Biomarkers of fibrosis and portal hypertension in Fontan-associated liver disease in children and adults

BACKGROUND

Fontan-associated liver disease (FALD) refers to structural and functional changes of the liver caused by the physiology of the Fontan palliation. Currently, liver biopsy is the gold standard to assess liver fibrosis of FALD.

AIM

Investigate biomarkers correlating with severity of liver biopsy fibrosis in FALD.

METHODS

A retrospective study of post-Fontan patients ≥ 10 years of age who underwent liver biopsy was conducted. Advanced liver disease (ALD) was defined as bridging fibrosis and/or cirrhosis on liver biopsy. AST-to-platelet ratio index (APRI), Fibrosis-4 (FIB-4) and Liver Stiffness Measurement (LSM) from FibroScan were used as non-invasive fibrosis scores.

RESULTS

Sixty-six patients (26/47; 55.3% adults and 13/19 children; 68.4%) had ALD on biopsy. ALD was associated with lower platelet count (151 vs. 198 K/uL, p = 0.003), higher APRI (0.64 vs. 0.32, p = 0.01), higher FIB-4 (0.64 vs. 0.32, p = 0.02). Liver fibrosis score correlated with APRI (0.34, p = 0.02) and FIB-4 (0.47, p = 0.001) in adults. LSM had a high sensitivity at 81.3% with 45.5% specificity at a cut-off 18.5 kPa.

CONCLUSIONS

APRI and FIB-4 had modest discrimination to identify adults with advanced liver disease, but not children, indicating that these values may be followed as a marker of FALD progression in older patients.

Apixaban for Prevention of Thromboembolism in Pediatric Heart Disease

BACKGROUND

Children with heart disease frequently require anticoagulation for thromboprophylaxis. Current standard of care (SOC), vitamin K antagonists or low-molecular-weight heparin, has significant disadvantages.

OBJECTIVES

The authors sought to describe safety, pharmacokinetics (PK), pharmacodynamics, and efficacy of apixaban, an oral, direct factor Xa inhibitor, for prevention of thromboembolism in children with congenital or acquired heart disease.

METHODS

Phase 2, open-label trial in children (ages, 28 days to <18 years) with heart disease requiring thromboprophylaxis. Randomization 2:1 apixaban or SOC for 1 year with intention-to-treat analysis.

PRIMARY ENDPOINT

a composite of adjudicated major or clinically relevant nonmajor bleeding. Secondary endpoints: PK, pharmacodynamics, quality of life, and exploration of efficacy.

RESULTS

From 2017 to 2021, 192 participants were randomized, 129 apixaban and 63 SOC. Diagnoses included single ventricle (74%), Kawasaki disease (14%), and other heart disease (12%). One apixaban participant (0.8%) and 3 with SOC (4.8%) had major or clinically relevant nonmajor bleeding (% difference -4.0 [95% CI: -12.8 to 0.8]). Apixaban incidence rate for all bleeding events was nearly twice the rate of SOC (100.0 vs 58.2 per 100 person-years), driven by 12 participants with ≥4 minor bleeding events. No thromboembolic events or deaths occurred in either arm. Apixaban pediatric PK steady-state exposures were consistent with adult levels.

CONCLUSIONS

In this pediatric multinational, randomized trial, bleeding and thromboembolism were infrequent on apixaban and SOC. Apixaban PK data correlated well with adult trials that demonstrated efficacy. These results support the use of apixaban as an alternative to SOC for thromboprophylaxis in pediatric heart disease. (A Study of the Safety and Pharmacokinetics of Apixaban Versus Vitamin K Antagonist [VKA] or Low Molecular Weight Heparin [LMWH] in Pediatric Subjects With Congenital or Acquired Heart Disease Requiring Anticoagulation; NCT02981472).

The Fontan Udenafil Exercise Longitudinal Trial: Subgroup Analysis

The Pediatric Heart Network's Fontan Udenafil Exercise Longitudinal (FUEL) Trial (Mezzion Pharma Co. Ltd., NCT02741115) demonstrated improvements in some measures of exercise capacity and in the myocardial performance index following 6 months of treatment with udenafil (87.5 mg twice daily). In this post hoc analysis, we evaluate whether subgroups within the population experienced a differential effect on exercise performance in response to treatment. The effect of udenafil on exercise was evaluated within subgroups defined by baseline characteristics, including peak oxygen consumption (VO2), serum brain-type natriuretic peptide level, weight, race, gender, and ventricular morphology. Differences among subgroups were evaluated using ANCOVA modeling with fixed factors for treatment arm and subgroup and the interaction between treatment arm and subgroup. Within-subgroup analyses demonstrated trends toward quantitative improvements in peak VO2, work rate at the ventilatory anaerobic threshold (VAT), VO2 at VAT, and ventilatory efficiency (VE/VCO2) for those randomized to udenafil compared to placebo in nearly all subgroups. There was no identified differential response to udenafil based on baseline peak VO2, baseline BNP level, weight, race and ethnicity, gender, or ventricular morphology, although participants in the lowest tertile of baseline peak VO2 trended toward larger improvements. The absence of a differential response across subgroups in response to treatment with udenafil suggests that the treatment benefit may not be restricted to specific sub-populations. Further work is warranted to confirm the potential benefit of udenafil and to evaluate the long-term tolerability and safety of treatment and to determine the impact of udenafil on the development of other morbidities related to the Fontan circulation.Trial Registration NCT0274115.

Researching COVID to enhance recovery (RECOVER) pediatric study protocol: Rationale, objectives and design

Importance

The prevalence, pathophysiology, and long-term outcomes of COVID-19 (post-acute sequelae of SARS-CoV-2 [PASC] or "Long COVID") in children and young adults remain unknown. Studies must address the urgent need to define PASC, its mechanisms, and potential treatment targets in children and young adults.

Observations

We describe the protocol for the Pediatric Observational Cohort Study of the NIH's RE searching COV ID to E nhance R ecovery (RECOVER) Initiative. RECOVER-Pediatrics is an observational meta-cohort study of caregiver-child pairs (birth through 17 years) and young adults (18 through 25 years), recruited from more than 100 sites across the US. This report focuses on two of five cohorts that comprise RECOVER-Pediatrics: 1) a de novo RECOVER prospective cohort of children and young adults with and without previous or current infection; and 2) an extant cohort derived from the Adolescent Brain Cognitive Development (ABCD) study ( n =10,000). The de novo cohort incorporates three tiers of data collection: 1) remote baseline assessments (Tier 1, n=6000); 2) longitudinal follow-up for up to 4 years (Tier 2, n=6000); and 3) a subset of participants, primarily the most severely affected by PASC, who will undergo deep phenotyping to explore PASC pathophysiology (Tier 3, n=600). Youth enrolled in the ABCD study participate in Tier 1. The pediatric protocol was developed as a collaborative partnership of investigators, patients, researchers, clinicians, community partners, and federal partners, intentionally promoting inclusivity and diversity. The protocol is adaptive to facilitate responses to emerging science.

Conclusions and Relevance

RECOVER-Pediatrics seeks to characterize the clinical course, underlying mechanisms, and long-term effects of PASC from birth through 25 years old. RECOVER-Pediatrics is designed to elucidate the epidemiology, four-year clinical course, and sociodemographic correlates of pediatric PASC. The data and biosamples will allow examination of mechanistic hypotheses and biomarkers, thus providing insights into potential therapeutic interventions.

Clinical Trialsgov Identifier

Clinical Trial Registration: http://www.clinicaltrials.gov . Unique identifier: NCT05172011.

Biomarker sST2 in Adults with Transposition of the Great Arteries Palliated by Mustard Procedure: A Five-Year Follow-up

The Mustard procedure was an early cardiac surgery for transposition of the great arteries (TGA). Despite being successful, it has been associated with long-term arrhythmias and heart failure. A key factor complicating management in adults with congenital heart disease (CHD) is the deficiency of biomarkers predicting outcome. Soluble suppression of tumorogenicity-2 (sST2) is secreted by cardiomyocytes in response to mechanical strain and fibrosis. We hypothesized that adults with a Mustard procedure would have higher levels of sST2 than healthy individuals, and this would correlate with clinical outcome. We performed a single-center study in patients managed during childhood with a Mustard procedure versus age-matched controls. Clinical and demographic data were collected and biomarkers (sST2, cTnI, BNP, lipid panel, insulin, and glucose) were obtained. There were 18 patients (12 male) in the Mustard cohort and 18 patients (6 male) in the control group (22-49 years, mean of 35.8 vs. mean 32.6 years, respectively, p = ns). Nine Mustard subjects were NYHA class II, and 9 subjects were class III. The control group was asymptomatic. sST2 in the Mustard group was elevated in 56% vs. 17% in controls (p = 0.035). Of the Mustard subjects with elevated sST2, 60% had elevated cTnI and BNP, and 90% had low HDL. Over five years, the Mustard patients with elevated sST2 values had greater medication use, arrhythmias, hospitalizations, and ablation/pacer implantations than Mustard subjects with normal sST2. Mustard subjects with elevated sST2 had other biomarker abnormalities and clinically worse outcomes. Thus, sST2 may add a predictive value to cardiac-related morbidity and mortality.

Examination of Adverse Reactions After COVID-19 Vaccination Among Patients With a History of Multisystem Inflammatory Syndrome in Children

Importance

Data are limited regarding adverse reactions after COVID-19 vaccination in patients with a history of multisystem inflammatory syndrome in children (MIS-C). The lack of vaccine safety data in this unique population may cause hesitancy and concern for many families and health care professionals.

Objective

To describe adverse reactions following COVID-19 vaccination in patients with a history of MIS-C.

Design, Setting, and Participants

In this multicenter cross-sectional study including 22 North American centers participating in a National Heart, Lung, and Blood Institute, National Institutes of Health-sponsored study, Long-Term Outcomes After the Multisystem Inflammatory Syndrome in Children (MUSIC), patients with a prior diagnosis of MIS-C who were eligible for COVID-19 vaccination (age ≥5 years; ≥90 days after MIS-C diagnosis) were surveyed between December 13, 2021, and February 18, 2022, regarding COVID-19 vaccination status and adverse reactions.

Exposures

COVID-19 vaccination after MIS-C diagnosis.

Main Outcomes and Measures

The main outcome was adverse reactions following COVID-19 vaccination. Comparisons were made using the Wilcoxon rank sum test for continuous variables and the χ2 or Fisher exact test for categorical variables.

Results

Of 385 vaccine-eligible patients who were surveyed, 185 (48.1%) received at least 1 vaccine dose; 136 of the vaccinated patients (73.5%) were male, and the median age was 12.2 years (IQR, 9.5-14.7 years). Among vaccinated patients, 1 (0.5%) identified as American Indian/Alaska Native, non-Hispanic; 9 (4.9%) as Asian, non-Hispanic; 45 (24.3%) as Black, non-Hispanic; 59 (31.9%) as Hispanic or Latino; 53 (28.6%) as White, non-Hispanic; 2 (1.1%) as multiracial, non-Hispanic; and 2 (1.1%) as other, non-Hispanic; 14 (7.6%) had unknown or undeclared race and ethnicity. The median time from MIS-C diagnosis to first vaccine dose was 9.0 months (IQR, 5.1-11.9 months); 31 patients (16.8%) received 1 dose, 142 (76.8%) received 2 doses, and 12 (6.5%) received 3 doses. Almost all patients received the BNT162b2 vaccine (347 of 351 vaccine doses [98.9%]). Minor adverse reactions were observed in 90 patients (48.6%) and were most often arm soreness (62 patients [33.5%]) and/or fatigue (32 [17.3%]). In 32 patients (17.3%), adverse reactions were treated with medications, most commonly acetaminophen (21 patients [11.4%]) or ibuprofen (11 [5.9%]). Four patients (2.2%) sought medical evaluation, but none required testing or hospitalization. There were no patients with any serious adverse events, including myocarditis or recurrence of MIS-C.

Conclusions and Relevance

In this cross-sectional study of patients with a history of MIS-C, no serious adverse events were reported after COVID-19 vaccination. These findings suggest that the safety profile of COVID-19 vaccination administered at least 90 days following MIS-C diagnosis appears to be similar to that in the general population.

Metabolomics analysis reveals dysregulation in one carbon metabolism in Friedreich Ataxia

Friedreich Ataxia (FA) is a rare and often fatal autosomal recessive disease in which a mitochondrial protein, frataxin (FXN), is severely reduced in all tissues. With loss of FXN, mitochondrial metabolism is severely disrupted. Multiple therapeutic approaches are in development, but a key limitation is the lack of biomarkers reflecting the activity of FXN in a timely fashion. We predicted this dysregulated metabolism would present a unique metabolite profile in blood of FA patients versus Controls (Con). Plasma from 10 FA and 11 age and sex matched Con subjects was analyzed by targeted mass spectrometry and untargeted NMR. This combined approach yielded quantitative measurements for 540 metabolites and found 59 unique metabolites (55 from MS and 4 from NMR) that were significantly different between cohorts. Correlation-based network analysis revealed several clusters of pathway related metabolites including a cluster associated with one‑carbon (1C) metabolism composed of formate, sarcosine, hypoxanthine, and homocysteine. Receiver operator characteristics analyses demonstrated an excellent ability to discriminate between Con and FA with AUC values >0.95. These results are the first reported metabolomic analyses of human patients with FA. The metabolic perturbations, especially those related to 1C metabolism, may serve as a valuable biomarker panel of disease progression and response to therapy. The identification of dysregulated 1C metabolism may also inform the search for new therapeutic targets related to this pathway.

Cardiovascular Research in Friedreich Ataxia: Unmet Needs and Opportunities

Friedreich Ataxia (FRDA) is an autosomal recessive disease in which a mitochondrial protein, frataxin, is severely decreased in its expression. In addition to progressive ataxia, patients with FRDA often develop a cardiomyopathy that can be hypertrophic. This cardiomyopathy is unlike the sarcomeric hypertrophic cardiomyopathies in that the hypertrophy is associated with massive mitochondrial proliferation within the cardiomyocyte rather than contractile protein overexpression. This is associated with atrial arrhythmias, apoptosis, and fibrosis over time, and patients often develop heart failure leading to premature death. The differences between this mitochondrial cardiomyopathy and the more common contractile protein hypertrophic cardiomyopathies can be a source of misunderstanding in the management of these patients. Although imaging studies have revealed much about the structure and function of the heart in this disease, we still lack an understanding of many important clinical and fundamental molecular events that determine outcome of the heart in FRDA. This review will describe the current basic and clinical understanding of the FRDA heart, and most importantly, identify major gaps in our knowledge that represent new directions and opportunities for research.

Myocardial Perfusion Reserve in Children with Friedreich Ataxia

Children with Friedreich's ataxia (FA) are at risk of perioperative morbidity and mortality from severe unpredictable heart failure. There is currently no clear way of identifying patients at highest risk. We used myocardial perfusion reserve (MPR), an MRI technique used to assess the maximal myocardial blood flow above baseline, to help determine potential surgical risk in FA subjects. In total, seven children with genetically confirmed FA, ages 8-17 years, underwent MPR stress testing using regadenoson. Six of the seven demonstrated impaired endocardial perfusion during coronary hyperemia. The same six were also found to have evidence of ongoing myocardial damage as illustrated by cardiac troponin I leak (range 0.04-0.17 ng/mL, normal < 0.03 ng/mL). None of the patients had a reduced ejection fraction (range 59-74%) or elevated insulin level (range 2.46-14.23 mCU/mL). This retrospective study shows that children with FA develop MPR defects early in the disease process. It also suggests MPR may be a sensitive tool to evaluate underlying cardiac compromise and could be of use in directing surgical management decisions in children with FA.

Metabolic profiles identify circulating biomarkers associated with heart failure in young single ventricle patients

BACKGROUND

Children and young adults with single ventricle (SV) heart disease frequently develop heart failure (HF) that is intractable and difficult to treat. Our understanding of the molecular and biochemical reasons underlying this is imperfect. Thus, there is an urgent need for biomarkers that predict outcome and provide a rational basis for treatment, and advance our understanding of the basis of HF.

OBJECTIVE

We sought to determine if a metabolomic approach would provide biochemical signatures of HF in SV children and young adults. If significant, these analytes might serve as biomarkers to predict outcome and inform on the biological mechanism(s) of HF.

METHODS

We applied a multi-platform metabolomics approach composed of mass spectrometry (MS) and nuclear magnetic resonance (NMR) which yielded 495 and 26 metabolite measurements respectively. The plasma samples came from a cross-sectional set of young SV subjects, ages 2-19 years with ten control (Con) subjects and 16 SV subjects. Of the SV subjects, nine were diagnosed as congestive HF (SVHF), and 7 were not in HF. Metabolomic data were correlated with clinical status to determine if there was a signature associated with HF.

RESULTS

There were no differences in age, height, weight or sex between the 3 cohorts. However, statistical analysis of the metabolomic profiles using ANOVA revealed 44 metabolites with significant differences between cohorts including 41 profiled by MS and 3 by NMR. These metabolites included acylcarnitines, amino acids, and bile acids, which distinguished Con from all SV subjects. Furthermore, metabolite profiles could distinguish between SV and SVHF subjects.

CONCLUSION

These are the first data to demonstrate a clear metabolomic signature associated with HF in children and young adults with SV. Larger studies are warranted to determine if these findings are predictive of progression to HF in time to provide intervention.

Cardiomyocyte microRNA-150 confers cardiac protection and directly represses pro-apoptotic small proline-rich protein 1A

MicroRNA-150 (miR-150) is downregulated in patients with multiple cardiovascular diseases and in diverse mouse models of heart failure (HF). miR-150 is significantly associated with HF severity and outcome in humans. We previously reported that miR-150 is activated by β-blocker carvedilol (Carv) and plays a protective role in the heart using a systemic miR-150 KO mouse model. However, mechanisms that regulate cell-specific miR-150 expression and function in HF are unknown. Here, we demonstrate that potentially novel conditional cardiomyocyte–specific (CM-specific) miR-150 KO (miR-150 cKO) in mice worsens maladaptive cardiac remodeling after myocardial infarction (MI). Genome-wide transcriptomic analysis in miR-150 cKO mouse hearts identifies small proline–rich protein 1a (Sprr1a) as a potentially novel target of miR-150. Our studies further reveal that Sprr1a expression is upregulated in CMs isolated from ischemic myocardium and subjected to simulated ischemia/reperfusion, while its expression is downregulated in hearts and CMs by Carv. We also show that left ventricular SPRR1A is upregulated in patients with HF and that Sprr1a knockdown in mice prevents maladaptive post-MI remodeling. Lastly, protective roles of CM miR-150 are, in part, attributed to the direct and functional repression of proapoptotic Sprr1a. Our findings suggest a crucial role for the miR-150/SPRR1A axis in regulating CM function post-MI.

Results of the FUEL Trial

BACKGROUND

The Fontan operation creates a total cavopulmonary connection, a circulation in which the importance of pulmonary vascular resistance is magnified. Over time, this circulation leads to deterioration of cardiovascular efficiency associated with a decline in exercise performance. Rigorous clinical trials aimed at improving physiology and guiding pharmacotherapy are lacking.

METHODS

The FUEL trial (Fontan Udenafil Exercise Longitudinal) was a phase III clinical trial conducted at 30 centers. Participants were randomly assigned udenafil, 87.5 mg twice daily, or placebo in a 1:1 ratio. The primary outcome was the between-group difference in change in oxygen consumption at peak exercise. Secondary outcomes included between-group differences in changes in submaximal exercise at the ventilatory anaerobic threshold, the myocardial performance index, the natural log of the reactive hyperemia index, and serum brain-type natriuretic peptide.

RESULTS

Between 2017 and 2019, 30 clinical sites in North America and the Republic of Korea randomly assigned 400 participants with Fontan physiology. The mean age at randomization was 15.5±2 years; 60% of participants were male, and 81% were white. All 400 participants were included in the primary analysis with imputation of the 26-week end point for 21 participants with missing data (11 randomly assigned to udenafil and 10 to placebo). Among randomly assigned participants, peak oxygen consumption increased by 44±245 mL/min (2.8%) in the udenafil group and declined by 3.7±228 mL/min (-0.2%) in the placebo group (P=0.071). Analysis at ventilatory anaerobic threshold demonstrated improvements in the udenafil group versus the placebo group in oxygen consumption (+33±185 [3.2%] versus -9±193 [-0.9%] mL/min, P=0.012), ventilatory equivalents of carbon dioxide (-0.8 versus -0.06, P=0.014), and work rate (+3.8 versus +0.34 W, P=0.021). There was no difference in change of myocardial performance index, the natural log of the reactive hyperemia index, or serum brain-type natriuretic peptide level.

CONCLUSIONS

In the FUEL trial, treatment with udenafil (87.5 mg twice daily) was not associated with an improvement in oxygen consumption at peak exercise but was associated with improvements in multiple measures of exercise performance at the ventilatory anaerobic threshold.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT02741115.

Nicotinamide mononucleotide requires SIRT3 to improve cardiac function and bioenergetics in a Friedreich's ataxia cardiomyopathy model

Increasing NAD+ levels by supplementing with the precursor nicotinamide mononucleotide (NMN) improves cardiac function in multiple mouse models of disease. While NMN influences several aspects of mitochondrial metabolism, the molecular mechanisms by which increased NAD+ enhances cardiac function are poorly understood. A putative mechanism of NAD+ therapeutic action exists via activation of the mitochondrial NAD+-dependent protein deacetylase sirtuin 3 (SIRT3). We assessed the therapeutic efficacy of NMN and the role of SIRT3 in the Friedreich's ataxia cardiomyopathy mouse model (FXN-KO). At baseline, the FXN-KO heart has mitochondrial protein hyperacetylation, reduced Sirt3 mRNA expression, and evidence of increased NAD+ salvage. Remarkably, NMN administered to FXN-KO mice restores cardiac function to near-normal levels. To determine whether SIRT3 is required for NMN therapeutic efficacy, we generated SIRT3-KO and SIRT3-KO/FXN-KO (double KO [dKO]) models. The improvement in cardiac function upon NMN treatment in the FXN-KO is lost in the dKO model, demonstrating that the effects of NMN are dependent upon cardiac SIRT3. Coupled with cardio-protection, SIRT3 mediates NMN-induced improvements in both cardiac and extracardiac metabolic function and energy metabolism. Taken together, these results serve as important preclinical data for NMN supplementation or SIRT3 activator therapy in Friedreich's ataxia patients.

Results of a phase I/II multi-center investigation of udenafil in adolescents after fontan palliation

BACKGROUND

The Fontan operation results in a circulation that is dependent on low pulmonary vascular resistance to maintain an adequate cardiac output. Medical therapies that lower pulmonary vascular resistance may augment cardiac output and improve long-term outcomes.

OBJECTIVES

This phase I/II clinical trial conducted by the Pediatric Heart Network was designed to evaluate short-term safety, pharmacokinetics (PK), and preliminary efficacy of udenafil in adolescents following Fontan.

METHODS

A 5-day dose-escalation trial was conducted in five study cohorts of six subjects each (37.5, 87.5, and 125 mg daily, 37.5 and 87.5 mg by mouth twice daily). A control cohort with 6 subjects underwent exercise testing only. Adverse events (AEs) were recorded, PK samples were collected on study days six through eight, and clinical testing was performed at baseline and day five.

RESULTS

The trial enrolled 36 subjects; mean age 15.8 years (58% male). There were no significant differences in subject characteristics between cohorts. No drug-related serious AEs were reported during the study period; 24 subjects had AEs possibly or probably related to study drug. Headache was the most common AE, occurring in 20 of 30 subjects. The 87.5 mg bid cohort was well tolerated, achieved the highest maximal concentration (506 ng/mL) and the highest average concentration over the dosing interval (279 ng/mL), and was associated with a suggestion of improvement in myocardial performance. Exercise performance did not improve in any of the dosing cohorts.

CONCLUSIONS

Udenafil was well-tolerated at all dosing levels. The 87.5 mg bid cohort achieved the highest plasma drug level and was associated with a suggestion of improvement in myocardial performance. These data suggest that the 87.5 mg bid regimen may be the most appropriate for a Phase III clinical trial.

Progressive mitochondrial protein lysine acetylation and heart failure in a model of Friedreich's ataxia cardiomyopathy

INTRODUCTION

The childhood heart disease of Friedreich's Ataxia (FRDA) is characterized by hypertrophy and failure. It is caused by loss of frataxin (FXN), a mitochondrial protein involved in energy homeostasis. FRDA model hearts have increased mitochondrial protein acetylation and impaired sirtuin 3 (SIRT3) deacetylase activity. Protein acetylation is an important regulator of cardiac metabolism and loss of SIRT3 increases susceptibility of the heart to stress-induced cardiac hypertrophy and ischemic injury. The underlying pathophysiology of heart failure in FRDA is unclear. The purpose of this study was to examine in detail the physiologic and acetylation changes of the heart that occur over time in a model of FRDA heart failure. We predicted that increased mitochondrial protein acetylation would be associated with a decrease in heart function in a model of FRDA.

METHODS

A conditional mouse model of FRDA cardiomyopathy with ablation of FXN (FXN KO) in the heart was compared to healthy controls at postnatal days 30, 45 and 65. We evaluated hearts using echocardiography, cardiac catheterization, histology, protein acetylation and expression.

RESULTS

Acetylation was temporally progressive and paralleled evolution of heart failure in the FXN KO model. Increased acetylation preceded detectable abnormalities in cardiac function and progressed rapidly with age in the FXN KO mouse. Acetylation was also associated with cardiac fibrosis, mitochondrial damage, impaired fat metabolism, and diastolic and systolic dysfunction leading to heart failure. There was a strong inverse correlation between level of protein acetylation and heart function.

CONCLUSION

These results demonstrate a close relationship between mitochondrial protein acetylation, physiologic dysfunction and metabolic disruption in FRDA hypertrophic cardiomyopathy and suggest that abnormal acetylation contributes to the pathophysiology of heart disease in FRDA. Mitochondrial protein acetylation may represent a therapeutic target for early intervention.

Post-translational modifications in mitochondria: protein signaling in the powerhouse

There is an intimate interplay between cellular metabolism and the pathophysiology of disease. Mitochondria are essential to maintaining and regulating metabolic function of cells and organs. Mitochondrial dysfunction is implicated in diverse diseases, such as cardiovascular disease, diabetes and metabolic syndrome, neurodegeneration, cancer, and aging. Multiple reversible post-translational protein modifications are located in the mitochondria that are responsive to nutrient availability and redox conditions, and which can act in protein-protein interactions to modify diverse mitochondrial functions. Included in this are physiologic redox signaling via reactive oxygen and nitrogen species, phosphorylation, O-GlcNAcylation, acetylation, and succinylation, among others. With the advent of mass proteomic screening techniques, there has been a vast increase in the array of known mitochondrial post-translational modifications and their protein targets. The functional significance of these processes in disease etiology, and the pathologic response to their disruption, are still under investigation. However, many of these reversible modifications act as regulatory mechanisms in mitochondria and show promise for mitochondrial-targeted therapeutic strategies. This review addresses the current knowledge of post-translational processing and signaling mechanisms in mitochondria, and their implications in health and disease.

Widespread and enzyme-independent Nε-acetylation and Nε-succinylation of proteins in the chemical conditions of the mitochondrial matrix

Alterations in mitochondrial protein acetylation are implicated in the pathophysiology of diabetes, the metabolic syndrome, mitochondrial disorders, and cancer. However, a viable mechanism responsible for the widespread acetylation in mitochondria remains unknown. Here, we demonstrate that the physiologic pH and acyl-CoA concentrations of the mitochondrial matrix are sufficient to cause dose- and time-dependent, but enzyme-independent acetylation and succinylation of mitochondrial and nonmitochondrial proteins in vitro. These data suggest that protein acylation in mitochondria may be a chemical event facilitated by the alkaline pH and high concentrations of reactive acyl-CoAs present in the mitochondrial matrix. Although these results do not exclude the possibility of enzyme-mediated protein acylation in mitochondria, they demonstrate that such a mechanism may not be required in its unique chemical environment. These findings may have implications for the evolutionary roles that the mitochondria-localized SIRT3 deacetylase and SIRT5 desuccinylase have in the maintenance of metabolic health.

Common data elements for clinical research in Friedreich's ataxia

To reduce study start-up time, increase data sharing, and assist investigators conducting clinical studies, the National Institute of Neurological Disorders and Stroke embarked on an initiative to create common data elements for neuroscience clinical research. The Common Data Element Team developed general common data elements, which are commonly collected in clinical studies regardless of therapeutic area, such as demographics. In the present project, we applied such approaches to data collection in Friedreich's ataxia (FRDA), a neurological disorder that involves multiple organ systems. To develop FRDA common data elements, FRDA experts formed a working group and subgroups to define elements in the following: ataxia and performance measures; biomarkers; cardiac and other clinical outcomes; and demographics, laboratory tests, and medical history. The basic development process included identification of international experts in FRDA clinical research, meeting by teleconference to develop a draft of standardized common data elements recommendations, vetting of recommendations across the subgroups, and dissemination of recommendations to the research community for public comment. The full recommendations were published online in September 2011 at http://www.commondataelements.ninds.nih.gov/FA.aspx. The subgroups' recommendations are classified as core, supplemental, or exploratory. Template case report forms were created for many of the core tests. The present set of data elements should ideally lead to decreased initiation time for clinical research studies and greater ability to compare and analyze data across studies. Their incorporation into new, ongoing studies will be assessed in an ongoing fashion to define their utility in FRDA.

Cardiomyopathy in Friedreich ataxia: clinical findings and research

Friedreich ataxia is the most common human ataxia and results from inadequate production of the frataxin protein, most often the result of a triplet expansion in the nuclear FXN gene. The gene cannot be transcribed to generate the messenger ribonucleic acid for frataxin. Frataxin is an iron-binding protein targeted to the mitochondrial matrix. In its absence, multiple iron-sulfur-dependent proteins in mitochondria and the cytosol lack proper assembly, destroying mitochondrial and nuclear function. Mitochondrial oxidant stress may also participate in ongoing cellular injury. Although progressive and debilitative ataxia is the most prominent clinical finding, hypertrophic cardiomyopathy with heart failure is the most common cause of early death in this disease. There is no cure. In this review the authors cover recent basic and clinical findings regarding the heart in Friedreich ataxia, offer recommendations for clinical management of the cardiomyopathy in this disease, and point out new research directions to advance the field.

Friedreich's ataxia reveals a mechanism for coordinate regulation of oxidative metabolism via feedback inhibition of the SIRT3 deacetylase

Friedreich's ataxia (FRDA) is the most common inherited human ataxia and is caused by a deficiency in the mitochondrial protein frataxin. Clinically, patients suffer from progressive spinocerebellar degeneration, diabetes and a fatal cardiomyopathy, associated with mitochondrial respiratory chain defects. Recent findings have shown that lysine acetylation regulates mitochondrial function and intermediary metabolism. However, little is known about lysine acetylation in the setting of pathologic energy stress and mitochondrial dysfunction. We tested the hypothesis that the respiratory chain defects in frataxin deficiency alter mitochondrial protein acetylation. Using two conditional mouse models of FRDA, we demonstrate marked hyperacetylation of numerous cardiac mitochondrial proteins. Importantly, this biochemical phenotype develops concurrently with cardiac hypertrophy and is caused by inhibition of the NAD(+)-dependent SIRT3 deacetylase. This inhibition is caused by an 85-fold decrease in mitochondrial NAD(+)/NADH and direct carbonyl group modification of SIRT3, and is reversed with excess SIRT3 and NAD(+) in vitro. We further demonstrate that protein hyperacetylation may be a common feature of mitochondrial disorders caused by respiratory chain defects, notably, cytochrome oxidase I (COI) deficiency. These findings suggest that SIRT3 inhibition and consequent protein hyperacetylation represents a negative feedback mechanism limiting mitochondrial oxidative pathways when respiratory metabolism is compromised, and thus, may contribute to the lethal cardiomyopathy in FRDA.

A TAT-frataxin fusion protein increases lifespan and cardiac function in a conditional Friedreich's ataxia mouse model

Friedreich's ataxia (FRDA) is the most common inherited human ataxia and results from a deficiency of the mitochondrial protein, frataxin (FXN), which is encoded in the nucleus. This deficiency is associated with an iron-sulfur (Fe-S) cluster enzyme deficit leading to progressive ataxia and a frequently fatal cardiomyopathy. There is no cure. To determine whether exogenous replacement of the missing FXN protein in mitochondria would repair the defect, we used the transactivator of transcription (TAT) protein transduction domain to deliver human FXN protein to mitochondria in both cultured patient cells and a severe mouse model of FRDA. A TAT-FXN fusion protein bound iron in vitro, transduced into mitochondria of FRDA deficient fibroblasts and reduced caspase-3 activation in response to an exogenous iron-oxidant stress. Injection of TAT-FXN protein into mice with a conditional loss of FXN increased their growth velocity and mean lifespan by 53% increased their mean heart rate and cardiac output, increased activity of aconitase and reversed abnormal mitochondrial proliferation and ultrastructure in heart. These results show that a cell-penetrant peptide is capable of delivering a functional mitochondrial protein in vivo to rescue a very severe disease phenotype, and present the possibility of TAT-FXN as a protein replacement therapy.

Downregulation of doxorubicin-induced myocardial apoptosis accompanies postnatal heart maturation

Doxorubicin is a highly effective chemotherapeutic agent used for treating a wide spectrum of tumors, but its usage is limited because of its dose-dependent cardiotoxicity, especially in pediatric patients. Accumulating evidence indicates that caspase-dependent apoptosis contributes to the cardiotoxicity of doxorubicin. However, less attention has been paid to the effects of age on doxorubicin-induced apoptosis signaling in myocardium. This study focused on investigating differential apoptotic sensitivity between neonatal and adult myocardium, in particular, between neonatal and adult cardiomyocytes in vivo. Our results show that caspase-3 activity in normal mouse hearts decreased by ≥ 20-fold within the first 3 wk after birth, associated with a rapid downregulation in the expression of key proapoptotic proteins in intrinsic and extrinsic pathways. This rapid downregulation of caspase-3 activity was confirmed by immunostaining for cleaved caspase-3 and terminal deoxynucleotidyl transferase dUTP-mediated nick-end label staining. Doxorubicin treatment induced a dose-dependent increase in caspase-3 activity and apoptosis in neonatal mouse hearts, and both caspase-8 and caspase-9 activations were involved. Using transgenic mice with a nuclear localized LacZ reporter gene to label cardiomyocytes in vivo, we observed a fourfold higher level of doxorubicin-induced cardiomyocyte apoptosis in 1-wk-old mice compared with that in 3-wk-old mice. This study points to a major difference in apoptotic signaling in doxorubicin cardiotoxicity between neonatal and adult mouse hearts and reveals a critical transition from high to low susceptibility to doxorubicin-induced apoptosis during postnatal heart maturation.

Tbx20 transcription factor is a downstream mediator for bone morphogenetic protein-10 in regulating cardiac ventricular wall development and function

Bone morphogenetic protein 10 (BMP10) belongs to the TGFβ-superfamily. Previously, we had demonstrated that BMP10 is a key regulator for ventricular chamber formation, growth, and maturation. Ablation of BMP10 leads to hypoplastic ventricular wall formation, and elevated levels of BMP10 are associated with abnormal ventricular trabeculation/compaction and wall maturation. However, the molecular mechanism(s) by which BMP10 regulates ventricle wall growth and maturation is still largely unknown. In this study, we sought to identify the specific transcriptional network that is potentially mediated by BMP10. We analyzed and compared the gene expression profiles between α-myosin heavy chain (αMHC)-BMP10 transgenic hearts and nontransgenic littermate controls using Affymetrix mouse exon arrays. T-box 20 (Tbx20), a cardiac transcription factor, was significantly up-regulated in αMHC-BMP10 transgenic hearts, which was validated by quantitative RT-PCR and in situ hybridization. Ablation of BMP10 reduced Tbx20 expression specifically in the BMP10-expressing region of the developing ventricle. In vitro promoter analysis demonstrated that BMP10 was able to induce Tbx20 promoter activity through a conserved Smad binding site in the Tbx20 promoter proximal region. Furthermore, overexpression of Tbx20 in myocardium led to dilated cardiomyopathy that exhibited ventricular hypertrabeculation and an abnormal muscular septum, which phenocopied genetically modified mice with elevated BMP10 levels. Taken together, our findings demonstrate that the BMP10-Tbx20 signaling cascade is important for ventricular wall development and maturation.

TAT fusion protein transduction into isolated mitochondria is accelerated by sodium channel inhibitors

Stringent control of ion and protein transport across the mitochondrial membranes is required to maintain mitochondrial function and biogenesis. In particular, the inner mitochondrial membrane is generally impermeable to proteins entering the matrix except via tightly regulated protein import mechanisms. Recently, cell penetrant peptides have been shown to move across the inner mitochondrial membrane in a manner suggesting an independent mechanism. HIV-1 transactivator of transcription (TAT) is an arginine-rich cell penetrant peptide, 47YGRKKRRQRRR57, which can transduce full-length proteins not only across the cell membrane but also into intracellular organelles. In this study, we investigated the ability of a TAT-containing protein to move into the mitochondrial matrix. Using a novel FACS assay for isolated, purified mitochondria, we show that TAT can deliver a modified fluorescent protein, mMDH-GFP, to the matrix of mitochondria and it is subsequently processed by the matrix peptidases. In addition, transduction of TAT-mMDH-GFP into mitochondria is independent of canonical protein import pathways as well as mitochondrial membrane potential. In direct contrast to published reports regarding the cell membrane where the sodium channel inhibitor, amiloride, blocks endocytosis and inhibits TAT transduction, TAT transduction into mitochondria is markedly increased by this same sodium channel inhibitor. These results confirm that the cell penetrant peptide, TAT, can readily transduce a protein cargo into the mitochondrial matrix. These results also demonstrate a novel role for mitochondrial sodium channels in mediating TAT transduction into mitochondria that is independent of endocytotic mechanisms. The mechanism of TAT transduction into mitochondria therefore is distinctly different from transduction across the cell membrane.

The Heart in Friedreich's Ataxia: Basic Findings and Clinical Implications

Friedreich's Ataxia is the most common inherited ataxia in man. It is a mitochondrial disease caused by severely reduced expression of the iron binding protein, frataxin. A large GAA triplet expansion in the human FRDA gene encoding this protein inhibits expression of this gene. It is inherited in an autosomal recessive pattern and typically diagnosed in childhood. The primary symptoms include severe and progressive neuropathy, and a hypertrophic cardiomyopathy that may cause death. The cardiomyopathy is difficult to treat and is frequently associated with arrhythmias, heart failure, and intolerance of cardiovascular stress, such as surgeries. Innovative approaches to therapy, such as histone deacetylase inhibitors, and enzyme replacement with cell penetrant peptide fusion proteins, hold promise for this and other similar mitochondrial disorders. This review will focus on the basic findings of this disease, and the cardiomyopathy associated with its diagnosis.

Mitochondrial acetylation and diseases of aging

In recent years, protein lysine acetylation has emerged as a prominent and conserved regulatory posttranslational modification that is abundant on numerous enzymes involved in the processes of intermediary metabolism. Well-characterized mitochondrial processes of carbon utilization are enriched in acetyl-lysine modifications. Although seminal discoveries have been made in the basic biology of mitochondrial acetylation, an understanding of how acetylation states influence enzyme function and metabolic reprogramming during pathological states remains largely unknown. This paper will examine our current understanding of eukaryotic acetate metabolism and present recent findings in the field of mitochondrial acetylation biology. The implications of mitochondrial acetylation for the aging process will be discussed, as well as its potential implications for the unique and localized metabolic states that occur during the aging-associated conditions of heart failure and cancer growth.

Cardiomyopathy of Friedreich's ataxia: use of mouse models to understand human disease and guide therapeutic development

Friedreich's ataxia is a multisystem disorder of mitochondrial function affecting primarily the heart and brain. Patients experience a severe cardiomyopathy that can progress to heart failure and death. Although the gene defect is known, the precise function of the deficient mitochondrial protein, frataxin, is not known and limits therapeutic development. Animal models have been valuable for understanding the basic events of this disease. A significant need exists to focus greater attention on the heart disease in Friedreich's ataxia, to understand its long-term outcome, and to develop new therapeutic strategies using existing medications and approaches. This review discusses some key features of the cardiomyopathy in Friedreich's ataxia and potential therapeutic developments.

Calcification after myocardial infarction is independent of amniotic fluid stem cell injection

Ischemic heart disease remains one of the most common causes of mortality in developed countries. Recently, stem cell therapy is being considered for treating ischemic heart diseases. On the other hand, there has been evidence of chondro-osteogenic mass formation after stem cell injection in the heart. In a recent publication, Chiavegato et al. (J Mol Cell Cardiol. 42 (2007) 746-759) has suggested that amniotic fluid-derived stem (AFS) cells cause chondro-osteogenic masses in the infarcted heart. The goal of the current study was to further examine the formation of such masses, specifically, the role of AFS cells in this process. Our results confirm the presence of similar bone-like masses in the left ventricular wall of infarcted rats; however, this phenomenon occurred independent of AFS cell injection into the myocardium. Moreover, AFS cell injection did not increase the presence of chondro-osteogenic masses. Echocardiographic analysis of large infarctions in rats frequently revealed the presence of echogenic structures in the left ventricular wall. We further demonstrated a significant relationship between the infarction size and chondro-osteogenic formation and subsequent decrease in cardiac function. Collectively, our study indicates that chondro-osteogenic differentiation can take place in infarcted rat heart independent of cell injection. These results have significant implications for future design and testing of stem cell therapy for treatment of cardiac muscle diseases.

Negative regulation of Stat3 by activating PTPN11 mutants contributes to the pathogenesis of Noonan syndrome and juvenile myelomonocytic leukemia

Noonan syndrome (NS) is an autosomal dominant congenital disorder characterized by multiple birth defects including heart defects and myeloproliferative disease (MPD). Approximately 50% of NS patients have germline gain-of-function mutations in PTPN11, which encodes the protein-tyrosine phosphatase, Shp2. We provide evidence that conditional ablation of Stat3 in hematopoietic cells and cardiac valvular tissues leads to myeloid progenitor hyperplasia and pulmonary stenosis due to the leaflet thickening, respectively. Consistently, STAT3 activation is significantly compromised in peripheral blood cells from NS patients bearing Shp2-activating mutations. Biochemical and functional analyses demonstrate that activated Shp2 is able to down-regulate Tyr(P)-Stat3 and that constitutively active Stat3 rescues activating mutant Shp2-induced granulocyte-macrophage colony-stimulating factor hypersensitivity in bone marrow cells. Collectively, our work demonstrates that Stat3 is an essential signaling component potentially contributing to the pathogenesis of NS and juvenile myelomonocytic leukemia caused by PTPN11 gain-of-function mutations.

Acute doxorubicin cardiotoxicity is associated with p53-induced inhibition of the mammalian target of rapamycin pathway

BACKGROUND

Doxorubicin is used to treat childhood and adult cancer. Doxorubicin treatment is associated with both acute and chronic cardiotoxicity. The cardiotoxic effects of doxorubicin are cumulative, which limits its chemotherapeutic dose. Free radical generation and p53-dependent apoptosis are thought to contribute to doxorubicin-induced cardiotoxicity.

METHODS AND RESULTS

Adult transgenic (MHC-CB7) mice expressing cardiomyocyte-restricted dominant-interfering p53 and their nontransgenic littermates were treated with doxorubicin (20 mg/kg cumulative dose). Nontransgenic mice exhibited reduced left ventricular systolic function (predoxorubicin fractional shortening [FS] 61+/-2%, postdoxorubicin FS 45+/-2%, mean+/-SEM, P<0.008), reduced cardiac mass, and high levels of cardiomyocyte apoptosis 7 days after the initiation of doxorubicin treatment. In contrast, doxorubicin-treated MHC-CB7 mice exhibited normal left ventricular systolic function (predoxorubicin FS 63+/-2%, postdoxorubicin FS 60+/-2%, P>0.008), normal cardiac mass, and low levels of cardiomyocyte apoptosis. Western blot analyses indicated that mTOR (mammalian target of rapamycin) signaling was inhibited in doxorubicin-treated nontransgenic mice but not in doxorubicin-treated MHC-CB7 mice. Accordingly, transgenic mice with cardiomyocyte-restricted, constitutively active mTOR expression (MHC-mTORca) were studied. Left ventricular systolic function (predoxorubicin FS 64+/-2%, postdoxorubicin FS 60+/-3%, P>0.008) and cardiac mass were normal in doxorubicin-treated MHC-mTORca mice, despite levels of cardiomyocyte apoptosis similar to those seen in doxorubicin-treated nontransgenic mice.

CONCLUSIONS

These data suggest that doxorubicin treatment induces acute cardiac dysfunction and reduces cardiac mass via p53-dependent inhibition of mTOR signaling and that loss of myocardial mass, and not cardiomyocyte apoptosis, is the major contributor to acute doxorubicin cardiotoxicity.

A mouse model for juvenile doxorubicin-induced cardiac dysfunction

Doxorubicin (DOX) is a potent antitumor agent. DOX can also induce cardiotoxicity, and high cumulative doses are associated with recalcitrant heart failure. Children are particularly sensitive to DOX-induced heart failure. The ability to genetically modify mice makes them an ideal experimental system to study the molecular basis of DOX-induced cardiotoxicity. However, most mouse DOX studies rely on acute drug administration in adult animals, which typically are analyzed within 1 wk. Here, we describe a juvenile mouse model of chronic DOX-induced cardiac dysfunction. DOX treatment was initiated at 2 wk of age and continued for a period of 5 wk (25 mg/kg cumulative dose). This resulted in a decline in cardiac systolic function, which was accompanied by marked atrophy of the heart, low levels of cardiomyocyte apoptosis, and decreased growth velocity. Other animals were allowed to recover for 13 wk after the final DOX injection. Cardiac systolic function improved during this recovery period but remained depressed compared with the saline injected controls, despite the reversal of cardiac atrophy. Interestingly, increased levels of cardiomyocyte apoptosis and concomitant myocardial fibrosis were observed after DOX withdrawal. These data suggest that different mechanisms contribute to cardiac dysfunction during the treatment and recovery phases.

Mitochondrial trifunctional protein defects: clinical implications and therapeutic approaches

The mitochondrial trifunctional protein (MTP) is a heterotrimeric protein that consists of four alpha-subunits and four beta-subunits and catalyzes three of the four chain-shortening reactions in the mitochondrial beta-oxidation of long-chain fatty acids. Families with recessively inherited MTP defects display a spectrum of maternal and fetal phenotypes. Current management of patients with MTP defects include long-term dietary therapy of fasting avoidance, low-fat/high-carbohydrate diet with restriction of long-chain fatty acid intake and substitution with medium-chain fatty acids. These dietary approaches appear promising in the short-term, but the long-term outcome of patients treated with dietary intervention is largely unknown. Potential therapeutic approaches targeted at correcting the metabolic defect will be discussed. We will discuss the potential use of protein transduction domains that cross the mitochondrial membranes for the treatment of mitochondrial disorders. In addition, we discuss the phenotypes of MTP in a heterozygous state and potential ways to intervene to increase hepatic fatty acid oxidative capacity.

Mitochondrial protein import and human health and disease

The targeting and assembly of nuclear-encoded mitochondrial proteins are essential processes because the energy supply of humans is dependent upon the proper functioning of mitochondria. Defective import of mitochondrial proteins can arise from mutations in the targeting signals within precursor proteins, from mutations that disrupt the proper functioning of the import machinery, or from deficiencies in the chaperones involved in the proper folding and assembly of proteins once they are imported. Defects in these steps of import have been shown to lead to oxidative stress, neurodegenerative diseases, and metabolic disorders. In addition, protein import into mitochondria has been found to be a dynamically regulated process that varies in response to conditions such as oxidative stress, aging, drug treatment, and exercise. This review focuses on how mitochondrial protein import affects human health and disease.

The pathogenesis of pulmonary contusion: an open chest model in the rat

BACKGROUND

Chemokines direct leukocytes to areas of inflammation or injury. In general, CC chemokines (MCP-1, MIP-1alpha, RANTES) are chemoattractants for mononuclear cells and CXC (CINC-1, MIP-2alpha) for polymorphonuclear cells (PMNs). Herein we describe an open chest model of pulmonary contusion (PC) in a rodent (rat) and have identified a possible role for CC and CXC chemokines in the pathogenesis of PC.

METHODS

Sprague-Dawley rats (350 g) underwent thoracotomy. The exposed lung was struck with a piston at 5.2 m/s (150 J/M2). Blood, bronchoalveolar lavage (BAL), and lung tissue were collected at 3 hours and 24 hours after injury. PaO2/FiO2 (P/F) ratio was calculated at 15-minute intervals for 3 hours after contusion. Serum was evaluated for cytokine and chemokine expression using ELISA. Cell count/differential was performed on BAL, and lung tissue was obtained for histologic analysis, protein expression and wet to dry weights. Data are reported as pg/mL +/- SE. Data were analyzed using Student's t test to identify significant differences (p < or = 0.05 significant) between sham and injured animals.

RESULTS

Piston impact caused PC based upon morphologic and histologic criteria. BAL cell count and lung wet to dry weights were increased and P/F ratio was decreased after PC. Systemic levels of IL-ra, MCP-1, and the CXC chemokines MIP-2alpha and CINC-1 were significantly elevated at 3 hours when sham and injured animals were compared. All chemokines were found to be significantly elevated at 24 hours, consistent with the early PMN and subsequent mononuclear infiltration observed in the contused lung. Pulmonary expression of TNF-alpha, IL-1beta, CINC-1, MIP-2alpha, ICAM-1, and elastase were increased and activated systemic neutrophils showed increased CD-11b.

CONCLUSION

A model of PC is described in which innate inflammation is activated locally and systemically. Systemic levels of CC and CXC chemokines are increased after PC. This correlates with elevated PMN CD-11b expression, enhanced pulmonary ICAM-1 expression, and mononuclear and PMN infiltration into the lung and alveolar space. Elevated levels of CC and CXC chemokines are seen after PC and may be involved in the lung's inflammatory response to injury.

Overexpression of bone morphogenetic protein 10 in myocardium disrupts cardiac postnatal hypertrophic growth

Postnatal cardiac hypertrophies have traditionally been classified into physiological or pathological hypertrophies. Both of them are induced by hemodynamic load. Cardiac postnatal hypertrophic growth is regarded as a part of the cardiac maturation process that is independent of the cardiac working load. However, the functional significance of this biological event has not been determined, mainly because of the difficulty in creating an experimental condition for testing the growth potential of functioning heart in the absence of hemodynamic load. Recently, we generated a novel transgenic mouse model (alphaMHC-BMP10) in which the cardiac-specific growth factor bone morphogenetic protein 10 (BMP10) is overexpressed in postnatal myocardium. These alphaMHC-BMP10 mice appear to have normal cardiogenesis throughout embryogenesis, but develop to smaller hearts within 6 weeks after birth. alphaMHC-BMP10 hearts are about half the normal size with 100% penetrance. Detailed morphometric analysis of cardiomyocytes clearly indicated that the compromised cardiac growth in alphaMHC-BMP10 mice was solely because of defect in cardiomyocyte postnatal hypertrophic growth. Physiological analysis further demonstrated that the responses of these hearts to both physiological (e.g. exercise-induced hypertrophy) and pathological hypertrophic stimuli remain normal. In addition, the alphaMHC-BMP10 mice develop subaortic narrowing and concentric myocardial thickening without obstruction by four weeks of age. Systematic analysis of potential intracellular pathways further suggested a novel genetic pathway regulating this previously undefined cardiac postnatal hypertrophic growth event. This is the first demonstration that cardiac postnatal hypertrophic growth can be specifically modified genetically and dissected out from physiological and pathological hypertrophies.

Preparation of ribosomes loaded with truncated nascent proteins to study ribosome binding to mammalian mitochondria

Supporting a co-translational model of protein import into mitochondria, we have previously shown that ribosome-nascent chain complexes (RNCs) specifically bind to mitochondria. When producing RNCs using the rabbit reticulocyte lysate in vitro translation system, it was necessary to maximize ribosome loading with truncated nascent proteins because it had a direct impact on RNC binding. We describe here the optimal conditions for preparing RNCs. We show that translation temperature and reaction time are two critical factors, with 30 degrees Celsius and 15min being optimal, respectively. We also show that transcription reactions can be used directly in the translation reaction to create RNCs.

Development of a finite element-based injury metric for pulmonary contusion part I: model development and validation

Pulmonary contusion is the most commonly identified thoracic soft tissue injury in an automobile crash and after blunt chest trauma and affects 10-17% of all trauma admissions. The mortality associated with pulmonary contusions is significant and is estimated to be 10-25%. Thus, there is a need to develop a finite element model based injury metric for pulmonary contusion for the purpose of predicting outcome. This will enable current and future finite element models of the lung to incorporate an understanding of how stress and strain may be related to contusion injuries. This study utilizes 14 impacts onto male Sprague-Dawley rats. In 5 of these tests, a calibrated weight (46 g) is dropped from a height of 44 cm directly onto the lungs of intubated, anesthetized rats in situ. Contused volume is estimated from MicroPET scans of the lung and normalized on the basis of liver uptake of 18F-FDG. The lungs are scanned at 24 hours, 7 days, and 28 days (15 scans), and the contused volume is measured. In addition, 9 controlled mechanical tests on in situ rat lung are used for model development and validation. Identical impacts are performed on a finite element model of the rat lung. The finite element model is developed from CT scans of normal rat and scaled to represent average rat lung volume. First principal strain is chosen as a candidate injury metric for pulmonary contusion. The volume of contused tissue at the three time points measured using PET is compared to the strain level achieved by a corresponding volume in the finite element model. For PET scans (n=5 scans per time point), the average contusion volume was 4.2 cm3 at 24 hours, 2.8 cm3 at 7 days, and 0.39 cm3 at 28 days. These volumes were used to identify threshold peak first principal strain levels measured by the finite element model. Maximum first principal strain from the finite element model for the three volume levels (4.2, 2.8, and 0.39 cm3) was 3.5%, 8.8%, and 35% strain, respectively. Furthermore, the lung model exhibited exponential decay in principal strain threshold as more of the lung volume was considered, correlating to the precise and well defined volume of the contusion as it healed. The results of this study may be used to establish an injury metric to predict pulmonary contusion due to an impact to the lungs. The results may be used to improve finite element models of the human body, which may then be used to tune stiffnesses of interior components of automobiles and tune safety systems for maximum mitigation of this serious injury.

Mitochondrial Trifunctional Protein Defects: Molecular Basis and Novel Therapeutic Approaches

Mitochondrial trifunctional protein (MTP) is a complex protein that catalyzes the last three steps of long chain fatty acid oxidation. MTP defects have emerged recently as important inborn errors of metabolism because of their clinical implications. These disorders are recessively inherited and display a spectrum of clinical phenotypes in affected children including hepatic dysfunction, cardiomyopathy, neuro-myopathy, and may cause sudden unexpected infant death if undiagnosed and untreated. Interestingly, mothers who carry fetuses with MTP defects develop life-threatening complications during pregnancy. Recently, we delineated disease-causing mutations in MTP and reported the molecular basis for the pediatric and fetal-maternal genotype-phenotype correlations. Current management of patients with MTP defects include long-term dietary therapy of fasting avoidance, low fat diet with the restriction of long chain fatty acid intake and substitution with medium chain fatty acids. The long-term outcome of patients treated by dietary modifications remains unknown. Thus, treatment that aims at correcting the metabolic defect remains the therapy of choice for this disorder. Currently, we are exploring the potential use of protein transfection domains (PTD) for treatment of these disorders. We have shown that the transactivator of transcription (TAT) peptide from the human immunodeficiency virus can deliver proteins to mitochondria. We have further developed methods to localize these proteins to mitochondria by including a mitochondrial targeting in the fusion protein construct. Finally, we have shown that the fusion protein can cross the placenta and was detectable in the fetus and newborn pups. The practical therapeutic implications of this novel approach will be discussed.

Evaluation of the Quantitative Capability of a High-Resolution Positron Emission Tomography Scanner for Small Animal Imaging

OBJECTIVE

The quantitative capability of a positron emission tomography scanner for small animal imaging was evaluated in this study.

METHODS

The microPET P4 (Concorde Microsystems, Knoxville, TN) scanner's capability for dynamic imaging and corrections for radioactive decay, dead time, and attenuation were evaluated. Rat brain and heart studies with and without attenuation correction were compared. A calibration approach to convert the data to nanocuries per milliliter was implemented. Calibration factors were determined using calibration phantoms of 2 sizes with and without attenuation correction. Quantitation was validated using the MiniPhantom (Data Spectrum, Chapel Hill, NC) with hot features (5:1 ratio) of different sizes (4, 6.4, 8, 13, and 16 mm).

RESULTS

The microPET P4 scanner's ability to acquire dynamic studies and to correct for decay, dead time, and attenuation was demonstrated. The microPET P4 scanner provided accurate quantitation to within 6% for features larger than 10 mm. Sixty percent of object contrast was retained for features as small as 4 mm.

CONCLUSIONS

The microPET P4 scanner can provide accurate quantitation.

Transactivator of transcription fusion protein transduction causes membrane inversion

The transactivator of transcription (TAT) protein transduction domain is an 11-amino acid positively charged peptide that has been shown to pull diverse molecules across cell membranes in vitro and in vivo. Fusion proteins constructed with TAT rapidly enter and exit cells and have been shown to cross intracellular membranes as well. Electrostatic interactions between TAT and the cell membrane have been implicated as a part of the mechanism of transduction. Here, we report that TAT transduction causes membrane phospholipid rearrangement as evidenced by detection of phosphatidylserine on the outer surface of the cell membrane. Furthermore, these rearrangements can be blocked by positively charged polylysine, further implicating electrostatic interactions as a part of the mechanism. Neither apoptosis nor necrosis is induced in these cells after exposure to TAT. We conclude that the process of TAT.GFP transduction causes phosphatidylserine to translocate from the inner to the outer leaflet of the plasma membrane. These results provide insight into the mechanism of TAT protein transduction domain transduction.

Video-assisted ductal ligation in premature infants

BACKGROUND

Video-assisted thoracic surgery has been shown to be a safe and effective method of closing the patent ductus arteriosus in infants and children. We have applied this technique in low birth weight premature infants and now report our experience.

METHODS

Since 1996, we have used video-assisted thoracic surgery ligation as the treatment of choice for all patent ductus arteriosus, including 100 performed on premature infants (23 to 31 weeks' gestation, mean 25.6 weeks; 0.420 to 1.5 kg, mean 0.859 kg). A modification of our previously described technique was used with a three-port approach. All patients had some degree of symptoms of congestive failure with failure to wean from ventilatory support or oxygen dependency. Five infants had associated patent foramen, and 1 had a small ventricular septal defect.

RESULTS

All 100 procedures were performed in the operating room. One infant was found to have a coarctation, and the procedure was aborted. The remaining 99 were successfully ligated, although three were converted to an open procedure (3%) because of coagulopathy, poor pulmonary compliance, or hemodynamic instability. There were no procedure-related deaths; however, 15 infants subsequently died of complications of prematurity, including enterocolitis, sepsis, and late respiratory failure. Six infants had chest tubes left in place for coagulopathy, effusions, suspected air leak, and existing empyema. There were six residual pneumothoraces, four requiring treatment.

CONCLUSIONS

Video-assisted thoracic surgery is a safe and effective technique for patent ductus arteriosus ligation in premature infants, including those with very low and extremely low birth weight.

Ribosomes specifically bind to mammalian mitochondria via protease-sensitive proteins on the outer membrane

The interaction of ribosomes with specific components of membranes is one of the central themes to the co-translational targeting and import of proteins. To examine ribosome binding to mammalian mitochondria, we used ribosome-nascent chain complexes (RNCs) to follow the in vitro binding of ribosomes that correspond to the initial targeting stage of proteins. Mitochondria were found to contain a limited number of RNC binding sites on the outer membrane. It required more than twice the amount of non-translating ribosomes to inhibit RNC binding by one-half, indicating that RNCs have a competitive binding advantage. In addition, we found that RNCs bind mainly through the ribosomal component and not the nascent chain. RNCs bind via protease-sensitive proteins on the outer membrane, as well as by protease-insensitive components suggesting that two classes of receptors exist. We also show that binding is sensitive to cation conditions. Nearly all of the binding was inhibited in 0.5 m KCl, indicating that they interact with the membrane primarily through electrostatic interactions. In addition, disruption of RNC structure by removing magnesium causes the complete inhibition of binding under normal binding conditions indicating that it is the intact ribosome that is crucial for binding and not the nascent chain. These findings support the hypothesis that the outer mitochondrial membrane contains receptors specific for ribosomes, which would support the conditions necessary for co-translational import.