# Longitudinal Plasma Metabolomics by GC–MS and LC–MS During Total Parenteral Nutrition After Gastrointestinal Surgery

## TL;DR

This study tracks changes in blood metabolites over 72 hours in patients receiving total parenteral nutrition after gastrointestinal surgery, revealing patterns in amino acids and other metabolites.

## Contribution

The study introduces a longitudinal untargeted metabolomics approach to characterize early systemic metabolic changes during TPN after surgery.

## Key findings

- Early TPN administration increases amino acids like glycine, isoleucine, and tryptophan within 24 hours.
- Metabolic changes persist and expand over 72 hours, with coordinated shifts in amino acids and carbohydrate-related metabolites.
- Untargeted metabolomics reveals time-dependent patterns in plasma metabolites during postoperative TPN.

## Abstract

Background: Total parenteral nutrition (TPN) is widely used after major gastrointestinal surgery; however, its early systemic metabolic effects and temporal adaptation patterns remain incompletely characterized. This study applied a longitudinal plasma metabolomics approach to investigate time-dependent metabolic changes during early TPN administration. Methods: Plasma samples were collected from patients undergoing gastrointestinal surgery before TPN initiation (baseline, T0) and at 24 h (T1), 48 h (T2), and 72 h (T3). Untargeted metabolomic profiling was performed using complementary gas chromatography–mass spectrometry (GC–MS) and liquid chromatography–mass spectrometry (LC–MS) platforms. In total, 111 metabolites were detected. Analysis of variance (ANOVA) with baseline (T0) as the reference identified time-point–specific metabolic alterations during TPN administration. Results: At 24 h (T1), nominally significant increases were observed in glycine, tryptophan, isoleucine, and methionine, accompanied by decreases in sarcosine and oxalic acid. At 48 h (T2), elevated levels of glycine, isoleucine, valine, and phenylalanine persisted, while sarcosine, oxalic acid, and myo-inositol remained decreased. By 72 h (T3), sustained increases in glycine, isoleucine, valine, phenylalanine, proline, alanine, and tryptophan were accompanied by reduced levels of sarcosine, oxalic acid, and glucopyranose, reflecting coordinated alterations across multiple metabolite classes. Conclusions: Overall, the results demonstrated a distinct longitudinal metabolomic pattern characterized by increases in circulating amino acids and time-dependent changes in carbohydrate- and lipid-related metabolites within the first 72 h of TPN. This exploratory, time-resolved metabolomic study in 37 patients highlights the utility of untargeted metabolomics for characterizing early metabolic adaptation to parenteral nutrition and supporting postoperative metabolic monitoring.