Most evidence of activity derives from in vitro and animal studies for oligomeric proanthocyanidin complexes (OPCs) or grapeseed extract; however, some clinical studies are also available. The stilbene resveratrol (3, 4′, 5 trihydroxystilbene) has also been the focus of much investigation and exhibits anti-inflammatory, antithrombotic, anticarcinogenic and antibacterial activities, but it is uncertain whether significant amounts are present in the seeds and GSE.
Grapeseed PC extract has demonstrated excellent free radical scavenging abilities, in both test tube and animal models, and provided significantly greater effects than vitamins C, E and beta-carotene. In vitro tests have further identified a vitamin E sparing effect, in which proanthocyanidins prevent vitamin E loss and cause alpha-tocopherol radicals to revert to their antioxidant form.
INHIBITS PLATELET AGGREGATION
Grapeseed extract has been shown to inhibit platelet aggregation, and combining extracts of grapeseed and grape skin produces a far greater antiplatelet effect in test tubeand ex vivo tests. Inhibition of platelet function was confirmed more recently by Vitseva et al (2005).
STABILISES CAPILLARY WALLS AND ENHANCES DERMAL WOUND HEALING
In vivo studies have found that proanthocyanidins stabilise the capillary wall and prevent increases in capillary permeability when chemically induced in tests such as carrageenan-induced hindpaw oedema and dextran-induced. Components in grapeseed extract have the ability to cross-link collagen fibres, thereby strengthening the collagen matrix. Clinical studies confirm that grapeseed extract improves capillary resistance when used at a dose of 150 mg daily. Not unexpectedly, research has also identified wound healing properties.
A 2002 study in mice found that topical application of grapeseed PCs considerably accelerated wound contraction and closure and provided additional support during the wound healing process. It has been shown that a grapeseed extract preparation containing 5000 ppm resveratrol facilitates oxidant-induced vascular endothelial growth factor expression in keratinocytes in vitro, which may account for its beneficial effects in promoting dermal wound healing and resolution of related skin disorders.
Several in vitro studies have demonstrated that proanthocyanidins from Vitis vinifera strongly suppress tumour growth and have cytotoxic activity against a range of cancer cells, including breast, lung, prostate and gastric adenoma cells. More specifically, PCs from grapeseeds exerted antitumour properties in several animal models. One study also found that grapeseed proanthocyanidins enhanced the growth and viability of human gastric mucosal cells at the same time.
In vitro evidence suggests grapeseed extract has anti-inflammatory activity. Two compounds isolated from Vitis vinifera exhibit non-specific inhibitory activity against COX-1 and -2.
Considering that grapeseed extract demonstrates antioxidant, antiplatelet and anti-inflammatory actions, it may have a role in the prevention of cardiovascular disease. A number of researchers have investigated this issue further, mainly using animal models. One series of studies was conducted by Bagchi et al (2003) using a natural, standardised, water-ethanol extract made from California red grapeseeds, which contained approximately 75-80% oligomeric PCs and 3-5% monomeric proanthocyanidins. According to in vivo research, treatment with grapeseed extract provided resistance to myocardial ischaemia-reperfusion injury, better post-ischaemic ventricular recovery and reduced incidence of reperfusion-induced ventricular fibrillation and ventricular tachycardia, as compared with corresponding control animals. Another study using a hamster atherosclerosis model found that 50 and 100 mg GSE/kg body weight led to a 49% and 63% reduction in foam cells respectively. Additionally, cholesterol and triglyceride lowering activity has been reported.
Protection against chemically induced multi-organ toxicity has also been reported. Results from a clinical study suggest that grapeseed extract increases the rhodopsin content of the retina or accelerates its regeneration after exposure to bright light.