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Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana.
Correspondence to Dr. K.J. Kelly, Indiana University School of Medicine, Division of Nephrology, 950 W. Walnut Street, RII 202, Indianapolis, IN 46202-5116. Phone: 317-274-7453; Fax: 317-274-8575;
| Abstract |
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(TNF-
) and interleukin-1 (IL-1) after renal ischemia in the mouse. In the present study, an animal model of bilateral renal ischemia was used to test the hypothesis that cytokines released with renal ischemia have effects on other organ systems. Increased levels of immunoreactive TNF-
and IL-1 and intercellular adhesion molecule-1 mRNA were found in the heart after renal ischemia in the rat. This was accompanied by increases in myeloperoxidase activity, an index of tissue leukocyte infiltration, in the heart as well as the liver and lung. Functional changes in the heart 48 h after renal ischemia included increases in left ventricular end diastolic diameter, left ventricular end systolic diameter, and decreased fractional shortening by echocardiography. Evidence of apoptosis of cardiac cells was also found 48 h after an abbreviated period of renal ischemia insufficient to induce azotemia but not bilateral nephrectomy (which resulted in significant renal failure), suggesting that renal ischemia but not uremia is necessary for the apoptosis observed. It was also found that blocking the action of TNF-
limited cardiac apoptosis. Renal ischemia results in distant effects and the alterations observed in the heart may be important in the morbidity and mortality observed clinically. E-mail: kajkelly@iupui.edu | Introduction |
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Although myocardial depressant factors have been postulated, the pathophysiology of cardiac dysfunction in ARF remains unclear (9). Leukocytes have long been thought to be important in cardiac dysfunction after ischemia (10), and agents that block leukocyte function or localization protect against injury (1113). An elevated white cell (WBC) count markedly increases the risk of acute myocardial infarction in humans (14), and removing WBC from cardioplegia solution improves myocardial function in stressed piglet hearts (15).
Leukocyte localization to sites of injury or inflammation is largely mediated by adhesion receptors (16). The initial rolling of leukocytes on activated endothelium is mediated by members of the selectin family. This allows exposure of WBC to inflammatory mediators such as interleukin-1 (IL-1) and tumor necrosis factor-
(TNF-
) and activation of the rolling leukocytes. Adhesion receptors, including intercellular adhesion molecule-1 (ICAM-1), on endothelial cells interact with their counterreceptors on leukocytes, resulting in immobilization of leukocytes on the endothelium and diapedesis of WBC across the vessel wall. ICAM-1 expression is increased by IL-1 and TNF-
in vitro (16). A significant body of data demonstrates the detrimental effects of these cytokines on the heart. The negative effects include left ventricular dysfunction and apoptosis of both cardiac myocytes and endothelial cells (17).
We have previously reported increases in the systemic levels of IL-1 and TNF-
after renal ischemia in an animal model (18). The purpose of the present study was to investigate the effect of these systemic increases in inflammatory mediators on the heart.
| Materials and Methods |
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action, polyclonal anti-TNF-
antibody (1 mg/kg; Endogen, Inc, Woburn, MA) was administered intravenously to some animals at the time of ischemia. Sham surgery consisted of an identical surgical procedure with the exception of application of microaneurysm clamps. In some experiments, mouse antibody against intercellular adhesion molecule-1 (ICAM-1) (20) or vehicle (0.9% NaCl) was administered intravenously at the time of ischemia. To determine whether renal failure was necessary for the changes observed, in another series of experiments, different periods of ischemia (15, 30, and 45 min) were employed. Bilateral nephrectomy (which produced renal failure without ischemia) was performed by ligating both renal arteries and veins through a midline incision after insuring adequate anesthesia. Both kidneys were removed, and the incision was closed in two layers. Blood was obtained via tail vein for determination of hematocrit as well as urea nitrogen and creatinine (by standard urease and picric acid reactions).
TNF-
Levels
TNF-
in sera obtained before surgery or 1, 2, 6, 24, or 48 h after ischemia or sham surgery was determined by immunoassay using reagents available from R & D Systems (Minneapolis, MN) according to the manufacturers protocol (18).
Fluorescence Microscopy
A Zeiss confocal microscope (LSM 510) equipped with UV, Argon, and Helium lasers was used. Pieces from the in situ fixed hearts were preserved in 20% sucrose before 10-µm frozen sections were obtained. Sections were stained with rabbit anti-rat IL-1 or anti-rat TNF-
polyclonal antibody (Endogen, Inc., Woburn, MA) followed by FITC-conjugated goat anti-rabbit antibody (Amersham Pharmacia Biotech, Piscataway, NJ) and then FITC-conjugated donkey anti-goat antibody (Amersham) and DAPI (a nuclear stain, Molecular Probes, Eugene, OR). Control sections were stained with secondary and tertiary antibodies only (21).
Northern Analysis
Renal RNA was isolated using TRI reagent (Molecular Research Center, Cincinnati, OH) according to the manufacturers protocol (22). Blots were probed with 32P-labeled ICAM-1 (23) as described previously (18). Membranes were exposed for 24 to 72 h and read by PhosphorImager (Molecular Dynamics, Sunnyvale, CA).
Myeloperoxidase (MPO) Activity
MPO activity, used as an indicator of leukocyte infiltration, was measured as described previously (19). Briefly, aliquots of supernatants of tissue homogenates were analyzed using o-dianisidine dihydrochloride and H2O2. MPO activity was normalized to protein content and expressed as percent increase over animals subjected to sham surgery.
Echocardiographic Analysis
Rats were lightly anesthetized with pentobarbital (30 mg/kg). M-mode echocardiograms were obtained from the short axis view of the left ventricle at the tip of the mitral valve leaflets using an Interspec-ATL Apogee X200 ultrasound machine (Ambler, PA) with a dynamically focused 9-mHz annular array transducer. Tracings were interpreted without knowledge of the experimental group. Left ventricular (LV) end diastolic dimension (EDD) and anterior (interventricular septal; AWT) and posterior wall thicknesses (PWT) were measured by the leading edge method at the time of maximum diastolic dimension. LV end systolic dimension (ESD) was determined at the time of the maximum anterior motion of the posterior wall.
TUNEL Reaction
Forty-eight hours after surgery, hearts were perfusion fixed with 4% paraformaldehyde, sectioned at 4 microns, and the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) reaction (Promega, Madison, WI) was performed according to the manufacturers protocol. All nuclei were counterstained with propidium iodine or DAPI. TUNEL-positive nuclei were quantified as percent of total nuclei in coded sections. The negative control was incubated without enzyme (terminal deoxynucleotidyl transferase), and the positive control was treated with DNAse before the TUNEL reaction. To assess the specificity of the TUNEL reaction in this model, nuclear morphology after DAPI staining was examined in a subset of the TUNEL-positive nuclei (21).
DNA Electrophoresis
Given the experimental difficulty of identifying apoptosis in tissue sections (24), DNA electrophoresis was also used to document apoptosis. Cardiac DNA was extracted using TRI reagent according to the manufacturers protocol. Electrophoresis was carried out using a 1% agarose gel. DNA was visualized by staining with ethidium bromide.
Sphygmomanometry
Systolic BP was measured by tail cuff using an IITC (Woodland Hills, CA) amplifier before anesthesia, after anesthesia but before surgery, during surgery, and 6 and 24 h after renal ischemia or sham surgery.
Statistical Analyses
Data are expressed as means ± 1 SE. ANOVA was used to determine if differences among mean values reached statistical significance. t test was used for comparisons between groups. Tukey test was used to correct for multiple comparisons. The null hypothesis was rejected at P < 0.05.
| Results |
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Levels
after experimental renal ischemia/reperfusion (18). IL-1 was increased 1 and 2 h after ischemia and returned to basal levels by 4 h. In the present study, we further define the increases in systemic TNF-
. Before ischemia and after sham surgery, TNF-
was undetectable in the serum. TNF-
increased by 1 h post-ischemia, increased further at 2 h and remained elevated compared with levels after sham surgery for 24 h, but levels were not significantly different from the sham surgery group 48 h post-ischemia (Figure 1).
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was seen 6, 24, and 48 h after renal ischemia (30 min; Figure 2), both proximal to blood vessels and in multinucleated cells. No staining was apparent after sham surgery.
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antibody at the time of renal ischemia when compared with hearts from the group subjected to ischemia only (Figure 8). Examination of the DAPI channel alone (21) in 20 TUNEL-positive nuclei showed nuclear condensation and/or fragmentation consistent with apoptosis (data not shown).
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| Discussion |
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Cytokines are thought to be important in the pathophysiology of congestive heart failure (29,30). Overexpression of TNF-
in the heart results in severely impaired cardiac function, myocyte apoptosis, and leukocyte infiltration of the heart (31). In the isolated rat heart, perfusion with TNF-
results in a decrease in left ventricular developed pressure (LVDP) and coronary vasoconstriction (32). TNF-
mediated apoptosis is one of the proposed mechanisms for its association with cardiac dysfunction (31). Increased plasma TNF-
has been found in human CHF (33). However, trials with the TNF-
receptor antagonist etanercept or antiTNF-
antibody (infliximab) in human CHF did not improve death rate or hospitalization for CHF (34). Chronic treatment with IL-1 in the dog results in sustained myocardial dysfunction, WBC infiltration of the heart, and increased cardiac myeloperoxidase activity. Myocardial dysfunction can be prevented by blocking adhesion receptors (35).
In vitro, cytokines such as TNF-
and IL-1 upregulate adhesion receptors such as ICAM-1 on endothelia. Adhesion receptors mediate the localization of WBC to sites of injury or inflammation. The interaction of adhesion receptors, including ICAM-1, on endothelial cells with their counter-receptors on leukocytes facilitates the immobilization of leukocytes on the endothelium, WBC exposure to cytokines, and activation and diapedesis of WBC across the vessel wall (16).
In this study, we found increases in immunoreactive IL-1 and TNF-
and increases in ICAM-1 mRNA levels in the heart after renal ischemia. These increases were accompanied by increased cardiac MPO activity, consistent with leukocyte infiltration and activation in the heart. The increases in MPO activity could be prevented by administration of anti-ICAM-1 antibody at the time of ischemia. It is possible that anti-ICAM-1 prevents leukocyte infiltration of the heart after renal ischemia. We have previously demonstrated that treatment with anti-ICAM-1 antibody at the time of renal ischemia results in preservation of renal function (19). Thus, an alternate explanation for the lack of increase in cardiac MPO after renal ischemia and anti-ICAM-1 antibody is the lack of renal failure in this setting.
We assessed the functional significance of the changes observed in the heart using echocardiography. Echocardiography can be used to assess the risk of death in patients with essential hypertension (36). We thus used echocardiography to evaluate cardiac function in rats with renal failure and found evidence of impaired cardiac function 48 h after renal ischemia. At this time, there was no difference in systolic BP, hematocrit, or body weight between the sham surgery and renal ischemia groups.
Loss of cardiomyocytes is also believed to be critical in the pathogenesis of congestive heart failure. Transgenic models have shown that apoptosis alone can result in heart failure (37). The increase in cardiac apoptosis we observed after renal ischemia may account for the decrease in cardiac function post-ischemia. Although renal failure can result in hemodynamic changes, the controls used were subjected to the same anesthetic and sham surgery, and no differences in systolic BP were observed. Renal ischemia, but not uremia, was critical in the induction of apoptosis in the heart, because TUNEL-positive cells were found after 15 min of renal ischemia (which did not produce renal failure), but not bilateral nephrectomy (which resulted in significant renal failure). Nephrectomy produces renal failure without inflammation. In contrast, cisplatin-mediated renal injury, which may have an inflammatory component (38), increases the number of TUNEL-positive cells in the heart.
To our knowledge, this is the first demonstration of alterations in cardiac function after experimental renal ischemia. Decreases in cardiac index and stroke volume have been observed after intestinal ischemia/reperfusion in the rat (39). Injury to the contralateral kidney has been demonstrated with unilateral renal ischemia (40). Alterations in phagocyte function have also been demonstrated after renal injury (41). Ischemia/reperfusion injury in several models (for example, intestine [42], liver [43], muscle [44], and contralateral lung [(45]) result in lung injury, although pulmonary dysfunction was not found after renal ischemia/reperfusion (46). Renal dysfunction has also been demonstrated after ischemic injury in other organ systems (47). In many of these systems, dysfunction in other organ systems was associated with increased systemic levels of cytokines after ischemic injury (39,43,47,48). Experimental renal ischemia has also been shown to stimulate the production of granulocyte-colony stimulating factor by the kidney and IL-10 by the liver (49).
In summary, this study demonstrates multiple alterations in the heart after renal ischemia. The changes include increases in mRNA levels of the adhesion receptor intercellular adhesion molecule-1, myeloperoxidase activity, and presence of apoptosis. This is accompanied by left ventricular dilation and decreased fractional shortening. If similar changes occur in human acute renal failure, the decreased cardiac function may be an important determinant of the unacceptably high mortality in acute renal failure.
| Acknowledgments |
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| References |
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