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.

Comparative effects of valsartan in combination with cilnidipine or amlodipine on cardiac remodeling and diastolic dysfunction in Dahl salt-sensitive rats.

Angiotensin receptor blockers (ARBs) are often supplemented with calcium channel blockers (CCBs) for treatment of hypertension. We recently showed that the L/N-type CCB cilnidipine has superior cardioprotective effects compared with the L-type CCB amlodipine in Dahl salt-sensitive (DS) rats. We have now compared the effects of the ARB valsartan combined with cilnidipine or amlodipine on cardiac pathophysiology in DS rats. DS rats fed a high-salt diet from 6 weeks of age were treated with vehicle, valsartan alone (10 mg kg(-1) per day), or valsartan combined with either cilnidipine (1 mg kg(-1) per day) or amlodipine (1 mg kg(-1) per day) from 7 to 11 weeks. The salt-induced increase in systolic blood pressure apparent in the vehicle group was attenuated similarly in the three drug treatment groups. Valsartan-cilnidipine attenuated left ventricular (LV) fibrosis and diastolic dysfunction as well as cardiac oxidative stress and inflammation to a greater extent than did valsartan alone or valsartan-amlodipine. In addition, the increases in urinary excretion of dopamine and epinephrine as well as in cardiac renin-angiotensin-aldosterone-system (RAAS) gene expression apparent in vehicle-treated rats were attenuated to a greater extent by valsartan-cilnidipine than by the other two treatments. Valsartan-cilnidipine thus attenuated LV remodeling and diastolic dysfunction more effectively than did valsartan or valsartan-amlodipine in rats with salt-sensitive hypertension, and this superior cardioprotective action of valsartan-cilnidipine compared with valsartan-amlodipine is likely attributable, at least in part, to the greater antioxidant and antiinflammatory effects associated with both greater inhibition of cardiac RAAS gene expression and N-type calcium channel blockade.

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.

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.

Dipeptidyl peptidase-4 modulates left ventricular dysfunction in chronic heart failure via angiogenesis-dependent and -independent actions.

BACKGROUND: The inhibition of dipeptidyl peptidase-4 (DPP4) protects the heart from acute myocardial ischemia. However, the role of DPP4 in chronic heart failure independent of coronary artery disease remains unclear. METHODS AND RESULTS: We first localized the membrane-bound form of DPP4 to the capillary endothelia of rat and human heart tissue. Diabetes mellitus promoted the activation of the membrane-bound form of DPP4, leading to reduced myocardial stromal cell-derived factor-1α concentrations and resultant angiogenic impairment in rats. The diabetic rats exhibited diastolic left ventricular dysfunction (DHF) with enhanced interstitial fibrosis caused partly by the increased ratio of matrix metalloproteinase-2 to tissue inhibitor of metalloproteinase-2 in a DPP4-dependent fashion. Both genetic and pharmacological DPP4 suppression reversed the stromal cell-derived factor-1α-dependent microvasculopathy and DHF associated with diabetes mellitus. Pressure overload induced DHF, which was reversed by DPP4 inhibition via a glucagon-like peptide-1/cAMP-dependent mechanism distinct from that for diabetic heart. In patients with DHF, the circulating DPP4 activity in peripheral veins was associated with that in coronary sinus and with E/e', an echocardiographic parameter representing DHF. Comorbid diabetes mellitus increased the circulating DPP4 activities in both peripheral veins and coronary sinus. CONCLUSIONS: DPP4 inhibition reverses DHF via membrane-bound DPP4/stromal cell-derived factor-1α-dependent local actions on angiogenesis and circulating DPP4/glucagon-like peptide-1-mediated inotropic actions. Myocardium-derived DPP4 activity in coronary sinus can be monitored by peripheral vein sampling, which partly correlates with DHF index; thus, circulating DPP4 may potentially serve as a biomarker for monitoring DHF.

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.

mGlu5 receptor and protein kinase C implicated in the development and induction of neuropathic pain following chronic ethanol consumption.

The central mechanisms of neuropathic pain following chronic ethanol consumption are poorly understood. We previously reported that the levels of metabotropic glutamate 5 (mGlu5) receptor and phosphorylated-protein kinase C (PKC) were significantly increased in the spinal cord following chronic ethanol consumption. The aim of this study was to investigate whether mGlu5 receptor and PKC inhibitors directly attenuate the neuropathic pain-like state induced by chronic ethanol treatment in rats. A significant decrease in the mechanical nociceptive threshold was observed 5 weeks of chronic ethanol consumption. This hyperalgesia was significantly attenuated by repeated i.p. injection of (S)-2,6-diamino-N-[[1-(oxotridecyl)-2-piperidinyl]methyl] hexanamide dihydrochloride (NPC15437), a selective PKC inhibitor, once a day for a week after 4 weeks of ethanol treatment. Furthermore, this hyperalgesia was also significantly attenuated by repeated i.p. injection of 6-methyl-2-[phenylethynyl]-pyridine (MPEP), a selective mGlu5 receptor inhibitor, once a day for a week after 4 weeks of ethanol treatment. Furthermore, the hyperalgesia that developed after 5 weeks of ethanol treatment was significantly suppressed by a single i.p. post-injection with either NPC15437 or MPEP. These findings constitute direct evidence that spinal mGlu5 receptor and PKC play substantial roles in the development and maintenance of an ethanol-dependent neuropathic pain-like state in rats.