This study, employing Mendelian Randomization (MR), provides genetic evidence of a causal relationship between the GM and IS. Our analysis indicates that specific microbial groups such as genus Ruminiclostridium increase the risk of IS, while order Burkholderiales appears to have a potential role in reducing the risk. Mediation analysis reveals potential mediating roles of metabolites such as Pyruvate and Arachidonate between genus Ruminiclostridium and IS. Metabolites such as Apolipoprotein A1, Total lipids in medium HDL, Concentration of medium HDL particles, Phospholipids in medium HDL, and Total concentration of lipoprotein particles may play significant mediating roles between order Burkholderiales and IS. This suggests that GM may directly influence stroke risk by regulating key metabolic pathways. These metabolites play crucial roles in energy metabolism and cellular signaling, and their aberrant expression may directly affect vascular function and inflammatory states, which are vital physiological processes in the development of stroke.
Specifically, we found that genus Ruminiclostridium reduces Pyruvate levels, while Pyruvate plays a neuroprotective role in IS. Pyruvate is beneficial as it helps to clear harmful glutamate from the blood and brain, reducing excitotoxicity that may exacerbate stroke injury[28]. Studies using animal models have shown that administering Pyruvate can significantly lower glutamate levels, thereby reducing brain damage and improving recovery outcomes in IS[28]. Existing research indicates that Pyruvate plays a critical role in regulating inflammation and preventing oxidative stress, key mechanisms in IS injury. Pyruvate has been shown to support mitochondrial function and reduce oxidative damage in neuronal cells, potentially reducing the severity of IS outcomes. These findings support exploring Pyruvate as a therapeutic agent in clinical settings, to mitigate IS injury by protecting neurons from excitotoxicity and oxidative stress[29, 30]. Moreover, our study demonstrates that genus Ruminiclostridium may lead to reduced levels of Pyruvate, thereby increasing the risk of IS. Additionally, we found that genus Ruminiclostridium increases Arachidonate levels, which is considered to be involved in inflammation processes and atherosclerosis, although its role in the risk of IS remains controversial[31]. In this study, we found that Arachidonate may increase the risk of IS.
We also found that order Burkholderiales increases levels of metabolites such as Apolipoprotein A1, Total lipids in medium HDL, Concentration of medium HDL particles, Phospholipids in medium HDL, and Total concentration of lipoprotein particles. The relationship between Apolipoprotein A1 (ApoA1) and IS has been revealed in multiple studies, suggesting that ApoA1 may serve as a useful biomarker for predicting and monitoring the progression of IS. Higher levels of ApoA1 are generally associated with a lower risk of recurrent stroke and better prognosis in stroke patients. Studies have shown that ApoA1 levels are inversely related to the severity of intracranial atherosclerosis and can predict the recurrence of cerebrovascular events[32–34]The specific roles of Total lipids in medium HDL, Concentration of medium HDL particles, Phospholipids in medium HDL, and Total concentration of lipoprotein particles in relation to IS are not directly studied. However, given the established role of high-density lipoprotein (HDL) related markers in cardiovascular health, they might also be important in the context of stroke. High levels of HDL and its components are generally associated with better cardiovascular health, and due to their roles in lipid transport and protection against atherosclerosis, they might help reduce the risk of stroke and facilitate better recovery. Our study indicates that order Burkholderiales reduces the risk of IS by increasing these beneficial lipoprotein levels.
Additionally, our findings were further validated for stability of the causal relationships through the BWMR method, showing that the relationships between genus Coprobacter, genus Ruminiclostridium, and order Burkholderiales with IS are consistent across multiple statistical models. This consistency underscores the reliability of our findings and also highlights potential therapeutic targets, which could aid in developing treatment strategies aimed at specific microbial groups to reduce the risk of stroke. Analyses of genetic correlation and overlap, such as those using LDSC and GPA, further revealed extensive genetic interactions between GM and IS. These analyses provide additional evidence supporting the role of GM in stroke, possibly by indirectly influencing the risk of stroke through effects on the host’s genetic background.
However, although our study provides detailed insights into the causal relationship between GM and IS, it has some limitations. Firstly, our analysis relies on publicly available GWAS data, which may limit our complete assessment of the types and quantities of GM taxa. Furthermore, although our methods can reduce potential confounders and reverse causality, they cannot entirely eliminate non-genetic interferences. Lastly, as our study is based on European population data, it is difficult to avoid impacts caused by racial differences. Additionally, due to the considerable individual variability of GM, which can be influenced by medication or other lifestyle and dietary habits and diseases, and the more lenient threshold settings for instrumental variables compared to conventional MR analysis, there is a risk of result heterogeneity.
Future research should validate these findings through more comprehensive datasets and diversified populations, and explore more complex biological mechanisms between GM and stroke. Overall, by integrating large-scale GWAS data and advanced statistical methods, this study strengthens the scientific understanding of the role of the gut microbiome in the pathophysiology of IS offering potential directions for future prevention and treatment strategies.