Roles of oxidative stress and the mineralocorticoid receptor in cardiac pathology in a rat model of metabolic syndrome.

Oxidative stress and the mineralocorticoid receptor (MR) are implicated in the pathogenesis of salt-induced left ventricular (LV) diastolic dysfunction associated with metabolic syndrome (MetS). We recently characterized DahlS.Z-Lepr(fa) /Lepr(fa) (DS/obese) rats, derived from a cross between Dahl salt-sensitive and Zucker rats, as a new animal model of MetS. We investigated the pathophysiological roles of increased oxidative stress and MR activation in cardiac injury with this model. DS/obese rats were treated with the antioxidant tempol (1 mmol/L in drinking water) or the selective MR antagonist eplerenone (15 mg/kg per day, per os) for 5 weeks beginning at 10 weeks of age. The increased systolic blood pressure and LV hypertrophy that develop in untreated DS/obese rats were substantially ameliorated by eplerenone but not by tempol. Eplerenone also attenuated LV fibrosis and diastolic dysfunction more effectively than did tempol in DS/obese rats, whereas cardiac oxidative stress and inflammation were reduced similarly by both drugs. Both the ratio of plasma aldosterone concentration to plasma renin activity and cardiac expression of the MR and serum/glucocorticoid-regulated kinase 1 genes were decreased to a greater extent by eplerenone than by tempol. Our results indicate that both increased oxidative stress and MR activation in the heart may contribute to the development of LV remodeling and diastolic dysfunction in DS/obese rats. The superior cardioprotective action of eplerenone is likely attributable to its greater antihypertensive effect, which is likely related to its greater inhibition of aldosterone-MR activity in the cardiovascular system.

Dietary salt restriction improves cardiac and adipose tissue pathology independently of obesity in a rat model of metabolic syndrome.

BACKGROUND: Metabolic syndrome (MetS) enhances salt sensitivity of blood pressure and is an important risk factor for cardiovascular disease. The effects of dietary salt restriction on cardiac pathology associated with metabolic syndrome remain unclear. METHODS AND RESULTS: We investigated whether dietary salt restriction might ameliorate cardiac injury in DahlS.Z-Lepr(fa)/Lepr(fa) (DS/obese) rats, which are derived from a cross between Dahl salt-sensitive and Zucker rats and represent a model of metabolic syndrome. DS/obese rats were fed a normal-salt (0.36% NaCl in chow) or low-salt (0.0466% NaCl in chow) diet from 9 weeks of age and were compared with similarly treated homozygous lean littermates (DahlS.Z-Lepr(+)/Lepr(+), or DS/lean rats). DS/obese rats fed the normal-salt diet progressively developed hypertension and showed left ventricular hypertrophy, fibrosis, and diastolic dysfunction at 15 weeks. Dietary salt restriction attenuated all of these changes in DS/obese rats. The levels of cardiac oxidative stress and inflammation and the expression of cardiac renin-angiotensin-aldosterone system genes were increased in DS/obese rats fed the normal-salt diet, and dietary salt restriction downregulated these parameters in both DS/obese and DS/lean rats. In addition, dietary salt restriction attenuated the increase in visceral adipose tissue inflammation and the decrease in insulin signaling apparent in DS/obese rats without reducing body weight or visceral adipocyte size. Dietary salt restriction did not alter fasting serum glucose levels but it markedly decreased the fasting serum insulin concentration in DS/obese rats. CONCLUSIONS: Dietary salt restriction not only prevents hypertension and cardiac injury but also ameliorates insulin resistance, without reducing obesity, in this model of metabolic syndrome.

Premature cardiac senescence in DahlS.Z-Lepr(fa)/Lepr(fa) rats as a new animal model of metabolic syndrome.

Aging is accelerated by metabolic and cardiovascular diseases, and the risk of these diseases increases with age. Obesity is an important risk factor for many age-related diseases and is linked to reduced telomere length in white blood cells. We investigated whether cardiac senescence might be enhanced in DahlS.Z-Lepr(fa)/Lepr(fa) (DS/obese) rats, which we recently established as a new animal model of metabolic syndrome. The heart of DS/obese rats was compared with that of homozygous lean littermates (DahlS.Z-Lepr+/Lepr+, or DS/lean, rats). DS/obese rats manifested hypertension as well as left ventricular hypertrophy, fibrosis, and diastolic dysfunction at 18 weeks of age. Myocardial oxidative stress and inflammation were increased in DS/obese rats compared with DS/lean rats. Telomere length in myocardial cells did not differ between the two rat strains, whereas telomerase activity and expression of the telomerase reverse transcriptase gene were increased in DS/obese rats. Expression of the senescence-associated genes for checkpoint kinase 2 (Chk2), p53, and p21 as well as that of genes related to the renin-angiotensin-aldosterone system were also up-regulated in the DS/obese rat heart. Our results indicate that DS/obese rats undergo premature cardiac senescence as well as cardiac remodeling in association with the development of diastolic dysfunction in these animals.

Glucocorticoids activate cardiac mineralocorticoid receptors in adrenalectomized Dahl salt-sensitive rats.

We previously showed that selective mineralocorticoid receptor (MR) blockade by eplerenone is cardioprotective in Dahl salt-sensitive (DS) rats. To clarify the consequences of glucocorticoid-mediated MR activation in these animals, we investigated the effects of exogenous corticosterone on blood pressure as well as cardiac remodeling and function after adrenalectomy. DS rats were subjected to adrenalectomy at 6 weeks of age and thereafter fed a high-salt diet and administered corticosterone (20 mg/kg per day) or vehicle. Systolic blood pressure was higher in the corticosterone group than in the vehicle group at 7 weeks and thereafter. By 11 weeks, corticosterone had reduced left ventricular (LV) mass and induced LV diastolic dysfunction. The ratio of collagen type I to type III mRNA levels in the left ventricle was increased in the corticosterone group compared with the vehicle group. Administration of a non-antihypertensive dose of the MR antagonist spironolactone (20 mg/kg per day) from 6 weeks inhibited the effects of corticosterone on both the collagen type I to type III mRNA ratio and diastolic function without affecting the decrease in LV mass. Spironolactone attenuated both the increase in NADPH oxidase activity in the left ventricle and coronary vascular inflammatory responses apparent in the corticosterone group. These results indicate that exogenous glucocorticoids induce hypertension, cardiac remodeling, and diastolic dysfunction in adrenalectomized DS rats fed a high-salt diet. The cardiac effects of exogenous glucocorticoids are likely attributable, at least in part, to myocardial oxidative stress and coronary vascular inflammation induced by glucocorticoid-activated MRs.

Effects of salt status and blockade of mineralocorticoid receptors on aldosterone-induced cardiac injury.

The mineralocorticoid aldosterone regulates sodium and water homeostasis in the human body. The combination of excess aldosterone and salt loading induces hypertension and cardiac damage. However, little is known of the effects of aldosterone on blood pressure and cardiac pathophysiology in the absence of salt loading. We have now investigated the effects of salt status and blockade of mineralocorticoid receptors (MRs) on cardiac pathophysiology in uninephrectomized Sprague-Dawley rats implanted with an osmotic minipump to maintain hyperaldosteronism. The rats were fed a low-salt (0.0466% NaCl in chow) or high-salt (0.36% NaCl in chow plus 1% NaCl in drinking water) diet in the absence or presence of treatment with a subdepressor dose of the MR antagonist spironolactone (SPL). Aldosterone excess in the setting of low salt intake induced substantial cardiac remodeling and diastolic dysfunction without increasing blood pressure. These effects were accompanied by increased levels of oxidative stress and inflammation as well as increased expression of genes related to the renin-angiotensin and endothelin systems in the heart. All of these cardiac changes were completely blocked by the administration of SPL. On the other hand, aldosterone excess in the setting of high salt intake induced hypertension and a greater extent of cardiac injury, with the cardiac changes being only partially attenuated by SPL in a manner independent of its antihypertensive effect. The combination of dietary salt restriction and MR antagonism is thus a promising therapeutic option for the management of hypertensive patients with hyperaldosteronism or relative aldosterone excess.

Calorie restriction attenuates cardiac remodeling and diastolic dysfunction in a rat model of metabolic syndrome.

Calorie restriction (CR) can modulate the features of obesity-related metabolic and cardiovascular diseases. We have recently characterized DahlS.Z-Lepr(fa)/Lepr(fa) (DS/obese) rats, derived from a cross between Dahl salt-sensitive and Zucker rats, as a new animal model of metabolic syndrome. DS/obese rats develop hypertension and manifest left ventricular remodeling and diastolic dysfunction, as well as increased cardiac oxidative stress and inflammation. We have now investigated the effects of CR on cardiac pathophysiology in DS/obese rats. DS/obese rats were fed either normal laboratory chow ad libitum or a calorie-restricted diet (65% of the average food intake for ad libitum) from 9 to 13 weeks. Age-matched homozygous lean (DahlS.Z-Lepr(+)/Lepr(+) or DS/lean) littermates served as controls. CR reduced body weight in both DS/obese and DS/lean rats, as well as attenuated the development of hypertension in DS/obese rats without affecting blood pressure in DS/lean rats. CR also reduced body fat content, ameliorated left ventricular hypertrophy, fibrosis, and diastolic dysfunction, and attenuated cardiac oxidative stress and inflammation in DS/obese rats. In addition, it increased serum adiponectin concentration, as well as downregulated the expression of angiotensin-converting enzyme and angiotensin II type 1A receptor genes in the heart of DS/obese rats. Our results thus show that CR attenuated obesity and hypertension, as well as left ventricular remodeling and diastolic dysfunction in DS/obese rats, with these latter effects being associated with reduced cardiac oxidative stress and inflammation.

Glucocorticoid-induced hypertension and cardiac injury: effects of mineralocorticoid and glucocorticoid receptor antagonism.

Glucocorticoids are widely administered for the treatment of various disorders, although their long-term use results in adverse effects associated with glucocorticoid excess. We investigated the pathophysiological roles of glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs) in the cardiac changes induced by exogenous corticosterone in rats. Corticosterone or vehicle was injected twice daily in rats from 8 to 12 weeks of age. The effects of the GR antagonist RU486, the MR antagonist spironolactone, or both agents on corticosterone action were also determined. Corticosterone induced hypertension, left ventricular (LV) fibrosis, and LV diastolic dysfunction. Neither RU486 nor spironolactone affected corticosterone-induced hypertension, whereas spironolactone, but not RU486, attenuated the effects of corticosterone on LV fibrosis and diastolic function. Corticosterone also increased cardiac oxidative stress and inflammation in a manner sensitive to spironolactone but not to RU486. The corticosterone-induced LV atrophy was not affected by either RU486 or spironolactone. Our results implicate MRs in the cardiac fibrosis and diastolic dysfunction, but not MRs or GRs in the cardiac atrophy, induced by corticosterone. Neither MRs nor GRs appear to contribute to corticosterone-induced hypertension.

Comparison of the effects of cilnidipine and amlodipine on cardiac remodeling and diastolic dysfunction in Dahl salt-sensitive rats.

OBJECTIVE: The L/N-type calcium channel blocker (CCB) cilnidipine suppresses sympathetic nerve activity and has a superior renoprotective effect compared with L-type CCBs such as amlodipine. The cardioprotective action of cilnidipine has remained largely uncharacterized, however. We have now investigated the effects of cilnidipine, in comparison with amlodipine, on cardiac pathophysiology in rats with salt-sensitive hypertension. METHODS: Dahl salt-sensitive rats fed a high-salt diet from 6 weeks of age were treated with vehicle (LVH group), amlodipine (3 mg/kg per day), or cilnidipine (3 mg/kg per day) from 7 to 11 weeks. RESULTS: The salt-induced increase in SBP apparent in LVH rats was attenuated to a similar extent by treatment with amlodipine or cilnidipine. The two drugs also similarly inhibited the development of left ventricular (LV) hypertrophy. However, cilnidipine attenuated the increase in relative wall thickness as well as ameliorated LV perivascular and interstitial fibrosis and diastolic dysfunction to a greater extent than did amlodipine. In addition, cilnidipine treatment was associated with greater inhibition of cardiac oxidative stress, inflammation, and renin-angiotensin system (RAS) gene expression. The decrease in cardiac norepinephrine content apparent in LVH rats was similarly inhibited by both drugs. CONCLUSIONS: Cilnidipine attenuated LV fibrosis and diastolic dysfunction as well as LV concentricity to a greater extent than did amlodipine in Dahl salt-sensitive rats. The superior cardioprotective action of cilnidipine is likely attributable, at least in part, to the greater antioxidant and anti-inflammatory effects associated with inhibition of cardiac RAS gene expression observed with this drug.

Effects of estrogen on cardiovascular injury in ovariectomized female DahlS.Z-Lepr(fa)/Lepr(fa) rats as a new animal model of metabolic syndrome.

Although recent clinical trials have found an increased incidence of cardiovascular disease in women on estrogen replacement therapy, the underlying mechanism remains unclear. We have recently characterized DahlS.Z-Lepr(fa)/Lepr(fa) (DS/obese) rats, derived from a cross between Dahl salt-sensitive and Zucker rats, as a new animal model of metabolic syndrome. We have now examined the effects of estrogen replacement on cardiac pathophysiology in ovariectomized female DS/obese (Ovx-DS/obese) rats. Animals subjected to ovariectomy at 7 weeks of age were implanted subcutaneously with a 60-day release pellet containing 0.5 mg of 17ß-estradiol (E(2)) or placebo at 8 weeks. Age-matched female homozygous lean littermates (DahlS.Z-Lepr(+)/Lepr(+) or DS/lean rats) of DS/obese rats served as controls. Animals were maintained on a normal diet and were subjected to echocardiography followed by various pathological analyses at 13 weeks of age. Ovx-DS/obese rats manifested hypertension at 7 weeks of age and thereafter and showed left ventricular (LV) fibrosis and diastolic dysfunction at 13 weeks. Treatment with E(2) attenuated hypertension in Ovx-DS/obese rats but had no effect on blood pressure in ovariectomized female DS/lean (Ovx-DS/lean) rats. E(2) treatment exacerbated LV fibrosis and diastolic dysfunction, as well as further increased cardiac oxidative stress and inflammation in Ovx-DS/obese rats, and it elicited similar effects in Ovx-DS/lean rats. E(2) reduced food intake, body weight, and visceral fat content in both Ovx-DS/obese and Ovx-DS/lean rats. E(2) treatment attenuated hypertension and obesity but exacerbated LV fibrosis and diastolic dysfunction in Ovx-DS/obese rats, with these latter effects being associated with increased cardiac oxidative stress and inflammation.

Cardiac remodeling and diastolic dysfunction in DahlS.Z-Lepr(fa)/Lepr(fa) rats: a new animal model of metabolic syndrome.

We recently characterized male DahlS.Z-Lepr(fa)/Lepr(fa) (Dahl salt-sensitive (DS)/obese) rats, which were established from a cross between Dahl salt-sensitive and Zucker rats, as a new animal model of metabolic syndrome (MetS). We have now investigated cardiac pathophysiology and metabolic changes in female DS/obese rats in comparison with homozygous lean female littermates (DahlS.Z-Lepr(+)/Lepr(+), or DS/lean, rats). Animals were maintained on a normal diet and were subjected to echocardiography followed by various pathological analyses at 15 weeks of age. Systolic blood pressure was significantly higher in female DS/obese rats than in DS/lean females at 12 weeks of age and thereafter. The survival rate of DS/obese rats was significantly lower than that of DS/lean rats at 15 weeks. Body weight, as well as visceral and subcutaneous fat mass were significantly increased in DS/obese rats, which also manifested left ventricular (LV) diastolic dysfunction and marked LV hypertrophy and fibrosis. In addition, myocardial oxidative stress and inflammation were increased in DS/obese rats compared with DS/lean rats. Serum insulin and triglyceride levels as well as the ratio of low-density lipoprotein- to high-density lipoprotein-cholesterol levels were markedly elevated in DS/obese rats, whereas fasting serum glucose concentrations were similar in the two rat strains. The phenotype of female DS/obese rats is similar to that of MetS in humans. These animals also develop salt-sensitive hypertension and LV diastolic dysfunction as well as LV hypertrophy and fibrosis, and these changes are associated with increased cardiac oxidative stress and inflammation.

Angiotensin-converting enzyme inhibition promotes coronary angiogenesis in the failing heart of Dahl salt-sensitive hypertensive rats.

BACKGROUND: The biologic response to angiotensin-converting enzyme (ACE) inhibitors may be influenced by the local environment. The effect of ACE inhibition on coronary angiogenesis was investigated in a rat model of hypertensive heart failure. METHODS AND RESULTS: Dahl salt-sensitive (DS) rats fed a high-salt diet from 6 weeks of age were treated with a nonantihypertensive dose of the ACE inhibitor perindopril or vehicle from 9 to 18 weeks. Treatment of rats with perindopril attenuated the heart failure as well as cardiac hypertrophy and fibrosis that were manifest in the vehicle-treated animals. Myocardial capillary density as well as the expression of the bradykinin B(2) receptor, endothelial nitric oxide synthase, and vascular endothelial growth factor were reduced in the heart of vehicle-treated rats compared with that of nonhypertensive control rats, and all of these changes were attenuated by treatment with perindopril. CONCLUSIONS: These results indicate that ACE inhibition by perindopril promotes myocardial capillary formation as well as attenuates cardiac remodeling and failure in a manner independent from the antihypertensive effect of the drug in DS hypertensive rats. The beneficial cardiac effects of perindopril were associated with activation of the bradykinin-nitric oxide pathway in the heart.

Mechanism underlying the efficacy of combination therapy with losartan and hydrochlorothiazide in rats with salt-sensitive hypertension.

Although thiazide diuretics are commonly used to supplement angiotensin receptor blockers for treatment of hypertension, the mechanism underlying the therapeutic effects of this drug combination remains unclear. We investigated the antihypertensive and cardioprotective effects of combination therapy with losartan (LOS) and hydrochlorothiazide (HCTZ), in comparison with those of either drug alone, in Dahl salt-sensitive hypertensive rats. Rats fed a high-salt diet from 6 weeks of age were treated with LOS, HCTZ, both drugs (COMB) and vehicle from 6 to 11 weeks. The salt-induced increase in systolic blood pressure was attenuated moderately by LOS and to a greater extent by HCTZ and COMB. Left ventricular (LV) hypertrophy and fibrosis, diastolic dysfunction, as well as angiotensin-converting enzyme and angiotensin II type 1A (AT(1A)) receptor gene expression were attenuated similarly by LOS and HCTZ and more so by COMB. LOS downregulated expression of the AT(1A) receptor gene, without affecting that of the AT(2) receptor gene, in the aorta. In contrast, neither HCTZ nor COMB affected aortic expression of the AT(1A) receptor gene, but both markedly upregulated that of the AT(2) receptor gene. The salt-induced decrease in the plasma concentration of nitric oxide metabolites was attenuated substantially by LOS and abolished by both HCTZ and COMB. In conclusion, the combination of LOS and HCTZ attenuated hypertension, as well as LV remodeling and diastolic dysfunction, more effectively than did LOS or HCTZ alone in rats with salt-sensitive hypertension. Modulation of the cardiac and vascular renin-angiotensin system may have contributed to these beneficial effects of the drug combination.