Potentiation of human polymorphonuclear leukocyte activation by atrial natriuretic peptide. Inhibitory effect of carnitine congeners

Immunomodulation and immunopharmacology in heart failure

The immune system is intimately involved in the pathophysiology of heart failure. However, it is currently underused as a therapeutic target in the clinical setting. Moreover, the development of novel immunomodulatory therapies and their investigation for the treatment of patients with heart failure are hampered by the fact that currently used, evidence-based treatments for heart failure exert multiple immunomodulatory effects. In this Review, we discuss current knowledge on how evidence-based treatments for heart failure affect the immune system in addition to their primary mechanism of action, both to inform practising physicians about these pleiotropic actions and to create a framework for the development and application of future immunomodulatory therapies. We also delineate which subpopulations of patients with heart failure might benefit from immunomodulatory treatments. Furthermore, we summarize completed and ongoing clinical trials that assess immunomodulatory treatments in heart failure and present several therapeutic targets that could be investigated in the future. Lastly, we provide future directions to leverage the immunomodulatory potential of existing treatments and to foster the investigation of novel immunomodulatory therapeutics.

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.

Pleiotropic Roles of Atrial Natriuretic Peptide in Anti-Inflammation and Anti-Cancer Activity

Simple Summary

The relationship between inflammation and carcinogenesis, as well as the response to anti-tumor therapy, is intimate. Atrial natriuretic peptides (ANPs) play a pivotal role in the homeostatic control of blood pressure, electrolytes, and water balance. In addition, ANPs exert immune-modulatory effects in the tissue microenvironment, thus exhibiting a fascinating ability to prevent inflammation-related tumorigenesis and cancer recurrence. In cancers, ANPs show anti-proliferative effects through several molecular pathways. Furthermore, ANPs attenuate the side effects of cancer therapy. Therefore, ANPs have potential therapeutic value in tumors. Here, we summarized the roles of ANPs in diverse aspects of the immune system and the molecular mechanisms underlying the anti-cancer effects of ANPs, contributing to the development of ANP-based anti-cancer agents.

Abstract

The atrial natriuretic peptide (ANP), a cardiovascular hormone, plays a pivotal role in the homeostatic control of blood pressure, electrolytes, and water balance and is approved to treat congestive heart failure. In addition, there is a growing realization that ANPs might be related to immune response and tumor growth. The anti-inflammatory and immune-modulatory effects of ANPs in the tissue microenvironment are mediated through autocrine or paracrine mechanisms, which further suppress tumorigenesis. In cancers, ANPs show anti-proliferative effects through several molecular pathways. Furthermore, ANPs attenuate the side effects of cancer therapy. Therefore, ANPs act on several hallmarks of cancer, such as inflammation, angiogenesis, sustained tumor growth, and metastasis. In this review, we summarized the contributions of ANPs in diverse aspects of the immune system and the molecular mechanisms underlying the anti-cancer effects of ANPs.

Use of high-resolution metabolomics for the identification of metabolic signals associated with traffic-related air pollution

BACKGROUND

High-resolution metabolomics (HRM) is emerging as a sensitive tool for measuring environmental exposures and biological responses. The aim of this analysis is to assess the ability of high-resolution metabolomics (HRM) to reflect internal exposures to complex traffic-related air pollution mixtures.

METHODS

We used untargeted HRM profiling to characterize plasma and saliva collected from participants in the Dorm Room Inhalation to Vehicle Emission (DRIVE) study to identify metabolic pathways associated with traffic emission exposures. We measured a suite of traffic-related pollutants at multiple ambient and indoor sites at varying distances from a major highway artery for 12 weeks in 2014. In parallel, 54 students living in dormitories near (20 m) or far (1.4 km) from the highway contributed plasma and saliva samples. Untargeted HRM profiling was completed for both plasma and saliva samples; metabolite and metabolic pathway alternations were evaluated using a metabolome-wide association study (MWAS) framework with pathway analyses.

RESULTS

Weekly levels of traffic pollutants were significantly higher at the near dorm when compared to the far dorm (p < 0.05 for all pollutants). In total, 20,766 metabolic features were extracted from plasma samples and 29,013 from saliva samples. 45% of features were detected and shared in both plasma and saliva samples. 1291 unique metabolic features were significantly associated with at least one or more traffic indicator, including black carbon, carbon monoxide, nitrogen oxides and fine particulate matter (p < 0.05 for all significant features), after controlling for confounding and false discovery rate. Pathway analysis of metabolic features associated with traffic exposure indicated elicitation of inflammatory and oxidative stress related pathways, including leukotriene and vitamin E metabolism. We confirmed the chemical identities of 10 metabolites associated with traffic pollutants, including arginine, histidine, γ‑linolenic acid, and hypoxanthine.

CONCLUSIONS

Using HRM, we identified and verified biological perturbations associated with primary traffic pollutant in panel-based setting with repeated measurement. Observed response was consistent with endogenous metabolic signaling related to oxidative stress, inflammation, and nucleic acid damage and repair. Collectively, the current findings provide support for the use of untargeted HRM in the development of metabolic biomarkers of traffic pollution exposure and response.

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.

Genome-wide analysis of the transcriptional response to porcine reproductive and respiratory syndrome virus infection at the maternal/fetal interface and in the fetus

Background

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection of pregnant pigs can result in congenital infection and ultimately fetal death. Little is known about immune responses to infection at the maternal-fetal interface and in the fetus itself, or the molecular events behind virus transmission and disease progression in the fetus. To investigate these processes, RNA-sequencing of two sites, uterine endothelium with adherent placental tissue and fetal thymus, was performed 21 days post-challenge on four groups of fetuses selected from a large PRRSV challenge experiment of pregnant gilts: control (CON), uninfected (UNINF), infected (INF), and meconium-stained (MEC) (n = 12/group). Transcriptional analyses consisted of multiple contrasts between groups using two approaches: differential gene expression analysis and weighted gene co-expression network analysis (WGCNA). Biological functions, pathways, and regulators enriched for differentially expressed genes or module members were identified through functional annotation analyses. Expression data were validated by reverse transcription quantitative polymerase chain reaction (RTqPCR) carried out for 16 genes of interest.

Results

The immune response to infection in endometrium was mainly adaptive in nature, with the most upregulated genes functioning in either humoral or cell-mediated immunity. In contrast, the expression profile of infected fetal thymus revealed a predominantly innate immune response to infection, featuring the upregulation of genes regulated by type I interferon and pro-inflammatory cytokines. Fetal infection was associated with an increase in viral load coupled with a reduction in T cell signaling in the endometrium that could be due to PRRSV-controlled apoptosis of uninfected bystander cells. There was also evidence for a reduction in TWIST1 activity, a transcription factor involved in placental implantation and maturation, which could facilitate virus transmission or fetal pathology through dysregulation of placental function. Finally, results suggested that events within the fetus could also drive fetal pathology. Thymus samples of meconium-stained fetuses exhibited an increase in the expression of pro-inflammatory cytokine and granulocyte genes previously implicated in swine infectious disease pathology.

Conclusions

This study identified major differences in the response to PRRSV infection in the uterine endometrium and fetus at the gene expression level, and provides insight into the molecular basis of virus transmission and disease progression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2720-4) contains supplementary material, which is available to authorized users.

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.

Role and interactions of annexin A1 and oestrogens in the manifestation of sexual dimorphisms in cerebral and systemic inflammation

BACKGROUND AND PURPOSE

Gender differences in inflammation are well described, with females often showing more robust, oestrogen-associated responses. Here, we investigated the influence of gender, oestrogen and the anti-inflammatory protein annexin A1 (AnxA1) on lipopolysaccharide (LPS)-induced leukocyte-endothelial cell interactions in murine cerebral and mesenteric microvascular beds.

EXPERIMENTAL APPROACH

Intravital microscopy was used to visualize and quantify the effects of LPS (10 μg·per mouse i.p.) on leukocyte-endothelial interactions in male and female wild-type (WT) mice. The effects of ovariectomy ± oestrogen replacement were examined in WT and AnxA1-null (AnxA1(-/-) ) female mice.

KEY RESULTS

LPS increased leukocyte adherence in the cerebral and mesenteric beds of both male and female WT mice; females showed exacerbated responses in the brain versus males, but not the mesentery. Ovariectomy further enhanced LPS-induced adhesion in the brain but not the mesentery; its effects were reversed by oestrogen treatment. OVX AnxA1(-/-) mice also showed exaggerated adhesive responses to LPS in the brain. However, these were unresponsive to ovariectomy and, paradoxically, responded to oestrogen with a pronounced increase in basal and LPS-induced leukocyte adhesion in the cerebrovasculature.

CONCLUSIONS AND IMPLICATIONS

Our data confirm the fundamental role of AnxA1 in limiting the inflammatory response in the central and peripheral microvasculature. They also (i) show that oestrogen acts via an AnxA1-dependent mechanism to protect the cerebral, but not the mesenteric, vasculature from the damaging effects of LPS and (ii) reveal a paradoxical and potentially toxic effect of the steroid in potentiating the central response to LPS in the absence of AnxA1.

Atrial natriuretic peptide increases inflammation, infarct size, and mortality after experimental coronary occlusion

Acute coronary artery occlusion triggers the release of atrial natriuretic peptide (ANP) from the heart. ANP affects vasodilation, natriuresis, and inflammation, but the integrated biological effects of ANP on myocardial infarction are unknown. To elucidate these effects, the left anterior coronary artery was ligated in anesthetized, ANP-deficient (ANP(-/-)) and congenic wild-type (ANP(+/+)) mice. The survival of ANP(-/-) mice was markedly better (56%) at 30 days postinfarction than the survival of ANP(+/+) mice (20%, P < 0.01). Surviving mice were comparable initially, but ANP(-/-) mice developed more cardiac hypertrophy (P < 0.001) and had lower contractility indexes 30 days after infarction (P < 0.05). An analysis 24 h after coronary occlusion showed that ANP(-/-) mice had smaller infarcts than ANP(+/+) mice (62.6 +/- 12.1 vs. 100.8 +/- 3.8%, P < 0.001) adjusted for comparable areas at risk for ischemia. The administration of ANP to ANP(-/-) mice via osmotic minipumps significantly enlarged infarct size to levels comparable with those observed in ANP(+/+) mice (P < 0.05). There was no difference in neutrophil migration into the noninfarcted myocardium of ANP(-/-) mice undergoing actual versus sham-operated coronary occlusion. By comparison, after coronary occlusion, the neutrophil infiltration into the myocardium was enhanced in ANP(+/+) (P < 0.0005) and ANP(-/-) mice administered ANP (P < 0.0005). The expression of P-selectin, a molecule that mediates neutrophil adhesion, was significantly greater after coronary occlusion in the vasculature of ANP(+/+) or ANP(-/-) mice treated with ANP than in ANP(-/-) mice (P < 0.002). Taken together, these results indicate that ANP increases P-selectin, neutrophil infiltration, infarct size, and mortality following experimental coronary occlusion.

Expression of natriuretic peptide receptor mRNA and functional response to atrial natriuretic peptide and C-type natriuretic peptide in rainbow trout (Oncorhynchus mykiss) head kidney leucocytes

The stimulatory effect of vasomodulatory natriuretic peptide hormones on macrophages and peripheral blood leucocytes in mammals is well-established. However, the relationship in lower vertebrates has not been characterised. Expression of atrial natriuretic peptide, ventricular natriuretic peptide and C-type natriuretic peptide-1, and the guanylyl cyclase-linked (GC) natriuretic peptide receptor-A and -B-type receptors (NPR-A and NPR-B, respectively) was determined by PCR from the mRNA of rainbow trout head kidney leucocytes yielding gene fragments with 100% homology to the same respective natriuretic peptide and NPR-A and -B sequences obtained from other rainbow trout tissues. A mixed population of isolated rainbow trout head kidney leucocytes was stimulated in vitro with trout atrial natriuretic peptide (specific NPR-A agonist) and trout C-type natriuretic peptide (NPR-A and -B agonist) as well as the cGMP agonist 8-bromo-cGMP or the GC inhibitor 8-bromo-phenyl-eutheno-cGMP. Respiratory burst was stimulated by trout atrial natriuretic peptide, trout C-type natriuretic peptide-1 and 8-bromo-cGMP in a dose dependant manner with the highest activity as a result of stimulation with trout C-type natriuretic peptide-1 in excess of that achieved by phorbol myristate acetate (PMA). Equimolar concentrations of the inhibitor, inhibited the respiratory burst caused by the natriuretic peptides and 8-bromo-cGMP. The natriuretic peptide receptors on rainbow trout head kidney leucocytes appear to have a stimulatory function with regard to respiratory burst that is activated through a cGMP second messenger pathway and the natriuretic peptides expressed in the head kidney leucocytes may well act in a paracrine/autocrine manner.

Role of natriuretic peptide signaling in modulating asthma and inflammation

Atrial natriuretic peptide (ANP), the C-terminal peptide comprising residues 99-126 of the pro-ANP hormone, has been studied for 3 decades for its cardiovascular effects. Recent reports suggest that it plays a significant role in modulation of the immune system. Immune cells, including macrophages, dendritic cells, and T lymphocytes, express receptors for ANP. ANP plays a significant role in shaping the early immune response to environmental antigens and may play a critical role in the interaction between cells of the innate and adaptive immune systems; it also appears to be involved in polarizing the immune response to allergens. Thus, ability to alter the magnitude of natriuretic peptide receptor A (NPRA) signaling could be exploited to develop therapeutics for several allergic diseases, including asthma. This report will review and critically evaluate the role of the ANP pathway in asthma and inflammation.

The sodium/hydrogen exchanger: a possible mediator of immunity

Immune cells such as macrophages and neutrophils provide the first line of defence of the immune system using phagocytosis, cytokine and chemokine synthesis and release, as well as Reactive Oxygen Species (ROS) generation. Many of these functions are positively coupled with cytoplasmic pH (pHi) and/or phagosomal pH (pHp) modification; an increase in pHi represents an important signal for cytokine and chemokine release, whereas a decrease in pHp can induce an efficient antigen presentation. However, the relationship between pHi and ROS generation is not well understood. In immune cells two main transport systems have been shown to regulate pHi: the Na+/H+ Exchanger (NHE) and the plasmalemmal V-type H+ ATPase. NHE is a family of proteins which exchange Na+ for H+ according to their concentration gradients in an electroneutral manner. The exchanger also plays a key role in several other cellular functions including proliferation, differentiation, apoptosis, migration, and cytoskeletal organization. Since not much is known on the relationship between NHE and immunity, this review outlines the contribution of NHE to different aspects of innate and adaptive immune responses such as phagosomal acidification, NADPH oxidase activation and ROS generation, cytokine and chemokine release as well as T cell apoptosis. The possibility that several pro-inflammatory diseases may be modulated by NHE activity is evaluated.

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.

Peritoneal macrophages function modulation by L-carnitine in aging rats

BACKGROUND AND AIMS

The aging process is associated with a progressive decline in physiological functions involving immune response in most species. The aim of the present study was to determine the effect of L-carnitine on impaired macrophages function in aged rats.

METHODS

Superoxide anion production, chemotaxis and phagocytic activity were studied in peritoneal macrophages obtained from young (2 months old) and aged (24 months old) rats. L-carnitine (50 mg/kg bw) or control vehicle was orally gavaged into young and aged rats for 30 consecutive days.

RESULTS

The peritoneal macrophages of the aged rats exhibited an increase in superoxide anion generation and a decline in chemotaxis and phagocytic index by comparison with the young rats. Superoxide anion production in aged rats was significantly reduced by L-carnitine treatment, as accompanied by a significant enhancement of chemotactic activity, which was restored to control levels observed in young rats. The age-related reduction in phagocytic index was only slightly, but not significantly, restored by L-carnitine administration, however.

CONCLUSION

The findings suggest that L-carnitine administration may be useful in reversing some age-related changes.

Pharmacological potentiation of natriuretic peptide limits polymorphonuclear neutrophil-vascular cell interactions

OBJECTIVE

Activated polymorphonuclear neutrophils (PMNs) are the main source of circulating neutral endopeptidase (NEP). We tested the hypothesis that NEP inhibition could potentiate the effect of atrial natriuretic peptide (ANP) on PMN-vascular cell interactions in vitro.

METHODS AND RESULTS

ANP alone and its potentiation by retrothiorphan, the NEP inhibitor, significantly inhibited superoxide, lysozyme, and matrix metalloproteinase (MMP)-9 release by N-formyl-Met-Leu-Phe-stimulated PMNs. Activated PMNs degraded exogenous ANP, which was prevented by NEP inhibition. Hypoxia significantly increased the adhesion of PMNs to endothelial cells and their subsequent MMP-9 release by 60% and 150%, respectively (P<0.01). ANP and its potentiation by retrothiorphan limited PMN adhesion to hypoxic endothelial cells and thus decreased their MMP-9 release (P<0.01). Smooth muscle cells (SMCs) incubated with conditioned medium of N-formyl-Met-Leu-Phe-stimulated PMNs exhibited morphological and biochemical changes characteristic of apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling positivity, nuclear condensation/fragmentation, poly ADP-ribose polymerase cleavage, and DNA laddering). SMC detachment and subsequent apoptosis could be related to leukocyte elastase-induced pericellular proteolysis, inasmuch as both events are inhibited by elastase inhibitors. ANP and its potentiation by retrothiorphan were able to limit elastase release, fibronectin degradation, and SMC apoptosis.

CONCLUSIONS

ANP potentiation by NEP inhibition could limit PMN activation and its consequences on vascular cells.

The atrial natriuretic peptide as a regulator of Kupffer cell functions

Kupffer cells (KCs), the resident macrophages of the liver, contribute prominently to liver injury by inflammatory mediators. Pre-conditioning with the atrial natriuretic peptide (ANP), known also as a regulator of macrophage functions, attenuates hepatic ischemia-reperfusion injury. Therefore, the aim of this study was to determine the presence of functional ANP receptors on isolated KCs and to investigate whether this hepatoprotective hormone influences the activation of KCs. KCs were isolated by collagenase/pronase digestion followed by elutrial centrifugation and cultured for 1 to 3 days. Intracellular cyclic guanosine 3'5'-monophosphate (cGMP) concentrations were measured by radioimmunoassay after treating the cells with sodium nitroprusside or ANP. KCs were stimulated with bacterial lipopolysaccharide in the presence or absence of ANP, and inflammatory mediators were determined. Phagocytosis was assayed using Coumarin-labeled latex particles and flow cytometric analysis. Treatment of KCs with ANP but not with sodium nitroprusside resulted in a significant elevation of intracellular cGMP levels indicating functional type A natriuretic peptide receptors (NPR-As). ANP significantly reduced lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNFalpha) secretion, paralleled by an increased cell-associated TNFalpha. LPS-induced TNFalpha mRNA expression was not affected. ANP significantly increased phagocytotic activity of KCs via NPR-A. No effect of ANP on LPS-activated inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 protein levels, iNOS mRNA expression, nitric oxide, and PGE2-production was observed. We demonstrated functional cGMP-dependent ANP receptors in isolated rat KCs. ANP reduced TNFalpha release possibly by influencing post-translational processing of TNFalpha in LPS-activated KCs. In addition, we demonstrated that ANP enhances phagocytosis in KCs. These effects may contribute to the hepatoprotective actions of ANP.

Leukotriene B(4) promotes reactive oxidant generation and leukocyte adherence during acute hypoxia

Acute systemic hypoxia produces rapid leukocyte adherence in the rat mesenteric microcirculation, although the underlying mechanisms are not fully known. Hypoxia is known to increase reactive oxygen species (ROS) generation, which could result in formation of the lipid inflammatory mediator leukotriene B(4) (LTB(4)). The goal of this study was to examine the role of LTB(4) in hypoxia-induced microvascular alterations. Using intravital microscopy, we determined the effect of the LTB(4) antagonist, LTB(4)-dimethyl amide (LTB(4)-DMA), on ROS generation and leukocyte adherence in mesenteric venules during hypoxia. Exogenous LTB(4) increased ROS generation to 144 +/- 8% compared with control values and also promoted leukocyte adherence. These responses to LTB(4) were blocked by pretreating the mesentery with LTB(4)-DMA. Leukopenia did not significantly attenuate the LTB(4)-induced increase in ROS generation (142 +/- 12.1%). LTB(4)-DMA substantially, though not completely, reduced hypoxia-induced ROS generation from 66 +/- 18% to 11 +/- 4% above control values. Hypoxia-induced leukocyte adherence was significantly attenuated by LTB(4)-DMA. Our results support a role for LTB(4) in the mechanism of hypoxia-induced ROS generation and leukocyte adherence in the rat mesenteric microcirculation.

Down-regulation of L-selectin expression in neutrophils by nonsteroidal anti-inflammatory drugs: role of intracellular ATP concentration

L-selectin is an adhesion molecule that plays an essential role in the early events of the inflammatory response. Our group has recently described that several nonsteroidal anti-inflammatory drugs (NSAIDs) are able to induce both in vivo and in vitro the shedding of L-selectin in neutrophils through an unknown mechanism. In this work, we have studied potential mechanisms involved in the shedding of L-selectin induced by NSAIDs. This effect of NSAIDs did not involve any detectable intracellular calcium flux. Pretreatment of neutrophils either with Ro 31-8220 and H7, 2 specific inhibitors of protein kinase C (PKC), or with inhibitors of protein tyrosine kinases such as tyrphostin A25 or herbimycin A did not prevent the NSAID-mediated L-selectin shedding. However, the KD-IX-73-4, an inhibitor of L-selectin proteolysis was able to block the effect of NSAIDs on L-selectin expression. Remarkably, NSAIDs caused a variable reduction in the neutrophil intracellular ATP concentration that highly correlated with the differential ability of NSAIDs to trigger L-selectin shedding (r = 0.8, P &lt; .01). In agreement with this finding, azide plus 2-deoxy-D-glucose, 2 metabolic blockers, also induced a rapid L-selectin shedding (65% ± 8%) without affecting the neutrophil viability, activation, or expression level of other surface molecules with soluble isoforms such as CD16 and CD59. These data indicate that the maintenance of L-selectin on the neutrophil surface requires energy consumption, which suggests that L-selectin is shed in neutrophils by default. Interestingly, NSAIDs seem to cause the shedding of L-selectin, at least in part, through the reduction of the intracellular ATP concentration.

Down-regulation of L-selectin expression in neutrophils by nonsteroidal anti-inflammatory drugs: role of intracellular ATP concentration

L-selectin is an adhesion molecule that plays an essential role in the early events of the inflammatory response. Our group has recently described that several nonsteroidal anti-inflammatory drugs (NSAIDs) are able to induce both in vivo and in vitro the shedding of L-selectin in neutrophils through an unknown mechanism. In this work, we have studied potential mechanisms involved in the shedding of L-selectin induced by NSAIDs. This effect of NSAIDs did not involve any detectable intracellular calcium flux. Pretreatment of neutrophils either with Ro 31-8220 and H7, 2 specific inhibitors of protein kinase C (PKC), or with inhibitors of protein tyrosine kinases such as tyrphostin A25 or herbimycin A did not prevent the NSAID-mediated L-selectin shedding. However, the KD-IX-73-4, an inhibitor of L-selectin proteolysis was able to block the effect of NSAIDs on L-selectin expression. Remarkably, NSAIDs caused a variable reduction in the neutrophil intracellular ATP concentration that highly correlated with the differential ability of NSAIDs to trigger L-selectin shedding (r = 0.8, P < .01). In agreement with this finding, azide plus 2-deoxy-D-glucose, 2 metabolic blockers, also induced a rapid L-selectin shedding (65% ± 8%) without affecting the neutrophil viability, activation, or expression level of other surface molecules with soluble isoforms such as CD16 and CD59. These data indicate that the maintenance of L-selectin on the neutrophil surface requires energy consumption, which suggests that L-selectin is shed in neutrophils by default. Interestingly, NSAIDs seem to cause the shedding of L-selectin, at least in part, through the reduction of the intracellular ATP concentration.

Sequence of metabolic changes during X-ray-induced apoptosis

A cell population undergoing apoptosis usually contains varying proportions of cells in the diverse stages of the process, from very early continuously through to secondary necrosis. This heterogeneity acts as a confounding factor in metabolic studies if a general population is investigated. Using fluorescent probes and multiparameter flow cytometry, we report on metabolic changes occurring during X-ray-induced apoptosis in human peripheral blood lymphocytes and relate the observed alterations to cells at various phases of the process assessed by monitoring the progressive loss of selective plasma membrane permeability. Data show that alterations of mitochondria cardiolipin and a reduction of plasma membrane potential are rather early events as they commence in cells which still possess an impermeable plasma membrane. Conversely, mitochondrial transmembrane potential is impaired only when plasma membrane permeability starts to be altered, that is, in relatively later apoptotic cells, thereby reflecting the complexity of mitochondria demise during apoptosis. The prooxidant/antioxidant balance is altered in cells in early apoptosis with a correlated increase of prooxidants and depletion of thiols, the latter indicative for the progressive impairment of this detoxifying mechanism. The imbalance in prooxidant/antioxidant remained evident through apoptosis suggesting that oxidative damage starts early and then continues, eventually leading to cellular disruption. Assessing cell transit through the apoptotic process and coupling the observed metabolic changes to selected stages of the process enables one to improve the understanding of the temporary sequence of biochemical phenomena occurring in a given model.

Effects of atrial natriuretic peptide on phagocytosis and respiratory burst in murine macrophages

Atrial natriuretic peptide (ANP) is known to affect cardiovascular physiology displaying both hormone- and neurotransmitter characteristics. However, there is increasing evidence that ANP possesses additional biological activities referring to the immune system. To further strengthen this hypothesis the effect of ANP on two major functions of macrophages, i.e., phagocytosis and respiratory burst was tested. Both parameters were analyzed by flow cytometry employing bone marrow derived macrophages and the murine macrophage cell line J774. In both cell types preincubation with ANP dose dependently (10(-10)-10(-7) M) increases ingestion of opsonized fluorescent latex particles. The respiratory burst activity was monitored by oxidation of dihydrorhodamine-123 in cells stimulated either with phorbol-myristate (PMA, 10 ng/ml) or formyl-Met-Leu-Phe (fMLP, 1 microM). In both cases preexposure of cells to ANP (10(-8)-10(-6) M) for 2 h enhances reactive oxygen production. The data demonstrate an influence of ANP on important defense mechanisms of macrophages and thus extend the knowledge regarding the pharmacological profile of this natriuretic peptide.