New insights into the pathogenesis and management of steroid-resistant asthma

Proinflammatory cytokines regulate human glucocorticoid receptor gene expression and lead to the accumulation of the dominant negative beta isoform: a mechanism for the generation of glucocorticoid resistance

Inflammatory responses in many cell types are coordinately regulated by the opposing actions of NF-kappaB and the glucocorticoid receptor (GR). The human glucocorticoid receptor (hGR) gene encodes two protein isoforms: a cytoplasmic alpha form (GRalpha), which binds hormone, translocates to the nucleus, and regulates gene transcription, and a nuclear localized beta isoform (GRbeta), which does not bind known ligands and attenuates GRalpha action. We report here the identification of a tumor necrosis factor (TNF)-responsive NF-kappaB DNA binding site 5' to the hGR promoter that leads to a 1.5-fold increase in GRalpha mRNA and a 2.0-fold increase in GRbeta mRNA in HeLaS3 cells, which endogenously express both GR isoforms. However, TNF-alpha treatment disproportionately increased the steady-state levels of the GRbeta protein isoform over GRalpha, making GRbeta the predominant endogenous receptor isoform. Similar results were observed following treatment of human CEMC7 lymphoid cells with TNF-alpha or IL-1. The increase in GRbeta protein expression correlated with the development of glucocorticoid resistance.

Mechanisms of glucocorticoid reduction in asthmatic subjects treated with intravenous immunoglobulin

BACKGROUND

Intravenous immunoglobulin (IVIG) has been used as an oral glucocorticoid (GC)-sparing agent in patients with steroid-dependent asthma. Despite its use, little is known regarding its mechanism of action.

OBJECTIVE

We sought to determine whether the GC-sparing effects of IVIG in severe asthma are related to improved GC receptor (GCR)-binding affinity and subsequent enhanced GC sensitivity.

METHODS

In an open-label study, 11 steroid-dependent asthmatic subjects (6 GC-insensitive, 5 GC-sensitive) received monthly infusions of IVIG (2 g/kg) for 6 months. Peak expiratory flow rates and oral GC dose were recorded daily, and spirometry was performed monthly. Blood was drawn for lymphocyte stimulation assays and GCR assays at baseline and after 3 and 6 months of therapy. Lymphocytes were stimulated ex vivo with PHA in the presence and absence of IVIG and increasing concentrations of dexamethasone (DEX).

RESULTS

IVIG resulted in significant reductions in oral GC dose (P <.02), number of GC bursts (P =.033), and hospitalizations (P =.001) after 6 months of IVIG. Those with GC-insensitive asthma responded equally well to IVIG as those with GC-sensitive asthma. Associated with the improved clinical efficacy, IVIG acted synergistically with DEX in suppressing lymphocyte activation as measured by a shift in the DEX dose-response curve by 1 log-fold (P =.03). IVIG therapy was also associated with significantly improved GCR-binding affinity (P =.01).

CONCLUSIONS

IVIG resulted in significant reductions in oral GC requirements and hospitalizations in a group of patients with severe asthma, with IVIG being as effective in patients with GC-insensitive asthma as in patients with GC-sensitive asthma. IVIG therapy acted synergistically with DEX in suppressing lymphocyte activation and significantly improved GCR-binding affinity after 3 and 6 months of therapy.

Individual variations in lymphocyte-responses to glucocorticoids in patients with bronchial asthma: comparison of potencies for five glucocorticoids

Glucocorticoids (GCs) are known to be effective for bronchial asthma, however, a considerable number of asthma patients fail to respond to GC despite the onset of serious side effects. Here we examined individual sensitivities to five clinically-used GCs in 40 asthma patients and 100 healthy subjects. Peripheral-blood mononuclear cells (PBMCs) were isolated from these subjects, and their in vitro sensitivities to hydrocortisone, prednisolone, methylprednisolone, dexamethasone, and betamethasone were determined with a mitogen-assay procedure. The number of PBMCs positive to IL-2 receptors (IL-2Rs) as well as soluble IL-2R (sIL-2R) levels in serum were concomitantly measured in asthma patients, and relationships between these cytokine indices and PBMC-sensitivities to GCs were also examined. Large individual variations in GC IC50s have been observed in PBMCs from asthma subjects, especially in prednisolone IC50s (ranged from 1 to 10,000 ng/ml). When compared with healthy subjects, asthma patients tend to show PBMC-resistance to prednisolone (p < 0.05). Moreover, potencies of methylprednisolone on PBMC-blastogenesis were > 10 times higher than those of prednisolone in both healthy subjects and asthmatics (p < 0.01). In asthma patients, IC50s of hydrocortisone, prednisolone and betamethasone against PBMC-blastogenesis were significantly correlated with elevated percentages of IL-2R-positive PBMCs (p < 0.05), while the IC50 of methylprednisolone showed no such correlation. sIL-2R levels did not correlate with IC50s of any of the GCs examined. Thus, the results showed that a part of asthma patients exhibited PBMC-resistance to GCs, especially to prednisolone. Methylprednisolone potency was unexpectedly higher (> 10 times) than prednisolone potency. Our results also raised the possibility that PBMC-resistance to prednisolone in asthma may correlate with an increase in IL-2R positive PBMCs.