Tetrahedral DNA loaded siCCR2 restrains M1 macrophage polarization to ameliorate pulmonary fibrosis in chemoradiation-induced murine model.

Idiopathic pulmonary fibrosis (IPF) is a chronic lethal disease in the absence of demonstrated efficacy for preventing progression. Although macrophage-mediated alveolitis is determined to participate in myofibrotic transition during disease development, the paradigm of continuous macrophage polarization is still under-explored due to lack of proper animal models. Here, by integrating 2.5 U/kg intratracheal Bleomycin administration and 10 Gy thorax irradiation at day 7, we generated a murine model with continuous alveolitis-mediated fibrosis, which mimics most of the clinical features of our involved IPF patients. In combination with data from scRNA-seq of patients and a murine IPF model, a decisive role of CCL2/CCR2 axis in driving M1 macrophage polarization was revealed, and M1 macrophage was further confirmed to boost alveolitis in leading myofibroblast activation. Multiple sticky-end tetrahedral framework nucleic acids conjunct with quadruple ccr2-siRNA (FNA-siCCR2) was synthesized in targeting M1 macrophages. FNA-siCCR2 successfully blocked macrophage accumulation in pulmonary parenchyma of the IPF murine model, thus preventing myofibroblast activation and leading to the disease remitting. Overall, our studies lay the groundwork to develop a novel IPF murine model, reveal M1 macrophages as potential therapeutic targets, and establish new treatment strategy by using FNA-siCCR2, which are highly relevant to clinical scenarios and translational research in the field of IPF.

Comparison of neurally adjusted ventilatory assist and synchronized intermittent mandatory ventilation in preterm infants after patent ductus arteriosus ligation: a retrospective study.

OBJECTIVE: This study aimed to compare the efficacy of neurally adjusted ventilatory assist (NAVA) to synchronized intermittent mandatory ventilation (SIMV) in preterm infants requiring mechanical ventilation after patent ductus arteriosus (PDA) ligation. METHODS: A retrospective analysis was conducted on intubated preterm infants who underwent PDA ligation at our hospital from July 2021 to January 2023. Infants were divided into NAVA or SIMV groups based on the ventilation mode after surgery. RESULTS: Fifty preterm infants were included. During treatment, peak inspiratory pressure (PIP) and mean airway pressure (MAP) were lower with NAVA compared to SIMV (PIP: 19.1 ± 2.9 vs. 22.4 ± 3.6 cmH2O, P < 0.001; MAP: 9.1 ± 1.8 vs. 10.9 ± 2.7 cmH2O, P = 0.002). PaO2 and PaO2/FiO2 were higher with NAVA (PaO2: 94.0 ± 11.7 vs. 84.8 ± 15.8 mmHg, P = 0.031; PaO2/FiO2: 267 [220-322] vs. 232 [186-290] mmHg, P = 0.025). Less sedation was required with NAVA (midazolam: 1.5 ± 0.5 vs. 1.1 ± 0.3 µg/kg/min, P < 0.001). CONCLUSION: Compared to SIMV, early use of NAVA post PDA ligation in preterm infants was associated with decreased PIP and MAP. Early NAVA was also associated with reduced sedation needs and improved oxygenation. However, further studies are warranted to quantify the benefits of NAVA ventilation.

Improved Tumor Infiltration and Immunomodulation for Tumor Therapy: A Pathway Based on Tetrahedral Framework Nucleic Acids Coupled Bacterial Nanocells.

Growing evidence indicates that the tumor microenvironment (TME) can be combined with other therapeutic modalities, including cytotoxic chemotherapy and targeted therapies, to produce unanticipated results in oncology treatment. Here, we proposed a novel bacterial nanomaterial capable of targeting peritumoral biofilm and modulating TME. It was based on tetrahedral framework nucleic acids (T) that were chemically attached to aptamer AS1411 and 5-fluorouracil (AT5). Additionally, the oral pathogenic bacterium Streptococcus mutans (S.m) was employed as a biocarrier for synergetic biofilm targeting and immunomodulation. In this article, the effect of AT5-coupled S.m-derived nanocells (S.m-AT5) was investigated in vitro and in vivo. Due to bacteria aggregation in the tumor-specific biofilm, these nanocells released greater medication concentrations. Furthermore, they exerted an immunomodulatory effect by stimulating the maturation of dendritic cells (DCs) and regulation of T cells. This chemo-immunostimulation combination has a powerful antitumor impact. It may also be an advanced approach for boosting the survival rate of cancer patients.

Tetrahedral Framework Nucleic Acids Inhibit Muscular Mitochondria-Mediated Apoptosis and Ameliorate Muscle Atrophy in Sarcopenia.

Sarcopenia is known as age-related muscle atrophy, which influences over a quarter of the elderly population worldwide. It is characterized by a progressive decline in muscle mass, strength, and performance. To date, clinical treatments in sarcopenia are limited to rehabilitative interventions and dietary supplements. Tetrahedral framework nucleic acids (tFNAs) represent a novel kind of DNA-based nanomaterial with superior antiapoptosis capacity in cells, tissues, organs, and systems. In our study, the therapeutic effect of tFNAs treatment on sarcopenia was evaluated both in vivo and in vitro. Results from muscular biophysiological characteristics demonstrated significant improvement in muscle function and endurance in the aged mouse model, and histologic examinations also showed beneficial morphological changes in muscle fibers. In vitro, DEX-induced sarcopenic myotube atrophy was also ameliorated through the inhibition of mitochondria-mediated cell apoptosis. Collectively, tFNAs treatment might serve as an alternative option to deal with sarcopenia in the near future.

Selective deficiency of UCP-1 and adropin may lead to different subtypes of anti-neutrophil cytoplasmic antibody-associated vasculitis.

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease that is prone to respiratory and renal failures. Its major target antigens are serine protease 3 (PR3) and myeloperoxidase (MPO), but the determinants of PR3 and MPO subtypes are still unclear. Uncoupling protein-1 (UCP-1) and adropin (Adr) regulate mutually and play an important role in endothelial cell injury. In this study, adropin and UCP-1 knockout (AdrKO and UCP-1-KO) models were established on the basis of C57BL/6 J mice. The results showed that UCP-1-KO and AdrKO mice similar to AAV: significant inflammatory cell infiltration, vascular wall damage, and erythrocyte extravasation. The pathological basis of AdrKO was that endothelial cells adhered and activated neutrophils to release MPO, and the core gene was peroxisome proliferator-activated receptor gamma (PPARG). However, UCP-1-KO induced PR3 release, and the accumulation and expression of tissue factor on the vascular wall, and the core gene was peroxisome proliferator-activated receptor delta (PPARD). The present study verified that the subtypes of AAV may be genetically different diseases and it also provide novel experimental evidence for clinical differentiation of the two subtypes.

Effects of Puerarin-Loaded Tetrahedral Framework Nucleic Acids on Osteonecrosis of the Femoral Head.

Osteonecrosis of the femoral head (ONFH) is recognized as a common refractory orthopedic disease that causes severe pain and poor quality of life in patients. Puerarin (Pue), a natural isoflavone glycoside, can promote osteogenesis and inhibit apoptosis of bone mesenchymal stem cells (BMSCs), demonstrating its great potential in the treatment of osteonecrosis. However, its low aqueous solubility, fast degradation in vivo, and inadequate bioavailability, limit its clinical application and therapeutic efficacy. Tetrahedral framework nucleic acids (tFNAs) are promising novel DNA nanomaterials in drug delivery. In this study, tFNAs as Pue carriers is used and synthesized a tFNA/Pue complex (TPC) that exhibited better stability, biocompatibility, and tissue utilization than free Pue. A dexamethasone (DEX)-treated BMSC model in vitro and a methylprednisolone (MPS)-induced ONFH model in vivo is also established, to explore the regulatory effects of TPC on osteogenesis and apoptosis of BMSCs. This findings showed that TPC can restore osteogenesis dysfunction and attenuated BMSC apoptosis induced by high-dose glucocorticoids (GCs) through the hedgehog and Akt/Bcl-2 pathways, contributing to the prevention of GC-induced ONFH in rats. Thus, TPC is a promising drug for the treatment of ONFH and other osteogenesis-related diseases.

Tetrahedral Framework Nucleic Acids: A Novel Strategy for Antibiotic Treating Drug-Resistant Infections.

Antibiotic multiresistance (AMR) has emerged as a major threat to human health as millions of people die from AMR-related problems every year. As has been witnessed during the global COVID-19 pandemic, the significantly increased demand for antibiotics has aggravated the issue of AMR. Therefore, there is an urgent need to find ways to alleviate it. Tetrahedral framework nucleic acids (tFNAs) are novel nanomaterials that are often used as drug delivery platforms because of their structural diversity. This study formed a tFNAs-antibiotic compound (TAC) which has a strong growth inhibitory effect on Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA) in vitro owing to the increased absorption of antibiotics by bacteria and improved drug movement across cell membranes. We established a mouse model of systemic peritonitis and local wound infections. The TAC exhibited good biosafety and improved the survival rate of severely infected mice, promoting the healing of local infections. In addition to the better transport of antibiotics to the target, the TAC may also enhance immunity by regulating the differentiation of M1 and M2 macrophages, providing a new option for the treatment of infections.

Hypomagnesemia with Secondary Hypocalcemia (HSH): a Case Report.

BACKGROUND: Hypomagnesemia with secondary hypocalcemia (HSH) is a genetic disorder arising from the body's impaired capacity to absorb and retain magnesium (Mg2+) consumed through diet. Consequently, Mg2+ levels in blood are significantly reduced, a condition referred to as hypomagnesemia. Insufficient levels of Mg2+ and calci-um (Ca2+) can lead to neurological complications that manifest during infancy, such as painful muscle spasms (tet-any) and seizures. METHODS: We reported a case of HSH involving a 10-year-old male patient from a Han Chinese family. He was admitted due to recurrent convulsions experienced over the past two years. The patient's initial episode occurred two years prior, when he collapsed without apparent cause and exhibited limb numbness, convulsions, and a disordered state of consciousness, accompanied by hypocalcemia. Cranial CT scans revealed multiple symmetrical calcifications in the basal ganglia, corona radiata, and cerebellar dentate nucleus. RESULTS: During the hospital stay, the patient was administered the following treatments: Calcium Carbonate and Vitamin D3 Tablets (1.5 g of calcium carbonate and 125 IU of Vitamin D3 per tablet, 1 tablet/time) once daily, Calcitriol Soft Capsules (0.25 µg of calcitriol per capsule, 1 capsule/time) twice daily, Potassium Chloride Sustained-release Tablets (0.5 g of potassium chloride per tablet, 1 tablet/time) thrice daily, Potassium Aspartate and Mag-nesium Aspartate Tablets (158 mg of potassium aspartate and 140 mg of magnesium aspartate per tablet, 1 tablet/ time) thrice daily, and intravenous infusions of Magnesium Sulfate Injection (2.5 g/time) twice daily. After three days in the hospital, the patient's initial symptoms subsided, resulting in discharge with a prescription of ongoing oral medications including Calcium Carbonate and Vitamin D3 Tablets, Calcitriol Soft Capsules, and Potassium Aspartate and Magnesium Aspartate Tablets, with the same usage and dosage as the above three drugs. A month subsequent, the serum levels of Mg2+, Ca2+, potassium (K+), and phosphorus were 0.96 mmol/L, 2.52 mmol/L, 4.06 mmol/L, and 1.63 mmol/L, respectively. CONCLUSIONS: Primary HSH is an uncommon manifestation of parathyroid hypoplasia, clinically characterized by low levels of Mg2+, Ca2+, and K+ in the blood. Our findings serve to enrich and consolidate the knowledge for future case studies and follow-up investigations.

Tetrahedral Framework Nucleic Acids Can Alleviate Taurocholate-Induced Severe Acute Pancreatitis and Its Subsequent Multiorgan Injury in Mice.

Severe acute pancreatitis (SAP) is an inflammatory disease of the pancreas accompanied by tissue injury and necrosis. It not only affects the pancreas but also triggers a systemic inflammatory response that leads to multiorgan failure or even death. Moreover, there is no effective treatment currently that can reverse the disease progression. In this study, tetrahedral framework nucleic acids (tFNAs) were utilized to treat SAP in mice for the first time and proved to be effective in suppressing inflammation and preventing pathological cell death. Serum levels of pancreatitis-related biomarkers witnessed significant changes after tFNAs treatment. Reduction in the expression of certain cytokines involved in local and systemic inflammatory response were observed, together with alteration in proteins related to cell death and apoptosis. Collectively, our results demonstrate that tFNAs could both alleviate SAP and its subsequent multiorgan injury in mice, thus offering a novel and effective option to deal with SAP in the future.

Antiepilepticus Effects of Tetrahedral Framework Nucleic Acid via Inhibition of Gliosis-Induced Downregulation of Glutamine Synthetase and Increased AMPAR Internalization in the Postsynaptic Membrane.

More than 15 million out of 70 million patients worldwide do not respond to available antiepilepticus drugs (AEDs). With the emergence of nanomedicine, nanomaterials are increasingly being used to treat many diseases. Here, we report that tetrahedral framework nucleic acid (tFNA), an assembled nucleic acid nanoparticle, showed an excellent ability to the cross blood-brain barrier (BBB) to inhibit M1 microglial activation and A1 reactive astrogliosis in the hippocampus of mice after status epilepticus. Furthermore, tFNA inhibited the downregulation of glutamine synthetase by alleviating oxidative stress in reactive astrocytes and subsequently reduced glutamate accumulation and glutamate-mediated neuronal hyperexcitability. Meanwhile, tFNA promotes α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) internalization in the postsynaptic membrane by regulating AMPAR endocytosis, which contributed to reduced calcium influx and ultimately reduced hyperexcitability and spontaneous epilepticus spike frequencies. These findings demonstrated tFNA as a potential AED and that nucleic acid material may be a new direction for the treatment of epilepsy.

Immune disguise: the mechanisms of Neu5Gc inducing autoimmune and transplant rejection.

Organ (stem cell) transplantation is the most effective treatment for advanced organ failure. Neu5Gc (N-hydroxyacetylneuraminic acid) is a pathogenic non-human sialic acid, which is very similar to the molecular structure of Neu5Ac (N-acetylneuraminic acid) in human body. Neu5Gc has the function of "immune disguise", which is the main obstacle to transplantation. Gene knockout such as cytidine monophosphate-N-acetylneuraminidase (CMAH) reduces donor antigenicity, making xenotransplantation from fiction to reality. Exploring the immune disguise event in this emerging field has become a hot topic in the research of transplantation immune tolerance mechanism.

APE1 senses DNA single-strand breaks for repair and signaling.

DNA single-strand breaks (SSBs) represent the most abundant type of DNA damage. Unrepaired SSBs impair DNA replication and transcription, leading to cancer and neurodegenerative disorders. Although PARP1 and XRCC1 are implicated in the SSB repair pathway, it remains unclear how SSB repair and SSB signaling pathways are coordinated and regulated. Using Xenopus egg extract and in vitro reconstitution systems, here we show that SSBs are first sensed by APE1 to initiate 3'-5' SSB end resection, followed by APE2 recruitment to continue SSB end resection. Notably, APE1's exonuclease activity is critical for SSB repair and SSB signaling pathways. An APE1 exonuclease-deficient mutant identified in somatic tissue from a cancer patient highlighted the significance of APE1 exonuclease activity in cancer etiology. In addition, APE1 interacts with APE2 and PCNA, although PCNA is dispensable for APE1's exonuclease activity. Taken together, we propose a two-step APE1/APE2-mediated mechanism for SSB end resection that couples DNA damage response with SSB repair in a eukaryotic system.

Tetrahedral Framework Nucleic Acids Induce Immune Tolerance and Prevent the Onset of Type 1 Diabetes.

A failure in immune tolerance leads to autoimmune destruction of insulin-producing ß-cells, leading to type 1 diabetes (T1D). Inhibiting autoreactive T cells and inducing regulatory T cells (Tregs) to re-establish immune tolerance are promising approaches to prevent the onset of T1D. Here, we investigated the ability of tetrahedral framework nucleic acids (tFNAs) to induce immune tolerance and prevent T1D in nonobese diabetic (NOD) mice. In prediabetic NOD mice, tFNAs treatment led to maintenance of normoglycemia and reduced incidence of diabetes. Moreover, the tFNAs (250 nM) treatment preserved the mass and function of ß-cells, increased the frequency of Tregs, and suppressed autoreactive T cells, leading to immune tolerance. Collectively, our results demonstrate that tFNAs treatment aids glycemic control, provides ß-cell protection, and prevents the onset of T1D in NOD mice by immunomodulation. These results highlight the potential of tFNAs for the prevention of autoimmune T1D.

Noninvasive high-frequency oscillatory ventilation versus bi-level positive pressure ventilation in premature infants with respiratory failure: A retrospective study.

Objectives: Noninvasive high-frequency oscillatory ventilation (nHFOV) is a novel respiratory support mode for premature infants. This retrospective study aimed to compare the effect of nHFOV and bi-level nasal continuous positive airway pressure (BiPAP) in premature infants with neonatal respiratory failure (NRF) as initial noninvasive ventilation (NIV) support mode. Methods: We retrospectively analyzed medical records of preterm infants admitted to the tertiary neonatal intensive care units (NICUs) of Fujian Maternal and Child Health Hospital from January 2019 to December 2020. Preterm infants with the gestational age of 25-34 weeks, diagnosed with NRF, used nHFOV or BiPAP as the initial respiratory support mode were analyzed. The rates of invasive mechanical ventilation (IMV) within the first seven days after birth and adverse outcomes were compared between the two groups. Results: Two hundred fifty-five preterm infants were analyzed (128 in nHFOV group,127 in BiPAP group). There was no significant difference in baseline characteristics between the two groups. Compared with the BiPAP group, the nHFOV group had significantly lower need for IMV within the first seven days after birth (18/128 vs. 33/127, p = 0.01) and PCO2 at 12 and 24 hours post-treatment (46.34±5.24mmHg vs. 51.18±4.83mmHg, P<0.01; 40.72±4.02mmHg vs. 42.50±3.86mmHg, P<0.01). The incidence of BPD, ROP, air leak syndromes, IVH≥ grade 3, PVL, NEC≥II stage, abdominal distension, and nasal trauma were similar between the two groups. Conclusion: nHFOV significantly reduced the need for IMV and improved the elimination of CO2 compared with BiPAP in preterm infants with NRF without increasing the incidence of adverse effects.

A non-canonical role for the DNA glycosylase NEIL3 in suppressing APE1 endonuclease-mediated ssDNA damage.

The DNA glycosylase NEIL3 has been implicated in DNA repair pathways including the base excision repair and the interstrand cross-link repair pathways via its DNA glycosylase and/or AP lyase activity, which are considered canonical roles of NEIL3 in genome integrity. Compared with the other DNA glycosylases NEIL1 and NEIL2, Xenopus laevis NEIL3 C terminus has two highly conserved zinc finger motifs containing GRXF residues (designated as Zf-GRF). It has been demonstrated that the minor AP endonuclease APE2 contains only one Zf-GRF motif mediating interaction with single-strand DNA (ssDNA), whereas the major AP endonuclease APE1 does not. It appears that the two NEIL3 Zf-GRF motifs (designated as Zf-GRF repeat) are dispensable for its DNA glycosylase and AP lyase activity; however, the potential function of the NEIL3 Zf-GRF repeat in genome integrity remains unknown. Here, we demonstrate evidence that the NEIL3 Zf-GRF repeat was associated with a higher affinity for shorter ssDNA than one single Zf-GRF motif. Notably, our protein-protein interaction assays show that the NEIL3 Zf-GRF repeat but not one Zf-GRF motif interacted with APE1 but not APE2. We further reveal that APE1 endonuclease activity on ssDNA but not on dsDNA is compromised by a NEIL3 Zf-GRF repeat, whereas one Zf-GRF motif within NEIL3 is not sufficient to prevent such activity of APE1. In addition, COMET assays show that excess NEIL3 Zf-GRF repeat reduces DNA damage in oxidative stress in Xenopus egg extracts. Together, our results suggest a noncanonical role of NEIL3 in genome integrity via its distinct Zf-GRF repeat in suppressing APE1 endonuclease-mediated ssDNA breakage.

Bioswitchable Delivery of microRNA by Framework Nucleic Acids: Application to Bone Regeneration.

MicroRNAs (miRs) play an important role in regulating gene expression. Limited by their instabilities, miR therapeutics require delivery vehicles. Tetrahedral framework nucleic acids (tFNAs) are potentially applicable to drug delivery because they prominently penetrate tissue and are taken up by cells. However, tFNA-based miR delivery strategies have failed to separate the miRs after they enter cells, affecting miR efficiency. In this study, an RNase H-responsive sequence is applied to connect a sticky-end tFNA (stFNA) and miR-2861, which is a model miR, to target the expression of histone deacetylase 5 (HDAC5) in bone marrow mesenchymal stem cells. The resultant bioswitchable nanocomposite (stFNA-miR) enables efficient miR-2861 unloading and deployment after intracellular delivery, thereby inhibiting the expression of HDAC5 and promoting osteogenic differentiation. stFNA-miR also facilitated ideal bone repair via topical injection. In conclusion, a versatile miR delivery strategy is offered for various biomedical applications that necessitate modulation of gene expression.

Broadening the biocompatibility of gold nanorods from rat to Macaca fascicularis: advancing clinical potential.

BACKGROUND: The biomedical field has used gold nanorods (GNRs) for decades; however, clinical trials and translation is limited except gold nanoshells. The preparation of gold nanoshells is more complex than that of polyethylene glycol-modified GNRs (PEG-GNRs), and it is difficult to ensure uniform thickness. It is important to encourage and broaden the use of the star member (PEG-GNRs) of gold nanoparticles family for clinical translation. Existing studies on PEG-GNRs are limited with no relevant systematic progression in non-human primates. Herein, we assessed the systematic biocompatibility of PEG-GNRs in rats and clinically relevant Macaca fascicularis. RESULTS: In this small animal study, we administrated multiple doses of PEG-GNRs to rats and observed good biocompatibility. In the non-human primate study, PEG-GNRs had a longer blood half-life and produced a negligible immune response. Histological analysis revealed no significant abnormality. CONCLUSIONS: PEG-GNRs were well-tolerated with good biocompatibility in both small animals and large non-human primates. The information gained from the comprehensive systemic toxicity assessment of PEG-GNRs in M. fascicularis will be helpful for translation to clinical trials.

Tetrahedral Framework Nucleic Acids Deliver Antimicrobial Peptides with Improved Effects and Less Susceptibility to Bacterial Degradation.

Antimicrobial peptides (AMPs) have been an attractive alternative to traditional antibiotics. However, considerable efforts are needed to further enhance their antimicrobial effects and stability against bacterial degradation. Tetrahedral framework nucleic acids (tFNAs), a new class of three-dimensional nanostructures, have been utilized as a delivery vehicle. In this study, tFNAs were combined for the first time with an antimicrobial peptide GL13K, and the effects of the resultant complexes against Escherichia coli (sensitive to GL13K) and Porphyromonas gingivalis (capable of degrading GL13K) were investigated. tFNA-based delivery enhanced the effects of GL13K against E. coli. The tFNA vehicle both increased bacterial uptake and promoted membrane destabilization. Moreover, it enhanced the effects of GL13K against P. gingivalis by protecting the peptide against degradation in the protease-rich extracellular environment. Therefore, tFNA provides a delivery vehicle for AMPs targeting a broad range of disease.

[Tetrahedral Framework Nucleic Acids and Human Health].

In recent years, tetrahedral framework nucleic acids (tFNAs) have become a hot topic in the field of DNA nanomaterials due to their excellent mechanical, chemical and biological properties. By taking advantage of these merits, tFNAs of varied sizes and modification methods have been designed and applied in diverse fields such as regenerative medicine, biosensors, and tumor treatment to promote human health. This paper reviews the current research progress of tFNAs in human health-related fields, and the future challenges in the clinical applications of tFNAs.

Distinct roles of XRCC1 in genome integrity in Xenopus egg extracts.

Oxidative DNA damage represents one of the most abundant DNA lesions. It remains unclear how DNA repair and DNA damage response (DDR) pathways are co-ordinated and regulated following oxidative stress. While XRCC1 has been implicated in DNA repair, it remains unknown how exactly oxidative DNA damage is repaired and sensed by XRCC1. In this communication, we have demonstrated evidence that XRCC1 is dispensable for ATR-Chk1 DDR pathway following oxidative stress in Xenopus egg extracts. Whereas APE2 is essential for SSB repair, XRCC1 is not required for the repair of defined SSB and gapped plasmids with a 5'-OH or 5'-P terminus, suggesting that XRCC1 and APE2 may contribute to SSB repair via different mechanisms. Neither Polymerase beta nor Polymerase alpha is important for the repair of defined SSB structure. Nonetheless, XRCC1 is important for the repair of DNA damage following oxidative stress. Our observations suggest distinct roles of XRCC1 for genome integrity in oxidative stress in Xenopus egg extracts.