The changing face of esophageal malignancy

Risk assessment of esophageal adenocarcinoma using γ-H2AX assay

BACKGROUND

Mutagen-induced DNA damage as measured in peripheral blood lymphocytes (PBL) has been associated with increased risks of cancers. The formation of γ-H2AX is an early cellular response to DNA double-strand breaks (DSB). We hypothesize that higher level of radiation-induced γ-H2AX in PBLs may be associated with an increased risk of esophageal adenocarcinoma.

METHODS

Laser scanning cytometer-based immunocytochemical method was used to measure baseline and irradiation-induced γ-H2AX levels in PBLs from 211 patients with esophageal adenocarcinoma and 211 healthy controls. The ratio of induced γ-H2AX level to baseline level was used to evaluate individual susceptibility to DSBs. Relative risks for esophageal adenocarcinoma associated with γ-H2AX were assessed by multivariable logistic regression analysis.

RESULTS

Radiation-induced γ-H2AX level and the γ-H2AX ratio were significantly higher in cases than in controls. Dichotomized at the median in controls, a significantly increased risk for esophageal adenocarcinoma was observed in association with high γ-H2AX ratio [OR = 2.94; 95% confidence interval (CI), 1.83-4.72]. Quartile analyses showed significant dose-response associations between higher γ-H2AX ratio and increased risk of esophageal adenocarcinoma (Ptrend, 1.64E-06). In addition, joint effect between γ-H2AX ratio and smoking was observed: smokers who had high γ-H2AX ratio exhibited the highest risk of esophageal adenocarcinoma (OR = 5.53; 95% CI, 2.71-11.25) compared with never smokers with low γ-H2AX ratio.

CONCLUSION

Radiation-induced DNA damage assessed by γ-H2AX ratio is associated with an increased risk of esophageal adenocarcinoma.

IMPACT

γ-H2AX assay is a new and robust method to measure DSB damage in PBLs, which can be used to assess mutagen sensitivity and esophageal adenocarcinoma risk.

Circulating lymphangiogenic growth factors in gastrointestinal solid tumors, could they be of any clinical significance?

Metastasis is the principal cause of cancer mortality, with the lymphatic system being the first route of tumor dissemination. The glycoproteins VEGF-C and VEGF-D are members of the vascular endothelial growth factor (VEGF) family, whose role has been recently recognized as lymphatic system regulators during embryogenesis and in pathological processes such as inflammation, lymphatic system disorders and malignant tumor metastasis. They are ligands for the VEGFR-3 receptor on the membrane of the lymphatic endothelial cell, resulting in dilatation of existing lymphatic vessels as well as in vegetation of new ones (lymphangiogenesis). Their determination is feasible in the circulating blood by immunoabsorption and in the tissue specimen by immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR). Experimental and clinicopathological studies have linked the VEGF-C, VEGF-D/VEGFR3 axis to lymphatic spread as well as to the clinical outcome in several human solid tumors. The majority of these data are derived from surgical specimens and malignant cell series, rendering their clinical application questionable, due to subjectivity factors and post-treatment quantification. In an effort to overcome these drawbacks, an alternative method of immunodetection of the circulating levels of these molecules has been used in studies on gastric, esophageal and colorectal cancer. Their results denote that quantification of VEGF-C and VEGF-D in blood samples could serve as lymph node metastasis predictive biomarkers and contribute to preoperative staging of gastrointestinal malignancies.

Dietary mineral and trace element intake and squamous cell carcinoma of the esophagus in a Chinese population

Few studies have been conducted in low-selenium areas of China to assess the relationships between dietary intake of selenium and zinc and the risk of squamous cell carcinoma of the esophagus (SCCE). We studied dietary mineral and trace element intake and risk of SCCE in a population- based, case-control study in Taixing, China, in 2000. A total of 218 SCCE patients and 415 population healthy controls were interviewed using a standard dietary and health questionnaire. The median and quartiles were calculated to represent the average level and distribution of selected dietary minerals and trace elements estimated by the Chinese Standard Tables of Food Composition. The adjusted odds ratios (ORs) comparing the highest with the lowest quartiles were 0.30 (95% confidence intervals, CIs = 0.13-0.67) for selenium intake and 0.28 (95% CI = 0.11-0.70) for zinc intake with obvious dose-dependent patterns (P values for trend = 0.01). The adjusted OR for the combined effect of selenium and zinc intake was 0.53 (95% CI = 0.29-0.96) after controlling for potential confounding factors, including age, gender, educational level, body mass index, and total energy intake. Our results suggested that the potential joint effect of zinc and selenium might contribute to SCCE risk. Increased dietary intake of selenium and zinc may decrease the risk of SCCE in a low-selenium area of China.

Deficiency of cell cycle checkpoints and DNA repair system predispose individuals to esophageal cancer

Cell cycle checkpoints and DNA repair capacity are critical for the maintenance of genome integrity. We hypothesized that, in comparison to healthy controls, esophageal cancer patients might have a higher frequency of deficiencies in cell cycle checkpoints and/or DNA repair system. Using flow cytometry and comet assay, we assessed the gamma-radiation-induced S phase and G2-M phase accumulation, and benzo(a)pyrene-diol-epoxide (BPDE)- and gamma-radiation-induced DNA damage, in peripheral blood lymphocytes of 99 newly diagnosed esophageal cancer patients and 112 age-, gender-, and ethnicity-matched healthy controls. The mean gamma-radiation-induced cell accumulation at G2-M phase was significantly lower in esophageal cancer patients than the control subjects (case versus control: 5.27%+/-5.11% versus. 7.06%+/-5.04%, P = 0.013). The less G2-M phase cell accumulation resulted in a significant increased risk for esophageal cancer with an odds ratio of 2.08 (95% confidence interval 1.15-3.77). After normalization to baseline S fraction, the radiation-induced increment in the 4N/2N ratio was also significantly lower in esophageal cancer patients than in controls (case versus control: 0.76% versus 1.04%, P = 0.0039). The less increment in the radiation-induced 4N/2N ratio was associated with 2.24(95% confidence interval 1.22-4.11)-fold increase of esophageal cancer risk. We also compared the mutagen-induced DNA damage level among individuals with different S or G2-M phase cell accumulation. We found that the less G2-M phase accumulation was associated with both high BPDE induced and gamma-radiation-induced DNA damage in the healthy controls (P for trend = 0.023 and 0.015, respectively). Similar pattern was observed for S phase accumulation (P for trend = 0.033 and 0.022, respectively). However, such association was not seen in esophageal cancer patients. This study provides the first molecular epidemiologic evidence linking increased esophageal cancer risk with defects in cell-cycle checkpoints and DNA repair capacity.

Induction of cyclooxygenase-2 by benzo[a]pyrene diol epoxide through inhibition of retinoic acid receptor-beta 2 expression

Benzo[a]pyrene diol epoxide (BPDE, a carcinogen present in tobacco smoke and environmental pollution) has been shown to suppress retinoic acid receptor-beta2 (RAR-beta(2)) and induce cyclooxygenase-2 (COX-2) expression. Restoration of RAR-beta(2) inhibited growth and colony formation of esophageal cancer cells, which was correlated with COX-2 suppression. In this study, we investigated the molecular mechanisms for RAR-beta(2)-mediated suppression of COX-2 expression using BPDE as a tool. We found that BPDE-induced COX-2 expression was through inhibition of RAR-beta(2) and consequently, induction of epidermal growth factor receptor (EGFR), extracellular signal-regulated protein kinases 1/2 (Erk1/2) phosphorylation, and c-Jun expression. Esophageal cancer cells that do not express RAR-beta(2) did not respond to BPDE for induction of COX-2. BPDE was also unable to induce COX-2 expression after RAR-beta(2) expression was manipulated in these esophageal cancer cells. Furthermore, BPDE induced time-dependent methylation of RAR-beta(2) gene promoter in esophageal cancer cells. Transfection of RAR-beta(2) expression vector into esophageal cancer cells suppressed expression of EGFR, Erk1/2 phosphorylation, c-Jun, and COX-2. In addition, co-treatment of RAR-beta(2)-positive cells with BPDE and the MEK1/2 inhibitor U0126 caused little change in c-Jun and COX-2 expression. This study demonstrated that BPDE-suppressed expression of RAR-beta(2) results in COX-2 induction and restoration of RAR-beta(2) expression reduces COX-2 protein in esophageal cancer cells, thereby further supporting our previous finding that RAR-beta(2) plays an important role in suppressing esophageal carcinogenesis.

Predictors of esophageal cancer risk: assessment of susceptibility to DNA damage using comet assay

Individuals' susceptibility to DNA damage could be identified by mutagen-challenged assays. We tested the hypothesis that susceptibility to DNA damage, measured by comet assay, may be associated with increased esophageal cancer (EC) risk. We recruited 102 subjects with previously untreated EC and 112 healthy controls. Baseline (untreated), benzo[a]pyrene diol epoxide (BPDE)-induced, and gamma-radiation-induced DNA damage were quantified by the Olive tail moment parameter. The mean tail moment was significantly higher in cases than in controls at baseline (case vs. control: 2.6 vs. 1.9, P < 0.01), after BPDE induction (case vs. control: 3.8 vs. 2.7, P < 0.01), and after gamma-radiation-induction (case vs. control: 5.0 vs. 3.8, P < 0.01). When data were dichotomized with the median values in the controls, a significantly increased risk for EC was observed for high baseline tail moment [odds ratio (OR) = 5.7, 95% confidence interval (CI) = 2.9-11.4], high BPDE-induced tail moment (OR = 5.8, 95% CI = 2.9-11.8), and high gamma-radiation-induced tail moment (OR = 4.6, 95% CI = 2.4-8.8). Further, the association between DNA damage and EC was stronger in never smokers than in ever smokers. Compared with subjects not sensitive to both mutagens, individuals sensitive to only one mutagen showed a 3.4-fold risk for EC and those sensitive to both mutagens showed an 8.7-fold risk for EC. Thus, we conclude that susceptibility to DNA damage as assessed by comet assay might help identify individuals with high EC risk.

Helicobacter pylori infection: a protective factor for esophageal squamous cell carcinoma in a Taiwanese population

AIM

Many researchers have reported the inverse relationship between Helicobacter pylori (H. pylori) infection and esophageal adenocarcinoma risk, but very few studies have examined the association between H. pylori infection and the development of esophageal squamous-cell carcinoma (ESCC). Therefore, the aim of this study is to evaluate the relationship between H. pylori infection and ESCC risk.

METHOD

Subjects were cancer cases, pathologically proven to have ESCC, in two large medical centers in Kaohsiung metropolitan of southern Taiwan between August 2000 and May 2003. Controls were from the healthy subjects who lived in Kaohsiung metropolitan and voluntarily participated in one large multiyear of gene-environmental study. In total, 127 cases (116 males and 11 females) and 171 controls (161 males and 10 females) were recruited in the same period of time for interviews. H. pylori seropositivity was determined by an enzyme-linked immunosorbant assay measuring IgG.

RESULTS

A total of 28 (22.1%) and 74 (43.3%) out of 127 cases and 171 controls, respectively, had positive H. pylori infection. After adjusting for other covariates, subjects with positive H. pylori infections had a significantly reduced risk (adjusted odds ratio (AOR) = 0.51; 95% CI = 0.27-0.96; p= 0.037) of developing ESCC than those without. This result was even more pronounced in the groups of younger subjects, nonsmokers, or nondrinkers. In addition, among the 117 cancer patients who provided information about site of cancer lesion, the present study found that subjects with cancer lesions in the lower third of the esophagus had significantly fewer positive H. pylori infections (AOR = 0.34; 95% CI = 0.14-0.80; p= 0.013) than controls.

CONCLUSION

Our findings suggest that H. pylori infection may protect against the development of ESCC. Additional studies are needed to confirm these findings.

New approaches to the role of diet in the prevention of cancers of the alimentary tract

Cancers of the alimentary tract are, collectively, amongst the major causes of morbidity and deaths from cancer across the world today. Of the 10 million new cases of cancer diagnosed in 2000, about 2.3 million were cancers of the pharynx, oesophagus, stomach or colorectum. Nevertheless, epidemiological studies indicate that cancers of the digestive organs are also amongst the most susceptible to modification by dietary factors. International variations in incidence suggest that round three quarters of all sporadic colorectal cancers are attributable to diet. Even within the relatively uniform environment of the European Union, there are variations in the incidence of colorectal and oesophageal cancers of about two- and six-fold, respectively. Carcinomas of the alimentary tract arise from epithelial cells via distinct sequences of neoplastic change, which require a large fraction of an individual's lifespan. The best characterised of these is the adenoma-carcinoma sequence of colorectal carcinogenesis, in which progressive loss of differentiation and normal morphology in a growing lesion is associated with the acquisition of somatic mutations, and of aberrant methylation of CpG-islands, leading to gene silencing. These molecular events are accompanied by functional changes, including increased mitosis and evasion of apoptosis. There is little evidence that diet exerts its effects primarily through food-borne carcinogens that can be identified and eliminated from the food-chain. It is far more probable that the adverse effects of diet are caused largely by over-consumption of energy, coupled with inadequate intakes of protective substances, including micronutrients, dietary fibre and a variety of phytochemicals. The latter are biologically active secondary plant metabolites, many of which modify cell proliferation and induce apoptosis in vitro. There is growing evidence that such effects also occur in vivo, and that they can suppress the progress of neoplasia. Carcinomas of the oesophagus, stomach and colon all appear to be partially preventable by diets rich in fruits and vegetables. Plant foods contain a variety of components including micronutrients, polyunsaturated fatty acids, and secondary metabolites such as glucosinolates and flavonoids, many of which can inhibit cell proliferation and induce apoptosis, and which may well act synergistically when combined in the human diet. The future challenge is to fully characterise and evaluate these effects at the cellular and molecular level, so at to exploit their full potential as protective mechanisms for the population as a whole.