Cytoplasmic lipid droplets in nervous system tumour cell lines : size and lipid species as analysed by 1H nuclear magnetic resonance spectroscopy

Active biogenesis of cytoplasmic lipid droplets (LDs) is reported in different types of cancer cells. LDs are linked to cancer cell proliferation, apoptosis and differentiation. The chemical nature of lipids in LDs is poorly understood and revealing their chemical composition may provide novel information of lipid metabolism in cancers. Gradient ultracentrifugation was performed to isolate LDs from five nervous system tumour cell lines. Nile red staining was used to estimate the size of LDs and validate the isolation procedure. 1H NMR spectroscopy was performed from the chloroform/methanol extracts of whole cells and the isolated LDs. NMR lipid signal intensity from different lipid species was measured to compare the lipid compositions. The average diameter of LDs in cancer cells was 0.21±0.02 μm, with a widely varying size range up to 1.48 μm. 1H NMR spectroscopic analysis revealed that the LDs contain phosphatidylcholine, cholesterol and cholesterol ester with saturated, mono-unsaturated and polyunsaturated fatty acid species. The content of the isolated LDs differed between the tumor cell lines with variability seen in unsaturated fatty acids, cholesterol and lipids containing choline head groups however the mean fatty acid chain length remained similar across the cell lines. The lipid composition of LDs was also found to be different from whole cell extracts. In conclusion, we have shown that the composition of LDs differs between tumour cell lines, suggesting a functional link between these structures and cancer specific pathways