Background: Retinoic acid (RA) is a powerful differentiation agent. Barrett’s oesophagus occurs when duodeno-gastro-oesophageal reflux causes squamous epithelium (SE) tissue to become columnar epithelium tissue by an unknown mechanism. The bile acid lithocholic acid (LCA) competes for the retinoid X receptor retinoid binding site. Hence, RA pathways may be implicated in Barrett’s oesophagus.
Methods: RA activity in tissues and cell lines treated with all-trans retinoic acid (ATRA) with or without LCA was assessed using a reporter. Expression of p21 was determined by real-time PCR in Barrett’s oesophagus cell lines with or without LCA. SE and Barrett’s oesophagus biopsy specimens were exposed to 100 μM of ATRA or 20 mM of a RA inhibitor, citral, in organ culture for >72 h. Characteristics of treated specimens, compared with untreated controls, were analysed by immunohistochemical analysis (cytokeratins (CKs), vimentin) and RT-PCR (CKs). Confocal microscopy assessed temporal changes in co-localisation of CK8/18 and vimentin. Cell proliferation was assessed by bromo-deoxyuridine incorporation and immunohistochemical analysis for Ki67 and p21.
Results: RA biosynthesis was increased in Barrett’s oesophagus compared with SE (p<0.001). LCA and ATRA caused a synergistic increase in RA signalling as shown by increased p21 (p<0.01). Morphological and molecular analysis of SE exposed to ATRA showed columnar differentiation independent of proliferation. Metaplasia could be induced from the stromal compartment alone and vimentin expression co-localised with CK8/18 at 24 h, which separated into CK8/18-positive glands and vimentin-positive stroma by 48 h. Citral-treated Barrett’s oesophagus led to phenotypic and immunohistochemical characteristics of SE, which was independent of proliferation.
Conclusion: RA activity is increased in Barrett’s oesophagus and is induced by LCA. Under conditions of altered RA activity and an intact stroma, the oesophageal phenotype can be altered independent of proliferation.
- ATRA, all-trans retinoic acid
- BrdU, bromo-deoxyuridine
- CK, cytokeratin
- Ct, cycle threshold
- GAPDH, glyceraldehyde-3-phosphate dehydrogenase
- LCA, lithocholic acid
- RA, retinoic acid
- RARE, retinoic acid response elements
- RT-PCR, real-time PCR
- SE, squamous epithelium
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Published Online First 21 December 2006
Competing interests: None.