Intestinal carotenoid absorption

Carotenoids are highly lipophilic an active area of research concerns how carotenoids interact with and affect membrane systems (see Chapters 2 and 10). Also, the lipid solubility of these compounds has important implications for carotenoid intestinal absorption (see Chapter 17) models such as the Caco-2 cell model are being used to conduct detailed studies of carotenoid absorption/ competition for absorption (Chapter 18). The lipid solubility of these carotenoids also leads to the aggregation of carotenoids (see Chapter 3). Carotenoids aggregate both in natural and artificial systems, with implications for carotenoid excited states (see Chapter 8). This has implications for a new indication for carotenoids, namely, serving as potential materials for harnessing solar energy. 

FURR H c and clark r m (1997) Intestinal absorption and tissue distribution of carotenoids. J Nutr Biochem. 8(7) 364-77. 

In contrast to previous in vivo models, this in vitro model provides the possibility of dissociating experimentally two important processes of intestinal absorption cellular uptake and secretion. Under conditions mimicking the postprandial state (taurocholate/oleic acid supplementation), differentiated Caco-2 cells were able to (1) take up carotenoids at the apical sides and incorporate them into CMs and (2) secrete them at the basolateral sides associated with CM fractions. Using this approach, the extent of absorption of P-carotene through Caco-2 cell monolayers after 16 hr of incubation was 11.2%, a value falling within the in vivo range (9 to 22%). ° - Of the total amount of P-carotene secreted, 78% was associated with the two CM fractions and 10% with the VLDL fraction. ... 

This in vitro approach thus has a great potential for studying the intestinal absorption processes of carotenoids and other pigments. It is important to note the existence of several clones isolated from the parent Caco-2 cell line that can be used for studying... 

During, A. and Harrison, E.H., Intestinal absorption and metabolism of carotenoids insights from cell culture. Arch. Biochem. Biophys., 430, 77, 2004. 

Borel, R, Factors affecting intestinal absorption of highly lipophilic food microconstituents (fat-soluble vitamins, carotenoids and phytosterols), Clin. Chem. Lab. Med., 41, 979, 2003. 

Baskaran, V, Sugawara, T., and Nagao, A., Phospholipids affect the intestinal absorption of carotenoids in mice. Lipids, 38, 705, 2003. 

Yonekura, L and Nagao, A, 2007. Intestinal absorption of dietary carotenoids. Mol Nutr Food Res 51, 107-115. 

Mechanisms of Intestinal Absorption of Carotenoids Insights from In Vitro Systems... 

An In Vitro Model to Study Intestinal Absorption of Carotenoids.370... 

The first study was conducted to determine whether carotenoids and cholesterol share common pathways (transporters) for their intestinal absorption (During et al., 2005). Differentiated Caco-2 cells on membranes were incubated (16 h) with a carotenoid (1 pmol/L) with or without ezetimibe (EZ Zetia, an inhibitor of cholesterol transport), and with or without antibodies against the receptors, cluster determinant 36 (CD36) and scavenger receptor class B, type I (SR-BI). Carotenoid transport in Caco-2 cells (cellular uptake + secretion) was decreased by EZ (lOmg/L) as follows P-C and a-C (50% inhibition) P-cryptoxanthin and LYC (20%) LUT ZEA (1 1) (7%). EZ reduced cholesterol transport by 31%, but not retinol transport. P-Carotene transport was also inhibited by anti-SR-BI, but not by anti-CD36. The inhibitory effects of EZ and anti-SR-BI on P-C transport... 

B18. Bohm, V., and Bitsch, R., Intestinal absorption of lycopene from different matrices and interactions to other carotenoids, the lipid status, and the antioxidant capacity of human plasma. Ear. J.Nutr. 38,118-125 (1999). 

Finckh, B. Kontush, A. Commentz, J. Flubner, C. Burdelski, M. Kohlschiitter, A. 1995. Monitoring of ubiquinol-10, ubiquinone-10, carotenoids, and tocopherols in neonatal plasma microsamples using high-performance liquid chromatography with coulometric electrochemical detection. Anal. Biochem. 232 210-216. Fleshman, M.K. Cope, K.A. Novotny, J.A. Riedl, K. Schwartz, S.J. Jones, P.J. Baer, D.J. Harrison, E.H. 2010. Efficiency of intestinal absorption of P-carotene (BC) is not correlated with cholesterol (CHL) absorption in humans. FASEB J. 24S 539.4. 

Both drugs and compounds naturally present in foods may compete with vitamins for absorption. Chlorpromazine, tricyclic antidepressants, and some antimalarial dmgs inhibit the intestinal transport and metabolism of riboflavin (Section 7.4.4) carotenoids lacking vitamin A activity compete with /S-carotene for intestinal absorption and metabolism (Section 2.2.2.2) and alcohol inhibits the active transport of thiamin across the intestinal mucosa (Section 6.2). 

Fig. 1. The structures of key retinoids and their precursors. Fish convert retinyl esters (e.g. retinyl palmitate (RP)) and carotenoids (e.g. /3-carotene) to retinol in the gut lumen prior to intestinal absorption. Retinyl esters (e.g. RP) stored in the liver are synthesized from retinol by lecithin retinol acyltransferase (LRAT) and acyl CoAiretinol acyltransferase (ARAT). The retinyl esters are mobilized through their conversion to retinol by retinyl ester hydrolase (REH), which is then transported in the circulation to various sites in the body. Retinol is further metabolized within specific tissues to retinal by alcohol dehydrogenases (ADH) or short-chain dehydrogenase/reductase. Retinal is converted to the two major biologically active forms of retinoic acid (RA) (all-trans and 9-cis RA). Retinaldehyde dehydrogenase 2 (Raldh2) synthesizes all-trans RA from all-trans precursors and 9-cis RA form 9-cis precursors.

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