Phosphorylated metabolites in tumors, tissues, and cell lines

First proof-of-concept of UC/HILIC for extending the versatility of the current art of supercritical fluid separation

Supercritical Fluid Chromatography (SFC), a high-throughput separation technique, has been widely applied as a promising routine method in pharmaceutical, pesticides, and metabolome analysis in the same way as conventional liquid chromatography and gas chromatography. Unified chromatography (UC), an advanced version of SFC, which applied gradient elution with mobile phase changing continuously from supercritical to subcritical and to liquid states, can further extend the SFC applications. UC mostly applying the popular mobile phase of 95%:5%/Methanol:Water with additives allows to analyze many hydrophilic compounds. However, many of phosphorylated metabolites or multi carboxylic acids show very poor peak shapes or even can't be eluted under UC conditions, thus hampering the UC's metabolome coverage. In this study, we proposed the first proof-of-concept of UC/HILIC, a novel strategy to extend the current UC metabolome coverage by employing an aqueous gradient right after the UC gradient on a single packed column in a single measurement. The proposed method showed significant improvement regarding the chromatographic performance and metabolome coverage, while still maintaining the precision and high throughput in comparison with conventional UC methods.

Application of 31P NMR spectroscopy to monitor chemotherapy-associated changes of serum phospholipids in patients with malignant lymphomas

31P spectra were obtained from 22 healthy volunteers and 35 patients with malignant lymphomas. Sera from patients were collected at the time of diagnosis and at several time-points during therapy. Long-term follow-up studies showed a good correlation between the 31P NMR spectra of sera and the clinically evident response of the disease to the chemotherapy. During therapy leading to remission resonance from phospholipids increased progressively resulting in spectra similar to those seen in normal sera. By contrast, in patients who did not respond to therapy the intensities of the phospholipid peaks remained relatively low or became progressively reduced as the disease progressed. To understand the source of the spectral differences, we also examined the concentrations of high-density lipoprotein, low-density lipoprotein, cholesterol, and triglycerides. In individuals responding to the treatment, both high-density lipoprotein and cholesterol increased to the point where they were statistically equivalent to those from healthy volunteers.

Simultaneous extraction of cellular lipids and water-soluble metabolites: evaluation by NMR spectroscopy

A method for simultaneous extraction of lipids and water-soluble metabolites from a single cell sample was developed and optimized for NMR spectroscopy. Intermediary metabolites in cultured M2R mouse melanoma cells and changes therein in response to challenge with melanotropin were studied by 31P and 13C NMR. Cells were extracted with methanol, chloroform, and water (1:1:1, v/v/v). The contents of the chloroform and methanol-water phases were separated and quantitatively recovered. The contents of the upper and lower phases compared well with the homologous fractions obtained by perchloric acid and Folch's lipid extraction methods. The pH of the extracts remained within the physiologic range, eliminating potential deleterious effect on cellular metabolites. The water phase contained minimal amounts of salts, making these extracts amenable to subsequent analytical procedures. Obtaining lipid- and water-soluble metabolites from the same sample enables characterization of metabolic pathways that bridge the two cellular components in a quantitative manner.

NOE enhancements and T1 relaxation times of phosphorylated metabolites in human calf muscle at 1.5 Tesla

Nuclear Overhauser effect (NOE) enhancements and relaxation times of 31P metabolites in human calf were measured in 12 volunteers (4 men and 8 women) at 1.5 T using a dual tuned four-ring birdcage. The NOE enhancements of inorganic phosphate (Pi), phosphocreatine (PCr), gamma-, alpha-, and beta-nucleoside triphosphate (NTP) from 19 measurements were 0.51 +/- 0.10, 0.64 +/- 0.03, 0.53 +/- 0.03, 0.56 +/- 0.08, and 0.47 +/- 0.05, respectively. The relaxation times were independent of proton irradiation and from 23 measurements were 3.49 +/- 0.35, 4.97 +/- 0.58, 4.07 +/- 0.36, 2.90 +/- 0.25, and 3.61 +/- 0.25 s for Pi, PCr, gamma-, alpha-, and beta-NTP, respectively. No significant differences between gender and age were observed for either NOE enhancements or relaxation times. Also, among nine volunteers, we observed no significant differences in T1 between the coupled and decoupled cases.

Magnetic resonance spectroscopy detects metabolic differences between seven Dunning rat prostate tumor sublines with different biological behavior

In this study, it was investigated whether prostate tumor biological parameters correlate with metabolic profiles. 1H and 31P magnetic resonance spectra were acquired from perchloric acid extracts of seven Dunning R-3327 prostate tumor sublines. Several metabolic ratios, for example, phosphocholine/total phosphate, choline/total creatine, and inositol/total creatine, did not correlate specifically with one biological characteristics but, based on each of these ratios, the well-differentiated, nonmetastatic, and hormone-dependent sublines could be discriminated from the poorly differentiated or anaplastic, metastatic, and hormone-independent sublines. The glycerophosphoethanolamine/total phosphate, glycerophosphocholine/total phosphate, and phosphocreatine/total phosphate ratios correlated with differentiation grade, and the differences in glycerophosphorylglycerol/total phosphate ratio between metastatic and nonmetastatic sublines was highly significant. No correlation for hormonal sensitivity with any of the metabolites measured could be found, neither by 31P nor by 1H MRS.

Characterization of a phosphonium analog of choline as a probe in 31P NMR studies of phospholipid metabolism

Tumors and transformed cells have been shown by 31P NMR to contain elevated concentrations of two phosphomonoesters, phosphorylcholine and phosphorylethanolamine, involved in phospholipid metabolism. In order to understand the biochemical basis for these phenomena new methods are needed to allow for analysis of the relevant metabolic pathways in intact cells. One such promising tool may be phosphonium-choline, a 31P NMR-visible analog of choline in which the trimethyl-ammonium group of choline has been replaced with a trimethyl-phosphonium moiety. As shown previously [Sim et al. Biochem. J. 154, 303 (1976)], this compound is non-toxic and readily metabolized by cultured cells into phospholipids. In this paper we describe in greater detail some of the chemical and NMR spectroscopic properties of this material. Most significantly we show here that the chemical shift of phosphonium-choline is sensitive to the phosphorylation state of the analog and that the phosphonium nucleus is NMR-visible even after its incorporation into phospholipid. The unique properties of this analog should make it possible to use high-field 31P NMR to follow the flux of phosphonium-choline through the Kennedy pathway in intact perfused cells cultures.

Intracellular acidosis in murine fibrosarcomas coincides with ATP depletion, hypoxia, and high levels of lactate and total Pi

Bioenergetic and metabolic status of murine FSaII tumours were evaluated using 31P MRS, acid extracts ('global' techniques) and quantitative bioluminescence ('microregional' assay). Data obtained from s.c. tumours of varying sizes (44-600 mm3) have been correlated with the oxygenation status evaluated using O2-sensitive needle electrodes. beta-NTP/Pi and phosphocreatine (PCr)/Pi ratios derived from 31P MRS were positively correlated to the median tissue pO2 values. pH declined during growth with intracellular acidosis being evident in tumours > 350 mm3. Whereas lactic acid formation greatly contributed to this decline in small- and medium-sized tumours, ATP hydrolysis and slowing down of the activities of pumps involved in pHi regulation seem to be major factors responsible for intracellular acidification in bulky tumours. PCr levels decreased at an early growth stage, whilst ATP concentrations dropped in bulky malignancies only, coinciding with a decrease in adenylate energy charge and a substantial rise in the levels of total Pi. MRS observable (mobile) Pi was consistently lower than [Pi] measured in acid extracts. On average, median pO2 values of ca 10 mmHg represent a critical threshold for energy metabolism. At higher median O2 tensions, levels of ATP, phosphomonoester and total Pi were relatively constant. This coincided with intracellular alkalosis or neutrality and stable adenylate ratios. On average, median pO2 values < 10 mmHg coincided with intracellular acidosis, ATP depletion, a drop in energy charge and rising Pi levels.

Evaluation of radiation injury by 1H and 31P NMR of human urine

1H and 31P NMR techniques were applied to study the changes in metabolite profiles in human urine resulting from radiation exposure following the Chernobyl reactor accident. In cases of acute leukemia and different accumulated doses of external radiation (from 0.20 to 4.00 Sv), the proton spectra were classified on the basis of the peaks due to N-trimethyl groups, creatinine, citrate, glycine, and hippurate. Unidentified resonances were observed between 15.9 and 21.4 ppm in six phosphorus spectra of patients with preleukemia and acute leukemia. Characteristic spectral changes were similar for external radiation and incorporation-induced internal irradiation. The spectral patterns described may serve as a criterion of radiation injury.

Characterization of human prostate cancer, benign prostatic hyperplasia and normal prostate by in vitro 1H and 31P magnetic resonance spectroscopy

In vitro 1H and 31P magnetic resonance spectra were acquired from perchloric acid extracts of human prostate tissue obtained by transurethral resection. This included tissue of patients with benign prostatic hyperplasia and prostatic adenocarcinoma; one tissue sample was obtained from a patient without any sign of BPH or malignancy. Major resonances in the magnetic resonance spectra were assigned to prostate compounds and were quantified. The citrate/lactate, citrate/total choline, phosphocholine/total creatinine, choline/total creatine, alanine/total creatine, phosphoethanolamine/total phosphate, phosphocholine/total phosphate and glycerophosphoethanolamine/total phosphate ratios were statistically different for the prostate cancer samples as compared with the BPH specimens. These observations may contribute to the understanding of in vivo magnetic resonance spectra of the prostate and indicate that magnetic resonance spectroscopy can aid in the diagnosis of prostate malignancy.

A new NMR airlift bioreactor used in 31P-NMR studies of itaconic acid producing Aspergillus terreus

An airlift bioreactor for in-vivo NMR studies of cells is described. The 10-mm diameter airlift reactor was constructed for studies of mycelial/pellet forming organisms, grown in suspension. With this device 161 MHz 31P-NMR spectra of living Aspergillus terreus cells, producing itaconic acid, have been obtained. Signals were observed for intra- and extracellular orthophosphate, glycerol-3-phosphorylethanolamine (GPE), glycerol-3-phosphorylcholine (GPC), sugar phosphates and polyphosphate. The spectra also showed broad overlapping resonances in the shift range of NAD(H) and NADP(H). Polyphosphate disappeared when the respiratory gas was exchanged for pure N2. The intracellular pH was estimated at 6.2. In spectra of cell extracts approx. 60 peaks were observed in the range of 20 to -22 ppm, and they confirmed the appearance of the metabolites observed in living cells.

Esophageal cancer phospholipid characterization by 31P NMR

Phospholipid extracts of surgical tissue specimens from 18 patients, consisting of normal esophagus, distal esophageal tumor and normal stomach, were analyzed using 31P NMR. The prominent phospholipids detected in these tissues included cardiolipin (CL), phosphatidylethanolamine plasmalogen, phosphatidylethanolamine (PE), phosphatidylserine (PS), sphingomyelin (SPH), phosphatidylinositol (PI), phosphatidylcholine plasmalogen and phosphatidylcholine (PC). Very small quantities of the phospholipids lysophosphatidylcholine, phosphatidic acid, phosphatidylglycerol, and an uncharacterized phospholipid at -0.13 delta also were detected in some of the 54 tissue specimens analyzed. The mean relative concentrations of these phospholipids, in mole percentages of total detected phosphorus, were determined from the acquired spectra and used to differentiate among the three tissue groups. The relative concentrations of the following phospholipids differed significantly (p < 0.001) among the respective tissue groups: normal esophagus vs esophageal tumor, PS, SPH, PI, PC; normal esophagus vs normal stomach, CL, PE, PS, SPH; esophageal tumor vs normal stomach, CL, PE. Membrane phospholipids implicated in modulating the growth and metastases of tumors of epithelial origin can be profiled to discriminate among normal esophagus, distal esophageal tumor and normal stomach using 31P NMR.

In vivo 31P nuclear magnetic resonance spectroscopy of experimental murine tumours and human tumour xenografts: effects of blood flow modification

The effect of hydralazine on tumours appears to vary depending on tumour type. Blood flow and radiation sensitivity decrease more in murine tumours than human tumour xenografts. In this study a comparison between various tumour types has been made using in vivo 31P nuclear magnetic resonance spectroscopy (NMRS) to follow the metabolic responses occurring after clamping or intravenous administration of hydralazine (5 mg kg-1). Large increases in the Pi/total phosphate ratio were found with the murine sarcomas, KHT and RIF-1 implanted into C3H/He mice. However little or no effect was seen for the two human xenografted tumours, HX118 and HT29 implanted in MFI nu/nu/01a mice. An intermediate response was observed for KHT tumours grown in nu/nu mice. All tumours showed a large response to clamping. The anaesthetic Hypnorm/Hypnovel has a great influence on the response of the tumour metabolism to hydralazine appearing to both prolong and increase the changes induced. There is evidence to support the theory that the changes in 31P spectra are related to the oxygen status of the tumours.

Tumors growing in irradiated tissue: oxygenation, metabolic state, and pH

Experimental tumors growing in irradiated tissue have been used to study the biological differences characteristic of locally recurrent tumors. Animal tumors were early generation isotransplants of a spontaneous fibrosarcoma in a C3Hf/Sed mouse, designated FSa-II. Since the hypoxic cell fraction of tumors growing in irradiated tissue is increased, these tumors are assumed to be metabolically deprived with hypoperfusion and acidosis. In this study we directly measured the oxygen partial pressure (pO2) distribution, metabolic state, and pH of tumors growing in an irradiated tumor bed using oxygen sensitive electrodes and 31P-NMR. The results confirmed a three-fold increase in the number of pO2 readings less than or equal to 2.5 mmHg and also showed increased acidosis with a 0.17 unit decrease in pHNMR. When tumors growing in pre-irradiated tissue reached approximately 100 mm3 in volume, a high frequency of gross and microscopic necrosis and hemorrhage was already observed. Consistent with these observations, the phosphocreatine/inorganic phosphate (PCr/Pi) and nucleoside triphosphate/inorganic phosphate (NTP/Pi) ratios were significantly lower in the tumors in a pre-irradiated bed compared to tumors in a non-irradiated bed (PCr/Pi: 0.51 vs 0.79, p less than 0.05; and NTP/Pi: 0.64 vs 0.93, p less than 0.05). The longitudinal relaxation time (T1) of Pi was numerically shorter in control tumors (consistent with the better tissue oxygenation), but this did not reach statistical significance (2.09 +/- .11 sec vs 2.25 +/- .16 sec).

Identification of a naturally occurring methyl-ester of phosphate, methyl-phosphorylcholine (methyl-2-(N,N,N trimethylamino) ethyl phosphate), in the eggs of the sea urchin S. purpuratus

A novel metabolite of choline, phosphorylcholine methyl ester, has been identified in the eggs of S. purpuratus wherein it is present at approximately 1 mM concentration. To the best of our knowledge, this is the first instance of a phosphoryl-methyl-ester to be observed in nature. The compound appears to be species specific, since it has not been observed in other species such as L. pictus and P. depressus. In S. purpuratus its distribution is confined to the ovary, eggs and embryos, and is absent from young animals following metamorphosis.

Metabolic studies of galactosemic cataract

Experimental diabetic and galactosemic animal models are widely used to study diabetes-induced complications. Galactose feeding can rapidly produce cataract, retinopathy and nephropathy; it is therefore favored over the diabetic model. Although the common feature for both models is the activation of aldose reductase, there are substantial differences between the two--not only does the rate of cataract progression differ but the metabolic patterns are far more complex than for polyol production alone. We here present the result of a comparison between diabetic and galactosemic lenses and show the differences in phosphorus and aldose metabolism, cell integrity and osmotic environment.

Metabolic studies with NMR spectroscopy of the alga Dunaliella salina trapped within agarose beads

A technique for the entrapment of the unicellular algae Dunaliella salina in agarose beads and their perfusion during NMR measurements is presented. The trapped cells maintained their ability to proliferate under normal growth conditions, and remained viable and stable under steady-state conditions for long periods during NMR measurements. Following osmotic shock in the dark, prominent changes were observed in the intracellular level of ATP and polyphosphates, but little to no changes in the intracellular pH or orthoposphate content. When cells were subjected to hyperosmotic shock, the ATP level decreased. The content of NMR-visible polyphosphates decreased as well, presumably due to the production of longer, NMR-invisible structures. Following hypoosmotic shock, the ATP content increased and longer polyphosphates were broken down to shorter, more mobile polymers.