Dual deletion of guanylyl cyclase-A and p38 mitogen-activated protein kinase in podocytes with aldosterone administration causes glomerular intra-capillary thrombi

Natriuretic peptides exert not only blood-lowering but also kidney-protective effects through guanylyl cyclase-A (GC-A), a natriuretic peptide receptor. Signaling through GC-A has been shown to protect podocytes from aldosterone-induced glomerular injury, and a p38 mitogen-activated protein kinase (MAPK) inhibitor reduced glomerular injury in aldosterone-infused podocyte-specific GC-A knockout mice. To explore the role of p38 MAPK in podocytes, we constructed podocyte-specific p38 MAPK and GC-A double knockout mice (pod-double knockout mice). Unexpectedly, aldosterone-infused and high salt-fed (B-ALDO)-treated pod-double knockout mice resulted in elevated serum creatinine, massive albuminuria, macrophage infiltration, foot process effacement, nephrin and podocin reduction, and additionally, intra-capillary fibrin thrombi, indicating endothelial injury. Microarray analysis showed increased plasminogen activator inhibitor-1 (PAI-1) in glomeruli of B-ALDO-treated pod-double knockout mice. In B-ALDO-treated pod-double knockout mice, PAI-1 increased in podocytes, and treatment with PAI-1 neutralizing antibody ameliorated intra-capillary thrombus formation. In vitro, deletion of p38 MAPK by the CRISPR/Cas9 system and knockdown of GC-A in human cultured podocytes upregulated PAI-1 and transforming growth factor- β1 (TGF-β1). When p38 MAPK knockout podocytes, transfected with a small interfering RNA to suppress GC-A, were co-cultured with glomerular endothelial cells in a transwell system, the expression of TGF-β1 was increased in glomerular endothelial cells. PAI-1 inhibition ameliorated both podocyte and endothelial injury in the transwell system signifying elevated PAI-1 in podocytes is a factor disrupting normal podocyte-endothelial crosstalk. Thus, our results indicate that genetic dual deletion of p38 MAPK and GC-A in podocytes accelerates both podocyte and endothelial injuries, suggesting these two molecules play indispensable roles in podocyte function.

Molecular Mechanism of Blood Pressure Regulation through the Atrial Natriuretic Peptide

Simple Summary

Atrial natriuretic peptide (ANP) is a cardiac peptide hormone that was identified by Kangawa and Matsuo in 1984. In Japan, ANP has been used as an intravenous drug for the treatment of acute heart failure since 1995. Because ANP has a hypotensive effect, it is important to avoid excessive lowering of blood pressure when ANP is used. Recently, a compound that inhibits neutral endopeptidase, the enzyme that degrades ANP, has been developed (angiotensin receptor-neprilysin inhibitor (ARNI)). ARNI has been approved worldwide for the treatment of chronic heart failure and has been authorized in Japan as an antihypertensive drug. However, it is not understood exactly how ANP exerts its hypotensive effect. In this review, we discuss the molecular mechanism of the blood pressure-regulating effects of ANP, focusing on our recent findings.

Abstract

Natriuretic peptides, including atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), have cardioprotective effects and regulate blood pressure in mammals. ANP and BNP are hormones secreted from the heart into the bloodstream in response to increased preload and afterload. Both hormones act through natriuretic peptide receptor 1 (NPR1). In contrast, CNP acts through natriuretic peptide receptor 2 (NPR2) and was found to be produced by the vascular endothelium, chondrocytes, and cardiac fibroblasts. Based on its relatively low plasma concentration compared with ANP and BNP, CNP is thought to function as both an autocrine and a paracrine factor in the vasculature, bone, and heart. The cytoplasmic domains of both NPR1 and NPR2 display a guanylate cyclase activity that catalyzes the formation of cyclic GMP. NPR3 lacks this guanylate cyclase activity and is reportedly coupled to G_i-dependent signaling. Recently, we reported that the continuous infusion of the peptide osteocrin, an endogenous ligand of NPR3 secreted by bone and muscle cells, lowered blood pressure in wild-type mice, suggesting that endogenous natriuretic peptides play major roles in the regulation of blood pressure. Neprilysin is a neutral endopeptidase that degrades several vasoactive peptides, including natriuretic peptides. The increased worldwide clinical use of the angiotensin receptor-neprilysin inhibitor for the treatment of chronic heart failure has brought renewed attention to the physiological effects of natriuretic peptides. In this review, we provide an overview of the discovery of ANP and its translational research. We also highlight our recent findings on the blood pressure regulatory effects of ANP, focusing on its molecular mechanisms.

Endothelial Natriuretic Peptide Receptor 1 Play Crucial Role for Acute and Chronic Blood Pressure Regulation by Atrial Natriuretic Peptide

BACKGROUND

ANP (atrial natriuretic peptide), acting through NPR1 (natriuretic peptide receptor 1), provokes hypotension. Such hypotension is thought to be due to ANP inducing vasodilation via NPR1 in the vasculature; however, the underlying mechanism remains unclear. Here, we investigated the mechanisms of acute and chronic blood pressure regulation by ANP.

METHODS AND RESULTS

Immunohistochemical analysis of rat tissues revealed that NPR1 was abundantly expressed in endothelial cells and smooth muscle cells of small arteries and arterioles. Intravenous infusion of ANP significantly lowered systolic blood pressure in wild-type mice. ANP also significantly lowered systolic blood pressure in smooth muscle cell-specific Npr1-knockout mice but not in endothelial cell-specific Npr1-knockout mice. Moreover, ANP significantly lowered systolic blood pressure in Nos3-knockout mice. In human umbilical vein endothelial cells, treatment with ANP did not influence nitric oxide production or intracellular Ca²⁺ concentration, but it did hyperpolarize the cells. ANP-induced hyperpolarization of human umbilical vein endothelial cells was inhibited by several potassium channel blockers and was also abolished under knockdown of RGS2 (regulator of G-protein signaling 2), an GTPase activating protein in G-protein α-subunit. ANP increased Rgs2 mRNA expression in human umbilical vein endothelial cells but failed to lower systolic blood pressure in Rgs2-knockout mice. Endothelial cell-specific Npr1-overexpressing mice exhibited lower blood pressure than did wild-type mice independent of RGS2, and showed dilation of arterial vessels on synchrotron radiation microangiography.

CONCLUSIONS

Together, these results indicate that vascular endothelial NPR1 plays a crucial role in ANP-mediated blood pressure regulation, presumably by a mechanism that is RGS2-dependent in the acute phase and RGS2-independent in the chronic phase.

P0143OPPOSING EFFECTS OF P38 MAPK IN PODOCYTES ON ALDOSTERONE-INDUCED GLOMERULAR INJURY IN POD-GC-A CKO MICE

Background and Aims

Previously, we demonstrated that uninephrectomized aldosterone-infused, high salt-fed podocyte-specific guanylyl cyclase-A (natriuretic peptide receptor 1) conditional KO (pod-GC-A cKO) mice exhibited glomerular injury and that pharmacological inhibition of p38 MAPK ameliorates podocyte damage. However, the effects of genetic deletion of p38 MAPK in podocytes of pod-GC-A cKO mice have been unclarified.

Method

We generated p38 MAPK(fl/fl);Nephrin-Cre (pod-p38 MAPK cKO) mice and p38 MAPK(fl/fl);GC-A(fl/fl);Nephrin-Cre (pod-p38MAPK/GC-A DKO) mice. For induction of glomerular injury, we treated them with aldosterone and high salt at 2 months of age for 3 weeks without nephrectomy (B-ALDO). In vitro, we examined the effect of p38 MAPK inhibitor in cultured human podocytes transfected with GC-A siRNA.

Results

B-ALDO-treated pod-p38 MAPK/GC-A DKO mice resulted in significant elevation of serum Cr (0.29 ± 0.04 mg/dl), massive albuminuria (42,660 ± 20,200 μg/mgCr) and severe foot process effacement in addition to intracapillary fibrin thrombi which indicated endothelial damage. Vehicle-treated DKO mice, B-ALDO-treated pod-GC-A cKO mice, and B-ALDO-treated pod-p38 MAPK cKO showed normal serum Cr levels (0.14 ± 0.01, 0.18 ± 0.02, 0.20 ± 0.01 mg/dl, respectively), mild increase of albuminuria (223 ± 6.5, 1,496 ± 592, 649 ± 303 μg/mgCr, respectively) and only segmental foot process effacement. Blood pressure was not elevated in either mutant mice compared with that of B-ALDO control mice. Furthermore, glomerular mRNA expressions of MCP-1, PAI-1, and FN were upregulated and that of VEGF-A was downregulated in DKO mice. In vitro, suppression of GC-A mRNA by siRNA in combination with p38 MAPK inhibitor downregulated VEGF mRNA in human cultured podocytes. Our previous works showed that pharmacological inhibition of p38 MAPK in the whole body ameliorated podocyte damage, whereas our current result showed that genetic deletion of p38 MAPK in podocytes aggravated renal injury. In order to explain the discrepancy in these results, we added an analysis of podocyte specific GC-A fl/fl p38 fl/+ cKO mice. Pod GC-A fl/fl p38 fl/+ cKO mice exhibited considerably milder renal damage than pod GC-A fl/fl p38 fl/fl double cKO mice.

Conclusion

Genetic complete p38 MAPK deletion in GC-A-nul podocytes exacerbated aldosterone-induced glomerular endothelial cell injury as well as podocytes, and resulted in renal dysfunction, probably through VEGF downregulation, whereas partial p38 MAPK inhibition in podocytes ameliorated aldosterone-induced glomerular injury in pod-GC-A cKO mice. These results suggest a certain level of p38 MAPK in podocytes is necessary to protect endothelial and epithelial cells from aldosterone-induced renal injury.

Deficiency of Cardiac Natriuretic Peptide Signaling Promotes Peripartum Cardiomyopathy-Like Remodeling in the Mouse Heart

BACKGROUND

The maternal circulatory system and hormone balance both change dynamically during pregnancy, delivery, and the postpartum period. Although atrial natriuretic peptides and brain natriuretic peptides produced in the heart control circulatory homeostasis through their common receptor, NPR1, the physiologic and pathophysiologic roles of endogenous atrial natriuretic peptide/brain natriuretic peptide in the perinatal period are not fully understood.

METHODS

To clarify the physiologic and pathophysiologic roles of the endogenous atrial natriuretic peptide/brain natriuretic peptide-NPR1 system during the perinatal period, the phenotype of female wild-type and conventional or tissue-specific Npr1-knockout mice during the perinatal period was examined, especially focusing on maternal heart weight, blood pressure, and cardiac function.

RESULTS

In wild-type mice, lactation but not pregnancy induced reversible cardiac hypertrophy accompanied by increases in fetal cardiac gene mRNAs and ERK1/2 (extracellular signaling-regulated kinase) phosphorylation. Npr1-knockout mice exhibited significantly higher plasma aldosterone level than did wild-type mice, severe cardiac hypertrophy accompanied by fibrosis, and left ventricular dysfunction in the lactation period. Npr1-knockout mice showed a high mortality rate over consecutive pregnancy-lactation cycles. In the hearts of Npr1-knockout mice during or after the lactation period, an increase in interleukin-6 mRNA expression, phosphorylation of signal transducer and activator of transcription 3, and activation of the calcineurin-nuclear factor of the activated T cells pathway were observed. Pharmacologic inhibition of the mineralocorticoid receptor or neuron-specific deletion of the mineralocorticoid receptor gene significantly ameliorated cardiac hypertrophy in lactating Npr1-knockout mice. Anti-interleukin-6 receptor antibody administration tended to reduce cardiac hypertrophy in lactating Npr1-knockout mice.

CONCLUSIONS

These results suggest that the characteristics of lactation-induced cardiac hypertrophy in wild-type mice are different from exercise-induced cardiac hypertrophy, and that the endogenous atrial natriuretic peptide/brain natriuretic peptide-NPR1 system plays an important role in protecting the maternal heart from interleukin-6-induced inflammation and remodeling in the lactation period, a condition mimicking peripartum cardiomyopathy.

Ghrelin and the heart

Ghrelin, a growth hormone-releasing peptide that was first discovered in the stomach of rats in 1999, is an endogenous ligand of growth hormone secretagogue receptor. Ghrelin exerts its potent growth hormone-releasing and orexigenic activities by binding to specific receptors in the brain. Subsequent studies showed that ghrelin participates in the regulation of diverse processes, including energy balance, body weight maintenance, and glucose and fat metabolism, and demonstrated that ghrelin is beneficial for treatment of cardiac diseases. In animal models of chronic heart failure, administration of ghrelin improves cardiac function and remodeling, and these findings were recapitulated in human patients with heart failure. Also in animal models, ghrelin administration effectively diminishes pulmonary hypertension induced by monocrotaline or chronic hypoxia. In addition, repeated administration of ghrelin to cachectic chronic obstructive pulmonary disease patients has positive effects on body composition, including amelioration of muscle wasting, improvement of functional capacity, and sympathetic activity. Moreover, administration of ghrelin early after myocardial infarction decreases the frequency of fatal arrhythmia and improved the survival rate. In ghrelin-deficient mice, both exogenous and endogenous ghrelin protects against fatal arrhythmia and promotes remodeling after myocardial infarction. Although the mechanisms underlying the effects of ghrelin on the cardiovascular system have not been fully elucidated, some evidence suggests that its beneficial effects are mediated through both direct actions on cardiovascular cells and regulation of autonomic nervous system activity. Therefore, ghrelin is a promising novel therapeutic agent for cardiac disease.

Adipocyte-specific expression of C-type natriuretic peptide suppresses lipid metabolism and adipocyte hypertrophy in adipose tissues in mice fed high-fat diet

C-type natriuretic peptide (CNP) is expressed in diverse tissues, including adipose and endothelium, and exerts its effects by binding to and activating its receptor, guanylyl cyclase B. Natriuretic peptides regulate intracellular cGMP and phosphorylated vasodilator-stimulated phosphoprotein (VASP). We recently revealed that overexpression of CNP in endothelial cells protects against high-fat diet (HFD)-induced obesity in mice. Given that endothelial CNP affects adipose tissue during obesity, CNP in adipocytes might directly regulate adipocyte function during obesity. Therefore, to elucidate the effect of CNP in adipocytes, we assessed 3T3-L1 adipocytes and transgenic (Tg) mice that overexpressed CNP specifically in adipocytes (A-CNP). We found that CNP activates the cGMP–VASP pathway in 3T3-L1 adipocytes. Compared with Wt mice, A-CNP Tg mice showed decreases in fat weight and adipocyte hypertrophy and increases in fatty acid β-oxidation, lipolysis-related gene expression, and energy expenditure during HFD-induced obesity. These effects led to decreased levels of the macrophage marker F4/80 in the mesenteric fat pad and reduced inflammation. Furthermore, A-CNP Tg mice showed improved glucose tolerance and insulin sensitivity, which were associated with enhanced insulin-stimulated Akt phosphorylation. Our results suggest that CNP overexpression in adipocytes protects against adipocyte hypertrophy, excess lipid metabolism, inflammation, and decreased insulin sensitivity during HFD-induced obesity.

A New Secretory Peptide of Natriuretic Peptide Family, Osteocrin, Suppresses the Progression of Congestive Heart Failure After Myocardial Infarction

RATIONALE

An increase of severe ischemic heart diseases results in an increase of the patients with congestive heart failure (CHF). Therefore, new therapies are expected in addition to recanalization of coronary arteries. Previous clinical trials using natriuretic peptides (NPs) prove the improvement of CHF by NPs.

OBJECTIVE

We aimed at investigating whether OSTN (osteocrin) peptide potentially functioning as an NPR (NP clearance receptor) 3-blocking peptide can be used as a new therapeutic peptide for treating CHF after myocardial infarction (MI) using animal models.

METHODS AND RESULTS

We examined the effect of OSTN on circulation using 2 mouse models; the continuous intravenous infusion of OSTN after MI and the OSTN-transgenic (Tg) mice with MI. In vitro studies revealed that OSTN competitively bound to NPR3 with atrial NP. In both OSTN-continuous intravenous infusion model and OSTN-Tg model, acute inflammation within the first week after MI was reduced. Moreover, both models showed the improvement of prognosis at 28 days after MI by OSTN. Consistent with the in vitro study binding of OSTN to NPR3, the OSTN-Tg exhibited an increased plasma atrial NP and C-type NP, which might result in the improvement of CHF after MI as indicated by the reduced weight of hearts and lungs and by the reduced fibrosis.

CONCLUSIONS

OSTN might suppress the worsening of CHF after MI by inhibiting clearance of NP family peptides.

Overexpression of C-type Natriuretic Peptide in Endothelial Cells Protects against Insulin Resistance and Inflammation during Diet-induced Obesity

The endogenous peptide C-type natriuretic peptide (CNP) binds its receptor, guanylyl cyclase B (GCB), and is expressed by endothelial cells in diverse tissues. Because the endothelial cells of visceral adipose tissue have recently been reported to play a role in lipid metabolism and inflammation, we investigated the effects of CNP on features of obesity by using transgenic (Tg) mice in which CNP was placed under the control of the Tie2 promoter and was thus overexpressed in endothelial cells (E-CNP). Here we show that increased brown adipose tissue thermogenesis in E-CNP Tg mice increased energy expenditure, decreased mesenteric white adipose tissue (MesWAT) fat weight and adipocyte hypertrophy, and prevented the development of fatty liver. Furthermore, CNP overexpression improved glucose tolerance, decreased insulin resistance, and inhibited macrophage infiltration in MesWAT, thus suppressing pro-inflammation during high-fat diet–induced obesity. Our findings indicate an important role for the CNP produced by the endothelial cells in the regulation of MesWAT hypertrophy, insulin resistance, and inflammation during high-fat diet–induced obesity.

Endothelium-Derived C-Type Natriuretic Peptide Contributes to Blood Pressure Regulation by Maintaining Endothelial Integrity

We previously reported the secretion of C-type natriuretic peptide (CNP) from vascular endothelial cells and proposed the existence of a vascular natriuretic peptide system composed of endothelial CNP and smooth muscle guanylyl cyclase-B (GC-B), the CNP receptor, and involved in the regulation of vascular tone, remodeling, and regeneration. In this study, we assessed the functional significance of this system in the regulation of blood pressure in vivo using vascular endothelial cell–specific CNP knockout and vascular smooth muscle cell–specific GC-B knockout mice. These mice showed neither the skeletal abnormality nor the early mortality observed in systemic CNP or GC-B knockout mice. Endothelial cell–specific CNP knockout mice exhibited significantly increased blood pressures and an enhanced acute hypertensive response to nitric oxide synthetase inhibition. Acetylcholine-induced, endothelium-dependent vasorelaxation was impaired in rings of mesenteric artery isolated from endothelial cell–specific CNP knockout mice. In addition, endothelin-1 gene expression was enhanced in pulmonary vascular endothelial cells from endothelial cell–specific CNP knockout mice, which also showed significantly higher plasma endothelin-1 concentrations and a greater reduction in blood pressure in response to an endothelin receptor antagonist than their control littermates. By contrast, vascular smooth muscle cell–specific GC-B knockout mice exhibited blood pressures similar to control mice, and acetylcholine-induced vasorelaxation was preserved in their isolated mesenteric arteries. Nonetheless, CNP-induced acute vasorelaxation was nearly completely abolished in mesenteric arteries from vascular smooth muscle cell–specific GC-B knockout mice. These results demonstrate that endothelium-derived CNP contributes to the chronic regulation of vascular tone and systemic blood pressure by maintaining endothelial function independently of vascular smooth muscle GC-B.

RETRACTED: Protective effects of ghrelin on cisplatin-induced nephrotoxicity in mice

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Authors. The Authors express that: although main outcome is correct, there are some errors in calculation, statistical analysis, description for sample numbers and data preparation including, using the common control and vehicle group already reported in the other paper. Those experiments were performed at the same time but, we lacked explanation for those condition (Cancer Chemother Pharmacol. 2015;75:123-9). Taken together, we decided to retract this article due to those errors.

Atrial natriuretic peptide protects against cisplatin-induced granulocytopenia

PURPOSE

Granulocytopenia is the major toxicity associated with cisplatin treatment. Atrial natriuretic peptide (ANP) is a cardiac hormone used clinically for the treatment of acute heart failure in Japan. ANP exerts a wide range of protective effects on various organs, including the heart, blood vessels, lungs, and kidneys. This study's objective was to investigate the protective effects of ANP on cisplatin-induced granulocytopenia in mice.

METHODS

The mice were divided into two groups: cisplatin with vehicle and cisplatin with ANP. ANP (1.5 μg/kg/min via osmotic pump, subcutaneously) or vehicle administration was started 1 day before cisplatin injection until the mice were killed. At 0, 2, 4, 8, and 14 days after cisplatin injection (16 mg/kg, intraperitoneally as a single dose), the white blood cell, red blood cell, and platelet counts were measured in the peripheral blood in both groups. The numbers of total and live cells and colony-forming unit-granulocyte-macrophage (CFU-GM) colonies in the bone marrow of the mice were also examined. In addition, at 0, 0.5, 1, and 2 days after cisplatin injection, serum granulocyte colony-stimulating factor (G-CSF) levels were measured.

RESULTS

ANP significantly attenuated the white blood cell count decrease in the peripheral blood 2 and 4 days after cisplatin injection. ANP also attenuated the decrease in the number of live cells and CFU-GM colonies in bone marrow 2, 4, and 8 days after cisplatin injection. ANP significantly increased serum G-CSF levels 1 day after cisplatin injection.

CONCLUSIONS

ANP has protective effects in cisplatin-induced granulocytopenia, with increased G-CSF production.

Effects of Adrenomedullin on Doxorubicin-Induced Cardiac Damage in Mice

Doxorubicin (DOX) is one of the best known anticancer drugs, and is used in the treatment of lymphoma, lung cancer, stomach cancer, and a number of other cancers. However, DOX has some serious side effects, the worst being lethal heart failure. Occasionally, its side effects result in the cessation of the anticancer treatment, thus having a serious adverse influence on prognosis. Agents that can be administered as alternative prophylactics or to ameliorate the side effects of DOX will be useful in increasing the safety and efficacy of anticancer therapy. Adrenomedullin (AM) is a peptide hormone secreted by many organs, including the heart; it has an organ-protective effect, including antiapoptotic, anti-inflammatory, and antioxidative stress. Blood AM levels increase with heart failure; endogenic AM has been suggested in order to protect the heart. Furthermore, exogenous AM administration has shown therapeutic effects for heart failure in patients. However, it is unclear whether AM can protect the heart against drug-induced cardiac injury in vivo. The present study was performed in order to investigate the effects of AM on DOX-induced cardiac damage. Male BALB/c mice were treated with DOX and/or AM. Exogenous AM improved the survival ratio of DOX-treated mice. In addition, AM reduced serum lactate dehydrogenase (LDH) levels following DOX treatment. On pathological examination, AM was shown to inhibit DOX-induced cardiac tissue damage, mitochondrial abnormality, and cell death. These findings suggest that AM has a protective effect against DOX-induced cardiac damage.

Importance of Endogenous Atrial and Brain Natriuretic Peptides in Murine Embryonic Vascular and Organ Development

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) bind to the receptor guanylyl cyclase (GC)-A, leading to diuresis, natriuresis, and blood vessel dilation. In addition, ANP and BNP have various angiogenic properties in ischemic tissue. When breeding mice devoid of GC-A, we noted significant skewing of the Mendelian ratio in the offspring, suggesting embryonic lethality due to knockout of GC-A. Consequently, we here investigated the roles of endogenous ANP and BNP in embryonic neovascularization and organ morphogenesis. Embryos resulting from GC-A(-/-) × GC-A(+/-) crosses developed hydrops fetalis (HF) beginning at embryonic day (E)14.5. All embryos with HF had the genotype GC-A(-/-). At E17.5, 33.3% (12 of 36) of GC-A(-/-) embryos had HF, and all GC-A(-/-) embryos with HF were dead. Beginning at E16.0, HF-GC-A(-/-) embryos demonstrated poorly developed superficial vascular vessels and sc hemorrhage, the fetal side of the placenta appeared ischemic, and vitelline vessels on the yolk sac were poorly developed. Furthermore, HF-GC-A(-/-) embryos also showed abnormal constriction of umbilical cord vascular vessels, few cardiac trabeculae and a thin compact zone, hepatic hemorrhage, and poor bone development. Electron microscopy of E16.5 HF-GC-A(-/-) embryos revealed severe vacuolar degeneration in endothelial cells, and the expected 3-layer structure of the smooth muscle wall of the umbilical artery was indistinct. These data demonstrate the importance of the endogenous ANP/BNP-GC-A system not only in the neovascularization of ischemic tissues but also in embryonic vascular development and organ morphogenesis.

Phase II study of the immune-checkpoint inhibitor ipilimumab plus dacarbazine in Japanese patients with previously untreated, unresectable or metastatic melanoma

PURPOSE

Ipilimumab (IPI), a monoclonal antibody against immune-checkpoint receptor cytotoxic T lymphocyte antigen-4, is designed to enhance antitumor T cell function. IPI 10 mg/kg plus dacarbazine (DTIC) significantly improved overall survival in a phase 3 study involving predominantly Caucasian patients, with an adverse event (AE) profile similar to that of IPI monotherapy. We conducted a single-arm, phase 2 study to evaluate the safety and efficacy of IPI plus DTIC in Japanese patients.

METHODS

Previously untreated patients with unresectable stage III or IV melanoma received IPI 10 mg/kg plus DTIC 850 mg/m(2) every 3 weeks for four doses (q3w × 4), followed by DTIC q3w × 4 and then IPI every 12 weeks until disease progression or intolerable toxicity.

RESULTS

All 15 treated patients reported drug-related AEs, the most common of which were increases in alanine aminotransferase (n = 12, 80 %) and aspartate aminotransferase (n = 11, 73 %). Treatment-related serious AEs were reported in 11 (73 %) patients. Nine patients (60 %) discontinued treatment due to drug-related toxicities. Immune-related AEs (irAEs) were reported in 14 patients (93 %). The most frequent irAEs were liver (n = 12, 80 %) and skin (n = 10, 67 %) toxicities. Five deaths were reported; all were caused by progressive disease. Efficacy evaluation showed one complete response, one partial response and four patients with stable disease. Best overall response rate was 13 % (2/15), and the disease control rate was 40 % (6/15). The study was terminated early due to frequent, high-grade liver toxicities.

CONCLUSIONS

IPI 10 mg/kg plus DTIC 850 mg/m(2) was not considered tolerable in the Japanese patient population. ClinicalTrials.gov identifier: NCT01681212.

Endogenous ghrelin attenuates pressure overload-induced cardiac hypertrophy via a cholinergic anti-inflammatory pathway

Cardiac hypertrophy, which is commonly caused by hypertension, is a major risk factor for heart failure and sudden death. Endogenous ghrelin has been shown to exert a beneficial effect on cardiac dysfunction and postinfarction remodeling via modulation of the autonomic nervous system. However, ghrelin's ability to attenuate cardiac hypertrophy and its potential mechanism of action are unknown. In this study, cardiac hypertrophy was induced by transverse aortic constriction in ghrelin knockout mice and their wild-type littermates. After 12 weeks, the ghrelin knockout mice showed significantly increased cardiac hypertrophy compared with wild-type mice, as evidenced by their significantly greater heart weight/tibial length ratios (9.2±1.9 versus 7.9±0.8 mg/mm), left ventricular anterior wall thickness (1.3±0.2 versus 1.0±0.2 mm), and posterior wall thickness (1.1±0.3 versus 0.9±0.1 mm). Furthermore, compared with wild-type mice, ghrelin knockout mice showed suppression of the cholinergic anti-inflammatory pathway, as indicated by reduced parasympathetic nerve activity and higher plasma interleukin-1β and interleukin-6 levels. The administration of either nicotine or ghrelin activated the cholinergic anti-inflammatory pathway and attenuated cardiac hypertrophy in ghrelin knockout mice. In conclusion, our results show that endogenous ghrelin plays a crucial role in the progression of pressure overload-induced cardiac hypertrophy via a mechanism that involves the activation of the cholinergic anti-inflammatory pathway.

Efficacy and safety of dapagliflozin monotherapy in Japanese patients with type 2 diabetes inadequately controlled by diet and exercise

AIMS

To evaluate the efficacy and safety of the selective sodium glucose co-transporter 2 inhibitor dapagliflozin in Japanese patients with type 2 diabetes mellitus (T2DM) inadequately controlled by diet and exercise.

METHODS

Patients received placebo or dapagliflozin (5 or 10 mg) once daily for 24 weeks. The primary outcome measure was change from baseline in glycated haemoglobin (HbA1c).

RESULTS

Patients (N = 261) had modestly elevated baseline HbA1c (mean ≈ 7.5%) and most had mild or moderate renal impairment (estimated glomerular filtration rate range 43-103 ml/min/1.73 m(2)). Greater reductions in mean HbA1c level were observed with dapagliflozin (5 mg, -0.41%; 10 mg, -0.45%) than with placebo (-0.06%) at week 24 and these were greater in patients with higher baseline HbA1c levels. Fasting plasma glucose (FPG) was also significantly reduced with dapagliflozin (5 mg, -8.6 mg/dl; 10 mg, -13.7 mg/dl) compared with placebo (+5.8 mg/dl). Dapagliflozin significantly reduced body weight (5 mg, -2.13 kg; 10 mg, -2.22 kg) compared with placebo (-0.84 kg). Overall, 47.7 and 64.8% of patients with dapagliflozin 5 and 10 mg, respectively, and 51.7% with placebo experienced ≥ 1 adverse event, mostly mild or moderate, and unrelated to study treatment. Two patients on dapagliflozin 10 mg reported hypoglycaemia. Four patients across all groups reported events suggestive of genital infection and four of urinary tract infection. No events of pyelonephritis were reported.

CONCLUSION

Dapagliflozin (5 and 10 mg) was well tolerated and effective in reducing HbA1c, FPG and body weight over 24 weeks in Japanese patients with T2DM inadequately controlled by diet and exercise.

Ghrelin and the cardiovascular system

Ghrelin is a peptide that was originally isolated from the stomach. It exerts potent growth hormone (GH)-releasing and orexigenic activities. Several studies have highlighted the therapeutic benefits of ghrelin for the treatment of cardiovascular disease. In animal models of chronic heart failure, the administration of ghrelin improved cardiac function and remodeling; these findings were replicated in human patients with heart failure. Moreover, in an animal study, ghrelin administration effectively reduced pulmonary hypertension induced by chronic hypoxia. In addition, repeated administration of ghrelin to cachectic patients with chronic obstructive pulmonary disease had positive effects on overall body function, including muscle wasting, functional capacity and sympathetic activity. The administration of ghrelin early after myocardial infarction (MI) reduced fatal arrhythmia and related mortality. In ghrelin-deficient mice, both exogenous and endogenous ghrelin were protective against fatal arrhythmia and promoted remodeling after MI. Although the mechanisms underlying the effects of ghrelin on the cardiovascular system remain unclear, there are indications that its beneficial effects are mediated through both direct physiological actions, including increased GH levels, improved energy balance and direct actions on cardiovascular cells, and regulation of autonomic nervous system activity. Therefore, ghrelin is a promising novel therapeutic agent for cardiovascular disease.

One dose of oral hexarelin protects chronic cardiac function after myocardial infarction

Both hexarelin and its natural analog ghrelin exert comparable cardioprotective activities. A single dose of ghrelin administered at the very acute phase after experimental myocardial infarction positively affects cardiac function in chronic heart failure. Therefore, this study aimed to determine whether a single dose of oral hexarelin has the same effect in the chronic disease phase. Myocardial infarction or sham operation was generated by left coronary artery ligation in male C57BL/6J mice, which subsequently received one dose of hexarelin or vehicle treatment by oral gavage 30 min after operation. Although the mortality within 14 days after myocardial infarction did not differ between the groups, hexarelin treatment protected cardiac function in the chronic phase as evidenced by higher ejection fraction and fractional shortening, as well as lower lung weight/body weight and lung weight/tibial length ratios, compared with vehicle treatment. Hexarelin treatment concurrently lowered plasma epinephrine and dopamine levels, and shifted the balance of autonomic nervous activity toward parasympathetic nervous activity as evidenced by a smaller low/high-frequency power ratio and larger normalized high-frequency power on heart rate variability analysis. The results first demonstrate that one dose of oral hexarelin treatment potentially protects chronic cardiac function after acute myocardial infarction, and implicate that activating growth hormone secretagogue receptor 1a might be beneficial for cardioprotection, although other mechanism may also be involved.

Lack of salt-inducible kinase 2 (SIK2) prevents the development of cardiac hypertrophy in response to chronic high-salt intake

Cardiac left ventricle hypertrophy (LVH) constitutes a major risk factor for heart failure. Although LVH is most commonly caused by chronic elevation in arterial blood pressure, reduction of blood pressure to normal levels does not always result in regression of LVH, suggesting that additional factors contribute to the development of this pathology. We tested whether genetic preconditions associated with the imbalance in sodium homeostasis could trigger the development of LVH without concomitant increases in blood pressure. The results showed that the presence of a hypertensive variant of α-adducin gene in Milan rats (before they become hypertensive) resulted in elevated expression of genes associated with LVH, and of salt-inducible kinase 2 (SIK2) in the left ventricle (LV). Moreover, the mRNA expression levels of SIK2, α-adducin, and several markers of cardiac hypertrophy were positively correlated in tissue biopsies obtained from human hearts. In addition, we found in cardiac myocytes that α-adducin regulates the expression of SIK2, which in turn mediates the effects of adducin on hypertrophy markers gene activation. Furthermore, evidence that SIK2 is critical for the development of LVH in response to chronic high salt diet (HS) was obtained in mice with ablation of the sik2 gene. Increases in the expression of genes associated with LVH, as well as increases in LV wall thickness upon HS, occurred only in sik2^+/+ but not in sik2^−/− mice. Thus LVH triggered by HS or the presence of a genetic variant of α-adducin requires SIK2 and is independent of elevated blood pressure. Inhibitors of SIK2 may constitute part of a novel therapeutic regimen aimed at prevention/regression of LVH.

Atrial natriuretic peptide inhibits lipopolysaccharide-induced acute lung injury

OBJECTIVES

We recently reported that administration of atrial natriuretic peptide during the perioperative period has prophylactic effects with respect to not only cardiovascular but also respiratory complications following pulmonary resection. However, its mechanisms are not well understood. The objective of the present study was to investigate the mechanism of the prophylactic effects of atrial natriuretic peptide in an acute lung injury model.

METHODS

For the evaluation of the early phase of pulmonary inflammation, in vitro and in vivo studies using lipopolysaccharide were used. In the in vitro study, the effects of atrial natriuretic peptide on the induction of E-selectin by lipopolysaccharide in human pulmonary artery endothelial cells were evaluated. In the in vivo study, the effects of atrial natriuretic peptide on lipopolysaccharide-induced inflammatory cell infiltration and cytokine levels including tumor necrosis factor-alpha and interleukin-6 in the bronchoalveolar lavage fluid in the lungs of C57/B6 mice were examined. The number of myeloperoxidase-positive staining cells in the tissue sections of the lung of lipopolysaccharide-administered C57/B6 mice was also evaluated.

RESULTS

Atrial natriuretic peptide significantly attenuated the up-regulation of E-selectin expression induced by lipopolysaccharide in human pulmonary artery endothelial cells. There were significantly lower cell counts and levels of tumor necrosis factor-alpha and interleukin-6 in the bronchoalveolar lavage fluid of atrial natriuretic peptide-treated mice compared to control mice after lipopolysaccharide injection. In addition, there were significantly fewer myeloperoxidase-positive cells in atrial natriuretic peptide-treated mice than in control mice after lipopolysaccharide injection.

CONCLUSIONS

Atrial natriuretic peptide had a protective effect in the lipopolysaccharide-induced acute lung injury model. Atrial natriuretic peptide may be of value in therapeutic strategies aimed at the treatment of acute lung injury such as pneumonia or acute respiratory distress syndrome.

Hexarelin treatment in male ghrelin knockout mice after myocardial infarction

Both ghrelin and the synthetic analog hexarelin are reported to possess cardioprotective actions that are mainly exerted through different receptors. However, their effects on acute myocardial infarction have not been compared in vivo. This study aimed to clarify whether hexarelin treatment can compensate for ghrelin deficiency in ghrelin-knockout mice and to compare the effects of hexarelin (400 nmol/kg/d, sc) and equimolar ghrelin treatment after myocardial infarction. Myocardial infarction was produced by left coronary artery ligation in male ghrelin-knockout mice, which then received ghrelin, hexarelin, or vehicle treatment for 2 weeks. The mortality within 2 weeks was significantly lower in the hexarelin group (6.7%) and ghrelin group (14.3%) than in the vehicle group (50%) (P < .05). A comparison of cardiac function 2 weeks after infarction showed that in the ghrelin and hexarelin treatment groups, cardiac output was greater, whereas systolic function, represented by ejection fraction, and diastolic function, represented by dP/dt min (peak rate of pressure decline), were significantly superior compared with the vehicle group (P < .05). Hexarelin treatment was more effective than ghrelin treatment, as indicated by the ejection fraction, dP/dt max (peak rate of pressure rise), and dP/dt min. Telemetry recording and heart rate variability analysis demonstrated that sympathetic nervous activity was clearly suppressed in the hexarelin and ghrelin groups relative to the vehicle group. Our data demonstrated that hexarelin treatment can result in better heart function than ghrelin treatment 2 weeks after myocardial infarction in ghrelin-knockout mice, although both hormones have similar effects on heart rate variability and mortality.

Efficacy and safety of dapagliflozin as a monotherapy for type 2 diabetes mellitus in Japanese patients with inadequate glycaemic control: a phase II multicentre, randomized, double-blind, placebo-controlled trial

AIM

Dapagliflozin is a selective sodium-glucose co-transporter 2 (SGLT2) inhibitor under development as a treatment for type 2 diabetes mellitus (T2DM). This study assessed the efficacy and safety of dapagliflozin monotherapy in Japanese T2DM patients with inadequate glycaemic control.

METHODS

Patients (n = 279) were randomized to receive dapagliflozin (1, 2.5, 5 or 10 mg/day) or placebo once daily for 12 weeks. The primary endpoint was change from baseline in haemoglobin A1c (HbA1c) at week 12. Secondary endpoints included change from baseline in fasting plasma glucose (FPG) and proportion of patients achieving HbA1c <7.0% at week 12.

RESULTS

Significant reductions in HbA1c were seen with all dapagliflozin doses (-0.11 to -0.44%) versus placebo (+0.37%). Reductions were also observed in FPG with dapagliflozin (-0.87 to -1.77 mmol/l [-15.61 to -31.94 mg/dl]) versus placebo (+0.62 mmol/l [+11.17 mg/dl]). No significant difference in the proportion of patients achieving HbA1c levels <7.0% was noted with dapagliflozin versus placebo. Adverse events (AEs) were more frequent with dapagliflozin (40.7-53.8%) versus placebo (38.9%) and were mostly mild/moderate in intensity. Three hypoglycaemic events were reported (1 each with placebo, dapagliflozin 2.5 mg and 10 mg). The frequency of signs and symptoms suggestive of urinary tract or genital infections was 0-3.8 and 0-1.8% respectively with dapagliflozin and 1.9 and 0% with placebo. No AEs of pyelonephritis were observed.

CONCLUSIONS

Compared with placebo, dapagliflozin significantly reduced hyperglycaemia over 12 weeks with a low risk of hypoglycaemia in Japanese T2DM patients with inadequate glycaemic control.

Excessive sympathoactivation and deteriorated heart function after myocardial infarction in male ghrelin knockout mice

We have previously demonstrated the protective role of endogenous ghrelin against malignant arrhythmias in the very acute phase of myocardial infarction (MI). However, the role of endogenous ghrelin in the chronic phase is unknown. Therefore, the aim of the current study was to focus on the effects of endogenous ghrelin on cardiac function and sympathetic activation after acute MI. In 46 ghrelin-knockout (KO) and 41 wild-type (WT) male mice, MI was produced by left coronary artery ligation. The mortality due to heart failure within 2 weeks was 0% in WT and 10.9% in KO (P < 0.05). At the end of this period, lung weight/tibial length, atrial natriuretic peptide and brain natriuretic peptide transcripts, end-systolic and end-diastolic volumes were all significantly greater in KO mice, whereas systolic function, represented by ejection fraction (16.4 ± 4.7% vs 25.3 ± 5.1%), end-systolic elastance, and preload-recruitable stroke work, was significantly inferior to that in WT mice (P < 0.05). Telemetry recording and heart rate variability analysis showed that KO mice had stronger sympathetic activation after MI than did WT mice. Metoprolol treatment and ghrelin treatment in KO mice prevented excessive sympathetic activation, decreased plasma epinephrine and norepinephrine levels, and improved heart function and survival rate after MI. Our data demonstrate that endogenous ghrelin plays a crucial role in protecting heart function and reducing mortality after myocardial infarction, and that these effects seem to be partly the result of sympathetic inhibition.

Ghrelin prevents incidence of malignant arrhythmia after acute myocardial infarction through vagal afferent nerves

Ghrelin is a GH-releasing peptide mainly excreted from the stomach. Ghrelin administration has been shown to inhibit cardiac sympathetic nerve activity (CSNA), reduce malignant arrhythmia, and improve prognosis after acute myocardial infarction (MI). We therefore investigated the effects and potential mechanisms of the action of endogenous ghrelin on survival rate and CSNA after MI by using ghrelin-knockout (KO) mice. MI was induced by left coronary artery ligation in 46 KO mice and 41 wild-type mice. On the first day, malignant arrhythmia-induced mortality was observed within 30 min of the ligation and had an incidence of 2.4% in wild-type and 17.4% in KO mice (P < 0.05). We next evaluated CSNA by spectral analysis of heart rate variability. CSNA, represented by the low frequency/high frequency ratio, was higher in KO mice at baseline (2.18 ± 0.43 vs. 0.98 ± 0.09; P < 0.05), and especially after MI (25.5 ± 11.8 vs. 1.4 ± 0.3; P < 0.05), than in wild-type mice. Ghrelin (150 μg/kg, s.c.) 15 min before ligation suppressed the activation of CSNA and reduced mortality in KO mice. Further, this effect of ghrelin was inhibited by methylatropine bromide (1 mg/kg, i.p.) or by perineural treatment of both cervical vagal trunks with capsaicin (a specific afferent neurotoxin). Our data demonstrated that both exogenous and endogenous ghrelin suppressed CSNA, prevented the incidence of malignant arrhythmia, and improved the prognosis after acute MI. These effects are likely to be via the vagal afferent nerves.

Natriuretic peptide receptor guanylyl cyclase-A protects podocytes from aldosterone-induced glomerular injury

Natriuretic peptides produced by the heart in response to cardiac overload exert cardioprotective and renoprotective effects by eliciting natriuresis, reducing BP, and inhibiting cell proliferation and fibrosis. These peptides also antagonize the renin-angiotensin-aldosterone system, but whether this mechanism contributes to their renoprotective effect is unknown. Here, we examined the kidneys of mice lacking the guanylyl cyclase-A (GC-A) receptor for natriuretic peptides under conditions of high aldosterone and high dietary salt. After 4 weeks of administering aldosterone and a high-salt diet, GC-A knockout mice, but not wild-type mice, exhibited accelerated hypertension with massive proteinuria. Aldosterone-infused GC-A knockout mice had marked mesangial expansion, segmental sclerosis, severe podocyte injury, and increased oxidative stress. Reducing the BP with hydralazine failed to lessen such changes; in contrast, blockade of the renin-angiotensin-aldosterone system markedly reduced albuminuria, ameliorated podocyte injury, and reduced oxidative stress. Furthermore, treatment with the antioxidant tempol significantly reduced albuminuria and abrogated the histologic changes. In cultured podocytes, natriuretic peptides inhibited aldosterone-induced mitogen-activated protein kinase phosphorylation. Taken together, these results suggest that renoprotective properties of the endogenous natriuretic peptide/GC-A system may result from the local inhibition of the renin-angiotensin-aldosterone system and oxidative stress in podocytes.

One dose of ghrelin prevents the acute and sustained increase in cardiac sympathetic tone after myocardial infarction

Acute myocardial infarction (MI) increases sympathetic nerve activity (SNA) to the heart, which exacerbates chronic cardiac deterioration. The hormone ghrelin, if administered soon after an MI, prevents the increase in cardiac SNA and improves early survival prognosis. Whether these early beneficial effects of ghrelin also impact on cardiac function in chronic heart failure has not yet been addressed and thus was the aim of this study. MI was induced in Sprague Dawley rats by ligating the left coronary artery. One bolus of saline (n = 7) or ghrelin (150 μg/kg, sc, n = 9) was administered within 30 min of MI. Two weeks after the infarct (or sham; n = 7), rats were anesthetized and cardiac function was evaluated using a Millar pressure-volume conductance catheter. Cardiac SNA was measured using whole-nerve electrophysiological techniques. Untreated-MI rats had a high mortality rate (50%), evidence of severe cardiac dysfunction (ejection fraction 28%; P < 0.001), and SNA was significantly elevated (102% increase; P = 0.03). In comparison, rats that received a single dose of ghrelin after the MI tended to have a lower mortality rate (25%; P = NS) and no increase in SNA, and cardiac dysfunction was attenuated (ejection fraction of 43%; P = 0.014). This study implicates ghrelin as a potential clinical treatment for acute MI but also highlights the importance of therapeutic intervention in the early stages after acute MI. Moreover, these results uncover an intricate causal relationship between early and chronic changes in the neural control of cardiac function in heart failure.

The sphingosine-1-phosphate transporter Spns2 expressed on endothelial cells regulates lymphocyte trafficking in mice

The bioactive lysophospholipid mediator sphingosine-1-phosphate (S1P) promotes the egress of newly formed T cells from the thymus and the release of immature B cells from the bone marrow. It has remained unclear, however, where and how S1P is released. Here, we show that in mice, the S1P transporter spinster homolog 2 (Spns2) is responsible for the egress of mature T cells and immature B cells from the thymus and bone marrow, respectively. Global Spns2-KO mice exhibited marked accumulation of mature T cells in thymi and decreased numbers of peripheral T cells in blood and secondary lymphoid organs. Mature recirculating B cells were reduced in frequency in the bone marrow as well as in blood and secondary lymphoid organs. Bone marrow reconstitution studies revealed that Spns2 was not involved in S1P release from blood cells and suggested a role for Spns2 in other cells. Consistent with these data, endothelia-specific deletion of Spns2 resulted in defects of lymphocyte egress similar to those observed in the global Spns2-KO mice. These data suggest that Spns2 functions in ECs to establish the S1P gradient required for T and B cells to egress from their respective primary lymphoid organs. Furthermore, Spns2 could be a therapeutic target for a broad array of inflammatory and autoimmune diseases.

Ghrelin and cardiovascular diseases

In 1999, a peptide from the stomach called ghrelin was discovered, which exerts potent growth hormone releasing powers. Subsequent studies revealed that it exerts a potent orexigenic action. In addition, the beneficial effects of ghrelin in cardiovascular diseases have been recently suggested. In humans as well as in animals, administration of ghrelin improves cardiac function and remodeling in chronic heart failure. In an animal model for myocardial infarction, ghrelin treatment early after coronary ligation effectively reduces fatal arrhythmia and, consequently, mortality, suggesting the potential therapeutic role of the peptide in acute myocardial infarction. Although how ghrelin may influence the cardiovascular system is not fully understood, the cardiovascular beneficial effects are mediated possibly through a combination of various actions, such as an increase in growth hormone level, an improvement in energy balance, direct actions to the cardiovascular cells, and regulation of the autonomic nervous activity. Of note, current experimental evidence suggests that ghrelin may act centrally to decrease sympathetic nervous system activity through peripheral afferent nerve. Thus, administration of ghrelin might become a unique new therapy for cardiovascular diseases.

Natriuretic Peptide Signaling via Guanylyl Cyclase (GC)-A: An Endogenous Protective Mechanism of the Heart

Atrial and brain natriuretic peptides (ANP and BNP, respectively) are cardiac hormones, secretions of which are markedly upregulated during cardiac failure, making their plasma levels clinically useful diagnostic markers. ANP and BNP exert potent diuretic, natriuretic and vasorelaxant effects, which are mediated via their common receptor, guanylyl cyclase (GC)-A (also called natriuretic peptide receptor (NPR)-A). Mice deficient for GC-A are mildly hypertensive and show marked cardiac hypertrophy and fibrosis that is disproportionately severe, given their modestly higher blood pressure. Indeed, the cardiac hypertrophy seen in these mice is enhanced in a blood pressure-independent manner and is suppressed by cardiomyocyte-specific overexpression of GC-A. These results suggest that the actions of a local cardiac ANP/BNP-GC-A system are essential for maintenance of normal cardiac architecture. In addition, GC-A was shown to exert its cardioprotective effects by inhibiting angiotensin II-induced hypertrophic signaling, and recent evidence suggests that regulator of G protein signaling (RGS) subtype 4 is involved in the GC-A-mediated inhibition of Gαq-coupled hypertrophic signal transduction. Furthermore, several different groups have reported that functional mutations in the promoter region of the human GC-A gene are associated with essential hypertension and ventricular hypertrophy. These findings suggest that endogenous GC-A protects the heart from pathological hypertrophic stimuli, and that humans who express only low levels of GC-A are genetically predisposed to cardiac remodeling and hypertension.

Natriuretic peptide system: an overview of studies using genetically engineered animal models

The mammalian natriuretic peptide system, consisting of at least three ligands and three receptors, plays critical roles in health and disease. Examination of genetically engineered animal models has suggested the significance of the natriuretic peptide system in cardiovascular, renal and skeletal homeostasis. The present review focuses on the in vivo roles of the natriuretic peptide system as demonstrated in transgenic and knockout animal models.

Centrally administered ghrelin activates cardiac vagal nerve in anesthetized rabbits

Although central ghrelin has cardioprotective effect through inhibiting sympathetic nerve activity, the effects of central ghrelin on cardiac vagal nerve remain unknown. We investigated the effects of centrally administered ghrelin on cardiac autonomic nerve activities using microdialysis technique. A microdialysis probe was implanted in the right atrial wall adjacent to the sinoatrial node of an anesthetized rabbit and was perfused with Ringer's solution containing a cholinesterase inhibitor, eserine. After injection of ghrelin (1 nmol) into the right lateral cerebral ventricle, norepinephrine (NE) and acetylcholine (ACh) concentrations in the dialysate samples were measured as indices of NE and ACh release from nerve endings to the sinoatrial node using high-performance liquid chromatography. Heart rate was 270±4 bpm at baseline and decreased gradually after ghrelin injection to 234±9 bpm (P<0.01) at 60-80 min, followed by gradual recovery. Dialysate ACh concentration was 5.5±0.8 nM at baseline and increased gradually after ghrelin injection to 8.8±1.2 nM (P<0.01) at 60-80 min; the concentration started to decrease gradually from 100 to 120 min after injection reaching 5.6±0.8 nM at 160-180 min. Central ghrelin did not change mean arterial pressure or dialysate NE concentration. The elevated dialysate ACh concentration declined rapidly after transection of cervical vagal nerves. These results indicate that centrally administered ghrelin activates cardiac vagal nerve.

Interleukin-6 as an independent predictor of future cardiovascular events in high-risk Japanese patients: comparison with C-reactive protein

Inflammation is associated with the development of atherosclerotic vascular lesions and some inflammatory parameters are used as cardiovascular (CV) risk markers. The present study was designed to assess the predictive power of interleukin (IL)-6 for future CV events. In 121 Japanese patients with multiple CV risk factors and/or disease, serum concentrations of IL-6 and high sensitive C-reactive protein (hs-CRP) were measured. During follow-up periods (mean, 2.9 years) after the baseline assessment, 50 patients newly experienced CV events such as stroke/transient ischemic attack (n=10), heart failure hospitalization (n=6), acute coronary syndrome (n=7), and revascularization for coronary artery disease (n=15) and peripheral arterial disease (n=12). The serum level of IL-6, but not hs-CRP, was significantly higher in patients who had CV events than in event-free subjects (3.9±2.6 and 3.0±2.2 pg/mL, P=0.04). When the patients were divided into three groups by tertiles of basal levels of IL-6 (<1.85, 1.85-3.77, and ≥3.77 pg/mL), cumulative event-free rates by the Kaplan-Meier method were decreased according to the increase in basal IL-6 levels (65%, 50%, and 19% in the lowest, middle, and highest tertiles of IL-6, respectively; log-rank test, P=0.002). By univariate Cox regression analysis, previous CV disease, creatinine clearance, and serum IL-6 levels were significantly associated with CV events during follow-up. Among these possible predictors, the highest tertile of IL-6 was only an independent determinant for the morbidity in the multivariate analysis (hazard ratio 2.80 vs. lowest tertile, P=0.006). These findings indicate that IL-6 is a powerful independent predictor of future CV events in high-risk Japanese patients, suggesting its predictive value is superior to that of hs-CRP.

Impaired recovery of blood flow after hind-limb ischemia in mice lacking guanylyl cyclase-A, a receptor for atrial and brain natriuretic peptides

OBJECTIVE

Atrial and brain natriuretic peptides (ANP and BNP, respectively) function via guanylyl cyclase (GC)-A, resulting in diuresis, natriuresis, and blood vessel dilation. Here, we investigated the role of endogenous ANP/BNP-GC-A signaling on reparative vascular remodeling using a hind-limb ischemia model.

METHODS AND RESULTS

In GC-A-deficient mice (GC-A-KO), hind-limb ischemia resulted in autoamputation or severe ulcers in 60% of mice (6/10) during the 28-day observation period. In wild-type (WT) mice, partial amputation or mild ulcers were detected in only 20% of mice (2/10). Laser Doppler perfusion imaging revealed that the recovery of blood flow in the ischemic limb was significantly inhibited in GC-A-KO mice compared with WT mice. Immunostainings with anti-PECAM-1 antibody demonstrated that, in GC-A-KO, the capillary density of the ischemic tissue was significantly diminished compared to WT. Furthermore, bone marrow transplantation showed the predominant role of GC-A on local ischemic tissue rather than on vascular progenitor cells mobilized from bone marrow during vascular remodeling. In cultured human endothelial cells, ANP treatment significantly stimulated mRNA expressions of vascular endothelial growth factor and endothelial nitric oxide synthase via Erk1/2-dependent mechanism.

CONCLUSIONS

These results suggest that endogenous ANP and BNP play important roles in reparative vascular remodeling in ischemic tissue.

Therapeutic potential of ghrelin in cardiac diseases

It has recently been revealed that ghrelin, a hormone discovered in the stomach, has a potential therapeutic role in the treatment of diseased hearts. In human patients with heart failure and in animal models, repeated subcutaneous administration of ghrelin improves cardiac dysfunction and remodeling. Moreover, ghrelin treatment early after myocardial infarction effectively reduces fatal arrhythmia and, consequently, mortality. The beneficial effects of ghrelin result from a growth hormone increase, an orexigenic effect, direct actions to the cardiovascular cells and its potent inhibitory action on sympathetic nervous activity, which is excessively activated in cardiac diseases. These results suggest that ghrelin could be a promising novel therapeutic agent for cardiac diseases.

C-type natriuretic peptide is a Schwann cell-derived factor for development and function of sensory neurones

Cyclic GMP (cGMP) is known to play important roles for neuronal development and neurite pathfinding. However, the regulatory mechanism that governs the synthesis of cGMP in the nervous system is not well defined. In the present study, we examined the role of C-type natriuretic peptide (CNP), which increases intracellular cGMP upon binding to its receptor, guanylyl cyclase (GC)-B, in the peripheral nervous system. Immunohistochemistry revealed that CNP is demonstrated in Schwann cells, whereas GC-B mRNA is highly expressed in dorsal root ganglion (DRG) neurones. In cultured DRG neurones, GC-B was demonstrated in dendrites of TrkA-positive cells, where it co-exists with cGMP-dependent protein kinase I (cGKI), the major intracellular mediator of cGMP actions. Addition of CNP in the culture medium increased the density of fine neurites, which was accompanied by the increase in phosphorylation of vasodilator-stimulated phosphoprotein, a cGKI substrate. Furthermore, in mice deficient for the CNP gene (CNP-KO), the numbers of TrkA-positive DRG neurones were diminished. Likewise, there were much less cGKI-positive neurones in DRG and cGKI-positive fibres in the dorsal spinal cord of CNP-KO than wild-type mice. Finally, the bone deformity-rescued CNP-KO mice displayed a decreased response to formalin-induced pain compared to wild-type. Taken together, these results suggest that CNP is derived from Schwann cells and plays an important role for the development and function of nociceptive sensory neurones.

Early ghrelin treatment after myocardial infarction prevents an increase in cardiac sympathetic tone and reduces mortality

Acute myocardial infarction (MI) initiates an increase in cardiac sympathetic nerve activity (CSNA), which ultimately exacerbates chronic cardiac dysfunction. Ghrelin (Ghr), a GH-releasing peptide, is an effective treatment for improving cardiac function in chronic heart failure. Ghr also suppresses renal sympathetic nerve activity (SNA) and, therefore, may have important therapeutic benefits in the early stages of acute MI: by reducing CSNA. In this study we hypothesized that early Ghr administration may prevent an increase in CSNA in the acute phase after MI. CSNA was continuously recorded in urethane-anaesthetized rats before and for 5 h after acute MI (or sham). MI was induced by ligation of the left anterior descending coronary artery. Rats received an injection of either saline or Ghr (150 microg/kg, sc) 1 min, or 2 h, after the infarct. CSNA remained stable during the 5-h recording duration in sham rats. MI induced a maximal 110% increase in SNA, which was prevented in rats that received Ghr 1 min after infarct. When Ghr was injected 2 h after MI (SNA had increased by approximately 85%), SNA decreased to pre-MI activity. Importantly, early Ghr administration significantly reduced the high mortality rate associated with MI (61% mortality in untreated MI rats cf. approximately 23% in Ghr-treated MI rats). These results show that early Ghr treatment prevents the increase in CSNA after MI, which may contribute to the improved chances of survival. Whether these early beneficial effects of Ghr also have long-term benefits for improving cardiac function is an area that requires further investigation.