Vitrification of rabbit tissues with propylene glycol and trehalose

A previous study had suggested the use of a mixture of propanediol and trehalose for the preservation of tissues by vitrification. In this paper, we describe experiments in which stepwise procedures were developed for adding these cryoprotectants to high final concentrations in two rabbit tissues-carotid artery and cornea. The tissue concentration of the additives was measured at the end of each step so that the temperature of the next step could be chosen to reduce toxicity but avoid freezing. This process was arrested when a concentration had been reached that should permit vitrification if the tissues were cooled rapidly to -175 degrees C. They were stored at that temperature; warmed rapidly by conduction; the cryoprotectants removed by stepwise dilution; and appropriate active functions measured. These were contraction and relaxation for arteries and endothelial integrity and ability to control stromal swelling for the corneas. In control experiments the exposure and functional assays were carried out without vitrification. It was shown that the tissue concentration of propanediol was 33%w/w in artery and 30% in cornea. These permitted cooling to -175 degrees C without freezing but devitrification occurred during the warming of the arteries, though not of the corneas, despite the lower tissue concentration reached in the cornea. The function of the vitrified arteries was severely reduced but the endothelium of the corneas was substantially intact although we were unable to demonstrate any ability to control stromal swelling during normothermic perfusion. It appears that concentrations of cryoprotectants sufficient to prevent freezing in these tissues during cooling were well tolerated so long as appropriate stepwise means of addition and removal were used. Devitrification during warming remained a major problem with arteries, but not with corneas. We suggest that the composition of the aqueous phase in the tissue with respect to components other than the vitrifying agents may be crucial here and that the search for agents that will suppress devitrification is an important avenue for further study.