Biochemical alterations and tissue viability in at-1 prostate tumor tissue after in vitro cryodestruction

This study tested the effect of freezing with cryosurgically-achievable freezing rates and end-point temperatures on plasma membrane integrity, protein synthetic activity, and cell survival in cryotreated rat AT-1 prostate tumor tissue. Freezing damage to the cell membranes, as assessed by protein leakage from the tissue, was approximately equal at all freeze rates. Protein synthetic activity, measured by the incorporation of radioactive methionine into secreted and total cellular protein, was lost in all treatments except the most moderate (5°C/min→-20°C and 10°C/min→-40°C). Loss of chromatin from the nucleus by predominantly necrotic pathways was evident in all tissue but the preservation of intact DNA was correlated with cell survival at 5°C/min →-20°C and control. Histologic examination of the tissue after in vitro cryotreatment was consistent with extensive tissue destruction in samples cooled by LN2 immersion, at 50°C/min →-90°C or 35°C/min → -75°C, marginal survival in samples cooled at 10°C/min → -40°C, and the highest survival in samples cooled at 5°C/min →-20°C compared to control. These results show that freezing results in biochemical damage that reflects loss of cell viability, and that for the freezing rates and endpoint temperatures tested cell damage is maximal at freeze rates greater than 10°C/min to endpoint temperatures below -40°C. Evidence suggests that of the freezing parameters tested, an end-point temperature < -40°C is the determining factor in tissue destruction.