Circulating vitamin levels mediate the causal relationship between gut microbiota and cholecystitis: a two-step bidirectional Mendelian randomization study

Abstract

Background: The relationship between gut microbiota and the occurrence of cholecystitis remains unclear. Existing research lacks a clear understanding of how circulating vitamin levels modulate this relationship. Therefore, our study aims to investigate whether circulating vitamin levels mediate the causal relationship between gut microbiota and cholecystitis using a two-step bidirectional Mendelian randomization approach.

Methods: In this study, we initially employed Linkage Disequilibrium Score Regression (LDSC) analysis to assess the genetic correlation of five circulating vitamin level genome-wide association study (GWAS) summary datasets, thereby avoiding potential sample overlap. Subsequently, we conducted a two-step analysis to investigate the causal effects between gut microbiota and cholecystitis. In the second step, we explored the causal relationship between circulating vitamin levels and cholecystitis and identified the mediating role of vitamin D. The primary method used for causal analysis was the inverse variance-weighted approach. We performed additional sensitivity analyses to ensure result robustness, including the cML-MA method and reverse Mendelian randomization (MR) analysis.

Results: An increment of one standard deviation in RuminococcaceaeUCG003 was associated with a 25% increased risk of cholecystitis (OR = 1.25, 95%CI = 1.01-1.54, p = 0.04), along with a 3% decrease in 25-hydroxyvitamin D levels (OR = 0.97, 95%CI = 0.944-0.998, p = 0.04). However, following the rigorous Bonferroni correction, every one standard deviation decrease in circulating vitamin D levels was associated with a 33% increased risk of cholecystitis (OR = 0.67, 95%CI = 0.49-0.90, p = 0.008, P_adjust = 0.04). Thus, the potential link between gut microbiota and cholecystitis risk might be mediated by circulating vitamin D levels (proportion mediated = 5.5%). Sensitivity analyses provided no evidence of pleiotropy.

Conclusion: Our study results suggest that an elevated abundance of specific gut microbiota is associated with an increased susceptibility to cholecystitis, with the causal relationship being mediated by circulating vitamin D levels. Further large-scale randomized controlled trials are necessary to validate the causal effects of gut microbiota on cholecystitis risk. This study provides novel insights into cholecystitis prevention through the regulation of gut microbiota.

Keywords: Mendelian randomization; causal relationship; cholecystitis; circulating vitamin levels; gut microbiota.

Figure 1

The schematic diagram of the study design (the figure illustrates the design and principles of this study, demonstrating the interactions among gut microbiota, cholecystitis, and multiple circulating vitamin levels). The dashed arrows in the figure represent the reverse Mendelian randomization studies conducted in this research.

Figure 2

The complete results plot of the Mendelian randomization analysis between 211 gut microbiota taxa and gallbladder inflammation (the figure displays the results of three major Mendelian randomization analyses involving 211 taxa of gut microbiota and gallbladder inflammation. It also presents the results of the cML-MA analysis conducted to mitigate the effects of multicollinearity at the relevant levels).

Figure 3

The step-by-step flowchart of the Mendelian randomization analysis (the figure specifically presents the basic assumptions and principles of all Mendelian randomizations conducted in this study and clearly indicates the level of pleiotropy of genes that are correlated and unrelated). (A) A bidirectional Mendelian randomization analysis was conducted to assess the causal relationship between gut microbiota and cholecystitis. (B) A univariable Mendelian randomization analysis was performed to assess the causal relationship between different circulating vitamin levels and cholecystitis. (C) A bidirectional Mendelian randomization analysis was conducted to assess the causal relationship between gut microbiota and circulating vitamin D levels.

Figure 4

The results plot of LDSC analysis for genetic correlation between different circulating vitamin levels’ GWAS summary data (the figure showcases the genetic correlations among different circulating vitamin levels and combines the p-values from the LDSC analysis results. rg, genetic correlation).

Figure 5

Mediation effect of circulating vitamin D levels in the causal association between RuminococcaceaeUCG003 and cholecystitis [the figure shows that the risk of cholecystitis is increased when the abundance of RuminococcaceaeUCG003 increases, with an effect size of 0.22. 25-hydroxyvitamin D levels decreased with increasing abundance of RuminococcaceaeUCG003, with an effect value of −0.03. The risk of cholecystitis increased with a decrease in circulating vitamin D levels, with an effect size of −0.41. The association between gut microbiota and risk of cholecystitis is mediated by circulating vitamin D levels (proportion mediated = 5.5%)].