Carotenoids biological activities

Many carotenoids function in humans as vitamin A precursors however, not all carotenoids have provitamin A activity (Table 3). Of the biologically active carotenoids, -carotene has the greatest activity. Despite the fact that theoretically one molecule of -carotene is a biological source of two molecules of vitamin A, this relationship is not observed and 6 p.g -carotene is equivalent to 1 p. vitamin A. Although -carotene and vitamin A have complementary activities, they caimot totally replace each other. Because the conversion of -carotene to vitamin A is highly regulated, toxic quantities of vitamin A cannot accumulate and -carotene can be considered as a safe form of vitamin A (8). 

The ready availability of carotenoid oxidation products through chemical methods will facilitate their use as standard identification tools in complex media such as biological fluids, and enable in vitro investigation of their biological activity. Moreover, these studies can help reveal the mechanisms by which they can be chemically or biochemically cleaved in vivo. 

Wang, X.D., Carotenoid oxidative/degradative prodncts and their biological activities, in Carotenoids in Health and Disease, Krinsky, S.T.M. and Sies, H., Eds., Marcel Dekker, New York, 2004, 313. 

The research into the biological activities of chlorophylls developed over the past 20 years is also important although very few in vivo assays concerning then-potential health benefits have been performed. Far fewer studies have focused on chlorophylls in comparison to carotenoids. Efforts to stabilize chlorophylls in pro-... 

BIOPHYSICAL AND BIOLOGICAL ACTIVITY OF HYDROPHILIC CAROTENOIDS AND CAROTENOID AGGREGATES... 

Wang, X. D. (2004). Carotenoid oxidative/degradative products and their biological activities. Carotenoids in Health and Disease. N. I. Krinsky, S. T. Mayne and H. Sies, eds. New York Marcel Dekker, pp. 313-335. 

McNulty, H., R. F. Jacob et al. (2008). Biologic activity of carotenoids related to distinct membrane physicochemical interactions. Am. J. Cardiol. 101(10A) 20D-29D. 

Stahl, W., Nicolai, S., Briviba, K., Hanusch, M., Broszeit,G., Peters, M., Martin, H.D., Sies, H., 1997. Biological activities of natural and synthetic carotenoids Induction of gap junctional communication and singlet oxygen quenching. Carcinogenesis. 18, 89-92. 

Similarly to carotenoids, flavonoids also show considerable biological activity. Their beneficial effect in cancer and heart diseases has been proven many times [86-89], It has further been established that flavonoids improve cardiovascular remodelling and vascular function in NO-deficient hypertension [90], Moreover, flavonoid intake reduces the risk of chronic diseases [91], and beneficially influences inflammations [92], and ulcer formation [93,94],... 

Besides the great pigment classes such as carotenoids, flavonoids, anthocyanins and chlorophylls a wide variety of other pigments have been separated, quantitated and identified by different liquid chromatograpchic techniques. The chemical structures of these pigments show high diversity. Unfortunately, in the majority of cases the biological activity of these... 

Vitamin A (retinol, 6.1) is the parent of a range of compounds known as retinoids, which possess the biological activity of vitamin A. In general, animal foods provide preformed vitamin A as retinyl esters (e.g. 6.5, which are easily hydrolysed in the gastrointestinal tract) while plant foods provide precursors of vitamin A, i.e. carotenoids. Only carotenoids with a /3-ionone ring (e.g. /1-carotene) can serve as vitamin A precursors. /3-Carotene (6.6)... 

The fat-soluble vitamins comprise vitamins A, D, E, and K, whose biological activities are attributed to a number of structurally related compounds known as vitamers. Also included are those carotenoids that are precursors of vitamin A. Recommended dietary allowances (RDAs) based on human epidemiological and experimental animal studies have been published in the United States for vitamins A, D, E, and K (1). Other countries and international bodies have compiled similar recommendations. In the United States and Canada, fluid milk is supplemented by law with vitamin D to a level of 400 international units per quart (10 /zg/0.95 L) to meet the RDA of 10 p%. Other commodities, such as margarine, milk products, ready-to-eat breakfast cereals, and dietetic foods, are commonly supplemented with vitamins A, D, and E. Except for infant formulas, vitamin K is not added to foods. The addition of vitamins to a particular processed food is intended to provide a specific proportion of the RDA. 

From a nutritional viewpoint, the carotenoids are classified as provitamins and inactive carotenoids. To have vitamin A activity, the carotenoid molecule must incorporate a molecule of retinol, i.e., an unsubstituted /3-ionone ring with an 11-carbon polyene chain. /3-carotene (C40H56, MW = 536.88), the most ubiquitous provitamin A carotenoid, is composed of two molecules of retinol joined tail to tail thus the compound possesses maximal (100%) vitamin A activity. The structures of all other provitamin A carotenoids incorporate one molecule of retinol and hence theoretically contribute 50% of the biological activity of /3-carotene. Among the 600 or so carotenoids that exist in nature, only about 50 possess vitamin A activity in varying degrees of potency. 

The biological activities of carotenoids, such as (3-carotene, are related to their provitamin A activity within the body (Clinton, 1998). Since lycopene lacks the (3-ionic ring structure, it does not have any provitamin A activity (Stahl and Sies, 1996). The biological effects of lycopene in humans have therefore been attributed to mechanisms other than vitamin A. Two major hypotheses have been proposed to explain the anticarcinogenic and antiatherogenic activities of lycopene oxidative and nonoxidative mechanisms. The proposed mechanisms for the role of lycopene in the prevention of chronic diseases are summarized in Figure 6. 

Vitamins are essential nutrients, which must be supplied exogenously. They are organic compounds with indispensable biological activities as coenzymes in a multitude of cellular metabolic processes. Vitamin A, retinoids (vitamin A-derivatives), carotenoids, vitamin D, vitamin E, and vitamin K are fat-soluble, vitamin C and vitamins of the B-complex are water-soluble. This is of importance for gastrointestinal absorption in oral supplementation as well as the transdermal penetration for topical applications. 

Molnar, P., Kawase, M., Satoh, K., Sohara, Y., Tanaka, T., Tani, S., Sakagami, H., Nakashima, H., Motohashi, N., Cyemant, N. and Molnar, J. (2005) Biological activity of carotenoids in red paprika, Valencia orange and golden delicious apple. Phytotherapy Research 19(8), 700-707. 

The term vitamin A can include any compound with the biological activity of the vitamin provitamin A carotenoids, retinol, and its active metabolites. 

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