Molecular targets for steroids in airway vascular smooth muscle

Rapid permissive action of dexamethasone on the regulation of blood pressure in a rat model of septic shock

Glucocorticoids (GCs) play a vital role in the regulation of blood pressure by their permissive effects in potentiating vasoactive responses to catecholamines through glucocorticoid receptors. GCs achieve this function by controlling vascular smooth muscle tone. Clinically, low to moderate doses of GCs are generally used in the treatment of septic shock in recent years. GCs are now known to have both genomic and non-genomic effects. While genomic effects of GCs were well studied, few non-genomic effects were reported, much less the non-genomic mechanisms. One of the most important characters of their non-genomic effects is short latency. The aim of this study was to determine whether GCs can rapidly regulate blood pressure by their permissive action on norepinephrine (NE). Adrenalectomized rats were subjected to cecal ligation and puncture to induce septic shock. The septic rats displayed a significant decrease in the blood pressure response to NE. Dexamethasone (DEX) rapidly restores this hyporeactivity to NE in adrenalectomized septic rats. Further studies showed that DEX potentiates the NE-induced shrinkage and actin cytoskeleton rearrangement of single cell from mesenteric arteries in a short time. These findings suggest that GCs probably exert their permissive actions on the pressure response to NE through rapid non-genomic mechanisms. In this article, we found that as an adjunctive therapy for septic shock, the use of GCs may involve a rapid permissive action, and non-genomic effects of GCs may be involved in these processes.

Organic cation transporter 3 (OCT3) is localized to intracellular and surface membranes in select glial and neuronal cells within the basolateral amygdaloid complex of both rats and mice

Organic cation transporter 3 (OCT3) is a high-capacity, low-affinity transporter that mediates corticosterone-sensitive uptake of monoamines including norepinephrine, epinephrine, dopamine, histamine and serotonin. OCT3 is expressed widely throughout the amygdaloid complex and other brain regions where monoamines are key regulators of emotional behaviors affected by stress. However, assessing the contribution of OCT3 to the regulation of monoaminergic neurotransmission and monoamine-dependent regulation of behavior requires fundamental information about the subcellular distribution of OCT3 expression. We used immunofluorescence and immuno-electron microscopy to examine the cellular and subcellular distribution of the transporter in the basolateral amygdaloid complex of the rat and mouse brain. OCT3-immunoreactivity was observed in both glial and neuronal perikarya in both rat and mouse amygdala. Electron microscopic immunolabeling revealed plasma membrane-associated OCT3 immunoreactivity on axonal, dendritic, and astrocytic processes adjacent to a variety of synapses, as well as on neuronal somata. In addition to plasma membrane sites, OCT3 immunolabeling was also observed associated with neuronal and glial endomembranes, including Golgi, mitochondrial and nuclear membranes. Particularly prominent labeling of the outer nuclear membrane was observed in neuronal, astrocytic, microglial and endothelial perikarya. The localization of OCT3 to neuronal and glial plasma membranes adjacent to synaptic sites is consistent with an important role for this transporter in regulating the amplitude, duration, and physical spread of released monoamines, while its localization to mitochondrial and outer nuclear membranes suggests previously undescribed roles for the transporter in the intracellular disposition of monoamines.

The use of inhaled corticosteroids in pediatric asthma: update

Despite the availability of several formulations of inhaled corticosteroids (ICS) and delivery devices for treatment of childhood asthma and despite the development of evidence-based guidelines, childhood asthma control remains suboptimal. Improving uptake of asthma management plans, both by families and practitioners, is needed. Adherence to daily ICS therapy is a key determinant of asthma control and this mandates that asthma education follow a repetitive pattern and involve literal explanation and physical demonstration of the optimal use of inhaler devices. The potential adverse effects of ICS need to be weighed against the benefit of these drugs to control persistent asthma especially that its safety profile is markedly better than oral glucocorticoids. This article reviews the key mechanisms of inhaled corticosteroid action; recommendations on dosage and therapeutic regimens; potential optimization of effectiveness by addressing inhaler technique and adherence to therapy; and updated knowledge on the real magnitude of adverse events.

Mechanisms of glucocorticoid action and insensitivity in airways disease

Glucocorticoids are the mainstay for the treatment of chronic inflammatory diseases including asthma and chronic obstructive pulmonary disease (COPD). However, it has been recognized that glucocorticoids do not work well in certain patient populations suggesting reduced sensitivity. The ultimate biologic responses to glucocorticoids are determined by not only the concentration of glucocorticoids but also the differences between individuals in glucocorticoid sensitivity, which is influenced by multiple factors. Studies are emerging to understand these mechanisms in detail, which would help in increasing glucocorticoid sensitivity in patients with chronic airways disease. This review aims to highlight both classical and emerging concepts of the anti-inflammatory mechanisms of glucocorticoids and also review some novel strategies to overcome steroid insensitivity in airways disease.

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.

Chronic mild stress-induced depression-like symptoms in rats and abnormalities in catecholamine uptake in small arteries

OBJECTIVE

Major depression and cardiovascular diseases have a strong comorbidity; however, the reason for this is unknown. In the chronic mild stress (CMS) model of depression, only a fraction of rats develop a major feature of depression-anhedonia-like behavior, whereas other rats are stress resilient. Previous studies suggested that CMS rats also have increased total peripheral vascular resistance.

METHODS

On the basis of CMS-induced changes of sucrose intake, a reliable measure for anhedonia, rats were divided into "resilient" and "anhedonic" groups. An interaction between hedonic status and vascular function was studied after 4 and 8 weeks of CMS exposure in vitro in wire myograph on saphenous arteries and mesenteric small arteries (MSAs) from these rats.

RESULTS

When comparing the different experimental rat groups, arterial sensitivities to noradrenaline (NA) were similar under control conditions, but in the presence of the neuronal reuptake inhibitor cocaine, arteries from anhedonic rats were more sensitive to NA. No change in perivascular innervation was found, but elevated expression of neuronal NA transporter was detected. Inhibition of extraneuronal uptake with corticosterone (1 μM) suggests that this transport is diminished in MSAs after CMS. The corticosterone-sensitive transporter organic cation cotransporter 2 was shown to be reduced in MSAs after CMS. No CMS-induced changes in the corticosterone-sensitive transport were found in saphenous arteries.

CONCLUSIONS

Our results indicate that CMS-induced depression-like symptoms in rats are associated with changes in catecholamine uptake pathways in the vascular wall, which potentially modulates the effect of sympathetic innervation of resistance arteries.

Rapid corticosteroid effect on beta(2)-adrenergic airway and airway vascular reactivity in patients with mild asthma

BACKGROUND

Long-term glucocorticoid therapy has been suggested to improve airway and airway vascular smooth muscle responsiveness to inhaled beta(2)-agonists in patients with asthma.

OBJECTIVE

We sought to assess whether a single dose of an inhaled glucocorticoid acutely potentiates beta(2)-adrenergic airway and airway vascular smooth muscle reactivity in asthma.

METHODS

In 10 asthmatic and 10 healthy subjects, airway blood flow and FEV(1) were measured before and 30 minutes after fluticasone or placebo inhalation and 15 minutes after the subsequent inhalation of racemic albuterol (0.6 mg or 1.25 mg) or (R)-albuterol (0.3 mg or 0.6 mg).

RESULTS

In healthy subjects all albuterol formulations increased airway blood flow equally after placebo or fluticasone pretreatment. In asthmatic subjects airway blood flow response was blunted after placebo and acutely restored after fluticasone pretreatment. Fluticasone pretreatment did not increase FEV(1) responses to any albuterol formulation, except 0.6 mg racemic albuterol.

CONCLUSION

A single dose of an inhaled glucocorticoid restores beta(2)-adrenergic airway vasodilator responses in patients with mild asthma. The mechanism of this rapid glucocorticoid effect remains to be clarified.