Maturational changes in airway remodeling after chronic exposure to ovalbumin in sensitized guinea pigs: role of cell renewal of airway resident cells

[Effects of montelukast sodium and bacterial lysates on airway remodeling and expression of transforming growth factor-β1 and Smad7 in guinea pigs with bronchial asthma]

OBJECTIVE

To study the effect of montelukast sodium (MK), a leukotriene receptor antagonist, and bacterial lysates (OM-85BV), used alone or in combination, on airway remodeling and the expression of transforming growth factor-β1 (TGF-β1) and Smad7 in guinea pigs with bronchial asthma and their correlation.

METHODS

A total of 40 male Hartley guinea pigs were randomly divided into normal control group, asthma group, MK group, OM-85BV group, and MK+OM-85BV group, with 8 guinea pigs in each group. Intraperitoneal injection of 10% ovalbumin (OVA) for sensitization and aerosol inhalation of 1% OVA for challenge were performed to establish a model of airway remodeling of asthma in all of the groups apart from the normal control group, which were treated with normal saline. In the stage of challenge by aerosol inhalation, the guinea pigs in the MK, OM-85BV, and MK+OM-85BV groups were given corresponding suspension by gavage, and those in the normal control and asthma groups were given an equal volume of normal saline by gavage. Bronchoalveolar lavage fluid (BALF) of the guinea pigs was collected within 24 hours after challenge, and ELISA was used to measure the levels of TGF-β1 and Smad7 in BALF. The guinea pigs were sacrificed and the pathological section of lung tissue was prepared to observe the degree of airway remodeling. An image analysis technique was used to measure perimeter of the basement membrane (Pbm), total bronchial wall area (Wat), and airway bronchial smooth muscle area (Wam). Pearson linear regression was used to investigate the correlation between two variables.

RESULTS

According to the lung pathological section, compared with the normal control group, the asthma, MK, OM-85BV, and MK+OM-85BV groups had significant thickening of bronchial smooth muscle and alveolar wall, significantly higher Wat/Pbm and Wam/Pbm, a significantly higher level of TGF-β1, and a significantly lower level of Smad7 (P<0.05). Compared with the asthma group, the MK, OM-85BV, and MK+OM-85BV groups had a significant improvement in pathological injury, significantly lower Wat/Pbm and Wam/Pbm, a significantly lower level of TGF-β1, and a significantly higher level of Smad7 (P<0.05). The MK+OM-85BV group had significantly greater improvements than the MK group and the OM-85BV group (P<0.05). The expression of TGF-β1 was negatively correlated with that of Smad7 and positively correlated with Wat/Pbm and Wam/Pbm, and the expression of Smad7 was negatively correlated with Wat/Pbm and Wam/Pbm (P<0.01).

CONCLUSIONS

MK and OM-85BV, used alone or in combination, can reduce airway remodeling in guinea pigs with asthma, and MK combined with OM-85BV has the best effect, possibly by reducing TGF-β1 expression, increasing Smad7 expression, and improving the TGF-β1/Smad7 imbalance.

Changes in lung sounds during asthma progression in a guinea pig model

BACKGROUND

Lung sound analysis is useful for objectively evaluating airways even in children with asymptomatic asthma. However, the relationship between lung sounds and morphological changes in the airways has not been elucidated. We examined the relationship between lung sounds and chronic morphological changes in the airways during the progression of asthma from onset in guinea pigs.

METHODS

Eleven male guinea pigs were examined; of these, seven were used as asthma models and four as controls. The asthma models were sensitized and repeatedly challenged by inhaling albumin chicken egg. We measured lung sounds and lung function twice a week for 21 weeks. After the final antigen challenge, the lungs were excised for histological examination. We measured the ratio of airway wall thickness to the total airway area and the ratio of the internal area to the total airway area in the trachea, third bronchi, and terminal bronchioles.

RESULTS

Among the lungs sounds, the difference between the two groups was greatest with respect to inspiratory sound intensity. The ratio of airway wall thickness to the total airway area of the terminal bronchioles was greater in the asthma models than in the controls, and it correlated best with the changes in inspiratory sound intensity in the 501-1000-Hz range (r = 0.76, p < 0.003).

CONCLUSIONS

Lung sound intensity in the middle frequency range from 501 to 1000 Hz correlated with peripheral airway wall thickness. Inspiratory sound intensity appeared to be an indicator of morphological changes in small airways in asthma.

Endotoxin inhalation alters lung development in neonatal mice

BACKGROUND

Childhood asthma is a significant public health problem. Epidemiologic evidence suggests an association between childhood asthma exacerbations and early life exposure to environmental endotoxin. Although the pathogenesis of endotoxin-induced adult asthma is well studied, questions remain about the impact of environmental endotoxin on pulmonary responsiveness in early life.

METHODS

We developed a murine model of neonatal/juvenile endotoxin exposures approximating those in young children and evaluated the lungs inflammatory and remodeling responses.

RESULTS

Persistent lung inflammation induced by the inhalation of endotoxin in early life was demonstrated by the influx of inflammatory cells and pro-inflammatory mediators to the airways and resulted in abnormal alveolarization.

CONCLUSIONS

Results of this study advance the understanding of the impact early life endotoxin inhalation has on the lower airways, and demonstrates the importance of an experimental design that approximates environmental exposures as they occur in young children.

Characteristic features of allergic airway inflammation in a murine model of infantile asthma

BACKGROUND

The pathophysiology of infantile asthma may differ from that in older children or in adults, partly because of the different immune response depending upon maturation. In adult mice, the sensitizing dose of antigen is known to be critical to the polarized development of helper T cell subsets and allergic airway inflammation. We wanted to know the characteristics of allergic airway inflammation of infantile asthma by developing a murine model.

METHODS

BALB/C mice at different stages of maturation (juvenile: 3 days after birth; adult: 8 weeks of age) were sensitized with 10 or 1,000 microg ovalbumin (OVA) or vehicle. The animals were then challenged with aerosolized OVA or saline once a day during 6 consecutive days. After the final challenge, bronchial hyperresponsiveness (BHR), bronchoalveolar lavage fluid (BALF), histological changes in the airways and immunological status were examined.

RESULTS

In both juvenile and adult animals, sensitization with 10 microg OVA induced the T helper 2 response (elevated IL-4 and decreased IFN-gamma levels). BHR, airway eosinophilia, the inflammatory cell infiltration, goblet cell metaplasia (GCM), and IgE antibody production were more prominent in animals given this dose than 1,000 microg OVA. Among these responses, GCM as well as BALF IL-4, and BHR were comparable between juvenile and adult animals, whereas other parameters were lower in juvenile animals, especially in those given 1,000 microg OVA.

CONCLUSION

GCM and, consequently, airway mucus hypersecretion may be an important component of allergic airway inflammation in infantile asthma.