Tear Protein Biomarkers for Ocular Mucous Membrane Pemphigoid Uncovered Using Targeted LC-MS/MS

Mucous membrane pemphigoid (MMP) is a multisystemic rare
autoimmune
disease affecting the skin and mucous membranes. Ocular involvement
is characterized by chronic conjunctival inflammation causing scar
formation, leading to corneal opacification and vision loss. Conjunctival
biopsies are currently used to confirm diagnosis, and the associated
immunosuppression treatments prescribed can have serious consequences
on patients. To address these challenges, a noninvasive approach to
collect patient tears using untargeted and targeted liquid chromatography-tandem
mass spectrometry (LC-MS/MS) analyses has been developed to identify
a list of potential biomarkers of ocular MMP. Samples were collected
on Schirmer strips and subjected to tryptic digestion and LC-MS/MS
analysis. Three cohorts of patients were studied, and targeted LC-scheduled
multiple reaction monitoring (LC-sMRM) methods were developed for
the verification of putative biomarkers. The comparison of three groups
of patients, those diagnosed with ocular MMP, non-ocular MMP, and
lichen planus, another ocular cicatricial conjunctivitis disorder,
yielded 56 biomarkers of interest. Proteins distinguishing MMP patients
with and without ocular involvement were linked to the extracellular
matrix, metabolism, and neutrophil degranulation. The
comparison between MMP and lichen planus patients highlighted lower
levels of metabolic enzymes in the latter. This study highlights the
use of multiple patient cohorts and tailored targeted quantitative
proteomics methods for the discovery of biomarkers for diagnostic
and prognostic purposes.