Carotenoids and cancer in animal models.

As evidence accumulated from epidemiological studies that beta-carotene acts as a chemopreventive agent with respect to inhibiting the appearance of certain types of tumors in humans, attention focused on animal models as a means of extending our understanding of carotenoid function. Unfortunately, most animals used in research are "white fat" animals, and require large amounts of carotenoids in their diets to obtain significant blood and tissue levels. Even with these limitations, beta-carotene, a provitamin A carotenoid, as well as canthaxanthin, a non-provitamin A carotenoid, have been shown to protect animals against UV-induced skin tumors, UV and carcinogen-induced tumors, and carcinogen treatment alone. Similar observations have been made in cell and organ cultures where carotenoids have been shown to prevent malignant transformation and nuclear damage. Although the mechanism of this protection is still unclear, the evidence continues to accumulate that carotenoids may possess intrinsic chemopreventive action with respect to tumor formation.