Thrombopoietin levels in sepsis and septic shock - a systematic review and meta-analysis.

OBJECTIVES: Sepsis is a life-threatening condition implicating an inadequate activation of the immune system. Platelets act as modulators and contributors to immune processes. Indeed, altered platelet turnover, thrombotic events, and changes in thrombopoietin levels in systemic inflammation have been reported, but thrombopoietin-levels in sepsis and septic-shock have not yet been systematically evaluated. We therefore performed a meta-analysis of thrombopoietin (TPO)-levels in patients with sepsis. METHODS: Two independent reviewers screened records and full-text articles for inclusion. Scientific databases were searched for studies examining thrombopoietin levels in adult sepsis and septic-shock patients until August 1st 2022. RESULTS: Of 95 items screened, six studies met the inclusion criteria, including 598 subjects. Both sepsis and severe sepsis were associated with increased levels of thrombopoietin (sepsis vs. control: standardized mean difference 3.06, 95 % CI 1.35-4.77; Z=3.50, p=0.0005) (sepsis vs. severe sepsis: standardized mean difference -1.67, 95 % CI -2.46 to -0.88; Z=4.14, p<0.0001). TPO-levels did not show significant differences between severe sepsis and septic shock patients but differed between sepsis and inflammation-associated non-septic controls. Overall, high heterogeneity and low sample size could be noted. CONCLUSIONS: Concluding, increased levels of thrombopoietin appear to be present both in sepsis and severe sepsis with high heterogeneity but thrombopoietin does not allow to differentiate between severe sepsis and septic-shock. TPO may potentially serve to differentiate sepsis from non-septic trauma and/or tissue damage related (systemic) inflammation. Usage of different assays and high heterogeneity demand standardization of methods and further large multicenter trials.

Nuclease activity and protein A release of Staphylococcus aureus clinical isolates determine the virulence in a murine model of acute lung infection.

Staphylococcus aureus is a common cause of hospital-acquired pneumonia associated with high mortality. Adequate clinical treatment is impeded by increasing occurrence of antibiotic resistances. Understanding the underlying mechanisms of its virulence during infections is a prerequisite to finding alternative treatments. Here, we demonstrated that an increased nuclease activity of a S. aureus isolate from a person with cystic fibrosis confers a growth advantage in a model of acute lung infection compared to the isogenic strain with low nuclease activity. Comparing these CF-isolates with a common MRSA-USA300 strain with similarly high nuclease activity but significantly elevated levels of Staphylococcal Protein A (SpA) revealed that infection with USA300 resulted in a significantly increased bacterial burden in a model of murine lung infection. Replenishment with the cell wall-bound SpA of S. aureus, which can also be secreted into the environment and binds to tumor necrosis factor receptor -1 (TNFR-1) to the CF-isolates abrogated these differences. In vitro experiments confirmed significant differences in spa-expression between USA300 compared to CF-isolates, thereby influencing TNFR-1 shedding, L-selectin shedding, and production of reactive oxygen species through activation of ADAM17.

Bioactive Nanogels Mimicking the Antithrombogenic Nitric Oxide-Release Function of the Endothelium.

Nitric oxide (NO) plays a significant role in controlling the physiology and pathophysiology of the body, including the endothelial antiplatelet function and therefore, antithrombogenic property of the blood vessels. This property of NO can be exploited to prevent thrombus formation on artificial surfaces like extracorporeal membrane oxygenators, which when come into contact with blood lead to protein adsorption and thereby platelet activation causing thrombus formation. However, NO is extremely reactive and has a very short biological half-life in blood, so only endogenous generation of NO from the blood contacting material can result into a stable and kinetically controllable local delivery of NO. In this regards, highly hydrophilic bioactive nanogels are presented which can endogenously generate NO in blood plasma from endogenous NO-donors thereby maintaining a physiological NO flux. It is shown that NO releasing nanogels could initiate cGMP-dependent protein kinase signaling followed by phosphorylation of vasodilator-stimulated phosphoprotein in platelets. This prevents platelet activation and aggregation even in presence of highly potent platelet activators like thrombin, adenosine 5'-diphosphate, and U46619 (thromboxane A2 mimetic).

Role of S100A8/A9 in Platelet-Neutrophil Complex Formation during Acute Inflammation.

Acute respiratory distress syndrome (ARDS) due to pulmonary infections is associated with high morbidity and mortality. Upon inflammation, the alarmin S100A8/A9 is released and stimulates neutrophil recruitment mainly via binding to Toll-like receptor 4 (TLR4). TLR4 is also expressed on platelets, which modulate the immune response through direct interaction with leukocytes. In a murine model of Klebsiella pneumoniae-induced pulmonary inflammation, global S100A9 deficiency resulted in diminished neutrophil recruitment into the lung alveoli and neutrophil accumulation in the intravascular space, indicating an impaired neutrophil migration. A lack of TLR4 on platelets resulted in reduced neutrophil counts in the whole lung, emphasising the impact of TLR4-mediated platelet activity on neutrophil behaviour. Flow cytometry-based analysis indicated elevated numbers of platelet-neutrophil complexes in the blood of S100A9-/- mice. Intravital microscopy of the murine cremaster muscle confirmed these findings and further indicated a significant increase in neutrophil-platelet complex formation in S100A9-/- mice, which was reversed by administration of the S100A8/A9 tetramer. An in vitro bilayer assay simulated the murine alveolar capillary barrier during inflammation and validated significant differences in transmigration behaviour between wild-type and S100A9-/- neutrophils. This study demonstrates the role of S100A8/A9 during platelet-neutrophil interactions and neutrophil recruitment during pulmonary inflammation.

Glutamine prevents acute kidney injury by modulating oxidative stress and apoptosis in tubular epithelial cells.

Acute kidney injury (AKI) represents a common complication in critically ill patients that is associated with increased morbidity and mortality. In a murine AKI model induced by ischemia/reperfusion injury (IRI), we show that glutamine significantly decreases kidney damage and improves kidney function. We demonstrate that glutamine causes transcriptomic and proteomic reprogramming in murine renal tubular epithelial cells (TECs), resulting in decreased epithelial apoptosis, decreased neutrophil recruitment, and improved mitochondrial functionality and respiration provoked by an ameliorated oxidative phosphorylation. We identify the proteins glutamine gamma glutamyltransferase 2 (Tgm2) and apoptosis signal-regulating kinase (Ask1) as the major targets of glutamine in apoptotic signaling. Furthermore, the direct modulation of the Tgm2-HSP70 signalosome and reduced Ask1 activation resulted in decreased JNK activation, leading to diminished mitochondrial intrinsic apoptosis in TECs. Glutamine administration attenuated kidney damage in vivo during AKI and TEC viability in vitro under inflammatory or hypoxic conditions.

Targeting Procalcitonin Protects Vascular Barrier Integrity.

Rationale: Capillary leakage frequently occurs during sepsis and after major surgery and is associated with microvascular dysfunction and adverse outcome. Procalcitonin is a well-established biomarker in inflammation without known impact on vascular integrity. Objectives: We determined how procalcitonin induces endothelial hyperpermeability and how targeting procalcitonin protects vascular barrier integrity. Methods: In a prospective observational clinical study, procalcitonin levels were assessed in 50 patients who underwent cardiac surgery and correlated to postoperative fluid and vasopressor requirements along with sublingual microvascular functionality. Effects of the procalcitonin signaling pathway on endothelial barrier and adherens junctional integrity were characterized in vitro and verified in mice. Inhibition of procalcitonin activation by dipeptidyl-peptidase 4 (DPP4) was evaluated in murine polymicrobial sepsis and clinically verified in cardiac surgery patients chronically taking the DPP4 inhibitor sitagliptin. Measurements and Main Results: Elevated postoperative procalcitonin levels identified patients with 2-fold increased fluid requirements (P < 0.01), 1.8-fold higher vasopressor demand (P < 0.05), and compromised microcirculation (reduction to 63.5 ± 2.8% of perfused vessels, P < 0.05). Procalcitonin induced 1.4-fold endothelial and 2.3-fold pulmonary capillary permeability (both Ps < 0.001) by destabilizing VE-cadherin. Procalcitonin effects were dependent on activation by DPP4, and targeting the procalcitonin receptor or DPP4 during sepsis-induced hyperprocalcitonemia reduced capillary leakage by 54 ± 10.1% and 60.4 ± 6.9% (both Ps < 0.01), respectively. Sitagliptin before cardiac surgery was associated with augmented microcirculation (74.1 ± 1.7% vs. 68.6 ± 1.9% perfused vessels in non-sitagliptin-medicated patients, P < 0.05) and with 2.3-fold decreased fluid (P < 0.05) and 1.8-fold reduced vasopressor demand postoperatively (P < 0.05). Conclusions: Targeting procalcitonin's action on the endothelium is a feasible means to preserve vascular integrity during systemic inflammation associated with hyperprocalcitonemia.

Remote ischemic preconditioning causes transient cell cycle arrest and renal protection by a NF-κB-dependent Sema5B pathway.

Acute kidney injury increases morbidity and mortality, and previous studies have shown that remote ischemic preconditioning (RIPC) reduces the risk of acute kidney injury after cardiac surgery. RIPC increases urinary high mobility group box protein-1 (HMGB1) levels in patients, and this correlates with kidney protection. Here, we show that RIPC reduces renal ischemia-reperfusion injury and improves kidney function in mice. Mechanistically, RIPC increases HMGB1 levels in the plasma and urine, and HMGB1 binds to TLR4 on renal tubular epithelial cells, inducing transcriptomic modulation of renal tubular epithelial cells and providing renal protection, whereas TLR4 activation on nonrenal cells was shown to contribute to renal injury. This protection is mediated by activation of induction of AMPKα and NF-κB; this induction contributes to the upregulation of Sema5b, which triggers a transient, protective G1 cell cycle arrest. In cardiac surgery patients at high risk for postoperative acute kidney injury, increased HMGB1 and Sema5b levels after RIPC were associated with renal protection after surgery. The results may help to develop future clinical treatment options for acute kidney injury.

C/EBPδ-induced epigenetic changes control the dynamic gene transcription of S100a8 and S100a9.

The proinflammatory alarmins S100A8 and S100A9 are among the most abundant proteins in neutrophils and monocytes but are completely silenced after differentiation to macrophages. The molecular mechanisms of the extraordinarily dynamic transcriptional regulation of S100a8 and S100a9 genes, however, are only barely understood. Using an unbiased genome-wide CRISPR/Cas9 knockout (KO)-based screening approach in immortalized murine monocytes, we identified the transcription factor C/EBPδ as a central regulator of S100a8 and S100a9 expression. We showed that S100A8/A9 expression and thereby neutrophil recruitment and cytokine release were decreased in C/EBPδ KO mice in a mouse model of acute lung inflammation. S100a8 and S100a9 expression was further controlled by the C/EBPδ antagonists ATF3 and FBXW7. We confirmed the clinical relevance of this regulatory network in subpopulations of human monocytes in a clinical cohort of cardiovascular patients. Moreover, we identified specific C/EBPδ-binding sites within S100a8 and S100a9 promoter regions, and demonstrated that C/EBPδ-dependent JMJD3-mediated demethylation of H3K27me3 is indispensable for their expression. Overall, our work uncovered C/EBPδ as a novel regulator of S100a8 and S100a9 expression. Therefore, C/EBPδ represents a promising target for modulation of inflammatory conditions that are characterized by S100a8 and S100a9 overexpression.

Platelets orchestrate the resolution of pulmonary inflammation in mice by T reg cell repositioning and macrophage education.

Beyond hemostasis, platelets actively participate in immune cell recruitment and host defense, yet their potential in the resolution of inflammatory processes remains unknown. Here, we demonstrate that platelets are recruited into the lung together with neutrophils during the onset of inflammation and alongside regulatory T (T reg) cells during the resolution phase. This partnering dichotomy is regulated by differential adhesion molecule expression during resolution. Mechanistically, intravascular platelets form aggregates with T reg cells, a prerequisite for their recruitment into the lung. This interaction relies on platelet activation by sCD40L and platelet P-selectin binding to PSGL-1 on T reg cells. Physical platelet-T reg cell interactions are necessary to modulate the transcriptome and instruct T reg cells to release the anti-inflammatory mediators IL-10 and TGFß. Notably, the presence of platelet-T reg cell aggregates in the lung was also required for macrophage transcriptional reprogramming, polarization toward an anti-inflammatory phenotype, and effective resolution of pulmonary inflammation. Thus, platelets partner with successive immune cell subsets to orchestrate both the initiation and resolution of inflammation.

[Inflammation and perioperative organ dysfunction]. / Inflammation und perioperative Organdysfunktion.

The immune system is an effective defense against invading pathogens and is accompanied by recruitment of immune cells and initiation of an inflammatory reaction. This can also be triggered by noninfectious stimuli, e.g. a large surgical intervention and cause severe tissue destruction and organ dysfunction. The organism cannot distinguish many stimuli that are released during a large surgical intervention from exogenous pathogens. Therefore, there is a high risk for the occurrence of systemic inflammatory reactions, particularly in large surgical interventions. This excessive immune response leads to release of proinflammatory cytokines, endothelial dysfunction, damage to the glycocalyx, activation of leukocytes as well as tissue and organ destruction. This article summarizes the molecular principles of the surgery-associated inflammatory reaction, the differentiation from other inflammatory complications and treatment options.

Systemic Inflammatory Response Syndrome After Surgery: Mechanisms and Protection.

The immune system is an evolutionary hallmark of higher organisms that defends the host against invading pathogens and exogenous infections. This defense includes the recruitment of immune cells to the site of infection and the initiation of an inflammatory response to contain and eliminate pathogens. However, an inflammatory response may also be triggered by noninfectious stimuli such as major surgery, and, in case of an overshooting, still not comprehensively understood reaction, lead to tissue destruction and organ dysfunction. Unfortunately, in some cases, the immune system may not effectively distinguish between stimuli elicited by major surgery, which ideally should only require a modest inflammatory response, and those elicited by trauma or pathogenic infection. Surgical procedures thus represent a potential trigger for systemic inflammation that causes the secretion of proinflammatory cytokines, endothelial dysfunction, glycocalyx damage, activation of neutrophils, and ultimately tissue and multisystem organ destruction. In this review, we discuss and summarize currently available mechanistic knowledge on surgery-associated systemic inflammation, demarcation toward other inflammatory complications, and possible therapeutic options. These options depend on uncovering the underlying mechanisms and could include pharmacologic agents, remote ischemic preconditioning protocols, cytokine blockade or clearance, and optimization of surgical procedures, anesthetic regimens, and perioperative inflammatory diagnostic assessment. Currently, a large gap between basic science and clinically confirmed data exists due to a limited evidence base of translational studies. We thus summarize important steps toward the understanding of the precise time- and space-regulated processes in systemic perioperative inflammation.

Effects of Different Doses of Remote Ischemic Preconditioning on Kidney Damage Among Patients Undergoing Cardiac Surgery: A Single-Center Mechanistic Randomized Controlled Trial.

OBJECTIVES: We have previously shown that remote ischemic preconditioning reduces acute kidney injury (acute kidney injury) in high-risk patients undergoing cardiopulmonary bypass and that the protective effect is confined to patients who exhibit an increased urinary tissue inhibitor of metalloproteinases-2 and insulin-like growth factor-binding protein 7 in response to remote ischemic preconditioning. The purpose of this study was to determine the optimal intensity of remote ischemic preconditioning to induce required [tissue inhibitor of metalloproteinases-2]*[insulin-like growth factor-binding protein 7] changes and further explore mechanisms of remote ischemic preconditioning. DESIGN: Observational and randomized controlled, double-blind clinical trial. SETTING: University Hospital of Muenster, Germany. PATIENTS: High-risk patients undergoing cardiac surgery as defined by the Cleveland Clinic Foundation Score. INTERVENTIONS: In the interventional part, patients were randomized to receive either one of four different remote ischemic preconditioning doses (3 × 5 min, 3 × 7 min, 3 × 10 min remote ischemic preconditioning, or 3 × 5 min remote ischemic preconditioning + 2 × 10 min remote ischemic preconditioning in nonresponders) or sham-remote ischemic preconditioning (control). MEASUREMENTS AND MAIN RESULTS: The primary endpoint of the interventional part was change in urinary [tissue inhibitor of metalloproteinases-2]*[insulin-like growth factor-binding protein 7] between pre- and postintervention. To examine secondary objectives including acute kidney injury incidence, we included an observational cohort. A total of 180 patients were included in the trial (n = 80 observational and n = 100 randomized controlled part [20 patients/group]). The mean age was 69.3 years (10.5 yr), 119 were men (66.1%). Absolute changes in [tissue inhibitor of metalloproteinases-2]*[insulin-like growth factor-binding protein 7] were significantly higher in all remote ischemic preconditioning groups when compared with controls (p < 0.01). Although we did not observe a dose-response relationship on absolute changes in [tissue inhibitor of metalloproteinases-2]*[insulin-like growth factor-binding protein 7] across the four different remote ischemic preconditioning groups, in the 15 patients failing to respond to the lowest dose, nine (60%) responded to a subsequent treatment at a higher intensity. Compared with controls, fewer patients receiving remote ischemic preconditioning developed acute kidney injury within 72 hours after surgery as defined by both Kidney Disease: Improving Global Outcomes criteria (30/80 [37.5%] vs 61/100 [61.0%]; p = 0.003). CONCLUSIONS: All doses of remote ischemic preconditioning significantly increased [tissue inhibitor of metalloproteinases-2]*[insulin-like growth factor-binding protein 7] and significantly decreased acute kidney injury compared with controls. High-dose remote ischemic preconditioning could stimulate [tissue inhibitor of metalloproteinases-2]*[insulin-like growth factor-binding protein 7] increases in patients refractory to low-dose remote ischemic preconditioning.

The integrin-linked kinase is required for chemokine-triggered high-affinity conformation of the neutrophil ß2-integrin LFA-1.

Neutrophil adhesion and extravasation into tissue at sites of injury or infection depend on binding of the integrin lymphocyte function-associated antigen 1 (LFA-1) to ICAM-1 expressed on activated endothelial cells. The activation-dependent conformational change of LFA-1 to the high-affinity conformation (H+) requires kindlin-3 binding to the ß2-integrin cytoplasmic domain. Here we show that genetic deletion of the known kindlin interactor integrin-linked kinase (ILK) impaired neutrophil adhesion and extravasation in the cremaster muscle and in a clinically relevant model of renal ischemia reperfusion injury. Using in vitro microfluidic adhesion chambers and conformation-specific antibodies, we show that knockdown of ILK in HL-60 cells reduced the conformational change of ß2-integrins to the H+ conformation. Mechanistically, we found that ILK was required for protein kinase C (PKC) membrane targeting and chemokine-induced upregulation of its kinase activity. Moreover, PKC-α deficiency also resulted in impaired leukocyte adhesion in bone marrow chimeric mice. Mass spectrometric and western blot analyses revealed stimulation- and ILK-dependent phosphorylation of kindlin-3 upon activation. In summary, our data indicate an important role of ILK in kindlin-3-dependent conformational activation of LFA-1.

Intravascular adhesion and recruitment of neutrophils in response to CXCL1 depends on their TRPC6 channels.

Here we report a novel role for TRPC6, a member of the transient receptor potential (TRPC) channel family, in the CXCL1-dependent recruitment of murine neutrophil granulocytes. Representing a central element of the innate immune system, neutrophils are recruited from the blood stream to a site of inflammation. The recruitment process follows a well-defined sequence of events including adhesion to the blood vessel walls, migration, and chemotaxis to reach the inflammatory focus. A common feature of the underlying signaling pathways is the utilization of Ca2+ ions as intracellular second messengers. However, the required Ca2+ influx channels are not yet fully characterized. We used WT and TRPC6-/- neutrophils for in vitro and TRPC6-/- chimeric mice (WT mice with WT or TRPC6-/- bone marrow cells) for in vivo studies. After renal ischemia and reperfusion injury, TRPC6-/- chimeric mice had an attenuated TRPC6-/- neutrophil recruitment and a better outcome as judged from the reduced increase in the plasma creatinine concentration. In the cremaster model CXCL1-induced neutrophil adhesion, arrest and transmigration were also decreased in chimeric mice with TRPC6-/- neutrophils. Using atomic force microscopy and microfluidics, we could attribute the recruitment defect of TRPC6-/- neutrophils to the impact of the channel on adhesion to endothelial cells. Mechanistically, TRPC6-/- neutrophils exhibited lower Ca2+ transients during the initial adhesion leading to diminished Rap1 and ß2 integrin activation and thereby reduced ICAM-1 binding. In summary, our study reveals that TRPC6 channels in neutrophils are crucial signaling modules in their recruitment from the blood stream in response to CXCL1. KEY POINT: Neutrophil TRPC6 channels are crucial for CXCL1-triggered activation of integrins during the initial steps of neutrophil recruitment.

Anesthesia-induced immune modulation.

PURPOSE OF REVIEW: Surgery, invasive procedures and anesthesia itself may induce an inflammatory response in the patient. This represents an evolutionary inherited and conserved response of the host to environmental stimuli and may lead to both beneficial and potentially harmful effects. This review highlights the mechanisms of anesthesia-induced and perioperative immune modulation. RECENT FINDINGS: The innate and adaptive immune system serve the host in protection against invading pathogens. Yet, an inflammatory immune response may also be induced by different noninfectious stimuli, for example invasive perioperative procedures and the surgical trauma itself. These stimuli may lead to the activation of the immune system with the consequence of perturbation of cell, tissue of even organ functions in cases of an overshooting immune response. Several perioperative factors have been identified that modulate the immune response, for example different anesthetic drugs and surgical tissue injury, but their impact on immune system modulation may also vary with respect to the procedural context and include both pro-inflammatory and anti-inflammatory effects. SUMMARY: The current review will highlight the current knowledge on the perioperative anesthesia-induced and surgery-induced modulation of the immune response and also address possible intervention strategies for the development of future therapeutic approaches.

6% Hydroxyethyl starch (HES 130/0.4) diminishes glycocalyx degradation and decreases vascular permeability during systemic and pulmonary inflammation in mice.

BACKGROUND: Increased vascular permeability is a pathophysiological hallmark of sepsis and results in increased transcapillary leakage of plasma fluid, hypovolemia, and interstitial edema formation. 6% hydroxyethyl starch (HES 130/0.4) is commonly used to treat hypovolemia to maintain adequate organ perfusion and oxygen delivery. The present study was designed to investigate the effects of 6% HES 130/0.4 on glycocalyx integrity and vascular permeability in lipopolysaccharide (LPS)-induced pulmonary inflammation and systemic inflammation in mice. METHODS: 6% HES 130/0.4 or a balanced electrolyte solution (20 ml/kg) was administered intravenously 1 h after cecal ligation and puncture (CLP) or LPS inhalation. Sham-treated animals receiving 6% HES 130/0.4 or the electrolyte solution served as controls. The thickness of the endovascular glycocalyx was visualized by intravital microscopy in lung (LPS inhalation model) or cremaster muscle (CLP model). Syndecan-1, hyaluronic acid, and heparanase levels were measured in blood samples. Vascular permeability in the lungs, liver, kidney, and brain was measured by Evans blue extravasation. RESULTS: Both CLP induction and LPS inhalation resulted in increased vascular permeability in the lung, liver, kidney, and brain. 6% HES 130/0.4 infusion led to significantly reduced plasma levels of syndecan-1, heparanase, and hyaluronic acid, which was accompanied by a preservation of the glycocalyx thickness in postcapillary venules of the cremaster (0.78 ± 0.09 µm vs. 1.39 ± 0.10 µm) and lung capillaries (0.81 ± 0.09 µm vs. 1.49 ± 0.12 µm). CONCLUSIONS: These data suggest that 6% HES 130/0.4 exerts protective effects on glycocalyx integrity and attenuates the increase of vascular permeability during systemic inflammation.

Perioperative Inflammation and Its Modulation by Anesthetics.

Surgery and other invasive procedures, which are routinely performed during general anesthesia, may induce an inflammatory response in the patient. This inflammatory response is an inherent answer of the body to the intervention and can be both beneficial and potentially harmful. The immune system represents a unique evolutionary achievement equipping higher organisms with an effective defense mechanism against exogenous pathogens. However, not only bacteria might evoke an immune response but also other noninfectious stimuli like the surgical trauma or mechanical ventilation may induce an inflammatory response of varying degree. In these cases, the immune system activation is not always beneficial for the patients and might carry the risk of concomitant, harmful effects on host cells, tissues, or even whole organ systems. Research over the past decades has contributed substantial information in which ways surgical patients may be affected by inflammatory reactions. Modulations of the patient's immune system may be evoked by the use of anesthetic agents, the nature of surgical trauma and the use of any supportive therapy during the perioperative period. The effects on the patient may be manifold, including various proinflammatory effects. This review focuses on the causes and effects of inflammation in the perioperative period. In addition, we also highlight possible approaches by which inflammation in the perioperative may be modulated in the future.

Cathepsin G Controls Arterial But Not Venular Myeloid Cell Recruitment.

BACKGROUND: Therapeutic targeting of arterial leukocyte recruitment in the context of atherosclerosis has been disappointing in clinical studies. Reasons for such failures include the lack of knowledge of arterial-specific recruitment patterns. Here we establish the importance of the cathepsin G (CatG) in the context of arterial myeloid cell recruitment. METHODS: Intravital microscopy of the carotid artery, the jugular vein, and cremasteric arterioles and venules in Apoe-/-and CatG-deficient mice (Apoe-/-Ctsg-/-) was used to study site-specific myeloid cell behavior after high-fat diet feeding or tumor necrosis factor stimulation. Atherosclerosis development was assessed in aortic root sections after 4 weeks of high-fat diet, whereas lung inflammation was assessed after inhalation of lipopolysaccharide. Endothelial deposition of CatG and CCL5 was quantified in whole-mount preparations using 2-photon and confocal microscopy. RESULTS: Our observations elucidated a crucial role for CatG during arterial leukocyte adhesion, an effect not found during venular adhesion. Consequently, CatG deficiency attenuates atherosclerosis but not acute lung inflammation. Mechanistically, CatG is immobilized on arterial endothelium where it activates leukocytes to firmly adhere engaging integrin clustering, a process of crucial importance to achieve effective adherence under high-shear flow. Therapeutic neutralization of CatG specifically abrogated arterial leukocyte adhesion without affecting myeloid cell adhesion in the microcirculation. Repetitive application of CatG-neutralizing antibodies permitted inhibition of atherogenesis in mice. CONCLUSIONS: Taken together, these findings present evidence of an arterial-specific recruitment pattern centered on CatG-instructed adhesion strengthening. The inhibition of this process could provide a novel strategy for treatment of arterial inflammation with limited side effects.

Gnb isoforms control a signaling pathway comprising Rac1, Plcß2, and Plcß3 leading to LFA-1 activation and neutrophil arrest in vivo.

Chemokines are required for leukocyte recruitment and appropriate host defense and act through G protein-coupled receptors (GPCRs), which induce downstream signaling leading to integrin activation. Although the α and ß subunits of the GPCRs are the first intracellular molecules that transduce signals after ligand binding and are therefore indispensable for downstream signaling, relatively little is known about their contribution to lymphocyte function-associated antigen 1 (LFA-1) activation and leukocyte recruitment. We used knockout mice and short hairpin RNA to knock down guanine nucleotide binding protein (GNB) isoforms (GNB1, GNB2, GNB4, and GNB5) in HL60 cells and primary murine hematopoietic cells. Neutrophil function was assessed by using intravital microscopy, flow chamber assays, and chemotaxis and biochemistry studies. We unexpectedly discovered that all expressed GNB isoforms are required for LFA-1 activation. Their downregulation led to a significant impairment of LFA-1 activation, which was demonstrated in vitro and in vivo. Furthermore, we showed that GPCR activation leads to Ras-related C3 botulinum toxin substrate 1 (Rac1)-dependent activation of both phospholipase C ß2 (Plcß2) and Plcß3. They act nonredundantly to produce inositol triphosphate-mediated intracellular Ca(2+) flux and LFA-1 activation that support chemokine-induced arrest in vivo. In a complex inflammatory disease model, Plcß2-, Plcß3-, or Rac1-deficient mice were protected from lipopolysaccharide-induced lung injury. Taken together, we demonstrated that all Gnb isoforms are required for chemokine-induced downstream signaling, and Rac1, Plcß2, and Plcß3 are critically involved in integrin activation and leukocyte arrest.

Acute kidney injury: definition, diagnosis and epidemiology.

Acute kidney injury (AKI) is a common complication in hospitalized patients and great efforts by leading experts have been made in order to establish common definitions of AKI. The clinical use of these consensus definitions has led to a substantially improved understanding of AKI. In addition, the consensus definitions allow to compare AKI incidence and outcomes between different patient populations. As a result, it has become evident that AKI in the Western population represents a clinical syndrome with an incidence close to that of myocardial infarction. The aim of this review is to revisit the current concepts and definitions of AKI, to highlight its diagnosis, and to emphasize its epidemiological characteristics. Here, we will focus on the available literature reporting the epidemiology of AKI in critically ill patients. Sepsis, major surgery, and nephrotoxic drugs are the main causes of AKI in these patients, and its occurrence is associated with an increased risk for sustained chronic kidney injury. We also discuss the concept of renal angina as a possible future concept for improved clinical risk stratification to detect AKI. In this regard, we emphasize the importance of the use of novel biomarkers in the diagnosis of AKI, as they hold the potential to improve early diagnosis and prevention in the clinical setting.