PARP-1 inhibition induces a late increase in the level of reactive oxygen species in cells after ionizing radiation

The Ribonuclease ZC3H12A is required for self-inflicted DNA breaks after DNA damage in small cell lung cancer cells

Radiotherapy is the first line treatment for small cell lung cancer (SCLC); However, radio-resistance accompanies with the treatment and hampers the prognosis for SCLC patients. The underlying mechanisms remains elusive. Here we discovered that self-inflicted DNA breaks exist in SCLC cells after radiation. Moreover, using nuclease siRNA screening combined with high-content ArrayScan™ cell analyzer, we identified that Ribonuclease ZC3H12A is required for the self-inflicted DNA breaks after radiation and for SCLC cell survival after DNA damage. ZC3H12A expression was increased in response to DNA damage and when ZC3H12A was knocked down, the DNA repair ability of the cells was impaired, as evidenced by decreased expression of the DNA damage repair protein BRCA1, and increased γH2AX at DNA damage sites. Colony formation assay demonstrates that ZC3H12A knocked down sensitized small cell lung cancer radiotherapy. Therefore, the Ribonuclease ZC3H12A regulates endogenous secondary breaks in small cell lung cancer and affects DNA damage repair. ZC3H12A may act as an important radiotherapy target in small cell lung cancer.

Self-inflicted DNA breaks in cell differentiation and cancer

Self-inflicted DNA strand breaks are canonically linked with cell death pathways and the establishment of genetic diversity in immune and germline cells. Moreover, this form of DNA damage is an established source of genome instability in cancer development. However, recent studies indicate that nonlethal self-inflicted DNA strand breaks play an indispensable but underappreciated role in a variety of cell processes, including differentiation and cancer therapy responses. Mechanistically, these physiological DNA breaks originate from the activation of nucleases, which are best characterized for inducing DNA fragmentation in apoptotic cell death. In this review, we outline the emerging biology of one critical nuclease, caspase-activated DNase (CAD), and how directed activation or deployment of this enzyme can lead to divergent cell fate outcomes.

PARP-1: a critical regulator in radioprotection and radiotherapy-mechanisms, challenges, and therapeutic opportunities

Background: Since its discovery, poly (ADP-ribose) polymerase 1 (PARP-1) has been extensively studied due to its regulatory role in numerous biologically crucial pathways. PARP inhibitors have opened new therapeutic avenues for cancer patients and have gained approval as standalone treatments for certain types of cancer. With continued advancements in the research of PARP inhibitors, we can fully realize their potential as therapeutic targets for various diseases. Purpose: To assess the current understanding of PARP-1 mechanisms in radioprotection and radiotherapy based on the literature. Methods: We searched the PubMed database and summarized information on PARP inhibitors, the interaction of PARP-1 with DNA, and the relationships between PARP-1 and p53/ROS, NF-κB/DNA-PK, and caspase3/AIF, respectively. Results: The enzyme PARP-1 plays a crucial role in repairing DNA damage and modifying proteins. Cells exposed to radiation can experience DNA damage, such as single-, intra-, or inter-strand damage. This damage, associated with replication fork stagnation, triggers DNA repair mechanisms, including those involving PARP-1. The activity of PARP-1 increases 500-fold on DNA binding. Studies on PARP-1-knockdown mice have shown that the protein regulates the response to radiation. A lack of PARP-1 also increases the organism's sensitivity to radiation injury. PARP-1 has been found positively or negatively regulate the expression of specific genes through its modulation of key transcription factors and other molecules, including NF-κB, p53, Caspase 3, reactive oxygen species (ROS), and apoptosis-inducing factor (AIF). Conclusion: This review provides a comprehensive analysis of the physiological and pathological roles of PARP-1 and examines the impact of PARP-1 inhibitors under conditions of ionizing radiation exposure. The review also emphasizes the challenges and opportunities for developing PARP-1 inhibitors to improve the clinical outcomes of ionizing radiation damage.

Molecular Mechanisms of Takotsubo Syndrome

Takotsubo syndrome (TTS) is a severe but reversible acute heart failure syndrome that occurs following high catecholaminergic stress. TTS patients are similar to those with acute coronary syndrome, with chest pain, dyspnoea and ST segment changes on electrocardiogram, but are characterised by apical akinesia of the left ventricle, with basal hyperkinesia in the absence of culprit coronary artery stenosis. The pathophysiology of TTS is not completely understood and there is a paucity of evidence to guide treatment. The mechanisms of TTS are thought to involve catecholaminergic myocardial stunning, microvascular dysfunction, increased inflammation and changes in cardiomyocyte metabolism. Here, we summarise the available literature to focus on the molecular basis for the pathophysiology of TTS to advance the understanding of the condition.

Cancer cells use self-inflicted DNA breaks to evade growth limits imposed by genotoxic stress

Genotoxic therapy such as radiation serves as a frontline cancer treatment, yet acquired resistance that leads to tumor reoccurrence is frequent. We found that cancer cells maintain viability during irradiation by reversibly increasing genome-wide DNA breaks, thereby limiting premature mitotic progression. We identify caspase-activated DNase (CAD) as the nuclease inflicting these de novo DNA lesions at defined loci, which are in proximity to chromatin-modifying CCCTC-binding factor (CTCF) sites. CAD nuclease activity is governed through phosphorylation by DNA damage response kinases, independent of caspase activity. In turn, loss of CAD activity impairs cell fate decisions, rendering cancer cells vulnerable to radiation-induced DNA double-strand breaks. Our observations highlight a cancer-selective survival adaptation, whereby tumor cells deploy regulated DNA breaks to delimit the detrimental effects of therapy-evoked DNA damage.

Molecular mechanisms of chemo- and radiotherapy resistance and the potential implications for cancer treatment

Cancer is a leading cause of death worldwide. Surgery is the primary treatment approach for cancer, but the survival rate is very low due to the rapid progression of the disease and presence of local and distant metastasis at diagnosis. Adjuvant chemotherapy and radiotherapy are important components of the multidisciplinary approaches for cancer treatment. However, resistance to radiotherapy and chemotherapy may result in treatment failure or even cancer recurrence. Radioresistance in cancer is often caused by the repair response to radiation-induced DNA damage, cell cycle dysregulation, cancer stem cells (CSCs) resilience, and epithelial-mesenchymal transition (EMT). Understanding the molecular alterations that lead to radioresistance may provide new diagnostic markers and therapeutic targets to improve radiotherapy efficacy. Patients who develop resistance to chemotherapy drugs cannot benefit from the cytotoxicity induced by the prescribed drug and will likely have a poor outcome with these treatments. Chemotherapy often shows a low response rate due to various drug resistance mechanisms. This review focuses on the molecular mechanisms of radioresistance and chemoresistance in cancer and discusses recent developments in therapeutic strategies targeting chemoradiotherapy resistance to improve treatment outcomes.

Glucagon-Like Peptide 1 Attenuates Lipotoxicity-Induced Islet Dysfunction in ApoE-/- Mice

AIM

Glucagon-like peptide-1 (GLP1) is known to decrease glucagon release and may be beneficial for the reduction of elevated blood glucose. However, its role and mechanism of action in diabetes remain elusive. This study aimed to examine the function of GLP1 and analyze the mechanism of effect that GLP1exerts on inducible nitric oxide synthase (iNOS) in diabetic mice.

METHODS

A diabetes model was established in ApoE-/- mice fed a high-fat diet and treated with GLP1 and/or lentivirus-expressing PARP1. PARP1, iNOS, and inflammatory factors in islets were detected by Western blot and ELISA. Islet α cells and β cells and CD8+ T lymphocytes were detected by immunostaining. Islet-cell apoptosis was detected by TUNEL.

RESULTS

GLP1 inhibited the expression of PARP1 and iNOS in islets, alleviated decrease in β cells, and suppressed cell apoptosis induced by the high-fat diet. Moreover, GLP1 recovered the decline in insulin sensitivity and glucose tolerance in ApoE-/- mice fed the high-fat diet, and the effects of GLP1 were related to the inhibition of COX2 and NFκB expression.

CONCLUSION

GLP1 significantly alleviated the decrease in β-cell numbers, suppressed β-cell apoptosis induced by the high-fat diet, inhibited the expression of iNOS, and alleviated inflammatory islet injury via inhibiting the COX2-NFκB pathway.

Autophagy suppresses radiation damage by activating PARP-1 and attenuating reactive oxygen species in hepatoma cells

Purpose: To investigate the relationship between autophagy and radiation damage of human hepatoma cells and to explore the role of reactive oxygen species (ROS). Materials and methods: HepG2 cells were exposed to X-rays, then the protein expressions of microtubule-associated protein 1 light chain 3 (LC3) and poly ADP-ribose polymerase-1 (PARP-1) were measured by Western blot assay, the formation of autophagosomes was detected by an autophagy detection kit, the intracellular ROS level was measured by flow cytometer, and DNA damage was evaluated by the incidence of micronuclei (MN). A CCK-8 kit was used to measure the proliferation ability of irradiated cells with or without N-acetyl-l-cysteine (NAC) treatment. In some experiments, the hepatoma cells were transferred with LC3 siRNA or PARP-1 siRNA before irradiation. Results: The protein expressions of LC3 and PARP-1 and the inductions of autophagosomes and intracellular ROS were increased in the irradiated HepG2 cells. Pretreatment of cells with NAC relieved the irradiation-induced inhibition of cell proliferation. When HepG2 cells were transfected with the LC3 siRNA, the over-expression of PARP-1 was diminished in the irradiated cells. Compared with the control group, the inhibitions of LC3 and PARP-1 increased ROS level in the irradiated HepG2 cells and hence sensitized radiation responses of both proliferation inhibition and MN induction. Conclusion: Autophagy upregulates the expression of PARP-1 and relieves radiation damage by reducing the generation of ROS.

ROS Reduction Does Not Decrease the Anticancer Efficacy of X-Ray in Two Breast Cancer Cell Lines

Radiotherapy is effective on a large number of cancer types and is one of the most frequently administrated treatments for cancer patients. The anticancer efficacy of X-ray radiotherapy has been frequently correlated with reactive oxygen species (ROS) elevation, which is also a limiting factor for its toxicity on normal tissues. Here, we found that although 4-10 Gy X-rays could significantly reduce cell numbers in both MDA-MB-231 and MCF-7 breast cancer cells, the ROS level changes are less in MCF-7 cells than in MDA-MB-231 cells. Moreover, although both the ROS scavenger N-acetyl-L-cysteine (NAC) and 1 T static magnetic field (SMF) could reduce X-ray-induced ROS elevation, they did not prevent X-ray-induced cell number reduction or cell death increase, which is significantly different from cisplatin. These results demonstrate that although the anticancer efficacy of cisplatin on two breast cancer cell lines is dependent on ROS, the anticancer efficacy of X-ray is not. Moreover, by testing 19 different cell lines, we found that 1 T SMF could effectively reduce ROS levels in multiple cell lines by 10-20%, which encourages further studies to investigate whether SMF could be used as a potential "physical antioxidant" in the future.

Nitrosative Stress as a Modulator of Inflammatory Change in a Model of Takotsubo Syndrome

Previous studies have shown that patients with Takotsubo syndrome (TS) have supranormal nitric oxide signaling, and post-mortem studies of TS heart samples revealed nitrosative stress. Therefore, we first showed in a female rat model that isoproterenol induces TS-like echocardiographic changes, evidence of nitrosative stress, and consequent activation of the energy-depleting enzyme poly(ADP-ribose) polymerase-1. We subsequently showed that pre-treatment with an inhibitor of poly(ADP-ribose) polymerase-1 ameliorated contractile abnormalities. These findings thus add to previous reports of aberrant β-adrenoceptor signaling (coupled with nitric oxide synthase activation) to elucidate mechanisms of impaired cardiac function in TS and point to potential methods of treatment.

Soft tissue sarcomas: new opportunity of treatment with PARP inhibitors?

BACKGROUND

Poly(ADP-ribose) polymerases (PARP) are a large family of enzymes involved in several cellular processes, including DNA single-strand break repair via the base-excision repair pathway. PARP inhibitors exert antitumor activity by both catalytic PARP inhibition and PARP-DNA trapping, moreover PARP inhibition represents a potential synthetic lethal approach against cancers with specific DNA-repair defects. Soft tissue sarcoma (STSs) are a heterogeneous group of mesenchymal tumors with locally destructive growth, high risk of recurrence and distant metastasis.

OBJECTIVES

The purpuse of this review is to provide an overview of the main preclinical and clinical data on use of PARPi in STSs and of effect and safety of combination of PARPi with irradiation.

RESULTS

Due to numerous genomic alterations in STSs, the DNA damage response pathway can offer an interesting target for biologic therapy. Preclinical and clinical studies showed promising results, with the most robust evidences of PARPi efficacy obtained on Ewing sarcoma bearing EWS-FLI1 or EWS-ERG genomic fusions. The activity of PARP inhibitors resulted potentiated by chemotherapy and radiation. Although mechanisms of synergisms are not completely known, combination of radiation therapy and PARP inhibitors exerts antitumor effect by accumulation of unrepaired DNA damage, arrest in G2/M, activity both on oxic and hypoxic cells, reoxygenation by effect on vessels and promotion of senescence. Early trials have shown a good tolerance profile.

CONCLUSIONS

The use of PARP inhibitors in advanced stage STSs, alone or combined in multimodal treatments, is of great interest and warrants further investigations.

The role of base excision repair in the development of primary open angle glaucoma in the Polish population

Glaucoma is a leading cause of irreversible blindness in developing countries. Previous data have shown that progressive loss of human TM cells may be connected with chronic exposure to oxidative stress. This hypothesis may suggest a role of the base excision repair (BER) pathway of oxidative DNA damage in primary open angle glaucoma (POAG) patients. The aim of our study was to evaluate an association of BER gene polymorphism with a risk of POAG. Moreover, an association of clinical parameters was examined including cup disk ratio (c/d), rim area (RA) and retinal nerve fiber layer (RNFL) with glaucoma progression according to BER gene polymorphisms. Our research included 412 patients with POAG and 454 healthy controls. Gene polymorphisms were analyzed by PCR-RFLP. Heidelberg Retinal Tomography (HRT) clinical parameters were also analyzed. The 399 Arg/Gln genotype of the XRCC1 gene (OR 1.38; 95% CI 1.02-1.89 p = 0.03) was associated with an increased risk of POAG occurrence. It was indicated that the 399 Gln/Gln XRCC1 genotype might increase the risk of POAG progression according to the c/d ratio (OR 1.67; 95% CI 1.07-2.61 P = 0.02) clinical parameter. Moreover, the association of VF factor with 148 Asp/Glu of APE1 genotype distribution and POAG progression (OR 2.25; 95% CI 1.30-3.89) was also found. Additionally, the analysis of the 324 Gln/His MUTYH polymorphism gene distribution in the patient group according to RNFL factor showed that it might decrease the progression of POAG (OR 0.47; 95% CI 0.30-0.82 P = 0.005). We suggest that the 399 Arg/Gln polymorphism of the XRCC1 gene may serve as a predictive risk factor of POAG.

X-ray induced DNA damage and repair in germ cells of PARP1(-/-) male mice

Poly(ADP-ribose)polymerase-1 (PARP1) is a nuclear protein implicated in DNA repair, recombination, replication, and chromatin remodeling. The aim of this study was to evaluate possible differences between PARP1^−/− and wild-type mice regarding induction and repair of DNA lesions in irradiated male germ cells. Comet assay was applied to detect DNA damage in testicular cells immediately, and two hours after 4 Gy X-ray irradiation. A similar level of spontaneous and radiation-induced DNA damage was observed in PARP1^−/− and wild-type mice. Conversely, two hours after irradiation, a significant level of residual damage was observed in PARP1^−/− cells only. This finding was particularly evident in round spermatids. To evaluate if PARP1 had also a role in the dynamics of H2AX phosphorylation in round spermatids, in which γ-H2AX foci had been shown to persist after completion of DNA repair, we carried out a parallel analysis of γ-H2AX foci at 0.5, 2, and 48 h after irradiation in wild-type and PARP1^−/− mice. No evidence was obtained of an effect of PARP1 depletion on H2AX phosphorylation induction and removal. Our results suggest that, in round spermatids, under the tested experimental conditions, PARP1 has a role in radiation-induced DNA damage repair rather than in long-term chromatin modifications signaled by phosphorylated H2AX.

Crosstalk between apoptosis, necrosis and autophagy

Apoptosis and necrosis are the two major modes of cell death, the molecular mechanisms of which have been extensively studied. Although initially thought to constitute mutually exclusive cellular states, recent findings reveal cellular contexts that require a balanced interplay between these two modes of cellular demise. Several death initiator and effector molecules, signaling pathways and subcellular sites have been identified as key mediators in both processes, either by constituting common modules or alternatively by functioning as a switch allowing cells to decide which route to take, depending on the specific situation. Importantly, autophagy, which is a predominantly cytoprotective process, has been linked to both types of cell death, serving either a pro-survival or pro-death function. Here we review the recent literature that highlights the intricate interplay between apoptosis, necrosis and autophagy, focusing on the relevance and impact of this crosstalk in normal development and in pathology. This article is part of a Special Section entitled: Cell Death Pathways.

Autophagy, apoptosis, mitoptosis and necrosis: interdependence between those pathways and effects on cancer

Cell death is a fundamental ingredient of life. Thus, not surprisingly more than one form of cell death exists. Several excellent reviews on various forms of cell death have already been published but manuscripts describing interconnection and interdependence between such processes are uncommon. Here, what follows is a brief introduction on all three classical forms of cell death, followed by a more detailed insight into the role of p53, the master regulator of apoptosis, and other forms of cell death. While discussing p53 and also the role of caspases in cell death forms, we offer insight into the interplay between autophagy and apoptosis, or necrosis, where autophagy may initially serve pro-survival functions. The review moves further to present some details about less researched forms of programmed cell death, namely necroptosis, necrosis and mitoptosis. These "mixed" forms of cell death allow us to highlight the interconnected nature of cell death forms, particularly apoptosis and necrosis. The interdependence between apoptosis, autophagy and necrosis, and their significance for cancer development and treatment are also analyzed in further parts of the review. In the concluding parts, the afore-mentioned issues will be put in perspective for the development of novel anti-cancer therapies.

Early treatment of radiation-induced heart damage in rats by caffeic acid phenethyl ester

The study is designed to determine the therapeutic effect of caffeic acid phenethyl ester (CAPE) in minimizing radiation-induced injuries in rats. Rats were exposed to 7Gy gamma radiation, 30min later rats were injected with CAPE (10μmol/kg body, i.p.) for 7 consecutive days. Rats were sacrificed at 8 and 15 days after starting the experiment. Gamma-irradiation induced significant increase in malondialdehyde (MDA) level and xanthine oxidase (XO) and adenosine deaminase (ADA) activities, and significant decrease in total nitrate/nitrite (NO(x)) level and glutathione peroxidise (GPx), superoxide dismutase (SOD) and catalase activities in heart tissue and augmented lipid fractions levels and activities of lactate dehydrogenase (LDH), creatine phosphokinase (CPK) and aspartate transaminase (AST) in serum. Irradiated rats early treated with CAPE showed significant decrease in MDA, XO and ADA and significant increase in NO(x) and SOD in heart tissue and in serum enzymes compared with irradiated group. Serum lipid profiles and cardiac enzymes were restored.

CONCLUSION

CAPE could exhibits curable effects on gamma irradiation-induced cardiac-oxidative impairment in rats.