Deoxyribonucleic Acid Damage Research Articles

Interactions of Zinc Oxide Nanostructures with Mammalian Cells: Cytotoxicity and Photocatalytic Toxicity.

This article presents a state-of-the-art review and analysis of literature studies on the morphological structure, fabrication, cytotoxicity, and photocatalytic toxicity of zinc oxide nanostructures (nZnO) of mammalian cells. nZnO with different morphologies, e.g., quantum dots, nanoparticles, nanorods, and nanotetrapods are toxic to a wide variety of mammalian cell lines due to in vitro cell–material interactions. Several mechanisms responsible for in vitro cytotoxicity have been proposed. These include the penetration of nZnO into the cytoplasm, generating reactive oxygen species (ROS) that degrade mitochondrial function, induce endoplasmic reticulum stress, and damage deoxyribonucleic acid (DNA), lipid, and protein molecules. Otherwise, nZnO dissolve extracellularly into zinc ions and the subsequent diffusion of ions into the cytoplasm can create ROS. Furthermore, internalization of nZnO and localization in acidic lysosomes result in their dissolution into zinc ions, producing ROS too in cytoplasm. These ROS-mediated responses induce caspase-dependent apoptosis via the activation of B-cell lymphoma 2 (Bcl2), Bcl2-associated X protein (Bax), CCAAT/enhancer-binding protein homologous protein (chop), and phosphoprotein p53 gene expressions. In vivo studies on a mouse model reveal the adverse impacts of nZnO on internal organs through different administration routes. The administration of ZnO nanoparticles into mice via intraperitoneal instillation and intravenous injection facilitates their accumulation in target organs, such as the liver, spleen, and lung. ZnO is a semiconductor with a large bandgap showing photocatalytic behavior under ultraviolet (UV) light irradiation. As such, photogenerated electron–hole pairs react with adsorbed oxygen and water molecules to produce ROS. So, the ROS-mediated selective killing for human tumor cells is beneficial for cancer treatment in photodynamic therapy. The photoinduced effects of noble metal doped nZnO for creating ROS under UV and visible light for killing cancer cells are also addressed.

Zinc deficient diet increases the toxicity of bisphenol A in rat testis.

Zinc (Zn) plays an important role in maintaining the process of spermatogenesis and reproductive health. Bisphenol A (BPA), an endocrine disrupting chemical is known to be a reproductive toxicant in different animal models. The present study was designed to study the effect of two of the utmost determinative factors (Zn deficient condition and influence of toxicant BPA) on germ cell growth and overall male reproductive health in the testis, epididymis, and sperm using (a) biochemical, (b) antioxidant, (c) cellular damage, (d) apoptosis, and (e) protein expression measurements. Rats were divided into Control (normal feed and water), BPA (100 mg/kg/d), zinc deficient diet (ZDD; fed with ZDD), and BPA + ZDD for 8 weeks. Body and organ weights, sperm motility and counts, and sperm head morphology were evaluated. The histology of testes, epididymides, and prostate wasinvestigated. Testicular deoxyribonucleic acid (DNA) damage was evaluated by Halo and Comet assay, apoptosis of sperm and testes were quantified by TUNEL assay. Serum protein electrophoretic patterns and testicular protein expressions such as Nrf-2, catalase, PCNA, and Keap1 were analyzed by Western blot analysis. The results showed that BPA significantly increased the testicular, epididymal, and prostrate toxicity in dietary Zn deficient condition due to testicular hypozincemia, hypogonadism, increased cellular and DNA damage, apoptosis, as well as perturbations in protein expression.

Effects of DNA Damage and Oxidative Stress in Human Bronchial Epithelial Cells Exposed to PM2.5 from Beijing, China, in Winter.

Epidemiological studies have corroborated that respiratory diseases, including lung cancer, are related to fine particulate matter (<2.5 μm) (PM2.5) exposure. The toxic responses of PM2.5 are greatly influenced by the source of PM2.5. However, the effects of PM2.5 from Beijing on bronchial genotoxicity are scarce. In the present study, PM2.5 from Beijing was sampled and applied in vitro to investigate its genotoxicity and the mechanisms behind it. Human bronchial epithelial cells 16HBE were used as a model for exposure. Low (67.5 μg/mL), medium (116.9 μg/mL), and high (202.5 μg/mL) doses of PM2.5 were used for cell exposure. After PM2.5 exposure, cell viability, oxidative stress markers, DNA (deoxyribonucleic acid) strand breaks, 8-OH-dG levels, micronuclei formation, and DNA repair gene expression were measured. The results showed that PM2.5 significantly induced cytotoxicity in 16HBE. Moreover, the levels of reactive oxygen species (ROS), malondialdehyde (MDA), and cellular heme oxygenase (HO-1) were increased, and the level of glutathione (GSH) was decreased, which represented the occurrence of severe oxidative stress in 16HBE. The micronucleus rate was elevated, and DNA damage occurred as indicators of the comet assay, γ-H2AX and 8-OH-dG, were markedly enhanced by PM2.5, accompanied by the influence of 8-oxoguanine DNA glycosylase (OGG1), X-ray repair cross-complementing gene 1 (XRCC1), and poly (ADP-ribose) polymerase-1 (PARP1) expression. These results support the significant role of PM2.5 genotoxicity in 16HBE cells, which may occur through the combined effect on oxidative stress and the influence of DNA repair genes.

2-Monokloropropandiol (2-MCPD)’nin Sitotoksik Etkilerinin Fare TM3 Leydig ve TM4 Sertoli Hücreleri Üzerinde in vitro Değerlendirilmesi

Amaç: 2-monokloropropandiol (2-MCPD), 3-monokloropropandiol (3-MCPD) ve esterleri ile glisidil yağ asidi esteri (GE), gıda veya gıda işlem kaynaklı kontaminantlar olarak adlandırılmaktadır. Bu gıda kontaminantlarının başta palmiye yağı olmak üzere bitkisel yağlar, margarinler, pasta ve kek gibi işlem görmüş gıdalarda ve bebek mamalarında tespit edilmesi, güvenlikleri konusundaki ilgiyi arttırmıştır. Avrupa Gıda Güvenliği Otoritesi’nin (European Food Safety Authority, EFSA) Mayıs 2016 yılında yayınlamış olduğu bilimsel görüşe göre bitkisel yağ ve işlenmiş gıdalarda bulunan GE, 3-MCPD, 2-MCPD ve bunların yağ asidi esterlerinin insan sağlığı için zararlı olduğu raporlanmıştır. Ancak 2-MCPD toksisitesi hakkında yeterli veri olmadığı için tam bir değerlendirme yapılamamıştır. Bu amaçla 2-MCPD’nin, TM3 Leydig ve TM4 Sertoli hücre hatları üzerinde in vitro sitotoksik, apoptotik etkileri ve deoksiribonükleik asit (DNA) hasarı yapma potansiyeli değerlendirilmiştir.&#x0D; Gereç ve Yöntem: Hücre canlılığı, 3-(4,5-dimetiltiyazol-2-il)-2,5-difeniltetrazolyum bromid (MTT) ve nötral kırmızısı alım (NRU) yöntemleri ile değerlendirilmiştir. Akış sitometrisi ile hücre ölüm tipinin belirlenmesinde aneksin V-FITC/PI ikili boyama kiti kullanılmıştır. Genotoksisite değerlendirmesinde komet yöntemi uygulanmıştır. &#x0D; Bulgular: Hücre canlılık yöntemleri sonucu 2-MCPD’nin test edilen konsantrasyonlarda 1000 µM’a kadar sitotoksik olmadığı tespit edilmiştir. Aynı zamanda 2-MCPD’nin, sub-toksik konsantrasyonlarda (1-1000 µM) her iki hücre hattında da (TM3 Leydig ve TM4 Sertoli hücreleri) DNA hasarını indüklemediği bulunmuştur. &#x0D; Sonuç: 2-MCPD, her ne kadar test edilen konsantrasyonlarda (1-1000 µM) sitotoksik ve apoptotik etki göstermese de daha yüksek konsantrasyonlarda hücre ölümüne ve DNA hasarına neden olabilir. Ancak bu yüksek konsantrasyonlar günlük maruziyet dozlarından çok uzaktır.

Changes in the levels of comet parameters before and after fluoxetine therapy in major depression patients.

Major depression belongs to mood disorders and characterized by worthlessness, no interest or happiness in any activity; lasting for atleast two weeks. Etio-pathological changes of major depression include oxidative stress leading to free radical synthesis which causes damage to carbohydrates, proteins, lipids and nucleic acids. Nucleic acid damage can be identified by either single or double strand breaks and for quantitative estimation of the same, neutral or alkaline comet assay is performed. Fluoxetine is the drug of choice for treatment of major depression having antioxidant function. In the current study eighty drug naïve major depression patients were recruited and comet parameters namely total comet length, head diameter and tail length were measured before starting the treatment and after completion of eight week fluoxetine therapy. The levels of comet parameters were higher in females than males suggesting higher prevalence of major depression among females. On categorizing into three age groups, the numbers of major depression patients belonging to 18–30 year age group were higher than 31–40 and 41–50 year age groups. All the parameters of deoxyribonucleic acid damage were reduced after eight week of fluoxetine therapy indicating that fluoxetine has anti-oxidant action along with its antidepressant properties, which cause reversal of oxidative stress induced damage occurring during major depression.

Preventive effect of Euphorbia royleana Boiss on diabetes induced by streptozotocin via modulating oxidative stress and deoxyribonucleic acid damage

Oxidative stress is associated with streptozotocin induced diabetes. The present study was conducted to investigate the anti-oxidant, anti-diabetic and genotoxic effects of Euphorbia royleana Boiss. stem’s crude extract in rats. Better inhibitory concentration (IC50) of methanolic extract in alpha amylase and antioxidant assays along with improvement in hyperglycemia can be linked with the presence of phenolic acids and flavonoids determined quantitatively by HPLC. The declining superoxide dismutase, catalase activities, and hydrogen peroxide concentrations were restored at the dose of 500 mg/kg. The methanolic extract turned out to be Class I genotoxic at 100 µg/mL. Moreover, improvement in histopathological changes of pancreas, liver and kidney were also observed.

ATM-mediated DNA double-strand break response facilitated oncolytic Newcastle disease virus replication and promoted syncytium formation in tumor cells.

Deoxyribonucleic acid (DNA) damage response (DDR) is the fundamental cellular response for maintaining genomic integrity and suppressing tumorigenesis. The activation of ataxia telangiectasia-mutated (ATM) kinase is central to DNA double-strand break (DSB) for maintaining host-genome integrity in mammalian cells. Oncolytic Newcastle disease virus (NDV) can selectively replicate in tumor cells; however, its influence on the genome integrity of tumor cells is not well-elucidated. Here, we found that membrane fusion and NDV infection triggered DSBs in tumor cells. The late replication and membrane fusion of NDV mechanistically activated the ATM-mediated DSB pathway via the ATM-Chk2 axis, as evidenced by the hallmarks of DSBs, i.e., auto-phosphorylated ATM and phosphorylated H2AX and Chk2. Immunofluorescence data showed that multifaceted ATM-controlled phosphorylation markedly induced the formation of pan-nuclear punctum foci in response to NDV infection and F-HN co-expression. Specific drug-inhibitory experiments on ATM kinase activity further suggested that ATM-mediated DSBs facilitated NDV replication and membrane fusion. We confirmed that the Mre11-RAD50-NBS1 (MRN) complex sensed the DSB signal activation triggered by NDV infection and membrane fusion. The pharmacological inhibition of MRN activity also significantly inhibited intracellular and extracellular NDV replication and syncytia formation. Collectively, these data identified for the first time a direct link between the membrane fusion induced by virus infection and DDR pathways, thereby providing new insights into the efficient replication of oncolytic NDV in tumor cells.

Mechanism Analysis of Coix Seed in Gastric Cancer Treatment Based on Biological Network Modules

Coix seed, the mature seed of Coix lacryma-jobi L., is a traditional herb widely used in various cancer adjuvant treatments; however, its mechanism is unknown. The aim of this study was to reveal the multitarget mechanisms of Coix seed in the treatment of gastric cancer (GC) by biological network and modular analysis methods. Forty-one ingredients and 482 targets of Coix seed and 165 GC-related genes were obtained from databases. Twelve on-target genes ( AICDA, CASP3, EP300, ERBB2, FGFR2, IL12A, IL12B, IL1B, LOX, TJP1, TP53, and TRIB3) of Coix seed overlapped with GC-related genes. Using compound-target and protein–protein interaction network analyses, we discovered the core targets of Coix seed. Markov cluster algorithm-based modular analysis identified 5 potential module targets of Coix seed for GC. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis demonstrated the vast actions of Coix seed, which involve pathways in cancer, the cell cycle, receptor signal transduction, deoxyribonucleic acid damage response, transcriptional regulation, apoptosis, and cell connections. This study elucidated the potential mechanisms of Coix seed on GC, which may lead to the development of an effective drug. Additionally, this study showed the feasibility of network and modular analysis methods to investigate traditional Chinese medicinal herbal mechanisms and may provide a new angle for further research in the field of anticancer mechanisms and multitarget drugs.

The Close Interplay of Nitro-Oxidative Stress, Advanced Glycation end Products and Inflammation in Inflammatory Bowel Diseases.

Inflammatory Bowel Disease (IBD) exhibits no defined aetiology. However, factors such as genetic and nitro-oxidative stress are associated with chronic inflammation and IBD progression to Colorectal Cancer (CRC). The present review discusses the association of nitro-oxidative stress, inflammation and Advanced Glycation End products (AGE) and their corresponding receptor (RAGE) in IBD and examines the connection between these factors and nuclear factors, such as Nuclear Factor Kappa B (NF-κB), factorerythroid 2-related factor-2 (Nrf2), and p53 Mutant (p53M). We searched the PubMed, ScienceDirect and Web of Science databases using a combination of the following terms: IBD, CRC, oxidative stress, inflammation, NF-κB, Nrf2, p53M, AGE and RAGE. Oxidative stress and inflammation activated two cellular pathways, the nuclear expression of pro-inflammatory, pro-oxidant and pro-oncogenic genes based on NF-κB and p53M, which is associated with NF-κB activation, Deoxyribonucleic acid (DNA) damage and the expression of pro-oncogenic genes. Nrf2 stimulates the nuclear expression of enzymatic and non-enzymatic antioxidant systems and anti-inflammatory genes, and is inhibited by chronic oxidative stress, NF-κB and p53M. AGE/RAGE are involved in inflammation progression because RAGE polymorphisms and increased RAGE levels are found in IBD patients. Alterations of these pathways in combination with oxidative damage are responsible for IBD symptoms and the progression to CRC. IBD is an inflammatory and nitro-oxidative stress-based bowel disease. Achieving a molecular understanding of the biochemical events and their complicated interactions will impact basic and applied research, animal models, and clinical trials.

Antioxidant characterization and in vitro DNA damage protection potential of some Indian fenugreek (Trigonella foenum-graecum) cultivars: effect of solvents

Indian fenugreek cultivars were characterized for their antioxidant properties and bioactive compounds were quantified using high performance liquid chromatography (HPLC). The extraction efficiencies were compared for two extraction solvents [aqueous ethanol (50%) and methanol]. The bioactive properties studied were total phenolic content (TPC), total flavonoids content (TFC), condensed tannin content (CTC), 2,2'-Azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS+), 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, total antioxidant capacity (TAC), and reducing power activity (RPA). Aqueous ethanol extracts showed higher TPC, TFC, ABTS+, TAC and RPA as compared to methanol. However, methanolic extracts showed higher CTC and DPPH activity. Higher TPC [45.3 and 45.4mg gallic acid equivalents (GAE)/g dry weight basis (dwb)], DPPH (93.0 and 93.2%), ABTS+ (98.3 and 98.5%), RPA [40.9 and 44.9mg quercetin equivalents (QE)/g dwb], were observed for cv.RMT-143 and cv.RMT-365, respectively. TFC (20.5mg catechin equivalents (CE)/g dwb) and CTC (9.3mg CE/g dwb) were found the highest for cv. Kasoori methi. Quantification of phenolic compounds using HPLC revealed higher amount of gallic acid (in Kasoori methi), ascorbic and p-coumaric acid (HM-57), benzoic and cinnamic acid (RMT-143) and catechol (only in RMT-365). Significant (p < 0.05) protection against in vitro plasmid deoxyribonucleic acid (DNA) (pBR322) oxidative damage was observed for fenugreek extracts.

Increased chemotherapy-induced ovarian reserve loss in women with germline BRCA mutations due to oocyte deoxyribonucleic acid double strand break repair deficiency

To assess whether woman who have BRCA mutations (WBM) experience more declines in ovarian reserve after chemotherapy treatment, as it induces oocyte death by deoxyribonucleic acid (DNA) damage, and BRCA mutations result in DNA damage repair deficiency. Longitudinal cohort study. Academic centers. The 108 evaluable women with breast cancer were stratified into those never tested (negative family history; n = 35) and those negative (n = 59) or positive (n = 14) for a pathogenic BRCA mutation. Sera were longitudinally obtained before and 12-24 months after chemotherapy treatment, assayed for antimüllerian hormone (AMH), and adjusted for age at sample collection. Ovarian recovery, defined as the geometric mean of the after chemotherapy age-adjusted AMH levels compared with baseline levels. Compared with the controls, the before chemotherapy treatment AMH levels were 24% and 34% lower in those negative or positive for BRCA mutations, consistent with accelerated ovarian aging in WBM. The WBM had a threefold difference in AMH recovery after chemotherapy treatment (1.6%), when compared with BRCA negative (3.7%) and untested/low risk controls (5.2%). Limiting the analysis to the most common regimen, doxorubicin and cyclophosphamide followed by paclitaxel, showed similar results. These findings were mechanistically confirmed in an invitro mouse oocyte BRCA knockdown bioassay, which showed that BRCA deficiency results in increased oocyte susceptibility to doxorubicin. Women who have pathogenic BRCA mutations are more likely to lose ovarian reserve after chemotherapy treatment, suggesting an emphasis on fertility preservation. Furthermore, our findings generate the hypothesis that DNA repair deficiency is a shared mechanism between aging, infertility, and cancer. NCT00823654.

Polo-like kinase 1 as a promising diagnostic biomarker and potential therapeutic target for hepatocellular carcinoma.

Hepatocellular carcinoma is a major cause of cancer mortality worldwide. The outcome of hepatocellular carcinoma depends mainly on its early diagnosis. To date, the performance of traditional biomarkers is unsatisfactory. Polo-like kinase 1 is a serine/threonine kinase that plays essential roles in cell cycle progression and deoxyribonucleic acid damage. Moreover, polo-like kinase 1 knockdown decreases the survival of hepatocellular carcinoma cells; therefore, polo-like kinase 1 is an attractive target for anticancer treatments. Nobiletin, a natural polymethoxy flavonoid, exhibits a potential antiproliferative effect against a wide variety of cancers. This study targets to identify a reliable diagnostic biomarker for hepatocellular carcinoma and provide a potential therapeutic target for its treatment. Polo-like kinase 1 levels were analyzed in 44 hepatocellular carcinoma patients, 33 non-hepatocellular carcinoma liver cirrhosis patients and 15 healthy controls using the enzyme-linked immunosorbent assay method. Receiver operating characteristics curve analysis was used to establish a predictive model for polo-like kinase 1 relative to α-fetoprotein in hepatocellular carcinoma diagnosis. Furthermore, in the in vitro study, gene expressions were assessed by quantitative polymerase chain reaction in two human hepatocellular carcinoma cell lines after treatment with doxorubicin and polo-like kinase 1 inhibitor volasertib (Vola) either alone or in combination with nobiletin. Cell viability was also determined using the crystal violet assay.: Serum polo-like kinase 1 levels in hepatocellular carcinoma patients were significantly higher than liver cirrhosis and control groups (p < 0.0001). Polo-like kinase 1 showed a reasonable sensitivity, specificity, positive predictive value, and negative predictive value in hepatocellular carcinoma diagnosis. Moreover, nobiletin improved inhibition of cell growth induced by Vola and doxorubicin. Regarding reverse transcription polymerase chain reaction results, nobiletin suppressed expressions of polo-like kinase 1 and proliferating cell nuclear antigen and elevated expressions of P53, poly (ADPribose) polymerase 1, and caspase-3. Nobiletin/doxorubicin and nobiletin/Vola showed a significant increase in caspase-3 activity indicating cell apoptosis. Polo-like kinase 1 may be a potential biomarker for hepatocellular carcinoma diagnosis and follow-up during treatment with chemotherapies. In addition, nobiletin synergistically potentiates the doxorubicin and Vola-mediated anticancer effect that may be attributed partly to suppression of polo-like kinase 1 and proliferating cell nuclear antigen expression and enhancement of chemotherapy-induced apoptosis.

A Sublime Technique to Solve DNA-Repair Model

Deoxyribonucleic acid (DNA) is an essential macromolecule for all known varieties of life and its damage is a life-threatening structure. The DNA double-strand breaks (DSBs) are considered as one of the most rigorous kinds of DNA damage and an error in its repairing mechanism stimulates cancer and also causes lethality in cells with various genetic disorders. In this article, we have exhibited a numerical solution of an ordinary differential equation based biological model to overcome the error for estimating the average number of DSBs per cell time. This model is called DNA repair Model (DRM) and to solve this model a Modified Adomian decomposition method with new polynomials (MADMNP) is applied. The convergence of the aforesaid method is established and the order of error is also dissertated. To solve DRM, this method provides an improved scheme to estimate the average number of DSBs per cell time in comparison to Adomain decomposition method (ADM) and Laplace ADM with Pad`e approximation (LADM-Pad`e). In this respect, a comparison table and a two-dimensional comparison graph are provided by considering a numerical example.

Early vascular ageing in chronic kidney disease: impact of inflammation, vitamin K, senescence and genomic damage.

Chronic kidney disease (CKD) is a clinical model of premature ageing characterized by cardiovascular disease, persistent uraemic inflammation, osteoporosis muscle wasting and frailty. The accelerated early vascular ageing (EVA) process mediated by medial vascular calcification (VC) is a hallmark of senescence as well as a strong predictor of cardiovascular morbidity and mortality in the CKD population. Current clinical therapeutic strategies and novel treatments for VC have not yet been proven to prevent or reverse VC progression in patients with CKD. Knowledge of the fundamental mechanism underlying EVA is urgently needed to identify and develop novel and efficient therapeutic targets for VC and EVA. An accumulating body of evidence indicates that deoxyribonucleic acid (DNA) damage–induced cellular senescence and ‘inflammaging’ may largely contribute to such pathological conditions characterized by accelerated EVA. Growing evidence shows that nuclear factor erythroid 2–related factor 2 (NRF2) signalling and vitamin K play a crucial role in counteracting oxidative stress, DNA damage, senescence and inflammaging, whereby NRF2 activation and vitamin K supplementation may provide a novel treatment target for EVA. In this review we discuss the link between senescence and EVA in the context of CKD, with a focus on the role of NRF2 and vitamin K in DNA damage signalling, senescence and inflammaging.

A new open-source GPU-based microscopic Monte Carlo simulation tool for the calculations of DNA damages caused by ionizing radiation - Part II: sensitivity and uncertainty analysis.

Calculations of deoxyribonucleic acid (DNA) damages involve many parameters in the computation process. As these parameters are often subject to uncertainties, it is of central importance to comprehensively quantify their impacts on DNA single-strand break (SSB) and double-strand break (DSB) yields. This has been a challenging task due to the required large number of simulations and the relatively low computational efficiency using CPU-based MC packages. In this study, we present comprehensive evaluations on sensitivities and uncertainties of DNA SSB and DSB yields on 12 parameters using our GPU-based MC tool, gMicroMC. We sampled one electron at a time in a water sphere containing a human lymphocyte nucleus and transport the electrons and generated radicals until 2Gy dose was accumulated in the nucleus. We computed DNA damages caused by electron energy deposition events in the physical stage and the hydroxyl radicals at the end of the chemical stage. We repeated the computations by varying 12 parameters: (a) physics cross section, (b) cutoff energy for electron transport, (c)-(e) three branching ratios of hydroxyl radicals in the de-excitation of excited water molecules, (f) temporal length of the chemical stage, (g)-(h) reaction radii for direct and indirect damages, (i) threshold energy defining the threshold damage model to generate a physics damage, (j)-(k) minimum and maximum energy values defining the linear-probability damage model to generate a physics damage, and (l) probability to generate a damage by a radical. We quantified sensitivity of SSB and DSB yields with respect to these parameters for cases with 1.0 and 4.5keV electrons. We further estimated uncertainty of SSB and DSB yields caused by uncertainties of these parameters. Using a threshold of 10% uncertainty as a criterion, threshold energy in the threshold damage model, maximum energy in the linear-probability damage model, and probability for a radical to generate a damage were found to cause large uncertainties in both SSB and DSB yields. The scaling factor of the cross section, cutoff energy, physics reaction radius, and minimum energy in the linear-probability damage model were found to generate large uncertainties in DSB yields. We identified parameters that can generate large uncertainties in the calculations of SSB and DSB yields. Our study could serve as a guidance to reduce uncertainties of parameters and hence uncertainties of the simulation results.

BRCA Mutational Status is a Promising Predictive Biomarker for Platinum- based Chemotherapy in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) can be distinguished from other breast malignancies by the lack of expression of estrogen receptors (ER), progesterone receptors (PR) as well as human epidermal growth factor receptor 2 (HER2). TNBC is associated with adverse clinical outcomes and high risk of metastasis. Currently, several clinical and translational reports are focusing on developing targeted therapies for this aggressive cancer. In addition to approved targeted drugs such as poly(ADP-ribose) polymerase inhibitors (PARPi) and immune-checkpoint inhibitors, platinum-based chemotherapy is still a cornerstone therapeutic option in TNBC. However, despite the observed improved outcomes with platinum- based chemotherapy in TNBC, there is still a large proportion of patients who do not respond to this treatment, hence, the need for predictive biomarkers to stratify TNBC patients and therefore, avoiding unwanted toxicities of these agents. With the emergence of genetic testing, several recent studies suggested mutations in breast cancer susceptibility gene (BRCA) in TNBC patients as important predictors of outcomes. These mutations alter the homologous recombination repair (HRR) mechanisms leading to genomic instability. Consequently, sensitivity to platinum-based treatments in this subpopulation of TNBC patients may be explained by cell death enhanced by deoxyribonucleic acid (DNA) damage induced by these potent anticancer drugs. Through this paper, we review several recent studies on this topic to better understand the mechanisms and discuss the potential of BRCA mutational status as a predictive biomarker of platinum-based chemotherapy in TNBC.

Deoxyribonucleic acid damage and its detection

Deoxyribonucleic acid damage and its detection

Minibeam radiation therapy: A micro‐ and nano‐dosimetry Monte Carlo study

Minibeam radiation therapy (MBRT) is an innovative strategy based on a distinct dose delivery method that is administered using a series of narrow (submillimetric) parallel beams. To shed light on the biological effects of MBRT irradiation, we explored the micro- and nanodosimetric characteristics of three promising MBRT modalities (photon, electron, and proton) using Monte Carlo (MC) calculations. Irradiation with proton (100MeV), electron (300MeV), and photon (effective energy of 69keV) minibeams were simulated using Geant4 MC code and the Geant4-DNA extension, which allows the simulation of energy transfer points with nanometric accuracy. As the target of the simulations, cells containing spherical nuclei with or without a detailed description of the DNA (deoxyribonucleic acid) geometry were placed at different depths in peak and valley regions in a water phantom. The energy deposition and number of events in the cell nuclei were recorded in the microdosimetry study, and the number of DNA breaks and their complexity were determined in the nanodosimetric study, where a multi-scale simulation approach was used for the latter. For DNA damage assessment, an adapted DBSCAN clustering algorithm was used. To compare the photon MBRT (xMBRT), electron MBRT (eMBRT), and proton MBRT (pMBRT) approaches, we considered the treatment of a brain tumor located at a depth of 75mm. Both mean energy deposition at micrometric scale and DNA damage in the "valley" cell nuclei were very low as compared with these parameters in the peak region at all depths for xMBRT and at depths of 0 to 30mm and 0 to 50mm for eMBRT and pMBRT, respectively. Only the charged minibeams were favorable for tumor control by producing similar effects in peak and valley cells after 70mm. At the micrometer scale, the energy deposited per event pointed to a potential advantage of proton beams for tumor control, as more aggressive events could be expected at the end of their tracks. At the nanometer scale, all three MBRT modalities produced direct clustered DNA breaks, although the majority of damage (>93%) was composed of isolated single strand breaks. The pMBRT led to a significant increase in the proportion of clustered single strand breaks and double-strand breaks at the end of its range as compared to the entrance (7% at 75mm vs 3% at 10mm) in contrast to eMBRT and xMBRT. In the latter cases, the proportions of complex breaks remained constant, irrespective of the depth and region (peak or valley). Enhanced normal tissue sparing can be expected with these three MBRT techniques. Among the three modalities, pMBRT offers an additional gain for radioresistant tumors, as it resulted in a higher number of complex DNA damage clusters in the tumor region. These results can aid understanding of the biological mechanisms of MBRT.

One-electron oxidation of TAT-motif triplex DNA and the ensuing Hoogsteen hydrogen-bonding dissociation.

One-electron oxidation of adenine (A) leads initially to the formation of adenine radical cation (A•+). Subsequent deprotonation of A•+ can provoke deoxyribonucleic acid (DNA) damage, which further causes senescence, cancer formation, and even cell death. However, compared with considerable reports on A•+ reactions in free deoxyadenosine (dA) and duplex DNA, studies in non-B-form DNA that play critical biological roles are rare at present. It is thus of vital importance to explore non-B-form DNA, among which the triplex is an emerging topic. Herein, we investigate the deprotonation behavior of A•+ in the TAT triplex with continuous A bases by time-resolved laser flash photolysis. The rate constants for the one-oxidation of triplex 8.4 × 108 M-1 s-1 and A•+ deprotonation 1.3 × 107 s-1 are obtained. The kinetic isotope effect of A•+ deprotonation in the TAT triplex is 1.8, which is characteristic of a direct release of the proton into the solvent similar to free base dA. It is thus elucidated that the A•+ proton bound with the third strand is most likely to be released into the solvent because of the weaker Hoogsteen H-bonding interaction and the presence of the highly mobile hydration waters within the third strand. Additionally, it is confirmed through Fourier transform infrared spectroscopy that the deprotonation of A•+ results in the dissociation of the third strand and disruption of the secondary structure of the triplex. These results provide valuable kinetic data and in-depth mechanistic insights for understanding the adenine oxidative DNA damage in the triplex.

Alkaline Comet Assay as a Predictor of DNA Damage in Medical Radiation Workers

The study was aimed to examine the deoxyribonucleic acid (DNA) damage level between medical and non-medical radiation workers using the comet assay method. The radiation-exposed group (29 subjects) and the control group (29 subjects) were chosen from the administration staff. The assessment of single-strand DNA damage hosted by peripheral blood lymphocyte was performed using the alkaline comet assay, the tail length and long-tailed DNA were measured to detect the DNA damage. An independent sample t-test was used to assess the statistical difference between groups. The results showed that comet tail length mean measured in the exposed worker’s group was 25.57±4.4 μm whereas the mean percentage of long-tailed DNA was 6.97±1.53. In the control group, the mean tail length was 23.15±7.57 μm and the long-tailed nucleus percentage was 5.65±1.99. Mean values for the tail length measured were no significantly higher in the exposed group compared to the control group (P=0.15), whereas the percentage of long-tailed nuclei was significantly higher in the exposed group compared to the control group (P=0.007) . The observed single-strand DNA can be measured by using the alkaline comet assay. The DNA damage can be influenced by radiation exposure in medical radiation workers.