Impact of microparticles released during murine systemic inflammation on macrophage activity and reactive nitrogen species regulation

Microparticles (MPs) packaged with numerous bioactive molecules are essential vehicles in cellular communication in various pathological conditions, including systemic inflammation, Whereas MPs are studied mostly upon isolation, their detection in vivo is limited. Impact of MPs might depend on target cell type and cargo they carry; thus herein, we aimed at verifying MPs' impact on macrophages. Unlike neutrophils, monocytes/macrophages are rather inactive during sepsis, and we hypothesized this might be at least partially controlled by MPs. For the above reasons, we focused on the detection of MPs with intravital microscopy (IVM) and report the presence of putative neutrophil-derived MPs in the vasculature of cremaster muscle of endotoxemic mice. Subsequently, we characterized MPs isolated not only from their blood but also from the peritoneal cavity and observed differences in their size, concentration, and cargo. Such MPs were then used to study their impact on RAW 264.7 macrophage cell line performance (cell viability/activity, cytokines, oxygen, and nitrogen reactive species). Addition of MPs to macrophages with or without co-stimulation with lipopolysaccharide did not affect respiratory burst, somewhat decreased mitochondrial activity but increased inducible nitric oxide synthase (iNOS) expression, and NO production especially in case of plasma-derived MPs. The latter MPs carried more iNOS-controlling ceruloplasmin than those discharged into the peritoneal cavity. We conclude that MPs can be detected in vivo with IVM and their cellular origin identified. They are heterogeneous in nature depending on the site of their release. Consequently, microparticles released during systemic inflammation to various body compartments differentially affect macrophages.

Large extracellular vesicle (EV) and neutrophil extracellular trap (NET) interaction captured in vivo during systemic inflammation

Extracellular vesicles (EVs) and neutrophil extracellular traps (NETs) are pivotal bioactive structures involved in various processes including inflammation. Herein we report the interactions between EVs and NETs during murine endotoxemia studied in situ directly in the vasculature (cremaster muscle, liver sinusoids) using intravital microscopy (IVM). We captured NETs and EV release in real time by both non- and polarized neutrophils in liver but not in cremaster vasculature. When comparing numbers of circulating EVs of various origin (nanoparticle tracking analysis-NTA, flow cytometry) with those interacting with endothelium and NETs (IVM) we observed that whereas platelet and monocyte/macrophage-derived EVs dominate in blood and peritoneal lavage, respectively, mostly neutrophil-derived EVs interact with the vascular lining, NETs and leukocytes. Despite the interaction, NETs do not affect EV formation as NET release inhibition did not alter EV release. However, EVs inhibit NETs formation and in particular, erythrocyte-derived EVs downregulate NET release and this effect is mediated via Siglec-E-dependent interactions with neutrophils. Overall, we report that EVs are present in NETs in vivo and they do modulate their release but the process in not bidirectional. Moreover, EVs isolated from body fluids might not reflect their importance in direct endothelial- and leukocyte-related interactions.

Impact of endogenous and exogenous nitrogen species on macrophage extracellular trap (MET) formation by bone marrow-derived macrophages

Macrophage extracellular traps (METs) represent a novel defense mechanism in the antimicrobial arsenal of macrophages. However, mechanisms of MET formation are still poorly understood and this is at least partially due to the lack of reliable and reproducible models. Thus, we aimed at establishing a protocol of MET induction by bone marrow-derived macrophages (BMDMs) obtained from cryopreserved and then thawed bone marrow (BM) mouse cells. We report that BMDMs obtained in this way were morphologically (F4/80+) and functionally (expression of inducible nitric oxide (NO) synthase and NO production) differentiated and responded to various stimuli of bacterial (lipopolysaccharide, LPS), fungal (zymosan) and chemical (PMA) origin. Importantly, BMDMs were successfully casting METs composed of extracellular DNA (extDNA) serving as their backbone to which proteins such as H2A.X histones and matrix metalloproteinase 9 (MMP-9) were attached. In rendered 3D structure of METs, extDNA and protein components were embedded in each other. Since studies had shown the involvement of oxygen species in MET release, we aimed at studying if reactive nitrogen species (RNS) such as NO are also involved in MET formation. By application of NOS inhibitor - L-NAME or nitric oxide donor (SNAP), we studied the involvement of endogenous and exogenous RNS in traps release. We demonstrated that L-NAME halted MET formation upon stimulation with LPS while SNAP alone induced it. The latter phenomenon was further enhanced in the presence of LPS. Taken together, our findings demonstrate that BMDMs obtained from cryopreserved BM cells are capable of forming METs in an RNS-dependent manner.

Synergistic Action of MCL-1 Inhibitor with BCL-2/BCL-XL or MAPK Pathway Inhibitors Enhances Acute Myeloid Leukemia Cell Apoptosis and Differentiation

Acute myeloid leukemia (AML) is a hematological malignancy characterized by excessive proliferation of abnormal myeloid precursors accompanied by a differentiation block and inhibition of apoptosis. Increased expression of an anti-apoptotic MCL-1 protein was shown to be critical for the sustained survival and expansion of AML cells. Therefore, herein, we examined the pro-apoptotic and pro-differentiating effects of S63845, a specific inhibitor of MCL-1, in a single-agent treatment and in combination with BCL-2/BCL-XL inhibitor, ABT-737, in two AML cell lines: HL-60 and ML-1. Additionally, we determined whether inhibition of the MAPK pathway had an impact on the sensitivity of AML cells to S63845. To assess AML cells' apoptosis and differentiation, in vitro studies were performed using PrestoBlue assay, Coulter electrical impedance method, flow cytometry, light microscopy and Western blot techniques. S63845 caused a concentration-dependent decrease in the viability of HL-60 and ML-1 cells and increased the percentage of apoptotic cells. Combined treatment with S63845 and ABT-737 or MAPK pathway inhibitor enhanced apoptosis but also induced differentiation of tested cells, as well as altering the expression of the MCL-1 protein. Taken together, our data provide the rationale for further studies regarding the use of MCL-1 inhibitor in combination with other pro-survival protein inhibitors.

Biological Properties of Heparins Modified with an Arylazopyrazole-Based Photoswitch

Unfractionated heparin (UFH) and enoxaparin (Enox) were substituted with a photoswitch (PS) showing quantitative trans-cis and cis-trans photoisomerizations. Long half-life of the cis photoisomer enabled comparison of the properties of heparins substituted with both PS photoisomers. Hydrodynamic diameter, D_h, of UFH-PS decreased upon trans-cis photoisomerization, the change being more pronounced for UFH-PS with a higher degree of substitution (DS), while D_h of Enox-PS did not significantly change. The anticoagulative properties of substituted heparins were significantly attenuated compared to non-substituted compounds. The interaction of UFH-PS with HSA, lysozyme, and protamine was studied with ITC. Under serum-free conditions, UFH-PS-trans with a high DS stimulated proliferation of murine fibroblasts, while UFH-PS-cis decreased the viability of these cells. Under serum conditions, both UFH-PS-cis and UFH-PS-trans decreased cell viability, the reduction for UFH-PS-cis being higher than that for UFH-PS-trans. Neither Enox-PS-trans nor Enox-PS-cis influenced the viability at concentrations prolonging aPTT, while at higher concentrations their cytotoxicity did not differ.

Itaconate Suppresses Formation of Neutrophil Extracellular Traps (NETs): Involvement of Hypoxia-Inducible Factor 1α (Hif-1α) and Heme Oxygenase (HO-1)

Neutrophil extracellular traps (NETs) immobilize pathogens during early stages of systemic inflammation but as the reaction progresses they become detrimental to endothelial cells and the organ-specific cells. For this reason it would be of importance to control their formation by either physiological or pharmacological means. Endogenously, formation of NETs is under control of cellular and whole organism metabolism as shown previously in the course of bacterial systemic inflammation, obesity or the combination of the two. Numerous leukocytes are subjected to immunometabolic regulation and in macrophages exposure to lipopolysaccharide (LPS) leads to two breaks in the Krebs cycle that impact this cell functioning. As a consequence of the first break, anti-microbial itaconic acid (itaconate) is produced whereas the second break activates hypoxia-inducible factor-1α (Hif-1α). In turn, itaconate activates transcription of the anti-inflammatory nuclear factor erythroid 2-related factor 2 (Nrf2) which upregulates cyto-protective heme oxygenase (HO-1). Here we report that exogenously added derivative of the itaconic acid, 4-octyl itaconate (4-OI), diminishes formation of NETs by neutrophils of either normal (lean) or obese mice, and independently of the age of the animals or immunoaging. Elucidating the mechanism of this inhibition we unravel that although Nrf2/HO-1 expression itself is not altered by 4-OI, it is up-regulated when compared against the NET formation while Hif-1α is downregulated in 4-OI-pre-treated LPS-stimulated neutrophils in either way. We further show that blockage of Hif-1α by its specific inhibitor diminishes NET release as does inhibition by 4-OI. Also inhibition of HO-1 activity correlates with diminished LPS-induced NET release upon pre-treatment with 4-OI albeit LPS alone induced NETs are not HO-1-dependent. In summary, we unravel that 4-OI inhibits NET formation by murine neutrophils independently of their origin (health vs. metabolically challenged animals) and the age of individuals/immunosenescence via inhibition of Hif-1α and induction of HO-1.

Metabolic Pathways Involved in Formation of Spontaneous and Lipopolysaccharide-Induced Neutrophil Extracellular Traps (NETs) Differ in Obesity and Systemic Inflammation

Obesity manifests itself with low-grade chronic inflammation that shapes immune responses during infection. Albeit obese individuals are at risk of higher mortality due to comorbidities, they are better protected from systemic inflammation. Recently, we showed that in the vasculature of obese mice kept on high-fat diet (HFD), neutrophils produce less neutrophil extracellular traps (NETs) than in lean controls (normal diet, ND). NETs are used by neutrophils to counteract severe infection, but they also cause collateral damage. Hardly anything is known about metabolic requirements for their formation, especially in the context of obesity and/or sepsis. Thus, we aimed to study the immunometabolism of NET formation by application of ex vivo neutrophil analyses (Seahorse analyzer, selective inhibitors, confocal imaging) and intravital microscopy. The obtained data show that glycolysis and/or pentose phosphate pathway are involved in NETs release by ND neutrophils in both physiological and inflammatory conditions. In contrast, such cells of septic HFD mice utilize these routes only to spontaneously cast NETs, while after secondary ex vivo activation they exhibit so called "exhausted phenotype", which manifests itself in diminished NET release despite high glycolytic potential and flexibility to oxidize fatty acids. Moreover, impact of ATP synthase inhibition on NET formation is revealed. Overall, the study shows that the neutrophil potential to cast NETs depends on both the metabolic and inflammatory state of the individual.

Scrutinizing Mechanisms of the 'Obesity Paradox in Sepsis': Obesity Is Accompanied by Diminished Formation of Neutrophil Extracellular Traps (NETs) Due to Restricted Neutrophil-Platelet Interactions

Systemic inflammation is a detrimental condition associated with high mortality. However, obese individuals seem to have higher chances of surviving sepsis. To elucidate what immunological differences exist between obese and lean individuals we studied the course of endotoxemia in mice fed high-fat diet (HFD) and ob/ob animals. Intravital microscopy revealed that neutrophil extracellular trap (NET) formation in liver vasculature is negligible in obese mice in sharp contrast to their lean counterparts (ND). Unlike in lean individuals, neutrophil influx is not driven by leptin or interleukin 33 (IL-33), nor occurs via a chemokine receptor CXCR2. In obese mice less platelets interact with neutrophils forming less aggregates. Platelets transfer from ND to HFD mice partially restores NET formation, and even further so upon P-selectin blockage on them. The study reveals that in obesity the overexaggerated inflammation and NET formation are limited during sepsis due to dysfunctional platelets suggesting their targeting as a therapeutic tool in systemic inflammation.

On Neutrophil Extracellular Trap (NET) Removal: What We Know Thus Far and Why So Little

Although neutrophil extracellular traps (NETs) were discovered only 16 years ago, they have already taken us from heaven to hell as we learned that apart from beneficial trapping of pathogens, they cause, or contribute to, numerous disorders. The latter is connected to their persistent presence in the blood or tissue, and we hardly know how they are removed in mild pathophysiological conditions and why their removal is impaired in multiple severe pathological conditions. Herein, we bring together all data available up till now on how NETs are cleared—from engaged cells, their phenotypes, to involved enzymes and molecules. Moreover, we hypothesize on why NET removal is challenged in multiple disorders and propose further directions for studies on NET removal as well as possible therapeutic strategies to have them cleared.

Reduced Neutrophil Extracellular Trap (NET) Formation During Systemic Inflammation in Mice With Menkes Disease and Wilson Disease: Copper Requirement for NET Release

Neutrophil extracellular traps (NETs) contribute to pathological disorders, and their release was directly linked to numerous diseases. With intravital microscopy (IVM), we showed previously that NETs also contribute to the pathology of systemic inflammation and are strongly deposited in liver sinusoids. Over a decade since NET discovery, still not much is known about the metabolic or microenvironmental aspects of their formation. Copper is a vital trace element essential for many biological processes, albeit its excess is potentially cytotoxic; thus, copper levels are tightly controlled by factors such as copper transporting ATPases, ATP7A, and ATP7B. By employing IVM, we studied the impact of copper on NET formation during endotoxemia in liver vasculature on two mice models of copper excess or deficiency, Wilson (ATP7B mutants) and Menkes (ATP7A mutants) diseases, respectively. Here, we show that respective ATP7 mutations lead to diminished NET release during systemic inflammation despite unaltered intrinsic capacity of neutrophils to cast NETs as tested ex vivo. In Menkes disease mice, the in vivo effect is mostly due to diminished neutrophil infiltration of the liver as unmutated mice with a subchronic copper deficiency release even more NETs than their controls during endotoxemia, whereas in Wilson disease mice, excess copper directly diminishes the capacity to release NETs, and this was further confirmed by ex vivo studies on isolated neutrophils co-cultured with exogenous copper and a copper-chelating agent. Taken together, the study extends our understanding on how microenvironmental factors affect NET release by showing that copper is not a prerequisite for NET release but its excess affects the trap casting by neutrophils.

Imaging of Neutrophils and Neutrophil Extracellular Traps (NETs) with Intravital (In Vivo) Microscopy

As we have learned during recent years, neutrophils are not just simple foot soldiers of the innate immune system with a restricted set of pro-inflammatory functions, and instead, they perform sophisticated functions (some of them only recently discovered) both in innate and adaptive immune responses. Neutrophil behavior and functioning should best be studied in situ, at locations where they are executed in a living organism, especially considering that neutrophils are mobile cells, performing their functions in distal body sites and various organs. For this herein we describe an approach to detect neutrophil presence/behavior in various organs (skin, muscle, liver) of alive mice, that is, intravital imaging/microscopy. We describe all surgeries required prior to imaging and share our methods of detection of neutrophils and neutrophil extracellular traps (NETs).

To NET or not to NET:current opinions and state of the science regarding the formation of neutrophil extracellular traps

Since the discovery and definition of neutrophil extracellular traps (NETs) 14 years ago, numerous characteristics and physiological functions of NETs have been uncovered. Nowadays, the field continues to expand and novel mechanisms that orchestrate formation of NETs, their previously unknown properties, and novel implications in disease continue to emerge. The abundance of available data has also led to some confusion in the NET research community due to contradictory results and divergent scientific concepts, such as pro- and anti-inflammatory roles in pathologic conditions, demarcation from other forms of cell death, or the origin of the DNA that forms the NET scaffold. Here, we present prevailing concepts and state of the science in NET-related research and elaborate on open questions and areas of dispute.

Age is the work of art? Impact of neutrophil and organism age on neutrophil extracellular trap formation

Neutrophil extracellular traps or NETs are released by highly activated neutrophils in response to infectious agents, sterile inflammation, autoimmune stimuli and cancer. In the cells, the nuclear envelop disintegrates and decondensation of chromatin occurs that depends on peptidylarginine deiminase 4 (PAD4) and neutrophil elastase (NE). Subsequently, proteins from neutrophil granules (e.g., NE, lactoferrin and myeloperoxidase) and the nucleus (histones) bind to decondensed DNA and the whole structure is ejected from the cell. The DNA decorated with potent antimicrobials and proteases can act to contain dissemination of infection and in sterile inflammation NETs were shown to degrade cytokines and chemokines via serine proteases. On the other hand, overproduction of NETs, or their inadequate removal and prolonged presence in vasculature or tissues, can lead to bystander damage or even initiation of diseases. Considering the pros and cons of NET formation, it is of relevance if the stage of neutrophil maturation (immature, mature and senescent cells) affects the capacity to produce NETs as the cells of different age-related phenotypes dominate in given (pathological) conditions. Moreover, the immune system of neonates and elderly individuals is weaker than in adulthood. Is the same pattern followed when it comes to NETs? The overall importance of individual and neutrophil age on the capacity to release NETs is reviewed in detail and the significance of these facts is discussed.

Decreased expression of the β2 integrin on tumor cells is associated with a reduction in liver metastasis of colorectal cancer in mice

BACKGROUND

Lymphocyte Function-Associated Antigen-1 (LFA-1; CD18/CD11a) is one of the main adhesion molecules used by immune cells to infiltrate the liver under inflammatory conditions. Recently, the expression of this integrin has also been reported on several solid tumors, including colorectal cancer. However, its functional role in the metastatic progression to the liver remains unknown. Using in vitro assays and an experimental orthotopic in vivo model of liver metastasis, we aimed to elucidate the role of tumor LFA-1 in the metastatic progression by means of the partial depletion of the β₂ subunit of LFA-1, required for integrin activation, firm adhesion and signaling.

METHODS

To do so, we evaluated the effects of β₂ reduction on the murine colon carcinoma C26 cell line on their pro-metastatic features in vitro and their metastatic potential in vivo in a mouse model of colon carcinoma metastasis to the liver.

RESULTS

The reduction in β₂ integrin expression correlated with a slower proliferation, and a reduced adhesion and migration of C26 cells in an in vitro setting. Additionally, tumor cells with a reduced in β₂ integrin expression were unable to activate the liver sinusoidal endothelial cells (LSECs). This resulted in a recovery of the cytotoxic potential of liver lymphocytes which is compromised by LSECs activated by C26 cells. This was related to the abrogation of RNA expression of inflammatory and angiogenic cytokines by C26 cells after their activation with sICAM-1, the main ligand of β₂α_L. Furthermore, in vivo tumor cell retention and metastasis were profoundly reduced, along with a decrease in the recruitment and infiltration of myeloid derived suppressor cells (MDSCs) and lymphocytes to the liver.

CONCLUSION

Taken together, our findings uncovered the modulatory role for the tumor β₂ subunit of the LFA-1 integrin in the metastatic progression of colorectal cancer to the liver by impairing activation of liver endothelium and thus, the local immune response in the liver. Besides, this integrin also showed to be critical in vivo for tumor cell retention, cytokine release, leukocyte recruitment and metastasis development. These data support a therapeutical potential of the integrin LFA-1 as a target for the treatment of colorectal liver metastasis.

CXCL9-Derived Peptides Differentially Inhibit Neutrophil Migration In Vivo through Interference with Glycosaminoglycan Interactions

Several acute and chronic inflammatory diseases are driven by accumulation of activated leukocytes due to enhanced chemokine expression. In addition to specific G protein-coupled receptor-dependent signaling, chemokine-glycosaminoglycan (GAG) interactions are important for chemokine activity in vivo. Therefore, the GAG-chemokine interaction has been explored as target for inhibition of chemokine activity. It was demonstrated that CXCL9(74-103) binds with high affinity to GAGs, competed with active chemokines for GAG binding and thereby inhibited CXCL8- and monosodium urate (MSU) crystal-induced neutrophil migration to joints. To evaluate the affinity and specificity of the COOH-terminal part of CXCL9 toward different GAGs in detail, we chemically synthesized several COOH-terminal CXCL9 peptides including the shorter CXCL9(74-93). Compared to CXCL9(74-103), CXCL9(74-93) showed equally high affinity for heparin and heparan sulfate (HS), but lower affinity for binding to chondroitin sulfate (CS) and cellular GAGs. Correspondingly, both peptides competed with equal efficiency for CXCL8 binding to heparin and HS but not to cellular GAGs. In addition, differences in anti-inflammatory activity between both peptides were detected in vivo. CXCL8-induced neutrophil migration to the peritoneal cavity and to the knee joint were inhibited with similar potency by intravenous or intraperitoneal injection of CXCL9(74-103) or CXCL9(74-93), but not by CXCL9(86-103). In contrast, neutrophil extravasation in the MSU crystal-induced gout model, in which multiple chemoattractants are induced, was not affected by CXCL9(74-93). This could be explained by (1) the lower affinity of CXCL9(74-93) for CS, the most abundant GAG in joints, and (2) by reduced competition with GAG binding of CXCL1, the most abundant ELR+ CXC chemokine in this gout model. Mechanistically we showed by intravital microscopy that fluorescent CXCL9(74-103) coats the vessel wall in vivo and that CXCL9(74-103) inhibits CXCL8-induced adhesion of neutrophils to the vessel wall in the murine cremaster muscle model. Thus, both affinity and specificity of chemokines and the peptides for different GAGs and the presence of specific GAGs in different tissues will determine whether competition can occur. In summary, both CXCL9 peptides inhibited neutrophil migration in vivo through interference with GAG interactions in several animal models. Shortening CXCL9(74-103) from the COOH-terminus limited its GAG-binding spectrum.

Differential inhibition of activity, activation and gene expression of MMP-9 in THP-1 cells by azithromycin and minocycline versus bortezomib: A comparative study

Gelatinase B or matrix metalloproteinase-9 (MMP-9) (EC 3.4.24.35) is increased in inflammatory processes and cancer, and is associated with disease progression. In part, this is due to MMP-9-mediated degradation of extracellular matrix, facilitating influx of leukocytes into inflamed tissues and invasion or metastasis of cancer cells. MMP-9 is produced as proMMP-9 and its propeptide is subsequently removed by other proteases to generate proteolytically active MMP-9. The significance of MMP-9 in pathologies triggered the development of specific inhibitors of this protease. However, clinical trials with synthetic inhibitors of MMPs in the fight against cancer were disappointing. Reports on active compounds which inhibit MMP-9 should be carefully examined in this regard. In a considerable set of recent publications, two antibiotics (minocycline and azythromycin) and the proteasome inhibitor bortezomib, used in cancers, were reported to inhibit MMP-9 at different stages of its expression, activation or activity. The current study was undertaken to compare and to verify the impact of these compounds on MMP-9. With exception of minocycline at high concentrations (>100 μM), the compounds did not affect processing of proMMP-9 into MMP-9, nor did they affect direct MMP-9 gelatinolytic activity. In contrast, azithromycin specifically reduced MMP-9 mRNA and protein levels without affecting NF-κB in endotoxin-challenged monocytic THP-1 cells. Bortezomib, although being highly toxic, had no MMP-9-specific effects but significantly upregulated cyclooxygenase-2 (COX-2) activity and PGE₂ levels. Overall, our study clarified that azithromycin decreased the levels of MMP-9 by reduction of gene and protein expression while minocycline inhibits proteolytic activity at high concentrations.

Metallothionein 2 and Heat Shock Protein 72 Protect Allolobophora chlorotica from Cadmium But Not Nickel or Copper Exposure: Body Malformation and Coelomocyte Functioning

Earthworms serve as good indicators of heavy metal contamination due to their innate sensitivity towards soil pollution. However, to date, not many studies have focused on endogeic earthworms, such as the omnipresent Allolobophora chlorotica. The current study was designed to verify whether this earthworm could serve as a novel distinctively susceptible species for environmental contamination studies. We show that the dermal exposure to Cu, Ni, and Cd affected the mortality and morphology of A. chlorotica, and the number and functioning of coelomocytes. These features particularly were pronounced in animals treated with Ni and Cu and interestingly to a lesser extend with Cd. In contrast, Cd induced a strong expression of metallothioneins (MT-2) and heat shock proteins (HSP72). The presence of MT-2 was detected not only in coelomocytes but also in the intestine, blood vessels, and epidermis. In conclusion, Allolobophora chlorotica coelomocytes are adopted to respond differentially to various heavy metals, generating powerful response towards potentially most dangerous exogenous non-essential elements.

Conservative Mechanisms of Extracellular Trap Formation by Annelida Eisenia andrei: Serine Protease Activity Requirement

Formation of extracellular traps (ETs) capturing and immobilizing pathogens is now a well-established defense mechanism added to the repertoire of vertebrate phagocytes. These ETs are composed of extracellular DNA (extDNA), histones and antimicrobial proteins. Formation of mouse and human ETs depends on enzymes (i) facilitating decondensation of chromatin by citrullination of histones, and (ii) serine proteases degrading histones. In invertebrates, initial reports revealed existence of ETs composed of extDNA and histones, and here we document for the first time that also coelomocytes, immunocompetent cells of an earthworm Eisenia andrei, cast ETs which successfully trap bacteria in a reactive oxygen species (ROS)-dependent and -independent manner. Importantly, the formation of ETs was observed not only when coelomocytes were studied ex vivo, but also in vivo, directly in the earthworm coelom. These ETs were composed of extDNA, heat shock proteins (HSP27) and H3 histones. Furthermore, the formation of E. andrei ETs depended on activity of serine proteases, including elastase-like activity. Moreover, ETs interconnected and hold together aggregating coelomocytes, a processes proceeding encapsulation. In conclusion, the study confirms ET formation by earthworms, and unravels mechanisms leading to ET formation and encapsulation in invertebrates.

Effects of aliphatic polyesters on activation of the immune system: studies on macrophages

There is a constant search for biodegradable polymers with biocompatible characteristics. However, the reported materials are rarely tested for their immunostimulatory properties, which is an important issue as immune cells activated by the polymers might cause their rejection and lead to further injury to the host tissues. Therefore, the aim of the present study was to determine if biodegradable polymers are able to activate RAW 264.7 macrophages. Aliphatic polyesters, poly(L-lactide) (PLLA), poly(L-lactide-co-trimethylene carbonate) (PLTMC), poly(glycolide-co-L-lactide) (PGLA), poly(glycolide-co-L-lactide-co-ε-caprolactone) (PGLCap) and poly(glycolide-co-ε-caprolactone) (PGCap), processed into foils by slip-casting, were characterized in terms of their structure ((1)H-NMR, GPC, DSC) and surface properties (chemical composition, water contact angle, surface free energy, topography and roughness). RAW 264.7 cells were cultured on the materials for 3 or 5 days and their adherence, numbers of apoptotic/necrotic cells, as well as production of several cytokines/chemokines and other inflammation-related molecules (matrix metalloproteinases, nitric oxide) was evaluated. The study demonstrated that PLLA and PGLA did not influence macrophage activation and survival. In contrast, PLTMC, PGLCap and PGCap significantly decreased macrophage adherence, increased ratio of apoptosis and up-regulated synthesis/release of numerous inflammatory mediators. Thus, the latter materials might initiate an undesired inflammatory reaction. The above effects of the polymers were attributed to their high hydrophobicity and low polarity due to the presence of ε-caproyl blocks (PGLCap and PGCap), and/or high flexibility and susceptibility to mechanical deformation due to low glasstransition temperature (PLTMC, PGLCap and PGCap). In conclusion, while PLLA and PGLA do not affect macrophage functioning, the other materials (PLTMC, PGLCap, PGCap) up-regulate macrophage activity.

Effective activation of antioxidant system by immune-relevant factors reversely correlates with apoptosis of Eisenia andrei coelomocytes

Oxidative stress is harmful to the microbes but also to the host, and may result in bystander damage or death. Because of this, respiratory burst triggered in phagocytes by pathogens is counteracted by production of antioxidative factors. The aim of this work was to examine effectiveness of the latter system in earthworms Eisenia andrei by induction of reactive oxygen species, lipofuscin and phenoloxidase by natural (LPS, zymosan, Micrococus luteus) and synthetic (phorbol ester, PMA) stimulants. The compounds impaired numbers, viability (increased apoptosis) and composition of coelomocytes, and triggered the antioxidant activity of catalase and selenium-dependent glutathione peroxidase. The natural pathogenic compounds, unlike PMA, strongly activated antioxidative responses that diminished cell apoptosis. Moreover, repeated exposure to the same or different pathogenic compounds did not induce respiratory burst exhausted phenotype showing that coelomocytes are constantly at bay to withstand numerous infections. The current study reveals importance and efficiency of the oxidative-antioxidative systems in annelids but also confirms its evolutionary conservatism and complexity even in lower taxa of the animal kingdom.

An iminosugar-based heparanase inhibitor heparastatin (SF4) suppresses infiltration of neutrophils and monocytes into inflamed dorsal air pouches

Local infiltration of inflammatory cells is regulated by a number of biological steps during which the cells likely penetrate through subendothelial basement membranes that contain heparan sulfate proteoglycans. In the present study, we examined whether administration of heparastatin (SF4), an iminosugar-based inhibitor of heparanase, could suppress local inflammation and degradation of heparan sulfate proteoglycans in basement membranes. In a carrageenan- or formyl peptide-induced dorsal air pouch inflammation model, the number of infiltrated neutrophils and monocytes was significantly lower in mice after topical administration of heparastatin (SF4). The concentration of chemokines MIP-2 and KC in pouch exudates of drug-treated mice was similar to control. In a zymosan-induced peritonitis model, the number of infiltrated cells was not altered in drug-treated mice. To further test how heparastatin (SF4) influences transmigration of inflammatory neutrophils, its suppressive effect on migration and matrix degradation was examined in vitro. In the presence of heparastatin (SF4), the number of neutrophils that infiltrated across a Matrigel-coated polycarbonate membrane was significantly lower, while the number of neutrophils passing through an uncoated membrane was not altered. Lysate of bone marrow-derived neutrophils released sulfate-radiolabeled macromolecules from basement membrane-like extracellular matrix, which was suppressed by heparastatin (SF4). Heparan sulfate degradation activity was almost completely abolished after incubation of lysate with protein G-conjugated anti-heparanase monoclonal antibody, strongly suggesting that the activity was due to heparanase-mediated degradation. Taken together, in a dorsal air pouch inflammation model heparastatin (SF4) potentially suppresses extravasation of inflammatory cells by impairing the degradation of basement membrane heparan sulfate.

Imaging the dynamic platelet-neutrophil response in sterile liver injury and repair in mice

Although platelets have been extensively studied in hemostasis and inflammation, their role is not well understood in sterile liver injury and repair. Using a thermally induced focal liver injury and repair model and multichannel spinning disk confocal microscopy allowed visualization of the dynamic behavior of platelets and neutrophils in this insult. Platelets instantaneously adhered to molecularly altered sinusoidal endothelium adjacent to the afflicted area, paving approximately 200 µm abutting the injury. Platelets remained adherent for at least 4 hours, but dissipated by 8 hours. The early recruitment occurred by GPIIbIIIa (CD41) and the later recruitment was dependent upon both GPIIbIIIa and GPIb (CD42B). Platelets did not occlude the vessels, but rather paved the altered endothelium. Endothelin-induced vasoconstriction by hepatic stellate cells, and not platelet accumulation or coagulation, was responsible for temporarily restricted perfusion around the injury. Neutrophils crawled into the injury from significant distances through the sinusoids. The crawling neutrophils required the platelet-paved endothelium given that very little neutrophil recruitment was noted in thrombocytopenic or CD41-deficient mice. As platelets slowly dissipated, neutrophil recruitment was also halted. Previous work suggested that platelets binding to immobilized neutrophils induced neutrophil extracellular trap (NET) formation in response to infection as well as during thrombosis and other forms of sterile injury. In this model of neutrophils crawling on immobilized platelets, very few NETs were observed and no additional injury was noted. In fact, GPIIbIIIa-deficient mice had delayed repair.

CONCLUSION

In a liver model of sterile injury and repair, platelets play a critical role in forming a substratum and pave the way for neutrophils to enter the injured site for subsequent repair.

A dynamic spectrum of monocytes arising from the in situ reprogramming of CCR2+ monocytes at a site of sterile injury

Monocytes are recruited from the blood to sites of inflammation, where they contribute to wound healing and tissue repair. There are at least two subsets of monocytes: classical or proinflammatory (CCR2(hi)CX3CR1(low)) and nonclassical, patrolling, or alternative (CCR2(low)CX3CR1(hi)) monocytes. Using spinning-disk confocal intravital microscopy and mice with fluorescent reporters for each of these subsets, we were able to track the dynamic spectrum of monocytes that enter a site of sterile hepatic injury in vivo. We observed that the CCR2(hi)CX3CR1(low) monocytes were recruited early and persisted for at least 48 h, forming a ringlike structure around the injured area. These monocytes transitioned, in situ, from CCR2(hi)Cx3CR1(low) to CX3CR1(hi)CCR2(low) within the ringlike structure and then entered the injury site. This phenotypic conversion was essential for optimal repair. These results demonstrate a local, cytokine driven reprogramming of classic, proinflammatory monocytes into nonclassical or alternative monocytes to facilitate proper wound-healing.

Interference with glycosaminoglycan-chemokine interactions with a probe to alter leukocyte recruitment and inflammation in vivo

In vivo leukocyte recruitment is not fully understood and may result from interactions of chemokines with glycosaminoglycans/GAGs. We previously showed that chlorite-oxidized oxyamylose/COAM binds the neutrophil chemokine GCP-2/CXCL6. Here, mouse chemokine binding by COAM was studied systematically and binding affinities of chemokines to COAM versus GAGs were compared. COAM and heparan sulphate bound the mouse CXC chemokines KC/CXCL1, MIP-2/CXCL2, IP-10/CXCL10 and I-TAC/CXCL11 and the CC chemokine RANTES/CCL5 with affinities in the nanomolar range, whereas no binding interactions were observed for mouse MCP-1/CCL2, MIP-1α/CCL3 and MIP-1β/CCL4. The affinities of COAM-interacting chemokines were similar to or higher than those observed for heparan sulphate. Although COAM did not display chemotactic activity by itself, its co-administration with mouse GCP-2/CXCL6 and MIP-2/CXCL2 or its binding of endogenous chemokines resulted in fast and cooperative peritoneal neutrophil recruitment and in extravasation into the cremaster muscle invivo. These local GAG mimetic features by COAM within tissues superseded systemic effects and were sufficient and applicable to reduce LPS-induced liver-specific neutrophil recruitment and activation. COAM mimics glycosaminoglycans and is a nontoxic probe for the study of leukocyte recruitment and inflammation invivo.

Impact of poly(L-lactide) versus poly(L-lactide-co-trimethylene carbonate) on biological characteristics of fibroblasts and osteoblasts

Bone tissue loss due to injury or disease often requires application ofautologous tissue grafts or artificial biomaterials to fill the fracture. Synthetic biomaterials provide temporary structural support for bone tissue and can be subsequently colonized by host tissue-specific cells. One of the most investigated groups of biomaterials are degradable polymers that naturally decompose in tissues with time. In particular aliphatic polyesters such as polylactides were reported to fulfill biocompatibility requirements as they induce a minor or lack an immune response and integrate with the surrounding tissue. Here we report on the biological effects of two polymers: poly(L-lactide) (PLLA) and a copolymer of L-lactide and trimethylene carbonate (PLTMC) on osteoblasts (MG-63) and fibroblasts (L-929). Osteoblasts are bone forming cells that are in the closest contact with the potential implant while fibroblasts produce the stroma forming the extracellular matrix (ECM) and along with macrophages initiate inflammation. We detected that both types of cells adhered better to PLLA than to PLTMC which might be related to the more rough surface of the former. However, both polymers, but especially PLTMC, increased apoptotic death of both cell types. Moreover, in contrast to PLLA, PLTMC modulated the production of some immune-related mediators by fibroblasts: it increased nitric oxide production and synthesis of numerous pro-inflammatory factors, cytokines (TNF-a and IL-6) activating leukocytes, and ECM-degrading MMP-9 which facilitates leukocyte migration. Thus, overall, our data suggest that PLTMC is less cytocompatible than PLLA.

Carp neutrophilic granulocytes form extracellular traps via ROS-dependent and independent pathways

Neutrophil extracellular traps (NETs) have recently been described as an important innate defense mechanism that leads to immobilization and killing of invading pathogens. NETs have been identified in several species, but the mechanisms involved in NET formation and their role in infection have not been well determined yet. Here we show that upon in vitro stimulation with different immunostimulants of bacterial, fungal or viral origin, carp neutrophilic granulocytes rapidly release NET structures. We analyzed the composition of these structures and the kinetics of their formation by confocal microscopy, by quantifying the levels of extracellular DNA and the release of enzymes originating from neutrophilic granules: myeloperoxidase, neutrophil elastase and matrix metalloproteinase 9 (MMP-9). Profiles of NET release by carp neutrophils as well as their enzyme composition are stimulus- and time-dependent. This study moreover provides evidence for a stimulus-dependent selective requirement of reactive oxygen species in the process of NET formation. Collectively the results support an evolutionary conserved and strictly regulated mechanism of NET formation in teleost fish.

Leptin stimulation of cell cycle and inhibition of apoptosis gene and protein expression in OVCAR-3 ovarian cancer cells

The OVCAR-3 cell line expressing the long (ObRb) and short (ObRt) isoforms of leptin receptor mRNA was used to analyze the effect of leptin on the expression of selected genes and proteins involved in the cell cycle and apoptosis. OVCAR-3 cells were exposed to 2, 20, 40, and 100 ng/ml of leptin. Cell proliferation was determined using the alamarBlue cell viability test and flow cytometry. Apoptosis was measured using a cellular DNA fragmentation ELISA kit. The expression of selected cell cycle and apoptosis genes was evaluated by real-time PCR and confirmed by western blot. The stimulatory action of leptin on cell proliferation was observed as an increase in cells in the S and G2/M phases. Up-regulation of genes responsible for inducing cell proliferation and suppression of genes responsible for inhibition of proliferation were noted. Western blots revealed increased expression of cyclins D and A and inhibition of p21WAF1/CIP1 protein expression by leptin. Inhibition of DNA fragmentation was observed under all leptin doses. Suppression of genes involved in the extrinsic and intrinsic apoptotic pathway was observed. Western blots illustrated decreased Bad, TNFR1, and caspase 6 protein expression in response to leptin treatment. Leptin promotes ovarian cancer cell line growth by up-regulating genes and proteins responsible for inducing cell proliferation as well as down-regulating pro-apoptotic genes and proteins in apoptotic pathways. Results of this study warrant examining the relationship between the risk of ovarian cancer and elevated leptin levels in obese women.

Modulation of zymosan-induced peritonitis by riboflavin co-injection, pre-injection or post-injection in male Swiss mice

AIMS

We compared the effects of riboflavin pre-injection, co-injection and post-injection on several symptoms of zymosan-induced peritonitis in male Swiss mice. Additionally, the effects of i.p. injection of riboflavin itself were elucidated.

MAIN METHODS

Peritonitis was induced in Swiss mice (50 animals) by i.p. zymosan (Z; 40mg/kg) injection. Riboflavin (R; 0, 20, 50, or 100mg/kg) was applied either alone or in combination with zymosan. In the latter case riboflavin was administered either together with zymosan (R group), or 30min before zymosan (R-Z group), or 1h later (Z-R group). The nociceptive response was evaluated by counting body writhes. The peritoneal exudates retrieved 4h after the R or Z injection were analyzed for the numbers and apoptosis of polymorphonuclear leukocytes (PMNs), and levels of metalloproteinase 9 (MMP-9), nitric oxide, and inflammatory cytokines, IL-12p70, TNFα, MCP-1, IL-6, IL-10, IFNγ.

KEY FINDINGS

Riboflavin itself induced nociceptive-related body writhes and a moderate inflammatory response manifested by PMN influx and the release of some cytokines and MMP-9. In contrast, antinociceptive properties of riboflavin were significant in the ZR group co-injected with the lowest dose of riboflavin (ZR20). At the 4th hour of zymosan-induced peritonitis an intraperitoneal accumulation of PMNs was decreased in the riboflavin-treated groups and cytokine profiles were modified according to riboflavin dose and the time of injection.

SIGNIFICANCE

Riboflavin itself induces low-grade nociception and inflammation while its effects on zymosan-induced inflammation are dependent on the dose and time of its application: either before or during inflammation.

Morphine-modulated mast cell migration and proliferation during early stages of zymosan-induced peritonitis in CBA mice

We have previously shown that supplementation of inflammation-inducing zymosan with a high dose ofmorphine inhibits peritoneal influx ofleukocytes in Swiss, C57C3H, Balb/c, and C57BL/6 strains but not in CBA mice. We have also reported that the different pattern of the response to morphine treatment might be, at least partially, due to the inter-strain differences in the peritoneal mast cell (P-MC) number (high in CBA mice versus other strains) and P-MC specific features (high sensitivity to degranulation upon morphine treatment in CBA mice). The aim of the present study was to investigate the mechanism of morphine action on P-MC in CBA mice. In particular, the effects of morphine on the proliferation and migration of P-MC in CBA mice with ongoing zymosan-induced peritonitis modulated by morphine were studied. Morphine alone acted as a strong chemoattractant for P-MC of CBA mice and this effect was opioid receptor-independent. Moreover, flow cytometric analysis showed that i.p. morphine injection induced significant proliferation of P-MC in CBA mice. Therefore, we conclude that the lack of anti-inflammatory effects of morphine during peritonitis in CBA mice might result not only from a unique sensitivity of CBA mast cells to morphine-induced degranulation but also from the fact that mast cell numbers increase at the inflammatory focus. The latter might be due to morphine-induced mast cell proliferation and/or migration.

Strain-specific effects of riboflavin supplementation on zymosan-induced peritonitis in C57BL/6J, BALB/c and CBA mice

AIMS

We investigated the effects of riboflavin (vitamin B2) on the kinetics of zymosan-induced peritonitis in three strains of mice.

MAIN METHODS

Peritonitis was induced in males of C57BL/6J, BALB/c and CBA mice by intraperitoneal injection of zymosan (40 mg/kg) or zymosan supplemented with riboflavin (50mg/kg). During the first 45 min of inflammation the pain symptoms were scored. At the selected time points (4, 6, 8, 10, 24, and 30 h) the mice were sacrificed and peritoneal exudates were retrieved. Leukocytes, among them polymorphonuclear cells (PMNs) and macrophages (Mac3(+) cells) were counted. Levels of inducible nitric oxide synthase (iNOS) were measured in cell pellets while supernatants were used for measurements of nitric oxide, cytokine/chemokines (IL-6, IL-10, MCP-1, IFNγ, TNF-α, and IL-12p70), and matrix metalloproteinase-9 (MMP-9).

KEY FINDING

A riboflavin ip injection induced pain symptoms itself, but reduced zymosan-induced pain in C57BL/6J and CBA strains of mice when coinjected with zymosan. In comparison with the mice injected with zymosan only, riboflavin coinjection prolonged inflammation in C57BL/6J mice due to prolonged macrophage accumulation; inhibited peritoneal leukocytes (PTL) accumulation in BALB/c due to inhibited influx of macrophages and PMNs; and inhibited PTL accumulation in CBA mice due to delayed PMN influx. These effects corresponded with the delayed (C57BL/6J) or inhibited (BALB/c and CBA) expression of iNOS in PTL lysates, and with the prolonged (C57BL/6) or inhibited (BALB/c) intraperitoneal accumulation of MMP-9. Moreover, cytokine accumulation was affected in a strain-specific way.

SIGNIFICANCE

Riboflavin is antinociceptive during yeast-induced peritonitis, but its anti-inflammatory effects are strain-specific.

Resident peritoneal macrophages and mast cells are important cellular sites of COX-1 and COX-2 activity during acute peritoneal inflammation

INTRODUCTION

Cyclooxygenases (COXs) play important roles during inflammation. While reports on COX-2 function in inflammation preceded those on COX-1, it is now well established that both isoforms participate in this process. During inflammation, COX expression was reported in inflammatory leukocytes, but much less is known about their presence in tissue- resident leukocytes. The aim was thus to verify the expression and activity of the COX isoforms in resident peritoneal mast cells and macrophages during acute peritonitis.

MATERIALS AND METHODS

Zymosan peritoneal inflammation was induced in C57BL/6J mice and COX-1 and COX-2 expression was evaluated by RT-PCR (mRNA level) and immunocytochemistry (protein level). COX activity was assessed by a specific assay and prostaglandin production by ELISA. Furthermore, some mice were selectively depleted of either peritoneal mast cells or macrophages and then COX activity was determined.

RESULTS

The study revealed that both COXs are expressed/active at the peak of inflammation, but COX-2 predominates during resolution. The expressions of the COXs were detectable in both populations of resident peritoneal leukocytes. In peritoneal macrophages both isoforms were active even during the late phases of peritonitis and the cells significantly contributed to PGE(2) and PGD(2) synthesis. The most striking observation was that resident macrophages are critical for PGD(2) production during the resolution of inflammation.

CONCLUSIONS

This study documents that both COX isoforms participate in all stages of acute inflammation and that tissue-resident leukocytes, especially macrophages, are important sites of COX-1/COX-2 expression and prostaglandin synthesis.

Altered apoptosis of inflammatory neutrophils in MMP-9-deficient mice is due to lower expression and activity of caspase-3

Matrix metalloproteinase 9 (MMP-9) is a Zn(2+)-dependent endopeptidase that degrades some of the components of basement membranes and extracellular matrix and thus participates in leukocyte infiltration during inflammation. In a model of zymosan peritonitis, neutrophil infiltration in MMP-deficient (MMP-9(-/-)) mice was significantly weaker at the time of their maximal influx in wild-type mice (6h). However, during the late stages of peritonitis (24h) an extended accumulation of neutrophils was observed in MMP-9(-/-)versus the wild-type mice. Recently, we reported that the ratio of apoptosis of inflammatory leukocytes is impaired in MMP-9(-/-) mice during late peritonitis and the process depends on COX-1-driven PGE(2). Here we scrutinized the alterations in apoptotic mechanisms by comparisons between MMP-9(-/-) and the wild-type mice. Altered apoptosis occurred only during late (24h) peritonitis and concerned only neutrophils, and not macrophages, mast cells or lymphocytes. Furthermore, expression and activity of caspases was altered in MMP-9(-/-) animals, delayed for caspase-8 and -9, and decreased in the case of caspase-3. Also the expression of Bax/Bcl-2 proteins was changed in MMP-9(-/-) mice. These changes, and in particular the impaired neutrophil apoptosis and weaker caspase-3 activity, were restored by the selective COX-1 inhibition. We conclude that in mice lacking MMP-9 the enhanced COX-1-PGE(2) decreases caspase-3 expression and activity leading to impaired apoptosis of inflammatory neutrophils resulting in abnormal accumulation of the cells at the inflammatory focus. The data also reinforce the notion that MMP-9 is a key enzyme in neutrophil biology.

Inflammatory macrophages, and not only neutrophils, die by apoptosis during acute peritonitis

The central paradigm says that during inflammation, after completing their function, granulocytes die apoptotically in periphery to avoid destruction of self-tissues. Here we aimed to investigate the kinetic aspect of inflammatory leukocyte apoptosis and verify whether apart from neutrophils also other inflammatory leukocytes numerously undergo apoptosis. We observed that in physiological conditions, less than 7% of either resident peritoneal macrophages or lymphocytes die apoptotically. The studies on a model of acute zymosan-induced peritoneal inflammation revealed that there are two waves of inflammatory leukocyte apoptosis. The first wave corresponds to the time of maximal neutrophil accumulation in peritoneum (6h) and the apoptotic death indeed concerns mostly neutrophils (over 30% of those cells), but also more macrophages die at this time (>10%). The second wave (at 3 days) concerns mostly macrophages (20% versus 3-6% for other populations) and coincides with the resolution of inflammation and the dominant presence of macrophages. In contrast, numbers of apoptotic T (1-3%) and B (approximately 5%) cells do not significantly change during the whole peritonitis. The two waves of apoptosis concur with an increase of caspase-8, -9 and -3 at the transcript and activity levels. The apoptosis inducer TNF-alpha is produced only during first hours while nitric oxide throughout all inflammation. Moreover, during the whole course of peritonitis the expression of pro-apoptotic Bax dominates over anti-apoptotic Bcl-2. In conclusion, we characterized kinetics of apoptotic death of inflammatory leukocytes during acute peritoneal inflammation and revealed that both phagocyte populations (neutrophils and macrophages) die numerously in peritoneum.

Effects of macrophage depletion on peritoneal inflammation in swiss mice, edible frogs and goldfish

SWISS mice, edible frogs and goldfish i.p. injected with zymosan (Z groups) develop peritoneal inflammation connected with a massive intraperitoneal accumulation of leukocytes, which is significantly diminished in mice and fish (but not frogs) by supplementation of zymosan with morphine (ZM groups). In order to check the putative role of resident peritoneal macrophages in morphine-modulated zymosan-induced peritonitis, some animals were depleted of resident macrophages by repeated i.p. injections of clodronate-liposomes (CL) followed by Z or ZM injection. In SWISS mice such CL-induced removal ofMac-3-positive cells (macrophages) resulted in an enhanced influx and prolonged accumulation of polymorphonuclear leukocytes (PMNs) in CL-Z and CL-ZM groups in comparison with their counterparts with intact macrophages. Nevertheless, supplementation of zymosan with morphine inhibited the early stages of peritonitis in CL-treated animals as it did in untreated mice. This indicates that intact peritoneal macrophages of SWISS mice are important for limiting PMN accumulation, perhaps mainly through the release of IL-10, but are not critical for the induction of anti-inflammatory effects of morphine during the early stages of peritonitis. Unexpectedly, macrophage depletion in CL-treated frogs and fish resulted in a lack of a typical peritonitis in both Z and ZM groups of these ectothermic animals.

Neutrophil elastase activity compensates for a genetic lack of matrix metalloproteinase-9 (MMP-9) in leukocyte infiltration in a model of experimental peritonitis

Extracellular proteolysis of basement membranes and matrix is required for leukocyte diapedesis and migration to the inflammatory focus. Neutrophil elastase (NE) and matrix metalloproteinases (MMPs) are among the enzymes involved in these processes, as shown in mice genetically deprived of such enzymes. However, studies with MMP-9(-/-) mice revealed that albeit neutrophil influx is impaired initially in these animals versus controls, neutrophilia is subsequently augmented during later stages of zymosan peritonitis. MMP-9 as a MMP and NE as a serine protease belong to different enzyme classes. As MMP-9 and NE are produced by neutrophils and have similar biological effects on matrix remodeling, it was evaluated whether enhanced NE activity might compensate for the lack of MMP-9. In genetically uncompromised mice, two waves of NE expression and activity during zymosan peritonitis were observed in inflammatory neutrophils and macrophages at the time of influx of the respective cell populations into the peritoneum. Additionally, NE expression was associated with the activity of resident peritoneal mast cells and macrophages, as their depletion reduced NE activity. Most importantly, the NE mRNA and protein expression and activity were enhanced significantly in MMP-9(-/-) mice during late stages of zymosan peritonitis. In addition, the application of a selective NE inhibitor restrained enhanced neutrophil accumulation significantly. In conclusion, during acute peritoneal inflammation, NE expression and activity increase gradually, facilitating leukocyte influx. Moreover, increased NE activity might compensate for a genetic lack of MMP-9 (as detected in MMP-9(-/-) mice), resulting in delayed accumulation of neutrophils during late zymosan peritonitis.

Role of lymphocytes in the course of murine zymosan-induced peritonitis

OBJECTIVE AND DESIGN

To investigate a putative role of lymphocytes in a murine model of zymosan peritonitis.

MATERIAL OR SUBJECTS

Rag-deficient mice (KO) and their counterparts (WT) (13 animals in each group).

TREATMENT

Mice were injected i. p. with zymosan (2 mg/ml, 0.5 ml/mouse) and sacrificed either 30 min or 6 h post-treatment.

METHODS

At 30 min of inflammation vascular permeability was assessed by peritoneal leakage of i. v. injected Evans blue. At 6 h of peritonitis leukocyte numbers were estimated (Turk's staining), and MMP-2 and -9 presence (zymography). Levels of inflammatory mediators were evaluated by either ELISA (PGE(2), KC) or Cytometric Bead Array (IL-6, IL-10, MCP-1, IFN-gamma, TNF-alpha, and IL-12p70). The Amount of nitric oxide (NO) was measured by the Greiss reaction. Differences between WT and KO mice were analyzed by Student's t-test (p </=0.05).

RESULTS

During zymosan peritonitis, there was a decreased production of IFN-alpha (p = 0.03) and IL-10 (p = 0.03) and elevated synthesis of NO (p = 0.0001) in KO mice compared with WT controls. Despite this, no alterations in major events of peritonitis (vascular permeability and neutrophil infiltration) were detected in KO mice.

CONCLUSIONS

Lymphocytes do not have a significant impact on zymosan peritonitis in mice.

Increased cyclooxygenase activity impairs apoptosis of inflammatory neutrophils in mice lacking gelatinase B/matrix metalloproteinase-9

Matrix metalloproteinase-9 (MMP-9)/gelatinase B plays an important role in neutrophil infiltration during inflammation and cyclooxygenases (COX-1 and COX-2) and their products are important regulators of inflammation. Recently, we reported that a genetic lack of MMP-9 impairs neutrophil infiltration during early zymosan-induced peritonitis but at later stages (> 24 hr) neutrophils persist in the peritoneal cavity. Here we show that this is the result of impaired apoptosis of MMP-9(-/-)-derived leucocytes. As enhanced COX-1 expression was reported in MMP-9(-/-) mice, we evaluated the hypothesis that altered COX expression induced the above phenomenon as COX-dependent prostaglandins can act either anti-apoptotically (PGE(2)) or pro-apoptotically (PGD(2)). The current data demonstrate that messenger RNA and protein expression of both COX isoforms and their activities are increased in MMP-9(-/-) mice during late peritonitis. Application of selective COX inhibitors revealed enhanced COX-1-dependent PGE(2) production and impaired COX-2-dependent PGD(2) synthesis in MMP-9(-/-) mice. Most importantly, inhibition of COX-1 abolished prolonged neutrophil accumulation in the peritoneal cavity of MMP-9(-/-) mice and increased apoptosis of inflammatory leucocytes. Similarly, weaker apoptosis of MMP-9(-/-) bone marrow neutrophils treated in vitro with zymosan was reversed by COX-1 inhibition. In conclusion, enhanced COX-1 expression is responsible for persistent neutrophil presence in the peritoneum of MMP-9(-/-) mice because of increased synthesis of anti-apoptotic PGE(2). In non-transgenic mice, however, inflammatory leucocytes die apoptotically in the late stages of peritonitis as a result of COX-2-dependent PGD(2) activity. Overall, we show a dependence of COX expression on the presence of MMP-9.

Expression profiles of matrix metalloproteinase 9 in teleost fish provide evidence for its active role in initiation and resolution of inflammation

Matrix metalloproteinase 9 (MMP-9) belongs to a family of zinc-dependent endopeptidases. As a consequence of its ability to cleave structural extracellular matrix molecules, mammalian MMP-9 is associated with vital inflammatory processes such as leucocyte migration and tissue remodelling and regeneration. Interestingly, MMP-9 genes have been identified in fish, but functional data are still limited and focus on the involvement of MMP-9 in embryonic development, reproduction and post-mortem tenderization. Here, we describe the involvement of MMP-9 in the innate immunity of carp. In carp, MMP-9 was most notably expressed in classical fish immune organs and in peritoneal and peripheral blood leucocytes, indicating a role of MMP-9 in immune responses. In our well-characterized zymosan-induced peritonitis model for carp, we analysed expression of the MMP-9 gene and the gelatinolytic levels of both pro- and activated forms of MMP-9. The biphasic profile of MMP-9 mRNA expression indicated involvement during the initial phase of inflammation and during the later phase of tissue remodelling. Also, in vitro stimulation of carp phagocytes with lipopolysaccharide or concanavalin A increased MMP-9 gene expression, with a peak at 24 hr. The increase of MMP-9 mRNA correlated with the peak of MMP-9 gelatinolytic level in culture supernatants. These results provide evidence for an evolutionarily conserved and relevant role of MMP-9 in the innate immune response.

Gelatinase B/MMP-9 as an inflammatory marker enzyme in mouse zymosan peritonitis: comparison of phase-specific and cell-specific production by mast cells, macrophages and neutrophils

Neutrophil infiltration during zymosan peritonitis depends on matrix metalloproteinase-9 (MMP-9) activity as it is impaired both in MMP-9(-/-) and gelatinase inhibitor-treated animals. The producer cells of MMP-9 and their relative contribution are not known. The aim of this study was to identify and compare the cellular sources, timing and intensity of MMP-9 induction by zymosan in the murine peritoneal cavity. We detected MMP-9 mRNA in unstimulated peritoneal leukocytes and its levels increased after zymosan administration. To detect MMP-9 by flow cytometry, we selected and compared two specific monoclonal antibodies. We show that MMP-9 protein was absent in control peritoneal macrophages, whereas already at 30min of peritonitis almost all macrophages were producing the enzyme. Conversely, MMP-9 was constitutively present in unstimulated mast cells. Macrophages turned out to be prevalent MMP-9 producers in the early phase of peritonitis. During later stages macrophages kept the high expression of MMP-9 for at least 6h of inflammation. In contrast, the early phase expression of MMP-9 by neutrophils was limited albeit the highest percentage of MMP-9(+) neutrophils was observed at 2h but absolute numbers of the MMP-9 carrying neutrophils were low at that time. In contrast, during the late phase of peritonitis neutrophils became major producers of MMP-9 as they numerously infiltrated peritoneum. In conclusion, the study reports detection of MMP-9 at the single-cell level during peritonitis, demonstrates unexpectedly fast MMP-9 expression in macrophages and reveals quantitatively phase-specific contribution of mast cells, macrophages and neutrophils.

Resident peritoneal leukocytes are important sources of MMP-9 during zymosan peritonitis: superior contribution of macrophages over mast cells

Metalloproteinase 9 (MMP-9) is crucial for normal neutrophil infiltration into zymosan-inflamed peritoneum. During the course of zymosan peritonitis MMP-9 is produced in a biphasic-manner as its presence is detectable as early as 30 min post zymosan and then between 2 and 8 h of inflammation. As inflammatory leukocytes were shown to produce MMP-9 we asked if also resident leukocytes, mast cells and macrophages, contribute to its production. And furthermore, if their contribution is limited only to the early phase of inflammation or extends to the later stages. For this purpose some mice were depleted of either resident macrophages or functional mast cells and expression of MMP-9 in peritoneal leukocytes and its release to the exudate were monitored. It turned out that depletion of peritoneal macrophages decreased both MMP-9 content in the leukocytes and its release to the inflammatory exudate at 30 min and 6h of peritonitis. The functional depletion of mast cells also caused a significant decrease in the production/release of MMP-9 that was especially apparent at the early time point (30 min). Moreover, the study shows concomitant kinetics of MMP-9 expression in leukocytes and its release to the exudatory fluid. The findings indicate that resident tissue leukocytes, and among them especially macrophages, constitute an important source of MMP-9 during acute peritoneal inflammation. Overall, the study shows that resident tissue leukocytes, mostly macrophages, constitute an important cellular source(s) of inflammation-related factors and should be regarded as possible targets of anti-inflammatory treatment.

Enhanced early vascular permeability in gelatinase B (MMP-9)-deficient mice: putative contribution of COX-1-derived PGE2 of macrophage origin

Increased vascular permeability leading to vascular leakage is a central feature of all inflammatory reactions and is critical for the formation of an inflammatory exudate. The leakage occurs because of gap formation between endothelial cells and breakdown of the basement membrane barriers. The present study aimed to investigate the role of gelatinase B [matrix metalloproteinase 9 (MMP-9)], known to be involved in neutrophil exudation, in changes of vascular permeability at the early stages of acute zymosan peritonitis. We show that although MMP-9 is being released already within the first minutes of peritonitis, its lack, induced pharmacologically or genetically, does not decrease but rather increases vasopermeability. In mice treated with an inhibitor of gelatinases (A and B), a tendency to increased vasopermeability existed, and in MMP-9-/- mice [knockout (KO)], the difference was statistically significant in comparison with their controls. Moreover, in intact KO mice, significantly augmented production of prostaglandin E(2) (PGE(2)) of cyclooxygenase 1 (COX-1) origin was detected, and depletion of peritoneal macrophages, but not mast cells, decreased vasopermeability in KO mice. Thus, the increase of vasopermeability observed on KO mice is a result of the increased production of COX-1-derived PGE(2) by peritoneal macrophages. We conclude that genetic deficiency in gelatinase B might lead to the development of a compensatory mechanism involving the COX pathway.

Gelatinase B/matrix metalloproteinase-9 contributes to cellular infiltration in a murine model of zymosan peritonitis

Murine zymosan-induced peritonitis represents a well-defined model of acute inflammation. However, the molecular mechanisms by which leukocytes degrade basement membranes during extravasation into the peritoneum are not clear. Gelatinase B (MMP-9) is thought to participate in cellular migration, yet its role in leukocyte transmigration through endothelia during inflammation remains controversial. The aim of the present study was to evaluate the role of MMP-9 in the cell influx during zymosan-induced experimental peritonitis. In zymosan-treated Balb/c mice MMP-9 and its natural inhibitor (tissue inhibitor of metalloproteinase 1 - TIMP-1) were present in the peritoneal fluid and plasma at the time of peritoneal neutrophil (polymorphonuclear leukocyte - PMN) infiltration and persisted there until the time of monocytes/macrophages influx. To probe the function of gelatinases, gelatinase B-deficient mice (MMP-9(-/-)) were used as well as Balb/c mice treated with cyclic CTTHWGFTLC (INH), a specific peptide inhibitor of gelatinases. The studies revealed that in either group of mice deprived of MMP-9 activity, PMN infiltration was impaired at the time of their maximal extravasation (6h) while tumor necrosis factor alpha (TNF-alpha), cytokine-induced neutrophil chemoattractant (KC) and interleukin 10 (IL-10) levels were not changed. At later stages (24 h post-zymosan) a significant increase in PMNs was observed in MMP-9(-/-) mice, but not in the inhibitor-treated mice, in comparison to their respective controls. Moreover, intraperitoneal (i.p.) injection of recombinant mouse pro-MMP-9 induced leukocyte accumulation in peritoneum. Collectively, the findings indicate that gelatinase B participates in leukocyte transmigration; however, its function can be compensated by other mechanisms.

Shedding light on vascular permeability during peritonitis: role of mast cell histamine versus macrophage cysteinyl leukotrienes

The inflammatory response consists of sequential steps that are essentially the same whatever the cause and wherever the site. The main purpose of inflammation is to bring fluid, proteins, and cells from the blood into the damaged tissues. Therefore there are mechanisms that allow cells and proteins to gain access to extravascular sites, where and when they are needed if damage and infection has occurred. A critical process for formation of inflammatory exudate is an increase in permeability of local blood vessels. Vasopermeability changes can be usually attributed to mast cells and their mediators but recent studies reveal that also macrophages can be involved in this process. This short commentary discusses new data on cellular origin of major vasoactive mediators, and their receptors during peritoneal inflammation in mice.

Early vascular permeability in murine experimental peritonitis is co-mediated by resident peritoneal macrophages and mast cells: crucial involvement of macrophage-derived cysteinyl-leukotrienes

The initial phase of zymosan-induced peritonitis involves an increase of vascular permeability (peak at 30 min) that is correlated with high levels of vasoactive eicosanoids, namely, prostaglandins (PGI2 and PGE2) of cyclooxygenase-1 origin (as estimated by RT-PCR) and cysteinyl-leukotrienes. Previously, we showed that the increase of vascular permeability can be attributed only partially to mast cells and their histamine, as seen in mast cell-deficient WBB6F1-W/Wv mice. Thus we aimed to identify the major cellular source(s) that mediate vasopermeability, as well as particular vasoactive mediators operating in this model. For this purpose, some mice were selectively depleted of either peritoneal macrophages or mast cells, and/or they were treated with several pharmacologic inhibitors of cyclooxygenase- and lipoxygenase-metabolic pathways. More-over, macrophage-depleted mast cell-deficient WBB6F1-W/Wv mice and their controls (+/+) were used. The macrophage depletion always caused a profound decrease of both vascular permeability and lipid-mediator levels, which was particularly pronounced for leukotrienes, whereas the effects of mast-cell depletion were less severe. The macrophage/mast-cell co-mediation of vasopermeability was also revealed in thioglycolate-induced peritonitis, as well as the macrophage origin of cysteinyl-leukotrienes. Taken together, these findings demonstrate that the resident peritoneal macrophages are in fact the main contributors to the vasopermeability at the early stages of zymosan-induced peritonitis.

Critical role of mast cells in morphine-mediated impairment of zymosan-induced peritonitis in mice

OBJECTIVE AND DESIGN

Zymosan-induced peritoneal inflammation is significantly inhibited in mice injected with an irritant supplemented with morphine. The aim of the present study was to examine the putative mast cell involvement in this inhibition.

SUBJECTS

Peritonitis was induced in WBB6FI mice (genetically mast cell-deficient W/Wv and their control littermaters +/+) and in Balb/c mice, with normal mast cells (MC) and mast cell-depleted (MCx) by pretreatment with compound 48/80. Bone marrow leukocytes from intact Balb/c mice were tested for their sensitivity to chemoattractants after in vitro incubation with morphine (10(-6) M), with or without preincubation with naltrexone (10(-8) M). Control cells were incubated in medium only.

TREATMENT

Peritonitis was induced by i.p. injection of either zymosan only (Z, 2 mg/ml) or zymosan supplemented with morphine (ZM, M: 20 mg/kg), without or with pretreatment with naltrexone (NZM, N: 5 mg/kg).

METHODS

Thirty minutes after induction of peritonitis, the histamine levels (ELISA) and vascular permeability (Evans blue leakage) were measured. At 6 h, the number of exudatory leukocytes (haemocytometer) and chemotaxis/chemoattractant level (48-well chemotactic chamber) were estimated.

RESULTS

(1) At 6 h of peritonitis, the number of exudatory leukocytes and levels of plasma chemoattractants were significantly lower in animals injected with zymosan supplemented with morphine (ZM) than in Z and NZM groups of WBB6F1 and Balb/c mice, but only in those with normal mast cells, and not in their mast cell-deficient/depleted counterparts. (2) In contrast, at 30 minutes, vascular permeability and histamine levels were higher in ZM than in Z group of mice with normal mast cells (MC), but not in those depleted of mast cells (MCx). (3) In vitro preincubation of leukocytes with morphine inhibited their migratory activity only towards peritoneal fluid from zymosan-treated MC mice but not from their MCx counterparts.

CONCLUSIONS

Mast cell-derived factors are involved in morphine-mediated impairment of zymosan-induced peritonitis in mice.