Experimental carcinogenesis on the oropharyngeal mucosa of rats with hydrochloric acid, sodium nitrate and pepsin

Bile reflux and hypopharyngeal cancer (Review)

Laryngopharyngeal reflux, a variant of gastroesophageal reflux disease, has been considered a risk factor in the development of hypopharyngeal cancer. Bile acids are frequently present in the gastroesophageal refluxate and their effect has been associated with inflammatory and neoplastic changes in the upper aerodigestive tract. Recent in vitro and in vivo studies have provided direct evidence of the role of acidic bile refluxate in hypopharyngeal carcinogenesis and documented the crucial role of NF-κB as a key mediator of early oncogenic molecular events in this process and also suggested a contribution of STAT3. Acidic bile can cause premalignant changes and invasive squamous cell cancer in the affected hypopharynx accompanied by DNA damage, elevated p53 expression and oncogenic mRNA and microRNA alterations, previously linked to head and neck cancer. Weakly acidic bile can also increase the risk for hypopharyngeal carcinogenesis by inducing DNA damage, exerting anti-apoptotic effects and causing precancerous lesions. The most important findings that strongly support bile reflux as an independent risk factor for hypopharyngeal cancer are presented in the current review and the underlying mechanisms are provided.

Re-evaluation of sodium nitrate (E 251) and potassium nitrate (E 252) as food additives

The Panel on Food Additives and Nutrient Sources added to Food (ANS) provided a scientific opinion re-evaluating the safety of sodium nitrate (E 251) and potassium nitrate (E 252) when used as food additives. The current acceptable daily intakes (ADIs) for nitrate of 3.7 mg/kg body weight (bw) per day were established by the SCF (1997) and JECFA (2002). The available data did not indicate genotoxic potential for sodium and potassium nitrate. The carcinogenicity studies in mice and rats were negative. The Panel considered the derivation of an ADI for nitrate based on the formation of methaemoglobin, following the conversion of nitrate, excreted in the saliva, to nitrite. However, there were large variations in the data on the nitrate-to-nitrite conversion in the saliva in humans. Therefore, the Panel considered that it was not possible to derive a single value of the ADI from the available data. The Panel noticed that even using the highest nitrate-to-nitrite conversion factor the methaemoglobin levels produced due to nitrite obtained from this conversion would not be clinically significant and would result to a theoretically estimated endogenous N-nitroso compounds (ENOC) production at levels which would be of low concern. Hence, and despite the uncertainty associated with the ADI established by the SCF, the Panel concluded that currently there was insufficient evidence to withdraw this ADI. The exposure to nitrate solely from its use as a food additive was estimated to be less than 5% of the overall exposure to nitrate in food based on a refined estimated exposure scenario. This exposure did not exceed the current ADI (SCF, 1997). However, if all sources of exposure to dietary nitrate are considered (food additive, natural presence and contamination), the ADI would be exceeded for all age groups at the mean and the highest exposure.

The In Vitro Effect of Acidic-Pepsin on Nuclear Factor KappaB Activation and Its Related Oncogenic Effect on Normal Human Hypopharyngeal Cells

Background

Extra-esophageal carcinogenesis has been widely discussed in relation to the chronic effects of laryngopharyngeal reflux and most prominently with pepsin historically central to this discussion. With refluxate known to include gastric (pepsin) and duodenal (bile) fluids, we recently demonstrated the mechanistic role of NF-κB in mediating the preneoplastic effects of acidic-bile. However, the role of pepsin in promoting hypopharyngeal premalignant events remains historically unclear. Here, we investigate the in vitro effect of acidic-pepsin on the NF-κB oncogenic pathway to better define its potential role in hypopharyngeal neoplasia.

Methods

Human hypopharyngeal primary cells (HHPC) and keratinocytes (HHK) were repetitively exposed to physiologic pepsin concentrations (0.1 mg/ml) at pH 4.0, 5.0 and 7.0. Cellular localization of phospho-NF-κB and bcl-2 was determined using immunofluorescence and western blotting. NF-κB transcriptional activity was tested by luc reporter and qPCR. Analysis of DNA content of pepsin treated HHK and HHPC was performed using Fluorescence-activated-cell sorting assay. To explore a possible dose related effect, pepsin concentration was reduced from 0.1 to 0.05 and 0.01 mg/ml.

Results

At physiologic concentration, acidic-pepsin (0.1 mg/ml at pH 4.0) is lethal to most normal hypopharyngeal cells. However, in surviving cells, no NF-κB transcriptional activity is noted. Acidic-pepsin fails to activate the NF-κB or bcl-2, TNF-α, EGFR, STAT3, and wnt5α but increases the Tp53 mRNAs, in both HHPC and HHK. Weakly acidic-pepsin (pH 5.0) and neutral-pepsin (pH 7.0) induce mild activation of NF-κB with increase in TNF-α mRNAs, without oncogenic transcriptional activity. Lower concentrations of pepsin at varying pH do not produce NF-κB activity or transcriptional activation of the analyzed genes.

Conclusion

Our findings in vitro do not support the role of acidic-pepsin in NF-κB related hypopharyngeal carcinogenesis.

miR-21, miR-155, miR-192, and miR-375 Deregulations Related to NF-kappaB Activation in Gastroduodenal Fluid-Induced Early Preneoplastic Lesions of Laryngeal Mucosa In Vivo

Gastroduodenal refluxate found in the upper aerodigestive tract is not clinically uncommon. We recently demonstrated the neoplastic potential of gastroduodenal fluids (GDF) on hypopharyngeal mucosa, via NF-κB, using in vitro and in vivo models. Here we will explore the in vivo effect of GDF on laryngeal mucosa (LM) to induce early preneoplastic lesions related to NF-κB activation, along with deregulation of specific microRNA (miRNA) markers previously linked to laryngeal cancer. We used histological, immunohistochemical, automated quantitative analysis and quantitative polymerase chain reaction to examine LM from 35 C57Bl/6J mice previously treated with topical GDF against corresponding controls (4 experimental and 3 control groups; 5 mice/group). Our analysis showed that GDF produced early preneoplastic lesions in treated LM related to NF-κB activation. LM treated by acid and bile combination demonstrated significantly higher expression of the analyzed cell proliferation markers (Ki67, CK14, ∆Np63), oncogenic p-STAT3, and changes of cell adhesion molecules (E-cadherin, ϐ-catenin) versus untreated LM or LM exposed to acid alone (P < .0005). Furthermore, acidic bile but not neutral bile appeared to accelerate the expression of “oncomirs” miR-21, miR-155, and miR-192 (acidic bile versus neutral bile, P < .0001), while reducing tumor suppressor miR-375 (acidic bile versus neutral bile, P = .0137), previously linked to NF-κB and laryngeal cancer. Finally, acidic bile induced reduction of miR-34a, miR-375, and miR-451a, exhibiting an inverse correlation with NF-κB activation. SIGNIFICANCE: Bile in combination with acid has a selective tumorigenic effect on LM, inducing deregulation of “oncomirs” and tumor suppressor miRNAs, produced by NF-κB activation with molecular and early histopathological alterations linked to neoplastic transformation. Systematic acid suppression may in part convey a protective role.

Experimental model of smoking and simulation of reflux with acid and pepsin in rats

PURPOSE: To develop experimental models to evaluate the effects of hydrochloric acid associated with the pepsin instilled in the mucosa of the upper esophagus and the esophagogastric junction of young male rats Wistar, simulating injury caused by gastroesophageal reflux on the mucosa of aero-digestive tract in humans as well as the action of the risk exposure of mucosa to cigarette smoke. METHODS: Fifty young male Wistar rats divided in 5 groups with 10 animals each one, respectively simulating pharyngo-laryngeal reflux and gastroesophageal reflux, pharyngo-laryngeal reflux and smoking, smoking only, gastroesophageal reflux and control group. RESULTS: The histopathologic studies no recorded neoplasias, only mild changes and no significant alterations. The hemo-oximetry (carboxyhemoglobin and methemoglobim) and CO2 concentration confirm that the animals were submitted to high intensity of exposure to carcinogens in tobacco and its derivatives. CONCLUSION: The experimental models were highly efficient, practical, easy to use and economical and can be employed in other similar studies to determine the harmful effects by smoking and reflux.

Laryngopharyngeal reflux: current concepts and questions

PURPOSE OF REVIEW

Laryngopharyngeal reflux is a widely recognized disorder. Yet, decades after its initial description, debate persists regarding pathophysiology, diagnosis, and treatment. This review addresses current literature on laryngopharyngeal reflux and identifies areas of controversy and future opportunities for research.

RECENT FINDINGS

Despite numerous research efforts, the diagnosis and treatment of laryngopharyngeal reflux remain elusive and unproven. Acid-induced changes in laryngopharyngeal mucosa have been confirmed by histologic evidence. However, the implications of this for laryngeal symptoms and signs are unclear. Diagnosis remains controversial, confounded by lack of standardization and accepted, evidence-based norms. Whereas treatment is generally believed by clinicians to be effective in alleviating symptoms and signs attributed to laryngopharyngeal reflux, incontrovertible data confirming efficacy are scarce. Confounding the issues further, there are numerous studies that purport to show that various widely used treatments are not effective, although the scientific merit of virtually all of these studies has been challenged.

SUMMARY

Laryngopharyngeal reflux remains a controversial diagnosis. Treatment with proton pump inhibitors persists despite weak evidence supporting or refuting their utility, and well designed studies are needed to understand diagnosis, treatment, pathyophysiology, and long-term health consequences of laryngopharyngeal reflux and its treatment.