Causal effects of gut microbiome on endometriosis: a two-sample mendelian randomization study

The microbiome's influence on obesity: mechanisms and therapeutic potential

In 2023, the World Obesity Atlas Federation concluded that more than 50% of the world's population would be overweight or obese within the next 12 years. At the heart of this epidemic lies the gut microbiota, a complex ecosystem that profoundly influences obesity-related metabolic health. Its multifaced role encompasses energy harvesting, inflammation, satiety signaling, gut barrier function, gut-brain communication, and adipose tissue homeostasis. Recognizing the complexities of the cross-talk between host physiology and gut microbiota is crucial for developing cutting-edge, microbiome-targeted therapies to address the global obesity crisis and its alarming health and economic repercussions. This narrative review analyzed the current state of knowledge, illuminating emerging research areas and their implications for leveraging gut microbial manipulations as therapeutic strategies to prevent and treat obesity and related disorders in humans. By elucidating the complex relationship between gut microflora and obesity, we aim to contribute to the growing body of knowledge underpinning this critical field, potentially paving the way for novel interventions to combat the worldwide obesity epidemic.

The effects of saturated and unsaturated fatty acids on MASLD: a Mendelian randomization analysis and in vivo experiment

BACKGROUND

Excessive intake of fatty acids is a key factor contributing to metabolic dysfunction-associated steatotic liver disease (MASLD). However, the effects of saturated fatty acids (SFA) and unsaturated fatty acids (UFA) on the development of MASLD are uncertain. Therefore, we conducted two-sample Mendelian randomization studies and animal experiments to explore the effects of SFA, monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) on the risk of developing MASLD.

METHODS

The genetic summary data of exposures and outcome were retrieved from genome-wide association studies (GWASs) and used for five Mendelian randomization methods. A comprehensive sensitivity analysis was performed to verify the robustness of the results. Mice were subjected to different diets followed by assessment of severity of steatosis based on a histological score and determination of hepatic triglyceride levels to investigate the relationships between SFA, MUFA, PUFA and MASLD.

RESULTS

The Mendelian randomization results showed that MUFA (odds ratio: 1.441, 95% confidence interval: 1.078-1.927, P = 0.014) was causally associated with the incidence of MASLD. SFA and PUFA were not causally associated with the incidence of MASLD. Sensitivity analysis did not identify any significant bias in the results. The animal experiment results showed that a MUFA-enriched diet significantly contributed to the development of hepatic steatosis (P < 0.001).

CONCLUSION

SFA and PUFA did not have a significant causal effect on MASLD, but MUFA intake is a risk factor for MASLD. A MUFA-enriched diet increased the incidence of macrovesicular steatosis and the hepatic triglyceride levels. Therefore, replacing MUFA intake with a moderate intake of PUFA might help reduce the risk of MASLD.

The causality between gut microbiota and endometriosis: a bidirectional Mendelian randomization study

Background

Observational studies and animal experiments had suggested a potential relationship between gut microbiota abundance and pathogenesis of endometriosis (EMs), but the relevance of this relationship remains to be clarified.

Methods

We perform a two-sample bidirectional Mendelian randomization (MR) analysis to explore whether there is a causal correlation between the abundance of the gut microbiota and EMs and the direction of causality. Genome-wide association study (GWAS) data ukb-d-N80, finn-b-N14-EM, and MiBinGen were selected. Inverse variance weighted (IVW), weighted median, and MR Egger are selected for causal inference. The Cochran Q test, Egger intercept test, and leave-one-out analysis are performed for sensitivity analyses.

Results

In the primary outcome, we find that a higher abundance of class Negativicutes, genus Dialister, genus Enterorhabdus, genus Eubacterium xylanophilum group, genus Methanobrevibacter and order Selenomonadales predict a higher risk of EMs, and a higher abundance of genus Coprococcus and genus Senegalimassilia predict a lower risk of EMs. During verifiable outcomes, we find that a higher abundance of phylum Cyanobacteria, genus Ruminococcaceae UCG002, and genus Coprococcus 3 predict a higher risk of EMs, and a higher abundance of genus Flavonifracto, genus Bifidobacterium, and genus Rikenellaceae RC9 predict a lower risk of EMs. In primary reverse MR analysis, we find that EMs predict a lower abundance of the genus Eubacterium fissicatena group, genus Prevotella7, genus Butyricicoccus, family Lactobacillaceae, and a higher abundance of genus Ruminococcaceae UCG009. In verifiable reverse MR analysis, we find that EMs predict a lower abundance of the genus Ruminococcaceae UCG004 and a higher abundance of the genus Howardella.

Conclusion

Our study implies a mutual causality between gut microbiota abundance and the pathogenesis of EMs, which may provide a novel direction for EMs diagnosis, prevention, and treatment, may promote future functional or clinical analysis.

Causal associations among gut microbiota, 1400 plasma metabolites, and asthma: a two-sample Mendelian randomization study

Background

Emerging evidence indicates a correlation between imbalances in intestinal microbiota and changes in plasma metabolites in the progression of asthma. However, the causal link between these factors remains unclear.

Methods

A two-sample Mendelian randomization (MR) study was employed to evaluate the potential causal connection between gut microbiota, plasma metabolites, and asthma susceptibility. Gut microbiota data from expansive genome-wide genotype studies and 16S fecal microbiome datasets were examined by the MiBioGen Alliance. Asthma data were procured from the FinnGen biobank analysis, while comprehensive Genome-Wide Association Studies (GWAS) summary statistics for plasma metabolites were derived from the NHGRI-EBI GWAS Catalog. Fluctuations in intestinal flora and plasma metabolites in asthma patients were evaluated using the weighted mode method. Additionally, pleiotropic and heterogeneity analyses were performed to ascertain the reliability of the findings.

Results

Upon examining the gut microbiota through MR with the IVW method, alongside tests for heterogeneity and pleiotropy, findings reveal a negative association between the abundance of the Christensenellaceae R.7 group and asthma risk. In contrast, the Bifidobacterium and Prevotella 7 genera exhibit a positive association with asthma risk, indicating they may be potential risk factors (p < 0.05). Furthermore, MR analysis of 1,400 metabolites employing Weighted median, IVW, and Weighted mode methods resulted in p-values below 0.05. Subsequent tests for pleiotropy and heterogeneity showed that the levels of 3,5-dichloro-2,6-dihydroxybenzoic acid have a negative correlation with asthma, whereas the phenylalanine to phosphate ratio has a positive correlation, suggesting their potential as risk factors for asthma (p < 0.05).

Conclusion

The current Mendelian randomization study provides evidence supporting a potential causal link between specific gut microbiota taxa, plasma metabolites, and asthma. These findings offer novel perspectives for future research and the development of treatment and prevention strategies for asthma.

Unraveling the relationship between gut microbiota and site-specific endometriosis: a Mendelian randomization analysis

Background

Although numerous studies have illustrated the connection between gut microbiota and endometriosis, a conspicuous gap exists in research focusing on the pathogenesis of endometriosis at various sites and its linkage with infertility.

Methods

In this study, we used a two-sample Mendelian randomization analysis to investigate the effect of gut microbiota on the development of endometriosis in different regions, including the uterus, ovary, fallopian tube, pelvic peritoneum, vagina, and rectovaginal septum, as well as the intestine. Additionally, we explored the correlation between gut microbiota and endometriosis-induced infertility. Genetic associations with gut microbes were obtained from genome-wide association study (GWAS) datasets provided by the MiBioGen consortium, whereas endometriosis-related GWAS data were sourced from the FinnGen dataset. In our analysis, single-nucleotide polymorphisms were used as instrumental variables, with the primary estimation of the causal effect performed via the inverse variance weighting method. Our sensitivity analyses incorporated heterogeneity tests, pleiotropy tests, and the leave-one-out method.

Results

We identified associations at the genus level between four bacterial communities and endometriosis. Subsequently, several associations between the gut microbiota and various subtypes of endometriosis at different anatomical sites were recognized. Specifically, three genera were linked with ovarian endometriosis, six genera were associated with tubal endometriosis, four genera showed links with pelvic peritoneum endometriosis, five genera were connected with vaginal and rectovaginal septum endometriosis, and seven genera demonstrated linkages with intestinal endometriosis. Additionally, one genus was associated with adenomyosis, and three genera exhibited associations with endometriosis-induced infertility.

Conclusion

Our study elucidates associations between gut microbiota and site-specific endometriosis, thereby augmenting our understanding of the pathophysiology of endometriosis. Moreover, our findings pave the way for potential therapeutic strategies targeting gut microbiota for individuals grappling with endometriosis-related infertility.

Gut Microbiota and Endometriosis: Exploring the Relationship and Therapeutic Implications

Endometriosis is a common inflammatory disease affecting women of reproductive age, characterized by the growth of endometrial tissue beyond the uterus. In addition to gynecological manifestations, many endometriosis patients experience gastrointestinal symptoms, indicating a potential association between gut health and the disease. Recent studies have revealed alterations in the gut microbiota of individuals with endometriosis, including reduced diversity, microbial composition imbalances, and pathogenic bacteria. These changes can disrupt immune function, increase inflammation, and contribute to the chronic inflammatory state observed in endometriosis. Moreover, dysregulation of intestinal permeability may further exacerbate gastrointestinal symptoms in affected individuals. Understanding the role of the gut microbiota and intestinal permeability in endometriosis can provide valuable insights into disease pathogenesis, aid in non-invasive diagnostic approaches, and open new avenues for therapeutic interventions. Probiotics, in particular, have shown promise in improving endometriosis-associated pain symptoms and reducing endometriotic lesions in animal models. This review suggests that additional research and well-designed clinical trials are necessary to validate the potential diagnostic and therapeutic benefits of manipulating the gut microbiota in managing endometriosis and its gastrointestinal symptoms, thereby improving the quality of life for those affected.