Three of the major biochemical pathways implicated in the pathogenesis of hyperglycemia induced vascular damage (the hexosamine pathway, the advanced glycation end product (AGE) formation pathway and the diacylglycerol (DAG)-protein kinase C (PKC) pathway) are activated by increased availability of the glycolytic metabolites glyceraldehyde-3-phosphate and fructose-6-phosphate. We have discovered that the lipid-soluble thiamine derivative benfotiamine can inhibit these three pathways, as well as hyperglycemia-associated NF-kappaB activation, by activating the pentose phosphate pathway enzyme transketolase, which converts glyceraldehyde-3-phosphate and fructose-6-phosphate into pentose-5-phosphates and other sugars. In retinas of diabetic animals, benfotiamine treatment inhibited these three pathways and NF-kappaB activation by activating transketolase, and also prevented experimental diabetic retinopathy. The ability of benfotiamine to inhibit three major pathways simultaneously might be clinically useful in preventing the development and progression of diabetic complications.

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Apoptosis has been identified as a mechanism of pancreatic islet beta-cell death in autoimmune diabetes. Proinflammatory cytokines are candidate mediators of beta-cell death in autoimmune diabetes, and these cytokines can induce beta-cell death by apoptosis. In the present study, we examined whether transfection of human islet beta-cells with an anti-apoptotic gene, bcl-2, can prevent cytokine-induced beta-cell destruction. Human islet beta-cells were transfected by a replication-defective herpes simplex virus (HSV) amplicon vector that expressed the bcl-2 gene (HSVbcl-2) and, as a control, the same HSV vector that expressed a beta-galactosidase reporter gene (HSVlac). Two-color immunohistochemical staining revealed that 95+/-3% of beta-cells transfected with HSVbcl-2 expressed Bcl-2 protein compared with 14+/-3% of beta-cells transfected with HSVlac and 19+/-4% of nontransfected beta-cells. The bcl-2-transfected beta-cells were fully protected from impaired insulin secretion and destruction resulting from incubation for 5 days with the cytokine combination of interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma. In addition, the bcl-2-transfected islet cells were significantly protected from cytokine-induced lipid peroxidation and DNA fragmentation. These results demonstrate that cytokine-induced beta-cell dysfunction and death involve mechanisms subject to regulation by an anti-apoptotic protein, Bcl-2. Therefore, bcl-2 gene therapy has the potential to protect human beta-cells in pancreatic islets, or islet grafts, from immune-mediated damage in type 1 diabetes.

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