Some recent applications of 1H NMR spectroscopy in vivo

Administration and (1)H MRS detection of histidine in human brain: application to in vivo pH measurement

Measurement of histidine in vivo offers the potential for tissue pH measurement using routinely performed (1)H MR spectroscopy. In the brain, however, histidine concentrations are generally too low for reliable measurement. By using oral loading of histidine, this study demonstrates that brain concentrations can be significantly increased, enabling detection of histidine by localized (1)H MR measurements and making in vivo pH measurement possible. In studies carried out on healthy human subjects at 1.5 T, a consistent spectral quality downfield from water was achieved using a PRESS sequence at short echo times. Measurements at different TE values helped to characterize the downfield spectral region. Histidine loading of 400 mg/kg of body weight increased brain histidine levels by approximately 0.8 mM, with maximum histidine concentration reached 4 to 7 hr after consumption. The pH calculated from histidine resonances was 6.96, and a hyperventilation study demonstrated the potential for measuring altered pH.

Determination of metabolite and nucleotide concentrations in proliferating lymphocytes by 1H-NMR of acid extracts

Nuclear magnetic resonance (NMR) studies of extracts have proven to be a powerful window onto the intracellular machinery of cells and tissues. The major advantages of in vitro 1H-NMR, namely chemical preservation, simultaneous detection, identification, and quantitation of compounds, and sensitivity to a large variety of classes of compounds, are employed in this study to characterize the metabolic course of mitogen-stimulated proliferation of human peripheral lymphocytes. A reliable method to quantitate amino acids, metabolic intermediates, soluble membrane lipid precursors, and purine, pyridine and pyrimidine nucleotides is presented, using samples as small as 30 mg wet weight. A total of 53 substances were detected in lymphocytes and other blood cells. During the course of lymphocyte culture, changes in intracellular concentrations of lactate, taurine, inositol and nucleotides, including NAD, IMP and high-energy phosphates, were especially marked. 1H-NMR compares favorably to 31P-NMR and to HPLC, and is especially attractive in light of expectations for future in vivo application.

Intracellular pH in human skeletal muscle by 1H NMR

We report here the in vivo observation of the imidazole protons (C-2 and C-4) of carnosine (beta-Ala-His) by 1H NMR at 4.7 T in human skeletal muscle. The relationship between the pH and chemical shift of the C-2 and C-4 resonances was determined analytically. These titration curves were used to measure the resting pH of human muscle in vivo, 7.01 x 0.04 (C-2 proton) and 6.97 +/- 0.10 (C-4 proton). An in vivo titration curve of the C-2 proton resonance was determined by interleaving 1H and 31P NMR spectra after exhaustive exercise, during which muscle pH recovers from an acidic value of 6.1. We observed excellent agreement between the pH values as determined by the C-2 resonance of carnosine and that of inorganic phosphate. Carnosine provides an excellent pH indicator since (i) its concentration is relatively stable and (ii) it allows measurement of proton metabolites and pH to be achieved through the same coil, thus enabling a better signal/noise ratio and better localization.