Per Liss

Reactive oxygen species cause diabetes-induced decrease in renal oxygen tension

Aims/hypothesisAugmented formation of reactive oxygen species (ROS) induced by hyperglycaemia has been suggested to contribute to the development of diabetic nephropathy. This study was designed to evaluate the influence of streptozotocin (STZ)-induced diabetes mellitus, as well as the effects of preventing excessive ROS formation by α-tocopherol treatment, on regional renal blood flow, oxygen tension and oxygen consumption in anaesthetized Wistar Furth rats.MethodsNon-diabetic and STZ-diabetic rats were investigated after 4 weeks with or without dietary treatment with the radical scavenger DL-α-tocopherol (vitamin E, 5%). A laser-Doppler technique was used to measure regional renal blood flow, whilst oxygen tension and consumption were measured using Clark-type microelectrodes.ResultsRenal oxygen tension, but not renal blood flow, was lower throughout the renal parenchyma of diabetic rats when compared to non-diabetic control rats. The decrease in oxygen tension was most pronounced in the renal medulla. Renal cellular oxygen consumption was markedly increased in diabetic rats, predominantly in the medullary region. Diabetes increased lipid peroxidation and protein carbonylation in the renal medulla. Treatment with α-tocopherol throughout the course of diabetes prevented diabetes-induced disturbances in oxidative stress, oxygen tension and consumption. The diabetic animals had a renal hypertrophy and a glomerular hyperfiltration, which were unaffected by α-tocopherol treatment.Conclusions/interpretationWe conclude that oxidative stress occurs in kidneys of diabetic rats predominantly in the medullary region and relates to augmented oxygen consumption and impaired oxygen tension in the tissue.

Chronically decreased oxygen tension in rat pancreatic islets transplanted under the kidney capsule.

BACKGROUND A factor of potential importance in the failure of islet grafts is poor or inadequate engraftment of the islets in the implantation organ. This study measured the oxygen tension and blood perfusion in 1-, 2-, and 9-month-old islet grafts. METHODS The partial pressure of oxygen was measured in pancreatic islets transplanted beneath the renal capsule of diabetic and nondiabetic recipient rats with a modified Clark electrode (outer tip diameter 2-6 microm). The size of the graft (250 islets) was by purpose not large enough to cure the diabetic recipients. The oxygen tension in islets within the pancreas was also recorded. Blood perfusion was measured with the laser-Doppler technique. RESULTS Within native pancreatic islets, the partial pressure of oxygen was approximately 40 mm Hg (n=8). In islets transplanted to nondiabetic animals, the oxygen tension was approximately 6-7 mm Hg 1, 2, and 9 months posttransplantation. No differences could be seen between the different time points after transplantation. In the diabetic recipients, an even more pronounced decrease in graft tissue oxygen tension was recorded. The mean oxygen tension in the superficial renal cortex surrounding the implanted islets was similar in all groups (approximately 15 mm Hg). Intravenous administration of glucose (0.1 gxkg(-1)x min(-1)) did not affect the oxygen tension in any of the investigated tissues. The islet graft blood flow was similar in all groups, measuring approximately 50% of the blood flow in the kidney cortex. CONCLUSION The oxygen tension in islets implanted beneath the kidney capsule is markedly lower than in native islets up to 9 months after transplantation. Moreover, persistent hyperglycemia in the recipient causes an even further decrease in graft oxygen tension, despite similar blood perfusion. To what extent this may contribute to islet graft failure remains to be determined.

Intrarenal oxygen tension measured by a modified Clark electrode at normal and low blood pressure and after injection of x-ray contrast media

Abstract The oxygen tension (pO2) in the rat kidney was studied using a Clark microelectrode with a guard cathode behind the sensing cathode. The mean (± SEM) outer tip diameter of the electrodes used was 5.5 ± 1.9 μm. The zero-pO2 current amounted to 12.5 ± 0.9 pA at 37°C; at air saturation it was 252 ± 22.9 pA. Rats with a systolic blood pressure (BP) above 80 mmHg (where 1 mmHg = 133 Pa) showed an average pO2 in the cortex of 45 ± 2 mmHg and in the outer medulla of 31 ±1 mmHg. In rats with a BP below 80 mmHg a paradoxically high outer medullary pO2 of 40 ± 4 mmHg was found, while the pO2 in the cortex was 27 ± 4 mmHg. Changes in pO2 were also noted in the renal cortex and outer medulla after intravenous injections of the x-ray contrast medium diatrizoate (370 mg iodine/ml). In rats with normal BP, injection of diatrizoate caused a slight fall in pO2 in the renal cortex, from 42 ± 4 to 38 ±4 mmHg. In the medulla pO2 decreased significantly from 34 ± 6 to 20 ±4 mmHg. Ringer’s solution did not induce any changes.

Polyol-pathway-dependent disturbances in renal medullary metabolism in experimental insulin-deficient diabetes mellitus in rats

Aims/hypothesisThe renal medullary region is particularly vulnerable to reduced oxygen concentration because of its low blood perfusion and high basal oxygen consumption. This study investigated renal metabolic changes in relation to the previously observed decreased oxygen tension in streptozotocin-induced diabetic rats.MethodsBlood perfusion, oxygen tension and consumption, interstitial pH, and glycolytic and purine-based metabolites were determined in the renal cortex and the medulla of non-diabetic and diabetic animals by, respectively, laser Doppler flowmetry, oxygen and pH microelectrodes, and microdialysis. The importance of increased polyol pathway activity for the observed alterations was investigated by daily treatment with the aldose reductase inhibitor AL-1576 throughout the course of diabetes.ResultsThe diabetes-induced decrease in renal oxygen tension, due to augmented oxygen consumption, did not result in manifest hypoxia in either the cortical or the medullary region, as evaluated by microdialysis measurements of purine-based metabolites. The profound alterations in medullary oxygen metabolism were, however, associated with an increased lactate : pyruvate ratio and a concomitantly decreased pH. Notably, the renal medullary changes in oxygen tension, oxygen consumption, lactate : pyruvate ratio and pH were preventable by inhibition of aldose reductase.Conclusions/interpretationSubstantial metabolic changes were observed in the renal medulla in diabetic animals. These disturbances seemed to be mediated by increased polyol pathway activity and could be prevented by inhibition of aldose reductase.

Activation of Hypoxia-Inducible Factors Prevents Diabetic Nephropathy

Hyperglycemia results in increased oxygen consumption and decreased oxygen tension in the kidney. We tested the hypothesis that activation of hypoxia-inducible factors (HIFs) protects against diabetes-induced alterations in oxygen metabolism and kidney function. Experimental groups consisted of control and streptozotocin-induced diabetic rats treated with or without chronic cobalt chloride to activate HIFs. We elucidated the involvement of oxidative stress by studying the effects of acute administration of the superoxide dismutase mimetic tempol. Compared with controls, diabetic rats displayed tissue hypoxia throughout the kidney, glomerular hyperfiltration, increased oxygen consumption, increased total mitochondrial leak respiration, and decreased tubular sodium transport efficiency. Diabetic kidneys showed proteinuria and tubulointerstitial damage. Cobalt chloride activated HIFs, prevented the diabetes-induced alterations in oxygen metabolism, mitochondrial leak respiration, and kidney function, and reduced proteinuria and tubulointerstitial damage. The beneficial effects of tempol were less pronounced after activation of HIFs, indicating improved oxidative stress status. In conclusion, activation of HIFs prevents diabetes-induced alteration in kidney oxygen metabolism by normalizing glomerular filtration, which reduces tubular electrolyte load, preventing mitochondrial leak respiration and improving tubular transport efficiency. These improvements could be related to reduced oxidative stress and account for the reduced proteinuria and tubulointerstitial damage. Thus, pharmacologic activation of the HIF system may prevent development of diabetic nephropathy.

Differentiating between effects of streptozotocin per se and subsequent hyperglycemia on renal function and metabolism in the streptozotocin-diabetic rat model

The animal model with streptozotocin (STZ)‐induced diabetes mellitus is associated with progressive renal disturbances. The aim of this study was to differentiate between toxic effects of STZ and the effect of hyperglycemia. Previous studies have been limited to investigating the influence of STZ on glomerular filtration rate (GFR), albuminuria and renal morphology. The present study presents a new approach when transplanting β‐cells to cure the STZ‐treated animals and extends the evaluation to include both renal function and oxygen metabolism.

Oscillations in oxygen tension and insulin release of individual pancreatic ob/ob mouse islets.

Aims/hypothesis. The role of beta-cell metabolism for generation of oscillatory insulin release was investigated by simultaneous measurements of oxygen tension (pO2) and insulin release from individual islets of Langerhans.¶Methods. Individual islets isolated from the ob/ob-mice were perifused. Insulin in the perifusate was measured with a sensitive ELISA and pO2 with a modified Clark-type electrode inserted into the islets.¶Results. In the presence of 3 mmol/l d-glucose, pO2 was 102 ± 9 mmHg and oscillatory (0.26 ± 0.04 oscillations/min). Corresponding insulin measurements showed oscillatory release with similar periodicity (0.25 ± 0.02 oscillations/min). When the d-glucose concentration was increased to 11 mmol/l, pO2 decreased by 30 % to 72 ± 10 mmHg with maintained frequency of the oscillations. Corresponding insulin secretory rate rose from 5 ± 2 to 131 ± 16 pmol · g–1· s–1 leaving the frequency of the insulin pulses unaffected. The magnitude of glucose-induced change in pO2 varied between islets but was positively correlated to the amount of insulin released (r2 = 0.85). When 1 mmol/l tolbutamide was added to the perifusion medium containing 11 mmol/l glucose no change in average oscillatory pO2 was observed despite a doubling in the secretory rate. When 8 mmol/l 3-oxymethyl glucose was added to perifusion medium containing 3 mmol/l d-glucose, neither pO2 nor insulin release of the islets were changed. Temporal analysis of oscillations in pO2 and insulin release revealed that maximum respiration correlated to maximum or close to maximum insulin release.¶Conclusion/interpretation. The temporal relation between oscillations in pO2 and insulin release supports a role for metabolic oscillations in the generation of pulsatile insulin release. [Diabetologia (2000) 43: 1313–1318]

Renal Effects of CO2 and Iodinated Contrast Media in Patients Undergoing Renovascular Intervention: A Prospective, Randomized Study

PURPOSE CO2 gas has been proposed for use instead of iodinated contrast media in angiographic examinations in patients at risk of developing renal failure from contrast media. The influence of intraarterial injection of CO2 with small added amounts of ioxaglate (200 mgI/mL) or ioxaglate alone on renal function in patients with suspected renal artery stenosis was studied in a prospective, randomized study. MATERIALS AND METHODS One hundred twenty-three patients underwent renovascular intervention (n = 83) and/or renal angiography (n = 40) for suspected renal artery stenosis. Patients with a serum creatinine concentration less than 200 micromol/L (n = 82) were randomized prospectively to receive CO2 with small added amounts of ioxaglate (n = 37) or only ioxaglate (n = 45). Patients with serum creatinine levels greater than 200 micromol/L (n = 41) were not randomized and initially received CO2. Serum creatinine concentrations were measured within 1 day before and 1 day, 2 days, and 2-3 weeks after the procedure. RESULTS The amount of injected CO2 did not relate to an increase in serum creatinine level. In the randomized groups, and also when the whole patient sample was considered, the amount of injected iodine was significantly correlated (P = .011) with an increase in serum creatinine level and a decrease in estimated creatinine clearance after 2 days. Among the randomized patients, one in the CO2 group and three in the ioxaglate group had a more than 25% increase in serum creatinine level within the first 2 days after the intervention. CONCLUSION The risk of impairment of renal function is lower after injection of CO2 with small amounts of added ioxaglate compared with injection of a larger amount of ioxaglate alone. The larger the amount of administered iodinated contrast medium, the greater the risk of development of renal failure.

Use of a modified oxygen microelectrode and laser-Doppler flowmetry to monitor changes in oxygen tension and microcirculation in a flap

Flap failure is a clinical problem in free tissue transfer, and there is no reliable device for monitoring the tissue. Differentiating between an arterial occlusion and venous congestion is also a problem. A study was undertaken to monitor viability in a pedicled groin flap and to compare two different monitoring methods. The oxygen tension in the flap, measured with a modified Clark-type microelectrode (tip diameter = 3 to 8 &mgr;m; 90 percent response within 2.6 ± 0.5 seconds), was compared with changes in blood flow in the flap, measured with a laser-Doppler probe. In 11 Sprague-Dawley rats, the changes in oxygen tension and blood flow in the pedicled groin flap were studied after clamping and subsequent reperfusion of the artery or vein. After occlusion of the artery to the flap, oxygen tension decreased to a stable value (i.e., the recording level remained unchanged for 30 seconds), from 19.7 ± 1.8 to 0.3 ± 0.1 mmHg, after 193 ± 25 seconds; blood flow decreased to a stable value, from 117 ± 21 to 54 ± 18 perfusion units, after 26 ± 6 seconds. Clamping of the vein resulted in a decrease in oxygen tension, from 17.1 ± 1.8 to 1.4 ± 0.7 mmHg, after 416 ± 67 seconds, and blood flow decreased to a stable value, from 90 ± 14 to 35 ± 6 perfusion units, after 107 ± 27 seconds. The results of this study show that there is a difference in oxygen tension and blood flow responses between arterial and venous occlusion and that it may be possible with both methods to distinguish arterial from venous occlusion. However, although oxygen tension measurements are slightly slower in response than laser-Doppler measurements, the values are more reliable as a diagnostic tool for interpretation of a vessel occlusion.

The roles of NADPH-oxidase and nNOS for the increased oxidative stress and the oxygen consumption in the diabetic kidney.

Sustained hyperglycaemia induces increased renal oxygen consumption resulting in reduced oxygen availability in the diabetic kidney. We investigated the roles of the nicotinamide adenine dinucleotide phosphate (NADPH)‐oxidase and the neuronal nitric oxide synthase (nNOS) for the increased oxygen consumption in streptozotocin‐diabetic rats.