Comparative analysis of telmisartan and olmesartan on cardiac function in the transgenic (mRen2)27 rat

Targeting peroxisome proliferator-activated receptors: A new strategy for the treatment of cardiac fibrosis

Cardiac fibrosis is a pathogenic factor of many cardiovascular diseases (CVD), which seriously affects people's life, and health and causes huge economic losses. Increasing evidence has shown that peroxisome proliferator-activated receptors (PPARs) can regulate the progression of cardiac fibrosis. For the first time, this review systematically summarizes the literature on cardiac fibrosis from the perspective of PPARs from 2010 to 2020. Moreover, the role of each PPARs in cardiac fibrosis was clarified in this scientific revision from the perspectives of pharmacologically active substances, known agonists, natural extract compounds, and nucleic-acid-based drugs in different CVD models. Furthermore, the combination of multiple PPARs on the treatment of cardiac fibrosis is discussed. This scientific review provides new ideas for targeting PPARs in the treatment of cardiac fibrosis and provides strategies for the development of new, safe, and effective pharmacological antagonists against cardiac fibrosis based on PPAR activity.

Western diet induces renal artery endothelial stiffening that is dependent on the epithelial Na+ channel

Consumption of a Western diet (WD) induces central aortic stiffening that contributes to the transmittance of pulsatile blood flow to end organs, including the kidney. Our recent work supports that endothelial epithelial Na⁺ channel (EnNaC) expression and activation enhances aortic endothelial cell stiffening through reductions in endothelial nitric oxide (NO) synthase (eNOS) and bioavailable NO that result in inflammatory and oxidant responses and perivascular fibrosis. However, the role that EnNaC activation has on endothelial responses in the renal circulation remains unknown. We hypothesized that cell-specific deletion of the α-subunit of EnNaC would prevent WD-induced central aortic stiffness and protect the kidney from endothelial dysfunction and vascular stiffening. Twenty-eight-week-old female αEnNaC knockout and wild-type mice were fed either mouse chow or WD containing excess fat (46%), sucrose, and fructose (17.5% each). WD feeding increased fat mass, indexes of vascular stiffening in the aorta and renal artery (in vivo pulse wave velocity and ultrasound), and renal endothelial cell stiffening (ex vivo atomic force microscopy). WD further impaired aortic endothelium-dependent relaxation and renal artery compliance (pressure myography) without changes in blood pressure. WD-induced renal arterial stiffening occurred in parallel to attenuated eNOS activation, increased oxidative stress, and aortic and renal perivascular fibrosis. αEnNaC deletion prevented these abnormalities and support a novel mechanism by which WD contributes to renal arterial stiffening that is endothelium and Na⁺ channel dependent. These results demonstrate that cell-specific EnNaC is important in propagating pulsatility into the renal circulation, generating oxidant stress, reduced bioavailable NO, and renal vessel wall fibrosis and stiffening.

Enhanced endothelium epithelial sodium channel signaling prompts left ventricular diastolic dysfunction in obese female mice

OBJECTIVE

Enhanced activation of cell specific mineralocorticoid receptors (MRs) in obesity plays a key role in the development of cardiovascular disease including cardiac diastolic dysfunction as a critical prognosticator. Our previous investigations demonstrated that selective endothelium MR activation promotes a maladaptive inflammatory response and fibrosis in cardiovascular tissue in female mice fed a western diet (WD), and this was associated with expression and activation of the epithelial sodium channel on the surface of endothelial cells (EnNaC). However, the specific role of EnNaC signaling in the development of cardiac stiffness and diastolic dysfunction has not been examined. We hypothesized that targeted inhibition of EnNaC with low dose amiloride would prevent WD-induced diastolic dysfunction by suppressing abnormal endothelial permeability, inflammation and oxidative stress, and myocardial fibrosis.

MATERIALS/METHODS

Four week-old female C57BL6/J mice were fed a WD with or without a low dose of amiloride (1mg/kg/day) for 16weeks. Left ventricular cardiac function was evaluated by magnetic resonance imaging. In addition, we examined coronary vessel and cardiac remodeling, fibrosis, macrophage infiltration using immunohistochemistry, western blot and real time PCR.

RESULTS

Amiloride, an antagonist of EnNaC, attenuated WD-induced impairment of left ventricular initial filling rate and relaxation time. Cardiac diastolic dysfunction was associated with increases in coronary endothelium remodeling and permeability that paralleled WD-induced increases in F-actin and fibronectin, decreased expression of claudin-5 and occludin, and increased macrophage recruitment, M1 polarization, cardiac oxidative stress, fibrosis and maladaptive remodeling.

CONCLUSION

Our data support the concept that EnNaC activation mediates endothelium permeability which, in turn, promotes macrophage infiltration, M1 polarization, and oxidative stress, resulting in cardiac fibrosis and diastolic dysfunction in females with diet induced obesity.

Cardiovascular disease progression in female Zucker Diabetic Fatty rats occurs via unique mechanisms compared to males

Population studies have shown that compared to diabetic men, diabetic women are at a higher risk of cardiovascular disease. However, the mechanisms underlying this gender disparity are unclear. Our studies in young murine models of type 2 diabetes mellitus (T2DM) and cardiovascular disease show that diabetic male rats develop increased cardiac fibrosis and suppression of intracardiac anti-fibrotic cytokines, while premenopausal diabetic female rats do not. This protection from cardiac fibrosis in female rats can be an estrogen-related effect. However, diabetic female rats develop early subclinical myocardial deformation, cardiac hypertrophy via elevated expression of pro-hypertrophic miR-208a, myocardial damage, and suppression of cardio-reparative Angiotensin II receptor 2 (Agtr2). Diabetic rats of both sexes exhibit a reduction in cardiac capillary density. However, diabetic female rats have reduced expression of neuropilin 1 that attenuates cardiomyopathy compared to diabetic male rats. A combination of cardiac hypertrophy and reduced capillary density likely contributed to increased myocardial structural damage in diabetic female rats. We propose expansion of existing cardiac assessments in diabetic female patients to detect myocardial deformation, cardiac hypertrophy and capillary density via non-invasive imaging, as well as suggest miR-208a, AT2R and neuropilin 1 as potential therapeutic targets and mechanistic biomarkers for cardiac disease in females.

Mineralocorticoid receptor blockade prevents Western diet-induced diastolic dysfunction in female mice

Overnutrition/obesity predisposes individuals, particularly women, to diastolic dysfunction (DD), an independent predictor of future cardiovascular disease. We examined whether low-dose spironolactone (Sp) prevents DD associated with consumption of a Western Diet (WD) high in fat, fructose, and sucrose. Female C57BL6J mice were fed a WD with or without Sp (1 mg·kg(-1)·day(-1)). After 4 mo on the WD, mice exhibited increased body weight and visceral fat, but similar blood pressures, compared with control diet-fed mice. Sp prevented the development of WD-induced DD, as indicated by decreased isovolumic relaxation time and an improvement in myocardial performance (<Tei index) and septal annular velocity (<E'-to-A' ratio), as assessed by echocardiography, as well as decreased diastolic relaxation time/increased diastolic initial filling rate, as assessed by MRI. The relationship between passive sarcomere length of cardiac myocytes and ventricular pressure was monitored using di-8-ANEPPS staining of the t-tubule network in hearts ex vivo. Sp administration led to longer sarcomere lengths at each pressure indicative of improved ventricular compliance in WD-fed mice. Sp also prevented left ventricular hypertrophy, interstitial fibrosis, and oxidative stress. Sp prevented the WD-induced increased expression of myocardial proinflammatory M1 macrophage markers monocyte chemoattractant protein-1 and CD11c and increased the expression of the anti-inflammatory M2 macrophage marker CD206. These findings demonstrate that WD-induced DD is associated with increased oxidant stress, fibrosis, and immune dysregulation. Mineralocorticoid receptor antagonism enhanced M2 macrophage polarization and ameliorated oxidant stress and fibrosis. This work supports a novel blood pressure-independent effect of MR antagonism as a strategy to prevent diet-induced DD in women. Mineralocorticoid antagonism; low-dose spironolactone; aldosterone;high-fat diet; high-fructose diet; oxidative stress; inflammation; cardiac hypertrophy; myocardial compliance.

Uric acid promotes left ventricular diastolic dysfunction in mice fed a Western diet

The rising obesity rates parallel increased consumption of a Western diet, high in fat and fructose, which is associated with increased uric acid. Population-based data support that elevated serum uric acids are associated with left ventricular hypertrophy and diastolic dysfunction. However, the mechanism by which excess uric acid promotes these maladaptive cardiac effects has not been explored. In assessing the role of Western diet-induced increases in uric acid, we hypothesized that reductions in uric acid would prevent Western diet-induced development of cardiomyocyte hypertrophy, cardiac stiffness, and impaired diastolic relaxation by reducing growth and profibrotic signaling pathways. Four-weeks-old C57BL6/J male mice were fed excess fat (46%) and fructose (17.5%) with or without allopurinol (125 mg/L), a xanthine oxidase inhibitor, for 16 weeks. The Western diet-induced increases in serum uric acid along with increases in cardiac tissue xanthine oxidase activity temporally related to increases in body weight, fat mass, and insulin resistance without changes in blood pressure. The Western diet induced cardiomyocte hypertrophy, myocardial oxidative stress, interstitial fibrosis, and impaired diastolic relaxation. Further, the Western diet enhanced activation of the S6 kinase-1 growth pathway and the profibrotic transforming growth factor-β1/Smad2/3 signaling pathway and macrophage proinflammatory polarization. All results improved with allopurinol treatment, which lowered cardiac xanthine oxidase as well as serum uric acid levels. These findings support the notion that increased production of uric acid with intake of a Western diet promotes cardiomyocyte hypertrophy, inflammation, and oxidative stress that lead to myocardial fibrosis and associated impaired diastolic relaxation.

Salt loading exacerbates diastolic dysfunction and cardiac remodeling in young female Ren2 rats

OBJECTIVE

Recent data would suggest pre-menopausal insulin resistant women are more prone to diastolic dysfunction than men, yet it is unclear why. We and others have reported that transgenic (mRen2)27 (Ren2) rats overexpressing the murine renin transgene are insulin resistant due to oxidative stress in insulin sensitive tissues. As increased salt intake promotes inflammation and oxidative stress, we hypothesized that excess dietary salt would promote diastolic dysfunction in transgenic females under conditions of excess tissue Ang II and circulating aldosterone levels.

MATERIALS/METHODS

For this purpose we evaluated cardiac function in young female Ren2 rats or age-matched Sprague-Dawley (SD) littermates exposed to a high (4%) salt or normal rat chow intake for three weeks.

RESULTS

Compared to SD littermates, at 10weeks of age, female Ren2 rats fed normal chow showed elevations in left ventricular (LV) systolic pressures, LV and cardiomyocyte hypertrophy, and displayed reductions in LV initial filling rate accompanied by increases in 3-nitrotyrosine content as a marker of oxidant stress. Following 3weeks of a salt diet, female Ren2 rats exhibited no further changes in LV systolic pressure, insulin resistance, or markers of hypertrophy but exaggerated increases in type 1 collagen, 3-nitrotryosine content, and diastolic dysfunction. These findings occurred in parallel with ultrastructural findings of pericapillary fibrosis, increased LV remodeling, and mitochondrial biogenesis.

CONCLUSION

These data suggest that a diet high in salt in hypertensive female Ren2 rats promotes greater oxidative stress, maladaptive LV remodeling, fibrosis, and associated diastolic dysfunction without further changes in LV systolic pressure or hypertrophy.

Dipeptidylpeptidase inhibition is associated with improvement in blood pressure and diastolic function in insulin-resistant male Zucker obese rats

Diastolic dysfunction is a prognosticator for future cardiovascular events that demonstrates a strong correlation with obesity. Pharmacological inhibition of dipeptidylpeptidase-4 (DPP-4) to increase the bioavailability of glucagon-like peptide-1 is an emerging therapy for control of glycemia in type 2 diabetes patients. Accumulating evidence suggests that glucagon-like peptide-1 has insulin-independent actions in cardiovascular tissue. However, it is not known whether DPP-4 inhibition improves obesity-related diastolic dysfunction. Eight-week-old Zucker obese (ZO) and Zucker lean rats were fed normal chow diet or diet containing the DPP-4 inhibitor, linagliptin (LGT), for 8 weeks. Plasma DPP-4 activity was 3.3-fold higher in ZO compared with Zucker lean rats and was reduced by 95% with LGT treatment. LGT improved echocardiographic and pressure volume-derived indices of diastolic function that were impaired in ZO control rats, without altering food intake or body weight gain during the study period. LGT also blunted elevated blood pressure progression in ZO rats involving improved skeletal muscle arteriolar function, without reducing left ventricular hypertrophy, fibrosis, or oxidative stress in ZO hearts. Expression of phosphorylated- endothelial nitric oxide synthase (eNOS)(Ser1177), total eNOS, and sarcoplasmic reticulum calcium ATPase 2a protein was elevated in the LGT-treated ZO heart, suggesting improved Ca(2+) handling. The ZO myocardium had an abnormal mitochondrial sarcomeric arrangement and cristae structure that were normalized by LGT. These studies suggest that LGT reduces blood pressure and improves intracellular Cai(2+) mishandling and cardiomyocyte ultrastructure, which collectively result in improvements in diastolic function in the absence of reductions in left ventricular hypertrophy, fibrosis, or oxidative stress in insulin-resistant ZO rats.

Renin inhibition and AT(1)R blockade improve metabolic signaling, oxidant stress and myocardial tissue remodeling

OBJECTIVE

Strategies that block angiotensin II actions on its angiotensin type 1 receptor or inhibit actions of aldosterone have been shown to reduce myocardial hypertrophy and interstitial fibrosis in states of insulin resistance. Thereby, we sought to determine if combination of direct renin inhibition with angiotensin type 1 receptor blockade in vivo, through greater reductions in systolic blood pressure (SBP) and aldosterone would attenuate left ventricular hypertrophy and interstitial fibrosis to a greater extent than either intervention alone.

MATERIALS/METHODS

We utilized the transgenic Ren2 rat which manifests increased tissue expression of murine renin which, in turn, results in increased renin-angiotensin system activity, aldosterone secretion and insulin resistance. Ren2 rats were treated with aliskiren, valsartan, the combination (aliskiren+valsartan), or vehicle for 21 days.

RESULTS

Compared to Sprague-Dawley controls, Ren2 rats displayed increased systolic blood pressure, elevated serum aldosterone levels, cardiac tissue hypertrophy, interstitial fibrosis and ultrastructural remodeling. These biochemical and functional alterations were accompanied by increases in the NADPH oxidase subunit Nox2 and 3-nitrotyrosine content along with increases in mammalian target of rapamycin and reductions in protein kinase B phosphorylation. Combination therapy contributed to greater reductions in systolic blood pressure and serum aldosterone but did not result in greater improvement in metabolic signaling or markers of oxidative stress, fibrosis or hypertrophy beyond either intervention alone.

CONCLUSIONS

Thereby, our data suggest that the greater impact of combination therapy on reductions in aldosterone does not translate into greater reductions in myocardial fibrosis or hypertrophy in this transgenic model of tissue renin overexpression.

Abnormal amounts of intracellular calcium regulatory proteins in SHRSP.Z-Leprfa/IzmDmcr rats with metabolic syndrome and cardiac dysfunction

Metabolic syndrome is known to increase the risk of abnormal cardiac structure and function, which are considered to contribute to increased incidence of cardiovascular disease and mortality. We previously demonstrated that ventricular hypertrophy and diastolic dysfunction occur in SHRSP.Z-Leprfa/IzmDmcr (SHRSP fatty) rats with metabolic syndrome. The aim of this study was to investigate the possible mechanisms underlying abnormal heart function in SHRSP fatty rats. The amount of sarcoplasmic reticulum Ca2+-ATPase (SERCA) 2a, phospholamban (PLB) protein, and Ser16-phosphorylated PLB was decreased in cardiomyocytes from SHRSP fatty rats compared with those from control Wistar–Kyoto rats at 18 weeks of age, and the PLB-to-SERCA2a ratio was increased. Left ventricular developed pressure was unchanged, and coronary flow rate and maximum rate of left ventricular pressure decline (−dP/dt) was decreased in SHRSP fatty rats. Treatment with telmisartan reversed the abnormalities of PLB amount, coronary flow rate, and −dP/dt in SHRSP fatty rats. These results indicate that abnormal amounts of intracellular Ca2+ regulatory proteins in cardiomyocytes, leading to reduced intracellular Ca2+ reuptake into the sarcoplasmic reticulum, may play a role in the diastolic dysfunction in SHRSP fatty rats and that these effects are partially related to decreased coronary circulation. Telmisartan may be beneficial in protecting against disturbances in cardiac function associated with metabolic syndrome.

Overweight female rats selectively breed for low aerobic capacity exhibit increased myocardial fibrosis and diastolic dysfunction

The statistical association between endurance exercise capacity and cardiovascular disease suggests that impaired aerobic metabolism underlies the cardiovascular disease risk in men and women. To explore this connection, we applied divergent artificial selection in rats to develop low-capacity runner (LCR) and high-capacity runner (HCR) rats and found that disease risks segregated strongly with low running capacity. Here, we tested if inborn low aerobic capacity promotes differential sex-related cardiovascular effects. Compared with HCR males (HCR-M), LCR males (LCR-M) were overweight by 34% and had heavier retroperitoneal, epididymal, and omental fat pads; LCR females (LCR-F) were 20% heavier than HCR females (HCR-F), and their retroperitoneal, but not perireproductive or omental, fat pads were heavier as well. Unlike HCR-M, blood pressure was elevated in LCR-M, and this was accompanied by left ventricular (LV) hypertrophy. Like HCR-F, LCR-F exhibited normal blood pressure and LV weight as well as increased spontaneous cage activity compared with males. Despite normal blood pressures, LCR-F exhibited increased myocardial interstitial fibrosis and diastolic dysfunction, as indicated by increased LV stiffness, a decrease in the initial filling rate, and an increase in diastolic relaxation time. Although females exhibited increased arterial stiffness, ejection fraction was normal. Increased interstitial fibrosis and diastolic dysfunction in LCR-F was accompanied by the lowest protein levels of phosphorylated AMP-actived protein kinase [phospho-AMPK (Thr(172))] and silent information regulator 1. Thus, the combination of risk factors, including female sex, intrinsic low aerobic capacity, and overweightness, promote myocardial stiffness/fibrosis sufficient to induce diastolic dysfunction in the absence of hypertension and LV hypertrophy.

Sex differences in baroreflex sensitivity, heart rate variability, and end organ damage in the TGR(mRen2)27 rat

The aim of this investigation was to evaluate sex differences in baroreflex and heart rate variability (HRV) dysfunction and indexes of end-organ damage in the TG(mRen2)27 (Ren2) rat, a model of renin overexpression and tissue renin-angiotensin-aldosterone system overactivation. Blood pressure (via telemetric monitoring), blood pressure variability [BPV; SD of systolic blood pressure (SBP)], spontaneous baroreflex sensitivity, HRV [HRV Triangular Index (HRV-TI), standard deviation of the average NN interval (SDNN), low and high frequency power (LF and HF, respectively), and Poincaré plot analysis (SD1, SD2)], and cardiovascular function (pressure-volume loop analysis and proteinuria) were evaluated in male and female 10-wk-old Ren2 and Sprague Dawley rats. The severity of hypertension was greater in Ren2 males (R2-M) than in Ren2 females (R2-F). Increased BPV, suppression of baroreflex gain, decreased HRV, and associated end-organ damage manifested as cardiac dysfunction, myocardial remodeling, elevated proteinuria, and tissue oxidative stress were more pronounced in R2-M compared with R2-F. During the dark cycle, HRV-TI and SDNN were negatively correlated with SBP within R2-M and positively correlated within R2-F; within R2-M, these indexes were also negatively correlated with end-organ damage [left ventricular hypertrophy (LVH)]. Furthermore, within R2-M only, LVH was strongly correlated with indexes of HRV representing predominantly vagal (HF, SD1), but not sympathetic (LF, SD2), variability. These data demonstrated relative protection in females from autonomic dysfunction and end-organ damage associated with elevated blood pressure in the Ren2 model of hypertension.

Angiotensin II activation of mTOR results in tubulointerstitial fibrosis through loss of N-cadherin

BACKGROUND/AIMS

Angiotensin (Ang) II contributes to tubulointerstitial fibrosis. Recent data highlight mammalian target of rapamycin (mTOR)/S6 kinase 1 (S6K1) signaling in tubulointerstitial fibrosis; however, the mechanisms remain unclear. Thereby, we investigated the role of Ang II on mTOR/S6K1-dependent proximal tubule (PT) injury, remodeling, and fibrosis.

METHODS

We utilized young transgenic Ren2 rats (R2-T) and Sprague-Dawley rats (SD-T) treated with the Ang type 1 receptor (AT(1)R) blocker telmisartan (2 mg · kg(-1) · day(-1)) or vehicle (R2-C; SD-C) for 3 weeks to examine PT structure and function.

RESULTS

Ren2 rats displayed increased systolic blood pressure, proteinuria and increased PT oxidant stress and remodeling. There were parallel increases in kidney injury molecule-1 and reductions in neprilysin and megalin with associated ultrastructural findings of decreased clathrin-coated pits, endosomes, and vacuoles. Ren2 rats displayed increased Serine(2448) phosphorylation of mTOR and downstream S6K1, in concert with ultrastructural basement membrane thickening, tubulointerstitial fibrosis and loss of the adhesion molecule N-cadherin. Telmisartan treatment attenuated proteinuria as well as the biochemical and tubulointerstitial structural abnormalities seen in the Ren2 rats.

CONCLUSIONS

Our observations suggest that Ang II activation of the AT(1)R contributes to PT brush border injury and remodeling, in part, due to enhanced mTOR/S6K1 signaling which promotes tubulointerstitial fibrosis through loss of N-cadherin.

Mineralocorticoid receptor blockade improves diastolic function independent of blood pressure reduction in a transgenic model of RAAS overexpression

There is emerging evidence that aldosterone can promote diastolic dysfunction and cardiac fibrosis independent of blood pressure effects, perhaps through increased oxidative stress and inflammation. Accordingly, this investigation was designed to ascertain if mineralocorticoid receptor blockade improves diastolic dysfunction independently of changes in blood pressure through actions on myocardial oxidative stress and fibrosis. We used young transgenic (mRen2)27 [TG(mRen2)27] rats with increases in both tissue ANG II and circulating aldosterone, which manifests age-related increases in hypertension and cardiac dysfunction. Male TG(mRen2)27 and age-matched Sprague-Dawley rats were treated with either a low dose (∼1 mg·kg(-1)·day(-1)) or a vasodilatory, conventional dose (∼30 mg·kg(-1)·day(-1)) of spironolactone or placebo for 3 wk. TG(mRen2)27 rats displayed increases in systolic blood pressure and plasma aldosterone levels as well as impairments in left ventricular diastolic relaxation without changes in systolic function on cine MRI. TG(mRen2)27 hearts also displayed hypertrophy (left ventricular weight, cardiomyoctye hypertrophy, and septal wall thickness) as well as fibrosis (interstitial and perivascular). There were increases in oxidative stress in TG(mRen2)27 hearts, as evidenced by increases in NADPH oxidase activity and subunits as well as ROS formation. Low-dose spironolactone had no effect on systolic blood pressure but improved diastolic dysfunction comparable to a conventional dose. Both doses of spironolactone caused comparable reductions in ROS/3-nitrotryosine immunostaining and perivascular and interstitial fibrosis. These data support the notion mineralocorticoid receptor blockade improves diastolic dysfunction through improvements in oxidative stress and fibrosis independent of changes in systolic blood pressure.