The effects of freezing versus supercooling on vascular cells: implications for balloon cryoplasty

To investigate the effects of supercooling, a phase whereby cells are below 0 degrees C but still in a liquid state, and freezing, the phase when cells become solid, of vascular cells in culture.

Bovine aortic endothelial cells and smooth muscle cells were supercooled to -10 degrees C with or without freezing for 3, 30, or 60 seconds and then rewarmed to 37 degrees C for 24 hours. Viability was assessed by means of trypan blue exclusion, and apoptosis was assessed with the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) assay.

Viability of smooth muscle cells decreased 49% after freezing versus supercooling (P< .05). Endothelial cells maintained greater viability rates. A 19.5% smooth muscle cell apoptotic rate was observed after freezing, whereas smooth muscle cell supercooling yielded rates of only 11% (P< .05). A 4.17% endothelial cell apoptotic rate was observed after freezing, whereas supercooled endothelial cells yielded a 1.76% rate (P< .05).

Freezing results in decreased viability and increased apoptosis compared to supercooling in both cell lines. Smooth muscle cells appear more susceptible to freezing. The biologic effects of freezing on vascular cells may elucidate the mechanisms behind the enhanced patency after cryoplasty of atherosclerotic lesions.