Bile reflux and hypopharyngeal cancer (Review)

Abstract

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.

Keywords: DNA damage; NF‑κB; bile reflux; conjugated bile acids; deoxycholic acid; head and neck cancer; hypopharyngeal cancer; hypopharyngeal squamous cell carcinoma; in vivo; laryngopharyngeal reflux.

Figure 1.

The mechanistic role of NF-κB in the mRNA oncogenic phenotype induced by bile reflux in hypopharyngeal carcinogenesis. Acidic bile induces constitutive activation of NF-κB via TNF-α, EGFR or TLR, which promotes the transcriptional activation of genes with inflammatory, anti-apoptotic or oncogenic function, such as IL6, IL1β, TNF-α, BCL2L1, EGFR, cREL, STAT3, ΔNp63 and WNT5A. Activation of NF-κB under acidic bile exposure also induces overexpression of AKT1, suggesting acidic bile may contribute to the PI3K/AKT1 downstream pathway, which is frequently activated in HNSCC. In addition, NF-κB is able to upregulate the expression of PTGS2 (COX-2), supporting its regulatory role in inflammatory and cancer-related downstream signaling pathways. Finally, acidic bile-induced NF-κB activation may prevent the upregulation of wild-type TP53 expression.

Figure 2.

The mechanistic role of NF-κB in the miRNA oncogenic phenotype induced by bile reflux in hypopharyngeal carcinogenesis. Chronic stimulation of laryngopharyngeal mucosa by acidic bile induces constitutive activation of NF-κB, producing upregulation of ‘oncomiRs’ miR-21, miR-155 and miR-192, previously associated with oncogenic signaling pathways in head and neck cancer and GERD. The acidic bile-induced activation of NF-κB in treated hypopharyngeal mucosa is capable of downregulating ‘tumor suppressor’ miR-34a, miR-451a, miR-375, miR-99a and miR-504, are known to control the cell cycle and are frequently affected in head and neck cancer. Acidic bile-induced expression levels of ‘oncomiRs’ exhibited an inverse correlation with ‘tumor suppressor’ miRNAs that appears to be regulated by NF-κB. miRNA/miR, microRNA; GERD, gastroesophageal reflux disease; HNSCC, head and neck squamous cell carcinoma.

Figure 3.

Schematic representation of proposed interactions between acidic bile-induced NF-κB activation and alterations of cancer-related mRNA and miRNA phenotypes in hypopharyngeal cancer. NF-κB inhibition provided evidence of strong interactions between acidic bile-induced and cancer-related oncogenic mRNA and miRNA phenotypes in treated hypopharyngeal cells. miRNA/miR, microRNA.

Figure 4.

Schematic representation of the proposed mechanism of bile reflux-induced hypopharyngeal cancer. Bile refluxate is capable of inducing DNA damage, such as double-strand DNA breaks and oxidative damage and significant activation of NF-κB and its related anti-apoptotic pathways, leading to malignant transformation of laryngopharyngeal mucosa and invasive cancer.