Hansen Experimental Physics Laboratory, Stanford University, Stanford, California, USA.
Invest Ophthalmol Vis Sci. 2011 Mar 28;52(3):1780-7. doi: 10.1167/iovs.10-5917.
Subthreshold retinal phototherapy demonstrated clinical efficacy for the treatment of diabetic macular edema without visible signs of retinal damage. To assess the range of cellular responses to sublethal hyperthermia, expression of the gene encoding a 70 kDa heat shock protein (HSP70) was evaluated after laser irradiation using a transgenic reporter mouse.
One hundred millisecond, 532 nm laser exposures with 400 μm beam diameter were applied to the retina surrounding the optic nerve in 32 mice. Transcription from the HSP70 promoter was assessed relative to the control eye using a bioluminescence assay at 7 hours after laser application. The retinal pigmented epithelium (RPE) viability threshold was determined with a fluorescence assay. A computational model was developed to estimate temperature and the extent of cell damage.
A significant increase in HSP70 transcription was found at exposures over 20 mW, half the threshold power for RPE cell death. Computational modeling estimated peak temperature T = 49°C at HSP70 expression threshold. At RPE viability threshold, T = 57°C. Similar temperatures and damage indices were calculated for clinical subvisible retinal treatment parameters.
Beneficial effects of laser therapy have been previously shown to extend beyond those resulting from destruction of tissue. One hundred millisecond laser exposures at approximately half the threshold power of RPE damage induced transcription of HSP70, an indication of cellular response to sublethal thermal stress. A computational model of retinal hyperthermia can guide further optimization of laser parameters for nondamaging phototherapy.
亚阈光凝已被证实对糖尿病性黄斑水肿具有临床疗效，而不会出现可见的视网膜损伤迹象。为了评估细胞对亚致死性热应激的反应范围，利用转基因报告鼠评估了激光照射后编码 70kDa 热休克蛋白（HSP70）的基因表达。
使用 532nm 激光，以 400μm 的光斑直径对视神经周围的视网膜进行 100ms 的照射。在激光照射后 7 小时，采用生物发光法评估相对于对照眼的 HSP70 启动子转录情况。采用荧光法测定视网膜色素上皮（RPE）细胞的存活阈值。建立了一个计算模型，用于估计温度和细胞损伤程度。
在超过 20mW 的照射下，发现 HSP70 转录显著增加，这是 RPE 细胞死亡的半阈值功率。计算模型估计 HSP70 表达阈值时的峰值温度 T=49°C。在 RPE 存活阈值时，T=57°C。计算出的类似温度和损伤指数也适用于临床亚可见视网膜治疗参数。
先前的激光治疗有益效果已被证明超出了组织破坏所产生的效果。在大约为 RPE 损伤阈值功率的一半的情况下进行 100ms 的激光照射，可诱导 HSP70 的转录，表明细胞对亚致死性热应激的反应。视网膜过热的计算模型可以指导进一步优化非破坏性光疗的激光参数。
