Magnetization‒transfer ³¹P NMR of biochemical exchange in vivo: Application to creatine kinase kinetics

Abstract

Abstract. Phosphorus-31 saturation-transfer NMR spectroscopy provides an elegant means to study fluxes through the creatine kinase reaction in human skeletal muscle. To obtain reliable quantitative kinetic information, experimental imperfections, such as incomplete saturation and radiofrequency bleed over need to be addressed appropriately. In resting muscle, creatine kinase was near equilibrium both in normal controls and in a patient with impaired oxidative phosphorylation. Oral intake of high doses of creatine monohydrate for several days resulted in significantly increased concentrations of phosphocreatine but had no measurable effect on the phosphocreatine resynthesis rate in resting muscle.Abbreviations ADP = adenosine 5 -diphosphate; ATP = adenosine 5 -triphosphate; CK = creatine kinase; Cr = creatine; MEALS = mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes; NMR = nuclear magnetic resonance; PCr = phosphocreatine; PDE = phosphodiesters; P i = inorganic phosphate; PME = phosphomonoesters; PP = phosphorylation potential; RF = radiofrequency; ST = saturation transfer.

Magnetic resonance spectroscopy in patients with MELAS

“…Resting-state control spectra were recorded in 10 volunteers (m 6, f 4; 25.9F4.6 years). An exhaustive review of strategies to extract bioenergetic data from dynamic 31 They were obtained from simultaneous fits of the time courses of the PCr and g-ATP signals in both types of MT experiments (i.e., saturation of PCr or g-ATP) as detailed elsewhere [28]. The corresponding fluxes are given by v for =k +1 Â[PCr] and v rev =k À1 Â [ATP].…”

“…Details of the MT technique are given elsewhere [28,30]. Briefly, frequency-selective saturation was achieved by a DANTE (delays alternating with nutations for tailored excitation) [31] pulse train (bandwidth 15 Hz) preceding the readout pulse by a variable delay (series of nine spectra, delay 27-4025 ms, TR 5 s, NAC 32).…”

“…Absolute metabolite concentrations, however, are only available from 5 patients [15,18], whereas the other studies are limited to qualitative data or metabolite ratios. Additional results from 31 P MRS of the brain in five patients [2,[21][22][23] and of skeletal muscle in 13 patients [2,18,[24][25][26][27][28] were also published. Consistent metabolic abnormalities are elevated Lac and decreased NAA as well as indications of impaired mitochondrial function in brain and muscle.…”

“…Changes of the PCr and g-ATP peak areas (a.u.=arbitrary units) depending on the delay time s as obtained from 31 P MT experiments in skeletal muscle of patient 5[28] involving saturation of (A) the g-ATP resonance and (B) the PCr resonance.…”

Three‐dimensional mapping of the creatine kinase enzyme reaction rate in muscles of the lower leg

“…Besides providing measurement of the concentration of several key metabolites, 31 P‐MRS also allows the assessment of metabolic turnover rates in resting muscles by means of magnetization transfer (MT) methods . Tissues with high energy demand (such as the skeletal muscle, heart or brain) buffer against adenosine triphosphate (ATP) depletion via a reservoir of energy in the form of phosphocreatine (PCr), which is utilized by the creatine kinase (CK) enzyme reaction to recycle adenosine diphosphate (ADP) rapidly back to ATP . Alteration in the kinetics of the CK reaction rate appears to play a central role in many disease states, including ischemic heart disease , heart failure , stroke and congenital myopathies , inflammatory myopathies , type 2 diabetes and peripheral artery disease .…”