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Deprecated: Implicit conversion from float 243.2 to int loses precision in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 534 NMR+Biomed 2015 ; 28 (11): 1455-62 Nephropedia Template TP
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31P-MRS of Healthy Human Brain: ATP synthesis, Metabolite Concentrations, pH, and T1 Relaxation Times #MMPMID26404723
Ren J; Sherry AD; Malloy CR
NMR Biomed 2015[Nov]; 28 (11): 1455-62 PMID26404723show ga
The conventional method for measuring brain ATP synthesis is 31P saturation transfer (ST), a technique typically dependent on prolonged pre-saturation at ?-ATP. In this study, ATP synthesis rate in resting human brain is evaluated using EBIT (Exchange Kinetics by Band Inversion Transfer), a technique based on slow recovery of ?-ATP magnetization in the absence of B1 field following co-inversion of PCr and ATP resonances with a short adiabatic pulse. The unidirectional rate constant for the Pi ? ?-ATP reaction is 0.21 ± 0.04 sec?1 and the ATP synthesis rate is 9.9 ± 2.1 mmol/min/kg in human brain (n = 12 subjects), consistent with the results by ST. Therefore EBIT could be a useful alternative to ST in studying brain energy metabolism in normal physiology and under pathological conditions. In addition to ATP synthesis, all detectable 31P signals are analyzed to determine the brain concentration of phosphorus metabolites including UDPG at ~ 10 ppm, a previously reported resonance in liver tissues and now confirmed in human brain. Inversion recovery measurements indicate that UDPG, like its diphosphate analogue NAD, has a shorter apparent T1 than monophosphates (Pi, PMEs and PDEs) but longer than triphosphate ATP, highlighting the significance of 31P-31P dipolar mechanism in T1 relaxation of polyphosphates. Another interesting finding is the observation of ~40% shorter T1 at intracellular Pi relative to extracellular Pi, attributed to the modulation by the intracellular phosphoryl exchange reaction Pi ? ?-ATP. The sufficiently separated intra- and extra-cellualr Pi signals also permit the distinction of pH between intra- and extra-cellular environments (pH 7.0 vs pH 7.4). In summary, the quantitative 31P MRS in combination with ATP synthesis, pH and T1 relaxation measurements may offer a promising tool to detect biochemical alternations at early stages of brain dysfunctions and diseases.