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Characterization of vitamin D uptake in Caco-2 TC7 cells. (A) Comparison of vitamin D3 and vitamin D2 uptake by differentiated Caco-2 TC-7 cell monolayers at 378C at low concentrations. (B) Cholecalciferol uptake by differentiated Caco-2 TC-7 cell monolayers at 378C at high concentrations. (C) Effect of temperature and transport direction on cholecalciferol uptake by differentiated Caco-2 TC-7 monolayers.
Scope: It is assumed that vitamin D is absorbed by passive diffusion. However, since cholecalciferol (vitamin D 3 ) and cholesterol display similar structures, we hypothesized that common absorption pathways may exist. Methods and results: Cholecalciferol apical transport was first examined in human Caco-2 and transfected Human embryonic kidney (HEK) cells. Cholecalciferol uptake was then valuated ex vivo and in vivo, using either wild-type mice, mice overexpressing Scavenger Receptor class B type I (SR-BI) at the intestinal level or mice treated or not with ezetimibe. Cholecalciferol uptake was concentration-, temperature-and direction-dependent, and was significantly impaired by a co-incubation with cholesterol or tocopherol in Caco-2 cells. Moreover Block Lipid Transport-1 (SR-BI inhibitor) and ezetimibe glucuronide (Niemann-Pick C1 Like 1 inhibitor) significantly decreased cholecalciferol transport. Transfection of HEK cells with SR-BI, Cluster Determinant 36 and Niemann-Pick C1 Like 1 significantly enhanced vitamin D uptake, which was significantly decreased by the addition of Block Lipid Transport-1, sulfo-N-succinimidyl oleate (Cluster Determinant 36 inhibitor) or ezetimibe glucuronide, respectively. Similar results were obtained in mouse intestinal explants. In vivo, cholecalciferol uptake in proximal intestinal fragments was 60% higher in mice overexpressing SR-BI than in wild-type mice (p a 0.05), while ezetimibe effect remained non-significant. Conclusion: These data show for the first time that vitamin D intestinal absorption is not passive only but involves, at least partly, some cholesterol transporters.
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In vitro release profile of curcumin from C-SLNs by dialysis method. Scope: Curcumin, a molecule with pluripharmacological properties, was loaded into solid lipid nanoparticles (SLNs) with a view to improve its oral bioavailability (BA). Methods and results: Curcumin-loaded solid lipid nanoparticle