In Vitro 31P MR Chemical Shifts of In Vivo-Detectable Metabolites at 3T as a Basis Set for a Pilot Evaluation of Skeletal Muscle and Liver 31P Spectra with LCModel Software

Most in vivo 31P MR studies are realized on 3T MR systems that provide sufficient signal intensity for prominent phosphorus metabolites. The identification of these metabolites in the in vivo spectra is performed by comparing their chemical shifts with the chemical shifts measured in vitro on high-field NMR spectrometers. To approach in vivo conditions at 3T, a set of phantoms with defined metabolite solutions were measured in a 3T whole-body MR system at 7.0 and 7.5 pH, at 37 °C. A free induction decay (FID) sequence with and without 1H decoupling was used. Chemical shifts were obtained of phosphoenolpyruvate (PEP), phosphatidylcholine (PtdC), phosphocholine (PC), phosphoethanolamine (PE), glycerophosphocholine (GPC), glycerophosphoetanolamine (GPE), uridine diphosphoglucose (UDPG), glucose-6-phosphate (G6P), glucose-1-phosphate (G1P), 2,3-diphosphoglycerate (2,3-DPG), nicotinamide adenine dinucleotide (NADH and NAD+), phosphocreatine (PCr), adenosine triphosphate (ATP), adenosine diphosphate (ADP), and inorganic phosphate (Pi). The measured chemical shifts were used to construct a basis set of 31P MR spectra for the evaluation of 31P in vivo spectra of muscle and the liver using LCModel software (linear combination model). Prior knowledge was successfully employed in the analysis of previously acquired in vivo data.

Mineral Intake and Clinical Symptoms in Adult Patients with Hypophosphatasia

Background Hypophosphatasia (HPP) is a rare inherited metabolic disorder characterized by deficient activity of the tissue-nonspecific alkaline phosphatase entailing impaired turnover of phosphorus metabolites. Dietary mineral intake is suspected to influence clinical symptoms of HPP, but scientific evidence is missing. Methods Cross-sectional matched-pairs study collecting comprehensive data on nutrient intake in 20 HPP patients and 20 unaffected, age- and gender-matched controls. Dietary information and clinical symptoms were documented in detail over 7 consecutive days using structured diaries. Results Baseline data and type of energy-supplying nutrients were balanced between both groups. Median nutritional intake of phosphorus and calcium were significantly lower in HPP patients versus controls, which is partially attributable to lower energy consumption in HPP patients. Differences regarding phosphorus and calcium (Ca/P) ratio and uptake of magnesium, zinc, and vitamin B6 were not statistically significant. Both high (≥ 1375 mg/d) and low intakes (< 1100 mg/d) of phosphorus were significantly associated with an increased frequency of neuropsychiatric symptoms (P = 0.02). Similarly, very high and very low intake of calcium was significantly associated with musculoskeletal (P < 0.01), gastrointestinal (P = 0.02), and neuropsychiatric (P < 0.001) symptoms. An increased Ca/P ratio was associated with increased tiredness/fatigue (P < 0.01), whereas a decreased Ca/P was associated with gastrointestinal issues (P = 0.01). Conclusion Phosphorus and calcium intake seem reduced in HPP patients along with reduced total energy consumption. Particularly high as well as very low absolute or unbalanced phosphorus and calcium intake are associated with an increased frequency of clinical symptoms.

Growth-related changes of phosphorus metabolites in VX-2 carcinoma implanted into rabbit thigh muscle: in vivo 31P MR spectroscopy

The purpose of this study was to evaluate the usefulness of in vivo 31P magnetic resonance spectroscopy (MRS) for monitoring changes in growth-related phosphate metabolite concentration and intracellular pH value in rabbit thigh muscle implanted with VX-2 carcinoma. The time-course magnetic resonance imaging (MRI) and in vivo 31P MRS were examined weekly in the course of 10 weeks following the onset of a VX-2 carcinoma implantation. The spectra were quantitatively analyzed to obtain vital information on the time course variation of the phosphorus metabolites and intracellular pH value according to the tumor growth. Elevation in the concentrations of phosphormonoesters (PME), inorganic phosphate (Pi), and phosphodiesters (PDE) was observed over the time course of 3-4 weeks after the implantation of VX2 carcinoma, while the rest of the metabolites, PCr and ATP tended to be constant. The concentration changes of PME, Pi, and PDE were positively correlated with the volumes of tumor necrosis. The intracellular pH values decreased with the time course of tumor growth and the volumes of tumor necrosis. In vivo 31P MRS is capable of non-invasive monitoring of intracellular pH values as well as the concentration changes of phosphate metabolites during tumor growth.

Transgenic livers expressing mitochondrial and cytosolic CK: mitochondrial CK modulates free ADP levels

The function of creatine kinase (CK) and its effect on phosphorus metabolites was studied in livers of transgenic mice expressing human ubiquitous mitochondrial CK (CK-Mit) and rat brain CK (CK-B) isoenzymes and their combination.31P NMR spectroscopy and saturation transfer were recorded in livers of anesthetized mice to measure high-energy phosphates and hepatic CK activity. CK reaction velocity was related to total enzyme activity irrespective of the isoenzyme expressed, and it increased with increasing concentrations of creatine (Cr). The fluxes mediated by both isoenzymes in both directions (phosphocreatine or ATP synthesis) were equal. Over a 20-fold increase in CK-Mit activity (28–560 μmol · g wet wt−1 · min−1), the fraction of phosphorylated Cr increased 1.6-fold. Hepatic free ADP concentrations calculated by assuming equilibrium of the CK-catalyzed reaction in vivo decreased from 84 ± 9 to 38 ± 4 nmol/g wet wt. Calculated free ADP levels in mice expressing high levels of CK-B (920–1,635 μmol · g wet wt−1 · min−1) were 52 ± 6 nmol/g wet wt. Mice expressing both isoenzymes had calculated free ADP levels of 36 ± 4 nmol/g wet wt. These findings indicate that CK-Mit catalyzes its reaction equally well in both directions and can lower hepatic apparent free ADP concentrations.

31P NMR quantitation of phosphorus metabolites in rat heart and skeletal muscle in vivo

The aim of this study was to examine two methods of 31P NMR quantitation of phosphocreatine (PCr), ATP, and Pi in rat heart and skeletal muscle in vivo. The first method employed an external standard of phenylphosphonic acid (PPA; 10 mM), and the second method used an enzymatic measurement of tissue ATP equated to the area under the βATP peak. With the use of the external standard, the concentrations of ATP, PCr, and Pi in the rat heart were 4.48 ± 0.33, 9.21 ± 0.65, and 2.25 ± 0.16 μmol/g wet wt, respectively. With the use of the internal ATP standard, measured on the same tissue, the contents (means ± SE) were 4.78 ± 0.19, 9.83 ± 0.18, and 2.51 ± 0.33 μmol/g wet wt, respectively ( n = 7). In skeletal muscle, ATP, PCr, and Pi were 6.09 ± 0.19, 23.44 ± 0.88, and 1.81 ± 0.18 μmol/g wet wt using the PPA standard and 6.03 ± 0.19, 23.30 ± 1.30, and 1.82 ± 0.19 μmol/g wet wt using the internal ATP standard ( n = 6). There was no significant difference for each metabolite as measured by the two methods of quantification in heart or skeletal muscle. The results validate the use of an external reference positioned symmetrically above the coil and imply that each has similar NMR sensitivities (similar signal amplitude per mole of 31P between PPA and tissue phosphorus compounds). We conclude that PCr, ATP, and Pi are nearly 100% visible in the normoxic heart and nonworking skeletal muscle given the errors of measurement.