The Protection Of Sildenafil Against Steroid Induced Avascular Necrosis Of Femoral Head

Objective As a common bone disease, osteonecrosis of the femoral head（SONFH）is apathological process that many kinds of factors cause the destruction of the femoral head blood supplyleading to the death of bone marrow cells and bone cell. Currently the treatment of steroid-inducedosteonecrosis progresses slowly, patients often haven’t obtained adequate therapy until osteonecrosishappened, which does harm to the quality of patient’s work and life seriously. Most of the patients requiretotal hip replacement because there are no effective measures to prevent this disorder as a result of itsunclear pathogenesis. So it’s significant to intervene the development of steroid-induced femoral headosteonecrosis and study its pathogenesis, as also to improve the preventative and curative techniques..Sildenafil as a hemorheologic agent has the functions of dilating the smooth muscle of blood vessles andinhibiting platelet activation, aggregation and secretion, which results in expansion of blood vessels andincreasing intra-vascular blood flow. However, the definite role of sildenafil in femoral head necrosis isunclear. In this experiment, we explore the feasibility and molecular mechanism of sildenafil in SONFHwith establishing animal models of femoral head necrosis and intervening with this drug to provideexperimental basis of prevention of steroid induced SONFH.Methods30healthy C57BL/6mice postnatal eight weeks were randomly divided into3groups (n=10): controlgroup (group A), endotoxin/hormone group (group B), endotoxin/hormone/sildenafil group (group C).There was no difference in the weight and the number of gender among three groups with t test (P＞0.05).The mice in group B and C were treated with endotoxin by intraperitoneal injection in a dose of50ug/kgper day for two days and with methylprednisolone sodium succinate in a dose of20mg/kg per day for fourdays in the same way. At the same time, the mice in group C were injected with sildenafil in a dose of2mg/(kg d) until been decapitated (injection for28days in total). The mice were observed every day untilall of them had been killed4weeks later, then we compared the morphological characters of femoral headsfrom the experimental mice among different groups and processed these samples and hepatic tissue withHE and immunohistochemical staining, as well as analyzed the change of PKG in the tissue of liver,kidney and femoral head with Western Blot. The data from different groups were performed byanalysis of variance and the data comparing in pairs were performed by SNK test using SPSS17.0software.Summary statistics was expressed at mean±SD, P value less than0.05was considered statisticallysignificant.Results The appearance, the articular cartilage surface and morphology of the femoral heads fromthree groups are all normal. The hepatic tissue and femoral heads of Group A are normal. In the group B,the hepatic cells are swelling significantly and there are small fat vacuoles in cells, the structure of hepaticcords is not clear and the hepatic sinusoid becomes narrower. The trabecular bone of femoral head becomesthin and sparse, partly with visible fracture. For Group C, the morphology of the liver and femoral head issimilar to group A. The situation is between Group A and Group B.The femoral head empty bone pit rate ofGroup B is higher than Group A and C (P <0.01), and there is no difference between Group A and C(P>0.05). In Group A, the OPG brown granules distribute more widely and OPGL brown granules are rare,the positive staining rate is low. In Group B, the expression of OPG is rare and OPGL expressionsignificantly increases4weeks later after hormones been given. In Group C, OPG brown granules arecommon, OPGL brown granules are rare. The OPG and OPGL expression of Group C is slightly lowerand higher than Group A respectively. Comparing with Group A and C, the OPG local expression offemoral head in Group B decreases obviously,and the OPGL local expression rises obviously.Thedifferences have statistical significance (P <0.01). There is no difference between Group A and Group C inOPG and OPGL positive expression levels (P>0.05). Comparing with Group A and C, the PKG expressionin femoral head,liver and kidney drops significantly(P<0.01). The PKG expression between Group A and Chas little difference(P>0.05).Conclusion1. Sildenafil has obvious preventative effect on liver lipid metabolism disorder induced by hormone.2. Sildenafil could improve osteocyte metabolism and protect bone cells by affecting the activity ofbone cells and osteoblasts, in order to prevent bone resorption, promote bone formation and bone repair.3. sildenafil could resist hormones that have the effect on OPG and OPGL expression, whichcontribute to the proliferation of osteoblast cells, inhibit the activity of osteoclasts and effectivelyimprove bone metabolism and status of bone biomechanics. In conclusion，sildenafil has the effect of preventing early stage of SONFH by inhibiting thephosphodiesterase type5(PDE5) expression (phosphodiesterase is the negative regulatory factor ofNO-cGMP pathway), suppressing contraction of smooth muscle of vessles, dilating blood vessles,preventing ischemia of the femoral head, inhibiting sequential necrosis of the osteocytes, resistinghormones that have the effect on OPG and OPGL expression, and so on.