Abdominal radiation initiates apoptotic mechanism in rat femur bone marrow cells in vivo that is reversed by IGF-1 administration

Administration of necrostatin-1 ameliorates glucocorticoid-induced osteonecrosis of the femoral head in rats

Glucocorticoid (GC)-induced osteonecrosis of the femoral head (ONFH) is a serious complication of glucocorticoid treatment and is characterized by dysfunctional bone reconstruction at necrotic sites. Our previous study confirmed the protective potential of necrostatin-1, a selective blocker of necroptosis, in glucocorticoid-induced osteoporosis. In this study, rat models of GC-induced ONFH were established to evaluate the effects of necrostatin-1 on osteonecrotic changes and repair processes. Osteonecrosis was verified by histopathological staining. An analysis of trabecular bone architecture was performed to evaluate osteogenesis in the osteonecrotic zone. Then, necroptotic signaling molecules such as RIP1 and RIP3 were examined by immunohistochemistry. Histopathological observations indicated that necrostatin-1 administration reduced the incidence of osteonecrosis and the osteogenic response in subchondral areas. Additionally, bone histomorphometry demonstrated that necrostatin-1 intervention could restore bone reconstruction in the necrotic zone. The protective mechanism of necrostatin-1 was related to the inhibition of RIP1 and RIP3. Necrostatin-1 administration alleviated GC-induced ONFH in rats by attenuating the formation of necrotic lesions, recovering the function of osteogenesis, and suppressing glucocorticoid-induced osteocytic necroptosis by inhibiting the expression of RIP1 and RIP3.

Oxidative stress due to radiation in CD34(+) hematopoietic progenitor cells: protection by IGF-1

Radiation exerts direct as well as indirect effects on DNA through the generation of reactive oxygen species (ROS). Irradiated hematopoietic progenitor cells (HPCs) experience DNA strand breaks, favoring genetic instability, due to ROS generation. Our aim was to study the effect of a range of radiation doses in HPCs and the possible protective mechanisms activated by insulin-like growth factor-1 (IGF-1). ROS generation was evaluated, in the presence or absence of IGF-1 in liquid cultures of human HPCs-CD34(+) irradiated with 1-, 2- and 5-Gy X-rays, using a flow cytometry assay. Manganese superoxide dismutase (MnSOD) expression was studied by western blot analysis and visualized by an immunofluorescence assay. Apoptosis was estimated using the following assays: Annexin-V assay, DNA degradation assay, BCL-2/BAX mRNA and protein levels and caspase-9 protein immunofluorescence visualization. Viability and clonogenic potential were studied in irradiated HPCs. The generation of superoxide anion radicals at an early and a late time point was increased, while the hydrogen peroxide generation at a late time point was stable. IGF-1 presence further enhanced the radiation-induced increase of MnSOD at 24 h post irradiation. IGF-1 inhibited the mitochondria-mediated pathway of apoptosis by regulating the m-RNA and protein expression of BAX, BCL-2 and the BCL-2/BAX ratio and by decreasing caspase-9 protein expression. IGF-1 presence in culture media of irradiated cells restored the clonogenic capacity and the viability of HPCs as well. In conclusion, IGF-1 protects HPCs-CD34(+) from radiation effects, by eliminating the oxidative microenvironment through the enhancement of MnSOD activation and by regulating the mitochondria-mediated pathway of apoptosis.

A rat model of early stage osteonecrosis induced by glucocorticoids

BACKGROUND

Glucocorticoid (GC)-induced osteonecrosis (ON) is an important complication of medical therapy. The exact pathomechanisms of ON has not been clearly elucidated. There is a need for a reproducible animal model that better approximates the clinical scenario.

METHODS

To determine the genetic susceptibility of rats to develop GC-induced femoral head ON, we evaluated 5 different inbred strains of rats (Spontaneous Hypertensive Rat, Wistar Kyoto, Wistar Furth, SASCO Fisher and Lewis). Prednisone pellets (dosage of 1.82-2.56 mg/kg/day) were implanted subcutaneously for 90. After 90 days, the femurs were resected and examined histologically and radiographically. Pathological and histological examination was performed. Hematoxylin and eosin (H & E) staining was used to delineate the femoral head osteonecrosis lesions as well as abnormalities of articular cartilage and growth plate.

RESULTS

The greatest differences in H & E staining were seen in the Wistar Kyoto and Wistar Furth groups. In these groups 4 out of 5 and 3 out of 5, respectively, steroid-induced rats revealed growth plate disruption with acellular areas. The TUNEL apoptosis staining assay for apoptosis revealed that 4 out of 5 of Wistar Kyoto rats, 5 out of 5 of Wistar Furth, 2 out of 4 of surviving Lewis and 2 out of 2 of the surviving spontaneous hypertensive rats had apoptotic osteocytes in trabeculae, whereas none of the Fisher rats showed apoptotic osteocytes.

CONCLUSIONS

We postulate that Wistar Kyoto, Wistar Furth and spontaneous hypertensive rats may be strains of rats more susceptible to develop ON of the femoral head while Fisher rats were the most resistant.