Measurement of myo-inositol in biological systems by mass spectrometric and in vivo H-1 magnetic resonance spectroscopic techniques

Cells utilize myo-inositol for osmoregulation and phosphatidylinositol sign aling. Mass spectrometric and in vivo magnetic resonance spectroscopic tech niques have been complementarily used in our laboratories to investigate br ain myo-inositol metabolism. Mass spectrometric quantitation methods are su rveyed focusing primarily on derivatization reactions, gas chromatographic separation and detection of ions. Monitoring of the m/z 373 fragment ion ge nerated from acetate derivative provides precise quantitation of myo-inosit ol in biological matrices. The technique and its clinical applications are discussed. Measurement of myo-inositol transport using a stable isotope tec hnique is illustrated for cultured neurons. In addition, the possible use o f the technique in probing phosphatidylinositol turnover is discussed. An in vivo H-1 magnetic resonance spectroscopic technique is described for measuring the absolute concentration of myo-inositol in human brain. Magnet ic resonance spectroscopy with short echo-time enables detection of the res onance peak of myo-inositol (3.56 ppm) when the water resonance peak is sup pressed by narrow band radio-frequency pulses. The review focuses on an ext ernal reference method involving collection of data from the human subject and the phantom containing aqueous myo-inositol standard solution in the sa me scanning session. The method takes into account differences in longitudi nal and transverse relaxation time constants of myo-inositol between brain tissue and aqueous solution. Application of the technique is illustrated by measuring brain myo-inositol in Down syndrome adults and Alzheimer disease patients. Advantages and limitations of this noninvasive technique in moni toring metabolic processes are discussed.