Beneficial effects of myocyte preconditioning on contractile processes after cardioplegic arrest

The effects of epinephrine on outcomes of normothermic and therapeutic hypothermic cardiopulmonary resuscitation

OBJECTIVE

To investigate the effects of epinephrine when administered during either normothermic or therapeutic hypothermic cardiopulmonary resuscitation on postresuscitation myocardial and cerebral function and survival.

DESIGN

Prospective, randomized, placebo-controlled experimental study.

SETTING

University-affiliated animal research laboratory.

SUBJECTS

Thirty-two healthy male Sprague-Dawley rats.

INTERVENTIONS

Ventricular fibrillation was induced and untreated for 8 mins. The animals were then randomly assigned to one of four groups: normothermic placebo control; normothermic epinephrine; hypothermic placebo control; and hypothermic epinephrine. Hypothermia was initiated coincident with the start of cardiopulmonary resuscitation. The blood temperature was reduced and maintained at 32 ± 0.2°C and continued for 4 hrs after resuscitation. Normothermic animals were maintained at 37 ± 0.2°C. Either placebo or epinephrine (20 μg/kg) was administered 5 mins after the start of cardiopulmonary resuscitation and 3 mins before defibrillation.

MEASUREMENTS AND MAIN RESULTS

Postresuscitation cardiac output, ejection fraction, and myocardial performance index were measured hourly for 4 hrs after resuscitation; neurologic deficit scores were measured daily for 7 days, and durations of survival were observed for up to 3 mos. Except for three normothermic control animals, all animals were resuscitated. When epinephrine was administered during normothermic cardiopulmonary resuscitation, postresuscitation myocardial function was severely impaired when compared with the normothermic control group. However, postresuscitation myocardial function was significantly better in animals treated with epinephrine during hypothermic cardiopulmonary resuscitation when compared with hypothermic controls. This was associated with significantly fewer postresuscitation ventricular arrhythmias, less ST-segment elevation, better postresuscitation neurologic deficit scores, and longer duration of survival.

CONCLUSIONS

Epinephrine, when administered during normothermic cardiopulmonary resuscitation, significantly increases the severity of postresuscitation myocardial dysfunction and decreases the duration of survival. These detrimental effects of epinephrine, however, no longer exist when it is administered during therapeutic hypothermic cardiopulmonary resuscitation.

Trafficking of the membrane type-1 matrix metalloproteinase in ischemia and reperfusion: relation to interstitial membrane type-1 matrix metalloproteinase activity

BACKGROUND

The matrix metalloproteinases (MMPs) contribute to regional remodeling after prolonged periods of ischemia and reperfusion (I/R), but specific MMP types activated during this process remain poorly understood. A novel class, the membrane-type MMPs (MT-MMPs), has been identified in the myocardium, but activity of these MMP types has not been assessed in vivo, particularly during I/R.

METHODS AND RESULTS

Pigs (30 kg, n=8) were instrumented with microdialysis catheters to measure MT1-MMP activity in both ischemic and nonischemic (remote) myocardium. A validated MT1-MMP fluorogenic substrate was infused through the microdialysis system, and changes in fluorescence were reflective of MT1-MMP activity at steady state, during ischemia (90 minutes), and during reperfusion (120 minutes). At peak ischemia, MT1-MMP activity was increased by >40% in the ischemic region, with no change in the remote region, which persisted with reperfusion (P<0.05). After I/R, MT1-MMP abundance was increased by >50% (P<0.05). Differential centrifugation revealed that the endosomal fraction (which contains subcellular organelles) within the ischemic myocardium was associated with a >135% increase in MT1-MMP (P<0.05). Furthermore, in an isolated left ventricular myocyte model of I/R, hypoxia (simulated ischemia) induced a >70% increase in MT1-MMP abundance in myocytes, and confocal microscopy revealed MT1-MMP internalization during this time period and reemergence to the membrane with reperfusion.

CONCLUSIONS

These unique results demonstrate that a specific MMP type, MT1-MMP, is increased in abundance and activity with I/R and is likely attributed, at least in part, to changes in intracellular trafficking.

Protein kinase C isoform-dependent myocardial protection by ischemic preconditioning and potassium cardioplegia

OBJECTIVE

Ischemic preconditioning combined with potassium cardioplegia does not always confer additive myocardial protection. This study tested the hypothesis that the efficacy of ischemic preconditioning under potassium cardioplegia is dependent on protein kinase C isoform.

METHODS

Isolated and crystalloid-perfused rat hearts underwent 5 cycles of 1 minute of ischemia and 5 minutes of reperfusion (low-grade ischemic preconditioning) or 3 cycles of 5 minutes of ischemia and 5 minutes of reperfusion (high-grade ischemic preconditioning) or time-matched continuous perfusion. These hearts received a further 5 minutes of infusion of normal buffer or oxygenated potassium cardioplegic solution. The isoform nonselective protein kinase C inhibitor chelerythrine (5 micromol/L) was administered throughout the preischemic period. All hearts underwent 35 minutes of normothermic global ischemia followed by 30 minutes of reperfusion. Isovolumic left ventricular function and creatine kinase release were measured as the end points of myocardial protection. Distribution of protein kinase C alpha, delta, and epsilon in the cytosol and the membrane fractions were analyzed by Western blotting and quantified by a densitometric assay.

RESULTS

Low-grade ischemic preconditioning was almost as beneficial as potassium cardioplegia in improving functional recovery; left ventricular developed pressure 30 minutes after reperfusion was 70 +/- 15 mm Hg (P <.01) in low-grade ischemic preconditioning and 77 +/- 14 mm Hg (P <.001) in potassium cardioplegia compared with values found in unprotected control hearts (39 +/- 12 mm Hg). Creatine kinase release during reperfusion was also equally inhibited by low-grade ischemic preconditioning (18.2 +/- 10.6 IU/g dry weight, P <.05) and potassium cardioplegia (17.6 +/- 6.7 IU/g, P <.01) compared with control values. However, low-grade ischemic preconditioning in combination with potassium cardioplegia conferred no significant additional myocardial protection; left ventricular developed pressure was 80 +/- 17 mm Hg, and creatine kinase release was 14.8 +/- 11.0 IU/g. In contrast, high-grade ischemic preconditioning with potassium cardioplegia conferred better myocardial protection than potassium cardioplegia alone; left ventricular developed pressure was 121 +/- 16 mm Hg (P <.001), and creatine kinase release was 8.3 +/- 5.8 IU/g (P <.05). Chelerythrine itself had no significant effect on functional recovery and creatine kinase release in the control hearts, but it did inhibit the salutary effects not only of low-grade and high-grade ischemic preconditioning but also those of potassium cardioplegia. Low-grade ischemic preconditioning and potassium cardioplegia enhanced translocation of protein kinase C alpha to the membrane, whereas high-grade ischemic preconditioning also enhanced translocation of protein kinase C delta and epsilon. Chelerythrine inhibited translocation of all 3 protein kinase C isoforms.

CONCLUSIONS

These results suggest that myocardial protection by low-grade ischemic preconditioning and potassium cardioplegia are mediated through enhanced translocation of protein kinase C alpha to the membrane. It is therefore suggested that activation of the novel protein kinase C isoforms is necessary to potentiate myocardial protection under potassium cardioplegia.

Cellular and molecular therapeutic targets for treatment of contractile dysfunction after cardioplegic arrest

Transient left ventricular (LV) dysfunction can occur after hypothermic hyperkalemic cardioplegic arrest. This laboratory has developed an isolated LV myocyte system of simulated cardioplegic arrest and rewarming in order to examine cellular and molecular events that may contribute to the LV dysfunction after cardioplegic arrest. Contractile function was examined using high-speed video microscopy after reperfusion and rewarming. After cardioplegic arrest and reperfusion, indices of myocyte contractility were reduced by over 40% from normothermic control values. The capacity of the myocyte to respond to an inotropic stimulus was examined through beta-adrenergic receptor stimulation with isoproterenol. After cardioplegic arrest, the contractile response to isoproterenol was reduced by over 50% from normothermic values. The next series of studies focused upon preventing these changes in myocyte contractile processes after cardioplegic arrest. First, the cardioplegic solutions were augmented with adenosine or an ATP-sensitive potassium channel opener, aprikalim. Both adenosine and aprikalim augmentation significantly improved myocyte function compared with cardioplegia alone values. A potential intracellular mechanism for the protective effects of either adenosine or the ATP-sensitive potassium channel is the activation of protein kinase C (PKC). A brief period of PKC activation before cardioplegic arrest provided protective effects on myocyte contractility with subsequent reperfusion and rewarming. In another set of studies, the potential protective effects of the active form of thyroid hormone (T3) were examined. In myocytes pretreated with T3, myocyte contractile function and beta-adrenergic responsiveness were significantly improved after hypothermic cardioplegic arrest and rewarming. Thus, endogenous means of providing improved myocardial protection during prolonged cardioplegic arrest can be achieved through a brief period of PKC activation or pretreatment with T3. Future studies, which more carefully deduce the basis for these pretreatment effects, will likely yield novel methods by which to protect myocyte contractile processes during cardioplegic arrest.

Protein kinase C activation before cardioplegic arrest: beneficial effects on myocyte contractility

OBJECTIVE

A potential intracellular mechanism for the protective effects of myocardial preconditioning is the activation of protein kinase C. The present study tested the hypothesis that a brief period of protein kinase C activation before cardioplegic arrest would provide protective effects on myocyte contractility with subsequent reperfusion and rewarming.

METHODS

Left ventricular porcine myocytes were assigned to the following treatments: (1) Protein kinase C/cardioplegia: Protein kinase C activation in myocytes (n = 39) for 3 minutes with a phorbol ester (10(-9) mol/L of phorbol 12-myristate 13-acetate) in oxygenated, normothermic (37 degrees C) cell media. Protein kinase C activation was followed by 2 hours of cardioplegic arrest (K+, 24 mEq/L; HCO3-, 30 mEq/L; 4 degrees C) and a 5-minute reperfusion period (37 degrees C media). (2) Cardioplegia: Myocytes (n = 31), 2 hours of cardioplegic arrest, and a 5-minute reperfusion and rewarming period. Myocyte contractility was measured by means of high-speed videomicroscopy. For comparison purposes, contractile function was examined in myocytes (n = 70) under normothermic control conditions.

RESULTS

Myocyte shortening velocity was reduced after cardioplegic arrest when compared with normothermic values (22.3 +/- 1.6 vs 48.8 +/- 2.0 microm/sec, p < 0.0001). Protein kinase C activation before cardioplegic arrest normalized myocyte shortening velocity (48.8 +/- 2.5 microm/sec). Co-incubation with phorbol 12-myristate 13-acetate and chelerythrine (10(-6) mol/L), an inhibitor of protein kinase C, before cardioplegic arrest abolished the protective effects of phorbol 12-myristate 13-acetate pretreatment.

CONCLUSION

These results suggest that an endogenous means of providing improved myocardial protection during prolonged cardioplegic arrest can be achieved through a brief period of protein kinase C activation.

Left ventricular diastolic function after coronary artery bypass grafting: a correlative study with three different myocardial protection techniques

BACKGROUND

This study was designed to examine the effect of myocardial protection on diastolic function after cardiac operations.

METHODS

Subjects were patients with normal preoperative diastolic function who were scheduled for coronary artery bypass grafting. Group I received anterograde cardioplegia; group II received anterograde and retrograde cardioplegia; and group III was protected with ventricular fibrillation and intermittent aortic crossclamping. Operations were performed with mild hypothermia and ventricular venting through the left superior pulmonary vein in all cases. Left ventricular diastolic function was evaluated with pulsed-wave Doppler transesophageal echocardiography (samples at the mitral valve leaflet: four-chamber view) and left superior pulmonary vein flow velocity. The flow patterns were stored on videotape and sent to an independent investigator for analysis. Left ventricular ejection fraction was calculated with transesophageal echocardiography (short-axis view, two-dimensional and M-mode).

RESULTS

Left ventricular diastolic function, as measured by the ratio between the peak velocities during early filling and atrial contraction and by systolic diastolic superior pulmonary venous flow ratio, was significantly impaired in all three groups 5 minutes after discontinuation of cardiopulmonary bypass. At 1 hour after operation, these values had returned to control levels only in group III. There was an increased incidence of supraventricular arrhythmias in group III. There were no significant hemodynamic differences among the three groups.

CONCLUSIONS

Left ventricular diastolic function was severely impaired after cardiopulmonary bypass. The degree of impairment depended on the myocardial protection used. The impairment in diastolic function was less when ventricular fibrillation and intermittent aortic crossclamping were used, and greater when anterograde and retrograde cardioplegia were used.

Protective effects of adenosine on myocyte contractility during cardioplegic arrest

BACKGROUND

Adenosine delivery to the left ventricular myocardium has been demonstrated to provide protective effects in the setting of ischemia and reperfusion. However, whether adenosine has direct protective effects on isolated myocytes in the setting of cardioplegic arrest was unclear.

METHODS

Isolated porcine left ventricular myocytes were assigned to one of the following treatment groups: (1) cardioplegia: 24 mEq/L K+, 4 degrees C for 2 hours followed by rewarming (cell media, 37 degrees C; n = 29); (2) cardioplegia augmented with adenosine (1 to 200 micromol/L) followed by rewarming (n = 98); and (3) normothermic control (cell media, 37 degrees C, 2 hours; n = 175). Myocyte contractility was measured by computer-aided videomicroscopy.

RESULTS

Cardioplegic arrest and rewarming reduced myocyte shortening velocity compared with normothermic control (25.3 +/- 2.5 microm/s versus 50.9 +/- 1.4 microm/s, p < 0.05). Adenosine-augmented cardioplegic arrest improved myocyte contractility with rewarming in a concentration-dependent fashion. For example, cardioplegia augmented with 10 micromol/L adenosine improved myocyte shortening velocity by 33% (33.6 +/- 3.0 microm/s versus 25.3 +/- 2.5 microm/s, p < 0.05), whereas 200 micromol/L adenosine improved shortening velocity by 97% (49.9 +/- 3.4 microm/s vs 25.3 +/- 2.5 microm/s, p < 0.05) compared with conventional cardioplegia.

CONCLUSIONS

This study demonstrated concentration-dependent protective effects of adenosine-augmented cardioplegia on myocyte contractile function with subsequent reperfusion and rewarming. These results suggest that stimulation of putative myocyte adenosine receptors may provide enhanced protective effects on myocyte contractile processes during cardioplegic arrest.

Preconditioning improves cardiac function after global ischemia, but not after cold cardioplegia

BACKGROUND

Ischemic preconditioning reduces infarct size and cardiac dysfunction during reperfusion. Preconditioning may offer myocardial protection in open heart operations.

METHODS

The effect of preconditioning before ischemia and cardioplegia was investigated in Langendorff-perfused rat hearts in the following groups. First, group 1 received two episodes of 3-minute ischemia and 5-minute reperfusion before 25 minutes of global (37 degrees C) ischemia and 60 minutes of reperfusion. Group 2 served as ischemic controls to group 1. Groups 3, 5, and 7 were preconditioned as described, before 3.5, 4, or 5 hours of cold (6 degrees to 8 degrees C) St. Thomas' II cardioplegia and 1 hour of reperfusion (37 degrees C). Groups 4, 6, and 8 were cardioplegic controls to groups 3, 5, and 7 (n = 17 in groups 1 and 2, and n = 10 in groups 3 to 8).

RESULTS

Preconditioning before warm ischemia attenuated the ischemia-induced increase of left ventricular end-diastolic pressure (3 +/- 1 versus 17 +/- 4 mm Hg; p < 0.01) (mean +/- standard error of the mean), the reduction of coronary flow (14 +/- 1 versus 9 +/- 0.5 mL/min; p < 0.001) and heart rate (252 +/- 19 versus 198 +/- 18 beats/min; p < 0.04), and the incidence of ventricular fibrillation (2 of 17 versus 10 of 17 hearts; p < 0.04) at the start of reperfusion. However, preconditioning did not influence postischemic cardiac function or the release of lactate dehydrogenase in any of the cardioplegia groups.

CONCLUSIONS

Ischemic preconditioning improved post-ischemic cardiac function after warm global ischemia, but did not protect cold cardioplegic hearts, perhaps because of the time span used.