The Study Of Preventive Effect And Mechanism Of HG On Glucocorticoids Induced Osteoporosis

Objective: Osteoporosis is the most common metabolic disease characterized by loss of the normal density of bone, resulting in fragile bone and a higher risk of fractures. Glucocorticoid-induced osteoporosis (GIO) is the most common form of secondary osteoporosis. However, recent studies have also demonstrated different or even contradictive outcomes on whether the glucocorticoids inhibit or increase biological activity of the skeletal cells. Our study is to determine the different influence of Dexamethasone on cancellous and cortical bone, and also to study preventive effect and mechanism of Chinese medicine HUGU capsule (HG) on glucocorticoids induced osteoporosis by histomorphometry and biomechanicm in SD rats.Methods: 60 SPF 3-month-old SD female rats were randomly divided into six groups: normal group, model group, Gusongbao group (positive control group) and HG capsules low, medium and high dose group (Ctrl, Mod, GSB, HG-L, HG-M, HG-H), 10 in each group. The left tibia (proximal tibia metaphyses, PTM) and middle (middle part of tibia shaft, TX) were taken for bone histomorphometry, the left side of the femur (Left Femur, LF) and fifth lumbar vertebrae (the 5th Lumbar Vertebra, LV5) were taken for bone biomechanical test.Results:1. The effect of Dex and HG on body weight soft tissue The body weights of ctrl were gradually increased in 6 weeks; while Dex retarded rat growth or even body weights was decreased, and there were significant differences in body weight between the two groups. As unexpected, the HG-L, M and H groups did not increase the body weight in 45 days compared with Mod group.The soft tissues were weighed and found the liver, spleen, kidney, uterus and thymus with Dex treatment were significantly decreased compared with the ctrl group. The HG-L and M increased weight of kidney (P<0.05)and the weight of kidney in HG-M is higher than GSB group (P<0.05).2. The effect of Dex and HG on TX by bone histomorphometryStatic parameter: Dex was found to significantly reduce cortical bone (%Ct.Ar) and enlarge bone marrow cavity area (%Ma.Ar) compared with the ctrl group (P <0.01).Dynamic parameters displayed that Dex not only reduced the percent labeling perimeter and bone formation rate, but also increased bone resorption perimeter compared with the Ctrl group on endosteum surface. However, such changes were not found on periosteum surface.The HG-L and M groups prevented Dex induced cortical bone loss (% Ct.Ar) and marrow cavity area (% Ma.Ar) enlargement (P <0.01). These effects can also be resulted by the GSB Group. Compared with Dex group, endosteal surface % E L.Pm were all found to be higher (56.37%, 73.71%, 52.15%) in the HG-L, M and H groups. In addition, endosteal surface % E L.Pm in three groups is higher than GSB(P<0.05). Furthermore, the HG-L and M groups increased E-BFR/BS (125.36%, 155.36%) (P<0.05, P<0.01) in dose-dependent manner. As expected, the HG-M and HG-H were found to decrease %E-Er.Pm(P<0.01).3. The effect of Dex and HG on PTM by bone histomorphometryBoth static and dynamic parameters were found that the cancellous bone was not statistically changed in the Dex and Ctrl roup. However, by contrast Mod group, the HG-M increased cancellous bone (%Tb.Ar) (p<0.05), which even higher than Ctrl and GSB group (p<0.05). Only HG-H group could elevated Tb.Wi (p<0.05).Dynamic data showed that the HG-M increased MAR(P<0.01)which is not only higher than HG-L, but also higher than GSB group(P<0.05). As the same like TX results that the HG-M was also found to decrease Oc.N , which is lower than HG-L(P<0.05).4 The effect of Dex and HG on biomechanical properties of cortical bone and cancellous boneIn Dex treatment, the mechanical properties of the femur and vertebrae (maximum load, maximum stress, and maximum strain) were not weakening. As we expected, the all HG doses did not influence the mechanical properties of the femur by the three point bending; However, the HG-M was found to increase Max load , Max deflection and Max deflection in cancellouse bone of LV by contrast Dex group.Conclusion1. Short-term, small amount of Dex (45d ,2.5 mg kg-1,twice per week ) was found to lead to cortical bone loss, and did not affect the cancellous bone. The biomechanical properties of cortical bone were not weakened due to the change of geometrical shape in cortical bone. These results of the study showed the different effects of Dex on different parts of the skeleton with earlier influence on the cortical than the cancellous bone. This result suggests that future research should pay more attention on the cortical bone other than overly emphasizing the cancellous bone.2. Chinese medicine HG can prevent Dex-induce cortical bone loss, and the effect of HG-M is was found to be better than HG-L,H. The mechanism of cortical bone gain may be related to the increasing effect of HG on endosteal bone percent labeling paramenter and bone formation rate as well as the decreasing effect on osteoclast bone resorption.Although Dex was not shown to induce cancellous bone loss,the HG-M was found to promote cancellous bone formation and mineralization, as well as to inhibit bone resorption compared with Dex group. Moreover, the HG-M improved the mechanical properties for LV cancellous bone. Our results indicated that HG has the potential effect to prevent Dex-induce secondary osteoporosis(GIO).