8-oxo-2'-deoxyguanosine suppresses allergy-induced lung tissue remodeling in mice

DNA oxidation after exercise: a systematic review and meta-analysis

Purpose: 8-Hydroxy-2'-deoxyguanosine (8-OHdG) is a byproduct of DNA oxidation resulting from free radical attacks. Paradoxically, treatment with 8-OHdG accelerates tissue healing. The aim of this study is to quantify the 8-OHdG response after a single session of exercise in both trained and untrained adults. Methods: A systematic review and meta-analysis of exercise intervention studies measuring changes in blood 8-OHdG following resistance exercise and aerobic exercise were conducted. The literature search included Web of Science, PubMed, BASE, and Scopus, with publications up to February 2023 included. Subgroup analysis of training status was also conducted. Results: Sixteen studies involving 431 participants met the eligibility criteria. Resistance exercise showed a medium effect on increasing circulating 8-OHdG levels (SMD = 0.66, p < 0.001), which was similar for both trained and untrained participants. However, studies on aerobic exercise presented mixed results. For trained participants, a small effect of aerobic exercise on increasing circulating 8-OHdG levels was observed (SMD = 0.42; p < 0.001). In contrast, for untrained participants, a large effect of decreasing circulating 8-OHdG levels was observed, mostly after long-duration aerobic exercise (SMD = -1.16; p < 0.05). Similar to resistance exercise, high-intensity aerobic exercise (5-45 min, ≥75% VO2max) significantly increased circulating 8-OHdG levels, primarily in trained participants. Conclusion: Pooled results from the studies confirm an increase in circulating 8-OHdG levels after resistance exercise. However, further studies are needed to fully confirm the circulating 8-OHdG response to aerobic exercise. Increases in 8-OHdG after high-intensity aerobic exercise are observed only in trained individuals, implicating its role in training adaptation. Systematic Review Registration: [https://Systematicreview.gov/], identifier [CRD42022324180].

Protective effect of exogenous 8-oxo-2'-deoxyguanosine on Drosophila melanogaster larval stages under heat shock

The influence of exogenous 8-oxo-2'-deoxyguanosine on the development of Drosophila melanogaster under normal conditions, and under the influence of short-term heat shock was studied. It was shown that 8-oxo-2'-deoxyguanosine was not toxic at concentrations of up to 1 μM. A tendency to accelerate larval development and fly emergence was observed under the influence of this compound in our experiments. Short-term heat shock causes a 50-80% decrease in the number of larvae that complete development. The addition of exogenous 8-oxo-2'-deoxyguanosine to the food before thermal influence negates this effect and brings the levels of the imago emergence indicators back to the basal level. The obtained results are further evidence of the possible bioregulatory and adaptogen functions of 8-oxo-2'-deoxyguanosine.

Oxidized Cell-Free DNA Role in the Antioxidant Defense Mechanisms under Stress

The present study focuses on the investigation of the oxidized cell-free DNA (cfDNA) properties in several experimental models, including cultured cerebellum cells, peripheral blood lymphocytes (PBL), plasma, and hippocampus under an acute and chronic unpredictable stress model in rats. Firstly, our study shows that Spectrum Green fluorescence-labeled oxidized cfDNA fragments were transferred into the cytoplasm of 80% of the cerebellum culture cells; meanwhile, the nonoxidized cfDNA fragments do not pass into the cells. Oxidized cfDNA stimulates the antioxidant mechanisms and induction of transcription factor NRF2 expression, followed by an activation of NRF2 signaling pathway genes-rise of Nrf2 and Hmox1 gene expression and consequently NRF2 protein synthesis. Secondly, we showed that stress increases plasma cfDNA concentration in rats corresponding with the duration of the stress exposure. At the same time, our study did not reveal any significant changes of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) level in PBL of rats under acute or chronic stress, probably due to the significantly increased Nrf2 expression, that we found in such conditions. 8-oxodG is one of the most reliable markers of DNA oxidation. We also found an increased level of 8-oxodG in the hippocampal homogenates and hippocampal dentate gyrus in rats subjected to acute and chronic stress. Taken together, our data shows that oxidized cfDNA may play a significant role in systemic and neuronal physiological mechanisms of stress and adaptation.

Therapeutic Effects of Topical 8-Oxo-2'-deoxyguanosine on Ethanol-Induced Ocular Chemical Injury Models

PURPOSE

To evaluate the therapeutic effects of topical 8-oxo-2'-deoxyguanosine (8-oxo-dG) on experimental ocular chemical injury models.

METHODS

We created ocular chemical injury models with 8-week-old BALB/c mice (n = 70) by applying 100% ethanol; the mice were then treated with 8-oxo-dG eye drops 10 and 5 mg/mL and phosphate-buffered saline (PBS) twice daily. After 7 days, clinical findings such as corneal integrity, clarity, and neovascularization were assessed. Histology, immunohistochemistry findings, and inflammatory cytokine levels using real-time polymerase chain reactions in the corneas of the mice were also analyzed.

RESULTS

Topical application of 8-oxo-dG eye drops resulted in a significant improvement of epithelial defects and clarity, dose dependently (each P < 0.001). Inflammatory cell infiltration and corneal stromal edema were also decreased in the 8-oxo-dG-treated mice compared with PBS-treated controls, based on hematoxylin and eosin staining. The expressions of F4/80 and neutrophil elastase-positive inflammatory cells and IL-1 and TNF-α cytokine levels were significantly reduced in the 8-oxo-dG group compared with the PBS group (each P < 0.01).

CONCLUSIONS

Topical 8-oxo-dG application showed an excellent therapeutic effect in ocular chemical injury models by suppressing inflammation.

Oxidatively generated base modifications in DNA: Not only carcinogenic risk factor but also regulatory mark?

The generation of DNA modifications in cells is in most cases accidental and associated with detrimental consequences such as increased mutation rates and an elevated risk of malignant transformation. Accordingly, repair enzymes involved in the removal of the modifications have primarily a protective function. Among the well-established exceptions of this rule are 5-methylcytosine and uracil, which are generated in DNA enzymatically under controlled conditions and fulfill important regulatory functions in DNA as epigenetic marks and in antibody diversification, respectively. More recently, considerable evidence has been obtained that also 8-oxo-7,8-dihydroguanine (8-oxoG), a frequent pro-mutagenic DNA modification generated by endogenous or exogenous reactive oxygen species (ROS), has distinct roles in the regulation of both transcription and signal transduction. Thus, the activation of transcription by the estrogen receptor, NF-κB, MYC and other transcription factors was shown to depend on the presence of 8-oxoG in the promoter regions and its recognition by the DNA repair glycosylase OGG1. The lysine-specific histone demethylase LSD1, which produces H₂O₂ as a by-product, was indentified as a local generator of 8-oxoG in some of these cases. In addition, a complex of OGG1 with the excised free substrate base was demonstrated to act as a guanine nucleotide exchange factor (GEF) for small GTPases such as Ras, Rac and Rho, thus stimulating signal transduction. The various findings and intriguing novel mechanisms suggested will be described and compared in this review.

The role of 8-oxoguanine DNA glycosylase-1 in inflammation

Many, if not all, environmental pollutants/chemicals and infectious agents increase intracellular levels of reactive oxygen species (ROS) at the site of exposure. ROS not only function as intracellular signaling entities, but also induce damage to cellular molecules including DNA. Among the several dozen ROS-induced DNA base lesions generated in the genome, 8-oxo-7,8-dihydroguanine (8-oxoG) is one of the most abundant because of guanine’s lowest redox potential among DNA bases. In mammalian cells, 8-oxoG is repaired by the 8-oxoguanine DNA glycosylase-1 (OGG1)-initiated DNA base excision repair pathway (OGG1–BER). Accumulation of 8-oxoG in DNA has traditionally been associated with mutagenesis, as well as various human diseases and aging processes, while the free 8-oxoG base in body fluids is one of the best biomarkers of ongoing pathophysiological processes. In this review, we discuss the biological significance of the 8-oxoG base and particularly the role of OGG1–BER in the activation of small GTPases and changes in gene expression, including those that regulate pro-inflammatory chemokines/cytokines and cause inflammation.

Expression of airway remodeling proteins in mast cell activated by TGF-β released in OVA-induced allergic responses and their inhibition by low-dose irradiation or 8-oxo-dG

Allergic asthma is characterized by chronic airway remodeling, which is associated with the expression of extracellular matrix proteins (ECM) by TGF-β. However, to date there are no reports demonstrating that structural proteins are directly expressed in mast cells. This study aimed to investigate whether ECM proteins are expressed in mast cells activated with antigen/antibody reaction, and whether the resolution effects of irradiation or 8-oxo-dG may contribute to allergic asthma prevention. Bone marrow-derived mast cells (BMMCs) were activated with DNP-HSA/anti-DNP IgE antibody (act-BMMCs). C57BL/6 mice were sensitized and challenged with ovalbumin (OVA) to induce allergic asthma. Mice were treated orally with 8-oxo-dG or exposed to whole body irradiation (using (137)Cs gamma ray at a dose of 0.5 Gy) for three consecutive days 24 h after OVA challenge. Expression of extracellular matrix (ECM) proteins, TGF-β signaling molecules and NF-κB/AP-1 was determined in the BMMCs, bronchoalveolar lavage (BAL) cells or lung tissues using Western blot, polymerase chain reaction (PCR) and electrophoretic mobility shift assay (EMSA), respectively. Act-BMMCs increased expression of ECM proteins, TGF-β/TGF-β receptor I, TGF-β signaling molecules and cytokines; and increased both NF-κB and AP-1 activity. In addition, the population of mast cells; expression of mast cell markers, TGF-β signaling molecules, ECM proteins/amounts; OVA-specific serum IgE level; numbers of goblet cells; airway hyperresponsiveness; cytokines/chemokines were increased in BAL cells and lung tissues of OVA-challenged mice. All of the above end points were reduced by irradiation or 8-oxo-dG in vitro and in vivo, respectively. The data suggest that mast cells induce expression of ECM proteins through TGF-β produced in inflammatory cells of OVA mice and that post treatment of irradiation or 8-oxo-dG after OVA-challenge may reduce airway remodeling through down-regulating mast cell re-activation by TGF-β/Smad signals.

Foxp3(+)-Treg cells enhanced by repeated low-dose gamma-irradiation attenuate ovalbumin-induced allergic asthma in mice

Gamma radiation is used for several therapeutic indications such as cancers and autoimmune diseases. Low-dose whole-body γ irradiation has been shown to activate immune responses in several ways, however, the effect and mechanism of irradiation on allergic asthma remains poorly understood. This study investigated whether or not irradiation exacerbates allergic asthma responses and its potential mechanism. C57BL/6 mice were sensitized and challenged with ovalbumin (OVA) to induce asthma. The mice received whole-body irradiation once daily for 3 consecutive days with a dose of 0.667 Gy using (137)Cs γ rays 24 h before every OVA challenge. Repeated low-dose irradiation reduced OVA-specific IgE levels, the number of inflammatory cells including mast cells, goblet cell hyperplasia, collagen deposition, airway hyperresponsiveness, expression of inflammatory cytokines, CCL2/CCR2, as well as nuclear factor kappa B (NF-κB) and activator protein-1 activities. All of these factors were increased in BAL cells and lung tissue of OVA-challenged mice. Irradiation increased the number of Treg cells, expression of interleukin (IL)-10, IL-2 and IL-35 in BAL cells and lung tissue. Irradiation also increased Treg cell-expressed Foxp3 and IL-10 by NF-κB and RUNX1 in OVA-challenged mice. Furthermore, while Treg cell-expressing OX40 and IL-10 were enhanced in lung tissue or act-bone marrow-derived mast cells (BMMCs) with Treg cells, but BMMCs-expressing OX40L and TGF-β were decreased. The data suggest that irradiation enhances Foxp3(+)- and IL-10-producing Treg cells, which reduce OVA-induced allergic airway inflammation and tissue remodeling through the down-regulation of migration by the CCL2/CCR2 axis and activation of mast cells via OX40/OX40L in lung tissue of OVA-challenged mice.

8-Hydroxy-2-deoxyguanosine prevents plaque formation and inhibits vascular smooth muscle cell activation through Rac1 inactivation

8-Hydroxy-2-deoxyguanosine (8-OHdG), a marker of oxidative stress, has been recently rediscovered to inhibit Rac1 in neutrophils and macrophages, thereby inhibiting Rac1-linked functions of these cells, including reactive oxygen species production through NADPH oxidase activation, phagocytosis, chemotaxis, and cytokine release. In vascular smooth muscle cells (VSMCs), reactive oxygen species also induce abnormal proliferation and migration leading to progression of atherosclerosis. Based upon the involvement of reactive oxygen species in phagocytic cells and VSMCs during the atherosclerotic process, we hypothesized that 8-OHdG could have antiatherosclerotic action and tested this hypothesis in an experimentally induced atherosclerosis in mice. Partially ligated ApoE knockout mice, a more physiologically relevant model of low and oscillatory flow, developed an advanced lesion in 2 weeks, and orally administered 8-OHdG significantly reduced plaque formation along with reduced superoxide formation, monocyte/macrophage infiltration, and extracellular matrix (ECM) accumulation. The effects of 8-OHdG observed in primary VSMCs were consistent with the in vivo effects of 8-OHdG and were inhibitory to angiotensin II or platelet-derived growth factor-induced production of reactive oxygen species, proliferation, migration, and ECM production. Also, angiotensin II-induced Rac1 activity in VSMCs was significantly inhibited by 8-OHdG, and transfection of constitutively active Rac1 reversed the inhibitory effect of 8-OHdG on VSMC activation. Molecular docking study showed that 8-OHdG stabilizes Rac1-GEF complex, indicating the physical contact of 8-OHdG with Rac1. These findings highly suggest that the antiatherosclerotic effect of 8-OHdG is mediated by inhibition of Rac1 activity. In conclusion, our results show a novel action of orally active 8-OHdG in suppressing atherosclerotic plaque formation in vivo and VSMC activation in vitro through inhibition of Rac1, which emphasizes a new therapeutic avenue to benefit atherosclerosis.

Grape seed extract attenuates lung parenchyma pathology in ovalbumin-induced mouse asthma model: an ultrastructural study

Due to the growing incidence of asthma and because of the non-specificity and side effects of the conventional drugs, the development of novel agents for the treatment of asthma has become considerably important. Natural plant products offer promising alternatives for the development of effective and safe treatments. Grape seed extract (GSE) is one such phytochemical supplement that has been shown to have potent antioxidant and anti-inflammatory effects. Thus, the present study aimed to investigate the effect of GSE to suppress lung parenchyma pathology and inflammation in ovalbumin-induced murine asthma model. Ovalbumin exposure was associated with many pathological and morphometric alterations in the lungs of asthmatic mice. The alterations involved alveolar size reduction, alveolar wall thickening, cellular infiltration and blood capillary congestion, as well as significant increase in the number of type II pneumocytes and lamellar bodies. However, GSE significantly ameliorated of the pathological changes of ovalbumin-induced asthma. The results support the possibility of GSE as an effective, safe anti-inflammatory dietary supplement to attenuate the pathogenicity of asthma. While these preliminary results appear promising, further studies are required to elucidate the precise mechanism of the modulatory effect of GSE on asthma remodeling.

CXCR4 regulates migration of lung alveolar epithelial cells through activation of Rac1 and matrix metalloproteinase-2

Restoration of the epithelial barrier following acute lung injury is critical for recovery of lung homeostasis. After injury, alveolar type II epithelial (ATII) cells spread and migrate to cover the denuded surface and, eventually, proliferate and differentiate into type I cells. The chemokine CXCL12, also known as stromal cell-derived factor 1α, has well-recognized roles in organogenesis, hematopoiesis, and immune responses through its binding to the chemokine receptor CXCR4. While CXCL12/CXCR4 signaling is known to be important in immune cell migration, the role of this chemokine-receptor interaction has not been studied in alveolar epithelial repair mechanisms. In this study, we demonstrated that secretion of CXCL12 was increased in the bronchoalveolar lavage of rats ventilated with an injurious tidal volume (25 ml/kg). We also found that CXCL12 secretion was increased by primary rat ATII cells and a mouse alveolar epithelial (MLE12) cell line following scratch wounding and that both types of cells express CXCR4. CXCL12 significantly increased ATII cell migration in a scratch-wound assay. When we treated cells with a specific antagonist for CXCR4, AMD-3100, cell migration was significantly inhibited. Knockdown of CXCR4 by short hairpin RNA (shRNA) caused decreased cell migration compared with cells expressing a nonspecific shRNA. Treatment with AMD-3100 decreased matrix metalloproteinase-14 expression, increased tissue inhibitor of metalloproteinase-3 expression, decreased matrix metalloproteinase-2 activity, and prevented CXCL12-induced Rac1 activation. Similar results were obtained with shRNA knockdown of CXCR4. These findings may help identify a therapeutic target for augmenting epithelial repair following acute lung injury.

8-Hydroxydeoxyguanosine: Not mere biomarker for oxidative stress, but remedy for oxidative stress-implicated gastrointestinal diseases

Reactive oxygen species (ROS) attack guanine bases in DNA easily and form 8-hydroxydeoxyguanosine (8-OHdG), which can bind to thymidine rather than cytosine, based on which, the level of 8-OHdG is generally regarded as a biomarker of mutagenesis consequent to oxidative stress. For example, higher levels of 8-OHdG are noted in Helicobacter pylori-associated chronic atrophic gastritis as well as gastric cancer. However, we have found that exogenous 8-OHdG can paradoxically reduce ROS production, attenuate the nuclear factor-κB signaling pathway, and ameliorate the expression of proinflammatory mediators such as interleukin (IL)-1, IL-6, cyclo-oxygenase-2, and inducible nitric oxide synthase in addition to expression of nicotinamide adenine dinucleotide phosphate oxidase (NOX)-1, NOX organizer-1 and NOX activator-1 in various conditions of inflammation-based gastrointestinal (GI) diseases including gastritis, inflammatory bowel disease, pancreatitis, and even colitis-associated carcinogenesis. Our recent finding that exogenous 8-OHdG was very effective in either inflammation-based or oxidative-stress-associated diseases of stress-related mucosal damage has inspired the hope that synthetic 8-OHdG can be a potential candidate for the treatment of inflammation-based GI diseases, as well as the prevention of inflammation-associated GI cancer. In this editorial review, the novel fact that exogenous 8-OHdG can be a functional molecule regulating oxidative-stress-induced gastritis through either antagonizing Rac-guanosine triphosphate binding or blocking the signals responsible for gastric inflammatory cascade is introduced.