Abstract:

Objective To observe the influence of glucocorticoid(GC) on the expressions of high mobility group protein B1(HMGB1), receptor of advanced glycation endproducts(RAGE), osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) in bone tissue of the rats,and to discuss the related mechanism in glucocorticoid-induced osteoporosis. Methods 48 healthy adult male SD rats were randomly divided into low dose of GC (LGC) group (n=12),medium dose of GC (MGC) group(n=12),high dose of GC(HGC) group(n=12),and control group(n=12).The rats in LGC,MGC and HGC groups were treated by intramuscular injection of prednisolone 7.0,12.5 and 25.0 mg·kg^-1, respectively,and the rats in control group were only treated by the same volume of normal saline.All the rats receieved the injection twice a week.After 4 weeks of intervention,all the rats were sacrificed.ELISA method was used to detect the serum HMGB1,OPG,and RANKL levels of the rats;HE staining method was used to detect the pathomorphology of bone tissue of the rats;Immunohistochemistry and Western blotting method were used to detect the expression levels of HMGB1,RAGE,OPG and RANKL protein in the bone tissue of rats. Results The ELISA results showed that the serum HMGB1 levels of the rats in GC groups had no significant differences compared with control group;the OPG levels were lower than that in control group,and they were decreased with the increase of the GC dose,and there were significant differences between HGC group and control,LGC,MGC groups (P<0.05);the serum RANKL levels of the rats in GC groups were higher thanthat in control group and they were increased in a dose-dependent manner;there were significant differences between HGC group and control,LGC,MGC groups (P<0.05).The HE staning results showed that the femur tissue of the rats in LGC group was close to normal bone tissue;a lot of bone trabecular which already had a reduced thickness in MGC group were found,and replaced by granulation tissue,the dead osteocytes and empty osteocyte lacunae were easy to encounter;the bone trabecula of the rats in HGC group were seriously compromised,and the adipocytes almost replacing the hematopoietic cells in the marrow cavity were hyperplasia and hypertrophy which render them abnormal appearance,and the necrotic bone marrow and discontinuous bone chips were also found.The immunohistochemistry and Western blotting results showed that the HMGB1 protein levels in bone tissue of the rats in GC groups were increased compared with control group (P<0.05),and there were significant differences between different doses of GC groups(P<0.05);the RAGE protein levels in bone tissue of the rats had no significant differences between various groups;the OPG protein levels in bone tissue of the rats in GC groups were decreased compared with control group (P<0.05),and there were significant differences between different doses of GC groups (P<0.05); the RANKL protein levels in bone tissue of the rats in MGC and HGC groups were increased compared with control group (P<0.05),and the RANKL protein level in MD group was lower than that in HGC group (P<0.05). Conclusion After the rats are treated with excess GC,the levels of HMGB1 in bone tissue is increased and the proportion of OPG/RANKL is decreased which may be one of the pathogenesis of osteoporosis.

Key words: glucocorticoid, high mobility group protein B1, receptor of advanced glycation endproducts, osteoprotegerin, receptor activator of nuclear factor-κB ligand