Inhibition of cytokine secretion from adipocytes by 1,25-dihydroxyvitamin D ₃ via the NF-κB pathway

Adipose tissue inflammation is an important pathological process in obese people, associated with diabetes and cardiovascular disease. We hypothesized that 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] inhibits cytokine secretion from adipocytes via direct inhibition of transcription factor nuclear factor-κB (NF-κB). We utilized two different human models. Bone marrow-derived human mesenchymal stromal cells (hMSCs) differentiated into adipocytes, and adipocytes isolated from biopsies stimulated with lipopolysaccharide (LPS) were treated with or without 1,25(OH)₂D₃. Expression and secretion of interleukin-6 (IL-6) were measured by quantitative RT-PCR analysis and ELISA. Assessment of NF-κB nuclear translocation, DNA binding activity was per formed by immunofluorescence (IF) and electrophoretic mobility assay (EMSA). Inhibitor κB (IκB) and its phosphorylation were detected by Western blot (WB) analysis. Simultaneous 1,25(OH)₂D₃ cotreatment significantly reduced LPS-stimulated (10 ng/ml) IL-6 secretion dose dependently by 15% at 10^-10 M and 26% at 10^-7 M (P<0.05) in hMSCs, while preincubation with 1,25(OH)₂D₃ (10^-7 M) for 24 h reduced IL-6 secretion by 24 and 35% (P<0.001) and mRNA levels by 34 and 30% (P<0.05) in hMSCs and isolated adipocytes, respectively. 1,25(OH)2D3 suppressed LPS-stimulated IκB phosphorylation-medi ated NF-κB translocation into the nucleus were evident from WB, IF, and EMSA. 1,25(OH) ₂D₃ inhibits LPSstimulated IL-6 secretion in two human adipocyte models via interference with NF-κB signaling.