Alterations of the respiratory burst of polymorphonuclear leukocytes from diabetic children. A chemiluminescence study

Vitreous levels of vascular cell adhesion molecule and vascular endothelial growth factor in patients with proliferative diabetic retinopathy: a case-control study

OBJECTIVE

To evaluate the intravitreous concentration of vascular cell adhesion molecule (VCAM)-1 in diabetic patients with proliferative diabetic retinopathy (PDR) and the relationship of VCAM-1 with vascular endothelial growth factor (VEGF).

RESEARCH DESIGN AND METHODS

Serum and vitreous fluid samples were obtained simultaneously at the onset of vitrectomy from 20 diabetic patients with PDR and 20 nondiabetic control subjects with nonproliferative ocular disease. Both groups were matched by serum levels of VCGM-1 and VEGF. VCAM-1 and VEGF were determined by enzyme-linked immunosorbent assay. Statistics were determined using the Mann-Whitney U test and Spearman's rank correlation test.

RESULTS

The intravitreous concentration of VCAM-1 was signifcantly elevated in diabetic patients with PDR compared with control subjects (26 ng/ml [19-118] vs. 22 ng/ml [20-47], P < 0.05). A direct correlation between VCAM-1 and total vitreous proteins was detected in diabetic patients (r = 0.64, P = 0.003), but not in control subjects. After adjusting for total intravitreous proteins, VCAM-1 was significantly lower in diabetic patients with PDR than in control subjects (8.2 ng/ml [4-31.4] vs. 43.1 ng/ml [9.7-100], P < 0.001). Intravitreous VEGF concentrations were higher in patients with PDR than in control subjects in absolute terms (1.34 ng/ml [0.16-6.22] vs. 0.009 ng/ml [0.009-0.044], P < 0.0001) and after correcting for total vitreal proteins (0.33 ng/ml [0.01-2.3] vs. 0.013 ng/ml [0.003-0.035], P = 0.0001). Finally, the vitreous ratio of VCAM-1 to proteins correlated with the vitreous ratio of VEGF to proteins in both diabetic patients (r = 0.74, P = 0.001) and control subjects (r = 0.84, P = 0.005).

CONCLUSIONS

The low proportion of VCAM-1 in relation to total vitreal proteins observed in diabetic patients with PDR suggests that VCAM-1 is quenched by diabetic retina. In addition, the direct correlation detected between VCAM-1 and VEGF suggests that cellular adhesion and neovascularization may be linked processes.

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.

Plasma membrane polarity of polymorphonuclear leucocytes from children with primary ciliary dyskinesia

BACKGROUND

Polymorphonuclear leucocytes (PMN) from subjects with primary ciliary dyskinesia (PCD) can have abnormal locomotory systems. The locomotory activity of PMN is the result of biochemical events mediated by the plasma membrane. In this study we investigated plasma membrane polarity of PMN from children with PCD.

DESIGN

Membrane polarity was studied in 11 children with PCD and in healthy controls by measuring the steady-state fluorescence excitation and emission spectra of 2-dimethylamino[6-lauroyl]naphthalene (Laurdan), which is known to be incorporated at the hydrophobic-hydrophilic interface of the bilayer, displaying spectral sensitivity to the polarity of its surroundings. Laurdan shows a marked steady-state emission red shift in polar solvents, with respect to nonpolar solvents. Moreover, the effect of the microtubule disassembling agent colchicine on PMN membrane polarity was evaluated.

RESULT

Our results show a red shift of the fluorescence excitation and emission spectra of Laurdan in PMN from the PCD group with respect to the control group. These data indicate an increase in membrane polarity of PMN from the PCD group. Treatment of PMN with colchicine induced a red shift in the Laurdan excitation and emission spectra with the same trend observed in PMN from the PCD group.

CONCLUSION

PMN from children with PCD are characterized by an increased plasma membrane polarity. These changes could be the basis of the modifications in the locomotory activities of PMN. The observed alterations may be attributed to abnormalities in the cytoskeleton.

Plasma membrane fluidity and polarity of polymorphonuclear leukocytes from children with type I diabetes mellitus

Polymorphonuclear leukocytes (PMN) from diabetic subjects have been found to be abnormal in various functional activities. These activities are mediated by the plasma membrane. This study was designed to evaluate plasma membrane fluidity and polarity in children with type I diabetes mellitus using fluorescence spectroscopy. PMN membrane fluidity and polarity were assessed in a group of 32 diabetic children. Membrane fluidity was investigated by measuring steady-state fluorescence anisotropy and fluorescence decay of 1-[4-trimethylammonium-phenyl]-6-phenyl- 1,3,5-hexatriene (TMA-DPH), whereas membrane polarity was studied by measuring the steady-state fluorescence emission and excitation spectra of 2-dimethylamino[6-lauroyl]-naphthalene (Laurdan). TMA-DPH and Laurdan are known to be incorporated at the hydrophobic-hydrophilic interface of the bilayer. Our data show a significant increase in steady-state fluorescence anisotropy in diabetic PMN that reflects a decrease in membrane fluidity, and a decrease in TMA-DPH lifetime distribution indicating a decrease in membrane heterogeneity. Laurdan shows a blue shift of the fluorescence emission and a red shift of the excitation spectra in diabetic PMN with respect to the control group, indicating a decrease in membrane polarity. The results demonstrate a decrease in the phospholipid order at the membrane surface and a decrease in membrane polarity in diabetic PMN. These alterations in the physico-chemical properties of the plasma membrane could be the basis of the modifications in functional activities of PMN. The changes in the plasma membrane of PMN could be the result of metabolic and chemical modification associated with type I diabetes.

Inhibition of phospholipase D and superoxide generation by glucose in diabetic neutrophils

Diabetics are prone to infection, in part, due to neutrophil dysfunction and impaired superoxide generation. The mechanism of impaired superoxide generation in diabetes remains unknown. We report herein that neutrophils from poorly controlled diabetics have impaired ability to generate superoxide in response to N-formyl-Met-Leu-Phe (FMLP) but not to 4 beta-phorbol 12-myristate 13-acetate (PMA). Phosphatidic acid, a phospholipase D (PLD) -mediated product of membrane phosphatidylcholine is decreased in response to FMLP. The impaired superoxide generation and activation of phospholipase D are readily reversible once the diabetic neutrophils are incubated in normal glucose concentration. These data show that decreased superoxide generation by neutrophils in insulin-dependent diabetics is, in part, due to impaired activation of phospholipase D and is solely due to high glucose concentrations.

Production of superoxide anion by polymorphonuclear leukocytes from diabetic patients with or without diabetic retinopathy

Oxygen free radicals have been implicated in the pathogenesis of diabetic microangiopathy. The production of superoxide anion (O2-.) by polymorphonuclear leukocytes (PMNs) from 45 insulin-dependent diabetes mellitus patients in the resting state and in response to a soluble stimulus (phorbol myristate acetate) was measured spectrophotometrically and compared with that of 15 age and sex matched controls. The resting superoxide anion production by PMNs from diabetic patients was significantly higher than that of controls (2.17 +/- 1.32 and 1.35 +/- 0.6 nmol/10(5) cells/60 min respectively; p = 0.037). In contrast, PMNs from diabetic patients released significantly lower levels of superoxide anion compared to controls in response to phorbol myristate acetate stimulation (2.33 +/- 2.04 and 3.55 +/- 0.98 nmol/10(5) cells/60 min respectively; p = 0.044). The stimulated superoxide anion production was significantly higher in diabetic patients with retinopathy compared to diabetic patients without retinopathy (2.7 +/- 2.08 and 1.3 +/- 1.6 nmol/10(5) cells/60 min respectively; p = 0.02). Furthermore, stimulated PMNs from diabetic patients with proliferative retinopathy generated superoxide anion at significantly higher rates than did those from diabetics with nonproliferative retinopathy or without retinopathy (3.8 +/- 1.5, 2.08 +/- 2.1 and 1.3 +/- 1.6 nmol/10(5) cells/60 min respectively; p = 0.005). These results suggest that reactive oxygen species produced by PMNs may play a role in the progression of diabetic retinopathy.

Serum factor from diabetic patients with or without retinopathy stimulates superoxide anion production by normal polymorphonuclear leukocytes

Oxygen free radicals (OFRs) have been implicated in the pathogenesis of diabetic microangiopathy. The effects of serum from insulin-dependent diabetes mellitus patients with or without retinopathy on the production of superoxide anion by normal polymorphonuclear leukocytes (PMNs) were measured spectrophotometrically and compared with that of age matched controls. Superoxide anion production by PMNs incubated with serum from retinopathy-free patients or patients with retinopathy was significantly higher than that of controls (P=0.0002 and 0.0001, respectively). Furthermore, superoxide anion production by PMNs incubated with serum from patients with retinopathy was significantly higher than retinopathy-free patients (P=0.02). These observations suggest that a diabetic serum factor provoked a significant generation of superoxide anion in normal PMNs, a phenomenon found parallel to the presence of retinopathy, indicating that OFRs may play a role in the progression of diabetic retinopathy. The nature of this serum factor remains to be clarified.

Polymorphonuclear leukocyte-generated oxygen metabolites decrease beat frequency of human respiratory cilia

We investigated the effect of polymorphonuclear leukocyte (PMN)-generated oxygen metabolites on the ciliary beat frequency. PMNs were incubated with human respiratory cilia obtained by nasal brushing. The oxidative metabolism was stimulated by opsonized zymosan, and ciliary beat frequency was evaluated before and after activation of PMNs. Ciliary beat frequency was studied using video microscopy. Our results demonstrate a significant decrease in ciliary beat frequency after activation of PMNs. This effect was reduced by catalase. These data suggest that the PMN-generated oxygen metabolites, particularly H2O2, decrease beat frequency of human respiratory cilia.

Vascular permeability in diabetics and implications for therapy

Several factors contribute to increased vascular permeability in diabetes mellitus, namely hyperglycaemia leading to increased production of diacylglycerol and thence protein kinase C, non-enzymatic glucosylation generating free radicals and lipid peroxides, sorbitol formation, loss of endothelial cell surface heparan sulphates, and the action of arachidonate derivatives that affect endothelial cell contractility. In view of the importance of oxidative damage, serious consideration must be given to therapeutic regimens that utilise vitamin E or ascorbic acid or D-myoinositol. Probucol is an available antioxidant whose properties have received insufficient attention. The oleate of monounsaturated oil diets is likewise anti-oxidant. Furthermore there is a possibility of replacing lost surface heparan sulphates.

Effect of nedocromil sodium on polymorphonuclear leukocyte plasma membrane

The effect of nedocromil sodium on the plasma membrane fluidity of polymorphonuclear leukocytes (PMNs) was investigated by measuring steady-state fluorescence anisotropy of 1-[4-trimethylammonium-phenyl]-6-phenyl- 1,3,5-hexatriene (TMA-DPH) incorporated in the membrane. Our results show that nedocromil sodium 300 muM significantly decreased membrane fluidity of PMNs. The decrease in membrane fluidity of PMNs induced by fMLP was abolished in the presence of nedocromil sodium. These data suggest that nedocromil sodium interferes with the plasma membranes of PMNs and modulates their activities.

Impairment of the oxygen-dependent microbicidal mechanisms of polymorphonuclear neutrophils in patients with type 2 diabetes is not associated with increased susceptibility to infection

Phagocytosis, bactericidal capacity and some selected parameters of oxygen-dependent bactericidal mechanisms were evaluated in 20 patients with type 2 diabetes being in similar (intermediate) state of metabolic control and in 15 healthy individuals. Polymorphonuclear neutrophils (PMNs) from diabetics showed normal ability to phagocytose staphylococci, a decreased Intracellular bacteria killing, the impaired stimulated superoxide anion (O2-) and hydrogen peroxide (H2O2) production and the low intracellular myeloperoxidase activity. The obtained data seem to indicate that the decreased bacterial killing by PMNs isolated from diabetics are partly at least related to an impairment of the oxygen-dependent bactericidal mechanisms. Since none of the diabetic patients suffered from recurrent infection the clinical significance of our finding is still uncertain.

Use of Laurdan fluorescence in studying plasma membrane organization of polymorphonuclear leukocytes during the respiratory burst

The changes in plasma membrane polarity of polymorphonuclear leukocytes (PMN) during the activation of the respiratory burst were investigated by measuring the steady-state fluorescence emission spectra of 2-dimethylamino(6-lauroyl) naphthalene (Laurdan), which is known to be incorporated at the hydrophobic-hydrophilic interface of the bilayer, displaying spectral sensitivity to the polarity of its surroundings. Laurdan shows a marked steady-state emission blue shift in nonpolar solvents, with respect to polar solvents. Our results show a blue shift of the fluorescence emission spectra of Laurdan during activation of PMN with phorbol myristate acetate or N-formyl-methionyl-leucyl-phenylalanine. These results suggest that the activation of the respiratory burst of PMN is accompanied by a decrease in polarity in the hydrophobic-hydrophilic interface of the plasma membrane.

Oxygen radical production is increased in macrophages from diabetes prone BB rats

Macrophages from autoimmune diabetes prone BB rats were found to produce radical oxygen intermediates (ROI) at an enhanced rate when compared to diabetes resistant BB or normal Wistar rats. The release of ROI was determined by chemiluminescence using in parallel luminol and lucigenin as detector molecules. In diabetes prone BB rats the spontaneous release of ROI was upregulated in macrophages from different compartments, i.e. peritoneum and spleen. Also, maximal output of ROI after activation of macrophages either in vivo by injection of Corynebacterium parvum or in vitro by LPS and IFN was highest for cells from diabetes prone BB rats. This macrophage abnormality was seen in animals prior to recognizable islet inflammation and also was present at the level of macrophages grown in vitro from precursor cells of diabetes prone BB rats. Hypersecretion of oxygen radicals may contribute to Beta cell loss and diabetes development in BB rats.

Photon emission of phagocytes in relation to stress and disease

Phagocytes, the first-line cells of the body's defence mechanisms against invading pathogens, kill microorganisms by means of lysosomal degradative enzymes and highly toxic reactive oxygen intermediates. The reactive oxygen compounds are produced, in a process called the 'respiratory burst', by the NADPH oxidase complex in plasma membranes, and by myeloperoxidase in phagolysosomes after degranulation. These processes generate electronically excited states which, on relaxation, emit photons, giving rise to phagocyte chemiluminescence (CL). This paper describes the conditions for the measurement of CL, and reviews the activity of phagocytes from individuals undergoing stress or disease. The capability of phagocytes to emit photons reflects remarkably well the pathophysiological state of the host. In many cases even the magnitude of the stress, the presence of a pathogen in the body, or the activity of the disease can be estimated. Physiological changes, e.g. in the reproductive cycle, can also be predicted.

Alterations in membrane fluidity of diabetic polymorphonuclear leukocytes

Plasma membrane fluidity of polymorphonuclear leukocytes was investigated in 28 patients with insulin dependent diabetes mellitus and 30 healthy controls. Membrane fluidity was measured by steady-state fluorescence anisotropy of 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) incorporated into the plasma membrane. The fluorescence anisotropy values in resting (unstimulated) polymorphonuclear leukocytes from diabetic subjects were significantly higher than those of controls (0.318 +/- 0.003 vs 0.287 +/- 0.003, P less than 0.001). The addition of the respiratory burst stimulus phorbol myristate acetate induced a stable increase in fluorescence anisotropy values in both groups. Fluorescence anisotropy values of stimulated polymorphonuclear leukocytes from the diabetic and control groups were not significantly different (P greater than 0.05). These data demonstrate a decrease in plasma membrane fluidity of resting polymorphonuclear leukocytes obtained from diabetic subjects. This finding could be in part explained by an increase in their basal respiratory burst activity.

Effect of oral administration of bacterial extracts on the bactericidal capacity of polymorphonuclear leucocytes in children with recurrent respiratory infections

The effect of orally administered bacterial extracts given intermittently over 16 weeks on the bactericidal capacity of polymorphonuclear leucocytes (PMNs) in children with recurrent respiratory infections was investigated using a luminol-amplified chemiluminescence assay. Chemiluminescence of PMNs stimulated with zymosan or N-formyl-methionyl-leucyl-phenylalanine (fMLP) before and after treatment with bacterial extracts or intramuscular benzanthine penicillin was evaluated. Chemiluminescence induced by opsonized zymosan increased significantly (P less than 0.05) after treatment with bacterial extracts, whereas no significant changes were observed in the fMLP-stimulated PMNs. Long-acting penicillin treatment did not significantly affect zymosan- or fMLP-stimulated chemiluminescence. The data suggest that orally administered bacterial extracts can increase the opsonic capacity of serum and thus the bactericidal capacity of PMNs in subjects with recurrent respiratory infections.

Changes of fluorescence anisotropy in plasma membrane of human polymorphonuclear leukocytes during the respiratory burst phenomenon

Steady state fluorescence anisotropy (rs) of TMA-DPH was measured to study the effect of respiratory burst activation with PMA, FMLP, and PAF on the physico-chemical structure of PMNs plasma membrane. Our results show a significant increase in rs during the respiratory burst activation. In the presence of NADPH-oxidase inhibitor DPI, only PAF induces changes in rs values. This suggests a non-specific effect of PAF on plasma membrane. Azide, which induces a supranormal release of H2O2, fails to increase the basal rs value after activation. Moreover, the catalase does not abolish the increase in rs induced upon activation. This rules out the possibility that changes of rs during the respiratory burst activation are attributed mainly to H2O2 release. We conclude that multiple processes accompanying the respiratory burst activation are responsible for the changes in the physico-chemical properties of PMNs plasma membrane.