Anthocyanin-rich extracts, as well as pure anthocyanins, have shown relatively more effective chemoprevention towards tumorigenesis at directly accessible targets such as gastrointestinal tract (oral, esophagus, colon, etc.) and skin, than other sites in animal models suggesting that the low absorption into the plasma limits their ability to exert protective effects on tissues that require delivery of nutrients through the blood.
Freeze-dried black raspberries were found to reduce azoxymethane (AOM)-induced aberrant crypt foci (ACF), colon tumors, and the level of urinary deoxyguanosine in male F344 rats. The chemoprotective activity of anthocyanin-rich extracts from bilberry, chokeberry, and grape was investigated by assessing multiple biomarkers of colon cancer in male F344 rats treated with AOM.
Total ACF were reduced significantly in colon tissues of rats receiving a diet enhanced with bilberry, chokeberry, and grape compared with the control group. The number of large ACF was also reduced in bilberry and chokeberry diet groups.
Rats fed with bilberry/grape anthocyanin-rich diets had lower COX-2 mRNA expression of gene. A significant reduction in fecal bile acids was observed and the levels of urinary 8-hydroxyguanosine were similar among rats fed different diets. Protective roles of anthocyanin-rich extracts from those fruits were shown in colon carcinogenesis and multiple mechanisms of action appear to be involved.
The possible chemopreventive effects of berry fruits (blueberries, blackberries, and cranberries) were compared with other fruit types (plums, mangoes, pomegranate, and watermelon) on AOM-induced ACF in F344 male rats. Among these fruits, blueberry and pomegranate contributed the most significant reductions in the formation of AOM-induced ACF. Anthocyanins have also been shown to inhibit the development of cancer in animals with hereditary predisposition to cancer.
Cyanidin 3-glucoside, the most abundant anthocyanin in berries, was investigated for the colorectal adenoma formation in ApcMin mice. Ingestion of cyanidin 3-glucoside reduced adenoma load dose-dependently. After supplementation of 0.3% of cyanidin 3-glucoside in the diet for 12 weeks, adenoma numbers were decreased by 45% compared to controls, suggesting that it could be a potential chemopreventive agent for human colorectal cancer.
Freeze-dried strawberries, freeze-dried black raspberries and freeze-dried blueberries were fed to F-344 rats in the diets before repeatedly treating with N-nitrosomethylbenzylamine (NMBA). At 30 weeks, strawberries and black raspberries were found to significantly inhibit NMBA-induced esophageal tumor multiplicity in a dosedependant manner in the rat esophagus.
Animals fed 5 and 10% freeze-dried strawberries and freeze-dried black raspberries in the diet after NMBA treatment significantly reduced tumor multiplicity by 38 and 31% for strawberries, 62 and 43 % for black raspberries.
Blueberries did not inhibit the initiation and progression of NMBA-induced tumorigenesis in the rat esophagus. A significant decrease in O6-methylguanine adducts was observed in the esophageal DNA of animals fed with strawberries or black raspberries, but not with blueberries.
Both freeze-dried strawberries and black raspberries appear to possess bioactive compounds for potential inhibition of both initiation and promotion/progression during NMBA-induced esophageal tumorigenesis. Both the anthocyanin-rich fraction and the ellagitannins-rich residue of black raspberries effectively reduced NMBA-induced tumors in the rat esophagus, suggesting anthocyanins and ellagitannins appear to be important for the chemopreventive effects of berries.
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1. Clinical evaluation in humans
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