Secretory phospholipase A2 is required to produce histologic changes associated with gastroduodenal reflux in a murine model

Simvastatin Inhibits Histologic Changes Associated with Gastroduodenal Reflux in a Murine Model

BACKGROUND

Observational studies demonstrate a protective effect of statins on the development and progression of esophageal adenocarcinoma. The role of statins in the prevention of reflux-induced esophageal changes remains unknown.

AIMS

Using a mixed gastroduodenal reflux mouse model, we hypothesized that oral administration of simvastatin would attenuate reflux-induced mucosal changes of the distal esophagus.

METHODS

Human Barrett's (CPB) and esophageal adenocarcinoma (FLO1 and OE19) cells were treated with simvastatin. Cell proliferation and apoptosis were evaluated using the MTS proliferation and annexin V apoptosis assays, respectively. A reflux mouse model was generated by performing a side-to-side anastomosis between the gastroesophageal junction and first portion of the duodenum (duodeno-gastroesophageal anastomosis, DGEA). DGEA mice were fed a standard or simvastatin-containing diet following surgery. Mice were euthanized 6 weeks post-operatively.

RESULTS

Simvastatin significantly decreased proliferation and increased apoptosis in all cell lines. Compared to control animals, mice undergoing DGEA who were fed a standard diet demonstrated a fourfold increase in mucosal thickness and significant increase in proliferating cells (p < 0.0001). DGEA mice fed a simvastatin-containing diet had an attenuated response to reflux, with a significant reduction in mucosal hyperplasia and proliferation (p < 0.0001). DGEA mice fed a simvastatin-containing diet demonstrated significant upregulation of procaspase-3 (p = 0.009) and cleaved caspase-3 (p = 0.034) in the distal esophagus.

CONCLUSIONS

We demonstrate for the first time a reduction in reflux-induced histologic changes of the distal esophagus following oral administration of simvastatin in vivo. These findings identify simvastatin as a potential preventative agent to inhibit the development and progression of reflux-induced esophageal injury.

Toll-like Receptor 4 Mediates Reflux-Induced Inflammation in a Murine Reflux Model

Dysregulation of toll-like receptor (TLR) signaling within the gastrointestinal epithelium has been associated with uncontrolled inflammation and tumorigenesis. We sought to evaluate the role of TLR4 in the development of gastroesophageal reflux-mediated inflammation and mucosal changes of the distal esophagus. Verified human esophageal Barrett's cells with high grade dysplasia (CPB) and esophageal adenocarcinoma cells (OE33) were treated with deoxycholic acid for 24 hours. Cells were pretreated with a TLR4-specific inhibitor peptide 2 hours prior to deoxycholic acid treatment. Inflammatory markers were evaluated using immunoblotting and enzyme-linked immunosorbent assay. A surgical reflux mouse model was generated by performing a side-to-side anastomosis between the second portion of the duodenum and the gastroesophageal junction. Control animals underwent laparotomy with incision and closure of the esophagus superior to the gastroesophageal junction (sham procedure). Esophageal sections were evaluated using hematoxylin and eosin staining and immunohistochemistry. Deoxycholic acid increased expression of inflammatory markers including intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and interleukin 8. Pretreatment with a TLR4 inhibitor significantly decreased deoxycholic acid-induced inflammatory marker expression. C3H/HeNCrl mice demonstrated a significant increase in mucosal hyperplasia and proliferation following DGEA compared to sham procedure. TLR4 mutant mice (C3H/HeJ) undergoing DGEA demonstrated an attenuated hyperplastic and proliferative response compared to C3H/HeNCrl mice. Inhibition of TLR4 signaling attenuates reflux-induced inflammation in vivo. These findings identify TLR4 inhibition as a potential therapeutic target to halt the progression of pathologic esophageal changes developing in the setting of chronic gastroesophageal reflux disease.

Expression of Adhesion Molecules in a Gastroduodenal Reflux Murine Model

BACKGROUND

Various adhesion molecules including intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) have been shown to play a role in inflammation as well as contribute to tumor progression and prognosis. We hypothesized that gastroduodenal reflux upregulates ICAM-1 and VCAM-1 expression in the distal esophagus, serving as possible early markers of pathologic esophageal disease.

METHODS

Normal human esophageal epithelial cells (HET1A), Barrett's cells (CPB), and esophageal adenocarcinoma cells (FLO1 and OE33) were treated with deoxycholic acid (DCA) at increasing concentrations for 24 hours. Adhesion molecule expression was assessed using immunoblotting. A surgical mouse reflux model was generated by performing a side-to-side anastomosis between the gastroesophageal junction and the first portion of the duodenum (duodeno-gastroesophageal anastomosis, DGEA). Esophageal sections were evaluated using H&E staining, immunohistochemistry, and immunofluorescence.

RESULTS

DCA induced a significant increase in ICAM-1 and VCAM-1 expression in HET1A, CPB, FLO1, and OE33 cells. Animals undergoing DGEA demonstrated a significant increase in mucosal hyperplasia (p<0.0001) and cellular proliferation (p<0.0001) compared to control animals. Immunofluorescence and western blot analysis of the lower esophagus demonstrated significant upregulation of ICAM-1 (p=0.005), with no change in VCAM-1 expression (p=0.82).

CONCLUSIONS

Our results reveal that ICAM-1 and VCAM-1 are upregulated in response to in vitro reflux treatment of normal esophageal epithelial cells. However, upon investigation using a mouse reflux model, ICAM-1 is noticeably upregulated without a concomitant increase in VCAM-1. These findings identify ICAM-1, but not VCAM-1, as a potential player in early esophageal disease developing from chronic reflux exposure.

Secretory Phospholipase A2 Inhibition Attenuates Adhesive Properties of Esophageal Barrett's Cells

BACKGROUND

Gastroesophageal reflux and Barrett's esophagus are significant risk factors for the development of esophageal adenocarcinoma. Group IIa secretory phospholipase A₂ (sPLA₂) catalyzes the production of various proinflammatory metabolites and plays a critical role in promoting reflux-induced inflammatory changes within the distal esophagus. We hypothesized that inhibition of sPLA₂ in human Barrett's cells would attenuate adhesion molecule expression via decreased activation of nuclear factor kappa B (NF-κB) and decrease cell proliferation, possibly mitigating the invasive potential of Barrett's esophagus.

MATERIALS AND METHODS

Normal human esophageal epithelial cells (HET1A) and Barrett's cells (CPB) were assayed for baseline sPLA₂ expression. CPB cells were treated with a specific inhibitor of sPLA₂ followed by tumor necrosis factor-α. Protein expression was evaluated using immunoblotting. Cell proliferation was assessed using an MTS cell proliferation assay kit. Statistical analysis was performed using the Student's t-test or analysis of variance, where appropriate.

RESULTS

CPB cells demonstrated higher baseline sPLA₂ expression than HET1A cells (P = 0.0005). Treatment with 30 μM sPLA₂ inhibitor significantly attenuated intercellular adhesion molecule-1 (P = 0.004) and vascular cell adhesion molecule-1 (P < 0.0001) expression as well as decreased NF-κB activation (P = 0.002). sPLA₂ inhibition decreased cell proliferation in a dose-dependent manner (P < 0.001 for 15, 20, and 30 μM doses).

CONCLUSIONS

sPLA₂ inhibition in human Barrett's cells decreases cellular adhesive properties and NF-κB activation as well as decreases cell proliferation, signifying downregulation of the inflammatory response and possible attenuation of cellular malignant potential. These findings identify sPLA₂ inhibition as a potential chemopreventive target for premalignant lesions of the esophagus.

A novel murine model of esophageal nonerosive reflux disease: from inflammation to impairment in mucosal integrity

Nonerosive reflux disease (NERD) is a highly prevalent phenotype of the gastroesophageal reflux disease. In this study, we developed a novel murine model of NERD in mice with microscopic inflammation and impairment in the epithelial esophageal barrier. Female Swiss mice were subjected to the following surgical procedure: the transitional region between the forestomach and the glandular portion of the stomach was ligated, and a nontoxic ring was placed around the duodenum near the pylorus. The control group underwent sham surgery. The animals were euthanized at 1, 3, 7, and 14 days after surgery. Survival and body weight were monitored daily. Esophageal wet weight, macroscopic lesion, histopathological alterations, myeloperoxidase (MPO) activity, cytokine levels, transepithelial electrical resistance (TEER), and mucosal permeability were evaluated. The survival rate was 78% at 14 days, with mild loss in body weight. Surgery did not induce erosive esophagitis but instead induced microscopic inflammation and increased esophageal wet weight, IL-6, keratinocyte-derived cytokine (KC) levels, and MPO activity with maximal peak between 3 and 7 days and resolution at 14 days postsurgery. Epithelial esophageal barrier was evaluated in operated mice at 7 and 14 days postsurgery; a decrease in TEER and increase in the esophageal epithelial permeability were observed compared with the sham-operated group. In addition, the inhibition of acid secretion with omeprazole significantly prevented the esophageal inflammation and impairment of barrier function at 7 days postsurgery. Thus we established a novel experimental model of NERD in mice, which can contribute to understanding the pathophysiological events associated with NERD.NEW & NOTEWORTHY In this study, we standardized an experimental model of nonerosive reflux disease (NERD) in mice. This model involves an acute inflammatory response followed by impaired esophageal mucosal integrity, even in the absence of inflammation. Thus this model can serve for evaluation of pathophysiological aspects of NERD and open new perspectives for therapeutic strategies for patients with this disorder.

Columnar metaplasia in a surgical mouse model of gastro-esophageal reflux disease is not derived from bone marrow-derived cell

The incidence of esophageal adenocarcinoma has increased in the last 25 years. Columnar metaplasia in Barrett's mucosa is assumed to be a precancerous lesion for esophageal adenocarcinoma. However, the induction process of Barrett's mucosa is still unknown. To analyze the induction of esophageal columnar metaplasia, we established a mouse gastro-esophageal reflux disease (GERD) model with associated development of columnar metaplasia in the esophagus. C57BL/6 mice received side-to-side anastomosis of the esophagogastric junction with the jejunum, and mice were killed 10, 20, and 40 weeks after operation. To analyze the contribution of bone marrow-derived cells to columnar metaplasia in this surgical GERD model, some mice were transplanted with GFP-marked bone marrow after the operation. Seventy-three percent of the mice (16/22) showed thickened mucosa in esophagus and 41% of mice (9/22) developed columnar metaplasia 40 weeks after the operation with a mortality rate of 4%. Bone marrow-derived cells were not detected in columnar metaplastic epithelia. However, scattered epithelial cells in the thickened squamous epithelia in regions of esophagitis did show bone marrow derivation. The results demonstrate that reflux induced by esophago-jejunostomy in mice leads to the development of columnar metaplasia in the esophagus. However, bone marrow-derived cells do not contribute directly to columnar metaplasia in this mouse model.

MicroRNA and its roles in esophageal cancer

Esophageal cancer is the eighth most common cancer and causes the sixth highest cancer-related mortality worldwide. The 5-year survival of patients suffering from esophageal cancer in either advanced stage or metastasis is less than 20%. MicroRNAs are small, well conserved, non-coding RNA molecules that either repress translation or promote mRNA degradation based on the degree of complementary between miRNAs and mRNAs. Based on biogenesis and function of microRNAs, specific microRNA profiles, either from cancerous tissues or serum, were able to serve as diagnostic and prognostic biomarkers of esophageal cancer and predicted the effectiveness of surgery and chemoradiotherapy. MicroRNAs could also influence the biological behaviors of esophageal cancer cells, such as cellular proliferation, apoptosis, invasion and metastasis. MicroRNAs were also associated with multi-drug resistance of esophageal cancer. Further studies on the roles of microRNAs in esophageal cancer would provide a strategy to prevent and treat esophageal cancer, and reverse multi-drug resistance of esophageal cancer.

Circulating phospholipase-A2 activity in obstructive sleep apnea and recurrent tonsillitis

OBJECTIVE

Phospholipase A2 (PLA2) plays a major part in growth regulation, differentiation and inflammation. It has been proposed as an evaluating marker for infection and inflammation. The aim of this study was to investigate activity of serum type II secretory PLA2 (sPLA2 IIa) in obstructive sleep apnea (OSA) and recurrent infective tonsillitis (RT) in children.

METHODS

Activity of serum sPLA2 IIa was determined in children who underwent tonsillectomy, including OSA in 126 cases and RT in 60. Serum enzyme activities were measured using the standard assay with Diheptanoyl Thio-Phosphatidylcholin as substrate.

RESULTS

The sPLA2 IIa activity of serum was significantly higher in RT than in OSA (P<0.01). Serum sPLA2 IIa activity in the RT patients was positively correlated with BMI (r=0.26; P=0.02), which was not apparent in OSA (r=0.14; P=0.09).

CONCLUSION

This study suggests that serum sPLA2 IIa activity may be considered as a supportive diagnostic marker in suspected or clinically unclear cases of RT children.

Lung cancer cell invasion and expression of intercellular adhesion molecule-1 (ICAM-1) are attenuated by secretory phospholipase A₂ inhibition

OBJECTIVE

Invasive lung tumors are associated with intercellular adhesion molecule-1 (ICAM-1) expression. Secretory phospholipase A(2) (sPLA(2)) enzymes produce inflammatory mediators that stimulate ICAM-1 expression, and upregulation of PLA(2) activity can enhance metastasis. We hypothesize a link between sPLA(2) activity, ICAM-1 expression, and tumor cell invasion. We propose that inhibition of sPLA(2) modulates ICAM-1 expression in cancer cells and attenuates their invasiveness.

METHODS

Human lung adenocarcinoma cells (A549) were treated with an ICAM-1 blocking antibody and assayed for invasion. Lung cancer cells (A549 and H358) were then treated with an sPLA(2) inhibitor and evaluated by immunoblotting for ICAM-1 expression. Next cells (A549) treated with sPLA(2) inhibitor were assayed for invasion. Finally, sPLA(2) messenger RNA and protein expression were evaluated by quantitative reverse-transcriptase polymerase chain reaction and immunofluorescence microscopy, respectively. Statistical analysis was performed by the Student t test or analysis of variance, as appropriate.

RESULTS

Antibody blockade of ICAM-1 decreased lung cancer cell invasion. sPLA(2) inhibition significantly reduced ICAM-1 expression and invasion. sPLA(2) inhibition also significantly decreased sPLA(2) mRNA expression and immunofluorescent staining of sPLA(2).

CONCLUSIONS

sPLA(2) plays a significant role in mediating the inflammatory signals that induce ICAM-1 expression in lung cancer cells. Inhibition of the enzyme can significantly decrease ICAM-1 expression and subsequent cancer cell invasion. This lays the groundwork for further investigation into the cellular mechanisms of sPLA(2) and its role in lung cancer.

Secretory phospholipase A2 inhibition attenuates intercellular adhesion molecule-1 expression in human esophageal adenocarcinoma cells

BACKGROUND

Esophageal adenocarcinoma is an aggressive malignancy, with most patients succumbing to metastatic disease. The presence of intercellular adhesion molecule-1 (ICAM-1) in these cancer cells contributes to their metastatic potential. The ICAM-1 production in other cell types is stimulated by the actions of phospholipase enzymes. We hypothesize that inhibition of the enzyme secretory phospholipase A2 (sPLA2), which contributes to the growth potential of normal esophageal mucosa and esophageal cancer cells, may attenuate ICAM-1 production and nuclear factor-kappa beta activation in human esophageal adenocarcinoma cells.

METHODS

The FLO-1 verified human esophageal adenocarcinoma cells were treated with 5-(4-benzyloxyphenyl)-4S-(7-phenylheptanoylamino) pentanoic acid, a specific inhibitor of group IIa sPLA2 (5 μM, 10 μM, and 15 μM doses), followed by tumor necrosis factor-alpha stimulation (20 ng/mL). Cells and medium were collected and analyzed by immunoblotting, flow cytometry, and enzyme-linked immunosorbent assay. Statistical analysis was performed using analysis of variance with the Fisher's least significant difference post-hoc test.

RESULTS

Treatment with sPLA2 inhibitor attenuated total cellular ICAM-1 expression in a dose-dependent manner (p<0.005). Cell-surface and secreted ICAM-1 expression decreased significantly with sPLA2 inhibitor treatment (p<0.001 and p<0.05, respectively). sPLA2 inhibition attenuated nuclear factor-kappa beta activation dose-dependently (p<0.05).

CONCLUSIONS

Esophageal adenocarcinoma has significant metastatic potential, and inhibiting its metastasis would significantly advance the treatment of this disease. We demonstrate here that treatment of human esophageal adenocarcinoma cells with sPLA2 inhibitor attenuates the expression of ICAM-1, a marker of metastatic potential, and nuclear factor-kappa beta activation, suggesting a common pathway between the two. These findings identify inhibition of sPLA2 as a potential therapeutic target for esophageal adenocarcinoma.

Gastroduodenal reflux induces group IIa secretory phospholipase A(2) expression and activity in murine esophagus

Exposure of esophageal epithelium to gastric and duodenal contents results in the histologic changes of hyperproliferation and mucosal thickening. We have previously shown that presence of secretory phospholipase A(2) (sPLA(2)) is necessary to produce these histologic changes in a murine model of gastroduodenal reflux. We sought to determine the influence of gastroduodenal reflux (GDR) on sPLA(2) protein and mRNA levels as well as enzyme activity in esophageal tissue. BALB/c (sPLA(2)(+/+)) mice (n= 28) underwent side-to-side surgical anastomosis of the first portion of the duodenum and GE junction (DGEA) resulting in continuous exposure of esophageal mucosa to mixed gastric and duodenal contents. Sham control mice (n= 14) underwent laparotomy, esophagotomy and closure. Real-time RT PCR was used to quantitate the influence of GDR on group IIa sPLA(2) expression. Immunofluorescent staining was quantitated by digital microscopy using a specific antibody to identify and locate sPLA(2) protein. A colorimetric assay was used to quantify total sPLA(2) activity after standardization of protein levels. Statistical analysis was conducted using Student's t-test. Group IIa sPLA(2) mRNA and protein levels were increased at 4 and 8 weeks compared with sham controls. This increase occurred in a time-dependent manner and correlated with esophageal mucosal thickness. Furthermore, sPLA(2) enzyme activity was increased significantly at 4 and 8 weeks compared with untreated controls. The expression of group IIa sPLA(2) as well as sPLA(2) activity is induced by GDR. This novel finding indicates that sPLA(2) may play a role in the development of the histologic changes produced by GDR in esophageal mucosa.

The secretory phospholipase A2 gene is required for gastroesophageal reflux-related changes in murine esophagus

BACKGROUND

The initial response of esophageal mucosa to gastroduodenal reflux is inflammation and hyperplasia. Secretory phospholipase A(2) (sPLA(2)) is a known mediator of gut inflammation, and its levels are increased in Barrett's esophagus. We hypothesized that the sPLA(2) gene is required to produce esophageal mucosal hyperplasia in response to gastroduodenal reflux.

METHODS

C57BL/6 (n = 5) sPLA(2) (-/-) mice and C57BL/6( Cg-Tg(PLA2G2A)703N16 ) mice (n = 4) sPLA(2) (-/+) underwent a side-to-side surgical anastomosis between the duodenum and gastroesophageal junction (DGEA). Control animals [sPLA(2) (-/-) (n = 5), sPLA(2) (-/+) (n = 4)] underwent laparotomy with incision and repair of the esophagus. Tissue was harvested after 4 weeks, and H&E staining was performed to quantify esophageal mucosal thickness. Ki67 and sPLA(2) immunostaining were performed to quantitate differences in cell division and sPLA(2) expression.

RESULTS

Mice expressing human sPLA(2) had a 2.5-fold increase in thickness of the esophageal mucosa as compared to controls (p = 0.01). A 6.5-fold increase in proliferation (p = 0.02) and a twofold increase in sPLA(2) expression (p = 0.04) were demonstrated in animals exposed to gastroduodenal reflux.

CONCLUSIONS

The presence of sPLA(2) is necessary for early mucosal hyperplasia produced by exposure of the esophagus to gastroduodenal contents. sPLA(2) expression is upregulated by gastroduodenal reflux, strengthening its role as a critical mediator of early mucosal hyperplasia.

Barrett's esophagus: where do we stand?

Barrett's esophagus (BE) is a precursor for esophageal adenocarcinoma, which has an increased incidence rate over the last few decades. Its importance stems from the poor five-year survival of esophageal adenocarcinoma and current data that suggest a survival benefit when surveillance programs are implemented. In this review, we will cover the pathophysiology and natural history of BE and the different endoscopic findings. The prevalence of BE in different geographic areas and the incidence of high-grade dysplasia and adenocarcinoma in this patient population is reviewed. Recent recommendation for screening and surveillance of BE has been covered in this review as well as the efficacy of nonconventional imaging modalities and endoscopic ablation therapies.