Experimental strategies for in vivo 13 C NMR spectroscopy

Abstract

In vivo carbon-13 (C) MRS opens unique insights into the metabolism of intact organisms, and has led to major advancements in the understanding of cellular metabolism under normal and pathological conditions in various organs such as skeletal muscles, the heart, the liver and the brain. However, the technique comes at the expense of significant experimental difficulties. In this review we focus on the experimental aspects of non-hyperpolarized C MRS in vivo. Some of the enrichment strategies which have been proposed so far are described; the various MRS acquisition paradigms to measureC labeling are then presented. Finally, practical aspects of C spectral quantification are discussed.

Characterization of the Tumor Microenvironment and Tumor–Stroma Interaction by Non-invasive Preclinical Imaging

“…Tumor glycolysis is typically assessed by in vivo PET using the cellular entrapment of 18 F-FDG, after uptake of 18 F-FDG by glucose transporters (GLUT-1, GLUT-3; often overexpressed in cancer) and subsequent phosphorylation by hexokinase II ( 256 , 275 ). While it is quite insensitive, 13 C MRS has been applied preclinically to evaluate glycolysis and the 13 C labeling of downstream metabolites ( 275 – 277 ). Detection sensitivity of 13 C MRS can be significantly improved by magnetization transfer techniques or indirect inverse detection ( 276 , 277 ).…”

“…While it is quite insensitive, 13 C MRS has been applied preclinically to evaluate glycolysis and the 13 C labeling of downstream metabolites ( 275 – 277 ). Detection sensitivity of 13 C MRS can be significantly improved by magnetization transfer techniques or indirect inverse detection ( 276 , 277 ). Hyperpolarization of 13 C-labeled substrates increases detection sensitivity up to 10,000-fold, with the caveats that the hyperpolarization is short lived and currently limited to few substrates, including glucose ( 64 , 275 , 276 , 278 , 279 ).…”

“…Various in vitro models mimicking the TME, such as cocultures between stromal and tumor cells or CAF-derived exosomes and cancer cells ( 326 ), 3D culture systems ( 327 ), bioreactors for live cell studies ( 20 , 277 , 328 – 330 ) have been developed to understand the nature and mechanisms behind tumor–stroma interactions by, e.g., gene expression microarrays from cocultures ( 331 ).…”

In Vitro Gut Metabolism of [U‐13C]‐Quinic Acid, The Other Hydrolysis Product of Chlorogenic Acid

“…In vitro studies of substrates being transformed by the gut microbiota may take advantage of metabolomics techniques (e.g., LC–MS, GC–MS, and NMR) to monitor substrate changes along experimental time, and identify intermediates and products . The use of stable isotopic‐labeled substrates, such as 13 C‐labels, is an elegant way to selectively identify intermediates from gut metabolism produced over time, in a qualitative and/or quantitative ways …”

Quantification of muscle triglyceride synthesis rate requires an adjustment for total triglyceride content

“…The incorporation of a tracer (e.g., [ 13 C16]-palmitate) into imTGs can be assessed either by using magnetic resonance spectroscopy (MRS) or by a direct measurement of the tracer enrichment of imTGs in lipid extracts of muscle biopsy samples (7)(8)(9)(10). The use of MRS is the less invasive approach, but this procedure has not been well established (10). Measurement of tracer incorporation into the imTGs of muscle samples requires obtaining muscle biopsy samples, a somewhat invasive procedure but one widely used.…”