Pitting Phosphate Transport Inhibitors Against Vascular Calcification

Biomimetic transformation of polyphosphate microparticles during restoration of damaged teeth

OBJECTIVE

In the present study, we investigated the fusion process between amorphous microparticles of the calcium salt of the physiological polymer comprising orthophosphate units, of inorganic polyphosphate (polyP), and enamel.

METHODS

This polymer was incorporated as an ingredient into toothpaste and the fusion process was studied by electron microscopy and by synchrotron-based X-ray tomography microscopy (SRXTM) techniques.

RESULTS

The data showed that toothpaste, supplemented with the amorphous Ca-polyP microparticles (aCa-polyP-MP), not only reseals tooth defects on enamel, like carious lesions, and dentin, including exposed dentinal tubules, but also has the potential to induce re-mineralization in the enamel and dentin regions. The formation of a regeneration mineralic zone on the tooth surface induced by aCa-polyP-MP was enhanced upon exposure to artificial saliva, as demonstrated by SRXTM. Energy dispersive X-ray analysis revealed an increase in the calcium/phosphorus atomic ratio of the enamel deposits to values characteristic for the particles during the treatment with polyP applied in the toothpaste, indicating a fusion of the particles with the tooth mineral.

SIGNIFICANCE

Our results suggest that toothpaste enriched with aCa-polyP-MP is a promising biomimetic material for accelerating enamel and dentin restoration.

Mechanistic insights into vascular calcification in CKD

Cardiovascular disease begins early in the course of renal decline and is a life-limiting problem in patients with CKD. The increased burden of cardiovascular disease is due, at least in part, to calcification of the vessel wall. The uremic milieu provides a perfect storm of risk factors for accelerated calcification, but elevated calcium and phosphate levels remain key to the initiation and progression of vascular smooth muscle cell calcification in CKD. Vascular calcification is a highly regulated process that involves a complex interplay between promoters and inhibitors of calcification and has many similarities to bone ossification. Here, we discuss current understanding of the process of vascular calcification, focusing specifically on the discrete and synergistic effects of calcium and phosphate in mediating vascular smooth muscle cell apoptosis, osteochondrocytic differentiation, vesicle release, calcification inhibitor expression, senescence, and death. Using our model of intact human vessels, factors initiating vascular calcification in vivo and the role of calcium and phosphate in driving accelerated calcification ex vivo are described. This work allows us to link clinical and basic research into a working theoretical model to explain the pathway of development of vascular calcification in CKD.

The presence of open dentinal tubules affects the biological properties of dental pulp cells ex vivo

To investigate the effects of open dentinal tubules on the morphological and functional characteristics of dental pulp cells. Morphological changes in human dental pulp cells that were seeded onto dentin discs with open dentinal tubules were investigated on days 1, 2, 4, and 10 of culture using scanning electron microscopy and fluorescence microscopy. Samples collected on days 1, 3, 6, 8, and 10 of culture were evaluated for cell proliferation rate and alkaline phosphatase activity. Cultured human dental pulp cells developed a columnar or polygonal morphology and monopolar cytoplasmic processes that extended into the dentinal tubules. The cells formed a multilayer and secreted an extracellular matrix onto the cell surface. Scanning electron microscopy and fluorescence microscopy revealed polarized organization of odontoblasts. Cells seeded onto dentin discs proliferated minimally but showed high levels of ALP activity. Dental pulp cells seeded onto treated dentin discs develop an odontoblastlike phenotype, which may be a potential alternative for use in experimental research on dentinogenesis.

A calcimimetic (R-568), but not calcitriol, prevents vascular remodeling in uremia

Renal insufficiency increases cardiovascular risk, accelerates atherogenesis, and causes vascular wall remodeling. Here we evaluated the effect of the calcimimetic R-568 and non-hypercalcemic doses of calcitriol on vascular structure. Subtotal nephrectomy was produced in Sprague-Dawley rats followed by treatment with R-568, calcitriol, or vehicle for 12 weeks. The aortic wall was significantly thicker in vehicle-treated uremic rats than in those with a sham-operation but R-568-treated uremic rats had a lower value. In contrast, calcitriol increased wall thickness in both the sham-operated and uremic groups. The calcification score, measured by von Kossa staining, and the number of proliferating cells in the intima and media were significantly higher in the calcitriol-treated uremic group. The expression of the calcium sensing receptor was higher in the intima of sham-operated and uremic rats treated with R-568 compared to animals treated with vehicle or calcitriol, while the expression of the vitamin D receptor was upregulated by both calcitriol and R-568. Our study shows that in uremic rats, calcitriol increased while R-568 attenuated media calcification and proliferation of vascular smooth muscle and endothelial cells.