RNA-Seq Profiling of Neutrophil-Derived Microvesicles in Alzheimer's Disease Patients Identifies a miRNA Signature That May Impact Blood-Brain Barrier Integrity

(1) Background: Systemic infection is associated with increased neuroinflammation and accelerated cognitive decline in AD patients. Activated neutrophils produce neutrophil-derived microvesicles (NMV), which are internalised by human brain microvascular endothelial cells and increase their permeability in vitro, suggesting that NMV play a role in blood–brain barrier (BBB) integrity during infection. The current study investigated whether microRNA content of NMV from AD patients is significantly different compared to healthy controls and could impact cerebrovascular integrity. (2) Methods: Neutrophils isolated from peripheral blood samples of five AD and five healthy control donors without systemic infection were stimulated to produce NMV. MicroRNAs isolated from NMV were analysed by RNA-Seq, and online bioinformatic tools were used to identify significantly differentially expressed microRNAs in the NMV. Target and pathway analyses were performed to predict the impact of the candidate microRNAs on vascular integrity. (3) Results: There was no significant difference in either the number of neutrophils (p = 0.309) or the number of NMV (p = 0.3434) isolated from AD donors compared to control. However, 158 microRNAs were significantly dysregulated in AD NMV compared to controls, some of which were associated with BBB dysfunction, including miR-210, miR-20b-5p and miR-126-5p. Pathway analysis revealed numerous significantly affected pathways involved in regulating vascular integrity, including the TGFβ and PDGFB pathways, as well as Hippo, IL-2 and DNA damage signalling. (4) Conclusions: NMV from AD patients contain miRNAs that may alter the integrity of the BBB and represent a novel neutrophil-mediated mechanism for BBB dysfunction in AD and the accelerated cognitive decline seen as a result of a systemic infection.

Hypoxia Increases the Potential for Neutrophil-mediated Endothelial Damage in Chronic Obstructive Pulmonary Disease

Rationale: Patients with chronic obstructive pulmonary disease (COPD) experience excess cardiovascular morbidity and mortality, and exacerbations further increase the risk of such events. COPD is associated with persistent blood and airway neutrophilia and systemic and tissue hypoxia. Hypoxia augments neutrophil elastase release, enhancing capacity for tissue injury. Objective: To determine whether hypoxia-driven neutrophil protein secretion contributes to endothelial damage in COPD. Methods: The healthy human neutrophil secretome generated under normoxic or hypoxic conditions was characterized by quantitative mass spectrometry, and the capacity for neutrophil-mediated endothelial damage was assessed. Histotoxic protein concentrations were measured in normoxic versus hypoxic neutrophil supernatants and plasma from patients experiencing COPD exacerbation and healthy control subjects. Measurements and Main Results: Hypoxia promoted PI3Kγ-dependent neutrophil elastase secretion, with greater release seen in neutrophils from patients with COPD. Supernatants from neutrophils incubated under hypoxia caused pulmonary endothelial cell damage, and identical supernatants from COPD neutrophils increased neutrophil adherence to endothelial cells. Proteomics revealed differential neutrophil protein secretion under hypoxia and normoxia, and hypoxia augmented secretion of a subset of histotoxic granule and cytosolic proteins, with significantly greater release seen in COPD neutrophils. The plasma of patients with COPD had higher content of hypoxia-upregulated neutrophil-derived proteins and protease activity, and vascular injury markers. Conclusions: Hypoxia drives a destructive "hypersecretory" neutrophil phenotype conferring enhanced capacity for endothelial injury, with a corresponding signature of neutrophil degranulation and vascular injury identified in plasma of patients with COPD. Thus, hypoxic enhancement of neutrophil degranulation may contribute to increased cardiovascular risk in COPD. These insights may identify new therapeutic opportunities for endothelial damage in COPD.

Fibrinogen αC-subregions critically contribute blood clot fibre growth, mechanical stability, and resistance to fibrinolysis

Fibrinogen is essential for blood coagulation. The C-terminus of the fibrinogen α-chain (αC-region) is composed of an αC-domain and αC-connector. Two recombinant fibrinogen variants (α390 and α220) were produced to investigate the role of subregions in modulating clot stability and resistance to lysis. The α390 variant, truncated before the αC-domain, produced clots with a denser structure and thinner fibres. In contrast, the α220 variant, truncated at the start of the αC-connector, produced clots that were porous with short, stunted fibres and visible fibre ends. These clots were mechanically weak and susceptible to lysis. Our data demonstrate differential effects for the αC-subregions in fibrin polymerisation, clot mechanical strength, and fibrinolytic susceptibility. Furthermore, we demonstrate that the αC-subregions are key for promoting longitudinal fibre growth. Together, these findings highlight critical functions of the αC-subregions in relation to clot structure and stability, with future implications for development of novel therapeutics for thrombosis.

Elimination of fibrin γ-chain cross-linking by FXIIIa increases pulmonary embolism arising from murine inferior vena cava thrombi

The onset of venous thromboembolism, including pulmonary embolism, represents a significant health burden affecting more than 1 million people annually worldwide. Current treatment options are based on anticoagulation, which is suboptimal for preventing further embolic events. In order to develop better treatments for thromboembolism, we sought to understand the structural and mechanical properties of blood clots and how this influences embolism in vivo. We developed a murine model in which fibrin γ-chain cross-linking by activated Factor XIII is eliminated (FGG3X) and applied methods to study thromboembolism at whole-body and organ levels. We show that FGG3X mice have a normal phenotype, with overall coagulation parameters and platelet aggregation and function largely unaffected, except for total inhibition of fibrin γ-chain cross-linking. Elimination of fibrin γ-chain cross-linking resulted in thrombi with reduced strength that were prone to fragmentation. Analysis of embolism in vivo using Xtreme optical imaging and light sheet microscopy demonstrated that the elimination of fibrin γ-chain cross-linking resulted in increased embolization without affecting clot size or lysis. Our findings point to a central previously unrecognized role for fibrin γ-chain cross-linking in clot stability. They also indirectly indicate mechanistic targets for the prevention of thrombosis through selective modulation of fibrin α-chain but not γ-chain cross-linking by activated Factor XIII to reduce thrombus size and burden, while maintaining clot stability and preventing embolism.

Neutrophil-Derived Microvesicle Induced Dysfunction of Brain Microvascular Endothelial Cells In Vitro

The blood-brain barrier (BBB), composed of brain microvascular endothelial cells (BMEC) that are tightly linked by tight junction (TJ) proteins, restricts the movement of molecules between the periphery and the central nervous system. Elevated systemic levels of neutrophils have been detected in patients with altered BBB function, but the role of neutrophils in BMEC dysfunction is unknown. Neutrophils are key players of the immune response and, when activated, produce neutrophil-derived microvesicles (NMV). NMV have been shown to impact the integrity of endothelial cells throughout the body and we hypothesize that NMV released from circulating neutrophils interact with BMEC and induce endothelial cell dysfunction. Therefore, the current study investigated the interaction of NMV with human BMEC and determined whether they altered gene expression and function in vitro. Using flow cytometry and confocal imaging, NMV were shown to be internalized by the human cerebral microvascular endothelial cell line hCMEC/D3 via a variety of energy-dependent mechanisms, including endocytosis and macropinocytosis. The internalization of NMV significantly altered the transcriptomic profile of hCMEC/D3, specifically inducing the dysregulation of genes associated with TJ, ubiquitin-mediated proteolysis and vesicular transport. Functional studies confirmed NMV significantly increased permeability and decreased the transendothelial electrical resistance (TEER) of a confluent monolayer of hCMEC/D3. These findings indicate that NMV interact with and affect gene expression of BMEC as well as impacting their integrity. We conclude that NMV may play an important role in modulating the permeability of BBB during an infection.

Microvesicles in vascular homeostasis and diseases. Position Paper of the European Society of Cardiology (ESC) Working Group on Atherosclerosis and Vascular Biology

Microvesicles are members of the family of extracellular vesicles shed from the plasma membrane of activated or apoptotic cells. Microvesicles were initially characterised by their pro-coagulant activity and described as "microparticles". There is mounting evidence revealing a role for microvesicles in intercellular communication, with particular relevance to hemostasis and vascular biology. Coupled with this, the potential of microvesicles as meaningful biomarkers is under intense investigation. This Position Paper will summarise the current knowledge on the mechanisms of formation and composition of microvesicles of endothelial, platelet, red blood cell and leukocyte origin. This paper will also review and discuss the different methods used for their analysis and quantification, will underline the potential biological roles of these vesicles with respect to vascular homeostasis and thrombosis and define important themes for future research.

Experimental Approaches to Study Endothelial Responses to Shear Stress

SIGNIFICANCE

Shear stress controls multiple physiological processes in endothelial cells (ECs).

RECENT ADVANCES

The response of ECs to shear has been studied using a range of in vitro and in vivo models.

CRITICAL ISSUES

This article describes some of the experimental techniques that can be used to study endothelial responses to shear stress. It includes an appraisal of large animal, rodent, and zebrafish models of vascular mechanoresponsiveness. It also describes several bioreactors to apply flow to cells and physical methods to separate mechanoresponses from mass transport mechanisms.

FUTURE DIRECTIONS

We conclude that combining in vitro and in vivo approaches can provide a detailed mechanistic view of vascular responses to force and that high-throughput systems are required for unbiased assessment of the function of shear-induced molecules. Antioxid. Redox Signal. 25, 389-400.

Factor XIII A-Subunit V34L Variant Affects Thrombus Cross-Linking in a Murine Model of Thrombosis

OBJECTIVE

Factor XIII (FXIII) cross-links fibrin upon activation by thrombin. Activation involves cleavage at residue 37 by thrombin, releasing an activation peptide. A common polymorphism (valine to leucine variant at residue 34, V34L), located in the activation peptide, has been associated with increased activation rates and paradoxically a protective effect in cardiovascular disease. There is, currently, no data available on the effects of V34L from in vivo models of thrombosis. We examined the effect of FXIII V34L on clot formation and cross-linking in vivo.

APPROACH AND RESULTS

We generated a panel of full-length recombinant human FXIII-A2 variants with amino acid substitutions in the activation peptide to investigate the effect of these variants on activation rate, and we used wild-type, V34L, and alanine to glycine variant at residue 33 variants to study the effects of varying FXIII activation rate on thrombus formation in a murine model of FeCl3 injury. FXIII activation assay showed that residues 29, 30, 33, and 34 play a critical role in thrombin interaction. Full-length recombinant human FXIII-A2 V34L has significant effects on clot formation, structure, and lysis in vitro, using turbidity assay. This variant influenced fibrin cross-linking but not size of the thrombus in vivo.

CONCLUSIONS

Mutations in the activation peptide of full-length recombinant FXIII regulate activation rates by thrombin, and V34L influences in vivo thrombus formation by increased cross-linking of the clot.

Roles of fibrin α- and γ-chain specific cross-linking by FXIIIa in fibrin structure and function

Factor XIII is responsible for the cross-linking of fibrin γ-chains in the early stages of clot formation, whilst α-chain cross-linking occurs at a slower rate. Although γ- and α-chain cross-linking was previously shown to contribute to clot stiffness, the role of cross-linking of both chains in determining clot structure is currently unknown. Therefore, the aim of this study was to determine the role of individual α- and γ-chain cross-linking during clot formation, and its effects on clot structure. We made use of a recombinant fibrinogen (γQ398N/Q399N/K406R), which does not allow for γ-chain cross-linking. In the absence of cross-linking, intact D-D interface was shown to play a potential role in fibre appearance time, clot stiffness and elasticity. Cross-linking of the fibrin α-chain played a role in the thickening of the fibrin fibres over time, and decreased lysis rate in the absence of α2-antiplasmin. We also showed that α-chain cross-linking played a role in the timing of fibre appearance, straightening fibres, increasing clot stiffness and reducing clot deformation. Cross-linking of the γ-chain played a role in fibrin fibre appearance time and fibre density. Our results show that α- and γ-chain cross-linking play independent and specific roles in fibrin clot formation and structure.

L- and P-selectins collaborate to support leukocyte rolling in vivo when high-affinity P-selectin-P-selectin glycoprotein ligand-1 interaction is inhibited

P-selectin glycoprotein ligand-1 (PSGL-1) binding to P-selectin controls early leukocyte rolling during inflammation. Interestingly, antibodies and pharmacological inhibitors (eg, rPSGL-Ig) that target the N-terminus of PSGL-1 reduce but do not abolish P-selectin-dependent leukocyte rolling in vivo whereas PSGL-1-deficient mice have almost no P-selectin-dependent rolling. We have investigated mechanisms of P-selectin-dependent, PSGL-1-independent rolling using intravital microscopy. Initially we used fluorescent microspheres to study the potential of L-selectin and the minimal selectin ligand sialyl Lewis(x) (sLe(x)) to interact with postcapillary venules in the absence of PSGL-1. Microspheres coated with combinations of L-selectin and sLe(x) interacted with surgically stimulated cremaster venules in a P-selectin-dependent manner. Microspheres coated with either L-selectin or sLe(x) alone showed less evidence of interaction. We also investigated leukocyte rolling in the presence of PSGL-1 antibody or inhibitor (rPSGL-Ig), both of which partially inhibited P-selectin-dependent leukocyte rolling. Residual rolling was substantially inhibited by L-selectin-blocking antibody or a previously described sLe(x) mimetic (CGP69669A). Together these data suggest that leukocytes can continue to roll in the absence of optimal P-selectin/PSGL-1 interaction using an alternative mechanism that involves P-selectin-, L-selectin-, and sLe(x)-bearing ligands.

The anti-inflammatory effects of a selectin ligand mimetic, TBC-1269, are not a result of competitive inhibition of leukocyte rolling in vivo

Selectins and their ligands support leukocyte rolling, facilitating the subsequent firm adhesion and migration that occur during inflammation. TBC-1269 (Bimosiamose), a structural mimetic of natural selectin ligands, inhibits P-, E-, and L-selectin in vitro, has anti-inflammatory effects in vivo, and recently underwent phase II clinical trials for childhood asthma and psoriasis. We studied whether the anti-inflammatory effects of TBC-1269 could be related to leukocyte rolling in vivo. Although TBC-1269 inhibited rolling of a murine leukocyte cell line on murine P-selectin in vitro and thioglycollate-induced peritonitis in vivo, it did not alter leukocyte rolling in mouse cremaster venules. TBC-1269 reduced neutrophil recruitment in thioglycollate-induced peritonitis in wild-type and P-selectin-/- mice but not in E-selectin-/- mice. We suggest that the in vivo effects of TBC-1269 may be mediated through E-selectin but do not appear to involve leukocyte rolling.

Alveolar Macrophage Apoptosis Contributes to Pneumococcal Clearance in a Resolving Model of Pulmonary Infection

The role of alveolar macrophages (AM) in host defense against pulmonary infection has been difficult to establish using in vivo models. This may reflect a reliance on models of fulminant infection. To establish a unique model of resolving infection, with which to address the function of AM, C57BL/6 mice received low-dose intratracheal administration of pneumococci. Administration of low doses of pneumococci produced a resolving model of pulmonary infection characterized by clearance of bacteria without features of pneumonia. AM depletion in this model significantly increased bacterial outgrowth in the lung. Interestingly, a significant increase in the number of apoptotic AM was noted with the low-dose infection as compared with mock infection. Caspase inhibition in this model decreased AM apoptosis and increased the number of bacteremic mice, indicating a novel role for caspase activation in pulmonary innate defense against pneumococci. These results suggest that AM play a key role in clearance of bacteria from the lung during subclinical infection and that induction of AM apoptosis contributes to the microbiologic host defense against pneumococci.

Recombinant P-selectin glycoprotein ligand-1 directly inhibits leukocyte rolling by all 3 selectins in vivo: complete inhibition of rolling is not required for anti-inflammatory effect

Selectin-dependent leukocyte rolling is one of the earliest steps of an acute inflammatory response and, as such, contributes to many inflammatory diseases. Although inhibiting leukocyte rolling with selectin antagonists is a strategy that promises far-reaching clinical benefit, the perceived value of this strategy has been limited by studies using inactive, weak, or poorly characterized antagonists. Recombinant P-selectin glycoprotein ligand-1-immunoglobulin (rPSGL-Ig) is a recombinant form of the best-characterized selectin ligand (PSGL-1) fused to IgG, and is one of the best prospects in the search for effective selectin antagonists. We have used intravital microscopy to investigate the ability of rPSGL-Ig to influence leukocyte rolling in living blood vessels and find that it can reduce rolling dependent on each of the selectins in vivo. Interestingly, doses of rPSGL-Ig required to reverse pre-existing leukocyte rolling are 30-fold higher than those required to limit inflammation, suggesting additional properties of this molecule. In support of this, we find that rPSGL-Ig can bind the murine chemokine KC and inhibit neutrophil migration toward this chemoattractant in vitro.

Caspase-1-deficient mice have delayed neutrophil apoptosis and a prolonged inflammatory response to lipopolysaccharide-induced acute lung injury

Caspase-1, the prototypic caspase, is known to process the cytokines IL-1beta and IL-18 to mature forms but it is unclear whether, like other caspases, it can induce apoptosis by activation of downstream protease cascades. Neutrophils are known to express caspase-1, to release IL-1beta and to undergo rapid, caspase-dependent apoptosis. We examined apoptosis and IL-1beta production in peripheral blood neutrophils of caspase-1-deficient and wild-type mice. Constitutive apoptosis of caspase-1-deficient neutrophils was delayed compared with wild-type neutrophils and LPS-mediated inhibition of apoptosis was absent, but caspase-1-deficient neutrophils were susceptible to Fas-mediated apoptosis. LPS-stimulated IL-1beta production was absent from caspase-1-deficient neutrophils. To ascertain whether these differences in apoptosis and IL-1beta production would alter the response to acute lung injury, we studied pulmonary neutrophil accumulation following intratracheal administration of LPS. Caspase-1-deficient mice showed increased, predominantly neutrophilic pulmonary inflammation, but inflammation had resolved in both wild-type and deficient animals by 72 h after LPS instillation. IL-1beta production was increased in wild-type lungs but was also detected in caspase-1-deficient mice. We conclude that caspase-1 modulates apoptosis of both peripheral blood and inflammatory neutrophils, but is not essential for IL-1beta production in the lung.

A novel method for isolation of neutrophils from murine blood using negative immunomagnetic separation

Inappropriate neutrophil activation has been implicated in the pathology of several clinically important inflammatory conditions. Although murine models are extensively used in the investigation of such pathological processes, a reliable method by which viable, quiescent neutrophils can be isolated from murine blood has not been developed. Here we describe a novel method based on negative immunomagnetic separation, which yields highly pure populations of murine neutrophils. Blood is incubated with a cocktail of antibodies against specific cell markers on unwanted cells, and then with secondary antibody-coated magnetic beads. After running the preparation through a column within a magnetic field, labeled cells are retained, and a neutrophil-rich effluent is collected. This method yields a >95% pure suspension of >97% viable neutrophils, recovering approximately 70% of neutrophils from whole blood. Flow cytometric analysis shows little difference in surface L-selectin and CD18 expression on isolated neutrophils compared with neutrophils in whole blood, indicating that neutrophils are minimally activated bythe isolation process. Stimulation with phorbol 12-myristate 13-acetate (PMA) reduced L-selectin andincreased CD18 expression. Isolated neutrophilsmigrate under agarose in response to fMLP, and fluorescently labeled neutrophils transfused into recipient mice interact with postcapillary venules in a manner comparable to endogenous leukocytes. These findings show that neutrophils isolated using this method can be used for inflammatory studies in vitro and in vivo.

Dominant role of L- and P-selectin in mediating CXC chemokine-induced neutrophil migration in vivo

The role of selectins in neutrophil emigration in response to the CXC chemokines KC and MIP-2 was investigated in wild type and P-selectin deficient mice. Intrapleural injection of KC or MIP-2 induced a rapid and specific neutrophil accumulation. Emigration 2 h after KC or MIP-2 was reduced 83 - 88% by anti-L-selectin mAb and 53 - 63% by anti-P-selectin mAb. Co-administration of anti-L- and P-selectin mAbs abolished neutrophil migration induced by either chemokine. An anti-E-selectin mAb tested alone did not affect KC-induced neutrophil migration after 2 or 4 h. Moreover, anti-E-selectin did not have an additive inhibitory effect on KC-induced neutrophil migration compared with P-selectin blockade alone. This was found when neutrophil migration was measured at 2 and 4 h after KC. Despite a blood neutrophilia, neutrophil migration at 2 and 4 h after KC was markedly smaller (by approximately 90%) in P-selectin deficient mice compared with wild type animals. Responses at both time points were not decreased further in animals given E-selectin mAb but were reduced to the PBS control level in the presence of anti-L-selectin. In vitro study of cultured murine endothelial cells demonstrated that KC can directly increase cell surface P-selectin expression. These data suggest that CXC chemokine-induced neutrophil accumulation is dependent on both neutrophil L-selectin and a rapid upregulation of endothelial P-selectin but there is no evidence for E-selectin induction.

Differential effects of CD18, CD29, and CD49 integrin subunit inhibition on neutrophil migration in pulmonary inflammation

Neutrophil migration to lung alveoli is a characteristic of lung diseases and is thought to occur primarily via capillaries rather than postcapillary venules. The role of adhesion molecules CD18 and CD29 on this migration in a mouse model of lung inflammation has been investigated. The number of neutrophils present in bronchoalveolar lavage fluid was determined 4 h after intratracheal instillation of LPS (0.1-1 microg) or murine recombinant KC (CXC chemokine, 0.03-0.3 microg). Both stimuli produced a dose-related increase in neutrophil accumulation. Intravenous anti-mouse CD18 mAb, 2E6 (0.5 mg/mouse), significantly (p < 0.001) attenuated LPS (0.3 microg)- but not KC (0.3 microg)-induced neutrophil accumulation. The anti-mouse CD29 mAb, HM beta 1-1 (0.02 mg/mouse), significantly (p < 0.05) inhibited both LPS (0.3 microg)- and KC (0.3 microg)-induced neutrophil migration. A second mAb to CD18 (GAME-46) and both F(ab')(2) and Fab of HM beta 1-1 produced similar results to those above, while coadministration of mAbs did not result in greater inhibition. Electron microscopy studies showed that CD29 was involved in the movement of neutrophils from the interstitium into alveoli. The effect of mAbs to CD49 (alpha integrin) subunits of CD29 was also examined. mAbs to CD49e and CD49f inhibited both responses, while anti-CD49b and CD49d significantly inhibited responses to KC only. These data suggest that CD29 plays a critical role in neutrophil migration in pulmonary inflammation and that CD49b and CD49d mediate CD18-independent neutrophil accumulation.

Effect of peroxynitrite on plasma extravasation, microvascular blood flow and nociception in the rat

1. Peroxynitrite (ONOO-) is a cytotoxic species, formed by the reaction between nitric oxide and superoxide free radicals, that may be involved in inflammation. In this study we have investigated the effect of peroxynitrite on plasma extravasation and microvascular blood flow in the dorsal skin and on nociceptive responses in the hind paw of the rat. 2. Male Wistar rats were anaesthetized and their dorsal skin shaved. Plasma extravasation was measured by the extravascular accumulation of 125I-labelled albumin over 0-45 min and 0-240 min. Blood flow was measured by laser-Doppler flowmetry over 0-240 min. Studies in the hind paw were carried out in the conscious rat. Hind paw weight changes were determined by volume displacement and nociception by a mechanical hyperalgesia technique. 3. Intradermal (i.d.) peroxynitrite (100-200 nmol site-1) produced a significant (P < 0.01) dose-dependent increase in plasma extravasation in dorsal skin over 0-45 min which was not increased over 45-240 min. Plasma extravasation was significantly (P < 0.001) decreased in rats pretreated with the anti-inflammatory steroid dexamethasone (1 mg kg-1, i.v.; -180 min), but not modulated by treatment with the hydrogen peroxide deactivator catalase (2200 u site-1), or the superoxide scavenger superoxide dismutase (500 u site-1), effective doses of the tachykinin NK1 antagonist SR140333 (1 nmol site-1), the cyclo-oxygenase inhibitor indomethacin (358 mumol site-1), or combined pretreatment with mepyramine (histamine H1-receptor antagonist; 2.8 nmol site-1) and methysergide (5-HT antagonist; 1.9 nmol site-1). 4. Microvascular blood flow was significantly (P < 0.05) increased 30 and 120 min after i.d. peroxynitrite (100 nmol site-1) in dorsal skin and remained raised until the end of the recording period (240 min). The increase in blood flow was unaffected by dexamethasone (1 mg kg-1, i.v.; -180 min) or indomethacin (10 mg kg-1, s.c.; -30 min). 5. Hind paw volume was significantly (P < 0.001) increased 30 min after intraplantar peroxynitrite (87.5 and 175 nmol paw-1) and remained raised for the duration of the experiment (360 min). By comparison, nociception was not altered by intraplantar peroxynitrite. 6. These data indicate that peroxynitrite can cause an increase in both plasma extravasation and blood flow, suggesting that peroxynitrite could be of biological relevance to microvascular responses. These findings may be of importance in the pathology of inflammatory diseases in which peroxynitrite formation occurs.

Effect of the inducible nitric oxide synthase inhibitors aminoguanidine and L-N6-(1-iminoethyl)lysine on zymosan-induced plasma extravasation in rat skin

The effect of nitric oxide synthase (NOS) inhibitors on plasma extravasation in a rat model of zymosan-induced inflammation has been investigated. Plasma extravasation was determined in response to intradermal test agents over 0 to 45 min or 0 to 4 h by the accumulation of i.v. injected 125I-labeled human serum albumin. Zymosan (1-100 microg/site) produced a dose- and time-dependent plasma extravasation. N(G)-nitro-L-arginine methyl ester (30-300 nmol/site), but not aminoguanidine (AG; 10-300 nmol/site) or L-N6-(1-iminoethyl)lysine (L-NIL; 10-300 nmol/site), significantly (p &lt; 0.01) inhibited zymosan-induced (10 microg/site) plasma extravasation over 0 to 45 min. However, both AG and L-NIL produced significant (p &lt; 0.05) inhibition over 0 to 4 h. The inhibition produced by AG was reversed by i.v. L-arginine or by coinjection of the vasodilator, calcitonin gene-related peptide. Zymosan (10-100 microg/site) induced an increase in dermal blood flow (laser-Doppler flowmetry) and this was inhibited by AG. Neutrophils were depleted selectively with antiserum, but this did not affect plasma extravasation except at the highest dose of zymosan (100 microg/site). Furthermore, zymosan-induced edema was not modified at either time point by pretreatment with the cyclooxygenase inhibitor indomethacin (30 micromol/kg, s.c., -30 min). In conclusion, in this model of dermal inflammation, it is suggested that inducible NOS inhibitors selectively remove an inducible NOS component that, at least in part, acts to increase microvascular blood flow and thus the edema formation observed during 0 to 4 h. There is no evidence of a contributory role for neutrophils or cyclooxygenase products in this model.

Effect of the inducible nitric oxide synthase inhibitors aminoguanidine and L-N6-(1-iminoethyl)lysine on zymosan-induced plasma extravasation in rat skin

The effect of nitric oxide synthase (NOS) inhibitors on plasma extravasation in a rat model of zymosan-induced inflammation has been investigated. Plasma extravasation was determined in response to intradermal test agents over 0 to 45 min or 0 to 4 h by the accumulation of i.v. injected 125I-labeled human serum albumin. Zymosan (1-100 microg/site) produced a dose- and time-dependent plasma extravasation. N(G)-nitro-L-arginine methyl ester (30-300 nmol/site), but not aminoguanidine (AG; 10-300 nmol/site) or L-N6-(1-iminoethyl)lysine (L-NIL; 10-300 nmol/site), significantly (p < 0.01) inhibited zymosan-induced (10 microg/site) plasma extravasation over 0 to 45 min. However, both AG and L-NIL produced significant (p < 0.05) inhibition over 0 to 4 h. The inhibition produced by AG was reversed by i.v. L-arginine or by coinjection of the vasodilator, calcitonin gene-related peptide. Zymosan (10-100 microg/site) induced an increase in dermal blood flow (laser-Doppler flowmetry) and this was inhibited by AG. Neutrophils were depleted selectively with antiserum, but this did not affect plasma extravasation except at the highest dose of zymosan (100 microg/site). Furthermore, zymosan-induced edema was not modified at either time point by pretreatment with the cyclooxygenase inhibitor indomethacin (30 micromol/kg, s.c., -30 min). In conclusion, in this model of dermal inflammation, it is suggested that inducible NOS inhibitors selectively remove an inducible NOS component that, at least in part, acts to increase microvascular blood flow and thus the edema formation observed during 0 to 4 h. There is no evidence of a contributory role for neutrophils or cyclooxygenase products in this model.