Parahydrogen hyperpolarization offers a relatively accessible way of increasing NMR signals by approximately three orders of magnitude over what is offered by the regular means of NMR sensitivity. If applied to biofluids, it could allow to detect metabolites and metabolic information that would otherwise be inaccessible due low analyte abundance, below the usual Limit of Detection (LoD) of NMR. However, combining parahydrogen hyperpolarization, which is based on chemical interactions between an organometallic catalyst and metabolites in the sample, with the complexity of biological mixtures can be challenging.
Herein we will present the necessary considerations for achieving compatibility of parahydrogen hyperpolarization with human biofluids and show the first proof of concept applications that demonstrate the available information. Using a parahydrogen hyperpolarization technique called non-hydrogenative PHIP (nhPHIP), we have conducted a urinary pharmacokinetics study on mid-nanomolar concentration analytes [1]. Further, it was shown that parahydrogen hyperpolarization is robust enough for compiling spectral libraries for assignment of hyperpolarized signals [2] and that it can be applied to minimally treated urine, producing highly information rich hyperpolarized NMR spectra [3]. We are now extending the application scope towards sensitivity enhanced nhPHIP analysis of blood samples, which is often the more relevant biofluid to study the metabolic state of a subject. However, blood is also a very different sample matrix that has mandated development of different sample preparation protocols.
We will give an overview of metabolite classes in biofluids that we have worked with: starting with nicotinamide derivatives, moving to nucleosides and nucleotides, and most recently, to oligopeptides. We argue that, based on these examples, parahydrogen hyperpolarization is ready for targeted analysis in biofluids, but could potentially also be applied to untargeted metabolomics studies in the near future.