Selective Retina Therapy Reduces Bruch's Membrane Thickness and Retinal Pigment Epithelium Pathology in Age-Related Macular Degeneration Mouse Models

Nanosecond laser induces proliferation and improved cellular health within the retinal pigment epithelium

Background

Age-related macular degeneration (AMD) is a leading cause of vision loss in those over 60 years of age. Although there are limited interventions that may prevent the development or progression of disease, more efficacious treatments are required. Short-pulsed laser treatment shows promise in delaying progression of early disease. This work details how nanosecond laser influences the retinal pigment epithelium (RPE), the principal cell type implicated in AMD.

Methods

C57BL/6J mice (3-month-old) underwent monocular nanosecond laser treatment to assess short-term RPE response, while 9-month-old C57BL/6J and ApoEnull mice were similarly treated and longer-term responses investigated after 3 months. Human tissue was also obtained after 2 nanosecond laser treatments (1 month apart). RPE proliferation was assessed using bromodeoxyuridine and RPE gene change explored using qPCR and RNAseq. Melanin and lipofuscin content were quantified using histological techniques.

Results

Nanosecond laser induced RPE proliferation in treated and fellow mouse eyes, with monolayer repair occurring within 3 days. This was replicated in human tissue, albeit over a longer duration (1-4 weeks). Wildtype animals showed no overt change in RPE gene expression after short or longer post-treatment durations, while laser treated ApoEnull animals showed increased Mertk and Pedf expression, and a reduced number of dysregulated aging genes in treated and fellow eyes after 3 months. Furthermore, melanin and lipofuscin content were restored to wildtype levels in laser-treated ApoEnull RPE, while melanolipofuscin granules were reduced within treated regions of human RPE.

Conclusion

This work shows nanosecond laser stimulates RPE proliferation and results in an improved cellular phenotype. These data provide a biological basis for the prophylactic use of nanosecond lasers in AMD.

Understanding the Ocular Hypertension Model in Mice Induced by Dexamethasone-21-Acetate - Implications for Glaucoma Research

PURPOSE

This study aimed to assess the effectiveness of monocular and bilateral injections of Dexamethasone-21-acetate (Dex-21-Ac) into the murine fornix twice a week as a glucocorticoid-induced ocular hypertension model and investigated potential systemic side effects.

METHODS

Dex-21-Ac was administered twice weekly in three groups: bilateral injections, monocular injections, and a control group receiving the vehicle solution bilateral. After 21 days, enucleated eyes were examined using immunocytochemistry (ICC), and organ histology was performed.

RESULTS

All groups receiving Dex-21-Ac injections had a significant increase in intraocular pressure (IOP). Monocular injections also resulted in a significant increase in IOP in the fellow eye. The Dex-21-Ac-treated groups showed a bilateral increase in IOP of approximately 8 mmHg, accompanied by elevated expression of alpha smooth muscle actin and fibronectin in the anterior chamber angle. There were no significant changes in weight progression. Hepatic steatosis was observed in all Dex-21-Ac-treated animals, and some suffered from residual neuromuscular blockade under fentanyl anesthesia.

CONCLUSION

Bilateral injections of Dex-21-Ac twice a week lead to a significant increase in daytime IOP and fibrotic changes in the trabecular meshwork. Unilateral application has a significant impact on the fellow eye. Local dexamethasone leads to notable systemic effects independent of changes in animal weight. Considering liver damage and associated influence on metabolization, hepatically eliminated injection anesthetics may lead to overdosing and are not recommended. They should be replaced by inhalation anesthesia.

Regenerative Retinal Laser and Light Therapies (RELITE): Proposal of a New Nomenclature, Categorization, and Trial Reporting Standard

OBJECTIVES

Numerous laser and light therapies have been developed to induce regenerative processes in the choroid/retinal pigment epithelium (RPE)/photoreceptor complex, leaving the neuroretina undamaged. These therapies are applied to the macula for the treatment of various diseases, most prominently diabetic maculopathy, retinal vein occlusion, central serous chorioretinopathy, and age-related macular degeneration. However, the abundance of technologies, treatment patterns, and dosimetry protocols has made understanding these therapies and comparing different approaches increasingly complex and challenging. To address this, we propose a new nomenclature system with a clear categorization that will allow for better understanding and comparability between different laser and light modalities. We propose this nomenclature system as an open standard that may be adapted in future toward new technical developments or medical advancements.

METHODS

A systematic literature review of reported macular laser and light therapies was conducted. A categorization into a standardized system was proposed and discussed among experts and professionals in the field. This paper does not aim to assess, compare, or evaluate the efficacy of different laser or dosimetry techniques or treatment patterns.

RESULTS

The literature search yielded 194 papers describing laser techniques, 50 studies describing dosimetry, 272 studies with relevant clinical trials, and 82 reviews. Following the common therapeutic aim, we propose "regenerative retinal laser and light therapies (RELITE)" as the general header. We subdivided RELITE into four main categories that refer to the intended physical and biochemical effects of temperature increase (photothermal therapy, PTT), RPE regeneration (photomicrodisruption therapy, PMT), photochemical processes (photochemical therapy, PCT), and photobiomodulation (photobiomodulation therapy, PBT). Further, we categorized the different dosimetry approaches and treatment regimens. We propose the following nomenclature system that integrates the most important parameters to enable understanding and comparability: Pattern-Dosimetry-Exposure Time/Frequency, Duty Cycle/Irradiation Diameter/Wavelength-Subcategory-Category.

CONCLUSION

Regenerative retinal laser and light therapies are widely used for different diseases and may become valuable in the future. A precise nomenclature system and strict reporting standards are needed to allow for a better understanding, reproduceable and comparable clinical trials, and overall acceptance. We defined categories for a systematic therapeutic goal-based nomenclature to facilitate future research in this field.

Replenishing IRAK-M expression in retinal pigment epithelium attenuates outer retinal degeneration

Chronic inflammation is a constitutive component of many age-related diseases, including age-related macular degeneration (AMD). Here, we identified interleukin-1 receptor-associated kinase M (IRAK-M) as a key immunoregulator in retinal pigment epithelium (RPE) that declines during the aging process. Rare genetic variants of IRAK3, which encodes IRAK-M, were associated with an increased likelihood of developing AMD. In human samples and mouse models, IRAK-M abundance in the RPE declined with advancing age or exposure to oxidative stress and was further reduced in AMD. Irak3-knockout mice exhibited an increased incidence of outer retinal degeneration at earlier ages, which was further exacerbated by oxidative stressors. The absence of IRAK-M led to a disruption in RPE cell homeostasis, characterized by compromised mitochondrial function, cellular senescence, and aberrant cytokine production. IRAK-M overexpression protected RPE cells against oxidative or immune stressors. Subretinal delivery of adeno-associated virus (AAV)-expressing human IRAK3 rescued light-induced outer retinal degeneration in wild-type mice and attenuated age-related spontaneous retinal degeneration in Irak3-knockout mice. Our data show that replenishment of IRAK-M in the RPE may redress dysregulated pro-inflammatory processes in AMD, suggesting a potential treatment for retinal degeneration.

Effects of Fucoidans on Activated Retinal Microglia

Sulfated marine polysaccharides, so-called fucoidans, have been shown to exhibit anti-inflammatory and immunomodulatory activities in retinal pigment epithelium (RPE). In this study, we tested the effects of different fucoidans (and of fucoidan-treated RPE cells) on retinal microglia to investigate whether its anti-inflammatory effect can be extrapolated to the innate immune cells of the retina. In addition, we tested whether fucoidan treatment influenced the anti-inflammatory effect of RPE cells on retinal microglia. Three fucoidans were tested (FVs from Fucus vesiculosus, Fuc1 and FucBB04 from Laminaria hyperborea) as well as the supernatant of primary porcine RPE treated with fucoidans for their effects on inflammatory activated (using lipopolysaccharide, LPS) microglia cell line SIM-A9 and primary porcine retinal microglia. Cell viability was detected with a tetrazolium assay (MTT), and morphology by Coomassie staining. Secretion of tumor necrosis factor alpha (TNFα), interleukin 1 beta (IL1β) and interleukin 8 (IL8) was detected with ELISA, gene expression (NOS2 (Nitric oxide synthase 2), and CXCL8 (IL8)) with qPCR. Phagocytosis was detected with a fluorescence assay. FucBB04 and FVs slightly reduced the viability of SIM-A9 and primary microglia, respectively. Treatment with RPE supernatants increased the viability of LPS-treated primary microglia. FVs and FucBB04 reduced the size of LPS-activated primary microglia, indicating an anti-inflammatory phenotype. RPE supernatant reduced the size of LPS-activated SIM-A9 cells. Proinflammatory cytokine secretion and gene expression in SIM-A9, as well as primary microglia, were not significantly affected by fucoidans, but RPE supernatants reduced the secretion of LPS-induced proinflammatory cytokine secretion in SIM-A9 and primary microglia. The phagocytosis ability of primary microglia was reduced by FucBB04. In conclusion, fucoidans exhibited only modest effects on inflammatorily activated microglia by maintaining their cell size under stimulation, while the anti-inflammatory effect of RPE cells on microglia irrespective of fucoidan treatment could be confirmed, stressing the role of RPE in regulating innate immunity in the retina.

Replenishing Age-Related Decline of IRAK-M Expression in Retinal Pigment Epithelium Attenuates Outer Retinal Degeneration

Unchecked, chronic inflammation is a constitutive component of age-related diseases, including age-related macular degeneration (AMD). Here we identified interleukin-1 receptor-associated kinase (IRAK)-M as a key immunoregulator in retinal pigment epithelium (RPE) that declines with age. Rare genetic variants of IRAK-M increased the likelihood of AMD. IRAK-M expression in RPE declined with age or oxidative stress and was further reduced in AMD. IRAK-M-deficient mice exhibited increased incidence of outer retinal degeneration at earlier ages, which was further exacerbated by oxidative stressors. The absence of IRAK-M disrupted RPE cell homeostasis, including compromised mitochondrial function, cellular senescence, and aberrant cytokine production. IRAK-M overexpression protected RPE cells against oxidative or immune stressors. Subretinal delivery of AAV-expressing IRAK-M rescued light-induced outer retinal degeneration in wild-type mice and attenuated age-related spontaneous retinal degeneration in IRAK-M-deficient mice. Our data support that replenishment of IRAK-M expression may redress dysregulated pro-inflammatory processes in AMD, thereby treating degeneration.

Investigation of the Influence of Pulse Duration and Application Mode on Microsecond Laser Microsurgery of the Retinal Pigment Epithelium

Optical microsurgery confined to the retinal pigment epithelium (RPE) requires locally optimized laser parameters and reliable real-time feedback dosimetry (RFD) to prevent unwanted neuroretinal overexposure. This study aimed to compare pulses of different durations and application modes (single, ramp, burst). Moreover, optical coherence tomography (OCT)-based RFD was investigated in an ex vivo experiment, utilizing nine porcine eyes that were exposed to laser pulses of 8, 12, 16 and 20 µs duration (wavelength: 532 nm, exposure area: 90 × 90 µm², radiant exposure: 247 to 1975 mJ/µm²). Simultaneously, time-resolved OCT M-scans were recorded (central wavelength: 870 nm, scan rate: 85 kHz) for RFD. Post irradiation, retinal changes were assessed with color fundus photography (CFP) and cross-sectional OCT B-scans. RPE cell damage was quantified via fluorescence-based cell viability assay and compared to the OCT dosimetry feedback. Our experiments indicate cumulative RPE damage for pulse bursts of 16 µs and 20 µs, whereas no cumulative effects were found for pulse durations of 8 µs and 12 µs applied in ramp mode. According to statistical analysis, OCT-RFD correctly detected RPE cell damage with 96% sensitivity and 97% specificity using pulses of 8 µs duration in ramp mode.

Current and Novel Therapeutic Approaches for Treatment of Diabetic Macular Edema

Diabetic macular edema (DME) is a major ocular complication of diabetes mellitus (DM), leading to significant visual impairment. DME's pathogenesis is multifactorial. Focal edema tends to occur when primary metabolic abnormalities lead to a persistent hyperglycemic state, causing the development of microaneurysms, often with extravascular lipoprotein in a circinate pattern around the focal leakage. On the other hand, diffusion edema is due to a generalized breakdown of the inner blood-retinal barrier, leading to profuse early leakage from the entire capillary bed of the posterior pole with the subsequent extravasation of fluid into the extracellular space. The pathogenesis of DME occurs through the interaction of multiple molecular mediators, including the overexpression of several growth factors, including vascular endothelial growth factor (VEGF), insulin-like growth factor-1, angiopoietin-1, and -2, stromal-derived factor-1, fibroblast growth factor-2, and tumor necrosis factor. Synergistically, these growth factors mediate angiogenesis, protease production, endothelial cell proliferation, and migration. Treatment for DME generally involves primary management of DM, laser photocoagulation, and pharmacotherapeutics targeting mediators, namely, the anti-VEGF pathway. The emergence of anti-VEGF therapies has resulted in significant clinical improvements compared to laser therapy alone. However, multiple factors influencing the visual outcome after anti-VEGF treatment and the presence of anti-VEGF non-responders have necessitated the development of new pharmacotherapies. In this review, we explore the pathophysiology of DME and current management strategies. In addition, we provide a comprehensive analysis of emerging therapeutic approaches to the treatment of DME.

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

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.

Physiological response of the retinal pigmented epithelium to 3-ns pulse laser application, in vitro and in vivo

BACKGROUND

To treat healthy retinal pigmented epithelium (RPE) with the 3-ns retinal rejuvenation therapy (2RT) laser and to investigate the subsequent wound-healing response of these cells.

METHODS

Primary rat RPE cells were treated with the 2RT laser at a range of energy settings. Treated cells were fixed up to 7 days post-irradiation and assessed for expression of proteins associated with wound-healing. For in vivo treatments, eyes of Dark Agouti rats were exposed to laser and tissues collected up to 7 days post-irradiation. Isolated wholemount RPE preparations were examined for structural and protein expression changes.

RESULTS

Cultured RPE cells were ablated by 2RT laser in an energy-dependent manner. In all cases, the RPE cell layer repopulated completely within 7 days. Replenishment of RPE cells was associated with expression of the heat shock protein, Hsp27, the intermediate filament proteins, vimentin and nestin, and the cell cycle-associated protein, cyclin D1. Cellular tight junctions were lost in lased regions but re-expressed when cell replenishment was complete. In vivo, 2RT treatment gave rise to both an energy-dependent localised denudation of the RPE and the subsequent repopulation of lesion sites. Cell replenishment was associated with the increased expression of cyclin D1, vimentin and the heat shock proteins Hsp27 and αB-crystallin.

CONCLUSIONS

The 2RT laser was able to target the RPE both in vitro and in vivo, causing debridement of the cells and the consequent stimulation of a wound-healing response leading to layer reformation.

Photobiomodulation therapy in age-related macular degeneration

PURPOSE OF REVIEW

To review the available data supporting the use of photobiomodulation therapy (PBT) in the treatment of age-related macular degeneration (AMD).

RECENT FINDINGS

PBT might be used in treating nonexudative AMD. Limited evidence suggests that exudative AMD may also benefit from PBT.

SUMMARY

The optimal device would deliver doses of 60 J/cm2 or more with a multiwavelength composition through the pupil over short treatment intervals. Safe upper limits have not been established. More studies are needed to evaluate the efficacy of PBT in treating exudative and nonexudative AMD.

Subthreshold Nano-Second Laser Treatment and Age-Related Macular Degeneration

The presence of drusen is an important hallmark of age-related macular degeneration (AMD). Laser-induced regression of drusen, first observed over four decades ago, has led to much interest in the potential role of lasers in slowing the progression of the disease. In this article, we summarise the key insights from pre-clinical studies into the possible mechanisms of action of various laser interventions that result in beneficial changes in the retinal pigment epithelium/Bruch's membrane/choriocapillaris interface. Key learnings from clinical trials of laser treatment in AMD are also summarised, concentrating on the evolution of laser technology towards short pulse, non-thermal delivery such as the nanosecond laser. The evolution in our understanding of AMD, through advances in multimodal imaging and functional testing, as well as ongoing investigation of key pathological mechanisms, have all helped to set the scene for further well-conducted randomised trials to further explore potential utility of the nanosecond and other subthreshold short pulse lasers in AMD.

Retinal pigment epithelial responses based on the irradiation density of selective retina therapy

PURPOSE

We evaluated the response of the retinal pigment epithelium (RPE) to high-density (HD) or low-density (LD)-selective retina therapy (SRT) with real-time feedback-controlled dosimetry (RFD) in rabbits.

METHODS

Sixteen eyes of 8 Chinchilla Bastard rabbits underwent SRT with RFD (527-nm wavelength, 1.7-μs pulse duration), using automatically titrated pulse energy, by using optoacoustic dosimetry or real-time reflectometry. Fifty-six 25-μJ SRT, including LD-SRT (1-spot or 2-spot-spacing) and HD-SRT (4-spot, 7-spot, or 9-spot-no-spacing), were applied per eye. Color fundus photography and fundus fluorescein angiography (FFA) were used to confirm SRT spots 1-h post-SRT. Light microscopy and scanning electron microscopy (SEM) were performed at 2-h, 3-day, 7-day, and 1-month post-treatment.

RESULTS

We tested 896 spots irradiated by SRT with RFD and confirmed that SRT lesions were adequate, based on invisibility on fundoscopy and visibility on FFA. On SEM, at 2-h post-SRT, flattened RPE cells were observed in the center of the SRT lesion. While normal RPE cells were clearly observed between LD-SRT lesions, healthy RPE cells were rare in HD-SRT lesions at 2-h post-treatment. At 7-day post-SRT, SEM revealed completely restored LD-SRT lesions with small or large RPE cells with microvilli, whereas HD-SRT lesions were covered with RPE cells without microvilli. At 1-month post-SRT, SEM revealed restored RPE cells with microvilli in HD-SRT lesions. On light microscopy, both HD- and LD-SRT lesions were completely restored with adjacent RPE cells and spared photoreceptors at 1-month post-treatment.

CONCLUSIONS

Although both HD- and LD-SRT lesions had recovered at 1-month post-SRT, LD-SRT lesions healed faster than HD-SRT lesions.

Retina in a dish: Cell cultures, retinal explants and animal models for common diseases of the retina

For many retinal diseases, including age-related macular degeneration (AMD), glaucoma, and diabetic retinopathy (DR), the exact pathogenesis is still unclear. Moreover, the currently available therapeutic options are often unsatisfactory. Research designed to remedy this situation heavily relies on experimental animals. However, animal models often do not faithfully reproduce human disease and, currently, there is strong pressure from society to reduce animal research. Overall, this creates a need for improved disease models to understand pathologies and develop treatment options that, at the same time, require fewer or no experimental animals. Here, we review recent advances in the field of in vitro and ex vivo models for AMD, glaucoma, and DR. We highlight the difficulties associated with studies on complex diseases, in which both the initial trigger and the ensuing pathomechanisms are unclear, and then delineate which model systems are optimal for disease modelling. To this end, we present a variety of model systems, ranging from primary cell cultures, over organotypic cultures and whole eye cultures, to animal models. Specific advantages and disadvantages of such models are discussed, with a special focus on their relevance to putative in vivo disease mechanisms. In many cases, a replacement of in vivo research will mean that several different in vitro models are used in conjunction, for instance to analyze and validate causative molecular pathways. Finally, we argue that the analytical decomposition into appropriate cell and tissue model systems will allow making significant progress in our understanding of complex retinal diseases and may furthermore advance the treatment testing.

Modulation of inflammatory processes by thermal stimulating and RPE regenerative laser therapies in age related macular degeneration mouse models

Purpose

Inflammatory processes play a major role within the multifactorial pathogenesis of age-related macular degeneration (AMD). Neuroretina sparing laser therapies, thermal stimulation of the retina (TSR) and selective retina therapy (SRT), are known to reduce AMD-like pathology in vitro and in vivo. We investigated the effect of TSR and SRT on inflammatory processes in AMD mouse models.

Methods

One randomized eye of 8 months old apolipoprotein (Apo)E and 9 months old nuclear factor (erythroid-derived 2) -like 2 (NRF2) knock out mice were treated by TSR (10 ms, 532 nm, 50 µm² spot size, mean 4.5 W, ~200 spots) or SRT (~1.4 µs pulses, 532 nm, 50 µm spot size, 100 Hz over 300 ms, mean 2.5 µJ per pulse, ~200 spots). Fellow eyes, untreated knock out mice and wild-type BL/6J mice acted as controls. All mice were examined funduscopically and by optical coherence tomography (OCT) at the day of laser treatment. Mice were euthanized and enucleated either 1 day or 7 days after laser treatment and examined by gene expression analysis of 84 inflammatory genes.

Results

The inflammatory gene expression profile of both knock out models compared to healthy BL/6J mice suggests a regulation of pro- and anti-inflammatory processes especially concerning T-cell activity and immune cell recruitment. TSR resulted in downregulation of several pro-inflammatory cell-mediators both in ApoE -/- and NRF2-/- mice compared to treatment naïve litter mates one day after treatment. In contrast, SRT induced pro-inflammatory cell-mediators connected with necrosis one day after treatment as expected following laser-induced selective RPE cell death. Seven days after laser treatment, both findings were reversed.

Conclusions

Both TSR and SRT influence inflammatory processes in AMD mouse models. However, they act conversely. TSR leads to anti-inflammatory processes shortly after laser therapy and induces immune-cell recruitment one week after treatment. SRT leads to a quick inflammatory response to laser induced RPE necrotic processes. One week after SRT inflammation is inhibited. It remains unclear, if and to what extent this might play a role in a therapeutic or preventive approach of both laser modalities on AMD pathology.