title: Relevance of N-nitrosamines to esophageal cancer in China.
abstract: Studies on the relevance of the N-nitrosamines to esophageal cancer in China are reviewed. Esophageal cancer is a complex and multifactorial problem. Although a causal association between nitrosamines exposure and esophageal cancer in China has not yet been rigorously established, exposure of Lin-Xian subjects to nitrosamines either directly or as a result of their in vivo formation has been detected in our study. Several N-nitrosamines (NDMA, NDEA, NMBzA, NPyr, NPip, and NSAR) in gastric juice collected from Lin-Xian inhabitants have been detected. A correlation was found between the lesions of esophageal epithelium and the amount of nitrosamines present. In addition, the amounts of N-nitrosamino acids (N-nitrosoproline, N-nitrosothiazolidine 4-carboxylic acid, NSAR, and nitrates) excreted in 24-hr urine of subjects in Lin-Xian were significantly higher than those in Fan-Xian, indicating a higher exposure to N-nitroso compound and their precursors of the inhabitants in the high-risk area. The effect of nitrosamines on human esophagus has been investigated at the cellular levels. The amounts of O6-MedG in DNA of esophageal or stomach mucosa of patients from Lin-Xian were higher than that from Europe (Lyon and Essen). The presence of O6-MedG in the human fetal esophagus cultured with NMBzA was also detected. These findings indicate that the elevated levels of O6-MedG in esophageal DNA could be the result of a recent exposure to N-nitroso compounds or a genetically determined reduced cellular capacity for repair of O6-MedG from DNA. The hyperplasia was induced in the esophagus of human fetus that cultured with NMBzA for 2 weeks to 2 months. The intervention studies of esophageal cancer in Lin-Xian have been pursued. Intake of moderate doses of ascorbic acids by Lin-Xian subjects effectively reduced the urinary levels of N-nitrosamino acids to those found in un-dosed subjects in the low-risk area. If N-nitroso compounds are formed in vivo and are among the causative factors of esophageal cancer in Lin-Xian, ascorbic acid appears to be effective in lowering the body burden of these carcinogenic compounds. Thus, the plan of chemoprevention is carried out in Lin-Xian.
mesh_terms: D001205:Ascorbic Acid / Q000627:therapeutic use; D002681:China; D004247:DNA / Q000032:analysis; D004812:Epidemiologic Methods; D004938:Esophageal Neoplasms / Q000139:chemically induced* / Q000453:epidemiology / Q000517:prevention & control; D004947:Esophagus / Q000196:embryology / Q000473:pathology; D005260:Female; D005750:Gastric Juice / Q000032:analysis; D006147:Guanine / Q000031:analogs & derivatives / Q000032:analysis; D006801:Humans; D006965:Hyperplasia; D009602:Nitrosamines / Q000009:adverse effects*; D011247:Pregnancy; D013997:Time Factors
chemical_list: D009602:Nitrosamines; D006147:Guanine; D004247:DNA; C008449:O-(6)-methylguanine; D001205:Ascorbic Acid