N-acetyl aspartate estimation: a potential method for determining neuronal loss in the transmissible spongiform encephalopathies

Neurodegenerative pathology is typical of the transmissible spongiform encephalopathies (TSEs), and is thought to underlie clinical disease. Some morphometric studies have shown early focal neurone loss, but the full extent of TSE induced neuronal loss in the central nervous system is not known, and can only be accurately estimated using intensive morphometric techniques. We have used a murine scrapie model in which we determined the levels of N-acetyl aspartate (NAA), a putative neuronal marker, by both high-performance liquid chromatography and high resolution, proton magnetic resonance spectroscopy in samples taken sequentially from the hippocampus. This scrapie model develops severe neuronal loss in the hippocampus, and the NAA levels showed a significant positive correlation with our previous morphometric estimates of neurone number. NAA measurement may therefore provide a practical alternative to intensive morphometric techniques in the investigation of neurodegeneration in the TSEs.

Urinary levels of creatine and other metabolites in the assessment of polymyositis and dermatomyositis

BACKGROUND

A simple and reliable method is needed to assess disease activity and monitor the efficacy of therapy in polymyositis (PM) and dermatomyositis (DM). This study used in vitro proton ((1)H) magnetic resonance spectroscopy (MRS) to explore whether excretion of urinary metabolites can be used as a reliable marker of disease in PM and DM patients.

METHODS

Urine samples were obtained from PM/DM patients (n=34), healthy controls (50) and subjects with known muscle-wasting conditions including adult-onset muscular dystrophy (8), stroke patients (10), rheumatoid arthritis (RA) patients on steroids (13) and not on steroids (16) and patients with alcoholic myopathy (12). Levels of urinary metabolites were then correlated with creatine kinase (CK) activities and quadriceps muscle strength.

RESULTS

Creatine was detected in the urine in 26 of 35 patients with PM/DM, four of 60 cases with other medical disorders (including one with adult-onset dystrophy, one with a stroke and two with RA who were not on steroids) and 10 of 50 healthy controls. The urinary creatine/creatinine ratio exceeded 0.4 in 20 patients with PM/DM but no patients with other medical disorders and no healthy controls. These differences were highly significant (P<0.001) by Kruskal-Wallis test (comparing all groups) and by Mann-Whitney U-tests (comparing individual groups with PM/DM cases). Citrate, glycine, choline-containing compounds and taurine levels were significantly increased in PM/DM when compared with controls. There were positive correlations between CK activities and choline-containing compounds (r=0.78, P=0.0006) and also between CK activities and betaine (r=0.57, P=0.026).

CONCLUSIONS

This study shows significant differences in the urinary levels of creatine, choline-containing metabolites, betaine and citrate in PM/DM subjects compared with controls, although further work is required to elucidate the underlying metabolic processes.

Influence of undersampling on magnetic resonance imaging measurements of intra-abdominal adipose tissue

OBJECTIVE

Single-slice magnetic resonance imaging (MRI) and computed tomography (CT) are finding increasing use as methods to estimate visceral fat content in human studies. To assess the validity of this approach, we have compared single- and multi-slice MRI methods for the measurement of intra-abdominal adipose tissue content.

MEASUREMENTS

Multi-slice whole-body MR images and single-slices at the level of L2-L3 and L4-L5 were obtained from 59 healthy female volunteers chosen to cover a wide range of body size, and from 17 healthy female volunteers before and after a 6-month exercise intervention.

RESULTS

Taking the group as a whole, significant correlation between multi-slice and single-slices was observed (L2-L3: r=0.56; P<0.01; L4-L5: r=0.76; P<0.01). However, the ranking of subjects according to their intra-abdominal fat content was significantly altered by the choice of MRI strategy, especially using L2-L3 methodology. Whole-body (-23.8+/-20.0%; P<0.01) and single-slice (L2-L3: -31.03+/-35.0%; P<0.01; L4-L5: -22.1+/-37.24%; p<0.05) MRI methods also detected a significant decrease in intra-abdominal fat following the exercise protocol, although the latter techniques gave rise to increased spreading of the data from the mean. These results suggest that the use of single-slice imaging techniques can lead to inconsistencies in the estimation of intra-abdominal fat content, which in turn can have significant effects on data interpretation.

CONCLUSION

Single-slice MRI appears to be suitable for assessing changes in intra-abdominal fat content in interventional studies, especially in large cohort of subjects, where each subject can serve as its own control. However, for accurate determination of an individual's intra-abdominal fat content, and intersubject comparison, only multi-slice imaging will give precise results.

Fast and reproducible method for the direct quantitation of adipose tissue in newborn infants

The role of body fat content and distribution in infants is becoming an area of increasing interest, especially as perception of its function appears to be rapidly evolving. Although a number of methods are available to estimate body fat content in adults, many are of limited use in infants, especially in the context of regional distribution and internal depots. In this study we developed and implemented a whole-body magnetic resonance imaging (MRI)-based protocol that allows fast and reproducible measurements of adipose tissue content in newborn infants, with an intra-observer variability of <2.4% and an inter-observed variability of <7%. The percentage total body fat for this cohort of infants ranged from 13.3-22.6% (mean and standard deviation: 16.6 +/- 2.9%), which agrees closely with published data. Subcutaneous fat accounted for just over 89% of the total body fat, whereas internal fat corresponded to almost 11%, most of which was nonabdominal fat. There were no gender differences in total or regional body fat content. These results show that whole-body MRI can be readily applied to the study of adipose tissue content and distribution in newborn infants. Furthermore, its noninvasive nature makes it an ideal method for longitudinal and interventional studies in newborn infants.

Evidence for altered hepatic gluconeogenesis in patients with cirrhosis using in vivo 31-phosphorus magnetic resonance spectroscopy

BACKGROUND AND AIMS

Alterations in gluconeogenesis in the diseased liver can be assessed non-invasively using magnetic resonance spectroscopy by measuring changes in phosphomonoester resonance which contains information regarding several metabolites, including the phosphorylated intermediates of the gluconeogenic pathway.

METHODS

31P magnetic resonance spectroscopy was used to determine changes in phosphomonoesters following bolus infusions of 2.8 mmol/kg L-alanine in five patients with functionally compensated cirrhosis and in five patients with functionally decompensated cirrhosis.

RESULTS

Compared with six healthy volunteers, baseline phosphomonoester values were elevated by 35% (p<0.05) in the compensated cirrhosis group and by 57% (p<0.01) in the decompensated cirrhosis group. Following alanine infusion, phosphomonoesters in healthy volunteers increased by 46% from baseline values (p<0.01), in patients with compensated cirrhosis by 27% (p<0.02) but those with decompensated cirrhosis showed no increase from baseline. There was a reduction in the percentage of inorganic phosphate signal in all subjects.

CONCLUSIONS

By analysing changes in phosphomonoester and inorganic phosphate resonances it is possible to discern clear metabolic differences between healthy volunteers and patients with cirrhosis of varying severity using magnetic resonance spectroscopy. Those patients with functionally decompensated cirrhosis have higher percentage baseline phosphomonoester values but the absence of phosphomonoester elevation following L-alanine infusion suggests that they are unable to mount a significant metabolic response with a progluconeogenic stimulus.

Visceral adipose tissue and metabolic complications of obesity are reduced in Prader-Willi syndrome female adults: evidence for novel influences on body fat distribution

Visceral obesity is detrimental to health, but the mechanisms controlling body fat distribution are not fully understood. In premenopausal adult females (30 nonobese, 14 obese [body mass index >30 kg/m(2)]), variance in fasting insulin, glucose, insulin/glucose ratio, C-peptide/insulin ratio, triglycerides, and high-density lipoprotein/low-density lipoprotein-cholesterol ratio, were independently influenced by visceral but not total sc or abdominal sc adipose tissue, as measured by whole-body magnetic resonance imaging. Adult females with Prader-Willi syndrome (n = 13) had significantly reduced visceral adiposity, compared with obese controls (visceral/total sc adipose tissue ratio: 0.067 +/- 0.017 vs. 0.108 +/- 0.021), independent of their total adiposity (P < 0.001), or use of exogenous sex steroids. This is in contrast to that expected by their physical inactivity, hypogonadism, adult GH deficiency, and psychiatric problems. Females with Prader-Willi syndrome not receiving sex steroids (n = 8) had significantly reduced fasting insulin, insulin/glucose ratio, and triglycerides and increased C-peptide/insulin ratio, compared with obese controls, adjusting for total (P < 0.05) but not visceral adiposity (P = 0.3-0.6), supporting their association. The cause of the reduced visceral adiposity in Prader-Willi syndrome may reflect novel hormonal, hypothalamic, and/or genetic influences on body fat distribution.

Physical properties of erythrocyte ghosts that determine susceptibility to secretory phospholipase A2

Artificial membranes may be resistant or susceptible to catalytic attack by secretory phospholipase A(2) (sPLA(2)) depending on the physical properties of the membrane. Living cells are normally resistant but become susceptible during trauma, apoptosis, and/or a significant elevation of intracellular calcium. Intact erythrocytes and ghosts were studied to determine whether the principles learned from artificial systems apply to biological membranes. Membrane properties such as phospholipid and/or protein composition, morphology, and microscopic characteristics (e.g. fluidity) were manipulated by preparing ghosts under different experimental conditions such as in the presence or absence of divalent cations with or without ATP. The properties of each membrane preparation were assessed by biochemical and physical means (fluorescence spectroscopy and electron and two-photon microscopy using the membrane probes bis-pyrene and laurdan) and compared with sPLA(2) activity. The properties that appeared most relevant were the degree of phosphatidylserine exposure on the outer face of the membrane and changes to the membrane physical state detected by bis-pyrene and laurdan. Specifically, vulnerability to hydrolysis by sPLA(2) was associated with an increase in bilayer order apparently reflective of expansion of membrane regions of diminished fluidity. These results argue that the general principles identified from studies with artificial membranes apply to biological systems.

Mechanisms by which intracellular calcium induces susceptibility to secretory phospholipase A2 in human erythrocytes

Exposure of human erythrocytes to the calcium ionophore ionomycin rendered them susceptible to the action of secretory phospholipase A(2) (sPLA(2)). Analysis of erythrocyte phospholipid metabolism by thin-layer chromatography revealed significant hydrolysis of both phosphatidylcholine and phosphatidylethanolamine during incubation with ionomycin and sPLA(2). Several possible mechanisms for the effect of ionomycin were considered. Involvement of intracellular phospholipases A(2) was excluded since inhibitors of these enzymes had no effect. Assessment of membrane oxidation by cis-parinaric acid fluorescence and comparison to the oxidants diamide and phenylhydrazine revealed that oxidation does not participate in the effect of ionomycin. Incubation with ionomycin caused classical physical changes to the erythrocyte membrane such as morphological alterations (spherocytosis), translocation of aminophospholipids to the outer leaflet of the membrane, and release of microvesicles. Experiments with phenylhydrazine, KCl, quinine, merocyanine 540, the calpain inhibitor E-64d, and the scramblase inhibitor R5421 revealed that neither phospholipid translocation nor vesicle release was required to induce susceptibility. Results from fluorescence spectroscopy and two-photon excitation scanning microscopy using the membrane probe laurdan argued that susceptibility to sPLA(2) is a consequence of increased order of membrane lipids.

Binding of steroidogenic acute regulatory protein to synthetic membranes suggests an active molten globule

Steroidogenic acute regulatory protein (StAR) mediates cholesterol transport from the outer to the inner mitochondrial membrane during steroid biosynthesis. The mechanism of StAR's action is not established. To address mechanistic issues, we assessed the binding of StAR to artificial membranes by fluorescence resonance energy transfer using endogenous StAR tryptophan residues as the donor and dansyl-phosphatidylethanolamine in the bilayer as the acceptor. Mixing StAR with dansyl-labeled vesicles composed of phosphatidylcholine increased the fluorescence intensity of dansyl emission excited at 280 nm by 10-40%. This interaction was dependent on pH, with a maximum at pH 3.0-3.5 and essentially no change above pH 5. Binding experiments at different temperatures and various combinations of phosphatidylcholine, phosphatidylglycerol, cardiolipin, and cholesterol showed that binding involves an electrostatic step and one or more other steps. Although binding prefers a thermodynamically ordered bilayer, the rate-limiting step occurs either when the bilayer is in a fluid state or when there is cholesterol-induced membrane heterogeneity. Experiments with fluorescence and light scattering indicate that StAR binding promotes ordering and aggregation of anionic membranes. The inactive StAR mutant R182L had lower affinity for the membrane, and the partially active mutant L275P had intermediate affinity. Far-UV CD spectroscopy of StAR in PC membranes show more beta-structure than in aqueous buffers, and the presence of cardiolipin or cholesterol in the membrane fosters a molten globule state. Our data suggest that StAR binds to membranes in a partially unfolded molten globule state that is relevant to the activity of the protein.

In vivo evaluation of the effects of continuous exercise on skeletal muscle triglycerides in trained humans

Magnetic resonance spectroscopy (1H MRS) and imaging (MRI) were used to investigate the effects of a bout of moderate prolonged exercise on intra (IMCL)- and extramyocellular lipid (EMCL) utilization in the soleus, tibialis anterior, and gastrocnemius muscles of five trained human subjects. MRI and 1H MRS measurements were obtained before and after a 90 min run on a calibrated treadmill at a velocity corresponding to 64 +/- 1.5% of each subjects' maximal rate of oxygen consumption. There were significant decreases in IMCL following exercise in the tibialis (pre: 22.37 +/- 4.33 vs. post: 15.16 +/- 3.25 mmol/kg dry wt; P < 0.01) and soleus (pre: 36.93 +/- 1.45 vs. post: 29.85 +/- 2.44 mmol/kg dry wt; P < 0.01) muscles. There was also a decrease in the gastrocnemius muscle, although this did not reach the level of significance (pre: 33.78 +/- 5.35 vs. post: 28.48 +/- 5.44 mmol/kg dry weight; P < 0.10). No significant changes were observed in EMCL or subcutaneous fat. In conclusion, this study showed that IMCL were significantly utilized in the tibialis and soleus muscles of aerobically endurance-trained humans. The absence of significant utilization of IMCL in the gastrocnemius may reflect differences in fiber type and/or intensity of contraction for each muscle group.

Stimulation by interleukin-6 and inhibition by tumor necrosis factor of cortisol release from bovine adrenal zona fasciculata cells through their receptors

Interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) are synthesized and released from adrenal cells. Therefore, the effects of TNF-alpha and IL-6 on cortisol release from bovine zona fasciculata (ZF) cells were investigated. IL-6 (10-1000 pg/mL) significantly increased basal and adrenocorticotropic hormone (ACTH)-stimulated cortisol release in a concentration-dependent manner. This stimulatory effect of IL-6 became apparent at intervals as short as 4 h and continued through 24 h. IL-6 also potentiated the cortisol release stimulated by the adenylyl cyclase activator forskolin. By contrast, TNF-alpha (0.1-10 ng) inhibited basal and ACTH-stimulated cortisol release in a concentration-dependent manner. The inhibitory effects of TNF-alpha on cortisol release were significant at time intervals as short as 4 h and continued through 24 h. TNF-alpha inhibited forskolin-stimulated cortisol release. Binding studies demonstrated that ZF cells have IL-6 receptors (100 receptors/cell, Kd of 7.5 x 10(-11)) and TNF receptors (200 receptors/cell, Kd of 2.4 x 10(-9) M). Immunohistochemical analysis provided evidence that the majority of ZF cells have IL-6 receptors, TNF type 1 receptors, and TNF type 2 receptors. Because IL-6 and TNF-alpha are released from the adrenal cortex and these cytokines modify the release of cortisol from the ZF, IL-6 and TNF-alpha may play a paracrine or autocrine role in the regulation of adrenal function.

Activities and interactions among phospholipases A2 during thapsigargin-induced S49 cell death

The purpose of this study was to determine the roles of calcium-dependent phospholipase A2 (cPLA2) and calcium-independent phospholipase A2 (iPLA2) in thapsigargin-induced membrane susceptibility to secretory phospholipase A2 (sPLA2) and programmed cell death. 3H-arachidonic acid release was observed in the presence of thapsigargin. This release was inhibited partially by an inhibitor of iPLA2 (BEL) and completely by an inhibitor of both cPLA2 and iPLA2 (MAFP) suggesting that these enzymes were active during apoptosis. The process of cell death did not require the activity of either enzyme since neither inhibitor impeded the progression of apoptosis. However, both inhibitors increased the susceptibility of the membrane to sPLA2 in the presence of thapsigargin. In the case of BEL, this effect appeared to involve direct induction of apoptosis in a sub-population of the cells independent of the action of iPLA2. In conclusion, the results suggested that cPLA2 and iPLA2 are active during thapsigargin-induced apoptosis in S49 cells and that cPLA2 tempers the tendency of the cells to become susceptible to sPLA2 during apoptosis.

Investigation of human low-density lipoprotein by (1)H nuclear magnetic resonance spectroscopy: mobility of phosphatidylcholine and sphingomyelin headgroups characterizes the surface layer

The resolution of the trimethyl headgroup resonance of phosphatidylcholine (PC) and sphingomyelin (SM) in the intact human low-density lipoprotein (LDL) (1)H NMR spectrum at 600 MHz enabled the investigation of LDL surface structure and phospholipid-apoB interactions. We have previously shown that a higher proportion of PC headgroups (25-35% of total PC in LDL) compared to SM were tightly bound to apoB and therefore NMR-invisible [Murphy, H. C., et al. (1997) Biochem. Biophys. Res. Commun. 234 (3), 733-737]. In the present study, we have investigated the mobility of phospholipid (PL) headgroups, using (1)H NMR spin-spin (T(2)) relaxation measurements, in LDL isolated from nine volunteers. We show that both PC and SM exist in two additional and distinct environments indicated by the biexponential behavior of the relaxation decays in each case. The data showed that 36% of PC headgroups had a short T(2) component, mean T(2) of 31 ms, and 64% had a longer T(2) component of 54 ms. Approximately 15% of SM headgroups had a short T(2) component (mean T(2) of 27 ms) and 85% had a longer T(2) component of 78 ms. Therefore the majority of SM headgroups (85%) were more mobile than PC (P < 0.001) and since PC headgroups in organic media were more mobile than SM, we conclude that the characteristic high mobility of LDL SM is not an intrinsic property but arises from a high degree of order in molecular packing of the surface PL of human LDL. We suggest that because PC and SM interact differentially with cholesterol and possibly with neighboring phospholipids, this results in the formation of relatively long-lived microdomains of PL in vivo.

Assessing gene expression in vivo: magnetic resonance imaging and spectroscopy

Recent developments in magnetic resonance imaging and spectroscopy afford the possibility of detecting and assessing transfer, expression and subsequent therapeutic changes of effector or marker transgenes noninvasively. In the field of MR imaging, 'smart' MR contrast agents are being developed, so called because they change their conformational structure and in so doing induce MR detectable changes in a given tissue. These agents become 'switched on' in response to physiological changes brought about by the enzymatic action of a given gene product (enzymes), and are being developed for use in intact cells, isolated organs and animal models. Ultimately, these agents hold the promise of bridging the gap between the laboratory and the patient with noninvasive detection of transgene expression in vivo in man. Similarly, magnetic resonance spectroscopy is being developed as a noninvasive method to assess transgene expression indirectly by means of MR visible intracellular markers. These markers take the form of intracellular endo/exogenous metabolites associated with exogenous enzyme expression and function. Again, this technique will be applicable to a variety of different situations, from cell suspensions through to clinical imaging of the whole body. In this article the unique opportunities for laboratory-based and clinical studies afforded by MR techniques are discussed.

Bioenergetic targeting during organ preservation: (31)P magnetic resonance spectroscopy investigations into the use of fructose to sustain hepatic ATP turnover during cold hypoxia in porcine livers

During liver preservation, ATP supplies become depleted, leading to loss of cellular homeostatic controls and a cascade of ensuing harmful changes. Anaerobic glycolysis is unable to prolong ATP production for a significant period because of metabolic blockade. Our aim was to promote glycolysis during liver cold hypoxia by supplying fructose as an additional substrate, compared to supplementation with an equivalent concentration of glucose. Porcine livers (two groups; n = 5 in each) were retrieved by clinical harvesting techniques and subjected to two cycles of cold hypoxia and oxygenated hypothermic reperfusion. In the second cycle of reperfusion, the perfusate was supplemented with either 10 mmol/L glucose (Group 1) or 10 mmol/L fructose (Group 2). During reperfusion in both groups, similar levels of ATP were detected by phosphorus magnetic resonance spectroscopy ((31)P MRS). However, during subsequent hypoxia, ATP was detected for much longer periods in the fructose-perfused group. The rate of ATP loss was sevenfold slower during hypoxia in the presence of fructose than in the presence of glucose (ATP consumption of -7.2 x 10(-3)% total (31)P for Group 1 versus -1.0 x 10(-3)% total (31)P for Group 2; P < 0. 001). The changes in ATP were mirrored by differences in other MRS-detectable intermediates; e.g., inorganic phosphate was significantly higher during subsequent hypoxia in Group 1 (45.7 +/- 2.7% total (31)P) than in Group 2 (33.7 +/- 1.1% total (31)P; P < 0. 01). High-resolution MRS of liver tissue extracts demonstrated that fructose was metabolized mainly via fructose 1-phosphate. We conclude that fructose supplied by brief hypothermic perfusion may improve the bioenergetic status of cold hypoxic livers by sustaining anaerobic glycolysis via a point of entry into the pathway that is different from that for glucose.

Preferential loss of visceral fat following aerobic exercise, measured by magnetic resonance imaging

The aim of this study was to use whole-body magnetic resonance imaging (MRI) together with biochemical and anthropometric measurements to study the influence of regular moderate exercise with no dietary intervention on adipose tissue distribution in nonobese healthy women. We found significant decreases in both total (28.86+/-2.24 vs. 27.00+/-2.27 liters, P < 0.05) and regional fat depots (visceral fat: 1.68+/-0.21 vs. 1.26+/-0.18 liters, P < 0.01) using whole-body MRI despite no significant change in body weight, body mass index, or the waist-to-hip ratio. Interestingly, no changes in body fat content were found using anthropometry or impedance. There was a significant increase in high density lipoprotein cholesterol (1.58+/-0.06 vs. 1.66+/-0.08 mmol/L P < 0.02) following exercise although there were no changes in other blood lipids such as triglycerides. In summary, moderate aerobic exercise over a period of 6 mon resulted in a preferential loss in visceral fat in nonobese healthy women, and this may help to explain some of the health benefits associated with regular and moderate physical activity.

Susceptibility of S49 lymphoma cell membranes to hydrolysis by secretory phospholipase A(2) during early phase of apoptosis

During cell death, plasma membranes of cells become vulnerable to attack by extracellular secretory phospholipase A(2). The purpose of this study was to identify the timing of this phenomenon relative to other events that occur during the process of cell death. Death was induced in S49 murine lymphoma cells by treatment with dexamethasone, dibutyryl cAMP, ionomycin, thapsigargin, or heat shock (1 h at 43 degrees C). The appearance of membrane susceptibility to secretory phospholipase A(2) was compared to the following apoptotic events: loss of mitochondrial membrane potential, phosphatidylserine exposure in the outer leaflet of the cell membrane, early DNA damage assessed by the comet assay, and changes in cell size and internal complexity assessed by flow cytometry. Each inducer of death was distinct in the time course of events produced. Although dead cells were susceptible to the action of phospholipase A(2), live cells (impermeable to propidium iodide) also became vulnerable to the enzyme during characteristic time courses after exposure to each inducer. In fact, susceptibility to sPLA(2) was observed in each case prior to or concurrent with the earliest of the markers of apoptosis. These results demonstrate that the onset of susceptibility to sPLA(2) is an early event in apoptosis suggesting that changes in membrane structure may be relevant to initial aspects of the apoptotic process.

Increased availability of central benzodiazepine receptors in patients with chronic hepatic encephalopathy and alcohol related cirrhosis

BACKGROUND/AIMS

To measure cerebral benzodiazepine receptor binding using (11)C-flumazenil positron emission tomography in patients with stable chronic hepatic encephalopathy, who were also characterised by proton magnetic resonance spectroscopy.

METHODS

Six abstinent patients of mean age 61 years with alcohol related cirrhosis and grade I-II hepatic encephalopathy and 11 matched healthy volunteers were studied. Each patient's encephalopathy was defined according to clinical, psychometric, electroencephalographic, and magnetic resonance spectroscopy criteria. Using positron emission tomography, the brain volume of distribution of (11)C-flumazenil was obtained; this reflects benzodiazepine receptor availability. Proton magnetic resonance spectra were acquired at 1.5 T using a multivoxel technique; peak area ratios were calculated for choline, glutamine/glutamate, N-acetylaspartate, and creatine resonances.

RESULTS

The mean volume of distribution of (11)C-flumazenil was significantly higher in the cortex, cerebellum, and the basal ganglia in the patients compared with controls (p<0.001). In the patient group, the mean glutamine/glutamate to creatine ratio was significantly increased and the mean choline to creatine ratio was significantly decreased in all brain areas, compared with healthy volunteers. However, the N-acetylaspartate to creatine ratio was unchanged compared with controls.

CONCLUSIONS

The spectroscopy results reflect the cerebral metabolic derangement associated with hepatic encephalopathy. Stable grade I-II chronic hepatic encephalopathy in alcohol related cirrhosis may be associated with increased cerebral benzodiazepine receptor availability. However, a direct effect of previous chronic exposure to alcohol cannot be excluded.

Cortical dysfunction in non-demented Parkinson's disease patients: a combined (31)P-MRS and (18)FDG-PET study

Regional cerebral phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) was performed in 10 non- demented Parkinson's disease patients and nine age-matched control subjects. Five of the patients undergoing (31)P-MRS and four additional Parkinson's disease patients had cerebral 2-[(18)F]fluoro-2-deoxy-D-glucose PET ((18)FDG-PET), the results of which were compared with those of eight age-matched control subjects. All Parkinson's disease patients underwent neuropsychological testing including performance and verbal subtests of the Wechsler Adult Intelligence Scale-Revised, Boston Naming Test, Controlled Oral Word Association test (FAS Test) and California Learning Test to exclude clinical dementia. (31)P MR spectra from right and left temporo-parietal cortex, occipital cortex and a central voxel incorporating basal ganglia and brainstem were obtained. (31)P MR peak area ratios of signals from phosphomonoesters (PMEs), inorganic phosphate (P(i)), phosphodiesters (PDEs), alpha-ATP, gamma-ATP and phosphocreatine (PCr) relative to beta-ATP were measured. Relative percentage peak areas of PMEs, P(i), PDEs, PCr, and alpha-, beta- and gamma-ATP signals were also measured with respect to the total (31)P-MRS signal. Significant bilateral increases in the P(i)/beta-ATP ratio were found in temporoparietal cortex (P = 0.002 right and P = 0.014 left cortex) for the non-demented Parkinson's disease patients compared with controls. In the right temporoparietal cortex, there was also a significant increase in the mean relative percentage P(i) (P = 0.001). (18)FDG-PET revealed absolute bilateral reductions in glucose metabolism after partial volume effect correction in posterior parietal and temporal cortical grey matter (P < 0.01 and P < 0.05, respectively) for the Parkinson's disease group, using both volume of interest analysis and statistical parametric mapping. There were significant correlations between right temporoparietal P(i)/beta-ATP ratios and estimated reductions in performance IQ (r = 0.96, P < 0.001). Left temporoparietal P(i)/beta-ATP ratios correlated with full scale IQ and verbal IQ (r = -0.82, P = 0.006, r = -0.86, P = 0.003, respectively). In summary, temporoparietal cortical hypometabolism was seen in non-demented Parkinson's disease patients with both (31)P-MRS and (18)FDG-PET, suggesting that both glycolytic and oxidative pathways are impaired. This dysfunction may reflect either the presence of primary cortical pathology or deafferentation of striato-cortical projections. (31)P-MRS and (18)FDG-PET may both provide useful predictors of future cognitive impairment in a subset of Parkinson's disease patients who go on to develop dementia.

Diversity in levels of intracellular total creatine and triglycerides in human skeletal muscles observed by (1)H-MRS

We used (1)H-magnetic resonance spectroscopy to noninvasively determine total creatine (TCr), choline-containing compounds (Cho), and intracellular (IT) and extracellular (between-muscle fibers) triglycerides (ET) in three human skeletal muscles. Subjects' (n = 15 men) TCr concentrations in soleus [Sol; 100.2 +/- 8.3 (SE) mmol/kg dry wt] were lower (P < 0.05) than those in gastrocnemius (Gast; 125.3 +/- 9.2 mmol/kg dry wt) and tibialis anterior (TA; 123. 7 +/- 8.8 mmol/kg dry wt). The Cho levels in Sol (35.8 +/- 3.6 mmol/kg dry wt) and Gast (28.5 +/- 3.5 mmol/kg dry wt) were higher (P < 0.001 and P < 0.01, respectively) compared with TA (13.6 +/- 2. 4 mmol/kg dry wt). The IT values were found to be 44.8 +/- 4.6 and 36.5 +/- 4.2 mmol/kg dry wt in Sol and Gast, respectively. The IT values of TA (24.5 +/- 4.5 mmol/kg dry wt) were lower than those of Sol (P < 0.01) and Gast (P < 0.05). There were no differences in ET [116.0 +/- 11.2 (Sol), 119.1 +/- 18.5 (Gast), and 91.4 +/- 19.2 mmol/kg dry wt (TA)]. It is proposed that the differences in metabolite levels may be due to the differences in fiber-type composition and deposition of metabolites due to the adaptation of different muscles during locomotion.

Conflicting MRI signals from gliosis and neuronal vacuolation in prion diseases

Magnetic resonance imaging (MRI) has given inconsistent results when used as a non-invasive diagnostic tool for Creutzfeldt-Jakob disease (CJD). In order to understand this finding, we studied a hamster model of scrapie by in vivo MRI and histopathology. Vacuolation of neurones/neuropil and gliosis were found to correlate with hypo-intense and hyper-intense changes in the conventional T2-weighted MR images, respectively. These opposing effects were shown to give rise to normal images of a scrapie-affected brain undergoing severe neurodegeneration, and may underlie the variability of previous CJD MRI data.

Cerebral proton and phosphorus-31 magnetic resonance spectroscopy in patients with subclinical hepatic encephalopathy

BACKGROUND/AIMS

In vivo magnetic resonance spectroscopy can be used to study cerebral metabolism non-invasively. We aimed to correlate 1H and 31P magnetic resonance spectral abnormalities in the brains of patients with subclinical hepatic encephalopathy.

METHODS

Eighteen patients were studied at 1.5T, with combined 1H and 31P magnetic resonance spectra obtained from multiple voxels in the cerebral cortex and basal ganglia. Peak area ratios of choline, glutamine/glutamate, relative to creatine in the 1H spectra and percentage phosphomonoesters, phosphodiesters and betaNTP signals relative to total 31P signals in the 31P spectra were measured.

RESULTS

Six patients did not complete the full examination - 31P results are available from 12 patients only. Relative to creatine, there were reductions in choline and elevations in glutamine/glutamate, varying across the brain with choline significantly reduced in occipital cortex (p<0.05) and glutamine/glutamate most significantly elevated in temporo-parietal cortex (p<0.0001). Percentage phosphomonoester (p<0.05), phosphodiester (p<0.05) and betaNTP (p<0.005) signals were significantly decreased in basal ganglia spectra. No correlation was found between the magnitude of 1H and 31P MRS changes, except between percentage phosphodiester decrease and glutamine/glutamate to creatine increase in occipital cortex.

CONCLUSION

The results of this study point to a multifactorial aetiology for this condition.