Mechanism of cryoinjury in biological systems

Abstract

A new hypothesis, based on the assumption that intracellular water remains liquidlike below 0 °C and therefore its vapor pressure (vp) is greater than that of ice, is proposed to explain the mechanism of cryoinjury. On cooling, extra-cellular ice forms and a vp difference, Δ p, is created which increases with decreasing temperatures. A spontaneous process of water desorption and subsequent redistribution is prompted by the nonequilibrium state. Injury is the result of dehydration at slow cooling rates and membrane rupture at rapid rates. Penetrating cryoprotective agents improve survival rate by diminishing the migration rate and Δ p. The latter is achieved by lowering the vp of the intracellular fluid colligatively and increasing the vp of the extracellular solid. Differential thermal analysis of the aqueous solutions of glycerine, DMSO, and ammonium acetate provides experimental evidence that at concentrations at which these cryoprotective agents render full protection for red blood cells the frozen solid is amorphous glass instead of crystalline. Nonpenetrating agents protect only extracellular glass formation. Certain additives increase membrane permeability which at slow cooling rates is beneficial. The dimensional changes and thermogram of potato samples during temperature cycles are explicable by the proposed model. It is shown that the hypothesis is compatible with the most important modes of freezing injury already proposed, suggesting the primary cause leading to the creation under which they became operational.