Aging-Related Early Changes in Markers of Ventricular and Matrix Remodeling After Reperfused ST-Segment Elevation Myocardial Infarction in the Canine Model
Effect of Early Therapy With an Angiotensin II Type 1 Receptor Blocker
Background— Elderly patients with reperfused ST-segment-elevation myocardial infarction are at increased risk for left ventricular remodeling. Extracellular matrix damage has been implicated in early remodeling. We hypothesized that aging results in enhanced early reperfusion injury and left ventricular remodeling after reperfused ST-segment-elevation myocardial infarction and that early therapy initiated at the time of reperfusion with an angiotensin II type 1 receptor blocker such as candesartan attenuates age-related increases in reperfusion injury and remodeling.
Methods and Results— We randomized 3 groups of dogs (age, 1 to 2, 2.1 to 5, and 5.1 to 10 years) with reperfused ST-segment-elevation myocardial infarction (90 minutes of ischemia, 2 hours of reperfusion) to therapy with placebo or candesartan (1 mg/kg CV-11974) over 30 minutes from the onset of reperfusion. Reperfusion in placebo groups was associated with aging-related changes in the ischemic zones in markers of damage (increased ischemic injury, infarct size [as percent risk], cardiomyocyte apoptosis, blood flow impairment, no reflow), structural remodeling (increased left ventricular dilation and dysfunction), extracellular matrix remodeling (increased expression of secretory leucocyte protease inhibitor, secreted protein acidic and rich in cysteine, osteopontin, a disintegrin and metalloproteinase-10 and -17, and matrix metalloproteinase-9 and -2), and inflammation (increased inducible nitric oxide synthase, proinflammatory cytokines interleukin-6 and tumor necrosis factor-α, and transforming growth factor-β1; decreased antiinflammatory cytokine interleukin-10). Compared with placebo, candesartan attenuated these age-dependent changes.
Conclusion— Aging results in age-dependent early increases in markers of damage and adverse structural and matrix remodeling after ST-segment-elevation myocardial infarction reperfused after 90 minutes of ischemia, and early therapy initiated at the time of reperfusion with the angiotensin II type 1 receptor blocker candesartan attenuates these changes. This strategy needs clinical confirmation.
Received February 22, 2010; accepted May 20, 2010.
We hypothesized that aging results in enhanced early reperfusion injury and left ventricular (LV) remodeling after reperfused ST-segment-elevation myocardial infarction (STEMI) and that early therapy initiated at the time of reperfusion with an angiotensin II (AngII) receptor blocker (ARB) such as candesartan attenuates the increase in reperfusion injury and LV remodeling.
Editorial see p 322
Clinical Perspective on p 351
Cumulative evidence suggests that prevention of early LV remodeling during STEMI is of critical importance, especially in the elderly. Early remodeling leads to progressive dilation, which affects outcome,1,2 and elderly STEMI patients are at increased risk for LV remodeling.3–5 Acute STEMI patients reperfused by percutaneous coronary intervention after >90 minutes of ischemia develop LV remodeling that persists despite medical therapy initiated during recovery.6 Although reperfusion aimed at improving flow to myocardium at risk7 has proven benefits,4 it results in reperfusion injury with damage of the myocardium through necrosis and apoptosis8–10 and of the extracellular matrix (ECM)11,12 through increased matrix metalloproteinases (MMPs).12–14 Although increased MMP relative to tissue inhibitors of MMP (TIMPs) is a generally accepted pathway leading to early ECM damage and LV remodeling,12–15 failure of MMP inhibition initiated during recovery after acute STEMI to limit LV remodeling16 suggests that ECM damage had occurred earlier and/or other matrix proteins besides MMPs might contribute to damage.5,17–20 In a recent study on the effect of aging on early LV remodeling, reperfused STEMI resulted in increased early expression of MMPs, other matrix proteins such as secretory leucocyte protease inhibitor (SLPI), secreted protein acidic and rich in cysteine (SPARC), and osteopontin, and inflammatory cytokines in young dogs. Augmentation of this response in older dogs was associated with enhanced reperfusion damage and LV remodeling.17
Emerging evidence suggests that interactions between matrix proteins and inflammatory cytokines may modulate ECM damage.5,17–20 Thus, the protease inhibitor SLPI,18,19 the matricellular proteins SPARC and osteopontin,5,17 and the matrixins a disintegrin and metalloproteinase (ADAM)-10 and ADAM-1720 have all been suggested to interact with inflammatory cytokines and alter MMPs; thus, they affect LV remodeling and/or reperfusion injury.5,17–20
AngII is known to increase with aging in the LV,21 to exacerbate acute ischemic injury,5 and to regulate ECM homeostasis.5,12 Experimentally, ARBs given before ischemia limit acute ischemia/reperfusion injury,22 suppress early increases in MMP-9 and limit LV remodeling,13 or limit infarct size and attenuate LV remodeling.22 However, the approach used in those studies (ie, therapy before ischemia) is not clinically feasible. One study that initiated ARB therapy 1 hour after STEMI without reperfusion showed a decrease in infarct size and LV remodeling.23 Moreover, all these studies involved only young animals. Here, we sought to determine the effect of aging on early reperfusion injury and markers of structural and matrix remodeling in the well-characterized preclinical in vivo canine model of reperfusion 90 minutes after STEMI and the impact of early therapy initiated at the time of reperfusion with an ARB.
Animal Preparation and Protocol
As described previously17 (see the Methods section in the online-only Data Supplement), healthy mongrel dogs were anesthetized, were instrumented for hemodynamic recordings, and had reperfused STEMI induced by ligation of the middle left anterior descending coronary artery for 90 minutes followed by ligature release for reperfusion (Figure 1).
Three groups with increasing age (group 1: 1 to 2 years, n=29; group 2: 2.1 to 5 years, n=29; group 3: 5.1 to 10 years, n=29) were studied first (batch 1), 69 (23 per group) with reperfused STEMI and 18 age-matched sham-operated dogs (6 per group). STEMI groups were randomized to intravenous infusions of saline placebo or candesartan (CV-11974, the active metabolite of candesartan-cilexitil, a gift from AstraZeneca Canada) over 30 minutes from the onset of reperfusion. We confirmed that the dose of candesartan (1 mg/kg) inhibited pressor responses to AngII (0.25 μg/kg)22,23 and did not decrease blood pressure >10% from baseline.
Echocardiograms and Hemodynamics
Two-dimensional echocardiograms and Doppler, ECGs, and left atrial and arterial pressures were recorded at repeated intervals and analyzed (Figure 1) as described previously (see Methods in the online-only Data Supplement).17,22–25
Tissue Sampling, Infarct Size, and Apoptosis
As previously described (see Methods in the online-only Data Supplement),13,17,22–25 the risk region was defined by monastral blue dye, and all hearts were arrested in diastole. Transmural samples were taken from the ischemic zone (IZ) and non-IZ of STEMI hearts and corresponding sites in risk and nonrisk regions of sham hearts for biochemical assays (Figure 1B). Transverse sections were processed for infarct size (triphenyltetrazolium chloride [TTC] method, computerized planimetry, and histopathology) and for cardiomyocyte apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling assay and α-sarcomeric actin staining).
Zymographic MMP Activity
As described previously,17,24,25 degradative activities of MMP-9 and MMP-2 were measured by zymography (see Methods in the online-only Data Supplement).
Immunoblot Analyses, RNA Isolation, and Real-Time Polymerase Chain Reaction
As described previously (see also Methods in the online-only Data Supplement),17,25 frozen LV samples were processed and probed with antibody against TIMP-1, TIMP-3, TIMP-4, MMP-2, MMP-9, interleukin (IL)-6, nitric oxide (NO) synthases (NOSs; endothelial [eNOS], inducible [iNOS], neuronal [nNOS]), tumor necrosis factor (TNF)-α, transforming growth factor (TGF)-β1, IL-10, SLPI, SPARC, osteopontin, ADAM-10, ADAM-17, and actin. RNA isolation and quantitative real-time polymerase chain reaction for SLPI, SPARC, and osteopontin were done (see Table I in the online-only Data Supplement).
Myocardial Blood Flow and No Reflow
Regional blood flow (see Methods in the online-only Data Supplement) was measured by left atrial colored microsphere injections26,27 in 58 dogs 2 hours after reperfusion (batch 1: 40 STEMI [22 placebo, 18 candesartan], 18 sham) and in 24 STEMI dogs (batch 2: 12 placebo, 12 candesartan) 90 minutes after occlusion and at 10 minutes and 2 hours after reperfusion. The latter 24 dogs also had left atrial injections of thioflavin-S (TFL), a fluorescent marker of capillary perfusion to define no-reflow zones.10
Infarct Size and Systolic Function 3 Days After Reperfusion
In another 24 dogs (batch 3), infarct size and systolic function were measured 72 hours after reperfused STEMI (see Methods in the online-only Data Supplement).
Analyses were done in blinded fashion with ANOVA for group comparisons; ANOVA and Student-Newman-Keuls test for differences within and between groups; repeated-measures ANOVA for within-group comparisons of serial in vivo functional and remodeling data; linear regression analysis to compare infarct with risk region sizes and exponential regression to compare infarct/risk with flow, with the significance of R values and slopes by ANOVA; and χ2 test with Yates correction for deaths between treatment groups. Data are shown as mean±SEM. Significance was set at P<0.05.
Aging and STEMI Deaths
Thirteen of the 113 dogs in short-term studies (87 in batch 1, 26 batch 2) and placebo studies (2 in group 1, 5 in group 2, 6 in group 3) but no dogs in the candesartan groups died (χ2=8.11, P=0.004) of ventricular fibrillation between 1.5 and 2 hours after reperfusion or 3 to 3.5 hours after occlusion. Two of the 26 dogs in batch 3 died 1.5 hours after reperfusion in placebo group 3. All deaths were excluded from analysis.
Age-Related Increases in Infarct Size, Apoptosis, and Ischemic Injury
We analyzed TTC infarct size and apoptosis in 58 dogs (21 in group 1, 18 in group 2, 19 in group 3). Mean ages were 1.74, 4.4, and 7.7 years, which correspond to 12, 31, and 54 human years (http://www.onlineconversion.com/dogyears.htm), respectively. Both sham and STEMI hearts showed age-dependent trends consistent with aging: mild increases in LV mass (Table II in the online-only Data Supplement) and increases in wall thickness, collagen volume fraction, and cardiomyocyte size in nonischemic regions on histopathology and morphometry in formalin-fixed hearts (not shown). STEMI hearts showed age-related increases in infarct size (by 73% in grams, by 42% as percent LV, by 33% as percent risk region) and in apoptosis by 75% (Table II in the online-only Data Supplement and Figure 2A through 2E). Compared with placebo, candesartan attenuated the age-dependent increases in infarct size and apoptosis with lesser benefit in older dogs (Figure 2B through E).
Percent changes after reperfusion in Figures 2F and 3⇓ refer to the change over the interval between the onset of reperfusion (reperfusion baseline just after 90 minutes of left anterior descending occlusion) and just after 2 hours of reperfusion, expressed as a percent of the reperfusion baseline value. Compared with sham, placebo STEMI groups showed age-dependent increases in ischemic injury (reflected in increased sum of ST-segment elevations in ECG leads I, II, aVL, and V4) after reperfusion (Tables III through V in the online-only Data Supplement). Compared with placebo, the candesartan groups showed a trend (statistically nonsignificant) toward less percent increases in injury (Figure 2F).
Age-Related Postreperfusion Deterioration in Hemodynamics
Compared with sham, placebo STEMI groups showed an age-dependent decrease in blood pressure and increase in left atrial pressure (index of LV filling pressure) after reperfusion but no change in heart rate (Tables III through V and Figure I in the online-only Data Supplement). Compared with placebo, candesartan blunted the age-dependent postreperfusion decrease in blood pressure and increase in left atrial pressure (Figure I in the online-only Data Supplement).
Age-Related Adverse LV Remodeling and Dysfunction
Compared with sham, placebo groups showed an age-dependent increase in LV asynergy, end-diastolic and end-systolic volumes, and diastolic dysfunction; a decrease in ejection fraction; but no change in infarct expansion and thinning during reperfusion (Figure 3A through 3I and Tables III through V in the online-only Data Supplement). Compared with placebo, candesartan attenuated the age-related augmentations in systolic and diastolic dysfunction and dilation after reperfused STEMI (Figure 3A through 3I and Tables IV and V in the online-only Data Supplement); however, incremental benefits reflected in percent increase in ejection fraction were less for group 3 than for group 1 (Figure 3A through 3I).
Age-Related Increase in MMP-9 and MMP-9/TIMP-3 Ratio
Levels of matrix proteins for sham in Figures 4 and 5⇓ are for samples from the risk region corresponding to IZs of reperfused STEMI hearts. Compared with sham, placebo groups showed age-dependent robust increases in MMP-9 protein and zymographic activity, as well as modest increases in TIMP-3 protein and MMP-9 activity/TIMP-3 protein ratio in the IZ that were normalized by candesartan (Figure 4A through 4C and 4G). Compared with sham, placebo groups also showed age-dependent modest increases in MMP-2 protein and activity and modest increases in TIMP-1 protein that were suppressed by candesartan (Figure 4D through 4F). MMP-2 activity/TIMP-1 protein ratios were similar in placebo groups and unaltered by candesartan (Figure 4H). TIMP-4 protein levels did not change (Figure 4I).
Age-Related Changes in Other Matrix Proteins
Compared with sham, placebo-reperfused STEMI groups showed robust age-related increases in SLPI, SPARC, and osteopontin protein and mRNA levels in the IZs, and candesartan suppressed the increases in all 3 groups, although the effect was more pronounced in group 3 than in groups 1 and 2 (Figure 5A through F). In addition, placebo-reperfused STEMI showed robust age-related increases in ADAM-10 and -17 proteins in the IZs; these increases were attenuated by candesartan (Figure 5G and 5H).
Age-Related Changes in Inflammatory Cytokines and NOSs
Compared with sham, reperfused STEMI induced robust age-related increases in TNF-α, TGF-β1, and IL-6 in the IZs, and candesartan attenuated these increases and prevented the age-related decrease in IL-10 in the IZs of the 3 groups (Figure 6A through 6D). Reperfused STEMI also induced robust age-related increase in iNOS and decreases in eNOS and nNOS in the IZs (Figure 6E through 6G). Candesartan suppressed the increase in iNOS and reversed the decrease in eNOS in groups 1 and 2; it mostly blunted the decrease in nNOS and actually enhanced the level in group 3 (Figure 6E through 6G).
Age-Related Increase in Flow Impairment in No-Reflow Zones
Impairment of blood flow was more severe in inner no-reflow zones (TTC negative, mostly TFL negative) than in outer zones (TTC negative, mixed TFL negative and TFL positive) 90 minutes after left anterior descending occlusion and 2 hours after reperfusion, and the severity increased from groups 1 to 3 (Figure 7; Table VI in the online-only Data Supplement). The improvement in inner and outer flows by 2 hours after reperfusion was blunted in placebo groups 2 and 3 compared with group 1 (P<0.05 to 0.001). By 2 hours after reperfusion in the placebo groups, inner flows were still <0.2 mL · min−1 · g−1, whereas outer flows were >0.5 mL · min−1 · g−1 in group 1 but <0.5 mL · min−1 · g−1 in group 2 and <0.2 mL · min−1 · g−1 in group 3. Candesartan improved inner and outer flows in all 3 groups, with final inner flows >0.2 mL · min−1 · g−1 and outer flows >0.5 mL · min−1 · g−1 in groups 1 and 2 and >0.3 mL · min−1 · g−1 in group 3, suggesting a trend toward decreased no reflow. In transverse sections at the low papillary level, compared with placebo, candesartan decreased (P<0.001) no-reflow areas (TFL-negative area as percent of the TTC-negative infarct area) across groups (group 1, 54±3% versus 27±1%; group 2, 66±2% versus 35±1%; group 3, 85±3% versus 64±2%).
Linear regressions between infarct size and risk region suggested less infarction with candesartan than placebo for the same area at risk, although the difference between the slopes did not achieve statistical significance (Figure 8A). Exponential regressions of infarct size as percent risk versus inner and outer infarct blood flows showed lower relations with candesartan than placebo, suggesting less damage for the same level of flow (Figure 8B). Strong positive correlations were found between infarct size and diastolic or systolic volumes and between matrix proteins and diastolic or systolic volumes (Table VII and Figures II and III in the online-only Data Supplement).
Infarct Size and Systolic Function 3 Days After Reperfusion
As with 2-hour reperfusion, reperfusion for 72 hours resulted in age-dependent increases in TTC infarct size, echocardiographic volumes, and systolic dysfunction that were attenuated by candesartan (Table VIII and Figure IV in the online-only Data Supplement). However, there was a further increase in LV asynergy between 2 and 72 hours of reperfusion in the placebo groups, consistent with progressive damage, which was attenuated in the candesartan groups.
There are 3 new findings in this study. First, there was an age-dependent augmentation of ischemic injury, infarct size, cardiomyocyte apoptosis, impairment of blood flow in infarct regions, severity of no reflow, early LV remodeling, and LV systolic and diastolic dysfunction after reperfused STEMI. Second, reperfused STEMI induced early age-dependent increases in expression of MMPs known to degrade ECM in the reperfused IZs; importantly, these changes were associated with parallel increases in other matrix proteins and concomitant changes in cytokines known to modulate ECM. Third, therapy initiated at the time of reperfusion 90 minutes after STEMI with the ARB candesartan attenuated these early age-dependent changes in reperfusion damage, matrix proteins, inflammatory cytokines, and LV remodeling and dysfunction.
Other studies of reperfused STEMI with 90 minutes of ischemia have shown progression of myocardial damage after reperfusion in young dogs.10,28 Recently, adult dogs were found to have larger infarcts and more apoptosis than young dogs after reperfused STEMI.17 Here, we show an incremental effect of age on damage across 3 groups of young, adult, and older dogs and an inhibitory effect of candesartan on age-dependent myocardial damage evidenced by decreased ischemic injury, infarct size, and cardiomyocyte apoptosis, implying that AngII plays a role in the age-dependent augmentation of early myocardial damage. However, this benefit was less marked in the older groups, probably as a result of age-related increases in LV AngII.21
Studies have shown that myocardial blood flow is a major determinant of damage after STEMI with7,10,29 and without30,31 reperfusion in young dogs. Other studies showed expansion of microvascular damage in young dogs32 and the area of anatomic no reflow in young rats.33 Because increased AngII can aggravate blood flow impairment through vasoconstriction, an ARB can improve flow via intact vessels and thereby reduce reperfusion injury, as shown in many studies.12,13,22–25 Here, candesartan attenuated the age-related aggravation of blood flow impairment in infarct regions and severe depression of flow in no-reflow areas, improved flow in the outer and some inner regions, and decreased areas of anatomic no reflow, implying that AngII plays a role in the age-dependent augmentation of early microvascular damage and no reflow.
Our finding of less infarction for the same level of collateral blood flow with candesartan compared with placebo (Figure 8B) suggests that other mechanisms besides flow may be involved. Emerging evidence suggests that ARBs may attenuate the surge of reactive oxygen species that occurs after ischemic reperfusion8 and thereby reduce oxidative stress and improve mitochondrial metabolism and function. Studies in young dogs have shown that an ARB given before STEMI-reperfusion reduces reperfusion damage, suppresses posttranslational modifications of ATP/δ, inhibits NO-related modifications,24 and improves metabolic and functional proteins.34 In addition, aging increases AngII21 and reactive oxygen species,35 and both can contribute to damage. Thus, AngII increases mitochondrial reactive oxygen species, leading to mitochondrial dysfunction, opening of the permeability transition pore, and cell death.36 AngII also induces oxidative stress by enhancing generation of NO and NADPH oxidase–derived superoxide, thereby promoting peroxynitrite formation,36 which increases reperfusion injury.37 Additionally, AngII induces eNOS uncoupling, switching from NO to superoxide production,36 which contributes to reperfusion injury.37 Importantly, aging cardiomyocytes have increased cytosolic and mitochondrial reactive oxygen species production and increased susceptibility to apoptosis and necrosis,35 and ARBs have been suggested to limit age-related mitochondrial dysfunction.36
Other evidence suggests that early ECM damage in IZs contributes to early infarct remodeling and LV dilation after STEMI,5,13,15 that early LV dilation begets dilation,1,2 and that AngII regulates ECM homeostasis and drives LV remodeling.12 MMPs, secreted as latent pro-MMPs, degrade ECM after activation and are inhibited by specific TIMPs.12 The gelatinases MMP-9 and -2 digest denatured collagens (gelatins) and other ECM proteins. Early increase in and activation of MMP-9 and -2 have been implicated in early LV remodeling after reperfused STEMI.5,13,17,24 In particular, an early increase in MMP-9,14 associated with an increased MMP-9/TIMP-3 ratio,13 appears to be an important pathway to ECM damage and LV dilation.12,13 Here, aging augmented the early surge not only in MMPs but also in other matrix proteins (ie, SPARC, osteopontin, ADAMs) and protease inhibitors (ie, SLPI, TIMPs), and candesartan attenuated all these changes. This implies that AngII plays a role in the age-related augmentation of MMP release and/or activation and in the release of the other matrix proteins. Strong positive correlations between levels of the MMPs and matrix proteins with diastolic and systolic volumes suggest that they contributed to age-related aggravation of LV remodeling and dysfunction. Because immunohistochemical staining for AngII increased across sham groups and was reduced by candesartan in the STEMI groups (data not shown), aging-related increase in LV AngII21 might have contributed to the enhanced early postreperfusion surges in matrix proteins. Scanning electron microscopy showed ECM damage in reperfused STEMI (not shown), but the changes were not quantifiable.
The finding that candesartan concurrently attenuated or reversed aging-related changes in markers of inflammation (ie, augmented early surges in iNOS, TNF-α, TGF-β1, and IL-6 and decreases in eNOS, nNOS, and IL-10) implicates AngII in the changes. Additionally, the changes likely contributed to early reperfusion damage and LV remodeling. Evidence suggests that interactions among matrix proteins, inflammatory cytokines, and NOSs can aggravate the imbalance between MMPs and TIMPs, thereby leading to enhanced reperfusion damage, ECM damage, and LV remodeling.5,18,19,38,39 AngII is known to increase inflammation, which modulates reperfusion damage via inflammatory cytokines (ie, proinflammatory IL-6 and TNF-α, antiinflammatory IL-10 and TGF-β1) that in turn regulate matrix proteins and NOSs.5,39 Reperfused STEMI is known to induce early inflammatory cell infiltration, inflammatory cytokine activation,5,17,25 and MMP activation.5,38 Acute upregulation of proinflammatory cytokines (such as IL-6 and TNF-α) leads to increased MMP-9, MMP-2, reactive oxygen species, iNOS-derived NO, peroxynitrite, cardiomyocyte apoptosis, and reperfusion injury,24,37–40 which in turn leads to ECM damage and LV dysfunction.
The matrix proteins may have contributed to the changes in MMPs and/or TIMPs either directly or indirectly via interactions in proinflammatory cytokines and iNOS. Studies have shown that ADAM-17 activates proinflammatory cytokine TNF-α,20 whereas TIMP-3 inhibits ADAM-17 and -1020,41 and MMP-9.42 Aged TIMP-3–null mice show increased MMP-9, ECM degradation, and LV dilation.41 Both ADAMs can alter integrins (cell-surface matrix receptors), disrupt cell-matrix interactions, degrade ECM, and contribute to LV dilation.20 SLPI suppresses MMP-9 and inflammation18 and ischemia/reperfusion injury.19 SPARC limits postinfarct remodeling but increases TGF-β1 and MMP activity in acute STEMI.5 Osteopontin limits postinfarct LV dilation but interacts with integrins, activates inflammation, and increases iNOS, MMP-2, and MMP-9 in acute STEMI.5,17 Increased TGF-β1 suppresses inflammation and decreases reperfusion injury by inhibiting increases in MMP-1.43 Taken together, this evidence suggests that matrix proteins like cytokines may exert different effects in acute and chronic settings; acutely here, the net result of their interactions appears to favor adverse LV remodeling, and candesartan attenuates this effect.
Here, we used repeated 2-dimensional echocardiographic imaging as before2,13,15,17,22–25 and demonstrated age-related early increases during reperfusion (ie, onset to 2 hours later) in LV systolic and diastolic dysfunction and volumes. Although candesartan attenuated these age-related augmentations in LV systolic and diastolic dysfunction and dilation, the benefit was less in older groups. Our findings suggest that the benefits were related to the decrease in myocardial damage, decrease in flow impairment and no reflow, and decrease in ECM damage. Improved hemodynamics with attenuation of the decrease in blood pressure and increase in left atrial pressure may have contributed. Candesartan-induced attenuation of stunning,22,24,34 AngII type 2 receptor–mediated effects,22 and a possible “permissive” interaction with the known isoflurane anesthetic–induced preconditioning action may also have contributed.
First, our findings suggest that age is an important determinant of reperfusion injury. Second, matrix proteins besides MMPs may participate in age-related augmentation of early reperfusion damage and remodeling. Third, reperfusion damage occurs with reperfusion after 90 minutes of ischemia, with progression of damage and expansion of no-reflow areas, as found in young animals here and reported by others,8–10,28,32,33 and is augmented by aging. Fourth, intravenous candesartan initiated at the time of reperfusion 90 minutes after STEMI attenuates but does not altogether abolish age-related increases in damage and remodeling at both 2 and 72 hours after reperfusion. Because elderly STEMI patients are seldom reperfused before 90 minute from the onset of ischemia,4,5 this approach may be clinically relevant. Because vasodilator-induced hypotension can offset benefits by decreasing perfusion,4,5,12,31 we used low-dose candesartan, which did not decrease blood pressure >10% and did not cause hypotension during reperfusion. Whether other ARBs and ACE inhibitors produce similar benefits is likely but needs confirmation.
We focused on short-term candesartan therapy and early changes and did not study long-term effects during infarct healing. Cognizant of limitations of the dog model, we measured infarct size as percent risk and collateral blood flow.
Aging results in age-dependent early increases in markers of damage and adverse structural and matrix remodeling after STEMI reperfused after 90-minute ischemia. Early therapy initiated at the time of reperfusion with the ARB candesartan attenuates these changes.
Source of Funding
This work was supported in part by grants MOP 79461 and IAP99003 (to Dr Jugdutt) from the Canadian Institutes of Health Research, Ottawa, Ontario, Canada.
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Prevention of early left ventricular remodeling during ST-segment-elevation myocardial infarction is of critical importance, especially in the elderly. Early remodeling leads to progressive ventricular enlargement that affects outcome, and elderly ST-segment-elevation myocardial infarction patients are at greater risk for remodeling. Acute ST-segment-elevation myocardial infarction patients reperfused by percutaneous coronary intervention after 90 minutes of ischemia develop left ventricular remodeling that persists despite medical therapy initiated during recovery. Although reperfusion has proven benefits, it results in injury with myocardial and extracellular matrix damage. Although increased matrix metalloproteinase is a generally accepted pathway leading to early extracellular matrix damage and ventricular remodeling, failure of metalloproteinase inhibition initiated during recovery after ST-segment-elevation myocardial infarction to limit ventricular remodeling suggests that damage had occurred earlier and/or other matrix proteins besides metalloproteinases contributed to damage. We present evidence that aging increases reperfusion damage and markers of left ventricular structural remodeling (echocardiographic ventricular enlargement and dysfunction) and matrix remodeling (novel matrix proteins besides metalloproteinases), as well as inflammatory cytokines that contribute to early extracellular matrix degradation and early ventricular remodeling and dysfunction. Because angiotensin II is known to increase with aging, to exacerbate ischemic injury, and to regulate extracellular matrix homeostasis, we tested early therapy, given intravenously at the time of reperfusion (as a relevant clinical approach at the time of percutaneous coronary intervention), with an angiotensin II receptor blocker and demonstrate attenuation, but not abolition, of the deleterious aging-related changes. Because elderly ST-segment-elevation myocardial infarction patients are seldom reperfused before 90 minutes of ischemia, this strategy may be relevant but requires clinical confirmation.
The online-only Data Supplement is available with this article at http://circ.ahajournals.org/cgi/content/full/CIRCULATIONAHA.110.948190/DC1.