<p>Radiotherapy is one of the most common therapeutic methods for treatment of many types of cancer. Despite many decades of development and experience there is much to improve, both in efficacy of treatment and to decrease the incidences of adverse healthy tissue reactions. Around 20 % of the radiotherapy patients show a broad range in the severity of normal tissue reactions to radiotherapy, and dose limits are governed by severe reactions in the most radiosensitive patients (< 5 %). Identification of patients with low, moderate or high clinical radiosensitivity before commencing of radiotherapy would allow individual adaptation of the maximum dose with an overall increase in the cure rate. Characterization of factors that may modify the biological effects of ionizing radiation has been a subject of intense research efforts. Still, there is no assay currently available that can reliably predict the clinical radiosensitivity. The aim of this work has been to investigate the role of oxidative stress in individual radiosensitivity and evaluate novel markers of radiation response, which could be adapted for clinical use.</p><p>8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), a general marker of oxidative stress, is one of the major products of interaction of ionizing radiation with DNA and the nucleotide pool of the cell. As 8-oxo-dG is highly mutagenic due to incorrect base pairing with deoxyadenosine, various repair mechanisms recognize and remove 8-oxo-dG. The repaired lesions are released from cells to the extracellular milieu (serum, urine and cell culture medium) where they can be detected as markers for free radical reactions with the nucleic acids.</p><p>Significant variations in background levels as well as in radiation induced levels of 8-oxo-dG in urine have been demonstrated in breast cancer patients (paper 1). Two major patterns were observed: high background and no therapy-related increase vs. low background and significant increase during radiotherapy for the radiosensitive and non radiosensitive patients respectively.</p><p>Studies in paper 2 indicated major contribution of the nucleotide pool to the extracellular 8-oxo-dG levels. The results also implicated induction of prolonged endogenous oxidative stress in the irradiated cells. RNA “knock-down” experiments on the nucleotide pool sanitization enzyme hMTH1 in paper 3 lend further experimental evidence to this assumption.</p><p>The applicability of 8-oxo-dG as a diagnostic marker of oxidative stress was demonstrated in paper 4. Studies on dialysis patients revealed a good correlation between inflammatory responses (known to be associated with persistent oxidative stress) and extracellular 8-oxo-dG.</p><p>In summary, our results confirm that extracellular 8-oxo-dG is a sensitive <i>in vivo</i> biomarker of oxidative stress, primarily formed by oxidative damage of dGTP in the nucleotide pool with a potential to become a clinical tool for prediction of individual responses to radiotherapy.</p>

Radiotherapy is one of the most common therapeutic methods for treatment of many types of cancer. Despite many decades of development and experience there is much to improve, both in efficacy of treatment and to decrease the incidences of adverse healthy tissue reactions. Around 20 % of the radiotherapy patients show a broad range in the severity of normal tissue reactions to radiotherapy, and dose limits are governed by severe reactions in the most radiosensitive patients (&lt; 5 %). Identification of patients with low, moderate or high clinical radiosensitivity before commencing of radiotherapy would allow individual adaptation of the maximum dose with an overall increase in the cure rate. Characterization of factors that may modify the biological effects of ionizing radiation has been a subject of intense research efforts. Still, there is no assay currently available that can reliably predict the clinical radiosensitivity. The aim of this work has been to investigate the role of oxidative stress in individual radiosensitivity and evaluate novel markers of radiation response, which could be adapted for clinical use. 8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), a general marker of oxidative stress, is one of the major products of interaction of ionizing radiation with DNA and the nucleotide pool of the cell. As 8-oxo-dG is highly mutagenic due to incorrect base pairing with deoxyadenosine, various repair mechanisms recognize and remove 8-oxo-dG. The repaired lesions are released from cells to the extracellular milieu (serum, urine and cell culture medium) where they can be detected as markers for free radical reactions with the nucleic acids. Significant variations in background levels as well as in radiation induced levels of 8-oxo-dG in urine have been demonstrated in breast cancer patients (paper 1). Two major patterns were observed: high background and no therapy-related increase vs. low background and significant increase during radiotherapy for the radiosensitive and non radiosensitive patients respectively. Studies in paper 2 indicated major contribution of the nucleotide pool to the extracellular 8-oxo-dG levels. The results also implicated induction of prolonged endogenous oxidative stress in the irradiated cells. RNA “knock-down” experiments on the nucleotide pool sanitization enzyme hMTH1 in paper 3 lend further experimental evidence to this assumption. The applicability of 8-oxo-dG as a diagnostic marker of oxidative stress was demonstrated in paper 4. Studies on dialysis patients revealed a good correlation between inflammatory responses (known to be associated with persistent oxidative stress) and extracellular 8-oxo-dG. In summary, our results confirm that extracellular 8-oxo-dG is a sensitive in vivo biomarker of oxidative stress, primarily formed by oxidative damage of dGTP in the nucleotide pool with a potential to become a clinical tool for prediction of individual responses to radiotherapy.

Pesticides are among the most pervasive environmental contaminants and they are an important potential risk for human health. Agricultural workers are constantly exposed to pesticide spray, drift and residues in the soil and foliage. Many agricultural pesticides are readily absorbed by the body, through contact with the skin, the respiratory track, the eyes, and the gastrointestinal system. Multiple studies have reported a strong association between pesticide exposure and various health outcomes including cancer. Oxidative stress and DNA damage have been proposed as mechanisms linking pesticide exposure to health effects and neurological diseases. The focus of the present translational study is to examine the relationship between human exposure to the organophosphate pesticide azinphos methyl (AZM) and oxidative stress by measuring biomarkers of oxidative stress in biological fluids (i.e., urine, serum) and peripheral blood lymphocytes (PBLs) of agricultural workers. The findings from these field studies will be validated in vitro by examining cultures of human lymphocytes treated with AZM for similar biomarkers of oxidative stress. Since the collection of PBLs from study participants is highly invasive and not suitable for studies involving younger subjects, we also examined buccal cells for biomarkers of oxidative stress (i.e., DNA damage) as a more universal source of human tissue to assess oxidative stress in pesticide exposed individuals. We demonstrated in this study that AZM induces oxidative stress and causes DNA damage in human tissues. Agricultural workers who had been exposed to AZM showed elevated serum levels of lipid peroxides, increased urinary levels of 8-OH-dG, and lymphocytes from these individuals showed increased DNA damage and associated changes in oxidative DNA repair enzymes. Biomarkers of oxidative stress were also elevated in human lymphocytes treated with physiologically relevant concentrations of AZM. In cultures of human lymphocytes, AZM caused a concentration-dependent loss of viability and associated increases in ROS and a reduction in intracellular GSH. We also demonstrated that viable leukocytes from the oral cavity can be readily obtained from humans and these buccal cells can be used to assess DNA damage following exposure to occupational and environmental genotoxicants. We also noted that oral leukocytes are especially sensitive to cryopreservation with DMSO and thus, these cells must be cryoprotected with 5% DMSO to preserve the viability of these cells for subsequent biochemical studies. In summary, these in vivo and in vitro studies demonstrated that AZM induces oxidative stress in a dose-dependent matter and that oral lymphocytes are a good source of human tissue for assessing DNA damage and possibly other biochemical changes. The possible health implications of the variations in these biomarkers of oxidative stress and DNA damage are undetermined. Yet the findings from these studies have provided a strong foundation for determining the mechanism by which pesticide induce oxidative stress, to explore the putative relationship between pesticide-induced oxidative stress and disease (e.g. cancer, neurodegenerative disorders) and determine whether tissue damage in humans is brought about by direct or by indirect action of organophosphate pesticides. / Graduation date: 2010