Changes in levels of purine and pyrimidine nucleotides during acute hypoxia and recovery in neonatal rat brain

Relationship between [18F]FDG PET/CT and metabolomics in patients with colorectal cancer

INTRODUCTION

Advances in metabolomics have significantly improved cancer detection, diagnosis, treatment, and prognosis.

OBJECTIVES

To investigate the relationship between metabolic tumor volume (MTV) using 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) positron emission tomography (PET)/ computed tomography (CT) and metabolomics data in patients with colorectal cancer (CRC).

METHODS

The metabolome in tumor tissues was analyzed using capillary electrophoresis time-of-flight mass spectrometry in 33 patients with newly diagnosed CRC who underwent FDG PET/CT before treatment and had tumor tissue post-surgery. Based on the FDG PET data, MTV was calculated and was dichotomized according to the median value, and tumors were divided into low-MTV and high-MTV tumors. Metabolomics data were compared between the low-MTV and high-MTV tumors.

RESULTS

The levels of most glycolysis-related metabolites were not different between low-MTV and high-MTV tumors. The level of component of the initial part of the tricarboxylic acid (TCA) cycle, citrate, was significantly lower in the high-MTV tumor than in the low-MTV tumor. The TCA intermediate succinate level was significantly higher in the high-MTV tumor than in the low-MTV tumor. In contrast, the TCA intermediate fumarate level was significantly lower in the high-MTV tumor than in the low-MTV tumor. The levels of many amino acids were significantly higher in the high-MTV tumor than in the low-MTV tumor.

CONCLUSIONS

Although preliminary, these results suggest that tumors with high FDG metabolism in CRC may obtain more energy by using a reverse reaction of the TCA cycle and amino-acid metabolism. However, further research is required to clarify this relationship.

Lactate dehydrogenases promote glioblastoma growth and invasion via a metabolic symbiosis

Lactate is a central metabolite in brain physiology but also contributes to tumor development. Glioblastoma (GB) is the most common and malignant primary brain tumor in adults, recognized by angiogenic and invasive growth, in addition to its altered metabolism. We show herein that lactate fuels GB anaplerosis by replenishing the tricarboxylic acid (TCA) cycle in absence of glucose. Lactate dehydrogenases (LDHA and LDHB), which we found spatially expressed in GB tissues, catalyze the interconversion of pyruvate and lactate. However, ablation of both LDH isoforms, but not only one, led to a reduction in tumor growth and an increase in mouse survival. Comparative transcriptomics and metabolomics revealed metabolic rewiring involving high oxidative phosphorylation (OXPHOS) in the LDHA/B KO group which sensitized tumors to cranial irradiation, thus improving mouse survival. When mice were treated with the antiepileptic drug stiripentol, which targets LDH activity, tumor growth decreased. Our findings unveil the complex metabolic network in which both LDHA and LDHB are integrated and show that the combined inhibition of LDHA and LDHB strongly sensitizes GB to therapy.

Intracellular ATP Concentration and Implication for Cellular Evolution

Crystalline lens and striated muscle exist at opposite ends of the metabolic spectrum. Lens is a metabolically quiescent tissue, whereas striated muscle is a mechanically dynamic tissue with high-energy requirements, yet both tissues contain millimolar levels of ATP (>2.3 mM), far exceeding their underlying metabolic needs. We explored intracellular concentrations of ATP across multiple cells, tissues, species, and domains to provide context for interpreting lens/striated muscle data. Our database revealed that high intracellular ATP concentrations are ubiquitous across diverse life forms including species existing from the Precambrian Era, suggesting an ancient highly conserved role for ATP, independent of its widely accepted view as primarily "metabolic currency". Our findings reinforce suggestions that the primordial function of ATP was non-metabolic in nature, serving instead to prevent protein aggregation.

Zinc-α2-glycoprotein as an inhibitor of amine oxidase copper-containing 3

Zinc-α2-glycoprotein (ZAG) is a major plasma protein whose levels increase in chronic energy-demanding diseases and thus serves as an important clinical biomarker in the diagnosis and prognosis of the development of cachexia. Current knowledge suggests that ZAG mediates progressive weight loss through β-adrenergic signalling in adipocytes, resulting in the activation of lipolysis and fat mobilization. Here, through cross-linking experiments, amine oxidase copper-containing 3 (AOC3) is identified as a novel ZAG binding partner. AOC3-also known as vascular adhesion protein 1 (VAP-1) and semicarbazide sensitive amine oxidase (SSAO)-deaminates primary amines, thereby generating the corresponding aldehyde, H2O2 and NH3. It is an ectoenzyme largely expressed by adipocytes and induced in endothelial cells during inflammation. Extravasation of immune cells depends on amine oxidase activity and AOC3-derived H2O2 has an insulinogenic effect. The observations described here suggest that ZAG acts as an allosteric inhibitor of AOC3 and interferes with the associated pro-inflammatory and anti-lipolytic functions. Thus, inhibition of the deamination of lipolytic hormone octopamine by AOC3 represents a novel mechanism by which ZAG might stimulate lipolysis. Furthermore, experiments involving overexpression of recombinant ZAG reveal that its glycosylation is co-regulated by oxygen availability and that the pattern of glycosylation affects its inhibitory potential. The newly identified protein interaction between AOC3 and ZAG highlights a previously unknown functional relationship, which may be relevant to inflammation, energy metabolism and the development of cachexia.

Protein Glycosylation and Tumor Microenvironment Alterations Driving Cancer Hallmarks

Decades of research have disclosed a plethora of alterations in protein glycosylation that decisively impact in all stages of disease and ultimately contribute to more aggressive cell phenotypes. The biosynthesis of cancer-associated glycans and its reflection in the glycoproteome is driven by microenvironmental cues and these events act synergistically toward disease evolution. Such intricate crosstalk provides the molecular foundations for the activation of relevant oncogenic pathways and leads to functional alterations driving invasion and disease dissemination. However, it also provides an important source of relevant glyco(neo)epitopes holding tremendous potential for clinical intervention. Therefore, we highlight the transversal nature of glycans throughout the currently accepted cancer hallmarks, with emphasis on the crosstalk between glycans and the tumor microenvironment stromal components. Focus is also set on the pressing need to include glycans and glycoconjugates in comprehensive panomics models envisaging molecular-based precision medicine capable of improving patient care. We foresee that this may provide the necessary rationale for more comprehensive studies and molecular-based intervention.

The kinetic characteristics of human and trypanosomatid phosphofructokinases for the reverse reaction

Eukaryotic ATP-dependent phosphofructokinases (PFKs) are often considered unidirectional enzymes catalysing the transfer of a phospho moiety from ATP to fructose 6-phosphate to produce ADP and fructose 1,6-bisphosphate. The reverse reaction is not generally considered to occur under normal conditions and has never been demonstrated for any eukaryotic ATP-dependent PFKs, though it does occur in inorganic pyrophosphate-dependent PFKs and has been experimentally shown for bacterial ATP-dependent PFKs. The evidence is provided via two orthogonal assays that all three human PFK isoforms can catalyse the reverse reaction in vitro, allowing determination of kinetic properties. Additionally, the reverse reaction was shown possible for PFKs from three clinically important trypanosomatids; these enzymes are contained within glycosomes in vivo. This compartmentalisation may facilitate reversal, given the potential for trypanosomatids to have an altered ATP/ADP ratio in glycosomes compared with the cytosol. The kinetic properties of each trypanosomatid PFK were determined, including the response to natural and artificial modulators of enzyme activity. The possible physiological relevance of the reverse reaction in trypanosomatid and human PFKs is discussed.

Untargeted metabolomic analysis and pathway discovery in perinatal asphyxia and hypoxic-ischaemic encephalopathy

Elucidating metabolic effects of hypoxic-ischaemic encephalopathy (HIE) may reveal early biomarkers of injury and new treatment targets. This study uses untargeted metabolomics to examine early metabolic alterations in a carefully defined neonatal population. Infants with perinatal asphyxia who were resuscitated at birth and recovered (PA group), those who developed HIE (HIE group) and healthy controls were all recruited at birth. Metabolomic analysis of cord blood was performed using direct infusion FT-ICR mass spectrometry. For each reproducibly detected metabolic feature, mean fold differences were calculated HIE vs. controls (ΔHIE) and PA vs. controls (ΔPA). Putative metabolite annotations were assigned and pathway analysis was performed. Twenty-nine putatively annotated metabolic features were significantly different in ΔPA after false discovery correction ( q < 0.05), with eight of these also significantly altered in ΔHIE. Altered putative metabolites included; melatonin, leucine, kynurenine and 3-hydroxydodecanoic acid which differentiated between infant groups (ΔPA and ΔHIE); and D-erythrose-phosphate, acetone, 3-oxotetradecanoic acid and methylglutarylcarnitine which differentiated across severity grades of HIE. Pathway analysis revealed ΔHIE was associated with a 50% and 75% perturbation of tryptophan and pyrimidine metabolism, respectively. We have identified perturbed metabolic pathways and potential biomarkers specific to PA and HIE, which measured at birth, may help direct treatment.

New perspectives on the roles of pyrimidines in the central nervous system

Since 1956, when exogenous uridine and cytidine were found to be necessary for the maintenance of perfused rat brain function, the co-existence of de novo synthesis, salvage pathways and removal of pyrimidine bases in the CNS has been a controversial subject. Here, we review studies on metabolites and enzymes of pyrimidine metabolism through more than 60 years. In view of known and newly-described inherited pyrimidine and purine disorders - some with complex clinical profiles of neurological impairments - we underline the necessity to investigate how the different pathways work together in the developing brain and then sustain plasticity, regeneration and neuro-transmission in the adult CNS. Experimentally, early incorporation studies in animal brain slices and homogenates with radio-labelled nucleosides or precursors demonstrated salvage activity or de novo synthesis. Later, the nucleoside transporters and organic anionic transporters underlying uptake of metabolites and anti-pyrimidine drugs in the CNS were identified. Recently, the expression of de novo enzymes in glial cells and neurons was verified using (immuno) histochemical and in-situ-hybridization techniques. Adult brain was shown to take up or produce all pyrimidine (deoxy) ribonucleosides or, after uptake and phosphorolysis of nucleosides, to make use of ribose for different purposes, including energy. More recently, non-canonical pyrimidine bases (5mC, 5hmC) have been found most notably in brain, pointing to considerable postreplicative DNA metabolism, with the need for pyrimidine-specific enzymes. Even more perspectives are emerging, with advances in genome analysis and in the manipulation of expression from the gene.

Cooperation between NMDA-Type Glutamate and P2 Receptors for Neuroprotection during Stroke: Combining Astrocyte and Neuronal Protection

Excitotoxicity is the principle mechanism of acute injury during stroke. It is defined as the unregulated accumulation of excitatory neurotransmitters such as glutamate within the extracellular space, leading to over-activation of receptors, ionic disruption, cell swelling, cytotoxic Ca2+ elevation and a feed-forward loop where membrane depolarisation evokes further neurotransmitter release. Glutamate-mediated excitotoxicity is well documented in neurons and oligodendrocytes but drugs targeting glutamate excitotoxicity have failed clinically which may be due to their inability to protect astrocytes. Astrocytes make up ~50% of the brain volume and express high levels of P2 adenosine triphosphate (ATP)-receptors which have excitotoxic potential, suggesting that glutamate and ATP may mediate parallel excitotoxic cascades in neurons and astrocytes, respectively. Mono-cultures of astrocytes expressed an array of P2X and P2Y receptors can produce large rises in [Ca2+]i; mono-cultured neurons showed lower levels of functional P2 receptors. Using high-density 1:1 neuron:astrocyte co-cultures, ischemia (modelled as oxygen-glucose deprivation: OGD) evoked a rise in extracellular ATP, while P2 blockers were highly protective of both cell types. GluR blockers were only protective of neurons. Neither astrocyte nor neuronal mono-cultures showed significant ATP release during OGD, showing that cell type interactions are required for ischemic release. P2 blockers were also protective in normal-density co-cultures, while low doses of combined P2/GluR blockers where highly protective. These results highlight the potential of combined P2/GluR block for protection of neurons and glia.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.

GTP is an allosteric modulator of the interaction between the guanylate-binding protein 1 and the prosurvival kinase PIM1

GBP1 and PIM1 are known to interact with a molar ratio 1:1. GBP1:PIM1 binding initiates a signaling pathway that induces resistance to common chemotherapeutics such as paclitaxel. Since GBP1 is a large GTPase which undergoes conformational changes in a nucleotide-dependent manner, we investigated the effect of GTP/GDP binding on GBP1:PIM1 interaction by using computational and biological studies. It resulted that only GTP decreases the formation of the GBP1:PIM1 complex through an allosteric mechanism, putting the bases for the identification of new compounds potentially able to revert resistance to paclitaxel.

The role of extracellular adenosine in chemical neurotransmission in the hippocampus and Basal Ganglia: pharmacological and clinical aspects

Now there is general agreement that the purine nucleoside adenosine is an important neuromodulator in the central nervous system, playing a crucial role in neuronal excitability and synaptic/non-synaptic transmission in the hippocampus and basal ganglia. Adenosine is derived from the breakdown of extra- or intracellular ATP and is released upon a variety of physiological and pathological stimuli from neuronal and non-neuronal sources, i.e. from glial cells and exerts effects diffusing far away from release sites. The resultant elevation of adenosine levels in the extracellular space reaches micromolar level, and leads to the activation A₁, A_2A, A_2B and A₃ receptors, localized to pre- and postsynaptic as well as extrasynaptic sites. Activation of presynaptic A₁ receptors inhibits the release of the majority of transmitters including glutamate, acetylcholine, noradrenaline, 5-HT and dopamine, whilst the stimulation of A_2A receptors facilitates the release of glutamate and acetylcholine and inhibits the release of GABA. These actions underlie modulation of neuronal excitability, synaptic plasticity and coordination of neural networks and provide intriguing target sites for pharmacological intervention in ischemia and Parkinson’s disease. However, despite that adenosine is also released during ischemia, A₁ adenosine receptors do not participate in the modulation of excitotoxic glutamate release, which is nonsynaptic and is due to the reverse operation of transporters. Instead, extrasynaptic A1 receptors might be responsible for the neuroprotection afforded by A₁ receptor activation.

Hypoxic regulation of glycosylation via the N-acetylglucosamine cycle

Glucose is an energy substrate, as well as the primary source of nucleotide sugars, which are utilized as donor substrates in protein glycosylation. Appropriate glycosylation is necessary to maintain the stability of protein, and is also important in the localization and trafficking of proteins. The dysregulation of glycosylation results in the development of a variety of disorders, such as cancer, diabetes mellitus and emphysema. Glycosylation is kinetically regulated by dynamically changing the portfolio of glycosyltransferases, nucleotide sugars, and nucleotide sugar transporters, which together form a part of what is currently referred to as the ”Glycan cycle”. An excess or a deficiency in the expression of glycosyltransferases has been shown to alter the glycosylation pattern, which subsequently leads to the onset, progression and exacerbation of a number of diseases. Furthermore, alterations in intracellular nucleotide sugar levels can also modulate glycosylation patterns. It is observed that pathological hypoxic microenvironments frequently occur in solid cancers and inflammatory foci. Hypoxic conditions dramatically change gene expression profiles, by activating hypoxia-inducible factor-1, which mediates adaptive cellular responses. Hypoxia-induced glycosyltransferases and nucleotide sugar transporters have been shown to modulate glycosylation patterns that are part of the mechanism associated with cancer metastasis. Hypoxia-inducible factor-1 also induces the expression of glucose transporters and various types of glycolytic enzymes, leading to shifts in glucose metabolic patterns. This fact strongly suggests that hypoxic conditions are an important factor in modulating various nucleotide sugar biosynthetic pathways. This review discusses some of the current thinking of how hypoxia alters glucose metabolic fluxes that can modulate cellular glycosylation patterns and consequently modify cellular functions, particularly from the standpoint of the N-acetylglucosamine cycle, a part of the ”Glycan cycle”.

P2 receptor-mediated modulation of neurotransmitter release-an update

Presynaptic nerve terminals are equipped with a number of presynaptic auto- and heteroreceptors, including ionotropic P2X and metabotropic P2Y receptors. P2 receptors serve as modulation sites of transmitter release by ATP and other nucleotides released by neuronal activity and pathological signals. A wide variety of P2X and P2Y receptors expressed at pre- and postsynaptic sites as well as in glial cells are involved directly or indirectly in the modulation of neurotransmitter release. Nucleotides are released from synaptic and nonsynaptic sites throughout the nervous system and might reach concentrations high enough to activate these receptors. By providing a fine-tuning mechanism these receptors also offer attractive sites for pharmacotherapy in nervous system diseases. Here we review the rapidly emerging data on the modulation of transmitter release by facilitatory and inhibitory P2 receptors and the receptor subtypes involved in these interactions.

Dynamic remodelling of synapses can occur in the absence of the parent cell body

Background

Retraction of nerve terminals is a characteristic feature of development, injury and insult and may herald many neurodegenerative diseases. Although morphological events have been well characterized, we know relatively little about the nature of the underlying cellular machinery. Evidence suggests a strong local component in determining which neuronal branches and synapses are lost, but a greater understanding of this basic neurological process is required. Here we test the hypothesis that nerve terminals are semi-autonomous and able to rapidly respond to local stimuli in the absence of communication with their parent cell body.

Results

We used an isolated preparation consisting of distal peripheral nerve stumps, associated nerve terminals and post-synaptic muscle fibres, maintained in-vitro for up to 3 hrs. In this system synapses are intact but the presynaptic nerve terminal is disconnected from its cell soma. In control preparations synapses were stable for extended periods and did not undergo Wallerian degneration. In contrast, addition of purines triggers rapid changes at synapses. Using fluorescence and electron microscopy we observe ultrastructural and gross morphological events consistent with nerve terminal retraction. We find no evidence of Wallerian or Wallerian-like degeneration in these preparations. Pharmacological experiments implicate pre-synaptic P2X7 receptor subunits as key mediators of these events.

Conclusion

The data presented suggest; first that isolated nerve terminals are able to regulate connectivity independent of signals from the cell body, second that synapses exist in a dynamic state, poised to shift from stability to loss by activating intrinsic mechanisms and molecules, and third that local purines acting at purinergic receptors can trigger these events. A role for ATP receptors in this is not surprising since they are frequently activated during cellular injury, when adenosine tri-phosphate is released from damaged cells. Local control demands that the elements necessary to drive retraction are constitutively present. We hypothesize that pre-existing scaffolds of molecular motors and cytoskeletal proteins could provide the dynamism required to drive such structural changes in nerve terminals in the absence of the cell body.

Purinergic modulation of microglial cell activation

Microglial cells are resident macrophages in the brain and their activation is an important part of the brain immune response and the pathology of the major CNS diseases. Microglial activation is triggered by pathological signals and is characterized by morphological changes, proliferation, phagocytosis and the secretion of various cytokines and inflammatory mediators, which could be both destructive and protective for the nervous tissue. Purines are one of the most important mediators which regulate different aspects of microglial function. They could be released to the extracellular space from neurons, astrocytes and from the microglia itself, upon physiological neuronal activity and in response to pathological stimuli and cellular damage. Microglial activation is regulated by various subtypes of nucleotide (P2X, P2Y) and adenosine (A₁, A(₂A) and A₃) receptors, which control ionic conductances, membrane potential, gene transcription, the production of inflammatory mediators and cell survival. Among them, the role of P2X₇ receptors is especially well delineated, but P2X₄, various P2Y, A₁, A(₂A) and A₃ receptors also powerfully participate in the microglial response. The pathological role of microglial purine receptors has also been demonstrated in disease models; e.g., in ischemia, sclerosis multiplex and neuropathic pain. Due to their upregulation and selective activation under pathological conditions, they provide new avenues in the treatment of neurodegenerative and neuroinflammatory illnesses.

Supersensitivity of P2X receptors in cerebrocortical cell cultures after in vitro ischemia

Neuronally enriched primary cerebrocortical cultures were exposed to glucose-free medium saturated with argon (in vitro ischemia) instead of oxygen (normoxia). Ischemia did not alter P2X7 receptor mRNA, although serum deprivation clearly increased it. Accordingly, P2X7 receptor immunoreactivity (IR) of microtubuline-associated protein 2 (MAP2)-IR neurons or of glial fibrillary acidic protein (GFAP)-IR astrocytes was not affected; serum deprivation augmented the P2X7 receptor IR only in the astrocytic, but not the neuronal cell population. However, ischemia markedly increased the ATP- and 2'-3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP)-induced release of previously incorporated [3H]GABA. Both Brilliant Blue G and oxidized ATP inhibited the release of [3H]GABA caused by ATP application; the Brilliant Blue G-sensitive, P2X7 receptor-mediated fraction, was much larger after ischemia than after normoxia. Whereas ischemic stimulation failed to alter the amplitude of ATP- and BzATP-induced small inward currents recorded from a subset of non-pyramidal neurons, BzATP caused a more pronounced increase in the frequency of miniature inhibitory postsynaptic currents (mIPSCs) after ischemia than after normoxia. Brilliant Blue G almost abolished the effect of BzATP in normoxic neurons. Since neither the amplitude of mIPSCs nor that of the muscimol-induced inward currents was affected by BzATP, it is assumed that BzATP acts at presynaptic P2X7 receptors. Finally, P2X7 receptors did not enhance the intracellular free Ca2+ concentration either in proximal dendrites or in astrocytes, irrespective of the normoxic or ischemic pre-incubation conditions. Hence, facilitatory P2X7 receptors may be situated at the axon terminals of GABAergic non-pyramidal neurons. When compared with normoxia, ischemia appears to markedly increase P2X7 receptor-mediated GABA release, which may limit the severity of the ischemic damage. At the same time we did not find an accompanying enhancement of P2X7 mRNA or protein expression, suggesting that receptors may become hypersensitive because of an increased efficiency of their transduction pathways.

Purine and pyrimidine metabolism and electrocortical brain activity during hypotension in near-term lambs

BACKGROUND

Insufficient cerebral O2 supply leads to cellular energy failure and loss of brain cell function. The relationship between the severity of cellular energy failure due to hemorrhagic hypotension and the loss of electrocortical brain activity (ECBA), as a measure of brain cell function, is not yet fully elucidated in near-term born lambs.

OBJECTIVES

To study the relationship between cerebral purine and pyrimidine metabolism, as a measure of brain cell energy failure, and brain cell function after hemorrhagic hypotension in near-term born lambs.

METHODS

Eight near-term lambs (term 147 days) were delivered at 131 days of gestation. After a stabilization period, mean arterial blood pressure was reduced till 30% of baseline by withdrawal of blood. Cerebrospinal fluid (CSF) was obtained at the end of the hypotensive period (2.5 h). CSF from 8 siblings was used for comparison. HPLC was used to determine purine and pyrimidine metabolites in CSF, as a measure of cellular energy failure. ECBA was calculated as the root mean square value of a band-filtered (2-16 Hz) one-channel EEG.

RESULTS

Values of guanosine, inosine, hypoxanthine, xanthine and uridine were significantly higher, while ECBA was significantly lower after hemorrhagic hypotension than control values. The concentrations of inosine, hypoxanthine, xanthine and uridine were significantly negatively linearly related to ECBA.

CONCLUSIONS

Brain cell function is negatively related to concentrations of inosine, hypoxanthine, xanthine and uridine in the CSF after hemorrhagic hypotension in near-term born lambs.

Purine and pyrimidine metabolism and electrocortical brain activity during hypoxemia in near-term lambs

Insufficient cerebral O(2) supply leads to brain cell damage and loss of brain cell function. The relationship between the severity of hypoxemic brain cell damage and the loss of electrocortical brain activity (ECBA), as measure of brain cell function, is not yet fully elucidated in near-term newborns. We hypothesized that there is a strong relationship between cerebral purine and pyrimidine metabolism, as measures of brain cell damage, and brain cell function during hypoxemia. Nine near-term lambs (term, 147 d) were delivered at 131 (range, 120-141) d of gestation. After a stabilization period, prolonged hypoxemia (fraction of inspired oxygen, 0.10; duration, 2.5 h) was induced. Mean values of carotid artery blood flow, as a measure of cerebral blood flow, and ECBA were calculated over the last 3 min of hypoxemia. At the end of the hypoxemic period, cerebral arterial and venous blood gases were determined and CSF was obtained. CSF from 11 normoxemic siblings was used for baseline values. HPLC was used to determine purine and pyrimidine metabolites in CSF, as measures of brain cell damage. Concentrations of purine and pyrimidine metabolites were significantly higher in hypoxemic lambs than in their siblings, whereas ECBA was lower in hypoxemic lambs. Significant negative linear relationships were found between purine and pyrimidine metabolite concentrations and, respectively, cerebral O(2) supply, cerebral O(2) consumption, and ECBA. We conclude that brain cell function is related to concentrations of purine and pyrimidine metabolites in the CSF. Reduction of ECBA indeed reflects the measure of brain damage due to hypoxemia in near-term newborn lambs.

Early biochemical and histological alterations in rat corticoencephalic cell cultures following metabolic damage and treatment with modulators of mitochondrial ATP-sensitive potassium channels

The present study was aimed at characterizing alterations of the nucleotide content and morphological state of rat corticoencephalic cell cultures subjected to metabolic damage and treatment with modulators of mitochondrial ATP-dependent potassium channels (mitoK(ATP)). In a first series of experiments, in vitro ischemic changes of the contents of purine and pyrimidine nucleoside diphosphates and triphosphates were measured by high performance liquid chromatography (HPLC) and the corresponding histological alterations were determined by celestine blue/acid fuchsin staining. As an ischemic stimulus, incubation with a glucose-free medium saturated with argon was used. Ischemia decreased the levels of adenosine, guanine and uridine triphosphate (ATP, GTP, UTP) and increased the levels of the respective dinucleotides ADP and UDP, whereas the GDP content was not changed. Both 5-hydroxydecanoate (5-HD) and diazoxide failed to alter the contents of nucleoside diphosphates and triphosphates, when applied under normoxic conditions. 5-HD (30 microM) prevented the ischemia-induced changes of nucleotide and nucleoside levels. Diazoxide (300 microM), either alone or in combination with 5-hydroxydecanoate (30 microM) was ineffective. Pyruvate (5 mM) partially reversed the effects of ischemia or ischemia plus 2-deoxyglucose (20mM) in the incubation medium. Diazoxide (300 microM) and 5-HD (30 microM) had no effect in the presence of pyruvate (5mM) and 2-deoxyglucose (20mM). Staining the cells with celestine blue/acid fuchsin in order to classify them as intact, reversibly or profoundly injured, revealed a protective effect of 5-HD. When compared with 5-HD, diazoxide, pyruvate and 2-deoxyglucose had similar but less pronounced effects. In conclusion, these results suggest a protective role of 5-hydroxydecanoate on early corticoencephalic nucleotide and cell viability alterations during ischemia.

Early biochemical and histological changes during hyperbaric or normobaric reoxygenation after in vitro ischaemia in primary corticoencephalic cell cultures of rats

In a first series of experiments, the morphological changes of corticoencephalic cells by ischaemia were determined by staining with celestine blue-acid fuchsin in order to classify cells as intact, dark basophilic (supposedly reversibly injured) and preacidophilic or acidophilic (profoundly injured). Hypoxia and glucose-deprivation (in vitro ischaemia) markedly decreased the number of intact cells and correspondingly increased the number of both reversibly and profoundly damaged cells. The morphological characteristics indicated a partial recovery during reoxygenation either in the absence or presence of glucose and irrespective of whether normobaric or hyperbaric oxygen was used. In a second series of experiments, nucleoside triphosphate and diphosphate levels were determined in corticoencephalic cultures by high-performance liquid chromatography. Hypoxia in combination with glucose-deficiency markedly decreased the ATP:ADP, GTP:GDP and UTP:UDP ratios. A still larger fall of these ratios was observed both after normobaric and hyperbaric reoxygenation. In contrast, both normobaric and hyperbaric reoxygenation in the presence of glucose led to an almost complete recovery near the control normoxic values. In conclusion, the histological changes were not adequately reflected by changes in the nucleoside triphosphate:diphosphate ratios and, in addition, hyperbaric oxygen had neither favourable nor unfavourable effects on the early morphological and functional restitution of ischaemically damaged cells under the conditions of the present study.

Alterations of purine and pyrimidine nucleotide contents in rat corticoencephalic cell cultures following metabolic damage and treatment with openers and blockers of ATP-sensitive potassium channels

Rat corticoencephalic cell cultures were investigated by high performance liquid chromatography for changes in the levels of adenosine 5'-triphosphate (ATP), guanosine 5'-triphosphate (GTP), uridine 5'-triphosphate (UTP), cytidine 5'-triphosphate (CTP), and the respective nucleoside diphosphates. Hypoxia was induced by gassing the incubation medium for 30 min with 100% argon. Removal of glucose was caused by washing the cultures in glucose-free medium at the beginning of the 30 min incubation period. Whereas hypoxia or glucose-deficiency alone failed to alter the nucleotide levels, the combination of these two manipulations was clearly inhibitory. Diazoxide (300 microM) an opener of ATP-dependent potassium channels (K(ATP)) did not alter the nucleotide contents either in a normoxic and glucose-containing medium, or a hypoxic and glucose-free medium. By contrast, the K(ATP) channel antagonist tolbutamide (300 microM) aggravated the hypoxic decrease of nucleotide levels in a glucose-free medium, although it was ineffective in a normoxic and glucose-containing medium. Hypoxia and glucose-deficiency decreased the ATP/ADP and UTP/UDP ratios, but failed to change the GTP/GDP ratio. Diazoxide and tolbutamide (300 microM each) had no effect on the nucleoside triphosphate/diphosphate ratios either during normoxic or during hypoxic conditions. In conclusion, corticoencephalic cultures are rather resistant to in vitro ischemia. Although they clearly respond to the blockade of plasmalemmal K(ATP) channels (plasmaK(ATP)) by tolbutamide, these channels appear to be maximally open as a consequence of the fall in intracellular nucleotides and, therefore, diazoxide has no further effect.

Purine and pyrimidine salvage in whole rat brain. Utilization of ATP-derived ribose-1-phosphate and 5-phosphoribosyl-1-pyrophosphate generated in experiments with dialyzed cell-free extracts

The object of this work stems from our previous studies on the mechanisms responsible of ribose-1-phosphate- and 5-phosphoribosyl-1-pyrophosphate-mediated nucleobase salvage and 5-fluorouracil activation in rat brain (Mascia, L., Cappiello M., Cherri, S., and Ipata, P. L. (2000) Biochim. Biophys. Acta 1474, 70-74; Mascia, L., Cotrufo, T., Cappiello, M., and Ipata, P. L. (1999) Biochim. Biophys. Acta 1472, 93-98). Here we show that when ATP at "physiological concentration" is added to dialyzed extracts of rat brain in the presence of natural nucleobases or 5-fluorouracil, adenine-, hypoxanthine-, guanine-, uracil-, and 5-fluorouracil-ribonucleotides are synthesized. The molecular mechanism of this peculiar nucleotide synthesis relies on the capacity of rat brain to salvage purine and pyrimidine bases by deriving ribose-1-phosphate and 5-phosphoribosyl-1-pyrophosphate from ATP even in the absence of added pentose or pentose phosphates. The levels of the two sugar phosphates formed are compatible with those of synthesized nucleotides. We propose that the ATP-mediated 5-phosphoribosyl-1-pyrophosphate synthesis occurs through the action of purine nucleoside phosphorylase, phosphopentomutase, and 5-phosphoribosyl-1-pyrophosphate synthetase. Furthering our previous observations on the effect of ATP in the 5-phosphoribosyl-1-pyrophosphate-mediated 5-fluorouracil activation in rat liver (Mascia, L., and Ipata, P. L. (2001) Biochem. Pharmacol. 62, 213-218), we now show that the ratio [5-phosphoribosyl-1-pyrophosphate]/[ATP] plays a major role in modulating adenine salvage in rat brain. On the basis of our in vitro results, we suggest that massive ATP degradation, as it occurs in brain during ischemia, might lead to an increase of the intracellular 5-phosphoribosyl-1-pyrophosphate and ribose-1-phosphate pools, to be utilized for nucleotide resynthesis during reperfusion.

Rapid assay for one-run determination of purine and pyrimidine nucleotide contents in neocortical slices and cell cultures

The present study describes the measurement of endogenous nucleoside di- and triphosphate contents (ATP, GTP, UTP, CTP, ADP, GDP and UDP) in rat neocortical brain slices and mixed neuronal/astrocytic corticoencephalic cultures. Determination was by means of anion-exchange HPLC using a binary gradient of 0.3 M ammonium carbonate and water. In addition, a new method is described for the identification of nucleoside triphosphates, using digestion of the nucleotides by phosphoglycerate kinase and partial splitting of nucleoside diphosphates to shift the equilibrium of the phosphoglycerate kinase reaction in direction of breakdown of nucleoside triphosphates. Finally, the determination of the sum of creatine and creatine phosphate is suggested as an alternative reference value instead of protein under conditions when cells are cultured in protein-containing medium.

Tolbutamide attenuates diazoxide-induced aggravation of hypoxic cell injury

ATP-dependent potassium (KATP) channels of neurons are closed in the presence of physiological levels of intracellular ATP and open when ATP is depleted during hypoxia or metabolic damage. The present study investigates hypoxic alterations of purine and pyrimidine nucleotide levels supposed to intracellularly modulate KATP channels. In addition, the effects of the KATP channel activator diazoxide and its antagonist tolbutamide were investigated on ATP, GTP, CTP and UTP levels in slices of the parietal cortex. Hypoxia was evoked by saturation of the medium with 95% N2-5% CO2 instead of 95% O2-5% CO2 for 5 min. Nucleotide contents were measured by anion-exchange HPLC in neutralized perchloric acid extracts obtained from slices frozen immediately at the end of incubation. Hypoxia per se decreased purine and pyrimidine nucleoside triphosphate contents. Thus, ATP and GTP contents were reduced to 69.9 and 77.6% of the respective normoxic levels. UTP and CTP contents were even more decreased (to 60.9 and 41.6%),, probably because the salvage pathway of these pyrimidine nucleotides is less effective than that of the purine nucleotides ATP and GTP. While tolbutamide (30 microM) had no effect on the hypoxia-induced decrease of nucleotides, diazoxide at 300, but not 30 microM aggravated the decline of ATP, UTP and CTP to 51.8, 37.5 and 28.5% of the contents observed at normoxia; GTP levels also showed a tendency to decrease after diazoxide application. Tolbutamide (300 microM) antagonized the effects of diazoxide (300 but not 30 microM aggravated the decline of ATP, UTP and CTP to 51.8, 37.5 and 28.5% of the contents observed at normoxia; GTP levels also showed a tendency to decrease after diazoxide application. Tolbutamide (300 microM) antagonized the effects of diazoxide (300 MicroM). Nucleoside diphosphate (ADP, GDP and UDP) levels were uniformly increased by hypoxia. There was no hypoxia-induced increase of ADP contents in the presence of tolbutamide (300 microM). The ATP/ADP, GTP/GDP and UTP/UDP ratios uniformly declined at a low pO2. However, only the ATP/ADP ratio was decreased further by diazoxide (300 microM). The observed alterations in nucleotide contents may be of importance for long- and short-term processes related to acute cerebral hypoxia. Thus, hypoxia-induced alterations of purine and pyrimidine nucleotide levels may influence the open state of KATP-channels during the period of reversible hypoxic cerebral injury. Furthermore, alterations during the irreversible period of cerebral injury may also arise, as a consequence of decreased pyrimidine nucleotide contents affecting cell survival viaprotein and DNA synthesis.

Effects of mexiletine on ATP sensitive K+ channel of rat skeletal muscle fibres: a state dependent mechanism of action

1. The effects of mexiletine were evaluated on the ATP-sensitive K+ channel (K(ATP)) of rat skeletal muscle fibres using patch clamp techniques. The effects of mexiletine were studied on macropatch currents 20 s (maximally activated), 8 min (early stage of rundown) and 15 min (late stage of rundown) after excision in the absence or in the presence of internal ADP (50-100 microM) or UDP (500 microM). In addition, the effects of mexiletine were tested on single channel. 2. In the absence of ADP and UDP, mexiletine inhibited the current through maximally activated channels with an IC50 of -5.58+/-0.3 M. Nucleoside diphosphates shifted the current versus mexiletine concentration relationship to the right on the log concentration axis. UDP (500 microM) was more efficacious than ADP (50-100 microM) in this effect. 3. At the early stage of rundown, the sensitivity of the channel to mexiletine was reduced and nucleoside diphosphates, particularly UDP, antagonized the effect of mexiletine. At the late stage of rundown, mexiletine did not affect the currents. 4. At the single channel level, 1 microM mexiletine reduced the mean burst duration by 63% and prolonged the arithmetic mean closed time intervals between the bursts of openings without altering the open time and closed time distributions. Mexiletine did not affect the single channel conductance. 5. These results show that in skeletal muscle, mexiletine is a state-dependent K(ATP) channel inhibitor which either acts through the nucleotide binding site or a site allosterically coupled to it.

Neuroprotective effect of YM-39558 in focal cerebral ischemia in cats

We studied the effect of YM-39558, orotic acid ethylester, in a focal cerebral ischemia model in anesthetized cats. YM-39558 has good permeability across the blood brain barrier, and in the brain is hydrolyzed to orotic acid, the main active substance. Cats were subjected to permanent occlusion of the middle cerebral artery (MCA) for 6 h, then killed and examined histologically. Treatment with YM-39558 (intravenous infusion of 11.8 mg (10 mg as orotic acid)/6 ml per kg per h) starting 15 min after MCA occlusion markedly reduced the volume of ischemic damage (from 2450 +/- 82 mm3 of the cerebral hemisphere in the saline-treated cats to 1644 +/- 123 mm3 in the YM-39558-treated cats, P < 0.01). In contrast, YM-39558 (2.26 and 1.18 mg/0.8 ml per kg per h) showed no significant protective effect on ischemic damage. No significant differences were observed between saline- and YM-39558-treated cats concerning physiological variables including brain temperature. This evidence for the neuroprotective efficacy of YM-39558 in gyrencephalic species suggests its therapeutic potential in the treatment of stroke in humans.

Neuroprotective effect of YM-39558, orotic acid ethylester, in gerbil forebrain ischemia

We studied the effects of orotic acid and YM-39558 (2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid ethyl ester), orotic acid ethylester, on delayed neuronal death of hippocampal CA1 neurons induced by transient forebrain ischemia. Our data indicated that YM-39558 had high permeability across the blood brain barrier and was hydrolyzed to orotic acid, the active substance, in the brain. The neuronal damage was reduced significantly in animals intraperitoneally treated with YM-39558 (100 mg/kg x 3) after ischemia, but not with orotic acid in the same way. The results also suggested that the maintenance of a few ten micromolar orotic acid in cerebrospinal fluid were needed for its neuroprotective effects.

The importance of the measurement of ATP depletion and subsequent cell damage with an estimate of size and nature of the market for a practicable method: a review designed for technology transfer

ATP is the energy currency of cells. ATP depletion is a central process in pathogenesis, in particular ischaemia, hypoxia and hypoglycaemia. ATP depletion in cells can be indirectly measured from the increased concentrations of extracellular hypoxanthine, a central intermediate in the metabolism of ATP. Cell damage secondary to ATP depletion can also be measured from extracellular hypoxanthine. The relevant biochemistry and physiology is briefly reviewed. Since market size is needed for investment decisions that would allow technology transfer, the numbers of hypoxanthine analyses that are clinically justified from the extensive published evidence are calculated per million population from UK, Norwegian and other evidence. The concentration of oxygen in blood is measured to estimate whether mitochondrial oxidative phosphorylation is adequate. Measurements of bicarbonate are used to estimate anaerobic glycolysis. Since the indirect estimation of ATP depletion is a major objective of blood gas and acid-base analyses, the number of such analyses per million population provides a good estimate of potential market size for a more direct method of estimating ATP depletion. A method is required for the rapid, dispersed emergency analyses needed clinically. Routes for method development are indicated. Competition, risks, acceptability, consumer motivation and timetables are indicated for the development phase. There are medicolegal pressures, especially in the USA, for the proposed advances to be widely used.

Post-ischaemic treatment with orotic acid prevents neuronal injury in gerbil brain ischaemia

We studied the effects of orotic acid, a precursor of pyrimidine nucleotide, on delayed neuronal death of hippocampal CA1 neurones induced by global cerebral ischaemia in Mongolian gerbils. Neuronal damage was significantly reduced in animals treated with orotic acid 2 h before ischaemia at doses of 100, 200 or 300 mg kg-1, i.p. A dose of 300 mg kg-1 given 24 h after ischaemia also suppressed CA1 neuronal damage, but had no effect when given at 48 or 72 h. These results demonstrate a protective effect of orotic acid on ischaemic neuronal damage with a wide therapeutic time window.

Physiological concentrations of purines and pyrimidines

The concentrations of bases, nucleosides, and nucleosides mono-, di- and tri-phosphate are compared for about 600 published values. The data are predominantly from mammalian cells and fluids. For the most important ribonucleotides, average concentrations +/- SD (microM) are: ATP, 3,152 +/- 1,698; GTP, 468 +/- 224; UTP, 567 +/- 460 and CTP, 278 +/- 242. For deoxynucleosides-triphosphate (dNTP), the concentrations in dividing cells are: dATP, 24 +/- 22; dGTP, 5.2 +/- 4.5; dCTP, 29 +/- 19 and dTTP 37 +/- 30. By comparison, dUTP is usually about 0.2 microM. For the 4 dNTPs, tumor cells have concentrations of 6-11 fold over normal cells, and for the 4 NTPs, tumor cells also have concentrations 1.2-5 fold over the normal cells. By comparison, the concentrations of NTPs are significantly lower in various types of blood cells. The average concentration of bases and nucleosides in plasma and other extracellular fluids is generally in the range of 0.4-6 microM; these values are usually lower than corresponding intracellular concentrations. For phosphate compounds, average cellular concentrations are: Pi, 4400; ribose-1-P, 55; ribose-5-P, 70 and P-ribose-PP, 9.0. The metal ion magnesium, important for coordinating phosphates in nucleotides, has values (mM) of: free Mg2+, 1.1; complexed-Mg, 8.0. Consideration of experiments on the intracellular compartmentation of nucleotides shows support for this process between the cytoplasm and mitochondria, but not between the cytoplasm and the nucleus.

Brain purines in a genetic mouse model of Lesch-Nyhan disease

Mice carrying a mutation in the gene encoding the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) have recently been produced to provide an animal model for Lesch-Nyhan disease. The current studies were conducted to characterize the consequences of the mutation on the expression of HPRT and to characterize potential changes in brain purine content in these mutants. Our results indicate that the mutant animals have no detectable HPRT-immunoreactive material on western blots and no detectable HPRT enzyme activity in brain tissue homogenates, confirming that they are completely HPRT deficient (HPRT-). Despite the absence of HPRT-mediated purine salvage, the animals have apparently normal brain purine content. However, de novo purine synthesis, as measured by [14C]formate incorporation into brain purines, is accelerated four- to fivefold in the mutant animals. This increase in the synthesis of purines may protect the HPRT- mice from potential depletion of brain purines despite complete impairment of HPRT-mediated purine salvage.

Protective effect of adenosine on the anoxic damage of hippocampal slice

To investigate the effect of adenosine on anoxic damage of brain tissue, energy metabolism in relation to neural activity was studied using hippocampal slices from the guinea-pig. For the index of energy metabolism, adenosine triphosphate and creatine phosphate in each slice were measured and also postsynaptic potentials (population spike potentials) were recorded in the granule cell layer of the slices. After preparation of the slices, one group of slices was incubated for 120 min in standard medium and another in the medium containing adenosine (5 mM). The adenosine triphosphate content of the former group was 8.8 mmol/kg protein whereas that of the latter was 15.8 mmol/kg protein. During deprivation of oxygen and glucose, adenosine triphosphate and creatine phosphate in the control slices and the slices treated with adenosine decreased rapidly. Adenosine did not alter the rate of consumption of high energy phosphates in both slices. The pretreatment of slices with adenosine (5 mM), however, considerably enhanced the recovery of the adenosine triphosphate level during reoxygenation with glucose after deprivation of oxygen and glucose for 15 and 30 min. Postsynaptic potentials in the granule cell layer of the slice were recorded before and after 10, 15, 20 or 25 min deprivation of oxygen and glucose in the control slice and the slices pretreated with adenosine (5 mM) for 60 min. In the control slices, postsynaptic potentials in one of 10 slices could be recorded after 60 min reoxygenation following 15 min anoxia/aglycemia, while postsynaptic potentials in 10 of 15 slices treated with adenosine could be detected even after 15 min of anoxia/aglycemia. Thus the functional recovery of postsynaptic potentials agreed well with the results of the recovery of adenosine triphosphate level in the slices treated with adenosine. These results indicate that adenosine has a protective effect against anoxic/aglycemic damage of brain tissue by facilitating the resynthesis of tissue adenosine triphosphate during the recovery period.

Opposite alterations in cerebrospinal fluid uridine after severe cerebral ischemia or intrathecal blood injection

1. Rats which survived hypoglycemia by insulin, hypoxia by 10% O2, or ischemia by carotid ligation and hypotension to 40 mm Hg, evidenced no changes in cerebrospinal fluid (CSF) uridine. Animals which died soon after the above interventions or as a result of KCl-induced cardiac arrest had elevated CSF uridine concentrations. 2. Injection of whole blood or the soluble contents of lysed blood cells into the lateral ventricle of rats reduced CSF uridine to less than one-half normal at 24 hrs but values returned to normal 3 days later. Changes in hypoxanthine resembled those of uridine, but were less dramatic, whereas xanthine concentrations were largely unaltered. Intraventricular injection of plasma or saline did not alter CSF uridine. 3. It seems most likely that low CSF uridine concentrations previously reported in head injury patients may be secondary to the effects of blood cell contents in the cerebrospinal fluid, rather than responses to altered metabolism in neurons or glia cells.

Perinatal exposure to anoxia alone does not alter the susceptibility to amygdaloid-kindled seizures in the adult rabbit

It is suggested that asphyxia on newborns increases the susceptibility to epileptic syndromes. The effect of perinatal and postnatal anoxia on subsequent seizure susceptibility was assessed by amygdaloid kindling in adult rabbits. Rabbits from 1 day pre-term to 53 days were exposed to 100% N2 for an average of 7 min or until the heart rate was reduced by 70%. Non-anoxic littermates served as controls. At 2 months of age, animals were implanted with bilateral amygdalae electrodes. After a postsurgical recovery period, afterdischarge (AD) thresholds were determined for the electrode sites and a kindling paradigm was performed. There were no significant differences in the rate of kindling in all groups studied (control, anoxic at 1 day pre-term or at term, anoxic at 44 and 53 days). These results demonstrate that perinatal anoxia did not alter the seizure susceptibility in the adult rabbit kindling model.

Carbohydrate and energy metabolism during the evolution of hypoxic-ischemic brain damage in the immature rat

The brain damage that evolves from perinatal cerebral hypoxia-ischemia may involve lingering disturbances in metabolic activity that proceed into the recovery period. To clarify this issue, we determined the carbohydrate and energy status of cerebral tissue using enzymatic, fluorometric techniques in an experimental model of perinatal hypoxic-ischemic brain damage. Seven-day postnatal rats were subjected to unilateral common carotid artery ligation followed by 3 h of hypoxia with 8% oxygen at 37 degrees C. This insult is known to produce tissue injury (selective neuronal necrosis or infarction) predominantly in the cerebral hemisphere ipsilateral to the carotid artery occlusion in 92% of the animals. Rat pups were quick-frozen in liquid nitrogen at 0, 1, 4, 12, 24, or 72 h of recovery; littermate controls underwent neither ligation nor hypoxia. Glucose in both cerebral hemispheres was nearly completely exhausted during hypoxia-ischemia, with concurrent increases in lactate to 10 mmol/kg. During recovery, glucose promptly increased above control values, suggesting an inhibition of glycolytic flux, as documented in the ipsilateral cerebral hemisphere by measurement of glucose utilization (CMRglc) at 24 h. Tissue lactate declined rapidly during recovery but remained slightly elevated in the ipsilateral hemisphere for 12 h. Phosphocreatine (P approximately Cr) and ATP in the ipsilateral cerebral hemisphere were 14 and 26% of control (p less than 0.001) at the end of hypoxia-ischemia; total adenine nucleotides (ATP + ADP + AMP) also were partially depleted (-46%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine metabolism in neurons and astrocytes in primary cultures

Metabolic fate of [8-14C]adenosine was studied in primary cultures of either astrocytes or neurons from the mouse brain. In astrocytes the main metabolic route was the formation of nucleotides. Thus, synthesis of adenosine triphosphate (ATP) amounted to about 0.2 nmol X min-1 X mg-1 protein. The deamination occurred less rapidly. The total rate of formation of inosine was difficult to establish because a considerable amount of labeled inosine accumulated in the medium. The initial incorporation of radioactivity into inosine in the medium was extremely rapid, probably because of the action of an ectoenzyme. However, the labeling of inosine in the medium also continued to increase slowly throughout the incubation, maybe as a result of release of intracellularly formed inosine. The total inosine formation rate during the incubation amounted to at most 0.1 nmol X min-1 X mg-1. Hypoxanthine was formed at a corresponding rate but was released to a lesser extent. In neurons much less label was incorporated into ATP. The major metabolite was inosine, formed intracellularly at a rate of 0.2 nmol X min-1 X mg-1. In addition, there was an immediate rapid labeling of inosine (and to a lesser extent hypoxanthine) in the medium, again suggesting the action of an ectoenzyme. Neither neurons nor astrocytes released a measurable amount of nucleotides to the medium. The cellular differences in adenosine metabolism are probably of relevance for the interpretation of adenosine metabolism in brain in situ. The ectoenzyme may be of importance for rapid termination of the neuromodulator activity of adenosine, and the rapid nucleotide formation in astrocytes is in agreement with a high metabolic activity of these cells.

Effect of deafferentation on the levels of uric acid in the spinal cord of the rat

In previous studies we reported that the rat spinal cord contains relatively high levels of uric acid and that the levels in a rat model of bilateral chronic pain, experimental adjuvant arthritis. In this report we evaluate the changes in UA in the unilaterally deafferented rat, a preparation which has also been used to study chronic pain. Uric acid was measured by high-pressure liquid chromatography with electrochemical detection in the spinal cord of rats that underwent unilateral, multiple cervical dorsal rhizotomy. Compared to control and sham-operated rats, there was a significant increase in the level of uric acid in the dorsal quadrant of the spinal cord ipsilateral to the dorsal rhizotomy. This increase was present at 1 and 4 weeks after surgery. At 1 week, we also observed a small but statistically insignificant increase in uric acid levels in the dorsal quadrant contralateral to the deafferentation and in sham-operated rats. Four weeks after surgery the levels of UA in all regions except for the deafferented dorsal quadrant returned to normal. The possibility was raised that the changes in uric acid reflect an increase in purinergic metabolism in the spinal cord secondary to the increased activity of the dorsal horn neurons that occurs with deafferentation.

Behavioral abnormalities and seizure susceptibility in rat after neonatal anoxia

Wistar rat pups were exposed to 99.99%-nitrogen gas for 10 minutes at 4 days of age, and then their behavior and susceptibility to pentylentetrazol (PTZ) induced seizure were investigated at the ages of 28 and 56 days. Neonatal anoxic rats exhibited hyperactivity in the open field examination and motor coordination disturbance in the inclined screen test, hyperirritability to the startle response and high susceptibility to PTZ at the age of 28 days. However, these behavioral changes and high susceptibility to PTZ were improved with development and there were no longer significant difference from controls rats at 56 days of age except the wire maneuver test. These results suggested that neonatal total anoxia could produce transient dysfunction of the developing brain, including increased susceptibility to seizure and behavioral abnormalities.

Cyanide-induced chronic partial asphyxia in vitro: neurochemical abnormalities and reversal by magnesium

Neuronal cortical cell cultures obtained from fetal mice were subjected to increasing concentrations of sodium cyanide (10-500 microM) for 6 days in order to simulate prolonged partial asphyxia. Various neurochemical assays were performed to determine if certain cell types were preferentially more affected. Choline acetyltransferase activity was reduced significantly from control values at cyanide concentrations greater than 100 microM; there were similar reductions on a percentage basis in high-affinity uptake of beta-alanine and GABA and in clonazepam-displaceable benzodiazepine (BDZ) binding which reflected the neuronal BDZ receptor population. Ro5-4864-displaceable BDZ binding, a nonneuronal marker, was increased significantly. More modest reductions were apparent in specific BDZ binding and in protein content. Although a particular vulnerability of a specific cell type was not demonstrated, there was more neurochemical than morphologic evidence of cellular dysfunction. Co-exposure of the cultures to magnesium along with the highest concentrations of cyanide substantially prevented both neurochemical and morphologic abnormalities. These results lend further support to the concept that excitatory neurotransmitters may be implicated in the neuronal damage produced by hypoxia.