Phytonutrient – Resveratrol
THIS is a phytonutrient commonly found in grapes. It is a stilbenoid and one of a group of plant chemicals known as polyphenols.
Stilbenoids are secondary products of heartwood formation in trees that can act as phytoalexin.
Phytoalexins are phytochemicals with antimicrobial properties, synthesised by plants in response to pathogenic attacks.
When there is an attack (bacterial or fungal), the phytoalexins are quickly synthesised and accumulate rapidly at the region of attack.
Resveratrol is an example of a phytoalexin. This is in keeping with the dual role of phytochemicals as part of plant defense systems and their health enhancing roles in humans.
Sources of resveratrol
One of the commonest sources of resveratrol is the skin of red grapes and by extension red wine becomes another important source. This is so because red wine is fermented with the skin. On the other hand white wine is not fermented with the skin and so its resveratrol content is low. Other sources of resveratrol include blue berries, raspberry, mulberry, peanuts (raw or boiled), cocoa powder and dark chocolate. Resveratrol can also be found in the seed of muscadine grapes.
Mechanism of action, disease prevention and health benefits of resveratrol
A lot of research work have been carried out and are ongoing concerning resveratrol. Most of these works have been conducted in test tubes, cell cultures and on animals. A few have been on human beings and so far promising and positive results have shown that resveratrol has a lot of health benefits in humans. One issue that has to be addressed so as to improve the function of resveratrol in the human body is that of bioavailability.
The concentration of resveratrol that can be attained in the blood circulation and tissues by oral consumption is far less than that which gives positive results in test tubes and cell cultures.
The cardiovascular system
There are certain properties of resveratrol and mechanism of action that make it a potent preventive against cardiovascular diseases. These include the following:
Prevention of atherosclerosis
In the development of atherosclerosis, inflammatory white blood cells are usually attracted from the blood to the arterial walls by vascular cell adhesion molecules. From here plaques, known as atheromas are formed which eventually occlude the lumen of the artery. Resveratrol has been found to inhibit the adhesion molecules and prevent plaque formation.
Peripheral vascular resistance increases the risk of hypertension and other cardiovascular diseases. Vascular smooth muscle cell proliferation increases this resistance and increases the risk of atherosclerosis. Resveratrol opposes this smooth muscle cell proliferation.
Endothelial nitric oxide synthase is the enzyme that catalyses the production of nitric oxide in the endothelial cells. Nitric oxide on its own causes relaxation (vasodilatation) of the arteries. Resveratrol stimulates and supports the action of the enzyme involved in nitric oxide production. In the absence of nitric oxide synthase and the support of resveratrol, vasoconstriction sets in. Vasoconstriction increases the risk of hypertension and other cardiovascular diseases.
Resveratrol inhibits platelet aggregation and prevents the formation of thrombosis – blood clots in the walls of the arteries. When this thrombus gets separated from the arterial wall and flows freely in the circulation it becomes known as an embolus. An embolus can block a coronary or a cerebral artery and give rise to myocardial infaction or stroke. Resveratrol prevents this clot formation.
Resveratrol has been found to be effective against tumours that it can make direct contact with, such as cancer of the skin and that of the gastrointestinal tract. It has also been discovered to exhibit anticancer activities against cancer of the breast in animal studies. Several other cancers have also been found to be influenced by resveratrol.
Mechanism of action of resveratrol against cancer is as follows:
In cancer, cells no longer respond to DNA signals and they proliferate uncontrollably. Also, cancer cells do not respond to cell death signals that initiate programmed cell death (apoptosis). Resveratrol induces apoptosis and arrests cell proliferation in several different types of cancer.