Autocrine regulation of inducible nitric-oxide synthase in macrophages by atrial natriuretic peptide

Reversal of the detrimental effects of social isolation on ischemic cerebral injury and stroke-associated pneumonia by inhibiting small intestinal T-cell migration into the brain and lung

Social isolation (ISO) is associated with an increased risk and poor outcomes of ischemic stroke. However, the roles and mechanisms of ISO in stroke-associated pneumonia (SAP) remain unclear. Adult male mice were single- or pair-housed with an ovariectomized female mouse and then subjected to transient middle cerebral artery occlusion. Isolated mice were treated with the natriuretic peptide receptor A antagonist A71915 or anti-gamma-delta (γδ) TCR monoclonal antibody, whereas pair-housed mice were treated with recombinant human atrial natriuretic peptide (rhANP). Subdiaphragmatic vagotomy (SDV) was performed 14 days before single- or pair-housed conditions. We found that ISO significantly worsened brain and lung injuries relative to pair housing, which was partially mediated by elevated interleukin (IL)-17A levels and the migration of small intestine-derived inflammatory γδ T-cells into the brain and lung. However, rhANP treatment or SDV could ameliorate ISO-exacerbated post-stroke brain and lung damage by reducing IL-17A levels and inhibiting the migration of inflammatory γδ T-cells into the brain and lung. Our results suggest that rhANP mitigated ISO-induced exacerbation of SAP and ischemic cerebral injury by inhibiting small intestine-derived γδ T-cell migration into the lung and brain, which could be mediated by the subdiaphragmatic vagus nerve.

Natriuretic peptide receptor-C mediates the inhibitory effect of atrial natriuretic peptide on neutrophil recruitment to the lung during acute lung injury

Atrial natriuretic peptide (ANP) protects against acute lung injury (ALI), but the receptor that mediates this effect is not known. Transgenic mice with 0 (knockout), 1 (heterozygote), or 2 (wild-type) functional copies of Npr3, the gene that encodes for natriuretic peptide receptor-C (NPR-C), were treated with intravenous infusion of ANP or saline vehicle before oropharyngeal aspiration of Pseudomonas aeruginosa (PA103) or saline vehicle. Lung injury was assessed 4 h following aspiration by measurement of lung wet/dry (W/D) weight, whole lung leukocyte and cytokine levels, and protein, leukocyte, and cytokine concentration in bronchoalveolar lavage fluid (BALF). PA103 induced acute lung injury as evidenced by increases in lung W/D ratio and protein concentration in BALF. The severity of PA103-induced lung injury did not differ between NPR-C genotypes. Treatment with intravenous ANP infusion reduced PA103-induced increases in lung W/D and BALF protein concentration in all three NPRC genotypes. PA103 increased the percentage of leukocytes that were neutrophils and cytokine levels in whole lung and BALF in NPR-C wild-type and knockout mice. This effect was blunted by ANP in wild-type mice but not in the NPR-C knockout mice. NPR-C does not mediate the protective effect of ANP on endothelial cell permeability in settings of PA103-induced injury but may mediate the effect of ANP on inhibition of the recruitment of neutrophils to the lung and thereby attenuate the release of inflammatory cytokines.

RhANP attenuates endotoxin-derived cognitive dysfunction through subdiaphragmatic vagus nerve-mediated gut microbiota-brain axis

BACKGROUND

Atrial natriuretic peptide (ANP) secreted from atrial myocytes is shown to possess anti-inflammatory, anti-oxidant and immunomodulatory effects. The aim of this study is to assess the effect of ANP on bacterial lipopolysaccharide (LPS)-induced endotoxemia-derived neuroinflammation and cognitive impairment.

METHODS

LPS (5 mg/kg) was given intraperitoneally to mice. Recombinant human ANP (rhANP) (1.0 mg/kg) was injected intravenously 24 h before and/or 10 min after LPS injection. Subdiaphragmatic vagotomy (SDV) was performed 14 days before LPS injection or 28 days before fecal microbiota transplantation (FMT). ANA-12 (0.5 mg/kg) was administrated intraperitoneally 30 min prior to rhANP treatment.

RESULTS

LPS (5.0 mg/kg) induced remarkable splenomegaly and an increase in the plasma cytokines at 24 h after LPS injection. There were positive correlations between spleen weight and plasma cytokines levels. LPS also led to increased protein levels of ionized calcium-binding adaptor molecule (iba)-1, cytokines and inducible nitric oxide synthase (iNOS) in the hippocampus. LPS impaired the natural and learned behavior, as demonstrated by an increase in the latency to eat the food in the buried food test and a decrease in the number of entries and duration in the novel arm in the Y maze test. Combined prophylactic and therapeutic treatment with rhANP reversed LPS-induced splenomegaly, hippocampal and peripheral inflammation as well as cognitive impairment. However, rhANP could not further enhance the protective effects of SDV on hippocampal and peripheral inflammation. We further found that PGF mice transplanted with fecal bacteria from rhANP-treated endotoxemia mice alleviated the decreased protein levels of hippocampal polyclonal phosphorylated tyrosine kinase receptor B (p-TrkB), brain-derived neurotrophic factor (BDNF) and cognitive impairment, which was abolished by SDV. Moreover, TrkB/BDNF signaling inhibitor ANA-12 abolished the improving effects of rhANP on LPS-induced cognitive impairment.

CONCLUSIONS

Our results suggest that rhANP could mitigate LPS-induced hippocampal inflammation and cognitive dysfunction through subdiaphragmatic vagus nerve-mediated gut microbiota-brain axis.

Protective Renal Effects of Atrial Natriuretic Peptide: Where Are We Now?

Atrial natriuretic peptide belongs to the family of natriuretic peptides, a system with natriuretic, diuretic, and vasodilator effects that opposes to renin-angiotensin system. In addition to its classic actions, atrial natriuretic peptide exerts a nephroprotective effect given its antioxidant and anti-inflammatory properties, turning it as a beneficial agent against acute and chronic kidney diseases. This minireview describes the most relevant aspects of atrial natriuretic peptide in the kidney, including its renal synthesis, physiological actions through specific receptors, the importance of its metabolism, and its potential use in different pathological scenarios.

Very-Short-Term Sleep Deprivation Slows Early Recovery of Lymphocytes in Septic Patients

Sleep plays an important role in immune function. However, the effects of very-short-term sleep deprivation on the early recovery of immune function after sepsis remain unclear. This study was conducted in the intensive care unit to investigate the effects of 2 consecutive days of sleep deprivation (SD) on lymphocyte recovery over the following few days in septic patients who were recovering from a critical illness. The patients' self-reports of sleep quality was assessed using the Richards–Campbell Sleep Questionnaire at 0 and 24 h after inclusion. The demographic, clinical, laboratory, treatment, and outcome data were collected and compared between the good sleep group and poor sleep group. We found that 2 consecutive days of SD decreased the absolute lymphocyte count (ALC) and ALC recovery at 3 days after SD. Furthermore, post-septic poor sleep decreased the plasma levels of atrial natriuretic peptide (ANP) immediately after 2 consecutive days of SD. The ANP levels at 24 h after inclusion were positively correlated with ALC recovery, the number of CD3⁺ T cells, or the number of CD3⁺ CD4⁺ cells in the peripheral blood on day 5 after inclusion. Our data suggested that very-short-term poor sleep quality could slow down lymphocyte recovery over the following few days in septic patients who were recovering from a critical illness. Our results underscore the significance of very-short-term SD on serious negative effects on the immune function. Therefore, it is suggested that continuous SD or several short-term SD with short intervals should be avoided in septic patients.

Cardiovascular Pleiotropic Effects of Natriuretic Peptides

Atrial natriuretic peptide (ANP) is a cardiac hormone belonging to the family of natriuretic peptides (NPs). ANP exerts diuretic, natriuretic, and vasodilatory effects that contribute to maintain water–salt balance and regulate blood pressure. Besides these systemic properties, ANP displays important pleiotropic effects in the heart and in the vascular system that are independent of blood pressure regulation. These functions occur through autocrine and paracrine mechanisms. Previous works examining the cardiac phenotype of loss-of-function mouse models of ANP signaling showed that both mice with gene deletion of ANP or its receptor natriuretic peptide receptor A (NPR-A) developed cardiac hypertrophy and dysfunction in response to pressure overload and chronic ischemic remodeling. Conversely, ANP administration has been shown to improve cardiac function in response to remodeling and reduces ischemia-reperfusion (I/R) injury. ANP also acts as a pro-angiogenetic, anti-inflammatory, and anti-atherosclerotic factor in the vascular system. Pleiotropic effects regarding brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) were also reported. In this review, we discuss the current evidence underlying the pleiotropic effects of NPs, underlying their importance in cardiovascular homeostasis.

Cardiomyokines from the heart

The heart is regarded as an endocrine organ as well as a pump for circulation, since atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were discovered in cardiomyocytes to be secreted as hormones. Both ANP and BNP bind to their receptors expressed on remote organs, such as kidneys and blood vessels; therefore, the heart controls the circulation by pumping blood and by secreting endocrine peptides. Cardiomyocytes secrete other peptides besides natriuretic peptides. Although most of such cardiomyocyte-derived peptides act on the heart in autocrine/paracrine fashions, several peptides target remote organs. In this review, to overview current knowledge of endocrine properties of the heart, we focus on cardiomyocyte-derived peptides (cardiomyokines) that act on the remote organs as well as the heart. Cardiomyokines act on remote organs to regulate cardiovascular homeostasis, systemic metabolism, and inflammation. Therefore, through its endocrine function, the heart can maintain physiological conditions and prevent organ damage under pathological conditions.

Atrial natriuretic peptide reduces inflammation and enhances apoptosis in rat acute pancreatitis

AIM

We previously reported that atrial natriuretic peptide (ANP) reduces serum amylase and intrapancreatic trypsinogen activation in the onset of acute pancreatitis whereas secretin increases them. In the present work, we sought to establish the effect of ANP and secretin on the inflammatory response and cell death in experimental acute pancreatitis.

METHODS

The expression and activity of key inflammatory mediators and apoptosis were evaluated in the presence or absence of the atrial peptide, secretin or both in cerulein-induced acute pancreatitis in rats. Also, ultrastructural changes in pancreatic acinar cells were assessed by transmission electron microscopy.

RESULTS

ANP significantly reduced NF-κB activation and TNF-α intrapancreatic levels. Furthermore, it decreased inducible nitric oxide synthase and cyclooxygenase 2 expression and activity while it diminished myeloperoxidase activity. ANP also stimulated apoptosis as shown by caspase-3 expression and activation as well as TUNEL assay. These findings correlated well with the ultrastructural changes observed in the exocrine pancreas. Although secretin reduced various inflammatory markers, it also diminished caspase-3 activation and the overall response was the aggravation of the disease as reflected by the ultrastructural alterations of pancreatic acinar cells. In the presence of ANP, various effects evoked by secretin were antagonized.

CONCLUSION

Present findings show that ANP significantly attenuated the severity of acute pancreatitis in the rat by inducing apoptosis and reducing the inflammatory response and further suggest that ANP may have eventual therapeutic implications in the disease and/or in medical interventions at risk of its developing like endoscopic retrograde cholangiopancreatography.

Classical activation of macrophages and vardenafil

Inhibitors of phosphodiesterase 5 (PDE5) – sildenafil citrate (Viagra; Pfizer) and vardenafil hydrochloride (Levitra; Bayer/GlaxoSmithKline) – approved for the treatment of erectile dysfunction and pulmonary arterial hypertension also rescue the loss of cystic fibrosis (CF) chloride channel function and the mislocalization of F508del-CFTR in affected tissues in CF. Can PDE5 inhibitors provide a therapeutic strategy which combines ability to correct the basic ion transport defect and to control de-regulated lung inflammation in CF?

Yeast-mediated mRNA delivery polarizes immuno-suppressive macrophages towards an immuno-stimulatory phenotype

Macrophages have increasingly gained interest as a therapeutic target since they represent an integral component of the tumor microenvironment. In fact, M2 macrophage accumulation in solid tumors is associated with poor prognosis and therapy failure. Therefore, reprogramming M2 macrophages towards an M1 phenotype with anti-tumor activity by gene therapy represents a promising therapeutic approach. Herein, we describe recombinant Saccharomyces cerevisiae as a novel gene delivery vehicle for primary human macrophages. Opsonized S. cerevisiae was taken up efficiently by M2 macrophages and initiated the expression of pro-inflammatory cytokines. Recombinant yeast delivered functional nucleic acids to macrophages, especially when constitutively biosynthesized mRNA was used as cargo. Interestingly, expression of the protein encoded for by the delivered nucleic acid was higher in M2 cells when compared to M1 macrophages. Finally, the delivery of mRNA coding for the pro-inflammatory regulators MYD88 and TNF to M2 macrophages induced a prolonged upregulation of pro-inflammatory and cytotoxic cytokines in these cells, suggesting their successful re-education towards an anti-tumor M1 phenotype. Our results suggest the use of yeast-based gene delivery as a promising approach for the treatment of pathologic conditions that may benefit from the presence of M1-polarized macrophages, such as cancer.

Atrial natriuretic peptide down-regulates LPS/ATP-mediated IL-1β release by inhibiting NF-kB, NLRP3 inflammasome and caspase-1 activation in THP-1 cells

Atrial natriuretic peptide (ANP) is an hormone/paracrine/autocrine factor regulating cardiovascular homeostasis by guanylyl cyclase natriuretic peptide receptor (NPR-1). ANP plays an important role also in regulating inflammatory and immune systems by altering macrophages functions and cytokines secretion. Interleukin-1β (IL-1β) is a potent pro-inflammatory cytokine involved in a wide range of biological responses, including the immunological one. Unlike other cytokines, IL-1β production is rigorously controlled. Primarily, NF-kB activation is required to produce pro-IL-1β; subsequently, NALP3 inflammasome/caspase-1 activation is required to cleave pro-IL-1β into the active secreted protein. NALP3 is a molecular platform capable of sensing a large variety of signals and a major player in innate immune defense. Due to their pleiotropism, IL-1β and NALP3 dysregulation is a common feature of a wide range of diseases. Therefore, identifying molecules regulating IL-1β/NALP3/caspase-1 expression is an important step in the development of new potential therapeutic agents. The aim of our study was to evaluate the effect of ANP on IL-1β/NALP3/caspase-1 expression in LPS/ATP-stimulated human THP1 monocytes. We provided new evidence of the direct involvement of ANP/NPR-1/cGMP axis on NF-kB/NALP3/caspase-1-mediated IL-1β release and NF-kB-mediated pro-IL-1β production. In particular, ANP inhibited both NF-kB and NALP3/caspase-1 activation leading to pro- and mature IL-1β down-regulation. Our data, pointing out a modulatory role of this endogenous peptide on IL-1β release and on NF-kB/NALP3/caspase-1 activation, indicate an important anti-inflammatory and immunomodulatory effect of ANP via these mechanisms. We suggest a possible employment of ANP for the treatment of inflammatory/immune-related diseases and IL-1β/NALP3-associated disorders, affecting millions of people worldwide.

Atrial natriuretic peptide down-regulates neutrophil recruitment on inflamed endothelium by reducing cell deformability and resistance to detachment force

BACKGROUND

Recombinant atrial natriuretic peptide (ANP) is administered in patients with acute heart failure in Japan to improve renal function and hemodynamics, but its anti-inflammatory effect on activated leukocytes may also contribute to its therapeutic efficacy.

OBJECTIVE

Examine unconventional role of ANP in neutrophil adhesion to inflamed endothelium.

METHODS

Human neutrophils were perfused over endothelial monolayers in a microfluidic lab-chip assay. Cell rheology was assessed by micropipette aspiration to assess changes in cortical tension and viscosity. Fluorescence microscopy was applied to measure adhesive contact area and β2-integrin focal bond formation.

RESULTS

ANP inhibited neutrophil rolling and firm adhesion without influencing the upregulation of cellular adhesion molecules on endothelium or the regulation of high affinity CD18 and shedding of L-selectin during neutrophil activation. Exposed to fluid shear, integrin mediated arrest was disrupted with ANP treatment, which elicited formation of long tethers and diminished cell spreading and contact. This correlated with a ∼40% increase in neutrophil viscosity and a reduction in the adhesive footprint.

CONCLUSIONS

A decrease in cell deformation and neutrophil flattening with ANP results in fewer integrin bond clusters, which translates to higher tensile forces and impaired adhesion strengthening and cell detachment.

Signaling pathways involved in renal oxidative injury: role of the vasoactive peptides and the renal dopaminergic system

The physiological hydroelectrolytic balance and the redox steady state in the kidney are accomplished by an intricate interaction between signals from extrarenal and intrarenal sources and between antinatriuretic and natriuretic factors. Angiotensin II, atrial natriuretic peptide and intrarenal dopamine play a pivotal role in this interactive network. The balance between endogenous antioxidant agents like the renal dopaminergic system and atrial natriuretic peptide, by one side, and the prooxidant effect of the renin angiotensin system, by the other side, contributes to ensuring the normal function of the kidney. Different pathological scenarios, as nephrotic syndrome and hypertension, where renal sodium excretion is altered, are associated with an impaired interaction between two natriuretic systems as the renal dopaminergic system and atrial natriuretic peptide that may be involved in the pathogenesis of renal diseases. The aim of this review is to update and comment the most recent evidences about the intracellular pathways involved in the relationship between endogenous antioxidant agents like the renal dopaminergic system and atrial natriuretic peptide and the prooxidant effect of the renin angiotensin system in the pathogenesis of renal inflammation.

Atrial natriuretic peptide: an old hormone or a new cytokine?

Atrial natriuretic peptide (ANP) a cardiovascular hormone mainly secreted by heart atria in response to stretching forces induces potent diuretic, natriuretic and vasorelaxant effects and plays a major role in the homeostasis of blood pressure as well as of water and salt balance. The hormone can also act as autocrine/paracrine factor and modulate several immune functions as well as cytoprotective effects. ANP contributes to innate immunity being able to: (i) stimulate the host defense against extracellular microbes by phagocytosis and Reactive Oxygen Species (ROS) release; (ii) inhibit the synthesis and release of proinflammatory markers such as TNF-α, IL-1, MCP-1, nitric oxide (NO), cyclooxygenase-2 (COX-2); (iii) inhibit the expression of adhesion molecules such as ICAM-1 and E-selectin. ANP can also affect the adaptive immunity being able to: (i) reduce the number of CD4(+) CD8(+) lymphocytes as well as to increase the CD4(-) CD8(-) cells; (ii) stimulate the differentiation of naïve CD4(+) cells toward the Th2 and/or Th17 phenotype. The hormone shows protective effects during: (i) ventricular hypertrophy and myocardial injury; (ii) atherosclerosis and hypertension by the induction of antiproliferative effects; (iii) oxidative stress counteracting the dangerous effects of ROS; (iv) growth of tumors cells by the induction of apoptosis or necrosis. Since not much is known about of the role of ANP locally produced and released by non-cardiac cells, this review outlines the contribution of ANP in different aspect of innate as well as adaptive immunity also with respect to the excessive cell growth in physiological and/or pathological conditions.

Phosphodiesterase 2A is a major negative regulator of iNOS expression in lipopolysaccharide-treated mouse alveolar macrophages

PDE2A is a dual-function PDE that is stimulated by cGMP to hydrolyze cAMP preferentially. In a two-hit model of ALI, we found previously that PDE2A decreased lung cAMP, up-regulated lung iNOS, and exacerbated ALI. Recent data suggest that macrophage iNOS expression contributes to ALI but later, promotes lung-injury resolution. However, macrophage iNOS is increased by cAMP, suggesting that PDE2A could negatively regulate macrophage iNOS expression. To test this, we examined the effects of manipulating PDE2A expression and function on LPS-induced iNOS expression in a mouse AM cell line (MH-S) and primary mouse AMs. In MH-S cells, LPS (100 ng/ml) increased PDE2A expression by 15% at 15 min and 50% at 6 h before decreasing at 24 h and 48 h. iNOS expression appeared at 6 h and remained increased 48 h post-LPS. Compared with control Ad, Ad.PDE2A-shRNA enhanced LPS-induced iNOS expression further by fourfold, an effect mimicked by the PDE2A inhibitor BAY 60-7550. Adenoviral PDE2A overexpression or treatment with ANP decreased LPS-induced iNOS expression. ANP-induced inhibition of iNOS was lost by knocking down PDE2A and was not mimicked by 8-pCPT-cGMP, a cGMP analog that does not stimulate PDE2A activity. Finally, we found that in primary AMs from LPS-treated mice, PDE2A knockdown also increased iNOS expression, consistent with the MH-S cell data. We conclude that increased AM PDE2A is an important negative regulator of macrophage iNOS expression.

Downregulation of the glucocorticoid-induced leucine zipper (GILZ) promotes vascular inflammation

OBJECTIVE

Glucocorticoid-induced leucine zipper (GILZ) represents an anti-inflammatory mediator, whose downregulation has been described in various inflammatory processes. Aim of our study was to decipher the regulation of GILZ in vascular inflammation.

APPROACH AND RESULTS

Degenerated aortocoronary saphenous vein bypass grafts (n = 15), which exhibited inflammatory cell activation as determined by enhanced monocyte chemoattractrant protein 1 (MCP-1, CCL2) and Toll-like receptor 2 (TLR2) expression, showed significantly diminished GILZ protein and mRNA levels compared to healthy veins (n = 23). GILZ was also downregulated in human umbilical vein endothelial cells (HUVEC) and macrophages upon treatment with the inflammatory cytokine TNF-α in a tristetraprolin (ZFP36, TTP)- and p38 MAPK-dependent manner. To assess the functional implications of decreased GILZ expression, we determined NF-κB activation after GILZ knockdown by siRNA and found that NF-κB activity and inflammatory gene expression were significantly enhanced. Importantly, ZFP36 is induced in TNF-α-activated HUVEC as well as in degenerated vein bypasses. When atheroprotective laminar shear stress was employed, GILZ levels in HUVEC increased on mRNA and protein level. Laminar flow also counteracted TNF-α-induced ZFP36 expression and GILZ downregulation. MAP kinase phosphatase 1 (MKP-1, DUSP1), a negative regulator of ZFP36 expression, was distinctly upregulated under laminar shear stress conditions and downregulated in degenerated vein bypasses.

CONCLUSION

Our data show a diminished expression of the anti-inflammatory mediator GILZ in the inflamed vasculature and indicate that GILZ downregulation requires the mRNA binding protein ZFP36. We suggest that reduced GILZ levels play a role in cardiovascular disease.

Influence of regular physical activity and caloric restriction on β-adrenergic and natriuretic peptide receptor expression in retroperitoneal adipose tissue of OLETF rats

The mechanisms underlying exercise-induced increases in adipose tissue blood flow and lipolysis involve both β-adrenergic receptor (βAR)- and natriuretic peptide receptor (NPR)-dependent processes. We hypothesized that daily wheel running (RUN) would increase the expression of NPR1, NPR2, βAR2 and βAR3 in retroperitoneal (RP) and epididymal (EPI) adipose tissues of obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Four-week-old OLETF rats were assigned to sedentary (SED, n = 6), calorie-restricted (CR, n = 8; fed 70% of SED) or RUN groups (n = 8). Rats were killed at 40 weeks of age. By design, body weight and adiposity were similar between RUN and CR animals, but each was lower than SED (P < 0.01). Compared with SED, RP depots of RUN rats exhibited 1.7- to 3.2-fold greater NPR1, NPR2, βAR2 and βAR3 mRNA levels (all P < 0.05). There were no differences between CR and SED in the expression of these genes in RP adipose tissues, and there were no differences in gene expression among groups in EPI adipose tissues. At the protein level, βAR2 and βAR3 were elevated in RUN and CR groups relative to the SED group in RP adipose tissues. In order to gain insight into the mechanisms underlying the activity-induced increases in NPR and βAR mRNAs, RP adipose tissue explants from Wistar rats were treated with atrial natriuretic peptide (ANP), adrenaline and/or S-nitroso-N-acetyl-dl-penicillamine (SNAP; a nitric oxide donor) in organ culture experiments. SNAP synergistically enhanced adrenaline- and ANP-stimulated increases in NPR2 and βAR2 mRNA levels. Our data suggest that physical activity-induced increases in nitric oxide interact with adrenaline and ANP to trigger the induction of NPR and βAR mRNAs in the RP adipose tissue depot of the OLETF rat.

Glucocorticoid-induced leucine zipper is downregulated in human alveolar macrophages upon Toll-like receptor activation

Induction of the glucocorticoid-induced leucine zipper (GILZ) by glucocorticoids plays a role in their antiinflammatory action, whereas GILZ expression is reduced under inflammatory conditions. The mechanisms regulating GILZ expression during inflammation, however, have not yet been characterized. Here, we investigated GILZ expression in human alveolar macrophages (AMs) following Toll-like receptor (TLR) activation. Macrophages were shown to predominantly express GILZ transcript variant 2. Lipopolysaccharide-treated AMs, THP-1 cells, and lungs of lipopolysaccharide-exposed mice displayed decreased GILZ protein and mRNA levels. The effect was strictly dependent on the adapter molecule MyD88, as shown by using specific ligands or a knockdown strategy. Investigations on the functional significance of GILZ downregulation performed by GILZ knockdown revealed a proinflammatory response, as indicated by increased cytokine expression and NF-κB activity. We found that TLR activation reduced GILZ mRNA stability, which was mediated via the GILZ 3'-untranslated region. Finally, involvement of the mRNA-binding protein tristetraprolin (TTP) is suggested, since TTP overexpression or knockdown modulated GILZ expression and TTP was induced in a MyD88-dependent fashion. Taken together, our data show a MyD88- and TTP-dependent GILZ downreg-ulation in human macrophages upon TLR activation. Suppression of GILZ is mediated by mRNA destabilization, which might represent a regulatory mechanism in macrophage activation.

Overexpression of the IGF2-mRNA binding protein p62 in transgenic mice induces a steatotic phenotype

BACKGROUND & AIMS

The insulin-like growth-factor 2 (IGF2) mRNA binding protein p62 is highly expressed in hepatocellular carcinoma tissue. Still, its potential role in liver disease is largely unknown. In this study, we investigated pathophysiological implications of p62 overexpression in mice.

METHODS

We generated mice overexpressing p62 under a LAP-promotor. mRNA expression levels and stability were examined by real-time RT-PCR. Allele-specific expression of Igf2 and H19 was assessed after crossing mice with SD7 animals. The Igf2 downstream mediators pAKT and PTEN were determined by Western blot.

RESULTS

Hepatic p62 overexpression neither induced inflammatory processes nor liver damage. However, 2.5week old transgenic animals displayed a steatotic phenotype and improved glucose tolerance. p62 overexpression induced the expression of the imprinted genes Igf2 and H19 and their transcriptional regulator Aire (autoimmune regulator). Neither monoallelic expression nor mRNA stability of Igf2 and H19 was affected. Investigating Igf2 downstream signalling pathways showed increased AKT activation and attenuated PTEN expression.

CONCLUSIONS

The induction of a steatotic phenotype implies that p62 plays a role in hepatic pathophysiology.

Stimulation of natriuretic peptide receptor C attenuates accumulation of reactive oxygen species and nitric oxide synthesis in ammonia-treated astrocytes

Oxidative and nitrosative stress contribute to ammonia-induced astrocytic dysfunction in hepatic encephalopathy. Treatment of cultured astrocytes with 5 mmol/L ammonium chloride ('ammonia') increased the production of reactive oxygen species (ROS), including the toxic NADPH oxidase reaction product, •O(2)(-). Atrial natriuretic peptide (ANP), natriuretic peptide C and a selective natriuretic peptide receptor (NPR)-C ligand, cANP((4-23),) each decreased the total ROS content both in control cells and cells treated with ammonia. However, attenuation of •O(2)(-) accumulation by ANP and cANP((4-23),) was observed in ammonia-treated cells only and the effect of cANP((4-23)) was decreased when the NADPH oxidase-regulatory protein G(iα-2) was blocked with a specific anti-G(iα-2) antibody. Although in contrast to ANP, cANP((4-23)) did not elevate the cGMP content in control astrocytes, it decreased cAMP content and reduced the expression of G(iα-2), the NADPH oxidase-regulatory protein. The results show the presence of functional NPR-C in astrocytes, activation of which (i) attenuates basal ROS production, and (ii) prevents excessive accumulation of the toxic ROS species, •O(2)(-) by ammonia. Ammonia, ANP and cANP((4-23)) added separately, each stimulated formation of NO(x) (nitrates + nitrites) which was associated with up-regulation of the activity [cANP((4-23))] or/and expression (ammonia) of the endothelial isoform of nitric oxide synthase. However, the ammonia-induced increase of NO(x) was not augmented by co-addition of ANP, and was reduced to the control level by co-addition of cANP((4-23)) , indicating that activation of NPR-C may also reduce nitrosative stress. Future hepatic encephalopathy therapy might include the use of cANP((4-23)) or other NPR-C agonists to control oxidative/nitrosative stress induced by ammonia.

Atrial natriuretic peptide and oxidative stress

Atrial natriuretic peptide (ANP) is a hormone, produced mainly by cardiomyocytes, with a major role in cardiovascular homeostatic mechanisms such as natriuresis and vasodilation, which serve to regulate blood pressure. However, ANP also acts as an autocrine/paracrine factor on other targets such as kidney, lung, thymus, liver and the immune system. ANP participates in the regulation of cell growth and proliferation, and evidence is accumulating that these effects are associated with the generation of reactive oxygen species (ROS). In vascular cells and cardiomyocytes ANP stimulates the antioxidant defense, but in other systems such as hepatoblastoma and macrophages ANP may produce either antioxidant or prooxidant effects, depending on experimental conditions and cell context. At present very little is known on the relationship between ANP and ROS production in the normal homeostatic processes or during the development of cardiovascular diseases and cancer. Our current knowledge of the role of ANP in signaling pathways leading to the generation of intracellular messengers such as diacylglycerol (DAG), and guanosine 3'-5'-cyclic monophosphate has been examined in order to clarify the mechanisms by which the hormone may counteract or contribute to the potentially dangerous effects of free radicals.

GREBP, a cGMP-response element-binding protein repressing the transcription of natriuretic peptide receptor 1 (NPR1/GCA)

NPR1/GCA (natriuretic peptide receptor 1/guanylyl cyclase A) expression is controlled by several agents, including ANP (atrial natriuretic peptide). After ANP stimulation, NPR1/GCA down-regulates the transcriptional activity of its gene via a cGMP-dependent mechanism. Because we previously identified a cis-acting element responsible for this cGMP sensitivity, we proceed here to explore novel putative protein binding to cGMP-response element (cGMP-RE). Using the yeast one-hybrid technique with a human kidney cDNA library, we identified a strong positive clone able to bind cGMP-RE. The clone was derived from 1083-bp-long cDNA of a gene of yet unknown function localized on human chromosome 1 (1p33.36). We named this new protein GREBP (for cGMP-response element-binding protein). DNA binding assays showed 18-fold higher cGMP-RE binding capacity than the controls, whereas an electromobility shift assay indicated a specific binding for the cGMP-RE, and chromatin immunoprecipitation confirmed the binding of GREBP to the element under physiological conditions. By acting on cGMP-RE, GREBP inhibited the expression of a luciferase-coupled NPR1 promoter construct. In H295R cells, ANP heightened GREBP expression by 60% after just 3 h of treatment while inhibiting NPR1/GCA expression by 30%. Silencing GREBP with specific small interfering RNA increased the activity of the luciferase-coupled NPR1 promoter and GCA/NPR1 mRNA levels. GREBP is a nuclear protein mainly expressed in the heart. We report here the existence of a human-specific gene that acts as a transcriptional repressor of the NPR1/GCA gene.

Natriuretic peptides and cardiovascular damage in the metabolic syndrome: molecular mechanisms and clinical implications

Natriuretic peptides are endogenous antagonists of vasoconstrictor and salt- and water-retaining systems in the body's defence against blood pressure elevation and plasma volume expansion, through direct vasodilator, diuretic and natriuretic properties. In addition, natriuretic peptides may play a role in the modulation of the molecular mechanisms involved in metabolic regulation and cardiovascular remodelling. The metabolic syndrome is characterized by visceral obesity, hyperlipidaemia, vascular inflammation and hypertension, which are linked by peripheral insulin resistance. Increased visceral adiposity may contribute to the reduction in the circulating levels of natriuretic peptides. The dysregulation of neurohormonal systems, including the renin-angiotensin and the natriuretic peptide systems, may in turn contribute to the development of insulin resistance in dysmetabolic patients. In obese subjects with the metabolic syndrome, reduced levels of natriuretic peptides may be involved in the development of hypertension, vascular inflammation and cardio vascular remodelling, and this may predispose to the development of cardiovascular disease. The present review summarizes the regulation and function of the natriuretic peptide system in obese patients with the metabolic syndrome and the involvement of altered bioactive levels of natriuretic peptides in the pathophysiology of cardiovascular disease in patients with metabolic abnormalities.

Human plasmacytoid dendritic cells express an atrial natriuretic peptide receptor, guanylyl cyclase-A

Atrial natriuretic peptide is a cardiovascular hormone secreted mainly by the cardiac atria and regulates the volume-pressure homeostasis. The action of ANP is mediated by GC-A. We previously reported that human monocyte-derived dendritic cells express GC-A and respond to ANP with polarization toward a Th2-inducing phenotype. In the present study, we explored the possibility that pDC are subjected to immunoregulation via the ANP/GC-A system. We examined GC-A expression on blood pDC and found that GC-A was not expressed on fresh pDC but was induced after stimulation with CpG-oligodeoxynucleotide AAC-30, IL-3, or interleukin-3 plus CD40 ligand. Activated pDC responded to ANP with an increase in cGMP production, indicating that GC-A expressed on pDC was functional. We investigated whether tonsillar pDC express GC-A by immunohistochemistry and immunofluorescence staining. We found that GC-A(+) HLA-DR(+) cells were present in the T-cell areas and the perivascular areas. Flow cytometric analysis with tonsillar cells confirmed that lineage(-) CD123(high) pDC express GC-A. These results indicate that the ANP/GC-A system is involved in immune regulation through pDC in secondary lymphoid organs.

cGMP in the vasculature

Cyclic guanosine 3', 5'-monophosphate (cGMP) plays an integral role in the control of vascular function. Generated from guanylate cyclases in response to the endogenous ligands, nitric oxide (NO) and natriuretic peptides (NPs), cGMP influences a number of vascular cell types and regulates vasomotor tone, endothelial permeability, cell growth and differentiation, as well as platelet and blood cell interactions. Reciprocal regulation of the NO-cGMP and NP-cGMP pathways is evident in the vasculature such that one cGMP generating system may compensate for the dysfunction of the other. Indeed, aberrant cGMP production and/or signalling accompanies many vascular disorders such as hypertension, atherosclerosis, coronary artery disease and diabetic complications. This chapter highlights the main vascular functions of cGMP, its role in disease and the resulting current and potential therapeutic applications. With respect to pulmonary hypertension, heart failure and erectile dysfunction, as well as cGMP signal transduction, the reader is specifically referred to other dedicated chapters.

cGMP and cGMP-dependent protein kinase in platelets and blood cells

Platelets are specialized adhesive cells that play a key role in normal and pathological hemostasis through their ability to rapidly adhere to subendothelial matrix proteins (platelet adhesion) and to other activated platelets (platelet aggregation). NO plays a crucial role in preventing platelet adhesion and aggregation. In platelets, cGMP synthesis is catalyzed by sGC, whereas PDE2, PDE3 and PDE5 are responsible for cGMP degradation. Stimulation of cGK by cGMP leads to phosphorylation of multiple target substrates. These substrates inhibit elevation of intracellular calcium, integrin activation, cytoskeletal reorganization, and platelet granule secretion, events normally associated with platelet activation. The NO/cGMP pathway also plays a significant role in many other blood cell types in addition to platelets. In leukocytes, depending on the specific cell type, cGMP signaling regulates gene expression, differentiation, migration, cytokine production, and apoptosis.

Attenuated activation of macrophage TLR9 by DNA from virulent mycobacteria

Alveolar macrophages are the first line of host defence against mycobacteria, but an insufficient host response allows survival of bacteria within macrophages. We aimed to investigate the role of Toll-like receptor 9 (TLR9) activation in macrophage defence against mycobacteria. Human in vitro differentiated macrophages as well as human and mouse alveolar macrophages showed TLR9 mRNA and protein expression. The cells were markedly activated by DNA isolated from attenuated mycobacterial strains (H37Ra and Mycobacterium bovis BCG) as assessed by measuring cytokine expression by real-time PCR, whereas synthetic phosphorothioate-modified oligonucleotides had a much lower potency to activate human macrophages. Intracellular replication of H37Ra was higher in macrophages isolated from TLR9-deficient mice than in macrophages from wild-type mice, whereas H37Rv showed equal survival in cells from wild-type or mutant mice. Increased bacterial survival in mouse macrophages was accompanied by altered cytokine production as determined by Luminex bead assays. In vivo infection experiments also showed differential cytokine production in TLR9-deficient mice compared to wild-type animals. Both human monocyte-derived macrophages as well as human alveolar macrophages showed reduced activation upon treatment with DNA isolated from bacteria from virulent (M. bovis and H37Rv) compared to attenuated mycobacteria. We suggest attenuated TLR9 activation contributes to the insufficient host response against virulent mycobacteria.

Natriuretic peptides: an update on bioactivity, potential therapeutic use, and implication in cardiovascular diseases

The natriuretic peptide system includes three known peptides: atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). They contribute to the regulation of cardiovascular homeostasis through diuretic, natriuretic, and vasodilatory properties. Among them, ANP has received particular attention because of its effects on blood pressure regulation and cardiac function. Although the potential for its therapeutic application in the treatment of hypertension and heart failure has been evaluated in several experimental and clinical investigations, no pharmacological approach directly targeted at modulation of ANP levels has ever reached the stage of being incorporated into clinical practice. Recently, ANP has also received attention as being a possible cardiovascular risk factor, particularly in the context of hypertension, stroke, obesity, and metabolic syndrome. Abnormalities in either peptide levels or peptide structure are thought to underlie its implied role in mediating cardiovascular diseases. Meanwhile, BNP has emerged as a relevant marker of left ventricular (LV) dysfunction and as a useful predictor of future outcome in patients with heart failure. This review deals with the major relevant findings related to the cardiovascular and metabolic effects of natriuretic peptides, to their potential therapeutic use, and to their role in mediating cardiovascular diseases.

The ANP-cGMP-protein kinase G pathway induces a phagocytic phenotype but decreases inflammatory gene expression in microglial cells

Reactive gliosis is a prominent feature of CNS injury that involves dramatic changes in glial cell morphology together with increased motility, phagocytic activity, and release of inflammatory mediators. We have recently demonstrated that stimulation of the cGMP-protein kinase G (PKG) pathway by NO or atrial natriuretic peptide (ANP) regulates cytoskeleton dynamics and motility in rat astrocytes in culture. In this work, we show that the cGMP-PKG pathway stimulated by ANP, but not by NO, regulates microglial cell morphology by inducing a dramatic reorganization in the actin cytoskeleton. Both ANP (0.01-1.0 microM) and the permeable cGMP analog, dibutyryl-cGMP (1-100 microM), promote a rapid (maximal at 30 min) and concentration-dependent increase in size, rounding, and lamellipodia and filopodia formation in rat brain cultured microglia. These morphological changes involve an augment and redistribution of F-actin and result in increased phagocytic activity. ANP-induced rearrangements in actin cytoskeleton and inert particle phagocytosis are prevented by the PKG inhibitor, Rp-8-Br-PET-cGMPS (0.5 microM), and involve inhibition of RhoA GTPase and activation of Rac1 and Cdc42. However, ANP does not induce NO synthase Type 2 (NOS-2) or tumor necrosis factor-alpha expression and is able to decrease lipopolysaccharide (LPS)-elicited induction of these inflammatory genes. The morphological changes and the decrease of LPS-induced NOS-2 expression produced by ANP in cultured microglia are also observed by immunostaining in organotypic cultures from rat hippocampus. These results suggest that stimulation of the ANP-cGMP-PKG pathway in microglia could play a beneficial role in the resolution of neuroinflammation by removing dead cells and decreasing levels of proinflammatory mediators.

The inhibitory effect of simvastatin on the ADMA-induced inflammatory reaction is mediated by MAPK pathways in endothelial cells

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is emerging as a key contributor for endothelial dysfunction associated with inflammation. Statins can inhibit vascular inflammatory reaction and improve endothelial function. The aim of this study was to investigate in human endothelial cells the signaling pathways of ADMA-induced inflammatory reaction and potential inhibitory effects of simvastatin. Endothelial cells were cultured and used for all of the studies. Tumor necrosis factor-alpha(TNF-alpha) and soluble intercellular adhesion molecule-1 (sICAM-1) were determined by enzyme-linked immunosorbent assay. Nuclear factor-kappaB (NF-kappaB) was assayed by electrophoretic mobility shift assay. The activation of mitogen-activated protein kinases (MAPKs), including p38 MAPK and extracellular signal-related kinase (ERK(1/2)), were characterized by Western blot analysis. Treatment with ADMA (3-30 micromol/L) increased the concentration of sICAM-1 in a dose-dependent manner. ADMA (30 micromol/L) significantly enhanced the concentrations of TNF-alpha and sICAM-1, the activity of NF-kappaB and the phosphorylation of p38 MAPK and ERK(1/2). The increased secretion of TNF-alpha and sICAM-1 and the increased activity of NF-kappaB by ADMA were altered by SB203580 (5 micromol/L) or PD98059 (20 micromol/L), but not by LY294002 (20 micromol/L). Simvastatin (0.1, 0.5, or 2.5 micromol/L) markedly inhibited the elevated concentrations of TNF-alpha and sICAM-1, the activity of NF-kappaB, and the phosphorylation of p38 MAPK and ERK(1/2) induced by ADMA. Simvastatin inhibited ADMA-induced inflammatory reaction by p38 MAPK and ERK(1/2) pathways in cultured endothelial cells.

Natriuretic peptide responsive, cyclic guanosine monophosphate producing structures in the guinea pig bladder

PURPOSE

We examined the localization of natriuretic peptide responsive, cyclic guanosine monophosphate producing cells in the guinea pig bladder.

MATERIALS AND METHODS

The bladder was removed from male guinea pigs sacrificed by cervical dislocation. The lateral wall of the bladder was cut into strips 2 mm thick. The tissue pieces were incubated in the presence of human atrial natriuretic peptide, rat brain natriuretic peptide and C-type natriuretic peptide or the nitric oxide donor DEANO (diethylamine NONOate or 1,1-diethyl-2-hydroxy-2-nitrosohydrazine) (Sigma). Cyclic guanosine monophosphate immunoreactivity was localized using an antibody against formaldehyde fixed cyclic guanosine monophosphate.

RESULTS

Atrial natriuretic peptide and brain natriuretic peptide stimulated cyclic guanosine monophosphate synthesis in suburothelial interstitial cells, whereas C-type natriuretic peptide was not effective. In contrast, DEANO stimulated cyclic guanosine monophosphate synthesis in urothelial umbrella cells, suburothelial interstitial cells, muscle interstitial cells and neurons. The effect of atrial natriuretic peptide and brain natriuretic peptide was not inhibited by ODQ (1H-[1, 2, 4]oxadiazolo[4-3a]quinoxalin-1-one), an inhibitor of nitric oxide responsive soluble guanylyl cyclase.

CONCLUSIONS

To our knowledge our findings show for the first time a localized effect of atrial natriuretic peptide and brain natriuretic peptide to the suburothelial cells of the guinea pig bladder. These cells express the soluble guanylyl cyclase and particulate guanylyl cyclase-A isoforms. The specific physiological role of these cells is not known but it was suggested that they may be involved in the generation or modulation of sensation. The results imply a role for natriuretic peptide-cyclic guanosine monophosphate signaling in the processing of sensory information in the bladder.

Relationship between protective effects of rosiglitazone on endothelium and endogenous nitric oxide synthase inhibitor in streptozotocin-induced diabetic rats and cultured endothelial cells

BACKGROUND

Previous investigations have indicated that the level of asymmetric dimethylarginine (ADMA) is increased in diabetic patients and animals, and rosiglitazone has a protective effect on the endothelium. In the present study, we tested the relationship between protective effects of rosiglitazone and ADMA in streptozotocin (STZ)-induced diabetic rats and cultured endothelial cells.

METHODS

Blood samples were collected from carotid artery. Vasodilator responses to acetylcholine (ACh) in the isolated aortic rings were measured, and serum concentrations of glucose, lipid, nitrite/nitrate, ADMA and tumour necrosis factor-alpha (TNF-alpha) were determined. Cultured endothelial cells were treated with ADMA, and the concentrations of intercellular adhesion molecule (ICAM-1), TNF-alpha, and the activity of nuclear factor-kappaB (NF-kappaB) were determined.

RESULTS

Vasodilator responses to ACh were decreased markedly and the serum concentrations of TNF-alpha, nitrite/nitrate and ADMA were increased significantly in diabetic rats. Rosiglitazone (3, 10 or 30 mg/kg) produced a significant reduction of the inhibition of vasodilator responses to ACh, but had no effect on the serum concentrations of glucose, lipid, nitrite/nitrate and ADMA in diabetic rats. ADMA (30 microM) significantly increased the activity of NF-kappaB and elevated the levels of ICAM-1 and TNF-alpha, and pre-treatment with rosiglitazone (10 or 30 microM) markedly inhibited the increased activity of NF-kappaB and reduced the elevated levels of TNF-alpha and ICAM-1 induced by ADMA in cultured endothelial cells.

CONCLUSIONS

Rosiglitazone improves endothelial function in diabetic rats, which is related to the reduction of the inflammatory response induced by ADMA.

Predominant Effect of A-Type Natriuretic Peptide on Reduction of Oxidative Stress During the Treatment of Patients With Heart Failure

BACKGROUND

Oxidative stress plays an important role in the pathogenesis of heart failure and was investigated in the present study of the role of exogenous A-type natriuretic peptide (ANP) in the patients with heart failure and in cultured neonatal rat cardiomyocytes.

METHODS AND RESULTS

The first protocol was to examine if an infusion of human ANP (carperitide) changed serum levels of TRX (thioredoxin) during the treatment of patients with heart failure compared with conventional therapy using furosemide. Protocol 2 investigated whether ANP had a direct antioxidant action on the failing heart by measuring TRX gene expression and reactive oxygen species (ROS) production in cultured neonatal rat cardiomyocytes. In Protocol 1, 8 patients were treated with only an intravenous bolus of furosemide and 11 patients with only an intravenous infusion of carperitide for 24 h. Serum TRX levels significantly decreased at 4 h (p<0.03) and at 24 h (p<0.05) in the carperitide group, whereas they decreased slightly but were not significantly different in the furosemide group. In Protocol 2, it was found that a low dose of exogenous ANP of 10(-9) mol/L significantly suppressed TRX expression and ROS production in cardiomyocytes.

CONCLUSION

Carperitide infusion has a predominantly antioxidant action, in addition to improving the hemodynamics of patients with acute heart failure. Furthermore, carperitide infusion should have a direct antioxidant effect on the failing heart.

Renal protective role of atrial natriuretic peptide in acute sodium overload-induced inflammatory response

BACKGROUND

The present study was performed to explore the effect of exogenous infusions of atrial natriuretic peptide (ANP) on the early inflammatory response during acute sodium overload in normal rats.

METHODS

Sprague Dawley rats were exposed to acute sodium overload (Na 1.5 M). Nonhypotensive doses of ANP (1 and 5 microg x kg(-1) x h(-1)) were infused simultaneously with sodium or after sodium infusion in order to evaluate prevention or reversion of the inflammatory response, respectively. We determined inflammation markers in renal tissue by immunohistochemistry.

RESULTS

Creatinine clearance was not reduced in any case. Sodium tubular reabsorption increased after sodium overload (334.3 +/- 18.7 vs. control 209.6 +/- 27.0 mEq x min(-1), p < 0.05) without changes in mean arterial pressure. This increase was prevented (228.9 +/- 26.4; p < 0.05) and reversed (231.5 +/- 13.9; p < 0.05) by ANP-5 microg x kg(-1) x h(-1). Sodium overload increased the expression of: RANTES (38.4.3 +/- 0.8 vs. 2.9 +/- 0.6%, p < 0.001), transforming-growth-factor-beta(1) (35.3 +/- 1.0 vs. 5.0 +/- 0.7%, p < 0.001), alpha-smooth muscle actin (15.6 +/- 0.7 vs. 3.1 +/- 0.3%, p < 0.001), NF-kappaB (9.4 +/- 1.3 to 2.2 +/- 0.5 cells/mm(2), p < 0.001), HIF-1alpha (38.2 +/- 1.7 to 8.4 +/- 0.8 cells/mm(2), p < 0.001) and angiotensin II (35.9 +/- 1.3 to 8.2 +/- 0.5%, p < 0.001). ANP-5 microg x kg(-1) x h(-1) prevented and reversed inflammation: RANTES (9.2 +/- 0.5 and 6.9 +/- 0.7, p < 0.001); transforming growth factor-beta(1) (13.2 +/- 0.7 and 10.2 +/- 0.5, p < 0.001) and alpha-smooth muscle actin (4.1 +/- 0.4 and 5.2 +/- 0.4, p < 0.001). Both prevention and reversion by ANP were associated with downregulation of NF-kappaB (3.2 +/- 0.4 and 2.8 +/- 0.5, p < 0.001) and angiotensin II (8.2 +/- 0.5 and 9.1 +/- 0.7, p < 0.001) and diminished hypoxia evaluated through HIF-1alpha expression (8.4 +/- 0.8 and 8.8 +/- 0.7, p < 0.001).

CONCLUSION

Our study provides evidence supporting a protective role of ANP in both prevention and reversion of renal inflammation in rats with acute sodium overload.

Expression and activity of cGMP-dependent phosphodiesterases is up-regulated by lipopolysaccharide (LPS) in rat peritoneal macrophages

It has been shown that cyclic GMP (cGMP) modulates the inflammatory responses of macrophages, but the underlying molecular mechanisms are still poorly understood. Looking for proteins potentially regulated by cGMP in rat peritoneal macrophages (PMs), in this study we analyzed expression and activity of cGMP-hydrolyzing and cGMP-regulated phosphodiesterases (PDEs). It was found that freshly isolated peritoneal exudate macrophages (PEMs) express enzymes belonging to families PDE1-3, PDE5, PDE10, and PDE11. Analysis of substrate specificity, sensitivity to inhibitors, and subcellular localization showed that PDE2 and PDE3 are the main cGMP-regulated PDE isoforms in PEMs. The profile of PDE expression was altered by maintaining PEMs in culture and treatment with bacterial endotoxin (LPS). After 24 h culture, PDE5 was not present and the levels of PDE2, PDE3, and PDE11 were markedly decreased. However, their expression and activity was recovered after treatment of cultured cells with LPS. A similar pattern of changes was observed for the expression of TNFalpha, but not for guanylyl cyclase A (GC-A). LPS up-regulated PDE expression also in resident peritoneal macrophages (RPMs), although not all PDEs present in PEMs were detected in RPMs. Taken together, our results show that in rat PMs expression of cGMP-dependent PDEs positively correlates with the activation state of cells. Moreover, the fact that most of these PDEs hydrolyze also cAMP indicates that cGMP can play a role of potent regulator of cAMP signaling in macrophages.

ANP inhibits LPS-induced stimulation of rat microglial cells by suppressing NF-kappaB and AP-1 activations

Atrial natriuretic peptide (ANP) contributes to the inhibition of such causes of inflammation as the lipopolysaccharide (LPS)-induced productions of nitric oxide (NO) and proinflammatory cytokines [including interleukin-1 (IL-1)] in macrophages. In the present study we used primary cultures of rat brain macrophage-like cells (i.e., microglial cells) to investigate whether ANP binding to its receptors inhibits LPS-induced microglial activation via effects on the activation of the proinflammatory transcription factors NF-kappaB and AP-1. The productions of NO and IL-1, as well as morphological changes, were examined to assess LPS-induced activation of microglial cells. Our RT-PCR study revealed that rat microglial cells express the mRNAs for ANP receptors (types A, B, and C) and that for the ANP molecule. LPS (100 ng/ml)-stimulated microglial cells showed increases in nitrite (a relatively stable metabolite of NO) and IL-1 concentrations, and in the expression of IL-1 mRNA, as well as a morphological change from an amoeboid shape to a multipolar (mostly bipolar, but sometimes tripolar) rod shape. These effects were all significantly inhibited by treatment with ANP (at 10(-6)M or less). The inhibition by ANP of the LPS-induced nitrite response was abrogated by a NP-receptor antagonist, HS-142-1 (100 ng/ml). NF-kappaB and AP-1 activities were enhanced in LPS-stimulated microglial cells, and these enhancements were significantly suppressed by ANP (10(-6)M). These results suggest that ANP inhibits LPS-stimulated activities in microglial cells through activation of microglial ANP receptors, leading to inhibitions of NF-kappaB and AP-1.

Metalloporphyrins inactivate caspase-3 and -8

Activation of caspases represents one of the earliest biochemical indicators for apoptotic cell death. Therefore, measurement of caspase activity is a widely used and generally accepted method to determine apoptosis in a wide range of in vivo and in vitro settings. Numerous publications characterize the role of the heme-catabolizing enzyme heme oxygenase-1 (HO-1) in regulating apoptotic processes. Different metalloporphyrins representing inducers and inhibitors of this enzyme are often used, followed by assessment of apoptotic cell death. In the present work, we found that caspase-3-like activity, as well as activity of caspase-8 measured in either Fas (CD95) ligand-treated Jurkat T-lymphocytes or by the use of recombinant caspase-3 or -8, was inhibited by different metalloporphyrins (cobalt(III) protoporphyrin IX, tin and zinc(II) protoporphyrin-IX). Moreover, employing the mouse model of Fas-induced liver apoptosis these properties of porphyrins could also be demonstrated in vivo. The metalloporphyrins were shown to inhibit caspase-3-mediated PARP cleavage. Molecular modeling studies demonstrated that porphyrins can occupy the active site of caspase-3 in an energetically favorable manner and in a binding mode similar to that of known inhibitors. The data shown here introduce metalloporphyrins as direct inhibitors of caspase activity. This finding points to the need for careful employment of metalloporphyrins as modulators of HO-1.

Zinc-mediated inhibition of cyclic nucleotide phosphodiesterase activity and expression suppresses TNF-alpha and IL-1 beta production in monocytes by elevation of guanosine 3',5'-cyclic monophosphate

The trace element zinc affects several aspects of immune function, such as the release of proinflammatory cytokines from monocytes. We investigated the role of cyclic nucleotide signaling in zinc inhibition of LPS-induced TNF-alpha and IL-1beta release from primary human monocytes and the monocytic cell line Mono Mac1. Zinc reversibly inhibited enzyme activity of phosphodiesterase-1 (PDE-1), PDE-3, and PDE-4 in cellular lysate. It additionally reduced mRNA expression of PDE-1C, PDE-4A, and PDE-4B in intact cells. Although these PDE can also hydrolyze cAMP, only the cellular level of cGMP was increased after incubation with zinc, whereas cAMP was found to be even slightly reduced due to inhibition of its synthesis. To investigate whether an increase in cGMP alone is sufficient to inhibit cytokine release, the cGMP analogues 8-bromo-cGMP and dibutyryl cGMP as well as the NO donor S-nitrosocysteine were used. All three treatments inhibited TNF-alpha and IL-1beta release after stimulation with LPS. Inhibition of soluble guanylate cyclase-mediated cGMP synthesis with LY83583 reversed the inhibitory effect of zinc on LPS-induced cytokine release. In conclusion, inhibition of PDE by zinc abrogates the LPS-induced release of TNF-alpha and IL-1beta by increasing intracellular cGMP levels.

Inducible nitric oxide synthase (iNOS) in tumor biology: the two sides of the same coin

Inducible nitric oxide synthase (iNOS) is one of three key enzymes generating nitric oxide (NO) from the amino acid l-arginine. iNOS-derived NO plays an important role in numerous physiological (e.g. blood pressure regulation, wound repair and host defence mechanisms) and pathophysiological (inflammation, infection, neoplastic diseases, liver cirrhosis, diabetes) conditions. iNOS is the synthase isoform most commonly associated with malignant disease. Nevertheless, the role of iNOS during tumor development is highly complex, and incompletely understood. Both promoting and deterring actions have been described, presumably depending upon the local concentration of iNOS within the tumor microenvironment. In particular, pivotal effects such as malingnant transformation, angiogenesis, and metastasis are modulated by iNOS. On the other hand, NO derived from macrophages has a potentially cytotoxic/cytostatic effect upon tumor cells. Hence, therapeutical interference with iNOS activity is of considerable interest, especially in tumors where metastatic activity, host defence mechanisms and the level of differentiation seem to be correlated to iNOS expression. This review will aim to summarize the dual actions of iNOS as simultaneous tumor promoter and suppressor.

Nitric oxide inhibits IFN-alpha production of human plasmacytoid dendritic cells partly via a guanosine 3',5'-cyclic monophosphate-dependent pathway

NO, a free radical gas, is known to be critically involved not only in vascular relaxation but also in host defense. Besides direct bactericidal effects, NO has been shown to inhibit Th1 responses and modulate immune responses in vivo, although the precise mechanism is unclear. In this study, we examined the effect of NO on human plasmacytoid dendritic cells (pDCs) to explore the possibility that NO might affect innate as well as adaptive immunity through pDCs. We found that NO suppressed IFN-alpha production of pDCs partly via a cGMP-dependent mechanism, which was accompanied by down-regulation of IFN regulatory factor 7 expression. Furthermore, treatment of pDCs with NO decreased production of IL-6 and TNF-alpha and up-regulated OX40 ligand expression. In accordance with these changes, pDCs treated with NO plus CpG-oligodeoxynucleotide AAC-30 promoted differentiation of naive CD4(+) T cells into a Th2 phenotype. Moreover, pDCs did not express inducible NO synthase even after treatment with AAC-30, LPS, and several cytokines. These results suggest that exogenous NO and its second messenger, cGMP, alter innate as well as adaptive immune response through modulating the functions of pDCs and may be involved in the pathogenesis of certain Th2-dominant allergic diseases.

The role of atrial natriuretic peptide in the immune system

Atrial natriuretic peptide (ANP) is a hormone predominately produced by the heart atria which regulates the water and salt balance as well as blood pressure homeostasis. Being expressed in various parts of the immune system a link of the peptide to the immune system has been proposed. In fact, this review focus on effects of ANP in the immune system and reports about the role of the peptide in innate immune functions as well as in the adaptive immune response.

Fenofibrate decreases asymmetric dimethylarginine level in cultured endothelial cells by inhibiting NF-κB activity

Previous investigations have demonstrated that endogenous inhibitors of nitric oxide synthase (NOS), such as asymmetric dimethylarginine (ADMA), contribute importantly to endothelial dysfunction, and that fenofibrate has a protective effect on the endothelium in rats treated with low-density lipoprotein (LDL) by reducing ADMA levels. In the present study, we explored further the possible mechanism underlying inhibition of ADMA generation by fenofibrate in cultured human umbilical vein endothelial cells (HUVECs). Endothelial injury was induced in cultured HUVECs by incubation with oxidative LDL (ox-LDL) and the levels of ADMA, lactate dehydrogenase (LDH), NO and tumour necrosis factor-alpha (TNF-alpha) in the conditioned medium were measured. Cell viability and the activity of dimethylarginine dimethylaminohydrolase (DDAH) and nuclear factor-kappaB (NF-kappaB) in the cultured HUVECs were also determined. Incubation of HUVECs with ox-LDL (100 microg/ml) for 24 h markedly elevated ADMA, LDH and TNF-alpha in the conditioned medium and significantly increased the activity of NF-kappaB, concomitantly with a significant decrease in the activity of DDAH and the content of NO. Pretreatment with fenofibrate (3, 10 or 30 microM) significantly inhibited the increases in ADMA, LDH and TNF-alpha, attenuated the decreased levels of NO and the decreased activity of DDAH and prevented the activation of NF-kappaB. Similar effects were observed in the presence of pyrrolidine dithiocarbamate (PDTC, 10 microM), an antagonist of NF-kappaB. The beneficial effects of fenofibrate on cultured endothelial cells were abolished by MK-886, a specific peroxisome proliferator-activated receptor-alpha (PPARalpha) antagonist. The present results suggest that fenofibrate inhibits ox-LDL-induced endothelial cell damage by decreasing ADMA and increasing DDAH activity, and the protective effects of fenofibrate on endothelial cells may be related to reduction of NF-kappaB activity by activation of the PPARalpha receptor.

Selective up-regulation of PDE1B2 upon monocyte-to-macrophage differentiation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a major regulator of monocyte to macrophage differentiation. In both humans and mice, the main phenotype of decreased GM-CSF function is pulmonary proteinosis due to aberrant function of alveolar macrophages. Recently, this cytokine has been shown to up-regulate a cyclic nucleotide phosphodiesterase, PDE1B. Two PDE1B variants with unique N-terminal sequences, PDE1B1 and PDE1B2, have been identified. Here, we report that the previously uncharacterized PDE1B2 is selectively increased by GM-CSF by stimulation of transcription at a previously unknown transcriptional start site. Analysis of the exon and intron organization of the PDE1B gene reveals that PDE1B2 has a different N-terminal sequence because of a separate first exon that is located 11.5 kb downstream from the PDE1B1 first exon. By using 5'-RACE, alignment of EST sequences, and a luciferase-reporter system, we provide evidence that PDE1B2 has a separate transcriptional start site from PDE1B1 that can be activated by monocyte differentiation. Furthermore, IL-4 treatment in the presence of GM-CSF, which shifts the differentiation from a macrophage to a dendritic cell phenotype, suppresses the up-regulation of PDE1B2. Induction of PDE1B2 is also found in T cells upon activation by PHA. Therefore, PDE1B2 may have a regulatory role in multiple immune cell types. Last, characterization of the catalytic properties of recombinant PDE1B2 shows that it prefers cGMP over cAMP as a substrate and, thus, is likely to regulate cGMP in macrophages. Also, PDE1B2 has a nearly 3-fold lower EC(50) for activation by calmodulin than PDE1B1.

Direct ANP inhibition of hypoxia-induced inflammatory pathways in pulmonary microvascular and macrovascular endothelial monolayers

Atrial natriuretic peptide (ANP) has been shown to reduce hypoxia-induced pulmonary vascular leak in vivo, but no explanation of a mechanism has been offered other than its vasodilatory and natriuretic actions. Recently, data have shown that ANP can protect endothelial barrier functions in TNF-alpha-stimulated human umbilical vein endothelial cells. Therefore, we hypothesized that ANP actions would inhibit pulmonary vascular leak by inhibition of TNF-alpha secretion and F-actin formation. Bovine pulmonary microvascular (MVEC) and macrovascular endothelial cell (LEC) monolayers were stimulated with hypoxia, TNF-alpha, or bacterial endotoxin (LPS) in the presence or absence of ANP, and albumin flux, NF-kappa B activation, TNF-alpha secretion, p38 mitogen-activated protein kinase (MAPK), and F-actin (stress fiber) formation were assessed. In Transwell cultures, ANP reduced hypoxia-induced permeability in MVEC and TNF-alpha-induced permeability in MVEC and LEC. ANP inhibited hypoxia and LPS increased NF-kappa B activation and TNF-alpha synthesis in MVEC and LEC. Hypoxia decreased activation of p38 MAPK in MVEC but increased activation of p38 MAPK and stress fiber formation in LEC; TNF-alpha had the opposite effect. ANP inhibited an activation of p38 MAPK in MVEC or LEC. These data indicate that in endothelial cell monolayers, hypoxia activates a signal cascade analogous to that initiated by inflammatory agents, and ANP has a direct cytoprotective effect on the pulmonary endothelium other than its vasodilatory and natriuretic properties. Furthermore, our data show that MVEC and LEC respond differently to hypoxia, TNF-alpha-stimulation, and ANP treatment.