The non-peptidyl low molecular weight radical scavenger IAC protects human pancreatic islets from lipotoxicity

Chronic exposure to high free fatty acids (FFA) can lead to irreversible damage of beta-cell accounting for impaired insulin secretion. Multiple mechanisms concur in generating the damage, but activation of oxidative stress may contribute to the final toxic effect. To better understand the phenomenon of lipotoxicity in human beta-cells, we evaluated the effects of 24-h pre-culture with 1.0 mmol/l FFA on the function, survival and mRNA expression of several enzymes involved in the generation and scavenging of reactive oxygen species (ROS).

Human islets, prepared by collagenase digestion and density gradient purification from 9 pancreases of multiorgan donors, were incubated for 24-h in the presence 1.0 mmol/l long-chain mixture (oleate:palmitate, 2:1) FFA, with or without 100 micromol/l IAC, a non-peptidyl low molecular weight radical scavenger. At the end of incubation period, insulin secretion was measured by static incubation, and mRNA expression of insulin, Cu/Zn-SOD, Mn-SOD, Catalase, Glutathione peroxidase (GSH-px) and HO-1 by quantitative Real-Time RT-PCR. Nitrotyrosine levels were determined by an ELISA technique.

As compared to control incubation (Ctrl, no FFA), exposure to FFA was associated with impaired insulin release and reduced insulin mRNA expression. The presence of IAC in the incubation medium increased insulin release significantly and prevented changes in mRNA expression. Exposure to FFA was associated with oxidative stress as indicated by a significant accumulation of nitrotyrosine and IAC restrained such an increase. mRNA expression of Cu/Zn-SOD, Mn-SOD, Catalase, GSH-Px, and HO-1 were all modified after FFA exposure. These changes were partially prevented in the presence of IAC.

In human islets 24-h exposure to high FFA causes oxidative stress associated with changes of several enzymes involved in ROS scavenging. These effects were prevented by the use of an antioxidant molecule.