Robin Hinmon

Allogeneic Mesenchymal Precursor Cell Therapy to Limit Remodeling After Myocardial Infarction : The Effect of Cell Dosage

BACKGROUND This experiment assessed the dose-dependent effect of a unique allogeneic STRO-3-positive mesenchymal precursor cell (MPC) on postinfarction left ventricular (LV) remodeling. The MPCs were administered in a manner that would simulate an off-the-self, early postinfarction, preventative approach to cardiac cell therapy in a sheep transmural myocardial infarct (MI) model. METHODS Allogeneic MPCs were isolated from male crossbred sheep. Forty-six female sheep underwent coronary ligation to produce a transmural LV anteroapical infarction. One hour after infarction, the borderzone myocardium received an injection of 25, 75, 225, or 450 x 10(6) MPCs, or cell medium. Echocardiography was performed at 4 and 8 weeks after MI to quantify LV end-diastolic (LVEDV) and end-systolic volumes (LVESV), ejection fraction (EF), and infarct expansion. CD31 and smooth muscle actin (SMA) immunohistochemical staining was performed on infarct and borderzone specimens to quantify vascular density. RESULTS Compared with controls, low-dose (25 and 75 x 10(6) cells) MPC treatment significantly attenuated infarct expansion and increases in LVEDV and LVESV. EF was improved at all cell doses. CD31 and SMA immunohistochemical staining demonstrated increased vascular density in the borderzone only at the lower cell doses. There was no evidence of myocardial regeneration within the infarct. CONCLUSION Allogeneic STRO-3 positive MPCs attenuate the remodeling response to transmural MI in a clinically relevant large-animal model. This effect is associated with vasculogenesis and arteriogenesis within the borderzone and infarct and is most pronounced at lower cell doses.

Single dose GLP-1-Tf ameliorates myocardial ischemia/reperfusion injury.

BACKGROUND Glucagon-like peptide-1 (GLP-1) has insulinomimetic, insulinotropic, and antiapoptotic properties that may make it a useful adjunct to reperfusion therapy for myocardial infarction (MI); however, GLP-1 has a short plasma half-life. Fusion of GLP-1 to human transferrin (GLP-1-Tf) significantly prolongs drug half-life. MATERIALS AND METHODS We tested the ability of single dose GLP-1-Tf to limit myocardial ischemia (30 min)/reperfusion (180 min) injury in rabbits. Nineteen animals were untreated controls. The pre-ischemic group (n=10) was given 10mg/kg of GLP-1-Tf 12 h before ischemia. Immediately after reperfusion, the post-ischemic group (n=10) received GLP-1-Tf (10 mg/kg) and the Tf group (n=4) received transferrin alone. RESULTS Infarct size as a percentage of the area at risk was 59.1% ± 1.3%, 45.7% ± 1.9%, 44.1% ± 3.3%, 59.7% ± 2.0% in the control group, pre-ischemic group, post-ischemic group, and Tf group, respectively (P<0.05 for both GLP-1-Tf treatments group versus control). GLP-1-Tf reduced the apoptotic index from 4.67% ± 0.40% in the control group to 3.15% ± 0.46% in the pre-ischemic group and to 2.66% ± 0.40% in the post-ischemic group (P<0.05 for both GLP-1-Tf treatments versus control). The size of the wall motion abnormality and ejection fraction was significantly improved in the post-ischemic group relative to the control group. Serum GLP-1 levels were 239.8 ± 25.7 μg/mL in the post-ischemic group, 27.9 ± 5.8 μg/mL in the pre-ischemic group, and undetectable in the control group. CONCLUSION GLP-1-Tf limits myocardial reperfusion injury whether given prior to the onset of ischemia or given at reperfusion. GLP-1-Tf may also limit myocardial stunning at high serum levels of the drug.

Mild Hypothermia to Limit Myocardial Ischemia-Reperfusion Injury: Importance of Timing

BACKGROUND Hypothermia during ischemia has been shown to reduce myocardial reperfusion injury. We sought to establish the cardioprotective effect of very mild total-body hypothermia (<or= 2.5 degrees C) and to determine whether the application of hypothermia at different points during the ischemia-reperfusion period influenced the degree of myocardial salvage. METHODS Rabbits were subjected to 30 minutes of myocardial ischemia followed by 3 hours of reperfusion. Twenty-five animals were maintained at normal temperature (39.5 degrees C) throughout the experiment (W-W-W group). All other animals were cooled to reduce left atrial temperature 2.0 degrees C to 2.5 degrees C. Eleven animals reached goal temperature before coronary occlusion (C-C-C group), in 14 animals cooling was initiated at coronary occlusion (W-C0-C group), in 8 animals cooling was initiated 15 minutes after coronary occlusion (W-C15-C group), in 5 animals cooling was initiated 25 minutes after coronary occlusion (W-C25-C group), and in 13 animals cooling was started concurrently with reperfusion (W-W-C group). Infarct size as a percentage of the risk area (I/AR) was determined by a double staining-planimetry technique. RESULTS Goal temperature was achieved before reperfusion in the C-C-C and W-C0-C groups but was not achieved until the reperfusion period in the other treatment groups. Infarct size was 59.0 +/- 1.2% in the W-W-W group and was reduced in all cooling groups (C-C-C = 30.4 +/- 4.9%; W-C0-C = 33.4 +/- 5.0%; W-C15-C = 42.4 +/- 1.4%; W-C25-C = 44.1 +/- 2.3%; W-W-C = 50.5 +/- 4.1%). The temperature at reperfusion correlated most strongly with infarct size (r = 0.72, p < 1 x 10(-12)). CONCLUSIONS Very mild hypothermia affords a significant cardioprotective effect. Temperature at the time of reperfusion most strongly correlates with the degree of myocardial salvage.

Cyclosporine Preserves Mitochondrial Morphology After Myocardial Ischemia/Reperfusion Independent of Calcineurin Inhibition

BACKGROUND Opening of the mitochondrial permeability transition pore (MPTP) has been shown to contribute to myocardial ischemia/reperfusion injury. We sought to demonstrate that the myocardial protective effect of inhibiting MPTP opening with cyclosporine A (CsA) results in stabilization of mitochondrial morphology and is independent of CsA-induced calcineurin inhibition. METHODS Thirty-seven rabbits were divided into three groups: control (n = 15), CsA (MPTP and calcineurin inhibitor, n = 12), or FK506 (calcineurin inhibitor, n = 10). Each group received a 1-hour infusion of either a saline vehicle, 25 mg/kg CsA or 1 mg/kg FK506. All animals underwent 30 minutes of regional ischemia and 3 hours of reperfusion. Myocardial infarct size was determined using Evans blue dye and triphenyltetrazolium chloride. In situ oligo ligation was used to assess apoptotic cell death. Transmission electron microscopy was used to quantitatively evaluate morphologic differences in the mitochondria between groups. RESULTS Infarct size in the CsA group (39% +/- 3%) was significantly reduced compared with the control group (60% +/- 2%, p < 0.001) and FK506 group (55% +/- 3%, p = 0.001). Apoptotic cell death was also attenuated in the CsA group (1.2% +/- 0.5%) compared with the control group (4.3% +/- 0.8%, p = 0.01) and FK506 group (4.1% +/- 0.9%, p = 0.05). Transmission electron microscopy revealed a preservation of normal mitochondrial morphology and a reduction in the percentage of disrupted mitochondria in the CsA group (20% +/- 7%) compared with the control group (53% +/- 12%) and FK506 group (47% +/- 9%). CONCLUSIONS Cyclosporine A-induced MPTP inhibition preserves mitochondrial morphology after myocardial ischemia/reperfusion and limits myocyte necrosis and apoptosis. These effects are independent of calcineurin inhibition.

Quantifying Acute Myocardial Injury Using Ratiometric Fluorometry

Early reperfusion is the best therapy for myocardial infarction (MI). Effectiveness, however, varies significantly between patients and has implications for long-term prognosis and treatment. A technique to assess the extent of myocardial salvage after reperfusion therapy would allow for high-risk patients to be identified in the early post-MI period. Mitochondrial dysfunction is associated with cell death following myocardial reperfusion and can be quantified by fluorometry. Therefore, we hypothesized that variations in the fluorescence of mitochondrial nicotinamide adenine dinucleotide (NADH) and flavoprotein (FP) can be used acutely to predict the degree of myocardial injury. Thirteen rabbits had coronary occlusion for 30 min followed by 3 h of reperfusion. To produce a spectrum of infarct sizes, six animals were infused cyclosporine A prior to ischemia. Using a specially designed fluorometric probe, NADH and FP fluorescence were measured in the ischemic area. Changes in NADH and FP fluorescence, as early as 15 min after reperfusion, correlated with postmortem assessment infarct size (r=0.695, p<0.01). This correlation strengthened with time (r=0.827, p<0.01 after 180 min). Clinical application of catheter-based myocardial fluorometry may provide a minimally invasive technique for assessing the early response to reperfusion therapy.

Rotating Frame Spin Lattice Relaxation in a Swine Model of Chronic, Left Ventricular Myocardial Infarction

T1ρ relaxation times were quantified in a swine model of chronic, left ventricular myocardial infarction. It was found that there were low frequency relaxation mechanisms that suppress endogenous contrast at low spin‐lock amplitudes and in T2‐weighted images. A moderate amplitude spin‐locking pulse could overcome these relaxation mechanisms. Relaxation dispersion data were measured over a range of RF field amplitudes, and a model was formulated to include dipole–dipole relaxation modulated by molecular rotation and an apparent exchange mechanism. These techniques may find some use in the clinic for the observation of chronic, left ventricular cardiac remodeling. Magn Reson Med, 2010.

Very Mild Hypothermia During Ischemia and Reperfusion Improves Postinfarction Ventricular Remodeling

BACKGROUND Mild hypothermia (< 4 degrees C) improves myocardial salvage after infarct reperfusion in animals and in early clinical studies. In this experiment the effect of mild hypothermia during ischemia and early reperfusion on long-term postinfarction left ventricular (LV) remodeling was assessed in an ovine infarct model. METHODS In the initial phase of the experiment the effect of progressive degrees of hypothermia on infarct size was quantified. Thirty-eight male sheep were subjected to 1 hour of ischemia using a standardized anteroapical infarct followed by 3 hours of reperfusion. Temperature was maintained at either 39.5 degrees C (n = 11), 38.5 degrees C (n = 7), 37.5 degrees C (n = 7), 36.5 degrees C (n = 7), or 35.5 degrees C (n = 6) for the entire period of ischemia and reperfusion. The area at risk (AR) and infarct size as a percentage of AR (I/AR) were determined with a double staining and planimetry technique. In the second phase of the study, chronic post-infarction remodeling was assessed in animals with nonreperfused infarcts (n = 6), 1 hour of ischemia followed by reperfusion at 39.5 degrees C (n = 6) and 1 hour of ischemia followed by reperfusion at 37.5 degrees C (n = 6). Remodeling was determined at 8 weeks after infarction using echocardiography. RESULTS The I/AR in the 39.5 degrees C, 38.5 degrees C, 37.5 degrees C, 36.5 degrees C, and the 35.5 degrees C groups was 71.8 +/- 3.0%, 63.1 +/- 1.9%, 49.4 +/- 1.4%, 38.7 +/- 1.4%, and 21.7 +/- 2.2%, respectively (p < 0.05 between all groups). In the chronic study LV end systolic volume at 8 weeks after infarction was 81 +/- 8 mL in the nonreperfused group, 57 +/- 4 mL in the 39.5 degrees C reperfusion group, and 41 +/- 3 mL in the 37.5 degrees C reperfusion group (p < 0.05 for between group differences). CONCLUSIONS Subtle degrees of hypothermia can significantly improve immediate myocardial salvage and long-term LV remodeling after infarct reperfusion.

Regional Heterogeneity of Myocardial Reperfusion Injury: Effect of Mild Hypothermia

BACKGROUND Mild hypothermia confers a myocardial protective effect that may make it a useful adjunct to reperfusion therapy for myocardial infarction (MI). The effect of temperature on the extent and distribution of myocardial reperfusion injury in a collateral deficient ovine model was studied. METHODS Topical cooling maintained left atrial temperature at 39.5 degrees C (n = 8), 38.5 degrees C (n = 5), 37.5 degrees C (n = 6), 36.5 degrees C (n = 6), or 35.5 degrees C (n = 5) in sheep prior to 1 hour of coronary occlusion to produce an anteroapical myocardial risk area (AR) followed by 3 hours of reperfusion. A dual staining and planimetry technique was used to assess infarct size as a percentage of the AR in 3 myocardial short axis slices that included the entire AR (slice 1= most apical; slice 3= most basal). The subendocardial, midmyocardial, and subepicardial extent in short axis of the infarct was also assessed in each slice. Microspheres assessed transmural blood flow. RESULTS At 39.5 degrees C there was a long-axis gradient in myocardial injury that was most severe at the apex and lessened toward the base. The midmyocardial region was most susceptible to injury at all long axis levels. Temperature reduction (as little as 1 degrees C) was associated with improved salvage that was most pronounced in the apical subendocardium and least in the basilar midmyocardium. Reperfusion at 39.5 degrees C resulted in severe transmural microvascular injury (no-reflow) that was completely obviated at temperatures below 38.5 degrees C. CONCLUSIONS Myocardial reperfusion injury varies over the long and short LV axes. Mild hypothermia preferentially improves myocardial salvage at the LV apex. Small temperature changes can dramatically affect microvascular integrity.

Sex-related resistance to myocardial ischemia-reperfusion injury is associated with high constitutive ARC expression

The female sex has been associated with improved myocardial salvage after ischemia and reperfusion (I/R). Estrogen, specifically 17beta-estradiol, has been demonstrated to mediate this phenomenon by limiting cardiomyocyte apoptosis. We sought to quantitatively assess the effect of sex, ovarian hormone loss, and I/R on myocardial Bax, Bcl-2, and apoptosis repressor with caspase recruitment domain (ARC) expression. Male (n = 48), female (n = 26), and oophorectomized female (n = 20) rabbits underwent 30 min of regional ischemia and 3 h of reperfusion. The myocardial area at risk and infarct size were determined using a double-staining technique and planimetry. In situ oligo ligation was used to assess apoptotic cell death. Western blot analysis was used to determine proapoptotic (Bax) and antiapoptotic (Bcl-2 and ARC) protein levels in all three ischemic groups and, additionally, in three nonischemic groups. Infarct size (43.7 +/- 3.2%) and apoptotic cell death (0.51 +/- 0.10%) were significantly attenuated in females compared with males (56.4 +/- 1.6%, P < 0.01, and 4.29 +/- 0.95%, P < 0.01) and oophorectomized females (55.7 +/- 3.4%, P < 0.05, and 4.36 +/- 0.51%, P < 0.01). Females expressed significantly higher baseline ARC levels (3.62 +/- 0.29) compared with males (1.78 +/- 0.18, P < 0.01) and oophorectomized females (1.08 +/- 0.26, P < 0.01). Males expressed a significantly higher baseline Bax-to-Bcl-2 ratio (4.32 +/- 0.99) compared with females (0.65 +/- 0.13, P < 0.01) and oophorectomized females (0.42 +/- 0.10, P < 0.01). I/R significantly reduced Bax-to-Bcl-2 ratios in males. In all other groups, ARC levels and Bax-to-Bcl-2 ratios did not significantly change. These results support the conclusion that in females, endogenous estrogen limits I/R-induced cardiomyocyte apoptosis by producing a baseline antiapoptotic profile, which is associated with estrogen-dependent high constitutive myocardial ARC expression.

Infarction induced myocardial apoptosis and ARC activation.

BACKGROUND Apoptosis is thought to play a role in infarction induced ventricular remodeling. Apoptosis repressor with caspase recruitment domain (ARC) has been shown to limit cardiomyocytes apoptosis; however, its role in the pathogenesis of heart failure is not established. This study examines the regional and temporal relationships of apoptosis, ARC, and remodeling. METHODS Myocardium was harvested from the infarct borderzone and remote regions of the left ventricle (LV) at 2 (n=8), 8 (n=6), and 32 (n=5) wk after MI. Activated ARC was compared with myocardial apoptosis in each region at each time. Both were then compared with the progression of remodeling. RESULTS LV systolic volume increased by a factor 1.56±0.06 and 2.09±0.07 at 2 and 8 wk, respectively then stabilized by 32 wk (2.08±0.18). Activated ARC was elevated at 2 wk, diminished at 8 wk, and increased again at 32 wk in both regions. Apoptosis was elevated at 2 wk, and further increased at 8 wk. By 32 wk, apoptosis had diminished significantly. CONCLUSIONS In a large animal infarction model, remodeling varied directly with the degree of apoptosis and inversely with ARC activation, suggesting that ARC acts as a natural regulatory phenomenon that limits apoptosis induced ventricular remodeling.