Intestinal absorption and metabolism of antioxidants from plants and their suppressive effects against oxidative stress

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The absorption analysis using rat everted small intestine demonstrated that luteolin was converted to glucuronides during passing through the intestinal mucosa and that luteolin 7-ο-b-glucoside was absorbed after hydrolysis to luteolin. Free luteolin, its conjugates and methylated conjugates were present in rat plasma after dosing. This suggests that some luteolin can escape the intestinal conjugation and the hepatic sulfation/ methylation. LC/MS analysis showed that the main conjugate which circulates in the blood was a monoglucuronide of the unchanged aglycone. The plasma concentration of luteolin and its conjugates reached the highest level 15 min and 30 min after dosing with luteolin in propyleneglycol, respectively. The excretory recovery of luteolin and its conjugates in rats was about 4%. Luteolin and its conjugates were also detected in human serum, and the highest peak was observed 2-3h after oral administration.In order to evaluate the antioxidant effect of absorbed luteolin in human serum, TBARS and the content of vitamin C in the serum treated with 2,2 azobis(2 aminopropane)-dihydrochloride(AAPH) were determined. The serum obtained after oral administration of luteolin showed a protective effect against lipid peroxidation and vitamin C degradation. on the other hand, preadministration of luteolin and aG-rutin reduced the frequency of MNRETs in peripheral blood and suppressed vitamin C degradation in bone marrow when mice were exposed to doxorubicin. These results suggest that absorbed flavonoids show antioxidant activity in the coordinate manner with ascorbic acid.