Inhibition of apoptosis in polymorphonuclear neutrophils from burn patients

Role of oxidative stress in induction of trans-differentiation of neutrophils in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disorder whose etiopathology involves an interplay between genetic and environmental factors, with oxidative stress being a key contributory factor. This study aimed to establish the impact, if any, of an oxidative, pro-inflammatory milieu upon trans-differentiation of neutrophils and disease progression. In the synovial fluid (SF) and peripheral blood sourced from patients with RA (n = 40) along with healthy controls (n = 25), the proportion of neutrophil-dendritic (N-DC) cell hybrids, i.e. CD66b⁺/CD83⁺ was characterized in terms of their antigen presentation (HLA-DR, CD80, andCD86) and cell adhesion and migration (ICAM-1, VCAM-1, and CD62L) properties, along with their ability to generate reactive oxygen species (ROS). In the SF of RA cases, the raised levels of circulating and intra-neutrophilic pro-inflammatory cytokines/chemokines were accompanied by an enhanced proportion of CD66b⁺ neutrophils, that co-expressed features of antigen presenting cells (APCs) namely CD83, HLA-DR, CD80, CD86, ICAM-1, VCAM-1, and decreased CD62L. These N-DCs as compared to canonical neutrophils demonstrated a higher generation of ROS, and their frequency positively correlated with disease activity score (DAS28). An ex-vivo functional assay validated that oxidative stress supported trans-differentiation and could be attenuated by a free radical scavenger. Taken together, the pro-inflammatory microenvironment in the SF of patients with RA coupled with a higher generation of ROS promoted the trans-differentiation of neutrophils into N-DCs, suggesting the inclusion of anti-oxidants as an add-on therapeutic strategy to limit trans-differentiation.

Molecular Mechanisms for Regulation of Neutrophil Apoptosis under Normal and Pathological Conditions

Neutrophils are one of the main cells of innate immunity that perform a key effector and regulatory function in the development of the human inflammatory response. Apoptotic forms of neutrophils are important for regulating the intensity of inflammation and restoring tissue homeostasis. This review summarizes current data on the molecular mechanisms of modulation of neutrophil apoptosis by the main regulatory factors of the inflammatory response-cytokines, integrins, and structural components of bacteria. Disturbances in neutrophil apoptosis under stress are also considered, molecular markers of changes in neutrophil lifespan associated with various diseases and pathological conditions are presented, and data on pharmacological agents for modulating apoptosis as potential therapeutics are also discussed.

Neutrophils in Biomaterial-Guided Tissue Regeneration: Matrix Reprogramming for Angiogenesis

Biomaterial-guided in situ tissue regeneration uses biomaterials to stimulate and guide the body's endogenous, regenerative processes to drive functional tissue repair and regeneration. To be successful, cell migration into the biomaterials is essential, which requires angiogenesis to maintain cell viability. Neutrophils, the first cells responding to an implanted biomaterial, are now known to play an integral part in angiogenesis in multiple tissues and exhibit considerable potential for driving angiogenesis in the context of tissue regeneration. In terms of biomaterial-guided in situ tissue regeneration, harnessing the proangiogenic potential of the neutrophil through its robust secretion of matrix metalloproteinase 9 (MMP-9) may provide a mechanism to improve biomaterial performance by initiating matrix reprogramming. This review will discuss neutrophils as matrix reprogrammers and what is currently known about their ability to create a microenvironment that is more conducive for angiogenesis and tissue regeneration through the secretion of MMP-9. It will first review a set of ground-breaking studies in tumor biology and then present an overview of what is currently known about neutrophils and MMP-9 in biomaterial vascularization. Finally, it will conclude with potential strategies and considerations to engage neutrophils in biomaterial-guided angiogenesis and in situ tissue regeneration. Impact statement This review draws attention to a highly neglected topic in tissue engineering, the role of neutrophils in biomaterial-guided tissue regeneration and angiogenesis. Moreover, it highlights their abundant secretion of matrix metalloproteinase 9 (MMP-9) for matrix reprogramming, a topic with great potential yet to be vetted in the literature. It presents strategies and considerations for designing the next generation of immunomodulatory biomaterials. While there is literature discussing the overall role of neutrophils in angiogenesis, there are a limited number of review articles focused on this highly relevant topic in the context of biomaterial integration and tissue regeneration, making this a necessary and impactful article.

Does Neutrophil Phenotype Predict the Survival of Trauma Patients?

According to the World Health Organization (WHO), trauma is responsible for 10% of deaths and 16% of disabilities worldwide. This is considerably higher than those for malaria, tuberculosis, and HIV/AIDS combined. While the human suffering and death caused by injury is well-recognized, injury has a significant medical care cost. Better prediction of the state of trauma patients in the days immediately after trauma may reduce costs. Traumatic injuries to multiple organs can cause dysfunction in all systems of the body especially the immune system placing patients at high risk of infections and inflammatory complications which are often fatal. Neutrophils are the most abundant leukocyte in the human circulation and are crucial for the prevention of microbial disease. Significant changes in neutrophil functions such as enhanced chemotaxis, Neutrophil extracellular trap (NET)-induced cell death (NETosis), and phagocytosis occur early after injury followed by prolonged functional defects such as phagocytosis, killing mechanisms, and receptor expression. Analysis of these changes may improve the prediction of the patient's condition over time. We provide a comprehensive and up-to-date review of the literature investigating the effect of trauma on neutrophil phenotype with an underlying goal of using this knowledge to examine the predictive potential of neutrophil alterations on secondary complications in patients with traumatic injuries. We conclude that alterations in neutrophil surface markers and functions may be potential biomarkers that predict the outcome of trauma patients.

Targeting junctional adhesion molecule-C ameliorates sepsis-induced acute lung injury by decreasing CXCR4+ aged neutrophils

Sepsis is a severe inflammatory condition associated with high mortality. Transmigration of neutrophils into tissues increases their lifespan to promote deleterious function. Junctional adhesion molecule-C (JAM-C) plays a pivotal role in neutrophil transmigration into tissues. We aim to study the role of JAM-C on the aging of neutrophils to cause sepsis-induced acute lung injury (ALI). Sepsis was induced in C57BL/6J mice by cecal ligation and puncture (CLP) and JAM-C expression in serum was assessed. Bone marrow-derived neutrophils (BMDN) were treated with recombinant mouse JAM-C (rmJAM-C) ex vivo and their viability was assessed. CLP-operated animals were administrated with either isotype IgG or anti-JAM-C Ab at a concentration of 3 mg/kg and after 20 h, aged neutrophils (CXCR4⁺ ) were assessed in blood and lungs and correlated with systemic injury and inflammatory markers. Soluble JAM-C level in serum was up-regulated during sepsis. Treatment with rmJAM-C inhibited BMDN apoptosis, thereby increasing their lifespan. CLP increased the frequencies of CXCR4⁺ neutrophils in blood and lungs, while treatment with anti-JAM-C Ab significantly reduced the frequencies of CXCR4⁺ aged neutrophils. Treatment with anti-JAM-C Ab significantly reduced systemic injury markers (alanine aminotransferase, aspartate aminotransferase, and lactate dehydrogenase) as well as systemic and lung inflammatory cytokines (IL-6 and IL-1β) and chemokine (macrophage inflammatory protein-2). The blockade of JAM-C improved lung histology and reduced neutrophil contents in lungs of septic mice. Thus, reduction of the pro-inflammatory aged neutrophils by blockade of JAM-C has a novel therapeutic potential in sepsis-induced ALI.

PKD regulates actin polymerization, neutrophil deformability, and transendothelial migration in response to fMLP and trauma

Neutrophils are important mediators of the innate immune defense and of the host response to a physical trauma. Because aberrant infiltration of injured sites by neutrophils was shown to cause adverse effects after trauma, we investigated how neutrophil infiltration could be modulated at the cellular level. Our data indicate that protein kinase D (PKD) is a vital regulator of neutrophil transmigration. PKD phosphorylates the Cofilin-phosphatase Slingshot-2L (SSH-2L). SSH-2L in turn dynamically regulates Cofilin activity and actin polymerization in response to a chemotactic stimulus for neutrophils, for example, fMLP. Here, we show that inhibition of PKD by two specific small molecule inhibitors results in broad, unrestricted activation of Cofilin and strongly increases the F-actin content of neutrophils even under basal conditions. This phenotype correlates with a significantly impaired neutrophil deformability as determined by optical stretcher analysis. Consequently, inhibition of PKD impaired chemotaxis as shown by reduced extravasation of neutrophils. Consequently, we demonstrate that transendothelial passage of both, neutrophil-like NB4 cells and primary PMNs recovered from a hemorrhagic shock trauma model was significantly reduced. Thus, inhibition of PKD may represent a promising modulator of the neutrophil response to trauma.

A novel role for coinhibitory receptors/checkpoint proteins in the immunopathology of sepsis

Coinhibitory molecules, such as PD-1, CTLA-4, 2B4, and BTLA, are an important new family of mediators in the pathophysiology of severe bacterial and/or fungal infection, as well as the combined insults of shock and sepsis. Further, the expression of these molecules may serve as indicators of the immune status of the septic individual. Using PD-1:PD-L as an example, we discuss in this review how such checkpoint molecules may affect the host response to infection by mediating the balance between effective immune defense and immune-mediated tissue injury. Additionally, we explore how the up-regulation of PD-1 and/or PD-L1 expression on not only adaptive immune cells (e.g., T cells), but also on innate immune cells (e.g., macrophages, monocytes, and neutrophils), as well as nonimmune cells during sepsis and/or shock contributes to functional alterations often with detrimental sequelae.

The role of complement in the acute phase response after burns

Severe burns induce a complex systemic inflammatory response characterized by a typical prolonged acute phase response (APR) that starts approximately 4-8h after-burn and persists for months up to a year after the initial burn trauma. During this APR, acute phase proteins (APPs), including C-reactive protein (CRP) and complement (e.g. C3, C4 and C5) are released in the blood, resulting amongst others, in the recruitment and migration of inflammatory cells. Although the APR is necessary for proper wound healing, a prolonged APR can induce local tissue damage, hamper the healing process and cause negative systemic effects in several organs, including the heart, lungs, kidney and the central nervous system. In this review, we will discuss the role of the APR in burns with a specific focus on complement.

High performance mass spectrometry based proteomics reveals enzyme and signaling pathway regulation in neutrophils during the early stage of surgical trauma

PURPOSE

In clinical conditions trauma is associated with high mortality and morbidity. Neutrophils play a key role in the development of multiple organ failure after trauma EXPERIMENTAL DESIGN: To have a detailed understanding of the neutrophil activation at primary stages after trauma, neutrophils are isolated from control and surgical trauma rats in this study. Extracted proteins are analyzed using nano liquid chromatography coupled with tandem mass spectrometry.

RESULTS

A total of 2924 rat neutrophil proteins are identified in our analysis, of which 393 are found differentially regulated between control and trauma groups. By using functional pathways analysis of the 190 proteins up-regulated in surgical trauma, we found proteins related to transcription initiation and protein biosynthesis. On the other hand, among the 203 proteins down-regulated in surgical trauma we found enrichment for proteins of the immune response, proteasome degradation and actin cytoskeleton. Overall, enzyme prediction analysis revealed that regulated enzymes are directly involved in neutrophil apoptosis, directional migration and chemotaxis. Our observations are then confirmed by in silico protein-protein interaction analysis.

CONCLUSIONS AND CLINICAL RELEVANCE

Collectively, our results reveal that neutrophils drastically regulate their biochemical pathways after the early stages of surgical trauma, showing lower activity. This implies higher susceptibility of the trauma patients to infection and bystander tissues damage.

Cytochrome c modulates the mitochondrial signaling pathway and polymorphonuclear neutrophil apoptosis in bile duct-ligated rats

It has been observed that polymorphonuclear neutrophils (PMN) increase in number and function during obstructive jaundice (OJ). However, the precise mechanisms underlying PMN apoptosis during OJ remain poorly understood. The aim of the present study was to investigate the modulation of cytochrome c (Cytc) on the mitochondrial signaling pathway in bile duct-ligated (BDL) rats and the effect on PMN apoptosis following the intravenous administration of Cytc. Rats were randomly divided into four groups: A control group, a sham group, a BDL group and a BDL + Cytc group (rats with common bile duct ligation as well as Cytc intravenous injection). Blood samples were collected from the inferior vein cava for biochemical analysis and separation of the PMN. PMN apoptosis was evaluated using flow cytometry. The mitochondrial membrane potential (ΔΨm) of PMN was detected by rhodamine-123 staining. The Cytc protein expression levels were examined using western blotting. PMN mitochondria were observed using transmission electron microscopy. The results of the present study revealed that the PMN apoptosis rate in rats decreased gradually from 12 to 72 h following BDL to levels that were significantly lower than those of the control group and the sham group. Compared with the corresponding time point of the BDL group, the BDL + Cytc group showed a significantly increased PMN apoptosis rate. The mean fluorescence intensity (MFI) of ΔΨm decreased from 12 to 72 h following BDL, and was significantly increased compared with the control and sham groups. MFI in the BDL + Cytc group was higher compared with that in the BDL group. Cytc expression levels increased in the mitochondria and decreased in the cytoplasm from the 12 to 72 h in the BDL group, which was significantly different from that in the control and sham groups at the corresponding time points. Compared with the BDL group, Cytc expression levels in the cytoplasm for the BDL + Cytc group tended to gradually and significantly increase. Morphological changes in PMN mitochondria were marginal in BDL rats and marked in the BDL + Cytc group. In the BDL rats, PMN apoptosis was inhibited, a process induced by the mitochondrial apoptotic signaling pathway in which Cytc has an important role. High ΔΨm in the mitochondria and decreased Cytc expression levels in the cytoplasm result in PMN apoptosis inhibition. Intravenous injection of Cytc may help compensate for the lack of Cytc proteins in the cytoplasm, inducing PMN apoptosis following BDL.

Burn-Evoked Reactive Oxygen Species Immediately After Injury are Crucial to Restore the Neutrophil Function Against Postburn Infection in Mice

Although reactive oxygen species (ROS) basically play beneficial roles to maintain host homeostasis against external disturbance/stress including infection, excessive ROS generation by activated neutrophils can sometimes cause organ damage. We investigated the role of burn-induced ROS generation in the injured hosts, focusing on postburn infection. C57BL/6 mice received a 20% full-thickness burn injury. In these mice, the burn-induced ROS generation was inhibited during and immediately after injury by pretreatment with superoxide dismutase (at 1 h before and immediately before injury), or the subsequent ROS production was inhibited posttreatment with superoxide dismutase (at 1 and 2 h after injury), which could not scavenge the ROS produced immediately after injury. As expected, inhibition of ROS production during/immediately after injury reduced the burn-induced pulmonary damage at 6 h, whereas inhibition of the subsequent ROS production did not lead to any improvements. Burn injury rendered the mice susceptible to bacterial infection at 5 days after injury and impaired bactericidal activity of neutrophils. Nevertheless, inhibition of the ROS production during/immediately after injury did not improve the burn-induced susceptibility to infection or the neutrophil dysfunction. Interestingly, inhibition of the subsequent ROS production potently restored the neutrophil functions and hematopoietic function of the bone marrow myelocytes, thereby improving the postburn infection. Thus, although the inhibition of burn-evoked ROS generation is effective against burn-induced organ injury, it may be ineffective against postburn infection. Preservation of the immediate burn-evoked ROS production, but the inhibition of subsequent ROS production, may be crucial to protect against postburn infection.

Staurosporine resistance in inflammatory neutrophils is associated with the inhibition of caspase- and proteasome-mediated Mcl-1 degradation

Apoptosis resistance in activated neutrophils is known to be associated with collateral damage of surrounding tissue, as well as immune and organ dysfunction. Thus, the safe removal of neutrophils by apoptosis induction represents a prerequisite for the resolution of inflammation. Here, we report that intrinsic apoptosis resistance in human neutrophils, isolated from severely injured patients, is based on enhanced stabilization of antiapoptotic myeloid cell leukemia 1 and subsequent impairment of downstream apoptotic pathways. Whereas extrinsic apoptosis induction by the activation of Fas death receptor on inflammatory neutrophils was accompanied by caspase- and proteasome-mediated myeloid cell leukemia 1 degradation, intrinsic apoptosis induction by staurosporine led to a significant stabilization of myeloid cell leukemia 1 protein, which impeded on truncated forms of B cell lymphoma 2-associated X protein and B cell lymphoma 2 homology domain 3-interacting domain death translocation and subsequent cytochrome c release from the mitochondria. We show further that profound inhibition of myeloid cell leukemia 1 degradation is based on the inhibition of caspases and sustained activation of kinases involved in cell survival, such as Akt. Accordingly, impeded myeloid cell leukemia 1 phosphorylation on Ser159 by glycogen synthase kinase 3 and protein ubiquitination has been demonstrated. Inhibition of myeloid cell leukemia 1 activity markedly increased sensitivity to staurosporine-induced cell death. Altogether, these results provide new insights into the mechanisms underlying myeloid cell leukemia 1-mediated apoptosis resistance to staurosporine under inflammatory situations and should be considered for the development of novel therapeutic strategies.

Design, synthesis and antiproliferative activity of novel heterobivalent hybrids based on imidazo[2,1-b][1,3,4]thiadiazole and imidazo[2,1-b][1,3]thiazole scaffolds

Heterobivalent ligands constituted by two different pharmacophores that bind to different molecular targets or to two distinct sites on the same molecular target could be one of the methods used for the treatment of cancer. In view of the importance of imidazo[1,2-b][1,3]thiazole and imidazo[1,2-b][1,3,4]thiadiazole as privileged structures for the preparation of novel anticancer agents, we decided to explore the synthesis and biological evaluation of molecular conjugates comprising these fused bicyclic systems tethered at their C-6 position by a meta-(α-bromoacryloylamido)phenyl moiety. We found that most of the hybrid compounds displayed high antiproliferative activity toward a wide panel of cancer cell lines, with one-digit micromolar to submicromolar 50% inhibitory concentrations (IC50). We have observed that selected compounds 7d, 7e, 7n and 8c induced apoptosis, which was associated with the release of cytochrome c and cleavage of multiple caspases. Overexpression of the protective mitochondrial protein Bcl-2 did not confer protection to cell death induced by these compounds.

The impact of trauma on neutrophil function

A well described consequence of traumatic injury is immune dysregulation, where an initial increase in immune activity is followed by a period of immune depression, the latter leaving hospitalised trauma patients at an increased risk of nosocomial infections. Here, we discuss the emerging role of the neutrophil, the most abundant leucocyte in human circulation and the first line of defence against microbial challenge, in the initiation and propagation of the inflammatory response to trauma. We review the findings of the most recent studies to have investigated the impact of trauma on neutrophil function and discuss how alterations in neutrophil biology are being investigated as potential biomarkers by which to predict the outcome of hospitalised trauma patients. Furthermore, with trauma-induced changes in neutrophil biology linked to the development of such post-traumatic complications as multiple organ failure and acute respiratory distress syndrome, we highlight an area of research within the field of trauma immunology that is gaining considerable interest: the manipulation of neutrophil function as a means by which to potentially improve patient outcome.

Synthesis and biological evaluation of hydroxycinnamic acid hydrazide derivatives as inducer of caspase-3

In order to generate compounds with superior antitumor activity and reduced toxicity, twelve new hydroxycinnamic acid hydrazide derivatives were synthesized and evaluated for their antiproliferative activities against two cancer cell lines (H1299 lung carcinoma cells and MCF-7 breast cancer cells), and compared to two normal counterparts (NL-20 lung epithelial cells and H184B5F5/M10 breast cells) by MTT method. The results demonstrated that some of these compounds possessed good antiproliferative activity against the two cancer cell lines. Among them, compound 2c was active against the growth of H1299 lung carcinoma cells with IC50 values of 1.50 μM, which was more active than the positive topotecan (IC50 = 4.18 μM). Simultaneously, it showed lower cytotoxic effects on normal NL-20 lung epithelial cells (IC50 > 10 μM). Mechanism studies indicated that it induced cell cycle arrest at G2/M phase followed by activation of caspase-3, and consequently caused the cell death. Further studies on the structure optimization are ongoing.

Evaluation of neutrophil apoptosis in horses with acute abdominal disease

OBJECTIVE

To quantify peripheral blood neutrophil apoptosis in equine patients with acute abdominal disease (ie, colic) caused by strangulating or nonstrangulating intestinal lesions and compare these values with values for horses undergoing elective arthroscopic surgery.

ANIMALS

20 client-owned adult horses.

PROCEDURES

Peripheral blood was collected from horses immediately prior to and 24 hours after surgery for treatment of colic (n = 10) or elective arthroscopic surgery (10), and neutrophils were counted. Following isolation by means of a bilayer colloidal silica particle gradient and culture for 24 hours, the proportion of neutrophils in apoptosis was detected by flow cytometric evaluation of cells stained with annexin V and 7-aminoactinomycin D. Values were compared between the colic and arthroscopy groups; among horses with colic, values were further compared between horses with and without strangulating intestinal lesions.

RESULTS

Percentage recovery of neutrophils was significantly smaller in preoperative samples (median, 32.5%) and in all samples combined (35.5%) for the colic group, compared with the arthroscopy group (median, 66.5% and 58.0%, respectively). No significant differences in the percentages of apoptotic neutrophils were detected between these groups. Among horses with colic, those with strangulating intestinal lesions had a significantly lower proportion of circulating apoptotic neutrophils in postoperative samples (median, 18.0%) than did those with nonstrangulating lesions (66.3%).

CONCLUSIONS AND CLINICAL RELEVANCE

The smaller proportion of apoptotic neutrophils in horses with intestinal strangulation suggested that the inflammatory response could be greater or prolonged, compared with that of horses with nonstrangulating intestinal lesions. Further investigations are needed to better understand the relationship between neutrophil apoptosis and inflammation during intestinal injury.

Modulation of Neutrophil Apoptosis and the Resolution of Inflammation through β2 Integrins

Precise control of the neutrophil death program provides a balance between their defense functions and safe clearance, whereas impaired regulation of neutrophil death is thought to contribute to a wide range of inflammatory pathologies. Apoptosis is essential for neutrophil functional shutdown, removal of emigrated neutrophils, and timely resolution of inflammation. Neutrophils receive survival and pro-apoptosis cues from the inflammatory microenvironment and integrate these signals through surface receptors and common downstream mechanisms. Among these receptors are the leukocyte-specific membrane receptors β2 integrins that are best known for regulating adhesion and phagocytosis. Accumulating evidence indicate that outside-in signaling through the β2 integrin Mac-1 can generate contrasting cues in neutrophils, leading to promotion of their survival or apoptosis. Binding of Mac-1 to its ligands ICAM-1, fibrinogen, or the azurophilic granule enzyme myeloperoxidase suppresses apoptosis, whereas Mac-1-mediated phagocytosis of bacteria evokes apoptotic cell death. Mac-1 signaling is also target for the anti-inflammatory, pro-resolving mediators, including lipoxin A4, aspirin-triggered lipoxin A4, and resolvin E1. This review focuses on molecular mechanisms underlying Mac-1 regulation of neutrophil apoptosis and highlights recent advances how hierarchy of survival and pro-apoptosis signals can be harnessed to facilitate neutrophil apoptosis and the resolution of inflammation.

Molecular mechanisms underlying delayed apoptosis in neutrophils from multiple trauma patients with and without sepsis

Delayed neutrophil apoptosis and overshooting neutrophil activity contribute to organ dysfunction and subsequent organ failure in sepsis. Here, we investigated apoptotic signaling pathways that are involved in the inhibition of spontaneous apoptosis in neutrophils isolated from major trauma patients with uneventful outcome as well as in those with sepsis development. DNA fragmentation in peripheral blood neutrophils showed an inverse correlation with the organ dysfunction at d 10 after trauma in all patients, supporting the important role of neutrophil apoptosis regulation for patient's outcome. The expression of the antiapoptotic Bcl-2 protein members A1 and Mcl-1 were found to be diminished in the septic patients at d 5 and d 10 after trauma. This decrease was also linked to an impaired intrinsic apoptosis resistance, which has been previously shown to occur in neutrophils during systemic inflammation. In patients with sepsis development, delayed neutrophil apoptosis was found to be associated with a disturbed extrinsic pathway, as demonstrated by reduced caspase-8 activity and Bid truncation. Notably, the expression of Dad1 protein, which is involved in protein N-glycosylation, was significantly increased in septic patients at d 10 after trauma. Taken together, our data demonstrate that neutrophil apoptosis is regulated by both the intrinsic and extrinsic pathway, depending on patient's outcome. These findings might provide a molecular basis for new strategies targeting cell death pathways in apoptosis-resistant neutrophils during systemic inflammation.

Regulation of neutrophil survival/apoptosis by Mcl-1

Neutrophil granulocytes have the shortest lifespan among leukocytes in the circulation and die via apoptosis. At sites of infection or tissue injury, prolongation of neutrophil lifespan is critical for effective host defense. Apoptosis of inflammatory neutrophils and their clearance are critical control points for termination of the inflammatory response. Evasion of neutrophil apoptosis aggravates local injury and leads to persistent tissue damage. The short-lived prosurvival Bcl-2 family protein, Mcl-1 (myeloid cell leukemia-1), is instrumental in controlling apoptosis and consequently neutrophil lifespan in response to rapidly changing environmental cues during inflammation. This paper will focus on multiple levels of control of Mcl-1 expression and function and will discuss targeting Mcl-1 as a potential therapeutic strategy to enhance the resolution of inflammation through accelerating neutrophil apoptosis.

Increased serum soluble Fas after major trauma is associated with delayed neutrophil apoptosis and development of sepsis

Introduction

Deregulated apoptosis and overshooting neutrophil functions contribute to immune and organ dysfunction in sepsis and multiple organ failure (MOF). In the present study, we determined the role of soluble Fas (sFas) in the regulation of posttraumatic neutrophil extrinsic apoptosis and the development of sepsis.

Methods

Forty-seven major trauma patients, 18 with and 29 without sepsis development during the first 10 days after trauma, were enrolled in this prospective study. Seventeen healthy volunteers served as controls. Blood samples from severely injured patients were analyzed at day 1, day 5 and day 9 after major trauma. sFas levels, plasma levels of neutrophil elastase (PMNE) and levels of interleukin (IL)-6 were quantified by enzyme-linked immunosorbent assay and related to patients' Sequential Organ Failure Assessment (SOFA) score and Multiple Organ Dysfunction Score (MODS). Neutrophil apoptosis was determined by propidium iodide staining of fragmented DNA and flow cytometry. sFas-mediated effects on neutrophil apoptosis were investigated in cells cultured with agonistic anti-Fas antibodies in the presence of recombinant sFas, sFas-depleted serum or untreated serum from septic patients.

Results

Serum levels of sFas in patients who later developed sepsis were significantly increased at day 5 (P < 0.01) and day 9 (P < 0.05) after trauma compared with patients with uneventful recovery. Apoptosis of patient neutrophils was significantly decreased during the observation period compared with control cells. Moreover, Fas-mediated apoptosis of control neutrophils was efficiently inhibited by recombinant sFas and serum from septic patients. Depletion of sFas from septic patient sera diminished the antiapoptotic effects. In septic patients, sFas levels were positively correlated with SOFA at day 1 (r = 0.7, P < 0.001), day 5 (r = 0.62, P < 0.01) and day 9 (r = 0.58, P < 0.01) and with PMNE and leukocyte counts (r = 0.49, P < 0.05 for both) as well as MODS at day 5 (r = 0.56, P < 0.01) after trauma.

Conclusions

Increased sFas in patients with sepsis development impairs neutrophil extrinsic apoptosis and shows a positive correlation with the organ dysfunction scores and PMNE. Therefore, sFas might be a therapeutic target to prevent posttrauma hyperinflammation and sepsis.

Pharmacotherapy for prevention and treatment of acute respiratory distress syndrome: current and experimental approaches

The acute respiratory distress syndrome (ARDS) arises from direct and indirect injury to the lungs and results in a life-threatening form of respiratory failure in a heterogeneous, critically ill patient population. Critical care technologies used to support patients with ARDS, including strategies for mechanical ventilation, have resulted in improved outcomes in the last decade. However, there is still a need for effective pharmacotherapies to treat ARDS, as mortality rates remain high. To date, no single pharmacotherapy has proven effective in decreasing mortality in adult patients with ARDS, although exogenous surfactant replacement has been shown to reduce mortality in the paediatric population with ARDS from direct causes. Several promising therapies are currently being investigated in preclinical and clinical trials for treatment of ARDS in its acute and subacute, exudative phases. These include exogenous surfactant therapy, β₂-adrenergic receptor agonists, antioxidants, immunomodulating agents and HMG-CoA reductase inhibitors (statins). Recent research has also focused on prevention of acute lung injury and acute respiratory distress in patients at risk. Drugs such as captopril, rosiglitazone and incyclinide (COL-3), a tetracycline derivative, have shown promising results in animal models, but have not yet been tested clinically. Further research is needed to discover therapies to treat ARDS in its late, fibroproliferative phase. Given the vast number of negative clinical trials to date, it is unlikely that a single pharmacotherapy will effectively treat all patients with ARDS from differing causes. Future randomized controlled trials should target specific, more homogeneous subgroups of patients for single or combination therapy.

Interleukin-18 delays neutrophil apoptosis following alcohol intoxication and burn injury

Studies have shown that burn patients who are intoxicated at the time of injury are more susceptible to infection and have a higher incidence of mortality. A major cause of death in burn and trauma patients regardless of their alcohol (EtOH) exposure is multiple organ dysfunction, which is driven in part by the systemic inflammatory response and activated neutrophils. Neutrophils are short lived and undergo apoptosis to maintain homeostasis and resolution of inflammation. A delay in apoptosis of neutrophils is one important mechanism which allows for their prolonged presence and the release of potentially harmful enzymes. The purpose of this study was to examine whether EtOH intoxication combined with burn injury influences neutrophil apoptosis and whether IL-18 plays any role in this setting. To accomplish this investigation, rats were gavaged with EtOH (3.2 g/kg) 4 h before being subjected to sham or burn injury of ~12.5% of the total body surface area, and then killed on d 1 after injury. Peripheral blood neutrophils were isolated and lysed. The lysates were analyzed for pro- and antiapoptotic proteins. We found that EtOH combined with burn injury prolonged neutrophil survival. This prolonged neutrophil survival was accompanied by a decrease in the levels of the neutrophil proapoptotic protein Bax, and an increase in antiapoptotic proteins Mcl-1 and Bcl-xl. Administration of IL-18 antibody following burn injury normalized the levels of Bax, Mcl-1 and Bcl-xl. The decrease in caspase-3 and DNA fragmentation observed following EtOH and burn injury was also normalized in rats treated with anti-IL-18 antibody. These findings suggest that IL-18 delays neutrophil apoptosis following EtOH and burn injury by modulating the pro- and antiapoptotic proteins.

Mcl-1-mediated impairment of the intrinsic apoptosis pathway in circulating neutrophils from critically ill patients can be overcome by Fas stimulation

The systemic inflammatory response syndrome and subsequent organ failure are mainly driven by activated neutrophils with prolonged life span, which is believed to be due to apoptosis resistance. However, detailed underlying mechanisms leading to neutrophil apoptosis resistance are largely unknown, and possible therapeutic options to overcome this resistance do not exist. Here we report that activated neutrophils from severely injured patients exhibit cell death resistance due to impaired activation of the intrinsic apoptosis pathway, as evidenced by limited staurosporine-induced mitochondrial membrane depolarization and decreased caspase-9 activity. Moreover, we found that these neutrophils express high levels of antiapoptotic Mcl-1 and low levels of proapoptotic Bax protein. Mcl-1 up-regulation was dependent on elevated concentrations of GM-CSF in patient serum. Accordingly, increased Mcl-1 protein stability and GM-CSF serum concentrations were shown to correlate with staurosporine-induced apoptosis resistance. However, cross-linking of neutrophil Fas by immobilized agonistic anti-Fas IgM resulted in caspase-dependent mitochondrial membrane depolarization and apoptosis induction. In conclusion, the observed impairment of the intrinsic pathway and the resulting apoptosis resistance may be overcome by immobilized agonistic anti-Fas IgM. Targeting of neutrophil Fas by immobilized agonistic effector molecules may represent a new therapeutic tool to limit neutrophil hyperactivation and its sequelae in patients with severe immune disorders.

Cell death and stress signaling in glycogen storage disease type I

Cell death has been traditionally classified in apoptosis and necrosis. Apoptosis, known as programmed cell death, is an active form of cell death mechanism that is tightly regulated by multiple cellular signaling pathways and requires ATP for its appropriate process. Apoptotic death plays essential roles for successful development and maintenance of normal cellular homeostasis in mammalian. In contrast to apoptosis, necrosis is classically considered as a passive cell death process that occurs rather by accident in disastrous conditions, is not required for energy and eventually induces inflammation. Regardless of different characteristics between apoptosis and necrosis, it has been well defined that both are responsible for a wide range of human diseases. Glycogen storage disease type I (GSD-I) is a kind of human genetic disorders and is caused by the deficiency of a microsomal protein, glucose-6-phosphatase-α (G6Pase-α) or glucose-6-phosphate transporter (G6PT) responsible for glucose homeostasis, leading to GSD-Ia or GSD-Ib, respectively. This review summarizes cell deaths in GSD-I and mostly focuses on current knowledge of the neutrophil apoptosis in GSD-Ib based upon ER stress and redox signaling.

A role for IL-18 in human neutrophil apoptosis

Decreased neutrophil apoptosis is associated with persistent inflammation, the severity of which correlates with serum IL-18 levels. IL-18 receptors as well as Toll-like receptors, including Toll-like receptor 4, a receptor for LPS, possess a highly conserved intracellular domain called "Toll-IL-1R domain" and activate overlapping signaling pathways. Here, we show that IL-18 modulates neutrophil apoptosis and compare its mechanism of action with LPS. We found that both IL-18 and LPS decreased neutrophil apoptosis in a similar dose- and time-dependent fashion. However, pretreatment with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 increased apoptosis more effectively in IL-18- than in LPS-stimulated cells, whereas the ERK inhibitor PD98059 had the same effect in both. In contrast, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 had no influence on apoptosis at all. Neutrophils constitutively expressed mRNA for IL-18 receptor beta, but little or no receptor alpha, both of which increased during coculture with either IL-18 or LPS in a time- and dose-dependent manner. Of the Bcl-2 family, antiapoptotic A1/Bfl-1 tended to increase on IL-18 and LPS stimulation, but was further increased despite increased apoptosis in the presence of MAPK inhibitors. Thus, human neutrophils can express mRNA for IL-18 receptors alpha and beta, and IL-18, like LPS, inhibits neutrophil apoptosis by activating PI3K and ERK pathways but not p38MAPK. However, PI3K may play more important role(s) in IL-18- than in LPS-induced inhibition of apoptosis. Mitogen-activated protein kinases seem to mediate antiapoptotic signals through factors other than Bcl-2 gene family expression.

Epithelial cell apoptosis and neutrophil recruitment in acute lung injury-a unifying hypothesis? What we have learned from small interfering RNAs

In spite of protective ventilatory strategies, Acute Lung Injury (ALI) remains associated with high morbidity and mortality. One reason for the lack of therapeutic options might be that ALI is a co-morbid event associated with a diverse family of diseases and, thus, may be the result of distinct pathological processes. Among them, activated neutrophil- (PMN-) induced tissue injury and epithelial cell apoptosis mediated lung damage represent two potentially important candidate pathomechanisms that have been put forward. Several approaches have been undertaken to test these hypotheses, with substantial success in the treatment of experimental forms of ALI. With this in mind, we will summarize these two current hypotheses of ALI briefly, emphasizing the role of apoptosis in regulating PMN and/or lung epithelial cell responses. In addition, the contribution that Fas-mediated inflammation may play as a potential biological link between lung cell apoptosis and PMN recruitment will be considered, as well as the in vivo application of small interfering RNA (siRNA) as a novel approach to the inhibition of ALI and its therapeutic implications.

Role of polymorphonuclear neutrophils on infectious complications stemming from Enterococcus faecalis oral infection in thermally injured mice

Thermally injured mice are susceptible to Enterococcus faecalis translocation. In this study, the role of polymorphonuclear neutrophils (PMN) on the development of sepsis stemming from E. faecalis translocation was studied in SCID-beige (SCIDbg) mice depleted of PMN (SCIDbgN mice) or macrophages (Mphi) and PMN (SCIDbgMN mice). Sepsis was not developed in SCIDbgN mice orally infected with E. faecalis, while the orally infected pathogen spread systemically in the same mice inoculated with PMN from thermally injured mice (TI-PMN). SCIDbgMN mice were shown to be greatly susceptible to sepsis caused by E. faecalis translocation, while orally infected E. faecalis did not spread into sepsis in the same mice that were previously inoculated with Mphi from unburned SCIDbg mice (resident Mphi). In contrast, orally infected E. faecalis spread systemically in SCIDbgMN mice inoculated with resident Mphi and TI-PMN, while all SCIDbgMN mice inoculated in combination with resident Mphi and PMN from unburned SCIDbg mice survived after the infection. After cultivation with TI-PMN in a dual-chamber transwell, resident Mphi converted to alternatively activated Mphi, which are inhibitory on the generation of classically activated Mphi (typical effector cells in host antibacterial innate immunities). TI-PMN were characterized as immunosuppressive PMN (PMN-II) with abilities to produce cc-chemokine ligand-2 and IL-10. These results indicate that PMN-II appearing in response to burn injury impair host antibacterial resistance against sepsis stemming from E. faecalis translocation through the conversion of resident Mphi to alternatively activated Mphi.

Constitutive neutrophil apoptosis: mechanisms and regulation

Neutrophil constitutive death is a critical cellular process for modulating neutrophil number and function, and it plays an essential role in neutrophil homeostasis and the resolution of inflammation. Neutrophils die due to programmed cell death or apoptosis. In this article, we review recent studies on the mechanism of neutrophil apoptosis. The involvement of caspase, calpain, reactive oxygen species, cellular survival/death signaling pathways, mitochondria, and BCL-2 family member proteins are discussed. The fate of neutrophils can be influenced within the inflammatory microenvironment. We summarize the current understanding regarding the modulation of neutrophil apoptotic death by various extracellular stimuli such as proinflammatory cytokines, cell adhesion, phagocytosis, red blood cells, and platelets. The involvement of neutrophil apoptosis in infectious and inflammatory diseases is also addressed.

Apoptosis in Critical Illness: A Primer for the Intensivist

The complexities of the cell cycle have occupied a prominent place in the history of cellular biology. Recognition of the process of mitosis dates back over a century, when Fol, Butschli, and Strasburger identified a network of intracellular points and lines, then called the karyokinetic figure, and today known as the mitotic apparatus. This discovery, dating to 1873, laid the foundation for the discovery of chromosomes and, later, the fundamental biologic processes of mitosis and meiosis [1]. But, while cellular growth and proliferation were understood to be essential to the emergence of multicellular organisms, the corollary — that controlled cell death must be part of this calculus of cellular homeostasis — was not appreciated until quite recently. Although cell death was first described in 1859 by Virchow, it took more than a century to appreciate the importance of programmed cell death as a physiological process that eliminated unwanted cells [2]. The term ‘apoptosis’ was coined in 1972 by Kerr, Wyllie, and Currie to describe a distinct type of cell death characterized by the degradation of cellular constituents into membrane-bound apoptotic bodies [3]. Since then, recognition of the importance of apoptosis in health and disease, and an understanding of its cellular mechanisms, has increased exponentially.

Apoptosis in Critical Illness: A Primer for the Intensivist

The complexities of the cell cycle have occupied a prominent place in the history of cellular biology. Recognition of the process of mitosis dates back over a century, when Fol, Butschli, and Strasburger identified a network of intracellular points and lines, then called the karyokinetic figure, and today known as the mitotic apparatus. This discovery, dating to 1873, laid the foundation for the discovery of chromosomes and, later, the fundamental biologic processes of mitosis and meiosis [1]. But, while cellular growth and proliferation were understood to be essential to the emergence of multicellular organisms, the corollary — that controlled cell death must be part of this calculus of cellular homeostasis — was not appreciated until quite recently. Although cell death was first described in 1859 by Virchow, it took more than a century to appreciate the importance of programmed cell death as a physiological process that eliminated unwanted cells [2]. The term ‘apoptosis’ was coined in 1972 by Kerr, Wyllie, and Currie to describe a distinct type of cell death characterized by the degradation of cellular constituents into membrane-bound apoptotic bodies [3]. Since then, recognition of the importance of apoptosis in health and disease, and an understanding of its cellular mechanisms, has increased exponentially.

“Systemic apoptotic response” after thermal burns

The systemic pathophysiologic changes following thermal injuries affect multiple organs and body systems leading to clinical manifestations including shock, intestinal alterations, respiratory and renal failure, immunosuppression and others. Recent advances in the comprehension of mechanisms underlying systemic complications of thermal injuries have contributed to uncover part of the cellular and molecular basis that underlie such changes. Recently, programmed cell death (apoptosis) has been considered playing an important role in the development of such pathological events. Therefore, investigators utilizing animal models and clinical studies involving human primates have produced a large body of information suggesting that apoptosis is associated with most of the tissue damages triggered by severe thermal injuries. In order to draw the attention on the important role of apoptosis on systemic complications of thermal injuries, in this review we describe most of these studies, discuss possible cellular and molecular mechanisms and indicate ways to utilize them for the development of therapeutic strategies by which apoptosis may be prevented or counteracted.

Circulating levels of cytochrome c after resuscitation from cardiac arrest: a marker of mitochondrial injury and predictor of survival

Ca(2+) overload and reactive oxygen species can injure mitochondria during ischemia and reperfusion. We hypothesized that mitochondrial injury occurs during cardiac resuscitation, causing release of cytochrome c to the cytosol and bloodstream while activating apoptotic pathways. Plasma cytochrome c was measured using reverse-phase HPLC and Western immunoblotting in rats subjected to 4 or 8 min of untreated ventricular fibrillation and 8 min of closed-chest resuscitation followed by 240 min of postresuscitation hemodynamic observation. A sham group served as control. Plasma cytochrome c rose progressively to levels 10-fold higher than in sham rats 240 min after resuscitation (P < 0.01), despite reversal of whole body ischemia (decreases in arterial lactate). Cytochrome c levels were inversely correlated with left ventricular stroke work (r = -0.40, P = 0.02). Western immunoblotting of left ventricular tissue demonstrated increased levels of 17-kDa cleaved caspase-3 fragments in the cytosol. Plasma cytochrome c was then serially measured in 12 resuscitated rats until the rat died or cytochrome c returned to baseline. In three survivors, cytochrome c rose slightly to <or=2 microg/ml and returned to baseline within 96 h. In nine nonsurvivors, cytochrome c rose progressively to significantly higher maximal levels [4.6 (SD 2.0) vs. 1.6 (SD 0.3) microg/ml, P = 0.029] and at faster rates [0.7 (SD 0.5) vs. 0.1 (SD 0.1) microg.ml(-1).h(-1), P = 0.046] than in survivors. Plasma cytochrome c may represent a novel in vivo marker of mitochondrial injury after resuscitation from cardiac arrest that relates inversely with survival outcome.

Apoptosis and necrosis: a review for surgeons

BACKGROUND

Orderly cell death, termed apoptosis, features a morphology that is distinct from necrotic, or accidental, cell death. As the body of literature on apoptotic cell death grows, it is difficult for practicing surgeons to stay current with the involved mechanisms and their biologic significance.

METHODS

A MEDLINE/PubMed literature search was conducted, followed by manual crossreferencing, to identify relevant articles published in the English language between 1972 and 2004.

RESULTS

Apoptosis is now known to be involved in numerous disease states. Ischemia-reperfusion injury and acute pancreatitis are but two surgical entities in which the balance of apoptotic and necrotic cell death has a profound effect on clinical outcome. Similarly, the timing and extent of apoptosis in immune cells are important factors that determine the outcome of septic patients.

CONCLUSIONS

As already demonstrated in animal models, further research in this field will target opportunities for therapeutic intervention, making it increasingly important for clinicians to be familiar with apoptosis and necrosis, and their roles in normal and pathologic states.

Endotoxin inhibits apoptosis but induces primary necrosis in neutrophils

Lipopolysaccharide (LPS) is known to prolong the functional lifespan of neutrophils at a site of infection by preventing apoptosis through inhibitor of apoptosis proteins (IAPs). We hypothesized that the increased neutrophil lifespan ultimately leads to a larger fraction of cells undergoing uncontrolled, primary necrosis. Diluted venous whole blood was incubated with increasing concentrations of LPS for up to 36 hr. The percentages of apoptotic, necrotic and viable neutrophils were assessed using the Annexin V/propidium iodide flow cytometric assay. LPS led to a reduction of neutrophil apoptosis and increased the number of viable cells at 12, 24, and 36 hr of incubation. At the same time intervals, there was a significant increase in the percentage of cells undergoing primary necrosis for all concentrations of LPS (e.g., 10 ng/ml LPS at 24 h produced a mean increase from 9.6% in controls to 30.6%, p < 0.001). This increase in direct neutrophil necrosis following LPS activation may amplify local proinflammatory effects through less well controlled release of neutrophil contents into surrounding tissue.

Aminopeptidase N (CD13) Regulates Tumor Necrosis Factor-α-induced Apoptosis in Human Neutrophils

Neutrophil apoptosis plays a central role in the resolution of granulocytic inflammation. We have shown previously that tumor necrosis factor-alpha (TNFalpha) enhances the rate of neutrophil apoptosis at early time points via a mechanism involving both TNF receptor (TNFR) I and TNFRII. Here we reveal a marked but consistent variation in the magnitude of the pro-apoptotic effect of TNFalpha in neutrophils isolated from healthy donors, and we show that inhibition of cell surface aminopeptidase N (APN) using actinonin, bestatin, or inhibitory peptides significantly enhanced the efficacy of TNFalpha-induced killing. Notably, an inverse correlation is shown to exist between neutrophil APN activity and the sensitivity of donor cells to TNFalpha-induced apoptosis. Inhibition of cell surface APN appears to interfere with the shedding of TNFRI, and as a consequence results in augmented TNFalpha-induced apoptosis, cell polarization, and TNFalpha-primed, formyl-methionyl-leucyl-phenylalanine-stimulated respiratory burst. Of note, actinonin and bestatin had no effect on TNFRII expression under resting or TNFalpha-stimulated conditions and did not alter CXCRI or CXCRII expression. These data suggest significant variation in the activity of APN/CD13 on the cell surface of neutrophils in normal individuals and reveal a novel mechanism whereby APN/CD13 regulates TNFalpha-induced apoptosis via inhibition of TNFRI shedding. This has therapeutic relevance for driving neutrophil apoptosis in vivo.

Kinetics of pulmonary neutrophil recruitment and clearance in a natural and spontaneously resolving model of airway inflammation

BACKGROUND

Neutrophil apoptosis and phagocytic clearance have been proposed as key determinants affecting the resolution of airway inflammation. Objective To determine the kinetics of neutrophil priming, recruitment, activation and subsequent clearance in a naturally occurring equine disease model of neutrophilic pulmonary inflammation.

METHODS AND RESULTS

A 5 h mouldy hay/straw challenge in hypersensitive horses induced transient pulmonary dysfunction lasting 4 days. At 24 h circulating neutrophils were primed and displayed delayed rates of spontaneous apoptosis in vitro. Neutrophil numbers in the airspaces peaked at 5 h and then fell abruptly, returning to pre-challenge levels by 4 days. Airspace neutrophils demonstrated increased respiratory burst activity compared with circulating cells and equine neutrophil elastase 2A concentrations increased in parallel with neutrophil numbers indicating in vivo priming and degranulation. The number of apoptotic neutrophils and proportion of alveolar macrophages containing phagocytosed apoptotic neutrophils increased significantly at 24 h and 4 days post-challenge corresponding to the period of most rapid neutrophil clearance.

CONCLUSION

This is the first demonstration of spontaneous neutrophil apoptosis and phagocytic removal in a natural disease model of airway inflammation and provides critical kinetic data to support the hypothesis that this clearance pathway plays a central role in the resolution of neutrophilic inflammation.

Regulation of Fas-mediated apoptosis in neutrophils after surgery-induced acute inflammation

BACKGROUND

Neutrophils undergo rapid Fas-mediated apoptosis during in vitro culture. The purpose of this study was to investigate the effects of surgical stress upon the Fas-mediated apoptotic response in circulating neutrophils.

MATERIALS AND METHODS

Blood samples were drawn from eight patients with a mandibular prognathism, and who had undergone a bilateral sagittal split ramus osteotomy, at 2 days before, and at 1 and 5 days after surgery. The circulating neutrophils in each blood sample were then evaluated for their susceptibility to Fas-mediated apoptosis in either the presence or the absence of autogenous plasma.

RESULTS

Fas-induced apoptosis in the neutrophils of these surgically treated patients was found to be slightly accelerated at 1 day postoperatively in the presence of FBS, compared with 2 days preoperatively and 5 days postoperatively. However, we obtained different results for these experiments in the presence of autogenous plasma. The Fas-induced apoptotic response levels in the neutrophils at day 1 postsurgery following exposure to autogenous plasma were significantly suppressed compared with the levels at both 2 days preoperatively and 5 days postoperatively. The Fas expression levels on the cell surface of the neutrophils were not altered, but the levels of soluble Fas (sFas) in the plasma were reduced to almost inverse levels during the postoperative periods. The levels of granulocyte-macrophage colony-stimulating factor, interleukin-6, and interleukin-8 levels in the plasma were also markedly raised in the plasma from each of these patients at 1 day postoperatively. However, the anti-apoptotic effects of the plasma on the Fas-mediated neutrophil apoptosis were not influenced by the addition of their neutralizing antibodies for these cytokines. The suppressive effects of postoperative plasma on Fas-mediated neutrophil apoptosis were blocked by the phosphatidylinositol 3-kinase (PI 3-K) inhibitors, LY294002, and wortmannin. Additionally, these effects were also abrogated by the extracellular signal-regulated kinase (ERK) inhibitor, PD98059, but not by the p38 mitogen-activated protein kinase inhibitor, SB203580.

CONCLUSIONS

The increase in sFas levels in the plasma of patients with acute inflammation may lead to the inhibition of Fas-mediated neutrophil apoptosis. Moreover, the activation of the PI 3-K and ERK signaling-dependent pathways may, in part, also contribute to the down-regulation of the Fas-mediated apoptotic response in neutrophils.

Modulation of neutrophil apoptosis in plasma of patients after orthognathic surgery

BACKGROUND

Human neutrophils undergo rapid apoptosis during in vitro culture. The aim of this study was to investigate the role of interleukin-8 (IL-8) on neutrophil apoptosis in surgery-induced inflammation.

MATERIALS AND METHODS

Blood samples were drawn from 21 patients with mandibular prognathism 2 days before, and 1 and 5 days after orthognathic surgery. The IL-8 levels in the separated plasma were measured using an ELISA kit. The expression of two receptors for IL-8, CXCR1, and CXCR2, and their role in neutrophil apoptosis was evaluated using a flow cytometer.

RESULTS

The IL-8 levels in the plasma were correlated with acute inflammatory markers, such as peripheral blood neutrophil counts and C-reactive protein levels. Both IL-8 receptors were markedly raised in patient-derived neutrophils 1 day post-operatively. Recombinant IL-8 (0-100 ng/ml) suppressed apoptosis in fresh-isolated neutrophils from healthy donors dose-dependently. Neutrophil apoptosis 1 day post-operatively was slightly accelerated in the presence of fetal bovine serum compared to the value 2 days pre-operatively and 5 days post-operatively. In contrast, in the presence of autogenous plasma, neutrophil apoptosis was significantly suppressed 1 day post-operatively compared to the value 2 days pre-operatively and 5 days post-operatively. Moreover, the anti-apoptotic effect of plasma on neutrophil apoptosis was partially decreased by the addition of anti-IL-8 neutralizing antibody.

CONCLUSIONS

These results suggest that circulating neutrophils are susceptible to augmentation by IL-8 through the reinforcement of IL-8 receptors in acute inflammatory conditions. Furthermore, IL-8 may, in part, contribute to the regulation of neutrophil survival during the inflammatory response.

In Vitro Effect of Nitrogen and He-Ne Laser on the Apoptosis of Human Polymorphonuclear Cells from Burn Cases and Healthy Volunteers

OBJECTIVE

The aim of this study was to examine the effect of He-Ne and nitrogen lasers on the apoptosis of PMN in normal versus burn patients.

BACKGROUND DATA

Nitrogen and He-Ne laser exposure increases the apoptotic death rate for human macrophages. Inflammation is a major consequence of thermal injury, and polymorphonuclear cell (PMN) infiltration exacerbates inflammatory process through the release of proinflammatory cytokines. The apoptotic death instead of necrotic death of PMN under the situation may help to resolve inflammation.

METHODS

Ten healthy volunteers and 10 burn cases (30-50% burn surface) were included in the study. The PMN was separated by dextran sedimentation and density gradient centrifugation before suspending in RPMI-1640 medium supplemented with autologus serum. The cell suspension aliquoted in microwells was exposed to nitrogen (wavelength of 337 nm with power output of 3 mW) and He-Ne (LGN model no. 111, Russia, wavelength of 632.8 nm with power output of 3 mW) lasers for 10 and 5 min. The wells not exposed to laser were used as controls. After 24-36 h of incubation, the apoptotic rates were measured as percentage by morphological studies on acridine orange-ethidium bromide stained preparation using fluorescent microscope.

RESULTS

Percentage of apoptotic death increases from 32.9% (SD +/- 4.14) in control PMN to 41.97% (SD +/- 14) in PMN exposed to nitrogen laser for 5 min and further increased to 62.7% (SD +/- 15.11) with nitrogen laser exposure for 10 min. He-Ne laser exposure for 10 min increased apoptotic cell percentage to 41.9%. Increased apoptosis in PMN exposed to nitrogen laser was statistically significant (p < 0.03) both for PMN from healthy subjects and burn cases. It was significantly elevated (p = 0.005) only for PMN from healthy volunteers exposed to He-Ne laser for 10 min but not among He-Ne exposed PMN from burn cases.

CONCLUSIONS

These observations support the therapeutic application of nitrogen laser to reduce inflammation and improve wound healing for burn cases.

Limiting burn extension by transient inhibition of Connexin43 expression at the site of injury

Extension of a burn wound over the first 24h following injury is recognised clinically, and leads to diagnostic and therapeutic dilemmas. In the central nervous system, a similar spread of damage, beyond the initial injury, can occur via the spread of death signals from injured cells to their healthy neighbours via Connexin43 (Cx43) gap junction channels. In the skin, Cx43 is expressed in the basal epidermis and in fibroblasts and dermal appendages. We have used Cx43 specific antisense oligodeoxynucleotide approach to transiently down-regulate Cx43 protein in the early stages of partial thickness cutaneous burn wound healing. Antisense ODNs reduce the spread of tissue damage and neutrophil infiltration around the wound following injury. Epithelial cell proliferation is increased and the rate of wound closure is accelerated, compared to controls. Resultant scarring is smaller with less granulation tissue and more dermal appendages than controls. These findings suggest that Cx43 antisense treatment speeds partial thickness burn wound healing and reduces scarring. We suggest that this approach may provide an effective adjunct to managing partial thickness burn wounds.

Intestinal Epithelial Cells Modulate PMN Activation and Apoptosis Following Bacterial and Hypoxic Challenges

BACKGROUND

The post-ischemic gut may serve to prime and activate neutrophils which may lead to the subsequent development of the systemic inflammatory response syndrome (SIRS) and multiple organ failure. However, the initiating event which may trigger this immunoinflammatory cascade from the gut is unknown. Recent studies have indicated that intestinal epithelial cells (IEC) play an integral role in generating and transmitting signals between luminal bacteria and the host cells in the underlying gut tissues. The purpose of this study was to investigate the ability of IEC to modulate PMN responses to bacteria and/or hypoxia/reoxygenation (H/R) challenges in vitro.

METHODS

Caco2 cell monolayers were established in a two-chamber cell culture system. Neutrophils from normal human volunteers were placed in the basal chamber and the cell co-culture exposed to either apical bacteria (E. coli) and/or H/R challenge. PMN apoptosis, and percentage of CD11b expression, superoxide anion production, and elastase release were subsequently quantitated.

RESULTS

Coculture of PMNs with Caco2 cells led to a significant reduction in neutrophil apoptosis in both normoxic and H/R conditions. CD11b expression was increased in PMNs exposed to bacteria but the greatest expression was noted with PMN cocultured with Caco2 cells and H/R. Superoxide anion production was increased in all groups following either H/R or bacterial challenge and H/R. Elastase release was highest in neutrophils following H/R and exposure to E. coli.

CONCLUSION

IEC modulate PMN response to bacteria and H/R insults. This results in the production of activated neutrophils with an exaggerated lifespan which may promote remote organ failure. Attempts to modulate this response may be useful in preventing multiple organ failure following severe traumatic shock.

Leukocyte apoptosis and its significance in sepsis and shock

Sepsis and multiple organ failure continue to be significant problems among trauma, burn, and the critically ill patient population. Thus, a number of laboratories have focused on understanding the role of altered apoptotic cell death in contributing to immune and organ dysfunction seen in sepsis and shock. Immune cells that undergo altered apoptotic changes include neutrophils, macrophages, dendritic cells, as well as various lymphocyte populations. Evidence of epithelial as well as endothelial cell apoptotic changes has also been reported. Although mediators such as steroids, tumor necrosis factor, nitric oxide, C5a, and Fas ligand (FasL) appear to contribute to the apoptotic changes, their effects are tissue- and cell population-selective. As inhibiting Fas-FasL signaling (e.g., gene deficiency, Fas fusion protein, or Fas short interfering RNA administration), caspase inhibition (caspase mimetic peptides), and/or the overexpression of downstream antiapoptotic molecules (e.g., Bcl-2, Akt) improve survival of septic mice, it not only demonstrates the pathological significance of this process but points to novel targets for the treatment of sepsis.

The CD11/CD18 (beta2) integrins modulate neutrophil caspase activation and survival following TNF-alpha or endotoxin induced transendothelial migration

Neutrophils (PMN) are short-lived cells but their survival is often prolonged in inflammation. The beta2 (CD11/CD18) integrins are involved in PMN migration into inflammation but their role in PMN survival is not well understood. We investigated the role of beta2 integrins in PMN caspase activation, a key enzyme cascade in apoptosis. After 20 h, caspase activation (Western blotting) was markedly decreased in PMN cultured on fibrinogen, a ligand for Mac-1 (CD11b/CD18), but not on fibronectin or albumin. In the presence of TNF-alpha or endotoxin (LPS), blockade of CD18 (beta2 chain) with mAb markedly increased caspase activation in PMN on fibrinogen. PMN which migrated through endothelium in vitro in response to TNF-alpha, LPS, IL-1alpha, IL-8 or C5a contained 58% fewer active caspase positive PMN after 20 h than non-migrated PMN remaining on the endothelium. When beta2 (CD18) integrin or lymphocyte function antigen (LFA)-1 (CD11a) plus Mac1 (CD11b) were blocked by mAb (intact or Fab'), the proportion of migrated PMN (but not of non-migrated PMN) with active caspases was significantly increased (2-4-fold) and this was associated with accelerated PMN apoptosis and death. Thus, engagement of ligands on extracellular matrix and endothelium by the beta2 integrins Mac-1 and LFA-1 plays a role in delaying apoptosis in PMN recruited in response to LPS and TNF-alpha. Inhibition of beta2 integrin function may not only inhibit PMN infiltration, but also accelerate PMN clearance from inflamed tissue.

Polymorphonuclear neutrophils in posttraumatic osteomyelitis: cells recovered from the inflamed site lack chemotactic activity but generate superoxides

The pathogenesis of posttraumatic osteomyelitis, one of the major complications after orthopedic surgery, is not yet understood. Formation of bacterial biofilms on the implant is presumed, conferring resistance to antibiotic therapy and probably also to the host defense mechanisms. In that context, the polymorphonuclear neutrophils (PMN) having infiltrated the infected site were recovered and characterized phenotypically and functionally. Loss of CD62L and upregulation of CD14 were seen, as was expression of CD83. Expression of the latter is dependent on de novo protein synthesis and thus is indicative of an extended life span and a transdifferentiation of the PMN at the infected site. The infiltrated PMN had lost their chemotactic activity, whereas the capacity to produce superoxides was preserved and in some patients even enhanced. In vitro experiments done in parallel showed that long-term culture with interferon-gamma resulted in similar alterations of PMN: loss of chemotactic activity, whereas other functions of PMN, such generation of superoxides and phagocytosis of opsonized bacteria, were preserved or even enhanced. The loss of the migratory capacity of PMN having already emigrated from the blood vessel to the infected site is not expected to affect the host defense negatively. Assuming, however, that bacteria are organized as a biofilm and that infiltration into this biofilm is required for phagocytosis of the bacteria, our data could to some extent explain why despite being activated, the PMN are not able to control the infection. By releasing their cytotoxic, proteolytic, and collagenolytic potential, PMN might instead contribute to tissue destruction and eventually to osteolysis.