Current medical treatments for degenerative disc disease are limited and the available surgical treatments to remove the perturbed discs while stabilizing the new spinal construct are costly and invasive with associated risks of morbidity. Leading research is focused on less invasive methods to reverse or prevent intervertebral disc degeneration. Most rely on costly new drugs and devices. However, new implantations with mobile prostheses or even engineered tissues have brought a new spectrum of complications and hurdles to be addressed. Biological repair or regeneration of the intervertebral disc has been advocated with recent advances in recombinant therapeutic proteins. Many growth factors including bone morphogenetic protein (BMP) have been investigated on the aspect of biological repair and have been proved preliminarily with their anabolic effects on the intervertebral disc cells. Nonetheless, concerns still remain with these recombinant human growth factors since they either participate in undesired blood vessel ingrowth at the intervertebral disc or their given doses are normally much over the physiological levels to obtain effectiveness. In addition, costs for using these biofactors have not yet reached affordable. The proposed study will investigate a treatment for disc degeneration with the potential for substantially lower cost. Our previous work indicated that the common cholesterol-lowing drug simvastatin stimulated endogenous BMP-2 expression and in turn increased the chondrogenic phenotype expression of intervertebral disc cells cultured in vitro, and also the disc degeneration induced by a stab injury was fully reversed when injecting simvastatin that was loaded in a thermosensative, biodegradable polymer into nucleus pulposus of the perturbed discs in our rat model. In this study, we would like to extend our investigation to the defined animal models with IVD degeneration to further characterize the safety and effectiveness of using simvastatin specifically for the treatment of degenerative disc disease as an off-label indication of statins. We hypothesize that controlled release of simvastain from an injectable, degradable polymer will retard the progress of disc degeneration and may further regenerate intradiscal tissues. We will use stab injury (annulotomy) perturbation on intervertebral discs at predetermined levels of Sprague-Dawley rat's caudal spine to develop each category of disc degeneration that will be graded according to imaging, morphological and histological assessments. Grades with intact structure of annulus fibrosus will be indicated to the injection with simvastatin loaded in the polymer. Doses of the drug will be administered in an escalating manner and will be last until predetermined sacrifice time points to characterize the optimal dosage as well as the effective duration. Finally, a Yucatan minipig model will be utilized to further evaluate whether perturbed discs can restore the inherent biomechanical functions and anatomical features of interbody space after being treated with simvastatin to provide an insight in the development and implementation of future clinical trials.
A prevalent cholesterol-lowing drug simvastatin has recently been investigated to stimulate bone cells to secrete a growth factor that can augment bone tissue growth. This mechanism is thought to be critical as well for cells in the intervertebral disc to regenerate tissue substances. It is then proposed in this study to observe the potential to inject simvastatin into degenerative disc to retard the progression of degenerative disc disease and also help repair the aberrant tissues.
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