Efeitos do ultrassom pulsado de baixa intensidade na proliferação e mineralização de pré-osteoblastos in vitro

Abstract

Low-intensity pulsed ultrasound (LIPUS) has been proposed as a high potential therapeutic technique for the treatment of metabolic bone diseases and fractures with delayed healing. However, recent investigations have shown controversial results, suggesting the need for more studies on the understanding of biological responses and the standardization of methods and parameters. For this reason, the present study aimed to evaluate the effect of ultrasound on the proliferation and mineralization of osteoblasts using in vitro bioassays. Pre-osteoblastic MC3T3-E1 cells were used and treated with therapeutic pulsed ultrasound, 20%, frequency of 1MHz and 0,2W/cm2 of intensity. In the study of cellular proliferation, intracellular calcium, TGF-β1, magnesium and osteopontin and osteocalcin mRNA levels, NF-κB1 and p38α were evaluated. In addition, nifedipine and rapamycin were used to investigate the proliferation pathways. Initially, the results showed an increase in proliferation of MC3T3-E1 and a decrease in calcium and magnesium content in supernatant with LIPUS exposure. In addition, LIPUS increased calcium deposition, activated NF-κB1 and mTOR complex via p38α and promoted a decrease in TGF-β1 synthesis, which is an inhibitor of cell growth. On cell mineralization assays, we evaluated mineral nodules deposition and expression of osteocalcin mRNA, collagen concentrations on culture supernatant, phosphate, calcium, TGF- β1 and ALP on cell lysates. The results showed that US stimulates the mineralization of preosteoblasts 192h after treatment by stimulating osteocalcin mRNA expression, calcium and phosphate uptake amd consequent formation of HA. Later, in different experimental conditions, the results showed that LIPUS had the ability to stimulate pre-osteoblastic mineralization with decreased concentration of collagen, calcium and phosphate in the cell supernatant 192 hours after treatment. It also changed the alkaline phosphatase concentration, as well as the osteocalcin gene expression.