Benjamin E. Reinking

Essential Roles of an Intercalated Disc Protein, mXinβ, in Postnatal Heart Growth and Survival

Rationale: The Xin repeat-containing proteins mXin&agr; and mXin&bgr; localize to the intercalated disc of mouse heart and are implicated in cardiac development and function. The mXin&agr; directly interacts with &bgr;-catenin, p120-catenin, and actin filaments. Ablation of mXin&agr; results in adult late-onset cardiomyopathy with conduction defects. An upregulation of the mXin&bgr; in mXin&agr;-deficient hearts suggests a partial compensation. Objective: The essential roles of mXin&bgr; in cardiac development and intercalated disc maturation were investigated. Methods and Results: Ablation of mXin&bgr; led to abnormal heart shape, ventricular septal defects, severe growth retardation, and postnatal lethality with no upregulation of the mXin&agr;. Postnatal upregulation of mXin&bgr; in wild-type hearts, as well as altered apoptosis and proliferation in mXin&bgr;-null hearts, suggests that mXin&bgr; is required for postnatal heart remodeling. The mXin&bgr;-null hearts exhibited a misorganized myocardium as detected by histological and electron microscopic studies and an impaired diastolic function, as suggested by echocardiography and a delay in switching off the slow skeletal troponin I. Loss of mXin&bgr; resulted in the failure of forming mature intercalated discs and the mislocalization of mXin&agr; and N-cadherin. The mXin&bgr;-null hearts showed upregulation of active Stat3 (signal transducer and activator of transcription 3) and downregulation of the activities of Rac1, insulin-like growth factor 1 receptor, protein kinase B, and extracellular signal-regulated kinases 1 and 2. Conclusions: These findings identify not only an essential role of mXin&bgr; in the intercalated disc maturation but also mechanisms of mXin&bgr; modulating N-cadherin-mediated adhesion signaling and its crosstalk signaling for postnatal heart growth and animal survival.

Cardiomyopathy in offspring of diabetic rats is associated with activation of the MAPK and apoptotic pathways.

BackgroundMaternal diabetes affects the developing fetal cardiovascular system. Newborn offspring of diabetic mothers can have a transient cardiomyopathy. We hypothesized that cardiomyopathic remodeling is associated with activation of the mitogen activated protein kinase (MAPK) signaling and apoptotic pathways.MethodsTo evaluate the effects of moderate and severe maternal hyperglycemia, pregnant rats were made diabetic with an injection of 50 mg/kg of streptozotocin. Moderately well controlled maternal diabetes was achieved with twice daily glucose checks and insulin injections. No insulin was given to severely diabetic dams. Offspring of moderate and severe diabetic mothers (OMDM and MSDM, respectively) were studied on postnatal days 1 (NB1) and 21 (NB21). Echocardiograms were performed to evaluate left ventricular (LV) dimensions and function. Myocardial MAPK and apoptotic protein levels were measured by Western blot.ResultsOMDM had increased cardiac mass at NB1 compared to controls that normalized at NB21. OSDM demonstrated microsomia with relative sparing of cardiac mass and a dilated cardiomyopathy at NB1. In both models, there was a persistent increase in the HW:BW and significant activation of MAPK and apoptotic pathways at NB21.ConclusionThe degree of maternal hyperglycemia determines the type of cardiomyopathy seen in the offspring, while resolution of both the hypertrophic and dilated cardiomyopathies is associated with activation of MAPK signaling and apoptotic pathways.

Sertraline exposure leads to small left heart syndrome in adult mice

Background:Sertraline, a selective serotonin reuptake inhibitor (SSRI), is the most commonly prescribed therapy for maternal depression. Epidemiologic studies have linked SSRI exposure with decreased fetal growth, altered autonomic regulation, and cardiac malformations. We hypothesized that SSRI exposure decreases left-ventricular (LV) volumes and increases adult sympathetic nervous system activation, resulting in increased adult heart rates.Methods:C57BL/6 mice received saline or sertraline (5 or 15 mg/kg/day i.p.) on postnatal days 1–14. Adult phenotypes were assessed at 5 mo.Results:Sertraline-exposed mice had smaller LV internal diameters in diastole (control 4.0 ± 0.1 mm, SSRI 3.7 ± 0.1 mm, P < 0.05), decreased stroke volumes (control 46 ± 2.6 µl, SSRI 37 ± 2.3 µl, P < 0.05), higher heart rates (control 530 ± 13 beats per minute (bpm), SSRI 567 ± 6 bpm, P <0.05), and increased urinary excretion of noradrenaline (control 174 ± 29.4 ng/ml, SSRI 276 ± 35.1 ng/ml, P < 0.05). These changes were associated with increased cerebral serotonin transporter (5-HTT) expression.Conclusion:Neonatal sertraline exposure causes long-term changes in cardiac morphology and physiology. We speculate that early-life SSRI exposure impairs cardiomyocyte growth and central serotonin signaling, leading to a small left heart syndrome in adult mice.

Programming of Adult Cardiovascular Disease following Exposure to Late-Gestation Hyperglycemia

Background: In utero exposure to hyperglycemia is becoming increasingly prevalent as the number of women entering pregnancy with type II diabetes, or developing gestational diabetes, increases. Both animal studies and epidemiologic investigations have found cardiovascular abnormalities in adult offspring of hyperglycemic mothers (OHM). Objective: We hypothesized that adult OHM would have abnormal cardiac function in vivo and increased susceptibility to ischemia. Methods: Pregnant rats were made diabetic on day 12 of gestation. Serum glucose was monitored twice daily and insulin provided to maintain serum glucose at 200–400 mg/dl. Offspring were fostered to normal mothers after birth. Adult OHM were studied at 8–10 months of age with echocardiography to assess in vivo cardiac function and isolated hearts to determine the response to ischemia. Results: Echocardiography found significant diastolic dysfunction in male OHM compared to male controls. In isolated hearts, baseline cardiac function and left ventricular compliance was significantly diminished in male OHM compared to controls. Ischemia caused a significant decline in heart function in controls and female OHM, while function in male OHM remained unchanged. Conclusions: Adult male OHM demonstrate programmed cardiac dysfunction. Given the growing number of pregnancies complicated by hyperglycemia, additional assessment of cardiac function of adults born to diabetic mothers may be warranted.

Norwood Reconstruction Using Continuous Coronary Perfusion: A Safe and Translatable Technique

BACKGROUND Continuous coronary perfusion during Norwood reconstruction offers the theoretic advantage of less postoperative cardiac dysfunction. The avoidance of a cardiac and circulatory arrest period allows time for a more deliberate aortic reconstruction while the heart remains beating. This single-center study was designed to compare patient results using this method vs standard cardiac arrest for Norwood reconstruction. METHODS A retrospective review was done of 32 patients undergoing Norwood reconstruction from November 2004 to July 2011. The operations in the most recent 16 consecutive patients were performed under deep hypothermia with constant coronary and cerebral perfusion. Continuous coronary perfusion was provided by a cannula inserted into the proximal aorta. The operations in the prior 16 consecutive patients were performed using deep hypothermia, selective cerebral perfusion, and cardioplegic arrest during aortic reconstruction. RESULTS Survival in the beating-heart group was 87.5% (14 of 16) vs 62.5% (10 of 16) in the standard group (p = 0.22). No patients in the beating-heart group required extracorporeal membrane oxygenation vs 3 in the standard group. Postoperative cardiac function was similar for both groups. The beating-heart cohort had lower peak lactate levels (8.2 mEq/L) than the standard group (10.7 mEq/L, p = 0.022). CONCLUSIONS This study presents the largest series of Norwood operations in which the entire aorta is augmented while delivering continuous coronary perfusion. The technique is applicable to any size aorta and represents a safe alternative because outcomes for survival, freedom from extracorporeal membrane oxygenation, postoperative cardiac function, and lactate levels were all noninferior compared with the standard technique.

Maternal Hyperglycemia Directly and Rapidly Induces Cardiac Septal Overgrowth in Fetal Rats

Cardiac septal overgrowth complicates 10–40% of births from diabetic mothers, but perplexingly hyperglycemia markers during pregnancy are not reliably predictive. We thus tested whether fetal exposure to hyperglycemia is sufficient to induce fetal cardiac septal overgrowth even in the absence of systemic maternal diabetes. To isolate the effects of hyperglycemia, we infused glucose into the blood supply of the left but not right uterine horn in nondiabetic pregnant rats starting on gestational day 19. After 24 h infusion, right-sided fetuses and dams remained euglycemic while left-sided fetuses were moderately hyperglycemic. Echocardiograms in utero demonstrated a thickened cardiac septum among left-sided (glucose-exposed, 0.592 ± 0.016 mm) compared to right-sided (control, 0.482 ± 0.016 mm) fetuses. Myocardial proliferation was increased 1.5 ± 0.2-fold among left-sided compared to right-sided fetuses. Transcriptional markers of glucose-derived anabolism were not different between sides. However, left-sided fetuses exhibited higher serum insulin and greater JNK phosphorylation compared to controls. These results show that hyperglycemic exposure is sufficient to rapidly induce septal overgrowth even in the absence of the myriad other factors of maternal diabetes. This suggests that even transient spikes in glucose may incite cardiac overgrowth, perhaps explaining the poor clinical correlation of septal hypertrophy with chronic hyperglycemia.

Mycotic aneurysm in a child with history of coarctation of the aorta repair

A mycotic aneurysm is a rare condition occasionally seen in patients with a history of prior cardiac or vascular surgery. Here we report the presentation of a mycotic aneurysm in a pediatric patient at the site of prior aortic coarctation repair. This patients initial presentation suggested rheumatologic or oncologic disease, and after diagnosis he continued to show evidence of splenic, renal and vascular injury distal to the mycotic aneurysm site while being treated with antibiotics. We discuss the diagnosis, treatment and management of this condition.

Oral oestrogen reverses ovariectomy-induced morning surge hypertension in growth-restricted mice

Perinatal growth restriction (GR) is associated with heightened sympathetic tone and hypertension. We have previously shown that naturally occurring neonatal GR programmes hypertension in male but not female mice. We therefore hypothesized that intact ovarian function or post-ovariectomy (OVX) oestrogen administration protects GR female mice from hypertension. Utilizing a non-interventional model that categorizes mice with weanling weights below the tenth percentile as GR, control and GR adult mice were studied at three distinct time points: baseline, post-OVX and post-OVX with oral oestrogen replacement. OVX elicited hypertension in GR mice that was significantly exacerbated by psychomotor arousal (systolic blood pressure at light to dark transition: control 122 ± 2; GR 119 ± 2; control-OVX 116 ± 3; GR-OVX 126 ± 3 mmHg). Oestrogen partially normalized the rising blood pressure surge seen in GR-OVX mice (23 ± 7% reduction). GR mice had left ventricular hypertrophy, and GR-OVX mice in particular had exaggerated bradycardic responses to sympathetic blockade. For GR mice, a baseline increase in baroreceptor reflex sensitivity and high frequency spectral power support a vagal compensatory mechanism, and that compensation was lost following OVX. For GR mice, the OVX-induced parasympathetic withdrawal was partially restored by oestrogen (40 ± 25% increase in high frequency spectral power, P<0.05). In conclusion, GR alters cardiac morphology and cardiovascular regulation. The haemodynamic consequences of GR are attenuated in ovarian-sufficient or oestrogen-replete females. Further investigations are needed to define the role of hormone replacement therapy targeted towards young women with oestrogen deficiency and additional cardiovascular risk factors, including perinatal GR, cardiac hypertrophy and morning surge hypertension.

Impact of neonatal sertraline exposure on the post-myocardial infarction outcomes of adult male mice.

Abstract: Neonatal exposure to a selective serotonin reuptake inhibitor (SSRI) leads to decreased left ventricular volumes and sympathetic activation in adult mice. We hypothesized this neonatal SSRI exposure–induced small left heart syndrome would increase post–myocardial infarction (MI) morbidity and mortality. C57BL/6 mice received saline or sertraline (5 mg/kg intraperitoneally) on postnatal days 1–14. At 5 months, male mice underwent coronary artery ligation and were monitored by radiotelemetry until death or 4 weeks after ligation. After ligation, SSRI-exposed mice had increased heart rates (SSRI, 516 ± 13 bpm; control, 470 ± 15 bpm; P < 0.05). SSRI-exposed mice had significant reductions in left ventricular systolic volumes both before and after coronary ligation (SSRI: baseline = 20 ± 3 &mgr;L, post-MI = 37 ± 10 &mgr;L; control: baseline = 30 ± 3 &mgr;L, post-MI = 65 ± 23 &mgr;L). Post-MI echocardiography showed significantly decreased ejection fraction in control mice (baseline = 60% ± 4%, post-MI = 41% ± 2%, P < 0.01) but not the SSRI-exposed mice (baseline = 65% ± 3%, post-MI = 53% ± 7%). Neonatal SSRI exposure did not significantly alter post-MI survival. We conclude that the preexisting SSRI-induced small left heart syndrome may provide protection from post-MI ventricular dilation.

Bovine arch anatomy influences recoarctation rates in the era of the extended end-to-end anastomosis

Objectives: Arch branching has never been shown to influence recoarctation after extended end‐to‐end anastomosis via thoracotomy, yet in each study bovine arch identification is grossly underreported. This study aims to (1) assess chart review reliability in bovine arch identification; (2) determine recoarctation risk with a bovine arch; and (3) explore an anatomic explanation for recurrent arch obstruction based on arch anatomy. Patients: A total of 49 consecutive patients underwent thoracotomy with extended end‐to‐end aortic coarctation repair at a single institution (2007‐2012). Methods: Echocardiograms from these patients were reviewed for arch anatomy and compared with the echocardiographic reports. Recurrent arch obstruction was defined as an echocardiographic gradient across the repair of 20 mm Hg or greater. For cases with angiographic images (n = 17), a scaled clamping distance between the left subclavian artery and the maximal proximal clamp location on orthogonal projections was then calculated across arch anatomies. Results: Chart review identified 6.1% (3/49) of patients with a bovine arch compared with 28.6% (14/49) on targeted image review. A total of 28.6% (4/14) of patients with a bovine arch had a follow‐up gradient of 20 mm Hg or greater. Only 5.7% (2/35) of patients with normal arch branching had a follow‐up gradient of 20 mm Hg or greater. The mean clamping index was significantly diminished in patients with bovine arch anatomy. Conclusions: Arch anatomy often goes undocumented on preoperative imaging, yet children undergoing extended end‐to‐end repair with bovine arch anatomy are at a significantly increased risk of recoarctation. This may be due to a reduced clampable distance to facilitate repair. These results should be considered in the preoperative assessment, parental counseling, and surgical approach for children with discrete aortic coarctation.