Hypernatremia and Intercalated Disc Edema Synergistically Exacerbate Long QT Syndrome Type 3 Phenotype

Background: Cardiac voltage-gated sodium channel gain-of-function prolongs repolarization in the Long-QT Syndrome Type 3 (LQT3). Previous studies suggest that narrowing the perinexus within the intercalated disc, leading to rapid sodium depletion, attenuates LQT3-associated action potential duration (APD) prolongation. However, it remains unknown whether extracellular sodium concentration modulates APD prolongation during sodium channel gain-of-function. We hypothesized that elevated extracellular sodium concentration and widened perinexus synergistically prolong APD in LQT3. Methods and Results: LQT3 was induced with anemone toxin type II (ATXII) in Langendorff-perfused guinea pig hearts (n=20). Sodium concentration was increased from 145 to 160 mM. Perinexal expansion was induced with mannitol or the sodium channel β1-subunit adhesion domain antagonist (βadp1). Epicardial ventricular action potentials were optically mapped. Individual and combined effects of varying clefts and sodium concentrations were simulated in a computational model. With ATXII, both mannitol and βadp1 significantly widened the perinexus and prolonged APD, respectively. The elevated sodium concentration alone significantly prolonged APD as well. Importantly, the combination of elevated sodium concentration and perinexal widening synergistically prolonged APD. Computational modeling results were consistent with animal experiments. Conclusions: Concurrently elevating extracellular sodium and increasing intercalated disc edema prolongs repolarization more than the individual interventions alone in the LQT3. This synergistic effect suggests an important clinical implication that hypernatremia in the presence of cardiac edema can markedly increase LQT3-associated APD prolongation. Therefore, this is the first study to provide evidence of a tractable and effective strategy to mitigate LQT3 phenotype by managing patient sodium levels and preventing cardiac edema.

P3099Lymphatic insufficiency increases cardiac edema after myocardial infarction as assessed by novel magnetic resonance TRAFFn and T2 relaxation times

Introduction The role of cardiac lymphatic system in myocardial infarction (MI) is still unclear. A new method to detect and characterize MI without contrast agent is a relaxation along a fictitious field in nth rotating frame (RAFFn). The RAFFn takes advantage of the fictitious magnetic field, which is produced by a fast sweep of an effective radio frequency field, to increase a spin locking field strength without increasing the specific absorption rate. MI is detected as increased RAFFn relaxation times and cardiac edema by an increased T2 relaxation time. We have shown earlier that MI size can be accurately measured by the RAFFn relaxation times. Purpose To study the effects of the lack of cardiac lymphatic system on MI and cardiac edema in a mouse model. Methods Transgenic (TG) mice expressing soluble decoy VEGF receptor 3 (sVEGFR3) thus blocking lymphatic vessel formation in the heart and wild type (WT) control mice were used. MI was induced in 13–17 week old TG (n=11) and WT (n=14) mice by ligating the left anterior descending coronary artery. The RAFFn (TRAFF2 and TRAFF4), a continuous wave T1ρ and a T2 relaxation times were acquired at time points 0, 3, 7 and 21 days after the MI at 9.4 T. Histological sections were stained with hematoxylin eosin and Sirius red to assess cellularity and MI area. An Area of difference (AOD) was determined by subtracting MI areas based on TRAFF2, TRAFF4 and T1ρ maps from MI area based on T2 maps. Results MI size based on the TRAFF4 and T2 relaxation time maps were larger at early time points 3 and 7 days post MI in the WT group compared to the TG group (Figure 1A-B, p<0.05). However, the MI size was significantly larger in the T2 relaxation time map in the TG group compared to the WT group at the last time point and interaction between the groups were significant as a function of time (Figure 1A-B, p<0.05). The AOD values, which reflect cardiac edema, increased in the TG group as a function of time (Figure 1C, p<0.001). TRAFF2, TRAFF4 (Figure 1D), T1ρ and T2 relaxation times increased significantly (≈50%, p<0.001) after the MI compared to remote areas in both groups. In the WT group, the lymphatic vessel network is fully functional and removes edema efficiently between days 3 and 21 after the MI, while in the TG group the MI area in T2 map is relative stable indicating insufficient edema removal, caused by the lymphatic deficiency and insufficient lymphangiogenesis in the TG group. The MIs were also verified based on Sirius red stained histology (Figure 1E). Figure 1 Conclusion Lymphatic deficiency increases cardiac edema (AOD values) 7–21 days after MI as compared to the WT group. Results support the importance of cardiac lymphatic vessels for healing after MI. Effects of the lymphatics on MI can be detected based on the MI size difference based on the TRAFFn and the T2 relaxation times. Acknowledgement/Funding Doctoral Programme of Molecular Medicine

ACUTE TOXICITY OF BISPHENOL A INDUCED PHENOTYPIC CHANGES ON ZEBRAFISH (DANIO RERIO) DURING EARLY DEVELOPMENT

Bisphenol A (BPA) has been considered as a weak environmental estrogen, as similar to estradiol that has a potential in stimulating some cellular responses and phenotype changes. In addition, the ecological impacts of BPA to aquatic organisms have been increasingly raised at environmental relevant concentrations that potentially may affect to human health at early–life. This study used 3-day old zebrafish larvae (Danio rerio) as a model for toxicological testing. The semistatic testing was conducted to investigate the effects of different BPA concentrations (5 mg/L, 6 mg/L, 7 mg/L, 8 mg/L and 9 mg/L) that induced morphorlogical and physiological changes during the early development. As the results, the LC50-24hrs, LC50-48hrs, LC50-72hrs and LC50-96hrs were determined as 9.503 mg/L, 8.688 mg/L, 7.328 mg/L and 6.669 mg/L, respectively. Phenotypic analysis revealed that toxicity caused cardiac edema. The result obtained from this research provided relevant information for environmental and human risk assessments.

Developmental Toxicity Assay for Food Additive Tartrazine Using Zebrafish (Danio rerio) Embryo Cultures

Tartrazine (TTZ) is an azo dye used as a colorant in food products, drugs, and cosmetics. The present study evaluates the impacts of TTZ on embryonic development of zebrafish ( Danio rerio). Laboratory-raised D. rerio embryos (n = 20/concentration) were exposed to graded dilutions of TTZ (0, 0.1, 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 75, and 100 mM) from gastrulation stage (5.25 hours postfertilization [hpf]) until hatching and developmental trajectory was traced up to day 7. The no observed effect concentration (NOEC), median lethal concentration (LC50), median effective concentration (EC50), and teratogenic index (TI) were calculated. Exposure of embryos to < 10 mM TTZ had no effects; 20 to 30 mM TTZ caused tail bending, cardiac and yolk sac edema in 50% of larvae; in 30 to 50 mM TTZ-exposed embryos the heart rates declined along with the above mentioned deformities, causing mortality within 96 to 144 hpf; development ceased completely at 75 to 100 mM concentration. The NOEC and LC50 were recorded at 5 and 29.4 mM dose, respectively. The EC50 values for heart rate, cardiac edema, tail bending, and hatching success were at 59.60, 53.81, 98.28, and 58.97 mM with TI quotient 0.49, 0.54, 0.29, and 0.49, respectively. We conclude that TTZ is not embryo toxic/teratogenic for zebrafish embryos up to a dose level of 10 mM concentration.

Abstract 10378: Characterization of Changes in Cardiac Structure and Function in Mice Treated With Anthracyclines Using Serial Cardiac Magnetic Resonance Imaging

Introduction: Anthracyclines are a standard chemotherapeutic agent. However, the anthracyclines are associated with a late reduction in left ventricular ejection fraction (LVEF) and heart failure. Pathologically, anthracycline-induced cardiotoxicity (AIC) is characterized by the development of cardiac edema and fibrosis and cardiac magnetic resonance (CMR) is the gold-standard imaging technique for edema and fibrosis. Hypothesis: We hypothesized that a) cardiac edema and fibrosis would be detected by CMR after anthracyclines and b) edema and fibrosis would provide prognostic information. Methods: We performed a longitudinal CMR and histological study of 45 wild-type mice randomized to doxorubicin (DOX, n=30, 5 mg/kg/week for 5 weeks) or placebo (n=15). Measurements were performed at baseline, 5, 10, and 20 weeks after DOX or placebo. Measures of interest were LVEF, myocardial edema and fibrosis. Edema was assessed by T2 mapping, fibrosis by calculating the extracellular volume (ECV) from pre- and post-contrast T1 measurements. Results: In DOX-treated mice vs. placebo, myocardial edema at 5 weeks was increased (T2 values of 32±4 vs. 21±3 ms, P<0.05, Fig. A), while LVEF was unchanged. At 10 weeks, there was a reduction in LVEF (54±6 vs. 63±5% μL, P<0.05) and an increase in myocardial fibrosis (ECV of 0.34±0.03 vs. 0.27±0.03, P<0.05, Fig. B). There was a correlation between T2 measures and cardiac water weight (r=0.79, P=0.007, Fig. C) and between the ECV and histological myocardial fibrosis (r=0.90, P<0.001; Fig. D). Both the early increase in edema and the sub-acute increase in fibrosis predicted the late DOX-induced mortality (P<0.001, Fig. E and F). Conclusions: Our data suggest that, in mice, CMR can detect the early increase in edema and sub-acute increase in fibrosis after anthracyclines, that an increase in edema precedes a reduction in LVEF, that the increase in edema and fibrosis are linked and both are predictive of late animal mortality.