Yoshiro Naito

Augmented Diurnal Variations of the Cardiac Renin-Angiotensin System in Hypertensive Rats

Abstract—There are several controversies concerning the enhanced gene expression of cardiac renin-angiotensin system components in spontaneously hypertensive rats (SHR) compared with their normotensive control Wistar-Kyoto (WKY) rats. We hypothesized that these discrepancies arise from circadian fluctuations in gene expression. We examined the circadian mRNA expression of renin, angiotensinogen, ACE, and angiotensin type 1a (AT1a) and type 2 (AT2) receptors in the hearts of SHR and WKY rats by real-time quantitative reverse transcription–polymerase chain reaction. The cardiac mRNA expression of the renin-angiotensin system components showed circadian oscillations in both SHR and WKY rats. The amplitudes of these circadian fluctuations were greater in the SHR than in the WKY rats. The mRNA levels of the renin-angiotensin system components were also increased in the SHR compared with the WKY rats at many time points (especially during the dark phase). However, the levels of ACE, AT1a receptor, and AT2 receptor mRNA in the SHR and WKY rats were almost the same during the late light phase. In contrast to mRNA expression, ACE activity was similar both at the time of maximum and minimum mRNA expression. The AT1 receptor antagonist candesartan upregulated AT1a receptor mRNA and downregulated ACE mRNA at specific time points only in the SHR group. Our findings of differential diurnal expression of cardiac renin-angiotensin system genes in SHR and WKY rats appear to explain the discrepancies between prior studies. However, the physiological relevance of the differential circadian mRNA expression of the renin-angiotensin system components remains to be elucidated.

A Novel Role for Tumor Necrosis Factor–Like Weak Inducer of Apoptosis (TWEAK) in the Development of Cardiac Dysfunction and Failure

Background— Tumor necrosis factor–like weak inducer of apoptosis (TWEAK), a member of the tumor necrosis factor superfamily, is a multifunctional cytokine known to regulate cellular functions in contexts of injury and disease through its receptor, fibroblast growth factor–inducible molecule 14 (Fn14). Although many of the processes and downstream signals regulated by the TWEAK/Fn14 pathway have been implicated in the development of cardiac dysfunction, the role of TWEAK in the cardiovascular system is completely unknown. Methods and Results— Herein, we demonstrate that mouse and human cardiomyocytes express the TWEAK receptor Fn14. Furthermore, we determine that elevated circulating levels of TWEAK, induced via transgenic or adenoviral-mediated gene expression in mice, result in dilated cardiomyopathy with subsequent severe cardiac dysfunction. This phenotype was mediated exclusively by the Fn14 receptor, independent of tumor necrosis factor-α, and was associated with cardiomyocyte elongation and cardiac fibrosis but not cardiomyocyte apoptosis. Moreover, we find that circulating TWEAK levels were differentially upregulated in patients with idiopathic dilated cardiomyopathy compared with other forms of heart disease and normal control subjects. Conclusions— Our data suggest that TWEAK/Fn14 may be important in regulating myocardial structural remodeling and function and may play a role in the pathogenesis of dilated cardiomyopathy.

Adaptive response of the heart to long-term anemia induced by iron deficiency

Anemia is common in patients with chronic heart failure and an independent predictor of poor prognosis. Chronic anemia leads to left ventricular (LV) hypertrophy and heart failure, but its molecular mechanisms remain largely unknown. We investigated the mechanisms, including the molecular signaling pathway, of cardiac remodeling induced by iron deficiency anemia (IDA). Weanling Sprague-Dawley rats were fed an iron-deficient diet for 20 wk to induce IDA, and the molecular mechanisms of cardiac remodeling were evaluated. The iron-deficient diet initially induced severe anemia, which resulted in LV hypertrophy and dilation with preserved systolic function associated with increased serum erythropoietin (Epo) concentration. Cardiac STAT3 phosphorylation and VEGF gene expression increased by 12 wk of IDA, causing angiogenesis in the heart. Thereafter, sustained IDA induced upregulation of cardiac hypoxia inducible factor-1alpha gene expression and maintained upregulation of cardiac VEGF gene expression and cardiac angiogenesis; however, sustained IDA promoted cardiac fibrosis and lung congestion, with decreased serum Epo concentration and cardiac STAT3 phosphorylation after 20 wk of IDA compared with 12 wk. Upregulation of serum Epo concentration and cardiac STAT3 phosphorylation is associated with a beneficial adaptive mechanism of anemia-induced cardiac hypertrophy, and later decreased levels of these molecules may be critical for the transition from adaptive cardiac hypertrophy to cardiac dysfunction in long-term anemia. Understanding the mechanism of cardiac maladaptation to anemia may lead to a new strategy for treatment of chronic heart failure with anemia.

Increased circulating interleukin-18 in patients with congestive heart failure

Accumulating evidence suggests that proinflammatory cytokines such as tumour necrosis factor (TNF) α, interleukin (IL)-1β, and IL-6 are likely to be involved in the pathogenesis of advanced cardiac failure. Cytokine actions directly identified to date include promotion of systemic catabolism, myocardial depression, cardiac hypertrophy, and apoptosis of myocytes in congestive heart failure (CHF). IL-18, a new member of the IL-1 family, is a proinflammatory cytokine with multiple biologic functions.1 In concert with IL-12, IL-18 stimulates Th1 mediated immune responses; by itself, IL-18 can stimulate Th2 cytokine production. IL-18, originally named as an interferon γ inducing factor (IGIF),2 can induce TNFα and IL-6 in murine macrophages.3 Pomerantz and colleagues demonstrated that IL-18 is expressed in vascular endothelial cells and macrophages in human heart, and that IL-18 binding protein, which is derived from a gene distinct from the IL-18 receptor gene and can neutralise IL-18 actions, reduces human myocardial reperfusion injury after 30 minutes of ischaemia.4,5 We hypothesised that IL-18 might contribute to immune activation and cardiac dysfunction in congestive heart failure. In this study we examined serum concentrations of IL-18 in patients with CHF to examine whether the cytokine was involved in the pathophysiology of this syndrome. Subjects included 34 consecutively recruited patients (20 men and 14 women aged 42–83 years, mean 64 years) who had chronic, stable symptomatic heart failure representing New York Heart Association (NYHA) functional class II–IV for more than two …

Dietary Iron Restriction Prevents Hypertensive Cardiovascular Remodeling in Dahl Salt-Sensitive Rats

Iron accumulation is associated with the pathogenesis of several cardiovascular diseases. However, the preventive effects of iron restriction (IR) against cardiovascular disease remain obscure. We investigated the effects of dietary IR on cardiovascular pathophysiology and the involved mechanism in Dahl salt-sensitive rats. Dahl salt-sensitive rats were provided either a normal or high-salt (HS) diet. Another subset of Dahl salt-sensitive rats were fed an HS with iron-restricted (HS+IR) diet for 11 weeks. Dahl salt-sensitive rats given an HS diet developed hypertension, heart failure, and decreased a survival rate after 11 weeks on the diet. In contrast, IR attenuated the development of hypertension and heart failure, thereby improving survival rate. Dietary IR suppressed cardiovascular hypertrophy, fibrosis, and inflammation in HS rats. The phosphorylation of Akt, AMP-activated protein kinase, and endothelial nitric oxide synthase was decreased in the aorta of HS rats, whereas they were ameliorated by the IR diet. Aortic expression of the cellular iron import protein transferrin receptor 1, and the iron storage protein ferritin H-subunit, was upregulated in HS rats. IR also attenuated proteinuria and increased oxidative stress in the HS group. NG-nitro-l-arginine methyl ester abolished the beneficial effects of IR and decreased survival rate in HS+IR rats. Dietary IR had protective effects on salt-induced hypertension, cardiovascular remodeling, and proteinuria through the inhibition of oxidative stress, and maintenance of Akt, AMP-activated protein kinase, and endothelial nitric oxide synthase in the aorta. IR could be an effective strategy for prevention of HS-induced organ damage in salt-sensitive hypertensive patients.

Intraleaflet haemorrhage is associated with rapid progression of degenerative aortic valve stenosis

AIMS The haemorrhage in the plaque (intraplaque haemorrhage) plays a critical role in the progression of atherosclerosis. The purpose of this study is to clarify whether the haemorrhage in the aortic valve leaflet (intraleaflet haemorrhage) accelerates the progression of aortic valve stenosis (AS). METHODS AND RESULTS We examined specimens of aortic valve leaflets obtained from 36 patients who had undergone aortic valve replacement for degenerative AS and in whom echocardiographic data were available just before the operation and at least 180 days before the last study. The stenotic valves were examined by immunohistochemistry to detect intraleaflet haemorrhage with antibody against glycophorin A, an erythrocyte-specific protein. The progression of AS was assessed by annualized change in the aortic valve area (ΔAVA: cm(2)/year). The patients were divided into two groups, namely the rapid progression group (ΔAVA ≥ 0.1 cm(2)/year) and the slow progression group (ΔAVA < 0.1 cm(2)/year), according to the reported average progression rate of AS. Intraleaflet haemorrhage was observed in 78 % of the specimens. Intraleaflet haemorrhage was associated with neovascularization and macrophage infiltration. The areas of intraleaflet haemorrhage and macrophage infiltration were greater in the rapid progression group than in the slow progression group. Multivariate analysis has shown that the area of intraleaflet haemorrhage was the sole independent factor that positively correlated with ΔAVA. CONCLUSIONS Intraleaflet haemorrhage was frequently observed in the valve leaflets of degenerative AS and associated with a rapid progression of AS.

Serum interleukin-6 and C-reactive protein are markedly elevated in acute decompensated heart failure patients with left ventricular systolic dysfunction.

Cytokines play important roles in heart failure (HF). We examined whether cytokine levels are different in acute decompensated heart failure (ADHF) patients between with left ventricular systolic dysfunction (LVSDF) and with preserved LV ejection function (PLVEF). We studied 81 HF patients who were admitted to our hospital with acute decompensation. They were divided into two groups: LVSDF (LVEF)<45% and PLVEF (LVEF45%). Serum interleukin-6 (IL-6), highly sensitive C-reactive protein (hsCRP), tumor necrosis factor alpha (TNF-alpha), and IL-18 and plasma brain natriuretic peptide (BNP) were measured on admission and at discharge. On admission, IL-6 and hsCRP were higher in LVSDF than in PLVEF. IL-6 and hsCRP decreased after treatment in LVSDF, but not in PLVEF, while plasma BNP levels decreased in both HF with treatment. There was no difference in TNF-alpha or in IL-18 level between LVSDF and PLVEF, and they did not change after treatment in either group. In conclusion, cytokine profiles were different in ADHF between those with LVSDF and PLVEF. Activation of IL-6-hsCRP pathway may play a specific role in ADHF with LVSDF.

Inhibition of the Cardiomyocyte-Specific Kinase TNNI3K Limits Oxidative Stress, Injury, and Adverse Remodeling in the Ischemic Heart

Blocking the activity of a cardiomyocyte-specific protein kinase with a small-molecule inhibitor reduces oxidative stress, myocyte death, and adverse remodeling in the ischemic heart. Blocking Cardiac Kinase Prevents Heart Damage Restoring blood flow after a heart attack is essential; yet, rapid reperfusion of blood can cause adverse effects on heart cells (cardiomyocytes) via oxidative damage, calcium overload, and inflammation. To limit these effects, Vagnozzi and colleagues developed an inhibitor that targets a cardiomyocyte-specific kinase called TNNI3K, which may be intimately involved in signaling events after ischemia (blockage of blood flow) and reperfusion. The authors first confirmed that TNNI3K is up-regulated in tissues from patients with heart failure who were undergoing transplant. Mice that overexpressed active TNNI3K had larger infarcts than those with an inactive form of the kinase, as well as worse ischemic injury and cardiomyocyte death. Conversely, deletion of Tnni3k reduced infarct size and prevented cardiomyocyte death in mice. From the human tissues, the kinase appeared to be limited to cardiomyocytes, which lends itself to targeted therapy. Vagnozzi et al. administered two different small-molecule inhibitors during reperfusion to mice with ischemic injury and observed a reduction in left ventricle dysfunction, progressive remodeling, and fibrosis (a hardening of the heart tissue). The authors believe that these functional benefits stem from a concomitant reduction in superoxide production, p38 activation, and infarct size. This inhibition strategy will need to be tested in a large-animal model before translation. If successful, it could find immediate application to patients with chronic ischemic cardiomyopathy, where recurrent ischemia is followed by reperfusion. Percutaneous coronary intervention is first-line therapy for acute coronary syndromes (ACS) but can promote cardiomyocyte death and cardiac dysfunction via reperfusion injury, a phenomenon driven in large part by oxidative stress. Therapies to limit this progression have proven elusive, with no major classes of new agents since the development of anti-platelets/anti-thrombotics. We report that cardiac troponin I–interacting kinase (TNNI3K), a cardiomyocyte-specific kinase, promotes ischemia/reperfusion injury, oxidative stress, and myocyte death. TNNI3K-mediated injury occurs through increased mitochondrial superoxide production and impaired mitochondrial function and is largely dependent on p38 mitogen-activated protein kinase (MAPK) activation. We developed a series of small-molecule TNNI3K inhibitors that reduce mitochondrial-derived superoxide generation, p38 activation, and infarct size when delivered at reperfusion to mimic clinical intervention. TNNI3K inhibition also preserves cardiac function and limits chronic adverse remodeling. Our findings demonstrate that TNNI3K modulates reperfusion injury in the ischemic heart and is a tractable therapeutic target for ACS. Pharmacologic TNNI3K inhibition would be cardiac-selective, preventing potential adverse effects of systemic kinase inhibition.

Effect of iron restriction on renal damage and mineralocorticoid receptor signaling in a rat model of chronic kidney disease.

Objective: Iron is associated with the pathogenesis of chronic kidney disease (CKD). Activation of mineralocorticoid receptor signaling is implicated in CKD; however, a link between iron and mineralocorticoid receptor signaling in CKD remains unknown. We have previously shown that long-term dietary iron restriction leads to increased sodium and decreased potassium excretions in the rat urine. Herein, we investigated the effect of iron restriction on renal damage and mineralocorticoid receptor signaling in a rat model of CKD. Methods: CKD was induced by 5/6 nephrectomy in Sprague–Dawley rats. CKD rats were divided into untreated and dietary iron-restricted groups. Results: CKD rats exhibited proteinuria, glomerulosclerosis, tubulointerstitinal damage, and podocyte injury. In contrast, these changes were attenuated by 16 weeks of iron-restricted diet. Consistent with these findings, iron restriction suppressed increased gene expression of collagen type III, transforming growth factor-&bgr;, CD68, and tumor necrosis factor-&agr; in the CKD kidney. Importantly, increased expression of nuclear mineralocorticoid receptor and SGK1, a key downstream effector of mineralocorticoid receptor signaling, in the CKD kidney was markedly attenuated by iron restriction. Of interest, expression of cellular iron transport proteins, transferrin receptor 1, and divalent metal transporter 1 was increased in the CKD renal tubules, along with increased iron accumulation, superoxide production, and urinary iron excretion. CKD rats also developed hypertension, although iron restriction suppressed the development of hypertension. Conclusion: Taken together, these data uncover a novel effect of iron restriction on renal damage and hypertension through the inhibition of renal mineralocorticoid receptor signaling.

Impaired expression of duodenal iron transporters in Dahl salt-sensitive heart failure rats.

Objective Anemia is common in patients with heart failure and several factors have been thought to cause anemia in heart failure. Despite vigorous studies, the mechanism underlying the pathophysiology of anemia in heart failure is unknown. We investigated the iron regulating system in Dahl salt-sensitive heart failure rats to elucidate the mechanism of anemia in heart failure. Methods Dahl salt-sensitive rats were provided either a normal or high-salt diet to initiate heart failure progression. A further subset of Dahl salt-sensitive rats underwent an iron-deficient diet to induce iron deficiency anemia (IDA). Results Dahl salt-sensitive rats, which develop diastolic heart failure, gradually showed hypertension and anemia after 8 weeks of high-salt diet. Although serum iron levels were decreased, erythropoietin levels were increased in the IDA and heart failure groups. Hepatic expression of hepcidin, a central regulator of iron metabolism, was downregulated in both IDA and heart failure groups. Duodenal cytochrome b (Dcyt-b), divalent metal transporter 1 (DMT-1), and ferroportin are the crucial regulators of intestinal iron transport and absorption. Duodenal expression levels of these molecules were markedly upregulated in the IDA group, but not in the heart failure group. Moreover, intestinal expression of hypoxia-inducible factor-2α, a critical regulator of the transcription of Dcyt-b and DMT-1, was upregulated in the IDA group, but not in the heart failure group. Conclusion Duodenal iron transporters expression was impaired in Dahl heart failure rats. Our data suggest that impaired duodenal iron absorption may occur in Dahl heart failure rats. Understanding the mechanism of abnormal iron regulating system may lead to new therapeutic strategies in anemia with heart failure.