The aim of this study is to characterize lipid peroxidation mechanisms that are interfering with the insulin signaling pathway in a type 2 diabetes model. As a result of enhanced lipid peroxidation in diabetes, toxic end- products such as 4-hydroxynonenal accumulate and may chemically modify the insulin signaling proteins, contributing to the development of insulin resistance. An emerging hypothesis relates inflammation and a proinflammatory stage as causative factors leading to the overproduction of reactive oxygen and nitrogen species (ROS/RNS) in the disease, with increasing evidence for the involvement of inducible nitric oxide synthase (iNOS) and the deleterious peroxynitrite. The expression of iNOS is upregulated by most, if not all, inducers of insulin resistance as well, and therefore considerable amount of data implies the role of the enzyme in insulin resistance-related processes. My preliminary data demonstrate that both in type 1 and type 2 diabetes, lipid radicals were formed in the liver. The extensive protein radical formation and 4- hydroxynonenal accumulation is mediated by hydroxyl radical production; the lipid radical formation and lipid peroxidation were initiated by the hydroxyl radical derived from iNOS overexpression; this finding suggests peroxynitrite involvement as a primary oxidant. Moreover, a similar pattern of lipid radical production exists in a type 2 diabetic rat model with significant iNOS involvement; and the end product 4-hydroxynonenal may interfere with the insulin signaling pathway by making chemical modification on the insulin receptor substrate protein. In this proposal, I intend to further extend these initial studies by 1 - investigating the role of iNOS- driven free radical-dependent initiation of lipid peroxidation in a model of obese type 2 diabetes; 2 - characterizing lipid peroxidation-driven mechanisms underlying the progression of insulin resistance in type 2 diabetic animals; 3 - investigating potential pharmacologic treatments to attenuate and/or delay lipid peroxidation-mediated damage and insulin resistance in type 2 diabetes. These questions compose the core of the work described in this proposal which I believe will profoundly impact our understanding of oxidative stress and free radical mechanisms in diabetes, obesity and insulin resistance.
The proposal has the potential to impact our understanding of the mechanisms underlying insulin resistance, and its relation to an inflammatory stage in diabetes, to obesity and enhanced lipid free radical production. I believe that understanding these mechanisms is fundamental to rationally developing new therapies for the ultimate prevention and/or amelioration of diabetic complications and insulin resistance.
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