Role of calcium-phosphorous disorders in the progression of renal failure

Among factors related to disturbed calcium-phosphate metabolism in chronic kidney disease, the following must be mainly considered as potential culprits in the progression of renal dysfunction: hyperphosphatemia, hyperparathyroidism, lack of active vitamin D, and possibly excess of the phosphaturic hormone FGF 23. Early experimental work suggested a parathyroid hormone (PTH)-independent beneficial role of phosphate restriction on progression in rats (animals with physiologic hyperphosphatemia), so that the generalization of the data is uncertain. Recent observational studies also found a correlation between S-phosphate and progression, but it remains uncertain whether the relationship is causal. There is very little direct experimental or clinical evidence for a role of PTH in accelerating progression, although the PTH1 receptor is expressed in podocytes and PTH affects podocyte function (i.e., Kf). It is undoubtedly a candidate that requires more sophisticated investigation. Recently, it has been shown that progression is significantly attenuated by calcimimetics (and equally by parathyroidectomy), but it is currently impossible to exclude a confounding effect of lower blood pressure values. The most solid evidence for an impact on progression exists for active vitamin D. In the past, it was widely assumed that vitamin D was nephrotoxic. In retrospect, nephrotoxicity was the result of hypercalcemia. Recent evidence is overwhelming that 1,25(OH)(2)D-3 and its analogues attenuate progression in noninflammatory and inflammatory models of chronic kidney disease. The main target cells identified so far are podocytes and mesangial cells. It is currently unknown whether the novel phosphaturic hormones have an impact on progression.