Inhibition of carcinogenesis by polyphenols: evidence from laboratory investigations

Abstract

Many plant polyphenolic compounds have been shown to have cancer-preventing activities in laboratory studies. For example, tea and tea preparations have been shown to inhibit tumorigenesis in a variety of animal models of carcinogenesis, involving organ sites such as the skin, lungs, oral cavity, esophagus, stomach, liver, pancreas, small intestine, colon, and prostate. In some of these models, inhibitory activity was demonstrated when tea was administered during the initiation, promotion, or progression stage of carcinogenesis. The cancer-preventing activities of these and other polyphenols, such as curcumin, genistein, and quercetin, are reviewed. In studies in vitro, many of these compounds have been shown to affect signal transduction pathways, leading to inhibition of cell growth and transformation, enhanced apoptosis, reduced invasive behavior, and slowed angiogenesis. However, the concentrations used in cell culture studies were much higher than those found in vivo. If we propose mechanisms for cancer prevention on the basis of cell line experiments, then these activities must be demonstrated in vivo. The bioavailability, ie, tissue and cellular concentrations, of dietary polyphenols is a determining factor in their cancer-preventing activity in vivo. For example, compounds such as curcumin are effective when applied topically to the skin or administered orally to affect the colon but are not effective in internal organs such as the lungs. More in-depth studies on bioavailability should facilitate correlation of mechanisms determined in vitro with in vivo situations, increase our understanding of dose-response relationships, and facilitate extrapolation of results from animal studies to human situations.

Inhibition of carcinogenesis by tea constituents

“…Some of the results have been reviewed previously [1][2][3][4][5][6][7][8]. Table 1 summarizes the results of 120 studies published since the year 1991.…”

Possible Controversy over Dietary Polyphenols: Benefits vs Risks

“…Dietary phytochemicals including flavonoids, polyunsaturated fatty acids, tocopherols, and others have been the subject of increasing amounts of research for their potential beneficial effects as both disease preventive and therapeutic agents (1,2). For example, the major polyphenolic compounds in green tea (Camellia sinensis, Theaceae), the catechins, have been extensively studied for their cancer preventive activity and have shown activity in a number of animal models of carcinogenesis at organ sites including the lung, prostate, oral cavity, intestine, colon, liver, and skin (3).…”

Sunscreens and Antioxidants as Photo-protective Measures: An update

“…* Hydroxicinnamic acids such ascaffeic or ferulic acids prevent UVB-induced erythema in vivo and in vitro, and decrease UVinduced oxidative damage in skin cells and lymphocytes [10][11][12][13]. * Polyphenolics such as flavonoids and phenolic acids, green tea polyphenols, resveratrol, astaxanthin have been found useful [14]. * Anthocyanins and tannins, present in several fruits such as grapes, pears act by inhibiting UVB-dependent activation of NF-kB, MAP kinase and COX-2 pathways downstream of the signalling kinases MKK4, MEK1, and Raf-1 [15,16].…”