Selective retina therapy and thermal stimulation of the retina: different regenerative properties - implications for AMD therapy

Abstract

Background Selective Retina Therapy (SRT), a photodisruptive micropulsed laser modality that selectively destroys RPE cells followed by regeneration, and Thermal Stimulation of the Retina (TSR), a stimulative photothermal continuous wave laser modality that leads to an instant sublethal temperature increase in RPE cells, have shown therapeutic effects on Age-related Macular Degeneration (AMD) in mice. We investigate the differences between both laser modalities concerning RPE regeneration. Methods For PCR array, 6 eyes of murine AMD models, apolipoprotein E and nuclear factor erythroid-derived 2- like 2 knock out mice respectively, were treated by neuroretina-sparing TSR or SRT. Untreated litter mates were controls. Eyes were enucleated either 1 or 7 days after laser treatment. For morphological analysis, porcine RPE/choroid organ cultures underwent the same laser treatment and were examined by calcein vitality staining 1 h and 1, 3 or 5 days after irradiation. Results TSR did not induce the expression of cell-mediators connected to cell death. SRT induced necrosis associated cytokines as well as inflammation 1 but not 7 days after treatment. Morphologically, 1 h after TSR, there was no cell damage. One and 3 days after TSR, dense chromatin and cell destruction of single cells was seen. Five days after TSR, there were signs of migration and proliferation. In contrast, 1 h after SRT a defined necrotic area within the laser spot was seen. This lesion was closed over days by migration and proliferation of adjacent cells. Conclusions SRT induces RPE cell death, followed by regeneration within a few days. It is accompanied by necrosis induced inflammation, RPE proliferation and migration. TSR does not induce immediate RPE cell death; however, migration and mitosis can be seen a few days after laser irradiation, not accompanied by necrosis-associated inflammation. Both might be a therapeutic option for the treatment of AMD.

Long-Term Multimodal Imaging Analysis of Selective Retina Therapy Laser Lesions

“…In porcine organ cultures, closure of SRT-induced defects caused by migration and proliferation were observed within five days. However, those cells showed an altered morphology and SRT treatment increased active MMP expression, resulting in the pathologically swollen Bruch's membrane becoming thinner [6]. It is stated that this leads to a restored and rejuvenated RPE but may also explain altered FAF due to altered morphology and metabolism.…”

“…SRT has been shown to thin a pathologically thickened Bruch membrane, regenerate the rejuvenated RPE and lead to decreased vascular endothelial growth factor (VEGF) release and increased release of the VEGF antagonist, pigment epithelium-derived factor (PEDF) [6]. Thus, SRT could also be a promising therapy option for age-related macular degeneration (AMD).…”

“…The microvaporization-induced local RPE defects are closed by the proliferation and migration of neighboring pigment epithelial cells [5]. It is postulated that these remodeling processes contribute to the restructuring of the blood-retinal barrier, the improvement of metabolic functions of the RPE and therefore act as a rejuvenating therapy for the RPE [6]. The regenerating RPE cells subsequently form a functional closed tissue structure.…”

“…SRT has shown therapeutic success in central serous chorioretinopathy and diabetic macular edema [8,[10][11][12]. No side effects or complications of this procedure have been reported so far [5,6,12,13]. One problem in the clinical application of SRT is that neither the optimal irradiation parameters nor the standard treatment strategies regarding the application geometry of laser foci, the number of spots and repetitive treatment regimens have been reported and so far are only based on common therapeutic regimes of conventional laser coagulation treatment [8].…”