Effect of tea beverages on aldehyde oxidase activity.

Aldehyde oxidase (AO) plays an important role in metabolizing antitumor and antiviral drugs, including methotrexate, cyclophosphamide and acyclovir. Green tea and its catechins have been shown to modulate the activities of various xenobiotic-metabolizing cytochrome P450 species, both in vivo and in vitro, but their effect on AO has not been studied. Therefore, we evaluated the effect of tea beverages on AO activity in rat and human liver cytosol. We also investigated the influence of several catechins on AO activity in rat liver cytosol. AO activity was evaluated in terms of oxidation of N-1-methylnicotinamide to N-1-methyl-2-pyridone-5-carboxamide and N-1-methyl-4-pyridone-3-carboxamide. Bottled green tea beverages at 10% (vol/vol) inhibited AO activity by 90.0-93.5%, while at 1.0% (vol/vol), they reduced AO activity by 73.9-90.0%. At 0.1% (vol/vol), green tea II and III, which have high contents of catechins and their derivatives, inhibited AO activity by 24.3% and 38.8%, respectively. Bottled mineral water had no effect. AO activity was inhibited potently by epicatechin and epicatechin gallate. These results indicate that the AO-inhibitory activity of tea beverages is predominantly due to catechins and their derivatives. Thus, consumption of tea beverages may cause a decrease of AO activity, which may result in reduced clearance of drugs that are AO substrates.