Portal Vein Tryptophan Pathway Analysis Reveals Gut-Mediated Inflammatory Pathway Predominance in HCV Infection.

Peripheral tryptophan and kynurenine were elevated while indolelactate and xanthurenate were reduced during active HCV infection.

• HCV infected patients were evaluated during infection (HCVi, n=24) and 6 months after sofosbuvir/velpatasvir mediated sustained virologic response (SVR, n=19)
• All changes were statistically significant at p<0.05
• Both peripheral and portal blood were sampled at both time points
• Treatment used was sofosbuvir/velpatasvir (NCT02400216)

In portal blood during HCV infection, the kynurenine/tryptophan ratio and kynurenine were increased, whereas indoleacetate and xanthurenate were decreased.

• All portal blood metabolite changes were statistically significant at p<0.05
• The kynurenine/tryptophan ratio is a marker of IDO1-mediated inflammatory pathway activation
• Elevated portal kynurenine specifically suggests upregulation of gut-mediated pro-inflammatory pathways
• Portal and peripheral blood were collected simultaneously allowing direct comparison between compartments

Tryptophan metabolites positively correlated with hepatic activity index, gamma-glutamyl transferase, total bilirubin, spleen volume/height ratio, and pro-inflammatory cytokines.

• Pro-inflammatory cytokines showing positive correlation included CXCL9, CXCL10, TNFα, IL6, and IL-12p40
• Clinical parameters correlated included hepatic activity index, gamma-glutamyl transferase, total bilirubin, and spleen volume/height ratio
• Liver biopsies, portal and peripheral blood collection, and stool sampling were performed at both time points
• These correlations link tryptophan pathway dysregulation to markers of liver inflammation and disease severity

Tryptophan metabolites negatively correlated with gut microbes Dorea longicatena and Qiania dongpingenesis.

• Stool sampling was performed at both time points (during infection and 6 months after SVR)
• Both Dorea longicatena and Qiania dongpingenesis showed negative correlations with tryptophan metabolites
• These correlations link the gut microbiome composition to tryptophan pathway activity in HCV
• Multi-omics integration was used to assess these microbiome-metabolite relationships

The study design evaluated tryptophan metabolites before and after sofosbuvir/velpatasvir-mediated sustained virologic response, allowing within-patient comparison of HCV infection and recovery states.

• HCVi group: n=24 patients evaluated during active infection
• SVR group: n=19 patients evaluated 6 months after achieving sustained virologic response
• The study was registered under NCT02400216
• Assessments included liver biopsies, portal and peripheral blood collection, and stool sampling at both time points
• Statistical analyses assessed metabolite abundance during infection and recovery, and their associations with cytokines, clinical parameters, and the microbiome

The study identified several limitations including small sample size, absence of quantitative values for all pathway metabolites, and reliance on correlative rather than causative associations.

• Sample size was limited to 24 patients during infection and 19 patients after SVR
• Not all tryptophan pathway metabolites had quantitative values available
• Mechanistic interpretation is limited due to correlative rather than causative study design
• Authors call for future studies with larger cohorts and functional analyses to clarify causal mechanisms and evaluate therapeutic potential of targeting the tryptophan pathway