GERD is associated with shortened telomeres in the squamous epithelium of the distal esophagus.

Telomeres are repetitive DNA sequences located at the ends of chromosomes. Telomeres are shortened by repeated cell divisions and by oxidative DNA damage, and cells with critically shortened telomeres cannot divide. We hypothesized that chronic gastroesophageal reflux disease (GERD)-induced injury of the esophageal squamous epithelium results in progressive telomeric shortening that eventually might interfere with mucosal healing. To address our hypothesis, we compared telomere length and telomerase activity in biopsy specimens of esophageal squamous epithelium from GERD patients and control patients. Endoscopic biopsies were taken from the esophageal squamous epithelium of 38 patients with GERD [10 long-segment Barrett's esophagus (LSBE), 15 short-segment (SSBE), 13 GERD without Barrett's esophagus] and 16 control patients without GERD. Telomere length was assessed using the terminal restriction fragment assay, and telomerase activity was studied by the PCR-based telomeric repeat amplification protocol assay. Patients with GERD had significantly shorter telomeres in the distal esophagus than controls [8.3 +/- 0.5 vs. 10.9 +/- 1.5 (SE) Kbp, P = 0.043]. Among the patients with GERD, telomere length in the distal esophagus did not differ significantly in those with and without Barrett's esophagus (LSBE 7.9 +/- 0.8, SSBE 8.6 +/- 0.9, GERD without BE 8.7 +/- 1.0 Kbp). No significant differences in telomerase activity in the distal esophagus were noted between patients with GERD and controls (4.0 +/- 0.39 vs. 5.2 +/- 0.53 RIUs). Telomeres in the squamous epithelium of the distal esophagus of patients who have GERD, with and without Barrett's esophagus, are significantly shorter than those of patients without GERD despite similar levels of telomerase activity.

Spontaneous immortalization of clinically normal colon-derived fibroblasts from a familial adenomatous polyposis patient.

Normal human diploid cells do not spontaneously immortalize in culture, but instead enter replicative senescence after a finite number of population doublings. Ablation of key checkpoint arrest or cancer-suppressor genes, through dominantly inherited germline mutation (p53+/-, Li-Fraumeni) or viral oncogene expression (SV40 large T, HPV16/18, and E6/E7) can lead to escape from senescence, additional doublings, and entrance into crisis phase, where immortal clones emerge at low frequency. In the vast majority of cases, telomerase is reactivated and telomeres are stabilized. Here we describe the spontaneous immortalization of clinically normal fibroblasts derived from colonic stroma of a familial adenomatous polyposis (FAP) patient. The preimmortal (C26C) and the spontaneously immortalized derivative (C26Ci) cells are heterozygous for a characterized germline mutation in exon 15 of the adenomatous polyposis coli gene. Immortalization was accompanied by spontaneous reactivation of endogenous telomerase and establishment of telomeres at presenescent lengths. Normal checkpoint behavior is retained and a diploid karyotype is maintained. These cells provide a valuable new addition to the limited number of spontaneously immortalized human cell types, particularly fibroblast cells, and will be useful in experimentally determining the functional pathways in neoplastic development and in the identification of potential molecular targets for cancer chemoprevention.

Intestinal metaplasia at the gastroesophageal junction: Barrett's, bacteria, and biomarkers.

For patients found to have intestinal metaplasia at the gastroesophageal junction, technical problems can make it difficult to distinguish short-segment Barrett's esophagus from intestinal metaplasia of the gastric cardia. Whereas the risk of malignancy for the former condition seems to be higher than that for the latter, the distinction between these conditions can have practical clinical implications. Immunostaining for cytokeratins has been proposed as a means to distinguish intestinal metaplasia of esophageal and gastric origins. We review recent data on this issue, and conclude that immunostaining for cytokeratins has no clear advantages over other biomarkers that have been proposed for identifying Barrett's esophagus (e.g., mucin histochemistry, mAb Das-1 immunoreactivity). Presently, the importance of intestinal metaplasia at the gastroesophageal junction remains unclear, and the clinical utility of biomarkers in distinguishing short-segment Barrett's esophagus from intestinal metaplasia of the gastric cardia has not yet been established.

Bypass of telomere-dependent replicative senescence (M1) upon overexpression of Cdk4 in normal human epithelial cells.

Many stimuli causing 'stress' or DNA damage in cells can produce phenotypes that overlap with telomere-based replicative senescence. In epithelial systems, the p16/RB pathway may function as a stress senescence-signaling pathway independent of telomere shortening. Overexpressing cyclin-dependent kinase 4 (Cdk4) in human epidermal keratinocytes and human mammary epithelial cells not only prevents the p16(INK4a)-associated premature growth arrest due to telomere-independent stress (e.g., inadequate culture conditions), but also bypasses the ensuing telomere-dependent senescence (M1). Overexpressed Cdk4 in epithelial cells induces a dramatic upregulation of p16(INK4a) and milder upregulation of p53 and p21(WAF1), which become unresponsive to UV irradiation. Despite the high levels of these checkpoint factors, Cdk4-overexpressing cells divide in an apparently normal regulated fashion, are able to respond to changes in calcium levels, retain the stem cell phenotype, and fully differentiate and stratify. These results suggest that the differentiation pathways in Cdk4-overexpressing cells remain intact.

Hallmarks of cancer progression in Barrett's oesophagus.

CONTEXT: Hanahan and Weinberg proposed in 200 that carcinogenesis involves DNA changes that enable cells to:provide their own growth signals, ignore growth-inhibitory signals, avoid apoptosis, replicate without limit, sustain angiogenesis, and invade and proliferate in unnatural locations. The metaplastic cells of Barrett's oesophagus are predisposed to develop these cancer hallmarks. STARTING POINT: The genetic changes that have been described in Barrett's oesophagus can be categorised according to the predominant cancer hallmark affected. For example, M Auvinen and colleagues recently observed abnormalities in the expression of vascular endothelial growth factors (VEGFs) in Barrett's oesophagus (J Clin Oncol 2002; 20: 2971-79). These abnormalities can be categorised as those that affect angiogenesis, a process that is essential for the development and progression of tumours. WHERE NEXT? The cancer hallmarks of Barrett's oesophagus provide a framework to categorise the genetic abnormalities described and to further understanding of the genetic events that underlie oesophageal carcinogenesis.

Management of Anticoagulation for Gastrointestinal Endoscopic Procedures.

Endoscopic procedures, particularly those requiring mucosal biopsy or polypectomy, are associated with an increased risk of gastrointestinal bleeding during or after procedure. This risk is increased in patients treated with chronic anticoagulant therapy. Anticoagulant therapy needs to be withheld for certain high-risk endoscopic procedures to prevent bleeding complications. However, this may expose some patients to an increased risk of thromboembolic complications during this period, particularly in patients with recent episodes of venous or arterial thromboembolism and those with prosthetic mechanical valves. Identifying patients at a high risk for thromboembolic complications and more aggressively managing their anticoagulant regimen (by switching to heparin) in preparation for the endoscopic procedure decreases the length of time they remain unanticoagulated and helps minimize complications. Low molecular weight heparin as a bridging therapy in preparation for endoscopic procedures can obviate unnecessary hospitalization and is an attractive strategy for managing high-risk patients.