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

Background We have previously reported that 1 alpha ,25-dihydroxyvitamin D-3 [1 alpha ,25(OH)(2)D-3] 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-alpha (TNF-alpha) initiates an inflammatory cascade during peritonitis, the aim of the present study was to investigate the effect of 1 alpha ,25(OH)(2)D-3 on the production of TNF-alpha by human peritoneal macrophages (HPMs). Methods. HPMs were obtained from patients on CAPD. Cells were incubated with various concentrations of 1 alpha ,25(OH)(2)D-3, 1 alpha ,24(S) dihydroxyvitamin D-2 [1 alpha ,24(S)(OH)(2)D-2] Or 25-hydroxyvitamin D-3 (25-OH-D-3) for 16 hours. This was followed by lipopolysaccharide (LPS; 1 mug/mL) incubation for 2.5 to 6 hours. TNF-alpha protein production was determined by enzyme-linked immunosorbent assay. TNF-alpha mRNA was assayed by the reverse transcriptase-polymerase chain reaction procedure, using internal synthetic mRNA standards for quantitative results. Results. Incubation of HPMs with 1 alpha ,25(OH)(2)D-3 prior to stimulation with LPS dose dependently inhibited the expression of TNF-alpha on both mRNA and protein levels. Similar results were obtained with the less calcemic vitamin D-2 analogue 1 alpha ,24(S)(OH)(2)D-2. Incubation of HPMs with 25-OH-D-3 also revealed a down-regulation of TNF-alpha. expression. Since this down-regulatory effect was blocked by ketoconazole, it is likely that this effect was caused by the conversion of 25-OH-D-3 into 1 alpha ,25(OH)(2)D-3 by HPMs. Conclusions. 1 alpha ,25(OH)(2)D-3 has a potent inhibitory effect on the production of TNF-alpha by LPS-activated HPMs. We hypothesize that 1 alpha ,25(OH)(2)D-3 may constitute a regulatory mechanism that, by controlling the intensity of the inflammatory response of the peritoneum, will moderate tissue damage during peritonitis.