Spin-spin relaxation of the phosphodiester resonance in the 31P NMR spectrum of human brain. The determination of the concentrations of phosphodiester components

Altered high-energy phosphate and membrane metabolism in Pelizaeus–Merzbacher disease using phosphorus magnetic resonance spectroscopy

Pelizaeus–Merzbacher disease is an X-linked recessive leucodystrophy of the central nervous system caused by mutations affecting the major myelin protein, proteolipid protein 1. The extent of the altered in vivo neurochemistry of protein, proteolipid protein 1 duplications, the most common form of Pelizaeus–Merzbacher disease, is, however, poorly understood. Phosphorus magnetic resonance spectroscopy is the only in vivo technique that can assess the biochemistry associated with high-energy phosphate and membrane phospholipid metabolism across different cortical, subcortical and white matter areas. In this cross-sectional study, whole-brain, multi-voxel phosphorus magnetic resonance spectroscopy was acquired at 3 T on 14 patients with Pelizaeus–Merzbacher disease with protein, proteolipid protein 1 duplications and 23 healthy controls (all males). Anabolic and catabolic levels of membrane phospholipids (phosphocholine and phosphoethanolamine, and glycerophosphoethanolamine and glycerophosphocholine, respectively), as well as phosphocreatine, inorganic orthophosphate and adenosine triphosphate levels relative to the total phosphorus magnetic resonance spectroscopy signal from 12 different cortical and subcortical areas were compared between the two groups. Independent of brain area, phosphocholine, glycerophosphoethanolamine and inorganic orthophosphate levels were significantly lower (P = 0.0025, P < 0.0001 and P = 0.0002) and phosphocreatine levels were significantly higher (P < 0.0001) in Pelizaeus–Merzbacher disease patients compared with controls. Additionally, there was a significant group-by-brain area interaction for phosphocreatine with post-hoc analyses demonstrating significantly higher phosphocreatine levels in patients with Pelizaeus–Merzbacher disease compared with controls across multiple brain areas (anterior and posterior white matter, superior parietal lobe, posterior cingulate cortex, hippocampus, occipital cortex, striatum and thalamus; all P ≤ 0.0042). Phosphoethanolamine, glycerophosphoethanolamine and adenosine triphosphate levels were not significantly different between groups. For the first-time, widespread alterations in phosphorus magnetic resonance spectroscopy metabolite levels of Pelizaeus–Merzbacher disease patients are being reported. Specifically, increased high-energy phosphate storage levels of phosphocreatine concomitant with decreased inorganic orthophosphate across multiple areas suggest a widespread reduction in the high-energy phosphate utilization in Pelizaeus–Merzbacher disease, and the membrane phospholipid metabolite deficits suggest a widespread degradation in the neuropil content/maintenance of patients with Pelizaeus–Merzbacher disease which includes axons, dendrites and astrocytes within cortex and the myelin microstructure and oligodendrocytes within white matter. These results provide greater insight into the neuropathology of Pelizaeus–Merzbacher disease both in terms of energy expenditure and membrane phospholipid metabolites. Future longitudinal studies are warranted to investigate the utility of phosphorus magnetic resonance spectroscopy as surrogate biomarkers in monitoring treatment intervention for Pelizaeus–Merzbacher disease.

Glycerophosphocholine and Glycerophosphoethanolamine Are Not the Main Sources of the In Vivo (31)P MRS Phosphodiester Signals from Healthy Fibroglandular Breast Tissue at 7 T

PURPOSE

The identification of the phosphodiester (PDE) (31)P MR signals in the healthy human breast at ultra-high field.

METHODS

In vivo (31)P MRS measurements at 7 T of the PDE signals in the breast were performed investigating the chemical shifts, the transverse- and the longitudinal relaxation times. Chemical shifts and transverse relaxation times were compared with non-ambiguous PDE signals from the liver.

RESULTS

The chemical shifts of the PDE signals are shifted -0.5 ppm with respect to glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE), and the transverse and longitudinal relaxation times for these signals are a factor 3 to 4 shorter than expected for aqueous GPC and GPE.

CONCLUSION

The available experimental evidence suggests that GPC and GPE are not the main source of the PDE signals measured in fibroglandular breast tissue at 7 T. These signals may predominantly originate from mobile phospholipids.

Increased sensitivity of 31P MRSI using direct detection integrated with multi-echo polarization transfer (DIMEPT)

Here, we show that the sensitivity of (31)P MRSI of (31)P spins J-coupled to protons can be increased by almost a factor of three when compared with an optimal direct detection free induction decay. By direct detection integrated with multi-echo polarization transfer (DIMEPT), multiple signals from polarization transfer and direct detection can be acquired in one repetition time, with minimal mutual interference, provided that the number of refocusing pulses in the multi-echo polarization transfer part is even. The DIMEPT sequence was implemented on a 7-T body scanner and tested on a phantom and on the breasts of five healthy volunteers. The in vivo signal-to-noise ratio (SNR) enhancement for the J-coupled phosphomonoesters was 270% when compared with an Ernst angle pulse-acquire sequence. However, the phosphodiester signals, presumably mainly mobile phospholipids, had T2 values that were too short to be enhanced. Uncoupled (31)P spins, with sufficiently long T2 values, such as inorganic phosphate, were SNR enhanced by a factor of 1.9 relative to an Ernst-angle excitation pulse-acquire sequence by multi-echo direct detection.

Distribution and potential role of cytosolic water-soluble phosphodiesters in fish

The distribution of water-soluble phosphodiesters (WSPDEs) visible by nuclear magnetic resonance (NMR) in some intact tissues of rainbow trout (Oncorhynchus mykiss walbaum) and in perchloric extracts after partial purification was examined by (31)P NMR spectroscopy. The compounds of interest were serine ethanolamine phosphate (SEP), threonine ethanolamine phosphate (TEP), glycerophosphorylcholine (GPC), and glycerophosphorylethanolamine (GPE). TEP and SEP were mostly accumulated in the heart and less accumulated in the kidney of intact trout. After the extraction procedure, two additional minor resonances were visible and identified as GPC and GPE. The liver of trout contained large amounts of GPE. Similar investigations were conducted by (31)P NMR on hearts and kidneys of two elasmobranchs (Scyliorhinus canicula, Raja clavata) and four teleosts (Anguilla anguilla, Sparus auratus, Dicentrarchus labrax, Scophtlhalmus maximus); comparison with the trout data showed striking interspecies differences in the identity of WSPDEs. All teleosts, except eel and turbot, accumulated predominantly TEP. However, in elasmobranchs, first GPC and then GPE were the major compounds. Whatever the studied species, the relative abundances in the heart and kidney were similar. In the last two decades, two hypotheses were proposed to explain the occurrence of high levels of cytosoluble phosphodiesters: these compounds may constitute an index of phospholipid catabolism or a protective mechanism through which phospholipid levels are kept high. To test them and elucidate the role of these compounds in membrane phospholipid regulation in fish, we investigated the effects of two physiological stresses, that is, seawater adaptation and induced myocardial ischemia, on trout cytosolic phosphodiester levels. A 32.5-min ischemic stress caused no effect on SEP and TEP levels. On the contrary, significant osmotic stress induced changes in the PDEs levels: 2 d after transfer from freshwater to seawater or from seawater to freshwater, both tissues displayed a transient decrease of TEP; however, a 2-d stay in seawater after transfer from freshwater caused a rise in SEP concentration, whereas a 2-d stay in freshwater after transfer decreased SEP level. In conclusion, our experiments suggest a relationship between the high levels of cytosoluble phosphodiesters observed in some fish tissues and resistance to stress.

Signal enhancement through heteronuclear polarisation transfer in in-vivo 31P MR spectroscopy of the human brain

Significant (31)P NMR signal enhancement through heteronuclear polarisation transfer was obtained in model solutions and in vivo on a 1.5-T whole-body MR scanner equipped with two RF channels. The much higher population differences involved in proton Zeeman energy levels can be transferred to the (31)P levels with the refocused INEPT (insensitive nucleus enhancement by polarisation transfer) double-resonance experiment by means of a series of simultaneously applied broadband RF pulses. INEPT achieves a polarisation transfer from (1)H to (31)P spin states by directly reordering the populations in spin systems with heteronuclear scalar coupling. Thus, only the (31)P NMR signal of metabolites with scalar (1)H-(31)P coupling is amplified, while the other metabolite signals in the spectra are suppressed. Compared to Ernst-angle excitation, a repetition-time-dependent signal enhancement of eta=(29+/-3)% for methylene diphosphonic acid (MDPA) and eta=(56+/-1)% for phosphorylethanolamine (PE) was obtained on model solutions through optimisation of the temporal parameters of the pulse experiment. The results are in good agreement with numerical calculations of the theoretical model for the studied spin systems. With optimised echo times, in-vivo (31)P signal enhancement of the same order was obtained in studies of the human brain.

Prefrontal membrane phospholipid metabolism of child and adolescent offspring at risk for schizophrenia or schizoaffective disorder: an in vivo 31P MRS study

In vivo (31)P magnetic resonance spectroscopy ((31)P MRS) studies have shown abnormal membrane phospholipid metabolism in the prefrontal cortex (PF) in the early course of schizophrenia. It is unclear, however, whether these alterations also represent premorbid risk indicators in schizophrenia. In this paper, we report in vivo (31)P MRS data on children and adolescents at high risk (HR) for schizophrenia. In vivo (31)P MRS studies of the PF were conducted on 16 nonpsychotic HR offspring of parents with schizophrenia or schizoaffective disorder, and 37 age-matched healthy comparison (HC) subjects. While 11 of the HR subjects had evidence of Axis I psychopathology (HR-P), five HR subjects had none (HR-NP). We quantified the freely mobile phosphomonoester (PME) and phosphodiester (PDE) levels reflecting membrane phospholipid precursors and breakdown products, respectively, and the relatively broad signal underlying PDE and PME peaks, comprised of less mobile molecules with PDE and PME moieties (eg, synaptic vesicles and phosphorylated proteins). Compared to HC subjects, HR subjects had reductions in freely mobile PME; the differences were accounted for mainly by the HR-P subjects. Additionally, HR-P subjects showed increases in the broad signal underlying the PME and PDE peaks in the PF. To conclude, these data demonstrate new evidence for decreased synthesis of membrane phospholipids and possibly altered content or the molecular environment of synaptic vesicles and/or phosphoproteins in the PF of young offspring at risk for schizophrenia. Follow-up studies are needed to examine the predictive value of these measures for future emergence of schizophrenia in at-risk individuals.

In vivo magnetic resonance spectroscopy and its application to neuropsychiatric disorders

In vivo magnetic resonance spectroscopy (MRS) is the only noninvasive imaging technique that can directly assess the living biochemistry in localized brain regions. In the past decade, spectroscopy studies have shown biochemical alterations in various neuropsychiatric disorders. These first-generation studies have, in most cases, been exploratory but have provided insightful biochemical information that has furthered our understanding of different brain disorders. This review provides a brief description of spectroscopy, followed by a literature review of key spectroscopy findings in schizophrenia, affective disorders, and autism. In schizophrenia, phosphorus spectroscopy studies have shown altered metabolism of membrane phospholipids (MPL) during the early course of the illness, which is consistent with a neurodevelopmental abnormality around the critical period of adolescence when the illness typically begins. Children and adolescents who are at increased genetic risk for schizophrenia show similar MPL alterations, suggesting that schizophrenia subjects with a genetic predisposition may have a premorbid neurodevelopmental abnormality. Independent of medication status, bipolar subjects in the depressive state tended to have higher MPL precursor levels and a deficit of high-energy phosphate metabolites, which also is consistent with major depression, though these results varied. Further bipolar studies are needed to investigate alterations at the early stage. Lastly, associations between prefrontal metabolism of high-energy phosphate and MPL and neuropsychological performance and reduced N-acetylaspartate in the temporal and cerebellum regions have been reported in individuals with autism. These findings are consistent with developmental alterations in the temporal lobe and in the cerebellum of persons with autism. This paper discusses recent findings of new functions of N-acetylaspartate.

Neurochemical investigation of the schizophrenic brain by in vivo phosphorus magnetic resonance spectroscopy

Abnormal phospholipid metabolisms may play important roles in the pathophysiology of schizophrenia. Phosphorus magnetic resonance spectroscopy (31P-MRS) offers a new method for studying phosphorus-related metabolism in vivo. A decrease in the level of phosphomonoesters (PME) and an increase in the level of phosphodiesters (PDE) has been demonstrated in the prefrontal lobe of neuroleptic-naive schizophrenic patients. Most of the studies in medicated schizophrenic patients have shown decreased PME and/or increased PDE. The decreased PME in the frontal lobe appears to be associated with negative symptoms and poor working memory performance. 1H-decoupled 31P-MRS revealed a reduction in the phosphocholine element of PME and an elevation in the mobile phospholipids of PDE in the prefrontal region of medicated schizophrenic patients. PDE were elevated in the temporal lobes of neuroleptic-naive schizophrenic patients, and this increase was partially normalized by haloperidol administration. Data about the temporal lobes of medicated schizophrenic patients have not been consistent. Except for the reduction in the adenosine triphosphate (ATP) in the basal ganglia and the correlation between the increase in the frontal lobe phosphocreatine (PCr) and negative symptomatology, data related to changes in high-energy phosphates are contradictory. No consensus on the effect of neuroleptics on phosphorus metabolites has been achieved. Methodological problems inherent in 31P-MRS may have contributed to the confusion in understanding available data. Future directions of MRS studies are suggested in the last section of the paper.

Postprocessing method to segregate and quantify the broad components underlying the phosphodiester spectral region of in vivo (31)P brain spectra

In a typical, in vivo (31)P brain spectrum, the phosphomonoester (PME) and phosphodiester (PDE) spectral region not only contains signals from freely mobile PMEs and PDEs (which are anabolic and catabolic products of membrane phospholipids) but also signals of broader underlying lineshapes from less-mobile molecules. In general, either the PME and PDE resonances are quantified as a combined value of freely mobile metabolites plus less-mobile molecules or the broader underlying signal is reduced/eliminated prior to or post data collection. In this study, a postprocessing method that segregates and quantifies the individual contributions of the freely mobile metabolites and the less-mobile molecules is introduced. To demonstrate the precision and accuracy of the method, simulated data and in vivo (31)P brain spectroscopy data of healthy individuals were quantified. The ability to segregate and quantify these various PME and PDE contributions provides additional spectral information and improves the accuracy of the interpretation of (31)P spectroscopy results. Magn Reson Med 45:390-396, 2001.

Changes in levels of phosphorus metabolites in temporal lobes of drug-naive schizophrenic patients

OBJECTIVE

The authors examined phospholipids and high-energy phosphorus metabolism in the temporal lobes of drug-naive schizophrenic patients.

METHOD

In vivo 31P magnetic resonance spectroscopy was performed on 17 first-episode, drug-naive schizophrenic patients and 17 age- and gender-matched healthy subjects.

RESULTS

Patients showed higher levels of phosphodiesters and lower levels of phosphomonoesters than the comparison group. Phosphocreatine levels were increased in the left temporal lobes of patients.

CONCLUSIONS

The results suggest disturbed membrane phospholipid metabolism in both temporal lobes and decreased energy demands in the left temporal lobes of drug-naive schizophrenic patients.

31Phosphorus magnetic resonance spectroscopy of the dorsolateral prefrontal region in schizophrenics--a study including 50 patients and 36 controls

BACKGROUND

In a preliminary study we found decreased phosphodiester (PDE)% values and an increased phosphomonoester (PME)/phosphodiester ratio in the dorsolateral prefrontal region (DLPFR) of 13 chronic schizophrenics vs. 14 controls using 31phosphorus magnetic resonance spectroscopy (31P-MRS). Since these results are in contrast to the findings of other groups, we increased our study group to a total of 50 chronic schizophrenics on stable neuroleptic medication and 36 controls to minimize the possibility of a chance result due to small sample size.

METHODS

An image-selected in vivo 31P-MRS method on a Philips Gyroscan ACS II scanner working at 1.5 T was used.

RESULTS

We could confirm our earlier findings of decreased PDE% levels in schizophrenics. Additionally, we found phosphocreatine (PCr)% and PCr/adenosine triphosphate (ATP) to be increased in the schizophrenics. While no association between PME% and PDE% with neuroleptic medication was found, ATP% correlated positively and PCr/ATP negatively with the chlorpromazine equivalent dose.

CONCLUSIONS

The decreased PDE% levels might be characteristic only for chronic, neuroleptic-treated patients. The finding of altered high-energy phosphate levels can be interpreted as an indication of decreased energy-demanding processes in the DLPFR of the investigated patients compared to controls.

Multiple regression analysis of relationship between frontal lobe phosphorus metabolism and clinical symptoms in patients with schizophrenia

We investigated the differences among diagnostic types of 36 schizophrenic patients in the brain phosphorus metabolism in the frontal lobe. We performed phosphorus-31 magnetic resonance spectroscopy (31P-MRS) in the frontal region in patients with schizophrenia of the catatonic (n = 4), disorganized (n = 8), paranoid (n = 10) and undifferentiated (n = 14) types. In the disorganized type, the PME level was significantly decreased compared to those in the other three types, while the phosphodiester (PDE) level tended to be higher, although not significantly, than those in the other types. Using multiple regression analysis, we investigated whether or not the clinical symptoms were correlated with the brain phosphorus metabolism. An increased motor retardation factor score was significantly correlated with decreased PME level, whereas more severe emotional withdrawal and blunted affect were associated with increased PDE level. These results suggest that altered membrane phospholipid metabolism in the frontal region may be associated with negative symptoms and that schizophrenia of the disorganized type is associated with more severe negative symptoms and may present more severe brain abnormalities compared to the other types.

31P-NMR determinations of cytosolic phosphodiesters in turtle hearts

As part of our ongoing research on cardiac hypoxia tolerance we have conducted 31P nuclear magnetic resonance (NMR) studies of isolated, perfused, working hearts from freshwater turtles, animals that are well known for their ability to tolerate prolonged periods of anoxia. A striking feature of turtle heart spectra is an extremely high concentration of NMR visible phosphodiesters (PDEs). Cardiac spectra from mammals, on the other hand, typically exhibit only a small resonance in the PDE region. Our aim in this study was to compare myocardial PDE profiles between the highly hypoxia tolerant western painted turtle (Chrysemys picta bellii) and the relatively hypoxia sensitive softshelled turtle (Trionyx spinifer) in order to begin to rest the hypothesis that high constitutive levels of cytosolic PDEs may play a role in conferring hypoxia and ischemia tolerance on the myocardium. We also collected 31P-NMR spectra of PCA extracts of tissue from these species and from Kemp's ridley sea turtles (Lepidochelys kempi), as well as spectra from isolated hearts and PCA extracts of red-eared sliders (Trachemys [formerly Pseudemys] scripta]). Total NMR visible phosphodiesters make up 24 +/- 8.6% of the total NMR visible phosphorus in Chrysemys hearts, 20.7 +/- 5.9% in Trachemys hearts, but only 12.2 +/- 5.1% in Trionyx hearts (P < 0.05). We have identified three distinct PDEs in turtle hearts: glycerophosphorylcholine (GPC); glycerophosphorylethanolamine (GPE); and serine ethanolamine phosphodiester (SEP). SEP is the dominant compound in Chrysemys and Trachemys (79.3 +/- 10.2% and 84.7 +/- 3.7% of total PDE, respectively), while GPC is most abundant in Trionyx (74.0 +/- 4.3% of total PDE) and Lepidochelys (not quantitated). The function of this class of compounds is unclear but it has been suggested that cytosolic PDEs may function as lysophospholipase inhibitors, a role that would decrease the rate of membrane phospholipid turnover. Our comparative data suggest that cytosolic PDEs could play a role in phospholipid sparing during anoxic or ischemic stress in turtles but a direct test of this hypothesis awaits future experimentation.

Phosphorus magnetic resonance spectroscopy in schizophrenia: correlation between membrane phospholipid metabolism in the temporal lobe and positive symptoms

1. To determine any correlations between phosphorus metabolites in the temporal lobes and clinical symptoms in schizophrenic patients, the authors performed 31phosphorus magnetic resonance spectroscopy in 31 medicated patients and age- and sex- matched normal subjects. 2. Schizophrenic patients demonstrated an increased level of phosphodiesters (PDE) in the temporal lobes bilaterally and a decreased level of beta-adenosine triphosphate (beta-ATP) in the left temporal lobe. 3. A significant positive correlation was observed between the level of PDE in the left temporal lobe and the score of positive symptoms on the Brief Psychiatric Rating Scale. 4. These results suggest that altered membrane phospholipid metabolism in the left temporal lobe is associated with neuroleptic-resistant positive symptoms in schizophrenic patients.

In vivo detection of myelin phospholipids in multiple sclerosis with phosphorus magnetic resonance spectroscopic imaging

The goal of this study was to investigate myelin phospholipids in vivo in multiple sclerosis lesions and normal-appearing white matter by evaluating the spectral broad component from phosphorus 31 magnetic resonance spectroscopic imaging data. The phospholipid broad component was reduced nearly 35% (p < 0.001) in both lesions and in normal-appearing white matter in multiple sclerosis subjects compared to control subjects, suggesting reduced myelin phospholipid concentration or altered relaxation times.

31P magnetic resonance spectroscopy of the medial temporal lobe of schizophrenic patients with neuroleptic-resistant marked positive symptoms

31P magnetic resonance spectroscopy was performed in 16 mediated schizophrenic patients with neuroleptic-resistant marked positive symptoms and in 16 healthy volunteers matched for age and sex in order to determine what changes in phosphorus metabolites are detected in such patients as compared to the controls. The schizophrenic patients showed an increased level of phosphodiesters in the bilateral medial temporal lobes. They also showed a decrease in the level of beta-ATP in the left medial temporal lobe. These findings suggest that schizophrenic patients with prominent positive symptoms refractory to neuroleptics may have a disturbance of bilateral membrane phospholipid and left-sided high-energy phosphate metabolism in the medial temporal lobe.

An assessment of spin-echo rotating-frame imaging for spatially localized determination of short T2 relaxation times in vivo

The rotating frame of localized spectroscopy can be augmented by the inclusion of a refocusing pulse to enable the measurement of T2 relaxation times. This technique is particularly appropriate for determining short relaxation parameters due to the absence of time consuming switched B(omicron) field gradients. We have evaluated the accuracy of this protocol by measuring localized T2s in the range of 1 to 20 ms. Preliminary data obtained from muscle and liver of normal and iron overloaded human subjects are also presented.

Studies of human tumors by MRS: a review

The literature describing 31P, 1H, 13C, 23Na and 19F MRS in vivo in human cancers is reviewed. Cancers have typical metabolic characteristics in 31P and 1H MRS including high levels of phospholipid metabolites and a cellular pH more alkaline than normal. These alone are not specific for cancer but are diagnostic in appropriate clinical settings. Some metabolic characteristics appear to be prognostic indices and correlation with treatment response is emerging as an important potentially cost-effective use of MRS in oncology. 19F MRS examines pharmacokinetics of 5-fluorouracil and by demonstrating its retention predicts response of a cancer to treatment. Current needs include improvement of diagnostic specificity by use of techniques like multivoxel MRS, proton decoupling of 31P, short echo time and fat-suppressed 1H MRS, 13C MRS direct or via 1H-observe, and statistical analysis of multiple spectral features. Trials in large populations in well defined clinical settings are needed to determine if MRS can provide independent prognostic indices useful in cancer management.