The effect of endostatin on angiogenesis and osteogenesis of steroid-induced osteonecrosis of the femoral head in a rabbit model.

Objective: This study aimed to investigate whether endostatin, a crucial anti-angiogenic factor, plays a negative role in angiogenesis and osteogenesis and aggravates the progression of osteonecrosis of the femoral head induced by steroid use in a rabbit model.

Methods: 66 New Zealand white rabbits were randomly divided into four groups: glucocorticoid model (GC) group (GC group, n = 18), glucocorticoid model and endostatin group (GC;ES group, n = 18), ES group (ES group, n = 18), and blank control group (CON group, n = 12). In the GC group, 10 μg/ kg lipopolysaccharide (LPS) was intravenously injected into the ear margin, and 24h after LPS injection, 20 mg/kg GC methylprednisolone (MPS) was injected into the gluteus muscle three times, each time at an interval of 24h. The animals of the GC;ES group were given as same treatment as the GC group, except for the addition of ES. MPS was not used in the ES group and CON group. ES group was only given ES, while the CON group was only given the same amount of normal saline. All animals successfully established models of femoral head necrosis, and then the difference among the Immunohistochemistry, Quantitative polymerase chain reaction (qPCR) analysis, Enzyme-linked immunosorbent assay, Biomechanical test, etracyclline-calcein double labeling, and Van Gieson staining indices were compared among the four groups.

Results: The combination of MPS and LPS was successful in establishing the femoral head necrosis model in New Zealand white rabbits. The incidence of osteonecrosis after MPS and LPS intervention was 70% (7/10), while that plus ES was 100% (10/10). At the same time, after MPS and LPS intervention, while the empty bone lacuna rate of the femoral head was significantly increased, the number of osteo- blasts was decreased. Also, the expressions of CD31 positive cells, Runx2, Osterix, COL1A1, and VEGF mRNA in the femoral head were decreased, and the levels of osteogenesis-related protein b-ALP, OCN, and angiogenic factor VEGF in the femoral head were decreased. The percentage of the trabecular bone area (%Tb.Ar), trabecular thickness (Tb.Th), trabecular number (Tb.N), labeled perimeter percent (%L.Pm), mineral apposition rate (MAR), and bone formation rate (BFR/BS) in the femoral head after MPs and LPS intervention detected by tetracycline calcein double labeling and Van Gieson staining decreased significantly, except trabecular separation (Tb.Sp) increased significantly. The compressive strength (CS), elastic modulus (EM), and strain energy (SE) of the femoral head examed by biomechanical measurement decreased significantly. All the above changes were more obvious after adding ES intervention. ES mRNA in the femoral head was undifferentiated and increased in the GC, ES, and GC;ES group compared with group CON.

Conclusion: This study has revealed that ES can inhibit angiogenesis and osteogenesis in the femoral head and aggravate the occurrence and development of femoral head necrosis. Thus, antiangiogenic factors may play an important role in the pathogenesis of ONFH.