Stable Isotope Probing and Raman Spectroscopy for Monitoring Carbon Flow in a Food Chain and Revealing Metabolic Pathway

In vivo metabolic fingerprinting of neutral lipids with hyperspectral stimulated Raman scattering microscopy

Metabolic fingerprinting provides valuable information on the physiopathological states of cells and tissues. Traditional imaging mass spectrometry and magnetic resonance imaging are unable to probe the spatial-temporal dynamics of metabolites at the subcellular level due to either lack of spatial resolution or inability to perform live cell imaging. Here we report a complementary metabolic imaging technique that is based on hyperspectral stimulated Raman scattering (hsSRS). We demonstrated the use of hsSRS imaging in quantifying two major neutral lipids: cholesteryl ester and triacylglycerol in cells and tissues. Our imaging results revealed previously unknown changes of lipid composition associated with obesity and steatohepatitis. We further used stable-isotope labeling to trace the metabolic dynamics of fatty acids in live cells and live Caenorhabditis elegans with hsSRS imaging. We found that unsaturated fatty acid has preferential uptake into lipid storage while saturated fatty acid exhibits toxicity in hepatic cells. Simultaneous metabolic fingerprinting of deuterium-labeled saturated and unsaturated fatty acids in living C. elegans revealed that there is a lack of interaction between the two, unlike previously hypothesized. Our findings provide new approaches for metabolic tracing of neutral lipids and their precursors in living cells and organisms, and could potentially serve as a general approach for metabolic fingerprinting of other metabolites.

Microworms swallow the nanobait: the use of nanocoated microbial cells for the direct delivery of nanoparticles into Caenorhabditis elegans

The application of in vivo models in assessing the toxicity of nanomaterials is currently regarded as a promising way to investigate the effects of nanomaterials on living organisms. In this paper we introduce a novel method to deliver nanomaterials into Caenorhabditis elegans nematodes. Our approach is based on using nanoparticle-coated microbial cells as "nanobait", which are ingested by nematodes as a sole food source. We found that nematodes feed on the nanocoated bacteria (Escherichia coli) and microalgae (Chlorella pyrenoidosa) ingesting them via pharyngeal pumping, which results in localization of nanoparticles inside the digestive tract of the worms. Nanoparticles were detected exclusively inside the intestine, indicating the efficient delivery based on microbial cells. Delivery of iron oxide nanoparticles results in magnetic labelling of living nematodes, rendering them magnetically-responsive. The use of cell-mediated delivery of nanoparticles can be applied to investigate the toxicity of polymer-coated magnetic nanoparticles and citrate-capped silver nanoparticles in Caenorhabditis elegans in vivo.