Conserved responses to trichostatin A in rodent lungs exposed to endotoxin or stretch

Potential therapeutic interventions of plant-derived isoflavones against acute lung injury

Acute lung injury (ALI) is a life-threatening syndrome that possibly leads to high morbidity and mortality as no therapy exists. Several natural ingredients with negligible adverse effects have recently been investigated to possibly inhibit the inflammatory pathways associated with ALI at the molecular level. Isoflavones, as phytoestrogenic compounds, are naturally occurring bioactive compounds that represent the most abundant category of plant polyphenols (Leguminosae family). A broad range of therapeutic activities of isoflavones, including antioxidants, chemopreventive, anti-inflammatory, antiallergic and antibacterial potentials, have been extensively documented in the literature. Our review exclusively focuses on the possible anti-inflammatory, antioxidant role of botanicals'-derived isoflavones against ALI and their immunomodulatory effect in experimentally induced ALI. Despite the limited scope covering their molecular mechanisms, isoflavones substantially contributed to protecting from ALI via inhibiting toll-like receptor 4 (TLR4)/Myd88/NF-κB pathway and subsequent cytokines, chemokines, and adherent proteins. Nonetheless, future research is suggested to fill the gap in elucidating the protective roles of isoflavones to alleviate ALI concerning antioxidant potentials, inhibition of the inflammatory pathways, and associated molecular mechanisms.

Inflammatory processes during acute respiratory distress syndrome: a complex system

PURPOSE OF REVIEW

ARDS is a severe pulmonary disease characterized by inflammation. However, inflammation-directed therapies have yet failed to improve the outcome in ARDS patients. One of the reasons may be the underestimated complexity of inflammation. Here, we summarize recent insights into the complex interrelations between inflammatory circuits.

RECENT FINDINGS

Gene expression analysis from animal models or from patients with ARDS, sepsis or trauma show an enormous number of differentially expressed genes with highly significant overlaps between the various conditions. These similarities, however, should not obscure the complexity of inflammation. We suggest to consider inflammation in ARDS as a system controlled by scale-free networks of genome-wide molecular interaction with hubs (e.g. NFκB, C/EBPβ, ATF3), exhibiting nonlinear emergence and the ability to adapt, meaning for instance that mild and life-threatening inflammation in ARDS are distinct processes. In order to comprehend this complex system, it seems necessary to combine model-driven simulations, data-driven modelling and hypothesis-driven experimental studies. Recent experimental studies have illustrated how several regulatory circuits interact during pulmonary inflammation, including the resolution of inflammation, the inflammasome, autophagy and apoptosis.

SUMMARY

We suggest that therapeutic interventions in ARDS should be based on a systems approach to inflammation.

Attenuated Airway Epithelial Cell Interleukin-22R1 Expression in the Infant Nonhuman Primate Lung

Respiratory tract infections are a leading cause of morbidity and mortality in children under 5 years of age. Increased susceptibility to infection is associated with deficiencies in immunity during early childhood. Airway epithelium represents the first line of mucosal defense against inhaled pathogens. However, little is known about epithelial immune mechanisms in the maturing lung. IL-22 and its receptor IL-22R1 are important in host defense and repair of epithelial barriers. The objective of this study was to determine whether a quantitative difference in IL-22R1 exists between infant and adult airways using the rhesus macaque monkey as a model of childhood lung development. Immunofluorescence staining of tracheal tissue revealed minimal expression of IL-22R1 in epithelium at 1 month of age, with a progressive increase in fluorescence-positive basal cells through 1 year of age. Western blot analysis of tracheal lysates confirmed significant age-dependent differences in IL-22R1 protein content. Further, primary tracheobronchial epithelial cell cultures established from infant and adult monkeys showed differential IL-22R1 mRNA and protein expression in vitro. To begin to assess the regulation of age-dependent IL-22R1 expression in airway epithelium, the effect of histone deacetylase and DNA methyltransferase inhibitors was evaluated. IL-22R1 mRNA in adult cultures was not altered by 5-aza-2'-deoxycytidine or trichostatin A. IL-22R1 mRNA in infant cultures showed no change with 5-aza-2'-deoxycytidine but was significantly increased after trichostatin A treatment; however, IL-22R1 protein did not increase concurrently. These data suggest that IL-22R1 in airway epithelium is regulated, in part, by epigenetic mechanisms that are dependent on chronologic age.

Protective effects of thoracic epidural anesthesia on hypoxia-induced acute lung injury in rabbits

The mechanism underlying the effect of thoracic epidural anesthesia (TEA) on hypoxia-induced acute lung injury (ALI) is currently unknown. In the present study, a rabbit acute lung injury model was established to investigate the effects of TEA on inflammatory factors, pulmonary surfactant and ultrastructure. A total of 56 rabbits were randomly assigned to four groups (n=14 per group): Control group (Group C), hypoxia group (Group H), sevoflurane group (Group S) and combined sevoflurane-epidural anesthesia group (Group ES). The ALI model was considered to have been successfully induced when the ratio of arterial oxygen partial pressure to fractional inspired oxygen was <300. The correct placement of a catheter for TEA was confirmed using epidurography. ALI was maintained for 3 h. Arterial blood samples were collected from all groups during spontaneous breathing (T₀) and at 3 h after ALI induction (T₅) in order to evaluate the serum levels of interleukin (IL)-6, IL-8 and IL-10. Bronchoalveolar lavage fluid was harvested to determine the total phospholipid, saturated phosphatidylcholine and total protein levels. Furthermore, the dry/wet weight ratio and the mRNA expression levels of IL-6, IL-8 and IL-10 in the lung tissue were determined using ELISA. In addition, light and transmission electron microscopy and histological techniques were used to examine the morphology of alveolar type II cells in the rat lung tissue. The results indicate that changes of serum IL-6, IL-8 and IL-10 levels following ALI were consistent with the changes in the mRNA expression levels of IL-6, IL-8 and IL-10 in the lung tissue. TEA attenuated these changes and thus reduced the severity of the ALI. In addition, TEA improved the alveolar structure, reduced the number of polymorphonuclear cells and mitigated the damage of lamellar bodies. In summary, the results of the present study indicate that TEA reduces lung tissue damage by inhibiting systemic and local inflammation, decreasing the inactivation of pulmonary surfactant and improving the alveolar ultrastructure following ALI.

Ventilation-induced lung injury

Mechanical ventilation (MV) is, by definition, the application of external forces to the lungs. Depending on their magnitude, these forces can cause a continuum of pathophysiological alterations ranging from the stimulation of inflammation to the disruption of cell-cell contacts and cell membranes. These side effects of MV are particularly relevant for patients with inhomogeneously injured lungs such as in acute lung injury (ALI). These patients require supraphysiological ventilation pressures to guarantee even the most modest gas exchange. In this situation, ventilation causes additional strain by overdistension of the yet non-injured region, and additional stress that forms because of the interdependence between intact and atelectatic areas. Cells are equipped with elaborate mechanotransduction machineries that respond to strain and stress by the activation of inflammation and repair mechanisms. Inflammation is the fundamental response of the host to external assaults, be they of mechanical or of microbial origin and can, if excessive, injure the parenchymal tissue leading to ALI. Here, we will discuss the forces generated by MV and how they may injure the lungs mechanically and through inflammation. We will give an overview of the mechanotransduction and how it leads to inflammation and review studies demonstrating that ventilator-induced lung injury can be prevented by blocking pathways of mechanotransduction or inflammation.

Novel therapeutic strategies for lung disorders associated with airway remodelling and fibrosis

Inflammatory cell infiltration, cytokine release, epithelial damage, airway/lung remodelling and fibrosis are central features of inflammatory lung disorders, which include asthma, chronic obstructive pulmonary disease, acute respiratory distress syndrome and idiopathic pulmonary fibrosis. Although the lung has some ability to repair itself from acute injury, in the presence of ongoing pathological stimuli and/or insults that lead to chronic disease, it no longer retains the capacity to heal, resulting in fibrosis, the final common pathway that causes an irreversible loss of lung function. Despite inflammation, genetic predisposition/factors, epithelial-mesenchymal transition and mechanotransduction being able to independently contribute to airway remodelling and fibrosis, current therapies for inflammatory lung diseases are limited by their ability to only target the inflammatory component of the disease without having any marked effects on remodelling (epithelial damage and fibrosis) that can cause lung dysfunction independently of inflammation. Furthermore, as subsets of patients suffering from these diseases are resistant to currently available therapies (such as corticosteroids), novel therapeutic approaches are required to combat all aspects of disease pathology. This review discusses emerging therapeutic approaches, such as trefoil factors, relaxin, histone deacetylase inhibitors and stem cells, amongst others that have been able to target airway inflammation and airway remodelling while improving related lung dysfunction. A better understanding of the mode of action of these therapies and their possible combined effects may lead to the identification of their clinical potential in the setting of lung disease, either as adjunct or alternative therapies to currently available treatments.

Epigenetics in asthma and COPD

Epigenetic mechanisms are likely to play a role in many complex diseases, the extent of which we only beginning to understand. COPD and asthma are two respiratory diseases subject to strong environmental influences depending on underlying genetic susceptibility. Epigenetic mechanisms such as DNA methylation, histone modification and microRNA may be involved in these processes by modulating environmental effects to influence disease development. Given their demonstrated modifiable nature, epigenetic mechanisms may open new possibilities for therapeutic intervention. Here we give an overview of recent developments in the field of respiratory epigenetics in relation to asthma and COPD in the context of our current understanding of mechanisms leading to such diseases.

Using the one-lung method to link p38 to pro-inflammatory gene expression during overventilation in C57BL/6 and BALB/c mice

INTRODUCTION

The mechanisms of ventilator-induced lung injury (VILI), including the role of MAP kinases, are frequently studied in different mouse strains. A useful model for such studies is the isolated perfused mouse lung. As a further development we present the one-lung method that permits to continue perfusion and ventilation of the right lung after removal of the left lung. This method was used to compare the effect of high pressure ventilation (HPV) on pro-inflammatory signaling events in two widely used mouse strains (C57BL/6, BALB/c) and to further define the role of p38 in VILI.

METHODS

Lungs were perfused and ventilated for 30 min under control conditions before they were randomized to low (8 cm H(2)O) or high (25 cm H(2)O) pressure ventilation (HPV) for 210 min, with the left lung being removed after 180 min. In the left lung we measured the phosphorylation of p38, JNK, ERK and Akt kinase, and in the right lung gene expression and protein concentrations of Il1b, Il6, Tnf, Cxcl1, Cxcl2, and Areg.

RESULTS

Lung mechanics and kinase activation were similar in both mouse strains. HPV increased all genes (except Tnf in BALB/c) and all mediators in both strains. The gene expression of mRNA for Il1b, Il6, Cxcl1 and Cxcl2 was higher in BALB/c mice. Backward regression of the kinase data at t = 180 min with the gene and protein expression data at t = 240 min suggested that p38 controls HPV-induced gene expression, but not protein production. This hypothesis was confirmed in experiments with the p38-kinase inhibitor SB203580.

CONCLUSIONS

The one-lung method is useful for mechanistic studies in the lungs. While C57BL/6 show diminished pro-inflammatory responses during HPV, lung mechanics and mechanotransduction processes appear to be similar in both mouse strains. Finally, the one-lung method allowed us to link p38 to gene expression during VILI.

Effects of the histone deacetylase inhibitor, trichostatin A, in a chronic allergic airways disease model in mice

There is a need for new asthma therapies that can concurrently address airway remodeling, airway hyperresponsiveness and progressive irreversible loss of lung function, in addition to inhibiting inflammation. Histone deacetylase inhibitors (HDACi) alter gene expression by interfering with the removal of acetyl groups from histones. The HDACi trichostatin A (TSA) has pleiotropic effects targeting key pathological processes in asthma including inflammation, proliferation, angiogenesis and fibrosis. The aim was to evaluate the effects of TSA treatment in a mouse model of chronic allergic airways disease (AAD). Wild-type BALB/c mice with AAD were treated intraperitoneally with 5 mg/kg TSA or vehicle control. Airway inflammation was assessed by bronchoalveolar lavage fluid (BALF) cell counts and histological examination of lung tissue sections. Remodeling was assessed by morphometric analysis and airway hyperresponsiveness was assessed by invasive plethysmography. TSA-treated mice had a reduced number of total inflammatory cells and eosinophils within the BALF as compared to vehicle-treated mice (both p < 0.05). Furthermore, airway remodeling changes were significantly reduced with TSA compared to vehicle-treated mice, with fewer goblet cells (p < 0.05), less subepithelial collagen deposition (p < 0.05) and attenuated airway hyperresponsiveness at the highest methacholine dose. These findings demonstrate that treatment with an HDACi can concurrently reduce structural airway remodeling changes and airway hyperresponsiveness, in addition to attenuating airway inflammation in a chronic AAD model. This has important implications for the development of novel treatments for severe asthma.

Controversies Surrounding the Potential Use of Histone Deacetylase Inhibitors for the Treatment of Asthma

Management of asthma with long-acting β2-adrenergic receptor agonists and corticosteroids is exceptionally effective for the majority of asthma patients. However, corticosteroid insensitivity or resistance remains a significant clinical problem for a significant proportion of patients, requiring the investigation of new potential therapeutics for asthma. Histone deacetylase inhibitors represent a different class of compounds that have been evaluated for their potential antiasthmatic effects. Although accumulating evidence is indicating beneficial effects in rodent models of allergic airways disease, the potential use of histone deacetylase inhibitors in asthma remains controversial given their mechanisms of action. The aim of this paper is to provide an overview of histone deacetylases and pharmacological modifiers of these enzymes. The discussion represents a balanced account of the emerging evidence indicating the beneficial effects of histone deacetylase inhibitors in inflammatory lung diseases. The potential problems associated with the use of this class of compounds in asthma are also carefully considered.

Models and mechanisms of acute lung injury caused by direct insults

Acute lung injury (ALI) and its more severe form acute respiratory distress syndrome (ARDS) are life-threatening diseases that are characterized by acute onset, pulmonary inflammation, oedema due to increased vascular permeability and severe hypoxemia. Clinically, ARDS can be divided into ARDS due to direct causes such as pneumonia, aspiration or injurious ventilation, and due to extrapulmonary indirect causes such as sepsis, severe burns or pancreatitis. In order to identify potential therapeutic targets, we asked here whether common molecular mechanisms can be identified that are relevant in different models of the direct form of ALI/ARDS. To this end, we reviewed three widely used models: (a) one based on a biological insult, i.e. instillation of bacterial endotoxins; (b) one based on a chemical insult, i.e. instillation of acid; and (c) one based on a mechanical insult, i.e. injurious ventilation. Studies were included only if the mediator or mechanism of interest was studied in at least two of the three animal models listed above. As endpoints, we selected neutrophil sequestration, permeability, hypoxemia (physiological dysfunction) and survival. Our analysis showed that most studies have focused on mechanisms of pulmonary neutrophil sequestration and models with moderate forms of oedema. The underlying mechanisms that involve canonical inflammatory pathways such as MAP kinases, CXCR2 chemokines, PAF, leukotrienes, adhesions molecules (CD18, ICAM-1) and elastase have been defined relatively well. Further mechanisms including TNF, DARC, HMGB1, PARP, GADD45 and collagenase are under investigation. Such mechanisms that are shared between the three ALI models may represent viable therapeutic targets. However, only few studies have linked these pathways to hypoxemia, the most important clinical aspect of ALI/ARDS. Since moderate oedema does not necessarily lead to hypoxemia, we suggest that the clinical relevance of experimental studies can be further improved by putting greater emphasis on gas exchange.

Histone deacetylases and their role in asthma

OBJECTIVE

The aim of this article is to provide an overview of the classical histone deacetylase (HDAC) enzymes and HDAC inhibitors. The discussion is focused on the potential anti-asthmatic effects of this group of compounds.

METHODS

Medline was used with the search terms, "asthma and HDAC," "asthma and Trichostatin A," "asthma and valproic acid," "allergic airways disease and HDAC," "allergic airways disease and Trichostatin A," and "allergic airways disease and valproic acid." Manuscripts from the past decade were accessed. Historical literature dating from the 1960s was accessed for the use of anti-epileptics in the treatment of asthma.

RESULTS

Preliminary clinical trials with anti-epileptic drugs including the well-known HDAC inhibitor, valproic acid, have shown long-lasting anti-asthmatic effects providing the basis for the evaluation of this class of compounds in asthma. Studies using the prototypical HDAC inhibitor, Trichostatin A, in well-established murine models of allergic airways disease have also indicated beneficial effects.

CONCLUSION

Although the precise mechanisms are still controversial, inhibition of airway hyperresponsiveness and agonist-induced contraction as well as anti-inflammatory effects have been described for HDAC inhibitors in asthma.

Inhibition of histone deacetylase causes emphysema

In patients with chronic obstructive pulmonary disease (COPD), histone deacetylase (HDAC) expression and activity are reduced in the lung tissue. However, whether HDAC activity controls the maintenance of the lung alveolar septal structures has not been investigated. To explore the consequences of HDAC inhibition and address the question of whether HDAC inhibition causes lung cell apoptosis and emphysema, male Sprague-Dawley rats and human pulmonary microvascular endothelial cells (HPMVEC) were treated with trichostatin A (TSA), a specific inhibitor of HDACs. Chronic TSA treatment increased the alveolar air space area, mean linear intercept, and the number of caspase-3-positive cells in rat lungs. TSA suppressed hypoxia-inducible factor-1α (HIF-1α), VEGF, and lysyl oxidase (LOX) and increased microtubule-associated protein-1 light chain 3 (LC3), p53, and miR34a microRNA expression in both rat lungs and cultured HPMVEC. Gene silencing of HDAC2 using small interfering RNA (siRNA) in cultured HPMVEC resulted in the suppression of HIF-1α, VEGF, and LOX and an increase of p53 expression. These data indicate that HDAC inhibition causes emphysema and that HDAC-dependent mechanisms contribute to the maintenance of the adult lung structure. Our results also suggest that the increase in apoptosis, as a consequence of HDAC inhibition, is associated with decreased VEGF and HIF-1α expression.