Soluble L-selectin attenuates tumor necrosis factor-alpha-mediated leukocyte adherence and vascular permeability: a protective role for elevated soluble L-selectin in sepsis

Plasma soluble L-selectin in medicated patients with schizophrenia and healthy controls

Immune dysfunction has been implicated in the pathophysiology of schizophrenia. Leukocyte migration to the site of inflammation is a fundamental step of immune response which involves P-, E-, and L-selectins. Elevated selectin levels have been reported in un-medicated first-episode patients with schizophrenia but not in medicated patients with multi-episode schizophrenia. We measured fasting plasma soluble P-, E-, and L-selectin in 39 medicated patients with multi-episode schizophrenia and 19 healthy controls. In patients, psychotic symptom severity and cognitive function were assessed with the Positive and Negative Syndrome Scale (PANSS) and the NIH Toolbox Cognitive Test Battery respectively. C-reactive protein (CRP) and Body Mass Index (BMI) were measured in patients and controls. Comparison of selectin levels between patients and controls was done with t-tests and linear regression. Pearson correlation coefficients between plasma selectins and PANSS and cognitive measures were calculated. Geometric mean plasma soluble L-selectin level was lower in patients compared to controls from unadjusted (606.7 ± 1.2 ng/ml vs. 937.7 ± 1.15 ng/ml, p < 0.001) and adjusted analyses (β = 0.59; CI 0.41 to 0.88, p = 0.011). There was a trend towards higher plasma soluble P-selectin in patients compared to controls (90.4 ± 1.2ng/ml vs. 71.8 ± 1.2ng/ml, p = 0.059) in the unadjusted analysis. There was no association between the selectins and psychotic symptoms or cognitive function in the patients. In addition, the selectins were not significantly associated with CRP or BMI. The limitations of this study include small sample size and unavailability of information on medications and blood cell counts. The potential utility of soluble L-selectin as a biomarker of antipsychotic exposure in patients with schizophrenia and the concomitant change in immune response with the use of antipsychotics should be further evaluated.

NSAIDs: learning new tricks from old drugs

Nonsteroidal anti-inflammatory drugs (NSAIDs) comprise a heterogeneous group of pharmacological agents used for the symptomatic treatment of fever, pain, and inflammation. Although the main mechanism of action of NSAIDs consists of inhibiting prostaglandin synthesis by blocking the enzyme cyclooxygenase (COX), clinical, and experimental data strongly indicate the existence of additional mechanisms. Some of the COX-independent effects are related to the ability of NSAIDs to penetrate biological membranes and disrupt important molecular interactions necessary for a wide array of cellular functions, including cell adhesion. These effects, in particular those that interfere with L-selectin function in neutrophils during the inflammatory response, may contribute to the anti-inflammatory properties that NSAIDs exert in vivo. Recent contributions in this field have shown that the anti-L-selectin effect of NSAIDs is related to the NADPH-oxidase-dependent generation of superoxide anion at the plasma membrane. These findings might represent a novel approach for developing new and effective anti-inflammatory compounds with a better safety profile than the currently available NSAIDs.

Soluble L-Selectin as an Independent Biomarker of Bronchial Asthma

BACKGROUND

We sought to determine the association of plasma level of soluble L-selectin (sL-selectin) and F206L polymorphism of L-selectin with asthma.

METHODS

A total of 90 asthmatic patients and 90 sex- and age-matched healthy controls were enrolled. The plasma level of sL-selectin was measured by enzyme-linked immunosorbent assay (ELISA) method. An amplification refractory mutation system polymerase chain reaction was performed to detect F206L polymorphism of L-selectin.

RESULTS

The mean plasma levels of sL-selectin was significantly higher in the patients with asthma than the controls (2113 ± 466 vs. 1664 ± 322 ng/ml, P = 0.001). Logistic regression analysis after adjustment for age, sex, and body mass index demonstrated that plasma levels of sL-selectin are an independent biomarkers for asthma (odds ratio [OR], 1.86; 95% confidence interval [95% CI], 1.42-2.24). The area under the receiver operating characteristic (ROC) curve for sL-selectin was 0.792, 95% CI (0.732-0.862), P = 0.0001. Individuals with the minor homozygote of F206L polymorphism of L-selectin demonstrated a higher level of sL-selectin than the major homozygous (2319 ± 732 vs. 1917 ± 453 ng/ml, P = 0.02). No association was found between F206L polymorphism of L-selectin with asthma.

CONCLUSION

Our study suggests that plasma level of sL-selectin is an independent biomarker for asthma.

Soluble adhesion molecules as markers for sepsis and the potential pathophysiological discrepancy in neonates, children and adults

Sepsis is a severe and life-threatening systemic inflammatory response to infection that affects all populations and age groups. The pathophysiology of sepsis is associated with aberrant interaction between leukocytes and the vascular endothelium. As inflammation progresses, the adhesion molecules that mediate these interactions become shed from cell surfaces and accumulate in the blood as soluble isoforms that are being explored as potential prognostic disease biomarkers. We critically review the studies that have tested the predictive value of soluble adhesion molecules in sepsis pathophysiology with emphasis on age, as well as the underlying mechanisms and potential roles for inflammatory shedding. Five soluble adhesion molecules are associated with sepsis, specifically, E-selectin, L-selectin and P-selectin, intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. While increased levels of these soluble adhesion molecules generally correlate well with the presence of sepsis, their degree of elevation is still poorly predictive of sepsis severity scores, outcome and mortality. Separate analyses of neonates, children and adults demonstrate significant age-dependent discrepancies in both basal and septic levels of circulating soluble adhesion molecules. Additionally, a range of both clinical and experimental studies suggests protective roles for adhesion molecule shedding that raise important questions about whether these should positively or negatively correlate with mortality. In conclusion, while predictive properties of soluble adhesion molecules have been researched intensively, their levels are still poorly predictive of sepsis outcome and mortality. We propose two novel directions for improving clinical utility of soluble adhesion molecules: the combined simultaneous analysis of levels of adhesion molecules and their sheddases; and taking age-related discrepancies into account. Further attention to these issues may provide better understanding of sepsis pathophysiology and increase the usefulness of soluble adhesion molecules as diagnostic and predictive biomarkers.

Bench-to-bedside review: Immunoglobulin therapy for sepsis - biological plausibility from a critical care perspective

Sepsis represents a dysregulated host response to infection, the extent of which determines the severity of organ dysfunction and subsequent outcome. All trialled immunomodulatory strategies to date have resulted in either outright failure or inconsistent degrees of success. Intravenous immunoglobulin (IVIg) therapy falls into the latter category with opinion still divided as to its utility. This article provides a narrative review of the biological rationale for using IVIg in sepsis. A literature search was conducted using the PubMed database (1966 to February 2011). The strategy included the following text terms and combinations of these: IVIg, intravenous immune globulin, intravenous immunoglobulin, immunoglobulin, immunoglobulin therapy, pentaglobin, sepsis, inflammation, immune modulation, apoptosis. Preclinical and extrapolated clinical data of IVIg therapy in sepsis suggests improved bacterial clearance, inhibitory effects upon upstream mediators of the host response (for example, the nuclear factor kappa B (NF-κB) transcription factor), scavenging of downstream inflammatory mediators (for example, cytokines), direct anti-inflammatory effects mediated via Fcγ receptors, and a potential ability to attenuate lymphocyte apoptosis and thus sepsis-related immunosuppression. Characterizing the trajectory of change in immunoglobulin levels during sepsis, understanding mechanisms contributing to these changes, and undertaking IVIg dose-finding studies should be performed prior to further large-scale interventional trials to enhance the likelihood of a successful outcome.

Regulation of L-selectin expression by trauma-relevant cytokines

The leukocyte adhesion molecule L-selectin is important for the rolling of neutrophil granulocytes (PMN), the first step of the cascade leading to adhesion, diapedesis, and subsequent organ dysfunction. The activation of leukocytes in the posttraumatic course is assumed to be induced by different pro-inflammatory cytokines. In the present study, we investigated the effects of stimulation with pro- and anti-inflammatory cytokines on the L-selectin surface expression on PMN. Twenty patients admitted to our institution for elective operations of the lower extremities were enrolled in a prospective clinical study. For the measurement of L-selectin expression, blood was taken before the operation (0 h), as well as 24 h and 48 h postoperatively. Without and after incubation with different pro- and anti-inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-10), the surface expression of L-selectin was detected using an anti-L-selectin-specific antibody and flow cytometry. L-selectin surface expression without any stimulation showed a non-significant increase 48 h after the operation (63.6±6.6 ng/ml at 0 h, 95.2±10.5 ng/ml at 48 h). Stimulation with TNF-α resulted in a significant decrease of L-selectin expression at 0 h (25.6±2.7 ng/ml; p<0.05) and 24 h (18.3±2.5 ng/ml; p<0.05), but not at 48 h (39.8±4.2 ng/ml). No significant differences were observed after stimulation with IL-1β, IL-6, and IL-10 in comparison to the non-stimulated group. The study results indicate that the primary pro-inflammatory cytokine TNF-α regulates the L-selectin surface expression on PMN after surgical trauma. Therefore, a regulation of neutrophil activation on this level might be crucial in the development of posttraumatic complications.

IL-17 promotes p38 MAPK-dependent endothelial activation enhancing neutrophil recruitment to sites of inflammation

Neutrophilic inflammation plays an important role in lung tissue destruction occurring in many chronic pulmonary diseases. Neutrophils can be recruited to sites of inflammation via the action of the cytokine IL-17. In this study, we report that IL-17RA and IL-17RC mRNA expression is significantly increased in asthmatic bronchoscopic biopsies and that these receptors are not only expressed on epithelial and inflammatory cells but also on endothelial cells. IL-17 potently stimulates lung microvascular endothelial cells to produce chemoattractants (CXCL8 and derivatives of the 5-lipoxygenase pathway) that selectively drive neutrophil but not lymphocyte chemotaxis. Moreover, IL-17 promotes endothelial activation by inducing the expression of endothelial adhesion markers (E-selectin, VCAM-1, and ICAM-1) in a p38 MAPK-dependent manner. This increased expression of adhesion molecules stimulates the trans-endothelial migration of neutrophils, as well as the transmigration of HT-29 colon carcinoma cells, suggesting a further role in promoting lung metastasis. Finally, IL-17 increased neutrophil adhesion to the endothelium in vivo as determined by intravital microscopy of mice cremaster muscle. Overall, our results demonstrate that IL-17 is a potent activator of the endothelium in vivo leading to neutrophil infiltration. Therefore, preventing neutrophil recruitment by blocking the action of IL-17 on endothelial cells may prove to be highly beneficial in diseases in which neutrophilic inflammation plays a key role.

Systemic inflammation increases cancer cell adhesion to hepatic sinusoids by neutrophil mediated mechanisms

Interactions between endothelial selectins and selectin ligands expressed on tumor cells have been implicated in the binding of circulating metastatic cancer cells to the vascular endothelium during extravasation. Moreover, there is mounting evidence that inflammatory environments can accelerate the progression of metastasis by neutrophil mediated mechanisms. In this study, a physiologically relevant in vivo model of early metastasis coupled with intravital microscopy was used to visualize the trafficking of tumor cells within the liver vasculature in real time. Using GFP-labeled Lewis lung carcinoma subline H-59 cells, we show here that disrupting the interactions between endothelial selectins and tumor cell selectin ligands diminished tumor cell recruitment to the liver. Furthermore, systemic inflammation induced by intravenous injection of lipopolysaccharide significantly enhanced the metastatic potential of these lung carcinoma cells by increasing their propensity to adhere to the liver sinusoidal endothelium. Confocal microscopy revealed frequent colocalization of cancer cells with neutrophils and neutrophil depletion in vivo significantly attenuated the lipopolysaccharide-induced increase in H-59 cell adhesion. Although direct selectin-selectin ligand interactions contributed significantly to tumor cell adhesion to sinusoidal endothelial cells, we show here that in addition, interactions between adherent neutrophils within the inflamed sinusoids and circulating tumor cells may further increase tumor cell arrest in the liver.

L-selectin shedding in sepsis limits leukocyte mediated microvascular injury at remote sites

BACKGROUND

Increased soluble L-selectin levels have been shown to attenuate local inflammation-mediated microvascular leakage, and failure to generate high levels has been associated with increased risk of acute respiratory distress syndrome in septic patients. We hypothesized that failure to shed L-selectin in systemic inflammation would result in increased local inflammation-induced leukocyte adherence and microvascular leakage.

METHODS

Using intraperitoneal lipopolysaccharide (LPS) or control bicarbonate buffered saline (BBS) and intrascrotal TNFalpha or BBS, mice were randomized to systemic inflammation (LPSip + BBSis), local inflammation (BBSip + TNFis), both (LPSip + TNFis), or control (BBSip+BBSis). Furthermore, mice received intraperitoneal L-selectin Sheddase inhibitor (Ro31-9790) or control vector. With intravital microscopy on cremaster muscle, we measured leukocyte-endothelial cell interactions and microvascular leakage (permeability index). Surface L-selectin was measured by flow cytometry (MCF).

RESULTS

Without Ro31-9790, systemic inflammation attenuated increases induced by local inflammation in leukocyte adherence and vascular leakage. Ro31-9790 significantly increased adherence and leakage in systemic and systemic + local inflammation. L-selectin was shed progressively by increasing degrees of inflammation. Ro31-9790 limited this shedding of L-selectin.

CONCLUSION

In systemic inflammation, L-selectin shedding is required to limit local inflammation-mediated leukocyte adherence and microvascular leakage. Failure to shed L-selectin may increase leukocyte-mediated end-organ injury in septic patients.

Cysteinyl leukotriene 2 receptor-mediated vascular permeability via transendothelial vesicle transport

Cysteinyl leukotrienes (CysLTs) are potent mediators of inflammation synthesized by the concerted actions of 5-lipoxygenase (5-LO), 5-LO-activating protein (FLAP), leukotriene C(4) synthase, and additional downstream enzymes, starting with arachidonic acid substrate. CysLTs produced by macrophages, eosinophils, mast cells, and other inflammatory cells activate 3 different high-affinity CysLT receptors: CysLT(1)R, CysLT(2)R, and GPR 17. We sought to investigate vascular sites of CysLT(2)R expression and the role and mechanism of this receptor in mediating vascular permeability events. Vascular expression of CysLT(2)R was investigated by reporter gene expression in a novel CysLT(2)R deficient-LacZ mouse model. CysLT(2)R was expressed in small, but not large, vessels in mouse brain, bladder, skin, and cremaster muscle. Intravital, in addition to confocal and electron, microscopy investigations using FITC-labeled albumin in cremaster postcapillary venule preparations indicated rapid CysLT-mediated permeability, which was blocked by application of BAY-u9773, a dual CysLT(1)R/CysLT(2)R antagonist or by CysLT(2)R deficiency. Endothelial human CysLT(2)R overexpression in mice exacerbated vascular leakage even in the absence of exogenous ligand. The enhanced vascular permeability mediated by CysLT(2)R takes place via a transendothelial vesicle transport mechanism as opposed to a paracellular route and is controlled via Ca(2+) signaling. Our results reveal that CysLT(2)R can mediate inflammatory reactions in a vascular bed-specific manner by altering transendothelial vesicle transport-based vascular permeability.

Sepsis: emerging role of nitric oxide and selectins

Sepsis--a state of systemic bacterial infection--often leads to multiorgan failure and is associated with high mortality despite the recent advances achieved in intensive care treatment. Many of the ill effects of sepsis are attributed to an abnormally enhanced host inflammatory response that leads to neutrophil recruitment and activation involving selectins, a class of adhesion molecules, in the initial stages. Nitric oxide and its various isoforms have also been implicated in various vascular alterations and directly participate in the cellular toxicity in sepsis. This review briefly describes the role of selectins and nitric oxide in experimental and clinical sepsis as well as the therapeutic outcomes of blocking therapies.

Intrauterine undernutrition in rats interferes with leukocyte migration, decreasing adhesion molecule expression in leukocytes and endothelial cells

Experimental and epidemiologic data have shown that malnutrition predisposes individuals to infections. Immune responses are compromised, particularly in undernourished children. Therefore, we investigated the migratory capacity of leukocytes, using the intravital microscopy technique, in male Wistar rats (8-9 wk of age) that were undernourished in utero after their dams were fed 50% less food than the amount consumed by control dams. The number of leukocytes rolling along the venular endothelium, sticking after stimulation with leukotriene B4, tumor necrosis factor-alpha (TNF-alpha) or zymosan-activated plasma, or migrating after TNF-alpha stimulation was significantly reduced in the undernourished rat offspring. Compared with nourished rat offspring, undernourished offspring had significantly reduced numbers of circulating leukocytes, higher blood pressure, and higher leukocyte rolling velocity (V(WBC)), as well as a higher ratio between V(WBC) and RBC velocity (V(RBC)). Endothelial P-selectin and intercellular adhesion molecule-1 (ICAM-1) expression, analyzed by immunohistochemistry, and basal leukocyte L-selectin expression, analyzed by flow cytometry, were significantly reduced in the undernourished rat offspring. Because the groups did not differ in leukocyte CD11/18 expression, endothelial expression of platelet-endothelial cell adhesion molecule-1, or venular blood flow velocity and, consequently, venular shear rate, we conclude that intrauterine undernutrition in rats reduces leukocyte migration, downregulates endothelial expression of P-selectin and ICAM-1, as well as leukocyte expression of L-selectin, while reducing leukocyte counts. The higher V(WBC) and V(WBC)/V(RBC) ratio may also play a role in this reduced leukocyte migration. Our data suggest that this phenomenon is involved in the increased predisposition to infections in undernourished subjects.

Intravital microscopy for the study of mouse microcirculation in anti-inflammatory drug research: Focus on the mesentery and cremaster preparations

Intravital microscopy is an extremely useful tool used as a qualitative and quantitative way of observing leukocyte-endothelial cell interactions in-vivo. This present article reviews the methods of the technique of intravital microscopy, in particular focussing on the mesentery and cremaster preparations. It focuses on how to actually carry out the experiments required to directly observe and localize the changes in the function of the microcirculation. Where necessary the reader is asked to refer to a selection of highly acclaimed publications, which should enable the reader to truly appreciate, and if necessary perform, the technique of intravital microscopy.

Science review: Cell membrane expression (connectivity) regulates neutrophil delivery, function and clearance

As the principal cellular component of the inflammatory host defense and contributor to host injury after severe physiologic insult, the neutrophil is inherently coupled to patient outcome in both health and disease. Extensive research has focused on the mechanisms that regulate neutrophil delivery, function, and clearance from the inflammatory microenvironment. The neutrophil cell membrane mediates the interaction of the neutrophil with the extracellular environment; it expresses a complex array of adhesion molecules and receptors for various ligands, including mediators, cytokines, immunoglobulins, and membrane molecules on other cells. This article presents a review and analysis of the evidence that the neutrophil membrane plays a central role in regulating neutrophil delivery (production, rolling, adhesion, diapedesis, and chemotaxis), function (priming and activation, microbicidal activity, and neutrophil-mediated host injury), and clearance (apoptosis and necrosis). In addition, we review how change in neutrophil membrane expression is synonymous with change in neutrophil function in vivo. Employing a complementary analysis of the neutrophil as a complex system, neutrophil membrane expression may be regarded as a measure of neutrophil connectivity, with altered patterns of connectivity representing functionally distinct neutrophil states. Thus, not only does the neutrophil membrane mediate the processes that characterize the neutrophil lifecycle, but characterization of neutrophil membrane expression represents a technology with which to evaluate neutrophil function.

Recent developments in the treatment of sepsis

Despite advances in supportive care, septic shock remains a major cause of morbidity and mortality. With the identification of the systemic inflammatory response as a major component in the pathogenesis of the septic shock syndrome, much of the recent work has focused on modulating this response. This includes antiendotoxin therapies in patients with Gram-negative sepsis, and therapies to modulate the pro-inflammatory mediators produced in response to infection, such as TNF-alpha, platelet-activating factor and complement. High-flow haemofiltration has the potential advantage of clearing both endotoxin and pro-inflammatory mediators. Antithrombotic strategies have been investigated and have yielded the first major success in the treatment of sepsis with activated protein C. Nitric oxide produces the cardiovascular features of sepsis and investigators have looked at both reducing its production and mopping up the excess. Attempts to reduce apoptosis have been a new focus in the treatment of sepsis. There have also been recent developments in supportive care suggesting a role for vasopressin and replacement corticosteroid therapy.

Targets for pharmacological intervention of endothelial hyperpermeability and barrier function

Many diseases share the common feature of vascular leakage, and endothelial barrier dysfunction is often the underlying cause. The subsequent stages of endothelial barrier dysfunction contribute to endothelial hyperpermeability. Vasoactive agents induce loss of junctional integrity, a process that involves actin-myosin interaction. Subsequently, the interaction of leukocytes amplifies leakage by the leukocyte-derived mediators. The processes mainly occur at the postcapillary venules. The whole microvascular bed, including the capillaries, becomes involved in vascular leakage by the induction of angiogenesis. Plasma leakage results from gaps between endothelial cells as well as by the induction of transcellular transport pathways. Several mechanisms can improve endothelial barrier function, depending on the tissue affected and the cause of hyperpermeability. They include blockade of specific receptors and elevation of cyclic AMP (cAMP) by agents such as beta(2)-adrenergic agents. However, current therapies based on these principles often fail. Recent research has identified several new promising targets for pharmacological therapy. Endogenous compounds were also found with barrier-improving characteristics. Important insights were obtained in the different pathways involved in barrier dysfunction. Such insights regard the regulation of endothelial contraction and endothelial junction integrity: inhibitors of RhoA activation and Rho kinase represent a potentially valuable group of agents with endothelial hyperpermeability reducing properties, and strategies to target vascular endothelial growth factor (VEGF)-mediated edema are under current investigation. In clinical practice, not only tools to improve an impaired endothelial barrier function are necessary. Sometimes, a controlled, temporal, and local increase in permeability can also be desired, for example, with the aim to enhance drug delivery. Therefore, vessel leakiness is also being exploited to enable tissue access of liposomes, viral vectors, and other therapeutic agents that do not readily cross healthy endothelium. This review discusses strategies for targeting signaling molecules in therapies for diseases involving altered endothelial permeability.