Systemic bone loss and induction of coronary vessel disease in a rat model of chronic inflammation

Clinically, osteopenia or low bone mass has been observed in a variety of chronic inflammatory diseases, and elevated proinflammatory mediators have implicated this process. The purpose of this study was to develop an in vivo model of bone loss induced by chronic systemic inflammation. Time-release pellets designed to deliver one of three doses of LPS: Low (3.3 μg/day), High (33.3 μg/day), or Placebo over 90 days, were implanted subcutaneously in 3-month-old male Sprague–Dawley rats (n = 8/group). Neutrophil counts, indicative of ongoing inflammation, were elevated (P < 0.05) in both LPS groups at 30 days post-implant and remained significantly elevated in the High dose throughout the 90-day study period. At the end of the study, bone loss occurred in the femur as indicated by decreased bone mineral density (BMD) in both LPS-treated groups, but vertebral BMD was reduced in the High dose animals only. Microcomputed tomography revealed that trabecular bone volume (BV/TV) of the proximal tibial metaphysis tended to be reduced in the High dose LPS group. Deleterious effects on trabecular number (TbN) and trabecular separation (TbSp) were observed in both LPS-treated groups, but only the High dose group reached statistical significance. These alterations in trabecular microarchitecture resulted in compromised biomechanical properties. No changes in cortical thickness, porosity, or area of the tibia midshaft were evident at either dose of LPS. Up-regulation of the proinflammatory mediators, cyclooxygenase (COX)-2, interleukin (IL)-1, and tumor necrosis factor (TNF)-α was demonstrated in the metaphyseal region where the deleterious effects of LPS were observed. In addition to these alterations in bone, trichrome staining indicated changes in the coronary arterioles, consistent with vascular disease. Utilization of a LPS time-release pellet appears to provide an in vivo model of chronic inflammation-induced bone loss and a potentially novel system to study concurrent development of osteopenia and vascular disease.