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J Am Coll Cardiol, 2005; 46:1036-1042, doi:10.1016/j.jacc.2005.05.067
(Published online 7 September 2005). © 2005 by the American College of Cardiology Foundation |
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* McGill University, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Canada
Cardiovascular Institute, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania
Cardiovascular Medicine, Kyushu University, Fukuoka, Japan
Massachusetts General Hospital, Boston, Massachusetts
|| Department of Family and Preventive Medicine, School of Medicine, University of Utah, Salt Lake City, Utah
¶ Department of Medicine, Jefferson Medical College, Philadelphia, Pennsylvania
# New York Medical College, Valhalla, New York
Manuscript received March 4, 2005; revised manuscript received April 27, 2005, accepted May 3, 2005.
* Reprint requests and correspondence: Dr. Dennis M. McNamara, Heart Failure/Transplantation Program, Cardiovascular Institute, University of Pittsburgh Medical Center, 566 Scaife Hall, 200 Lothrop Street, Pittsburgh, Pennsylvania 15213 (Email: mcnamaradm{at}upmc.edu).
| Abstract |
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BACKGROUND: Apoptosis may limit ventricular recovery. We examined the myocardial expression of Fas, Fas ligand (FasL), tumor necrosis factor (TNF)-alpha, and TNF receptor 1 (TNFR1), and myocardial recovery in patients from the multicenter Intervention in Myocarditis and Acute Cardiomyopathy (IMAC) study.
METHODS: Endomyocardial biopsy samples were obtained in 20 patients with recent-onset (<6 months) idiopathic dilated cardiomyopathy (left ventricular ejection fraction [LVEF]
0.40). The LVEF was assessed at baseline and at 6 and 12 months by nuclear scans. Myocardial expression was assessed by ribonuclease (RNase) protection, normalized to a constitutively active gene (glyceraldehydes 3-phosphate dehydrogenase [GAPDH]) and reported as percent GAPDH expression. The change in LVEF at 6 and 12 months was compared by tertiles of expression.
RESULTS: For all patients (14 men, 6 women; age 46.5 ± 10.7 years), the mean LVEF was 0.28 ± 0.05 at baseline and 0.40 ± 0.14 at six months. Patients in the highest tertile of Fas expression had minimal improvement at six months (
EF = 0.03 ± 0.05) when compared with the intermediate (
EF = 0.10 ± 0.13) and lowest tertiles (
EF = 0.21 ± 0.11, change in LVEF by tertile, p = 0.006). A similar relationship was seen with TNFR1 expression (highest tertile,
EF = 0.06 ± 0.07; lowest tertile,
EF = 0.21 ± 0.11, p = 0.02). In contrast with Fas and TNFR1, expression of TNF-alpha and FasL did not predict recovery of LV function.
CONCLUSIONS: In cardiomyopathy of recent onset, increased expression of Fas and TNFR1 was associated with minimal recovery of LV function. Apoptosis limits myocardial recovery, and represents a potential target for therapeutic intervention.
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In patients with chronic heart failure, loss of myocytes caused by apoptosis or programmed cell death results in progressive myocardial dysfunction (4,5). Fas is a transmembrane cell surface receptor that plays a critical role in apoptosis (6). When engaged by the signaling peptide Fas ligand (FasL), the receptor initiates a cascade that leads to proteolysis and programmed cell death. Other cytokines are important in this pathway, and the interaction of tumor necrosis factor (TNF)-alpha and its receptor, TNFR1, also leads to apoptosis. Patients with progressive left ventricular dysfunction and chronic heart failure have elevated levels of soluble Fas that correlate with prognosis (711). In addition, levels of serum FasL are increased in patients with myocarditis and correlate with severity of heart failure (11). The impact of myocardial expression of mediators of apoptosis on myocardial recovery has not been previously evaluated in cardiomyopathy of recent onset.
We examined the myocardial expression of Fas and FasL, their relationship to expression of the proinflammatory cytokines TNF-alpha and its receptor TNFR1, and their impact on subsequent myocardial recovery in a series of patients with recent-onset cardiomyopathy.
| Methods |
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0.40, were within six months of their onset of cardiac symptoms, and had an extensive evaluation including right heart catheterization and right ventricular biopsy. Baseline assessment of LVEF by radionuclide scan was performed, and LVEF was reassessed at 6 and 12 months after presentation. Gene expression. Samples were immediately frozen in liquid nitrogen and stored at 80°C until analysis. To measure myocardial gene expression, total ribonucleic acid (RNA) was extracted from frozen tissues by using an acid guanidium thiocyanate-phenol-chloroform method. A commercially available multi-probe RNase protection assay kit (Riboquant, PharMingen, San Diego, California) was used to evaluate transcript levels, with the assay performed according to the manufacturers protocol. The value of each hybridized probe was quantified by the PhosphoImager using ImageQuant software (Molecular Dynamics, Sunnyvale, California) and normalized to that of a constitutively active gene, glyceraldehydes 3-phosphate dehydrogenase (GAPDH) included in each template set as an internal control (arbitrarily set as = 1). Myocardial levels of mRNA for TNF-alpha, TNF receptor-1 (TNFR1), Fas, FasL, and Fas-associated death domain-like interleukin-1-beta-converting enzyme (FLICE) were then expressed as percents of GAPDH mRNA level.
Statistical analysis. Statistical analysis was performed using the statistics software SPSS (SPSS Inc., Chicago, Illinois). Results are presented as mean values ± standard deviation. Patients were grouped into tertiles based on gene expression of Fas, FasL, TNF, and TNFR1. For continuous variables, assessment of significant differences between ordered tertile means was performed by one-way analysis of variance; significance of a linear trend across ordered means is reported. An exact version of the Mantel-Haentzsel trend test was used to compare distributions of all categorical variables by ordered tertiles. Pearsons correlation coefficient was used as a measure of linear association between two variables. Differences were considered significant at a value of p < 0.05.
| Results |
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Impact of medical therapy on LV recovery. Beta-blocker therapy was used by 3 of 20 (15%) of patients at baseline, 5 (25%) at 6 months, and 6 (30%) at 12 months. The low percentage of patients on beta-blockers was reflective of evolving practice guidelines during the time of enrollment (1996 to 1998). The percentage of patients on beta-blockers by Fas tertile (low, intermediate, high) was not significantly different at baseline (Tables 1 and 2) or at 6 or 12 months. The mean LVEF was significantly higher for patients on beta-blockers at 12-month follow-up, (n = 6, LVEF = 0.50 ± 14) when compared with those not on therapy (n = 14, LVEF = 0.35 ± 0.10, p = 0.01). Therefore, to ensure that beta-blocker therapy was not acting as a confounder, analysis of the change in EF by Fas tertile was repeated exclusively in patients not treated with beta-blockers during follow-up. Even in this smaller cohort (n = 14), high Fas expression remained significantly linked to less improvement in LVEF for both the 6-month (p = 0.014) and the 12-month (p = 0.017) end points. For the small subset (n = 6) on beta-blockers, the improvement in LVEF seemed to be greater for patients on beta-blockers from the lowest Fas tertile (n = 3, increase in LVEF = 0.30 ± 0.10) than for those in higher tertiles of Fas expression (n = 3, change in EF = 0.12 ± 0.21); however, this was not significant given the limited number of patients.
All patients were on ACEI therapy at study entry. The ACEI dose was increased in 8 of 20 patients (40%) during follow-up. The number of patients with an increase in ACEI therapy was similar in all Fas tertiles (43%, 43%, 33%, p = 0.92), and was not associated with increased LVEF (ACE increased, n = 8; LVEF = 0.40 ± 0.16; not increased, LVEF = 0.40 ± 0.11; p = 0.92). Although statistical power was limited in the smaller subsets, tertiles of Fas expression seemed predictive of subsequent LV recovery in both groups for the 6-month (ACE not increased, p = 0.05; ACE increased, p = 0.10) and 12-month end points (ACE not increased, p = 0.08; ACE increased, p = 0.02).
| Discussion |
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In the IMAC study of acute cardiomyopathy and myocarditis, biopsy status, hemodynamic assessment, and metabolic stress testing all failed to predict subsequent improvements in LVEF (12). In cardiomyopathy of recent onset, the percentage of patients with biopsy-proven myocarditis in published series is variable, with as few as 10% showing inflammatory infiltrates (14). Evidence of cellular inflammation on biopsy does not seem to predict clinical outcome (1). In fact, patients with fulminant myocarditis seem to have a significant chance of complete recovery (15). For patients with recent-onset cardiomyopathy, the utility of endomyocardial biopsy remains uncertain and the procedure is not routinely performed. However, the findings of the current investigation suggest that the incorporation of gene expression profiles may significantly improve the predictive value of myocardial assessment.
The Fas/FasL system is involved in the pathogenesis of autoimmune myocarditis (16) and peripartum cardiomyopathy (17). Elevated levels of soluble Fas and FasL have been shown in patients with myocarditis (10) and chronic congestive heart failure (69), and have been found to predict clinical outcomes (11). The TNFR1 receptor, when activated by TNF-alpha, induces several cellular processes, including apoptosis (18). Patients with increased expression of Fas and TNFR1 may be showing a more profound response to myocardial injury, resulting in increased cell death and diminished potential for recovery. Alternatively, these patients may have undergone biopsy at a more advanced stage of disease progression, in which increase in programmed cell death is evident. Whether increased expression represents a distinct response to injury or a simply a different stage of the inflammatory/apoptotic response cannot be determined by the current study.
Male gender was associated with higher Fas and TNFR1 expression. The murine model of autoimmune disease shows significant gender differences in the expression of genes associated with programmed cell death (19). Testosterone stimulates apoptosis in vitro in renal tubular cells, and may contribute to the more rapid progression of diabetic nephropathy in men (20). In a rat ischemia-reperfusion model, reduction of androgens through surgical castration or hormonal therapy decreases pro-inflammatory and pro-apoptotic gene expression and facilitates myocardial recovery (21). The tendency of androgens to stimulate cytokine and pro-apoptotic gene expression would theoretically limit myocardial recovery in men relative to women and may underlie the male predominance in idiopathic dilated cardiomyopathy (22).
Plasma levels of TNF-alpha are elevated in patients with new-onset cardiomyopathy and correlate with myocardial expression (19). The current study shows a strong correlation between myocardial expression of Fas and TNF-alpha consistent with the role of TNF in initiating the apoptotic pathway. Despite this correlation, TNF-alpha and FasL expression were not predictive of recovery of left ventricular function, suggesting that receptor expression is more reflective of myocardial processes that lead to apoptosis than the circulating ligands. Additionally, the role of TNF-alpha in acute cardiomyopathy is complex; TNF-alpha plays a role in cell survival and protection through induction of the transcription factor nuclear factor kappa-beta (18). The overall impact of TNF expression on LV recovery may therefore represent a synthesis of these two competing roles: protection from viral injury and facilitation of apoptosis.
In acute viral myocarditis, cytokine expression and apoptosis may be beneficial and facilitate viral clearing. Although the current cohort is defined by the recent onset of symptoms, they seem to be beyond the stage of an acute viral trigger. No patient was febrile at the time of endomyocardial biopsy, all had normal white cell counts, and only one had histologic evidence of lymphocytic myocarditis. The apparent negative impact of cytokine and apoptotic myocardial expression in this cohort may reflect a later post-viral stage of this disorder, and the current study cannot address the potential protective role in acute viral myocarditis.
There are several limitations to this study. Given the limited myocardial tissue available, protein levels of Fas and TNFR1 were not assessed. In addition, immunohistochemistry quantifying apoptotic nuclei was not performed. Soluble Fas and FasL were not assessed in the serum, and this study cannot address the predictive value of these more accessible peripheral markers of apoptosis. We have previously shown that circulating TNF correlates with myocardial expression (23). In addition, as with routine histology, biopsy studies of gene expression may be subject to sampling error because of regional variations. However, previous studies of myocardial gene expression in the right ventricle septum showed significant correlation with expression in the left ventricular free wall (24). Finally, patients in this study were part of a larger randomized trial of immune globulin therapy, and we cannot rule out that an interaction with the randomized therapy may have impacted the results. The absence of any impact of treatment of immune globulin on subsequent LVEF in the larger trial diminishes this possibility (12).
This study is the first to suggest that the gene expression profile from an endomyocardial biopsy predicts subsequent LV recovery for patients with recent-onset cardiomyopathy. Activation of apoptotic pathways, as delineated by higher Fas and TNFR1 expression, denotes a subset of patients unlikely to recover LV function, whereas patients with minimal Fas and TNFR1 expression experienced a dramatic increase in LVEF during subsequent follow-up. Whether patients with higher Fas and TNFR1 expression were showing a differential response to injury or were captured at a later phase of their illness remains a question for further study. In contrast to the role of the ligands TNF-alpha and FasL, high expression of the receptors Fas and TNFR1 seems to limit LV recovery and may represent targets for therapeutic intervention.
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