The combination of metallothionein and superoxide dismutase protects pancreatic β cells from oxidative damage

Abstract

Reactive oxygen species are considered an important cause of the death of pancreatic β cells, thereby triggering the development of type 2 diabetes as well as failure of islet transplantation. The biological properties of metallothionein (MT) and superoxide dismutase (SOD) are likely to be related to their antioxidant and free-radical scavenging abilities, but their access across biological membranes is limited. We investigated whether Tat-MT and Tat-SOD fusion protein could be introduced into islets by a novel protein transduction technology and protect them from oxidative damage. We used 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and Annexin V/propidium iodide assays to analyse cell viability, and assessed expression of apoptosis marker proteins by Western blotting. We examined the protective effect of Tat-MT and Tat-SOD on the development of diabetes and on graft failure after syngeneic islet transplantation into Otsuka Long Evans Tokushima Fatty (OLETF) rats and Imprinting Control Region (ICR) mice, respectively. Tat-MT and Tat-SOD were successfully delivered into the rat islets, and reactive oxygen species, nitric oxide, glucolipotoxicity-induced cell death, cytokine injury, and DNA fragmentation due to ischaemia-reperfusion in pancreatic β cells were significantly reduced. In addition Tat-MT and Tat-SOD treatment protected OLETF rats from developing diabetes, and enhanced the survival of antioxidant-treated islets transplanted into the renal capsules of diabetic mice. Transduction of Tat-MT and Tat-SOD proteins offers a new strategy for protecting against the development of diabetes by relieving oxidative stress.