Cyclic hydrostatic pressure and particles increase synthesis of 1,25-dihydroxyvitamin D3 by human macrophages in vitro

Human peripheral blood macrophages were isolated, cultured and exposed to pressure (similar to that found in the human joint) and/or particles. Synthesis of 1,25-dihydroxyvitamin D3 by macrophages was assayed using high pressure liquid chromatography and in situ hybridization. Synthesis of 1,25-dihydroxyvitamin D3 but not 24,25-dihydroxyvitamin D3 was increased in macrophages under pressure. In situ hybridization demonstrated an increase in 1α-hydroxylase expression in response to pressure or particles and simultaneous exposure to both stimuli generated higher expression of 1α-hydroxylase. In conclusion, this is the first study to demonstrate that mechanical loading, in the form of pressure, stimulates 1,25-dihydroxyvitamin D3 synthesis in human macrophages. These findings have implications for the in vivo situation, as they suggest that 1,25-dihydroxyvitamin D3 could be one factor stimulating osteoclastic bone resorption in pathologies, such as arthritis or implant loosening, where intra-articular or intra-osseous pressure is raised or where wear particles interact with macrophages.