Novel strategies of Raman imaging for monitoring intracellular retinoid metabolism in cancer cells

We developed a label-free Raman method for whole-cell biochemical imaging to detect molecular processes that occur in normal and cancer brain cells due to retinol transport in human cancers at the level of isolated organelles. Our approach allows the creation of biochemical maps of lipid droplets, mitochondria and nuclei in single cells. The maps were capable of discriminating triglycerides (TAG) from retinyl ester (RE) in lipid droplets (LD), providing an excellent tool to monitor intracellular retinoid metabolism. We detected spectral changes that arose in proteins and lipids due to retinoid metabolism in human cell lines of normal astrocytes and high-grade cancer cells of glioblastoma as well as in human medulloblastoma and glioblastoma tissue. Raman imaging is an effective tool for monitoring of retinoids and retinol binding proteins involved in carcinogenesis, as monitored by the unique spectral signatures of vibrations. We found two functionally distinct lipid droplets: TAG-LD, for energy storage, and RE-LD, for regulating the level of apo-CRBP1 in cytosol. Raman polarization measurements revealed the occurrence of conformational changes affecting discrete regions of proteins associated with retinol binding. Aberrant expression of retinoids and retinol binding proteins in human tumours were localized in lipid droplets, mitochondria and nuclei according Raman imaging.