Characterization of a structurally intact in situ lung model and comparison of naphthalene protein adducts generated in this model vs lung microsomes.

Airway epithelial cells are a susceptible site for injury by ambient air toxicants such as naphthalene that undergo P450-dependent metabolic activation. The metabolism of naphthalene in Clara cells to reactive intermediates that bind covalently to proteins correlates with cell toxicity. Although several proteins adducted by reactive naphthalene metabolites were identified in microsomal incubations, new methods that maintain the structural integrity of the lung are needed to examine protein targets. Therefore, we developed a method that involves inflation of the lungs via the trachea with medium containing (14)C-naphthalene followed by incubation in situ. The viability of this preparation is supported by maintenance of glutathione levels, rates of naphthalene metabolism, and exclusion of ethidium homodimer-1 from airway epithelium. Following in situ incubation, the levels of adduct per milligram of protein were measured in proteins obtained from bronchoalveolar lavage, epithelial cells, and remaining lung. The levels of adducted proteins obtained in lavage and epithelial cells were similar and were 20-fold higher than those in residual lung tissue. (14)C-Labeled adducted proteins were identified by matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry (MS) and quadrupole-TOF MS/MS. Major adducted proteins include cytoskeletal proteins, proteins involved in folding and translocation, ATP synthase, extracellular proteins, redox proteins, and selenium binding proteins. We conclude that in situ incubation maintains structural integrity of the lung while allowing examination of reactive intermediate activation and interaction with target cell proteins of the lung. The proteins adducted and identified from in situ incubations were not the same proteins identified from microsomal incubations.

Smooth muscle development during postnatal growth of distal bronchioles in infant rhesus monkeys.

Development of smooth muscle in conducting airways begins early in fetal life. Whereas the pattern and regulation of smooth muscle differentiation are well-defined, the impact of airway growth on the process is not. To evaluate the transformations in organization during postnatal growth, smooth muscle bundle organization (size, abundance, and orientation) was mapped in five generations of distal airways of infant rhesus monkeys (5 days and 1, 2, 3, and 6 mo old). On the basis of direct measurement of the bronchiole proximal to the terminal bronchiole, length increased by 2-fold, diameter by 1.35-fold, and surface area by 2.8-fold between 5 days and 6 mo of age. Smooth muscle bundle size was greater in proximal bronchioles than in respiratory bronchioles and did not change with age. However, relative bundle size decreased in proportion to airway size as the airways grew. Relative bundle abundance was constant regardless of airway generation or age. The distribution of smooth muscle bundle orientation changed with age in each airway generation, and there were significant changes in the terminal and respiratory bronchioles. We conclude that smooth muscle undergoes marked organizational changes as airways grow during postnatal development.