Metabolite signal

To obtain absolute concentrations of metabolites, calibration techniques are necessary. For this purpose an external calibration compound of known concentration can be measured to which the metabolite signals are referenced. Another possibility is the use of spectral signals from a tissue compound with known concentration serving as internal reference. 

Coruzzi G, Bush DR. 2001. Nitrogen and carbon nutrient and metabolite signaling in plants. Plant Physiol 125 61-64. 

Bouwmeester, H.J., Matusova, R., Zhongkui, S., Beale, M.H. Secondary metabolite signalling in host-parasitic plant interactions.Curr Opin Plant Biol 2003 6 358-364. 

A typical metabolite profiling analysis involves the following steps (i) metabolite extraction that often has to be adapted on a case-by-case basis depending on the type of sample and analytical platform chosen (ii) sample preparation which may include partial purification and derivatization steps (iii) instrumental analysis of sample (iv) detection and quantification of metabolite signals to generate a data matrix that summarizes the detected signals and their intensity data and (v) statistical analysis of metabolite profiles (67). 

Kugel H, Roth B, Pillekamp F, Kruger K, Schulte O, von Gontard A, Benz-Bohm G (2003) Proton spectroscopic metabolite signal relaxation times in preterm infants a prerequisite for quantitative spectroscopy in infant brain. J Magn Reson Imaging 17 634-640... 

Fig. 24. Results from the fit of a single voxel from a. /-refocused PRESS MRSI data set acquired at 4.1 T with 40 ms TE. (a) The top spectrum is the spectral data (thin line) overlaid with the fit result (heavy line), the middle spectrum is spectral data with only the baseline fit overlaid, and the bottom spectrum is the residual spectrum, (b) An expanded plot of the metabolite signal only (with baseline fit subtracted) in the top spectrum and the summed metabolite fits (without baseline) in the middle spectrum. The bottom spectrum contains the labelled, individual metabolite fits, with the vertical scale increased by 2. Reproduced with permission from B. J. Soher, K. Young, V. Govindaraju and A. A. Maudsley, Magn. Reson. Med., 1998, 40, 822. 1998 John Wiley and Sons.

Hwang JH, Graham GD, Behar KL, Alger JR, Prichard JW, et al. 1996. Short echo time proton magnetic resonance spectroscopic imaging of macromolecule and metabolite signal intensities in the human brain. Magn Reson Med 35 633-639. 

To improve reproducibility in MRSI in human brain, simultaneous acquisition of the internal water reference and metabolite signals was evaluated. Use of singular value decomposition techniques and finite impulse response filters proved effective in separating water and metabolite signals and providing estimations of the metabolite concentrations. 

Relative water intensity when compared with concentrations of metabolites of interest, + + + indicates that few metabolite signals can be observed without water suppression due to dynamic range problems. 

MR spectroscopic results were frequently expressed in terms of peak ratios however, this resulted in doubt about whether one metabolite is elevated or another decreased. Absolute concentration values can eliminate such problems this is especially important when metabolite changes are studied in disease process. The advantage of quantitating MRI data by using water signal in vivo is that the water signal and metabolite signals are obtained under the same conditions. 

Draper, J., Enot, D. R, Rarker, D., Beckmann, M., Snowdon, S., Lin, W., and Zubair, H. 2009. Metabolite signal identification in accurate mass metabolomics data with MZedDB, an interactive m/z annotation tool utilizing predicted ionization behaviour "rules." BMC Bioinformatics 10 227. 

The subscripts c and m correspond to the concentration reference and the in vivo metaboHte respectively, f is the number of equivalent nuclei contributing to the ECR/metabolite signal, and T is the in vivo/ECK temperature. The in vivo and phantom VOI volumes are assumed equal. 

Bouwmeester HJ, Matusova R, Zhongkui S, Beale MH (2003) Secondary metabolite signalling in host-parasitic plant interactions. CurrOpin Plant Biol 6 358-364. doi 10.1016/S1369-5266(03)00065-7... 

Ghasemzadeh MB, Capella P, Mitchell K, Adams RN (1993) Real-time monitoring of electrically stimulated norepinephrine release in rat thalamus I. Resolution of transmitter and metabolite signal components. J Neurochem 60 442-448. 

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