Proanthocyanidins are a group of chemical compounds found in many types of plants and are an important part of the human diet. Proanthocyanidins belong to a larger category of plant chemicals called flavonoids. Proanthocyanidins are sometimes called OPCs, an abbreviation for oligomeric procyanidins, or PCOs, an abbreviation for procyanidolic oligomers, both classes of nutrients belonging to the flavonoid family.
A variety of plants contain proanthocyanidins, including teas, black currant, bilberry, cranberry, grape seed, and grape skin. These useful antioxidant chemicals are also found in making red wines.
Although proanthocyanidins have been sold in Europe since the 1980s, they have not appeared in U.S. markets as therapeutic and nutritional supplements. Nutritional supplements containing proanthocyanidins are sold alone or in combination with other agents as tablets and capsules. Some health experts recommend that individuals consume between 50 and 100 milligrams of proanthocyanidins per day.
The proanthocyanidins present in red wine are thought to contribute to the "French Paradox," a hypothesis that attributes lower occurrence of heart disease in countries where moderate amounts of wine are a regular part of the diet.
Proanthocyanidins are not classified as essential nutrients, as no symptoms or medical conditions have been linked to the absence of flavonoids in the diet. However, many experts believe that proanthocyanidins may play a role in treating chronic venous insufficiency. The effects of proanthocyanidins on capillary fragility, retinopathy, and sunburn are more tentative. It has also been suggested that proanthocyanidins may help to treat varicose veins and pancreatic insufficiency, but there is a significant lack of any type of clinical evidence to support these uses. Human clinical trials evaluating proanthocyanidins in prevention, treatment, or cure of any medical condition are not currently available.
Flavonoids, leucoanthocyanin, leukocyanidin, oligomeric proanthocyanidin (OPC), procyanidolic oligomers (PCO), pycnogenol.
proanthocyanidin content in selected foods
theory and evidence
A 2007 study by Du et al. observed a notable induction of antioxidant enzymes occurring in a concentration-dependent fashion when cardiac H9C2 cells were incubated with micromolar concentrations of proanthocyanidin B4 or catechin. The authors propose that proanthocyanidin B4 or catechin pretreatment reduced the accumulation of intracellular reactive oxygen species (ROS) and cardiac cell apoptosis, which was induced by xanthine oxidase (XO)/xanthine. The authors therefore propose that by inducing endogenous antioxidant enzymes, grape seed polyphenols may offer protection against cardiac cell apoptosis. This mechanism may explain the cardioprotective properties of grape seed extract.
A 2005 article by Erdman et al. discussed the risk and safety assessments of supporting heart health via the intake of certain flavonoids. The article also proposed several mechanisms of action for flavonoids.
A 2005 study by Hernandez-Vallejo et al. found that apple procyanidins are capable of reproducing the inhibition of lipoprotein secretion and cholesteryl ester synthesis. The results are similar to the mechanism of action of polyphenols that results from an impaired lipid availability. This impaired lipid availability could possibly cause intestinal lipoprotein secretion to be inhibited. It could also add to the hypolipidemic effect that these compounds have exhibited in vivo.
A 2003 study by Shao et al. observed an increase in cell death and reactive oxygen species generation when laboratory animals were exposed to higher concentrations of grape seed proanthocyanidin extract. The increase in cell death and reactive oxygen species was measured by lactate dehydrogenase release and propidium iodide uptake.
A 2002 study by Pataki et al. observed the cardioprotective effects of grape seed proanthocyanidins against reperfusion-induced injury. It was proposed that grape seed proanthocyanidins demonstrate these effects by directly or indirectly reducing or removing the free radicals that occur in the myocardium after ischemia reperfusion.
A 2002 study by Bagchi et al. found that proanthocyanidins derived from grape seeds demonstrate cellular protection.
A 2001 study by Spencer et al. found that 3'-O-methylepicatechin exerts a protective effect against stress-induced cell death. The studies described in the article also suggest that the most significant bioactive forms of procyanidins and flavanol monomers in vivo are probably the conjugates and/or metabolites of epicatechin.
A 2000 study by Subarnas et al. evaluated the activity of proanthocyanidins taken from the roots of Polypodium feei fern in controlling pain and reducing inflammation. The writhing response of rats to pain induced by 0.7% acetic acid was significantly reduced at doses of 50 and 100mg/kg. At the dose of 100 mg/kg, the proanthocyanidins offered pain protection at a rate of 76.23 higher than that of 59.85% acetylsalicylic acid (59.84 %) at a dose of 50 mg/kg. In a separate anti-inflammatory test, the proanthocyanidin compound significantly inhibited the rats' plantar edema, which was induced by 1% of carrageenan; however, this activity was only observable at a higher dose of 200 mg/kg. The findings of these studies suggest that proanthocyanidin from Polypodium feei roots may possess analgesic and anti-inflammatory activities. The authors suggest that the inhibition of prostaglandin biosynthesis may be the mechanism of action, because the proanthocyanidin fraction inhibited cyclooxygenase, but not 5-lypoxygenase enzymes.
A 1999 study by Costantini et al. found that the rapid reduction in the swelling of the lower limbs in humans, which was observed in the course of the study, can be explained by the oligomeric proanthocyanidins' mechanism of action.
A 1983 study by Borzeix et al. discussed the mechanism of action of procyanidolic oligomers. The authors propose that these chemicals may cause an increase in the resistance of the tight junctions in arteriolar capillaries. This action may therefore interfere with the rise in pressure that normally occurs at the time that blood is injected.