A97-08 Sepsis Reprograms the Gut Barrier to Release Microbial Acetate Into the Blood

Introduction/Rationale Gut microbial metabolites, such as acetate, are protective in animal models of sepsis. Yet how these gut-derived metabolites reach the bloodstream during infection is unknown. Although sepsis increases gut permeability, it is unknown whether gut metabolites enter the circulation through passive barrier breakdown or through an active, regulated transport process. We sought to distinguish between these two mechanisms using complementary in vivo approaches. Methods We performed a series of in vivo mouse experiments to identify the pathways by which gut permeability increases in sepsis. We modeled sepsis in mice using systemic endotoxin (5 mg/kg intraperitoneally) or vehicle. Twenty-four hours after injection, we assessed gut permeability using two complementary approaches. In one cohort, we performed histology on fixed intestinal tissue (hematoxylin and eosin). In a separate cohort, we measured blood acetate levels by liquid chromatography-mass spectrometry and quantified gene expression in gut tissue by quantitative polymerase chain reaction. We used simple linear regression to quantify correlations between metabolites and gene expression. Results Sepsis did not cause intestinal epithelial necrosis but instead increased gut permeability by upregulating claudin-2, a pore-forming tight-junction protein that drives sodium flux from the blood into the gut lumen. Claudin-2 expression was strongly and positively correlated with blood acetate levels (Figure 1A; R2=0.90; P = 0.003). SMCT-1, a transporter that utilizes gut sodium to transport acetate into the blood, was also upregulated in sepsis and strongly correlated with claudin-2 (Figure 1B; R2=0.80; P = 0.006), consistent with a coordinated, sodium-dependent program for acetate transport into the bloodstream. Conclusions In sepsis, gut microbial acetate enters the bloodstream through active, regulated gut permeability pathways, rather than passive barrier breakdown. Regulated export of gut microbial metabolites may represent a host-adaptive response to infection. In future work, we will pharmacologically modulate claudin-2 and SMCT1 during sepsis to test their causal roles in gut-blood acetate dissemination.