# A Systematic Study of the Hepatic–Intestinal First-Pass Effect and Excretion Pathways of Punicalagin Based on UPLC-MS/MS

## TL;DR

This study identifies that punicalagin's poor oral bioavailability is mainly due to intestinal metabolism rather than liver processing, with most of the compound being excreted in feces.

## Contribution

The study introduces a UPLC-MS/MS workflow to quantify punicalagin's first-pass metabolism and excretion pathways in rats.

## Key findings

- Punicalagin has an absolute oral bioavailability of ~3.49%.
- Intestinal first-pass metabolism accounts for 95.95% extraction, compared to 13.94% hepatic extraction.
- Elimination is primarily fecal, with minimal urinary excretion of metabolites.

## Abstract

Punicalagin, the major polyphenol in pomegranate peel, shows broad bioactivity but suffers from poor oral bioavailability. Whether hepatic or intestinal first-pass processes dominate this limitation remains unresolved. We developed a quantitative UPLC-MS/MS workflow to dissect punicalagin’s first-pass disposition and elimination in rats. Sprague–Dawley rats received punicalagin by intravenous, portal vein, oral, or intraduodenal dosing; plasma exposure was quantified by UPLC-MS/MS and analyzed noncompartmentally. We also profiled urinary and fecal excretion of punicalagin and key metabolites (punicalin, ellagic acid, urolithin C and urolithin A) to define biotransformation and clearance. Punicalagin displayed an absolute oral bioavailability of ~3.49%. First-pass analysis revealed modest hepatic extraction (~13.94%) but near-complete intestinal extraction (95.95%), identifying intestinal first-pass metabolism as the dominant barrier to systemic exposure. Consistently, parent and metabolites were eliminated mainly in feces, whereas urine contained only trace conjugated urolithin A. Collectively, these findings demonstrate that the poor oral bioavailability of punicalagin is driven primarily by extensive intestinal first-pass metabolism rather than hepatic clearance, and that its feces-dominant elimination is compatible with widespread hydrolysis and microbiota-mediated conversion within the gut. This work provides a pharmacokinetic framework to guide strategies aimed at improving oral delivery and systemic exposure of punicalagin.