Hypotension and resistance to lipopolysaccharide-induced shock in transgenic mice overexpressing adrenomedullin in their vasculature

Sandwich immunoassay for adrenomedullin precursor and its practical application

Adrenomedullin (ADM) is a multifaceted peptide hormone involved in numerous physiological processes, including vascular stability, vasodilation, angiogenesis, and anti-inflammatory responses. The processing of ADM results in several fragments, including midregional proadrenomedullin (MR-proADM), and glycine-extended ADM (ADM-Gly) and bioactive ADM (bio-ADM). MR-proADM, the stable ADM fragment, and bio-ADM, the active form of ADM with a short half-life, have been shown to be potent biomarkers in a variety of pathologies. ADM-Gly, the direct precursor of bio-ADM, is a predominant form in human plasma, but remains less understood and least investigated. This study presents the development of a specific immunoluminometric assay for the quantification of ADM-Gly and offers a robust one-step approach for large-scale sample screening. Applied to human and rodent plasma, it elucidates the release kinetics and plasma half-life of ADM-Gly. Our findings confirm the predominance of ADM-Gly in healthy individuals and its significant release under pathological conditions. Our immunoluminometric assay enables precise measurement of ADM-Gly, advancing research into ADM-related pathophysiology and supporting its use as a biomarker and therapeutic target in various diseases.

A Focus on the Pathophysiology of Adrenomedullin Expression: Endothelitis and Organ Damage in Severe Viral and Bacterial Infections

Adrenomedullin (ADM) is a peptide hormone produced primarily in the adrenal glands, playing a crucial role in various physiological processes. As well as improving vascular integrity and decreasing vascular permeability, ADM acts as a vasodilator, positive inotrope, diuretic, natriuretic and bronchodilator, antagonizing angiotensin II by inhibiting aldosterone secretion. ADM also has antihypertrophic, anti-apoptotic, antifibrotic, antioxidant, angiogenic and immunoregulatory effects and antimicrobial properties. ADM expression is upregulated by hypoxia, inflammation-inducing cytokines, viral or bacterial substances, strength of shear stress, and leakage of blood vessels. These pathological conditions are established during systemic inflammation that can result from infections, surgery, trauma/accidents or burns. The ability to rapidly identify infections and the prognostic, predictive power makes it a valuable tool in severe viral and bacterial infections burdened by high incidence and mortality. This review sheds light on the pathophysiological processes that in severe viral or bacterial infections cause endothelitis up to the development of organ damage, the resulting increase in ADM levels dosed through its more stable peptide mid-regional proadrenomedullin (MR-proADM), the most significant studies that attest to its diagnostic and prognostic accuracy in highlighting the severity of viral or bacterial infections and appropriate therapeutic insights.

Receptor activity-modifying proteins of adrenomedullin (RAMP2/3): Roles in the pathogenesis of ARDS

Acute respiratory distress syndrome (ARDS) is a life-threatening lung condition characterized by widespread inflammation and pulmonary edema. Adrenomedullin (AM), a bioactive peptide with various functions, is expected to be applied in treating ARDS. Its functions are regulated primarily by two receptor activity-modifying proteins, RAMP2 and RAMP3, which bind to the AM receptor calcitonin receptor-like receptor (CLR). However, the roles of RAMP2 and RAMP3 in ARDS remain unclear. We generated a mouse model of ARDS via intratracheal administration of lipopolysaccharide (LPS), and analyzed the pathophysiological significance of RAMP2 and RAMP3. RAMP2 expression declined with LPS administration, whereas RAMP3 expression increased at low doses and decreased at high doses of LPS. After LPS administration, drug-inducible vascular endothelial cell-specific RAMP2 knockout mice (DI-E-RAMP2-/-) showed reduced survival, increased lung weight, and had more apoptotic cells in the lungs. DI-E-RAMP2-/- mice exhibited reduced expression of Epac1 (which regulates vascular endothelial cell barrier function), while RAMP3 was upregulated in compensation. In contrast, after LPS administration, RAMP3-/- mice showed no significant changes in survival, lung weight, or lung pathology, although they exhibited significant downregulation of iNOS, TNF-α, and NLRP3 during the later stages of inflammation. Based on transcriptomic analysis, RAMP2 contributed more to the circulation-regulating effects of AM, whereas RAMP3 contributed more to its inflammation-regulating effects. These findings indicate that, while both RAMP2 and RAMP3 participate in ARDS pathogenesis, their functions differ distinctly. Further elucidation of the pathophysiological significance and functional differences between RAMP2 and RAMP3 is critical for the future therapeutic application of AM in ARDS.

Adrenomedullin Therapy in Moderate to Severe COVID-19

The 2019 coronavirus (COVID-19) pandemic is still in progress, and a significant number of patients have presented with severe illness. Recently introduced vaccines, antiviral medicines, and antibody formulations can suppress COVID-19 symptoms and decrease the number of patients exhibiting severe disease. However, complete avoidance of severe COVID-19 has not been achieved, and more importantly, there are insufficient methods to treat it. Adrenomedullin (AM) is an endogenous peptide that maintains vascular tone and endothelial barrier function. The AM plasma level is markedly increased during severe inflammatory disorders, such as sepsis, pneumonia, and COVID-19, and is associated with the severity of inflammation and its prognosis. In this study, exogenous AM administration reduced inflammation and related organ damage in rodent models. The results of this study strongly suggest that AM could be an alternative therapy in severe inflammation disorders, including COVID-19. We have previously developed an AM formulation to treat inflammatory bowel disease and are currently conducting an investigator-initiated phase 2a trial for moderate to severe COVID-19 using the same formulation. This review presents the basal AM information and the most recent translational AM/COVID-19 study.

Mid-Regional Proadrenomedullin (MR-proADM) and Microcirculation in Monitoring Organ Dysfunction of Critical Care Patients With Infection: A Prospective Observational Pilot Study

Introduction: Microvascular alterations are involved in the development of organ injury in critical care patients. Mid-regional proadrenomedullin (MR-proADM) may predict organ damage and its evolution. The main objective of this study was to assess the correlation between MR-proADM and microvascular flow index (MFI) in a small cohort of 20 adult critical care patients diagnosed with infection, sepsis, or septic shock. Further objectives were to evaluate the correlation between the clearance of MR-proADM and the variables of microcirculation and between MR-proADM and the Sequential Organ Failure Assessment (SOFA) score.

Materials and Methods: This is a prospective observational pilot study. Inclusion criteria: consecutive adult patients admitted to intensive care unit (ICU) for or with infection-related illness. Daily measurement of MR-proADM and calculation of the SOFA score from admission in ICU to day 5. Repeated evaluations of sublingual microcirculation, collection of clinical data, and laboratory tests.

Results: Primary outcome: MR-proADM was not significantly correlated to the MFI at admission in ICU. A clearance of MR-proADM of 20% or more in the first 24 h was related to the improvement of the MFIs and MFIt [percentual variation of the MFIs + 12.35 (6.01–14.59)% vs. +2.23 (−4.45–6.01)%, p = 0.005; MFIt +9.09 (4.53–16.26)% vs. −1.43 (−4.36–3.12)%, p = 0.002].

Conclusion: This study did not support a direct correlation of MR-proADM with the MFI at admission in ICU; however, it showed a good correlation between the clearance of MR-proADM, MFI, and other microvascular variables. This study also supported the prognostic value of the marker. Adequately powered studies should be performed to confirm the findings.

Adrenomedullin: A Novel Therapeutic for the Treatment of Inflammatory Bowel Disease

Adrenomedullin (AM) is a bioactive peptide with various physiological functions, including vasodilation, angiogenesis, anti-inflammation, organ protection, and tissue repair. AM suppresses inflammatory cytokine production in the intestinal mucosa, improves vascular and lymphatic regeneration and function, mucosal epithelial repair, and immune function in the intestinal bacteria of animal models with intestinal inflammation. We have been promoting translational research to develop novel therapeutic agents for inflammatory bowel disease (IBD) using AM and have started clinical research for IBD patients since 2010. A multicenter clinical trial is currently underway in Japan for patients with refractory ulcerative colitis and Crohn’s disease. Moreover, since current AM administration is limited to continuous intravenous infusion, the development of a subcutaneous formulation using long-acting AM is underway for outpatient treatment.

Adrenomedullin Ameliorates Pulmonary Fibrosis by Regulating TGF-ß-Smads Signaling and Myofibroblast Differentiation

Pulmonary fibrosis is an irreversible, potentially fatal disease. Adrenomedullin (AM) is a multifunctional peptide whose activity is regulated by receptor activity-modifying protein 2 (RAMP2). In the present study, we used the bleomycin (BLM)-induced mouse pulmonary fibrosis model to investigate the pathophysiological significance of the AM-RAMP2 system in the lung. In heterozygous AM knockout mice (AM+/-), hydroxyproline content and Ashcroft scores reflecting the fibrosis severity were significantly higher than in wild-type mice (WT). During the acute phase after BLM administration, FACS analysis showed significant increases in eosinophil, monocyte, and neutrophil infiltration into the lungs of AM+/-. During the chronic phase, fibrosis-related molecules were upregulated in AM+/-. Notably, nearly identical changes were observed in RAMP2+/-. AM administration reduced fibrosis severity. In the lungs of BLM-administered AM+/-, the activation level of Smad3, a receptor-activated Smad, was higher than in WT. In addition, Smad7, an antagonistic Smad, was downregulated and microRNA-21, which targets Smad7, was upregulated compared to WT. Isolated AM+/- lung fibroblasts showed less proliferation and migration capacity than WT fibroblasts. Stimulation with TGF-β increased the numbers of α-SMA-positive myofibroblasts, which were more prominent among AM+/- cells. TGF-β-stimulated AM+/- myofibroblasts were larger and exhibited greater contractility and extracellular matrix production than WT cells. These cells were α-SMA (+), F-actin (+), and Ki-67(-) and appeared to be nonproliferating myofibroblasts (non-p-MyoFbs), which contribute to the severity of fibrosis. Our findings suggest that in addition to suppressing inflammation, the AM-RAMP2 system ameliorates pulmonary fibrosis by suppressing TGF-β-Smad3 signaling, microRNA-21 activity and differentiation into non-p-MyoFbs.

Diagnostic and prognostic blood biomarkers in vascular dementia: From the viewpoint of ischemic stroke

Reliable quantitative blood biomarkers are important in vascular dementia (VaD) because early diagnosis and therapeutic intervention are effective in preventing progression of dementia. Although many blood biomarkers for acute ischemic stroke (AIS) or VaD have been reported, there are few reliable blood biomarkers. VaD and AIS have similar pathological conditions that are associated with small vessel disease (SVD) such as oxidative stress, inflammation, endothelial dysfunction, and neuronal injury. Therefore, it may be possible to find superior blood biomarkers of VaD among AIS blood biomarkers. Owing to recent developments, noncoding RNAs such as microRNA and long noncoding RNA, which can be analyzed using a single drop of blood, are also particularly reliable VaD markers because they stably reflect brain tissue damage. A multimarker combining several blood biomarkers or artificial intelligence technology may also be beneficial to compensate for insufficiencies of a single blood biomarker. This review describes the blood biomarkers of VaD and how they are related to blood biomarkers of AIS.

Lack of adrenomedullin in mouse endothelial cells results in defective angiogenesis, enhanced vascular permeability, less metastasis, and more brain damage

Adrenomedullin (AM) is a vasodilating peptide involved in the regulation of circulatory homeostasis and in the pathophysiology of certain cardiovascular diseases. AM plays critical roles in blood vessels, including regulation of vascular stability and permeability. To elucidate the autocrine/paracrine function of AM in endothelial cells (EC) in vivo, a conditional knockout of AM in EC (AM(EC-KO)) was used. The amount of vascularization of the matrigel implants was lower in AM(EC-KO) mice indicating a defective angiogenesis. Moreover, ablation of AM in EC revealed increased vascular permeability in comparison with wild type (WT) littermates. In addition, AM(EC-KO) lungs exhibited significantly less tumor growth than littermate WT mice using a syngeneic model of metastasis. Furthermore, following middle cerebral artery permanent occlusion, there was a significant infarct size decrease in animals lacking endothelial AM when compared to their WT counterparts. AM is an important regulator of EC function, angiogenesis, tumorigenesis, and brain response to ischemia. Studies of AM should bring novel approaches to the treatment of vascular diseases.

Immunoneutralization of procalcitonin as therapy of sepsis

Prior studies have demonstrated that the prohormone, procalcitonin (ProCT), and its component calcitonin precursors (CTpr) are increased in the serum of septic patients, correlate with the severity of the illness, and persist for relatively long periods of time. Animal studies in septic hamsters have revealed that the administration of ProCT is toxic and that immunoneutralization with IgG that is reactive to this molecule significantly improves survival. A large animal model of a very rapidly lethal polymicrobial sepsis has been developed in the pig in order to measure continuous physiological and metabolic parameters and also to compare the effects in this animal of an immunoneutralization, which is performed late in the course of the disease, to an identical, but early, therapy. Based upon the physiological and metabolic parameters, the late therapy, which was initiated during the fourth hour at a time when pigs were nearly moribund, was found to be as beneficial as early therapy. In both late and early therapy, the only animals to survive at the predetermined time of euthanasia were those which had received immunoneutralization therapy.

Dysregulation of intracellular calcium transporters in animal models of sepsis-induced cardiomyopathy

Sepsis-induced cardiomyopathy (SIC) develops as the result of myocardial calcium (Ca) dysregulation. Here we reviewed all published studies that quantified the dysfunction of intracellular Ca transporters and the myofilaments in animal models of SIC. Cardiomyocytes isolated from septic animals showed, invariably, a decreased twitch amplitude, which is frequently caused by a decrease in the amplitude of cellular Ca transients (ΔCai) and sarcoplasmic reticulum (SR) Ca load (CaSR). Underlying these deficits, the L-type Ca channel is downregulated, through mechanisms that may involve adrenomedullin-mediated redox signaling. The SR Ca pump is also inhibited, through oxidative modifications (sulfonylation) of one reactive thiol group (on Cys) and/or modulation of phospholamban. Diastolic Ca leak of ryanodine receptors is frequently increased. In contrast, Na/Ca exchange inhibition may play a partially compensatory role by increasing CaSR and ΔCai. The action potential is usually shortened. Myofilaments show a bidirectional regulation, with decreased Ca sensitivity in milder forms of disease (due to troponin I hyperphosphorylation) and an increase (redox mediated) in more severe forms. Most deficits occurred similarly in two different disease models, induced by either intraperitoneal administration of bacterial lipopolysaccharide or cecal ligation and puncture. In conclusion, substantial cumulative evidence implicates various Ca transporters and the myofilaments in SIC pathology. What is less clear, however, are the identity and interplay of the signaling pathways that are responsible for Ca transporters dysfunction. With few exceptions, all studies we found used solely male animals. Identifying sex differences in Ca dysregulation in SIC becomes, therefore, another priority.

A pilot study on the diagnostic accuracy of proadrenomedullin and proatrial natriuretic Peptide in lower respiratory tract infections

Background :

Pneumonia is the leading cause of death among infectious diseases in developed countries. However, the severity of pneumonia requiring hospitalization often makes the initial diagnosis difficult because of an equivocal clinical picture or interpretation of the chest film. The objective of the present study was to assess the usefulness of the plasma levels of mid-regional proadrenomedullin (MR-proADM) and mid-regional proatrial natriuretic peptide (MR-proANP) in differentiating pneumonia from other lower respiratory tract infections (LRTIs).

Methods :

A retrospective study was conducted. The plasma levels of MR-proADM and MR-proANP were measured in 85 patients hospitalized for LRTIs, 56 of whom with diagnosis of pneumonia and 29 with other LRTIs.

Results :

The patients with pneumonia had increased MR-proADM levels (median 1.46 nmol/L [IQR 25-75, 0.82-2.02 nmol/L]) compared with the patients with other LRTIs (median 0.88 nmol/mL [0.71-1.39 nmol/L]) (p= 0.04). However, the MR-proANP levels did not show differences between the groups. The optimal threshold of MR-proADM to predict pneumonia was 1.5 nmol/L, which yielded a sensitivity of 51.7% (95% CI, 38.0-65.3), a 79.3% specificity (95% CI, 60.3-92.0), and an odds ratio of 6.64 (95% CI, 1.32-32.85). The combination of this parameter with C-reactive protein in an “and” rule increased the specificity for detecting pneumonia significantly.

Conclusion :

MR-proADM levels (but not MR-proANP levels) are increased in patients with pneumonia although its discriminatory power is moderate.

Adrenomedullin Function in Vascular Endothelial Cells: Insights from Genetic Mouse Models

Adrenomedullin is a highly conserved peptide implicated in a variety of physiological processes ranging from pregnancy and embryonic development to tumor progression. This review highlights past and present studies that have contributed to our current appreciation of the important roles adrenomedullin plays in both normal and disease conditions. We provide a particular emphasis on the functions of adrenomedullin in vascular endothelial cells and how experimental approaches in genetic mouse models have helped to drive the field forward.

Overexpression of Bcl-2 in vascular endothelium inhibits the microvascular lesions of diabetic retinopathy

Recent studies on the pathogenesis of diabetic retinopathy have focused on correcting adverse biochemical alterations, but there have been fewer efforts to enhance prosurvival pathways. Bcl-2 is the archetypal member of a group of antiapoptotic proteins. In this study, we investigated the ability of overexpressing Bcl-2 in vascular endothelium to protect against early stages of diabetic retinopathy. Transgenic mice overexpressing Bcl-2 regulated by the pre-proendothelin promoter were generated, resulting in increased endothelial Bcl-2. Diabetes was induced with streptozotocin, and mice were sacrificed at 2 months of study to measure superoxide generation, leukostasis, and immunohistochemistry, and at 7 months to assess retinal histopathology. Diabetes of 2 months duration caused a significant decrease in expression of Bcl-2 in retina, upregulation of Bax in whole retina and isolated retinal microvessels, and increased generation of retinal superoxide and leukostasis. Seven months of diabetes caused a significant increase in the number of degenerate (acellular) capillaries in diabetic animals. Furthermore, overexpression of Bcl-2 in the vascular endothelium inhibited the diabetes-induced degeneration of retinal capillaries and aberrant superoxide generation, but had no effect on Bax expression or leukostasis. Therefore, overexpression of Bcl-2 in endothelial cells inhibits the capillary degeneration that is characteristic of the early stages of diabetic retinopathy, and this effect seems likely to involve inhibition of oxidative stress.

Midregional proadrenomedullin as a prognostic tool in community-acquired pneumonia

BACKGROUND

Midregional proadrenomedullin (MR-proADM) is a potential prognostic biomarker in patients with community-acquired pneumonia (CAP). Previous work has been hampered by sample size and illness spectrum limits. We sought to describe the pattern of MR-proADM in a broad CAP cohort, confirm its prognostic role, and compare its performance to procalcitonin, a novel biomarker of infection.

METHODS

We conducted a multicenter prospective cohort study in 28 community and teaching EDs. Patients with a clinical and radiographic diagnosis of CAP were enrolled. We stratified MR-proADM levels a priori into quartiles and quantified severity of illness using the pneumonia severity index (PSI); and confusion (abbreviated mental test score of <or= 8), urea >or= 7 mmol/L, respiratory rate >or= 30 breaths/min, BP < 90 mm Hg systolic or < 60 mm Hg diastolic, age >or= 65 years (CURB-65). The primary outcome was 30-day mortality.

RESULTS

A total of 1,653 patients formed the study cohort. MR-proADM levels consistently rose with PSI class and 30-day mortality (p < 0.001). MR-proADM had a higher area under the curve for 30-day mortality than procalcitonin (0.76 vs 0.65, respectively; p < 0.001), but adding MR-proADM to the PSI in all subjects minimally improved performance. Among low-risk subjects (PSI classes I to III), mortality was low and did not differ by MR-proADM quartile. However, among high-risk subjects (PSI class IV/V; n = 546), subjects in the highest MR-proADM quartile (n = 232; 42%) had higher 30-day mortality than those in MR-proADM quartiles 1 to 3 (23% vs 9%, respectively; p < 0.0001). Similar results were seen with CURB-65. MR-proADM and procalcitonin levels were generally concordant; only 6% of PSI class IV/V subjects in the highest MR-proADM quartile had very low procalcitonin levels (< 0.1 ng/mL).

CONCLUSIONS

In our multicenter CAP cohort, MR-proADM levels correlate with increasing severity of illness and death. High MR-proADM levels offer additional risk stratification in high-risk CAP patients, but otherwise MR-proADM levels do not alter PSI-based risk assessment in most CAP patients.

Regulation of nitric oxide signalling by thrombospondin 1: implications for anti-angiogenic therapies

In addition to long-term regulation of angiogenesis, angiogenic growth factor signalling through nitric oxide (NO) acutely controls blood flow and haemostasis. Inhibition of this pathway may account for the hypertensive and pro-thrombotic side effects of the vascular endothelial growth factor antagonists that are currently used for cancer treatment. The first identified endogenous angiogenesis inhibitor, thrombospondin 1, also controls tissue perfusion, haemostasis and radiosensitivity by antagonizing NO signalling. We examine the role of these and other emerging activities of thrombospondin 1 in cancer. Clarifying how endogenous and therapeutic angiogenesis inhibitors regulate vascular NO signalling could facilitate development of more selective inhibitors.

The GPCR modulator protein RAMP2 is essential for angiogenesis and vascular integrity

Adrenomedullin (AM) is a peptide involved both in the pathogenesis of cardiovascular diseases and in circulatory homeostasis. The high-affinity AM receptor is composed of receptor activity-modifying protein 2 or 3 (RAMP2 or -3) and the GPCR calcitonin receptor-like receptor. Testing our hypothesis that RAMP2 is a key determinant of the effects of AM on the vasculature, we generated and analyzed mice lacking RAMP2. Similar to AM-/- embryos, RAMP2-/- embryos died in utero at midgestation due to vascular fragility that led to severe edema and hemorrhage. Vascular ECs in RAMP2-/- embryos were severely deformed and detached from the basement membrane. In addition, the abnormally thin arterial walls of these mice had a severe disruption of their typically multilayer structure. Expression of tight junction, adherence junction, and basement membrane molecules by ECs was diminished in RAMP2-/- embryos, leading to paracellular leakage and likely contributing to the severe edema observed. In adult RAMP2+/- mice, reduced RAMP2 expression led to vascular hyperpermeability and impaired neovascularization. Conversely, ECs overexpressing RAMP2 had enhanced capillary formation, firmer tight junctions, and reduced vascular permeability. Our findings in human cells and in mice demonstrate that RAMP2 is a key determinant of the effects of AM on the vasculature and is essential for angiogenesis and vascular integrity.

Mice heterozygous for adrenomedullin exhibit a more extreme inflammatory response to endotoxin-induced septic shock

Adrenomedullin (AM) is a highly conserved peptide that can act as a potent vasodilator, anti-microbial factor and anti-inflammatory factor. Several studies have implicated diverse roles for AM in regulating the inflammatory and hemodynamic responses to septic shock. Moreover, during sepsis the receptors that mediate AM signaling [calcitonin receptor-like receptor (calcrl) and receptor activity modifying proteins (RAMP) 2 and 3] undergo dynamic and robust changes in their expression. Although numerous studies have used animal models to study the role of administered or increased AM in septic animals, genetic studies to determine the consequences of reduced AM during septic shock have not yet been performed. Here, we used a murine model of lipopolysaccharide (LPS)-induced septic shock to assess the inflammatory response in mice heterozygous for the AM gene. Following LPS challenge, AM(+/-) mice had higher expression of TNF-alpha and IL-1beta than LPS-treated wild-type (WT) controls. Consequently, serum TNF-alpha was also significantly elevated in LPS-treated AM(+/-) mice compared to WT LPS-treated mice. We also observed higher serum levels of liver enzymes, suggesting more advanced end-organ damage in mice with genetically reduced AM. Finally, we found that RAMP2 and calcrl expression levels were markedly reduced in LPS-treated mice, whereas RAMP3 expression was significantly elevated. Importantly, these changes in receptor gene expression were conserved in AM(+/-) mice, demonstrating that AM peptide itself does not impact directly on the expression of the genes encoding its receptors. We, therefore, conclude that during septic shock the dynamic modulation of AM and its receptors primarily functions to dampen the inflammatory response.

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.

Rapid zygosity determination in mice by SYBR Green real-time genomic PCR of a crude DNA solution

We examined whether crude DNA extracts prepared from gene-engineered mouse tissues are suitable as a template for zygosity determination by SYBR Green real-time genomic PCR. A crude DNA solution was prepared by brief incubation with lysis buffer containing ear, tail, or fetus of ROSA26 mouse, a gene-trapped strain carrying the beta-galactosidase (beta-gal) gene. Five serially diluted crude DNA samples (original, 2-, 4-, 8-, 16-diluted) were next prepared and then subjected to three-step (95 degrees C, 60 degrees C and 72 degrees C) reactions of real-time PCR to detect the beta-gal gene and the receptor-activity-modifying protein 3 (ramp3) gene (as an internal reference gene). The slopes of standard curves obtained from the real-time PCR indicated that amplification efficiency was approximately 99%, and the efficiencies of target and reference were almost equal. With this system, we next determined the zygosity of mice derived from mating heterozygous ROSA26 females and males, and found a sharp distinction in zygosity, wild-type, heterozygous and homozygous. Assessment of crude DNA samples from other gene-engineered mice including B6ZP3Cre-Tg, B6rAM-Tg, and Ramp2-gene-targeted strains revealed that our method was effective for determination of zygosity. The present method is more convenient and rapid than formerly published methods employing purified genomic DNA as a template. Our method will be particularly useful for experiments requiring rapid and accurate genotyping of gene-modified animals/fetuses.

Adrenomedullin ameliorates lipopolysaccharide-induced acute lung injury in rats

Adrenomedullin (AM), an endogenous peptide, has been shown to have a variety of protective effects on the cardiovascular system. However, the effect of AM on acute lung injury remains unknown. Accordingly, we investigated whether AM infusion ameliorates lipopolysaccharide (LPS)-induced acute lung injury in rats. Rats were randomized to receive continuous intravenous infusion of AM (0.1 microg x kg(-1) x min(-1)) or vehicle through a microosmotic pump. The animals were intratracheally injected with either LPS (1 mg/kg) or saline. At 6 and 18 h after intratracheal instillation, we performed histological examination and bronchoalveolar lavage and assessed the lung wet/dry weight ratio as an index of acute lung injury. Then we measured the numbers of total cells and neutrophils and the levels of tumor necrosis factor (TNF)-alpha and cytokine-induced neutrophil chemoattractant (CINC) in bronchoalveolar lavage fluid (BALF). In addition, we evaluated BALF total protein and albumin levels as indexes of lung permeability. LPS instillation caused severe acute lung injury, as indicated by the histological findings and the lung wet/dry weight ratio. However, AM infusion attenuated these LPS-induced abnormalities. AM decreased the numbers of total cells and neutrophils and the levels of TNF-alpha and CINC in BALF. AM also reduced BALF total protein and albumin levels. In addition, AM significantly suppressed apoptosis of alveolar wall cells as indicated by cleaved caspase-3 staining. In conclusion, continuous infusion of AM ameliorated LPS-induced acute lung injury in rats. This beneficial effect of AM on acute lung injury may be mediated by inhibition of inflammation, hyperpermeability, and alveolar wall cell apoptosis.

Adrenomedullin reduces vascular hyperpermeability and improves survival in rat septic shock

OBJECTIVE

Current therapies of sepsis and septic shock require administration of a large volume of fluid to maintain hemodynamic stability. The vasoregulatory peptide adrenomedullin has been shown to prevent the transition to the fatal hypocirculatory septic state by poorly understood mechanisms. We tested the hypothesis that therapeutic administration of adrenomedullin would reduce vascular hyperpermeability, thereby contributing to improved hemodynamics and survival.

DESIGN

Prospective randomized controlled animal study.

SUBJECTS

Male Sprague-Dawley rats (270 g).

INTERVENTIONS

We used 4.8 x 10(3) U/kg of Staphylococcus aureus alpha-toxin, a pore-forming exotoxin, to induce vascular leakage and circulatory shock in rats. The infusion rate was 24 microg/kg per hour. Adrenomedullin was started 1 h after alpha-toxin administration.

MEASUREMENT AND RESULTS

Infusion of alpha-toxin in rats induced cardiocirculatory failure resulting in a 6-h mortality of 53%. alpha-Toxin provoked massive vascular hyperpermeability, which was indicated by an enrichment of Evans blue dye albumin in the tissues of lung, liver, ileum and kidney. Plasma fluid loss led to a significant hemoconcentration. Hemodynamic impairment observed after alpha-toxin infusion was closely correlated to vascular hyperpermeability. Therapeutic administration of 24 microg/kg per hour adrenomedullin reduced 6-h mortality from 53% to 7%. Stabilization of the endothelial barrier by adrenomedullin was indicated by reduced extravasation of albumin and plasma fluid and may have contributed to hemodynamic improvement.

CONCLUSIONS

These data suggest that adrenomedullin-related reduction of vascular hyperpermeability might represent a novel and important mechanism contributing to the beneficial effects of this endogenous vasoregulatory peptide in sepsis and septic shock.

Adrenomedullin gene expression differences in mice do not affect blood pressure but modulate hypertension-induced pathology in males

Adrenomedullin (AM) is a potent vasodilator peptide in plasma at picomolar levels. Polymorphisms in the human AM gene have been associated with genetic predisposition to diabetic nephropathy and proteinuria with essential hypertension, and numerous studies have demonstrated that endogenous AM plays a role in protecting the heart and kidneys from fibrosis resulting from cardiovascular disease. Elevated plasma levels of AM are associated with pregnancy and sepsis and with cardiovascular stress and hypertension. However, there are no reports of the effects of genetic differences in the expression of the endogenous AM gene and of gender on blood pressure in these circumstances or on the pathological changes accompanying hypertension. To address these questions, we have generated mice having genetically controlled levels of AM mRNA ranging from approximately 50% to approximately 140% of wild-type levels. These modest changes in AM gene expression have no effect on basal blood pressure. Although pregnancy and sepsis increase plasma AM levels, genetically reducing AM production does not affect the transient hypotension that occurs during normal pregnancy or that is induced by treatment with lipopolysaccharide. Nor does the reduction of AM affect chronic hypertension caused by a renin transgene. However, 50% normal expression of AM enhances cardiac hypertrophy and renal damage in male, but not female, mice with a renin transgene. These observations suggest that the effect of gender on the role of AM in counteracting cardiovascular damage in humans merits careful evaluation.

Evolutionary history of the calcitonin gene-related peptide family in vertebrates revealed by comparative genomic analyses

The calcitonin gene-related peptide (CGRP) family is composed of CGRP, amylin and adrenomedullin (AM) in mammals. In teleost fish, AM forms an independent subfamily of five members (AM1-5), which inspired us to trace the evolutionary history of the CGRP family throughout vertebrates by comparative genomic approach. Linkage mapping and synteny analyses of the CGRP family genes in medaka, Oryzias latipes, revealed that AM1/CGRP, AM2/amylin, and AM5 genes were located on respective proto-chromosomes before the divergence of teleost lineage. In teleost fish, additional whole genome duplication generated AM1/4, CGRP1/2, AM2/3, but one of the duplicated amylin and AM5 genes was silenced. In mammals, the amylin or AM2 gene was translocated to different chromosomes, while the CGRP gene was multiplied in tandem to generate CGRP-alpha,beta, and recently identified calcitonin receptor-stimulating peptide genes. Based on these data, we identified a novel AM5 gene in several mammalian species as we previously did for AM2.

Adrenomedullin inhibits angiotensin II-induced oxidative stress via Csk-mediated inhibition of Src activity

We have demonstrated that adrenomedullin (AM) protects against angiotensin II (ANG II)-induced cardiovascular damage through the attenuation of increased oxidative stress observed in AM-deficient mice. However, the mechanism(s) that underlie this activity remain unclear. To address this question, we investigated the effect of AM on ANG II-stimulated reactive oxygen species (ROS) production in cultured rat aortic vascular smooth muscle cells (VSMCs). ANG II markedly increased ROS production through activation of NADPH oxidase. This effect was significantly attenuated by AM in a concentration-dependent manner. This effect was mimicked by dibutyl-cAMP and blocked by pretreatment with N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide hydrochloride (H-89), a protein kinase A inhibitor, and CGRP(8-37), an AM/CGRP receptor antagonist. This inhibitory effect of AM was also lost following the expression of a constitutively active Src. Moreover, AM intersected ANG II signaling by inducing COOH-terminal Src kinase (Csk) activation that, in turn, inhibits Src activation. These data, for the first time, demonstrate that AM attenuates the ANG II-induced increase in ROS in VSMCs via activation of Csk, thereby inhibiting Src activity.

Markers for sepsis diagnosis: what is useful?

Timely diagnosis of the different severities of septic inflammation is potentially lifesaving because therapies that have been shown to lower mortality should be initiated early. Sepsis and severe sepsis are accompanied by clinical and laboratory signs of systemic inflammation but patients with inflammation caused by noninfectious causes may present with similar signs and symptoms. It is important to identify markers for an early diagnosis of sepsis and organ dysfunction. This article presents currently interesting sepsis biomarkers. Other novel markers and their potential role are discussed.

Receptor activity-modifying proteins: RAMPing up adrenomedullin signaling

Adrenomedullin (AM) is a 52-amino-acid multifunctional peptide that circulates in the plasma in the low picomolar range and can exert a multitude of biological effects through an autocrine/paracrine mode of action. The mechanism by which AM transduces its signal represents a novel and pharmacologically tractable paradigm in G protein-coupled receptor signaling. Since its discovery in 1993, the study of AM has emerged into a new field of research with nearly 1800 publications that rivals the renown of other common factors like angiopoetin (1015 publications) and ghrelin (1550 publications). Despite the tremendous strides made in recent years toward unveiling the biochemical and cellular functions of AM, we are still lagging in our understanding of the essential roles of AM in normal and disease physiology. As discussed in this current review, a concerted effort to combine information from clinical, genomic, biochemical, and genetic mouse model sources can provide a focused view to help define the physiological functions of AM. Specifically, we find that certain conditions, such as pregnancy, cardiovascular disease, and sepsis, are associated with robust and dynamic changes in the expression of AM and AM receptor proteins, which together represent an elegant mechanism for altering the physiological responsiveness or function of AM. Thus, the modulation of AM signaling may be further exploited for therapeutic strategies in the management and treatment of human disease.

Adrenomedullin and CGRP interact with endogenous calcitonin-receptor-like receptor in endothelial cells and induce its desensitisation by different mechanisms

Adrenomedullin (AM) and calcitonin gene-related peptide (CGRP) are related peptides with distinct pharmacological profiles. Calcitonin-receptor-like receptor (CRLR, now known as CL) can function as either an AM receptor or a CGRP receptor, when cotransfected with receptor-activity-modifying proteins (RAMPs) that define ligand-binding specificity. The aim of the present study was to determine the role of endogenously expressed CL (EndoCL) in generating endogenous AM and CGRP receptors. We raised anti-human CL antibody and identified microvascular endothelial cells (MVECs) as a major CL-expressing cell type in tissues by immunohistochemistry. Cultured MVECs continue to express EndoCL as well as fully active endogenous AM- and CGRP-sensitive receptors in vitro, as demonstrated by the ability of both peptides to induce migration and Akt phosphorylation. We therefore tested the hypothesis that endothelial EndoCL can interact with both AM and CGRP by examining receptor internalisation and desensitisation (loss of the ability to induce Akt phosphorylation). We found that agonist-mediated internalisation of EndoCL occurs in response to AM but not CGRP in MVECs. However, AM-induced EndoCL internalisation was blocked by antagonists of both AM and CGRP receptors: AM(22-52) and CGRP(8-37), respectively. Furthermore, AM-induced EndoCL internalisation resulted in desensitisation not only of AM but also of CGRP receptors. Finally, CGRP also induced desensitisation of both endogenous AM and CGRP receptors, but did not mediate EndoCL internalisation despite interaction with this receptor. Thus, EndoCL interacts with both AM and CGRP, and simultaneously acts as a receptor for both peptides (i.e acting as an endogenous AM/CGRP receptor) in endothelial cells. Interaction with either ligand is sufficient to induce EndoCL desensitisation to both AM and CGRP, but differential mechanisms are involved since only AM induces EndoCL internalisation. These novel findings regarding regulation of EndoCL function in endothelial cells are likely to be of importance in conditions where AM or CGRP levels are elevated, such as cardiovascular disease, diabetes and inflammation.

Urocortin and adrenomedullin prevent lethal endotoxemia by down-regulating the inflammatory response

Urocortin 1 (UCN) and adrenomedullin (AM) are two neuropeptides that have emerged as potential endogenous anti-inflammatory factors based on their production by and binding to immune cells. Because human septic shock involves excessive inflammatory cytokine production, we investigated the effect of UCN and AM in the production of inflammatory mediators and their therapeutic actions in two models of septic shock. Both peptides down-regulated the production of inflammatory mediators by endotoxin-activated macrophages. The administration of UCN or AM protected against lethality after cecal ligation and puncture or after injection of bacterial endotoxin and prevented septic shock-associated histopathology, such as infiltration of inflammatory cells and intravascularly disseminated coagulation in various target organs. The therapeutic effect of UCN and AM was mediated by decreasing the local and systemic levels of a wide spectrum of inflammatory mediators, including cytokines, chemokines, and the acute phase protein serum amyloid A. Importantly, UCN or AM treatment was therapeutically effective in established endotoxemia. In conclusion, UCN and AM could represent two multistep therapeutic agents for human septic shock to be used in combination with other immunomodulatory agents or complementary as anti-inflammatory factors to other therapies.

Pathophysiologic and therapeutic implications of adrenomedullin in cardiovascular disorders

Adrenomedullin (AM) is a vasodilator peptide that originally isolated from pheochromocytoma tissue. However, the mRNA is expressed in the normal adrenal gland, heart, kidney and blood vessels. The human AM gene is located in the short arm of chromosome 11 and is composed of 4 exons. There are 2 single nucleotide polymorphisms in introns 1 and 3, and the 3'-end of the AM gene is flanked by a microsatellite marker of cytosine-adenine repeats that is associated with an increased risk of developing hypertension and diabetic nephropathy. AM gene expression is promoted by various stimuli, including inflammation, hypoxia, oxidative stress, mechanical stress and activation of the renin-angiotensin and sympathetic nervous systems. The AM gene promoter region possessed binding site for several transcription factors, including nuclear factor for interleukin-6 expression (NF-IL6) and activator protein 2 (AP-2). Further, plasma AM levels are increased in patients with various cardiovascular diseases, including hypertension, heart failure and renal failure. These findings suggest that AM plays a role in the development of or response to cardiovascular disease. Indeed, experimental and clinical studies have demonstrated that systemic infusion of AM may have a therapeutic effect on myocardial infarction, heart failure and renal failure. Further, vasopeptidase inhibitors which augment the bioactivity of endogenous AM may benefit patients with hypertension and arteriosclerosis. Finally, the angiogenic and cytoprotective properties of AM may have utility in revascularization and infarcted myocardium and ischemic limbs. Because of the potential clinical benefits of AM, indications for use and optimal dosing strategies should be established.

Perturbation of endothelial junction proteins by Staphylococcus aureus alpha-toxin: inhibition of endothelial gap formation by adrenomedullin

Endothelial hyperpermeability is a hallmark of an inflammatory reaction and contributes to tissue damage in severe infections. Loss of endothelial cell-cell adhesion leads to intercellular gap formation allowing paracellular fluid flux. Although Staphylococcus aureus alpha-toxin significantly contributed to staphylococci disease, little is known about its mechanism of endothelial hyperpermeability induction. Here, we demonstrate that in a model of isolated perfused rat ileum discontinuation of capillary vascular-endothelial-cadherin (VE-cadherin) was observed after bolus application of S. aureus alpha-toxin being inhibited by the endogenous peptide adrenomedullin (ADM). In vitro, alpha-toxin exposure induced loss of immunoreactivity of VE-cadherin and occludin in human cultured umbilical vein endothelial cells. Likewise, ADM blocked alpha-toxin-related junctional protein disappearance from intercellular sites. Additionally, cyclic AMP elevation was shown to stabilize endothelial barrier function after alpha-toxin application. Although no RhoA activation was noted after endothelial alpha-toxin exposure, inhibition of Rho kinase and myosin light chain kinase blocked loss of immunoreactivity of VE-cadherin and occludin as well as intercellular gap formation. In summary, stabilization of endothelial junctional integrity as indicated by interendothelial immunostaining might be an interesting approach to stabilize endothelial barrier function in severe S. aureus infections.

Differential induction of adrenomedullin, interleukins and tumour necrosis factor-alpha by lipopolysaccharide in rat tissues in vivo

The aim of the present study was to determine the temporal changes in tissue adrenomedullin (AM) and cytokine contents and cytokine and preproAM mRNA levels in the kidney, liver, adrenal gland and spleen of lipopolysaccharide (LPS)-treated rats. Rats were injected with LPS (10 mg/kg, i.p.). Radioimmunoassay and solution hybridization-RNase protection assays were used to follow the changes in AM and its mRNA levels, respectively; ELISA and reverse transcription-polymerase chain reaction were used to follow the changes in cytokines and their mRNA levels, respectively. In the kidney, the preproAM mRNA levels were increased 1 and 3 h after LPS treatment, whereas AM levels were decreased at 3 h. Interleukin (IL)-6 and IL-1beta levels were increased at 3 and 6 h, respectively. The preproAM mRNA levels were elevated in the liver 3 h after LPS injection. Concentrations of tumour necrosis factor (TNF)-alpha and IL-1beta were increased at l and 6 h, respectively. There were no changes in the levels of either preproAM mRNA or AM in the adrenal gland and the spleen. In the spleen, TNF-alpha levels were elevated at 1 and 3 h after LPS injection and IL-1beta was elevated at 1 and 6 h after LPS injection, whereas in the adrenal gland IL-1beta was elevated at 6 h after injection. The mRNA levels of the three cytokines were elevated at all three time intervals examined in the kidney, liver, adrenal gland and spleen, with the exception that TNF-alpha mRNA was not elevated in the adrenal gland at 6 h after LPS injection and IL-1beta mRNA was not elevated in the spleen at 3 and 6 h. The plasma concentrations of TNF-alpha were increased at 1 and 3 h after LPS injection, whereas plasma concentration of IL-1beta and IL-6 were elevated at 3 and 6 h for both. The present results suggest that the biosynthesis and secretion of AM may be differentially regulated in various tissues of rats injected with LPS and that AM may interact with cytokines during inflammation.

Autocrine peptide mediators of cerebral endothelial cells and their role in the regulation of blood-brain barrier

A unique feature of cerebral endothelial cells (CECs) is the formation of the blood-brain barrier (BBB), which contributes to the stability of the brain microenvironment. CECs are capable of producing several substances mediating endothelium-dependent vasorelaxation or vasoconstriction, regulating BBB permeability, and participating in the regulation of cell-cell interactions during inflammatory and immunological processes. The chemical nature of these mediators produced by CECs ranges from gaseous anorganic molecules (e.g. nitric oxide) through lipid mediators (e.g. prostaglandins) to peptides. Peptide mediators are a large and diverse family of bioactive molecules which can elicit multiple effects on cerebral endothelial functions. In this review, we summarize current knowledge of peptide mediators produced by CECs, such as adrenomedullin, angiotensin, endothelin and several others and their role in the regulation of BBB functions.

Adrenomedullin protects rat cerebral endothelial cells from oxidant damage in vitro

Increased permeability and reduced cerebral endothelial cell (CEC) viability induced by oxidative stress are the hallmarks of the blood-brain barrier disruption. In our experiments hydrogen peroxide (H2O2, 0.5 mM) induced a continuous decrease of the transendothelial electrical resistance (TEER) and resulted in intercellular gap formations in cultured rat CECs. Adrenomedullin (AM) increased TEER, enhanced peripheral localization of F-actin bands and attenuated the increased permeability induced by H2O2. Furthermore, AM treatment preserved mitochondrial membrane potential, attenuated cytochrome c release, and consequently improved CEC viability in H2O2 treated cultures. These results suggest that AM treatment protects CECs against oxidative injury.

Adrenomedullin treatment abolishes ileal mucosal hypoperfusion induced by Staphylococcus aureus α-toxin—An intravital microscopic study on an isolated rat ileum

OBJECTIVE

Disturbances of intestinal microcirculation associated with sepsis and septic shock result in diminished mucosal oxygenation. Tissue hypoxia as well as mediator formation may lead to intestinal mucosa dysfunction. As a consequence, bacteria and their products as well as gut-derived inflammatory mediators may further perpetuate septic and inflammatory events. Adrenomedullin is produced in the mucosa of the gastrointestinal tract and has been shown to improve survival in experimental sepsis. Using pore-forming Staphylococcus aureus alpha-toxin as a potent initiator of inflammatory reactions, we tested the hypothesis that exogenously added adrenomedullin improves ileal mucosal perfusion.

DESIGN

Prospective, experimental study.

SETTING

University laboratory.

SUBJECTS

Isolated perfused ileum from male Sprague-Dawley rats

INTERVENTIONS

Adrenomedullin treatment of S. aureus alpha-toxin infused ileum.

MEASUREMENT AND MAIN RESULTS

An infusion of alpha-toxin (0.05 microg/mL) induced a significant decrease of red blood cell velocity in villus terminal arterioles from 1.7 to 0.7 mm/sec assessed by intravital microscopy. This was accompanied by a significant reduction of mucosal hemoglobin oxygenation from 71.8% to 17.5% and impaired oxygen uptake. At constant bulk flow and oxygen delivery, these data indicate a redistribution of blood perfusion away from mucosa. Subsequent intervention with 0.1 microM adrenomedullin redistributed blood flow back toward the mucosa, causing an improvement of mucosal hemoglobin oxygenation and of organ oxygen uptake.

CONCLUSION

These data suggest that exogenously added adrenomedullin protects ileum mucosa by diminishing alpha-toxin-induced microcirculatory disturbances. Further investigations will have to clarify the therapeutic potential of adrenomedullin in sepsis-related gut dysfunction.

Expression of the adrenomedullin gene in adipose tissue

Adrenomedullin (AM) is a potent vasodilating peptide originally isolated from human pheochromocytoma cells. This report concerns the expression and secretion of AM from adipose tissue. Northern blot analysis demonstrated marked expression of AM mRNA in mouse adipose tissue. Expression levels in adipose tissues were 2.5-3.2 times higher than in the kidney. AM mRNA level in mature adipocytes was 7.3 times higher than in the stroma-vascular fraction of adipose tissue. In mature adipocyte culture, time-dependent increase of AM peptide concentration in the culture medium was detected. AM expression was also detected in human subcutaneous adipose tissue. Adipose AM expression significantly increased in obesity mouse model, high-fat diet fed mice and ob/ob mice. These results suggest that adipose tissue, especially mature adipocytes, is major source of AM in the body, and that adipocyte-derived AM plays a pathophysiological role in obesity.

LPS regulates a set of genes in primary murine macrophages by antagonising CSF-1 action

We previously reported that bacterial products such as LPS and CpG DNA down-modulated cell surface levels of the Colony Stimulating Factor (CSF)-1 receptor (CSF-1R) on primary murine macrophages in an all-or-nothing manner. Here we show that the ability of bacterial products to down-modulate the CSF-1R rendered bone marrow-derived macrophages (BMM) unresponsive to CSF-1 as assessed by Akt and ERK1/2 phosphorylation. Using toll-like receptor (tlr)9 as a model CSF-1-repressed gene, we show that LPS induced tlr9 expression in BMM only when CSF-1 was present, suggesting that LPS relieves CSF-1-mediated inhibition to induce gene expression. Using cDNA microarrays, we identified a cluster of similarly CSF-1 repressed genes in BMM. By real time PCR we confirmed that the expression of a selection of these genes, including integral membrane protein 2B (itm2b), receptor activity-modifying protein 2 (ramp2) and macrophage-specific gene 1 (mpg-1), were repressed by CSF-1 and were induced by LPS only in the presence of CSF-1. This pattern of gene regulation was also apparent in thioglycollate-elicited peritoneal macrophages (TEPM). LPS also counteracted CSF-1 action to induce mRNA expression of a number of transcription factors including interferon consensus sequence binding protein 1 (Icsbp1), suggesting that this mechanism leads to transcriptional reprogramming in macrophages. Since the majority of in vitro studies on macrophage biology do not include CSF-1, these genes represent a set of previously uncharacterised LPS-inducible genes. This study identifies a new mechanism of macrophage activation, in which LPS (and other toll-like receptor agonists) regulate gene expression by switching off the CSF-1R signal. This finding also provides a biological relevance to the well-documented ability of macrophage activators to down-modulate surface expression of the CSF-1R.

Adrenomedullin gene delivery alleviates hypertension and its secondary injuries of cardiovascular system

Adrenomedullin (AM) is a hypotensive peptide that functions as an important regulator in the cardiovascular and renal systems. The current study explored the potential therapeutic effects of delivering the human AM cDNA via a novel double-stranded adeno-associated virus vector (dsAAV) on hypertension and related complications in spontaneously hypertensive rats (SHR). A single dose of dsAAV-AM vector administered by tail vein injection into adult SHR resulted in significant reduction of systolic blood pressure at 2 weeks after gene delivery. This effect was observed through the entire duration of the experiment period (up to 16 weeks). Administration of dsAAV-AM also resulted in a decrease in total urine microalbumin content. Left ventricle and cardiomyocyte hypertrophy, fibrosis in the heart, glomerular sclerosis, and tubular injuries in the kidney were significantly reduced. Moreover, deterioration of hemodynamic variables was prevented in treated rats, as compared with the control groups. We conclude that AAV-mediated AM delivery can render a longterm and stable reduction of hypertension and protect against renal injury and cardiac remodeling in the spontaneously hypertensive rat model. Further preclinical studies are warranted for the development of a gene therapy strategy for human hypertension.

RELAXANT EFFECT OF ADRENOMEDULLIN ON BOVINE ISOLATED IRIS SPHINCTER MUSCLE UNDER RESTING CONDITIONS

1. The mechanisms involved in the fine adjustment of iris sphincter muscle tone are largely unknown. The aim of the present study was to clarify the effects of adrenomedullin on the resting tension of the bovine isolated iris sphincter muscle. 2. The motor activity of the bovine isolated iris sphincter muscle was measured isometrically. The effects of adrenomedullin on resting tension were analysed in the presence of indomethacin. The presence of adrenomedullin mRNA in the preparation was determined by reverse transcription-polymerase chain reaction. Immunolabelling for adrenomedullin was also performed. 3. Adrenomedullin significantly decreased the resting tension of the muscle. The relaxant effect of adrenomedullin was significantly inhibited by adrenomedullin (22-52), a putative antagonist for the adrenomedullin receptor, or calcitonin gene-related peptide (CGRP) (8-37), a putative antagonist for the CGRP1 receptor. The relaxant effect was almost completely blocked by a combination of adrenomedullin (22-52) and CGRP (8-37). 4. The relaxant effect of adrenomedullin was also significantly diminished by 2',5'-dideoxyadenosine, an inhibitor of adenylate cyclase, N(G)-nitro-L-arginine, an inhibitor of nitric oxide synthesis, or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase. 5. Reverse transcription-polymerase chain reaction analysis showed that adrenomedullin mRNA was expressed in the muscle strip. Immunopositive staining for adrenomedullin was detected in blood vessel cells and in the iris sphincter muscle cells. 6. These results suggest that adrenomedullin may be an autocrine and paracrine regulator of the resting tension of the iris sphincter muscle. Its biological effects may be due to the direct involvement of adrenomedullin receptors and also to the stimulation of CGRP1 receptors. The stimulation of these receptors by the peptide leads to the activation of adenylate cyclase and soluble guanylate cyclase and subsequent relaxation of the muscle strip.

Adrenomedullin reduces Staphylococcus aureus alpha-toxin-induced rat ileum microcirculatory damage

OBJECTIVE

Increased microvascular permeability and perfusion mismatch are hallmarks of sepsis or septic shock. The intestinal mucosa is very sensitive to tissue hypoxia. Intestinal mucosa dysfunction may allow translocation of bacteria and their products, thereby perpetuating sepsis and inflammation. Staphylococcus aureus alpha-toxin is a major pathogenicity determinant of this bacterium, provoking cardiovascular collapse. Current evidence suggests that the endogenous peptide adrenomedullin stabilizes circulatory homeostasis in systemic inflammatory response. Using alpha-toxin as a well-defined strong initiator of an inflammatory reaction, we tested the hypothesis that exogenously applied adrenomedullin stabilizes gut microcirculation.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Isolated, perfused ileum from male Sprague-Dawley rats and human umbilical vein endothelial cells.

INTERVENTIONS

Administration of S. aureus alpha-toxin before or after infusion of adrenomedullin.

MEASUREMENTS AND MAIN RESULTS

Injection of a bolus of 1 microg of alpha-toxin in the superior mesenteric artery in a constant-flow, blood-perfused preparation of rat ileum increased perfusion pressure and relative hemoglobin concentration and decreased mucosal hemoglobin oxygen saturation. Continuous infusion of adrenomedullin (0.1 micromol/L) significantly reduced these alpha-toxin-related effects. Severe microvascular hyperpermeability observed in alpha-toxin-exposed ileum was abolished by adrenomedullin pretreatment. In addition, adrenomedullin blocked alpha-toxin-induced endothelial myosin light chain phosphorylation, endothelial cell contraction, and subsequent loss of endothelial barrier function in vitro. Treatment of alpha-toxin (infusion of 0.05 microg/mL)-exposed ileum with adrenomedullin (0.1 micromol/L) started 10 mins after onset of toxin application also significantly reduced superior mesenteric artery pressure and permeability increase.

CONCLUSIONS

In summary, these data suggest that exogenous adrenomedullin protects ileum by reducing alpha-toxin-induced microcirculatory disturbances and by stabilizing endothelial barrier function.

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.

The vasoactive peptide adrenomedullin is secreted by adipocytes and inhibits lipolysis through NO-mediated beta-adrenergic agonist oxidation

Adipocytes are known to secrete a number of adipokines, but many adipocyte secretions and their functional importance remain to be characterized. This work shows that human white adipocytes and 3T3-F442A-derived adipocytes produce adrenomedullin (AM) and that AM acts in an autocrine/paracrine way on lipid metabolism by extracellular inactivation of isoproterenol, a beta-adrenergic agonist. AM is described as a counter-regulatory factor involved in the control of cardiovascular homeostasis. This peptide is believed to protect the heart from several complications implicated in obesity-linked cardiomorbidity, such as arterial hypertension, cardiac fibrosis, and decreased sinusal variability. The exact source of circulating AM remains a matter of debate, although endothelial and vascular smooth muscle cells seem to be important sites of production. We show that human adipose cells and 3T3-F442A-derived adipocytes express AM receptors and secrete AM. The function of this feature was investigated in 3T3-F442A cell line at the level of lipolysis regulation. AM inhibited beta-adrenergic-stimulated lipolysis by a nitric oxide (NO)-dependent mechanism, inducing a significant decrease in pD2 value for isoproterenol (8.6 +/- 0.2 vs. 9.8 +/- 0.1, P<0.001). This effect is cGMP-independent since it occurred in the presence of the NO-sensitive guanylate cyclase inhibitor ODQ. It is apparently mediated by a novel extracellular mechanism. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) demonstrated that AM-produced NO oxidized isoproterenol to generate its aminochrome, namely isoprenochrome. Isoprenochrome amounts were increased 3.62 +/- 1.13-fold in cell culture media (P<0.05). We describe for the first time that AM down-regulates lipolysis in adipocytes through the chemical modification of a beta-agonist.