Low phagocytic activity of resident peritoneal macrophages in diabetic mice: relevance to the formation of advanced glycation end products

Mechanisms of the hypoglycaemic and immunopotentiating effects of Nigella sativa L. oil in streptozotocin-induced diabetic hamsters

The aim of this study was to elucidate the mechanisms underlying the hypoglycaemic effect of N. sativa oil (Nigella sativa oil) in streptozotocin (STZ)-induced diabetic hamsters, in terms of hepatic glucose production, and to investigate the possible immunopotentiating effect of N. sativa oil on peritoneal macrophages. Diabetes was induced by intraperitoneal injection of 65 mg/kg body weight of STZ. Treatment with N. sativa oil commenced 6 weeks after induction of diabetes at a dose of 400 mg/kg body weight by gastric gavage. Isolated hepatocytes were collected using collagenase to determine liver glucose production. Phagocytic activity was evaluated by injection of fluorescent latex (2 microm diameter) intraperitoneally, followed 24 h later by collection of peritoneal macrophages. N. sativa oil reduced blood glucose from 391+/-3.0 mg/dl before treatment to 325+/-4.7, 246+/-5.9, 208+/-2.5 and 179+/-3.1 mg/dl after the first, second, third and fourth weeks of treatment, respectively. Hepatic glucose production from gluconeogenic precursors (alanine, glycerol and lactate) was significantly lower in treated hamsters. Treatment with N. sativa oil significantly increased the phagocytic activity and phagocytic index of peritoneal macrophages and lymphocyte count in peripheral blood compared with untreated diabetic hamsters. Our data indicate that the hypoglycaemic effect of N. sativa oil is due to, at least in part, a decrease in hepatic gluconeogenesis, and that the immunopotentiating effect of N. sativa oil is mediated through stimulation of macrophage phagocytic activity either directly or via activation of lymphocytes.

Insulin receptor substrate-2-dependent interleukin-4 signaling in macrophages is impaired in two models of type 2 diabetes mellitus

We have shown previously that hyperinsulinemia inhibits interferon-alpha-dependent activation of phosphatidylinositol 3-kinase (PI3-kinase) through mammalian target of rapamycin (mTOR)-induced serine phosphorylation of insulin receptor substrate (IRS)-1. Here we report that chronic insulin and high glucose synergistically inhibit interleukin (IL)-4-dependent activation of PI3-kinase in macrophages via the mTOR pathway. Resident peritoneal macrophages (PerMPhis) from diabetic (db/db) mice showed a 44% reduction in IRS-2-associated PI3-kinase activity stimulated by IL-4 compared with PerMPhis from heterozygote (db/+) control mice. IRS-2 from db/db mouse PerMPhis also showed a 78% increase in Ser/Thr-Pro motif phosphorylation without a difference in IRS-2 mass. To investigate the mechanism of this PI3-kinase inhibition, 12-O-tetradecanoylphorbol-13-acetate-matured U937 cells were treated chronically with insulin (1 nm, 18 h) and high glucose (4.5 g/liter, 48 h). In these cells, IL-4-stimulated IRS-2-associated PI3-kinase activity was reduced by 37.5%. Importantly, chronic insulin or high glucose alone did not impact IL-4-activated IRS-2-associated PI3-kinase. Chronic insulin + high glucose did reduce IL-4-dependent IRS-2 tyrosine phosphorylation and p85 association by 54 and 37%, respectively, but did not effect IL-4-activated JAK/STAT signaling. When IRS-2 Ser/Thr-Pro motif phosphorylation was examined, chronic insulin + high glucose resulted in a 92% increase in IRS-2 Ser/Thr-Pro motif phosphorylation without a change in IRS-2 mass. Pretreatment of matured U937 cells with rapamycin blocked chronic insulin + high glucose-dependent IRS-2 Ser/Thr-Pro motif phosphorylation and restored IL-4-dependent IRS-2-associated PI3-kinase activity. Taken together these results indicate that IRS-2-dependent IL-4 signaling in macrophages is impaired in models of type 2 diabetes mellitus through a mechanism that relies on insulin/glucose-dependent Ser/Thr-Pro motif serine phosphorylation mediated by the mTOR pathway.

Metabolic, endocrine, and immune effects of stress hyperglycemia in a rabbit model of prolonged critical illness

Stress hyperglycemia is frequent in critically ill patients. The aim of this study was to investigate the effect of blood glucose control with insulin on endocrine, metabolic, and immune function in an animal model of severe injury. Seventy-two hours after alloxan injection and exogenous insulin infusion combined with continuous iv parenteral nutrition, male New Zealand White rabbits received a burn injury and were allocated to a normoglycemic (n = 17) or hyperglycemic (n = 13) group. In the normoglycemic group, blood glucose levels were kept between 3.3 and 6.1 mmol/liter by insulin infusion, whereas in the hyperglycemic group blood glucose levels were maintained at 13.8-16.6 mmol/liter. Blood was drawn for biochemical analysis at regular time points. At 24 and 72 h after burn injury, immune function of monocytes was assessed in vitro. Maintenance of normoglycemia with exogenous insulin after severe trauma to a large extent prevented weight loss, lactic acidosis, and hyponatremia. Furthermore, within 3 d after injury, the intervention improved phagocytosis of monocytes investigated in fresh cells by more than a mean 150% (P = 0.006) and after 24-h incubation with or without lipopolysaccharide by more than a mean 4-fold (P = 0.001) and 2-fold (P = 0.05), respectively. Oxidative killing after 24-h incubation was also improved by 2-fold (P = 0.05), but no effect on chemotaxis was detected. Concomitantly, inflammation and stress-induced growth hormone hypersecretion were suppressed. Prevention of catabolism, acidosis, excessive inflammation, and impaired innate immune function may explain previously documented beneficial effects of intensive insulin therapy on outcome of critical illness.

Immune response modulation in acutely ethanol-intoxicated, acutely diabetic male and female rats

We examined how acute diabetes mellitus and acute ethanol intoxication modulate factors that mediate immune responses as a basis for explaining the increased susceptibility to infection in these two conditions. Our working hypothesis is that ethanol intoxication in diabetes compromises host defense mechanisms to a greater extent than observed in each condition alone. Male and female rats were made diabetic with streptozotocin (65 mg/kg, i.p.). Forty-eight hours after administration of streptozotocin, rats either received no treatment (control group) or were treated with (1) ethanol (bolus injection of 1.75 g/kg, followed by a 3-h infusion at the rate of 300 mg/kg/h), (2) lipopolysaccharide [(LPS); 0.9 mg/kg], or (3) a combination of LPS+ethanol. At the end of 3 h, rats were killed, and the livers were digested by perfusion with collagenase-containing Hanks' balanced salt solution to isolate hepatocytes and Kupffer cells. To measure chemokine generation, hepatocytes (2.5x10(5) cells per well) and Kupffer cells (1x10(6) cells per well) were cultured for 20 h, and the supernatant was used to measure cytokine-induced neutrophil chemoattractant (CINC) and regulated on activation, normal T-cell expressed and secreted (RANTES) chemokines. Phagocytosis by Kupffer cells was measured by flow cytometry and expressed as mean channel fluorescence intensity (MCF). Induction of diabetes as well as treatment of nondiabetic rats with LPS, ethanol, or LPS+ethanol caused depression of MCF values of Kupffer cells. However, treatment of the diabetic male and female rats with LPS and LPS+ethanol increased the MCF values relative to those of Kupffer cells obtained from untreated diabetic rats, but administration of ethanol to diabetic rats did not have a similar effect. The induction of diabetes caused an increase in CINC generation by Kupffer cells obtained from male rats, but not from female rats. This diabetes-induced elevation of chemoattractant factor was decreased when diabetic animals were treated with LPS, ethanol, or LPS+ethanol, and the sex difference was obliterated. Thus, the induction of diabetes as well as treatment with LPS, ethanol, or LPS+ethanol in nondiabetic rats depressed the phagocytic capability of Kupffer cells, whereas the presence of endotoxemia (administration of the endotoxin LPS) or administration of LPS+ethanol reversed the diabetic effect, but ethanol intoxication did not. These findings seem to indicate a persistence of depression of host defense capacity in the ethanol-intoxicated diabetic condition. This is further reinforced by the depression of the diabetes-induced enhancement of chemotaxis when the diabetic rats became intoxicated.

Advanced glycation endproducts induce changes in glucose consumption, lactate production, and ATP levels in SH-SY5Y neuroblastoma cells by a redox-sensitive mechanism

Advanced glycation endproducts (AGEs) accumulate on long-lived proteins, including beta-amyloid plaques in Alzheimer's disease, and are suggested to contribute to neuronal dysfunction and cell death. We have investigated the effects of a model AGE upon glucose metabolism and energy production in a neuroblastoma cell line. AGEs decrease cellular ATP levels and increase glucose consumption and lactate production. All of the AGE-induced metabolic changes can be attenuated by antioxidants such as (R+)-alpha-lipoic acid and 17beta-estradiol. These antioxidants may become useful drugs against (AGE-mediated) effects in neurodegeneration through their positive effects on cellular energy metabolism.

Dysfunction of dermal fibroblasts induced by advanced glycation end-products (AGEs) and the contribution of a nonspecific interaction with cell membrane and AGEs

Advanced glycation end-products (AGEs) have been reported to accumulate in the dermal skin. However, it remains unknown whether the AGEs interact with the dermal fibroblasts and influence their function. Previously, we demonstrated that AGEs hastened photoaging of the skin by means of active oxygen species such as *O(2)(-), H(2)O(2), and *OH, generated during UVA irradiation. The purpose of the present study was to clarify the influence of AGEs on the functions of dermal fibroblasts under physiological conditions. It was found that AGEs decreased both hyaluronic acid (HA) synthesis and activity of elastase-type matrix metalloproteinase (ET-MMP). Because the reactions of both HA synthesis and ET-MMP were found to take place at the cell membrane region, it appeared that AGEs modulated cellular dysfunction through an interaction with the cell membrane. To clarify the mechanisms of these dysfunction in relation to AGEs, we examined the interaction between AGEs and cell membranes, and obtained the following results: (1) AGEs associated with the cell membranes and liposomal membrane prepared with phosphatidyl choline; (2) AGEs hydrophobically modified the circumstances of the cell membrane and liposome membrane as evaluated by experiments using a fluorescence probe; (3) AGEs increased the fluidity of the cell membrane and liposomal membrane as estimated by ESR spin-labeling using 5-doxylstearic acid; and (4) AGEs accelerated lactate dehydrogenase (LDH) leakage from the cells. On the basis of these experimental results, we proposed that AGEs modulated cell function through a nonspecific interaction with the membranes of dermal fibroblasts.

Phagocytosis--the mighty weapon of the silent warriors

Professional phagocytes, comprising polymorphonuclear neutrophils and monocyte/macrophage cells, play an important role in the host defense. Any defect in their function exposes the organism to microbial intruders terminating in fatal diseases. The functional responses of the phagocytes to bacterial and fungal infections include chemotaxis, actin assembly, migration, adhesion, aggregation, phagocytosis, degranulation, and reactive oxygen species production. Superoxide generation by phagocytic NADPH oxidase is an imperative step toward bacterial killing. Phagocytes participate in inflammatory reactions and exert tumoricidal activity. They are supported by serum factors such as immunoglobulins, cytokines, complement, the acute phase reactant C-reactive protein, production of antibacterial proteins, and others. In addition to their principal task to eliminate bacteria, they are engaged in removing damaged, senescent, and apoptotic cells. Engulfed cell debris, large particles such as latex beads, fat, and oil droplets, are examples of phagocytic activity illustrated in the present review with transmission and scanning electron microscope micrographs. Numerous factors, such as diseases and stressful conditions, affect the engulfing activity of the professional phagocytes. Our experience regarding the impaired phagocytic capacity of cells in patients with diabetes and chronic renal failure is discussed. The results obtained in our laboratory from experiments detecting the effect of strenuous physical exercise, hypothermia, fasting, and abdominal photon irradiation on the phagocytic capacity of human polymorphonuclear neutrophils and rat peritoneal macrophages are hereby summarized and the reports on those subjects in the recent literature are reviewed. A variety of assays are applied for quantifying phagocytosis. Flow cytometry based on incubation of phagocytic cells with fluorescent conjugated particles and measuring the amount of fluorescence as an indicator of the engulfing capacity of the cells is a useful method. A direct visualization of the ingested particles using light or electron microscopy is a valuable tool for estimation of phagocytic function. In our hands, the use of semithin sections of embedded phagocytes following their incubation with latex particles provided satisfactory results for measuring the total number of phagocytic cells, as well as the internalizing capacity of each individual cell. Microbiological assays, the nitroblue tetrazolium test, quantitation of antibody- and antigen-mediated phagocytosis, as well as methods reviewed in detail in other reports are additional applications for determination of this intricate process.

Effect of hyperglycemia on the basal cytosolic free calcium level, calcium signal and tyrosine-phosphorylation in human T-cells

In this study, we investigated the effect of in vitro hyperglycemia on the function of human T-cells (Jurkat cells). Hyperglycemic conditions caused concentration-dependent elevation of basal cytosolic free calcium level and reduced calcium signal (activation capacity), either after ionomycin or monoclonal anti-CD3 antibody treatments. Similar changes were observed if cells were treated with the calcineurin inhibitor Cyclosporin-A. We found that tyrosine-phosphorylation after anti-CD3 treatment was also impaired. High glucose concentrations in the tissue culture medium are also associated with increased non-enzymatic glycation of T-cell proteins. We propose that the increased glycation of proteins involved in calcium transport and/or intracellular signal transduction in T-cells accounts for the abnormal calcium sequestration and calcium mediated signal transduction.

In vitro effect of advanced glycation end-products on human polymorphonuclear superoxide production

BACKGROUND

Advanced glycation end-products (AGEs) are elevated in the sera of diabetic patients. The latter are prone to severe bacterial infections. Advanced glycation end-products have been shown to modulate immune competent cell activities. In this study we examined the in vitro effect of advanced glycation end-products on superoxide anion generation by human polymorphonuclear leukocytes.

MATERIALS AND METHODS

Advanced glycation end-products were prepared by incubation of bovine serum albumin (BSA) with glucose for 90 days. Superoxide production was measured as the superoxide dismutase-inhibitable reduction of ferricytochrome c. The effect of advanced glycation end-products on superoxide production was evaluated in both baseline (nonstimulated) and stimulated (by either formyl-methionyl-leucyl-phenylalanine, or phorbol-myristate-acetate) polymorphonuclear leukocytes.

RESULTS

The baseline superoxide production of polymorphonuclear leukocytes was significantly increased by advanced glycation end-products in a dose-dependent manner. In contrast, in stimulated polymorphonuclear leukocytes advanced glycation end-products significantly inhibited superoxide production, again in a dose-dependent manner. This inhibitory effect of advanced glycation end-products was observed after dialyzing AGE-BSA, thereby eliminating the possible influence of reactive carbohydrates. No modification of superoxide production was seen with BSA and only a mild inhibitory effect of glucose at high concentrations.

CONCLUSIONS

Advanced glycation end-products depress superoxide production by stimulated polymorphonuclear leukocytes. As superoxide plays an essential role in bactericidal activity, this polymorphonuclear leukocyte dysfunction may be a contributory factor to the increased prevalence and severity of bacterial infection seen in diabetic patients.

Regeneration of pancreatic beta cells from intra-islet precursor cells in an experimental model of diabetes

We previously reported that new beta cells differentiated in pancreatic islets of mice in which diabetes was produced by injection of a high dose of the beta cell toxin streptozotocin (SZ), which produces hyperglycemia due to rapid and massive beta cell death. After SZ-mediated elimination of existing beta cells, a population of insulin containing cells reappeared in islets. However, the number of new beta cells was small, and the animals remained severely hyperglycemic. In the present study, we tested whether restoration of normoglycemia by exogenous administered insulin would enhance beta cell differentiation and maturation. We found that beta cell regeneration improved in SZ-treated mice animals that rapidly attained normoglycemia following insulin administration because the number of beta cells per islet reached near 40% of control values during the first week after restoration of normoglycemia. Two presumptive precursor cell types appeared in regenerating islets. One expressed the glucose transporter-2 (Glut-2), and the other cell type coexpressed insulin and somatostatin. These cells probably generated the monospecific cells containing insulin that repopulated the islets. We conclude that beta cell neogenesis occurred in adult islets and that the outcome of this process was regulated by the insulin-mediated normalization of circulating blood glucose levels.