Discovery and Qualification of Candidate Urinary Biomarkers of Disease Activity in Lupus Nephritis

Lupus nephritis (LN)
is a severe clinical manifestation of systemic
lupus erythematosus (SLE) associated with significant morbidity and
mortality. Assessment of severity and activity of renal involvement
in SLE requires a kidney biopsy, an invasive procedure with limited
prognostic value. Noninvasive biomarkers are needed to inform treatment
decisions and to monitor disease activity. Proteinuria is associated
with disease progression in LN; however, the composition of the LN
urinary proteome remains incompletely characterized. To address this,
we profiled LN urine samples using complementary mass spectrometry-based
methods:  protein gel fractionation, chemical labeling using
tandem mass tags, and data-independent acquisition. Combining results
from these approaches yielded quantitative information on 2573 unique
proteins in urine from LN patients. A multiple-reaction monitoring
(MRM) method was established to confirm eight proteins in an independent
cohort of LN patients, and seven proteins (transferrin, α-2-macroglobulin,
haptoglobin, afamin, α-1-antitrypsin, vimentin, and ceruloplasmin)
were confirmed to be elevated in LN urine compared to healthy controls.
In this study, we demonstrate that deep mass spectrometry profiling
of a small number of patient samples can identify high-quality biomarkers
that replicate in an independent LN disease cohort. These biomarkers
are being used to inform clinical biomarker strategies to support
longitudinal and interventional studies focused on evaluating disease
progression and treatment efficacy of novel LN therapeutics.