Microbiome Dysbiosis: A Pathological Mechanism at the Intersection of Obesity and Glaucoma

Increased Intestinal Inflammation and Permeability in Glaucoma

Objective

Evidence suggests that dysbiosis of the gut microbiota plays a pivotal role in the development of glaucoma. This dysbiosis is commonly associated with chronic intestinal inflammation and increased intestinal permeability. However, the understanding of intestinal inflammation and permeability in glaucoma remains insufficient. This study aims to investigate the potential relationship between fecal inflammation and permeability markers and glaucoma.

Methods

We recruited 114 glaucoma patients and 75 healthy controls. Levels of fecal lactoferrin (Lf) and alpha-1 antitrypsin (AAT) were quantified using enzyme linked immunosorbent assay (ELISA) to compare both biomarkers between groups and across different severity grades of glaucoma. Logistic regression analysis was used to assess the association between these fecal biomarkers and glaucoma. The severity of glaucoma was assessed based on the mean deviation (MD) in the visual field.

Results

In this study, we observed elevated levels of fecal Lf and AAT in glaucoma patients. The proportion of glaucoma patients with abnormal fecal Lf levels (≥ 7.25 µg/g) was significantly higher than that of the controls (p = 0.012). A positive correlation was noted between fecal Lf and AAT (rho = 0.20, p = 0.006). After adjusting for age and sex, multivariable logistic regression analysis indicated that both fecal Lf (OR = 1.11, 95% CI: 1.01-1.21, p = 0.026) and AAT (OR = 1.01, 95% CI: 1.01-1.02, p < 0.001) positively correlated with glaucoma. These biomarkers might reflect glaucoma severity, with significant differences in fecal Lf levels observed between moderate and severe stages, but not in the early stage. Furthermore, increasing levels of fecal AAT correlated with greater severity of glaucomatous injury and a larger vertical cup-to-disc ratio (VCDR) (p < 0.05).

Conclusion

This study suggests an increase in intestinal inflammation and permeability in glaucoma, further indicating the importance of the 'gut-retina axis' in the pathogenesis of the disease and potentially offering new therapeutic avenues.

Investigating the uncertain causal link between gut microbiota and glaucoma: A genetic correlation and Mendelian randomisation study

BACKGROUND

Glaucoma is the most common cause of irreversible blindness, and gut microbiota (GM) is associated with glaucoma. Whether this association represents a causal role remains unknown. This study aims to assess the potential association and causal link between GM and various forms of glaucoma, emphasising the need for cautious interpretation of the strength of these associations.

METHODS

Employing a two-sample bidirectional Mendelian randomisation (MR) framework with false discovery rate correction and various sensitivity analyses, supplemented by genetic correlation analysis via linkage disequilibrium score regression (LDSC) and colocalisation for European summary-level data between MiBioGen consortium and FinnGen Study, we sought to explore the relationship between GM and glaucoma.

RESULTS

While certain microbial taxa showed potential associations with glaucoma subtypes (e.g., Erysipelotrichaceae with primary angle closure glaucoma, Senegalimassilia with exfoliation glaucoma), the overall findings suggest a complex and not definitively causal relationship between GM and glaucoma. Notably, reverse MR analysis did not establish a significant causal effect of glaucoma on GM composition, and no consistent genetic correlations were observed between GM and glaucoma.

CONCLUSIONS

While our study provides some evidence of associations between specific GM taxa and glaucoma, the results underscore the complexity of these relationships and the need for further research to clarify the potential causal links. The findings highlight the importance of interpreting the gut-eye axis with caution and suggest that while GM may play a role in glaucoma, it is unlikely to be a predominant causal factor.

Microbiome as an endocrine organ and its relationship with eye diseases: Effective factors and new targeted approaches

Microbiome is an endocrine organ that refers to both the complicated biological system of microbial species that colonize our bodies and their genomes and surroundings. Recent studies confirm the connection between the microbiome and eye diseases, which are involved in the pathogenesis of eye diseases, including age-related macular disorders, diabetic retinopathy, glaucoma, retinitis pigmentosa, dry eye, and uveitis. The aim of this review is to investigate the microbiome in relation to eye health. First, a brief introduction of the characteristics of the gut microorganisms terms of composition and work, the role of dysbiosis, the gut microbiome and the eye microbiome in the progression of eye illnesses are highlighted, then the relationship among the microbiome and the function of the immune system and eye diseases, the role of inflammation and aging and the immune system, It has been reviewed and finally, the control and treatment goals of microbiome and eye diseases, the role of food factors and supplements, biotherapy and antibiotics in relation to microbiome and eye health have been reviewed.

Innovative treatments for obesity and NAFLD: A bibliometric study on antioxidants, herbs, phytochemicals, and natural compounds

The increasing scientific interest in antioxidants and naturally derived compounds as potential remedies for obesity and non-alcoholic fatty liver disease (NAFLD) has led to extensive research. The objective of this bibliometric analysis is to present an updated perspective on the topic of antioxidants, herbs, phytochemicals, and natural compounds, in the control of obesity and NAFLD, to identify new areas for future research. Publications from the years 2012-2022 were retrieved using the Scopus database. The research trends were analyzed using the Biblioshiny and VOSviewer tools. The field has seen a significant increase in research activity, as indicated by an annual growth rate of 10 % in the number of published manuscripts. China, Korea, and the USA emerged as the most prominent contributors in this specific field, supported by their notable volumes of publications and citations. The density analysis revealed that the most frequently occurring authors' keywords related to herbal species are, in rank order, Camelia sinensis, Momordica charantia, Curcuma longa, Ilex paraguariensis, Panax ginseng, Moringa oleifera, Garcinia cambogia, Garcinia mangostana, Zingiber officinale, and Cinnamomum verum. In the group of antioxidants, phytochemicals, and natural compounds, the top 10 were resveratrol, curcumin, quercetin, vitamin E, alpha-lipoic acid, vitamin C, chlorogenic acid, lycopene, fucoxanthin, and berberine. The co-occurrence analysis unveiled significant themes and potential trends, including a notable interest in the impact of herbal species, antioxidants, phytochemicals, and natural compounds on obesity and NAFLD through the modulation of the gut microbiome. Another recurring theme that arises, is the ongoing investigation of molecular targets that demonstrate anti-adipogenesis properties. The analysis presented in this study provides valuable insights for researchers investigating the efficacy of antioxidants, herbs, phytochemicals, and natural compounds in addressing obesity and NAFLD. Through the use of bibliometric methods, the study offers a comprehensive overview. Furthermore, the findings of this analysis can serve as a foundation for future research in this specific domain.

Exploring the Ocular Surface Microbiome and Tear Proteome in Glaucoma

Although glaucoma is a leading cause of irreversible blindness worldwide, its pathogenesis is incompletely understood, and intraocular pressure (IOP) is the only modifiable risk factor to target the disease. Several associations between the gut microbiome and glaucoma, including the IOP, have been suggested. There is growing evidence that interactions between microbes on the ocular surface, termed the ocular surface microbiome (OSM), and tear proteins, collectively called the tear proteome, may also play a role in ocular diseases such as glaucoma. This study aimed to find characteristic features of the OSM and tear proteins in patients with glaucoma. The whole-metagenome shotgun sequencing of 32 conjunctival swabs identified Actinobacteria, Firmicutes, and Proteobacteria as the dominant phyla in the cohort. The species Corynebacterium mastitidis was only found in healthy controls, and their conjunctival microbiomes may be enriched in genes of the phospholipase pathway compared to glaucoma patients. Despite these minor differences in the OSM, patients showed an enrichment of many tear proteins associated with the immune system compared to controls. In contrast to the OSM, this emphasizes the role of the proteome, with a potential involvement of immunological processes in glaucoma. These findings may contribute to the design of new therapeutic approaches targeting glaucoma and other associated diseases.

Obesity, body fat distribution and eye diseases

BACKGROUND

The prevalence of obesity, a chronic disease, is increasing, and obesity is now considered a global epidemic. Eye diseases are also increasing worldwide and have serious repercussions on quality of life as well as increasingly high costs for the community. The relationships between obesity and ocular pathologies are not yet well clarified and are not pathologically homogeneous: they seem to be somehow linked to excess body fat, especially to the distribution of adipose tissue and its ectopic deposits.

PURPOSE

Our objective was to examine the associations between obesity and anthropometric indices, including body mass index (BMI), waist circumference (WC), and the waist/hip ratio (WHR), and the risk of most widespread eye diseases, with particular attention given to the most significant metabolic mechanisms.

METHODS

This article provides a narrative overview of the effect of obesity and anthropometric measurements of body fat on prevalent eye diseases. We used the MEDLINE/PubMed, CINAHL, EMBASE, and Cochrane Library databases from 1984 to 2024. In addition, we hand-searched references from the retrieved articles and explored a number of related websites. A total of 153 publications were considered.

RESULTS

There is significant evidence that obesity is associated with several eye diseases. Waist circumference (WC) and the waist/hip ratio (WHR) have been observed to have stronger positive associations with eye diseases than BMI.

CONCLUSIONS

Obesity must be considered a significant risk factor for eye diseases; hence, a multidisciplinary and multidimensional approach to treating obesity, which also affects ocular health, is important. In the prevention and treatment of eye diseases related to obesity, lifestyle factors, especially diet and physical activity, as well as weight changes, both weight loss and weight gain, should not be overlooked.

LEVEL OF EVIDENCE

Level V narrative review.

Microbial Dynamics in Ophthalmic Health: Exploring the Interplay between Human Microbiota and Glaucoma Pathogenesis

The human microbiome has a crucial role in the homeostasis and health of the host. These microorganisms along with their genes are involved in various processes, among these are neurological signaling, the maturation of the immune system, and the inhibition of opportunistic pathogens. In this sense, it has been shown that a healthy ocular microbiota acts as a barrier against the entry of pathogens, contributing to the prevention of infections. In recent years, a relationship has been suggested between microbiota dysbiosis and the development of neurodegenerative diseases. In patients with glaucoma, it has been observed that the microbiota of the ocular surface, intraocular cavity, oral cavity, stomach, and gut differ from those observed in healthy patients, which may suggest a role in pathology development, although the evidence remains limited. The mechanisms involved in the relationship of the human microbiome and this neurodegenerative disease remain largely unknown. For this reason, the present review aims to show a broad overview of the influence of the structure and composition of the human oral and gut microbiota and relate its dysbiosis to neurodegenerative diseases, especially glaucoma.

Altered ocular surface microbiota in obesity: a case-control study

Purpose

This study aimed to investigate the composition of ocular surface microbiota in patients with obesity.

Methods

This case-control study, spanning from November 2020 to March 2021 at Henan Provincial People's Hospital, involved 35 patients with obesity and an equivalent number of age and gender-matched healthy controls. By employing 16S rRNA sequencing, this study analyzed the differences in ocular surface microbiota between the two groups. The functional prediction analysis of the ocular surface microbiota was conducted using PICRUSt2.

Results

The alpha diversity showed no notable differences in the richness or evenness of the ocular surface microbiota when comparing patients with obesity to healthy controls (Shannon index, P=0.1003). However, beta diversity highlighted significant variances in the microbiota composition of these two groups (ANOSIM, P=0.005). LEfSe analysis revealed that the relative abundances of Delftia, Cutibacterium, Aquabacterium, Acidovorax, Caulobacteraceae unclassified, Comamonas and Porphyromonas in patients with obesity were significantly increased (P<0.05). Predictive analysis using PICRUSt2 highlighted a significant enhancement in certain metabolic pathways in patients with obesity, notably xenobiotics metabolism via cytochrome P450 (CYP450), lipid metabolism, and the oligomerization domain (NOD)-like receptor signaling pathway (P<0.05).

Conclusions

Patients with obesity exhibit a distinct ocular surface core microbiome. The observed variations in this microbiome may correlate with increased activity in CYP450, changes in lipid metabolism, and alterations in NOD-like receptor signaling pathways.

Shedding light on eye disease in obesity: A review

Obesity is known to be associated with numerous ocular manifestations, including but not limited to, diabetic retinopathy (DR), age-related macular degeneration (AMD), cataracts, glaucoma, and dry eye disease. This review aims to provide an overview of the ophthalmological findings in obesity. A literature search was conducted using PubMed and Cochrane databases for studies describing randomized clinical trials, meta-analyses, systematic reviews, and observational studies published from 1 January 2017 to 1 April 2023. The search terms used included relevant keywords such as 'obesity', 'body mass index', 'waist-to-hip ratio', 'bariatric', 'ophthalmology', 'eye disease', 'myopia', 'retinopathy', 'glaucoma', and 'cataract'. This literature search was performed on 1 April 2023. Obesity is associated with increased risk of developing DR, a sight-threatening complication of diabetes mellitus. Similarly, obesity has been shown to increase risk of AMD, cataracts, glaucoma, and ocular surface disease. Multiple mechanisms linking obesity to ophthalmic disease have been proposed. Adipose tissue produces various inflammatory cytokines that can affect ocular tissues, leading to disease progression. Additionally, obesity is associated with systemic metabolic changes that can influence ocular health. Bariatric surgery has been shown to be protective against development of ophthalmic disease. Obesity is a significant risk factor for several ophthalmological diseases. Healthcare providers should encourage weight loss in patients with overweight or obesity to prevent or delay the onset of ocular complications. Further research is needed to better understand the underlying mechanisms of this association, and to identify effective strategies for preventing or managing ophthalmic disease in patients with obesity.

Effect of the gut microbiome in glaucoma risk from the causal perspective

OBJECTIVE

Evidence from observational studies has reported possible associations between the gut microbiome (GM) and glaucoma. However, the causal effect of GM on glaucoma risk remains to be determined.

METHODS AND ANALYSIS

We conducted two-sample bidirectional Mendelian randomisation (MR) analyses to explore the causal association between GM and glaucoma. Genome-wide association study summary statistics of 196 GM taxa (n=18 340) and glaucoma (18 902 cases and 358 375 controls) were obtained from MiBioGen and FinnGen Consortium. Inverse variance weighted, MR-Egger, weighted median, weighted mode, Mendelian Randomisation Pleiotropy Residual Sum and Outlier, MR-Egger intercept and Cochran's Q statistical analyses were used to supplement MR results and sensitivity analysis. An independent cohort from the Medical Research Council (MRC) Integrative Epidemiology Unit at the University of Bristol (MRC-IEU) Consortium (1715 cases and 359 479 controls) was used to validate causal effects.

RESULTS

Results of the MR analysis suggested that the family Oxalobacteraceae (OR 0.900, 95% CI 0.843 to 0.961, p=0.002) and the genus Eggerthella (OR 0.881, 95% CI 0.811 to 0.957, p=0.003) had a negative effect on glaucoma, whereas the genus Bilophila (OR 1.202, 95% CI 1.074 to 1.346, p=0.001), LachnospiraceaeUCG010 (OR 1.256, 95% CI 1.109 to 1.423, p=0.0003) and Ruminiclostridium 9 (OR 1.258, 95% CI 1.083 to 1.461, p=0.003) had a positive effect on glaucoma. Among these, the positive causal effect of LachnospiraceaeUCG010 (OR 1.002, 95% CI 1.000 to 1.004, p=0.033) on glaucoma was replicated in an independent cohort.

CONCLUSION

This MR analysis from large population studies demonstrated the causal effect of GM on glaucoma risk and supported the role of GM in influencing glaucoma susceptibility.

Exploring public interest in gut microbiome dysbiosis, NAFLD, and probiotics using Google Trends

Scientific interest related to the role of gut microbiome dysbiosis in the pathogenesis of non-alcoholic fatty liver disease (NAFLD) has now been established and is constantly growing. Therefore, balancing dysbiosis, through probiotics, would be a potential therapy. In addition to scientific interest, on the other hand, it is important to evaluate the interest in these topics among the population. This study aimed to analyze, temporally and geographically, the public's interest in gut microbiome dysbiosis, NAFLD, and the use of gut probiotics. The most widely used free tool for analyzing online behavior is Google Trends. Using Google Trends data, we have analyzed worldwide volume searches for the terms "gut microbiome", "dysbiosis", "NAFLD" and "gut probiotic" for the period from 1, January 2007 to 31 December 2022. Google's relative search volume (RSV) was collected for all terms and analyzed temporally and geographically. The RSV for the term "gut microbiome" has a growth rate of more than 1400% followed, by "gut probiotics" (829%), NAFLD (795%), and "dysbiosis" (267%) from 2007 to 2012. In Australia and New Zealand, we found the highest RSV score for the term "dysbiosis" and "gut probiotics". Moreover, we found the highest RSV score for the term "NAFLD" in the three countries: South Korea, Singapore, and the Philippines. Google Trends analysis showed that people all over the world are interested in and aware of gut microbiome dysbiosis, NAFLD, and the use of gut probiotics. These data change over time and have a geographical distribution that could reflect the epidemiological worldwide condition of NAFLD and the state of the probiotic market.

Role of Perturbated Hemostasis in MASLD and Its Correlation with Adipokines

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) continues to rise, making it one of the most prevalent chronic liver disorders. MASLD encompasses a range of liver pathologies, from simple steatosis to metabolic dysfunction-associated steatohepatitis (MASH) with inflammation, hepatocyte damage, and fibrosis. Interestingly, the liver exhibits close intercommunication with fatty tissue. In fact, adipose tissue could contribute to the etiology and advancement of MASLD, acting as an endocrine organ that releases several hormones and cytokines, with the adipokines assuming a pivotal role. The levels of adipokines in the blood are altered in people with MASLD, and recent research has shed light on the crucial role played by adipokines in regulating energy expenditure, inflammation, and fibrosis in MASLD. However, MASLD disease is a multifaceted condition that affects various aspects of health beyond liver function, including its impact on hemostasis. The alterations in coagulation mechanisms and endothelial and platelet functions may play a role in the increased vulnerability and severity of MASLD. Therefore, more attention is being given to imbalanced adipokines as causative agents in causing disturbances in hemostasis in MASLD. Metabolic inflammation and hepatic injury are fundamental components of MASLD, and the interrelation between these biological components and the hemostasis pathway is delineated by reciprocal influences, as well as the induction of alterations. Adipokines have the potential to serve as the shared elements within this complex interrelationship. The objective of this review is to thoroughly examine the existing scientific knowledge on the impairment of hemostasis in MASLD and its connection with adipokines, with the aim of enhancing our comprehension of the disease.

The role of the microbiota in glaucoma

Glaucoma is a common irreversible vision loss disorder because of the gradual loss of retinal ganglion cells (RGCs) and the optic nerve axons. Major risk factors include elder age and high intraocular pressure (IOP). However, high IOP is neither necessary nor sufficient to cause glaucoma. Some non-IOP signaling cascades can mediate RGC degeneration. In addition, gender, diet, obesity, depression, or anxiety also contribute to the development of glaucoma. Understanding the mechanism of glaucoma development is crucial for timely diagnosis and establishing new strategies to improve current IOP-reducing therapies. The microbiota exerts a marked influence on the human body during homeostasis and disease. Many glaucoma patients have abnormal compositions of the microbiota (dysbiosis) in multiple locations, including the ocular surface, intraocular cavity, oral cavity, stomach, and gut. Here, we discuss findings in the last ten years or more about the microbiota and metabolite changes in animal models, patients with three risk factors (aging, obesity, and depression), and glaucoma patients. Antigenic mimicry and heat stress protein (HSP)-specific T-cell infiltration in the retina may be responsible for commensal microbes contributing to glaucomatous RGC damage. LPS-TLR4 pathway may be the primary mechanism of oral and ocular surface dysbiosis affecting glaucoma. Microbe-derived metabolites may also affect glaucoma pathogenesis. Homocysteine accumulation, inflammatory factor release, and direct dissemination may link gastric H. pylori infection and anterior chamber viral infection (such as cytomegalovirus) to glaucoma. Potential therapeutic protocols targeting microbiota include antibiotics, modified diet, and stool transplant. Later investigations will uncover the underlying molecular mechanism connecting dysbiosis to glaucoma and its clinical applications in glaucoma management.

The Role of Gut Microbiota in Glaucoma Progression and Other Retinal Diseases

As a rapidly growing field, microbiota research offers novel approaches to promoting ocular health and treating major retinal diseases, such as glaucoma. Gut microbiota changes throughout life; however, certain patterns of population changes have been increasingly associated with specific diseases. It has been well established that a disrupted microbiome contributes to central nervous system diseases, including Alzheimer disease, Parkinson disease, multiple sclerosis, and glioma, suggesting a prominent role of microbiome in neurodegenerative diseases. This review summarizes the progress in identifying significant changes in the microbial composition of patients with glaucoma by compiling studies on the association between microbiota and disease progression. Of interest is the relationship between increased Firmicutes/Bacteroidetes ratio in patients with primary open-angle glaucoma, increased taurocholic acid, decreased glutathione, and a reduction in retinal ganglion cell survival. Connecting these microbes to specific metabolites sheds light on the pathogenic mechanism and novel treatment strategies. In summary, the current review synthesizes the findings of several studies investigating the effects of shifting bacterial population in retinal diseases, particularly glaucoma, with the aim to identify the current direction of treatment and help direct future endeavors.

Gut Microbiome in the Progression of NAFLD, NASH and Cirrhosis, and Its Connection with Biotics: A Bibliometric Study Using Dimensions Scientific Research Database

There is growing evidence that gut microbiota dysbiosis is linked to the etiopathogenesis of nonalcoholic fatty liver disease (NAFLD), from the initial stage of disease until the progressive stage of nonalcoholic steatohepatitis (NASH) and the final stage of cirrhosis. Conversely, probiotics, prebiotics, and synbiotics have shown promise in restoring dysbiosis and lowering clinical indicators of disease in a number of both preclinical and clinical studies. Additionally, postbiotics and parabiotics have recently garnered some attention. The purpose of this bibliometric analysis is to assess recent publishing trends concerning the role of the gut microbiome in the progression of NAFLD, NASH and cirrhosis and its connection with biotics. The free access version of the Dimensions scientific research database was used to find publications in this field from 2002 to 2022. VOSviewer and Dimensions' integrated tools were used to analyze current research trends. Research into the following topics is expected to emerge in this field: (1) evaluation of risk factors which are correlated with the progression of NAFLD, such as obesity and metabolic syndrome; (2) pathogenic mechanisms, such as liver inflammation through toll-like receptors activation, or alteration of short-chain fatty acids metabolisms, which contribute to NAFLD development and its progression in more severe forms, such as cirrhosis; (3) therapy for cirrhosis through dysbiosis reduction, and research on hepatic encephalopathy a common consequence of cirrhosis; (4) evaluation of diversity, and composition of gut microbiome under NAFLD, and as it varies under NASH and cirrhosis by rRNA gene sequencing, a tool which can also be used for the development of new probiotics and explore into the impact of biotics on the gut microbiome; (5) treatments to reduce dysbiosis with new probiotics, such as Akkermansia, or with fecal microbiome transplantation.