Effect of epinephrine on glucose metabolism and hydrogen peroxide content in incubated rat macrophages

A past and present overview of macrophage metabolism and functional outcomes

In 1986 and 1987, Philip Newsholme et al. reported macrophages utilize glutamine, as well as glucose, at high rates. These authors measured key enzyme activities and consumption and production levels of metabolites in incubated or cultured macrophages isolated from the mouse or rat intraperitoneal cavity. Metabolic pathways essential for macrophage function were then determined. Macrophages utilize glucose to generate (i) ATP in the pathways of glycolysis and mitochondrial oxidative phosphorylation, (ii) glycerol 3-phosphate for the synthesis of phospholipids and triacylglycerols, (iii) NADPH for the production of reactive oxygen species (ROS) and (iv) ribose for the synthesis of RNA and subsequently production and secretion of protein mediators (e.g. cytokines). Glutamine plays an essential role in macrophage metabolism and function, as it is required for energy production but also provides nitrogen for synthesis of purines, pyrimidines and thus RNA. Macrophages also utilize fatty acids for both energy production in the mitochondria and lipid synthesis essential to plasma membrane turnover and lipid meditator production. Recent studies utilizing metabolomic approaches, transcriptional and metabolite tracking technologies have detailed mitochondrial release of tricarboxylic acid (TCA) intermediates (e.g. citrate and succinate) to the cytosol, which then regulate pro-inflammatory responses. Macrophages can reprogramme their metabolism and function according to environmental conditions and stimuli in order to polarize phenotype so generating pro- or anti-inflammatory cells. Changes in macrophage metabolism result in modified function/phenotype and vice versa. The plasticity of macrophage metabolism allows the cell to quickly respond to changes in environmental conditions such as those induced by hormones and/or inflammation. A past and present overview of macrophage metabolism and impact of endocrine regulation and the relevance to human disease are described in this review.

The Role of Acute Intermittent Hypoxia in Neutrophil-Generated Superoxide, Sympathovagal Balance, and Vascular Function in Healthy Subjects

Introduction: Recurrent hypoxia (HPX), a hallmark of the obstructive sleep apnea (OSA), impairs autonomic balance, and increases arterial blood pressure (BP). Oxidative stress is one of the mechanisms involved in these alterations. The cumulative effect of acute intermittent HPX and the chronicity may determine whether the response crosses the threshold from having protective value to pathology. However, the impact of acute intermittent HPX–reoxygenation on markers of oxidative stress in healthy individuals remains to be fully understood.

Objective: To analyze the effects of the acute intermittent HPX on the generation of neutrophil-derived superoxide, sympathovagal balance, and vascular function in healthy subjects.

Methods: We applied six cycles of intermittent HPX (10% O₂ and 90% N₂) for 5 min followed by 2 min of room-air in 15 healthy volunteers (34 ± 2 years; 22.3 ± 0.46 kg/m²), without OSA (polysomnography), during wakefulness. During the experimental protocol, we recorded O₂ saturation, end-tidal CO₂, heart rate (HR), systolic, and diastolic BP, cardiac output (CO) and peripheral resistance (PR). Cardiac sympathovagal balance was determined by HR variability analysis (low frequency and high frequency bands, LF/HF). Superoxide generation in polymorphonuclear neutrophil cells were established using relative luminescence units (PMNs RLU) at baseline (pre-HPX) and immediately after hypoxia induction (post-HPX6).

Results: The studied subjects had normal levels of BP, plasma glucose, lipid profile, and inflammatory marker (C-reactive protein). Acute intermittent HPX increased HR, systolic BP, CO, and decreased PR. Additionally, acute intermittent HPX increased PMNs RLU, measured post-HPX6 (470 ± 50 vs. 741 ± 135, P < 0.05). We found a similar increase in LF/HF post-HPX6 (0.91 ± 0.11 vs. 2.85 ± 0.40, P < 0.05). PR was diminished from pre-HPX to post-HPX6 (1.0 ± 0.03 vs. 0.85 ± 0.06, P < 0.05). Further analysis showed significant association between O₂ saturation and PMNs RLU (R = −0.62, P = 0.02), and with LF/HF (R = −0.79, P = 0.02) post-HPX6. In addition, an association was found between PMNs RLU and PR post-HPX6 (R = 0.58, P = 0.04).

Conclusion: Acute exposure to intermittent HPX not only increased superoxide generation in neutrophils, but also impaired cardiac sympathovagal balance in healthy subjects. These data reinforce the role of intermittent HPX in superoxide generation on neutrophils, which may lead to an impairment in peripheral vascular resistance.

Multianalyte Microphysiometry of Macrophage Responses to Phorbol Myristate Acetate, Lipopolysaccharide, and Lipoarabinomannan

This study examined the hypothesis that mycobacterial antigens generate different metabolic responses in macrophages as compared to gram-negative effectors and macrophage activators. The metabolic activation of macrophages by PMA is a useful tool for studying virulent agents and can be compared to other effectors. While phorbol myristate acetate (PMA) is commonly used to study macrophage activation, the concentration used to create this physiological response varies. The response of RAW-264.7 macrophages is concentration-dependent, where the metabolic response to high concentrations of PMA decreases suggesting deactivation. The gram-negative effector, lipopolysaccharide (LPS), was seen to promote glucose and oxygen production which were used to produce a delayed onset of oxidative burst. Pre-incubation with interferon-γ (IFN-γ) increased the effect on cell metabolism, where the synergistic effects of IFN-γ and LPS immediately initiated oxidative burst. These studies exhibited a stark contrast with lipoarabinomannan (LAM), an antigenic glycolipid component associated with the bacterial genus Mycobacterium. The presence of LAM effectively inhibits any metabolic response preventing consumption of glucose and oxygen for the promotion of oxidative burst and to ensure pathogenic proliferation. This study demonstrates for the first time the immediate inhibitory metabolic effects LAM has on macrophages, suggesting implications for future intervention studies with Mycobacterium tuberculosis.

Endurance training restores peritoneal macrophage function in post-MI congestive heart failure rats

Congestive heart failure (CHF) induces a state of immune activation, and peritoneal macrophages (Mφs) may play an important role in the development and progression of one such condition. Moderate endurance training modulates peritoneal Mφ function. We evaluated the effect of endurance training on different stages of the phagocytic process and in the production of interleukin-6 (IL-6), interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) after LPS stimulation. Either ligation of the left coronary artery or Sham operations were performed in adult Wistar rats. After 4 wk, control (Sham operated) and MI (ligation of the left coronary artery) animals were randomly assigned to either a sedentary (Sham-operated sedentary, n = 7 and MI sedentary, n = 10) or a trained group (Sham-operated trained, n = 8 and MI trained, n = 8). Trained rats ran on a treadmill (0% grade at 13–20 m/min) for 60 min/day, 5 days/wk, for 8–10 wk, whereas sedentary rats had only limited activity. Training increased maximal oxygen uptake normalized for body weight (ml·kg−1·min−1), as well as skeletal muscle citrate synthase maximal activity, when compared with sedentary groups. The resident and total cell number, the chemotaxis index, and the production of TNF-α stimulated by LPS were significantly higher in the MI sedentary group when compared with the Sham sedentary group. Moderate endurance training reversed these alterations promoted by post-MI. These results demonstrate that moderate intensity exercise training modulates peritoneal Mφ function and induces beneficial metabolic effects in rats with post-MI CHF.

Role of central mu-opioid receptors in the modulation of nitric oxide production by splenocytes

Previous studies have shown that administration of morphine results in alterations of splenic macrophage nitric oxide production. The present studies were conducted to determine the subtype of opioid receptor involved in the modulation of macrophage nitric oxide production. Moreover, the present work was directed at determining whether nitric oxide production is regulated through opioid receptors in the central nervous system (CNS) or via opioid receptors found directly on splenocytes. The study shows that intracerebroventricular (i.c.v.) administration of the mu-selective opioid agonist, DAMGO, to rats dose-dependently increases the production of nitric oxide by splenocytes stimulated with toxic shock syndrome toxin (TSST-1). The effect of DAMGO is blocked by prior i.c.v. administration of N-methylnaltrexone. In contrast, i.c.v. administration of the kappa-selective agonist, U69,593, and the delta-selective agonist, DPDPE, have no significant effect on the production of nitric oxide. Furthermore, the in vitro administration of DAMGO, DPDPE, or U69,593 to splenocytes cultures does not significantly alter the production of nitric oxide by splenocytes. In addition, the present work shows that elevation of nitric oxide production by i.c.v. administration of DAMGO produces functional changes in splenic lymphocytes. Collectively, these results indicate that mu-opioid receptors within the CNS are involved in the regulation of splenic nitric oxide production.

Changes in the TBARs content and superoxide dismutase, catalase and glutathione peroxidase activities in the lymphoid organs and skeletal muscles of adrenodemedullated rats

Thiobarbituric acid reactant substances (TBARs) content, and the activities of glucose-6-phosphate dehydrogenase (G6PDh), citrate synthase (CS), Cu/Zn- and Mn-superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPX) were measured in the lymphoid organs (thymus, spleen, and mesenteric lymph nodes (MLN)) and skeletal muscles (gastrocnemius and soleus) of adrenodemedullated (ADM) rats. The results were compared with those obtained for sham-operated rats. TBARs content was reduced by adrenodemedullation in the lymphoid organs (MLN) (28%), thymus (40%) and spleen (42%)) and gastrocnemius muscle (67%). G6PDh activity was enhanced in the MLN (69%) and reduced in the spleen (28%) and soleus muscle (75%). CS activity was reduced in all tissues (MLN (75%), spleen (71%), gastrocnemius (61%) and soleus (43%)), except in the thymus which displayed an increment of 56%. Cu/Zn-SOD activity was increased in the MLN (126%), thymus (223%), spleen (80%) and gastrocnemius muscle (360%) and was reduced in the soleus muscle (31%). Mn-SOD activity was decreased in the MLN (67%) and spleen (26%) and increased in the thymus (142%), whereas catalase activity was reduced in the MLN (76%), thymus (54%) and soleus muscle (47%). It is particularly noteworthy that in ADM rats the activity of glutathione peroxidase was not detectable by the method used. These data are consistent with the possibility that epinephrine might play a role in the oxidative stress of the lymphoid organs. Whether this fact represents an important mechanism for the establishment of impaired immune function during stress remains to be elucidated.

Hormonal regulation of superoxide dismutase, catalase, and glutathione peroxidase activities in rat macrophages

This study examined the effects of glycocorticoids, insulin, thyroxine, and epinephrine upon the activities of CuZn- and Mn-superoxide dismutases (SOD), catalase, and glutathione peroxidase (GPX) and upon hydrogen peroxide production in rat macrophages obtained from the intraperitoneal cavity. The experiments were performed in vivo under conditions causing hormonal dysfunctions: adrenal demedullation, dexamethasone treatment, thyroidectomy, administration of L-tri-iodothyronine (T3) and L-thyroxine (T4), and diabetes. Macrophages were also cultured for 24 hr in the presence of dexamethasone, thyroid hormones, and insulin as to evaluate possible interferences caused in vivo by changes in other hormones. The results indicated that these hormones do control the activities of the antioxidant enzymes and hydrogen peroxide production both in vivo and in vitro. Insulin increased the activities of CuZn-SOD, catalase, and GPX and reduced that of Mn-SOD. Thyroid hormones raised the activities of CuZn- and Mn-SOD and decreased that of GPX, whereas glucocorticoids reduced both Mn-SOD and GPX. The removal of the adrenal medulla caused a decrease of Mn-SOD and GPX activities in the macrophages. Hydrogen peroxide production was increased by insulin and reduced by thyroid hormones and glucocorticoids. The changes in antioxidant enzyme activities caused by these hormones in macrophages may indicate important mechanisms for the establishment of impaired immune function in endocrine pathologies.

Effect of adrenaline and phorbol myristate acetate or bacterial lipopolysaccharide on stimulation of pathways of macrophage glucose, glutamine and O2 metabolism. Evidence for cyclic AMP-dependent protein kinase mediated inhibition of glucose-6-phosphate dehydrogenase and activation of NADP+-dependent 'malic' enzyme

Adrenaline has recently been shown to stimulate both glucose metabolism and H2O2 release by macrophages but the activity of the key pentose phosphate pathway enzyme, glucose-6-phosphate dehydrogenase (which generates the NADPH crucial for the reduction of molecular oxygen), was reduced under these conditions [Costa Rosa, Safi, Cury and Curi (1992) Biochem. Pharmacol. 44, 2235-2241]. We report here that adrenaline activates another NADPH-producing enzyme, NADP(+)-dependent 'malic' enzyme, while also inhibiting glucose-6-phosphate dehydrogenase, via cyclic AMP-dependent protein kinase (PKA) activation. Regulation of glucose-6-phosphate dehydrogenase activity by PKA has not been reported elsewhere. The sparing of some glucose from pentose phosphate pathway consumption may be important in the provision of glycerol 3-phosphate which in the macrophage may be required for new phospholipid synthesis. Glutamine oxidation was also stimulated by adrenaline thus providing increased substrate (malate) for NADP(+)-dependent 'malic' enzyme and therefore shifting some of the burden of NADPH production from glucose to glutamine metabolism. We also report a novel synergistic effect of adrenaline and some bacterial products and/or gamma-interferon in stimulating secretory and metabolic pathways in macrophages which may be a part of a larger network of signals that lead to enhanced macrophage activity.