Dysbiosis in the Gut Microbiome in Streptozotocin-Induced Diabetes Rats and Follow-Up During Retinal Changes

Association between Gut Microbiota Compositions with MicrovascularComplications in Individuals with Diabetes: A Systematic Review

BACKGROUND

Diabetes is one of the chronic and very complex diseases that can lead to microvascular complications. Recent evidence demonstrates that dysbiosis of the microbiota composition might result in low-grade, local, and systemic inflammation, which contributes directly to the development of diabetes mellitus and its microvascular consequences.

OBJECTIVE

The aim of this systematic review was to investigate the association between diabetes microvascular complications, including retinopathy, neuropathy, nephropathy, and gut microbiota composition.

METHODS

A systematic search was carried out in PubMed, Scopus, and ISI Web of Science from database inception to March 2023. Screening, data extraction, and quality assessment were performed by two independent authors. The Newcastle-Ottawa Quality Assessment Scale was used for quality assessment.

RESULTS

About 19 articles were selected from 590 retrieved articles. Among the included studies, nephropathy has been studied more than other complications of diabetes, showing that the composition of the healthy microbiota is changed, and large quantities of uremic solutes that cause kidney injury are produced by gut microbes. Phyla, including Fusobacteria and Proteobacteria, accounted for the majority of the variation in gut microbiota between Type 2 diabetic patients with and without neuropathy. In cases with retinopathy, an increase in pathogenic and proinflammatory bacteria was observed.

CONCLUSION

Our results revealed that increases in Bacteroidetes, Proteobacteria and Fusobacteria may be associated with the pathogenesis of diabetic nephropathy, neuropathy, and retinopathy. In view of the detrimental role of intestinal dysbiosis in the development of diabetes-related complications, gut microbiota assessment may be used as a biomarker in the future and interventions that modulate the composition of microbiota in individuals with diabetes can be used to prevent and control these complications.

Effect of Benaglutide on Gut Microbiota and Fecal Metabolites in Patients with Type 2 Diabetes Mellitus

Objective

Benaglutide is a glucagon-like peptide-1 receptor agonist (GLP-1RA) that has been approved in the treatment of type 2 diabetes mellitus (T2DM). It is known to lead to significant weight loss, and it is hypothesized that changes in gut microbiota may play a significant role in such weight loss. However, it is unclear how gut microbiota and metabolites change as a result of benaglutide treatment.

Methods

Healthy participants and patients with T2DM were included in this study. They received differentiated treatments, and stool specimens were collected separately. These stool specimens were subjected to 16S ribosomal RNA amplicon and metagenomic sequencing to create fecal metabolomic profiles. The diversity of gut microbiota and metabolic products in the stools of each participant was analyzed.

Results

The data showed that Faecalibacterium prausnitzii was abundant in the gut microbiota of the control group, which was entirely made up of healthy individuals; however, it showed a statistically significant decrease in patients with T2DM treated with metformin alone, while no significant decrease was observed in patients treated with metformin combined with benaglutide. A metagenomic analysis revealed that benaglutide could improve the fecal microbiota diversity in patients with T2DM. Furthermore, there was a statistically significant correlation between the changes in the metabolites of patients with T2DM and the changes in their gut microbiota (including F. prausnitzii) after treatment with metformin and benaglutide.

Conclusion

These findings suggest that the weight-reducing effect of benaglutide is attributed to its ability to normalize the gut microbiota of patients with T2DM, particularly by increasing the abundance of F. prausnitzii.

Intraocular Microbiome in Diabetes and Diabetic Retinopathy: A Pilot Study

INTRODUCTION

The objective of this study was to compare the microbiome in the aqueous humour and gut of people with diabetes mellitus (DM) with and without diabetic retinopathy (DR).

METHODS

This was a prospective controlled study. The study included 17 people undergoing intraocular surgery in their naïve eyes. Stool samples were obtained in the perioperative period; aqueous humour samples of sufficient quantity were obtained in 12 people during intraocular surgery. Dietary information was obtained using a previously validated questionnaire. The gut and aqueous humour samples were assessed for microbiome using 16S rRNA gene sequencing coupled with QIIME and R software.

RESULTS

Aqueous humour was analysed in 12 people: 4 each healthy controls, people with DM, and people with DR. There were minor differences at the phyla levels, but the aqueous humour microbiomes of healthy controls, DM, and DR formed three distinct clusters on heat map analysis with discriminatory genera. This genera-level clustering was more apparent for the intraocular than the gut microbiome. In people with DM and DR, we identified genera unique to the eye or the gut. There was a consistent reduction in the abundance of anti-inflammatory bacteria in people with DR than DM.

CONCLUSIONS

There is a difference in intraocular and gut microbiome regardless of disease or health. Our preliminary findings indicate distinctive features of the intraocular microbiome in people with DR compared with those without it. While this distinctiveness appears more evident in aqueous humour than in the gut, it needs further confirmation with larger studies.

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.

Evidence Suggesting the Role of Gut Dysbiosis in Diabetic Retinopathy

Purpose

Gut dysbiosis has been identified and tested in human trials for its role in diabetes mellitus (DM). The gut-retina axis could be a potential target for retardation of diabetic retinopathy (DR), a known complication of DM. This study reviews the evidence suggesting gut dysbiosis in DR.

Methods

The published literature in the past 5 years was reviewed using predetermined keywords and articles. The review intended to determine changes in gut microbiome in DR, the hypothesized mechanisms linking to the gut-retina axis, its predictive potential for progression of DR, and the possible therapeutic targets.

Results

The gut microbiota of people with DM differ from those without it, and the gut microbiota of people with DR differ from those without it. The difference is more significant in the former (DM versus no DM) and less significant in the latter (DM without DR versus DM with DR). Early research has suggested mechanisms of the gut-retina axis, but these are not different from known changes in the gut microbiome of people with DM. The current evidence on the predictive value of the gut microbiome in the occurrence and progression of DR is low. Therapeutic avenues targeting the gut-retina axis include lifestyle changes, pharmacologic inhibitors, probiotics, and fecal microbiota transplantation.

Conclusions

Investigating the therapeutic utility of the gut ecosystem for DM and its complications like DR is an emerging area of research. The gut-retina axis could be a target for retardation of DR but needs longitudinal regional studies adjusting for dietary habits.

Unconventional avenues to decelerated diabetic retinopathy

Diabetic retinopathy (DR) is an important microvascular complication of diabetes mellitus (DM), causing significant visual impairment worldwide. Current gold standards for retarding the progress of DR include blood sugar control and regular fundus screening. Despite these measures, the incidence and prevalence of DR and vision-threatening DR remain high. Given its slowly progressive course and long latent period, opportunities to contain or slow DR before it threatens vision must be explored. This narrative review assesses the recently described unconventional strategies to retard DR progression. These include gut-ocular flow, gene therapy, mitochondrial dysfunction-oxidative stress, stem cell therapeutics, neurodegeneration, anti-inflammatory treatments, lifestyle modification, and usage of phytochemicals. These therapies impact DR directly, while some of them also influence DM control. Most of these strategies are currently in the preclinical stage, and clinical evidence remains low. Nevertheless, our review suggests that these approaches have the potential for human use to prevent the progression of DR.

Gut mycobiome dysbiosis in rats showing retinal changes indicative of diabetic retinopathy

The current study compared the gut mycobiomes of diabetic rats generated by a streptozotocin chemical challenge, diabetic rats with retinal changes and normal control rats over a period of 4 months. Sustained increase in blood sugar levels (>150 mg/dL) confirmed the induction of diabetes. Histology and immunohistochemistry were used to identify changes in the retinal tissues in the diabetic rats indicative of the animals progressing into diabetic retinopathy. Gut mycobiomes generated using faecal DNA, indicated dysbiosis at the genus level in both diabetic (DM) and diabetic rats with retinal changes (DRC) when compared with the control rats. In Tables 3–6 the specific genera that were significantly increased/decreased in DM1 and DM2 and in DRC1 and DRC2 respectively compared to the respective controls CT1-CT4 rats are listed. Further, the mycobiomes of the DM and DRC rats separated into distinct clusters following heat-map analysis of the discriminating genera. In addition, β-diversity analysis separated the mycobiomes of DM and DRC rats from that of the control rats, but the mycobiomes of diabetic rats and diabetic rats with retinal changes showed an overlap. Based on the inferred functions of the discriminating genera in the mycobiomes, we speculated that increase in pathogenic fungi might contribute to the inflammatory status both in diabetic rats and rats showing retinal changes.