To investigate the role of the nervous system of bone in steroid-induced osteonecrosis in rabbits

Metabolic Disorders and Mineral Density of the Bone Tissue in the Early Pathogenesis of Osteonecrosis: Study on Rabbits with Steroid-Induced Osteonecrosis

The relationship between the appearance of bone metabolism disorders and the onset of steroid-induced osteonecrosis remains unclear. We studied the time course of calcium, phosphorus, osteocalcin, alkaline phosphatase, and mineral density of bone tissue in the subchondral bone of the femoral head of rabbits injected with steroids and attempted to precisely determine the time when disorders in bone metabolism started in animals with steroid-induced osteonecrosis. We detected bone metabolism disorders involved in the early pathogenesis of steroid-induced osteonecrosis, which were the cause, but not the result of this condition.

Relation between the development of osteoporosis and osteonecrosis following glucocorticoid in a rabbit model

BACKGROUND

There has been a recent increase in the number of patients suffering from bone and joint diseases, as a consequence of corticosteroids administration. There are more patients treated with low dose of GCs under long-term conditions in clinical, such as effect of GCs on Rheumatoid arthritis, Crohn's disease and Asthma patients. Hence, it was difficult for doctor to determine which problem occur first - OP or ON; however, there was no clinical report previously in the literature, and there was no effective animal model of OP and ON about low dose GCs. This study was conducted to develop rabbit models of glucocorticoid (GC)-induced femoral head ON and OP and to investigate the temporal relationship between the occurrence of the two events following administration of glucocorticoids.

MATERIALS AND METHODS

Fifty six, 6 months old female rabbits were randomly divided into the GC group and control group (C). Rabbits received gluteal injections of methylprednisolone sodium succinate once a day for 4 weeks, while normal saline solution in the control group. Rabbits were sacrificed at 0, 2, 4, and 8 weeks. Hip magnetic resonance imaging was performed before the rabbits were sacrificed. Serum calcium (Ca), phosphorus (P), total cholesterol, and triglyceride levels were also measured. The bone mineral density (BMD) of femoral head and the femoral shaft were measured by dual-energy X-ray absorptiometry. The trabecular parameters of the femur and the 4(th) lumbar vertebrae (L4) were measured with a micro-computed tomography (μ-CT). Also, the femoral head was stained with hematoxylin-eosin staining.

RESULTS

At 4 weeks in the GC group, the BMD of the femur reduced 33% and 22% in the femoral head and shaft; there was irregular intermediate to high T2-weighted images signals; μ-CT showed microfractures and cystic changes in the femoral head and L4 at 4 weeks. At 8 weeks in the GC group, the classical "line-like sign" indicating ON of the femoral head was observed in 64.3% of the rabbits.

CONCLUSION

A rabbit model of GC-induced OP and ON was developed by repetitive injection with small doses of GCs in the gluteal region. OP was observed at 4 weeks while ON developed at 8 weeks and followed a clear temporal pattern.

Abnormal subchondral bone microstructure following steroid administration is involved in the early pathogenesis of steroid-induced osteonecrosis

Loss of bone microstructure integrity is thought to be related to osteonecrosis. But the relationship between the time when bone microstructure integrity loss appears and the onset of osteonecrosis has not yet been determined. Our study demonstrated abnormal changes of subchondral bone microstructure involved in the early pathogenesis of osteonecrosis.

INTRODUCTION

Using a rabbit model, we investigated the changes of subchondral bone microstructure following steroid administration to identify the onset of abnormal bone microstructure development in steroid-induced osteonecrosis.

METHODS

Fifty-five adult female Japanese White rabbits (mean body weight 3.5 kg; mean age 24 months) were used and randomly divided among three time points (3, 7, and 14 days) consisting of 15 rabbits each, received a single intramuscular injection of methylprednisolone acetate (MP; Pfizer Manufacturing Belgium NV) at a dose of 4 mg/kg, and a control group consisting of 10 rabbits was fed and housed under identical conditions but were not given steroid injections. A micro-CT scanner was applied to detect changes in the trabecular region of subchondral bone of excised femoral head samples. Parameters including bone volume fraction (BV/TV), bone surface (BS), trabecular bone pattern factor (Tb.Pf), trabecular thickness/number/separation (Tb.Th, Tb.N, and Tb.Sp), and structure model index (SMI) were evaluated using the software CTAn (SkyScan). After micro-CT scans, bilateral femoral heads were cut in the coronal plane at a thickness of 4 μm. The sections were then stained with haematoxylin-eosin and used for the diagnosis of osteonecrosis and the rate of development of osteonecrosis.

RESULTS

The BV/TV, BS, Tb.Th and Tb.N demonstrated a time-dependent decline from 3, 7, and 14 days compared with the control group, while the Tb.Pf, Tb.Sp and SMI demonstrated an increase at 3, 7, and 14 days compared with the control group. For the histopathology portion, osteonecrosis was not seen 3 days after steroid treatment, but was present 7 days after treatment and was obvious 14 days after treatment. Furthermore, the rate of osteonecrosis appearing between 7 and 14 days was not significantly different. In addition, the presence and variation of BV/TV, BS, Tb.Pf, Tb.Th, Tb.N, and SMI demonstrated significant changes at 7 days compared with the control group except Tb.Sp (at 14 days) and this is the time when osteonecrosis is thought to occur in this model.

CONCLUSION

This study demonstrated that osteonecrosis in rabbits is chronologically associated with changes in subchondral bone microstructure.

Role of the local bone renin‑angiotensin system in steroid‑induced osteonecrosis in rabbits

The specific pathogenesis of steroid‑induced osteonecrosis (ON) is yet to be elucidated and until recently effective prophylactic therapies have not been available. The local renin‑angiotensin system (RAS) exists in the bone and has an important role in local bone regulation. However, to the best of our knowledge, the interrelation between local bone RAS and steroid‑induced ON is yet to be investigated. In the present study, 45 rabbits were injected with a single intramuscular dose of 20 mg/kg methylprednisolone acetate (MPA) and were sacrificed 1 (group A), 2 (group B) and 3 (group C) weeks subsequent to MPA administration (n=15 per group). Ten rabbits were used as a control group (group N). The presence or absence of ON in the bilateral femoral heads was examined histopathologically. The mRNA and protein expression of components of the RAS, including angiotensin II (Ang II), angiotensin converting enzyme (ACE) and Ang II type 1 (AT1) and Ang II type 2 (AT2) receptors, were detected in the bone. Significant changes in Ang II, ACE, and AT1 and AT2 receptor expression were observed in the bone of the rabbits in the different groups. Moreover, the expression of Ang II and ACE was highest one week subsequent to administration of the glucocorticoid methylprednisolone and the expression of the AT1 and AT2 receptors was highest two weeks following methylprednisolone administration. ON occurs most significantly at three weeks following the administration of MPA in this animal model, thus the changes in Ang II, ACE and AT1 and AT2 receptor expression preceded this. The present study found that ON was strongly associated with the activation of the local bone RAS in rabbits.

Experimental animal models of osteonecrosis

Osteonecrosis (ON) or avascular necrosis (AVN) is a common bone metabolic disorder, mostly affecting femoral head. Although many biological, biophysical, and surgical methods have been tested to preserve the femoral head with ON, none has been proven fully satisfactory. It lacks consensus on an optimal approach for treatment. This is due, at least in part, to the lack of ability to systematically compare treatment efficacy using an ideal animal model that mimics full-range osteonecrosis of femoral head (ONFH) in humans with high incidence of joint collapse accompanied by reparative reaction adjacent to the necrotic bone in a reproducible and accessible way. A number of preclinical animal ON models have been established for testing potential efficacy of various modalities developed for prevention and treatment of ON before introduction into clinics for potential applications. This paper describes a number of different methods for creating animal experimental ON models. Advantages and disadvantages of such models are also discussed as reference for future research in battle against this important medical condition.