Beta-carotene and aryl hydrocarbon hydroxylase in the rat: an effect of beta-carotene independent of vitamin A activity.
Animal models demonstrate a cancer-protective effect of vitamin A. However, human epidemiologic studies correlate the intake of the precursor, beta-carotene, rather than active vitamin A, to a reduced risk for certain cancers. This suggests that beta-carotene may have cancer-protective properties independent of its vitamin A activity. In the present rat study, effects of beta-carotene or active vitamin A on carcinogen metabolizing enzyme activity were evaluated. The activity of intestinal aryl hydrocarbon hydroxylase (AHH, EC 1.14.14.1) was higher in rats fed a purified diet supplemented with beta-carotene than in rats fed the control diet containing adequate vitamin A as retinyl palmitate (165 +/- 30 vs. 90 +/- 18 pmol/min x mg), P less than (0.05). Supplementing the control diet with retinyl acetate had no effect. This AHH-enhancing effect of beta-carotene on the activity of the intestinal mucosal enzyme was not seen on the hepatic enzyme, which is consistent with the nearly complete conversion of beta-carotene to vitamin A prior to reaching the liver. These results demonstrate an effect of beta-carotene on carcinogen metabolism which is independent of its vitamin A activity. This may help explain human epidemiologic data, and may lead to further work which would allow for prudent dietary recommendations toward a reduction in cancer risk.
Edes
T E
TE
Department of Medicine, Harry S. Truman Memorial Veterans Hospital, Columbia, MO.
Thornton
W
W
Shah
J
J
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D001580:Benzopyrenes / Q000008:administration & dosage / Q000494:pharmacology; D001835:Body Weight / Q000187:drug effects; D002338:Carotenoids / Q000378:metabolism* / Q000494:pharmacology; D004032:Diet; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014801:Vitamin A / Q000494:pharmacology; D019207:beta Carotene
D001580:Benzopyrenes; D019207:beta Carotene; D014801:Vitamin A; D002338:Carotenoids; D001189:Aryl Hydrocarbon Hydroxylases