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,
,,,1
* Department of Physiology, Queen’s University, Kingston, Ontario, Canada:
Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, USA;
Department of Medicine, Duke University Medical Center, Durham, North Carolina, USA; and
Department of Physiology, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada
1 Correspondence: Department of Physiology, Queen’s University, 18 Stuart St., Kingston, Ontario K7L 3N6, Canada. E-mail: melol{at}post.queensu.ca
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Key Words: echocardiography • gene therapy • ischemia • myocardial infarction • reperfusion • viruses
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. Biliverdin is further reduced to bilirubin by biliverdin reductase (1)
. The by-products of heme catabolism exert a broad spectrum of cytoprotective effects (1
2
3)
, indicating that HO-1 plays an obligatory role in the cellular adaptation to stress. Bilirubin is a potent antioxidant that scavenges peroxyl radicals and reduces peroxidation of membrane lipids and proteins (2)
. CO exerts powerful anti-inflammatory and anti-apoptotic effects (3)
, and free iron stimulates the synthesis of the iron binding protein ferritin, which reduces the formation of free radicals and up-regulates several key cytoprotective genes (4)
.
We reported previously a pre-emptive gene therapy strategy for myocardial protection from ischemia and reperfusion (I/R) injury using adeno-associated virus (AAV) to deliver HO-1 to the heart (5)
. Our results showed that delivery of HO-1 gene to the left ventricle (LV) by AAV several wk in advance of coronary artery ligation leads to a marked acute myocardial protection in a rat model of acute I/R injury. We reported comparable results after delivery of the free radical scavenging enzyme extracellular superoxide dismutase (ecSOD) gene (6)
. Thus, the predelivery of antioxidant genes such as HO-1 or ecSOD with a vector system capable of prolonged transgene expression (i.e., AAV) may be a useful protective therapeutic strategy for patients at high risk of incurring myocardial injury.
Although the acute cardioprotective effect of HO-1 overexpression is well established (1
2
3
4
, 7
, 8)
, the long-term effects of HO-1 gene delivery on postinfarction LV function and structure are not known. Soon after infarction, the LV undergoes a complex and highly dynamic process of remodeling whereby the extracellular matrix is degraded by metalloproteinases leading to expansion of the infarct (9)
. This is followed by healing of the infarct during which fibroblasts proliferate and deposit collagen to form a reparative infarct scar (9
, 10)
. In the later stages, the noninfarcted myocardium also undergoes remodeling, resulting in further dilation of the LV and increased propensity for contractile dysfunction and failure. Proinflammatory cytokines and ROS released after MI play a central role in initiating the process of postinfarction LV remodeling by activating metalloproteinases and by stimulating fibroblast proliferation (11
, 12)
. We postulate that the enhanced resistance to I/R injury conferred by overexpression of HO-1 may preserve long-term LV function after myocardial infarction. In addition, HO-1 may directly reduce fibrosis and prevent postinfarction negative LV remodeling.
In the current study we assessed the time-dependent effects of HO-1 gene delivery on post-MI LV function and LV wall and chamber dimensions using echocardiographic imaging and morphometric methods. To gain further insight into the mechanism underlying the long-term therapeutic effect of HO-1 gene therapy, we examined the direct effect of HO-1 on cardiac fibroblast proliferation and phenotypic conversion in vivo and in vitro. Our data show that predelivery of HO-1 to the myocardium by AAV leads to marked functional recovery, reduced interstitial fibrosis and absence of ventricular remodeling when examined at 3 months after MI. These findings support the premise that pre-emptive delivery of HO-1 gene by AAV may be a useful strategy for protection from ischemia-induced LV dysfunction and remodeling.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Vector construction and virus production
The construction of the AAV2 plasmid encoding human heme oxygenase-1 (hHO-1) was described previously (5
, 6)
(Fig. 1
B). Packaging, propagation, and purification of AAV2 viral particles were carried out at the Harvard Gene Therapy Initiative Core Facility (Boston, MA, USA) by standard methods (13)
.
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Intramyocardial gene delivery and acute I/R injury
Intramyocardial gene delivery and acute myocardial I/R injury were carried out as described previously (5)
. Two groups of animals were treated with 4 x 1011 genome particle of AVV-hHO-1 or AAV-LacZ (Fig. 1A, C, D
). Acute myocardial I/R injury was induced 7–8 wk after gene delivery by ligation of the proximal LAD for 30 min (Fig. 1A
). All surgical and experimental procedures were approved by the Queen’s University Animal Care Committee and by the Harvard Medical Area Standing Committee on Animals.
Echocardiography
Two groups of rats (n=8) treated with AAV-hHO-1 or AAV-LacZ were used for echocardiographic assessment of LV function and chamber dimensions. Measurements were made 24 h prior to acute I/R injury and at 1.5 and 3 months after acute I/R injury. In preparation for echocardiographic examinations, rats were anesthetized with isoflurane. Heart rates ranged from 350 to 400 bpm during measurements. Echocardiography was performed using a 6–15 MHz Ultraband Intraoperative Linear Array probe and a Sonos 5500 echocardiograph (Philips Ultrasound, Andover, MA, USA). Images were obtained from the parasternal short and long axes and analyzed with an off-line analysis program. Endocardial borders were traced and systolic and diastolic areas and volumes were calculated.
Histological and immunohistochemical analysis of myocardial injury and fibrosis
At 4 days, 1.5 and 3 months after I/R, hearts were arrested in diastole with 0.2N KCl, fixed by perfusion at constant pressure (100 cm H2O) with 10% formalin, harvested, and postfixed in the same fixative for 12 h. Paraffin sections (5 µm thickness) were stained with Masson’s trichrome stain (Accustain, Sigma Chemicals) or with picrosirius red for myocardial interstitial collagen deposition and visualization. Three sequential transverse sections corresponding to the apical, middle, and basal regions of the infarct were used to prepare sections for morphometric quantification of fibrosis. Five sections from different levels of each region were analyzed. Collagen-positive areas were calculated for each section using Sigma Scan Pro 5 (SPSS Inc., Chicago, IL, USA). Percent fibrosis was expressed as the ratio of fibrotic area to total LV area. For calculation of wall thickness, the distance between the endocardial and epicardial circumference was determined separately in each section at the anterior wall, posterior wall, and septum. A minimum of five measurements were taken and averaged for each section. The wall-thinning index was calculated as the ratio of anterior to posterior wall thickness. For immunohistochemical detection of myofibroblasts, sections prepared 4 days after I/R were stained with 
-smooth muscle actin monoclonal antibody (Sigma Chemicals).
Myocardial collagen I, III content
Interstitial collagen I and III content was determined in total protein homogenates prepared from infarcted LV tissue from both groups. Protein samples were fractionated on 8% SDS-PAGE gels, transferred to Hybond-P membranes (Amersham, Oakville, Ontario), and incubated for 2 h with 1:10,000 mouse monoclonal anti-collagen III antibody (Sigma C-7805) or 1:400 goat polyclonal anti-collagen I antibody (Southern Biotech),, then incubated for 30 min with horseradish peroxidase-conjugated anti-mouse IgG or anti-goat IgG. Immunodetection was carried out by enhanced chemiluminescence.
Cardiac fibroblast isolation, culture, and retroviral transduction
Cardiac fibroblasts were isolated from male Sprague-Dawley rats (200–250 g) by perfusion with digestion buffer (0.4 U/mL collagenase (type 1A, Sigma C-9891), 180 U/mL hyaluronidase (type 1S, Sigma H-3506), and 50 µM CaCl2 in Krebs-Henseleit buffer) at 37°C for 20 min in a Langendorff apparatus. The ventricles were minced and incubated for 20 min at 37°C with digestion buffer supplemented with 5840 U/mL trypsin type IX-S (Sigma T-0303) and 55 µM CaCl2. The digest was filtered through an 80 µm nylon mesh and the filtrate was centrifuged at room temperature for 4 min at 800 x g. The cell pellet was suspended in high glucose Dulbecco’s modified Eagle’s medium containing 10% fetal bovine serum (FBS, Hyclone), 100 U/mL penicillin, 0.1 mg/mL streptomycin, 2.5 µg/mL amphotericin B and 0.05 mg/mL gentamicin, and the cell suspension was plated into two 100 mm plastic dishes and maintained at 37°C in 5% CO2. At 1st passage, > 99% of the isolated cells stain positive for vimentin. The cells were transduced at 40% confluence with MSCV-HO-1 or MSCV-LacZ retroviral vectors for 24 h in full medium supplemented with 8 µg/mL polybrene (Fig. 1E
). We obtained 
30% transduction efficiency (Fig. 1F
) and 2- to 5-fold increases in HO-1 protein levels (Fig. 1G
) after two rounds of infection.
Cardiac fibroblast proliferation
To determine fibroblast proliferation, first passage cells were seeded in 24-well plates at a density of 10,000 cells/well and cultured for 24 h. After 48 h of serum starvation the cells were incubated in either serum-free medium or full medium containing 10% FBS for 24 h. DNA synthesis was determined in the final 6 by the addition of 1 mCi/mL [3H]-thymidine (Perkin-Elmer, Norwalk, CT, USA) to the culture medium. The radioactivity was counted in a scintillation counter. Six replicates were performed for each experiment.
Myofibroblast conversion
For assessment of phenotypic conversion, fibroblasts were transduced with either MSCV-HO-1 or MSCV-LacZ and plated in 4-chamber culture slides at a density of 10,000 cells/chamber in complete growth medium. After 24 or 48 h, the cells were fixed in methanol for 10 min at –20°C and stained for smooth muscle -actin using a commercially available kit (Sigma, IMMH-2).
Metalloproteinase activity
Matrix metalloproteinase (MMP) activity in tissue homogenates and in cultured cardiac fibroblasts was measured by zymography as described by Hawkes et al. (14)
. For determination of myocardial MMP activity, 5 µg protein were used. Fibroblasts were maintained in serum-free medium for 48 h and the medium was harvested, freeze-dried, and reconstituted in H2O in 1/20 of the original volume. Proteins were separated on 10% nonreducing SDS-PAGE gels containing 0.1% gelatin. Purified MMP-2 (Chemicon, CA, USA) was used as a positive control. The gels were incubated for 18 h at 37°C in development buffer (50 mM Tris-HCl, pH 8.8, 5 mM CaCl2, 0.05% sodium azide) and stained for 4 h with Coomassie blue. To confirm that the bands on the zymograms were due to matrix metalloproteinase activity, parallel zymograms were incubated in developing buffer containing 5 mM EDTA.
Statistical analysis
Results are shown as mean ± SE. Unpaired t test was used to compare differences in echocardiographic parameters, wall thickness, fibroblast proliferation, and myofibroblast conversion. Linear regression analysis was used to compare the relationship between myocardial injury and fibrosis in both groups of animals. One-way ANOVA was used to compare time course differences in collagen levels and fibrosis. P < 0.05 was considered to indicate statistical significance.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. The percent changes in ejection fraction (EF) and LV dimensions relative to preinfarct values are summarized in Table 2
. Two animals in the LacZ control group died before the 1.5 month follow-up. One animal in the HO-1 group died during echocardiography and was excluded. EF was significantly reduced in the LacZ and HO-1-treated animals 1.5 months after infarction relative to preinfarction levels (Table 1)
. However, the reduction in EF was markedly greater in the LacZ control animals (n=6) than in the HO-1-treated animals (n=7) (Table 2)
. Three months after infarction, EF recovered fully in the HO-1 (n=7), but only partially in the LacZ-treated animals (n=6) (Tables 1
, 2)
. End diastolic (EDD) and end systolic (ESD) dimensions were significantly increased at 1.5 months after I/R in both groups (Table 1)
. However, the relative increase in chamber dimensions was greater in the LacZ group (Table 2)
. Three months after I/R, EDD and ESD dimensions returned to near preinfarction levels in the HO-1-treated animals, but remained elevated in the LacZ group (Table 2)
. Significant increases in long axis dimensions were also seen in the LacZ-treated animals, but not in the HO-1-treated animals at 1.5 and 3 months after I/R (Tables 1
, 2)
. No significant changes in septal or posterior wall thickness were seen in either group.
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HO-1 gene transfer prevents ventricular remodeling after acute myocardial I/R injury
Postinfarction fibrosis and chamber remodeling is generally thought to be complete during the first 3 months after I/R injury (15)
. Thus, we assessed the development of fibrosis and chamber remodeling during this period. The gross histomorphological appearance of the left ventricle 3 months after I/R in the LacZ- and HO-1-treated animals is shown in Fig. 2
. No thinning (Fig. 2A
) or fibrosis (Fig. 2B
) of the anterior wall was seen in the HO-1-treated animals. In contrast, significant thinning of the anterior wall occurred in the LacZ-treated animals (Fig. 2C
). The infarcted tissue was largely replaced by collagen (Fig. 2D
). Anterior wall thickness in the LacZ animals at 3 months after MI was markedly reduced compared with the HO-1-treated animals (Fig. 2E
) (n=3 for both, P<0.05). In concordance with the echocardiographic data, no significant differences in posterior wall (Fig. 2F
) or septal wall (Fig. 2G
) thickness was seen between the two groups. The wall thinning ratio (AWT/PWT) indicated that the anterior wall thickness was reduced by 50% in the LacZ group relative to the HO-1 group (Fig. 2H
).
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HO-1 gene transfer reduces interstitial collagen deposition after I/R injury
We followed the time course of LV fibrosis in the LacZ- and HO-1-treated animals for the first 3 months after I/R injury. Evidence of fibrosis was seen as early as 1 wk after I/R. In the HO-1-treated animals, fibrosis was markedly attenuated and remained relatively constant throughout the duration of the experiment (Fig. 3
A–C), with minimal interstitial collagen deposition (Fig. 3D, E
). In contrast, the LacZ-treated animals showed progressive fibrosis over the 3 month duration of the experiment (Fig. 3F-J
), associated with extensive accumulation of interstitial collagen (Fig. 3I, J
). Morphometric assessment showed that the fibrotic area remained unchanged in the HO-1-treated animals (n=3–6) (Fig. 3K
). However, a time-dependent increase in fibrotic area was seen in the LacZ animals (Fig. 3L
).
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We assessed the relationship beween infarct size and fibrosis in adjacent biventricular sections from the HO-1 and LacZ-treated animals at 1.5 (Fig. 4
A) and 3 months (Fig. 4B
) after I/R injury in both groups by quantifying the infarcted area and the corresponding fibrotic area. As expected, there was a high correlation (r2>0.75) between infarct size and fibrosis at 1.5 (Fig. 4A
) and 3 months (Fig. 4B
) after I/R in both groups. However, the slope of the regression line between infarct size and fibrosis was smaller in the HO-1-treated animals than in the LacZ-treated control animals at both time points, suggesting that the HO-1-treated animals have an attenuated fibrotic response after myocardial infarction that is, at least partially independent of infarct size.
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To further characterize the degree of fibrosis and remodeling after I/R, we determined the time course of interstitial collagen I and III accumulation and metalloproteinase activity in the infarcted tissue in both groups in the 3 months following I/R injury (Fig. 5
). Collagen I and II are the predominant species found in interstitial cardiac fibrosis, comprising >80% of the extracellular matrix (9
, 16)
At 1 month after I/R, no difference in collagen I was seen between the two groups (n=5) (Fig. 5A
). Collagen I levels rose at two months after I/R in the LacZ animals and remained elevated until the end of the experiment at 3 months (Fig. 5A
). In contrast, the levels of collagen I decreased in the HO-1-treated group relative to one month and remained at this level for the duration of the experiment (Fig. 5A
). At 2 and 3 months after I/R collagen I levels in the HO-1-treated animals were markedly lower than in the LacZ control animals. The time course of collagen III followed a similar pattern in the LacZ and HO-1 groups. (Fig. 5B
). However, the levels of collagen III were significantly higher in the LacZ group than in the HO-1 group at 3 months (LacZ, n=3; HO-1, n=4, P<0.009). Metalloproteinase activity in infarcted myocardium was primarily associated with MMP-2 (Fig. 5C
). No difference in MMP-2 activity was seen between the HO-1 LacZ-treated groups in the immediate and 24 h postreperfusion period. However there was a significant time-dependent increase in MMP-2 activity in the LacZ-treated control animals at 1 and 3 months after I/R (n=4, P<0.05).
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HO-1 gene transfer reduces cardiac fibroblast proliferation
We studied the effect of HO-1 overexpression on cardiac fibroblast proliferation in vivo four days after I/R and in vitro on serum-stimulated cardiac fibroblast proliferation under normoxic conditions, and in response to hypoxia and reoxygenation (24 h hypoxia, 1% O2:24 h reoxygenation). Accumulation of -smooth muscle actin-positive myofibroblasts in the infarcted myocardium was markedly decreased in the HO-1-overexpressing animals (Fig. 6
A) compared with the LacZ-treated control animals (Fig. 6B
). HO-1 overexpression in cultured cardiac fibroblasts did not significantly affect thymidine incorporation in unstimulated cells in either normoxic (Fig. 6C
) or hypoxic (Fig. 6D
) conditions. However, HO-1 reduced thymidine incorporation significantly in serum-stimulated cells relative to the LacZ-control cells in both normoxic and hypoxic conditions. Hypoxia and reoxygenation exerted a mild potentiating effect on thymidine incorporation by serum-stimulated fibroblasts, but this was not affected by HO-1 overexpression (Fig. 6D
).
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HO-1 gene transfer does not affect myofibroblast conversion
We investigated the effect of HO-1 overexpression on basal and TGF-ß-stimulated myofibroblast conversion and expression of extracellular matrix proteins and growth factors. Basal rate of phenotypic conversion in LacZ-transduced cells was 8% after 24 h in serum free conditions as evidenced by the number of cells showing positive -smooth muscle actin immunoreactivity (Fig. 7
A, G). HO-1 overexpression did not significantly affect the basal rate of myofibroblast conversion (Fig. 7B, G
). Stimulation of the cells with 0.5–2.0 ng/mL TGF-ß led to dose-dependent increases in basal myofibroblast conversion (Fig. 7C, E, G
), and this was not affected by HO-1 overexpression (Fig. 7D, F, G
). Secreted metalloproteinase activity (primarily gelatinase MMP-2) did not differ significantly in serum-free conditioned medium from LacZ- or HO-1-transduced fibroblasts in normoxic conditions or after exposure to hypoxia and reoxygenation (Fig. 7H
). Similarly, no significant differences in secreted MMP-2 protein (Fig. 7I
) or cellular TGF-ß (Fig. 7J
) were found between the control and HO-1 transduced cells in either normoxic or hypoxic conditions. We measured mRNA level of collagen I and III under basal and TGF-ß-stimulated conditions in control and HO-1-transduced fibroblasts using RT-PCR. Using primers that specifically distinguish the two collagen species, no significant differences were found between the LacZ- and HO-1-transduced cells in basal or stimulated conditions (Fig. 7K
).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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or ecSOD (6)
to the myocardium with AAV vector confers protection from acute I/R injury. These findings suggested that this may be a useful pre-emptive gene therapy strategy for sustained myocardial protection in patients with or at high risk of developing myocardial infarction. Here we report morphological and echocardiographic evidence that pre-emptive delivery of HO-1 to the myocardium prevents LV remodeling and promotes recovery of function after myocardial infarction. Thus, these findings support the premise that predelivery of HO-1 gene by AAV may have potential therapeutic value as a strategy for protection from ischemia-induced LV remodeling and failure.
The mechanism underlying the anti-remodeling action after MI in the HO-1-treated animals is not fully understood. Our results indicate that the relationship between infarct size and fibrosis is significantly attenuated in the HO-1-treated animals, suggesting that HO-1 overexpression confers antifibrogenic properties to the infarcted myocardium. Indeed, our data show markedly lower myofibroblast abundance and decreased collagen I and MMP-2 levels in the infarcted area in the HO-1-treated animals compared with the LacZ control animals in the intervening 3 months after MI. This coincides with the period during which fibrosis and LV remodeling are nearly complete in rats (9
, 15
, 16)
. Collagen I is the predominant interstitial fibrillar collagen species and plays an essential role in myocardial interstitial fibrosis (9
, 16)
, and MMP-2 is ubiquitously expressed by cardiomyocytes and fibroblasts in infarcted myocardium and is involved in postinfarction extracellular matrix remodeling (17
18
19)
. The mechanism leading to fibrosis and LV remodeling is complex. The injured cardiomyocytes release proinflammatory cytokines, chemokines and ROS that stimulate fibroblast proliferation and metalloproteinase activity in a paracrine fashion (11
, 12
, 15
, 16
, 19
20
21
22)
. The by-products of heme catabolism exert a plethora of cytoprotective effects that may reduce acute myocardial injury and mitigate the development of fibrosis (2
3
4)
. For example, administration of a water solube carbon monoxide releasing molecule (CORM-3) at the time of reperfusion has recently been reported to markedly reduce infarct size in mice (23)
. Similarly, exogenous bilirubin administration was reported to reduce infarct size and to enhance postischemic myocardial functional recovery in isolated rat hearts (24)
. Since CO and bilirubin exerts powerful anti-inflammatory and antioxidant effects, it is plausible that an increase in the basal levels of these meadiators by exogenous HO-1 overexpression may decrease the release of profibrotic mediators from the injured myocytes, thereby attenuating myocardial fibrosis and LV remodeling. In this regard, it is interesting to note HO-1 null mice show increased myocardial fibrosis after chronic exposure to hypoxia (25)
. However, the direct role of CO and bilirubin in myocardial remodeling and fibrosis have not yet been investigated.
In addition, HO-1 may exert direct anti-fibrogenic effects. Our results indicate that HO-1 overexpression decreases serum-induced proliferation of cardiac fibroblasts without affecting phenotypic conversion into myofibroblasts. Furthermore, HO-1 overexpression attenuates the proproliferative effect of simulated ischemia/reperfusion on the cultured fibroblasts. HO-1 does not alter collagen I and III gene expression or the secretion of MMP by cardiac fibroblasts, indicating that any direct anti-fibrotic effect of HO-1 is likely mediated by reduced cell proliferation. Thus, HO-1 may exert dual anti-fibrotic effects in the myocardium after I/R by inhibiting the release of paracrine fibrogenic factors from the ischemic myocytes and by directly inhibiting the stimulation of fibroblast proliferation by ROS. The signaling mechanism linking HO-1 to inhibition of cardiac fibroblast proliferation is not known. Previous studies have reported the ability of carbon monoxide to inhibit vascular smooth muscle cell proliferation by up-regulating the cell cycle inhibitory protein p21 (26)
. However, the inhibitory effect of HO-1 on cell cycle progression appears to be cell type-specific (27)
.
Our results show complete recovery of function and normalization of ventricular dimensions in the HO-1-treated animals 3 months after MI. However, the echocardiographic data also show partial recovery of function and chamber dimensions in the LacZ-treated animals. This rebound in LV function and dimensions may be due, in part, to exclusion of animals with large infarcts from the later time point because of premature death. Three out of the eight LacZ-treated animals used for echocardiography died of natural causes by the end of the experiment, whereas no deaths due to natural causes were registered in the HO-1-treated animals. However, the possibility that additional factors may contribute to the recovery in the control animals cannot be excluded. Reperfusion has been reported to lead to early recovery of function in a significant percentage of patients with MI (28)
. In contrast, our results show that EF remains markedly depressed in the LacZ-treated animals as late as 6 wk after MI, suggesting that functional recovery, if any, in the control animals is a late event. However, this possibility is not supported by the histomorphological data showing progressive thinning and fibrosis of the infarcted LV wall in LacZ-treated animals. These changes in LV wall structure have been reported to lead to impairment of systolic and diastolic function in infarcted rat hearts (22)
.
From a therapeutic standpoint, our findings may have implications as a anti-remodeling strategy for high risk patients with coronary artery disease. A significant number of patients are not suited for surgical revascularization (28)
, and may be at risk of cumulative injury resulting from multiple episodes of I/R injury. For these patients, a strategy that could simultaneously confer protection of the myocytes from acute I/R insults and prevent the activation of mechanisms involved in chronic pathological LV remodeling would be ideal. We have recently reported that AAV-HO-1 confers significant myocardial protection against multiple transient I/R episodes (29)
. Thus, exogenous overexpression of HO-1 using either viral vectors (5
, 6
, 29)
or pharmacological inducers or mimetics of HO-1 activity (23
, 24)
may provide a strategy to potentiate native protective responses in the myocardium in patients at high risk of myocardial injury. Such pre-emptive approaches represent a significant departure from the current anti-remodeling therapeutic strategies that focus on rescue and/or reversal of injury, as opposed to prevention, and whose efficacy is limited by a narrow time window for successful therapeutic intervention (30)
. In contrast, a preventive strategy obviates the constraint of time and provides sustained protection against the deleterious effects of I/R injury with one single administration of the therapeutic gene.
In summary, the current study demonstrates the efficacy of pre-emptive exogenous delivery and overexpression of HO-1 by AAV in preventing pathological ventricular remodeling after acute myocardial infarction. We conclude that AAV-mediated delivery of cytoprotective genes such as HO-1 may be a useful strategy for prevention of left ventricular remodeling and failure due to myocardial infarction in patients with severe coronary artery disease.
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ACKNOWLEDGMENTS |
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Received for publication July 12, 2005. Accepted for publication October 5, 2005.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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 N. G. Abraham and A. Kappas Pharmacological and Clinical Aspects of Heme Oxygenase Pharmacol. Rev., March 1, 2008; 60(1): 79 - 127. [Abstract] [Full Text] [PDF]
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