Parahydrogen hyperpolarization of minimally altered urine samples for sensitivity enhanced NMR metabolomics

Abstract

Parahydrogen hyperpolarization has been shown to enhance NMR sensitivity in urine analysis by several orders of magnitude if urine samples are prepared by solid phase extraction (SPE). We present a...

Understanding Parahydrogen Hyperpolarized Urine Spectra: The Case of Adenosine Derivatives

“…Signal assignment is arguably the most notable limitation hindering wider adoption of the technique. Since hydride signals do not carry as much structural information as traditional NMR, the only reliable way of assigning signals has proven to be internal standard addition [4,7,9]. The most practical pulse sequence for hyperpolarized chemosensing [6], which can also be carried out as very fast experiments [20], resolves hydride signals (red in Figure 1) according to their mutual zero quantum (ZQ) frequency in the indirect dimension of 2D spectra.…”

“…10 ppm region [4]. Furthermore, the complexity of published hyperpolarized urine spectra [6][7][8][9] demonstrates that even the catalyst's limited chemical scope allows for the detection of large numbers of metabolites. The list of known 2 binding analytes is growing and includes, on top of nitrogenous heteroaromatics, pyruvate [10], tagged oligopeptides [11,12], amino acids [13,14], nitriles [15], and sulfur heteroaromatics [16], suggesting the chemoselectivity envelope is wide.…”

“…The method is not quantitative in the same way as traditional 1 H NMR, since multipulse NMR detection schemes and analyte-specific complex 3 dissociation kinetics [17], hydrogen exchange rate and relaxation [18] properties are involved. However, similarly to regular 2D NMR [19], quantification can be achieved by analyte-specific calibration curves [4][5][6][7][8][9]13]. When exact values are not necessary, concentrations can be estimated by comparison of signals representing chemically similar analytes [13].…”

“…Notably, chemical shifts of hydride signals of different complexes 3 have proven to be largely identical in methanolic urine samples and in simple methanol solutions [7]. Consequently, it should be feasible to compile libraries of analyte signals, which could be applied for signal assignment in complex samples.…”

“…In particular, the parahydrogen (pH 2 ) hyperpolarized chemosensing technique [4] has been used for the study of various biological mixtures such as flavor compounds in coffee extracts [4] and whiskey [5]. A modification of the technique has been demonstrated to work in SPE extracts of human urine [6] and in (almost) whole urine [7], allowing for the detection of endogenous urinary metabolites below the LOD of regular NMR.…”