Polyphenols - another type of phytochemical

Another probably more significant group of phytochemicals are the polyphenols. These are molecules of various sizes but which have more than one phenolic unit in their structure. Examples of polyphenols are flavonoids, lignins and tannins.

One of the oldest functions of polyphenols might be protection against UV damage. But polyphenols tend to have varied and complex biological roles. Some of these roles include antioxidation, cell signalling and insect/herbivore signalling.

The non-flavonoid polyphenol, curcumin, for example, is principle member of a family of co

ngeners found in turmeric.

Turmeric itself is a rhizome and a relative of the ginger. The Chinese call it the 'yellow ginger', and the Malays call it 'kunyit'. It's biological activity is recognized in in many cultures and is listed in many traditional pharmacopoieas. It is best known however for the yellow flavouring used in many curries.

Curcumin is however, actually, poorly absorbed when taken orally. The reason has been attributed to poor absorption and rapid metabolism and elimination. It has been shown to induce apoptosis of cancer cells, and thus thought to have anti-cancer properties in the colon. Some clinical studies have also shown that curcumin taken in gram amounts over a period of time can inhibit CYP1A2 while enhancing CYP2A6. Apparently, when given in these large amounts, significant absorption occurs to enable enzyme inhibition. In vitro work suggest inhibition also of CYP2B6 and CYP3A4. Curcumin is otherwise quite harmless even in large doses and therefore appear to serve only the purpose of discouraging eating of the raw rhizome. Although quite flavourful when cooked with other spices, the raw turmeric root is quite unpalatable due to the bitter and pungent taste of curcuminoids.

Similar to the alkaloids, the polyphenols interact extensively with drug metabolizing enzymes and membrane transporters. These interactions are not limited to direct interactions with the proteins, but are also mediated through interaction with regulatory processes of the various enzyme and transporter genes.