The anti-inflammatory activity of 1,25-dihydroxyvitamin D₃ in macrophages

In a previous study we demonstrated a down-regulatory effect of vitamin D active metabolite (1,25(OH)₂D₃) and its vitamin D₂ analog (1,24(OH)₂D₂) on TNFα expression in macrophages. We also found an inhibitory effect in the physiological concentration (10^-10 M) of 1,25(OH)₂D₃ which was dose-dependent. This down-regulation, caused by the decrease in NFκB activity by 1,25(OH)₂D₃ and 1,24(OH)₂D₂, was demonstrated in P388D1 cells transfected with NFκB reporter gene (p NFκB-Luc) and by EMSA. In our present study we investigated the processes leading to reduced NFκB activity on P388D1 cells. A decrease in nuclei NFκB-p65 and an increase in cytosolic NFκB-p65, were measured, while no changes in total NFκB-p65 mRNA and protein levels were observed. Simultaneously, a significant increase in both mRNA and protein levels of the NFκB-cytosolic inhibitor, IκBα, were determined. The half-life of IκBα-mRNA increased, with a parallel decrease in the phosphorylation of its protein, as the first step of ubiquitinization and degradation. The present results demonstrate that 1,25(OH)₂D₃ and 1,24(OH)₂D₂ inhibit TNFα expression in macrophages, by increasing IκBα and decreasing NFκB activity. Since NFκB is a major transcription factor for TNFα and other inflammatory mediators, these findings suggest that 1,25(OH)₂D₃ and 1,24(OH)₂D₂ may be used therapeutically as anti-inflammatory agents.