Vasavi Mohan, Ponnala Shivani, Gujjari Kusumanjali, Boddu Prabhakar, Bharatula Ravi Shankar, Prasad Rupender, Ahuja Yog Raj, Hasan Qurratulain
Department of Genetics and Molecular Medicine, Gastroenterology and Biochemistry, Kamineni Hospitals, Hyderabad, India.
Tumori. 2006 Mar-Apr;92(2):155-62. doi: 10.1177/030089160609200212.
Chronic inflammation leading to malignancy in the esophagus may be due to errors in mismatch repair (MMR) genes such as hMLH1. Promoter hypermethylation has been suggested as the main cause of hMLH1 silencing. In this study we assessed hMLH1 promoter hypermethylation in a range of esophageal diseases. Further, we evaluated the role of factors affecting the methylation cycle: (1) methylenetetrahydrofolate reductase (MTHFR) C677T mutation and (2) serum homocysteine levels.
We endoscopically and histologically categorized 124 paired tissue and blood samples from patients into cancer, precancer, reflux esophagitis, other inflammatory esophagitis and controls (endoscopically normal). Restriction enzyme-based methylation analysis was carried out to assess hMLH1 promoter hypermethylation.
hMLH1 promoter hypermethylation in tissue was seen in 63.5% of patients with cancer and 53.8% of those with precancer, which was significantly increased when compared with controls (P < 0.001). There appears to be an increasing degree of hMLH1 hypermethylation with disease progression. Patients with gastroesophageal reflux disease (GERD) showed a high degree of hMLH1 hypermethylation (88.8%), indicating that local environment due to reflux may be promoting hypermethylation. We suggest that GERD is a progressive condition with an increased risk for developing into cancer. Only 14.5% of cases exhibited hypermethylation both in tissue and blood. Hence, we conclude that hMLH1 promoter hypermethylation is a tissue-specific change in the esophagus and blood testing cannot be used as a noninvasive tool to assess it. DNA methylation is dependent on the methylation cycle; MTHFR is a major enzyme in this pathway. MTHFR mutations did not correlate with hypermethylation or clinical pathology (P > 0.5). Elevated homocysteine levels, independent of MTHFR mutation, correlated significantly with hMLH1 hypermethylation in tissue (P < 0.005). Our study shows that hMLH1 hypermethylation in tissue may be the primary event caused by endogenous/exogenous factors in esophageal diseases, aiding disease progression.
导致食管癌的慢性炎症可能归因于错配修复（MMR）基因如hMLH1的错误。启动子高甲基化被认为是hMLH1沉默的主要原因。在本研究中，我们评估了一系列食管疾病中hMLH1启动子的高甲基化情况。此外，我们还评估了影响甲基化循环的因素的作用：（1）亚甲基四氢叶酸还原酶（MTHFR）C677T突变；（2）血清同型半胱氨酸水平。
我们通过内镜检查和组织学检查，将124例患者的配对组织和血液样本分为癌症组、癌前病变组、反流性食管炎组、其他炎症性食管炎组和对照组（内镜检查正常）。采用基于限制性内切酶的甲基化分析来评估hMLH1启动子的高甲基化情况。
63.5%的癌症患者和53.8%的癌前病变患者的组织中观察到hMLH1启动子高甲基化，与对照组相比显著增加（P < 0.001）。随着疾病进展，hMLH1高甲基化程度似乎在增加。胃食管反流病（GERD）患者表现出高度的hMLH1高甲基化（88.8%），表明反流引起的局部环境可能促进高甲基化。我们认为GERD是一种进行性疾病，发展为癌症的风险增加。仅14.5%的病例在组织和血液中均表现出高甲基化。因此，我们得出结论，hMLH1启动子高甲基化是食管中的一种组织特异性变化，血液检测不能用作评估它的非侵入性工具。DNA甲基化依赖于甲基化循环；MTHFR是该途径中的一种主要酶。MTHFR突变与高甲基化或临床病理无关（P > 0.5）。同型半胱氨酸水平升高，与MTHFR突变无关，与组织中hMLH1高甲基化显著相关（P < 0.005）。我们的研究表明，组织中hMLH1高甲基化可能是食管疾病中内源性/外源性因素引起的主要事件，有助于疾病进展。
