Antioxidant properties of a dry product from Vitis vinifera seeds (Leucoselect) in rat liver endoplasmic reticulum / Propiedades antioxidantes de un producto seco de semillas de Vitis vinifera (Leucoselect) en retículo endoplásmico de hígado de rata

Leucoselect is a commercial dry product obtained from grape seeds and enriched in procyanidins, which display antioxidant activity in virtue to their ability to scavenge oxygen free radicals and to chelate transition metal ions. The hypoxanthine/xanthine oxidase and Cu2+/ascorbate systems are capable of generating reactive oxygen species; the latter system can also promote non-specific binding of copper ions to proteins. Therefore, we assessed the ability of Leucoselect to inhibit oxidative phenomena elicited by both oxidative systems on rat liver microsomes: lipid peroxidation, oxidation of protein thiols, and inhibition of the cytochrome P450 system. The antioxidant activity of Leucoselect was a reflection of its ability to scavenge oxygen free radicals, chelate copper ions, and protect microsomal membranes through direct interaction. These mechanisms were displayed in a dependent manner with the type of biomolecule studied and also with the oxidative system employed, which is an interesting phenomenon to consider when evaluating the antioxidant activity of herbal products.

Leucoselect es un producto comercial seco obtenido de semillas de uva y enriquecido en procianidinas, las cuales presentan actividad antioxidante debido a su capacidad para atrapar radicales libres y quelar metales de transición. Los sistemas hipoxantina/xantina oxidasa y Cu2+/ascorbato generan especies reactivas del oxígeno; este último sistema también promueve la unión inespecífica de iones cobre a proteínas. Por lo tanto, evaluamos la capacidad de Leucoselect para inhibir los fenómenos oxidativos producidos por ambos sistemas oxidantes en microsomas hepáticos de rata: lipoperoxidación, oxidación de tioles proteicos e inhibición de la actividad del sistema citocromo P450. La actividad antioxidante de Leucoselect fue un reflejo de su capacidad de atrapar radicales libres del oxígeno, quelar iones cobre y proteger membranas microsómicas por interacción directa. Dichos mecanismos se manifestaron en forma dependiente del tipo de biomolécula estudiada y del sistema oxidante empleado, fenómeno interesante de considerar al evaluar la actividad antioxidante de preparados herbales.

Microsomal UDP-glucuronyltransferase in rat liver: oxidative activation.

Activation of microsomal UDP-glucuronyltransferase (UDPGT) activity by treatment of hepatic microsomes with either detergents or Fe(3+)/ascorbate pro-oxidant system has been reported; however, definite mechanisms underlying these effects have not been clarified. In this work, we characterize Fe(3+)/ascorbate-induced activation of UDPGT activity prior to solubilization with Triton X-100 and after the oxidation process provoked the solubilization of the enzyme. We observed a time-dependent increase in UDPGT activity up to 20 min. incubation of the microsomes with Fe(3+)/ascorbate (3-times); after 20 min. incubation, however, we observed a time-dependent decrease in this activity to basal levels after 4 hr incubation. Treatment of microsomes with 0.1% Triton X-100 (5 min.) lead to a similar increase in UDPGT activity; higher detergent concentrations produced a dose-dependent decrease in this activity to basal levels with 1% Triton X-100. Interestingly, UDPGT activity was susceptible to activation only when associated to microsomal membranes and the loss of activation correlated with the solubilization of this activity. UDPGT activation by either Fe(3+)/ascorbate or Triton X-100 was correlated with an increase in p-nitrophenol apparent K(m) and V(max) values. This activation was prevented or reversed by the reducing agents glutathione, cysteine or dithiothreitol when it was induced by the Fe(3+)/ascorbate. Furthermore, the latter provoked a significant decrease in microsomal thiol content, effect not observed after treatment with Triton X-100. Our results suggest that the main mechanism responsible for Fe(3+)/ascorbate-induced UDPGT activation is likely to be the promotion of protein sulfhydryl oxidation; this mechanism appears to be different from detergent-induced UDPGT activation.