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J Am Coll Cardiol, 2001; 38:1693-1700 © 2001 by the American College of Cardiology Foundation |


* Oxidative Stress Clinical Research Group and Division of Critical Care, Department of Medicine, Taipei Veterans General Hospital, and National Yang-Ming University School of Medicine, Taipei, Taiwan
Institute of Sports Science, Taipei Physical Education College, Taipei, Taiwan
Department of Biochemistry, College of Medicine, National Taiwan University, Taipei, Taiwan
Manuscript received January 23, 2001; revised manuscript received July 10, 2001, accepted August 9, 2001.
* Reprint requests and correspondence: Dr. Kelvin Tsai, Oxidative Stress Clinical Research Group and Division of Critical Care, Department of Medicine, Taipei Veterans General Hospital, 2F, 201, Section 2, Shih-Pai Rd., Taipei, 112, Taiwan
kctsai{at}vghtpe.gov.tw
| Abstract |
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The purpose of this study was to examine the changes in leukocyte mitochondrial transmembrane potential (MTP) and its association with apoptosis in congestive heart failure (CHF).
BACKGROUND
Congestive heart failure is a heterogeneous syndrome with multiple hemodynamic, neuroendocrine and immune abnormalities. Although edematous CHF may be associated with endotoxemia and increased cytokine production, peripheral blood leukocyte functions in advanced CHF remain unclear.
METHODS
Thirty patients with acute decompensated CHF (mean age [± SEM] 74.9 ± 3.1 years) and 20 healthy controls underwent determination of MTP, intracellular oxidants and apoptosis in three subsets of peripheral blood leukocytes. The measurements were repeated after the time of recompensation.
RESULTS
Patients with acute CHF showed marked MTP reduction and increased intracellular oxidant formation in three subsets of leukocytes upon entry into the study. These changes were more prominent in patients with peripheral edema. The decline in MTP was correlated with the severity of the peripheral edema and plasma concentration of cortisol, nitrogen metabolites and tumor necrosis factor-alpha (p < 0.01). After clinical stabilization, MTP gradually recovered. Leukocytes underwent increased propensity of apoptosis one week after the time of recompensation.
CONCLUSIONS
The mitochondrial depolarization and apoptosis of leukocytes in decompensated heart failure suggest that CHF is associated with severity-dependent impairments in leukocyte function. Accentuated hormonal and cytokine abnormalities and increased circulating oxidants may contribute to these changes. Early and aggressive management of advanced heart failure is helpful in the recovery of these immune abnormalities.
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Cellular energization status is crucial to the activity and vitality of cells (11). Mitochondrial transmembrane potential (MTP), the driving force of cellular adenosine triphosphate (ATP) formation, is an important determinant of the energization status and physiological activity of the cell, and also constitutes an obligate step in cell-death programs (1215). A reduction in MTP can be triggered by various apoptotic inducers such as glucocorticoids, ischemia, reactive oxygen species (16), tumor necrosis factor-alpha (TNF-
) (17) and nitrogen metabolites (18). These inducers may cause functional disturbance in mitochondrial respiratory chain components or the inappropriate opening of the permeability transition (PT) pores, resulting in mitochondrial depolarization and MTP disruption (13). The mitochondrial functional status of immunocompetent cells in patients with CHF has not been investigated yet.
Because the extent of neuroendocrine and immune disturbances in CHF patients is correlated with the severity of heart failure and hemodynamic parameters (2,7,19), it is tempting to speculate that these abnormalities may be more prominent at the deterioration stage of CHF. To gain further insight into the mixed and complex responses of the immune system to CHF, we conducted a prospective, observational study to investigate peripheral blood leukocyte MTP and its propensity for apoptosis in 30 decompensated CHF patients. The study subjects were grouped according to whether peripheral edema existed or not, and were sequentially gauged to evaluate time-sequence changes after appropriate management of CHF.
| Methods |
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Hemodynamic monitoring. Twenty of the 35 included patients (8 in the endematous group and 12 in the nonedematous group) underwent pulmonary artery cannulation with a balloon-tipped, flow-directed, 7F Swan-Ganz catheter through the internal jugular or subclavian vein. Pressure waveforms were recorded in the right atrium, pulmonary trunk and pulmonary artery wedge positions. Cardiac output was determined by applying the thermo-dilution method.
Blood sampling. Immediately upon fulfillment of the inclusion criteria, 10 ml of venous blood was obtained by venipuncture for sampling. Part of the blood (5 ml) was anticoagulated with heparin and assayed immediately for various fluorescence stainings (see subsequent text). The remaining blood samples were EDTA-anticoagulated, centrifuged and stored in a frozen state at 70°C. Repeated blood sampling was performed under fasting states at the time of hemodynamic recompensation (mean duration 5.6 ± 2.4 days after admission) and one week thereafter.
Cell isolation. The heparinized blood was divided into several 200 µl aliquots. Each aliquot was treated with 3 ml of 1:10 erythrocyte lysing buffer (PharMingen, San Diego, California) for 10 min. The supernatant was discarded and the cells were washed with phosphate-buffered saline and resuspended with Hanks balanced salt solution (Gibco BRL, Paisley, Scotland) to approximately 105 cells/ml. The viability of leukocytes was confirmed to be more than 95% by trypan blue exclusion.
For assaying DNA fragmentation, polymorphonuclear leukocytes (PMN) and peripheral blood mononuclear cells (PBMC) were separated from whole blood by Histopaque-1119 (Sigma, St. Louis, Missouri) and Ficoll-Hypaque (Pharmacia, Uppsala, Sweden) centrifugation. After isolation and resuspension, the cells were fixed with 1% paraformaldehyde and 70% ethanol and stored under 70°C for further assay.
Cell labeling. Aliquots of leukocytes were labeled separately with the following fluorescent probes. The MTP was specified by incorporating the fluorochrome 5,5',6,6'-tetrachloro-1,1'3,3'-tetraethylbenzimidazolcarbocyanine iodide (JC-1) (Molecular Probes, Eugene, Oregon) in cell staining. The leukocyte suspension was incubated with 5 µmol/l JC-1 for 20 min at 37°C. After staining, JC-1 was incorporated into the mitochondria, where it either formed monomers (green fluorescence, 527 nm) or, at high MTP, aggregates (red fluorescence, 590 nm). The ratio between fluorescence intensity of JC-1 aggregates and monomers can reliably reflect MTP (20). In addition, intracellular oxidants were evaluated by incubating the cells with 20 µmol/l 2',7'-dichlorofluorescein (DCF) diacetate (Molecular Probes) for 20 min at 37°C (21).
The DNA fragmentation assay. The DNA fragmentation of nuclei was assessed using terminal deoxynucleotidyltransferase to incorporate fluorescein-isothiocyanate-dUTP into nuclei (TUNEL assay), following the manufacturers protocol (APO-BRDU Kit, PharMingen, San Diego, California) (22). The percentage of apoptosis was calculated as the number of cells in the high fluorescence intensity population divided by the total number of cells (PMN or PBMC) analyzed.
Flow-cytometric evaluation. Fluorescence was analyzed by cytometry using a FACScan (Becton Dickinson, San Jose, California) fitted with an air-cooled argon laser emitting at 488 nm. During analysis, a gate was set on the dot plot of forward and side scatter to include PMN, monocytes or lymphocytes. The identity of cell populations in each analysis was confirmed by counterstaining with CD45 and CD14 antibody reagents (23). The total number of events from each sample was made such that at least 5,000 events were collected for each cell population. To ensure consistency of data among the different measurements, the photomultiplier values of the detector in FL1 and FL2 remained constant and were set at 450 V throughout all the experiments. All the analyzing procedures were undertaken within 3 h after blood sampling.
Associating plasma factors.
For the following assays, EDTA-anticoagulated plasma samples were used. Nitrogen metabolites, including nitrites and nitrates, were measured by a modified Griess method (BIOXYTECH Nitric Oxide Non-Enzymatic Assay, Oxis, Portland, Oregon), with a detection sensitivity of 1 µmol/l. Lipid peroxides (including malondialdehyde and 4-hydroxyalkenals) were analyzed by a colorimetric assay kit (LPO assay kit, CalBiochem, San Diego, California), with a detection limit of 0.1 µmol/l. Cortisol was assayed by a radioimmunoassay (RIA) kit (DSL-2000 Cortisol RIA kit, Diagnostic Systems, Webster, Texas), with a detection sensitivity of 2.7 nmol/l. Both TNF-
and interleukin-6 (IL-6) concentrations were measured using ultrasensitive ELISA kits (BioSource, Camarillo, California), with a minimum detectable range of 1.7 pg/ml and 0.7 pg/ml, respectively.
Statistics. All continuous data were expressed as mean ± SEM. Time-sequence changes and group comparisons were assessed by the Mann-Whitney U test or two-way analysis of variance (ANOVA) models with repeated-measures ANOVA methods when appropriate. Spearman rank correlation or Pearsons product moment correlation analyses were used to establish the relation between variables. A p value < 0.01 was considered statistically significant.
| Results |
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Apoptosis. The DNA fragmentation assay revealed a delayed appearance of apoptotic leukocytes in CHF subjects one week after the time of recompensation (Fig. 2). The percentage of apoptotic cells was higher in PMN (up to 42.9%) than in PBMC (up to 20.8%). Leukocytes from patients with edematous CHF showed a higher percentage of apoptosis than those of nonedematous subjects, but the difference did not reach statistical significance except that at one week for PBMC (p < 0.01 by Mann-Whitney U test).
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and IL-6) concentrations during the observation period. Plasma nitrite/nitrate levels increased approximately two-fold from admission, as compared with the control value. More prominent changes were noted in plasma lipid peroxide levels, with the increase reaching sevenfold compared with the control value. The increases in plasma oxidants were more pronounced in the edematous subjects. Plasma cortisol levels increased significantly from admission in the edematous CHF subjects, and the levels normalized one week after the time of recompensation. Finally, plasma TNF-
and IL-6 levels markedly increased in patients with edematous CHF, and remained supranormal throughout the study period.
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(p < 0.01).
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| Discussion |
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Possible mechanisms underlying MTP disruption.
Several factors may potentially contribute to the leukocyte MTP disruption in patients with CHF. First, increased intracellular oxidants, as evidenced by increased DCF fluorescence, may lead to oxidation of carrier molecules in the respiratory chain and/or mitochondria pyridine nucleotides, which either hamper the respiratory coupling or induce mitochondrial PT (16) with resultant MTP disruption. Second, increased DCF fluorescence might also signify greater production of mitochondrial reactive nitrogen species such as nitric oxide or peroxynitrite (21), which is able to cause reversible or irreversible inhibition of respiratory enzymes and lead to MTP disruption (2426). Alternatively, increased plasma nitrogen metabolites, probably secondary to endothelial nitric oxide synthase activation by endotoxemia and increased circulating cytokine in edematous CHF (27,28), may also trigger MTP disruption in leukocytes (9). Third, plasma TNF-
, with the potential to deplete cells of nicotinamide adenosine diphosphate (NAD) and adenosine triphosphate (ATP) due to the activation of poly-ADP-ribose polymerase (29), is another culprit in mitochondrial depolarization. Although it was unclear whether the plasma concentration of TNF-
in our CHF patients was adequate to elicit these changes, the fact that leukocytes from patients with CHF have both enhanced expression of surface TNF-
receptors and more responsiveness to TNF-
(30) seems to heighten this possibility. Finally, cortisol also seems to be a potential contributor of MTP disruption (31,32). The plasma concentration of cortisol increased to about 500 nmol/l in our CHF patients, exceeding concentrations that were able to induce lymphocyte MTP disruption and apoptosis in vitro (33).
Disruption and apoptosis of MTP. Recent evidence proposed the paradigm that the reduction in MTP may constitute an early and committed step in cell apoptosis (14,15). The dissipation in MTP may induce apoptotic programs by disturbing mitochondrial ATP production and by inducing the release of mitochondrial matrix solutes, cytochrome C, and other pro-apoptotic factors (34). In the present study, a significant percentage (23.5%) of peripheral blood PMN underwent apoptosis at the decompensated stage of CHF. Intriguingly, the propensity of PMN apoptosis increased for a period after the time of recompensation. Also, PBMC underwent apoptosis at this stage. It seems that these phenomena may reflect the temporal effect of downstream events in the apoptotic program induced by mitochondrial depolarization.
Comparisons between edematous and nonedematous CHF.
The increased plasma concentrations of TNF-
and IL-6 in CHF patients, especially those with peripheral edema, corroborate previous findings (1). The in-crease in inflammatory cytokines may potentially augment phagocytic oxidant production and lead to more intravascular oxidants, as shown by Keith et al. (2) and our study (Fig. 3B). Our study further demonstrates a two-fold increase in plasma nitrogen metabolites and a 1.5-fold increase in plasma cortisol in the edematous CHF patients. Because all these factors have the potential to induce mitochondrial depolarization and apoptosis, the greater degree of their abnormalities seems to account for the more prominent leukocyte dysfunctions in the edematous CHF patients. The significant correlation of MTP levels with the severity of peripheral edema renders further support to this notion.
Possible clinical implications. The CHF-related immune alterations seem to be multifold and remain to be clarified. Congestive heart failure with peripheral edema or cachexia has been shown to be associated with immune activation and increased circulating pro-inflammatory cytokines (1,35). Conversely, reduced host defenses, as evidenced by an increased susceptibility to pneumonia, have also been reported in CHF patients (36). The present study further explores the pathomechanisms underlying the immune disturbances associated with CHF by demonstrating an impaired leukocyte mitochondria functional status and an increased propensity for apoptosis in severe and untreated heart failure. These phenomena may constitute a pivotal facet of immune dysfunction in advanced CHF. That leukocyte dysfunction partly improved after the restoration of hemodynamic functions may underscore the importance of early and aggressive management of advanced heart failure.
Study limitations. Unlike well-controlled laboratory investigations where a single variable can be manipulated at a time, circulating leukocytes are under simultaneous influence by a number of contributing factors, making a definite conclusion very difficult to reach. In addition, medications used in the treatments of CHF, such as catecholamines, also have the potential to induce lymphocyte apoptosis (37), thus making the interpretation of this studys results more complex. Cautions must also be taken in the interpretation of the results of the TUNEL assay, as it may be too sensitive to detect not only the specific DNA fragmentations in apoptosis, but also the nicks in DNA that were produced by topoisomerase (38) or the random DNA degradation occurring during necrosis (39,40). Further in-depth studies are demanded to verify the different pathways that are involved in the immune abnormalities associated with acute CHF.
Conclusions. Congestive heart failure is a state of physiological stress. The stress resides not only in the level of cardiovascular function, but also at the cell level, as exemplified by leukocyte mitochondrial depolarization and apoptosis. The impaired functional status of peripheral blood leukocytes may impair host defenses in the acute deterioration stage of CHF. Successful management of CHF not only improves the patients hemodynamic status but also restores the leukocyte energization status. These findings may shed new light on both the pathogenesis and the treatment of immune disturbances in CHF.
| Footnotes |
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| References |
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and tumor necrosis factor receptors in the failing human heart. Circulation. 1996;93:704711This article has been cited by other articles:
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