Accumulating evidence has implicated that GLP-1 may have a beneficial effect on cardiovascular and renal diseases but the mechanism is not fully understood. Here we show that GLP-1 analog, liraglutide, inhibits oxidative stress and albuminuria in streptozotocin (STZ)-induced type 1 diabetes mellitus rats, via a protein kinase A (PKA)-mediated inhibition of renal NAD(P)H oxidases. Diabetic rats were randomly treated with subcutaneous injections of liraglutide (0.3 mg/kg/12 h) for 4 weeks. Oxidative stress markers (urinary 8-hydroxy-2'-deoxyguanosine and renal dihydroethidium staining), expression of renal NAD(P)H oxidase components, transforming growth factor-β (TGF-β), fibronectin and urinary albumin excretion were measured. In vitro effect of liraglutide was evaluated using cultured renal mesangial cells. Administration of liraglutide did not affect plasma glucose levels or body weights in STZ diabetic rats, but normalized oxidative stress markers, expression of NAD(P)H oxidase components, TGF-β, fibronectin in renal tissues and urinary albumin excretion, all of which were significantly increased in diabetic rats. In addition, in cultured renal mesangial cells, incubation with liraglutide for 48 h inhibited NAD(P)H-dependent superoxide production evaluated by lucigenin chemiluminescence in a dose-dependent manner. This effect was reversed by both PKA inhibitor H89 and adenylate cyclase inhibitor SQ22536, but not by Epac2 inhibition via its small interfering RNA. Liraglutide may have a direct beneficial effect on oxidative stress and diabetic nephropathy via a PKA-mediated inhibition of renal NAD(P)H oxidase, independently of a glucose-lowering effect.

Intrauterine environment may influence the health of postnatal offspring. There have been many studies on the effects of maternal high-fat diet (HFD) on diabetes and glucose metabolism in offspring. Here, we investigated the effects in male and female offspring. C57/BL6J mice were bred and fed either control diet (CD) or HFD from conception to weaning, and offspring were fed CD or HFD from 6 to 20 wk. At 20 wk, maternal HFD induced glucose intolerance and insulin resistance in offspring. Additionally, liver triacylglycerol content, adipose tissue mass, and inflammation increased in maternal HFD. In contrast, extending previous observations, insulin secretion at glucose tolerance test, islet area, insulin content, and PDX-1 mRNA levels in isolated islets were lower in maternal HFD in males, whereas they were higher in females. Oxidative stress in islets increased in maternal HFD in males, whereas there were no differences in females. Plasma estradiol levels were lower in males than in females and decreased in offspring fed HFD and also decreased by maternal HFD, suggesting that females may be protected from insulin deficiency by inhibiting oxidative stress. In conclusion, maternal HFD induced insulin resistance and deterioration of pancreatic ␤-cell function, with marked sex differences in adult offspring accompanied by adipose tissue inflammation and liver steatosis. Additionally, our results demonstrate that potential mechanisms underlying sex differences in pancreatic ␤-cell function may be related partially to increases in oxidative stress in male islets and decreased plasma estradiol levels in males.

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The Joslin Medalist Study characterized people affected with type 1 diabetes for 50 years or longer. More than 35% of these individuals exhibit no to mild diabetic retinopathy (DR), independent of glycemic control, suggesting the presence of endogenous protective factors against DR in a subpopulation of patients. Proteomic analysis of retina and vitreous identified retinol binding protein 3 (RBP3), a retinol transport protein secreted mainly by the photoreceptors, as elevated in Medalist patients protected from advanced DR. Mass spectrometry and protein expression analysis identified an inverse association between vitreous RBP3 concentration and DR severity. Intravitreal injection and photoreceptor-specific overexpression of RBP3 in rodents inhibited the detrimental effects of vascular endothelial growth factor (VEGF). Mechanistically, our results showed that recombinant RBP3 exerted the therapeutic effects by binding and inhibiting VEGF receptor tyrosine phosphorylation. In addition, by binding to glucose transporter 1 (GLUT1) and decreasing glucose uptake, RBP3 blocked the detrimental effects of hyperglycemia in inducing inflammatory cytokines in retinal endothelial and Müller cells. Elevated expression of photoreceptor-secreted RBP3 may have a role in protection against the progression of DR due to hyperglycemia by inhibiting glucose uptake via GLUT1 and decreasing the expression of inflammatory cytokines and VEGF.

Aims/hypothesis We have previously shown a negative correlation between serum bilirubin levels and prevalence of type 2 diabetes, suggesting that bilirubin inhibits development of this disease. To confirm this hypothesis, we investigated whether administration of biliverdin, the precursor of bilirubin, protects against the deterioration of glucose tolerance in db/db mice, a rodent model of type 2 diabetes. Methods Biliverdin (20 mg/kg daily) was orally administered to 5-week-old db/db mice for 4 weeks. After 4 weeks of treatment, i.p. glucose tolerance and insulin tolerance tests were performed. Insulin content was evaluated by immunostaining and ELISA. Oxidative stress markers (8-hydroxy-2′-deoxyguansosine and dihydroethidium staining) and expression of NADPH oxidase components Pdx1 and Bax were also evaluated in isolated islets. Results Treatment with biliverdin partially prevented worsening of hyperglycaemia and glucose intolerance in db/db mice. This effect was accompanied by a significant increase in insulin content and Pdx1 expression, and a significant decrease of apoptosis and Bax expression in pancreatic islets from db/db mice. At the same time, levels of oxidative stress markers and NADPH oxidase component production in islets were normalised. Biliverdin had little effect on HOMA of insulin resistance or insulin resistance evaluated by insulin tolerance tests. Conclusions/interpretation Biliverdin may protect against progressive worsening of glucose tolerance in db/db mice, mainly via inhibition of oxidative stress-induced beta cell damage.

There has been a concern that sodium-glucose cotransporter 2 (SGLT2) inhibitors could reduce skeletal muscle mass and function. Here, we examine the effect of canagliflozin (CANA), an SGLT2 inhibitor, on slow and fast muscles from nondiabetic C57BL/6J mice. In this study, mice were fed with or without CANA under ad libitum feeding, and then evaluated for metabolic valuables as well as slow and fast muscle mass and function. We also examined the effect of CANA on gene expressions and metabolites in slow and fast muscles. During SGLT2 inhibition, fast muscle function is increased, as accompanied by increased food intake, whereas slow muscle function is unaffected, although slow and fast muscle mass is maintained. When the amount of food in CANA-treated mice is adjusted to that in vehicle-treated mice, fast muscle mass and function are reduced, but slow muscle was unaffected during SGLT2 inhibition. In metabolome analysis, glycolytic metabolites and ATP are increased in fast muscle, whereas glycolytic metabolites are reduced but ATP is maintained in slow muscle during SGLT2 inhibition. Amino acids and free fatty acids are increased in slow muscle, but unchanged in fast muscle during SGLT2 inhibition. The metabolic effects on slow and fast muscles are exaggerated when food intake is restricted. This study demonstrates the differential effects of an SGLT2 inhibitor on slow and fast muscles independent of impaired glucose metabolism, thereby providing new insights into how they should be used in patients with diabetes, who are at a high risk of sarcopenia.

Rationale: Activation of monocytes/macrophages by hyperlipidemia associated with diabetes and obesity contributes to the development of atherosclerosis. PKCδ expression and activity in monocytes were increased by hyperlipidemia and diabetes with unknown consequences to atherosclerosis. Objective: To investigate the effect of PKCδ activation in macrophages on the severity of atherosclerosis. Methods and Results: PKCδ expression and activity were increased in Zucker diabetic rats. Mice with selective deletion of PKCδ in macrophages were generated by breeding PKCδ flox/flox mice with LyzM-Cre and ApoE−/− mice (MPKCδKO/ApoE−/− mice) and studied in atherogenic (AD) and very high fat diet (HFD). Mice fed AD and HFD exhibited hyperlipidemia, but only HFD fed mice had insulin resistance and mild diabetes. Surprisingly, MPKCδKO/ApoE−/− mice exhibited accelerated aortic atherosclerotic lesions by 2-fold vs. ApoE−/− mice on AD or HFD. Splenomegaly was observed in MPKCδKO/ApoE−/− mice on AD and HFD, but not on regular chow. Both the AD or HFD increased macrophage numbers in aortic plaques and spleen by 1.7 and 2-fold, respectively, in MPKCδKO/ApoE−/− vs. ApoE−/− mice due to decreased apoptosis (62%) and increased proliferation (1.9 fold), and not due to uptake, with parallel increased expressions of inflammatory cytokines. Mechanisms for the increased macrophages in MPKCδKO/ApoE−/− were associated with elevated phosphorylation levels of pro-survival cell signaling proteins, Akt and FoxO3a, with reduction of pro-apoptotic protein Bim associated with PKCδ induced inhibition of P85/PI3K. Conclusion: Accelerated development of atherosclerosis induced by insulin resistance and hyperlipidemia may be partially limited by PKCδ isoform activation in the monocytes, which decreased its number and inflammatory responses in the arterial wall.

Exogenous insulin decreased atherosclerosis by lowering inflammatory cytokines, macrophages, and plasma lipids in HFD-induced hyperlipidemia, insulin resistant and mildly diabetic ApoE mice.