Causal relationship of gut microbiota and metabolites on cognitive performance: A mendelian randomization analysis

Exploring causal links in the gut-brain axis: a Mendelian randomization study of gut microbiota, metabolites, and cognition

The causal mediation effects of metabolites between gut microbiota and cognitive phenotypes remain unclear. Guided by the gut-brain axis mechanism, this study employed systematic Mendelian randomization (MR) to investigate these mediation pathways and their implications for functional food development. Univariate MR analysis was performed to estimate the causality of 211 gut microbial taxa (n = 18 340) and 452 serum metabolites (n = 7824) on general cognitive (n = 257 700), non-cognitive (n = 510 795), and specific cognitive phenotypes (n ≈ 2500) using genome-wide association study data. Inverse-variance weighted estimation was adopted as the primary method, with MR sensitivity analyses performed to complement the results. Metabolic pathway analysis was employed to enrich metabolic profiles, while two-step MR was used to screen mediation pathways. We revealed seven causal associations between microbiotas or metabolites and cognitive phenotypes (FDR < 0.05). Increased abundance of the order Clostridiales id.1863 was associated with better cognitive traits (OR = 1.14, 95%CI = 1.06-1.22, P = 2.06 × 10-4), while 1-linoleoylglycerophosphoethanolamine was also positively associated with cognitive traits (OR = 1.61, 95%CI = 1.33-1.95, P = 8.17 × 10-7). Seven significant metabolic pathways were enriched, including alpha-linolenic acid and linoleic acid metabolism, highlighting the potential role of omega-3 and omega-6 fatty acids in cognitive health. We further identified two significant mediation pathways linking the gut microbiota to cognitive phenotypes through metabolites. Notably, homostachydrine (39.1%) was found to mediate a proportion of the impact of the genus Turicibacter on emotion recognition (indirect effect: β = 0.105, 95%CI = 0.006-0.259, p = 2.60 × 10-2). This study provides evidence for causal relationships between gut microbiota, serum metabolites, and cognitive function, supporting the gut-brain axis mechanism. Our findings suggest potential targets for the development of functional food and personalized nutrition to improve cognitive health.

Healthy dietary patterns, cognition and dementia risk: current evidence and context

Approximately 60 million individuals worldwide are currently living with dementia. As the median age of the world's population rises, the number of dementia cases is expected to increase markedly, and to affect ∼150 million individuals by 2050. This will create a huge and unsustainable economic and social burden across the globe. Although promising pharmacological treatment options for Alzheimer's disease - the most common cause of dementia - are starting to emerge, dementia prevention and risk reduction remain vital. In this review, we present evidence from large-scale epidemiological studies and randomised controlled trials to indicate that adherence to healthy dietary patterns could improve cognitive function and lower dementia risk. We outline potential systemic (e.g. improved cardiometabolic health, lower inflammation, modified gut microbiome composition/metabolism, slower pace of aging) and brain-specific (e.g. lower amyloid-β load, reduced brain atrophy and preserved cerebral microstructure and energetics) mechanisms of action. We also explore current gaps in our knowledge and outline potential directions for future research in this area. Our aim is to provide an update on current state of the knowledge, and to galvanise research on this important topic.

Elucidating the causal relationship between gut microbiota, metabolites, and diabetic nephropathy in European patients: Revelations from genome-wide bidirectional mendelian randomization analysis

Objective

Previous observational studies suggest a potential link between gut microbiota, metabolites, and diabetic nephropathy. However, the exact causal relationship among these factors remains unclear.

Method

We conducted a two-sample bidirectional Mendelian randomization study using summary statistics from the IEU OpenGWAS Project database to investigate gut microbiota, metabolites, and diabetic nephropathy. A range of methods, including inverse variance weighting, MR-Egger, weighted median, and simple median, were applied to examine causal associations. Sensitivity analyses were performed to assess the robustness of the results. Additionally, reverse Mendelian randomization analysis was conducted, treating significant gut microbiota as the outcome, to evaluate effects and perform sensitivity testing. This comprehensive approach provided an in-depth assessment of the interactions among gut microbiota, metabolites, and diabetic nephropathy.

Result

The Inverse Variance Weighted estimates revealed that the abundance of Lachnospiraceae, Parasutterella, and Eubacterium exhibited negative causal effects on diabetic nephropathy, while Coprococcus, Sutterella, Faecalibacterium prausnitzii, and Bacteroides vulgatus showed protective causal effects against the condition. However, reverse Mendelian randomization analysis did not identify any significant associations between diabetic nephropathy and the identified gut microbiota. Furthermore, the estimates indicated that Cholesterol, Pyridoxate, Hexanoylcarnitine, X-12007, Octanoylcarnitine, 10-nonadecenoate (19:1n9), X-12734, and the average number of double bonds in a fatty acid chain had negative causal effects on diabetic nephropathy. In contrast, Methionine, Glycodeoxycholate, X-06351, 1-stearoylglycerol (1-monostearin), 5-dodecenoate (12:1n7), X-13859, 2-hydroxyglutarate, Glycoproteins, Phospholipids in IDL, and the concentration of small HDL particles demonstrated protective causal effects. Notably, sensitivity analyses did not detect any heterogeneity or horizontal pleiotropy, ensuring the robustness of the findings.

Conclusion

Modulating gut microbiota diversity and composition offers a promising strategy for improving the incidence and prognosis of diabetic nephropathy. This highlights the need for future clinical trials focusing on microbiome-based interventions, potentially utilizing microbiome-dependent metabolites. Such approaches could transform the treatment and management of diabetic nephropathy and its associated risk factors, paving the way for more effective therapeutic strategies to combat this debilitating condition.

Gut microbiota and risk of ankylosing spondylitis

OBJECTIVE

Observational studies have established a connection between gut microbiota and ankylosing spondylitis (AS) risk; however, whether the observed associations are causal remains unclear. Therefore, we conducted a two-sample Mendelian randomization (MR) analysis to assess the potential causal associations of gut microbiota with AS risk.

METHODS

Instrumental variants of gut microbiota were obtained from the MiBioGen consortium (n = 18,340) and the Dutch Microbiome Project (n = 7738). The FinnGen consortium provided genetic association summary statistics for AS, encompassing 2860 cases and 270,964 controls. We used the inverse-variance weighted (IVW) method as the primary analysis, supplemented with the weighted median method, maximum likelihood-based method, MR pleiotropy residual sum and outlier test, and MR-Egger regression. In addition, we conducted a reverse MR analysis to assess the likelihood of reverse causality.

RESULTS

After the Bonferroni correction, species Bacteroides vulgatus remained statistically significantly associated with AS risk (odds ratio (OR) 1.55, 95% confidence interval (CI) 1.22-1.95, P = 2.55 × 10-4). Suggestive evidence of associations of eleven bacterial traits with AS risk was also observed (P < 0.05 by IVW). Among them, eight were associated with an elevated AS risk (OR 1.37, 95% CI 1.07-1.74, P = 0.011 for phylum Verrucomicrobia; OR 1.31, 95% CI 1.03-1.65, P = 0.026 for class Verrucomicrobiae; OR 1.17, 95% CI 1.01-1.36, P = 0.035 for order Bacillales; OR 1.31, 95% CI 1.03-1.65, P = 0.026 for order Verrucomicrobiales; OR 1.43, 95% CI 1.13-1.82, P = 0.003 for family Alcaligenaceae; OR 1.31, 95% CI 1.03-1.65, P = 0.026 for family Verrucomicrobiaceae; OR 1.31, 95% CI 1.03-1.65, P = 0.026 for genus Akkermansia; OR 1.55, 95% CI 1.19-2.02, P = 0.001 for species Sutterella wadsworthensis). Three traits exhibited a negative association with AS risk (OR 0.68, 95% CI 0.53-0.88, P = 0.003 for genus Dialister; OR 0.84, 95% CI 0.72-0.97, P = 0.020 for genus Howardella; OR 0.75, 95% CI 0.59-0.97, P = 0.026 for genus Oscillospira). Consistent associations were observed when employing alternate MR methods. In the reverse MR, no statistically significant correlations were detected between AS and these bacterial traits.

CONCLUSION

Our results revealed the associations of several gut bacterial traits with AS risk, suggesting a potential causal role of gut microbiota in AS development. Nevertheless, additional research is required to clarify the mechanisms by which these bacteria influence AS risk. Key Points • The association of gut microbiota with AS risk in observational studies is unclear. • This MR analysis revealed associations of 12 gut bacterial traits with AS risk.

Investigating Causal Associations between the Gut Microbiota and Dementia: A Mendelian Randomization Study

Background: The causal association of specific gut microbiota with dementia remains incompletely understood. We aimed to access the causal relationships in which one or more gut microbiota account for dementia. Method: Using data from the MiBioGen and FinnGen consortia, we employed multiple Mendelian randomization (MR) approaches including two-sample MR (TSMR), multivariable MR (MVMR), and Bayesian model averaging MR to comprehensively evaluate the causal associations between 119 genera and dementia, and to prioritize the predominant bacterium. Result: We identified 21 genera that had causal effects on dementia and suggested Barnesiella (OR = 0.827, 95%CI = 0.722-0.948, marginal inclusion probability [MIP] = 0.464; model-averaged causal estimate [MACE] = -0.068) and Allisonella (OR = 0.770, 95%CI = 0.693-0.855, MIP = 0.898, MACE = -0.204) as the predominant genera for AD and all-cause dementia. Conclusions: These findings confirm the causal relationships between specific gut microbiota and dementia, highlighting the necessity of multiple MR approaches in gut microbiota analysis, and provides promising genera as potential novel biomarkers for dementia risk.

Effects of electroacupuncture on postoperative cognitive dysfunction and its underlying mechanisms: a literature review of rodent studies

With the aging of the population, the health of the elderly has become increasingly important. Postoperative cognitive dysfunction (POCD) is a common neurological complication in elderly patients following general anesthesia or surgery. It is characterized by cognitive decline that may persist for weeks, months, or even longer. Electroacupuncture (EA), a novel therapy that combines physical nerve stimulation with acupuncture treatment from traditional Chinese medicine, holds potential as a therapeutic intervention for preventing and treating POCD, particularly in elderly patients. Although the beneficial effects of EA on POCD have been explored in preclinical and clinical studies, the reliability of EA is limited by methodological shortcomings, and the underlying mechanisms remain largely unexplored. Therefore, we have synthesized existing evidence and proposed potential biological mechanisms underlying the effects of EA on neuroinflammation, oxidative stress, autophagy, the microbiota-gut-brain axis, and epigenetic modification. This review summarizes recent advances in EA and POCD, provides a theoretical foundation, explores potential molecular mechanisms for the prevention and treatment of POCD, and offers a basis for conducting relevant clinical trials.