Molecular, Cellular, and Clinical Evidence That Sodium-Glucose Cotransporter 2 Inhibitors Act as Neurohormonal Antagonists When Used for the Treatment of Chronic Heart Failure

Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce the risk of cardiovascular death and hospitalization for heart failure in patients with chronic heart failure. Initially, these drugs were believed to have a profile similar to diuretics or hemodynamically active drugs, but they do not rapidly reduce natriuretic peptides or cardiac filling pressures, and they exert little early benefit on symptoms, exercise tolerance, quality of life, or signs of congestion. Clinically, the profile of SGLT2 inhibitors resembles that of neurohormonal antagonists, whose benefits emerge gradually during sustained therapy. In experimental models, SGLT2 inhibitors produce a characteristic pattern of cellular effects, which includes amelioration of oxidative stress, mitigation of mitochondrial dysfunction, attenuation of proinflammatory pathways, and a reduction in myocardial fibrosis. These cellular effects are similar to those produced by angiotensin converting enzyme inhibitors, β-blockers, mineralocorticoid receptor antagonists, and neprilysin inhibitors. At a molecular level, SGLT2 inhibitors induce transcriptional reprogramming of cardiomyocytes that closely mimics that seen during nutrient deprivation. This shift in signaling activates the housekeeping pathway of autophagy, which clears the cytosol of dangerous cytosolic constituents that are responsible for cellular stress, thereby ameliorating the development of cardiomyopathy. Interestingly, similar changes in cellular signaling and autophagic flux have been seen with inhibitors of the renin-angiotensin system, β-blockers, mineralocorticoid receptor antagonists, and neprilysin inhibitors. The striking parallelism of these molecular, cellular, and clinical profiles supports the premise that SGLT2 inhibitors should be regarded as neurohormonal antagonists when prescribed for the treatment of heart failure with a reduced ejection fraction.

Cardio-omentopexy Reduces Cardiac Fibrosis and Heart Failure After Experimental Pressure Overload

BACKGROUND

The pedicled greater omentum has been shown to offer benefit in ischemic heart disease for both animal models and human patients. The impact of cardio-omentopexy in a pressure overload model of left ventricular hypertrophy (LVH) is unknown.

METHODS

LVH was created in rats by banding the ascending aorta after right thoracotomy (n = 23). Sham surgery was performed in 12 additional rats. Six weeks after banding, surviving LVH rats were assigned to cardio-omentopexy by left thoracotomy (LVH+Om, n = 8) or sham left thoracotomy (LVH, n = 8). Sham rats also underwent left thoracotomy for cardio-omentopexy (Sham+Om, n = 6); the remaining rats underwent sham left thoracotomy (Sham, n = 6).

RESULTS

Echocardiography 10 weeks after cardio-omentopexy revealed LV end-systolic diameter, cardiomyocyte diamter, and myocardial fibrosis in the LVH group were significantly increased compared with the LVH+Om, Sham+Om, and Sham groups (p < 0.01). LV ejection fraction of the LVH group was lower than the LVH+Om group (p < 0.01). Gene expression analysis revealed significantly lower levels of sarcoendoplasmic reticulum calcium adenosine triphosphatase 2b in LVH rats than in the LVH+Om, Sham+Om, and Sham groups (p < 0.01). In contrast, collagen type 1 α 1 chain, lysyl oxidase-like protein 1, nuclear protein-1, and transforming growth factor- β1 in the LVH group were significantly higher than in the LVH+Om cohort (p < 0.01), consistent with a reduced fibrotic phenotype after omentopexy. Lectin staining showed myocardial capillary density of the LVH group was significantly lower than all other groups (p < 0.01).

CONCLUSIONS

Cardio-omentopexy reduced cardiac dilation, contractile dysfunction, cardiomyocyte hypertrophy, and myocardial fibrosis, while maintaining other molecular indicators of contractile function in this LVH model.

MiR-18a-5p inhibits endothelial-mesenchymal transition and cardiac fibrosis through the Notch2 pathway

Hyperglycemia plays a crucial role in the pathogenesis of diabetic complications; however, the mechanisms underlying diabetic cardiac fibrosis remain unclear. Endothelial cells are known to contribute to cardiac fibrosis through endothelial-mesenchymal transition (EndMT) under high glucose stimulation. Here we investigated the expression of miR-18a-5p and examined its functional role in human aortic valvular endothelial cells (HAVECs). Using HAVECs, we revealed that miR-18a-5p regulated high glucose-induced EndMT. Moreover, high glucose levels induced Notch2 expression, which promoted EndMT, resulting in the downregulation of vascular endothelial cadherin and CD31 and upregulation of fibroblast-specific protein-1, α-smooth muscle actin, fibronectin, and vimentin. Furthermore, Notch2 was identified as a target of miR-18a-5p. Our data showed that the overexpression of miR-18a-5p could downregulate Notch2 expression and subsequently suppress EndMT. In conclusion, our findings demonstrated that miR-18a-5p/Notch2 signaling pathway participates in the regulation of high glucose-induced EndMT, and may act as a novel promising target for myocardial fibrosis in diabetic cardiomyopathy.

NOD1 activation in cardiac fibroblasts induces myocardial fibrosis in a murine model of type 2 diabetes

Cardiac fibrosis and chronic inflammation are common complications in type 2 diabetes mellitus (T2D). Since nucleotide oligomerization-binding domain 1 (NOD1), an innate immune receptor, is involved in the pathogenesis of insulin resistance and diabetes outcomes, we sought to investigate its involvement in cardiac fibrosis. Here, we show that selective staining of cardiac fibroblasts from T2D (db/db;db) mice exhibits up-regulation and activation of the NOD1 pathway, resulting in enhanced NF-κB and TGF-β signalling. Activation of the TGF-β pathway in cardiac fibroblasts from db mice was prevented after inhibition of NF-κB with BAY-11-7082 (BAY). Moreover, fibrosis progression in db mice was also prevented by BAY treatment. Enhanced TGF-β signalling and cardiac fibrosis of db mice was dependent, at least in part, on the sequential activation of NOD1 and NF-κB since treatment of db mice with a selective NOD1 agonist induced activation of the TGF-β pathway, but co-administration of a NOD1 agonist plus BAY, or a NOD1 inhibitor prevented the NOD1-induced fibrosis. Therefore, NOD1 is involved in cardiac fibrosis associated with diabetes, and establishes a new mechanism for the development of heart fibrosis linked to T2D.

Exercise training reduces cardiac dysfunction and remodeling in ovariectomized rats submitted to myocardial infarction

The aim of this study was to evaluate whether exercise training (ET) prevents or minimizes cardiac dysfunction and pathological ventricular remodeling in ovariectomized rats subjected to myocardial infarction (MI) and to examine the possible mechanisms involved in this process. Ovariectomized Wistar rats were subjected to either MI or fictitious surgery (Sham) and randomly divided into the following groups: Control, OVX+SHAM_SED, OVX+SHAM_ET, OVX+MI_SED and OVX+MI_ET. ET was performed on a motorized treadmill (5x/wk, 60 min/day, 8 weeks). Cardiac function was assessed by ventricular catheterization and Dihydroethidium fluorescence (DHE) was evaluated to analyze cardiac oxidative stress. Histological analyses were made to assess collagen deposition, myocyte hypertrophy and infarct size. Western Blotting was performed to analyze the protein expression of catalase and SOD-2, as well as Gp91phox and AT1 receptor (AT1R). MI-trained rats had significantly increased in +dP/dt and decreased left ventricular end-diastolic pressure compared with MI-sedentary rats. Moreover, oxidative stress and collagen deposition was reduced, as was myocyte hypertrophy. These effects occurred in parallel with a reduction in both AT1R and Gp91phox expression and an increase in catalase expression. SOD-2 expression was not altered. These results indicate that ET improves the functional cardiac parameters associated with attenuation of cardiac remodeling in ovariectomized rats subjected to MI. The mechanism seems to be related to a reduction in the expression of both the AT1 receptor and Gp91phox as well as an increase in the antioxidant enzyme catalase, which contributes to a reduction in oxidative stress. Therefore, ET may be an important therapeutic target for the prevention of heart failure in postmenopausal women affected by MI.

AdipoR1/APPL1 potentiates the protective effects of globular adiponectin on angiotensin II-induced cardiac hypertrophy and fibrosis in neonatal rat atrial myocytes and fibroblasts

Atrial hypertrophy and fibrosis are essential pathological features of atrial fibrillation. Recently, adiponectin has become a protein of interest due to its beneficial effects on cardiovascular diseases. However, the molecular mechanism of atrial structural remodeling and signaling pathways evoked by adiponectin remain unclear. In the present study, we investigated the cardioprotective effect of globular adiponectin (gAcrp) on angiotensin II-induced atrial hypertrophy and fibrosis in neonatal Sprague-Dawley rat. To further investigate the molecular mechanisms underlying the preventive effect of gAcrp, transfection of cells with siRNA was used to suppress the mRNA expression of adiponectin receptor 1 (AdipoR1) and its downstream adaptor protein APPL1. Non-silencing-Cy-3 labelled siRNA was used to determine transfection efficiency using fluorescence microscopy. The expression of atrial natriuretic peptide and procollagen type1 α-1, hypertrophy marker and fibrosis one, respectively, was detected by real-time PCR. Furthermore, the expression of adenosine monophosphate-activated protein kinase (AMPK), phosphatidylinositol 3-kinase (PI3K) and Akt was detected by western blotting. In addition, nuclear p65 translocation activity was analyzed by EMSA supershift assay. Our results showed that AdipoR1 and the adaptor protein APPL1 mediated the protective effects of gAcrp. In addition, the function of adiponectin and phosphorylation of AMPK were prominently diminished by inhibition of PI3K. Furthermore, nuclear factor-κB (NF-κB) transcription was diminished by the specific inhibition of AMPK. Taken together, AMPK pivotally interacts with NF-κB and PI3K, mediating the cardioprotective effect of adiponectin, and may serve as a therapeutic target for preventing atrial hypertrophy and fibrosis. Our present study suggests that gAcrp could ameliorate AngII-induced cardiac hypertrophy and fibrosis in rat atrial cells, which is mediated by the activation of AMPK signaling pathways. APPL1 and AdipoR1 are the key factors involved in the downstream of gAcrp approach.

Reduction of chronic graft injury with a new HTK-based preservation solution in a murine heart transplantation model

OBJECTIVE

Aim of this study was to evaluate a new histidine-tryptophan-ketoglutarate (HTK)-based preservation solution on chronic isograft injury in comparison to traditional HTK solution.

METHODS

Hearts of C57BL/6J (H-2b) mice were stored for 15 h in 0-4 °C cold preservation solution and then transplanted heterotopically into C57BL/6J (H-2b) mice. Three groups were evaluated: HTK, the base solution of a new preservation solution and hearts without cold ischemia (control). Time to restoration of heartbeat was measured (re-beating time). Strength of the heartbeat was palpated daily and scored on a 4-level scale (palpation score). Animals were sacrificed after 60 days of observation (24 h for TGF-β expression). The transplanted hearts were evaluated histologically for myocardial damage, vasculopathy and interstitial fibrosis. TGF-β expression was assessed immunohistologically. All investigators were blinded to the groups. ANOVA and LSD post hoc test were used for statistical analysis.

RESULTS

The re-beating time was significantly shorter in hearts stored in the new solution (10.3±2.6 min vs. HTK 14.2±4.1 min; p<0.05). The palpation score was significantly higher in hearts stored in the new solution (2.3±0.4 vs. HTK 1.6±0.5; p<0.01). Hearts stored in the new solution showed a lower myocardial injury score (1.8±0.2 vs. HTK 2.2±0.7), less interstitial fibrosis (4.8±1.9% vs. HTK 8.5±3.8%, p<0.05), less vasculopathy (14.7±6.9% vs. 22.0±23.2%; p=0.06) and lower TGF-β1-expression (6.6±1.4% vs. HTK 12.0±4.6%).

CONCLUSION

The new HTK-based solution reduces the chronic isograft injury. This protective effect is likely achieved through several modifications and supplements into the new solution like N-acetyl-L-histidine, glycine, alanine, arginine and sucrose.

Hyperthermia treatment prevents angiotensin II-mediated atrial fibrosis and fibrillation via induction of heat-shock protein 72

We tested the hypothesis that atrial fibrosis and atrial fibrillation (AF) evoked by angiotensin II (AII) could be prevented by the induction of heat-shock protein 72 (HSP72) by hyperthermia (HT). In cultured atrial fibroblasts isolated from male Sprague-Dawley rats, HT (42 degrees C) was applied for 30 min. AII (100 nmol/L) was added to the medium 8 h later. HT induced the expression of HSP72, which was associated with the attenuation of AII-induced extracellular signal-regulated kinase (ERK1/ERK2) phosphorylation, alpha-smooth muscle actin (alpha-SMA) expression, transforming growth factor-beta(1) secretion, collagen synthesis, and expression of collagen type I and tissue inhibitor of metalloproteinases-1. A small interfering RNA targeting HSP72 abolished these anti-fibrotic effects of HT. In male Sprague-Dawley rats in vivo, an osmotic mini-pump was subcutaneously implanted for continuous infusion of AII (400 ng/kg/min). Whole-body HT (43 degrees C, 20 min) was applied 24 h before and 7, 14, and 21 days after the start of the AII infusion. Repeated HT led to the induction of HSP72 expression, which resulted in an attenuation of AII-induced left atrial fibrosis. In an electrophysiological study using isolated perfused heart, continuous AII caused slowing of interatrial conduction without affecting atrial refractoriness. In AII-treated hearts, extrastimuli from the right atrial appendage resulted in a high incidence of repetitive atrial responses, which were suppressed by treatment with HT. Our results suggest that HT treatment is effective in suppressing AII-mediated atrial fibrosis and AF via induction of HSP72 at least in parts, and is thus expected to be a novel strategy for prevention of AF.

[Effect of astragaloside on myocardial fibrosis in chronic myocarditis]

OBJECTIVE

To investigate the effect of astragaloside (Astr), one of the active components of the Chinese medical herb Astragulus membranaceus, on cardiac fibrosis in chronic myocarditis and its relevant mechanisms.

METHODS

Eighty mice were randomized into 3 groups, the control group (n=20), the model group (n=30) and the Astr group (n=30). Mice in the model group and the Astr group were monthly intraperitoneally inoculated with CVB3, but to the control group equal amount of culture fluid was given instead. Mice in the control and the model group were fed with drinking water while those in the Astr group with drinking water containing Astr-sodium carboxymethycellulose at a concentration of 300 mg/L. All the survived mice were sacrificed 3 months later. Heart tissue of mice was stained by picrosirius red for calculating collagen volume fraction (CVF) with an automatic image analysis system. Expressions of transforming growth factor beta1 (TGF-beta1), platelet derived growth factor (PDGF), matrix metalloproteinase 1 (MMP-1), tissue inhibitor of metalloproteinase 1 (TIMP-1), MMP-13 and MMP-14 in heart tissue were detected by Western blot analysis.

RESULTS

As compared with the model group, in the Astr group, the mortality and CVF were significantly lower (53.3% vs. 23.3%, chi2 = 4.23, P < 0.05), and (17.4 +/- 1.2% vs. 8.6 +/- 0.9%, chi2 = 5.38, P < 0.05), respectively. As compared with the control group, Western blot analysis showed that expression of TGF-beta1 was decreased, MMP-1 and TIMP-1 were down-regulated, while expressions of MMP-13 and MMP-14 were up-regulated after Astr treatment.

CONCLUSION

Astr could lower the mortality and alleviate the myocardial fibrosis of mice with chronic myocarditis. Its antifibrotic effect might be realized by way of inhibiting TGF-beta1 expression and up-regulating the expressions of MMP-13 and MMP-14 in the heart tissues.

The adenosine A1 receptor antagonist SLV320 reduces myocardial fibrosis in rats with 5/6 nephrectomy without affecting blood pressure

BACKGROUND AND PURPOSE

Myocardial fibrosis is an unwanted effect associated with chronic renal failure. The adenosine system is involved in cardiac and renal function. Therefore, we investigated the novel selective adenosine A(1) receptor antagonist SLV320 focusing on its potential in preventing cardiomyopathy in rats with 5/6 nephrectomy.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were allocated to 4 groups of 12 rats each: 5/6 nephrectomy (5/6 NX), 5/6 NX plus SLV320 (10 mg kg(-1) d(-1) mixed with food), sham and sham plus SLV320. Study duration was 12 weeks, blood pressure was assessed repeatedly. At study end kidney function was assessed, blood samples and hearts were taken for histology/immunohistochemistry. Pharmacological properties of SLV320 were assessed using receptor binding and enzyme assays and in vivo.

KEY RESULTS

SLV320 is a selective and potent adenosine A(1) antagonist in vitro (Ki=1 nM) with a selectivity factor of at least 200 versus other adenosine receptor subtypes. Functional A(1) antagonism was demonstrated in vivo. In rats with 5/6 NX SLV320 significantly decreased albuminuria by about 50%, but did not alter glomerular filtration rate (GFR). SLV320 normalized cardiac collagen I+III contents in 5/6 NX rats. SLV320 prevented nephrectomy-dependent rise in plasma levels of creatinine kinase (CK), ALT and AST. Blood pressure did not differ between study groups.

CONCLUSION

SLV320 suppresses cardiac fibrosis and attenuates albuminuria without affecting blood pressure in rats with 5/6 nephrectomy, indicating that selective A(1) receptor antagonists may be beneficial in uraemic cardiomyopathy.

Alpha-linolenic acid-enriched diet prevents myocardial damage and expands longevity in cardiomyopathic hamsters

Randomized clinical trials have demonstrated that the increased intake of omega-3 polyunsaturated fatty acids significantly reduces the risk of ischemic cardiovascular disease, but no investigations have been performed in hereditary cardiomyopathies with diffusely damaged myocardium. In the present study, delta-sarcoglycan-null cardiomyopathic hamsters were fed from weaning to death with an alpha-linolenic acid (ALA)-enriched versus standard diet. Results demonstrated a great accumulation of ALA and eicosapentaenoic acid and an increased eicosapentaenoic/arachidonic acid ratio in cardiomyopathic hamster hearts, correlating with the preservation of myocardial structure and function. In fact, ALA administration preserved plasmalemma and mitochondrial membrane integrity, thus maintaining proper cell/extracellular matrix contacts and signaling, as well as a normal gene expression profile (myosin heavy chain isoforms, atrial natriuretic peptide, transforming growth factor-beta1) and a limited extension of fibrotic areas within ALA-fed cardiomyopathic hearts. Consequently, hemodynamic indexes were safeguarded, and more than 60% of ALA-fed animals were still alive (mean survival time, 293+/-141.8 days) when all those fed with standard diet were deceased (mean survival time, 175.9+/-56 days). Therefore, the clinically evident beneficial effects of omega-3 polyunsaturated fatty acids are mainly related to preservation of myocardium structure and function and the attenuation of myocardial fibrosis.

Decorin-mediated Transforming Growth Factor-β Inhibition Ameliorates Adverse Cardiac Remodeling

BACKGROUND

Implantation of a left ventricular assist device (LVAD) has been shown to induce regression of fibrosis in patients with congestive heart failure (CHF) and improve myocardial function. The mechanism of reverse remodeling after mechanical circulatory support (MCS), however, has not been fully characterized. In this study we examined the anti-fibrotic effects of decorin, an extracellular matrix (ECM) proteoglycan, on the transforming growth factor-beta (TGF-beta) pathway.

METHODS

Human myocardial tissue samples were obtained from patients undergoing LVAD implantation and again following subsequent transplantation after a sustained period of MCS. The specimens were examined by utilizing different molecular and histologic techniques, including human cardiac fibroblast in vitro studies. We assessed gene expression, mRNA and protein levels.

RESULTS

We found a significant decrease in interstitial fibrosis after MCS, with a decrease in collagen mRNA transcription rates, serving as an indirect measurement of collagen synthesis. Both the mRNA and protein levels of decorin were significantly increased after a period of MCS. Decorin mRNA was up-regulated by 44% after MCS (p < 0.01), which paralleled the increase in interstitial decorin deposition (p < 0.001). In addition, p-SMAD2, a molecular marker downstream of the TGF-beta pathway, was found to be inactivated after MCS (p < 0.02). Moreover, cultured human cardiac fibroblasts exposed to TGF-beta demonstrated decreased collagen production when exogenous decorin was added (p < 0.03).

CONCLUSIONS

The decorin molecule is potentially involved in reverse cardiac remodeling, by directly inhibiting the TGF-beta pathway and its pro-fibrotic effects on the failing human heart.

Inhibition of Urokinase-Type Plasminogen Activator or Matrix Metalloproteinases Prevents Cardiac Injury and Dysfunction During Viral Myocarditis

Background— Acute viral myocarditis is an important cause of cardiac failure in young adults for which there is no effective treatment apart from general heart failure therapy. The present study tested the hypothesis that increased expression of the proteinases urokinase-type plasminogen activator (uPA) and matrix metalloproteinases (MMPs) is implicated in cardiac inflammation, injury, and subsequent failure during Coxsackievirus-B3 (CVB3)–induced myocarditis.

Methods and Results— First, we showed increased expression and activity of uPA and MMP-9 in wild-type mice at 7 days of CVB3-induced myocarditis. Targeted deletion of uPA, which resulted in reduced MMP activity and cytokine expression or inhibition of MMPs by adenoviral gene overexpression of tissue inhibitor of metalloproteinases-1, decreased cardiac inflammation and reduced myocardial necrosis at 7 days and decreased cardiac fibrosis at 35 days after CVB3 infection. Importantly, loss of uPA or MMP activity prevented CVB3-induced cardiac dilatation and dysfunction, as determined by serial echocardiography.

Conclusions— Loss of uPA or MMP activity reduces the cardiac inflammatory response after CVB3 infection, thereby protecting against cardiac injury, dilatation, and failure during CVB3-induced myocarditis.

Antifibrotic activity of an inhibitor of group IIA secretory phospholipase A2 in young spontaneously hypertensive rats

The development of fibrosis in the chronically hypertensive heart is associated with infiltration of inflammatory cells and cardiac hypertrophy. In this study, an inhibitor of the proinflammatory enzyme, group IIA human secretory phospholipase A2 (sPLA2-IIA), has been found to prevent collagen deposition as an important component of cardiovascular remodeling in a rat model of developing chronic hypertension. Daily treatment of young male spontaneously hypertensive rats (SHR) with an sPLA2-IIA inhibitor (KH064, 5-(4-benzyloxyphenyl)-4S-(phenyl-heptanoylamino)-pentanoic acid, 5 mg/kg/day p.o.) prevented increases in the content of perivascular (SHR 20.6 +/- 0.9%, n = 5; SHR+KH064 14.0 +/- 1.2%, n = 5) and interstitial (SHR 7.9 +/- 0.3%, n = 6; SHR+KH064 5.4 +/- 0.7%, n = 6) collagen in the left ventricle of rat hearts, but did not affect numbers of infiltrating monocytes/macrophages, left ventricular hypertrophy (SHR 2.88 +/- 0.08, n = 12; SHR+KH064 3.09 +/- 0.08 mg/g body weight, n = 9), increased systolic blood pressure, or thoracic aortic responses. This selective antifibrotic activity suggests that sPLA2-IIA may have an important but specific role in cardiac fibrosis, and that its inhibitors could be useful in dissecting molecular pathways leading to fibrotic conditions.

Aldosterone mediates angiotensin II-induced interstitial cardiac fibrosis via a Nox2-containing NADPH oxidase

Angiotensin (ANG) II (AngII) and aldosterone contribute to the development of interstitial cardiac fibrosis. We investigated the potential role of a Nox2-containing NADPH oxidase in aldosterone-induced fibrosis and the involvement of this mechanism in AngII-induced effects. Nox2-/- mice were compared with matched wild-type controls (WT). In WT mice, subcutaneous (s.c.) AngII (1.1 mg/kg/day for 2 wk) significantly increased NADPH oxidase activity, interstitial fibrosis (11.5+/-1.0% vs. 7.2+/-0.7%; P<0.05), expression of fibronectin, procollagen I, and connective tissue growth factor mRNA, MMP-2 activity, and NF-kB activation. These effects were all inhibited in Nox2-/- hearts. The mineralocorticoid receptor antagonist spironolactone inhibited AngII-induced increases in NADPH oxidase activity and the increase in interstitial fibrosis. In a model of mineralocorticoid-dependent hypertension involving chronic aldosterone infusion (0.2 mg/kg/day) and a 1% Na Cl diet ("ALDO"), WT animals exhibited increased NADPH oxidase activity, pro-fibrotic gene expression, MMP-2 activity, NF-kB activation, and significant interstitial cardiac fibrosis (12.0+/-1.7% with ALDO vs. 6.3+/-0.3% without; P<0.05). These effects were inhibited in Nox2-/- ALDO mice (e.g., fibrosis 6.8+/-0.8% with ALDO vs. 5.8+/-1.0% without ALDO; P=NS). These results suggest that aldosterone-dependent activation of a Nox2-containing NADPH oxidase contributes to the profibrotic effect of AngII in the heart as well as the fibrosis seen in mineralocorticoid-dependent hypertension.

Poly(ADP-ribose) polymerase-1-deficient mice are protected from angiotensin II-induced cardiac hypertrophy

Poly(ADP-ribose) polymerase-1 (PARP), a chromatin-bound enzyme, is activated by cell oxidative stress. Because oxidative stress is also considered a main component of angiotensin II-mediated cell signaling, it was postulated that PARP could be a downstream target of angiotensin II-induced signaling leading to cardiac hypertrophy. To determine a role of PARP in angiotensin II-induced hypertrophy, we infused angiotensin II into wild-type (PARP(+/+)) and PARP-deficient mice. Angiotensin II infusion significantly increased heart weight-to-tibia length ratio, myocyte cross-sectional area, and interstitial fibrosis in PARP(+/+) but not in PARP(-/-) mice. To confirm these results, we analyzed the effect of angiotensin II in primary cultures of cardiomyocytes. When compared with PARP(-/-) cardiomyocytes, angiotensin II (1 microM) treatment significantly increased protein synthesis in PARP(+/+) myocytes, as measured by (3)H-leucine incorporation into total cell protein. Angiotensin II-mediated hypertrophy of myocytes was accompanied with increased poly-ADP-ribosylation of nuclear proteins and depletion of cellular NAD content. When cells were treated with cell death-inducing doses of angiotensin II (10-20 microM), robust myocyte cell death was observed in PARP(+/+) but not in PARP(-/-) myocytes. This type of cell death was blocked by repletion of cellular NAD levels as well as by activation of the longevity factor Sir2alpha deacetylase, indicating that PARP induction and subsequent depletion of NAD levels are the sequence of events causing angiotensin II-mediated cardiomyocyte cell death. In conclusion, these results demonstrate that PARP is a nuclear integrator of angiotensin II-mediated cell signaling contributing to cardiac hypertrophy and suggest that this could be a novel therapeutic target for the management of heart failure.

Protection from angiotensin II-induced cardiac hypertrophy and fibrosis by systemic lentiviral delivery of ACE2 in rats

Angiotensin converting enzyme 2 (ACE2), a newly discovered member of the renin-angiotensin system (RAS), is a potential therapeutic target for the control of cardiovascular disease owing to its key role in the formation of vasoprotective peptides from angiotensin II. The aim of the present study was to evaluate whether overexpression of ACE2 could protect the heart from angiotensin II-induced hypertrophy and fibrosis. Lentiviral vector encoding mouse ACE2 (lenti-mACE2) or GFP was injected intracardially in 5-day-old Sprague-Dawley rats. This resulted in expression of mACE2 in cardiac tissue for the duration of the study. Infusion of 200 ng kg-1 min-1 angiotensin II for 4 weeks resulted in an 80 mmHg increase in systolic blood pressure, a significant increase in the heart weight to body weight ratio (HW:BW), and marked myocardial fibrosis in control rats. Transduction with lenti-mACE2 resulted in significant attenuation of the increased HW:BW and myocardial fibrosis induced by angiotensin II infusion. These observations demonstrate that ACE2 overexpression results in protective effects on angiotensin II-induced cardiac hypertrophy and fibrosis.

Reduction of ventricular hypertrophy and fibrosis in spontaneously hypertensive rats by L-arginine

The purpose of this experiment was to explore long-term L-arginine administration on ventricular hypertrophy and cardiac fibrosis in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. Twenty-four rats of each strain at eight wks of age were divided into two groups--one receiving L-arginine and the other vehicle for twelve wks. Arterial pressure (AP) and heart rate were monitored. At 20 wks of age, the rats' rings of thoracic aorta were isolated to record isometric tension. The study measured left ventricular weight (LVW), body weight (BW), left ventricular (LV) contents of cGMP, and collagen volume fraction (LVCVF). Histological examination of the LV tissue determined changes in cardiomyocytes. Administration of L-arginine did not alter the AP change in SHR, but reduced the AP in WKY after six wks. Our results showed a significantly higher LVW/BW ratio and LVCVF in vehicle-treated SHR compared to levels in corresponding WKY, whereas, the LV cGMP and nitrite/nitrate measurements were higher in vehicle-treated WKY than in SHR. L-Arginine treatment decreased LVW/BW ratio and LVCVF, while increasing the levels of LV cGMP and nitrite/nitrate only in SHR, consistent with histopathological examinations that showed L-arginine prevented cardiomyocytes from thickness and hypertrophy. Our results suggested that the mechanism of reduction in ventricular hypertrophy and fibrosis following long-term L-arginine administration in SHR may stem from increased myocardial nitric oxide-cGMP signaling, independent of AP and EDV of thoracic aorta.

Effect of endothelin blockade on early cardiovascular remodeling in the one-clip-two-kidney hypertension of the rat

BACKGROUND

In models of hypertension and of renal failure, pharmacological blockade of the ET(A) receptor has been shown to cause some inconsistent lowering of blood pressure (BP) and lesser left ventricular hypertrophy (LVH). The effects of ET(A) receptor blockade (ET(A)-RB) on vascular remodeling and their potential relation to BP lowering, have not been clarified.

DESIGN

The experimental study in male Sprague-Dawley rats was designed to compare four experimental groups: (1) sham-operated controls (sham); (2) untreated rats with one-clip-two-kidney (1C-2K) renovascular hypertension; (3) 1C-2K rats treated with the ACE inhibitor (ACE-i) trandolapril (0.3 mg/kg b.w./day), and (4) 1C-2K rats treated with the ET(A)-RB LU-135252 (50 mg/kg b.w./day). BP was measured weekly by tail plethysmography. After 3 weeks, animals were sacrificed and cardiac, aortic and mesenteric artery morphology was evaluated using morphometric and stereological techniques.

RESULTS

Systolic BP was significantly higher in 1C-2K rats compared to sham. BP was not significantly affected by ET(A)-RB, but was significantly lowered by the ACE-i. Despite no significant change in BP, ET(A)-RB treatment led to a significantly less volume density of the cardiac interstitium (sham 1.40 +/- 0.18, 1C-2K 2.66 +/- 0.56, 1C-2K + ACE-i 1.88 +/- 0.38, 1C-2K + ET(A)-RB 2.15 +/- 0.37%). In contrast, ET(A)-RB had no significant effect on left ventricular/body weight ratio (sham 2.85 +/- 0.26, 1C-2K 2.96 +/- 0.33, 1C-2K + ACE-i 2.54 +/- 0.22 and 1C-2K + ET(A)-RB 3.15 +/- 0.44 mg/g) or on wall thickness of intramyocardial arteries.

CONCLUSIONS

The ET(A)-RB LU-135252 ameliorated the development of myocardial fibrosis in a short-term hyperreninemic normal salt model of experimental hypertension nearly as effectively as an ACE-i. This effect of LU-135252 is independent of systemic BP. In contrast to findings in other models, ET(A) receptor blockade had no significant effect on LVH or vascular remodeling. Only the ACE-i but not the ET(A)-RB prevented structural changes of small intramyocardial arteries and of the aorta.

Protection From Ischemic Heart Injury by a Vigilant Heme Oxygenase-1 Plasmid System

Although human heme oxygenase-1 (hHO-1) could provide a useful approach for cellular protection in the ischemic heart, constitutive overexpression of hHO-1 may lead to unwanted side effects. To avoid this, we designed a hypoxia-regulated hHO-1 gene therapy system that can be switched on and off. This vigilant plasmid system is composed of myosin light chain-2v promoter and a gene switch that is based on an oxygen-dependent degradation domain from the hypoxia inducible factor-1-alpha. The vector can sense ischemia and switch on the hHO-1 gene system, specifically in the heart. In an in vivo experiment, the vigilant hHO-1 plasmid or saline was injected intramyocardially into myocardial infarction mice or sham operation mice. After gene transfer, expression of hHO-1 was only detected in the ischemic heart treated with vigilant hHO-1 plasmids. Masson trichrome staining showed significantly fewer fibrotic areas in vigilant hHO-1 plasmids-treated mice compared with saline control (43.0%+/-4.8% versus 62.5%+/-3.3%, P<0.01). The reduction of interstitial fibrosis is accompanied by an increase in myocardial hHO-1 expression in peri-infarct border areas, concomitant with higher Bcl-2 levels and lower Bax, Bak, and caspase 3 levels in the ischemic myocardium compared with saline control. By use of a cardiac catheter, heart from vigilant hHO-1 plasmids-treated mice showed improved recovery of contractile and diastolic performance after myocardial infarction compared with saline control. This study documents the beneficial regulation and therapeutic potential of vigilant plasmid-mediated hHO-1 gene transfer. This novel gene transfer strategy can provide cardiac-specific protection from future repeated bouts of ischemic injury.

Effects of ACE Inhibition versus Non-ACE Inhibitor Antihypertensive Treatment on Myocardial Fibrosis in Patients with Arterial Hypertension

BACKGROUND AND PURPOSE

In experimental arterial hypertension, left ventricular hypertrophy (LVH) becomes pathologic with impaired myocardial function if myocardial fibrosis occurs. Myocardial fibrosis is associated with activated circulating or local renin-angiotensin-aldosterone systems. The primary objective of this retrospective study was to determine whether patients with arterial hypertension treated with angiotensin-converting enzyme inhibitors (ACEI) have less myocardial fibrosis than patients on non-ACEI treatment.

MATERIAL AND METHODS

We examined left ventricular (LV) endomyocardial biopsies of 97 consecutive patients with hypertensive heart disease due to primary hypertension treated with either any ACEI for at least 6 months (n = 34; HTN + ACEI) or non-ACEI antihypertensive drugs (n = 63; HTN). Normal hearts designated for heart transplantation served as controls (n = 23; CTR). Myocyte diameter (MyoD) and collagen volume fraction (CVF) were measured by morphometry, and pro-matrix metalloproteinases (proMMPs) 2 and 9 by zymography. In a subset of 35 patients, LV myocardial stiffness was determined by left heart catheterization with calculation of stiffness constant k.

RESULTS

In HTN + ACEI or HTN, MyoD (21.8 +/- 0.3 micro m and 22.4 +/- 0.3 micro m, respectively) and CVF (5.3 +/- 0.6% and 7.6 +/- 0.7%, respectively) were increased (p < 0.01) compared with CTR (16.0 +/- 0.4 micro m and 0.5 +/- 0.2%, respectively). In HTN + ACEI, CVF was significantly lower (p < 0.02) and proMMP 2 was higher (0.063 +/- 0.013 OD/mg) compared with HTN (0.037 +/- 0.006 OD/mg; p < 0.05) while no significant difference of MyoD was evident. We found no correlation between CVF and MyoD (r = 0.13; p = 0.47), a positive correlation between k and CVF (r = 0.71; p < 0.00001), and no correlation between k and MyoD (r = 0.22; p = 0.24).

CONCLUSION

In patients with hypertensive heart disease, myocyte hypertrophy and myocardial fibrosis are present. Myocardial fibrosis and not myocyte hypertrophy determines myocardial stiffness. ACEI appear to diminish myocardial fibrosis associated with enhanced collagen degradation irrespective of LVH regression.

Sub-Depressor Dose of Angiotensin Type-1 Receptor Blocker Inhibits Transforming Growth Factor-β-Mediated Perivascular Fibrosis in Hypertensive Rat Hearts

Recently, we have shown that pressure overload transiently induces transforming growth factor-beta-mediated fibroblast proliferation and reactive myocardial fibrosis that extends from the perivascular space. However, the upper stream event of transforming growth factor-beta induction has remained unknown. Thus, we sought to determine whether angiotensin II mediates the fibrotic process in pressure-overloaded hearts. Male Wistar rats were administered orally everyday 0.1 mg/kg per day of candesartan, an angiotensin type-1 receptor blocker, or the vehicle from Day 7, and underwent a suprarenal aortic constriction (AC) at Day 0. This dose was the maximum dose of candesartan that does not induce the depressor effect in AC rats. In AC+ vehicle (control) rats, pressure overload induced myocardial transforming growth factor-beta expression and perivascular fibroblast proliferation at Day 3 and thereafter left ventricular hypertrophy associated with cardiomyocyte hypertrophy and perivascular fibrosis. AC+ candesartan rats showed suppressed transforming growth factor-beta expression and reduced number of proliferating fibroblasts, while not changing arterial pressure. Furthermore, perivascular fibrosis, but not myocyte hypertrophy, was significantly inhibited associated with reduced collagen mRNA expression. In conclusion, angiotensin II may play a role in reactive myocardial fibrosis in pressure-overloaded hearts, through the mechanism independent of hemodynamic change.

Tissue Angiotensin-converting enzyme activity plays an important role in pressure overload-induced cardiac fibrosis in rats

It has been widely assumed that the cardiac angiotensin-generating system plays an important role in the development and maintenance of cardiac remodeling caused by pressure overload. The roles of angiotensin-converting enzyme (ACE) in pressure overload-induced cardiac hypertrophy and fibrosis in rats were investigated. Pressure overload was achieved by constricting the abdominal aorta above the renal arteries. After they underwent surgery, the rats were treated with a low or high dose of the ACE inhibitor imidapril (0.07 and 0.7 mg/kg/d s.c.) with an osmotic pump for 4 weeks. High-dose imidapril prevented the increase in blood pressure, cardiac hypertrophy, and fibrosis. Low-dose imidapril inhibited only cardiac fibrosis. ACE activity in the myocardium, but not in serum, was significantly increased in the rats with the banded aorta, and ACE immunoreactivity was increased in the areas of fibrosis. These changes were markedly reduced by both doses of imidapril. These results suggest that the increased local ACE expression contributes to the development of pressure overload-induced cardiac fibrosis but is not responsible for hypertrophy in rats.

Spironolactone and captopril attenuates isoproterenol-induced cardiac remodelling in rats

The role of renin-angiotensin-aldosterone system in cardiac remodelling was studied in isoproterenol-induced cardiac hypertrophy in rats. The effects of captopril and spironolactone were compared. Isoproterenol treatment increased ventricular to body weight ratio (4.6 vs 3.7) and collagen area (22.6 vs 8.2%), and reduced systolic (89.93 vs 107.5 mm Hg) and diastolic (59.6 vs 70.8 mm Hg) pressure. In these animals, captopril decreased systolic (67.4 mm Hg) and diastolic pressure (31.9 mm Hg), whereas spironolactone regressed systolic pressure to control values (101.2 mm Hg). Captopril and spironolactone prevented cardiac hypertrophy (4.01 and 3.95). However, only spironolactone prevented myocardial fibrosis (11.3%).

Low dose carvedilol inhibits progression of heart failure in rats with dilated cardiomyopathy

The cardioprotective properties of carvedilol (a vasodilating beta-adrenoceptor blocking agent) were studied in a rat model of dilated cardiomyopathy induced by autoimmune myocarditis. Twenty-eight days after immunization, surviving Lewis rats (32/43=74%) were divided into three groups to be given 2 mg kg(-1) day(-1) (Group-C2, n=10) or 20 mg kg(-1) day(-1) (Group-C20, n=10) of carvedilol, or vehicle (0.5% methylcellulose, Group-V, n=12). After oral administration for 2 months, body weight, heart weight (HW), heart rate (HR), rat alpha-atrial natriuretic peptide (r-ANP) in blood, central venous pressure (CVP), mean blood pressure (mean BP), peak left ventricular pressure (LVP), left ventricular end-diastolic pressure (LVEDP), +/-dP dt(-1) and area of myocardial fibrosis were measured. Values were compared with those for normal Lewis rats (Group-N, n=10). Two out of 12 (17%) rats in Group-V died from day 28 to day 42 after immunization. No rat died in Groups-C2, -C20 and -N. Although the CVP, mean BP, LVP and +/-dP dt(-1) did not differ among the three groups, the HW, HR and r-ANP in Group-C2 (1.14+/-0.03, 339+/-16 and 135+/-31) and Group-C20 (1.23+/-0.04, 305+/-8 and 156+/-24) were significantly lower than those in Group-V (1.36+/-0.04 g, 389+/-9 beats min(-1) and 375+/-31 pg ml(-1), respectively). The LVEDP in Group-C2 was significantly lower than that in Group-V (7.4+/-1.4 and 12.2+/-1.2 mmHg, respectively, P<0. 05). The area of myocardial fibrosis in Group-C2 was smaller than that in Group-V (12+/-1 and 31+/-2%, P<0.01). These results indicate that a low dose of carvedilol has beneficial effects on dilated cardiomyopathy.

Beta-adrenergic receptor blockade arrests myocyte damage and preserves cardiac function in the transgenic G(salpha) mouse

Transgenic (TG) mice with cardiac G(salpha) overexpression exhibit enhanced inotropic and chronotropic responses to sympathetic stimulation, but develop cardiomyopathy with age. We tested the hypothesis that cardiomyopathy in TG mice with G(salpha) overexpression could be averted with chronic beta-adrenergic receptor (beta-AR) blockade. TG mice and age-matched wild-type littermates were treated with the beta-AR blocker propranolol for 6-7 months, starting at a time when the cardiomyopathy was developing but was not yet severe enough to induce significant cardiac depression (9.5 months of age), and ending at a time when cardiac depression and cardiomyopathy would have been clearly manifest (16 months of age). Propranolol treatment, which can induce cardiac depression in the normal heart, actually prevented cardiac dilation and the depressed left ventricular function characteristic of older TG mice, and abolished premature mortality. Propranolol also prevented the increase in myocyte cross-sectional area and myocardial fibrosis. Myocyte apoptosis, already apparent in 9-month-old TG mice, was actually eliminated by chronic propranolol. This study indicates that chronic sympathetic stimulation over an extended period is deleterious and results in cardiomyopathy. Conversely, beta-AR blockade is salutary in this situation and can prevent the development of cardiomyopathy.

Pharmacologic agents on cardiovascular mass, coronary dynamics and collagen in aged spontaneously hypertensive rats

OBJECTIVE

To determine whether antihypertensive treatment could alter hypertension and age-related progressive impairment of coronary hemodynamics and cardiac fibrosis in aged spontaneously hypertensive rats (SHR).

DESIGN

Old SHR were given their respective therapy for 3 months. To differentiate between hypertension and age-related changes, a comparison was made between left and right ventricular indices since the right ventricle was not exposed to pressure overload.

METHODS

Male, 65-week-old spontaneously SHR were divided into three groups and were given either vehicle, felodipine (30 mg/kg per day) or enalapril (30 mg/kg per day). After 12 weeks of the respective treatments, systemic and coronary hemodynamics (radionuclide-labelled microspheres), right and left ventricular and aortic mass indices, and right and left ventricular hydroxyproline concentrations (an estimate of collagen) were determined.

RESULTS

Arterial pressure and total peripheral resistance were reduced to the same extent in SHRs treated with either felodipine or enalapril; however, compared to the control rats, enalapril was more effective in reducing left ventricular and aortic mass indices. Both agents also improved coronary hemodynamics of both ventricles in aged SHR but enalapril was more effective as indicated by a greater increase in coronary flow reserve and a greater decrease in minimal coronary vascular resistance. Furthermore, enalapril but not felodipine reduced left ventricular hydroxyproline concentration; and right ventricular hydroxyproline concentration increased with felodipine but remained unchanged with enalapril.

CONCLUSIONS

Both enalapril and felodipine ameliorated adverse cardiovascular effects of hypertension in the aged SHRs within 12 weeks, as demonstrated by reduced arterial pressure, diminished left ventricular mass, and improved coronary hemodynamics. Enalapril also decreased aortic mass and left ventricular collagen concentration and appeared to be more effective in improving coronary hemodynamics than felodipine, possibly as a result, in part, of reduced myocardial fibrosis.

Basic fibroblast growth factor increased regional myocardial blood flow and limited infarct size of acutely infarcted myocardium in dogs

Basic fibroblast growth factor (bFGF), a growth factor potent in promoting angiogenesis, has been shown to reduce infarct size in experimentally induced acute myocardial infarction. However, the effect of bFGF on regional myocardial blood flow (Qm) in the acutely infarcted myocardium has not been well clarified. In 20 open-chest dogs, the left anterior descending (LAD) coronary artery was occluded and animals were maintained in this condition for 4 weeks. In eight of these dogs, bFGF (300 microg) was injected into the myocardium supplied by the LAD and the artery was ligated (bFGF group), and in the other 12 dogs, saline was injected (control group). Nonradioactive colored microspheres were used to measure Qm. The amount of viable myocardium as percent of visual field in the microscope and the extent of fibrosis scored histologically from 0 to 5 in the infarcted area 4 weeks after occlusion were measured. In the outer layer, the Qm values immediately after and 4 weeks after occlusion were 26 +/- 2% and 70 +/- 6%, respectively, in the control group, and 46 +/- 5% and 121 +/- 13%, respectively, in the bFGF group. The Qm at both times in the bFGF group was significantly higher than the corresponding control group values (p < 0.01). The Qm at 4 weeks in the inner and the middle layers also significantly increased in the bFGF group. There was more viable myocardium (control vs bFGF group; 41 +/- 5 vs 61 +/- 7%, p < 0.05) and less fibrosis (3.1 +/- 0.2 vs 2.0 +/- 0.4, p < 0.01) at the outer layer in the bFGF group. It was found that bFGF caused a marked increase in Qm, an increase of viable myocardium, and a decrease of fibrosis in the infarcted myocardium in dogs.

Angiotensin converting enzyme inhibition modulates cardiac fibroblast growth

BACKGROUND

The progression of left ventricular hypertrophy and cardiac fibrosis in hypertensive heart disease is influenced by sex and age. Although angiotensin converting enzyme inhibition has been shown to prevent progression of the disease in postmenopausal women, the interaction of angiotensin II and estrogen in this process before and after the menopause is poorly understood.

OBJECTIVE

To investigate the influence of the angiotensin converting enzyme inhibitor moexiprilat on serum, estrogen and angiotensin II-induced cardiac fibroblast growth.

METHODS

Neonatal rat cardiac fibroblasts were incubated with 1 and 10% fetal calf serum, 10(-7) mol/l angiotensin II, 10(-9) mol/l estrone, 10(-9) mol/l 17beta-estradiol and 10(-8) mol/l moexiprilat. Proliferation was measured in terms of incorporation of bromodeoxyuridine. Western blot analysis was performed using antibodies directed against the growth-related immediate early genes c-fos and Sp-1. All experiments were performed at least three times.

RESULTS

Fetal calf serum stimulated cardiac fibroblast proliferation (1% fetal calf serum 2.0+/-0.028-fold; 10% fetal calf serum 2.7+/-0.028-fold). Angiotensin II and estrone stimulated proliferation of cardiac fibroblasts grown in the absence of fetal calf serum (angiotensin II 4.2+/-0.075-fold; estrone 2.9+/-0.034-fold) and further increased proliferation in the presence of 1% fetal calf serum (angiotensin 11 4.3+/-0.072-fold); estrone 3.8+/-0.045-fold) and 10% fetal calf serum (angiotensin II 4.8+/-0.112-fold; estrone 4.1+/-0.047-fold). Coincubation with moexiprilat specifically inhibited proliferation induced by angiotensin II and estrone but not by serum, and angiotensin II type 1 receptor blockade inhibited angiotensin II-induced but not estrone-induced cell growth. Western blot analysis showed that the expression of c-fos and Sp-1 was induced in a time-dependent fashion by angiotensin II (to maxima of 5.0-fold for c-fos and 3.0-fold for Sp-1) and estrone (15.2-fold for c-fos and 6.2-fold for Sp-1). This effect was completely inhibited by moexiprilat.

CONCLUSIONS

Angiotensin converting enzyme inhibition modulates cardiac fibroblast growth induced by angiotensin II and estrone. This mechanism might contribute to the beneficial effects of angiotensin converting enzyme inhibition in postmenopausal patients with hypertensive heart disease.

Aldosterone escape during ACE inhibitor therapy in chronic heart failure

In the setting of chronic heart failure (CHF), therapy with angiotensin converting enzyme (ACE) inhibitors generally reduces serum aldosterone levels acutely. However, long-term ACE inhibition is associated with aldosterone suppression that is weak, variable, and unsustained, i.e. aldosterone 'escape'. Magnesium loss caused by aldosterone and by diuretics can contribute to coronary artery spasm and arrhythmias. Aldosterone can block noradrenaline uptake by the myocardium; extracellular catecholamines may lead to arrhythmias and ischaemia. Aldosterone has been shown to have an acute arrhythmogenic effect as well as a potential detrimental effect on baroreflex function, a marker of prognosis in CHF. Both angiotensin II and aldosterone may stimulate myocardial fibrosis, which is associated with a higher incidence of malignant ventricular arrhythmias. ACE inhibition initiated early in the progression of CHF may prevent development of patchy myocardial fibrosis and its inherent arrhythmias and thus reduce the incidence of sudden death. Spironolactone therapy added to the regimen of an ACE inhibitor and diuretic can induce natriuresis and magnesium retention, increase myocardial noradrenaline uptake, and reduce the incidence of arrhythmias.

Systolic ventricular dysfunction and heart failure due to coronary microangiopathy in hypertensive heart disease

Left ventricular hypertrophy in arterial hypertension is characterized by myocyte hypertrophy, myocardial fibrosis, and structural changes of the intramural coronary arteries. Hypertensives with or without left ventricular hypertrophy have a reduced coronary vasodilator reserve due to alterations of the coronary microcirculation. The impairment in coronary vasodilator reserve is likely to initiate a process of malperfusion and malnutrition concomitant with increased metabolic demands. Further, malperfusion is supported by an increase in diastolic filling pressure, which will enhance the extravascular component of coronary resistance. The sum of interactions of these structural alterations of myocardium, interstitium, and coronary vasculature are likely to initiate and maintain a process of myocardial malperfusion and malnutrition, which can provoke functional depression of the myocardial performance, a loss of contractile proteins, an increase in interstitial fibrosis, and, not least, an overall decrease in contractile function in long-standing cardiac hypertrophy. Finally, the reversal of these processes by adequate antihypertensive treatment may contribute to renormalization of cardiac function and to prevention of late cardiac failure in hypertensive heart disease.

Trandolapril decreases prevalence of ventricular ectopic activity in middle-aged SHR

BACKGROUND

Although severe arrhythmias are still a major problem in patients with left ventricular hypertrophy (LVH), the relationship between ventricular remodeling and its regression or prevention, and the prevalence of ventricular premature beats (VPB) or more sustained arrhythmias are still poorly explored in hypertensive heart disease.

METHODS AND RESULTS

Holter monitoring was used to quantify supraventricular premature beats and VPB and heart rate (HR) in middle-aged spontaneously hypertensive rats (SHR) and Wistar rats treated for 3 months with trandolapril (ACE inhibitor, 0.3 mg/kg per day). Hypertrophy and fibrosis were morphometrically determined. Statistical analysis was performed with the use of simple regression and multivariate data analysis (cluster and correspondence analysis). SHR have higher cardiac mass and fibrosis, more VPB, and a decreased HR. Cluster analysis demonstrated that trandolapril was only effective in SHR. Trandolapril significantly reduced cardiac hypertrophy, fibrosis, and VPB incidence and increased the HR. Simple regression analysis showed that VPB incidence correlated to both hypertrophy and fibrosis. Correspondence analysis evidenced a strong correlation between hypertrophy, fibrosis, and VPB, but only for severe hypertrophy, and the correlation disappeared for moderate hypertrophy.

CONCLUSIONS

After trandolapril treatment, the regression of VPB incidence not only is linked to hypertrophy and fibrosis, but additional causal factors also are involved including the myocardial phenotype and new calcium metabolism. Our model of Holter monitoring in conscious middle-aged SHR and multivariate data analysis might be useful in correlating myocardial structural modifications and ectopic activity.

Protective effect of clentiazem against epinephrine-induced cardiac injury in rats

We investigated the effects of clentiazem, a 1,5-benzothiazepine calcium antagonist, on epinephrine-induced cardiomyopathy in rats. With 2-week chronic epinephrine infusion, 16 of 30 rats died within 4 days, and severe ischemic lesions and fibrosis of the left ventricles were observed. In epinephrine-treated rats, left atrial and left ventricular papillary muscle contractile responses to isoproterenol were reduced, but responses to calcium were normal or enhanced compared to controls. Left ventricular alpha and beta adrenoceptor densities were also reduced compared to controls. Treatment with clentiazem prevented epinephrine-induced death (P < .05), and attenuated the ventricular ischemic lesions and fibrosis, in a dose-dependent manner. Left atrial and left ventricular papillary muscle contractile responses to isoproterenol were reduced compared to controls in groups treated with clentiazem alone, but combined with epinephrine, clentiazem restored left atrial responses and enhanced left ventricular papillary responses to isoproterenol. On the other hand clentiazem did not prevent epinephrine-induced down-regulation of alpha and beta adrenoceptors. Interestingly, clentiazem, infused alone, resulted in decreased adrenergic receptor densities in the left ventricle. Clentiazem also did not prevent the enhanced responses to calcium seen in the epinephrine-treated animals, although the high dose of clentiazem partially attenuated the maximal response to calcium compared to epinephrine-treated animals. In conclusion, clentiazem attenuated epinephrine-induced cardiac injury, possibly through its effect on the adrenergic pathway.

Myocardial fibrosis: role of angiotensin II and aldosterone

In this report we review the replacement (i.e., scarring) and reactive (i.e., perivascular and interstitial fibrosis) fibrous tissue responses found in the myocardium in response to effector hormones of the renin-angiotensin-aldosterone system. Experimental data are presented to indicate: a) endogenous or exogenous elevations in plasma angiotensin II are associated with acute cardiac myocyte necrosis and subsequent microscopic scarring; b) chronic elevations in plasma aldosterone (ALDO), relative to Na+ intake, are associated with a perivascular and interstitial fibrosis of the coronary and systemic circulations and are also seen in response to chronic administration of the mineralocorticoid hormone deoxycorticosterone (DOC); and c) chronic mineralocorticoid excess, due to ALDO or DOC, is associated with enhanced urinary K+ excretion, cardiac myocyte necrosis and scarring. Pharmacologic agents which interfere with these effector hormones (e.g., ACE inhibition and ALDO receptor antagonism) protect the myocardium against this pathologic structural remodeling created by the reactive and replacement (reparative) fibrosis. Evidence is also presented to indicate that chronic ACE inhibition is associated with a regression in reactive myocardial fibrosis. Based on these experimental findings we would suggest that clinical trials are indicated to address the prevention and regression of myocardial fibrosis--an important determinant of pathologic structural remodeling and abnormal myocardial stiffness.

Ramipril prevents left ventricular hypertrophy with myocardial fibrosis without blood pressure reduction: a one year study in rats

1. Angiotensin converting enzyme (ACE)-inhibitors have been demonstrated to be effective in the treatment of cardiac hypertrophy when used in antihypertensive doses. The aim of our one year study with an ACE-inhibitor in rats was to separate local cardiac effects produced by a non-antihypertensive dose from those on systemic blood pressure when an antihypertensive dose was used. 2. Rats made hypertensive by aortic banding were subjected to chronic oral treatment for one year with an antihypertensive dose of the ACE inhibitor, ramipril 1 mg kg-1 daily, (RA 1 mg) or received a low dose of 10 micrograms kg-1 daily (RA 10 micrograms) which did not affect high blood pressure. 3. Chronic treatment with the ACE-inhibitor prevented left ventricular hypertrophy in the antihypertensive rats as did the low dose which had no effects on blood pressure. Similar effects were observed on myocardial fibrosis. Plasma ACE activity was inhibited in the RA 1 mg but not in the RA 10 micrograms group although conversion of angiotensin (Ang) I to Ang II in isolated aortic strips was suppressed in both treated groups. Plasma catecholamines were increased in the untreated control group, but treatment with either dose of ramipril normalized the values. The myocardial phosphocreatine to ATP ratio (an indicator of the energy state in the heart) was reduced in the vehicle control group whereas the hearts from treated animals showed a normal ratio comparable to hearts from sham-operated animals. 4. After one year, five animals were separated from each group, treatment withdrawn, and housed for additional six months. In the RA 1 mg group, blood pressure did not reach the value of the control vehicle group and surprisingly, left ventricular hypertrophy and myocardial fibrosis did not recur in animals during withdrawal of treatment.5. These data show that long term ACE inhibitor treatment with ramipril in antihypertensive and non-antihypertensive doses prevented cardiac hypertrophy and myocardial fibrosis. This protective effect was still present after 6 months treatment withdrawal.

Effect of captopril on the prevention and regression of myocardial cell hypertrophy and interstitial fibrosis in pressure overload cardiac hypertrophy

This article reports on the effects of captopril on both the prevention and the regression of myocardial cell hypertrophy and interstitial fibrosis in experimental animals (rats) with pressure overloaded hearts. Constriction of the abdominal aorta just below the diaphragm during periods of 20 days (prevention experiment) and 40 days (regression experiment) resulted in hypertension and cardiac hypertrophy. In the prevention experiment, captopril was able to inhibit the development of high blood pressure levels and cardiac hypertrophy in aortic-constricted rats. Similarly, the treatment of sham-operated rats with captopril led to a reduction in the weight of the heart and in the myocyte diameter compared with controls. The myocyte volume fraction of the left ventricles of both aortic-constricted and sham-operated animals that were treated with captopril was significantly diminished compared with that of the control group. The interstitial collagen volume fraction of all experimental groups was elevated as compared with the control group. As a consequence, the ratios of myocytes to interstitial collagen in groups of aortic-constricted rats, aortic-constricted rats that were treated with captopril, and sham-operated rats that were treated with captopril were reduced compared with the control group; that is, although captopril was able to prevent myocardial cell hypertrophy after aortic constriction, it could not prevent the maintenance of a normal ratio of myocytes to interstitial collagen, which was due to increased collagen volume fraction. In the regression experiment, captopril lowered high blood pressure levels and augmented heart weights to control values. The mean myocyte transverse diameter in aortic-constricted rats that were treated with captopril was significantly smaller than that of controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial fibrosis in aging germ-free and conventional Lobund-Wistar rats: the protective effect of diet restriction

The influences of diet restriction and germ-free environment on aging were studied in 127 male Lobund-Wistar rats ranging in age from 7 to 48 months. There was an age-related increase in collagen deposition of the heart, particularly involving the left ventricle. The degree of fibrosis was significantly less extensive in middle and old age rats (18 mo, 30 mo, 32+ mo) maintained on a restricted diet. No clear-cut influence of germ-free environment was apparent. No amyloid was detected in 175 tissue sections examined from hearts, lungs, and livers.

Enalapril prevents cardiac fibrosis and arrhythmias in hypertensive rats

To evaluate the effects of hypertension on cardiac hypertrophy, on myocardial structure, and on ventricular arrhythmias, 27 3-month-old spontaneously hypertensive rats were treated with enalapril (10 mg/kg) daily for 11 months and compared with 26 untreated control rats. Systolic arterial pressure was significantly decreased in treated rats, and at the end of the experiment, it was 199 +/- 3 mm Hg (treated) versus 237 +/- 3 mm Hg (controls) (p less than 0.001). At this time, spontaneous arrhythmias and induced arrhythmias either by programmed electrical stimulation (train of stimuli +1 or 2 extrastimuli) or by trains of eight stimuli at decreasing coupling intervals were observed in isolated heart preparations. Comparing enalapril-treated and control rats, spontaneous arrhythmias (9 of 27 versus 20 of 26, respectively; p less than 0.01), programmed stimulation-induced arrhythmias (3 of 26 versus 12 of 23, respectively; p less than 0.01), and trains of stimuli-induced arrhythmias (4 of 26 versus 14 of 19, respectively, p less than 0.001) were less frequent in the enalapril group. Left ventricular weight was decreased in treated rats by 18% (p less than 0.001). Enalapril administration diminished the fraction of myocardium occupied by foci of replacement fibrosis normally occurring in control rats by 59% (p less than 0.001). Finally, a significant correlation was found between left ventricular weight, the extent of myocardial fibrosis, and the occurrence of ventricular fibrillation. It was concluded that chronic treatment with enalapril, which resulted in attenuation of systemic arterial pressure by limiting cardiac hypertrophy and myocardial fibrosis, decreases the propensity of the heart of hypertensive rats to arrhythmogenesis.

[Antihypertensive effect of bopindolol on stroke-prone spontaneously hypertensive rats (SHRSP)]

The antihypertensive effect of bopindolol, a long-acting beta-adrenoceptor blocking agent, was investigated in stroke-prone spontaneously hypertensive rats (SHRSP). One group received tap water during the period of 8 to 32 weeks of age. The average dose of bopindolol administered was calculated from water intake to be approximately 1.4 mg/kg/day. The lowering effect in blood pressure of bopindolol was apparent at the age of 14 weeks, and this continued up to the end of the experiment. Bopindolol significantly reduced the heart rate. Plasma levels of urea nitrogen (BUN), triglyceride, and phospholipid of SHRSP treated with bopindolol were lower than those of the control SHRSP. One of the 8 control SHRSP died, and no rats treated with bopindolol died during the experiment. The histopathological study revealed that three of the control SHRSP had cerebral apoplexy, whereas there was no evidence of cerebral apoplexy in the treated SHRSP. Chronic treatment of bopindolol clearly alleviated myocardial fibrosis and hypertrophic changes in the left ventricular wall of the heart. Decreases in the incidence of proliferative arteritis and malignant nephrosclerosis in the kidney and necrotizing arteritis of the mesenteric arteries were observed in SHRSP treated with bopindolol. The data presented indicate that bopindolol is a powerful antihypertensive agent.