Although β-carotene has been considered to be a key cancer preventive agent in green and yellow vegetables, other types of carotenoids, such as α-carotene, may also contribute to anticarcinogenic action, since these carotenoids usually coexist with β-carotene and are detectable in human blood and tissues. In this study, we compared the inhibitory effect of natural α-carotene, obtained from palm oil, with that of β-carotene on spontaneous liver carcinogenesis in C3H/He male mice. The mean number of hepatomas per mouse was significantly decreased by α-carotene supplementation (per os administration in drinking water at a concentration of 0.05%, ad libitum) as compared with that in the control group (P < 0.001, Student's t test). On the other hand, β-carotene, at the same dose as α-carotene, did not show any such significant difference from the control group. Furthermore, we also compared the antitumor-promoting activity of α-carotene with that of β-carotene against two-stage mouse lung carcinogenesis (initiator, 4-nitroquinoline 1-oxide; promoter, glycerol). α-Carotene, but not β-carotene, reduced the number of lung tumors per mouse to about 30% of that in the control group (P < 0.001, Student's t test). The higher potency of the antitumor-promoting action of α-carotene compared to β-carotene was confirmed in other experimental systems; e.g., α-carotene was also found to have a stronger effect than β-carotene in suppressing the promoting activity of 12-O-tetradecanoylphorbol-13-acetate on skin carcinogenesis in 7,12-dimethylbenz[a]anthracene-initiated mice.
These results suggest that not only β-carotene, but also other types of carotenoids, such as a-carotene, may play an important role in cancer prevention.
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Supported in part by grants from the Ministry of Education, Science, and Culture; the Smoking Research Foundation; and the Plant Science Research Foundation, Faculty of Agriculture, Kyoto University, Japan.