Endocrine Abstracts

Introduction: Corticosteroid Binding Globulin (CBG) binds >85% of plasma cortisol and modulates free cortisol levels. Observations in vitro show that CBG is cleaved by neutrophil elastase (NE), a mechanism proposed to reduce CBG binding affinity and increase free cortisol availability to inflamed tissues. However, detection of cleaved CBG in vivo in human plasma is controversial, and any influence of NE on CBG cleavage has not been tested in vivo. We hypothesised that the endogenous NE inhibitor elafin reduces CBG cleavage and thus free plasma cortisol. We tested this in humans using coronary artery bypass graft (CABG) surgery as a model of acute neutrophil-mediated inflammation.

Methods: In a randomised double-blind placebo-controlled parallel group clinical trial, 35 patients undergoing CABG surgery were randomised 1:1 to intravenous elafin 200 mg or saline placebo administered after induction of anaesthesia. Blood samples were taken at baseline (time 0, skin incision) and 2, 6 and 24 hours postoperatively. We measured elafin (LC-MS); plasma elastase activity (fluorometric assay); IL-6, TNF-alpha, NE and CBG (all ELISAs); CBG binding capacity (radioligand-saturation assay); total cortisol (LC-MS) and free cortisol (isotopic dilution and ultrafiltration). Data were analysed as area under the curve from 0-24h or by two-way ANOVA.

Results: With placebo, NE increased from baseline 91.4 ± 10.0 to peak 894.4 ± 108.4 ng/ml at 2h, accompanied by increased IL-6 and TNF-alpha. Elafin infusion resulted in >1000-fold higher plasma concentrations than those of endogenous elafin, with marked reduction in elastase activity (mean AUC_0-24; 3.83 ± 1.99 vs 8.04 ± 2.97 units/mL). Plasma CBG concentrations fell >30% between 0-2h in both treatment groups, then remained unchanged to 24h; this was mirrored by reduced binding capacity, unaffected by elafin. Total cortisol rose dramatically, a fourfold increase between 2-6h in both groups. Free cortisol fraction doubled over 0-6h from 16.4 ± 0.44 to 30.7 ± 6.1 % in placebo, while elafin tended to increase free cortisol concentration (mean difference 24.3 nM, 95% CI -1.33 to 49.9, P=0.062).

Discussion: The fall in plasma CBG and increase in total and free cortisol during CABG surgery is in keeping with published studies in humans during sepsis. We also noted an increase in cytokines which downregulate hepatic CBG production. However, we did not find evidence that the fall in CBG is mediated by increased cleavage by NE. Further studies are needed to assess any effects on CBG cleavage of NE inhibition in target tissues or more potently in serum.