Analysis of DNA damage via single-cell electrophoresis

Analysis of Single- and Double-Stranded DNA Damage in Osteoblastic Cells after Hyperbaric Oxygen Exposure

(1) Background: Hyperbaric oxygen (HBO) exposure induces oxidative stress that may lead to DNA damage, which has been observed in human peripheral blood lymphocytes or non-human cells. Here, we investigated the impact of hyperbaric conditions on two human osteoblastic cell lines: primary human osteoblasts, HOBs, and the osteogenic tumor cell line SAOS-2. (2) Methods: Cells were exposed to HBO in an experimental hyperbaric chamber (4 ATA, 100% oxygen, 37 °C, and 4 h) or sham-exposed (1 ATA, air, 37 °C, and 4 h). DNA damage was examined before, directly after, and 24 h after exposure with an alkaline comet assay and detection of γH2AX+53BP1 colocalizing double-strand break (DSB) foci and apoptosis. The gene expression of TGFß-1, HO-1, and NQO1, involved in antioxidative functions, was measured with qRT-PCR. (3) Results: The alkaline comet assay showed significantly elevated levels of DNA damage in both cell lines after 4 h of HBO, while the DSB foci were similar to sham. γH2AX analysis indicated a slight increase in apoptosis in both cell lines. The increased expression of HO-1 in HOB and SAOS-2 directly after exposure suggested the induction of an antioxidative response in these cells. Additionally, the expression of TGF-ß1 was negatively affected in HOB cells 4 h after exposure. (4) Conclusions: in summary, this study indicates that osteoblastic cells are sensitive to the DNA-damaging effects of hyperbaric hyperoxia, with the HBO-induced DNA damage consisting largely of single-strand DNA breaks that are rapidly repaired.

Ultrasensitive biosensing of thiram based on detection of the DNA damage induced by thiram: Application to investigation of protective effects of extra virgin olive oil against DNA damage

In this work, a novel electrochemical biosensor was fabricated based on modification of a glassy carbon electrode (GCE) with nafion-DNA/gold nanoparticles/poly-ethylenedioxy pyrrole/multi-walled carbon nanotubes-ionic liquid (NF-DNA/Au NPs/PEDOP/MWCNTs-IL/GCE) with the aim of amperometric detection of the DNA damage induced by thiram (TH). By incubation of the biosensor with the TH, the TH was intercalated within DNA, and the exposed DNA released negative charges at the surface of the biosensor which repelled the probe molecules and caused the amperometric response of the biosensor to be decreased. Protective effects of extra virgin olive oil (EVOO) on the DNA damage induced by the TH were investigated by recording amperometric responses of the biosensor in the presence of EVOO, and the results confirmed that the response of the biosensor didn't change to confirm the protective effects of the EVOO on preventing the DNA damage induced by the TH. A novel and sensitive electroanalytical method was developed for determination of the TH in two linear ranges including 1-6 pM and 7-10 pM based on amperometric detection of the DNA damage induced by the TH which gave a LOD of 0.31 pM. The developed methodology in this work was successful in detection of the DNA damage induced by TH, detection of protective effects of EVOO on preventing DNA damage and determination of the TH in real matrices.

Simultaneous estimation of rates of DNA damage induced by three important chemotherapy drugs by a novel electrochemical biosensor assisted by chemometric multivariate calibration methods

In this work, a novel electrochemical biosensor assisted by multivariate calibration methods was developed for simultaneous estimation of rates of DNA damage induced by doxorubicin (DX), daunorubicin (DR) and idarubicin (ID), and also to simultaneous determination of the drugs. A glassy carbon electrode was efficiently modified and used as the biosensing platform. Binding and interactions of DX, DR and ID with DNA were modeled by molecular docking methods, and theoretical information was completed by experimental results. The methylene blue was able to intercalate within the DNA structure and by incubation of the biosensor with DX or DR or ID, the methylene blue was replaced by drug and therefore, the voltammetric signal of the biosensor was changed due to the exposed DNA and repelling the electrochemical probe molecules carrying negative charge. The DNA damage induced by each drug was individually monitored by differential pulse voltammetry and then, rates of DNA damage were calibrated and validated by mixture design and multivariate calibration methods. The developed multivariate calibration model constructed based on vectorization of the data was able to simultaneous detection of the rates of DNA damage induced by all the three drugs. The change in the biosensor response in the presence of the drugs was also modeled by multivariate calibration methods to simultaneous determination of the drugs.

Developing an elegant and integrated electrochemical-theoretical approach for detection of DNA damage induced by 4-nonylphenol

In this work, a novel biosensor was fabricated for detection of DNA damage induced by 4-nonylphenol (NP) and also determination of NP. To achieve this goal, a glassy carbon electrode (GCE) was modified with chitosan (Chit), gold nanoparticles (Au NPs) and DNA-multiwalled carbon nanotubes (DNA-MWCNTs). Then, the DNA-MWCNTs/Au NPs/Chit/GCE was incubated with methylene blue (MB) to obtain MB-DNA-MWCNTs/Au NPs/Chit/GCE in which MB was used as the redox indicator. The modifications applied to the GCE were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopic (EDS) and theoretical evidence. MB is a derivative of anthraquinone which can intercalate into double helix structure of DNA. By treating MB-DNA-MWCNTs/Au NPs/Chit/GCE with NP, a higher R _ct was observed because the insertion of the NP may result in a more negative charge environment on the DNA surface which hinders accessibility of [Fe(CN)₆]^3-/4- anion to the electrode surface. Change in the EIS response of the biosensor in the presence of NP was used to develop a novel system for monitoring the DNA damage induced by NP. The EIS technique was also used to develop a sensitive electroanalytical method for determination of NP.

Fabrication of a novel biosensor for biosensing of bisphenol A and detection of its damage to DNA

In this work, a novel electrochemical biosensor has been fabricated based on step-by-step modification of a glassy carbon electrode (GCE) with methylene blue (MB)-DNA/multiwalled carbon nanotubes (MWCNTs)-chitosan (CS)/palladium nanoparticles (Pd NPs)/fullerene C₆₀ (C₆₀) for voltammetric and impedimetric detection of DNA damage induced by bisphenol A (BPA). Modifications applied to the GCE were characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy. The EIS and DPV responses of the biosensor were increased and decreased, respectively, by the DNA damage induced by BPA which led us to develop novel systems for detection of DNA damage. Our records confirmed that the biosensor was able to rapid and sensitive detection of DNA damage induced by BPA. Finally, according to the developed systems for detection of DNA damage, we have developed voltammetric and impedimetric methods for determination of BPA.

Carcinogens and DNA damage

Humans are variously and continuously exposed to a wide range of different DNA-damaging agents, some of which are classed as carcinogens. DNA damage can arise from exposure to exogenous agents, but damage from endogenous processes is probably far more prevalent. That said, epidemiological studies of migrant populations from regions of low cancer risk to high cancer risk countries point to a role for environmental and/or lifestyle factors playing a pivotal part in cancer aetiology. One might reasonably surmise from this that carcinogens found in our environment or diet are culpable. Exposure to carcinogens is associated with various forms of DNA damage such as single-stand breaks, double-strand breaks, covalently bound chemical DNA adducts, oxidative-induced lesions and DNA-DNA or DNA-protein cross-links. This review predominantly concentrates on DNA damage induced by the following carcinogens: polycyclic aromatic hydrocarbons, heterocyclic aromatic amines, mycotoxins, ultraviolet light, ionising radiation, aristolochic acid, nitrosamines and particulate matter. Additionally, we allude to some of the cancer types where there is molecular epidemiological evidence that these agents are aetiological risk factors. The complex role that carcinogens play in the pathophysiology of cancer development remains obscure, but DNA damage remains pivotal to this process.

Bio-monitoring of DNA damage in matchstick industry workers from Peshawar Khyber Pakhtunkhwa, Pakistan

BACKGROUND

Safety protocols are usually neglected in most of the matchstick industries rendering the laborer prone to various occupational hazards.

OBJECTIVE

The present study highlights DNA damage among matchstick factory workers (n = 92) against a control group (n = 48) of healthy individuals.

METHODS

Genotoxicity was measured in peripheral blood lymphocytes of the test subjects using a Single Cell Gel Electrophoresis assay (SCGE/comet assay).

RESULTS

Our results substantiate a high Total Comet Score (TCS) for factory workers (74.5 ± 47.0) when compared to the control group (53.0 ± 25.0) (P ≤ 0.001). Age and duration of occupational exposure had no significant effect (P > 0.05) on TCS value. As for job function, the TCS value was greatest in sweepers (91.0 ± 56.1) and lowest in box-making operators (26.0 ± 25.0) indicating that waste disposal poses the higher risk of DNA damage.

CONCLUSIONS

Our study corroborates that matchstick chemicals can potentially damage the DNA of exposed subjects.

Persistent Organochlorine Pollutants in Placentas Sampled from Women in Croatia and an Evaluation of Their DNA Damaging Potential In Vitro

This study investigated the levels and distribution of 17 polychlorinated biphenyls (PCBs) and organochlorine pesticides (HCB, α-HCH, β-HCH, γ-HCH, p,p'-DDE, p,p'-DDD, and p,p'-DDT) in placenta samples from women living in the coastal area of Croatia. During November 2012 to February 2013, 51 placenta samples were collected from healthy mothers. This study presents the first report about Croatian placenta samples. Each of the analysed compounds were found in all of the samples; all of the maximum values were < 1 ng g^-1 w.w., and the highest median value found for PCB-28 was 11.2 pg g^-1 w.w. PCBs and organochlorine pesticide (OCPs) present in placenta samples were tested for their genotoxic potential using the alkaline comet assay. The alkaline comet assay is one of the most reliable methods in assessing the DNA lesions that occurs in direct interaction of a chemical and the genome. The detected levels of PCBs and OCPs in the placenta did not pose a significant risk to the children's DNA during embryonic and foetal growth following short-term exposure. PCB and OCP concentrations in the placenta samples did not induce any significant primary damage to DNA in terms of DNA strand breaks and changes in the primary chemical structure, which could be detected by the alkaline comet assay.

Hypoxia induces universal but differential drug resistance and impairs anticancer mechanisms of 5-fluorouracil in hepatoma cells

Hepatocellular carcinoma (HCC) is one of the most refractory cancers. The mechanisms by which hypoxia further aggravates therapeutic responses of advanced HCC to anticancer drugs remain to be clarified. Here, we report that hypoxia (1% O₂) caused 2.55-489.7-fold resistance to 6 anticancer drugs (sorafenib, 5-fluorouracil [5-FU], gemcitabine, cisplatin, adriamycin and 6-thioguanine) in 3 HCC cell lines (BEL-7402, HepG2 and SMMC-7721). Among the 6 drugs, sorafenib, the sole one approved for HCC therapy, inhibited proliferation with little influence from hypoxia and displayed the smallest variation among the 3 HCC cell lines tested. By contrast, the inhibition of proliferation by 5-FU, which has been extensively tested in clinical trials but has not been approved for HCC therapy, was severely affected by hypoxia and showed a large variation among these cell lines. In 5-FU-treated HCC cells, hypoxia reduced the levels of basal thymidylate synthase (TS) and functional TS, leading to decreased dTMP synthesis and DNA replication. Hypoxia also affected the accumulation of FdUTP and its misincorporation into DNA. Consequently, both single-strand breaks and double-strand breaks in DNA were reduced, although hypoxia also inhibited DNA repair. In 5-FU-treated HCC cells, hypoxia further abated S-phase arrest, alleviated the loss of mitochondrial membrane potential, diminished the activation of caspases, and finally resulted in reduced induction of apoptosis. Thus, hypoxia induces universal but differential drug resistance. The extensive impacts of hypoxia on the anticancer mechanisms of 5-FU contributes to its hypoxia-induced resistance in HCC cells. We propose that hypoxia-induced drug resistance and interference of hypoxia with anticancer mechanisms could be used as candidate biomarkers in selecting and/or developing anticancer drugs for improving HCC therapy.

Antioxidant and antigenotoxic potential of Ramaria largentii Marr & D. E. Stuntz, a wild edible mushroom collected from Northeast Romania

Ramaria largentii Marr & D. E. Stuntz (orange coral mushroom) is a wild edible mushroom whose chemical composition and bioactivity have not been investigated. Herein, we present a study on the phenolic constituents, antioxidant and antigenotoxic effects of a hydromethanolic extract of the fruiting bodies. Total phenolic content, estimated by Folin-Ciocalteu assay, was found to be 42.33 ± 0.18 mg GAE/g. Protocatechuic and vanillic acids were detected by HPLC-DAD-ESI-MS. The extract showed good free radical scavenging and reducing capacities (EC₅₀ = 64.3 ± 0.2 and 61.54 ± 0.46 μg/mL, respectively). In normal Vero cells, the extract (100, 200 and 300 μg/mL) showed no genotoxic potential and moreover, almost completely protected DNA against H₂O₂-induced damage (2.09-7.91% tail DNA) (24 and 48 h pre-treatment). Taken together, the results of our study show that Ramaria largentii extract is devoid of genotoxicity and has a remarkable DNA protective activity against H₂O₂-induced damage.

A model for the control of DNA integrity by the sperm nuclear matrix

The highly condensed chromatin of mammalian spermatozoa is usually considered to be biologically inert before fertilization. However, we have demonstrated that even in this compacted state, sperm chromatin is subject to degradation at open configurations associated with the nuclear matrix through a process we have termed sperm chromatin fragmentation (SCF). This suggests that a mechanism exists to monitor the health of spermatozoa during transit through the male reproductive tract and to destroy the genome of defective sperm cells. The site of DNA damage in SCF, the matrix attachment sites, are the same that we hypothesize initiate DNA synthesis in the zygote. When sperm that have damaged DNA are injected into the oocyte, the newly created zygote responds by delaying DNA synthesis in the male pronucleus and, if the damage is severe enough, arresting the embryo's development. Here we present a model for paternal DNA regulation by the nuclear matrix that begins during sperm maturation and continues through early embryonic development.

Double-stranded DNA breaks hidden in the neutral Comet assay suggest a role of the sperm nuclear matrix in DNA integrity maintenance

We used a mouse model in which sperm DNA damage was induced to understand the relationship of double-stranded DNA (dsDNA) breaks to sperm chromatin structure and to the Comet assay. Sperm chromatin fragmentation (SCF) produces dsDNA breaks located on the matrix attachment regions, between protamine toroids. In this model, epididymal sperm induced to undergo SCF can religate dsDNA breaks while vas deferens sperm cannot. Here, we demonstrated that the conventional neutral Comet assay underestimates the epididymal SCF breaks because the broken DNA ends remain attached to the nuclear matrix, causing the DNA to remain associated with the dispersion halo, and the Comet tails to be weak. Therefore, we term these hidden dsDNA breaks. When the Comet assay was modified to include an additional incubation with sodium dodecyl sulfate (SDS) and dithiothreitol (DTT) after the conventional lysis, thereby solubilizing the nuclear matrix, the broken DNA was released from the matrix, which resulted in a reduction of the sperm head halo and an increase in the Comet tail length, exposing the hidden dsDNA breaks. Conversely, SCF-induced vas deferens sperm had small halos and long tails with the conventional neutral Comet assay, suggesting that the broken DNA ends were not tethered to the nuclear matrix. These results suggest that the attachment to the nuclear matrix is crucial for the religation of SCF-induced DNA breaks in sperm. Our data suggest that the neutral Comet assay identifies only dsDNA breaks that are released from the nuclear matrix and that the addition of an SDS treatment can reveal these hidden dsDNA breaks.