SEARCH · PubMed Health

Results for “hyperammonemia”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,009 records · Page 56Linked to original sources

PubMed1997

Role of the mitochondrial permeability transition in salicylate toxicity to cultured rat hepatocytes: implications for the pathogenesis of Reye's syndrome.

Aspirin is strongly implicated in the pathogenesis of Reye's syndrome, a childhood disorder characterized by hyperammonemia, microvesicular steatosis, and encephalopathy. Previously, we showed that salicylate, the active metabolite of aspirin, induces the mitochondrial permeability transition (MPT) in isolated mitochondria, as do several other chemicals implicated in Reye's-related disorders. Opening of a high conductance, cyclosporin A-sensitive pore in the mitochondrial inner membrane causes the MPT, leading to swelling, depolarization, and uncoupling of oxidative phosphorylation. The goal of this study was to characterize the role of the MPT in salicylate toxicity to cultured rat hepatocytes. Salicylate (0.3-5 mM) caused concentration-dependent cell killing. In Krebs-Ringer buffer, half-maximal cell killing occurred 150 min after 3 mM salicylate. Increasing Ca2+ enhanced salicylate lethality. Salicylate-dependent cell killing was blocked by 0.5-5 microM cyclosporin A and its nonimmunosuppresive analog, 4-methylvaline cyclosporin, implicating the MPT in the pathogenesis of cell killing. The contribution of the MPT to lethal cell injury was confirmed by laser scanning confocal microscopy, which demonstrated the redistribution of the fluorophore calcein from the cytosol into mitochondria prior to cell killing, an event blocked by cyclosporin A. Salicylate toxicity was enhanced at high extracellular Ca2+. In the range of 10-100 microM, several chemically diverse calcium antagonists blocked or reduced salicylate toxicity including verapamil, diltiazem, chlorpromazine, nifedipine, and nisoldipine. Calcium antagonists also blocked the increase of mitochondrial free Ca2+ in high Ca2+ buffer, as determined by confocal imaging of the fluorophore Rhod-2. These data with salicylate suggest that onset of the MPT may be the common pathophysiologic mechanism causing mitochondrial injury in Reye's syndrome and Reye's-related drug toxicities. Further, elevated intramitochondrial Ca2+ may be a predisposing condition promoting onset of the MPT by Reye's-related chemicals.

Animals↗

PubMed1993

Two different families of NMDA receptors in mammalian brain: physiological function and role in neuronal development and degeneration.

The data from purification, ligand binding, reconstitution and immunochemical studies indicate that there is a group of small molecular size proteins (30 to 70 kDa) that form what appear to be NMDA receptor complexes. Based on cell biological studies of the expression and localization of one of the subunits of this complex, the glutamate-binding subunit, it appears that this putative NMDA receptor plays a key role in neuronal sensitivity to NMDA and in neuronal survival in early development. However, brain neurons quite clearly express another family of proteins which have all functional characteristics of an NMDA receptor plus a great degree of variability that can account for the varieties of NMDA receptors found in brain. This family of NMDA receptors, the NMDAR1 and NMDAR2, are not homologous to the small molecular size proteins of the previously described receptor complex that was isolated from synaptic membranes. If brain neurons are indeed expressing two very diverse families of proteins that function as glutamate/NMDA receptors, this must be an indication that either there is a very selective expression of one of these forms in specific neurons or neuronal compartments, or that one of these forms of the receptor plays an important role in unique functions of the cell, such as synaptic plasticity or neurodegeneration. As more information is gathered about the structure and function of these receptors, a better understanding of the expression and role of these families of receptor proteins in normal neuronal excitability will be achieved. This enhanced level of understanding about the function and activity of these receptors will be needed in order to identify more precisely the NMDA receptors most affected in pathological conditions such as hyperammonemia.

Alternative Splicing↗

PubMed1999

Brain tryptophan/serotonin perturbations in metabolic encephalopathy and the hazards involved in the use of psychoactive drugs.

Several combined pathogenetic factors such as hyperammonemia, different brain tryptophan metabolic disturbances and serotonin physiological/pharmacological alterations not yet defined in all details, will often give rise to the clinical neuropsychiatric condition known as hepatic encephalopathy (HE). Indeed, to this the probable exposure to novel potent CNS-monoamine acting drugs today may put such patients at certain risk for other pharmacodynamic (PD) responses than usually are expected from these "safe" drugs. Moreover, with a compromised liver function in HE, also pharmacokinetic (PK) features for the drugs are likely changed in these patients. Thus, the ultimate clinical outcome by this probable but unknown PD/PK-deviation for such psychoactive drugs when given to HE-patients needs further clarification. Accordingly, delineation of both PD- and PK-effects in experimental HE should shed light on this issue of relevance for monoamine-active drug safety as well as on some further details in the complex tryptophan/monoamine-related pathophysiology that comes into play in HE.

Animals↗

PubMed1990

New roles of carnitine metabolism in ammonia cytotoxicity.

High levels of ammonia in blood and brain due to metabolic disorders are associated with neurological abnormalities. Although the mechanism of ammonia toxicity at the CNS level is still unknown, alterations in brain energy metabolism, in neurotransmitter function and direct effects on nervous impulse have been proposed. In most hyperammonemic conditions morphological changes in the liver and brain have been demonstrated, especially in mitochondria, endoplasmic reticulum and lysosomes, together with an accumulation of intracellular lipids. The treatment of hyperammonemias is uncertain and mostly directed to reduce the level of circulating ammonia; there is no current therapy aimed to counteract the molecular effects of ammonia. Administration of carnitine prevents acute ammonia toxicity and enhances the efficacy of ammonia elimination as urea and glutamine. In addition the cytotoxic effects of ammonia, possibly arising from lipid peroxidation, are ameliorated by carnitine. These data indicate the feasibility of utilization of carnitine in the therapy of human hyperammonemic syndromes, both for reducing the levels of ammonia and preventing its toxic effects.

Ammonia↗

PubMed1990

Ammonia metabolism in normal and portacaval-shunted rats.

Ammonia is generated from a large number of metabolically important reactions. Despite its central importance in whole body nitrogen homeostasis excess ammonia is neurotoxic and its concentration must be kept low. Ammonia generated in most extrahepatic tissues is detoxified by incorporation into glutamine (amide). This glutamine may be used in a number of biosynthetic reactions (e.g. in pyrimidine synthesis). Alternatively, as a means of maintaining nitrogen balance, glutamine may be released to the blood. Resting skeletal muscle is particularly important 1) as a "sink" for removal of blood ammonia, and 2) as a major source of circulating glutamine. However, during vigorous exercise skeletal muscle may become a net contributor of ammonia to the blood. A few tissues and cell types (e.g. lymphocytes, macrophages, enterocytes, colonocytes, thymocytes, fibroblasts, bone) and tumors exhibit marked rates of glutamine utilization. In the kidney, glutamine is an important source of urinary ammonia. Ammonia generated from 1) the breakdown of nitrogenous substances in the gut, and 2) from the use of glutamine as a metabolic fuel in the small intestine, is taken up by the liver wherein it is detoxified by conversion to urea and to a lesser extent, glutamine. Some portal vein glutamine acts as a source of urea nitrogen. Ultimately, however, most excess ammonia nitrogen is detoxified indirectly (via glutamine (blood)----glutamine (small intestine)----ammonia (portal vein) or directly in the liver as urea. Portal-systemic shunting of blood, as occurs in chronic cirrhosis of the liver or following the surgical construction of a portacaval shunt results in portal blood bypassing the normal ammonia detoxification machinery of the liver. Under this condition blood ammonia levels rise markedly, increasing the burden on extrahepatic tissues, such as skeletal muscle, brain, and kidney, in maintaining ammonia homeostasis. The most commonly employed animal model of human liver disease is the rat in which an end-to-side portacaval shunt (PCS) has been surgically constructed. Brain glutamine synthetase activity is not increased in PCS rats and in some areas of the brain there may even be a decrease in activity. The brain glutamine synthetase appears to be working at near maximal capacity. Thus, the PCS rats exhibit profound neurological dysfunction when administered ammonium salts in amounts easily tolerated by normal animals. Because of the limited capacity of brain to remove excess ammonia, a rational approach to the treatment of patients with liver disease should include a regimen directed toward lowering the associated hyperammonemia.

Ammonia↗

PubMed1994

Possible role of neuropeptide Y in experimental cancer anorexia.

The efficacy of NPY to elicit feeding in TB rats was reduced prior to the onset of overt anorexia, with the feeding response decreasing further as anorexia developed. Hypothalamic concentration of NPY was reduced in TB rats, with the magnitude of the decrease paralleling the degree of anorexia. Binding affinity of NPY to hypothalamic membranes taken from TB rats suggested decreased binding affinity with no change in receptor number. Infusing ammonium salts at a concentration and rate necessary to increase blood ammonia levels to the degree observed in TB rats, produced anorexia and decreased NPY feeding. These results suggest that NPY feeding systems are abnormal in TB rats and that hyperammonemia may be of primary importance in this dysfunction.

Ammonia↗

PubMed1990

Carrier detection in a partially dominant X-linked disease: ornithine transcarbamylase deficiency.

Ornithine transcarbamylase (OTC) deficiency is an X-linked disease responsible for lethal neonatal hyperammonemia in males. Partial OTC deficiency also occurs in females and can be responsible for life-threatening hyperammonemic comas in heterozygotes (15%). Increased orotic acid excretion occurs in both symptomatic and asymptomatic carriers, especially under protein loading tests. The disease is therefore partially dominant with neonatal lethality in the hemizygous male; the fraction of new mutations has previously been estimated to be low in males (point estimation = 0, upper bound of the confidence interval = 0.16) and 57% in females. Genetic counseling in this disease is difficult because it is not clear whether a negative protein loading test rules out carrier status. In an attempt to determine how reliable the test is for carrier detection, we investigated ten obligate carriers for orotic acid excretion; considering all data available, we concluded that the test is rarely negative in obligate carriers (8%). Consequently, a negative test in a mother decreases the minimum risk of being a carrier from 84% a priori to 30% if she had an affected son and from 43% a priori to 5% if she had a heterozygous daughter. Finally, the diagnosis of a new mutation in the germ cells of the maternal grandfather in one particular family could be ascertained by extensive DNA analysis.

Bayes Theorem↗

PubMed1992

Phenotype of disease in three patients with identical mutations in methylmalonyl CoA mutase.

We have previously identified a mutation in the gene for methylmalonyl CoA mutase in a patient with the mut- phenotype of methylmalonic aciduria. This mutation (G717V) interferes with the binding of the deoxyadenosylcobalamin cofactor to the apoenzyme producing a mutant holoenzyme that is defective, but not completely inactive, in vitro. This report describes the clinical phenotype associated with this mutation in the original patient and two additional patients who are homozygous for this allele. All three patients presented in the first years of life with multiple episodes of life-threatening organic acidosis and hyperammonemia. None had evidence of disease in the perinatal period, and all three have low-normal intelligence. These three children exhibit a distinctive phenotype of disease that is intermediate between the fulminant and benign forms of methylmalonic aciduria. These data suggest that this phenotype is the specific consequence of the G717V mutation, and that the degree of residual enzyme activity associated with the G717V mutation is close to the threshold required in vivo for maintaining metabolic homeostasis.

Acidosis↗

PubMed1990

Hyperaminoacidemia in epileptic children treated with valproic acid.

Serum amino acids were determined in 22 epileptic children treated with valproic acid. This treatment caused hypocarnitinemia in all, and hyperammonemia in 16. Regardless of the blood ammonia levels, values for glutamic acid, arginine, glycine, serine and alanine were higher than those of normal controls, while aspartic acid and ornithine were lower. These findings suggest that valproate causes intramitochondrial dysfunction of the urea cycle.

Adolescent↗

PubMed1988

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: review of 18 reported patients.

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMG-CoA lyase) is an inborn error of leucine catabolism which often leads to life-threatening illness in the neonatal period. The cardinal clinical features include severe infantile hypoglycemia, metabolic acidosis, hepatomegaly, lethargy or coma and apnea. Hyperammonemia is variable. There is a characteristic absence of ketosis. Considerable heterogeneity has been observed in clinical and biochemical presentation. Acute episodes of illness have been mistaken for Reye syndrome. The pattern of organic acids in the urine includes large amounts of 3-hydroxy-3-methylglutaric, 3-methyl-glutaconic, 3-methylglutaric and 3-hydroxyisovaleric acids. Smaller, but appreciable levels of glutaric, adipic and other dicarboxylic acids may also be excreted in the urine. Lactic acid may be present in sizable amounts at times of acute illness. The primary defect is a deficiency of 3-hydroxy-3-methylglutaryl-coenzyme A lyase, a key enzyme in the cycle of ketogenesis.

Amino Acid Metabolism, Inborn Errors↗

PubMed1984

Systemic carnitine deficiency: benefit of oral carnitine supplements vs. persisting biochemical abnormalities.

A patient is described who was admitted with a condition similar to the Reye syndrome at the age of 9 months. Hypoglycemia, hyperammonemia, hepatomegaly, and lethargy were present. The plasma concentrations of free and acylcarnitine were extremely low and the urine contained excessive amounts of dicarboxylic acids. Extensive biochemical and histological investigations of biopsied liver and muscle led to the diagnosis of systemic carnitine deficiency. The patient was put on oral carnitine treatment, upon which he remained clinically well. A prolonged fasting test during this treatment gave abnormal results: there was no ketonemia, but an increase of omega-oxidation of fatty acids. In spite of the treatment the liver and muscle carnitine content remained below normal.

Carnitine↗

PubMed1979

Hyperdibasicaminoaciduria in a Turkish infant without evident protein intolerance.

The first patient of Turkish descent with hyperdibasicaminoaciduria is described. Recurrent diarrhea was observed only during the first three months of life. The infant exhibited low plasma levels of ornithine and arginine. Intestinal absorption of lysine was decreased. Hyperammonemia was noticed only after an i.v. alanine load. It was prevented by addition of arginine.

Arginine↗

PubMed1986

Rett syndrome revisited: a patient with biotin dependency.

A patient with Rett syndrome (cerebral atrophy associated with hyperammonemia) was studied. Primary defects of urea cycle enzymes were excluded as causes of the disorder. The analysis of urinary organic acids showed a moderate increase of lactate, methylcitrate, tiglyglycine and 3-hydroxisovalerate, indicating an abnormality of multiple carboxylases. Biotin supplementation reversed the urinary abnormalities. In fibroblasts grown with a low biotin medium propionylCoA and 3-methylcrotonylCoA carboxylase activities were reduced. Holocarboxylase synthetase activity was normal (Vmax and Km). Surprisingly the biotinidase in fibroblasts was not decreased. The data indicate that some patients with Rett syndrome might suffer from a biotin-dependent defect of unknown nature.

Amino Acids↗

PubMed1995

Lysinuric protein intolerance in pregnancy: case report with successful outcome.

We present a 28-year-old pregnant woman who exhibited intolerance to lysinuric protein. However, she gave birth to a normal child without serious maternal complications. Since four of seven similar patients reported previously developed serious complications such as hemorrhage and eclampsia, patients with lysinuric protein intolerance are considered to be at high risk during pregnancy. A successful outcome can be achieved, provided that the anemia, thrombocytopenia, toxemia and hyperammonemia are well controlled.

Adult↗

PubMed1991

Neurotoxicity of ammonia and fatty acids: differential inhibition of mitochondrial dehydrogenases by ammonia and fatty acyl coenzyme A derivatives.

In several metabolic encephalopathies, hyperammonemia and organic acidemia are consistently found. Ammonia and fatty acids (FAs) are neurotoxic: previous workers have shown that ammonia and FAs can act singly, in combination, or synergistically, in inducing coma in experimental animals. However, the biochemical mechanisms underlying the neurotoxicity of ammonia and FAs have not been fully elucidated. FAs are normally converted to their corresponding CoA derivatives (CoAs) once they enter cells and it is known that these fatty acyl CoAs can alter intermediary metabolism. The present study was initiated to determine the effects of ammonia and fatty acyl CoAs on brain mitochondrial dehydrogenases. At a pathophysiological level (2 mM), ammonia is a potent inhibitor of brain mitochondrial alpha-ketoglutarate dehydrogenase complex (KGDHC). Only at toxicological levels (10-20 mM) does ammonia inhibit brain mitochondrial NAD(+)- and NADP(+)- linked isocitrate dehydrogenase (NAD-ICDH, NADP-ICDH), and NAD(+)-linked malate dehydrogenase (MDH) and liver mitochondrial NAD-ICDH. Butyryl- (BCoA), octanoyl- (OCoA), and palmitoyl (PCoA) CoA were potent inhibitors of brain mitochondrial KGDHC, with IC50 values of 11, 20, and 25 microM, respectively; moreover, the inhibitory effect of fatty acyl CoAs and ammonia were additive. At levels of 250 microM or higher, both OCoA (IC50 = 1.15 mM) and PCoA (IC50 = 470 microM) inhibit brain mitochondrial NADP-ICDH; only at higher levels (0.5-1 mM) does BCoA inhibit this enzyme (by 30-45%). Much less sensitive than KGDHC and NADP-ICDH, brain mitochondrial NAD-ICDH is only inhibited by 1 mM BCoA, OCoA, and PCoA by 22%, 35%, and 44%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Acyl Coenzyme A↗

PubMed1993

High ammonia diet: its effect on the glial fibrillary acidic protein (GFAP).

The effect of a recent hyperammonemic model, consisting of a high ammonia diet for 3, 7, 15, 45, and 90 days, on glial fibrillary acidic protein (GFAP) in the rat spinal cord and on blood ammonia levels has been studied. The high ammonia diet was prepared by mixing a standard diet with ammonium acetate (20% wt/wt); in addition, 5 mM of ammonium acetate was added to the water supply. GFAP contents were determined by means of immunoblotting analysis. The results demonstrated that this high ammonia diet model neither induces significant changes in GFAP immunoreactivity, nor modifies total protein concentration, and only induces significant blood hyperammonemic levels in the first days of treatment. An adaptive response to the diet is suggested and discussed to explain these results. A relation between ammonia and GFAP expression is suggested because transient hyperammonemia induces transient, although no significant, changes on GFAP expression.

Ammonia↗

PubMed1994

Functional relationship between ammonia and gangliosides in brain.

The functional significance of ammonia production in brain under physiological or pathological conditions is not clearly known. NH4+ stimulates Na+, K+ activated ATPase causing stabilization of neuronal membranes of which gangliosides are major structural components. Moreover ammonia is known to inhibit lysosomal enzymes which include enzymes degrading gangliosides. Gangliosides have been shown to stimulate neuritogenesis in neuronal cultures and prevent the damage of the neurons from glutamate toxicity particularly in areas of brain ischemia. Hyperammonemia without any behavioural changes was induced in experimental rats by intraperitoneal administration of either a single dose (0.8 mmol/100 g wt.) or by six 'hourly' doses (0.6 mmol/100 g wt.) of ammonium acetate. An increase in the content of gangliosides along with a rise in the content of GD1A and GD1B without any change in beta-galactosidase and N-acetylhexosaminidase was observed in cerebral cortex, cerebellum, and brain stem, following the administration of single dose of ammonium acetate. Gangliosides, after extraction from the different brain regions, were estimated by the thiobarbituric acid method and expressed in terms of sialic acid. Individual gangliosides were separated and estimated by thin layer chromatography using resorcinol as the staining agent. These results suggest that ammonia production in the neuronal pathways in brain either as a result of repeated stimulation under physiological conditions or as a result of focal ischemia or injury, may likewise cause an increase in the content of gangliosides which may help in neuritic growth (physiological conditions facilitating synaptic plasticity) and may exert a protective effect on the neurons in the ischemic area against glutamate toxicity.

Acetates↗

PubMed1988

Changes in glutamate-cycle enzyme mRNA levels in a rat model of hepatic encephalopathy.

To detect possible changes in the regulation of glutamate/gamma-aminobutyric acid (GABA) enzymes at the level of gene expression in a thioacetamide-induced rat model of acute hepatic encephalopathy, we have examined changes in the mRNAs of four glutamate/GABA enzymes by quantitative RNA blot hybridization analysis. Such changes could reflect cell adaptation to excess ammonia or some other associated metabolic stress. The mRNA levels of glutamate dehydrogenase (GDH) decreased similarly in three different brain regions, whereas those of glutamine synthetase (GS) and glutaminase (GA) increased. The mRNA levels of glutamate decarboxylase (GAD) were unchanged. The results indicate that some effect of liver damage, presumably hyperammonemia, affected the expression of some, but not all, genes associated with ammonia and glutamate metabolism in the brain. This adaptation of gene expression to secondary effects of ammonia on brain amino acid neurotransmitter metabolism or brain energy metabolism could play a role in the physiological changes observed in hepatic encephalopathy.

Amino Acids↗