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Query: UMLS:C0038454 (stroke)
 147,016 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fetal cortex from 16- and 17-day-old embryonic rats was transplanted into the parietal cortex of 12 adult rats rendered ischemic by temporary intraluminal occlusion of the middle cerebral artery. Ischemic injury in the host cortex adjacent to all nine surviving transplants was demonstrated with hematoxylin and eosin and cresyl violet strains. Nicotidamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemical studies revealed a normal number of NADPH-d-positive neurons, whereas acetylcholinesterase (AChE) staining revealed many more AChE-positive neurons in the transplants compared to the host parietal cortex. This could be due to: 1) selective survival of AChE neurons in the transplants compared to the host cortex; 2) increased expression of AChE in transplanted neurons; 3) induction of AChE in normally AChE-negative neurons; or 4) decreased transport of the AChE enzyme from the perikarya to fibers in surviving transplanted neurons. Many fibers positive for AChE and NADPH-d crossed between the host and transplant, although fiber density in the transplants was less than in normal host cortex. These results should encourage future investigation of whether similar transplants improve neurological function following experimental stroke.
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PMID:Neuronal changes in fetal cortex transplanted to ischemic adult rat cortex. 319 96

Yeast NADPH-sulfite reductase (hydrogen sulfide:NADP+ oxidoreductase, EC 1.8.1.2) is a complex hemoflavoprotein. The Strokes radius was determined to be 80 A by gel filtration and the molecular weight was estimated to be 604,000. The minimal molecular weight calculated from flavin and heme content was 306,000, indicating that this enzyme contains two FAD, two FMN and two hemes per molecule. The enzyme consists of two types of subunit, alpha and beta, having molecular weights of 116,000 and 167,000, respectively. The subunit structure is suggested to be alpha 2 beta 2. The secondary structure, the amino acid composition and the isoelectric point were also investigated. The Km values for sulfite and NADPH were 17 microM and 10 microM, respectively. Sulfite and NADPH affected the reaction velocity to give parallel Lineweaver-Burk plots, indicating the involvement of the 'ping-pong' mechanism in the overall reaction. NADP+ inhibited the reaction competitively with NADPH and noncompetitively with sulfite. Inhibition by sulfide was partially noncompetitive with both substrates but very weak. These results are discussed and compared with sulfite reductase from Escherichia coli.
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PMID:Studies on yeast sulfite reductase. IV. Structure and steady-state kinetics. 675

Three isozymes of nitric oxide (NO) synthase (EC 1.14.13.39) have been identified and the cDNAs for these enzymes isolated. In humans, isozymes I (in neuronal and epithelial cells), II (in cytokine-induced cells), and III (in endothelial cells) are encoded for by three different genes located on chromosomes 12, 17, and 7, respectively. The deduced amino acid sequences of the human isozymes show less than 59% identity. Across species, amino acid sequences for each isoform are well conserved (> 90% for isoforms I and III, > 80% for isoform II). All isoforms use L-arginine and molecular oxygen as substrates and require the cofactors NADPH, 6(R)-5,6,7,8-tetrahydrobiopterin, flavin adenine dinucleotide, and flavin mononucleotide. They all bind calmodulin and contain heme. Isoform I is constitutively present in central and peripheral neuronal cells and certain epithelial cells. Its activity is regulated by Ca2+ and calmodulin. Its functions include long-term regulation of synaptic transmission in the central nervous system, central regulation of blood pressure, smooth muscle relaxation, and vasodilation via peripheral nitrergic nerves. It has also been implicated in neuronal death in cerebrovascular stroke. Expression of isoform II of NO synthase can be induced with lipopolysaccharide and cytokines in a multitude of different cells. Based on sequencing data there is no evidence for more than one inducible isozyme at this time. NO synthase II is not regulated by Ca2+; it produces large amounts of NO that has cytostatic effects on parasitic target cells by inhibiting iron-containing enzymes and causing DNA fragmentation. Induced NO synthase II is involved in the pathophysiology of autoimmune diseases and septic shock. Isoform III of NO synthase has been found mostly in endothelial cells. It is constitutively expressed, but expression can be enhanced, eg, by shear stress. Its activity is regulated by Ca2+ and calmodulin. NO from endothelial cells keeps blood vessels dilated, prevents the adhesion of platelets and white cells, and probably inhibits vascular smooth muscle proliferation.
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PMID:Nitric oxide synthase isozymes. Characterization, purification, molecular cloning, and functions. 751 53

Potent and selective inhibition of neuronal nitric oxide synthase (nNOS) compared to endothelial NOS (eNOS) and inducible NOS (iNOS) may be useful to treat cerebral ischemia (stroke) and other neurodegenerative diseases. S-Methyl-L-thiocitrulline (Me-TC) and S-ethyl-L-thiocitrulline (Et-TC) inhibited the oxidation of L-arginine and the L-arginine-independent oxidation of NADPH by nNOS from human brain. Me-TC and Et-TC were slow, tight binding inhibitors of nNOS with second-order association rate constants (kon) of 2.6 x 10(5) M-1 s-1 and 1.3 x 10(5) M-1 s-1, respectively. The respective dissociation rate constants (koff) were 3 x 10(-4) s-1 and 0.7 x 10(-4) s-1. Thus, the Kd values calculated from koff/kon were 1.2 and 0.5 nM, respectively. L-Arginine was a competitive inhibitor of Me-TC and Et-TC binding with competition constant (Ks) values of 2.2 and 2.7 microM, respectively. The Km of nNOS for L-arginine was 1.6 microM. The active site concentration of nNOS was estimated by titration with Et-TC. Based on this active site concentration, a kcat of 0.4 s-1 for the oxidation of L-arginine, was calculated. Me-TC and Et-TC were less potent inhibitors of human iNOS (Ki values of 34 and 17 nM, respectively) and human eNOS (Ki values of 11 and 24 nM). Thus, Me-TC and Et-TC were 10- and 50-fold, respectively, more potent inhibitors of nNOS than eNOS. Furthermore, Me-TC was also 17-fold selective for rat nNOS in neuronal tissue compared to rat eNOS in vascular endothelium, suggesting that Me-TC may be selective for nNOS in vivo and therefore, may be therapeutically useful to treat neurodegenerative diseases.
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PMID:Potent and selective inhibition of human nitric oxide synthases. Selective inhibition of neuronal nitric oxide synthase by S-methyl-L-thiocitrulline and S-ethyl-L-thiocitrulline. 752 10

Oxidized irwN has been proposed as a mediator of the free radical-induced damage that occurs during cerebral ischemia. Dihydroriboflavin, a compound produced from riboflavin (B2) by NADPH-dependent flavin reductase, rapidly reduces oxidized iron. Since treatment with riboflavin offers protection from ischemic injury in other tissues, we tested the effect of pretreatment with B2 on brain edema formation during focal ischemia. Two different models of middle cerebral artery occlusion (MCAO) in rats were tested: transcranial electrocautery and intracarotid occlusion with a nylon thread. Groups of 6-8 animals were treated with 7.5 mg of B2/kg or saline vehicle 1 h before MCAO and brain water content was determined after 4 h of ischemia. Pretreatment with B2 reduced total hemisphere edema formation from 0.37 +/- 0.05 to 0.19 +/- 0.05 mg/g dry wt. (48% protection, p < 0.01) following transcranial MCAO. Edema was greater following MCAO with the intra-carotid thread (0.54 +/- 0.05 ml/g) but protection by B2 was less (21%). We conclude that pretreatment with B2 reduces ischemic brain injury, perhaps by reacting with oxidized iron. However, the larger stroke produced by the thread MCAO method makes it more difficult to observe protection following brief ischemia in this model.
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PMID:Riboflavin reduces edema in focal cerebral ischemia. 797 77

NADPH-dependent methemoglobin reductase, first detected in erythrocytes sixty years ago, has subsequently been purified and characterized as a methylene blue reductase and a flavin reductase. The reductase plays no role in methemoglobin reduction under normal conditions, but its activity serves as the basis for the treatment of methemoglobinemia with methylene blue or flavin. On-going studies demonstrate that this cytosolic protein is also present in liver and that its primary structure distinguishes it from other known proteins. The bovine erythrocyte reductase tightly binds hemes, porphyrins, and fatty acids with resulting loss of activity. Pyrroloquinoline quinone serves as a high-affinity substrate of the reductase, suggesting that this naturally-occurring compound may be a physiological substrate. The ability of the reductase to catalyze the intracellular reduction of administered riboflavin to dihydroriboflavin suggested that this system might be exploited to protect tissues from oxidative damage. This hypothesis was supported by our finding that dihydroriboflavin reacts rapidly with Fe(IV)O and Fe(V)O oxidation states of hemeproteins, states that have been implicated in tissue damage associated with ischemia and reperfusion. Preliminary studies demonstrate that, as predicted, administration of low concentrations of riboflavin protects isolated rabbit heart from reoxygenation injury, rat lung from injury resulting from systemic activation of complement, and rat brain from damage caused by four hours of ischemia. Data from these animal studies suggest that flavin therapy holds promise in protecting tissue from the oxidative injuries of myocardial infarction, acute lung injury, stroke, and a number of other clinical conditions.
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PMID:Evidence that NADPH-dependent methemoglobin reductase and administered riboflavin protect tissues from oxidative injury. 841 88

The gaseous signal molecule, nitric oxide (NO*), is generated enzymatically by NO synthase (NOS) from L-arginine. Overproduction of NO contributes to cell and tissue damage as sequelae of infection and stroke. Strategies to suppress NO synthesis rely heavily on guanidino-substituted L-arginine analogs (L-NAME, L-NA, L-NMMA, L-NIO) as competitive inhibitors of NOS, which are often used in high doses to compete with millimolar concentrations of intracellular arginine. We show that these analogs are also a source for non-enzymatically produced NO. Enzyme-independent NO release occurs in the presence of NADPH, glutathione, L-cysteine, dithiothreitol and ascorbate. This non-enzymatic synthesis of NO can produce potentially toxic, micromolar concentrations of NO and can oppose the effects of NOS inhibition. NO production driven by NOS inhibitors was demonstrated ex vivo in the central nervous and peripheral tissues of gastropod molluscs Aplysia and Pleurobranchaea using electron paramagnetic resonance and spin-trapping techniques. These results have important implications for therapeutic regulation of NO homeostasis.
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PMID:Non-enzymatic production of nitric oxide (NO) from NO synthase inhibitors. 991 69

Modern molecular biology has revealed vast numbers of large and complex proteins and genes that regulate body function. By contrast, discoveries over the past ten years indicate that crucial features of neuronal communication, blood vessel modulation and immune response are mediated by a remarkably simple chemical, nitric oxide (NO). Endogenous NO is generated from arginine by a family of three distinct calmodulin- dependent NO synthase (NOS) enzymes. NOS from endothelial cells (eNOS) and neurons (nNOS) are both constitutively expressed enzymes, whose activities are stimulated by increases in intracellular calcium. Immune functions for NO are mediated by a calcium-independent inducible NOS (iNOS). Expression of iNOS protein requires transcriptional activation, which is mediated by specific combinations of cytokines. All three NOS use NADPH as an electron donor and employ five enzyme cofactors to catalyze a five-electron oxidation of arginine to NO with stoichiometric formation of citrulline. The highest levels of NO throughout the body are found in neurons, where NO functions as a unique messenger molecule. In the autonomic nervous system NO functions NO functions as a major non-adrenergic non-cholinergic (NANC) neurotransmitter. This NANC pathway plays a particularly important role in producing relaxation of smooth muscle in the cerebral circulation and the gastrointestinal, urogenital and respiratory tracts. Dysregulation of NOS activity in autonomic nerves plays a major role in diverse pathophysiological conditions including migraine headache, hypertrophic pyloric stenosis and male impotence. In the brain, NO functions as a neuromodulator and appears to mediate aspects of learning and memory. Although endogenous NO was originally appreciated as a mediator of smooth muscle relaxation, NO also plays a major role in skeletal muscle. Physiologically muscle-derived NO regulates skeletal muscle contractility and exercise-induced glucose uptake. nNOS occurs at the plasma membrane of skeletal muscle which facilitates diffusion of NO to the vasculature to regulate muscle perfusion. nNOS protein occurs in the dystrophin complex in skeletal muscle and NO may therefore participate in the pathophysiology of muscular dystrophy. NO signalling in excitable tissues requires rapid and controlled delivery of NO to specific cellular targets. This tight control of NO signalling is largely regulated at the level of NO biosynthesis. Acute control of nNOS activity is mediated by allosteric enzyme regulation, by posttranslational modification and by subcellular targeting of the enzyme. nNOS protein levels are also dynamically regulated by changes in gene transcription, and this affords long-lasting changes in tissue NO levels. While NO normally functions as a physiological neuronal mediator, excess production of NO mediates brain injury. Overactivation of glutamate receptors associated with cerebral ischemia and other excitotoxic processes results in massive release of NO. As a free radical, NO is inherently reactive and mediates cellular toxicity by damaging critical metabolic enzymes and by reacting with superoxide to form an even more potent oxidant, peroxynitrite. Through these mechanisms, NO appears to play a major role in the pathophysiology of stroke, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis.
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PMID:Endogenous nitric oxide synthesis: biological functions and pathophysiology. 1063 Jun 82

The heme oxygenase (HO) and nitric oxide (NO) synthase (NOS) systems display notable similarities as well as differences. HO and NOS are both oxidative enzymes using NADPH as an electron donor. The constitutive forms of the enzyme are differentially activated, with calcium entry stimulating NOS by binding to calmodulin, whereas calcium entry activates protein kinase C to phosphorylate and activate HO2. Although both NO and carbon monoxide (CO) stimulate soluble guanylyl cyclase to form cGMP, NO also S-nitrosylates selected protein targets. Both involve constitutive and inducible biosynthetic enzymes. However, functions of the inducible forms are virtual opposites. Macrophage-inducible NOS generates NO to kill other cells, whereas HO1 generates bilirubin to exert antioxidant cytoprotective effects and also provides cytoprotection by facilitating iron extrusion from cells. The neuronal form of HO, HO2, is also cytoprotective. Normally, neural NO in the brain seems to exert some sort of behavioral inhibition. However, excess release of NO in response to glutamate's N-methyl-d-aspartate receptor activation leads to stroke damage. On the other hand, massive neuronal firing during a stroke presumably activates HO2, leading to neuroprotective actions of bilirubin. Loss of this neuroprotection after HO inhibition by mutant forms of amyloid precursor protein may mediate neurotoxicity in Familial Alzheimer's Disease. NO and CO both appear to be neurotransmitters in the brain and peripheral autonomic nervous system. They also are physiologic endothelial-derived relaxing factors for blood vessels. In the gastrointestinal pathway, NO and CO appear to function as coneurotransmitters, both stimulating soluble guanylyl cyclase to cause smooth muscle relaxation.
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PMID:Neural roles for heme oxygenase: contrasts to nitric oxide synthase. 1157 59

Oxidative stress occurs in the brain due to stroke, Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, trauma, aging and other conditions. Analysis of the effects of oxidative stress can involve quantitation of brain GSH, GSSG, NADPH and NADP. Reliable and rapid assays have been developed for these compounds and will be presented in detail. The assays have been used to analyze the effects of brain oxidative stress. Thermodynamic calculations can be performed to find the observed electrochemical potentials of the GSSG/GSH and the NADP/NADPH couples during oxidative stress. The biochemical consequences of these thermodynamic changes in the cell will be discussed as well as the defense mechanisms available to the cell to recover from oxidative stress.
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PMID:Brain oxidative stress--analytical chemistry and thermodynamics of glutathione and NADPH. 1189 24


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