SAT-LB136 A Proteomic Approach to Identify Circulating Glucocorticoid Responsive Proteins in Humans

Glucocorticoids used in pharmacological doses for the treatment of a variety of medical conditions, and endogenous glucocorticoid excess - Cushing’s syndrome, may result in several adverse effects, but currently there is no clinically useful biomarker of glucocorticoid activity. We have applied a proteomic approach to the discovery of glucocorticoid-responsive proteins potentially measurable in human serum samples. To minimise the masking by abundant serum proteins, we conducted discovery proteomics on the secretome of ex vivo-stimulated peripheral blood mononuclear cells (PBMC) isolated from 12 volunteers. The PBMC were divided into 4 treatment groups; +/- dexamethasone 100 ng/mL (dex) for 4h, or +/- dex for 24h. In all treatment groups, media was changed to serum free for 3h before collection. Media samples were processed for proteomics, with 561 and 273 proteins analysed by label-free quantification (LFQ) for the 4h and 24h secretome, respectively. Paired statistical analysis at the 2 time points generated a shortlist of 43 candidate biomarker proteins, which was verified using a multiple reaction monitoring (MRM) assay, confirming the differential secretion of 12 proteins at both 4h and 24 h. Five proteins were selected for validation using enzyme linked immunosorbent assay (ELISA) in an independent cohort: β2 microglobulin (B2M), lysozyme C (LYZ), high-mobility group protein 2 (HMG2), nucleophosmin (NPM1) and nucleolin (NCL). Twenty new volunteers (10M and 10F) had venous blood drawn at baseline and 12h after 4 mg oral dex. Four proteins were detectable by ELISA, three of which showed statistically significant change in concentration. Serum LYZ and NPM1 significantly decreased following dex: LYZ - 101 ± 5.5 vs 67 ± 4.4 ng/mL, (P<0.0001); NPM1 - 17.4 ± 1.0 vs 14.3 ± 0.9 ng/mL, (P<0.01), while HMG2 significantly increased - 819 ± 34 vs 984 ± 60 pg/mL (P<0.01). These results demonstrate that an ex vivo proteomic approach using PBMC in conditioned media can identify glucocorticoid-responsive proteins measurable in human serum.