Metabolism of Choline and Deuterated Choline Detected by 1H-14N 2D Heteronuclear Single-Quantum Coherence (HSQC) NMR.

Choline is an essential nutrient that plays a critical role in tumor growth. Choline levels can be detected by proton (1H) MR spectroscopy (MRS) in vivo, whereas active (dynamic) choline metabolism can be studied with deuterated choline and 2H MRS. The detected 1H and 2H choline signals represent the sum of choline, phosphocholine (PC) and glycerophosphocholine (GPC), preventing a detailed characterization of choline metabolism. Here we have developed a two-dimensional (2D) NMR method that allows the simultaneous detection of all protonated and deuterated choline-related compounds in excised tissue. The methodology relies on the high 1H detection sensitivity and chemical shift dispersion to distinguish between choline types, the sensitivity of the 14N chemical shift toward deuteration of nearby methyl groups and the presence of a 1H-14N scalar coupling between 14N and CH2 groups. With optimized sequence parameters, the utility of the method is demonstrated on extracts from cultured cancer cells, blood plasma and rat brain and brain tumor tissues.