Carotenoid absorption

The measurement of carotenoid absorption is fraught with difficulties and riddled with assumptions, and it is therefore a complex matter. Methods may rely on plasma concentration changes provoked by acute or chronic doses, oral-faecal mass balance method variants and compartmental modelling. 

A group of competing reactions takes place when carotenoids are exposed to light. When the incidence of light energy overlaps the carotenoid absorption region. 

Independent Pathways of Retinol and Carotenoid Absorption in Caco-2 Cells ... 

Carotenoid absorption and metabolism have been comprehensively reviewed (Erdman et al., 1993 Parker, 1996 van Vliet, 1996 Furr and Clark, 1997 Yeum and Russell, 2002) and this chapter will focus only on recent advances in these areas. A particular emphasis will be placed on studies that used in vitro and cell culture models as tools to understand better the mechanisms of absorption on the molecular level. 

Thus, in contrast to previous in vivo models, this in vitro model provides the possibility of dissociating experimentally two important processes of the intestinal carotenoid absorption cellular uptake and secretion. Under conditions mimicking the postprandial state (TC OA supplementation), differentiated Caco-2 cells were able (1) to take up carotenoids at the apical side and to incorporate them into CM and (2) to secrete them at the basolateral side, associated with CM fractions. In this model, no attempt has yet been made to reproduce the in vivo physiochemical conditions occurring in the intestinal lumen, such as carotenoid release from the food matrix and solubilization into mixed lipid micelles. Carotenoids were delivered to Caco-2 cells in aqueous suspension with Tween 40 (During et al., 2002). Using this cell culture system in conjunction with an in vitro... 

THE HUMAN CACO-2 INTESTINAL CELL MODEL A VALUABLE TOOL FOR STUDYING CAROTENOID ABSORPTION... 

Competition resulting in a decrease of global carotenoid absorption can occur at many steps of the digestion process, including the transfer of carotenoids into mixed micelles, transport across... 

In conclusion, the Caco-2 cell monolayer model has given original data on the competition effect of several nutrients on carotenoid uptake. Most of these data have been confirmed in several in vivo studies, including clinical studies, confirming that this model is a valuable tool to study competition effects on 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. 

Nevertheless, the avena coleoptile exhibits a curvature to unilateral UV-illumina-tion with a satisfactory log-linear response/time relationship38) (the bending mode is similar to that observed for the second positive curvature which develops from the coleoptile base cf. 2.2). Fig. 5 338) shows that the double-peaked action spectrum does not match neither flavin (Fig. 5 5,16S)) nor carotenoid absorption (Fig. 5 4,183)), most likely excluding both as photoreceptors. The growth hormone auxin (cf. 2.4 and Scheme 1) has been discussed to be a possible photoreceptor. However, in this case, this is not supported by the action spectrum either. 

Dietary fats are required for carotenoid uptake by intestinal cells. Fats have an important role in the continuation of the process of carotenoid absorption, because the human intestine is incapable of secreting significant quantities of chylomicrons into the bloodstream in the absence of fats (Ornelas-Paz and others 2008b). Some studies have suggested that at least 5 g/day of dietary fat are required for suitable (3-carotene absorption (West and Castenmiller 1998), whereas others suggested the consumption... 

The type and amount of carotenoids consumed affects carotenoid absorption. Absorption of (3-carotene from large doses is independent of dose size (Tanumihardjo 2002). The response of (3-carotene in serum and milk was similar in women supplemented with 60 or 210 mg of (3-carotene (Canfield and others 1997). In contrast, small carotenoid doses are more efficiently absorbed than large ones (West and Castenmiller 1998 Furusho and others 2000 Tanumihardjo 2002). 

Subject-related Factors Limiting Carotenoid Absorption... 

Studies in humans and animals suggest that carotenoid absorption depends on several factors including vitamin A status. Sklan and others (1989) demonstrated that vitamin A supplementation reduced (3-carotene and canthaxanthin absorption in chickens. Dietary carotenoids absorption and bioconversion to vitamin A varied inversely with the vitamin A status of Philippine children (Ribaya-Mercado and others 2000). Some studies (Lecomte and others 1994 Albanes and others 1997) have suggested a possible negative effect of alcohol consumption on carotenoid absorption however,... 

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