Antitumor-Promoting Effects of Polyphenolic Extracts from Seedless and Seeded Indian Grapes

Abstract

Grapes, the widely consumed fruits, are rich in polyphenols. The biological and chemopreventive activities of grape seed polyphenols have been demonstrated, while similar information regarding crude polyphenolic extracts from whole grapes and their components (pulp plus skin, seeds), particularly the seedless varieties, is lacking. Cancer chemoprevention can be achieved by inhibition of either initiation or promotion/progression stages of carcinogenesis. This study involves the determination of the polyphenolic content extracted from green (Pandhari sahebi, Thompson seedless) and black cultivars (Bangalore blue, Sharad seedless) of Indian grapes and their components (whole grapes, pulp plus skin, and seeds). Comparative evaluation of antitumor-promoting effects of seedless and seeded grape polyphenolic extracts (GPEs) was carried out in carcinogen-initiated and 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted S/RVCri-ba mouse skin and stomach, as well as esophagus of ICRC mice. The yield of crude polyphenolic extracts from whole grapes and their components varied between 3% and 51%. The total polyphenolic content expressed as mg catechin equivalents/g crude polyphenolic extract ranged from 0.47 to 701 in seeded grapes and 1.49 to 28.30 in seedless varieties. Both seedless and seeded GPEs possessed antitumor-promoting activity in target tissues of mice as is evident from their ability to delay tumor formation along with a significant decrease in tumor multiplicity and incidence. Marked and sustained epidermal hyperplasia observed in 7,12-dimethylbenz(a)anthracene-initiated and TPA-promoted mice was greatly reduced on pretreatment with GPE or catechin. The polyphenolic extracts from Sharad seedless and seeds of Bangalore blue showed the strongest suppressing activity comparable to catechin than the corresponding whole grapes. The results suggest that the chemopreventive activity of polyphenols extracted from seedless grape cultivars was as effective as that of the seeded variety and these may have beneficial effects in disease states, especially cancer.