Unchanged cardiac angiotensin II levels accompany losartan-sensitive cardiac injury due to nitric oxide synthase inhibition

Cardiac Protection by Oral Sodium Thiosulfate in a Rat Model of L-NNA-Induced Heart Disease

Hypertension contributes to cardiac damage and remodeling. Despite the availability of renin-angiotensin system inhibitors and other antihypertensive therapies, some patients still develop heart failure. Novel therapeutic approaches are required that are effective and without major adverse effects. Sodium Thiosulfate (STS), a reversible oxidation product of hydrogen sulfide (H₂S), is a promising pharmacological entity with vasodilator and anti-oxidant potential that is clinically approved for the treatment of calciphylaxis and cyanide poisoning. We hypothesized that Sodium Thiosulfate improves cardiac disease in an experimental hypertension model and sought to investigate its cardioprotective effects by direct comparison to the ACE-inhibitor lisinopril, alone and in combination, using a rat model of chronic nitric oxide (NO) deficiency. Systemic nitric oxide production was inhibited in Sprague Dawley rats by administering N-ω-nitro-l-arginine (L-NNA) with the food for three weeks, leading to progressive hypertension, cardiac dysfunction and remodeling. We observed that STS, orally administered via the drinking water, ameliorated L-NNA-induced heart disease. Treatment with STS for two weeks ameliorated hypertension and improved systolic function, left ventricular hypertrophy, cardiac fibrosis and oxidative stress, without causing metabolic acidosis as is sometimes observed following parenteral administration of this drug. STS and lisinopril had similar protective effects that were not additive when combined. Our findings indicate that oral intervention with a H₂S donor such as STS has cardioprotective properties without noticeable side effects.

Development of an experimentally useful model of acute myocardial infarction: 2/3 nephrectomized triple nitric oxide synthases-deficient mouse

We investigated the effect of subtotal nephrectomy on the incidence of acute myocardial infarction (AMI) in mice deficient in all three nitric oxide synthases (NOSs). Two-thirds nephrectomy (NX) was performed on male triple NOSs(-/-) mice. The 2/3NX caused sudden cardiac death due to AMI in the triple NOSs(-/-) mice as early as 4months after the surgery. The 2/3NX triple NOSs(-/-) mice exhibited electrocardiographic ST-segment elevation, reduced heart rate variability, echocardiographic regional wall motion abnormality, and accelerated coronary arteriosclerotic lesion formation. Cardiovascular risk factors (hypertension, hypercholesterolemia, and hyperglycemia), an increased number of circulating bone marrow-derived vascular smooth muscle cell (VSMC) progenitor cells (a pro-arteriosclerotic factor), and cardiac up-regulation of stromal cell-derived factor (SDF)-1α (a chemotactic factor of the progenitor cells) were noted in the 2/3NX triple NOSs(-/-) mice and were associated with significant increases in plasma angiotensin II levels (a marker of renin-angiotensin system activation) and urinary 8-isoprostane levels (a marker of oxidative stress). Importantly, combined treatment with a clinical dosage of an angiotensin II type 1 receptor blocker, irbesartan, and a calcium channel antagonist, amlodipine, markedly prevented coronary arteriosclerotic lesion formation and the incidence of AMI and improved the prognosis of those mice, along with ameliorating all those pro-arteriosclerotic parameters. The 2/3NX triple NOSs(-/-) mouse is a new experimentally useful model of AMI. Renin-angiotensin system activation, oxidative stress, cardiovascular risk factors, and SDF-1α-induced recruitment of bone marrow-derived VSMC progenitor cells appear to be involved in the pathogenesis of AMI in this model.

Target organ cross talk in cardiorenal syndrome: animal models

The combination of chronic kidney disease (CKD) and heart failure (HF) is associated with an adverse prognosis. Although clinical studies hint at a specific bidirectional interaction between HF and CKD, insight into the pathogenesis of cardiorenal syndrome (CRS) remains limited. We review available evidence on cardiorenal interactions from animal models of CKD and HF and discuss several studies that employed a "double-hit" model to research organ cross talk between the heart and kidneys. Regarding cardiac changes in CKD models, parameters of cardiac remodeling are equivocal and cardiac systolic function generally remains preserved. Structural changes include hypertrophy, fibrosis, and microvasculopathy. In models of HF, data on renal pathology are mostly limited to functional hemodynamic changes. Most double-hit models were unable to show that combined renal and cardiac injury induces additive damage to both organs, perhaps because of the short study duration or absence of organ failure. Because of this lack of "dual-failure" models, we have developed two rat models of combined CKD and HF in which renal dysfunction induced by a subtotal nephrectomy preceded cardiac dysfunction. Cardiac dysfunction was induced either functionally by nitric oxide depletion or structurally by myocardial infarction. In both models, we found that cardiac remodeling and failure were worse in CKD rats compared with controls undergoing the same cardiac insult. Variables of renal damage, like glomerulosclerosis and proteinuria, were also further worsened by combined cardiorenal injury. These studies show that target organ cross talk does occur in CRS. These models may be useful for interventional studies in rats.

Connecting chronic and recurrent stress to vascular dysfunction: no relaxed role for the renin-angiotensin system

The renin-angiotensin system (RAS) is classically considered to be a protective system for volume balance and is activated during states of volume depletion. Interestingly, one of the major pathways activating the system is the sympathetic nervous system, also the primary mediator of the acute stress response. When one further examines the cells mediating the immune site of the response, which is primarily an inflammatory response leading to defense at a locally injured area, these cells all express the ANG II type 1 receptor (AGTR1). Scattered throughout the literature are reports indicating that acute and chronic stress can activate renin and increase plasma levels of components of the RAS. Moreover, there are reports describing that ANG II can modulate the distribution and function of immune cells. Since the inflammatory response is also implicated to be central in the initiation and progression of vascular damage, we propose in this review that recurrent acute stress and chronic stress can induce a state with inflammation, due to ANG II-mediated activation of inflammatory cells, specifically monocytes and lymphocytes. Such a proposal would explain a lot of the observations regarding RAS components in inflammatory cells. Despite its attractiveness, substantial research in this area would be required to substantiate this hypothesis.

Mechanisms of Hypertension Induced by Nitric Oxide (NO) Deficiency: Focus on Venous Function

Loss of endothelial cell-derived nitric oxide (NO) in hypertension is a hallmark of arterial dysfunction. Experimental hypertension created by the removal of NO, however, involves mechanisms in addition to decreased arterial vasodilator activity. These include augmented endothelin-1 (ET-1) release, increased sympathetic nervous system activity, and elevated tissue oxidative stress. We hypothesized that increased venous smooth muscle (venomotor) tone plays a role in Nomega-nitro-L-arginine (LNNA) hypertension through these mechanisms. Rats were treated with the NO synthase inhibitor LNNA (0.5 g/L in drinking water) for 2 weeks. Mean arterial pressure of conscious rats was 119 +/- 2 mm Hg in control and 194 +/- 5 mm Hg in LNNA rats (P<0.05). Carotid arteries and vena cava were removed for measurement of isometric contraction. Maximal contraction to norepinephrine was modestly reduced in arteries from LNNA compared with control rats whereas the maximum contraction to ET-1 was significantly reduced (54% control). Maximum contraction of vena cava to norepinephrine (37% control) also was reduced but no change in response to ET-1 was observed. Mean circulatory filling pressure, an in vivo measure of venomotor tone, was not elevated in LNNA hypertension at 1 or 2 weeks after LNNA. The superoxide scavenger tempol (30, 100, and 300 micromol kg(-1), IV) did not change arterial pressure in control rats but caused a dose-dependent decrease in LNNA rats (-18 +/- 8, -26 +/- 15, and -54 +/- 11 mm Hg). Similarly, ganglionic blockade with hexamethonium caused a significantly greater fall in LNNA hypertensive rats (76 +/- 9 mm Hg) compared with control rats (35 +/- 10 mm Hg). Carotid arteries, vena cava, and sympathetic ganglia from LNNA rats had higher basal levels of superoxide compared with those from control rats. These data suggest that while NO deficiency increases oxidative stress and sympathetic activity in both arterial and venous vessels, the impact on veins does not make a major contribution to this form of hypertension.

Estradiol Metabolites Attenuate Renal and Cardiovascular Injury Induced by Chronic Nitric Oxide Synthase Inhibition

Our previous studies in rodent models of nephropathy demonstrate that 2-hydroxyestradiol (2HE), an estradiol metabolite with little estrogenic activity, exerts renoprotective effects. In vivo, 2HE is readily converted to 2-methoxyestradiol (2ME), a major estradiol metabolite with no estrogenic activity. The goal of this study was to determine whether 2ME has renal and cardiovascular protective effects in vivo. First, the acute (90 minutes) and chronic (14 days) effects of 2ME (10 microg/kg/h) on blood pressure and renal function were examined in normotensive and spontaneously hypertensive rats (SHR). Second, a rat model of cardiovascular and renal injury induced by chronic nitric oxide synthase inhibition (N-nitro-L-arginine; 40 mg/kg/d; LNNA group) was used to examine the protective effects of estradiol metabolites. Subsets of LNNA-treated rats were administered either 2HE or 2ME (10 microg/kg/h via osmotic minipump; LNNA+2ME and LNNA+2HE groups, respectively. 2-Methoxyestradiol had no acute or chronic effects on blood pressure or renal function in normotensive animals or on hypertension in SHR. Prolonged, 5-week NOS inhibition induced severe cardiovascular and renal disease and high mortality (75%, LNNA group). 2ME, but not 2HE, significantly decreased elevated blood pressure and attenuated the reduction in GFR. 2HE delayed the onset of proteinuria, whereas no proteinuria was detected in the 2-ME group. 2HE and 2ME reduced mortality rate by 66% and 83%, respectively (P < 0.001). In the kidney, 2HE and 2ME abolished LNNA-induced interstitial and glomerular inflammation, attenuated glomerular collagen IV synthesis, and inhibited glomerular and tubular cell proliferation. In the heart, 2HE and 2ME markedly reduced vascular and interstitial inflammation and reduced collagen synthesis and vascular/interstitial cell proliferation. This study provides the first evidence that, in a model of severe cardiovascular and renal injury, 2-methoxyestradiol (a major nonestrogenic estradiol metabolite) exerts renal and cardiovascular protective effects and reduces mortality.

Gene expression of energy and protein metabolism in hearts of hypertensive nitric oxide- or GSH-depleted mice

Hypertension demands cardiac synthetic and metabolic adaptations to increased afterload. We studied gene expression in two models of mild hypertension without overt left ventricular hypertrophy using the NO synthase inhibitor nitro-L-arginine (L-NNA) and the glutathione depletor buthionine-S,R-sulfoximine (BSO). Mice were administered L-NNA, BSO, or water for 8 weeks. RNA of left ventricles was pooled per group, reverse transcribed, Cy3 and Cy5 labeled, and hybridized to cDNA microarrays. Normalized log(2) Cy3/Cy5 ratios of > or =0.7 or < or =-0.7 were considered significant. L-NNA and BSO both caused hypertension. Gene expression was regulated in cytoskeletal components in both models, protein synthesis in L-NNA-treated mice, and energy metabolism in BSO-treated mice. Energy metabolism genes shared several common transcription factor-binding sites such as Coup-Tf2, of which gene expression was increased in BSO-treated mice, and COMP-1. Characterization of the left ventricular adaptations as assessed with gene expression profiles reveals differential expression in energy and protein metabolism related to the pathogenetic background of the hypertension.

Fiftieth anniversary of aldosterone: from discovery to cardiovascular therapy

Half a century after the elucidation of its molecular structure, aldosterone is generating the greatest interest, not in the fields of endocrinology or renal medicine but in cardiology-where aldosterone over-activation is now perceived as detrimental in heart failure (HF) and ischaemic heart disease. Clinically, excess aldosterone is associated with higher morbidity and mortality after myocardial infarction (MI) and HF. The Randomised Aldactone Evaluation Study (RALES) study in severe chronic heart failure and the Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival (EPHESUS) study in post-MI heart failure have shown that use of non-selective and selective aldosterone receptor antagonists, respectively, improves prognosis. The pathophysiological mechanisms underpinning these damaging aldosterone-mediated cardiovascular effects are still being elucidated, but prime candidates include cardiomyocyte necrosis and apoptosis, and myocardial fibrosis resulting in adverse cardiac remodelling, coronary vasculopathy, tachyarrhythmia and positive feedback activation of the renin-angiotensin-aldosterone system. Practical points for consideration when instigating therapy include preferential use of aldosterone receptor antagonists to maintain electrolyte balance whenever loop or thiazide diuretics are used (vulnerable HF patients require higher ranges of potassium and magnesium to minimise propensity for tachyarrthythmia), for renoprotection and for counteracting aldosterone breakthrough despite adequate ACE inhibition; use of the minimum doses of loop diuretics required to lessen activation of the renin-angiotensin-aldosterone system in HF; use of selective aldosterone receptor antagonists to avoid gynaecomastia/mastalgia and impotence; and prophylactic use of aldosterone receptor antagonists to improve prognosis.

Effectiveness of Angiotensin-Converting Enzyme Inhibitor or Angiotensin II Receptor Blocker on Atrial Natriuretic Peptide

The aim of this study was to evaluate the effectiveness of an angiotensin-converting enzyne inhibitor (ACEI, quinapril) or angiotensin II receptor blocker (ARB, candesartan) on atrial natriuretic peptide (ANP) activity in rats with hypertension induced by nitric oxide (NO) inhibition. ACEI and ARB have a number of pharmacologic effects, including blood pressure reduction, myocardial preservation, and an unknown effect in the circulation. The changes in ANP in NO inhibitor-induced hypertensive rats were evaluated in order to elucidate the interaction between ANP and NO in the regulation of blood pressure. Thirty-six rats were divided into 4 groups and administered the experimental agents for 8 weeks: group CONTROL was given regular food (n=9), group N(G)-nitro-L-arginine (L-NNA) was administered L-NNA (25 mg. kg(-1). day(-1), n=9), group ACEI was administered L-NNA and quinapril (10 mg. kg(-1). day(-1), n=9), and group ARB was administered L-NNA and candesartan (10 mg. kg(-1). day(-1), n=9). Blood pressure, plasma ANP, atrial ANP, ANP mRNA, and ANP granules were measured. A significant elevation in blood pressure was observed in group L-NNA. However, there were no increases in plasma ANP (L-NNA: 138.8+/-64.4, CONTROL: 86.7+/-36.4), ANP mRNA (L-NNA: 2.2+/-1.0, CONTROL: 1.7+/-0.5) or ANP granules (L-NNA: 61.1+/-10.2, CONTROL: 64.5+/-8.5). No increase in blood pressure was seen in groups ACEI and ARB. However, plasma ANP (ACEI: 1,392.3+/-1,034.4, ARB: 1,142.8+/-667.3), ANP mRNA (ACEI: 52.8+/-29.1, ARB: 42.9+/-21.2), and ANP granules (ACEI: 122.5+/-23.4, ARB: 136.3+/-33.2) increased significantly. NO inhibitor-induced hypertension caused no changes in ANP concentrations. However, the ACEI and ARB had a direct effect on the induction of ANP secretion. The findings suggest that ANP secretion is directly effected by ACEI and ARB, which seems to play a key role in lowering blood pressure, relieving heart failure symptoms, and preserving the myocardium.

Attenuation of hypertension, cardiomyocyte hypertrophy, and myocardial fibrosis by beta-adrenoceptor blockers in rats under long-term blockade of nitric oxide synthesis

The effects of propranolol and atenolol were investigated on arterial hypertension, cardiomyocyte hypertrophy, and ventricular ischaemic lesions induced by an 8-week treatment with the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME; 20 mg/rat per day) in Wistar rats. Propranolol and atenolol (30 mg/rat per day each) were given in the drinking water concomitantly to L-NAME. Treatment with L-NAME induced marked arterial hypertension and cardiomyocyte hypertrophy, both of which were significantly reduced by propranolol and atenolol. A marked repairing fibrosis was also observed in L-NAME-treated rats and this was significantly attenuated in animals receiving the beta-blockers. In L-NAME group, 33% mortality was observed, whereas all the animals from the other groups survived. Our study demonstrates that propranolol and atenolol reduce arterial hypertension, cardiomyocyte hypertrophy and myocardial fibrosis induced by L-NAME, suggesting that beta-blockers are of beneficial value in treatment of vascular and cardiac alterations caused by chronic nitric oxide deficiency.