Carotenoids alpha-carotene

Cuscuta australis R. Brown Dou Tu Si (Dodder) (seed, aerial part) Carotenoids, alpha-carotene-5, 6-epoxide, taraxanthin, lutein.48 For fever, constipation, diuretic. 

In addition to the actual forms of vitamin A, related compounds, known as carotenes, are found in several fruits and vegetables. Carotene is also called (1) provitamin A, because it can be converted to vitamin A in the body and (2) precursor of vitamin A, because it precedes vitamin A. At least 10 of the carotenoids found in plants can be converted with varying efficiencies into vitamin A. Four of these carotenoids alpha-carotene, beta-carotene, gamma-carotene, and crypto-xanthine (the main carotenoid of corn)—are of particular importance due to their provitamin A activity. Of the four, beta-carotene (see Fig. V-25) has the highest vitamin A activity and provides about two-thirds of the vitamin A necessary for human nutrition. 

Some non-enzymatic antioxidants play a key role in these defense mechanisms. These are often vitamins (A, C, E, K), minerals (zinc, selenium), caretenoids, organosulfur compounds, allyl sulfide, indoles, antioxidant cofactors (coenzyme Qio)> and polyphenols (flavonoids and phenolic acids) [1,37]. Further, there is good evidence that bilirubin and uric acid can act as antioxidants to help neutralize certain free radicals [38]. Alpha-carotene, lycopene, lutein, and zeaxanthine [39] can be considered subgroups of carotenoids [40] that are effective antioxidant compounds. 

A concern has been raised that phytosterol doses that are effective for cholesterol reduction may impair the absorption and lower blood concentrations of fat-soluble vitamins and antioxidants. A number of studies showed that phytosterols had no effect on plasma concentrations of vitamin D, retinol, or plasma-lipid-standardized alpha-tocopherol. Moreover, the reports of the effect of phytosterols on concentrations of blood carotenoids (lutein, lycopene, and alpha-carotene) are controversial. There seems to be general agreement that phytosterol doses >1 g/d significantly decrease LDL-C standardized beta-carotene concentrations however, it remains to be determined whether a reported 15-20% reduction in beta-carotene due to phytosterol supplementation is associated with adverse health effects. Noakes et al. found that consumption of one or more carotenoid-rich vegetable or fruit servings a day was sufficient to prevent lowering of plasma carotenoid concentrations in 46 subjects with hypercholesterolemia treated with 2.3 g of either sterol or stanol esters. 

Vitamin A is a family of fat-soluble vitamins, of which retinol is the most active form. Beta-carotene is a provitamin carotenoid that is converted to retinol more efficiently than other provitamin carotenoids. Other provitamin carotenoids include alpha-carotene and (trivial names) b-cryptoxanthin, lycopene, lutein, and zeaxanthin they are widely available in foods. 

El 60 Carotenoids, Alpha-, Beta-, Gamma-carotene 192 E302 Calcium Ascorbate 660... 

Nutrient Content high in protein, prebiotic fiber, antioxidant vitamins A and C, B vitamins, dietary minerals Phytochemical Content high in carotenoids (alpha- and beta-carotene, beta-cryptoxanthin, lutein, violaxanthin), polyphenols (quercetin, gallic acid, gallotannins, rhamnetin, cyanidin and xanthone glycosides, including mangiferin, mainly in skin)... 

High Phytochemical Content carotenoids (alpha- and beta-carotene, beta-cryptoxanthin, lutein, violaxanthin) polyphenols (anthocyanins, proanthocyanidins, ellagic acid)... 

Fig. 5.3 Carotenoid biosynthesis in maize endosperm. Compounds IPP, isopentenyl pyrophosphate FPP, famesyl pyrophosphate GGPP, geranylgeranyl pyrophosphate DMAPP, dimethallyl pyrophosphate. Carotenoid biosynthetic pathway enzymes PSY, phytoene synthase PDS, phytoene desaturase ZDS, zetacarotene desaturase ISO, carotene isomerase LCY-B, lycopene beta cyclase LCY-E, lycopene epsilon cyclase HYD-B, beta-carotene hydroxylase HYD-E, alpha-carotene hydroxylase Isonrenoid biosynthetic pathway enzymes IPPI (IPP isomerase) GGPPS (GGPP synthase). Structures are not representative of the geometrical isomer substrates (e.g. Z-phytoene is a bent structure).

Compared to other fruits and vegetable, carotenoid accumulation in maize endosperm is orders of magnitude lowerThe primary compounds accumulating are zeaxanthin and lutein, the ratio of which is highly variable and further accompanied by smaller amounts of the provitamin A compounds, alpha-carotene, betacarotene, and betacryptoxanthin. The earlier pathway intermediates are generally not detected, unless there is a mutation conferring a block in the pathway but which... 

Antioxidants derived from foods help to protect against free radical damage. Carotenoids are a very important class of antioxidants, as are vitamins A, C, and E. Carotenoids, including alpha carotene, beta carotene, lycopene, lutein, and zexanthin, have been demonstrated to protect against skin cancer, prostate cancer, and atherosclerosis, among others. Higher blood antioxidant levels have been correlated with lower blood levels of C-reactive protein (CRP), and thus lower inflammation of the blood vessels (and less atherosclerotic plaque). 

The presence of other carotenoids can affect the absorption of carotenoids into intestinal mucosal cells, since carotenoids can compete for absorption or facilitate the absorption of another. Data on carotenoid interactions are not clear. Human studies show that /3-carotene decreases lutein absorption, while lutein has either no effect or a lowering effect on /3-carotene absorption. Although not confirmed in humans, the inhibitory effect of lutein on /3-carotene absorption might be partly attributed to the inhibition of the /3-carotene cleavage enzyme by lutein shown in rats. Beta-carotene also seemed to lower absorption of canthaxanthin, whereas canthaxanthin did not inhibit /3-carotene absorption. Studies showed that /3-carotene increased lycopene absorption, although lycopene had no effect on /3-carotene. Alpha-carotene and cryptoxanthin show high serum responses to dietary intake compared to lutein. In addition, cis isomers of lycopene seem to be more bioavailable than the -trans, and selective intestinal absorption of a)X-trans /3-carotene occurs, as well as conversion of the 9-cis isomer to sW-trans /3-carotene. It is clear, then, that selective absorption of carotenoids takes place into the intestinal mucosal cell. 

Carotenoids Alpha- and beta-carotene cryptoxanthin, lutein, lycopene, zeaxanthin Quench singlet and triplet oxygen, increase cell-cell communication Red, orange and yellow fruits and vegetables, egg yolk, butter fat, margarine... 

It is well known that excessive intake of P-carotene may lead to carotenodermia (yellow skin), and it is undoubtedly the case that some carotenoid is directly lost via the skin or through photo-oxidation in the skin. As far as is known the carotenoids are not cytotoxic or genotoxic even at concentrations up to 10 times the normal plasma concentration which may cause carotenodermia. However, they are associated with amenorrhoea in girls who may be consuming bizarre diets and, in long-term supplementation studies, with an increase in lung cancer (The Alpha-tocopherol, Beta-carotene Cancer Prevention Study Group, 1994). 

Holick, C.N. et al., Dietary carotenoids, serum beta-carotene, and retinol and risk of lung cancer in the alpha-tocopherol, beta-carotene cohort study, Am. J. Epidemiol., 156, 536, 2002. 

Albanes, D. et al., Effect of supplemental P-carotene, cigarette smoking and alcohol consumption on serum carotenoids in alpha-tocopherol, P-carotene cancer prevention study, Am. J. Clin. Nutn, 66, 366, 1976. 

The interaction of carotenoids with cigarette smoke has become a subject of interest since the results of the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study Group 1994 (ATBC) and CARET (Omenn et al. 1996) studies were released. P-Carotene has been hypothesized to promote lung carcinogenesis by acting as a prooxidant in the smoke-exposed lung. Thus, the autoxidation of P-carotene in the presence of cigarette smoke was studied in model systems (toluene) (Baker et al. 1999). The major product was identified as 4-nitro-P-carotene, but apocarotenals and P-carotene epoxides were also encountered. 

Albanes D, Virtamo J, Taylor PR, Rautalahti M, Pietinen P and Heinonen OP. 1997. Effects of supplemental 3-carotene, cigarette smoking, and alcohol consumption on serum carotenoids in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. Am J Clin Nutr 66 366—372. 

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