[Show abstract][Hide abstract] ABSTRACT: This study demonstrates that in mice subjected to hypoxia-ischemia (HI) brain injury isoflurane anesthesia initiated upon reperfusion limits a release of mitochondrial oxidative radicals by inhibiting a recovery of complex-I dependent mitochondrial respiration. This significantly attenuates an oxidative stress and reduces the extent of HI brain injury. Neonatal mice were subjected to HI, and at the initiation of reperfusion were exposed to isoflurane with or without mechanical ventilation. At the end of HI and isoflurane exposure cerebral mitochondrial respiration, H2O2 emission rates were measured followed by an assessment of cerebral oxidative damage and infarct volumes. At 8 weeks after HI navigational memory and brain atrophy were assessed. In vitro, direct effect of isoflurane on mitochondrial H2O2 emission was compared to that of complex-I inhibitor, rotenone. Compared to controls, 15 minutes of isoflurane anesthesia inhibited recovery of the compex I-dependent mitochondrial respiration and decreased H2O2 production in mitochondria supported with succinate. This was associated with reduced oxidative brain injury, superior navigational memory and decreased cerebral atrophy compared to the vehicle-treated HI-mice. Extended isoflurane anesthesia was associated with sluggish recovery of cerebral blood flow (CBF) and the neuroprotection was lost. However, when isoflurane anesthesia was supported with mechanical ventilation the CBF recovery improved, the event associated with further reduction of infarct volume compared to HI-mice exposed to isoflurane without respiratory support. Thus, in neonatal mice brief isoflurane anesthesia initiated at the onset of reperfusion limits mitochondrial release of oxidative radicals and attenuates an oxidative stress. This novel mechanism contributes to neuroprotective action of isoflurane. The use of mechanical ventilation during isoflurane anesthesia counterbalances negative effect of isoflurane anesthesia on recovery of cerebral circulation which potentiates protection against reperfusion injury.
[Show abstract][Hide abstract] ABSTRACT: Hyperoxia inhibits pulmonary bioenergetics, causing delayed alveolarization in mice. We hypothesized that, mechanical ventilation (MV) also causes bioenergetics failure to support alveolarization. To test this hypothesis, neonatal mice were ventilated with room air for eight hours (prolonged) or for two hours (brief) with 15μL/g (aggressive) tidal volume (Tv), or for eight hours with 8μL/g (gentle) Tv. At 24 hours or 10 days of recovery lung mitochondria were examined for: ADP-phosphorylating respiration using complex-I (C-I), complex-II (C-II), or cytochrome c oxidase (C-IV) dependent substrates, ATP production rate and activity of C-I and C-II. A separate cohort of mice was exposed to 2,4-dinitrophenol (DNP), known uncoupler of oxidative phosphorylation. At 10 days of recovery pulmonary alveolarization and VEGF expression was assessed. Sham-operated littermates were used as a control. At 24 hours following aggressive MV mitochondrial ATP production rates and activity of C-I and C-II were significantly decreased compared to controls. However, at 10 days of recovery only mice exposed to prolonged-aggressive MV continued to have significantly depressed mitochondrial respiration. This was associated with significantly poorer alveolarization and VEGF expression. In contrast, mice exposed to brief-aggressive or prolonged-gentle exhibited restored mitochondrial ADP-phosphorylation and normal alveolarization and pulmonary VEGF content. Exposure to DNP fully replicated the phenotype consistent with alveolar developmental arrest. Our data suggest that in the immature lungs bioenergetics failure to support normal development is caused by aggressive and prolonged ventilation and should be considered as a fundamental mechanism for development of bronchopulmonary dysplasia in premature neonates.
No preview · Article · Aug 2013 · American Journal of Respiratory Cell and Molecular Biology
[Show abstract][Hide abstract] ABSTRACT: Nelfinavir (NLF), an antiretroviral agent, preserves mitochondrial membranes integrity and protects mature brain against ischemic injury in rodents. Our study demonstrates that in neonatal mice NLF significantly limits mitochondrial calcium influx, the event associated with protection of the brain against hypoxic-ischemic insult (HI). Compared to the vehicle-treated mice, cerebral mitochondria from NLF-treated mice exhibited a significantly greater tolerance to the Ca(2+)-induced membrane permeabilization, greater ADP-phosphorylating activity and reduced cytochrome C release during reperfusion. Pre-treatment with NLF or Ruthenium red (RuR) significantly improved viability of murine hippocampal HT-22 cells, reduced Ca(2+) content and preserved membrane potential (Ψm) in mitochondria following oxygen-glucose deprivation (OGD). Following histamine-stimulated Ca(2+) release from endoplasmic reticulum, in contrast to the vehicle-treated cells, the cells treated with NLF or RuR also demonstrated reduced Ca(2+) content in their mitochondria, the event associated with preserved Ψm. Because RuR inhibits mitochondrial Ca(2+) uniporter, we tested whether the NLF acts via the mechanism similar to the RuR. However, in contrast to the RuR, in the experiment with direct interaction of these agents with mitochondria isolated from naïve mice, the NLF did not alter mitochondrial Ca(2+) influx, and did not prevent Ca(2+) induced collapse of the Ψm. These data strongly argues against interaction of NLF and mitochondrial Ca(2+) uniporter. Although the exact mechanism remains unclear, our study is the first to show that NLF inhibits intramitochondrial Ca(2+) flux and protects developing brain against HI-reperfusion injury. This novel action of NLF has important clinical implication, because it targets a fundamental mechanism of post-ischemic cell death: intramitochondrial Ca(2+) overload → mitochondrial membrane permeabilization → secondary energy failure.
[Show abstract][Hide abstract] ABSTRACT: Oxidative stress and Ca(2+) toxicity are mechanisms of hypoxic-ischemic (HI) brain injury. This work investigates if partial inhibition of mitochondrial respiratory chain protects HI brain by limiting a generation of oxidative radicals during reperfusion. HI insult was produced in p10 mice treated with complex I (C-I) inhibitor, pyridaben, or vehicle. Administration of P significantly decreased the extent of HI injury. Mitochondria isolated from the ischemic hemisphere in pyridaben-treated animals showed reduced H(2)O(2) emission, less oxidative damage to the mitochondrial matrix, and increased tolerance to the Ca(2+)-triggered opening of the permeability transition pore. A protective effect of pyridaben administration was also observed when the reperfusion-driven oxidative stress was augmented by the exposure to 100% O(2) which exacerbated brain injury only in vehicle-treated mice. In vitro, intact brain mitochondria dramatically increased H(2)O(2) emission in response to hyperoxia, resulting in substantial loss of Ca(2+) buffering capacity. However, in the presence of the C-I inhibitor, rotenone, or the antioxidant, catalase, these effects of hyperoxia were abolished. Our data suggest that the reperfusion-driven recovery of C-I-dependent mitochondrial respiration contributes not only to the cellular survival, but also causes oxidative damage to the mitochondria, potentiating a loss of Ca(2+) buffering capacity. This highlights a novel neuroprotective strategy against HI brain injury where the major therapeutic principle is a pharmacological attenuation, rather than an enhancement of mitochondrial oxidative metabolism during early reperfusion.
Full-text · Article · Feb 2012 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
[Show abstract][Hide abstract] ABSTRACT: Reperfusion triggers an oxidative stress. We hypothesized that mild hypoxemia in reperfusion attenuates oxidative brain injury following hypoxia-ischemia (HI). In neonatal HI-mice, the reperfusion was initiated by reoxygenation with room air (RA) followed by the exposure to 100%, 21%, 18%, 15% oxygen for 60 minutes. Systemic oxygen saturation (SaO(2)), cerebral blood flow (CBF), brain mitochondrial respiration and permeability transition pore (mPTP) opening, markers of oxidative injury, and cerebral infarcts were assessed. Compared with RA-littermates, HI-mice exposed to 18% oxygen exhibited significantly decreased infarct volume, oxidative injury in the brain mitochondria and tissue. This was coupled with improved mitochondrial tolerance to mPTP opening. Oxygen saturation maintained during reperfusion at 85% to 95% was associated (r=0.57) with the best neurologic outcome. Exposure to 100% or 15% oxygen significantly exacerbated brain injury and oxidative stress. Compared with RA-mice, hyperoxia dramatically increased reperfusion CBF, but exposure to 15% oxygen significantly reduced CBF to values observed during the HI-insult. Mild hypoxemia during initial reperfusion alleviates the severity of HI-brain injury by limiting the reperfusion-driven oxidative stress to the mitochondria and mPTP opening. This suggests that at the initial stage of reperfusion, a slightly decreased systemic oxygenation (SaO(2) 85% to 95%) may be beneficial for infants with birth asphyxia.
Full-text · Article · Nov 2011 · Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism
[Show abstract][Hide abstract] ABSTRACT: Caused by a polyglutamine expansion in the huntingtin protein, Huntington's disease leads to striatal degeneration via the transcriptional dysregulation of a number of genes, including those involved in mitochondrial biogenesis. Here we show that transglutaminase 2, which is upregulated in HD, exacerbates transcriptional dysregulation by acting as a selective corepressor of nuclear genes; transglutaminase 2 interacts directly with histone H3 in the nucleus. In a cellular model of HD, transglutaminase inhibition de-repressed two established regulators of mitochondrial function, PGC-1alpha and cytochrome c and reversed susceptibility of human HD cells to the mitochondrial toxin, 3-nitroproprionic acid; however, protection mediated by transglutaminase inhibition was not associated with improved mitochondrial bioenergetics. A gene microarray analysis indicated that transglutaminase inhibition normalized expression of not only mitochondrial genes but also 40% of genes that are dysregulated in HD striatal neurons, including chaperone and histone genes. Moreover, transglutaminase inhibition attenuated degeneration in a Drosophila model of HD and protected mouse HD striatal neurons from excitotoxicity. Altogether these findings demonstrate that selective TG inhibition broadly corrects transcriptional dysregulation in HD and defines a novel HDAC-independent epigenetic strategy for treating neurodegeneration.
Full-text · Article · Sep 2010 · EMBO Molecular Medicine
[Show abstract][Hide abstract] ABSTRACT: Cysteine S-conjugate β-lyases are pyridoxal 5′-phosphate-containing enzymes that catalyze β-elimination reactions with cysteine S-conjugates that possess a good leaving group in the β-position. The end products are aminoacrylate and a sulfur-containing fragment. The aminoacrylate tautomerizes and hydrolyzes to pyruvate and ammonia. The mammalian cysteine S-conjugate β-lyases thus far identified are enzymes involved in amino acid metabolism that catalyze β-lyase reactions as non-physiological side reactions. Most are aminotransferases. In some cases the lyase is inactivated by reaction products. The cysteine S-conjugate β-lyases are of much interest to toxicologists because they play an important key role in the bioactivation (toxication) of halogenated alkenes, some of which are produced on an industrial scale and are environmental contaminants. The cysteine S-conjugate β-lyases have been reviewed in this journal previously (Cooper and Pinto in Amino Acids 30:1–15, 2006). Here, we focus on more recent findings regarding: (1) the identification of enzymes associated with high-M
r cysteine S-conjugate β-lyases in the cytosolic and mitochondrial fractions of rat liver and kidney; (2) the mechanism of syncatalytic inactivation of rat liver mitochondrial aspartate aminotransferase by the nephrotoxic β-lyase substrate S-(1,1,2,2-tetrafluoroethyl)-l-cysteine (the cysteine S-conjugate of tetrafluoroethylene); (3) toxicant channeling of reactive fragments from the active site of mitochondrial aspartate aminotransferase to susceptible proteins in the mitochondria; (4) the involvement of cysteine S-conjugate β-lyases in the metabolism/bioactivation of drugs and natural products; and (5) the role of cysteine S-conjugate β-lyases in the metabolism of selenocysteine Se-conjugates. This review emphasizes the fact that the cysteine S-conjugate β-lyases are biologically more important than hitherto appreciated.
[Show abstract][Hide abstract] ABSTRACT: Mitochondrial dysfunction is a central feature of a number of acute and chronic neurodegenerative conditions, but clinically approved therapeutic interventions are only just emerging. Here we demonstrate the potential clinical utility of low molecular weight inhibitors of the hypoxia inducible factor prolyl-4-hydroxylases (HIF PHDs) in preventing mitochondrial toxin-induced cell death in mouse striatal neurons that express a "knock-in" mutant Huntingtin allele. Protection from 3-nitropropionic acid (3-NP, a complex II inhibitor)-induced toxicity by HIF PHD inhibition occurs without rescue of succinate dehydrogenase activity. Although HIF-1alpha mRNA is dramatically induced by mutant huntingtin, HIF-1alpha depletion by short interfering RNAs (siRNA) does not affect steady-state viability or protection from 3-NP-induced death by HIF PHD inhibitors in these cells. Moreover, 3-NP-induced complex II inhibition in control or mutant striatal neurons does not lead to activation of HIF-dependent transcription. HIF PHD inhibition also protects cortical neurons from 3-NP-induced cytotoxicity. Protection of cortical neurons by HIF PHD inhibition correlates with enhanced VEGF but not PGC-1alpha gene expression. Together, these findings suggest that HIF PHD inhibitors are promising candidates for preventing cell death in conditions such as Huntington's disease and Alzheimer's disease that are associated with metabolic stress in the central nervous system.
[Show abstract][Hide abstract] ABSTRACT: Aberrant transglutaminase (TG) activity has been implicated in the pathology of numerous diseases, including Huntington's disease and Alzheimer's disease. To fully characterize the role of TGs in these disorders, it is important that simple quantifiable assays be made available. The most commonly used assay currently employed requires significant time and a radioactive substrate. The assay described here uses a biotinylated substrate in conjunction with a dot blot apparatus to eliminate the use of radioactive substrates and allows relative transglutaminase activity to be measured simultaneously with minimal sample preparation in a large number of samples containing purified enzyme, cell extracts, or tissue homogenates.
[Show abstract][Hide abstract] ABSTRACT: The present work documents the first example of an enzyme-catalyzed beta-elimination of a thioether from a sulfonium cysteine S-conjugate. beta-(S-Tetrahydrothiophenium)-L-alanine (THT-A) is the cysteine S-conjugate of busulfan. THT-A slowly undergoes a nonenzymatic beta-elimination reaction at pH 7.4 and 37 degrees C to yield tetrahydrothiophene, pyruvate, and ammonia. This reaction is accelerated by 1) rat liver, kidney, and brain homogenates, 2) isolated rat liver mitochondria, and 3) pyridoxal 5'-phosphate (PLP). A PLP-dependent enzyme in rat liver cytosol that catalyzes a beta-lyase reaction with THT-A was identified as cystathionine gamma-lyase. This unusual drug metabolism pathway represents an alternate route for intermediates in the mercapturate pathway.
Full-text · Article · Sep 2008 · Drug metabolism and disposition: the biological fate of chemicals
[Show abstract][Hide abstract] ABSTRACT: Rat kidney glutamine transaminase K (GTK) exhibits broad specificity both as an aminotransferase and as a cysteine S-conjugate beta-lyase. The beta-lyase reaction products are pyruvate, ammonium and a sulfhydryl-containing fragment. We show here that recombinant human GTK (rhGTK) also exhibits broad specificity both as an aminotransferase and as a cysteine S-conjugate beta-lyase. S-(1,1,2,2-Tetrafluoroethyl)-l-cysteine is an excellent aminotransferase and beta-lyase substrate of rhGTK. Moderate aminotransferase and beta-lyase activities occur with the chemopreventive agent Se-methyl-l-selenocysteine. l-3-(2-Naphthyl)alanine, l-3-(1-naphthyl)alanine, 5-S-l-cysteinyldopamine and 5-S-l-cysteinyl-l-DOPA are measurable aminotransferase substrates, indicating that the active site can accommodate large aromatic amino acids. The alpha-keto acids generated by transamination/l-amino acid oxidase activity of the two catechol cysteine S-conjugates are unstable. A slow rhGTK-catalyzed beta-elimination reaction, as measured by pyruvate formation, was demonstrated with 5-S-l-cysteinyldopamine, but not with 5-S-l-cysteinyl-l-DOPA. The importance of transamination, oxidation and beta-elimination reactions involving 5-S-l-cysteinyldopamine, 5-S-l-cysteinyl-l-DOPA and Se-methyl-l-selenocysteine in human tissues and their biological relevance are discussed.
Full-text · Article · Jul 2008 · Archives of Biochemistry and Biophysics