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 procedure as well as during tissue culture and cryopreservation, we have measured the glutathione redox state (GSH/GSSG) of islets. Human islets were purified by standard techniques from organ donors, cultured, and cryopreserved. Glucose-induced insulin release was monitored in parallel during static incubations to assess the function of the islets. Cultured human islets responded by a 2.2-fold increase in insulin release to a glucose challenge. After cryopreservation the hormonal response 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 cryopreservation to 12.2 +/- 3.4, suggesting that the freezing and thawing procedures imposed oxidative stress on the islets. To explore this hypothesis further, cryopreserved islets were treated with the antioxidant butylated hydroxyanisole (BHA). Islets exposed to BHA showed an improved glucose-induced insulin release and had an increased insulin content. BHA also protected the islets when they were exposed to alloxan, a free radical generating agent. However, after cryopreservation, BHA treatment did not modify the glutathione redox state. Although the BHA effect could not be explained merely by a change in the glutathione redox state, it is not precluded that redox changes of other cell components ameliorate the glucose sensitivity of the beta cells. Further studies will be needed to determine possible ways of improving islet cryopreservation with antioxidant treatments and particularly, to validate the present observations by in vivo experiments in the context of clinical islet transplantation.