John M. Pearce

Analysis of phospholipid molecular species in brain by 31P NMR spectroscopy

Techniques are described for the 31P NMR analysis of glycerophospholipid (PL) headgroup and molecular species in brain. The 31P NMR spectrum of PLs from human temporal cortex, solubilized in aqueous Na cholate, typically showed 3 major resonances, assigned to phosphatidylcholine (PC) molecular species containing 0, 1, or 2 fully saturated acyl chains. Less species resolution was obtained for the other PL headgroups under these conditions. Alkylacyl‐ and alkenylacyl‐PC were readily discerned using the CHCl3‐CH3OH‐H2O solvent method. The chain‐length, temperature, and species dependences of the 31P NMR chemical shifts were explored in model PLs. Assignments of signals from phosphatidylethanolamine (PE) subclasses were confirmed in the sodium‐cholate system by lipase‐mediated selective hydrolysis of bovine‐brain PE. The utility of 31P NMR to monitor enzymatic PL oxidation was further demonstrated. Possible changes in PL composition with postmortem interval (PMI) in rat brain were examined. No significant changes were seen in PL headgroup or PC species composition with PMI at up to 18 hours. Where comparable, the Na‐cholate‐solubilization and solvent methods gave similar quantitative results for headgroup analysis on the same samples. The present work demonstrates the feasibility and utility of the dual system for analysis of PLs in brain. Magn Reson Med 44:215–223, 2000.

31P NMR spectroscopy of phospholipid metabolites in postmortem schizophrenic brain.

Evidence has been accumulating that schizophrenia involves abnormalities in the composition and metabolism of cell membrane phospholipids (PLs) in the brain. In vivo 31P MRS has been used to measure the metabolic precursors and degradation products of PL metabolism in schizophrenia. Because in vivo line widths are substantially broader than in solution, only the broad phosphomonoester (PME) and phosphodiester bands, or partly resolved resonances of individual metabolites, are typically measured in vivo in the 31P spectrum. In addition to poor resolution, the relatively low signal‐to‐noise ratio (SNR) makes precise quantitation difficult. An alternative with substantially better resolution and precision for quantitation is high‐resolution NMR spectroscopy of extracts of samples from postmortem brain. Here we determine absolute concentrations of the individual PL metabolites phosphocholine (pc), phosphoethanolamine (pe), glycerophosphocholine (gpc), and glycerophosphoethanolamine in aqueous extracts of tissue from frontal, temporal, and occipital cortex of postmortem brain for schizophrenics, controls, and patients with other mental illnesses (psychiatric controls [PC]) using high‐resolution 31P NMR spectroscopy. For the complete groups, which included both males and females, there were no statistically significant differences for schizophrenics vs. controls for any of the four PL metabolites in any of the three brain regions. Trends (0.05 < P < 0.10) were noted for increased gpc in schizophrenia in all three regions. PC differed from both controls and schizophrenics in several measures. When only males were considered, gpc was significantly (P < 0.05) elevated in all three brain regions in schizophrenia. Magn Reson Med 59:469–474, 2008.

PHOSPHOLIPID COMPOSITION OF POSTMORTEM SCHIZOPHRENIC BRAIN BY 31P NMR SPECTROSCOPY

Cell membrane abnormalities due to changes in phospholipid (PL) composition and metabolism have been implicated in schizophrenia pathogenesis. That work has generally assessed membrane phospholipids from nonneural tissues such as erythrocytes and platelets. High‐resolution 31P NMR spectroscopy was used to characterize PLs of gray matter in postmortem brain for 20 schizophrenics, 20 controls, and 7 patients with other mental illnesses (psychiatric controls). Tissues from frontal, temporal, and occipital cortices were extracted with hexane–isopropanol, and 31P NMR spectra were obtained in an organic–solvent system to resolve the major PL classes (based on headgroups) and subclasses (based on linkage at the sn − 1 position). Surprisingly, repeated‐measures multivariate analysis of variance revealed no overall differences among the groups. There were no significant differences (P < .05) among the three groups for any individual PL subclass, including lysophospholipids. The sum of all phosphatidylethanolamine headgroups was significantly lower for schizophrenics than for controls or psychiatric controls in the frontal cortex. The present results are minimally correlated with previous results for aqueous PL metabolites on these same samples. The metabolite changes measured by in vivo 31P MRS in schizophrenia do not appear to reflect PL concentration changes. The present results offer very little support for the phospholipid hypothesis of schizophrenia. Magn Reson Med 61:28–34, 2009.

Phospholipid abnormalities in postmortem schizophrenic brains detected by 31P nuclear magnetic resonance spectroscopy: a preliminary study

It has been hypothesized that schizophrenia arises from cell membrane abnormalities due to changes in phospholipid (PL) composition and metabolism. We have used high resolution, in vitro 31P nuclear magnetic resonance (NMR) to characterize the PLs in left frontal cortex (gray matter) of postmortem brain from four schizophrenics and five controls. High resolution 31P NMR spectra were obtained in an organic-solvent system to resolve PL classes (headgroups) and in a sodium-cholate, aqueous dispersion system to resolve phosphatidylcholine (PC) molecular species. Multivariate analysis which included the major PC molecular species and phosphatidylinositol (PI) showed a significant difference between schizophrenics and controls. Analysis of specific interactions showed that the PI was significantly higher in the schizophrenic group than in the control group. There were no differences between the two groups for other individual PL classes, or for individual PL subclasses determined by the linkage type at the sn-1 position on glycerol. There was a trend for total PL content to be higher in schizophrenics than in controls. There was no evidence for elevated lysophosphatidylcholine or lysophosphatidylethanolamine in schizophrenia. The intensity of the PC peak representing molecular species with one saturated and one unsaturated (one or two double bonds) acyl chain was higher for the schizophrenic group than for the control group. Although these results are not in complete agreement with previous studies, they support the idea that PL abnormalities occur in the brain in schizophrenia and that fatty acid metabolism may be abnormal.

Imaging of brain tumors with paramagnetic vesicles targeted to phosphatidylserine

To investigate paramagnetic saposin C and dioleylphosphatidylserine (SapC‐DOPS) vesicles as a targeted contrast agent for imaging phosphatidylserine (PS) expressed by glioblastoma multiforme (GBM) tumors.

Localized 7Li MR spectroscopy: In vivo brain and serum concentrations in the rat

The brain concentration of lithium (Li) in treated rats was measured using a recently developed method based on in vivo 7Li PRESS localized MRS. Comparison was made to the corresponding serum concentration at two treatment durations. The brain and serum Li concentrations were highly correlated with each other, more so than found previously for humans. The brain and serum Li concentrations also correlated with dose. Both the brain Li concentration and the serum concentration at 16.1 days of treatment correlated with the corresponding measure at 6.6 days. After correction of the brain Li concentrations for reduced 7Li MRS visibility, the mean brain/serum Li ratio for rats was close to unity, unlike most previous values found for humans. However, in some individual cases the ratio deviated substantially from the mean, suggesting that serum Li is not always a reliable indicator of brain Li. Magn Reson Med 52:1087–1092, 2004.

Localized 7Li MR spectroscopy and spin relaxation in rat brain in vivo

Localized 7Li MR point‐resolved spectroscopy (PRESS) was developed as a technique to measure lithium (Li) concentration in rat brain in vivo. Localized 7Li spectra could be obtained at 4.7 T in a 0.7‐ml voxel in rat brain over the entire therapeutic range of serum Li for humans. Localized 7Li spin‐lattice (T1) and spin–spin (T2) relaxation times were measured. Measured intensities were corrected for spin relaxation effects and 7Li MR visibility in vivo. The average T1 was 3.3 ± 0.9 sec, and the average T2 was 82 ± 20 ms. Neither T1 nor T2 correlated with brain concentration. No statistically significant change was found in either T1 or T2 from ∼7–17 days of Li dosing. Magn Reson Med 52:164–168, 2004.

Estimating intracellular lithium in brain in vivo by localized 7Li magnetic resonance spectroscopy.

The therapeutic mechanism of action of lithium (Li) in bipolar disorder is unknown. While Li is presumed to work intracellularly in the brain, the fraction of intracellular Li in the brain in vivo is not known. It has not yet been possible to determine, directly and noninvasively, the intra‐ to extracellular distribution of Li in human brain in vivo. Lithium‐7 (7Li) MR is the only technique available for measuring noninvasively the concentration of Li in the brain in vivo. Here the individual components of biexponential 7Li transverse (T2) relaxation in rat brain in vivo are identified with intra‐ and extracellular Li, and used to estimate its compartmental distribution. Intracellular T2 was 14.6 ± 6.9 ms, while extracellular T2 was 160 ± 52 ms in nine rats. The fraction of intracellular brain Li ranged from 37% to 75% (mean: 63 ± 11%). Further, the biexponential T2 results provided the basis for estimating Li compartmental distribution from monoexponential T2 decays using a simple linear approximation. The fraction of intracellular Li estimated from monoexponential T2 decays agreed with the corresponding biexponential estimates in most cases. Magn Reson Med 60:21–26, 2008.

Lithium compartmentation in brain by 7Li MRS: effect of total lithium concentration

In previous work at 4.7 T, the individual components of biexponential 7Li transverse (T2) spin relaxation in rat brain in vivo were tentatively identified with intra‐ and extracellular Li. The goal in this work was to estimate Lis compartmental distribution as a function of total Li concentration in brain from the biexponential decays. Here a localized, biexponential 7Li T2 MR spin‐relaxation study with isotopically enriched 7LiCl is reported in rat brain in vivo at 7 T. Additionally, a simple linear interpolation using the biexponential T2 values to estimate intracellular Li from individual monoexponential T2 decays was assessed. Intracellular T2 was 14.8 ± 4.3 ms and extracellular T2 was 295 ± 61 ms. The fraction of intracellular brain Li ranged from 37.3 to 64.8% (mean 54.5 ± 6.7%) and did not correlate with total Li concentration. The estimated intracellular Li concentration ranged from 47 to 80% (mean 68.3 ± 8.5%) of the total brain Li concentration and was highly correlated with it. The monoexponential estimates of the intracellular‐Li fractions and derived concentrations averaged about 15% higher than the corresponding biexponential estimates. This work supports the previous conclusion that a large fraction of Li in the brain is within the intracellular compartment. Copyright