Maternal administration of APAP induces angiogenesis disorders in mouse placenta via SOCS3/JAK1/STAT3 pathway.

Acetaminophen (APAP, also known as paracetamol) is a commonly used antipyretic and analgesic that is considered safe to use during pregnancy. However, a growing body of research indicates that gestational administration of APAP increased the risk of neurodevelopmental, reproductive and genitourinary disorders in offspring, alongside impairments in placental development. Notably, over-dosed APAP exhibits direct toxicity to endothelial cells, but there is very limited research investigating the impact of APAP on placental angiogenesis, a gap we aim to address in this study. Pregnant mice were gavaged with APAP (15, 50 and 150 mg/kg/d) from embryonic day 11.5 (E11.5) to E13.5. Administration of 150 mg/kg/d APAP leads to low birth weight (LBW) of the offspring and disordered vascular structures within the labyrinthine (Lab) layer of the placenta. This disruption is accompanied by a significant increase in Suppressor of Cytokine Signaling 3 (SOCS3) level, a negative regulator of the Janus kinase signal transducer 1 and activator of the transcription 3 (JAK1/STAT3) signaling. Meanwhile, Human umbilical vein endothelial Cells (HUVECs) with the treatment of 3 mM APAP exhibited reduced cell viability, whereas 1 mM APAP significantly affected the proliferation, migration, invasion and angiogenic capacities of HUVECs. Further, SOCS3 was up-regulated in HUVECs, accompanied by inhibition of JAK1/STAT3 pathways. Knocking-down SOCS3 in HUVECs restored the nuclear translocation of STAT3 and efficiently promoted cellular capacity of tube formation. Overall, short-term maternal administration of overdosed APAP impairs angiogenic capacities of fetal endothelial cells via SOCS3/JAK1/STAT3 pathway in the mouse placenta. This study reveals that overdose of APAP during pregnancy may adversely affect placental angiogenesis, emphasizing the importance of adhering to the safe principles of smallest effective dose for the shortest required durations.

V-ATPase B2 promotes microglial phagocytosis of myelin debris by inactivating the MAPK signaling pathway.

Microglial phagocytosis of myelin debris is a crucial process for promoting myelin regeneration in conditions such as multiple sclerosis (MS). Vacuolar-ATPase B2 (V-ATPase B2) has been implicated in various cellular processes, but its role in microglial phagocytosis and its potential impact on MS-related responses remain unclear. In this study, we employed BV-2 murine microglial cells to investigate the influence of V-ATPase B2 on the phagocytosis of myelin debris by microglia. The results revealed that V-ATPase B2 expression increased in response to myelin debris exposure. Overexpression of V-ATPase B2 significantly enhanced BV-2 phagocytosis of myelin debris. Additionally, V-ATPase B2 overexpression shifted microglial polarization towards an anti-inflammatory M2 phenotype, coupled with decreased lysosomal pH and enhanced lysosome degradation capacity. Moreover, endoplasmic reticulum (ER) stress inhibitor, 4-PBA, reversed the effects of V-ATPase B2 silencing on ER stress, M2 polarization, and lysosomal degradation of BV-2 cells. The MAPK pathway was inhibited upon V-ATPase B2 overexpression, contributing to heightened myelin debris clearance by BV-2 cells. Notably, MAPK pathway inhibition partially attenuated the inhibitory effects of V-ATPase B2 knockdown on myelin debris clearance. In conclusion, our findings reveal a pivotal role for V-ATPase B2 in promoting microglial phagocytosis of myelin debris by regulating microglial polarization and lysosomal function via the MAPK signaling pathway, suggesting that targeting V-ATPase B2 may hold therapeutic potential for enhancing myelin debris clearance and modulating microglial responses in MS and related neuroinflammatory disorders.

Acute kidney injury prediction model utility in premature myocardial infarction.

The incidence of premature myocardial infarction (PMI) has been rising and acute kidney injury (AKI) occurring in PMI patients severely impacts prognosis. This study aimed to develop and validate a prediction model for AKI specific to PMI patients. The MIMIC-Ⅲ-CV and MIMIC-Ⅳ databases were utilized for model derivation of PMI patients. Single-center data served for external validation. There were 571 and 182 AKI patients in the training set (n = 937) and external validation set (n = 292) cohorts, respectively. Finally, a 7-variable model consisting of: Sequential Organ Failure Assessment (SOFA) score, coronary artery bypass grafting (CABG), ICU stay time, loop diuretics, estimated glomerular filtration rate (eGFR) HCO3- and Albumin was developed, achieving an AUC of 0.85 (95% CI: 0.83-0.88) in the training set. External validation also confirmed model robustness. This model may assist clinicians in the early identification of patients at elevated risk for PMI. Further validation is warranted before clinical application.

Maternal Administration of Acetaminophen Affects Meiosis Through its Metabolite NAPQI Targeting SIRT7 in Fetal Oocytes.

Aim: Acetaminophen (APAP) is clinically recommended as analgesic and antipyretic among pregnant women. However, accumulating laboratory evidence shows that the use of APAP during pregnancy may alter fetal development. Since fetal stage is a susceptible window for early oogenesis, we aim to assess the potential effects of maternal administration of APAP on fetal oocytes. Results: Pregnant mice at 14.5 dpc (days post-coitus) were orally administered with APAP (50 and 150mg/kg.bw/day) for 3 days; meanwhile, 14.5 dpc ovaries were collected and cultured with APAP or its metabolite N-acetyl-p-benzoquinone imine (NAPQI; 5 and 15 µM) for 3 days. It showed that APAP caused meiotic aberrations in fetal oocytes through its metabolite NAPQI, including meiotic prophase I (MPI) progression delay and homologous recombination defects. Co-treatment with nicotinamide (NAM) or nicotinamide riboside chloride (NRC), nicotinamide adenine dinucleotide (NAD+) supplements, efficiently restored the MPI arrest, whereas the addition of the inhibitor of sirtuin 7 (SIRT7) invalidated the effect of the NAD+ supplement. In addition, RNA sequencing revealed distorted transcriptomes of fetal ovaries treated with NAPQI. Furthermore, the fecundity of female offspring was affected, exhibiting delayed primordial folliculogenesis and puberty onset, reduced levels of ovarian hormones, and impaired developmental competence of MII oocytes. Innovation: These findings provide the first known demonstration that NAPQI, converted from maternal administration of APAP, disturbs meiotic process of fetal oocytes and further impairs female fecundity in adulthood. The concomitant oral dosing with NAM further supports the benefits of NAD+ supplements on oogenesis. Conclusion: Short-term administration of APAP to pregnant mouse caused meiotic aberrations in fetal oocytes by its metabolite NAPQI, whereas co-treatment with NAD+ supplement efficiently relieves the adverse effects by interacting with SIRT7.

Structural Basis of Low-Molecular-Weight Thiol Glycosylation in Lincomycin A Biosynthesis.

The involvement of low-molecular-weight thiols in the biosynthesis of natural products is rarely reported. During lincomycin A biosynthesis, ergothioneine (EGT) is incorporated in the S-glycosylation catalyzed by LmbT. In contrast to the widely reported glycosylation of nitrogen and oxygen atoms, the glycosylation of sulfur atoms is less studied. In particular, the crystal structure of enzymes that glycosylate thiols on small molecules rather than peptides has not been reported. Here, we report the crystal structures of LmbT in apo form and in complex with GDP and EGT S-conjugated lincosamine. We found that LmbT has a characteristic glycosyltransferase type B fold, which forms a symmetric homotetramer. The substrates are bound deeply in the catalytic cleft. Consistent with the substrate structure, LmbT does not have the large peptide binding groove of the previously reported S-glycosyltransferase. Combined with site-directed mutagenesis, we propose a catalytic mechanism for the unusual EGT-mediated S-glycosylation in natural product biosynthesis.

Exploring the role of sphingolipid-related genes in clinical outcomes of breast cancer.

Background: Despite tremendous advances in cancer research, breast cancer (BC) remains a major health concern and is the most common cancer affecting women worldwide. Breast cancer is a highly heterogeneous cancer with potentially aggressive and complex biology, and precision treatment for specific subtypes may improve survival in breast cancer patients. Sphingolipids are important components of lipids that play a key role in the growth and death of tumor cells and are increasingly the subject of new anti-cancer therapies. Key enzymes and intermediates of sphingolipid metabolism (SM) play an important role in regulating tumor cells and further influencing clinical prognosis. Methods: We downloaded BC data from the TCGA database and GEO database, on which we performed in depth single-cell sequencing analysis (scRNA-seq), weighted co-expression network analysis, and transcriptome differential expression analysis. Then seven sphingolipid-related genes (SRGs) were identified using Cox regression, least absolute shrinkage, and selection operator (Lasso) regression analysis to construct a prognostic model for BC patients. Finally, the expression and function of the key gene PGK1 in the model were verified by in vitro experiments. Results: This prognostic model allows for the classification of BC patients into high-risk and low-risk groups, with a statistically significant difference in survival time between the two groups. The model is also able to show high prediction accuracy in both internal and external validation sets. After further analysis of the immune microenvironment and immunotherapy, it was found that this risk grouping could be used as a guide for the immunotherapy of BC. The proliferation, migration, and invasive ability of MDA-MB-231 and MCF-7 cell lines were dramatically reduced after knocking down the key gene PGK1 in the model through cellular experiments. Conclusion: This study suggests that prognostic features based on genes related to SM are associated with clinical outcomes, tumor progression, and immune alterations in BC patients. Our findings may provide insights for the development of new strategies for early intervention and prognostic prediction in BC.

Integrating single-cell RNA-seq and bulk RNA-seq to construct prognostic signatures to explore the role of glutamine metabolism in breast cancer.

Background: Although breast cancer (BC) treatment has entered the era of precision therapy, the prognosis is good in the case of comprehensive multimodal treatment such as neoadjuvant, endocrine, and targeted therapy. However, due to its high heterogeneity, some patients still cannot benefit from conventional treatment and have poor survival prognoses. Amino acids and their metabolites affect tumor development, alter the tumor microenvironment, play an increasingly obvious role in immune response and regulation of immune cell function, and are involved in acquired and innate immune regulation; therefore, amino acid metabolism is receiving increasing attention. Methods: Based on public datasets, we carried out a comprehensive transcriptome and single-cell sequencing investigation. Then we used 2.5 Weighted Co-Expression Network Analysis (WGCNA) and Cox to evaluate glutamine metabolism-related genes (GRGs) in BC and constructed a prognostic model for BC patients. Finally, the expression and function of the signature key gene SNX3 were examined by in vitro experiments. Results: In this study, we constituted a risk signature to predict overall survival (OS) in BC patients by glutamine-related genes. According to our risk signature, BC patients can obtain a Prognostic Risk Signature (PRS), and the response to immunotherapy can be further stratified according to PRS. Compared with traditional clinicopathological features, PRS demonstrated robust prognostic power and accurate survival prediction. In addition, altered pathways and mutational patterns were analyzed in PRS subgroups. Our study sheds some light on the immune status of BC. In in vitro experiments, the knockdown of SNX3, an essential gene in the signature, resulted in a dramatic reduction in proliferation, invasion, and migration of MDA-MB-231 and MCF-7 cell lines. Conclusion: We established a brand-new PRS consisting of genes associated with glutamine metabolism. It expands unique ideas for the diagnosis, treatment, and prognosis of BC.

Characteristics, Prognosis, and Prediction Model of Heart Failure Patients in Intensive Care Units Based on Preserved, Mildly Reduced, and Reduced Ejection Fraction.

Background: Heart failure (HF) patients in intensive care units (ICUs) are rather poorly studied based on varying left ventricular ejection fraction (LVEF) classification. Characteristics and prognosis of patients in ICUs with HF with mildly reduced ejection fraction (HFmrEF), HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF) require further clarification. Methods: Data involving clinical information and 4-year follow-up records of HF patients were extracted and integrated from the Medical Information Mart for Intensive Care III (MIMIC-III) database. Tests were carried out to identity differences among these three HF subtypes. Prognostic analyses were performed using Kaplan-Meier survival analysis and Cox proportional-hazards regression modeling. To develop a novel prediction nomogram, forward selection was used as the best-fit model. Prognostic heterogeneity of the subgroups prespecified by stratification factors in pairwise comparisons was presented using forest plots. Results: A total of 4150 patients were enrolled in this study. HFmrEF had the lowest all-cause mortality rate during the 4-year follow-up, which was significantly different from HFrEF and HFpEF (Log-Rank p < 0.001). The Cox proportional-hazards regression model also showed that a comparison of HFrEF versus HFmrEF indicated a hazard ratio (HR) of 0.76 (95% CI 0.61-0.94, p = 0.011) and HFrEF versus HFpEF indicated a HR 0.93 (95% CI 0.82-1.07, p = 0.307). Following a multivariable analysis, 13 factors were confirmed as independent. A new nomogram was established and quantified with a concordance index (C-index) of 0.70 (95% CI 0.67-0.73), and the internal validation indicated the accuracy of the model. Stratification factors such as a history of coronary artery bypass grafting (CABG) and comorbidity of chronic obstructive pulmonary disease (COPD) induced prognostic heterogeneity among the three subtypes. Conclusions: Clinical characteristics and prognosis significantly varied among the three subtypes of HF patients in ICUs, with HFmrEF patients achieving the best prognosis. The novel prediction model, tailored for this population, showed a satisfying prediction ability.

Peptide-based electrochemical sensor with nanogold enhancement for detecting rheumatoid arthritis.

Rheumatoid arthritis (RA), an autoimmune and chronic inflammatory disorder, is an incurable disease. We developed a peptide-based electrochemical sensor using electrochemical impedance spectroscopy that can be used to detect autoantibodies for RA diagnostics. We first validated that the developed peptide showed high sensitivity and could compliment the current gold standard method of an anti-cyclic citrullinated peptide antibody (anti-CCP) ELISA. The developed peptide can be modified on the nanogold surface of the working electrode of sensing chips through the method of a self-assembling monolayer. The sensing process was first optimized using a positive control cohort and a healthy control cohort. Subsequently, 10 clinically confirmed samples from RA patients and five healthy control samples were used to find the threshold value of the impedance between RA and healthy subjects. Furthermore, 10 clinically confirmed samples but with low values of anti-CCP autoantibodies were used to evaluate the sensitivity of the present method compared to the conventional method. The proposed method showed better sensitivity than the current conventional anti-CCP ELISA method.

RIPK3 collaborates with RIPK1 to inhibit MAVS-mediated signaling during black carp antiviral innate immunity.

Both the activation and attenuation of MAVS/IFN signaling are critical for host defensing against viral infection and thus lead to an elaborate regulation of MAVS-mediated signaling. However, the regulatory mechanisms concerning MAVS/IFN signaling in teleost fish are not well understood. RIPK3 has been identified as a key regulator of necroptosis, apoptosis, and inflammatory signaling in human and mammals. Here we report the identification of the RIPK3 homologue from black carp Mylopharyngodon piceus (bcRIPK3) and describe its role in regulating MAVS/IFN signaling. qPCR results demonstrated that bcRIPK3 was transcriptionally activated in response to poly (I:C) or LPS stimulation. Immunoblot assay and immunofluorescent staining assay showed that bcRIPK3 was a cytosolic protein with molecular weights of 47 kDa. Like its mammalian counterparts, bcRIPK3 exhibited a conserved function in inducing cell death. The reporter assay and plaque assay showed that overexpression of bcRIPK3 restricted bcMAVS-activated transcription of the interferon promoters of black carp and zebrafish, and suppressed bcMAVS-mediated antiviral activity. Notably, EPC cells co-expressing bcRIPK3, bcRIPK1 and bcMAVS presented much attenuated antiviral activity than the cells co-expressing bcRIPK3 and bcMAVS; and the subsequent co-IP assay identified the interaction between bcRIPK3 and bcRIPK1. Our findings collectively elucidate for the first time in teleost that black carp RIPK3 interacts with RIPK1 to inhibit MAVS-mediated antiviral signaling.

Stromal Score-Based Gene Signature: A Prognostic Prediction Model for Colon Cancer.

BACKGROUND: Growing evidence has revealed the crucial roles of stromal cells in the microenvironment of various malignant tumors. However, efficient prognostic signatures based on stromal characteristics in colon cancer have not been well-established yet. The present study aimed to construct a stromal score-based multigene prognostic prediction model for colon cancer. METHODS: Stromal scores were calculated based on the expression profiles of a colon cancer cohort from TCGA database applying the ESTIMATE algorithm. Linear models were used to identify differentially expressed genes between low-score and high-score groups by limma R package. Univariate, LASSO, and multivariate Cox regression models were used successively to select the prognostic gene signature. Two independent datasets from GEO were used as external validation cohorts. RESULTS: Low stromal score was demonstrated to be a favorable factor to the overall survival of colon cancer patients in TCGA cohort (p = 0.0046). Three hundred and seven stromal score-related differentially expressed genes were identified. Through univariate, LASSO, and multivariate Cox regression analyses, a gene signature consisting of LEP, NOG, and SYT3 was recognized to build a prognostic prediction model. Based on the predictive values estimated by the established integrated model, patients were divided into two groups with significantly different overall survival outcomes (p < 0.0001). Time-dependent Receiver operating characteristic curve analyses suggested the satisfactory predictive efficacy for the 5-year overall survival of the model (AUC value = 0.733). A nomogram with great predictive performance combining the multigene prediction model and clinicopathological factors was developed. The established model was validated in an external cohort (AUC value = 0.728). In another independent cohort, the model was verified to be of significant prognostic value for different subgroups, which was demonstrated to be especially accurate for young patients (AUC value = 0.763). CONCLUSION: The well-established model based on stromal score-related gene signature might serve as a promising tool for the prognostic prediction of colon cancer.

Black carp TRADD suppresses MAVS/IFN signaling during the innate immune activation.

Tumor necrosis factor receptor 1 (TNFR1) associated death domain protein (TRADD) is a pivotal adaptor in TNF signaling pathway and up-regulates MAVS/IFN signaling pathway in human and mammal. However, the role of TRADD in teleost fish remains obscure. To reveal the function of teleost TRADD in the innate immune response, the TRADD homologue (bcTRADD) of black carp (Mylopharyngodon piceus) has been cloned and the function of bcTRADD is investigated in this study, which shares similar functional domain to its mammalian counterpart. bcTRADD mRNA expression level increased in response to different stimuli, including LPS, poly (I:C) and virus infection in host cells. bcTRADD activated the transcriptional activity of NF-κB promoter in the reporter assay; however, showed hardly any effect on the transcriptional activity of IFN promoter. It was interesting that black carp mitochondria antiviral signaling protein (bcMAVS)-activated IFN promoter transcription were dramatically depressed by bcTRADD and the C-terminal death domain of bcTRADD was indispensable for its regulation of bcMAVS. Accordingly, the plaque assay result showed that EPC cells co-expressing bcMAVS and bcTRADD presented much attenuated antiviral activity than EPC cells expressing bcMAVS alone. Knockdown of bcTRADD slightly promoted the antiviral ability of the host cells against SVCV. The current data support the conclusion that bcTRADD suppresses MAVS-mediated antiviral signaling, which is different to its mammalian counterpart.

Black carp RIPK1 negatively regulates MAVS-mediated antiviral signaling during the innate immune activation.

Receptor-interacting serine/threonine protein kinase 1 (RIPK1) is an important regulator of necroptosis and involved in innate immune response in human and mammal; however, its function in teleost fish mains largely unknown. In this paper, the RIPK1 homologue of black carp (Mylopharyngodon piceus) has been cloned and characterized to explore its role in immunity. Black carp RIPK1 (bcRIPK1) possesses the similar structure to its mammalian counterpart, which has been identified as a cytosolic protein by immunofluorescence staining. Overexpressed bcRIPK1 in host cells led to the decreased transcription of interferon (IFN) and interferon stimulated genes, and exogenous bcRIPK1 in EPC cells led to the decreased transcription of interferon promoters in reporter assay. Our previous study has identified that black carp MAVS (bcMAVS) functions as an antiviral adaptor protein against both grass carp reovirus (GCRV) and spring viremia of carp virus (SVCV). The reporter assay showed that the IFN-inducing ability of bcMAVS was dampened by bcRIPK1 and the plaque assay demonstrated that the antiviral activity of bcMAVS was inhibited by bcRIPK1. The immunofluorescent staining and co-immunoprecipitation identified the interaction between these two molecules. Thus, the data generated in this paper support the conclusion that bcRIPK1 interacts with bcMAVS and negatively regulates bcMAVS-mediated antiviral signaling.

Black carp TRAFD1 restrains MAVS-mediated antiviral signaling during the innate immune activation.

TRAFD1 negatively regulates TLR and RLR signaling in human and mammal; however, its role in teleost fish remains unknown. In this paper, the TRAFD1 homologue has been cloned and characterized from black carp (Mylopharyngodon piceus). Black carp TRAFD1 (bcTRAFD1) consists of 567 amino acids and shows low similarity to that of mammalian TRAFD1, which has been identified as a cytosolic protein through immunofluorescence staining. When co-expressed with bcTRAFD1, the IFN promoter-inducing ability of black carp MAVS (bcMAVS) was obviously dampened in the luciferase reporter assay. Accordingly, bcMAVS-mediated antiviral activity against grass carp reovirus (GCRV) and spring viremia of carp virus (SVCV) was potently repressed by bcTRAFD1 in plaque assay. And the co-immunoprecipitation assay between bcTRAFD1 and bcMAVS has identified the association between these two molecules. Thus, our data supports the conclusion that bcTRAFD1 interacts with bcMAVS and negatively regulates bcMAVS-mediated antiviral signaling during the innate immune activation, which sheds a light on the regulation of MAVS in teleost.

[Effects of pretreatment with recombinant human B-type natriuretic peptide on infarct size in patients with acute ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention].

OBJECTIVES: To investigate whether the administration of recombinant human B-type natriuretic peptide (rhBNP) before primary percutaneous coronary intervention (PCI) could further limit the infract size, improve left ventricular function, and alleviate cardiac dilation in patients with acute ST-segment elevation myocardial infarction(STEMI). METHODS: A total of 93 consecutive patients presenting chest pain within 12 hours from the onset, suspicious of first STEMI located at anterior wall undergoing primary PCI, were eligible for enrollment and randomly assigned to either rhBNP group (rhBNP administration starting at 5 min before PCI, 1.5 µg/kg bolus intravenous injection followed by 0.007 5-0.03 µg·kg(-1)·min(-1) for up to 120 hours, n=48) or nitroglycerin (NIT) group (NIT treatment starting at 5 min before PCI, 10-100 µg/min intravenous infusion for 120 hours, n=45). Primary PCI was performed in both groups using post-conditioning (PC) technique. TIMI flow grade, corrected TIMI frame count, and TIMI myocardial perfusion grade were compared between the two groups at the time of infarct related artery (IRA) re-patency. The levels of serum creatine kinase MB isoenzyme (CK-MB) and troponin I (TnI) were measured. Echocardiography was performed at baseline 7 days and 6 months later. RESULTS: Baseline characteristics were similar between the two groups. The percentage of TIMI grade 3 and TIMI myocardial perfusion grade 3 after PCI both tended to be higher in rhBNP group than those in NIT group (95.8%(46/48) vs. 86.7%(39/45), P=0.162) and (72.9%(35/48) vs. 62.2%(28/45), P=0.500). The corrected TIMI frame count was significantly decreased in rhBNP group (21.0±8.7 vs. 28.2±14.8, P=0.005). The myocardial infarct size expressed as the AUC of CK-MB ((3 249±1 101) U/L vs. (4 474±1 661)U/L, P=0.010) or AUC of TnI ((3 670±942) µg/L vs. (4 541±1 098) µg/L, P=0.021) was significantly decreased in rhBNP group compared with those in NIT group. At 7 days after primary PCI, the left ventricular ejection fraction (LVEF) tended to be higher (P>0.05), while the E/e' index and wall motion score index (WMSI) ((11.95±3.31 vs. 14.60±4.09, P=0.030) and (1.74±0.17 vs. 2.40±0.55, P<0.001)) were significantly improved in rhBNP group compared with those in NIT group. BNP level was also significantly lower in rhBNP group compared that in NIT group ((68.3±37.8) ng/L vs. (129.4±64.4) ng/L, P<0.001). During 6-month follow-up, LVEF and WMSI were significantly improved in rhBNP group compared those in NIT group(51.7%±12.7% vs. 46.9%±9.6%, P=0.024 and 1.69±0.35 vs. 1.92±0.47, P=0.020). CONCLUSION: Administration of rhBNP before PCI with post-conditioning procedure can further improve myocardial perfusion, limit myocardial infarct size, ameliorate cardiac dysfunction and postpone left ventricular early-stage and long-term remodeling in STEMI patients undergoing primary PCI.

Genotoxic Klebsiella pneumoniae in Taiwan.

BACKGROUND: Colibactin is a nonribosomal peptide-polyketide synthesized by multi-enzyme complexes encoded by the pks gene cluster. Colibactin-producing Escherichia coli have been demonstrated to induce host DNA damage and promote colorectal cancer (CRC) development. In Taiwan, the occurrence of pyogenic liver abscess (PLA) has been suggested to correlate with an increasing risk of CRC, and Klebsiella pneumoniae is the predominant PLA pathogen in Taiwan. METHODOLOGY/PRINCIPAL FINDINGS: At the asn tRNA loci of the newly sequenced K. pneumoniae 1084 genome, we identified a 208-kb genomic island, KPHPI208, of which a module identical to the E. coli pks colibactin gene cluster was recognized. KPHPI208 consists of eight modules, including the colibactin module and the modules predicted to be involved in integration, conjugation, yersiniabactin production, microcin production, and unknown functions. Transient infection of BALB/c normal liver cells with K. pneumoniae 1084 increased the phosphorylation of histone H2AX, indicating the induction of host DNA damage. Colibactin was required for the genotoxicity of K. pneumoniae 1084, as it was diminished by deletion of clbA gene and restored to the wild type level by trans-complementation with a clbA coding plasmid. Besides, BALB/c mice infected with K. pneumoniae 1084 exhibited enhanced DNA damage in the liver parenchymal cells when compared to the isogenic clbA deletion mutant. By PCR detection, the prevalence of pks-positive K. pneumoniae in Taiwan is 25.6%, which is higher than that reported in Europe (3.5%), and is significantly correlated with K1 type, which predominantly accounted for PLA in Taiwan. CONCLUSIONS: Our knowledge regarding how bacteria contribute to carcinogenesis has just begun. The identification of genotoxic K. pneumoniae and its genetic components will facilitate future studies to elucidate the molecular basis underlying the link between K. pneumoniae, PLA, and CRC.