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Lookup NU author(s): Professor Brian Walker
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
Corticosteroid-binding globulin (CBG) transports glucocorticoids in blood and is a serine proteaseinhibitor family member. Human CBG has a reactive center loop (RCL) which, when cleaved byneutrophil elastase (NE), disrupts its steroid-binding activity. Measurements of CBG levels are typicallybased on steroid-binding capacity or immunoassays. Discrepancies in enzyme-linked immunosorbentassays (ELISAs) using monoclonal antibodies that discriminate between intact versus RCL-cleaved CBGhave been interpreted as evidence that CBG with a cleaved RCL and low affinity for cortisol exists in thecirculation. We examined the biochemical properties of plasma CBG in samples with discordant ELISAmeasurements and sought to identify RCL-cleaved CBG in human blood samples. Plasma CBG bindingcapacity and ELISA values were consistent in arterial and venous blood draining skeletal muscle, liverand brain, as well as from a tissue (adipose) expected to contain activated neutrophils in obese individuals. Moreover, RCL-cleaved CBG was undetectable in plasma from critically ill patients, irrespective of whether their ELISA measurements were concordant or discordant. We found no evidence of RCL cleaved CBG in plasma using a heat-dependent polymerization assay, and CBG that resistsimmunoprecipitation with a monoclonal antibody designed to specifically recognize an intact RCL, boundsteroids with a high affinity. In addition, mass spectrometry confirmed the absence of NE-cleaved CBG inplasma in which ELISA values were highly discordant. Human CBG with a NE-cleaved RCL and lowaffinity for steroids is absent in blood samples, and CBG ELISA discrepancies likely reflect structural differences that alter epitopes recognized by specific monoclonal antibodies.
Author(s): Hill LA, Vassiliadi DA, Dimopoulos I, Anderson AJ, Boyle LD, Kilgour AHM, Stimson RH, Machado Y, Overall CM, Walker BR, Lewis JG, Hammond GL
Publication type: Article
Publication status: Published
Journal: Journal of Endocrinology
Online publication date: 31/01/2019
Acceptance date: 28/09/2018
Date deposited: 06/11/2018
ISSN (print): 0022-0795
ISSN (electronic): 1479-6805
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