Cryopreservation studies with porcine corneas

A new technique for the cryopreservation of rabbit corneas in 20% w/w dimethylsulfoxide, which has been shown to preserve significant structural and functional integrity of the endothelium, was tested in porcine corneas.

The characteristics of uptake of dimethylsulfoxide into porcine corneas were measured using proton ( 1 H) nuclear magnetic resonance (NMR) spectroscopy. The effect on structural integrity of exposure to 20% w/w dimethylsulfoxide without freezing was first assessed using vital staining (acridine orange and propidium iodide), and optimum temperature conditions for addition and removal of the cryoprotectant were derived. The effects on structural integrity of cryopreservation in 15% and 20% w/w dimethylsulfoxide, and of reducing the degree of cell swelling during cryoprotectant removal following cryopreservation, were then evaluated.

The characteristics of uptake of dimethylsulfoxide from a 10% w/w solution fitted a single exponential, resulting in a maximum tissue concentration of 14.6% when the addition occurred on ice, and 18.5% when the addition took place at room temperature. The toxic effects of dimethylsulfoxide in porcine corneas were highly temperature dependent and only evident after removal of the cryoprotectant. Unlike rabbit corneas, cryopreservation of porcine corneas in 15% and 20% w/w dimethylsulfoxide induced substantial endothelial injury which was not improved by reducing the degree of cell swelling that occurred during removal of the cryoprotectant.

Porcine corneas were substantially more susceptible to the toxic effects of dimethyl sulfoxide, and to cryopreservation injury, than rabbit corneas. These results underline the importance of species variation in animal studies aimed at the cryopreservation of human tissue for transplantation.