NMR-visible
lipid signals detected in vivo by 1H MRS are associated with tumour aggression and believed to arise from cytoplasmic lipid droplets. High-resolution magic angle spinning (HRMAS) 1H MRS and
Nile Red staining were performed on human brain tumour biopsy specimens to investigate how NMR-visible
lipid signals relate to viable cells and levels of
necrosis across different grades of
glioma. Presaturation spectra were acquired from 24 adult human
astrocytoma biopsy samples of grades II (8), III (2) and IV (14) using HRMAS 1H MRS and quantified using LCModel to determine
lipid concentrations. Each biopsy sample was then refrozen, cryostat sectioned, and stained with
Nile Red, to determine the number of lipid droplets and droplet size distribution, and with Haematoxylin and
Eosin, to determine cell density and percentage
necrosis. A strong correlation (R=0.92, P<0.0001) was found between the number of
Nile Red-stained droplets and the approximately 1.3 ppm
lipid proton concentration by 1H MRS. Droplet sizes ranged from 1 to 10 microm in diameter, and the size distribution was constant independent of tumour grade. In the non-necrotic biopsy samples, the number of lipid droplets correlated with cell density, whereas in the necrotic samples, there were greater numbers of droplets that showed a positive correlation with percentage
necrosis. The correlation between 1H MRS
lipid signals and number of
Nile Red-stained droplets, and the presence of lipid droplets in the non-necrotic biopsy specimens provide good evidence that the in vivo NMR-visible
lipid signals are cytoplasmic in origin and that formation of lipid droplets precedes
necrosis.