BACKGROUND DNA hypermethylation of tumor suppressor genes is observed in precancerous lesions and oral cancer of individuals with the habits of betel quid (BQ) chewing. SIRT1 has been identified as playing a role in the maintenance of epithelial integrity, and its alteration is often related to carcinogenesis. However, the methylation and transcription status of SIRT1 in patients with BQ chewing-related oral cancer has not been investigated. We examined the methylation status of SIRT1 in paraffin-embedded tissue samples of oral squamous cell carcinoma (OSCC) obtained from BQ chewing and non-chewing patients and in tissue samples from healthy control subjects. In addition, we examined whether the hypermethylation of SIRT1 followed by its transcriptional downregulation in the human gingival epithelial cells could be caused by arecoline, a major component of BQ. Furthermore, we investigated the methylation status of SIRT1 in smear samples of macroscopically healthy buccal mucosa from subjects with a habit of BQ chewing. RESULTS SIRT1 was significantly hypermethylated in tissue samples of OSCC from BQ chewers and non-chewers than in oral mucosa from healthy control subjects. Results also showed that the hypermethylation level of SIRT1 was significantly higher in OSCC of patients with BQ chewing habits than in those of non-chewing habits (p < 0.05). Our in vitro model showed that hypermethylation is followed by downregulation of the transcriptional level of SIRT1 (p < 0.05). The methylation levels of SIRT1 in the smear samples obtained from BQ chewing individuals were significantly higher than those in the samples obtained from individuals that did not chew BQ. The duration of BQ chewing habits was correlated positively to the frequency of SIRT1 hypermethylation (p < 0.05). CONCLUSIONS Our results suggest that DNA hypermethylation of SIRT1 is involved in the occurrence of oral cancer in BQ chewing patients and that hypermethylation in the oral mucosa of BQ chewers could be a predictive marker for the occurrence of malignant transformation. This is the first report that showed DNA hypermethylation in clinically healthy oral epithelium of BQ chewers. Our study shows evidence that DNA hypermethylation may be an early event of oral carcinogenesis prior to observable clinical changes.

中文翻译：

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槟榔咀嚼引起的sirtuin 1（SIRT1）的DNA超甲基化-可能是恶性转化的预测生物标记。

背景技术在具有槟榔（BQ）咀嚼习惯的个体的癌前病变和口腔癌中观察到了肿瘤抑制基因的DNA超甲基化。SIRT1已被确定在维持上皮完整性中发挥作用，其改变通常与致癌作用有关。然而，尚未研究与咀嚼相关的口腔癌患者中SIRT1的甲基化和转录状态。我们检查了从BQ咀嚼和非咀嚼患者获得的口腔鳞状细胞癌（OSCC）的石蜡包埋组织样品以及健康对照受试者的组织样品中SIRT1的甲基化状态。此外，我们研究了SIRT1在人齿龈上皮细胞中的过度甲基化及其转录下调是否可能是由于槟榔碱引起的，BQ的主要组成部分。此外，我们调查了具有BQ咀嚼习惯的宏观健康口腔黏膜涂片样本中SIRT1的甲基化状态。结果与健康对照对象的口腔粘膜相比，BQ咀嚼和非咀嚼的OSCC组织样品中SIRT1的甲基化程度明显更高。结果还显示，BQ咀嚼习惯患者的OSCC中SIRT1的高甲基化水平显着高于非咀嚼习惯患者（p <0.05）。我们的体外模型显示，高甲基化后SIRT1的转录水平下调（p <0.05）。从BQ咀嚼个体获得的涂片样本中，SIRT1的甲基化水平明显高于从没有咀嚼BQ个体获得的样本中的SIRT1甲基化水平。BQ咀嚼习惯的持续时间与SIRT1高甲基化的频率呈正相关（p <0.05）。结论我们的结果表明，SIRT1的DNA高甲基化与BQ咀嚼患者口腔癌的发生有关，而BQ咀嚼器口腔黏膜中的高甲基化可能是恶性转化发生的预测标志。这是第一份显示BQ咀嚼物临床上健康的口腔上皮中DNA甲基化程度较高的报告。我们的研究表明，DNA高甲基化可能是可观察到的临床变化之前口腔癌发生的早期事件。结论我们的结果表明，SIRT1的DNA高甲基化与BQ咀嚼患者口腔癌的发生有关，并且BQ咀嚼器口腔黏膜中的高甲基化可能是恶性转化发生的预测标志。这是第一份显示BQ咀嚼物临床上健康的口腔上皮中DNA甲基化程度较高的报告。我们的研究表明，DNA高甲基化可能是可观察到的临床变化之前口腔癌发生的早期事件。结论我们的结果表明，SIRT1的DNA高甲基化与BQ咀嚼患者口腔癌的发生有关，并且BQ咀嚼器口腔黏膜中的高甲基化可能是恶性转化发生的预测标志。这是第一份显示BQ咀嚼物临床上健康的口腔上皮中DNA甲基化程度较高的报告。我们的研究表明，DNA高甲基化可能是可观察到的临床变化之前口腔癌发生的早期事件。