Evaluation of31P high-resolution magic angle spinning of intact tissue samples

Abstract

The first detailed evaluation is presented of high-resolution (31)P MRS using magic angle spinning (MAS) of intact tissue samples and comparison with the conventional method of studying tissue extracts. The main motivation is that MAS leaves the sample intact at the end of the study for histopathological evaluation. While MAS of tissue samples has previously been demonstrated for (1)H MRS, (31)P MRS is better suited to study of the phospholipid metabolites of importance in cancer. Samples of rhabdomyosarcoma and RIF-1 experimental tumours were maintained at 4 degrees C, spun at 3 kHz and measured in 28-min acquisitions at 11.7 and 14 T. Metabolite stability was evaluated using four sequential 28-min acquisitions. High-resolution MRS was performed on extracts of the same tissue samples. (31)P HR-MAS yielded well-resolved high-resolution spectra, showing peaks from phosphoethanolamine (PE), phosphocholine (PC), inorganic phosphate, glycerophosphoethanolamine and glycerophosphocholine, with linewidths in the range 3-20 Hz. In tumour samples there was no significant change in peak areas over a 2-h period, while peaks sensitive to pH (inorganic phosphate, PE and PC) showed a small change in chemical shift, corresponding to a change of 0.13 +/- 0.06 pH units. Tissue metabolite concentrations showed good agreement with concentrations measured from extracts of the same pieces of tissue. For calculation of metabolite concentrations, the measurement of a reference compound in a separate measurement is more robust than using the signal from a reference compound in the rotor with the sample. Compared with performing tissue extracts, use of MAS of intact tissue samples requires less preparation, is quicker and permits the same sample to be used for subsequent histopathology. The methodology has particular application in studying phospholipid metabolism in cancer and in monitoring tumour response to treatment, where concentrations of phospholipid-related metabolites are found to alter following response to a wide range of anti-cancer therapies.