Causal associations between gut microbiota, circulating inflammatory proteins, and epilepsy: a multivariable Mendelian randomization study

Abstract

Background: Previous studies have suggested that gut microbiota (GM) may be involved in the pathogenesis of epilepsy through the microbiota-gut-brain axis (MGBA). However, the causal relationship between GM and different epilepsy subtypes and whether circulating inflammatory proteins act as mediators to participate in epileptogenesis through the MGBA remain unclear. Therefore, it is necessary to identify specific GM associated with epilepsy and its subtypes and explore their underlying inflammatory mechanisms for risk prediction, personalized treatment, and prognostic monitoring of epilepsy.

Methods: We hypothesized the existence of a pathway GM-inflammatory proteins-epilepsy. We found genetic variants strongly associated with GM, circulating inflammatory proteins, epilepsy and its subtypes, including generalized and partial seizures, from large-scale genome-wide association studies (GWAS) summary data and used Multivariate Mendelian Randomization to explore the causal relationship between the three and whether circulating inflammatory proteins play a mediating role in the pathway from GM to epilepsy, with inverse variance weighted (IVW) method as the primary statistical method, supplemented by four methods: MR-Egger, weighted median estimator (WME), Weighted mode and Simple mode.

Results: 16 positive and three negative causal associations were found between the genetic liability of GM and epilepsy and its subtypes. There were nine positive and nine negative causal associations between inflammatory proteins and epilepsy and its subtypes. Furthermore, we found that C-X-C motif chemokine 11 (CXCL11) levels mediated the causal association between Genus Family XIII AD3011 group and epilepsy.

Conclusion: Our study highlights the possible causal role of specific GM and specific inflammatory proteins in the development of epilepsy and suggests that circulating inflammatory proteins may mediate epileptogenesis through the MGBA.

Keywords: Mendelian randomization; epilepsy; gut microbiota; inflammatory proteins; microbiota-gut-brain-axis.

Figure 1

The overall flowchart of this study Step 1-1A represents the causal associations of gut microbiota on epilepsy and subtypes. Step 1-1B represents the reverse causal associations between gut microbiota and epilepsy and its subtypes. Step 1-2A represents the causal associations of inflammatory proteins on epilepsy and subtypes. Step 1-2B represents the reverse causal associations between inflammatory proteins and epilepsy and its subtypes. Step 1-3 represents the causal relationship between gut microbiota significantly associated with epilepsy and its subtypes and inflammatory proteins significantly associated with epilepsy and its subtypes. Each Univariate MR performs the procedure in the dashed box on the right. Step 2-1 represents incorporating positive microbiota and positive proteins obtained from Step 1 into Multivariate MR. Step 2-2 represents the detailed design of this Multivariate MR study of the causal associations of gut microbiota with the risk of epilepsy and its subtypes. MR, Mendelian randomization; GWAS, genome-wide association studies; WME, weighted median estimator; SNP, single nucleotide polymorphism; IVs, instrumental variables.

Figure 2

Cyclic heat map of causality associated with epilepsy (A-C) represent causal associations of GM with epilepsy and its subtypes, (D-F) represent causal associations of inflammatory proteins with epilepsy and its subtypes, and the innermost circle represents the OR value of the IVW method, the outermost abbreviation of (A-C) consists of the initial capitalization of taxa names of GM plus the number of GM, and the outermost abbreviations of (A-F) are shown in Supplementary Table S10 . IVW, inverse variance weighted; MR-Egger, Mendelian randomization of Egger regression; WM, weighted median estimator; Q, Cochran’s Q test; GE, Generalized Epilepsy; FE, Focal Epilepsy.

Figure 3

IVW method results on causal associations between GM and epilepsy and its subtypes. Nsnps, number of single nucleotide polymorphisms; OR, odds ratio; CI, confidence intervals.

Figure 4

IVW method results on causal associations between circulating inflammatory proteins and epilepsy and its subtypes. Nsnps, number of single nucleotide polymorphisms; OR, odds ratio; CI, confidence intervals; CXCL11, C-X-C motif chemokine 11; TNF-β, Tumor necrosis factor-β; TNFSF12, Tumor necrosis factor ligand superfamily member 12; VEGF-A, Vascular endothelial growth factor A; CXCL1, C-X-C motif chemokine 1; CXCL9, C-X-C motif chemokine 9; IL-15RA, Interleukin-15 receptor subunit alpha; IL-6, interleukin-6; LIF, Leukemia inhibitory factor; TRAIL, TNF-related apoptosis-inducing ligand; CCL25, C-C motif chemokine 25; EIF4EBP1, Eukaryotic translation initiation factor 4E-binding protein 1; FGF21, Fibroblast growth factor 21; IL-20RA, Interleukin- 20 receptor subunit alpha; TNFSF14, Tumor necrosis factor ligand superfamily member 14; VEGF-A, Vascular endothelial growth factor A.