PPARγ-dependent and -independent effects of Rosiglitazone on lipotoxic human pancreatic islets

We explored the in vitro effects of Rosiglitazone (RZG), a PPAR gamma agonist, on human pancreatic islet dysfunctions induced by chronic free fatty acid exposure. We demonstrated that RZG beneficial effects on insulin secretion and apoptosis did not imply PDX-1 or insulin gene modulation. It rather involved, through a PPAR gamma-dependent mechanism, a reduction of NOS overexpressed in lipotoxic islets. This reduction likely led to the restoration of ATP level and insulin secretion as well as the decrease in apoptosis. More interestingly, we also demonstrated that RZG beneficial effects involved PPAR gamma-independent mechanisms. RZG treatment led to a limitation of oxidative stress exemplified by an increase of GPx and SOD expression. It also increased UCP2 expression that seemed to display antioxidant action in this model. Thus, RZG did not appear to exert a direct action on insulin expression but rather an indirect action on insulin secretion and apoptosis, through PPAR gamma-dependent and -independent mechanisms, via regulation of nitrogen and oxygen reactive species injury. (c) 2007 Elsevier Inc. All rights reserved.