Raman spectroscopy and imaging of beta-carotene in live corpus luteum cells

Raman spectroscopy has been used to identify and locate beta-carotene within individual living luteal cells. The cells were either freshly prepared or cultured; the latter was incubated in the presence or absence of beta-carotene in the form of enriched bovine high-density lipoprotein. Luteal cells were investigated using several Raman spectroscopic and imaging techniques. These techniques did not give accurate concentration levels of beta-carotene within parts of the cell but illustrated the distribution of the molecule. Freshly prepared luteal cells were found to contain an appreciable concentration of beta-carotene. Over a period of several days, the concentration gradually reduced to a nearly undetectable level; similar results were found for cells cultured in the absence of the beta-carotene. For cells cultured in the presence of beta-carotene, the molecular concentration was maintained for as long as 2 weeks. The Raman spectra of fragmented cells showed that the beta-carotene is predominantly localised in the lipid-rich cell components, with the concentration highest in the microsomal fraction. The Raman imaging techniques revealed that beta-carotene was spread over the entire volume of the luteal cells with higher levels occurring at distinct sites, including the surface.