Objective: To investigate the effect of low-level laser irradiation (LLLI) on bone mineral density (BMD), bone structures, bone biomechanical properties and bone metabolism in senile osteoporosis, and to explore a relatively more secure and effective way to prevent and treat osteoporosis.
Materials and methods: Sprague-Dawley (SD) male rats at different age stages (4 months old, 12 months old and 20 months old) were selected and randomly divided into six groups. The rats in the treatment group were treated with LLLI for 12 weeks, and then the microstructure of bones was analyzed by micro-computed tomography (micro-CT) scanning. The biomechanical indexes of the femur were detected by the three-point bending test. Levels of the blood calcium (Ca)2+, blood phosphorus (P)3+, urine Ca, urine P and urine creatinine (CREA) were detected using an automatic biochemical analyzer. The contents of serum osteocalcin (OCN) and bone alkaline phosphatase (BAP) were measured by enzyme-linked immunosorbent assay (ELISA). The bone formation rate (BFR) was analyzed by double fluorescent labeling with calcein and tetracycline. Hematoxylin and eosin (HE) staining and toluidine blue staining were used to analyze the number of bone marrow osteoblasts and adipocytes.
Results: Micro-CT results showed that compared with those in the young group, the bone mineral density (BMD) in the old group was significantly decreased, and the trabecular microstructure was seriously damaged. LLLI could significantly enhance the BMD and improve the damage to the trabecular microstructure; the three-point bending test revealed that LLLI could significantly improve the biomechanical properties and enhance the mechanical strength of the femur in the old group; the biochemical analysis showed that LLLI could significantly reduce Ca and P losses and elevate the levels of serum BAP and OCN; the bone histomorphology analysis results indicated that LLLI could increase BFR and mineral apposition rate (MAR), increase the number of osteoblasts and decrease the number of adipocytes in the bone marrow in the old group.
Conclusions: LLLI can effectively improve osteoporosis, increase BMD, improve bone structure and improve bone biomechanical properties in old rats; at the same time, it increases the levels of serum BAP and OCN and the number of osteoblasts in the bone marrow, suggesting that the osteogenesis function of osteoblasts is enhanced.