Regulation of TNF-α by 1α,25-dihydroxyvitamin D3 in human macrophages from CAPD patients

Abstract

Background: We have previously reported that 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3] accumulates in the dialysis fluid of uremic patients treated by continuous ambulatory peritoneal dialysis (CAPD). It has been reported that this metabolite regulates the production of cytokines by monocytes/macrophages. Since tumor necrosis factor-α (TNF-α) initiates an inflammatory cascade during peritonitis, the aim of the present study was to investigate the effect of 1α,25(OH)2D3 on the production of TNF-α by human peritoneal macrophages (HPMs). Methods: HPMs were obtained from patients on CAPD. Cells were incubated with various concentrations of 1α,25(OH)2D3, 1α,24(S) dihydroxyvitamin D2 [1α,24(S)(OH)2D2] or 25-hydroxyvitamin D3 (25-OH-D3) for 16 hours. This was followed by lipopolysaccharide (LPS; 1 μg/mL) incubation for 2.5 to 6 hours. TNF-α protein production was determined by enzyme-linked immunosorbent assay. TNF-α mRNA was assayed by the reverse transcriptase-polymerase chain reaction procedure, using internal synthetic mRNA standards for quantitative results. Results: Incubation of HPMs with 1α,25(OH)2D3 prior to stimulation with LPS dose dependently inhibited the expression of TNF-α on both mRNA and protein levels. Similar results were obtained with the less calcemic vitamin D2 analogue 1α,24(S)(OH)2D2. Incubation of HPMs with 25-OH-D3 also revealed a down-regulation of TNF-α expression. Since this down-regulatory effect was blocked by ketoconazole, it is likely that this effect was caused by the conversion of 25-OH-D3 into 1α,25(OH)2D3 by HPMs. Conclusions: 1α,25(OH)2D3 has a potent inhibitory effect on the production of TNF-α by LPS-activated HPMs. We hypothesize that 1α,25 (OH)2D3 may constitute a regulatory mechanism that, by controlling the intensity of the inflammatory response of the peritoneum, will moderate tissue damage during peritonitis.