Percutaneous Transluminal Coronary Angioplasty (PTCA) has become a widely used pro-cedure for the treatment of coronary artery disease (CAD). However, restenosis at the site of PTCA remains a persistent problem. Restenosis following PTCA involves a fibroproliferative response to vascular injury and numerous attempts to modify this response, either through pharmacological interventions or mechanical devices, have met with very limited success. It is felt that by understanding the cellular and molecular mechanisms that underlie this fibroproliferative response to injury, more effective strategies to prevent restenosis can be explored. One mechanism that has been shown to be important in restenosis in the rat is the migration of vascular smooth muscle cells (VSMCs) from the media of the vascular wall to the in-tima. Recent studies by LCS scientists in cultured VSMCs suggest that the MMP-2 Type IV metalloproteinase (MMP-2) may be important in this process. Using gelatin zymography on extracts from carotid artery tissue isolated at varying time points following injury, we previously demonstrated the presence of the MMP-2 protein. To further clarify the in vivo relevance of this enzyme to the arterial response to injury, experiments involving the rat carotid injury model were performed. De-endotheliazation was performed with a embolectomy catheter and vessels were subsequently harvested at the appropriate time points. Preliminary findings with immunocytochemistry, in situ hybridization studies, and the ribonuclease protection assay reveal parallel results. The mRNA and protein for the MMP-2 gene was ex- pressed at moderate levels in uninjured vessels and decreased in expression a early time points. Within 5-7 days following injury expression increased and peaked at 14-21 days. The functional significance of these changes in vivo is presently under investigation. Treatment for restenosis is dependent on the development of an effective means of intravascular site-specific delivery. We recently began studies using a unique sustained-release biodegradable microcapsule. Initial experiments using Texas-red labeled albumin (TRA) incorporated into the microcapsules showed penetration of the TRA into the media in vessels from which the adventitia had been removed. Based upon preliminary results obtained about the potential role of MMP-2 in VSMC migration, we initiated in vivo studies using a peptide inhibitor of metalloproteinase activity. The peptide inhibitor was incorporated into the microcapsule and applied to the outside of the rat carotid artery that had under-gone vascular injury. The results of these experiments are pending.
