Growth hormone in the tumor microenvironment

ABSTRACT Tumor development is a multistep process whereby local mechanisms enable somatic mutations during preneoplastic stages. Once a tumor develops, it becomes a complex organ composed of multiple cell types. Interactions between malignant and non-transformed cells and tissues create a tumor microenvironment (TME) comprising epithelial cancer cells, cancer stem cells, non-tumorous cells, stromal cells, immune-inflammatory cells, blood and lymphatic vascular network, and extracellular matrix. We review reports and present a hypothesis that postulates the involvement of growth hormone (GH) in field cancerization. We discuss GH contribution to TME, promoting epithelial-to-mesenchymal transition, accumulation of unrepaired DNA damage, tumor vascularity, and resistance to therapy. Arch Endocrinol Metab. 2019;63(6):568-75

Increased ROS production and DNA damage in monocytes are biomarkers of aging and atherosclerosis

BACKGROUND: New evidence demonstrates that aging and dyslipidemia are closely associated with oxidative stress, DNA damage and apoptosis in some cells and extravascular tissues. However, in monocytes, which are naturally involved in progression and/or resolution of plaque in atherosclerosis, this concurrence has not yet been fully investigated. In this study, we evaluated the influence of aging and hypercholesterolemia on serum pro-inflammatory cytokines, oxidative stress, DNA damage and apoptosis in monocytes from apolipoprotein E-deficient (apoE-/-) mice compared with age-matched wild-type C57BL/6 (WT) mice. Experiments were performed in young (2-months) and in old (18-months) male wild-type (WT) and apoE-/- mice. RESULTS: Besides the expected differences in serum lipid profile and plaque formation, we observed that atherosclerotic mice exhibited a significant increase in monocytosis and in serum levels of pro-inflammatory cytokines compared to WT mice. Moreover, it was observed that the overproduction of ROS, led to an increased DNA fragmentation and, consequently, apoptosis in monocytes from normocholesterolemic old mice, which was aggravated in age-matched atherosclerotic mice. CONCLUSIONS: In this study, we demonstrate that a pro-inflammatory systemic status is associated with an impairment of functionality of monocytes during aging and that these parameters are fundamental extra-arterial contributors to the aggravation of atherosclerosis. The present data open new avenues for the development of future strategies with the purpose of treating atherosclerosis.

DNA damage in Wistar Kyoto rats exercised during pregnancy

Abstract Purpose: To evaluate DNA damage levels in pregnant rats undergoing a treadmill exercise program. Methods: Wistar Kyoto rats were allocated into two groups (n= 5 animals/group): non-exercise and exercise. The pregnant rats were underwent an exercise protocol on a treadmill throughout pregnancy. Exercise intensity was set at 50% of maximal capacity during maximal exercise testing performed before mating. Body weight, blood pressure and glucose levels, and triglyceride concentration were measured during pregnancy. At day 10 post-natal, the animals were euthanized and maternal blood samples were collected for DNA damage. Results: Blood pressure and glucose levels and biochemical measurements showed no significant differences. Increased DNA damage levels were found in exercise group compared to those of non-exercise group (p<0.05). Conclusion: The exercise intensity protocol used in the study might have been exhaustive leading to maternal increased DNA damage levels, demonstrating the relevance of an adequate protocol of physical exercise.

Protein carbonyl content: a novel biomarker for aging in HIV/AIDS patients

Abstract Background: The major complications of “treated” Human Immunodeficiency Virus (HIV) infection are cardiovascular disease, malignancy, renal disease, liver disease, bone disease, and perhaps neurological complications, which are phenomena of the normal aging process occurring at an earlier age in the HIV-infected population. The present study is aimed to explore protein carbonyl content as a biomarker for detecting oxidative DNA damage induced ART toxicity and/or accelerated aging in HIV/AIDS patients. Objective: To investigate the potential of carbonyl content as a biomarker for detecting oxidative Deoxyribonucleic acid (DNA) damage induced Antiretroviral Theraphy (ART) toxicity and/or accelerated aging in HIV/AIDS patients. Methods: In this case–control study a total 600 subjects were included. All subjects were randomly selected and grouped as HIV-negative (control group) (n = 300), HIV-infected ART naive (n = 100), HIV-infected on first line ART (n = 100), and HIV-infected on second line ART (n = 100). Seronegative control subjects were age- and sex-matched with the ART naive patients and the two other groups. Carbonyl protein was determined by the method described in Levine et al. DNA damage marker 8-OH-dG was determined using 8-hydroxy-2-deoxy Guanosine StressXpress ELA Kit by StressMarq Biosciences. Results: Protein carbonyl content levels and oxidative DNA damage were significantly higher (p < 0.05) in HIV-infected patients on second line ART and HIV-infected patients on first line ART than ART naive patients and controls. In a linear regression analysis, increased protein carbonyl content was positively associated with increased DNA damage (OR: 0.356; 95% CI: 0.287–0.426) p < 0.05. Conclusions: Carbonyl content may has a role as a biomarker for detecting oxidative DNA damage induced ART toxicity and/or accelerated aging in HIV/AIDS patients. Larger studies are warranted to elucidate the role of carbonyl content as a biomarker for premature aging in HIV/AIDS patients.

Association of oxidative stress and DNA damage with grafting time in patients with multiple myeloma and lymphoma submitted to autologous hematopoietic stem cell transplantation / Associação do estresse oxidativo e dano ao DNA com o tempo de enxertia em pacientes com mieloma múltiplo e linfomas submetidos a transplante autólogo de células-tronco hematopoéticas

ABSTRACT The aim of the study was to investigate the association between oxidative stress and DNA damage with grafting time in patients submitted to autologous hematopoietic stem-cell transplantation (HSCT). The study included 37 patients submitted to autologous HSCT diagnosed with Multiple Myeloma (MM) and lymphoma (Hodgkin’s and non-Hodgkin’s). Biomarkers of oxidative stress and DNA damage index (DI) were performed at baseline (pre-CR) of the disease and during the conditioning regimen (CR), one day after the HSCT, ten days after HSCT and twenty days after HSCT, as well as in the control group consisting of 30 healthy individuals. The outcomes showed that both groups of patients had an hyperoxidative state with high DI when compared to baseline and to the control group and that the CR exacerbated this condition. However, after the follow-up period of the study, this picture was re-established to the baseline levels of each pathology. The study patients with MM showed a mean grafting time of 10.75 days (8 to 13 days), with 10.15 days (8 to 15 days) for the lymphoma patients. In patients with MM, there was a negative correlation between the grafting time and the basal levels of GPx (r = -0.54; p = 0.034), indicating that lower levels of this important enzyme are associated with a longer grafting time. For the DI, the correlation was a positive one (r = 0.529; p = 0.030). In the group with lymphoma, it was observed that the basal levels of NOx were positively correlated with grafting time (r = 0.4664, p = 0.032). The data indicate the potential of these biomarkers as predictors of toxicity and grafting time in patients with MM and Lymphomas submitted to autologous HSCT.

RESUMO O objetivo do estudo foi investigar a associação entre estresse oxidativo e dano ao DNA com o tempo de enxertia em pacientes submetidos ao transplante de células-tronco hematopoéticas autólogo (TCTH). Participaram do estudo 37 pacientes submetidos ao TCTH autólogo com diagnóstico de mieloma múltiplo (MM) e Linfomas (Hodgkin e não Hodgkin). Biomarcadores de estresse oxidativo e índice de dano ao DNA (ID) foram determinados no estado basal (Pré-RC) das doenças e durante o regime de condicionamento (RC), um dia após o TCTH, dez dias após o TCTH e vinte dias após o TCTH e no grupo controle composto por 30 individuos saudáveis. Os resultados demonstraram que os dois grupos de pacientes apresentaram um estado hiperoxidativo com elevado ID quando comparados ao estado basal e ao grupo controle e que o RC exacerbou essa condição. No entanto, após o tempo de acompanhamento do estudo, esse quadro foi reestabelecido ao estado basal de cada patologia. Os pacientes do estudo com MM apresentaram uma média do tempo de enxertia de 10,75 dias (8 a 13 dias), e de 10,15 dias (8 a 15 dias) para o grupo Linfoma. Nos pacientes com MM houve uma correlação negativa entre o tempo de enxertia e os níveis basais de GPx (r=-0,54; p=0,034), indicando que níveis mais baixos de GPx estão relacionados a um maior tempo de enxertia, e para o ID, a correlação foi positiva (r=0,529; p=0,030). No grupo com Linfoma, observou-se que os níveis basais de NOx correlacionaram-se positivamente com o tempo de enxertia (r= 0,4664; p=0,032). Os dados apontam para o potencial desses biomarcadores como preditores da toxicidade e do tempo de enxertia em pacientes com MM e Linfomas submetidos ao TCTH autólogo

Relevance of prognostic factors in the decision-making of stem cell transplantation in Myelodysplastic Syndromes / Relevância dos fatores prognósticos na decisão do transplante de células-tronco na Síndrome Mielodisplásica

ABSTRACT The hematopoietic stem cell transplantation (HSCT) is the only curative alternative for Myelodysplastic Syndrome (MDS), but many patients are not eligible for this treatment, as there are several limiting factors, especially in the case of patients with low-risk MDS. The aim of this study is to discuss the factors that can guide the decision-making on referring or not a patient to HSCT. Three cases of MDS, two of which were submitted to HSCT are presented. We intend to report the difficulties in referring patients with MDS to transplant and the prognostic factors that contribute to define eligibility.

RESUMO O transplante de células-tronco hematopoéticas (TCTH) é a única alternativa curativa para Síndrome Mielodisplásica (SMD), porém muitos pacientes não são elegíveis para esta opção, pois existem diversos fatores limitantes, principalmente no caso de pacientes com SMD de baixo risco. O objetivo do estudo é discutir os fatores que podem orientar a decisão no encaminhamento ou não para o TCTH. São apresentados três casos de SMD, dos quais dois foram submetidos ao TCTH. Nos propomos a relatar as dificuldades no encaminhamento dos pacientes com SMD ao transplante e os fatores prognósticos que contribuem para definir a elegibilidade.

Low-level red laser therapy alters effects of ultraviolet C radiation on Escherichia coli cells

Low-level lasers are used at low power densities and doses according to clinical protocols supplied with laser devices or based on professional practice. Although use of these lasers is increasing in many countries, the molecular mechanisms involved in effects of low-level lasers, mainly on DNA, are controversial. In this study, we evaluated the effects of low-level red lasers on survival, filamentation, and morphology of Escherichia colicells that were exposed to ultraviolet C (UVC) radiation. Exponential and stationary wild-type and uvrA-deficientE. coli cells were exposed to a low-level red laser and in sequence to UVC radiation. Bacterial survival was evaluated to determine the laser protection factor (ratio between the number of viable cells after exposure to the red laser and UVC and the number of viable cells after exposure to UVC). Bacterial filaments were counted to obtain the percentage of filamentation. Area-perimeter ratios were calculated for evaluation of cellular morphology. Experiments were carried out in duplicate and the results are reported as the means of three independent assays. Pre-exposure to a red laser protected wild-type and uvrA-deficient E. coli cells against the lethal effect of UVC radiation, and increased the percentage of filamentation and the area-perimeter ratio, depending on UVC fluence and physiological conditions in the cells. Therapeutic, low-level red laser radiation can induce DNA lesions at a sub-lethal level. Consequences to cells and tissues should be considered when clinical protocols based on this laser are carried out.

Low-intensity red and infrared laser effects at high fluences on Escherichia coli cultures

Semiconductor laser devices are readily available and practical radiation sources providing wavelength tenability and high monochromaticity. Low-intensity red and near-infrared lasers are considered safe for use in clinical applications. However, adverse effects can occur via free radical generation, and the biological effects of these lasers from unusually high fluences or high doses have not yet been evaluated. Here, we evaluated the survival, filamentation induction and morphology of Escherichia coli cells deficient in repair of oxidative DNA lesions when exposed to low-intensity red and infrared lasers at unusually high fluences. Cultures of wild-type (AB1157), endonuclease III-deficient (JW1625-1), and endonuclease IV-deficient (JW2146-1) E. coli, in exponential and stationary growth phases, were exposed to red and infrared lasers (0, 250, 500, and 1000 J/cm2) to evaluate their survival rates, filamentation phenotype induction and cell morphologies. The results showed that low-intensity red and infrared lasers at high fluences are lethal, induce a filamentation phenotype, and alter the morphology of the E. coli cells. Low-intensity red and infrared lasers have potential to induce adverse effects on cells, whether used at unusually high fluences, or at high doses. Hence, there is a need to reinforce the importance of accurate dosimetry in therapeutic protocols.

Evaluación de la calidad de vida de pacientes bipolares chilenos: propiedades psicométricas y utilidad diagnóstica de la versión chilena del cuestionario Quality of Life Bipolar Disorder (QoL.BD-CL) / Assessment of a version adapted and translated into Spanish of the Quality of Life Bipolar Disorder Questionnaire

Background: The Quality of life Bipolar Disorder (QoL.BD) Questionnaire specifically measures quality of life in patients with bipolar disorder. Aim: To adapt a version translated into Spanish of the questionnaire and assess its validity in Chilean patients. Material and Methods: The QoL. BD was adapted to the Chilean population through the back-translation method and then administered to 32 adult patients with a bipolar disorder and 31 subjects without the disease, both groups with similar socioeconomic status. To confirm the diagnosis, the International Neuropsychiatric Interview (MINI), Young (YMRS) and Hamilton (HAM-D) scales were applied. Quality of life was assessed using the SF-36v.2 survey. We determined internal consistency, reliability, convergent validity, the cut-off point, and the sensibility and specificity of the scale. Results: The Chilean version of the Questionnaire [QoL. BD-CL] had a high reliability (α = 0.95) and a high validity in reference to external criteria (correlation coefficients with SF-36 ranging from 0.453 and 0.819; p < 0.01). A cut-off point of 170, with sensitivity of 87.9% and specificity of 80% was determined. Conclusions: QoL.BD-CL has adequate psychometric properties, as well as an adequate sensitivity and specificity to distinguish between negative and positive perceptions of life quality in Chilean patients with bipolar disorders.

Evaluación bioquímica de trabajadores rurales expuestos a pesticidas / Biochemical evaluation on rural workers exposed to pesticides

Los pesticidas utilizados en agricultura pueden representar un riesgo potencial para la salud de los agricultores expuestos y para el medio ambiente. El objetivo de este trabajo fue evaluar trabajadores frutihortícolas expuestos a plaguicidas, categorizados por: exposición directa (n = 45), exposición indirecta (n = 50) y controles (n = 50) mediante biomarcadores de exposición y efecto: colinesterasa (ChE), acetilcolinesterasa (AChE), catalasa (CAT), peroxidación de lípidos (TBARS), Indice de Daño Ensayo Cometa (IDEC) e Indice de Daño Ensayo Reparación (IDER). Los resultados indican: a) inhibición significativa de AChE (p < 0.001) en expuestos directos e indirectos; b) aumento en los niveles de TBARS (p < 0.001) en los directos; c) reducción de CAT significativa (p < 0.01) y d) aumento de IDEC e IDER (p < 0.001) en ambos grupos. Los resultados obtenidos reflejan modificaciones en el balance oxidativo junto con daño al ADN en los trabajadores estudiados. Estos hallazgos representan una contribución en la evaluación subclínica de exposición a agroquímicos en nuestro país.

Pesticides are used in agriculture to protect crops but may represent a potential risk to farmers and the environment. The aim of this work was to evaluate horticultural workers exposed to pesticide, categorized by: direct exposure (n = 45), indirect exposure (n = 50) and controls (n = 50) using exposure and effect biomarkers: cholinesterase (ChE), acetylcholinesterase (AChE), catalase (CAT), lipid peroxidation (TBARS), Damage Index Comet Assay (IDEC) and Damage Index Repair Assay (IDER). Our results show: a) an AChE inhibition in directly and indirectly exposed population (p < 0.001), b) significant increase in the levels of TBARS in direct exposure (p < 0.001), c) the CAT reduction was significant (p < 0.01), d) a significant increase in IDEC and IDER in both exposed groups (p < 0.001). Our results evidence variations in oxidative balance and DNA damage in exposed workers. These findings represent a contribution to the sub-clinical evaluation of subjects exposed to agrochemicals in our country.

Hot water extract of Chlorella vulgaris induced DNA damage and apoptosis

OBJECTIVES: The aim of this study was to determine the antiproliferative and apoptotic effects of hot water extracts of Chlorella vulgaris on hepatoma cell line HepG2. INTRODUCTION: The search for food and spices that can induce apoptosis in cancer cells has been a major study interest in the last decade. Chlorella vulgaris, a unicellular green algae, has been reported to have antioxidant and anti-cancer properties. However, its chemopreventive effects in inhibiting the growth of cancer cells have not been studied in great detail. METHODS: HepG2 liver cancer cells and WRL68 normal liver cells were treated with various concentrations (0-4 mg/ml) of hot water extract of C. vulgaris after 24 hours incubation. Apoptosis rate was evaluated by TUNEL assay while DNA damage was assessed by Comet assay. Apoptosis proteins were evaluated by Western blot analysis. RESULTS: Chlorella vulgaris decreased the number of viable HepG2 cells in a dose dependent manner (p < 0.05), with an IC50 of 1.6 mg/ml. DNA damage as measured by Comet assay was increased in HepG2 cells at all concentrations of Chlorella vulgaris tested. Evaluation of apoptosis by TUNEL assay showed that Chlorella vulgaris induced a higher apoptotic rate (70 percent) in HepG2 cells compared to normal liver cells, WRL68 (15 percent). Western blot analysis showed increased expression of pro-apoptotic proteins P53, Bax and caspase-3 in the HepG2 cells compared to normal liver cells WRL68, and decreased expression of the anti-apoptotic protein Bcl-2. CONCLUSIONS: Chlorella vulgaris may have anti-cancer effects by inducing apoptosis signaling cascades via an increased expression of P53, Bax and caspase-3 proteins and through a reduction of Bcl-2 protein, which subsequently lead to increased DNA damage and apoptosis.

Oxidative stress & male infertility.

The male factor is considered a major contributory factor to infertility. Apart from the conventional causes for male infertility such as varicocoele, cryptorchidism, infections, obstructive lesions, cystic fibrosis, trauma, and tumours, a new and important cause has been identified: oxidative stress. Oxidative stress is a result of the imbalance between reactive oxygen species (ROS) and antioxidants in the body. It is a powerful mechanism that can lead to sperm damage, deformity and eventually, male infertility. This review discusses the physiological need for ROS and their role in normal sperm function. It also highlights the mechanism of production and the pathophysiology of ROS in relation to the male reproductive system and enumerate the benefits of incorporating antioxidants in clinical and experimental settings.

Clinical relevance of oxidative stress and sperm chromatin damage in male infertility: an evidence based analysis

Oxidative stress (OS) in the reproductive tract is now a real entity and concern due to the potential harmful effects of high levels of reactive oxygen species (ROS) on sperm number, motility, quality, and function including damage to sperm nuclear DNA. Evaluation of OS related damage to non-functional sperm is highly relevant as intracytoplasmic sperm injection (ICSI) technique, an effective therapy for severe male factor infertility, bypasses the majority of reproductive tract deficiencies. Despite the controversial findings in the existing literature, there is now enough evidence to show that sperm DNA damage is detrimental to reproductive outcomes. In addition, spermatozoa of infertile men are suggested to carry more DNA damage than do the spermatozoa from fertile men. Besides impairment of fertility such damage is likely to increase the transmission of genetic diseases during the assisted reproductive procedures. Standardization of protocols to assess reactive oxygen species and DNA damage is very important in introducing these tests in such clinical practice. Thus evaluation of seminal ROS levels and extent of sperm DNA damage especially in an infertile male may help develop new therapeutic strategies and improve success of assisted reproductive techniques (ART).

El nucléolo como un regulador del envejecimiento celular / The nucleolus as a regulator of cellular senescence

El nucléolo, considerado únicamente como el sitio de síntesis de los ribosomas, actualmente representa una estructura nuclear dinámica que participa en la regulación de importantes procesos celulares. Numerosas evidencias han demostrado que el envejecimiento celular es una de las diversas funciones que son controladas por el nucléolo. Las mutaciones en las proteínas de localización nucleolar promueven el envejecimiento prematuro en levaduras y humanos. La carencia de represión en la transcripción de genes que codifican para el ARNr que se encuentran dañados, y las mutaciones en las helicasas del ADN encargadas de minimizar la formación de círculos extra-cromosómicos del ADN que codifica para el ARNr, provocan modificaciones en la estructura del nucléolo e inducen envejecimiento prematuro en levaduras. De igual manera, en los humanos la carencia de las helicasas del ADN localizadas en el nucléolo y que participan en el mantenimiento de la integridad genómica, favorecen el desarrollo de aquellas enfermedades asociadas con el envejecimiento acelerado. Además, la presencia de algunos componentes de la telomerasa en el nucléolo, indica que parte de la biosíntesis de esta enzima se realiza en esta estructura nuclear, sugiriendo una conexión entre el nucléolo y la síntesis de los telómeros en la regulación del envejecimiento celular. Por otra parte, el nucléolo secuestra proteínas para regular su actividad biológica durante el inicio o término de la vida replicativa celular.

The nucleolus has been considered originally only as the site for the ribosome synthesis, but now it is well known that it represents a dynamic nuclear structure involved in important cellular processes. Several evidences have demonstrated that the nucleolus regulates the cellular senescence. Specific mutations on the DNAs codifying for nucleolar proteins induced premature senescence from yeast to human. The failure to repress the genes transcription codifying for damaged rRNA, and the mutations in DNA helicases, which minimizes the formation of DNA extra-chromosomal circles codifying for rRNA, modify the nucleolar structure and induce premature senescence in yeast. Similarly, in humans, the reduction of these DNA helicases levels, which are localized in the nucleoli and participate in maintenance of genomic integrity, helps to the development of those diseases associated with premature senescence. Furthermore, the presence in the nucleolus of some telomerase components, indicates that part of the biosynthesis of this enzyme occurred in this nuclear structure; suggesting a communication between the nucleolus and the synthesis of the telomeres in the regulation of cell senescence. On the other hand, the nucleolus sequesters proteins to regulate its own biological activity, from the start to the end of cellular replication. In addition this nuclear structure is involved in the biosynthesis of most cellular ribonucleoprotein particles, as well as in cell cycle regulation, making it central to gene expression. In conclusion, the nucleolus became a multifunctional subnuclear structure involved from cell proliferation to cell senescence.

Increased DNA Damage of Lymphocytes in Korean Male Smokers / 예방의학회지

OBJECTIVE: The purpose of this study was to evaluate the levels of DNA damage in human lymphocytes caused by smoking and other lifestyle factors. METHODS: The study population consisted of 173 normal healthy male adults from 21 to 59 years old. The demographic and lifestyle variables were obtained from administered questionnaires. The level of lymphocytic DNA damage in the peripheral blood was evaluated by the Comet assay. Statistical analyses were done by general linear model analysis and Dunnett's multiple comparison. RESULTS: The difference in DNA damage between smokers and non-smokers was statistically significant. The means for the Tail%DNA were found to be 10.48 in the current smokers and 9.60 in the non-smokers (p<0.05). The tail moment means were 1.58 and 1.45 (p<0.05) for the current smokers and non-smokers, respectively. The number of cigarettes smoked per day did not result in a significant difference in the level of DNA damage among the smokers. Other lifestyle factors such as age, and drinking and exercise habits were not related to DNA damage. CONCLUSIONS: The DNA damage in the lymphocytes of smokers was found to be significantly higher than that for non-smokers. However, the number of cigarettes smoked per day was not related to DNA damage. Further study is needed to evaluate the relationship between the amount of smoking and level of damage to DNA. In addition, the status of DNA repair activities should be assessed.

Application of the age-associated injure in mitochondrial DNA / 法医学杂志

Nowadays, the injury in human mitochondrial DNA (mtDNA) is well known to accumulate in various tissues with age. It's significant to further investigate and then apply it to estimation of the age at parenchymas.

Progression of the manner of cardiomyocyte death and its potential significance in forensic medicine / 法医学杂志

The manner of cell death is a hotspot of medical researchers. Apoptosis and necrosis were considered as two manners of cell death in the past. But recently a new manner of cell death--oncosis is gradually accepted by the pathologists. Oncosis is different from apoptosis in morphologic, mechanism and the role in cardiovascular diseases. In this paper, the progression of the research about manner of the cardiomyocyte death and its significance in forensic medicine in recent years was reviewed.

Reactive oxygen species and oxidative DNA damage.

Reactive oxygen species (ROS) such as the superoxide anion radical (O2.-) hydrogen peroxide (H2O2) and hydroxyl radical (.OH) have been implicated in the pathophysiology of various states, including ischemia reperfusion injury, haemorrhagic shock, atherosclerosis, heart failure, acute hypertension and cancer. The free radicals, nitric oxide (NO) and O2.- react to form peroxynitrite (ONOO-), a potent cytotoxic oxidant. A potential mechanism of oxidative damage is the nitration of tyrosine residues of protein, peroxidation of lipids, degradation of DNA and oligonucleosomal fragments. Several mechanisms are responsible for the protection of the cells from potential cytotoxic damage caused by free radicals. Cells have developed various enzymatic and nonenzymatic defense systems to control excited oxygen species, however, a certain fraction escapes the cellular defense and may cause permanent or transient damage to nucleic acids within the cells, leading to such events as DNA strand breakage and disruption of Ca2+ metabolism. There is currently great interest in the possible role of ROS in causing DNA damage that leads to cancer and spontaneous mutations. A high rate of oxidative damage to mammalian DNA has been demonstrated by measuring oxidized DNA bases excreted in urine after DNA repair. The rate of oxidative DNA damage is directly related to the metabolic rate and inversely related to life span of the organism.