Update in asthma 2006

Protocols to Evaluate Cigarette Smoke-Induced Lung Inflammation and Pathology in Mice

Cigarette smoking is a major cause of chronic obstructive pulmonary disease (COPD). Inhalation of cigarette smoke causes inflammation of the airways, airway wall remodelling, mucus hypersecretion and progressive airflow limitation. Much of the disease burden and health care utilisation in COPD is associated with the management of its comorbidities and infectious (viral and bacterial) exacerbations (AECOPD). Comorbidities, in particular skeletal muscle wasting, cardiovascular disease and lung cancer markedly impact on disease morbidity, progression and mortality. The mechanisms and mediators underlying COPD and its comorbidities are poorly understood and current COPD therapy is relatively ineffective. Many researchers have used animal modelling systems to explore the mechanisms underlying COPD, AECOPD and comorbidities of COPD with the goal of identifying novel therapeutic targets. Here we describe a mouse model that we have developed to define the cellular, molecular and pathological consequences of cigarette smoke exposure and the development of comorbidities of COPD.

Anti-inflammatory and immunosuppressive effects of the enaminone E121

Asthma is a chronic inflammatory disease of the airways. The treatment of asthma is far from optimal and hence the need for novel therapeutic agents exists. The purpose of this study was to assess the anti-asthma effects of an enaminone, E121, and also its effects on human peripheral blood mononuclear cell proliferation and cytokine release. The effects of E121 were assessed in an ovalbumin-induced model of airway inflammation and airway hyperresponsiveness. In addition, the effects of E121 on phytohemagglutinin (PHA), anti-CD3 monoclonal antibody and lipopolysaccharide (LPS)-induced human peripheral blood mononuclear cell proliferation and cytokine release, respectively, were assessed. Treatment of mice with E121 significantly decreased the ovalbumin-induced increase in airway total cell influx and eosinophil infiltration and this was associated with an inhibition of ovalbumin-induced airway hyperresponsiveness. Moreover, E121 reduced PHA and anti-CD3-induced human peripheral blood mononuclear cell proliferation in vitro. E121 also inhibited PHA, anti-CD3 monoclonal antibody and LPS-induced cytokine release from human peripheral blood mononuclear cell cultures. These findings indicate that E121 exhibits anti-inflammatory and immunosuppressive activities.

The Saudi Initiative for Asthma

The Saudi Initiative for Asthma (SINA) provides up-to-date guidelines for healthcare workers managing patients with asthma. SINA was developed by a panel of Saudi experts with respectable academic backgrounds and long-standing experience in the field. SINA is founded on the latest available evidence, local literature, and knowledge of the current setting in Saudi Arabia. Emphasis is placed on understanding the epidemiology, pathophysiology, medications, and clinical presentation. SINA elaborates on the development of patient-doctor partnership, self-management, and control of precipitating factors. Approaches to asthma treatment in SINA are based on disease control by the utilization of Asthma Control Test for the initiation and adjustment of asthma treatment. This guideline is established for the treatment of asthma in both children and adults, with special attention to children 5 years and younger. It is expected that the implementation of these guidelines for treating asthma will lead to better asthma control and decrease patient utilization of the health care system.

Effect of proinflammatory cytokines on regulation of sarcoplasmic reticulum Ca2+ reuptake in human airway smooth muscle

Airway inflammation leads to increased intracellular Ca(2+) ([Ca(2+)](i)) levels in airway smooth muscle (ASM) cells. Sarcoplasmic reticulum Ca(2+) release and reuptake are key components of ASM [Ca(2+)](i) regulation. Ca(2+) reuptake occurs via sarcoendoplasmic reticulum Ca(2+) ATPase (SERCA) and is regulated by the inhibitory protein phospholamban (PLB) in many cell types. In human ASM, we tested the hypothesis that inflammation increases PLB, thus inhibiting SERCA function, and leading to maintained [Ca(2+)](i) levels. Surprisingly, we found that human ASM does not express PLB protein (although mRNA is detectable). Overnight exposure to the proinflammatory cytokines TNFalpha and IL-13 did not induce PLB expression, raising the issue of how SERCA is regulated. We then found that direct SERCA phosphorylation (via CaMKII) occurs in human ASM. In fura-2-loaded human ASM cells, we found that the CaMKII antagonist KN-93 significantly slowed the rate of fall of [Ca(2+)](i) transients induced by ACh or bradykinin (in zero extracellular Ca(2+)), suggesting a role for CaMKII-mediated SERCA regulation. SERCA expression was decreased by cytokine exposure, and the rate of fall of [Ca(2+)](i) transients was slowed in cells exposed to TNFalpha and IL-13. Cytokine effects on Ca(2+) reuptake were unaffected by additional exposure to KN-93. These data indicate that in human ASM, SERCA is regulated by mechanisms such as CaMKII and that airway inflammation maintains [Ca(2+)](i) levels by decreasing SERCA expression and slowing Ca(2+) reuptake.

CD38 plays a dual role in allergen-induced airway hyperresponsiveness

The multifunctional surface protein CD38 acts as a receptor with ecto-enzymatic activity, hydrolyzing NAD to generate several products known to exhibit Ca2+-mobilizing properties. Although CD38 is a convenient marker of immune cell development, and an indicator of progression for several diseases, it is not restricted to the immune compartment. To determine the potentially multilayered involvement of CD38 in allergen-induced airway inflammation and hyperreactivity, we dissected the potential role of CD38 as a regulator of immunity, but also pulmonary function. CD38-deficient and wild-type (WT) mice were sensitized and airway challenged with ovalbumin, and subsequently analyzed regarding their level of airway hyperresponsiveness (AHR) in response to methacholine. Parameters of lung inflammation were also analyzed. Similar sets of measurements were obtained from reciprocal bone marrow swapping experiments between CD38(-/-) and WT mice. Mice lacking CD38 exhibit strongly reduced AHR, which is accompanied by a decrease in typical hallmarks of pulmonary inflammation, including eosinophilia and lymphocytic lung infiltrates, as well as Th2-cytokine levels (IL-4, -5, and -13). Antigen-specific immunoglobulin (Ig)E and IgG1 antibody titers are substantially reduced, consistent with CD38 being crucial for mounting a primary humoral systemic immune response. Reconstitution of lethally irradiated, lung-shielded, CD38-deficient mice with WT bone marrow does not restore WT levels of airway hyperreactivity, nor mucus secretion. The opposite experiment, transferring CD38(-/-) bone marrow into WT mice, also shows reduced AHR levels. These studies demonstrate that CD38 not only acts as a key modulator of the immune response, but also plays an equally important role as an intrinsic pulmonary component.

Corticosteroid-resistant asthma is associated with classical antimicrobial activation of airway macrophages

BACKGROUND

The cause of corticosteroid-resistant (CR) asthma is unknown.

OBJECTIVE

We sought to perform gene microarray analyses by using bronchoalveolar lavage (BAL) cells from well-characterized subjects with CR asthma and subject with corticosteroid-sensitive (CS) asthma to elucidate the differential expression of genes that contribute to the development of corticosteroid resistance.

METHODS

The patients were characterized as having CR or CS asthma based on FEV(1) percent predicted improvement after a 1-week course of oral prednisone. Expression of selected gene targets was verified by means of real-time PCR and ELISA.

RESULTS

Microarray analyses demonstrated significantly higher levels (>3-fold increase, P < .05) of transcripts for TNF-alpha, IL-1 alpha, IL-1 beta, IL-6, CXCL1, CXCL2, CXCL3, CXCL8 (IL-8), CCL3, CCL4, and CCL20 in BAL cells of subjects with CR asthma. These findings, confirmed by means of RT-PCR in additional BAL samples, were consistent with classical macrophage activation by bacterial products. In contrast, markers of alternatively activated macrophages, arginase I and CCL24, were decreased. Genes associated with activation of the LPS signaling pathway (early growth response 1, dual-specificity phosphatase 2, molecule possessing ankyrin repeats induced by LPS, and TNF-alpha-induced protein 3) were significantly increased in BAL samples from subjects with CR asthma (P < .05). These patients had significantly higher amounts (1444.0 +/- 457.3 pg/mg total protein) of LPS in BAL fluid than seen in subjects with CS asthma (270.5 +/- 216.0 pg, P < .05), as detected by using the LAL assay and confirmed by means of gas chromatographic/mass spectrometric analysis. Prolonged exposure to LPS induced functional steroid resistance to dexamethasone in normal human monocytes, as demonstrated by persistently increased IL-6 levels in the presence of dexamethasone.

CONCLUSIONS

Classical macrophage activation and induction of LPS signaling pathways along with high endotoxin levels detected in BAL fluid from subjects with CR asthma suggest that LPS exposure might contribute to CR asthma.

Role of CD38 in TNF-alpha-induced airway hyperresponsiveness

CD38 is involved in normal airway function, IL-13-induced airway hyperresponsiveness (AHR), and is also regulated by tumor necrosis factor (TNF)-alpha in airway smooth muscle (ASM) cells. This study aimed to determine whether TNF-alpha-induced CD38 upregulation in ASM cells contributes to AHR, a hallmark of asthma. We hypothesized that AHR would be attenuated in TNF-alpha-exposed CD38-deficient (CD38KO) mice compared with wild-type (WT) controls. Mice (n = 6-8/group) were intranasally challenged with vehicle control or TNF-alpha (50 ng) once and every other day during 1 or 4 wk. Lung inflammation and AHR, measured by changes in lung resistance after inhaled methacholine, were assessed 24 h following the last challenge. Tracheal rings were incubated with TNF-alpha (50 ng/ml) to assess contractile changes in the ASM. While a single TNF-alpha challenge caused no airway inflammation, both multiple-challenge protocols induced equally significant inflammation in CD38KO and WT mice. A single intranasal TNF-alpha challenge induced AHR in the WT but not in the CD38KO mice, whereas both mice developed AHR after 1 wk of challenges. The AHR was suppressed by extending the challenges for 4 wk in both mice, although to a larger magnitude in the WT than in the CD38KO mice. TNF-alpha increased ASM contractile properties in tracheal rings from WT but not from CD38KO mice. In conclusion, CD38 contributes to TNF-alpha-induced AHR after a brief airway exposure to the cytokine, likely by mediating changes in ASM contractile responses, and is associated with greater AHR remission following chronic airway exposure to TNF-alpha. The mechanisms involved in this remission remain to be determined.

The synergistic interactions of allergic lung inflammation and intratracheal cationic protein

RATIONALE

Airways hyperresponsiveness (AHR) is a hallmark feature of asthma, and can be caused by various disparate mechanisms. Mouse models of AHR have been useful for studying these mechanisms in isolation, but such models still typically do not exhibit the same degree of AHR as seen in severe human asthma. We hypothesized that more severe AHR in mice could be achieved by imbuing them with more than one mechanism of AHR.

OBJECTIVES

We sought to determine if the airway wall thickening accompanying allergic inflammation and the exaggerated smooth muscle shortening induced by intratracheal cationic protein could act together to produce a severe form of AHR.

METHODS

We used the forced oscillation technique to measure methacholine responsiveness in BALB/c mice that had been sensitized and challenged with ovalbumin followed by an intratracheal instillation of poly-l-lysine.

MEASUREMENTS AND MAIN RESULTS

We found that both ovalbumin and poly-l-lysine treatment alone caused moderate levels of AHR. When the two treatments were combined, however, they synergized in terms of their effect on lung stiffness to an extent that could even be fatal, reflecting a significantly enhanced level of airway closure.

CONCLUSIONS

Our results suggest that mechanistic synergy between airway wall thickening and exaggerated smooth muscle shortening produces a more germane mouse model of asthma that may have particular relevance to the pathophysiology of the acute severe asthma exacerbation.