Vitamin D Auto-Paracrine System Is Involved in Modulation of Glucocorticoid-Induced Changes in AngiogenesisBone Remodeling Coupling

Abstract EN

Osteoporosis is a devastating side effect of chronic glucocorticoid (GC) treatment.

Despite the crucial role of vitamin D (VD) in bone homeostasis, the precise molecular mechanisms of its action on GC-induced disturbances of bone remodeling remain undefined.

The study was performed to elucidate the relation of VD status to GC-induced changes of the angiogenesis/osteogenesis/bone resorption coupling in bone tissue.

Female Wistar rats received prednisolone (5 mg/kg of b.w.) with or without VD3 (1000 IU/kg of b.w., for 30 days).

Biomechanical parameters of rat femurs were assessed by the three-point bending test.

The levels of calcium, inorganic phosphate, activity of total alkaline phosphatase (ALP), and its isoenzymes were determined spectrophotometrically.

Vascular endothelial growth factor-A (VEGF-A) and caspase-3 protein levels were detected by western blotting.

Vdr and Cyp27b1 mRNAs were measured by qRT-PCR.

Receptor activator of nuclear factor κB (RANK) expression in bone sections was visualized immunohistochemically.

Serum 25(OH)D was assayed by ELISA.

GC administration led to a decrease in maximal load (by 1.2-fold) and stiffness and toughness (by 1.3-fold), which was accompanied by a 3-fold reduction of 25(OH)D level, an elevation of the ALP bone isoenzyme activity in serum, hypocalcaemia, and hypophosphatemia.

Along with prednisolone-induced VD deficiency, an impaired synthesis of Vdr (−30%) and Cyp27b1 (+71%) mRNA was observed, reflecting deregulation of bone tissue VD-auto-/paracrine system.

GC caused an increase in caspase-3 content, suppressed the synthesis of the osteoclastic marker RANK, and altered angiogenesis/osteogenesis coupling by significantly reducing the level of VEGF-A.VD3 treatment restored serum 25(OH)D content and the expression of key components of the VD-auto-/paracrine system.

VD3 supplementation diminished cell apoptosis and strongly improved angiogenesis/osteogenesis coupling as well as mineral metabolism and biomechanical parameters of femurs in GC-administered rats.

Thus, VD3 can have a beneficial effect on the correction of GC-induced pathological changes in bone remodeling.