Induction Of DNA Single-strand Breaks Research Articles

Dispensability of HPF1 for cellular removal of DNA single-strand breaks.

In response to DNA damage, the histone PARylation factor 1 (HPF1) regulates PARP1/2 activity, facilitating serine ADP-ribosylation of chromatin-associated factors. While PARP1/2 are known for their role in DNA single-strand break repair (SSBR), the significance of HPF1 in this process remains unclear. Here, we investigated the impact of HPF1 deficiency on cellular survival and SSBR following exposure to various genotoxins. We found that HPF1 loss did not generally increase cellular sensitivity to agents that typically induce DNA single-strand breaks (SSBs) repaired by PARP1. SSBR kinetics in HPF1-deficient cells were largely unaffected, though its absence partially influenced the accumulation of SSB intermediates after exposure to specific genotoxins in certain cell lines, likely due to altered ADP-ribosylation of chromatin. Despite reduced serine mono-ADP-ribosylation, HPF1-deficient cells maintained robust poly-ADP-ribosylation at SSB sites, possibly reflecting PARP1 auto-poly-ADP-ribosylation at non-serine residues. Notably, poly-ADP-ribose chains were sufficient to recruit the DNA repair factor XRCC1, which may explain the relatively normal SSBR capacity in HPF1-deficient cells. These findings suggest that HPF1 and histone serine ADP-ribosylation are largely dispensable for PARP1-dependent SSBR in response to genotoxic stress, highlighting the complexity of mechanisms that maintain genomic stability and chromatin remodeling.

The protective effects of empagliflozin on DNA oxidative changes in a model of vascular endothelial and smooth muscle cells damaged by oxidized cholesterol

BackgroundDiabetes patients often suffer chronic vascular complications resulting from endothelial dysfunction, smooth muscle cell (SMC) proliferation, inflammation and disturbed oxidative balance. Empagliflozin is one of three approved sodium-glucose cotransporter 2 (SGLT2) inhibitors for type 2 diabetes mellitus. The aim of this studywas to determine the protective and repairing effect of EMPA in a model of vascular endothelial and SMC damage with 25-hydroxycholesterol (25-OHC). MethodsHuman umbilical vascular endothelial cells (HUVECs) and SMCs were treated with compounds which induce DNA single-strand breaks (SSBs) and subjected to comet assay. Oxidative DNA damage was detected using endonuclease III (Nth) or human 8 oxoguanine DNA glycosylase (hOOG1). Reactive oxygen species (ROS) formation was determined by the fluorescence of a 6-carboxy-2′,7′-dichlorodihydrofluoresce probe in diacetate (H2DCFDA). Results25-OHC-stimulated SMCs showed greater resistance to ROS generation and DNA damage compared to HUVECs. In both experimental models, EMPA treatment was associated with lower ROS production and DNA damage, including oxidative damage to purines and pyrimidines. This effect was not dose-dependent. EMPA was found to counteract this DNA damage by inhibiting ROS production. ConclusionsIt appears that the EMPA induced indirect repair of DNA by inhibiting ROS production.

The protective effect of dabigatran and rivaroxaban on DNA oxidative changes in a model of vascular endothelial damage with oxidized cholesterol

Background: Atherosclerotic plaques are unstable, and their release may result in thrombosis; therefore, currently, antiplatelet therapy with anticoagulants is recommended for the treatment of acute coronary syndrome. The aim of this study was to assess the effect of oxidized cholesterol on human umbilical vascular endothelial cells (HUVECs). The study also examines the protective and repairing effect of dabigatran and rivaroxaban in a model of vascular endothelial damage with 25-hydroxycholesterol (25-OHC). Methods: HUVECs were treated with compounds induce DNA single-strand breaks (SSBs) using the comet assay. Oxidative DNA damage was detected using endonuclease III (Nth) or human 8 oxoguanine DNA glycosylase (hOOG1). Reactive oxygen species (ROS) formation was determined using flow cytometry. Results: 25-hydroxycholesterol caused DNA SSBs, induced oxidative damage and increased ROS in the HUVECs; ROS level was lowered by dabigatran and rivaroxaban. Only dabigatran was able to completely repair the DNA SSBs induced by oxysterol. Dabigatran was able to reduce the level of oxidative damage of pyrimidines induced by oxysterol to the level of control cells. Conclusions: Observed changes strongly suggest that the tested anticoagulants induced indirect repair of DNA by inhibiting ROS production. Furthermore, dabigatran appears to have a higher antioxidant activity than rivaroxaban.

Inhibitor of protein kinases 1-(4-chlorobenzyl)-3-chloro-4-(3-trifluoromethylphenylamino)-1Н-pyrrole-2,5-dione induces DNA damage and apoptosis in human colon carcinoma cells

Background. The heterocyclic scaffolds are in the list of key structural blocks used at synthesis of novel biologically active compounds. Materials and Methods. The present study addressed the evaluation of the mecha­nisms of the DNA damaging and pro-apoptotic actions in vitro of the maleimide derivative 1-(4-chlorobenzyl)-3-chloro-4-(3-trifluoromethylphenylamino)-1Н-pyrrole-2,5-dione (MI-1) targeting human colon carcinoma cells of HCT116 line. The Western-blot analysis was used to study changes in apoptosis-associated proteins, DNA comet assay under alkaline conditions was applied for evaluation of the DNA-damaging events, and Barton’s assay with diphenylamine was applied for measuring the level of DNA fragmentation in human colon carcinoma cells treated with MI-1 compound. Results. The results of the Western-blot analysis demonstrated that MI-1 induced the apoptosis in HCT116 cells via mitochondria-dependent pathway. It activated caspase 3 via its cleavage in the treated human colon carcinoma cells. Besides, MI-1 increased the content of mitochondria-specific proteins: endonuclease G (EndoG) and the pro-apoptotic cytosolic protein protease-activating factor 1 (Apaf1). At the same time, MI-1 reduced the level of the anti-apoptotic Bcl-2 protein in HCT116 cells. The DNA comet analysis under alkaline conditions of the targeted human colon carcinoma cells of HCT116 line demonstrated that MI-1 induced DNA single-strand breaks in line with the olive tail moment of 13.2. The results of the colorimetric diphenylamine assay in HCT116 cells have shown that cell treatment with MI-1 increased the content of fragmented DNA to 14.2 %. Conclusions. The anti-proliferative action of MI-1 in human colon carcinoma cells of HCT116 line is associated with apoptosis induction via mitochondria-dependent pathway, as well as the DNA damage through single-strand breaks and DNA fragmentation. These data suggest that the 1-(4-chlorobenzyl)-3-chloro-4-(3-trifluoromethylpheny­l­amino)-1Н-pyrrole-2,5-dione (MI-1) might be a promising agent for suppression of growth of colon tumor cells. Keywords: 1Н-pyrrole-2,5-diones, apoptosis, Western-blot assay, comet assay, single-strand breaks, Barton’s assay, DNA fragmentation

Ochratoxin A-induced genotoxic and epigenetic mechanisms lead to Alzheimer disease: its modulation with strategies.

Ochratoxin A (OTA) is a naturally occurring mycotoxin mostly found in food items including grains and coffee beans. It induces DNA single-strand breaks and has been considered to be carcinogenic. It is recognized as a serious threat to reproductive health both in males and females. OTA is highly nephrotoxic and carcinogenic, and its potency changes evidently between species and sexes. There is a close association between OTA, mutagenicity, carcinogenicity, and genotoxicity, but the underlying mechanisms are not clear. Reports regarding genotoxic effects in relation to OTA which leads to the induction of DNA adduct formation, protein synthesis inhibition, perturbation of cellular energy production, initiation of oxidative stress, induction of apoptosis, influences on mitosis, induction of cell cycle arrest, and interference with cytokine pathways. All these mechanisms are associated with nephrotoxicity, hepatotoxicity, teratotoxicity, immunological toxicity, and neurotoxicity. OTA administration activates various mechanisms such as p38 MAPK, JNKs, and ERKs dysfunctions, BDNF disruption, TH overexpression, caspase-3 and 9 activation, and ERK-1/2 phosphorylation which ultimately lead to Alzheimer disease (AD) progression. The current review will focus on OTA in terms of recent discoveries in the field of molecular biology. The main aim is to investigate the underlying mechanisms of OTA in regard to genotoxicity and epigenetic modulations that lead to AD. Also, we will highlight the strategies for the purpose of attenuating the hazards posed by OTA exposure.

Clothianidin induces DNA damage and oxidative stress in bronchial epithelial cells.

Clothianidin (CHN) is a member of the neonicotinoid group of insecticides. Its oxidative and DNA damage potential for human lung cells are not known. Therefore, the present study was designed to examine the effects of CHN on DNA damage and oxidative stress in human bronchial epithelial cells (BEAS-2B) treated with CHN for 24, 72, and 120 hr. Our results indicate that CHN decreased cell viability in a concentration-dependent manner. CHN induced DNA single-strand breaks because alkaline comet parameters such as tail intensity, DNA in the tail, tail moment, and tail length increased. All CHN concentrations also significantly induced the formation of DNA double-strand breaks (DSBs) because it increased phosphorylated H2AX protein foci for all treatment times and p53-binding protein 1 foci for all treatments except for the lowest concentration (0.15 mM) of 120-hr treatment. DNA damage caused by DNA DSBs was not repaired in a 24-hr recovery period. CHN also induced oxidative stress by decreasing reduced glutathione and increasing lipid peroxidation. These results make it necessary to conduct studies about the detailed carcinogenic potential of CHN in humans because it can induce both oxidative and DNA damage.

The Protective Effect of Dabigatran and Rivaroxaban on DNA Oxidative Changes in a Model of Vascular Endothelial Damage with Oxidized Cholesterol.

Background: Atherosclerotic plaques are unstable, and their release may result in thrombosis; therefore, currently, antiplatelet therapy with anticoagulants is recommended for the treatment of acute coronary syndrome. The aim of this study was to assess the effect of oxidized cholesterol on human umbilical vascular endothelial cells (HUVECs). The study also examines the protective and repairing effect of dabigatran and rivaroxaban in a model of vascular endothelial damage with 25-hydroxycholesterol (25-OHC). Methods: HUVECs were treated with compounds induce DNA single-strand breaks (SSBs) using the comet assay. Oxidative DNA damage was detected using endonuclease III (Nth) or human 8 oxoguanine DNA glycosylase (hOOG1). Reactive oxygen species (ROS) formation was determined using flow cytometry. Results: 25-hydroxycholesterol caused DNA SSBs, induced oxidative damage and increased ROS in the HUVECs; ROS level was lowered by dabigatran and rivaroxaban. Only dabigatran was able to completely repair the DNA SSBs induced by oxysterol. Dabigatran was able to reduce the level of oxidative damage of pyrimidines induced by oxysterol to the level of control cells. Conclusions: Observed changes strongly suggest that the tested anticoagulants induced indirect repair of DNA by inhibiting ROS production. Furthermore, dabigatran appears to have a higher antioxidant activity than rivaroxaban.

Complex genetic interactions between DNA polymerase β and the NHEJ ligase.

Mammalian cells possess multiple pathways for repairing various types of DNA damage. Although the molecular mechanisms of each DNA repair pathway have been analyzed by biochemical analysis and cell biological analysis, interplay between different pathways has not been fully elucidated. In this study, using human Nalm-6-mutant cell lines, we analyzed the relationship between the base excision repair factor DNA polymerase β (POLβ) and DNA ligase IV (LIG4), which is essential for DNA double-strand break (DSB) repair by non-homologous end-joining (NHEJ). We found that cells lacking both POLβ and LIG4 grew significantly more slowly than either single mutant, indicating cooperative functions of the two proteins in normal cell growth. To further investigate the genetic interaction between POLβ and LIG4, we examined DNA damage sensitivity of the mutant cell lines. Our results suggested that NHEJ acts as a backup pathway for repairing alkylation damage (when converted into DSBs) in the absence of POLβ. Surprisingly, despite the critical role of POLβ in alkylation damage repair, cells lacking POLβ exhibited increased resistance to camptothecin (a topoisomerase I inhibitor that induces DNA single-strand breaks), irrespective of the presence or absence of LIG4. A LIG4-independent increased resistance associated with POLβ loss was also observed with ionizing radiation; however, cells lacking both POLβ and LIG4 were more radiosensitive than either single mutant. Taken together, our findings provide novel insight into the complex interplay between different DNA repair pathways.

Helicobacter pylori-Induced DNA Damage Is a Potential Driver for Human Gastric Cancer AGS Cells.

Helicobacter pylori is a major cause of gastric cancer. This study was aimed to explore the characteristic of DNA damage induced by H. pylori infection in gastric cancer AGS cells. After infection with H. pylori, the reactive oxygen species (ROS) levels in AGS cells were significantly higher than those in the uninfected cells. Cells with longer comet tails were detected after infection with H. pylori. The number of apurinic/apyrimidinic endonuclease 1- and phosphorylated H2AX-positive cells was significantly increased compared with the number of negative control cells. The expression of pChk1 and pChk2 was significantly upregulated by H. pylori infection. Cell growth was inhibited after H. pylori infection. All these results were dose dependent. The cell alterations were more significant upon infection with H. pylori at a multiplicity of infection (MOI) of 100:1 than at an MOI of 50:1. H. pylori infection can induce DNA single-strand breaks, DNA double-strand breaks, and cell cycle checkpoint activation after ROS generation in the gastric cancer cell line AGS, which is a potential driver for gastric cancer.

Inhibition of ATR Potentiates Acute Myeloid Leukemia Cells to the RNA Pol I Transcription Inhibitor CX-5461

Inhibition of ATR Potentiates Acute Myeloid Leukemia Cells to the RNA Pol I Transcription Inhibitor CX-5461

Uranyl acetate induced DNA single strand breaks and AP sites in Chinese hamster ovary cells

The aim of this study is to characterize the genotoxicity of depleted uranium (DU) in Chinese Hamster Ovary cells (CHO) with mutations in various DNA repair pathways. CHO cells were exposed to 0–300 μM of soluble DU as uranyl acetate (UA) for 0–48 h. Intracellular UA concentrations were measured via inductively coupled mass spectrometry (ICP-MS) and visualized by transmission electron microscopy (TEM). Cytotoxicity was assessed in vitro by clonogenic survival assay. DNA damage response was assessed via Fast Micromethod® to determine UA-induced DNA single strand breaks. Results indicate that UA is entering the CHO cells, with the highest concentration localizing in the nucleus. Clonogenic assays show that UA is cytotoxic in each cell line with the greatest cytotoxicity in the base excision repair deficient EM9 cells and the nuclear excision repair deficient UV5 cells compared to the non-homologous end joining deficient V3.3 cells and the parental AA8 cells after 48 h. This indicates that UA is producing single strand breaks and forming UA-DNA adducts rather than double strand breaks in CHO cells. Fast Micromethod® results indicate an increased amount of single strand breaks in the EM9 cells after 48 h UA exposure compared to the V3.3 and AA8 cells. These results indicate that DU induces DNA damage via strand breaks and uranium-DNA adducts in treated cells. These results suggest that: (1) DU is genotoxic in CHO cells, and (2) DU is inducing single strand breaks rather than double strand breaks in vitro.

Antigenotoxic properties of Paliurus spina-christi Mill fruits and their active compounds

BackgroundPaliurus spina-christi Mill. (PS) fruits are widely used for different medical purposes in Turkey. Like in many medicinal herbs the studies concerning their activity, the activities of PS are also not well clarified. The aim of this study is to evaluate the antigenotoxicity of the compounds isolated and identified from the extracts of PS fruits.MethodsThe active compounds were separated, isolated, and determined by chromatographic methods and their structural elucidation was performed by Nuclear Magnetic Resonance (NMR) methods. The compounds were obtained from either ethyl acetate (EA) or n-butanol extracts. The cytotoxicities of the compounds using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and the antigenotoxic activities of the compounds using the alkaline single cell gel electrophoresis techniques (comet assay) were evaluated in Chinese hamster lung fibroblast (V79) cell lines.ResultsThe isolated major compounds were identified as (+/−) catechins and gallocatechin from EA fraction and rutin from n-butanol fraction of PS fruits. Their chemical structures were identified by 1H-NMR, 13C-NMR, HMBC, and HMQC techniques. Half-maximal inhibitory concentration of catechins, gallocatechin, and rutin were found to be 734 μg/mL, 220 μg/mL, and 1004 μg/mL, respectively. The methanolic extract of PS (1-100 μg/mL) alone did not induce DNA single-strand breaks while catechins (1-100 μg/mL), gallocatechin (1-50 μg/mL), and rutin (1-50 μg/mL) significantly reduced H2O2-induced DNA damage.ConclusionIt has been suggested that PS fruits and their compounds catechins, gallocatechin and rutin may have beneficial effects in oxidative DNA damage. It seems that PS fruits may be used in protection of the disorders related to DNA damage.

Aqueous and enzyme-extracted phenolic compounds from brewers' spent grain (BSG): Assessment of their antioxidant potential

Brewers' spent grain (BSG) is a major coproduct of the brewing industry and a potential valuable source of protein, cell wall polysaccharides, lignin, lipid, and phenolic compounds. The aim of this study was to assess the antioxidant potential of phenolic extracts isolated from BSG using cell wall degrading enzymes, Depol 740L, Shearzyme and, Ultraflo Max. The phenolic extracts were prepared from black BSG (derived from barley grains roasted at 200°C) and pale BSG (derived from malted barley grains). The phenolic extracts protected against hydrogen peroxide (H2O2)-induced DNA single strand breaks in U937 cells as assessed using the comet assay. The extracts also protected against a H2O2 challenge in HepG2 cells, as assessed by measuring the cellular content of glutathione (GSH) and the activity of cellular antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT). Enzyme-extracted black and pale BSG phenolic extracts protected against oxidant-induced DNA damage and enhanced the cellular antioxidant activity in cells. Practical applications Enzyme-extraction may be an effective alternative to conventional solvent extraction for the isolation of novel bioactive components, such as phenolics, from Brewers' spent grain. The BSG extracts may be used as a source of functional ingredients for the development of foods with potential benefits to human health.

Exposure to volatile anaesthetics is not followed by a massive induction of single-strand DNA breaks in operation theatre personnel.

Volatile anaesthetics such as halothane, isoflurane and others were expected to produce a health challenge for operation room personnel because of prolonged occupational exposure to anaesthetic gases. To estimate a molecular background of adverse health effects, a cohort of 100 exposed individuals was studied by the single-cell gene electrophoresis (comet assay) test. DNA lesions in lymphocytes of the exposed group did not differ significantly compared with non-exposed blood donors. Then, the exposed group was further divided according to job position. A highest level of DNA lesions was established in nurses but without significant difference compared with other groups. When a time period of exposure was taken into account, a tendency to cumulate DNA lesions was found only in the group of anaesthesiologists. A very weak genotoxic effect established in this study is discussed in relation to DNA repair, adaptative response and potential self-elimination of sensitive individuals.

Abstract PL05-04: PARP trapping versus PARP catalytic inhibition and coupling with TDP1

Abstract The five clinical PARP inhibitors (veliparib, olaparib, niraparib, rucaparib and talazoparib) are potent submicromolar competitive NAD+ inhibitors for PARP1 and PARP2, thereby blocking PARylation reactions [i.e. formation of poly(ADPribose) polymers]. In addition, PARP trapping, which determines the anticancer activity of PARP inhibitor as single agents, is drug-specific, and PARP inhibitors can be ranked according to their PARP trapping potency: talazoparib >> niraparib ≈ olaparib ≈ rucaparib > veliparib. We will review evidence that PARP trapping is the primary cytotoxic mechanism of PARP inhibitors as single agents and that cancer-specific DNA repair alterations as well as SLFN11 expression determine the cytotoxicity of trapped PARP-DNA complexes in cancers beyond BRCA inactivation. Used in combination in cellular models, PARP inhibitors are highly synergistic with alkylating agent (temozolomide or methyl methanesulfonate) and topoisomerase I (Top1) inhibitors (camptothecin and its clinical derivatives (topotecan and irinotecan) and the non-camptothecin indenoisoquinoline Top1 inhibitors in clinical development (LMP400, LMP776 and LMP744). Both alkylating agents and Top1 inhibitors induce DNA single-strand breaks sensed by PARP. Yet, the molecular mechanisms of synergy are different. For alkylating agents (temozolomide and MMS), both PARP trapping and PARylation inhibition account for the synergy, whereas for Top1 inhibitors, there is no involvement of PARP trapping and it is PARylation inhibition that deters the coupling of PARP with the repair enzyme, tyrosyl-DNA phosphodiesterase, TDP1. We will review the molecular pharmacology differences between PARP inhibitors as single agents and the rationale for choosing among different PARP inhibitors in combination with alkylating agents or Top1 inhibitors based on trapping vs. catalytic inhibition. Citation Format: Yves G. Pommier, Junko Murai. PARP trapping versus PARP catalytic inhibition and coupling with TDP1. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr PL05-04.

O6.1 - Classification of PARP inhibitors based on PARP trapping and catalytic inhibition, and rationale for combinations

ABSTRACT All PARP inhibitors in clinical development (veliparib, olaparib, niraparib, rucaparib, and talazoparib) are potent submicromolar competitive NAD+ inhibitors for PARP1 and PARP2, thereby blocking PARylation reactions [i.e. formation of poly(ADPribose) polymers]. In addition, PARP trapping, which determines the anticancer activity of PARP inhibitor as single agents, is drug-specific, and PARP inhibitors can be ranked according to their PARP trapping potency: talazoparib >> niraparib ≈ olaparib ≈ rucaparib > veliparib. The highly synergistic effects of PARP inhibitors in combination with alkylating agent (temozolomide or methyl methanesulfonate) and topoisomerase I (Top1) inhibitors (camptothecins and indenoisoquinolines) are well documented. Both classes of drugs induce DNA single-strand breaks sensed by PARP. Yet, the molecular mechanisms of synergy are different. For alkylating agents (temozolomide and MMS), both PARP trapping and PARylation inhibition account for the synergy, whereas for Top1 inhibitors, there is no involvement of PARP trapping and it is PARylation inhibition deters the coupling of PARP with the repair enzyme, tyrosyl-DNA phosphodiesterase TDP1. We will review the differences between PARP inhibitors and the rationale for choosing among different PARP inhibitors in combination with alkylating agents or Top1 inhibitors.

Single-cell gel electrophoresis assay in the ten spotted live-bearer fish, Cnesterodon decemmaculatus (Jenyns, 1842), as bioassay for agrochemical-induced genotoxicity

The ability of two 48 percent chlorpyrifos-based insecticides (Lorsban* 48E® and CPF Zamba®), two 50 percent pirimicarb-based insecticides (Aficida® and Patton Flow®), and two 48 percent glyphosate-based herbicides (Panzer® and Credit®) to induce DNA single-strand breaks in peripheral blood erythrocytes of Cnesterodon decemmaculatus (Jenyns, 1842) (Pisces, Poeciliidae) exposed under laboratory conditions was evaluated by the single-cell gel electrophoresis (SCGE) assay. In those fish exposed to Lorsban* 48E®, CPF Zamba®, Aficida®, Patton Flow®, Credit®, and Panzer®, a significant increase of the genetic damage was observed for all formulations regardless of the harvesting time. This genotoxic effect was achieved by an enhancement of Type II-IV comets and a concomitant decrease of Type 0-I comets over control values. A regression analysis revealed that the damage varied as a negative function of the exposure time in those Lorsban* 48E®- and Aficida®-treated fish. On the other hand, a positive correlation between damage increase and exposure time was achieved after Patton Flow® and Credit® treatment. Finally, no correlation was observed between increase in the genetic damage and exposure time after treatment with CPF Zamba® or Panzer®. These results highlight that all agrochemicals inflict primary genotoxic damage at the DNA level at sublethal concentrations, regardless of the exposure time of the aquatic organisms under study, at least within a period of 96h of treatment.

Electromagnetic fields act via activation of voltage‐gated calcium channels to produce beneficial or adverse effects

The direct targets of extremely low and microwave frequency range electromagnetic fields (EMFs) in producing non-thermal effects have not been clearly established. However, studies in the literature, reviewed here, provide substantial support for such direct targets. Twenty-three studies have shown that voltage-gated calcium channels (VGCCs) produce these and other EMF effects, such that the L-type or other VGCC blockers block or greatly lower diverse EMF effects. Furthermore, the voltage-gated properties of these channels may provide biophysically plausible mechanisms for EMF biological effects. Downstream responses of such EMF exposures may be mediated through Ca2+/calmodulin stimulation of nitric oxide synthesis. Potentially, physiological/therapeutic responses may be largely as a result of nitric oxide-cGMP-protein kinase G pathway stimulation. A well-studied example of such an apparent therapeutic response, EMF stimulation of bone growth, appears to work along this pathway. However, pathophysiological responses to EMFs may be as a result of nitric oxide-peroxynitrite-oxidative stress pathway of action. A single such well-documented example, EMF induction of DNA single-strand breaks in cells, as measured by alkaline comet assays, is reviewed here. Such single-strand breaks are known to be produced through the action of this pathway. Data on the mechanism of EMF induction of such breaks are limited; what data are available support this proposed mechanism. Other Ca2+-mediated regulatory changes, independent of nitric oxide, may also have roles. This article reviews, then, a substantially supported set of targets, VGCCs, whose stimulation produces non-thermal EMF responses by humans/higher animals with downstream effects involving Ca2+/calmodulin-dependent nitric oxide increases, which may explain therapeutic and pathophysiological effects.

Sulforaphane induces DNA single strand breaks in cultured human cells

Sulforaphane (SFR), an isothiocyanate from cruciferous vegetables, possesses growth-inhibiting and apoptosis-inducing activities in cancer cell lines. Recently, SFR has been shown to promote the mitochondrial formation of reactive oxygen species (ROS) in human cancer cell lines. The present study was undertaken to see whether SFR-derived ROS might cause DNA damage in cultured human cells, namely T limphoblastoid Jurkat and human umbilical vein endothelial cells (HUVEC). 1–3 h treatments with 10–30 μM SFR elicited intracellular ROS formation (as assayed with dihydrorhodamine, DHR, oxidation) as well as DNA breakage (as assessed with fast halo assay, FHA). These effects lacked cell-type specificity, since could be observed in both Jurkat and HUVEC. Differential-pH FHA analysis of damaged DNA showed that SFR causes frank DNA single strand breaks (SSBs); no DNA double strand breaks (DSBs) were found within the considered treatment times (up to 3 h). SFR-derived ROS were formed at the mitochondrial respiratory chain (MRC) level: indeed rotenone or myxothiazol (MRC Complex I and III inhibitors, respectively) abrogated ROS formation. Furthermore ROS were not formed in Jurkat cells pharmacologically depleted of respiring mitochondria (MRC−/Jurkat). Formation of ROS was causally linked to the induction of SSBs: indeed all the experimental conditions capable of preventing ROS formation also prevented the damage of nuclear DNA from SFR-intoxicated cells. As to the toxicological relevance of SSBs, we found that their prevention slightly but significantly attenuated SFR cytotoxicity, suggesting that high-dose SFR toxicity is the result of a complex series of events among which GSH depletion seems to play a pivotal role. In conclusion, the present study identifies a novel mechanism contributing to SFR toxicity which – since DNA damage is a prominent mechanism underlying the cytotoxic activity of established antineoplastic agents – might help to exploit the therapeutic value of SFR in anticancer drug protocols.

PARP-3 Is a Mono-ADP-ribosylase That Activates PARP-1 in the Absence of DNA

The PARP-3 protein is closely related to the PARP-1 and PARP-2 proteins, which are involved in DNA repair and genome maintenance. Here, we characterized the biochemical properties of human PARP-3. PARP-3 is able to ADP-ribosylate itself as well as histone H1, a previously unknown substrate for PARP-3. PARP-3 is not activated upon binding to DNA and is a mono-ADP-ribosylase, in contrast to PARP-1 and PARP-2. PARP-3 interacts with PARP-1 and activates PARP-1 in the absence of DNA, resulting in synthesis of polymers of ADP-ribose. The N-terminal WGR domain of PARP-3 is involved in this activation. The functional interaction between PARP-3 and PARP-1 suggests that it may have a role in DNA repair. However, here we report that PARP-3 small interfering RNA-depleted cells are not sensitive to the topoisomerase I poison camptothecin, inducing DNA single-strand breaks, and repair these lesions as efficiently as wild-type cells. Altogether, these results suggest that the interaction between PARP-1 and PARP-3 is unrelated to DNA single-strand break repair.