Pulsed Electromagnetic Fields Stimulation Prevents Steroid-induced Osteonecrosis In Rats

Part1Effects of PEMF on the BMD and BMC of the proximal femur in steroid-treated ratsObjective:The purpose of the study was to investigate the effects of pulsed electromagnetic fields (PEMF) stimulation on the bone mineral density (BMD) and bone mineral content (BMC) of the proximal femur in steroid-treated rats.Methods:Seventy-two male adult Wistar rats were divided into three groups and treated as follows.(1) PEMF stimulation group (PEMF group, n=24):intravenously injected with lipopolysaccharide (LPS,10μg/kg) on day0and intramuscularly injected with methylprednisolone acetate (MPSL,20mg/kg) on days1,2and3, then subjected to PEMF stimulation4h per day for1to8weeks.(2) Methylprednisolone-treated group (MPSL group, n=24):injected the same dose of LPS and MPSL as the PEMF group but without exposure to PEMF.(3) Control group (PS group, n=24):injected0.9%saline in the same mode at the same time points. Six rats were randomly selected and killed from each group, and analyzed the BMD and BMC of the proximal femur1,2,4and8weeks after the last MPSL (or saline) injection.Results:There were no differences of BMD and BMC values between PEMF and PS groups at all time points (P>0.05). In the MPSL group, BMD and BMC values were significantly lower than the PS group from2to8weeks (P<0.05), and significantly lower than the PEMF group at4and8weeks(P<0.05).Conclusions:PEMF stimulation can prevent the loss of bone mass and maintain the BMD and BMC in steroid-treated rats. Part2Effects of PEMF on the serum lipid levels in steroid-treated ratsObjective:The purpose of the study was to investigate the effects of PEMF stimulation on the serum lipid levels in steroid-treated rats.Methods:Seventy-two male adult Wistar rats were divided into three groups and treated as follows.(1) PEMF stimulation group (PEMF group, n=24):intravenously injected with LPS (10μg/kg) on day0and intramuscularly injected with MPSL (20mg/kg) on days1,2and3, then subjected to PEMF stimulation4h per day for1to8weeks.(2) Methylprednisolone-treated group (MPSL group, n=24):injected the same dose of LPS and MPSL as the PEMF group but without exposure to PEMF.(3) Control group (PS group, n=24):injected0.9%saline in the same mode at the same time points. Six rats were randomly selected and killed from each group, and analyzed the levels of triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL) and high-density lipoprotein cholesterol (HDL)1,2,4and8weeks after the last MPSL (or saline) injection.Results:There were no differences of the values of TG, TC and LDL/HDL between PEMF and PS groups at all time points (P>0.05). Compared with the PEMF and PS groups, the values of TG, TC and LDL/HDL were significantly higher at all time points (P<0.05).Conclusions:PEMF stimulation can prevent hyperlipidemia in steroid-treated rats, and that might be one of the underlying mechanisms of preventing steroid-induced osteonecrosis. Part3Effects of PEMF on the mRNA and protein expression of TGF-β1and BMP-2in the proximal femur in steroid-treated ratsObjective:The purpose of the study was to investigate the effects of PEMF stimulation on the mRNA and protein expression of transforming growth factor β1(TGF-β1) and bone morphogenetic protein2(BMP-2) in the proximal femur in steroid-treated rats.Methods:Seventy-two male adult Wistar rats were divided into three groups and treated as follows.(1) PEMF stimulation group (PEMF group, n=24):intravenously injected with LPS (10μg/kg) on day0and intramuscularly injected with MPSL (20mg/kg) on days1,2and3, then subjected to PEMF stimulation4h per day for1to8weeks.(2) Methylprednisolone-treated group (MPSL group, n=24):injected the same dose of LPS and MPSL as the PEMF group but without exposure to PEMF.(3) Control group (PS group, n=24):injected0.9%saline in the same mode at the same time points. Six rats were randomly selected and killed from each group, and analyzed the mRNA and protein expression of TGF-β1and BMP-2in the proximal femur1,2,4and8weeks after the last MPSL (or saline) injection.Results:Compared with the PEMF and PS groups, the mRNA and protein expression of TGF-β1and BMP-2were significantly lower in the MPSL group at all time points (P <0.05). Compared with the MPSL and PS groups, the mRNA expression of TGF-β1and BMP-2increased, reaching a peak1week after PEMF treatment, and remained high for4weeks, then declined at8weeks, whereas the protein expression of TGF-β1and BMP-2increased, reaching a peak at2weeks after PEMF treatment, and remained high for8weeks.Conclusions:PEMF stimulation can increase the mRNA and protein expression of TGF-β1and BMP-2in the proximal femur in steroid-treated rats, and that might be one of the underlying mechanisms of preventing steroid-induced osteonecrosis. Part4Effects of PEMF on the incidence of osteonecrosis in the proximal femur in steroid-treated rats and the underlying mechanismsObjective:The purpose of the study was to investigate the effects of PEMF stimulation on the incidence of osteonecrosis in the proximal femur in steroid-treated rats and explore the underlying mechanisms.Methods:Seventy-two male adult Wistar rats were divided into three groups and treated as follows.(1) PEMF stimulation group (PEMF group, n=24):intravenously injected with LPS (10pg/kg) on day0and intramuscularly injected with MPSL (20mg/kg) on days1,2and3, then subjected to PEMF stimulation4h per day for1to8weeks.(2) Methylprednisolone-treated group (MPSL group, n=24):injected the same dose of LPS and MPSL as the PEMF group but without exposure to PEMF.(3) Control group (PS group, n=24):injected0.9%saline in the same mode at the same time points. Six rats were randomly selected and killed from each group, and analyzed the incidence of osteonecrosis in the proximal femur1,2,4and8weeks after the last MPSL (or saline) injection.Results:The incidence of osteonecrosis in the PEMF group (29%) was significantly lower than that observed in the MPSL group (75%)(P<0.05), while no osteonecrosis was observed in the PS group.Conclusions:PEMF stimulation can significantly decrease the incidence of steroid-induced osteonecrosis in the proximal femur, and the underlying mechanisms involve decreased serum lipid levels and increased the mRNA and protein expression of TGF-β1and BMP-2.