Mitsumasa Ohyanagi

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.

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.

OCT Assessment of Thin-Cap Fibroatheroma Distribution in Native Coronary Arteries

OBJECTIVES We evaluated the geographic distribution of thin-cap fibroatheromas (TCFAs) in the coronary arteries using optical coherence tomography (OCT), a high-resolution imaging modality. BACKGROUND Plaque rupture is the most frequent cause of acute myocardial infarction (AMI). It has been recognized that TCFA is the primary plaque type at the site of plaque rupture. METHODS We performed 3-vessel OCT examinations in 55 patients: 35 AMI and 20 stable angina pectoris patients. The criteria for TCFA in an OCT image was a lipid-rich plaque with fibrotic cap thickness <65 microm. The distance between each TCFA location and the respective coronary artery ostium was measured with motorized OCT imaging pullback. The total length of all 3 coronary arteries imaged by OCT pullbacks was 82 +/- 21 mm in the left anterior descending coronary artery (LAD), 67 +/- 26 mm in the left circumflex coronary artery (LCx), and 104 +/- 32 mm in the right coronary artery (RCA). RESULTS OCT detected 94 TCFAs in 165 coronary arteries. The minimum fibrous-cap thickness of TCFAs was 57.4 +/- 5.4 microm in AMI patients, and 55.9 +/- 7.3 microm in stable angina pectoris patients (p = 0.4). Of the total of 94 TCFAs, 28 were detected in the LAD, 18 in the LCx, and 48 in the RCA. Most LAD TCFAs were located between 0 and 30 mm from the LAD ostium (76%). Conversely, LCx and RCA TCFAs were evenly distributed throughout the entire coronary length. The clustering of the TCFAs was similar in culprit segments as compared with nonculprit segments. In AMI patients, most LAD TCFAs were distributed near side branches, mainly positioned opposite the side branch bifurcation. CONCLUSIONS Three-vessel OCT imaging showed that TCFAs tend to cluster in predictable spots within the proximal segment of the LAD, but develop relatively evenly in the LCx and RCA arteries.

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 …

Frequency and predictor of coronary thin-cap fibroatheroma in patients with acute myocardial infarction and stable angina pectoris a 3-vessel optical coherence tomography study.

To the Editor: Autopsy studies suggest that the main mechanisms of acute myocardial infarction (AMI) are plaque ruptures followed by thrombus formation ([1][1]). Post-mortem studies have shown that rupture-prone plaques, known as thin-cap fibroatheromas (TCFAs), have certain characteristics: a thin

Eicosapentaenoic Acid Improves Endothelial Function in Hypertriglyceridemic Subjects Despite Increased Lipid Oxidizability

BackgroundEpidemiologic investigations suggest that fish oil, which contains eicosapentaenoic acid (EPA), has favorable cardiovascular effects. Fish oil improves endothelial function in subjects with hypercholesterolemia or diabetes. However, controversy persists regarding relationships between primary hypertriglyceridemia and endothelial dysfunction. Moreover, lipoproteins are more susceptible to oxidation in vitro after incorporation of fish oil. MethodsWe determined the effects of EPA on serum lipids, susceptibility of low-density lipoproteins (LDL) and very-low-density lipoproteins (VLDL) to oxidation, and endothelial function in hypertriglyceridemic (HTG) subjects. In 8 men with untreated primary hypertriglyceridemia (plasma triglyceride between 150 and 500 mg/dL) and 7 control subjects (triglyceride below 150 mg/dL), forearm blood flow (FBF) responses were tested. In HTG subjects, this was repeated 3 months after initiation of EPA (1800 mg / day). Cu2+-induced oxidation of VLDL and LDL was determined by serial measurement of conjugated dienes. We used lag time, which corresponded to the period when the lipoproteins were resistant to oxidation, as a parameter of oxidizability. FBF responses to acetylcholine and sodium nitroprusside were determined by strain-gauge plethysmography. ResultsPlasma triglyceride in HTG subjects fell 31% with EPA supplementation. Before EPA, VLDL and LDL lag times in HTG subjects were shorter than in control subjects. EPA further reduced lag time for VLDL but not LDL. The FBF response to acetylcholine (but not to nitroprusside) was significantly less in HTG subjects before EPA than in control subjects. EPA normalized the FBF response to acetylcholine. ConclusionsEPA improves endothelial function in HTG subjects despite increasing in VLDL oxidizability.

Aldosterone induces interleukin-18 through endothelin-1, angiotensin II, Rho/Rho-kinase, and PPARs in cardiomyocytes

Aldosterone (Aldo) is recognized as an important risk factor for cardiovascular diseases. IL-18 induces myocardial hypertrophy, loss of contractility of cardiomyocytes, and apoptosis leading myocardial dysfunction. However, so far, there have been few reports concerning the interaction between Aldo and IL-18. The present study examined the effects and mechanisms of Aldo on IL-18 expression and the roles of peroxisome proliferator-activated receptor (PPAR) agonists in rat cardiomyocytes. We used cultured rat neonatal cardiomyocytes stimulated with Aldo to measure IL-18 mRNA and protein expression, Rho-kinase, and NF-kappaB activity. We also investigated the effects of PPAR agonists on these actions. Aldo, endothelin-1 (ET-1), and angiotensin II (ANG II) increased IL-18 mRNA and protein expression. Mineralocorticoid receptor antagonists, endothelin A receptor antagonist, and ANG II receptor antagonist inhibited Aldo-induced IL-18 expression. Aldo induced ET-1 and ANG II production in cultured media. Moreover, Rho/Rho-kinase inhibitor and statin inhibited Aldo-induced IL-18 expression. On the other hand, Aldo upregulated the activities of Rho-kinase and NF-kappaB. PPAR agonists attenuated the Aldo-induced IL-18 expression and NF-kappaB activity but not the Rho-kinase activity. Our findings indicate that Aldo induces IL-18 expression through a mechanism that involves, at a minimum, ET-1 and ANG II acting via the Rho/Rho-kinase and PPAR/NF-kappaB pathway. The induction of IL-18 in cardiomyocytes by Aldo, ET-1, and ANG II might, therefore, cause a deterioration of the cardiac function in an autocrine and paracrine fashion. The inhibition of the IL-18 expression by PPAR agonists might be one of the mechanisms whereby the beneficial cardiovascular effects are exerted.

CorrespondenceResearch CorrespondenceFrequency and Predictor of Coronary Thin-Cap Fibroatheroma in Patients With Acute Myocardial Infarction and Stable Angina Pectoris: A 3-Vessel Optical Coherence Tomography Study

To the Editor: Autopsy studies suggest that the main mechanisms of acute myocardial infarction (AMI) are plaque ruptures followed by thrombus formation ([1][1]). Post-mortem studies have shown that rupture-prone plaques, known as thin-cap fibroatheromas (TCFAs), have certain characteristics: a thin

Effects of endothelium-derived hyperpolarizing factor and nitric oxide on endothelial function in femoral resistance arteries of spontaneously hypertensive rats.

In hypertension, endothelium-dependent relaxation is attenuated and this attenuation contributes to the increased peripheral resistance. However, the role of endothelium-derived hyperpolarizing factor (EDHF) in the arteries of hypertensive rats remains unclear. Therefore, the aim of this study was to evaluate the role of EDHF in the femoral resistance arteries of hypertensive rats. The femoral resistance arteries were isolated from 5-, 15- and 25-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY). Changes in internal diameter were examined with videomicroscopy. EDHF-mediated dilatation was determined by differences between the degree of acetylcholine (ACh)-induced dilatation in the presence of NG-monomethy-L-arginine (L-NMMA) plus a prostaglandin I2 inhibitor (indomethacin) and the degree of such dilatation in the presence of L-NMMA, indomethacin and KCl. Charybdotoxin (CTx) and apamin (a Ca2+-activated K+ channel [KCa] inhibitor)−sensitive EDHF dilatation was also compared between in 5-, 15- and 25-week-old SHR and WKY. ACh-induced vasodilatation was not different between 5-week-old SHR and WKY. There was no difference between NO- and EDHF-mediated vasodilatation in 5-week-old rats. ACh-induced vasodilatation was weaker in 15-week-old SHR than in WKY. NO-mediated vasodilatation did not differ between the two groups. EDHF-mediated dilatation was attenuated in SHR but not in WKY. ACh-induced dilatation was weaker in 25-week-old SHR than in WKY. NO- and EDHF-mediated vasodilatation were attenuated in SHR but not WKY. EDHF-mediated vasodilatation was attenuated before the loss of NO-mediated vasodilatation in the femoral resistance arteries of SHR. The attenuation of this vasodilatation was mediated by the CTx plus apamin–sensitive EDHF.

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.