Longitudinal Urinary Protein Variability in Participants of the Space Flight Simulation Program

Urine
is a valuable material for the diagnosis of renal pathologies
and to investigate the effects of their treatment. However, the variability
in protein abundance in the context of normal homeostasis remains
a major challenge in urinary proteomics. In this study, the analysis
of urine samples collected from healthy individuals, rigorously selected
to take part in the MARS-500 spaceflight simulation
program, provided a unique opportunity to estimate normal concentration
ranges for an extended set of urinary proteins. In order to systematically
identify and reliably quantify peptides/proteins across a large sample
cohort, a targeted mass spectrometry method was developed. The performance
of parallel reaction monitoring (PRM) analyses was improved by implementing
tight control of the monitoring windows during LC–MS/MS runs,
using an on-the-fly correction routine. Matching the experimentally
obtained MS/MS spectra with reference fragmentation patterns allowed
dependable peptide identifications to be made. Following optimization
and evaluation, the targeted method was applied to investigate protein
abundance variability in 56 urine samples, collected from six volunteers
participating in the MARS-500 program. The intrapersonal
protein concentration ranges were determined for each individual and
showed unexpectedly high abundance variation, with an average difference
of 1 order of magnitude.