Mechanisms of airway hypersecretion and novel therapy

Oxytetracycline Inhibits Mucus Secretion and Inflammation in Human Airway Epithelial Cells

Oxytetracycline is a broad-spectrum antibiotic, but its nonantibacterial effects in the human respiratory tract are unknown. In this study, the effects of oxytetracycline on mucus secretion and inflammation were examined by PCR and ELISA in the human airway epithelial cell line NCI-H292. Oxytetracycline (10 μg/mL) significantly inhibited TNF-α-induced MUC5AC gene expression and MUC5AC protein levels in NCI-H292 cells. It also downregulated IL-8 and IL-1β gene expression and IL-1β protein levels. Our findings demonstrated that oxytetracycline suppressed mucus production and inflammation in human respiratory epithelial cells, providing further evidence for the usefulness of oxytetracycline for human airway inflammatory diseases.

Blocking of thromboxane A₂ receptor attenuates airway mucus hyperproduction induced by cigarette smoke

Cigarette smoking is one of the risk factors for chronic obstructive pulmonary disease (COPD). In this study, we investigated the effects of thromboxane A2 (TxA2) receptor antagonists on airway mucus production induced by cigarette smoke. Rats were exposed to cigarette smoke 1h/day, 6 days/week for 4 weeks. Seratrodast (2, 5, 10mg/kg day) was administered intragastrically prior to smoke exposure. Thromboxane B2 (TxB2) in the bronchoalveolar lavage fluid and lung tissues was determined by enzyme immunoassay. Airway mucus production was determined by alcin-blue/periodic acid sthiff (AB-PAS) staining, Muc5ac immunohistochemical staining, and RT-PCR. The phosphorylation of ERK and p38 was evaluated by Western blotting. Seratrodast reduced the overproduction of TxB2 in both bronchoalveolar lavage fluid and lung tissues. Cigarette smoke exposure markedly increased AB/PAS-stained goblet cells and rat Muc5ac expression in the airway, which was significantly attenuated by seratrodast administration. The induced phosphorylation of ERK and p38 was also attenuated by seratrodast. TxA2 receptor antagonist could reduce Muc5ac production induced by cigarette smoke in vivo, possibly through the mitogen-activated protein kinases (MAPK) signaling pathway.

Asian sand dust enhances allergen-induced th2 allergic inflammatory changes and mucin production in BALB/c mouse lungs

Purpose

Recent studies have reported that Asian sand dust (ASD) has a potential risk of aggravating airway inflammation. The purpose of this study was to investigate the effect of ASD on inflammation and mucin production in the airways of allergic mice.

Methods

Forty BALB/c female mice were divided into four groups: saline (group 1); ASD (group 2); ovalbumin (OVA) alone (group 3); and OVA+ASD (group 4). OVA-specific immunoglobulin E (IgE) in serum and interleukin (IL)-4, IL-5, IL-13, and interferon-gamma (IFN-γ) in bronchoalveolar lavage fluid (BALF) were measured by enzyme-linked immunosorbent assay (ELISA). Hematoxylin & eosin (H&E) and Periodic acid-Schiff (PAS) staining was performed on lung tissues. In addition, immunohistochemical staining for IL-4, IL-5, MUC5AC, and transforming growth factor alpha (TGF-α) was conducted.

Results

Serum IgE levels were significantly higher in group 4 than in group 3 (P<0.05). IL-4 and IL-5 in BALF were significantly higher in group 4 than in group 3 (P<0.05, respectively). Based on H&E staining, inflammatory cell numbers were significantly greater in group 4 than in the other groups (P<0.05). The number of PAS-positive cells was also significantly greater in groups 3 and 4 than in groups 1 and 2 (P<0.05). The numbers of IL-4 and IL-5-positive cells were higher in group 4 than in group 3 (P<0.05). The number of MUC5AC and TGF-α-positive cells were also higher in group 4 than in group 3 (P<0.05).

Conclusions

Our data suggest that ASD increases cytokine expression and mucin production in an allergic murine model. The increased inflammatory reactions were related to cytokine production.

Muco-ciliary differentiation of nasal epithelial cells is decreased after wound healing in vitro

BACKGROUND

Epithelial damage and modifications of cell differentiation are frequent in airway diseases with chronic inflammation, in which transforming growth factor-beta1 (TGF-beta1) plays an important role. The aim of this study was to evaluate the differentiation of human nasal epithelial cells (HNEC) after wound healing and the potential effects of TGF-beta1.

METHODS

Basal, mucus, and ciliated cells were characterized by cytokeratin-14, MUC5AC, and betaIV tubulin immunodetection, respectively. Their expression was evaluated in situ in nasal polyps and in an in vitro model of wound healing in primary cultures of HNEC after wound closure, under basal conditions and after TGF-beta1 supplementation. Using RT-PCR, the effects of TGF-beta1 on MUC5AC and DNAI1 genes, specifically transcribed in mucus and ciliated cells, were evaluated.

RESULTS

In situ, high TGF-beta1 expression was associated with low MUC5AC and betaIV tubulin expression. In vitro, under basal conditions, MUC5AC expression remained stable, cytokeratin-14 expression was strong and decreased with time, while betaIV tubulin expression increased. Transforming growth factor-beta1 supplementation downregulated MUC5AC and betaIV tubulin expression as well as MUC5AC and DNAI1 transcripts.

CONCLUSION

After a wound, differentiation into mucus and ciliated cells was possible and partially inhibited in vitro by TGF-beta1, a cytokine that may be involved in epithelial remodeling observed in chronic airway diseases.

The inhibitory effects of rebamipide on cigarette smoke-induced airway mucin production

Cigarette smoke may be the main cause of chronic bronchitis. Exposure of cigarette smoke induces the recruitment of inflammatory cells in the airway epithelium, and release of the tumor necrosis factor alpha (TNFalpha) from airways. Previous reports have shown that cigarette smoke induces goblet cell metaplasia by activating an epidermal growth factor receptor (EGFR) cascade, and that this results in mucin production. Rebamipide (2-(4-chlorobenzoylamino)-3-[2(1H)-quinolinon-4-yl] propionic acid, OPC-12759) directly inhibits the production of superoxide (O2-) and inhibits proinflammatory cytokines (such as TNFalpha and IL-8). In the present study, we aimed to analyze the inhibitory effects of rebamipide on TNFalpha and EGFR activation after cigarette smoke treatment in vitro and in vivo. NCl-H292 cells and Sprague-Dawley rats were used for in vitro and in vivo studies. In vitro studies, cigarette smoke solution was found to increase TNFalpha secretion, and EGFR-specific tyrosine phosphorylation, and to elevate MUC5AC production. These effects were inhibited dose-dependently by pretreatment with rebamipide (MUC5AC protein levels were inhibited from 44% to 17%, P<0.05). In vivo studies, cigarette smoke was found to cause inflammatory cell recruitment and to increase the secretion of TNFalpha in bronchoalveolar lavage (BAL) fluids (from 198+/-78 to 2270+/-158 pg/ml, P<0.01). Moreover, the pretreatment of rats with rebamipide inhibited goblet cell metaplasia and TNFalpha secretion, dose-dependently (from 2270+/-158 to 1377+/-112 pg/ml, P<0.05). In conclusion, the exposure of airway epithelium to cigarette smoke-induced TNFalpha production, neutrophil recruitment, activated EGFR, and caused MUC5AC mucin synthesis. Moreover, rebamipide was found to prevent this cigarette smoke-induced TNFalpha release, and mucin production.

Management of acute severe asthma

Asthma is a chronic inflammatory disorder that results in recurrent episodes of reversible airflow obstruction. Lung hyperinflation results from obstruction or dynamic airway collapse during exhalation. Obstruction and dynamic hyperinflation both play a deleterious role in asthma. Patients who present with asthma have increased inspiratory work of breathing due to lung hyperinflation and auto-positive end-expiratory pressure (auto-PEEP). The goal of acute care treatment is to reverse bronchoconstriction and inflammation, thus reducing dynamic hyperinflation, so that breathing is restored to baseline, unlabored, quiet breathing.

Mucosal changes in rhinitis medicamentosa

To evaluate the nasal mucosal changes in rhinitis medicamentosa (RM), especially those related to goblet cells and subepithelial glands, we studied specimens of the inferior turbinate mucosa from 8 patients with RM, 8 patients with chronic hypertrophic rhinitis (CHR), and 5 patients with normal nasal mucosa. All specimens were assessed by electron microscopy and immunohistochemical study. Under a scanning electron microscope, hyperplasia of goblet cells was most prominent in the RM group, and an increased number of gland openings was evident in the RM and CHR groups. In addition, the immunoreactivity of epidermal growth factor receptor staining was strongest in the hyperplastic epithelium of the RM group. According to our results, it is feasible that the mucosa of patients with RM is in a chronic inflammatory, hypersecretory state. Degenerative changes in the secretory elements may cause impairment of mucociliary transport and may be responsible for the nasal obstruction and posterior nasal drip in RM.

Role of hyaluronan and reactive oxygen species in tissue kallikrein-mediated epidermal growth factor receptor activation in human airways

In human airways, oxidative stress-induced submucosal gland cell hypertrophy and hyperplasia, histological features of chronic bronchitis, have been linked to epidermal growth factor receptor (EGFR) activation. To explore mechanisms of oxidative stress-induced EGFR activation and signaling, primary cultures of human tracheal submucosal gland (SMG) cells were used to assess EGFR ligand release, EGFR phosphorylation, p44/42 MAPK phosphorylation, and mucin 5AC synthesis in response to reactive oxygen species generated by xanthine/xanthine oxidase (X/XO). Exposure to X/XO increased release of epidermal growth factor (EGF) from these cells, thereby activating EGFR, phosphorylating MAPK, and increasing mucin 5AC production. The importance of EGF was confirmed by transfection of small interfering RNA inhibiting pro-EGF production, which resulted in inhibition of EGFR and MAPK phosphorylation despite X/XO exposure. Blocking signaling by using specific protease inhibitors showed that tissue kallikrein (TK) processed pro-EGF in response to X/XO. Airway TK is bound and inactivated by luminal hyaluronan (HA), and treatment of submucosal gland cells with X/XO induced HA depolymerization and TK activation. These events were blocked by reactive oxygen species scavengers and addition of exogenous excess HA and TK inhibitors. Thus, HA plays a crucial role in regulating airway TK activity and thereby TK-mediated release of active EGF from human SMG cells. Sustained HA depolymerization is expected to cause TK activation, EGF release, and EGFR signaling and to lead to SMG cell hypertrophy and hyperplasia as well as mucus hypersecretion with subsequent airflow obstruction.

Osmotic stimuli increase clearance of mucus in patients with mucociliary dysfunction

Mucociliary dysfunction results in mucus accumulation, airway obstruction, bacterial colonization, recurrent infective exacerbations, and an increase in morbidity and mortality. Studies in patients with cystic fibrosis, established that inhalation of hypertonic saline (HS) increases clearance of mucus acutely in a dose-dependent manner. Clearance over 90 min was 23.8 +/- 4.0% and 26.0 +/- 3.1% in response to 7% and 12% saline, which was significantly enhanced compared to 12.7 +/- 1.4% and 19.7 +/- 3.1% in response to 0.9% and 3% saline. Mannitol (approximately 300 mg) inhaled as a dry powder had a marked acute effect in patients with bronchiectasis. Clearance over 75 min was 34.0 +/- 5.0% with mannitol, 17.4 +/- 3.8% with control, and 11.7 +/- 4.4% at baseline. Further studies in patients with bronchiectasis showed that mannitol reduces the 24-h retention of radiolabeled mucus, suggesting that the effect of mannitol extends beyond the acute phase. Mannitol helped patients to clear mucus within 2 h that would have taken 24 h to clear without mannitol. A further study in CF patients showed that mannitol was equally effective as 6% HS at improving ciliary and cough clearance. The total clearance over 120 min with mannitol (27.6 +/- 3.7%) and with HS (31.0 +/- 5.5%) was significantly increased compared to their respective controls (18.6 +/- 3.8% and 20.9 +/- 3.6%). These preliminary results suggest that long-term treatment with HS or mannitol may benefit patients with mucociliary dysfunction.