beta-glycerophosphate, a phosphate donor, and uremic sera induce osteopontin (OPN) expression in bovine vascular smooth muscle cells (VSMCs). However, the correlations of serum phosphorus level with OPN expression, and blood urea nitrogen (BUN) level with OPN expression in humans have not previously been reported. The purpose of the current study is to compare the expression of OPN in VSMCs with clinical data in patients with end-stage renal disease (ESRD). The radial arteries of 33 patients (21 male and 12 female patients) were examined to determine the expression of OPN and collagen type I (Col I) by immunohistochemistry. The correlation of the expression of bone matrix proteins with clinical data was analyzed. Between the low-serum phosphorus (<6 mg/dL) group and high-serum phosphorus (> or =6 mg/dL) group, significant differences were detected in the expression of OPN (P = 0.0049) and the levels of BUN (P = 0.0005), serum phosphorus (P < 0.0001) and calcium x phosphorus products (P < 0.0001). Moreover, between the low-BUN (<70 mg/dL, N = 19) group and high-BUN (> or =70 mg/dL) group, significant differences were detected in the expression of OPN (P = 0.0039) and the levels of BUN (P = 0.0002), serum phosphorus (P = 0.0002) and calcium x phosphorus products (P = 0.0003). We have shown that hyperphosphatemia or azotemia is associated with the expression of OPN in VSMCs in patients with ESRD.