ObjectiveTo investigate whether signal molecule mitogen-activated protein kinases (MAPKs) involves in the process of the mineralization and maturation of rat calvarial osteoblasts promoted by 50 Hz, 0.6 mT pulsed electromagnetic fields. MethodsRat calvarial osteoblasts were obtained by enzyme digestion from the skull of 6 neonatal Wistar rats of SPF level. The primary osteoblasts were treated in 50 Hz and 0.6 mT pulsed electromagnetic fields for 0, 5, 10, 20, 40, 60, and 120 minutes; the protein expression of phosphorylated MAPKs was detected by Western blot. The osteoblasts were randomly divided into group A (control group), group B (low frequency pulse electromagnetic fields treatment group), group C (SB202190 group), and group D (SB202190+low frequency pulse electromagnetic fields treatment group); the alkaline phosphatase (ALP) activities were tested after corresponding treatment for 1, 4, and 7 days. The corresponding treated more than 90% confluenced osteoblasts were cultured under condition of osteogenic induction, then ALP staining and alizarin red staining were carried out at 9 and 12 days respectively. ResultsThe results of Western blot showed that there was no significant changes in the protein expressions of phosphorylated level of extracellular signal-related kinases 1/2 and c-Jun amino N-terminal kinases 1/2 in 50 Hz, 0.6 mT pulsed electromagnetic fields P>0.05), but the phosphorylated level of p38 began to increase at 5 minutes, peaked at 40 minutes, then gradually decreased, and it was significantly higher at 5-120 minutes than at 0 minute (P<0.05). After the activities of p-p38 was inhibited by inhibitor SB202190, the ALP activities, positive colonies and area of ALP and calcified nodules of group B were significantly higher than groups A, C, and D (P<0.05). Conclusionp38 is one of the signal molecules involved in the process of the mineralization and maturation of rat calvarial osteoblasts promoted by 50 Hz, 0.6 mT pulsed electromagnetic fields.
Studying effects of 50 Hz sinusoidal electromagnetic fields (SEMFs) with different intensities on peak bone mass (PBM) of rats may provide a theoretical basis for application of electromagnetic clinical field. 30 female SD rats, 6 weeks of age, were randomly divided into three groups: the control group, 0.1 mT electromagnetic field group (EMFs) and 0.6 mT EMFs. The EMFs groups were treated for 3 h/day. After 8 weeks, we examined their bone mineral densities (BMD), measured their bone biomechanical properties, and made serum levels of osteocalcin (OC), tartrate-resistant acid phosphatase 5b (TRACP 5b), and histomorphometry. It was found that the BMD (P < 0.01), maximum mechanical load (P < 0.01) in the 0.1 mT group were significantly higher than those in the control group, and Yield strength (P < 0.05), the analyses of serum bone turnover markers and histomorphometric parameters were better than those in the control group (P < 0.05). However, the 0.6 mT group did not have significantly difference comparing with that in the control group. This study proved that 50 Hz 0.1 mT SEMFs can increased BMD, bone strength, and bone tissue microstructure. Therefore, 50 Hz 0.1 mT SEMFs can improve peak bone mass of rats.
The present research is to investigate the time effect of sinusoidal electromagnetic fields (SEMFs) at different exposure time on the biomechanical properties in rats, and to find a best time for improving biomechanical properties. Forty female SD rats were randomly divided into five groups, i.e. control group, 45 min SEMFs group, 90 min SEMFs group, 180 min SEMFs group, and 270 min SEMFs group. In addition to the control group, other groups were exposed to 50 Hz and 0.1 mT magnetic field every day for the corresponding time periods. After eight weeks, bone mineral density (BMD), bone biomechanics, bone tissue morphology, micro-CT and pathological examination were performed. The results showed that there was no abnormal pathological finding in the experimental groups. In the 90 min SEMFs group, BMD, femur maximum load, elastic modulus, yield strength, trabecular number (Tb.N), trabecular thickness (Tb.Th) and trabecular area (Tb.Ar) percentage were all significantly higher than those in the control group (P＜0.01), and trabecular separation (Tb.Sp) was significantly lower than that of the control group (P＜0.01). However, for other experimental groups, some indices showed statistical significance compared to the control group (P＜0.05), but some did not (P>0.05). This study showed that under 50 Hz and 0.1 mT SEMFs, 90 min is the best time that can effectively increase bone mineral density, improve the bone tissue microstructure organization and the biomechanical properties.