Kiyoko Takemiya

Pressure-independent effects of angiotensin II on hypertensive myocardial fibrosis.

Abstract—Angiotensin II (Ang II) is implicated in the proinflammatory process in various disease situations. Thus, we sought to determine the role of Ang II in early inflammation-induced fibrosis of pressure-overloaded (PO) hearts. PO was induced by suprarenal aortic constriction (AC) at day 0 in male Wistar rats, and they were orally administered 0.1 mg/kg per day candesartan every day from day −7. This was the maximum dose of candesartan that did not change arterial pressure in hypertensive rats with AC (AC rats). In AC rats, cardiac angiotensin-converting enzyme (ACE) activity was transiently enhanced after day 1 and peaked at day 3, declining to lower levels by day 14, whereas serum ACE activity was not changed. In AC rats, PO induced early fibroinflammatory changes (monocyte chemoattractant factor [MCP]-1 and transforming growth factor [TGF]-&bgr; expression, perivascular macrophage accumulation, and fibroblast proliferation), and thereafter, left ventricular hypertrophy developed, featuring myocyte hypertrophy, intramyocardial arterial wall thickening, and perivascular and interstitial fibroses. Candesartan suppressed the induction of MCP-1 and TGF-&bgr; and reduced macrophage accumulation and fibroblast proliferation in PO hearts. Candesartan significantly prevented perivascular and interstitial fibrosis. However, candesartan did not affect myocyte hypertrophy and arterial wall thickening. In conclusion, a subdepressor dose of candesartan prevented the MCP-1–mediated inflammatory process and reactive myocardial fibrosis in PO hearts. Ang II might play a key role in reactive fibrosis in hypertensive hearts, independent of arterial pressure changes.

Pressure Overload–Induced Transient Oxidative Stress Mediates Perivascular Inflammation and Cardiac Fibrosis through Angiotensin II

Oxidative stress is implicated in the pathogenesis of various cardiovascular diseases. We have shown that in Wistar rats with a suprarenal aortic constriction (AC), pressure overload–induced transient perivascular inflammation (monocyte chemoattractant protein-1 [MCP-1] induction and macrophage accumulation) in the early phase is the determinant of reactive myocardial fibrosis and resultant diastolic dysfunction in the late phase. Thus, we investigated the role of reactive oxygen species production in cardiac remodeling in AC rats. Superoxide production and the footprint of lipid peroxidation were assessed using dihydroethidium staining and immunohistostaining against 4-hydroxy-2-nonenal (4-HNE), respectively. In sham rats, dihydroethidium and 4-HNE signals were scarcely found in the heart. At day 3, AC rats showed dihydroethidium signals mainly in the intramyocardial arterial wall, whereas modest 4-HNE staining was observed diffusely in the myocardium. These signals declined to lower levels by day 14 despite sustained hypertension. Chronic administration of a subdepressor dose of an angiotensin II type 1 receptor blocker candesartan reduced the pressure overload–induced dihydroethidium and 4-HNE signals at day 3. Moreover, candesartan decreased MCP-1 induction and macrophage infiltration at day 3 and prevented myocardial fibrosis at day 14, without affecting left ventricle and myocyte hypertrophy. In conclusion, acute pressure overload induced self-limited superoxide production mainly in the vascular wall. The reactive oxygen species production would contribute to the perivascular inflammation and subsequent myocardial fibrosis. Angiotensin II was suggested to have a pressure-independent effect on the reactive oxygen species production.

Roles of Intercellular Adhesion Molecule-1 in Hypertensive Cardiac Remodeling

Abstract—Recently, we have shown that in rats with a suprarenal abdominal aortic constriction (AC), pressure overload induces early perivascular fibro-inflammatory changes (transforming growth factor [TGF]-&bgr; induction and fibroblast proliferation) within the first week after AC and then causes the development of cardiac remodeling (myocyte hypertrophy and reactive myocardial fibrosis) associated with diastolic dysfunction. Intercellular adhesion molecule (ICAM)-1 is implicated in the recruitment of leukocytes, especially macrophages, in various inflammatory situations. Thus, we sought to investigate the causal relation of ICAM-1 to macrophage recruitment and cardiac remodeling in AC rats. In AC rats, immunoreactive ICAM-1 was observed transiently on endothelial cells of the intramyocardial coronary arterioles after day 1, with a peak at day 3, returning to baseline by day 7. Also, ED1+ macrophage accumulation was found in the area adjacent to the arteries expressing ICAM-1. Chronic treatment with an anti–ICAM-1 neutralizing antibody, but not with control IgG, remarkably reduced the accumulations of macrophages and proliferative fibroblasts and inhibited the upregulation of TGF-&bgr; expression. Furthermore, the neutralizing antibody significantly prevented myocardial fibrosis without affecting arterial pressure and left ventricular and myocyte hypertrophy. In conclusion, ICAM-1 expression was induced by pressure overload in the intramyocardial arterioles, and triggered perivascular macrophage accumulation. In pressure-overloaded hearts, a crucial role in ICAM-1–mediated macrophage accumulation was suggested in the development of myocardial fibrosis, through TGF-&bgr; induction and fibroblast activation.

Rho-kinase inhibition reduces neointima formation after vascular injury by enhancing Bax expression and apoptosis.

Summary: Recently, we have shown that a specific Rho‐kinase inhibitor, Y27632 (R‐(+)‐trans‐N‐(4‐pyridyl)‐4‐(1‐aminoethyl)‐ cyclohexanecarboxamide), prevents neointima formation after vascular injury associated with increased terminal deoxynucleotidyl transferase‐mediated dUTP nickend labeling (TUNEL)+ smooth muscle cells. Because the mechanism of the action of Y27632 remains unclear, we investigated the expression changes in Bcl family proteins, apoptosis regulators of smooth muscle cells, in the rat carotid artery after balloon injury (BI). Y27632 (BI + Y group) or saline (BI group) was administered peritoneally from Day 1 to Day 14 after BI. Y27632 markedly prevented neointima formation at Day 14. In the BI group, TUNEL+ smooth muscle cells were transiently increased in the neointima, but not in the media, with a peak at Day 7, returning to a lower level by Day 14. Y27632 significantly increased TUNEL+ smooth muscle cells at Days 7 and 14. Smooth muscle cell apoptosis was confirmed by electron microscopic examination. At Day 14, although proapoptotic Bax was slightly, but not significantly, increased in the BI group, it was significantly upregulated in the BI + Y group. Antiapoptotic Bcl‐xL was upregulated in the BI group, and the upregulated Bcl‐xL was not affected by Y27632. These findings indicate that Rho‐kinase inhibition induces neointimal smooth muscle cell apoptosis through Bax upregulation, resulting in reduced neointima formation.

Hypertension Opens the Flood Gates to the Gut Microbiota

There continues to be a rapidly evolving interest in the role of the gut microbiome in cardiovascular disease. It has long been known that the gut microbiome has a fundamentally mutualistic, symbiotic relationship with the human host. However, from earlier observations using mice grown in germ-free environments to more recent advances in identifying unique metabolic products of the gut microbiome,1 the data have led to a compelling story linking cardiovascular disease to the trillions of prokaryotic organisms that live in the human gut. Article, see p 312 In this issue of Circulation Research , Santisteban et al2 have provided provocative data demonstrating very definitively that, in 2 different animal models of hypertension, there is decreased expression of several tight junction proteins in the gut and a concomitant increase in intestinal permeability. Furthermore, their data show that in the spontaneously hypertensive rat model, the increase in permeability is a result of increased sympathetic nerve activity before the development of hypertension. They therefore conclude that there is a direct, causal link between the sympathetic nerve activity derived from the central nervous system and increased gut permeability (Figure). They further hypothesize that the changes in gut permeability result in hypertension and cause a shift in the types of bacteria that are present in the gut. Finally, they have shown that the changes in sympathetic activity resulting in increased gut permeability are also associated with an increase in inflammatory cells within the intestinal wall thus …