Serum parathyroid hormone and phosphate influence the levels of circulating CD34+ cells in uremia.

BACKGROUND

Parathyroid hormone (PTH) is an active stimulator of bone marrow osteoblasts; it is involved in the niche organization, ie the bone marrow microenvironment which controls the turnover and the fate of endothelial progenitor cells (EPCs). PTH stimulates EPC production; this action can be measured by counting the number of circulating CD34+ cells.

METHODS

This observational cross-sectional study aimed to verify this effect in 3 groups of hemodialysis patients with different serum PTH levels. The first group consisted of 11 patients affected by secondary hyperparathyroidism (SHPTH group, serum PTH levels >500 pg/ml); the second group consisted of 10 patients with serum PTH levels between 150 and 500 pg/ml (TargetPTH group); the third group consisted of 10 patients with serum PTH levels below the treatment target after parathyroidectomy (PTx group, serum PTH levels <150 pg/ml). Serum PTH, calcium (Ca), phosphorus (P), alkaline phosphatases (ALP), urea nitrogen, albumin and hemoglobin were measured. Flow cytofluorimetry with CD45+ sequential gating was effected; therefore, CD34+ cells could be analyzed.

RESULTS

The SHPTH group showed significantly higher values of serum PTH, P and ALP (respectively, p<0.0001, p<0.033 and p<0.0001), and significantly lower values of circulating CD34+ cells (both in absolute and percent terms) in the SHPTH and in the TargetPTH groups (for both, p<0.0001). Two models of multiple regression analysis built with circulating CD34+ cells (expressed as percentage in the first one and as absolute values in the second one) as dependent variables showed that only serum PTH and P values were inversely associated with both.

CONCLUSIONS

Our data suggest that an inverse relationship exists in uremic patients among circulating CD34+ cells and serum P and PTH levels. The count of circulating CD34+ cells might represent a novel biomarker for the assessment of the cardiovascular risk for dialysis patients.