Gut microbiota influences pathological angiogenesis in obesity-driven choroidal neovascularization

The role of immune modulators in age-related macular degeneration

We provide an overview of the expanding literature on the role of cytokines and immune mediators in pathophysiology of age-related macular degeneration (AMD). Although many immunological mediators have been linked to AMD pathophysiology, the broader mechanistic picture remains unclear with substantial variations in the levels of evidence supporting these mediators. Therefore, we reviewed the literature considering the varying levels of supporting evidence. A Medical Subject Headings (MeSH) term-based literature research was conducted in September, 2023, consisting of the MeSH terms "cytokine" and "Age-related macular degeneration" connected by the operator "AND". After screening the publications by title, abstract, and full text, a total of 146 publications were included. The proinflammatory cytokines IL-1β (especially in basic research studies), IL-6, IL-8, IL-18, TNF-α, and MCP-1 are the most extensively characterised cytokines/chemokines, highlighting the role of local inflammasome activation and altered macrophage function in the AMD pathophysiology. Among the antiinflammatory mediators IL-4, IL-10, and TGF-β were found to be the most extensively characterised, with IL-4 driving and IL-10 and TGF-β suppressing disease progression. Despite the extensive literature on this topic, a profound understanding of AMD pathophysiology has not yet been achieved. Therefore, further studies are needed to identify potential therapeutic targets, followed by clinical studies.

Complement proteins and complement regulatory proteins are associated with age-related macular degeneration stage and treatment response

BACKGROUND

Dysregulation of the complement system is involved in development of age-related macular degeneration (AMD). The complement cascade is regulated by membrane bound complement regulatory proteins (Cregs) on mononuclear leukocytes among others. This study aims to investigate systemic complement proteins and Cregs in AMD stages and their association with treatment response in neovascular AMD (nAMD).

METHODS

In this clinical prospective study, treatment-naïve patients with nAMD, intermediate AMD (iAMD) and healthy controls were recruited and systemic complement proteins C3, C3a and C5a were investigated with electrochemiluminescence immunoassays, and Creg expression (CD35, CD46 and CD59) on T cells (CD4 + and CD8+) and monocytes (classical, intermediate and non-classical) investigated with flow cytometry. Treatment response in nAMD patients was evaluated after loading dose and after one year, and categorized as good, partial or poor. Complement proteins and Creg expression levels were compared between healthy controls, iAMD and nAMD, as well as between good, partial and poor nAMD treatment response groups. Polymorphisms in the CFH and ARMS2 genes were analyzed and compared to complement proteins and Creg expression levels in nAMD patients.

RESULTS

One hundred patients with nAMD, 34 patients with iAMD and 61 healthy controls were included. 94 nAMD patients completed the 1-year follow-up. Distribution of treatment response in nAMD was 61 (65%) good, 26 (28%) partial, and 7 (7%) poor responders. The distribution of 1-year treatment response was 50 (53%) good, 33 (36%) partial, and 11 (11%) poor responders. The concentrations of systemic C3, C3a, and the C3a/C3-ratio were significantly increased in patients with nAMD compared to healthy controls (P < 0.001, P = 0.002, and P = 0.035, respectively). Systemic C3 was also increased in iAMD compared to healthy controls (P = 0.031). The proportion of CD46 + CD4 + T cells and CD59 + intermediate monocytes were significantly decreased in patients with nAMD compared to healthy controls (P = 0.018 and P = 0.042, respectively). The post-loading dose partial treatment response group had significantly lower concentrations of C3a and C5a compared to the good response group (P = 0.005 and P = 0.042, respectively). The proportion of CD35 + monocytes was significantly lower in the 1-year partial response group compared to the 1-year good response group (P = 0.039). High-risk CFH genotypes in nAMD patients was associated with increased C3a, C3a/C3-ratio, and expression levels of CD35 + CD8 + T cells and CD46 + classical monocytes, while expression level of CD46 + non-classical monocytes was decreased.

CONCLUSION

Elevated concentrations of systemic complement proteins were found in patients with iAMD and nAMD. Decreased Creg expression levels were found in patients with nAMD. Partially responding nAMD patients had a dysregulated complement system and Cregs compared to good responders.

Gut microbiota and eye diseases: A review

Recent studies reveal that alterations in gut microbiota play a significant role in the progression of various diseases, including those affecting the eyes. The association between gut microbiota and eye health is an emerging focus of research. This review seeks to summarize the connection between the gut microbiome and specific eye conditions, such as ocular surface diseases, funduscopic disorders and immune-mediated eye diseases. Gut microbiota may influence these conditions by regulating the immune system or altering metabolites, thereby contributing to disease development. Strategies like probiotics, antibiotics, dietary modifications, and fecal transplants show promise in addressing these issues. This review examines how the gut microbiome may be linked to the pathogenesis of eye diseases, providing fresh therapeutic perspectives for ophthalmology.

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.

From Gut to Eye: Exploring the Role of Microbiome Imbalance in Ocular Diseases

Background: The gut microbiome plays a crucial role in human health, and recent research has highlighted its potential impact on ocular health through the gut-eye axis. Dysbiosis, or an imbalance in the gut microbiota, has been implicated in various ocular diseases. Methods: A comprehensive literature search was conducted using relevant keywords in major electronic databases, prioritizing recent peer-reviewed articles published in English. Results: The gut microbiota influences ocular health through immune modulation, maintenance of the blood-retinal barrier, and production of beneficial metabolites. Dysbiosis can disrupt these mechanisms, contributing to ocular inflammation, tissue damage, and disease progression in conditions such as uveitis, age-related macular degeneration, diabetic retinopathy, dry eye disease, and glaucoma. Therapeutic modulation of the gut microbiome through probiotics, prebiotics, synbiotics, and fecal microbiota transplantation shows promise in preclinical and preliminary human studies. Conclusions: The gut-eye axis represents a dynamic and complex interplay between the gut microbiome and ocular health. Targeting the gut microbiome through innovative therapeutic strategies holds potential for improving the prevention and management of various ocular diseases.

Housing RCS rats under specific pathogen-free conditions mildly ameliorates retinal degeneration and alters intestine microbiota

Retinitis pigmentosa (RP) is a genetic blinding disease with over 80 causative genes. Disease progression varies between patients with similar genetic backgrounds. We assessed the association between environment, gut microbiota, and retinal degeneration in the RP rat model Royal College of Surgeons (RCS). The rats were born and raised for two generations under specific pathogen-free (SPF, n = 69) or non-SPF conditions (n = 48). At the age of four weeks, SPF rats had significantly shorter dark-adapted a-wave and dark and light-adapted b-wave implicit times by electroretinogram (p = 0.014, p = 9.5*10-6, p = 0.009, respectively). The SPF rats had significantly less photoreceptor apoptosis at ages four, eight, and twelve weeks (all p < 0.022), significantly thicker debris zone at age 14 weeks, and smaller hypofluorescent lesions in SPF rats at ages 10-16 weeks, especially in the inferior retina. The non-SPF rats had significantly higher microbiota alpha diversity (p = 0.037) and failed to present the age-related maturation of Proteobacteria, Spirochaetes, Actinobacteria, and Bacteroidetes seen in SPF conditions. Specific microbial amplicon sequence variants were reduced in rats with more severe retinal degeneration. Our data suggest an environmental effect on retinal deterioration in RCS rats. These findings may lead to the development of novel microbiome-related interventions for retinal degeneration.

Pharmacomicrobiomics in precision cancer therapy: bench to bedside

The burgeoning field of pharmacomicrobiomics offers promising insights into the intricate interplay between the microbiome and cancer, shaping responses to diverse treatment modalities. This review aims to analyze the molecular mechanisms underlying interactions between distinct microbiota types and cancer, as well as their influence on treatment outcomes. We explore how the microbiome impacts antitumor immunity, and response to chemotherapy, immunotherapy, and radiation therapy, unveiling its multifaceted roles in cancer progression and therapy resistance. Moreover, we discuss the challenges hindering the development of microbiome-based interventions in cancer therapy, including standardization, validation, and clinical translation. By synthesizing clinical evidence, we underscore the transformative potential of harnessing pharmacomicrobiomics in guiding cancer treatment decisions, paving the way for improved patient outcomes in clinical practice.

Gut microbiota-derived indole-3-acetic acid suppresses high myopia progression by promoting type I collagen synthesis

High myopia (HM) is a leading cause of blindness worldwide with currently no effective interventions available. A major hurdle lies in its often isolated perception as a purely ocular morbidity, disregarding potential systemic implications. Recent evidence suggests the existence of a gut-eye axis; however, the role of gut microbiota in the pathogenesis of HM remains largely unexplored. Herein, we provide a potential crosstalk among HM's gut dysbiosis, microbial metabolites, and scleral remodeling. Utilizing 16S rRNA gene sequencing, we observed an altered gut microbiota profile in HM patients with a significant reduction in probiotic abundance compared with healthy controls. Subsequent targeted metabolic profiling revealed a notable decrease in plasma levels of the gut microbiota-derived metabolite indole-3-acetic acid (3-IAA) among HM patients, which is closely associated with the reduced probiotics, both negatively correlated with HM severity. Genetic analyses determined that gut microbiota are causally associated with myopia risk. Importantly, when mice subjected to HM modeling receive fecal microbiota transplantation from healthy donors, there is an increase in 3-IAA plasma levels and simultaneous retardation of HM progression along with better maintenance of collagen type I alpha 1 (COL1A1) expression in the sclera. Furthermore, 3-IAA gavage achieves similar effects. Mechanistic investigations confirm the transcriptional activation of COL1A1 by 3-IAA via promoting the enrichment of SP1 to its promoter. Together, our findings provide novel insights into the gut microbiota-eye axis in the pathogenesis of HM and propose new strategies for HM intervention by remodeling the gut microbiota and indole supplementation.

What is the impact of microbiota on dry eye: a literature review of the gut-eye axis

BACKGROUND

Dry eye is a chronic and multifactorial ocular surface disease caused by tear film instability or imbalance in the microenvironment of the ocular surface. It can lead to various discomforts such as inflammation of the ocular surface and visual issues. However, the mechanism of dry eye is not clear, which results in dry eye being only relieved but not cured in clinical practice. Finding multiple environmental pathways for dry eye and exploring the pathogenesis of dry eye have become the focus of research. Studies have found that changes in microbiota may be related to the occurrence and development of dry eye disease.

METHODS

Entered the keywords "Dry eye", "Microbiota", "Bacteria" through PUBMED, summarised the articles that meet the inclusion criteria and then filtered them while the publication time range of the literature was defined in the past 5 years, with a deadline of 2023.A total of 13 clinical and 1 animal-related research articles were screened out and included in the summary.

RESULTS

Study found that different components of bacteria can induce ocular immune responses through different receptors present on the ocular surface, thereby leading to an imbalance in the ocular surface microenvironment. Changes in the ocular surface microbiota and gut microbiota were also found when dry eye syndrome occurs, including changes in diversity, an increase in pro-inflammatory bacteria, and a decrease in short-chain fatty acid-related bacterial genera that produce anti-inflammatory effects. Fecal microbiota transplantation or probiotic intervention can alleviate signs of inflammation on the ocular surface of dry eye animal models.

CONCLUSIONS

By summarizing the changes in the ocular surface and intestinal microbiota when dry eye occurs, it is speculated and concluded that the intestine may affect the occurrence of eye diseases such as dry eye through several pathways and mechanisms, such as the occurrence of abnormal immune responses, microbiota metabolites- intervention of short-chain fatty acids, imbalance of pro-inflammatory and anti-inflammatory factors, and release of neurotransmitters, etc. Analyzing the correlation between the intestinal tract and the eyes from the perspective of microbiota can provide a theoretical basis and a new idea for relieving dry eyes in multiple ways in the future.

Gut microbial dysbiosis in the pathogenesis of leukemia: an immune-based perspective

Leukemias are a set of clonal hematopoietic malignant diseases that develop in the bone marrow. Several factors influence leukemia development and progression. Among these, the gut microbiota is a major factor influencing a wide array of its processes. The gut microbial composition is linked to the risk of tumor development and the host's ability to respond to treatment, mostly due to the immune-modulatory effects of their metabolites. Despite such strong evidence, its role in the development of hematologic malignancies still requires attention of investigators worldwide. In this review, we make an effort to discuss the role of host gut microbiota-immune crosstalk in leukemia development and progression. Additionally, we highlight certain recently developed strategies to modify the gut microbial composition that may help to overcome dysbiosis in leukemia patients in the near future.

The Conjunctival Microbiome and Dry Eye: What We Know and Controversies

ABSTRACT

Dry eye disease is a common multifactorial condition that may be idiopathic or associated with autoimmune conditions, such as Sjogren syndrome. Commensal microorganisms modify immune responses, so it is relevant to understand how they modify such immune-mediated diseases. Microbiota in the gut regulate inflammation in the eye, and conversely, severe inflammation of the ocular surface results in alteration of gut microbiome. The conjunctiva microbiome can be analyzed using 16S or shotgun metagenomics. The amount of microbial DNA in ocular surface mucosa relative to human DNA is limited compared with the case of the intestinal microbiome. There are challenges in defining, harvesting, processing, and analyzing the microbiome in the ocular surface mucosa. Recent studies have shown that the conjunctiva microbiome depends on age, presence of local and systemic inflammation, and environmental factors. Microbiome-based therapy, such as the use of oral probiotics to manage dry eye disease, has initial promising results. Further longitudinal studies are required to investigate the alteration of the conjunctival microbiome after local therapy and surgery.

Causal influence of gut microbiota on small cell lung cancer: a Mendelian randomization study

BACKGROUND

Previous studies have hinted at a significant link between lung cancer and the gut microbiome, yet their causal relationship remains to be elucidated.

METHODS

GWAS data for small cell lung cancer (SCLC) was extracted from the FinnGen consortium, comprising 179 cases and 218 613 controls. Genetic variation data for 211 gut microbiota were obtained as instrumental variables from MiBioGen. Mendelian randomization (MR) was employed to determine the causal relationship between the two, with inverse variance weighting (IVW) being the primary method for causal analysis. The MR results were validated through several sensitivity analyses.

RESULTS

The study identified a protective effect against SCLC for the genus Eubacterium ruminantium group (OR = 0.413, 95% CI: 0.223-0.767, p = 0.00513), genus Barnesiella (OR = 0.208, 95% CI: 0.0640-0.678, p = 0.00919), family Lachnospiraceae (OR = 0.319, 95% CI: 0.107-0.948, p = 0.03979), and genus Butyricimonas (OR = 0.376, 95% CI: 0.144-0.984, p = 0.04634). Conversely, genus Intestinibacter (OR = 3.214, 95% CI: 1.303-7.926, p = 0.01125), genus Eubacterium oxidoreducens group (OR = 3.391, 95% CI: 1.215-9.467, p = 0.01973), genus Bilophila (OR = 3.547, 95% CI: 1.106-11.371, p = 0.03315), and order Bacillales (OR = 1.860, 95% CI: 1.034-3.347, p = 0.03842) were found to potentially promote the onset of SCLC.

CONCLUSION

We identified potential causal relationships between certain gut microbiota and SCLC, offering new insights into microbiome-mediated mechanisms of SCLC pathogenesis, resistance, mutations, and more.

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.

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.

A narrative review on dietary components and patterns and age-related macular degeneration

Age-related macular degeneration (AMD) is one of the most prevalent eye diseases among the ageing population worldwide. It is a leading cause of blindness in individuals over 55, particularly in industrialised Western countries. The prevalence of AMD increases with age, and genetic factors and environmental influences are believed to contribute to its development. Among the environmental factors, diet plays a significant role in AMD. This review explores the association between dietary components, dietary patterns and AMD. Various nutrients, non-nutrient substances and dietary models that have the potential to counteract oxidative stress and inflammation, which are underlying mechanisms of AMD, are discussed. Consuming fruits, vegetables, fish and seafood, whole grains, olive oil, nuts and low-glycaemic-index foods has been highlighted as beneficial for reducing the risk of AMD. Adhering to the Mediterranean diet, which encompasses these elements, can be recommended as a dietary pattern for AMD. Furthermore, the modulation of the gut microbiota through dietary interventions and probiotics has shown promise in managing AMD.

Epidemiology of geographic atrophy and its precursor features of intermediate age-related macular degeneration

Globally age-related macular degeneration (AMD) is a leading cause of blindness with a significant impact on quality of life. Geographic atrophy (GA) is the atrophic late form of AMD and its prevalence increases markedly with age with around 1 in 5 persons aged 85 and above having GA in at least one eye. Bilateral GA leads to severe visual impairment thus posing a significant burden on patients, careers and health providers. The incidence and prevalence of GA varies across different geographic regions, with the highest rates in those of European ancestry. Although heterogeneity in definitions of GA and reporting strategy can explain some of the discrepancies, the data overall are consistent in showing a lower prevalence in other ethnicities such as those of Asian heritage. This is at present unexplained but thought to be due to the existence of protective factors such as differences in eye pigmentation, diet, environmental exposures and genetic variability. This review covers key aspects of the prevalence and incidence of the ocular precursor features of GA (large drusen, pigmentary abnormalities and reticular pseudo-drusen), the late stage of GA and factors that have been known to be associated with modifying risk including systemic, demographic, environment, genetic and ocular. Understanding the global epidemiology scenario is crucial for the prevention of and management of patients with GA.

Associations Between Autoimmune Disease and the Development of Age-Related Macular Degeneration

Purpose

The pathogenesis of age-related macular degeneration (AMD) likely implicates the dysregulation of immune response pathways. Several studies demonstrate that the pathogenic elements of AMD resemble those of autoimmune diseases, yet the association between AMD development and most autoimmune diseases remain unexplored.

Methods

We conducted a case-control analysis of patients ages 55 and older with new-onset International Classification of Diseases (ICD) coding of dry, wet, or unspecified AMD between 2005 and 2019 in the Merative MarketScan Commercial and Medicare Databases. The diagnosis of an autoimmune disease was defined by an outpatient or inpatient claim with a relevant ICD code in the 12 months before the index visit. Conditional multivariable logistic regression, adjusted for AMD risk factors, was used to calculate odd ratios and 95% confidence intervals.

Results

We identified 415,027 cases with new-onset ICD coding for AMD matched with propensity scores to 414,853 controls. In total, 16.1% of cases and 15.9% of controls were diagnosed with any autoimmune disease. The diagnosis of any autoimmune disease did not affect the odds of new-onset ICD coding for AMD in multivariable regression (OR = 1.01; 95% CI, 0.999-1.02). Discoid lupus erythematosus (OR = 1.29; 95% CI, 1.12-1.48), systemic lupus erythematosus (SLE) (OR = 1.21; 95% CI, 1.15-1.27), giant cell arteritis (OR = 1.19; 95% CI, 1.09-1.30), Sjogren's syndrome (OR = 1.17; 95% CI, 1.09-1.26), and Crohn's disease (OR = 1.13; 95% CI, 1.06-1.22) increased the odds of a new-onset ICD coding for AMD.

Conclusions

Most autoimmune diseases do not affect the odds of developing AMD but several common autoimmune disorders such as SLE and Crohn's disease were associated with modestly increased odds of AMD. Further studies are needed to validate and investigate the underlying mechanisms of these associations.

Microbiota in cancer: molecular mechanisms and therapeutic interventions

The diverse bacterial populations within the symbiotic microbiota play a pivotal role in both health and disease. Microbiota modulates critical aspects of tumor biology including cell proliferation, invasion, and metastasis. This regulation occurs through mechanisms like enhancing genomic damage, hindering gene repair, activating aberrant cell signaling pathways, influencing tumor cell metabolism, promoting revascularization, and remodeling the tumor immune microenvironment. These microbiota-mediated effects significantly impact overall survival and the recurrence of tumors after surgery by affecting the efficacy of chemoradiotherapy. Moreover, leveraging the microbiota for the development of biovectors, probiotics, prebiotics, and synbiotics, in addition to utilizing antibiotics, dietary adjustments, defensins, oncolytic virotherapy, and fecal microbiota transplantation, offers promising alternatives for cancer treatment. Nonetheless, due to the extensive and diverse nature of the microbiota, along with tumor heterogeneity, the molecular mechanisms underlying the role of microbiota in cancer remain a subject of intense debate. In this context, we refocus on various cancers, delving into the molecular signaling pathways associated with the microbiota and its derivatives, the reshaping of the tumor microenvironmental matrix, and the impact on tolerance to tumor treatments such as chemotherapy and radiotherapy. This exploration aims to shed light on novel perspectives and potential applications in the field.

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.

Gut Microbiome and Retinopathy of Prematurity

Retinopathy of prematurity (ROP), a leading cause of childhood blindness worldwide, is strongly associated with gestational age and weight at birth. Yet, many extremely preterm infants never develop ROP or develop only mild ROP with spontaneous regression. In addition, a myriad of other factors play a role in the retinal pathology, one of which may include the early gut microbiome. The complications associated with early gestational age include dysbiosis of the dynamic neonatal gut microbiome, as evidenced by the development of often concomitant conditions, such as necrotizing enterocolitis. Given this, alongside growing evidence for a gut-retina axis, there is an increasing interest in how the early intestinal environment may play a role in the pathophysiology of ROP. Potential mechanisms include dysregulation of vascular endothelial growth factor and insulin-like growth factor 1. Furthermore, the gut microbiome may be impacted by other known risk factors for ROP, such as intermittent hypoxia and sepsis treated with antibiotics. This mini-review summarizes the literature supporting these proposed avenues, establishing a foundation to guide future studies.

The Emerging Role of Gut Microbiota in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a progressive, degenerative retinal disease that is a leading cause of blindness globally. Although multiple risk factors have been identified regarding disease incidence and progression, including smoking, genetics, and diet, the understanding of AMD pathogenesis remains unclear. As such, primary prevention is lacking, and current treatments have limited efficacy. More recently, the gut microbiome has emerged as an influential player in various ocular pathologies. As mediators of metabolism and immune regulation, perturbations in gut microbiota may impart significant effects distally on the neuroretina and its adjacent tissues, termed the gut-retina axis. In this review, key studies over the past several decades are summarized, both in humans and in animal models, which shed insight on the relationships between the gut microbiome and retinal biology and their implications for AMD. The literature linking gut dysbiosis with AMD is examined, along with preclinical animal models and techniques apt for studying the role of gut microbiota in AMD pathogenesis, which include interactions with systemic inflammation, immune regulation, chorioretinal gene expression, and diet. As understanding of the gut-retina axis continues to advance, so too will the possibility for more accessible and effective prevention and therapy of this vision-threatening condition.

Gut-spine axis: a possible correlation between gut microbiota and spinal degenerative diseases

As society ages, the number of patients with spinal degenerative diseases (SDD) is increasing, posing a major socioeconomic problem for patients and their families. SDD refers to a generic term for degenerative diseases of spinal structures, including osteoporosis (bone), facet osteoarthritis (joint), intervertebral disk degeneration (disk), lumbar spinal canal stenosis (yellow ligament), and spinal sarcopenia (muscle). We propose the term "gut-spine axis" for the first time, given the influence of gut microbiota (GM) on the metabolic, immune, and endocrine environment in hosts through various potential mechanisms. A close cross-talk is noted between the aforementioned spinal components and degenerative diseases. This review outlines the nature and role of GM, highlighting GM abnormalities associated with the degeneration of spinal components. It also summarizes the evidence linking GM to various SDD. The gut-spine axis perspective can provide novel insights into the pathogenesis and treatment of SDD.

Insights into the liver-eyes connections, from epidemiological, mechanical studies to clinical translation

Maintenance of internal homeostasis is a sophisticated process, during which almost all organs get involved. Liver plays a central role in metabolism and involves in endocrine, immunity, detoxification and storage, and therefore it communicates with distant organs through such mechanisms to regulate pathophysiological processes. Dysfunctional liver is often accompanied by pathological phenotypes of distant organs, including the eyes. Many reviews have focused on crosstalk between the liver and gut, the liver and brain, the liver and heart, the liver and kidney, but with no attention paid to the liver and eyes. In this review, we summarized intimate connections between the liver and the eyes from three aspects. Epidemiologically, we suggest liver-related, potential, protective and risk factors for typical eye disease as well as eye indicators connected with liver status. For molecular mechanism aspect, we elaborate their inter-organ crosstalk from metabolism (glucose, lipid, proteins, vitamin, and mineral), detoxification (ammonia and bilirubin), and immunity (complement and inflammation regulation) aspect. In clinical application part, we emphasize the latest advances in utilizing the liver-eye axis in disease diagnosis and therapy, involving artificial intelligence-deep learning-based novel diagnostic tools for detecting liver disease and adeno-associated viral vector-based gene therapy method for curing blinding eye disease. We aim to focus on and provide novel insights into liver and eyes communications and help resolve existed clinically significant issues.

The Association of Antibiotic Use and the Odds of a New-Onset ICD Code Diagnosis of Age-Related Macular Degeneration: A Large National Case-Control Study

Purpose

The widespread use of antibiotics has many well-documented impacts on the human microbiome, which may be associated with the development of various inflammatory diseases. Despite age-related macular degeneration (AMD) featuring an inflammatory pathogenesis, the relationship between antibiotics and AMD has remained unexplored. We conducted the first study to determine the association between antibiotic exposure and a new-onset International Classification of Diseases (ICD) diagnosis of AMD.

Methods

We performed a case-control analysis of patients aged 55 and older with new-onset AMD between 2008 and 2017 from a nationwide commercial health insurance claims database. Exposure to antibiotics in the two years before the index date was determined for cases and controls matched one-to-one by age, year, region, anemia, hypertension, and a comorbidity index. Conditional multivariable logistic regression, adjusted for AMD risk factors, was performed to calculate odd ratios (OR) and 95% confidence intervals (CI).

Results

Among the antibiotic classes, exposure to aminoglycosides (OR = 1.24; 95% CI, 1.22-1.26) and fluoroquinolones (OR = 1.13; 95% CI, 1.12-1.14) was associated with the greatest odds of a new-onset ICD code diagnosis of AMD. Broad-spectrum antibiotics were associated with nearly three times greater odds of a new-onset ICD code diagnosis of AMD (OR = 1.15; 95% CI, 1.13-1.16) compared to narrow-spectrum antibiotics (OR = 1.05; 95% CI, 1.03-1.07). We also identified a frequency- and duration-dependent association, with a greater cumulative number of antibiotic prescriptions or day supply of antibiotics conferring increased odds of a new-onset ICD code diagnosis of AMD.

Conclusions

Greater cumulative exposure to antibiotics, particularly fluoroquinolones, aminoglycosides, and those with broader-spectrum coverage, may be associated with the development of AMD, a finding that requires further investigation using prospective studies.

Causal Effects of Gut Microbiota on Age-Related Macular Degeneration: A Mendelian Randomization Study

Purpose

Recently, the association between gut microbiota and age-related macular degeneration (AMD) through the gut-retina axis has attracted great interest. However, the causal relationship between them has not been elucidated. Using publicly available genome-wide association study summary statistics, we conducted a two-sample Mendelian randomization (MR) analysis to examine the causal relationship between the gut microbiota and the occurrence of AMD.

Methods

The study used a variety of quality control techniques to select instrumental single nucleotide polymorphisms (SNPs) with strong exposure associations. We used a set of SNPs as instrumental variable that were below the genome-wide statistical significance threshold (5 × 10-8). Additionally, a separate group of SNPs below the locus-wide significance level (1 × 10-5) were selected as instrumental variables to ensure a comprehensive conclusion. Inverse variance-weighted (IVW) analysis was the primary technique we used to examine causality in order to confirm the validity of our findings. The MR-Egger intercept test, Cochran's Q test, and leave-one-out sensitivity analysis were used to evaluate the horizontal pleiotropy, heterogeneities, and stability of the genetic variants.

Results

IVW results showed that genus Anaerotruncus (P = 5.00 × 10-3), genus Candidatus Soleaferrea (P = 1.83 × 10-2), and genus unknown id.2071 (P = 3.12 × 10-2) were protective factors for AMD. The Eubacterium oxidoreducens group (P = 3.17 × 10-2), genus Faecalibacterium (P = 2.67 × 10-2), and genus Ruminococcaceae UCG-011 (P = 4.04 × 10-2) were risk factors of AMD. No gut microbiota (GM) taxa were found to be causally related to AMD at the phylum, class, order, and family levels (P > 0.05). The robustness of MR results were confirmed by heterogeneity and pleiotropy analysis. (P > 0.05). We also performed a bidirectional analysis, which showed that genus Anaerotruncus, genus Candidatus Soleaferrea, genus unknown id.2071 and the Eubacterium oxidoreducens group had an interaction with AMD, whereas genus Faecalibacterium showed only a unilateral unfavorable effect on AMD.

Conclusions

We confirmed a causal relationship between AMD and GM taxa, including the Eubacterium oxidoreducens group, Faecalibacterium, Ruminococcaceae UCG-011, Anaerotruncus, and Candidatus Soleaferrea. These strains have the potential to serve as new biomarkers, offering valuable insights into the treatment and prevention of AMD.

Targeting the Gut-Eye Axis: An Emerging Strategy to Face Ocular Diseases

The human microbiota refers to a large variety of microorganisms (bacteria, viruses, and fungi) that live in different human body sites, including the gut, oral cavity, skin, and eyes. In particular, the presence of an ocular surface microbiota with a crucial role in maintaining ocular surface homeostasis by preventing colonization from pathogen species has been recently demonstrated. Moreover, recent studies underline a potential association between gut microbiota (GM) and ocular health. In this respect, some evidence supports the existence of a gut-eye axis involved in the pathogenesis of several ocular diseases, including age-related macular degeneration, uveitis, diabetic retinopathy, dry eye, and glaucoma. Therefore, understanding the link between the GM and these ocular disorders might be useful for the development of new therapeutic approaches, such as probiotics, prebiotics, symbiotics, or faecal microbiota transplantation through which the GM could be modulated, thus allowing better management of these diseases.

Gut microbiota and eye diseases: a bibliometric study and visualization analysis

Introduction

Recently the role of gut microbial dysbiosis in many ocular disorders, including but not limited to uveitis, age-related macular degeneration (AMD), diabetic retinopathy (DR), dry eye, keratitis and orbitopathy is a hot research topic in the field. Targeting gut microbiota to treat these diseases has become an unstoppable trend. Bibliometric study and visualization analysis have become essential methods for literature analysis in the medical research field. We aim to depict this area's research hotspots and future directions by bibliometric software and methods.

Methods

We search all the related publications from the Web of Science Core Collection. Then, CiteSpace was applied to analyze and visualize the country distributions, dual-map overlay of journals, keyword bursts, and co-cited references. VOSviewer was employed to identify authors, co-cited authors, journals and co-cited journals and display the keyword co-occurrence networks.

Results

A total of 284 relevant publications were identified from 2009 to 2023. The number of studies has been small in the first five years and has grown steadily since 2016. These studies were completed by 1,376 authors from 41 countries worldwide, with the United States in the lead. Lin P has published the most papers while Horai R is the most co-cited author. The top journal and co-cited journal are both Investigative Ophthalmology & Visual Science. In the keyword co-occurrence network, except gut microbiota, inflammation becomes the keyword with the highest frequency. Co-citation analyses reveal that gut dysbiosis is involved in common immune- and inflammation-mediated eye diseases, including uveitis, diabetic retinopathy, age-related macular degeneration, dry eye, and Graves' orbitopathy, and the study of microbiomes is no longer limited to the bacterial populations. Therapeutic strategies that target the gut microbiota, such as probiotics, healthy diet patterns, and fecal microbial transplantation, are effective and critical to future research.

Conclusions

In conclusion, the bibliometric analysis displays the research hotspots and developmental directions of the involvement of gut microbiota in the pathogenesis and treatment of some ocular diseases. It provides an overview of this field's dynamic evolution and structural relationships.

Mendelian randomization analysis reveals causal relationships between gut microbiome and optic neuritis

BACKGROUND

It is unclear whether gut microbiota (GM) affects the risk of optic neuritis (ON) through the "gut-brain" axis and the "gut-retina" axis. To examine the causal relationship between GM and ON, we conducted Mendelian randomization (MR) study.

METHODS

Up to 18,340 samples of 24 population-based cohorts were included in genome-wide association study (GWAS) of 196 GM taxa. ON outcomes were selected from the FinnGen GWAS (951 ON cases and 307,092 controls). In addition, the GWAS based on UK Biobank (UKB) (105 ON cases and 456,243 controls) was used for further exploration. Inverse variance weighted (IVW) was carried out to estimate their effects on ON risk and the MR assumptions were evaluated in sensitivity analyses.

RESULTS

Among the 196 GM taxa, the IVW results confirmed that Family -Peptococcaceae (P = 2.17 × 10-3), Genus- Hungatella (P = 4.57 × 10-3) and genus-Eubacterium_rectale_group (P = 0.02) were correlated with the risk of ON based on Finngen GWAS. Based on data from UKB, Genus- Eubacterium_hallii_group (P = 1.50 × 10-3) and Genus- Ruminococcaceae_UCG_002 (P = 0.02) were correlated with the risk of ON. At the phylum, class and order levels, no GM taxa were causally related to ON (P > 0.05). Heterogeneity (P > 0.05) and pleiotropy (P > 0.05) analysis confirmed the robustness of the MR results.

CONCLUSION

Our MR findings support the causal effect of specific GM taxa on ON. GM may affect the risk of ON through the "gut-brain" axis and the "gut-retina" axis. However, further research is needed to confirm the relevant mechanism of the relationship between GM and ON.

Gut Microbiota and the Microvasculature

The gut microbiota is increasingly recognized as an actuating variable shaping vascular development and endothelial cell function in the intestinal mucosa but also affecting the microvasculature of remote organs. In the small intestine, colonization with gut microbiota and subsequent activation of innate immune pathways promotes the development of intricate capillary networks and lacteals, influencing the integrity of the gut-vascular barrier as well as nutrient uptake. Since the liver yields most of its blood supply via the portal circulation, the hepatic microcirculation steadily encounters microbiota-derived patterns and active signaling metabolites that induce changes in the organization of the liver sinusoidal endothelium, influencing immune zonation of sinusoids and impacting on metabolic processes. In addition, microbiota-derived signals may affect the vasculature of distant organ systems such as the brain and the eye microvasculature. In recent years, this gut-resident microbial ecosystem was revealed to contribute to the development of several vascular disease phenotypes.

The Link Between Gastrointestinal Microbiome and Ocular Disorders

The gut-eye axis has been hypothesized to be a factor in many eye pathologies. This review examines papers from PubMed about this topic. Bacterial commensals could either be protective by regulating the immune system or prove to be damaging to the gut mucosal wall and incite an inflammatory process. The balance between the two appears to be crucial in maintaining eye health. Imbalances have been implicated in ophthalmologic conditions. The use of probiotics, dietary modifications, antibiotics, and faecal microbiota transplant in mice with pathologies such as those encountered in our practice appears to reverse disease course or at least prevent its progression. Clinical trials are currently underway to investigate their clinical significance in diseased patients.

The gut-retina axis: a new perspective in the prevention and treatment of diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular lesion that occurs as a complication of diabetes mellitus. Many studies reveal that retinal neurodegeneration occurs early in its pathogenesis, and abnormal retinal function can occur in patients without any signs of microvascular abnormalities. The gut microbiota is a large, diverse colony of microorganisms that colonize the human intestine. Studies indicated that the gut microbiota is involved in the pathophysiological processes of DR and plays an important role in its development. On the one hand, numerous studies demonstrated the involvement of gut microbiota in retinal neurodegeneration. On the other hand, alterations in gut bacteria in RD patients can cause or exacerbate DR. The present review aims to underline the critical relationship between gut microbiota and DR. After a brief overview of the composition, function, and essential role of the gut microbiota in ocular health, and the review explores the concept of the gut-retina axis and the conditions of the gut-retina axis crosstalk. Because gut dysbiosis has been associated with DR, the review intends to determine changes in the gut microbiome in DR, the hypothesized mechanisms linking to the gut-retina axis, and its predictive potential.

Alterations in Faecal and Serum Metabolic Profiles in Patients with Neovascular Age-Related Macular Degeneration

Neovascular age-related macular degeneration (nAMD) is a common and multifactorial disease in the elderly that may lead to irreversible vision loss; yet the pathogenesis of AMD remains unclear. In this study, nontargeted metabolomics profiling using ultra-performance liquid chromatography coupled with Q-Exactive Orbitrap mass spectrometry was applied to discover the metabolic feature differences in both faeces and serum samples between Chinese nonobese subjects with and without nAMD. In faecal samples, a total of 18 metabolites were significantly altered in nAMD patients, and metabolic dysregulations were prominently involved in glycerolipid metabolism and nicotinate and nicotinamide metabolism. In serum samples, a total of 29 differential metabolites were founded, involved in caffeine metabolism, biosynthesis of unsaturated fatty acids, and purine metabolism. Two faecal metabolites (palmitoyl ethanolamide and uridine) and three serum metabolites (4-hydroxybenzoic acid, adrenic acid, and palmitic acid) were selected as potential biomarkers for nAMD. Additionally, the significant correlations among dysregulated neuroprotective, antineuroinflammatory, or fatty acid metabolites in faecal and serum and IM dysbiosis were found. This comprehensive metabolomics study of faeces and serum samples showed that alterations in IM-mediated neuroprotective metabolites may be involved in the pathophysiology of AMD, offering IM-based nutritional therapeutic targets for nAMD.

Bifidobacterium promotes retinal ganglion cell survival by regulating the balance of retinal glial cells

INTRODUCTION

Optic nerve injury is a leading cause of irreversible blindness worldwide. The retinal ganglion cells (RGCs) and their axons cannot be regenerated once damaged. Therefore, reducing RGC damage is crucial to prevent blindness. Accordingly, we aimed to investigate the potential influence of the gut microbiota on RGC survival, as well as the associated action mechanisms.

METHODS

We evaluated the effects of microbiota, specifically Bifidobacterium, on RGC. Optic nerve crush (ONC) was used as a model of optic nerve injury. Vancomycin and Bifidobacterium were orally administered to specific pathogen-free (SPF) mice.

RESULTS

Bifidobacterium promoted RGC survival and optic nerve regeneration. The administration of Bifidobacterium inhibited microglia activation but promoted Müller cell activation, which was accompanied by the downregulation of inflammatory cytokines and upregulation of neurotrophic factors and retinal ERK/Fos signaling pathway activation.

CONCLUSIONS

Our study demonstrates that Bifidobacterium-induced changes in intestinal flora promote RGC survival. The protective effect of Bifidobacterium on RGC can be attributed to the inhibition of microglia activation and promotion of Müller cell activation and the secondary regulation of inflammatory and neurotrophic factors.

The Role of Retinal Pigment Epithelial Cells in Age-Related Macular Degeneration: Phagocytosis and Autophagy

Age-related macular degeneration (AMD) causes vision loss in the elderly population. Dry AMD leads to the formation of Drusen, while wet AMD is characterized by cell proliferation and choroidal angiogenesis. The retinal pigment epithelium (RPE) plays a key role in AMD pathogenesis. In particular, helioreceptor renewal depends on outer segment phagocytosis of RPE cells, while RPE autophagy can protect cells from oxidative stress damage. However, when the oxidative stress burden is too high and homeostasis is disturbed, the phagocytosis and autophagy functions of RPE become damaged, leading to AMD development and progression. Hence, characterizing the roles of RPE cell phagocytosis and autophagy in the pathogenesis of AMD can inform the development of potential therapeutic targets to prevent irreversible RPE and photoreceptor cell death, thus protecting against AMD.

Anti-inflammatory properties of antiangiogenic fucoidan in retinal pigment epithelium cells

Age-related macular degeneration (AMD) is a multifactorial disease in which angiogenesis, oxidative stress and inflammation are important contributing factors. In this study, we investigated the anti-inflammatory effects of a fucoidan from the brown algae Fucus vesiculosus (FV) in primary porcine RPE cells. Inflammation was induced by lipopolysaccharide (LPS), polyinosinic:polycytidylic acid (Poly I:C), Pam2CSK4 (Pam), or tumor necrosis factor alpha (TNF-α). Cell viability was tested with thiazolyl blue tetrazolium bromide (MTT) test, barrier function by measuring transepithelial electric resistance (TEER), interleukin 6 (IL-6) and interleukin 8 (IL-8) secretion in ELISA, retinal pigment epithelium-specific 65 kDa protein (RPE65) and protectin (CD59) expression in Western blot, gene expression with quantitative polymerase chain reaction (qPCR) (IL6, IL8, MERTK, PIK3CA), and phagocytotic activity in a microscopic assay. FV fucoidan did not influence RPE cell viability. FV fucoidan reduced the Poly I:C proinflammatory cytokine secretion of IL-6 and IL-8. In addition, it decreased the expression of IL-6 and IL-8 in RT-PCR. LPS and TNF-α reduced the expression of CD59 in Western blot, this reduction was lost under FV fucoidan treatment. Also, LPS and TNF-α reduced the expression of visual cycle protein RPE65, this reduction was again lost under FV fucoidan treatment. Furthermore, the significant reduction of barrier function after Poly I:C stimulation is ameliorated by FV fucoidan. Concerning phagocytosis, however, the inflammation-induced reduction was not improved by FV fucoidan. FV and proinflammatory milieu did not relevantly influence phagocytosis relevant gene expression either. In conclusion, we show that fucoidan from FV can reduce proinflammatory stimulation in RPE induced by toll-like receptor 3 (TLR-3) activation and is of high interest as a potential compound for early AMD treatment.

Pivotal Role of Intestinal Microbiota and Intraluminal Metabolites for the Maintenance of Gut-Bone Physiology

Intestinal microbiota, and their mutual interactions with host tissues, are pivotal for the maintenance of organ physiology. Indeed, intraluminal signals influence adjacent and even distal tissues. Consequently, disruptions in the composition or functions of microbiota and subsequent altered host-microbiota interactions disturb the homeostasis of multiple organ systems, including the bone. Thus, gut microbiota can influence bone mass and physiology, as well as postnatal skeletal evolution. Alterations in nutrient or electrolyte absorption, metabolism, or immune functions, due to the translocation of microbial antigens or metabolites across intestinal barriers, affect bone tissues, as well. Intestinal microbiota can directly and indirectly alter bone density and bone remodeling. Intestinal dysbiosis and a subsequently disturbed gut-bone axis are characteristic for patients with inflammatory bowel disease (IBD) who suffer from various intestinal symptoms and multiple bone-related complications, such as arthritis or osteoporosis. Immune cells affecting the joints are presumably even primed in the gut. Furthermore, intestinal dysbiosis impairs hormone metabolism and electrolyte balance. On the other hand, less is known about the impact of bone metabolism on gut physiology. In this review, we summarized current knowledge of gut microbiota, metabolites and microbiota-primed immune cells in IBD and bone-related complications.

Early-life peripheral infections reprogram retinal microglia and aggravate neovascular age-related macular degeneration in later life

Pathological neovascularization in age-related macular degeneration (nvAMD) drives the principal cause of blindness in the elderly. While there is a robust genetic association between genes of innate immunity and AMD, genome-to-phenome relationships are low, suggesting a critical contribution of environmental triggers of disease. Possible insight comes from the observation that a past history of infection with pathogens such as Chlamydia pneumoniae, or other systemic inflammation, can predispose to nvAMD in later life. Using a mouse model of nvAMD with prior C. pneumoniae infection, endotoxin exposure, and genetic ablation of distinct immune cell populations, we demonstrated that peripheral infections elicited epigenetic reprogramming that led to a persistent memory state in retinal CX3CR1+ mononuclear phagocytes (MNPs). The immune imprinting persisted long after the initial inflammation had subsided and ultimately exacerbated choroidal neovascularization in a model of nvAMD. Single-cell assay for transposase-accessible chromatin sequencing (scATAC-seq) identified activating transcription factor 3 (ATF3) as a central mediator of retina-resident MNP reprogramming following peripheral inflammation. ATF3 polarized MNPs toward a reparative phenotype biased toward production of proangiogenic factors in response to subsequent injury. Therefore, a past history of bacterial endotoxin-induced inflammation can lead to immunological reprograming within CNS-resident MNPs and aggravate pathological angiogenesis in the aging retina.

Systemic Cytokines in Retinopathy of Prematurity

Retinopathy of prematurity (ROP), a vasoproliferative vitreoretinal disorder, is the leading cause of childhood blindness worldwide. Although angiogenic pathways have been the main focus, cytokine-mediated inflammation is also involved in ROP etiology. Herein, we illustrate the characteristics and actions of all cytokines involved in ROP pathogenesis. The two-phase (vaso-obliteration followed by vasoproliferation) theory outlines the evaluation of cytokines in a time-dependent manner. Levels of cytokines may even differ between the blood and the vitreous. Data from animal models of oxygen-induced retinopathy are also valuable. Although conventional cryotherapy and laser photocoagulation are well established and anti-vascular endothelial growth factor agents are available, less destructive novel therapeutics that can precisely target the signaling pathways are required. Linking the cytokines involved in ROP to other maternal and neonatal diseases and conditions provides insights into the management of ROP. Suppressing disordered retinal angiogenesis via the modulation of hypoxia-inducible factor, supplementation of insulin-like growth factor (IGF)-1/IGF-binding protein 3 complex, erythropoietin, and its derivatives, polyunsaturated fatty acids, and inhibition of secretogranin III have attracted the attention of researchers. Recently, gut microbiota modulation, non-coding RNAs, and gene therapies have shown promise in regulating ROP. These emerging therapeutics can be used to treat preterm infants with ROP.

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

The rate at which obesity is becoming an epidemic in many countries is alarming. Obese individuals have a high risk of developing elevated intraocular pressure and glaucoma. Additionally, glaucoma is a disease of epidemic proportions. It is characterized by neurodegeneration and neuroinflammation with optic neuropathy and the death of retinal ganglion cells (RGC). On the other hand, there is growing interest in microbiome dysbiosis, particularly in the gut, which has been widely acknowledged to play a prominent role in the etiology of metabolic illnesses such as obesity. Recently, studies have begun to highlight the fact that microbiome dysbiosis could play a critical role in the onset and progression of several neurodegenerative diseases, as well as in the development and progression of several ocular disorders. In obese individuals, gut microbiome dysbiosis can induce endotoxemia and systemic inflammation by causing intestinal barrier malfunction. As a result, bacteria and their metabolites could be delivered via the bloodstream or mesenteric lymphatic vessels to ocular regions at the level of the retina and optic nerve, causing tissue degeneration and neuroinflammation. Nowadays, there is preliminary evidence for the existence of brain and intraocular microbiomes. The altered microbiome of the gut could perturb the resident brain-ocular microbiome ecosystem which, in turn, could exacerbate the local inflammation. All these processes, finally, could lead to the death of RGC and neurodegeneration. The purpose of this literature review is to explore the recent evidence on the role of gut microbiome dysbiosis and related inflammation as common mechanisms underlying obesity and glaucoma.

Past history of obesity triggers persistent epigenetic changes in innate immunity and exacerbates neuroinflammation

Age-related macular degeneration is a prevalent neuroinflammatory condition and a major cause of blindness driven by genetic and environmental factors such as obesity. In diseases of aging, modifiable factors can be compounded over the life span. We report that diet-induced obesity earlier in life triggers persistent reprogramming of the innate immune system, lasting long after normalization of metabolic abnormalities. Stearic acid, acting through Toll-like receptor 4 (TLR4), is sufficient to remodel chromatin landscapes and selectively enhance accessibility at binding sites for activator protein-1 (AP-1). Myeloid cells show less oxidative phosphorylation and shift to glycolysis, ultimately leading to proinflammatory cytokine transcription, aggravation of pathological retinal angiogenesis, and neuronal degeneration associated with loss of visual function. Thus, a past history of obesity reprograms mononuclear phagocytes and predisposes to neuroinflammation.

Alterations of the intestinal microbiota in age-related macular degeneration

Purpose

Age-related macular degeneration (AMD) is the leading cause of vision loss in those over the age of 50. Recently, intestinal microbiota has been reported to be involved in the pathogenesis of ocular diseases. The purpose of this study was to discover more about the involvement of the intestinal microbiota in AMD patients.

Methods

Fecal samples from 30 patients with AMD (AMD group) and 17 age- and sex-matched healthy controls (control group) without any fundus disease were collected. DNA extraction, PCR amplification, and 16S rRNA gene sequencing of the samples were performed to identify intestinal microbial alterations. Further, we used BugBase for phenotypic prediction and PICRUSt2 for KEGG Orthology (KO) as well as metabolic feature prediction.

Results

The intestinal microbiota was found to be significantly altered in the AMD group. The AMD group had a significantly lower level of Firmicutes and relatively higher levels of Proteobacteria and Bacteroidota compared to those in the control group. At the genus level, the AMD patient group showed a considerably higher proportion of Escherichia-Shigella and lower proportions of Blautia and Anaerostipes compared with those in the control group. Phenotypic prediction revealed obvious differences in the four phenotypes between the two groups. PICRUSt2 analysis revealed KOs and pathways associated with altered intestinal microbiota. The abundance of the top eight KOs in the AMD group was higher than that in the control group. These KOs were mainly involved in lipopolysaccharide biosynthesis.

Conclusion

The findings of this study indicated that AMD patients had different gut microbiota compared with healthy controls, and that AMD pathophysiology might be linked to changes in gut-related metabolic pathways. Therefore, intestinal microbiota might serve as non-invasive indicators for AMD clinical diagnosis and possibly also as AMD treatment targets.

The role of the gut microbiome in eye diseases

The gut microbiome is a complex ecosystem of microorganisms and their genetic entities colonizing the gastrointestinal tract. When in balanced composition, the gut microbiome is in symbiotic interaction with its host and maintains intestinal homeostasis. It is involved in essential functions such as nutrient metabolism, inhibition of pathogens and regulation of immune function. Through translocation of microbes and their metabolites along the epithelial barrier, microbial dysbiosis induces systemic inflammation that may lead to tissue destruction and promote the onset of various diseases. Using whole-metagenome shotgun sequencing, several studies have shown that the composition and associated functional capacities of the gut microbiome are associated with age-related macular degeneration, retinal artery occlusion, central serous chorioretinopathy and uveitis. In this review, we provide an overview of the current knowledge about the gut microbiome in eye diseases, with a focus on interactions between the microbiome, specific microbial-derived metabolites and the immune system. We explain how these interactions may be involved in the pathogenesis of age-related macular degeneration, retinal artery occlusion, central serous chorioretinopathy and uveitis and guide the development of new therapeutic approaches by microbiome-altering interventions for these diseases.

Gut microbiota contributes to the methionine metabolism in host

Methionine (Met) metabolism provides methyl groups for many important physiological processes and is implicated in multiple inflammatory diseases associated with the disrupted intestinal microbiota; nevertheless, whether intestinal microbiota determines Met metabolism in the host remains largely unknown. Here, we found that gut microbiota is responsible for host Met metabolism by using various animal models, including germ-free (GF) pigs and mice. Specifically, the Met levels are elevated in both GF pigs and GF mice that mainly metabolized to S-adenosine methionine (SAM) in the liver. Furthermore, antibiotic clearance experiments demonstrate that the loss of certain ampicillin- or neomycin-sensitive gut microbiota causes decreased Met in murine colon. Overall, our study suggests that gut microbiota mediates Met metabolism in the host and is a prospective target for the treatment of Met metabolism-related diseases.

Innate immunity dysregulation in aging eye and therapeutic interventions

The prevalence of eye diseases increases considerably with age, resulting in significant vision impairment. Although the pathobiology of age-related eye diseases has been studied extensively, the contribution of immune-related changes due to aging remains elusive. In the eye, tissue-resident cells and infiltrating immune cells regulate innate responses during injury or infection. But due to aging, these cells lose their protective functions and acquire pathological phenotypes. Thus, dysregulated ocular innate immunity in the elderly increases the susceptibility and severity of eye diseases. Herein, we emphasize the impact of aging on the ocular innate immune system in the pathogenesis of infectious and non-infectious eye diseases. We discuss the role of age-related alterations in cellular metabolism, epigenetics, and cellular senescence as mechanisms underlying altered innate immune functions. Finally, we describe approaches to restore protective innate immune functions in the aging eye. Overall, the review summarizes our current understanding of innate immune functions in eye diseases and their dysregulation during aging.

Immune response in retinal degenerative diseases - Time to rethink?

Retinal degeneration comprises a group of diseases whereby either the retinal neurons or the neurovascular unit degenerates leading to the loss of visual function. Although the initial cause varies in different conditions, inflammation is known to play an important role in disease pathogenesis. Recent advances in molecular and cell biology and systems biology have yielded unexpected findings, including the heterogeneity of immune cells in the degenerative retina, bidirectional neuron-microglia cross talk, and links to the gut microbiome. Here we discuss the immune response in retinal degenerative conditions, taking into account both regional (retinal) and systemic factors. We propose to classify retinal degeneration into dry and wet forms based on whether the blood-retinal barrier (BRB) is breached and fluid is accumulated in retinal parenchyma. The dry form has a relatively intact BRB and is characterised by progressive retinal thinning. Immune response to degenerative insults is dominated by the retinal defence system, which remains to be regulated by neurons. In contrast, the wet form has retinal oedema due to BRB damaged. Inflammation is executed by infiltrating immune cells as well as the retinal defence system. The gut microbiome will have easy access to the retina in wet retinal degeneration and may affect significantly retinal immune response.

The pathophysiological mechanisms underlying diabetic retinopathy

Diabetic retinopathy (DR) is the most common complication of diabetes mellitus (DM), which can lead to visual impairment and even blindness in severe cases. DR is generally considered to be a microvascular disease but its pathogenesis is still unclear. A large body of evidence shows that the development of DR is not determined by a single factor but rather by multiple related mechanisms that lead to different degrees of retinal damage in DR patients. Therefore, this article briefly reviews the pathophysiological changes in DR, and discusses the occurrence and development of DR resulting from different factors such as oxidative stress, inflammation, neovascularization, neurodegeneration, the neurovascular unit, and gut microbiota, to provide a theoretical reference for the development of new DR treatment strategies.

Inside out: Relations between the microbiome, nutrition, and eye health

Age-related macular degeneration (AMD) is a complex disease with increasing numbers of individuals being afflicted and treatment modalities limited. There are strong interactions between diet, age, the metabolome, and gut microbiota, and all of these have roles in the pathogenesis of AMD. Communication axes exist between the gut microbiota and the eye, therefore, knowing how the microbiota influences the host metabolism during aging could guide a better understanding of AMD pathogenesis. While considerable experimental evidence exists for a diet-gut-eye axis from murine models of human ocular diseases, human diet-microbiome-metabolome studies are needed to elucidate changes in the gut microbiome at the taxonomic and functional levels that are functionally related to ocular pathology. Such studies will reveal new ways to diminish risk for progression of- or incidence of- AMD. Current data suggest that consuming diets rich in dark fish, fruits, vegetables, and low in glycemic index are most retina-healthful during aging.