Tear biomarkers of depression and post-traumatic stress disorder in US Veterans

Abstract

Purpose : Inflammation has been associated with depression and anxiety. In this study, we examine correlations between inflammatory proteins in tears and symptoms of depression and PTSD-associated anxiety.

Methods : 39 individuals from the Miami Veterans Affairs eye clinic were prospectively recruited. All filled out questionnaires regarding depression (Patient Health Questionnaire 9, PHQ-9) and PTSD-associated anxiety (Post Traumatic Stress Disorder Checklist-Military Version, PCL-M). Anesthetized tears were collected from the right eye using a Schirmer’s strip (5-minute collection) then stored at -80^oC until protein extraction. Information about other features was collected, including demographics and Schirmer strip wetting length. For quantitative determination of 23 inflammatory proteins, a multiplex assay system was custom designed from ThermoFisher and run with reagents, standards, and protocols supplied by the vendor. Pearson correlations examined associations between symptoms of depression, PTSD, and tear inflammatory proteins. Multivariable models were built to examine the impact of potential confounders.

Results : The mean age of the population was 61±13 years, 95% self-identified as male, 69% as Black, and 15% as Hispanic. The mean PHQ-9 score was 11.3±8.1 (0-27) and the mean PCL-M score was 45.2±20.1 (range 17-85). Symptoms of depression and PTSD-associated anxiety were highly correlated (r=0.82, p<0.005). Both scores positively correlated with Intercellular Adhesion Molecule 1 (ICAM-1) (PHQ9: r=0.36, p=0.03; PCL-M: r=0.36, p=0.03) and Interleukin 8 (IL-8) (PHQ9: r=0.38, p=0.02; PCL-M: r=0.38, p=0.02). In addition, depression was positively associated with IL-1α, IL-1β, Macrophage Inflammatory Protein-1 (MIP-1) α and β (r~0.35 for all). When demographics, Schirmer length, and all measured proteins were included in a multivariable model, MIP-1 α remained associated with depression (standardized β 0.37) and IL-8 with anxiety (β 0.38).

Conclusions : Several tear proteins are associated with symptoms of depression and PTSD-associated anxiety in a US Veteran sample. Past research has linked higher serum levels of these inflammatory markers to depression and anxiety; thus, tear biomarkers may be a less-invasive analysis tool. More research is needed to investigate whether tear biomarkers can help with the diagnosis of mental health disorders or aid in evaluating the impact of treatment.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.