Metformin, A Potential Role in Age-Related Macular Degeneration: A Systematic Review and Meta-Analysis

Anti-Inflammatory Potential of the Anti-Diabetic Drug Metformin in the Prevention of Inflammatory Complications and Infectious Diseases Including COVID-19: A Narrative Review

Metformin, a widely used first-line anti-diabetic therapy for the treatment of type-2 diabetes, has been shown to lower hyperglycemia levels in the blood by enhancing insulin actions. For several decades this drug has been used globally to successfully control hyperglycemia. Lactic acidosis has been shown to be a major adverse effect of metformin in some type-2 diabetic patients, but several studies suggest that it is a typically well-tolerated and safe drug in most patients. Further, recent studies also indicate its potential to reduce the symptoms associated with various inflammatory complications and infectious diseases including coronavirus disease 2019 (COVID-19). These studies suggest that besides diabetes, metformin could be used as an adjuvant drug to control inflammatory and infectious diseases. In this article, we discuss the current understanding of the role of the anti-diabetic drug metformin in the prevention of various inflammatory complications and infectious diseases in both diabetics and non-diabetics.

The Association Between Metformin Use and New-Onset ICD Coding of Geographic Atrophy

Purpose

Metformin has been suggested to protect against the development of age-related macular degeneration (AMD) in multiple observational studies. However, the association between metformin and geographic atrophy (GA), a debilitating subtype of AMD, has not been analyzed.

Methods

We conducted a case-control study of patients ages 60 years and older with new-onset International Classification of Diseases (ICD) coding of GA in the Merative MarketScan Commercial and Medicare Databases between 2017 and 2021. Cases were matched with propensity scores estimated by age, region, hypertension, and Charlson Comorbidity Index to a control without GA of the same year. Exposure to metformin was assessed for cases and controls in the year prior to their index visit. Conditional multivariable logistic regression, adjusting for AMD risk factors, was used to calculate odd ratios and 95% confidence intervals (CIs). This study design and analysis were repeated in a sample of patients without diabetes.

Results

In the full sample, we identified 10,505 cases with GA and 10,502 matched controls without GA. In total, 1149 (10.9%) cases and 1277 (12.2%) controls were exposed to metformin, and in multivariable regression, metformin decreased the odds of new-onset ICD coding of GA by 12% (95% CI, 0.79-0.99). In the sample of patients without diabetes, we identified 7611 cases with GA and 7608 matched controls without GA. Twenty-nine (0.4%) cases and 63 (0.8%) controls were exposed to metformin, and in multivariable regression, metformin decreased the odds of new-onset ICD coding of GA by 47% (95% CI, 0.33-0.83).

Conclusions

Metformin may hold promise as a noninvasive, alternative agent to prevent the development of GA. This finding is notable due to shortcomings in recently approved therapeutics for GA and metformin's overall ease of use and few adverse effects. Additional studies are required to explore our findings further and motivate a clinical trial.

Metformin Use and Age-Related Macular Degeneration in Patients Without Diabetes

Importance

Metformin use may protect against the development of age-related macular degeneration (AMD) based on results from observational studies. However, its potential effectiveness among patients without diabetes remains unclear.

Objective

To assess the association between metformin use and the development of AMD in patients without diabetes.

Design, Setting, and Participants

This case-control study used data from 2006 to 2017 in the Merative MarketScan Research Database, a nationwide insurance claims database that includes between 27 and 57 million patients in the US with primary or Medicare supplemental health insurance. Cases with AMD and controls without AMD aged 55 years or older were matched 1:1 by year, age, anemia, hypertension, region, and Charlson Comorbidity Index score. Then, cases and matched controls without a diagnosis of diabetes were selected. In subgroup analyses, cases with dry AMD and their matched controls were identified to explore the association between metformin use and AMD staging in patients without diabetes. Data were analyzed between March and September 2023.

Exposures

Exposure to metformin in the 2 years prior to the index date (ie, date of AMD diagnosis in cases and date of a randomly selected eye examination for controls) was assessed from the claims database and categorized into quartiles based on cumulative dose (1-270, 271-600, 601-1080, and >1080 g/2 y). Exposure to other antidiabetic medications was also noted.

Main Outcomes and Measures

Odds of new-onset AMD development as assessed by multivariable conditional logistic regression after adjusting for known risk factors for AMD, including female sex, hyperlipidemia, smoking, and exposures to other antidiabetic medications. Asymptotic Cochran-Armitage tests for trend were also performed.

Results

We identified 231 142 patients with any AMD (mean [SD] age, 75.1 [10.4] years; 140 172 females [60.6%]) and 232 879 matched controls without AMD (mean [SD] age, 74.9 [10.5] years; 133 670 females [57.4%]), none of whom had a diagnosis of diabetes. The sample included 144 147 cases with dry AMD that were matched to 144 530 controls. In all, 2268 (1.0%) cases and 3087 controls (1.3%) were exposed to metformin in the 2 years before their index visit. After data adjustment, exposure to any metformin was associated with reduced odds of any AMD development (adjusted odds ratio [AOR], 0.83; 95% CI, 0.74-0.87), specifically in the dosing quartiles of 1 to 270, 271 to 600, and 601 to 1080 g/2 y. Any metformin use was also associated with a reduced odds of developing dry AMD (AOR, 0.85; 95% CI, 0.79-0.92), specifically in the dosing quartiles of 1 to 270 and 271 to 600 g/2 y. Adjusted odds ratios for any AMD and dry AMD development did not differ across the dosing quartiles. Asymptotic Cochran-Armitage tests for trend revealed 2-sided P = .51 and P = .66 for the any and dry AMD samples, respectively.

Conclusions and Relevance

In this case-control study of a population without a diagnosis of diabetes, metformin use was associated with reduced odds of developing AMD. This association does not appear to be dose dependent. These findings provide further impetus to study metformin's usefulness in protecting against AMD in prospective clinical trials.

Oral Metformin Inhibits Choroidal Neovascularization by Modulating the Gut-Retina Axis

Purpose

Emerging data indicate that metformin may prevent the development of age-related macular degeneration (AMD). Whereas the underlying mechanisms of metformin's anti-aging properties remain undetermined, one proposed avenue is the gut microbiome. Using the laser-induced choroidal neovascularization (CNV) model, we investigate the effects of oral metformin on CNV, retinal pigment epithelium (RPE)/choroid transcriptome, and gut microbiota.

Methods

Specific pathogen free (SPF) male mice were treated via daily oral gavage of metformin 300 mg/kg or vehicle. Male mice were selected to minimize sex-specific differences to laser induction and response to metformin. Laser-induced CNV size and macrophage/microglial infiltration were assessed by isolectin and Iba1 immunostaining. High-throughput RNA-seq of the RPE/choroid was performed using Illumina. Fecal pellets were analyzed for gut microbiota composition/pathways with 16S rRNA sequencing/shotgun metagenomics, as well as microbial-derived metabolites, including small-chain fatty acids and bile acids. Investigation was repeated in metformin-treated germ-free (GF) mice and antibiotic-treated/GF mice receiving fecal microbiota transplantation (FMT) from metformin-treated SPF mice.

Results

Metformin treatment reduced CNV size (P < 0.01) and decreased Iba1+ macrophage/microglial infiltration (P < 0.005). One hundred forty-five differentially expressed genes were identified in the metformin-treated group (P < 0.05) with a downregulation in pro-angiogenic genes Tie1, Pgf, and Gata2. Furthermore, metformin altered the gut microbiome in favor of Bifidobacterium and Akkermansia, with a significant increase in fecal levels of butyrate, succinate, and cholic acid. Metformin did not suppress CNV in GF mice but colonization of microbiome-depleted mice with metformin-derived FMT suppressed CNV.

Conclusions

These data suggest that oral metformin suppresses CNV, the hallmark lesion of advanced neovascular AMD, via gut microbiome modulation.

Association of lipid-lowering drugs and antidiabetic drugs with age-related macular degeneration: a meta-analysis in Europeans

BACKGROUND/AIMS

To investigate the association of commonly used systemic medications with prevalent age-related macular degeneration (AMD) in the general population.

METHODS

We included 38 694 adults from 14 population-based and hospital-based studies from the European Eye Epidemiology consortium. We examined associations between the use of systemic medications and any prevalent AMD as well as any late AMD using multivariable logistic regression modelling per study and pooled results using random effects meta-analysis.

RESULTS

Between studies, mean age ranged from 61.5±7.1 to 82.6±3.8 years and prevalence ranged from 12.1% to 64.5% and from 0.5% to 35.5% for any and late AMD, respectively. In the meta-analysis of fully adjusted multivariable models, lipid-lowering drugs (LLD) and antidiabetic drugs were associated with lower prevalent any AMD (OR 0.85, 95% CI=0.79 to 0.91 and OR 0.78, 95% CI=0.66 to 0.91). We found no association with late AMD or with any other medication.

CONCLUSION

Our study indicates a potential beneficial effect of LLD and antidiabetic drug use on prevalence of AMD across multiple European cohorts. Our findings support the importance of metabolic processes in the multifactorial aetiology of AMD.

Metformin regulates the LIN28B‑mediated JNK/STAT3 signaling pathway through miR‑140‑3p in subretinal fibrosis

Subretinal fibrosis (SF) is an important cause of submacular neovascularization that leads to permanent vision loss, but has no effective clinical treatment. The present study examined the influence of metformin on SF, and investigated whether the mechanism involves the microRNA (miR)-140-3p/LIN28B/JNK/STAT3-mediated regulation of oxidative stress, angiogenesis and fibrosis-associated indicators. A mouse model of laser-induced SF was established. In addition, an ARPE-19 fibrotic cell model was established using TGF-β1. A Cell Counting Kit-8 assay was used to examine cell viability. Flow cytometry was used to measure reactive oxygen species levels, and western blotting was used to detect the levels of proteins associated with epithelial-mesenchymal transition (EMT), signaling and fibrosis. The levels of superoxide dismutase, malondialdehyde, glutathione-peroxidase and catalase were measured using kits. Scratch assays and Transwell assays were used to assess cell migration and invasion, respectively, and reverse transcription-quantitative PCR was used to determine the levels of miR-140-3p and LIN28B. Dual-luciferase assays were used to verify the targeting relationship between miR-140-3p and LIN28B, and coimmunoprecipitation was used to confirm the interaction between LIN28B and JNK. Masson staining and hematoxylin and eosin staining were used to examine collagenous fibers and the histopathology of eye tissue. In ARPE-19 cells induced by TGF-β1, metformin promoted miR-140-3p expression and inhibited LIN28B expression and JNK/STAT3 pathway activation, thereby inhibiting oxidative stress, EMT and fibrosis in ARPE-19 cells. The overexpression of LIN28B or treatment with the JNK/STAT3 agonist anisomycin partially reversed the inhibitory effect of metformin on oxidative stress and fibrosis in ARPE-19 cells. The dual-luciferase reporter assay and coimmunoprecipitation assay showed that miR-140-3p targeted the 3' untranslated region of LIN28B mRNA and inhibited LIN28B expression. LIN28B targeted and bound to JNK and regulated the JNK/STAT3 pathway. Therefore, it may be concluded that metformin can promote miR-140-3p expression, inhibit LIN28B and then inhibit the JNK/STAT3 pathway to alleviate SF.

Association of metformin use with risk of newly onset neovascular age-related macular degeneration development

PURPOSE

To investigate if metformin use reduces the odds of developing new neovascular AMD (nAMD).

METHODS

This is a case-control study of 86,930 subjects with new diagnoses of nAMD and 86,918 matched controls using the Merative™ Marketscan® Research Databases. Subjects were analyzed using multivariable conditional logistic regression to identify the risks of various exposures on developing nAMD. A subgroup analysis of 22,117 diabetic cases and 21,616 diabetic controls was also performed.

RESULTS

Metformin use was associated with reduced odds ratio (OR) of developing nAMD (OR 0.95, 95% confidence interval 0.91-0.98) in full sample and diabetic cohort particularly in patients without any diabetic retinopathy (DR) -an effect that persisted after Bonferroni correction. In the diabetic cohort without DR, reduced OR was observed at 24-month cumulative doses of 1 to 300g, 301 to 630g, and 631 to 1080g.

CONCLUSIONS

Metformin use was associated with reduced OR of nAMD, particularly in patients without DR. The protective effect was noted for 24-month cumulative doses below 1080g. Metformin may be a novel preventive strategy for nAMD.

Age-Related Macular Degeneration in an Ageing Society - Current Epidemiological Research

Epidemiological studies on age-related macular degeneration (AMD) provide crucial data on the frequency of early and late forms as well as associated risk factors. The increasing number of population-based cross-sectional and longitudinal cohort studies in Germany and Europe with published data is making prevalence and incidence estimators for AMD more robust, although they show mostly method-related fluctuations. This review article brings together the latest published epidemiological measures for AMD from Germany and Central as well as Western Europe. Based on this data and population figures for Germany and Europe, prevalence is projected, and future trends are forecasted. The epidemiological evidence for AMD-associated risk factors is also improving, especially through meta-analyses within large consortia with correspondingly high case numbers. This review article summarizes the latest findings and resulting recommendations for prevention approaches. Additionally, it discusses treatment options and future challenges.

Association of Metformin and Other Diabetes Medication Use and the Development of New-Onset Dry Age-Related Macular Degeneration: A Case-Control Study

Purpose

To investigate if metformin use is associated with decreased odds of developing new non-neovascular ("dry") age-related macular degeneration (AMD).

Methods

Case-control study examining 194,135 cases with diagnoses of new-onset AMD between 2008 and 2017 and 193,990 matched controls in the Merative MarketScan Research Databases. The diabetic subgroup included 49,988 cases and 49,460 controls. Multivariable conditional logistic regressions identified the risks of exposures on the development of dry AMD. Main outcome measures were odds ratios (ORs) of developing dry AMD with metformin use.

Results

In multivariable conditional logistic regression, any metformin use was associated with decreased odds of developing dry AMD (OR = 0.97; 95% confidence interval [CI], 0.95-0.99). This protective effect was noted for cumulative 2-year doses of metformin of 1 to 270 g (OR = 0.93; 95% CI, 0.90-0.97) and 271 to 600 g (OR = 0.92; 95% CI, 0.89-0.96). In a diabetic subgroup, metformin use below 601 g per 2 years decreased the odds of developing dry AMD (1-270 g: OR = 0.95; 95% CI, 0.91-0.99; 271-600 g: OR = 0.92; 95% CI, 0.89-0.96). Unlike in diabetic patients with diabetic retinopathy, diabetic patients without diabetic retinopathy had decreased odds of developing dry AMD with any metformin use (OR = 0.97; 95% CI, 0.94-0.998) and cumulative two-year doses of 1 to 270 g (OR 0.96; 95% CI, 0.91-0.998) and 271 to 600 g (OR = 0.92; 95% CI, 0.88-0.96).

Conclusions

Metformin use was associated with decreased odds of developing dry AMD. The protective effect was observed for cumulative 2-year doses below 601 g. In diabetics, this association persisted, specifically in those without diabetic retinopathy. Therefore, metformin may be a strategy to prevent development of dry AMD.

Association of Metformin With the Development of Age-Related Macular Degeneration

Importance

Age-related macular degeneration (AMD) is a leading cause of blindness with no treatment available for early stages. Retrospective studies have shown an association between metformin and reduced risk of AMD.

Objective

To investigate the association between metformin use and age-related macular degeneration (AMD).

Design, Setting, and Participants

The Diabetes Prevention Program Outcomes Study is a cross-sectional follow-up phase of a large multicenter randomized clinical trial, Diabetes Prevention Program (1996-2001), to investigate the association of treatment with metformin or an intensive lifestyle modification vs placebo with preventing the onset of type 2 diabetes in a population at high risk for developing diabetes. Participants with retinal imaging at a follow-up visit 16 years posttrial (2017-2019) were included. Analysis took place between October 2019 and May 2022.

Interventions

Participants were randomly distributed between 3 interventional arms: lifestyle, metformin, and placebo.

Main Outcomes and Measures

Prevalence of AMD in the treatment arms.

Results

Of 1592 participants, 514 (32.3%) were in the lifestyle arm, 549 (34.5%) were in the metformin arm, and 529 (33.2%) were in the placebo arm. All 3 arms were balanced for baseline characteristics including age (mean [SD] age at randomization, 49 [9] years), sex (1128 [71%] male), race and ethnicity (784 [49%] White), smoking habits, body mass index, and education level. AMD was identified in 479 participants (30.1%); 229 (14.4%) had early AMD, 218 (13.7%) had intermediate AMD, and 32 (2.0%) had advanced AMD. There was no significant difference in the presence of AMD between the 3 groups: 152 (29.6%) in the lifestyle arm, 165 (30.2%) in the metformin arm, and 162 (30.7%) in the placebo arm. There was also no difference in the distribution of early, intermediate, and advanced AMD between the intervention groups. Mean duration of metformin use was similar for those with and without AMD (mean [SD], 8.0 [9.3] vs 8.5 [9.3] years; P = .69). In the multivariate models, history of smoking was associated with increased risks of AMD (odds ratio, 1.30; 95% CI, 1.05-1.61; P = .02).

Conclusions and Relevance

These data suggest neither metformin nor lifestyle changes initiated for diabetes prevention were associated with the risk of any AMD, with similar results for AMD severity. Duration of metformin use was also not associated with AMD. This analysis does not address the association of metformin with incidence or progression of AMD.

Role of Oxidative Stress in Ocular Diseases: A Balancing Act

Redox homeostasis is a delicate balancing act of maintaining appropriate levels of antioxidant defense mechanisms and reactive oxidizing oxygen and nitrogen species. Any disruption of this balance leads to oxidative stress, which is a key pathogenic factor in several ocular diseases. In this review, we present the current evidence for oxidative stress and mitochondrial dysfunction in conditions affecting both the anterior segment (e.g., dry eye disease, keratoconus, cataract) and posterior segment (age-related macular degeneration, proliferative vitreoretinopathy, diabetic retinopathy, glaucoma) of the human eye. We posit that further development of therapeutic interventions to promote pro-regenerative responses and maintenance of the redox balance may delay or prevent the progression of these major ocular pathologies. Continued efforts in this field will not only yield a better understanding of the molecular mechanisms underlying the pathogenesis of ocular diseases but also enable the identification of novel druggable redox targets and antioxidant therapies.

Association Between Oral Metformin Use and the Development of Age-Related Macular Degeneration in Diabetic Patients: A Systematic Review and Meta-Analysis

Purpose

Metformin is a biguanide derivative that is commonly used for the treatment of diabetes mellitus (DM). It demonstrates antioxidative, anti-inflammatory, and antiangiogenic activity within the ocular tissue and thus may be implicated in the treatment of age-related macular degeneration (AMD). However, epidemiological studies have shown conflicting results.

Methods

The Ovid MEDLINE/Embase, Cochrane Library, and Web of Science databases were systematically searched from inception through August 3, 2022. Studies reporting the association between metformin use and odds of AMD were enrolled. Adjusted odds ratios (ORs) of AMD were extracted and pooled with random-effects model meta-analysis. Subgroup analyses based on AMD subtypes, ethnicity, study design, sex, and confirmation of AMD diagnosis were conducted.

Results

A total of 9 observational studies with 1,446,284 participants were included in the analysis. The meta-analysis showed that metformin use was associated with a significant reduction in the odds of AMD (pooled ORs = 0.81, 95% confidence interval [CI] = 0.70-0.93). Subgroup analyses revealed that metformin use was not significantly associated with dry or wet AMD. Black (pooled ORs = 0.61, 95% CI = 0.58-0.64) and Hispanic populations (pooled ORs = 0.85, 95% CI = 0.81-0.89) demonstrated significantly lower odds of AMD.

Conclusions

This systematic review and meta-analysis found that patients with DM with metformin usage were at lower odds of developing AMD. Future prospective clinical trials are needed to confirm this association.

Using Advanced Bioinformatics Tools to Identify Novel Therapeutic Candidates for Age-Related Macular Degeneration

Purpose

Age-related macular degeneration (AMD) is the most common cause of aging-related blindness in the developing world. Although medications can slow progressive wet AMD, currently, no drugs to treat dry-AMD are available. We use a systems or in silico biology analysis to identify chemicals and drugs approved by the Food and Drug Administration for other indications that can be used to treat and prevent AMD.

Methods

We queried National Center for Biotechnology Information to identify genes associated with AMD, wet AMD, dry AMD, intermediate AMD, and geographic atrophy to date. We combined genes from various AMD subtypes to reflect distinct stages of disease. Enrichment analysis using the ToppGene platform predicted molecules that can influence AMD genes. Compounds without clinical indications or with deleterious effects were manually filtered.

Results

We identified several drug/chemical classes that can affect multiple genes involved in AMD. The drugs predicted from this analysis include antidiabetics, lipid-lowering agents, and antioxidants, which could theoretically be repurposed for AMD. Metformin was identified as the drug with the strongest association with wet AMD genes and is among the top candidates in all dry AMD subtypes. Curcumin, statins, and antioxidants are also among the top drugs correlating with AMD-risk genes.

Conclusions

We use a systematic computational process to discover potential therapeutic targets for AMD. Our systematic and unbiased approach can be used to guide targeted preclinical/clinical studies for AMD and other ocular diseases.

Translational Relevance

Advanced bioinformatics models identify novel chemicals and approved drug candidates that can be efficacious for different subtypes of AMD.

NF-κB Regulation by Gut Microbiota Decides Homeostasis or Disease Outcome During Ageing

Human beings and their indigenous microbial communities have coexisted for centuries, which led to the development of co-evolutionary mechanisms of communication and cooperation. Such communication machineries are governed by sophisticated multi-step feedback loops, which typically begin with the recognition of microbes by pattern recognition receptors (PRRs), followed by a host transcriptional response leading to the release of effector molecules. Our gastrointestinal tract being the main platform for this interaction, a variety of host intestinal cells tightly regulate these loops to establish tolerance towards the microbial communities of the gut and maintain homeostasis. The transcription factor, nuclear factor kappa B (NF-κB) is an integral component of such a communication apparatus, which plays a critical role in determining the state of homeostasis or inflammation associated with dysbiosis in the host. Here we outline the crucial role of NF-κB in host response to microbial cues in the context of ageing and associated diseases.

Association of Diabetes Medication With Open-Angle Glaucoma, Age-Related Macular Degeneration, and Cataract in the Rotterdam Study

Importance

Recent studies suggest that the diabetes drug metformin has a protective effect on open-angle glaucoma (OAG) and age-related macular degeneration (AMD). However, studies have not addressed the critical issue of confounding by indication, and associations have not been evaluated in a large prospective cohort.

Objective

To determine the association between diabetes medication and the common eye diseases OAG, AMD, and cataract and to evaluate their cumulative lifetime risks in a large cohort study.

Design, Setting, and Participants

This cohort study included participants from 3 independent cohorts from the prospective, population-based Rotterdam Study between April 23, 1990, and June 25, 2014. Participants were monitored for incident eye diseases (OAG, AMD, cataract) and had baseline measurements of serum glucose. Data on diabetes medication use and data from ophthalmologic examinations were gathered.

Exposures

Type 2 diabetes (T2D) and the diabetes medications metformin, insulin, and sulfonylurea derivatives.

Main Outcomes and Measures

Diagnosis and cumulative lifetime risk of OAG, AMD, and cataract.

Results

This study included 11 260 participants (mean [SD] age, 65.1 [9.8]; 6610 women [58.7%]). T2D was diagnosed in 2406 participants (28.4%), OAG was diagnosed in 324 of 7394 participants (4.4%), AMD was diagnosed in 1935 of 10 993 participants (17.6%), and cataract was diagnosed in 4203 of 11 260 participants (37.3%). Untreated T2D was associated with a higher risk of OAG (odds ratio [OR], 1.50; 95% CI, 1.06-2.13; P = .02), AMD (OR, 1.35; 95% CI, 1.11-1.64; P = .003), and cataract (OR, 1.63; 95% CI, 1.39-1.92; P < .001). T2D treated with metformin was associated with a lower risk of OAG (OR, 0.18; 95% CI, 0.08-0.41; P < .001). Other diabetes medication (ie, insulin, sulfonylurea derivates) was associated with a lower risk of AMD (combined OR, 0.32; 95% CI, 0.18 to 0.55; P < .001). The cumulative lifetime risk of OAG was lower for individuals taking metformin (1.5%; 95% CI, 0.01%-3.1%) than for individuals without T2D (7.2%; 95% CI, 5.7%-8.7%); the lifetime risk of AMD was lower for individuals taking other diabetes medication (17.0%; 95% CI, 5.8%-26.8% vs 33.1%; 95% CI, 30.6%-35.6%).

Conclusions and Relevance

Results of this cohort study suggest that, although diabetes was clearly associated with cataract, diabetes medication was not. Treatment with metformin was associated with a lower risk of OAG, and other diabetes medication was associated with a lower risk of AMD. Proof of benefit would require interventional clinical trials.

Nutraceuticals/Drugs Promoting Mitophagy and Mitochondrial Biogenesis May Combat the Mitochondrial Dysfunction Driving Progression of Dry Age-Related Macular Degeneration

In patients with age-related macular degeneration (AMD), the crucial retinal pigment epithelial (RPE) cells are characterized by mitochondria that are structurally and functionally defective. Moreover, deficient expression of the mRNA-editing enzyme Dicer is noted specifically in these cells. This Dicer deficit up-regulates expression of Alu RNA, which in turn damages mitochondria—inducing the loss of membrane potential, boosting oxidant generation, and causing mitochondrial DNA to translocate to the cytoplasmic region. The cytoplasmic mtDNA, in conjunction with induced oxidative stress, triggers a non-canonical pathway of NLRP3 inflammasome activation, leading to the production of interleukin-18 that acts in an autocrine manner to induce apoptotic death of RPE cells, thereby driving progression of dry AMD. It is proposed that measures which jointly up-regulate mitophagy and mitochondrial biogenesis (MB), by replacing damaged mitochondria with “healthy” new ones, may lessen the adverse impact of Alu RNA on RPE cells, enabling the prevention or control of dry AMD. An analysis of the molecular biology underlying mitophagy/MB and inflammasome activation suggests that nutraceuticals or drugs that can activate Sirt1, AMPK, Nrf2, and PPARα may be useful in this regard. These include ferulic acid, melatonin urolithin A and glucosamine (Sirt1), metformin and berberine (AMPK), lipoic acid and broccoli sprout extract (Nrf2), and fibrate drugs and astaxanthin (PPARα). Hence, nutraceutical regimens providing physiologically meaningful doses of several or all of the: ferulic acid, melatonin, glucosamine, berberine, lipoic acid, and astaxanthin, may have potential for control of dry AMD.

Metformin and retinal diseases in preclinical and clinical studies: Insights and review of literature

Metformin is one of the most prescribed drugs in the world giving potential health benefits beyond that of type 2 diabetes (T2DM). Emerging evidence suggests that it may have protective effects for retinal/posterior segment diseases including diabetic retinopathy (DR), age-related macular degeneration (AMD), inherited retinal degeneration such as retinitis pigmentosa (RP), primary open angle glaucoma (POAG), retinal vein occlusion (RVO), and uveitis. Metformin exerts potent anti-inflammatory, antiangiogenic, and antioxidative effects on the retina in response to pathologic stressors. In this review, we highlight the broad mechanism of action of metformin through key preclinical studies on animal models and cell lines used to simulate human retinal disease. We then explore the sparse but promising retrospective clinical data on metformin's potential protective role in DR, AMD, POAG, and uveitis. Prospective clinical data is needed to clarify metformin's role in management of posterior segment disorders. However, given metformin's proven broad biochemical effects, favorable safety profile, relatively low cost, and promising data to date, it may represent a new therapeutic preventive and strategy for retinal diseases.

Pathogenic mitochondrial dysfunction and metabolic abnormalities

Herein we trace links between biochemical pathways, pathogenesis, and metabolic diseases to set the stage for new therapeutic advances. Cellular and acellular microorganisms including bacteria and viruses are primary pathogenic drivers that cause disease. Missing from this statement are subcellular compartments, importantly mitochondria, which can be pathogenic by themselves, also serving as key metabolic disease intermediaries. The breakdown of food molecules provides chemical energy to power cellular processes, with mitochondria as powerhouses and ATP as the principal energy carrying molecule. Most animal cell ATP is produced by mitochondrial synthase; its central role in metabolism has been known for >80 years. Metabolic disorders involving many organ systems are prevalent in all age groups. Progressive pathogenic mitochondrial dysfunction is a hallmark of genetic mitochondrial diseases, the most common phenotypic expression of inherited metabolic disorders. Confluent genetic, metabolic, and mitochondrial axes surface in diabetes, heart failure, neurodegenerative disease, and even in the ongoing coronavirus pandemic.

Therapeutic potential of PGC-1α in age-related macular degeneration (AMD) - the involvement of mitochondrial quality control, autophagy, and antioxidant response

INTRODUCTION

Age-related macular degeneration (AMD) is the leading, cause of sight loss in the elderly in the Western world. Most patients remain still without any treatment options. The targeting of Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), a transcription co-factor, is a putative therapy against AMD.

AREAS COVERED

The characteristics of AMD and their possible connection with PGC-1α as well as the transcriptional and post-transcriptional control of PGC-1α are discussed. The PGC-1α-driven control of mitochondrial functions, and its involvement in autophagy and antioxidant responses are also examined. Therapeutic possibilities via drugs and epigenetic approaches to enhance PGC-1α expression are discussed. Authors conducted a search of literature mainly from the recent decade from the PubMed database.

EXPERT OPINION

Therapy options in AMD could include PGC-1α activation or stabilization. This could be achieved by a direct elevation of PGC-1α activity, a stabilization or modification of its upstream activators and inhibitors by chemical compounds, like 5-Aminoimidazole-4-carboxamide riboside, metformin, and resveratrol. Furthermore, manipulations with epigenetic modifiers of PGC-1α expression, including miRNAs, e.g. miR-204, are considered. A therapy aimed at PGC-1α up-regulation may be possible in other disorders besides AMD, if they are associated with disturbances in the mitochondria-antioxidant response-autophagy axis.

Long-Term Oral Treatment with Non-Hypoglycemic Dose of Glibenclamide Reduces Diabetic Retinopathy Damage in the Goto-KakizakiRat Model

Diabetic retinopathy (DR) remains a major cause of vision loss, due to macular edema, retinal ischemia and death of retinal neurons. We previously demonstrated that acute administration of glibenclamide into the vitreous, or given orally at a non-hypoglycemic dose, protected the structure and the function of the retina in three animal models that each mimic aspects of diabetic retinopathy in humans. In this pilot study, we investigated whether one year of chronic oral glibenclamide, in a non-hypoglycemic regimen (Amglidia^®, 0.4 mg/kg, Ammtek/Nordic Pharma, 5 d/week), could alleviate the retinopathy that develops in the Goto-Kakizaki (GK) rat. In vivo, retinal function was assessed by electroretinography (ERG), retinal thickness by optical coherence tomography (OCT) and retinal perfusion by fluorescein and indocyanin green angiographies. The integrity of the retinal pigment epithelium (RPE) that constitutes the outer retinal barrier was evaluated by quantitative analysis of the RPE morphology on flat-mounted fundus ex vivo. Oral glibenclamide did not significantly reduce the Hb1Ac levels but still improved retinal function, as witnessed by the reduction in scotopic implicit times, limited diabetes-induced neuroretinal thickening and the extension of ischemic areas, and it improved the capillary coverage. These results indicate that low doses of oral glibenclamide could still be beneficial for the prevention of type 2 diabetic retinopathy. Whether the retinas ofpatients treated specifically with glibenclamideare less at risk of developing diabetic complications remains to be demonstrated.

Management of type 2 diabetes mellitus in older adults: eight case studies with focus SGLT-2 inhibitors and metformin

Objectives: Sodium-glucose co-transporter-2 (SGLT-2) inhibitors have been recently introduced for type 2 diabetes treatment with significant cardiovascular, renal benefits. Yet, they have frequently been refrained in older adults. Metformin is regarded the first-line diabetes therapy for all ages; still it is associated with weight loss and frailty in older adults. We aimed to outline our experience with three oldest-old patients with high cardiovascular risk managed with SGLT-2 inhibitors, and five patients with anorexia/weight loss managed by metformin cessation. Methods: We outlined demographics, comorbidities, geriatric syndromes, functional status, and diabetes duration, and presented the changes in frailty by noting pre-intervention and post-intervention frailty scores. We outlined benefits and side effects related to SGLT-2 inhibitors, and the deprescription reasons and represcription practices of metformin therapy. We gave details on baseline and current diabetes treatment, overall medication regimen, and current status of the patients. Results: Among the case studies with SGLT-2 inhibitors, two patients were frail and reversed to pre-frailty status after SGLT-2 intervention, while the third patient was and remained robust. All patients had clinical improvements with better blood pressure and glucose control. Among the case studies treated with metformin, all were frail before the cessation of metformin. Four reversed to pre-frailty and one became robust after intervention. Conclusion: The findings of our case studies suggest considering SGLT-2 inhibitors in patients with accompanying heart failure/high cardiovascular risk factors and cessation of metformin in those with malnutrition/malnutrition risk. These approaches have potential to improve frailty and inappropriate medication use in diabetic older adults.