LINE1 methylation levels in pre-diagnostic leukocyte DNA and future renal cell carcinoma risk

Higher levels of LINE1 methylation in blood DNA have been associated with increased kidney cancer risk using post-diagnostically collected samples; however, this association has never been examined using pre-diagnostic samples. We examined the association between LINE1 %5mC and renal cell carcinoma (RCC) risk using pre-diagnostic blood DNA from the United States-based, Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) (215 cases/436 controls), and the Alpha-tocopherol, Beta-carotene Cancer Prevention Study (ATBC) of Finnish male smokers (191 cases/575 controls). Logistic regression adjusted for age at blood draw, study center, pack-years of smoking, body mass index, hypertension, dietary alcohol intake, family history of cancer, and sex was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) using cohort and sex-specific methylation categories. In PLCO, higher, although non-significant, RCC risk was observed for participants at or above median methylation level (M2) compared to those below the median (M1) (OR: 1.37, 95% CI: 0.96–1.95). The association was stronger in males (M2 vs. M1, OR: 1.54, 95% CI: 1.00–2.39) and statistically significant among male smokers (M2 vs. M1, OR: 2.60, 95% CI: 1.46–4.63). A significant interaction for smoking was also detected (<i>P</i>-interaction: 0.01). No association was found among females or female smokers. Findings for male smokers were replicated in ATBC (M2 vs. M1, OR: 1.31, 95% CI: 1.07–1.60). In a pooled analysis of PLCO and ATBC male smokers (281cases/755controls), the OR among subjects at or above median methylation level (M2) compared to those below the median (M1) was 1.89 (95% CI: 1.34–2.67, <i>P</i>-value: 3 x 10^–4); a trend was also observed by methylation quartile (<i>P</i>-trend: 0.002). These findings suggest that higher LINE1 methylation levels measured prior to cancer diagnosis may be a biomarker of future RCC risk among male smokers.

此前已有研究基于诊断后采集的样本，发现血液DNA中较高的LINE1甲基化水平与肾癌风险升高存在关联，但该关联尚未有诊断前采集的样本加以验证。本研究借助美国前列腺、肺、结直肠和卵巢癌筛查试验（Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, PLCO）（215例病例/436例对照）以及芬兰男性吸烟者的α-生育酚、β-胡萝卜素癌症预防研究（Alpha-tocopherol, Beta-carotene Cancer Prevention Study, ATBC）（191例病例/575例对照）中诊断前采集的血液DNA样本，探讨了LINE1的5-甲基胞嘧啶（5mC）占比与肾细胞癌（renal cell carcinoma, RCC）风险之间的关联。本研究采用按队列及性别分层的甲基化分类方法，通过校正采血年龄、研究中心、吸烟包年数、体重指数、高血压病史、膳食酒精摄入量、癌症家族史以及性别的logistic回归模型，计算比值比（OR）与95%置信区间（CI）。在PLCO队列中，与甲基化水平低于中位数的受试者（M1组）相比，甲基化水平处于中位数及以上的受试者（M2组）的肾细胞癌风险虽未达到统计学显著性，但呈现升高趋势（OR: 1.37, 95% CI: 0.96–1.95）。该关联在男性群体中更为显著（M2组vs.M1组，OR: 1.54, 95% CI: 1.00–2.39），且在男性吸烟者中达到统计学显著性（M2组vs.M1组，OR: 2.60, 95% CI: 1.46–4.63）；同时检测到吸烟存在显著的交互作用（交互P值: 0.01）。在女性群体及女性吸烟者中未观察到此类关联。男性吸烟者的上述关联在ATBC队列中得到了重复验证（M2组vs.M1组，OR: 1.31, 95% CI: 1.07–1.60）。对PLCO与ATBC队列的男性吸烟者（共281例病例/755例对照）进行合并分析后发现，与M1组受试者相比，M2组受试者的肾细胞癌风险OR值为1.89（95% CI: 1.34–2.67, P值: 3×10^–4）；按甲基化四分位数分组也观察到了剂量反应趋势（趋势P值: 0.002）。上述研究结果表明，在癌症诊断前检测到的较高LINE1甲基化水平，或可作为男性吸烟者未来肾细胞癌风险的生物标志物。