Mutations in fumarate hydratase (FH) lead to the accumulation of fumarate, considered to be an ‘oncometabolite’ due to the wide-ranging consequences of its accumulation in the cell. Here, we demonstrate that Raman spectroscopy (RS) can detect and map fumarate in living cells. We highlight the presence of three main peaks at 1281±2cm-1, 1403±2cm-1 and 1657±2cm-1. In live cells, we measure an average fumarate concentration of 10 mM in FH-proficient cells compared to 23 mM for FH-deficient cells, in agreement with prior mass spectrometry measurements. Future studies will focus on enhancing sensitivity using coherent or surface enhanced Raman methods.
Oxidative stress in cancer is implicated in tumor progression, being associated with increased therapy resistance and metastasis. Conventional approaches for monitoring oxidative stress in tissue such as high-performance liquid chromatography and immunohistochemistry are bulk measurements and destroy the sample, meaning that longitudinal monitoring of cancer cell heterogeneity remains elusive. Raman spectroscopy has the potential to overcome this challenge, providing a chemically specific, label free readout from single living cells. Here, we applied a standardized protocol for label-free confocal Raman micro-spectroscopy in living cells to monitor oxidative stress in bronchial cells. We used a quartz substrate in a commercial cell chamber contained within a microscope incubator providing culture media for cell maintenance. We studied the effect of a potent reactive oxygen species inducer, tert-butyl hydroperoxide (TBHP), and antioxidant, N-acetyl-L-cysteine (NAC) on living cells from a human bronchial epithelial cells (HBEC). We found that the Raman bands corresponding to nucleic acids, proteins and lipids were significantly different (p<0.05) for control, TBHP, and NAC. Encouragingly, partial least squares discriminant analysis applied to our data showed high sensitivity and specificity for identification of control (87.3%, 71.7%), NAC (92.3%, 85.1%) and TBHP (86.9%, 92.9%). These results suggest that confocal Raman micro-spectroscopy may be able to monitor the biological impact of oxidative and reductive processes in cells, hence enabling longitudinal studies of oxidative stress in therapy resistance and metastasis at the single cell level.
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