| Lung cancer (LC) is the most common malignant primary-tumor. According to WHO statistics, about 14.1 million new cancer cases occur in 2012 worldwide. There are 1.8 million new lung cancer cases accounting for about 13% of total cancer diagnoses. LC is the leading cause of cancer-related deaths in both developed and developing countries. In some areas, such as Xuanwei city of Yunnan province, the incidence of lung cancer is ranked the first place among all the cities in China. Numerous LC studies conducted in Xuanwei indicated that high incidence rate of LC is mainly associated with indoor air pollution from use of coal that contains carcinogens polycyclic aromatic hydrocarbons.Due to the recently increased environmental pollution and population aging, more and more people were diagnosed with LC. However, most patients were already in late-stage LC when diagnosed, because of lack of effective biomarkers for early detection of LC. As a result, the morbidity and mortality of LC still increase yearly and the 5-year survival rate has been less than 17%. Developing effective biomarkers is essential for early detection and early treatment of lung cancer and is a key to improve the prognosis and survival of LC. Studies have shown that the occurrence and development of human tumors significantly correlated with aberrant DNA methylation. Abnormal methylation on tumor-related genes occurs in cancerous cells before tumorigenesis, which could be excellent biomarkes of lung cancer screening and early diagnosis. DNA methylation-based biomarkers have an important role for the prevention and detection of LC, and for determination of effect of environmental carcinogens on the development of lung cancer.In this study, two tumor suppressor genes were chosen to investigate DNA methylation aberration in LC. In addition, BPDE-DNA adducts, an indicator for exposure to environmental carcinogens, was determined on LC tissues. The correlation between DNA methylation and BPDE-DNA adducts in lung cancer were explored in order to discover potential biomarkers for early-detection of lung cancer, and to evaluate the cancer related damage caused by environmental carcinogens on lung tissues.LC tissue-samples of lung cancer from 23 patients were collected from surgical treatment, in which 9 patients come from high-risk areas. According to statistical analysis, the number of male patients of LC were more than the female patients, and the average age of lung cancer patients from high-risk areas are obviously lower than that of other places. The methylation levels of RASSF1A and TBX5 genes in lung cancer patients were detected by bisulfite sequencing PCR. There are 8 of total 23 LC patients with high methylation level in RASSF1A gene (34.78%) and 14 samples with high methylation level in TBX5 gene (60.87%). In addition, we found that higher methylation level of RASSF1A and TBX5 appeared in lung cancer tissues than in the corresponding paracancerous tissues (P<0.001 and P<0.005 respectively). In some LC samples, the amounts of methylation of RASSF1A and TBX5 were correlated (R2=0.65), especially in one SCLC patient with both high methylation level of RASSF1A and TBX5. Finally, the correlation analysis showed that the methylation level of RASSF1A and TBX5 in male patients were higher than in female patients. Although no significant correlation was found between age and methylation level in general, in patients diagnosed as early stage LC, a positive correlation between the methylation levels of RASSF1A/TBX5 gene existed.The localization and quantification of BPDE-DNA adducts in LC tissues were analyzed by immunofluorescence assay. Results showed that BPDE-DNA adducts were expressed in both cell nuclear and cytoplasm and distributed in the surface of bronchial mucosa and in areas near lung alveolar. Furthermore, BPDE-DNA adducts were found in proliferating tumor cells, which revealed that BPDE-DNA could be inherited along with the proliferation of lung tumor cells after entering. The results of correlation analysis with clinical characteristics showed no significant difference between BPDE-DAN adducts and the gender of patients, and the expression of BPDE-DNA adducts in LC patients of age of 50-70 old was higher than patients at with other ages. Moreover, there was a trend of increasing BPDE-DNA adducts amount in LC patients with the clinical stage from â… A to â…¡ A, which demonstrated a positive relevance between BPDE-DNA adducts in early-stage LC.The relationship between the content of BPDE-DNA adducts and the level of DNA methylation in LC was analyzed. The results showed that no correlation was found between the methylation levels of RASSF1A gene with BPDE-DNA adducts content. while the methylation levels of TBX5 gene rose gradually with the increase of BPDE-DNA adducts expression (P=0.018)In summary, this study revealed that abnormal methylation of RASSF1A and TBX5 can be used as potential biomarkers for early diagnosis of LC. The malignancy of early lung cancer could be assessed by the concentration of BPDE-DNA adducts which can be reflected by methylation level of gene.TBX5 gene methylation could be an effective marker for assessment of damage effect induced by environmental carcinogens (PAHs). |
PDF Full Text Request