Lycopene induces gap junctional communication between cells, which is considered to be a basis for protection against cancer development (Zhang et al., 1991). This property is independent of its antioxidant activity. Lycopene has also been reported to alleviate coronary heart disease. This action is thought to be related to its antioxidant activity through preventing the oxidation of serum lipoproteins (Bramley, 2000; Packer et al., 1999).
Garlic (Allium sativum L.) bulbs have been used as a food with medicinal properties since ancient times. Many consider garlic as a cure-all. Animal and clinical studies have shown that garlic is effective in treating atherosclerosis, bringing down high blood pressure and high cholesterol levels, especially low-density lipoprotein (LDL) cholesterol, the so-called bad cholesterol. It also provides relief from gastrointestinal disorders (Hasler, 2000; Robbers and Tyler, 2000).
Garlic contains organosulphur compounds or thiosulphinates as active ingredients. Allicin has been shown to be responsible for most of its antimicrobial, antimycotic, antiviral, hypocholesterolaemic, hypotensive and antioxidant activities. Allicin is also responsible for the typically strong odour of garlic. It evolves from odourless sulphur containing the amino acid derivative alliin by the action of the enzyme alliinase. Alliin, which is present in garlic at c. 1 per cent, is immediately converted to allicin by bruising or crushing garlic cloves. One mg of alliin produces c.0.5 mg of allicin (Lawson, 1998; Blumenthal et al., 2000).
Distillation of garlic bulbs yields an essential oil (0.1—0.4 per cent) rich in allylsul-phides (e.g. diallyldisulphide), ajoenes and vinyldithiins as decomposition products of allicin and other related thiosulphinates. Ajoene, a self-condensation product of allicin, is an antithrombotic agent of garlic, at least as potent as aspirin (Koch and Lawson, 1996; Lawson, 1998).
Epidemiological and clinical studies to prove the anticancer activity of garlic have produced inconclusive and conflicting results. This is largely due to the use of a wide variety of garlic products in investigations. Garlic consumption substantially increases the anticoagulant effects of warfarin and is not recommended for people on warfarin treatment. It is also not recommended during lactation (Blumenthal et al., 2000; Mahady et al., 2001).
Flax (Linum usitatissimum L.) is one of the earliest cultivated crops. Apart from textile use of its fibres, flax seed has been used for food for the last c. 10,000 years. Worldwide, flax seed is used as a mild laxative as well as a poultice for topical application to treat inflammations and similar skin conditions. In the USA, it is consumed as a component of health food or nutraceutical products such as baked foods, breads, bars, breakfast cereals, granolas, etc. (Hasler, 2000).
Flax seed contains fixed oil (30—45 per cent) with 52—76 per cent linolenic acid, proteins (20—25 per cent), mucilage (3—10 per cent), steroids, cyanogenic glycosides (0.1—1.5 per cent) composed mostly of linustatin, neolinustatin, linamarin, lotaus-tralin, high content of soluble and insoluble fibre and secoisolariciresinol diglucoside (SDG) and matairesinol, precursors of lignans, enterodiol and enterolactone (Westcott and Muir, 2000). Lignans are diphenolic compounds containing a 2,3-dibenzylbutane structure. Enterodiol and enterolactone possess weak oestrogenic and anti-oestrogenic activities suggesting a possible preventive role in oestrogen-dependent cancers. Preventive effects on colon cancer have been shown in animal studies. Flax seed supplementation has been shown to lower serum cholesterol (Oomah and Mazza, 2000; Blumenthal et al., 2000).
Clinical studies suggested that flax seed supplementation has been successfully used in treating various disorders such as types of cancer and lupus nephritis. It reduces atherogenic risk in hyperlipidemic patients, improves arterial function and positively affects platelet composition and function (Oomah and Mazza, 2000).
Anticarcinogenic, hypolipidemic activities of flax seed as well as its beneficial effects in treating systemic lupus erythematosus (SLE) and rheumatoid arthritis have been put down to its high content of a-linolenic acid and secoisolariciresinol (Blumenthal et al., 2000).
A standardized dry extract of the dried leaves of Ginkgo biloba L. (GBE) contains 24 per cent flavonoids (mostly flavone glycosides and quercetin) and 6 per cent terpenes (mainly ginkgolides composed of 2.9 per cent bilobalide and 3.1 per cent ginkgolides A, B, C and J) (Braquet, 1988; Ahlemeyer and Krieglstein, 1998).
GBE is widely used and is sold as a prescription and over-the-counter (OTC) drug both in solid and liquid dosage forms for its beneficial effects on the circulatory system as a safe and efficacious drug. It is used in the treatment of cerebral dysfunction symptoms, dementia, vertigo, tinnitus and peripheral arterial occlusive disease. There are also indications that it is an effective antioxidant with free-radical scavenging activity (Hori et al., 1997; Foster and Tyler, 2000).
Due to the necessity to use high doses, GBE instead of the herb itself is used. Therefore, unless standardized extracts are used no beneficial effects of Ginkgo can be achieved. Recommended doses are 120—240 mg standardized dry extract (2 times or 3 times a day) in solid or liquid forms for oral use (Halpern, 1998; Blumenthal et al., 2000; Mahady et al., 2001).
St John's wort
Leaves and flowering tops of Hypericum perforatum L. (Hypericaceae) have in recent years become quite popular for their antidepressant properties. The plant has been known to mankind since time immemorial for the wound-healing properties of its olive oil macerate which acquires a reddish colour when exposed to sun for several weeks. This red oil is highly valued since it can be applied externally and internally to relieve inflammations and promote healing. The colour and the activity are related to the presence of hypericin, a reddish dianthrone pigment. Excessive use of this herb induces photosensitivity on exposure to direct sunlight. The damage is characterized by dermatitis and inflammation of the skin and mucous membranes. In Germany, St John's wort is an approved medicine and licensed as a medicinal tea. It is marketed in various dosage forms to treat mild depression Leung and Foster, 1996; Foster and Tyler, 2000).
In the USA, it is widely used as a dietary supplement in various forms such as alcoholic tincture, aqueous infusion for oral use, oil infusion for topical use and standardized dry extract in capsules and tablets. United States Pharmacopoeia (USP) notes the safety of St John's wort and has published a monograph for assessing its purity. USP requires not less than 0.2 per cent of hypericin and pseudohypericin combined and not less than 3.0 per cent of hyperforin (Anon., 1999).
Several clinical studies have confirmed the antidepressant action of St John's wort extracts in humans. St John's wort contains 6.5—15 per cent catechic tannins and proanthocyanidins (e.g., catechin, epicatechin, leucocyanidin); flavonoids (e.g. hyperoside — up to 2 per cent; rutin — up to 1.6 per cent; quercetin — up to 0.3 per cent); biflavonoids (c.0.26 per cent biapigenins); phloroglucinol derivatives (e.g. hyperforin — up to 4 per cent); 0.05—1.0 per cent essential oil containing mainly higher n-alkanes; 0.05—0.15 per cent naphthodianthrones (e.g. hypericin and pseudohypericin); xan-thones (up to 10 ppm); sterols; and vitamins (A and C) (Reuter, 1998; Blumenthal et al., 2000; Mahady et al., 2001).
For the constituents of St John's wort the following activities have been reported: hypericin (antiviral), pseudohypericin (antiviral), hyperforin (antibacterial, wound-healing, neurotransmitter inhibitor, potential anticarcinogenic), biapigenins (anti-inflammatory, antiulcerogenic, probably sedative), proanthocyanidins (antioxidant, antimicrobial, antiviral, vasorelaxant), xanthones (antidepressant, antimicrobial, antiviral, diuretic, cardiotonic, monoamine oxidase inhibitor), quercitrin (in vitro MAO inhibitor) (AHP, 1997).
Recommended doses for St John's wort products are as follows: powdered or chopped herb: 2—4 g daily; fluid extract 1:1 (g/ml): 2 ml, 2 times daily; dry extract 5—7:1:300 mg, 3 times daily; oily macerate: directly apply on affected areas (Blumenthal et al., 2000).
Echinacea has been a popular remedy since the early 20 th century in the USA and Europe for preventing and treating the common cold, influenza and upper respiratory tract infections. It is considered as a potent immunostimulant and also used to treat vaginal candidiasis (Bauer and Wagner, 1990; Foster and Tyler, 2000).
Roots and herbs of Echinacea purpurea, E. pallida and E. angustifolia are used as sources of echinacea products. Fresh pressed juice of the aerial parts with 22 per cent ethanol by volume as a preservative and alcoholic extract of the roots are approved for use. Echinacea polysaccharides are responsible for its immune-stimulant effect. Stimulation of phagocytosis is apparently enhanced by the alkamides (isobutylamides), glyco-proteins and cichoric acid. Roots and herbs of official Echinacea species contain caffeic acid derivatives, alkamides and polysaccharides as active ingredients (Bauer, 1998).
Korean ginseng (Panax ginseng C.A. Meyer) (Araliaceae) and American ginseng (P. quinquefolius L.) are two species used as the principal sources of ginseng. The former grows in Korea, northern China and parts of Siberia where it is harvested from the wild. In this form it is known as 'white ginseng'. It may sometimes be bleached and dried, or sometimes processed and sold as 'red ginseng'. American ginseng is harvested from wild sources and cultivated, especially in China (Blumenthal et al., 2000).
In Chinese medicine, it is used as a general tonic to provide energy and considered as a panacea (cure-all). However, recent randomized, controlled clinical trials did not provide substantive evidence to support its purported ergogenic effects in healthy subjects. Some evidence is available for treating erectile dysfunction and age-associated memory-impairment with ginseng. It is also an antioxidant and immune stimulant. Ginseng is generally considered as an aphrodisiac (Robbers and Tyler, 2000).
Active principles responsible for most of ginseng's activities are believed to be gin-senosides (or panaxosides). These are a series of triterpenoid saponins. Ginseng root contains 2—3 per cent ginsenosides with Rg1, Rc, Rd, Rb1, Rb2 and Rb0 being the most important (Sticher, 1998).
The German Commission E suggested a daily dose of ginseng as 1—2 g of root per day for up to three months, or 200—600 mg of standardized extracts (4—7 per cent ginsenosides) (Blumenthal et al., 2000; Mahady et al., 2001).
Dietary fibre is composed mainly of non-starch polysaccharides and lignin. Water-soluble forms of dietary fibre includes pectins, beta-glucans, gums and mucilages while the insoluble portion consists of cellulose, lignin and hemicelluloses. Barley and oats have greater contents of soluble fibre than do wheat and maize. The use of dietary fibre in human diet has been shown to have association with heart disease, cancer, diabetes and obesity. Wheat bran may have an effect on oestrogen metabolism as well (Kritchevsky and Bonefield, 1994).
Phytates and phytate derivatives (e.g. phytic acid) are found in flax, wheat germ and bran (Thompson, 1994). These compounds possess antioxidant properties with potential use in food preservation. They also have hypocholesterolemic, anticarcino-genic, hypolipidemic and hypoglycemic effects (Oomah and Mazza, 2000).
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