Concentration-Dependent Effects of Boric Acid on Osteogenic Differentiation of Vascular Smooth Muscle Cells

Vascular calcification can be triggered by oxidative stress and inflammation. Although boron possesses antioxidant and anti-inflammatory properties, its effect on osteogenic differentiation of vascular smooth muscle cells (VSMCs) has yet to be examined. Therefore, we aimed to investigate the effect of boric acid (BA), the main form of boron in body fluids, on the osteogenic differentiation of VSMCs. Following the isolation of VSMCs, the effects of BA on cell proliferation were determined by MTT. The impact of various BA concentrations on the osteogenic differentiation of VSMCs was evaluated by Alizarin red S and alkaline phosphatase (ALP) stainings and the o-cresolphthalein complexone method. In addition, mRNA expressions of osteogenic-related (Runx2 and ALP) and antioxidant system-related genes (Nrf2 and Nqo1) were detected using qRT-PCR analysis. BA treatments did not alter the proliferation of VSMCs. Osteogenic differentiation of VSMCs treated with 100 and 500 μM BA (moderate and high plasma concentrations) was no different from untreated cells. However, increased osteogenic differentiation was observed with the lowest blood level (2 μM) and extremely high BA concentration (1000 μM). Consistent with these results, mRNA expression of Runx2 increased with 2 and 1000 μM BA treatments, while Nrf2 and Nqo1 expressions increased significantly with 100 and 500 μM BA. BA has different effects on VSMCs at various concentrations. The low blood level and too high BA concentration appear detrimental as they increase the osteogenic differentiation of VSMCs in vitro. We propose to investigate BA's effects and mechanism of action on vascular calcification in vivo.