Title:
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Analysis of cell membrane lipids using Raman spectroscopy
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Ceramide accumulates in Cystic Fibrosis (CF) airways and ceramide reduction decreased
inflammation, susceptibility to Pseudomonas aeruginosa (Pa) infection, mortality and mobility. The
research undertaken here aimed to evaluate the anti-inflammatory effect of sphingolipid-modifying
drugs in LPS-stimulated bronchial epithelial cells. Moreover, the use of Raman Spectroscopy to
identify-the distribution of biomembrane lipids was evaluated.
Firstly, Raman markers of selected lipids were determined and their specificity and changes
of lipid-derived Raman peaks due to bio-compound interaction were confirmed in solution.
Secondly, membrane lipids within cells were investigated using Surface-enhanced Raman
Spectroscopy (SERS) employing silver nanoparticles (NPs) and self-assembled thiols monolayers
I
(SAMs). NPs and S03--terminated SAMs promote a weak SERS, compared to choline-, methyl- or OHterminated
SAMs. However, cellular lipid signals were not detected, SERS combined with confocal
Raman microscopy gave enriched Raman spectra, but the signal was unstable and was not suitable
for analyses , Thirdly, the anti-inflammatory effect of amitriptyline and miglustat on Pa LPS-induced
inflammation in CF and non-CF cell lines was investigated. LPS from a clinical Pa isolate failed to
induce inflammation, compared to commercially available LPS and bacterial lysate. Neither of the
drugs suppressed LPS-induced inflammation, in contrast to dexamethasone, and cell lines responded
to treatments similarly. Finally, using Raman spectroscopy combined with principal component
analysis, the distribution of cellular components (DNA, RNA, proteins), and lipids
(phosphatidylcholine, sphingomyelin, phosphatidylinositol, cholesterol) in LPS-stimulated cells pretreated
with amitriptyline or sphingomyelinase was semiquantitatively imaged: CF cells expressed
more sphingomyelin than non-CF cells. Sphingomyelin was reduced by sphingomyelinase, but
increased by amitriptyline and LPS, suggesting that sphingomyelin was not associated with
inflammation.
Overall Raman spectroscopy techniques have potential for the label-free study of the cellular
lipid composition; however, further improvements in the sensitivity are needed. The observation
that miglustat and amitriptyline target LPS-independent immune responses needs further
investigations.
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