Eye Drops of Metformin Prevents Fibrosis After Glaucoma Filtration Surgery in Rats via Activating AMPK/Nrf2 Signaling Pathway

M2 macrophages promote subconjunctival fibrosis through YAP/TAZ signalling

PURPOSE

To evaluate the role of M2 macrophages in subconjunctival fibrosis after silicone implantation (SI) and investigate the underlying mechanisms.

MATERIALS AND METHODS

A model of subconjunctival fibrosis was established by SI surgery in rabbit eyes. M2 distribution and collagen deposition were evaluated by histopathology. The effects of M2 cells on the migration (using wound-scratch assay) and activation (by immunofluorescence and western blotting) of human Tenon's fibroblasts (HTFs) were investigated.

RESULTS

There were more M2 macrophages (CD68+/CD206+ cells) occurring in tissue samples around silicone implant at 2 weeks postoperatively. Dense collagen deposition was observed at 8 weeks after SI. In vitro experiment showed M2 expressed high level of CD206 and transforming growth factor-β1 (TGF-β1). The M2-conditioned medium promoted HTFs migration and the synthesis of collagen I and fibronectin. Meanwhile, M2-conditioned medium increased the protein levels of TGF-β1, TGF-βR II, p-Smad2/3, yes-associated protein (YAP), and transcriptional coactivator with PDZ-binding motif (TAZ). Verteporfin, a YAP inhibitor, suppressedTGF-β1/Smad2/3-YAP/TAZ pathway and attenuated M2-induced extracellular matrix deposition by HTFs.

CONCLUSIONS

TGF-β1/Smad2/3-YAP/TAZ signalling may be involved in M2-induced fibrotic activities in HTFs. M2 plays a key role in promoting subconjunctival fibrosis and can serve as an attractive target for anti-fibrotic therapeutics.

17β-estradiol inhibits TGF-β-induced collagen gel contraction mediated by human Tenon fibroblasts via Smads and MAPK signaling pathways

AIM

To investigate the impact of 17β-estradiol on the collagen gels contraction (CGC) and inflammation induced by transforming growth factor (TGF)-β in human Tenon fibroblasts (HTFs).

METHODS

HTFs were three-dimensionally cultivated in type I collagen-generated gels with or without TGF-β (5 ng/mL), 17β-estradiol (12.5 to 100 µmol/L), or progesterone (12.5 to 100 µmol/L). Then, the collagen gel diameter was determined to assess the contraction, and the development of stress fibers was analyzed using immunofluorescence staining. Immunoblot and gelatin zymography assays were used to analyze matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) being released into culture supernatants. Enzyme-linked immunosorbent assay (ELISA) and reverse transcription-quantitative polymerase chain reaction (RT-PCR) were used to detect interleukin (IL)-6, monocyte chemoattractant proteins (MCP)-1, and vascular endothelial growth factor (VEGF) in HTFs at the translational and transcriptional levels. The phosphorylation levels of Sma- and Mad-related proteins (Smads), mitogen-activated protein kinases (MAPKs), and protein kinase B (AKT) were measured by immunoblotting. Statistical analysis was performed using either the Tukey-Kramer test or Student's unpaired t-test to compare the various treatments.

RESULTS

The CGC caused by TGF-β in HTFs was significantly inhibited by 17β-estradiol (25 to 100 µmol/L), and a statistically significant difference was observed when comparing the normal control group with 17β-estradiol concentrations exceeding 25 µmol/L (P<0.05). The suppressive impact of 17β-estradiol became evident 24h after administration and peaked at 72h (P<0.05), whereas progesterone had no impact. Moreover, 17β-estradiol attenuated the formation of stress fibers, and the production of MMP-3 and MMP-1 in HTFs stimulated by TGF-β. The expression of MCP-1, IL-6, and VEGF mRNA and protein in HTFs were suppressed by 100 µmol/L 17β-estradiol (P<0.01). Additionally, the phosphorylation of Smad2 Smad3, p38, and extracellular signal-regulated kinase (ERK) were downregulated (P <0.01).

CONCLUSION

17β-estradiol significantly inhibits the CGC and inflammation caused by TGF-β in HTFs. This inhibition is likely related to the suppression of stress fibers, inhibition of MMPs, and attenuation of Smads and MAPK (ERK and p38) signaling. 17β-estradiol may have potential clinical benefits in preventing scar development and inflammation in the conjunctiva.

Ocular Delivery of Metformin for Sustained Release and in Vivo Efficacy

Metformin is known to lower inflammation, independent of its anti-diabetic action. Thus, topical metformin can be a therapeutic strategy for managing ocular inflammation associated with diabetes. To achieve this and address the issues of ocular retention and controlled release an in situ gel of metformin was developed. The formulations were prepared using sodium hyaluronate, hypromellose, and gellan gum. The composition was optimized by monitoring gelling time/capacity, viscosity, and mucoadhesion. MF5 was selected as the optimized formulation. It showed both chemical and physiological compatibility. It was found to be sterile and stable. MF5 exhibited sustained release of metformin for 8h that fitted best with zero-order kinetics. Further, the release mode was found to be close to the Korsmeyer-Peppas model. Supported by an ex vivo permeation study, it showed potential for prolonged action. It showed a significant reduction in ocular inflammation that was comparable to that of the standard drug. MF5 shows translational potential as a safe alternative to steroids for managing ocular inflammation.

Immunomodulatory and Antioxidant Drugs in Glaucoma Treatment

Glaucoma, a group of diseases characterized by progressive retinal ganglion cell loss, cupping of the optic disc, and a typical pattern of visual field defects, is a leading cause of severe visual impairment and blindness worldwide. Elevated intraocular pressure (IOP) is the leading risk factor for glaucoma development. However, glaucoma can also develop at normal pressure levels. An increased susceptibility of retinal ganglion cells to IOP, systemic vascular dysregulation, endothelial dysfunction, and autoimmune imbalances have been suggested as playing a role in the pathophysiology of normal-tension glaucoma. Since inflammation and oxidative stress play a role in all forms of glaucoma, the goal of this review article is to present an overview of the inflammatory and pro-oxidant mechanisms in the pathophysiology of glaucoma and to discuss immunomodulatory and antioxidant treatment approaches.

Metformin protects against retinal ischemia/reperfusion injury through AMPK-mediated mitochondrial fusion

Retinal ischemia/reperfusion (I/R) injury is a common pathological process responsible for cellular damage in glaucoma, diabetic retinopathy and hypertensive retinopathy. Metformin is a biguanide drug that exerts strong effects on multiple diseases. This study aims to evaluate the protective effect of metformin against retinal I/R injury and its underlying mechanism. I/R induced reduction in retina thickness and cell number in ganglion cell layer, and metformin alleviated I/R-induced retinal injury. Both retinal I/R and simulated ischemia/reperfusion (SIR) in R28 cells down-regulated expression of mitochondrial fusion protein Mfn2 and OPA1, which led to mitochondrial fission. Metformin also alleviated damage in R28 cells, and reversed the alteration in Mfn2 and OPA1, mitochondrial fission and mitochondrial membrane potential (MMP) disruption-induced by I/R or SIR as well. Intriguingly, inhibition of AMPK by compound C or siRNA prevented metformin-mediated up-regulation of Mfn2 and OPA1. Compound C and knockdown of Mfn2 or OPA1 dramatically alleviated the protective effect of metformin against intracellular ROS generation, MMP disruption, mitochondrial fission and loss of RGCs in ganglion cell layer induced by SIR or I/R. Moreover, scavenging mitochondrial ROS (mito-ROS) by mito-TEMPO exerted the similar protection against I/R-induced retinal injury or SIR-induced damage in R28 cells as metformin. Our data show for the first time that metformin protects against retinal I/R injury through AMPK-mediated mitochondrial fusion and the decreased mito-ROS generation. These findings might also repurpose metformin as a therapeutic agent for retinal I/R injury.

Oxidative Stress: A Suitable Therapeutic Target for Optic Nerve Diseases?

Optic nerve disorders encompass a wide spectrum of conditions characterized by the loss of retinal ganglion cells (RGCs) and subsequent degeneration of the optic nerve. The etiology of these disorders can vary significantly, but emerging research highlights the crucial role of oxidative stress, an imbalance in the redox status characterized by an excess of reactive oxygen species (ROS), in driving cell death through apoptosis, autophagy, and inflammation. This review provides an overview of ROS-related processes underlying four extensively studied optic nerve diseases: glaucoma, Leber's hereditary optic neuropathy (LHON), anterior ischemic optic neuropathy (AION), and optic neuritis (ON). Furthermore, we present preclinical findings on antioxidants, with the objective of evaluating the potential therapeutic benefits of targeting oxidative stress in the treatment of optic neuropathies.

Carboxymethyl chitosan regulates macrophages polarization to inhibit early subconjunctival inflammation in conjunctival injury

Persistent subconjunctival inflammation leads to subconjunctival fibrosis and eventual visual impairment. There is an unmet need for how to effectively inhibit subconjunctival inflammation. Herein, the effect of carboxymethyl chitosan (CMCS) on subconjunctival inflammation was investigated and the mechanism was involved. The evaluation of cytocompatibility demonstrated that CMCS had good biocompatibility. The in vitro results showed that CMCS inhibited secretions of pro-inflammatory cytokines (IL-6, TNF-α, IL-8 and IFN-γ) and chemokines (MCP-1), and downregulated TLR4/MyD88/NF-κB pathway in M1. The in vivo results displayed that CMCS alleviated conjunctival edema and congestion, and improved conjunctival epithelial reconstruction significantly. Both in vitro and in vivo results demonstrated that CMCS inhibited the infiltration of macrophages and reduced the expressions of iNOS, IL-6, IL-8 and TNF-α in the conjunctiva. Given that CMCS indicated the activities of inhibiting M1 polarization, NF-κB pathway, and subconjunctival inflammation, which may be employed as a potent treatment for subconjunctival inflammation.

Autophagy in glaucoma pathogenesis: Therapeutic potential and future perspectives

Glaucoma is a common blinding eye disease characterized by progressive loss of retinal ganglion cells (RGCs) and their axons, progressive loss of visual field, and optic nerve atrophy. Autophagy plays a pivotal role in the pathophysiology of glaucoma and is closely related to its pathogenesis. Targeting autophagy and blocking the apoptosis of RGCs provides emerging guidance for the treatment of glaucoma. Here, we provide a systematic review of the mechanisms and targets of interventions related to autophagy in glaucoma and discuss the outlook of emerging ideas, techniques, and multidisciplinary combinations to provide a new basis for further research and the prevention of glaucomatous visual impairment.

Recent developments of neuroprotective agents for degenerative retinal disorders

Retinal degeneration is a debilitating ocular complication characterized by the progressive loss of photoreceptors and other retinal neurons, which are caused by a group of retinal diseases affecting various age groups, and increasingly prevalent in the elderly. Age-related macular degeneration, diabetic retinopathy and glaucoma are among the most common complex degenerative retinal disorders, posing significant public health problems worldwide largely due to the aging society and the lack of effective therapeutics. Whilst pathoetiologies vary, if left untreated, loss of retinal neurons can result in an acquired degeneration and ultimately severe visual impairment. Irrespective of underlined etiology, loss of neurons and supporting cells including retinal pigment epithelium, microvascular endothelium, and glia, converges as the common endpoint of retinal degeneration and therefore discovery or repurposing of therapies to protect retinal neurons directly or indirectly are under intensive investigation. This review overviews recent developments of potential neuroprotectants including neuropeptides, exosomes, mitochondrial-derived peptides, complement inhibitors, senolytics, autophagy enhancers and antioxidants either still experimentally or in clinical trials. Effective treatments that possess direct or indirect neuroprotective properties would significantly lift the burden of visual handicap.

AGTR1 blocker attenuates activation of Tenon's capsule fibroblasts after glaucoma filtration surgery via the NF-κB signaling pathway

Activation of Tenon's capsule fibroblasts limits the success rate of glaucoma filtration surgery (GFS), the most efficacious therapy for patients with glaucoma. Angiotensin type 1 receptor (AGTR1) is involved in tissues remodeling and fibrogenesis. However, whether AGTR1 is involved in the progress of fibrogenesis after GFS is not fully elucidated. The aim of this study was to investigate the role of an AGTR1 in scar formation after GFS and the potential anti-fibrosis effect of AGTR1 blocker. AGTR1 expression level was increased in subconjunctival tissues in a rat model of GFS and transforming growth factor-beta 2 (TGF-β2)-induced human Tenon's capsule fibroblasts (HTFs). AGTR1 blocker treatment suppressed TGF-β2-induced HTF migration and α-smooth muscle actin (α-SMA) and fibronectin (FN) expression. AGTR1 blocker treatment also attenuated collagen deposition and α-SMA and FN expression in subconjunctival tissues of the rat model after GFS. Moreover, AGTR1 blocker decreased TGF-β2-induced P65 phosphorylation, P65 nuclear translocation, and nuclear factor kappa B (NF-κB) luciferase activity. Additionally, BAY 11-7082 (an NF-κB inhibitor) significantly suppressed HTF fibrosis. In conclusion, our results indicate that AGTR1 is involved in scar formation after GFS. The AGTR1 blocker attenuates subconjunctival fibrosis after GFS by inhibiting the NF-κB signaling pathway. These findings indicate that targeting AGTR1 is a potential approach to attenuate fibrosis after GFS.

Metformin attenuates the epithelial-mesenchymal transition of lens epithelial cells through the AMPK/TGF-β/Smad2/3 signalling pathway

Posterior capsule opacification (PCO) is a common ocular fibrosis disease related to the epithelial-mesenchymal transition (EMT) of human lens epithelial cells (HLECs). However, safe and effective drugs that prevent or treat PCO are lacking. Metformin (Mtf) has been used to treat fibrosis-related diseases affecting many organs and tissues, but its effect on ocular fibrosis-related diseases is unclear. We investigated whether Mtf can inhibit EMT and fibrosis in HLECs to prevent and treat PCO and elucidated the potential molecular mechanism. Here, we established an HLEC model of TGF-β-induced EMT and found that 400 μM Mtf inhibited vertical and lateral migration and EMT-related gene and protein expression in HLECs. Smad2/3 are downstream molecules of TGF-β that enter the nucleus to regulate EMT-related gene expression during the occurrence and development of PCO. We revealed that Mtf suppressed TGF-β-induced Smad2/3 phosphorylation and nuclear translocation. Mtf induces AMP-activated protein kinase (AMPK) phosphorylation. In this study, we found that Mtf induced the activation of AMPK phosphorylation in HLECs. To further explore the mechanism of Mtf, we pretreated HLECs with Compound C (an AMPK inhibitor) to repeat the above experiments and found that Compound C abolished the inhibitory effect of Mtf on HLEC EMT and the TGF-β/Smad2/3 signalling pathway. Thus, Mtf targets AMPK phosphorylation to inhibit the TGF-β/Smad2/3 signalling pathway and prevent HLEC EMT. Notably, we first illustrated the AMPK/TGF-β/Smad2/3 signalling pathway in HLECs, which may provide a new therapeutic strategy for PCO.

Metformin and Glaucoma-Review of Anti-Fibrotic Processes and Bioenergetics

Glaucoma is the leading cause of irreversible blindness globally. With an aging population, disease incidence will rise with an enormous societal and economic burden. The treatment strategy revolves around targeting intraocular pressure, the principle modifiable risk factor, to slow progression of disease. However, there is a clear unmet clinical need to find a novel therapeutic approach that targets and halts the retinal ganglion cell (RGC) degeneration that occurs with fibrosis. RGCs are highly sensitive to metabolic fluctuations as a result of multiple stressors and thus their viability depends on healthy mitochondrial functioning. Metformin, known for its use in type 2 diabetes, has come to the forefront of medical research in multiple organ systems. Its use was recently associated with a 25% reduced risk of glaucoma in a large population study. Here, we discuss its application to glaucoma therapy, highlighting its effect on fibrotic signalling pathways, mitochondrial bioenergetics and NAD oxidation.

Newly-found functions of metformin for the prevention and treatment of age-related macular degeneration

Metformin (MET), a first-line oral agent used to treat diabetes, exerts its function mainly by activating adenosine monophosphate-activated protein. The accumulation of oxidized phospholipids in the outer layer of the retina plays a key role in retinal pigment epithelium (RPE) cells death and the formation of choroidal neovascularization (CNV), which mean the development of age-related macular degeneration (AMD). Recent studies have shown that MET can regulate lipid metabolism, inhibit inflammation, and prohibit retinal cell death and CNV formation due to various pathological factors. Here, newly discovered functions of MET that may be used for the prevention and treatment of AMD were reviewed.

Knockdown of FAM225B inhibits the progression of the hypertrophic scar following glaucoma surgery by inhibiting autophagy

The formation of a hypertrophic scar (HS) may lead to failure of glaucoma surgery. Long non-coding RNAs (lncRNAs) are involved in the formation of HSs. Moreover, family with sequence similarity 225 member B (FAM225B) is upregulated in HS. However, the role of the lncRNA FAM225B in HS remains unknown. Thus, the present study aimed to investigate the function of FAM225B in HS. Scar fibroblasts were isolated from patients who had undergone glaucoma surgery. Western blotting was used to detect the expressions of Bax, Bcl-2, cleaved caspase 3, p62, ATG7 and Beclin 1, and reverse transcription-quantitative PCR (RT-qPCR) were conducted to determine the level of FAM225B in scar fibroblasts. Microtubule associated protein 1 light chain 3 α staining was performed to examine autophagosomes in scar fibroblasts. Furthermore, cell proliferation was evaluated via 5-ethynyl-2′-deoxyuridine staining. Flow cytometry was conducted to determine cell apoptosis and the levels of reactive oxygen species (ROS) in scar fibroblasts. The cell migratory ability was assessed using a Transwell assay. The results demonstrated that FAM225B knockdown significantly attenuated scar fibroblast proliferation and induced apoptosis. Additionally, transfection of scar fibroblasts with FAM225B small interfering RNA (siRNA) significantly increased the ROS levels and significantly decreased the migration of scar fibroblasts. The FAM225B overexpression-induced increase of scar fibroblast proliferation and migration was significantly reversed by 3-methyladenine administration. The results suggested that knockdown of FAM225B significantly inhibited the proliferation of scar fibroblasts by inhibiting autophagy. Therefore, knockdown of FAM225B could inhibit scar fibroblast proliferation after glaucoma surgery by inhibiting autophagy. These findings may provide a novel perspective of developing treatment strategy for the patients with HSs after glaucoma surgery.