IN VIVO MECHANISMS OF LOCAL STATIN-INDUCED BONE

DESCRIPTION (provided by applicant): The broad, long-term objective of this research is to develop practical approaches for the local application of biochemical preparations to stimulate controlled craniofacial bone growth, important for the repair of osseous defects. Simvastatin is a promising candidate, but causes soft tissue inflammation. How statins manipulate the local bone turnover sequence, the cells and mediators involved, and how to optimize bone formation and minimize inflammation need further investigation. The following hypotheses are proposed: 1) Local application of simvastatin initiates bone growth in a dose-dependent manner and 2) initiates peripheral soft tissue inflammation at higher doses than required for bone growth; 3) Bone growth induced by local application of simvastatin is mediated by nitric oxide synthase (NOS), bone morphogenetic protein (BMP-2) and cyclooxygenase (COX-2) pathways. The Specific Aims with accompanying research design and methods are: Aim 1. Characterize the dose effect of simvastatin on the mandibular bone growth and adjacent soft tissue inflammation. An in vivo rat bilateral mandible model will be used which allows active drug (simvastatin) to be delivered supraperiosteally at varying doses in a sustained-release vehicle (methylcellulose) under an occlusive membrane (polylactic acid) on one side of the mandible, and control vehicle/membrane on the other side. This permits statin effects on bone turnover (resorption/apposition) to be monitored histomorphometrically across time. Aim 2. Test the role of NOS, BMP-2 and inflammation (COX) in simvastatin-induced bone growth by measurement of local levels and/or co-administration of inhibitors of NOS and COX-2. NOS, BMP-2 and COX will be quantitated with immunoassays of mandibular soft-tissue homogenates. The vehicle/membrane system allows inhibitors of suspected mediators of statin-induced bone growth/inflammation (L-NAME for NOS and NS398 for COX-2) to be added to optimal simvastatin doses in additional animals to determine how reduction of these mediators affects the bone formation, histomorphometrically. A positive control will be mevalonate (statins inhibit mevalonate) added to the statin vehicle/membrane. Defining optimal doses of simvastatin (possibly combined with anti-inflammatory drugs), which allow high bone growth and low inflammation (and associated side effects), as well as identification of important host mediators, will allow development of promising therapeutic strategies for local bone growth in alveolar and craniofacial bone defects.