Yoko Irukayama-Tomobe

Effects of exercise training of 8 weeks and detraining on plasma levels of endothelium-derived factors, endothelin-1 and nitric oxide, in healthy young humans.

Vascular endothelial cells produce nitric oxide (NO), which is a potent vasodilator substance and has been proposed as having antiatherosclerotic property. Vascular endothelial cells also produce endothelin-1 (ET-1), which is a potent vasoconstrictor peptide and has potent proliferating activity on vascular smooth muscle cells. Therefore, ET-1 has been implicated in the progression of atheromatous vascular disease. Because exercise training has been reported to produce an alteration in the function of vascular endothelial cells in animals, we hypothesized that exercise training influences the production of NO and ET-1 in humans. The purpose of the present study was to examine whether chronic exercise could influence the plasma levels of NO (measured as the stable end product of NO, i.e., nitrite/nitrate [NOx]) and ET-1 in humans. Eight healthy young subjects (20.3 +/- 0.5 yr old) participated in the study and exercised by cycling on a leg ergometer (70% VO2max for 1 hour, 3-4 days/week) for 8 weeks. Venous plasma concentrations of NOx and ET-1 were measured before and after (immediately before the end of 8-week exercise training) the exercise training, and also after the 4th and 8th week after the cessation of training. The VO2max significantly increased after exercise training. After the exercise training, the plasma concentration of NOx significantly increased (30.69 +/- 3.20 vs. 48.64 +/- 8.16 micromol/L, p < 0.05), and the plasma concentration of ET-1 significantly decreased (1.65 +/- 0.14 vs. 1.23 +/- 0.12 pg/mL, p < 0.05). The increase in NOx level and the decrease in ET-1 level lasted to the 4th week after the cessation of exercise training and these levels (levels of NOx and ET-1) returned to the basal levels (the levels before the exercise training) in the 8th week after the cessation of exercise training. There was a significant negative correlation between plasma NOx concentration and plasma ET-1 concentration. The present study suggests that chronic exercise causes an increase in production of NO and a decrease in production of ET-1 in humans, which may produce beneficial effects (i.e., vasodilative and antiatherosclerotic) on the cardiovascular system.

Endothelin-1–Induced Cardiac Hypertrophy Is Inhibited by Activation of Peroxisome Proliferator–Activated Receptor-α Partly Via Blockade of c-Jun NH2-Terminal Kinase Pathway

Background—Peroxisome proliferator-activated receptor-&agr; (PPAR-&agr;) is a lipid-activated nuclear receptor that negatively regulates the vascular inflammatory gene response by interacting with transcription factors, nuclear factor-&kgr;B, and AP-1. However, the roles of PPAR-&agr; activators in endothelin (ET)-1–induced cardiac hypertrophy are not yet known. Methods and Results—First, in cultured neonatal rat cardiomyocytes, a PPAR-&agr; activator, fenofibrate (10 &mgr;mol/L), and PPAR-&agr; overexpression markedly inhibited the ET-1–induced increase in protein synthesis. Second, fenofibrate markedly inhibited ET-1–induced increase in c-Jun gene expression and phosphorylation of c-Jun and JNK. These results suggest that this PPAR-&agr; activator interferes with the formation and activation of AP-1 protein induced by ET-1 in cardiomyocytes. Third, fenofibrate significantly inhibited the increase of ET-1 mRNA level by ET-1, which was also confirmed by luciferase assay. Electrophoretic mobility shift assay revealed that fenofibrate significantly decreased the ET-1–stimulated or phorbol 12-myristate 13-acetate–stimulated AP-1 DNA binding activity, and the nuclear extract probe complex was supershifted by anti-c-Jun antibody. Fourth, 24 hours after aortic banding (AB) operation, fenofibrate treatment significantly inhibited left ventricular hypertrophy and hypertrophy-related gene expression pattern (ET-1, brain natriuretic peptide, and &bgr;-myosin heavy chain mRNA) in AB rats. Conclusions—These results suggest that PPAR-&agr; activation interferes with the signaling pathway of ET-1–induced cardiac hypertrophy through negative regulation of AP-1 binding activity, partly via inhibition of the JNK pathway in cultured cardiomyocytes. We also revealed that fenofibrate treatment inhibited left ventricle hypertrophy and phenotypic changes in cardiac gene expression in AB rats in vivo.

Essential Role of p38 Mitogen-activated Protein Kinase in Contact Hypersensitivity

The present study was designed to elucidate the role of p38 mitogen-activated protein kinase (p38) in the pathogenesis of inflammation, using a mouse contact hypersensitivity (CHS) model induced by 2,4-dinitro-1-fluorobenzene (DNFB). Ear swelling was induced by challenge with DNFB, accompanied by infiltration of mononuclear cells, neutrophils, and eosinophils and a marked increase in mRNA levels of cytokines such as interleukin (IL)-2, interferon (IFN)-γ, IL-4, IL-5, IL-1β, IL-18, and tumor necrosis factor-α in the challenged ear skin. Both ear swelling and the number of infiltrated cells in DNFB-challenged ear skin were significantly inhibited by treatment with SB202190, a p38 inhibitor. Furthermore, the DNFB-induced expression of all cytokines except IL-4 was significantly inhibited by treatment with SB202190. Ribonuclease protection assay revealed that the mRNA levels of chemokines such as IP-10 and MCP-1 in ear skin were markedly increased at 24 h after challenge with DNFB. The induction of these chemokines was significantly inhibited by treatment with SB202190. In p38α +/− mice, both ear swelling and infiltration of cells induced by DNFB were reduced compared with those in wild-type mice. However, induction of cytokines by DNFB was also observed in p38α +/− mice, although the induction of IFN-γ, IL-5, and IL-18 was typically reduced compared with that in wild-type mice. Challenge with DNFB slightly induced IP-10 and MCP-1 mRNA in p38α +/− mice, with weaker signals than those in SB202190-treated wild-type mice. These results suggest that p38 plays a key role in CHS and is an important target for the treatment of CHS.

Involvement of Endogenous Endothelin-1 in Exercise-Induced Redistribution of Tissue Blood Flow An Endothelin Receptor Antagonist Reduces the Redistribution

Background—Endothelin-1 (ET-1) is a potent endothelium-derived vasoconstrictor peptide. Exercise results in a significant redistribution of tissue blood flow, which greatly increases blood flow in active muscles but decreases it in the splanchnic circulation. We reported that exercise causes an increase of ET-1 production in the internal organ and then hypothesized that ET-1 participates in the exercise-induced redistribution of tissue blood flow. We investigated the effects of acute endothelin-A (ETA)-receptor blockade on regional tissue blood flow during exercise in rats. Methods and Results—Regional blood flow in the kidney, spleen, stomach, intestine, and muscles was measured using the microsphere technique before and during treadmill running of 30 minutes duration at 30 m/min after pretreatment with either an ETA-receptor antagonist (TA-0201; 0.5 mg/kg) or vehicle in rats. Blood flow in the kidney, spleen, stomach, and intestine was decreased by exercise, but the magnitude of the decrease after pretreatment with TA-0201 was significantly smaller than that after pretreatment with vehicle. Furthermore, the increase in blood flow to active muscles induced by exercise was significantly smaller in rats pretreated with TA-0201 than those pretreated with vehicle. Conclusions—The present study revealed that ET-1-mediated vasoconstriction participates in the decrease of blood flow in the internal organs of rats during exercise, and therefore, that these actions of endogenous ET-1 partly contribute to the increase of blood flow in active muscles during exercise. The data suggest that endogenous ET-1 participates in the exercise-induced redistribution of tissue blood flow.

Aromatic D-amino acids act as chemoattractant factors for human leukocytes through a G protein-coupled receptor, GPR109B

GPR109B (HM74) is a putative G protein-coupled receptor (GPCR) whose cognate ligands have yet to be characterized. GPR109B shows a high degree of sequence similarity to GPR109A, another GPCR that was identified as a high-affinity nicotinic acid (niacin) receptor. However, the affinity of nicotinic acid to GPR109B is very low. In this study, we found that certain aromatic D-amino acids, including D-phenylalanine, D-tryptophan, and the metabolite of the latter, D-kynurenine, decreased the activity of adenylate cyclase in cells transfected with GPR109B cDNA through activation of pertussis toxin (PTX)-sensitive G proteins. These D-amino acids also elicited a transient rise of intracellular Ca2+ level in cells expressing GPR109B in a PTX-sensitive manner. In contrast, these D-amino acids did not show any effects on cells expressing GPR109A. We found that the GPR109B mRNA is abundantly expressed in human neutrophils. D-phenylalanine and D-tryptophan induced a transient increase of intracellular Ca2+ level and a reduction of cAMP levels in human neutrophils. Furthermore, knockdown of GPR109B by RNA interference inhibited the D-amino acids-induced decrease of cellular cAMP levels in human neutrophils. These D-amino acids induced chemotactic activity of freshly prepared human neutrophils. We also found that D-phenylalanine and D-tryptophan induced chemotactic responses in Jurkat cells transfected with the GPR109B cDNA but not in mock-transfected Jurkat cells. These results suggest that these aromatic D-amino acids elicit a chemotactic response in human neutrophils via activation of GPR109B.

Association of an orexin 1 receptor 408Val variant with polydipsia-hyponatremia in schizophrenic subjects.

BACKGROUND Primary polydipsia is a common complication in patients with chronic psychoses, particularly schizophrenia. Disease pathogenesis is poorly understood, but one contributory factor is thought to be dopamine dysregulation caused by prolonged treatment with neuroleptics. Both angiotensin-converting enzyme (ACE) and orexin (hypocretin) signaling can modulate drinking behavior through interactions with the dopaminergic system. METHODS We performed association studies on the insertion/deletion (I/D) sequence polymorphism of ACE and single nucleotide polymorphisms within the prepro-orexin (HCRT), orexin receptor 1 (HCRTR1), and orexin receptor 2 (HCRTR2) genes. Genotypes were determined by polymerase chain reaction amplification, followed by either electrophoretic separation or direct sequencing. RESULTS The ACE I/D polymorphism showed no association with polydipsic schizophrenia. Screening of the orexin signaling system detected a 408 isoleucine to valine mutation in HCRTR1 that showed significant genotypic association with polydipsic-hyponatremic schizophrenia (p = .012). The accumulation of this mutation was most pronounced in polydipsic versus nonpolydipsic schizophrenia (p = .0002 and p = .008, for the respective genotypic and allelic associations). The calcium mobilization properties and the protein localization of mutant HCRTR1 seem to be unaltered. CONCLUSION Our preliminary data suggest that mutation carriers might have an increased susceptibility to polydipsia through an undetermined mechanism.

Activation of peroxisome proliferator-activated receptor-alpha decreases endothelin-1-induced p38 mitogen-activated protein kinase activation in cardiomyocytes.

Endothelin-1 (ET-1) is synthesized and secreted by cardiomyocytes and induces cardiac hypertrophy. Peroxisome proliferator-activated receptor-α (PPAR-α) is a lipid-activated nuclear receptor that negatively regulates the vascular inflammatory gene response by interacting with transcription factors, such as nuclear factor-κB and activator protein-1 (AP-1). We reported that PPAR-α activator, fenofibrate (10 μM), and PPAR-α overexpression markedly inhibited the ET-1-induced increase in protein synthesis in cultured neonatal rat cardiomyocytes. Activation of protein kinase C and one or more of the mitogen-activated protein kinase cascades by ET-1 induces many of the features of hypertrophy.We demonstrated that PPAR-α activation significantly inhibits ET-1-induced cardiac hypertrophy through negative regulation of AP-1 binding activity partly secondary to inhibition of the JNK pathway. Zechner et al. demonstrated a significant role of p38 mitogen-activated protein kinase (p38) in myocardial cell hypertrophic growth and gene expression. Therefore, we investigated the effect of fenofibrate on ET-1-induced p38 activation in cardiomyocytes. The phosphorylation of p38 was transiently increased after 15 and 30 minutes of stimulation with ET-1, which was significantly inhibited by fenofibrate (10 μM). Neither application of ET-1 nor fenofibrate treatment affected the expression level of p38 in cardiomyocytes. These results suggest that the negative effect of the PPAR-α activator, fenofibrate, on ET-1-induced cardiac hypertrophy may be partly due to inhibition of the p38 signaling pathway.

The benefit of medium-chain triglyceride therapy on the cardiac function of SHRs is associated with a reversal of metabolic and signaling alterations

The spontaneously hypertensive rat (SHR) is a model of cardiomyopathy that displays a genetic defect in cardiac fatty acid (FA) translocase/CD36, a plasma membrane long-chain FA transporter. Therapy with medium-chain FAs, which do not require CD36-facilitated transport, has been shown to improve cardiac function and hypertrophy in SHRs despite persistent hypertension. However, little is known about the underlying molecular mechanisms. The aim of this study was to document the impact of medium-chain triglyceride (MCT) therapy in SHRs on the expression level and activity of metabolic enzymes and signaling pathways. Four-week-old male SHRs were administered MCT (SHR-MCT) or long-chain triglyceride (SHR-LCT) for 16 wk. We used Wistar-Kyoto (WKY) rats as controls (WKY-MCT and WKY-LCT). The SHR-MCT group displayed improved cardiac dysfunction [as assessed by left ventricular (LV) end-diastolic pressure and the positive and negative first derivatives of LV pressure/P value], a shift in the beta-myosin heavy chain (MHC)-to-alpha-MHC ratio, and cardiac hypertrophy compared with the SHR-LCT group without an effect on blood pressure. Administration of MCT of SHRs reversed the LCT-induced reduction in the cardiac FA metabolic enzymatic activities of long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and medium-chain acyl-CoA dehydrogenase (MCAD). In the SHR-MCT group, the protein expression and transcriptional regulation of myocardial peroxisome proliferator-activated receptor-alpha, which regulates the transcription of LCHAD and MCAD genes, corresponded to the changes seen in those enzymatic activities. Furthermore, MCT intake caused an inhibition of JNK activation in SHR hearts. Collectively, the observed changes in the myocardial activity of metabolic enzymes and signaling pathways may contribute to the improved cardiac dysfunction and hypertrophy in SHRs following MCT therapy.

The peroxisome proliferator-activated receptor alpha activator fenofibrate inhibits endothelin-1-induced cardiac fibroblast proliferation.

Endothelin-1 has been known to promote tissue fibrosis. We previously reported in our animal experiments that a peroxisome proliferator-activated receptor α (PPARα) inhibited cardiac fibrosis with suppression of endothelin-1 production, and it was also reported that PPARα activation suppressed the production of c-jun, which is a component of activator protein-1. The objective of this study is to clarify on the in vitro level that PPARα activators inhibited cardiac fibroblast proliferation via their suppressive action on c-jun expression. We investigated the effects of the PPARα activator fenofibrate (10 μM) on DNA synthesis in neonatal rat cardiac fibroblasts by [3H]thymidine incorporation. The [3H]thymidine incorporation in cardiac fibroblasts showed an increase of 1.1-fold by endothelin-1 (10-8 M) stimulation. Fenofibrate treatment showed significant inhibition of [3H]thymidine incorporation in both endothelin-1-stimulated and non-stimulated fibroblasts. Additionally, we also evaluated mRNA expressions of cjun and c-fos in the fibroblasts by the reverse transcriptionpolymerase chain reaction method. Fenofibrate treatment markedly reduced c-jun mRNA expression, whereas it did not affect c-fos mRNA expression. In conclusion, we demonstrated that the PPARα activator fenofibrate inhibited endothelin-1-induced proliferation of cardiac fibroblasts and also inhibited non-stimulated proliferation. This inhibition of proliferation may be caused by up-regulation of p27Kip1 by suppressing c-jun expression.

Nonpeptide orexin type-2 receptor agonist ameliorates narcolepsy-cataplexy symptoms in mouse models

Significance Narcolepsy-cataplexy is a debilitating disorder characterized by excessive daytime sleepiness (sleep attacks) and cataplexy, a sudden bilateral loss of muscle tone often triggered by emotion. The disease is caused by a selective loss of hypothalamic neurons producing the neuropeptide orexin. Currently, only symptomatic therapies are available for narcolepsy. Here, we examine the pharmacological effect of YNT-185, a nonpeptide, selective agonist for the orexin type-2 receptor in mouse models of narcolepsy-cataplexy. We show that peripheral administration of YNT-185 significantly ameliorates the narcolepsy symptoms in model mice, providing a proof-of-concept for the mechanistic treatment of narcolepsy with orexin receptor agonists. YNT-185 also promotes wakefulness in wild-type mice, suggesting that orexin receptor agonists may be useful for treating sleepiness due to other causes. Narcolepsy-cataplexy is a debilitating disorder of sleep/wakefulness caused by a loss of orexin-producing neurons in the lateroposterior hypothalamus. Genetic or pharmacologic orexin replacement ameliorates symptoms in mouse models of narcolepsy-cataplexy. We have recently discovered a potent, nonpeptide OX2R-selective agonist, YNT-185. This study validates the pharmacological activity of this compound in OX2R-transfected cells and in OX2R-expressing neurons in brain slice preparations. Intraperitoneal, and intracerebroventricular, administration of YNT-185 suppressed cataplexy-like episodes in orexin knockout and orexin neuron-ablated mice, but not in orexin receptor-deficient mice. Peripherally administered YNT-185 also promotes wakefulness without affecting body temperature in wild-type mice. Further, there was no immediate rebound sleep after YNT-185 administration in active phase in wild-type and orexin-deficient mice. No desensitization was observed after repeated administration of YNT-185 with respect to the suppression of cataplexy-like episodes. These results provide a proof-of-concept for a mechanistic therapy of narcolepsy-cataplexy by OX2R agonists.