Systemic bioavailability of inhaled steroids: the importance of appropriate and comparable methodology

A Severe Asthma Disease Signature from Gene Expression Profiling of Peripheral Blood from U-BIOPRED Cohorts

RATIONALE

Stratification of asthma at the molecular level, especially using accessible biospecimens, could greatly enable patient selection for targeted therapy.

OBJECTIVES

To determine the value of blood analysis to identify transcriptional differences between clinically defined asthma and nonasthma groups, identify potential patient subgroups based on gene expression, and explore biological pathways associated with identified differences.

METHODS

Transcriptomic profiles were generated by microarray analysis of blood from 610 patients with asthma and control participants in the U-BIOPRED (Unbiased Biomarkers in Prediction of Respiratory Disease Outcomes) study. Differentially expressed genes (DEGs) were identified by analysis of variance, including covariates for RNA quality, sex, and clinical site, and Ingenuity Pathway Analysis was applied. Patient subgroups based on DEGs were created by hierarchical clustering and topological data analysis.

MEASUREMENTS AND MAIN RESULTS

A total of 1,693 genes were differentially expressed between patients with severe asthma and participants without asthma. The differences from participants without asthma in the nonsmoking severe asthma and mild/moderate asthma subgroups were significantly related (r = 0.76), with a larger effect size in the severe asthma group. The majority of, but not all, differences were explained by differences in circulating immune cell populations. Pathway analysis showed an increase in chemotaxis, migration, and myeloid cell trafficking in patients with severe asthma, decreased B-lymphocyte development and hematopoietic progenitor cells, and lymphoid organ hypoplasia. Cluster analysis of DEGs led to the creation of subgroups among the patients with severe asthma who differed in molecular responses to oral corticosteroids.

CONCLUSIONS

Blood gene expression differences between clinically defined subgroups of patients with asthma and individuals without asthma, as well as subgroups of patients with severe asthma defined by transcript profiles, show the value of blood analysis in stratifying patients with asthma and identifying molecular pathways for further study. Clinical trial registered with www.clinicaltrials.gov (NCT01982162).

Mometasone furoate: an inhaled glucocorticoid for the management of asthma in adults and children

Mometasone furoate has been available for clinical use, starting with a dermatologic preparation, for nearly 20 years. An inhaled format of the drug for management of asthma had been in development during the last decade and has been available for clinical use for 6 years as a dry powder inhaler delivering either 100 mcg or 200 mcg per dose. It has a long half-life and is suitable for daily dosing. The drug is approved for use in the USA for the treatment of asthma in patients aged 4 years or over. Mometasone furoate is a topically potent glucocorticoid with a favorable risk-benefit profile. A wide variety of randomized clinical trials have shown the drug to have a clinically beneficial effect on asthma comparable to fluticasone propionate, and to permit the reduction or withdrawal of oral glucocorticoid therapy in patients with asthma. Mometasone furoate has approximately 1% oral bioavailability but does produce systemic glucocorticoid effects from the drug released from the lung and its metabolites. These effects are minimal when mometasone is used appropriately at low or moderate doses.

A sensitive liquid chromatography-tandem mass spectrometry method for the quantification of mometasone furoate in human plasma

A robust, rapid, selective and sensitive liquid chromatography-negative atmospheric pressure chemical ionization (LC-(APCI(-))-MS-MS) method has been developed for the quantification of mometasone furoate (MF) in human plasma utilizing a solid-phase extraction clean-up step and 13C-fluticasone propionate as internal standard. The intra- and inter-day coefficients of variation were < or = 15% and the lower limit of quantification (LLOQ) was 15 pg/ml. This method is ideally suited for pharmacokinetic investigations of low MF levels following inhalation of MF.

Human receptor kinetics, tissue binding affinity, and stability of mometasone furoate

Mometasone furoate (MF) is a topically used glucocorticoid with high anti-inflammatory potency. In contrast to the wealth of data derived from clinical studies, information about the molecular pharmacology of the compound is lacking or contradictory. Thus, we elucidated the characteristics of receptor binding kinetics and receptor affinity in a bioassay. Metabolite formation was determined in human plasma and lung tissue as well as binding affinity to human lung tissue. Fast and extensive association of MF to the human glucocorticoid receptor was observed while the dissociation of the MF-receptor complex was faster compared to fluticasone propionate (FP). The relative receptor affinity of MF was calculated as 2200 (dexamethasone = 100, FP = 1800) and confirmed in a bioassay measuring the induction of the glucocorticoid regulated protein CD163 in human monocytes. In plasma and human lung tissue MF formed a 9,11-epoxy degradation product. The binding affinity of MF to human lung tissue was low compared to FP due to fast redistribution from tissue into plasma. These molecular pharmacological properties are in accordance with clinical data.

Significant receptor affinities of metabolites and a degradation product of mometasone furoate

Mometasone furoate (MF) is a highly potent glucocorticoid used topically to treat inflammation in the lung, nose and on the skin. However, so far no information has been published on the human glucocorticoid receptor activity of the metabolites or degradation products of MF. We have now determined the relative receptor binding affinities of the known metabolite 6beta-OH MF and the degradation product 9,11-epoxy MF to understand their possible contribution to undesirable systemic side effects. In competition experiments with human lung glucocorticoid receptors we have determined the relative receptor affinities (RRA) of these substances with reference to dexamethasone (RRA = 100). We have discovered that 6beta-OH MF and 9,11-epoxy MF display RRAs of 206 +/- 15 and 220 +/- 22, respectively. This level of activity is similar to that of the clinically used inhaled corticosteroid flunisolide (RRA 180 +/- 11). Furthermore we observed that 9,11-epoxy MF is a chemically reactive metabolite. In recovery experiments with human plasma and lung tissue we found a time dependent decrease in extractability of the compound. Hence, we provide data that might contribute to the understanding of the pharmacokinetics as well as the clinical effects of MF.

Deposition and effects of inhaled corticosteroids

Inhaled corticosteroids are now recommended as maintenance therapy for all but the mildest cases of asthma, and may be delivered by a variety of devices and formulations. Drug delivery may be assessed by both in vitro and in vivo methods. Although drug deposition in the lungs is expected to predict clinical response, this relationship is often masked by the flat nature of corticosteroid dose-response curves. The effects of inhaled corticosteroids depend not only upon the pharmacology of the drug being administered, but also upon its delivery system, with more efficient devices not only improving therapeutic effect but also potentially increasing systemic adverse effects. Modern delivery systems that enhance drug targeting to the lungs make it possible to use lower dosages of inhaled corticosteroid, such that the clinical response is maintained but systemic exposure reduced.

The use of inhaled corticosteroids in adult asthma

Inhaled corticosteroids modify some but not all features of airway inflammation seen in asthma. ICS remain the most effective class of medications currently available to treat persistent asthma and result in few clinically relevant adverse effects when used in low-moderate doses. ICS activity is enhanced when used in combination with LABA and, to a lesser degree, LTRAs. ICS are well tolerated in adults. Daily doses of ICS may not be required to exceed 200 micrograms of FP equivalents. From an economic standpoint, ICS provide health care savings because of reductions in asthma hospitalization. The impact of early introduction of ICS in the disease course of asthma remains unresolved. The use of ICS in patients whose asthma is mild, with essentially normal lung function, and infrequent symptoms also remains unstudied. For the time being, ICS remain the first line of asthma treatment for adults with persistent disease.