Methylomic biomarkers for magnesium deficiency and colon neoplasia prevention

 描述(由申请人提供)：五项使用镁耐量测试的美国研究表明，50%的参与者患有镁缺乏。镁耐量测试是镁状态的“金标准”测试。在我们正在进行的美国试验中，我们发现了类似的结果。随着越来越多的人认识到镁在人类健康中的重要性，最近，美国联邦膳食参考摄入量委员会(DRI)选择了镁来更新DRI。在美国和其他镁缺乏高危人群中，镁摄入量高与结直肠癌、胰岛素抵抗、代谢综合征、2型糖尿病和心血管疾病(CVD)的风险降低有关。相反，在镁缺乏风险不高的人群中，高镁摄入量与总死亡率(如总癌症、结直肠癌和心血管疾病)的增加有关，特别是在钙摄入量低的情况下。这些观察表明，高镁摄入量和疾病风险之间的关联可能完全不同于潜在的镁状态。由于主要的局限性，镁耐量试验不在常规临床实践中使用，也很少用于研究中。相反，血清镁用于临床诊断。然而，血清镁在识别镁缺乏者方面表现得非常差。迫切需要开发可实施的、灵敏的、特异的生物标志物，以便容易地用于识别镁缺乏者。如果没有这样的标记物，就不可能制定有效的策略，通过针对那些因镁缺乏而有患常见疾病风险的人，将不良影响降至最低。众所周知，DNA甲基化变化是由环境暴露，包括营养物质诱导的，当环境暴露消失时，这种变化是可逆的。DNA中的胞嘧啶修饰主要有两种类型，5-羟甲基胞嘧啶(5-HMC)和5-甲基胞嘧啶(5-MC)。5-MC常与基因表达受抑有关。5-羟甲基纤维素(5-HMC)是由5-MC氧化生成的，它特异性地富含在表达的基因中，在激活和/或维持基因表达方面起着关键作用。然而，目前的表观基因组图谱平台不能区分5-HMC和5-MC。就在最近，我们的合作者Chuan He博士(HHMI Investigator)建立了一种新的、最先进的技术-TAB-Seq&TAB-Array协议，它可以在基因组中分离5-HMC和5-MC。我们的初步研究表明，镁的摄入或治疗显著影响甲基化能力、5-MC和5-HMC生物标志物。我们的发现提示，血白细胞5-HMC/5-MC生物标志物可能是比血清镁更敏感的镁缺乏生物标志物。因此，一项全面的表观基因组关联研究可能有助于确定镁缺乏最敏感的5-HMC/5-MC生物标志物。我们建议在“个性化预防结直肠癌试验[PPCCT，R01CA149633；Pi，Dai&Yu]”中，通过一项4阶段的EWAS研究，确定镁缺乏的5-HMC/5-MC生物标记物，共有240名参与者。镁耐量试验将作为金标准。最后，使用新确定的生物标志物，我们将评估12周镁治疗是否仅在镁缺乏者的直肠组织中降低了TRPM7的表达，而TRPM7在镁稳态和结直肠癌发生中是必不可少的。

 DESCRIPTION (provided by applicant): Five US studies using the Mg tolerance test, the "gold standard" test of Mg status, indicated that >50% participants had Mg deficiency. In our ongoing US trial, we have found a similar result. In growing recognition of the importance of Mg in human health, very recently, Mg was selected by the US Federal Dietary Reference Intake (DRI) Committee to update the DRI. In US and other populations at high risk of Mg deficiency, high Mg intake has been linked to reduced risk of colorectal neoplasia, insulin resistance, metabolic syndrome, type 2 diabetes, and cardiovascular disease (CVD). Conversely, in populations not at high risk of Mg deficiency, high Mg intake has been related to increased risk of total mortality (e.g. total cancer, colorectal cancer, and CVD), particularly when calcium intak is low. These observations suggest that the associations between high Mg intake and disease risks may completely differ by the underlying Mg status. Due to major limitations, the Mg tolerance test is not used in conventional clinical practice and rarely used in research. Instead, serum Mg is used for clinical diagnosis. However, serum Mg performs very poorly at identifying those with Mg deficiency. There is a great need to develop implementable, sensitive, and specific biomarkers which can be easily used for identifying people with Mg deficiency. Without such a marker, it is impossible to develop effective strategies that minimize adverse effects by targeting those who, as a result of Mg deficiency, are at risk of common diseases. It is known that DNA methylation changes are inducible by environmental exposures, including nutrients, and reversible when the exposure disappears. There are two major types of cytosine modifications in DNA, 5-hydroxymethylcytosine (5-hmC) and 5-methylcytosine (5-mC). 5-mC is often associated with suppressed gene expression. 5-hmC, generated by the oxidation of 5-mC, is specifically enriched in expressed genes and plays a critical role in activating and/or maintaining gene expression. However, current epigenomic profiling platforms cannot distinguish 5-hmC from 5-mC. Just recently, our collaborator, Dr. Chuan He (HHMI Investigator), established a novel and state of the art technique, TAB-Seq & TAB-Array protocol, which can separate 5-hmC from 5-mC in the genome. Our pilot studies indicate that Mg intake or treatment significantly affects methylation capacity, 5-mC and 5-hmC biomarkers. Our findings suggest blood leukocyte 5-hmC/5-mC biomarkers may serve as more sensitive biomarkers to identify Mg deficiency than serum Mg. Thus, a comprehensive epigenome-wide association study (EWAS) may help to identify the most sensitive 5-hmC/ 5- mC biomarkers for Mg deficiency. We propose to identify 5-hmC/5-mC biomarkers for Mg deficiency by a 4- phase EWAS study in the "Personalized Prevention of Colorectal Cancer Trial [PPCCT, R01CA149633; PI, Dai & Yu]" with a total of 240 participants. Mg tolerance test will be used as the gold standard. Finally, using newly identified biomarkers, we will evaluate if 12-week Mg treatment reduces TRPM7 expression, essential in Mg homeostasis and colorectal carcinogenesis, in rectal tissues only among those with Mg deficiency.