Session5 1400-1700 Monday, September11,1995 Research ! Room B-1 5.1 Photodynamic Therapy Delivered Via a Scavenger- Receptor Mediated Photosensitizer Prevents Intimal Hyperplasia T. NAGAE, B. TROMBERG, S. ITO, M. BERNS, S. ISHIMARU and S.E. WILSON, Irvine, California, USA and Tokyo, Japan Photosensitizers, such as Photofrin 1l or Chloroaluminum- suifouate accumulate at sites of arterial injury. We have exploited this property to develop a model of photodynamic therapy (PDT) for intimal hyperplasia. Our hypothesis is that localization of a photosensitizer to areas of intimal hyperplas- tia will allow highly specific PDT ablation of hyperplastic lesions. We have previously shown that the fluorescent probe [maleylated-bovine serum albumin (maI-BSA) conjugated with Texas-Red] can be selectively targeted to the macrophages recruited during formation of hyperplasia via a receptor- mediated mechanism. In this study, the photosensitizer chlor- ine 6 (Cle6) was conjugated to maI-BSA. Endothelial cells, smooth muscle cells, and macrophages were tested for uptake of BSA/CIe6. Macrophages were found to concentrate the photosensitizer in a manner characteristic of a receptor- mediated process. In Sprague-Dawley rats weighing 350-450 gm, arterial wall injury was produced by withdrawing an inflated 2-F Fogarty balloon catheter through the abdominal aorta to create a model of intimal hyperplasia. Fluorescent compounds were injected two weeks after injury. Four hours following injection, the injured aorta was irradiated externally with an argon-pumped dye laser tuned to emit 661 nm of light energy. We employed two total radiant exposures: 20 J/cm 2 (Cle6, n = 3; maI-BSA-Cle6, n = 3) and 40 J/cm 2 (Cle6, n = 3; mal-BSA/Cle6, n = 3; no drug, n = 3). Forty-eight hours after PDT, the arteries were excised and examined histologically, and the cross-sectional areas of damaged neointimal cells compared. Intimal hyperplastic cells were significantly dam- aged in the mal-BSA/Cle6 injected group (20J, 67%; 40J, 87%) versus Cle6 group (0-20%). CONCLUSION: From this in vivo study, we conclude that mal-BSA/CIe6 is taken up efficiently by a macrophage medi- ated scavenger pathway, localizes in areas of intimal hyper- plastia, and functions effectively as a photosensitizer for PDT. Treatment of photosensitized, neointimal macrophages with 661 nm of light irradiation is effective in limiting formation of intimal hyperplasia in this model of arterial wall injury. 5.2 Effect of Heparin on Distal Anastomotic lntimal Hyperplasia (DAIH) V.S. SOTTIURAI, M. COOPER, J. GILMORE, A. STEPHEN& N. MCHALE and D. LEWIS, New Orleans, Louisiana Heparin is known to inhibit vascular myoblast proliferation, migration and matrix synthesis. This study was undertaken to determine (1) whether heparin inhibits (DAIH), (2) DAIH distibution, and (3) the histocytology of DAIH. Thirty-five adult mongrel dogs received aortoiliac dacron bifurcated grafts with heparin impregnation in one limb followed by collagen coating of both limbs. Grafts were explanted at 2, 4, and 6-8 months for determination of DAIH formation, localization, characterization and comparison of graft limb patency. Ten animals died prior to explantation, 25/35 anim- als were explanted on schedule. 29/35 grafts were analysed for DAIH according to the protocol. 18/29 graft analysed were occluded. The distribution of the patent grafts were: at 2 months 1/8; at 4 months 3/7; at 6-8 months 3/10. DAIH, a multi-interlamination o~ myoblasts alternating with fibrocol- lagen occurred specifically at the toe>heel>floor. DAIH plotted against time is summarized below. DAIH is attenuated by heparin only after the superimposed collagen coating is dissolved in 6-8 weeks. The inhibiting effects of heparin on myoblasts ceases after its release in 2-6 weeks. This explains the benefits to the 4-month group mostly in this model. This study supports the tenet that controlling DAIH by controlling myoblast activity using heparin requires uninterrupted treatment. Because flow turbulence, the princip- al mechanism responsible for DAIH formation is always present in the end-to-side distal anastomosis. 5.3 Thrombin is an Important Factor in the Development of Intimal Hyperplasia After Arterial Injury M. DRY]SKI, S. FREBELIUS, P. SVENBERG, U. HEDIN andJ. SWEDENBORG, Buffalo, New York, USA and Stockholm, Sweden Thrombm is a mitogen for smooth muscle cells (SMC) in tissue culture and it has been suggested that it could be one of the factors contributing to the development of intimal hyperplasia after arterial injury. In addition, thrombin appears on the vessel wall shortly after balloon catheter denudation in an experimental arterial injury model, but its appearance could be prevented if the animals are treated with thrombin inhibi- tors such as hirudin or heparin. The present study was designed to evaluate the effect of thrombin inhibition on the development of intimal hyperplasia after balloon catheter injury in the rat carotid artery. A specific thrombin inhibitor, recombinant hirudin, was administered as three i.v. bolus injections at one hour intervals, the first dose given either immediately or six hours after injury. The animals were sacrificed two weeks after injury. The index of intimal SMC proliferation was the maximum intima to media area ratio (I/M). The control animals developed a marked intimal thickening (1/M 0.88). The animals treated with hirudin given immediately after injury (total dose of 300 I~g/kg) exhibited significantly less intimal hyperplasia (I/M 0.14). Using a lower hirudin dose (total dose of 30 I~g/kg) the increase in I/M ratio was 0.36. If the first hirudin dose was administrated 6 hours after injury (total dose of 300 I~g/kg) no decrease in the I/M ratio was noted (I/M 0.91), The APTT levels were significantly CARDIOVASCULAR SURGERY SEPTEMBER 1995 23