Glucose metabolism in the developing cerebral cortex as detected by 1H(13C) nuclear magnetic resonance spectroscopy ex vivo

Metabolism of [1-13C]glucose was monitored in superfused cerebral cortex slice preparations from 1-, 2-, and 5-week-old rats using 1H-observed/13C-edited (1H(13C)) NMR spectroscopy. The rate of label incorporation into glutamate C-4 did not differ among the three age groups: 0.52-0.67% of total 1H NMR-detected glutamate/min. This was rather unexpected, as oxygen uptake proceeded at 1.1 +/- 0.1, 1.9 +/- 0.1, and 2.0 +/- 0.1 mumol/min/g wet weight in brain slices prepared from 1-, 2-, and 5-week-old animals, respectively. Steady-state glutamate C-4 fractional enrichments in the slice preparations were approximately 23% in all age groups. In the acid extracts of slices glutamate C-4 enrichments were smaller, however, in 1- and 2-week-old (17.8 +/- 1.7 and 16.8 +/- 0.8%, respectively) than in 5-week-old rats (22.7 +/- 0.7%) after 75 min of incubation with 5 mM [1-13C]glucose. We add a new assignment to the 1H(13C) NMR spectroscopy, as acetate C-2 was detected in slice preparations from 5-week-old animals. In the acid extracts of slice preparations acetate C-2 was labeled by approximately 30% in 5-week-old rats but by 15% in both 1- and 2-week-old animals, showing that the turnover rate was increased in 5-week-old animals. In the extracts 3-4% of the C-6 of N-acetyl-aspartate (NAA; CH3 of the acetyl group) contained label as determined by both NMR and mass spectrometry, which indicated that there was no significant labeling to other carbons in NAA.(ABSTRACT TRUNCATED AT 250 WORDS)

Spectral lineshape determination by self-deconvolution

A data-processing method is described for the determination of spectral lineshapes using deconvolution of the data with an initial estimate of the same spectrum, referred to as self-deconvolution. The method is demonstrated using computer-simulation studies and experimental data, and is shown to accurately determine amplitude and phase lineshape distortions which may be caused by field inhomogeneity and gradient eddy-current effects. The results indicate that the method is robust in the presence of noise and errors in the initial spectral estimate. Once the spectral lineshape is determined it can be incorporated into a parametric spectral-analysis procedure, thereby reducing the number of parameters to be determined and improving the accuracy of the fit. A proposed application of the method is for spatially resolved in vivo NMR studies where local susceptibility effects and gradient eddy-current effects cause significant deviation of the spectral lineshape from a Lorentzian lineshape.

Cerebral white matter in the centrum semiovale exhibits a larger N-acetyl signal than does gray matter in long echo time 1H-magnetic resonance spectroscopic imaging

Long echo time (272 ms) 1H magnetic resonance spectroscopic imaging was used to measure the relative magnitudes of the N-acetylaspartate (NAA) signal in a variety of anatomically defined brain structures (centrum semiovale, thalamus, medial frontal cortex, and genu of the corpus callosum) composed primarily of gray matter or white matter. Six normal young adult humans aged 30-40 were studied. With a 95% level of statistical confidence, the white matter in the centrum semiovale (CSO) produced a more intense NAA signal than did the gray matter in the thalamus and the frontal cortex. Differences between the white matter regions were also noted. The CSO white matter's NAA signal yielded a larger NAA signal than did the white matter of the genu of the corpus callosum. Possible reasons for the anatomical variation in the cerebral NAA signal intensity are discussed.

Polymorphic amino acid variations in HLA-DQ are associated with systematic physical property changes and occurrence of IDDM. Members of the Swedish Childhood Diabetes Study

The association between human leukocyte antigen (HLA) and insulin-dependent diabetes was studied in a large population-based investigation using genotyping of 425 new-onset patients, 0-14 years of age, and 367 matched control subjects. As many as 97% of patients compared with 75% of control subjects were positive for one or several of DQA1*0301, DQA1*0501, DQB1*0302, or DQB1*0201. Asp-57 DQB was present among 28% of patients, indicating that this residue alone does not confer protection. Combining Asp-57 DQB1 with either Arg-52 DQA1 or Leu-69 DQA1 did not explain susceptibility or protection either. DQA1*0301-DQB1*0302 (DQ8) and DQA1*0301-DQB1*0301 (DQ7) are identical except for four amino acid substitutions in the beta-chain, but DQ8 was positively (odds ratio 8.07; P < 0.001) and DQ7 negatively (odds ratio 0.38; P < 0.001) associated with the disease. Molecular modeling was used to determine whether physiochemical properties such as steric factors and surface electrostatic potentials also differ in a systematic way for various DQ molecules. Amino acids were substituted systematically at the four polymorphic sites, and the solvent-accessible surfaces and electrostatic potentials were computed for each molecule. Dramatic alterations in electrostatic potential were seen for double substitutions at position 45 (G45E) and 57 (A57D) of DQB1. The variation of physicochemical properties due to polymorphic substitutions may be significant to the mechanism of HLA-DQ association with insulin-dependent diabetes, via the effect these property variations have on peptide antigen binding selectivity and subsequent interactions with specific T-cell receptors.

Proton magnetic resonance spectroscopy and gadolinium-DTPA perfusion imaging of asymptomatic MRI white matter lesions

In the elderly, asymptomatic white matter hyperintensities are common on T2-weighted magnetic resonance imaging (MRI). In symptomatic patients, such MRI appearances correlate with varied postmortem findings including demyelination or stroke. What structural correlates underlie the T2 hyperintensities in patients whose lesions are asymptomatic is controversial. Therefore, in order to investigate the underlying metabolism and perfusion in white matter lesions (exhibiting T2 hyperintensity), 13 patients underwent proton magnetic resonance spectroscopy and dynamic gadolinium-DTPA perfusion-weighted MR imaging. N-acetyl aspartate (NA) levels were reduced in the lesions compared with age-matched controls (P = 0.031), implying neuronal/axonal loss. Creatine levels were also reduced (P = 0.001). Choline levels were unchanged in the lesions. Lactate was identified in the lesions of 5 of the 13 patients. Although not statistically significant, perfusion studies exhibited a trend toward lower cerebral blood volumes in patients with high grade extracranial carotid stenosis and lactate-containing lesions. These findings suggest that neuronal/axonal loss underlies the majority of T2-weighted asymptomatic lesions in the older population, and in many cases these changes may be due to chronic ischemia.

Metabolic abnormalities and grade of encephalopathy in acute hepatic failure

Acute hepatic failure is associated with many biochemical abnormalities in plasma and brain. Changes that correlate well with the degree of behavioral impairment may be important factors in the development of encephalopathy. We measured the concentrations of intermediary metabolites, ammonia, and amino acids in brain and plasma and the rate of whole-brain glucose utilization in rats with an acutely devascularized liver. In all rats an estimate of the grade of encephalopathy (reflected by behavioral impairment) was made. Rats underwent portacaval shunting and hepatic artery ligation (or sham operation) and were kept normoglycemic and normothermic thereafter. We sampled blood and whole brain (by near-instantaneous freeze-blowing) 2, 4, or 6 h later. There were no alterations in levels of high-energy phosphate metabolites in the brain or in metabolites associated with the glycolytic pathway and Krebs cycle, except lactate and pyruvate. Brain glucose use was decreased similarly at all times after surgery. Levels of ammonia and many amino acids were increased in brain and plasma; brain aspartate, glutamate, and arginine levels were decreased. The increases in content of plasma ammonia and brain glutamine, proline, alanine, and aromatic amino acids and the decreases in brain aspartate and glutamate were most strongly correlated with behavioral impairment.

Protection by alcuronium of muscarinic receptors against chemical inactivation and location of the allosteric binding site for alcuronium

We have found earlier that the neuromuscular blocker alcuronium binds to cardiac muscarinic receptors simultaneously with their specific antagonist [3H]methyl-N-scopolamine ([3H]NMS) and allosterically increases their affinity to this ligand. Nothing is known about the allosteric site with which alcuronium interacts. To gain an insight, we have now investigated how the binding of [3H]NMS is affected by agents known to modify specific residues in proteins and how their effects are altered by alcuronium. Reagents that covalently modify the tyrosyl residues (p-nitrobenzenesulfonyl fluoride and 4-chloro-7-nitrobenzofurazan) and the carboxyl groups of aspartate and glutamate [1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N,N'-dicyclohexylcarbodiimide, and N-ethyl-5-phenylisoxazolium-3'-sulfonate] blocked the binding of [3H]NMS to receptors in rat heart atria. Their action was probably due to the modification of tyrosyl and aspartyl residues directly in the muscarinic binding sites because it was antagonized by atropine and carbamoylcholine. Alcuronium and gallamine, another allosteric ligand, also protected the [3H]NMS binding sites against the inactivation by tyrosine- and carboxyl-directed chemical modifiers just as well as by benzilylcholine mustard, known to attach covalently to the muscarinic binding sites. Protection by alcuronium has also been observed on cerebrocortical muscarinic receptors. The effect of alcuronium indicates that the drug interferes with the access of chemical modifiers to the muscarinic sites. In view of the unspecific nature of most of the modifiers used (with regard to muscarinic mechanisms), the protection by alcuronium appears to be best explained on the assumption that the drug binds in close vicinity of the "classical" muscarinic site and sterically blocks the access to this site.

Evaluation of cerebral gray and white matter metabolite differences by spectroscopic imaging at 4.1T

Using a 4.1T whole body system, we have acquired 1H spectroscopic imaging (SI) data of N-acetyl (NA) compounds, creatine (CR), and choline (CH) with nominal voxel sizes of 0.5 cc (1.15 cc after filtering). We have used the SI data to estimate differences in cerebral metabolites of human gray and white matter. To evaluate the origin of an increased CR/NA and CH/NA ratios in gray matter relative to white matter, we measured the T1 and T2 of CR, NA, and CH in gray and white matter using moderate resolution SI imaging. In white matter the T2s of NA, CR, and CH were 233 +/- 27, 141 +/- 18, and 167 +/- 20 ms, respectively, and 227 +/- 27, 140 +/- 16, and 189 +/- 25 ms in gray matter. The T1 values for NA, CR, and CH were 1267 +/- 141, 1487 +/- 146, and 1111 +/- 136 ms in gray matter and 1260 +/- 154, 1429 +/- 233, and 1074 +/- 146 ms in white matter. After correcting for T1 and T2 losses, creatine content was significantly lower in white matter than gray (P < 0.01, t-test), with a white/gray content ratio of 0.8, in agreement with biopsy and in vivo measurements at 1.5 and 2.0T.

Charge state specific facile gas-phase cleavage of Asp 75-Met 76 peptide bond in the alpha-chain of human apohemoglobin probed by electrospray ionization mass spectrometry

Herein, we present the first example of charge state specific facile gas-phase cleavage of an aspartic acid-methionine peptide linkage. This cleavage (Asp 75-Met 76) was observed in the alpha-chain of human adult hemoglobin (Hb) and was probed by electrospray ionization mass spectrometry. This specific conformational and/or charge density dependent dissociation was observed primarily in the [M + 11H]11+ and [M + 12H]12+ species. A mechanism involving an intramolecular proton transfer from the protonated carboxyl side chain of Asp 75 to the neighboring Met 76 residue yielding an anhydride moiety at the C-terminal of the Asp 75 is proposed. Dramatic differences in dissociation of [M + 13H]13+ and [M + 14H]14+ species were observed.

Temporal lobe epilepsy: presurgical localization with proton chemical shift imaging

PURPOSE

To assess two-dimensional phase-encoded proton chemical shift imaging for potential clinical application in presurgical localization of temporal lobe epilepsy (TLE).

MATERIALS AND METHODS

Interictal chemical shift imaging studies were performed in 25 patients (17 unilateral, eight bilateral epileptogenic abnormalities) and 12 healthy volunteers. Results were compared with those of electroencephalography. For each temporal lobe, the volume of interest (VOI) included mesial, lateral, anterior, and posterior areas.

RESULTS

The epileptogenic zone was characterized by an abnormal pattern of decreased signal intensity in the N-acetylaspartate (NAA) peak, either increased or unchanged choline (Cho) level relative to creatine (Cr) signal intensity, and, occasionally, elevated lactate level. NAA/Cho was the most sensitive and reliable quantitative marker for abnormality. The sensitivity and specificity of this technique compared with EEG were 90% and 85%, respectively. The difference in NAA/Cho between epileptogenic and normal temporal lobes was highly significant (P < .001). No statistically significant difference was found between normal temporal lobes and patients' uninvolved temporal lobes.

CONCLUSION

NAA/Cho is an excellent marker for localizing the epileptogenic zone in TLE.

Simultaneous single-cell recording and microdialysis within the same brain site in freely behaving rats: a novel neurobiological method

We present a method for performing intracerebral microdialysis in freely behaving rats while recording the firing of neurons within the dialysis site. Studying hippocampal theta cells and complex-spike cells with this technique, it has been found that: (1) when the microdialysis fluid contained only artificial cerebrospinal fluid, both types of neurons displayed normal electrical activity, (2) the simultaneous single-cell recording/microdialysis procedure could be readily performed for as long as 3 days, and (3) inclusion of drugs into the microdialysis fluid, at appropriate concentrations, caused clear changes in firing pattern. For example, microdialysis with 1% lidocaine completely abolished, whereas that with 50 mM K+ markedly increased, the neuronal electrical activity. These cellular changes developed without apparent EEG or behavioral manifestations and were reversible. In some of the experiments, the extracellular concentrations of glutamate and aspartate in the recording/dialysis site were also measured. The described method allows the extracellular environment of recorded brain cells to be manipulated by drugs delivered through the microdialysis probe and simultaneously allows determination of the neurochemical composition of that environment over a remarkably long period of time and in intact, physiologically functioning, neural network. Such studies will provide new insights into the molecular basis of neuronal activity in the brain in the context of behavior, including learning.

Correlation between choline level and Gd-DTPA enhancement in patients with brain metastases of mammary carcinoma

Single voxel 1H double spin-echo MR spectroscopy was used to examine 15 cases of brain metastasis of mammary carcinoma (18 lesions) in relation to Gd-DTPA enhanced MR imaging. For lesions larger than 50% of MRS voxel size, there was significant correlation between Gd-DTPA-enhanced MRI signal and MRS-detected signal of choline (Cho) containing compounds (r = 0.86, P < 0.01; n = 8). The observed loss of correlation when including the smaller lesions was overcome by correcting for partial volume effects (r = 0.69, P < 0.002; n = 18). Metastasis spectra showed increased Cho compared with control spectra, except for those lesions showing detectable lactate (Lact) signal. The detection of Lact in four of the larger lesions coincided with comparatively low levels of creatine (Cr) and Cho and heterogeneous Gd-DTPA enhancement (Cr) and Cho and heterogeneous Gd-DTPA enhancement (ring-enhancement). It was concluded that in brain metastases of mammary carcinoma Lact represents a product of ischemia preceding/during tissue decay resulting in central necrosis, rather than tumor specific metabolism resulting in increased glycolysis.

Chemical modification of Penicillium 1,2-alpha-D-mannosidase by water-soluble carbodi-imide: identification of a catalytically important aspartic acid residue

1,2-alpha-D-Mannosidase from Penicillium citrinum was inactivated by chemical modification with 1-ethyl-3-(3-dimethylamino-propyl)carbodi-imide (EDC). Most of the activity was lost after modification in the absence of a nucleophile, glycine ethyl ester. 1-Deoxymannojirimycin (dMM), a competitive inhibitor of the enzyme, showed partial protection against the inactivation. After the modification by EDC without the presence of a nucleophile, proteolytic digests of the enzyme were analysed by reversed-phase h.p.l.c. and a unique peptide was shown to decrease when dMM was present during the modification. The peptide was absent from the digests of unmodified enzyme. The amino acid sequence of the peptide (A; Ile-Gly-Pro) was identical in part with that of the adjacent peptide (B; Ile-Gly-Pro-Asp-Ser-Trp-Gly-Trp-Asp-Pro-Lys). When cholecystokinin tetrapeptide (Trp-Met-Asp-Phe-NH2) was modified by EDC alone, the modified peptide could be separated from unmodified peptide by reversed-phase h.p.i.c., and Edman degradation was stopped before the modified aspartic acid residue. This suggested that, in the enzyme, peptide A was derived from peptide B by the modification. Consequently, Asp-4 in peptide B was assumed to be masked by dMM during the modification, and to be involved in the interaction of the enzyme with its substrate.

Age estimation by aspartic acid racemization in dentin of deciduous teeth

In forensic dental medicine, one of the most important endeavors is the estimation of age. We have studied the method of age assessment using the D/L ratio of aspartic acid from the dentin. The age of deciduous teeth has been estimated by measuring the racemization reaction of this amino acid. The results of the present study indicated that the measured D/L ratio for the dentin of deciduous teeth was highly correlated with the real age (r = 0.824 - 0.981 (sigma = +/- 0.5 to +/- 1.3). These results indicate that age can be accurately estimated from the dentin of deciduous teeth, as it can when permanent teeth are used, and that the D/L ratio is more highly correlated with age than is the eruption time of permanent teeth.

Localized brain proton MRS metabolic patterns in HIV-related encephalopathies

We have examined 9 healthy volunteers and 63 HIV-patients (16 asymptomatic patients and 47 patients with clinical AIDS-dementia complex, ADC) by magnetic resonance spectroscopy (MRS) and imaging (MRI) on a Siemens Magnetom SP63 (1.5 T). Proton MRS of the brain was performed at 63 MHz using the PRESS sequence (echo time = 135 ms, TR = 1.6 s). Four main results have been found: (1) HIV-related encephalopathy induces significant modifications of brain metabolism analyzed by MRS and the most sensitive metabolic parameter is the N-acetyl-aspartate/Choline ratio, (2) the correlation between MRS and MRI is good in 75% of patients, (3) in 4 of the 16 neuro-asymptomatic patients (i.e. 25%) a metabolic encephalopathy was found while MRI was still normal, and (4) MR spectra describe 3 different pathological metabolic patterns in the brain of HIV patients. Two patterns might correspond to the two entities of HIV-induced lesions i.e. HIV encephalitis and HIV-related progressive leukoencephalopathy.

[Determination of taurine, L-glutamine, vitamin U and L-aspartic acid in pharmaceuticals by high-performance liquid chromatography with pre-column derivatization]

A pre-column derivatization method for the high-performance liquid chromatographic determination of taurine (1), L-glutamine (2), vitamin U (3) and L-aspartic acid (4) in pharmaceuticals has been developed. The optimum requirements for the derivatization conditions and the stability of resulting derivatives were discussed. The compounds were converted into DNT derivatives through the amino group by reaction with sodium 2,6-dinitro-4-trifluoromethylbenzenesulfonate (DNTS) in 50% sodium borate at 60 degrees C for 30 min (1), at 60 degrees C for 90 min (2), at 60 degrees C for 80 min (3) and at 80 degrees C for 90 min (4). After the reaction mixtures were acidified with dil. HCl, the derivatives were separated on a Cosmosil 3C18 (4.6 mm i.d. x 50 mm) column using 1% acetic acid-methanol (13:7) containing 2 mM sodium 1-heptanesulfonate as mobile phase with a ultra violet detector at 280 nm. The precisions of the analytical values expressed as the coefficient of variation were below 2.0%. The recoveries of 1-4 added to various commercial samples were in the range of 97.8-100.6%.

High-resolution 1H-magnetic resonance spectroscopy of pediatric posterior fossa tumors in vitro

High-resolution proton magnetic resonance (MR) spectroscopy was performed on perchlorate extracts of tumors (24 cases) or peritumoral vermis (five cases) obtained at surgery. Fifteen tumors were typical cerebellar astrocytomas and nine were posterior fossa primitive neuroectodermal tumors/medulloblastomas. Spectra obtained from the five samples of peritumoral vermis revealed a pattern of metabolites similar to that reported for cerebellar tissue, but concentrations of most metabolites were low, perhaps due to dilution from peritumoral edema. The astrocytomas were characterized by high levels of valine, alanine, and choline, an increase in the choline:N-acetylaspartate (NAA) ratio, and a shift from glutamate to glutamine. Elevations in lactate, pyruvate, and glucose were the result of ischemia during sampling. The primitive neuroectodermal tumors/medulloblastomas were distinguished from astrocytomas by a greater increase in the choline:NAA ratio, a smaller decrease in the glutamate:glutamine ratio, and a relative increase in glycine, taurine, and inositol levels. These metabolic patterns may be of value diagnostically as in vivo MR spectroscopy achieves higher resolution.

Identification of the major brown shrimp (Penaeus aztecus) allergen as the muscle protein tropomyosin

Shrimp, a major seafood allergen, was investigated as a model food allergen. Extracts from both shrimp (Penaeus aztecus) meat and cooking fluid contain a substantial and similar amount of allergenic activity. A 36-kD allergen, demonstrated in both extracts by SDS-PAGE/Western blot analysis, reacted with 28/34 (82%) sera from shrimp-sensitive, skin test and RAST-positive, individuals. This allergen, named Pen a I, was isolated by SDS-PAGE; its amino acid composition was rich in aspartic and glutamic acids. A 21-residue peptide, obtained from endoproteinase Lys-C digested Pen a I by high-performance liquid chromatography, demonstrated significant homology (60-87%) with the muscle protein tropomyosin from various species and origins. The greatest homology (87%) was noted with tropomyosin of the fruit fly (Drosophila melanogaster) reflecting the phylogenic relationship between these two arthropods. These studies demonstrate that tropomyosin is the major shrimp allergen. Although the amino acid sequence of this shrimp muscle protein shares considerable homology with tropomyosins of other species including man, significant differences remain in allergenic activity.

Three-dimensional echo-planar MR spectroscopic imaging at short echo times in the human brain

PURPOSE

To demonstrate the feasibility of three-dimensional echo-planar spectroscopic imaging (EPSI) at short echo time (13 msec) with a conventional clinical imager in the human brain.

MATERIALS AND METHODS

Periodic inversions of a readout gradient were used during data acquisition to simultaneously encode chemical shift and one spatial dimension in one excitation. Aliasing artifacts were avoided with a modified acquisition-and-processing method based on oversampling. A double outer-volume suppression technique that adapts to the ovoid brain shape was used to strongly reduce extracranial lipid resonances.

RESULTS

Three-dimensional spatial encoding in vivo of eight sections with 32 x 32 voxels each (0.75 cm3) was performed in 34 minutes with four signal averages. The spectral resolution and signal-to-noise ratio (S/N) of resonances of inositol, choline, creatine, glutamate and glutamine, and N-acetyl aspartate were consistent with those previously recorded with conventional phase encoding.

CONCLUSION

EPSI substantially reduces acquisition time for three-dimensional spatial encoding and yields a spectral quality similar to that obtained with conventional techniques without affecting the S/N per unit time and unit volume.

Targeting glucose oxidase at aspartate and glutamate residues with organic two-electron redox mediators

The bimolecular rate constants for the reactions of five organic two-electron redox mediators with reduced glucose oxidase (GOx) were determined by measuring voltammetric electrocatalytic currents at glassy carbon electrodes in the presence of excess glucose under anaerobic conditions. The mediators studied were thionine, brilliant cresyl blue, azure A, daunomycin, and dopamine, and the bimolecular rate constants for electron transfer between GOx and the oxidized mediator (M-1 s-1) are 1.6 x 10(4), 4.0 x 10(2), 9.8 x 10(2), 9.0 x 10(3), and 1.2 x 10(6), respectively. GOx was covalently derivatized using 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide and N-hydroxysulfosuccinimide to form amide bonds between the aliphatic primary amine groups on daunomycin and dopamine and carboxylate side chains of aspartate and glutamate residues. Derivatives with 2.5 +/- 0.1 daunomycin groups and 4 +/- 1 dopamine groups were obtained, with activities of 50% and 75%, respectively, relative to native GOx in a dye-peroxidase assay. Although the daunomycin derivative did not show measurable intramolecular electron-transfer rates, the dopamine derivative rapidly transfers electrons from active-site FADH2 groups to the oxidized (quinone) form of dopamine. Because the heterogeneous oxidation of dopamine is relatively slow, the currents measured at +0.75 V vs Ag/AgCl were not at their limiting (plateau) values, and only a minimum value of the intramolecular rate constant (4.5 s-1) could be determined. This value is > 20 times larger than values obtained for GOx-ferrocene derivatives in which surface lysine residues were covalently modified using identical coupling reagents and similar reaction conditions. This work shows that targeting GOx carboxylate groups with electron-transfer mediators may represent a promising approach to the design of reagentless glucose biosensors.

Variations in the amino acid composition of cyanophycin in the cyanobacterium Synechocystis sp. PCC 6308 as a function of growth conditions

Gas chromatography-mass spectrometry studies of the nitrogen isotopic composition of the N-trifluoroacetyl n-butyl ester derivatives of the amino acids from isolated hydrolyzed cyanophycin from 15N-enriched cells led to two major findings: (1) the amino acid composition of this granular polypeptide, isolated using procedures optimized for extracting and purifying cyanophycin from cells in the stationary growth phase, varied with the culture growth condition; (2) the rate of incorporation of exogenous nitrate differed for each nitrogen atom of the amino acid constituents of cyanophycin or cyanophycin-like polypeptide. Arginine and aspartic acid were the principle components of cyanophycin isolated from exponentially growing cells and from light-limited stationary phase cells, with glutamic acid as an additional minor component. The cyanophycin-like polypeptide from nitrogen-limited cells contained only aspartic and glutamic acids, but no arginine. The glutamic acid content decreased and arginine content increased as nitrate was provided to nitrogen-limited cells. These cells rapidly incorporated nitrate at different rates at each cyanophycin nitrogen site: guanidino nitrogens of arginine > aspartic acid > alpha-amino nitrogen of arginine > glutamic acid. Little media-derived nitrogen was incorporated into cyanophycin of exponentially growing cells during one cellular doubling time.

Quantitative proton spectroscopy of canine brain: in vivo and in vitro correlations

Quantitative, single-voxel proton NMR spectroscopy of normal brain was performed in five adult beagle dogs using the cerebral water signal as an internal intensity reference. The same brain regions were then rapidly isolated and frozen using a pneumatic biopsy drill, perchloric acid extracted, and analyzed by biochemical assay and high-resolution NMR spectroscopy. The concentrations of the major resonances in the in vivo and in vitro spectra were compared, and good agreement was found between the different measurements. The in vivo spectra contained three peaks at 3.21, 3.04, and 2.02 ppm, which are usually assigned to trimethylamines (TMA), creatines, and N-acetyl derivatives (NAc), which corresponded to be the following metabolite concentration values: 1.7 +/- 0.6, 7.7 +/- 2.1, and 10.9 +/- 2.7 mumol/g wet weight respectively. In vitro, the following metabolite concentrations were measured: glycerophosphocholine (GPC) 1.3 +/- 0.2, phosphocholine (PC) 0.5 +/- 0.1, phosphocreatine (PCr) 2.6 +/- 0.4, creatine (Cr) 5.9 +/- 1.4, and N-Acetyl aspartate (NAA) 8.9 +/- 1.8 mumol/g wet weight. Therefore, the 3.21 ppm resonance observed in the in vivo spectrum is predominantly GPC and PC in a ratio of 2.6:1, the 3.04 ppm resonance is Cr and PCr in a ratio of 2.3:1, and the 2.02 ppm resonance is predominantly (approximately 80%) NAA with small contributions from N-acetylaspartylglutamate (NAAG) and glutamate. The data presented here validate the technique of water referencing as a simple and convenient means of quantitating single-voxel in vivo proton NMR spectra of the brain.

Prospective utility of cerebral proton magnetic resonance spectroscopy in monitoring HIV infection and its associated neurological impairment

Neurological manifestations of HIV disease occur in most adults and children with AIDS. Many of those affected will inevitably suffer clinical neurological deficits involving mental function, movement, and sensation. Surprisingly, there are not as yet adequate monitoring systems to predict the onset and/or progression of HIV infection of the CNS. Neurological, neuropsychological, CSF, and magnetic resonance imaging (MRI) analyses cannot accurately detect mental deterioration during advancing HIV disease. Reports suggest that in vivo proton MR spectroscopy (1H MRS) of the brain could be a predictor of virus-induced neurological deterioration. H MRS can measure N-acetylaspartate (NAA), a metabolite present only in neurons. Decreased NAA reflects neuronal loss seen during HIV infection of brain. To uncover possible associations between NAA levels and HIV-induced neurological disease we performed serial 1H MRS brain tests in HIV-infected patients with or at risk for encephalopathy. Serial testing, for 1 year, of 10 patients showed that brain NAA levels decreased in all HIV-infected subjects. The most severe NAA reductions were associated with progressive neurological impairment. These findings suggest that NAA can be used as a noninvasive measure of neuronal loss in patients with HIV disease. Most important, the results suggest that 1H MRS could be used to monitor therapeutics directed against HIV infection within the CNS.

Experimental study of the mechanism of seizure induction: changes in the concentrations of excitatory amino acids in the epileptic focus of the cat amygdaloid kindling model

L-glutamate (Glu) and L-aspartate (Asp) are two major excitatory amino acids that may be involved in seizure susceptibility and seizure induction. The concentrations of Glu and Asp were measured by microdialysis in the epileptic focus in a cat amygdaloid kindling model. Sequential changes in Glu and Asp (before, during, and after seizure) were measured in the partial seizure (S4) and generalized seizure (S6) groups. By stimulation at and 50 microA below the partial seizure-triggering threshold in the S4 group and the generalized seizure-triggering threshold in the S6 group, Glu was released from the epileptic focus in the S4 group, and both Glu and Asp were released in the S6 group after seizure and stimulation (below threshold), and the amount of Glu and/or Asp release determined seizure induction. Excitatory amino acids may be the trigger of seizure induction in the cat amygdaloid kindling model.