Statius van Eps R G, Adili F, LaMuraglia G M
Division of Vascular Surgery, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Cardiovasc Res. 1997 Aug;35(2):334-40. doi: 10.1016/s0008-6363(97)00120-x.
Procedurally related vascular injury results in a smooth muscle cell (SMC) proliferative response which is in part initiated by SMC release of mitogens, including basic fibroblast growth factor (bFGF). This injury-induced proliferative response is believed to be a key event in intimal hyperplasia development. Photodynamic therapy (PDT), a novel approach found to be effective in inhibiting experimental intimal hyperplasia, produces cytotoxic free radicals resulting in localized SMC eradication. However, this form of SMC injury does not induce an inflammatory or proliferative response in the vessel wall. This study investigated whether PDT-generated free radicals could inactivate cell-associated bFGF normally released with cell injury.
PDT of bovine SMC was performed in vitro with the photosensitizer CASPc (5 micrograms/ml) and 675 nm laser light using three different fluences: 10, 50, and 100 J/cm2. After PDT, SMC viability was determined with the tetrazolium salt (MTT) assay and cell-associated bFGF was quantitated by ELISA. A SMC mitogenesis assay was utilized to detect cell-associated bFGF activity released with SMC injury.
In a dose-dependent manner, PDT-generated free radicals reduced cell-associated bFGF levels. After PDT with 100 J/cm2, cell-associated bFGF content was reduced by 88% (P < 0.0002). Of special interest was the finding that PDT with 10 J/cm2 significantly (P < 0.0002) reduced cell viability to around 50%, without affecting cellular bFGF levels. Consequently, a higher PDT dose (100 J/cm2) was needed to significantly (P < 0.001) inhibit the SMC mitogenic response associated with SMC injury.
These results provide a mechanism to explain how, unlike mechanical or other forms of SMC injury, optimal doses of PDT can locally eradicate medial vascular SMC without resulting in a bFGF-induced initiation of cell proliferation.
与手术相关的血管损伤会引发平滑肌细胞（SMC）增殖反应，部分原因是SMC释放包括碱性成纤维细胞生长因子（bFGF）在内的促有丝分裂原。这种损伤诱导的增殖反应被认为是内膜增生发展中的关键事件。光动力疗法（PDT）是一种被发现可有效抑制实验性内膜增生的新方法，它能产生细胞毒性自由基，导致局部SMC消除。然而，这种形式的SMC损伤不会在血管壁中引发炎症或增殖反应。本研究调查了PDT产生的自由基是否能使细胞损伤时正常释放的细胞相关bFGF失活。
使用光敏剂CASPc（5微克/毫升）和675纳米激光对牛SMC进行体外PDT，采用三种不同的能量密度：10、50和100焦/平方厘米。PDT后，用四氮唑盐（MTT）法测定SMC活力，并用酶联免疫吸附测定法（ELISA）对细胞相关bFGF进行定量。利用SMC有丝分裂原测定法检测SMC损伤时释放的细胞相关bFGF活性。
PDT产生的自由基以剂量依赖方式降低细胞相关bFGF水平。在100焦/平方厘米的PDT后，细胞相关bFGF含量降低了88%（P<0.0002）。特别值得关注的是，10焦/平方厘米的PDT显著（P<0.0002）将细胞活力降低至约50%，而不影响细胞bFGF水平。因此，需要更高剂量的PDT（100焦/平方厘米）才能显著（P<0.001）抑制与SMC损伤相关的SMC有丝分裂反应。
这些结果提供了一种机制，用以解释为何与机械性或其他形式的SMC损伤不同，最佳剂量的PDT能局部消除血管中层SMC，而不会导致bFGF诱导的细胞增殖启动。
