Aims/hypothesis Endoplasmic reticulum (ER) stress has been implicated in glucose-induced beta cell dysfunction. However, its causal role has not been established in vivo. Our objective was to determine the causal role of ER stress and its link to oxidative stress in glucose-induced beta cell dysfunction in vivo. Methods Healthy Wistar rats were infused i.v. with glucose for 48 h to achieve 20 mmol/l hyperglycaemia with or without the co-infusion of the superoxide dismutase mimetic tempol (TPO), or the chemical chaperones 4-phenylbutyrate (PBA) or tauroursodeoxycholic acid (TUDCA). This was followed by assessment of beta cell function and measurement of ER stress markers and superoxide in islets.Results Glucose infusion for 48 h increased mitochondrial superoxide and ER stress markers and impaired beta cell function. Co-infusion of TPO, which we previously found to reduce mitochondrial superoxide and prevent glucoseinduced beta cell dysfunction, reduced ER stress markers.Similar to findings with TPO, co-infusion of PBA, which decreases mitochondrial superoxide, prevented glucoseinduced beta cell dysfunction in isolated islets. TUDCA was also effective. Also similar to findings with TPO, PBA prevented beta cell dysfunction during hyperglycaemic clamps in vivo and after hyperglycaemia (15 mmol/l) for 96 h. Conclusions/interpretation Here, we causally implicate ER stress in hyperglycaemia-induced beta cell dysfunction in vivo. We show that: (1) there is a positive feedback cycle between oxidative stress and ER stress in glucose-induced beta cell dysfunction, which involves mitochondrial superoxide; and (2) this cycle can be interrupted by superoxide dismutase mimetics as well as chemical chaperones, which are of potential interest to preserve beta cell function in type 2 diabetes.

-We have shown that oxidative stress is a mechanism of free fatty acid (FFA)-induced ␤-cell dysfunction. Unsaturated fatty acids in membranes, including plasma and mitochondrial membranes, are substrates for lipid peroxidation, and lipid peroxidation products are known to cause impaired insulin secretion. Therefore, we hypothesized that mice overexpressing glutathione peroxidase-4 (GPx4), an enzyme that specifically reduces lipid peroxides, are protected from fat-induced ␤-cell dysfunction. GPx4-overexpressing mice and their wild-type littermate controls were infused intravenously with saline or oleate for 48 h, after which reactive oxygen species (ROS) were imaged, using dihydrodichlorofluorescein diacetate in isolated islets, and ␤-cell function was assessed ex vivo in isolated islets and in vivo during hyperglycemic clamps. Forty-eight-hour FFA elevation in wild-type mice increased ROS and the lipid peroxidation product malondialdehyde and impaired ␤-cell function ex vivo in isolated islets and in vivo, as assessed by decreased disposition index. Also, islets of wild-type mice exposed to oleate for 48 h had increased ROS and lipid peroxides and decreased ␤-cell function. In contrast, GPx4-overexpressing mice showed no FFA-induced increase in ROS and lipid peroxidation and were protected from the FFA-induced impairment of ␤-cell function assessed in vitro, ex vivo and in vivo. These results implicate lipid peroxidation in FFA-induced ␤-cell dysfunction. oxidative stress; lipid peroxide; glutathione peroxidase 4; lipotoxicity; ␤-cell dysfunction; in vivo CHRONIC EXPOSURE of pancreatic ␤-cells to free fatty acids (FFA) impairs ␤-cell function (21). Although not all studies are concordant (45), a growing body of evidence implicates oxidative stress as a mechanism of FFA-induced ␤-cell dysfunction (9,38,46,60,67). Pancreatic ␤-cells have low antioxidant defenses (34) and are thus susceptible to reactive oxygen species (ROS)-induced decrease in function and viability (37,47). We have demonstrated previously that 1) prolonged elevation of plasma FFA in rats impairs glucose-stimulated insulin secretion (GSIS) in vivo during hyperglycemic clamps and ex vivo in freshly isolated islets and 2) the treatment with the antioxidants N-acetylcysteine, taurine, or tempol, which decreases islet ROS measured with dihydrodichlorofluorescein diacetate (H 2 DCF-DA), prevents the impairing effects of FFA on ␤-cell function (51). Zhang et al. (72) confirmed our findings in rats (51) in a different model of prolonged FFA elevation. Our group has also shown that the antioxidant taurine alleviates FFA-induced impairment in ␤-cell function in humans (68).The type and cellular localization of ROS in FFA-induced ␤-cell dysfunction are still unclear. We have demonstrated that cytosolic superoxide plays a causal role in fat-induced ␤-cell dysfunction (32); however, since the antioxidants N-acetylcysteine and taurine, which do not decrease superoxide, were also effective in restoring ␤-cell function (51), other ROS are implicated in addition ...

The study suggests a significant role of ATR corneal astigmatism in good uncorrected distance and near vision after monofocal IOL implantation.

Aims/hypothesisThe activation of NADPH oxidase has been implicated in NEFA-induced beta cell dysfunction. However, the causal role of this activation in vivo remains unclear. Here, using rodents, we investigated whether pharmacological or genetic inhibition of NADPH oxidase could prevent NEFA-induced beta cell dysfunction in vivo.MethodsNormal rats were infused for 48 h with saline or oleate with or without the NADPH oxidase inhibitor apocynin. In addition, NADPH oxidase subunit p47phox-null mice and wild-type littermate controls were infused with saline or oleate for 48 h. This was followed by measurement of NADPH oxidase activity, reactive oxygen species (ROS) and superoxide imaging and assessment of beta cell function in isolated islets and hyperglycaemic clamps.ResultsOleate infusion in rats increased NADPH oxidase activity, consistent with increased total but not mitochondrial superoxide in islets and impaired beta cell function in isolated islets and during hyperglycaemic clamps. Co-infusion of apocynin with oleate normalised NADPH oxidase activity and total superoxide levels and prevented beta cell dysfunction. Similarly, 48 h NEFA elevation in wild-type mice increased total but not mitochondrial superoxide and impaired beta cell function in isolated islets. p47phox-null mice were protected against these effects when subjected to 48 h oleate infusion. Finally, oleate increased the levels of total ROS, in both models, whereas inhibition of NADPH oxidase prevented this increase, suggesting that NADPH oxidase is the main source of ROS in this model.Conclusions/interpretationThese data show that NADPH-oxidase-derived cytosolic superoxide is increased in islets upon oleate infusion in vivo; and whole-body NADPH-oxidase inhibition decreases superoxide in concert with restoration of islet function.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-013-2858-4) contains peer-reviewed but unedited supplementary material, which is available to authorised users.