Natural Polyphenols (Vegetable Tannins) as Drugs:  Possible Modes of Action

Natural products from plants and microorganisms traditionally have provided the pharmaceutical industry with one of its most important sources of "lead" compounds in the search for new drugs and medicines. Over the past two decades, researchers have also turned to many of the traditional folk medicines - invariably a "cocktail" of natural products - to uncover the scientific basis of their remedial effects, endeavors which have their roots as much in a desire to improve the efficacy as to enhance the ethics of modern medical practice. In this context, particular attention has been given by various groups in the Far East, Europe, and America to those traditional herbal medicines rich in polyphenols (vegetable tannins). Some typical examples of such medicines and the polyphenols which they contain are shown. The ripe fruits of hawthorn (Crataegus sp.) provide one of the best tonic remedies for the heart and circulatory system. They act in a normalizing way upon the heart, depending on the need, stimulating or depressing its activity. Hawthorn is a rich source of the flavan-3-ol (-)-epicatechin and proanthocyanidins related to (-)-epicatechin (1), e.g., epicatechin-(4 beta arrow right 8)-epicatechin [procyanidin B sub(2) (2)]. Meadowsweet is likewise one of the best digestive remedies available. It acts to protect and soothe the mucous membranes of the digestive tract, reducing excess acidity and easing nausea. It is used in the treatment of heartburn, hyperactivity, gastritis, and peptic ulceration and relieves the pain of rheumatism. Its gentle astringency is very useful in the treatment of diarrhea in children. Two of its principal polyphenolic constituents are tellimagrandin II (3) and rugosin D (4); the latter polyphenol is formally derived by loss of two hydrogen atoms from two molecules of the "monomer" tellimagrandin II. Very recently, and related generally to this area of research, there has arisen a considerable interest in the possibility that the impact of several diseases which afflict mankind may be ameliorated, if not prevented, by the simple expedient of improving the dietary intake of nutrients with antioxidant properties. Their role has been described with varying degrees of certitude as follows: important, vitamin E; thought to be important, vitamin C; probably important, beta -carotene and carotenoids; possibly important, plant phenolics (such as tannins and flavonoids). Thus, although proof of a cause and effect relationship does not exis