The relation between single/double or repeated tea catechin ingestions and plasma antioxidant activity in humans.

OBJECTIVE: The purpose of this study was to investigate the effects of single/double or repeated intake of a normal amount of tea catechin on plasma catechin concentrations and antioxidant activity in young women. DESIGN: First, after an overnight fast, five healthy subjects were given water or single/double dose(s) of tea polyphenol extract (164 mg tea catechins containing 61% epigallocatechin gallate in 190 ml water). Blood samples were taken before and 30, 60 and 180 min after the ingestion. Second, 16 healthy subjects ingested the tea polyphenol extract three times a day at mealtimes for 7 days followed by withdrawal of tea polyphenol extract for 7 days. Blood samples were taken before and after ingestion, and 7 days after the withdrawal of tea catechin. Subjects were prohibited from drinking any beverages containing polyphenols or antioxidant supplements during the study period. Catechin and other antioxidant concentrations in the plasma were measured, and changes in antioxidant activity were evaluated by ferric reducing ability of plasma assay. RESULTS: Single/double ingestion of tea polyphenol extract did not cause an increase in the antioxidant activity. There was no also change in antioxidant activity after the ingestion of tea polyphenol extract for 7 days. Plasma-free epigallocatechin gallate concentration remained at the pre-study level; however, the plasma FRAP value decreased significantly at 7 days after the withdrawal of tea polyphenol extract. Decreases in endogenous antioxidants in the plasma, including vitamin C and bilirubin, were also observed 7 days after withdrawal of tea polyphenol. CONCLUSIONS: The results suggest that continuous daily intake of tea catechins affects the concentrations of endogenous antioxidants in the plasma and has the potential to maintain total antioxidant activity.

Docosahexaenoic acid supplementation-increased oxidative damage in bone marrow DNA in aged rats and its relation to antioxidant vitamins.

We compared the influence of docosahexaenoic acid (DHA) supplementation on oxidative DNA damage in bone marrow between young and aged rats. As a marker of oxidative DNA damage, 8-hydroxydeoxyguanosine (8-OHdG) in DNA was analyzed. Young (5-week-old) and aged (100-week-old) female Wistar rats were given DHA (300mg/kg body weight/day) or vehicle (control) orally for 12 weeks. The 8-OHdG in the bone marrow in the aged DHA group was significantly higher than that in the other groups. Vitamin E concentrations, however, did not differ among the groups regardless of the DHA supplementation. Vitamin C (ascorbic acid) concentrations in the aged control group were approximately 1/2 those in the young control group. The concentrations of vitamin C tended to be higher in the young DHA group and lower in the aged DHA group when compared to their respective control groups. Changes in the concentrations of vitamin C and vitamin E in plasma were similar to those in the bone marrow. The activity of hepatic l-gulono- gamma -lactone oxidase, an enzyme responsible for vitamin C synthesis, corresponded well to the concentrations of vitamin C in the bone marrow and the plasma. These results suggest that in aged rats, but not young rats, excess supplementation of DHA induces oxidative DNA damage in bone marrow and that the decrease in vitamin C synthesis in aged rats is involved in the mechanisms of DNA damage.

Analytical method of measuring tea catechins in human plasma by solid-phase extraction and HPLC with electrochemical detection.

We developed an analytical method for measuring tea catechins in plasma by solid-phase extraction (SPE), followed by HPLC with a coulometric electrochemical detector. The plasma was mixed with an equal volume of acetonitrile to precipitate protein, and catechins in the resulting supernatant were extracted by SPE, using a C18 cartridge. To correct the extraction efficiency, ethyl gallate was simultaneously added with acetonitrile as an internal standard. Plasma samples were treated in microtubes, and evaporation and SPE were performed by the use of a vacuum centrifuge and vacuum manifold for SPE. The use of these instruments allowed the handling of a large number of samples simultaneously. In this method, (-)-epicatechin (EC), (-)-epicatechin-3-O-gallate (ECg), (-)-epigallocatechin (EGC), (-)-epigallocatechin-3-O-gallate (EGCg), and ethyl gallate could be detected as a single peak with high sensitivity. For an analysis of the conjugated form of catechins, plasma samples were treated with glucuronidase and sulfatase. Type H-2 beta-glucuronidase effectively digested the conjugated forms, and the enzyme also converted EGCg and ECg to their nongallated form. When the concentrations of catechins in plasma were analyzed in subjects who took a single dose of catechin liquid, the concentration of free EGCg in plasma reached a maximum of 300 nM at 1 h after intake; those of the other free form of catechins increased only slightly after the intake. The concentration of total catechins (free+conjugated forms) in plasma increased up to 2 h after the intake.