Sphingosine 1-phosphate (S1P) has been discovered to be a critical regulator of bone metabolism. Very recently, we found that higher circulating S1P levels were associated with higher rate of prevalent osteoporotic fracture in human.

This was a cross-sectional study of 16 patients who underwent hip replacement surgeries. Bone marrow fluids were obtained during hip surgeries, and the S1P levels were measured using a competitive enzyme-linked immunosorbent assay (ELISA) assay. Bone mineral densities (BMDs) at various skeletal sites were obtained using dual energy X-ray absorptiometry.

Among 16 patients, 4 patients were undergone operations due to hip fractures, and the others were done by any other causes. Bone marrow S1P levels were significantly lower in patients with hip fractures than in those without, before and after adjusting for confounding factors ( P =0.047 and 0.025, respectively). We failed to demonstrate significant associations between bone marrow S1P levels and any BMD values (γ=0.026-0.482, P =0.171-0.944).

In conjunction with our previous findings, these suggest that the effects of gradient between peripheral blood and bone marrow, but not S1P itself, may be the most critical on bone metabolism.