apigenin inhibited 79-95% at 10 μM concentrations. The remaining polyphenols were either less potent or noninhibitory of acetaldehyde formation at similar concentrations in these screening tests. Results are relevant to the known preventive effects of folic acid against alcohol-induced breast cancer and to their potential preventive actions if added to foods or alcoholic beverages.

Further studies on the potential contribution of acetaldehyde accumulation and oxidative stress in rat mammary tissue in the alcohol drinking promotion of breast cancer

There is available evidence supporting a positive association between alcohol intake and risk of breast cancer. However, there is limited information regarding possible mechanisms for this effect. Past studies from our laboratory suggest that acetaldehyde accumulation in mammary tissue after alcohol intake may be of particular relevance and that cytosolic and microsomal in situ bioactivation of ethanol to acetaldehyde and free radicals and the resulting stimulation of oxidative stress could be a significant early event related to tumor promotion. In the present studies repetitive alcohol drinking for 28 days was found to produce significant decreases in the mammary tissue content of GSH and alpha tocopherol and in glutathione S‐transferase or glutathione reductase activities. In contrast, glutathione peroxidase activity was slightly increased. Malondialdehyde determinations did not show the occurrence of lipid peroxidation while the xylenol orange procedure gave positive results. The mammary microsomal metabolism of ethanol to acetaldehyde was not induced after an acute dose of ethanol or acetone able to induce the activity of its liver counterpart. The cytosolic pathway of alcohol metabolism instead was significantly enhanced by these two treatments. No increased generation of comet images was found either in mammary tissue or in liver under the experimental conditions tested. Results suggest that, while acetaldehyde accumulation in mammary tissue could be a critical event resulting from increasing production of acetaldehyde in situ plus an additional amount of it arriving via blood, other factors such as poor handling of the accumulated acetaldehyde could be also relevant. Copyright

Inhibition of rat mammary microsomal oxidation of ethanol to acetaldehyde by plant polyphenols

We previously reported that the microsomal fraction from rat mammary tissue is able to oxidize ethanol to acetaldehyde, a mutagenic-carcinogenic metabolite, depending on the presence of NADPH and oxygen but not inhibited by carbon monoxide or other cytochrome P450 inhibitors. The process was strongly inhibited by diphenyleneiodonium, a known inhibitor of NADPH oxidase, and by nordihydroguaiaretic acid, an inhibitor of lipoxygenases. This led us to suggest that both enzymes could be involved. With the purpose of identifying natural compounds present in food with the ability to decrease the production of acetaldehyde in mammary tissue, in the present studies, several plant polyphenols having inhibitory effects on lipoxygenases and of antioxidant nature were tested as potential inhibitors of the rat mammary tissue microsomal pathway of ethanol oxidation. We included in the present screening study 32 polyphenols having ready availability and that were also tested against the rat mammary tissue cytosolic metabolism of ethanol to acetaldehyde. Several polyphenols were also able to inhibit the microsomal ethanol oxidation at concentrations as low was 10-50 μM. The results of these screening experiments suggest the potential of several plant polyphenols to prevent in vivo production and accumulation of acetaldehyde in mammary tissue.

Preventive Effects of Plant Polyphenols in the Promotion of Mammary Cancer and Testicular Damage Induced by Alcohol Drinking

Excessive alcohol drinking promotes mammary cancer in women and deleterious effects to testes in males. Evidence about the need of ethanol bioactivation to acetaldehyde and promotion of oxidative stress on these harmful effects of alcohol drinking is reviewed. In situ relevant pathways of acetaldehyde formation exist in the microsomal and cytosolic fractions of mammary tissue which are accompanied of its poor detoxication and this lead to acetaldehyde accumulation. This accumulative process, the oxidative stress promoted, and the pro-estrogenic effects of alcohol might be involved in the carcinogenic action of alcohol drinking. Acetaldehyde formation and ethanol promoted oxidative stress also occurs in the cytosolic and microsomal fractions of the testes. In this chapter, the inhibitory effects of several polyphenols on these pathways of acetaldehyde formation in both tissues at very low concentrations were studied. These effects and the known antioxidant properties of plant polyphenols open the possibility for future preventive studies of both pathologies.

Acetaldehyde Content and Oxidative Stress in the Deleterious Effects of Alcohol Drinking on Rat Uterine Horn

After alcohol exposure through a standard Lieber and De Carli diet for 28 days, a severe atrophy in the rat uteirne horn was observed, accompanied by significant alterations in its epithelial cells. Microsomal pathway of acetaldehyde production was slightly increased. Hydroxyl radicals were detected in the cytosolic fraction, and this was attributed to participation of xanthine oxidoreductase. They were also observed in the microsomal fraction in the presence of NADPH generating system. No generation of 1-hydroxyethyl was evidenced. The t-butylhydroperoxide-induced chemiluminescence analysis of uterine horn homogenates revealed a significant increase in the chemiluminiscence emission due to ethanol exposure. In the animals repeatedly exposed to alcohol, sulfhydryl content from uterine horn proteins was decreased, but no significant changes were observed in the protein carbonyl content from the same samples. Minor but significant decreasing changes were observed in the GSH content accompanied by a tendency to decrease in the GSH/GSSG ratio. A highly significant finding was the diminished activity content of glutathione peroxidase. Results suggest that acetaldehyde accumulation plus the oxidative stress may play an additional effect to the alcohol-promoted hormonal changes in the uterus reported by others after chronic exposure to alcohol.