Phosphorus 31 NMR of neuroblastoma clonal lines. Effect of cell confluency state and dibutyryl cyclic AMP

ATP, the 31P Spectral Modulus, and Metabolism

Adenosine triphosphate (ATP) has a high intracellular millimolar concentration (ca. 2.4 mM) throughout the phylogenetic spectrum of eukaryotes, archaea, and prokaryotes. In addition, the function of ATP as a hydrotrope in the prevention of protein aggregation and maintenance of protein solubilization is essential to cellular, tissue, and organ homeostasis. The 31P spectral modulus (PSM) is a measure of the health status of cell, tissue, and organ systems, as well as of ATP, and it is based on in vivo 31P nuclear magnetic resonance (31P NMR) spectra. The PSM is calculated by dividing the area of the 31P NMR integral curve representing the high-energy phosphates by that of the low-energy phosphates. Unlike the difficulties encountered in measuring organophosphates such as ATP or any other phosphorylated metabolites in a conventional 31P NMR spectrum or in processed tissue samples, in vivo PSM measurements are possible with NMR surface-coil technology. The PSM does not rely on the resolution of individual metabolite signals but uses the total area derived from each of the NMR integral curves of the above-described spectral regions. Calculation is based on a simple ratio of the high- and low-energy phosphate bands, which are conveniently arranged in the high- and low-field portions of the 31P NMR spectrum. In practice, there is essentially no signal overlap between these two regions, with the dividing point being ca. -3 δ. ATP is the principal contributor to the maintenance of an elevated PSM that is typically observed in healthy systems. The purpose of this study is to demonstrate that (1) in general, the higher the metabolic activity, the higher the 31P spectral modulus, and (2) the modulus calculation does not require highly resolved 31P spectral signals and thus can even be used with reduced signal-to-noise spectra such as those detected as a result of in vivo analyses or those that may be obtained during a clinical MRI examination. With increasing metabolic stress or maturation of metabolic disease in cells, tissues, or organ systems, the PSM index declines; alternatively, with decreasing stress or resolution of disease states, the PSM increases. The PSM can serve to monitor normal homeostasis as a diagnostic tool and may be used to monitor disease processes with and without interventional treatment.

Effect of glucose and confluency on phosphorus metabolites of perfused human prostatic adenocarcinoma cells as determined by 31P MRS

A series of perfused cell 31P MRS studies were conducted using a well established human prostate adenocarcinoma cell line (DU 145) at different phases of growth, and exposed to varying glucose concentrations during growth. The spectral characteristics of perfused DU 145 cells were compared with the same cells grown in nude mice (xenografts). Perfused DU 145 cells had lower levels of inorganic phosphate and phosphocreative relative to in vivo nude mice xenografts. 31P MR spectra obtained from perfused cells at different phases of growth and exposed to varying glucose concentrations during grown suggest that increases in diphosphodiester levels are associated with high glucose concentrations and confluency. Perfused DU 145 cells grown in 5.5 mM glucose and harvested at log phase of growth best reflected the phosphorus MR spectra of the same cell line grown in nude mice.

Comparative 31P and 1H NMR studies on rat astrocytes and C6 glioma cells in culture

Rat astroglial cells in primary culture (95% enrichment) and C6 glioma cells were adapted to grow on microcarrier beads. In vivo 31P NMR spectra were collected from cell-covered beads perfused in the NMR tube. The NMR-visible phosphorylated metabolite contents of both cell types were determined using saturation factors calculated from the values of longitudinal relaxation times determined for C6 cells using progressive saturation experiments. On the other hand, the amounts of phosphorylated metabolites in cells were determined from proton decoupled 31P NMR spectra of cell perchloric acid extracts. The results indicate that the NTP and Pi contents of the normal and tumoral cells were similar, whereas the PCr level was higher in C6 cells and the NDP and phosphomonoester levels higher in astrocytes. The comparison of 1H NMR spectra of cell perchloric acid extracts evidenced larger inositol and alanine contents in C6 cells, whereas larger taurine and choline (and choline derivatives) contents were found in astrocytes. The Glu/Gln ratio was very different, 3.5 and 1 in C6 cells and astrocytes, respectively. In both cases, the more intense resonance in the 1H NMR spectrum was assigned to glycine. Based on the comparison of the metabolite content of a tumoral and a normal cell of glial origin, this work emphasizes the usefulness of a multinuclear NMR study in characterizing intrinsic differences between normal and tumoral cells.

31P nuclear magnetic resonance study of phospholipid metabolites in ischemic liver

To assess the metabolic alterations induced by normothermic hepatic ischemia, 31P nuclear magnetic resonance analysis was performed on liver samples using perchloric acid extraction. In particular, phosphomonoesters and phosphodiesters, the intermediary metabolites of membrane phospholipid turnover, were characterized precisely and quantitated. Phosphocholine and phosphoethanolamine, the precursors of phospholipid anabolism, did not change, while the phosphodiesters decreased. In contrast, alpha-glycerophosphate, which is both a precursor of phospholipid synthesis and the intermediary product of phospholipid degradation, markedly increased following 30 min of normothermic ischemia. These findings suggest that cellular phospholipids are actively degraded during normothermic hepatic ischemia.

Molecular insights into schizophrenia

A number of studies have demonstrated alterations in the structure and function of the frontal cortex in some schizophrenic patients. The possible etiology and pathogenesis of these abnormalities are unknown, but genetic and developmental causes are frequently mentioned. Recent in vivo 31P NMR studies of the dorsal prefrontal cortex have been conducted in eleven neuroleptic naive, first episode schizophrenic patients and compared with normal controls of comparable age, educational level and parental educational level. The findings in the schizophrenic patients are different from those of normal IQ adult autistic patients of comparable age and Alzheimer's patients but similar to normal elderly controls. These studies show decreased frontal lobe utilization of adenosine triphosphate in the schizophrenic patients which suggests a hypoactive dorsal prefrontal cortex. In addition, indices of membrane phospholipid metabolism are altered in the schizophrenic patients. However, the findings in the schizophrenic patients are quite similar to those observed in normal elderly controls and to those that normally occur to a lesser degree during adolescence. The phospholipid alterations observed in the schizophrenic patients are compatible with either premature aging or altered timing and exaggeration of the regressive events which occur during normal brain development. The changes in high-energy phosphate metabolism observed in the schizophrenic patients may prove to be state dependent, but the changes in membrane phospholipid metabolism could be related to molecular changes that precede the onset of clinical symptoms and brain structural changes in schizophrenia. These findings suggest new avenues of thinking about the pathogenesis and treatment of schizophrenia.

A perfusion system developed for 31P NMR study of melanoma cells at tissue-like density

A perfusion culture system has been developed for 31P NMR study of human uveal melanoma metabolism by adapting the Vitafiber I cartridge system (Amicon). 31P NMR spectra collected weekly during periods of up to 10 weeks demonstrated increasing levels of phosphorus metabolites as the anchorage-dependent cells grew to tissue-like density.

31P-NMR studies of normal and dystrophic chicken muscle

Phosphorus-31 nuclear magnetic resonance (31P-NMR) analysis was performed on normal (line 412) and dystrophic (line 413) superficial pectoralis muscles excised from chickens between 15 and 116 days after hatching. An apparent alteration in dystrophic muscle energy metabolism was abolished by pretreatment with curare and was attributed to muscle hyperexcitability. Time-dependent 31P-NMR studies demonstrated no apparent difference in the overall tissue adenosine triphosphatase (ATPase) activity of dystrophic as compared to normal muscle. After 55 days of age, a resonance signal attributed to serine ethanolamine phosphodiester (SEPDE) was observed only in dystrophic muscle. Adding the paramagnetic cation Mn2+ to the buffer surrounding the muscle resulted in an approximate 80% decrement in the dystrophic SEPDE signal without apparent alteration of the other phosphatic signals in either the normal or dystrophic muscle. This would argue against any generalized membrane defect in dystrophic chicken muscle and suggest that SEPDE is in a compartment accessible to Mn2+.

P-31 nuclear magnetic resonance analysis of brain: normoxic and anoxic brain slices

Perchloric acid extracts were prepared from liquid-N2-frozen gerbil and guinea pig brain slices studied under one of three conditions: O2-incubated, N2-incubated or O2-incubated recovery following N2 incubation. Mole percentages of the various phosphatic components contained in the extracts were determined by phosphorus-31 nuclear magnetic resonance spectroscopy. The brain slice extract spectrum revealed a previously unreported group of brain phosphodiesters at -0.73 delta relative to 85% orthophosphoric acid. Although the phosphatic profiles from O2-incubated slices from gerbils and guinea pigs revealed only minor species variations, which differed quantitatively rather than qualitatively, species-specific differences were made readily apparent and amplified by incubating brain slices under oxygen-deficient conditions. Despite these differences which were most prevalent during the recovery phase, the overall metabolic changes described herein in response to N2-incubation were in accord with the results obtained by other analytical techniques. Inorganic orthophosphate (2.63 delta) was increased, while nucleoside (principally, adenosine) triphosphate (alpha-, -10.92 delta, beta-, -21.45 delta, and gamma-, -5.80 delta) and phosphocreatine (-3.12 delta) levels were decreased in response to N2 incubation. In addition, inosine monophosphate (3.78 delta) was increased and the levels of a partially characterized acid-labile phosphate (0.85 delta, guinea pig) were decreased upon N2 incubation. Phosphoglyceride metabolism also appeared to be altered by oxygen deprivation (gerbil). These latter findings provide additional information concerning the metabolic responses of cerebral tissue to oxygen deficient conditions.

A hypothesis: noncyclic phosphodiesters may play a role in membrane control

The study of the metabolism of GPC and SEP has the potential to demonstrate a previously undiscovered method by which the cytosol can communicate with membrane.