A recent assessment of patients with difficult asthma identified subjects in whom exhaled NO levels remain markedly increased (17.5 ppb, 95% Cl 11.1 to 24.0 n=17) in spite of high dose corticosteroid therapy1. We have measured the ligand binding affinity of 3H-dexamethasone in PBMCs isolated from 10 patients assessed for difficult asthma. They were all taking oral corticosteroids but were selected in outpatients and consented for venesection of 100mls of blood required for this assay. Blood was drawn before their usual oral prednisolone was taken. Eight of the 10 patients had raised exhaled NO levels 25.6±4 ppb (95% Cl 15 - 36) despite confirmed two hour post dose prednisolone levels of 643±184 nmol/l measured at the same visit. The eosinophil count (0.56±0.15×109/L), serum ECP (83±22μg/L) and peripheral blood T cell activation marker (CD4/CD25 positive cells 16±2%) were raised. Cortisol, measured by HPLC in the same serum samples, was found to be supressed at 41±7 nmol/L. Two patients also had raised NO levels at 21 and 12 ppb but had undetectable serum prednisolone levels and raised cortisol (240±55 nmol/L) suggesting non compliance at that time The ability of dexamethasone to bind to GR was decreased in the nucleus ( Kd 40±7.5 nM) but not in the cytoplasm ( Kd 3.4 ±0.6 nM). There were more receptor sites per cell in the nuclear fraction (4000±850 versus 560±43 sites per cell). One patient was identified who had a high binding affinity in the nuclear and cytosolic fraction (1.7 nM and 1.2 nM) but very low receptor sites per cell in both fractions ( 959 and 700 sites per cell). Difficult asthma patients demonstrate relative steroid insensitivity for a range of inflammatory markers though serum cortisol was relatively sensitive. The altered ability of difficult asthmatics to respond to steroids may relate to their reduced nuclear GR affinity for dexamethasone or low receptor numbers.
|Issue number||SUPPL. 3|
|Publication status||Published - 1 Dec 2000|