Vitamin Retinol

Retinoic acid (vitamin A acid). Retinol (vitamin A... 

Fat-Soluble Retinol (vitamin A) Ergocalciferol (vitamin Dg) Cholecalciferol (vitamin Dg) n-Tocopherol (vitamin E) Vitamin K ... 

Transthyretin (TTR) A protein complex found in blood that binds both retinol (vitamin A) and thyroxine. 

A small but variable proportion of the carotenoids with one or two P-ionone rings (mainly P-carotene) are cleaved in the enterocytes to produce retinol (vitamin A). This process is very tightly controlled, so that too much vitamin A is not produced, although the control mechanism is not clear. Some cleavage of P-carotene can also occur in the liver, but this does not account for the turnover of P-carotene in the body. Small amounts of carotenoids are subject to enterohepatic circulation, but this does not account for losses. 

Zeegers, M.P. et al.. Are retinol, vitamin C, vitamin E, folate and carotenoids intake associated with bladder cancer risk Results from the Netherlands Cohort Study, Br. J. Cancer, 85, 977, 2001. 

Four deuteriated retinols, 26-29, with 3 to 5 deuterium atoms have been synthesized29 for metabolism of vitamin A studies in humans30. Deuterium has been introduced into appropriate intermediates, used in the reaction scheme shown in equation 12, by base-catalysed exchange with 2H20 or perdeuterioacetone. The numbering system for retinol (vitamin A alcohol) is shown in equation 12. 

While the human body can remove an excess of any water-soluble vitamin, excesses of fat-soluble vitamins are more serious. Early arctic explorers discovered that the Inuit regarded seal liver and polar bear liver as taboo and must not be eaten. Those explorers who ignored this advice risked retinol poisoning as the livers of both these species are rich in retinol (vitamin A) that can not be excreted. The effects of retinol poisoning are extremely unpleasant. It is for this reason that fortification with fat-soluble vitamins is not likely to be undertaken. 

The answer is d. (Hardman, p 1575.) Isotretinoin is actually a form of high-dose vitamin A therapy Vitamin A itself or retinol (vitamin A could be used, but they have less advantageous pharmacokinetic properties. Antibiotics such as tetracyclines are used in acne, but they have little effect on the nodulocystic form... 

Figure 12.8 Vitamin Ar All-tranj-retinol (Vitamin A alcohol) is usually referred to as Vitamin A,.

J. Boehnlein, A. Sakr, J. L. Lichtin, R. L. Bronaugh, Characterization of Esterase and Alcohol Dehydrogenase Activity in Skin. Metabolism of Retinyl Palmitate to Retinol (Vitamin A) During Percutaneous Absorption , Pharm. Res. 1994, 11, 1155-1159. 

Vitamin Ai (retinol) is derived in mammals by oxidative metabolism of plant-derived dietary carotenoids in the liver, especially -carotene. Green vegetables and rich plant sources such as carrots help to provide us with adequate levels. Oxidative cleavage of the central double bond of -carotene provides two molecules of the aldehyde retinal, which is subsequently reduced to the alcohol retinol. Vitamin Ai is also found in a number of foodstuffs of animal origin, especially eggs and dairy products. Some structurally related compounds, including retinal, are also included in the A group of vitamins. 

Zachman, R. D. (1989). Retinol (vitamin A) and the neonate Special problems of the human premature infant. Am. J. Clin. Nutr. 50, 413-424. 

Retinol (vitamin A) is found in foods of mammalian origin in the form of retinyl ester, or in fruits and vegetables as carotenoids with provitamin A activity, especially P-carotene (provitamin A). In enterocytes, retinol binds to cellular retinol-binding protein type II (CRBPII), which directs the esterification by the enzyme lecithin retinol acyltransferase (LRAT). 

The stability of some vitamins is influenced by aw. In general, the stability of retinol (vitamin A), thiamin (vitamin Bj) and riboflavin (vitamin B2) decreases with increasing aw. At low av (below 0.40), metal ions do not have a catalytic effect on the destruction of ascorbic acid. The rate of loss of ascorbic acid increases exponentially as aw increases. The photodegradation of riboflavin (Chapter 6) is also accelerated by increasing aw. 

The retinoids, a family of molecules that are related to retinol (vitamin A), are essential for vision, reproduction, growth, and maintenance of epithelial tissues. Retinoic acid, derived from oxidation of dietary retinol, mediates most of the actions of the retinoids, except for vision, which depends on retinal, the aldehyde derivative of retinol. 

VITAMIN A. This substance also has been referred to as retinol, axerophthol, biosterol, vitamin Ai, anti-xerophthalmic vitamin, and anti-infective vitamin. The physiological forms of the vitamin include Retinol (vitamin A ) and esters 3-dehydroretinol (vitamin A2) and esters 3-dehydroretinal (retinme-2) retinoic acid neovitamin A neo-b-vitamin Ai. The vitamin is required by numerous animal species. All vertebrates and some invertebrates convert plant dietary carotenoids in gut to vitamin Ai. which is absorbed. Most animal species store appreciable amounts... 

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