The Future of Stem Cells and Their Derivates in the Treatment of Glaucoma. A Critical Point of View

Future directions of glaucoma treatment: emerging gene, neuroprotection, nanomedicine, stem cell, and vascular therapies

PURPOSE OF REVIEW

The aim of this article is to summarize current research on novel gene, stem cell, neuroprotective, nanomedicine, and vascular therapies for glaucoma.

RECENT FINDINGS

Gene therapy using viral vectors and siRNA have been shown to reduce intraocular pressure by altering outflow and production of aqueous humor, to reduce postsurgical fibrosis with few adverse effects, and to increase retinal ganglion cell (RGC) survival in animal studies. Stem cells may treat glaucoma by replacing or stimulating proliferation of trabecular meshwork cells, thus restoring outflow facility. Stem cells can also serve a neuroprotective effect by differentiating into RGCs or preventing RGC loss via secretion of growth factors. Other developing neuroprotective glaucoma treatments which can prevent RGC death include nicotinamide, the NT-501 implant which secretes ciliary neurotrophic factor, and a Fas-L inhibitor which are now being tested in clinical trials. Recent studies on vascular therapy for glaucoma have focused on the ability of Rho Kinase inhibitors and dronabinol to increase ocular blood flow.

SUMMARY

Many novel stem cell, gene, neuroprotective, nanomedicine, and vascular therapies have shown promise in preclinical studies, but further clinical trials are needed to demonstrate safety and efficacy in human glaucomatous eyes. Although likely many years off, future glaucoma therapy may take a multifaceted approach.

Electrical, Electromagnetic, Ultrasound Wave Therapies, and Electronic Implants for Neuronal Rejuvenation, Neuroprotection, Axonal Regeneration, and IOP Reduction

The peripheral nervous system (PNS) of mammals and nervous systems of lower organisms possess significant regenerative potential. In contrast, although neural plasticity can provide some compensation, the central nervous system (CNS) neurons and nerves of adult mammals generally fail to regenerate after an injury or damage. However, use of diverse electrical, electromagnetic and sonographic energy waves are illuminating novel ways to stimulate neuronal differentiation, proliferation, neurite growth, and axonal elongation/regeneration leading to various levels of functional recovery in animals and humans afflicted with disorders of the CNS, PNS, retina, and optic nerve. Tools such as acupuncture, electroacupuncture, electroshock therapy, electrical stimulation, transcranial magnetic stimulation, red light therapy, and low-intensity pulsed ultrasound therapy are demonstrating efficacy in treating many different maladies. These include wound healing, partial recovery from motor dysfunctions, recovery from ischemic/reperfusion insults and CNS and ocular remyelination, retinal ganglion cell (RGC) rejuvenation, and RGC axonal regeneration. Neural rejuvenation and axonal growth/regeneration processes involve activation or intensifying of the intrinsic bioelectric waves (action potentials) that exist in every neuronal circuit of the body. In addition, reparative factors released at the nerve terminals and via neuronal dendrites (transmitter substances), extracellular vesicles containing microRNAs and neurotrophins, and intercellular communication occurring via nanotubes aid in reestablishing lost or damaged connections between the traumatized tissues and the PNS and CNS. Many other beneficial effects of the aforementioned treatment paradigms are mediated via gene expression alterations such as downregulation of inflammatory and death-signal genes and upregulation of neuroprotective and cytoprotective genes. These varied techniques and technologies will be described and discussed covering cell-based and animal model-based studies. Data from clinical applications and linkage to human ocular diseases will also be discussed where relevant translational research has been reported.

A bibliometric analysis of the application of stem cells in glaucoma research from 1999 to 2022

Background: Glaucoma, a neurodegenerative disease of the retina, is the leading cause of irreversible blindness. Stem cells have therapeutic potential for glaucoma. However, few bibliometric studies have been published in this field. Concerning a visual map, this article aims to characterize the research context, cooperation relationship, hotspots, and trends concerning the application of stem cells in glaucoma research. Methods: Publications focusing on stem cell research and glaucoma were retrieved from the Web of Science Core Collection. VOSviewer, CiteSpace, Microsoft Excel, and Scimago Graphica were used to map the contributions of countries or regions, authors, organizations, and journals. Journal Impact Factor data were obtained from the Web of Science Core Collection. We analyzed the tendencies, hotspots, and knowledge networks using VOSviewer, and CiteSpace. Results: We analyzed 518 articles published from 1999 through 2022. In the first decade, the number of articles in this field increased slowly, and there was a marked acceleration in publication frequency after 2010. The United States, China, and England were the main contributors. Yiqin Du was the most prolific author, and among the top 10 prolific writers, Keith R. Martin's work was cited most frequently. Investigative Ophthalmology and Visual Science, Experimental Eye Research, and Cornea published the most articles in this domain. The three most commonly co-cited journals were Investigative Ophthalmology and Visual Science, Experimental Eye Research, and Proceedings of the National Academy of Sciences of the United States of America. The Central South University, the University of Pittsburgh, and the National Institutes of Health National Eye Institute were highly prolific institutions in this research area. Our keywords analysis with VOSviewer suggested directions of future research and yielded the following recent key themes, extracellular vesicles, exosomes, mitochondria, growth factors, oxidative stress, and ocular diseases. Four co-cited references had a citation burst duration until 2022. Conclusion: With improvements in overall quality of life and demographic transitions toward population aging, research and clinical focus on eye care has increased, with glaucoma as a key area of emphasis. This study added to our understanding of the global landscape and Frontier hotspots in this field.

Optic Neuritis in Multiple Sclerosis—A Review of Molecular Mechanisms Involved in the Degenerative Process

Multiple sclerosis is a central nervous system inflammatory demyelinating disease with a wide range of clinical symptoms, ocular involvement being frequently marked by the presence of optic neuritis (ON). The emergence and progression of ON in multiple sclerosis is based on various pathophysiological mechanisms, disease progression being secondary to inflammation, demyelination, or axonal degeneration. Early identification of changes associated with axonal degeneration or further investigation of the molecular processes underlying remyelination are current concerns of researchers in the field in view of the associated therapeutic potential. This article aims to review and summarize the scientific literature related to the main molecular mechanisms involved in defining ON as well as to analyze existing data in the literature on remyelination strategies in ON and their impact on long-term prognosis.

Evaluation of neuroprotective and immunomodulatory properties of mesenchymal stem cells in an ex vivo retinal explant model

BACKGROUND

Glaucoma is a blinding degenerative neuropathy in which the death of retinal ganglion cells (RGCs) causes progressive loss of visual field and eventually vision. Neuroinflammation appears to be a key event in the progression and spread of this disease. Thus, microglial immunomodulation represents a promising therapeutic approach in which mesenchymal stem cells (MSCs) might play a crucial role. Their neuroprotective and regenerative potentials have already raised hope in animal models. Yet no definitive treatment has been developed, and some safety concerns have been reported in human trials. In the present study, we investigated the neuroprotective and immunomodulatory properties as well as the safety of MSCs in an ex vivo neuroretina explant model.

METHODS

Labeled rat bone marrow MSCs were placed in coculture with rat retinal explants after optic nerve axotomy. We analyzed the neuroprotective effect of MSCs on RGC survival by immunofluorescence using RBPMS, Brn3a, and NeuN markers. Gliosis and retinal microglial activation were measured by using GFAP, CD68, and ITGAM mRNA quantification and GFAP, CD68, and Iba1 immunofluorescence stainings. We also analyzed the mRNA expression of both 'M1' or classically activated state inflammatory cytokines (TNFα, IL1β, and IL6), and 'M2' or alternatively activated state microglial markers (Arginase 1, IL10, CD163, and TNFAIP6).

RESULTS

The number of RGCs was significantly higher in retinal explants cultured with MSCs compared to the control group at Day 7 following the optic nerve axotomy. Retinal explants cultured with MSCs showed a decrease in mRNA markers of gliosis and microglial activations, and immunostainings revealed that GFAP, Iba1, and CD68 were limited to the inner layers of the retina compared to controls in which microglial activation was observed throughout the retina. In addition, MSCs inhibited the M1 phenotype of the microglia. However, edema of the explants was observed in presence of MSCs, with an increase in fibronectin labeling at the surface of the explant corresponding to an epiretinal membrane-like phenotype.

CONCLUSION

Using an ex vivo neuroretina model, we demonstrated a neuroprotective and immunomodulatory effect of MSCs on RGCs. Unfortunately, the presence of MSCs also led to explant edema and epiretinal membrane formation, as described in human trials. Using the MSC secretome might offer the beneficial effects of MSCs without their potential adverse effects, through paracrine signaling.