Spin Probes as Scavengers of Free Radicals in Cells

Spin probes can be used to monitor biological membranes, including the penetration of different molecules into cells. The aim of the present studies was an investigation of the endocytosis process of two spin labels-2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-TEMPO (TEMPOL)-into yeast cells and a leukemia cell line (HL-60, ATCC CCL-240) by Electron Spin Resonance (ESR). The ESR method is helpful for the direct detection of free radicals. The cell incubation and endocytosis of spin probes were carried out at 310 K. In contrast, the ESR measurements of yeast cells and a leukemia cell line with spin probes were at 240 K. Spectral differentiation was observed; hence, the spin probes present in suspension and attached to the cell membrane could be distinguished. The ESR signal changes of spin probes depended on spin probe concentration, cell number, and type of cell (healthy/cancerous). Additionally, the effect of external factors (oxygen and vitamin C) on the ESR signal decay of spin markers in the cell solution was established. The experimental results prove that the spin probes (TEMPO and TEMPOL) could scavenge free radicals inside the cell. At the same time, the mechanism of spin probe interaction in suspension was determined based on the measurements at low temperatures.