Glucocorticoid decreases airway tone via a nongenomic pathway

Expression and purification of Gpr33, a candidate membrane receptor for cortisol

Membrane receptors for the sex steroids progesterone, estrogen, and androgens have been identified, and membrane receptors for the adrenocortical steroids glucocorticoids and mineralocorticoids have also been suggested to exist but have not yet been identified. Because of their diverse physiological actions, corticoids have been artificially synthesized and widely used as steroid drugs, and membrane receptors for corticoids are expected to become new drug targets. Therefore, there is a need to identify membrane glucocorticoid receptors (mGRs). To screen candidate mGRs, we identified two common amino acid sequences between membrane progesterone receptor (mPR) and membrane estrogen receptor (mER). We searched the protein database PROSITE for these common sequences. This led us to select GPR33 as a candidate mGR. To determine whether GPR33 can bind to corticoids, recombinant mouse Gpr33 (MGpr33) was expressed in Pichia yeast. Recombinant MGpr33, which was present as an oligomer in the membrane fraction, was found to bind to cortisol (hydrocortisone), a type of glucocorticoid. These results verified that GPR33 is a candidate membrane corticoid receptor. Denaturation by urea resulted in the generation of MGpr33 monomers and reduced the cortisol-binding activity of MGpr33, suggesting that MGpr33 may function as an oligomer. MGpr33 oligomers purified by two-step column chromatography using a Ni-NTA column and a Sephacryl S-300 gel filtration column retained the ability to bind cortisol. The purified fraction bound to cortisol with a Kd = 11.9 nM and Bmax = 1.19 nM. Furthermore, MGpr33 specifically bound to cortisol but not to estradiol, progesterone or testosterone. MGpr33 was found to be a candidate mGR that may function as an oligomer.

Non-genomic actions of steroid hormones on the contractility of non-vascular smooth muscles

Steroid hormones play an important role in physiological processes. The classical pathway of steroid actions is mediated by nuclear receptors, which regulate genes to modify biological processes. Non-genomic pathways of steroid actions are also known, mediated by cell membrane-located seven transmembrane domain receptors. Sex steroids and glucocorticoids have several membrane receptors already identified to mediate their rapid actions. However, mineralocorticoids have no identified membrane receptors, although their rapid actions are also measurable. In non-vascular smooth muscles (bronchial, uterine, gastrointestinal, and urinary), the rapid actions of steroids are mediated through the modification of the intracellular Ca2+ level by various Ca-channels and the cAMP and IP3 system. The non-genomic action can be converted into a genomic one, suggesting that these distinct pathways may interconnect, resulting in convergence between them. Sex steroids mostly relax all the non-vascular smooth muscles, except androgens and progesterone, which contract colonic and urinary bladder smooth muscles, respectively. Corticosteroids also induce relaxation in bronchial and uterine tissues, but their actions on gastrointestinal and urinary bladder smooth muscles have not been investigated yet. Bile acids also contribute to the smooth muscle contractility. Although the therapeutic application of the rapid effects of steroid hormones and their analogues for smooth muscle contractility disorders seems remote, the actions and mechanism discovered so far are promising. Further research is needed to expand our knowledge in this field by using existing experience. One of the greatest challenges is to separate genomic and non-genomic effects, but model molecules are available to start this line of research.

Diclofenac and dexamethasone modulate the effect of cannabidiol on the rat colon motility ex vivo

Introduction

Due to the growing interest in the use of cannabinoids in supportive therapies, they are increasingly used together with anti-inflammatory drugs. Cannabinoids inhibit gastrointestinal motility, while steroidal and nonsteroidal anti-inflammatory drugs influence motility in other ways. The aim of the research was to study the interactions between cannabidiol (CBD) and these two classes of anti-inflammatory drugs in the context of gastrointestinal motility. Dexamethasone (DEX) was selected as a steroidal drug and diclofenac (DCF) as a nonsteroidal counterpart.

Material and Methods

The experiments were performed on isolated rat colon strips in isometric conditions. The contractile response to acetylcholine (ACh) (1 μM) was measured with no substance applied as a control value and was measured after application of CBD (80 μM), DEX (100 μM), DCF (100 μM), or a combination of these substances.

Results

Cannabidiol strongly inhibited intestinal motility mediated by ACh application, DCF inhibited it non-significantly, while DEX intensified it. When CBD was co-administered with DEX, the combination inhibited intestinal motility non-significantly relative to the ACh-only control. Co-administration of CBD with DCF inhibited motility more than when these substances were administered separately.

Conclusion

Inhibition of the intestinal response to ACh is likely due to the synergistic effect of CBD and endogenous cannabinoids. Dexamethasone lessened the inhibitory effect of CBD, likely because of diminished availability of the arachidonic acid necessary for endogenous cannabinoid synthesis. However, diclofenac may increase endogenous cannabinoid synthesis, because of the greater availability of arachidonic acid caused by DCF blocking the cyclooxygenation pathway.

Genomic and non-genomic effects of glucocorticoids in respiratory diseases

Cortisol is an endogenous steroid hormone essential for the natural resolution of inflammation. Synthetic glucocorticoids (GCs) were developed and are currently amongst the most widely prescribed anti-inflammatory drugs in our modern clinical landscape owing to their potent anti-inflammatory activity. However, the extent of GC's effects has yet to be fully elucidated. Indeed, GCs modulate a broad spectrum of cellular activity, from their classical regulation of gene expression to acute non-genomic mechanisms of action. Furthermore, tissue specific effects, disease specific conditions, and dose-dependent responses complicate their use, with side-effects potentially plaguing their use. It is thus vital to outline and consolidate the effects of GCs, to demystify and maximize their therapeutic potential while avoiding pitfalls that would otherwise render them obsolete.

Non-genomic Effects of Glucocorticoids: An Updated View

Glucocorticoid (GC) anti-inflammatory effects generally require a prolonged onset of action and involve genomic processes. Because of the rapidity of some of the GC effects, however, the concept that non-genomic actions may contribute to GC mechanisms of action has arisen. While the mechanisms have not been completely elucidated, the non-genomic effects may play a role in the management of inflammatory diseases. For instance, we recently reported that GCs 'rapidly' enhanced the effects of bronchodilators, agents used in the treatment of allergic asthma. In this review article, we discuss (i) the non-genomic effects of GCs on pathways relevant to the pathogenesis of inflammatory diseases and (ii) the putative role of the membrane GC receptor. Since GC side effects are often considered to be generated through its genomic actions, understanding GC non-genomic effects will help design GCs with a better therapeutic index.

Interaction between corticosteroids and muscarinic antagonists in human airways

BACKGROUND

To date there is emerging clinical evidence to add long-acting anti-muscarinic agents (LAMAs) with inhaled corticosteroid (ICSs) in asthma, but the pharmacological rationale that supports the use of such a combination has not yet been explained. The aim of this study was to pharmacologically investigate the interaction between the ICS beclomethasone and the LAMA glycopyrronium on the human airway smooth muscle (ASM) tone.

METHODS

We investigated the rapid non-genomic bronchorelaxant effect of beclomethasone and glycopyrronium, administered alone and in combination, in human isolated bronchi and bronchioles. Experiments were carried out also in passively sensitized airways and the pharmacological analysis of drug interaction was performed by Bliss Independence method.

RESULTS

The acute administration of beclomethasone and glycopyrronium induced a significant relaxation of passively sensitized ASM pre-contracted with histamine, by causing submaximal/maximal inhibition of the contractile tone in both medium bronchi and bronchioles. Beclomethasone was characterized by a rapid non-genomic and epithelium independent bronchorelaxant effect. In passively sensitized airways, this effect seemed to be dependent by the activation of a Gsα--cyclic adenosine monophosphate (cAMP)--protein kinase A cascade. While no synergistic interaction was detected in non-sensitized bronchi, the beclomethasone/glycopyrronium combination synergistically enhanced the relaxation of passively sensitized medium and small bronchi. The synergistic interaction between beclomethasone and glycopyrronium was associated with an increase of cAMP concentrations.

CONCLUSIONS

Our study provides for the first time the pharmacological rationale for combining low doses of an ICS plus a LAMA.

G protein-coupled receptors: extranuclear mediators for the non-genomic actions of steroids

Steroids hormones possess two distinct actions, a delayed genomic effect and a rapid non-genomic effect. Rapid steroid-triggered signaling is mediated by specific receptors localized most often to the plasma membrane. The nature of these receptors is of great interest and accumulated data suggest that G protein-coupled receptors (GPCRs) are appealing candidates. Increasing evidence regarding the interaction between steroids and specific membrane proteins, as well as the involvement of G protein and corresponding downstream signaling, have led to identification of physiologically relevant GPCRs as steroid extranuclear receptors. Examples include G protein-coupled receptor 30 (GPR30) for estrogen, membrane progestin receptor for progesterone, G protein-coupled receptor family C group 6 member A (GPRC6A) and zinc transporter member 9 (ZIP9) for androgen, and trace amine associated receptor 1 (TAAR1) for thyroid hormone. These receptor-mediated biological effects have been extended to reproductive development, cardiovascular function, neuroendocrinology and cancer pathophysiology. However, although great progress have been achieved, there are still important questions that need to be answered, including the identities of GPCRs responsible for the remaining steroids (e.g., glucocorticoid), the structural basis of steroids and GPCRs' interaction and the integration of extranuclear and nuclear signaling to the final physiological function. Here, we reviewed the several significant developments in this field and highlighted a hypothesis that attempts to explain the general interaction between steroids and GPCRs.

Steroids and antihistamines synergize to inhibit rat's airway smooth muscle contractility

Both glucocorticoids and H1-antihistamines were widely used on patients with allergic rhinitis (AR) and obstructive airway diseases. However, their direct effects on airway smooth muscle were not fully explored. In this study, we tested the effectiveness of prednisolone (Kidsolone) and levocetirizine (Xyzal) on isolated rat trachea submersed in Kreb's solution in a muscle bath. Changes in tracheal contractility in response to the application of parasympathetic mimetic agents were measured. The following assessments of the drug were performed: (1) effect on tracheal smooth muscle resting tension; (2) effect on contraction caused by 10(-6) M methacholine; (3) effect of the drug on electrical field stimulation (EFS) induced tracheal smooth muscle contractions. The result revealed sole use of Kidsolone or Xyzal elicited no significant effect or only a little relaxation response on tracheal tension after methacholine treatment. The tension was 90.5 ± 7.5 and 99.5 ± 0.8 % at 10(-4) M for Xyzal and 10(-5) M for Kidsolone, respectively. However, a dramatically spasmolytic effect was observed after co-administration of Kidsolone and Xyzal and the tension dropped to 67.5 ± 13.6 %, with statistical significance (p < 0.05). As for EFS-induced contractions, Kidsolone had no direct effect but Xyzal could inhibit it, with increasing basal tension. In conclusion, using glucocorticoids alone had no spasmolytic effect but they can be synergized with antihistamines to dramatically relax the trachea smooth muscle within minutes. Therefore, for AR patients with acute asthma attack, combined use of those two drugs is recommended.

Nongenomic bronchodilating action elicited by dehydroepiandrosterone (DHEA) in a guinea pig asthma model

Primates secrete large amounts of the precursor steroid dehydroepiandrosterone (DHEA); in humans, its levels are low during childhood and start declining after the fourth decade. It has been postulated that the progressive decline in DHEA levels may be related with the severity of asthma associated with age. To determine whether DHEA may regulate the airway smooth muscle (ASM) activity, isolated tracheal rings with and without epithelium from male guinea pigs were isometrically recorded to characterize the response of ASM to DHEA at different concentrations on KCl- and carbachol (CCh)-induced contraction as well as on ovalbumin (OVA)-induced contraction in sensitized guinea pigs. Additionally, we used barometric plethysmography in sensitized guinea pigs in order to compare changes of the lung resistance increased by the antigen challenge to OVA in the absence and presence of different doses of DHEA. DHEA concentration-dependently abolished the contraction to KCl, CCh and OVA, and no differences were found in preparations with and without epithelium. DHEA-induced relaxation was not modified by the suppression of protein synthesis or transcription, pharmacological inhibition of nitric oxide (NO) synthase, nor by antagonist of β2-adrenergic receptors or an inhibitor of the 3β-HSD enzyme. Likewise, Ca(2+)-induced contraction in Ca(2+)-free depolarized tissues was antagonized by DHEA, and the contraction to the L-type voltage-dependent calcium channel activator (Bay K 8644) was inhibited by DHEA. Furthermore, DHEA prevented OVA-induced increases in lung resistance. These results indicate that DHEA-induced relaxation in ASM is a nongenomic (membrane) action and is not produced after its bioconversion. The data suggest that DHEA-induced relaxation is an epithelium- and NO-independent mechanism that involves a blockade of voltage-dependent calcium channels and possible non-selective cation channels.

Extraneuronal monoamine transporter mediates the permissive action of cortisol in the Guinea pig trachea: possible involvement of tracheal chondrocytes

Cortisol, a member of glucocorticoids, could potentiate the action of catecholamine by a non-genomic mechanism. Although this permissive effect has been well appreciated in the anti-asthmatic medication, the underlying signaling pathway has remained mysterious. Here, we show that extraneuronal monoamine transporter (EMT), a membraneous reuptake transporter for circulating catecholamine clearance, is the direct target of cortisol in its permissive effect. We found that BSA-conjugated cortisol, which functions as a cortisol but cannot penetrate cell membrane, enhanced the spasmolytic effect of β-adrenoceptor agonist (isoprenaline) in histamine-sensitized tracheal spirals of guinea pigs, and pharmacological inhibition of EMT with famotidine was powerful enough to imitate the permissive action of cortisol. To our surprise, EMT protein expression was high in the chondrocytes of tracheal cartilage, but was undetectable in tracheal smooth muscle cells. The functionality of EMT was further confirmed with measurement of catecholamine uptake by tracheal chondrocytes. Moreover, cortisol-initiated membrane signaling could activate protein kinase C (PKC), which phosphorylates EMT and induces its internalization via a lipid raft-dependent pathway. Both of the mechanisms slow down the reuptake process by chondrocytes, leading to extracellular catecholamine accumulation and results in a more profound adrenergic signaling activation in tracheal smooth muscle cells. Thus, an EMT-centered pathway was proposed to explain the permissive action of cortisol. Collectively, our results highlight the role of EMT in the crosstalk between glucocorticoid and catecholamine. EMT may represent a promising target for adrenergic signaling modulation.