Background: It has previously been observed that the insulin-producing cells of human pancreatic islets are more resistant to alloxan-, streptozotocin-, nitroprusside-, or cytokine-induced injury than those of mouse and rat islets.
Materials and methods: Human pancreatic islets were obtained from heart-beating organ donors. The expression of the stress proteins heat shock protein 70 (hsp70) and heme oxygenase and the anti-apoptosis gene bcl-2 was determined in isolated rat, mouse, and human islets, either cultured in vitro or transplanted under the kidney capsule of nude mice, using immunoblot analysis. Rat and human islet sensitive hydrogen peroxide was assess by glucose oxidation measurements. Isolated islets were also analyzed for their catalase and superoxide dismutase activities, and the islet cell levels of reduced glutathione were determined in response to hydrogen peroxide and nitroprusside. Programmed cell death in human and rat islets in response to streptozotocin was evaluated using TUNEL staining.
Results: Cultured human islets expressed higher contents of hsp70 than mouse and rat islets at basal conditions. Also after 4 weeks under the kidney capsule of normoglycemic mice, the hsp70 levels were higher in human islets than in rat islets. The expression of another stress protein, heme oxygenase (HO), was strongly increased in cultured rat islets, but was not affected in human islets. Expression of the bcl-2 gene could not be detected in human islets. In spite of this, 0.5 mM streptozotocin induced apotosis in rat but not in human islet cells. Hydrogen peroxide (0.1 and 0.4 mM) decreased glucose oxidation rates in rat but not in human islets. The levels of reduced glutathione were moderately decreased in human and rat islet cells and sharply decreased in mouse islet cells in response to hydrogen peroxide. Moreover, the activities of catalase and superoxide dismutase (SOD) were markedly lower in mouse islets than in human islets. The activity of catalase was lower in rat islets than in human islets.
Conclusion: Human islets differ clearly from mouse and rat islets in their increased expression of hsp70, catalase, and SOD, which may explain the increased resistance of human islets to beta cell toxins.