Interaction of Vitamin D-BODIPY With Fat Cells and the Link to Obesity-associated Vitamin D Deficiency

Obese individuals often exhibit vitamin D deficiency, potentially due to sequestration in fat cells. Little is known about how vitamin D₃ enters adipocytes and associates with the intracellular lipid droplet.

Newly differentiated human and mouse (3T3-L1) adipocytes and primary mouse adipocytes were treated with vitamin D₃ covalently linked to green fluorescent BODIPY (VitD-B) or Green BODIPY (GB) as control. Cells were exposed to 10-100 nM concentrations for various lengths of time (1-48 h). Fluorescence microscopy assessed vitamin D distribution.

VitD-B demonstrated stable incorporation into adipocytes without enzymatic cleavage, as HPLC showed no free vitamin D₃ after 72 h. Fluorescence microscopy showed GB uptake was rapid and persisted for 48 h. VitD-B uptake was more gradual compared to GB in the human and 3T3-L1 adipocytes. Primary mouse adipocytes exhibited similar uptake patterns, with VitD-B appearing within 1 h and fluorescence intensity increasing 1.2-fold at 8 h and 5.7-fold at 24 h. GB exhibited rapid fluorescence uptake in these same cells, 29-fold higher than VitD-B at 1 h. At 24 h, some VitD-B treated cells exhibited greater fluorescence intensity around the surface of the lipid droplets, which was not observed in GB. Isolated lipid droplets exhibited rapid and immediate uptake of both VitD-B and GB, indicating a strong affinity for these lipid structures. The time-dependent accumulation of vitamin D₃ in human adipocytes mirrored VitD-B uptake.

VitD-B is a reliable proxy for studying the dynamics of vitamin D₃ uptake in adipocytes.