Retinoids storage

Blaner, WS O Byme, SM Wongsiriroj, N Kluwe, J D Ambrosio, DM Jiang, H et al. Hepatic stellate cell lipid droplets a specialized lipid droplet for retinoid storage. Biochim Biophys Acta, 2009 1791 467-73. 

PENG Y s, PENG Y M, MCGEE D L and ALBERTS D s (1994) Carotenoids, tocopherols and retinoids in human buccal mucosal cells intra- and inter-individual variability and storage stability. J Clin Nutr 59(3) 636-43. 

Structurally, vitamin A and many synthetic retinoids consist of a (3-ionone ring, a polyunsaturated polyene chain, and a polar end group. The polar end group can exist in several oxidation states, as retinol, retinal, or retinoic acid. Retinol and retinyl esters are the most abundant vitamin A forms found in the body (Blaner and Olson, 1994). Retinol can be esterified with long-chain fatty acids (mainly palmitate, oleate, and stearate) to form retinyl esters, which are the body s storage form of vitamin A. Retinol also can undergo oxidation to retinal, which can be oxidized further to retinoic acid. The active... 

All-trans retinol then diffuses out of the outer segments (rod or cone) and into the retinal pigmented epithelium (RPE). The diffusion of all-trans-retinol out of the outer segments and into RPE cells is facilitated by interstitial retinoid binding protein (IRBP), which is localized in the extracellular matrix of the retina (22). IRBP binds all-trans-retinol as it diffuses out of the outer segment cells and is believed to facilitate transport of aM-trans-retinol to the RPE cell. Additionally, RPE cells directly acquire retinol from serum as described earlier. In both cases, retinol in the RPE cell is rapidly esterified by LRAT in a lecithin-dependent mechanism (22). Retinyl esters provide both a mechanism of storage for the RPE cell and/or provide a substrate for the isomerization reaction (22). 

Most retinoid reductions have been reported in response to organic contaminants, but other pollutants may affect storage levels. Lake trout (Salvelinus namaycush) inhabiting an area contaminated with iron-ore mine tailings had hepatic retinol and retinyl palmitate levels reduced by approximately 95%80. These fish also exhibited oxidative damage, providing indirect evidence that the loss of retinoid stores may be related to increased oxidative stress. 

All toxicology studies to date measuring retinoid levels in fish have focused on the storage forms as opposed to RA, which is the active form binding to the nuclear... 

Retinoic acid appears to regulate the activity, transport, storage, and metabolism of members of the vitamin A family by binding to and/or activating RAREs present in genes encoding retinoid-binding proteins or enzymes involved in RA biosynthesis. For example, a mechanism exists for... 

The storage of plasma or serum samples for periods of several years is now common in connection with health surveys of various kinds. Whether or not the values obtained for retinoids as well as for other labile substances such as vitamin E and ascorbic acid are still valid after extensive storage is of critical concern. Methodological problems did arise in two studies (Kark et al., 1981 Wald et al., 1980) in which plasma samples stored for long periods were analyzed for retinol relative to cancer risk. In Kark s study (1981) the history of the samples was not well documented, including the number of times that specific samples were frozen and thawed, and in Wald s study (1980) about one-fourth of the samples, including 40% of the samples from cancer subjects, arrived at the analytical laboratory in cracked tubes. 

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