The role of lipopolysaccharide in stimulating adrenomedullin production during polymicrobial sepsis

Evaluation of cardiac troponin I in serum and myocardium of rabbits with experimentally induced polymicrobial sepsis

Sepsis is a potentially life-threatening condition, and it is frequently complicated by myocardial damage. Data on myocardial damage in rabbit caecal ligation and puncture (CLP) models are limited, although numerous animal models have been used to study sepsis-associated myocardial damage. This study aimed to investigate the effect of CLP on cardiac muscle by measuring serum cardiac troponin I (cTnI) concentrations and by detecting both histopathological changes and cTnI immunoreactivity in cardiomyocytes in rabbits. After CLP was performed in rabbits, blood samples were taken from the jugular vein at 0, 4, 8, and 12 h for haematological and biochemical analyses. At the end of the experiment, all of the rabbits were euthanised to examine the histopathological changes and the cTnI immunoreactivity in cardiac muscle tissue. No changes in serum cTnI concentration were observed in the experimental group (EG) or control group (CG) at 0 and 4 h. In EG, the mean serum cTnI concentrations were 0.230 ± 0.209 and 1.177 ± 0.971 ng/ml at 8 and 12 h, respectively. In CG, the mean serum cTnI concentrations were 0.032 ± 0.014 and 0.031 ± 0.021 ng/ml at 8 and 12 h, respectively. Moreover, cytoplasmic cTnI immunoreactivity decreased in EG compared with that in CG (P<0.01). The results demonstrated that CLP induced a systemic inflammatory response and caused myocardial damage in rabbits.

Challenges of using lipopolysaccharides for cancer immunotherapy and potential delivery-based solutions thereto

Despite being one of the earliest Toll-like receptor (TLR)-based cancer immunotherapeutics discovered and investigated, the full extent of lipopolysaccharide (LPS) potentials within this arena remains hitherto unexploited. In this review, we will debate the challenges that have complicated the improvement of LPS-based immunotherapeutic approaches in cancer therapy. Based on their nature, those will be discussed with a focus on side effect-related, tolerance-related and in vivo model-related challenges. We will then explore how drug delivery strategies can be integrated within this domain to address such challenges in order to improve the therapeutic outcome, and will present a summary of the studies that have been dedicated thereto. This paper may inspire further developments based on reconciling the advantages of drug delivery and LPS-based cancer immunotherapy.

Adrenomedullin protects from experimental autoimmune encephalomyelitis at multiple levels

Adrenomedullin is a neuropeptide known for its cardiovascular activities and anti-inflammatory effects. Here, we investigated the effect of adrenomedullin in a model of experimental autoimmune encephalomyelitis (EAE) that mirrors chronic progressive multiple sclerosis. A short-term systemic treatment with adrenomedullin reduced clinical severity and incidence of EAE, the appearance of inflammatory infiltrates in spinal cord and the subsequent demyelination and axonal damage. This effect was exerted at multiple levels affecting both early and late events of the disease. Adrenomedullin decreased the presence/activation of encephalitogenic Th1 and Th17 cells and down-regulated several inflammatory mediators in peripheral lymphoid organs and central nervous system. Noteworthy, adrenomedullin inhibited the production by encephalitogenic cells of osteopontin and of Granulocyte Macrophage Colony-Stimulating Factor (GM-CSF), two critical cytokines in the development of EAE. At the same time, adrenomedullin increased the number of IL-10-producing regulatory T cells with suppressive effects on the progression of EAE. Furthermore, adrenomedullin generated dendritic cells with a semi-mature phenotype that impaired encephalitogenic responses in vitro and in vivo. Finally, adrenomedullin regulated glial activity and favored an active program of neuroprotection/regeneration. Therefore, the use of adrenomedullin emerges as a novel multimodal therapeutic approach to treat chronic progressive multiple sclerosis.

Role of adrenomedullin in Lyme disease

Borrelia burgdorferi stimulates a strong inflammatory response during infection of a mammalian host. To understand the mechanisms of immune regulation employed by the host to control this inflammatory response, we focused our studies on adrenomedullin, a peptide produced in response to bacterial stimuli that exhibits antimicrobial activity and regulates inflammatory responses by modulating the expression of inflammatory cytokines. Specifically, we investigated the effect of B. burgdorferi on the expression of adrenomedullin as well as the ability of adrenomedullin to dampen host inflammatory responses to the spirochete. The concentration of adrenomedullin in the synovial fluid of untreated Lyme arthritis patients was elevated compared with that in control osteoarthritis patient samples. In addition, coculture with B. burgdorferi significantly increased the expression of adrenomedullin in RAW264.7 macrophages through MyD88-, phosphatidylinositol 3-kinase (PI3-K)-, and p38-dependent signaling cascades. Furthermore, the addition of exogenous adrenomedullin to B. burgdorferi-stimulated RAW264.7 macrophages resulted in a significant decrease in the induction of proinflammatory cytokines. Taken together, these results suggest that B. burgdorferi increases the production of adrenomedullin, which in turn negatively regulates the B. burgdorferi-stimulated inflammatory response.

Milk fat globule epidermal growth factor-factor VIII is down-regulated in sepsis via the lipopolysaccharide-CD14 pathway

Phagocytosis prevents the release of potentially harmful or immunogenic materials from dying cells. Milk fat globule epidermal growth factor (EGF)-factor VIII (MFG-E8) mediates the clearance of apoptotic cells. We have previously shown that the administration of MFG-E8-rich exosomes from immature dendritic cells promotes the phagocytosis of apoptotic cells and improves survival in sepsis. Because endotoxin is elevated in polymicrobial sepsis, we hypothesized that down-regulation of MFG-E8 is mediated via the LPS-CD14 pathway, eventually leading to the accruement of apoptotic cells. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) in CD14-deficient (CD14(-/-)), TLR4-mutated and wild-type (WT) mice. In addition, endotoxemia was elicited by i.p. injection of LPS. LPS was also neutralized by pretreating CLP-induced WT mice with polymyxin B. Splenic MFG-E8 expression, phagocytic activity, and apoptosis were assessed 5 and 20 h after CLP or 5 h after LPS administration. In septic WT mice, MFG-E8 mRNA and protein levels were suppressed by 49 and 33%, respectively. Endotoxemia reduced MFG-E8 mRNA expression in a dose dependent manner and the down-regulation of MFG-E8 mRNA expression in CLP-induced sepsis was attenuated by polymyxin B. This CLP-induced suppression was not observed in both CD14(-/-) and TLR4-mutated mice. CLP significantly decreased phagocytic activity of peritoneal macrophages in WT (by 30%), but not in CD14(-/-) mice. CLP also induced significant apoptosis in the spleen of WT (by 61%), but less in CD14(-/-) mice. Thus, MFG-E8 production is down-regulated in sepsis by LPS-CD14 dependent fashion, leading to a reduction of phagocytosis of apoptotic cells.

Endotoxin downregulates peroxisome proliferator-activated receptor-gamma via the increase in TNF-alpha release

The nuclear receptor peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is anti-inflammatory in a cell-based system and in animal models of endotoxemia. We have shown that PPAR-gamma gene expression is downregulated in macrophages after lipopolysaccharide (LPS) stimulation. However, it remains unknown whether hepatic PPAR-gamma is altered in sepsis and, if so, whether LPS directly downregulates PPAR-gamma. To study this, rats were subjected to sepsis by cecal ligation and puncture (CLP). Hepatic tissues were harvested at 5, 10, and 20 h after CLP. PPAR-gamma gene expression and protein levels were determined by RT-PCR and Western blot analysis, respectively. The results showed that PPAR-gamma gene expression decreased at 10 and 20 h and that its proteins levels were reduced at 20 h after CLP. PPAR-gamma levels were also decreased in animals that were administered LPS. To determine the direct effects of LPS on PPAR-gamma downregulation, LPS binding agent polymyxin B (PMB) was administered intramuscularly after CLP. The administration of PMB significantly reduced plasma levels of endotoxin, but it did not prevent the downregulation of PPAR-gamma expression. We found that circulating levels of TNF-alpha still remained significantly elevated in PMB-treated septic animals. We, therefore, hypothesize that the decrease of PPAR-gamma expression is TNF-alpha dependent. To investigate this, Kupffer cells (KCs) were isolated from normal rats and stimulated with LPS or TNF-alpha. TNF-alpha significantly attenuated PPAR-gamma gene expression in KCs. Although LPS decreased PPAR-gamma in KCs, the downregulatory effect of LPS was blocked by the addition of TNF-alpha-neutralizing antibodies. Furthermore, the administration of TNF-alpha-neutralizing antibodies to animals before the onset of sepsis prevented the downregulation of PPAR-gamma in sepsis. We, therefore, conclude that LPS downregulates PPAR-gamma expression during sepsis via an increase in TNF-alpha release.

Activated protein C suppresses adrenomedullin and ameliorates lipopolysaccharide-induced hypotension

Activated protein C (APC) is an important modulator of vascular function that has antithrombotic and anti-inflammatory properties. Studies in humans have shown modulation of endotoxin-induced hypotension by recombinant human APC, drotrecogin alfa (activated), however, the mechanism for this effect is unclear. We have found that APC suppresses the induction of the potent vasoactive peptide adrenomedullin (ADM) and could downregulate lipopolysaccharide (LPS)-induced ADM messenger RNA (mRNA) and nitrite levels in cell culture. This effect was dependent on signaling through protease-activated receptor 1. Addition of 1400W, an irreversible inducible nitric oxide synthase (iNOS) inhibitor, inhibited LPS-induced ADM mRNA, suggesting that ADM induction is NO mediated. Furthermore, in a rat model of endotoxemia, APC (100 microg/kg, i.v.) prevented LPS (10 mg/kg, i.v.)-induced hypotension, and suppressed ADM mRNA and protein expression. APC also inhibited iNOS mRNA and protein levels along with reduction in NO by-products (NOx). We also observed a significant reduction in iNOS-positive leukocytes adhering to vascular endothelium after APC treatment. Moreover, we found that APC inhibited the expression of interferon-gamma (IFN-gamma), a potent activator of iNOS. In a human study of LPS-induced hypotension, APC reduced the upregulation of plasma ADM levels, coincident with protection against the hypotensive response. Overall, we demonstrate that APC blocks the induction of ADM, likely mediated by IFN-gamma and iNOS, and suggests a mechanism that may account for ameliorating LPS-induced hypotension. Furthermore, our data provide a new understanding for the role of APC in modulating vascular response to insult.

Ghrelin attenuates sepsis-induced acute lung injury and mortality in rats

RATIONALE

Our study has shown that plasma levels of ghrelin, a stomach-derived peptide, are significantly reduced in sepsis, and that ghrelin administration improves organ blood flow via a nuclear factor (NF)-kappaB-dependent pathway. However, it remains unknown whether ghrelin has any protective effects on severe sepsis-induced acute lung injury (ALI) and, if so, whether inhibition of NF-kappaB plays any role in it.

OBJECTIVES

To test the hypothesis that ghrelin reduces severe sepsis-induced ALI and mortality through inhibition of NF-kappaB.

METHODS

Sepsis was induced in rats by cecal ligation and puncture (CLP). Five hours after CLP, a bolus intravenous injection of 2 nmol of ghrelin was followed by continuous infusion of 12 nmol of ghrelin via a minipump for 15 hours. Samples were harvested 20 hours post-CLP (i.e., severe sepsis). Pulmonary levels of ghrelin and proinflammatory cytokines were measured by ELISA. NF-kappaB p65 and IkappaBalpha expression and NF-kappaB activity were measured by Western blot analysis and ELISA, respectively. Pulmonary blood flow was measured with radioactive microspheres. In additional animals, the necrotic cecum was excised 20 hours post-CLP and 10-day survival was recorded.

MEASUREMENTS AND MAIN RESULTS

Pulmonary levels of ghrelin decreased significantly 20 hours post-CLP. Ghrelin administration restored pulmonary levels of ghrelin, reduced lung injury, increased pulmonary blood flow, down-regulated proinflammatory cytokines, inhibited NF-kappaB activation, and improved survival in sepsis. Administration of a specific ghrelin receptor antagonist worsened the survival rate after CLP and cecal excision.

CONCLUSIONS

Ghrelin can be developed as a novel treatment for severe sepsis-induced ALI. The protective effect of ghrelin is mediated through inhibition of NF-kappaB.

Pro-inflammatory cytokines from Kupffer cells downregulate hepatocyte expression of adrenomedullin binding protein-1

Polymicrobial sepsis is characterized by an early, hyperdynamic phase followed by a late hypodynamic phase. Adrenomedullin (AM), a vasodilatory peptide, inhibits this transition from the early phase to the late phase. Adrenomedullin binding protein-1 (AMBP-1) enhances AM-mediated activities. The decrease of AMBP-1 levels in late sepsis reduces the vascular response to AM and produces the hypodynamic phase. Studies have indicated that the administration of LPS downregulates AMBP-1 production in the liver. Since hepatocytes are the primary source of AMBP-1 biosynthesis in the liver, we employed a co-culture strategy using hepatocyte and Kupffer cells to determine whether LPS directly or by increasing pro-inflammatory cytokines from Kupffer cells downregulates AMBP-1 production. Hepatocytes and Kupffer cells isolated from rats were co-cultured and treated with LPS for 24 h. LPS significantly attenuated AMBP-1 protein expression in a dose-dependent manner. Since AMBP-1 is basically a secretory protein, cell supernatants from co-culture cells treated with LPS were examined for AMBP-1 protein levels. LPS treatment caused a dose related decrease in AMBP-1 protein secretion. Similarly, LPS treatment produced a significant decrease in AMBP-1 protein expression in hepatocytes and Kupffer cells cultured using transwell inserts. LPS had no direct effect on AMBP-1 levels in cultured hepatocytes or Kupffer cells alone. To confirm that the observed effects in co-culture were due to the cytokines released from Kupffer cells, hepatocytes were treated with IL-1beta or TNF-alpha for 24 h and AMBP-1 expression was examined. The results indicated that both cytokines significantly inhibited AMBP-1 protein levels. Thus, pro-inflammatory cytokines released from Kupffer cells are responsible for downregulation of AMBP-1.

Cecal ligation and puncture

The model of cecal ligation and puncture (CLP) in rodents has been used extensively to investigate the clinical settings of sepsis and septic shock. This model produces a hyperdynamic, hypermetabolic state that can lead to a hypodynamic, hypometabolic stage, and eventual death. Blood cultures are positive for enteric organisms very early after CLP. The model has been widely used over the past 26 years and is highly versatile in adapting to a range of severity and testing objectives. It is inexpensive to prepare and technically straightforward. Aspects of sepsis research investigated using CLP include energetics, metabolism, resuscitation, antibiotic therapy, microbial factors, cardiovascular responses, immune function, mediator release, and cytokine expression patterns. The challenge of the small circulating blood volume in rodents can be overcome by using micromethods that enable analysis of small volumes, or alternatively, by using a large number of animals to obtain serial samples.

The anti-inflammatory effect of curcumin in an experimental model of sepsis is mediated by up-regulation of peroxisome proliferator-activated receptor-gamma

OBJECTIVE

Although phytochemical curcumin has been shown to possess anti-inflammatory properties, it remains unknown whether this agent has any beneficial effects in sepsis. The purpose of this study was to demonstrate whether curcumin protects septic animals and, if so, whether activation of peroxisome proliferator-activated receptor (PPAR)-gamma, an anti-inflammatory nuclear receptor, plays any role.

DESIGN

Prospective, controlled, and randomized animal study.

SETTING

A research institute laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

A bolus injection of 0.2 micromol of curcumin was given intravenously to male adult rats, followed by continuous infusion of curcumin (0.24 micromol/day) for 3 days via a primed 2-mL mini-pump. The rats were then subjected to sepsis by cecal ligation and puncture (CLP).

MEASUREMENTS AND MAIN RESULTS

Serum levels of liver enzymes (alanine aminotransferase and aspartate aminotransferase), lactate, albumin, and tumor necrosis factor (TNF)-alpha were measured at 20 hrs after CLP (i.e., late stage of sepsis). In addition, a 10-day survival curve was conducted following CLP and cecal excision with or without curcumin treatment. Furthermore, macrophages cell line RAW 264.7 cells were treated with curcumin followed by stimulation with endotoxin. TNF-alpha and PPAR-gamma expression were then measured. The results indicate that intravenous administration of curcumin before the onset of sepsis attenuated tissue injury, reduced mortality, and decreased the expression of TNF-alpha in septic animals. Similar results were also found when curcumin was administered after the onset of sepsis. Moreover, the down-regulated PPAR-gamma in the liver at 20 hrs after CLP was significantly improved by curcumin treatment. Concurrent administration of curcumin and GW9662, a specific PPAR-gamma antagonist, completely abolished the beneficial effects of curcumin under such conditions. In cultured RAW 264.7 cells, curcumin inhibited endotoxin-induced increases in TNF-alpha expression and markedly up-regulated PPAR-gamma expression without affecting cell viability. Curcumin also prevented morphologic alterations in macrophages induced by endotoxin.

CONCLUSIONS

The protective effect of curcumin makes it or its analogues strong candidates as a novel therapy for sepsis. The beneficial effect of curcumin appears to be mediated by up-regulation of nuclear receptor PPAR-gamma.

[Role of adrenomedullin in the pathogenesis and treatment of cardiovascular dysfunctions and sepsis]

Adrenomedullin (AM) is an endogenous vasodilatory peptide hormone, which plays a key role in the regulation and preservation of cardiovascular and pulmonary functions. Clinical and experimental studies have demonstrated that AM represents an alternative therapeutic option in the treatment of pulmonary hypertension. In addition, AM proved to be useful in the treatment of cardiovascular dysfunctions, such as arterial hypertension and congestive heart failure following myocardial infarction. Recent research has also shown that AM plays a pivotal role in the development of sepsis-associated hemodynamic and microcirculatory disorders. Experimental studies also suggest that infusion of exogenous AM might be a rational approach to prevent and treat hypodynamic septic shock. The objectives of this review article are to characterize the regulative properties of AM and to discuss clinical and experimental studies which allow to judge the role of AM in the setting of cardiovascular dysfunction and sepsis.

Possible involvement of adrenomedullin in lipopolysaccharide-induced small-intestinal motility changes in conscious rats

BACKGROUND

Adrenomedullin is a vasodilator peptide that displays a variety of effects, such as hypotension and vasodilatation. The aim of this study was to test the effect of intravenous adrenomedullin on the motility pattern of the small intestine, and the functional involvement of adrenomedullin in endotoxin-induced small-intestinal motility disturbance.

METHODS

Jejunal motility was recorded in fasted conscious rats, using miniature strain-gauge force transducers sutured to the serosal surface of the small-intestinal wall.

RESULTS

Intravenous administration of adrenomedullin at doses of 3, 6, and 10 microg/kg per min over 30 min disrupted phase 3 of the migrating motor complex, with the disruption lasting for 61.9 +/- 5.1, 52.2 +/- 10.6, and 74.1 +/- 25.2 min, respectively. The interval from drug administration to the onset of disruption decreased as the dose of adrenomedullin increased to 41.5 +/- 11.0, 11.6 +/- 3.4, and 0 min, respectively (P < 0.05). An increase in the motility index was also dose-dependent (P < 0.05) at these doses of adrenomedullin. Lipopolysaccharide (50 microg/kg) induced disruption of phase 3, which lasted for 138.7 +/- 5.4 min. Previous administration of the putative adrenomedullin-receptor antagonist, AM (22-52), at a 50 microg/kg dose, attenuated the disruption induced by lipopolysaccharide to 74.4 +/- 3.5 min (P < 0.01).

CONCLUSIONS

Our findings (1) suggest that intravenous adrenomedullin causes small-intestinal motility disturbances, and (2) support the hypothesis that adrenomedullin overproduction plays an important role in lipopolysaccharide-induced disruption of the motility pattern in the small intestine in rats.

Adrenomedullin gene expression and levels in the cardiovascular system after treatment with lipopolysaccharide

To study the effect of septicaemia, the temporal changes in tissue adrenomedullin (AM) and preproAM mRNA levels were studied in the heart and blood vessels after lipopolysaccharide (LPS) injection. Radioimmunoassay and solution hybridization-RNase protection assays were used to follow the changes in AM and its mRNA levels respectively after intraperitoneal injection of 10 mg/kg LPS in rats. The preproAM mRNA levels increased at 1 h in the right atrium after LPS injection, while the AM contents decreased at 1 h in the left atrium. The preproAM mRNA levels increased at 3 and 6 h in the left ventricle, whereas it increased at 6 h in the right ventricles after LPS injection. There was an increase in preproAM mRNA levels at 1 and 3 h in the mesenteric artery, while AM levels were increased at 1, 3 and 6 h. However, there were no such changes in the thoracic aorta. There were also increases in tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta and IL-6 in the heart, and in the mesenteric artery (TNF-alpha and IL-1beta) and in thoracic aorta (IL-1beta and IL-6). The present results suggest that the biosynthesis and secretion of AM may be increased in cardiovascular tissues of rats injected with LPS, and that AM may play multiple roles in inflammation.

Vascular Actions of Calcitonin Gene-Related Peptide and Adrenomedullin

This review summarizes the receptor-mediated vascular activities of calcitonin gene-related peptide (CGRP) and the structurally related peptide adrenomedullin (AM). CGRP is a 37-amino acid neuropeptide, primarily released from sensory nerves, whilst AM is produced by stimulated vascular cells, and amylin is secreted from the pancreas. They share vasodilator activity, albeit to varying extents depending on species and tissue. In particular, CGRP has potent activity in the cerebral circulation, which is possibly relevant to the pathology of migraine, whilst vascular sources of AM contribute to dysfunction in cardiovascular disease. Both peptides exhibit potent activity in microvascular beds. All three peptides can act on a family of CGRP receptors that consist of calcitonin receptor-like receptor (CL) linked to one of three receptor activity-modifying proteins (RAMPs) that are essential for functional activity. The association of CL with RAMP1 produces a CGRP receptor, with RAMP2 an AM receptor and with RAMP3 a CGRP/AM receptor. Evidence for the selective activity of the first nonpeptide CGRP antagonist BIBN4096BS for the CGRP receptor is presented. The cardiovascular activity of these peptides in a range of species and in human clinical conditions is detailed, and potential therapeutic applications based on use of antagonists and gene targeting of agonists are discussed.

Disassociated increases of adrenomedullin in the rat cerebrospinal fluid and plasma after salt loading and systemic administration of lipopolysaccharide

To determine the role of adrenomedullin (AM) in the fluid electrolyte homeostasis and endotoxin shock, cerebral spinal fluid (CSF) and plasma were sampled from rats after respective challenges. The AM levels were measured by a highly sensitive immunoassay. The AM levels in the CSF of the rats anesthetized with ether (10.7 +/- 0.60 fmol/ml) were significantly higher than those with isoflurane 5.17 +/- 0.70 fmol/ml, P < 0.01), while the plasma level did not differ significantly. The CSF levels of the rats received 2% saline drinking increased to 3 and 4 folds at day 5 and day 7, respectively, while the plasma levels did not differ from controls at both time points. The AM levels in CSF or plasma increased to 1.5 and 3 folds at 1.5 h after intraperitoneal (i.p.) administration of lipopolysaccharide (LPS, 5 mg/kg), reached 6.5 and 30 folds at 6 h, respectively, while no change was observed in the controls. The present findings suggest that AM in the CSF is regulated independently from that in the plasma, the centrally synthesized AM plays and important role in the regulation of the fluid electrolyte homeostasis. Furthermore, the circulatory AM plays an important role in the endotoxin shock.

Adrenomedullin is increased in the portal circulation during chronic sepsis in rats

BACKGROUND

A clinical hallmark of sepsis is an early, hyperdynamic cardiac phase (increased cardiac output) that degrades to a hypodynamic phase, which results in poor gut perfusion and subsequent gastrointestinal (GI) hypoxemia, tissue ischemia, necrosis and loss of gut barrier function. Studies in rat cecal-ligation and puncture suggest that the potent vasodilator adrenomedullin (AM) might initiate or maintain the hypodynamic phase. We hypothesize that AM expression is increased in acute Escherichia coli bacteremia and chronic E coli-Bacteroides fragilis sepsis.

METHODS

Acute bacteremia: male Sprague-Dawley rats were anesthetized (urethane/alpha-chloralose), tracheotomized, and cannulated for monitoring blood pressure (MABP) and heart rate (HR) and for infusion of E coli (10(9) colony-forming units [CFU] E coli per 1 mL normal saline) and blood sampling. Arterial blood was withdrawn for arterial blood gas (ABG) measurements every 60 minutes. After 6 hours, we harvested lung, liver, kidney, spleen, and small intestine tissue samples and drew arterial and portal blood for AM enzyme-linked immunosorbent assay (ELISA). Chronic sepsis: a sterile gauze pad was implanted and animals recovered for 5 days. Twenty-four hours (10(9) CFU E coli and 10(9) CFU B fragilis per 1 mL normal saline; 1 injection) or 72 hours (2 injections) after the inoculation of the back sponge, rats were anesthetized, intubated, and cannulated as above. MABP, HR, and ABG were measured for 1 hour before tissue and serum harvest for AM ELISA.

RESULTS

Sepsis increased HR and MABP in all groups. Acute sepsis caused a respiratory alkalosis and pH was also elevated in chronic sepsis. Serum AM levels were increased in all groups compared with baseline and remained elevated at every time point, but were not different between saline controls and septic animals at any time point, except for the portal serum from the 72-hour chronic sepsis, which was elevated.

CONCLUSIONS

These data suggest that surgical manipulation alone is sufficient to stimulate AM secretion, most probably from endothelial cells. While the AM levels were decreasing at 72 hours compared with 6 hours or 24 hours in the arterial blood and the saline control portal blood, it remained elevated in the septic portal samples, suggesting that the sepsis-induced increase of AM was derived from the gut by a different mechanism than that which elevated arterial serum levels.

Adrenomedullin and adrenomedullin binding protein-1 downregulate TNF-alpha in macrophage cell line and rat Kupffer cells

Recent studies have demonstrated that administration of adrenomedullin (AM) and AM binding protein-1 (AMBP-1) maintains cardiovascular stability and reduces mortality in sepsis. However, the mechanism responsible for the beneficial effect of AM/AMBP-1 remains unknown. The aim of this study therefore was to determine whether AM/AMBP-1 directly reduces lipopolysaccharide (LPS)-induced secretion of TNF-alpha from murine macrophage-like cell line RAW 264.7 cells and Kupffer cells isolated from normal rats. TNF-alpha release and gene expression were determined by ELISA and RT-PCR, respectively. The results indicated that LPS increased TNF-alpha production from RAW cells by 38-63-fold in a dose- and time-dependent manner. Although incubation with AM or AMBP-1 alone inhibited LPS-induced TNF-alpha release by 14-22% and 13-22%, respectively, AM and AMBP-1 in combination significantly suppressed TNF-alpha production (by 24-35%). Moreover, the upregulated TNF-alpha mRNA by LPS stimulation was significantly reduced by AM/AMBP-1, but not by AM or AMBP-1 alone. In the Kupffer cells primary culture, AM or AMBP-1 alone inhibited LPS-induced TNF-alpha production by 52% and 44%, respectively. Co-culture with AM/AMBP-1 markedly reduced TNF-alpha production (by 90%). Moreover, AM or AMBP-1 alone decreased TNF-alpha mRNA expression by 41% and 36%, respectively, whereas the combination of AM/AMBP-1 decreased its expression by 63%. These results indicate that AM and AMBP-1 in combination effectively suppress LPS-induced TNF-alpha expression and release especially from primary cultured Kupffer cells, suggesting that the downregulatory effect of AM/AMBP-1 on proinflammatory cytokine TNF-alpha may represent a mechanism responsible for their beneficial effects in preventing inflammatory responses and tissue damage in sepsis.

Adrenomedullin and adrenomedullin binding protein-1: their role in the septic response

Adrenomedullin (AM) is a recently discovered, potent vasodilatory peptide with activities including maintenance of cardiovascular and renal homeostasis. Studies have indicated that AM is important in initiating the hyperdynamic response during the early stage of sepsis, and reduction of the vascular effects of AM marks the transition from the initial hyperdynamic phase to the late hypodynamic phase in experimental sepsis. The decreased AM responsiveness in late sepsis may be related to alterations in the AM receptor binding characteristics and/or signaling pathways. Genetic experiments have provided useful information by enhancing AM gene expression. Moreover, a plasma protein which binds AM, adrenomedullin binding protein-1 (AMBP-1), was reported very recently and is just beginning to be investigated as an important modulator in the biphasic septic response. In this regard, our recent results have demonstrated that AMBP-1 synergistically enhanced AM-induced vascular relaxation in both sham and septic animals. It appears that decreased levels of AMBP-1 play a critical role in producing vascular AM hyporesponsiveness during the late stage of sepsis. Furthermore, administration of AM and AMBP-1 in combination prevented the transition from the hyperdynamic to hypodynamic response during the progression of polymicrobial sepsis. Thus, modulation of vascular responsiveness to AM by AMBP-1 may provide a novel approach for the management of sepsis.