# Molecular mechanisms and biomarkers of total parenteral nutrition-induced hepatotoxicity revealed by iTRAQ proteomics analysis

## TL;DR

This study identifies proteins and molecular pathways involved in liver damage caused by long-term intravenous nutrition using proteomic analysis.

## Contribution

The study reveals novel regulators, Elovl5 and Ptbp3, involved in TPN-induced liver injury through proteomic and functional analyses.

## Key findings

- Forty-eight proteins were differentially expressed in TPN-infused rats, with Elovl5 and Ptbp3 showing significant changes.
- Elovl5 and Ptbp3 knockdown reduced palmitic acid-induced liver cell toxicity and apoptosis.
- Palmitic acid-induced apoptosis involves histone modifications and activation of ASK1/JNK/p38 pathways.

## Abstract

Background/Aims: Total parenteral nutrition (TPN) provides medical nutrients intravenously to patients who cannot obtain proper nutrition through normal dietary means or enteral feeding. One significant concern is the risk of liver damage associated with long-term TPN use. In this study, the TPN-associated acute liver injury proteins and the molecular mechanisms underlying TPN oxidative stress were investigated through a quantitative proteomic survey. The proteomic changes between control and TPN infusion rats were analyzed by using the LC-MS/MS iTRAQ technology.

Methods: Rats were randomly assigned to saline infusion (control group) and TPN infusion (infusion rate of 30 mL/kg/h for 3 h). At the end of treatment, total liver samples from rats of control and TPN infusion groups were separated by iTRAQ-based quantitative proteomic identification. The effects of the differentially expressed proteins on the potential mechanism of hepatocytes were examined through flow cytometry. Additionally, siRNA-based assessments were conducted to examine the role of the endoplasmic reticulum stress (ER stress) as well as in vivo apoptosis of TPN-related liver cells.

Results: The effect of TPN on the biochemical markers of acute liver injury in the experimental rats was examined following palmitic acid treatment of live cells. Forty-eight proteins were differentially expressed between untreated control and TPN infusion liver tissues. The abundances of Elovl5 and Ptbp3 proteins were observed in TPN infusion (P < 0.05). Palmitic acid treatment of liver cells increased cell cytotoxicity and generated ROS, and increased the level of Elovl5 and Ptbp3, validated in the TPN infusion in vivo. The treatment of hepatocytes resulted in the activation of the caspases 3, caspase 9, accompanied by the expression and release of apoptotic molecules, cytochrome c, Bcl-2, Bcl-XL, p-IRE1α, and TRAF2. Elovl5 and Ptbp3 knockdown significantly regulated palmitic acid-mediated cytotoxicity of liver cells, including inhibition of apoptosis and ROS generation. Palmitic acid-mediated apoptotic induction was accompanied by histone H3K4 trimethylation of Elovl5 and Ptbp3 promoters, leading to enhanced transcription through the sustained phosphorylation of ASK1/JNK/p38 pathways.

Conclusions: The mechanism of palmitic acid-induced apoptosis cascade and ER stress in hepatocyte cells involves up-regulation of Elovl5 and Ptbp3. This study provides novel regulators underlying the effects of TPN on liver injury.