Hybrid Directed Hypergraph Learning and Forecasting of Skeleton-Based Human Poses.

Forecasting 3-dimensional skeleton-based human poses from the historical sequence is a classic task, which shows enormous potential in robotics, computer vision, and graphics. Currently, the state-of-the-art methods resort to graph convolutional networks (GCNs) to access the relationships of human joint pairs to formulate this problem. However, human action involves complex interactions among multiple joints, which presents a higher-order correlation overstepping the pairwise (2-order) connection of GCNs. Moreover, joints are typically activated by the parent joint, rather than driving their parent joints, whereas in existing methods, this specific direction of information transmission is ignored. In this work, we propose a novel hybrid directed hypergraph convolution network (H-DHGCN) to model the high-order relationships of the human skeleton with directionality. Specifically, our H-DHGCN mainly involves 2 core components. One is the static directed hypergraph, which is pre-defined according to the human body structure, to effectively leverage the natural relations of human joints. The second is dynamic directed hypergraph (D-DHG). D-DHG is learnable and can be constructed adaptively, to learn the unique characteristics of the motion sequence. In contrast to the typical GCNs, our method brings a richer and more refined topological representation of skeleton data. On several large-scale benchmarks, experimental results show that the proposed model consistently surpasses the latest techniques.

Long non­coding RNA L13Rik promotes high glucose-induced mesangial cell hypertrophy and matrix protein expression by regulating miR-2861/CDKN1B axis.

Background: Diabetic nephropathy (DN) is a frequent microvascular complication of diabetes. Glomerular mesangial cell (MC) hypertrophy occurs at the initial phase of DN and plays a critical role in the pathogenesis of DN. Given the role of long non coding RNA (lncRNA) in regulating MC hypertrophy and extracellular matrix (ECM) accumulation, our aim was to identify functional lncRNAs during MC hypertrophy. Methods: Here, an lncRNA, C920021L13Rik (L13Rik for short), was identified to be up-regulated in DN progression. The expression of L13Rik in DN patients and diabetic mice was assessed using quantitative real-time PCR (qRT-PCR), and the function of L13Rik in regulating HG-induced MC hypertrophy and ECM accumulation was assessed through flow cytometry and western blotting analysis. Results: The L13Rik levels were significantly increased while the miR-2861 levels were decreased in the peripheral blood of DN patients, the renal tissues of diabetic mice, and HG-treated MCs. Functionally, both L13Rik depletion and miR-2861 overexpression effectively reduced HG-induced cell hypertrophy and ECM accumulation. Mechanistically, L13Rik functioned as a competing endogenous RNA (ceRNA) to sponge miR-2861, resulting in the de-repression of cyclin-dependent kinase inhibitor 1B (CDKN1B), a gene known to regulate cell cycle and MC hypertrophy. Conclusions: Collectively, the current results demonstrate that up-regulated L13Rik is correlated with DN and may be a hopeful therapeutic target for DN.

Breviscapine alleviates podocyte injury by inhibiting NF-κB/NLRP3-mediated pyroptosis in diabetic nephropathy.

Podocyte injury is a critical factor in the pathogenesis of diabeticnephropathy (DN). Emerging evidence has demonstrated that breviscapine (Bre) exerts a renoprotective effect on diabetic rats. However, the effects of Bre on regulating podocyte injury under high glucose (HG) conditions remain unclear. In this study, an experimental mouse model of DN was induced by intraperitoneal injections of streptozotocin (STZ) in vivo. The effects of Bre on podocyte injury were assessed using cell counting kit-8 (CCK-8) assay, TdT-mediated dUTPnick-endlabelling (TUNEL) staining, quantitative real-time PCR (qRT‒PCR) and western blot analysis. We found that renal function was significantly decreased in diabetic mice, and this effect was blocked by Bre treatment. Bre effectively increased podocyte viability and inhibited HG-induced cell apoptosis. Furthermore, Bre ameliorated HG-induced podocyte injury, as evidenced by decreased α-smooth muscle actin (α-SMA) expression and increased podocin and synaptopodin expression. Mechanistically, Bre inhibited HG-induced nuclear factorkappaB (NF-κB) signalling activation and subsequently decreased NLR family pyrin domain containing 3 (NLRP3) inflammasome activation, resulting in a decrease in pyroptosis. Pharmacological inhibition of NLRP3 decreased HG-induced podocyte injury, whereas the NLRP3 agonist abrogated the effects of Bre on inhibiting podocyte injury. In summary, these results demonstrate that Bre alleviates HG-induced podocyte injury and improves renal function in diabetic mice, at least in part by inhibiting NF-κB/NLRP3-mediated pyroptosis.

Prevalence of osteoporosis in patients with diabetes mellitus: a systematic review and meta-analysis of observational studies.

BACKGROUND: Osteoporosis (OP) and diabetes mellitus (DM) are two major healthcare issues in the world. Numerous population based-studies have reported an increased prevalence of OP among individuals with DM, though, estimates vary significantly. PURPOSE: The objective of this study is to estimate the prevalence of OP in patients with DM. METHODS: To identify relevant literature, PubMed, Embase, Medline, CBM and Cochrane Library were searched for studies published from inception till July 2022, The search was conducted, and studies were included without countries and language restrictions. For full-text articles included in the study, the references were also independently searched. Random inverse variance-weighted models were used by Stata version 17.0 to estimate the prevalence of OP in patients with diabetes across studies. The heterogeneity was examined with I2 via the χ2 test on Cochrane's Q statistic. Subgroup analysis and meta-regression were used to explore potential sources of heterogeneity. Egger's test was used to assess publication bias. RESULTS: A high OP prevalence of 27.67% (95% confidence interval (CI) 21.37-33.98%) was found in a pooled analysis of 21 studies involving 11,603 T2DM patients. Methodological value of the included articles was high, with only three medium-quality studies and no low-quality studies. A significantly high heterogeneity (I2 = 98.5%) was observed. CONCLUSIONS: Worldwide, a high prevalence of OP was found in patients with T2DM. Therefore, strong measures to prevent and treat osteoporosis in diabetic patients are required. TRIAL REGISTRATION: This study has been registered on PROSPERO, number CRD42021286580 .

Higher modified dietary inflammatory index is associated with increased risk of osteoporosis in US adults: Data from NHANES.

Objective: The aim of this study was to study the relationship between modified dietary inflammatory index (MDII) score with osteoporosis (OP) in adult Americans. Methods: Data were extracted from the United States National Health and Nutrition Examination Survey (NHANES) (2007-2008, 2009-2010, 2013-2014, and 2017-2018). In this cross-sectional study, 5,446 participants were included and analyzed. Potential dietary inflammatory was assessed by MDII score (24-h recall), a composite method computed according to the relationship between nutrients and systemic pro-inflammatory cytokine level, and was further classified into tertiles. Weighted multivariable logistic regression analysis was employed to examine the associations between OP and MDII scores. Results: In weighted multivariable-adjusted logistic regression models, the highest tertile of MDII score was associated with an increased risk of OP [odds ratio (OR): 1.73, 95% confidence interval (95 CI%): 1.14-2.63]. In participants aged above 59 years, a higher MDII score showed a higher risk of OP (OR: 1.92; 95 CI%: 1.16-3.15). In the sex-stratified models, the results remained significant only among women (OR: 1.80; 95% CI: 1.02-3.17). In the menopausal status stratified model, after adjusting potential confounding variables, the association between the MDII score, either as a categorical (OR: 1.88; 95% CI: 1.07-3.13) or continuous variables (OR: 1.19; 95%CI: 1.02-1.38), and OP risk was significant among postmenopausal women. Conclusion: Our study indicates that a higher MDII score (pro-inflammatory effect) is significantly associated with an increased risk of OP in US adults, especially among those postmenopausal women more than 60 years. This study further supports that those dietary changes have the potential to prevent OP.

A Review on the Application of PD-1 Blockade in EBV-Associated Nasopharyngeal Carcinoma Immunotherapy.

Epstein-Barr virus (EBV) linked with nasopharyngeal carcinoma (NPC) is considered to be one of the most prevalent head and neck malignancies in East and Southeast Asia. Although radiotherapy and chemotherapy are effective treatments for NPC, they have immunosuppressive effects. Immunotherapy has got considerable attention of clinicians for cancer treatment in recent years due to proven success of PD-1/PD-L 1 inhibition in solid tumors trials. The distinct immunological environment of EBV-associated NPC presents a reasonable therapeutic target for PD-1/PD-L 1 inhibition. Immune checkpoint blockade therapy targeting the programmed cell death-1 (PD-1) and programmed cell death ligand-1 (PD-L 1) receptors have shown efficacy in early phase I clinical trials, with ongoing phase III clinical trials. Herein, we have extensively addressed the role of the PD-1/PD-L1 axis in the immunotherapy of EBV-associated NPC. Immunotherapeutic strategies are anticipated to enter mainstream clinical practise and provide long-term remissions in patients with severe NPC.

Performance Improvement of PVDF-HFP-Based Gel Polymer Electrolyte with the Dopant of Octavinyl-Polyhedral Oligomeric Silsesquioxane.

Gel polymer electrolytes have the advantages of both a solid electrolyte and a liquid electrolyte. As a transitional product before which a solid electrolyte can be comprehensively used, gel polymer electrolytes are of great research value. They can reduce the risk of spontaneous combustion and explosion caused by leakage during the use of conventional liquid electrolytes. Poly(vinylidene-fluoride-co-hexafluoropropylene) (PVDF-HFP), a material with excellent performance, has been widely utilized in the preparation of gel polymer electrolytes. Here, PVDF-HFP-based gel polymer membranes with polyvinyl pyrrolidone (PVP) pores were prepared using a phase inversion method, and Octavinyl-polyhedral oligomeric silsesquioxane (OVAPOSS) was doped to improve its temperature resistance as well as its ionic conductivity, to enhance its safety and electrochemical performance. The final prepared polymer membrane had a porosity of 85.06% and still had a certain mechanical strength at 160 °C without any shrinkage. The gel polymer electrolyte prepared with this polymer membrane had an ionic conductivity of 1.62 × 10-3 S·cm-1 at 30 °C, as well as an electrochemical window of about 5.5 V. The LiCoO2-Li button half-cell prepared therefrom had a specific capacity of 141 mAh·g-1 at a rate of 1C. The coulombic efficiency remained above 99% within 100 cycles and the capacity retention rate reached 99.5%, which reveals an excellent cycling stability.

Association of serum vitamin D level and nonalcoholic fatty liver disease: a meta-analysis.

We aimed to explore the potential link of serum vitamin D level with nonalcoholic fatty liver disease (NAFLD). PubMed, Embase and the Cochrane Library database were searched until the end of February 2018. Clinical studies with sufficient data investigating the relationship between serum vitamin D and NAFLD were included. The outcome data were processed to make an overall estimate of combined standardized mean differences (SMD) and pooled odds ratio (OR)/hazard ratios with 95% confidence intervals (CIs). Of the 309 initially retrieved studies, 15 studies of high quality involving a total of 20 096 participants (including 7803 NAFLD patients) were included in this meta-analysis. Meta-analysis of continuous data indicated that NAFLD patients had averagely 0.90 ng/ml lower levels of 25-hydroxyvitamin D compared with the non-NAFLD subjects (SMD -0.90; 95% CI: -1.29 to -0.52). Parallelly, pooled dichotomous data revealed that serum vitamin D level is negatively associated with NAFLD (OR = 0.64, 95% CI = 0.54-0.77), albeit with substantial heterogeneity. Next, subgroup analysis showed that Western NAFLD patients were more likely to be vitamin D deficient (OR = 0.60, 95% CI = 0.46-0.78). Finally, meta-regression showed that sample size, ethnic background, and diagnosis of NAFLD were possible sources of heterogeneity in the meta-analysis. Our results revealed that serum vitamin D level was inversely associated with an increased risk of NAFLD. Patients with hypovitaminosis D might benefit from extra supplement of vitamin D against the risk of NAFLD.

Development and Internal Validation of a Prediction Model to Estimate the Probability of Left-Ventricular Diastolic Dysfunction in Stable Maintenance Hemodialysis Patients without Clinical Heart Failure.

OBJECTIVE: To develop and internally validate a multivariable prediction model based on simple clinical record data and laboratory tests and to estimate the probability of left-ventricular diastolic dysfunction (LVDD) in stable maintenance hemodialysis (MHD) patients without clinical heart failure. DESIGN: Cross-sectional study. SETTING AND PARTICIPANTS: In all, 181 patients on MHD without clinical heart failure were eligible from the dialysis center of Tongren Hospital, Shanghai Jiao Tong University School of Medicine between October 2017 and September 2018. OUTCOMES: LVDD detected by echocardiography. MEASUREMENTS: We performed multivariable logistic regression using demographic, clinical, and laboratory data to identify predictors of LVDD with internal validation by using 200 bootstrap replications. RESULTS: Overall, 78 out of 181 (43.1%) patients were affected by LVDD. Predictors included in the LVDD Model were high-sensitive cardiac troponin T (OR 5.91 per 1-ln unit; 95% CI 2.17-16.13), B-type natriuretic peptide (OR 2.35 per 1-ln unit; 95% CI 1.14-4.86), and dialysis vintage (OR 1.04 per 1-month; 95% CI 1.01-1.07). The area (AUC) under the receiver operating characteristic curve of the Model was 0.871 (95% CI 0.811-0.932, p < 0.001). The calibration plot showed good agreement between predicted and observed probabilities with a calibration slope of 1.023 and intercept of -0.010. After internal validation, the Model maintained excellent discrimination (AUC 0.858, 95% CI 0.798-0.919) and good calibration (slope of 1.079, 95% CI 1.058-1.097 and intercept of -0.120, 95% CI -0.142 to -0.093). LVDD Model <0.23 can be used to rule out (sensitivity = 87.3%, negative likelihood ratio = 12.7%) and ≥0.44 can be used to rule in (specificity = 87.6%, positive likelihood ratio = 12.4%) echocardiography diagnosed LVDD. LIMITATION: External validation of the Model will be required. CONCLUSIONS: A model using routinely available simple clinical record data and laboratory tests can accurately predict the risk of LVDD in stable MHD patients. The Model and its cutoff values may be useful for early diagnosis and intervention of LVDD.

High-sensitive cardiac troponin T: a biomarker of left-ventricular diastolic dysfunction in hemodialysis patients.

OBJECTIVE: To identify the relationship between serum high-sensitive cardiac troponin T (hs-cTnT) and left ventricular diastolic dysfunction (LVDD) among maintenance hemodialysis patients and to further explore the value of hs-cTnT in evaluating and predicting LVDD in this special group of patients. METHODS: In a cross-sectional study, 152 dialysis patients with end-stage renal disease (ESRD) underwent Hs-cTnT measurement using the high sensitivity assay. Echocardiography measurements were carried out according to the American Society of Echocardiography recommendations and E/E' > 15 or E' < 7 cm/s was defined as diastolic dysfunction. Demographic, biochemical, and echocardiographic values of left ventricular mass index (LVMI), left ventricular ejection fraction (LVEF), left atrial diameter, early/late peak velocities ratio (E/A), early peak diastolic annular velocity (E') and E/E' were compared across quartiles of hs-cTnT. The association of plasma hs-cTnT concentrations with echocardiographic parameters was analyzed by Spearman's correlation. The relationship between serum hs-cTnT and LVDD parameters of E/E' and E' was analyzed using multivariate regression analysis, and the value of hs-cTnT on assessing LVDD was evaluated by receiver-operating characteristic (ROC) curves. RESULTS: The median value of hs-cTnT was 45 pg/ml (range 28-73). All patients had detectable hs-cTnT, while 88% had greater hs-cTnT than the 99th percentile of the general population (14 pg/ml). Serum hs-cTnT values showed a significantly positive correlation with E/E' (r = 0.739, p < 0.001) and LVMI (r = 0.608, p < 0.001), but showed a negative correlation with E' (r = - 0.554, p < 0.001). Serum hs-cTnT was not associated with LV systolic dysfunction. The associations of hs-cTnT with E/E' and E' persisted after multivariate adjustment for LVMI and comorbidities. In logistic multiple regression analysis, compared with the lowest quartile of hs-cTnT, the highest two quartiles were approximately 5 and 11 times more likely to have E/E' > 15 and 7 and 17 times more likely to have E' < 7 cm/s. The area under the ROC curve for hs-cTnT evaluating E/E' > 15 was 0.847 and evaluating E' < 7 cm/s was 0.799, which denoted a moderate accuracy. CONCLUSIONS: Our studies suggest that serum hs-cTnT may serve as a biomarker of LVDD in hemodialysis patients.

Development and in-house validation of a sensitive LC-MS/MS method for simultaneous quantification of gelsemine, koumine and humantenmine in porcine plasma.

Three monomers of G. elegans indole alkaloids (gelsemine, koumine and humantenmine) were simultaneously detected in porcine plasma for the first time with the development and validation of a sensitive and reliable LC-ESI-MS/MS method. Using a gradient mobile phase at a constant flow rate of 0.2 mL/min via electrospray ionization (positive ion mode) in a multiple reaction monitoring (MRM) scan, gelsemine, koumine and humantenmine were eluted, separated and detected at an appropriate retention time. The porcine plasma was prepared using protein precipitation with 1% formic acid-acetonitrile: methanol (2:1, v/v). Using matrix-matched calibration curves and weighted least squares linear regression, a good linearity (r2 > 0.99) was achieved with a concentration range of 0.1-200 µg/L for gelsemine, koumine and humantenmine; estimated LOD and LOQ values were 0.10 µg/L and 0.2 µg/L, respectively. The mean of the recoveries was in the range of 82.68-100.35% of porcine plasma at four different levels, and the intra-day and inter-day precision (CV) were lower than 15% with a range of 2.46-8.76% and 2.73-10.83%, respectively. The proposed method has proved to be suitable for accurate, quantitative determination of gelsemine, koumine and humantenmine in porcine plasma.

Association of Serum Vitamin D Level and Carotid Atherosclerosis: A Systematic Review and Meta-analysis.

Vitamin D deficiency is associated with an increased risk of subclinical atherosclerosis. To explore the potential link of the serum vitamin D level with carotid atherosclerosis, this meta-analysis assessed the correlation between vitamin D and carotid intima-media thickness as well as carotid atherosclerotic plaque. PubMed, Embase, Web of Science, and Cochrane Library databases were searched until the end of March 2017. Clinical studies investigating the relationship between vitamin D and carotid atherosclerosis were included. The outcome data were extracted according to the inclusion criteria and pooled for an effect estimate by a random-effects model. Of the 506 initially retrieved studies, 11 studies involving a total of 16,434 participants were included in the meta-analysis. Newcastle-Ottawa Quality Assessment Scale scores suggested that the included studies were of high quality. The pooled effects estimate showed that the serum vitamin D level was negatively associated with carotid atherosclerosis (odds ratio, 0.95; 95% confidence interval [CI], 0.93-0.96), with substantial heterogeneity among the individual studies (I2 = 54%). Furthermore, a subgroup analysis suggested that hypovitaminosis D was associated with an 0.85-fold decrease in the odds of having a higher carotid intima-media thickness (95% CI, 0.76-0.96; P < .05; I2 = 69%). Additionally, the pooled analysis also indicated that the serum vitamin D level was a protective factor against increased carotid plaque (odds ratio, 0.95; 95% CI, 0.93-0.97; P < .05; I2 = 29%). Funnel plots and the Egger regression test showed the absence of a publication bias. In this meta-analysis, we comprehensively revealed a close link between vitamin D deficiency and carotid atherosclerosis. Patients with hypovitaminosis D might have extra requirements for preventive and therapeutic measures against early atherosclerosis, thus reducing the cardiovascular disease risk in the long term.

Serum DLK1 is a potential prognostic biomarker in patients with hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is the sixth most prevalent cancer and the third most frequent cause of cancer-related death in developing countries, especially in East Asia and South Africa, and the identification of new biomarkers for early diagnosis and prognosis is needed. Delta-like 1 homologue (Drosophila) (DLK1) is expressed in malignancies and promotes cancer cell stemness and tumourigenicity, which makes this molecule a potential target for therapies directed against cancer stem/progenitor cells. Here, we aimed to assess the predictive value of DLK1 as a diagnostic and prognostic biomarker in HCC. With this purpose, serum DLK1 levels were detected using an enzyme-linked immunosorbent assay (ELISA) in serum specimens from 397 HCC patients, 114 healthy individuals, 43 patients with chronic hepatitis B virus (HBV) infection and 24 cirrhotic liver patients with HBV infection, and the correlation between DLK1 levels and clinical features was evaluated. Our data showed that the serum DLK1 level was significantly higher in HCC patients than in healthy individuals or patients with chronic HBV infection (HBV carriers) (P < 0.05). Moreover, the serum DLK1 levels were positively correlated with tumour size and α-fetoprotein (AFP) levels, but not with gender, age, histological grade, HBV infection, intrahepatic metastasis or cirrhosis in HCC patients. Kaplan-Meier analysis indicated that higher DLK1 levels were associated with shorter survival in HCC patients. These results suggest that the serum levels of DLK1 may serve as a prognostic biomarker for HCC patients.

[A nonlinear multi-compartment lung model for optimization of breathing airflow pattern].

It is difficult to select the appropriate ventilation mode in clinical mechanical ventilation. This paper presents a nonlinear multi-compartment lung model to solve the difficulty. The purpose is to optimize respiratory airflow patterns and get the minimum of the work of inspiratory phrase and lung volume acceleration, minimum of the elastic potential energy and rapidity of airflow rate changes of expiratory phrase. Sigmoidal function is used to smooth the respiratory function of nonlinear equations. The equations are established to solve nonlinear boundary conditions BVP, and finally the problem was solved with gradient descent method. Experimental results showed that lung volume and the rate of airflow after optimization had good sensitivity and convergence speed. The results provide a theoretical basis for the development of multivariable controller monitoring critically ill mechanically ventilated patients.

Caprin-1 is a novel microRNA-223 target for regulating the proliferation and invasion of human breast cancer cells.

MicroRNAs (miRNAs) are 21-22 nucleotides regulatory small non-coding RNAs that inhibit gene expression by binding to complementary sequences especially the 3' untranslated region (3'UTR) of mRNA. One miRNA can target many messenger RNAs, leading to a complex metabolic network. Previous studies have shown that miRNA-223 regulates migration and invasion of tumor cells and targets cytoplasmic activation/proliferation-associated protein-1 (Caprin-1). In the present study, we detected the expression of miRNA-223 and Caprin-1 in MCF-7, T-47D and MDA-MB-231 cancer cell lines, and MCF-10A normal breast cell line, and analyzed the role of miRNA-223 in Caprin-1-induced proliferation and invasion of human breast cancer cells. We found that miRNA-223 expression levels are significantly lower in MCF-7, T-47D and MDA-MB-231 cancer cells than in MCF-10A normal breast cells, while Caprin-1 expression is higher in cancer cells than in normal breast cells. The most malignant cancer cell line MDA-MB-231 has the lowest expression of miR-223, but the highest expression of Caprin-1. Further, we found that miR-223 targets the 3'UTR of Caprin-1 miRNA and down-regulates the expression of Caprin-1. We also found that over-expression of Caprin-1 can promote the proliferation and the invasion of breast cancer cells, but miRNA-223 can inhibit the proliferation and the invasion. miRNA-223-induced inhibition can be reversed by ectopic over-expression of Caprin-1. These findings suggest that miR-223 may suppress the proliferation and invasion of cancer cells by directly targeting Caprin-1. Our study also indicates that expression levels of miR-223 and Caprin-1 can be used to predict the state of cancer in breast cancer patient.

Cell-free DNA in blood is a potential diagnostic biomarker of breast cancer.

Breast cancer is a highly malignant disease in women. A convenient screening tool with high accuracy for early detection, not only in high-risk individuals but in the general population, is necessary. Two hundred breast cancer patients, 100 healthy controls and 100 hyperplasia patients were enrolled in this study. Samples were randomly assigned into training or testing cohorts. The receiver operating characteristic curve was used to explore the optimal concentration of cell-free DNA (GAPDH) in the training cohort and the cut-off point was validated in the testing cohort. The results showed that both in the training and testing cohorts, the overall accuracy of classification between cancer, healthy controls and hyperplasia was higher than 0.9. The sensitivity, specificity, positive predictive value and negative predictive value also reached 0.9, with the exception of the negative predictive value in the testing cohort. This study provides useful information on the use of concentration of free DNA for breast cancer detection. These findings need to be validated in a large prospective trial prior to clinical application.

Anisotropic conduction block and reentry in neonatal rat ventricular myocyte monolayers.

Anisotropy can lead to unidirectional conduction block that initiates reentry. We analyzed the mechanisms in patterned anisotropic neonatal rat ventricular myocyte monolayers. Voltage and intracellular Ca (Ca(i)) were optically mapped under the following conditions: extrastimulus (S1S2) testing and/or tetrodotoxin (TTX) to suppress Na current availability; heptanol to reduce gap junction conductance; and incremental rapid pacing. In anisotropic monolayers paced at 2 Hz, conduction velocity (CV) was faster longitudinally than transversely, with an anisotropy ratio [AR = CV(L)/CV(T), where CV(L) and CV(T) are CV in the longitudinal and transverse directions, respectively], averaging 2.1 ± 0.8. Interventions decreasing Na current availability, such as S1S2 pacing and TTX, slowed CV(L) and CV(T) proportionately, without changing the AR. Conduction block preferentially occurred longitudinal to fiber direction, commonly initiating reentry. Interventions that decreased gap junction conductance, such as heptanol, decreased CV(T) more than CV(L), increasing the AR and causing preferential transverse conduction block and reentry. Rapid pacing resembled the latter, increasing the AR and promoting transverse conduction block and reentry, which was prevented by the Ca(i) chelator 1,2-bis oaminophenoxy ethane-N,N,N',N'-tetraacetic acid (BAPTA). In contrast to isotropic and uniformly anisotropic monolayers, in which reentrant rotors drifted and self-terminated, bidirectional anisotropy (i.e., an abrupt change in fiber direction exceeding 45°) caused reentry to anchor near the zone of fiber direction change in 77% of monolayers. In anisotropic monolayers, unidirectional conduction block initiating reentry can occur longitudinal or transverse to fiber direction, depending on whether the experimental intervention reduces Na current availability or decreases gap junction conductance, agreeing with theoretical predictions.

Atrioventricular conduction and arrhythmias at the initiation of beating in embryonic mouse hearts.

To investigate cardiac physiology at the onset of heart beating in embryonic mouse hearts, we performed optical imaging of membrane potential (Vm) and/or intracellular calcium (Ca(i)). Action potentials and Ca(i) transients were detected in approximately 50% of mouse embryo hearts at E8.5, but in all hearts at E9.0, indicating that beating typically starts between E8-E9. Beating was eliminated by Ca channel blocker nifedipine and the I(f) blocker ZD7288, unaffected by tetrodotoxin and only mildly depressed by disabling sarcoplasmic (SR) and endoplasmic (ER) reticulum Ca cycling. From E8.5 to E10, conduction velocity increased from 0.2-1 mm/s to >5 mm/s in first ventricular and then atrial tissue, while remaining slow in other areas. Arrhythmias included atrioventricular reentry induced by adenosine. In summary, at the onset of beating, I(f)-dependent pacemaking drives both AP propagation and Ca(i) transient generation through activation of voltage-dependent Ca channels. Na channels and intracellular Ca cycling have minor roles.

Increased susceptibility of aged hearts to ventricular fibrillation during oxidative stress.

Oxidative stress with hydrogen peroxide (H(2)O(2)) readily promotes early afterdepolarizations (EADs) and triggered activity (TA) in isolated rat and rabbit ventricular myocytes. Here we examined the effects of H(2)O(2) on arrhythmias in intact Langendorff rat and rabbit hearts using dual-membrane voltage and intracellular calcium optical mapping and glass microelectrode recordings. Young adult rat (3-5 mo, N = 25) and rabbit (3-5 mo, N = 6) hearts exhibited no arrhythmias when perfused with H(2)O(2) (0.1-2 mM) for up to 3 h. However, in 33 out of 35 (94%) aged (24-26 mo) rat hearts, 0.1 mM H(2)O(2) caused EAD-mediated TA, leading to ventricular tachycardia (VT) and fibrillation (VF). Aged rabbits (life span, 8-12 yr) were not available, but 4 of 10 middle-aged rabbits (3-5 yr) developed EADs, TA, VT, and VF. These arrhythmias were suppressed by the reducing agent N-acetylcysteine (2 mM) and CaMKII inhibitor KN-93 (1 microM) but not by its inactive form (KN-92, 1 microM). There were no significant differences between action potential duration (APD) or APD restitution slope before or after H(2)O(2) in aged or young adult rat hearts. In histological sections, however, trichrome staining revealed that aged rat hearts exhibited extensive fibrosis, ranging from 10-90%; middle-aged rabbit hearts had less fibrosis (5-35%), whereas young adult rat and rabbit hearts had <4% fibrosis. In aged rat hearts, EADs and TA arose most frequently (70%) from the left ventricular base where fibrosis was intermediate ( approximately 30%). Computer simulations in two-dimensional tissue incorporating variable degrees of fibrosis showed that intermediate (but not mild or severe) fibrosis promoted EADs and TA. We conclude that in aged ventricles exposed to oxidative stress, fibrosis facilitates the ability of cellular EADs to emerge and generate TA, VT, and VF at the tissue level.

Oxidative-stress-induced afterdepolarizations and calmodulin kinase II signaling.

In the heart, oxidative stress caused by exogenous H(2)O(2) has been shown to induce early afterdepolarizations (EADs) and triggered activity by impairing Na current (I(Na)) inactivation. Because H(2)O(2) activates Ca(2+)/calmodulin kinase (CaMK)II, which also impairs I(Na) inactivation and promotes EADs, we hypothesized that CaMKII activation may be an important factor in EADs caused by oxidative stress. Using the patch-clamp and intracellular Ca (Ca(i)) imaging in Fluo-4 AM-loaded rabbit ventricular myocytes, we found that exposure to H(2)O(2) (0.2 to 1 mmol/L) for 5 to 15 minutes consistently induced EADs that were suppressed by the I(Na) blocker tetrodotoxin (10 micromol/L), as well as the I(Ca,L) blocker nifedipine. H(2)O(2) enhanced both peak and late I(Ca,L), consistent with CaMKII-mediated facilitation. By prolonging the action potential plateau and increasing Ca influx via I(Ca,L), H(2)O(2)-induced EADs were also frequently followed by DADs in response to spontaneous (ie, non-I(Ca,L)-gated) sarcoplasmic reticulum Ca release after repolarization. The CaMKII inhibitor KN-93 (1 micromol/L; n=4), but not its inactive analog KN-92 (1 micromol/L, n=5), prevented H(2)O(2)-induced EADs and DADs, and the selective CaMKII peptide inhibitor AIP (autocamtide-2-related inhibitory peptide) (2 micromol/L) significantly delayed their onset. In conclusion, H(2)O(2)-induced afterdepolarizations depend on both impaired I(Na) inactivation to reduce repolarization reserve and enhancement of I(Ca,L) to reverse repolarization, which are both facilitated by CaMKII activation. Our observations support a link between increased oxidative stress, CaMKII activation, and afterdepolarizations as triggers of lethal ventricular arrhythmias in diseased hearts.