Effects Of DNA Damage Research Articles

A Eukaryote-Featured Membrane Phospholipid Enhances Bacterial Formaldehyde Tolerance and Assimilation of One-Carbon Feedstocks.

Efficient bioassimilation of one-carbon (C1) feedstocks is often hindered by the toxicity of C1 substrates and/or intermediates. We compared the toxicity of several common C1 substrates/intermediates and found that formaldehyde imposes the highest toxicity on the representative bacterium Escherichia coli. Besides causing chromosomal DNA and protein damage effects, here, we revealed that formaldehyde greatly impairs cell membranes. To this end, here, we sought to remodel the cell membrane of E. coli by introducing a non-native, eukaryote-featured membrane phospholipid composition, phosphatidylcholine (PC). This engineered E. coli strain exhibited significantly increased membrane integrity, resulting in enhanced formaldehyde tolerance. When applied to C1 assimilation, the PC-harboring E. coli consumed up to 4.7 g/L methanol, which is 23-fold higher than that of the control strain (0.2 g/L). In summary, the present study highlights the detrimental impact of formaldehyde-induced membrane damage and thus underscores the significance of membrane remodeling in enhancing formaldehyde tolerance and facilitating the assimilation of C1 substrates.

Effect of Mexel®432 on DNA Damage in Haliotis Discus Hannai and Mesocentrotus Nudus

Mexel®432 is a surfactant-like substance that is a biosuppressant against marine fouling organisms. Therefore, to study the toxic effect of Mexel®432 on marine organisms, the wrinkled abalone and echinococcus was exposed to concentrations of 0.175 mg·L-1, 0.350 mg·L-1, 0.700 mg·L-1, 0.275 mg·L-1, 0.550 mg∙L−1, 1.100 mg·L-1 Mexel®432 solution, and single-cell gel electrophoresis (comet experiment) was used to detect different exposure times (0, 10, 20 d) DNA damage effect of digestive gland cells and echinococcus pallidae intestinal cells in wrinkled disc abalone, and tail DNA content, tail length, tail distance, and Olive tail distance were used as evaluation indexes. The results showed that different concentrations of Mexel®432 could cause DNA disintegration and tailing in digestive gland cells and intestinal cells in a short period of time (10 d), and with the increase of Mexel®432 concentration and the extension of exposure time, DNA deformation was obvious, the fragmentation increased, and the degree of damage was aggravated. When the concentration of Mexel®432 reaches 0.350 mg·L-1, it produces certain genotoxicity to the digestive gland cells of wrinkled abalone, and when the concentration of Mexel®432 reaches 1.1000 mg·L-1, it also has certain genotoxicity to the intestinal cells of Mesocentrotus nudus. The experimental results showed that Mexel®432 had a significant dose effect relationship on DNA damage in the cells of two biological tissues.

Effect of CAT gene polymorphism on sensitivity of human lymphocytes to genotoxic effect of organochlorine pesticide in vitro

Introduction. Over recent decades, toxicogenetic studies have focused on the issues of genome instability under the action of genotoxicants, taking into account biomarkers of sensitivity. The question about the genotoxic potential of chlorpyrifos remains open, since both positive and negative effects have been revealed in various tests. The aim of the study is the investigation of sensitivity of donor peripheral blood lymphocytes to chlorpyrifos in vitro and evaluation of the contribution of polymorphism of antioxidant defense system genes (CAT (rs1001179), SOD2 (rs4880)) to the response of human cells to the action of genotoxicant. Materials and methods. The DNA damaging effect of chlorpyrifos was assessed on lymphocytes from fifty two donors using DNA-comet assay with metabolic activation (+S9) and without it (–S9). The study of cytotoxic effects of chlorpyrifos on human lymphocytes was carried out using an automatic fluorescent cell analyzer ADAMII LS. Results. Chlorpyrifos had a pronounced cytotoxic effect on lymphocytes in most donors in the absence of metabolic activation system. With increasing concentration of the pesticide in the medium and time of cultivation, the viability of lymphocytes decreased, and the proportion of cells in late apoptosis and necrosis increased. Positive genotoxic effects were found on the cells of 33 donors (-S9). In the presence of the S9, mild but statistically significant effects were detected only on cells from 2 donors. % DNA values in the comet tail after exposure to the pesticide varied for cells from different donors. In the absence of metabolic activation, a statistically significant increase in the level of DNA damage was found in cells of individuals with genotype AA (homozygote for the minor allele) for the CAT G262A catalase gene (rs1001179), compared with homozygote for the dominant GG allele. Limitations. The genotoxicity of chlorpyryfos was studied in vitro. Conclusion. The results of the study shown cytotoxic and genotoxic effects of chlorpyrifos. The sensitivity of lymphocytes from different donors to the pesticide was found to be significantly different. The association of the level of DNA damage under exposure of chlorpyrifos in vitro with the G262A polymorphism of the catalase gene was found. The research also confirms the possibility of using a model test-system with peripheral blood lymphocytes to assess the potential genetic risk for humans and to study the contribution of gene polymorphism to individual sensitivity to the action of genotoxicants.

An RNA damage response network mediates the lethality of 5-FU in colorectal cancer

5-fluorouracil (5-FU), a major anti-cancer therapeutic, is believed to function primarily by inhibiting thymidylate synthase, depleting deoxythymidine triphosphate (dTTP), and causing DNA damage. Here, we show that clinical combinations of 5-FU with oxaliplatin or irinotecan show no synergy in human colorectal cancer (CRC) trials and sub-additive killing in CRC cell lines. Using selective 5-FU metabolites, phospho- and ubiquitin proteomics, and primary human CRC organoids, we demonstrate that 5-FU-mediated CRC cell killing primarily involves an RNA damage response during ribosome biogenesis, causing lysosomal degradation of damaged rRNAs and proteasomal degradation of ubiquitinated ribosomal proteins. Tumor types clinically responsive to 5-FU treatment show upregulated rRNA biogenesis while 5-FU clinically non-responsive tumor types do not, instead showing greater sensitivity to 5-FU's DNA damage effects. Finally, we show that treatments upregulating ribosome biogenesis, including KDM2A inhibition, promote RNA-dependent cell killing by 5-FU, demonstrating the potential for combinatorial targeting of this ribosomal RNA damage response for improved cancer therapy.

HUC-MSC-derived exosomes repaired the damage induced by hydroquinone to 16HBE cells via miR-221/PTEN pathway

Mesenchymal stem cell - originated exosomes (MSC-exo) are promising non-cellular treatment agents for various diseases. The present study aimed to explore whether human umbilical cord MSC - originated exosomes (HUC-MSC-exo) have the function of protecting human cells (16HBE) against the damage caused by HQ and the related mechanism. HUC-MSC-exo was isolated with differential gradient ultracentrifugation method and characterized by using transmission electron microscope (TEM). 16HBE cells were used as the tool cells and co-cultured with HUC-MSC-exo. Confocal laser scanning microscope was employed to confirm the ingestion of HUC-MSC-exo by 16HBE. Cell proliferation, migration, oxidative stress, DNA and chromosome damages of 16HBE were analyzed under HQ stress, and the role of miR-221/PTEN axis was investigated. Our data showed that under HQ stress, different groups of cells exhibited significantly decreased proliferation and migration abilities, and significant oxidative stress, DNA and chromosome damage effects. HUC-MSC-exo could alleviate the cytotoxic, oxidative stress and genotoxic damage effects of HQ on 16HBE cells. Mechanistically, HQ exposure up-regulated the level of miR-221 and down-regulated PTEN, while HUC-MSC-exo could significantly reduce the level of miR-221 and promote PTEN expression, which was involved in alleviating the toxic effects of HQ on 16HBE cells. Our data indicates that HUC-MSC-exo can alleviate the oxidative stress, cytotoxic and genotoxic effects of HQ on 16HBE cells via miR-221/PTEN pathway, and it may be a promising agent for protecting against the toxicity of HQ.

Changing of gamma-H2AX in peripheral blood mononuclear cells during concurrent chemoradiation in locally advanced rectal cancer patients: a potential response predictor.

The most detrimental effect of DNA damage from radiation is DNA double-strand breaks, making it critical to identify reliable biomarkers for treatment response in cancer therapy. Gamma-H2AX (γ-H2AX), a marker of DNA double-strand breaks, was evaluated in this study as a potential biomarker for treatment response in locally advanced rectal cancer patients undergoing preoperative concurrent chemoradiation (CCRT). Thirty patients with locally advanced rectal cancer received preoperative CCRT. Peripheral blood mononuclear cells (PBMCs) were collected at five time points: baseline, 24 hours after the first radiation fraction, mid-treatment, end of treatment, and six weeks post-CCRT. γ-H2AX levels were measured in these samples. MRI was used to assess treatment response based on magnetic resonance tumor regression grade (mrTRG). Patients were classified as responders or non-responders based on mrTRG. T-test and repeated measures analysis of variance (ANOVA) evaluated dynamic changes in γ-H2AX levels, and a multilevel linear regression model analyzed the relationship between γ-H2AX levels and treatment response. Nineteen out of thirty patients (63.33%) were classified as responders. Significant dynamic changes in γ-H2AX levels were observed between non-responders and responders (P=0.01). The multilevel linear regression model showed a trend towards increased γ-H2AX levels in responders [1.17, 95% confidence interval (CI): -0.02 to 2.34, P=0.053]. Significant differences in γ-H2AX levels were observed from baseline to mid-treatment, end of treatment, and six weeks post-CCRT. Pathologic complete response (pCR) after CCRT was associated with significantly higher γ-H2AX ratios compared to those without pCR (P=0.04). However, no significant difference was identified in the multilevel linear regression model. γ-H2AX may have potential as a biomarker for treatment response in locally advanced rectal cancer patients undergoing preoperative CCRT, although further validation is required.

The Allium cepa comet assay for environmental sample assessment: a scoping review.

The purposes of this review were to investigate the application of the comet assay in Allium cepa root cells to assess the genotoxicity of environmental samples and to analyse the experimental procedures employed. A literature search was performed selecting articles published between January 2000 and October 2023 from online databases using the combined search terms 'comet assay' and 'A. cepa'. Only 18 papers met the inclusion criteria. None of these were published in the first eight years (2000-2007), highlighting the increasing interest in using the comet assay on A. cepa to analyse environmental samples over the last decade. The majority of the selected studies (15/18, 83%) were performed on samples belonging to the water compartment on onion bulbs. Half of the selected studies (9/18) were conducted to demonstrate the DNA damaging effect of the sample, while the other half of the studies not only recognized the presence of genotoxic agents but also addressed possible remediation measures. Detailed analysis of the experimental procedures revealed heterogeneity in many key steps, such as exposure time, test controls, nuclei isolation solutions, duration of electrophoresis, and number of nuclei scored. This literature review has shown that the comet assay on A. cepa, although recognized as an appropriate tool, is underutilized in environmental toxicology. Greater standardization could lead to its more widespread use, providing valuable information on the genotoxicity of environmental samples and the ability of different processes to mitigate their negative effects on plants.

Design of a hybrid nanoscaled skin photoprotector by boosting the antioxidant properties of food waste-derived lignin through molecular combination with TiO2 nanoparticles

TiO2 nanoparticles loaded with pistachio shell lignin (8 % and 29 % w/w) were prepared by a hydrothermal wet chemistry approach. The efficient interaction at the molecular level of the biomacromolecule and inorganic component was demonstrated by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–Visible (UV–Vis), Fourier transform infrared (FT-IR), dynamic light scattering (DLS), and electron paramagnetic resonance (EPR) analysis. The synergistic combination of lignin and TiO2 nanoparticles played a key role in the functional properties of the hybrid material, which exhibited boosted features compared to the separate organic and inorganic phase. In particular, the hybrid TiO2-lignin nanoparticles showed a broader UV–Vis protection range and remarkable antioxidant performance in aqueous media. They could also better protect human skin explants from the DNA damaging effect of UV radiations compared to TiO2 as indicated by lower levels of p-H2A.X, a marker of DNA damage, at 6 h from exposure. In addition, the samples could protect the skin against the structural damage occurring 24 h post UV radiations by preventing the loss of keratin 10. These results open new perspectives in the exploitation of food-waste derived phenolic polymers for the design of efficient antioxidant materials for skin photoprotection in a circular economy perspective.

Exploring the LET dependence of DNA DSB repair kinetics using the DR DNA database.

The repair of DNA double-strand breaks is a crucial yet delicate process which is affected by a multitude of factors. In this study, our goal is to analyse the influence of the linear energy transfer (LET) on the DNA repair kinetics. By utilizing the database of repair of DNA and aggregating the results of 84 experiments, we conduct various model fits to evaluate and compare different hypothesis regarding the effect of LET on the rejoining of DNA ends. Despite the considerable research efforts dedicated to this topic over the past decades, our findings underscore the complexity of the relationship between LET and DNA repair kinetics. This study leverages big data analysis to capture overall trends that single experimental studies might miss, providing a valuable model for understanding how radiation quality impacts DNA damage and subsequent biological effects. Our results highlight the gaps in our current understanding, emphasizing the pressing need for further investigation into this phenomenon.

Conserved cysteine-switches for redox sensing operate in the cyclin-dependent kinase inhibitor p21(CIP/KIP) protein family

The cell cycle is a tightly regulated, dynamic process controlled by multiple checkpoints. When the prevention of cell cycle progression is needed, key effectors such as members of the p21 (CIP/KIP) inhibit cyclin-dependent kinases (CDKs). It is accepted that p21 does not sense DNA damage and that stress signals affect p21 indirectly. A plethora of DNA damaging events activate the tumor suppressor p53, which in turn transcriptionally activates p21, steeply changing its levels to reach CDK inhibition. The levels of p21 are also controlled by phosphorylation and ubiquitination events, which are relevant as they modulate p21 activity, localization, and stability. Intriguingly, here we report the first evidence of the direct control of p21 cell proliferation inhibition by DNA damaging signals. Specifically, we have identified a redox regulating mechanism that controls p21 capacity to reduce cell proliferation. Using the human p21 protein, we identified two cysteine-switches that independently regulate its cyclin-binding and linker (LH) modules respectively. Additionally, we provide a mechanistic explanation of how reactive cysteines embedded in unstructured regions of intrinsically disordered proteins respond to ROS without the guidance of protein structure, contributing to a vastly unexplored area of research. Cellular experiments utilizing p21KID mutants that disrupt disulfide-based switches demonstrate their impact on the capacity of p21 to inhibit cell cycle progression, thus highlighting the functional relevance of our findings. Furthermore, our investigation reveals that reactive cysteine residues are highly conserved across the Kinase Inhibitory Domain (KID) sequences of p21 proteins from higher eukaryotes, and the p27 and p57 human paralogs. We propose that the presence of conserved regulatory cysteines within the KIDs of p21 family members from multiple taxa provides those proteins with the capability for directly sensing ROS, enabling the direct regulation of cyclin kinase activity by ROS levels.

GL-V9 synergizes with oxaliplatin of colorectal cancer via Wee1 degradation mediated by HSP90 inhibition.

GL-V9 exhibited anti-tumour effects on various types of tumours. This study aimed to verify if GL-V9 synergized with oxaliplatin in suppressing colorectal cancer (CRC) and to explore the synergistic mechanism. The synergy effect was tested by MTT assays and the mechanism was examined by comet assay, western blotting and immunohistochemistry (IHC). Xenograft model was constructed to substantiated the synergy effect and its mechanism in vivo. GL-V9 was verified to enhance the DNA damage effect of oxaliplatin, so as to synergistically suppress colon cancer cells in vitro and in vivo. In HCT-116 cells, GL-V9 accelerated the degradation of Wee1 and induced the abrogation of cell cycle arrest and mis-entry into mitosis, bypassing the DNA damage response caused by oxaliplatin. Our findings suggested that GL-V9 binding to HSP90 was responsible for the degradation of Wee1 and the vulnerability of colon cancer cells to oxaliplatin. Functionally, overexpression of either HSP90 or WEE1 annulled the synergistic effect of GL-V9 and oxaliplatin. Collectively, our findings revealed that GL-V9 synergized with oxaliplatin to suppress CRC and displayed a promising strategy to improve the efficacy of oxaliplatin.

Multi-biomarker approach reveals the effects of heavy metal bioaccumulation in the foundation species Prosopis laevigata (Fabaceae).

Mining is a major economic activity in many developing countries. However, it disturbs the environment, producing enormous quantities of waste, known as mine tailings, which can have deleterious environmental impact, due to their high heavy metals (HM) content. Often, foundation species that establish on mine tailings are good candidates to study the effects of HM bioaccumulation at different levels of biological organization. Prosopis laevigata is considered a HM hyperaccumulator which presents attributes of a foundation species (FS) and establishes naturally on mine tailings. We evaluated the bioaccumulation of Cu, Pb, and Zn in P. laevigata foliar tissue, the leaf micro- and macro-morphological characters, DNA damage, and population genetic effects. In total, 80 P. laevigata individuals (20/site) belonging to four populations: The individuals from both sites (exposed and reference) bioaccumulated HMs (Pb > Cu > Zn). However, in the exposed individuals, Pb and Cu bioaccumulation was significantly higher. Also, a significant effect of macro- and micro-morphological characters was registered, showing significantly lower values in individuals from the exposed sites. In addition, we found significant differences in genotoxic damage in P. laevigata individuals, between the exposed and reference sites. In contrast, for the micro-morphological characters, none of the analyzed metals had any influence. P. laevigata did not show significant differences in the genetic structure and diversity between exposed and reference populations. However, four haplotypes and four private alleles were found in the exposed populations. Since P. laevigata is a species that establishes naturally in polluted sites and bioaccumulates HM in its foliar tissues, the resulting genetic, individual and population effects have not been severe enough to show detrimental effects; hence, P. laevigata can be a useful tool in phytoremediation strategies for soils polluted with Pb and Cu, maintaining its important ecological functions.

Sponge-derived alkaloid AP-7 as a sensitizer to cisplatin in the treatment of multidrug-resistant NSCLC via Chk1-dependent mechanisms.

Multidrug resistance is a substantial obstacle in treating non-small cell lung cancer (NSCLC) with therapies like cisplatin (DDP)-based adjuvant chemotherapy and EGFR-tyrosine kinase inhibitors (TKIs). Aaptamine-7 (AP-7), a benzonaphthyridine alkaloid extracted from Aaptos aaptos sponge, has been shown to exhibit a broad spectrum of anti-tumor activity. However, the anti-cancer activity of AP-7 in combination with DDP and its molecular mechanisms in multidrug-resistant NSCLC are not yet clear. Our research indicates that AP-7 bolsters the growth inhibition activity of DDP on multidrug-resistant NSCLC cells. AP-7 notably disrupts DDP-induced cell cycle arrest and amplifies DDP-induced DNA damage effects in these cells. Furthermore, the combination of AP-7 and DDP downregulates Chk1 activation, interrupts the DNA damage repair-dependent Chk1/CDK1 pathway, and helps to overcome drug resistance and boost apoptosis in multidrug-resistant NSCLC cells and a gefitinib-resistant xenograft mice model. In summary, AP-7 appears to enhance DDP-induced DNA damage by impeding the Chk1 signaling pathway in multidrug-resistant NSCLC, thereby augmenting growth inhibition, both in vitro and in vivo. These results indicate the potential use of AP-7 as a DDP sensitizer in the treatment of multidrug-resistant NSCLC.

Assessing the antioxidant properties of Naringin and Rutin and investigating their oxidative DNA damage effects in breast cancer

This work examines the capacity of Naringin and Rutin to influence the DNA damage response (DDR) pathway by investigating their interactions with key DDR proteins, including PARP-1, ATM, ATR, CHK1, and WEE1. Through a combination of in silico molecular docking and in vitro evaluations, we investigated the cytotoxic and genotoxic effects of these compounds on MDA-MB-231 cells, comparing them to normal human fibroblast cells (2DD) and quiescent fibroblast cells (QFC). The research found that Naringin and Rutin had strong affinities for DDR pathway proteins, indicating their capacity to specifically regulate DDR pathways in cancer cells. Both compounds exhibited preferential cytotoxicity towards cancer cells while preserving the vitality of normal 2DD fibroblast cells, as demonstrated by cytotoxicity experiments conducted at a dose of 10 µM. The comet experiments performed particularly on QFC cells provide valuable information on the genotoxic impact of Naringin and Rutin, highlighting the targeted initiation of DNA damage in cancer cells. The need to use precise cell models to appropriately evaluate toxicity and genotoxicity is emphasized by this discrepancy. In addition, ADMET and drug-likeness investigations have emphasized the pharmacological potential of these compounds; however, they have also pointed out the necessity for optimization to improve their therapeutic profiles. The antioxidant capabilities of Naringin and Rutin were assessed using DPPH and free radical scavenging assays at a concentration of 10 µM. The results confirmed that both compounds have a role in reducing oxidative stress, hence enhancing their anticancer effects. Overall, Naringin and Rutin show potential as medicines for modulating the DDR in cancer treatment. They exhibit selective toxicity towards cancer cells while sparing normal cells and possess strong antioxidant properties. This analysis enhances our understanding of the therapeutic uses of natural chemicals in cancer treatment, supporting the need for more research on their mechanisms of action and clinical effectiveness.

Preparation of Dearomatized p-Coumaric Acid Derivatives as DNA Damage Response Inhibitors with Potent In Vitro Antitumor Effect.

Our research group previously identified graviquinone (1) as a promising antitumor metabolite that is formed in situ when the antioxidant methyl caffeate scavenges free radicals. Furthermore, it exerted a DNA damaging effect on cancer cells and a DNA protective effect on normal keratinocytes. To expand and explore chemical space around qraviquinone, in the current work we synthesized 9 new alkyl-substituted derivatives and tested their in vitro antitumor potential. All new compounds bypassed ABCB1-mediated multidrug resistance and showed highly different cell line specificity compared with 1. All compounds were more potent in MDA-MB-231 than on MCF-7 cells. The n-butyl-substituted derivatives 2 and 8 modulated the cell cycle and inhibited the ATR-mediated phosphorylation of checkpoint kinase-1 in MCF-7 cells. As a significant expansion of our previous findings, our results highlight the potential antitumor value of alkyl-substituted graviquinone derivatives.

Ethyl pyruvate attenuates cellular adhesion and proliferation of diffuse large B-cell lymphoma by targeting c-Jun.

Diffuse large B-cell lymphoma (DLBCL) stands out as the most common type of malignant cancer, representing the majority of cases of non-Hodgkin's lymphoma. Ethyl pyruvate (EP) is a derivative of pyruvic acid and found to have potent anti-tumor properties. Despite its potential benefits, the impact of EP on DLBCL remains ambiguous. Our objective is to elucidate the role of EP in modulating the development of DLBCL. Analysis of cholecystokinin-8 (CCK-8) revealed that treatment with EP significantly diminished the viability of DLBCL cells. Furthermore, EP administration suppressed colony formation and hindered cell adhesion and invasion in DLBCL cells. Examination of cell cycle progression showed that EP treatment induced arrest at the G1 phase and subsequently reduced the S phase population in DLBCL cells. EP treatment consistently exhibited apoptosis-inducing properties in Annexin-V assays, and notably downregulated the expression of Bcl-2 while increasing levels of proapoptotic cleaved caspase 3 and BAX in DLBCL cells. Additionally, EP treatment decreased the overexpression of c-Jun in c-Jun-transfected DLBCL cells. Further, EP demonstrated DNA-damaging effects in TUNEL assays. In vivo, xenograft animal models revealed that EP treatment significantly mitigated DLBCL tumor growth and suppressed DLBCL cell adhesion to bone marrow stromal cells. In summary, these findings suggest that EP mitigates DLBCL progression by inducing apoptosis, inducing cell cycle arrest, and promoting DNA damage.

Comparative evaluation of zinc oxide nanoparticles (ZnONPs): Photocatalysis, antibacterial, toxicity and genotoxicity

This study compares the physicochemical, photocatalytic, antimicrobial, toxicity and genotoxic properties of zinc oxide nanoparticles (ZnONPs) produced by hydrothermal and sol–gel methods as an alternative biomaterial. The comparative antibacterial activities, toxicity and DNA damage effects of ZnONPs on Drosophila melanogaster were determined using different doses. The study also investigates the effects of ZnONPs on malondialdehyde (MDA) and glutathione (GSH) levels, as well as superoxide dismutase (SOD) and catalase (CAT) activity. The structural, optical, and morphological properties of ZnONPs were investigated using X-ray diffractometer (XRD), UV–Visible spectrophotometry (UV–Vis), and field emission scanning electron microscopy (FESEM). The photocatalytic activity of ZnONPs in methylene blue solution was determined, and a high photocatalytic efficiency of 87 % was achieved in a short time. ZnONPs were found to have a significant antimicrobial effect on Streptococcus mutans ATCC 10449. Additionally, ZnONPs were non-toxic doses and did not cause DNA damage. In conclusion, ZnONPs synthesized can be safely used as filling material and bracket material especially in the field of dentistry since they are non-toxic, have a strong antimicrobial effect on S. mutans and do not cause DNA damage.

Simulation of Radiation-Induced DNA Damage and Protection by Histones Using the Code RITRACKS.

(1) Background: DNA damage is of great importance in the understanding of the effects of ionizing radiation. Various types of DNA damage can result from exposure to ionizing radiation, with clustered types considered the most important for radiobiological effects. (2) Methods: The code RITRACKS (Relativistic Ion Tracks), a program that simulates stochastic radiation track structures, was used to simulate DNA damage by photons and ions spanning a broad range of linear energy transfer (LET) values. To perform these simulations, the transport code was modified to include cross sections for the interactions of ions or electrons with DNA and amino acids for ionizations, dissociative electron attachment, and elastic collisions. The radiochemistry simulations were performed using a step-by-step algorithm that follows the evolution of all particles in time, including reactions between radicals and DNA structures and amino acids. Furthermore, detailed DNA damage events, such as base pair positions, DNA fragment lengths, and fragment yields, were recorded. (3) Results: We report simulation results using photons and the ions 1H+, 4He2+, 12C6+, 16O8+, and 56Fe26+ at various energies, covering LET values from 0.3 to 164 keV/µm, and performed a comparison with other codes and experimental results. The results show evidence of DNA protection from damage at its points of contacts with histone proteins. (4) Conclusions: RITRACKS can provide a framework for studying DNA damage from a variety of ionizing radiation sources with detailed representations of DNA at the atomic scale, DNA-associated proteins, and resulting DNA damage events and statistics, enabling a broader range of future comparisons with experiments such as those based on DNA sequencing.

MCF-7 cell - derived exosomes were involved in protecting source cells from the damage caused by tributyltin chloride via transport function

Tributyltin chloride (TBTC) is a ubiquitous environmental pollutant with various adverse effects on human health. Exosomes are cell - derived signaling and substance transport vesicles. This investigation aimed to explore whether exosomes could impact the toxic effects caused by TBTC via their transport function. Cytotoxicity, DNA and chromosome damage caused by TBTC on MCF-7 cells were analyzed with CCK-8, flow cytometry, comet assay and micronucleus tests, respectively. Exosomal characterization and quantitative analysis were performed with ultracentrifugation, transmission electron microscope (TEM) and bicinchoninic acid (BCA) methods. TBTC content in exosomes was detected with Liquid Chromatography-Mass Spectrometry (LC-MS). The impacts of exosomal secretion on the toxic effects of TBTC were analyzed. Our data indicated that TBTC caused significant cytotoxicity, DNA and chromosome damage effects on MCF-7 cells, and a significantly increased exosomal secretion. Importantly, TBTC could be transported out of MCF-7 cells by exosomes. Further, when exosomal secretion was blocked with GW4869, the toxic effects of TBTC were significantly exacerbated. We concluded that TBTC promoted exosomal secretion, which in turn transported TBTC out of the source cells to alleviate its toxic effects. This investigation provided a novel insight into the role and mechanism of exosomal release under TBTC stress.

#2372 Investigating the effects of low-level and transient DNA damage on kidney health in a novel mouse model of aging

Abstract Background and Aims Increasing life expectancy worldwide underscores the importance of addressing the effects of aging on organ and cell function. Aging is characterized by a gradual decline in organ function that varies among individuals and is influenced by lifestyle choices and various external factors that induce DNA stress. This mismatch between kidney aging and an individual's lifespan contributes to the increase in end-stage renal disease. Among the kidney's constituent cells, the proximal tubules are frequently damaged by external factors such as ischemia and drugs. Our research has focused on DNA damage and its repair mechanisms (DDR) caused by these injuries, and we have previously shown that extensive DNA damage beyond the capacity of DDR or abnormalities in DDR cause cellular senescence in proximal tubules, resulting in incomplete renal repair after injury (Kishi et al. Sci Transl Med 2019, J Clin Invest 2019). In this study, we extend these studies and test whether acquired and mild DNA stress induces renal senescence using a novel mouse model of aging, the Inducible Changes to the Epigenome (ICE) mouse (Hayano et al. Cell. 2023). Method ICE mice were generated by mating I-PpoI STOP/+ mice with CreERT2/+ mice. I-PpoI, an endonuclease, cleaves DNA only upon administration of tamoxifen and the resulting DNA damage is subsequently repaired by the DDR. To induce transient DNA damage, 4- to 6-month-old mice were fed a tamoxifen-containing diet for 3 weeks and then housed until they reached 14 months of age. A comprehensive renal analysis was then performed, which included renal tissue evaluation, single-nucleus RNA sequencing, q-PCR, and Western blot analysis for phenotypic analysis of mouse kidneys. Results No significant histological changes were observed in the kidney tissues between the ICE mice and the control group, and the levels of interstitial fibrosis were comparable. To ensure unbiased evaluation, we performed single-nucleus RNA-seq. In ICE mice, there was an increased presence of proximal tubules with incomplete repair expressing KIM-1 and VCAM-1. In addition, ICE mice showed increased gene expression of DNA repair-related enzymes (Mgmt) in proximal tubules and evidence of cellular senescence. No differences in mitochondrial number or biosynthetic capacity were observed. Conclusion The consequences of short-term and transient DNA damage were found to have lasting effects on the kidney. In particular, significant changes were observed in the proximal tubules, where DNA instability and accelerated cellular senescence were evident, suggesting an impaired repair phenotype within the proximal tubules. This may be related to increased susceptibility to various external stimuli. For further detailed analysis, studies using proximal tubule-specific ICE mice are currently performed.