Phenotypic Shift of Adipocytes by Cholecalciferol and 1α,25 Dihydroxycholecalciferol in Relation to Inflammatory Status and Calcium Content

Recent experimental data seem to suggest a relevant role for 1,25[OH](2)cholecalciferol (1,25[OH](2)D-3) in adipocyte physiology and pathophysiology, with some studies showing adipogenic and pro-inflammatory properties, and others lipolytic and anti-inflammatory functions. Moreover, to our knowledge, the role of cholecalciferol (D-3) in adipocytes function is still not known. Therefore, the aim of this study was to investigate in vitro the effects of 1,25[OH](2)D-3, as well as of D-3, in 3T3-L1 adipocytes in basal and inflammatory conditions, testing the effects of different calcium concentrations in adipocytes culture medium. In 3T3-L1 adipocytes, CYP27A1 and CYP27B1 mRNA were detected in basal conditions and induced after D-3 treatment. Pre-treatment of 3T3-L1 adipocytes not only with 1,25[OH](2)D-3, but also with D-3 before inflammatory stimulation, significantly prevented the increase in gene expression and protein secretion of IL-6 and TNF-alpha, and significantly increased IL-10 mRNA and protein production compared with adipocytes treated only with lipopolysaccharide (LPS). Biological effects of D-3 were still present after inhibition of P450 activity with ketokonazole. LPS determined a decrease in cell area compared with controls, paralleled by a significant increase in optical density (OD) of lipid droplets, whereas 1,25[OH](2)D-3 and D-3 alone significantly increased adipocytes area and decreased OD. Pretreatment with both forms of vitamin D preserved cells from the reduction in their area observed after LPS treatment. LPS decreased more the area of cells grown in a high calcium medium than of adipocytes grown in a low calcium medium. In the presence of a high calcium medium, 1,25(OH)(2)D-3 treatment preserved cell area, maintaining its anti-inflammatory and adipogenic properties. In conclusion our results show that D-3, besides 1,25[OH](2)D-3, presents anti-inflammatory effects on 3T3-L1, as well as that adipocytes have the enzymatic pathways necessary to locally regulate the production of active forms of vitamin D, capable of influencing adipocyte phenotype and function.