Modulation of the defense mechanism of pancreatic islets against oxidative stress

Author(s)

Luiz Fabrizio Stoppiglia

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2006-03-27

Examining board members

Antonio Carlos Boschero; Silvana Bordin; Carla Roberta de Oliveira Carvalho; Anibal Eugenio Vercesi; Jose Camillo Novello

• Advisor: Antonio Carlos Boschero

Abstract

In diabetes mellitus, oxygen radicals are associated with loss of glucose-sensibility and destruction of b-cells. In this work, we investigated the tolerance of neonatal rat islets to stress induced by H2O2, the islets antioxidant defense mechanism and factors maintaining islet glucoseresponsiveness. Islets cultured with 1 mM of H2O2 increased 6 fold the glucose uptake and resisted H2O2-induced stress when cultured in media containing 20 mM of glucose. Glucose-induced catalase expression was shown to be necessary to islet cell-survival, although not sufficient. In low H2O2 concentrations, the activity of catalase is dependent on NADPH and we observed that even proteins with no catalytic activity could be antioxidants regenerated by NADPH. Mapping the peroxidase activity in islets, we observed sensibility to NADPH in nuclear and cytossolic fractions. Islets cultured with 20 mM of glucose and islets that survived after culture with H2O2 both showed increased activity of the pentose phosphate pathway, which generate cytossolic NADPH. Is theses islets, we verified that cytossolic production of NAD(P)H limits insulin secretion. Such islets generate NAD(P)H principally from oxidation of endogenous fuels in cytossol and mitochondria, in contrary of the most H2O2-sensible islets which use endogenous fuels exclusively in cytossol. Culture with 20 mM of glucose produced islets with high expression of the glycerol-phosphate NADH shuttle, where as culture with H2O2 selected islets with high expression of the mal/asp shuttle. Since both shuttles promote interchange between cytossol and mitochondria, we have concluded that the shuttle system together with NAD(P)H generation ability are critical factors in maintaining islet glucoseresponsiveness (AU)