Structure/function studies and the effects of memantine in monkeys with experimental glaucoma

Human umbilical cord mesenchymal stem cells derived-exosomes in diseases treatment

Exosomes are extracellular vesicles with the size of 40-100 nm in diameter and a density of 1.13-1.19 g/mL, containing proteins, mRNAs, miRNAs, and DNAs. Exosomes change the recipient cells biochemical features through biomolecules delivery and play a role in cellular communication. These vesicles are produced from body fluids and different cell types like mesenchymal stem cells (MSCs). Evidence suggests that mesenchymal stem cells-derived exosome (MSC-EXO) exhibit functions similar to MSCs with low immunogenicity and no tumorization. MSCs can also be isolated from a variety of sources including human umbilical cord (HUC). Because of the non-invasive collection method, higher proliferation and lower immunogenicity, HUCMSC-EXO has been frequently used in regenerative medicine and various diseases treatment compared to the other MSC-EXO resources. This review aimed to investigate the applications of HUCMSC-EXO in different diseases.

Hydrogen sulfide supplement attenuates the apoptosis of retinal ganglion cells in experimental glaucoma

Glaucoma is a group of neurodegenerative eye diseases characterized by progressive impairment of visual function due to loss of retinal ganglion cells (RGC). As hydrogen sulfide (H₂S) was reported to play a role in the process of glaucomatous neuropathy and improve RGC survival in experimental glaucoma, the authors aimed to investigate the anti-apoptosis effect of H₂S supplement in a rat glaucoma model, and further tried to explore the involved factors in the neuroprotection. A chronic ocular hypertension (COH) rat model induced by intracameral injection of cross-linking hydrogel was employed to simulate glaucoma and 288 rats were subjected to experimental procedures in the present study. After 4 weeks of sodium hydrosulfide (NaHS) administration following COH induction, the apoptosis of RGC isolated from experimented rats as well as apoptosis of neurons in ganglion cell layer (GCL), intrinsic apoptotic pathway activity, mitochondrial function, glial activation, NF-κB pathway activity, NADPH oxidase activity, autophagy activity and TNF-α level in retina were evaluated. The results showed that H₂S supplement effectively attenuated the apoptosis of RGC in experimental glaucoma, and the neuroprotection by H₂S might correlate with preservation of mitochondrial function, attenuation of oxidative stress, suppression of glial activation, inhibition of inflammatory pathways and downregulation of autophagy. Our study indicated that H₂S supplement resulted in significant neuroprotection through attenuation of RGC apoptosis which might be linked with multiple factors in experimental glaucoma. The new therapeutic strategy might potentially contribute to benefit glaucoma treatment, which is worth further concerns.

Memantine-Loaded PEGylated Biodegradable Nanoparticles for the Treatment of Glaucoma

Glaucoma is a multifactorial neurodegenerative disease associated with retinal ganglion cells (RGC) loss. Increasing reports of similarities in glaucoma and other neurodegenerative conditions have led to speculation that therapies for brain neurodegenerative disorders may also have potential as glaucoma therapies. Memantine is an N-methyl-d-aspartate (NMDA) antagonist approved for Alzheimer's disease treatment. Glutamate-induced excitotoxicity is implicated in glaucoma and NMDA receptor antagonism is advocated as a potential strategy for RGC preservation. This study describes the development of a topical formulation of memantine-loaded PLGA-PEG nanoparticles (MEM-NP) and investigates the efficacy of this formulation using a well-established glaucoma model. MEM-NPs <200 nm in diameter and incorporating 4 mg mL^-1 of memantine were prepared with 0.35 mg mL^-1 localized to the aqueous interior. In vitro assessment indicated sustained release from MEM-NPs and ex vivo ocular permeation studies demonstrated enhanced delivery. MEM-NPs were additionally found to be well tolerated in vitro (human retinoblastoma cells) and in vivo (Draize test). Finally, when applied topically in a rodent model of ocular hypertension for three weeks, MEM-NP eye drops were found to significantly (p < 0.0001) reduce RGC loss. These results suggest that topical MEM-NP is safe, well tolerated, and, most promisingly, neuroprotective in an experimental glaucoma model.

[EFFECT OF NMDA-RECEPTOR BLOCKERS ON THE DYNAMICS OF INTRAOCULAR PRESSURE IN RABBITS]

Experiments on rabbits with a model of acute temporary ocular hypertension created by intragastric administration of water (100 ml/kg) have been performed. It was found that intravenous administration or instillation into the eye of blocker of NMDA-receptor 1-adamantylethyloxy-3-morpholino-2- propanol hydrochloride (Ademol) unlike amantadine sulfate results in a significant decrease in intraocular pressure (IOP). It was also discovered that such ocular hypotensive effect takes place in animals with unchanged ophthalmotonus. Taking into account neuroretinoprotective and hypotensive ocular hypotensive properties of Ademol this drug appears to be perspective in the treatment of ischemic disorders of the retina and optic nerve, especially under the conditions of increased IOP.

Exosomes derived from MSCs ameliorate retinal laser injury partially by inhibition of MCP-1

Although accumulated evidence supports the notion that mesenchymal stem cells (MSCs) act in a paracrine manner, the mechanisms are still not fully understood. Recently, MSC-derived exosomes (MSC-Exos), a type of microvesicle released from MSCs, were thought to carry functional proteins and RNAs to recipient cells and play therapeutic roles. In the present study, we intravitreally injected MSCs derived from either mouse adipose tissue or human umbilical cord, and their exosomes to observe and compare their functions in a mouse model of laser-induced retinal injury. We found that both MSCs and their exosomes reduced damage, inhibited apoptosis, and suppressed inflammatory responses to obtain better visual function to nearly the same extent in vivo. Obvious down-regulation of monocyte chemotactic protein (MCP)-1 in the retina was found after MSC-Exos injection. In vitro, MSC-Exos also down-regulated MCP-1 mRNA expression in primarily cultured retinal cells after thermal injury. It was further demonstrated that intravitreal injection of an MCP-1-neutralizing antibody promoted the recovery of retinal laser injury, whereas the therapeutic effect of exosomes was abolished when MSC-Exos and MCP-1 were administrated simultaneously. Collectively, these results suggest that MSC-Exos ameliorate laser-induced retinal injury partially through down-regulation of MCP-1.

Neuroprotective Effects of Memantine in the Retina of Glaucomatous Rats: An Electron Microscopic Study

Purpose:

In this experimental study, the effects of systemic memantine administration on the retinal ultrastructure of experimentally induced glaucomatous rats were investigated.

Methods:

Twenty-four Wistar albino rats were included in this study. Glaucoma was induced by injecting sodium hyaluronate into the anterior chamber of the rats for a period of three weeks. As a control, 8 rats were sham treated (Group C). Glaucoma induced animals were divided into two groups; Group M (n = 8) received a single daily dose of 10 mg/kg memantine, and Group G received the same volume of saline (n = 8), via intraperitoneal route for a period of six weeks, starting with the induction of glaucoma. Then, all rats were sacrificed and the retinas were prepared for electron microscopic examination. Electron microscopic damage findings were graded between 0 and 4 and mean damage scores for each cell or layer was calculated for each group. Statistical comparison was made between group G and group M.

Results:

Including the photoreceptor cells, marked ultrastructural changes were observed in the retinas of the animals in group G. The ultrastructural changes in group M were modest and there was no significant cell death. Statistical findings indicated these results.

Conclusion:

Results of the present study suggest that memantine treatment, when started in the early phase of glaucomatous process, may help to preserve the retinal ultrastructure and thus prevent neuronal injury in experimentally induced glaucoma.

Current perspective of neuroprotection and glaucoma

Glaucoma is the second leading cause of blindness worldwide and is most notably characterized by progressive optic nerve atrophy and advancing loss of retinal ganglion cells (RGCs). The main concomitant factor is the elevated intraocular pressure (IOP). Existing treatments are focused generally on lowering IOP. However, both RGC loss and optic nerve atrophy can independently occur with IOP at normal levels. In recent years, there has been substantial progress in the development of neuroprotective therapies for glaucoma in order to restore vital visual function. The present review intends to offer a brief insight into conventional glaucoma treatments and discuss exciting current developments of mostly preclinical data in novel neuroprotective strategies for glaucoma that include recent advances in noninvasive diagnostics going beyond IOP maintenance for an enhanced global view. Such strategies now target RGC loss and optic nerve damage, opening a critical therapeutic window for preventative monitoring and treatment.

Relating Retinal Ganglion Cell Function and Retinal Nerve Fiber Layer (RNFL) Retardance to Progressive Loss of RNFL Thickness and Optic Nerve Axons in Experimental Glaucoma

PURPOSE

To relate changes in retinal function and retinal nerve fiber layer (RNFL) retardance to loss of RNFL thickness and optic nerve axon counts in a nonhuman primate (NHP) model of experimental glaucoma (EG).

METHODS

Bilateral longitudinal measurements of peripapillary RNFL thickness (spectral-domain optical coherence tomography, SDOCT; Spectralis), retardance (GDxVCC), and multifocal electroretinography (mfERG; VERIS) were performed in 39 NHP at baseline (BL; median, 5 recordings; range, 3-10) and weekly after induction of unilateral EG by laser photocoagulation of the trabecular meshwork. Multifocal ERG responses were high-pass filtered (>75 Hz) to measure high- and low-frequency component (HFC and LFC) amplitudes, including LFC features N1, P1, and N2. High-frequency component amplitudes are known to specifically reflect retinal ganglion cell (RGC) function. Complete (100%) axon counts of orbital optic nerves were obtained in 31/39 NHP.

RESULTS

Postlaser follow-up was 10.4 ± 7.9 months; mean and peak IOP were 18 ± 5 and 41 ± 11 mm Hg in EG eyes, 11 ± 2 and 18 ± 6 mm Hg in control (CTL) eyes. At the final available time point, RNFL thickness had decreased from BL by 14 ± 14%, retardance by 20 ± 11%, and the mfERG HFC by 30 ± 17% (P < 0.0001 each). Longitudinal changes in retardance and HFC were linearly related to RNFL thickness change (R2 = 0.51, P < 0.0001 and R2 = 0.22, P = 0.002, respectively); LFC N2 was weakly related but N1 or P2 (N1: R2 = 0.07, P = 0.11; P1: R2 = 0.04, P = 0.24; N2: R2 = 0.13, P = 0.02). At zero change from BL for RNFL thickness (Y-intercept), retardance was reduced by 11% (95% confidence interval [CI]: -15.3% to -6.8%) and HFC by 21.5% (95% CI: -28.7% to -14.3%). Relative loss of RNFL thickness, retardance, and HFC (EG:CTL) were each related to axon loss (R2 = 0.66, P < 0.0001; R2 = 0.42, P < 0.0001; R2 = 0.42, P < 0.0001, respectively), but only retardance and HFC were significantly reduced at zero relative axon loss (Y-intercept; retardance: -9.4%, 95% CI: -15.5% to -3.4%; HFC: -10.9%, 95% CI: -18.6% to -3.2%; RNFL thickness: +1.8%, 95% CI: -4.9% to +5.4%).

CONCLUSIONS

Retinal nerve fiber layer retardance and RGC function exhibit progressive loss from baseline before any loss of RNFL thickness or orbital optic nerve axons occurs in NHP EG. These in vivo measures might serve as potential biomarkers of early-stage glaucomatous damage preceding axon loss and RGC death.

The non-human primate experimental glaucoma model

The purpose of this report is to summarize the current strengths and weaknesses of the non-human primate (NHP) experimental glaucoma (EG) model through sections devoted to its history, methods, important findings, alternative optic neuropathy models and future directions. NHP EG has become well established for studying human glaucoma in part because the NHP optic nerve head (ONH) shares a close anatomic association with the human ONH and because it provides the only means of systematically studying the very earliest visual system responses to chronic intraocular pressure (IOP) elevation, i.e. the conversion from ocular hypertension to glaucomatous damage. However, NHPs are impractical for studies that require large animal numbers, demonstrate spontaneous glaucoma only rarely, do not currently provide a model of the neuropathy at normal levels of IOP, and cannot easily be genetically manipulated, except through tissue-specific, viral vectors. The goal of this summary is to direct NHP EG and non-NHP EG investigators to the previous, current and future accomplishment of clinically relevant knowledge in this model.