A rat surgical model of esophageal metaplasia and adenocarcinoma-induced by mixed reflux of gastric acid and duodenal contents

An improved surgical procedure to establish a gastroesophageal reflux model with a high incidence of Barrett's esophagus in rats

Barrett's esophagus (BE) is a complication of gastroesophageal reflux disease and is a precursor lesion of esophageal adenocarcinoma. In existing BE models, the incidence of BE is typically low and induction is usually time consuming. In the present study, a gastroesophageal reflux model with a high incidence of BE in rats. Rats were divided into a model group and a sham operation group, and anesthetized with an inhalation anesthesia machine. Stomach-jejunal anastomosis (SJA) and esophagus-jejunal anastomosis (EJA) were simultaneously performed in the model group. The distance between the Treitz ligament and the gastro-jejunal anastomosis was shortened to 3 cm. The distance between the SJA and the EJA was prolonged to 1–1.5 cm. However, 15/40 rats in the model group succumbed to post-surgical complications (mortality rate was 37.5%). The weight of surviving rats in the model group was significantly lower compared with the sham group rats post-surgery. Erosions and ulcers were common of the surviving rats in the model group, with an incidence of 80% (20/25). Squamous cell dysplasia was identified in 40% (10/25) of rats in model group. The modified model was well established within 16 weeks. Notably, the modified surgical procedure used enhanced the incidence of BE in rats from 47% in the EJGJ model (as establish by Zhang) to 100%. To conclude, this model can be used as a reliable animal model for basic research on BE.

Protective effects of quercetin against chronic mixed reflux esophagitis in rats by inhibiting the nuclear factor-κB p65 and interleukin-8 signaling pathways

OBJECTIVE

To observe the effects of quercetin on chronic mixed reflux esophagitis (RE) in rats by inhibiting the nuclear factor-κB p65 (NF-κBp65) and interleukin-8 (IL-8) signaling pathways.

METHODS

Forty-eight healthy male Sprague-Dawley rats were randomly divided into six groups, with 8 rats in each group: the normal intact group, the sham operation group, the RE control group, the RE group treated with omeprazole or 100 mg/kg and 200 mg/kg quercetin. The animals were sacrificed after 6 weeks of different interventions. The pathological characteristics of esophageal mucosa were observed according to the diagnostic criteria and the expressions of NF-κBp65 and IL-8 were assessed by immunohistochemistry and real-time polymerase chain reaction.

RESULTS

Compared with the RE control group, esophageal mucosal injury was improved and the expressions of NF-κBp65 and IL-8 were significantly decreased in the RE group treated with omeprazole or quercetin (P < 0.05). Compared with the omeprazole group, the gross and microscopic scores of esophageal mucosal injury and the expressions of NF-κBp65 and IL-8 in the 100 mg/kg and 200 mg/kg quercetin groups were not increased (P > 0.05). There was no statistically significant difference between the RE groups treated with 100 mg/kg quercetin and 200 mg/kg quercetin.

CONCLUSION

Quercetin can prevent esophageal mucosal injury in RE rats by suppressing the NF-κBp65 and IL- 8 signaling pathways.

Involvement of luminal nitric oxide in the pathogenesis of the gastroesophageal reflux disease spectrum

Over the last 3 decades, the incidence of esophageal adenocarcinoma has dramatically increased in Western countries; a similar increase may be observed in Asian countries in the near future. Esophageal adenocarcinoma arises from a sequential gastroesophageal reflux disease (GERD) spectrum from reflux erosive esophagitis, to Barrett's esophagus, and finally to esophageal adenocarcinoma. At present, gastric acid and bile are assumed to be primarily involved in the etiology of the GERD spectrum. We reported in 2002 that, at the gastroesophageal junction in humans, abundant amounts of nitric oxide (NO) are generated luminally through the entero-salivary re-circulation of dietary nitrate. Since then, we have carried out a series of experiments to demonstrate that NO diffuses into the adjacent epithelium at cytotoxic levels. This diffusion results in disruption of the epithelial barrier function, exacerbation of inflammation, acceleration of columnar transformation in the esophagus (Barrett's esophagus) via the induction of caudal-type homeobox 2, and the shifting of carcinogenic N-nitroso compound formation from the luminal to epithelial compartment. These results suggest that, in addition to conventionally recognized causative factors, luminal NO could also be involved in the pathogenesis of the GERD spectrum. In addition, we recently showed that there is a prominent gender-related difference in NO-related cytotoxicity in the esophagus and that estrogen attenuated the esophageal tissue damage via the estrogen receptor in female rats. The role of estrogen in attenuating the esophageal tissue damage in NO-related esophageal damage could explain the well-recognized male predominance in the GERD spectrum in humans.

Upper gastrointestinal cancer and reflux disease

There is a growing evidence that gastroesophageal reflux disease is related to several upper gastrointestinal cancers, mainly the esophageal adenocarcinoma and a certain type of gastric cardia adenocarcinoma. Currently, the incidence of gastroesophageal reflux disease is rapidly increasing in Korea. Therefore, there is a possibility of such increasing cancerous incidents, similar to the western worlds. In this article, the relationship between gastroesophageal reflux disease and several upper gastrointestinal cancers, the components of refluxate which has possible causal relationship with carcinogenesis, and the clinical implications of such relationship in the management of gastroesophageal reflux disease patients are discussed through the review of literature.

Exposure to gastric juice may not cause adenocarcinogenesis of the esophagus

AIM: To determine the effects of gastric juice on the development of esophageal adenocarcinoma (EAC).

METHODS: A animal model of duodenogastroesophageal reflux was established in Sprague-Dawley rats undergoing esophagoduodenostomy. The development of EAC and forestomach adenocarcinoma was investigated 40 wk after the treatment. Intraluminal pH and bile of the forestomach were measured.

RESULTS: There were no significant differences in pH (t = 0.117, P = 0.925) or bile (χ² = 0.036, P = 0.85) in the forestomach before and 40 wk after esophagoduodenostomy. There were also no significant differences between the model and controls during esophagoduodenostomy or 40 wk after esophagoduodenostomy. The incidence of intestinal metaplasia (88%) and intestinal metaplasia with dysplasia and adenocarcinoma (28%) in the esophagus in the model was higher than in the controls 40 wk after surgery (χ² = 43.06, P < 0.001 and χ² = 9.33, P = 0.002, respectively) and in the forestomach in the model (χ² = 32.05, P < 0.001 and χ² = 8.14, P = 0.004, respectively). The incidence rates of inflammation in the esophagus and forestomach were 100% and 96%, respectively (χ² = 1.02, P = 0.31) in the model, which was higher than in the esophageal control (6.8%) (χ² = 42.70, P < 0.001).

CONCLUSION: Gastric juice exposure may not cause intestinal metaplasia with dysplasia or adenocarcinoma of the forestomach and may not be related to EAC.

Effects of refluxate pH values on duodenogastroesophageal reflux-induced esophageal adenocarcinoma

AIM: To determine the effects of duodenogastric juice pH on the development of esophageal adenocarcinoma (EAC).

METHODS: An animal model of duodenogastroesophageal reflux was established using Sprague-Dawley (SD) rats undergoing esophagoduodenostomy (ED). The development of EAC was investigated in rats exposed to duodenogastric juice of different pH. The rats were divided into three groups: low-pH group (group A), high-pH group (group B) and a sham-operated group as a control (group C) (n = 30 rats in each group). The incidence of esophagitis, Barrett’s esophagus (BE), intestinal metaplasia with dysplasia and EAC was observed 40 wk after the treatment.

RESULTS: The incidence rate of esophagitis, BE, intestinal metaplasia with dysplasia and EAC was higher in groups A and B compared with the control group after 40 wk (P < 0.01), being 96% and 100% (P > 0.05), 88% and 82.4% (P > 0.05), 20% and 52.1% (P < 0.05), and 8% and 39% (P < 0.05), respectively.

CONCLUSION: Non-acidic refluxate increases the occurrence of intestinal metaplasia with dysplasia and EAC while the low-pH gastric juice exerts a protective effect in the presence of duodenal juice. The non-acid reflux is particularly important in the progression from BE to cancer. Therefore, control of duodenal reflux may be an important prophylaxis for EAC.

Exogenous luminal nitric oxide exposure accelerates columnar transformation of rat esophagus

Exposure of the esophageal mucosa to refluxed gastroduodenal contents is recognized to be an important risk factor for Barrett's esophagus (BE). At the human gastroesophageal junction, nitric oxide is generated luminally through the enterosalivary recirculation of dietary nitrate, and in cases with gastroesophageal reflux, the site of luminal nitric oxide generation could shift to the distal esophagus. The aim of this study is to investigate whether exogenous luminal nitric oxide could promote the development of BE in rats. Sodium nitrite plus ascorbic acid were administered to a rat surgical model of BE, in which the gastroduodenal contents were refluxed into the esophagus to generate exogenous luminal nitric oxide in the esophagus by the acid-catalyzed chemical reaction between the 2 reagents. The emergence of BE was evaluated histologically in the early phase (several weeks) after the surgery with or without exogenous nitric oxide administration. To elucidate the histogenesis of BE, CDX2, MUC2 and MUC6 expressions were investigated immunohistochemically. Coadministration of sodium nitrite plus ascorbic acid significantly accelerated the timing of emergence and increased the area of BE compared with controls. Administration of either reagent alone did not show any promotive effects on BE formation. Immunohistochemically, the columnar epithelium thus induced was similar to the specialized intestinal metaplasia in human BE. The results of this animal model study suggest that exogenous luminal nitric oxide could be involved in the pathogenesis of the columnar transformation of the esophagus. Further studies in human are warranted.

The role of an alginate suspension on pepsin and bile acids - key aggressors in the gastric refluxate. Does this have implications for the treatment of gastro-oesophageal reflux disease?

OBJECTIVES

During a reflux event the oesophagus is exposed to a heterogeneous mixture of gastric juice components. The role of non-acid components of the refluxate in causing damage to the oesophagus is now well established but no therapeutic option exists to address this.

METHODS

The role of Gaviscon Advance (GA), a raft-forming alginate suspension, in protecting the oesophagus from damage by pepsin and bile acids (aggressors) was investigated using a series of in-vitro models.

KEY FINDINGS

GA was able to dose-dependently inhibit pepsin activity over and above the neutralisation effect of the formulation. This was evident against both protein and collagen substrates using two distinct colorimetric assays. GA was able to retard the diffusion of pepsin and multiple bile acids using a Franz cell model. Using the raft-forming mode of action GA was able to remove both pepsin and multiple bile acids from a simulated reflux event. There was capacity in the GA raft to accommodate aggressors from multiple reflux events.

CONCLUSIONS

GA can specifically remove both pepsin and bile acids from the refluxate, limit their diffusion and affect enzymatic activity of pepsin. There is a role for GA to reduce the damaging potential of the refluxate and thus protect the oesophagus.

Carcinogenesis of the upper gastrointestinal tract induced by N-methyl-N'-nitro-nitrosoguanidine and reflux of duodenal contents in the rat

PURPOSE

To investigate the combined effects of reflux of duodenal contents through the pylorus and treatment with N-methyl-N'-nitro-nitrosoguanidine (MNNG) on the development of lesions in the glandular stomach, at the gastrojejunal anastomosis and in the forestomach of rats.

METHODS

Eighty Male Wistar rats were divided into 4 groups: G1: MNNG + Reflux, G2: Reflux, G3: MNNG and G4: Gastrostomy. MNNG was given in the drinking water (100 mg/ml) for 12 weeks and then two groups (G1 and G2) were submitted to a gastrojejunal anastomosis followed by section of the afferent loop and suture of both stumps to allow reflux of duodenal contents through the pylorus. The animals were sacrificed 18 and 36 weeks after surgery. The lesions obtained in the antral mucosa, at the gastrojejunal anastomosis and in the forestomach were analysed histologically.

RESULTS

Duodenal reflux induced proliferative lesions at both glandular and squamous mucosa of the stomach. In the antrum, adenomatous hyperplasia (AH) was observed in 20% and 50% of the animals at the 18th and 36th weeks respectively. Aditionally 85% of the animals presented AH at the gastrojejunal anastomosis and 60% developed squamous hyperplasia at the squamous portion of the stomach. MNNG treatment plus duodenal reflux enhanced the development of malignant tumors at both glandular and squamous mucosa, since there were 30% of antral adenocarcinomas and 45% of squamous carcinomas at the 18th week and the frequency of these malignant tumors rose to 50% in the antrum and 65% in the squamous mucosa at the 36th week.

CONCLUSION

The reflux of duodenal contents through the pylorus enhanced the development of proliferative lesions, benign and malignant, in the glandular stomach and in the forestomach of rats.