**6. Diseases associated with defects of oxidative DNA damage repair systems**

It is quite new and non conclusive that oxidative DNA damage might result in diseases. Increasing numbers of oxidatively modified DNA lesions are proposed to be appropriate, intermediate biomarkers of a disease endpoint. For this reason alone, the association between oxidative DNA damage and disease should be determined. As seen above , it is clear that oxidative DNA damage has effects upon cells other than mutation. Nevertheless, DNA mutation is perhaps one of the most important consequences of lesion persistence, evidenced by the presence of multiple systems to prevent lesion formation and, should damage occur, ensure rapid lesion removal; with the DNA repair systems responsible for the latter having much overlap of substrates, as discussed previously [Evans et al., 2004].

Cumulative oxidative DNA damage have a significant effect of the impairment on normal cellular repair mechanisms. In fact, one of the main etiological hypotheses linking genomic instability, mutagenesis and tumorigenesis is that of deficient cellular repair mechanisms due to extensive oxidative DNA damage and cellular injury [Ziech, 2011]. Clearly, reduced repair will result in elevated lesions and an increased risk of disease [Cooke et al., 2003]. ROS-mediated DNA damage in addition to ineffective DNA repair mechanisms are well established lesions common to many life threatening human diseases, including neurodegenerative diseases, atherosclerosis, cancer, and aging has invoked free radical reactions as an underlying mechanism of injury [Ziech, 2011]. Given the importance of mutation in carcinogenesis, cancer will be the first disease in which a role for oxidative DNA damage in its aetiology is considered [Evans et al., 2004].

#### **Cancer**

58 Selected Topics in DNA Repair

for the redox activation of transcription factors (e.g. p53) spontaneously oxidized at cysteine residues in DNA binding domains to establish DNA binding activity [Jayaraman et al., 1997]. Deletion of APE in mice causes embryonic lethality [Jayaraman et al., 1997]. Cells from mice with APE haploinsufficiency respond poorly to oxidative stress [Meira et al.,

The nick generated by the cleavage of the abasic site is filled in by either Pol or Pol / in the nucleus, and Pol in the mitochondria. Pol is the only DNA polymerase identified so far in vertebrate mitochondria and functions both as the replicative and the repair polymerase [Weissman et al., 2007, Kaguni, 2004]. Relevant to its role in BER, Pol has a dRP-lyase activity and can catalyze the 3'-end-processing necessary for short-patch BER

The final step in the BER pathway is ligation of the nick with the correct nucleotide by DNA polymerases. An adenosine triphosphate-dependent DNA ligase (Ligase [Lig]I or III) completes the repair process and restores the integrity of the helix by sealing the nick. In the nucleus, two distinct DNA ligases participate in BER, ligase I, which has been implicated in long-patch BER, and ligase III, implicated in short-patch. The human ligase III gene (*LIG3*) also encodes for a mitochondrial variant, with a putative MTS generated by an alternative downstream translation initiation site [Lakshmipathy & Campbell, 1999, Lakshmipathy & Campbell, 2001]. The localization of ligase III protein to mitochondria suggests, then, that this enzyme may perform the ligation step in mtBER. Accordingly, reduction of ligase III expression using an antisense strategy resulted in an increase in breaks in mtDNA

**6. Diseases associated with defects of oxidative DNA damage repair systems**  It is quite new and non conclusive that oxidative DNA damage might result in diseases. Increasing numbers of oxidatively modified DNA lesions are proposed to be appropriate, intermediate biomarkers of a disease endpoint. For this reason alone, the association between oxidative DNA damage and disease should be determined. As seen above , it is clear that oxidative DNA damage has effects upon cells other than mutation. Nevertheless, DNA mutation is perhaps one of the most important consequences of lesion persistence, evidenced by the presence of multiple systems to prevent lesion formation and, should damage occur, ensure rapid lesion removal; with the DNA repair systems responsible for the latter having much overlap of substrates, as discussed previously

Cumulative oxidative DNA damage have a significant effect of the impairment on normal cellular repair mechanisms. In fact, one of the main etiological hypotheses linking genomic instability, mutagenesis and tumorigenesis is that of deficient cellular repair mechanisms due to extensive oxidative DNA damage and cellular injury [Ziech, 2011]. Clearly, reduced repair will result in elevated lesions and an increased risk of disease [Cooke et al., 2003]. ROS-mediated DNA damage in addition to ineffective DNA repair mechanisms are well established lesions common to many life threatening human diseases, including neurodegenerative diseases, atherosclerosis, cancer, and aging has invoked free radical reactions as an underlying mechanism of injury [Ziech, 2011]. Given the importance of mutation in carcinogenesis, cancer will be the first disease in which a role for oxidative DNA

damage in its aetiology is considered [Evans et al., 2004].

2001].

[Longley et al., 1998].

[Evans et al., 2004].

[Lakshmipathy & Campbell, 2001].

The carcinogenicity of oxidative stress is primarily attributed to the genotoxicity of ROS in diverse cellular processes [ Ziech, 2011]. Oxidative mechanisms have been demonstrated to possess a potential role in the initiation, promotion, and malignant conversion (progression) stages of carcinogenesis [Cooke et al., 2003] . It has been suggested that some signaling system induces ROS that exhibit dual roles, cancer promoting and cancer suppresing, in tumorogenesis. ROS participate simultaneously in two signaling pathways that have inverse functions in tumorigenesis, Ras-Raf-MEK1/2-ERK1/2 signaling and the p38 mitogenactivated protein kinases (MAPK) pathway. Ras-Raf-MEK1/2-ERK1/2 signaling plays a role in oncogenesis, while the p38 MAPK pathway contributes to cancer suppression. The accumulation of intracellular ROS induced by oncogenic Ras is ERK-dependent during the activation of p38a [Pan et al., 2009)

Increased intracellular levels of ROS, induced by the Ras-Raf-MEK-ERK signaling cascade, may mediate the activation of the p38 pathway and act as an intermediate signal between the MEK-ERK and MKK3/6-p38 pathways. On the one hand, the activation of p38 mitogenactivated protein kinase (MAPK) is a prerequisite for ROS-mediated functions such as apoptotic cell death in cancer cells. On the other hand, inhibiting or scavenging ROS may attenuate the activation of p38-dependent pathways. Human cancer cell lines with high ROS levels display enhanced tumorigenicity and impaired p38α activation by ROS [Pan et al., 2009].

The effect of ROS by Ras may occur at the transcription level. GATA-6 is a component of the specific protein-DNA complexes at the nicotinamide adenine dinucleotide phosphate oxidase (Nox) 1 promoter, and is able to trans-activate the Nox1 promoter. GATA-6 is phosphorylated at serine residues by MEK-activated extracellular signal regulated kinase (ERK), which enhances GATA-6 DNA binding. The activity of the ROS-generating enzyme Nox1 is required for vascular endothelial growth factor (VEGF), a potent stimulator of tumor angiogenesis. Ras signaling enhances the transcription of Nox1 [Adachi et al., 2008]. A regulatory subunit, Rac, of the NADPH oxidase complex also involves the regulation of ROS [Heyworth et al., 1993, Kadara et al., 2008]. However, if extracellular signal-regulated kinase (ERK)-dependent phosphorylation of the transcription factor Sp1 and Sp1 binding to a VEGF promoter is inhibited, this activity does not occur [Pan et al., 2009].

Although some studies suggested that increased intracellular ROS elevate the activation of p38, these results have not been confirmed yet by the other researchers. It seems that further studies are needed to understand the mechanism of ROS in cancer.

Since the main purpose of this chapter is not to deal with the effect of ROS in tumorogenesis, we will explain the effect of ROS on DNA and DNA repair enzymes. ROS can cause direct oxidative DNA damage by increasing a cell's mutation.

Major oxidative DNA damage products including those of 8-oxo-7, 8-dihydroadenine (8 oxoAde), 8-oxo-7, 8-dihydroguanine (8-oxoGua), 8-oxo-7, 8-dihydro-2′-deoxyguanosine (8-oxodG), and 5, 6-dihydroxy-5, 6-dihydrothymine as well as the ring-open lesions of 4, 6-diamino-5-formamido-pyrimidine and 2, 6-diamino-4-hydroxy-5-formamidopyrimidine [Kohen & Nyska, 2002]. Of these oxidative products, 8-oxoGua is known to be a biomarker of oxidative stres and its mutagenicity in mammalian cells demonstrates an additional potential as an intermediate marker of a disease endpoint (e.g. cancer). Elevated levels of such DNA lesions have been noted in many tumor types and are strongly implicated in the etiology of cancer [Valko et al., 2006]. Approximately 50%

Effect of Oxidative Stress on DNA Repairing Genes 61

region of mtDNA, have been identified in various human cancers. In general, mtDNA is more susceptible to oxidative damage than nuclear DNA because (i) mitochondrial DNA is not protected by histones, (ii) mitochondrial DNA repair capacity is limited, and (iii) under physiological conditions, the mitochondria converts roughly 3–5% of O2 consumed into •O2− and subsequently H2O2. In addition, mtDNA is located in close proximity to the respiratory chain and thus is consequently readily exposed to ROS-induced oxidative damage. As a result, mtDNA has more than two orders of magnitude higher frequency of oxidative damage than that of nuclear DNA and significantly correlates with the

It is known that DNA alterations exist in atherosclerotic tissues and may play a fundamental role in the pathogenesis of this disease [Olinski et al., 2002, De Flora et al., 1997, Lee et al., 2001]. Elevated level of 8-OH-Gua found in the lesion of the aorta wall in atherosclerotic patients may be one of the events directly involved in the development of the disease [De Flora et al., 1997]. Oxidized low-density lipoprotein (LDL) might play an important role in the development of atherosclerotic lesions [Ross, 1993]. Interestingly, it has been found that oxidized LDL downregulates enzymes that take part in the BER pathways [Chen et al., 2000]. This DNA repair mechanism is responsible for the removal of 8-OH-Gua from cellular DNA [Dianov et al., 1998]. Therefore, it is possible that oxidized LDL that contributes directly to the development of atherosclerosis, may also be responsible for the high level of 8-OH-Gua observed in blood lymphocytes [Chen et al.,

Alzheimer's disease (AD), Huntington's disease and Parkinson's disease (PD) are neurodegenerative conditions, thought to be the result, in part, of chronic exposure to environmental neurotoxins, coupled with a genetic component. These diseases all have oxidative stress implicated in their pathogenesis [Lovell et al., 1999, Lezza et al., 1999, Alam et al., 1997, Zhang et al., 1999], and elevated levels of oxidative DNA damage have been measured in a broad range of neurological conditions [ Koppele et al., 1996, Alam et al., 2000]. Supportive of the studies showing elevated lesion levels are data derived from in vitro studies demonstrating that neurotransmitters such as dopamine and serotonin can generate DNA-damaging, free radical species [Spencer et. al., 1994, Wrona et al., 1998]. Overall, the role of oxidative stress in neurodegenerative disease appears undisputed. However, damage to lipid and protein, rather than DNA, appears to have been apportioned

The association between inflammation and oxidative stress is well documented [Wiseman et al., 1996, Khanna & Shiloh, 2009], with numerous studies of inflammatory conditions or infections reporting elevated levels of 8-OH-dG: hepatitis [Shimoda et al., 1994], hepatitis C infection [Farinati et al., 1999], and atopic dermatitis. An important source of the ROS are the bactericidal species (O2•– and H2O2), generated from the respiratory burst of invading neutrophils, macrophages, and eosinophils damaging surrounding tissue. Chronic inflammation, and the accompanying oxidative stress, has been closely linked to the pathogenesis of autoimmune diseases such as rheumatoid arthritis [Bashir et.al, 1993] and systemic lupus erythematosus [Lunec et.al., 1994], with free radical production resulting, not

the greatest significance [Markesbery, 1999, Christen, 2000, Smith et al., 2000].

development of cancer [Ralph et al., 2010].

**Cardiovascular disease** 

**Neurodegenerative diseases** 

**Inflammatory disease** 

2000].

higher rates of 8-oxoGua levels have been observed in lung, breast or prostate cancer patients when compared to otherwise healthy individuals [Tudek et al., 2010]. In addition, recent investigations have showed higher endogenous levels of 8-oxoGua in tumor tissues when compared to controls, thus suggesting oxidative DNA damage as a contributing factor in cancer development [Trachootham et al., 2009]. In addition, high levels of 8 oxoGua and possibly other DNA lesions are suggested as reliable risk factors associated with the transformation of benign to malignant tumors [Chen et al., 2007]. Furthermore, 8 oxoGua lesions are known to induce aberrant modifications in adjacent DNA a hypothesized mechanism that significantly contributes to the genetic instability and metastatic potential of tumor cells [Valko et al., 2006]. For example, formation of 8 oxoGua lesions has been shown to induce a cascade of adjacent DNA base mutations, such as GC → TA transversions in the *ras* oncogene [Bos, 1988] and *p53* tumour suppressor gene in lung and liver cancer [Valko et al.2006, Mos, 1988, Takahashi et al., 1989]. Under normal conditions, DNA repair mechanisms include OGG1, nei-like glycosylase 1 (NEIL1), APE1, and MutY homologue (MUTYH) (Evans et al. 2004). In addition, nucleotide excision repair (NER) may also participate in the process of removing the 8-OHdG lesion [Klaunig, 2010]. Several genes involved in the processing of oxidative DNA damage have been analysed in relation to human cancer risk in molecular epidemiological studies . Among these genes, allele polymorphic variants have been found in OGG1, XRCC1, Pol b, APE1 and MUTYH, which are associated with a varying extent increased cancer risk [Canbay et al., 2010, Agachan et al., 2009, Narter et al., 2009, Attar et al., 2010]. Several SNPs within hOGG1 have been reported [Kohno et al., 1998]. As polymorphisms in this gene alter glycosylase function and an individual's ability to repair oxidatively damaged DNA, they may contribute to carcinogenesis [Boiteaux & Radicella, 2000, Ide & Kotera, 2004, Shao et al., 2006]. Epidemiologic studies investigating the association between the SNPs of OGG1 have led to conflicting results. The variant allele of this SNP was shown to be associated with significantly increased risk of a number of human cancers, including lung [Hung et al., 2005, Li & Kong, 2008], esophageal [Xing et al., 2001], prostate [Xu et al., 2002], and gastric [Farinati et al., 2008] cancer but not with squamous cell carcinoma of the head and neck (SCCHN) [Zhang et al., 2004] or pancreatic cancer [McWilliams et al., 2008]. A total of eighteen polymorphisms in APE1 have been reported, among which Gln51His and Asp148Glu are the two most common SNPs. Associations between polymorphisms in APE1 and increased risk of lung, colon, breast, SCCHN, prostate, and pancreatic cancer have been reported, but with mixed results [Hung et al., 2005, Zhang et al., 2004, Goode et al., 2002, Jiao et al., 2006].

Studies relating to lung cancer and smoking have supported a potential role for ROS in cancer. Cigarette smoking is strongly linked to the aetiology of lung cancer [Hoffman & Wynder, 1986], being shown to increase the generation of free radical species [Church & Pryor, 1985] and elevate levels of oxidative DNA damage in human lungs [Asami et al., 1997, Agachan et al., 2009, ] and white blood cells [Kiyosawa et al., 1990, Lodovici et al., 2000], as well as to increase the repair of 8-OH-Gua [Asami et al., 1996] and lead to an increased urinary excretion of 8-OH-dG and 5-OHMeUra in smokers compared to nonsmokers [Loft et al., 1994, Pourcelot et al., 1999].

Recently ROS-mediated mutations in mitochondrial DNA (mtDNA) have emerged as an important contributor to human carcinogenesis [Freuhaug & Meyskens, 2007]. Mutations in mitochondrial genes encoding complexes I, III, IV and V, as well as within the hypervariable region of mtDNA, have been identified in various human cancers. In general, mtDNA is more susceptible to oxidative damage than nuclear DNA because (i) mitochondrial DNA is not protected by histones, (ii) mitochondrial DNA repair capacity is limited, and (iii) under physiological conditions, the mitochondria converts roughly 3–5% of O2 consumed into •O2− and subsequently H2O2. In addition, mtDNA is located in close proximity to the respiratory chain and thus is consequently readily exposed to ROS-induced oxidative damage. As a result, mtDNA has more than two orders of magnitude higher frequency of oxidative damage than that of nuclear DNA and significantly correlates with the development of cancer [Ralph et al., 2010].

### **Cardiovascular disease**

60 Selected Topics in DNA Repair

higher rates of 8-oxoGua levels have been observed in lung, breast or prostate cancer patients when compared to otherwise healthy individuals [Tudek et al., 2010]. In addition, recent investigations have showed higher endogenous levels of 8-oxoGua in tumor tissues when compared to controls, thus suggesting oxidative DNA damage as a contributing factor in cancer development [Trachootham et al., 2009]. In addition, high levels of 8 oxoGua and possibly other DNA lesions are suggested as reliable risk factors associated with the transformation of benign to malignant tumors [Chen et al., 2007]. Furthermore, 8 oxoGua lesions are known to induce aberrant modifications in adjacent DNA a hypothesized mechanism that significantly contributes to the genetic instability and metastatic potential of tumor cells [Valko et al., 2006]. For example, formation of 8 oxoGua lesions has been shown to induce a cascade of adjacent DNA base mutations, such as GC → TA transversions in the *ras* oncogene [Bos, 1988] and *p53* tumour suppressor gene in lung and liver cancer [Valko et al.2006, Mos, 1988, Takahashi et al., 1989]. Under normal conditions, DNA repair mechanisms include OGG1, nei-like glycosylase 1 (NEIL1), APE1, and MutY homologue (MUTYH) (Evans et al. 2004). In addition, nucleotide excision repair (NER) may also participate in the process of removing the 8-OHdG lesion [Klaunig, 2010]. Several genes involved in the processing of oxidative DNA damage have been analysed in relation to human cancer risk in molecular epidemiological studies . Among these genes, allele polymorphic variants have been found in OGG1, XRCC1, Pol b, APE1 and MUTYH, which are associated with a varying extent increased cancer risk [Canbay et al., 2010, Agachan et al., 2009, Narter et al., 2009, Attar et al., 2010]. Several SNPs within hOGG1 have been reported [Kohno et al., 1998]. As polymorphisms in this gene alter glycosylase function and an individual's ability to repair oxidatively damaged DNA, they may contribute to carcinogenesis [Boiteaux & Radicella, 2000, Ide & Kotera, 2004, Shao et al., 2006]. Epidemiologic studies investigating the association between the SNPs of OGG1 have led to conflicting results. The variant allele of this SNP was shown to be associated with significantly increased risk of a number of human cancers, including lung [Hung et al., 2005, Li & Kong, 2008], esophageal [Xing et al., 2001], prostate [Xu et al., 2002], and gastric [Farinati et al., 2008] cancer but not with squamous cell carcinoma of the head and neck (SCCHN) [Zhang et al., 2004] or pancreatic cancer [McWilliams et al., 2008]. A total of eighteen polymorphisms in APE1 have been reported, among which Gln51His and Asp148Glu are the two most common SNPs. Associations between polymorphisms in APE1 and increased risk of lung, colon, breast, SCCHN, prostate, and pancreatic cancer have been reported, but with mixed results

[Hung et al., 2005, Zhang et al., 2004, Goode et al., 2002, Jiao et al., 2006].

smokers [Loft et al., 1994, Pourcelot et al., 1999].

Studies relating to lung cancer and smoking have supported a potential role for ROS in cancer. Cigarette smoking is strongly linked to the aetiology of lung cancer [Hoffman & Wynder, 1986], being shown to increase the generation of free radical species [Church & Pryor, 1985] and elevate levels of oxidative DNA damage in human lungs [Asami et al., 1997, Agachan et al., 2009, ] and white blood cells [Kiyosawa et al., 1990, Lodovici et al., 2000], as well as to increase the repair of 8-OH-Gua [Asami et al., 1996] and lead to an increased urinary excretion of 8-OH-dG and 5-OHMeUra in smokers compared to non-

Recently ROS-mediated mutations in mitochondrial DNA (mtDNA) have emerged as an important contributor to human carcinogenesis [Freuhaug & Meyskens, 2007]. Mutations in mitochondrial genes encoding complexes I, III, IV and V, as well as within the hypervariable It is known that DNA alterations exist in atherosclerotic tissues and may play a fundamental role in the pathogenesis of this disease [Olinski et al., 2002, De Flora et al., 1997, Lee et al., 2001]. Elevated level of 8-OH-Gua found in the lesion of the aorta wall in atherosclerotic patients may be one of the events directly involved in the development of the disease [De Flora et al., 1997]. Oxidized low-density lipoprotein (LDL) might play an important role in the development of atherosclerotic lesions [Ross, 1993]. Interestingly, it has been found that oxidized LDL downregulates enzymes that take part in the BER pathways [Chen et al., 2000]. This DNA repair mechanism is responsible for the removal of 8-OH-Gua from cellular DNA [Dianov et al., 1998]. Therefore, it is possible that oxidized LDL that contributes directly to the development of atherosclerosis, may also be responsible for the high level of 8-OH-Gua observed in blood lymphocytes [Chen et al., 2000].

#### **Neurodegenerative diseases**

Alzheimer's disease (AD), Huntington's disease and Parkinson's disease (PD) are neurodegenerative conditions, thought to be the result, in part, of chronic exposure to environmental neurotoxins, coupled with a genetic component. These diseases all have oxidative stress implicated in their pathogenesis [Lovell et al., 1999, Lezza et al., 1999, Alam et al., 1997, Zhang et al., 1999], and elevated levels of oxidative DNA damage have been measured in a broad range of neurological conditions [ Koppele et al., 1996, Alam et al., 2000]. Supportive of the studies showing elevated lesion levels are data derived from in vitro studies demonstrating that neurotransmitters such as dopamine and serotonin can generate DNA-damaging, free radical species [Spencer et. al., 1994, Wrona et al., 1998]. Overall, the role of oxidative stress in neurodegenerative disease appears undisputed. However, damage to lipid and protein, rather than DNA, appears to have been apportioned the greatest significance [Markesbery, 1999, Christen, 2000, Smith et al., 2000].

#### **Inflammatory disease**

The association between inflammation and oxidative stress is well documented [Wiseman et al., 1996, Khanna & Shiloh, 2009], with numerous studies of inflammatory conditions or infections reporting elevated levels of 8-OH-dG: hepatitis [Shimoda et al., 1994], hepatitis C infection [Farinati et al., 1999], and atopic dermatitis. An important source of the ROS are the bactericidal species (O2•– and H2O2), generated from the respiratory burst of invading neutrophils, macrophages, and eosinophils damaging surrounding tissue. Chronic inflammation, and the accompanying oxidative stress, has been closely linked to the pathogenesis of autoimmune diseases such as rheumatoid arthritis [Bashir et.al, 1993] and systemic lupus erythematosus [Lunec et.al., 1994], with free radical production resulting, not

Effect of Oxidative Stress on DNA Repairing Genes 63

repair enzymes are important for oxidative DNA damage. If individual spesific biomarkers related DNA repair enzyme are found, new treatmant strategies would be developed to cure

Adachi Y, Shibai Y, Mitsushita J, Shang WH, Hirose K, Kamata T. 2008. Oncogenic Ras

Adly, AAM. 2010. Oxidative stress and disease: An updated review. *Res. J. Immunol.*, 3: 129-

Agaçhan B, Küçükhüseyin O, Aksoy P, Turna A, Yaylim I, Görmüs U, Ergen A, Zeybek U,

Alam ZI, Jenner A, Daniel SE, Lees AJ, Cairns N, Marsden CD, Jenner P, Halliwell B. 1997.

Altman SA, Zastawny TH, Randers-Eichhorn L, Cacciuttolo MA, Akman SA, Dizdaroglu

Asami S, Manabe H, Miyake J, Tsurudome Y, Hirano T, Yamaguchi R, Itoh H, Kasai H. 1997.

Asami S, Hirano T, Yamaguchi R, Tomioka Y, Itoh H, Kasai H. 1996. Increase of a type of

Attar R, Cacina C, Sozen S, Attar E, Agachan B. 2010. DNA repair genes in endometriosis.

Bashir S, Harris G, Denman MA, Blake DR, Winyard PG. 1993. Oxidative DNA damage and

Beckman JS, Ischiropoulos H, Zhu L, van der Woerd M, Smith C, Chen J, Harrison J, Martin

Beckman KB and Ames BN. 1998. The free radical theory of aging matures. *Physiol. Rev.,* 78,

Behrend, R. and Roosen, O. 1889. Synthese der Harnsa¨ure. *Liebigs Ann.Chem.*, 251, 235–256. Bielski BHJ and Cabelli DE. 1995. Superoxide and hydroxyl radical chemistry in aqueous

Boiteux S and Radicella JP.2000. The human OGG1 gene: Structure, functions, and its implication in the process of carcinogenesis. *Arch Biochem Biophys.,* 377, 1–8.

8-hydroxyguanine levels in substantia nigra, J. *Neurochem.* , 1196–1203. Alam ZI, Halliwell B, Jenner P. 2000. No evidence for increased oxidative damage to lipids,

proteins, or DNA in Huntington's disease. J. *Neurochem.,* 840–846

cells upon treatment with iron ions. *Free Radical Biol. Med.,* 897–902.

leukocytes by cigarette smoking. *Cancer Res*., 56; 2546–2549.

Babior BM.2000. The NADPH oxidase of endothelial cells. *IUBMB Life,* 50;267–269.

phenolics by peroxynitrite. *Arch Biochem Biophys.*, 298:438–445.

Liebman JF (eds). Chapman and Hall, London, pp. 66–104.

phosphorylation of GATA-6. *Oncogene* 27: 4921-4932

upregulates NADPH oxidase 1 gene expres s ion through MEK-ERK-dependent

Dalan B, Isbir T. 2009. Apurinic/apyrimidinic endonuclease (APE1) gene polymorphisms and lung cancer risk in relation to tobacco smoking. *Anticancer Res.,* 

Oxidative DNA damage in the Parkinsonian brain: an apparent selective increase in

M., Rao G. 1995. Formation of DNA–protein cross-links in cultured mammalian

Cigarette smoking induces an increase in oxidative DNA damage, 8 hydroxydeoxyguanosine, in a central site of the human lung. *Carcinogenesis,* 

oxidative DNA damage, 8-hydroxyguanine, and its repair activity in human

cellular sensitivity to oxidative stress in human autoimmune diseases. *Ann. Rheum.* 

JC, Tsai M.1992. Kinetics of superoxide dismutase- and iron-catalyzed nitration of

solution. In: *Active Oxygen in Chemistry*, Foote CS, Valentine JS, Greenberg A,

disease related oxidative DNA damage.

**8. References** 

145.

29(6):2417-20.

18;1763–1766.

*Dis.,* 52; 659–666.

547–581.

*Genet Mol Res.,* 6;9(2):629-36.

only in connective tissue damage, but also modified biomolecules being exposed to the systemic circulation, postulated to be the antigen driving autoantibody production [Weitzman & Gordon, 1990].

Elevated DNA levels of 8-OH-dG have been reported in lymphocytes from patients with RA, SLE, vasculitis or Behcet's disease. These same lymphocytes, from RA and SLE patients, also display increased sensitivity to hydrogen peroxide-induced cytotoxicity [Bashir et al., 1993].

#### **Ischemia-reperfusion injury**

The literature provides a growing number of reports in which levels of oxidative DNA damage are elevated in post-ischaemia-reperfusion. Elevated levels of urinary 8-OH-dG or dTg were reported following liver transplantation, which proposed to be due to ischemiareperfusion or reoxygenation injury [Thier et al., 1999, Loft et al., 1995]. Ischaemiareperfusion injury is a significant factor affecting morbidity and mortality following bypass and transplantation surgery, haemorrhagic or septic shock, myocardial infarction and multiple organ failure. During the period of ischaemia, xanthine dehydrogenase is converted to xanthine oxidase. Upon reperfusion, there is a "burst" of xanthine oxidase activity which, rather than transferring electrons to NAD+, transfers them to O2, generating superoxide, with the subsequent potential for generating other ROS and hence DNA damage. Endogenous levels of xanthine dehydrogenase vary from organ to organ and hence ischemia-reperfusion injury might be more relevant to some tissues than others. Human leukocytes appear to be sensitive to the genotoxic effects of ischemia-reperfusion (163) and therefore represent a potential surrogate tissue in which to study the effects of ischemiareperfusion that have affected a less accessible tissue.

#### **Aging**

Major theories of aging are grouped under two categories: damage accumulation aging and developmentally programmed aging. However, a developing (emerging) hypothesis described as the free radical theory of aging appears to have adopted elements of the former theories. The basis of the Harman's theory [Harman, 1956] suggested that aging occurs through the gradual accumulation of free radical damage to biomolecules. With age, antioxidant defences fail to scavenge all potentially damaging radical species that result in the insidious accumulation of damage and gradual loss of function [Beckman et al., 1998]. One of the few focussing upon DNA damage, is a report of an age-related increase in serum 8-OH-dG in apparently disease-free individuals over an age range of 15–91 years [Rattan et al., 1995]. Although this same trend was not evident in the urinary 8-OH-dG output of infants, a gradual increase was noted over the first month postpartum, which mirrored the velocity growth curve [Drury et al., 1998].

The accumulation of lesions can, in part, be explained by the discovery that DNA repair capability correlates with species-specific life span [168]. Furthermore, repair activity appears to decline with age, resulting in the persistence of damage and a subsequent increase in replication errors [Hirano et al., 1995].
