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Am J Physiol Heart Circ Physiol 281: H2612-H2618, 2001;
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Vol. 281, Issue 6, H2612-H2618, December 2001

PR-39 and PR-11 peptides inhibit ischemia-reperfusion injury by blocking proteasome-mediated Ikappa Balpha degradation

Jialin Bao1, Kaori Sato1, Min Li1, Youhe Gao1, Ruhul Abid2, William Aird2, Michael Simons1, and Mark J. Post1,3

1 Angiogenesis Research Center, 2 Division of Molecular Medicine, Beth Israel Deaconess Medical Center, 3 Angiogenesis Research Center, Dartmouth Medical School, Hanover, New Hampshire 03756


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

PR-39 inhibits proteasome-mediated Ikappa Balpha degradation and might protect against ischemia-reperfusion injury. We studied PR-39, its truncated form PR-11, and a mutant PR-11AAA, which lacks the ability to prevent Ikappa Balpha degradation, in a rat heart ischemia-reperfusion model. After 30 min of ischemia and 24 h of reperfusion, cardiac function, infarct size, neutrophil infiltration, and myeloperoxidase activity were measured. Intramyocardial injection of 10 nmol/kg PR-39 or PR-11 at the time of reperfusion reduced infarct size by 65% and 57%, respectively, which improved blood pressure, left ventricular systolic pressure, and relaxation and contractility (±dP/dt) compared with vehicle controls 24 h later. Neutrophil infiltration, myeloperoxidase activity, and the expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule 1 were reduced. Thus PR-39 and PR-11 effectively inhibit myocardial ischemia-reperfusion injury in the rat in vivo. This effect is mediated by inhibition of Ikappa Balpha degradation and subsequent inhibition of nuclear factor-kappa B-dependent adhesion molecules. The active sequence is located in the first 11 amino acids, suggesting a potential for oligopeptide therapy as an adjunct to revascularization.

rat; reactive oxygen species


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

DESPITE ADVANCES in the management of acute myocardial ischemia, limitation of ischemia-reperfusion injury remains an important clinical challenge. Recently, we demonstrated that a naturally occurring proline-arginine-rich PR-39 peptide selectively inhibits proteasome-mediated degradation of Ikappa Balpha , resulting in inactivation of transcription nuclear factor (NF)kappa B (7). Studies of acute myocardial infarction and acute pancreatitis models in mice demonstrated that systemic administration of the peptide reduced expression of leukocyte adhesion molecules, including intercellular adhesion molecule-1 (ICAM-1) and vascular adhesion molecule-1 (VCAM-1), as well as generally suppressed NFkappa B-dependent transcription (7). Activation of NFkappa B due to degradation of its cytoplasmic Ikappa Balpha inhibitor is an early event in myocardial ischemia-reperfusion injury (4, 17). This increase in NFkappa B-dependent transcription results in enhanced expression of endothelial adhesion molecules, including P-selectin (13), ICAM-1 (11), and VCAM-1 (27), and thus initiates rolling and transmigration of circulating neutrophils and monocytes (14). We hypothesized that locally administered PR-39 might protect against myocardial ischemia-reperfusion injury by suppressing NFkappa B-dependent expression of these adhesion molecules, thereby inhibiting accumulation and/or activation of invading white blood cells and reducing local inflammatory response.

To study the mechanism for PR-39 protection against ischemia-reperfusion injury, we investigated the effect of PR-39 and two derivatives: PR-11 and PR-11AAA. PR-11 comprises the first 11 amino acids of the PR-39 sequence, and in PR-11AAA the first three arginines are replaced by alanines, which block its inhibitory effect on tumor necrosis factor-alpha (TNF-alpha )-induced degradation of Ikappa Balpha in vitro. We find that intramyocardial injection of PR-39 and PR-11 into the area of myocardium at risk 30 min after occlusion of the proximal coronary artery and before restoration of blood flow inhibits ischemia-induced upregulation of ICAM-1 and VCAM-1 and decreases accumulation of neutrophils, resulting in reduction in the infarct size and enhanced preservation of myocardial function. At the same time, injections of PR-11AAA peptide had no effect on any of these end points. The data support the hypothesis that ischemia-induced activation of NFkappa B-dependent expression of endothelial adhesion molecules results in accumulation of neutrophils and subsequent ischemia-reperfusion injury. PR39 and PR-11 peptides are able to disrupt this cycle by preventing degradation of Ikappa Balpha by the proteasome pathway.


    METHODS
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Animal model. Male Sprague-Dawley rats (250-300 g) were anesthetized with ketamine 100 mg/kg and xylazine 10 mg/kg, intubated, and ventilated (Tidal volume: 2 ml, 55 min, model 683, Harvard Apparatus; Holliston, MA). An electrocardiogram (ECG) was recorded during ischemia-reperfusion and during the final study using needle electrodes. At the final study, the carotid artery was cannulated to record blood pressure and left ventricular pressure (LVP) using dedicated physiological monitors (model 200, Micro-Med; Louisville, KY) interfaced with a computer.

For ischemia-reperfusion, a left fifth intercostal thoracotomy was performed under sterile conditions. The pericardium was incised, and the left anterior descending coronary artery (LAD) was ligated for 30 min. At the start of reperfusion the animals were randomized to receive intramyocardial injections of PR-39, PR-11, PR-11AAA (250 µM, 40 µl/kg), or vehicle (phosphate-buffered saline, pH = 7.4) into the ischemic part of the heart in two equal injections. The chest was closed, and ECG and blood pressure were recorded for another 15 min. Successful ligation and reperfusion of the LAD were confirmed by ECG changes and discoloring of the subtended myocardium. After 24 h, the animal was reanesthetized and ventilated as before. The carotid artery was cannulated for aortic blood pressure and LVP recording. Subsequently, the LAD was religated at the previous level, and 0.3 ml 4% Evans blue was injected into the aorta 5 min before euthanasia. After harvest, the heart was processed for macroscopic, biochemical, and histologic analysis.

The study was compliant with the National Institutes of Health Guide for the Care and Use of Laboratory Animals (NIH Publication No. 85-23, Revised 1985) and was approved by the institutional Animal Care and Use Committee.

Analysis of physiological data. BP, ECG, LVP, contractility (+dP/dt) and relaxivity (-dP/dt), and the relaxation constant tau were recorded at 500 Hz and analyzed by the Digi-med system integrator model 200. Before ligation and at the final study, stable recordings of 10-15 min were obtained and physiological parameters were averaged over 5 min. Stable recordings were obtained during the last 10 min of ischemia and the last 5 min of reperfusion, and parameters were averaged over 2-5 min.

Area at risk and infarct areas calculation. The excised heart was rinsed with phosphate-buffered saline three times and cut in five cross sections (1 mm). Cross sections were incubated in 1% 2,3,5-triphenyltetrazolium chloride (Sigma; St. Louis, MO) for 25 min at 25°C. Digital photographs of the cross sections were made, and the area at risk, the vital area, and the infarcted area were delineated by an observer blinded to treatment using computer-assisted image analysis (Optimas 6.0).

Measurement of tissue myeloperoxidase activity and Western blot analysis. A cross section 2 mm apical from the ligature was divided into a nonischemic area and ischemic area (300-µg samples), snap frozen in liquid nitrogen, and stored at -80°C. Myocardial myeloperoxidase (MPO) activity was measured according to the method described by Mullane et al. (20). In brief, the frozen myocardial tissue was pulverized, weighed, and suspended in 1 ml of 50 mM potassium phosphate buffer solution (pH 6.0) containing 0.5% (wt/vol) hexadecyltrimethylammonium bromide (Sigma). The samples were then blended for 90 s (30 s, 3×), sonicated for 10 s, freeze-thawed three times with liquid nitrogen, and again sonicated for 10 s. Specimens were ultracentrifuged at 45,000 g for 15 min, and the volume of supernatant was measured. The supernatant (10 ml) was mixed with 290 µl of 50 mM potassium phosphate buffer solution (pH 6.0) containing 0.167 mg/ml o-dianisidine hydrochloride (Sigma) and 0.0005% (vol/vol) hydrogen peroxide. The change in absorbance at 460 nm was measured every 30 s for 4 min using a microplate reader. One unit of MPO activity was defined as the amount needed to degrade 1 mmol peroxide/min at 25°C, and the result was expressed as units of MPO per microgram of protein.

For Western blot analysis, the same samples were subjected to 10% SDS-PAGE and electrotransferred to an Immobilon-P membrane (Millipore, MA). Membranes were preincubated for 30 min in 3% milk-phosphate buffer solution and then incubated with either ICAM-1 (HA58 clone, Pharminogen; San Diego, CA), VCAM-1 (1.4C3 clone, Pharminogen), or Ikappa Balpha antibody (Santa Cruz; Santa Cruz, CA) for 1 h at room temperature. After being washed with phosphate-buffered saline, the membrane was incubated with IgG horseradish peroxidase (1:2,000) for 1 h. The membrane was again washed three times with phosphate-buffered saline and then developed using the ECL kit (Amersham), followed by exposure to Kodak XAR film. Equal loading of various samples was confirmed by Ponceau staining.

Histologic analysis. A cross section 3 mm apical from the ligature was fixed with 10% formaldehyde overnight, embedded in paraffin, sectioned into 5-µm sections, and stained with hematoxylin and eosin. From each section, five and two high power fields (HPF, 400×) were randomly selected from the area at risk and nonischemic area, respectively. In each HPF, polymorphonuclear neutrophils (PMNs) were counted by an experienced observer blinded to treatment assigned. The results were summated for final neutrophil counts.

PR-39 and PR-11. PR-39 and PR-11 peptides were synthesized by CS Bio (San Carlos, CA) and dissolved in sterile saline at a concentration of 250 µM. PR-11 is a carboxyl-end truncated form of PR-39 with 11 amino terminus amino acids remaining: Arg-Arg-Arg-Pro-Arg-Pro-Pro-Tyr-Leu-Pro-Arg. In PR-11AAA the first three arginines were replaced by alanines.

Ikappa Balpha Westerns. Ikappa B Westerns were performed as previously described (7). In brief, human umbilical vein endothelial cells (HUVEC) were exposed to TNF-alpha (5 ng/ml for 10 min) after 45 min of preincubation with PR-39, PR-11, PR-11AAA (all 500 nM), or the proteasome inhibitor MG132 (10 µM). Cells were lysed, and Ikappa Balpha levels were determined by Western blotting with a rabbit polyclonal antibody.

Measurement of reactive oxygen species. For detection of intracellular reactive oxygen species (ROS) level, human coronary adult endothelial cells at 80-90% confluence were serum starved overnight in EBM-2 (Clonetics) medium containing 0.5% serum in a 10-cm plate, were washed twice with prewarmed Hank's balanced salt solution (HBSS; GIBCO BRL), preincubated for 2 h with the PR peptides or known inhibitors, and then incubated in 5 ml HBSS containing 15 µM 2',7'-dichlorofluorescein diacetate (DCFH-DA; Molecular Probes) at 37°C for 30 min. For stimulated ROS measurement, the cells were incubated with phorbol myristate acetate (PMA) or N-phenylmethazonium methosulfate (PMS) for 1 h after 2 h of pretreatment with PR-39. Cells were washed with ice-cold HBSS, gently scraped from the plate, and resuspended in 1 ml of HBSS. DCF fluorescence was measured by fluorescence-assisted cell sorting (FACS, excitation wavelength = 485 nm, emission wavelength = 530 nm) by counting 20,000 viable cells (events) from each sample. Propidium iodide (5 µg/ml) was added to exclude dead cells. Each experiment was done in triplicate and repeated at least two times.

Matrigel pellet assay. Twenty C57/BL6 male mice weighing 20 g were anesthetized with 100 mg/kg ketamine ip. Regular Matrigel (Becton Dickinson; Bedford, MA) was mixed with 5 µg/ml PR-39 on ice. With the use of a 24-gauge needle, 0.5 ml of supplemented Matrigel was injected subcutaneously in the abdominal midline under sterile conditions. Two weeks later, the pellets were harvested and processed for histology. Thin sections (5 µm) were cut and stained with hematoxylin and eosin. Blood vessels (cell-lined tubes or circles containing red blood cells) were counted in 10 random HPF (×400 magnification) by an observer blinded to treatment, and the results were summated over the 10 HPFs

Statistical analysis. Data throughout the manuscript are expressed as means ± SE. Means of treatment groups are compared by ANOVA with least significant difference corrected post hoc analysis of group differences using StatView 5.0.1 (SAS Institute; Cary, NC). P values < 0.05 were considered statistically significant.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

PR-39 and PR-11, but not PR-11AAA, inhibit Ikappa Balpha degradation in endothelial cells. To test the effect of PR-39, PR-11, and PR-11AAA on proteasome-mediated degradation of Ikappa Balpha , we assessed intracellular Ikappa Balpha levels in HUVEC 45 min after exposure to TNF-alpha . Western blotting demonstrated complete disappearance of Ikappa Balpha in control cells (Fig. 1). At the same stimulus, pretreatment with either PR-39 or PR-11 (500 nM), but not with PR-11AAA, inhibited TNF-alpha -induced Ikappa Balpha degradation by 50 or 25%, respectively, compared with a general proteasome inhibitor MG132 at high concentration (10 µM).


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Fig. 1.   Western blot of Ikappa Balpha on human umbilical vein endothelial cells (HUVEC) cells stimulated with tumor necrosis factor-alpha (TNF-alpha ) and incubated with vehicle (veh), PR-39, PR-11, or MG-132. PR-39 and PR-11 both inhibit Ikappa Balpha degradation comparably to MG-132.

Rat myocardial ischemia-reperfusion model: acute effects of PR peptides injection. Ischemia was induced by ligation of the LAD in 36 rats, and reperfusion was successfully established in all animals after 30 min of ischemia. One animal in the vehicle (control) group died of ventricular fibrillation within 1 h of ligation, and three animals (1 from the vehicle group and 2 from the PR-39 group) died overnight after several hours of reperfusion. Sixteen rats (8 treated with vehicle and 8 with PR-39) were sham operated with the placement of a suture around the LAD without tying. Data from 48 animals (8 per group) were analyzed. No acute adverse effects of intramyocardial PR-39, PR-11, or PR-11AAA injections (hypotension, arrhythmias, myocardial rupture) were seen in this study.

Before and during ischemia, mean arterial blood pressure was similar in the four groups (Table 1). Shortly after reperfusion and after the intramyocardial injection of PR-39, PR-11, PR-11AAA, or vehicle, there were also no differences in mean arterial blood pressure and heart rate among the groups.

                              
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Table 1.   Mean arterial blood pressure and heart rate during ischemia-reperfusion

Myocardial area at risk and the left ventricular function. Area at risk, determined by Evans blue dye injection while the LAD was reoccluded, was similar in all groups (51.9 ± 3.6% in the vehicle group, 49.8 ± 2.7% in the PR-39 group, and 44.1 ± 3.2% in the PR-11 group, 53.5 ± 2.9 in PR-11AAA group, ANOVA, P = 0.34). Intramyocardial administration of either PR-39 or PR-11 resulted in a significant (64% and 57%, respectively, P < 0.0001 for both) reduction in the infarct size compared with the vehicle group (Fig. 2), whereas PR-11AAA treatment was similar to the vehicle (Fig. 2).


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Fig. 2.   A: injection of PR-39 with an HA-tag, visualized with an anti-HA antibody. Four hours after injection, PR-39 is diffused over a wide area (*). B: infarct size expressed as percentage of the area at risk. C: PR-39 and PR-11 reduced infarct size significantly (ANOVA: *P < 0.001), whereas PR-11AAA had no effect. n = 8 rats for each group.

After 24 h of reperfusion, cardiac function was better preserved in the PR-39 and PR-11 than in PR-11AAA or vehicle-treated animals, resulting in higher mean arterial pressures (Table 1, P < 0.05 compared with the vehicle group), higher left ventricular systolic pressures (P < 0.01 vs. vehicle), and higher +dP/dt and lower -dP/dt (P < 0.05 and P < 0.01 vs. vehicle, respectively). No differences in end-diastolic pressure, heart rate, or tau were observed at this time point (Table 1). In sham-operated rats, arterial pressure during surgery did not change. PR-39 had no effect on the left ventricular function on sham-operated rats 24 h after surgery. For instance, left ventricular systolic pressure was 94.4 ± 3.5 mmHg in vehicle and 94.6 ± 4.6 mmHg in PR-39-treated animals, and end-diastolic pressures were 9.1 ± 2.4 mmHg and 9.3 ± 2.3 mmHg, respectively

Myocardial neutrophil infiltration and MPO activity. To assess the impact of PR peptides on myocardial accumulation of white blood cells, we quantified the presence of PMNs on histologic sections of the myocardium after 24 h of reperfusion. In nonischemic territories of the heart, very small numbers of PMNs were counted, and there were no differences among the treatment groups. In contrast, analysis of the area at risk demonstrated high PMN counts and significant reduction in PR-39- and PR-11- but not in the PR-11AAA-treated animals (Fig. 3A).


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Fig. 3.   Neutrophil counts (A) and myeloperoxidase (MPO) activity (B) in the areas at risk. For each heart, a midventricle cross section was taken and 5 high power fields (HPFs, ×400) were randomly chosen for counting. Polymorphonuclear neutrophils (PMNs) were identified on the basis of their unique appearance in hemotoxylin and eosin-stained tissues. Neutrophil counts were consistently and significantly lower in the PR-39 and PR-11 (P = 0.0009 and P = 0.014, respectively). Number of neutrophils in the PR-11AAA-treated hearts were similar to vehicle controls (P = 0.64). Virtually no MPO activity is found in normal parts of the heart (P = 0.001 vs. ischemic). n = 8 rats in each group. PR-39 and PR-11 both inhibited MPO activity in the ischemic territory by 55% (P = 0.03 for PR-39 and P = 0.05 for PR-11). No difference was observed between PR-11AAA and vehicle treated hearts (P = 0.62). * P < 0.05; **P < 0.01.

To further confirm the inhibitory effect of PR39 and PR11 peptides on myocardial PMN accumulation, we assessed total myocardial MPO activity. MPO activity was significantly reduced in PR-39- and PR-11-treated groups by 55%, P = 0.04 and P = 0.02, respectively, with no reduction in the PR-11AAA group (Fig. 3B). Sham ischemia resulted in an MPO activity in the target area of 0.034 ± 0.008 U/mg protein (not significant compared with control area in ischemic hearts), which was not affected by PR39 treatment (0.040 ± 0.008 U/mg protein). In sham-operated animals PR-39 did not affect neutrophil count or MPO activity.

Reduction of ICAM-1, VCAM-1, and increase in Ikappa Balpha . Western analysis performed on samples from the area at risk 24 h after reperfusion showed a substantial reduction in ICAM-1 and VCAM-1 expression by PR-39 and PR-11, but not by PR-11AAA (Fig. 4), further supporting a reduction of NFkappa B-dependent protein expression and linking this pathway with reduction of neutrophil attraction into the area of reperfusion. Most likely the reduced NFkappa B effects were due to increased levels Ikappa Balpha levels in the ischemic areas of the hearts that were treated with PR-39 and PR-11 (Fig. 4)


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Fig. 4.   Western analysis of intercellular adhesion molecule-1 (ICAM-1) and vascular adhesion molecule-1 (VCAM-1) from the area at risk after 24 h of reperfusion. PR-39 and PR-11 reduced expression of these adhesion molecules, and PR-11AAA had no effect. Experiments were repeated 4 times on different samples from the treatment groups.

PR peptides do not exhibit anti-p47phox effect. A recently published study suggests that PR-39 interacts with the p47phox component of NADPH oxidase (15, 25) and that this interaction may result in reduced generation of ROS such as H2O2 and ONOO- that would in turn contribute to reduction in the ischemia-reperfusion injury. To evaluate this potential mechanism, we measured the formation of ROS in human cardiac adult endothelial cells in the presence of PR-39, PR-11, and a known inhibitor of NADPH oxidase diphenyleneiodonium (DPI). Neither PR-39 nor PR-11 inhibited the formation of ROS, whereas DPI (100 µM) reduced it by 70% (Fig. 5A). PMA and PMS stimulated ROS production 1.4- and 1.9-fold, respectively, which was not affected by preincubation with 5 µg/ml PR-39 (Fig. 5B). Because another aspect of PR-39 activity is the inhibition of proteasome-mediated degradation of hypoxia-inducible factor (HIF)-1alpha , we assessed PR-39-induced angiogenesis in p47phox knockout and heterozygous control mice. The extent of angiogenesis induced by the peptide was the same in both settings (Fig. 5C).


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Fig. 5.   PR-39 and reactive oxygen species (ROS). ROS basal (A) production by human cardiac adult endothelial cells. PR-39 and PR-11 (crosshatched bar: 0.1 nM, open bar: 1 nM, hatched bar 5 µM) did not inhibit the formation of ROS in these cells, whereas diphenyleneiodonium (DPI) inhibited by 70%. In phorbol myristate acetate (PMA)- and N-phenylmethazonium methosulfate (PMS)-stimulated endothelial cells (B) PR-39 (solid bar: vehicle, open bar: 1 nM, crosshatched bar: 5 µM) did not affect ROS production either. In the mouse Matrigel model in p47phox-/- mice, PR-39 induced angiogenesis, which was similar to that in heterozygous littermates (C).


    DISCUSSION
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

The principal findings of this study are that PR-39 peptide and its derivative PR-11, following local injection into the transiently ischemic region of the left ventricle, protect against ischemia-reperfusion injury through inhibition of degradation of Ikappa Balpha . This in turn resulted in reduced activation of NFkappa B-dependent events such as the expression of the adhesion molecules ICAM-1 and VCAM-1 on endothelial cells in the ischemic but viable myocardium. This was accompanied by a reduction in myocardial accumulation of PMN and a decrease in the severity of reperfusion injury as assessed by the infarct size and left ventricular function measures. A mutant form of PR11, PR-11AAA, a peptide that did not prevent TNF-alpha -induced Ikappa Balpha degradation in cultured endothelial cells, was not effective in preventing the expression of NFkappa B-dependent genes VCAM-1 and ICAM-1 in an ischemia-reperfusion injury model in the rat heart and did not reduce the size or severity of myocardial injury.

The evidence summarized in this study, including reduction in the number of infiltrating neutrophils, reduced MPO activity, and reduced infarct size in the PR-39/PR-11-treated hearts, strongly supports the concept that ischemia-induced activation of NFkappa B-dependent gene expression and, in particular, expression of adhesion molecules such as ICAM-1 and VCAM-1, underlies ischemia-reperfusion injury.

We propose that the ability of PR-39 and its PR-11 derivative peptides to block proteasome-mediated degradation of Ikappa Balpha is the mechanism through which these peptides exert their effect in ischemia-reperfusion injury. The ability of PR-39 to block ischemia-reperfusion injury has recently been demonstrated in several models, including the mesentery (15) and the heart (10). In the case of mesenteric ischemia, systemically administered PR-39 in the rat inhibited leukocyte rolling and adherence in the inflamed mesentery and reduced the extent of reperfusion injury. Likewise, systemic infusion of PR-39 in a mouse cardiac ischemia-reperfusion model reduced PMN accumulation, mitigated ischemia-reperfusion injury, lowered the extent of myocardial necrosis, and preserved left ventricular function (10). However, the molecular mechanism of this effect remained unclear. We have recently shown that PR-39 binds to the alpha 7-subunit of the 20S proteasome, resulting in inhibition of Ikappa Balpha (7) and HIF-1alpha degradation (18). Unlike the usual proteasome inhibitor, PR-39 activity appears to be relatively selective to these two proteins with no significant effect on overall cellular protein degradation and no activation of the heat shock response (7).

At the same time, other studies suggested an alternative mechanism of PR-39 activity. In particular, the presence of proline-rich sequence suggested the possibility of interactions with SH3 domain-containing proteins, including a transmembrane protein p130(Cas) (3) and the p47phox subunit of NADPH (25). Whereas the biological effect of a potential PR39-p130(Cas) interaction still remains unclear, it is highly unlikely that inhibition of NADPH activity mediates any of PR-39 biological activities. Several lines of evidence from this study support this conclusion. Although both PR-11 and PR-11AAA peptides in this study have the same putative SH3 domain-binding sequence, only PR-11 inhibited TNF-alpha -induced Ikappa Balpha degradation and VCAM/ICAM expression in vivo. Furthermore, neither PR-39 nor PR-11 blocked baseline or PMA/PMS-induced generation of ROS in cultured endothelial cells. Finally, PR-39 was able to induce angiogenesis in Matrigel pellets implanted in p47phox-/- mice, a process that depends on inactivation of proteasome-mediated HIF-1alpha degradation (7). Moreover, a recent study of ischemia-reperfusion in p47phox-/- mice demonstrated that the extent of reperfusion injury was comparable to heterozygote littermate control mice (9).

Whereas many factors could have contributed to the difference between this observation and the original reports of PR-39-mediated inhibition of NADPH activity (1, 15), including differences in species and cell types, the most likely explanation is in the amount of peptide used. The PR-39 concentration reportedly required for the anti-NADPH effect, 5 µM (15), is significantly higher than the dose employed in the study of Gao et al. (7) or in the present study (estimated tissue concentration of 250 nM, based on a 10% retention of PR-39 during the first hour, and a local distribution volume that is 100-fold larger than the injection volume as estimated from immunohistochemistry). In vitro, as little as 100 nM of PR-39 is sufficient to fully inhibit 20S proteasome activity (Y. Gao and M. Simons, unpublished observations). Thus it is highly unlikely that the inhibition of NADPH oxidase at physiological and therapeutic concentrations of PR-39 is relevant for mitigation of ischemia-reperfusion injury. Finally, it is unlikely that the documented angiogenic effect of PR-39 (18) has contributed to the reduction in infarct size in this model of acute ischemia-reperfusion given the short duration of reperfusion (24 h).

Evidence from other studies supports the concept that the inhibition of endothelial adhesion molecules or their CD11/CD18 leukocyte receptors protects against ischemia-reperfusion injury. Thus both the infarct size and the extent of neutrophil invasion after ischemia-reperfusion injury in ICAM-1- and CD18-deficient mice are reduced by more than 50% (19, 21). Infusion of a monoclonal antibody against ICAM-1 reduced myocardial infarct size in dog (8), rabbit (28), and rat (12, 26) models of ischemia-reperfusion injury. Likewise, neutralizing antibodies against the alpha 4-integrin (VLA4, CD49d), the receptor for VCAM-1, reduced cerebral infarcts in rats after transient ischemia (23). In addition to ICAM-1 and VCAM-1, E-selectin (24) and P-selectin (16) are considered important cytokine-induced and NFkappa B-mediated adhesion molecules in inflammatory processes such as ischemia-reperfusion injury (22). A novel synthetic proteasome inhibitor PS-519 reduced ischemia-reperfusion injury in the rat Langendorff preparation, which was associated with attenuation of P-selectin expression in the coronary microvasculature (2).

Thus there is firm experimental support for the concept that inhibition of NFkappa B-dependent gene expression by either gene disruption or inactivation of expressed proteins would result in amelioration of ischemic injury. PR-39 should be especially effective in this regard given its unique ability to selectively inhibit proteasome-mediated Ikappa Balpha degradation thereby inhibiting expression of relevant NFkappa B-dependent genes.

Recent clinical trials with antibodies against single adhesion molecules, including CD18 and CD11b administered in a systemic fashion, have produced disappointing results (5, 6). In contrast to this approach, we investigated local injections into the area at risk of peptides capable of suppressing the activation of all NFkappa B-dependent genes, including endothelial cell adhesion molecules. In our view, this strategy has great clinical potential, but this is clearly an area that requires further study in patients with coronary heart disease.

In conclusion, PR39 is an effective inhibitor of ischemia-reperfusion injury in the rat heart in vivo. The peptide limits the infarct size and prevents cardiac dysfunction after temporary coronary ligation by reducing influx of neutrophils. Its effect is most likely based on inhibition of the 20S proteasome-mediated degradation of Ikappa Balpha and subsequent inhibition of NFkappa B-dependent expression of adhesion molecules. The active sequence is located in the first 11 amino acids, suggesting a potential for oligopeptide therapy as an adjunct to revascularization.


    ACKNOWLEDGEMENTS

This study was supported through National Heart, Lung, and Blood Institute Grants HL-53793 and HL636-09, EIA Award 9940074 of the American Heart Association and by MicroHeart, Inc. M. Simons is an Established Investigator of the AAHA.


    FOOTNOTES

Address for reprint requests and other correspondence: M. J. Post, Angiogenesis Research Center, Dartmouth Hitchcock Medical Center HB 7700, 1 Medical Center Dr., Lebanon, NH 03756 (E-mail: Mark.J.Post{at}Hitchcock.org).

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 31 January 2001; accepted in final form 24 August 2001.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Al-Mehdi, AB, Zhao G, Dodia C, Tozawa K, Costa K, Muzykantov V, Ross C, Blecha F, Dinauer M, and Fisher AB. Endothelial NADPH oxidase as the source of oxidants in lungs exposed to ischemia or high K+. Circ Res 83: 730-737, 1998[Abstract/Free Full Text].

2.   Campbell, B, Adams J, Shin YK, and Lefer AM. Cardioprotective effects of a novel proteasome inhibitor following ischemia and reperfusion in the isolated perfused rat heart. J Mol Cell Cardiol 31: 467-476, 1999[Web of Science][Medline].

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Am J Physiol Heart Circ Physiol 281(6):H2612-H2618
0363-6135/01 $5.00 Copyright © 2001 the American Physiological Society



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