Chemopreventive Potential of Flavones, Flavonols, and their Glycosides.

Epidemiological studies have long indicated a possible role for dietary flavonoids, notably flavones and flavonols, in the prevention of a range of degenerative diseases, e.g. cancer, diabetes, cardiovascular diseases and neurological disorders like Parkinson’s and Alzheimer’s disease. The flavonoids are a large and variable group of compounds, comprising thousands of different structures. The bulk of the dietary flavonoids occur as glycosides. The effect of flavonoid aglycones and their corresponding glycosides on cell metabolism and aetiology of degenerative diseases has been a topic of interest for a number of decades. In contrast, the role of the metabolic products of dietary flavonoid that reach all parts of the human body through systemic circulation, has received much less attention. Studies on animal and human metabolism have shown that the amount flavone and flavonol glycosides is absorbed intact is negligible; the bulk is absorbed only after deglycosylation. Thus, dietary glycosides are not likely to play a direct role in chemoprevention. However, the sugar groups on glycosides can greatly affect the bioavailability of flavones and flavonols. Flavonoids linked with indigestible sugars are not absorbed in the small intestine, but are transported through the digestive tract to be degraded by gut bacteria in the large intestine. The compounds that directly play a tole in the prevention of degenerative diseases are most likely not dietary flavones themselves, but rather their metabolites and conjugation products.