# Proteomic Analysis of Tear Film in Dogs and Cats: Emerging Biomarkers of Cognitive Dysfunction and Neurodegenerative Disorders

## TL;DR

This paper reviews how proteins in pet animals' tears could help detect brain-related diseases like cognitive dysfunction and neurodegeneration in older dogs and cats.

## Contribution

The paper highlights tear film proteomics as a novel, non-invasive approach for identifying potential biomarkers of cognitive dysfunction in companion animals.

## Key findings

- Tear film contains proteins linked to inflammation, oxidative stress, and immune regulation, which are relevant to neurodegeneration.
- Tear-derived proteins may reflect molecular changes associated with cognitive dysfunction in aging dogs and cats.
- Integration of tear film proteomics with other biomarkers could improve diagnostic strategies for neurodegenerative disorders.

## Abstract

Cognitive dysfunction and neurodegenerative disorders are increasingly recognized in aging dogs and cats and represent an important and growing challenge in veterinary practice. These conditions are commonly diagnosed based on behavioral changes reported by owners, while objective and easily accessible biological markers that could support early detection or disease monitoring remain limited. Therefore, there is an important need for non-invasive diagnostic tools that can be applied safely and repeatedly in geriatric companion animals. Tear film, a fluid covering the ocular surface, contains numerous proteins derived from local tissues as well as from systemic circulation. In recent years, advances in proteomic techniques have enabled detailed analysis of the tear film protein composition in dogs and cats. Many of the identified proteins are involved in inflammation, oxidative stress, immune regulation, and cellular maintenance, which are biological processes known to play an important role in neurodegenerative changes and age-related cognitive decline in animals. These findings suggest that tear-derived proteins may provide indirect information on molecular alterations associated with cognitive dysfunction. This review summarizes current knowledge on proteomic studies of tear film in dogs and cats and discusses the potential relevance of tear-derived proteins as biomarkers of cognitive dysfunction and neurodegenerative processes. The advantages of tear film as a non-invasive and clinically practical sample are highlighted, along with current limitations of available studies. Improved understanding of tear film proteomics may contribute to the development of novel diagnostic and monitoring tools for cognitive dysfunction in companion animals.

Cognitive dysfunction and neurodegenerative disorders represent an increasing clinical challenge in aging dogs and cats, while objective and minimally invasive biomarkers for early detection and disease monitoring remain limited. Tear film is a biologically active fluid reflecting both local and systemic processes and offers a practical, non-invasive source of potential biomarkers in geriatric veterinary patients. Proteomic analyses of canine and feline tear film have revealed a complex protein composition, including molecules involved in inflammation, oxidative stress, immune regulation, and cellular homeostasis—processes implicated in neurodegeneration. However, growing evidence from human and veterinary research emphasizes the importance of CNS-specific and mechanistically informative biomarkers, such as markers of axonal injury, synaptic degeneration, and glial activation, which may provide a more precise framework for interpreting peripheral proteomic alterations. This review summarizes current knowledge on tear film proteomics in dogs and cats and discusses its potential relevance to cognitive dysfunction and neurodegenerative processes. Particular attention is given to the integration of tear-derived proteins with validated blood and cerebrospinal fluid biomarkers, as well as to methodological challenges and future research priorities. With appropriate standardization and clinical validation, tear film proteomics may contribute to the development of novel diagnostic and monitoring strategies for neurodegenerative disorders in companion animals.