Dinesh K. Kalra

THE ROLE OF CYTOKINES IN THE FAILING HUMAN HEART

Despite repeated attempts to develop a unifying hypothesis that explains the clinical syndrome of heart failure, no single conceptual paradigm has withstood the test of time. In this regard, recent studies have shown that a class of biologically active molecules, generically referred to as cytokines, are overexposed in heart failure. This article will review recent clinical and experimental material that suggest proinflammatory (stress activated) cytokines such as tumor necrosis factor-alpha (TFN-alpha), interleukin-1 (IL-1), and interleukin-6 (IL-6) may play a role in the pathogenesis of congestive heart failure. The scope of this article includes an overview of the biology of cytokines in the heart, as well as review of the clinical studies that have documented elevated levels of cytokines and cytokine receptors in patients with heart failure.

Angiotensin II Induces Tumor Necrosis Factor Biosynthesis in the Adult Mammalian Heart Through a Protein Kinase C–Dependent Pathway

Background—Previous studies suggest that angiotensin II (Ang II) upregulates the expression of tumor necrosis factor (TNF) in nonmyocyte cell types; however, the effect of Ang II on TNF expression in the adult mammalian heart is not known. Methods and Results—To determine whether Ang II was sufficient to provoke TNF biosynthesis in the adult heart, we examined the effects of Ang II in isolated buffer-perfused Langendorff feline hearts. Ang II (10−7 mol/L) treatment resulted in a time- and dose-dependent increase in myocardial TNF mRNA and protein biosynthesis in the heart as well as in cultured adult cardiac myocytes. The effects of Ang II on myocardial TNF mRNA and protein synthesis were mediated through the angiotensin type 1 receptor (AT1R), insofar as an AT1R antagonist (AT1a) blocked the effects of Ang II, whereas an angiotensin type 2 receptor (AT2R) antagonist (AT2a) had no effect. Stimulation with Ang II led to the activation of nuclear factor-&kgr;B and activator protein-1 (AP-1), two transcription factors that are important for TNF gene expression. Nuclear factor-&kgr;B activation was accompanied by phosphorylation of I&kgr;B&agr; on serine 32 as well as degradation of I&kgr;B&agr;, suggesting that the effects of Ang II were mediated through an I&kgr;B&agr;-dependent pathway. The important role of protein kinase C (PKC) was suggested by studies in which a phorbol ester triggered TNF biosynthesis, and a PKC inhibitor abrogated Ang II–induced TNF biosynthesis. Conclusions—These studies suggest that Ang II provokes TNF biosynthesis in the adult mammalian heart through a PKC-dependent pathway.

Load-Dependent and -Independent Regulation of Proinflammatory Cytokine and Cytokine Receptor Gene Expression in the Adult Mammalian Heart

Background—Although previous studies have examined the effects of acute hemodynamic pressure overload on proinflammatory cytokine gene expression, the effects of sustained hemodynamic overloading have not been examined. Methods and Results—Sustained hemodynamic pressure overloading was produced in mice by transverse constriction of the aorta. Proinflammatory cytokine and cytokine receptor gene expression were determined by ribonuclease protection assays (RPA) at 6 hours and at 3, 7, 14 and 35 days after banding. M-mode echocardiography was used to assess left ventricular structure and function at identical time points. RPA showed that tumor necrosis factor (TNF), interleukin (IL)-1&bgr;, and IL-6 mRNA levels were maximal at 6 hours and returned to baseline levels within 72 hours. There was a significant increase in IL-1RII and IL-6R&agr; receptor mRNA levels after overloading but no significant increase in TNFR1, TNFR2, IL-1RI, or gp130 mRNA levels. The transient increase in expression of proinflammatory cytokine gene expression was not explained by changes in left ventricular loading conditions, left ventricular wall stress, desensitization of proinflammatory genes, or decreased nuclear factor-&kgr;B activation. It is interesting that transverse constriction of the aorta provoked an increase in the expression of tristetraprolin, a homeostatic zinc finger protein that is known to destabilize TNF mRNA. Conclusion—Sustained hemodynamic overloading provokes a transient increase in proinflammatory cytokine and cytokine receptor gene expression; however, the decrease in proinflammatory cytokine gene expression occurred in the absence of changes in loading conditions, suggesting that the expression of proinflammatory cytokines in the heart is regulated, at least in part, by load-dependent and load-independent mechanisms.

Nitric Oxide Provokes Tumor Necrosis Factor-α Expression in Adult Feline Myocardium Through a cGMP-Dependent Pathway

BackgroundThe mechanism(s) responsible for the persistent coexpression of tumor necrosis factor-&agr; (TNF-&agr;) and nitric oxide (NO) in the failing heart is unknown. Methods and ResultsTo determine whether NO was sufficient to provoke TNF-&agr; biosynthesis, we examined the effects of an NO donor, S-nitroso-N-acetyl penicillamine (SNAP), in buffer-perfused Langendorff hearts. SNAP (1 &mgr;mol/L) treatment resulted in a time- and dose-dependent increase in myocardial TNF-&agr; mRNA and protein biosynthesis in adult cat hearts. The effects of SNAP were completely abrogated by a NO quenching agent, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (C-PTIO), and mimicked by sodium nitroprusside. Electrophoretic mobility shift assays demonstrated that SNAP treatment led to the rapid induction of nuclear factor kappa-beta (NF-&kgr;B) but not AP-1. The importance of the cGMP pathway in terms of mediating NO-induced TNF-&agr; biosynthesis was shown by studies that demonstrated that 8-bromo-cGMP mimicked the effects of SNAP and that the effects of SNAP could be completely abrogated using a cGMP antagonist, 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ), or protein kinase G antagonist (Rp-8-Br-cGMPS). SNAP and 8-Br-cGMP were both sufficient to lead to the site-specific phosphorylation (serine 32) and degradation of I&kgr;B&agr; in isolated cardiac myocytes. Finally, protein kinase G was sufficient to directly phosphorylate I&kgr;B&agr; on serine 32, a critical step in the activation of NF-&kgr;B. ConclusionsThese studies show that NO provokes TNF-&agr; biosynthesis through a cGMP-dependent pathway, which suggests that the coincident expression of TNF-&agr; and NO may foster self-sustaining positive autocrine/paracrine feedback inflammatory circuits within the failing heart.

Increased Myocardial Gene Expression of Tumor Necrosis Factor-α and Nitric Oxide Synthase-2: A Potential Mechanism for Depressed Myocardial Function in Hibernating Myocardium in Humans

Background—Whether cardioinhibitory cytokines are elevated in regions of hibernating myocardium and account in part for the depression in resting function is currently not known. Methods and Results—Thirteen patients with stable ischemic ventricular dysfunction scheduled for bypass surgery underwent preoperative dobutamine echocardiography (DE) and intraoperative myocardial biopsies. The numbers of copies of mRNA for the negatively inotropic cytokines tumor necrosis factor-&agr; (TNF-&agr;) and inducible nitric oxide synthase (NOS2) were quantified by reverse transcription–polymerase chain reaction. In normal segments, myocardial TNF-&agr; was barely detectable (1.2±0.4 copies per 106 copies of &bgr;-actin). A 13.7-fold increase in myocardial TNF-&agr; was observed in dysfunctional segments with a biphasic response to DE (contractile reserve and ischemia) and was highest (45.5-fold) in segments with ischemia and without contractile reserve (P <0.001). A similar graded increase was seen for NOS2. Cytokine results were also similar if analysis was performed using recovery of function at 3 months as the index of viability. The change in serum TNF-&agr; and nitrite levels from baseline to 3 months after surgery correlated inversely with both the change in ejection fraction and the number of DE viable segments (r =−0.92 to −0.93;P <0.001). Conclusions—TNF-&agr; and NOS2 gene expression is regionally upregulated in hibernating myocardium to a level intermediate between that of normal regions and ischemic regions without contractile reserve. This, along with a decline in serum cytokine levels after revascularization proportional to the extent of myocardial viability, suggests a contributing role for cardioinhibitory cytokines in the observed depression of function seen in hibernating myocardium.

Prevalence and Characteristics of Continuous Electrical Activity in Patients with Paroxysmal and Persistent Atrial Fibrillation

Background: Complex fractionated atrial electrograms (CFAEs) may play a role in the genesis of atrial fibrillation (AF). One type of CFAE is continuous electrical activity (CEA). The prevalence and characteristics of CEA in patients with paroxysmal and persistent AF are unclear.

Relation of tissue Doppler-derived myocardial velocities to serum levels and myocardial gene expression of tumor necrosis factor-alpha and inducible nitric oxide synthase in patients with ischemic cardiomyopathy having coronary artery bypass grafting

We evaluated the relation of segmental and annular tissue Doppler (TD) velocities to serum levels and myocardial gene expression of tumor necrosis factor-alpha (TNF-alpha) and inducible nitric oxide (NOS2) in humans. Seven patients with coronary artery disease underwent echocardiographic examination including TD imaging, along with transmural endomyocardial biopsies (2 biopsies per patient for a total of 14 specimens) at the time of bypass surgery. The specimens were analyzed for the number of mRNA copies of TNF-alpha and NOS2. In addition, serum levels of TNF-alpha and nitrite were determined before and after surgery. Normal segments (n = 7) had fewer numbers of mRNA copies of both TNF-alpha (54.6 vs 6.5, p = 0.002) and NOS2 (3,093 +/- 486 vs 661 +/- 259, p <0.001) than dysfunctional segments (n = 7). Peak systolic velocity (Sm) (13.3 +/- 1.4 vs 4.9 +/- 1.6 cm/s, p = 0.002) and early diastolic velocity (Em) (16.5 +/- 2.7 vs 8.8 +/- 1.3 cm/s, p = 0.02) were significantly higher in normal segments. A significant correlation was present among Em, Sm, and the number of mRNA copies of TNF-alpha and NOS2 at baseline and during infusion of dobutamine (r range -0.72 to -0.92, p <0.01 for all). Likewise, significant relations were present between the changes in serum cytokine levels and changes in the mitral annulus diastolic velocity, E/Ea ratio, and end-diastolic wall stress (r range 0.75 to 0.88, p </=0.05 for all). In conclusion, Sm and Em are strongly dependent on the regional levels of cytokine gene expression, which are known to have negative inotropic and lusitropic effects when overexpressed.

Cardiac magnetic resonance tissue tracking in right ventricle: Feasibility and normal values

PURPOSE To investigate right ventricular (RV) strain in patients without identified cardiac pathology using cardiac magnetic resonance tissue tracking (CMR TT). METHODS A total of 50 consecutive patients with no identified cardiac pathology were analyzed. RV longitudinal and circumferential strain was assessed by CMR TT. The age range was 4-81years with a median of 32years (interquartile range, 15 to 56years). RESULTS Analysis time per patient was <5min. The peak longitudinal strain (Ell) was -22.11±3.51%. The peak circumferential strains (Ecc) for global, basal, mid-cavity and apical segments were as follows: -11.69±2.25%, -11.00±2.45%, -11.17±3.36%, -12.90±3.34%. There were significant gender differences in peak Ecc at the base (P=0.04) and the mid-cavity (P=0.03) with greater deformation in females than in males. On Bland-Altman analysis, peak Ell (mean bias, 0.22±1.67; 95% CI -3.05 to 3.49) and mid-cavity Ecc (mean bias, 0.036±1.75; 95% CI, -3.39 to 3.47) had the best intra-observer agreement and inter-observer agreement, respectively. CONCLUSIONS RV longitudinal and circumferential strains can be quickly assessed with good intra-observer and inter-observer variability using TT.

Supraventricular tachycardia: What is the mechanism?

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Cardiac Imaging in the Diagnosis of Coronary Artery Disease

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