Emphysema and Metalloelastase Expression in Mouse Lung Induced by Cigarette Smoke

Abstract

Cigarette smoke (CS) causes pulmonary emphysema in humans and elastin degradation plays a key role in its pathogenesis. Previous studies on CS-exposed animals have been equivocal and have not clearly demonstrated the progression of the disease. In this study, morphometry was used to assess lung modifications to alveolar septa, airspaces, elastic and collagen fibers, and alveolar macrophages. Male (n = 40) C57/BL6 mice were exposed 3 times/day, whole body, to CS from three cigarettes for 10, 20, 30, or 60 days. Control groups (n = 10) were sham-smoked or received no exposure (day 0, n = 10). Morphometry included measurements of volume fraction of alveolar septa and airspaces, elastic and collagen fibers, and surface fraction of elastic fibers and alveolar septa. Morphometrical differences in mice after 60 days of exposure were greater than those after 10, 20, or 30 days, suggesting a progression of the disease. Inflammatory lesions in the lungs of mice contained significantly more metalloelastase (MMP-12) in macrophages at 10, 20, and 30 days than in controls of mice exposed for 60 days. These results suggest that elastin degradation took place during development of pulmonary changes in mice exposed to CS, and activation of MMPs specific for elastin may be a determining factor for susceptibility to emphysema.

Human matrix metalloproteinases: An ubiquitarian class of enzymes involved in several pathological processes

“…Inflammatory lesions in mouse lung exposed to cigarette smoke is also associated with a significant increase of alveolar macrophages expressing MMP-12 (Valença et al, 2004).…”

Role of matrix metalloproteinases in the development of airway inflammation and remodeling

“…Indeed, MMP-12 generates elastin-derived peptides and experiments performed in modified Boyden chambers have shown that these elastin-derived peptides are chemotactic for monocytes (26). In a more recent study, it was reported that inflammatory lesions in the lungs of mice contained significantly more MMP-12 in macrophages at 10, 20, and 30 days of cigarette smoke exposure than in control mice exposed to 60 days (27). These results suggest that elastin degradation took place during the development of pulmonary change in mice exposed to cigarette smoke and activation of elastin-specific MMPs may be a determining factor for susceptibility to emphysema (27).…”

Development and evaluation of an inhalation chamber for in vivo tests

“…This constant and unidirectional flow carries body smells, excrement smells, and gases expelled by the animals themselves, preventing them from contaminating the internal environment of the chamber. Constant air renewal into the chamber is an advantage compared to chambers working with controlled pressure (Hemenway and Stedman 1981, Lopes 2004, Pereira 2004, those which do not have unidirectional flow, in which the chamber air outlet is near to the entrance (Bung et al1984, Vincent and Guénette 1997, Schenkel et al 2009), and inhalation boxes (Valença et al 2004, Komyia et al 2006, Bradley et al 2007, Takemoto et al 2008, Ito and Ito 2011.…”

“…Furthermore, apparatus containing an inhalation box (Valença et al 2004, Komyia et al 2006, Bradley et al 2007, Takemoto et al 2008, Ito and Ito 2011 and those that do not present a unidirectional flow of insufflated material (Hemenway and Stedman 1981, Bung et al 1984, Vincent and Guénette 1997, Lopes 2004, Pereira 2004, Schenkel et al 2009) are prone to the accumulation and deposition of such test materials. This may result in the administration of more than the required dose due to both accumulation inside the chamber and deposition on the animals' bodies.…”

“…To this end, the use of an inhalation chamber enables in vivo studies by mimicking clinical use of the drug, and it is of the utmost importance in the development of a medicine designed for pulmonary administration. Such an apparatus is also important in evaluating the toxicity of smokes and vapors encountered in human daily life, such as cigarette smoke (Shimazu et al 1990, Sakano 1993, Lalonde et al 1994, Valença et al 2004. Matthew et al (2001) used a model similar to that proposed in this study to assess lung damage caused by inhalation of smoke derived from burning wood, as well as during fire events.…”