Prostacyclin prevents pulmonary endothelial cell apoptosis induced by cigarette smoke

Pulmonary vascular involvement in COPD

Alterations in pulmonary vessel structure and function are highly prevalent in patients with COPD. Vascular abnormalities impair gas exchange and may result in pulmonary hypertension, which is one of the principal factors associated with reduced survival in COPD patients. Changes in pulmonary circulation have been identified at initial disease stages, providing new insight into their pathogenesis. Endothelial cell damage and dysfunction produced by the effects of cigarette smoke products or inflammatory elements is now considered to be the primary alteration that initiates the sequence of events resulting in pulmonary hypertension. Cellular and molecular mechanisms involved in this process are being extensively investigated. Progress in the understanding of the pathobiology of pulmonary hypertension associated with COPD may provide the basis for a new therapeutic approach addressed to correct the imbalance between endothelium-derived vasoactive agents. The safety and efficacy of endothelium-targeted therapy in COPD-associated pulmonary hypertension warrants further investigation in randomized clinical trials.

Distal airways in mice exposed to cigarette smoke: Nrf2-regulated genes are increased in Clara cells

Cigarette smoke (CS) is the main risk factor for chronic obstructive pulmonary disease (COPD). Terminal bronchioles are critical zones in the pathophysiology of COPD, but little is known about the cellular and molecular changes that occur in cells lining terminal bronchioles in response to CS. We subjected C57BL/6 mice to CS (6 d/wk, up to 6 mo), looked for morphologic changes lining the terminal bronchioles, and used laser capture microdissection to selectively isolate cells in terminal bronchioles to study gene expression. Morphologic and immunohistochemical analyses showed that Clara cell predominance remained despite 6 months of CS exposure. Since Clara cells have a role in protection against oxidative stress, we focused on the expression of antioxidant/detoxification genes using microarray analysis. Of the 35 antioxidant/detoxification genes with at least 2.5-fold increased expression in response to 6 months of CS exposure, 21 were NF-E2-related factor 2 (Nrf2)-regulated genes. Among these were cytochrome P450 1b1, glutathione reductase, thioredoxin reductase, and members of the glutathione S-transferase family, as well as Nrf2 itself. In vitro studies using immortalized murine Clara cells (C22) showed that CS induced the stabilization and nuclear translocation of Nrf2, which correlated with the induction of antioxidant and detoxification genes. Furthermore, decreasing Nrf2 expression by siRNA resulted in a corresponding decrease in CS-induced expression of several antioxidant and detoxification genes by C22 cells. These data suggest that the protective response by Clara cells to CS exposure is predominantly regulated by the transcription factor Nrf2.

Molecular pathogenesis of emphysema

Emphysema is one manifestation of a group of chronic, obstructive, and frequently progressive destructive lung diseases. Cigarette smoking and air pollution are the main causes of emphysema in humans, and cigarette smoking causes emphysema in rodents. This review examines the concept of a homeostatically active lung structure maintenance program that, when attacked by proteases and oxidants, leads to the loss of alveolar septal cells and airspace enlargement. Inflammatory and noninflammatory mechanisms of disease pathogenesis, as well as the role of the innate and adaptive immune systems, are being explored in genetically altered animals and in exposure models of this disease. These recent scientific advances support a model whereby alveolar destruction resulting from a coalescence of mechanical forces, such as hyperinflation, and more recently recognized cellular and molecular events, including apoptosis, cellular senescence, and failed lung tissue repair, produces the clinically recognized syndrome of emphysema.

Impaired flow-mediated dilation is associated with low pulmonary function and emphysema in ex-smokers: the Emphysema and Cancer Action Project (EMCAP) Study

RATIONALE

Basic science research suggests a causal role for endothelial dysfunction in chronic obstructive pulmonary disease (COPD). Clinical studies examining endothelial function are lacking, particularly early in the disease. Flow-mediated dilation (FMD) is a physiologic measure of endothelial reactivity to endogenous nitric oxide.

OBJECTIVES

We hypothesized that lower FMD among former smokers would be associated with lower post-bronchodilator FEV(1), higher percentage of emphysema using computed tomography (CT) and lower diffusing capacity.

METHODS

We measured FMD, pulmonary function, and CT percentage of emphysema in a random sample of 107 cotinine-confirmed former smokers in the ongoing EMCAP study. FMD was defined as percentage change in the brachial artery diameter with reactive hyperemia. Generalized additive models were used to adjust for potential confounders and assess linearity.

MEASUREMENTS AND MAIN RESULTS

Mean age of participants was 71 +/- 5 years, 46% were female, and pack-years averaged 48 +/- 26. Mean FMD was 3.8 +/- 3.1%; mean post-bronchodilator FEV(1), 2.3 +/- 0.8 L; and mean CT percentage of emphysema, 26 +/- 10%. A 1 SD decrease in FMD was associated with a 132-ml (95% confidence interval, 16-248 ml; P = 0.03) decrement in post-bronchodilator FEV(1) and a 2.6% (95% confidence interval, 0.5-4.7%; P = 0.02) increase in CT percentage of emphysema in fully adjusted models. These associations were linear across the spectrum from normality to disease, independent of smoking history, and also significant among participants without COPD. Associations with diffusing capacity were consistent but nonsignificant (P = 0.09). The FMD-FEV(1) association was entirely attributable to percentage of emphysema.

CONCLUSIONS

Impaired endothelial function, as measured by FMD, was associated with lower FEV(1) and higher CT percentage of emphysema in former smokers early in COPD.