Site-specific inverse associations between FGF23 levels and marrow adiposity content at the proximal femur in post-menopausal women.

CONTEXT: Experimental studies have suggested that the autocrine/paracrine effects of bone-derived Fibroblast Growth Factor 23 (FGF23) inhibit adipogenesis and promote osteoblastic differentiation of bone marrow stroma cells.

OBJECTIVE

To examine whether there is relationship between circulating levels of FGF23 and bone marrow adiposity assessed by MRI.

DESIGN

This cross-sectional study included 199 postmenopausal women without apparent disorders in phosphate homeostasis.

SETTING

University Hospital of Lille, France.

MAIN OUTCOME MEASURE(S): C-terminal FGF23 (cFGF23, relative units (RU)/ml) and intact FGF23 (iFGF23, pg/ml). The Proton Density Fat Fraction (PDFF) of the lumbar spine and the proximal femur was assessed using MRI with chemical shift-based water-fat separation (WFI) and DXA of the hip and spine. Our main goal was to explore the relationships between PDFF, cFGF23, and iFGF23 levels in women who are postmenopausal. The relationships between cFG23, iFGF23, and body composition metrics were subsequently analyzed.

RESULTS

A significant positive correlation was observed between cFGF23 and iFGF23 (R = 0.534, p < 0.0001). Significant inverse associations were found between cFGF23, iFGF23, and femoral neck PDFF (reciprocally, coefficient β (95%CI), -1.35 (-2.49 to -0.21), p = 0.020 and - 1.66 (-3.00 to -0.32), p = 0.016) after adjustment for age, recent fragility fracture, BMI, eGFR, and BMD. Conversely, there were no notable associations identified between cFGF23, iFGF23, and lumbar spine PDFF, regardless of whether adjustment models were applied. No significant associations were found between cFGF23, iFGF23, and body composition parameters (total body fat and visceral adipose tissue).

CONCLUSIONS

An inverse association was found between cFGF23, iFGF23, and proximal femur PDFF (particularly femoral neck PDFF), but not with lumbar spine PDFF. Moreover, cFGF23 and iFGF23 levels were not associated with other adipose deposits.