Therapeutic potential of ghrelin in the treatment of heart failure

Ghrelin is a novel growth hormone (GH)-releasing peptide, isolated from the stomach, which has been identified as an endogenous ligand for the GH secretagogues receptor. The discovery of ghrelin indicates that the release of GH from the pituitary might be regulated, not only by hypothalamic GH-releasing hormone, but also by ghrelin derived from the stomach. Considering the haemodynamic and anabolic effects of GH, ghrelin may have beneficial effects on cardiac function and energy metabolism in heart failure through GH-dependent mechanisms. On the other hand, ghrelin has some GH-independent actions: ghrelin stimulates food intake and induces adiposity. Interestingly, ghrelin acts directly on the CNS to decrease sympathetic nerve activity. It also inhibits apoptosis of cardiomyocytes and endothelial cells. An experimental study has shown that repeated administration of ghrelin improves cardiac structure and function, and attenuates the development of cardiac cachexia in chronic heart failure (CHF). These results suggest that ghrelin has cardiovascular effects and regulates energy metabolism through GH-dependent and -independent mechanisms. Thus, administration of ghrelin may be a new therapeutic strategy for the treatment of severe CHF.

Increased plasma monocyte chemoattractant protein-1 level in idiopathic pulmonary arterial hypertension

OBJECTIVE

Monocyte chemoattractant protein-1 (MCP-1), a pro-inflammatory chemokine, has potent chemoattractant activity for monocytes/macrophages. We sought to investigate the clinical significance of MCP-1 in idiopathic pulmonary arterial hypertension (IPAH).

METHODS

This study included 28 patients with IPAH, seven patients with pulmonary arterial hypertension (PAH) related to collagen vascular disease, and 13 healthy subjects. Plasma MCP-1 levels were measured together with serum IL-6 and tumour necrosis factor-alpha (TNF-alpha) levels.

RESULTS

Circulating levels of MCP-1, IL-6 and TNF-alpha were significantly higher in patients with IPAH than in healthy controls, although they were lower than in patients with PAH related to collagen vascular disease. Plasma MCP-1 did not significantly correlate with any haemodynamic variables. However, plasma MCP-1 levels correlated negatively with the disease duration (time from symptom onset).

CONCLUSIONS

Plasma MCP-1 levels were elevated in patients with IPAH, and this elevation was particularly marked in the early stage of disease. Taking into account the chemoattractant activity of MCP-1, these results imply a contribution of MCP-1 to the development of pulmonary hypertension.

Physiological significance and therapeutic potential of adrenomedullin in pulmonary hypertension

Adrenomedullin (ADM) is a potent vasodilator peptide that was originally isolated from human pheochromocytoma. Its vasodilatory effect is mediated by cyclic adenosine 3',5'-monophosphate- and nitric oxide-dependent mechanisms. Earlier studies have demonstrated that ADM is secreted from various tissues, including vessels, heart, and lungs. In addition, there are specific receptors for ADM in the lungs. Plasma ADM level is elevated in proportion to the severity of pulmonary hypertension, and circulating ADM is partially metabolized in the lungs. These findings suggest that ADM plays an important role in the regulation of pulmonary vascular tone. Administration of ADM by intravenous or intratracheal delivery significantly decreased pulmonary arterial pressure and pulmonary vascular resistance in patients with pulmonary arterial hypertension. Furthermore, we have recently developed a new therapeutic strategy using ADM gene-modified endothelial progenitor cells (EPC). Intravenously administered ADM gene-modified EPC were incorporated into lung tissues and attenuated monocrotaline-induced pulmonary hypertension in rats. In addition, ADM has angiogenic and anti-apoptotic activities via activation of Akt and/or mitogen-activated protein kinase. These findings suggest that ADM may act not only as a vasodilator but also as a vasoprotective factor. Thus, ADM may be a promising endogenous peptide for the treatment of pulmonary hypertension.

Postexercise VO2 “Hump” phenomenon as an indicator for inducible myocardial ischemia in patients with acute anterior myocardial infarction

OBJECTIVES

At exercise testing with respiratory gas analysis in patients with inducible myocardial ischemia, we have occasionally observed abnormal transient oxygen uptake (VO2) components with a characteristic "Hump"-shaped morphology early after exercise, which may serve as an index for inducible ischemia. We examined this hypothesis in patients with anterior q-wave myocardial infarction in whom the accuracy to identify ischemia by exercise ECG is limited.

DESIGN

From patients with acute anterior q-wave infarction but without clinically overt heart failure who underwent pre-discharge exercise testing, we examined patients with (Group-I, n = 30) and without (Group-N, n = 29) inducible ischemia. To identify "Hump", postexercise VO2 (up to 4 min) standardized for peak VO2 was exponentially fitted with use of peak VO2 and VO2 of 90-240 s, yielding "expected VO2". "D-curve" was obtained by subtracting "expected VO2" from measured VO2.

RESULTS

Although exercise-induced ST depressions more frequently appeared in Group-I (27%) than in Group-N (3%, p < 0.05), the prevalence was low. D-curve peaked later (p < 0.01) and its value was greater (p < 0.05) in Group-I than in Group-N. When "Hump" was defined to be present if D-curve peaked > or =40 s and its peak value > or =15%, it was far more frequently found in Group-I (n = 17/30) than in Group-N (n = 1/29, p < 0.01). Thus, "Hump" could diagnose inducible ischemia with a sensitivity of 57% and a specificity of 97%.

CONCLUSIONS

Although not highly sensitive, postexercise VO2 "Hump" with its peak occurring around 60 s after exercise is a specific marker for inducible ischemia. The identification may be useful, particularly in patients with limited accuracy of exercise ECG such as those with q-wave anterior infarction.

Adrenomedullin: molecular mechanisms and its role in cardiac disease

Adrenomedullin (AM) is a potent, long-lasting vasoactive peptide originally isolated from human pheochromocytoma. Since its discovery, serum and tissue AM expression have been shown to be increased in experimental models and in patients with cardiac hypertrophy, myocardial infarction and end-stage heart failure with several beneficial effects. Considerable evidence exists for a wide range of autocrine, paracrine and endocrine mechanisms for AM which include vasodilatory, anti-apoptotic, angiogenic, anti-fibrotic, natriuretic, diuretic and positive inotropic. Thus, through regulation of body fluid or direct cardiac mechanisms, AM has additive and beneficial effects in the context of heart disease. Notable molecular mechanisms of AM include cyclic adenosine monophosphate, guanosine-3',5'-monophosphate, PI3K/Akt and MAPK-ERK-mediated cascades. Given the endogenous and multifunctional nature of AM, we consider this molecule to have great potential in the treatment of cardiovascular diseases. In agreement, early experimental and preliminary clinical studies suggest that AM is a new and promising therapy for cardiovascular diseases.

Monolayered mesenchymal stem cells repair scarred myocardium after myocardial infarction

Mesenchymal stem cells are multipotent cells that can differentiate into cardiomyocytes and vascular endothelial cells. Here we show, using cell sheet technology, that monolayered mesenchymal stem cells have multipotent and self-propagating properties after transplantation into infarcted rat hearts. We cultured adipose tissue-derived mesenchymal stem cells characterized by flow cytometry using temperature-responsive culture dishes. Four weeks after coronary ligation, we transplanted the monolayered mesenchymal stem cells onto the scarred myocardium. After transplantation, the engrafted sheet gradually grew to form a thick stratum that included newly formed vessels, undifferentiated cells and few cardiomyocytes. The mesenchymal stem cell sheet also acted through paracrine pathways to trigger angiogenesis. Unlike a fibroblast cell sheet, the monolayered mesenchymal stem cells reversed wall thinning in the scar area and improved cardiac function in rats with myocardial infarction. Thus, transplantation of monolayered mesenchymal stem cells may be a new therapeutic strategy for cardiac tissue regeneration.

Postnatal neovascularization by endothelial progenitor cells immortalized with the simian virus 40T antigen gene

Endothelial progenitor cells (EPCs) contribute to blood vessel formation in ischemic and tumorous tissues, but comprise only a small population in circulation. We attempted to immortalize putative EPCs from human cord blood. Human CD34+ cord blood cells were cultured in the presence of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (b-FGF), and transfected with a retroviral vector encoding the simian virus 40 large T (SV40T) antigen. This resulted in the immortalization of cord blood cells, leading to the establishment of several cell lines. One of these lines, HYCEC-1, exhibited a phenotype characteristic of the endothelial lineage, including expression of von Willebrand factor and VEGF receptor-2 (VEGFR-2/KDR/Flk-1) and uptake of acetylated-low density lipoprotein. Flow cytometric analysis revealed that HYCEC-1 cells were strongly positive for CD31 and CD146, moderately positive for CD144, weakly positive for CD133 and CD34, and negative for CD14 and CD45. HYCEC-1 cells formed capillary-like structures on basement matrix gel in vitro. Upon transplantation into the ischemic hind limb of nude rats, HYCEC-1 cells efficiently participated in neovascularization and augmented blood flow. The immortalized HYCEC-1 cells are suggested to be a class of EPCs that can efficiently participate in postnatal neovasculogenesis in the ischemic hind limb, and may also be a useful tool for studying tumor vessel formation.

Prostacyclin agonist with thromboxane synthase inhibitory activity (ONO-1301) attenuates bleomycin-induced pulmonary fibrosis in mice

The balance between prostacyclin and thromboxane A2 (TXA2) plays an important role in pulmonary homeostasis. However, little information is available regarding the therapeutic potency of these prostanoids for pulmonary fibrosis. We have recently developed ONO-1301, a novel long-acting prostacyclin agonist with thromboxane synthase inhibitory activity. Thus we investigated whether repeated administration of ONO-1301 attenuates bleomycin-induced pulmonary fibrosis in mice. After intratracheal injection of bleomycin or saline, mice were randomized to receive repeated subcutaneous administration of ONO-1301 or vehicle. Bronchoalveolar lavage (BAL) and histological analyses were performed at 3, 7, and 14 days after bleomycin injection. In vitro studies using mouse lung fibroblasts were also performed. ONO-1301 significantly attenuated the development of bleomycin-induced pulmonary fibrosis, as indicated by significant decreases in Ashcroft score and lung hydroxyproline content. ONO-1301 significantly reduced total cell count, neutrophil count, and total protein level in BAL fluid in association with a marked reduction of TXB2. A single administration of ONO-1301 significantly increased plasma cAMP level for >2 h. In vitro, ONO-1301 and a cAMP analog dose-dependently reduced cell proliferation in mouse lung fibroblasts. The reduction in cell proliferation by ONO-1301 was attenuated by a protein kinase A (PKA) inhibitor. Furthermore, bleomycin mice treated with ONO-1301 had a significantly higher survival rate than those given vehicle. These results suggest that repeated administration of ONO-1301 attenuates the development of bleomycin-induced pulmonary fibrosis and improves survival in bleomycin mice, at least in part by inhibition of TXA2 synthesis and activation of the cAMP/PKA pathway.

Ghrelin, a novel growth hormone-releasing peptide, in the treatment of cardiopulmonary-associated cachexia

Ghrelin is a novel growth hormone (GH)-releasing peptide, isolated from the stomach, which has been identified as an endogenous ligand for GH secretagogue receptor. The discovery of ghrelin indicates that the release of GH from the pituitary might be regulated not only by hypothalamic GH-releasing hormone, but also by ghrelin derived from the stomach. This peptide also stimulates food intake and induces adiposity through GH-independent mechanisms. In addition, ghrelin acts directly on the central nervous system to decrease sympathetic nerve activity. Thus, ghrelin plays important roles for maintaining GH release and energy homeostasis. Repeated administration of ghrelin improves body composition, muscle wasting, functional capacity, and sympathetic augmentation in cachectic patients with heart failure or chronic obstructive pulmonary disease. These results suggest that ghrelin has anti-cachectic effects through GH-dependent and independent mechanisms. Thus, administration of ghrelin may be a new therapeutic strategy for the treatment of cardiopulmonary-associated cachexia.

A Long-Acting Prostacyclin Agonist with Thromboxane Inhibitory Activity for Pulmonary Hypertension

RATIONALE

The balance between prostacyclin and thromboxane plays an important role in the regulation of pulmonary vascular tone. Recently, we developed ONO-1301, a novel, long-acting prostacyclin agonist with thromboxane synthase inhibitory activity.

OBJECTIVES

We investigated whether modulation of prostacyclin/thromboxane balance by ONO-1301 ameliorates monocrotaline-induced pulmonary hypertension in rats.

METHODS

After subcutaneous injection of monocrotaline or vehicle, rats were randomized to receive repeated subcutaneous administration of ONO-1301 or vehicle twice per day for 3 wk.

MEASUREMENTS AND MAIN RESULTS

There was significant development of pulmonary hypertension 3 wk after monocrotaline injection. Treatment with ONO-1301 significantly attenuated the increases in right ventricular systolic pressure and ratio of right ventricular weight to body weight in monocrotaline rats. Furthermore, ONO-1301 significantly attenuated the increase in medial wall thickness of peripheral pulmonary arteries in monocrotaline rats. The half-life of plasma ONO-1301 concentration after a single subcutaneous administration was approximately 5.6 h. A single administration of ONO-1301 increased plasma cyclic adenosine 3', 5'-monophosphate level, which lasted at least up to 8 h. Treatment with ONO-1301 significantly decreased plasma 11-dehydro-thromboxane B2, a metabolite of thromboxane, in monocrotaline rats. Finally, Kaplan-Meier survival curves demonstrated that repeated administration of ONO-1301 improved survival rate in monocrotaline rats compared with vehicle administration (80 vs. 30% in 6-wk survival).

CONCLUSIONS

Subcutaneous administration of a novel prostacyclin agonist (ONO-1301) markedly attenuated monocrotaline-induced pulmonary hypertension and improved survival in rats. The beneficial effects of ONO-1301 may occur through its long-lasting stimulation of cyclic adenosine 3', 5'-monophosphate and inhibition of thromboxane synthase.

Adrenomedullin is up-regulated in nitrofen-induced fetal pulmonary hypoplasia

BACKGROUND/PURPOSE

Pulmonary hypoplasia associated with congenital diaphragmatic hernia remains a major therapeutic problem. Adrenomedullin (AM), a multifunctional regulatory peptide, has been suggested to play a role in the mechanisms of fetal lung differentiation and maturation. The aim of this study was to investigate the pulmonary expression of AM in nitrofen-induced fetal pulmonary hypoplasia.

MATERIALS AND METHODS

Pulmonary hypoplasia was induced in timed-pregnant Sprague-Dawley rats after administration of 100 mg nitrofen on day 9.5 of gestation. Fetal and neonatal lungs were excised on gestational days 16.5, 19, and 21 and 1 hour after birth and divided into the following 3 groups: nitrofen with diaphragmatic defect, nitrofen without diaphragmatic defect, and control (without nitrofen). Pulmonary levels of AM and AM messenger RNA expression were measured by radioimmunoassay and real time quantitative reverse transcriptase polymerase chain reaction, respectively. Localization of pulmonary AM was identified by immunohistochemical staining.

RESULTS

There was a significant increase in pulmonary level of AM in the nitrofen-treated groups on gestational days 19 and 21. Real time quantitative reverse transcriptase polymerase chain reaction on gestational day 19 confirmed an increase of AM gene expression in the nitrofen-treated groups. Adrenomedullin immunoreactivity was more strongly expressed in airway epithelial cells in the nitrofen-treated groups than in the control.

CONCLUSION

Nitrofen up-regulates expression of AM in the fetal lung, which suggests that AM has some pathophysiological role in the differentiation and/or maturation processes of pulmonary hypoplasia in congenital diaphragmatic hernia.

Treatment of Cachexia With Ghrelin in Patients With COPD

STUDY OBJECTIVES

Ghrelin is a novel growth hormone (GH)-releasing peptide that also induces a positive energy balance by decreasing fat utility and stimulating feeding through GH-independent mechanisms. We investigated whether ghrelin improves cachexia and functional capacity in patients with COPD.

METHODS

This is an open-label pilot study. Human ghrelin (2 microg/kg bid) was IV administered to seven cachectic patients with COPD for 3 weeks. Food intake, body composition, muscle strength, exercise capacity, pulmonary function, and sympathetic nerve activity were examined before and after ghrelin therapy.

RESULTS

A single administration of ghrelin markedly increased serum GH (21-fold). Three-week treatment with ghrelin resulted in a significant increase in mean (+/- SEM) body weight (49.3 +/- 3.6 to 50.3 +/- 3.8 kg; p < 0.05). Food intake was significantly increased during ghrelin therapy. Ghrelin increased lean body mass and peripheral and respiratory muscle strength. Ghrelin significantly increased Karnofsky performance status score and the distance walked in 6 min (370 +/- 30 to 432 +/- 35 m; p < 0.05), although it did not significantly alter pulmonary function. Ghrelin attenuated the exaggerated sympathetic nerve activity, as indicated by a marked decrease in plasma norepinephrine level (889 +/- 123 to 597 +/- 116 pg/mL; p < 0.05).

CONCLUSIONS

These preliminary results suggest that repeated administration of ghrelin improves body composition, muscle wasting, functional capacity, and sympathetic augmentation in cachectic patients with COPD.

Transplantation of mesenchymal stem cells improves cardiac function in a rat model of dilated cardiomyopathy

BACKGROUND

Pluripotent mesenchymal stem cells (MSCs) differentiate into a variety of cells, including cardiomyocytes and vascular endothelial cells. However, little information is available about the therapeutic potency of MSC transplantation in cases of dilated cardiomyopathy (DCM), an important cause of heart failure.

METHODS AND RESULTS

We investigated whether transplanted MSCs induce myogenesis and angiogenesis and improve cardiac function in a rat model of DCM. MSCs were isolated from bone marrow aspirates of isogenic adult rats and expanded ex vivo. Cultured MSCs secreted large amounts of the angiogenic, antiapoptotic, and mitogenic factors vascular endothelial growth factor, hepatocyte growth factor, adrenomedullin, and insulin-like growth factor-1. Five weeks after immunization, MSCs or vehicle was injected into the myocardium. Some engrafted MSCs were positive for the cardiac markers desmin, cardiac troponin T, and connexin-43, whereas others formed vascular structures and were positive for von Willebrand factor or smooth muscle actin. Compared with vehicle injection, MSC transplantation significantly increased capillary density and decreased the collagen volume fraction in the myocardium, resulting in decreased left ventricular end-diastolic pressure (11+/-1 versus 16+/-1 mm Hg, P<0.05) and increased left ventricular maximum dP/dt (6767+/-323 versus 5138+/-280 mm Hg/s, P<0.05).

CONCLUSIONS

MSC transplantation improved cardiac function in a rat model of DCM, possibly through induction of myogenesis and angiogenesis, as well as by inhibition of myocardial fibrosis. The beneficial effects of MSCs might be mediated not only by their differentiation into cardiomyocytes and vascular cells but also by their ability to supply large amounts of angiogenic, antiapoptotic, and mitogenic factors.

Altered expression balance of matrix metalloproteinases and their inhibitors in human carotid plaque disruption: results of quantitative tissue analysis using real-time RT-PCR method

BACKGROUND

The balance between degradation and synthesis of extracellular matrix determines its content in atherosclerotic tissue. To examine the role of expression balance of matrix metalloproteinases (MMPs) to their inhibitors, tissue inhibitors of metalloproteinases (TIMPs) and tissue factor pathway inhibitor-2 (TFPI-2) in the development and disruption of atherosclerotic plaque, these gene expressions in human carotid plaque were quantitatively determined by real-time reverse transcription (RT)-polymerase chain reaction (PCR) method.

METHODS

Total RNA for cDNA synthesis was extracted from tissues in 24 patients with carotid endarterectomy. The amounts of cDNAs for MMP-1, -2, -3 and -9, TFPI-2 and TIMP-1, -2 and -3 were determined by real-time RT-PCR method, and normalized with glutaraldehyde 3-dehydrogenase.

RESULTS

In plaques, the expression MMP-1 (1.53+/-0.25, mean+/-S.E.M.), MMP-3 (1.99+/-0.59) and MMP-9 (2.00+/-0.51) was augmented compared to those in the adjacent control regions (0.60+/-0.16, 0.46+/-0.18 and 0.58+/-0.21, respectively, p<0.05). The expression of TFPI-2 was lower in plaques (0.32+/-0.08) than in controls (0.94+/-0.23, p<0.01). Although the expression of TIMP-1 was higher in plaques (1.28+/-0.23) than in controls (0.81+/-0.10, p<0.05), the indices of MMP-1/TIMP-1, MMP-3/TIMP-3 and MMP-9/TIMP-1 were still significantly higher in plaques. Interestingly, MMP-9 and the resulting MMP-9/TIMP-1 balance in plaques with disruption were significantly higher (3.36+/-1.52 and 1.66+/-0.12, n=11) than those in non-disrupted plaques (1.11+/-0.52 and 0.76+/-0.12, n=13, p<0.05).

CONCLUSION

With the decreased expression of TFPI-2, upregulation of MMPs in atherosclerotic plaque was disproportional to that of TIMPs, suggesting that imbalanced degradation and synthesis of extracellular matrix persists in advanced lesions, particularly in plaques with disruption.

Diagnostic value of epinephrine test for genotyping LQT1, LQT2, and LQT3 forms of congenital long QT syndrome

OBJECTIVES

The aim of this study was to test the hypothesis that epinephrine test may have diagnostic value for genotyping LQT1, LQT2, and LQT3 forms of congenital long QT syndrome (LQTS).

BACKGROUND

A differential response of dynamic QT interval to epinephrine infusion between LQT1, LQT2, and LQT3 syndromes has been reported, indicating the potential diagnostic value of the epinephrine test for genotyping the three forms.

METHODS

The responses of 12-lead ECG parameters to epinephrine were retrospectively examined in 15 LQT1, 10 LQT2, 8 LQT3, and 10 healthy volunteers to select the best ECG criteria for separating the four groups. The epinephrine test then was prospectively conducted in 42 probands clinically affected with LQTS, their 67 family members, and 10 new volunteers. The best criteria were applied in a blinded fashion to prospectively separate a different group of 31 LQT1, 23 LQT2, 6 LQT3, and 30 Control patients (10 genotype-negative LQT1, 10 genotype-negative LQT2 family members, and 10 volunteers).

RESULTS

The sensitivity (penetrance) by ECG diagnostic criteria was lower in LQT1 (68%) than in LQT2 (83%) or LQT3 (83%) before epinephrine and was improved with steady-state epinephrine in LQT1 (87%) and LQT2 (91%) but not in LQT3 (83%), without the expense of specificity (100%). The sensitivity and specificity to differentiate LQT1 from LQT2 were 97% and 96%, those from LQT3 were 97% and 100%, and those from Control were 97% and 100%, respectively, when Delta mean corrected Q-Tend >/=35 ms at steady state was used. The sensitivity and specificity to differentiate LQT2 from LQT3 or Control were 100% and 100%, respectively, when Delta mean corrected Q-Tend >/=80 ms at peak was used.

CONCLUSIONS

Epinephrine infusion is a powerful test to predict the genotype of LQT1, LQT2, and LQT3 syndromes as well as to improve the clinical diagnosis of genotype-positive patients, especially those with LQT1 syndrome.

Adrenomedullin regenerates alveoli and vasculature in elastase-induced pulmonary emphysema in mice

RATIONALE

Adrenomedullin, a potent vasodilator peptide, regulates cell growth and survival. However, whether adrenomedullin contributes to lung regeneration remains unknown.

OBJECTIVES

To investigate whether adrenomedullin influences the kinetics of bone marrow cells, and whether adrenomedullin promotes regeneration of alveoli and vasculature and thereby improves lung structure and function in elastase-induced emphysema in mice.

METHODS

Adrenomedullin or vehicle was randomly administered to C57BL/6 mice for 5 days. We counted the numbers of mononuclear cells and stem cell antigen-1-positive cells in circulating blood. After intratracheal injection of elastase or saline, mice were randomized to receive continuous infusion of adrenomedullin or vehicle for 14 days. Functional and histologic analyses were performed 28 days after treatment.

RESULTS

Twenty-eight days after elastase injection, destruction of the alveolar walls was observed. However, adrenomedullin infusion significantly inhibited the increase in lung volume, static lung compliance, and mean linear intercept in mice given elastase. Adrenomedullin increased the numbers of mononuclear cells and stem cell antigen-1-positive cells in circulating blood. Adrenomedullin significantly increased the number of bone marrow-derived cells incorporated into the elastase-treated lung. Some of these cells were positive for cytokeratin or von Willebrand factor. Infusion of adrenomedullin after the establishment of emphysema also had beneficial effects on lung structure and function. In vitro, addition of adrenomedullin attenuates elastase-induced cell death in alveolar epithelial cells and endothelial cells.

CONCLUSIONS

Adrenomedullin improved elastase-induced emphysema at least in part through mobilization of bone marrow cells and the direct protective effects on alveolar epithelial cells and endothelial cells.

Adrenomedullin: angiogenesis and gene therapy

Adrenomedullin (AM) is a potent, long-lasting vasodilator peptide that was originally isolated from human pheochromocytoma. AM signaling is of particular significance in endothelial cell biology since the peptide protects cells from apoptosis, promotes angiogenesis, and affects vascular tone and permeability. The angiogenic effect of AM is mediated by activation of Akt, mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2, and focal adhesion kinase in endothelial cells. Both AM and its receptor, calcitonin receptor-like receptor, are upregulated through a hypoxia-inducible factor-1-dependent pathway under hypoxic conditions. Thus AM signaling plays an important role in the regulation of angiogenesis in hypoxic conditions. Recently, we have developed a nonviral vector, gelatin. Positively charged gelatin holds negatively charged plasmid DNA in its lattice structure. DNA-gelatin complexes can delay gene degradation, leading to efficient gene transfer. Administration of AM DNA-gelatin complexes induces potent angiogenic effects in a rabbit model of hindlimb ischemia. Thus gelatin-mediated AM gene transfer may be a new therapeutic strategy for the treatment of tissue ischemia. Endothelial progenitor cells (EPCs) play an important role in endothelial regeneration. Interestingly, EPCs phagocytose ionically linked DNA-gelatin complexes in coculture, which allows nonviral gene transfer into EPCs. AM gene transfer into EPCs inhibits cell apoptosis and induces proliferation and migration, suggesting that AM gene transfer strengthens the therapeutic potential of EPCs. Intravenous administration of AM gene-modified EPCs regenerate pulmonary endothelium, resulting in improvement of pulmonary hypertension. These results suggest that in vivo and in vitro transfer of AM gene using gelatin may be applicable for intractable cardiovascular disease.