Dexamethasone inhibits the hexose monophosphate shunt in activated rat peritoneal macrophages by reducing hexokinase-dependent sugar uptake

The response of FDG uptake to immunosuppressive treatment on FDG PET/CT imaging for cardiac sarcoidosis

BACKGROUND

Immunosuppression is used to treat cardiac sarcoidosis, despite limited data. FDG PET/CT is used for detecting cardiac inflammation in patients with CS, yet there is variability in interpretation of FDG PET/CT. Our aim was to compare quantitative and qualitative interpretation of FDG PET/CT for CS in defining the FDG response to immunosuppression.

METHODS AND RESULTS

Patients with CS (N = 43 total studies from 17 patients) had serial FDG PET/CT studies before/after immunosuppression. FDG uptake was analyzed qualitatively (visually; FDG-positive segments) and quantitatively (SUVmax; cardiac metabolic volume and activity (CMV, CMA); volume above SUV thresholds 2.7 and 4.1 g/mL). Complete resolution of FDG uptake was common using CMA (10/17), CMV (10/17), but a 2.7 g/mL SUV threshold (13/17) and SUVmax (14/17) were more likely to define partial responses. In six patients imaged after a reduction in immunosuppression, 4/6 had a rebound quantitative FDG uptake.

CONCLUSIONS

Quantitative interpretation of FDG PET/CT in CS can detect changes in FDG uptake in response to immunosuppression. Further studies are needed to see if quantitative changes in FDG uptake are associated with improved outcomes.

A Mechanistic Basis for the Beneficial Effects of Caloric Restriction On Longevity and Disease: Consequences for the Interpretation of Rodent Toxicity Studies

Caloric restriction in rodents has been repeatedly shown to increase life span while reducing the severity and retarding the onset of both spontaneous and chemically induced neoplasms. These effects of caloric restriction are associated with a spectrum of biochemical and physiological changes that characterize the organism's adaptation to reduced caloric intake and provide the mechanistic basis for caloric restriction's effect on longevity. Here, we review evidence suggesting that the primary adaptation appears to be a rhythmic hypercorticism in the absence of elevated adrenocorticotropin (ACTH) levels. This characteristic hypercorticism evokes a spectrum of responses, including reduced body temperature and increased metabolic efficiency, decreased mitogenic response coupled with increased rates of apoptosis, reduced inflammatory response, reduced oxidative damage to proteins and DNA, reduced reproductive capacity, and altered drug-metabolizing enzyme expression. The net effect of these changes is to (1) decrease growth and metabolism in peripheral tissues to spare energy for central functions, and (2) increase the organism's capacity to withstand stress and chemical toxicity. Thus, caloric restriction research has uncovered an evolutionary mechanism that provides rodents with an adaptive advantage in conditions of fluctuating food supply. During periods of abundance, body growth and fecundity are favored over endurance and longevity. Conversely, during periods of famine, reproductive performance and growth are sacrificed to ensure survival of individuals to breed in better times. This phenomena can be observed in rodent populations that are used in toxicity testing. Improvements over the last 30 years in animal husbandry and nutrition, coupled with selective breeding for growth and fecundity, have resulted in several strains now exhibiting larger animals with reduced survival and increased incidence of background lesions. The mechanistic data from caloric restriction studies suggest that these large animals will also be more susceptible to chemically induced toxicity. This creates a problem in comparing tests performed on animals of different weights and comparing data generated today with the historical database. The rational use of caloric restriction to control body weight to within preset guidelines is a possible way of alleviating this problem.

Hexokinase II binding to mitochondria is necessary for Kupffer cell activation and is potentiated by ethanol exposure

Ethanol exposure promotes the development of steatohepatitis, which can progress to end stage liver disease. Kupffer cells have been documented to play a key role in the genesis and progression of alcoholic liver disease with ethanol exposure enhancing Kupffer cell activation. In the present study, we identified the binding of hexokinase II to the mitochondria as a requirement for LPS-induced activation of Kupffer cells and its potentiation by ethanol. LPS and ethanol exposure induced a reduction in sirtuin-3 activity. In turn, the decline of sirtuin-3 activity led to the activation of cyclophilin-D, which mediated an increased binding of hexokinase II to the mitochondria. Suppression of cyclophilin-D expression or enforced detachment of hexokinase II from the mitochondria abrogated the LPS- and ethanol-induced stimulation of Kupffer cells, preventing NADPH oxidase and inflammasome activation. Moreover, activation of AMP-activated protein kinase restored sirtuin-3 activity, thereby preventing LPS and ethanol from stimulating the binding of hexokinase II to the mitochondria and precluding NADPH oxidase and inflammasome activation.

Clostridium difficile infection in diabetes

Diabetes-related hospitalization and hospital utilization is a serious challenge to the health care system, a situation which may be further aggravated by nosocomial Clostridium difficile (C. difficile) infection (CDI). Studies have demonstrated that diabetes increases the risk of recurrent CDI with OR (95% CI) 2.99 (1.88, 4.76). C. difficile is a gram-positive, spore-forming anaerobic bacterium which is widely distributed in the environment. Up to 7% of healthy adults and up to 45% of infants may have asymptomatic intestinal carriage of C. difficile. A large number of strains of C. difficile have been identified. A number of PCR or sequence-based molecular typing methods are available for typing C. difficile isolates. C. difficile virulence evolved independently in the highly epidemic lineages, associated with the expression of toxin genes and other virulence factors. This article briefly reviews recent progresses in the bateriology of C. difficile and highlights the limited knowledge of potential mechanisms for the increased risk of CDI in diabetes which warrants further research.

Green tea catechins ameliorate adipose insulin resistance by improving oxidative stress

Epidemiological data have suggested that drinking green tea is negatively associated with diabetes, and adipose oxidative stress may have a central role in causing insulin resistance, according to recent findings. The aim of this work is to elucidate a new mechanism for green tea's anti-insulin resistance effect. We used obese KK-ay mice, high-fat diet-induced obese rats, and induced insulin resistant 3T3-L1 adipocytes as models. Insulin sensitivity and adipose reactive oxidative species (ROS) levels were detected in animals and adipocytes. The oxidative stress assay and glucose uptake ability assay were performed, and the effects of EGCG on insulin signals were detected. Green tea catechins (GTCs) significantly decreased glucose levels and increased glucose tolerance in animals. GTCs reduced ROS content in both models of animal and adipocytes. EGCG attenuated dexamethasone and TNF-α promoted ROS generation and increased glucose uptake ability. EGCG also decreased JNK phosphorylation and promoted GLUT-4 translocation. EGCG and GTCs could improve adipose insulin resistance, and exact this effect on their ROS scavenging functions.

Kinetics of glucose transport and sequestration in lactating bovine mammary glands measured in vivo with a paired indicator/nutrient dilution technique

To quantify kinetics of mammary glucose utilization in vivo, 24 paired glucose and extracellular indicator ( p-aminohippuric acid) dilution curves across intact bovine mammary glands were obtained after bolus injections into the external iliac artery. Dilution curves were analyzed using a compartmental capillary, convolution integration model. Four candidate submodels of glucose transport and metabolism in capillary supply zones were fit to the glucose dilution curves and evaluated. Model I, with one extracellular compartment for glucose and first-order unidirectional uptake, failed, indicating that efflux of glucose from the intracellular space could not be ignored. Model II, with first-order exchanges between extracellular and intracellular compartments and sequestration from the latter, was overdefined because unidirectional clearance of glucose was at least five times the blood flow rate and 20 times the net clearance rate. Model III, combining extracellular and intracellular space into one compartment, was superior in its goodness-of-fit to curves and identifiability of parameters. Michaelis-Menten parameters of sequestration were not identifiable. Parameters of the optimal compartmental capillary, convolution integration model were applicable to both the dynamics of injected glucose dilution and the steady-state background arteriovenous difference of glucose. Glucose sequestration followed first-order kinetics between 0 and 7 mM extracellular glucose with an average rate constant of 0.006 s−1 or a clearance of 44 ml/s. The ratio of intracellular to extracellular glucose distribution space was 0.34, which is considerably lower than the expected intracellular volume and suggests an intracellular occlusion compartment with which extracellular glucose rapidly exchanges.

Hexokinase translocation during neutrophil activation, chemotaxis, and phagocytosis: disruption by cytochalasin D, dexamethasone, and indomethacin

Neutrophils expend large amounts of energy to perform demanding cell functions. To better understand energy production and flow during cell activation, immunofluorescence microscopy was employed to determine the location of the key metabolic enzyme hexokinase during various conditions. Hexokinase is translocated from the neutrophil's cytosol to its periphery in response to N-formyl-methionyl-leucyl-phenylalanine (fMLP) and other activating stimuli, but not during exposure to the formyl peptide receptor antagonist N-tert-BOC-phe-leu-phe-leu-phe (Boc-PLPLP). Translocation was observed from 10(-6) to 10(-9)M fMLP. However, fMLP did not affect the intracellular distribution of lactate dehydrogenase. Hexokinase accumulated at the lamellipodium of cells exposured to an fMLP gradient whereas it localized to the phagosome after latex bead uptake. Thus, hexokinase is differentially translocated within cells depending upon the prevailing physiological conditions. Further studies noted that cytochalasin D, dexamethasone, and indomethacin blocked hexokinase translocation. Parallel regulation of reactive oxygen metabolite (ROM) production was shown. We speculate that hexokinase translocation participates in neutrophil activation.

Inhibition of microglial superoxide anion production by isoproterenol and dexamethasone

Microglia, like other tissue macrophages, are a component of the hypothalamic-pituitary endocrine-immune axis and, as such, are responsive to both neural and endocrine factors. Using cultured neonatal hamster microglia, we have examined the effect of isoproterenol, a beta-adrenergic agonist, and dexamethasone, a synthetic glucocorticoid, on superoxide anion production. For these experiments, microglia were pretreated with isoproterenol or dexamethasone and then induced to produce superoxide anion by exposure of the cells to phorbol myristate acetate (PMA). Our study demonstrates that the PMA-stimulated production of superoxide anion was decreased by acute (30 min) and chronic (24 h) pretreatment of the microglia with isoproterenol and was blocked by the beta-adrenergic receptor antagonist, propranolol. Since a rise in intracellular cAMP may be a prime factor in the inhibition of superoxide anion production in isoproterenol-treated cells, we used forskolin, a known activator of the adenylate cyclase in place of isoproterenol and re-investigate superoxide anion production. Short term exposures to forskolin produced a lower amount of superoxide anion than PMA-stimulated alone and, thus, mimicked the effect of isoproterenol. However, treatment with the same concentration of forskolin for 24 h prior to the induction of the NADPH oxidase did not significantly change PMA-stimulated superoxide anion production from untreated values. Thus, chronic exposure to forskolin produced a different effect than chronic exposure to isoproterenol. Isoproterenol and forskolin both increased immunoreactivity for the protein products of the early response genes, c-fos and c-jun. Pretreatment with dexamethasone for 24 h also inhibited superoxide anion production and was blocked by the protein synthesis inhibitor, cycloheximide. The simultaneous addition of varying concentrations of dexamethasone and 5 microM isoproterenol did not produce a greater inhibition in superoxide anion production than either agent alone. The down-regulation of microglial function by adrenergic agonists and by glucocorticoids provides a way in which the cytotoxicity of these immune cells can be reduced and may be a factor in the paracrine regulation of microglia.

Effects of ethanol on glucose transporter expression in cultured hippocampal neurons

Glucose transport was studied in primary hippocampal neuron cultures exposed to ethanol. Immunofluorescent staining with antibodies against neuron-specific enolase and glial fibrillary acidic protein identified approximately 95% of the cultured cells as neurons. Western blot analysis was conducted with polyclonal antisera to glucose transporter isoforms GLUT1 and GLUT3. As previously seen in astrocytes, GLUT1 protein was regulated by the culture medium glucose content. Exposure to 50 and 100 mM of ethanol for 5 hr induced dose-dependent reductions in GLUT1 and GLUT3 protein. In contrast, GLUT1 mRNA abundance was increased relative to controls under the same conditions. Glucose uptake, measured with the nonmetabolized analog, 2-deoxy-D-glucose, was reduced by 50 and 100 mM of ethanol in four experiments. These results indicate a direct effect of ethanol on neuronal glucose transporter expression, which may play a role in the neurotoxic effects of alcohol.

The relationship between sugar metabolism, transport and superoxide radical production in rat peritoneal macrophages

Dexamethasone inhibits sugar-dependent phorbol myristate acetate (PMA)-stimulated superoxide production and 2-deoxy-D-glucose (2-dGlc) transport in rat peritoneal macrophages (Rist, R.J., Jones, G.E. and Naftalin, R.J. (1991) Biochem. J. 278, 119-128; Rist, R.J. and Naftalin, R.J. (1991) Biochem J. 278, 129-135). Here it is shown that with glucose as a substrate, dexamethasone (0.1 microM) acts as a non-competitive inhibitor of PMA-induced superoxide production; decreasing the maximal rate of superoxide production (P < 0.001) without altering the Km. In contrast, with 2-dGlc as a substrate, dexamethasone shows competitive inhibition of PMA-stimulated superoxide production; increasing the Km of superoxide production, (P < 0.001) without altering the Vmax. The maximal rate of PMA-stimulated superoxide production with glucose as substrate is 10-12-fold in excess of the maximal rate with 2-dGlc as substrate. Diphenylene iodonium (DPI) is a non-competitive inhibitor of PMA-stimulated glucose-dependent superoxide production in macrophages, (Ki = 1-5 microM) and significantly reduces the activity of the PMA-induced hexose monophosphate shunt, (HMPS) (P < 0.01). However, DPI (1 microM) has no significant effect on the PMA-induced increase in 2-dGlc uptake, suggesting that the stimulus for HMPS activity and superoxide production is separate from the stimulus for hexose transport. A model is described which explains the observed differences in hexose transport and glucose- and 2-dGlc-dependent superoxide production in terms of the differences in metabolism of the two sugars. Accumulation of free 2-dGlc within the cytosol leads to saturation of hexokinase and hence, the effects of PMA and dexamethasone, which alter the coupling between hexokinase and the transporter, are only observed at low concentrations of 2-dGlc, where it is accumulated to sub-saturating levels. Since glucose is completely metabolized within the cell, PMA and dexamethasone increase and decrease, respectively, net uptake of sugar and superoxide production at all glucose concentrations.

Glucose- and phorbol myristate acetate-stimulated oxygen consumption and superoxide production in rat peritoneal macrophages is inhibited by dexamethasone

1. Rat peritoneal macrophages stimulated with phorbol 12-myristate 13-acetate (PMA) (40 nM) show an increase in the rate of oxygen consumption (measured with an O2 electrode) and the production of superoxide (measured by cytochrome c reduction), which are both dependent on the presence of exogenous glucose. There is a 1:1 correlation between the oxygen consumed and the superoxide produced over a range of glucose concentrations (0-10 mM). 2. Preincubation of macrophages with dexamethasone (1 microM) for 3 h significantly decreased the Vmax. for PMA-induced glucose-dependent oxygen consumption (P < 0.001) and glucose-dependent superoxide production (P < 0.001). However, dexamethasone did not significantly change the Km for glucose in either PMA-induced oxygen consumption or superoxide production. Dexamethasone is therefore a non-competitive inhibitor of PMA-stimulated glucose-dependent oxygen consumption (Ki = 0.83 +/- 0.09 microM) and superoxide generation (Ki = 0.87 +/- 0.09 microM). 3. The PMA-induced rate of oxygen consumption by macrophages was decreased at oxygen concentrations below approx. 15 microM. The Km of oxygen for PMA-induced oxygen consumption was 1.28 +/- 0.13 microM (n = 12), and this was not significantly different in the presence of dexamethasone; Km = 1.61 +/- 0.31 microM (n = 12). It is therefore concluded that in vivo macrophage superoxide production is not limited by external oxygen or glucose concentrations, even in hypoxic joints.

Augmented glucose use and pentose cycle activity in hepatic endothelial cells after in vivo endotoxemia

Glucose use and pentose cycle activity were determined in freshly isolated rat hepatic endothelial cells 3 hr after an intravenous injection of Escherichia coli lipopolysaccharide (0.1 mg/kg body weight), by use of [1-14C]glucose, [6-14C]glucose and [2-3H]glucose. Lipopolysaccharide treatment in vivo increased glucose use fivefold, whereas glucose oxidation in the pentose cycle was elevated from 0.2 to 1.5 nmol/hr/10(7) cells. In vitro incubation of endothelial cells from saline- and lipopolysaccharide-treated animals in the presence of phorbol 12-myristate 13-acetate (10(-6) mol/L) increased pentose cycle activity twofold and eightfold, respectively. Phorbol 12-myristate 13-acetate caused only a 40% to 60% increase in glycolysis in both groups. Addition of t-butyl hydroperoxide (0.5 mmol/L), a substrate for glutathione peroxidase, caused a 24-fold and 16-fold increase in the glucose flux through the pentose cycle in cells from saline- and lipopolysaccharide-treated rats, respectively. Oxidation of glucose through the Krebs cycle was also increased several-fold after t-butyl hydroperoxide administration. Depletion of cellular glutathione by N-ethylmaleimide (0.1 mmol/L) inhibited the phorbol 12-myristate 13-acetate-induced or t-butyl hydroperoxide-induced increase in the pentose cycle activity with no marked effects on glycolysis. Diphenyleneiodonium (0.1 mmol/L), an inhibitor of superoxide and nitric oxide synthesis inhibited the phorbol 12-myristate 13-acetate-induced increased pentose cycle activity with no effects on the t-butyl hydroperoxide-induced response.(ABSTRACT TRUNCATED AT 250 WORDS)

RP 54745, a potential antirheumatic compound. I. Inhibitor of macrophage stimulation and interleukin-1 production

RP 54745 is an amino-dithiole-one compound found to be active at micromolar concentration on the metabolism of stimulated macrophages, for example, the hexose monophosphate pathway (HMP) and the exocytosis of lysosomal enzymes. LPS-induced interleukin-1 (IL-1) production by murine peritoneal macrophages was also diminished by this compound in vitro as well as in vivo. This effect was confirmed at the mRNA level; at the concentration of 3 x 10(-6) M, the IL-1 alpha and beta mRNA signals were inhibited, whereas the TNF alpha mRNA signal was only slightly lessened. These observations were confirmed in vivo, with a dose of RP 54745 of 25 mg kg-1. These results led us to consider that RP 54745 might influence certain cells and cytokines implicated in the regulation of the immune system, the disfunctioning of which can lead to inflammatory disorders or autoimmune pathologies.