Aims/hypothesis Empagliflozin (EMPA), an inhibitor of the renal sodium-glucose cotransporter (SGLT) 2, reduces the risk of cardiovascular death in patients with type 2 diabetes. The underlying mechanism of this effect is unknown. ] m , through impairment of myocardial NHE flux, independent of SGLT2 activity.

Aims/hypothesis Sodium-glucose cotransporter 2 (SGLT2) inhibitors (SGLT2i) constitute a novel class of glucose-lowering (type 2) kidney-targeted agents. We recently reported that the SGLT2i empagliflozin (EMPA) reduced cardiac cytosolic Na þ ([Na þ ] c ) and cytosolic Ca 2þ ([Ca 2þ ] c ) concentrations through inhibition of Na þ /H þ exchanger (NHE). Here, we examine (1) whether the SGLT2i dapagliflozin (DAPA) and canagliflozin (CANA) also inhibit NHE and reduce [Na þ ] c ; (2) a structural model for the interaction of SGLT2i to NHE; (3) to what extent SGLT2i affect the haemodynamic and metabolic performance of isolated hearts of healthy mice. Methods Cardiac NHE activity and [Na þ ] c in mouse cardiomyocytes were measured in the presence of clinically relevant concentrations of EMPA (1 μmol/l), DAPA (1 μmol/l), CANA (3 μmol/l) or vehicle. NHE docking simulation studies were applied to explore potential binding sites for SGTL2i. Constant-flow Langendorff-perfused mouse hearts were subjected to SGLT2i for 30 min, and cardiovascular function, O 2 consumption and energetics (phosphocreatine (PCr)/ATP) were determined. Results EMPA, DAPA and CANA inhibited NHE activity (measured through low pH recovery after NH 4 þ pulse: EMPA 6.69 ± 0.09, DAPA 6.77 ± 0.12 and CANA 6.80 ± 0.18 vs vehicle 7.09 ± 0.09; p < 0.001 for all three comparisons) and reduced [Na þ ] c (in mmol/l: EMPA 10.0 ± 0.5, DAPA 10.7 ± 0.7 and CANA 11.0 ± 0.9 vs vehicle 12.7 ± 0.7; p < 0.001). Docking studies provided high binding affinity of all three SGLT2i with the extracellular Na þ -binding site of NHE. EMPA and CANA, but not DAPA, induced coronary vasodilation of the intact heart. PCr/ATP remained unaffected. Conclusions/interpretation EMPA, DAPA and CANA directly inhibit cardiac NHE flux and reduce [Na þ ] c , possibly by binding with the Na þ -binding site of NHE-1. Furthermore, EMPA and CANA affect the healthy heart by inducing vasodilation. The [Na þ ] c -lowering class effect of SGLT2i is a potential approach to combat elevated [Na þ ] c that is known to occur in heart failure and diabetes.

Zuurbier, Coert J., Cihan Demirci, Anneke Koeman, Hans Vink, and Can Ince. Short-term hyperglycemia increases endothelial glycocalyx permeability and acutely decreases lineal density of capillaries with flowing red blood cells. J Appl Physiol 99: [1471][1472][1473][1474][1475][1476] 2005. First published July 14, 2005; doi:10.1152/japplphysiol.00436.2005.-Hyperglycemia is becoming recognized as an important risk factor for microvascular dysfunction. We hypothesized that short-term hyperglycemia, either on the scale of hours or weeks, alters the barrier function and the volume of the endothelial glycocalyx and decreases functional capillary density and deformability of the red blood cells (RBCs). All experiments were performed in anesthetized, mechanically ventilated, C57BL/6 mice that were either normoglycemic, acutely hyperglycemic (25 mM) for 60 min due to infusion of glucose, or hyperglycemic (25 mM) for 2-4 wk (db/db mice). The glycocalyx was probed using 40-kDa Texas red dextran, which is known to permeate the glycocalyx, and 70-kDa FITC dextran, which has impaired access to the glycocalyx in healthy animals. Clearance of the dye from the blood was measured. An orthogonal polarization spectral imaging technique was used to visualize the number of capillaries with flowing RBCs of the dorsal flexor muscle. The data indicate that short-term hyperglycemia causes a rapid decrease of the ability of the glycocalyx to exclude 70-kDa dextran. No change in the vascular permeation of 40-kDa dextran was observed. Glycocalyx volume was not affected by short-term hyperglycemia. In addition, 1 h of hyperglycemia resulted in a 38% decrease of the lineal density of capillaries with flowing RBCs. This decreased lineal density was not observed in the 2-to 4-wk hyperglycemia model. Short-term hyperglycemia was without any effect on the deformablity of the RBCs. The data indicate that the described increased vascular permeability with hyperglycemia can be ascribed to an increased permeability of the glycocalyx, identifying the glycocalyx as a potential early target of hyperglycemia. vascular permeability; diabetes; skeletal muscle; db/db mice HYPERGLYCEMIA, EITHER IN ITS acute form, such as which may occur in hospitalized critically ill patients, or in its chronic form, such as is present in patients with diabetes mellitus, is associated with increased rates of morbidity and mortality and diminished clinical outcome. The central importance of a vascular pathology underlying the hyperglycemia-associated poor prognosis is becoming increasingly evident. Characteristics of hyperglycemia-induced vasculopathy include decreased endothelium-dependent vasodilation, increased capillary permeability for large proteins such as albumin, swelling of endothelial cells, decreased capillary dimensions and diameters, and thickening of the basal lamina (5,13,20,23,33,41).The endothelial cell glycocalyx, a 0.2-to 0.5-m matrix lining the luminal surface of all blood vessels, is a significant factor in microvascular regulation by its action on volum...

Volatile anesthetics and KMA induce hyperglycemia, which can be explained, at least partly, by impaired glucose-induced insulin release. The data indicate that the inhibition of insulin release by ISO is mediated by sarcolemmal K(ATP) channel activation. The use of PENTO and SPM is not associated with hyperglycemia. SPM and KMA reduce the antiapoptotic association of HK with mitochondria.

No abstract

This study evaluates the effects of anesthesia and fluid support on hemodynamic parameters of the mechanically ventilated mouse of four different strains. All experiments were performed at a similar surgical level of anesthesia, as indicated by the probing of the pedal withdrawal reflex. Three anesthetic regimens [fentanyl-fluanisone-midazolam (FFM), ketamine-medetomidine-atropine (KMA), and isoflurane (ISO)], four commonly used mouse strains (Swiss, CD-1, BalbC, and C57Bl6), and three different fluid support strategies (no fluid, 0.2 ml · h−1 · 10 g−1 of 6% polystarch solution, and 0.5 ml · h−1 · 10 g−1 saline) were studied. Mean arterial pressure (MAP) or heart rate (HR) was similar among the four strains of mice except a trend toward lower HR for the BalbC mice. In terms of MAP, KMA is the preferred anesthetic for the Swiss and CD-1 mice, whereas KMA or ISO are recommended for BalbC or C57Bl6 mice. In terms of HR, ISO is the preferred anesthetic for the Swiss, CD-1, and C57Bl6 strains. No differences in HR for the three anesthetics were observed for the BalbC strain. Compared with administration of no fluid, both saline and polystarch administration similarly increased MAP by 7 ± 2, 10 ± 2, and 11 ± 2 mmHg at t = 1, 2, and 3 h, respectively, whereas fluid administration was without effect on HR. Saline supplementation resulted in an increased dry-to-wet ratio of the heart and both fluid regimens decreased total hemoglobin in the blood from 12.6 ± 0.5 to 10.4 ± 0.5 g/100 ml. Saline administration was associated with blood acidosis (pH 7.20 ± 0.03) compared with the Haes (pH 7.29 ± 0.02) or no-fluid group (pH 7.34 ± 0.03), whereas Pco 2 was ∼30 mmHg for all groups. We conclude that at similar surgical levels of anesthesia, the preferable type of anesthesia (ISO or KMA, but never FFM) depends on the strain used and whether MAP or HR is the focus of study. Additional fluid support is beneficial in terms of raising arterial blood pressure, although this is at the cost of changes in organ water content and increased anemia.

Sodium glucose cotransporter 2 inhibitors (SGLT2i) are the first antidiabetic compounds that effectively reduce heart failure hospitalization and cardiovascular death in type 2 diabetics. Being explicitly designed to inhibit SGLT2 in the kidney, SGLT2i have lately been investigated for their off-target cardiac actions. Here, we review the direct effects of SGLT2i Empagliflozin (Empa), Dapagliflozin (Dapa), and Canagliflozin (Cana) on various cardiac cell types and cardiac function, and how these may contribute to the cardiovascular benefits observed in large clinical trials. SGLT2i impaired the Na+/H+ exchanger 1 (NHE-1), reduced cytosolic [Ca2+] and [Na+] and increased mitochondrial [Ca2+] in healthy cardiomyocytes. Empa, one of the best studied SGLT2i, maintained cell viability and ATP content following hypoxia/reoxygenation in cardiomyocytes and endothelial cells. SGLT2i recovered vasoreactivity of hyperglycemic and TNF-α-stimulated aortic rings and of hyperglycemic endothelial cells. Anti-inflammatory actions of Cana in IL-1β-treated HUVEC and of Dapa in LPS-treated cardiofibroblast were mediated by AMPK activation. In isolated mouse hearts, Empa and Cana, but not Dapa, induced vasodilation. In ischemia-reperfusion studies of the isolated heart, Empa delayed contracture development during ischemia and increased mitochondrial respiration post-ischemia. Direct cardiac effects of SGLT2i target well-known drivers of diabetes and heart failure (elevated cardiac cytosolic [Ca2+] and [Na+], activated NHE-1, elevated inflammation, impaired vasorelaxation, and reduced AMPK activity). These cardiac effects may contribute to the large beneficial clinical effects of these antidiabetic drugs.

Mitochondrial oxygen tension (mitoPO(2)) is a key parameter for cellular function, which is considered to be affected under various pathophysiological circumstances. Although many techniques for assessing in vivo oxygenation are available, no technique for measuring mitoPO(2) in vivo exists. Here we report in vivo measurement of mitoPO(2) and the recovery of mitoPO(2) histograms in rat liver by a novel optical technique under normal and pathological circumstances. The technique is based on oxygen-dependent quenching of the delayed fluorescence lifetime of protoporphyrin IX. Application of 5-aminolevulinic acid enhanced mitochondrial protoporphyrin IX levels and induced oxygen-dependent delayed fluorescence in various tissues, without affecting mitochondrial respiration. Using fluorescence microscopy, we demonstrate in isolated hepatocytes that the signal is of mitochondrial origin. The delayed fluorescence lifetime was calibrated in isolated hepatocytes and isolated perfused livers. Ultimately, the technique was applied to measure mitoPO(2) in rat liver in vivo. The results demonstrate mitoPO(2) values of approximately 30-40 mmHg. mitoPO(2) was highly sensitive to small changes in inspired oxygen concentration around atmospheric oxygen level. Ischemia-reperfusion interventions showed altered mitoPO(2) distribution, which flattened overall compared to baseline conditions. The reported technology is scalable from microscopic to macroscopic applications, and its reliance on an endogenous compound greatly enhances its potential field of applications.