Pyridoxamine and Aminoguanidine Attenuate the Abnormal Aggregation of ß-Tubulin and Suppression of Neurite Outgrowth by Glyceraldehyde-Derived Toxic Advanced Glycation End-Products.

Diabetes mellitus (DM) has been identified as a risk factor for the onset and progression of Alzheimer's disease (AD). In our previous study, we demonstrated that glyceraldehyde (GA)-derived toxic advanced glycation end-products (toxic AGEs, TAGE) induced similar alterations to those observed in AD. GA induced dysfunctional neurite outgrowth via TAGE-ß-tubulin aggregation, which resulted in the TAGE-dependent abnormal aggregation of ß-tubulin and tau phosphorylation in human neuroblastoma SH-SY5Y cells. However, the effects of inhibitors of AGE formation on dysfunctional neurite outgrowth caused by GA-induced abnormalities in the aggregation of ß-tubulin and tau phosphorylation remain unknown. Aminoguanidine (AG), an AGE inhibitor, and pyridoxamine (PM), a natural form of vitamin B6 (VB6), are effective AGE inhibitors. Therefore, the present study investigated whether AG or PM ameliorate TAGE-ß-tubulin aggregation and the suppression of neurite outgrowth by GA. The results obtained showed that AG and PM inhibited the formation of TAGE-ß-tubulin, mitigated the GA-induced suppression of neurite outgrowth, and reduced GA-mediated increases in tau phosphorylation levels. Collectively, these results suggest the potential of AG and PM to prevent the DM-associated onset and progression of AD.

The Effect of Glyceraldehyde-Derived Advanced Glycation End Products on ß-Tubulin-Inhibited Neurite Outgrowth in SH-SY5Y Human Neuroblastoma Cells.

Nutritional factors can affect the risk of developing neurological disorders and their rate of progression. In particular, abnormalities of carbohydrate metabolism in diabetes mellitus patients lead to an increased risk of neurological disorders such as Alzheimer's disease (AD). In this study, we investigated the relationship between nervous system disorder and the pathogenesis of AD by exposing SH-SY5Y neuroblastoma cells to glyceraldehyde (GA). We previously reported that GA-derived toxic advanced glycation end products (toxic AGEs, TAGE) induce AD-like alterations including intracellular tau phosphorylation. However, the role of TAGE and their target molecules in the pathogenesis of AD remains unclear. In this study, we investigated the target protein for TAGE by performing two-dimensional immunoblot analysis with anti-TAGE antibody and mass spectrometry and identified ß-tubulin as one of the targets. GA treatment induced TAGE-ß-tubulin formation and abnormal aggregation of ß-tubulin, and inhibited neurite outgrowth in SH-SY5Y cells. On the other hand, glucose-derived AGEs were also involved in developing AD. However, glucose did not make abnormal aggregation of ß-tubulin and did not inhibit neurite outgrowth. Understanding the underlying mechanism of TAGE-ß-tubulin formation by GA and its role in neurodegeneration may aid in the development of novel therapeutics and neuroprotection strategies.

Alternative Splicing for Activation of Coagulation Factor XIII-A in the Fish Retina After Optic Nerve Injury.

Factor XIII-A (FXIII-A), which has become known as cellular transglutaminase, plays important roles in mediating cross-linking reactions in various tissues. FXIII-A acts as one of the regeneration molecules in the fish retina and optic nerve after optic nerve injury and becomes activated at the site of injury within a few hours. Previous research has shown that activated FXIII-A induces neurite outgrowth from injured retinal ganglion cells and supports elongation of the regenerating optic nerve. However, the activation mechanism of FXIII-A remains unknown. Furthermore, the injured tissues do not express thrombin, a known activator of plasma FXIII. Here, we investigated the mRNA expression of FXIII-A based on two different regions, one encoding the activation peptide and the other encoding the enzymatic active site. We found that expression of the region encoding the activation peptide was markedly suppressed compared with the region encoding the active site. An overexpression study with a short-type FXIII-A cDNA lacking the activation peptide revealed induction of long neurite outgrowth in fish retinal explant cultures compared with full-length FXIII-A cDNA. The present findings suggest that alternative splicing may occur in the FXIII-A gene, resulting in deletion of the region encoding the activation peptide and thus allowing direct production of activated FXIII-A protein in the fish retina and optic nerve after optic nerve injury.

Talaumidin Promotes Neurite Outgrowth of Staurosporine-Differentiated RGC-5 Cells Through PI3K/Akt-Dependent Pathways.

Talaumidin, a tetrahydrofuran neolignan isolated from the root of Aristolochia arcuata, was an interesting small molecule with neurotrophic activity in the cultured neuron. Talaumidin can promote neurite outgrowth from neurons. However, the mechanism by which talaumidin exerts its neurotrophic actions on retinal neurons has not been elucidated to date. In this study, we describe that talaumidin has neurotrophic properties such as neurite outgrowth in neuroretinal cell line, RGC-5. Talaumidin promotes staurosporine-induced neurite outgrowth in RGC-5 cells. The neurite outgrowth effect of talaumidin was inhibited by phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, but not by Erk inhibitor, PD98059. These data suggest that talaumidin promotes neurite outgrowth through PI3K/Akt pathway and that the potential of talaumidin serves as a promising lead compound for the treatment of retinal degenerative disorders.

S-Nitrosylation Regulates Cell Survival and Death in the Central Nervous System.

Nitric oxide (NO), which is produced from nitric oxide synthase, is an important cell signaling molecule that is crucial for many physiological functions such as neuronal death, neuronal survival, synaptic plasticity, and vascular homeostasis. This diffusible gaseous compound functions as an effector or second messenger in many intercellular communications and/or cell signaling pathways. Protein S-nitrosylation is a posttranslational modification that involves the covalent attachment of an NO group to the thiol side chain of select cysteine residues on target proteins. This process is thought to be very important for the regulation of cell death, cell survival, and gene expression in the central nervous system (CNS). However, there have been few reports on the role of protein S-nitrosylation in CNS disorders. Here, we briefly review specific examples of S-nitrosylation, with particular emphasis on its functions in neuronal cell death and survival. An understanding of the role and mechanisms underlying the effects of protein S-nitrosylation on neurodegenerative/neuroprotective events may reveal a novel therapeutic strategy for rescuing neurons in neurodegenerative diseases.

Highly efficient uptake into cisplatin-resistant cells and the isomerization upon coordinative DNA binding of anticancer tetrazolato-bridged dinuclear platinum(II) complexes.

We examined the cytotoxicity and cellular uptake in L1210 murine leukemia cells, as well as the coordinative reaction with the guanine derivative 9-ethylguanine (9EtG), of a series of µ-hydroxo-µ-tetrazolato dinuclear platinum(II) complexes (tetrazolato-bridged complexes), [{cis-Pt(NH3)2}2(µ-OH)(µ-tetrazolato-N1,N2)](2+) (5-H-X) and [{cis-Pt(NH3)2}2(µ-OH)(µ-5-R-tetrazolato-N2,N3)](n+), where R = H (5-H-Y), CH3 (1), C6H5 (2), CH2COOCH2CH3 (3), or CH2COO(-) (4), and n = 2 (5-H-Y, 1-3) or 1 (4). Most tetrazolato-bridged complexes overcame cross-resistance to cisplatin and were more efficiently taken up into cisplatin-resistant cells (L1210R) than into parental cisplatin-sensitive cells (L1210), whereas cisplatin uptake into L1210R was decreased compared with that into L1210. The cellular uptake was most likely controlled by the total charge of the complexes. There was no correlation between the cytotoxicity and the kinetics of the coordinative reactions of 1-4 with 9EtG, but the isomerization involved in the reactions could contribute to determining the higher order structures of the compacted DNA. The cytotoxicity of tetrazolato-bridged complexes appears to correlate with the efficiency of cellular uptake and DNA compaction.

Glyceraldehyde caused Alzheimer's disease-like alterations in diagnostic marker levels in SH-SY5Y human neuroblastoma cells.

Clinical evidence has implicated diabetes mellitus as one of the risk factors for the development and progression of Alzheimer's disease (AD). However, the neurotoxic pathway activated due to abnormalities in glucose metabolism has not yet been identified in AD. In order to investigate the relationship between impaired cerebral glucose metabolism and the pathophysiology of AD, SH-SY5Y human neuroblastoma cells were exposed to glyceraldehyde (GA), an inhibitor of glycolysis. GA induced the production of GA-derived advanced glycation end-products (GA-AGEs) and cell apoptosis, glycolytic inhibition, decreases in the medium concentrations of diagnostic markers of AD, such as amyloid ß 1-42 (Aß42), and increases in tau phosphorylation. These results suggest that the production of GA-AGEs and/or inhibition of glycolysis induce AD-like alterations, and this model may be useful for examining the pathophysiology of AD.

Inflammation-related DNA damage and expression of CD133 and Oct3/4 in cholangiocarcinoma patients with poor prognosis.

Nitrative and oxidative DNA damage plays an important role in inflammation-related carcinogenesis. Chronic inflammation such as parasite infection and primary sclerosing cholangitis can be an etiological factor of cholangiocarcinoma. Using a proteomic approach and double-fluorescent staining, we identified high expression and colocalization of albumin and cytokeratin-19 in liver fluke-associated cholangiocarcinoma tissues, compared with normal livers from cholangiocarcinoma patients and cadaveric donors, respectively. Albumin was detected not only in cells of hyperplastic bile ducts and cholangiocarcinoma, but also in liver stem/progenitor cell origin, such as canal of Hering, ductules, and ductular reactions, suggesting the involvement of stem/progenitor cells in cholangiocarcinoma development. To clarify the involvement of liver stem/progenitor cells in cholangiocarcinoma, we examined several stem/progenitor cell markers (CD133, CD44, OV6, and Oct3/4) in cholangiocarcinoma tissues analyzed by immunohistochemical staining, and measured 8-oxodG levels by using HPLC-ECD as an inflammation-related DNA lesion. In addition, a stem/progenitor cell factor Bmi1, 8-nitroguanine (formed during nitrative DNA damage), DNA damage response (DDR) proteins (phosphorylated ATM and γ-H2AX), and manganese-SOD (Mn-SOD) were analyzed by immunohistochemistry. Stem/progenitor cell markers (CD133, OV6, CD44, and Oct3/4) were positively stained in 56, 38, 47, and 56% of 34 cholangiocarcinoma cases, respectively. Quantitative analysis of 8-oxodG revealed significantly increased levels in CD133- and/or Oct3/4-positive tumor tissues compared to negative tumor tissues, as well as 8-nitroguanine formation detected by immunohistochemistry. In the cases of CD44- and/or OV6-positive tissue, no significant difference was observed. Cholangiocarcinoma patients with CD133- and/or Oct3/4-positive tumor tissues showed significantly lower expression of Mn-SOD and higher DDR protein, γ-H2AX. Moreover, CD133- and/or Oct3/4-positive cholangiocarcinoma patients had significant associations with tumor histology types, tumor stage, and poor prognoses. Our results suggest that CD133 and Oct3/4 in cholangiocarcinoma are associated with increased formation of DNA lesions and the DDR protein, which may be involved in genetic instability and lead to cholangiocarcinoma development with aggressive clinical features.

Spontaneous occurrence of photoageing-like phenotypes in the dorsal skin of old SAMP1 mice, an oxidative stress model.

Skin photoageing is a complex, multifactorial process and both intrinsic and extrinsic factors may contribute to its pathogenesis. The ultraviolet-irradiated hairless mouse has been used as an animal model for photoageing, but this model mimics only the 'extrinsic' aspects. Here, we show that skin from old SAMP1 mice, a model for higher oxidative stress and senescence acceleration, exhibited histological and gene expression changes similar to those in human photoaged skin without ultraviolet irradiation. These changes include an increase in elastic fibre and glycosaminoglycan histologically, an upregulation of several proinflammatory cytokines and matrix metalloproteinases, and an increase in lipid peroxide. We propose that SAMP1 mice are a spontaneous animal model for photoageing caused by an exaggerated intrinsic mechanism, namely, higher oxidative status. This mouse model is useful to explore the link between oxidative stress and photoageing, and to evaluate the efficacy of antioxidants.

NMR study of xenotropic murine leukemia virus-related virus protease in a complex with amprenavir.

Xenotropic murine leukemia virus-related virus (XMRV) is a virus created through recombination of two murine leukemia proviruses under artificial conditions during the passage of human prostate cancer cells in athymic nude mice. The homodimeric protease (PR) of XMRV plays a critical role in the production of functional viral proteins and is a prerequisite for viral replication. We synthesized XMRV PR using the wheat germ cell-free expression system and carried out structural analysis of XMRV PR in a complex with an inhibitor, amprenavir (APV), by means of NMR. Five different combinatorially (15)N-labeled samples were prepared and backbone resonance assignments were made by applying Otting's method, with which the amino acid types of the [(1)H, (15)N] HSQC resonances were automatically identified using the five samples (Wu et al., 2006) [14]. A titration experiment involving APV revealed that one APV molecule binds to one XMRV PR dimer. For many residues, two distinct resonances were observed, which is thought to be due to the structural heterogeneity between the two protomers in the APV:XMRV PR=1:2 complex. PR residues at the interface with APV have been identified on the basis of chemical shift perturbation and identification of the intermolecular NOEs by means of filtered NOE experiments. Interestingly, chemical shift heterogeneity between the two protomers of XMRV PR has been observed not only at the interface with APV but also in regions apart from the interface. This indicates that the structural heterogeneity induced by the asymmetry of the binding of APV to the XMRV PR dimer is transmitted to distant regions. This is in contrast to the case of the APV:HIV-1 PR complex, in which the structural heterogeneity is only localized at the interface. Long-range transmission of the structural change identified for the XMRV PR complex might be utilized for the discovery of a new type of drug.

Molecular and enzymatic characterization of XMRV protease by a cell-free proteolytic analysis.

Xenotropic murine leukemia virus-related virus (XMRV) is a virus generated under artificial conditions by the recombination of 2 murine leukemia virus (MLV) proviruses, PreXMRV-1 and PreXMRV-2, during the in vivo passage of human prostate cancer cells in athymic nude mice. The molecular etiology of XMRV infection has not been characterized and its implication in human prostate cancer progression remains equivocal. As a step toward resolving this issue we developed an in vitro enzymatic assay system to characterize XMRV protease (PR)-mediated cleavage of host-cell proteins. Enzymatically-active XMRV PR protein was synthesized using a wheat-germ cell-free system. By monitoring cleavage activity of XMRV PR by AlphaScreen and 2-color immunoblot analyses, we revealed that the catalytic activity of XMRV PR is selectively blocked by the HIV PR inhibitor, Amprenavir, and identified several human tumor suppressor proteins, including PTEN and BAX, to be substrates of XMRV PR. This system may provide an attractive means for analyzing the function of retrovirus proteases and provide a technology platform for drug screening.

Oxidatively generated DNA damage induced by 3-amino-5-mercapto-1,2,4-triazole, a metabolite of carcinogenic amitrole.

Amitrole (3-amino-1,2,4-triazole) is a widely used herbicide. Amitrole induces thyroid and liver tumors in rodents. However, the mechanism of carcinogenesis by amitrole remains to be clarified. To clarify the mechanism of carcinogenesis induced by amitrole, we investigated the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a characteristic of oxidatively generated DNA damage, by an amitrole metabolite, 3-amino-5-mercapto-1,2,4-triazole (AMT), in the presence of Cu(II). The amount of 8-oxodG was increased by AMT in the presence of Cu(II). AMT-induced 8-oxodG formation was enhanced in deuterium oxide (D2O), which prolongs the half life of singlet oxygen (¹O2), more than that in H2O. Sodium azide and 1,4-diazabicyclo[2,2,2]-octane (DABCO), potent and relatively specific scavengers of ¹O2, inhibited AMT-mediated 8-oxodG formation. Bathocuproine, a Cu(I) chelator, also inhibited the 8-oxodG formation. On the other hand, typical OH scavengers did not inhibit the generation of 8-oxodG. AMT plus Cu(II) also induced piperidine-labile DNA lesions frequently at every guanine residue. These results suggest that ¹O2 and Cu(I) play an important role in DNA damage induced by AMT. It is concluded that oxidatively generated DNA damage induced by AMT via the generation of ¹O2 may contribute to carcinogenicity of amitrole.

Structure and real-time monitoring of the enzymatic reaction of APOBEC3G which is involved in anti-HIV activity.

Human apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3G (APOBEC3G) is known to play a role in intrinsic cellular immunity against human immunodeficiency virus type 1 (HIV-1). The antiretroviral activity of APOBEC3G is associated with hypermutation of viral DNA through cytidine deamination. APOBEC3G contains two cytidine deaminase domains that are characterized by a highly conserved zinc-coordinating motif. It is known that only the C-terminal domain of APOBEC3G (c-APOBEC3G) is involved in the catalytic activity. Here, we present the solution structure and the interaction with single-stranded DNA of c-APOBEC3G. Furthermore, we have succeeded for the first time in monitoring the deamination reaction of c-APOBEC3G in real-time using NMR signals. The monitoring has demonstrated that the deamination reaction occurs in a strict 3'-->5'

NMR assignments and the identification of the secondary structure of the anti-retroviral cytidine deaminase.

APOBEC3G (apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3G) is known to have a role in intrinsic cellular immunity against human immunodeficiency virus type1 (HIV-1). The antiretroviral activity of APOBEC3G (APO3G) is associated with the hypermutation of viral DNA through cytidine deamination. APO3G contains two cytidine deaminase domains that are characterised by highly conserved zinc-coordinating motif. It is known that only the C-terminal domain of APO3G (c-APO3G) has the catalytic activity. To shed light on the molecular mechanism of action by which APO3G inactivates HIV-1, we have undertaken the structural and binding studies by NMR. Here, we show the achievement of backbone assignments of c-APO3G and the identification of the secondary structure deduced from chemical shift index (CSI) and NOE data.

Neuronal toxicity of expanded polyglutamine depends on intracellular distribution in addition to the expression level.

The proteins that accumulate in pathologic lesions of neurodegenerative disorders are thought to be closely associated with neuronal cell damage. However, whether or not the formation of cytoplasmic or nuclear inclusions by expanded polyglutamine (polyQ) is directly toxic to neurons has been controversial to date. We prepared a culture model system in which polyQ tracts were transfected into Neuro2a, cells of neuronal origin, to study novel factors involved in cell toxicity of polyQ tracts to neuronal cells. Pathogenic polyQ tracts of 79 repeats (Q79C) when expressed in cytoplasm of Neuro2a cells changed in their intracellular distribution patterns from homogeneous, via punctate aggregates, to massive aggregates with incubation time. Some polyQ tracts formed nuclear inclusions. Cytoplasmic massive aggregates of Q79C tended to be associated with apoptotic fate of Neuro2a cells. Cells exhibiting cytoplasmic massive inclusions had the highest expression level of polyQ tracts among cells with four patterns of intracellular distribution. The elevation in the expression levels of polyQ tracts was not due to the difference in the initial transfection efficiency. When compared among cells expressing polyQ tracts at similar levels, damages were most remarkable in cells with cytoplasmic massive aggregate in terms of shrunken cellular and nuclear sizes. Cells with the other patterns of polyQ tract distribution such as cytoplasmic homogeneous, cytoplasmic punctate and nuclear inclusions were relatively spared. These data suggest that the severity of cell damages depends on the type of intracellular distribution of polyQ tracts, in addition to the expression level of polyQ tracts.

H2O2 accelerates cellular senescence by accumulation of acetylated p53 via decrease in the function of SIRT1 by NAD+ depletion.

It has been reported that p53 acetylation, which promotes cellular senescence, can be regulated by the NAD(+)-dependent deacetylase SIRT1, the human homolog of yeast Sir2, a protein that modulates lifespan. To clarify the role of SIRT1 in cellular senescence induced by oxidative stress, we treated normal human diploid fibroblast TIG-3 cells with H(2)O(2) and examined DNA cleavage, depletion of intracellular NAD(+), expression of p21, SIRT1, and acetylated p53, cell cycle arrest, and senescence-associated beta-galactosidase (SA-beta-gal) activity. DNA cleavage was observed immediately in TIG-3 cells treated with H(2)O(2), though no cell death was observed. NAD(+) levels in TIG-3 cells treated with H(2)O(2) were also decreased significantly. Pre-incubation with the poly (ADP-ribose) polymerase (PARP) inhibitor resulted in preservation of intracellular NAD(+) levels. The amount of acetylated p53 was increased in TIG-3 cells at 4h after H(2)O(2) treatment, while there was little to no decrease in SIRT1 protein expression. The expression level of p21 was increased at 12h and continued to increase for up to 24h. Additionally, exposure of TIG-3 cells to H(2)O(2) induced cell cycle arrest at 24h and increased SA-beta-gal activity at 48h. This pathway likely plays an important role in the acceleration of cellular senescence by oxidative stress.

Mutational analyses of a single-stranded telomeric DNA binding domain of fission yeast pot1: conflict with X-ray crystallographic structure.

To understand the telomere regulation mechanism in relation to cell aging and cancer, we examined the single-stranded telomeric DNA binding domain (ssDBD) of fission yeast telomere-binding protein Pot1 by constructing a series of deletion mutants. We found that Pot1(1-182) (amino acids 1-182) stably expressed in Escherichia coli without any degradation retained a stable folded structure and functional telomeric DNA binding activity, indicating that Pot1(1-182) corresponds to ssDBD. We investigated the amino acids of Pot1(1-182) involved in single-stranded telomeric DNA recognition by constructing a series of site-directed mutants. Although the previously reported X-ray crystallographic structure suggests that 12 amino acids contact the telomeric DNA, an electrophoretic mobility shift assay and isothermal titration calorimetry analyses of the binding ability of the site-directed mutants indicated that only five amino acids significantly contributed to telomeric DNA recognition. We conclude that the contribution to recognition is quite different in magnitude among the amino acids judged to contact the target by X-ray crystallographic structure.

Mechanism for manganese enhancement of dopamine-induced oxidative DNA damage and neuronal cell death.

Although the cause of dopaminergic cell death in Parkinson's disease is still poorly understood, there is accumulating evidence suggesting that metal ions can be involved in the processes. We investigated the effect of manganese on cell death and DNA damage in PC12 cells treated with dopamine. Mn(II) enhanced cell death induced by dopamine. Mn(II) also increased the 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) contents of DNA in PC12 cells treated with dopamine. To clarify the mechanism of cellular DNA damage, we investigated DNA damage induced by dopamine and Mn(II) using (32)P-labeled DNA fragments. Mn(II) enhanced Cu(II)-dependent DNA damage by dopamine. The Mn(II)-enhanced DNA damage was greatly increased by NADH. Piperidine and formamidopyrimidine-DNA glycosylase treatment induced cleavage sites mainly at T and G of the 5'-TG-3' sequence, respectively. Bathocuproine, a Cu(I) chelator, and catalase inhibited the DNA damage. Oxygen consumption and UV-visible spectroscopic measurements showed that Mn(II) enhanced autoxidation of dopamine with H(2)O(2) formation. These results suggest that reactive species derived from the reaction of H(2)O(2) with Cu(I) participates in Mn(II)-enhanced DNA damage by dopamine plus Cu(II). Therefore, it is concluded that oxidative DNA damage induced by dopamine in the presence of Mn(II), NADH, and Cu(II) is possibly linked to the degeneration of dopaminergic neurons.

Guanine-specific DNA damage induced by gamma-irradiated histone.

In gamma-irradiation, *OH is directly generated from water and causes DNA damage leading to carcinogenesis. Exposure of proteins to gamma-irradiation, in the presence of oxygen, gives high yields of hydroperoxides. To clarify whether these hydroperoxides, particularly those formed on DNA-binding histone proteins, participate in gamma-irradiation-induced carcinogenesis, experiments using 32P-labelled DNA fragments obtained from human cancer-related genes were undertaken. Histone protein-hydroperoxides induced significant DNA damage in the presence of Cu(I). Histone H1- and H3-hydroperoxides showed stronger DNA damage compared with histone H2A- and H4-hydroperoxides at 0.7 muM. Histone H1-hydroperoxides caused Cu(I)-dependent DNA damage predominantly at guanine residues, especially at 5'-GGC-3', 5'-GGA-3', 5'-GGT-3' and single G bases. In contrast, histone H3-hydroperoxides/Cu(I) induced DNA damage at 5'-G in GG sequences; this sequence specificity is identical with that generated by 2,2'-azobis (2-amidinopropane) dihydrochloride, which is known to produce peroxyl radicals (RO2*). The difference in site specificity of DNA damage induced by histone H1- and H3-hydroperoxides may arise from their amino acid composition or their mode of binding to DNA. The histone H1-hydroperoxides/Cu(I) system also induced 8-oxo-7,8-dihydro-2'-deoxyguanosine formation in calf thymus DNA. It is concluded that histone protein-hydroperoxides can induce guanine-specific DNA damage, which may contribute to gamma-irradiation-induced carcinogenesis.

(-)-Epigallocatechin gallate causes oxidative damage to isolated and cellular DNA.

Green tea catechins, especially (-)-epigallocatechin gallate (EGCG), are believed to mediate much of the cancer chemopreventive effects of tea. However, it was reported that green tea catechins enhanced colon carcinogenesis in rats. Experiments using 32P-labeled DNA fragments obtained from human cancer-related genes showed that catechins induced DNA damage in the presence of metals such as Cu(II) and Fe(III) complexes. In the presence of Fe(III)EDTA, the order of DNA damaging ability was EGCG approximately (-)-epigallocatechin>(-)-epicatechin gallate>>catechin. Catechins plus Fe(III)EDTA caused DNA damage at every nucleotide, most likely due to *OH generation from H(2)O(2). In the presence of Cu(II), the order was (-)-epigallocatechin>catechin>EGCG>(-)-epicatechin gallate. Cu(II)-mediated DNA damage by EGCG occurred most frequently at T and G residues, especially of 5'-TG-3' and GG sequences. Catalase and bathocuproine inhibited the Cu(II)-mediated DNA damage, suggesting the involvement of H(2)O(2) and Cu(I). In the presence of metal ions, increased amounts of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) were found in DNA treated with EGCG. Furthermore, EGCG increased amounts of 8-oxodG in HL-60 cells, but not in the H(2)O(2)-resistant clone HP100. When GSH was reduced by L-buthionine-[S, R]-sulfoximine, a low concentration of EGCG increased amounts of 8-oxodG in HL-60 cells, further supporting the involvement of H(2)O(2) in cellular DNA damage. It is concluded that EGCG can induce H(2)O(2) generation and subsequent damage to isolated and cellular DNA, and that oxidative DNA damage may mediate the potential carcinogenicity of EGCG.