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Am. J. Respir. Crit. Care Med., Volume 165, Number 4, February 2002, 449-455

Protective Effects of Cyclosporin A from Endotoxin-induced Myocardial Dysfunction and Apoptosis in Rats

HAROLD FAUVEL, PHILIPPE MARCHETTI, GUILLAUME OBERT, OLIVIER JOULAIN, CLAUDE CHOPIN, PIERRE FORMSTECHER, and RÉMI NEVIÈRE

INSERM U459, Faculté de Médecine 1, EA 2689, CHRU and Université de Lille 2, and Département de Physiologie, Faculté de Médecine Lille, Lille, France


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Myocardial depression can be demonstrated following administration of endotoxin. Proposed mechanisms of endotoxin-induced myocardial dysfunction include the release of proinflammatory mediators, focal myocardial ischemia, and the presence of activated leukocytes within the myocardium. Recently, myocardial caspase activation and mitochondria-related apoptotic events (i.e., release of cytochrome c) were demonstrated in the failing septic heart. Here, we tested the hypothesis that immunosuppressors, cyclosporin A and tacrolimus (FK 506), would improve inflammation, heart nuclear apoptosis, and myocardial dysfunction in endotoxin-treated rats. Myocardial contractility was assessed using an isolated heart preparation. Heart leukocyte infiltration was assessed by measurement of heart myeloperoxidase activity. Leukocyte activation was studied using the intravital microscopy of the mesenteric venule. Apoptosis was detected as myocardial DNA fragmentation, downstream caspase activation, and mitochondrial cytochrome c release. Both cyclosporin A and FK 506 reduced heart leukocyte sequestration and venular adhesion in endotoxin-treated rats. Cyclosporin A, which blocks mitochondrial cytochrome c release, was able to reduce endotoxin-induced myocardial end-stage nuclear apoptosis and heart dysfunction, whereas tacrolimus had no such effects. These effects could be related to the unique properties of cyclosporin A to act on mitochondria.

    INTRODUCTION
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Keywords: endotoxin; cardiomyocyte; mitochondria; cytochrome c; apoptosis

Human and animal studies have shown that myocardial contractile depression is an early manifestation of sepsis syndrome (1). Myocardial depression can be demonstrated in experimental animal models following administration of endotoxin, a lipopolysaccharide component of the outer membrane of gram-negative bacteria (2, 4, 5). Although the etiology of myocardial contractile dysfunction in this condition is incompletely described, potential mechanisms include the effects of circulating and locally produced "depressant substances" such as proinflammatory cytokines, for example, tumor necrosis factor (TNF)-alpha and nitric oxide (6), focal myocardial ischemia and necrosis (10), and the presence of activated leukocytes within the myocardium (11, 12).

In the heart, apoptosis may be activated under conditions such as cytokine stimulation. Indeed, proinflammatory cytokine TNF-alpha directly induces apoptosis of cardiomyocytes in vitro (13). Furthermore, we and other groups have recently shown that sepsis may also trigger apoptotic pathways in the heart and that these events may contribute to endotoxin-induced myocardial dysfunction (14). In most cases, the execution phase of the apoptotic process involves the participation of mitochondria as caspase activators (17, 18). Mitochondria release cytochrome c into the cytosol, where it binds to and induces oligomerization of Apaf-1 (19, 20). Once activated by cytochrome c, oligomerized Apaf-1 then binds procaspase-9, resulting in procaspase-9 proteolytic self-processing and activation of caspase-3, which participates as a terminal effector of apoptosis by cleaving crucial nuclear substrates (20). In sepsis, myocardial upstream and downstream caspase activation, as well as mitochondria-related apoptotic events such as release of cytochrome c, was recently demonstrated in the failing septic heart (15, 16).

A large body of evidence suggests that inflammation and apoptosis pathway activation contribute to endotoxin-induced myocardial dysfunction. In this context, we hypothetized that immunosuppressive compounds, that is, cyclosporin A (CsA) and tacrolimus (FK 506), would alter heart inflammation and apoptosis and ameliorate myocardial dysfunction in sepsis. Indeed, CsA and FK 506 are calcineurin inhibitors believed to exert their action through binding to cyclophilins and FK binding proteins, also known as immunophilins (21). When complexed with CsA and FK 506, the properties of immunophilins change, leading to the inhibition of the phosphatase calcineurin and subsequent inhibition of T cell activation. In addition, calcineurin inhibitors have been shown to inhibit cell apoptosis in vitro through mechanisms compatible with inhibition of mitochondrial permeability transition related to the opening of a megachannel in the inner mitochondrial membrane, cytochrome c release, and increases in levels of proteins of the Blc-2 family (22, 23). In vivo, analogues of CsA that block the mitochondrial permeability transition in isolated mitochondria are able to reduce reperfusion-induced myocardial dysfunction (22, 24, 25). Although these findings suggest that under certain conditions, calcineurin inhibitors may improve the function of the reperfused myocardium, the effects of CsA and FK 506 on endotoxin-induced myocardial inflammation and apoptosis have not been specifically addressed in the septic heart.

Therefore, in this study, we examined the protective effects of cyclosporin A and tacrolimus on myocardial dysfunction in heart from endotoxin-treated rats. The results of this study provide new pieces of information: (1) both CsA and FK 506 were able to reduce heart leukocyte sequestration, vascular leukocyte activation, and serum concentrations of TNF-alpha and (2) CsA, but not FK 506, was able to offer protection to endotoxin-induced myocardial cell apoptosis and improve myocardial function.

    METHODS
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Animal Preparation

Care and use of animals were in accordance with our institution's guidelines for the care and use of laboratory animals. Six groups of adult male Sprague-Dawley rats were studied, that is, saline-treated (control animals), endotoxin-treated (Endo. 10 mg/kg of endotoxin from Escherichia coli serotype 055:B5), CsA-treated (10 mg/kg) and FK 506-treated (3 mg/kg) control and endotoxin-treated rats. Four hours after treatment, rats were prepared for either physiological measurements or for in vitro assays.

Physiological Measurements

Isolated and perfused heart preparationMyocardial contractile function was studied using a modified Langendorff isolated heart preparation as we have previously described (26).

Leukocyte adhesion in the mesenteric venulesThe mesenteric microcirculation was observed with the use of an intravital microscope (Eclipse E800 Nikon microscope, Tokyo, Japan). As previously described, single unbranched mesenteric venules were selected for study of leukocyte rolling and adhesion (27, 28).

Biochemical Measurements

Cytokine determination and leukocyte countSerum levels of interleukin (IL)-1beta , IL-6, and TNF-alpha were determined by use of commercially available immunoassay kits (enzyme-linked immunosorbent assay [ELISA]). Circulating blood leukocytes and differential counts of leukocytes were performed.

Myeloperoxidase assayMyeloperoxidase (MPO) was extracted from homogenized tissue by suspending the pellets in 0.5% hexadecyl trimethylammonium bromide in 50 mM phosphate buffer and MPO activity was assayed spectrophotometrically as described (29, 30).

DNA fragmentation detectionFor the detection of oligonucleosomes, a cell death detection ELISA plus kit (Boehringer, Mannheim, Germany) was used according to the manufacturer's instructions. For electrophoresis, DNA was extracted from cardiac tissue (LV apex) using a commercially available isolation kit (Genzyme TACS, R&D Systems, MN) (15). The DNA obtained was used in a ligation mediated polymerase chain reaction (LM-PCR) assay according to the manufacturer's instructions (Clontech Laboratories, Palo Alto, CA) (15).

Caspase-3 activity and Western blot analysis for procaspase-3

For measurements of caspase-3 activity, heart proteins were diluted and incubated at 25° C with the colorimetric substrate Ac-DEVD-pNA (Biomol, Plymouth, PA) in 96-well microtiter plates. Cleavage of the p-nitroaniline (p-NA) dye from the peptide substrate was determined by the measure of absorbance of p-NA at 405 nm in a microplate reader Digiscan (Asys Hitech, Cincinnati, OH) (14, 15). Results were calibrated with known concentrations of p-NA and expressed in picomoles of substrate cleaved per minute and per microgram proteins at 25° C.

For procaspase-3 immunoblotting, fresh heart tissue was resuspended in RIPA buffer. Lysates were centrifugated at 14,000 × g and 200 µg of supernatant was loaded on 12.5% polyacrylamide gels, electrophoresed, and transferred as previously described (14). Procaspase-3 was detected using a polyclonal rabbit anti-procaspase-3 antibody (Santa Cruz Biotechnology Inc., Santa Cruz, CA), which recognizes the 32-kD unprocessed procaspase-3.

Isolation of mitochondria and swellingThe mitochondrial fraction was prepared as previoulsy described (31). For determination of swelling, mitochondria were washed and resuspended (1 mg/ml) in sucrose buffer. Mitochondrial swelling was estimated from the decrease in absorbance measured at 520 nm in a spectrophotometer as described (32). Large amplitude swelling was induced by addition of 320 µM calcium at the indicated time.

Western blot analysis for cytochrome c

Mitochondrial protein samples in loading buffer were run on 12% SDS-PAGE gels. The proteins on the gel were electrophoretically transferred to nitrocellulose membranes. After blocking, membranes were treated with mouse monoclonal anticytochrome c antibody (Pharmingen, Becton Dickinson Company). Membranes were then incubated with horseradish peroxidase-conjugated sheep anti-mouse immunoglobulin G (IgG) secondary antibody (Sanofi Diagnostics Pasteur, Bio-Rad), washed, and bound antibodies were detected using chemiluminescence with an ECL Plus kit (Amersham).

Statistical Analysis

For in vitro and in vivo studies, we tested for differences using ANOVA procedures (SPSS 9.0 for Windows, IL). Data are presented as means ± SEM throughout. A value of p < 0.05 was considered significant.

    RESULTS
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Cyclosporin A Prevented Endotoxin-induced Myocardial Dysfunction

As shown in Table 1, left ventricle (LV) developed pressure (LVDP) and its first derivatives (i.e., dP/dtmax and dP/dtmin) were significantly decreased 4 h after administration of endotoxin as compared with control animals. Coinjection of CsA (10 mg/kg) largely prevented LV systolic function alterations of endotoxin-treated hearts (n = 7 in each group). FK 506 (3 mg/kg) had no detectable effects on myocardial function in endotoxin-treated animals (n = 7 in each group) (Table 1). Animals cotreated with endotoxin and CsA exhibited LVDP-preload relationships that were shifted upward compared with animals treated with endotoxin alone, suggesting improved systolic myocardial performance (Figure 1). Animals cotreated with endotoxin and FK 506 exhibited LVDP-preload relationships that were similar to animals treated with endotoxin alone (Figure 1). CsA and FK 506 treatment had no effects on myocardial function in control animals (Table 1).

                              
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TABLE 1

 ASSESSMENT OF MYOCARDIAL FUNCTION*dagger


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Figure 1.   Effects of cyclosporin A (CsA) and tacrolimus (FK 506) on endotoxin-induced myocardial dysfunction. Changes in LV systolic performance in control hearts (squares) and in hearts 4 h after injection with endotoxin alone (triangles) or in association with either CsA (upside-down triangles) or FK 506 (diamonds) (n = 7 in each group). Results are displayed as mean ± SEM. Left ventricular (LV) end-diastolic pressure (LVEDP) was increased incrementally from -5 to +20 mm Hg in order to construct LV developed pressure (LVDP)-preload relationship curves. Compared with control, the LVDP- preload relationships were shifted downward (in the direction of LV systolic performance decrease) in endotoxin-treated rats and in endotoxin + FK 506-treated rats. Endotoxin + CsA-treated rat hearts exhibited a shift of LVDP-preload relationships upward compared with endotoxin-treated rat hearts (in the direction of LV systolic performance increase). Endotoxin + FK 506-treated rat hearts exhibited LVDP-preload relationships similar to endotoxin-treated rat hearts. CsA and FK 506 had no effects on LV function in control rats (data not shown). *p < 0.01 compared with control rats.

Cyclosporin A and Tacrolimus Reduced Endotoxin-induced Inflammation

CsA and FK 506 reduced serum TNF-alpha levels in endotoxin-treated rats but had no effects on IL-1beta and IL-6 levels (Figure 2A). Compared with control rats, heart MPO activity, an index of heart leukocyte infiltration, was increased in endotoxin-treated rats. CsA and FK 506 reduced heart MPO activities in endotoxin-treated rats (Figure 2B). Consistently, leukocyte adhesion on the mesenteric venule, a surrogate of vascular inflammation, was increased in endotoxin-treated rats compared with control rats. In endotoxin-treated rats, CsA and FK 506 administration provided significant reduction of adhesive interactions between leukocytes and venular endothelium (Table 2). Compared with endotoxin-treated rats, measured hemodynamic variables (i.e., mean arterial pressure and shear rate) were unchanged (Table 2) in CsA and FK 506 endotoxin-treated rats, which suggest that these compounds did not interfere with the physical forces that modulate leukocyte behavior within the microvasculature.


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Figure 2.   Effects of cyclosporin A (CsA) and tacrolimus (FK 506) on serum cytokine levels and heart leukocyte infiltration induced by endotoxin. (A) ELISA determination of inflammatory cytokines (IL-1beta , TNF-alpha , IL-6) levels in sera from treated rats (n = 8 in each group). Results are displayed as mean ± SEM. Cytokine levels increased in endotoxin-treated rats (*p < 0.01 compared with control rats). CsA and FK 506 reduced serum TNF-alpha levels in endotoxin-treated rats (dagger p < 0.01 compared with endotoxin-treated rats). (B) Compared with control rats, heart myeloperoxidase (MPO) activity, an index of heart leukocyte infiltration, increased in endotoxin-treated rats. CsA and FK 506 prevented heart MPO activities in endotoxin-treated rats. Results are displayed as mean ± SEM. (*p < 0.01 compared with control rats; n = 5 in each group; dagger p < 0.01 compared with endotoxin-treated rats.)

                              
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TABLE 2

 MEAN ARTERIAL BLOOD PRESSURE, MESENTERY VENULAR SHEAR RATE, CIRCULATING LEUKOCYTE COUNTS, AND MESENTERIC VENULE LEUKOCYTE ROLLING AND ADHESION IN CONTROL ANIMALS, ENDOTOXIN-TREATED RATS, AND CYCLOSPORIN A-TREATED AND TACROLIMUS-TREATED ENDOTOXEMIC RATS*dagger

Cyclosporin A Prevented Endotoxin-induced Myocardial Cell Nuclear Apoptosis

As shown in Figure 3A, significant nuclear DNA fragmentation detected by agarose gel electrophoresis was evident 4 h after endotoxin injection in the myocardium. Oligonucleosomal DNA fragmentation confirmed nuclear apoptosis 4 h after endotoxin injection (Figures 3A and 3B). CsA protected myocardial cells from DNA fragmentation induced by endotoxin, whereas FK 506 had no effects (Figure 3).


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Figure 3.   Cyclosporin A (CsA) and not tacrolimus (FK 506) prevented endotoxin-induced myocardial cell nuclear apoptosis. (A) Analysis by agarose gel electrophoresis shows endotoxin-induced nucleosomal ladders after LM-PCR assay (see METHODS), which were prevented by CsA and not by FK 506. (B) Oligonucleosomal DNA fragmentation confirmed nuclear apoptosis 4 h after endotoxin injection, which was reduced by CsA and not FK 506 treatment. Results are expressed as OD/µg proteins of seven independent experiments. Results are displayed as mean ± SEM. (*p < 0.01 compared with control rats; dagger p < 0.01 compared with endotoxin-treated rats).

Effects of Cyclosporin A and Tacrolimus on Endotoxin-induced Caspase-3 Activation

Four hours after endotoxin administration, caspase-3 activity assessed by measuring hydrolysis of the preferential substrate Ac-DEVD-pNA, increased in rat heart (n = 8 rats in each group) (Figure 4A). Results of immunoblotting (n = 4 in each group) indicated that in contrast to control hearts, the proteolytic activation of procaspase-3 was significant in endotoxin-treated myocardium (Figure 4B). Neither CsA nor FK 506 prevented proteolytic activation of procaspase-3 and caspase-3 activity increases in endotoxin-treated rat hearts.


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Figure 4.   Effects of cyclosporin A (CsA) and tacrolimus (FK 506) on endotoxin-induced caspase activation. (A) Effects of CsA and FK 506 on procaspase-3 cleavage. Immunoblotting for procaspase-3 was performed on heart lysates in control and endotoxin-treated rats. Protein levels of procaspase-3 (32 kD) were reduced in myocardium from endotoxin-treated rats compared with myocardium from control, which suggests caspase-3 activation (see METHODS). Four independent immunoblottings were scanned on a densitometer. The intensity of the values obtained were expressed in arbitrary units. Results are displayed as mean ± SEM. *p < 0.01 compared with control rats. (B) Effects of CsA and FK 506 on caspase-3 activity. Heart DEVDase enzymatic activities were measured 4 h after in vivo treatments with specific p-NA substrates as described in METHODS. Results are expressed as picomoles of substrates-p-NA hydrolyzed per minute and per microgram of proteins. Results are displayed as mean ± SEM (n = 8 in each group) made in duplicate. *p < 0.01 versus endotoxin-treated group.

Cyclosporin A Prevented Mitochondrial Cytochrome c Release in the Septic Heart

Results of immunoblotting indicated that cytochrome c, in contrast to normal hearts, was substantially reduced in the mitochondrial fraction of endotoxin-treated rat hearts (Figure 5). The reduction in mitochondrial cytochrome c observed in endotoxin-treated rats was prevented by CsA, but not by FK 506 (Figure 5).


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Figure 5.   Cyclosporin A (CsA) and not tacrolimus (FK 506) prevented the induction of the cytochrome c release in isolated mitochondria from endotoxin-treated hearts. (A) Proteins from the mitochondrial fractions were separated by 12% SDS-PAGE and were analyzed by immunoblotting for cytochrome c release (see METHODS). Four hours after injection, endotoxin reduced cytochrome c protein content into the mitochondrial fraction, which was prevented by CsA and not by FK 506. (B) Eight independent immunoblottings were scanned on a densitometer. The intensity of the values obtained were expressed in arbitrary units. Results are displayed as mean ± SEM. *p < 0.01 compared with control rats; dagger p < 0.01 compared with endotoxin-treated rats.

In Vitro Effects of Cyclosporin A and Tacrolimus on Heart Mitochondria Isolated from Control and Endotoxin-treated Rats

In these experiments, we have tested the capacity of CsA to inhibit mitochondria permeability transition (MPT) in our model of sepsis. Heart mitochondria were purified from control (Figure 6A) and endotoxin-treated rats (Figure 6B). Then, MPT was determined as large amplitude swelling after addition of a high dose of calcium, a standard protocol for the induction of permeability transition. As shown in Figure 5, no difference could be detected in the MPT-dependent colloidosmotic swelling induced by calcium of isolated mitochondria from control (Figure 5A) and endotoxin-treated rats (Figure 5B). As expected, preincubation of mitochondria with CsA fully inhibited calcium-induced PT (Figure 6). The MPT inhibitory effect of CsA was observed to the same extent on mitochondria from control and also on mitochondria from endotoxin-treated rats. In contrast, FK 506 was unable to protect mitochondria from MPT (Figure 6) even at high concentrations (data not shown).


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Figure 6.   Permeability transition of isolated mitochondria. Heart mitochondria derived from control (A) and endotoxin-treated rats (B) were monitored for changes in the absorbance (OD 520 nm) indicative of permeability transition-dependent swelling. As indicated by arrows, calcium (320 µM) was added to isolated mitochondria from control rats (closed squares) (A), preincubated for 5 min with cyclosporin A (CsA) (1 µM) (closed triangles) or preincubated for 5 min with tacrolimus (FK 506) (1 µM) (closed diamonds). The same experiments are realized on mitochondria from endotoxin-treated rats (open squares) (B), preincubated for 5 min with CsA (1 µM) (open triangles) or preincubated for 5 min with FK 506 (1 µM) (open diamonds). Results are displayed as mean ± SEM of four independent experiments. See RESULTS for comments.

    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

In this rat model of endotoxin-induced myocardial dysfunction, we found evidence of inflammation and end-stage apoptosis that may involve downstream caspase activation and mitochondria-related pathway events such as cytochrome c release. Pharmacological manipulation with immunosuppressors reduced endotoxin-induced inflammation and myocardial apoptosis. Both CsA and FK 506 reduced serum TNF-alpha levels, heart leukocyte sequestration, and venular endothelial adhesion in endotoxemic rats. CsA, but not FK 506, was able to offer protection from endotoxin-induced myocardial dysfunction and apoptosis. We speculated that the differential effects of the calcineurin inhibitors on myocardial dysfunction may be related to the unique effects of CsA on the mitochondrial function.

Proinflammatory mediators and leukocytes activated by proinflammatory cytokines contribute to the development of cardiovascular dysfunction associated with endotoxemia (2, 4, 7, 11, 12). The relevance of cytokine release and leukocyte adhesion in mediating cardiovascular dysfunction is illustrated by the finding that reduction of circulating cytokines and leukocyte activation attenuates endotoxin-induced cardiovascular dysfunction in shock models (33). In our model, endotoxin induced increases in TNF-alpha serum levels, heart MPO, and mesenteric endothelial-leukocyte interactions, which were mainly prevented by the administration of calcineurin inhibitors CsA and FK 506. These results are consistent with the finding that CsA and FK 506 modulate cytokine and adhesion molecule gene expression (36, 37) and attenuate cardiovascular failure by interfering with the processes of leukocyte adhesion and proinflammatory cytokine production in experimental models (37, 38).

Indeed, the identification of calcineurin as a target for the immunosuppressive drugs cyclosporin and FK 506 suggests a critical role for this phosphatase in the regulation of T cell reactivity and cytokine gene expression (22, 23). Cyclosporin and FK 506 inhibit calcineurin catalytic activity through complexes with cyclophilins and FKBP12, respectively. The mechanism whereby calcineurin promotes T-cell activation and cytokine activation has been largely attributed to the family of transcriptional regulators referred to as nuclear factor of activated T cells (NFAT). Dephosphorylation of NFAT and its translocation to the nucleus are followed by induction of several cytokines, including IL-2, IL-4, and TNF-alpha (39). Whereas NFAT factors are important downstream effectors, calcineurin also regulates activity of the transcriptional regulatory factors nuclear-kappa B, Elk-1, and myocyte enhancer factor-2 (39, 40). In addition, recent findings suggest that calcineurin promotes nitric oxide synthase, c-jun N-terminal kinase, extracellular signal-regulated kinase, and protein kinase C alpha  and theta  activation (40). Overall, these findings suggest a critical role for calcineurin in the regulation of several gene expressions (22, 23, 40) involved in the adaptative myocardial response to stress. Hence, inhibition of calcineurin activity may reduce endotoxin-induced cardiovascular inflammation and myocardial dysfunction. However, in our model of sepsis, CsA, but not FK 506, prevented myocardial dysfunction, suggesting that cyclosporin could improve myocardial function by interfering with different pathways. Indeed, in addition to their immunosuppressive effects, calcineurin inhibitors regulate processes of cellular apoptosis, suggesting that calcineurin is critical in death signaling (21, 41).

In the heart, apoptosis has been implicated as a major process in diseases including dilated cardiomyopathy, myocarditis, and ischemic reperfusion injury (42, 43). In cardiomyocytes, apoptosis pathways can also be activated under conditions such as cytokine and endotoxin stimulation, in vitro (13). Recently, we (14, 15) and other groups (16) have shown that in vivo, endotoxin induces myocardial apoptosis. In these studies, however, the observed small extent of cardiomyocyte nuclear apoptosis was likely insufficient to directly account for myocardial dysfunction. Therefore, it has been suggested that apoptotic pathways may be linked to myocardial dysfunction in other ways, involving multiple caspase activation and altered mitochondrial signaling. In the present study, we confirmed that endotoxin induces heart nuclear apoptosis as evidenced by detection of oligonucleosomes and electrophoresis DNA laddering (44). Consistent with previous results (13, 14, 16), we documented activation of apoptotic pathways in endotoxin-treated heart by measuring cytosolic activation of downstream caspase-3 and mitochondria cytochrome c release.

Growing evidence suggests that calcineurin participates in pathways of apoptotic death. Calcineurin inhibitors regulate apoptosis in cells stimulated by TNF-alpha and nitric oxide (23, 45). For example, cyclosporin and FK 506 potently inhibit cytotoxicity induced by TNF-alpha in rat hepatoma cells. Cyclosporin and FK 506 may oppose programmed cell death by inhibiting calcineurin activity, downstream caspase activaty, and mitochondrial signaling such as the mitochondrial pore transition and expression of Bcl-2. Consistently, in endotoxin-treated heart, CsA reduced heart internucleosomal DNA fragmentation. We found that neither cyclosporin nor FK 506 prevented increases in downstream caspase-3 activity, which was assessed by procaspase-3 protein level and DEVDase activity. However, cyclosporin, but not FK 506, prevented mitochondrial cytochrome c release in vivo and mitochondrial pore transition in vitro. These results suggest that in our model, cyclosporin may oppose cell death by inhibiting mitochondrial signaling (23, 41).

The differential effects of CsA and FK 506 on myocardial dysfunction could be related to their known opposite effects on mitochondrial permeability transition and cytochrome c release (21, 41). The mitochondrial permeability transition is caused by the opening of a nonspecific pore in the inner mitochondrial membrane under conditions of mitochondrial calcium overload, oxidative stress, and adenine nucleotide depletion (21, 32). CsA, but not FK 506, prevents in vitro mitochondrial permeability transition and cytochrome c release by blocking translocation of the matrix-specific cyclosporin D to the inner membrane of the mitochondria, thereby decreasing the mitochondrial megachannel sensibility to succinate and calcium ions and reducing mitochondrial swelling (21, 22). Indeed, we confirmed that CsA, as opposed to FK 506, prevented mitochondrial cytochrome c release in vivo in septic hearts and mitochondrial swelling in energized isolated mitochondria from control and septic hearts in vitro. However, in endotoxemic rats, CsA and FK 506 in vivo treatment effects on mitochondrial swelling were not tested because no differences between control and septic energized mitochondria were observed in our experimental setting. Overall, our results are consistent with previous studies showing that analogues of CsA inhibit the permeability transition pore and are able to provide myocardial protection (22, 24). Indeed, CsA provide protective effects in reoxygenated cardiac myocytes and reperfused heart (22, 24). The mechanisms of cyclosporin-induced myocardial protection remain speculative. It could be hypothetized, however, that beneficial effects of CsA on endotoxin-induced dysfunction may be related to independent mitochondria permeability transition effects (46), such as regulatory roles of immunophilins at the ryanodine receptor and antiapoptotic gene product bcl-2 (23, 39) and changes in nitric oxide production (50, 51).

In conclusion, these observations strongly suggest that (1) mitochondrial cytochrome c release may play an important role in the onset of end-stage nuclear apoptosis in endotoxemic heart and (2) CsA, which blocks cytochrome c release, was able to reduce endotoxin-induced heart end-stage nuclear apoptosis and myocardial dysfunction, which was not observed with FK 506. The precise mechanisms of the beneficial effects of cyclosporin warrant further investigations.

    Footnotes

Correspondence and requests for reprints should be addressed to Dr. Rémi Nevière, M.D., Ph.D., Département de Physiologie, Faculté de Médecine, 1, place de Verdun, Lille Cedex 59045, France. E-mail: rneviere{at}univ-lille2.fr

(Received in original form May 17, 2001 and accepted in revised form November 26, 2001).

This article has an online data supplement, which is accessible from this issue's table of contents online at www.atsjournals.org

Acknowledgments: This work was supported by IFR22, INSERM, Université de Lille 2, and by grants from MENRT and INSERM: Biologie et pathologie des régulations cellulaires. U459 and EA 2689 belong to IFR 22 (CHU, COL, INSERM, IRCL, Université Lille 2).
    References
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
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