Atta U. Shahbaz

FIBROSIS IN HYPERTENSIVE HEART DISEASE: MOLECULAR PATHWAYS AND CARDIOPROTECTIVE STRATEGIES

Fibrosis is a fundamental component of the adverse structural remodelling of myocardium found in hypertensive heart disease (HHD). A replacement fibrosis appears at sites of previous cardiomyocyte necrosis to preserve the structural integrity of the myocardium. Such scarring has adverse functional consequences. The extensive distribution of fibrosis involving the right and left heart suggests cardiomyocyte necrosis is widespread. Together, the loss of these contractile elements and fibrous tissue deposition in the form of stiff in-series and in-parallel elastic elements contribute to the progressive failure of this normally efficient muscular pump. Pathogenic mechanisms modulating fibrous tissue formation at sites of repair include auto/paracrine properties of locally generated angiotensin II and endothelin-1. This study focuses on the signal-transducer–effector pathway involved in cardiomyocyte necrosis and the crucial pathogenic role of intracellular calcium overloading, and the subsequent induction of oxidative stress originating within its mitochondria that dictates the opening of the mitochondrial permeability transition pore. The ensuing osmotic destruction of these organelles is followed by necrotic cell death. It is now further recognized that calcium overloading of cardiac myocytes and mitochondria functioning as pro-oxidant is pathophysiologically counterbalanced by an intrinsically coupled zinc entry, which serves as an antioxidant. The prospect of raising intracellular zinc by adjuvant nutriceutical supplementation can, therefore, be preferentially exploited to uncouple this intrinsically coupled calcium–zinc dyshomeostasis in favour of endogenous antioxidant defences. Novel cardioprotective strategies may thus be at hand and deserve to be explored further in the overall management of patients with HHD.

Temporal responses to intrinsically coupled calcium and zinc dyshomeostasis in cardiac myocytes and mitochondria during aldosteronism

Intracellular Ca(2+) overloading, coupled to induction of oxidative stress, is present at 4-wk aldosterone/salt treatment (ALDOST). This prooxidant reaction in cardiac myocytes and mitochondria accounts for necrotic cell death and subsequent myocardial scarring. It is intrinsically linked to increased intracellular zinc concentration ([Zn(2+)](i)) serving as an antioxidant. Herein, we addressed the temporal responses in coupled Ca(2+) and Zn(2+) dyshomeostasis, reflecting the prooxidant-antioxidant equilibrium, by examining preclinical (week 1) and pathological (week 4) stages of ALDOST to determine whether endogenous antioxidant defenses would be ultimately overwhelmed to account for this delay in cardiac remodeling. We compared responses in cardiomyocyte free [Ca(2+)](i) and [Zn(2+)](i) and mitochondrial total [Ca(2+)](m) and [Zn(2+)](m), together with biomarkers of oxidative stress and antioxidant defenses, during 1- and 4-wk ALDOST. At week 1 and compared with controls, we found: 1) elevations in [Ca(2+)](i) and [Ca(2+)](m) were coupled with [Zn(2+)](i) and [Zn(2+)](m); 2) increased mitochondrial H(2)O(2) production, cardiomyocyte xanthine oxidase activity, and cardiac and mitochondrial 8-isoprostane levels, counterbalanced by increased activity of antioxidant proteins, enzymes, and the nonenzymatic antioxidants that can be considered as cumulative antioxidant capacity; some of these enzymes and proteins (e.g., metallothionein-1, Cu/Zn-superoxide, glutathione synthase) are regulated by metal-responsive transcription factor-1; and 3) although these augmented antioxidant defenses were sustained at week 4, they fell short in combating the persistent intracellular Ca(2+) overloading and marked rise in cardiac tissue 8-isoprostane and mitochondrial transition pore opening. Thus a coupled Ca(2+) and Zn(2+) dyshomeostasis occurs early during ALDOST in cardiac myocytes and mitochondria that regulate redox equilibrium until week 4 when ongoing intracellular Ca(2+) overloading and prooxidants overwhelm antioxidant defenses.

Cation dyshomeostasis and cardiomyocyte necrosis: the Fleckenstein hypothesis revisited

An ongoing loss of cardiomyocytes to apoptotic and necrotic cell death pathways contributes to the progressive nature of heart failure. The pathophysiological origins of necrotic cell loss relate to the neurohormonal activation that accompanies acute and chronic stressor states and which includes effector hormones of the adrenergic nervous system. Fifty years ago, Albrecht Fleckenstein and coworkers hypothesized the hyperadrenergic state, which accompanies such stressors, causes cardiomyocyte necrosis based on catecholamine-initiated excessive intracellular Ca(2+) accumulation (EICA), and mitochondrial Ca(2+) overloading in particular, in which the ensuing dysfunction and structural degeneration of these organelles leads to necrosis. In recent years, two downstream factors have been identified which, together with EICA, constitute a signal-transducer-effector pathway: (i) mitochondria-based induction of oxidative stress, in which the rate of reactive oxygen metabolite generation exceeds their rate of detoxification by endogenous antioxidant defences; and (ii) the opening of the mitochondrial inner membrane permeability transition pore (mPTP) followed by organellar swelling and degeneration. The pathogenesis of stress-related cardiomyopathy syndromes is likely related to this pathway. Other factors which can account for cytotoxicity in stressor states include: hypokalaemia; ionized hypocalcaemia and hypomagnesaemia with resultant elevations in parathyroid hormone serving as a potent mediator of EICA; and hypozincaemia with hyposelenaemia, which compromise antioxidant defences. Herein, we revisit the Fleckenstein hypothesis of EICA in leading to cardiomyocyte necrosis and the central role played by mitochondria.

Hypoalbuminemia and Lymphocytopenia in Patients With Decompensated Biventricular Failure

Background:In patients hospitalized with decompensated biventricular failure having hypoalbuminemia and lymphocytopenia without underlying hepatic or renal disease, we addressed the presence of a protein-losing enteropathy (PLE). Methods:We studied 78 patients having a dilated cardiomyopathy, who were hospitalized with congestive heart failure (CHF) and hypoalbuminemia of uncertain origin. In the first 19 patients, we investigated the presence of PLE using Tc-Dex70 scintigraphy together with serum albumin 2 to 4 weeks later when compensation had been restored. In the next 59 patients, presenting with reduced serum albumin and relative lymphocyte count at admission, these parameters were again monitored (2–4 weeks) later when symptoms and signs of CHF had resolved. Results:PLE, documented by Tc-Dex70 scintigraphy, was found in 10 of 19 patients and whose hypoalbuminemia (2.7 ± 0.1 g/dL, mean ± standard error of mean) were corrected (3.3 ± 0.1 g/dL; P < 0.05) with the resolution of CHF, whereas in the 9 patients without a PLE, reduced baseline serum albumin (2.6 ± 0.1 g/dL) failed to improve on follow-up (2.6 ± 0.2 g/dL) in keeping with malnutrition. Relative lymphocyte count was reduced (14.6 ± 1.5%) in patients with PLE but was normal (21.4 ± 3.3%; P < 0.05) in those without PLE. Serum albumin and relative lymphocyte count were each reduced at admission (2.8 ± 0.1 g/dL and 14.4 ± 1.0%, respectively) in 59 patients and increased (P < 0.05) to normal values (3.5 ± 0.1 g/dL and 24.9 ± 1.0%) 2 to 4 weeks after they were compensated. Conclusions:Enteral losses of albumin and lymphocytes account for the reversible hypoalbuminemia and lymphocytopenia found in patients hospitalized with CHF having splanchnic congestion.

Uncoupling the coupled calcium and zinc dyshomeostasis in cardiac myocytes and mitochondria seen in aldosteronism.

Intracellular [Ca2+]i overloading in cardiomyocytes is a fundamental pathogenic event associated with chronic aldosterone/salt treatment (ALDOST) and accounts for an induction of oxidative stress that leads to necrotic cell death and consequent myocardial scarring. This prooxidant response to Ca2+ overloading in cardiac myocytes and mitochondria is intrinsically coupled to simultaneous increased Zn2+ entry serving as an antioxidant. Herein, we investigated whether Ca2+ and Zn2+ dyshomeostasis and prooxidant to antioxidant dysequilibrium seen at 4 weeks, the pathologic stage of ALDOST, could be uncoupled in favor of antioxidants, using cotreatment with a ZnSO4 supplement; pyrrolidine dithiocarbamate (PDTC), a Zn2+ ionophore; or ZnSO4 in combination with amlodipine (Amlod), a Ca2+ channel blocker. We monitored and compared responses in cardiomyocyte free [Ca2+]i and [Zn2+]i together with biomarkers of oxidative stress in cardiac myocytes and mitochondria. At week 4 of ALDOST and compared with controls, we found (1) an elevation in [Ca2+]i coupled with [Zn2+]i and (2) increased mitochondrial H2O2 production and increased mitochondrial and cardiac 8-isoprostane levels. Cotreatment with the ZnSO4 supplement alone, PDTC, or ZnSO4+Amlod augmented the rise in cardiomyocyte [Zn2+]i beyond that seen with ALDOST alone, whereas attenuating the rise in [Ca2+]i, which together served to reduce oxidative stress. Thus, a coupled dyshomeostasis of intracellular Ca2+ and Zn2+ was demonstrated in cardiac myocytes and mitochondria during 4-week ALDOST, where prooxidants overwhelm antioxidant defenses. This intrinsically coupled Ca2+ and Zn2+ dyshomeostasis could be uncoupled in favor of antioxidant defenses by selectively increasing free [Zn2+]i and/or reducing [Ca2+]i using cotreatment with ZnSO4 or PDTC alone or ZnSO4+Amlod in combination.

Cellular and molecular pathways to myocardial necrosis and replacement fibrosis

Fibrosis is a fundamental component of the adverse structural remodeling of myocardium present in the failing heart. Replacement fibrosis appears at sites of previous cardiomyocyte necrosis to preserve the structural integrity of the myocardium, but not without adverse functional consequences. The extensive nature of this microscopic scarring suggests cardiomyocyte necrosis is widespread and the loss of these contractile elements, combined with fibrous tissue deposition in the form of a stiff in-series and in-parallel elastic elements, contributes to the progressive failure of this normally efficient muscular pump. Cellular and molecular studies into the signal-transducer-effector pathway involved in cardiomyocyte necrosis have identified the crucial pathogenic role of intracellular Ca2+ overloading and subsequent induction of oxidative stress, predominantly confined within its mitochondria, to be followed by the opening of the mitochondrial permeability transition pore that leads to the destruction of these organelles and cells. It is now further recognized that Ca2+ overloading of cardiac myocytes and mitochondria serves as a prooxidant and which is counterbalanced by an intrinsically coupled Zn2+ entry serving as antioxidant. The prospect of raising antioxidant defenses by increasing intracellular Zn2+ with adjuvant nutriceuticals can, therefore, be preferentially exploited to uncouple this intrinsically coupled Ca2+–Zn2+ dyshomeostasis. Hence, novel yet simple cardioprotective strategies may be at hand that deserve to be further explored.

Mitochondria-targeted cardioprotection in aldosteronism

Chronic aldosterone/salt treatment (ALDOST) is accompanied by an adverse structural remodeling of myocardium that includes multiple foci of microscopic scarring representing morphologic footprints of cardiomyocyte necrosis. Our previous studies suggested that signal-transducer-effector pathway leading to necrotic cell death during ALDOST includes intramitochondrial Ca2+ overloading, together with an induction of oxidative stress and opening of the mitochondrial permeability transition pore (mPTP). To further validate this concept, we hypothesized that mitochondria-targeted interventions will prove to be cardioprotective. Accordingly, 8-week-old male Sprague-Dawley rats receiving 4 weeks ALDOST were cotreated with either quercetin, a flavonoid with mitochondrial antioxidant properties, or cyclosporine A (CsA), an mPTP inhibitor, and compared with ALDOST alone or untreated, age/sex-matched controls. We monitored mitochondrial free Ca2+ and biomarkers of oxidative stress, including 8-isoprostane and H2O2 production; mPTP opening; total Ca2+ in cardiac tissue; and collagen volume fraction to quantify replacement fibrosis, a biomarker of cardiomyocyte necrosis, and employed terminal deoxynucleotidyl transferase dUTP nick end labeling assay to address apoptosis in coronal sections of ventricular myocardium. Compared with controls, at 4 weeks ALDOST we found a marked increase in mitochondrial H2O2 production and 8-isoprostane levels, an increased propensity for mPTP opening, and greater concentrations of mitochondrial free [Ca2+]m and total tissue Ca2+, coupled with a 5-fold rise in collagen volume fraction without any terminal deoxynucleotidyl transferase dUTP nick end labeling-based evidence of cardiomyocyte apoptosis. Each of these pathophysiologic responses to ALDOST was prevented by quercetin or cyclosporine A cotreatment. Thus, mitochondria play a central role in initiating the cellular-subcellular mechanisms that lead to necrotic cell death and myocardial scarring. This destructive cycle can be interrupted and myocardium salvaged with its structure preserved by mitochondria-targeted cardioprotective strategies.

Calcium and zinc dyshomeostasis during isoproterenol-induced acute stressor state.

Acute hyperadrenergic stressor states are accompanied by cation dyshomeostasis, together with the release of cardiac troponins predictive of necrosis. The signal-transducer-effector pathway accounting for this pathophysiological scenario remains unclear. We hypothesized that a dyshomeostasis of extra- and intracellular Ca2+ and Zn2+ occurs in rats in response to isoproterenol (Isop) including excessive intracellular Ca2+ accumulation (EICA) and mitochondrial [Ca2+]m-induced oxidative stress. Contemporaneously, the selective translocation of Ca2+ and Zn2+ to tissues contributes to their fallen plasma levels. Rats received a single subcutaneous injection of Isop (1 mg/kg body wt). Other groups of rats received pretreatment for 10 days with either carvedilol (C), a β-adrenergic receptor antagonist with mitochondrial Ca2+ uniporter-inhibiting properties, or quercetin (Q), a flavonoid with mitochondrial-targeted antioxidant properties, before Isop. We monitored temporal responses in the following: [Ca2+] and [Zn2+] in plasma, left ventricular (LV) apex, equator and base, skeletal muscle, liver, spleen, and peripheral blood mononuclear cells (PBMC), indices of oxidative stress and antioxidant defenses, mitochondrial permeability transition pore (mPTP) opening, and myocardial fibrosis. We found ionized hypocalcemia and hypozincemia attributable to their tissue translocation and also a heterogeneous distribution of these cations among tissues with a preferential Ca2+ accumulation in the LV apex, muscle, and PBMC, whereas Zn2+ declined except in liver, where it increased corresponding with upregulation of metallothionein, a Zn2+-binding protein. EICA was associated with a simultaneous increase in tissue 8-isoprostane and increased [Ca2+]m accompanied by a rise in H2O2 generation, mPTP opening, and scarring, each of which were prevented by either C or Q. Thus excessive [Ca2+]m, coupled with the induction of oxidative stress and increased mPTP opening, suggests that this signal-transducer-effector pathway is responsible for Isop-induced cardiomyocyte necrosis at the LV apex.

Reduced Relative Lymphocyte Count in African-Americans With Decompensated Heart Failure

Background:A reduction in relative lymphocyte count (%L) has been reported in whites with heart failure that inversely correlated with jugular venous pressure thereby implicating systemic venous hypertension with splanchnic congestion. Objectives:To study whether a reduced %L (<20%) occurs in African-Americans (AA) with heart failure and to address pathophysiologic mechanisms having the potential to influence lymphocyte biology and survival, we monitored patients with or without systemic venous hypertension, hypoalbuminemia, hypovitaminosis D, and secondary hyperparathyroidism. Methods:In 131 AA (90 men; 53 ± 12 years): 113 were hospitalized, 50 with decompensated biventricular failure (DecompHF), 24 with acute left heart failure, and 39 with heart disease, but no heart failure (HDNHF); and 18 were outpatients with compensated heart failure. At the time of admission or outpatient visit, we monitored: white blood cell count and %L; and serum albumin, 25(OH)D, and parathyroid hormone (PTH). Results:White blood cell count did not differ among the groups, whereas %L was reduced only in those with DecompHF (15 ± 1%; P < 0.05) versus 25 ± 2% with left heart failure, 29 ± 1% in HDNHF, and 28 ± 3% in compensated heart failure. Serum albumin was reduced in DecompHF (2.8 ± 0.1; P < 0.05), but not in any of the other groups. Reduced 25(OH)D (<30 ng/mL), in keeping with hypovitaminosis D, was found in all AA, whereas elevated serum PTH (>65 pg/mL) was found only in those with DecompHF (123 ± 22 pg/mL). Conclusions:A relative lymphocytopenia, together with hypoalbuminemia and elevated PTH, were found only in hospitalized AA with DecompHF. These findings implicate splanchnic congestion and the enteric loss of lymphocytes and albumin with an associated secondary hyperparathyroidism.

Elevated Serum Cobalamin in Patients With Decompensated Biventricular Failure

Background:Serum cobalamin (vitamin B12), bound to transcobalamin II, is taken up by the endothelium of the hepatic vasculature via a receptor-mediated membrane transport process. We hypothesized hepatic congestion is associated with elevated serum B12 without hepatocyte necrosis. Methods and Results:Serum B12, aspartate and alanine transaminases, alkaline phosphatase, bilirubin (Bili), and brain natriuretic peptide (BNP) were monitored at the time of admission in 91 hospitalized patients: (a) 38 with decompensated biventricular failure having systemic venous distention, tricuspid regurgitation (TR), and echocardiographic evidence of inferior vena cava dilation and moderate to marked TR; (b) 18 with acute left heart failure having a myocardial infarction, an ischemic cardiomyopathy, or hypertensive heart disease; and (c) 35 without clinical evidence of failure despite myocardial infarction, pericarditis, or atrial arrhythmia. Serum cobalamin (normal 180–600 pg/mL) was elevated with biventricular failure (861.4 ± 53.0 pg/mL) compared with (P < 0.0001) left heart or no failure, where B12 remained normal. Serum aspartate, alanine, and alkaline phosphatase were normal in each group whereas Bili was increased (1.8 ± 0.2 mg/dL; P < 0.05) with biventricular failure. Plasma BNP was elevated in each group. Conclusions:Elevated cobalamin and Bili are respective biomarkers of hepatocellular dysfunction and cholestasis in patients having decompensated biventricular failure with systemic venous distention and TR without hepatocyte necrosis vis-à-vis left heart failure or in the absence of clinical failure. Elevated plasma BNP did not distinguish between the presence or absence of systemic venous congestion.