Tomoyuki Takayama

Endothelin stimulates an endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine, in experimental heart failure.

Congestive heart failure (CHF) is characterized by increased peripheral vascular resistance. Endothelin-1 (ET-1), a potent endothelium-derived vasoconstrictor, is present at increased concentrations in the plasma and contributes to the regulation of vascular tone in CHF. An endothelium-derived relaxing factor, nitric oxide (NO), also regulates vascular tone, but endothelium-dependent NO-mediated vasodilation is blunted in CHF. An endogenous NO synthase inhibitor, asymmetric dimethylarginine (ADMA), which inhibits NO production and endothelium-dependent relaxation, is present at increased levels in the plasma and plays a role in impaired endothelial function in CHF. However, at present, the relationship between ET-1 and impaired vascular relaxation in CHF is not well known. We hypothesized that ET-1 inhibits NO-mediated vasodilation via increased ADMA production in CHF, and that an endothelin receptor antagonist can prevent this increase in plasma ADMA levels. In the present study, we first examined whether circulating ADMA levels were increased in a dog model of CHF induced by 3 weeks of rapid ventricular pacing (n=5; 270 beats/min) compared with normal dogs (n=5). After 3 weeks of pacing, cardiac output had decreased significantly (1.56+/-0.16 compared with 2.93+/-0.25 litres/min; P<0.01) and systemic vascular resistance had increased (4653+/-374 compared with 3227+/-396 dyn.s.cm(-5); P<0.01) in dogs with CHF compared with normal dogs. Plasma levels of both ET-1 (4.95+/-0.83 compared with 2.12+/-0.39 pg/ml; P<0.05) and ADMA (3.27+/-0.49 compared with 1.91+/-0.25 nmol/ml; P<0.05) were significantly increased in CHF dogs. A significant positive correlation was observed between plasma ET-1 and ADMA levels (r=0.72, P<0.05). Secondly, we chronically administered an ET(A) receptor antagonist, TA-0201 (0.3 mg/kg; n=5), to paced CHF dogs. Drug administration started on day 8 of pacing and continued throughout the experiment. TA-0201 significantly increased cardiac output (2.58+/-0.24 litres/min; P<0.01) and suppressed the increases in plasma ADMA levels and systemic vascular resistance (2.36+/-0.30 nmol/ml and 2423+/-188 dyn.s.cm(-5) respectively; P<0.05 for each) compared with CHF dogs without TA-0201 treatment. In conclusion, ET-1 contributes to the regulation of vascular tone due, in part, to increased levels of an endogenous NO synthase inhibitor in CHF, and an ET(A) receptor antagonist can prevent the inhibition of NO production and the increased peripheral vascular resistance observed in CHF.

Transcardiac increase in tumor necrosis factor‐α and left ventricular end‐diastolic volume in patients with dilated cardiomyopathy

It remains unclear whether tumor necrosis factor (TNF)‐α and interleukin‐6 (IL‐6) are secreted from the failing heart and whether there is a relationship between the transcardiac gradients of these cytokines and left ventricular (LV) remodeling.

Relationship between transcardiac gradient of endothelin-1 and left ventricular remodelling in patients with first anterior myocardial infarction

Aims To evaluate whether plasma endothelin-1 (ET-1) is extracted or produced through the heart in patients with acute myocardial infarction (AMI), and the relationship between transcardiac extraction of plasma ET-1 and left ventricular (LV) remodelling. Methods and results We measured the plasma level of ET-1 in the aortic root (Ao) and coronary sinus (CS) in 48 consecutive patients, who received successful revascularization and enalapril, for a first anterior AMI. In the acute phase the plasma ET-1 level was significantly higher both in the Ao and the CS compared to the control subjects. However, the plasma ET-1 level was significantly lower in the CS than in the Ao in the acute phase and after 1 month. There were significant correlations between transcardiac extraction of ET-1 in the acute phase and LV ejection fraction and LV end-diastolic volume index (LVEDVI) after 1 month. Stepwise multivariate analysis showed that maximal creatine phosphokinase and transcardiac extraction of plasma ET-1 during the acute phase were independently and positively correlated with the absolute change in LVEDVI after 1 month. Conclusions These results indicate that elevated circulating ET-1 is extracted through the heart in patients with a first anterior AMI and that the extracted ET-1 plays a significant role in modulating post-infarct LV remodelling.

Chronic administration of phosphodiesterase type 5 inhibitor suppresses renal production of endothelin-1 in dogs with congestive heart failure.

Endothelin-1 (ET-1) and atrial natriuretic peptide (ANP) play important roles in the regulation of body fluid balance in congestive heart failure (CHF). Renal production of ET-1 increases in CHF and it is a significant independent predictor of sodium excretion. ANP inhibits the ET system through cGMP, a second messenger of ANP. However, in severe CHF, plasma cGMP levels reached a plateau despite the activation of ANP secretion. Thus, ANP does not seem to sufficiently oppose exaggerated ET-1 actions in severe CHF, partially due to the accelerated degradation of cGMP, through phosphodiesterase type 5 (PDE5). We examined the chronic effects of a PDE5 inhibitor, T-1032 (1 mg/kg per day, n=5), on renal function and renal production of ET-1 in dogs with CHF induced by rapid ventricular pacing (270 beats/min). Vehicle dogs were given a placebo (n=5) and normal dogs (n=5) served as normal controls without pacing. In this experimentally produced CHF, plasma levels of ET-1, ANP and cGMP were elevated and renal production of cGMP was increased compared with the normal group, associated with increases in renal expression of preproET-1 mRNA and the number of ET-1-positive cells in glomeruli. In the T-1032 group, systemic and renal production of cGMP were further increased compared with the vehicle group despite no significant difference in plasma ANP levels between the two groups. Subsequently, the agent significantly improved urine flow rate, sodium excretion rate and glomerular filtration rate (GFR) associated with reductions in renal expression of preproET-1 mRNA and the number of ET-1-positive cells compared with the vehicle group. Moreover, there was a significant negative correlation between the number of ET-1-positive cells and GFR (r=-0.802 and P<0.001 respectively). Our results indicate that chronic PDE5 inhibition ameliorates the antagonistic relationship between renal ANP and ET-1 through the cGMP pathway, subsequently preventing renal dysfunction during the progression of CHF.

Endogenous bradykinin suppresses myocardial fibrosis through the cardiac-generated endothelin system under chronic angiotensin-converting enzyme inhibition in heart failure

In congestive heart failure, angiotensin-converting enzyme inhibitors (ACEIs) may prevent cardiac fibrosis via interaction with both angiotensin II and endothelin-1, which enhance myocardial collagen synthesis. However, whether endogenous bradykinin with an ACEI modifies the cardiac collagen architecture, affecting the endothelin system, has not yet been fully elucidated. We evaluated the changes in circulating hormonal factors, myocardial fibrosis and cardiac gene expression closely linked with heart failure, using an orally active specific bradykinin type 2 receptor antagonist, FR173657 (0.3 mg/kg/day, n = 6), with an ACEI, enalapril (1 mg/kg/day), in dogs with tachycardia-induced congestive heart failure (270 p.p.m., 22 days) and compared the effects with enalapril alone (n = 6). Although there were no differences observed in blood pressure, plasma renin activity, aldosterone and endothelin-1 levels, combined FR173657 significantly increased the cardiac expression of preproendothelin- 1 mRNA (P < 0.05) and collagen type I and type III mRNA (P < 0.05), and cardiac collagen deposits (P < 0.05), and decreased eNOS gene expression (P < 0.05) in the left ventricle compared with the ACEI-treated group. Furthermore, there was a significant negative correlation between the expression of preproendothelin- 1 and eNOS mRNA levels (r = -0.708, P < 0.001). In conclusion, bradykinin may prevent cardiac fibrosis in part via suppression of the local endothelin system in the failing heart through the enhancement of nitric oxide production under chronic angiotensin-converting enzyme inhibition.

NADPH Oxidase Inhibition in Heart Failure Improved Vascular Function Associated with Changes in the Novel Genes Expression Revealed by Transcriptome Analysis

Vascular endothelium-dependent vasorelaxation is diminished and reduced skeletal muscle blood flow and correlates with the severity of symptoms in heart failure (HF) as a result of the significant elevation of superoxide anion (O2-) production. There are several sources of (O2-) production within vessels, but NADPH oxidase is present in vascular smooth muscle cells and endothelial cells. Therefore oxidative stress may attenuate endothelial function and inhibition of this action may become one of the strategies to treat HF. We previously investigated the global transcriptome analysis in tachycardia induced HF dogs and we selected four core genes, SOCS3, GADD45A, CDKN1A, and DUSP5 which were associated with the p53 pathway-related genes and the inflammatory interleukinrelated genes enhanced expression in HF. We examined therapeutic effects of apocynin (0.3 mg/kg/day) which suppressed generation of (O2-) on vascular endothelial function and those gene expressions in the femoral artery. Apocynin significantly increased % femoral blood flow responses by acetylcholine (HF 196.4 ± 24.7% vs. apocynin 342.2 ± 35.4%, P<0.05), suppressed O2 production (HF 17.9 ± 1.9 LU/mg/min vs. apocynin 12.89 ± 1.6 RLU/mg/ min, P<0.05) and NADPH oxidase activity (HF 124.9 ± 20.4 RLU/mg/min vs. apocynin 63.9 ± 14.7 RLU/mg/min P<0.05) in HF. The agent decreased the levels of SOCS3, GADD45A, CDKN1A and DUSP5 mRNAs expressions. Suppression of oxidative stress improved endothelial dysfunction in HF through pathways closely linked with cell cycles, proliferation, apoptosis and inflammation. We can conclude that the specific inhibition of NADPH oxidase will become one of the promising therapeutic targets in the treatment of HF mediating through novel vascular molecular mechanisms.