Neflamapimod inhibits endothelial cell activation, adhesion molecule expression, leukocyte attachment and vascular inflammation by inhibiting p38 MAPKα and NF-κB signaling

Neflamapimod, a selective inhibitor of the alpha isoform of p38 mitogen-activated protein kinase (MAPKα), was investigated for its potential to inhibit lipopolysaccharide (LPS)-induced activation of endothelial cells (ECs), adhesion molecule induction, and subsequent leukocyte attachment to EC monolayers. These events are known to contribute to vascular inflammation and cardiovascular dysfunction. Our results demonstrate that LPS treatment of cultured ECs and rats leads to significant upregulation of adhesion molecules, both in vitro and in vivo, which can be effectively inhibited by Neflamapimod treatment. Western blotting data further reveals that Neflamapimod inhibits LPS-induced phosphorylation of p38 MAPKα and the activation of NF-κB signaling in ECs. Additionally, leukocyte adhesion assays demonstrate a substantial reduction in leukocyte attachment to cultured ECs and the aorta lumen of rats treated with Neflamapimod. Consistent with vascular inflammation, LPS-treated rat arteries exhibit significantly diminished vasodilation response to acetylcholine, however, arteries from rats treated with Neflamapimod maintain their vasodilation capacity, demonstrating its ability to limit LPS-induced vascular inflammation. Overall, our data demonstrate that Neflamapimod effectively inhibits endothelium activation, adhesion molecule expression, and leukocyte attachment, thereby reducing vascular inflammation.

Hemoglobin increases leukocyte adhesion and initiates lung microvascular endothelial activation via Toll-like receptor 4 signaling

Cell-free hemoglobin is a pathophysiological driver of endothelial injury during sepsis and acute respiratory distress syndrome (ARDS), but the precise mechanisms are not fully understood. We hypothesized that hemoglobin (Hb) increases leukocyte adhesion and endothelial activation in human lung microvascular endothelial cells (HLMVEC). We stimulated primary HLMVEC, or leukocytes isolated from healthy human donors, with Hb (0.5 mg/mL) and found that leukocyte adhesion to lung endothelium in response to Hb is an endothelial-dependent process. Next, we stimulated HLMVEC with Hb over time (1, 3, 6, and 24 h) and found increased transcription and release of inflammatory cytokines (IL-1β, IL-8, and IL-6). In addition, Hb exposure variably upregulated transcription, total protein expression, and cell-surface localization of adhesion molecules E-selectin, P-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1). Since VCAM-1 was most upregulated by Hb, we further tested mechanisms for Hb-mediated upregulation of VCAM-1 in HLMVEC. Although upregulation of VCAM-1 was not prevented by hemoglobin scavenger haptoglobin, heme scavenger hemopexin, or inhibition of nod-like receptor protein 3 (NLRP3) signaling, blocking Toll-like receptor 4 (TLR4) with small molecule inhibitor TAK-242 (1 µM) prevented upregulation of VCAM-1 in response to Hb. Consistently, Hb increased nuclear factor-κB (NF-κB) activation and intracellular reactive oxygen species (ROS), which were both prevented by TLR4 inhibition. Together, these data demonstrate that Hb increases leukocyte-endothelial adhesion and activates HLMVEC through TLR4 signaling, indicating a potential mechanism for Hb-mediated pulmonary vascular injury during inflammatory and hemolytic conditions.

Development of experimental microfluidic device and methodology for assessing microrheological properties of blood

BACKGROUND AND OBJECTIVE

Microfluidics is a useful tool for investigating blood microrheology. The study aimed to present the development of a microfluidic device for assessing the microrheological properties of blood cells' suspensions and its application in patients with T2DM.

METHODS

A new microfluidic device was elaborated, connected to a system, including a microscope with a digital camera, a pump with a manometer and a computer with specially developed software. Blood cells' suspensions were investigated in a microchamber between two parallel optical slides within a 100μm distance. The motion of the blood cells in the microchamber was observed by the microscope and it was recorded and visualized by a digital camera. A method for evaluating the deformability of blood cells and a device for its implementation were used [1].

RESULTS

The pressure and flow rate ranges in the microfluidic device were specified by model suspensions of beta-ferroxy-hydroxide and red blood cells (RBC) suspensions. The pressure changes, realized by a pump (micropipette), connected to a manometer were established and the corresponding shear rates in the microfluidic device were determined. Data about the blood microrheological properties like RBC aggregation and deformability, leukocyte adhesion from a group of healthy volunteers and from patients with type 2 diabetes mellitus (T2DM) were obtained.

CONCLUSIONS

The developed device and experimental system is a promising tool for the study of blood microrheology.

CD47 Binding on Vascular Endothelial Cells Inhibits IL-17-Mediated Leukocyte Adhesion

To address the conflicting role of thrombospondin (TSP)-1 reported in acute and chronic pathologies, this study investigated the role of TSP-1 in regulating leukocyte recruitment and regulation of VCAM-1 expression using mouse models of uveitis. The spontaneously increased VCAM-1 expression and leukocyte adhesion in retinas of TSP-1-deficient mice suggested a TSP-1-mediated regulation of VCAM-1 expression. In a chronic uveitis model, induced by immunizing wild-type mice with specific interphotoreceptor retinoid-binding protein (IRBP) peptide, topically applied TSP-1-derived CD47-binding peptide significantly reduced the clinical disease course and retinal leukocyte adhesion as compared to the control peptide-treated group. In contrast, in LPS-mediated acute uveitis, TSP-1 deficiency significantly reduced the retinal leukocyte adhesion. The results of our in vitro study, using vascular endothelial cell (EC) cultures, demonstrate that unlike TNF-α, VCAM-1 expression induced by IL-17 is associated with a reduced expression of endogenous TSP-1. Such reduced endogenous TSP-1 expression in IL-17-stimulated ECs helps limit the CD36-mediated increased VCAM-1 expression, while favoring CD47-mediated inhibition of VCAM-1 expression and leukocyte adhesion. Thus, our study identifies TSP-1:CD47 interaction as a molecular pathway that modulates IL-17-mediated VCAM-1 expression, contributing to its anti-inflammatory effect in chronic inflammatory conditions.

TNF-α-activated eNOS signaling increases leukocyte adhesion through the S-nitrosylation pathway

Nitric oxide (NO) is a key factor in inflammation. Endothelial nitric oxide synthase (eNOS), whose activity increases after stimulation with proinflammatory cytokines, produces NO in endothelium. NO activates two pathways: 1) soluble guanylate cyclase-protein kinase G and 2) S-nitrosylation (NO-induced modification of free-thiol cysteines in proteins). S-nitrosylation affects phosphorylation, localization, and protein interactions. NO is classically described as a negative regulator of leukocyte adhesion to endothelial cells. However, agonists activating NO production induce a fast leukocyte adhesion, which suggests that NO might positively regulate leukocyte adhesion. We tested the hypothesis that eNOS-induced NO promotes leukocyte adhesion through the S-nitrosylation pathway. We stimulated leukocyte adhesion to endothelium in vitro and in vivo using tumor necrosis factor-α (TNF-α) as proinflammatory agonist. ICAM-1 changes were evaluated by immunofluorescence, subcellular fractionation, immunoprecipitation, and fluorescence recovery after photobleaching (FRAP). Protein kinase Cζ (PKCζ) activity and S-nitrosylation were evaluated by Western blot analysis and biotin switch method, respectively. TNF-α, at short times of stimulation, activated the eNOS S-nitrosylation pathway and caused leukocyte adhesion to endothelial cells in vivo and in vitro. TNF-α-induced NO led to changes in ICAM-1 at the cell surface, which are characteristic of clustering. TNF-α-induced NO also produced S-nitrosylation and phosphorylation of PKCζ, association of PKCζ with ICAM-1, and ICAM-1 phosphorylation. The inhibition of PKCζ blocked leukocyte adhesion induced by TNF-α. Mass spectrometry analysis of purified PKCζ identified cysteine 503 as the only S-nitrosylated residue in the kinase domain of the protein. Our results reveal a new eNOS S-nitrosylation-dependent mechanism that induces leukocyte adhesion and suggests that S-nitrosylation of PKCζ may be an important regulatory step in early leukocyte adhesion in inflammation.NEW & NOTEWORTHY Contrary to the well-established inhibitory role of NO in leukocyte adhesion, we demonstrate a positive role of nitric oxide in this process. We demonstrate that NO induced by eNOS after TNF-α treatment induces early leukocyte adhesion activating the S-nitrosylation pathway. Our data suggest that PKCζ S-nitrosylation may be a key step in this process.

Interleukin-1α Is a Central Regulator of Leukocyte-Endothelial Adhesion in Myocardial Infarction and in Chronic Kidney Disease

BACKGROUND

Cardiovascular diseases and chronic kidney disease (CKD) are highly prevalent, aggravate each other, and account for substantial mortality. Both conditions are characterized by activation of the innate immune system. The alarmin interleukin-1α (IL-1α) is expressed in a variety of cell types promoting (sterile) systemic inflammation. The aim of the present study was to examine the role of IL-1α in mediating inflammation in the setting of acute myocardial infarction (AMI) and CKD.

METHODS

We assessed the expression of IL-1α on the surface of monocytes from patients with AMI and patients with CKD and determined its association with atherosclerotic cardiovascular disease events during follow-up in an explorative clinical study. Furthermore, we assessed the inflammatory effects of IL-1α in several organ injury models in Il1a^-/- and Il1b^-/- mice and investigated the underlying mechanisms in vitro in monocytes and endothelial cells.

RESULTS

IL-1α is strongly expressed on the surface of monocytes from patients with AMI and CKD compared with healthy controls. Higher IL-1α surface expression on monocytes from patients with AMI and CKD was associated with a higher risk for atherosclerotic cardiovascular disease events, which underlines the clinical relevance of IL-1α. In mice, IL-1α, but not IL-1β, mediates leukocyte-endothelial adhesion as determined by intravital microscopy. IL-1α promotes accumulation of macrophages and neutrophils in inflamed tissue in vivo. Furthermore, IL-1α on monocytes stimulates their homing at sites of vascular injury. A variety of stimuli such as free fatty acids or oxalate crystals induce IL-1α surface expression and release by monocytes, which then mediates their adhesion to the endothelium via IL-1 receptor-1. IL-1α also promotes expression of the VCAM-1 (vascular cell adhesion molecule-1) on endothelial cells, thereby fostering the adhesion of circulating leukocytes. IL-1α induces inflammatory injury after experimental AMI, and abrogation of IL-1α prevents the development of CKD in oxalate or adenine-fed mice.

CONCLUSIONS

IL-1α represents a key mediator of leukocyte-endothelial adhesion and inflammation in AMI and CKD. Inhibition of IL-1α may serve as a novel anti-inflammatory treatment strategy.

Binding of Rap1 and Riam to Talin1 Fine-Tune β2 Integrin Activity During Leukocyte Trafficking

β2 integrins mediate key processes during leukocyte trafficking. Upon leukocyte activation, the structurally bent β2 integrins change their conformation towards an extended, intermediate and eventually high affinity conformation, which mediate slow leukocyte rolling and firm arrest, respectively. Translocation of talin1 to integrin adhesion sites by interactions with the small GTPase Rap1 and the Rap1 effector Riam precede these processes. Using Rap1 binding mutant talin1 and Riam deficient mice we show a strong Riam-dependent T cell homing process to lymph nodes in adoptive transfer experiments and by intravital microscopy. Moreover, neutrophils from compound mutant mice exhibit strongly increased rolling velocities to inflamed cremaster muscle venules compared to single mutants. Using Hoxb8 cell derived neutrophils generated from the mutant mouse strains, we show that both pathways regulate leukocyte rolling and adhesion synergistically by inducing conformational changes of the β2 integrin ectodomain. Importantly, a simultaneous loss of both pathways results in a rolling phenotype similar to talin1 deficient neutrophils suggesting that β2 integrin regulation primarily occurs via these two pathways.

CC16 Binding to α4β1 Integrin Protects against Mycoplasma pneumoniae Infection

Rationale CC16 (club cell secretory protein) is a pneumoprotein produced predominantly by pulmonary club cells. Circulating CC16 is associated with protection from the inception and progression of the two most common obstructive lung diseases (asthma and chronic obstructive pulmonary disease). Objectives Although exact mechanisms remain elusive, studies consistently suggest a causal role of CC16 in mediating antiinflammatory and antioxidant functions in the lung. We sought to determine any novel receptor systems that could participate in CC16's role in obstructive lung diseases. Methods Protein alignment of CC16 across species led to the discovery of a highly conserved sequence of amino acids, leucine-valine-aspartic acid (LVD), a known integrin-binding motif. Recombinant CC16 was generated with and without the putative integrin-binding site. A Mycoplasma pneumoniae mouse model and a fluorescent cellular adhesion assay were used to determine the impact of the LVD site regarding CC16 function during live infection and on cellular adhesion during inflammatory conditions. Measurements and Main Results CC16 bound to integrin α₄β₁), also known as the adhesion molecule VLA-4 (very late antigen 4), dependent on the presence of the LVD integrin-binding motif. During infection, recombinant CC16 rescued lung function parameters both when administered to the lung and intravenously but only when the LVD integrin-binding site was intact; likewise, neutrophil recruitment during infection and leukocyte adhesion were both impacted by the loss of the LVD site. Conclusions We discovered a novel receptor for CC16, VLA-4, which has important mechanistic implications for the role of CC16 in circulation as well as in the lung compartment.

ZNF667 attenuates leukocyte-endothelial adhesion via downregulation of P-selectin in skin flap following remote limb ischemic preconditioning

We assessed the effects and potential mechanism of romote ischemic preconditioning (RIPC) on leukocytes-endothelium cell adhesion in the flap microvessel after ischemia-reperfusion (I/R) injury. Eight hours after reperfusion, edema and intravascular leukocyte aggregation were reduced and microvessels were more obvious in the group with superficial inferior epigastric artery (SIEA) perforator flap (SIEA-flap) subjected to RIPC than in the I/R group. Zinc finger protein 667 (ZNF667) was significantly increased but P-selectin was decreased in the flaps subjected to RIPC, compared to those in the I/R group. The low expression of P-selectin was associated with ZNF667 expression and activation in human dermal microvascular endothelial cells in response to hypoxic preconditioning. ZNF667 bound to the P-selectin promoter region, suppressing its transcription through a special core sequence. The ablation of P-selectin by small interfering RNA effectively prevented the leukocytes-endothelium cell adhesion effect of ZNF667-knockdown. ZNF667 upregulation attenuates leukocyte-endothelial cell adhesion by negatively regulating the expression of P-selectin in SIEA-flap subjected to RIPC.

Pre-treatment with compound Danshen dripping pills prevents lipid infusion-induced microvascular dysfunction in mice

CONTEXT

Recent studies have shown compound Danshen dripping pills (CDDP) could improve microcirculation in ischemic/reperfusion injury and other microvascular disorders. The mechanism for CDDP's role in microcirculation is not clear.

OBJECTIVE

To explore the protective effects of CDDP on microvascular dysfunction.

MATERIALS AND METHODS

C57BL/6 male mice (6-8 weeks) were randomized into control, model and CDDP groups (n = 10), which were treated with normal saline or CDDP (105.30 mg/kg), respectively. Then, lipid emulsion and heparin were infused via mice jugular vein to establish systemic microvascular dysfunction model. Coronary flow reserve (CFR) and leukocytes adhesion on microvascular wall were measured. Relative CD11b and CD62L expression levels on neutrophils were measured by flow cytometric analysis. Expression level of forkhead box transcription factor O1 (FOXO1) mRNA was identified by real-time PCR.

RESULTS

Lipid infusion significantly attenuated the CFR (1.84 ± 0.14 vs. 2.65 ± 0.02) and increased the number of leukocytes adherent to microvascular wall in cremaster (4067.00 ± 581.20 cells/mm² vs. 10.67 ± 4.81 cells/mm²). The expression level of CD11b and FOXO1 in neutrophils was also up-regulated by lipid infusion. Pre-treatment with CDDP significantly improved CFR (2.57 ± 0.29 vs. 1.84 ± 0.14), decreased the number of leukocytes adherent to microvascular wall (2500.00 ± 288.70 cells/mm² vs. 4067.00 ± 581.20 cells/mm²) and down-regulated CD11b and FOXO1 expression. Discussion and conclusions: Pre-treatment with CDDP could prevent lipid infusion-induced systemic microvascular disorder including coronary and peripheral microvascular dysfunction. Down-regulated FOXO1 and decreased leukocyte adhesion might play an important role in the mechanisms of CDDP's efficacy.

Role of NO and S-nitrosylation in the Expression of Endothelial Adhesion Proteins That Regulate Leukocyte and Tumor Cell Adhesion

Leukocyte recruitment is one of the most important cellular responses to tissue damage. Leukocyte extravasation is exquisitely regulated by mechanisms of selective leukocyte-endothelium recognition through adhesion proteins in the endothelial cell surface that recognize specific integrins in the activated leukocytes. A similar mechanism is used by tumor cells during metastasis to extravasate and form a secondary tumor. Nitric oxide (NO) has been classically described as an anti-inflammatory molecule that inhibits leukocyte adhesion. However, the evidence available shows also a positive role of NO in leukocyte adhesion. These apparent discrepancies might be explained by the different NO concentrations reached during the inflammatory response, which are highly modulated by the expression of different nitric oxide synthases, along the inflammatory response and by changes in their subcellular locations.

Glucose-6-Phosphate Dehydrogenase Deficiency Activates Endothelial Cell and Leukocyte Adhesion Mediated via the TGFβ/NADPH Oxidases/ROS Signaling Pathway

Glucose-6-phosphate dehydrogenase (G6PD) deficiency, the most common genetic inherited trait among humans, affects ~7% of the global population, and is associated with excess risk of cardiovascular disease (CVD). Transforming growth factor-β (TGF-β) regulates immune function, proliferation, epithelial-mesenchymal transition, fibrosis, cancer, and vascular dysfunction. This study examined whether G6PD deficiencies can alter TGF-β-mediated NADPH oxidases (NOX) and cell adhesion molecules (CAM) in human aortic endothelial cells (HAEC). Results show that treatment with high glucose and the saturated free fatty acid palmitate significantly downregulated G6PD; in contrast, mRNA levels of TGF-β components, NOX and its activity, and reactive oxygen species (ROS) were significantly upregulated in HAEC. The expression levels of TGF-β and its receptors, NOX and its activity, and ROS were significantly higher in HG-exposed G6PD-deficient cells (G6PD siRNA) compared to G6PD-normal cells. The protein levels of adhesion molecules (ICAM-1 and VCAM-1) and inflammatory cytokines (MCP-1 and TNF) were significantly increased in HG-exposed G6PD-deficient cells compared to G6PD-normal cells. The adherence of monocytes (SC cells) to HAEC was significantly elevated in HG-treated G6PD-deficient cells compared to control cells. Pharmacological inhibition of G6PD enhances ROS, NOX and its activity, and endothelial monocyte adhesion; these effects were impeded by NOX inhibitors. The inhibition of TGF-β prevents NOX2 and NOX4 mRNA expression and activity, ROS, and adhesion of monocytes to HAEC. L-Cysteine ethyl ester (cell-permeable) suppresses the mRNA levels of TGF-β and its receptors, along with NOX2 and NOX4, and decreases NOX activity, ROS, and adhesion of monocytes to HAEC. This suggests that G6PD deficiency promotes TGF-β/NADPH oxidases/ROS signaling, the expression of ICAM-1 and VCAM-1, and the adhesion of leukocytes to the endothelial monolayer, which can contribute to a higher risk for CVD.

Model Particulate Drug Carriers Modulate Leukocyte Adhesion in Human Blood Flows

Drug carriers have been widely explored as a method of improving the efficacy of therapeutic drugs for a variety of diseases, including those involving inflammation. However, few of these formulations have advanced past clinical trials. There are still major gaps in our understanding of how drug carriers impact leukocytes, particularly in inflammatory conditions. In this work, we investigated how targeted and nontargeted drug carriers affect the function of leukocytes in blood flow. We explored three primary mechanisms: (1) collisions in blood flow disrupt leukocyte adhesion, (2) specific binding to the endothelium competes with leukocytes for binding sites, and (3) particle phagocytosis alters leukocyte phenotype, resulting in reduced adhesion. We find that each of these mechanisms contributes to significantly reduced leukocyte adhesion to an inflamed endothelium, and that particle phagocytosis may be the most significant driver of this effect. These results are crucial for understanding the totality of the impact of drug carriers on leukocyte behavior and response to inflammation and should inform the future design of any such drug carriers.

In contrast to Western diet, a plant-based, high-fat, low-sugar diet does not exacerbate retinal endothelial injury in streptozotocin-induced diabetes

Controversy remains about how diet affects the vascular endothelial dysfunction associated with disordered insulin-glucose homeostasis. It is postulated that the type and level of certain macronutrients contribute to endothelial dysfunction in vascular diabetes complications. However, it is not well understood how specific macronutrients affect the molecular inflammatory response under conditions of hyperglycemia. Here, we examined retinal microvascular endothelial injury in streptozotocin (STZ)-diabetic rats fed a laboratory Western diet (WD). WD, characterized by its high content of saturated fat, cholesterol, and sugar, significantly increased retinal leukocyte accumulation and endothelial injury in the STZ-diabetic rats. Suppression of endothelial NF-κB signaling in the STZ model reduced the WD-induced increase in leukocyte accumulation. To isolate the effect of dietary fat, we generated high-fat diets with varying fatty acid balance and type. These diets contained moderate amounts of carbohydrates but no sugar. We found that neither high levels of saturated or unsaturated fats per se increased retinal leukocyte accumulation and endothelial injury in the STZ-diabetic rat model but that the combination of high levels of dietary cholesterol with specific saturated fatty acids that are abundant in WD exacerbated leukocyte accumulation and endothelial injury in the retinas of STZ-diabetic rats.-Barakat, A., Nakao, S., Zandi, S., Sun, D., Schmidt-Ullrich, R., Hayes, K. C., Hafezi-Moghadam, A. In contrast to Western diet, a plant-based, high-fat, low-sugar diet does not exacerbate retinal endothelial injury in streptozotocin-induced diabetes.

Rapid changes in the microvascular circulation of skeletal muscle impair insulin delivery during sepsis

Sepsis costs the healthcare system $23 billion annually and has a mortality rate between 10 and 40%. An early indication of sepsis is the onset of hyperglycemia, which is the result of sepsis-induced insulin resistance in skeletal muscle. Previous investigations have focused on events in the myocyte (e.g., insulin signaling and glucose transport and subsequent metabolism) as the causes for this insulin-resistant state. However, the delivery of insulin to the skeletal muscle is also an important determinant of insulin action. Skeletal muscle microvascular blood flow, which delivers the insulin to the muscle, is known to be decreased during sepsis. Here we test whether the reduced capillary blood flow to skeletal muscle belies the sepsis-induced insulin resistance by reducing insulin delivery to the myocyte. We hypothesize that decreased capillary flow and consequent decrease in insulin delivery is an early event that precedes gross cardiovascular alterations seen with sepsis. This hypothesis was examined in mice treated with either lipopolysaccharide (LPS) or polymicrobial sepsis followed by intravital microscopy of the skeletal muscle microcirculation. We calculated insulin delivery to the myocyte using two independent methods and found that LPS and sepsis rapidly reduce insulin delivery to the skeletal muscle by ~50%; this was driven by decreases in capillary flow velocity and the number of perfused capillaries. Furthermore, the changes in skeletal muscle microcirculation occur before changes in both cardiac output and arterial blood pressure. These data suggest that a rapid reduction in skeletal muscle insulin delivery contributes to the induction of insulin resistance during sepsis.

Anti-inflammatory effects of a novel iron chelator, DIBI, in experimental sepsis

BACKGROUND

Iron catalyzes the generation of reactive oxygen species (ROS) as part of the innate antimicrobial defense. During sepsis, the dysregulated systemic inflammatory response to infection, iron homeostasis becomes disrupted, generating an excess of ROS causing damage to tissues. This can be potentially suppressed using iron chelators that selectively bind iron to prevent its participation in ROS-related inflammatory reactions.

OBJECTIVE

We hypothesize that administration of DIBI, a novel iron-chelator, attenuates the dysregulated systemic immune response and reduces tissue damage in experimental endotoxemia.

METHODS

Five groups of animals (n = 5-10) were included in this study: control, untreated endotoxemia, and endotoxemia animals treated with either DIBI-A, MAHMP, or DIBI-B. Intravital microscopy was performed on the intestine of anesthesized mice to observe leukocyte endothelial interactions and evaluate the intestinal microcirculation.

RESULTS

Treatment of endotoxemic mice with DIBI-B reduced the number of adhering leukocytes in submucosal collecting (V1) venules by 68%. DIBI-B, MAHMP, and DIBI-A were able to restore functional capillary density (FCD) in the intestinal muscle layer by 74%, 44%, and 11%, respectively.

CONCLUSIONS

DIBI-B reduces leukocyte recruitment and improves FCD in experimental endotoxemia, outperforming other chelators tested. These findings suggest a potential role for DIBI-B as a candidate drug for sepsis treatment.

Junctional Adhesion Molecules (JAMs): The JAM-Integrin Connection

Junctional adhesion molecules (JAMs) are cell surface adhesion receptors of the immunoglobulin superfamily. JAMs are involved in a variety of biological processes both in the adult organism but also during development. These include processes such as inflammation, angiogenesis, hemostasis, or epithelial barrier formation, but also developmental processes such as hematopoiesis, germ cell development, and development of the nervous system. Several of these functions of JAMs depend on a physical and functional interaction with integrins. The JAM – integrin interactions in trans regulate cell-cell adhesion, their interactions in cis regulate signaling processes originating at the cell surface. The JAM – integrin interaction can regulate the function of the JAM as well as the function of the integrin. Beyond the physical interaction with integrins, JAMs can regulate integrin function through intracellular signaling indicating an additional level of JAM – integrin cross-talk. In this review, we describe the various levels of the functional interplay between JAMs and integrins and the role of this interplay during different physiological processes.

In vivo observation of cerebral microcirculation after experimental subarachnoid hemorrhage in mice

Acute brain injury caused by subarachnoid hemorrhage is the major cause of poor prognosis. The pathology of subarachnoid hemorrhage likely involves major morphological changes in the microcirculation. However, previous studies primarily used fixed tissue or delayed injury models. Therefore, in the present study, we used in vivo imaging to observe the dynamic changes in cerebral microcirculation after subarachnoid hemorrhage. Subarachnoid hemorrhage was induced by perforation of the bifurcation of the middle cerebral and anterior cerebral arteries in male C57/BL6 mice. The diameter of pial arterioles and venules was measured by in vivo fluorescence microscopy at different time points within 180 minutes after subarachnoid hemorrhage. Cerebral blood flow was examined and leukocyte adhesion/albumin extravasation was determined at different time points before and after subarachnoid hemorrhage. Cerebral pial microcirculation was abnormal and cerebral blood flow was reduced after subarachnoid hemorrhage. Acute vasoconstriction occurred predominantly in the arterioles instead of the venules. A progressive increase in the number of adherent leukocytes in venules and substantial albumin extravasation were observed between 10 and 180 minutes after subarachnoid hemorrhage. These results show that major changes in microcirculation occur in the early stage of subarachnoid hemorrhage. Our findings may promote the development of novel therapeutic strategies for the early treatment of subarachnoid hemorrhage.

The Role of Gap Junction-Mediated Endothelial Cell-Cell Interaction in the Crosstalk between Inflammation and Blood Coagulation

Endothelial cells (ECs) play a pivotal role in the crosstalk between blood coagulation and inflammation. Endothelial cellular dysfunction underlies the development of vascular inflammatory diseases. Recent studies have revealed that aberrant gap junctions (GJs) and connexin (Cx) hemichannels participate in the progression of cardiovascular diseases such as cardiac infarction, hypertension and atherosclerosis. ECs can communicate with adjacent ECs, vascular smooth muscle cells, leukocytes and platelets via GJs and Cx channels. ECs dynamically regulate the expression of numerous Cxs, as well as GJ functionality, in the context of inflammation. Alterations to either result in various side effects across a wide range of vascular functions. Here, we review the roles of endothelial GJs and Cx channels in vascular inflammation, blood coagulation and leukocyte adhesion. In addition, we discuss the relevant molecular mechanisms that endothelial GJs and Cx channels regulate, both the endothelial functions and mechanical properties of ECs. A better understanding of these processes promises the possibility of pharmacological treatments for vascular pathogenesis.

Preconditioning with the BKCa channel activator NS-1619 prevents ischemia-reperfusion-induced inflammation and mucosal barrier dysfunction: roles for ROS and heme oxygenase-1

Activation of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels evokes cell survival programs that mitigate intestinal ischemia and reperfusion (I/R) inflammation and injury 24 h later. The goal of the present study was to determine the roles of reactive oxygen species (ROS) and heme oxygenase (HO)-1 in delayed acquisition of tolerance to I/R induced by pretreatment with the BK_Ca channel opener NS-1619. Superior mesentery arteries were occluded for 45 min followed by reperfusion for 70 min in wild-type (WT) or HO-1-null (HO-1^-/-) mice that were pretreated with NS-1619 or saline vehicle 24 h earlier. Intravital microscopy was used to quantify the numbers of rolling and adherent leukocytes. Mucosal permeability, tumor necrosis factor-α (TNF-α) levels, and HO-1 activity and expression in jejunum were also determined. I/R induced leukocyte rolling and adhesion, increased intestinal TNF-α levels, and enhanced mucosal permeability in WT mice, effects that were largely abolished by pretreatment with NS-1619. The anti-inflammatory and mucosal permeability-sparing effects of NS-1619 were prevented by coincident treatment with the HO-1 inhibitor tin protoporphyrin-IX or a cell-permeant SOD mimetic, Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), in WT mice. NS-1619 also increased jejunal HO-1 activity in WT animals, an effect that was attenuated by treatment with the BK_Ca channel antagonist paxilline or MnTBAP. I/R also increased postischemic leukocyte rolling and adhesion and intestinal TNF-α levels in HO-1^-/- mice to levels comparable to those noted in WT animals. However, NS-1619 was ineffective in preventing these effects in HO-1-deficient mice. In summary, our data indicate that NS-1619 induces the development of an anti-inflammatory phenotype and mitigates postischemic mucosal barrier disruption in the small intestine by a mechanism that may involve ROS-dependent HO-1 activity.NEW & NOTEWORTHY Antecedent treatment with the large-conductance Ca²⁺-activated K⁺ channel opener NS-1619 24 h before ischemia-reperfusion limits postischemic tissue injury by an oxidant-dependent mechanism. The present study shows that NS-1619-induced oxidant production prevents ischemia-reperfusion-induced inflammation and mucosal barrier disruption in the small intestine by provoking increases in heme oxygenase-1 activity.

Adiponectin treatment attenuates inflammatory response during early sepsis in obese mice

BACKGROUND

Morbid obesity increases the cost of care in critically ill patients. Sepsis is the leading cause of death in noncoronary intensive care units. Circulating cell-endothelial cell interactions in microcirculation are the rate-determining factors in any inflammation; obesity increases these interactions further. Adiponectin deficiency is implicated in increased cardiovascular risk in obese patients. We have shown that adiponectin deficiency increases microvascular dysfunction in early sepsis. In the present study, we investigated the effect of adiponectin replacement on nutritionally obese mice with early sepsis.

METHODS

We used cecal ligation and puncture model of sepsis in mice with diet-induced obesity (DIO) vs control diet (CTRL), with or without adiponectin treatment. We studied leukocyte/platelet adhesion in the cerebral microcirculation in early sepsis. We also studied the effect of adiponectin on free fatty acid (FFA)-fed and lipopolysaccharide-stimulated bone marrow-derived macrophages (BMDM) for mechanistic studies.

RESULTS

Leukocyte and platelet adhesion increased in the cerebral microcirculation of DIO and CTRL mice with early sepsis vs. sham; moreover cell adhesion in DIO-sepsis group was significantly higher than in the CTRL-sepsis group. Adiponectin replacement decreased leukocyte/platelet adhesion in CTRL and DIO mice. In FFA-fed BMDM, adiponectin treatment decreased tumor necrosis factor-alpha mRNA expression and increased sirtuin-1 (SIRT1) mRNA expression. Furthermore, using BMDM from SIRT1 knockout mice, we showed that the adiponectin treatment decreased inflammatory response in FFA-fed BMDM via SIRT1-dependent and -independent pathways.

CONCLUSION

Adiponectin replacement attenuates microvascular inflammation in DIO-sepsis mice. Mechanistically, adiponectin treatment in FFA-fed mouse macrophages attenuates inflammatory response via SIRT1-dependent and -independent pathways.

Trimethylamine N-Oxide Promotes Vascular Inflammation Through Signaling of Mitogen-Activated Protein Kinase and Nuclear Factor-κB

Background

The choline‐derived metabolite trimethylamine N‐oxide (TMAO) has been demonstrated to contribute to atherosclerosis and is associated with coronary artery disease risk.

Methods and Results

We explored the impact of TMAO on endothelial and smooth muscle cell function in vivo, focusing on disease‐relevant outcomes for atherogenesis. Initially, we observed that aortas of LDLR^−/− mice fed a choline diet showed elevated inflammatory gene expression compared with controls. Acute TMAO injection at physiological levels was sufficient to induce the same inflammatory markers and activate the well‐known mitogen‐activated protein kinase, extracellular signal–related kinase, and nuclear factor‐κB signaling cascade. These observations were recapitulated in primary human aortic endothelial cells and vascular smooth muscle cells. We also found that TMAO promotes recruitment of activated leukocytes to endothelial cells. Through pharmacological inhibition, we further showed that activation of nuclear factor‐κB signaling was necessary for TMAO to induce inflammatory gene expression in both of these relevant cell types as well as endothelial cell adhesion of leukocytes.

Conclusions

Our results suggest a likely contributory mechanism for TMAO‐dependent enhancement in atherosclerosis and cardiovascular risks.

Adenosine receptor activation improves microcirculation in experimental intestinal ischemia/reperfusion

Gut ischemia and reperfusion (IR), e.g. in small bowel transplantation or during resuscitation, may result in severe impairment of the intestinal microcirculation. Potential sequelae are mucosal damage, loss of intestinal barrier function, bacterial translocation, systemic inflammation, multiple organ failure and death. We hypothesized a protective role for extracellular adenosine signalling in intestinal IR injury. Using intravital microscopy we investigated the effects of the adenosine receptor (AR) agonist NECA (5'-N-ethyl carboxamide adenosine) on leukocyte-endothelial interactions and capillary perfusion in the intestinal microcirculation following intestinal IR. Six groups of Lewis rats (n = 44) were studied: control, NECA (5'-N-ethyl carboxamide adenosine), IR (30 minutes of intestinal ischemia, 2 hours of reperfusion), IR + NECA, IR + NECA + MRS1754 (A(2B)AR antagonist), IR + NECA + DPCPX (A(1)AR antagonist). All substances were administered i.v. immediately after declamping of the superior mesenteric artery. Intravital microscopy was performed after 2 hours of reperfusion. Following IR we observed a significant increase of leukocyte adhesion in the intestinal submucosal venules and a reduced capillary perfusion within the muscular layers. NECA reduced leukocyte activation and improved capillary perfusion significantly. Administration of A(2B)AR antagonist completely reversed the NECA effect, whereas A(1)AR inhibition only partially abolished the action of NECA. The data support the hypothesis that adenosine signalling is involved in intestinal IR injury. A(2B)AR may be more important than A(1)AR because A(2B)AR inhibition by MRS1754 completely reversed the effect of the adenosine receptor agonist NECA.

IV and IP administration of rhodamine in visualization of WBC-BBB interactions in cerebral vessels

Epi-illuminescence intravital fluorescence microscopy has been employed to study leukocyte-endothelial interactions in a number of brain pathologies. Historically, dyes such as Rhodamine 6G have been injected intravenously. However, intravenous injections can predispose experimental animals to a multitude of complications and requires a high degree of technical skill. Here, we study the efficacy of injecting Rhodamine 6G into the peritoneum (IP) for the purpose of analyzing leukocyte-endothelial interactions through a cranial window during real time intravital microscopy. After examining the number of rolling and adherent leukocytes through a cranial window, we found no advantage to the intravenous injection (IV). Additionally, we tested blood from both routes of injection by flow cytometry to gain a very precise picture of the two methods. The two routes of administration failed to show any difference in the ability to detect cells. The study supports the notion that IP Rhodamine 6G works as efficaciously as IV and should be considered a viable alternative in experimental design for investigations employing intravital microscopy. Facilitated intravital studies will allow for more exploration into cerebral pathologies and allow for more rapid translation from the laboratory to the patient with less chance of experimental error from failed IV access.

Oregonin from the Bark of Alnus japonica restrained ischemia-reperfusion-induced mesentery oxidative stress by inhibiting NADPH oxidase activation

OBJECTIVE

NADPH oxidase activation results in ROS overproduction that is the pathological basis of I/R injury. This study aimed to investigate potential effects of ORG on I/R-induced ROS production in rat mesenteric microvasculature and underlying mechanisms.

METHODS

Mesenteric I/R in Male Wistar rats (200~250 g) was induced by ligation of the mesenteric artery and vein for 10 minutes followed by reperfusion for 60 minutes by releasing of the occlusion. The rats were infused intravenously with or without ORG (5 mg/kg per hour) 10 minutes before ischemia (pretreatment) or 20 minutes after reperfusion (posttreatment). The DHR fluorescence intensity on, the leukocytes adherent to, and mast cell degranulation out of mesenteric venules were determined using an intravital microscope. NADPH oxidase subunit p47(phox) membrane translocation in intestine tissues was detected by Western blotting.

RESULTS

Pre- or posttreatment with ORG inhibited I/R-induced DHR fluorescence intensity on the venular walls and leukocytes adhesion, ORG pretreatment inhibited mast cell degranulation as well. Furthermore, the translocation of p47(phox) from cytosol to membrane was suppressed markedly by ORG after I/R.

CONCLUSIONS

The results suggested that ORG restrained I/R-induced ROS production, which might be correlated with its inhibitive effect on NADPH activation.

E-selectin ligand complexes adopt an extended high-affinity conformation

E-selectin is a cell-adhesion molecule of the vascular endothelium that promotes essential leukocyte rolling in the early inflammatory response by binding to glycoproteins containing the tetrasaccharide sialyl Lewis(x) (sLe(x)). Efficient leukocyte recruitment under vascular flow conditions depends on an increased lifetime of E-selectin/ligand complexes under tensile force in a so-called catch-bond binding mode. Co-crystal structures of a representative fragment of the extracellular E-selectin region with sLe(x) and a glycomimetic antagonist thereof reveal an extended E-selectin conformation, which is identified as a high-affinity binding state of E-selectin by molecular dynamics simulations. Small-angle X-ray scattering experiments demonstrate a direct link between ligand binding and E-selectin conformational transition under static conditions in solution. This permits tracing a series of concerted structural changes connecting ligand binding to conformational stretching as the structural basis of E-selectin catch-bond-mediated leukocyte recruitment. The detailed molecular view of the binding site paves the way for the design of a new generation of selectin antagonists. This is of special interest, since their therapeutic potential was recently demonstrated with the pan-selectin antagonists GMI-1070 (Rivipansel).

Resveratrol attenuates microvascular inflammation in sepsis via SIRT-1-Induced modulation of adhesion molecules in ob/ob mice

OBJECTIVE

Obesity, a sirtuin-1 (SIRT-1) -deficient state, increases morbidity and resource utilization in critically ill patients. SIRT-1 deficiency increases microvascular inflammation and mortality in early sepsis. The objective of the study was to study the effect of resveratrol (RSV), a SIRT-1 activator, on microvascular inflammation in obese septic mice.

METHODS

ob/ob and C57Bl/6 (WT) mice were pretreated with RSV versus dimethyl sulfoxide (DMSO) (vehicle) prior to cecal ligation and puncture (sepsis). We studied (1) leukocyte/platelet adhesion, (2) E-selectin, ICAM-1, and SIRT-1 expression in small intestine, and (3) 7-day survival. A group of RSV-treated mice received SIRT-1 inhibitor (EX-527) with sepsis induction, and leukocyte/platelet adhesion and E-selectin/ICAM-1 expression were studied. We treated endothelial (HUVEC) cells with RSV to study E-selectin/ICAM-1 and p65-acetylation (AC-p65) in response to lipopolysaccharide (LPS).

RESULTS

RSV treatment decreased leukocyte/platelet adhesion and E-selectin/ICAM-1 expression with increased SIRT-1 expression in septic ob/ob and WT mice, decreased E-selectin/ICAM-1 expression via increased SIRT-1 expression, and decreased AC-p65 expression in HUVEC. EX-527 abolished RSV-induced attenuation of microvascular inflammation in ob/ob septic mice. Finally, ob/ob mice in the sepsis+RSV group had significantly increased 7-day survival versus the sepsis+vehicle group.

CONCLUSIONS

RSV increases SIRT-1 expression in ob/ob septic mice to reduce microvascular inflammation and improves survival.

Inflammatory response of endothelial cells to a human endogenous retrovirus associated with multiple sclerosis is mediated by TLR4

The MSRV (multiple sclerosis-associated retrovirus) belongs to the human endogenous retrovirus HERV-W family. The envelope protein originating from the MSRV has been found in most patients with multiple sclerosis (MS). This protein (Env-ms) has pro-inflammatory properties for several types of immune cells and could therefore play a role in MS pathogenesis by promoting the leukocyte diapedesis observed in the central nervous system of patients. Our study aims to analyze the effects of Env-ms on the blood-brain barrier (BBB) at a molecular and functional level. We demonstrate that the recombinant MSRV envelope is able to stimulate several inflammatory parameters in a human BBB in vitro model, the HCMEC/D3 brain endothelial cell line. Indeed, Env-ms induces over-expression of ICAM-1, a major mediator of leukocyte adhesion to endothelial cells, in a dose-dependent manner as well as a strong dose-dependent production of the pro-inflammatory cytokines IL-6 and IL-8. Furthermore, using a silencing approach with siRNAs, we show that Env-ms is recognized via the Toll-like receptor 4 receptor, a pattern recognition receptor of innate immunity present on endothelial cells. We also show, using functional assays, that treatment of brain endothelial cells with Env-ms significantly stimulated the adhesion and the transmigration of activated immune cells through a monolayer of endothelial cells. These findings support the hypothesis that MSRV could be involved in the pathogenesis of MS disease or at least in maintenance of inflammatory conditions, thus fueling the auto-immune disorder. MSRV could also play a role in other chronic inflammatory diseases.

The CO donor CORM-2 inhibits LPS-induced vascular cell adhesion molecule-1 expression and leukocyte adhesion in human rheumatoid synovial fibroblasts

BACKGROUND AND PURPOSE

Infection with Gram-negative bacteria has been recognized as an initiator of rheumatoid arthritis, which is characterized by chronic inflammation and infiltration of immune cells. Carbon monoxide (CO) exhibits anti-inflammatory properties. Here we have investigated the detailed mechanisms of vascular cell adhesion molecule-1 (VCAM-1) expression induced by LPS and if CO inhibited LPS-induced leukocyte adhesion to synovial fibroblasts by suppressing VCAM-1 expression.

EXPERIMENTAL APPROACH

Human rheumatoid arthritis synovial fibroblasts (RASFs) were incubated with LPS and/or the CO-releasing compound CORM-2. Effects of LPS on VCAM-1 levels were determined by analysing mRNA expression, promoter activity, protein expression, and immunohistochemical staining. The molecular mechanisms were investigated by determining the expression, activation, and binding activity of transcriptional factors using target signal antagonists.

KEY RESULTS

CORM-2 significantly inhibited inflammatory responses in LPS-treated RASFs by down-regulating the expression of adhesion molecule VCAM-1 and leukocyte infiltration. The down-regulation of LPS-induced VCAM-1 expression involved inhibition of the expression of phosphorylated-NF-κB p65 and AP-1 (p-c-Jun, c-Jun and c-Fos mRNA levels). These results were confirmed by chromatin immunoprecipitation assay to detect NF-κB and AP-1 DNA binding activity.

CONCLUSIONS AND IMPLICATIONS

LPS-mediated formation of the TLR4/MyD88/TRAF6/c-Src complex regulated NF-κB and MAPKs/AP-1 activation leading to VCAM-1 expression and leukocyte adhesion. CORM-2, which liberates CO to elicit direct biological activities, attenuated LPS-induced VCAM-1 expression by interfering with NF-κB and AP-1 activation, and significantly reduced LPS-induced immune cell infiltration of the synovium.

Complement inhibition in a xenogeneic model of interactions between human whole blood and porcine endothelium

Xenotransplantation (xeno-Tx) is considered as an alternative solution to overcome the shortage of human donor organs. However, the success of xeno-Tx is hindered by immune reactions against xenogeneic cells (e. g. of porcine origin). More specifically, activation of innate immune mechanisms such as complement and triggering of the coagulation cascade occur shortly after xeno-Tx, and adhesion of human leukocytes to porcine endothelium is another early critical step mediating the immune attack. To investigate the therapeutic potential of complement inhibition in the context of xenogeneic interactions, we have employed a whole-blood model in the present study. Incubation of human blood with porcine endothelial cells (PAECs) led to activation of complement and coagulation as well as to increased leukocyte adhesion. The observed responses can be attributed to the pig-to-human xenogeneicity, since the presence of human endothelium induced a minor cellular and plasmatic inflammatory response. Importantly, complement inhibition using a potent complement C3 inhibitor, compstatin analogue Cp40, abrogated the adhesion of leukocytes and, more specifically, the attachment of neutrophils to porcine endothelium. Moreover, Cp40 inhibited the activation of PAECs and leukocytes, since the levels of the adhesion molecules E-selectin, ICAM-1, ICAM-2, and VCAM-1 on PAECs and the surface expression of integrin CD11b on neutrophils were significantly decreased. Along the same line, inhibition of CD11b resulted in decreased leukocyte adhesion. Taken together, our findings provide a better understanding of the mechanisms regulating the acute innate immune complications in the context of xeno-Tx and could pave the way for complement-targeting therapeutic interventions.

Role of high-mobility group box-1 protein in disruption of vascular barriers and regulation of leukocyte-endothelial interactions

High-mobility group box-1 protein (HMGB1) is a highly conserved non-histone DNA-binding protein present in the nuclei and cytoplasm of nearly all cell types. The results from recent research provide evidence that HMGB1 is secreted into the extracellular milieu and acts as a pro-inflammatory cytokine and exhibits angiogenic effects to fire the immunological response against the pathological effects. Recently, a great deal of evidence has indicated the critical importance of HMGB1 in mediating vascular barriers dysfunction by modulating the expression of adhesion molecules, such as intercellular adhesion molecule-1, vascular cell adhesion protein 1 and E-selectin on the surface of endothelial cells. Such process promotes the adhesion and migration of leukocytes across the endothelium, leading to breakdown of vascular barriers (blood-brain barrier and blood-retinal barrier) via modulating the expression, content, phosphorylation, and distribution of tight junction proteins. Therefore, here we give an abridged review to understand the mechanistic link between HMGB1 and vascular barriers dysfunction, including interaction with cell-surface receptors and intracellular signaling pathways.

Platelets, acting in part via P-selectin, mediate cytomegalovirus-induced microvascular dysfunction

Cytomegalovirus (CMV) infects a majority of the population worldwide. It has been implicated in cardiovascular disease, induces microvascular dysfunction, and synergizes with hypercholesterolemia to promote leukocyte and platelet recruitment in venules. Although platelets and platelet-associated P-selectin contribute to cardiovascular disease inflammation, their role in CMV-induced vascular responses is unknown. We assessed the role of platelets in CMV-induced microvascular dysfunction by depleting platelets and developing bone marrow chimeric mice deficient in platelet P-selectin. Wild-type and chimeric mice received mock or murine (m)CMV intraperitoneally. Five weeks later, some mice were switched to a high-cholesterol diet (HC) to investigate the synergism between mCMV and HC. Arteriolar vasodilation and recruitment of leukocytes and donor platelets in venules were measured at 11wk. mCMV with or without HC caused significant endothelial dysfunction in arterioles. Platelet depletion restored normal vasodilation in mCMV-HC but not mCMV-ND mice, whereas protection was seen in both groups for platelet P-selectin chimeras. Only mCMV + HC elevated leukocyte and platelet recruitment in venules. Leukocyte adhesion was reduced to mock levels by acute platelet depletion but was only partially decreased in platelet P-selectin chimeras. Platelets from mCMV-HC mice and, to a lesser extent, mCMV-ND but not mock-HC mice showed significant adhesion in mCMV-HC recipients. Our findings implicate a role for platelets, acting through P-selectin, in CMV-induced arteriolar dysfunction and suggest that the addition of HC leads to a platelet-dependent, inflammatory infiltrate that is only partly platelet P-selectin dependent. CMV appeared to have a stronger activating influence than HC on platelets and may represent an additional therapeutic target in vulnerable patients.

Improved in vitro blood compatibility of polycaprolactone nanowire surfaces

There are a multitude of polymeric materials currently utilized to prepare a variety of blood-contacting implantable medical devices. These devices include tissue grafts, coronary artery and vascular stents, and orthopedic implants. The thrombogenic nature of such materials can cause serious complications in patients, and ultimately lead to functional failure. To date, there is no truly hemocompatible biomaterial surface. Nanostructured surfaces improve cellular interactions but there is a limited amount of information regarding their blood compatibility. In this study, the in vitro blood compatibility of four different surfaces (control, PCL; nanowire, NW; collagen immobilized control, cPCL; collagen immobilized nanowire, cNW) were investigated for their use as interfaces for blood-contacting implants. The results presented here indicate enhanced in vitro blood compatibility of nanowire surfaces compared control surfaces. Although there were no significant differences in leukocyte adhesion, there was a decrease in platelet adhesion on NW surfaces. Scanning electron microscopy images showed a decrease in platelet/leukocyte complexes on cNW surfaces and no apparent complexes were formed on NW surfaces compared to PCL and cPCL surfaces. The increase in these complexes likely contributed to a higher expression of specific markers for platelet and leukocyte activation on PCL and cPCL surfaces. No significant differences were found in contact and complement activation on any surface. Further, thrombin antithrombin complexes were significantly reduced on NW surfaces. A significant increase in hemolysis and fibrinogen adsorption was identified on PCL surfaces likely caused by its hydrophobic surface. This work shows the improved blood-compatibility of nanostructured surfaces, identifying this specific nanoarchitecture as a potential interface for promoting the long-term success of blood-contacting biomaterials.

Epigenetic coordination of acute systemic inflammation: potential therapeutic targets

Epigenetic reprogramming of thousands of genes directs the course of acute systemic inflammation, which is highly lethal when dysregulated during sepsis. No molecular-based treatments for sepsis are available. A new concept supports that sepsis is an immunometabolic disease and that loss of control of nuclear epigenetic regulator sirtuin 1 (SIRT-1), a NAD(+) sensor directs immune and metabolic pathways during sepsis. SIRT-1, acting as homeostasis checkpoint, controls hyper- and hypo-inflammatory responses of sepsis at the microvascular interface, which disseminates inflammatory injury to cause multiple organ failure. Modifying SIRT-1 activity, which can prevent or treat established sepsis in mice, may provide a new way to treat sepsis by epigenetically restoring immunometabolic homeostasis.

Bone morphogenetic protein 2: a potential new player in the pathogenesis of diabetic retinopathy

Diabetic retinopathy (DR) is one of the most common complications of diabetes mellitus. Vision loss in DR principally occurs due to breakdown of the blood-retinal barrier (BRB), leading to macular edema, retinal detachment and inner retinal and vitreous hemorrhage. Several growth factors have been shown to play crucial role in the development of these vascular changes; however, the cellular and molecular mechanisms of DR are not yet fully revealed. In the current study we investigated the role of bone morphogenetic protein-2 (BMP2) in DR. We examined the changes in the protein levels of BMP2 in human vitreous and retina in addition to the mouse retina of streptozotocin-induced diabetes. To detect the source of BMP2 during diabetes, human retinal endothelial cells (hRECs) were subjected to high glucose (HG) for 5 days and levels of BMP2 protein were analyzed in conditioned media of these cells relative to control. We also evaluated the effect of BMP2 on the levels of VEGF in cultured rat Müller cells (rMC1). In addition, we tested the pro-inflammatory effects of BMP2 by examining its effect on leukocyte adhesion to cultured hRECs, and levels of adhesion molecules and cytokines production. Finally, the effect of different concentrations of BMP2 on permeability of confluent monolayer of hRECs was evaluated using FITC-Dextran flux permeability assay and by measuring Transcellular Electrical Resistance (TER) using Electric Cell-substrate Impedance Sensing (ECIS). Our results show, for the first time, the up-regulation of BMP2 in diabetic human and mouse retinas in addition to its detection in vitreous of patients with proliferative DR (72 ± 7 pg/ml). In vitro, hRECs showed upregulation of BMP2 in HG conditions suggesting that these cells are a potential source of BMP2 in diabetic conditions. Furthermore, BMP2 induced VEGF secretion by Müller cells in-vitro; and showed a dose response in increasing permeability of cultured hRECs. Meanwhile, BMP2 pro-inflammatory effects were recognized by its ability to induce leukocyte adhesion to the hRECs, intercellular adhesion molecule-1 (ICAM-1) and upregulation of interleukin-6 and 8 (IL-6 and IL-8). These results show that BMP2 could be a contributing growth factor to the development of microvascular dysfunction during DR via enhancing both pro-angiogenic and inflammatory pathways. Our findings suggest BMP2 as a potential therapeutic target to prevent/treat DR.

Expression of human CD46 modulates inflammation associated with GalTKO lung xenograft injury

Evaluation of lungs from GalTKO.hCD46 pigs, genetically modified to lack the galactose-α(1,3)-galactose epitope (GalTKO) and to express human CD46, a complement regulatory protein, has not previously been described. Physiologic, hematologic and biochemical parameters during perfusion with heparinized fresh human blood were measured for 33 GalTKO.hCD46, GalTKO (n = 16), and WT pig lungs (n = 16), and 12 pig lungs perfused with autologous pig blood. Median GalTKO.hCD46 lung survival was 171 min compared to 120 for GalTKO (p = 0.27) and 10 for WT lungs (p < 0.001). Complement activation, platelet activation and histamine elaboration were significantly reduced during the first 2 h of perfusion in GalTKO.hCD46 lungs compared to GalTKO (ΔC3a at 120' 812 ± 230 vs. 1412 ± 1047, p = 0.02; ΔCD62P at 120' 9.8 ± 7.2 vs. 25.4 ± 18.2, p < 0.01; Δhistamine at 60' 97 ± 62 vs. 189 ± 194, p = 0.03). We conclude that, in addition to significant down-modulation of complement activation, hCD46 expression in GalTKO lungs diminished platelet and coagulation cascade activation, neutrophil sequestration and histamine release. Because GalTKO.hCD46 lung failure kinetics correlated directly with platelet and neutrophil sequestration, coagulation cascade activation and a rise in histamine levels within the first hour of perfusion, further progress will likely depend upon improved control of these pathways, by rationally targeted additional modifications to pigs and pharmacologic interventions.

Caveolin-1 scaffolding domain promotes leukocyte adhesion by reduced basal endothelial nitric oxide-mediated ICAM-1 phosphorylation in rat mesenteric venules

Exogenously applied caveolin-1 scaffolding domain (CAV) has been shown to inhibit inflammatory mediator-induced nitric oxide (NO) production and NO-mediated increases in microvessel permeability. However, the effect of CAV on endothelial basal NO that prevents leukocyte adhesion remains unknown. This study aims to investigate the roles of exogenously applied CAV in endothelial basal NO production, leukocyte adhesion, and adhesion-induced changes in microvessel permeability. Experiments were conducted in individually perfused rat mesenteric venules. Microvessel permeability was determined by measuring hydraulic conductivity (Lp). NO was quantified with fluorescence imaging in DAF-2-loaded vessels. Perfusing venules with CAV inhibited basal NO production without affecting basal Lp. Resuming blood flow in CAV-perfused vessels significantly increased leukocyte adhesion. The firmly adherent leukocytes altered neither basal Lp nor adherens junction integrity. Increases in Lp occurred only upon formyl-Met-Leu-Phe application that induces release of reactive oxygen species from the adherent leukocytes. The application of NO synthase inhibitor showed similar results to CAV, and NO donor abolished CAV-mediated leukocyte adhesion. Immunofluorescence staining showed increases in binding of ICAM-1 to an adhesion-blocking antibody concurrent with a Src-dependent ICAM-1 phosphorylation following CAV perfusion. Pre-perfusing vessels with anti-ICAM-1 blocking antibody or a Src kinase inhibitor attenuated CAV-induced leukocyte adhesion. These results indicate that the application of CAV, in addition to preventing excessive NO-mediated permeability increases, also causes reduction of basal NO and promotes ICAM-1-mediated leukocyte adhesion through Src activation-mediated ICAM-1 phosphorylation. CAV-induced leukocyte adhesion was uncoupled from leukocyte oxidative burst and microvessel barrier function, unless in the presence of a secondary stimulation.

Interleukin-19 decreases leukocyte-endothelial cell interactions by reduction in endothelial cell adhesion molecule mRNA stability

Vascular endothelial cell (EC) inflammation is a key event in the pathogenesis of multiple vascular diseases. We tested the hypothesis that interleukin-19 (IL-19), an anti-inflammatory Th2 interleukin, could have a direct anti-inflammatory effect on ECs to decrease inflammation. IL-19 can significantly decrease tumor necrosis factor (TNF)-α-driven intracellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 mRNA and protein abundance in cultured human coronary artery ECs (P < 0.01). IL-19 treatment of ECs, but not monocytes, significantly reduced monocyte adhesion to EC monolayers (P < 0.01). In vivo, systemic administration of IL-19 could significantly reduce TNF-α-induced leukocyte rolling and adhesion in wild-type mice as assayed by intravital microscopy (P < 0.05). IL-19 does not reduce TNF-α-stimulated NF-κB activation in ECs but does decrease serine phosphorylation and cytoplasmic translocation of the mRNA stability factor HuR and significantly reduces stability of ICAM-1 and VCAM-1 mRNA (P < 0.01). These data are the first to report that IL-19 can reduce leukocyte-endothelial cell adhesion and the first to propose reduction in HuR-mediated mRNA stability of ICAM-1 and VCAM-1 as a mechanism. Expression of IL-19 by ECs may represent a protective mechanism to promote resolution of the vascular response to inflammation. Function of IL-19 outside of the immune system is a novel concept, suggesting that resident vascular cells can adopt a Th2 phenotype, and has important ramifications for numerous inflammatory diseases.

Comparative rheology of the adhesion of platelets and leukocytes from flowing blood: why are platelets so small?

We investigated rheological adaptation of leukocytes and platelets for their adhesive functions in inflammation and hemostasis, respectively. Adhesion and margination of leukocytes or platelets were quantified for blood perfused through capillaries coated with P-selectin or collagen, when flow rate, suspending phase viscosity, red cell aggregation, or rigidity was modified. Independent variation of shear rate and shear stress indicated that the ability of platelets to attach at higher levels than leukocytes was largely attributable to their smaller size, reducing their velocity before attachment, and, especially, drag after attachment. Increasing red cell aggregation increased the number of marginated and adhering leukocytes but inhibited platelet adhesion without effect on the number marginated. Increasing red cell rigidity tended to inhibit leukocyte adhesion but promote platelet adhesion. The effects on platelets may be explained by changes in the depth of the near-wall, red cell-depleted layer; broadening (or narrowing) this layer to greater (or less) than the platelet diameter would decrease (or increase) the normal force applied by red blood cells and make attachment less (or more) efficient. Thus different adhesive capabilities of leukocytes and platelets may arise from their differences in size, both directly because of influence on cell velocity and force experienced at the wall and indirectly through effects of size on margination in the bloodstream and interaction with the cell-free layer. In addition, red cell aggregation (of hitherto uncertain physiological significance) may be useful in promoting leukocyte adhesion in inflamed venules but inhibiting unwanted platelet deposition in veins.

Responses of the murine esophageal microcirculation to acute exposure to alkali, acid, or hypochlorite

BACKGROUND/PURPOSE

Although ingestion of alkali-based and/or hypochlorite-based household cleaners as well as strong acids remains a major cause of esophageal wall injury, little is known about the mechanisms that underlie the injury response to these toxic agents. This study examined the roles of vascular dysfunction and inflammation to the esophageal injury response to different caustic substances in mice.

METHODS

The esophageal responses to sodium hydroxide (10%, 5%, and 2.5%), potassium hydroxide (10%, 5%, and 2.5%), sodium hypochlorite (5.25%), and hydrochloric acid (10%, pH 2) were evaluated by intravital videomicroscopy and histopathology. Intravital microscopy was used to monitor changes in the diameter of arterioles and venules, the adhesion and movement of leukocytes in venules, and the time of cessation of arteriolar blood flow in mouse esophagus. The esophageal mucosa was exposed to caustic substances for 0 to 60 minutes before evaluation.

RESULTS

The higher concentrations of sodium hydroxide and potassium hydroxide elicited rapid stasis in both arterioles and venules, which was accompanied by arteriolar constriction and thrombosis. An accumulation of adherent leukocytes in venules was not observed with any agent. Histopathological evaluation revealed marked cellular and interstitial edema in the mucosa with alkali, whereas hydrochloric acid and sodium hypochlorite decreased the thickness epithelial layer.

CONCLUSION

These findings suggest that ischemia and thrombosis are dominant processes, whereas inflammation is less important in the pathogenesis of acute corrosive injury to the esophageal mucosa.

Lattice Boltzmann simulation of blood flow in digitized vessel networks

Efficient flow of red blood cells (RBCs) and white blood cells (WBCs) through the microcirculation is necessary for oxygen and nutrient delivery as well as immune cell function. Because blood is a dense particulate suspension, consisting of 40% RBCs by volume, it is difficult to analyze the physical mechanisms by which individual blood cells contribute to the bulk flow properties of blood. Both experimental and computational approaches are hindered by these non-Newtonian properties, and predicting macroscopic blood flow characteristics such as viscosity has historically been an empirical process. In order to examine the effect of the individual cells on macroscopic blood rheology, we developed a lattice Boltzmann model that considers the blood as a suspension of particles in plasma, accounting explicitly for cell-cell and cell-wall interactions. Previous studies have concluded that the abundance of leukocyte rolling in postcapillary venules is due to interactions between red blood cells and leukocytes as they enter postcapillary expansions. Similar fluid dynamics may be involved in the initiation of rolling at branch points, a phenomenon linked to atherosclerosis. The lattice Boltzmann approach is used to analyze the interactions of red and white blood cells as they flow through vascular networks digitized from normal and tumor tissue. A major advantage of the lattice-Boltzmann method is the ability to simulate particulate flow dynamically and in any geometry. Using this approach, we can accurately determine RBC-WBC forces, particle trajectories, the pressure changes in each segment that accompany cellular traffic in the network, and the forces felt by the vessel wall at any location. In this technique, intravital imaging using vascular contrast agents produces the network outline that is fed to the lattice-Boltzmann model. This powerful and flexible model can be used to predict blood flow properties in any vessel geometry and with any blood composition.

Correlation of leukocyte adhesiveness, adhesion molecule expression and leukocyte-induced contraction following balloon angioplasty

1. The aim of this study was to examine the changes in leukocyte adhesion and leukocyte-induced contraction in balloon-injured rabbit subclavian artery and to correlate these changes with vessel morphology and expression of adhesion molecules on the injured arteries. 2. Rabbits were anaesthetized and their left subclavian arteries were injured by balloon inflation and withdrawal followed by sacrifice at 2, 24, 48 h or 8 days after injury. The left and right subclavian arteries were removed and leukocytes were isolated from autologous rabbit blood. Leukocyte-induced contraction was measured in 5-HT precontracted artery rings and leukocyte adhesion was measured using (51)Cr-labelled leukocytes. Immunocytochemistry using paraffin-embedded tissue was employed to detect changes in the expression of adhesion molecules on injured arteries. 3. Autologous leukocytes caused a contraction of rabbit subclavian artery rings, which was prevented by L-NAME (10(-3) M). Balloon-induced injury abolished the contractile response to leukocytes, which correlated with loss of carbachol-induced relaxation 4. Balloon injury markedly enhanced the adhesiveness of the subclavian artery for leukocytes, most notably at 24 and 48 h after injury (1.7 and 1.8 fold respectively). Increased leukocyte adhesion at these two time points correlated with an upregulation of E-selectin, P-selectin and VCAM-1 expression on the remaining endothelium of the injured artery. 5. Vessel morphology revealed that balloon inflation had induced an infiltration of inflammatory cells into the vessel wall, the greatest increase being seen at 24 h after injury. 6. It is concluded that an increase in the expression of E-selectin, P-selectin and VCAM-1 following balloon-induced injury leads to enhanced leukocyte adhesion and migration into the injured vessel.

Mechanisms of gastroprotection by transdermal nitroglycerin in the rat

Nitric oxide (NO) donors prevent experimentally-induced gastric mucosal damage, but their clinical utility is limited by short duration of action or unsuitability of the pharmaceutical form employed. This study analyses the gastroprotection elicited by a clinically used mode of continuous administration of an NO donor, namely the nitroglycerin patch. Application to rats of a transdermal patch that releases doses of nitroglycerin comparable to those used in man (40, 80, 160 and 400 ng min(-1) rat(-1)) reduced gastric damage induced by indomethacin (25 mg kg(-1), p.o. or s.c.). The nitroglycerin patch (160 ng min(-1) rat(-1)) also diminished damage by oral administration (1 ml) of acidified bile salts (100 mg kg(-1) taurocholic acid in 150 mM HCl) or 50% ethanol. Transdermal nitroglycerin (160 ng min(-1) rat(-1)) did not influence basal gastric blood flow, as measured by lasser-doppler flowmetry, but prevented its reduction by indomethacin. Transdermal nitroglycerin (160 ng min(-1) rat(-1)) prevented in vivo leukocyte rolling and adherence in the rat mesentery microvessels superfused with indomethacin, as evaluated by intravital microscopy. The transdermal nitroglycerin patch protects the gastric mucosa from damage by mechanisms that involve maintenance of mucosal blood flow and reduction of leukocyte-endothelial cell interaction.

Rapid secretion of prestored interleukin 8 from Weibel-Palade bodies of microvascular endothelial cells

Interleukin (IL)-8, a C-X-C chemokine, activates integrin-mediated adhesion of neutrophils. Presentation of IL-8 on the endothelial cell surface may promote leukocyte extravasation. We found that cultured human microvascular endothelial cells from the intestine (HIMEC) and from nasal polyps (PMEC), but not human umbilical vein endothelial cells (HUVEC), contained IL-8 in intracellular granules that coexpressed von Willebrand factor (vWf ). This observation was corroborated by the immunohistochemical observation of double-positive granules (IL-8(+)vWf+) in vessels of small and large intestine, nasal mucosa, and skin, whereas umbilical cords revealed no endothelial IL-8. After treatment of HIMEC or PMEC with histamine or thrombin, a dramatic increase in supernatant IL-8 concentration was observed within 3 min, whereas no increase in IL-8 was detected in supernatants of identically treated HUVEC cultures. Histamine or thrombin treatment also caused IL-8-containing granules to rapidly disappear from HIMEC. In HUVEC, IL-8-containing granules were inducible by treatment with recombinant human IL-1beta for 24 h; additional histamine treatment doubled IL-8 secretion from HUVEC in the same rapid manner observed for mucosal EC. These data suggested that IL-8 prestored in microvascular endothelial cells may provide a rapid pathway for specific activation of neutrophil adhesion at sites of acute inflammation.

Modulation of cell adhesion molecule expression and function on human lung microvascular endothelial cells by inhibition of phosphodiesterases 3 and 4

1. Expression of cell adhesion molecules (CAM) on the lung microvascular endothelium is believed to play a key role in the recruitment of leukocytes in pulmonary inflammation. Moreover, regulation of CAM expression may be an important mechanism through which this inflammation may be controlled. Experimental evidence has suggested that combined phosphodiesterase (PDE) 3 and 4 inhibitors increase cyclic AMP levels within cells greater than inhibition of either isoenzyme alone. In the present study we assessed the effect of combinations of rolipram (PDE4 inhibitor), ORG 9935 (PDE3 inhibitor) and salbutamol (beta-agonist) on CAM expression and neutrophil or eosinophil adhesion to human lung microvascular endothelial cells (HLMVEC). 2. Tumour necrosis factor-alpha (TNF-alpha)-induced intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1 and E-selectin expression were measured on HLMVEC monolayers at 6 h by a specific ELISA technique in the presence of different combinations of medium, rolipram, ORG 9935 and salbutamol. 3. Rolipram in combination with salbutamol, but neither agent alone, inhibited TNF-alpha-induced E-selectin expression, whilst ICAM-1 and VCAM-1 expression were not affected. ORG 9935 had no significant effect on CAM expression alone. However, in combination with rolipram a syngergistic inhibition of VCAM-1 and E-selectin, but not ICAM-1, expression was observed. No further inhibition was seen in the additional presence of salbutamol. 4. Neutrophil adhesion to TNF-alpha-stimulated (6 h) HLMVEC was mainly E-selectin dependent in this model, as ENA2 an anti-E-selectin monoclonal antibody (mAb) abrogated neutrophil adhesion. Eosinophil adhesion was E-selectin-, ICAM-1- and VCAM-1-dependent, as assessed by the inhibitory activity of ENA2 and the ability of a mAb to the ICAM-1 ligand, CD18, and a mAb to the VCAM-1 ligand, VLA4, to attenuate adhesion. 5. Rolipram in the presence of salbutamol or ORG 9935 significantly inhibited neutrophil adherence to TNF-alpha-stimulated HLMVEC. Eosinophil adherence to monolayers was inhibited only when HLMVEC were activated in the presence of rolipram and ORG 9935. 6. Collectively, the findings presented in this manuscript suggest that inhibition of PDE4 with appropriate activation of adenylate cyclase is sufficient to inhibit induction of E-selectin expression on HLMVEC to a level that has functional consequences for neutrophil adhesion. In contrast, combined inhibition of PDE3 and 4 isoenzymes is necessary to inhibit VCAM-1 and to have inhibitory effects on eosinophil adhesion to activated HLMVEC. Upregulation of ICAM-1 expression on HLMVEC does not appear to be modulated by PDE3 and 4 inhibition. These data may have implications for the use of selective PDE4 inhibitors in lung inflammation.

An approach for studies of mediator-induced leukocyte rolling in the undisturbed microcirculation of the rat mesentery

1. Although intravital microscopy is the method of choice for observation of inflammatory leukocyte rolling and adhesion in small venules in vivo, a problem with this technique is that surgical exposure of suitable tissues per se triggers the rolling mechanism. In this study, we describe an approach to investigate induction of rolling in undisturbed microvessels. For this purpose, intravital microscopic observation of leukocyte rolling and adhesion in the rat mesentery was combined with histological determination of the intravascular concentrations of polymorphonuclear and mononuclear leukocytes (PMNL and MNL). 2. By relating the histologically determined number of intravascular leukocytes to either microvessel volume or to the erythrocyte concentration, the baseline MNL and PMNL content was found to be 3-6 fold higher in venules than in systemic blood. This increase in microvessel leukocyte concentration did not seem to be related to leukocyte-endothelium interactions, because the leukocyte concentration was similarly elevated in arterioles where rolling and adhesion did not take place. 3. Preparation of the rat mesentery for intravital microscopy time-dependently increased the venular PMNL concentration to over 100 fold the systemic PMNL concentration 45 min after exteriorization of the small intestine. The MNLs were much less responsive to the preparative manipulation. By treatment with the polysaccharide fucoidin (inhibits rolling but not firm adhesion per se), or by use of intravital microscopy immediately before tissue fixation, approximately 90% of the accumulated venular PMNLs were found to represent rolling cells. 4. Intraperitoneal injection of 10(-3) M histamine increased the venular PMNL (but not the MNL) concentration to almost 50 fold the systemic PMNL value. The histamine response did not vary with venular diameter, and the relative contribution of rolling vs firmly adherent cells to the PMNL, accumulation was again approximately 90%. Intraperitoneal injection of leukotriene C4, but not prostaglandin E2, caused a significant increase in venular PMNL concentration. 5. Systemic treatment with the anti-P-selectin monoclonal antibody PB1.3 had no effect on the histamine-induced venular PMNL accumulation (i.e. rolling) in female Wistar or male Sprague-Dawley rats. On the other hand, identical treatment with PB1.3 very effectively inhibited the histamine-induced PMNL response in the mesentery of rabbits. 6. In conclusion, we have shown that a histologically determined increase in leukocyte concentration in rat mesenteric venules may be used as an index of mediator-induced leukocyte rolling if the relative contribution of rolling and firm leukocyte adhesion is first determined, for example by the means described in this study. This relatively simple approach may be very useful for studying various aspects of leukocyte rolling when the 'spontaneous' rolling triggered by preparation of tissues for intravital microscopy is undesirable.

Characteristics of histamine-induced leukocyte rolling in the undisturbed microcirculation of the rat mesentery

1. The main objective of this study was to analyse the role and mode of action of the mast cell mediator histamine in leukocyte-endothelium interactions in small venules in vivo. For this purpose, we used a histological approach (combined with intravital microscopy) that allows studies of rapid mediator-induced venular leukocyte accumulation, reflecting leukocyte rolling, in the undisturbed microcirculation of the rat mesentery where rolling is normally absent. 2. We first examined the relative importance of histamine and 5-hydroxytryptamine (5-HT) in acute mast cell-dependent leukocyte recruitment. The mast cell secretagogue compound 48/80 (i.p. for 15 min) induced a marked venular accumulation of polymorphonuclear leukocytes (PMNL) which was almost abolished by combined histamine1 (H1)- and histamine2 (H2)-receptor blockade. In contrast, the 5-HT-receptor antagonist methysergide was inactive in this regard. Moreover, exogenous 5-HT was less active than exogenous histamine in evoking venular PMNL accumulation (histamine response dose-dependent; 5-HT response bell shaped). Prostaglandin D2 did not cause PMNL accumulation. 3. The venular PMNL response to exogenous histamine peaked between 15 min and 1 h, was still significantly elevated at 2 h, and then returned to prechallenge values after 3 h. At all time points, the histamine-induced PMNL accumulation was nearly abolished by i.v. treatment with the polysaccharide fucoidin (which blocks rolling but not firm adhesion per se), suggesting that the PMNL response to histamine was due to rolling rather than firm adhesion over the entire 3 h period. At no time point did histamine trigger accumulation of mononuclear leukocytes (MNL). 4. To examine the role of histamine-receptors in the histamine-induced PMNL accumulation (i.e. rolling), the animals were pretreated with diphenhydramine (H1-receptor antagonist), cimetidine, or ranitidine (H2-receptor antagonists). Diphenhydramine alone inhibited the venular PMNL response to histamine by 52%, while both H2-receptor antagonists were completely inactive. However, the combination of cimetidine and diphenhydramine reduced the histamine-induced PMNL rolling by 82%. Furthermore, in contrast to an H3-receptor agonist, challenge with either the H1-receptor agonist 2-thiazolylethylamine or two different H2-receptor agonists (impromidine, dimaprit) was sufficient to provoke significant venular PMNL accumulation. 5. Treatment with the nitric oxide-synthase inhibitor L-NAME did not affect the histamine-induced PMNL rolling. On the other hand, 3 h pretreatment with dexamethasone reduced the PMNL response to histamine by 73%, and flow cytometric analysis showed that the dexamethasone treatment almost completely inhibited binding of soluble P-selectin to rat isolated PMNLs. 6. We conclude that initial leukocyte recruitment after mast cell activation in the rat mesentery is critically dependent on histamine release. The cellular response to histamine was specifically due to PMNL rolling, involved activation of both H1- and H2-receptors, and lasted for 2 3 h. Moreover, the histamine-induced PMNL rolling was not dependent on nitric oxide synthesis, but was sensitive to glucocorticoid treatment, possibly via inhibition of expression or function of leukocytic P-selectin ligand(s).

Inhibitory effect of locally administered heparin on leukocyte rolling and chemoattractant-induced firm adhesion in rat mesenteric venules in vivo

1. Anti-inflammatory actions of heparin and related glycosaminoglycans have been described in the literature. Here, we used intravital microscopy of the rat mesentery microcirculation to examine effects of locally administered heparin on leukocyte rolling and chemoattractant-induced firm adhesion. 2. It was found that topical application of heparin reduced N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced leukocyte adhesion. Notably, the inhibitory action of heparin was not dose-dependent, but rather a biphasic dose-response was found, i.e. low (2 and 20 iu ml(-1)) and high (1000 iu ml(-1)) concentrations of heparin significantly reduced adhesion, whereas an intermediate dose (200 iu ml(-1)) was less effective. 3. Heparin, 2 and 20 iu ml(-1), decreased rolling leukocyte flux, while having no effect on blood flow or total leukocyte flux. By contrast, heparin, 200 and 1000 iu ml(-1), increased total leukocyte flux in parallel with a rise in volume blood flow resulting in recovery of the rolling leukocyte flux at these doses. Thus, the biphasic inhibitory action of heparin on fMLP-induced firm adhesion could in part be attributed to changes in leukocyte delivery (i.e. blood flow) and rolling leukocyte flux induced by heparin. 4. When compensating for the influence of different rolling levels on fMLP-evoked adhesion, a dose-related inhibitory effect of heparin on the firm adhesive response per se was revealed. Similar results were obtained in a static adhesion assay in vitro where heparin 200 and 1000 iu ml(-1) (but not 2 and 20 iu ml(-1)) significantly inhibited fMLP-induced leukocyte adhesion in the absence of any modulatory influence on changes in rolling. 5. Our data show that locally administered heparin inhibits leukocyte rolling as well as chemoattractant-induced firm adhesion in vivo which thus may contribute to the postulated anti-inflammatory activity of this compound. However, because of interference with several microvascular functions, strict dose-dependent responses to heparin treatment were not found, which illustrates the complex interplay between local blood flow, leukocyte rolling and chemoattractant-induced adhesion as determinants of leukocyte recruitment to tissues in inflammation.