Study on DNA strand breaks induced by sodium nitroprusside, a nitric oxide donor, in vivo and in vitro

Interpreting sperm DNA damage in a diverse range of mammalian sperm by means of the two-tailed comet assay

Key Concepts

The two-dimensional Two-Tailed Comet assay (TT-comet) protocol is a valuable technique to differentiate between single-stranded (SSBs) and double-stranded DNA breaks (DSBs) on the same sperm cell.

Protein lysis inherent with the TT-comet protocol accounts for differences in sperm protamine composition at a species-specific level to produce reliable visualization of sperm DNA damage.

Alkaline treatment may break the sugar–phosphate backbone in abasic sites or at sites with deoxyribose damage, transforming these lesions into DNA breaks that are also converted into ssDNA. These lesions are known as Alkali Labile Sites “ALSs.”

DBD–FISH permits the in situ visualization of DNA breaks, abasic sites or alkaline-sensitive DNA regions.

The alkaline comet single assay reveals that all mammalian species display constitutive ALS related with the requirement of the sperm to undergo transient changes in DNA structure linked with chromatin packing.

Sperm DNA damage is associated with fertilization failure, impaired pre-and post- embryo implantation and poor pregnancy outcome.

The TT is a valuable tool for identifying SSBs or DSBs in sperm cells with DNA fragmentation and can be therefore used for the purposes of fertility assessment.

Sperm DNA damage is associated with fertilization failure, impaired pre-and post- embryo implantation and poor pregnancy outcome. A series of methodologies to assess DNA damage in spermatozoa have been developed but most are unable to differentiate between single-stranded DNA breaks (SSBs) and double-stranded DNA breaks (DSBs) on the same sperm cell. The two-dimensional Two-Tailed Comet assay (TT-comet) protocol highlighted in this review overcomes this limitation and emphasizes the importance in accounting for the difference in sperm protamine composition at a species-specific level for the appropriate preparation of the assay. The TT-comet is a modification of the original comet assay that uses a two dimensional electrophoresis to allow for the simultaneous evaluation of DSBs and SSBs in mammalian spermatozoa. Here we have compiled a retrospective overview of how the TT-comet assay has been used to investigate the structure and function of sperm DNA across a diverse range of mammalian species (eutheria, metatheria, and prototheria). When conducted as part of the TT-comet assay, we illustrate (a) how the alkaline comet single assay has been used to help understand the constitutive and transient changes in DNA structure associated with chromatin packing, (b) the capacity of the TT-comet to differentiate between the presence of SSBs and DSBs (c) and the possible implications of SSBs or DSBs for the assessment of infertility.

Upregulation of N-acetylaspartic acid induces oxidative stress to contribute in disease pathophysiology

N-acetylaspartic acid (NAA) is predominantly present in brain and also present in lower amount in peripheral organs. The role of NAA in pathophysiology is poorly understood. Therefore the review was aimed to understand contribution of NAA in disease process. Amniotic fluid of mothers with Canavan disease (CD) fetus and patients with the disease show increased levels of NAA. Increase of this pathway is also reported in Parkinson's disease and type 2 diabetes. In HIV-related dementia, NAA is affected. Recent studies suggest that upregulation of NAA leads to oxidative stress including upregulation of nitric oxide and reducing potential antioxidants. NAA also leads to physiological abnormalities including walking disorder. These changes suggest that NAA contributes in disease pathophysiology.

Spectroscopic studies of the interaction between pirimicarb and calf thymus DNA

The interaction between pirimicarb and calf thymus DNA in physiological buffer (pH 7.4) was investigated with the use of Neutral Red (NR) dye as a spectral probe by UV-vis absorption, fluorescence and circular dichroism (CD) spectroscopy, as well as viscosity measurements and DNA melting techniques. The results revealed that an intercalation binding should be the interaction mode of pirimicarb to DNA. CD spectra indicated that pirimicarb induced conformational changes of DNA. The binding constants of pirimicarb with DNA were obtained by the fluorescence quenching method. The thermodynamic parameters, enthalpy change (ΔHθ) and entropy change (ΔSθ) were calculated to be -52.13±2.04 kJ mol(-1) and -108.8±6.72 J mol(-1) K(-1) according to the van't Hoff equation, which suggested that hydrogen bonds and van der Waals forces might play a major role in the binding of pirimicarb to DNA. Further, the alternative least squares (ALS) method was applied to resolve a complex two-way array of the absorption spectra data, which provided simultaneously the concentration information for the three reaction components, pirimicarb, NR and DNA-NR. This ALS analysis indicated that the intercalation of pirimicarb into the DNA by substituting for NR in the DNA-NR complex.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Upregulation of N-acetylaspartic acid resulting nitric oxide toxicity induces aspartoacylase mutations and protein interaction to cause pathophysiology seen in Canavan disease

Aspartoacylase (ASPA) converts N-acetylaspartic acid into aspartate and acetate. In Canavan disease (CD), N-acetylaspartic acid (NAA) is found to be increased and over 65 mutations including IVS4+1 G → T, deletion of introns and exons have been reported in the ASPA gene. These changes lead to severe form or mild form of CD. The present study was aimed to understand mechanism in the cause of mutations in ASPA and pathophysiology seen in patients with CD. We have reported that elevated levels of NAA induce inducible nitric oxide (iNOS) to produce nitric oxide toxicity in CD. Nitric oxide toxicity has been shown to induce several mutations including base change G → T and deletion and enhances protein interaction in several genes. Therefore we hypothesize that upregulation of NAA stimulates NOS and the resulting nitric oxide toxicity induces ASPA mutations and protein interaction to result pathophysiological abnormalities seen in patients with CD.

Requirement of inducible nitric-oxide synthase in lipopolysaccharide-mediated Src induction and macrophage migration

Previously, we have demonstrated the induction of Src in lipopolysaccharide (LPS)-stimulated macrophages. In this study, we observed that pharmacological blockade or knockout of inducible nitric-oxide synthase (iNOS) reduced LPS-mediated Src induction and macrophage migration. Either SNAP (a NO donor) or 8-Br-cGMP (a cGMP analogue) could rescue these defects in iNOS-null macrophages, which indicated the participation of NO/cGMP in LPS-elicited Src expression and mobilization. In addition, Src family kinase (SFK)-specific inhibitor, PP2, inhibited SNAP- and 8-Br-cGMP-evoked motility implicating the involvement of SFKs downstream of NO/cGMP. Analysis of the expression of SFKs indicated LPS dramatically induced Src, which could be attributable to the increased level of the src transcript. Attenuation of Src by src-specific siRNA reduced LPS- and SNAP-evoked mobilization in Raw264.7 macrophages, and reintroduction of avian Src could rescue their motility. Furthermore, LPS-mediated Src induction led to increased FAK Pi-Tyr-397 and Pi-Tyr-861, which was also iNOS-dependent. With these findings, we concluded that iNOS was important for LPS-mediated macrophage locomotion and Src was a critical player in this process.

Genetic instability in calamondin (Citrus madurensis Lour.) plants derived from somatic embryogenesis induced by diphenylurea derivatives

Somatic embryos were regenerated in vitro from calamondin style-stigma explants cultured in the presence of N (6)-benzylaminopurine (BAP) cytokinin and three synthetic phenylurea derivatives, N-(2-chloro-4-pyridyl)-N-phenylurea (4-CPPU), N-phenyl-N'-benzothiazol-6-ylurea (PBU) and N,N'-bis-(2,3-methilendioxyphenyl)urea (2,3-MDPU). The phenylurea derivative compounds tested at micromolar level (12 muM) were able to induce a percentage of responsive explants significantly higher from that obtained with BAP and hormone-free (HF) conditions. In order to verify the genetic stability of the regenerants, 27 plants coming from different embryogenic events were randomly selected from each different culture condition and evaluated for somaclonal variations using inter-simple sequence repeat and random amplified polymorphic DNA analyses. We observed that 2,3-MDPU and PBU gave 3.7% of somaclonal mutants, whereas 4-CPPU gave 7.4% of mutants. No somaclonal variability was observed when plantlets were regenerated in BAP or HF medium. Although diphenylurea derivatives show a higher embryogenic potential as compared to BAP, they induce higher levels of somaclonal variability. This finding should be taken in consideration when new protocols for clonal propagation are being developed.

Interaction of hyperbaric oxygen, nitric oxide, and heme oxygenase on DNA strand breaks in vivo

Hyperbaric oxygen (HBO), e.g. pure oxygen breathing at supra-atmospheric pressures, represents a well-suited model for investigating oxidative stress-induced DNA damage as well as protective mechanisms. While the induction of heme oxygenase-1 (HO-1) seems to be crucial for this protection against this DNA damage, the role of nitric oxide (NO) remains unclear. HO-1 expression is a major regulator of the inducible NO synthase (iNOS), and therefore we investigated the effect of the interaction between HBO, NO, and HO-1 on DNA damage. Prior to exposure to HBO (3 h at 3 bar ambient pressure) rats randomly received vehicle (HBO alone, 1 mL 0.9% saline, n=8), the NO donor molsidomine (SIN-10, 40 mg/kg, n=8) or the HO-1 blocker tin-mesopophyrin (Sn-MP, 50 micromol/kg, n=8). Additional groups received SIN-10 without exposure to HBO, i.e. breathing air under normobaric conditions for 3h (SIN-10 alone, 40 mg/kg, n=6), vehicle without HBO (negative controls, n=6), and ethylmethanesulfonate without HBO (EMS, 200 mg/kg) (positive controls n=4). Immediately after the 3 h HBO or air breathing period blood was analysed for DNA strand breaks (tail moment in the alkaline comet assay) and nitrite+nitrate (chemoluminescence). Whereas the tail moment was ten-fold higher after EMS than in the negative controls, there was no effect of HBO nor SIN-10 alone. Together with HBO, pretreatment with SIN-10 doubled the tail moment, and Sn-MP increased it by 50%. In contrast to Sn-MP or HBO alone, SIN-10 resulted in a five-fold increase of nitrite+nitrate concentrations. We conclude that both HO-1 blockade and excess NO release promote DNA damage during HBO exposure in vivo. The effect of HO-1 inhibition is probably independent of the regulatory function of HO-1 for iNOS.

Fullerene derivatives protect against oxidative stress in RAW 264.7 cells and ischemia-reperfused lungs

Fullerene derivatives have often been used as effective scavengers for reactive oxygen species (ROS). This study was designed to test whether polyhydroxylated fullerene derivatives [C(60)(OH)(7+/-2)] protect against oxidative stress in cultured RAW 264.7 cells and ischemia-reperfused (IR) lungs. In RAW 264.7 cells, sodium nitroprusside (SNP, 1 mM) and H(2)O(2) (400 microM) caused a marked (90%) decrease in cell viability, and this decrease was dose dependently reversed by pretreatment with C(60)(OH)(7+/-2) (10-50 microM). The increase in ROS production induced by SNP and H(2)O(2) was significantly suppressed by C(60)(OH)(7+/-2). Also, the decrease in mitochondrial membrane potential induced by SNP and H(2)O(2) was significantly reversed by C(60)(OH)(7+/-2). However, high concentration of C(60)(OH)(7+/-2) (1 and 1.5 mM) lead to cell death (apoptosis or necrosis). In the isolated rat lung, the increases in pulmonary artery pressure and capillary filtration pressure induced by SNP during IR were reversed significantly by C(60)(OH)(7+/-2) (10 mg/kg). These results indicate that polyhydroxylated fullerene derivatives C(60)(OH)(7+/-2) at low concentrations protect against oxidative stress in RAW 264.7 cells and IR lungs.

Nitric oxide promotes p53 nuclear retention and sensitizes neuroblastoma cells to apoptosis by ionizing radiation

Nitric oxide (NO) is a potent activator of the p53 tumor suppressor protein. However, the mechanisms underlying p53 activation by NO have not been fully elucidated. We previously reported that a rapid downregulation of Mdm2 by NO may contribute to the early phase of p53 activation. Here we show that NO promotes p53 nuclear retention and inhibits Mdm2-mediated p53 nuclear export. NO induces phosphorylation of p53 on serine 15, which does not require ATM but rather appears to depend on the ATM-related ATR kinase. An ATR-kinase dead mutant or caffeine, which blocks the kinase activity of ATR, effectively abolishes the ability of NO to cause p53 nuclear retention, concomitant with its inhibition of p53 serine 15 phosphorylation. Of note, NO enhances markedly the ability of low-dose ionizing radiation to elicit apoptotic killing of neuroblastoma cells expressing cytoplasmic wild-type p53. These findings imply that, through augmenting p53 nuclear retention, NO can sensitize tumor cells to p53-dependent apoptosis. Thus, NO donors may potentially increase the efficacy of radiotherapy for treatment of certain types of cancer.

Sper/NO-induced reversible proliferation inhibition and cycle arrests associated with a micronucleus induction in HSG cells

Nitric oxide (NO) is an important messenger molecule with multiple biological activities. In the present study, sper/NO, a NO generator, showed a biphasic effect on the proliferation of human salivary gland neoplastic (HSG) cells. Sper/NO of less than 20 micro M stimulated cells to depart from the G2/M phase and so enhanced cell division and cell proliferation. But sper/NO at higher concentrations restrained cell proliferation and blocked cell-cycle progression. Cells were mainly arrested in the G2/M phase and S phase when they were treated with 100-200 and 300-500 micro M sper/NO, respectively. A special S-phase peak was detected in a histogram of the cell-phase distribution of sper/NO-treated HSG. When the concentration of sper/NO increased, the S-phase peak shifted from early the G2/M-phase to later the G1-S-phase boundary. Sper/NO-induced cell-cycle arrests were reversible when the cells were released from NO stress for 48h and hence cell proliferation was recovered. In addition, micronucleus, but no apoptosis, was produced in the sper/NO-treated cells, and its yield tended to a saturation value with increasing concentrations of sper/NO. The sper/NO-induced effects were effectively eliminated or reduced by treating cells with PTIO, a NO-specific scavenger, indicating that NO is the main source of these effects.

Inhibitory effects of isoflavones on nitric oxide- or peroxynitrite-mediated DNA damage in RAW 264.7 cells and phiX174 DNA

The inhibitory effects of isoflavones (genistin, daidzin and their aglycones genistein, daidzein) on sodium nitroprusside (SNP; nitric oxide donor)- or peroxynitrite-mediated DNA damage in intact cells and in plasmid DNA was investigated. RAW 264.7 cells, a murine macrophage cell line, are capable of producing nitric oxide and superoxide anion. However, macrophages themselves are also shown to be more sensitive to nitric oxide or peroxynitrite, and were therefore used in these studies. Results from single-cell gel electrophoresis (the comet assay) showed that these isoflavones, at the concerning of 25-200 microM, inhibited the induction of nitric oxide- or peroxynitrite-mediated macrophage genotoxicity, with genistein showing the greatest inhibition. Genistein and daidzein, at a concentration of 1-25 microm, dose-dependently inhibited peroxynitrite-induced phiX174 DNA degradation based on the results of agarose gel electrophoretic analysis. Although SNP could increase the cellular GSH level, no significant differences in the glutathione content or the GSH:GSSG ratio were observed for genistein and daidzein in the presence or absence of SNP as compared with SNP-only treated RAW 264.7 cells. Exposure of RAW 264.7 cells to SNP caused the enzyme activities of GSH peroxidase, GSH reductase and catalase decrease to 44, 20 and 34% of that of untreated cells, respectively. On the contrary, exposure of RAW 264.7 cells to SNP in the presence of 100 microm of genistein or daidzein caused the enzyme activities of GSH peroxidase, GSH reductase and catalase decrease to 18, 9 and 12% (genistein) or 13, 9 and 19% (daidzein) of that of untreated cells, respectively. These results suggest that the inhibition by isoflavones of SNP- or peroxynitrite- mediated DNA damage could be attributed to their nitric oxide or peroxynitrite scavenging activities and their prevention of antioxidant enzyme inactivation.

Chromosomal aberrations, DNA strand breaks and gene mutations in nasopharyngeal cancer patients undergoing radiation therapy

Nasopharyngeal cancer (NPC) is a common disease in the south part of China, and its incidence is increasing in the southwest of China in recent years. Radiation therapy is the main therapeutic method for NPC in China. In this study, genetic changes were assessed in randomly selected nine NPC patients receiving radiation therapy by different genotoxical screening methods, the cytokinesis-block micronucleus test (CB-MNT), the buccal mucosa cell micronucleus test (BMC-MNT), the undivided lymphocyte micronucleus test (UL-MNT), chromosomal aberration (CA) test, the comet assay and the hprt gene mutation test (HPRT). Patients were used as self-control before receiving radiation therapy. Apart from the UL-MNT, all the methods detected genetic damages in NPC patients, though with different sensitivities. CB-MNT is the best biological indicator for evaluating genetic damage induced by radiation therapy in NPC patients; followed by CA and HPRT, while the BMC-MNT is simplest method as a potential biological indicator.