Fangping Chen

N-acetylcysteine reverses cardiac myocyte dysfunction in HIV-Tat proteinopathy.

HIV cardiomyopathy remains highly prevalent among the estimated 33 million HIV-infected individuals worldwide. This is particularly true in developing countries. Potential mechanisms responsible for myocardial dysfunction following HIV infection include direct effects of HIV proteins. We have previously reported that cardiac myocyte-specific expression of HIV-Tat (Tat) results in a murine cardiomyopathy model. We now report that Tat exhibits decreased myocardial ATP [wild type (WT) vs. Tat transgenic (TG), P < 0.01] and myocyte GSH levels (WT vs. TG, P < 0.01), decreased GSH/GSSG ratio (WT vs. TG, P < 0.01), increased H(2)O(2) levels (WT vs. TG, P < 0.05), and increased catalase (TG vs. WT, P < 0.05) and GPX1 (glutathione peroxidase 1) activities (WT vs. TG, P < 0.05), blunted cardiac myocyte positive inotropy (% peak shortening, WT vs. TG, P < 0.01; +dl/dt, WT vs. TG, P < 0.01) and negative inotropy (-dl/dt, WT vs. TG, P < 0.01), and blunted inotropic responses to Ca(2+) (P < 0.01, for each) and shortened anatomical and functional survival in vitro (P < 0.01). The sulfhydryl donor, N-acetylcysteine (NAC; 10(-4) M), completely reversed both the positive and negative inotropic defects in Tat; increased GSH (P < 0.01) and GSH/GSSG (P < 0.01); reversed H(2)O(2) level (P < 0.05) and GPX1 activity (P < 0.05); and normalized the blunted inotropic response to Ca(2+) (P < 0.01). NAC (10(-7)) M normalized duration of contractile function from <40 min to >120 min (P < 0.01), with no effect on GSH and GSH/GSSG. NAC (10(-4) M) reverses cardiac myocyte dysfunction and markers of oxidative stress. NAC (10(-7) M) enhances myocyte function independent of changes in glutathione. Elucidating the molecular mechanisms involved in the GSH-dependent and GSH-independent salutary effects of NAC should identify novel therapeutic targets for myocardial proteinopathies recently appreciated in human cardiomyopathies.

CXCR4 receptor antagonist blocks cardiac myocyte p38 MAP kinase phosphorylation by HIV gp120.

The prognosis for patients with human immunodeficiency virus (HIV) infection has improved remarkably as a result of effective antiretroviral therapy. This has resulted in an increased awareness of cardiac complications from HIV infection, including cardiomyopathy and overt heart failure. Mechanisms responsible for HIV cardiomyopathy and heart failure are unknown, but may include direct effects of HIV proteins on the heart. We have previously reported that the HIV envelope glycoprotein, gp120, has a p38 MAP kinase-dependent negative inotropic effect on adult rat ventricular myocytes (ARVM). This signaling pathway presumably results from the binding of gp120 to a specific receptor on the surface of cardiac myocytes. HIV gp120 has been shown to bind to CD4, CXCR4, and CCR5 receptors on lymphocytes and macrophages. Accordingly, we sought to determine if HIV gp120 regulated its negative inotropic effect through activation of one of these binding sites on cardiac myocytes. AMD3100, a highly selective CXCR4 receptor antagonist, reversed HIV gp120-induced negative inotropic effect on ARVM. AMD3100 also blocked HIV gp120 phosphorylation of both p38 MAP kinase and Troponin I. The binding of gp120 to the CXCR4 receptor on ARVM was confirmed by co-immunoprecipitation. We conclude that the negative inotropic effect of HIV gp120 is mediated by a novel signaling pathway that begins with binding to a cardiac myocyte CXCR4 receptor, followed by phosphorylation of both p38 MAP kinase and Troponin I.

p38 MAP kinase inhibitor reverses stress-induced myocardial dysfunction in vivo

Recent clinical reports strongly support the intriguing possibility that emotional stress alone is sufficient to cause reversible myocardial dysfunction in patients. We previously reported that a combination of prenatal stress followed by restraint stress (PS+R) results in echocardiographic evidence of myocardial dysfunction in anesthetized rats compared with control rats subjected to the same restraint stress (Control+R). We now report results of our catheter-based hemodynamic studies in both anesthetized and freely ambulatory awake rats, comparing PS+R vs. Control+R. Systolic function [positive rate of change in left ventricular pressure over time (+dP/dt)] was significantly depressed (P < 0.01) in PS+R vs. Control+R both under anesthesia (6,287 +/- 252 vs. 7,837 +/- 453 mmHg/s) and awake (10,438 +/- 741 vs. 12,111 +/- 652 mmHg/s). Diastolic function (-dP/dt) was also significantly depressed (P < 0.05) in PS+R vs. Control+R both under anesthesia (-5,686 +/- 340 vs. -7,058 +/- 458 mmHg/s) and awake (-8,287 +/- 444 vs. 10,440 +/- 364 mmHg/s). PS+R also demonstrated a significantly attenuated (P < 0.05) hemodynamic response to increasing doses of the beta-adrenergic agonist isoproterenol. Intraperitoneal injection of the p38 MAP kinase inhibitor SB-203580 reversed the baseline reduction in +dP/dt and -dP/dt as well as the blunted isoproterenol response. Intraperitoneal injection of SB-203580 also reversed p38 MAP kinase and troponin I phosphorylation in cardiac myocytes isolated from PS+R. Thus the combination of prenatal stress followed by restraint stress results in reversible depression in both systolic and diastolic function as well as defective beta-adrenergic receptor signaling. Future studies in this animal model may provide insights into the basic mechanisms contributing to reversible myocardial dysfunction in patients with ischemic and nonischemic cardiomyopathies.

N-acetylcysteine reverses cardiac myocyte dysfunction in a rodent model of behavioral stress

Compelling clinical reports reveal that behavioral stress alone is sufficient to cause reversible myocardial dysfunction in selected individuals. We developed a rodent stress cardiomyopathy model by a combination of prenatal and postnatal behavioral stresses (Stress). We previously reported a decrease in percent fractional shortening by echo, both systolic and diastolic dysfunction by catheter-based hemodynamics, as well as attenuated hemodynamic and inotropic responses to the β-adrenergic agonist, isoproterenol (ISO) in Stress rats compared with matched controls (Kan H, Birkle D, Jain AC, Failinger C, Xie S, Finkel MS. J Appl Physiol 98: 77-82, 2005). We now report enhanced catecholamine responses to behavioral stress, as evidenced by increased circulating plasma levels of norepinephrine (P < 0.01) and epinephrine (P < 0.01) in Stress rats vs. controls. Cardiac myocytes isolated from Stress rats also reveal evidence of oxidative stress, as indicated by decreased ATP, increased GSSG, and decreased GSH-to-GSSG ratio in the presence of increased GSH peroxidase and catalase activities (P < 0.01, for each). We also report blunted inotropic and intracellular Ca(2+) concentration responses to extracellular Ca(2+) (P < 0.05), as well as altered inotropic responses to the intracellular calcium regulator, caffeine (20 mM; P < 0.01). Treatment of cardiac myocytes with N-acetylcysteine (NAC) (10(-3) M) normalized calcium handling in response to ISO and extracellular Ca(2+) concentration and inotropic response to caffeine (P < 0.01, for each). NAC also attenuated the blunted inotropic response to ISO and Ca(2+) (P < 0.01, for each). Surprisingly, NAC did not reverse the changes in GSH, GSSG, or GSH-to-GSSG ratio. These data support a GSH-independent salutary effect of NAC on intracellular calcium signaling in this rodent model of stress-induced cardiomyopathy.

Diastolic dysfunction following HIV infection.

The development of myocardial dysfunction in patients following HIV infection continues to be widely reported [1–6]. Compelling evidence of surprisingly frequent diastolic dysfunction followed by systolic dysfunction is observed in both the pediatric and adult populations [1–6]. Basic mechanisms proposed to explain these clinical observations include direct effects of HIV proteins, or indirect effects of cytokines, co-infection, autoimmunity and antiretroviral toxicity [1,7]. The advent of highly active antiretroviral therapies (HAART) has prolonged survival, but has been considered a potential source of cardiovascular complications of HIV infection [1]. Recent clinical studies in countries lacking universal access to HAART have provided some insights into the relative importance of HIV infection as opposed to its pharmacotherapy in HIV cardiomyopathy. These recent studies indicate that HIV cardiomyopathy is more prevalent among patients with HIV alone compared with those patients with HIV who also received HAART [1–6]. Thus, HIV infection appears to contribute more to HIV cardiomyopathy than does its treatment. Human autopsy data identifying gp120 in the hearts of HIV cardiomyopathy patients prior to HAART also support its potential pathogenic role in this condition [8].