Circulation Research

Heritable cardiomyopathies are a class of heart diseases caused by variations in a number of genetic loci. Genetic variants on one allele lead to either a degraded protein, which causes a haploinsufficiency of that protein, or a nonfunctioning protein that subverts the molecular system within which the protein works. Over years, both of these mechanisms eventually lead to diseased heart tissue and symptoms of a failing heart. Most cardiomyopathy treatments repurpose heart failure drugs to manage these symptoms and avoid adverse outcomes. There are few therapies that correct the underlying pathogenic genetic or molecular mechanism. This review will reflect on this unmet clinical need in genetic cardiomyopathies and consider a variety of therapies that address the mechanism of disease rather than patient symptoms. These therapies are genetic, targeting a defective gene or transcript, or ameliorating a genetic insufficiency. However, there are also a number of small molecules under exploration that modulate downstream faulty protein products affected in cardiomyopathies.

Arrhythmogenic cardiomyopathy is an inherited heart muscle disorder, predisposing to sudden cardiac death, particularly in young patients and athletes. Pathological features include loss of myocytes and fibrofatty replacement of right ventricular myocardium; biventricular involvement is often observed. It is a cell-to-cell junction cardiomyopathy, typically caused by genetically determined abnormalities of cardiac desmosomes, which leads to detachment of myocytes and alteration of intracellular signal transduction. The diagnosis of arrhythmogenic cardiomyopathy does not rely on a single gold standard test but is achieved using a scoring system, which encompasses familial and genetic factors, ECG abnormalities, arrhythmias, and structural/functional ventricular alterations. The main goal of treatment is the prevention of sudden cardiac death. Implantable cardioverter defibrillator is the only proven lifesaving therapy; however, it is associated with significant morbidity because of device-related complications and inappropriate implantable cardioverter defibrillator interventions. Selection of patients who are the best candidates for implantable cardioverter defibrillator implantation is one of the most challenging issues in the clinical management.

Although the exchange of labeled water between blood and tissue in the heart has usually been assumed to be flow-limited, the outflow patterns of labeled water, relative to intravascular references, in a multiple indicator dilution experiment, have appeared to be anomalous in terms of the models used to explain the transport of less permeable substances. Data showing a change in the shape of the labeled water outflow curve after vasodilation and after the infusion of toxic doses of 2,4-dinitrophenol led us to propose a new model for labeled water permeation which includes barriers at both the capillary wall and the sarcolemmal membrane. This model explains adequately the form of the outflow curve, provides parameters related to the permeability at the two barriers, and gives an estimate of the ratio of the intracellular to interstitial space. Dinitrophenol infused intra-arterially in a dose sufficient to cause S-T elevation in the electrocardiogram is found to reduce the sarcolemmal water permeability by an order of magnitude, but to have no effect on capillary water permeability. We conclude that water transport in the heart is barrier-limited at both the capillary and sarcolemmal membranes and that sarcolemmal water permeability is probably mediated at least in part by a structure sensitive to the effects of dinitrophenol, presumably a protein channel. Since the outflow patterns of inert gases resemble that of labeled water, it is possible that oxygen distribution is also barrier-limited.

A model for capillary-tissue exchange in a uniformly perfused organ with uniform capillary transit times and no diffusional capillary interactions was designed to permit the exploration of the influences of various parameters on the interpretation of indicator-dilution curves obtained at the venous outflow following the simultaneous injection of tracers into the arterial inflow. These parameters include tissue geometric factors, longitudinal diffusion and volumes of distribution of tracers in blood and tissue, hematocrit, volumes of nonexchanging vessels and the sampling system, capillary permeability, P . capillary surface area, S , and flow of blood- or solute-containing fluid, F' _s . An assumption of instantaneous radial diffusion in the extravascular region is appropriate when intercapillary distances are small, as they are in the heart, or permeabilities are low, as they are for lipophobic solutes. Numerical solutions were obtained for dispersed input functions similar to normal intravascular dye-dilution curves. Axial extravascular diffusion showed a negligible influence at low permeabilities. The "instantaneous extraction" of a permeating solute can provide an estimate of PS/F' _s , the ratio of the capillary permeability-surface area product to the flow, when PS/F' _s lies between approximately 0.05 and 3.0; the limits of the range depend on the extravascular volume of distribution and the influences of intravascular dispersion. The most accurate estimates were obtained when experiments were designed so that PS/F' _s was between 0.2 and 1.0 or peak extractions were between 0.1 and 0.6.

Blocking brain mineralocorticoid receptors (MRs) reduces the high circulating levels of tumor necrosis factor (TNF)-α in heart failure (HF) rats. TNF-α and other proinflammatory cytokines activate neurons in the paraventricular nucleus (PVN) of hypothalamus, including corticotropin-releasing hormone (CRH) neurons, by inducing cyclooxygenase (COX)-2 activity and synthesis of prostaglandin E ₂ by perivascular cells of the cerebral vasculature. We tested the hypothesis that systemic treatment with a MR antagonist would reduce hypothalamic COX-2 expression and PVN neuronal activation in HF rats. Rats underwent coronary ligation to induce HF, confirmed by echocardiography, or sham surgery, followed by 6 weeks treatment with eplerenone (30 mg/kg per day, orally) or vehicle (drinking water). Eplerenone-treated HF rats had lower plasma TNF-α, interleukin (IL)-1β and IL-6, less COX-2 staining of small blood vessels penetrating PVN, fewer PVN neurons expressing Fra-like activity (indicating chronic neuronal activation), and fewer PVN neurons staining for TNF-α, IL-1β, and CRH than vehicle-treated HF rats. COX-2 and CRH protein expression in hypothalamus were 1.7- and 1.9-fold higher, respectively, in HF+vehicle versus sham+vehicle rats; these increases were attenuated (26% and 25%, respectively) in HF+eplerenone rats. Eplerenone-treated HF rats had less prostaglandin E ₂ in cerebrospinal fluid, lower plasma norepinephrine levels, lower left ventricular end-diastolic pressure, and lower right ventricle/body weight and lung/body weight ratios, but no improvement in left ventricular function. Treatment of HF rats with anticytokine agents, etanercept or pentoxifylline, produced very similar results. This study reveals a previously unrecognized effect of MR antagonism to minimize cytokine-induced central neural excitation in rats with HF.

Vai trò của các bất thường lipid trong bệnh sinh xơ cầu thận khu trú đã được nghiên cứu trong mô hình thận còn lại ở chuột về suy thận mạn. Những con chuột trải qua phẫu thuật cắt thận phải và nhồi máu hai phần ba thận trái (cắt thận 5/6) đã được điều trị bằng acid clofibric trong vòng 10 tuần. Cả nồng độ cholesterol huyết thanh và bài tiết albumin trong nước tiểu đều giảm đáng kể nhờ acid clofibric. Sau 10 tuần, tỷ lệ cầu thận có xơ cầu thận khu trú là 5 +/- 2% ở chuột điều trị bằng acid clofibric và 24 +/- 5% ở chuột không điều trị (p nhỏ hơn 0,01). Sự thanh thải inulin cao hơn ở chuột 5/6 cắt thận được điều trị so với chuột không điều trị (0,28 +/- 0,02 so với 0,22 +/- 0,02 ml/phút 100 g trọng lượng cơ thể, p nhỏ hơn 0,05). Trọng lượng cơ thể, trọng lượng thận, và huyết áp hệ thống không bị thay đổi đáng kể bởi acid clofibric. Các nghiên cứu vi kim tiêm, được thực hiện trên các nhóm chuột 5/6 cắt thận điều trị và không điều trị, đã chỉ ra rằng tỷ lệ lưu lượng lọc cầu thận đơn lẻ và áp lực mao mạch cầu thận đều tăng cao sau 4 tuần mổ. Tuy nhiên, acid clofibric không làm thay đổi đáng kể lưu lượng lọc cầu thận đơn lẻ (95 +/- 2,1 nl/phút ở nhóm điều trị so với 97,0 +/- 6,2 nl/phút ở nhóm không điều trị, p lớn hơn 0,05) hay áp lực mao mạch cầu thận (56,6 +/- 1,5 mm Hg ở nhóm điều trị so với 57,8 +/- 0,8 mm Hg ở nhóm không điều trị, p lớn hơn 0,05) ở chuột 5/6 cắt thận. Trong một bộ thí nghiệm khác, chuột 5/6 cắt thận được điều trị bằng chất ức chế cụ thể tổng hợp cholesterol, mevinolin. Mevinolin cải thiện nồng độ lipid trong huyết thanh và giảm albumin niệu ở chuột 5/6 cắt thận mà không gây thay đổi đáng kể trong huyết áp.(TÓM TẮT BỊ CẮT Ở 250 TỪ)

The present study was intended to define the interrelation among endocardial flow, endocardial function, and coronary arterial pressure during spontaneous autoregulation in the left ventricle of chronically instrumented unanesthetized dogs. Steady-state sonomicrometric measurements of regional function and epicardial coronary artery pressure were used to determine the lower pressure limit of endocardial autoregulation while global indexes of myocardial demand remained constant. Transmural wall thickening in the circumflex bed remained unchanged (+/- 5% of control values) until coronary pressure fell below 39 +/- 5.6 (SD) mm Hg. Endocardial segment shortening was similarly constant until coronary pressure fell below 42 +/- 7.4 mm Hg. There was no significant change in endocardial flow as coronary pressure was reduced over the autoregulatory plateau from 84 to 49 mm Hg (1.05-0.99 ml/min/g, p = NS). Below the critical pressure limits, small additional reductions in pressure were associated with marked reductions in both endocardial flow and function. The coronary pressure-function relation was linear as well as steep in this range for both wall thickening (r = 0.94 +/- 0.05) and segment shortening (r = 0.96 +/- 0.03). Although the relation between endocardial flow and function showed more variability than pressure-function relations at low pressures, wall thickening reductions and endocardial flow reductions related on a nearly one-to-one basis. The present study establishes that the coronary pressure-function relation can be used to define the lower limit of endocardial autoregulation. It also indicates that the lower pressure limit of endocardial autoregulation is considerably less than in anesthetized animals (40 vs. 70 mm Hg) and that steady-state flow above this limit is controlled more tightly. Although these differences may relate to systemic hemodynamics, it seems likely that general anesthesia and/or acute surgical instrumentation alter coronary autoregulation under at least some experimental circumstances.

We previously reported enhanced expression of the p67 ^phox and gp91 ^phox components of NAD(P)H oxidase in angiotensin (Ang) II–induced hypertension, suggesting de novo assembly in response to Ang II. To examine the direct involvement of NAD(P)H oxidases in Ang II–induced O ₂ ⁻ production, we designed a chimeric peptide that inhibits p47 ^phox association with gp91 ^phox in NAD(P)H oxidase (gp91ds- tat ). This was achieved by linking a 9-amino acid peptide (aa) derived from HIV-coat protein ( tat ) to a 9-aa sequence of gp91 ^phox (known to interact with p47 ^phox ). As a control, we constructed a chimera containing tat and a scrambled gp91 sequence (scramb- tat ). We found that gp91ds- tat decreased O ₂ ⁻ levels in aortic rings treated with Ang II (10 pmol/L) but had no effect on either the O ₂ ⁻ -generating enzyme xanthine oxidase or potassium superoxide–generated O ₂ ⁻ . We infused vehicle, Ang II (0.75 mg · kg ⁻¹ · d ⁻¹ ), Ang II+gp91ds- tat (10 mg · kg ⁻¹ · d ⁻¹ ), or Ang II+scramb- tat intraperitoneally in C57Bl/6 mice and measured systolic blood pressure (SBP) on days 0, 3, 5, and 7 of infusion. SBP increased by day 3 in mice given Ang II and Ang II+scramb- tat but was significantly lower with Ang II+gp91- tat . On day 7, SBP was still significantly inhibited in mice given Ang II+gp91ds- tat , whereas Ang II–induced O ₂ ⁻ production was inhibited throughout the aorta as detected by dihydroethidium staining, consistent with the ability of this inhibitor to block the various vascular NAD(P)H oxidase isoforms. These data support the hypothesis that inhibition of the interaction of p47 ^phox and gp91 ^phox (or its homologues) can block O ₂ ⁻ production and attenuate blood pressure elevation in mice.

Intracellular signaling pathway mediated by small GTPase Rho and its effector Rho-kinase plays an important role in regulation of vascular smooth muscle contraction and other cellular functions. We have recently demonstrated that Rho-kinase is substantially involved in angiotensin II–induced gene expressions and various cellular responses in vitro. However, it remains to be examined whether Rho-kinase is involved in the angiotensin II–induced cardiovascular hypertrophy in vivo and, if so, what mechanisms are involved. Long-term infusion of angiotensin II for 4 weeks caused hypertrophic changes of vascular smooth muscle and cardiomyocytes in rats. Both changes were significantly suppressed by concomitant oral treatment with fasudil, which is metabolized to a specific Rho-kinase inhibitor, hydroxyfasudil, after oral administration. Angiotensin II caused a perivascular accumulation of macrophages and Rho-kinase activation, both of which were also significantly suppressed by fasudil. Vascular NAD(P)H oxidase expression (nox1, nox4, gp91phox, and p22phox) and endothelial production of superoxide anions were markedly increased by angiotensin II, both of which were also significantly suppressed by fasudil. Thus, fasudil ameliorated the impaired endothelium-dependent relaxations caused by angiotensin II without affecting vasodilator function of vascular smooth muscle. These results provide evidence that Rho-kinase is substantially involved in the angiotensin II–induced cardiovascular hypertrophy in rats in vivo. The suppression of endothelial NAD(P)H oxidase upregulation and resultant superoxide production and the amelioration of endothelial vasodilator function may be involved in this process.