Characterization of the innate immune response to chronic aspiration in a novel rodent model

A review of current and novel therapies for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressively fibrotic interstitial lung disease that is associated with a median survival of 2-3 years from initial diagnosis. To date, there is no treatment approved for IPF in the United States, and only one pharmacological agent has been approved outside of the United States. Nevertheless, research over the past 10 years has provided us with a wealth of information on its histopathology, diagnostic work-up, and a greater understanding of its pathophysiology. Specifically, IPF is no longer thought to be a predominantly pro-inflammatory disorder. Rather, the fibrosis in IPF is increasingly understood to be the result of a fibroproliferative and aberrant wound healing cascade. The development of therapeutic targets has shifted in accord with this paradigm change. This review highlights the current understanding of IPF, and the recent as well as novel therapeutics being explored in clinical trials for the treatment of this devastating disease.

In the face of chronic aspiration, prolonged ischemic time exacerbates obliterative bronchiolitis in rat pulmonary allografts

Aspiration of gastric fluid into the lung mediates the development of obliterative bronchiolitis (OB) in orthotopic WKY-to-F344 rat pulmonary transplants that have been subjected to immunosuppression with cyclosporine. However, the contribution of ischemic time to this process remains unknown. In this study, the effect of long (n = 16) and short (n = 12) ischemic times (average of 6 h and of 73 min, respectively) on rat lung transplants receiving aspiration of gastric fluid was assessed. Long ischemic times (LIT) led to significantly (p < 0.05) greater development of OB (ratio of OB lesions/total airways = 0.45 ± 0.07, mean ± standard error) compared to short ischemic times (ratio = 0.19 ± 0.05). However, the development of OB was dependent on aspiration, as controls receiving aspiration with normal saline showed little development of OB, regardless of ischemic time (p < 0.05). These data suggest that LIT, while insufficient by itself to lead to OB, works synergistically with aspiration of gastric fluid to exacerbate the development of OB.

Gastrointestinal manifestations of scleroderma: recent progress in evaluation, pathogenesis, and management

Gastrointestinal (GI) involvement is frequent in scleroderma (systemic sclerosis [SSc]) and is the most frequent internal complication of the disease. Patients with GI involvement have impaired quality of life, and their prognosis may be one of severe impairment. Unfortunately, GI involvement is often noticed when severe complications have already occurred, is irreversible, and is difficult to manage. The past 2 to 3 years have been rich in exciting studies that we hope will help identify, prevent, treat, and monitor disease progression. Recent studies on the pathophysiology of GI tract disease could lead to advances in the treatment of GI tract involvement. The importance of treating gastroesophageal reflux (GER) has been reinforced by studies showing GER damage in almost all SSc patients, and the fact that GER damage is reversible if early treatment with proton pump inhibitors is introduced. Moreover, recent data showing a link between GER and interstitial lung disease in SSc underscore the importance of aggressive GER treatment in SSc patients. A novel lung pattern possibly related to GER also has been described. New, exciting data on gastric vascular antral ectasia have been published. Finally, malnutrition in SSc patients has been highlighted, and anorectal involvement has been emphasized.

Gastrointestinal manifestations of scleroderma: recent progress in evaluation, pathogenesis, and management

Gastrointestinal (GI) involvement is frequent in scleroderma (systemic sclerosis [SSc]) and is the most frequent internal complication of the disease. Patients with GI involvement have impaired quality of life, and their prognosis may be one of severe impairment. Unfortunately, GI involvement is often noticed when severe complications have already occurred, is irreversible, and is difficult to manage. The past 2 to 3 years have been rich in exciting studies that we hope will help identify, prevent, treat, and monitor disease progression. Recent studies on the pathophysiology of GI tract disease could lead to advances in the treatment of GI tract involvement. The importance of treating gastroesophageal reflux (GER) has been reinforced by studies showing GER damage in almost all SSc patients, and the fact that GER damage is reversible if early treatment with proton pump inhibitors is introduced. Moreover, recent data showing a link between GER and interstitial lung disease in SSc underscore the importance of aggressive GER treatment in SSc patients. A novel lung pattern possibly related to GER also has been described. New, exciting data on gastric vascular antral ectasia have been published. Finally, malnutrition in SSc patients has been highlighted, and anorectal involvement has been emphasized.

Pulmonary immune changes early after laparoscopic antireflux surgery in lung transplant patients with gastroesophageal reflux disease

BACKGROUND

The biologic mechanisms by which laparoscopic antireflux surgery (LARS) might influence the inflammatory process leading to bronchiolitis obliterans syndrome are unknown. We hypothesized that LARS alters the pulmonary immune profile in lung transplant patients with gastroesophageal reflux disease.

METHODS

In 8 lung transplant patients with gastroesophageal reflux disease, we quantified and compared the pulmonary leukocyte differential and the concentration of inflammatory mediators in the bronchoalveolar lavage fluid (BALF) 4 weeks before LARS, 4 weeks after LARS, and 12 months after lung transplantation. Freedom from bronchiolitis obliterans syndrome (graded 1-3 according to the International Society of Heart and Lung Transplantation guidelines), forced expiratory volume in 1 second trends, and survival were also examined.

RESULTS

At 4 weeks after LARS, the percentages of neutrophils and lymphocytes in the BALF were reduced (from 6.6% to 2.8%, P = 0.049, and from 10.4% to 2.4%, P = 0.163, respectively). The percentage of macrophages increased (from 74.8% to 94.6%, P = 0.077). Finally, the BALF concentration of myeloperoxide and interleukin-1β tended to decrease (from 2109 to 1033 U/mg, P = 0.063, and from 4.1 to 0 pg/mg protein, P = 0.031, respectively), and the concentrations of interleukin-13 and interferon-γ tended to increase (from 7.6 to 30.4 pg/mg protein, P = 0.078 and from 0 to 159.5 pg/mg protein, P = 0.031, respectively). These trends were typically similar at 12 months after transplantation. At a mean follow-up of 19.7 months, the survival rate was 75% and the freedom from bronchiolitis obliterans syndrome was 75%. Overall, the forced expiratory volume in 1 second remained stable during the first year after transplantation.

CONCLUSIONS

Our preliminary study has demonstrated that LARS can restore the physiologic balance of pulmonary leukocyte populations and that the BALF concentration of pro-inflammatory mediators is altered early after LARS. These results suggest that LARS could modulate the pulmonary inflammatory milieu in lung transplant patients with gastroesophageal reflux disease.

Reflux aspiration in children with neurodisability--a significant problem, but can we measure it?

Recurrent respiratory problems are common in children with severe neurodisability, and respiratory deterioration is a leading cause of premature death in this group. Although the etiology is multifactorial, recurrent pulmonary aspiration is thought to play a significant role. Gastroesophageal reflux is known to be common, as is oral-motor discoordination. Differentiating direct aspiration of food and saliva and gastric reflux aspiration is difficult and presents a challenge in managing patients and assessing their suitability for surgical antireflux procedures. This is particularly the case when children present with predominantly respiratory symptoms, where there may be direct aspiration, reflux aspiration, neither, or both. A clinical biomarker to identify and quantify reflux aspiration would therefore be useful in surgical assessment and may also be applicable as an outcome measure for clinical trials of antireflux surgery. In this review, we discuss the evidence base behind existing and potentially novel biomarkers of aspiration in bronchoalveolar lavage fluid. We highlight the limitations of the lipid-laden macrophage index, particularly with regard to its specificity and interrater/intrarater reliability. We discuss the laboratory methods available to measure promising new biomarkers (pepsin and bile acids) and highlight their potential advantages and disadvantages. Finally, to understand how aspiration causes clinical signs and symptoms in our patients, we need to study the effect of aspirated substances on the lung, and here we review the available in vivo and in vitro literature.

Chronic rejection pathology after orthotopic lung transplantation in mice: the development of a murine BOS model and its drawbacks

Almost all animal models for chronic rejection (CR) after lung transplantation (LTx) fail to resemble the human situation. It was our attempt to develop a representative model of CR in mice. Orthotopic LTx was performed in allografts receiving daily immunosuppression with steroids and cyclosporine. Controls included isografts and mice only undergoing thoracotomy (SHAM). Allografts were sacrificed 2, 4, 6, 8, 10 or 12 weeks after LTx. Pulmonary function was measured repeatedly in the 12w allografts, isografts and SHAM mice. Histologically, all allografts demonstrated acute rejection (AR) around the blood vessels and airways two weeks after LTx. This decreased to 50-75% up to 10 weeks and was absent after 12 weeks. Obliterative bronchiolitis (OB) lesions were observed in 25-50% of the mice from 4-12 weeks. Isografts and lungs of SHAM mice were normal after 12 weeks. Pulmonary function measurements showed a decline in FEV(0.1), TLC and compliance in the allografts postoperatively (2 weeks) with a slow recovery over time. After this initial decline, lung function of allografts increased more than in isografts and SHAM mice indicating that pulmonary function measurement is not a good tool to diagnose CR in a mouse. We conclude that a true model for CR, with clear OB lesions in about one third of the animals, but without a decline in lung function, is possible. This model is an important step forward in the development of an ideal model for CR which will open new perspectives in unraveling CR pathogenesis and exploring new treatment options.

Blocking TGFβ via Inhibition of the αvβ6 Integrin: A Possible Therapy for Systemic Sclerosis Interstitial Lung Disease

Interstitial lung disease (ILD) is a commonly encountered complication of systemic sclerosis (SSc) and accounts for a significant proportion of SSc-associated morbidity and mortality. Its pathogenesis remains poorly understood, and therapies that treat SSc ILD are suboptimal, at best. SSc ILD pathogenesis may share some common mechanisms with other fibrotic lung diseases, in which dysregulation of lung epithelium can contribute to pathologic fibrosis via recruitment or in situ generation and activation of fibroblasts. TGFβ, a master regulator of fibrosis, is tightly regulated in the lung by the integrin αvβ6, which is expressed at low levels on healthy alveolar epithelial cells but is highly induced in the setting of lung injury or fibrosis. Here we discuss the biology of αvβ6 and present this integrin as a potentially attractive target for inhibition in the setting of SSc ILD.

Gastroesophageal reflux therapy is associated with longer survival in patients with idiopathic pulmonary fibrosis

RATIONALE

Gastroesophageal reflux (GER) is highly prevalent in patients with idiopathic pulmonary fibrosis (IPF). Chronic microaspiration secondary to GER may play a role in the pathogenesis and natural history of IPF.

OBJECTIVES

To investigate the relationship between GER-related variables and survival time in patients with IPF.

METHODS

Regression analysis was used to investigate the relationship between GER-related variables and survival time in a retrospectively identified cohort of patients with well-characterized IPF from two academic medical centers.

MEASUREMENTS AND MAIN RESULTS

Two hundred four patients were identified for inclusion. GER-related variables were common in this cohort: reported symptoms of GER (34%), a history of GER disease (45%), reported use of GER medications (47%), and Nissen fundoplication (5%). These GER-related variables were significantly associated with longer survival time on unadjusted analysis. After adjustment, the use of GER medications was an independent predictor of longer survival time. In addition, the use of gastroesophageal reflux medications was associated with a lower radiologic fibrosis score. These findings were present regardless of center.

CONCLUSIONS

The reported use of GER medications is associated with decreased radiologic fibrosis and is an independent predictor of longer survival time in patients with IPF. These findings further support the hypothesis that GER and chronic microaspiration may play important roles in the pathobiology of IPF.

Severe airway epithelial injury, aberrant repair and bronchiolitis obliterans develops after diacetyl instillation in rats

BACKGROUND

Bronchiolitis obliterans (BO) is a fibrotic lung disease that occurs in a variety of clinical settings, including toxin exposures, autoimmunity and lung or bone marrow transplant. Despite its increasing clinical importance, little is known regarding the underlying disease mechanisms due to a lack of adequate small animal BO models. Recent epidemiological studies have implicated exposure to diacetyl (DA), a volatile component of artificial butter flavoring, as a cause of BO in otherwise healthy factory workers. Our overall hypothesis is that DA induces severe epithelial injury and aberrant repair that leads to the development of BO. Therefore, the objectives of this study were 1) to determine if DA, delivered by intratracheal instillation (ITI), would lead to the development of BO in rats and 2) to characterize epithelial regeneration and matrix repair after ITI of DA.

METHODS AND MAIN RESULTS

Male Sprague-Dawley rats were treated with a single dose of DA (125 mg/kg) or sterile water (vehicle control) by ITI. Instilled DA resulted in airway specific injury, followed by rapid epithelial regeneration, and extensive intraluminal airway fibrosis characteristic of BO. Increased airway resistance and lung fluid neutrophilia occurred with the development of BO, similar to human disease. Despite rapid epithelial regeneration after DA treatment, expression of the normal phenotypic markers, Clara cell secretory protein and acetylated tubulin, were diminished. In contrast, expression of the matrix component Tenascin C was significantly increased, particularly evident within the BO lesions.

CONCLUSIONS

We have established that ITI of DA results in BO, creating a novel chemical-induced animal model that replicates histological, biological and physiological features of the human disease. Furthermore, we demonstrate that dysregulated epithelial repair and excessive matrix Tenacin C deposition occur in BO, providing new insights into potential disease mechanisms and therapeutic targets.

Surgical correction of gastroesophageal reflux in lung transplant patients is associated with decreased effector CD8 cells in lung lavages: a case series

BACKGROUND

Lung transplantation is associated with a high incidence of gastroesophageal reflux disease (GERD). The presence of GERD is considered a risk factor for the subsequent development of obliterative bronchiolitis (OB), and surgical correction of GERD by gastric fundoplication (GF) may be associated with increased freedom from OB. The mechanisms underlying a protective effect from OB remain elusive. The objective of this study was to analyze the flow cytometric properties of BAL cells in patients who have undergone GF early after transplant.

METHODS

In a single-center lung transplant center, eight patients with GERD who were in the first transplant year underwent GF. Prior to and immediately following GF, BAL cells were analyzed by polychromatic flow cytometry. Spirometry was performed before and after GF.

RESULTS

GF was associated with a significant reduction in the frequency of BAL CD8 lymphocytes expressing the intracellular effector marker granzyme B, compared with the pre-GF levels. Twenty-six percent of CD8 cells were granzyme Bhi pre-GF compared with 12% of CD8 cells post-GF (range 8%-50% pre-GF, 2%-24% post-GF, P = .01). In contrast, GF was associated with a significant interval increase in the frequency of CD8 cells with an exhausted phenotype (granzyme Blo, CD127lo, PD1hi) from 12% of CD8 cells pre-GF to 24% post-GF (range 1.7%-24% pre-GF and 11%-47% post-GF, P = .05). No significant changes in spirometry were observed during the study interval.

CONCLUSIONS

Surgical correction of GF is associated with a decreased frequency of potentially injurious effector CD8 cells in the BAL of lung transplant recipients.

Gastroesophageal reflux incites interstitial lung disease in systemic sclerosis: clinical, radiologic, histopathologic, and treatment evidence

OBJECTIVES

Interstitial lung disease (ILD) is currently the main cause of death in systemic sclerosis (SSc) and has an unknown pathogenesis. Gastroesophageal reflux (GER) has been strongly implicated as a cause of ILD in several lung diseases, including SSc-ILD. This review summarizes clinical, radiologic, histopathologic, and treatment aspects of GER in SSc-ILD.

METHODS

The PubMed database was searched using the following keywords: "systemic sclerosis, scleroderma, interstitial lung disease, and gastroesophageal reflux." The research was limited to English-language studies that included SSc patients with ILD.

RESULTS

Pulmonary function tests were related with the presence of GER in several esophageal functional tests (esophageal endoscopy, pH monitoring, and manometric analysis). Regarding the histopathologic data, a pattern called centrilobular fibrosis was described in 21% of 28 lung biopsies, with a bronchocentric distribution and with an intraluminal content resembling gastric fluid. Radiologic evidence of esophageal dilation is very frequent in SSc patients, and consolidation with a patchy distribution was almost exclusively found in SSc patients with centrilobular fibrosis lung pattern. Furthermore, high levels of serum KL-6, a marker of epithelial injury, are indicative of active ILD in SSc disease.

CONCLUSIONS

The association of GER with SSc-ILD is strongly supported by several studies. An aggressive treatment for reflux is recommended in all SSc patients with ILD; however, future studies need to be performed to prove a long-term benefit.

Does chronic microaspiration cause idiopathic pulmonary fibrosis?

Idiopathic pulmonary fibrosis is a diffuse fibrotic lung disease of unknown etiology with no effective treatment. Emerging data support a role for chronic microaspiration (ie, subclinical aspiration of small droplets) in the pathogenesis and natural history of idiopathic pulmonary fibrosis. However, the precise relationship between chronic microaspiration and idiopathic pulmonary fibrosis remains unknown. Gastroesophageal reflux, a presumed risk factor for microaspiration, has been strongly associated with idiopathic pulmonary fibrosis with an estimated prevalence of up to 90%. This review aims to describe the relationship between chronic microaspiration and idiopathic pulmonary fibrosis by laying out the clinical and biologic rationale for this relationship and exploring the scientific evidence available. The gaps in our current understanding of the diagnosis of chronic microaspiration and idiopathic pulmonary fibrosis and the ongoing uncertainties in management and treatment will be highlighted. Defining the role of chronic microaspiration in idiopathic pulmonary fibrosis is essential as it has potential clinical, pathobiological, and treatment implications for this deadly disease.