Narimasa Takayama

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.

Exaggerated Blood Pressure Variability Superimposed on Hypertension Aggravates Cardiac Remodeling in Rats via Angiotensin II System-Mediated Chronic Inflammation

Hypertensive patients with large blood pressure variability (BPV) have aggravated end-organ damage. However, the pathogenesis remains unknown. We investigated whether exaggerated BPV aggravates hypertensive cardiac remodeling and function by activating inflammation and angiotensin II–mediated mechanisms. A model of exaggerated BPV superimposed on chronic hypertension was created by performing bilateral sinoaortic denervation (SAD) in spontaneously hypertensive rats (SHRs). SAD increased BPV to a similar extent in Wistar Kyoto rats and SHRs without significant changes in mean blood pressure. SAD aggravated left ventricular and myocyte hypertrophy and myocardial fibrosis to a greater extent and impaired left ventricular systolic function in SHRs. SAD induced monocyte chemoattractant protein-1, transforming growth factor-&bgr;, and angiotensinogen mRNA upregulations and macrophage infiltration of the heart in SHRs. The effects of SAD on cardiac remodeling and inflammation were much smaller in Wistar Kyoto rats compared with SHRs. Circulating levels of norepinephrine, the active form of renin, and inflammatory cytokines were not affected by SAD in Wistar Kyoto rats and SHRs. A subdepressor dose of candesartan abolished the SAD-induced left ventricular/myocyte hypertrophy, myocardial fibrosis, macrophage infiltration, and inductions of monocyte chemoattractant protein-1, transforming growth factor-&bgr;, and angiotensinogen and subsequently prevented systolic dysfunction in SHRs with SAD. These findings suggest that exaggerated BPV induces chronic myocardial inflammation and thereby aggravates cardiac remodeling and systolic function in hypertensive hearts. The cardiac angiotensin II system may play a role in the pathogenesis of cardiac remodeling and dysfunction induced by a combination of hypertension and exaggerated BPV.

Inhibition of Intrinsic Interferon-γ Function Prevents Neointima Formation After Balloon Injury

It is still controversial whether intrinsic interferon (IFN)-&ggr; promotes or attenuates vascular remodeling in hyperproliferative vascular disorders, such as neointima formation after balloon injury. Thus, we investigated whether inhibition of intrinsic IFN-&ggr; function prevents neointima formation. For this purpose, naked DNA plasmid encoding a soluble mutant of IFN-&ggr; receptor &agr;-subunit (sIFN&ggr;R; an IFN-&ggr; inhibitory protein) or mock plasmid was injected into the thigh muscle of male Wistar rats 2 days before balloon injury (day −2). sIFN&ggr;R gene transfer significantly elevated serum levels of sIFN&ggr;R protein for 2 weeks. In mock-treated rats, balloon injury induced smooth muscle cell proliferation in the neointima with a peak at day 7 and produced thick neointima at day 14. sIFN&ggr;R treatment reduced the number of proliferating intimal smooth muscle cells by 50% at day 7 and attenuated neointima formation with a 45% reduction of the intima/media area ratio at day 14. In mock-treated rats, at day 7, balloon injury induced phosphorylation of signal transducer and activator of transcription-1 and upregulations of IFN regulatory factor-1 (a transcription factor mediating IFN-&ggr; signal). Balloon injury also upregulated the key molecules of neointima formation, such as intercellular adhesion molecule-1 and platelet-derived growth factor &bgr;-receptor. These changes were suppressed by sIFN&ggr;R treatment. In conclusion, it is suggested that intrinsic IFN-&ggr; promotes neointima formation probably through IFN regulatory factor-1/intercellular adhesion molecule-1–mediated and platelet-derived growth factor–mediated mechanisms. Thus, inhibition of IFN-&ggr; signaling may be a new therapeutic target for prevention of neointima formation of hyperproliferative vascular disorders.

Simvastatin prevents large blood pressure variability induced aggravation of cardiac hypertrophy in hypertensive rats by inhibiting RhoA/Ras-ERK pathways.

Pronounced variability in blood pressure (BP) is an aggravating factor of hypertensive end-organ damage. However, its pathogenesis remains unknown. Statins have various protective effects on the cardiovascular system. Thus, we determined whether simvastatin would attenuate the aggravation of hypertensive cardiac remodeling in a rat model of hypertension with large BP variability, and also investigated the signaling mechanism involved in its effect. A model of hypertension with large BP variability was created by performing bilateral sinoaortic denervation (SAD) in spontaneously hypertensive rats (SHRs). A SAD or sham operation was performed in 12-week-old rats. Thereafter, simvastatin (0.2 mg kg−1 per day) or vehicle was intraperitoneally administered every day. After 6 weeks , telemetric recordings revealed that SAD enhanced BP variability without changing the mean BP. SAD increased myocyte hypertrophy, myocardial fibrosis and macrophage infiltration associated with the upregulation of brain natriuretic peptide (BNP), type I procollagen, transforming growth factor (TGF)-β and monocyte chemoattractant protein (MCP)-1, and activation of RhoA, Ras and ERK1/2. Simvastatin did not change the mean BP or BP variability in SAD-operated SHRs. In SAD-operated SHRs, simvastatin attenuated myocyte hypertrophy and BNP expression, as well as RhoA, Ras and ERK1/2 activities. In contrast, simvastatin did not change myocardial fibrosis, macrophage infiltration, or the expression of procollagen and TGF-β or MCP-1 in SAD-operated SHRs. Simvastatin did not affect serum lipid levels. In conclusion, simvastatin attenuated the large BP variability-induced aggravation of cardiac hypertrophy, but not myocardial fibrosis, in SHRs. The activation of RhoA/Ras–ERK pathways may contribute to the aggravation of cardiac hypertrophy by a combination of hypertension and large BP variability.

Enhanced cardiac inflammation and fibrosis in ovariectomized hypertensive rats: a possible mechanism of diastolic dysfunction in postmenopausal women.

Diastolic dysfunction is more prevalent in individuals with hypertension, particularly postmenopausal women; however, the pathogenesis of diastolic dysfunction remains unknown. Pressure overload activates cardiac inflammation, which induces myocardial fibrosis and diastolic dysfunction in rats with a suprarenal aortic constriction (AC). Therefore, we examined the effects of bilateral ovariectomy (OVX) on left ventricle (LV) remodeling, diastolic dysfunction and cardiac inflammation in hypertensive female rats. Rats were randomized to OVX+AC, OVX and AC groups as well as a Control group receiving sham operations for both the procedures. Rats underwent OVX at 6 weeks and AC at 10 weeks (Day 0). At Day 28, OVX did not appear to affect arterial pressure, cardiac hypertrophy or LV fractional shortening in AC rats. However, OVX increased myocardial fibrosis, elevated LV end-diastolic pressure and reduced the transmitral Doppler spectra early to late filling velocity ratio in AC rats. AC-induced transient myocardial monocyte chemoattractant protein-1 expression and macrophage infiltration, both of which peaked at Day 3 and were augmented and prolonged by OVX. At Day 28, dihydroethidium staining revealed superoxide generation in the intramyocardial arterioles in the OVX+AC group but not in the AC group. NOX1, a functional subunit of nicotinamide adenine dinucleotide phosphate oxidase, was upregulated only in the OVX+AC group at Day 28. Chronic 17β-estradiol replacement prevented the increases in macrophage infiltration, NOX1 upregulation, myocardial fibrosis and diastolic dysfunction in OVX+AC rats. In conclusion, we suggest that estrogen deficiency augments cardiac inflammation and oxidative stress and thereby aggravates myocardial fibrosis and diastolic dysfunction in hypertensive female rats. The findings provide insight into the mechanism underlying diastolic dysfunction in hypertensive postmenopausal women.

Molecular mechanism of aggravation of hypertensive organ damages by short-term blood pressure variability.

There is increasing evidence that not only the elevation of systolic and diastolic blood pressure (BP) but also the increase in BP variability (or fluctuation) are associated with hypertensive organ damages and the morbidity and mortality of cerebrovascular and cardiovascular events. However, the molecular mechanism whereby the increase in BP variability aggravates hypertensive organ damages remains unknown. Thus, we created a rat chronic model of a combination of hypertension and large BP variability by performing bilateral sino-aortic denervation in spontaneously hypertensive rat. A series of our studies using this model revealed that large BP variability induces chronic myocardial inflammation by activating local angiotensin II and mineralocorticoid receptor systems and thereby aggravates cardiac hypertrophy and myocardial fibrosis, leading to systolic dysfunction, in hypertensive hearts. In addition, large BP variability induces the aggravation of arteriolosclerotic changes and ischemic cortical fibrosis in hypertensive kidney via local angiotensin II system.