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      Update on the pathological processes, molecular biology, and clinical utility of N-acetylcysteine in chronic obstructive pulmonary disease

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          Chronic obstructive pulmonary disease (COPD) is a common and morbid disease characterized by high oxidative stress. Its pathogenesis is complex, and involves excessive oxidative stress (redox imbalance), protease/antiprotease imbalance, inflammation, apoptosis, and autoimmunity. Among these, oxidative stress has a pivotal role in the pathogenesis of COPD by initiating and mediating various redox-sensitive signal transduction pathways and gene expression. The protective physiological mechanisms of the redox balance in the human body, their role in the pathogenesis of COPD, and the clinical correlation between oxidative stress and COPD are reviewed in this paper. N-acetylcysteine (NAC) is a mucolytic agent with both antioxidant and anti-inflammatory properties. This paper also reviews the use of NAC in patients with COPD, especially the dose-dependent properties of NAC, eg, its effects on lung function and the exacerbation rate in patients with the disease. Earlier data from BRONCUS (the Bronchitis Randomized on NAC Cost-Utility Study) did not suggest that NAC was beneficial in patients with COPD, only indicating that it reduced exacerbation in an “inhaled steroid-naïve” subgroup. With regard to the dose-dependent properties of NAC, two recent randomized controlled Chinese trials suggested that high-dose NAC (1,200 mg daily) can reduce exacerbations in patients with COPD, especially in those with an earlier (moderately severe) stage of disease, and also in those who are at high risk of exacerbations. However, there was no significant effect on symptoms or quality of life in patients receiving NAC. Further studies are warranted to investigate the effect of NAC at higher doses in non-Chinese patients with COPD.

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          Most cited references 110

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          Cigarette smoke contains two very different populations of free radicals, one in the tar and one in the gas phase. The tar phase contains several relatively stable free radicals; we have identified the principal radical as a quinone/hydroquinone (Q/QH2) complex held in the tarry matrix. We suggest that this Q/QH2 polymer is an active redox system that is capable of reducing molecular oxygen to produce superoxide, eventually leading to hydrogen peroxide and hydroxyl radicals. In addition, we have shown that the principal radical in tar reacts with DNA in vitro, possibly by covalent binding. The gas phase of cigarette smoke contains small oxygen- and carbon-centered radicals that are much more reactive than are the tar-phase radicals. These gas-phase radicals do not arise in the flame, but rather are produced in a steady state by the oxidation of NO to NO2, which then reacts with reactive species in smoke such as isoprene. We suggest that these radicals and the metastable products derived from these radical reactions may be responsible for the inactivation of alpha 1-proteinase inhibitor by fresh smoke. Cigarette smoke oxidizes thiols to disulfides; we suggest the active oxidants are NO and NO2. The effects of smoke on lipid peroxidation are complex, and this is discussed. We also discuss the toxicological implications for the radicals in smoke in terms of a number of radical-mediated disease processes, including emphysema and cancer.
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            Decreased histone deacetylase activity in chronic obstructive pulmonary disease.

            Chronic obstructive pulmonary disease (COPD) is characterized by chronic airway inflammation that is greater in patients with advanced disease. We asked whether there is a link between the severity of disease and the reduction in histone deacetylase (HDAC) activity in the peripheral lung tissue of patients with COPD of varying severity. HDAC is a key molecule in the repression of production of proinflammatory cytokines in alveolar macrophages. HDAC activity and histone acetyltransferase (HAT) activity were determined in nuclear extracts of specimens of surgically resected lung tissue from nonsmokers without COPD, patients with COPD of varying severity, and patients with pneumonia or cystic fibrosis. Alveolar macrophages from nonsmokers, smokers, and patients with COPD and bronchial-biopsy specimens from nonsmokers, healthy smokers, patients with COPD, and those with mild asthma were also examined. Total RNA extracted from lung tissue and macrophages was used for quantitative reverse-transcriptase-polymerase-chain-reaction assay of HDAC1 through HDAC8 and interleukin-8. Expression of HDAC2 protein was quantified with the use of Western blotting. Histone-4 acetylation at the interleukin-8 promoter was evaluated with the use of a chromatin immunoprecipitation assay. Specimens of lung tissue obtained from patients with increasing clinical stages of COPD had graded reductions in HDAC activity and increases in interleukin-8 messenger RNA (mRNA) and histone-4 acetylation at the interleukin-8 promoter. The mRNA expression of HDAC2, HDAC5, and HDAC8 and expression of the HDAC2 protein were also lower in patients with increasing severity of disease. HDAC activity was decreased in patients with COPD, as compared with normal subjects, in both the macrophages and biopsy specimens, with no changes in HAT activity, whereas HAT activity was increased in biopsy specimens obtained from patients with asthma. Neither HAT activity nor HDAC activity was changed in lung tissue from patients with cystic fibrosis or pneumonia. Patients with COPD have a progressive reduction in total HDAC activity that reflects the severity of the disease. Copyright 2005 Massachusetts Medical Society.
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              Requirement for macrophage elastase for cigarette smoke-induced emphysema in mice.

              To determine which proteinases are responsible for the lung destruction characteristic of pulmonary emphysema, macrophage elastase-deficient (MME-/-) mice were subjected to cigarette smoke. In contrast to wild-type mice, MME-/- mice did not have increased numbers of macrophages in their lungs and did not develop emphysema in response to long-term exposure to cigarette smoke. Smoke-exposed MME-/- mice that received monthly intratracheal instillations of monocyte chemoattractant protein-1 showed accumulation of alveolar macrophages but did not develop air space enlargement. Thus, macrophage elastase is probably sufficient for the development of emphysema that results from chronic inhalation of cigarette smoke.

                Author and article information

                Int J Chron Obstruct Pulmon Dis
                Int J Chron Obstruct Pulmon Dis
                International Journal of COPD
                International Journal of Chronic Obstructive Pulmonary Disease
                Dove Medical Press
                06 August 2014
                : 9
                : 825-836
                Medical and Geriatric Department, Kwong Wah Hospital, Hong Kong Special Administrative Region
                Author notes
                Correspondence: Hoi Nam Tse, Medical and Geriatric Department, Kwong Wah Hospital, Waterloo Road, Yau Ma Tei, Hong Kong Special Administrative Region, Tel +852 2332 2311, Fax +852 3517 6209, Email drhoinam@
                © 2014 Tse and Tseng. This work is published by Dove Medical Press Limited, and licensed under Creative Commons Attribution – Non Commercial (unported, v3.0) License

                The full terms of the License are available at Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.



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