Laser-assisted targeted gene delivery to degenerated retina improves retinal function

Theoretical prediction of broadband ambient light optogenetic vision restoration with ChRmine and its mutants

Vision restoration is one of the most promising applications of optogenetics. However, it is limited due to the poor-sensitivity, slow-kinetics and narrow band absorption spectra of opsins. Here, a detailed theoretical study of retinal ganglion neurons (RGNs) expressed with ChRmine, ReaChR, CoChR, CatCh and their mutants, with near monochromatic LEDs, and broadband sunlight, halogen lamp, RGB LED light, and pure white light sources has been presented. All the opsins exhibit improved light sensitivity and larger photocurrent on illuminating with broadband light sources compared to narrow band LEDs. ChRmine allows firing at ambient sunlight (1.5 nW/mm2) and pure white light (1.2 nW/mm2), which is lowest among the opsins considered. The broadband activation spectrum of ChRmine and its mutants is also useful to restore color sensitivity. Although ChRmine exhibits slower turn-off kinetics with broadband light, high-fidelity spikes can be evoked upto 50 Hz. This limit extends upto 80 Hz with the improved hsChRmine mutant although it requires double the irradiance compared to ChRmine. The present study shows that ChRmine and its mutants allow activation of RGNs with ambient light which is useful for goggle-free white light optogenetic retinal prostheses with improved quality of restored vision.

Nanoactuator for Neuronal Optoporation

Light-driven modulation of neuronal activity at high spatial-temporal resolution is becoming of high interest in neuroscience. In addition to optogenetics, nongenetic membrane-targeted nanomachines that alter the electrical state of the neuronal membranes are in demand. Here, we engineered and characterized a photoswitchable conjugated compound (BV-1) that spontaneously partitions into the neuronal membrane and undergoes a charge transfer upon light stimulation. The activity of primary neurons is not affected in the dark, whereas millisecond light pulses of cyan light induce a progressive decrease in membrane resistance and an increase in inward current matched to a progressive depolarization and action potential firing. We found that illumination of BV-1 induces oxidation of membrane phospholipids, which is necessary for the electrophysiological effects and is associated with decreased membrane tension and increased membrane fluidity. Time-resolved atomic force microscopy and molecular dynamics simulations performed on planar lipid bilayers revealed that the underlying mechanism is a light-driven formation of pore-like structures across the plasma membrane. Such a phenomenon decreases membrane resistance and increases permeability to monovalent cations, namely, Na+, mimicking the effects of antifungal polyenes. The same effect on membrane resistance was also observed in nonexcitable cells. When sustained light stimulations are applied, neuronal swelling and death occur. The light-controlled pore-forming properties of BV-1 allow performing "on-demand" light-induced membrane poration to rapidly shift from cell-attached to perforated whole-cell patch-clamp configuration. Administration of BV-1 to ex vivo retinal explants or in vivo primary visual cortex elicited neuronal firing in response to short trains of light stimuli, followed by activity silencing upon prolonged light stimulations. BV-1 represents a versatile molecular nanomachine whose properties can be exploited to induce either photostimulation or space-specific cell death, depending on the pattern and duration of light stimulation.

Nanotechnology in Retinal Disease: Current Concepts and Future Directions

The retina is one of the most complex and extraordinary human organs affected by genetic, metabolic, and degenerative diseases, resulting in blindness for ∼1.3 million people in the United States and over 40 million people worldwide. This translates into a huge loss of productivity, especially among younger patients with inherited retinal diseases (IRDs) and diabetic retinopathy. Age-related macular degeneration accounts for 90% of all blindness cases worldwide. The prevalence of this condition is projected to reach over 5 million individuals over the next 3 decades. There are also >20 IRD phenotypes, affecting >2 million people worldwide. Nanobiotechnology uses nanotechnology for biological applications, making use of biological materials either conceptually or directly in the fabrication of new materials. Bionanotechnology, on the other hand, uses molecular biology for the purpose of creating nanostructures (ie, structures with at least 1 dimension <100 nm). Retinal applications of these technologies are developing at a rapid pace. This review includes the most current nanotechnological applications in retinal diagnostics, theranostics, drug delivery, and targeting, including the potential for nonviral vehicles such as liposomes, micelles, and dendrimers, which pose advantages over viral vectors in retinal drug delivery. Furthermore, we discuss current and future applications as surgical adjuncts and in regenerative medicine as they pertain to retinal disease. Structure and function of nanoparticles such as carbon nanotubules, quantum dots, and magnetic nanoparticles, as well as diagnostic technologies such as next-generation DNA sequencing and single-molecule bionanosensing, will also be discussed.

Gene-agnostic approaches to treating inherited retinal degenerations

Most patients with inherited retinal degenerations (IRDs) have been waiting for treatments that are "just around the corner" for decades, with only a handful of seminal breakthroughs happening in recent years. Highlighting the difficulties in the quest for curative therapeutics, Luxturna required 16 years of development before finally obtaining United States Food and Drug Administration (FDA) approval and its international equivalents. IRDs are both genetically and phenotypically heterogeneous. While this diversity offers many opportunities for gene-by-gene precision medicine-based approaches, it also poses a significant challenge. For this reason, alternative (or parallel) strategies to identify more comprehensive, across-the-board therapeutics for the genetically and phenotypically diverse IRD patient population are very appealing. Even when gene-specific approaches may be available and become approved for use, many patients may have reached a disease stage whereby these approaches may no longer be viable. Thus, alternate visual preservation or restoration therapeutic approaches are needed at these stages. In this review, we underscore several gene-agnostic approaches that are being developed as therapeutics for IRDs. From retinal supplementation to stem cell transplantation, optogenetic therapy and retinal prosthetics, these strategies would bypass at least in part the need for treating every individual gene or mutation or provide an invaluable complement to them. By considering the diverse patient population and treatment strategies suited for different stages and patterns of retinal degeneration, gene agnostic approaches are very well poised to impact favorably outcomes and prognosis for IRD patients.

ICG-mediated photodisruption of the inner limiting membrane enhances retinal drug delivery

Many groundbreaking therapies for the treatment of blindness require delivery of biologics or cells to the inner retina by intravitreal injection. Unfortunately, the advancement of these therapies is greatly hampered by delivery difficulties where obstruction of the therapeutics at the inner limiting membrane (ILM) represents the dominant bottleneck. In this proof-of-principle study, we explore an innovative light-based approach to locally ablate the ILM in a minimally invasive and highly controlled manner, thus making the ILM more permeable for therapeutics. More specifically, we demonstrate that pulsed laser irradiation of ILM-bound indocyanine green (ICG), a clinically applied ILM dye, results in the formation of vapor nanobubbles which can disrupt the bovine ILM as well as the extraordinary thick human ILM. We have observed that this photodisruption allows for highly successful retinal delivery of model nanoparticles which are otherwise blocked by the intact ILM. Strikingly, this treatment is furthermore able of enhancing the efficacy of mRNA-loaded lipid nanoparticles within the bovine retina by a factor of 5. In conclusion, this study provides evidence for a light-based approach to overcome the ILM which has the potential to improve the efficacy of all retinal therapies hampered by this delivery barrier.

The Landscape of Non-Viral Gene Augmentation Strategies for Inherited Retinal Diseases

Inherited retinal diseases (IRDs) are a heterogeneous group of disorders causing progressive loss of vision, affecting approximately one in 1000 people worldwide. Gene augmentation therapy, which typically involves using adeno-associated viral vectors for delivery of healthy gene copies to affected tissues, has shown great promise as a strategy for the treatment of IRDs. However, the use of viruses is associated with several limitations, including harmful immune responses, genome integration, and limited gene carrying capacity. Here, we review the advances in non-viral gene augmentation strategies, such as the use of plasmids with minimal bacterial backbones and scaffold/matrix attachment region (S/MAR) sequences, that have the capability to overcome these weaknesses by accommodating genes of any size and maintaining episomal transgene expression with a lower risk of eliciting an immune response. Low retinal transfection rates remain a limitation, but various strategies, including coupling the DNA with different types of chemical vehicles (nanoparticles) and the use of electrical methods such as iontophoresis and electrotransfection to aid cell entry, have shown promise in preclinical studies. Non-viral gene therapy may offer a safer and effective option for future treatment of IRDs.