| Summary: | The incidence of adenocarcinoma of the oesophagus (ACO) is rapidly rising, with the UK white male population currently experiencing the highest incidence worldwide. ACO arises on a background of Barrett's oesophagus (BO), a condition characterised by metastatic remodelling of the lower oesophagus in response to reflux of gastric contents. Previous work within our laboratory has shown that Barrett's epithelium expresses the gastrin activated CCK2 receptor, that gastrin stimulates proliferation of BO cells, and that Barrett's patients with the highest circulating gastrin concentrations are more likely to exhibit dysplasia. Patients diagnosed with BO are often prescribed proton pump inhibitors (PPIs) to reduce damage when acid reflux occurs. A common consequence of PPI usage is a significant increase in circulating gastrin concentration. The idea underlying the present study is that gastrin drives the progression of BO to ACO. If so, there is a need for biomarkers of the effect of gastrin on Barrett's epithelium that might be useful in tracking the progression of BO to ACO and in monitoring the effectiveness of novel anti-gastrin therapies. Circulating gastrin concentration was analysed by radioimmunoassay and related to putative biomarker mRNA and miRNA expression quantified by qPCR in gastric and oesophageal biopsies from BO patients. Using gastric adenocarcinoma cell lines expressing the CCK2 receptor and treated with gastrin, putative protein biomarkers were analysed using western blot. Treatment with PPIs was associated with significant increases in circulating gastrin in control and Barrett's patients. Abundance of CgA and HDC mRNA was also significantly elevated in gastric biopsies of both groups treated with PPIs. In gastric biopsies from patients with preneoplastic conditions CgA was significantly decreased in the highest risk group. Interestingly, BO biopsies exhibited a significantly lower abundance of CgA, MMP-1, MMP-7, COX-2 and SHH transcripts in patients with high circulating gastrin (>100 pM). In serum, miR-21, -221 and 222 abundances were significantly elevated when circulating gastrin was 30-100 pM but not >100 pM; tissue miR-221 and 222 was lower with gastrin >100 pM. The expression of putative biomarkers in vitro varied between cell lines, although TIMP-1 and MMP-1 exhibited consistent responses to gastrin. Unexpectedly, in stomach and BO biopsies, CCK2 receptor mRNA abundance was significantly depressed in patients with elevated circulating gastrin concentration. Whilst changes in CCK2 receptor expression relative to gastrin have been suggested previously, the regulatory mechanisms are not completely understood. This result was surprising and may account for the pattern of association of putative gastrin-regulated biomarkers and circulating gastrin. The result also has wider-reaching implications for the interpretation of previous studies and for the design of future studies of the effect of gastrin on the progression of preneoplastic conditions in the gastrointestinal tract.
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