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Obesity resulting from the delivery of an excess amount of energy to adipose tissue from glucose or free fatty acids is associated with insulin resistance and adipose tissue inflammation. Reactive oxygen species (ROS) have been implicated as contributors to both the onset and the progression of insulin resistance. ROS can be generated by overloading the mitochondrial oxidative phosphorylation system, and also by nicotinamide adenine dinucleotide phosphate oxidases (NOX) produced by either adipocytes, which only produce NOX4, or by macrophages, which produce mainly NOX2. The source of the ROS might differ in the early, intermediate and late stages of obesity, switching from NOX4-dependence in the early phases to NOX2-dependence, in the intermediate phase, and transiting to mitochondria-dependence later in the time course of obesity. Thus, depending on the stage of obesity, ROS can be generated by three distinct mechanisms: i.e., NOX4, NOX2, and mitochondria. In this review, we will discuss whether NOX4-, NOX2-, and/or mitochondria-derived ROS is/are causal in the onset of adipocyte insulin resistance as obesity progresses. Moreover, we will review the pathophysiological roles of NOX4, NOX2, and mitochondria-derived ROS on adipose tissue inflammation.
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Ageing is the most significant risk factor for a range of prevalent diseases, including cancer, cardiovascular disease, and diabetes. Accordingly, interventions are needed for delaying or preventing disorders associated with the ageing process, i.e., promotion of healthy ageing. Calorie restriction is the only nongenetic and the most robust approach to slow the process of ageing in evolutionarily divergent species, ranging from yeasts, worms, and flies to mammals. Although it has been known for more than 80 years that calorie restriction increases lifespan, a mechanistic understanding of this phenomenon remains elusive. Yeast silent information regulator 2 (Sir2), the founding member of the sirtuin family of protein deacetylases, and its mammalian homologue Sir2-like protein 1 (SIRT1), have been suggested to promote survival and longevity of organisms. SIRT1 exerts protective effects against a number of age-associated disorders. Caloric restriction increases both Sir2 and SIRT1 activity. This review focuses on the mechanistic insights between caloric restriction and Sir2/SIRT1 activation. A number of molecular links, including nicotinamide adenine dinucleotide, nicotinamide, biotin, and related metabolites, are suggested to be the most important conduits mediating caloric restriction-induced Sir2/SIRT1 activation and lifespan extension.
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Oxidative stress has been paid increasing attention to as an important causative factor for diabetic vascular complications. Among possible various sources, accumulating evidence has indicated that NAD(P)H oxidase may be the most important source for reactive oxygen species production in diabetic vascular tissues. The mechanisms underlying activation and up-regulation of NAD(P)H oxidase has been supposed to be mediated by high glucose-induced protein kinase C (PKC) activation. In this review article, activation of local renin-angiotensin II system induced by chymase activation is also shown to amplify such a PKC-dependent activation of NAD(P)H oxidase. Additionally, human evidence showing the beneficial effect of antioxidants on diabetic vascular complications. Bilirubin has been recognized as a strong endogenous antioxidant. Here markedly lower prevalence of vascular complications is shown in diabetic patients with Gilbert syndrome, a congenital hyperbilirubinemia, as well as reduced markers of oxidative stress and inflammation. Lastly, statin, angiotensin II receptor blocker, chymase inhibitor, bilirubin and biliverdin, PKC β isoform inhibitor, and glucagon-like peptide-1 analog, are shown to serve as antioxidants and have some beneficial effect on diabetic vascular complications, via inhibiting PKC-NAD(P)H oxidase activation, supporting the notion that this mechanism may be an effective therapeutic target for preventing diabetic vascular complications.
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