Non-Specific Particle Formation During Extracellular Vesicle Labelling With the Lipophilic Membrane Dye PKH26.

Area of Science:

• Extracellular Vesicle (EV) Research
• Biotechnology
• Fluorescent Labeling Techniques

Background:

• Current fluorescent labeling of extracellular vesicles (EVs) yields variable results, hindering research reproducibility.
• Lipophilic membrane dyes, like PKH26, often form non-specific particles, confounding EV detection and analysis.
• There is a critical need for validated, reproducible methods for EV fluorescent labeling.

Purpose of the Study:

• To optimize conditions for fluorescent labeling of EVs using PKH26, minimizing non-specific dye particle formation.
• To validate a refined labeling approach across in vitro and in vivo models of EV biodistribution.
• To investigate the impact of buffer conditions on PKH26 non-specific particle formation and EV labeling efficiency.

Main Methods:

• Optimized EV isolation using ultrafiltration and size exclusion chromatography.
• Investigated PKH26 non-specific particle formation under four different buffer conditions using single-EV spectral flow cytometry and transmission electron microscopy.
• Validated the optimized method in cell-based assays and in vivo mouse models using flow cytometry, immunofluorescence, and intravital imaging.

Main Results:

• Optimized buffer conditions, free of additional protein, significantly minimized non-specific PKH26 dye aggregates.
• Achieved efficient EV labeling with a substantially improved signal-to-noise ratio both in vitro and in vivo.
• Demonstrated that inadequate vehicle controls can lead to significant false positive data in EV studies.

Conclusions:

• Optimized buffer conditions provide a reproducible and validated method for PKH26 labeling of EVs, reducing artifacts.
• This improved labeling strategy is crucial for accurate assessment of EV trafficking in physiological and pathological contexts.
• Proper benchmarking of EV labeling techniques and inclusion of controls are essential for reliable experimental outcomes.