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Enhanced oxidative stress contributes to the pathogenesis of diabetes and its complications. Peroxiredoxin 6 (PRDX6) is a key regulator of cellular redox balance, with the peculiar ability to neutralize peroxides, peroxynitrite, and phospholipid hydroperoxides. In the current study, we aimed to define the role of PRDX6 in the pathophysiology of type 2 diabetes (T2D) using PRDX6 knockout (−/−) mice. Glucose and insulin responses were evaluated respectively by intraperitoneal glucose and insulin tolerance tests. Peripheral insulin sensitivity was analyzed by euglycemic-hyperinsulinemic clamp, and molecular tools were used to investigate insulin signaling. Moreover, inflammatory and lipid parameters were evaluated. We demonstrated that PRDX6−/− mice developed a phenotype similar to early-stage T2D caused by both reduced glucose-dependent insulin secretion and increased insulin resistance. Impaired insulin signaling was present in PRDX6−/− mice, leading to reduction of muscle glucose uptake. Morphological and ultrastructural changes were observed in islets of Langerhans and livers of mutant animals, as well as altered plasma lipid profiles and inflammatory parameters. In conclusion, we demonstrated that PRDX6 is a key mediator of overt hyperglycemia in T2D glucose metabolism, opening new perspectives for targeted therapeutic strategies in diabetes care.

Diabetic hyperglycaemia causes endothelial dysfunction mainly by impairing endothelial nitric oxide (NO) production. Moreover, hyperglycaemia activates several noxious cellular pathways including apoptosis, increase in reactive oxygen species (ROS) levels and diminishing Na(+)-K(+) ATPase activity which exacerbate vascular damage. Serum glucocorticoid kinase (SGK)-1, a member of the serine/threonine kinases, plays a pivotal role in regulating NO production through inducible NO synthase activation and other cellular mechanisms. Therefore, in this study, we aimed to investigate the protective role of SGK-1 against hyperglycaemia in human umbilical endothelial cells (HUVECs). We used retrovirus to infect HUVECs with either SGK-1, SGK-1Delta60 (lacking of the N-60 amino acids-increase SGK-1 activity) or SGK-1Delta60KD (kinase-dead constructs). We tested our hypothesis in vitro after high glucose and glucosamine incubation. Increase in SGK-1 expression and activity (SGK-1Delta60) resulted in higher production of NO, inhibition of ROS synthesis and lower apoptosis in endothelial cell after either hyperglycaemia or glucosamine treatments. Moreover, in this study, we showed increased GLUT-1 membrane translocation and Na(+)-K(+) ATPase activity in cell infected with SGK-1Delta60 construct. These results suggest that as in endothelial cells, an increased SGK-1 activity and expression reduces oxidative stress, improves cell survival and restores insulin-mediated NO production after different noxae stimuli. Therefore, SGK-1 may represent a specific target to further develop novel therapeutic options against diabetic vascular disease.

Liver has a principal role in glucose regulation and lipids homeostasis. It is under a complex control by substrates such as hormones, nutrients, and neuronal impulses. Insulin promotes glycogen synthesis, lipogenesis, and lipoprotein synthesis and inhibits gluconeogenesis, glycogenolysis, and VLDL secretion by modifying the expression and enzymatic activity of specific molecules. To understand the pathophysiological mechanisms leading to metabolic liver disease, we analyzed liver protein patterns expressed in a mouse model of diabetes by proteomic approaches. We used insulin receptor-knockout (IR−/−) and heterozygous (IR+/−) mice as a murine model of liver metabolic dysfunction associated with diabetic ketoacidosis and insulin resistance. We evaluated liver fatty acid levels by microscopic examination and protein expression profiles by orthogonal experimental strategies using protein 2-DE MALDI-TOF/TOF and peptic nLC-MS/MS shotgun profiling. Identified proteins were then loaded into Ingenuity Pathways Analysis to find possible molecular networks. Twenty-eight proteins identified by 2-DE analysis and 24 identified by nLC-MS/MS shotgun were differentially expressed among the three genotypes. Bioinformatic analysis revealed a central role of high-mobility group box 1/2 and huntigtin never reported before in association with metabolic and related liver disease. A different modulation of these proteins in both blood and hepatic tissue further suggests their role in these processes. These results provide new insight into pathophysiology of insulin resistance and hepatic steatosis and could be useful in identifying novel biomarkers to predict risk for diabetes and its complications.

Type 2 diabetes mellitus (T2DM) is associated with endothelial dysfunction, which leads to vascular complications. Endothelial progenitor cells (EPCs) are thought to be a subset of cells derived from the bone marrow that play a crucial role in the neovascularization of ischemic tissue and in the maintenance of endothelial cell integrity. In contrast, circulating endothelial cells (CECs) are of endothelial origin and become detached from the intima of blood vessels in response to pathological stimuli. The study investigated the effects of T2DM on subpopulations of EPCs and CECs in peripheral blood, as compared with the effects on unacylated (UAG) and acylated (AG) ghrelin levels, which have been shown recently to play an important role in endothelial dysfunction associated with diabetes. Using the high-performance flow cytometer FACSCanto, and UAG/AG ghrelin enzyme immunoassay kits, we analyzed whole peripheral blood samples from: (i) diabetic patients with a history of disease of less than 1 year and no clinical evidence of angiopathy, (ii) diabetic patients with long-standing disease with vascular complications, and (iii) healthy donors. We found that T2DM did not affect bone-marrow mobilization, but it altered the UAG/AG profile and decreased the number of highly differentiated EPCs (late EPCs) greatly. In addition, T2DM increased the number of CECs, together with the number of activated CECs. Our results suggest that: (i) the endothelial damage could be due mainly to altered maturation/commitment of EPCs, rather than a simple decrease in their production in the bone marrow; and (ii) EPC subpopulations and ghrelin levels could be useful markers to assess endothelial damage in diabetes.

BACKGROUND: The efficacy of Phosphodiesterase 5 (PDE5) inhibitors to re-establish endothelial function is reduced in diabetic patients. Recent evidences suggest that therapy with PDE5 inhibitors, i.e. sildenafil, may increase the expression of nitric oxide synthase (NOS) proteins in the heart and cardiomyocytes. In this study we analyzed the effect of sildenafil on endothelial cells in insulin resistance conditions in vitro. METHODOLOGY/PRINCIPAL FINDINGS: Human umbilical vein endothelial cells (HUVECs) were treated with insulin in presence of glucose 30 mM (HG) and glucosamine 10 mM (Gluc-N) with or without sildenafil. Insulin increased the expression of PDE5 and eNOS mRNA assayed by Real time-PCR. Cytofluorimetric analysis showed that sildenafil significantly increased NO production in basal condition. This effect was partially inhibited by the PI3K inhibitor LY 294002 and completely inhibited by the NOS inhibitor L-NAME. Akt-1 and eNOS activation was reduced in conditions mimicking insulin resistance and completely restored by sildenafil treatment. Conversely sildenafil treatment can counteract this noxious effect by increasing NO production through eNOS activation and reducing oxidative stress induced by hyperglycaemia and glucosamine. CONCLUSIONS/SIGNIFICANCE: These data indicate that sildenafil might improve NOS activity of endothelial cells in insulin resistance conditions and suggest the potential therapeutic use of sildenafil for improving vascular function in diabetic patients.