Human tear metabolites associated with nucleoside-signalling pathways in bacterial keratitis

Gauri Shankar Shrestha; Ajay Kumar Vijay; Fiona Stapleton; Andrew White; Russell Pickford; Nicole Carnt

doi:10.1016/j.exer.2023.109409

Human tear metabolites associated with nucleoside-signalling pathways in bacterial keratitis

Exp Eye Res. 2023 Mar:228:109409. doi: 10.1016/j.exer.2023.109409. Epub 2023 Feb 10.

Authors

Gauri Shankar Shrestha¹, Ajay Kumar Vijay², Fiona Stapleton², Andrew White³, Russell Pickford⁴, Nicole Carnt⁵

Affiliations

¹ School of Optometry and Vision Science, UNSW Sydney, Australia. Electronic address: g.shrestha@unsw.edu.au.
² School of Optometry and Vision Science, UNSW Sydney, Australia.
³ Department of Ophthalmology, Westmead Hospital, University of Sydney, Australia; Westmead Institute for Medical Research, University of Sydney, Australia.
⁴ Bioanalytical Mass Spectrometry Facility, UNSW Sydney, Australia.
⁵ School of Optometry and Vision Science, UNSW Sydney, Australia; Westmead Institute for Medical Research, University of Sydney, Australia; Institute of Ophthalmology, University College London, United Kingdom.

PMID: 36775205
DOI: 10.1016/j.exer.2023.109409

Abstract

Objective: The study aimed to profile and quantify tear metabolites associated with bacterial keratitis using both untargeted and targeted metabolomic platforms.

Methods: Untargeted metabolomic analysis using liquid-chromatography-Q Exactive-HF mass-spectrometry explored tear metabolites significantly associated with bacterial keratitis (n = 6) compared to healthy participants (n = 6). Differential statistics and principal component analysis determined meaningful metabolite differences between cases and controls. Purines and nucleosides were further quantified and compared between 15 cases and 15 controls in the targeted metabolomic platform using TSQ quantum access triple quadrupole mass spectrometry. Compound quantification was done by plotting the calibration curves and the difference in the compound levels was evaluated using the Wilcoxon rank-sum test.

Results: In the untargeted analysis, 49 tear metabolites (27 upregulated and 22 downregulated) were differentially expressed between cases and controls. The untargeted analysis indicated that the purine metabolism pathway was the most affected by bacterial keratitis. Metabolite quantification in the targeted analysis further confirmed the upregulation of xanthine (P = 0.02) and downregulation of adenine (P < 0.0001), adenosine (P < 0.0001) and cytidine (P < 0.0001) in the tears of participants with bacterial keratitis compared to that of healthy participants.

Conclusions: Bacterial keratitis significantly changes the tear metabolite profile, including five major compound classes such as indoles, amino acids, nucleosides, carbohydrates, and steroids. This study also indicates that tear fluids can be used to map the metabolic pathways and uncover metabolic markers associated with bacterial keratitis. Conceivably, the inhibition of nucleoside synthesis may contribute to the pathophysiology of bacterial keratitis because nucleosides are required for maintaining cellular energy homeostasis and immune adaptability.

Keywords: Bacterial keratitis; Mass spectrometry; Metabolites; Metabolomics; Nucleosides; Profiling; Purines; Tears.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Chromatography, Liquid
Humans
Keratitis*
Metabolomics / methods
Nucleosides*
Tandem Mass Spectrometry / methods

Substances

Nucleosides