catechin-gallate and protocatechuic-acid

Grapes are widely consumed in the world, and different grape varieties could exhibit distinctly different antioxidant activities. In this study, the free radical-scavenging and antioxidant activities of lipophilic, hydrophilic, and insoluble-bound fractions from 30 grape varieties were evaluated by ferric-reducing antioxidant powers (FRAP), Trolox equivalent antioxidant capacities (TEAC), total phenolic contents (TPC), and total flavonoid contents (TFC). The results indicated that the 30 grape varieties exhibited diverse FRAP values (1.289⁻11.767 μmol Fe(II)/g FW), TEAC values (0.339⁻4.839 μmol Trolox/g FW), TPC values (0.294⁻1.407 mg GAE/g FW) and TFC values (0.082⁻0.132 mg QE/g FW). Several grapes, such as Pearl Black Grape (Xinjiang), Summer Black Grape (Shaanxi), Pearl Green Grape (Xinjiang), Seedless Green Grape (Xinjiang), and Seedless Red Grape (Yunnan), exhibited strong free radical-scavenging and antioxidant activities, which could be consumed as good sources of natural antioxidants to prevent several diseases induced by oxidative stress, such as cardiovascular disease and cancer. Furthermore, several antioxidants were identified and quantified, including caffeic acid, catechin gallate, epicatechin, gallic acid, protocatechuic acid and rutin, which could contribute to the antioxidant activities of grapes.

Topics: Antioxidants; Caffeic Acids; Catechin; Free Radicals; Gallic Acid; Hydroxybenzoates; Oxidative Stress; Phenols; Plant Extracts; Rutin; Vitis

Flavonoids including tea catechins and gallic acid esters were characterized for their ability to inhibit o-methyltranslation of protocatechuic acid (PCA) to form vanillic acid (VA) in rat liver cytosolic preparations and cultured hepatocytes. Flavonols and flavones exhibited different behaviors in inhibiting the formation of VA between the cell-free enzymatic preparations and the intact cells. The underlying mechanism of the inhibitory effects of flavonols and flavones on PCA o-methylation in cultured hepatocytes may not be due to the inhibition of the enzyme activity of catechol o-methyl transferase (COMT). Catechin gallates inhibited PCA o-methylation in liver cytosolic preparations with markedly higher potency than other flavonoids. As compared with catechin gallates, ungallated catechins had two to three orders of magnitude lower efficiency in inhibiting cytosolic PCA o-methylation. Gallic acid esters inhibited cytosolic PCA o-methylation with strong potency almost equal to that of catechin gallates. These results suggest that the COMT-inhibitory activity of catechin gallates is derived from the presence of the galloyl moiety at the C3 position in the C-ring. Catechin gallates and gallic acid esters inhibited PCA o-methylation in cultured hepatocytes with two orders of magnitude lower efficacy than that in cytosolic preparations. The inhibitory effects of catechin gallates and gallic acid esters on cellular PCA o-methylation appear to be due to the direct inhibition of COMT activity.

Topics: Animals; Catechin; Catechol O-Methyltransferase; Cells, Cultured; Chromatography, High Pressure Liquid; Cytosol; Hepatocytes; Hydroxybenzoates; Liver; Male; Methylation; Rats; Rats, Wistar