Lipid droplets in prostate cancer cells and effect of irradiation studied by Raman microspectroscopy.

Lipid droplets (LDs) are key organelles in cancer cells proliferation, growth, and response to stress. These nanometric structures can aggregate to reach the size of microns becoming important cell components. Although it is known that LDs contain various lipids, their chemical composition is still under investigation. Moreover, their function in cell's response to exogenous factors is also not fully understood. Raman spectroscopy, together with chemometrics, has been shown to be a powerful tool for analytical analyses of cancer cell components on the subcellular level. It provides the opportunity to analyse LDs in a label-free manner in live cells. In the current study, this method was applied to investigate LDs composition in untreated and irradiated with X-ray beams prostate cancer cells. Raman mapping technique proved lipids accumulation in PC-3 cells and allowed visualization of LDs spatial distribution in cytoplasm. A heterogeneous composition of LDs was revealed by detailed analysis of Raman spectra. Interestingly, PC-3 cells were found to accumulate either triacylglycerols or cholesteryl esters. Finally, effect of X-ray radiation on the cells was investigated using Raman spectroscopy and fluorescence staining. Significant influence of LDs in the process of cell response was confirmed and time dependence of this phenomenon was determined.