Vitamin D Status of Mice Deficient in Scavenger Receptor Class B Type 1, Cluster Determinant 36 and ATP-Binding Cassette Proteins G5/G8

Classical lipid transporters are suggested to modulate cellular vitamin D uptake. This study investigated the vitamin D levels in serum and tissues of mice deficient in SR-B1 (Srb1-/-), CD36 (Cd36-/-) and ABC-G5/G8 (Abcg5/g8-/-) and compared them with corresponding wild-type (WT) mice. All mice received triple-deuterated vitamin D3 (vitamin D3-d3) for six weeks. All knockout mice vs. WT mice showed specific alterations in their vitamin D concentrations. Srb1-/- mice had higher levels of vitamin D3-d3 in the serum, adipose tissue, kidney and heart, whereas liver levels of vitamin D3-d3 remained unaffected. Additionally, Srb1-/- mice had lower levels of deuterated 25-hydroxyvitamin D3 (25(OH)D3-d3) in the serum, liver and kidney compared to WT mice. In contrast, Cd36-/- and WT mice did not differ in the serum and tissue levels of vitamin D3-d3, but Cd36-/- vs. WT mice were characterized by lower levels of 25(OH)D3-d3 in the serum, liver and kidney. Finally, Abcg5/g8-/- mice tended to have higher levels of vitamin D3-d3 in the serum and liver. Major alterations in Abcg5/g8-/- mice were notably higher levels of 25(OH)D3-d3 in the serum and kidney, accompanied by a higher hepatic mRNA abundance of Cyp27a1 hydroxylase. To conclude, the current data emphasize the significant role of lipid transporters in the uptake, tissue distribution and activation of vitamin D

Markers Indicating Body Vitamin D Stores and Responses of Liver and Adipose Tissues to Changes in Vitamin D Intake in Male Mice

Circulating 25-hydroxyvitamin D (25(OH)D) is regarded as the most reliable biomarker of vitamin D status. However, limited data exist concerning the suitability of 25(OH)D as an indicator of body vitamin D stores and the ability of adipose tissue to mobilize vitamin D. In the first study, in which male mice received different vitamin D3 doses for three weeks, we found strong linear response relationships between vitamin D3 intake and levels of vitamin D3 in the plasma (p < 0.001), liver (p < 0.001) and adipose tissues (p < 0.001), and strong positive correlations between plasma and tissue stores of vitamin D3 (p < 0.001). Plasma levels of 25(OH)D3 and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) showed weak or no correlations with tissue vitamin D3 stores. Data from a second study demonstrate a strong and rapid response of plasma 25(OH)D3 in vitamin D3-treated mice with a low vitamin D status. Additionally, mice fed a vitamin D-free diet showed a strong and rapid decline in vitamin D3 in the liver, whereas the decline in different adipose tissues was distinctly lower than that in the liver. To conclude, tissue stores of vitamin D3 were best reflected by plasma vitamin D3. In contrast to the liver, adipose tissues responded less sensitively to an absence of vitamin D intake