Analysis of the retinal capillary plexus layers in a murine model with diabetic retinopathy: effect of intravitreal injection of human CD34+ bone marrow stem cells

Novel Therapeutic Approaches for Treatment of Diabetic Retinopathy and Age-Related Macular Degeneration

Retina, a light-sensitive layer of tissue of the eye, requires high levels of oxygen for its physiology. Retinal ischemia occurs due to inadequate supply of blood to the retina and choroid. Retinal ischemia is implicated in the development or progression of many ocular diseases, such as diabetic retinopathy (DR) and age-related macular degeneration (AMD). To date, anti-vascular endothelial growth factor (VEGF) treatment has been widely used to manage neovascular diseases associated with retinal ischemia. Nonetheless, a substantial number of patients with DR or AMD still suffer from incomplete response and adverse effects related to its therapy with limitations. Therefore, research scientists have been developing and finding novel treatments to protect against or prevent vision loss in those diseases. In this review article, we summarize the recent novel therapeutic approaches for the treatment of ischemic retinopathy (e.g., cell therapy, advanced molecular targeting, or drug delivery). This summary enables further research to obtain more solid evidence of novel effective drug development in retinal ischemic diseases.

Animal models for the evaluation of retinal stem cell therapies

Retinal degeneration (RD) diseases leading to severe vision loss can affect photoreceptors (PRs) that are responsible for phototransduction, or retinal pigmented epithelium (RPE) providing support for PRs. Human pluripotent stem cell (hPSC)-based therapies are a potential approach for restoration of retinal structure in patients with currently incurable RD diseases. Currently, there are two targeted hPSC therapeutics: PR rescue and PR replacement. PR rescue involves the transplantation of RPE or other neural progenitors into the subretinal space to slow down or prevent further RD. RPE transplantation plays a critical role in preserving photoreceptors by providing trophic support and maintaining retinal integrity, particularly in diseases like age-related macular degeneration (AMD). Advances in RPE transplantation methods, such as polarized monolayer cultures and scaffold-based approaches, have shown promise in enhancing graft survival and integration. However, limitations include inconsistent integration, variable neurotrophic factor secretion, and immune rejection risks in non-autologous transplants. In PR replacement, stem cell-derived photoreceptor-like cells or photoreceptor progenitors (PRP) obtained are transplanted into the eye. While PRPs are commonly obtained from retinal organoids (ROs), alternative sources, such as early differentiation stages or direct differentiation protocols, are also utilized to enhance the efficiency and scalability of PRP generation. Challenges include achieving proper integration, forming outer segments, rosette formation, and avoiding immune rejection or tumorigenicity. Various animal models that simulate human RD diseases are being used for establishing surgical feasibility, graft survival and visual functional recovery but fail to replicate clinical immune challenges. Rodent models lack macula-like structures and have limited reliability in detecting subtle functional changes, while larger animal models pose ethical, logistical, and financial challenges. Immunocompromised models have been developed for minimizing xenograft issues. Visual functional testing for efficacy includes optokinetic testing (OKN), electroretinography (ERG), and electrophysiological recordings from the retina and brain. These tests often fail to capture the complexity of human visual recovery, highlighting the need for advanced models and improved functional testing techniques. This review aims to aggregate current knowledge about approaches to stem cell transplantation, requirements of animal models chosen for validating vision benefits of transplantation studies, advantages of using specific disease models and their limitations. While promising strides have been made, addressing these limitations remains essential for translating stem cell-based therapies into clinical success.

Advancements in utilizing CD34+ stem cells for repairing diabetic vascular damage

Diabetes-related vascular damage is a frequent complication of diabetes that results in structural and functional impairment of blood vessels. This damage significantly heightens the risk of cardiovascular events. CD34+ stem cells have shown great potential in the treatment of diabetes-related vascular damage due to their differentiation and vascular repair capabilities. This article provides a review of the research hotspots on the role and mechanisms of CD34+ stem cells in the repair of diabetes-related vascular damage, including changes in cell quantity and function during diabetes, as well as the latest research on activating, protecting, or repairing these cells to prevent or treat vascular damage. The article also summarizes the impact of diabetes on the mobilization and function of CD34+ stem cells, emphasizing how diabetes negatively affects their ability to promote angiogenesis. These deficits can result in various complications, including issues with small blood vessels, coronary heart disease, foot problems, and retinal complications. On the clinical side, the article highlights the positive effects of CD34+ stem cell therapy in improving vascular function and tissue repair in diabetic patients, while also mentioning the inconsistencies in results between diabetes models and clinical studies, which necessitate further research to optimize treatment strategies. It emphasizes the importance of enhancing the mobilization, homing, and repair capabilities of CD34+ stem cells, as well as combining them with other treatment methods, to develop more effective strategies for treating diabetes-related vascular damage.

Future Directions in Diabetic Retinopathy Treatment: Stem Cell Therapy, Nanotechnology, and PPARα Modulation

This narrative review focuses on innovative treatment approaches to diabetic retinopathy to meet the urgent demand for advancements in managing both the early and late stages of the disease. Recent studies highlight the potential of adipose stem cells and their secreted factors in mitigating the retinal complications of diabetes, with promising results in improving visual acuity and reducing inflammation and angiogenesis in diabetic retinopathy. However, caution is warranted regarding the safety and long-term therapeutic effects of adipose stem cells transplantation. Bone marrow mesenchymal stem cells can also mitigate retinal damage in diabetic retinopathy. Studies demonstrate that bone marrow mesenchymal stem cells-derived exosomes can suppress the Wnt/β-catenin pathway, reducing oxidative stress, inflammation, and angiogenesis in the diabetic retina, offering promise for future diabetic retinopathy treatments. Nanotechnology has the ability to precisely target the retina and minimize systemic side effects. Nanoparticles and nanocarriers offer improved bioavailability, sustained release of therapeutics, and potential for synergistic effects. They can be a new way of effective treatment and prevention of diabetic retinopathy. Activation and modulation of PPARα as a means for diabetic retinopathy treatment has been widely investigated in recent years and demonstrated promising effects in clinical trials. PPARα activation turned out to be a promising therapeutic method for treating dyslipidemia, inflammation, and insulin sensitivity. The combination of PPARα modulators with small molecules offers an interesting perspective for retinal diseases' therapy.

Clinical-grade human embryonic stem cell-derived mesenchymal stromal cells ameliorate diabetic retinopathy in db/db mice

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) hold great promise in the treatment of diabetic retinopathy (DR), as evidenced by increasing preclinical and clinical studies. However, the absence of standardized and industrialized clinical-grade donor cells hampers the continued development and large-scale clinical application of MSCs-based therapies for DR. Previously, we have identified a unique population of MSCs generated from a clinical-grade human embryonic stem cell (hESC) line under Good Manufacturing Practice conditions that could be a potential source to address the issues. Here, we investigated the therapeutic potential of the clinical-grade hESC line-derived MSCs (hESC-MSCs) on db/db mice with DR.

METHODS

hESC-MSCs were initially characterized by morphological assessment, flow cytometry analysis and trilineage differentiation assays. These cells (5 × 106 cells) were then transplanted intravenously into 12-week-old db/db mice via tail vein, with phosphate-buffered saline transplantation and untreated groups used as controls. The retinal alterations in neural functions and microvascular perfusions, and inflammatory responses in peripheral blood and retina were evaluated at 4 and 6 weeks after transplantation using electroretinography, optical coherence tomography angiography and flow cytometry, respectively. Body weight and fasting blood glucose (FBG) levels were also measured to investigate their systemic implications.

RESULTS

Compared with controls, intravenous transplantation of hESC-MSCs could significantly: (i) enhance impaired retinal electroretinography functions (including amplitudes of a-, b-wave and oscillatory potentials) at 4 weeks after transplantation; (ii) alleviate microvascular dysfunctions, especially in the inner retina with significance (including reducing non-perfusion area and increasing vascular area density) at 4 weeks after transplantation; (iii) decrease FBG levels at 4 weeks after transplantation and induce weight loss up to 6 weeks after transplantation and (iv) increase both peripheral blood and retinal interleukin-10 levels at 4 weeks after transplantation and modulate peripheral blood inflammatory cytokines and chemokines levels, such as monocyte chemotactic protein-1, up to 6 weeks after transplantation.

CONCLUSIONS

The findings of our study indicated that intravenous transplantation of hESC-MSCs ameliorated retinal neural and microvascular dysfunctions, regulated body weight and FBG and modulated peripheral blood and retinal inflammation responses in a mouse model of DR. These results suggest that hESC-MSCs could be a potentially effective clinical-grade cell source for the treatment of DR.

Advances in cell therapies using stem cells/progenitors as a novel approach for neurovascular repair of the diabetic retina

BACKGROUND

Diabetic retinopathy, a major complication of diabetes mellitus, is a leading cause of sigh-loss in working age adults. Progressive loss of integrity of the retinal neurovascular unit is a central element in the disease pathogenesis. Retinal ischemia and inflammatory processes drive interrelated pathologies such as blood retinal barrier disruption, fluid accumulation, gliosis, neuronal loss and/or aberrant neovascularisation. Current treatment options are somewhat limited to late-stages of the disease where there is already significant damage to the retinal architecture arising from degenerative, edematous and proliferative pathology. New preventive and interventional treatments to target early vasodegenerative and neurodegenerative stages of the disease are needed to ensure avoidance of sight-loss.

MAIN BODY

Historically, diabetic retinopathy has been considered a primarily microvascular disease of the retina and clinically it is classified based on the presence and severity of vascular lesions. It is now known that neurodegeneration plays a significant role during the pathogenesis. Loss of neurons has been documented at early stages in pre-clinical models as well as in individuals with diabetes and, in some, even prior to the onset of clinically overt diabetic retinopathy. Recent studies suggest that some patients have a primarily neurodegenerative phenotype. Retinal pigment epithelial cells and the choroid are also affected during the disease pathogenesis and these tissues may also need to be addressed by new regenerative treatments. Most stem cell research for diabetic retinopathy to date has focused on addressing vasculopathy. Pre-clinical and clinical studies aiming to restore damaged vasculature using vasoactive progenitors including mesenchymal stromal/stem cells, adipose stem cells, CD34+ cells, endothelial colony forming cells and induced pluripotent stem cell derived endothelial cells are discussed in this review. Stem cells that could replace dying neurons such as retinal progenitor cells, pluripotent stem cell derived photoreceptors and ganglion cells as well as Müller stem cells are also discussed. Finally, challenges of stem cell therapies relevant to diabetic retinopathy are considered.

CONCLUSION

Stem cell therapies hold great potential to replace dying cells during early and even late stages of diabetic retinopathy. However, due to the presence of different phenotypes, selecting the most suitable stem cell product for individual patients will be crucial for successful treatment.

Experiment-Based Interventions to Diabetic Retinopathy: Present and Advances

Diabetic retinopathy is the major blinding disease among working-age populations, which is becoming more significant due to the growth of diabetes. The metabolic-induced oxidative and inflammatory stress leads to the insult of neovascular unit, resulting in the core pathophysiology of diabetic retinopathy. Existing therapies focus on the inflammation, oxidation, and angiogenesis phenomena of diabetic retinopathy, without effect to radically cure the disease. This review also summarizes novel therapeutic attempts for diabetic retinopathy along with their advantages and disadvantages, mainly focusing on those using cellular and genetic techniques to achieve remission on a fundamental level of disease.