IMPROVED INSULIN-SECRETION OF CRYOPRESERVED HUMAN ISLETS BY ANTIOXIDANT TREATMENT

The viability of islets of Langerhans prior to grafting is believed to influence the clinical outcome of islet transplantation. To determine whether oxidative stress occurs during the isolation-purification pro cedure as well as during tissue culture and cryopreservation, we have measured the glutathione redox state (GSH/GSSG) of islets. Human islet s were purified by standard techniques from organ donors, cultured, an d cryopreserved. Glucose-induced insulin release was monitored in para llel during static incubations to assess the function of the islets. C ultured human islets responded by a 2.2-fold increase in insulin relea se to a glucose challenge. After cryopreservation the hormonal respons e was lower. Immediately after islet isolation the GSH/GSSG ratio was 25.2 +/- 5.2, and it increased slightly to 32.0 +/- 6.1 after 1-3 days in tissue culture. The GSH/GSSG decreased significantly after cryopre servation to 12.2 +/- 3.4, suggesting that the freezing and thawing pr ocedures imposed oxidative stress on the islets. To explore this hypot hesis further, cryopreserved islets were treated with the antioxidant butylated hydroxyanisole (BHA). Islets exposed to BHA showed an improv ed glucose-induced insulin release and had an increased insulin conten t. BHA also protected the islets when they were exposed to alloxan, a free radical generating agent. However, after cryopreservation, BHA tr eatment did not modify the glutathione redox state. Although the BHA e ffect could not be explained merely by a change in the glutathione red ox state, it is not precluded that redox changes of other cell compone nts ameliorate the glucose sensitivity of the beta cells. Further stud ies will be needed to determine possible ways of improving islet cryop reservation with antioxidant treatments and, particularly, to validate the present observations by in vivo experiments in the context of cli nical islet transplantation.