Abstract
Dietary habit is instrumental in about 50% of human colorectal cancers. Consumption of fruits and vegetables is associated with decreased risk of several types of cancer, including colorectal malignancy. These foods contain many non-nutritive as well as nutritive compounds, such as carotenoids, dithiolthiones, flavonoids, glucosinolates, indoles, isothiocyanates, monoterpenes, phenols, sterols, sulfhydryls and vitamins (including C, E and folate). There may be other unknown non-nutritive constituents in foods that can reduce cancer development. Studies using experimental chemical carcinogenesis models have indicated that several non-nutritive components, belonging to different chemical groups, in foods protect against certain types of cancer, including colorectal neoplasm. Many of these chemicals are known as potential "cancer chemopreventive agents" and are antioxidants that suppress carcinogenesis by (i) inhibiting phase I enzymes or blocking carcinogen formation, (ii) induction of phase II (detoxification) enzymes, (iii) scavenging DNA reactive agents, (iv) modulation of hormone homeostasis, (v) suppression of hyper-cell proliferation induced by carcinogen, (vi) induction of apoptosis, (vii) depression of tumor angiogenesis, and/or (viii) inhibition of certain phenotypic expressions of preneoplastic and neoplastic cells. Given the definite increase in the increase of colorectal cancer, we should determine the most effective mean of prevention and understand the mechanism(s) underlying successful prevention. There are critical interrelationships between diet, environmental factors and genetics that can affect cancer risk. However, non-nutritive compounds in fruits, vegetables and other dietary constituents (teas, spices and herbs) consumed as part of the diet have the ability to reduce cancer occurrence in pre-clinical animal carcinogenesis models. Although epidemiologic studies show similar associations, there have been very few intervention studies to date. This article describes our recent studies to determine whether several naturally occurring non-nutritive products from edible plants have any effective chemopreventive effects on colorectal carcinogenesis in rodents.
