Chronic Exposure to E-Cigarettes Elevates CYP2A5 Activity, Protein Expression, and Cotinine-Induced Production of Reactive Oxygen Species in Mice

Coumarin 7'-hydroxylase activity, a specific marker of CYP2A5 activity, and the protein level were measured in liver microsomes of male mice after chronic exposure to e-cigarettes (e-cigs) (2.4% nicotine). After exposure for 240 minutes per day for 5 days, the activity and the protein level in preproenkephalin (ppENK)-heterozygous [ppENK (+/-)] mice were significantly elevated (P <0.05) compared with the untreated control. This elevation was not due to deletion of the ppENK gene because the activity did not differ among untreated ppENK (+/-), ppENK (-/-), and wild-type ppENK (+/+) controls. Hence, the elevation can reasonably be attributed to nicotine exposure. The production of reactive oxygen species (ROS) upon incubation of the hepatic microsomes of these mice with cotinine was higher in microsomes from the e-cig-treated mice compared with the untreated controls (P < 0.01). Liquid chromatography mass spectrometry assay showed three oxidation products of cotinine, viz trans 3'-hydroxycotinine (3'-HC), 5'-hydroxycotinine (5'-HC), and cotinine N-oxide (CNO) in the plasma of these mice. The result identifies these three oxidation reactions as the source of the observed ROS and also shows that, in nicotine-treated mice, the appropriate "nicotine metabolite ratio" is (3'-HC + 5'-HC + CNO)/cotinine. The results suggest intriguing possibilities that 1) this metabolite ratio may correlate with plasma nicotine clearance and hence impact nicotine's psychoactive effects and 2) chronic e-cig treatment causes ROS-induced oxidative stress, which may play a major role in the regulation of CYP2A5 expression. Our present results clearly show that both the activity and the protein level of CYP2A5 are elevated by repeated exposure to nicotine. SIGNIFICANCE STATEMENT: Nicotine, the psychoactive ingredient of tobacco, is eliminated as the oxidation products of cotinine in reactions catalyzed by the enzymes CYP2A5 in mice and CYP2A6 in humans. This study shows that repeated exposure to e-cigarettes elevates the level of CYP2A5 and the formation of reactive oxygen species. The results suggest an intriguing possibility that CYP2A5 may be upregulated by chronic nicotine exposure due to oxidative stress caused by the oxidation of cotinine in this preclinical model of human smokers.

The Impact of Sex on Changes in Plasma Corticosterone and Cotinine Levels Induced by Nicotine in C57BL/6J Mice

We assessed if there were any sex-related differences in the ability of nicotine to increase plasma corticosterone secretion after single or repeated nicotine administration. For single-dose studies, male and female mice were habituated to the test room for 1 h and injected with saline or nicotine (0.25 or 1 mg/kg, subcutaneously (s.c.)). In repeated-dosing studies, mice were injected with saline or nicotine (1 mg/kg, s.c.) once daily for six days, and, on day 7, received nicotine (1 mg/kg, s.c.). Mice were then euthanized 15 min later, and trunk blood was collected for the measurement of corticosterone, nicotine, and cotinine. Our results showed that saline or nicotine each significantly increased plasma corticosterone levels in both males and females, with a greater response in female mice. Plasma corticosterone levels were increased in male but not female mice after being treated repeatedly compared to single nicotine administration. The level of cotinine, a biomarker of nicotine use, was significantly higher in female than in male mice. Taken together, these novel findings suggest that female mice respond to nicotine and the stress of handling more than male mice and provide for the first-time quantitative data on male–female differences in nicotine-induced elevations of corticosterone and cotinine plasma levels.

Faster flux of neurotransmitter glutamate during seizure - Evidence from 13C-enrichment of extracellular glutamate in kainate rat model

The objective is to examine how the flux of neurotransmitter glutamate from neurons to the extracellular fluid, as measured by the rate of ¹³C enrichment of extracellular glutamate (GLU_ECF), changes in response to seizures in the kainate-induced rat model of temporal-lobe epilepsy. Following unilateral intrahippocampal injection of kainate, GLU_ECF was collected by microdialysis from the CA1/CA3 region of awake rats, in combination with EEG recording of chronic-phase recurrent seizures and intravenous infusion of [2,5-¹³C]glucose. The ¹³C enrichment of GLU_ECF C5 at ~ 10 picomol level was measured by gas-chromatography mass-spectrometry. The rate of ¹³C enrichment, expressed as the increase of the fractional enrichment/min, was 0.0029 ± 0.0001/min in frequently seizing rats (n = 4); this was significantly higher (p < 0.01) than in the control (0.00167 ± 0.0001/min; n = 6) or in rats with infrequent seizures (0.00172 ± 0.0001/min; n = 6). This result strongly suggests that the flux of the excitatory neurotransmitter from neurons to the extracellular fluid is significantly increased by frequent seizures. The extracellular [¹²C + ¹³C]glutamate concentration increased progressively in frequently seizing rats. Taken together, these results strongly suggest that the observed seizure-induced high flux of glutamate overstimulated glutamate receptors, which triggered a chain reaction of excitation in the CA3 recurrent glutamatergic networks. The rate of ¹³C enrichment of extracellular glutamine (GLN_ECF) at C5 was 0.00299 ± 0.00027/min in frequently seizing rats, which was higher (p < 0.05) than in controls (0.00227 ± 0.00008/min). For the first time in vivo, this study examined the effects of epileptic seizures on fluxes of the neurotransmitter glutamate and its precursor glutamine in the extracellular fluid of the hippocampus. The advantages, limitations and the potential for improvement of this approach for pre-clinical and clinical studies of temporal-lobe epilepsy are discussed.

Nanostructured titanium phosphates prepared via hydrothermal reaction and their electrochemical Li- and Na-ion intercalation properties

A series of titanium phosphates with various morphologies are fabricated via a simple hydrothermal reaction of TiO₂ in H₃PO₄ aq.

Disinhibition reduces extracellular glutamine and elevates extracellular glutamate in rat hippocampus in vivo

Disinhibition was induced in the hippocampal CA1/CA3 region of normal adult rats by unilateral perfusion of the GABA(A)R antagonist, 4-[6-imino-3-(4-methoxyphenyl)pyridazin-1-yl] butanoic acid hydrobromide (gabazine), or a GABA(B)R antagonist, p-(3-aminopropyl)-p-diethoxymethyl-phosphinic acid (CGP 35348), through a microdialysis probe. Effects of disinhibition on EEG recordings and the concentrations of extracellular glutamate (GLU(ECF)), the major excitatory neurotransmitter, and of extracellular glutamine (GLN(ECF)), its precursor, were examined bilaterally in freely behaving rats. Unilateral perfusion of 10 μM gabazine in artificial CSF of normal electrolyte composition for 34 min induced epileptiform discharges which represent synchronized glutamatergic population bursts, not only in the gabazine-perfused ipsilateral hippocampus, but also in the aCSF-perfused contralateral hippocampus. The concentration of GLU(ECF) remained unchanged, but the concentration of its precursor, GLN(ECF), decreased to 73 ± 4% (n = 5) of the baseline during frequent epileptiform discharges, not only in the ipsilateral, but also in the contralateral hippocampus, where the change can be attributed to recurrent epileptiform discharges per se, with recovery to 95% of baseline when epileptiform discharges diminished. The blockade of GABA(B)R, by CGP 35348 perfusion in the ipsilateral hippocampus for 30 min, induced bilateral Na(+) spikes in extracellular recording. These can reasonably be attributed to somatic and dendritic action potentials and are indicative of synchronized excitatory activity. This disinhibition induced, in both hippocampi, (a) transient 1.6-2.4-fold elevation of GLU(ECF) which correlated with the number of Na(+) spike cluster events and (b) concomitant reduction of GLN(ECF) to ∼ 70%. Intracellular GLN concentration was measured in the hippocampal CA1/CA3 region sampled by microdialysis in separate groups of rats by snap-freezing the brain after 25 min of gabazine perfusion or 20 min of CGP perfusion when extracellular GLN (GLN(ECF)) was 60-70% of the pre-perfusion level. These intracellular GLN concentrations in the disinhibited hippocampi showed no statistically significant difference from the untreated control. This result strongly suggests that the observed decrease of GLN(ECF) is not due to reduced glutamine synthesis or decrease in the rate of efflux of GLN to ECF. This strengthens the likelihood that reduced GLN(ECF) reflects increased GLN uptake into neurons to sustain enhanced GLU flux during excitatory population bursts in disinhibited hippocampus. The results are consistent with the emerging concept that neuronal uptake of GLN(ECF) plays a major role in sustaining epileptiform activities in the kainate-induced model of temporal-lobe epilepsy.

Glucose-6-Phosphate Dehydrogenase in the Pentose Phosphate Pathway Is Localized in Vanadocytes of the Vanadium-Rich Ascidian, Ascidia sydneiensis samea

Ascidians are sessile marine animals known to accumulate high levels of vanadium selectively in vanadium-containing blood cells (vanadocytes). Almost all the vanadium accumulated in the vacuoles of vanadocytes is reduced to the +3 oxidation state via the +4 oxidation state, although vanadium is dissolved in the +5 oxidation state in sea water. Some of the reducing agents that participate in the reduction have been proposed. By chemical study, vanadium in the +5 oxidation state was reported to be reduced to the +4 oxidation state in the presence of NADPH. The present study revealed the existence of glucose-6-phosphodehydrogenase (G6PDH), the first enzyme to produce NADPH in the pentose phosphate pathway, in vanadocytes of a vanadium-rich ascidian. The results suggested that G6PDH conjugates the reduction of vanadium from the +5 through to the +4 oxidation state in vanadocytes of ascidians.

Chronic electrographic seizure reduces glutamine and elevates glutamate in the extracellular fluid of rat brain

Effects of spontaneous seizures on extracellular glutamate and glutamine were studied in the kainate-induced rat model of epilepsy in the chronic phase. Extracellular fluid from the CA1-CA3 regions of the hippocampus was collected with a 2-mm microdialysis probe every 2 min for 5h. EEG seizures with no or mild behavioral components caused 2- to 6-fold elevation of extracellular glutamate. Concomitantly, extracellular glutamine decreased at t=5h to 48% of the initial value (n=6). The changes in extracellular glutamate and glutamine correlated with the frequency and magnitude of seizure activity. In contrast, no change in either metabolite was observed in kainate-injected rats that did not undergo seizure during microdialysis (n=6). In hippocampal tissue (9.4 ± 1.1mg) that contained the region sampled by microdialysis and the site of kainate injection, intracellular glutamine concentration was significantly reduced in the seizure group, compared to that in no-seizure group. The observed elevation of extracellular glutamate strongly suggests that neurotransmitter glutamate was released at a rate faster than the rate of its uptake into glia, possibly due to down-regulation of the transporter. This reduces the availability of substrate glutamate for glutamine synthesis, as corroborated by the observed reduction of intracellular glutamine. This is likely to reduce the rate of glutamine efflux from glia and result in the observed decrease of extracellular glutamine. There remains an intriguing possibility that seizure-induced decrease of extracellular glutamine also reflects its increased uptake into neurons to replenish neurotransmitter glutamate during enhanced epileptiform activity.

Benzoate catalysis in the hydrolysis of endo-5-[4'(5')imidazolyl]-bicyclo[2.2.1]hept-endo- 2-yl trans-cinnamate: Implications for the charge-transfer mechanism of catalysis by serine proteases

The acceleration, by a factor of 2500, of the hydrolysis of endo-5-[4'(5')imidazolyl]bicyclo[2.2.1]hept-endo- 2-yl trans-cinnamate by 0.5 M sodium benzoate in 42 mol% dioxane in water can be explained without resort to operation of a "charge-relay" mechanism similar to that often postulated to account for the enzymatic activity of serine proteases. The degree of ionization of 4-methylimidazole and of sodium benzoate in 42 mol% dioxane in water at 60 degrees C have been measured by NMR spectroscopy.

Kinetics of glial glutamine efflux and the mechanism of neuronal uptake studied in vivo in mildly hyperammonemic rat brain

Kinetics of glial glutamine (GLN) transport to the extracellular fluid (ECF) and the mechanism of GLN(ECF) transport into the neuron--crucial pathways in the glutamine-glutamate cycle--were studied in vivo in mildly hyperammonemic rat brain, by NMR and microdialysis to monitor intra- and extracellular GLN. The minimum rate of glial GLN efflux, determined from the rate of GLN(ECF) increase during perfusion of alpha-(methylamino)isobutyrate (MeAIB), which inhibits neuronal GLN(ECF) uptake by sodium-coupled amino-acid transporter (SAT), was 2.88 +/- 0.22 micromol/g/h at steady-state brain [GLN] of 8.5 +/- 0.8 micromol/g. Our previous study showed that the rate of glutamine synthesis under identical experimental conditions was 3.3 +/- 0.3 micromol/g/h. At steady-state glial [GLN], this is equal to its efflux rate to the ECF. Comparison of the two rates suggests that SAT mediates at least 87 +/- 8% (= 2.88/3.3 x 100%) of neuronal GLN(ECF) uptake. While MeAIB induced > 2-fold elevation of GLN(ECF), no sustained elevation was observed during perfusion of the selective inhibitor of LAT, 2-amino-bicyclo[1,1,2]heptane-2-carboxylic acid (BCH), or of d-threonine, a putative selective inhibitor of ASCT2-mediated GLN uptake. The results strongly suggest that SAT is the predominant mediator of neuronal GLN(ECF) uptake in adult rat brain in vivo.

Suppression of glial glutamine release to the extracellular fluid studied in vivo by NMR and microdialysis in hyperammonemic rat brain

Release of glial glutamine (GLN) to the extracellular fluid (ECF), mainly mediated by the bidirectional system N transporter SN1, was studied in vivo in hyperammonemic rat brain, using (15)N-nuclear magnetic resonance (NMR) to monitor intracellular [5-(15)N]GLN and microdialysis/gradient (1)H-(15)N heteronuclear single-quantum correlation NMR to analyse extracellular [5-(15)N]GLN. GLN(ECF) was elevated to 2.4 +/- 0.2 mm after 4.5 h of intravenous ammonium acetate infusion. The [GLN(i)]/[GLN(ECF)] ratio (i = intracellular) was 9.6 +/- 0.9, compared with 17-20 in normal brain. GLN(ECF) then decreased substantially at t = 4.9 +/- 0.1 h. Comparison of the time-courses of intra- and extra-cellular [5-(15)N]GLN strongly suggested that the observed decrease reflects partial suppression of glial GLN release to ECF. Suppression also followed elevation of GLN(ECF) to 1.9 mM, resulting in a [GLN](i)/[GLN(ECF)] ratio of 8.4, upon perfusion of alpha-(methylamino)isobutyrate which inhibits neuronal uptake of GLN(ECF) mediated by sodium-coupled amino acid transporter (SAT). The results provide first evidence for bidirectional operation of SN1 in vivo, and clarify the effect of transmembrane GLN gradient on glial GLN release at physiological Na(+) gradient. Implications of the results for SN1 as an additional regulatory site in the glutamine/glutamate cycle and utility of this approach for examining the role of GLN in an experimental model of fulminant hepatic failure are discussed.

Quantitative determination of extracellular glutamine concentration in rat brain, and its elevation in vivo by system A transport inhibitor, alpha-(methylamino)isobutyrate

The basal concentration of glutamine in the extracellular fluid, [GLN(ECF)], was determined to be 385 +/- 16 microm in the cortico-striatal region of awake rats. This in vivo concentration was determined by measuring glutamine concentrations in dialysates collected at several flow rates (0.2-4 microL/min), and extrapolating to the concentration at zero flow-rate. Dialysate glutamine concentrations in the somatosensory cortex, hippocampus and thalamus showed no statistically significant difference. In these brain regions, [GLN(ECF)] was elevated 1.5- to 1.8-fold upon perfusion of 50-250 mmalpha-(methylamino)isobutyrate (MeAIB), a competitive inhibitor of glutamine uptake by system A amino acid transporter. The results show, for the first time, that MeAIB causes elevation of brain GLN(ECF)in vivo. The MeAIB-induced elevation of [GLN(ECF)] provides additional support for the current view that system A GLN transporter (Gln T/SAT 1) is the major pathway for the uptake of GLN(ECF) by neurons, while GLN release from glia is mainly mediated by a system N transporter (SN1) which is not inhibitable by MeAIB. The steady-state GLN(ECF) concentration and the effectiveness of MeAIB in inhibiting neuronal GLN uptake in vivo, reported in this study, will be useful, when combined with the known in vitro kinetic properties of the GLN transporters, for study of GLN transport in the intact brain.

13C enrichment of extracellular neurotransmitter glutamate in rat brain--combined mass spectrometry and NMR studies of neurotransmitter turnover and uptake into glia in vivo

13C-enrichment analysis of glutamate in the extracellular fluid (GLU(ECF): 2-3 microM) by gas-chromatography/mass-spectrometry (GCMS) was combined with in vivo NMR observation of whole-brain GLU (approximately10 mM) to study neurotransmitter uptake. Brain GLU C5 was 13C-enriched by intravenous [2,5-13C]glucose infusion. GLU(ECF) was collected by microdialysis from the cortico-striatal region of awake rats. The 13C-enrichment of basal dialysate GLU C5 during 0.75-1.25 hr of infusion was 0.263 +/- 0.01, very close to the enrichment of whole-brain GLU C5. The result strongly suggests that dialysate GLU consists predominantly of neurotransmitter GLU. For selective 13C-enrichment of neurotransmitter GLU, the whole-brain 13C-enrichment was followed by [12C]glucose infusion to chase 13C from the small glial GLU pool. This leaves [5-13C]GLU mainly in the large neuronal metabolic pool and the vesicular neurotransmitter pool. The uptake of synaptic [5-13C]GLU(ECF) into glia and metabolism to glutamine (GLN) were monitored in vivo by NMR observation of [5-13C,15N]GLN formed during 15NH4Ac infusion. The rate of GLN synthesis, derived from neurotransmitter GLU(ECF) (which provided 80-90% of the substrate) was 6.4 +/- 0.44 micromol/g/hr. Hence, the observed rate represents a reasonable estimate for the rate of glial uptake of GLU(ECF), a process that is crucial for protecting the brain from GLU excitotoxicity.

Glial uptake of neurotransmitter glutamate from the extracellular fluid studied in vivo by microdialysis and (13)C NMR

Glial uptake of neurotransmitter glutamate (GLU) from the extracellular fluid was studied in vivo in rat brain by (13)C NMR and microdialysis combined with gas-chromatography/mass-spectrometry. Brain GLU C5 was (13)C enriched by intravenous [2,5-(13)C]glucose infusion, followed by [(12)C]glucose infusion to chase (13)C from the small glial GLU pool. This leaves [5-(13)C]GLU mainly in the large neuronal metabolic pool and the vesicular neurotransmitter pool. During the chase, the (13)C enrichment of whole-brain GLU C5 was significantly lower than that of extracellular GLU (GLU(ECF)) derived from exocytosis of vesicular GLU. Glial uptake of neurotransmitter [5-(13)C]GLU(ECF) was monitored in vivo through the formation of [5-(13)C,(15)N]GLN during (15)NH(4)Ac infusion. From the rate of [5-(13)C,(15)N]GLN synthesis (1.7 +/- 0.03 micromol/g/h), the mean (13)C enrichment of extracellular GLU (0.304 +/- 0.011) and the (15)N enrichment of precursor NH(3) (0.87 +/- 0.014), the rate of synthesis of GLN (V'(GLN)), derived from neurotransmitter GLU(ECF), was determined to be 6.4 +/- 0.44 micromol/g/h. Comparison with V(GLN) measured previously by an independent method showed that the neurotransmitter provides 80-90% of the substrate GLU pool for GLN synthesis. Hence, under our experimental conditions, the rate of 6.4 +/- 0.44 micromol/g/h also represents a reasonable estimate for the rate of glial uptake of GLU(ECF), a process that is crucial for protecting the brain from GLU excitotoxicity.

In vivo microdialysis and gas-chromatography/mass-spectrometry for 13C-enrichment measurement of extracellular glutamate in rat brain

Extracellular glutamate (GLU(ECF)) was collected by microdialysis from the corticostriatal region of awake rats, at the basal level and after elevation by perfusion of GLU uptake inhibitor, L-trans-pyrrolidine-2,4-dicarboxylic acid. Concurrently, [2,5-(13)C]glucose was infused intravenously to 13C-enrich brain GLU predominantly at C5. The 13C enrichment of GLU(ECF) was measured, after tert-butyldimethylsilylation, by gas-chromatography/mass-spectrometry. Excellent signal-to-noise ratios of the analyte signals at three selected ion-pairs were achieved at approximately 20 pmol. The fractional 13C enrichment of basal dialysate GLU C5, collected during 0.75-1.25 h of [2,5-(13)C]glucose infusion, was 0.263+/-0.01, very close to the enrichment of whole-brain (predominantly intracellular) GLU C5 measured in parallel NMR study. The result strongly suggests that the dialysate GLU consists predominantly of neurotransmitter GLU, which was 13C-enriched in, and released from, neurons by exocytosis and had diffused to the dialysis probe; the label is undiluted by 12C-GLU(ECF) present before the enrichment. Hence, our result supports the view, proposed on the basis of Ca(2+)- and tetrodotoxin-sensitivity of dialysate GLU, that basal dialysate GLU in awake non-stimulated brain mainly represents neurotransmitter GLU. Isotope labeling provides a novel method for determining the extent to which dialysate GLU reflects synaptic GLU(ECF), and for measuring its turnover under physiological or pathological conditions.

The first in vivo observation of (13)C-(15)N coupling in mammalian brain

[5-(13)C,(15)N]Glutamine, with (1)J((13)C-(15)N) of 16 Hz, was observed in vivo in the brain of spontaneously breathing rats by (13)C MRS at 4.7 T. The brain [5-(13)C]glutamine peak consisted of the doublet from [5-(13)C,(15)N]glutamine and the center [5-(13)C,(14)N]glutamine peak, resulting in an apparent triplet with a separation of 8 Hz. The time course of formation of brain [5-(13)C,(15)N]glutamine was monitored in vivo with a time resolution of 20-35 min. This [5-(13)C,(15)N]glutamine was formed by glial uptake of released neurotransmitter [5-(13)C]glutamate and its reaction with (15)NH(3) catalyzed by the glia-specific glutamine synthetase. The neurotransmitter glutamate C5 was selectively (13)C-enriched by intravenous [2,5-(13)C]glucose infusion to (13)C-label whole-brain glutamate C5, followed by [(12)C]glucose infusion to chase (13)C from the small and rapidly turning-over glial glutamate pool, leaving (13)C mainly in the neurotransmitter [5-(13)C]glutamate pool, which is sequestered in vesicles until release. Hence, the observed [5-(13)C,(15)N]glutamine arises from a coupling between (13)C of neuronal origin and (15)N of glial origin. Measurement of the rate of brain [5-(13)C,(15)N]glutamine formation provides a novel noninvasive method of studying the kinetics of neurotransmitter uptake into glia in vivo, a process that is crucial for protecting the brain from glutamate excitotoxicity.

Syntheses, structures, stability, and insulin-like activities of peroxovanadium(V) complexes with a heteroligand

Several peroxovanadium(V) complexes were prepared with a tripodal or a quasi-tripodal tetradentate ligand. The structures of K(2)[VO(O(2))(nta)].2H(2)O and K[VO(O(2))(DL-cmhist)].H(2)O have been determined by X-ray crystallography (nta, nitrilotriacetate; cmhist, N-carboxymethylhistidinate). The structure of Cs[VO(O(2))(pda)].2H(2)O (pda, N-pyridylmethyliminodiacetate) has been estimated to be similar to that of K[VO(O(2))(DL-cmhist)].H(2)O. Each complex anion in these compounds adopts a distorted pentagonal bipyramidal structure, which is typical for heptacoordinate oxoperoxovanadium(V) complexes. The peroxide ion binds in a side-on fashion to the vanadium(V) center in the pentagonal plane. The peroxide anion in the cmhist complex dissociates rather easily in an acidic solution (pH approximately 3), while that in the other complexes stays intact under similar conditions. The in vitro insulin mimetic effect of the peroxovanadium(V) complexes has been evaluated by the inhibitory effect on free fatty acid (FFA) release in isolated rat adipocytes treated with epinephrine. The cmhist complex is effective, while the others are almost totally ineffective.

Subunit C of the vacuolar-type ATPase from the vanadium-rich ascidian Ascidia sydneiensis samea rescued the pH sensitivity of yeast vma5 mutants

A vanadium-accumulating ascidian, Ascidia sydneiensis samea, expresses vacuolar-type H(+)-ATPases (V-ATPases) on the vacuole membrane of the vanadium-containing blood cells known as vanadocytes. Previously, we showed that the contents of their vacuoles are extremely acidic and that a V-ATPase-specific inhibitor, bafilomycin A(1), neutralized the contents of the vacuoles. To understand the function of V-ATPase in vanadocytes, we isolated complementary DNA encoding subunit C of V-ATPase from vanadocytes because this subunit has been known to be responsible for the assembly of V-ATPases and to regulate the ATPase activity of V-ATPases. The cloned cDNA was 1443 nucleotides in length, and encoded a putative 384 amino acid protein. By expressing the ascidian cDNA for subunit C under the control of a galactose-inducible promoter, the pH-sensitive phenotype of the corresponding vma5 mutant of a budding yeast was rescued. This result showed that the ascidian cDNA for subunit C functioned in yeast cells.

Exclusive expression of transketolase in the vanadocytes of the vanadium-rich ascidian, Ascidia sydneiensis samea

Ascidians, especially those belonging to the Ascidiidae, are known to accumulate extremely high levels of vanadium in vanadocytes, one type of blood (coelomic) cell. Vanadium, which exists in the +5 oxidation state in seawater, is accumulated in the vanadocytes and reduced to the +3 oxidation state. We have been trying to characterize all of the polypeptides specific to vanadocytes and to specify the proteins that participate in the accumulation and reduction of vanadium. To date, we have localized three enzymes in vanadocytes: 6-phosphogluconate dehydrogenase (6-PGDH: EC 1.1.1.44), glucose-6-phosphate dehydrogenase (G6PDH: EC 1.1.1.49), and glycogen phosphorylase (GP: EC 2.4.1.1), all of which are involved in the pentose phosphate pathway. In the current study, we cloned a cDNA for transketolase, an essential and rate-limiting enzyme in the non-oxidative part of the pentose phosphate pathway, from vanadocytes. The cDNA encoded a protein of 624 amino acids, which showed 61.8% identity to the human adult-type transketolase gene product. By immunocytochemistry and immunoblot analyses, the transketolase was revealed to be a protein that was expressed only in vanadocytes and not in any of the more than ten other types of blood cell. This finding, taken together with the localized expression of the other three enzymes, strongly supports the hypothesis that the pentose phosphate pathway functions exclusively in vanadocytes.

[{Pt]

Prolonged evacuation of [{Pt(CO)(3)}(2)](2+) (1), the first homoleptic, dinuclear, cationic platinum(I) carbonyl complex, results in reversible disproportionation. Complex 1 was formed by dissolution of PtO(2) in concentrated H(2)SO(4) under an atmosphere of CO [Eq. (a)], and completely characterized by NMR ((13)C, (195)Pt), IR, and Raman spectroscopy.

In vivo detection of (15)N-coupled protons in rat brain by ISIS localization and multiple-quantum editing

Three-dimensional image-selected in vivo spectroscopy (ISIS) was combined with phase-cycled (1)H-(15)N heteronuclear multiple-quantum coherence (HMQC) transfer NMR for localized selective observation of protons J-coupled to (15)N in phantoms and in vivo. The ISIS-HMQC sequence, supplemented by jump-return water suppression, permitted localized selective observation of 2-5 micromol of [(15)N(indole)]tryptophan, a precursor of the neurotransmitter serotonin, through the (15)N-coupled proton in 20-40 min of acquisition in vitro at 4.7 T. In vivo, the amide proton of [5-(15)N]glutamine was selectively observed in the brain of spontaneously breathing (15)NH(4)(+)-infused rats, using a volume probe with homogeneous (1)H and (15)N fields. Signal recovery after three-dimensional localization was 72-82% in phantoms and 59 +/- 4% in vivo. The result demonstrates that localized selective observation of (15)N-coupled protons, with complete cancellation of all other protons except water, can be achieved in spontaneously breathing animals by the ISIS-HMQC sequence. This sequence performs both volume selection and heteronuclear editing through an addition/subtraction scheme and predicts the highest intrinsic sensitivity for detection of (15)N-coupled protons in the selected volume. The advantages and limitations of this method for in vivo application are compared to those of other localized editing techniques currently in use for non-exchanging protons.

Localized 15N NMR spectroscopy of rat brain by ISIS

Three-dimensional image-selected in vivo spectroscopy (ISIS), combined with proton-decoupled nuclear-Overhauser-enhanced 15N nuclear magnetic resonance (NMR), was used to localize [15N]metabolites, observed by a head coil, to the brain in rats. In spontaneously breathing anesthetized rats given intravenous [15N]ammonium acetate infusion, brain [5-15N]glutamine was observed in the localized spectrum with a v1/2 of 5 Hz in 19-28 min at 4.7 T, while the signal from blood [15N]urea was eliminated by the localization process. In rats given [15N]leucine infusion, the peak representing predominantly (89%) brain [15N]glutamate was observed, with elimination of the signal from muscle [15N]alanine. In vivo peak areas of the brain [15N]metabolites in the localized spectra were proportional to their concentrations. The advantages and limitations of localization by ISIS using a volume coil with a homogeneous B1 field are compared with those of localization by a surface coil for in vivo 15N NMR study of neurotransmitters in the brain.

A new insulin-mimetic vanadyl complex, (N-pyridylmethylaspartate)oxovanadium(IV) with VO(N2O2) coordination mode, and evaluation of its effect on uptake of D-glucose by Ehrlich ascites tumour cells

Because it has been confirmed that the vanadyl(IV) ion and its complexes act as insulin mimetics, a new organic vanadyl complex, (N-pyridylmethylaspartate)oxovanadium (VOPASP) with VO(N2O2) coordination mode, was prepared. Development of a simple and rapid in-vitro assay is needed for recognition of potent insulin-mimetic complexes. Treatment of Ehrlich ascites tumour cells with 2-deoxyglucose in the presence of vanadyl sulphate, or other vanadyl complexes with the same coordination mode (VOPASP, bis(picolinate)oxovanadium (VOPA) and bis(6-methyl picolinate)oxovanadium (VOMPA)), in the presence of 2-deoxy-D-[1-3H]glucose ([3H]deoxyglucose), resulted in concentration-dependent uptake of 2-deoxyglucose by the cells. The responses of the cells to the vanadyl complexes were reflected, in part, by results obtained from the free fatty acid-releasing assay using rat adipocytes. These results show that the in-vitro assay with Ehrlich ascites tumour cells provides an accurate and rapid assessment of glucose uptake by the cells. The assay is proposed as a means of predicting the insulin-mimetic activity of the vanadyl complexes and for studying the mechanism of action of the complexes.

6-Phosphogluconate dehydrogenase is a 45-kDa antigen recognized by S4D5, a monoclonal antibody specific to vanadocytes in the vanadium-rich ascidian Ascidia sydneiensis samea

We previously prepared a monoclonal antibody, S4D5, specific to vanadocytes, vanadium-containing blood cells, in the vanadium-rich ascidian Ascidia sydneiensis samea. Here, we demonstrate that a 45-kDa antigen recognized by S4D5 is 6-phosphogluconate dehydrogenase (6-PGDH), an enzyme of the pentose phosphate pathway, based on cDNA isolation of RNA samples from blood cells of the ascidian. Western blot analysis confirmed an abundance of 6-PGDH protein in the vanadocytes and localization of 6-PGDH in the soluble extract of the blood cells. Soluble protein exhibited a correspondingly high level of 6-PGDH enzymatic activity. Ascidians are known to selectively accumulate high levels of vanadium in vanadocytes, and the highest recorded concentration of accumulated vanadium is 350 mM, which is 10(7) times the concentration in sea water. Almost all vanadium ions are reduced to the +3 oxidation state via the +4 oxidation state in vanadocytes, indicating that reducing agents must participate in the accumulation. On the other hand, vanadium ions in the +5 oxidation state are reduced to the +4 oxidation state by the presence of NADPH in vitro. Together, these observations suggest that NADPH produced in the pentose phosphate pathway may conjugate the reduction of vanadium from the +5 oxidation state through the +4 oxidation state in vanadocytes of ascidians.

Rate of glutamate synthesis from leucine in rat brain measured in vivo by 15N NMR

The rate of glutamate synthesis from leucine by the branched-chain aminotransferase was measured in rat brain in vivo at steady state. The rats were fed exclusively by intravenous infusion of a nutrient solution containing [15N]leucine. The rate of glutamate synthesis from leucine, determined from the rate of increase of brain [15N]glutamate measured by 15N NMR and the 15N enrichments of brain and blood leucine analyzed by gas chromatography-mass spectrometry, was 0.7-1.8 micromol/g/h at a steady-state brain leucine concentration of 0.25 micromol/g. A comparison of the observed fractional 15N enrichments of brain leucine (0.42 +/- 0.03) and glutamate (0.21 +/- 0.015) showed that leucine provides approximately 50% of glutamate nitrogen under our experimental condition. From the observed rate (0.7-1.8 micromol/g) and the known Km of the branched-chain aminotransferase for leucine (1.2 mM), the rate of glutamate synthesis from leucine at physiological brain leucine concentration (0.11 micromol/g) was estimated to be 0.35-0.9 micromol/g/h, with leucine providing approximately 25% of glutamate nitrogen. The results strongly suggest that plasma leucine from dietary source, transported into the brain, is an important external source of nitrogen for replenishment of brain glutamate in vivo. Implications of the results for treatment of maple-syrup urine disease patients with leucine-restricted diet are discussed.

Glial alkalinization detected in vivo by 1H-15N heteronuclear multiple-quantum coherence-transfer NMR in severely hyperammonemic rat

Brain [5-15N] glutamine amide protons were selectively observed in vivo by 1H-15N heteronuclear multiple-quantum coherence-transfer NMR in spontaneously breathing, severely hyperammonemic rats during intravenous [15N]ammonium acetate infusion and the subsequent recovery period. The linewidth of brain [5-15N]-glutamine amide proton Hz increased from 36 +/- 2 Hz at 3.4 h to 58 +/- 6 Hz after 5.7 h of infusion, a net increase of 22 +/- 6 Hz. Concomitantly, brain ammonia concentration increased from 1.7 to 3.5 +/- 0.2 mumol/g and the rat progressed from grade III to grade IV encephalopathy. On recovery to grade III and decrease of brain ammonia concentration to 1.3 mumol/g, the linewidth returned to 37 +/- 2 Hz. In aqueous solution, [5-15N]glutamine amide proton Hz underwent a 17-Hz linebroadening when pH was raised from 7.1 to 7.5 at 37 degrees C, due to the increased rate of base-catalyzed exchange with water proton. Hence, linebroadening is a sensitive measure of changing intracellular pH. The 22-Hz linebroadening observed in vivo in severely hyperammonemic grade IV rats strongly suggests that the intracellular pH increases from 7.1 to about 7.4-7.5 in astrocytes where glutamine is synthesized and mainly stored. Probable mechanisms for the ammonia-induced alkalinization and decreased intraglial buffering capacity, as well as implications of the result for pathogenesis of hepatic encephalopathy, are discussed.

Severity of hyperammonemic encephalopathy correlates with brain ammonia level and saturation of glutamine synthetase in vivo

Correlation among in vivo glutamine synthetase (GS) activity, brain ammonia and glutamine concentrations, and severity of encephalopathy was examined in hyperammonemic rats to obtain quantitative information on the capacity of GS to control these metabolites implicated in the etiology of hepatic encephalopathy. Awake rats were observed for neurobehavioral impairments after ammonium acetate infusion to attain a steady-state blood ammonia concentration of 0.9 (group A) or 1.3 mumol/g (group B). As encephalopathy progressed from grade III to IV, brain ammonia concentration increased from 1.9 to 3.3 mumol/g and then decreased to 1.3 mumol/g on recovery to grade III. In contrast, brain glutamine concentration was 26, 23, and 21 mumol/g, respectively. NH(4+)-infused rats pretreated with L-methionine DL-sulfoximine reached grade IV when brain ammonia and glutamine concentrations were 3.0 and 5.5 mumol/g, respectively; severity of encephalopathy correlates with brain ammonia, but not glutamine. In vivo GS activity, measured by NMR, was 6.8 +/- 0.7 mumol/h/g for group A and 6.2 +/- 0.6 mumol/h/g for group B. Hence, the in vivo activity, shown previously to increase with blood ammonia over a range of 0.4-0.64 mumol/g, approaches saturation at blood ammonia > 0.9 mumol/g. This is likely to be the major cause of the observed accumulation of brain ammonia and the onset of grade IV encephalopathy.

[Effects of pulmonary rehabilitation in patients with chronic respiratory failure]

To evaluate the effects of pulmonary rehabilitation in patients with chronic respiratory failure, 43 patients with stable chronic respiratory failure were enrolled in a pulmonary rehabilitation program. The program included education, instruction in diaphragmatic breathing, respiratory muscle training, and exercise training (walking and riding a stationary bicycle). Patients were divided into 2 groups by the lowest SpO2 during a 12-minute-walk test done before rehabilitation: lowest SpO2 < 90% (Group A, 32 patients) and lowest SpO2 > or = 90% (Group B, 11 patients). In group A, SpO2 during exercise training was maintained over 90% by O2 inhalation, by load reduction, or by maintaining a slower walking speed. During 2 months of rehabilitation, the distance walked in 12 minutes and the maximum distance walked with an SpO2 > or = 90% significantly increased in both groups, but PaO2, VC, and FEV1 increased only in group A. In group A, the patients with chronic obstructive pulmonary disease had significant increases in PaO2, VC, and FEV1, but those with old tuberculosis sequelae had significant increases in PaO2 only. Pulmonary rehabilitation in patients with chronic respiratory failure may not only increase exercise tolerance but may also improve arterial oxygenation and pulmonary function.

Steady-state in vivo glutamate dehydrogenase activity in rat brain measured by 15N NMR

The in vivo activity of glutamate dehydrogenase (GDH) in the direction of reductive amination was measured in rat brain at steady-state concentrations of brain ammonia and glutamate after intravenous infusion of the substrate 15NH4+. The in vivo rate was determined from the steady-state fractional 15N enrichment of brain ammonia, measured by selective observation of 15NH4+ protons in brain extract by 1H-15N heteronuclear multiple-quantum coherence transfer NMR, and the rate of increase of brain [15N]glutamate and [2-15N]glutamine measured by 15N NMR. The in vivo GDH activity was 0.76-1.17 mumol/h/g, and 1.1-1.2 mumol/h/g at 1.0 +/- 0.17 mumol/g. Comparison of the observed in vivo GDH activity with the in vivo rates of glutamine synthesis and of phosphate-activated glutaminase suggests that, under mild hyperammonemia, GDH-catalyzed de novo synthesis can provide a minimum of 19% of the glutamate pool that is recycled from neurons to astrocytes through the glutamate-glutamine cycle.

Dependence of in vivo glutamine synthetase activity on ammonia concentration in rat brain studied by 1H - 15N heteronuclear multiple-quantum coherence-transfer NMR

The dependence of the in vivo rate of glutamine synthesis on the substrate ammonia concentration was studied in rat brain by 1H-15N heteronuclear multiple-quantum coherence-transfer NMR in combination with biochemical techniques. In vivo rates were measured at various steady-state blood and brain ammonia concentrations within the ranges 0.4-0.55 mumol/g and 0.86-0.98 mumol/g respectively, after low-rate intravenous 15NH4+ infusion (isotope chase). The rate of glutamine synthesis at steady state was determined from the change in brain [5-15N]glutamine levels during isotope chase, observed selectively through the amide proton by NMR, and 15N enrichments of brain glutamine and of blood and brain ammonia measured byN gas chromatography-MS. The in vivo rate (v) was 3.3-4.5 mumol/h per g of brain at blood ammonia concentrations (s) of 0.40-0.55 mumol/g. A linear increase of 1/v with 1/s permitted estimation of the in vivo glutamine synthetase (GS) activity at a physiological blood ammonia concentration to be 0.4-2.1 mumol/h per g. The observed ammonia-dependence strongly suggests that, under physiological conditions, in vivo GS activity is kinetically limited by sub-optimal in situ concentrations of ammonia as well as glutamate and ATP. Comparison of the observed in vivo GS activity with the reported in vivo rates of glutaminase and of gamma-aminobutyrate (GABA) synthesis suggests that, under mildly hyperammonaemic conditions, glutamine is synthesized at a sufficiently high rate to serve as a precursor of GABA, but glutaminase-catalysed hydrolysis of glutamine is too slow to be the sole provider of glutamate used for GABA synthesis.

Selective, in vivo observation of [5-15N]glutamine amide protons in rat brain by 1H-15N heteronuclear multiple-quantum-coherence transfer NMR

The amide protons of [5-15N]glutamine were selectively observed in vivo in the brains of anesthetized, spontaneously breathing rats after intravenous 15NH4+ infusion by 1H-15N heteronuclear multiple-quantum-coherence (HMQC) transfer NMR at 200 MHz for 1H. The peak intensity of the upfield amide proton was proportional to brain [5-15N]glutamine concentration. The 15N-decoupled amide-proton signal was observed in vivo in 2 min of acquisition at a brain [5-15N]glutamine concentration of 7.7 +/- 0.4 mumol/g, in < 8 min at 4.35 +/- 0.15 mumol/g, and in 17-34 min at 2.0 +/- 0.1 mumol/g. 1H signals not coupled to 15N were suppressed by phase cycling. The result suggests that 1H-15N HMQC will be useful for kinetic study of glutamine synthesis in rat brain in vivo at physiological concentrations of brain ammonia.

In vivo activity of glutaminase in the brain of hyperammonaemic rats measured by 15N nuclear magnetic resonance

The in vivo activity of phosphate-activated glutaminase (PAG) was measured in the brain of hyperammonaemic rat by 15N n.m.r. Brain glutamine was 15N-enriched by intravenous infusion of 15NH4+ until the concentration of [5-15N]glutamine reached 6.1 mumol/g. Further glutamine synthesis was inhibited by intraperitoneal injection of methionine-DL-sulphoximine, an inhibitor of glutamine synthetase, and the infusate was changed to 14NH4+ during observation of decrease in brain [5-15N]glutamine due to PAG and other glutamine utilization pathways. Progressive decrease in brain [5-15N]glutamine, PAG-catalysed production of 15NH4+ and its subsequent assimilation into glutamate by glutamate dehydrogenase were monitored in vivo by 15N n.m.r. Brain [5-15N]glutamine (15N enrichment of 0.35-0.50) decreased at a rate of 1.2 mumol/h per g of brain. The in vivo PAG activity, determined from the observed rate and the quantity of 15NH4+ produced and subsequently assimilated into glutamate and aspartate, was 0.9-1.3 mumol/h per g. This activity is less than 1.1% of the reported activity in vitro measured in rat brain homogenate at a 10 mM concentration of the activator Pi. Inhibition by ammonia (brain level 1.4 mumol/g) alone does not account for the observed low activity in vivo. The result strongly suggests that, in intact brain, PAG activity is maintained at a low level by a suboptimal in situ concentration of Pi and the strong inhibitory effect of glutamate. The observed PAG activity in vivo is lower than the reported in vivo activity of glutamate decarboxylase which converts glutamate into gamma-aminobutyrate (GABA). The result suggests that PAG-catalysed hydrolysis of glutamine is not the sole provider of glutamate used for GABA synthesis.

[Effects of inhaled furosemide after indomethacin premedication on bronchial hyperresponsiveness in patients with chronic congestive heart failure]

We studied the effects of inhaled furosemide (40 mg) on bronchial responsiveness to acetylcholine (ACh) in patients with chronic congestive heart failure who had been premedicated with indomethacin (75 mg/day) for five days. The measurement of bronchial responsiveness was performed by inhaling doses of ACh and calculating the provocative concentration of ACh needed to cause a 20% fall in FEV1.0 (PC20-ACh). Inhaled furosemide (N = 11) had no effect on resting pulmonary function but did cause a significant increase in the median value of PC20-ACh, from 7.58 to 11.9 mg/ml (p < 0.01). Irrespective of premedication with indomethacin, inhaled furosemide reduces bronchial hyperresponsiveness to ACh in patients with chronic congestive heart failure. Therefore, we speculate that the mechanism of bronchial hyperresponsiveness noticed in our patients is not related to prostaglandins such as PGE2 or PGI2.