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International Journal of Medical Sciences logoLink to International Journal of Medical Sciences
. 2024 Jan 1;21(2):376–395. doi: 10.7150/ijms.92131

Altered Gut Microbiota as a Potential Risk Factor for Coronary Artery Disease in Diabetes: A Two-Sample Bi-Directional Mendelian Randomization Study

Zhaopei Zeng 1,2,*, Junxiong Qiu 1,2,*, Yu Chen 3,*, Diefei Liang 4, Feng Wei 1,5, Yuan Fu 1, Jiarui Zhang 1, Xiexiao Wei 6, Xinyi Zhang 1, Jun Tao 1,2,#,, Liling Lin 2,7,#,, Junmeng Zheng 1,2,#,
PMCID: PMC10758148  PMID: 38169662

Abstract

The current body of research points to a notable correlation between an imbalance in gut microbiota and the development of type 2 diabetes mellitus (T2D) as well as its consequential ailment, coronary artery disease (CAD). The complexities underlying the association, especially in the context of diabetic coronary artery disease (DCAD), are not yet fully understood, and the causal links require further clarification. In this study, a bidirectional Mendelian randomization (MR) methodology was utilized to explore the causal relationships between gut microbiota, T2D, and CAD. By analyzing data from the DIAGRAM, GERA, UKB, FHS, and mibioGen cohorts and examining GWAS databases, we sought to uncover genetic variants linked to T2D, CAD, and variations in gut microbiota and metabolites, aiming to shed light on the potential mechanisms connecting gut microbiota with DCAD. Our investigation uncovered a marked causal link between the presence of Oxalobacter formigenes and an increased incidence of both T2D and CAD. Specifically, a ten-unit genetic predisposition towards T2D was found to be associated with a 6.1% higher probability of an increase in the Oxalobacteraceae family's presence (β = 0.061, 95% CI = 0.002-0.119). In a parallel finding, an augmented presence of Oxalobacter was related to an 8.2% heightened genetic likelihood of CAD (β = 0.082, 95% CI = 0.026-0.137). This evidence indicates a critical pathway by which T2D can potentially raise the risk of CAD via alterations in gut microbiota. Additionally, our analyses reveal a connection between CAD risk and Methanobacteria, thus providing fresh perspectives on the roles of TMAO and carnitine in the etiology of CAD. The data also suggest a direct causal relationship between increased levels of certain metabolites — proline, lysophosphatidylcholine, asparagine, and salicylurate — and the prevalence of both T2D and CAD. Sensitivity assessments reinforce the notion that changes in Oxalobacter formigenes could pose a risk for DCAD. There is also evidence to suggest that DCAD may, in turn, affect the gut microbiota's makeup. Notably, a surge in serum TMAO levels in individuals with CAD, coinciding with a reduced presence of methanogens, has been identified as a potentially significant factor for future examination.

Keywords: coronary artery disease, type 2 diabetes, causality, gut microbiota, metabolites, Mendelian randomization

Introduction

The diverse bacterial population within the human gut, numbering in the billions, plays a critical role in regulating host health and physiological functions 1. This microbial community is especially significant in the development and progression of various diseases, including cardiovascular maladies, metabolic disorders, neurogenic conditions, and immune system responses, with a particular impact on type 2 diabetes mellitus (T2D) and coronary artery disease (CAD) 2, 3. The imbalance of gut microbiota, known as dysbiosis, is increasingly acknowledged as a key contributor to metabolic imbalances, leading to persistent low-grade inflammation and oxidative stress, which are characteristic of T2D and its related health issues. Furthermore, the gut microbiota is known to participate actively in critical metabolic processes, contributing to the emergence of CAD by affecting inflammatory pathways and oxidative stress mechanisms 4. The likelihood of developing cardiovascular conditions is influenced by a confluence of factors, such as existing health conditions, lifestyle choices, and overall health 5, 6. Current research highlights the gut microbiota's significant role in mediating the risk and progression of CAD, particularly when it emerges as a secondary complication to diabetes 7.

Numerous studies have linked the gut microbiota to the development of T2D and CAD, highlighting the role of gut bacteria in the onset and progression of these conditions. It's well-documented that T2D significantly increases the risk of CAD, to an extent comparable to the risk associated with established heart diseases 8, 9. T2D-related issues such as hypertension and oxidative stress can lead to metabolic disturbances and impaired lipid metabolism, which in turn can cause both small and large vessel complications. These include a range of cardiovascular conditions that impact the arteries of various organs 10. Insulin resistance, a hallmark of T2D, is intricately connected to the composition of the gut microbiota 11. Specific bacterial species, including Butyrivibrio crossotus, Eubacterium siraeum, Streptococcus mutans, and Eggerthella lenta, play significant roles in regulating blood sugar levels by interacting with the gut's microbial ecosystem 12-14. Interestingly, shifts in the gut microbiome composition have been observed across different ethnic groups, including Asian and European populations, which have been shown to exhibit alterations in their gut microbiota in the context of T2D 15, 16.

Atherosclerotic cardiovascular conditions remain a leading contributor to disability and death among individuals with T2D. There is a growing body of evidence suggesting that the gut microbiota plays a crucial role in the development of atherosclerotic plaques 17, 18. The progression of atherosclerosis and CAD appears to be intricately linked to how the gut microbiota manages essential metabolic functions, notably affecting purine and lipid metabolism, as well as pathways related to oxidative stress and inflammation 5, 19.

The dynamic interplay between the gut microbiota's composition and diabetic coronary artery disease (DCAD) demands thorough investigation to establish direct causal links 20. It's increasingly critical to unravel how T2D enhances the susceptibility to CAD. Establishing causality in this domain is crucial not just for maintaining microbial equilibrium in the gut but also for developing strategies to prevent CAD.

Randomized controlled trials (RCTs) stand as the gold standard in epidemiological studies to determine causative relationships. However, their practical application can be restricted by logistical and ethical considerations. An alternative method, Mendelian randomization (MR), circumvents these limitations by employing genetic variants as proxies to draw causal inferences from observational data, thus minimizing confounder effects 21, 22. Leveraging the capabilities of MR, our research adopted a bidirectional two-sample MR method to substantiate the causal relationships between the gut microbiota and both T2D and CAD. Recent insights suggest that the interaction between gut microbiota and arterial health may play a role in how a lipid-rich diet contributes to atherosclerosis. Our MR examination of metabolites provides insights into their possible causative links with T2D and CAD 23.

Materials and Methods

Study Design

Our research aimed to explore the genetic underpinnings of gut microbiota profiles and their influence on the incidence of T2D and CAD. By implementing a bidirectional two-sample Mendelian Randomization (MR) model, we assessed combined datasets from extensive genome-wide association studies (GWAS), with this process depicted in Figure 1 and elaborated upon in Supplementary Table S1. Furthermore, we conducted a one-way two-sample MR analysis to probe into the interactions between specific metabolites and the occurrence of T2D and CAD, along with their impact on the composition of the gut microbiota.

Figure 1.

Figure 1

Framework for Bidirectional MR Analysis. This diagram details the methodological structure of our bidirectional Mendelian Randomization (MR) investigation, examining the cause-and-effect dynamics between gut microbiota and diseases such as type 2 diabetes (T2D) and coronary artery disease (CAD). Genetic data was primarily extracted from populations of European ancestry. The principal analysis method was inverse variance weighting (IVW), supplemented by sensitivity tests to ensure the reliability of the MR findings. After applying Bonferroni corrections, we identified significant causal links between three gut microbiota characteristics and T2D, and seven with CAD (P < 0.025, adjusted for two hypotheses). Notably, after adjustment for multiple testing (P < 2.36 × 10^-4, adjusted for 211 outcomes), no significant causal effect was observed between T2D/CAD and gut microbiota, although indicative causal links were noted.

Ethical Considerations and Methodological Conformance

This study incorporates data derived from GWAS databases that have undergone rigorous ethical scrutiny and received clearance for research utilization. The methodology adheres to the protocols established by Burgess and colleagues, and is in compliance with the recommendations outlined in the STROBE-MR guidelines for reporting observational research with Mendelian Randomization frameworks 24, 25.

Data Acquisition and Genetic Marker Selection for T2D Analysis

For our investigation into T2D, we extracted data from a genome-wide association study (GWAS) by Xue et al. 26, which utilized samples from the DIAGRAM, GERA, and UKB cohorts. This pivotal study provided deeper insights into the genetic underpinnings of T2D and pinpointed potential gene loci for more in-depth functional studies. The findings from Xue et al. emphasized the significant impact of rare genetic variations on the risk associated with T2D. Our selection of genetic markers was based on a significance cut-off of 5×10-8, and we incorporated a linkage disequilibrium (LD) filter with an r2 value above 0.01 within a 5000 kb range. We calculated F-statistics for individual SNPs to confirm the strength of the genetic instruments, ensuring that each had an F-value well above 10, which is indicative of their reliability for use in MR analysis.

Data Compilation for Coronary Artery Disease Investigation

For the assessment of CAD, we sourced information from an extensive GWAS meta-analysis undertaken by Nikpay et al. 27. This meta-analysis incorporated data from 48 distinct studies, totaling a cohort of 141,217 participants and close to 8.6 million SNPs. Instrumental variables selection for CAD mirrored the parameters set in the T2D analysis to maintain uniformity in our methodological approach.

Genomic Insights into Gut Microbiota

For our analysis of gut microbiota, we utilized data from the mibioGen initiative 28, noted for being the most comprehensive GWAS collection to date. This repository includes data from 24 cohort studies, primarily involving individuals of European ancestry. It provides GWAS results for 211 different bacterial groups, spanning 9 phyla, 16 classes, 20 orders, 35 families, and 131 genera. The selection of instrumental variables for this aspect of the study was determined with a P-value threshold of less than 1×10-5, considering the relatively small pool of loci detected. We adopted the same linkage disequilibrium clumping strategy as in our analyses of T2D and CAD to ensure the genetic markers' validity 29.

Compilation and Refinement of Metabolomic Data

We obtained our metabolomic data from a genome-wide association study by Rhee et al. 30, which analyzed blood metabolite profiles from 2,076 individuals of European descent participating in the Framingham Heart Study. This study focused on the relationship between gut microbiota and various host metabolites, taking into account numerous confounding factors such as age, gender, systolic blood pressure, antihypertensive drug use, body mass index (BMI), smoking status in diabetics, prevalence of cardiovascular diseases, and kidney function. These factors were adjusted to evaluate the correlations with 217 distinct metabolite concentrations in the dataset. For the subgroup analysis of metabolites, we set a P-value threshold of less than 1 × 10-5, consistent with the thresholds established in our prior analyses 31.

Methodology for Statistical Analysis and Deduction of Causality

We utilized the inverse-variance weighted (IVW) method to assess causal links between 211 microbiome characteristics and both T2D and CAD. This assessment was conducted within the framework of a two-sample bidirectional MR, leveraging paired GWAS summary statistics. To address the concerns of multiple hypothesis testing and the possibility of horizontal pleiotropy - the scenario where genetic variants might affect disease outcomes via multiple pathways - our analysis incorporated supplementary MR methodologies, including MR-PRESSO, the weighted median approach, and MR Egger. We rigorously tested for the presence of multi-trait pleiotropy using the MR-PRESSO global tests and Cochrane's Q-statistics 32.

Causal relationships inferred from the gut microbiota's impact on T2D and CAD were quantified using beta coefficients, complete with 95% confidence intervals. We implemented the Bonferroni method for correcting multiple comparisons, considering causal effects as significant at P-values less than 0.025 for two specific outcomes and less than 2.36 × 10-4 for the broader 211 outcomes. P-values falling between 0.05 and the Bonferroni threshold were interpreted as suggestive of potential causal links.

The robustness of the MR findings was quantified using the mRnd1 online tool. All harmonized data pertinent to our study are accessible in Supplementary Material Data 1, while Supplementary Material Data 2 elaborates on the comprehensive outcomes of the bidirectional MR analysis, encompassing the gut microbiota, T2D, CAD, and related metabolites. Our MR analyses were conducted in the R statistical framework (version 4.2.2), using the TwoSampleMR (version 0.5.6) and MRPRESSO (version 1.0) packages. The TwoSampleMR package was instrumental in integrating exposure and outcome information, based on a thorough compilation of SNP data, including allele information, effect magnitudes, allele frequencies, and standard error metrics.

Results

SNP Selection for T2D and CAD Analysis

In our study, we rigorously filtered SNPs, excluding those within a 5000-kilobase pair range showing linkage disequilibrium (LD) with an r2 value exceeding 0.01, and also removed any duplicates. This stringent selection process identified 1,745 SNPs linked to T2D and 2,801 SNPs associated with CAD, each meeting a significance threshold of P < 1×10-5. Following this, our bidirectional two-sample MR analysis provided substantial evidence indicating an elevated risk of CAD in the context of T2D, as elaborated in Supplementary Table S2.

Our MR analysis identified a total of 81 causal links, including those with potential associations where P < 0.05. This included five gut microbiota traits connected to T2D and ten to CAD, along with 16 metabolite traits associated with each condition. These findings were confirmed using MRPRESSO and leave-one-out analysis techniques, effectively ruling out instances of pleiotropy or heterogeneity. The reliability of these associations was further underscored by the F-statistics for the SNPs used in the MR analysis (see Tables 1-2, and Supplementary Tables S3-S4). A scatter plot in our report illustrates the trends and directionality of effects across different MR methodologies (see Figure 2).

Table 1.

Bidirectional MR Results of Type 2 diabetes and gut microbiota

Level Exposure Outcome Method NSNP Beta(95%CI) P Directional pleiotropy Cochrane's Q-statistic (P) Steiger P
Egger intercept (P) MRPRESSO RSSobs (P)
T2D on Gut microbiota
Genus T2D Butyrivibrio MR Egger 124 -0.108(-0.278,0.061) 0.212 0.001
(0.870)
151.361
(0.115)
143.251
(0.102)
6.51E-211
Weighted median 124 -0.067(-0.195,0.061) 0.305
IVW 124 -0.096(-0.169,-0.022) 0.011
Genus T2D Catenibacterium MR Egger 114 0.046(-0.127,0.22) 0.603 0.004
(0.530)
126.627
(0.378)
121.413
(0.277)
1.51E-202
Weighted median 114 0.044(-0.096,0.184) 0.537
IVW 114 0.096(0.02,0.172) 0.013
Genus T2D Olsenella MR Egger 124 0.011(-0.14,0.162) 0.886 0.005
(0.363)
135.497
(0.416)
122.308
(0.501)
5.77E-220
Weighted median 124 0.058(-0.072,0.188) 0.379
IVW 124 0.074(0.008,0.14) 0.027
Family T2D Oxalobacteraceae MR Egger 125 0.124(-0.011,0.258) 0.073 -0.005
(0.307)
154.722
(0.106)
136.319
(0.212)
1.47E-212
Weighted median 125 0.065(-0.037,0.167) 0.215
IVW 125 0.061(0.002,0.119) 0.043
Genus T2D Erysipelotrichaceae UCG003 MR Egger 14 0.203(-0.418,0.823) 0.534 -0.004
(0.842)
23.752
(0.097)
20.351
(0.087)
2.09E-15
Weighted median 14 0.173(0.011,0.334) 0.036
IVW 14 0.14(0.004,0.276) 0.043
Gut microbiota on T2D
Genus Lachnoclostridium T2D MR Egger 8 0.524(0.044,1.005) 0.076 -0.019(0.230) 6.420(0.706) 4.971(0.664) 1.16E-23
Weighted median 8 0.179(0.03,0.328) 0.019
IVW 8 0.206(0.095,0.316) 0.000
Genus Streptococcus T2D MR Egger 11 0.118(-0.239,0.474) 0.533 0.002(0.874) 19.848(0.147) 13.161(0.215) 4.19E-37
Weighted median 11 0.116(-0.013,0.245) 0.077
IVW 11 0.146(0.046,0.246) 0.004
Genus Actinomyces T2D MR Egger 5 0.289(-0.185,0.763) 0.318 -0.016(0.514) 3.149(0.837) 2.163(0.706) 4.13E-18
Weighted median 5 0.113(-0.008,0.234) 0.067
IVW 5 0.114(0.023,0.205) 0.014
Family Streptococcaceae T2D MR Egger 13 0.122(-0.218,0.462) 0.497 -0.002(0.867) 18.677(0.269) 13.621(0.326) 1.25E-44
Weighted median 13 0.087(-0.029,0.203) 0.143
IVW 13 0.093(0.006,0.18) 0.035
Genus unknown genus id.2041 T2D MR Egger 6 0.204(-0.072,0.48) 0.222 -0.010(0.472) 10.065(0.311) 6.910(0.227) 8.97E-19
Weighted median 6 0.058(-0.056,0.172) 0.319
IVW 6 0.099(0.006,0.192) 0.037

MR, mendelian randomization; T2D, Type 2 diabetes; IVW, inverse variance weighted; NSNPs, number of single nucleotide polymorphisms; beta, mendelian randomization effect estimate

Table 2.

Bidirectional MR Results of Coronary artery disease and gut microbiota

Level Exposure Outcome Method NSNP Beta(95%CI) P Directional pleiotropy Cochrane's Q-statistic (P) Steiger P
Egger intercept (P) MRPRESSO
RSSobs (P)
Gut Microbiota on CAD
Genus Oxalobacter CAD MR Egger 11 0.184(-0.075,0.444) 0.197 -0.016(0.447) 12.740(0.496) 4.155(0.940) 1.30E-36
Weighted median 11 0.085(0.013,0.156) 0.020
IVW 11 0.082(0.026,0.137) 0.004
Genus Turicibacter CAD MR Egger 10 0.042 (-0.143, 0.226) 0.827 0.008(0.676) 14.681(0.478) 7.201(0.616) 5.77E-40
Weighted median 10 0.085 (0.029, 0.142) 0.132
IVW 10 0.119 (0.076, 0.163) 0.006
Genus Butyricicoccus CAD MR Egger 8 -0.197(-0.381, -0.014) 0.080 0.007(0.426) 10.029(0.494) 4.227(0.753) 5.00E-24
Weighted median 8 -0.138(-0.279,0.003) 0.056
IVW 8 -0.131(-0.234, -0.028) 0.012
Genus unknown genus id.2071 CAD MR Egger 16 -0.392(-0.764, -0.02) 0.058 0.024(0.139) 28.083(0.141) 13.176(0.589) 9.07E-51
Weighted median 16 -0.119(-0.23, -0.008) 0.036
IVW 16 -0.101(-0.18, -0.021) 0.013
Family Clostridiales vadin BB60 group CAD MR Egger 15 -0.144(-0.345,0.057) 0.184 0.006(0.536) 9.383(0.945) 7.743(0.902) 2.85E-50
Weighted median 15 -0.086(-0.177,0.004) 0.062
IVW 15 -0.083(-0.153, -0.013) 0.021
Genus unknown genus id.1000000073 CAD MR Egger 15 -0.144(-0.345,0.057) 0.184 0.006(0.536) 9.383(0.940) 7.743(0.902) 2.85E-50
Weighted median 15 -0.086(-0.175,0.003) 0.057
IVW 15 -0.083(-0.153, -0.013) 0.021
Genus Clostridium innocuum group CAD MR Egger 9 0.094(-0.262,0.45) 0.620 -0.002(0.924) 14.581(0.30)9 8.562(0.381) 1.10E-28
Weighted median 9 0.028(-0.06,0.115) 0.537
IVW 9 0.077(0.011,0.142) 0.022
Class Lentisphaeria CAD MR Egger 8 -0.135(-0.371,0.1) 0.303 0.009(0.625) 5.244(0.908) 3.979(0.782) 3.79E-29
Weighted median 8 -0.061(-0.152,0.031) 0.194
IVW 8 -0.076(-0.144, -0.008) 0.028
Order Victivallales CAD MR Egger 8 -0.135(-0.371,0.1) 0.303 0.009(0.625) 5.244(0.897) 3.979(0.782) 3.79E-29
Weighted median 8 -0.061(-0.145,0.024) 0.160
IVW 8 -0.076(-0.144, -0.008) 0.028
Genus Bifidobacterium CAD MR Egger 14 0.087(-0.147,0.321) 0.482 0.000(0.972) 18.136(0.464) 11.777(0.546) 3.50E-58
Weighted median 14 0.125(0.014,0.235) 0.027
IVW 14 0.091(0.008,0.173) 0.031
CAD on Gut Microbiota
Genus CAD Veillonella MR Egger 36 0.023(-0.13,0.177) 0.77 0.009
(0.243)
34.134
(0.812)
29.682
(0.722)
1.80E-85
Weighted median 36 0.095(-0.001,0.192) 0.052
IVW 36 0.108(0.045,0.171) 0.001
Genus CAD Butyricicoccus MR Egger 36 -0.088(-0.199,0.024) 0.134 0.002
(0.678)
29.168
(0.934)
23.637
(0.928)
8.15E-91
Weighted median 36 -0.063(-0.131,0.005) 0.069
IVW 36 -0.066(-0.112, -0.019) 0.005
Family CAD Christensenellaceae MR Egger 10 0.05(-0.367,0.468) 0.819 0.01
(0.609)
17.859
(0.182)
11.086
(0.27)
4.40E-14
Weighted median 10 0.14(-0.005,0.285) 0.059
IVW 10 0.159(0.046,0.272) 0.006
Genus CAD Ruminococcaceae UCG004 MR Egger 36 0.007(-0.142,0.156) 0.928 0.008
(0.281)
34.257
(0.784)
30.473
(0.686)
5.60E-87
Weighted median 36 0.074(-0.023,0.171) 0.134
IVW 36 0.083(0.021,0.145) 0.009
Genus CAD Haemophilus MR Egger 36 0.064(-0.095,0.222) 0.438 0.002
(0.774)
42.824
(0.453)
35.787
(0.431)
7.65E-84
Weighted median 36 0.028(-0.071,0.128) 0.575
IVW 36 0.085(0.02,0.149) 0.010
Class CAD Gammaproteobacteria MR Egger 36 0.109(-0.008,0.225) 0.076 -0.005
(0.408)
38.906
(0.609)
28.717
(0.764)
3.77E-86
Weighted median 36 0.085(0.016,0.154) 0.016
IVW 36 0.063(0.015,0.111) 0.010
Family CAD Prevotellaceae MR Egger 36 0.098(-0.024,0.219) 0.124 -0.004
(0.533)
31.991
(0.865)
26.465
(0.85)
9.13E-91
Weighted median 36 0.023(-0.055,0.101) 0.563
IVW 36 0.062(0.012,0.112) 0.015
Genus CAD Coprococcus1 MR Egger 36 0.039(-0.074,0.153) 0.5 0.002
(0.74)
33.98
(0.803)
26.142
(0.86)
1.19E-89
Weighted median 36 0.045(-0.024,0.114) 0.203
IVW 36 0.057(0.01,0.104) 0.017
Genus CAD Lachnospiraceae UCG008 MR Egger 35 -0.08(-0.256,0.096) 0.38 0(0.973) 42.248
(0.401)
33.612
(0.486)
1.43E-83
Weighted median 35 -0.117(-0.223, -0.011) 0.03
IVW 35 -0.083(-0.156, -0.01) 0.025
Genus CAD Family XIII UCG001 MR Egger 36 -0.082(-0.211,0.046) 0.217 0.002
(0.699)
33.55
(0.819)
30.732
(0.674)
1.43E-89
Weighted median 36 -0.068(-0.144,0.009) 0.082
IVW 36 -0.059(-0.113, -0.006) 0.03
Genus CAD Methanobrevibacter MR Egger 34 -0.37(-0.667, -0.073) 0.02 0.024
(0.083)
37.82
(0.596)
32.384
(0.498)
6.55E-78
Weighted median 34 -0.141(-0.304,0.021) 0.088
IVW 34 -0.117(-0.224, -0.01) 0.032
Genus CAD Lachnospiraceae UCG010 MR Egger 36 -0.053(-0.188,0.082) 0.447 -0.001
(0.934)
40.419
(0.522)
38.02
(0.333)
3.35E-85
Weighted median 36 -0.033(-0.115,0.048) 0.42
IVW 36 -0.058(-0.113, -0.003) 0.038
Class CAD Methanobacteria MR Egger 34 -0.352(-0.647, -0.057) 0.026 0.023
(0.099)
40.407
(0.493)
35.488
(0.352)
1.44E-76
Weighted median 34 -0.166(-0.337,0.005) 0.057
IVW 34 -0.114(-0.223, -0.004) 0.042
Family CAD Methanobacteriaceae MR Egger 34 -0.352(-0.647, -0.057) 0.026 0.023
(0.099)
40.407
(0.494)
35.488
(0.352)
1.44E-76
Weighted median 34 -0.166(-0.332,0) 0.05
IVW 34 -0.114(-0.223, -0.004) 0.042
Order CAD Methanobacteriales MR Egger 34 -0.352(-0.647, -0.057) 0.026 0.023
(0.099)
40.407
(0.451)
35.488
(0.352)
1.44E-76
Weighted median 34 -0.166(-0.331, -0.001) 0.048
IVW 34 -0.114(-0.223, -0.004) 0.042
Family CAD Lachnospiraceae MR Egger 36 -0.11(-0.219, -0.001) 0.055 0.007
(0.217)
25.906
(0.969)
21.433
(0.965)
3.95E-95
Weighted median 36 -0.06(-0.125,0.004) 0.066
IVW 36 -0.046(-0.091, -0.002) 0.042
Family CAD Pasteurellaceae MR Egger 36 0.037(-0.127,0.201) 0.66 0.003
(0.692)
45.756
(0.349)
39.428
(0.278)
1.81E-83
Weighted median 36 0.012(-0.089,0.113) 0.822
IVW 36 0.068(0.001,0.134) 0.047
Order CAD Pasteurellales MR Egger 36 0.037(-0.127,0.201) 0.66 0.003
(0.692)
45.756
(0.324)
39.428
(0.278)
1.81E-83
Weighted median 36 0.012(-0.083,0.106) 0.81
IVW 36 0.068(0.001,0.134) 0.047
Genus CAD Prevotella9 MR Egger 36 0.024(-0.123,0.172) 0.748 0.004
(0.604)
26.219
(0.979)
20.101
(0.979)
2.75E-95
Weighted median 36 0.039(-0.048,0.127) 0.377
IVW 36 0.06(0,0.121) 0.05

MR, mendelian randomization; CAD, Coronary artery disease; IVW, inverse variance weighted; NSNP, number of single nucleotide polymorphisms; beta, mendelian randomization effect estimate

Figure 2.

Figure 2

Figure 2

Figure 2

MR Association Scatterplot for Gut Microbiota and Cardiometabolic Disorders. The scatterplot features in panels A1-B5 illustrate the relationship between various gut microbiota traits and T2D. Panels C1-D17 display associations with CAD, revealing the range of genetic correlations investigated in this study.

In the bidirectional MR framework where T2D was considered as the exposure factor influencing CAD, a significant P-value of less than 0.05 was observed. While this result did not meet the criteria of the Cochran's Q test for heterogeneity, the existence of a P-value below 0.05 in a multiplicative random effects model pointed to a potential causal relationship between T2D and CAD, as noted in Supplementary Table S2.

Impact of Gut Microbiota on T2D and CAD

In our investigation, we discerned nine distinct microbial taxa, spanning various taxonomic levels, that exhibit a positive causal relationship with both T2D and CAD. Regarding T2D, a genetic predisposition towards a greater abundance of the genera Lachnoclostridium, Streptococcus, Actinomyces, and the Streptococcaceae family was linked to a higher risk of the disease. Notably, a marked increase in Lachnoclostridium (β = 0.206, 95% CI = 0.095-0.316, P = 0.0002) was observed, indicating a significant rise in T2D risk (refer to Table 1). For CAD, elevated levels of Oxalobacter, Turicibacter, the Clostridium innocuum group, and Bifidobacterium were found to have a causative association with an increased risk, with Turicibacter showing a notable effect (β = 0.119, 95% CI = 0.076-0.163, P = 0.006), implying a considerable risk escalation for CAD (as shown in Table 2).

On the other hand, we identified that certain gut microbiota characteristics exhibit an inverse correlation with CAD risk. Specifically, the Lentisphaeria class, Victivallales order, Clostridiales vadin BB60 family, and Butyricicoccus genus demonstrated a protective effect, as evidenced by beta coefficients ranging from -0.234 to -0.008, suggesting they may mitigate CAD progression.

While our data analysis didn't reveal any significant negative causal effects of gut microbiota on T2D, it did indicate that certain microbes are associated with a reduced CAD risk, pointing towards their potential protective influence against the condition, as detailed in Table 2.

Effect of T2D and CAD on Gut Microbiota Dynamics

Our study explored the causal impact of T2D and CAD on the composition of gut microbiota, assessing causal links across 210 microbiotas for T2D and 211 for CAD. Four gut microbiotas exhibited positive causal links with T2D as a genetic factor, including the genera Catenibacterium, Olsenella, and Erysipelotrichaceae UCG-003, as well as the Oxalobacteraceae family. A genetic inclination towards T2D correlated with a heightened presence of these groups (Catenibacterium β = 0.096, 95% CI = 0.020-0.172, P = 0.013; Olsenella β = 0.074, 95% CI = 0.008-0.140, P = 0.027; Erysipelotrichaceae UCG-003 β = 0.140, 95% CI = 0.004-0.276, P = 0.043; Oxalobacteraceae β = 0.061, 95% CI = 0.002-0.119, P = 0.043), as indicated in Table 1. For CAD, an augmentation in several gut microbiota genera and families was noted, implying a possible connection post-Bonferroni adjustment (refer to Table 2).

In contrast, the Butyrivibrio genus showed a decrease in abundance with T2D, hinting at a possible protective role. Regarding CAD, a diminution in the abundance of certain gut microbiotas, such as Butyricicoccus and Methanobacteriaceae, was evident. Notably, the Methanobacteria genus displayed a significant reduction in abundance, suggesting a substantial protective influence against CAD.

To validate these conclusions, we conducted various sensitivity analyses, including MR-PRESSO, Cochrane's Q-test, and MR-Egger intercept tests. These procedures did not reveal any signs of heterogeneity or horizontal pleiotropy, thereby confirming the reliability of the identified causal relationships. Additionally, the F-values of the SNPs showing statistical significance consistently exceeded the threshold of 10, adding further credibility to our findings (as detailed in Supplementary Table S5).

Metabolomic Influences on T2D and CAD

In conducting a MR study, coupled with Bonferroni adjustments for dual hypotheses (setting the significance threshold at P < 0.025), we identified a subset of 22 metabolites from a total of 217, which were genetically associated with a reduced risk of T2D. This selection encompassed a diverse array of metabolite classes, including but not limited to sphingomyelin (specifically SM14_0), selected amino acids, lysophosphatidylcholine (notably LPC18_2), triacylglycerol (specifically TAG58_8), certain adenosine derivatives, salicylurate, and glycerol. These metabolites demonstrated beta effect sizes in the range of -0.072 to -0.010, indicating their inverse relationship with T2D risk. In contrast, an increase in specific metabolites such as taurocholate, phosphatidylcholine (particularly PC36_1), and suberic acid was found to be genetically correlated with an elevated risk of T2D, with beta effect sizes ranging from 0.011 to 0.067.

Metabolite-Gut Microbiota Interactions and CAD

In an analysis utilizing unidirectional MR, refined through Bonferroni adjustments (threshold set at P < 2.36 × 10-4), we were able to pinpoint four metabolites exhibiting causative links with both T2D and CAD. This assessment uncovered a negative causal association between proline levels and the presence of Eubacterium xylanophilum (yielding a beta coefficient of -0.038, within a 95% confidence interval of -0.058 to -0.019, and a P-value of 1.18×10-4). Furthermore, LPC18_2 demonstrated a causal relationship with alterations in four distinct gut microbiota taxa. Significantly, an inverse correlation was observed between asparagine and the genus Desulfovibrio (beta coefficient of -0.059, 95% CI between -0.090 and -0.028, P = 1.80×10-4), while the Bacteroidales S24-7 group showed a positive correlation. Additionally, salicylurate was identified as having causative connections with both the Christensenellaceae family and the genus Coprococcus1, as detailed in Supplementary Data 2.

Metabolite Associations with CAD

Utilizing a directional two-sample MR approach, followed by a Bonferroni correction accommodating dual hypotheses (establishing a significance threshold at P < 0.025), our analysis discerned associations of 16 metabolites with CAD. Within this group, seven metabolites, notably LPC18_2 and asparagine, were found to be genetically correlated with an increased predisposition to CAD. This correlation was quantified with beta effects spanning from 0.008 to 0.057. In contrast, a set of nine metabolites, which included amino acids like lysine and proline, exhibited a negative genetic association with CAD risk. The beta effect values for these metabolites varied from -0.067 to -0.007, as depicted in Figure 3.

Figure 3.

Figure 3

Forest Plots of MR-Derived Causal Estimates. Displayed here are the results from inverse variance-weighted MR analyses, examining the causal effects of different metabolites on T2D and CAD. Beta coefficients, along with 95% confidence intervals (CI), are shown, illustrating the variation in disease risk associated with each 10-unit increase in metabolite concentration. Analyzed metabolites include sphingomyelin (SM), lysophosphatidylcholine (LPC), triacylglycerol (TAG), phosphatidylcholine (PC), and cholesterol ester (CE).

Discussion

In this investigation, we explored the reciprocal genetic relationships between the composition of the gut microbiota and the incidence of T2D and CAD. Our findings identified causal links of five gut microbiota characteristics with T2D, and ten with CAD. Conversely, our results suggest potential causal relationships of T2D with five gut microbiota types, and CAD with eighteen types. Additionally, we noted that certain metabolites, particularly those related to energy and lipids, exhibit causal connections with both T2D and CAD 33, 34.

The study identified five gut microbiota changes associated with T2D and ten with CAD. Of these, three microbiota types were causally linked to T2D, and seven to CAD. A notable causal association was observed between the increase in Oxalobacteraceae family abundance and T2D. In a surprising finding, a rise in the genus Oxalobacter was positively associated with an increased risk of CAD 35, 36. Noteworthy was the discovery that both Turicibacter and the Clostridium innocuum group shared the same single nucleotide polymorphism (SNP), rs4869133, suggesting its significance in the heightened risk of CAD linked to gut microbiota. Furthermore, the Clostridiales vadin BB60 family, an unknown genus with the identifier id.1000000073, the Lentisphaeria class, and the Victivallales order all displayed identical SNPs in our final MR analysis. This genetic congruence might be attributed to the categorization of the unknown genus id.1000000073 under the Clostridiales vadin BB60 family, and a shared lineage between the Victivallales order and the Lentisphaeria class, indicating a limited range of genetic markers within these groups, as detailed in Table 3.

Table 3.

Particulars of SNPs used in MR analyses of gut microbiota

Exposure traits SNPs EA OA Beta Se samplesize P-value R2 F-statistic
Type 2 diabetes (P<1×10-12) rs2296173 G A 0.065 0.0087 62892 7.65773E-14 0.001 55.820
rs340874 C T 0.0626 0.0073 62892 8.40621E-18 0.001 73.536
rs2972144 G A 0.0913 0.0075 62892 2.55094E-34 0.002 148.190
rs243019 C T 0.0566 0.0071 62892 2.28981E-15 0.001 63.550
rs780094 C T 0.0692 0.0074 62892 5.15941E-21 0.001 87.448
rs17334919 T C -0.1398 0.0128 62892 6.68652E-28 0.002 119.287
rs13389219 T C -0.0722 0.0074 62892 2.1062E-22 0.002 95.194
rs6808574 C T 0.0552 0.0076 62892 4.38531E-13 0.001 52.753
rs11708067 G A -0.0965 0.0086 62892 5.93335E-29 0.002 125.909
rs6795735 T C -0.0558 0.0073 62892 1.63005E-14 0.001 58.428
rs7651090 G A 0.1204 0.0076 62892 3.8539E-57 0.004 250.972
rs1899951 T C -0.1118 0.0109 62892 1.63682E-24 0.002 105.204
rs1496653 G A -0.0769 0.0088 62892 2.57217E-18 0.001 76.364
rs1801214 T C 0.0903 0.0074 62892 5.51569E-34 0.002 148.906
rs459193 G A 0.0711 0.0083 62892 8.80846E-18 0.001 73.381
rs7729395 T C 0.1373 0.016 62892 1.10103E-17 0.001 73.638
rs7756992 G A 0.1297 0.0078 62892 5.99929E-62 0.004 276.497
rs1063355 G T 0.0709 0.0079 62892 3.71535E-19 0.001 80.545
rs17168486 T C 0.0742 0.0094 62892 2.17721E-15 0.001 62.309
rs2191348 T G 0.0652 0.0073 62892 3.44429E-19 0.001 79.772
rs13234269 A T -0.0583 0.0078 62892 6.9775E-14 0.001 55.866
rs849135 A G -0.0999 0.0072 62892 1.04112E-43 0.003 192.516
rs3802177 A G -0.1217 0.008 62892 2.32113E-52 0.004 231.420
rs516946 C T 0.0824 0.0085 62892 3.15864E-22 0.001 93.976
rs10974438 C A 0.0591 0.0075 62892 3.01301E-15 0.001 62.094
rs10811661 C T -0.1569 0.0098 62892 4.13238E-58 0.004 256.327
rs2796441 A G -0.0715 0.0073 62892 1.962E-22 0.002 95.933
rs1063192 A G 0.0634 0.0073 62892 3.29837E-18 0.001 75.428
rs4918796 C T 0.0623 0.0086 62892 4.01328E-13 0.001 52.478
rs7923866 T C -0.0972 0.0074 62892 9.33684E-40 0.003 172.532
rs11257655 T C 0.0737 0.0087 62892 1.96607E-17 0.001 71.762
rs7903146 T C 0.3059 0.0077 62892 1E-200 0.024 1578.256
rs10830963 G C 0.0909 0.008 62892 5.84655E-30 0.002 129.106
rs1552224 C A -0.1034 0.0101 62892 8.63575E-25 0.002 104.809
rs5215 T C -0.0678 0.0073 62892 2.08882E-20 0.001 86.261
rs10842994 T C -0.0755 0.0091 62892 1.01508E-16 0.001 68.835
rs2261181 T C 0.0985 0.0118 62892 9.1791E-17 0.001 69.680
rs825476 T C 0.0524 0.0073 62892 6.80456E-13 0.001 51.525
rs61953351 T G -0.07 0.0091 62892 1.97606E-14 0.001 59.172
rs1359790 A G -0.0796 0.008 62892 2.79512E-23 0.002 99.003
rs7177055 A G 0.0647 0.0079 62892 2.746E-16 0.001 67.074
rs7185735 G A 0.1056 0.0073 62892 1.59001E-47 0.003 209.258
rs77258096 A C -0.1171 0.0134 62892 1.7832E-18 0.001 76.367
rs8068804 A G 0.0587 0.0078 62892 4.41062E-14 0.001 56.635
rs9894220 G A -0.0585 0.0079 62892 1.51705E-13 0.001 54.835
rs8108269 G T 0.0644 0.0079 62892 3.11387E-16 0.001 66.453
coronary artery disease (P<1×10-10) rs67180937 G T 0.078807 0.0110551 42457 1.01E-12 0.001 50.816
rs7528419 G A -0.11453 0.011482 42457 1.97E-23 0.002 99.495
rs9970807 T C -0.12575 0.016695 42457 5.00E-14 0.001 56.734
rs115654617 A C 0.137846 0.0158314 42457 3.12E-18 0.002 75.814
rs12202017 G A -0.066813 0.0099612 42457 1.98E-11 0.001 44.988
rs55730499 T C 0.316641 0.0242403 42457 5.39E-39 0.004 170.631
rs186696265 T C 0.550351 0.0481949 42457 3.35E-30 0.003 130.400
rs9349379 G A 0.131836 0.0096527 42457 1.81E-42 0.004 186.539
rs2107595 A G 0.073415 0.0112951 42457 8.05E-11 0.001 42.246
rs11556924 T C -0.072569 0.0110605 42457 5.34E-11 0.001 43.048
rs2891168 G A 0.193401 0.0091877 42457 2.29E-98 0.010 443.102
rs2487928 A G 0.062633 0.0095049 42457 4.41E-11 0.001 43.422
rs1870634 G T 0.075878 0.0097113 42457 5.55E-15 0.001 61.049
rs1412444 T C 0.066812 0.0096809 42457 5.15E-12 0.001 47.630
rs2128739 C A -0.065565 0.0100568 42457 7.05E-11 0.001 42.503
rs2681472 G A 0.074114 0.0113331 42457 6.17E-11 0.001 42.766
rs4468572 C T 0.077234 0.0095277 42457 4.44E-16 0.002 65.711
rs4420638 G A 0.091906 0.0140977 42457 7.07E-11 0.001 42.500
rs56289821 A G -0.13361 0.0170415 42457 4.44E-15 0.001 61.470
rs28451064 A G 0.127571 0.015952 42457 1.33E-15 0.002 63.955
genus Lachnoclostridium id.11308 (P<1×10-5) rs12566975 T C -0.0468097 0.0105787 14306 9.57194E-06 0.001 19.580
rs1528479 A G 0.0497799 0.0111919 14306 9.63984E-06 0.001 19.783
rs615997 T C 0.0511752 0.0106491 14306 2.0268E-06 0.002 23.094
rs62285313 A G 0.0864203 0.0181565 14306 1.58332E-06 0.002 22.655
rs1031599 T G 0.078627 0.0175644 14306 6.31379E-06 0.001 20.039
rs3821998 C A -0.0864066 0.0192519 14306 6.72048E-06 0.001 20.144
rs4738679 A G 0.0520267 0.011404 14306 4.41754E-06 0.001 20.813
rs1997204 C T 0.108075 0.0242022 14306 5.97077E-06 0.001 19.941
rs62028349 G C 0.0469989 0.0105971 14306 9.17044E-06 0.001 19.670
rs72829893 G T 0.117472 0.0268103 14306 5.57763E-06 0.001 19.198
rs78068103 A G 0.0886199 0.0194248 14306 3.66522E-06 0.001 20.814
rs2385421 A G 0.0746186 0.0180734 14306 7.13724E-06 0.001 17.046
rs789029 C T -0.0641288 0.0137974 14306 3.75327E-06 0.002 21.603
rs6112314 A C -0.0561715 0.0108174 14306 2.43215E-07 0.002 26.964
genus Streptococcus id.1853 (P<1×10-5) rs11720390 G A 0.107024 0.0228121 14306 3.59484E-06 0.002 22.011
rs6806351 T C -0.0633829 0.0136647 14306 4.93867E-06 0.002 21.515
rs57646748 G A -0.0907696 0.0200344 14306 5.47545E-06 0.001 20.527
rs10028567 C T -0.0921167 0.0191881 14306 7.30348E-06 0.002 23.047
rs395407 C G 0.0792781 0.0173697 14306 4.36506E-06 0.001 20.832
rs77558518 A G -0.103999 0.0229714 14306 4.70858E-06 0.001 20.497
rs11764382 A G -0.0695345 0.0143671 14306 1.28632E-06 0.002 23.424
rs17708276 A G -0.0793955 0.0170628 14306 3.04096E-06 0.002 21.652
rs10448310 A G -0.0517935 0.0111324 14306 3.30704E-06 0.002 21.646
rs71481756 T G 0.0931048 0.0207949 14306 6.51478E-06 0.001 20.046
rs7916711 A G 0.102891 0.0217362 14306 0.000002717 0.002 22.407
rs1918540 A G -0.059639 0.0128148 14306 2.44068E-06 0.002 21.659
rs11110281 T C -0.137519 0.0227398 14306 2.58315E-09 0.003 36.572
rs2370083 G T -0.0816836 0.0185851 14306 9.75237E-06 0.001 19.317
rs72739637 A G 0.0959942 0.0193213 14306 1.03307E-06 0.002 24.684
rs6563952 C G -0.0827344 0.0180035 14306 5.8213E-06 0.001 21.118
rs4968759 A G -0.0515109 0.0112068 14306 3.7812E-06 0.001 21.127
rs9903102 C A -0.0709483 0.0155275 14306 4.17994E-06 0.001 20.878
genus Actinomyces id.423 (P<1×10-5) rs71315246 A G -0.0969809 0.021925 14306 9.82969E-06 0.001 19.566
rs34583783 G T 0.126596 0.0268461 14306 4.48528E-06 0.002 22.237
rs4073240 G A 0.0749687 0.0167368 14306 7.94273E-06 0.001 20.064
rs35011108 A G 0.232634 0.0512044 14306 6.33826E-06 0.001 20.641
rs4146653 G A 0.0985224 0.0214182 14306 4.49645E-06 0.001 21.159
rs10787984 G C 0.094316 0.0213513 14306 9.62299E-06 0.001 19.513
rs7915461 C T -0.18776 0.0401636 14306 5.91984E-06 0.002 21.855
rs2715439 T C -0.0746684 0.0164822 14306 6.27004E-06 0.001 20.523
family Streptococcaceae id.1850 (P<1×10-5) rs77968078 G A -0.0993013 0.0224788 14306 7.93341E-06 0.001 19.515
rs76717940 T A 0.150606 0.0334079 14306 3.08937E-06 0.001 20.323
rs6806351 T C -0.0619209 0.0135744 14306 6.93793E-06 0.001 20.808
rs10028567 C T -0.0934027 0.0190343 14306 3.72495E-06 0.002 24.079
rs57646748 G A -0.088021 0.019876 14306 7.88352E-06 0.001 19.612
rs395407 C G 0.0826855 0.0172536 14306 1.32559E-06 0.002 22.967
rs77558518 A G -0.104239 0.022806 14306 3.72195E-06 0.001 20.891
rs957755 T G -0.0642449 0.0142702 14306 7.41515E-06 0.001 20.268
rs2952251 G A 0.0639298 0.0126525 14306 3.72237E-07 0.002 25.530
rs28718126 A G 0.109069 0.0246868 14306 9.41044E-06 0.001 19.520
rs7916711 A G 0.0959639 0.021545 14306 6.32732E-06 0.001 19.839
rs16950051 A G 0.107008 0.0236973 14306 5.33814E-06 0.001 20.391
rs11110281 T C -0.130554 0.0225943 14306 1.40136E-08 0.002 33.387
rs2370083 G T -0.0842751 0.0184509 14306 4.25667E-06 0.001 20.862
rs72739637 A G 0.0927983 0.0192021 14306 1.82163E-06 0.002 23.355
rs6563952 C G -0.0801931 0.0178576 14306 8.70583E-06 0.001 20.166
rs35344081 G A 0.0609349 0.0129703 14306 2.63846E-06 0.002 22.072
rs9903102 C A -0.0693015 0.0154096 14306 4.91802E-06 0.001 20.226
rs4968759 A G -0.0544035 0.0111271 14306 8.91887E-07 0.002 23.905
unknown genus id.2041 (P<1×10-5) rs1032598 G A -0.0886426 0.0189039 14306 4.07587E-06 0.002 21.988
rs16843660 A G 0.234697 0.04907 14306 1.75344E-06 0.002 22.876
rs11941716 A G 0.101243 0.0224414 14306 9.0663E-06 0.001 20.353
rs249459 A G 0.0737341 0.0165018 14306 8.12307E-06 0.001 19.965
rs553072 G A 0.109193 0.0230198 14306 3.69097E-06 0.002 22.500
rs1962916 G A -0.0737876 0.0162232 14306 6.13847E-06 0.001 20.687
rs35703006 G T 0.0926669 0.0190779 14306 9.00762E-07 0.002 23.593
rs921383 G A 0.0723153 0.0159706 14306 7.72894E-06 0.001 20.503
rs2651663 A G -0.0762556 0.0168635 14306 5.64144E-06 0.001 20.448
rs2336448 T C 0.0773742 0.0160883 14306 1.42899E-06 0.002 23.130
rs7187855 A C 0.199941 0.0418308 14306 2.20602E-06 0.002 22.846
rs6514318 T C 0.128198 0.0281765 14306 5.37675E-06 0.001 20.701
genus Oxalobacter id.2978 (P<1×10-5) rs4428215 G A 0.130293 0.0242237 14306 7.51069E-08 0.002 28.931
rs36057338 G T 0.207847 0.0421439 14306 8.79812E-07 0.002 24.323
rs1569853 T C -0.138078 0.0296981 14306 3.64502E-06 0.002 21.617
rs6993398 G A 0.127217 0.0278855 14306 7.12771E-06 0.001 20.813
rs10464997 G A 0.137691 0.0294804 14306 3.29754E-06 0.002 21.814
rs12002250 A C 0.217122 0.0466317 14306 1.41504E-06 0.002 21.679
rs736744 T C -0.117882 0.0211262 14306 2.57472E-08 0.002 31.135
rs3862635 C T -0.172142 0.0394026 14306 9.18692E-06 0.001 19.086
rs11108500 A G -0.199099 0.0427327 14306 3.74283E-06 0.002 21.708
rs111966731 T C 0.213114 0.047162 14306 7.29861E-06 0.001 20.419
rs6071435 T A -0.105512 0.021489 14306 1.07431E-06 0.002 24.109
rs6000536 C T -0.130992 0.0253804 14306 2.06054E-07 0.002 26.637
genus Turicibacter id.2162 (P<1×10-5) rs149744580 A G 0.169883 0.0315478 14306 7.00971E-08 0.002 28.998
rs4869133 G A 0.131186 0.027197 14306 2.5537E-06 0.002 23.267
rs2221441 G C 0.0710364 0.015343 14306 3.45669E-06 0.001 21.436
rs3734633 G A -0.120957 0.02683 14306 5.31912E-06 0.001 20.325
rs55756211 T C -0.115115 0.0240708 14306 2.8053E-06 0.002 22.871
rs2952020 A G 0.0759019 0.0165764 14306 5.63313E-06 0.001 20.966
rs61265175 G C -0.0858591 0.0185778 14306 4.13676E-06 0.001 21.359
rs11054680 T C -0.104751 0.0226997 14306 2.30978E-06 0.001 21.295
rs4247078 G C -0.0710377 0.0155221 14306 5.46072E-06 0.001 20.945
rs11649454 G C 0.0950891 0.0203433 14306 3.26625E-06 0.002 21.848
rs7199484 G A -0.0731428 0.0160172 14306 5.7666E-06 0.001 20.853
rs12603364 T C 0.110861 0.0225598 14306 8.66603E-07 0.002 24.148
rs11666533 C T -0.111689 0.0248436 14306 7.37106E-06 0.001 20.211
rs2834977 T C -0.0959995 0.0208261 14306 3.95585E-06 0.001 21.248
genus Butyricicoccus id.2055 (P<1×10-5) rs12034718 G A -0.0701199 0.0158213 14306 9.57679E-06 0.001 19.643
rs10084203 G A -0.0549699 0.0123563 14306 8.58638E-06 0.001 19.791
rs56221232 T C 0.0828027 0.0167401 14306 7.61939E-07 0.002 24.467
rs2017189 T G 0.0506956 0.011024 14306 3.87258E-06 0.001 21.148
rs62478070 T G 0.224039 0.0494959 14306 5.93772E-06 0.001 20.488
rs4962426 T G -0.0614216 0.0135979 14306 7.38482E-06 0.001 20.403
rs7322368 C T -0.0815733 0.0183167 14306 5.51785E-06 0.001 19.834
rs12585793 T C -0.262206 0.0564729 14306 5.79189E-06 0.002 21.558
rs75238760 T A 0.0619423 0.0139942 14306 6.79704E-06 0.001 19.592
unknown genus id.2071 (P<1×10-5) rs4644504 T C -0.0969321 0.0216146 14306 5.81969E-06 0.001 20.111
rs11809762 G A -0.0934634 0.0190198 14306 1.68287E-06 0.002 24.147
rs11904514 A G 0.109498 0.0249839 14306 7.89951E-06 0.001 19.208
rs1809136 C G -0.0994594 0.0228638 14306 8.36989E-06 0.001 18.923
rs16823675 C T -0.0767515 0.0149973 14306 2.33346E-07 0.002 26.191
rs11684166 A G -0.0769635 0.0168349 14306 3.49116E-06 0.001 20.900
rs10200320 T C -0.0641139 0.0142769 14306 5.6607E-06 0.001 20.167
rs2898979 G C 0.0901515 0.0202199 14306 7.67291E-06 0.001 19.879
rs35740166 C T -0.112246 0.0226824 14306 8.39982E-07 0.002 24.489
rs17086536 C A -0.100851 0.022432 14306 3.3638E-06 0.001 20.213
rs34985298 G A -0.0623526 0.013772 14306 8.33758E-06 0.001 20.498
rs1455639 A G -0.0760307 0.0169831 14306 7.83899E-06 0.001 20.042
rs11195523 C A -0.0689278 0.0145351 14306 2.40121E-06 0.002 22.488
rs2939766 A G -0.0591611 0.013042 14306 7.01148E-06 0.001 20.577
rs76532867 T C 0.112353 0.0242364 14306 2.55859E-06 0.001 21.490
rs56975773 T A 0.113282 0.0248859 14306 7.65491E-06 0.001 20.721
rs12147596 C T -0.0719818 0.0141609 14306 2.86207E-07 0.002 25.838
rs72700702 T C -0.091726 0.0189005 14306 1.59272E-06 0.002 23.553
rs72707147 C T 0.110109 0.0244644 14306 6.84022E-06 0.001 20.257
rs6007642 C T -0.0791412 0.0177958 14306 9.95543E-06 0.001 19.777
family Clostridiales vadin BB60 group id.11286 rs7538034 T G -0.078598 0.0165982 14306 2.36706E-06 0.002 22.423
(P<1×10-5) rs6588624 A G 0.0662317 0.0138147 14306 1.79287E-06 0.002 22.985
rs13409132 A G -0.165419 0.0352154 14306 4.3723E-06 0.002 22.065
rs2191834 T G -0.0746375 0.0159136 14306 2.50196E-06 0.002 21.998
rs6755871 C G -0.0613825 0.0138976 14306 9.33061E-06 0.001 19.508
rs989682 A G 0.070194 0.0155364 14306 6.84715E-06 0.001 20.413
rs10517600 G T -0.0626993 0.0139364 14306 6.82763E-06 0.001 20.241
rs34088226 A G -0.117807 0.026924 14306 7.66214E-06 0.001 19.145
rs7725895 A G -0.116224 0.0240367 14306 3.94357E-06 0.002 23.380
rs66714985 A C 0.116908 0.0252447 14306 4.85333E-06 0.001 21.446
rs118104867 C T 0.214464 0.0455098 14306 3.43598E-06 0.002 22.207
rs10904722 C T -0.0672314 0.0147123 14306 5.04836E-06 0.001 20.883
rs17121075 G A 0.0769254 0.0172234 14306 7.91425E-06 0.001 19.948
rs55682560 C T -0.131519 0.0261319 14306 4.97038E-07 0.002 25.330
rs28691777 C T 0.137134 0.0266996 14306 6.95697E-07 0.002 26.380
rs7226487 A G -0.0643682 0.0138701 14306 3.58286E-06 0.002 21.537
rs9979874 G C -0.0738925 0.0150911 14306 1.05271E-06 0.002 23.975
unknown genus id.1000000073 (P<1×10-5) rs6588624 A G 0.0662317 0.0138147 14306 1.79287E-06 0.002 22.985
rs7538034 T G -0.078598 0.0165982 14306 2.36706E-06 0.002 22.423
rs2191834 T G -0.0746375 0.0159136 14306 2.50196E-06 0.002 21.998
rs13409132 A G -0.165419 0.0352154 14306 4.3723E-06 0.002 22.065
rs6755871 C G -0.0613825 0.0138976 14306 9.33061E-06 0.001 19.508
rs989682 A G 0.070194 0.0155364 14306 6.84715E-06 0.001 20.413
rs10517600 G T -0.0626993 0.0139364 14306 6.82763E-06 0.001 20.241
rs7725895 A G -0.116224 0.0240367 14306 3.94357E-06 0.002 23.380
rs34088226 A G -0.117807 0.026924 14306 7.66214E-06 0.001 19.145
rs66714985 A C 0.116908 0.0252447 14306 4.85333E-06 0.001 21.446
rs118104867 C T 0.214464 0.0455098 14306 3.43598E-06 0.002 22.207
rs10904722 C T -0.0672314 0.0147123 14306 5.04836E-06 0.001 20.883
rs17121075 G A 0.0769254 0.0172234 14306 7.91425E-06 0.001 19.948
rs55682560 C T -0.131519 0.0261319 14306 4.97038E-07 0.002 25.330
rs28691777 C T 0.137134 0.0266996 14306 6.95697E-07 0.002 26.380
rs7226487 A G -0.0643682 0.0138701 14306 3.58286E-06 0.002 21.537
rs9979874 G C -0.0738925 0.0150911 14306 1.05271E-06 0.002 23.975
genus Clostridium innocuum group id.14397 rs6577484 G A 0.160425 0.0360857 14306 8.40601E-06 0.001 19.764
(P<1×10-5) rs1948423 T A -0.108859 0.023425 14306 3.49406E-06 0.002 21.596
rs40656 C T 0.142664 0.0311021 14306 8.61529E-06 0.001 21.040
rs6890185 C T -0.113424 0.0233137 14306 1.12243E-06 0.002 23.669
rs4869133 G A -0.180591 0.0409505 14306 7.24453E-06 0.001 19.448
rs10074000 T C -0.102648 0.0227508 14306 6.99939E-06 0.001 20.357
rs71564433 T A -0.126746 0.0274657 14306 7.8001E-06 0.001 21.295
rs10506058 A G 0.0997048 0.0221926 14306 8.92442E-06 0.001 20.184
rs77845139 A G -0.114993 0.0257186 14306 8.40621E-06 0.001 19.992
rs61267978 T C 0.14708 0.0320875 14306 5.58509E-06 0.001 21.010
rs1942371 G A -0.157938 0.034187 14306 4.0634E-06 0.001 21.343
class Lentisphaeria id.2250 (P<1×10-5) rs72640280 A G 0.220207 0.0486196 14306 5.18036E-06 0.001 20.513
rs73113483 T A -0.131217 0.0288713 14306 8.66343E-06 0.001 20.656
rs2731834 G C -0.109438 0.023693 14306 4.24356E-06 0.001 21.335
rs11770843 C T 0.109431 0.0234879 14306 1.9073E-06 0.002 21.707
rs62570196 C T -0.21635 0.0439866 14306 1.07924E-06 0.002 24.192
rs2031282 A G 0.122368 0.0270329 14306 4.38258E-06 0.001 20.490
rs17114848 G A 0.152377 0.0324332 14306 4.05864E-06 0.002 22.073
rs1002941 A G -0.105025 0.0233484 14306 8.14836E-06 0.001 20.234
rs77599476 A G 0.230292 0.0480168 14306 1.86132E-06 0.002 23.002
rs2825714 A G -0.13741 0.0289246 14306 1.72211E-06 0.002 22.568
order Victivallales id.2254 (P<1×10-5) rs72640280 A G 0.220207 0.0486196 14306 5.18036E-06 0.001 20.513
rs73113483 T A -0.131217 0.0288713 14306 8.66343E-06 0.001 20.656
rs2731834 G C -0.109438 0.023693 14306 4.24356E-06 0.001 21.335
rs11770843 C T 0.109431 0.0234879 14306 1.9073E-06 0.002 21.707
rs62570196 C T -0.21635 0.0439866 14306 1.07924E-06 0.002 24.192
rs2031282 A G 0.122368 0.0270329 14306 4.38258E-06 0.001 20.490
rs1002941 A G -0.105025 0.0233484 14306 8.14836E-06 0.001 20.234
rs17114848 G A 0.152377 0.0324332 14306 4.05864E-06 0.002 22.073
rs77599476 A G 0.230292 0.0480168 14306 1.86132E-06 0.002 23.002
rs2825714 A G -0.13741 0.0289246 14306 1.72211E-06 0.002 22.568
genus Bifidobacterium id.436 (P<1×10-5) rs12022129 A G -0.0619356 0.0138937 14306 7.9965E-06 0.001 19.872
rs1961273 C T 0.0674036 0.0132319 14306 3.50865E-07 0.002 25.949
rs13020688 G A 0.0562696 0.0122617 14306 4.07258E-06 0.001 21.059
rs182549 T C -0.119703 0.0127294 14306 1.2782E-20 0.006 88.429
rs62181700 G A -0.0624643 0.0131205 14306 2.17245E-06 0.002 22.665
rs4567981 T A 0.0562084 0.0117923 14306 1.92832E-06 0.002 22.720
rs55888705 A G 0.0546319 0.0121139 14306 6.67022E-06 0.001 20.339
rs4957061 T C 0.0534239 0.0117431 14306 5.77936E-06 0.001 20.697
rs73797465 T G -0.0953566 0.0209236 14306 4.38157E-06 0.001 20.770
rs76671854 C G -0.0846055 0.0184003 14306 3.95667E-06 0.001 21.142
rs857444 C T 0.0558234 0.0121219 14306 0.000003571 0.001 21.208
rs2686790 C T -0.070741 0.0157926 14306 7.49894E-06 0.001 20.065
rs2491158 A G -0.0712624 0.015983 14306 8.04711E-06 0.001 19.879
rs10841473 G C -0.0624207 0.0129438 14306 1.6452E-06 0.002 23.256
rs7322849 T C 0.112428 0.0201813 14306 1.08368E-08 0.002 31.035
rs540489 T G -0.0637641 0.0138746 14306 5.19457E-06 0.001 21.121
rs75344046 C T 0.232354 0.0505979 14306 4.86351E-06 0.001 21.088
rs5746486 T C -0.0536216 0.0120801 14306 8.99953E-06 0.001 19.703

SNPs, single nucleotide polymorphisms; EA, effect allele; OA, other allele; Beta, effect estimate; SE, standard error

The anaerobic bacterium genus Oxalobacter, specialized in symbiosis and reliant solely on oxalic acid, was initially identified in the human gut and formally designated as Oxalobacter formigenes in 1985 37, 38. This bacterium has garnered significant attention in nephrolithiasis research due to correlations between heightened urinary oxalic acid excretion and the formation of oxalic acid kidney stones 39. Distinct variations in the gut microbiome have been noted in several studies comparing individuals with type 2 diabetes (T2D) and healthy controls. Key differences include a reduction in butyrate-producing gut microbiota, diminished levels of Akkermansia muciniphila, and an increased presence of pro-inflammatory bacterial species 40. Nonetheless, alterations in the abundance of Lachnoclostridium, Streptococcus, Actinomyces, and Streptococcaceae have been less frequently reported. Certain medications, like metformin, are known to modulate gut microbiota, thereby influencing insulin sensitivity and aiding in diabetes management. T2D may enhance the proliferation of Oxalobacter formigenes by inducing chronic intestinal inflammation and altering metabolic pathways related to oxalic acid processing 41, 42. This condition is characterized by heightened parasympathetic activity and local ATP release into the intestinal tract 43-45. The relatively unaffected colonization of Oxalobacter formigenes by other bacteria suggests a stable colonization characteristic of this genus 46. Research has examined various prevalent methods and conditions pertinent to probiotic strain production, particularly highlighting the resilience of the Group I Oxalobacter strain OxCC13 in lyophilized form and when mixed in yogurt 47. Human consumption of Oxalobacter in these forms may offer preventive benefits against CAD, although the understanding of Oxalobacter's role in CAD remains incomplete 48. A gut microbiota-based diagnostic model suggests that increased gut colonization by Oxalobacter formigenes might elevate CAD risk 49. This aligns with our study findings, though the underlying mechanisms require further elucidation 50.

Recent studies focusing on the interplay between T2D and gut microbiota have observed a reduction in gut microbiota species that produce butyric acid in individuals with prediabetes, aligning with previous findings 40, 41. In the context of intestinal dysbiosis associated with T2D, metformin has been shown to enhance the production of butyric and propionic acids and improve patients' ability to break down amino acids. Additionally, metformin's role in modifying gut microbiota composition, potentially aiding in T2D prognosis through an increase in butyric acid-producing bacteria, has been highlighted 51, 52. Past research, encompassing both animal models and epidemiological studies, has underscored the bidirectional relationship between gut microbiota and host health in the context of atherosclerotic cardiovascular disease. Notably, bacterial presence in atherosclerotic plaques has been documented 53-55. The gut microbiota's influence on the metabolism of short-chain fatty acids (SCFAs), including Prevotellaceae, Clostridium, and Anaerostipes, has been linked to CAD, echoing findings from this study 56. A significant observation is the decreased abundance of methanogens in individuals susceptible to CAD. Certain methanogens are known to convert Trimethylamine (TMA) into a less harmful derivative, trimethylamine N-oxide (TMAO), thus reducing TMAO production 57. In our study, though the P-value in the IVW method for TMAO was less than 0.05, it did not pass sensitivity analyses, suggesting a potential connection between altered gut microbiota in coronary atherosclerosis patients and increased TMAO levels due to impaired metabolism.

For individuals with DCAD, long-term medication complicates the reliability of isolated gut microbiota observations. This study suggests that intestinal bacteria play a regulatory role in the development of both T2D and CAD, with implications for both elevated and reduced risk. The discovery of certain gut flora causally linked to diabetes and coronary heart disease, previously unreported, opens up new avenues for therapeutic strategies and potential targets.

The composition and activity of the gut microbiome, influenced by dietary and environmental factors, play a crucial role in the abundance and utilization of various metabolites 58. Metabolomics research has linked bile acids, branched-chain amino acids (BCAAs), and by-products of intracellular fatty acid oxidation to diabetes, glycemic control, and insulin resistance. Despite some studies indicating a correlation between TMAO levels and an increased risk of major cardiovascular events, including CAD, other studies have not found a significant relationship between circulating TMAO concentrations and cardiovascular outcomes 59-62. In our research, TMAO did not exhibit a notable association with CAD risk. However, we observed a positive correlation between certain lipid metabolism markers, such as phosphatidylcholine and cholesterol, including lysophosphatidylcholine (LPC18_2) and cholesterol ester (CE18_2), and CAD risk, underlining the strong connection between lipid metabolism and CAD 63-65. Animal studies have shown that rats on a carnitine-rich diet experienced a reduction in aortic lesion size, irrespective of increased blood TMAO levels, hinting at a possible protective role of carnitine against atherosclerosis 66, 67. This finding aligns with the results from our MR analysis, reinforcing the potential significance of carnitine in atherosclerosis prevention 68.

When evaluating the findings of this research, certain limitations must be acknowledged. Firstly, despite utilizing the most comprehensive genome-wide association study (GWAS) database currently available for gut microbiota and metabolites, the limited number of single nucleotide polymorphisms (SNPs) reaching genome-wide significance might have led to the use of weaker instrumental variables. To mitigate this, we expanded the inclusion criteria for SNPs to a statistical threshold of P < 10-5, allowing for a broader SNP inclusion. Additionally, to ascertain that these SNPs were not weak instrumental variables, they were evaluated using F statistics, ensuring values greater than 10. Secondly, given the extensive number of base pairs in the genome-wide analysis, it's challenging to completely rule out the presence of polymorphisms. Moreover, the biological implications of the selected SNPs have not been comprehensively explored. However, in our study, no horizontal pleiotropy was identified, as confirmed by the application of methods like MRPRESSO and MR Egger. Thirdly, our MR analysis was predicated on the assumption of a linear relationship between the variables of interest, hence the possibility of non-linear interactions between the exposure and outcome cannot be entirely dismissed. Finally, the metabolite database employed in our study was subject to preliminary screening. This limitation meant that a comprehensive two-way MR analysis was not feasible. Future research, ideally with more complete GWAS data, will be necessary to corroborate and expand upon our findings.

Conclusion

The MR study conducted in our research provides insights into both the positive and negative causal effects of gut microbiota composition and metabolite levels on the occurrence of T2D and coronary artery disease (CAD). Our data supports the notion that the bacterial species Oxalobacter formigenes could be a contributory factor in CAD, particularly among individuals with diabetes. This study highlights a noteworthy link between the Methanobacteria class and CAD risk, paving the way for further exploration into the roles of TMAO and the protective potential of carnitine in the development of CAD. The findings present a new viewpoint on the influence of gut microbiota in the pathogenesis of CAD, providing valuable insights that could guide therapeutic approaches and the management of CAD in patients with T2D.

Supplementary Material

Supplementary figures and tables.

Supplementary data 1.

Supplementary data 2.

Acknowledgments

Our heartfelt thanks go to Xue and colleagues for their groundbreaking T2D GWAS meta-analysis, Nikpay and team for their exhaustive CAD GWAS meta-analysis, the MiBioGen consortium for their meta-analysis of gut microbiota GWAS, and the FHS consortium for their analysis in metabolite GWAS.

Financial Support

This investigation was financially supported by several grants: from the National Natural Science Foundation of China (Grant Numbers 82271806 and 82200483), the Natural Science Foundation of Guangdong Province (Grant Numbers 2022A1515110560, 2022A1515111053 and 2023A1515011687), the Guangzhou Basic Research Program's Basic and Applied Basic Research Project (Grant Number 202201011024), Guangzhou Science and Technology Plan Project (Grant Number 2023A03J0697), and the Sun Yat-sen Memorial Hospital, Sun Yat-sen University's Scientific Research Sailing Project (Grant Number YXQH2022017).

Ethics Statement

The genome-wide association studies (GWAS) used in this study received ethical approval from their respective review committees, as indicated in their original publications. Our study, employing summary-level data, did not necessitate additional ethical approval.

Data Accessibility

The data underpinning the conclusions of this article are detailed in the main text and supplementary materials, with direct references in Supplementary Table S1.

Author contributions

The study's conceptualization and design were led by Z. Zeng, J. Qiu, J. Tao, L. Lin, and J. Zheng. D. Liang, F. Wei, Y. Fu, J. Zhang, X. Zhang and X. Wei played key roles in data analysis and interpretation. Y. Chen provided statistical expertise and editorial assistance. Z. Zeng and J. Qiu drafted the initial manuscript. J. Tao, L. Lin, and J. Zheng oversaw the project. All authors participated in a thorough review and refinement of the manuscript and approved its final version for publication.

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Supplementary Materials

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Supplementary data 1.

Supplementary data 2.

Data Availability Statement

The data underpinning the conclusions of this article are detailed in the main text and supplementary materials, with direct references in Supplementary Table S1.


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