Victor G. Sharov

Effects of angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor antagonists in rats with heart failure. Role of kinins and angiotensin II type 2 receptors.

Angiotensin-converting enzyme inhibitors (ACEi) improve cardiac function and remodeling and prolong survival in patients with heart failure (HF). Blockade of the renin-angiotensin system (RAS) with an angiotensin II type 1 receptor antagonist (AT1-ant) may have a similar beneficial effect. In addition to inhibition of the RAS, ACEi may also act by inhibiting kinin destruction, whereas AT1-ant may block the RAS at the level of the AT1 receptor and activate the angiotensin II type 2 (AT2) receptor. Using a model of HF induced by myocardial infarction (MI) in rats, we studied the role of kinins in the cardioprotective effect of ACEi. We also investigated whether an AT1-ant has a similar effect and whether these effects are partly due to activation of the AT2 receptor. Two months after MI, rats were treated for 2 mo with: (a) vehicle; (b) the ACEi ramipril, with and without the B2 receptor antagonist icatibant (B2-ant); or (c) an AT1-ant with and without an AT2-antagonist (AT2-ant) or B2-ant. Vehicle-treated rats had a significant increase in left ventricular end-diastolic (LVEDV) and end-systolic volume (LVESV) as well as interstitial collagen deposition and cardiomyocyte size, whereas ejection fraction was decreased. Left ventricular remodeling and cardiac function were improved by the ACEi and AT1-ant. The B2-ant blocked most of the cardioprotective effect of the ACEi, whereas the effect of the AT1-ant was blocked by the AT2-ant. The decreases in LVEDV and LVESV caused by the AT1-ant were also partially blocked by the B2-ant. We concluded that (a) in HF both ACEi and AT1-ant have a cardioprotective effect, which could be due to either a direct action on the heart or secondary to altered hemodynamics, or both; and (b) the effect of the ACEi is mediated in part by kinins, whereas that of the AT1-ant is triggered by activation of the AT2 receptor and is also mediated in part by kinins. We speculate that in HF, blockade of AT1 receptors increases both renin and angiotensins; these angiotensins stimulate the AT2 receptor, which in turn may play an important role in the therapeutic effect of the AT1-ant via kinins and other autacoids.

Fish oil, but not flaxseed oil, decreases inflammation and prevents pressure overload-induced cardiac dysfunction

AIMS Clinical studies suggest that intake of omega-3 polyunsaturated fatty acids (omega-3 PUFA) may lower the incidence of heart failure. Dietary supplementation with omega-3 PUFA exerts metabolic and anti-inflammatory effects that could prevent left ventricle (LV) pathology; however, it is unclear whether these effects occur at clinically relevant doses and whether there are differences between omega-3 PUFA from fish [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] and vegetable sources [alpha-linolenic acid (ALA)]. METHODS AND RESULTS We assessed the development of LV remodelling and pathology in rats subjected to aortic banding treated with omega-3 PUFA over a dose range that spanned the intake of humans taking omega-3 PUFA supplements. Rats were fed a standard food or diets supplemented with EPA+DHA or ALA at 0.7, 2.3, or 7% of energy intake. Without supplementation, aortic banding increased LV mass and end-systolic and -diastolic volumes. ALA supplementation had little effect on LV remodelling and dysfunction. In contrast, EPA+DHA dose-dependently increased EPA and DHA, decreased arachidonic acid in cardiac membrane phospholipids, and prevented the increase in LV end-diastolic and -systolic volumes. EPA+DHA resulted in a dose-dependent increase in the anti-inflammatory adipokine adiponectin, and there was a strong correlation between the prevention of LV chamber enlargement and plasma levels of adiponectin (r = -0.78). Supplementation with EPA+DHA had anti-aggregatory and anti-inflammatory effects as evidenced by decreases in urinary thromboxane B(2) and serum tumour necrosis factor-alpha. CONCLUSION Dietary supplementation with omega-3 PUFA derived from fish, but not from vegetable sources, increased plasma adiponectin, suppressed inflammation, and prevented cardiac remodelling and dysfunction under pressure overload conditions.

Passive epicardial containment prevents ventricular remodeling in heart failure.

BACKGROUND We examined the effects of passive containment of the cardiac ventricles with a surgically placed epicardial prosthetic wrap on indexes of left ventricular (LV) remodeling in dogs with heart failure. METHODS Heart failure (LV ejection fraction 30% to 40%) was produced in 12 dogs by intracoronary microembolization. Six dogs underwent mid-sternotomy and pericardiotomy with placement of a preformed-knitted polyester device (Acorn Cardiac Support Device [CSD], Acorn Cardiovascular, Inc, St. Paul, MN) snugly around the ventricles and anchored to the atrioventricular groove. Six dogs did not undergo surgery and served as controls. Dogs were followed for 3 months prior to sacrifice. RESULTS In controls, LV end-diastolic volume increased after 3 months (67 +/- 12 versus 83 +/- 8 ml; p = 0.04), while in CSD-treated dogs, it decreased (68 +/- 10 versus 61 +/- 10 ml; p = 0.002). CSD-containment of LV size was associated with increased LV systolic fractional area of shortening, while in controls, fractional area of shortening decreased. CSD-treated dogs also showed amelioration of myocyte hypertrophy and attenuation of interstitial fibrosis compared to controls. CONCLUSIONS In dogs with heart failure, passive epicardial containment of the ventricles with the Acorn CSD ameliorates LV remodeling and improves LV systolic function.

Effects of ACE inhibition on cardiomyocyte apoptosis in dogs with heart failure

Cardiomyocyte apoptosis or programmed cell death has been shown to occur in end-stage explanted failed human hearts and in dogs with chronic heart failure (HF). We tested the hypothesis that early long-term monotherapy with an angiotensin-converting enzyme (ACE) inhibitor attenuates cardiomyocyte apoptosis in dogs with moderate HF. Left ventricular (LV) dysfunction (ejection fraction 30-40%) was produced in dogs by multiple sequential intracoronary microembolizations. Dogs were randomized to 3 mo of therapy with enalapril (Ena, 10 mg twice daily, n = 7) or to no therapy at all (control, n = 7). After 3 mo of therapy, dogs were euthanized and the hearts removed. Presence of nuclear DNA fragmentation (nDNAf), a marker of apoptosis, was assessed in frozen LV sections using the immunohistochemical deoxynucleotidal transferase-mediated dUTP-digoxigenin nick-end labeling (TUNEL) method. Sections were also stained with ventricular anti-myosin antibody to identify cells of cardiocyte origin. From each dog, 80 fields (×40) were selected at random, 40 from LV regions bordering old infarcts and 40 from LV regions remote from any infarcts, for quantifying the number of cardiomyocyte nDNAf events per 1,000 cardiomyocytes. The average number of cardiomyocyte nDNAf events per 1,000 cardiomyocytes was significantly lower in Ena-treated dogs compared with controls (0.81 ± 0.13 vs. 2.65 ± 0.81, P < 0.029). This difference was due to a significantly lower incidence of cardiomyocyte nDNAf events in LV regions bordering scarred tissue (infarcts) in Ena-treated dogs compared with controls. We conclude that early long-term Ena therapy attenuates cardiomyocyte apoptosis in dogs with moderate HF. Attenuation of cardiomyocyte apoptosis may be one mechanism by which ACE inhibitors preserve global LV function in HF.

Low Carbohydrate/High-Fat Diet Attenuates Cardiac Hypertrophy, Remodeling, and Altered Gene Expression in Hypertension

The effects of dietary fat intake on the development of left ventricular hypertrophy and accompanying structural and molecular remodeling in response to hypertension are not understood. The present study compared the effects of a high-fat versus a low-fat diet on development of left ventricular hypertrophy, remodeling, contractile dysfunction, and induction of molecular markers of hypertrophy (ie, expression of mRNA for atrial natriuretic factor and myosin heavy chain β). Dahl salt-sensitive rats were fed either a low-fat (10% of total energy from fat) or a high-fat (60% of total energy from fat) diet on either low-salt or high-salt (6% NaCl) chow for 12 weeks. Hearts were analyzed for mRNA markers of ventricular remodeling and activities of the mitochondrial enzymes citrate synthase and medium chain acyl-coenzyme A dehydrogenase. Similar levels of hypertension were achieved with high-salt feeding in both diet groups (systolic pressure of ≈190 mm Hg). In hypertensive rats fed low-fat chow, left ventricular mass, myocyte cross-sectional area, and end-diastolic volume were increased, and ejection fraction was decreased; however, these effects were not observed with the high-fat diet. Hypertensive animals on low-fat chow had increased atrial natriuretic factor mRNA, myosin heavy chain isoform switching (α to β), and decreased activity of citrate synthase and medium chain acyl-coenzyme A dehydrogenase, which were all attenuated by high-fat feeding. In conclusion, increased dietary lipid intake can reduce cardiac growth, left ventricular remodeling, contractile dysfunction, and alterations in gene expression in response to hypertension.

Ranolazine combined with enalapril or metoprolol prevents progressive LV dysfunction and remodeling in dogs with moderate heart failure

Acute intravenous infusion of ranolazine (Ran), an anti-ischemic/antiangina drug, was previously shown to improve left ventricular (LV) ejection fraction (EF) without a concomitant increase in myocardial oxygen consumption in dogs with chronic heart failure (HF). This study examined the effects of treatment with Ran alone and in combination with metoprolol (Met) or enalapril (Ena) on LV function and remodeling in dogs with HF. Dogs (n = 28) with microembolization-induced HF were randomized to 3 mo oral treatment with Ran alone [375 mg twice daily (bid); n = 7], Ran (375 mg bid) in combination with Met tartrate (25 mg bid; n = 7), Ran (375 mg bid) in combination with Ena (10 mg bid; n = 7), or placebo (PL; Ran vehicle bid; n = 7). Ventriculographic measurements of LV end-diastolic volume (EDV) and end-systolic volume (ESV) and LV EF were obtained before treatment and after 3 mo of treatment. In PL-treated dogs, EDV and ESV increased significantly. Ran alone prevented the increase in EDV and ESV seen in the PL group and significantly increased EF, albeit modestly, from 35 +/- 1% to 37 +/- 2%. When combined with either Ena or Met, Ran prevented the increase in EDV, significantly decreased ESV, and markedly increased EF compared with those of PL. EF increased from 35 +/- 1% to 40 +/- 1% with Ran + Ena and from 34 +/- 1% to 41 +/- 1% with Ran + Met. Ran alone or in combination with Ena or Met was also associated with beneficial effects at the cellular level on histomorphometric parameters such as hypertrophy, fibrosis, and capillary density as well as the expression for pathological hypertrophy and Ca2+ cycling genes. In conclusion, Ran prevented progressive LV dysfunction and global and cellular myocardial remodeling, and Ran in combination with Ena or Met improved LV function beyond that observed with Ran alone.

Effects of Dopamine β-Hydroxylase Inhibition With Nepicastat on the Progression of Left Ventricular Dysfunction and Remodeling in Dogs With Chronic Heart Failure

Background—Inhibition of dopamine β-hydroxylase (DBH) results in a decrease in norepinephrine synthesis. The present study was a randomized, blinded, placebo-controlled investigation of the long-term effects of therapy with the DBH inhibitor nepicastat (NCT) on the progression of left ventricular (LV) dysfunction and remodeling in dogs with chronic heart failure (HF). Methods and Results—Moderate HF (LV ejection fraction [LVEF] 30% to 40%) was produced in 30 dogs by intracoronary microembolization. Dogs were randomized to low-dose NCT (0.5 mg/kg twice daily, n=7) (L-NCT), high-dose NCT (2 mg/kg twice daily, n=7) (H-NCT), L-NCT plus enalapril (10 mg twice daily, n=8) (L-NCT+ENA), or placebo (PL, n=8). Transmyocardial (coronary sinus–arterial) plasma norepinephrine (tNEPI), LVEF, end-systolic volume, and end-diastolic volume were measured before and 3 months after initiating therapy. tNEPI levels were higher in PL compared with NL (86±20 versus 13±14 pg/mL, P<0.01). L-NCT alone and L-NCT+ENA reduced tNEPI t...

Reverse changes in cardiac substrate oxidation in dogs recovering from heart failure.

When recovering from heart failure (HF), the myocardium displays a marked plasticity and can regain normal gene expression and function; however, recovery of substrate oxidation capacity has not been explored. We tested whether cardiac functional recovery is matched by normalization of energy substrate utilization during post-HF recovery. HF was induced in dogs by pacing the left ventricle (LV) at 210-240 beats/min for 4 wk. Tachycardia was discontinued, and the heart was allowed to recover. An additional group was studied in HF, and healthy dogs served as controls (n = 8/group). Cardiac free fatty acids (FFAs) and glucose oxidation were measured with [3H]oleate and [14C]glucose. At 10 days of recovery, hemodynamic parameters returned to control values; however, the contractile response to dobutamine remained depressed, LV end-diastolic volume was 28% higher than control, and the heart mass-to-body mass ratio was increased (9.8 +/- 0.4 vs. 7.5 +/- 0.2 g/kg, P < 0.05). HF increased glucose oxidation (76.8 +/- 19.7 nmol.min(-1).g(-1)) and decreased FFA oxidation (20.7 +/- 6.4 nmol.min(-1).g(-1)), compared with normal dogs (24.5 +/- 6.3 and 51.7 +/- 9.6 nmol.min(-1).g(-1), respectively), and reversed to normal values at 10 days of recovery (25.4 +/- 6.0 and 46.6 +/- 6.7 nmol.min(-1).g(-1), respectively). However, similar to HF, the recovered dogs failed to increase glucose and fatty acid uptake in response to pacing stress. The activity of myocardial citrate synthase and aconitase was significantly decreased during recovery compared with that in control dogs (58 and 27% lower, respectively, P < 0.05), indicating a persistent reduction in mitochondrial oxidative capacity. In conclusion, cardiac energy substrate utilization is normalized in the early stage of post-HF recovery at baseline, but not under stress conditions.

Expression of cytoskeletal, linkage and extracellular proteins in failing dog myocardium.

In the setting of chronic heart failure (HF), progressive left ventricular (LV) dysfunction and chamber remodeling may be due, in part, to altered expression and disorganization of cytoskeletal, linkage and extracellular proteins. This brief review describes changes in expression of cytoskeletal, linkage and extracellular protein using LV tissue obtained from dogs with progressive HF produced by multiple sequential intracoronary microembolizations. LV tissue samples from 6 untreated HF dogs (LV ejection fraction 20% to 25%) and 3 normal dogs were used. Sections from freshly frozen tissue were prepared, immunostained for specific proteins and studies by confocal microscopy. In failing hearts, confocal microscopy showed disorganization of key cytoskeletal proteins that, when combined with the loss of myofilaments and sarcomeric skeleton, suggest substantial cardiomyocyte remodeling. Cardiomyocytes in areas bordering old infarcts invariably exhibited disorganization of α-actinin. The cytoskeleton protein desmin showed increased expression in areas of extensive fibrosis. Staining for pancadherin showed interruptions of intercalated disks in areas of intensive interstitial fibrosis. Observation of increased fibronectin and increased interstitial cellularity based on vimentin labeling is suggestive of ongoing fibrosis. Based on these findings, we conclude that the structural changes observed in failing LV myocardium of dogs with intracoronary microembolizations-induced HF are extensive and typical of those seen and previously described in LV myocardium of explanted failed human hearts. The observed structural changes in this experimental model of HF also support the notion that these cytoskeletal, linkage and extracellular disorganization of structural proteins may be important maladaptations that contribute, albeit in part, to the progression of LV dysfunction and remodeling characteristic of the HF state.

Atenolol Is Inferior to Metoprolol in Improving Left Ventricular Function and Preventing Ventricular Remodeling in Dogs with Heart Failure

Objectives: β-Blockers are standard therapy for patients with heart failure (HF). This study compared the effects of chronic monotherapy with 2 different β1-selective adrenoceptor blockers, namely atenolol and metoprolol succinate, on left ventricular (LV) function and remodeling in dogs with coronary microembolization-induced HF [LV ejection fraction (EF) 30–40%]. Methods: Twenty HF dogs were randomized to 3 months of therapy with atenolol (50 mg once daily, n = 6), metoprolol succinate (100 mg, once daily, n = 7) or to no therapy (control, n = 7). LV EF and volumes were measured before initiating therapy and after 3 months of therapy. The change (Δ) in EF and volumes between measurements before and after therapy was calculated and compared among study groups. Results: In controls, EF decreased and end-systolic volume increased. Atenolol prevented the decrease in EF and the increase in ESV. In contrast, metoprolol succinate significantly increased EF and decreased end-systolic volume. ΔEF was significantly higher and Δend-systolic volume significantly lower in metoprolol succinate-treated dogs compared to atenolol-treated dogs (EF: 6.0 ± 0.86% vs. 0.8 ± 0.85%, p < 0.05; end-systolic volume: –4.3 ± 0.81 ml vs. –1 ± 0.52 ml, p <0.05). Conclusions: In HF dogs, chronic therapy with atenolol does not elicit the same LV function and remodeling benefits as those achieved with metoprolol succinate.