Vascular calcification is a predominant symptom in chronic kidney disease (CKD) patients undergoing dialysis, leading to various cardiovascular complications. In the current study, we investigated a novel previously unknown systemic regulation of vascular calcification processes by peptides originating from the adrenal glands.

Homogenized bovine adrenal glands were separated using chromatographic fractionation. The fractions were assessed for effects on vascular calcification processes in vitro, ex vivo and in vivo in vitamin D3 plus nicotine elastocalcinosis rat model. Mass spectrometric analysis and comparison with pertinent databases led to the identification of potential mediators, which were further quantified in serum of end-stage renal disease patients undergoing dialysis and matched controls.

We identified an adrenal peptide controlling mesenchymal cell differentiation that regulates osteoblastic differentiation in the context of vascular calcification. It inhibits the transdifferentiation of aortic smooth muscle cells into osteoblast like cells, which drive the progression of vascular calcification. The peptide reduces the calcium content in cells and thoracic aortic rings under calcifying conditions, as well as in aortas from elastocalcinosis animals. This peptide is released from the parent peptide, chromogranin A, by enzymatic cleavage by calpain 1 and kallikrein and named Calcification Blocking Factor (CBF) owing to its protective effects against vascular calcification. CBF hinders the transdifferentiation of smooth musle cells into osteoblast-like cells within the vascular wall via the sodium-dependent phosphate transporter PIT-1. In addition it inhibits NF-κB activation and the subsequent BMP2/p-SMAD pathway, which is known to trigger vascular calcification. Arterial stiffness was significantly decreased in elastocalcinosis animals treated with CBF as measured by arterial pulse pressure measurement. Consistent with our preclinical results, there was a significant reduction in CBF concentration in patients with CKD who are predisposed to an increase in vascular calcification. Smaller fragments of the 19 amino acid (aa) peptide were analyzed to identify the active site of CBF, which revealed a smaller 6-8 aa sequence as the active site.

In conclusion, we identified a novel 19 aa inhibitor of vascular calcification, CBF, which is derived from the adrenal glands. Moreover, patients with CKD undergoing dialysis display a significantly lower concentration of CBF, emphasizing its prominent role in decreasing the risk of vascular calcification and consequently cardiovascular complicatiopns in these patients. These findings point towards a novel function of adrenal glands in regulation of vascular calcification.