Live cells may respond to disorders with metabolic changes, but direct observation of metabolites in living cells is difficult. The international team of scientists has now developed a class of remarkably small fluorophores called SCOTfluors. Colors emit light in the visible to near-infrared range and can be linked to common metabolites. The study was published in a journal Angewandte Chemie.
When a living cell changes its metabolism, due to an external signal or because something is wrong with it, the metabolism of the metabolites will change. Since metabolites are usually small molecules, cells need to be destroyed and metabolo to extract such changes. Alternatively, the metabolites may be labeled with a dye that is reflected by a fluorescence signal under a microscope.
However, conventional dyes are often much larger molecules than the metabolite to be labeled. A team of scientists led by Marc Vendrell at the University of Edinburgh, UK, has decided to develop the smallest fluorophores that can be attached to typical metabolites such as lipids, sugars, and carboxylic acids.
Fluorescent dyes typically contain fused aromatic rings that provide a conjugated electronic system, a chromophore. To minimize dye size, scientists have worked with nitrobenzodiazoles that contain only one benzene ring, an electronically active nitro group, and a fused diazo ring. This structure has proven to be beneficial in two ways: first, it is really small compared to other fluorescent dyes, and scientists can only tune the emission wavelengths by changing one atom in the molecule; for example by replacing the oxygen atom with nitrogen, sulfur, selenium or carbon.
To verify whether it is possible to monitor the metabolites by fluorescence labeling, scientists have attached fluorophores to either ceramide, which is a member of the sphingolipid, glucose, or lactic acid class. They then added labeled metabolites to human cell cultures and the metabolites could be localized in their respective organelles. It was even possible to combine lactate recycling rates in hypoxic or normoxic cells – cells that contain different levels of oxygen, as cancer cells do. They also fed labeled glucose to zebrafish embryos and tracked its intake into their developing brains.
The authors pointed out that another advantage could be the tunability of their mini-fluorophores, which they named SCOTfluors. They prepared various fluorophores using the same molecular platform and using similar synthetic steps. Not only could they label different metabolites in different colors, they were also able to track their uptake profiles in tumor cells simultaneously.
This work gives an example of how new, small fluorophores throw light into the fascinating metabolic apparatus of living cells.