Visibility of phospholipids in 31P NMR spectra of human breast tumours in vivo

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Abstract
The aims of this study were two-fold: to characterize the in vivo 31P NMR spectrum of human breast tumours by identifying the metabolites contributing to each peak; and to demonstrate changes in the detectability of the phosphodiester (PDE) peak at varying field strengths. This was achieved by obtaining 31P spectra from 23 patients in vivo at 1.5 T and also of 11 perchloric acid (PCA) extracts and 3 chloroform-methanol (CM) extracts of tumour biopsy samples at 9.4 T. In spectra acquired in vivo the percentage areas for each peak were: phosphomenoester (PME), 15%; Pi, 11%; PDE 35%; phosphocreatine, 5%; γ-NTP, 11%; α-NTP, 11% and β-NTP, 12% of the total spectral area. PCA extracts showed the PME peak to be > 70% phosphorylethanolamine whilst the PDE peak included almost equal proportions of glycerophosphorylethanolamine and glycerophosphorylcholine. CM extracts of tumours revealed additional metabolites in the PDE region suggesting that the large PDE peak observed in vivo could arise mainly from phospholipids. Spectra of human breast tumour xenografts examined in vivo at both 1.9 T and 9.4 T confirmed that the presence of a large PDE peak in vivo was a function of field strength. Further experiments with microsomal membranes from rat mammary tumours at 1.5 and 9.4 T demonstrated that phospholipids are more clearly visible at the lower field strength due to a substantial decrease in linewidth.