Cell biological and physicochemical aspects of arterial calcification

Phosphate: a stealthier killer than previously thought?

The kidneys excrete excess dietary phosphate, and patients with chronic kidney disease may suffer from phosphate overload and hyperphosphatemia. In chronic kidney disease, hyperphosphatemia has emerged as a risk factor for vascular calcification, cardiovascular mortality, left ventricular hypertrophy, and progression of chronic kidney disease. Serum phosphate at the upper limits of normal has also been associated with adverse outcomes in patients with relatively preserved kidney function. Of note, hyperphosphatemia is not a sensitive indicator of phosphate overload. In this regard, increased circulating fibroblast growth factor-23, a phosphatonin that is released in response to phosphate overload, is independently associated with adverse outcomes in patients with and without chronic kidney disease. Direct effects of extracellular phosphate on vascular calcification or cardiovascular cell biology; adverse consequences of adaptive mechanisms activated to limit phosphate overload, such as left ventricular hypertrophy induced by fibroblast growth factor-23; or epidemiological associations of additional cardiovascular risk factors with chronic kidney disease may underlie these observations. We now review the pathophysiology of phosphate, its relationship with cardiovascular outcomes, the potential consequences for patient care related to dietary phosphate and phosphate binders, and the clinical relevance for patients without overt chronic kidney disease.

A red herring in vascular calcification: 'nanobacteria' are protein-mineral complexes involved in biomineralization

Biomineralization at pathological extraosseous sites (i.e. vasculature and soft tissues) is associated with increased morbidity and mortality. So-called 'nanobacteria' have been described as pathogenic agents causing many diseases including calcification. Initially, their appearance, and having a content consisting of nucleic acids plus proteins and properties of growing structures, suggested that they were living organisms. However, it could be demonstrated that the so-called nanobacteria were in fact mineralizing nanoparticles that contain mineral and non-mineral compounds, that these particles bind to charged molecules and that supersaturation enables in vitro growth of these nanoparticles. Recent data indicate that nanoparticles consisting of protein-mineral complexes can be seen both in vitro and in vivo as precursors of matrix calcification.