EFFECTS OF S-NITROSOGLUTATHIONE (GSNO) ON THIOL HOMEOSTASIS OF PANCREATIC-ISLETS

The effects of the nitric oxide (NO) donor S-nitrosoglutathione (GSNO) on the thiol homeostasis of the rat pancreatic islets was studied by measuring: a) the activity of the glycolytic enzyme glyceraldehyde pho sphate dehydrogenase (GAPDH) which contains nitrosylable thiols critic ally involved in its catalytic function; b) the levels and redox of th e main intracellular low molecular weight thiol glutathione; c) the ab ility of mitochondrial dehydrogenases to reduce 4,5-dimetlhylthiazol-2 -yl)-3,5-diphenyltetrazolium bromide (MTT), The islet preparations in culture were incubated for 3 hours at 37 degrees C in the absence or p resence of low (250 mu M) and high (1 mM) concentrations of GSNO. The ability of GSNO to penetrate the islets and modify the intracellular t hiols of the beta-cells was demonstrated by the dramatic inhibition of GAPDH activity (by 79% and 98%, at the low and high GSNO levels, resp ectively); at the same time the total pool of glutathione dropped by 5 1% and 69%, with a slight decrease in the ratio of reduced/oxidized gl utathione, The decrease in the ability of the islets to reduce MTT par alleled the GSNO-induced modifications, These data indicate that the e xposure of pancreatic islets to GSNO, and probably to other nitrosylat ing agents, results in disruption of their thiol homeostasis with resu lting oxidative damage, This condition involves intracellular targets such as GAPDH and mag influence redox-sensitive elements involved in t he regulation of the beta-cell metabolism, ultimately influencing its survival. (C) 1997, Editrice Kurtis.