Carotenoid Transport Is Decreased and Expression of the Lipid Transporters SR-BI, NPC1L1, and ABCA1 Is Downregulated in Caco-2 Cells Treated with Ezetimibe

Abstract

Data suggest that intestinal carotenoid absorption is a facilitated process. The present study was conducted to determine whether carotenoids and cholesterol share common pathways (transporters) for their intestinal absorption. Differentiated Caco-2 cells on membranes were incubated (16 h) with a carotenoid (1 micromol/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 (10 mg/L) as follows: beta-carotene approximately alpha-carotene (50% inhibition) >> beta-cryptoxanthin approximately lycopene (20%) >> lutein:zeaxanthin (1:1) (7%). EZ reduced cholesterol transport by 31%, but not retinol transport. beta-Carotene transport was also inhibited by anti-SR-BI, but not by anti-CD36. The inhibitory effects of EZ and anti-SR-BI on beta-carotene transport were additive, indicating that they may have different targets. Finally, differentiated Caco-2 cells treated with EZ showed a significant decrease in mRNA expression for the surface receptors SR-BI, Niemann-Pick type C1 Like 1 protein (NPC1L1), and ATP-binding cassette transporter, subfamily A (ABCA1) and for the nuclear receptors retinoid acid receptor (RAR)gamma, sterol-regulatory element binding proteins (SREBP)-1 and -2, and liver X receptor (LXR)beta as assessed by real-time PCR analysis. The data indicate that 1) EZ is an inhibitor of carotenoid transport, an effect that decreases with increasing polarity of the carotenoid molecule, 2) SR-BI is involved in carotenoid transport, and 3) EZ may act, not only by interacting physically with cholesterol transporters as previously suggested, but also by downregulating expression of these proteins. The cellular uptake and efflux of carotenoids, like that of cholesterol, likely involve more than one transporter.

Phytoene, phytofluene, and lycopene from tomato powder differentially accumulate in tissues of male Fisher 344 rats

“…In CaCo-2 cells, differential and competitive uptake of α-carotene, β-carotene, lutein, and LYC has been reported [34]. Recently, scavenger receptor class B, type I (SR-BI) has been identified as a protein involved in intestinal transport of carotenoids in Caco-2 cells [35], and SR-BI is highly concentrated in human and rat liver and in steroidogenic tissues [36,37]. The specificity of transport and/or binding proteins is unclear, yet it is plausible that this specificity may depend on the number and/or location of conjugated double bonds present within carotenoids ( Figure 1).…”

β-Carotene conversion products and their effects on adipose tissue

“…At the intestinal level, b-carotene absorption is depending on three steps: (1) absorption at the enterocyte brush border membrane level, partly via the cholesterol transporters SR-BI and CD36 [11,71] but also by passive diffusion [83]; (2) enzymatic conversion of a fraction of absorbed b-carotene in a centric or eccentric fashion by the b-carotene 15,15 0 -monooxygenase BCMO1 (releasing retinal) or by the b-carotene 9 0 ,10 0 -dioxygenase, BCDO2 (releasing b-apo-10 0 -carotenal and b-ionone), respectively (Fig. 2, for review see [73].…”

The g.−762T>C polymorphism of the NPC1L1 gene is common in Chinese and contributes to a higher promoter activity and higher serum cholesterol levels

“…[22][23][24] Besides, our results were consistent with data reported by other group, NPC1L1 transcription activity was inhibited while cells were treated with ezetimibe. 25 In addition, it has been reported that NPC1L1 promoter is regulated mainly by SREBP-2, a transcription factor-regulated cholesterol metabolism-related genes expression. 17 Both putative sterol regulatory elements and Ying Yang-1 (YY1)-binding sites are present in the promoter region of NPC1L1, suggesting that these transcription factors may regulate the NPC1L1 gene expression.…”