Stimulators of AMP-activated protein kinase inhibit the respiratory burst in human neutrophils

The CAMKK/AMPK Pathway Contributes to Besnoitia besnoiti-Induced NETosis in Bovine Polymorphonuclear Neutrophils

Besnoitia besnoiti is an obligate intracellular apicomplexan parasite and the causal agent of bovine besnoitiosis. Bovine besnoitiosis has a considerable economic impact in Africa and Asia due to reduced milk production, abortions, and bull infertility. In Europe, bovine besnoitiosis is classified as an emerging disease. Polymorphonuclear neutrophils (PMN) are one of the most abundant leukocytes in cattle blood and amongst the first immunological responders toward invading pathogens. In the case of B. besnoiti, bovine PMN produce reactive oxygen species (ROS), release neutrophil extracellular traps (NETs), and show increased autophagic activities upon exposure to tachyzoite stages. In that context, the general processes of NETosis and autophagy were previously reported as associated with AMP-activated protein kinase (AMPK) activation. Here, we study the role of AMPK in B. besnoiti tachyzoite-induced NET formation, thereby expanding the analysis to both upstream proteins, such as the calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK), and downstream signaling and effector molecules, such as the autophagy-related proteins ULK-1 and Beclin-1. Current data revealed early AMPK activation (<30 min) in both B. besnoiti-exposed and AMPK activator (AICAR)-treated bovine PMN. This finding correlated with upstream responses on the level of CAMKK activation. Moreover, these reactions were accompanied by an augmented autophagic activity, as represented by enhanced expression of ULK-1 but not of Beclin-1. Referring to neutrophil effector functions, AICAR treatments induced both AMPK phosphorylation and NET formation, without affecting cell viability. In B. besnoiti tachyzoite-exposed PMN, AICAR treatments failed to affect oxidative responses, but led to enhanced NET formation, thereby indicating that AMPK and autophagic activation synergize with B. besnoiti-driven NETosis.

Adenosine 5'-monophosphate-activated protein kinase (AMPK) negatively regulates the immunity and resistance to Vibrio alginolyticus of white shrimp, Penaeus vannamei

Shrimp immunology is vital in establishing prophylactic and therapeutic strategies for controlling pathological problems that threaten shrimp production. Apart from dietary treatments, the adenosine 5'-monophosphate-activated protein kinase (AMPK), an important regulatory enzyme that restores cellular energy balance during metabolic and physiological stress, is known to have therapeutic potential to improve shrimp's defense mechanism. Despite this, studies targeting the AMPK pathway in shrimp exposed to stressful conditions are vastly limited. In this study, AMPK was knocked down to assess the immunological changes and white shrimp, Penaeus vannamei resistance to Vibrio alginolyticus infection. Shrimps were injected individually and simultaneously with dsRNA targeting specific genes such as AMPK, Rheb, and TOR, after which the hepatopancreas was analyzed for the different gene expressions. The gene expressions of AMPK, Rheb, and TOR were effectively suppressed after being treated with dsRNAs. The Western blot analysis further confirmed a reduction in the protein concentration of AMPK and Rheb in the hepatopancreas. The suppression of AMPK gene led to a robust increase in the shrimp's resistance to V. alginolyticus, whereas the activation of AMPK by metformin decreased the shrimp's disease resistance. Among the mTOR downstream targets, the HIF-1α expression in shrimp treated with dsAMPK significantly increased at 48 h but returned to normal levels when shrimp were treated with dsAMPK and either dsRheb or dsTOR. Immune responses such as respiratory burst, lysozyme activity, and phagocytic activity increased, while superoxide dismutase activity decreased following the knockdown of the AMPK gene compared to the control group. However, co-injection with dsAMPK and dsTOR or dsRheb restored immune responses to normal levels. Collectively, these results demonstrate that the inactivation of AMPK may ameliorate shrimp's innate immune response to recognize and defend against pathogens via the AMPK/mTOR1 pathway.

Mechanisms underlying unidirectional laminar shear stress-mediated Nrf2 activation in endothelial cells: Amplification of low shear stress signaling by primary cilia

Endothelial cells are sensitive to mechanical stress and respond differently to oscillatory flow versus unidirectional flow. This review highlights the mechanisms by which a wide range of unidirectional laminar shear stress induces activation of the redox sensitive antioxidant transcription factor nuclear factor-E2-related factor 2 (Nrf2) in cultured endothelial cells. We propose that fibroblast growth factor-2 (FGF-2), brain-derived neurotrophic factor (BDNF) and 15-Deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) are potential Nrf2 activators induced by laminar shear stress. Shear stress-dependent secretion of FGF-2 and its receptor-mediated signaling is tightly controlled, requiring neutrophil elastase released by shear stress, αvβ3 integrin and the cell surface glycocalyx. We speculate that primary cilia respond to low laminar shear stress (<10 dyn/cm2), resulting in secretion of insulin-like growth factor 1 (IGF-1), which facilitates αvβ3 integrin-dependent FGF-2 secretion. Shear stress induces generation of heparan-binding epidermal growth factor-like growth factor (HB-EGF), which contributes to FGF-2 secretion and gene expression. Furthermore, HB-EGF signaling modulates FGF-2-mediated NADPH oxidase 1 activation that favors casein kinase 2 (CK2)-mediated phosphorylation/activation of Nrf2 associated with caveolin 1 in caveolae. Higher shear stress (>15 dyn/cm2) induces vesicular exocytosis of BDNF from endothelial cells, and we propose that BDNF via the p75NTR receptor could induce CK2-mediated Nrf2 activation. Unidirectional laminar shear stress upregulates gene expression of FGF-2 and BDNF and generation of 15d-PGJ2, which cooperate in sustaining Nrf2 activation to protect endothelial cells against oxidative damage.

BAM15, a Mitochondrial Uncoupling Agent, Attenuates Inflammation in the LPS Injection Mouse Model: An Adjunctive Anti-Inflammation on Macrophages and Hepatocytes

Controlof immune responses through the immunometabolism interference is interesting for sepsis treatment. Then, expression of immunometabolism-associated genes and BAM15, a mitochondrial uncoupling agent, was explored in a proinflammatory model using lipopolysaccharide (LPS) injection. Accordingly, the decreased expression of mitochondrial uncoupling proteins was demonstrated by transcriptomic analysis on metabolism-associated genes in macrophages (RAW246.7) and by polymerase chain reaction in LPS-stimulated RAW246.7 and hepatocytes (Hepa 1-6). Pretreatment with BAM15 at 24 h prior to LPS in macrophages attenuated supernatant inflammatory cytokines (IL-6, TNF-α, and IL-10), downregulated genes of proinflammatory M1 polarization (iNOS and IL-1β), upregulated anti-inflammatory M2 polarization (Arg1 and FIZZ), and decreased cell energy status (extracellular flux analysis and ATP production). Likewise, BAM15 decreased expression of proinflammatory genes (IL-6, TNF-α, IL-10, and iNOS) and reduced cell energy in hepatocytes. In LPS-administered mice, BAM15 attenuated serum cytokines, organ injury (liver enzymes and serum creatinine), and tissue cytokines (livers and kidneys), in part, through the enhanced phosphorylated αAMPK, a sensor of ATP depletion with anti-inflammatory property, in the liver, and reduced inflammatory monocytes/macrophages (Ly6C +ve, CD11b +ve) in the liver as detected by Western blot and flow cytometry, respectively. In conclusion, a proof of concept for inflammation attenuation of BAM15 through metabolic interference-induced anti-inflammation on macrophages and hepatocytes was demonstrated as a new strategy of anti-inflammation in sepsis.

Candida Administration in Bilateral Nephrectomy Mice Elevates Serum (1→3)-β-D-glucan That Enhances Systemic Inflammation Through Energy Augmentation in Macrophages

Systemic inflammation, from gut translocation of organismal molecules, might worsen uremic complications in acute kidney injury (AKI). The monitoring of gut permeability integrity and/or organismal molecules in AKI might be clinically beneficial. Due to the less prominence of Candida albicans in human intestine compared with mouse gut, C. albicans were orally administered in bilateral nephrectomy (BiN) mice. Gut dysbiosis, using microbiome analysis, and gut permeability defect (gut leakage), which was determined by fluorescein isothiocyanate-dextran and intestinal tight-junction immunofluorescent staining, in mice with BiN-Candida was more severe than BiN without Candida. Additionally, profound gut leakage in BiN-Candida also resulted in gut translocation of lipopolysaccharide (LPS) and (1→3)-β-D-glucan (BG), the organismal components from gut contents, that induced more severe systemic inflammation than BiN without Candida. The co-presentation of LPS and BG in mouse serum enhanced inflammatory responses. As such, LPS with Whole Glucan Particle (WGP, a representative BG) induced more severe macrophage responses than LPS alone as determined by supernatant cytokines and gene expression of downstream signals (NFκB, Malt-1 and Syk). Meanwhile, WGP alone did not induced the responses. In parallel, WGP (with or without LPS), but not LPS alone, accelerated macrophage ATP production (extracellular flux analysis) through the upregulation of genes in mitochondria and glycolysis pathway (using RNA sequencing analysis), without the induction of cell activities. These data indicated a WGP pre-conditioning effect on cell energy augmentation. In conclusion, Candida in BiN mice accelerated gut translocation of BG that augmented cell energy status and enhanced pro-inflammatory macrophage responses. Hence, gut fungi and BG were associated with the enhanced systemic inflammation in acute uremia.

AMPK, metabolism, and vascular function

Adenosine monophosphate-activated protein kinase (AMPK) is a cellular energy sensor activated during energy stress that plays a key role in maintaining energy homeostasis. This ubiquitous signaling pathway has been implicated in multiple functions including mitochondrial biogenesis, redox regulation, cell growth and proliferation, cell autophagy and inflammation. The protective role of AMPK in cardiovascular function and the involvement of dysfunctional AMPK in the pathogenesis of cardiovascular disease have been highlighted in recent years. In this review, we summarize and discuss the role of AMPK in the regulation of blood flow in response to metabolic demand and the basis of the AMPK physiological anticontractile, antioxidant, anti-inflammatory, and antiatherogenic actions in the vascular system. Investigations by others and us have demonstrated the key role of vascular AMPK in the regulation of endothelial function, redox homeostasis, and inflammation, in addition to its protective role in the hypoxia and ischemia/reperfusion injury. The pathophysiological implications of AMPK involvement in vascular function with regard to the vascular complications of metabolic disease and the therapeutic potential of AMPK activators are also discussed.

AMP-activated protein kinase: A remarkable contributor to preserve a healthy heart against ROS injury

Heart failure is one of the leading causes of death and disability worldwide. Left ventricle remodeling, fibrosis, and ischemia/reperfusion injury all contribute to the deterioration of cardiac function and predispose to the onset of heart failure. Adenosine monophosphate-activated protein kinase (AMPK) is the universally recognized energy sensor which responds to low ATP levels and restores cellular metabolism. AMPK activation controls numerous cellular processes and, in the heart, it plays a pivotal role in preventing onset and progression of disease. Excessive reactive oxygen species (ROS) generation, known as oxidative stress, can activate AMPK, conferring an additional role of AMPK as a redox-sensor. In this review, we discuss recent insights into the crosstalk between ROS and AMPK. We describe the molecular mechanisms by which ROS activate AMPK and how AMPK signaling can further prevent heart failure progression. Ultimately, we review the potential therapeutic approaches to target AMPK for the treatment of cardiovascular disease and prevention of heart failure.

Activation of the AMP-related kinase (AMPK) induces renal vasodilatation and downregulates Nox-derived reactive oxygen species (ROS) generation

AMP-activated protein kinase (AMPK) is a cellular energy sensor activated during energy stress to stimulate ATP production pathways and restore homeostasis. AMPK is widely expressed in the kidney and involved in mitochondrial protection and biogenesis upon acute renal ischemia, AMPK activity being blunted in metabolic disease-associated kidney disease. Since little is known about AMPK in the regulation of renal blood flow, the present study aimed to assess the role of AMPK in renal vascular function. Functional responses to the selective AMPK activator A769662 were assessed in intrarenal small arteries isolated from the kidney of renal tumour patients and Wistar rats and mounted in microvascular myographs to perform simultaneous measurements of intracellular calcium [Ca²⁺]_i and tension. Superoxide (O₂^.-) and hydrogen peroxide (H₂O₂) production were measured by chemiluminescence and fluorescence and protein expression by Western blot. Activation of AMPK with A769662 increased AMPK_α phosphorylation at Thr-172 and induced potent relaxations compared to AICAR in isolated human and rat intrarenal arteries, through both endothelium-dependent mechanisms involving nitric oxide (NO) and intermediate-conductance calcium-activated potassium (IK_Ca) channels, as well as activation of ATP-sensitive (K_ATP) channels and sarcoplasmic reticulum Ca²⁺-ATP_ase (SERCA) in vascular smooth muscle (VSM). Furthermore, AMPK activator reduced NADPH oxidase 4 (Nox4) and Nox2-derived reactive oxygen species (ROS) production. These results demonstrate that A769662 has potent vasodilator and antioxidant effects in intrarenal arteries. The benefits of AMPK activation in rat kidney are reproduced in human arteries and therefore vascular AMPK activation might be a therapeutic target in the treatment of metabolic disease-associated kidney injury.

Activation of the AMP-related kinase (AMPK) induces renal vasodilatation and downregulates Nox-derived reactive oxygen species (ROS) generation

AMP-activated protein kinase (AMPK) is a cellular energy sensor activated during energy stress to stimulate ATP production pathways and restore homeostasis. AMPK is widely expressed in the kidney and involved in mitochondrial protection and biogenesis upon acute renal ischemia, AMPK activity being blunted in metabolic disease-associated kidney disease. Since little is known about AMPK in the regulation of renal blood flow, the present study aimed to assess the role of AMPK in renal vascular function. Functional responses to the selective AMPK activator A769662 were assessed in intrarenal small arteries isolated from the kidney of renal tumour patients and Wistar rats and mounted in microvascular myographs to perform simultaneous measurements of intracellular calcium [Ca²⁺]_i and tension. Superoxide (O₂^.-) and hydrogen peroxide (H₂O₂) production were measured by chemiluminescence and fluorescence and protein expression by Western blot. Activation of AMPK with A769662 increased AMPK_α phosphorylation at Thr-172 and induced potent relaxations compared to AICAR in isolated human and rat intrarenal arteries, through both endothelium-dependent mechanisms involving nitric oxide (NO) and intermediate-conductance calcium-activated potassium (IK_Ca) channels, as well as activation of ATP-sensitive (K_ATP) channels and sarcoplasmic reticulum Ca²⁺-ATP_ase (SERCA) in vascular smooth muscle (VSM). Furthermore, AMPK activator reduced NADPH oxidase 4 (Nox4) and Nox2-derived reactive oxygen species (ROS) production. These results demonstrate that A769662 has potent vasodilator and antioxidant effects in intrarenal arteries. The benefits of AMPK activation in rat kidney are reproduced in human arteries and therefore vascular AMPK activation might be a therapeutic target in the treatment of metabolic disease-associated kidney injury.

AMPK is essential for IL-10 expression and for maintaining balance between inflammatory and cytoprotective signaling

BACKGROUND

AMP-activated protein kinase (AMPK) exerts its anti-inflammatory effects by suppressing redox-sensitive nuclear factor kappa B (NF-κB) and pro-inflammatory cytokines including TNF-α. However, it is unclear whether AMPK regulates anti-inflammatory cytokine expressions in the presence of oxidative stress-induced inflammation. We sought to elucidate the mechanisms whereby AMPK regulates inflammatory cytokine expressions under NADPH oxidase (NOX)-induced oxidative stress.

METHODS

HT-29 human colonic epithelial cells transfected with AMPKα shRNA and mouse models with AMPKα knocked out in epithelial cells (AMPKα^fl/fl-Vil-Cre) or macrophages (AMPKα^fl/fl-Lyz2-Cre) were used to examine the effects of AMPK and NOX on signaling pathways and cytokine expressions.

RESULTS

In HT-29 cells, 5-hydroxytryptamine (5-HT)-induced NOX activity was enhanced by AMPKα silencing, and resulted in inflammatory cell death. AMPKα deletion specific for colon epithelial cells (AMPKα^fl/fl-Vil-Cre) or macrophages (AMPKα^fl/fl-Lyz2-Cre) intensified 5-HT- or dextran sulfate sodium (DSS)-induced upregulations of NOX2, TNF-α, and IL-6, but completely abolished basal and 5-HT- or DSS-induced upregulation of IL-10 in colon epithelium. Furthermore, 5-HT- and DSS-induced changes were accompanied by marked upregulations of increased inflammatory signaling pathways linked to NF-κB, AP-1, and STAT3 transcription factors, and to GATA, a cell fate-directing signaling. In addition, AMPKα deletion significantly fortified 5-HT- or DSS-induced downregulations of cytoprotective signaling pathways (Nrf2, HIF-1α, and KLF4).

CONCLUSION

Basal AMPKα maintains an anti-inflammatory state by inhibiting NOX, balancing pro-/anti-inflammatory signaling pathways, and directing IL-10 production. When these regulatory roles of AMPK are diminished by oxidative stress, colon epithelium undergoes inflammation despite IL-10 production.

Simultaneous and Positively Correlated NET Formation and Autophagy in Besnoitia besnoiti Tachyzoite-Exposed Bovine Polymorphonuclear Neutrophils

Given that B. besnoiti tachyzoites infect host endothelial cells of vessels in vivo, they become potential targets for professional phagocytes [e.g., polymorphonuclear neutrophils (PMN)] when in search for adequate host cells or in case of host cell lysis. It was recently reported that B. besnoiti-tachyzoites can efficiently be trapped by neutrophil extracellular traps (NETs) released by bovine PMN. So far, the potential role of autophagy in parasite-triggered NET formation is unclear. Thus, we here analyzed autophagosome formation and activation of AMP-activated protein kinase α (AMPKα) in potentially NET-forming innate leukocytes being exposed to B. besnoiti tachyzoites. Blood was collected from healthy adult dairy cows, and bovine PMN were isolated via density gradient centrifugation. Scanning electron microscopy confirmed PMN to undergo NET formation upon contact with B. besnoiti tachyzoites. Nuclear area expansion (NAE) analysis and cell-free and anchored NETs quantification were performed in B. besnoiti-induced NET formation. Interestingly, tachyzoites of B. besnoiti additionally induced LC3B-related autophagosome formation in parallel to NET formation in bovine PMN. Notably, both rapamycin- and wortmannin-treatments failed to influence B. besnoiti-triggered NET formation and autophagosome formation. Also, isolated NETs fail to induce autophagy suggesting independence between both cellular processes. Finally, enhanced phosphorylation of AMP activated kinase α (AMPKα), a key regulator molecule of autophagy, was observed within the first minutes of interaction in tachyzoite-exposed PMN thereby emphasizing that B. besnoiti-triggered NET formation indeed occurs in parallel to autophagy.

DNA methylation/hydroxymethylation regulate gene expression and alternative splicing during terminal granulopoiesis

Aim: To determine whether epigenetic modifications of DNA regulate gene expression and alternative splicing during terminal granulopoiesis. Materials & methods: Using whole genome bisulfite sequencing, reduced representation hydroxymethylation profiling and mRNA sequencing, we compare changes in DNA methylation, DNA hydroxymethylation, gene expression and alternative splicing in mouse promyelocytes and granulocytes. Results & conclusion: We show reduced DNA methylation at the promoters and enhancers of key granulopoiesis genes, indicating a regulatory role in the activation of lineage-specific genes during differentiation. Notably, increased DNA hydroxymethylation in exons is associated with preferential inclusion of specific exons in granulocytes. Overall, DNA methylation and hydroxymethylation changes at particular genomic loci may play specific roles in gene regulation or alternative splicing during terminal granulopoiesis. Data deposition: Whole genome bisulfite sequencing of mouse promyelocytes and granulocytes: Gene Expression Omnibus (GSE85517); mRNA sequencing of mouse promyelocytes and granulocytes: Gene Expression Omnibus (GSE48307); reduced representation 5-hydroxymethylation profiling of mouse promyelocytes and granulocytes: Bioproject (PRJNA495696).

Structural basis for ADP-dependent glucokinase inhibition by 8-bromo-substituted adenosine nucleotide

In higher eukaryotes, several ATP-utilizing enzymes known as hexokinases activate glucose in the glycolysis pathway by phosphorylation to glucose 6-phosphate. In contrast to canonical hexokinases, which use ATP, ADP-dependent glucokinase (ADPGK) catalyzes noncanonical phosphorylation of glucose to glucose 6-phosphate using ADP as a phosphate donor. Initially discovered in Archaea, the human homolog of ADPGK was described only recently. ADPGK's involvement in modified bioenergetics of activated T cells has been postulated, and elevated ADPGK expression has been reported in various cancer tissues. However, the physiological role of ADPGK is still poorly understood, and effective ADPGK inhibitors still await discovery. Here, we show that 8-bromo-substituted adenosine nucleotide inhibits human ADPGK. By solving the crystal structure of archaeal ADPGK in complex with 8-bromoadenosine phosphate (8-Br-AMP) at 1.81 Å resolution, we identified the mechanism of inhibition. We observed that 8-Br-AMP is a competitive inhibitor of ADPGK and that the bromine substitution induces marked structural changes within the protein's active site by engaging crucial catalytic residues. The results obtained using the Jurkat model of activated human T cells suggest its moderate activity in a cellular setting. We propose that our structural insights provide a critical basis for rational development of novel ADPGK inhibitors.

An in vitro comparative study of the antioxidant activity and SIRT1 modulation of natural compounds

Oxidative stress arises from an imbalance between the production of free radicals and antioxidant defences. Several studies have suggested that dietary antioxidants (such as polyphenols and berberine) may counteract oxidative stress through the involvement of the Sirtuin 1/Adenosine Monophosphate-Activated Protein Kinase (SIRT1/AMPK) pathway. The aim of this study was to evaluate the direct and specific antioxidant activity of some natural compounds, as well as their ability to modulate the expression of SIRT1 and the activation of AMPK. Quercetin, tyrosol, ferulic acid, catechin, berberine and curcumin were evaluated for their specific and direct antioxidant activity with TOSC assay. Their ability to modulate SIRT1 and AMPK was assessed by immunoblotting assay, while their cytotoxicity by CellTiter-Blue Cell Viability Assay. No statistically significant decrease (p > 0.05) in the number of viable cells was found upon challenging with the natural compounds. Quercetin exhibited the highest antioxidant activity against peroxyl radical and peroxinitrate derivates, while curcumin showed the best anti-hydroxyl activity with respect to the other compounds and, most importantly, respect to the reference antioxidants. Finally, all the tested compounds significantly increased the SIRT1 expression and the activation of AMPK. Our results clearly disclose the specific antioxidant activity of these natural compounds and their ability to increase SIRT1 expression and AMPK activation.

Adiponectin protects against lung ischemia-reperfusion injury in rats with type 2 diabetes mellitus

Adiponectin (APN) has been associated with the pathogenesis of acute brain, liver and heart injury. However, the role of APN in lung ischemia-reperfusion injury (LIRI) in diabetes mellitus remains unclear. To investigate this, the present study evaluated the effects of APN on lung dysfunction and pathological alterations in rats with type 2 diabetes mellitus via lung ischemia/reperfusion (I/R). The lung‑protective effects of APN globular domain (gAPN) in rats with type 2 diabetes mellitus were also investigated by measuring the oxygenation index, inflammatory cytokines, lung edema, histopathology, oxidative stress, apoptosis and the protein expression levels of phosphorylated 5'adenosine monophosphate‑activated protein kinase (p‑AMPK), endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS). The results of the present study demonstrated that the diabetes mellitus rats + I/R (DIR) group exhibited greater concentrations of tumor necrosis factor‑α and interleukin‑6, and increases in the wet‑weight to dry‑weight ratio, lung injury score, oxidative stress and cellular apoptosis. These effects were accompanied by lower pulmonary oxygenation compared with the normal rat + I/R (NIR) group (P<0.05). Additionally, all of these alterations were attenuated in the NIR + gAPN and DIR + gAPN groups compared with in the NIR and DIR groups, respectively. In the DIR group, the expression levels of p‑AMPK/AMPK and eNOS were significantly downregulated, and the levels of iNOS were upregulated, compared with those of the NIR group. Treatment with APN activated AMPK, increased eNOS expression and attenuated iNOS expression. The results of the present study demonstrated that APN exerted protective effects against LIRI via its anti‑inflammatory, antioxidative stress and anti‑apoptotic activities. These protective effects of APN were eliminated in rats with type 2 diabetes mellitus, in which LIRI was exacerbated. The present study indicated that APN may be a potential therapeutic agent for LIRI in type 2 diabetes mellitus.

Fatty Acid Oxidation Compensates for Lipopolysaccharide-Induced Warburg Effect in Glucose-Deprived Monocytes

Monocytes enter sites of microbial or sterile inflammation as the first line of defense of the immune system and initiate pro-inflammatory effector mechanisms. We show that activation with bacterial lipopolysaccharide (LPS) induces them to undergo a metabolic shift toward aerobic glycolysis, similar to the Warburg effect observed in cancer cells. At sites of inflammation, however, glucose concentrations are often drastically decreased, which prompted us to study monocyte function under conditions of glucose deprivation and abrogated Warburg effect. Experiments using the Seahorse Extracellular Flux Analyzer revealed that limited glucose supply shifts monocyte metabolism toward oxidative phosphorylation, fueled largely by fatty acid oxidation at the expense of lipid droplets. While this metabolic state appears to provide sufficient energy to sustain functional properties like cytokine secretion, migration, and phagocytosis, it cannot prevent a rise in the AMP/ATP ratio and a decreased respiratory burst. The molecular trigger mediating the metabolic shift and the functional consequences is activation of AMP-activated protein kinase (AMPK). Taken together, our results indicate that monocytes are sufficiently metabolically flexible to perform pro-inflammatory functions at sites of inflammation despite glucose deprivation and inhibition of the LPS-induced Warburg effect. AMPK seems to play a pivotal role in orchestrating these processes during glucose deprivation in monocytes.

Quercetin is a potent anti-atherosclerotic compound by activation of SIRT1 signaling under oxLDL stimulation

SCOPE

Atherosclerosis is believed to be an independent predictor of cardiovascular diseases. A growing body of evidence suggests that quercetin is a potent antioxidant and anti-inflammatory compound. The molecular mechanisms underlying its protective effects against oxidative stress in human endothelial cells remain unclear. This study was designed to confirm the hypothesis that quercetin inhibits oxidized LDL (oxLDL) induced endothelial oxidative damage by activating sirtuin 1 (SIRT1) and to explore the role of adenosine monophosphate activated protein kinase (AMPK), which is a negative regulator of Nicotinamide adenine dinucleotide phosphate-oxidase (NADPH oxidase) and free radicals.

METHODS AND RESULTS

Human umbilical vein endothelial cells were treated with oxLDL with or without quercetin pretreatment. We found that quercetin pretreatment increased SIRT1 mRNA expression. In fact, quercetin protected against oxLDL-impaired SIRT1 and AMPK activities and reduced oxLDL-activated NOX2 and NOX4. However, silencing SIRT1 and AMPK diminished the protective function of quercetin against oxidative injuries. The results also indicated that oxLDL suppressed AKT/endothelial NO synthase, impaired mitochondrial dysfunction, and enhanced reactive oxygen species formation, activating the Nuclear Factor Kappa B (NF-κB) pathway.

CONCLUSION

These results provide new insight regarding the possible molecular mechanisms of quercetin. Quercetin suppresses oxLDL-induced endothelial oxidative injuries by activating SIRT1 and modulating the AMPK/NADPH oxidase/AKT/endothelial NO synthase signaling pathway.

In adenosine A2B knockouts acute treatment with inorganic nitrate improves glucose disposal, oxidative stress, and AMPK signaling in the liver

Rationale: Accumulating studies suggest that nitric oxide (NO) deficiency and oxidative stress are central pathological mechanisms in type 2 diabetes (T2D). Recent findings demonstrate therapeutic effects by boosting the nitrate-nitrite-NO pathway, which is an alternative pathway for NO formation. This study aimed at investigating the acute effects of inorganic nitrate on glucose and insulin signaling in adenosine A_2B receptor knockout mice (A^−/−_2B), a genetic mouse model of impaired metabolic regulation.

Methods: Acute effects of nitrate treatment were investigated in aged wild-type (WT) and A^−/−_2B mice. One hour after injection with nitrate (0.1 mmol/kg, i.p.) or placebo, metabolic regulation was evaluated by intraperitoneal glucose and insulin tolerance tests. NADPH oxidase-mediated superoxide production and AMPK phosphorylation were measured in livers obtained from non-treated or glucose-treated mice, with or without prior nitrate injection. Plasma was used to determine insulin resistance (HOMA-IR) and NO signaling.

Results: A^−/−_2B displayed increased body weight, reduced glucose clearance, and attenuated overall insulin responses compared with age-matched WT mice. Nitrate treatment increased circulating levels of nitrate, nitrite and cGMP in the A^−/−_2B, and improved glucose clearance. In WT mice, however, nitrate treatment did not influence glucose clearance. HOMA-IR increased following glucose injection in the A^−/−_2B, but remained at basal levels in mice pretreated with nitrate. NADPH oxidase activity in livers from A^−/−_2B, but not WT mice, was reduced by nitrate treatment. Livers from A^−/−_2B displayed reduced AMPK phosphorylation compared with WT mice, and this was increased by nitrate treatment. Finally, injection with the anti-diabetic agent metformin induced similar therapeutic effects in the A^−/−_2B as observed with nitrate.

Conclusion: The A^−/−_2B mouse is a genetic mouse model of metabolic syndrome. Acute treatment with nitrate improved the metabolic profile in it, at least partly via reduction in oxidative stress and improved AMPK signaling in the liver.

The hypotensive effect of acute and chronic AMP-activated protein kinase activation in normal and hyperlipidemic mice

AMP-activated protein kinase (AMPK) is present in the arterial wall and is activated in response to cellular stressors that raise AMP relative to ADP/ATP. Activation of AMPK in vivo lowers blood pressure but the influence of hyperlipidemia on this response has not been studied. ApoE^−/− mice on high fat diet for 6 weeks and age-matched controls were treated with the AMPK activator, AICAR daily for two weeks. Under anesthesia, the carotid artery was cannulated for blood pressure measurements. Aortic tissue was removed for in vitro functional experiments and AMPK activity was measured in artery homogenates by Western blotting. ApoE^−/− mice had significantly raised mean arterial pressure; chronic AICAR treatment normalized this but had no effect in normolipidemic mice, whereas acute administration of AICAR lowered mean arterial pressure in both groups. Chronic AICAR treatment increased phosphorylation of AMPK and its downstream target acetyl-CoA carboxylase in normolipidemic but not ApoE^−/− mice. In aortic rings, AMPK activation induced vasodilation and an anticontractile effect, which was attenuated in ApoE^−/− mice. This study demonstrates that hyperlipidemia dysregulates the AMPK pathway in the arterial wall but this effect can be reversed by AMPK activation, possibly through improving vessel compliance.

NOX1 to NOX2 switch deactivates AMPK and induces invasive phenotype in colon cancer cells through overexpression of MMP-7

Background

Although matrix metalloproteinase (MMP)-7 expression is correlated with increased metastatic potential in human colon cancer cells, the underlying molecular mechanism of invasive phenotype remains unknown. In the current study, we investigated the regulatory effects of membrane NADPH oxidase (NOX) and AMP activated protein kinase (AMPK) on MMP-7 expression and invasive phenotype change in colon cancer cells.

Methods

Production of superoxide anion was measured by lucigenin chemiluminescence assay using whole cells and protein extracts (NADPH oxidase activity), and intracellular reactive oxygen species (ROS) by fluorescence microscopy using 2’,7’-dichlorofluorescein diacetate (DCF-DA). Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting were used to measure mRNA and protein levels, respectively. siRNA transfection was used to assess involvement of genes in cancer invasion, which were identified by Matrigel transwell invasion assay. Luciferase reporter assay was performed to identify transcription factors linked to gene expression.

Results

Under basal conditions, less invasive human colon cancer cells (HT29 and Caco-2) showed low MMP-7 expression but high NOX1 expression and AMPK phosphorylation. Treatment of HT29 and Caco-2 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) induced an invasive phenotype response along with corresponding increases in ROS production and NOX2 and MMP-7 expression as well as reduced AMPK phosphorylation, which resemble basal conditions of highly invasive human colon cancer cells (SW620 and HCT116). In addition, inverse regulation between AMPK phosphorylation and NOX2 and MMP-7 expression was observed in HT29 cells treated with different concentrations of exogenous hydrogen peroxide. TPA-induced invasive phenotype in HT29 cells was abolished by treatment with Vit. E, DPI, apocynin, and NOX2 siRNA but not NOX1 siRNA, indicating NOX2-derived ROS production induced an invasive phenotype. TPA-induced induction of MMP-7 expression was suppressed by AP-1, NF-κB, and MAPK (ERK, p38, and JNK) inhibitors, whereas TPA-induced expression of NOX2 and its regulators, p47phox and p67phox, was blocked by p38 and NF-κB inhibitors.

Conclusions

Molecular switch from NOX1 to NOX2 in colon cancer cells induces ROS production and subsequently enhances MMP-7 expression by deactivating AMPK, which otherwise inhibits stimulus-induced autoregulation of ROS and NOX2 gene expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0379-0) contains supplementary material, which is available to authorized users.

Oxidative stress-induced expression of HSP70 contributes to the inhibitory effect of 15d-PGJ2 on inducible prostaglandin pathway in chondrocytes

The inhibitory effect of 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2) on proinflammatory gene expression has been extensively documented and frequently ascribed to its ability to prevent NF-κB pathway activation. We and others have previously demonstrated that it was frequently independent of the peroxisome proliferator activated receptor (PPAR)γ activation. Here, we provide evidence that induction of intracellular heat shock protein (HSP)70 by oxidative stress is an additional regulatory loop supporting the anti-inflammatory effect of 15d-PGJ2 in chondrocytes. Using real-time quantitative PCR and Western blotting, we showed that 15d-PGJ2 stimulated HSP70, but not HSP27 expression while increasing oxidative stress as measured by spectrofluorimetry and confocal spectral imaging. Using N-acetylcysteine (NAC) as an antioxidant, we demonstrated further that oxidative stress was thoroughly responsible for the increased expression of HSP70. Finally, using an HSP70 antisense strategy, we showed that the inhibitory effect of 15d-PGJ2 on IL-1-induced activation of the NF-κB pathway, COX-2 and mPGES-1 expression, and PGE2 synthesis was partly supported by HSP70. These data provide a new anti-inflammatory mechanism to support the PPARγ-independent effect of 15d-PGJ2 in chondrocyte and suggest a possible feedback regulatory loop between oxidative stress and inflammation via intracellular HSP70 up-regulation. This cross talk is consistent with 15d-PGJ2 as a putative negative regulator of the inflammatory reaction.

Nox family NADPH oxidases: Molecular mechanisms of activation

NADPH oxidases of the Nox family are important enzymatic sources of reactive oxygen species (ROS). Numerous homologue-specific mechanisms control the activity of this enzyme family involving calcium, free fatty acids, protein-protein interactions, intracellular trafficking, and posttranslational modifications such as phosphorylation, acetylation, or sumoylation. After a brief review on the classic pathways of Nox activation, this article will focus on novel mechanisms of homologue-specific activity control and on cell-specific aspects which govern Nox activity. From these findings of the recent years it must be concluded that the activity control of Nox enzymes is much more complex than anticipated. Moreover, depending on the cellular activity state, Nox enzymes are selectively activated or inactivated. The complex upstream signaling aspects of these events make the development of "intelligent" Nox inhibitors plausible, which selectively attenuate disease-related Nox-mediated ROS formation without altering physiological signaling ROS. This approach might be of relevance for Nox-mediated tissue injury in ischemia-reperfusion and inflammation and also for chronic Nox overactivation as present in cancer initiation and cardiovascular disease.

5-aminoimidazole-4-carboxamide Riboside Induces Apoptosis Through AMP-activated Protein Kinase-independent and NADPH Oxidase-dependent Pathways

It is debatable whether AMP-activated protein kinase (AMPK) activation is involved in anti-apoptotic or pro-apoptotic signaling. AICAR treatment increases AMPK-α1 phosphorylation, decreases intracellular reactive oxygen species (ROS) levels, and significantly increases Annexin V-positive cells, DNA laddering, and caspase activity in human myeloid cell. AMPK activation is therefore implicated in apoptosis. However, AMPK-α1-knockdown THP-1 cells are more sensitive to apoptosis than control THP-1 cells are, suggesting that the apoptosis is AMPK-independent. Low doses of AICAR induce cell proliferation, whereas high doses of AICAR suppress cell proliferation. Moreover, these effects are significantly correlated with the downregulation of intracellular ROS, strongly suggesting that AICAR-induced apoptosis is critically associated with the inhibition of NADPH oxidase by AICAR. Collectively, our results demonstrate that in AICAR-induced apoptosis, intracellular ROS levels are far more relevant than AMPK activation.

AMPK activation by glucagon-like peptide-1 prevents NADPH oxidase activation induced by hyperglycemia in adult cardiomyocytes

Exposure of cardiomyocytes to high glucose concentrations (HG) stimulates reactive oxygen species (ROS) production by NADPH oxidase (NOX2). NOX2 activation is triggered by enhanced glucose transport through a sodium-glucose cotransporter (SGLT) but not by a stimulation of glucose metabolism. The aim of this work was to identify potential therapeutic approaches to counteract this glucotoxicity. In cultured adult rat cardiomyocytes incubated with 21 mM glucose (HG), AMP-activated protein kinase (AMPK) activation by A769662 or phenformin nearly suppressed ROS production. Interestingly, glucagon-like peptide 1 (GLP-1), a new antidiabetic drug, concomitantly induced AMPK activation and prevented the HG-mediated ROS production (maximal effect at 100 nM). α2-AMPK, the major isoform expressed in cardiomyocytes (but not α1-AMPK), was activated in response to GLP-1. Anti-ROS properties of AMPK activators were not related to changes in glucose uptake or glycolysis. Using in situ proximity ligation assay, we demonstrated that AMPK activation prevented the HG-induced p47phox translocation to caveolae, whatever the AMPK activators used. NOX2 activation by either α-methyl-d-glucopyranoside, a glucose analog transported through SGLT, or angiotensin II was also counteracted by GLP-1. The crucial role of AMPK in limiting HG-mediated NOX2 activation was demonstrated by overexpressing a constitutively active form of α2-AMPK using adenoviral infection. This overexpression prevented NOX2 activation in response to HG, whereas GLP-1 lost its protective action in α2-AMPK-deficient mouse cardiomyocytes. Under HG, the GLP-1/AMPK pathway inhibited PKC-β2 phosphorylation, a key element mediating p47phox translocation. In conclusion, GLP-1 induces α2-AMPK activation and blocks HG-induced p47phox translocation to the plasma membrane, thereby preventing glucotoxicity.

Perivascular fat, AMP-activated protein kinase and vascular diseases

Perivascular adipose tissue (PVAT) is an active endocrine and paracrine organ that modulates vascular function, with implications for the pathophysiology of cardiovascular disease (CVD). Adipocytes and stromal cells contained within PVAT produce mediators (adipokines, cytokines, reactive oxygen species and gaseous compounds) with a range of paracrine effects modulating vascular smooth muscle cell contraction, proliferation and migration. However, the modulatory effect of PVAT on the vascular system in diseases, such as obesity, hypertension and atherosclerosis, remains poorly characterized. AMP-activated protein kinase (AMPK) regulates adipocyte metabolism, adipose biology and vascular function, and hence may be a potential therapeutic target for metabolic disorders such as type 2 diabetes mellitus (T2DM) and the vascular complications associated with obesity and T2DM. The role of AMPK in PVAT or the actions of PVAT have yet to be established, however. Activation of AMPK by pharmacological agents, such as metformin and thiazolidinediones, may modulate the activity of PVAT surrounding blood vessels and thereby contribute to their beneficial effect in cardiometabolic diseases. This review will provide a current perspective on how PVAT may influence vascular function via AMPK. We will also attempt to demonstrate how modulating AMPK activity using pharmacological agents could be exploited therapeutically to treat cardiometabolic diseases.

Human resistin promotes neutrophil proinflammatory activation and neutrophil extracellular trap formation and increases severity of acute lung injury

Although resistin was recently found to modulate insulin resistance in preclinical models of type II diabetes and obesity, recent studies also suggested that resistin has proinflammatory properties. We examined whether the human-specific variant of resistin affects neutrophil activation and the severity of LPS-induced acute lung injury. Because human and mouse resistin have distinct patterns of tissue distribution, experiments were performed using humanized resistin mice that exclusively express human resistin (hRTN(+/-)(/-)) but are deficient in mouse resistin. Enhanced production of TNF-α or MIP-2 was found in LPS-treated hRtn(+/-/-) neutrophils compared with control Rtn(-/-/-) neutrophils. Expression of human resistin inhibited the activation of AMP-activated protein kinase, a major sensor and regulator of cellular bioenergetics that also is implicated in inhibiting inflammatory activity of neutrophils and macrophages. In addition to the ability of resistin to sensitize neutrophils to LPS stimulation, human resistin enhanced neutrophil extracellular trap formation. In LPS-induced acute lung injury, humanized resistin mice demonstrated enhanced production of proinflammatory cytokines, more severe pulmonary edema, increased neutrophil extracellular trap formation, and elevated concentration of the alarmins HMGB1 and histone 3 in the lungs. Our results suggest that human resistin may play an important contributory role in enhancing TLR4-induced inflammatory responses, and it may be a target for future therapies aimed at reducing the severity of acute lung injury and other inflammatory situations in which neutrophils play a major role.

AMPK activation--protean potential for boosting healthspan

AMP-activated kinase (AMPK) is activated when the cellular (AMP+ADP)/ATP ratio rises; it therefore serves as a detector of cellular "fuel deficiency." AMPK activation is suspected to mediate some of the health-protective effects of long-term calorie restriction. Several drugs and nutraceuticals which slightly and safely impede the efficiency of mitochondrial ATP generation-most notably metformin and berberine-can be employed as clinical AMPK activators and, hence, may have potential as calorie restriction mimetics for extending healthspan. Indeed, current evidence indicates that AMPK activators may reduce risk for atherosclerosis, heart attack, and stroke; help to prevent ventricular hypertrophy and manage congestive failure; ameliorate metabolic syndrome, reduce risk for type 2 diabetes, and aid glycemic control in diabetics; reduce risk for weight gain; decrease risk for a number of common cancers while improving prognosis in cancer therapy; decrease risk for dementia and possibly other neurodegenerative disorders; help to preserve the proper structure of bone and cartilage; and possibly aid in the prevention and control of autoimmunity. While metformin and berberine appear to have the greatest utility as clinical AMPK activators-as reflected by their efficacy in diabetes management-regular ingestion of vinegar, as well as moderate alcohol consumption, may also achieve a modest degree of health-protective AMPK activation. The activation of AMPK achievable with any of these measures may be potentiated by clinical doses of the drug salicylate, which can bind to AMPK and activate it allosterically.

Cells and mediators in diisocyanate-induced occupational asthma

PURPOSE OF REVIEW

Diisocyanates are the most common cause of occupational asthma in many industrialized countries, and various pathogenic mechanisms have been suggested to be involved. Occupational asthma causes airway remodeling unless diagnosed and treated within a proper time frame. However, treatment modalities are limited because of an insufficient understanding regarding underlying pathogenic mechanisms.

RECENT FINDINGS

Several immunological and nonimmunological mechanisms have been suggested, indicating that the pathogenesis of occupational asthma may be more complex than other types of asthma. Airway epithelial cells are the first to encounter diisocyanates and orchestrate various responses, such as cytokine release, oxidative stress generation, and autoantibody formation. Some evidence supports the involvement of adaptive immune responses. Additional evidence suggests that other mechanisms are involved in diisocyanate-induced occupational asthma. One such candidate mechanism is oxidative stress. Oxidative stress has been shown to trigger and aid in the development of diisocyanate-induced occupational asthma in human samples and genetic studies, and some therapeutic trials were performed based on this finding.

SUMMARY

Diisocyanate-induced occupational asthma may be caused by a complex interaction of innate and adaptive immune responses. The knowledge presented in this review may help lead to the development of new treatment modalities through an increased understanding of occupational asthma pathogenesis.

ETC-1002 regulates immune response, leukocyte homing, and adipose tissue inflammation via LKB1-dependent activation of macrophage AMPK

ETC-1002 is an investigational drug currently in Phase 2 development for treatment of dyslipidemia and other cardiometabolic risk factors. In dyslipidemic subjects, ETC-1002 not only reduces plasma LDL cholesterol but also significantly attenuates levels of hsCRP, a clinical biomarker of inflammation. Anti-inflammatory properties of ETC-1002 were further investigated in primary human monocyte-derived macrophages and in in vivo models of inflammation. In cells treated with ETC-1002, increased levels of AMP-activated protein kinase (AMPK) phosphorylation coincided with reduced activity of MAP kinases and decreased production of proinflammatory cytokines and chemokines. AMPK phosphorylation and inhibitory effects of ETC-1002 on soluble mediators of inflammation were significantly abrogated by siRNA-mediated silencing of macrophage liver kinase B1 (LKB1), indicating that ETC-1002 activates AMPK and exerts its anti-inflammatory effects via an LKB1-dependent mechanism. In vivo, ETC-1002 suppressed thioglycollate-induced homing of leukocytes into mouse peritoneal cavity. Similarly, in a mouse model of diet-induced obesity, ETC-1002 restored adipose AMPK activity, reduced JNK phosphorylation, and diminished expression of macrophage-specific marker 4F/80. These data were consistent with decreased epididymal fat-pad mass and interleukin (IL)-6 release by inflamed adipose tissue. Thus, ETC-1002 may provide further clinical benefits for patients with cardiometabolic risk factors by reducing systemic inflammation linked to insulin resistance and vascular complications of metabolic syndrome.

Immunometabolism of AMPK in insulin resistance and atherosclerosis

Obesity leads to insulin resistance and atherosclerosis, which precede Type 2 diabetes and cardiovascular disease. Immunometabolism addresses how metabolic and inflammatory pathways converge to maintain health and a contemporary problem is determining how obesity-induced inflammation precipitates chronic diseases such as insulin resistance and atherosclerosis. AMP-activated protein kinase (AMPK) is an important serine/threonine kinase well known for regulating metabolic processes and maintaining energy homeostasis. However, both metabolic and immunological AMPK-mediated effects play a role in disease. Pro-inflammatory mediators suppress AMPK activity and hinder lipid oxidation. In addition, AMPK activation curbs inflammation by directly inhibiting pro-inflammatory signaling pathways and limiting the build-up of specific lipid intermediates that elicit immune responses. In the context of obesity and chronic disease, these reciprocal responses involve both immune and metabolic cells. Therefore, the immunometabolism of AMPK-mediated processes and therapeutics should be considered in atherosclerosis and insulin resistance.

Ginkgo biloba extract attenuates oxLDL-induced endothelial dysfunction via an AMPK-dependent mechanism

Atherosclerosis is a complex inflammatory arterial disease, and oxidized low-density lipoprotein (oxLDL) is directly associated with chronic vascular inflammation. Previous studies have shown that Ginkgo biloba extract (GbE) acts as a therapeutic agent for neurological and cardiovascular disorders. However, the mechanisms mediating the actions of GbE are still largely unknown. In the present study, we tested the hypothesis that GbE protects against oxLDL-induced endothelial dysfunction via an AMP-activated protein kinase (AMPK)-dependent mechanism. Human umbilical vein endothelial cells were treated with GbE, followed by oxLDL, for indicated time periods. Results from Western blot showed that GbE inhibited the membrane translocation of the NADPH oxidase subunits p47(phox) and Rac-1 and attenuated the increase in protein expression of membrane subunits gp91 and p22(phox) caused by oxLDL-induced AMPK dephosphorylation and subsequent PKC activation. AMPK-α(1)-specific small interfering RNA-transfected cells that had been exposed to GbE followed by oxLDL revealed elevated levels of PKC and p47(phox). In addition, exposure to oxLDL resulted in reduced AMPK-mediated Akt/endothelial nitric oxide (NO) synthase signaling and the induction of phosphorylation of p38 mitogen-activated protein kinase, which, in turn, activated NF-κB-mediated inflammatory responses, such as the release of interleukin-8, the expression of the adhesion molecule, and the adherence of monocytic cells to human umbilical vein endothelial cells. Furthermore, oxLDL upregulated the expression of inducible NO synthase, thereby augmenting the formation of NO and protein nitrosylation. Pretreatment with GbE, however, exerted significant cytoprotective effects in a dose-dependent manner. Results from this study may provide insight into a possible molecular mechanism by which GbE protects against oxLDL-induced endothelial dysfunction.

AMP-activated protein kinase: an emerging drug target to regulate imbalances in lipid and carbohydrate metabolism to treat cardio-metabolic diseases

The adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor of energy metabolism at the cellular as well as whole-body level. It is activated by low energy status that triggers a switch from ATP-consuming anabolic pathways to ATP-producing catabolic pathways. AMPK is involved in a wide range of biological activities that normalizes lipid, glucose, and energy imbalances. These pathways are dysregulated in patients with metabolic syndrome (MetS), which represents a clustering of major cardiovascular risk factors including diabetes, lipid abnormalities, and energy imbalances. Clearly, there is an unmet medical need to find a molecule to treat alarming number of patients with MetS. AMPK, with multifaceted activities in various tissues, has emerged as an attractive drug target to manage lipid and glucose abnormalities and maintain energy homeostasis. A number of AMPK activators have been tested in preclinical models, but many of them have yet to reach to the clinic. This review focuses on the structure-function and role of AMPK in lipid, carbohydrate, and energy metabolism. The mode of action of AMPK activators, mechanism of anti-inflammatory activities, and preclinical and clinical findings as well as future prospects of AMPK as a drug target in treating cardio-metabolic disease are discussed.

Vinorelbine-induced oxidative injury in human endothelial cells mediated by AMPK/PKC/NADPH/NF-κB pathways

Vinorelbine tartrate (VNR), a semi-synthetic vinca alkaloid acquired from vinblastine, has extensively been used as an anticancer agent. However, VNR-induced oxidative damage may cause several side effects, such as venous irritation, vascular pain, and necrotizing vasculitis, thereby repressing clinical treatment efficiency. The molecular mechanisms underlying the induced oxidative stress in endothelial cells are still largely unknown. This study was designed to test the hypothesis that VNR induces oxidative injury through modulation of AMP-activated protein kinase (AMPK) and possible mechanisms were then explored. Human umbilical vein endothelial cells (HUVECs) were treated with VNR (5-0.625 μM) to produce oxidative damage. The VNR-mediated AMPK, PKC, and NADPH oxidase expressions were investigated by western blotting. Furthermore, several oxidative stress-induced oxidative damage markers as well as pro-inflammatory responses were also investigated. VNR treatment resulted in dephosphorylation of AMPK, which in turn led to an activation of NADPH oxidase by PKC; however, the phenomena were repressed by AICAR (an agonist of AMPK). Furthermore, VNR suppressed Akt/eNOS and enhanced p38 mitogen-activated protein kinase (MAPK), which in turn activated the NF-κB pathway. Furthermore, VNR facilitated several pro-inflammatory events, such as the adherence of monocytic THP-1 cells to HUVECs, pro-inflammatory cytokines release, and overexpression of adhesion molecular. Our results highlight a possible molecular mechanism for VNR-mediated endothelial dysfunction.

AMPK activation reduces vascular permeability and airway inflammation by regulating HIF/VEGFA pathway in a murine model of toluene diisocyanate-induced asthma

BACKGROUND

Occupational asthma is characterized by airway inflammation and hyperresponsiveness associated with increased vascular permeability. AMP-activated protein kinase (AMPK) has been suggested to be a novel signaling molecule modulating inflammatory responses.

OBJECTIVE

We sought to evaluate the involvement of AMPK in pathogenesis of occupational asthma and more specifically investigate the effect and molecular mechanisms of AMPK activation in regulating vascular permeability.

METHODS

The mechanisms of action and therapeutic potential of an AMPK activator, 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) were tested in a murine model of toluene diisocyanate (TDI)-induced asthma.

RESULTS

AICAR attenuated airway inflammation and hyperresponsiveness increased by TDI inhalation. Moreover, TDI-induced increases in levels of hypoxia-inducible factor (HIF)-1α, HIF-2α, vascular endothelial growth factor A (VEGFA), and plasma exudation were substantially decreased by treatment with AICAR. Our results also showed that VEGFA expression was remarkably reduced by inhibition of HIF-1α and HIF-2α with 2-methoxyestradiol (2ME2) and that an inhibitor of VEGFA activity, CBO-P11 as well as 2ME2 significantly suppressed vascular permeability, airway infiltration of inflammatory cells, and airway hyperresponsiveness induced by TDI. In addition, AICAR reduced reactive oxygen species (ROS) generation and levels of malondialdehyde and T-helper type 2 cytokines (IL-4, IL-5, and IL-13), while this agent enhanced expression of an anti-inflammatory cytokine, IL-10.

CONCLUSIONS

These results suggest that AMPK activation ameliorates airway inflammatory responses by reducing vascular permeability via HIF/VEGFA pathway as well as by inhibiting ROS production and thus may be a possible therapeutic strategy for TDI-induced asthma and other airway inflammatory diseases.

Regulation of NAD(P)H oxidases by AMPK in cardiovascular systems

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are ubiquitously produced in cardiovascular systems. Under physiological conditions, ROS/RNS function as signaling molecules that are essential in maintaining cardiovascular function. Aberrant concentrations of ROS/RNS have been demonstrated in cardiovascular diseases owing to increased production or decreased scavenging, which have been considered common pathways for the initiation and progression of cardiovascular diseases such as atherosclerosis, hypertension, (re)stenosis, and congestive heart failure. NAD(P)H oxidases are primary sources of ROS and can be induced or activated by all known cardiovascular risk factors. Stresses, hormones, vasoactive agents, and cytokines via different signaling cascades control the expression and activity of these enzymes and of their regulatory subunits. But the molecular mechanisms by which NAD(P)H oxidase is regulated in cardiovascular systems remain poorly characterized. Investigations by us and others suggest that adenosine monophosphate-activated protein kinase (AMPK), as an energy sensor and modulator, is highly sensitive to ROS/RNS. We have also obtained convincing evidence that AMPK is a physiological suppressor of NAD(P)H oxidase in multiple cardiovascular cell systems. In this review, we summarize our current understanding of how AMPK functions as a physiological repressor of NAD(P)H oxidase.

AMP-activated protein kinase, stress responses and cardiovascular diseases

AMPK (AMP-activated protein kinase) is one of the key players in maintaining intracellular homoeostasis. AMPK is well known as an energy sensor and can be activated by increased intracellular AMP levels. Generally, the activation of AMPK turns on catabolic pathways that generate ATP, while inhibiting cell proliferation and biosynthetic processes that consume ATP. In recent years, intensive investigations on the regulation and the function of AMPK indicates that AMPK not only functions as an intracellular energy sensor and regulator, but is also a general stress sensor that is important in maintaining intracellular homoeostasis during many kinds of stress challenges. In the present paper, we will review recent literature showing that AMPK functions far beyond its proposed energy sensor and regulator function. AMPK regulates ROS (reactive oxygen species)/redox balance, autophagy, cell proliferation, cell apoptosis, cellular polarity, mitochondrial function and genotoxic response, either directly or indirectly via numerous downstream pathways under physiological and pathological conditions.

The impact of various reactive oxygen species on the formation of neutrophil extracellular traps

The formation of neutrophil extracellular traps (NETs) depends on the generation of reactive oxygen species (ROS). Previous studies revealed that both NADPH oxidase and myeloperoxidase (MPO) are required for NET release. However, the contribution of various ROS as well as the role of mitochondria-derived ROS has not been addressed so far. In the present study we aimed to investigate in a systematic and comprehensive manner the contribution of various ROS and ROS-generating pathways to the PMA-induced NET release. By using specific inhibitors, the role of both NADPH oxidase- and mitochondria-derived ROS as well as the contribution of superoxide dismutase (SOD) and MPO on the NET release was assessed. We could demonstrate that NADPH oxidase function is crucial for the formation of NETs. In addition, we could clearly show the involvement of MPO-derived ROS in NET release. Our results, however, did not provide evidence for the role of SOD- or mitochondria-derived ROS in NET formation.

Aspirin prevents resistin-induced endothelial dysfunction by modulating AMPK, ROS, and Akt/eNOS signaling

BACKGROUND

Resistin, an adipocytokine, plays a potential role in cardiovascular disease and may contribute to increased atherosclerotic risk by modulating the activity of endothelial cells. A growing body of evidence suggests that aspirin is a potent antioxidant. We investigated whether aspirin mitigates resistin-induced endothelial dysfunction via modulation of reactive oxygen species (ROS) generation and explored the role that AMP-activated protein kinase (AMPK), a negative regulator of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, plays in the suppressive effects of aspirin on resistin-induced endothelial dysfunction.

METHODS

Human umbilical vein endothelial cells (HUVECs) were pretreated with various doses of aspirin (10-500 μg/mL) for 2 hours and then incubated with resistin (100 ng/mL) for an additional 48 hours. Fluorescence produced by the oxidation of dihydroethidium (DHE) was used to quantify the production of superoxide in situ; superoxide dismutase (SOD) and catalase activities were determined by an enzymatic assay; and protein levels of AMPK-mediated downstream signaling were investigated by Western blot.

RESULTS

Treatment of HUVECs with resistin for 48 hours resulted in a 2.9-fold increase in superoxide production; however, pretreatment with aspirin resulted in a dose-dependent decrease in production of superoxide (10-500 μg/mL; n = 3 experiments; all P < .05). Resistin also suppressed the activity of superoxide dismutase and catalase by nearly 50%; that result, however, was not observed in HUVECs that had been pretreated with aspirin at a concentration of 500 μg/mL. The membrane translocation assay showed that the levels of NADPH oxidase subunits p47(phox)and Rac-1 in membrane fractions of HUVECs were threefold to fourfold higher in cells that had been treated with resistin for 1 hour than in untreated cells; however, pretreatment with aspirin markedly inhibited resistin-induced membrane assembly of NADPH oxidase via modulating AMPK-suppressed PKC-α activation. Application of AMPKα1-specific siRNA resulted in increased activation of PKC-α and p47(phox). In addition, resistin significantly decreased AMPK-mediated downstream Akt/endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) signaling and induced the phosphorylation of p38 mitogen-activated protein kinases, which in turn activated NF-κB-mediated inflammatory responses such as the release of interleukin (IL)-6 and IL-8, the overexpression of adhesion molecules, and stimulation of monocytic THP-1 cell attachment to HUVECs (2.5-fold vs control; n = 3 experiments). Furthermore, resistin downregulated eNOS and upregulated inducible NO synthase (iNOS) expression, thereby augmenting the formation of NO and protein nitrosylation. Pretreatment with aspirin, however, exerted significant cytoprotective effects in a dose-dependent manner (P < .05).

CONCLUSIONS

Our findings suggest a direct connection between adipocytokines and endothelial dysfunction and provide further insight into the protective effects of aspirin in obese individuals with endothelial dysfunction.

Adiponectin and its globular fragment differentially modulate the oxidative burst of primary human phagocytes

Adiponectin (Acrp30) belongs to the family of C1q/tumor necrosis factor α (TNFα)-related proteins. Acrp30 circulates as multimers of high, middle, and low molecular weight. In this study, we detected Acrp30 and its globular fragment (gAcrp30) in synovial fluid from rheumatoid arthritis patients. Intriguingly, the LMW form was more abundant in synovial fluid than in serum from both rheumatoid arthritis patients and healthy subjects. We also investigated the effects of Acrp30 and gAcrp30 on reactive oxygen species (ROS) production via the phagocytic NADPH oxidase. Acrp30 inhibited fMLF-induced ROS production by human phagocytes, whereas gAcrp30 enhanced it. gAcrp30's effect is additive with TNFα, whereas Acrp30 inhibited TNFα-induced priming. gAcrp30 enhanced NOX-2 expression at the plasma membrane, with a concomitant increase in p47(phox) phosphorylation. Selective inhibitors of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase 1 (ERK1)/2 abrogated p47(phox) phosphorylation by gAcrp30. In contrast, p47(phox) phosphorylation was inhibited by Acrp30 in association with increased AMP-activated protein kinase (AMPK) phosphorylation in phagocytes. These results suggest that human phagocyte ROS production is regulated by different mechanisms selective for Acrp30 versus gAcrp30. An imbalance between gAcrp30 and higher molecular weight isoforms of Acrp30 might contribute to chronic inflammation by regulating NADPH oxidase.

NADPH oxidase: a target for the modulation of the excessive oxidase damage induced by overtraining in rat neutrophils

OBJECTIVE

The purpose of this study is to demonstrate that NADPH oxidase mediating the ROS production is the major pathway for ROS generation in neutrophils during exercise. NADPH oxidase, as a target can modulate oxidative damage induced by overtraining, which can be value to the prevention of exercise-induced immunosuppression.

METHODS

Thirty male Wistar rats were randomly divided into three groups: a negative control group (C, n = 10), an overtraining group (E, n = 10) and an overtraining + DPI intervention group (D, n =10). Groups E and D were trained on a standard treadmill with progressive load for 11 weeks. After 36-40 h from the last training, eight rats were randomly selected from each group, and blood was sampled from the orbital vein. ELISAs were used to measure serum cytokine levels and lipid peroxidation in blood plasma. Flow cytometry with Annexin V/PI double staining was used to measure neutrophil apoptosis and necrosis. DNA damage in lymphocytes was tested using single cell gel electrophoresis (SCGE). The co-localization between gp91(phox) and p47(phox) of the NADPH-oxidase was detected using immunocytochemistry and confocal microscopy.

RESULTS

1) Compared with group C, the concentrations of IL-1β, IL-8, and TNF-α were significantly increased and MCP-1, and CINC were significantly decreased in blood plasma from group E (P < 0.01 and P < 0.05, respectively). Concentrations of IL-1β and MCP-1 were decreased (P < 0.05), and IL-8 and TNF-α were significantly increased (P <0.05) in blood plasma from group D. MDA and MPO were elevated in plasma from groups E and D (P < 0.01 and P < 0.05, respectively). 2) Compared with group C, the percentage of neutrophils apoptosis were significantly elevated (P < 0.01) in both groups E and D, and the percentage of cell death was raised in group E (P < 0.05). No significant change was observed in group D. 3) Compared with group C, the number of comet cells, an indicator of DNA damage, was significantly increased (P < 0.01), and the width and tail length of comet cells were notably increased in group E, while no significant increase was observed in group D. 4) The p47(phox )protein translocated to the cell membrane and co-localized with the gp91(phox) subunit of NADPH oxidase in neutrophils activated by overtraining.

CONCLUSION

1) Excessive exercise led to an increased secretion of inflammatory cytokines and chemokines in peripheral blood, and it may have induced tissue inflammation 2) Overtraining can activate the NADPH oxidase-mediated overproduction of ROS, leading to increased lipid peroxidation. 3) NADPHoxidase in neutrophils as a target, was responsible for ROS, oxidative damage to phagocytes and lymphocytes and changes to inflammatory cytokines and immune regulatory factors all affect cellular immune functions and may be causative factors for exercise-induced immunosuppression.

Palmitate induces C-reactive protein expression in human aortic endothelial cells. Relevance to fatty acid-induced endothelial dysfunction

Circulating levels of free fatty acids are commonly elevated in patients with the metabolic syndrome and exert, through activating proinflammatory pathways, harmful effects of the vascular endothelium. In this study, we examined the effect of palmitate (PA) on endothelial C-reactive protein (CRP) expression and the role of CRP in PA-induced nitric oxide (NO) inhibition. Palmitate increased, in a dose-dependent manner, CRP protein expression and production in human aortic endothelial cells (HAECs). Induction of CRP protein was mimicked by ceramide, whereas bromopalmitate and other common free fatty acids such as oleate or linoleate were ineffective. Palmitate also elicited reactive oxygen species production in HAECs, an effect prevented by protein kinase C (PKC) inhibition and adenosine monophosphate-activated kinase (AMPK) activation. Palmitate-treated HAECs showed increased CRP messenger RNA expression and nuclear factor (NF)-κB activation. Induction of CRP expression by PA was prevented by antioxidants and normalized by PKC and mitogen-activated protein kinase inhibitors. Disrupting NF-κB and Janus kinase/signal transducers and activators of transcription pathways or inducing AMPK activation also suppressed the stimulatory effect of PA on CRP messenger RNA expression. Finally, in HAECs, PA reduced NO release, an effect reversed by anti-CRP antibody. These data demonstrate that PA-induced endothelial CRP expression involves PKC-driven oxidative stress, possibly through AMPK inhibition, and activation of downstream redox-sensitive signaling pathways, including NF-κB. They further support a role for endothelial cell-derived CRP as mediator of the suppressive effect of PA on NO production.