Pyrexia and acidosis act independently of neutrophil elastase reactive center loop cleavage to effect cortisol...

Area of Science:

• Biochemistry
• Endocrinology
• Molecular Biology

Background:

• Corticosteroid-binding globulin (CBG) is crucial for transporting cortisol and other steroids.
• Neutrophil elastase (NE) cleaves high-affinity CBG (haCBG) to low-affinity CBG (laCBG), altering its conformation.
• Physiological conditions like pyrexia and acidosis can impact CBG's binding properties.

Purpose of the Study:

• To investigate the binding profiles of various steroids to haCBG and laCBG under different temperature and pH conditions.
• To understand the effects of NE-mediated conversion, elevated temperature, and acidosis on CBG-steroid interactions.
• To explore the structural basis of altered CBG binding affinity.

Main Methods:

• Surface plasmon resonance (SPR) was employed to determine binding affinities for 19 steroids to haCBG and laCBG.
• Experiments were conducted at temperatures mimicking pyrexia (25, 37, 39°C) and pH levels mimicking acidosis (7.4, 7.0).
• Conformational antibody assays and molecular modeling were used to confirm structural changes and identify key residues.

Main Results:

• NE-mediated conversion of haCBG to laCBG caused a significant reduction (4-8 fold) in affinity for several steroids, including cortisol.
• CBG:cortisol binding affinity further decreased at 39°C compared to 37°C (3.5 fold).
• Both pyrexia and acidosis reduced CBG binding affinity for both haCBG and laCBG. NE cleavage eliminated RCL antibody binding, but pyrexia and acidosis did not.

Conclusions:

• CBG binding affinity for steroids is ligand-specific and diminished by NE cleavage, elevated temperature, and acidosis.
• Increased flexibility of Trp371 is proposed as a mechanism for temperature-induced cortisol release.
• The combined effects of NE cleavage, pyrexia, and acidosis likely enhance cortisol delivery in inflammatory conditions.