Phosphonoformic acid reduces hyperphosphatemia-induced vascular calcification via Pit-1.

OBJECTIVE: This study aimed to examine the mechanism of hyperphosphatemia-induced vascular calcification (HPVC). METHODS: Primary human aortic smooth muscle cells and rat aortic rings were cultured in Dulbecco's modified Eagle's medium supplemented with 0.9 mM or 2.5 mM phosphorus concentrations. Type III sodium-dependent phosphate cotransporter-1 (Pit-1) small interfering RNA and phosphonoformic acid (PFA), a Pit-1 inhibitor, were used to investigate the effects and mechanisms of Pit-1 on HPVC. Calcium content shown by Alizarin red staining, expression levels of Pit-1, and characteristic molecules for phenotypic transition of vascular smooth muscle cells were examined. RESULTS: Hyperphosphatemia induced the upregulation of Pit-1 expression, facilitated phenotypic transition of vascular smooth muscle cells, and led to HPVC in cellular and organ models. Treatment with Pit-1 small interfering RNA or PFA significantly inhibited Pit-1 expression, suppressed phenotypic transition, and attenuated HPVC. CONCLUSIONS: Our findings suggest that Pit-1 plays a pivotal role in the development of HPVC. The use of PFA as a Pit-1 inhibitor has the potential for therapeutic intervention in patients with HPVC. However, further rigorous clinical investigations are required to ensure the safety and efficacy of PFA before it can be considered for widespread implementation in clinical practice.

Apelin: A novel inhibitor of vascular calcification in chronic kidney disease.

BACKGROUND: Vascular calcification (VC) is closely related to cardiovascular events in chronic kidney disease (CKD). Apelin has emerged as a potent regulator of cardiovascular function, but its role in VC during CKD remains unknown. We determined whether apelin plays a role in phosphate-induced mineralization of human aortic smooth muscle cells (HASMCs) and in adenine-induced CKD rats with aortic calcification. METHODS AND RESULTS: In vitro, apelin-13 was found to inhibit calcium deposition in HASMCs (Pi(+) Apelin(+) group vs Pi(+) Apelin(-) group: 50.1 ± 6.21 ug/mg vs 146.67 ± 10.02 ug/mg protein, p = 0.012) and to suppress the induction of the osteoblastic transformation genes BMP-2, osteoprotegerin (OPG) and Cbfa1. This effect was mediated by interference of the sodium-dependent phosphate cotransporter (Pit-1) expression and phosphate uptake. In vivo, decreased plasma apelin levels (adenine(+) apelin(-) vs vehicle: 0.37 ± 0.09 ng/ml vs 0.68 ± 0.16 ng/ml, p = 0.003) and downregulation of APJ in the aorta were found in adenine-induced CKD rats with hyperphosphatemia (adenine(+) apelin(-) vs vehicle: 6.91 ± 0.23 mmoL/L vs 2.3 ± 0.07 mmoL/L, p = 0.001) and aortic calcification. Exogenous supplementation of apelin-13 normalized the level of the apelin/APJ system and significantly ameliorated aortic calcification, as well as the suppression of Runx2, OPG and Pit-1 expression. CONCLUSIONS: Apelin ameliorates VC by suppressing osteoblastic differentiation of VSMCs through downregulation of Pit-1. These results suggest apelin may have potential therapeutic value for treatment of VC in CKD.

Dexamethasone and cyclic AMP regulate sodium phosphate cotransporter (NaPi-IIb and Pit-1) mRNA and phosphate uptake in rat alveolar type II epithelial cells.

Alveolar epithelial type II (AT II) cells need phosphate (Pi) for surfactant synthesis. The Na-dependent (Na(d)) Pi transporters NaPi-IIb and Pit-1 are expressed in lung, but their expression, regulation, and function in AT II cells remain unclear. We studied NaPi-IIb and Pit-1 mRNA expression in cultured AT II cells isolated from adult rat lung, their regulation by agents known to enhance surfactant production, dexamethasone (dex) and dibutyryl cyclic AMP (cAMP), and the effects of dex and cAMP on Na(d) Pi uptake by this cell type. By Northern analysis, cultured AT II cells expressed both NaPi-IIb (4.8 and 4.0 kb) and Pit-1 (4.3 kb) mRNA. Treatment with 100 nmol/l dex for 24 h decreased the expression of both mRNAs (to 0.48 +/- 0.06 and 0.77 +/- 0.05, respectively, as compared to control), while 0.1 mmol/l cAMP stimulated NaPi-IIb (1.94 +/- 0.22) but not Pit-1 mRNA (0.90 +/- 0.05, compared to vehicle-treated cells). NaPi-IIb and Pit-1 proteins could not be identified by western analysis of plasma membrane preparations of cultured AT II cells. AT II cells take up Pi in a Na(d) manner. Uptake was slightly (to 0.78-fold of the control) decreased by 100 nmol/l dex but not affected by 0.1 mmol/l cAMP treatment. Although NaPi-IIb mRNA expression was maintained to some extent by AT II cells kept in primary culture, Pi uptake was more closely related to Pit-1 mRNA expression.