Intracellular Delivery of Liposome-encapsulated Finland Trityl Radical for EPR Oximetry
Tetrathiatriarylemthyl (TAM, trityl) radicals have found wide applications in electron paramagnetic resonance (EPR) oximetry. However, the biomedical applications of TAM radicals wereexclusively limited to extracellular region owing to their negatively charged nature. The intracellular delivery of TAM radicals still remains a challenge. In the present work, we report a liposome-based method to encapsulate the water-soluble Finland trityl radical CT-03 for its intracellular delivery. Using the thin lipid film hydration method, the CT-03-loaded liposomes were prepared from DSPC/cholesterol/DOTAP with a mean size of 167.5 ± 2.4 nm and zeta potential of 27.8 ± 0.8 mV. EPR results showed that CT-03 was entrapped into the liposomes and still exhibited good oxygen (O2) sensitivity. Moreover, CT-03 was successfully delivered into the HepG2 cells and HUVECs using the CT-03-loaded liposomes. Importantly, the combination of the liposome-encapsulated CT-03 and the other TAM radical CT02-H enabled simultaneous measurement of the intracellular and extracellular O2 concentrations and O2 consumption rates in HepG2 cells. Our present study provides a new approach for intracellular delivery of TAM radicals and could significantly expand their biomedical applications.