Reduced ability of neutrophils to produce active oxygen species in streptozotocin-induced diabetic rats

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.

Polymorphonuclear neutrophil dysfunctions in streptozotocin-induced type 1 diabetic rats

Since conflicting results have been reported on non-specific immune response in type 1 diabetes, this study evaluates polymorphonuclear neutrophil (PMN) functions in the infection free Long Evan diabetic rats (type 1) by using tests that include: polarization assay, phagocytosis of baker\'s yeasts (Saccharomyces cerevisiae) and nitroblue tetrazolium (NBT) dye reduction. Polarization assay showed that neutrophils from diabetic rats were significantly activated at the basal level compared to those from the controls (p < 0.001). After PMN activation with N-formylmethionyl-leucyl-phenylalanine (FMLP), control neutrophils were found to be more polarized than those of the diabetic neutrophils and the highest proportions of polarization were found to be 67 % and 57 % at 10(-7) M FMLP, respectively. In the resting state, neutrophils from the diabetic rats reduced significantly more NBT dye than that of the controls (p < 0.001). The percentages of phagocytosis of opsonized yeast cells by the neutrophils from control and diabetic rats were 87 % and 61 %, respectively and the difference was statistically significant (p < 0.001). Evaluation of the phagocytic efficiency of PMNs revealed that control neutrophils could phagocytose 381 +/- 17 whereas those from the diabetic rats phagocytosed 282 +/- 16 yeast cells, and the efficiency of phagocytosis varied significantly (p < 0.001). Further, both the percentages of phagocytosis and the efficiency of phagocytosis by the diabetic neutrophils were inversely related with the levels of their corresponding plasma glucose (p = 0.02; r = -0.498 and p < 0.05; r = -0.43, respectively), which indicated that increased plasma glucose reduced the phagocytic ability of neutrophils. Such relationship was not observed with the control neutrophils. These data clearly indicate that PMN functions are altered in the streptozotocin (STZ)-induced diabetic rats, and hyperglycemia may be the cause for the impairment of their functions leading to many infectious episodes.

Microscopic analysis of anastomotic healing in the intestine of normal and diabetic rats

PURPOSE

The mechanisms that cause diabetes to impair the development of anastomotic strength in the intestine are poorly understood. We investigated whether short-term uncontrolled diabetes causes alterations in microscopic aspects of anastomoses from the ileum and colon.

METHODS

Eighteen Wistar rats were rendered diabetic one week before operation by intravenous streptozotocin injection (50 mg/kg), resulting in nonfasting blood glucose levels of approximately 20 mmol/l. Another 18 age-matched rats were used as controls with a normal blood glucose range of 5 to 7 mmol/l. All rats underwent resection and anastomosis of both the ileum and colon. Animals were killed at one, three, or seven days after operation. Cellular and architectural parameters of anastomotic healing were scored in hematoxylin and eosin-stained sections. Anastomotic collagen content was analyzed by image analysis in picrosirius red-stained sections.

RESULTS

Anastomotic necrosis, edema, and epithelial recovery were not affected by diabetes. In diabetic rats, the number of polymorphonuclear cells and macrophages was significantly (P = 0.025 and 0.0002, respectively) increased in ileal anastomoses one and three days after operation. In colonic anastomoses, the number of polymorphonuclear cells was increased at one (P = 0.001) and seven (P = 0.014) days after operation. Repair of the submucosal-muscular layer in colonic anastomoses from diabetic rats was impaired seven days after surgery (P = 0.0071), but in ileal anastomoses no difference was found. In the anastomotic area, collagen deposition at postoperative Days 1, 3, and 7 remained unaffected by diabetes.

CONCLUSION

Experimental diabetes leads to alterations in cellular components involved in the early phase of repair of intestinal anastomoses but not to a reduced accumulation of wound collagen.

Effects of rhG-CSF on neutrophil functions and bone marrow parameters in diabetic rats

Neutrophils have an important role in the host defense. The elevated serum glucose levels of diabetics affect traditional host defenses such as neutrophil counts and functions. The causes of these impairments are not clear. We aimed to investigate changes of peripheral neutrophil counts and functions and their relation with bone marrow cells in diabetic rats. Thirty-two rats were divided into four equal groups. Group 1 were controls and Groups 2 and 4 were made diabetic by a single intraperitoneal injection of streptozotocin. Granulocyte colony stimulating factor (G-CSF) was injected subcutaneously into Groups 3 and 4. White blood cell count, neutrophil counts and function and bone marrow cell count were determined. Peripheral blood cell counts, neutrophil phagocytosis index were decreased but neutrophil adhesivity index was not different in the diabetes-induced group. There was a difference in circulating white blood cell counts and neutrophil counts between the rhG-CSF treated and non-treated groups. The phagocytosis index of neutrophil in diabetic rats was significantly diminished by rhG-CSF treatment. A hyperplasia of early cells of the myeloid series in G-CSF treated groups was observed when compared with those of nontreated groups (p<0.001). A significant decrease was noted in the number of mature marrow segmented cells diabetic groups (p<0.001). Finally, G-CSF has been shown to cause neutrophilia by acting as a releasing factor for mature marrow neutrophils in diabetic rats. These results suggest that G-CSF may be used to improve nonspecific immunity in diabetic patients.

Effects of granulocyte-macrophage colony-stimulating factor on incisional wound healing in an experimental diabetic rat model

The exact nature of poor wound healing in diabetes is uncertain. Neutrophils play a critical role in the host defense mechanism, and it is suggested that impaired neutrophil functions cause healing difficulties with or without infections in diabetic patients. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is used clinically when given systematically to increase the circulating neutrophils, but its wound-healing effects have not been systematically studied. This study was undertaken to examine the effects of GM-CSF on incisional wound healing in an experimental diabetic rat model. Forty rats were randomly divided into three groups, group I receiving saline as control, diabetes-induced group II receiving saline and diabetes-induced group III receiving GM-CSF. The anesthetized rats in all groups were wounded 21 days after diabetes induction by streptozotocin. Blood neutrophil counts and neutrophil fractions were also determined three days after wounding. Tensile strengths of wounded skin and the hydroxyproline (hyp) level of the wound were determined and wound healing processes were evaluated by light and electron microscopy, fourteen days after wounding. Neutrophil counts and phagocytosis were significantly increased in group III and neutrophil counts decreased in group II (p < 0.05). Although the hydroxyproline level of wound tissue significantly decreased in group II as compared with group III (p < 0.05), there was no differences of tensile strength between group II and III (p < 0.05). Wound score in group II was less than that in groups I and III (p < 0.05). It is concluded that PMN may have a role in modulating wound healing. GM-CSF may be useful for creating better wound healing healing. GM-CSF may be useful for creating better wound healing in risky patients such as diabetics.

Effect of epalrestat, an aldose reductase inhibitor, on the generation of oxygen-derived free radicals in neutrophils from streptozotocin-induced diabetic rats

Neutrophil function is impaired by a known mechanism in diabetic patients, thus increasing susceptibility to infections. We studied the effect of epalrestat, an aldose reductase inhibitor, on the generation of oxygen-derived free radicals and cytosolic sorbitol concentration in neutrophils from streptozotocin-induced diabetic rats. There were four groups: treated and untreated control and diabetic rats. Treated groups were given 0.075% epalrestat in their diet for 4 weeks from the induction of diabetes and were untreated for the subsequent 4 weeks. Oxygen radicals were measured as chemiluminescence amplified by a luciferin analog [Cypridina luciferin analog-dependent chemiluminescence (CLA-DCL), which is dependent on O2- generation] and luminol (L)-DCL, which is highly dependent on OCl- generation) in response to formyl-methonyl-leucyl-phenylalanine. Diabetes resulted in a significant decrease in CLA/L-DCL and a significant increase in sorbitol (P < 0.01); there was a negative correlation between sorbitol and CLA-DCL (P < 0.05) in diabetic groups. The 4-week treatment with epalrestat in the diabetic group completely prevented the increase in sorbitol and partially improved the CLA-DCL, although L-DCL was not significantly affected. After 4 weeks off treatment, CLA-DCL decreased and sorbitol increased. Treatment had no effect on serum insulin or glucose concentration. We conclude that an increase in sorbitol in neutrophils causes, in part, an impaired generation of O2-. Epalrestat improves the impaired O2- generation by preventing the sorbitol increase in streptozotocin-induced diabetic rats.

Effects of rhG-CSF on neutrophil functions and survival in sepsis induced diabetic rats

Diabetic patients are more prone to infection and evidence for an immunologic defect superimposed upon the metabolic abnormalities of diabetes is convincing. Neutrophils play a critical role in the host defense mechanism against various bacterial infections, and it is suggested that impaired neutrophil functions cause susceptibility to infections in diabetic patients. To explore the possibility that Granulocyte colony-stimulating factor (G-CSF) may be useful to prevent the morbidity and mortality caused by infections in diabetics. We studied the effect of G-CSF against septicemia in diabetic rats. Forty eight rats were divided into seven equal groups. The IInd, IVth-VIth groups were made diabetic by single intraperitoneal injection of streptozotocin. Fourth, VIth and VIIth groups were made septicemic by cecal ligation and perforation at the end of the second week of streptozotocin injection. G-CSF was subcutaneously injected into IIIrd, Vth and VIth groups. White blood cell count, neutrophil counts and function were determined. Rats in all groups were also observed for seven days for survival. White blood cells, neutrophil and lymphocyte counts and the neutrophil phagocytosis index decreased but neutrophil adherence rate was not different in diabetic group II (p<0.05). All these variables were significantly diminished in diabetes and sepsis-induced group IV (p<0.05). G-CSF injections improved all variables except neutrophil adherence. Cumulative survival ratio was better in G-CSF-injected group VI than in ceftriaxon-administrated group VII (p<0.05). In conclusion, G-CSF increased neutrophil counts, developed neutrophil functions and improved survival. These results suggest that G-CSF may be useful as a drug to prevent bacterial infection in diabetic patients.

Effect of tolrestat, an aldose reductase inhibitor, on neutrophil respiratory burst activity in diabetic patients

One hypothesis for the reduction in oxidative killing of neutrophils in diabetic patients is that increased polyol pathway activity during hyperglycemia reduces intracellular levels of nicotinamide adenine dinucleotide phosphate (NADPH), resulting in the reduction of neutrophil superoxide production during the respiratory burst. To test this hypothesis, we assessed the effect of tolrestat, an aldose reductase inhibitor, on neutrophil respiratory burst activity (NRBA) in diabetic patients. We measured fasting plasma glucose (FPG), hemoglobin A1 (HbA1), and NRBA levels in 79 diabetic patients and 48 normal controls. NRBA was reassessed in 34 patients after 4 weeks of tolrestat or placebo treatment, in seven controls after 4 weeks of tolrestat treatment, and in seven patients after 4 weeks of blood glucose control. NRBA was determined by flow cytometry, which detected fluorescent 2',7'-dichlorofluorescein (DCF) in neutrophils formed from 2',7'-dichlorofluorescein diacetate (DCF-DA) during phorbol myristate acetate (PMA)-induced respiratory bursts. Diabetic patients showed lower NRBA than the normal controls (mean cellular fluorescence, 438 +/- 103 v 668 +/- 101, mean +/- SD, P < .001). NRBA in diabetic patients showed a negative correlation with HbA1 (r = -.336, P < .005). Tolrestat treatment for 4 weeks in 17 patients restored the reduced NRBA to an almost normal level (relative NRBA, 0.55 +/- 0.20 v 0.99 +/- 0.36, P < .05) despite the fact that FPG level did not change (11.8 +/- 2.8 v 11.4 +/- 2.8 mmol/L). NRBA of these patients after tolrestat treatment was not significantly different from that of seven control subjects treated with tolrestat for 4 weeks. In 17 placebo-treated patients, there were no significant changes in NRBA and FPG level. The vigorous blood glucose control for 4 weeks in seven patients (16.6 +/- 2.1 v 8.6 +/- 2.3 mmol/L) also restored the reduced NRBA to almost normal (relative NRBA, 0.55 +/- 0.21 v 0.90 +/- 0.30, P < .05). The result that the reduced NRBA in diabetic patients was restored to almost normal either by tolrestat treatment or by blood glucose control strongly supports the hypothesis of this study.

Dexamethasone and methylprednisolone affect rat peritoneal phagocyte chemiluminescence after administration in vivo

Production of reactive oxygen compounds by peritoneal monocytes/macrophages was studied in rats exposed to dexamethasone or methylprednisolone in the drinking water. Luminol-amplified chemiluminescence was measured in preparations of peritoneal leukocytes activated ex vivo by serum opsonized zymosan, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) or phorbol 12-myristate 13-acetate (PMA). After dexamethasone administration for 1 day (approximately 0.13 mg/kg per 24 h) a significant reduction in chemiluminescence was found in cells stimulated with serum opsonized zymosan, while responses to fMLP and PMA stimulation were significantly reduced after 2 days. The maximal inhibition obtained after 5-8 days of dexamethasone administration (plasma levels < 5 nM) was 92.0 +/- 1.2%, 87.6 +/- 0.2% and 84.5 +/- 3.1% in cells stimulated with serum opsonized zymosan, fMLP and PMA, respectively. Administration of dexamethasone or methylprednisolone for 48 h gave a dose-dependent reduction of chemiluminescence. ED50 values of dexamethasone were estimated at 0.06-0.15 mg/kg for the different stimulators (plasma concentrations 5-10 nM). Estimated ED50 values for methylprednisolone were 35-36 mg/kg. Since the percentage of mononuclear phagocytes in the peritoneal cell population did not change significantly with dose or time of dexamethasone exposure, this study indicates that glucocorticoids have a depressive effect on the monocyte/macrophage 'respiratory burst' in vivo. The results are consistent with the hypothesis that these effects are mediated by glucocorticoid receptors. Although the pathway activated by serum opsonized zymosan was more rapidly inhibited than the fMLP- and PMA-activated pathways, the responses induced by the different stimulators were similarly affected, suggesting a modulation of common components in the activation pathways, possibly protein kinase C or the NADPH-oxidase complex, after administration of low pharmacological doses of glucocorticoids in vivo.

Increased receptor-mediated phospholipase D activation and Ca2+ mobilization in peritoneal polymorphonuclear leukocytes from streptozotocin-induced diabetic rats

Phospholipase D activation was investigated in peritoneal polymorphonuclear leukocytes from streptozotocin-induced diabetic rats. Stimulation of the cells with formyl-Met-Leu-Phe resulted in a time- and dose-dependent increase in phosphatidylethanol in the presence of ethanol, and this lipid formation in cells prepared from diabetic rats was enhanced as compared to that in the case of nondiabetic rats. Furthermore, the increase in the intracellular Ca2+ concentration was also enhanced in the stimulated cells from diabetic rats. Under the present conditions, N-acetyl-beta-glucosaminidase release and superoxide generation, which are known to be dependent on phospholipase D activation, were higher in the cells from diabetic rats than those in the cells from control rats. However, there was no difference in the dissociation constant and the number of binding sites for formyl-Met-Leu-Phe between the cells from diabetic and control rats. Phosphatidylethanol formation, N-acetyl-beta-glucosaminidase release and superoxide generation in response to ionomycin or 4 beta-phorbol 12-myristate 13-acetate were not enhanced in diabetic rat cells, as compared with those in control rat cells. These results suggest that receptor-mediated phospholipase D activation and Ca2+ mobilization are enhanced in diabetic rat polymorphonuclear leukocytes, which might be due to acceleration of receptor-mediated signaling.

Hypertonic glucose inhibits the production of oxygen-derived free radicals by rat neutrophils

We studied the influence of graded degrees of hypertonic glucose or sucrose on the generation of oxygen-derived free radicals by rat neutrophils. Hypertonic glucose and sucrose exerted dose- and time-dependent inhibition of chemiluminescence amplified by luciferin analog (CLA-DCL) and luminol (L-DCL) in response to fMLP. Hypertonic glucose was more effective to this chemiluminescence inhibition than hypertonic sucrose was. This inhibition of hypertonicity was more effective in CLA-DCL than in L-DCL. Although the production of superoxide anion measured by the reduction of ferricytochrome c was more inhibited by hypertonic glucose than by hypertonic sucrose, the myeloperoxidase activity was not affected by either glucose or sucrose hyperosmolarity. These data suggest that hyperosmotic state by itself and an additional direct glucose-toxicity may contribute to the impaired neutrophil function in the diabetic state.

Mechanism of inhibitory action of ketone bodies on the production of reactive oxygen intermediates (ROIS) by polymorphonuclear leukocytes

We determined an effect of acetoacetic acid (AcAc) and 3-hydroxybutyrate (3-OHB) on the production of reactive oxygen intermediates (ROIs) in polymorphonuclear leukocytes from healthy volunteers. Both AcAc and 3-OHB inhibited the luminol-dependent chemiluminescence (LDCL) activities assessed with initial slope and the inhibition rates were about 42%, 44% respectively by AcAc and 3-OHB when the leukocytes were preincubated with 10 mM AcAc or 3-OHB for 60 minutes. The LDCL activity was reduced by 16% and 42% following the addition of 1mM and 10 mM AcAc. The similar reduction of the LDCL activity was observed in the addition of 3-OHB. Either 3-OHB or AcAc failed to show a significant reduction of myeloperoxidase (MPO) activity. However, both 3-OHB and AcAc dose-dependently inhibited superoxide anion (O2-) production, measured by using cytochrome c. These data provided evidence that both 3-OHB and AcAc suppress neutrophil oxidative metabolism with respect with O2- production.