SLOW-MAS NMR METHODS TO STUDY METABOLIC PROCESSES IN VIVO AND IN VITRO
In vitro and in vivo 1H NMR spectroscopy is widely used to measure metabolic profiles in cells, tissues, animals, and humans and to use them, e.g., for diagnosis and therapy response evaluations. However, the spectra often suffer from poor resolution due to variations in the isotropic bulk magnetic susceptibility present in biological objects, resulting in a broadening of the NMR lines. In principle this broadening can be averaged to zero by the technique of magic angle spinning (MAS), where the sample is rotated about an axis making an angle of 54o44’ relative to the external magnetic field. However, a problem is that in a standard MAS experiment spinning speeds of a kHz or more are required in order to avoid the occurrence of spinning sidebands (SSBs) in the spectra, which renders analysis of the spectra difficult again. At these spinning speeds the large centrifugal forces cause severe structural damage in larger biological objects, so that this method cannot be used to study metabolic processes in intact samples. In solid state NMR several methods have been developed where slow MAS is combined with special radio frequency pulse sequences to eliminate spinning side bands or separate them from the isotropic spectrum so that a SSB-free high-resolution isotropic spectrum is obtained. It has been shown recently that two methods, phase-adjusted spinning sidebands (PASS) and phase-corrected magic angle turning (PHORMAT), can successfully be modified for applications in biological materials (1, 2). With PASS MAS speeds as low as 40 Hz can be employed, allowing non or minimally invasive in vitro studies of excised tissues and organs. This method was used, amongst other things, to study post mortem changes in the proton metabolite spectra in excised rabbit muscle tissue (3). With PHORMAT the NMR sensitivity is reduced and longer measuring times are required, but with this methodology the MAS speed can be reduced to ~1 Hz. This makes PHORMAT amenable for in vivo applications, as was demonstrated in a living mouse (4). In this presentation the principles and limitations of PASS and PHORMAT will be briefly discussed and illustrated with spectra obtained on a variety of biological objects. Moreover, it will be shown that PASS can be employed to study metabolic processes in biofilms and other living microbial systems. Finally, on-going work to develop PASS and PHORMAT spectroscopic imaging and to improve the performance of both techniques will be discussed. It is anticipated that slow- and ultra-slow-MAS will significantly enhance the utility of proton MR spectroscopy for biomedical research in living cell systems and live animals, and in future perhaps even in the clinic, in the latter case by rotating the external magnetic field rather than the patient.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 915317
- Report Number(s):
- PNNL-SA-49849; KP1402010; TRN: US200817%%316
- Resource Relation:
- Related Information: Magnetic Resonance in Food Science: The Multivariate Challenge, 156-165
- Country of Publication:
- United States
- Language:
- English
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