Disordered mineral metabolism and vascular calcification in nondialyzed chronic kidney disease patients

It is well established that abnormalities in mineral metabolism are apparent early in the course of chronic kidney disease (CKD) and result in clinically relevant consequences such as renal osteodystrophy. Furthermore, there is emerging evidence linking some of these abnormalities (hyperphosphatemia) to the high cardiovascular morbidity and mortality experienced by nondialyzed patients with CKD. Most studies have evaluated vascular calcification in patients with stage 5 CKD. Reports published over the last 2 years show that the process begins rather early in CKD and is particularly severe among elderly and type 2 diabetic patients. Furthermore, "calcium begets calcium", such that the calcification burden in early CKD is an important predictor of subsequent progression, including the rapid increase seen in stage 5 CKD. There is an increasing body of evidence that supports the thesis that elevated serum levels of phosphorus and calcium and deficiency of inhibitors of calcification (for example, fetuin-A) are important in the progression of vascular calcification in patients with end-stage renal disease. However, the concentrations of calcium and phosphorus shown to induce mineralization in cell culture studies are not observed in most patients until late in stage 4 or stage 5 CKD. Cross-sectional and longitudinal studies have also been unable to show a correlation between serum levels of markers of disordered mineral metabolism and severity of vascular calcification. Future studies should evaluate the pathogenetic role of phosphorus retention, which occurs early in the course of CKD, in the induction and/or progression of vascular calcification. Finally, there is a need to identify alternative pathogenetic mechanisms that may be important causes of the high calcification burden observed early in CKD.