Influence of lactic acid on the proliferation, metabolism, and differentiation of rabbit mesenchymal stem cells

Lactic acid, originated from degradation of biomaterials, cell cultures, and so on, would be a toxic compound in acute states. The present study was undertaken to ascertain whether the proliferation, metabolism, and differentiation of rabbit mesenchymal stem cells (rMSCs) were affected by additional lactic acid. Furthermore, this study aimed to determine whether this influence was due to decreasing pH, increasing osmotic pressure, or chemical action of lactate ion. It was shown that the proliferation and metabolism of MSCs were inhibited by decreasing pH or increasing lactate. However, when osmolarity was adjusted to the same level as that of sodium lactate using sodium chloride, cell proliferation was little affected by osmotic pressure. We also concluded that colony-forming potential and osteogenic differentiation capacity were significantly depressed by decreasing pH or increasing lactate. As was shown, this inhibition of lactate was not only due to osmotic pressure, but also mainly due to chemical action of lactate ion. However, we observed that acidifying extracellular medium and lactate ion promoted the retention of adipogenic differentiation potential of MSCs during in vitro expansion, which suggested that growth arrest and the decrease of osteogenic differentiation potential did not affect the adipogenic conversion of MSCs.