Papel Protetor dos Chás Provenientes da Camellia Sinensis sobre Atividade da Enzima Δ-ALA-d de Tecido Ovariano Inibida pelo Cádmio

Abstract

δ-aminolevulinate dehydratase (δ-ALA-D) is a thiol enzyme that catalyzes one of the initial reactions of heme biosynthesis. This enzyme is considered a marker protein for metal poisoning. Cadmium is a toxic pollutant, widely distributed in the environment, and human exposure results mainly from cigarette smoke, air pollution and consumption of food and water contaminated by the metal. Cadmium has a low excretion rate of the organism and high biological ha lf- life and for this reason it accumulates in the blood, kidney and liver as well as on reproductive organs including the ovaries. The pathogenesis of ovarian follicular damage and reduction of viability after exposure to cadmium has been associated with o xidative damage. Thus, antioxidant compounds may be an alternative therapy against cadmium toxicity. The present study evaluates the protective effect of Camellia sinensis (green, white and red teas) on the inhibition of ovarian δ-ALA-D activity induced by cadmium in vitro and ex vivo. The effect of cadmium chloride (IC 50 20μM), tea infusions (0.07 to 10 mg/ml) and individual catechins – epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), epigallocatechin gallate (EGCG) - were evaluated on bovine ovaries δ-ALA-D activity (in vitro). Furthermore, the composition of tea infusions was measured on a HPLC quantitative assay of catechins, gallic acid and purine alkaloids, and the content of total polyphenols was measured by Folin–Ciocalteu method. The green and white teas, at the highest concentrations studied, restored the δ-ALA-D activity inhibited by cadmium while red tea had no effect in vitro. Green tea has higher amount of phenolic content ( 757.24 mg GAE/mL ) and catechins (EGCG = 205.64 μg/mL; EC = 84.59 μg/mL; EGC = 75.53 μg/mL; ECG = 64.73 μg/mL) compared with white tea ( 499.37 mg GAE/mL ) (EGCG = 105.57 μg/mL; EC = 54.73 μg/mL; EGC = 81.96 μg/mL; ECG = 34.25 μg/mL) and red tea (272.39 mg GAE/mL) ( only detected ECG = 1.36 μg/mL). None of the tested catechins alone was effective in restoring the enzyme activity inhibited by cadmium. For the ex vivo experiments, mice received a single administration of CdCl 2 , at doses of 2.5 mg/kg and 5 mg/kg intraperitoneally, and green tea (250 mg/kg) administered orally. We found that acute exposure to cadmium at doses of 2.5 and 5 mg/kg inhibited (about 26% and 33%, respectively) δ-ALA-D activity of mice ovaries, and green tea was able to restore this inhibition. The greater effect observed in vitro by green tea as well as the protective role presented at the ex vivo study, could be attributed to the higher phenols content, but not catechins. In fact, the catechins were not able to restore the enzyme activity inhibited by cadmium, demonstrating that these compounds are not the key components responsible for the beneficial effect of green tea observed in this study. This study demonstrated the effectiveness of green tea in restoring the δ-ALA-D activity inhibited by cadmium in ovarian tissue.