In vitro assessment of cytotoxicity and labeling efficiency of ^99mTc-HMPAO with stromal vascular fraction of adipose tissue

Introduction: Noninvasive radionuclide imaging of cells using technetium99m-hexamethylpropyleneamine oxime (^99mTc-HMPAO) is a potential diagnostic tool for several applications. Herein we aimed to evaluate the labeling efficiency and cellular toxicity of ^99mTc-HMPAO with Stromal Vascular Fraction (SVF) of adipose tissue to develop a process tool for theranostic purposes, in particular imaging cardiac stem cell therapy. Methods: Ten million cells of SVF were labeled with ^99mTc-HMPAO complex and excess radiolabel was cleared off through washing in PBS. The labeling efficiency of ^99mTc-HMPAO was detected in labeled cells and their subsequent supernatant wash using isotope dose calibrator and gamma camera. The cytotoxicity was assessed for the comparative reactive oxygen species (ROS) by H₂DCFDDA, apoptotic events by annexin-V and TUNEL assay and mitochondrial potential by JC-1. Results: An encouraging labeling efficiency of 33% was observed with ^99mTc-HMPAO complex. The radionuclide labeling of SVF demonstrated significant safety profile as evaluated by apoptotic assays. Conclusion: ^99mTc-HMPAO labeling efficiency of 33% of total SV fraction would produce sufficient radioactive signals that would enable for in vivo tracking of cells by SPECT-CT. The radionuclide did not demonstrate any significant impact on the structural or functional organization of the labeled cells. Our study indicates that SVF can be safely labeled with ^99mTc-HMPAO without adverse cytotoxic events and for its potential role in imaging cardiac stem cell therapy.