OR19-05 Steroid:Corticosteroid-Binding Globulin Interactions; Effects of Neutrophil Elastase Cleavage, Pyrexia and Acidosis

Context Corticosteroid-binding globulin (CBG) transports cortisol and other steroid hormones(1,2). High-affinity CBG (haCBG) undergoes proteolysis of the reactive centre loop (RCL) by neutrophil elastase (NE) at inflammatory sites, liberating immunomodulatory cortisol and altering conformation to low-affinity CBG (laCBG). Pyrexia reduces CBG:cortisol binding affinity, an interaction at the RCL is speculated(3). Objective To measure the equilibrium binding constants of a panel of steroids to glycosylated haCBG and laCBG over temperature and pH ranges mimicking the pathophysiological conditions of septic shock. Design Surface plasmon resonance was used to determine the binding profiles of 19 steroid ligands to haCBG and laCBG at temperatures 25°C, 37°C and 39°C and pH 7.4 and 7.0. The RCL-recognizing 9G12 antibody was used to assess cleavage and epitope availability of the RCL across conditions. Results A 4–8 fold reduction in affinity for cortisol, cortisone, corticosterone, 11-deoxycortisol, progesterone, 17-hydroxyprogesterone and prednisolone occurred with NE-mediated haCBG-to-laCBG conversion, cortisol expectedly displayed the highest binding affinity. Binding affinity consistently decreased at higher temperatures and at acidic pH for both haCBG and laCBG. 9G12 antibody RCL binding was preserved for haCBG across temperatures. Conclusions These studies reveal that steroid binding to CBG is selective and in all cases reduced upon NE-mediated haCBG-to-laCBG transition. Moreover, reduced CBG:cortisol binding affinity at elevated temperature occurs with an intact and accessible RCL epitope, suggesting a non-RCL mechanism for the delivery of anti-inflammatory cortisol in pyrexia. Synergy of NE cleavage and pyrexia/acidosis may serve for local inflammatory site cortisol delivery and increase free cortisol. These findings demonstrate the modifiable hormone binding characteristics of CBG in (patho-)physiological conditions, supporting its significance in cortisol delivery in obviating systemic inflammation and multiorgan-organ failure in patients with septic shock and its association with mortality(4). 1. Pemberton PA, Stein PE, Pepys MB, et al. Hormone binding globulins undergo serpin conformational change in inflammation. Nature. 1988;336(6196):257–258. 2. Pugeat MM, Dunn JF, Nisula BC. Transport of steroid hormones: interaction of 70 drugs with testosterone-binding globulin and corticosteroid-binding globulin in human plasma. J Clin Endocrinol Metab. 1981;53(1):69–75. 3. Cameron A, Henley D, Carrell R, et al. Temperature-responsive release of cortisol from its binding globulin: a protein thermocouple. J Clin Endocrinol Metab. 2010;95(10):4689–4695. 4. Meyer EJ, Nenke MA, Rankin W, et al. Total and high-affinity corticosteroid-binding globulin depletion in septic shock is associated with mortality. Clin Endocrinol (Oxf). 2019;90(1):232–240.