Histidine–ImP Axis Links Gut, Liver and Vascular Injury in MASLD : Biomed Pharmacother | May 2026

Introduction

Metabolic Dysfunction-Associated Steatotic Liver Disease is increasingly recognized as a systemic disorder extending beyond hepatic steatosis and fibrosis. Cardiovascular disease remains the leading cause of mortality in MASLD, yet cardiovascular risk varies markedly among patients and is often poorly explained by liver disease severity or traditional metabolic risk factors alone. This discrepancy has intensified interest in microbiota-driven metabolic pathways linking the gut, liver and vascular system.

Problem Statement

Current models of MASLD inadequately explain why some patients develop disproportionate vascular and cardiometabolic complications despite similar hepatic disease burden. Novel mechanistic frameworks integrating microbial metabolism, host signaling and vascular inflammation are needed to better define biologic heterogeneity within MASLD.

Summary

This hypothesis-generating review proposes a novel gut–liver–vascular axis centered on microbial histidine metabolism and production of Imidazole Propionate (ImP). The authors suggest that altered microbial conversion of dietary L-histidine through the bacterial urdA pathway may represent a key mechanistic driver of both hepatic metabolic dysfunction and vascular inflammation in MASLD.

The proposed model centers on a dual pathogenic mechanism. First, enhanced microbial histidine metabolism reduces bioavailable histidine, potentially impairing protective signaling pathways mediated through TAAR1. Histidine depletion may therefore weaken anti-inflammatory, metabolic and vascular homeostatic responses. Simultaneously, excessive production and systemic accumulation of ImP exerts direct deleterious metabolic effects.

Experimental evidence reviewed in the article indicates that ImP interferes with insulin signaling within hepatocytes, thereby promoting hepatic steatosis and metabolic dysfunction. Beyond the liver, ImP also appears to activate proinflammatory and proatherogenic signaling cascades within endothelial tissue, suggesting a direct mechanistic bridge between intestinal microbial metabolism and cardiovascular injury.

The review additionally highlights the bacterial urdA enzyme pathway as a potential functional biomarker of pathogenic microbiota activity. The authors introduce the concept of an “ImP-positive/urdA-high” microbial biotype, which could represent a clinically important MASLD endophenotype characterized by persistent cardiometabolic and vascular risk despite otherwise similar hepatic disease severity.

This framework is especially important because it shifts focus from static taxonomic microbiome analysis toward functional microbial metabolism. Rather than simply identifying bacterial species abundance, the proposed model emphasizes metabolically active microbial pathways capable of directly modulating host cardiometabolic physiology.

The implications for precision medicine are substantial. Therapeutic strategies could theoretically target multiple levels of the histidine–ImP axis, including dietary histidine modulation, suppression of microbial urdA activity, inhibition of ImP production or blockade of downstream ImP-mediated inflammatory signaling. Such approaches may help identify and treat MASLD patients with residual cardiovascular risk not captured by conventional metabolic profiling.

Importantly, the review positions MASLD as a multidimensional gut-driven systemic disease rather than an isolated hepatic disorder. The proposed histidine–ImP pathway integrates microbiota metabolism, hepatic insulin resistance and vascular inflammation into a unified mechanistic model potentially explaining interpatient heterogeneity in disease expression and cardiovascular outcomes.

Overall, this integrative review introduces the histidine–imidazole propionate axis as a compelling new conceptual framework for understanding gut–liver–vascular crosstalk in MASLD. The model provides a strong rationale for future microbiota-guided precision stratification and targeted metabolic interventions aimed at both hepatic and cardiovascular complications of steatotic liver disease.