# A Pilot Proteomic Analysis of Tear Fluid in Domestic Cats with and Without Conjunctivitis Using MALDI–TOF/TOF Mass Spectrometry

## TL;DR

This study analyzed tear proteins in cats with and without conjunctivitis to better understand eye disease and potentially develop noninvasive diagnostic tools.

## Contribution

The study identifies nine tear proteins in cats, including lactoperoxidase and SBP1, which are reported in feline tears for the first time.

## Key findings

- Nine distinct tear proteins were identified, including immune and antimicrobial proteins like lactoperoxidase and lactotransferrin.
- Lactoperoxidase and SBP1 were detected in feline tears for the first time.
- Mean tear protein concentration was higher in cats with conjunctivitis, though the difference was not statistically significant.

## Abstract

Conjunctivitis is a common eye condition in cats; however, the biological changes that occur in tear fluid during inflammation are poorly understood. Tears contain many proteins that protect the ocular surface, and changes in these proteins may reflect disease processes. In this pilot study, we compared tear samples from healthy cats and cats with conjunctivitis. Tears were collected using Schirmer tear test strips, a method routinely used in veterinary clinics. Protein composition was analyzed using gel electrophoresis and a mass spectrometry technique that allows for identification of proteins from very small sample volumes. This method involves measuring the masses of protein fragments and matching them to known proteins in databases. Several proteins associated with immune defense and ocular surface protection were identified in feline tears. Some of these proteins are well characterized in other species, whereas others were detected in feline tears for the first time. Although no proteins were detected exclusively in cats with conjunctivitis, the mean total tear protein concentration was higher in affected cats; however, this difference was not statistically significant. These findings expand current knowledge of tear proteins in cats and highlight the need for larger quantitative investigations. A better understanding of tear protein profiles may support the development of noninvasive diagnostic tools and improved treatment strategies for feline eye diseases.

Feline conjunctivitis is a common ocular disorder; however, the molecular composition of feline tear fluid and its alterations during ocular surface inflammation remain poorly characterized. This pilot study aimed to explore the tear proteome of cats with conjunctivitis using matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI–TOF/TOF MS) and to compare findings with those from clinically healthy cats. Tear samples were collected using Schirmer tear test strips from healthy cats and cats diagnosed with conjunctivitis. Total protein concentration was measured by ultraviolet absorbance spectrophotometry, and tear proteins were separated by SDS–polyacrylamide gel electrophoresis, followed by in-gel trypsin digestion and MALDI–TOF/TOF MS analysis. Nine distinct tear proteins were identified, including antimicrobial and immune-related components such as lactoperoxidase, lactotransferrin, albumin, and immunoglobulin A constant region. Lactoperoxidase and SBP1 were identified in feline tear fluid for the first time. No proteins uniquely associated with conjunctivitis were detected. The mean total tear protein concentration was numerically higher in cats with conjunctivitis (13.06 ± 0.75 mg/mL) than in healthy cats (9.69 ± 0.67 mg/mL); however, this difference did not reach statistical significance (p = 0.095) and should be interpreted cautiously given the limited sample size. This pilot study provides preliminary insights into tear protein profiles in cats with conjunctivitis and highlights the need for larger quantitative investigations. These findings provide a preliminary framework for future studies aimed at further characterizing molecular alterations associated with feline ocular surface disorders.