Free radicals and grape seed proanthocyanidin extract: importance in human health and disease prevention
Introduction
Occupational exposure to chemically and structurally diverse environmental pollutants including pesticides, toxic chemical wastes, direct and second hand cigarette smoke, gasoline exhaust, urban air pollutants ozone and radiation, and physical stress, produce similar toxic effects on human health. These environmental pollutants have been demonstrated to produce enormous amounts of free radicals, resulting in oxidative deterioration of lipids, proteins and DNA, activation of procarcinogens, inhibition of cellular and antioxidant defense systems, depletion of sulfhydryls, altered calcium homeostasis, changes in gene expression and induction of abnormal proteins, and contribute significantly to human disease pathophysiology (Herman, 1982, Ames, 1992, Kehrer, 1993, Stohs and Bagchi, 1995). Antioxidants/free radical scavengers function as inhibitors at both initiation and promotion/propagation/transformation stages of tumor promotion/carcinogenesis and protect cells against oxidative damage (Halliwell et al., 1992). The potential role of the antioxidant vitamins such as vitamin C and E, β-carotene and proanthocyanidins, antioxidant minerals such as zinc and selenium, and antioxidant enzymes such as glutathione, superoxide dismutase and catalase, have been extensively studied in the prevention of numerous degenerative diseases including tumor growth and carcinogenesis (Halliwell et al., 1992). The following features are considered to evaluate the therapeutic potential of a given antioxidant:
- 1.
Absorption and bioavailability.
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Effective dose, safety and toxicity.
- 3.
Distribution in cells, tissues and extracellular fluids.
- 4.
Free radical scavenging ability.
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Metal chelating activity.
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Effects on gene expression.
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Interaction with cellular antioxidants/antioxidant enzymes.
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Detoxification of carcinogenic metabolites.
Epidemiological studies have demonstrated that five to seven servings of fresh fruits and vegetables, and two glasses of red wine per day can lead to a prolonged healthy life (German, 1997). Vegetables, fruits and their seeds are rich sources of vitamins C and E, and β-carotene, and/or protease inhibitors, compounds which might protect the organism against cancer (Hocman, 1989). Several plants have been reported to contain compounds including bioflavonoids and proanthocyanidins, ellipticine and taxol, indole derivatives, dithiolthiones, phytoestrogens, etc, which exhibit chemopreventive and/or anticancer properties (Hocman, 1989, Teel, 1992). These chemoprotective components have been demonstrated to inhibit oxidative stress and chemically induced carcinogenesis by the following mechanisms (Hocman, 1989):
- 1.
Modulation of metabolic functions so that toxins and carcinogens are not produced.
- 2.
Enhancement of detoxification pathways.
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Prevent interaction of the ultimate carcinogen with biological macromolecules.
The biological, pharmacological and medicinal properties of the bioflavonoids and proanthocyanidins have been extensively reviewed (Shahidi and Wanasundara, 1992, Suzuki, 1993, Jovanovic et al., 1994, Rice-Evans et al., 1996). Besides the free radical scavenging and antioxidant activity, proanthocyanidins exhibit vasodilatory, anticarcinogenic, anti-allergic, antiinflammatory, antibacterial, cardioprotective, immune-stimulating, anti-viral and estrogenic activities, as well as being inhibitors of the enzymes phospholipase A2, cyclooxygenase and lipooxygenase (Salah et al., 1995, Rice-Evans et al., 1996). The chemical properties of proanthocyanidins in terms of the availability of the phenolic hydrogens as hydrogen donating radical scavengers and singlet oxygen quenchers predicts their antioxidant activity (Chen et al., 1996, Rice-Evans et al., 1996). For a proanthocyanidin to be defined as an antioxidant it must satisfy two basic conditions: (i) when present in low concentrations relative to the substrate to be oxidized it can delay, retard, or prevent autooxidation or free radical-mediated oxidative injury; and (ii) the resulting product formed after scavenging must be stable through intramolecular hydrogen bonding on further oxidation (Shahidi and Wanasundara, 1992).
The total bioflavonoid/proanthocyanidin content in a typical fruit serving of 200 g is in the range of 50–500 mg, with apples having over 200 mg (Bravo, 1998). It has been demonstrated that proanthocyanidin content in the plasma can be maintained following regular intake of sufficient quantity of fresh fruits and vegetables or supplementation of bioavailable proanthocyanidins (Bravo, 1998). The absorption, distribution, metabolism and excretion of proanthocyanidins are governed by the chemical structures (Jimenez-Ramsey et al., 1994, Bravo, 1998). Distinct absorption and bioavailablity of various extractable proanthocyanidins, depending on their extractability with different solvents, was demonstrated by Jimenez-Ramsey et al. (1994). These authors demonstrated that proanthocyanidins soluble in water and ethanol are absorbed from the intestinal tract and extensively distributed in all tissues and plasma, while the proanthocyanidin fractions soluble in aqueous acetone but insoluble in water and ethanol are not at all bioavailable (Jimenez-Ramsey et al., 1994). Generally the dimer-, trimer- and tetrameric proanthocyanidins, also referred to as extractable proanthocyanidins or bioflavonoids, have been shown to be highly bioavailable and provide excellent health benefits. de Vries et al., 1998, Hollman and Katan, 1998 have further demonstrated that flavonoid glycosides are more bioavailable as compared to the pure aglycone. These low molecular proanthocyanidins are also known as sustained release antioxidants, and can remain in the plasma and tissues for up to 7–10 days and exert antioxidant properties, which is mechanistically different from other water soluble antioxidants. On the contrary, high molecular weight polymeric non-extractable proanthocyanidins are very potent scavengers of peroxyl radicals, but these are not absorbable or bioavailable at all. However, these high molecular weight proanthocyanidins can exert their antioxidant activity in the digestive tract and protect lipids, proteins and carbohydrates from oxidative damage during digestion and spare soluble antioxidants (Hagerman et al., 1998). In this paper, we have demonstrated the protective ability and biological efficacy of a novel IH636 grape seed proanthocyanidin extract (GSPE) in selected in vitro and in vivo models as well as in human clinical studies.
Section snippets
Occurrence
IH636 grape seed proanthocyanidin extract (GSPE, commercially available as ActiVin from InterHealth Nutraceuticals Incorporated, Benicia, CA) is a standardized water-ethanol extract from red grape seeds. It is worthwhile to mention that novel antioxidants including catechins and oligomeric proanthocyanidins (OPC) accumulate principally in the lignified portions of grape clusters, especially in the seeds (Kovac et al., 1995). HPLC studies in conjunction with GC-MS demonstrate that GSPE contains
Conclusions
Epidemiological evidence links high antioxidant status with low risk of degenerative disease including tumor promotion and cancer in humans. The increased consumption of fresh vegetables and fruits is usually associated with the decreased use of fish, meats and fats. Furthermore, supplementation of bioavailable and safe antioxidants are essential because we do not get enough antioxidant vitamins and minerals from foods and beverages we consume daily. These research studies demonstrate GSPE as a
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