Environmental Exposure and DNA Damage

我们的实验室对与暴露和癌症相关的遗传和表观遗传修饰广泛感兴趣。 结直肠癌是全球第四大常见癌症，红肉和加工肉类的消费与这种癌症的风险和死亡率增加有关。 特别是，食用红肉和在高温下烹饪的含有高水平杂环胺（HCAs）的肉类与结直肠腺瘤的风险增加有关。 HCAs是一种致癌和致突变的化合物，通过高温烹饪肉类中的芳香族氨基酸和肌酸酐的热解形成，特别是通过平底锅油炸。 我们招募了16名健康志愿者进行为期4周的对照喂养研究，其中8名受试者被随机分配到含有低温（100 ℃）或高温（250 ℃）烹饪肉类的饮食方案中，每个方案交叉设计2周。 其他8名受试者被随机分配到饮食方案，单独含有高温肉类饮食或结合3个假定的诱变剂抑制剂：十字花科蔬菜，酸奶，叶绿酸片，也在交叉设计。 与低温肉食相比，高温肉食增加了尿液和粪便的致突变性。 抑制剂饮食使靶结肠直肠细胞中的DNA损伤减少了近两倍。 据我们所知，这是第一次证明饮食因素可以减少油炸肉类相关致癌作用靶组织中的DNA损伤。 乳腺癌是女性最常见的癌症之一，但即使发病率稳定，死亡率下降，今年美国仍将有超过18万名女性被诊断出乳腺癌，超过4万名女性将死于乳腺癌。 最近的全基因组关联研究已经发现了几种与乳腺癌相关的多态性，尽管这些多态性的风险不大。 我们的研究小组正在测试某些DNA修饰与乳腺癌风险相关的假设。 这种改变可能是由环境和遗传因素决定的，预计会在妇女的一生中发生变化。 端粒是位于染色体末端的非编码双链重复序列，在维持基因组完整性方面起着关键作用。实验研究表明，端粒功能障碍可能是乳腺上皮细胞染色体异常的重要原因。研究表明，随着乳腺癌染色体畸变的增加，端粒长度逐渐缩短。然而，流行病学研究白细胞端粒长度和乳腺癌之间的关联已经产生了模棱两可的结果。我们在一项前瞻性队列研究中，对至少有一个姐妹患有乳腺癌的妇女进行了外周血端粒长度与乳腺癌风险的相关性研究。 我们比较了342例乳腺癌患者和735例非乳腺癌患者，并采用单管单色多重定量PCR测量了外周血中的相对端粒长度。 我们没有发现与端粒缩短相关的风险增加的证据。 表观遗传修饰，包括DNA甲基化，正越来越多地被认为是基因转录调控的重要决定因素，具有遗传性和获得性特征。 异常的DNA甲基化模式是癌变过程中最早和最常见的事件之一，最近的研究表明，与无疾病的女性相比，患有活动性卵巢癌的女性外周血替代组织的DNA表观遗传特征可能不同。 我们对900多名女性的外周血样本进行了全基因组DNA甲基化分析，以研究DNA甲基化模式是否与乳腺癌风险相关。 我们已经确定了一些与风险增加相关的甲基化位点，并正在继续进行数据分析。 表观遗传修饰的第二种形式是miRNA表达。 改变的miRNA表达是癌症的中心特征，并且已经显示miRNA表达特征与诊断、分期、预后和对治疗的反应相关。 癌症的表达模式显示出高组织特异性，使其成为癌症筛查的潜在标志物。 乳腺癌特异性miRNAs已被证明与分期、血管浸润、增殖指数和ER/PR状态相关。 最近，已经在人血浆和血清中发现了足够水平的miRNA以允许谱分析，具有足够的能力来区分患有转移性前列腺癌的男性与没有癌症的男性和患有卵巢癌的女性。 我们最近使用姐妹研究队列完成了对来自病例和非病例的400多份血清样本的检测，目前正在进行数据分析。

Our laboratory is broadly interested in both genetic and epigenetic modifications associated with exposure and cancer. Colorectal cancer is the fourth most common cancer worldwide, and consumption of red and processed meat has been associated with increased risk of and mortality from this cancer. In particular, consumption of red meat and meat cooked at high temperature containing elevated levels of heterocyclic amines (HCAs) is associated with increased risk of colorectal adenoma. HCAs are mutagenic and carcinogenic compounds formed through pyrolysis of aromatic amino acids and creatinine in meats cooked at high temperature, particularly by pan-frying. We enrolled 16 healthy volunteers in a 4-week controlled feeding study where 8 subjects were randomly assigned to dietary regimens containing meat cooked at either low (100C) or high temperature (250C), each for 2 weeks in a crossover design. The other 8 subjects were randomly assigned to dietary regimens containing the high-temperature meat diet alone or in combination with 3 putative mutagen inhibitors: cruciferous vegetables, yogurt, and chlorophyllin tablets, also in a crossover design. The high-temperature meat diet increased the mutagenicity of urine and feces compared to the low-temperature meat diet. The inhibitor diet decreased nearly twofold the DNA damage in target colorectal cells. To our knowledge, this is the first demonstration that dietary factors can reduce DNA damage in the target tissue of fried-meat associated carcinogenesis. Breast cancer is one of the most common cancers in women, yet even with a stabilizing incidence rate and decreased mortality, more than 180,000 women will be diagnosed and more than 40,000 women will die in the U.S. from the disease this year. Recent genome-wide association studies have identified several polymorphisms associated with breast cancer although risks from these polymorphisms are modest. Our group is testing the hypothesis that certain DNA modifications are associated with breast cancer risk. Such modifications may be determined by both environmental and genetic factors, and would be expected to change over a woman's lifetime. Telomeres are non-coding double-stranded repeats located at ends of chromosomes that play a critical role in maintaining genomic integrity. Experimental studies indicate that telomere dysfunction may be an important cause of chromosomal abnormalities in breast epithelium. Studies have demonstrated progressively shorter telomere length with increasing chromosomal aberrations in breast carcinomas. However, epidemiologic studies examining the association between leukocyte telomere length and breast cancer have yielded equivocal results. We examined telomere length in peripheral blood in relation to breast cancer risk in a prospective cohort study of women who have at least one sister with breast cancer. We compared 342 women with incident breast cancer to a set of 735 women without cancer sampled from the Sister Study cohort and measured relative telomere length in peripheral blood using single tube monochrome multiplex quantitative PCR. We found no evidence of increased risk associated with shortened telomeres. Epigenetic modifications, including DNA methylation, are being increasingly recognized as is being recognized as important determinants of gene transcriptional regulation that have both heritable and acquired characteristics. Aberrant DNA methylation patterns are among the earliest and most common events in carcinogenesis and recent studies suggest that the epigenetic profile of DNA from a surrogate tissue, peripheral blood, may differ between women with active ovarian cancer compared to women without disease. We have employed genome-wide profiling of DNA methylation in peripheral blood samples from more than 900 women in order to investigate whether the pattern of DNA methylation is associated with breast cancer risk. We have identified a number of methylation sites that are associated with increased risk and are continuing data analysis. A second form of epigenetic modification is miRNA expression. Altered miRNA expression is a central feature of cancer and miRNA expression signatures have been shown to be associated with diagnosis, stage, prognosis, and response to treatment. Expression patterns for cancer show high tissue specificity making them potential markers for cancer screening. Breast cancer specific miRNAs have been shown to correlate with stage, vascular invasion, proliferative index, and ER/PR status. Recently, sufficient levels of miRNAs have been found in human plasma and serum to permit profiling, with sufficient power to distinguish men with metastatic prostate cancer from men without cancer and women with ovarian cancer. We have recently completed assays on more than 400 serum samples from cases and non-cases using the Sister Study cohort and are in the process of data analysis.