• Beta-carotene metabolites enhance inflammation-induced oxidative DNA damage in lung epithelial cells.

      van Helden, Yvonne G.J.; Keijer, Jaap; Knaapen, Ad M.; Heil, Sandra G.; Briede, Jacob J.; Van Schooten, Frederik J.; Godschalk, Roger W.L. (2009-01-15)
      beta-Carotene (BC) intake has been shown to enhance lung cancer risk in smokers and asbestos-exposed subjects (according to the ATBC and CARET studies), but the mechanism behind this procarcinogenic effect of BC is unclear. Both smoking and asbestos exposure induce an influx of inflammatory neutrophils into the airways, which results in an increased production of reactive oxygen species and formation of promutagenic DNA lesions. Therefore, the aim of our study was to investigate the effects of BC and its metabolites (BCM) on neutrophil-induced genotoxicity. We observed that the BCM vitamin A (Vit A) and retinoic acid (RA) inhibited the H(2)O(2)-utilizing enzyme myeloperoxidase (MPO), which is released by neutrophils, thereby reducing H(2)O(2) conversion. Moreover, BC and BCM were able to increase (.)OH formation from H(2)O(2) in the Fenton reaction (determined by electron spin resonance spectroscopy). Addition of Vit A and RA to lung epithelial cells that were co-incubated with activated neutrophils resulted in a significant increase in the level of oxidized purines assessed by the formamidopyrimidine DNA glycosylase-modified comet assay. These data indicate that BCM can enhance neutrophil-induced genotoxicity by inhibition of MPO in combination with subsequent increased formation of hydroxyl radicals.
    • Bioactive components in foods.

      Manson, Margaret M.; Linseisen, Jakob; Rohrmann, Sabine; Sotiroudis, Theodore G.; Kyrtopoulos, Soterios A.; Hayes, John D.; Kelleher, Michael O.; Eggleston, Ian M.; de Kok, Theo M.; van Breda, Simone G.; et al. (The Nofer Institute of Occupational Medicine, 2007-04)
    • Bioactivity of Medicinal Bolivian Andean plants. Effects on cell proliferation and related processes.

      Rodrigo, Gloria C. (Lund University, 2012, 2012-11-22)
      Colon cancer is common in both developed and developing countries, and is responsible for at least 600,000 deaths globally every year. It is therefore the second most common cause of cancer-related mortality. Extensive studies are being conducted worldwide to find more effective drugs that can be used in cancer treatment. In these studies, phytochemicals have proven to be good sources for drug discovery. In Bolivia, there is a long tradition of using plants for medicinal purposes. The objective of the present thesis was to study the effects of extracts and compounds from medicinal plants in Bolivia on the growth of colon cancer (Caco-2) cells. Firstly, a survey of many plant extracts and some isolated compounds for their antiproliferative activity was performed. Sixty-six extracts from thirty-two medicinal plants and 15 extracts from 8 food plants were evaluated for antiproliferative activity in Caco-2 cells. Extracts from 7 plant species showed antiproliferative activity but in most of the preparations tested no cytotoxic activity was observed at the concentrations used. Secondly, some assays including DNA replication, DNA degradation, oligonucleosomal formation, and caspase-3 activity were performed to understand the mechanism by which the compounds isolated affect cell proliferation and cell death. Curcuphenol, isolated from Baccharis genistelloides and Myrmekioderma styx, and damsin and coronopilin, isolated from Ambrosia arborescens, were found to inhibit cell proliferation and to induce cell death in colon cancer cells. Further studies are needed to find new anti-cancer compounds in medicinal plants in Bolivia.
    • Biological activities of natural and semi-synthetic pseudo-guaianolides: Inhibition of transcription factors.

      Villagomez, Rodrigo (Media-Tryck, Lund University, Sweden, 2014, 2014-06)
      Damsin (1) is a natural sesquiterpene lactone (SL) isolated from Ambrosia arborescens Mill., a plant used in the Andes as antiinflammatory medicine. This natural product is an inhibitor of NF-κB, a protein complex that controls the transcription of many genes in mammalian cells, and has a potential for standing model for the development of new anti-cancer lead structures. In order to improve the anti-cancer activity, the chemistry of 1 was explored and in the process, dozens of derivatives were prepared. Damsin (1) inhibited cell proliferation, DNA biosynthesis and formation of cytoplasmic DNA histone complex in Caco-2 cells and further studies using the luciferase reporter system showed that it also inhibited expressions of NF-κB and STAT3. Therefore, the NF-κB inhibitory capacity of some derivatives was evaluated and two analogues, 31 and 32, were found to be more potent. In order to have a preliminary evaluation method of the derivatives, we developed fast and cheap biochemical assay to study the effect of SLs in the binding capacity of NF-κB (heterodimer RelA/p50) to the DNA recognition target. In this assay the compounds 21, 22, 24, 25 and 26 had a high dissociation capacity of the complex NF-κB/DNA. Finally, four compounds were selected for MS characterization studies with recombinant NF-κB, the most selective compound was 26 (compared with 1) by selective alkylation of Cys-38 and Cys-120 in RelA. The Cystein-38 is crucial for the transcriptional activity of NF-κB.
    • Biologically relevant oxidants and terminology, classification and nomenclature of oxidatively generated damage to nucleobases and 2-deoxyribose in nucleic acids.

      Cadet, Jean; Loft, Steffen; Olinski, Ryszard; Evans, Mark D.; Bialkowski, Karol; Richard Wagner, J.; Dedon, Peter C.; Moller, Peter; Greenberg, Marc M.; Cooke, Marcus S. (2012-04)
      A broad scientific community is involved in investigations aimed at delineating the mechanisms of formation and cellular processing of oxidatively generated damage to nucleic acids. Perhaps as a consequence of this breadth of research expertise, there are nomenclature problems for several of the oxidized bases including 8-oxo-7,8-dihydroguanine (8-oxoGua), a ubiquitous marker of almost every type of oxidative stress in cells. Efforts to standardize the nomenclature and abbreviations of the main DNA degradation products that arise from oxidative pathways are reported. Information is also provided on the main oxidative radicals, non-radical oxygen species, one-electron agents and enzymes involved in DNA degradation pathways as well in their targets and reactivity. A brief classification of oxidatively generated damage to DNA that may involve single modifications, tandem base modifications, intrastrand and interstrand cross-links together with DNA-protein cross-links and base adducts arising from the addition of lipid peroxides breakdown products is also included.
    • Biomarkers of carcinogen exposure and early effects.

      The Nofer Institute of Occupational Medicine, 2006
      The purpose of this review is to summarise the current situation regarding the types and uses of biomarkers of exposure and effect for the main classes of food-derived genotoxic carcinogens, and to consider some aspects of the intercomparison between these biomarkers. The biomarkers of exposure and early effects of carcinogens that have been most extensively developed are those for genotoxic agents and for compounds that generate hydroxyl radicals and other reactive radical species, and it is on these that this review is mostly concentrated.
    • Biomarkers of dietary intake of flavonoids and phenolic acids for studying diet-cancer relationship in humans.

      Linseisen, Jakob; Rohrmann, Sabine (2008-05)
      BACKGROUND: For many polyphenolic compounds found in plant-derived food, biological effects possibly relevant for cancer prevention have been shown. Since dietary intake estimates suffer from imprecision, the measurement of these compounds (or metabolites of) in biological specimens collected in epidemiological studies is expected to improve accuracy of exposure estimation. AIM OF THE STUDY: The current use of biomarkers in etiologic studies on polyphenolics and cancer risk is evaluated. In addition, available analytical methods are discussed with respect to the requirements for their integration in epidemiological studies, putting specific emphasis on the epidemiological validation of such markers. METHODS: The scientific literature was screened for epidemiologic studies on the relationship of flavonoid and phenolic acid concentrations in human specimens (i.e. blood, urine) and cancer risk. In addition, original data on intra- and inter-subject variability of several flavonoids and phenolic acids are presented. RESULTS: Although several techniques are used in bioavailability or short-term intervention studies, their integration in epidemiological studies is very limited. An exception are phytoestrogens where validated immunoassays allow the rapid measurement of large sample numbers with small sample volume. For several polyphenols, the data on the epidemiologic validity encourages for their use in epidemiological studies. CONCLUSIONS: There are valid possibilities for additional biomarkers of flavonoid and phenolic acid intake that are best applied in prospective studies with more than one biological sample per subject. Currently, a combination of a single biomarker measurement with long-term dietary intake estimates will probably be the most valuable choice to decrease measurement error in exposure data.
    • Biomarkers of exposure to vitamins A, C, and E and their relation to lipid and protein oxidation markers.

      Dragsted, Lars O. (2008-05)
      Since antioxidant vitamins may affect an organism's capacity for defence against reactive oxygen species, biological markers of the dietary exposure to these vitamins is of importance. There is also a need of effect biomarkers for determining the ability of these and other antioxidants to increase the overall antioxidant capacity and decrease the oxidative damage occurring in biological samples. This review is concerned with exposure markers and markers of lipid- or protein damage following intervention with vitamins A, C and E. While there are several high quality exposure markers available it is not possible to identify functional markers of lipid or protein oxidation, which respond reliably to human dietary intervention with vitamins A, C or E.
    • Biomarkers of oxidative damage to DNA and repair.

      Loft, Steffen; Hogh Danielsen, Pernille; Mikkelsen, Lone; Risom, Lotte; Forchhammer, Lykke; Moller, Peter (2008-10)
      Oxidative-stress-induced damage to DNA includes a multitude of lesions, many of which are mutagenic and have multiple roles in cancer and aging. Many lesions have been characterized by MS-based methods after extraction and digestion of DNA. These preparation steps may cause spurious base oxidation, which is less likely to occur with methods such as the comet assay, which are based on nicking of the DNA strand at modified bases, but offer less specificity. The European Standards Committee on Oxidative DNA Damage has concluded that the true levels of the most widely studied lesion, 8-oxodG (8-oxo-7,8-dihydro-2'-deoxyguanosine), in cellular DNA is between 0.5 and 5 lesions per 10(6) dG bases. Base excision repair of oxidative damage to DNA can be assessed by nicking assays based on oligonucleotides with lesions or the comet assay, by mRNA expression levels or, in the case of, e.g., OGG1 (8-oxoguanine DNA glycosylase 1), responsible for repair of 8-oxodG, by genotyping. Products of repair in DNA or the nucleotide pool, such as 8-oxodG, excreted into the urine can be assessed by MS-based methods and generally reflects the rate of damage. Experimental and population-based studies indicate that many environmental factors, including particulate air pollution, cause oxidative damage to DNA, whereas diets rich in fruit and vegetables or antioxidant supplements may reduce the levels and enhance repair. Urinary excretion of 8-oxodG, genotype and expression of OGG1 have been associated with risk of cancer in cohort settings, whereas altered levels of damage, repair or urinary excretion in case-control settings may be a consequence rather than the cause of the disease.
    • Biosynthesis of selenoproteins in cultured bovine mammary cells.

      Bruzelius, Katharina; Purup, Stig; James, Peter; Onning, Gunilla; Akesson, Bjorn (2008)
      The biosynthesis of selenoproteins was studied in relation to milk formation and mammary cell biology by incubating the bovine mammary cell line MAC-T with ((75)Se)selenite. Intracellular proteins and proteins secreted into the cell culture medium were separated by 2D electrophoresis, the selenoproteins were detected by autoradiography, and the proteins were identified by MALDI-TOF. Approximately 35 (75)Se-containing spots were found in the cell proteins from MAC-T cells. Among them, one-third showed high intensity. The strongest spot was identified as glutathione peroxidase 1. About 20 spots were observed in protein precipitated from cell culture medium, one-third of them being distinctly visible. In an attempt to study a perturbation of the system, the effect of retinoic acid (RA) on the formation of selenoproteins was investigated. The concentration of (75)Se in total cell protein was reduced by about 35% in cells cultured with RA compared with control cells, while the opposite effect was observed in protein precipitated from cell culture medium, which contained 60% more (75)Se in RA-treated samples than in controls. There were also indications that RA might affect different selenoproteins in different ways. The methods described provide a promising approach for further studies of the regulation of selenoprotein formation in the mammary gland.
    • Both replication bypass fidelity and repair efficiency influence the yield of mutations per target dose in intact mammalian cells induced by benzo[a]pyrene-diol-epoxide and dibenzo[a,l]pyrene-diol-epoxide.

      Lagerqvist, Anne; Hakansson, Daniel; Prochazka, Gabriela; Lundin, Cecilia; Dreij, Kristian; Segerback, Dan; Jernstrom, Bengt; Tornqvist, Margareta; Seidel, Albrecht; Erixon, Klaus; et al. (2008-08-02)
      Mutations induced by polycyclic aromatic hydrocarbons (PAH) are expected to be produced when error-prone DNA replication occurs across unrepaired DNA lesions formed by reactive PAH metabolites such as diol epoxides. The mutagenicity of the two PAH-diol epoxides (+)-anti-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) and (+/-)-anti-11,12-dihydroxy-13,14-epoxy-11,12,13,14-tetrahydrodibenzo[a,l]pyrene (DBPDE) was compared in nucleotide excision repair (NER) proficient and deficient hamster cell lines. We applied the (32)P-postlabelling assay to analyze adduct levels and the hprt gene mutation assay for monitoring mutations. It was found that the mutagenicity per target dose was 4 times higher for DBPDE compared to BPDE in NER proficient cells while in NER deficient cells, the mutagenicity per target dose was 1.4 times higher for BPDE. In order to investigate to what extent the mutagenicity of the different adducts in NER proficient cells was influenced by repair or replication bypass, we measured the overall NER incision rate, the rate of adduct removal, the rate of replication bypass and the frequency of induced recombination in the hprt gene. The results suggest that NER of BPDE lesions are 5 times more efficient than for DBPDE lesions, in NER proficient cells. However, DBPDE adducts block replication more efficiently and also induce 6 times more recombination events in the hprt gene than adducts of BPDE, suggesting that DBPDE adducts are, to a larger extent, bypassed by homologous recombination. The results obtained here indicate that the mutagenicity of PAH is influenced not only by NER, but also by replication bypass fidelity. This has been postulated earlier based on results using in vitro enzyme assays, but is now also being recognized in terms of forward mutations in intact mammalian cells.
    • Bulky DNA adduct formation and risk of bladder cancer.

      Castano-Vinyals, Gemma; Talaska, Glenn; Rothman, Nathaniel; Alguacil, Juan; Garcia-Closas, Montserrat; Dosemeci, Mustafa; Cantor, Kenneth P.; Malats, Nuria; Real, Francisco X.; Silverman, Debra; et al. (2007-10)
      Exposure to polycyclic aromatic hydrocarbons (PAHs) has been associated with risk of bladder cancer and with increased bulky DNA adduct levels in several studies, mainly in smokers. We investigated the relation between bulky PAH-DNA adducts in peripheral blood mononuclear cells and bladder cancer in nonsmoking subjects from a large hospital-based case-control study in Spain. Additionally, we examined the association between DNA adduct formation and several air pollution proxies. The study comprised 76 nonsmoking cases and 76 individually matched controls by sex, region of residence, age, and smoking status (never, former). To maximize the relevance of the DNA adduct measurement as a proxy of PAH exposure, subjects selected had not changed residence, occupation, and major lifestyle factors during the last 10 years. Bulky DNA adducts were measured using the (32)P-postlabeling technique, nuclease P1 treatment. The percentage of detectable adducts was higher in controls (41%) than in cases (32%) with an odds ratio of 0.75 (95% confidence interval, 0.36-1.58). In an analysis limited to controls, a higher percentage of DNA adducts was found among those whose last residence was in a big city (50%) compared with those living in villages (19%; P = 0.04). No consistent associations were found for other markers of air pollution. In this study, among nonsmokers with stable environmental and lifestyle factors, bulky DNA adducts were not associated with bladder cancer risk. Results do not support an association of bladder cancer risk with low-level exposure to PAHs as measured through the formation of bulky DNA adducts in peripheral mononuclear cells.
    • Bulky DNA adducts in white blood cells: a pooled analysis of 3,600 subjects.

      Ricceri, Fulvio; Godschalk, Roger W.; Peluso, Marco; Phillips, David H.; Agudo, Antonio; Georgiadis, Panagiotis; Loft, Steffen; Tjonneland, Anne; Raaschou-Nielsen, Ole; Palli, Domenico; et al. (2010-12)
      Bulky DNA adducts are markers of exposure to genotoxic aromatic compounds, which reflect the ability of an individual to metabolically activate carcinogens and to repair DNA damage. Polycyclic aromatic hydrocarbons (PAHs) represent a major class of carcinogens that are capable of forming such adducts. Factors that have been reported to be related to DNA adduct levels include smoking, diet, body mass index (BMI), genetic polymorphisms, the season of collection of biologic material, and air pollutants.
    • The cancer chemopreventive actions of phytochemicals derived from glucosinolates.

      Hayes, John D.; Kelleher, Michael O.; Eggleston, Ian M. (2008-05)
      This article reviews the mechanisms by which glucosinolate breakdown products are thought to inhibit carcinogenesis. It describes how isothiocyanates, thiocyanates, nitriles, cyano-epithioalkanes and indoles are produced from glucosinolates through the actions of myrosinase, epithiospecifier protein and epithiospecifier modifier protein released from cruciferous vegetables during injury to the plant. The various biological activities displayed by these phytochemicals are described. In particular, their abilities to induce cytoprotective genes, mediated by the Nrf2 (NF-E2 related factor 2) and AhR (arylhydrocarbon receptor) transcription factors, and their abilities to repress NF-kappaB (nuclear factor-kappaB) activity, inhibit histone deacetylase, and inhibit cytochrome P450 are outlined. Isothiocyanates appear to alter gene expression through modification of critical thiols in regulatory proteins such as Keap1 (Kelch-like ECH-associated protein 1) or IKK (IkappaB kinase), causing activation of Nrf2 and inactivation of NF-kappaB, respectively. Certain indoles act as ligands for AhR. Isothiocyanates and indoles are also capable of affecting cell cycle arrest and stimulating apoptosis. The mechanisms responsible for these anti-proliferative responses are discussed.
    • Cereal fiber intake may reduce risk of gastric adenocarcinomas: the EPIC-EURGAST study.

      Mendez, Michelle A.; Pera, Guillem; Agudo, Antonio; Bueno-de-Mesquita, H. Bas; Palli, Domenico; Boeing, Heiner; Carneiro, Fatima; Berrino, Franco; Sacerdote, Carlotta; Tumino, Rosario; et al. (2007-10-01)
      Numerous case-control studies suggest dietary fiber may reduce risk of gastric cancer, but this has not been confirmed prospectively. A previous case-control study reported reduced risk of gastric cardia adenocarcinomas associated with cereal fiber, but not with fruit or vegetable fiber. To date, different food sources of fiber have not been examined with respect to noncardia tumors or diverse histologic sub-types. This study prospectively examines associations between fiber from different food sources and incident gastric adenocarcinomas (GC) among more than 435,000 subjects from 10 countries participating in the European Prospective Investigation into Cancer and Nutrition study. Subjects aged 25-70 years completed dietary questionnaires in 1992-98, and were followed up for a median of 6.7 years. About 312 incident GCs were observed. The relative risk of GC was estimated based on cohort-wide sex-specific fiber intake quartiles using proportional hazards models to estimate hazards ratios (HRs) and 95% confidence intervals (CIs). Intakes of cereal fiber, but not total, fruit or vegetable fiber, were associated with reduced GC risk [adjusted HR for the highest vs. lowest quartile of cereal fiber 0.69, 0.48-0.99]. There was a strong inverse association for diffuse [HR 0.43, 0.22-0.86], but not intestinal type [HR 0.98, 0.54-1.80] tumors. Associations for cardia vs. noncardia tumors were similar to those for overall GC, although cardia associations did not reach significance. Cereal fiber consumption may help to reduce risk of GC, particularly diffuse type tumors. Further study on different food sources of fiber in relation to GC risk is warranted to confirm these relationships.
    • Challenges from new technologies and new biomarkers.

      Vineis, Paolo; Vermeulen, Roel; Geneletti, Sara; Minelli, Cosetta; Taioli, Emanuela; Thompson, John; Stromberg, Ulf; Kirsch-Volders, Micheline; Raluca, Mateuca; Matullo, Giuseppe (The Nofer Institute of Occupational Medicine, 2007)
    • Chromosomal changes: induction, detection methods and applicability in human biomonitoring.

      Mateuca, R.; Lombaert, N.; Aka, P.V.; Decordier, I.; Kirsch-Volders, M. (2006-11)
      The objective of this state of the art paper is to review the mechanisms of induction, the fate, the methodology, the sensitivity/specificity and predictivity of two major cytogenetic endpoints applied for genotoxicity studies and biomonitoring purposes: chromosome aberrations and micronuclei. Chromosomal aberrations (CAs) are changes in normal chromosome structure or number that can occur spontaneously or as a result of chemical/radiation treatment. Structural CAs in peripheral blood lymphocytes (PBLs), as assessed by the chromosome aberration (CA) assay, have been used for over 30 years in occupational and environmental settings as a biomarker of early effects of genotoxic carcinogens. A high frequency of structural CAs in lymphocytes (reporter tissue) is predictive of increased cancer risk, irrespective of the cause of the initial CA increase. Micronuclei (MN) are small, extranuclear bodies that arise in dividing cells from acentric chromosome/chromatid fragments or whole chromosomes/chromatids that lag behind in anaphase and are not included in the daughter nuclei in telophase. The cytokinesis-block micronucleus (CBMN) assay is the most extensively used method for measuring MN in human lymphocytes, and can be considered as a "cytome" assay covering cell proliferation, cell death and chromosomal changes. The key advantages of the CBMN assay lie in its ability to detect both clastogenic and aneugenic events and to identify cells which divided once in culture. Evaluation of the mechanistic origin of individual MN by centromere and kinetochore identification contributes to the high sensitivity of the method. A number of findings support the hypothesis of a predictive association between the frequency of MN in cytokinesis-blocked lymphocytes and cancer development. Recent advances in fluorescence in situ hybridization (FISH) and microarray technologies are modifying the nature of cytogenetics, allowing chromosome and gene identification on metaphase as well as in interphase. Automated scoring by flow cytometry and/or image analysis will enhance their applicability.
    • Circadian rhythms and chemical carcinogenesis: Potential link. An overview.

      Oesch-Bartlomowicz, Barbara; Weiss, Carsten; Dietrich, Cornelia; Oesch, Franz (2009-11)
      Circadian rhythm is an integral and not replaceable part of the organism's homeostasis. Its signalling is multidimensional, overlooking global networks such as chromatin remodelling, cell cycle, DNA damage and repair as well as nuclear receptors function. Understanding its global networking will allow us to follow up not only organism dysfunction and pathology (including chemical carcinogenesis) but well-being in general having in mind that time is not always on our side.
    • Circulating free DNA in plasma or serum as biomarker of carcinogenesis: practical aspects and biological significance.

      Gormally, Emmanuelle; Caboux, Elodie; Vineis, Paolo; Hainaut, Pierre (2008-08-27)
      The presence of small amounts of tumor DNA in cell free DNA (CFDNA) circulating in the plasma or serum of cancer patients was first demonstrated 30 years ago. Since then, overall plasma DNA concentration in cancer patients and genetic or epigenetic alterations specific to tumor DNA have been investigated in patients diagnosed with different types of cancer. The proportion of patients with altered CFDNA varies with the pathology and the nature of the marker. However, several studies have reported the presence of altered CFDNA in over 50% of cancer patients, suggesting that this marker may be common and amenable for a variety of clinical and epidemiological studies. Because the mechanisms and timing of CFDNA release in the blood stream are poorly understood, only few studies have addressed the use of CFDNA for early cancer detection or as a biomarker for mutagenesis and tumourigenesis in molecular epidemiology. In this review, we discuss the technical issues involved in obtaining, using and analyzing CFDNA in cancer or healthy subjects. We also summarize the literature available on the mechanisms of CDNA release as well as on cross-sectional or prospective studies aimed at assessing the clinical and biological significance of CFDNA. These studies show that, in some circumstances, CFDNA alterations are detectable ahead of cancer diagnosis, raising the possibility of exploiting them as biomarkers for monitoring cancer occurrence. Testing these hypotheses will require well-designed studies, assessing multiple markers with quantitative and sensitive methods, with adequate follow-up of subjects, and we provide recommendations for the development of such studies.
    • Combination of azathioprine and UVA irradiation is a major source of cellular 8-oxo-7,8-dihydro-2'-deoxyguanosine.

      Cooke, Marcus S.; Duarte, Tiago L.; Cooper, Deborah; Chen, Jie; Nandagopal, Sridevi; Evans, Mark D. (2008-12-01)
      Thiopurine antimetabolites, such as azathioprine (Aza) and 6-thioguanine (6-TG), are widely used in the treatment of cancer, inflammatory conditions and organ transplantation patients. Recent work has shown that cells treated with 6-TG and UVA generate ROS, with implied oxidatively generated modification of DNA. In a study of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in renal transplant patients, we provided the first in vivo evidence linking Aza and oxidatively damaged DNA. Using the hOGG1 comet assay, we herein demonstrate high levels of 8-oxodG and alkali-labile sites (ALS) in cells treated with biologically relevant doses of 6-TG, or Aza, plus UVA. This damage was induced dose-dependently. Surprisingly, given the involvement of 6-TG incorporation into DNA in its therapeutic effect, significant amounts of 8-oxodG and ALS were induced in quiescent cells, although less than in proliferating cells. We speculate that some activity of hOGG1 towards unirradiated, 6-TG treated cells, implies possible recognition of 6-TG or derivatives thereof. This is the first report to conclusively demonstrate oxidatively damaged DNA in cells treated with thiopurines and UVA. These data indicate that Aza-derived oxidative stress will occur in the skin of patients on Aza, following even low level UVA exposure. This is a probable contributor to the increased risk of non-melanoma skin cancer in these patients. However, as oxidative stress is unlikely to be involved in the therapeutic effects of Aza, intercepting ROS production in the skin could be a viable route by which this side effect may be minimised.