Objective: To examine the in vitro effects of low-level laser irradiation (LLLI) on proliferation and differentiation of human adipose-derived stromal cells (hASCs).
Methods: Cultured cells were exposed to different doses of LLLI with a semiconductor diode laser (980 nm; 100 mW-12 W power output). The effects of laser on proliferation were assessed daily up to seven days of culture in cells irradiated for four consecutive days with laser doses of 2, 4, 6 or 8 J/cm2, the cells without irradiation were used as controls. Half of the cells were changed to osteogenic medium (OM) when they had grown to 70% confluence. The hASCs both with and without osteogenic supplements were divided into three groups, and each group was irradiated at doses of 0, 2 and 4 J/cm2. In order to examine the in vitro effects of LLLI on osteogenic differentiation of hASCs, the alkaline phosphatase activity was assessed on day 7, and alizarin red staining (AR-S) and quantitative detection were assessed on days 14 and 21. The expression of osteoblast master genes (ALP and Runx2) were tested on days 7 and 14.
Results: The proliferation medium(PM)+LLLI4 J/cm2 group had the highest multiplication rate. In the groups with osteogenic supplements, LLLI increased alkaline phosphatase activity and mineralized nodule formation, and stimulated the expression of ALP and Runx2. Furthermore, the effect became more obvious at high dose.
Conclusion: Our data demonstrated that hASCs proliferation and osteogenic differentiation were enhanced by LLLI. With the increase of laser dose, the effect of LLLI would be enhanced at first, and then be decreased after reaching a peak.