Superoxide production by neutrophils from diabetics and normal subjects in response to glucose and galactose

The effect of high temperature on kinetics of reactive species generation in patients with type 2 diabetes

The excessive amount of reactive species under chronic inflammation, which are accompanied by an increase body temperature, lead to diabetic complications. Phagocyte NADPH oxidase is the key enzyme in these processes. The role of high temperature in its regulation in diabetes is not clear. The aim was to investigate the effect of high temperature on NADPH-oxidase-dependent generation of reactive species in diabetic patients. Chemiluminescent method was applied to assess respiratory burst kinetics initiated by opsonized zymosan in blood or phorbol ester in isolated granulocytes. Analyzing ROC curves, the main predictors and changes in stages of activation of NADPH oxidase were determined. Phosphoisoforms of p47^phox and p67^phox were quantified by immunoblotting. Response to opsonized zymosan was lower in all subjects at 40 °C vs 37 °C, its kinetic parameters (except T_max) were higher in blood of patients vs controls. Response rate was the main significant predictor to distinguish groups of subjects at 40 °C indicating NADPH oxidase upregulation in diabetes. Ca²⁺-dependent generation of reactive species by cells increased in both groups at 40 °C vs 37 °C, kinetic parameters were higher in patients. Initial phospho-p47^phox level was higher in patient cells vs ones in controls. It was increased by ionomycin, phorbol ester, or 40 °C in control cells and unchanged in patient ones. Phospho-p67^phox level was unchangeable in intact cells of healthy donors and patients at both temperatures. Excessive amounts of reactive species in patient cells were the consequence of granulocyte priming due to p47^phox phosphorylation. Thus, high temperature decreased phagocytosis- and enhanced Ca²⁺-dependent generation of reactive species making the differences between controls and patients less pronounced. The effect of temperature on the generation of reactive species in blood granulocytes is associated with activity of NADPH oxidase that can be a prospective therapeutic target for pathologies accompanied by inflammation including type 2 diabetes.

A Bittersweet Response to Infection in Diabetes; Targeting Neutrophils to Modify Inflammation and Improve Host Immunity

Chronic and recurrent infections occur commonly in both type 1 and type 2 diabetes (T1D, T2D) and increase patient morbidity and mortality. Neutrophils are professional phagocytes of the innate immune system that are critical in pathogen handling. Neutrophil responses to infection are dysregulated in diabetes, predominantly mediated by persistent hyperglycaemia; the chief biochemical abnormality in T1D and T2D. Therapeutically enhancing host immunity in diabetes to improve infection resolution is an expanding area of research. Individuals with diabetes are also at an increased risk of severe coronavirus disease 2019 (COVID-19), highlighting the need for re-invigorated and urgent focus on this field. The aim of this review is to explore the breadth of previous literature investigating neutrophil function in both T1D and T2D, in order to understand the complex neutrophil phenotype present in this disease and also to focus on the development of new therapies to improve aberrant neutrophil function in diabetes. Existing literature illustrates a dual neutrophil dysfunction in diabetes. Key pathogen handling mechanisms of neutrophil recruitment, chemotaxis, phagocytosis and intracellular reactive oxygen species (ROS) production are decreased in diabetes, weakening the immune response to infection. However, pro-inflammatory neutrophil pathways, mainly neutrophil extracellular trap (NET) formation, extracellular ROS generation and pro-inflammatory cytokine generation, are significantly upregulated, causing damage to the host and perpetuating inflammation. Reducing these proinflammatory outputs therapeutically is emerging as a credible strategy to improve infection resolution in diabetes, and also more recently COVID-19. Future research needs to drive forward the exploration of novel treatments to improve infection resolution in T1D and T2D to improve patient morbidity and mortality.

Modified kinetics of generation of reactive species in peripheral blood of patients with type 2 diabetes

Level of reactive species in blood is an important pathogenic factor in diabetes mellitus leading to dysfunctions of vascular endothelial and smooth muscle cells and coagulation system abnormality. A massive release of reactive species (respiratory burst), catalyzed by NADPH oxidase in blood phagocytes, is not well understood in diabetes. The work aimed to study kinetics of response to microbial particles in blood to specify changes in regulatory mechanisms of generation of reactive species in patients with type 2 diabetes. Production of reactive species in blood and isolated granulocytes was measured by luminol-dependent chemiluminescence. Respiratory burst was initiated by serum opsonized zymosan in blood samples and phorbol ester in cell samples. Kinetic parameters were calculated from experimental kinetic curves of chemiluminescence intensity. ROC curve analysis and mathematical modeling were used to reveal the most significant predictors and clarify specific mechanisms of NADPH oxidase activation. It was shown that kinetic parameters of response to opsonized zymosan (lag-time, response rate, amplitude, production of reactive species) were higher in blood of patients than controls. Amplitude and response rate were the most statistically significant predictors for distinguishing patients and controls at high glucose. It indicated NADPH oxidase activation was the target of hyperglycemia. Mathematical modeling showed hyperglycemia increased stability of NADPH oxidase complex, decreased synchronization of its assembling and elevated neutrophil capacity to phagocytosis in patients. Weak or no dependence of response kinetics on ionomycin concentration was shown in patients indicating changed Ca²⁺-dependent mechanism of NADPH oxidase activation. Hyperglycemia in type 2 diabetes causes disturbances in mechanisms of NADPH oxidase activation associated with both phagocytosis and the state of intracellular signaling systems, including Ca²⁺-dependent. We suggest that NADPH oxidase in blood granulocytes can be a promising target for clinical intervention improving management of diabetic complications associated with inflammation.

The association of plasma glucose, BHBA, and NEFA with postpartum uterine diseases, fertility, and milk production of Holstein dairy cows

The objective of this study was to investigate the association between the metabolic indicators such as nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHBA), and glucose during the transition period and the development of uterine diseases. In total, 181 Holstein dairy cows were enrolled in the study. Plasma glucose, NEFA, and BHBA concentrations were measured at -50, -6, 3, 7, and 14 days relative to parturition. All cows enrolled in the study were evaluated for retained placenta (RP), metritis, and endometritis. Metritis and RP were diagnosed and treated by trained farm personnel. Clinical endometritis was evaluated by a veterinarian at 35 days in milk using a Metricheck device. We found plasma glucose concentration to be associated with the occurrence of metritis and clinical endometritis. Moreover, cows with an increased calving-to-conception interval (>150 days) presented higher plasma glucose concentrations than cows that became pregnant within the first 150 days, whereas BHBA and NEFA were not associated with the occurrence of any uterine disorder. Receiver operating characteristic (ROC) curves were used in an attempt to determine the cow-level critical thresholds for the occurrence of metritis, and endometritis. In addition, pairwise comparisons of area under the curve (AUC) of ROC curves for the critical thresholds for glucose, BHBA, and NEFA predicting the same uterine disease were performed. Glucose at 3 days in milk was the best predictor for metritis and endometritis diagnosis, with AUC values of 0.66 and 0.67, respectively. Multivariable logistic regressions were performed and showed that cows with higher levels of glucose at Day 3 were at 6.6 times higher odds of being diagnosed with metritis, and 3.5 times higher odds of developing clinical endometritis, compared with cows with lower glucose levels. Finally, a simple linear regression analysis demonstrated a negative correlation between daily milk yield in the first and second weeks of lactation and plasma glucose concentrations measured at Days 7 and 14, respectively. Concentrations of NEFA and BHBA were not found to be associated with milk production.

Highest core temperature during cardiopulmonary bypass and rate of mediastinitis

Temperature control during cardiopulmonary bypass (CPB) may be related to rates of bacterial infection. We assessed the relationship between highest core temperature during CPB and rates of mediastinitis in 6955 consecutive isolated coronary artery bypass graft (CABG) procedures in northern New England.

The overall rate of mediastinitis was 1.1%. The association between highest core temperature and mediastinitis was different for diabetics than for nondiabetics. A multivariate model showed that there was a significant interaction between diabetes and temperature in their association with mediastinitis ( p = 0.015). Diabetic patients showed higher rates of mediastinitis as highest core temperature increased, from 0.7% in the ≤37°C group to 3.3% in the ≥38°C group ( ptrend = 0.002). Adjusted rates were similar. Nondiabetic patients did not show this trend ( ptrend = 0.998).

Among diabetic patients, a peak core body temperature > 37.9°C during CPB is a significant risk factor for development of mediastinitis. Avoidance of higher temperatures during CPB may lower the risk of mediastinitis for diabetic patients undergoing CABG surgery.

Association between systemic oxidative stress and insulin resistance/sensitivity indices - the PREDIAS study

OBJECTIVE

Systemic oxidative stress has been causally related to insulin resistance and the subsequent development of type 2 diabetes mellitus (T2D). We investigated associations between circulating oxidative stress markers and different surrogate indexes of insulin sensitivity/resistance.

PATIENTS

Cross-sectional data were obtained from 1183 subjects with normal glucose tolerance (NGT), 280 subjects with impaired glucose tolerance (IGT) and 69 newly detected T2D individuals entering the PREDIAS (prevention of diabetes) study.

MEASUREMENTS

Following oral glucose tolerance test, five different insulin sensitivity/resistance indices were estimated: homoeostasis model of insulin resistance (HOMA-IR), quantitative insulin sensitivity check index (QUICKI), early phase insulin release (EPIR), insulin sensitivity index (ISI) and disposition index (DI). Additionally, circulating phagocyte generation of reactive oxygen species (ROS) and plasma total antioxidant capacity (TAC) was measured.

RESULTS

After adjustment for five covariates, HOMA-IR was significantly increased in IGT and T2D subjects when compared to NGT subjects (P = 0·000). QUICKI (P = 0·000), ISI (P = 0·000), EPIR (0·005/0·012) and DI (P = 0·000) were significantly attenuated in IGT and T2D. The prevalence of IGT and T2D individuals increased with increasing ROS generation and TAC tertiles. Increased systemic ROS generation was paralleled by increased HOMA-IR (P < 0·001, tertile 1/T1/vs tertile 3/T3/), decreased QUICKI (P < 0·001, T1 vs T3) and decreased ISI (P < 0·05, T1 vs T3). A similar tendency for indices was observed when comparing TAC tertiles: increase in HOMA-IR, decrease in QUICKI and ISI (P < 0·001, T1 vs T3 each). EPIR and DI did not differ significantly across ROS generation and TAC tertiles.

CONCLUSIONS

Systemic oxidative stress is associated with elevated insulin resistance index HOMA-IR, and decreased insulin sensitivity surrogates QUICKI and ISI.

Strong glucose dependence of electron current in human monocytes

Reactive oxygen species (ROS) production by human monocytes differs profoundly from that by neutrophils and eosinophils in its dependence on external media glucose. Activated granulocytes produce vast amounts of ROS, even in the absence of glucose. Human peripheral blood monocytes (PBM), in contrast, are suspected not to be able to produce any ROS if glucose is absent from the media. Here we compare ROS production by monocytes and neutrophils, measured electrophysiologically on a single-cell level. Perforated-patch-clamp measurements revealed that electron current appeared after stimulation of PBM with phorbol myristate acetate. Electron current reflects the translocation of electrons through the NADPH oxidase, the main source of ROS production. The electron current was nearly abolished by omitting glucose from the media. Furthermore, in preactivated glucose-deprived cells, electron current appeared immediately with the addition of glucose to the bath. To characterize glucose dependence of PBM further, NADPH oxidase activity was assessed as hydrogen peroxide (H(2)O(2)) production and was recorded fluorometrically. H(2)O(2) production exhibited similar glucose dependence as did electron current. We show fundamental differences in the glucose dependence of ROS in human monocytes compared with human neutrophils.

Oxidant release is dramatically increased by elevated glucose concentrations in neutrophils from pregnant women

OBJECTIVE

To evaluate the mechanism of oxidative stress at glucose levels accompanying diabetic pregnancy. Specifically, we hypothesize that elevated glucose overwhelms hexose monophosphate shunt (HMS) down-regulation observed during pregnancy.

METHODS

Peripheral blood cells from normal healthy pregnant women were exposed to heightened glucose levels to provide an in vitro model of the effects of diabetic pregnancy. Changes in NAD(P)H, reactive oxygen species (ROS) and nitric oxide (NO) production were evaluated in single cells.

RESULTS

Altered metabolic dynamics, as judged by NAD(P)H autofluorescence of neutrophils from both pregnant and non-pregnant women, were observed during incubation with 14 mM glucose, a pathophysiologic level. In parallel, increased production of ROS and NO was observed. The ROS and NO levels attained in cells from pregnant women were greater than those observed in cells from non-pregnant women. Inhibitors of the HMS and NAD(P)H oxidase blocked these effects. These metabolic and oxidant changes required approximately one minute, suggesting that transient glucose spikes during pregnancy could trigger this response.

CONCLUSIONS

Elevated glucose levels enhance HMS activity and oxidant production in cells from pregnant women. This mechanism may be generally applicable in understanding the role of diabetes in materno-fetal health.

Increased polymorphonuclear leukocyte respiratory burst function in type 2 diabetes

The predisposition to infection and chronic inflammation in diabetes may in part be related to the effects of hyperglycemia or other metabolic abnormality on polymorphonuclear leukocytes (PMN). We evaluated oxidative respiratory burst activity (superoxide production) in non-stimulated and stimulated PMN from 70 stable type 2 Hispanic diabetic patients, as compared to 70 healthy Hispanic individuals without diabetes. The influences of protein kinase C (PKC) inhibitors and certain antibiotics on superoxide production were examined. Both resting and stimulated (PMA, zymosan) PMN from diabetic individuals produced more superoxide than PMN from controls. Inhibitors of PKC, a possible mediator of the augmented respiratory burst activity, decreased superoxide production in all (resting and stimulated) diabetic and control PMN. Azithromycin, which is markedly concentrated by PMN, profoundly inhibited superoxide generation in all groups of diabetic and control cells. PMN from Hispanic diabetic patients produced greater quantities of superoxide than non-diabetic controls. This increased oxidative respiratory burst activity may predispose to infection and chronic inflammation in diabetes. PKC inhibitors and azithromycin inhibited this respiratory burst response. The possible role of PKC (especially PKC beta) as the mediator of this augmented respiratory burst response requires further evaluation, and may lead to therapeutic studies with appropriate inhibitors.

Elevated glucose concentrations promote receptor-independent activation of adherent human neutrophils: an experimental and computational approach

Neutrophil activation plays integral roles in host tissue damage and resistance to infectious diseases. As glucose uptake and NADPH availability are required for reactive oxygen metabolite production by neutrophils, we tested the hypothesis that pathological glucose levels (>or=12 mM) are sufficient to activate metabolism and reactive oxygen metabolite production in normal adherent neutrophils. We demonstrate that elevated glucose concentrations increase the neutrophil's metabolic oscillation frequency and hexose monophosphate shunt activity. In parallel, substantially increased rates of NO and superoxide formation were observed. However, these changes were not observed for sorbitol, a nonmetabolizable carbohydrate. Glucose transport appears to be important in this process as phloretin interferes with the glucose-specific receptor-independent activation of neutrophils. However, LY83583, an activator of glucose flux, promoted these changes at 1 mM glucose. The data suggest that at pathophysiologic concentrations, glucose uptake by mass action is sufficient to activate neutrophils, thus circumventing the normal receptor transduction mechanism. To enable us to mechanistically understand these dynamic metabolic changes, mathematical simulations were performed. A model for glycolysis in neutrophils was created. The results indicated that the frequency change in NAD(P)H oscillations can result from the activation of the hexose monophosphate shunt, which competes with glycolysis for glucose-6-phosphate. Experimental confirmation of these simulations was performed by measuring the effect of glucose concentrations on flavoprotein autofluorescence, an indicator of the rate of mitochondrial electron transport. Moreover, after prolonged exposure to elevated glucose levels, neutrophils return to a "nonactivated" phenotype and are refractile to immunologic stimulation. Our findings suggest that pathologic glucose levels promote the transient activation of neutrophils followed by the suppression of cell activity, which may contribute to nonspecific tissue damage and increased susceptibility to infections, respectively.

Effect of acute hyperglycemia and/or hyperinsulinemia on polymorphonuclear functions in healthy subjects

Abnormal immune functions of polymorphonuclear (PMN) cells occur in a variety of pathophysiological conditions. There exists a close link between glucose metabolism and PMN functions. The aim of this study was to assess the effect of short-term hyperglycemia and/or hyperinsulinemia on phagocytosis and respiratory burst of PMN cells in healthy subjects in vivo. The study was performed on 12 healthy subjects (mean age, 26.9+/-1.6 years; body mass index, 24.4+/-0.84 kg/m(2)). Acute hyperglycemia and/or hyperinsulinemia was induced by three 4-hour-long clamp studies-hyperglycemic hyperinsulinemic clamp (HHC), hyperinsulinemic euglycemic clamp (HEC), and isolated hyperglycemic clamp with insulin secretion blockade (HGC). Polymorphonuclear cell phagocytosis and PMN cell respiratory burst (mean percentage and mean fluorescent intensity of phagocyting/activated PMN cells, phagocytic, and respiratory burst indexes) were evaluated by flow cytometry under basal and stimulated conditions. Results detected during clamp studies were compared with those found during a control study with saline infusion. Significant reductions in the mean percentage of phagocyting cells measured under basal conditions after the HHC (6.7%+/-1.3% vs 12.1%+/-4.3%; P<.05) and HGC (4.5% +/-1.8% vs 9.9%+/-2.1%; P<.05) were found in comparison with the pre-clamp study period; however, these results did not differ significantly from those detected during the control clamp (CC) study. Significantly higher phagocytic (115.1+/-65 vs 35.8 +/-18.6; P<.05) and respiratory burst indexes (16.5+/-3 vs 10.1+/-1.4; P<.05) measured under basal conditions were found after HEC in comparison with the pre-clamp data. However, these data did not differ significantly from those found after the CC study. No significant differences in other parameters of detected PMN cell immune functions were found after HHC, HEC, and HGC. In conclusion, immune functions of PMN cells were not significantly influenced by short-lasting hyperglycemia and/or hyperinsulinemia induced in vivo by clamp techniques in healthy subjects compared to changes induced by the CC study. Further studies on the short-term effect of glucose metabolism on PMN functions in diabetic patients should be considered necessary.

The roles of insulin and hyperglycemia in sepsis pathogenesis

Hyperglycemia is a risk marker of morbidity and mortality in acute critical illness, and insulin therapy seems to be beneficial in this patient group. Whether this is true for a population of sepsis patients, as such, has not been investigated in clinical trials, but evidence from in vitro studies and experimental sepsis suggests that this may be the case. The endocrinology of septic patients is characterized by a shift in the balance between insulin and its counter-regulatory hormones favoring the latter. This leads to prominent metabolic derangements composed of high release and low use of glucose, amino acids, and free fatty acids (FFA), resulting in increased blood levels of these substrates. Circulating, proinflammatory mediators further enhance this state of global catabolism. Increased levels of glucose and FFA have distinct effects on inflammatory signaling leading to additional release of proinflammatory mediators and endothelial and neutrophil dysfunction. Insulin has the inherent capability to counteract the metabolic changes observed in septic patients. Concomitantly, insulin therapy may act as a modulator of inflammatory pathways inhibiting the unspecific, inflammatory activation caused by metabolic substrates. Given these properties, insulin could conceivably be serving a dual purpose for the benefit of septic patients.

Determinants of Candidemia and Candidemia-Related Death in Cardiothoracic ICU Patients

STUDY OBJECTIVES

To develop and prospectively validate models of independent predictors of candidemia and candidemia-related death in cardiothoracic ICU (CICU) patients.

DESIGN

(1) An initial, prospective, one-center, case-control, independent predictor-model determining study; and (2) a prospective, two-center, model-validation study.

SETTING

The initial study was performed at the 14-bed CICU of the Onassis Cardiac Surgery Center, Athens, Greece; the model-validation study was performed at the Onassis Cardiac Surgery Center CICU and the 12-bed CICU of Henry Dunant General Hospital, Athens, Greece.

PATIENTS

In the initial study, 4,312 patients admitted to the Onassis Center CICU between March 1997 and October 1999 were considered for enrollment; 30 candidemic and 120 control patients (case/control ratio, 1/4) matched according to potential confounders were ultimately enrolled. In the model-validation study, 2,087 patients admitted to the Onassis and Henry Dunant CICUs between November 1999 and May 2002 were prospectively enrolled.

MEASUREMENTS AND RESULTS

Models of predictors of candidemia and associated death were constructed with stepwise logistic regression and subsequently validated. Independent candidemia predictors were ongoing invasive mechanical ventilation (IMV) > OR =10 days, hospital-acquired bacterial infection and/or bacteremia, cardiopulmonary bypass duration > 120 min, and diabetes mellitus. Model performance was as follows: sensitivity, 53.3%/57.9%; specificity, 100%/100%; positive predictive value (PPV), 100%/100%; negative predictive value (NPV), 88.9%/99.6%; and accuracy, 90.1%/99.6% (initial/model-validation study values, respectively). IMV > or =10 days and hospital-acquired bacterial infection/bacteremia were the two strongest candidemia predictors. APACHE (acute physiology and chronic health evaluation) II score > or =30 at candidemia onset independently predicted candidemia-related death with 80.0%/85.7% sensitivity, 80%/75% specificity, 66.7%/66.7% PPV, 88.9%/88.9% NPV, and 80.0%/78.9% accuracy (initial/model-validation study values, respectively).

CONCLUSIONS

We provided a set of easily determinable independent predictors of the occurrence of candidemia in CICU patients. Our results provide a rationale for implementing preventive measures in the form of independent predictor control, and initiating antifungal prophylaxis in high-risk CICU patients.

Impairment of type III group B Streptococcus-stimulated superoxide production and opsonophagocytosis by neutrophils in diabetes

The effect of hyperglycemia upon susceptibility to bacterial infection in diabetes mellitus is incompletely elucidated. The present experiments assessed the effect of hyperglycemia upon neutrophil-mediated phagocytosis of type III group B Streptococcus (GBS). Type III GBS was chosen for study because the incidence of invasive GBS disease is substantially increased in type 2 diabetic compared with nondiabetic subjects. The hypothesis tested was that severe hyperglycemia would alter neutrophil metabolism by diverting NADPH from superoxide production into the aldose reductase-dependent polyol pathway that converts glucose into sorbitol and thus would impair opsonophagocytosis (OP) of type III GBS. Neutrophils from 10 adults with type 2 diabetes had no intrinsic phagocytic defect under baseline glycemic conditions. After equilibration in 60 or 120 mM glucose or in 60 mM choline chloride, OP activity was reduced significantly (P < or = 0.03). Neutrophil superoxide production correlated with glucose concentration and also was significantly reduced during hyperglycemia (P < 0.05). Addition of III GBS capsular polysaccharide-specific IgG in a sufficient concentration supported efficient OP, even during hyperglycemia. Alrestatin, an aldose reductase inhibitor, increased superoxide production and significantly improved OP of type III GBS (P = 0.03). Thus, diversion of NADPH into the polyol pathway is one mechanism by which OP of GBS III is impaired during hyperglycemia, and this effect is mitigated when levels of capsular polysaccharide-specific IgG are sufficient.

Longer-term diabetic patients have a more frequent incidence of nosocomial infections after elective gastrectomy

Diabetes mellitus (DM) is one of the risk factors for the development of postoperative nosocomial infections in surgical patients. We conducted this retrospective study to elucidate the perioperative risk factors for postoperative nosocomial infections in diabetic patients undergoing elective gastrectomy. Chart review was performed on diabetic and nondiabetic patients undergoing elective gastrectomy for gastric malignancy from January 1992 through April 1999. Fourteen of the 83 diabetic patients, and 23 of the 284 nondiabetic patients developed postoperative nosocomial infections. Statistical comparisons of multiple variables were made between patients with and without postoperative nosocomial infections. In diabetic patients, univariate analysis showed that longer-term DM (especially longer than 10 yr) was associated with a significantly increased risk for postoperative nosocomial infections. Multiple logistic regression analysis showed that DM lasting longer than 10 yr was an independent risk factor for postoperative nosocomial infections (odds ratio, 6.8; 95% confidence interval, 1.7 to 27.1). In nondiabetic patients, similar analysis showed that age was an independent risk factor for postoperative nosocomial infections. We conclude that patients with longer-term DM had a significantly greater incidence of postoperative nosocomial infections after elective gastrectomy.

IMPLICATIONS

Postoperative nosocomial infection is one of the major problems in diabetic patients. This study demonstrated that postoperative nosocomial infections were more common in patients undergoing elective gastrectomy if they had diabetes mellitus longer than 10 yr.

Different effects of glucose on extracellular and intracellular respiratory burst response in normal human neutrophils activated with the soluble agonist fMet-Leu-Phe

AIMS

The study evaluated the effects of glucose concentration on the extracellular and intracellular activation of the respiratory burst in fMet-Leu-Phe-stimulated normal human neutrophils.

METHODS

Specific extracellular respiratory burst activity was measured as superoxide dismutase (SOD)-inhibitable cytochrome c reduction. Intracellular respiratory burst activity was studied using luminol-enhanced chemiluminescence in the presence of SOD and catalase, to quench extracellular chemiluminescence activity. Myeloperoxidase (MPO) release from activated neutrophils was studied by using the guaiacol technique.

RESULTS

The extracellular respiratory burst following activation with 1 microM fMet-Leu-Phe was significantly reduced at 15 and 25 mM D-glucose (9.5 +/- 1.0 and 8.5 +/- 0.8 nmol/10(6) cells and 10 min; P < 0.01 and P < 0.001, respectively) as compared with that at 5 mM glucose (10.3 +/- 1.0 nmol/10(6) cells and 10 min). When specifically studying the intracellular respiratory burst, no difference was found between the responses at 5, 15 or 25 mM glucose. Increasing glucose concentrations also reduced the secretion of MPO from fMet-Leu-Phe-activated neutrophils.

CONCLUSIONS

Elevated glucose concentrations inhibit the generation of extracellularly released reactive oxygen metabolites but have no effects on the intracellular respiratory burst in fMet-Leu-Phe-stimulated normal human neutrophils.

Insulin infusion improves neutrophil function in diabetic cardiac surgery patients

Diabetic patients are at increased risk of wound infection after major surgery, but the effect of perioperative glucose control on postoperative wound infection rates after surgery is uncertain. We tested the effect of an insulin infusion on perioperative neutrophil function in diabetic patients scheduled for coronary artery bypass surgery. Participants (n = 26) were randomly allocated to receive either aggressive insulin therapy (AIT) or standard insulin therapy (SIT) during surgery. Blood was drawn for neutrophil testing before surgery, 1 h after the completion of cardiopulmonary bypass, and on the first postoperative day. Neutrophil phagocytic activity decreased to 75% of baseline activity in the AIT group and to 47% of baseline activity in the SIT group (P < 0.05 between groups). No important differences in neutrophil antibody-dependent cell cytotoxicity were found. This study documents a potentially beneficial effect of continuous insulin therapy in diabetic patients who require major surgery.

IMPLICATIONS

A continuous insulin infusion and glucose control during surgery improves white cell function in diabetic patients and may increase resistance to infection after surgery.

Effects of the superoxide dismutase-mimic compound TEMPOL on oxidant stress-mediated endothelial dysfunction

The aim of this study was to investigate the effects of oxidant stress on endothelium-dependent and endothelium-independent arterial relaxation. For this, oxidant stress was generated by preincubation of rat aortic rings (RARs) in either 25 mM glucose (mimicking hyperglycemic stress) or 0.5 mM pyrogallol (a superoxide generator) and the effects of the superoxide dismutase (SOD)-mimetic compound 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy free radical (TEMPOL) on the vasorelaxant and cGMP-producing effects of acetylcholine (ACh) and glyceryl trinitrate (GTN) in control RARs and RARs exposed to oxidant stress were examined. Pyrogallol, and to a lesser extent high glucose concentration, enhanced the contractile response of RARs to phenylephrine and markedly inhibited the vasorelaxant response to ACh. Although they existed, the inhibitory effects of high glucose and pyrogallol on the vasorelaxant response to GTN were less profound, especially with pyrogallol. Moreover, both pyrogallol and high glucose concentration inhibited the basal and the ACh-induced vascular cyclic guanosine monophosphate (cGMP) production. Treatment with TEMPOL (1-5 mM) slightly increased the ACh and GTN-induced cGMP levels in control RARs but had a significant effect in high glucose and pyrogallol-pretreated RARs. Additionally, concomitant treatment of RARs with TEMPOL (5 mM) abolished the difference in the relaxation response between control RARs and RARs exposed to either pyrogallol or high glucose concentration. These results further support the theory that reactive oxygen species (ROS), especially superoxide, play a key role in mediation of endothelial dysfunction accompanying diabetes, probably through their effects on the ability of the endothelium to synthesize, release or respond to endogenous nitric oxide (NO) or NO donated by nitrovasodilators.