Postischemic inhibition of cerebral cortex pyruvate dehydrogenase

Baicalin attenuates neuronal damage associated with SDH activation and PDK2-PDH axis dysfunction in early reperfusion

BACKGROUND

Energy deficiency and oxidative stress are interconnected during ischemia/reperfusion (I/R) and serve as potential targets for the treatment of cerebral ischemic stroke. Baicalin is a neuroprotective antioxidant, but the underlying mechanisms are not fully revealed.

PURPOSE

This study explored whether and how baicalin rescued neurons against ischemia/reperfusion (I/R) attack by focusing on the regulation of neuronal pyruvate dehydrogenase kinase 2 (PDK2)-pyruvate dehydrogenase (PDH) axis implicated with succinate dehydrogenase (SDH)-mediated oxidative stress.

STUDY DESIGN

The effect of the tested drug was explored in vitro and in vivo with the model of oxygen-glucose deprivation/reoxygenation (OGD/R) and middle cerebral artery occlusion/reperfusion (MCAO/R), respectively.

METHODS

Neuronal damage was evaluated according to cell viability, infarct area, and Nissl staining. Protein levels were measured by western blotting and immunofluorescence. Gene expression was investigated by RT-qPCR. Mitochondrial status was also estimated by fluorescence probe labeling.

RESULTS

SDH activation-induced excessive production of reactive oxygen species (ROS) changed the protein expression of Lon protease 1 (LonP1) and hypoxia-inducible factor-1ɑ (HIF-1ɑ) in the early stage of I/R, leading to an upregulation of PDK2 and a decrease in PDH activity in neurons and cerebral cortices. Treatment with baicalin prevented these alterations and ameliorated neuronal ATP production and survival.

CONCLUSION

Baicalin improves the function of the neuronal PDK2-PDH axis via suppression of SDH-mediated oxidative stress, revealing a new signaling pathway as a promising target under I/R conditions and the potential role of baicalin in the treatment of acute ischemic stroke.

Effect of adjuvant thiamine and ascorbic acid administration on the neurologic outcomes of out-of-hospital cardiac arrest patients: A before-and-after study

AIM

This study aimed to evaluate the impact of early thiamine and ascorbic acid administration on the neurologic outcome in out-of-hospital cardiac arrest (OHCA) patients treated with targeted temperature management (TTM).

METHODS

This before-and-after cohort study used data extracted from two hospitals of the Korean Hypothermia Network prospective registry. The treatment group incorporated patients enrolled from December 2019 to May 2021, that received intravenous thiamine (200 mg) and ascorbic acid (3 g) at 12-hour intervals for a total of six doses. The control group incorporated those enrolled from May 2018 to November 2019. The one-month good neurologic outcome, defined as a Cerebral Performance Category score ≤ 2, between the groups was evaluated using inverse probability of treatment weighting (IPTW).

RESULTS

Among the 234 OHCA survivors with TTM, 102 were included in the treatment group and 132 were included in the control group. The one-month (31.4 % vs. 29.5 %, respectively; P = 0.76) good neurologic outcome rates did not differ between the treatment and control groups. After adjusting using the IPTW, vitamin supplementation was not associated with good neurologic outcome (odds ratio [OR], 1.134; 95 % confidence interval [CI], 0.644-1.999; P = 0.66). In subgroup analysis, vitamin administration was significantly associated with a good neurologic outcome in older (≥65 years) patients (adjusted OR, 5.53; 95 % CI, 1.21-25.23; P = 0.03).

CONCLUSION

Adjuvant thiamine and ascorbic acid administration in OHCA survivors with TTM did not improve their neurologic outcome after one month. Further clinical trials are warranted.

Mitochondrial complex I ROS production and redox signaling in hypoxia

Mitochondria are a main source of cellular energy. Oxidative phosphorylation (OXPHOS) is the major process of aerobic respiration. Enzyme complexes of the electron transport chain (ETC) pump protons to generate a protonmotive force (Δp) that drives OXPHOS. Complex I is an electron entry point into the ETC. Complex I oxidizes nicotinamide adenine dinucleotide (NADH) and transfers electrons to ubiquinone in a reaction coupled with proton pumping. Complex I also produces reactive oxygen species (ROS) under various conditions. The enzymatic activities of complex I can be regulated by metabolic conditions and serves as a regulatory node of the ETC. Complex I ROS plays diverse roles in cell metabolism ranging from physiologic to pathologic conditions. Progress in our understanding indicates that ROS release from complex I serves important signaling functions. Increasing evidence suggests that complex I ROS is important in signaling a mismatch in energy production and demand. In this article, we review the role of ROS from complex I in sensing acute hypoxia.

Repetitive mild traumatic brain injury-induced neurodegeneration and inflammation is attenuated by acetyl-L-carnitine in a preclinical model

Repetitive mild traumatic brain injuries (rmTBI) may contribute to the development of neurodegenerative diseases through secondary injury pathways. Acetyl-L-carnitine (ALC) shows neuroprotection through anti-inflammatory effects and via regulation of neuronal synaptic plasticity by counteracting post-trauma excitotoxicity. This study aimed to investigate mechanisms implicated in the etiology of neurodegeneration in rmTBI mice treated with ALC. Adult male C57BL/6J mice were allocated to sham, rmTBI or ALC + rmTBI groups. 15 rmTBIs were administered across 23 days using a modified weight drop model. Neurological testing and spatial learning and memory assessments via the Morris Water Maze (MWM) were undertaken at 48 h and 3 months. RT-PCR analysis of the cortex and hippocampus was undertaken for MAPT, GFAP, AIF1, GRIA, CCL11, TDP43, and TNF genes. Gene expression in the cortex showed elevated mRNA levels of MAPT, TNF, and GFAP in the rmTBI group that were reduced by ALC treatment. In the hippocampus, mRNA expression was elevated for GRIA1 in the rmTBI group but not the ALC + rmTBI treatment group. ALC treatment showed protective effects against the deficits displayed in neurological testing and MWM assessment observed in the rmTBI group. While brain structures display differential vulnerability to insult as evidenced by location specific postimpact disruption of key genes, this study shows correlative mRNA neurodegeneration and functional impairment that was ameliorated by ALC treatment in several key genes. ALC may mitigate damage inflicted in the various secondary neurodegenerative cascades and contribute to functional protection following rmTBI.

Clinical targeting of the cerebral oxygen cascade to improve brain oxygenation in patients with hypoxic-ischaemic brain injury after cardiac arrest

The cerebral oxygen cascade includes three key stages: (a) convective oxygen delivery representing the bulk flow of oxygen to the cerebral vascular bed; (b) diffusion of oxygen from the blood into brain tissue; and (c) cellular utilisation of oxygen for aerobic metabolism. All three stages may become dysfunctional after resuscitation from cardiac arrest and contribute to hypoxic-ischaemic brain injury (HIBI). Improving convective cerebral oxygen delivery by optimising cerebral blood flow has been widely investigated as a strategy to mitigate HIBI. However, clinical trials aimed at optimising convective oxygen delivery have yielded neutral results. Advances in the understanding of HIBI pathophysiology suggest that impairments in the stages of the oxygen cascade pertaining to oxygen diffusion and cellular utilisation of oxygen should also be considered in identifying therapeutic strategies for the clinical management of HIBI patients. Culprit mechanisms for these impairments may include a widening of the diffusion barrier due to peri-vascular oedema and mitochondrial dysfunction. An integrated approach encompassing both intra-parenchymal and non-invasive neuromonitoring techniques may aid in detecting pathophysiologic changes in the oxygen cascade and enable patient-specific management aimed at reducing the severity of HIBI.

Longitudinal Associations of Plasma TMAO and Related Metabolites with Cognitive Impairment and Dementia in Older Adults: The Cardiovascular Health Study

BACKGROUND

Animal studies suggest that gut microbiome metabolites such as trimethylamine N-oxide (TMAO) may influence cognitive function and dementia risk. However potential health effects of TMAO and related metabolites remain unclear.

OBJECTIVE

We examined prospective associations of TMAO, γ-butyrobetaine, crotonobetaine, carnitine, choline, and betaine with risk of cognitive impairment and dementia among older adults aged 65 years and older in the Cardiovascular Health Study (CHS).

METHODS

TMAO and metabolites were measured in stored plasma specimens collected at baseline. Incident cognitive impairment was assessed using the 100-point Modified Mini-Mental State Examination administered serially up to 7 times. Clinical dementia was identified using neuropsychological tests adjudicated by CHS Cognition Study investigators, and by ICD-9 codes from linked Medicare data. Associations of each metabolite with cognitive outcomes were assessed using Cox proportional hazards models.

RESULTS

Over a median of 13 years of follow-up, 529 cases of cognitive impairment, and 522 of dementia were identified. After multivariable adjustment for relevant risk factors, no associations were seen with TMAO, carnitine, choline, or betaine. In contrast, higher crotonobetaine was associated with 20-32% higher risk of cognitive impairment and dementia per interquintile range (IQR), while γ-butyrobetaine was associated with ∼25% lower risk of the same cognitive outcomes per IQR.∥Conclusion:These findings suggest that γ-butyrobetaine, crotonobetaine, two gut microbe and host metabolites, are associated with risk of cognitive impairment and dementia. Our results indicate a need for mechanistic studies evaluating potential effects of these metabolites, and their interconversion on brain health, especially later in life.

Acetyl-L-carnitine in chronic pain: A narrative review

Acetyl-L-carnitine (ALC) is an endogenous molecule that not only plays a role in energy metabolism, but also has antioxidant properties, protects from oxidative stress, modulates brain neurotransmitters such as acetylcholine, serotonin and dopamine, and acts on neurotrophic factors such as nerve growth factor (NGF) and metabotropic glutamate (mGlu) receptors by means of epigenetic mechanisms. Importantly, it induces mGlu2 expression at nerve terminals, thus giving rise to analgesia and preventing spinal sensitisation. It has also been found to have even long-term neurotrophic and analgesic activity in experimental models of chronic inflammatory and neuropathic pain. The aim of this narrative review is to summarise the current evidence regarding the use of ALC in patients with chronic pain, and cognitive and mood disorders, and investigate the rationale underlying its use in patients with fibromyalgia syndrome, which is characterised by nociplastic changes that increase the sensitivity of the nervous system to pain.

Cannabidiol modulation of oxidative stress and signalling

Cannabidiol (CBD), one of the primary non-euphoric components in the Cannabis sativa L. plant, has undergone clinical development over the last number of years as a therapeutic for patients with Lennox-Gastaut syndrome and Dravet syndromes. This phytocannabinoid demonstrates functional and pharmacological diversity, and research data indicate that CBD is a comparable antioxidant to common antioxidants. This review gathers the latest knowledge regarding the impact of CBD on oxidative signalling, with focus on the proclivity of CBD to regulate antioxidants and control the production of reactive oxygen species. CBD is considered an attractive therapeutic agent for neuroimmune disorders, and a body of literature indicates that CBD can regulate redox function at multiple levels, with a range of downstream effects on cells and tissues. However, pro-oxidant capacity of CBD has also been reported, and hence caution must be applied when considering CBD from a therapeutic standpoint. Such pro- and antioxidant functions of CBD may be cell- and model-dependent and may also be influenced by CBD dose, the duration of CBD treatment and the underlying pathology.

Pharmacologic neuroprotection in ischemic brain injury after cardiac arrest

Cardiac arrest has many implications for morbidity and mortality. Few interventions have been shown to improve return of spontaneous circulation (ROSC) and long-term outcomes after cardiac arrest. Ischemic-reperfusion injury upon achieving ROSC creates an imbalance between oxygen supply and demand. Multiple events occur in the postcardiac arrest period, including excitotoxicity, mitochondrial dysfunction, and oxidative stress and inflammation, all of which contribute to ongoing brain injury and cellular death. Given that complex pathophysiology underlies global brain hypoxic ischemia, neuroprotective strategies targeting multiple stages of the neuropathologic cascade should be considered as a means of mitigating secondary neuronal injury and improving neurologic outcomes and survival in cardiac arrest victims. In this review article, we discuss a number of different pharmacologic agents that may have a potential role in targeting these injurious pathways following cardiac arrest. Pharmacologic therapies most relevant for discussion currently include memantine, perampanel, magnesium, propofol, thiamine, methylene blue, vitamin C, vitamin E, coenzyme Q₁₀ , minocycline, steroids, and aspirin.

Enhancing Metabolic Imaging of Energy Metabolism in Traumatic Brain Injury Using Hyperpolarized [1-13C]Pyruvate and Dichloroacetate

Hyperpolarized magnetic resonance spectroscopic imaging (MRSI) of [1-¹³C]pyruvate metabolism has previously been used to assess the effects of traumatic brain injury (TBI) in rats. Here, we show that MRSI can be used in conjunction with dichloroacetate to measure the phosphorylation state of pyruvate dehydrogenase (PDH) following mild-to-moderate TBI, and that measurements can be repeated in a longitudinal study to monitor the course of injury progression and recovery. We found that the level of ¹³C-bicarbonate and the bicarbonate-to-lactate ratio decreased on the injured side of the brain four hours after injury and continued to decrease through day 7. Levels recovered to normal by day 28. Measurements following dichloroacetate administration showed that PDH was inhibited equally by PDH kinase (PDK) on both sides of the brain. Therefore, the decrease in aerobic metabolism is not due to inhibition by PDK.

Role of NAD+-Modulated Mitochondrial Free Radical Generation in Mechanisms of Acute Brain Injury

It is commonly accepted that mitochondria represent a major source of free radicals following acute brain injury or during the progression of neurodegenerative diseases. The levels of reactive oxygen species (ROS) in cells are determined by two opposing mechanisms—the one that produces free radicals and the cellular antioxidant system that eliminates ROS. Thus, the balance between the rate of ROS production and the efficiency of the cellular detoxification process determines the levels of harmful reactive oxygen species. Consequently, increase in free radical levels can be a result of higher rates of ROS production or due to the inhibition of the enzymes that participate in the antioxidant mechanisms. The enzymes’ activity can be modulated by post-translational modifications that are commonly altered under pathologic conditions. In this review we will discuss the mechanisms of mitochondrial free radical production following ischemic insult, mechanisms that protect mitochondria against free radical damage, and the impact of post-ischemic nicotinamide adenine mononucleotide (NAD⁺) catabolism on mitochondrial protein acetylation that affects ROS generation and mitochondrial dynamics. We propose a mechanism of mitochondrial free radical generation due to a compromised mitochondrial antioxidant system caused by intra-mitochondrial NAD⁺ depletion. Finally, the interplay between different mechanisms of mitochondrial ROS generation and potential therapeutic approaches are reviewed.

Time Course of Metabolomic Alterations in Cerebrospinal Fluid After Aneurysmal Subarachnoid Hemorrhage

Object: The aim of this study was to investigate metabolite levels in cerebrospinal fluid (CSF) in their time-dependent course after aneurysmal subarachnoid hemorrhage (aSAH) comparing them to patients harboring unruptured intracranial aneurysms. Methods: Eighty CSF samples of 16 patients were analyzed. The study population included patients undergoing endovascular/microsurgical treatment of ruptured intracranial aneurysms (n = 8), which were assessed for 9 days after aSAH. Control samples were collected from the basal cisterns in elective aneurysm surgery (n = 8). The CSF samples were consecutively collected with extraventricular drain (EVD) placement/intraoperatively, 6 h later, and daily thereafter (day 1-9). The endogenous metabolites were analyzed with a targeted quantitative and quality controlled metabolomics approach using the AbsoluteIDQ®p180Kit. Differences inbetween timepoints and compared to the control group were evaluated. Results: Numerous alterations of amino acid (AA) levels were detected within the first hours after bleeding. The highest mean concentrations occurred 1 week after aSAH. AA levels were continuously increasing over time starting 6 h after aSAH. Taurine concentration was highest briefly after aSAH starting to decrease already after 6 h (vs. day 1-9, p = 0.02). The levels of sphingomyelins/ phosphatidylcholines/ lysophosphatidylcholines/mono-unsaturated fatty acid chain were highly elevated on day 0 (compared to other timepoints or controls, p < 0.01) and decreased over the next several days to concentrations comparable to the control group. Carnitine concentrations were decreased after SAH (vs. day 7, p < 0.01), while they recovered within the next day. The Fischer ratio of branched-chain AA to aromatic AA was lowest immediately after SAH and increased in 7 days (p < 0.001). Conclusion: AA levels in CSF increased overtime and often differ from patients without SAH. There was a peak concentration of structural AA within the first 6 h after aneurysm treatment. Time-dependent alterations of CSF metabolites and compounds may elucidate pathophysiological processes after aSAH, providing potential predictors assessed non-invasively by routine lab testing.

Effect of l-carnitine supplementation on muscle cramps induced by stroke: A case report

l-carnitine, a compound responsible for transportation of acyl groups across cell membranes and modulating intracellular acyl-coenzyme A levels, is reported to reduce muscle cramps in patients with liver cirrhosis and diabetes and those on dialysis. A 79-y-old man with right-sided paralysis was admitted to our hospital and diagnosed with cerebral infarction. Nocturnal leg cramps appeared in the affected side and caused sleep disturbance. Supplementation with l-carnitine reduced the number of nocturnal leg cramps and alleviated sleep disturbance. It also plays an important role in nerve protection and treatment for carnitine deficiency. Patients with stroke-induced paralysis experience muscle wasting, which might reduce pooled carnitine in the affected side. This case suggests that stroke may cause localized carnitine deficiency, and l-carnitine supplementation might be effective for muscle cramps induced by stroke. To the best of our knowledge, this is the first case of l-carnitine supplementation for muscle cramps triggered by cerebral infarction.

Human brain blood flow and metabolism during isocapnic hyperoxia: the role of reactive oxygen species

KEY POINTS

It is unknown whether excessive reactive oxygen species (ROS) production drives the isocapnic hyperoxia (IH)-induced decline in human cerebral blood flow (CBF) via reduced nitric oxide (NO) bioavailability and leads to disruption of the blood-brain barrier (BBB) or neural-parenchymal damage. Cerebral metabolic rate for oxygen (CMR O 2 ) and transcerebral exchanges of NO end-products, oxidants, antioxidants and neural-parenchymal damage markers were simultaneously quantified under IH with intravenous saline and ascorbic acid infusion. CBF and CMR O 2 were reduced during IH, responses that were followed by increased oxidative stress and reduced NO bioavailability when saline was infused. No indication of neural-parenchymal damage or disruption of the BBB was observed during IH. Antioxidant defences were increased during ascorbic acid infusion, while CBF, CMR O 2 , oxidant and NO bioavailability markers remained unchanged. ROS play a role in the regulation of CBF and metabolism during IH without evidence of BBB disruption or neural-parenchymal damage.

ABSTRACT

To test the hypothesis that isocapnic hyperoxia (IH) affects cerebral blood flow (CBF) and metabolism through exaggerated reactive oxygen species (ROS) production, reduced nitric oxide (NO) bioavailability, disturbances in the blood-brain barrier (BBB) and neural-parenchymal homeostasis, 10 men (24 ± 1 years) were exposed to a 10 min IH trial (100% O₂ ) while receiving intravenous saline and ascorbic acid (AA, 3 g) infusion. Internal carotid artery blood flow (ICABF), vertebral artery blood flow (VABF) and total CBF (tCBF, Doppler ultrasound) were determined. Arterial and right internal jugular venous blood was sampled to quantify the cerebral metabolic rate of oxygen (CMR O 2 ), transcerebral exchanges (TCE) of NO end-products (plasma nitrite), antioxidants (AA and AA plus dehydroascorbic acid (AA+DA)) and oxidant biomarkers (thiobarbituric acid-reactive substances (TBARS) and 8-isoprostane), and an index of BBB disruption and neuronal-parenchymal damage (neuron-specific enolase; NSE). IH reduced ICABF, tCBF and CMR O 2 , while VABF remained unchanged. Arterial 8-isoprostane and nitrite TCE increased, indicating that CBF decline was related to ROS production and reduced NO bioavailability. AA, AA+DA and NSE TCE did not change during IH. AA infusion did not change the resting haemodynamic and metabolic parameters but raised antioxidant defences, as indicated by increased AA/AA+DA concentrations. Negative AA+DA TCE, unchanged nitrite, reductions in arterial and venous 8-isoprostane, and TBARS TCE indicated that AA infusion effectively inhibited ROS production and preserved NO bioavailability. Similarly, AA infusion prevented IH-induced decline in regional and total CBF and re-established CMR O 2 . These findings indicate that ROS play a role in CBF regulation and metabolism during IH without evidence of BBB disruption or neural-parenchymal damage.

Heptanoate is neuroprotective in vitro but triheptanoin post-treatment did not protect against middle cerebral artery occlusion in rats

Triheptanoin, the medium-chain triglyceride of heptanoate, has been shown to be anticonvulsant and neuroprotective in several neurological disorders. In the gastrointestinal tract, triheptanoin is cleaved to heptanoate, which is then taken up by the blood and most tissues, including liver, heart and brain. Here we evaluated the neuroprotective effects of heptanoate and its effects on mitochondrial oxygen consumption in vitro. We also investigated the neuroprotective effects of triheptanoin compared to long-chain triglycerides when administered after stroke onset in rats. Heptanoate pre-treatment protected cultured neurons against cell death induced by oxygen glucose deprivation and N-methyl-D-aspartate. Incubation of cultured astrocytes with heptanoate for 2 h increased mitochondrial proton leak and also enhanced basal respiration and ATP turnover, suggesting that heptanoate protects against oxidative stress and is used as fuel. However, continuous 72 h infusion of triheptanoin initiated 1 h after middle cerebral artery occlusion in rats did not alter stroke volume at 3 days or neurological deficit at 1 and 3 days relative to long-chain triglyceride control treatment.

Enhanced pyruvate dehydrogenase activity improves cardiac outcomes in a murine model of cardiac arrest

Rationale

Post-ischemic changes in cellular metabolism alter myocardial and neurological function. Pyruvate dehydrogenase (PDH), the limiting step in mitochondrial glucose oxidation, is inhibited by increased expression of PDH kinase (PDK) during ischemia/reperfusion injury. This results in decreased utilization of glucose to generate cellular ATP. Post-cardiac arrest (CA) hypothermia improves outcomes and alters metabolism, but its influence on PDH and PDK activity following CA are unknown. We hypothesized that therapeutic hypothermia (TH) following CA is associated with the inhibition of PDK activity and increased PDH activity. We further hypothesized that an inhibitor of PDK activity, dichloroacetate (DCA), would improve PDH activity and post-CA outcomes.

Methods and results

Anesthetized and ventilated adult female C57BL/6 wild-type mice underwent a 12-minute KCl-induced CA followed by cardiopulmonary resuscitation. Compared to normothermic (37°C) CA controls, administering TH (30°C) improved overall survival (72-hour survival rate: 62.5% vs. 28.6%, P<0.001), post-resuscitation myocardial function (ejection fraction: 50.9±3.1% vs. 27.2±2.0%, P<0.001; aorta systolic pressure: 132.7±7.3 vs. 72.3±3.0 mmHg, P<0.001), and neurological scores at 72-hour post CA (9.5±1.3 vs. 5.4±1.3, P<0.05). In both heart and brain, CA increased lactate concentrations (1.9-fold and 3.1-fold increase, respectively, P<0.01), decreased PDH enzyme activity (24% and 50% reduction, respectively, P<0.01), and increased PDK protein expressions (1.2-fold and 1.9-fold, respectively, P<0.01). In contrast, post-CA treatment with TH normalized lactate concentrations (P<0.01 and P<0.05) and PDK expressions (P<0.001 and P<0.05), while increasing PDH activity (P<0.01 and P<0.01) in both the heart and brain. Additionally, treatment with DCA (0.2 mg/g body weight) 30 min prior to CA improved both myocardial hemodynamics 2 hours post-CA (aortic systolic pressure: 123±3 vs. 96±4 mmHg, P<0.001) and 72-hour survival rates (50% vs. 19%, P<0.05) in normothermic animals.

Conclusions

Enhanced PDH activity in the setting of TH or DCA administration is associated with improved post-CA resuscitation outcomes. PDH is a promising therapeutic target for improving post-CA outcomes.

L-Carnitine and Acetyl-L-carnitine Roles and Neuroprotection in Developing Brain

L-Carnitine functions to transport long chain fatty acyl-CoAs into the mitochondria for degradation by β-oxidation. Treatment with L-carnitine can ameliorate metabolic imbalances in many inborn errors of metabolism. In recent years there has been considerable interest in the therapeutic potential of L-carnitine and its acetylated derivative acetyl-L-carnitine (ALCAR) for neuroprotection in a number of disorders including hypoxia-ischemia, traumatic brain injury, Alzheimer's disease and in conditions leading to central or peripheral nervous system injury. There is compelling evidence from preclinical studies that L-carnitine and ALCAR can improve energy status, decrease oxidative stress and prevent subsequent cell death in models of adult, neonatal and pediatric brain injury. ALCAR can provide an acetyl moiety that can be oxidized for energy, used as a precursor for acetylcholine, or incorporated into glutamate, glutamine and GABA, or into lipids for myelination and cell growth. Administration of ALCAR after brain injury in rat pups improved long-term functional outcomes, including memory. Additional studies are needed to better explore the potential of L-carnitine and ALCAR for protection of developing brain as there is an urgent need for therapies that can improve outcome after neonatal and pediatric brain injury.

Neuroprotective Effects of Acetyl-L-Carnitine on Neonatal Hypoxia Ischemia-Induced Brain Injury in Rats

Perinatal hypoxia ischemia (HI) is a significant cause of brain injury in surviving infants. Although hypothermia improves outcomes in some infants, additional therapies are needed since about 40% of infants still have a poor outcome. Acetyl-L-carnitine (ALCAR), an acetylated derivative of L-carnitine, protected against early changes in brain metabolites and mitochondrial function after HI on postnatal day (PND) 7 in a rat pup model of near-term HI injury. However, its efficacy in long-term structural and functional outcomes remains unexplored. We determined the efficacy of ALCAR therapy administered to rat pups after HI at PND 7, using both longitudinal in vivo magnetic resonance imaging and behavioral tests, in male and female rats. HI led to sex-specific behavioral impairment, with males exhibiting more global functional deficits than females. Interestingly, HI reduced the volume of the contralateral hemisphere in males only, suggesting that the brain injury is more diffuse in males than in females. Treatment with ALCAR improved both morphological and functional outcomes in both male and female rats. These results suggest that ALCAR may be a potential therapy for clinical use since the treatment attenuated the moderate injury produced under the experimental conditions used and improved the functional outcome in preclinical studies.

First Description of Reduced Pyruvate Dehydrogenase Enzyme Activity Following Subarachnoid Hemorrhage (SAH)

Object: Several previous studies reported metabolic derangements and an accumulation of metabolic products in the early phase of experimental subarachnoid hemorrhage (SAH), which may contribute to secondary brain damage. This may be a result of deranged oxygen utilization due to enzymatic dysfunction in aerobic glucose metabolism. This study was performed to investigate, if pyruvate dehydrogenase enzyme (PDH) is affected in its activity giving further hints for a derangement of oxidative metabolism.

Methods: Eighteen male Sprague-Dawley rats were randomly assigned to one of two experimental groups (n = 9): (1) SAH induced by the endovascular filament model and (2) sham-operated controls. Mean arterial blood pressure (MABP), intracranial pressure (ICP), and local cerebral blood flow (LCBF; laser-Doppler flowmetry) were continuously monitored from 30 min before until 3 h after SAH. Thereafter, the animals were sacrificed and PDH activity was measured by ELISA.

Results: PDH activity was significantly reduced in animals subjected to SAH compared to controls.

Conclusion: The results of this study demonstrate for the first time a reduction of PDH activity following SAH, independent of supply of substrates and may be an independent factor contributing to a derangement of oxidative metabolism, failure of oxygen utilization, and secondary brain damage.

Pyruvate dehydrogenase complex in cerebral ischemia-reperfusion injury

Pyruvate dehydrogenase (PDH) complex is a mitochondrial matrix enzyme that serves a critical role in the conversion of anaerobic to aerobic cerebral energy. The regulatory complexity of PDH, coupled with its significant influence in brain metabolism, underscores its susceptibility to, and significance in, ischemia-reperfusion injury. Here, we evaluate proposed mechanisms of PDH-mediated neurodysfunction in stroke, including oxidative stress, altered regulatory enzymatic control, and loss of PDH activity. We also describe the neuroprotective influence of antioxidants, dichloroacetate, acetyl-L-carnitine, and combined therapy with ethanol and normobaric oxygen, explained in relation to PDH modulation. Our review highlights the significance of PDH impairment in stroke injury through an understanding of the mechanisms by which it is modulated, as well as an exploration of neuroprotective strategies available to limit its impairment.

Thiamine as a neuroprotective agent after cardiac arrest

AIMS

Reduction of pyruvate dehydrogenase (PDH) activity in the brain is associated with neurological deficits in animals resuscitated from cardiac arrest. Thiamine is an essential co-factor of PDH. The objective of this study was to examine whether administration of thiamine improves outcomes after cardiac arrest in mice. Secondarily, we aimed to characterize the impact of cardiac arrest on PDH activity in mice and humans.

METHODS

Animal study: Adult mice were subjected to cardiac arrest whereupon cardiopulmonary resuscitation was performed. Thiamine or vehicle was administered 2min before resuscitation and daily thereafter. Mortality, neurological outcome, and metabolic markers were evaluated. Human study: In a convenience sample of post-cardiac arrest patients, we measured serial PDH activity from peripheral blood mononuclear cells and compared them to healthy controls.

RESULTS

Animal study: Mice treated with thiamine had increased 10-day survival (48% versus 17%, P<0.01) and improved neurological function when compared to vehicle-treated mice. In addition, thiamine markedly improved histological brain injury compared to vehicle. The beneficial effects of thiamine were accompanied by improved oxygen consumption in mitochondria, restored thiamine pyrophosphate levels, and increased PDH activity in the brain at 10 days. Human study: Post-cardiac arrest patients had lower PDH activity in mononuclear cells than did healthy volunteers (estimated difference: -5.8O.D./min/mg protein, P<0.001).

CONCLUSIONS

The provision of thiamine after cardiac arrest improved neurological outcome and 10-day survival in mice. PDH activity was markedly depressed in post-cardiac arrest patients suggesting that this pathway may represent a therapeutic target.

Pyruvate Dehydrogenase Activity and Quantity Decreases After Coronary Artery Bypass Grafting: a Prospective Observational Study

INTRODUCTION

Pyruvate dehydrogenase (PDH) is a key gatekeeper enzyme in aerobic metabolism. The main purpose of this study was to determine if PDH activity is affected by major stress in the form of coronary artery bypass grafting (CABG), which has previously been used as a model of critical illness.

METHODS

We conducted a prospective, observational study of patients undergoing CABG at an urban, tertiary care hospital. We included adult patients undergoing CABG with or without concomitant valve surgery. Measurements of PDH activity and quantity and thiamine were obtained prior to surgery, at the completion of surgery, and 6 h after surgery.

RESULTS

Fourteen patients were enrolled (aged 67 ± 10 years, 21% female). Study subjects had a mean 41.7% (SD, 27.7%) reduction in PDH activity after surgery and a mean 32.0% (SD, 31.4%) reduction 6h after surgery (P < 0.001). Eight patients were thiamine deficient (≤ 7 nmol/L) after surgery compared with none prior to surgery (P = 0.002). Thiamine level was significantly associated with PDH quantity at all time points (P = 0.01). Postsurgery lactate levels were inversely correlated with postsurgery thiamine levels (r = -0.58 and P = 0.04).

CONCLUSION

The stress of major surgery causes decreased PDH activity and quantity and depletion of thiamine levels.

In vivo longitudinal proton magnetic resonance spectroscopy on neonatal hypoxic-ischemic rat brain injury: Neuroprotective effects of acetyl-L-carnitine

PURPOSE

This study evaluated the longitudinal metabolic alterations after neonatal hypoxia-ischemia (HI) in rats and tested the neuroprotective effect of acetyl-L-carnitine (ALCAR) using in vivo proton short-TE Point-RESolved Spectroscopy method.

METHODS

Rice-Vannucci model was used on 7-day-old Sprague-Dawley rats. Data were acquired from contralateral and ipsilateral cortex and hippocampus, respectively at 4 time points (24-h, 72-h, 7-days, 28-days) post-HI. The effect of subcutaneous administration of ALCAR (100 mg/kg) immediately after HI, at 4-h, 24-h, and 48-h post-HI was determined.

RESULTS

Significant reductions in glutathione (P < 0.005), myo-inositol (P < 0.002), taurine (P < 0.001), and total creatine (P < 0.005) were observed at 24-h postinjury compared with the control group in the ipsilateral hippocampus of the HI rat pups. ALCAR-treated-HI rats had lower levels of lactate and maintained total creatine at 24-h and had smaller lesion size compared with the HI only rats.

CONCLUSION

Severe oxidative, osmotic stress, impaired phosphorylation, and a preference for anaerobic glycolysis were found in the ipsilateral hippocampus in the HI pups at 24-h postinjury. ALCAR appeared to have a neuroprotective effect if administered early after HI by serving as an energy substrate and promote oxidative cerebral energy producing and minimize anaerobic glycolysis.

BACE1 activity impairs neuronal glucose oxidation: rescue by beta-hydroxybutyrate and lipoic acid

Glucose hypometabolism and impaired mitochondrial function in neurons have been suggested to play early and perhaps causative roles in Alzheimer's disease (AD) pathogenesis. Activity of the aspartic acid protease, beta-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1), responsible for beta amyloid peptide generation, has recently been demonstrated to modify glucose metabolism. We therefore examined, using a human neuroblastoma (SH-SY5Y) cell line, whether increased BACE1 activity is responsible for a reduction in cellular glucose metabolism. Overexpression of active BACE1, but not a protease-dead mutant BACE1, protein in SH-SY5Y cells reduced glucose oxidation and the basal oxygen consumption rate, which was associated with a compensatory increase in glycolysis. Increased BACE1 activity had no effect on the mitochondrial electron transfer process but was found to diminish substrate delivery to the mitochondria by inhibition of key mitochondrial decarboxylation reaction enzymes. This BACE1 activity-dependent deficit in glucose oxidation was alleviated by the presence of beta hydroxybutyrate or α-lipoic acid. Consequently our data indicate that raised cellular BACE1 activity drives reduced glucose oxidation in a human neuronal cell line through impairments in the activity of specific tricarboxylic acid cycle enzymes. Because this bioenergetic deficit is recoverable by neutraceutical compounds we suggest that such agents, perhaps in conjunction with BACE1 inhibitors, may be an effective therapeutic strategy in the early-stage management or treatment of AD.

Potential protective effects of l-carnitine against neuromuscular ischemia-reperfusion injury: From experimental data to potential clinical applications

BACKGROUND & AIM

Ischemia-reperfusion (I/R) injury plays important role in morbidity and mortality in several pathologies, including myocardial infarction, ischemic stroke, acute kidney injury, trauma, and circulatory arrest. An imbalance in metabolic supply and tissue's demand during ischemia results in profound tissue hypoxia and microvascular dysfunction. Subsequently, reperfusion further results in activation of immune responses and cell death programs. l-carnitine and its derivatives have been administered to improve tolerance against I/R injury in various tissues. Anti-ischemic properties of l-carnitine and its derivative in neuromuscular organs will be reviewed here at the light of pertinent results from basic and clinical researches.

METHOD

All available in vitro and in vivo studies, patents, clinical trials, and meeting abstracts in English language that examined the protective effects of l-carnitine against I/R induced injury in neuromuscular organs were reviewed. Materials were obtained by searching ELSEVIER, web of knowledge, PubMed, Scopus, clinical trials, and Cochrane database of systematic reviews.

CONCLUSION

Although animal studies on central nervous system and some human studies on muscular system were in favors of effects of l-carnitine against I/R injury, however, more clinical trials are needed to clarify the clinical importance of l-carnitine as a treatment option to manage I/R-induced injury of neuromuscular system.

Delayed hyperoxic ventilation attenuates oxygen-induced free radical accumulation during early reperfusion after global brain ischemia

To compare the effect of immediate and delayed administration of oxygen on the accumulation of free radicals in ischemia-reperfusion animal models. Thirty-two adult male Mongolian gerbils with microdialysis probes implanted in the right hippocampal CA1 were divided randomly into four groups (eight each). One group was sham-operated (Sham group) whereas the other three groups were subjected to 10 min bilateral carotid artery occlusion (BCAO). BCAO-treated animals were then subjected to the following: (a) immediate 30% O2 (near normoxia, NO group), (b) immediate 100% O2 (hyperoxia, HO group), and (c) 30% O2 for 60 min, followed by 100% O2 for 60 min (delayed hyperoxia, DHO group). Hippocampal accumulation of hydroxyl radicals (•OH) during reperfusion was estimated by measuring 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA in microdialysis perfusate. Hippocampi were removed 2 h after perfusion to measure malondialdehyde, pyruvate dehydrogenase activity, indices of lipid peroxidation, and cellular respiration. At 24 h after BCAO, the histology of hippocampi was analyzed to rate the injury. Immediately after the onset of reperfusion, all groups showed markedly elevated DHBA, which returned to baseline over 1-2 h. Compared with the NO group, the HO group showed significantly higher peak DHBA and slower recovery. In contrast, the DHO group was not significantly different from the NO group in terms of the DHBA level. DHO animals also showed significantly lower hippocampal malondialdehyde accumulation and higher pyruvate dehydrogenase activity at 2 h after reperfusion versus the HO group. Histology analysis also showed animals in the DHO group with ameliorated injury compared with the HO group. Hydroxyl radical accumulation was more sensitive to O2 during early reperfusion. Delayed hyperoxia may re-establish oxidative metabolism while minimizing oxidative stress after CA.

Augmentation of normal and glutamate-impaired neuronal respiratory capacity by exogenous alternative biofuels

Mitochondrial respiratory capacity is critical for responding to changes in neuronal energy demand. One approach toward neuroprotection is the administration of alternative energy substrates ("biofuels") to overcome brain injury-induced inhibition of glucose-based aerobic energy metabolism. This study tested the hypothesis that exogenous pyruvate, lactate, β-hydroxybutyrate, and acetyl-L-carnitine each increase neuronal respiratory capacity in vitro either in the absence of or following transient excitotoxic glutamate receptor stimulation. Compared to the presence of 5 mM glucose alone, the addition of pyruvate, lactate, or β-hydroxybutyrate (1.0-10.0 mM) to either day in vitro (DIV) 14 or 7 rat cortical neurons resulted in significant, dose-dependent stimulation of respiratory capacity, measured by cell respirometry as the maximal O2 consumption rate in the presence of the respiratory uncoupler carbonyl cyanide-p-trifluoromethoxyphenylhydrazone. A 30-min exposure to 100 μM glutamate impaired respiratory capacity for DIV 14, but not DIV 7, neurons. Glutamate reduced the respiratory capacity for DIV 14 neurons with glucose alone by 25 % and also reduced respiratory capacity with glucose plus pyruvate, lactate, or β-hydroxybutyrate. However, respiratory capacity in glutamate-exposed neurons following pyruvate or β-hydroxybutyrate addition was still, at least, as high as that obtained with glucose alone in the absence of glutamate exposure. These results support the interpretation that previously observed neuroprotection by exogenous pyruvate, lactate, or β-hydroxybutyrate is at least partially mediated by their preservation of neuronal respiratory capacity.

Intraventricular albumin: an optional agent in experimental post-traumatic brain edema

HYPOTHESIS

Human albumin may be effective in the treatment of posttraumatic brain edema due to its hyperoncotic features. Therefore, the aim of the experimental study presented in this paper has two points: the first is to evaluate the efficacy of intraventricular hyperoncotic human albumin on post-traumatic brain edema and the second is to try to show the appropriate posttraumatic time window for albumin administration.

METHOD

Traumatic brain injury and subsequent edema was formed by a model of impact acceleration injury in rats. Human albumin was administered via intraventricular route by using a stereotactic head holder. All animals in each group were decapitated 24 hours after the procedure and the effect of albumin was evaluated by measurement of tissue specific gravity.

RESULTS

Tissue specific gravity decreased in edematous tissue (trauma indicator), increased after albumin administration at the 12th (p < 0.001), and both at the 1st and 12th hour of the trauma (edema treatment; p < 0.001). On the other hand, albumin administered at the 12th, and at both the 1st and 12th hours in the rats without trauma has caused the formation of the brain edema.

CONCLUSION

We conclude that human albumin is effective in cytotoxic, but not in vasogenic edema and exerts its best anti-edematous effect at the 12th hour of severe head trauma and this study may help future studies that will try to show the effects of albumin with different time modalities after severe head injury.

In the eye of the storm: mitochondrial damage during heart and brain ischaemia

We review research investigating mitochondrial damage during heart and brain ischaemia, focusing on the mechanisms and consequences of ischaemia-induced and/or reperfusion-induced: (a) inhibition of mitochondrial respiratory complex I; (b) release of cytochrome c from mitochondria; (c) changes to mitochondrial phospholipids; and (d) nitric oxide inhibition of mitochondria. Heart ischaemia causes inhibition of cytochrome oxidase and complex I, release of cytochrome c, and induction of permeability transition and hydrolysis and oxidation of mitochondrial phospholipids, but some of the mechanisms are unclear. Brain ischaemia causes inhibition of complexes I and IV, but other effects are less clear.

Serum albumin levels in ischemic stroke and its subtypes: correlation with clinical outcome

OBJECTIVE

Previous studies have associated low serum albumin levels with poor outcome in ischemic stroke. Animal studies also demonstrated neuroprotective effects of serum albumin in focal ischemia. However, there are very limited studies on the association of serum albumin levels with stroke outcome in ischemic stroke divided into subtypes. The present study was carried out to investigate the association of serum albumin levels with outcome in ischemic stroke and its subtypes.

METHODS

The study involved 560 patients. Serum albumin levels were estimated and follow-up interviews were conducted at 3 mo postevent to determine stroke outcome. The association between serum albumin levels and stroke outcome was evaluated by multiple logistic regression analysis after adjustment for potential confounders.

RESULTS

Low levels of albumin associated significantly with poor outcome (score of >3 on the modified Rankin Scale). The adjusted odds ratio was 1.972 (95% confidence interval, 1.103-4.001; P < 0.001). The recurrence of stroke and death rate also was high in patients with low levels of albumin compared with patients with elevated levels of albumin. The reduced level of serum albumin associated significantly with poor outcome in all the stroke subtypes classified according to TOAST (Trial of ORG 10172 in Acute Stroke Treatment).

CONCLUSIONS

Relatively high serum albumin levels in acute stroke decrease poor outcome.

Effect of hypoxia and hyperoxia on cerebral blood flow, blood oxygenation, and oxidative metabolism

Characterizing the effect of oxygen (O(2)) modulation on the brain may provide a better understanding of several clinically relevant problems, including acute mountain sickness and hyperoxic therapy in patients with traumatic brain injury or ischemia. Quantifying the O(2) effects on brain metabolism is also critical when using this physiologic maneuver to calibrate functional magnetic resonance imaging (fMRI) signals. Although intuitively crucial, the question of whether the brain's metabolic rate depends on the amount of O(2) available has not been addressed in detail previously. This can be largely attributed to the scarcity and complexity of measurement techniques. Recently, we have developed an MR method that provides a noninvasive (devoid of exogenous agents), rapid (<5 minutes), and reliable (coefficient of variant, CoV <3%) measurement of the global cerebral metabolic rate of O(2) (CMRO(2)). In the present study, we evaluated metabolic and vascular responses to manipulation of the fraction of inspired O(2) (FiO(2)). Hypoxia with 14% FiO(2) was found to increase both CMRO(2) (5.0±2.0%, N=16, P=0.02) and cerebral blood flow (CBF) (9.8±2.3%, P<0.001). However, hyperoxia decreased CMRO(2) by 10.3±1.5% (P<0.001) and 16.9±2.7% (P<0.001) for FiO(2) of 50% and 98%, respectively. The CBF showed minimal changes with hyperoxia. Our results suggest that modulation of inspired O(2) alters brain metabolism in a dose-dependent manner.

Decreased oxidative stress during glycolytic inhibition enables maintenance of ATP production and astrocytic survival

Depressed energy metabolism and oxidative stress are common features in many pathological situations in the brain, including stroke. In order to investigate astrocytic responses to such stress, we induced metabolic depression in cultured rat astrocytes. Iodoacetate (IA), an inhibitor of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used and resulted in a rapid inhibition of GAPDH activity. After 1h of GAPDH inhibition the ATP levels started to decrease and were completely abolished at 4h. In parallel, the activity of reactive oxygen species (ROS) was significantly increased, followed by extensive cell death involving flipping of phosphatidylserine and translocation of apoptosis-inducing factor, but not caspase-3 activation. When IA was combined with azide, a respiratory chain complex IV inhibitor, the ATP levels decreased immediately. Interestingly, with azide present, the ROS activity remained low and the astrocytes remained viable even at very low ATP levels. Addition of exogenous ROS-scavengers prevented the IA-induced ROS activity, the ATP levels were maintained and cell death was prevented. Similar protection could be obtained when astrocytes, prior to addition of IA, were incubated with substances known to activate the nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated endogenous antioxidant system. When IA was washed out, after a relatively moderate ATP depression, massive cell death occurred. This was efficiently prevented by addition of azide or ROS scavengers during the IA treatment or by pre-activation of the Nrf2 system. Our results demonstrate that astrocytes in culture can endure and recover from glycolytic inhibition if the ROS activity remained at a low level and suggest that oxidative stress can be an important component for astrocytic cell death following metabolic stress.

Quantitative imaging of mitochondrial and cytosolic free zinc levels in an in vitro model of ischemia/reperfusion

The role of zinc ion in cytotoxicity following ischemic stroke, prolonged status epilepticus, and traumatic brain injury remains controversial, but likely is the result of mitochondrial dysfunction. We describe an excitation ratiometric fluorescence biosensor based on human carbonic anhydrase II variants expressed in the mitochondrial matrix, permitting free zinc levels to be quantitatively imaged therein. We observed an average mitochondrial matrix free zinc concentration of 0.2 pM in the PC12 rat pheochromacytoma cell culture line. Cytoplasmic and mitochondrial free zinc levels were imaged in a cellular oxygen glucose deprivation (OGD) model of ischemia/reperfusion. We observed a significant increase in mitochondrial zinc 1 h following 3 h OGD, at a time point when cytosolic zinc levels were depressed. Following the increase, mitochondrial zinc levels returned to physiological levels, while cytosolic zinc increased gradually over a 24 h time period in viable cells. The increase in intramitochondrial zinc observed during reoxygenation after OGD may contribute to bioenergetic dysfunction and cell death that occurs with both in vitro and in vivo models of reperfusion.

Activation of protein kinase C delta following cerebral ischemia leads to release of cytochrome C from the mitochondria via bad pathway

BACKGROUND

The release of cytochrome c from the mitochondria following cerebral ischemia is a key event leading to cell death. The goal of the present study was to determine the mechanisms involved in post-ischemic activation of protein kinase c delta (δPKC) that lead to cytochrome c release.

METHODS/FINDINGS

We used a rat model of cardiac arrest as an in vivo model, and an in vitro analog, oxygen glucose deprivation (OGD) in rat hippocampal synaptosomes. Cardiac arrest triggered translocation of δPKC to the mitochondrial fraction at 1 h reperfusion. In synaptosomes, the peptide inhibitor of δPKC blocked OGD-induced translocation to the mitochondria. We tested two potential pathways by which δPKC activation could lead to cytochrome c release: phosphorylation of phospholipid scramblase-3 (PLSCR3) and/or protein phosphatase 2A (PP2A). Cardiac arrest increased levels of phosphorlyated PLSCR3; however, inhibition of δPKC translocation failed to affect the OGD-induced increase in PLSCR3 in synaptosomal mitochondria suggesting the post-ischemic phosphorylation of PLSCR3 is not mediated by δPKC. Inhibition of either δPKC or PP2A decreased cytochrome c release from synaptosomal mitochondria. Cardiac arrest results in the dephosphorylation of Bad and Bax, both downstream targets of PP2A promoting apoptosis. Inhibition of δPKC or PP2A prevented OGD-induced Bad, but not Bax, dephosphorylation. To complement these studies, we used proteomics to identify novel mitochondrial substrates of δPKC.

CONCLUSIONS

We conclude that δPKC initiates cytochrome c release via phosphorylation of PP2A and subsequent dephosphorylation of Bad and identified δPKC, PP2A and additional mitochondrial proteins as potential therapeutic targets for ischemic neuroprotection.

1,3-Dinitrobenzene-induced metabolic impairment through selective inactivation of the pyruvate dehydrogenase complex

Prolonged exposure to the chemical intermediate, 1,3-dinitrobenzene (1,3-DNB), produces neuropathology in the central nervous system of rodents analogous to that observed in various conditions of acute energy deprivation including thiamine deficiency and Leigh's necrotizing encephalopathy. Increased production of reactive intermediates in addition to induction of oxidative stress has been implicated in the neurotoxic mechanism of 1,3-DNB, but a clear metabolic target has not been determined. Here we propose that similar to thiamine deficiency, the effects of 1,3-DNB on metabolic status may be due to inhibition of the thiamine-dependent α-ketoacid dehydrogenase complexes. The effects of 1,3-DNB on astroglial metabolic status and α-ketoacid dehydrogenase activity were evaluated using rat C6 glioma cells. Exposure to 1,3-DNB resulted in altered morphology and biochemical dysfunction consistent with disruption of oxidative energy metabolism. Cotreatment with acetyl-carnitine or acetoacetate attenuated morphological and metabolic effects of 1,3-DNB exposure as well as increased cell viability. 1,3-DNB exposure inhibited pyruvate dehydrogenase complex (PDHc) and the inhibition correlated with the loss of lipoic acid (LA) immunoreactivity, suggesting that modification of LA is a potential mechanism of inhibition. Treatment with antioxidants and thiol-containing compounds failed to protect against loss of LA. Alternatively, inhibition of dihydrolipoamide dehydrogenase, the E3 component of the complex attenuated loss of LA. Collectively, these data suggest that 1,3-DNB impairs oxidative energy metabolism through direct inhibition of the PDHc and that this impairment is due to perturbations in the function of protein-bound LA.

Quo vadis 2010? - carpe diem: challenges and opportunities in pediatric traumatic brain injury

Traumatic brain injury (TBI) in infants and children remains a public health problem of enormous magnitude. It is a complex and heterogeneous condition that presents many diagnostic, therapeutic and prognostic challenges. A number of investigative teams are studying pediatric TBI both in experimental models and in clinical studies at the bedside. This review builds on work presented in a prior supplement to Developmental Neuroscience that was published in 2006, and addresses several active areas of research on this topic, including (1) the application of novel imaging methods, (2) the use of serum and/or CSF biomarkers of injury, (3) advances in neuromonitoring, (4) the development and testing of novel therapies, (5) developments in modeling pediatric TBI, (6) the consideration of a new approach to classification of pediatric TBI, and (7) assessing the potential impact of the development of pediatric and neonatal neurocritical care services on the management and outcome of pediatric TBI.

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.

Effect of short periods of normobaric hyperoxia on local brain tissue oxygenation and cerebrospinal fluid oxidative stress markers in severe traumatic brain injury

Preliminary evidence suggests local brain tissue oxygenation (PbtO(2)) values of <or=15 mm Hg following severe traumatic brain injury (TBI) represent brain tissue hypoxia. Accordingly, many neurotrauma units attempt to maintain PbtO(2) >or=20 mm Hg to avoid hypoxia. This study tested the impact of a short (2 h) trial of normobaric hyperoxia on measures of oxidative stress. We hypothesized this treatment would positively affect cerebral oxygenation but negatively affect the cellular environment via oxidative stress mechanisms. Cerebrospinal fluid (CSF) was serially assessed in 11 adults (9 male, 2 female), aged 26 +/- 1.8 years with severe TBI (Glasgow Coma Scale score, 6 +/- 1.4) before, during, and after a FiO(2) = 1.0 challenge for markers of oxidative stress, including lipid peroxidation (F(2)-isoprostane [ELISA]), protein oxidation (protein sulfhydryl [fluorescence]), and antioxidant defenses (total antioxidant reserve (AOR) [chemiluminescence] and glutathione [fluorescence]). Physiological parameters [PbtO(2), arterial oxygen content (PaO(2)), intracranial pressure (ICP), mean arterial pressure (MAP), and cerebral perfusion pressure (CPP)] were assessed at the same time points. Mean (+/-SD) PbtO(2) and PaO(2) levels significantly changed for each time point. Oxidative stress markers, antioxidant reserve defenses, and ICP, MAP, and CPP did not significantly change for any time period. These preliminary findings suggest that brief periods of normobaric hyperoxia do not produce oxidative stress and/or change antioxidant reserves in CSF. Additional studies are required to examine extended periods of normobaric hyperoxia in a larger sample.

Oxidative stress in cancer associated fibroblasts drives tumor-stroma co-evolution: A new paradigm for understanding tumor metabolism, the field effect and genomic instability in cancer cells

Loss of stromal fibroblast caveolin-1 (Cav-1) is a powerful single independent predictor of poor prognosis in human breast cancer patients, and is associated with early tumor recurrence, lymph node metastasis and tamoxifen-resistance. We developed a novel co-culture system to understand the mechanism(s) by which a loss of stromal fibroblast Cav-1 induces a "lethal tumor micro-environment." Here, we propose a new paradigm to explain the powerful prognostic value of stromal Cav-1. In this model, cancer cells induce oxidative stress in cancer-associated fibroblasts, which then acts as a "metabolic" and "mutagenic" motor to drive tumor-stroma co-evolution, DNA damage and aneuploidy in cancer cells. More specifically, we show that an acute loss of Cav-1 expression leads to mitochondrial dysfunction, oxidative stress and aerobic glycolysis in cancer associated fibroblasts. Also, we propose that defective mitochondria are removed from cancer-associated fibroblasts by autophagy/mitophagy that is induced by oxidative stress. As a consequence, cancer associated fibroblasts provide nutrients (such as lactate) to stimulate mitochondrial biogenesis and oxidative metabolism in adjacent cancer cells (the "Reverse Warburg Effect"). We provide evidence that oxidative stress in cancer-associated fibroblasts is sufficient to induce genomic instability in adjacent cancer cells, via a bystander effect, potentially increasing their aggressive behavior. Finally, we directly demonstrate that nitric oxide (NO) over-production, secondary to Cav-1 loss, is the root cause for mitochondrial dysfunction in cancer associated fibroblasts. In support of this notion, treatment with anti-oxidants (such as N-acetyl-cysteine, metformin and quercetin) or NO inhibitors (L-NAME) was sufficient to reverse many of the cancer-associated fibroblast phenotypes that we describe. Thus, cancer cells use "oxidative stress" in adjacent fibroblasts (i) as an "engine" to fuel their own survival via the stromal production of nutrients and (ii) to drive their own mutagenic evolution towards a more aggressive phenotype, by promoting genomic instability. We also present evidence that the "field effect" in cancer biology could also be related to the stromal production of ROS and NO species. eNOS-expressing fibroblasts have the ability to downregulate Cav-1 and induce mitochondrial dysfunction in adjacent fibroblasts that do not express eNOS. As such, the effects of stromal oxidative stress can be laterally propagated, amplified and are effectively "contagious"--spread from cell-to-cell like a virus--creating an "oncogenic/mutagenic" field promoting widespread DNA damage.

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.

Metabolic control analysis in a cellular model of elevated MAO-B: relevance to Parkinson's disease

We previously demonstrated that spare respiratory capacity of the TCA cycle enzyme alpha-ketoglutarate dehydrogenase (KGDH) was completely abolished upon increasing levels of MAO-B activity in a dopaminergic cell model system (Kumar et al., J Biol Chem 278:46432–46439, 2003). MAO-B mediated increases in H₂O₂ also appeared to result in direct oxidative inhibition of both mitochondrial complex I and aconitase. In order to elucidate the contribution that each of these components exerts over metabolic respiratory control as well as the impact of MAO-B elevation on their spare respiratory capacities, we performed metabolic respiratory control analysis. In addition to KGDH, we assessed the activities and substrate-mediated respiration of complex I, pyruvate dehydrogenase (PDH), succinate dehydrogenase (SDH), and mitochondrial aconitase in the absence and presence of complex-specific inhibitors in specific and mixed substrate conditions in mitochondria from our MAO-B elevated cells versus controls. Data from this study indicates that Complex I and KGDH are the most sensitive to inhibition by MAO-B mediated H₂O₂ generation, and could be instrumental in determining the fate of mitochondrial metabolism in this cellular PD model system.

Postischemic oxidative stress promotes mitochondrial metabolic failure in neurons and astrocytes

Oxidative stress and mitochondrial dysfunction have been closely associated in many subcellular, cellular, animal, and human studies of both acute brain injury and neurodegenerative diseases. Our animal models of brain injury caused by cardiac arrest illustrate this relationship and demonstrate that both oxidative molecular modifications and mitochondrial metabolic impairment are exacerbated by reoxygenation of the brain using 100% ventilatory O(2) compared to lower levels that maintain normoxemia. Numerous molecular mechanisms may be responsible for mitochondrial dysfunction caused by oxidative stress, including oxidation and inactivation of mitochondrial proteins, promotion of the mitochondrial membrane permeability transition, and consumption of metabolic cofactors and intermediates, for example, NAD(H). Moreover, the relative contribution of these mechanisms to cell injury and death is likely different among different types of brain cells, for example, neurons and astrocytes. In order to better understand these oxidative stress mechanisms and their relevance to neurologic disorders, we have undertaken studies with primary cultures of astrocytes and neurons exposed to O(2) and glucose deprivation and reoxygenation and compared the results of these studies to those using a rat model of neonatal asphyxic brain injury. These results support the hypothesis that release and or consumption of mitochondrial NAD(H) is at least partially responsible for respiratory inhibition, particularly in neurons.

Coordinate cis-[Cr(C₂O₄)(pm)(OH₂)₂]⁺ Cation as Molecular Biosensor of Pyruvate's Protective Activity Against Hydrogen Peroxide Mediated Cytotoxity

In this paper instrumental methods of carbon dioxide (CO₂) detection in biological material were compared. Using cis-[Cr(C₂O₄)(pm)(OH₂)₂]⁺ cation as a specific molecular biosensor and the stopped-flow technique the concentrations of CO₂ released from the cell culture medium as one of final products of pyruvate decomposition caused by hydrogen peroxide were determined. To prove the usefulness of our method of CO₂ assessment in the case of biological samples we investigated protective properties of exogenous pyruvate in cultured osteosarcoma 143B cells exposed to 1 mM hydrogen peroxide (H₂O₂) added directly to culture medium. Pyruvic acid is well known scavenger of H₂O₂ and, moreover, a molecule which is recognized as one of the major mediator of oxidative stress detected in many diseases and pathological situations like ischemia-reperfusion states. The pyruvate's antioxidant activity is described as its rapid reaction with H₂O₂, which causes nonenzymatic decarboxylation of pyruvate and releases of CO₂, water and acetate as final products. In this work for the first time we have correlated the concentration of CO₂ dissolved in culture medium with pyruvate's oxidant-scavenging abilities. Moreover, the kinetics of the reaction between aqueous solution of CO₂ and coordinate ion, cis-[Cr(C₂O₄)(pm)(OH₂)₂]⁺ was analysed. The results obtained enabled determination of the number of steps of the reaction studied. Based on the kinetic equations, rate constants were determined for each step.