顺铂对A549细胞DNA损伤修复生物标记物表达的影响

目的　研究顺铂对肺癌A5 49细胞中切除修复鼠缺陷交叉互补基因 2 (ERCC2 )蛋白、尿嘧啶DNA糖基化酶 (UDG)、细胞增殖核抗原 (PCNA)在肺癌和食管癌组织中表达水平的影响。方法　通过彗星试验、RT PCR和蛋白印记法研究 3种生物标记物在顺铂处理和未处理A5 49细胞之间的表达水平。分为染毒前、染毒 12h、染毒 2 4h、停止染毒 12h、停止染毒 2 4h 5个不同时间段组 ,每组细胞数均为 1× 10 6个 /ml。结果　在低浓度顺铂 (IC2 0 剂量 )作用下 ,染毒 2 4h内DNA损伤程度的变化与作用时间成正比 ,染毒 12h、2 4h尾相 (单位 :mm)分别为 5 0 2± 0 6 8和 7 2 2± 0 5 3,与阴性对照的尾相2 73± 0 2 9比较有明显差异。停止染毒 2 4h尾相为 3 6 4± 0 70 ,与阴性对照比较无明显差异。ERCC2、UDG和PCNA的mRNA水平和蛋白质水平在细胞染毒后均明显升高 ,染毒 2 4h后mRNA水平分别为 0 71± 0 0 8、0 74± 0 0 6和 0 82± 0 0 9,均明显高于阴性对照 (分别为 0 2 8± 0 0 5、0 31± 0 0 5和 0 37± 0 0 6 ) ;蛋白质表达水平分别为 4 37± 0 5 7、5 47± 0 46和 2 2 1± 0 47,均明显高于阴性对照(分别为 2 2 1± 0 47、2 5 4± 0 38和 3 2 1± 0 47)。停止染毒后 3种酶的mRNA分别为 0 31± 0     

ERCC1反义RNA降低肺癌细胞对苯并(a)芘所致DNA损伤的修复能力

目的 探讨核苷酸切除修复基因ERCCl在肺癌细胞修复苯并(a)芘所致DNA损伤中的作用。方法 构建表达ERCCl反义RNA的重组质粒,Lipofectin转染肺癌A549细胞,潮霉素筛选出稳定转染的细胞克隆;噻唑蓝法检测24h细胞生存力;Northern Blot分析细胞ERCCl基因mRNA表达水平;单细胞凝胶电泳技术检测DNA损伤程度,每组计算50个细胞损伤情况。结果 筛选出表达ERCCl反义RNA的7个阳性克隆,其生长特性与亲本细胞差别无显著性;内源性mRNA表达水平不同程度降低,为亲本细胞的12％-86％;DNA损伤修复速度减慢,10μmol/L苯并(a)芘作用24h后再孵育24h,修复程度为亲本细胞的29％-71％;相关分析表明DNA损伤修复程度与ERCClmRNA水平显著相关。结论 ERCCl反义RNA降低肺癌细胞对苯并(a)芘所致DNA损伤的修复能力。     

ERCC4基因遗传变异对焦炉工外周血淋巴细胞DNA损伤的影响

目的探讨焦炉作业工人核苷酸切除修复交叉互补组4基因（excision repair cross complementation group4，ERCC4）多态性和外周血淋巴细胞DNA损伤的关联。方法选择某焦化厂246名焦炉作业工人和127名对照者，运用彗星试验评价外周血淋巴细胞DNA损伤；根据Hapmap数据库筛选ERCC4基因的标签单核苷酸多态性位点（tagged-single nucleotide polymorphisms，TagSNPs），使用Taq—Man—MGB探针荧光标记聚合酶链反应方法对rs744154、rs3136079及rs318703个TagSNPs进行基因分型；运用PHASE2．0．2遗传分析软件计算单体型。结果焦炉工组外周血淋巴细胞的Olive尾矩（Olive TM）高于对照组（对数转换后分别为1．26±1．12及0．52±0．97），差异有统计学意义（P〈0．01）。焦炉工中，3个TagSNPs的不同基因型携带者Olive TM值的差异无统计学意义（P〉0．05），构建的不同单体型对携带者Olive TM值的差异亦无统计学意义（P〉0．05）；对照组中rs3136079位点TG杂合子携带者Olive TM值最低（0．26±0．96），明显低于野生型纯合子TT（0．66±0．98）及突变型纯合子GG携带者（0．66±0．51），差异均有统计学意义（P〈0．05），构建的CTG／CTG单体型对携带者Olive TM值最高（0．69±1．01），无CTG单体型携带者Olive TM值最低（0．25±0．80），差异无统计学意义（P=0．08）。结论ERCC4基因多态性对焦炉工外周血淋巴细胞DNA损伤程度无影响，但对照组中rs3136079位点TG杂合基因型携带者DNA损伤程度较轻，表明DNA损伤程度受遗传和环境因素交互作用的影响。     

Functional characterization of polymorphisms in DNA repair genes using cytogenetic challenge assays

A major barrier to understanding the role of polymorphic DNA repair genes for environmental cancer is that the functions of variant genotypes are largely unknown. Using our cytogenetic challenge assays, we conducted an investigation to address the deficiency. Using X-rays or ultraviolet (UV) light, we irradiated blood lymphocytes from 80 nonsmoking donors to challenge the cells to repair the induced DNA damage, and we analyzed expression of chromosome aberrations (CA) specific to the inducing agents. We have genotyped polymorphic DNA repair genes preferentially involved with base excision repair (BER) and nucleotide excision repair (NER) activities (XRCC1, XRCC3, APE1, XPD) corresponding to the repair of X-ray- and UV light-induced DNA damage, respectively. We expected that defects in specific DNA repair pathways due to polymorphisms would cause corresponding increases of specific CA. From our data, XRCC1 399Gln and XRCC3 241Met were associated with significant increases in chromosome deletions compared with the corresponding homozygous wild types (18.27 1.1 vs 14.79 1.2 and 18.22 0.99 vs 14.20 1.39, respectively); XPD 312Asn and XPD 751Gln were associated with significant increases in chromatid breaks compared with wild types (16.09 1.36 vs 11.41 0.98 and 16.87 1.27 vs 10.54 0.87, respectively), p < 0.05. The data indicate that XRCC1 399Gln and XRCC3 241Met are significantly defective in BER, and the XPD 312Asn and XPD 751Gln are significantly defective in NER. In addition, the variant genotypes interact significantly, with limited overlap of the two different repair pathways.     

DNA修复基因在基于铂类药物化疗的非小细胞肺鳞癌患者中的预后价值

目的了解DNA修复基因在接受以铂类药物为基础化疗的非小细胞肺癌(NSCLC)患者中不同病理类型的预后价值。 方法应用免疫组织化学技术检测121例NSCLC铂类药物化疗患者石蜡包埋病灶组织中多聚ADP-核糖聚合酶基因1(PARP1),切除修复交叉互补基因1(ERCC1),错配修复同源型2基因(MSH2),乳腺癌易感基因1(BRCA1)表达状态。分析NSCLC患者DNA修复基因的表达与临床病理特征之间的关系。并通过生存分析判断DNA修复基因的表达在不同病理类型中NSCLC化疗患者中的预后价值及是否为独立的预后指标。 结果ERCC1、PARP1、BRCA1、MSH2在非小细胞肺癌的表达均未显示与患者的性别、年龄、吸烟指数、临床TNM分期的相关性(P均>0.05)。在NSCLC腺癌组中ERCC1、PARP1、BRCA1、MSH2均不是判断预后的独立因素(P均>0.05)。鳞癌组中ERCC1、PARP1是预后判断独立因素(P=0.019,0.031)。 结论ERCC1、PARP1是基于铂类药物化疗的非小细胞肺鳞癌患者独立的预后指标。     

CYP2E1基因多态性和DNA损伤修复酶表达对肺癌易感性的影响

[目的]研究CYP2E1基因型与不同肺组织中切除修复鼠缺陷交叉互补基因2蛋白(ERCC2)、尿嘧啶DNA糖基化酶(UDG)、细胞增殖核抗原(PCNA)的表达水平的关系，探讨CYP2E1基因多态性对DNA稳定性和肺癌易感性的影响。[方法]通过免疫组织化学和原位杂交方法研究3种生物标志物在不同肺组织中蛋白质和mRNA的表达水平，同时采用PER-RFLP方法进行CYP2E1分型。[结果]在3种CYP2E1基因型(ww、mw、mm)中，ww和mm基因型对ERCC2的表达有明显影响，mw基因型对UDG的表达有明显影响，3种基因型均与PCNA的表达有关。交互分析结果显示CYP2E1多态性与UDG的表达存在交互作用。[结论]不同个体CYP2E1遗传多态性与DNA切除修复功能有关，并存在CYP2E1与UDG的交互作用，两者在肺癌易感性中均具有一定的作用。     

Assessment of abnormal DNA repair responses and genotoxic effects in lead exposed workers

BACKGROUND: One of the main sources of occupational exposure to lead (Pb) in Turkey is in workers of battery industries. Genotoxic studies in human populations exposed to this metal have had conflicting results. METHODS: Genotoxic effects of Pb were studied in blood cell samples from workers of battery manufactures exposed to Pb compounds by chromosomal aberration (CA) assay and X-ray induced challenge (XRC) assay to assess DNA damage and interference with DNA repair processes after an in vitro exposure of X-ray (1 Gy). The battery manufacturers (n=23) and 23 people who were not occupationally exposed to lead compounds were selected as a control group and classified into categories according to their blood lead levels. RESULTS: The CA frequencies in the exposed and control group were not significantly different (P>0.05) by conventional CA (CCA) assay, however, the XRC assay demonstrated significantly elevated CAs (P<0.05). Statistically non-significant but reduced DNA repair responses have also been observed in lead exposed workers. CONCLUSION: The results of this study showed significant increases in the CAs by XRC assay in Pb exposed workers compared to CCA assay. Our data suggests that Pb exposure may cause reduction in DNA repair capacity and these individuals will be more prone to DNA damage. Therefore, preventive measures should be improved against genotoxic risk in workplaces.     

Expression of DNA repair and metabolic genes in response to a flavonoid-rich diet

A diet rich in fruit and vegetables can be effective in the reduction of oxidative stress, through the antioxidant effects of phytochemicals and other mechanisms. Protection against the carcinogenic effects of chemicals may also be exerted by an enhancement of detoxification and DNA damage repair mechanisms. To investigate a putative effect of flavonoids, a class of polyphenols, on the regulation of the gene expression of DNA repair and metabolic genes, a 1-month flavonoid-rich diet was administered to thirty healthy male smokers, nine of whom underwent gene expression analysis. We postulated that tobacco smoke is a powerful source of reactive oxygen species. The expression level of twelve genes (APEX, ERCC1, ERCC2, ERCC4, MGMT, OGG1, XPA, XPC, XRCC1, XRCC3, AHR, CYP1A1) was investigated. We found a significant increase (P < 0.001) in flavonoid intake. Urinary phenolic content and anti-mutagenicity did not significantly change after diet, nor was a correlation found between flavonoid intake and urinary phenolic levels or anti-mutagenicity. Phenolic levels showed a significant positive correlation with urinary anti-mutagenicity. AHR levels were significantly reduced after the diet (P = 0.038), whereas the other genes showed a generalized up regulation, significant for XRCC3 gene (P = 0.038). Also in the context of a generalized up regulation of DNA repair genes, we found a non-significant negative correlation between flavonoid intake and the expression of all the DNA repair genes. Larger studies are needed to clarify the possible effects of flavonoids in vivo; our preliminary results could help to better plan new studies on gene expression and diet.     

ERCC2/XPD单核苷酸多态与苯并芘体外诱导DNA加合物损伤的关联性研究

目的评价环境致癌因子苯并芘(B[a]P)所致DNA损伤修复与ERCC2/XPD单核苷酸多态(SNP)的关联。方法收集282例辽宁地区汉族健康人群外周血8ml,常规提取淋巴细胞及DNA,采用Taqman实时定量PCR检测ERCC2/XPDLys751Gln(rs13181),Asp312Asn(rs1799793)和Arg156Arg(rs238406)的基因型;体外培养淋巴细胞,应用B[a]P及S9活化系统,诱导BPDE-DNA加合物的形成;高效液相色谱法检测BPDE-DNA加合物含量;分析BPDE-DNA加合物水平与ERCC2/XPD SNP位点的关联。结果携带ERCC2/XPD Arg156Arg位点AA基因型个体BPDE-DNA加合物水平显著高于CC基因型携带者;50～70岁和≥70岁年龄组人群的加合物水平高于≤30岁年龄组(P<0.05);多元线性回归分析同样显示,ERCC2/XPD Arg156Arg位点SNP及年龄对BPDE-DNA加合物含量的影响有统计学意义(P<0.05)。结论 ERCC2/XPD Arg156Arg位点A等位基因可能与BPDE-DNA加合物的DNA修复能力降低相关联,可能会增加肿瘤易感风险。     

高本底辐射居民DNA损伤修复能力研究

目的探讨小剂量慢性长期连续照射人群的DNA损伤修复能力。方法选择我国阳江天然放射性高本底辐射地区(HBRA)的53名50~59岁男性居民作为研究对象,另选择恩平市横坡镇(CA)出生并长大的年龄相仿的男性居民作为对照人群。分别抽取他们周围血5 ml,利用逆转录-聚合酶链反应(RT-PCR)测定周围血中有核细胞的Ku70基因、切除修复鼠缺陷交叉互补蛋白1(ERCC1)、错配修复hMSH2基因、O6-甲基鸟嘌呤甲基转移酶(MGMT)基因表达水平。结果在HBRA和CA组人群的周围血有核细胞中,Ku70基因表达水平分别为(0.438±0.351)、(0.389±0.271),ERCC1基因表达水平分别为(0.228±0.112)、(0.193±0.115),hMSH2基因表达水平分别为(0.365±0.222)、(0.279±0.214),MGMT基因表达水平分别为(0.585±0.319)、(0.414±0.365)。与对照组相比,高本底辐射居民Ku70、ERCC1、hMSH2水平略升高,但差异无统计学意义(P>0.05),MGMT基因表达增强,差异有统计学意义(P<0.05)。结论MG-MT基因可能参与了天然放射性...     

Inter-individual variation in nucleotide excision repair in young adults: effects of age, adiposity, micronutrient supplementation and genotype

Nucleotide excision repair (NER) is responsible for repairing bulky helix-distorting DNA lesions and is essential for the maintenance of genomic integrity. Severe hereditary impairment of NER leads to cancers such as those in xeroderma pigmentosum, and more moderate reductions in NER capacity have been associated with an increased cancer risk. Diet is a proven modifier of cancer risk but few studies have investigated the potential relationships between diet and NER. In the present study, the plasmid-based host cell reactivation assay was used to measure the NER capacity in peripheral blood mononuclear cells from fifty-seven volunteers aged 18-30 years before and after 6 weeks of supplementation with micronutrients (selenium and vitamins A, C and E). As a control, nine individuals remained unsupplemented over the same period. Volunteers were genotyped for the following polymorphisms in NER genes: ERCC5 Asp1104His (rs17655); XPC Lys939Gln (rs2228001); ERCC2 Lys751Gnl (rs13181); XPC PAT (an 83 bp poly A/T insertion-deletion polymorphism in the XPC gene). NER capacity varied 11-fold between individuals and was inversely associated with age and endogenous DNA strand breaks. For the first time, we observed an inverse association between adiposity and NER. No single polymorphism was associated with the NER capacity, although significant gene-gene interactions were observed between XPC Lys939Gln and ERCC5 Asp1104His and XPC Lys939Gln and ERCC2 Lys751Gnl. While there was no detectable effect of micronutrient supplementation on NER capacity, there was evidence that the effect of fruit intake on the NER capacity may be modulated by the ERCC2 Lys751Gnl single nucleotide polymorphism.     

XRCC3 and XPD/ERCC2 single nucleotide polymorphisms and the risk of cancer: a HuGE review

Hundreds of polymorphisms in DNA repair genes have been identified; however, for many of these polymorphisms, the impact on repair phenotype and cancer susceptibility remains uncertain. In this review, the authors focused on the x-ray repair cross-complementing protein group 3 (XRCC3) and xeroderma pigmentosum group D (XPD)/excision repair cross-complementing rodent repair deficiency (ERCC2) genes, because they are among the most extensively studied but no final conclusion has yet been drawn about their role in cancer occurrence. XRCC3 participates in DNA double-strand break/recombinational repair through homologous recombination to maintain chromosome stability. XPD/ERCC2 is a helicase involved in the nucleotide excision repair pathway, which recognizes and repairs many structurally unrelated lesions, such as bulky adducts and thymidine dimers. The authors identified a sufficient number of epidemiologic studies on cancer to perform meta-analyses for XPD/ERCC2 variants in codons 156, 312, and 751 and XRCC3 variants in codon 241. The authors evaluated all cancer sites to investigate whether DNA repair is likely to take place in a rather nonspecific manner for different carcinogens and different cancers. For the most part, the authors found no association between these genes and the cancer sites investigated, except for some statistically significant associations between XPD/ERCC2 single nucleotide polymorphisms and skin, breast, and lung cancers.     

醋酸铅染毒人外周血淋巴细胞诱发XRCC1、hOGG1基因表达变化的研究

目的 研究醋酸铅染毒人外周血淋巴细胞对XRCC1、hOGG1基因表达变化的影响。方法 用0、20、40和80μmol/L浓度醋酸铅染毒人外周血淋巴细胞24h, 采用qPCR法和Western-Blot法测定XRCC1、hOGG1基因的mRNA和蛋白表达水平。结果 与对照组相比,醋酸铅染毒诱导人外周血淋巴细胞XRCC1、hOGG1基因的mRNA和蛋白表达水平随醋酸铅染毒浓度增加而下降,差异有统计学意义(P<0.01)。结论 醋酸铅染毒抑制XRCC1、hOGG1基因表达水平,导致细胞对DNA损伤修复能力下降。     

Evidence for exposure-induced DNA repair abnormality is indicative of health and genetic risk

A recent focus has been targeted toward the development of functional biomarkers that can be used to predict disease more reliably. One such biomarker is the challenge assay for DNA repair deficiency. Briefly, the assay involves challenging lymphocytes in culture to a DNA damaging agent in vitro and determining the repair outcome in chromosome aberrations and/or DNA strand breaks. The aim is to show that individuals who have chronic exposure to toxic substances will develop exposure-induced DNA repair deficiencies. Many studies around the world have shown that the assay detects DNA repair deficiency in environmentally/occupationally exposed populations and with significant exposure dose–response relationship. The prediction of health risk was also validated. In addition, exposure-induced repair deficiency which was apparently passed through the germ cells had caused genetic consequences in a 3-generation population. The assay is simple to conduct and is more sensitive than some traditional biomarker assays. Together with the functional significance of the assay, the challenge assay can be used with confidence in population studies for health risk assessment.     

Unventilated indoor coal-fired stoves in Guizhou province, China: cellular and genetic damage in villagers exposed to arsenic in food and air

BACKGROUND: Inorganic arsenic (iAs) is a well-known human carcinogen recognized by the World Health Organization and the International Agency for Research on Cancer. Currently, most iAs studies in populations are concerned with drinking water and occupational arsenicosis. In Guizhou province, arsenicosis caused by the burning of coal in unventilated indoor stoves is an unusual type of exposure. Because the poisoning mechanism involved in arsenicosis is as yet unknown and no effective therapy exists, progress has been slow on the prevention and therapy of arsenicosis. OBJECTIVES: We examined the relationship between arsenic (As) exposure from the burning of coal in unventilated indoor stoves and genetic damage in humans, using cellular and molecular indices. We selected villagers from Jiaole township, Guizhou province, China, who had been exposed to milligram levels of As daily via food and air contaminated by the burning of As-containing coal in unventilated indoor stoves. RESULTS: The As-exposed subjects from Jiaole were divided into four groups according to skin lesion symptoms: nonpatients, mild, intermediate, and severe arsenicosis. Another 53 villagers from a town 12 km from Jiaole were recruited as the external control group. In the four groups of exposed subjects, As concentrations in urine and hair were 76-145 microg/L and 5.4-7.9 microg/g, respectively. These values were higher than those in the external control group, which had As concentrations of 46 microg/L for urine and 1.6 microg/g for hair. We measured sister chromatid exchange and chromosomal aberrations to determine human chromosome damage, and for DNA damage, we measured DNA single-strand breaks and DNA-protein cross-links. All measurements were higher in the four exposed groups compared with the external control group. DNA repair was impaired by As exposure, as indicated by the mRNA of O-6-methylguanine-DNA methyltransferase (MGMT), X-ray repair complementing defective repair in Chinese hamster cells 1 (XRCC1), and, to a lesser extent, by the mismatch repair gene hMSH2 mRNA. The expression of mutant-type p53 increased with aggravation of arsenicosis symptoms, whereas the expression of p16-INK4(p16) decreased. p53 mutated at a frequency of 30-17% in the carcinoma (n = 10) and precarcinoma (n = 12) groups. No mutation was found in p16, although deletion was evident. Deletion rates were 8.7% (n = 23) and 38.9% (n = 18) in noncarcinoma and carcinoma groups, respectively. CONCLUSIONS: The results showed that long-term As exposure may be associated with damage of chromosomes and DNA, gene mutations, gene deletions, and alterations of DNA synthesis and repair ability.     

焦化厂工人ERCC8基因多态性与外周血淋巴细胞DNA损伤的关系

[目的]探讨焦化厂工人ERCC8基因多态性与外周血淋巴细胞DNA损伤的关系。[方法]选择某焦化厂多环芳烃（PAHs）接触者207名焦炉作业工人和115名无PAHs接触及其他毒物暴露者，采集外周静脉血，分离淋巴细胞，使用单细胞凝胶电泳实验观察DNA损伤情况；采用TaqMan—MGB探针检测ERCC8基因分型；运用PHASE2．0．2遗传分析软件计算单倍型。[结果]接触组外周血淋巴细胞的Olive尾矩（Olive Tail Moment，OTM）高于对照组（经对数转换后分别为1．25±1．17和0．53±0．98），差异有极显著性（P〈0．01）。在接触组中，ERCC8基因Rs3117位点CT＋CC和TT基因型携带者外周血淋巴细胞的OTM分别为1．57±1．13和1．15±1．67，差异有统计学意义（P〈0．05）；启动区Rs158920位点CT＋TT和CC基因型携带者外周血淋巴细胞的OTM分别为1．14±1．21和1．24±1，17，差异无统计学意义（P〉0．05）。对照组中相应位点的OTM分别为0．54±0．93和0．56±1．00以及0．52±0．86和0．54±1．02，差异均无统计学意义（P〉0．05）。在接触组中，两个位点组成的单倍型对中CT／CT单倍型对和其他单倍型对携带者外周血淋巴细胞的OTM分别为1．20±1．17和1．36±1．17；对照组分别为0．54±1．02和0．51±0．91，两组差异均无统计学意义。[结论]接触组外周血淋巴细胞ERCC8基因Rs3117位点的不同基因型和DNA损伤的严重程度有关联。     

DNA Damage and Repair: Fruit and Vegetable Effects in a Feeding Trial

Epidemiologic studies have examined the association between fruit and vegetable (F&V) consumption and the risk of cancer. Several cancer-preventive mechanisms have been proposed, such as antioxidant properties and modulation of biotransformation enzyme activities; both may be associated with reducing DNA damage and hence the mutation rate. We investigated, in a randomized, controlled, crossover feeding trial, the effect of 10 servings/day of botanically defined F&V for 2 wk on endogenous DNA damage; resistance to γ -irradiation damage; and DNA repair capacity in lymphocytes, measured by the Comet assay. We also explored the association between the UGT1A1?28 polymorphism and serum bilirubin concentrations and DNA damage and repair measures. Healthy men (n = 11) and women (n = 17), age 20 to 40 yr, provided blood samples at the end of each feeding period. Overall, F&V did not affect DNA damage and repair measures in lymphocytes. The number of UGT1A1?28 alleles was inversely associated with sensitivity to γ -irradiation exposure and DNA repair capacity, but a biological mechanism to explain this association is unclear. A larger sample size is needed to investigate the association between bilirubin concentrations and endogenous DNA damage. With inconsistent findings in the literature, additional dietary intervention studies on the effect of F&V on DNA damage and repair are needed.     

Evidence that dietary supplementation with carotenoids and carotenoid-rich foods modulates the DNA damage: repair balance in human lymphocytes

Epidemiological evidence has shown that the habitual consumption of diets high in fruits and vegetables is associated with reduced risk of cancers. The challenge is to identify causal mechanisms of effect. The aim of the current study was to determine whether an increase in rate of removal of DNA single-strand breaks (SSB) following oxidative challenge could be provoked ex vivo in peripheral blood lymphocytes (PBL). The PBL were isolated from apparently healthy volunteers following dietary intervention with: (1) a mixed carotene capsule; (2) a daily portion of cooked minced carrots; (3) a matched placebo; (4) a portion of mandarin oranges; (5) vitamin C tablets. Single-cell gel electrophoresis was employed to measure baseline levels of SSB and DNA susceptibility to oxidative damage, and to monitor the number of SSB over 4 h, in both unchallenged and H2O2-treated PBL. The enzymatic capacity for repair of different types of DNA oxidative lesions was also measured using two related cell-free assays. There was no evidence that any of the dietary supplementation regimens altered baseline levels of SSB, provided any direct antioxidant protection or altered DNA repair capacity, with two exceptions: the number of SSB following exposure to H2O2 decreased more rapidly in PBL from volunteers given the mixed carotene capsules and repair patch synthesis activity in PBL increased from volunteers given the cooked carrots. These results suggest that carotenoids and carotenoid-rich foods can influence DNA damage:repair by modulation of discrete stages in the DNA repair mechanisms.