Effects of adrenomedullin on acute ischaemia-induced collateral development and mobilization of bone-marrow-derived cells

Adrenomedullin for steroid-resistant ulcerative colitis: a randomized, double-blind, placebo-controlled phase-2a clinical trial

BACKGROUND

Adrenomedullin (AM) is a bioactive peptide having many pleiotropic effects, including mucosal healing and immunomodulation. AM has shown beneficial effects in rodent models and in preliminary study for patients with ulcerative colitis (UC). We performed a clinical trial to investigate the efficacy and safety of AM in patients with UC.

METHODS

This was a multi-center, double-blind, placebo-controlled phase-2a trial evaluating 28 patients in Japan with steroid-resistant UC. Patients were randomly assigned to four groups and given an infusion of 5, 10, 15 ng/kg/min of AM or placebo for 8 h per day for 14 days. The primary endpoint was the change in Mayo scores at 2 weeks. Main secondary endpoints included the change in Mayo scores and the rate of clinical remission at 8 weeks, defined as a Mayo score 0.

RESULTS

No differences in the primary or secondary endpoints were observed among the four groups at 2 weeks. Despite the insufficient tracking rate, the Mayo score at 8 weeks was only significantly decreased in the high-dose AM group (15 ng/kg/min) compared with the placebo group (- 9.3 ± 1.2 vs. - 3.0 ± 2.8, P = 0.035), with its rate of clinical remission at 8 weeks being significantly higher (3/3, 100% vs. 0/2, 0%, P = 0.025). We noted mild but no serious adverse events caused by the vasodilatory effect of AM.

CONCLUSIONS

In this double-blind randomized trial, we observed the complete remission at 8 weeks in patients with steroid-resistant UC receiving a high dose of AM.

CLINICAL TRIAL REGISTRY

JAPIC clinical trials information; Japic CTI-205255 (200410115290). https://www.clinicaltrials.jp/cti-user/trial/Search.jsp .

An angiogenic role for adrenomedullin in choroidal neovascularization

Purpose

Adrenomedullin (ADM) has been shown to take part in physiological and pathological angiogenesis. The purpose of this study was to investigate whether ADM signaling is involved in choroidal neovascularization (CNV) using a mouse model.

Methods and Results

CNV was induced by laser photocoagulation in 8-week-old C57BL/6 mice. ADM mRNA expression significantly increased following treatment, peaking 4 days thereafter. The expression of ADM receptor (ADM-R) components (CRLR, RAMP2 and RAMP 3) was higher in CD31⁺CD45⁻ endothelial cells (ECs) than CD31⁻CD45⁻ non-ECs. Inflammatory stimulation upregulated the expression of ADM not only in cell lines but also in cells in primary cultures of the choroid/retinal pigment epithelium complex. Supernatants from TNFα-treated macrophage cell lines potentiated the proliferation of ECs and this was partially suppressed by an ADM antagonist, ADM (22–52). Intravitreous injection of ADM (22–52) or ADM neutralizing monoclonal antibody (mAb) after laser treatment significantly reduced the size of CNV compared with vehicle-treated controls (p<0.01).

Conclusions

ADM signaling is involved in laser-induced CNV formation, because both an ADM antagonist and ADM mAb significantly inhibited it. Suppression of ADM signaling might be a valuable alternative treatment for CNV associated with age-related macular degeneration.

Adrenomedullin as a growth and cell fate regulatory factor for adult neural stem cells

The use of stem cells as a strategy for tissue repair and regeneration is one of the biomedical research areas that has attracted more interest in the past few years. Despite the classic belief that the central nervous system (CNS) was immutable, now it is well known that cell turnover occurs in the mature CNS. Postnatal neurogenesis is subjected to tight regulation by many growth factors, cell signals, and transcription factors. An emerging molecule involved in this process is adrenomedullin (AM). AM, a 52-amino acid peptide which exerts a plethora of physiological functions, acts as a growth and cell fate regulatory factor for adult neural stem and progenitor cells. AM regulates the proliferation rate and the differentiation into neurons, astrocytes, and oligodendrocytes of stem/progenitor cells, probably through the PI3K/Akt pathway. The active peptides derived from the AM gene are able to regulate the cytoskeleton dynamics, which is extremely important for mature neural cell morphogenesis. In addition, a defective cytoskeleton may impair cell cycle and migration, so AM may contribute to neural stem cell growth regulation by allowing cells to pass through mitosis. Regulation of AM levels may contribute to program stem cells for their use in medical therapies.

Role of adrenomedullin in the growth and differentiation of stem and progenitor cells

Stem cells have captured the imagination of the general public by their potential as new therapeutic tools in the fight against degenerative diseases. This potential is based on their capability for self-renewal and at the same time for producing progenitor cells that will eventually provide the building blocks for tissue and organ regeneration. These processes are carefully orchestrated in the organism by means of a series of molecular cues. An emerging molecule which is responsible for some of these physiological responses is adrenomedullin, a 52-amino acid regulatory peptide which increases proliferation and regulates cell fate of stem cells of different origins. Adrenomedullin binds to specific membrane receptors in stem cells and induces several intracellular pathways such as those involving cAMP, Akt, or MAPK. Regulation of adrenomedullin levels may help in directing the growth and differentiation of stem cells for applications (e.g., cell therapy) both in vitro and in vivo.

Activation of hypoxia-inducible factor 1 in skeletal muscle cells after exposure to damaged muscle cell debris

Skeletal muscle damage provokes complex repair mechanisms including recruitment of leukocytes as well as activation of myogenic precursor cells such as satellite cells. To study muscle cell repair mechanisms after muscle fiber damage, we used an in vitro model of scrape-injured myotubes. Exposing vital C2C12 myoblasts and myotubes to cell debris of damaged myotubes revealed mRNA upregulation of adrenomedullin (ADM), insulin-like growth factors 1 and 2, metallopeptidase 9, and monocyte chemoattractant protein11. When cell debris was treated with ultrasound, frozen in liquid nitrogen, or heat inactivated before addition to C2C12 cells, gene expression was drastically reduced or completely absent. Moreover, incubations of myoblasts with debris separated by transwell inserts indicated that direct cell contact is required for gene induction. Incubation with albumin and PolyIC ruled out that ADM induction by cell debris simply results from increased protein or nucleic acid concentrations in the supernatant. Because the genes, which were upregulated by cell debris, are potential target genes of hypoxia-inducible factor (HIF), cells were analyzed for HIF-1α expression. Western blot analysis showed accumulation of the α-subunit upon contact to cell debris. Knockdown of HIF-1α in C2C12 cells proved that activation of HIF-1 in response to cell debris was responsible for upregulating ADM and monocyte chemoattractant protein 1. Furthermore, by incubating cells on gas-permeable culture dishes, we excluded a reduced pericellular pO2 induced by cell debris as the cause for ADM upregulation. Our data suggest that damaged myofibers activate HIF-1 in neighboring myotubes and precursor myoblasts by direct contact, concomitantly upregulating factors necessary for angiogenesis, tissue regeneration, and phagocyte recruitment.

Lack of adrenomedullin affects growth and differentiation of adult neural stem/progenitor cells

Adrenomedullin (AM) is a peptide hormone involved in the modulation of cellular growth, migration, apoptosis, and angiogenesis. These characteristics suggest that AM is involved in the control of neural stem/progenitor cell (NSPC) biology. To explore this hypothesis, we have obtained NSPC from the olfactory bulb of adult wild-type animals and brain conditional knockouts for adm, the gene that produces AM. Knockout NSPC contain higher levels of hyperpolymerized tubulin and more abundant filopodia than adm-containing cells, resulting in a different morphology in culture, whereas the size of the knockout neurospheres is smaller than that of the wild-types. Proliferation studies have demonstrated that adm-null NSPC incorporate less 5'-bromodeoxyuridine (BrdU) than their wild-type counterparts. In contrast, BrdU studies in the olfactory bulb of adult animals show more labeled cells in adm-null mice that in wild-types, suggesting that a compensatory mechanism exists that guarantees the sufficient production of neural cells in this organ. In NSPC differentiation tests, lack of adm results in significantly lower proportions of neurons and astrocytes and higher proportions of oligodendrocytes. The oligodendrocytes produced from adm-null neurospheres present an immature phenotype with fewer and shorter processes than adm-containing oligodendrocytes. Thus, AM is an important factor in regulating the proliferation and differentiation of adult NSPC and might be used to modulate stem cell renewal and fate in protocols destined to produce neural cells for regenerative therapies.

The HIF-1 response to simulated ischemia in mouse skeletal muscle cells neither enhances glycolysis nor prevents myotube cell death

Hypoxia-inducible factor (HIF) plays an important role in regulating gene expression in response to ischemia. Although activation of HIF-1 in muscle tissue was found during ischemia in vivo, the meaning and mechanisms in isolated cells are still incompletely understood. We studied activation of HIF-1 in skeletal muscle cells cultured in either their undifferentiated myoblast state or differentiated into myotubes. HIF-1 was activated in myoblasts and myotubes by hypoxia and simulated ischemia. Induction of adrenomedullin mRNA and, to a lesser extent, VEGF mRNA correlated well with the induction of HIF-1alpha protein in both cell types. Enzymes of glycolysis-like lactate dehydrogenase and pyruvate kinase showed upregulation of their mRNA only under hypoxic conditions but not during simulated ischemia. Phosphofructokinase mRNA showed no significant upregulation at all. Although HIF-1 was activated in myotubes during simulated ischemia, myotubes died preceded by a loss of ATP. Myoblasts survived simulated ischemia with no decrease in ATP or ATP turnover. Furthermore, pharmacological inhibition of HIF-1 hydroxylases by dimethyloxalylglycine (DMOG) increased HIF-1alpha accumulation and significantly upregulated the expression of adrenomedullin, VEGF, lactate dehydrogenase, and pyruvate kinase in myoblasts and myotubes. However, DMOG provided no protection from cell death. Our data indicate that HIF-1, although activated in myotubes during simulated ischemia, cannot protect against the loss of ATP and cell viability. In contrast, myoblasts survive ischemia and thus may play an important role during regeneration and HIF-1-induced revascularization.

Nonclassic Endogenous Novel Regulators of Angiogenesis

Angiogenesis, the process through which new blood vessels arise from preexisting ones, is regulated by several "classic" factors, among which the most studied are vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2). In recent years, investigations showed that, in addition to the classic factors, numerous endogenous peptides play a relevant regulatory role in angiogenesis. Such regulatory peptides, each of which exerts well-known specific biological activities, are present, along with their receptors, in the blood vessels and may take part in the control of the "angiogenic switch." An in vivo and in vitro proangiogenic effect has been demonstrated for erythropoietin, angiotensin II (ANG-II), endothelins (ETs), adrenomedullin (AM), proadrenomedullin N-terminal 20 peptide (PAMP), urotensin-II, leptin, adiponectin, resistin, neuropeptide-Y, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and substance P. There is evidence that the angiogenic action of some of these peptides is at least partly mediated by their stimulating effect on VEGF (ANG-II, ETs, PAMP, resistin, VIP and PACAP) and/or FGF-2 systems (PAMP and leptin). AM raises the expression of VEGF in endothelial cells, but VEGF blockade does not affect the proangiogenic action of AM. Other endogenous peptides have been reported to exert an in vivo and in vitro antiangiogenic action. These include somatostatin and natriuretic peptides, which suppress the VEGF system, and ghrelin, that antagonizes FGF-2 effects. Investigations on "nonclassic" regulators of angiogenesis could open new perspectives in the therapy of diseases coupled to dysregulation of angiogenesis.