Histone deacetylase-2 and airway disease

The increased expression of inflammatory genes in inflammatory lung diseases is regulated by acetylation of core histones, whereas histone deacetylase-2 (HDAC2) suppresses inflammatory gene expression. Corticosteroids suppress inflammatory genes in asthma by inhibiting histone acetyltransferase and in particular by recruiting HDAC2 to the nuclear factor-kappaB-activated inflammatory gene complex. This involves deacetylation of the acetylated glucocorticoid receptor. In COPD, severe asthma and asthmatics who smoke, HDAC2 is reduced, thus preventing corticosteroids from suppressing inflammation. The reduction in HDAC2 appears to be secondary to increased oxidative and nitrative stress in the lungs. Antioxidants and inhibitors of nitric oxide synthesis may therefore restore corticosteroid sensitivity in COPD, but this can also be achieved by low concentrations of theophylline and curcumin, which act as HDAC activators. Theophylline is a direct inhibitor of oxidant-activated phosphoinositide-3-kinase-delta, which is involved in inactivation of HDAC2. In the future selective PI3Kdelta inhibitors and more direct activators of HDAC2 may be used to treat corticosteroid-resistant inflammatory diseases of the lung, including COPD, severe asthma and asthma in smokers.

Inhibition of inducible nitric oxide synthase in respiratory diseases

Nitric oxide (NO) is a key physiological mediator and disturbed regulation of NO release is associated with the pathophysiology of almost all inflammatory diseases. A multitude of inhibitors of NOSs (nitric oxide synthases) have been developed, initially with low or even no selectivity against the constitutively expressed NOS isoforms, eNOS (endothelial NOS) and nNOS (neuronal NOS). In the meanwhile these efforts yielded potent and highly selective iNOS (inducible NOS) inhibitors. Moreover, iNOS inhibitors have been shown to exert beneficial anti-inflammatory effects in a wide variety of acute and chronic animal models of inflammation. In the present mini-review, we summarize some of our current knowledge of inhibitors of the iNOS isoenzyme, their biochemical properties and efficacy in animal models of pulmonary diseases and in human disease itself. Moreover, the potential benefit of iNOS inhibition in animal models of COPD (chronic obstructive pulmonary disease), such as cigarette smoke-induced pulmonary inflammation, has not been explicitly studied so far. In this context, we demonstrated recently that both a semi-selective iNOS inhibitor {L-NIL [N6-(1-iminoethyl)-L-lysine hydrochloride]} and highly selective iNOS inhibitors (GW274150 and BYK402750) potently diminished inflammation in a cigarette smoke mouse model mimicking certain aspects of human COPD. Therefore, despite the disappointing results from recent asthma trials, iNOS inhibition could still be of therapeutic utility in COPD, a concept which needs to be challenged and validated in human disease.

Nitric oxide synthase isoenzyme expression and activity in peripheral lung tissue of patients with chronic obstructive pulmonary disease

RATIONALE

Nitric oxide (NO) is increased in the lung periphery of patients with chronic obstructive pulmonary disease (COPD). However, expression of the NO synthase(s) responsible for elevated NO has not been identified in the peripheral lung tissue of patients with COPD of varying severity.

OBJECTIVES

METHODS

Protein and mRNA expression of nitric oxide synthase type I (neuronal NOS [nNOS]), type II (inducible NOS [iNOS]), and type III (endothelial NOS [eNOS]) were quantified by Western blotting and reverse transcription-polymerase chain reaction, respectively, in specimens of surgically resected lung tissue from nonsmoker control subjects, patients with COPD of varying severity, and smokers without COPD, and in a lung epithelial cell line (A549). The effects of nitrative/oxidative stress on NOS expression and activity were also evaluated in vitro in A549 cells. nNOS nitration was quantified by immunoprecipitation and dimerization of nNOS was detected by low-temperature SDS-PAGE/Western blot in the presence of the peroxynitrite generator, 3-morpholinosydnonimine-N-ethylcarbamide (SIN1), in vitro and in vivo.

MEASUREMENTS AND MAIN RESULTS

Lung tissue from patients with severe and very severe COPD had graded increases in nNOS (mRNA and protein) compared with nonsmokers and normal smokers. Hydrogen peroxide (H(2)O(2)) and SIN1 as well as the cytokine mixture (IFN-gamma, IL-1beta, and tumor necrosis factor-alpha) increased mRNA expression and activity of nNOS in A549 cells in a concentration-dependent manner compared with nontreated cells. Tyrosine nitration resulted in an increase in nNOS activity in vitro, but did not affect its dimerization.

CONCLUSIONS

Patients with COPD have a significant increase in nNOS expression and activity that reflects the severity of the disease and may be secondary to oxidative stress.

Nitration of distinct tyrosine residues causes inactivation of histone deacetylase 2

Histone deacetylases (HDACs) are key molecules involved in epigenetic regulation of gene expression. We have previously demonstrated that oxidative stress caused a reduction in HDAC2, resulting in amplified inflammation and reduced corticosteroid responsiveness. Here we showed nitrative/oxidative stress reduced HDAC2 expression via nitration of distinct tyrosine residues. Peroxynitrite, hydrogen peroxide and cigarette smoke-conditioned medium reduced HDAC2 expression in A549 epithelial cells in vitro. This reduction was due to increased proteasomal degradation following ubiquitination rather than reduction of mRNA expression or stability. HDAC2 was nitrated under nitrative/oxidative stress and in the peripheral lung tissues of smokers and patients with chronic obstructive pulmonary disease. Mutagenesis studies replacing tyrosine (Y) residues with alanine revealed that Y253 is at least partly responsible for the proteasomal degradation of HDAC2 under nitrative stress. Thus, nitration of distinct tyrosine residues modifies both the expression and activity of HDAC2, having an impact on epigenetic regulation.