The Vitamin D analogue TX 527 blocks NF-κB activation in peripheral blood mononuclear cells of patients with Crohn's disease

Crohn's disease (CD) is an inflammatory disease characterized by the activation of the immune system in the gut. Since tumor necrosis factor (TNF-α) plays an important role in the initiation and perpetuation of intestinal inflammation in CD, we investigated whether TX 527 [19-nor-14,20-bisepi-23-yne-1,25(OH)2D3], a Vitamin D analogue, could affect peripheral blood mononuclear cells (PBMC) proliferation and exert an immunosuppressive effect on TNF-α production in CD patients, and whether this immunosuppressive action could be mediated by NF-κB down-regulation. TX 527 significantly decreased cell proliferation and TNF-α levels. On activation, NF-κB, rapidly released from its cytoplasmatic inhibitor (IKB-α), transmigrates into the nucleus and binds to DNA response elements in gene promoter regions. The activation of NF-κB, stimulated by TNF-α, and its nuclear translocation together with the degradation of IKB-α were blocked by TX 527. At the same time, NF-κB protein levels present in cytoplasmic extracts decreased in the presence of TNF-α and increased when PBMC were incubated with TX 527. The results of our studies indicate that TX 527 inhibits TNF-α mediated effects on PBMC and the activation of NF-κB and that its action is mediated by Vitamin D receptor (VDR), which is activated when the cells are stimulated with TX 527.