Anastassia Todor

Reversal of Chronic Molecular and Cellular Abnormalities Due to Heart Failure by Passive Mechanical Ventricular Containment

Abstract— Passive mechanical containment of failing left ventricle (LV) with the Acorn Cardiac Support Device (CSD) was shown to prevent progressive LV dilation in dogs with heart failure (HF) and increase ejection fraction. To examine possible mechanisms for improved LV function with the CSD, we examined the effect of CSD therapy on the expression of cardiac stretch response proteins, myocyte hypertrophy, sarcoplasmic reticulum Ca2+-ATPase activity and uptake, and mRNA gene expression for myosin heavy chain (MHC) isoforms. HF was produced in 12 dogs by intracoronary microembolization. Six dogs were implanted with the CSD and 6 served as concurrent controls. LV tissue from 6 normal dogs was used for comparison. Compared with normal dogs, untreated HF dogs showed reduced cardiomyocyte contraction and relaxation, upregulation of stretch response proteins (p21ras, c-fos, and p38 &agr;/&bgr; mitogen-activated protein kinase), increased myocyte hypertrophy, reduced SERCA2a activity with unchanged affinity for calcium, reduced proportion of mRNA gene expression for &agr;-MHC, and increased proportion of &bgr;-MHC. Therapy with the CSD was associated with improved cardiomyocyte contraction and relaxation, downregulation of stretch response proteins, attenuation of cardiomyocyte hypertrophy, increased affinity of the pump for calcium, and restoration of &agr;- and &bgr;-MHC isoforms ratio. The results suggest that preventing LV dilation and stretch with the CSD promotes downregulation of stretch response proteins, attenuates myocyte hypertrophy and improves SR calcium cycling. These data offer possible mechanisms for improvement of LV function after CSD therapy.

Chronic therapy with metoprolol attenuates cardiomyocyte apoptosis in dogs with heart failure.

OBJECTIVES The purpose of this study was to determine if therapy with beta-blockade is associated with reduced cardiomyocyte apoptosis. BACKGROUND Chronic treatment with beta-adrenergic blocking agents has been shown to improve left ventricular (LV) ejection fraction and attenuate progressive LV remodeling in heart failure (HF). Cardiomyocyte apoptosis has also been shown to occur in the failing heart. METHODS Moderate HF was produced in 14 dogs by intracoronary microembolizations. Dogs were randomized to three months therapy with metoprolol (MET, 25 mg twice daily, n = 7) or to no therapy at all (n = 7). At the end of three months, dogs were sacrificed, and nuclear DNA fragmentation (nDNAf), a marker of apoptosis, was assessed in LV tissue using the TUNEL assay. The number of cardiomyocytes with positive nDNAf labeling per 1,000 was quantified in LV regions bordering old infarcts and in regions remote from infarcts. Endonuclease activity and expression of the antiapoptotic protein Bcl-2 and the proapoptotic proteins Bax and caspase-3 were also evaluated in LV tissue. RESULTS The number of nDNAf events per 1,000 cardiomyocytes was lower in dogs treated with MET compared with untreated dogs with HF in the border regions (0.35 +/- 0.07 vs. 5.32 +/- 0.77, p < 0.001) as well as the remote regions (0.07 +/- 0.05 vs. 0.39 +/- 0.12, p < 0.05). Endonuclease activity was also significantly lower in MET-treated compared with untreated dogs (25 +/- 3 vs. 37 +/- 2 ng [3H]DNA rendered soluble/min/mg protein). Western blotting for Bcl-2, Bax and caspase-3 showed increased expression of Bcl-2, decreased expression of caspase-3 and no change in Bax in MET-treated compared with untreated dogs. CONCLUSIONS Chronic therapy with MET attenuates cardiomyocyte apoptosis in dogs with moderate HF. Attenuation of ongoing cardiomyocyte loss through apoptosis may be one mechanism through which beta-blockers elicit their benefits in HF.

Effects of long-term therapy with bosentan on the progression of Left ventricular dysfunction and remodeling in dogs with heart failure

OBJECTIVES In this study, we examined the effects of long-term therapy with bosentan on the progression of LV dysfunction and remodeling in dogs with moderate HF. BACKGROUND Acute intravenous administration of bosentan, a mixed endothelin-1 type A and type B receptor antagonist, was shown to improve left ventricular (LV) function in patients and dogs with heart failure (HF). METHODS Left ventricular dysfunction was induced by multiple, sequential intracoronary microembolizations in 14 dogs. Embolizations were discontinued when LV ejection fraction (EF) was between 30% and 40%. Dogs were randomized to three months of therapy with bosentan (30 mg/kg twice daily, n = 7) or no therapy at all (control, n = 7). RESULTS In untreated dogs, EF decreased from 35 +/- 1% before initiating therapy to 29 +/- 1% at the end of three months of therapy (p = 0.001), and LV end-diastolic volume (EDV) and end-systolic volume (ESV) increased (EDV: 71 +/- 3 vs. 84 +/- 8 ml, p = 0.08; ESV: 46 +/- 2 vs. 60 +/- 6 ml, p = 0.03). By contrast, in dogs treated with bosentan, EF tended to increase from 34 +/- 2% before initiating therapy to 39 +/- 1% at the end of three months of therapy (p = 0.06), and EDV and ESV decreased (EDV: 75 +/- 3 vs. 71 +/- 4 ml, p = 0.05; ESV: 48 +/- 2 vs. 43 +/- 3 ml, p = 0.01). Furthermore, compared with untreated dogs, dogs treated with bosentan showed significantly less LV cardiomyocyte hypertrophy and LV volume fraction of interstitial fibrosis. CONCLUSIONS In dogs with moderate HF, long-term therapy with bosentan prevents the progression of LV dysfunction and attenuates LV chamber remodeling. The findings support the use of mixed endothelin-1 receptor antagonists as adjuncts to the long-term treatment of HF.

Hypoxia, angiotensin-II, and norepinephrine mediated apoptosis is stimulus specific in canine failed cardiomyocytes: a role for p38 MAPK, Fas-L and cyclin D1.

Apoptosis may contribute to the myocardial dysfunction associated with heart failure (HF). Activation of the p38 MAPK cascade can induce apoptosis in non‐cardiac cells through increased expression of Fas‐L, or through decreased expression of cyclin D1.

Inhibition of mitochondrial permeability transition pores by cyclosporine A improves cytochrome C oxidase function and increases rate of ATP synthesis in failing cardiomyocytes.

Background: We previously showed that mitochondrial respiratory function is abnormal in dogs with chronic heart failure (HF). Mitochondrial permeability transition pores (MPTP) can affect mitochondrial inner membrane potential (Δ < eqid1 > m) and mitochondrial function in normal cardiomyocytes. The potential impact of MPTP on Δ < eqid2 > m and mitochondrial respiratory function in HF has not yet been determined. We tested the hypothesis that cyclosporine A, a potent blocker of the MPTP, can improve mitochondrial function in HF. Methods: Cardiomyocytes were isolated from the left ventricular myocardium of 7 dogs with HF produced by intracoronary microembolizations and from 7 normal dogs. Cardiomyocytes were treated for 24 hours with cyclosporine A. Δ < eqid3 > m, cytochrome c oxidase protein expression, mitochondrial cytochrome c oxidase-dependent respiration (CDOR) and ATP synthesis were measured. Results: Δ < eqid4 > m, protein expression of cytochrome c oxidase, CDOR and the rate of ATP synthesis were decreased in HF compared to normal controls. Inhibition of MPTP in failing cardiomyocytes with low dose of cyclosporine A (0.2 μM) increased Δ < eqid5 > m, preserved expression of cytochrome c oxidase, improved CDOR and the rate of ATP synthesis. Conclusion: MPTP opening contributes to the loss of mitochondrial function observed in the failing heart. Inhibition of MPTP opening represents a potential therapeutic target for the treatment of HF.

Effects of the AT1-receptor antagonist eprosartan on the progression of left ventricular dysfunction in dogs with heart failure.

We examined the effects of eprosartan, an AT1 receptor antagonist, on the progression of left ventricular (LV) dysfunction and remodelling in dogs with heart failure (HF) produced by intracoronary microembolizations (LV ejection fraction, EF 30 to 40%). Dogs were randomized to 3 months of oral therapy with low‐dose eprosartan (600 mg once daily, n=8), high‐dose eprosartan (1200 mg once daily, n=8), or placebo (n=8). In the placebo group, LV end‐diastolic (EDV) and end‐systolic (ESV) volumes increased after 3 months (68±7 vs 82±9 ml, P<0.004, 43±1 vs 58±7 ml, P<0.003, respectively), and EF decreased (37±1 vs 29±1%, P<0.001). In dogs treated with low‐dose eprosartan, EF, EDV, and ESV remained unchanged over the course of therapy, whereas in dogs treated with high‐dose eprosartan, EF increased (38±1 vs 42±1%, P<0.004) and ESV decreased (41±1 vs 37±1 ml, P<0.006), Eprosartan also decreased interstitial fibrosis and cardiomyocyte hypertrophy. We conclude that eprosartan prevents progressive LV dysfunction and attenuates progressive LV remodelling in dogs with moderate HF and may be useful in treating patients with chronic HF.

Effects of Chronic Neutral Endopeptidase Inhibition on the Progression of Left Ventricular Dysfunction and Remodeling in Dogs with Moderate Heart Failure

AbstractBackground. The diuretic actions of endogenously produced atrial natriuretic factor (ANF) may be beneficial in the treatment of chronic heart failure (CHF). Neutral endopeptidase (NEP) is the primary enzyme responsible for the degradation of ANF. The present study investigates the effects of long-term NEP inhibition on the progression of left ventricular (LV) dysfunction and remodeling in dogs with moderate heart failure. Methods. LV dysfunction was produced in 12 dogs by multiple sequential intracoronary microembolizations. Embolizations were discontinued when LV ejection fraction (EF) was between 30–40%. Two weeks after the last embolization, dogs were randomized to 3 months of oral therapy with the NEP inhibitor ecadotril (100 mg, once daily, n = 6) or to no therapy at all (control, n = 6). Results. During the 3 months of follow-up, LV EF in control dogs decreased from 37 ± 1% to 28 ± 1% (P < 0.01) and LV end-diastolic volume (EDV) and end-systolic volume (ESV) increased (EDV: 72 ± 3 vs. 84 ± 5 ml, P < 0.01); ESV: 45 ± 1 vs. 60 ± 4 ml, P < 0.01). In dogs treated with ecadotril, LV EF (34 ± 1% vs. 37 ± 2%), EDV (79± 5 vs. 78± 6 ml) and ESV (52 ± 3 vs. 49 ± 4) remained essentially unchanged after 3 months of therapy. Histomorphometric measurements at the termination of the study showed that ecadotril was associated with significantly reduced cardiomyocyte hypertrophy compared to control. Conclusion. Early, long-term NEP inhibition with ecadotril prevents the progression of LV dysfunction and attenuates progressive LV remodeling in dogs with moderate heart failure.