Trans-Ocular Electric Current In Vivo Enhances AAV-Mediated Retinal Transduction in Large Animal Eye After Intravitreal Vector Administration

External stimuli-responsive drug delivery to the posterior segment of the eye

Posterior segment eye diseases represent the leading causes of vision impairment and blindness globally. Current therapies still have notable drawbacks, including the need for frequent invasive injections and the associated risks of severe ocular complications. Recently, the utility of external stimuli, such as light, ultrasound, magnetic field, and electric field, has been noted as a promising strategy to enhance drug delivery to the posterior segment of the eye. In this review, we briefly summarize the main physiological barriers against ocular drug delivery, focusing primarily on the recent advancements that utilize external stimuli to improve treatment outcomes for posterior segment eye diseases. The advantages of these external stimuli-responsive drug delivery strategies are discussed, with illustrative examples highlighting improved tissue penetration, enhanced control over drug release, and targeted drug delivery to ocular lesions through minimally invasive routes. Finally, we discuss the challenges and future perspectives in the translational research of external stimuli-responsive drug delivery platforms, aiming to bridge existing gaps toward clinical use.

Toward successful retinal drug delivery after intravitreal injection: Current strategies to overcome the inner limiting membrane

The global prevalence of retinal disorders leading to vision impairment and blindness is rising to significant numbers and is estimated to continuously increase in the coming years. Although many groundbreaking therapies are available in the expanding field of retinal gene and cell therapy, troublesome delivery after intravitreal (IVT) injection is currently complicating their clinical translation. In this regard, the inner limiting membrane (ILM), the basement membrane located between the vitreous and the retina, is recognized as the main obstacle hindering retinal entry. Overcoming this barrier might hence advance a plethora of potent therapeutics currently available but failing to enter the retina. Aware of the importance to address this drug delivery issue, this review will discuss the current proposed methods to tackle the ILM barrier. First, we will provide an overview of ILM characteristics in health and disease after which we will reflect on the relevance of the ILM barrier role for emerging advanced therapeutic strategies. Seeing the significance of ILM removal for those therapeutics, the current proposed surgical, pharmacological and physical strategies to bypass the ILM will furthermore be highlighted to encourage the entire field of retinal drug delivery after IVT injection forward.

Successful transduction of target gene mediated by adeno-associated virus 2 into lens epithelial cells in rats

The Adeno-Associated Virus (AAV) has emerged as a promising candidate for delivery of genetic material, exhibiting significant potential in various clinical applications. Although multiple AAV serotypes have been shown to transduce ocular tissues, there have been few studies of AAV transduction of lens epithelial cells (LECs) in the ocular. In this study, we compared the efficiency of intravitreal injection of six AAV serotypes (AAV2, AAV5, AAV6, AAV8, AAV9, and AAVDJ) to transduce lens and retina in rats, The expression and localization of the reporter gene ZsGreen in the lens and retina were examined using immunofluorescence staining, and the relative expression of ZsGreen mRNA was detected using RT-qPCR. Our results demonstrated that AAV2 had the highest efficiency in transducing LECs. All six AAV serotypes could transduce the retina. To validate this observation, we further constructed an AAV2 vector with exogenous gene senescence marker protein 30 (SMP30) and performed intravitreal injection to successfully overexpress SMP30 in LECs of rats. our results provide a basis for the use of AAV vector-mediated gene therapy for lens diseases.

Bruch's Membrane: A Key Consideration with Complement-Based Therapies for Age-Related Macular Degeneration

The complement system is crucial for immune surveillance, providing the body's first line of defence against pathogens. However, an imbalance in its regulators can lead to inappropriate overactivation, resulting in diseases such as age-related macular degeneration (AMD), a leading cause of irreversible blindness globally affecting around 200 million people. Complement activation in AMD is believed to begin in the choriocapillaris, but it also plays a critical role in the subretinal and retinal pigment epithelium (RPE) spaces. Bruch's membrane (BrM) acts as a barrier between the retina/RPE and choroid, hindering complement protein diffusion. This impediment increases with age and AMD, leading to compartmentalisation of complement activation. In this review, we comprehensively examine the structure and function of BrM, including its age-related changes visible through in vivo imaging, and the consequences of complement dysfunction on AMD pathogenesis. We also explore the potential and limitations of various delivery routes (systemic, intravitreal, subretinal, and suprachoroidal) for safe and effective delivery of conventional and gene therapy-based complement inhibitors to treat AMD. Further research is needed to understand the diffusion of complement proteins across BrM and optimise therapeutic delivery to the retina.

Gene Therapy to the Retina and the Cochlea

Vision and hearing disorders comprise the most common sensory disorders found in people. Many forms of vision and hearing loss are inherited and current treatments only provide patients with temporary or partial relief. As a result, developing genetic therapies for any of the several hundred known causative genes underlying inherited retinal and cochlear disorders has been of great interest. Recent exciting advances in gene therapy have shown promise for the clinical treatment of inherited retinal diseases, and while clinical gene therapies for cochlear disease are not yet available, research in the last several years has resulted in significant advancement in preclinical development for gene delivery to the cochlea. Furthermore, the development of somatic targeted genome editing using CRISPR/Cas9 has brought new possibilities for the treatment of dominant or gain-of-function disease. Here we discuss the current state of gene therapy for inherited diseases of the retina and cochlea with an eye toward areas that still need additional development.

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.