Lipid droplets (LDs) and lysosomes are important organelles in cellular metabolism and physiology, playing vital roles in maintaining intracellular homeostasis. LDs not only store and metabolize neutral lipids, but also contribute to energy balance, membrane dynamics, and lipid trafficking within cells. Dysfunctional LDs can lead to metabolic disorders and diseases like obesity, fatty liver diseases, diabetes, and certain cancers. Likewise, lysosomes are acidic organelles that significantly contribute to degrading cellular waste and maintaining cellular health. Irregularities in lysosome function can lead to various diseases, including lysosomal storage disorders, neurodegenerative and metabolic diseases, as well as cancer. Therefore, it is crucial to have reliable imaging tools for exploring these cellular structures.
Fluorescent probes represent a useful tool for studying specific structures or molecules within cells with spatiotemporal precision. These probes enable the visualization of cellular morphology, tracking of molecular processes, and studying biomolecules behaviour in real-time. 3-Difluoroborodipyrromethene (BODIPY) derivatives have stood out in this field due to their outstanding optical and physical properties, low phototoxicity and photobleaching, strong absorption, high quantum yield, and ease of synthesis. In this context, we report two BODIPY-based fluorescent probes, functionalized with formyl group or benzimidazole heterocyclic moiety at position 2 of the BODIPY core, designed for live cell imaging of lysosomes and lipid droplets. In vitro experiments using confocal microscopy in HeLa cells demonstrated the probe's ability to permeate the cell membrane and selectively label lysosomes and lipid droplets without causing any adverse effects on the cultured cells. These BODIPYs represent a promising tool for intracellular detection of lysosomes and lipid droplets through fluorescence imaging.
Great job! What is your perspective:
1. How do you assess the prospects for using your compounds to control/monitor/visualize singlet oxygen in cells?
2. Could the difference in the ability of the compounds 2 and 3 to stain cells be due to differences in the viscosity of the lysosomes and the lipid droplets?
Dr. Yulia Volkova
Thank you for your thoughtful and very interesting questions. I appreciate your interest in our work.
Regarding the application of our compounds as probes to monitor singlet oxygen levels within cells, while we haven't conducted specific evaluations for this purpose, our recent publication (doi: 10.1016/j.dyepig.2021.109784) reports the photophysical investigation of compound 2, including its singlet oxygen sensitization quantum yield. Further studies are needed to explore the potential of these compounds as singlet oxygen probes.
Concerning the staining behavior of compounds 2 and 3 in lipid droplets and lysosomes, respectively, literature reports (doi: 10.1021/acs.analchem.8b00590, 10.1016/j.snb.2022.132403) have showed probes whose fluorescence intensities increased with the increased viscosity in lysosomes and lipid droplets. Through our research, we observed that compound 3 exhibits pH sensitivity, with fluorescence enhancement at low pH values. We attribute this behavior to the protonation of the benzimidazole moiety linked to the BODIPY core in the acidic environment of lysosomes. A recent study from our group (doi: 10.3390/molecules27228065) on a similar BODIPY derivative further supports the use of pH-dependent fluorescence probes for lysosomal imaging. For compound 2, a more comprehensive investigation, potentially involving additional imaging techniques or cellular studies, is warranted to conclusively establish the role of viscosity in the observed differential staining patterns.
I hope these address your questions adequately.
