Low venular shear rates promote leukocyte-dependent recruitment of adherent platelets

The Endothelial Glycocalyx and Retinal Hemodynamics

PURPOSE

Previous studies suggest that the endothelial glycocalyx adds to vascular resistance, inhibits thrombosis, and is critical for regulating homogeneous blood flow and ensuring uniform red blood cell (RBC) distribution. However, these functions and consequences of the glycocalyx have not been examined in the retina. We hypothesize that the endothelial glycocalyx is a critical regulator of retinal hemodynamics and perfusion and decreases the propensity for retinal thrombus formation.

METHODS

Hyaluronidase and heparinase, which are endothelial glycocalyx-degrading enzymes, were infused into mice. Fluorescein isothiocyanate-dextran (2000 kDa) was injected to measure lumen diameter, while RBC velocity and distribution were measured using fluorescently labeled RBCs. The diameters and velocities were used to calculate retinal blood flow and shear rates. Mean circulation time was calculated by measuring the difference between arteriolar and venular mean transit times. Rose Bengal dye was infused, followed by illumination with a green light to induce thrombosis.

RESULTS

The acute infusion of hyaluronidase and heparinase led to significant increases in both arteriolar (7%) and venular (16%) diameters in the retina, with a tendency towards increased arteriolar velocity. In addition, the degradation caused a significant decrease in the venular shear rate (14%). The enzyme infusion resulted in substantial increases in total retinal blood flow (26%) and retinal microhematocrit but no changes in the mean circulation time through the retina. We also observed an enhanced propensity for retinal thrombus formation with the removal of the glycocalyx.

CONCLUSIONS

Our data suggest that acute degradation of the glycocalyx can cause significant changes in retinal hemodynamics, with increases in vessel diameter, blood flow, microhematocrit, pro-thrombotic conditions, and decreases in venular shear rate.

Enhanced Blood Clotting After Rewarming From Experimental Hypothermia in an Intact Porcine Model

Introduction: Due to functional alterations of blood platelets and coagulation enzymes at low temperatures, excessive bleeding is a well-recognized complication in victims of accidental hypothermia and may present a great clinical challenge. Still, it remains largely unknown if hemostatic function normalizes upon rewarming. The aim of this study was to investigate effects of hypothermia and rewarming on blood coagulation in an intact porcine model.

Methods: The animals were randomized to cooling and rewarming (n = 10), or to serve as normothermic, time-matched controls (n = 3). Animals in the hypothermic group were immersion cooled in ice water to 25°C, maintained at 25°C for 1 h, and rewarmed to 38°C (normal temperature in pigs) using warm water. Clotting time was assessed indirectly at different temperatures during cooling and rewarming using a whole blood coagulometer, which measures clotting time at 38°C.

Results: Cooling to 25°C led to a significant increase in hemoglobin, hematocrit and red blood cell count, which persisted throughout rewarming. Cooling also caused a transiently decreased white blood cell count that returned to baseline levels upon rewarming. After rewarming from hypothermia, clotting time was significantly shortened compared to pre-hypothermic baseline values. In addition, platelet count was significantly increased.

Discussion/Conclusion: We found that clotting time was significantly reduced after rewarming from hypothermia. This may indicate that rewarming from severe hypothermia induces a hypercoagulable state, in which thrombus formation is more likely to occur.

Live Intravital Intestine with Blood Flow Visualization in Neonatal Mice Using Two-photon Laser Scanning Microscopy

This protocol describes a novel technique to investigate the microcirculation dynamics underlying the pathology in the small intestine of neonatal mice using two-photon laser-scanning microscopy (TPLSM). Recent technological advances in multi-photon microscopy allow intravital analysis of different organs such as the liver, brain and intestine. Despite these advances, live visualization and analysis of the small intestine in neonatal rodents remain technically challenging. We herein provide a detailed description of a novel method to capture high resolution and stable images of the small intestine in neonatal mice as early as postnatal day 0. This imaging technique allows a comprehensive understanding of the development and blood flow dynamics in small intestine microcirculation.

Gold nanoparticles reduce inflammation in cerebral microvessels of mice with sepsis

Background

Sepsis is an emergency medical condition that can lead to death and it is defined as a life-threatening organ dysfunction caused by immune dysregulation in response to an infection. It is considered the main killer in intensive care units. Sepsis associated-encephalopathy (SAE) is mostly caused by a sepsis-induced systemic inflammatory response. Studies report SAE in 14–63% of septic patients. Main SAE symptoms are not specific and usually include acute impairment of consciousness, delirium and/or coma, along with electroencephalogram (EEG) changes. For those who recover from sepsis and SAE, impaired cognitive function, mobility and quality of life are often observed months to years after hospital discharge, and there is no treatment available today to prevent that. Inflammation and oxidative stress are key players for the SAE pathophysiology. Gold nanoparticles have been demonstrated to own important anti-inflammatory properties. It was also reported 20 nm citrate-covered gold nanoparticles (cit-AuNP) reduce oxidative stress. In this context, we tested whether 20 nm cit-AuNP could alleviate the acute changes caused by sepsis in brain of mice, with focus on inflammation. Sepsis was induced in female C57BL/6 mice by cecal ligation and puncture (CLP), 20 nm cit-AuNP or saline were intravenously (IV) injected 2 h after induction of sepsis and experiments performed 6 h after induction. Intravital microscopy was used for leukocyte and platelet adhesion study in brain, blood brain barrier (BBB) permeability carried out by Evans blue assay, cytokines measured by ELISA and real time PCR, cell adhesion molecules (CAMs) by flow cytometry and immunohistochemistry, and transcription factors, by western blotting.

Results

20 nm cit-AuNP treatment reduced leukocyte and platelet adhesion to cerebral blood vessels, prevented BBB failure, reduced TNF- concentration in brain, and ICAM-1 expression both in circulating polymorphonuclear (PMN) leukocytes and cerebral blood vessels of mice with sepsis. Furthermore, 20 nm cit-AuNP did not interfere with the antibiotic effect on the survival rate of mice with sepsis.

Conclusions

Cit-AuNP showed important anti-inflammatory properties in the brain of mice with sepsis, being a potential candidate to be used as adjuvant drug along with antibiotics in the treatment of sepsis to avoid SAE

Implications for maintaining vascular access device patency and performance: Application of science to practice

Introduction:

Vascular access devices are commonly inserted devices that facilitate the administration of fluids and drugs, as well as blood sampling. Despite their common use in clinical settings, these devices are prone to occlusion and failure, requiring replacement and exposing the patient to ongoing discomfort/pain, local vessel inflammation and risk of infection. A range of insertion and maintenance strategies are employed to optimize device performance; however, the evidence base for many of these mechanisms is limited and the mechanisms contributing to the failure of these devices are largely unknown.

Aims/objectives:

(1) To revisit existing understanding of blood, vessel physiology and biological fluid dynamics; (2) develop an understanding of the implications that different clinical practices have on vessel health, and (3) apply these understandings to vascular access device research and practice.

Method:

Narrative review of biomedical and bioengineering studies related to vascular access practice.

Results/outcomes:

Current vascular access device insertion and maintenance practice and policy are variable with limited clinical evidence to support the theoretical assumptions underpinning these regimens. This review demonstrates the physiological response to vascular access device insertion, flushing and infusion on the vein, blood components and blood flow. These appear to be associated with changes in intravascular fluid dynamics. Variable forces are at play that impact blood componentry and the endothelium. These may explain the mechanisms contributing to vascular access failure.

Conclusion:

This review provides an update to our current knowledge and understanding of vascular physiology and the hemodynamic response, challenging some previously held assumptions regarding vascular access device maintenance, which require further investigation.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Compartment syndrome causes systemic inflammation in a rat

Aims

Compartment syndrome results from increased intra-compartmental pressure (ICP) causing local tissue ischaemia and cell death, but the systemic effects are not well described. We hypothesised that compartment syndrome would have a profound effect not only on the affected limb, but also on remote organs.

Methods

Using a rat model of compartment syndrome, its systemic effects on the viability of hepatocytes and on inflammation and circulation were directly visualised using intravital video microscopy.

Results

We found that hepatocellular injury was significantly higher in the compartment syndrome group (192 PI-labelled cells/10-1 mm3, standard error of the mean (sem) 51) compared with controls (30 PI-labelled cells/10-1 mm3, sem 12, p < 0.01). The number of adherent venular white blood cells was significantly higher for the compartment syndrome group (5 leukocytes/30s/10 000 μm2, sem 1) than controls (0.2 leukocytes/30 s/10 000 μm2, sem 0.2, p < 0.01). Volumetric blood flow was not significantly different between the two groups, although there was an increase in the heterogeneity of perfusion.

Conclusions

Compartment syndrome can be accompanied by severe systemic inflammation and end organ damage. This study provides evidence of the relationship between compartment syndrome in a limb and systemic inflammation and dysfunction in a remote organ. Cite this article: Bone Joint J 2016; 98-B:1132–7.

Platelet-endothelial cell interaction in brain microvessels of angiotensin II type-2 receptor knockout mice following transient bilateral common carotid artery occlusion

The purpose of this study was to investigate the behavior of platelets (rolling and adhesion) in cerebral microvessels of angiotensin II type-2 receptor-knockout (AT2RKO) mice after transient bilateral carotid artery occlusion using intravital fluorescence microscopy. Twenty AT2RKO mice, consisting of 11 mice in the sham group and 9 mice in the ischemia reperfusion group (reperfusion after 15 min of bilateral, total carotid artery occlusion) were used in this study. The hole traversed the bone and dura mater, but arachnoid, pia mater, and cerebral parenchyma were preserved. Platelets were harvested from donor mice and stained using carboxyfluorescein diacetate succinimidyl ester. The number of platelets showing rolling and adhesion to pial vessels in AT2 deficient mice at 3 and 6 h after cerebral ischemia reperfusion was significantly higher than that in the sham group (P < 0.05). In addition, AT2 receptor has an inhibitory role in platelet rolling and adhesion after cerebral ischemia reperfusion.

Effect of salvianolic acid B on TNF-α induced cerebral microcirculatory changes in a micro-invasive mouse model

PURPOSE

To investigate the effects of salvianolic acid B (SAB) on tumor necrosis factor a (TNF-α) induced alterations of cerebral microcirculation with a bone-abrading model.

METHODS

The influences of craniotomy model and bone-abrading model on cerebral microcirculation were compared. The bone-abrading method was used to detect the effects of intracerebroventricular application of 40 μg/kg·bw TNF-α on cerebral venular leakage of fluorescein isothiocyanate (FITC)- albulmin and the rolling and adhesion of leukocytes on venules with fluorescence tracer rhodamine 6G. The therapeutical effects of SAB on TNF-α induced microcirculatory alteration were observed, with continuous intravenous injection of 5 mg/kg·h SAB starting at 20 min before or 20 min after TNF-α administration, respectively. The expressions of CD11b/CD18 and CD62L in leukocytes were measured with flow cytometry. Immunohistochemical staining was also used to detect E-selectin and ICAM-1 expression in endothelial cells.

RESULTS

Compared with craniotomy method, the bone-abrading method preserved a higher erythrocyte velocity in cerebral venules and more opening capillaries. TNF-α intervention only caused responses of vascular hyperpermeability and leukocyte rolling on venular walls, without leukocyte adhesion and other hemodynamic changes. Pre- or post-SAB treatment attenuated those responses and suppressed the enhanced expressions of CD11b/CD18 and CD62L in leukocytes and E-selectin and ICAM-1 in endothelial cells induced by TNF-α.

CONCLUSIONS

The pre- and post-applications of SAB during TNF-α stimulation could suppress adhesive molecular expression and subsequently attenuate the increase of cerebral vascular permeability and leukocyte rolling.

Adhesion Molecules: Master Controllers of the Circulatory System

This manuscript will review our current understanding of cellular adhesion molecules (CAMs) relevant to the circulatory system, their physiological role in control of vascular homeostasis, innate and adaptive immune responses, and their importance in pathophysiological (disease) processes such as acute lung injury, atherosclerosis, and pulmonary hypertension. This is a complex and rapidly changing area of research that is incompletely understood. By design, we will begin with a brief overview of the structure and classification of the major groups of adhesion molecules and their physiological functions including cellular adhesion and signaling. The role of specific CAMs in the process of platelet aggregation and hemostasis and leukocyte adhesion and transendothelial migration will be reviewed as examples of the complex and cooperative interplay between CAMs during physiological and pathophysiological processes. The role of the endothelial glycocalyx and the glycobiology of this complex system related to inflammatory states such as sepsis will be reviewed. We will then focus on the role of adhesion molecules in the pathogenesis of specific disease processes involving the lungs and cardiovascular system. The potential of targeting adhesion molecules in the treatment of immune and inflammatory diseases will be highlighted in the relevant sections throughout the manuscript.

IL-6 Mediates the Intestinal Microvascular Thrombosis Associated with Experimental Colitis

Inflammatory bowel diseases are associated with increased risk for thrombus formation both within the inflamed bowel and at distant sites. Although the increased propensity for distant organ thrombus development has been recapitulated in animal models of colitis and linked to interleukin-6 (IL-6), it remains unclear whether experimental colitis results in accelerated thrombus development within the inflamed bowel and whether IL-6 contributes to a local thrombogenic response. These issues related to thrombus formation within the inflamed bowel were addressed in mice with dextran sodium sulfate-induced colitis. Wild-type (WT) mice, IL-6 deficient (IL-6(-/-)) mice, and bone marrow chimeras (WT→WT and IL-6(-/-)→WT) were used. The effects of treatment with either an IL-6-blocking, IL-6Rα-blocking or gp130-blocking antibody were also evaluated. Disease activity index and colonic weight-to-length ratio (W/L) were used to monitor the development of colitis. Intravital videomicroscopy was used to study thrombus development (induced with the light/dye method) in mucosal vessels of the ascending colon. Thrombus development was significantly enhanced in WT colitic mice. Neither genetic deficiency nor immunoblockade of IL-6 significantly altered the disease activity index and W/L responses to dextran sodium sulfate treatment. However, colitis-induced thrombogenesis was attenuated in IL-6(-/-) mice and in WT mice treated with either the IL-6-blocking, IL-6Rα-blocking or gp130-blocking antibody. IL-6(-/-)→WT, but not WT→WT chimeras, exhibited a blunted thrombosis response to dextran sodium sulfate. These results indicate that experimental colitis is associated with accelerated thrombus development within the inflamed colon and that IL-6, derived from bone marrow-derived blood cells, is largely responsible for this response.

Drag-reducing polyethylene oxide improves microcirculation after hemorrhagic shock

BACKGROUND

Despite resuscitation after trauma, microcirculatory abnormalities are known to persist in post-shock multiorgan dysfunction. The high-molecular weight polymer polyethylene oxide (PEO) (>10(6) Da), a classic drag-reducing polymer, can improve hemorrhagic shock (HS)-induced hemodynamic abnormalities in rats.

MATERIALS AND METHODS

We examined the effects of PEO on microcirculation and on changes in multiple organs after shock. After the spinotrapezius muscle was prepared, HS was induced in Sprague-Dawley rats. Drug administration (normal saline or PEO) was performed 2 h after shock followed by infusion of shed blood.

RESULTS

The velocity, blood flow, and functional capillary density in the shock + PEO group were significantly higher than those in the shock + normal saline group. Moreover, the kidney, liver, and lung function was improved, resulting in prolonged survival time. Our findings indicate that intravenous infusion of PEO can ameliorate shock-associated organ dysfunction and prolong survival time in severe HS, which may be a result of increased arteriolar blood velocity, blood flow, and functional capillary density.

CONCLUSIONS

PEO could have potential clinical application in the treatment of shock-induced multiorgan dysfunction.

A focus on the role of platelets in liver regeneration: Do platelet-endothelial cell interactions initiate the regenerative process?

Platelets are involved in the early phases of liver regeneration. Moreover, platelet transfusion and thrombocytosis were recently shown to enhance hepatocyte proliferation. However, the precise mechanisms remain elusive. This review discusses the latest updates regarding the mechanisms by which platelets stimulate liver regeneration, focusing on their interactions with liver sinusoidal endothelial cells and on their fate within the liver. Following liver injury, platelets are recruited to and trapped within the liver, where they adhere to the endothelium. Subsequent platelet activation results in the release of platelet granules, which stimulate hepatocyte proliferation through activation of the Akt and ERK1/2 signalling pathways. Platelets activate liver sinusoidal endothelial cells, leading to the secretion of growth factors, such as interleukin-6. Finally, liver sinusoidal cells and hepatocytes can also internalize platelets, but the effects of this alternate process on liver regeneration remain to be explored. A better understanding of the mechanisms by which platelets stimulate liver regeneration could lead to improvement in post-operative organ function and allow hepatectomies of a greater extent to be performed.

The role of platelets in the recruitment of leukocytes during vascular disease

Besides their role in the formation of thrombus during haemostasis, it is becoming clear that platelets contribute to a number of other processes within the vasculature. Indeed, the integrated function of the thrombotic and inflammatory systems, which results in platelet-mediated recruitment of leukocytes, is now considered to be of great importance in the propagation, progression and pathogenesis of atherosclerotic disease of the arteries. There are three scenarios by which platelets can interact with leukocytes: (1) during haemostasis, when platelets adhere to and are activated on sub-endothelial matrix proteins exposed by vascular damage and then recruit leukocytes to a growing thrombus. (2) Platelets adhere to and are activated on stimulated endothelial cells and then bridge blood borne leukocytes to the vessel wall and. (3) Adhesion between platelets and leukocytes occurs in the blood leading to formation of heterotypic aggregates prior to contact with endothelial cells. In the following review we will not discuss leukocyte recruitment during haemostasis, as this represents a physiological response to tissue trauma that can progress, at least in its early stages, in the absence of inflammation. Rather we will deal with scenarios 2 and 3, as these pathways of platelet–leukocyte interactions are important during inflammation and in chronic inflammatory diseases such as atherosclerosis. Indeed, these interactions mean that leukocytes possess means of adhesion to the vessel wall under conditions that may not normally be permissive of leukocyte–endothelial cell adhesion, meaning that the disease process may be able to bypass the regulatory pathways which would ordinarily moderate the inflammatory response.

Time-dependent effect of clonidine on microvascular permeability during endotoxemia

BACKGROUND

Endothelial leakage with accompanying tissue edema and increased leukocyte adhesion are characteristics of the vascular inflammatory response. Tissue edema formation is a key mechanism in sepsis pathophysiology contributing to impaired tissue oxygenation and the development of shock. Sepsis mortality is directly associated with the severity of these microcirculatory alterations. Dysfunction of the sympathetic nervous system can have deleterious effects in generalized inflammation. This study evaluated the effect of the adrenergic alpha 2 agonist clonidine on microvascular permeability and leukocyte adhesion during endotoxemia.

METHODS

Macromolecular leakage, leukocyte adhesion, and venular wall shear rate were examined in mesenteric postcapillary venules of rats by using intravital microscopy (IVM). Lipopolysaccharide (LPS) (4mg/kg/h) or equivalent volumes of saline were continuously infused following baseline IVM at 0min. IVM was repeated after 60 and 120min in endotoxemic and nonendotoxemic animals. Clonidine (10μg/kg) was applied as an i.v. bolus. Animals received either (i) saline alone, (ii) clonidine alone, (iii) clonidine 45min prior to LPS, (iv) clonidine 10min prior to LPS, (v) clonidine 30min after LPS, or (vi) LPS alone. Due to nonparametric data distribution, Wilcoxon test and Dunn's multiple comparisons test were used for data analysis. Data were considered statistically significant at p<0.05.

RESULTS

LPS significantly increased microvascular permeability and leukocyte adhesion and decreased venular wall shear rate. Clonidine significantly reduced microvascular permeability when applied 45min before or 30min after LPS administration. Leukocyte adhesion and venular wall shear rate were not affected by clonidine during endotoxemia.

CONCLUSION

Clonidine reduces microvascular permeability in endotoxemic animals in a time-dependent manner. Adrenergic alpha 2 agonists might prove beneficial in stabilizing capillary leakage during inflammation.

Methods for assessing the effects of galectins on leukocyte trafficking

Numerous protocols exist for investigating leukocyte recruitment both in vitro and in vivo. Here we describe three of these methods; an in vitro flow chamber assay, intravital microscopy, and zymosan-induced peritonitis, and give details as to how they can be used to study the actions of galectins on this crucial process.

Emerging understanding of roles for arterioles in inflammation

Arterioles, capillaries, and venules all actively change their cellular functions and phenotypes during inflammation in ways that are essential for maintenance of homeostasis and self-defense, and are also associated with many inflammatory disorders. ECs, together with pericytes and ECM proteins, can regulate blood flow, the coagulation cascade, fluid and solute exchange, and leukocyte trafficking. While capillary and venular functions in inflammation are well characterized, the arteriolar contribution to inflammation has only recently come into focus. Arterioles differ from venules in structure, EC morphology, shear environment, expression, and distribution of surface ligands; hence, regulation and function of arteriolar wall cells during inflammation may also be distinct from venules. Recent work indicates that in response to proinflammatory stimuli, arterioles alter barrier function, and support leukocyte and platelet interactions through upregulation of adhesion molecules. This suggests that in addition to their role in blood flow regulation, arterioles may also participate in inflammatory responses. In this review, we will discuss mechanisms that characterize arteriolar responses to proinflammatory stimuli. We will detail how distinct arteriolar features contribute to regulation of barrier function and leukocyte-EC interactions in inflammation, and further highlight the potential priming effects of arteriolar responses on venular function and progression of inflammatory responses.

Silencing Bruton's tyrosine kinase in alveolar neutrophils protects mice from LPS/immune complex-induced acute lung injury

Previous observations made by our laboratory indicate that Bruton's tyrosine kinase (Btk) may play an important role in the pathophysiology of local inflammation in acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). We have shown that there is cross talk between FcγRIIa and TLR4 in alveolar neutrophils from patients with ALI/ARDS and that Btk mediates the molecular cooperation between these two receptors. To study the function of Btk in vivo we have developed a unique two-hit model of ALI: LPS/immune complex (IC)-induced ALI. Furthermore, we conjugated F(ab)2 fragments of anti-neutrophil antibodies (Ly6G1A8) with specific siRNA for Btk to silence Btk specifically in alveolar neutrophils. It should be stressed that we are the first group to perform noninvasive transfections of neutrophils, both in vitro and in vivo. Importantly, our present findings indicate that silencing Btk in alveolar neutrophils has a dramatic protective effect in mice with LPS/IC-induced ALI, and that Btk regulates neutrophil survival and clearance of apoptotic neutrophils in this model. In conclusion, we put forward a hypothesis that Btk-targeted neutrophil specific therapy is a valid goal of research geared toward restoring homeostasis in lungs of patients with ALI/ARDS.

Platelet dynamics during natural and pharmacologically induced torpor and forced hypothermia

Hibernation is an energy-conserving behavior in winter characterized by two phases: torpor and arousal. During torpor, markedly reduced metabolic activity results in inactivity and decreased body temperature. Arousal periods intersperse the torpor bouts and feature increased metabolism and euthermic body temperature. Alterations in physiological parameters, such as suppression of hemostasis, are thought to allow hibernators to survive periods of torpor and arousal without organ injury. While the state of torpor is potentially procoagulant, due to low blood flow, increased viscosity, immobility, hypoxia, and low body temperature, organ injury due to thromboembolism is absent. To investigate platelet dynamics during hibernation, we measured platelet count and function during and after natural torpor, pharmacologically induced torpor and forced hypothermia. Splenectomies were performed to unravel potential storage sites of platelets during torpor. Here we show that decreasing body temperature drives thrombocytopenia during torpor in hamster with maintained functionality of circulating platelets. Interestingly, hamster platelets during torpor do not express P-selectin, but expression is induced by treatment with ADP. Platelet count rapidly restores during arousal and rewarming. Platelet dynamics in hibernation are not affected by splenectomy before or during torpor. Reversible thrombocytopenia was also induced by forced hypothermia in both hibernating (hamster) and non-hibernating (rat and mouse) species without changing platelet function. Pharmacological torpor induced by injection of 5'-AMP in mice did not induce thrombocytopenia, possibly because 5'-AMP inhibits platelet function. The rapidness of changes in the numbers of circulating platelets, as well as marginal changes in immature platelet fractions upon arousal, strongly suggest that storage-and-release underlies the reversible thrombocytopenia during natural torpor. Possibly, margination of platelets, dependent on intrinsic platelet functionality, governs clearance of circulating platelets during torpor.

Molecular mechanisms underlying synergistic adhesion of sickle red blood cells by hypoxia and low nitric oxide bioavailability

The molecular mechanisms by which nitric oxide (NO) bioavailability modulates the clinical expression of sickle cell disease (SCD) remain elusive. We investigated the effect of hypoxia and NO bioavailability on sickle red blood cell (sRBC) adhesion using mice deficient for endothelial NO synthase (eNOS) because their NO metabolite levels are similar to those of SCD mice but without hypoxemia. Whereas sRBC adhesion to endothelial cells in eNOS-deficient mice was synergistically upregulated at the onset of hypoxia, leukocyte adhesion was unaffected. Restoring NO metabolite levels to physiological levels markedly reduced sRBC adhesion to levels seen under normoxia. These results indicate that sRBC adherence to endothelial cells increases in response to hypoxia prior to leukocyte adherence, and that low NO bioavailability synergistically upregulates sRBC adhesion under hypoxia. Although multiple adhesion molecules mediate sRBC adhesion, we found a central role for P-selectin in sRBC adhesion. Hypoxia and low NO bioavailability upregulated P-selectin expression in endothelial cells in an additive manner through p38 kinase pathways. These results demonstrate novel cellular and signaling mechanisms that regulate sRBC adhesion under hypoxia and low NO bioavailability. Importantly, these findings point us toward new molecular targets to inhibit cell adhesion in SCD.

Characterization of the shear stress regulation of CD18 surface expression by HL60-derived neutrophil-like cells

Shear stress-induced cleavage of cell surface CD18 integrins is reported to be part of an anti-inflammatory control mechanism that minimizes neutrophil activity in the blood under physiologic conditions. The cysteine protease, cathepsin B (catB), has been implicated in this mechanoregulatory mechanism, but its molecular dynamics remain to be elucidated. Moreover, attempts to do so using molecular approaches are hindered by the limited ex vivo life span of primary neutrophils. As an alternative, we explored the potential use of HL60-derived neutrophilic cells as a transfectable culture model that exhibits a shear-induced CD18 cleavage response comparable to primary neutrophils. HL60 cells were differentiated into neutrophil-like cells (dHL60-NCs) and exposed to laminar shear stress ([Formula: see text] for 10 min). Based on cytometric analyses, sheared cells cleaved CD18 and CD11a, but not CD11b, integrins. Treatment of cells with E64 or doxycycline prior to and during shear exposure inhibited CD18, but only attenuated CD11a, cleavage. Neither aprotinin nor pepstatin affected shear-induced CD18 or CD11a cleavage. Notably, dHL60-NCs expressed minimal catB. Thus, multiple cysteine proteases in addition to catB may cleave CD18 on sheared leukocytes. In fact, our findings indicate that multiple non-cysteine proteases also participate in the shear-related cleavage of CD11/CD18 heterodimers. Finally, shear-induced cleavage of CD18 and CD11a by dHL60-NCs was inhibited by fMLP concentrations of at least [Formula: see text]. Collectively, our findings indicate that shear-induced CD11/CD18 cleavage is phenotypic of neutrophilic cells, including those derived from HL60 cells. Moreover, our results verify shear stress as a key anti-inflammatory stimulus for neutrophils under physiologic conditions.

Superimposed traumatic brain injury modulates vasomotor responses in third-order vessels after hemorrhagic shock

BACKGROUND

Traumatic brain injury (TBI) and hemorrhagic shock (HS) are the leading causes of death in trauma. Recent studies suggest that TBI may influence physiological responses to acute blood loss. This study was designed to assess to what extent superimposed TBI may modulate physiologic vasomotor responses in third-order blood vessels in the context of HS.

METHODS

We have combined two established experimental models of pressure-controlled hemorrhagic shock (HS; MAP 50 mmHg/60 min) and TBI (lateral fluid percussion (LFP)) to assess vasomotor responses and microcirculatory changes in third-order vessels by intravital microscopy in a spinotrapezius muscle preparation. 23 male Sprague-Dawley rats (260-320 g) were randomly assigned to experimental groups: i) Sham, ii) HS, iii) TBI + HS, subjected to impact or sham operation, and assessed.

RESULTS

HS led to a significant decrease in arteriolar diameters by 20% to baseline (p < 0.01). In TBI + HS this vasoconstriction was less pronounced (5%, non-significant). At completed and at 60 minutes of resuscitation arteriolar diameters had recovered to pre-injury baseline values. Assessment of venular diameters revealed similar results. Arteriolar and venular RBC velocity and blood flow decreased sharply to < 20% of baseline in HS and TBI + HS (p < 0.01). Immediately after and at 60 minutes of resuscitation, an overshoot in arterial RBC velocity (140% of baseline) and blood flow (134.2%) was observed in TBI + HS.

CONCLUSION

Superimposed TBI modulated arteriolar and venular responses to HS in third-order vessels in a spinotrapezius muscle preparation. Further research is necessary to precisely define the role of TBI on the microcirculation in tissues vulnerable to HS.

Mild hypercholesterolemia blunts the proinflammatory and prothrombotic effects of hypertension on the cerebral microcirculation

Although an increased leukocyte and platelet adhesion is observed in cerebral venules of mice with either hypertension (HTN) or hypercholesterolemia (HCh), it remains unclear whether the combination of HTN and HCh exerts a comparable effect on leukocyte and platelet recruitment in the cerebral microvasculature. Thus, we examined whether HCh alters platelet and leukocyte adhesion, and blood-brain barrier (BBB) permeability, in cerebral venules in two models of murine HTN: DOCA salt-induced and angiotensin II (Ang II) induced. In both models, the mice were placed on either a normal or cholesterol-enriched diet. An enhanced recruitment of adherent leukocytes and platelets in cerebral venules was noted in both HTN models in the absence of HCh, but not in its presence. The Ang II-induced increase in BBB permeability was attenuated by HCh as well. Both total and high-density lipoprotein (HDL) cholesterol levels were elevated in the HCh mice. The HTN-induced increase in leukocyte and platelet adhesion was attenuated in apolipoprotein A-I transgenic mice (ApoA1-Tg) and blunted in wild-type mice treated with the ApoA1 mimetic peptide, 4F. Our findings indicate that mild HCh significantly blunts the cerebral microvascular responses to HTN and that HDL may have a role in mediating this beneficial effect of HCh.

Adiponectin-deficiency exaggerates sepsis-induced microvascular dysfunction in the mouse brain

Obesity increases circulating cell-endothelial cell interactions; an early marker of inflammation in laboratory model of sepsis, but little is known about the effect of different adipokines. Adiponectin is an anti-inflammatory adipokine secreted by adipocytes. Adiponectin deficiency is implicated in exaggerated proinflammatory phenotype in both obesity and sepsis via increased proinflammatory cytokine expression. However the effect of adiponectin deficiency on circulating cell-endothelial cell interactions in polymicrobial sepsis is unknown. Furthermore although brain dysfunction in septic patients is a known predictor of death, the pathophysiology involved is unknown. In the current study, we examined the effects of adiponectin deficiency on leukocyte (LA) and platelet adhesion (PA) in cerebral microcirculation of septic mice. Adiponectin deficient (Adipoq(-/-): Adko) and background strain C57Bl/6 (wild type (WT)) mice were used. Sepsis was induced using cecal ligation and puncture (CLP). We studied LA and PA in the cerebral microcirculation using intravital fluorescent video microscopy (IVM), blood brain barrier (BBB) dysfunction using Evans Blue (EB) leakage method and E-selectin expression using dual radiolabeling technique in different WT and Adko mice with CLP. Adiponectin deficiency significantly exaggerated LA (WT-CLP:201 ± 17; Adko-CLP: ± 53 cells/mm(2); P < 0.05) and PA (WT-CLP:125 ± 17; Adko-CLP:188 ± 20 cells/mm(2); P < 0.05) in cerebral microcirculation, EB leakage (WT-CLP:10 ± 3.7; Adko-CLP:24 ± 4.3 ng/g × µl plasma; P < 0.05) and E-selectin expression (WT-CLP:0.06 ± 0.11; Adko-CLP:0.44 ± 0.053 ng/g; P < 0.05) in the brain tissue of the mice with CLP. Furthermore, E-selectin monoclonal antibody (mAb) treatment attenuated cell adhesion and BBB dysfunction of Adko-CLP mice. Adiponectin deficiency is associated with exaggerated leukocyte and PA in cerebral microcirculation of mice with CLP via modulation of E-selectin expression.

Experimental Endotoxemia Induces Leukocyte Adherence and Plasma Extravasation Within the Rat Pial Microcirculation

Disturbance of capillary perfusions due to leukocyte adhesion, disseminated intravascular coagulation, tissue edema is critical components in the pathophysiology of sepsis. Alterations in brain microcirculation during sepsis are not clearly understood. The aim of this study is to gain an improved understanding of alterations through direct visualization of brain microcirculations in an experimental endotoxemia using intravital microscopy (IVM). Endotoxemia was induced in Lewis rats with Lipopolysaccharide (LPS, 15 mg/kg i.v.). The dura mater was removed via a cranial window to expose the pial vessels on the brain surface. Using fluorescence dyes, plasma extravasation of pial venous vessels and leukocyte-endothelial interaction were visualized by intravital microscopy 4 h after LPS administration. Plasma cytokine levels of IL1-β, IL-6, IFN-γ, TNF-α and KC/GRO were evaluated after IVM. A significant plasma extravasation of the pial venous vessels was found in endotoxemia rats compared to control animals. In addition, a significantly increased number of leukocytes adherent to the pial venous endothelium was observed in septic animals. Endotoxemia also induced a significant elevation of plasma cytokine levels of IL1-β, IL-6, IFN-γ, TNF-α and KC/GRO. Endotoxemia increased permeability in the brain pial vessels accompanied by an increase of leukocyte-endothelium interactions and an increase of inflammatory cytokines in the plasma.

Pathophysiology, treatment, and animal and cellular models of human ischemic stroke

Stroke is the world's second leading cause of mortality, with a high incidence of severe morbidity in surviving victims. There are currently relatively few treatment options available to minimize tissue death following a stroke. As such, there is a pressing need to explore, at a molecular, cellular, tissue, and whole body level, the mechanisms leading to damage and death of CNS tissue following an ischemic brain event. This review explores the etiology and pathogenesis of ischemic stroke, and provides a general model of such. The pathophysiology of cerebral ischemic injury is explained, and experimental animal models of global and focal ischemic stroke, and in vitro cellular stroke models, are described in detail along with experimental strategies to analyze the injuries. In particular, the technical aspects of these stroke models are assessed and critically evaluated, along with detailed descriptions of the current best-practice murine models of ischemic stroke. Finally, we review preclinical studies using different strategies in experimental models, followed by an evaluation of results of recent, and failed attempts of neuroprotection in human clinical trials. We also explore new and emerging approaches for the prevention and treatment of stroke. In this regard, we note that single-target drug therapies for stroke therapy, have thus far universally failed in clinical trials. The need to investigate new targets for stroke treatments, which have pleiotropic therapeutic effects in the brain, is explored as an alternate strategy, and some such possible targets are elaborated. Developing therapeutic treatments for ischemic stroke is an intrinsically difficult endeavour. The heterogeneity of the causes, the anatomical complexity of the brain, and the practicalities of the victim receiving both timely and effective treatment, conspire against developing effective drug therapies. This should in no way be a disincentive to research, but instead, a clarion call to intensify efforts to ameliorate suffering and death from this common health catastrophe. This review aims to summarize both the present experimental and clinical state-of-the art, and to guide future research directions.

Inhibition of cell adhesion by anti-P-selectin aptamer: a new potential therapeutic agent for sickle cell disease

Adhesive interactions between circulating sickle red blood cells (RBCs), leukocytes, and endothelial cells are major pathophysiologic events in sickle cell disease (SCD). To develop new therapeutics that efficiently inhibit adhesive interactions, we generated an anti-P-selectin aptamer and examined its effects on cell adhesion using knockout-transgenic SCD model mice. Aptamers, single-stranded oligonucleotides that bind molecular targets with high affinity and specificity, are emerging as new therapeutics for cardiovascular and hematologic disorders. In vitro studies found that the anti-P-selectin aptamer exhibits high specificity to mouse P-selectin but not other selectins. SCD mice were injected with the anti-P-selectin aptamer, and cell adhesion was observed under hypoxia. The anti-P-selectin aptamer inhibited the adhesion of sickle RBCs and leukocytes to endothelial cells by 90% and 80%, respectively. The anti-P-selectin aptamer also increased microvascular flow velocities and reduced the leukocyte rolling flux. SCD mice treated with the anti-P-selectin aptamer demonstrated a reduced mortality rate associated with the experimental procedures compared with control mice. These results demonstrate that anti-P-selectin aptamer efficiently inhibits the adhesion of both sickle RBCs and leukocytes to endothelial cells in SCD model mice, suggesting a critical role for P-selectin in cell adhesion. Anti-P-selectin aptamer may be useful as a novel therapeutic agent for SCD.

Cytomegalovirus infection leads to microvascular dysfunction and exacerbates hypercholesterolemia-induced responses

Cytomegalovirus (CMV) persistently infects more than 60% of the worldwide population. In immunocompetent hosts, it has been implicated in several diseases, including cardiovascular disease, possibly through the induction of inflammatory pathways. Cardiovascular risk factors promote an inflammatory phenotype in the microvasculature long before clinical disease is evident. This study determined whether CMV also impairs microvascular homeostasis and synergizes with hypercholesterolemia to exaggerate these responses. Intravital microscopy was used to assess endothelium-dependent and -independent arteriolar vasodilation and venular leukocyte and platelet adhesion in mice after injection with either mock inoculum or murine CMV (mCMV). Mice were fed a normal (ND) or high-cholesterol (HC) diet beginning at 5 weeks postinfection (p.i.), or a HC diet for the final 4 weeks of infection. mCMV-ND mice exhibited impaired endothelium-dependent vasodilation versus mock-ND at 9 and 12 weeks and endothelium-independent arteriolar dysfunction by 24 weeks. Transient mild leukocyte adhesion occurred in mCMV-ND venules at 7 and 21 weeks p.i. HC alone caused temporary arteriolar dysfunction and venular leukocyte and platelet recruitment, which were exaggerated and prolonged by mCMV infection. The time of introduction of HC after mCMV infection determined whether mCMV+HC led to worse venular inflammation than either factor alone. These findings reveal a proinflammatory influence of persistent mCMV on the microvasculature, and suggest that mCMV infection enhances microvasculature susceptibility to both inflammatory and thrombogenic responses caused by hypercholesterolemia.

Leucocyte/endothelium interactions and microvessel permeability: coupled or uncoupled?

In response to infections or tissue injury, circulating leucocytes adhere to and migrate from the vessel lumen to interstitial inflammatory sites to combat invading pathogens. However, these defensive actions may also cause host tissue injury and microvascular dysfunction through oxidative bursts or enzyme release. For decades, the interaction between leucocytes and microvessel walls has been considered as a critical event leading to organ dysfunction. Extensive investigations have therefore focused on blocking specific adhesive ligands to prevent tissue injury. However, anti-adhesion therapies have shown limited success in preventing vascular dysfunction in clinical trials. Numerous studies have demonstrated temporal and spatial dissociations of leucocyte adhesion and/or emigration from permeability increases. The mechanisms that initiate the adhesion cascade have been found to be distinct from those that trigger the leucocyte oxidative burst responsible for increasing microvessel permeability. Recent studies demonstrated that endothelial activation by inflammatory mediators is critical for initiating platelet adhesion and platelet-dependent leucocyte recruitment resulting in augmented increases in microvessel permeability. These new developments suggest that targeting endothelial activation via directly enhancing endothelial barrier function might be a more efficient strategy than focusing on anti-adhesion or platelet/leucocyte depletion to prevent vascular damage during inflammation. Owing to space limitations and the wide range of studies in the field, this article will not serve as a comprehensive review. Instead, it will highlight the emerging evidence of adhesion-uncoupled permeability changes and establish a basis for re-evaluating the coupled relationship between leucocyte/platelet activation and microvessel permeability to achieve a better understanding of permeability regulation during inflammation.

Obesity Exacerbates Sepsis-Induced Inflammation and Microvascular Dysfunction in Mouse Brain

OBJECTIVE

Obese patients with sepsis have higher morbidity and mortality than lean counterparts, but the mechanisms involved are unknown. The authors examined the inflammatory and thrombogenic responses of the cerebral microvasculature to sepsis induced by cecal ligation and perforation in obese and lean wild-type mice.

METHODS

Leukocyte and platelet adhesion in cerebral microvasculature and behavioral responses were measured in wild-type and obese mice 4 h postperforation. P-selectin expression in different vascular beds was assessed 6 h postperforation. The effects of immunoblockade of P-selectin, ICAM-1, and CD18 on leukocyte and platelet recruitment were evaluated in obese septic animals.

RESULTS

Cerebral venules of obese and wild-type mice assumed a proinflammatory and prothrombogenic phenotype 4 h post-perforation, with greatly exaggerated responses in obese mice compared to the lean counterparts. These enhanced responses were attenuated by blocking P-selectin, CD18, or ICAM-1. Obese mice also exhibited a more profound behavioral deficit after sepsis, which appears to be unrelated to the recruitment of leukocytes and platelets. Cecal ligation and perforation-induced P-selectin expression was greater in obese mice compared with lean counterparts.

CONCLUSIONS

These findings suggest that the increased morbidity to sepsis in obesity may result from exaggerated microvascular inflammatory and thrombogenic responses that include the activation of endothelial cells with subsequent expression of adhesion molecules, such as P-selectin.

A mouse model of yellow fluorescent protein (YFP) expression in hematopoietic cells to assess leukocyte-endothelial interactions in the microcirculation

In this study, we describe the use of intravital microscopy in a transgenic mouse model expressing yellow fluorescent protein (YFP) under the control of a monocyte specific promoter c-fms (CD115) to track and quantify specific leukocyte subsets. Flow cytometry on peripheral and bone marrow leukocytes revealed that YFP was predominantly expressed by CD11a(+), CD11b(+), and CD14(+) monocytes. In the bone marrow, 67+/-4% of Ly6C(high) F4/80(+) cells were YFP(high) while 55+/-1% of Ly6C(low) F4/80(+) cells were YFP(low) supporting the use of c-fms(YFP) expression as a marker of monocyte lineage. 70+/-7% of CD11b(+) F4/80(+) Ly6C(+) ("triple positive") cells expressed YFP. To assess leukocyte-endothelial interactions in YFP(+) cells in c-fms(YFP+) mice, we evaluated leukocyte adhesion, rolling and local shear stress responses in the cremasteric endothelium 4 h following administration of TNFalpha. TNFalpha resulted in a five-fold increase in adhesion of YFP(+) cells to the endothelium and provided superior discriminative ability in assessing rolling and adhesion events when compared with bright field microscopy. Additionally, when compared with Rhodamine-6G labeled leukocytes or GFP(+) cells in mice transplanted with green fluorescent protein (GFP) positive bone marrow, the level of detail observed in the c-fms(YFP+) was greater, with both GFP(+) and YFP(+) cells demonstrating superior signal to noise compared to bright field microscopy. A weak positive linear correlation between wall shear stress and YFP(+) cell adhesion (r(2)=0.20, p<0.05) was seen in the cremasteric microcirculation. Taken together, these data demonstrate the use of c-fms(YFP+) mice in identifying distinct monocyte subsets and highlight the potential of this model for real-time monocyte-endothelial interactions using intravital microscopy.

Nonimmune cells in inflammatory bowel disease: from victim to villain

Nonimmune cells have traditionally been viewed as target cells of the aberrant inflammatory process present in chronic immune-mediated conditions such as inflammatory bowel disease (IBD). However, the discovery that many of the functions traditionally attributed to immune cells are also performed by nonimmune cells has caused a shift to a multidirectional hypothesis in which nonimmune cells and acellular elements play active roles. Many types of interactions occur within this multidirectional system, and the difficulties associated with modeling these complex interactions currently limit our understanding of the cellular network that occurs in IBD. I describe the current knowledge of the roles played by nonimmune cells in the pathogenesis of IBD, as they emerge as crucial alternative targets for therapeutic intervention.

Dietary nitrite prevents hypercholesterolemic microvascular inflammation and reverses endothelial dysfunction

The nitrite anion is an endogenous product of mammalian nitric oxide (NO) metabolism, a key intermediate in the nitrogen cycle in plants, and a constituent of many foods. Research over the past 6 years has revealed surprising biological and cytoprotective activity of this anion. Hypercholesterolemia causes a proinflammatory phenotype in the microcirculation. This phenotype appears to result from a decline in NO bioavailability that results from a reduction in NO biosynthesis, inactivation of NO by superoxide, or both. Since nitrite has been shown to be potently cytoprotective and restore NO biochemical homeostasis, we investigated if supplemental nitrite could attenuate microvascular inflammation caused by a high cholesterol diet. C57Bl/6J mice were fed either a normal diet or a high cholesterol diet for 3 wk to induce microvascular inflammation. Mice on the high cholesterol diet received either nitrite-free drinking water or supplemental nitrite at 33 or 99 mg/l ad libitum in their drinking water. The results from this investigation reveal that mice fed a cholesterol-enriched diet exhibited significantly elevated leukocyte adhesion to and emigration through the venular endothelium as well as impaired endothelium-dependent relaxation in arterioles. Administration of nitrite in the drinking water inhibited the leukocyte adhesion and emigration and prevented the arteriolar dysfunction. This was associated with sparing of reduced tetrahydrobiopterin and decreased levels of C-reactive protein. These data reveal novel anti-inflammatory properties of nitrite and implicate the use of nitrite as a new natural therapy for microvascular inflammation and endothelial dysfunction associated with hypercholesterolemia.

Lactobacillus reuteri prevents colitis by reducing P-selectin-associated leukocyte- and platelet-endothelial cell interactions

Recent findings indicate that dextran sodium sulfate (DSS)-induced colitis is associated with a prothrombogenic phenotype, with P-selectin playing a major role in platelet recruitment. It has been suggested that probiotics may ameliorate colonic inflammation. We therefore investigated how treatment with Lactobacillus reuteri influenced P-selectin expression, leukocyte and platelet endothelial cell interactions, and colitis severity in DSS-treated rats. Rats were divided into the following four groups: nontreated, DSS treated (5% in drinking water for 9 days), L. reuteri, and L. reuteri and DSS treated. The rats were anesthetized with Inactin (120 mg/kg ip), and the dual radiolabeled monoclonal antibody technique was used to quantify P-selectin expression. Leukocyte-endothelial and platelet-endothelial cell interactions were studied in colonic venules with intravital microscopy. Colitis severity was assessed using a disease activity index. Disease activity index increased, as did the expression of P-selectin in the entire colon after DSS treatment, but both were reduced to control levels with L. reuteri pretreatment. The increased platelet- and leukocyte-endothelial cell interactions after DSS treatment were abolished by pretreatment with L. reuteri. L. reuteri protects against DSS-induced colitis in rats. The protection is associated with reduced P-selectin expression and a decrease in leukocyte- and platelet-endothelial cell interactions.

CD40/CD40L contributes to hypercholesterolemia-induced microvascular inflammation

Hypercholesterolemia is associated with phenotypic changes in endothelial cell function that lead to a proinflammatory and prothrombogenic state in different segments of the microvasculature. CD40 ligand (CD40L) and its receptor CD40 are ubiquitously expressed and mediate inflammatory responses and platelet activation. The objective of this study was to determine whether CD40/CD40L, in particular T-cell CD40L, contributes to microvascular dysfunction induced by hypercholesterolemia. Intravital microscopy was used to quantify blood cell adhesion in cremasteric postcapillary venules, endothelium-dependent vasodilation responses in arterioles, and microvascular oxidative stress in wild-type (WT) C57BL/6, CD40-deficient ((-/-)), CD40L(-/-), or severe combined immune deficient (SCID) mice placed on a normal (ND) or high-cholesterol (HC) diet for 2 wk. WT-HC mice exhibited an exaggerated leukocyte and platelet recruitment in venules and impaired vasodilation responses in arterioles compared with ND counterparts. A deficiency of CD40, CD40L, or lymphocytes attenuated these responses to HC. The HC phenotype was rescued in CD40L(-/-) and SCID mice by a transfer of WT T cells. Bone marrow chimeras revealed roles for both vascular- and blood cell-derived CD40 and CD40L in the HC-induced vascular responses. Hypercholesterolemia induced an oxidative stress in both arterioles and venules of WT mice, which was abrogated by either CD40 or CD40L deficiency. The transfer of WT T cells into CD40L(-/-) mice restored the oxidative stress. These results implicate CD40/CD40L interactions between circulating cells and the vascular wall in both the arteriolar and venular dysfunction elicited by hypercholesterolemia and identify T-cell-associated CD40L as a key mediator of these responses.

Cell adhesion molecules and ischemic stroke

OBJECTIVE

To describe the role of adhesion molecules in ischemic stroke.

METHODS

A PubMed search of literature pertaining to this study was conducted in April 2008 using specific keyword search terms pertaining to stroke and various listed subtopics related to adhesion molecules.

RESULTS

An important contribution of beta2-integrins (CD11/CD18), intercellular adhesion molecule and P-selectin in the recruitment of leukocytes as well as platelets in the post-ischemic cerebral microvasculature has been defined in related studies. Immunoblockade or genetic deletion of these adhesion molecules has been shown to reduce infarct volume, edema, behavioral deficits and/or mortality in different animal models of ischemic stroke. Anti-adhesion agents also appear to widen the therapeutic window for thrombolytic therapy in these experimental models. An emerging role of inflammatory signaling pathways has also been addressed in modulating adhesion properties of post-ischemic cerebral microvasculature. Despite the promising data obtained from animal studies, few clinical trials assessing anti-adhesion therapy in ischemic stroke have failed to show efficacy.

DISCUSSION

Several experiments using cell surface adhesion molecules as targets of stroke therapy are promising yet inadequate. Clinical trials using immune blockade of adhesion molecules by antibodies have failed due to immune reactions of the host. Further clinical trials are needed to test the efficacy of humanized antibodies or non-immunogenic agents that interfere with cell adhesion mechanisms. Adhesion blocking strategies seem to be effective particularly at reperfusion and use of these strategies with thrombolytic therapies justifies a continued effort to define the role of adhesion molecules in the pathophysiology of cerebral ischemia-reperfusion.

Thrombin mediates the extraintestinal thrombosis associated with experimental colitis

Recent evidence implicating tissue factor and the protein C pathway in the hypercoagulable state associated with intestinal inflammation suggests that thrombin is likely to contribute to this response. The objective of this study was to assess the role of thrombin in the extraintestinal thrombosis associated with experimental colitis. Thrombus formation was quantified in microvessels of the cremaster muscle in mice with dextran sodium sulfate (DSS)-induced colonic inflammation. The light/dye endothelial injury model was used to elicit thrombus formation in DSS colitic mice treated with either hirudin, heparin, or antithrombin III. The initiation and propagation/stabilization phases of thrombus formation were quantified using the time of onset of the thrombus and time to blood flow cessation, respectively. Thrombus formation was accelerated in arterioles of DSS colitic mice, as exhibited by significant reductions in the time of thrombus initiation and propagation/stabilization. Colitic mice treated with hirudin, heparin, or antithrombin III did not exhibit a significant change in the time of onset of the thrombus compared with untreated colitic mice. However, all three antithrombin agents largely prevented the DSS-induced reduction in the time to flow cessation following light/dye injury, with hirudin offering complete protection. These findings indicate that thrombin plays a major role in the extraintestinal thrombus formation associated with experimental colitis. Thrombin appears to contribute to the propagation/stabilization, rather than initiation, phase of the colitis-associated thrombogenesis at the distant vascular site. The results support the therapeutic use of antithrombin agents for reducing the risk of thromboembolism in patients with inflammatory bowel disease.

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.

Role of the protein C pathway in the extraintestinal thrombosis associated with murine colitis

BACKGROUND & AIMS

Chronic inflammatory bowel diseases (IBD) are associated with an increased risk for thromboembolism. Although thrombosis is known to contribute to the morbidity and mortality of patients with IBD, the underlying mechanisms that contribute to the genesis of a hypercoagulable state during intestinal inflammation remain poorly defined. The objective of this study was to determine whether the protein C pathway contributes to the enhanced extraintestinal thrombosis that is associated with dextran sodium sulfate (DSS)-induced colitis in mice.

METHODS

Microvascular thrombosis was induced in cremaster muscle microvessels of normal and colitic mice using a light/dye injury model. DSS colitis enhanced thrombus formation in cremaster arterioles of wild-type mice.

RESULTS

The DSS-induced thrombosis response was greatly attenuated in transgenic mice over expressing the endothelial protein C receptor. Activated protein C (APC), administered to colitic WT mice immediately prior to photoactivation, also afforded protection against thrombosis, and an anti-APC antibody enhanced thrombus formation.

CONCLUSIONS

These findings indicate that elevated APC levels, derived from either endogenous or exogenous sources, confer protection against the extraintestinal thrombosis that accompanies colonic inflammation.

Pathophysiological role of platelets and platelet system in acute pancreatitis

The most successful approach for restoring normal long-term glucose homeostasis in type I diabetes mellitus is whole-organ pancreas transplantation. Graft pancreatitis is observed in up to 20% of patients and may lead to loss of the transplanted organ. Several pathophysiological events have been implicated in this form of pancreatitis. The most important cause of early graft pancreatitis is ischemia/reperfusion (I/R)-related disturbance of microvascular perfusion with subsequent hypoxic tissue damage. Recently, considerable evidence accumulated that, among a variety of other pathophysiological events, the activation of platelets can contribute to I/R injury in the course of acute pancreatitis experimentally and clinically. This review summarizes the events affecting platelet function and, therefore, pancreatic microcirculation leading to acute pancreatitis. Therapeutic approaches and own results are presented.

Multiple pathogenic roles of microvasculature in inflammatory bowel disease: a Jack of all trades

The etiology of Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD), is still largely unknown. However, it is now clear that the abnormalities underlying pathogenesis of intestinal inflammation are not restricted to those mediated by classic immune cells but also involve nonimmune cells. In particular, advances in vascular biology have outlined a central and multifaceted pathogenic role for the microcirculation in the initiation and perpetuation of IBD. The microcirculation and its endothelial lining play a crucial role in mucosal immune homeostasis through tight regulation of the nature and magnitude of leukocyte migration from the intravascular to the interstitial space. Chronically inflamed IBD microvessels display significant alterations in microvascular physiology and function compared with vessels from healthy and uninvolved IBD intestine. The investigation into human IBD has demonstrated how endothelial activation present in chronically inflamed IBD microvessels results in a functional phenotype that also includes leakiness, chemokine and cytokine expression, procoagulant activity, and angiogenesis. This review contemplates the newly uncovered contribution of intestinal microcirculation to pathogenesis and maintenance of chronic intestinal inflammation. In particular, we assess the multiple roles of the microvascular endothelium in innate immunity, leukocyte recruitment, coagulation and perfusion, and immune-driven angiogenesis in IBD.

Multiple pathogenic roles of microvasculature in inflammatory bowel disease: a Jack of all trades

The etiology of Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD), is still largely unknown. However, it is now clear that the abnormalities underlying pathogenesis of intestinal inflammation are not restricted to those mediated by classic immune cells but also involve nonimmune cells. In particular, advances in vascular biology have outlined a central and multifaceted pathogenic role for the microcirculation in the initiation and perpetuation of IBD. The microcirculation and its endothelial lining play a crucial role in mucosal immune homeostasis through tight regulation of the nature and magnitude of leukocyte migration from the intravascular to the interstitial space. Chronically inflamed IBD microvessels display significant alterations in microvascular physiology and function compared with vessels from healthy and uninvolved IBD intestine. The investigation into human IBD has demonstrated how endothelial activation present in chronically inflamed IBD microvessels results in a functional phenotype that also includes leakiness, chemokine and cytokine expression, procoagulant activity, and angiogenesis. This review contemplates the newly uncovered contribution of intestinal microcirculation to pathogenesis and maintenance of chronic intestinal inflammation. In particular, we assess the multiple roles of the microvascular endothelium in innate immunity, leukocyte recruitment, coagulation and perfusion, and immune-driven angiogenesis in IBD.

In vivo imaging in mice reveals local cell dynamics and inflammation in obese adipose tissue

To assess physiological and pathophysiological events that involve dynamic interplay between multiple cell types, real-time, in vivo analysis is necessary. We developed a technique based on confocal laser microscopy that enabled us to analyze and compare the 3-dimensional structures, cellular dynamics, and vascular function within mouse lean and obese adipose tissue in vivo with high spatiotemporal resolution. We found increased leukocyte-EC-platelet interaction in the microcirculation of obese visceral adipose tissue in ob/ob and high-fat diet-induced obese mice. These changes were indicative of activation of the leukocyte adhesion cascade, a hallmark of inflammation. Local platelet activation in obese adipose tissue was indicated by increased P-selectin expression and formation of monocyte-platelet conjugates. We observed upregulated expression of adhesion molecules on macrophages and ECs in obese visceral adipose tissue, suggesting that interactions between these cells contribute to local activation of inflammatory processes. Furthermore, administration of anti-ICAM-1 antibody normalized the cell dynamics seen in obese visceral fat. This imaging technique to analyze the complex cellular interplay within obese adipose tissue allowed us to show that visceral adipose tissue obesity is an inflammatory disease. In addition, this technique may prove to be a valuable tool to evaluate potential therapeutic interventions.

Roles of platelet and endothelial cell COX-1 in hypercholesterolemia-induced microvascular dysfunction

Aspirin is a common preventative therapy in patients at risk for cardiovascular diseases, yet little is known about how aspirin protects the vasculature in hypercholesterolemia. The present study determines whether aspirin, nitric oxide-releasing aspirin (NCX-4016), a selective cyclooxygenase (COX)-1 inhibitor (SC560), or genetic deficiency of COX-1 prevents the inflammatory and prothrombogenic phenotype assumed by hypercholesterolemic (HC) venules. Aspirin or NCX-4016 (60 mg/kg) was administered orally for the last week of a 2-wk HC diet. COX-1-deficient (COX-1(-/-)) and wild-type (WT) mice were transplanted with WT (WT/COX-1(-/-)) or COX-1(-/-) (COX-1(-/-)/WT) bone marrow, respectively. HC-induced adhesion of platelets and leukocytes in murine intestinal venules, observed with intravital fluorescence microscopy, was greatly attenuated in aspirin-treated mice. Adhesion of aspirin-treated platelets in HC venules was comparable to untreated platelets, whereas adhesion of SC560-treated platelets was significantly attenuated. HC-induced leukocyte and platelet adhesion in COX-1(-/-)/WT chimeras was comparable to that in SC560-treated mice, whereas the largest reductions in blood cell adhesion were in WT/COX-1(-/-) chimeras. NCX-4016 treatment of platelet recipients or donors attenuated leukocyte and platelet adhesion independent of platelet COX-1 inhibition. Platelet- and endothelial cell-associated COX-1 promote microvascular inflammation and thrombogenesis during hypercholesterolemia, yet nitric oxide-releasing aspirin directly inhibits platelets independent of COX-1.