In vivo MR studies of glycine and glutathione metabolism in a rat mammary tumor

• Published in: NMR in biomedicine 2012-02, Vol.25 (2), p.271-278
• Main Authors: Thelwall, Peter E., Simpson, Nicholas E., Rabbani, Zahid N., Clark, M. Daniel, Pourdeyhimi, Roxana, Macdonald, Jeffrey M., Blackband, Stephen J., Gamcsik, Michael P.
• Format: Article
• Language: English
• Subjects: Animals; Carbon Isotopes; Female; glutathione; Glutathione - metabolism; Glycine - metabolism; Magnetic Resonance Spectroscopy - methods; Mammary Neoplasms, Animal - metabolism; Mammary Neoplasms, Animal - pathology; Mass Spectrometry; metabolism; Neoplasm Transplantation; Rats; Rats, Inbred F344; serine; Subcutaneous Tissue - pathology; trans-sulfuration
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.1745

The metabolism of glycine into glutathione was monitored noninvasively in vivo in intact rat mammary adenocarcinomas (R3230Ac) by MRI and MRS. Metabolism was tracked by following the isotope label from intravenously infused [2‐13C]‐glycine into the glycinyl residue of glutathione. Signals from [2‐13C]‐glycine and γ‐glutamylcysteinyl‐[2‐13C]‐glycine (13C‐glutathione) were detected by nonlocalized 13C spectroscopy, as these resonances are distinct from background signals. In addition, using spectroscopic imaging methods, heterogeneity in the in vivo tumor distribution of glutathione was observed. In vivo spectroscopy also detected isotope incorporation from [2‐13C]‐glycine into both the 2‐ and 3‐carbons of serine. Analyses of tumor tissue extracts showed single‐ and multiple‐label incorporation from [2‐13C]‐glycine into serine from metabolism through the serine hydroxymethyltransferase and glycine cleavage system pathways. Mass spectrometric analysis of extracts also showed that isotope‐labeled serine is further metabolized via the trans‐sulfuration pathway, as 13C isotope labels appear in both the glycinyl and cysteinyl residues of glutathione. Our studies demonstrate the use of MRI and MRS for the monitoring of tumor metabolic processes central to oxidative stress defense. Copyright © 2011 John Wiley & Sons, Ltd. In vivo 13C chemical shift imaging was used to detect the heterogeneous metabolism of [2‐13C]‐glycine into the glycyl residue of glutathione in an intact rat mammary tumor. In addition, the analysis of tumor extracts indicated that additional label incorporation into the cysteinyl residue of glutathione occurred as glycine was metabolized into serine via serine hydroxymethyltransferase and the glycine cleavage system, and then into cysteine through the trans‐sulfuration pathway.