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Biomedical subjects

Niels C Riedemann

Publications and source records attributed to Niels C Riedemann.

At least 19 recordsLinked to original sources
PubMed2006

Divergent signaling pathways in phagocytic cells during sepsis.

Neutrophil accumulation in the lung plays a pivotal role in the pathogenesis of acute lung injury during sepsis. Directed movement of neutrophils is mediated by a group of chemoattractants, especially CXC chemokines. Local lung production of CXC chemokines is intensified during experimental sepsis induced by cecal ligation and puncture (CLP), as reflected by rising levels of MIP-2 and cytokine-induced neutrophil chemoattractant-1 in bronchoalveolar lavage fluids. Alveolar macrophages are primed and blood neutrophils are down-regulated for production of MIP-2 and cytokine-induced neutrophil chemoattractant production in response to LPS and C5a. Under these conditions of stimulation, activation of MAPKs (p38, p42/p44) occurs in sham neutrophils but not in CLP neutrophils, while under the same conditions phosphorylation of p38 and p42/p44 occurs in both sham and CLP alveolar macrophages. These data indicate that, under septic conditions, there is impaired signaling in neutrophils and enhanced signaling in alveolar macrophages, resulting in CXC chemokine production, and C5a appears to play a pivotal role in this process. As a result, CXC chemokines increase in lung, setting the stage for neutrophil accumulation in lung during sepsis.

Amino Acid Sequence↗
PubMed2005

Evidence for a functional role of the second C5a receptor C5L2.

During experimental sepsis in rodents after cecal ligation and puncture (CLP), excessive C5a is generated, leading to interactions with C5aR, loss of innate immune functions of neutrophils, and lethality. In the current study, we have analyzed the expression of the second C5a receptor C5L2, the putative "default" or nonsignaling receptor for C5a. Rat C5L2 was cloned, and antibody was developed to C5L2 protein. After CLP, blood neutrophils showed a reduction in C5aR followed by its restoration, while C5L2 levels gradually increased, accompanied by the appearance of mRNA for C5L2. mRNA for C5L2 increased in lung and liver during CLP. Substantially increased C5L2 protein (defined by binding of 125I-anti-C5L2 IgG) occurred in lung, liver, heart, and kidney after CLP. With the use of serum IL-6 as a marker for sepsis, infusion of anti-C5aR dramatically reduced serum IL-6 levels, while anti-C5L2 caused a nearly fourfold increase in IL-6 when compared with CLP controls treated with normal IgG. When normal blood neutrophils were stimulated in vitro with LPS and C5a, the antibodies had similar effects on release of IL-6. These data provide the first evidence for a role for C5L2 in balancing the biological responses to C5a.

Amino Acid Sequence↗
PubMed2005

Relationship of acute lung inflammatory injury to Fas/FasL system.

There is mounting evidence that apoptosis plays a significant role in tissue damage during acute lung injury. To evaluate the role of the apoptosis mediators Fas and FasL in acute lung injury, Fas (lpr)- or FasL (gld)-deficient and wild-type mice were challenged with intrapulmonary deposition of IgG immune complexes. Lung injury parameters ((125)I-albumin leak, accumulation of myeloperoxidase, and wet lung weights) were measured and found to be consistently reduced in both lpr and gld mice. In wild-type mice, lung injury was associated with a marked increase in Fas protein in lung. Inflamed lungs of wild-type mice showed striking evidence of activated caspase-3, which was much diminished in inflamed lungs from lpr mice. Intratracheal administration of a monoclonal Fas-activating antibody (Jo2) in wild-type mice induced MIP-2 and KC production in bronchoalveolar lavage fluids, and a murine alveolar macrophage cell line (MH-S) showed significantly increased MIP-2 production after incubation with this antibody. Bronchoalveolar lavage fluid content of MIP-2 and KC was substantially reduced in lpr mice after lung injury when compared to levels in wild-type mice. These data suggest that the Fas/FasL system regulates the acute lung inflammatory response by positively affecting CXC-chemokine production, ultimately leading to enhanced neutrophil influx and tissue damage.

Animals↗
PubMed2004

Regulatory role of C5a on macrophage migration inhibitory factor release from neutrophils.

There is evidence that C5a and macrophage migration inhibitory factor (MIF) both play important roles in experimental sepsis. Humans with sepsis also show elevated levels of both mediators in the blood. Regulation of MIF during sepsis is poorly understood. We now demonstrate that neutrophil depletion greatly reduced serum MIF levels in rats and mice during the onset of sepsis after cecal ligation and puncture. In vitro, C5a induced MIF release from rat and mouse neutrophils. In vivo blockade of C5aR or absence of C5aR led to significantly reduced MIF generation during the onset of sepsis. C5a-induced release in vitro of MIF from neutrophils appeared to be due to up-regulation of MIF in cytoplasmic granules of neutrophils via activation of the protein kinase B signaling pathway together with involvement of PI3K. Our data suggest that C5a plays a role in enhancing MIF release from neutrophils in vitro and during sepsis. These findings represent a previously unrecognized function of C5a and neutrophils in the appearance of MIF in sepsis.

Animals↗
PubMed2004

Stat3 activation in acute lung injury.

Stat3 plays diverse roles in biological processes including cell proliferation, survival, apoptosis, and inflammation. Very little is known regarding its activation and function in the lung during acute inflammation. We now show that Stat3 activation was triggered in lungs and in alveolar macrophages after intrapulmonary deposition of IgG immune complexes in rats. Low levels of constitutive Stat3 were observed in normal rat lungs as determined by the EMSA. Stat3 activity in whole lung extracts increased 2 h after initiation of IgG immune complex deposition, reaching maximal levels by 4 h, whereas Stat3 activation was found in alveolar macrophages as early as 30 min after onset of injury. Expression and activation of Stat3 mRNA, protein, and protein phosphorylation was accompanied by increased gene expression of IL-6, IL-10, and suppressor of cytokine signaling-3 in whole lung tissues. Both Tyr(705) and Ser(727) phosphorylation were involved in Stat3 activation as assessed in whole lung extracts. C5a (complement 5, fragment a) per se can induce phosphorylation of Ser(727) of Stat3. In vivo, Stat3 activation was dramatically suppressed by depletion of neutrophils or lung macrophages, resulting in reduced gene expression of IL-6 and IL-10 in whole lung tissues. Using blocking Abs to IL-6, IL-10, and C5a, Stat3 activation induced by IgG immune complexes was markedly diminished. These data suggest in the lung injury model used that activation of Stat3 in lungs is macrophage dependent and neutrophil dependent. IL-6, IL-10, and C5a contribute to Stat3 activation in inflamed rat lung.

Animals↗
PubMed2004

Disturbed homeostasis of lung intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 during sepsis.

Cecal ligation and puncture (CLP)-induced sepsis in mice was associated with perturbations in vascular adhesion molecules. In CLP mice, lung vascular binding of (125)I-monoclonal antibodies to intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 revealed sharp increases in binding of anti-ICAM-1 and significantly reduced binding of anti-VCAM-1. In whole lung homogenates, intense ICAM-1 up-regulation was found (both in mRNA and in protein levels) during sepsis, whereas very little increase in VCAM-1 could be measured although some increased mRNA was found. During CLP soluble VCAM-1 (sVCAM-1) and soluble ICAM-1 (sICAM-1) appeared in the serum. When mouse dermal microvascular endothelial cells (MDMECs) were incubated with serum from CLP mice, constitutive endothelial VCAM-1 fell in association with the appearance of sVCAM-1 in the supernatant fluids. Under the same conditions, ICAM-1 cell content increased in MDMECs. When MDMECs were evaluated for leukocyte adhesion, exposure to CLP serum caused increased adhesion of neutrophils and decreased adhesion of macrophages and T cells. The progressive build-up in lung myeloperoxidase after CLP was ICAM-1-dependent and independent of VLA-4 and VCAM-1. These data suggest that sepsis disturbs endothelial homeostasis, greatly favoring neutrophil adhesion in the lung microvasculature, thereby putting the lung at increased risk of injury.

Animals↗
PubMed2004

Role of C5a-C5aR interaction in sepsis.

C5a-C5aR signaling plays an essential role in innate immunity of neutrophils. However, excessive interaction of C5a-C5aR results in harmful effects in these cells. In sepsis, robust generation of C5a occurs; blockade of either C5a or C5aR greatly improves survival in experimental sepsis following cecal ligation and puncture (CLP). The beneficial effects derived from C5a-C5aR interaction are associated with preservation of neutrophil innate immune functions (chemotaxis, phagocytosis, respiratory burst), attenuation of the inflammatory reaction, amelioration of coagulopathy, alteration in adhesion molecule expression, and modulation of apoptosis. Following CLP, C5aR expression is significantly elevated in organs, perhaps setting the stage for C5a-induced organ dysfunction. In contrast, C5aR content on neutrophils drops significantly at early stages of sepsis and progressively increases at later time points. Re-expression of C5aR on neutrophils during sepsis appears to be associated with the functional recovery of neutrophil innate immune functions. Following CLP, there is a positive correlation between C5aR content on blood neutrophils and survival of individual animals; high levels of C5aR on neutrophils are associated with survival, whereas low levels of C5aR on neutrophils predict mortality. These data suggest that in sepsis C5a-C5aR signaling is excessive, resulting in paralysis of neutrophil function. Interception of either C5a or C5aR dramatically improves survival during experimental sepsis.

Animals↗
PubMed2003

Regulatory role of C5a in LPS-induced IL-6 production by neutrophils during sepsis.

Experimental sepsis in rodents occurring after cecal ligation/puncture (CLP) is associated with excessive complement activation and a systemic inflammatory response. The proinflammatory mediator IL-6 has recently been shown to be an important inducer of the C5a receptor (C5aR) during sepsis. We now provide evidence that serum IL-6 production during sepsis in rats was reduced in neutrophil-depleted animals and that absence of C5aR in mice as well as antibody-blockade of C5a in rats significantly reduced serum levels of IL-6 during sepsis. Lipopolysaccharide (LPS)-induced production in vitro of IL-6 by neutrophils was significantly enhanced in the co-presence of C5a, likely due to transcriptional up-regulation of IL-6. Production of IL-6 in neutrophils by LPS was NF-kappaB dependent (but not on the presence of p50) and dependent on phosphorylation of p38-mitogen activated protein kinase (MAPK) as well as p44/p42 MAPK (ERK1/2) but not on phosphorylation of c-Jun N-terminal kinases (JNK1/2). C5a stimulation of neutrophils elicited a rapid phosphorylation of ERK1/2 and p38 MAPK. Accordingly, we suggest that induction of IL-6 after CLP is neutrophil and C5a/C5aR dependent, likely due to the ability of C5a to cause activation of ERK1/2 and p38 MAPK signaling pathways.

Animals↗
PubMed2003

Neutrophil C5a receptor and the outcome in a rat model of sepsis.

Complement fragment 5a (C5a)-C5a receptor (C5aR) signaling plays an essential role in neutrophil innate immunity. Blockade of either the ligand or the receptor improves survival rates in experimental sepsis. In the current study, sepsis was induced in rats by cecal ligation/puncture. Early in sepsis C5aR content on neutrophils significantly dropped, reached the nadir at 24 h after onset of sepsis, and progressively elevated thereafter. Western-blot, RT-PCR, and confocal microscopy analyses revealed that the loss and re-expression of C5aR during sepsis might be due, at least in part, to the receptor internalization and reconstitution. The reduction and reconstitution of C5aR correlate with the loss and restoration of innate immune functions of blood neutrophils (chemotaxis and reactive oxygen species production), respectively. Quantitative measurements of C5aR on blood neutrophils are highly predictive of survival or death during sepsis. These data suggest that neutrophil C5aR content represents an essential component of an efficient defense system in sepsis and may serve as a prognostic marker for the outcome.

Animals↗
PubMed2003

A key role of C5a/C5aR activation for the development of sepsis.

In recent studies, evidence has been provided for complement activation early during the onset of experimental sepsis. Excessive production of the anaphylatoxin C5a thereby appears to elicit various harmful effects. Blockade of C5a or C5a receptor (C5aR) at the start of experimental sepsis has been demonstrated to greatly improve survival in rodents. There is evidence that C5a, during the onset of sepsis, enhances the production of various proinflammatory mediators in different cell types. Besides its known, other proinflammatory effects, recent work suggested an inhibitory role of C5a for innate-immune functions of phagocytic cells (phagocytosis, reactive oxygen species production, chemotaxis) during experimental sepsis. This review article provides an overview of the important role of C5a/C5aR activation for the onset and development of sepsis.

Animals↗
PubMed2003

Protective effects of IL-6 blockade in sepsis are linked to reduced C5a receptor expression.

IL-6 is known to be an important pro- and anti-inflammatory cytokine, which is up-regulated during sepsis. Our previous work has suggested a role for IL-6 in the up-regulation of C5aR in sepsis. We reported earlier that interception of C5a or C5aR results in improved outcomes in experimental sepsis. Using the cecal ligation/puncture (CLP) model in mice, we now demonstrate that treatment with anti-IL-6 Ab (anti-IL-6) results in significantly improved survival, dependent on the amount of Ab infused. CLP animals showed significantly increased binding of 125I-labeled anti-C5aR to organs when compared to either control mice at 0 h or CLP animals infused with normal rabbit 125I-labeled IgG. Binding of 125I-labeled anti-C5aR to lung, liver, kidney, and heart was significantly decreased in anti-IL-6-treated animals 6 h after CLP. RT-PCR experiments with mRNA isolated from various organs obtained 3, 6, and 12 h after CLP demonstrated increased C5aR mRNA expression during the onset of sepsis, which was greatly suppressed in CLP mice treated with anti-IL-6. These data suggest that IL-6 plays an important role in the increased expression of C5aR in lung, liver, kidney, and heart during the development of sepsis in mice and that interception of IL-6 leads to reduced expression of C5aR and improved survival.

Amino Acid Sequence↗
PubMed2003

Regulatory effects of iNOS on acute lung inflammatory responses in mice.

The role of endogenous NO in the regulation of acute lung injury is not well defined. We investigated the effects of inducible nitric oxide synthase (iNOS) and endothelial NOS (eNOS) on the acute inflammatory response in mouse lungs. Acute lung injury was induced by intratracheal instillation of bacterial lipopolysaccharide (LPS) into wild-type (WT) mice and mice deficient in iNOS (iNOS(-/-)) or eNOS (eNOS(-/-)). Endpoints of inflammatory injury were myeloperoxidase (MPO) content and leak of albumin into lung. Inflammatory injury was similar in WT and eNOS(-/-) mice but was substantially increased in iNOS(-/-) mice. Bronchoalveolar lavage (BAL) fluids of iNOS(-/-) and WT mice showed similar levels of CXC chemokines (MIP-2, KC) but enhanced levels of CC chemokines (MCP-1, MCP-3). Increased lung content of MPO in iNOS(-/-) mice was reduced by anti-MCP-1 to values found in WT mice. In vitro stimulation of microvascular endothelial cells with LPS and IFN gamma revealed elevated production of CXC and CC chemokines in cells from iNOS(-/-) mice when compared to endothelial cells from iNOS(+/+) mice. Peritoneal macrophages from iNOS(-/-) donors also revealed increased production of CC chemokines after stimulation with LPS and interferon (IFN gamma). These data indicate that absence of iNOS causes enhanced lung inflammatory responses in mice which may be related to enhanced production of MCP-1 by endothelial cells and macrophages. It appears that iNOS affects the lung inflammatory response by regulating chemokine production.

Acute Disease↗
PubMed2003

Regulation by C5a of neutrophil activation during sepsis.

In sepsis, there is evidence that excessive C5a generation leads to compromised innate immune functions, being associated with poor outcome. We now report that in vitro exposure of neutrophils to C5a causes increased levels of IkappaBalpha, decreased NF-kappaB-dependent gene transcription of TNFalpha, and decreased lipopolysaccharide (LPS)-induced TNFalpha production. Similar findings were obtained with neutrophils from cecal ligation/puncture (CLP)-induced septic rats. Such changes were reversed by antibody-induced in vivo blockade of C5a. In contrast, in vitro exposure of alveolar macrophages to C5a and LPS resulted in enhanced production of TNFalpha and no increase in IkappaBalpha. These data suggest that CLP-induced sepsis causes a C5a-dependent dysfunction of neutrophils, which is characterized by altered signaling associated with NF-kappaB activation.

Animals↗
PubMed2003

Novel strategies for the treatment of sepsis.

The history of therapeutic interventions in clinical trials for sepsis has been referred to as the "graveyard for pharmaceutical companies." That is now set to change, as research provides hope for new approaches that will be therapeutically effective in humans with sepsis.

Animals↗
PubMed2003

Anti-complement strategies in experimental sepsis.

Using the cecal ligation/puncture (CLP) model of sepsis in rodents, evidence was obtained for excessive activation of the complement system, which leads to nearly total loss of innate immune protective functions of blood neutrophils. These defects are associated with profound defects in chemotaxis, respiratory burst (H2O2 production) and phagocytosis. The molecular mechanisms of these defects are linked to the complement activation product C5a. In CLP rats and mice, the C5a receptor (C5aR) is widely up-regulated in organs, in part owing to the production of interleukin-6 (IL-6). The up-regulation of C5aR in the thymus is linked to C5a-dependent induction of apoptosis in thymocytes, as revealed by caspase activation, increased binding of C5a and DNA laddering. Such events in thymocytes are prevented if rats first are treated with anti-C5a or with anti-C5aR at the time of CLP. Treatment of CLP rats and mice with anti-C5a, anti-IL-6 or anti-C5aR dramatically improves survival rates after CLP, indicating a linkage between C5a and C5aR in the harmful outcomes of sepsis in rodents. Studies are underway in humans with sepsis to determine whether similar mechanisms are in play.

Animals↗
PubMed2003

The enigma of sepsis.

Sepsis remains a serious cause of morbidity and mortality, and the pathophysiology of the disease is not clear. The definition of the clinical manifestations of sepsis is ever evolving. This review discusses the search for effective therapeutic interventions, hurdles in translational sepsis research, and new therapies in development in current clinical trials.

Animals↗
PubMed2003

Anti-inflammatory strategies for the treatment of sepsis.

Sepsis leads to an overwhelming inflammatory response of the host and is usually accompanied by well-known clinical symptoms (fever, tachycardia, leukocytosis, and so on) and the accompanying systemic inflammatory response syndrome (SIRS). Accordingly, most efforts to develop treatment strategies for sepsis have focused on those designed to counteract overactivation of the inflammatory system. Despite intensive research into identifying targets in sepsis, most of the resulting clinical trials have been based on experimental data and have resulted in no beneficial effects (i.e., survival). Recombinant activated protein C (APC) represents the first treatment that has led to restricted approval for use in sepsis in the USA and worldwide. This article reviews approaches to anti-inflammatory treatment in sepsis and provides an outlook into ongoing clinical trials as well as new treatments that have not yet been evaluated in the clinical setting.

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