O'Neill J, Fasching A, Pihl L, Patinha D, Franzén S, Palm F. Acute SGLT inhibition normalizes O 2 tension in the renal cortex but causes hypoxia in the renal medulla in anaesthetized control and diabetic rats. Am J Physiol Renal Physiol 309: F227-F234, 2015. First published June 3, 2015 doi:10.1152/ajprenal.00689.2014.-Early stage diabetic nephropathy is characterized by glomerular hyperfiltration and reduced renal tissue PO 2. Recent observations have indicated that increased tubular Na ϩ -glucose linked transport (SGLT) plays a role in the development of diabetes-induced hyperfiltration. The aim of the present study was to determine how inhibition of SLGT impacts upon PO 2 in the diabetic rat kidney. Diabetes was induced by streptozotocin in Sprague-Dawley rats 2 wk before experimentation. Renal hemodynamics, excretory function, and renal O 2 homeostasis were measured in anesthetized control and diabetic rats during baseline and after acute SGLT inhibition using phlorizin (200 mg/kg ip). Baseline arterial pressure was similar in both groups and unaffected by SGLT inhibition. Diabetic animals displayed reduced baseline PO 2 in both the cortex and medulla. SGLT inhibition improved cortical PO 2 in the diabetic kidney, whereas it reduced medullary PO 2 in both groups. SGLT inhibition reduced Na ϩ transport efficiency [tubular Na ϩ transport (TNa)/renal O2 consumption (QO2)] in the control kidney, whereas the already reduced TNa/QO 2 in the diabetic kidney was unaffected by SGLT inhibition. In conclusion, these data demonstrate that when SGLT is inhibited, renal cortex PO 2 in the diabetic rat kidney is normalized, which implies that increased proximal tubule transport contributes to the development of hypoxia in the diabetic kidney. The reduction in medullary PO 2 in both control and diabetic kidneys during the inhibition of proximal Na ϩ reabsorption suggests the redistribution of active Na ϩ transport to less efficient nephron segments, such as the medullary thick ascending limb, which results in medullary hypoxia. diabetes; oxgen consumption; renal hypoxia; sodium-glucose linked transport; sodium transport DIABETES affects up to 220 million people worldwide (15). Diabetic nephropathy is a renal complication of type 1 and type 2 diabetes and is a major cause of morbidity and mortality affecting up to 40% of diabetic patients (9). More recently, Na ϩ -glucose linked transport (SGLT) inhibition has become a frontline pharmacological target in the treatment of diabetes because of its ability to lower blood glucose levels by promoting the excretion of glucose by the kidney.Indeed, in a healthy kidney, 99% of filtered glucose is reabsorbed, mostly via high-capacity SGLT2, which is expressed in the brush-border membrane of the proximal tubule in the S1 segment (39), and, to a lesser extent, via low-capacity SGLT1, which is expressed in the S3 segment of the proximal tubule (2). Glucose is transported out of proximal tubules and into the surrounding interstitium via glucose transporter 2. The reabsorption of glucose ...

BACKGROUND AND PURPOSEActivation of the intrarenal renin-angiotensin system (RAS) and increased renal medullary hydrogen peroxide (H2O2) contribute to hypertension. We examined whether H2O2 mediated hypertension and intrarenal RAS activation induced by angiotensin II (Ang II). ) was given to Ang II-treated rats, from day 7 to day 14. Systolic blood pressure was measured throughout the study. H2O2, angiotensin AT1 receptor and Nox4 expression and nuclear factor-kB (NF-kB) activation were evaluated in the kidney. Plasma and urinary H2O2 and angiotensinogen were also measured. EXPERIMENTAL APPROACH KEY RESULTSAng II increased H2O2, AT1 receptor and Nox4 expression and NF-kB activation in the renal medulla, but not in the cortex. Ang II raised plasma and urinary H2O2 levels, increased urinary angiotensinogen but reduced plasma angiotensinogen. PEG-catalase had a short-term antihypertensive effect and transiently suppressed urinary angiotensinogen. PEG-catalase decreased renal medullary expression of AT1 receptors and Nox4 in Ang II-infused rats. Renal medullary NF-kB activation was correlated with local H2O2 levels and urinary angiotensinogen excretion. Loss of antihypertensive efficacy was associated with an eightfold increase of plasma angiotensinogen. CONCLUSIONS AND IMPLICATIONSThe renal medulla is a major target for Ang II-induced redox dysfunction. H2O2 appears to be the key mediator enhancing intrarenal RAS activation and decreasing systemic RAS activity. The specific control of renal medullary H2O2 levels may provide future grounds for the treatment of hypertension. AbbreviationsAng II, angiotensin II; DPI, diphenylene iodonium; EMSA, electrophoretic mobility shift assay; fEMSA, fluorescent electrophoretic mobility shift assay; GPx, glutathione peroxidase; L-NAME, nitro-L-arginine methylester; MPO, myeloperoxidase; PEG, polyethylene glycol; RAS, renin-angiotensin system; RFU, relative fluorescence units; ROS, reactive oxygen species; SBP, systolic blood pressure; SHR, spontaneously hypertensive rats; SOD, superoxide dismutase BJP British Journal of Pharmacology

Increased angiotensin II (ANG II) or adenosine can potentiate each other in the regulation of renal hemodynamics and tubular function. Diabetes is characterized by hyperfiltration, yet the roles of ANG II and adenosine receptors for controlling baseline renal blood flow (RBF) or tubular Na(+) handling in diabetes is presently unknown. Accordingly, the changes in their functions were investigated in control and 2-wk streptozotocin-diabetic rats after intrarenal infusion of the ANG II AT1 receptor antagonist candesartan, the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), or their combination. Compared with controls, the baseline blood pressure, RBF, and renal vascular resistance (RVR) were similar in diabetics, whereas the glomerular filtration rate (GFR) and filtration fraction (FF) were increased. Candesartan, DPCPX, or the combination increased RBF and decreased RVR similarly in all groups. In controls, the GFR was increased by DPCPX, but in diabetics, it was decreased by candesartan. The FF was decreased by candesartan and DPCPX, independently. DPCPX caused the most pronounced increase in fractional Na(+) excretion in both controls and diabetics, whereas candesartan or the combination only affected fractional Li(+) excretion in diabetics. These results suggest that RBF, via a unifying mechanism, and tubular function are under strict tonic control of both ANG II and adenosine in both control and diabetic kidneys. Furthermore, increased vascular AT1 receptor activity is a contribution to diabetes-induced hyperfiltration independent of any effect of adenosine A1 receptors.

Growing evidence supports a central role of NADPH oxidases (NOXs) in the regulation of platelets, which are circulating cells involved in both hemostasis and thrombosis. Here, the use of Nox1−/− and Nox1+/+ mice as experimental models of human responses demonstrated a critical role of NOX1 in collagen‐dependent platelet activation and pathological arterial thrombosis, as tested in vivo by carotid occlusion assays. In contrast, NOX1 does not affect platelet responses to thrombin and normal hemostasis, as assayed in tail bleeding experiments. Therefore, as NOX1 inhibitors are likely to have antiplatelet effects without associated bleeding risks, the NOX1‐selective inhibitor 2‐acetylphenothiazine (2APT) and a series of its derivatives generated to increase inhibitory potency and drug bioavailability were tested. Among the 2APT derivatives, 1‐(10H‐phenothiazin‐2‐yl)vinyl tert‐butyl carbonate (2APT‐D6) was selected for its high potency. Both 2APT and 2APT‐D6 inhibited collagen‐dependent platelet aggregation, adhesion, thrombus formation, superoxide anion generation, and surface activation marker expression, while responses to thrombin or adhesion to fibrinogen were not affected. In vivo administration of 2APT or 2APT‐D6 led to the inhibition of mouse platelet aggregation, oxygen radical output, and thrombus formation, and carotid occlusion, while tail hemostasis was unaffected. Differently to in vitro experiments, 2APT‐D6 and 2APT displayed similar potency in vivo. In summary, NOX1 inhibition with 2APT or its derivative 2APT‐D6 is a viable strategy to control collagen‐induced platelet activation and reduce thrombosis without deleterious effects on hemostasis. These compounds should, therefore, be considered for the development of novel antiplatelet drugs to fight cardiovascular diseases in humans.

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