Susanna Scafidi

Mitochondrial mechanisms of cell death and neuroprotection in pediatric ischemic and traumatic brain injury

There are several forms of acute pediatric brain injury, including neonatal asphyxia, pediatric cardiac arrest with global ischemia, and head trauma, that result in devastating, lifelong neurologic impairment. The only clinical intervention that appears neuroprotective is hypothermia initiated soon after the initial injury. Evidence indicates that oxidative stress, mitochondrial dysfunction, and impaired cerebral energy metabolism contribute to the brain cell death that is responsible for much of the poor neurologic outcome from these events. Recent results obtained from both in vitro and animal models of neuronal death in the immature brain point toward several molecular mechanisms that are either induced or promoted by oxidative modification of macromolecules, including consumption of cytosolic and mitochondrial NAD(+) by poly-ADP ribose polymerase, opening of the mitochondrial inner membrane permeability transition pore, and inactivation of key, rate-limiting metabolic enzymes, e.g., the pyruvate dehydrogenase complex. In addition, the relative abundance of pro-apoptotic proteins in immature brains and neurons, and particularly within their mitochondria, predisposes these cells to the intrinsic, mitochondrial pathway of apoptosis, mediated by Bax- or Bak-triggered release of proteins into the cytosol through the mitochondrial outer membrane. Based on these pathways of cell dysfunction and death, several approaches toward neuroprotection are being investigated that show promise toward clinical translation. These strategies include minimizing oxidative stress by avoiding unnecessary hyperoxia, promoting aerobic energy metabolism by repletion of NAD(+) and by providing alternative oxidative fuels, e.g., ketone bodies, directly interfering with apoptotic pathways at the mitochondrial level, and pharmacologic induction of antioxidant and anti-inflammatory gene expression.

Neuroprotection by acetyl-L-carnitine after traumatic injury to the immature rat brain.

Traumatic brain injury (TBI) is the leading cause of mortality and morbidity in children and is characterized by reduced aerobic cerebral energy metabolism early after injury, possibly due to impaired activity of the pyruvate dehydrogenase complex. Exogenous acetyl-L-carnitine (ALCAR) is metabolized in the brain to acetyl coenzyme A and subsequently enters the tricarboxylic acid cycle. ALCAR administration is neuroprotective in animal models of cerebral ischemia and spinal cord injury, but has not been tested for TBI. This study tested the hypothesis that treatment with ALCAR during the first 24 h following TBI in immature rats improves neurologic outcome and reduces cortical lesion volume. Postnatal day 21–22 male rats were isoflurane anesthetized and used in a controlled cortical impact model of TBI to the left parietal cortex. At 1, 4, 12 and 23 h after injury, rats received ALCAR (100 mg/kg, intraperitoneally) or drug vehicle (normal saline). On days 3–7 after surgery, behavior was assessed using beam walking and novel object recognition tests. On day 7, rats were transcardially perfused and brains were harvested for histological assessment of cortical lesion volume, using stereology. Injured animals displayed a significant increase in foot slips compared to sham-operated rats (6 ± 1 SEM vs. 2 ± 0.2 on day 3 after trauma; n = 7; p < 0.05). The ALCAR-treated rats were not different from shams and had fewer foot slips compared to vehicle-treated animals (2 ± 0.4; n = 7; p< 0.05). The frequency of investigating a novel object for saline-treated TBI animals was reduced compared to shams (45 ± 5% vs. 65 ± 10%; n = 7; p < 0.05), whereas the frequency of investigation for TBI rats treated with ALCAR was not significantly different from that of shams but significantly higher than that of saline-treated TBI rats (68 ± 7; p < 0.05). The left parietal cortical lesion volume, expressed as a percentage of the volume of tissue in the right hemisphere, was significantly smaller in ALCAR-treated than in vehicle-treated TBI rats (14 ± 5% vs. 28 ± 6%; p < 0.05). We conclude that treatment with ALCAR during the first 24 h after TBI improves behavioral outcomes and reduces brain lesion volume in immature rats within the first 7 days after injury.

Metabolism of acetyl-L-carnitine for energy and neurotransmitter synthesis in the immature rat brain.

J. Neurochem. (2010) 114, 820–831.

Delayed cerebral oxidative glucose metabolism after traumatic brain injury in young rats

Traumatic brain injury (TBI) results in a cerebral metabolic crisis that contributes to poor neurologic outcome. The aim of this study was to characterize changes in oxidative glucose metabolism in early periods after injury in the brains of immature animals. At 5 h after controlled cortical impact TBI or sham surgery to the left cortex, 21–22 day old rats were injected intraperitoneally with [1,6‐13C]glucose and brains removed 15, 30 and 60 min later and studied by ex vivo 13C‐NMR spectroscopy. Oxidative metabolism, determined by incorporation of 13C into glutamate, glutamine and GABA over 15–60 min, was significantly delayed in both hemispheres of brain from TBI rats. The most striking delay was in labeling of the C4 position of glutamate from neuronal metabolism of glucose in the injured, ipsilateral hemisphere which peaked at 60 min, compared with the contralateral and sham‐operated brains, where metabolism peaked at 30 and 15 min, respectively. Our findings indicate that (i) neuronal‐specific oxidative metabolism of glucose at 5–6 h after TBI is delayed in both injured and contralateral sides compared with sham brain; (ii) labeling from metabolism of glucose via the pyruvate carboxylase pathway in astrocytes was also initially delayed in both sides of TBI brain compared with sham brain; (iii) despite this delayed incorporation, at 6 h after TBI, both sides of the brain showed apparent increased neuronal and glial metabolism, reflecting accumulation of labeled metabolites, suggesting impaired malate aspartate shuttle activity. The presence of delayed metabolism, followed by accumulation of labeled compounds is evidence of severe alterations in homeostasis that could impair mitochondrial metabolism in both ipsilateral and contralateral sides of brain after TBI. However, ongoing oxidative metabolism in mitochondria in injured brain suggests that there is a window of opportunity for therapeutic intervention up to at least 6 h after injury.

A multicenter outcomes analysis of children with severe viral respiratory infection due to human metapneumovirus.

Objective: To investigate the impact of human metapneumovirus on morbidity and mortality outcomes in children with severe viral respiratory infection. Design: Retrospective cohort study. Setting: ICU, either PICU or cardiac ICU, at three urban academic tertiary care children’s hospitals. Patients: All patients admitted to an ICU with laboratory-confirmed human metapneumovirus infection between January 2010 and June 2011. Interventions: We captured demographic and clinical data and analyzed associated morbidity and mortality outcomes. Measurements and Main Results: There were 111 patients with laboratory-confirmed human metapneumovirus admitted to an ICU at one of the three participating institutions during the period of study. The median hospital length of stay was 7 days (interquartile range 4–18 days) and median ICU length of stay was 4 days (interquartile range 1–10 days). Ten patients (9%) did not survive to discharge. Predisposing factors associated with increased mortality included female gender (p = 0.002), presence of a chronic medical condition (p = 0.04), and hospital acquisition of human metapneumovirus infection (p = 0.006). Adjusting for female gender, chronic medical conditions, hospital acquisition of infection and severity of illness score, logistic regression analysis demonstrated that female gender, hospital acquisition of infection, and chronic medical conditions each independently increased the odds of mortality (odds ratios 14.8, 10.7, and 12.7, respectively). Conclusions: Analysis of our results suggests that there is substantial morbidity and mortality associated with severe viral respiratory infection due to human metapneumovirus in children. Female gender, hospital acquisition of human metapneumovirus infection, and presence of chronic medical conditions each independently increases mortality. The burden of illness from human metapneumovirus on the ICU in terms of resource utilization may be considerable.

A multicenter outcomes analysis of children with severe rhino/enteroviral respiratory infection.

Objectives: To investigate the impact of human rhino/enteroviruses on morbidity and mortality outcomes in children with severe viral respiratory infection. Design: Retrospective cohort study. Setting: The ICU, either PICU or cardiac ICU, at three urban academic tertiary-care children’s hospitals. Patients: All patients with laboratory-confirmed human rhino/enteroviruses infection between January 2010 and June 2011. Interventions: We captured demographic and clinical data and analyzed associated morbidity and mortality outcomes. Measurements and Main Results: There were 519 patients included in our analysis. The median patient age was 2.7 years. The median hospital and ICU lengths of stay were 4 days and 2 days, respectively. Thirty-four percent of patients had a history of asthma, and 25% of patients had a chronic medical condition other than asthma. Thirty-two percent of patients required mechanical ventilation. Eleven patients (2.1%) did not survive to hospital discharge. The rate of viral coinfection was 12.5% and was not associated with mortality. Predisposing factors associated with increased mortality included immunocompromised state (p < 0.001), ICU admission severity of illness score (p < 0.001), and bacterial coinfection (p = 0.003). Conclusions: There is substantial morbidity associated with severe respiratory infection due to human rhino/enteroviruses in children. Mortality was less severe than reported in other respiratory viruses such as influenza and respiratory syncytial virus. The burden of illness from human rhino/enteroviruses in the ICU in terms of resource utilization may be considerable.

Longitudinal in vivo developmental changes of metabolites in the hippocampus of Fmr1 knockout mice

Fragile X syndrome (FXS) is the most common form of inherited mental retardation and is studied in the Fmr1 knockout (KO) mouse, which models both the anatomical and behavioral changes observed in FXS patients. In vitro studies have shown many alterations in synaptic plasticity and increased density of immature dendritic spines in the hippocampus, a region involved in learning and memory. In this study, magnetic resonance imaging (MRI) and 1H magnetic resonance spectroscopy (MRS) were used to determine in vivo longitudinal changes in volume and metabolites in the hippocampus during the critical period of early myelination and synaptogenesis at post‐natal days (PND) 18, 21, and 30 in Fmr1 KO mice compared with wild‐type (WT) controls. MRI demonstrated an increase in volume of the hippocampus in the Fmr1 KO mouse compared with controls. MRS revealed significant developmental changes in the ratios of hippocampal metabolites N‐acetylaspartate (NAA), myo‐inositol (Ins), and taurine to total creatine (tCr) in Fmr1 KO mice compared with WT controls. Ins was decreased at PND 30, and taurine was increased at all ages studied in Fmr1 KO mice compared with controls. An imbalance of brain metabolites in the hippocampus of Fmr1 KO mice during the critical developmental period of synaptogenesis and early myelination could have long‐lasting effects that adversely affect brain development and contribute to ongoing alterations in brain function.

552: A multi-center outcomes analysis of children with severe respiratory infection caused by rhinovirus

A multi-center outcomes AnAlysis of children with severe respirAtory infection cAused by rhinovirus Michael Spaeder1, Jason Custer2, Alison Miles3, Lisa Razzi4, Nicholas Morin2, Susanna Scafidi3, Melania Bembea3, Xiaoyan Song1; 1Childrens National Medical Center, Washington, DC, 2University of Maryland Medical Center, Baltimore, MD, 3Johns Hopkins Medical Institutions, Baltimore, MD, 4Biostatistics Center, George Washington University, Rockville, MD