Objective: This study aimed to investigate the effect of low-intensity pulsed laser (LIPL; 650 nm, 2 mW) irradiation on mRNA expression of receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG) in rat calvarial cells.
Materials and methods: Cultured cells were treated with LIPL irradiation of 1.14 J/cm(2) (group A) or 2.28 J/cm(2) (group B), and non-irradiated cells (group C) were used as controls. The changes in cell numbers, alkaline phosphatase (ALP) activity, RANKL, and OPG mRNA expression in the three study groups was determined using MTT, UV/VIS spectrophotometry, and RT-PCR analyses.
Results: The cell numbers in groups A and B increased significantly (7.52% and 8.80%, respectively), as did ALP activity (71.95% and 88.20%, respectively), compared with group C (p < 0.001). Meanwhile, RANKL and OPG mRNA expression in group A were 51.06% lower and 3.35 times higher, respectively, than those seen in the controls (p < 0.05), and the RANKL:OPG mRNA ratio in group A was 81.82% lower than that in group C (p < 0.005).
Conclusion: LIPL irradiation may directly promote osteoblast proliferation and differentiation, and indirectly inhibit osteoclast differentiation, by downregulating the RANKL:OPG mRNA ratio in osteoblasts. Thus LIPL irradiation may play an important role in bone remodeling, and should be valuable for the treatment of bone diseases such as osteoporosis.