Uracil in DNA: consequences for carcinogenesis and chemotherapy

The synthesis of thymidylate (TMP) occupies a convergence of two critical metabolic pathways: folate metabolism and pyrimidine biosynthesis. Thymidylate is formed from deoxyuridylate (dUMP) using N(5),N(10)-methylene tetrahydrofolate. The metabolic relationship between dUMP, TMP, and folate has been the subject of cancer research from prevention to chemotherapy. Thymidylate stress is induced by nutritional deficiency of folic acid, defects in folate metabolism, and by antifolate and fluoropyrimidine chemotherapeutics. Both classes of chemotherapeutics remain mainstay treatments against solid tumors. Because of the close relationship between dUMP and TMP, thymidylate stress is associated with increased incorporation of uracil into DNA. Genomic uracil is removed by uracil DNA glycosylases of base excision repair (BER). Unfortunately, BER is apparently problematic during thymidylate stress. Because BER requires a DNA resynthesis step, elevated dUTP causes reintroduction of genomic uracil. BER strand break intermediates are clastogenic if not repaired. Thus, BER during thymidylate stress appears to cause genome instability, yet might also contribute to the mechanism of action for antifolates and fluoropyrimidines. However, the precise roles of BER and its components during thymidylate stress remain unclear. In particular, links between BER and downstream events remain poorly defined, including damage signaling pathways and homologous recombination (HR). Evidence is growing that HR responds to persistent BER strand break intermediates and DNA damage signaling pathways mediate cross talk between BER and HR. Examination of crosstalk among BER, HR, and damage signaling may shed light on decades of investigation and provide insight for development of novel chemopreventive and chemotherapeutic approaches.     

Supplementation with Watermelon Extract Reduces Total Cholesterol and LDL Cholesterol in Adults with Dyslipidemia under the Influence of the MTHFR C677T Polymorphism

Dyslipidemia and genetic polymorphisms are associated with increased risk for developing cardiovascular diseases, and watermelon appears to have the potential to improve hyperlipidemia due to the presence of nutrients such as arginine and citrulline.

Objective: To test the hypolipidemic effect of watermelon extract (Citrullus lanatus) and the influence of the methylenetetrahydrofolate reductase genotype (MTHFR C677T) on supplementation response.

Methods: This is an experimental clinical phase II randomized and double-blind study. Forty-three subjects with dyslipidemia were randomly divided into 2 groups: experimental (n = 22) and control (n = 21) groups. The subjects were supplemented daily for 42 days with 6 g of watermelon extract or a mixture of carbohydrates (sucrose/glucose/fructose).

Results: The use of watermelon extract reduced plasma total cholesterol (p < 0.05) and low-density lipoprotein (p < 0.01) without modifying triglycerides, high-density lipoprotein, and very low-density lipoprotein values. Only carriers of the T allele (MTHFR C677T) showed decreasing concentrations of low-density lipoprotein (p < 0.01). No changes in anthropometric parameters analyzed were observed. This is the first study to demonstrate the beneficial effect of the consumption of watermelon extract in reducing plasma levels of lipids in humans. The MTHFR C677T polymorphism did not affect the plasma lipid concentration but made individuals more responsive to treatment with watermelon.

Conclusions: The consumption of this functional food represents an alternative therapy in the combined treatment of patients with dyslipidemia, promoting health and minimizing the development of risk factors for cardiovascular diseases.     

中国北方少数民族人群同型半胱氨酸代谢酶的遗传多态性

目的 了解我国北方地区3个少数民族人群中MTHFR和CBS基因的遗传多态性,获得MTHFR C677T和A1298 C 以及CBS T833C和G919A位点的群体遗传学数据。方法 应用PCR-RFLP,PCR-ARMS技术分别调查了吉林延边朝鲜族、新疆乌鲁木齐维吾尔族和回族新生儿的基因型分布。结果 回族和朝鲜族MTHFR677纯合突变频率为16.7％和20.9％,与中国北方人群的总体水平基本一致,而维吾尔族人群纯合突变频率(5.3％)低于其它民族,但差异无显著性(P>0.05);朝鲜族人群CBS基因T833 C纯合突变频率(7％)低于其它两个民族(15.8％～16.7％)。结论 CBS T833 C位点多态性也可能存在群体差异。     

The effect of C677T mutation of methylene tetrahydrofolate reductase gene and plasma folate level on hyperhomocysteinemia in patients with meningomyelocele

To evaluate the relationship between genotypes of methylene tetrahydrofolate reductase (MTHFR), and plasma folate and homocysteine (Hcy) levels in meningomyelocele, 21 Korean patients, 47 of their family members, and 43 healthy controls were recruited. The presence of C677T mutation in the MTHFR gene and plasma concentrations of folate/Hcy were investigated. The genotype frequency of C677T mutation was not higher in study groups (patients and family members). The plasma folate concentration showed no difference either between the study and the control groups or among MTHFR-genotypic groups. The plasma Hcy concentration in homozygotes in the study group was higher than that in the control group, and higher than that in heterozygotes when plasma folate levels were low (P=0.006). Although neither MTHFR genotype nor plasma folate/Hcy level plays a definite part on its own, they seem to have an additive effect on the occurrence of meningomyelocele. Our results support folate supplementation for the prevention of hyperhomo- cysteinemia and meningomyelocele. Received: 11 November 1999 Revised: 3 April 2000     

中国汉族人群NR3C1 MTHFR和IGFBP3基因多态性及DNA甲基化与激素性股骨头坏死风险的相关分析

目的 探究NR3C1、MTHFR和IGFBP3基因多态性及DNA甲基化状态与激素性股骨头坏死(SONFH)之间的关系。方法 本病例对照研究中,选自合肥及周边地区包括79例短期冲击或长期口服糖皮质激素治疗SONFH的患者为病例组,114例服用糖皮质激素但未发生SONFH的患者为对照组。评估两组NR3C1、MTHFR和IGFBP3基因中的5个单核苷酸多态性(SNPs),这些SNPs由iMLDR进行基因分型。采用MethylTarget技术检测阳性位点(CpG位点)的甲基化水平,利用e QTLD技术分析以上3个基因的SNPs与甲基化水平的相互作用。结果 病例组与对照组相比,rs3110697 A/G基因型携带者患病风险低;在隐性遗传模型下,rs3110697 A等位基因携带者患病风险低;CpG位点IGFBP3_ 2-143、MTHFR_1-36、MTHFR_1-77、MTHFR_1-139、MTHFR_2-42、NR3C1_2-163、NR3C1_4-47甲基化水平差异显著,差异有统计学意义(P<0.05);共有10对SNPs与甲基化位点线性回归检验差异有统计学意义(P<0.05)。结论 SONFH是一种多基因病,其3个关联基因NR3C1、MTHFR和IGFBP3中的SNPs与DNA甲基化水平均存在广泛交互作用,有助于进一步建立SONFH基因调控模型指导临床诊疗。     

Methylenetetrahydrofolate reductase C677T gene polymorphism and the association with dyslipidemia in type 2 diabetic Palestinian patients

BackgroundDyslipidemia in diabetes is common and characterized by hypertriglyceridemia with decreased levels of high‐density lipoprotein. The objective of this study was to assess the prevalence of MTHFR C677T polymorphism in Palestinian T2DM patients and to investigate the association between this polymorphism and lipid profile in diabetic patients with and without dyslipidemia.MethodsA total of 208 T2DM patients including 98 with dyslipidemia and 110 without dyslipidemia were enrolled in this study. The MTHFR C677T genotyping was conducted by PCR‐RFLP followed by agarose gel electrophoresis.ResultsThere were no significant differences in either the genotype distribution or allele frequency in T2DM patients with or without dyslipidemia (37.8% CC, 54% CT, 8.2% TT vs. 48.2% CC, 41.8% CT, 11% TT; p = 0.209). However, among the dyslipidemic group, the TT carriers have a higher HDL level (46.8 ± 17.8) compared to (CC+CT) carriers (34.68 + 11.9) (p = 0.01). In the group without dyslipidemia, there was a significant elevation in diastolic blood pressure (DBP) among the CC carriers (83.6 ± 10.6) compared to those who carried at least one mutant allele (CT+TT) (78.1 ± 11.1) (p = 0.009).ConclusionsThe study shows that in our Palestinian population the MTHFR 677TT genotype lowers DBP significantly in patients without dyslipidemia and is related to increased level of HDL in diabetic dyslipidemia patients.     

Linkage disequilibrium of MTHFR genotypes 677C/T-1298A/C in the German population and association studies in probands with neural tube defects(NTD)

A number of studies have demonstrated that the common polymorphism 677C→T in the gene encoding 5, 10-methylenetetrahydrofolate reductase (MTHFR) leads to a thermolabile variant with decreased enzyme activity and to mildly elevated plasma homocysteine. 677TT homozygosity was shown to be more frequent in NTD probands compared with controls in some studies. Recently, another polymorphism, 1298A→C, in the MTHFR gene was described and combined heterozygosity 677CT/1298AC was suggested to be an additional risk factor for NTD. The present study examines the genotype and haplotype distribution of the two polymorphisms in the German population and evaluates the impact on NTD individuals and their relatives. To determine the haplotype of all individuals tested, we developed an easy-to-perform ARMS-RFLP test. Our data show that the two polymorphisms are in linkage disequilibrium in the general population and in NTD individuals. There was no statistically significant difference in allele and genotype frequency between probands (patients, fetuses) and controls (P > 0.10) and between observed and expected values for mother–child pairs (P > 0.80). Taking into account gender, an increased rate of 677CT heterozygotes was found in affected and unaffected males compared to affected and unaffected females. A family-based association study using a multiallelic transmission disequilibrium test (TDT) also shows that transmission rates do not deviate significantly from equilibrium (P > 0.50). Thus, our data provide no evidence for an association between NTD phenotype and MTHFR 677C/T-1298A/C genotypes and haplotypes. Am. J. Med. Genet. 87:23–29, 1999. © 1999 Wiley-Liss, Inc.     

Methylenetetrahydrofolate (MTHFR), the One-Carbon Cycle,and Cardiovascular Risks

The 5-10-methylenetetrahydrofolate reductase (MTHFR) enzyme is vital for cellular homeostasis due to its key functions in the one-carbon cycle, which include methionine and folate metabolism and protein, DNA, and RNA synthesis. The enzyme is responsible for maintaining methionine and homocysteine (Hcy) balance to prevent cellular dysfunction. Polymorphisms in the MTHFR gene, especially C677T, have been associated with various diseases, including cardiovascular diseases (CVDs), cancer, inflammatory conditions, diabetes, and vascular disorders. The C677T MTHFR polymorphism is thought to be the most common cause of elevated Hcy levels, which is considered an independent risk factor for CVD. This polymorphism results in an amino acid change from alanine to valine, which prevents optimal functioning of the enzyme at temperatures above 37 °C. Many studies have been conducted to determine whether there is an association between the C677T polymorphism and increased risk for CVD. There is much evidence in favour of this association, while several studies have concluded that the polymorphism cannot be used to predict CVD development or progression. This review discusses current research regarding the C677T polymorphism and its relationship with CVD, inflammation, diabetes, and epigenetic regulation and compares the evidence provided for and against the association with CVD.     

MTHFR基因多态性与中年男性冠状动脉病变程度的相关研究

目的 探讨四氢叶酸还原酶C677T基因多态性与中年男性冠状动脉病变程度。方法 选择2015年1月~2016年10月经冠脉造影确诊的128例山东沿海地区汉族中年男性冠心病患者（冠脉狭窄＞50%）,其中急性心肌梗死36例,按照国际心脏病学会和WHO冠心病诊断标准将128例冠心病患者分为急性冠脉综合征（ACS）组67例和稳定性心绞痛（SAP）组61例,并选110例冠脉正常者作为对照组。通过循环酶法测定血浆同型半胱氨酸浓度和PCR荧光法检测MTHER C677T基因型,观察血浆同型半胱氨酸浓度和MTHFRC677T基因型分布与冠脉病变的关系。结果 冠心病组血浆同型半胱氨酸水平明显高于对照组,差异有统计学意义（P＜0.01）,ACS组明显高于SAP组,差异有统计学意义（P＜0.01）。冠状动脉三支病变组血浆同型半胱氨酸水平明显高于单支病变组,差异有统计学意义（P＜0.01）,且高于双支病变组,差异有统计学意义（P＜0.05）。另外,双支病变组高于单支病变组,差异有统计学意义（P＜0.05）。冠心病组TT基因型、T等位基因频率明显高于对照组,差异有统计学意义（P＜0.01）;CT基因型高于对照组,差异有统计学意义（P＜0.05）。ACS组TT基因型高于SAP组,差异有统计学意义（P＜0.05）,T等位基因频率明显高于SAP组,差异有统计学意义（P＜0.01）。冠状动脉三支病变组TT基因型、T等位基因频率高于单支病变组,差异有统计学意义（P均＜0.05）。结论 MTHERC677T基因多态性及血浆同型半胱氨酸浓度参与山东沿海地区汉族中年男性冠状动脉粥样硬化病变的发生发展,且与冠脉病变严重程度有关。     

MTHFR与MTRR基因相关突变与H型高血压相关性分析

目的 探讨亚甲基四氢叶酸还原酶(MTHFR)、甲硫氨酸合成酶还原酶(MTRR)基因多态性与H型高血压的相关性。方法 选取2017-04~2017-10西安北方医院55例H型高血压患者样本做为病例组,37例孕妇样本作为健康对照组,使用PCR熔解曲线法检测两组人群MTHFR基因677C＞T、1298A＞C和MTRR基因66A＞G位点的多态性,分析两组人群的基因型及分布,采用循环酶法检测血清同型半胱氨酸(Hcy)水平。结果 与孕妇健康对照组相比,H型高血压组MTHFR677C＞T的T等位基因频率显著升高(χ²=10.172,P<0.01),而MTHFR1298A＞C和MTRR66A＞G差异无统计学意义(P>0.05)。此外,H型高血压组血清Hcy明显高于孕妇健康对照组(P＜0.01),血清Hcy水平在MTHFR677C＞T的基因型间差异有统计学意义(P＜0.05),但在MTHFR1298A＞C和MTRR66A＞G的基因型间差异无统计学意义(P>0.05)。结论 MTHFR677C＞T中T等位基因与H型高血压密切相关,也与Hcy水平升高相关,但未发现MTHFR1298A＞C和MTRR66A＞G与H型高血压及Hcy水平升高有关。