Lecithin-Cholesterol Acyltransferase activity during maturation of human preovulatory follicles with different concentrations of ascorbate, α-tocopherol and nitrotyrosine.

The LCAT enzyme transfers an acyl chain from lecithin to cholesterol or oestradiol, thus playing a crucial role in reverse cholesterol transport and follicular synthesis of potent long-lived estrogens. The mechanism of catalysis is biphasic, as it is based on a phospholipase activity and an esterifying activity. Sulfhydryl groups were previously reported to be required for the esterification step. LCAT was previously shown to be inhibited by thiol oxidants, such as peroxynitrite. Peroxynitrite also converts tyrosine to nitrotyrosines. We found, in fluids of human preovulatory follicles, high levels of nitrotyrosine (N-Tyr) associated with low LCAT activity, and vice versa. Follicular fluids were also analysed for their levels of oestradiol (E) and progesterone (P). The E/P ratio, which decreases as ovulation approaches, was used to evaluate the maturation status of each follicle. The enzyme activity was negatively correlated with the E/P ratio. Ascorbate (Asc) and alpha-tocopherol (Toc) were titrated in follicular fluid and plasma to evaluate their accumulation or consumption into the follicle. High LCAT activity was found in follicular fluids where Asc and Toc accumulated, while lower activity was associated with Asc and Toc consumption. The consumption of both the antioxidants was positively correlated with the E/P ratio. The results suggest that, as the follicle maturation progresses, the Toc and Asc levels increase in the fluid thus preventing LCAT from oxidative damage and loss of activity