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Biomedical subjects

B D Ross

Publications and source records attributed to B D Ross.

At least 19 recordsLinked to original sources
PubMed1996

Hypoxic encephalopathy after near-drowning studied by quantitative 1H-magnetic resonance spectroscopy.

Early prediction of outcome after global hypoxia of the brain requires accurate determination of the nature and extent of neurological injury and is cardinal for patient management. Cerebral metabolites of gray and white matter were determined sequentially after near-drowning using quantitative 1H nuclear magnetic resonance spectroscopy (MRS) in 16 children. Significant metabolite abnormalities were demonstrated in all patients compared with their age-matched normal controls. Severity of brain damage was quantified from metabolite concentrations and ratios. Loss of N-acetylaspartate, a putative neuronal marker, from gray matter preceded that observed in white matter and was more severe. Total creatine decreased, while lactate and glutamine/glutamate concentrations increased. Changes progressed with time after injury. A spectroscopic prognosis index distinguished between good outcome (n = 5) and poor outcome (n = 11) with one false negative (bad outcome after borderline MRS result) and no false positive results (100% specificity). The distinction was made with 90% sensitivity early (after 48 h) and became 100% later (by days 3 and 4). This compared with 50-75% specificity and 70-100% sensitivity based upon single clinical criteria. MRS performed sequentially in occipital gray matter provides useful objective information which can significantly enhance the ability to establish prognosis after near-drowning.

Brain↗
PubMed1996

Noninvasive assessment of the relative roles of cerebral antioxidant enzymes by quantitation of pentose phosphate pathway activity.

Cerebral pentose phosphate pathway (PPP) plays a role in the biosynthesis of macromolecules, antioxidant defense and neurotransmitter metabolism. Studies on this potentially important pathway have been hampered by the inability to easily quantitate its activity, particularly in vivo. In this study we review the use of [1,6-13C2,6,6-2H2]glucose for measuring the relative activities of the PPP and glycolysis in a single incubation in cultured neurons and in vivo, when combined with microdialysis techniques. PPP activity in primary cerebrocortical cultures and in the caudate putamem of the rat in vivo was quantitated from data obtained by GC/MS analysis of released labeled lactate following metabolic degradation of [1,6-13C2,6,6-2H2]glucose. Exposure of cultures to H2O2 resulted in stimulation of PPP activity in a concentration-dependent fashion and subsequent cell death. Chelation of iron during H2O2 exposure exerted a protective effect thus implicating the participation of the Fenton reaction in mediating damage caused by the oxidative insult. Partial inhibition of glutathione peroxidase, but not catalase, was extremely toxic to the cultures reflecting the pivotal role of GPx in H2O2 detoxification. These results demonstrate the ability to dynamically monitor PPP activity and its response to oxidative challenges and should assist in facilitating our understanding of antioxidant pathways in the CNS.

Animals↗
PubMed1996

Assessment of the role of the glutathione and pentose phosphate pathways in the protection of primary cerebrocortical cultures from oxidative stress.

Reactive oxygen species have been implicated in neuronal injury associated with various neuropathological disorders. However, little is known regarding the relationship between antioxidant enzyme capacity and resultant toxicity. The antioxidant pathways of primary cerebrocortical cultures were directly examined using a novel technique that measures pentose phosphate pathway (PPP) activity, which is enzymatically coupled to glutathione peroxidase (GPx) detoxification of hydrogen peroxide (H2O2). PPP activity was quantified from data obtained by gas chromatography/mass spectrometry analysis of released labeled lactate following metabolic degradation of [1,6-(13)C2, 6,6-(2)H2] glucose by cerebrocortical cultures. The antioxidant capacity of these cultures was systematically evaluated using H2O2, and the resultant toxicity was quantified by lactate dehydrogenase release. Exposure of primary mixed and purified astrocytic cultures to H2O2 caused stimulation of PPP activity in a concentration-dependent fashion from 0.25 to 22.2% and from 6.9 to 66.7% of glucose metabolized to lactate through the PPP, respectively. In the mixed cultures, chelation of iron before H2O2 exposure was protective and resulted in a correlation between PPP saturation and toxicity. Conversely, addition of iron, inhibition of GPx, or depletion of glutathione decreased H2O2-induced PPP stimulation and increased toxicity. These results implicate the Fenton reaction, reflect the pivotal role of GPx in H2O2 detoxification, and contribute to our understanding of the etiological role of free radicals in neuropathological conditions.

Amitrole↗
PubMed1996

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.

Ammonia↗
PubMed1996

Proton magnetic resonance spectroscopy: the new gold standard for diagnosis of clinical and subclinical hepatic encephalopathy?

Human hepatic encephalopathy (HE) is identified by a new noninvasive test, proton magnetic resonance spectroscopy (1H MRS) applied to the brain in a few minutes. Chemical changes identified by 1H MRS are elevated glutamine, decreased choline and decreased myoinositol. The specific association with HE is proven by clinical studies in patients with cirrhosis, overt and subclinical HE, by the appearance of the same changes after transjugular intrahepatic portasystemic shunt, and by their complete reversal by liver transplantation. The importance of the new marker, myoinositol, may lie in its role as an osmolyte regulating cell volume in the astrocytes. Other roles are also postulated. Progress in the management of both HE and subclinical hepatic encephalopathy may depend upon finding means, short of liver transplantation, which will restore cerebral choline and myoinositol. The finding of identical changes in experimental animals simplifies the search.

Animals↗
PubMed1995

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.

Ammonia↗
PubMed1995

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.

Adenosine Triphosphate↗
PubMed1995

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.

Ammonia↗
PubMed1995

Role of increased cerebral myo-inositol in the dementia of Down syndrome.

The purpose of this study was to determine cerebral myo-inositol (mI) in adults with Down syndrome (DS), and to trace the chronobiology of DS to Alzheimer disease (AD). AD has characteristic neuropathology of neurofibrillary plaques and tangles; indirect evidence links this to earlier deposition of beta-amyloid. Elevated mI, which distinguishes AD from other common dementias, is also elevated in 23 young patients who have DS without dementia. In one patient who has DS with dementia, mI is elevated and N-acetylaspartate (NAA) decreased. The similarity to AD is striking and may suggest a progressive neurochemical disorder in which elevation of mI precede loss of NAA in both AD and DS.

Adolescent↗
PubMed1995

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.

Amides↗
PubMed1995

Proton magnetic resonance spectroscopy in children with acute central nervous system injury.

Single voxel proton magnetic resonance spectroscopy (1H-MRS) was used in 30 infants and children with acute central nervous system injuries to determine the value of changes in specific metabolite ratios in predicting outcome. The mean age of all patients was 38 +/- 52 months and the mean time of study after insult was 7 +/- 5 days. 1H-MRS was determined in the occipital gray and parietal white matter (8 cm3 volume, STEAM sequence with TE = 20 ms, TR = 3,000 ms). Data were expressed as ratios of different metabolite peak areas including N-acetylaspartate (NA), choline-containing compounds (Ch), creatine and phosphocreatine (Cr), and lactate (Lac). Statistically significant differences were observed when patients with good/moderate (G/M) outcomes (n = 17; mean age: 46 months) were compared to patients with bad outcomes (n = 10; mean age: 26 months). NA/Cr and NA/Ch were significantly lower in the bad outcome group (NA/Cr = 1.15 +/- 0.38; NA/Ch = 1.18 +/- 0.52) compared to the G/M group (NA/Cr = 1.41 +/- 0.28, P < .05; NA/Ch = 1.98 +/- 0.81, P < .01). Lactate was present in 80% of bad outcome patients and in none of the G/M group (P < .0001). Using a linear discriminant analysis and combining 4 clinical variables (Glasgow Coma Scale score, initial pH and glucose, number of days unconscious at time of 1H-MRS) allows classification of 94% of patients into their correct outcome group. Use of spectroscopy variables (NA/Cr, NA/Ch, Ch/Cr, presence of lactate) alone correctly classified 81% of patients. The combination of clinical and 1H-MRS variables correctly classified 100% of patients. Our findings suggest that 1H-MRS adds information which, in combination with clinical examination, may be useful in outcome assessment in children with serious acute central nervous system injury.

Acute Disease↗
PubMed1995

Dynamic measurements of cerebral pentose phosphate pathway activity in vivo using [1,6-13C2,6,6-2H2]glucose and microdialysis.

Cerebral pentose phosphate pathway (PPP) activity has been linked to NADPH-dependent anabolic pathways, turnover of neurotransmitters, and protection from oxidative stress. Research on this potentially important pathway has been hampered, however, because measurement of regional cerebral PPP activity in vivo has not been possible. Our efforts to address this need focused on the use of a novel isotopically substituted glucose molecule, [1,6-13C2,6,6-2H2]glucose, in conjunction with microdialysis techniques, to measure cerebral PPP activity in vivo, in freely moving rats. Metabolism of [1,6-13C2,6,6-2H2]glucose through glycolysis produces [3-13C]lactate and [3-13C,3,3-2H2]lactate, whereas metabolism through the PPP produces [3-13C,3,3-2H2]lactate and unlabeled lactate. The ratios of these lactate isotopomers can be quantified using gas chromatography/mass spectrometry (GC/MS) for calculation of PPP activity, which is reported as the percentage of glucose metabolized to lactate that passed through the PPP. Following addition of [1,6-13C2,6,6-2H2]glucose to the perfusate, labeled lactate was easily detectable in dialysate using GC/MS. Basal forebrain and intracerebral 9L glioma PPP values (mean +/- SD) were 3.5 +/- 0.4 (n = 4) and 6.2 +/- 0.9% (n = 4), respectively. Furthermore, PPP activity could be stimulated in vivo by addition of phenazine methosulfate, an artificial electron acceptor for NADPH, to the perfusion stream. These results show that the activity of the PPP can now be measured dynamically and regionally in the brains of conscious animals in vivo.

Animals↗
PubMed1995

Probable Alzheimer disease: diagnosis with proton MR spectroscopy.

PURPOSE: To distinguish probable Alzheimer disease (AD) from other dementias (ODs) and normality in the elderly. MATERIALS AND METHODS: A double-blind trial of proton magnetic resonance (MR) spectroscopy was performed, principally in gray matter, in the occipital cortex of 114 patients with dementia (AD [n = 65], OD [n = 39], or frontal lobe dementia [FLD] [n = 10]), 98 patients without dementia, and 32 healthy control subjects. RESULTS: Reduced levels of N-acetylaspartate (NAA) (P < .0005) and increased levels of myo-inositol (MI) (P < .0005) characterize AD. Patients with OD had significantly reduced levels of NAA (P < .01) but normal levels of MI (P [vs AD] < .0005). When MI/NAA was used, AD was distinguished from normality with 83% sensitivity and 98% specificity. When MI/creatine was used, OD was distinguished from AD and FLD with a negative predictive rate of 80%, sensitivity of 82%, and specificity of 64%. CONCLUSION: Hydrogen-1 MR spectroscopy enables identification of mild to moderate AD with a specificity and sensitivity that suggest clinical utility.

Aged↗
PubMed1995

Human cerebral osmolytes during chronic hyponatremia. A proton magnetic resonance spectroscopy study.

The pathogenesis of morbidity associated with hyponatremia is postulated to be determined by the state of intracellular cerebral osmolytes. Previously inaccessible, these metabolites can now be quantitated by proton magnetic resonance spectroscopy. An in vivo quantitative assay of osmolytes was performed in 12 chronic hyponatremic patients (mean serum sodium 120 meq/liter) and 10 normal controls. Short echo time proton magnetic resonance spectroscopy of occipital gray and parietal white matter locations revealed dramatic reduction in the concentrations of several metabolites. In gray matter, myo-inositol was most profoundly reduced at 49% of control value. Choline containing compounds were reduced 36%, creatine/phosphocreatine 19%, and N-acetylaspartate 11% from controls. Similar changes were found in white matter. Recovery of osmolyte concentrations was demonstrated in four patients studied 8-14 wk later. These results are consistent with a reversible osmolyte reduction under hypoosmolar stress in the intact human brain and offer novel suggestions for treatment and monitoring of this common clinical event.

Aged↗
PubMed1994

Measurement of pentose phosphate-pathway activity in a single incubation with [1,6-13C2,6,6-2H2]glucose.

The isotopically substituted molecule D-[1,6-13C2,6,6-2H2]glucose is introduced for measuring the relative activities of the pentose phosphate pathway (PPP) and glycolysis in a single incubation. PPP activity in cultured cells was determined by gas chromatography/mass spectrometric analysis of lactate produced by cells incubated with [1,6-13C2,6,6-2H2]glucose. Two other isotopes, [1,5,6-13C3]glucose and [6-13C,1,6,6-2H3]glucose, were not satisfactory for measurements of this activity. This method has four advantages over the traditional one in which 14CO2 production from [1-14C]glucose and [6-14C]glucose is compared: (1) repeated measurements can be made on a single set of cells, (2) only a single incubation is required, (3) extensive CO2 production by Krebs-cycle activity does not interfere with the measurements and (4) it is not necessary to measure the amount of glucose consumed in order to calculate relative activities of the PPP and glycolysis. Preliminary observation indicates that rat brain PPP activity may be measured in vivo with [1,6-13C2,6,6-2H2]glucose when combined with microdialysis techniques.

Animals↗