The Experiment Study On Pathogenesis Of Osteoporosis After Spinal Cord Injury And Effect Of Bcl-2 On TNF-a Induced Apoptosis In Osteoblasts

Background: Osteoporosis is one of complications due to spinal cord injury (SCI). Osteoporosis after SCI lead to increased bone mass loss as well as decreased biomechanics quality which often result in pathologic fractures below the injured level with the incidence of 20% or so reported by some researchers. Nowadays there are so much research works on clinical practice, and little attention focus on experimental research. The establishment of the animal model would contribute to the investigation of pathogenesis. prevention and treatment for this disease.The aim of the first part of study is to evaluate the possibility of rats with SCI being used as an experimental model of osteoporosis after SCI by examining the bone turnover status, bone mineral density and biomechanical competence of the bone. Also, pathogenesis mechanism of osteoporosis due to SCI was investigated. Method: SCI model was established by cutting off the distal thoracic spinal cord of rats; The investigation of biochemical values relating to bone resorption and formation, bone mineral density and biomechanics were performed; Ultrastructural investigation of bone were performed; BMP, IL-6 and TNF- a proteins in the bone were examined by using immunochemical stain combined with the imaging analysis techniques. Results: Calculus of the bladder was found in the SCI animals 6 week after injuries. Biochemical date demonstrated serum calcium, urine calcium, and urine calcium/creatinine rose dramatically compared with control groups at week 1,3,6.(PO.05, 0.01, 0.05; PO.001, 0.001, 0.01; PO.05, 0.01, 0.01, respectively). Serum total alkaline phosphates dropped significantly at week 1 (P<0.01), and then returned to normal level at week 3,6. Bone mineral density measured by dual energy x-ray absorption at proximal of tibia, distal and proximal of femur showed a significant fall(P<0.05, 0.01, 0.05). There are significant decrease in value of maximum load, energy absorption capacity and structural rigidity in femoral neck through bending test after 6 weeks (P<0. 01, 0.05, 0.05). Ultrastructural investigation revealed little endoplasmic reticulum and Golgi apparatus were found in osteoblast and vacuole changes of mitochondrion indicating the low activity of osteoblast. Also, condensation of heterochromatin collected under the edge of nuclear membrane indicating the apoptosis were also found in osteoblasts. No differences were found between the SCI and control group in osteoblast ultrastructure at week 3. There were four basic changes in ultrastructure of osteocytes as follows. First, osteocytic dissolve characterized by decreased organelles. enlargement of bone lacuna, increasing concentrated wadding material and forming of osmium -favored stratum. Second, degenerative osteocytes revealed decreased organelles. sake-like change and some cells without integrated wall. Third, some typical necrosis cell showed nuclear pycnosis and cell collapsed. Fourth, changes such as bubble and bud. heterochromatin condensation, edge collection of heterochromatin under the nuclear membrane suggested apoptotic osteocytes. The expression of tumor necrosis factor-a (TNF-a) rose at week 1 significantly and returned to normal at week 6. Immunochemistry stain of bone morphogenetic protein (BMP) and interleukin-6 (IL-6) were more intensive in SCI groups at week 6 than that in control groups (PO.05, 0.05,respectfully), however, no difference was found between two groups at week 1. Conclusions: Osteoporosis develops at week 6 in rats suffering from SCI. Rats underwent SCI have a similar changes in bone turnover, bone loss site and the risk of fracture, so could be used as the animal model for osteoporosis after SCI. Decreased vigor and increased possibility of fall of total live osteoblasts resulted fromthe apoptosis may contributed to the decreased bone forming ability in early state. Dissolve, degeneration, necrosis and apoptosis of osteocytes are the probable causes for decoupling. The data collected from the alteration of the immunochemistry indicated that cytokine play...