Superoxide dismutase decreases early reperfusion release of conjugated dienes following regional canine ischemia

Controlled cardiac reoxygenation does not improve myocardial function following global myocardial ischemia

BACKGROUND

It has been shown that abrupt re-exposure of ischemic myocardium to oxygen can lead to increased peroxidative damage to myocytes (oxygen paradox). Controlled cardiac reoxygenation, as an adjunct to substrate-enhanced cardioplegia, has been shown to improve myocardial function and limit reperfusion injury when utilizing standardized hyperoxic cardiopulmonary bypass (CPB). The objective of our study was to evaluate the effect of controlled reoxygenation on myocardial function following global ischemia employing normoxic CPB.

STUDY DESIGN

Nineteen female swine (30-40kg) were placed on vented, normoxic CPB. They were subjected to 45-50min of unprotected global ischemia (aortic cross clamping) followed by 30min of controlled cardiac reperfusion utilizing substrate-enhanced cardioplegia. Group 1 maintained normoxic pO(2) (O(2) tension of 90-110mmHg). In Group 2, reoxygenation was titrated gradually and increased from venous to arterial levels (O(2) tensions from 40 to 110mmHg over 15min). We measured coronary sinus blood samples for CK, CK-MB, nitric oxide, and conjugated dienes at baseline, 5min into the cardioplegic resuscitation, 5min after the cross clamp removal, and just prior to the termination of the study. Hearts were pathologically studied and scored for evidence of tissue peroxidation.

RESULTS

Although not significantly different, Group 1 (normoxic reperfusion) animals were more likely to wean from CPB (p=0.141) and had a higher mean arterial pressure (p=0.556). In Group 1, conjugated dienes were significantly higher 5min into the resuscitative protocol (p=0.018) and at the termination of bypass (p=0.035). Five of six animals in Group 1 eventually attained normal sinus rhythm as opposed to three out of 13 in Group 2 (p=0.041). There was no significant difference in histology scoring between the two groups for tissue peroxidation.

CONCLUSION

This study of controlled cardiac reoxygenation in a lethal ischemic swine model failed to demonstrate that the use of controlled reoxygenation on the myocardial function following global ischemia was better with maintained normoxic pO(2) (with O(2) tensions of 90-110mmHg) than when reoxygenation was titrated gradually and increased from venous to arterial levels (O(2) tensions from 40 to 110mmHg over 15min).

Neurologic Preservation by Na+-H+ Exchange Inhibition Prior to 90 Minutes of Hypothermic Circulatory Arrest

BACKGROUND

The effects of pretreatment with cariporide (HOE 642 Aventis Pharma, Strasbourg-Cedex, France), a Na+-H+ exchanger (NHE) blocker, were studied in a cerebral ischemia-reperfusion model of hypothermic arrest.

METHODS

Fifteen Yorkshire-Duroc pigs (37.1 +/- 4.2 kg) underwent femoral-jugular bypass and 90 minutes of deep hypothermic circulatory arrest at 19 degrees C. Ten animals were untreated, whereas 5 received 5 mg/kg of intravenous cariporide before cooling. After rewarming and off cardiopulmonary bypass, the pigs were weaned from anesthesia and followed for 24 hours. A standardized neurologic scoring system assessed brain functional recovery. Biochemical markers were used to analyze cellular injury. Control studies without circulatory arrest were done in 2 animals that underwent similar cooling and rewarming.

RESULTS

Neurologic recovery was rapid and complete in the nonischemic controls and in all pretreated animals. Conversely, at 24 hours, all untreated pigs exhibited a cloudy or stuporous level of consciousness, abnormal positioning, and with only one exception, could not sit or stand. The gradation of neurologic score (evaluating central nervous system, motor and sensory functions, respiration condition, level of consciousness, and behavior) was 0 +/- 0 (0 = normal, 500 = brain death) in the treated group, compared with 124 +/- 59 in the untreated animals. Biochemical analysis showed every variable of whole-body injury (including conjugated dienes (p < 0.05), serum aspartate amino transferase (p < 0.01), creatine kinase p < 0.001) and endothelin-1 (p < 0.001) to be higher in the untreated group.

CONCLUSIONS

NHE function alters experimental brain ischemia-reperfusion damage. These observations imply that NHE inhibition therapy before ischemia may improve neurologic protection in adult and infant patients undergoing cerebral ischemia during procedures that use hypothermic circulatory arrest.

Reduction of systolic and diastolic dysfunction by retrograde coronary sinus perfusion during off-pump coronary surgery

OBJECTIVES

We evaluated the protective effects of retrograde coronary sinus perfusion to offset potential systolic and diastolic dysfunction (myocardial stunning) after temporary regional ischemia needed for off-pump coronary artery bypass grafting.

METHODS

Twenty Yorkshire-Duroc pigs (31.8 +/- 3.9 kg) underwent 15 minutes of mid-left anterior descending coronary artery ischemia in the beating heart. In 8 pigs, no protective measures were used. In 12 pigs, an aorta-coronary sinus shunt (with conventional cannulas) allowed retrograde perfusion during temporary ischemia; in 6 of these pigs, no leakage to the right atrium was ensured. Regional endocardial contraction was measured with sonomicrometer crystals. Systolic dysfunction (impaired regional shortening), diastolic dysfunction (contraction extending into early diastole), and coronary sinus nitric oxide and endothelin-1 levels were recorded.

RESULTS

Before ischemia, contraction did not extend into the diastolic interval. During ischemia, paradoxic bulging occurred in all hearts except in the occlusive coronary sinus shunt group (16% +/- 6% of baseline, P <.01). Sixty minutes after ischemia, systolic segment shortening recovered 36% +/- 24% without retrograde perfusion versus 56% +/- 20% and 61% +/- 14% with coronary sinus shunting (P <.05). Diastolic dysfunction (as percentage of diastolic time in contraction) was 38% +/- 16% in the nontreated group versus 22% +/- 22% and 9% +/- 9% (P <.05) after shunting and occlusive shunting, respectively. This correlated with a left ventricular end-diastolic pressure increase of 4 mm Hg in the ischemic group versus no change in the retrograde perfusion groups. Nitric oxide decreased 15% without shunting and increased 8% after occlusive coronary sinus shunting (P <.05).

CONCLUSIONS

Retrograde coronary sinus perfusion during simulated off-pump coronary revascularization diminishes systolic and diastolic dysfunction. An aortic-coronary sinus shunt is a rapid, recognized approach that can improve myocardial muscle and endothelial safety during off-pump coronary artery bypass grafting.

Myocyte and endothelial effects of preconditioning the jeopardized heart by inhibiting Na/H exchange

OBJECTIVES

The preconditioning effects of the adjunctive, cardiac-specific sodium-hydrogen ion exchange inhibitor cariporide (cariporide mesilate, HOE 642) were studied in hearts subjected to 30 minutes of normothermic ischemia and reperfusion to assess myocardial and endothelial changes.

METHODS

Sixteen Yorkshire-Duroc pigs (27-34 kg) receiving cardiopulmonary bypass underwent either cardiopulmonary bypass alone (control, n = 4) or 30 minutes of normothermic ischemia, followed by 30 minutes of blood reperfusion (n = 12). Six hearts were treated with 5 mg/kg cariporide administered intravenously 15 minutes before ischemia.

RESULTS

Cardiopulmonary bypass alone caused no changes. Conversely, 30 minutes of global normothermic ischemia caused 33% mortality and, in survivors, depression of left ventricular function to 22% +/- 6% of baseline preload recruitable stroke work and increased creatine kinase MB by 406% (88 +/- 13 U/L), conjugated dienes by 17% (161 +/- 0.2 AU/mL), and myeloperoxidase activity by 297% (0.036 +/- 0.005 U/g). Myocardial edema developed (3.5% water gain). Coronary sinus endothelin 1 increased by 111% (2.05 +/- 0.38 pg/mL), and nitric oxide production decreased by 10%. These adverse effects were limited by pretreatment with cariporide, which allowed complete survival and restored preload recruitable stroke work to 78% +/- 11%. Measurements of creatine kinase MB, conjugated dienes, myeloperoxidase, water, and endothelin 1 returned to baseline values, and nitric oxide production was accentuated 3-fold.

CONCLUSIONS

These observations show that adjunctive pretreatment with cariporide delays myocardial and endothelial injury during ischemia and reperfusion, limits oxygen-derived radical injury, restores function, reduces edema, and preserves endothelin and nitric oxide balance at normal values. The myeloperoxidase changes show that less white blood cell adherence supports reduced reperfusion endothelial damage.

Timing of treatment for myocardial reperfusion injury

Early reperfusion of acute myocardial infarctions halts cell death due to ischemia but causes further injury, probably by oxidant mechanisms. We identified the window of opportunity during which antioxidants must be present in therapeutic concentrations to prevent reperfusion injury during 90 min of ischemia and 48 h of reperfusion in 57 dogs. We examined the effect on myocardial infarct size of intravenous infusion of N-2-mercaptopropionyl glycine (MPG), a diffusible antioxidant with a plasma half-time of 7 min, by using a series of protocols with a range of timing. Whereas infusions of MPG for > or =3 h reduced infarct size by approximately 50%, infusions for 1 h only (the first, second or third hours of reperfusion) caused only small reductions. A statistical analysis that focused on identifying components of group membership responsible for differences revealed that duration of treatment was a major determinant of infarct size. If begun any time within the first hour of reperfusion, infusions of > or =3 h markedly diminished infarct size. Because reperfusion injury proceeds for the first 3 h of reperfusion, but decreases thereafter, adequate protection is needed for > or =3 of the first 4 h of reperfusion, but more prolonged protection is not necessary.

Delayed cardioplegic reoxygenation reduces reoxygenation injury in cyanotic immature hearts

BACKGROUND

Hypoxemic developing hearts are susceptible to oxygen-mediated damage that occurs after reintroduction of molecular oxygen. This unintended hypoxemic/reoxygenation injury leads to lipid peroxidation and membrane damage and may contribute to postoperative cardiac dysfunction. Biochemical and functional status are improved by delaying reoxygenation on cardiopulmonary bypass (CPB) until cardioplegic arrest.

METHODS

Six immature piglets (3 to 5 kg) without hypoxemia underwent 30 minutes of cardioplegic arrest during 1 hour of CPB. Fourteen others underwent 2 hours of hypoxemia on ventilator before reoxygenation on CPB. Reflecting our clinical routine, 9 were reoxygenated on CPB for 5 minutes followed by 30 minutes of cardioplegic arrest and 25 minutes of reperfusion. The other 5 were put on hypoxemic CPB for 5 minutes, before being reoxygenated during cardioplegic arrest for 30 minutes followed by 25 minutes of reperfusion.

RESULTS

Cardioplegic arrest (no hypoxemia group) caused no functional or biochemical changes. In contrast, by preceding hypoxemia with subsequent reoxygenation on CPB (no treatment group) we found 39.5% decrease in antioxidant reserve capacity, 1,212% increase in myocardial conjugated diene production, significant increase in coronary sinus blood conjugated dienes, and an 81% reduction of left ventricular contractility, all of which were statistically significant (p < 0.05) when compared with the no hypoxemia group. Conversely, delaying reoxygenation until cardioplegic arrest (treatment group) resulted in 33.1% improvement in antioxidant reserve capacity, 91.7% less conjugated diene production, lower coronary sinus blood conjugated diene levels, and a 95% improved contractility, all of which were significant (p < 0.05) when compared with the no treatment group.

CONCLUSIONS

A reoxygenation injury associated with lipid peroxidation and decreased postbypass contractility occurs in cyanotic immature hearts when reoxygenated on CPB. Delaying reoxygenation until cardioplegic arrest by starting CPB with ambient partial pressure of oxygen results in significantly improved myocardial status.

The use of cis-parinaric acid to measure lipid peroxidation in cardiomyocytes during ischemia and reperfusion

cis-Parinaric acid (PnAc), a fluorescent, polyunsaturated fatty acid, was used to measure lipid peroxidation during simulated ischemia and reperfusion in cultured neonatal rat cardiomyocytes. PnAc was used both as free fatty acid, inserted in the membranes following cultivation of the cells, as well as constituent of the cellular complex lipids by metabolically integrating the fatty acid during growth. In the insertion experiments a pre-incubation with DL-aminocarnitine, an inhibitor of beta-oxidation, was necessary to prevent loss of fluorescent signal. Such a pre-incubation resulted in an enrichment of PnAc in the sarcolemma: In pre-treated cells 57 +/- 1.3% of total inserted PnAc is present in the sarcolemma compared to 27 +/- 5.7% in cells containing the integrated probe. Both methods to introduce PnAc into the cells were compared with respect to their sensitivity for an externally applied oxidative stress and thereafter lipid peroxidation during simulated ischemia and reperfusion was assayed. Going from normoxic to ischemic conditions lipid peroxidation did not increase and remained at a low level. When the ischemic cells were subsequently subjected to reperfusion (reintroduction of both oxygen and glucose), large scale lipid peroxidation was obvious. When, on the other hand, oxygen alone was reintroduced (reoxygenation) no increased lipid peroxidation was observed. These observations led to the conclusion that ischemia does not lead to an enhanced lipid peroxidation and that resumption of metabolic activity during reperfusion is necessary to induce lipid peroxidation.

Nitric-oxide-induced reoxygenation injury in the cyanotic immature heart is prevented by controlling oxygen content during initial reoxygenation

Reintroduction of high levels of molecular oxygen after a hypoxic period is followed by a burst of nitric oxide (NO), peroxynitrite, and oxygen free radicals (OFR), which are highly cytotoxic. This study indicates that hyperoxic reoxygenation of cyanotic immature hearts on cardiopulmonary bypass (CPB) induces a reoxygenation injury and that, by reducing NO and OFR production during institution of CPB with subsequent reoxygenation under blood cardioplegic arrest, this oxygen-related damage can be avoided and biochemical and functional status improved. Of 25 immature piglets (3-5 kg, two to three weeks old), 6 underwent one hour of CPB including thirty minutes of aortic clamping with substrate-enriched modified blood cardioplegia (hypocalcemic, alkalotic, and hyperosmolar; warm induction-cold replenishment-warm reperfusion) without preceding hypoxia (controls). Nineteen others were made hypoxic (arterial [Po2] 20-30 mmHg) for up to two hours by lowering the fraction of inspired oxygen (FIO2) on ventilator. These hypoxic piglets were then reoxygenated on CPB at different Po2 levels (hyperoxic, normoxic, or hypoxic) for five minutes, followed by the aforementioned blood cardioplegic (BCP) arrest regimen. Myocardial conjugated diene (CD) production as a marker of lipid peroxidation, and NO production, determined as its spontaneous oxidation products, nitrite (NO2-) and nitrate (NO3-), were assessed during blood cardioplegic induction, and antioxidant reserve capacity was determined by incubating myocardium in the oxidant t-butylhydroperoxide (t-BHP). Myocardial function was evaluated from end-systolic elastance (Ees, conductance catheter). Blood cardioplegic arrest caused no functional or biochemical changes in normoxic control immature piglets. In contrast, brief reoxygenation at PO2 > 400 mmHg, followed by BCP-arrest (hyperoxic) resulted in marked CD production (42 +/- 4 vs 3 +/- 1 A233 nm/minute/100 g; P < 0.05), and NO production (4500 +/- 500 vs 450 +/- 32 mmol/minute/100 g; P < 0.05) during blood cardioplegic induction, reduced antioxidant reserve capacity (malondialdehyde [MDA] at 4.0 mM of t-BHP: 1342 +/- 59 vs 958 +/- 50 nM/g protein; P < 0.05), and caused profound myocardial dysfunction; Ees recovered only 21 +/- 2% (vs 104 +/- 7; P < 0.05), despite the blood cardioplegic regimen shown to be cardioprotective in control normoxic piglets. Conversely, controlling initial PO2 to normoxic (100 mmHg) or hypoxic (20-30 mmHg) levels reduced lipid peroxidation (CD production 16 +/- 2, 2 +/- 1 A233nm/minute/100 g) and NO production (1264 +/- 736, 270 +/- 182 mmol/minute/100 g), restored antioxidant reserve capacity (MDA at 4.0 mM of t-BHP: 940 +/- 95, 982 +/- 88 nM/g protein), and allowed significant functional recovery (58 +/- 11% and 83 +/- 8%), in a PO2-dependent fashion. The authors conclude that reoxygenation of hypoxemic immature hearts by initiating hyperoxic CPB causes oxidant-related damage characterized by lipid peroxidation, enhanced NO production, and reduced antioxidants, leading to functional depression that nullifies the cardioprotective effects of blood cardioplegia. These detrimental effects can be reduced in a PO2-dependent fashion by controlling initial PO2 on CPB and subsequent reoxygenation during blood cardioplegic arrest.

Oxidative insult associated with hyperoxic cardiopulmonary bypass in the infantile heart and lung

Cardiopulmonary bypass (CPB) per se alters many factors simultaneously, including free radical generation, which suggests that conventional hyperoxic CPB may produce oxidative injury in the infantile heart and lung. This study tests the hypothesis that CPB provokes oxidative cardiopulmonary changes and pulmonary endothelial dysfunction in immature piglets that can be prevented by free radical scavengers. We studied 15 2- to 3-week-old piglets. Five served as a control without CPB. Ten piglets underwent 60 min of CPB with a membrane oxygenator (Sarns). In 5 of these 10, the bypass prime was supplemented with N-mercaptopropionylglycine (MPG: 80 mg/kg) plus catalase (50,000 U/kg), whereas the others were not treated. Pre- and post-bypass cardiopulmonary function was measured in terms of left ventricular end-systolic elastance [Ees] by a conductance catheter, the arterial/alveolar pO2 ratio (a/A ratio) and static lung compliance. Conjugated dienes (A233 nm/mg lipid) were measured to detect lipid peroxidation in heart and lung tissue, and myocardial antioxidant reserve capacity [malondialdehyde (MDA) production in cardiac tissue incubated with the oxidant t-butyl hydroperoxide (t-BHP)] was assessed to detect oxidative changes. Pulmonary vascular resistance (PVR) and transpulmonary nitric oxide (NO) production were measured to assess pulmonary endothelial injury. Myocardial antioxidant reserve capacity was significantly reduced after 60 min of CPB, compared to control animals (MDA 779 +/- 100 vs 470 +/- 30 nmol/g protein, p < 0.05 at t-BHP 2.0 mmol/L), without evidence of lipid peroxidation or myocardial dysfunction. Pulmonary vascular resistance after CPB was dramatically increased (83 +/- 12 to 212 +/- 30, p < 0.05) without any change in lung function. In parallel to pulmonary vasoconstriction, NO production was significantly decreased after CPB (from 8.8 +/- 1.4 to 2.5 +/- 0.5 mmol/min/kg, p < 0.05). The addition of antioxidants (MPG+catalase) to the prime significantly improved myocardial antioxidant status (MDA: 604 +/- 30 vs 779 +/- 100 nmol/g protein, p < 0.05) and pulmonary vascular resistance (114 +/- 29 vs 212 +/- 30, p < 0.05 vs no-treatment group). In conclusion, the present study confirms that 1) Cardiopulmonary bypass produces substantial oxidative stress in normal immature myocardium, as assessed by reduced antioxidant reserve capacity; 2) CPB impairs pulmonary endothelial function, characterized by NO production, resulting in pulmonary vasoconstriction; and 3) These deleterious effects can be prevented by the addition of antioxidants (MPG/catalase) to the pump prime.

Decreased free radical scavengers with reperfusion after coronary angioplasty in patients with acute myocardial infarction

Early reperfusion after myocardial infarction improves survival rate and is thought to preserve myocardial function, but the reperfusion of ischemic tissue may release oxygen free radicals, which could adversely affect left ventricular function and diminish the beneficial effects of reperfusion. Measurements related to free radical scavenging (plasma and erythrocyte enzyme systems, which are involved in free radical control, alpha-tocopherol, selenium, and manganese superoxide dismutase) may be indirect markers of free radical production. We evaluated 10 patients undergoing coronary angioplasty within 4 hours of myocardial infarction to measure the impact of abrupt reperfusion on free radical scavenger-related indexes. Pulmonary artery samples were taken before, immediately after, and 3 hours after angioplasty. During reperfusion, significant reductions occurred in alpha-tocopherol (1.1 +/- 0.3 mg/dl before, 0.9 +/- 0.2 mg/dl immediately after [p = 0.03], and 0.8 +/- 0.2 mg/dl 3 hours after percutaneous transluminal coronary angioplasty [p = 0.02]), and selenium levels (13.7 +/- 2.4 micrograms/dl before, 12.9 +/- 2.4 micrograms/dl immediately after, and 10.2 +/- 3.0 micrograms/dl 3 hours after angioplasty [p = 0.0006]). Erythrocyte markers (glutathione peroxidase and superoxide dismutase) were not altered by reperfusion, possibly reflecting the relatively long half-life of the erythrocyte. The erythrocyte glutathione peroxidase value before reperfusion in patients (30.8 +/- 5.1 IU/gm of hemoglobin) was lower than in a control group (36.1 +/- 6.5 IU/gm of hemoglobin; p = 0.01). Thus the decrease in plasma alpha-tocopherol and selenium after reperfusion in this group of patients may reflect a general alteration in plasma free radical scavenger levels, suggesting consumption of plasma free radical scavengers with reperfusion after acute myocardial infarction.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. VI. Counteraction of oxidant damage by exogenous antioxidants: N-(2-mercaptopropionyl)-glycine and catalase

This study tests the hypothesis that antioxidants administered before reoxygenation can reduce oxygen-mediated damage and improve myocardial performance. Of 25 Duroc-Yorkshire piglets (2 to 3 weeks, 3 to 5 kg) five underwent 60 minutes of cardiopulmonary bypass without hypoxemia (control group), and five others underwent 30 minutes of hypoxemia on cardiopulmonary bypass with a circuit primed with oxygen tension about 25 mm Hg blood followed by reoxygenation on cardiopulmonary bypass (no treatment). In vitro studies were performed to obtain the optimal dosage of the antioxidants N-(2-mercaptopropionyl)-glycine and and catalase to be used in subsequent in vivo experimental studies; cardiac homogenates were incubated in 0 to 5 mmol/L concentrations of the oxidant t-butylhydroperoxide and malondialdehyde production was measured. Fifteen piglets were made hypoxemic on cardiopulmonary bypass for 30 minutes, and the antioxidants N-(2-mercaptopropionyl)-glycine at either 30 or 80 mg/kg body weight or N-(2-mercaptopropionyl)-glycine, 30 mg/kg body weight, and catalase, 50,000 U/kg body weight, were added to the cardiopulmonary bypass circuit 15 minutes before reoxygenation. Left ventricular contractility, which was expressed as end-systolic elastance, was measured by conductance catheter before hypoxemia and after reoxygenation. Myocardial antioxidant reserve capacity was determined after reoxygenation by incubating cardiac homogenates in the oxidant t-butylhydroperoxide and measuring subsequent malondialdehyde elution. The in vitro bioassay studies showed a dose-dependent reduction of lipid peroxidation with N-(2-mercaptopropionyl)-glycine, with maximal benefits of a 40% decrease and malondialdehyde elaboration occurring with N-(2-mercaptopropionyl)-glycine and catalase compared with untreated cardiac homogenates. Cardiopulmonary bypass (no hypoxemia) caused no oxidant damage or changes in contractile function after cardiopulmonary bypass. Reoxygenation without treatment raised conjugated diene levels 57%,* lowered antioxidant reserve capacity 51%,* and was associated with only 38%* recovery of contractile function (p < 0.05 vs control). In contrast, treatment with antioxidants avoided lipid peroxidation, maintained antioxidant reserve capacity, and resulted in a dose-dependent improvement in left ventricular contractility with complete recovery occurring in N-(2-mercaptopropionyl)-glycine and catalase-treated piglets (*p < 0.05 vs no treatment). This study confirms the occurrence of hypoxemic/reoxygenation injury in immature hearts placed on cardiopulmonary bypass and shows that biochemical and functional damage can be counteracted by adding antioxidants to the cardiopulmonary bypass priming fluid. Contractile function improved in a dose-dependent manner, and oxygen-mediated damage could be avoided by mercaptopropionyl glycine/catalase treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of hypoxemic/reoxygenation injury: without aortic clamping. IX. Importance of avoiding perioperative hyperoxemia in the setting of previous cyanosis

This study of an in vivo infantile piglet model of compensated hypoxemia tests the hypothesis that reoxygenation on hyperoxemic cardiopulmonary bypass produces oxygen-mediated myocardial injury that can be limited by normoxemic management of cardiopulmonary bypass and the interval after cardiopulmonary bypass. Twenty-five immature piglets (< 3 weeks old) were placed on 120 minutes of cardiopulmonary bypass and five piglets served as a biochemical control group without cardiopulmonary bypass. Five piglets underwent cardiopulmonary bypass without hypoxemia (cardiopulmonary bypass control). Twenty others became hypoxemic on cardiopulmonary bypass for 60 minutes by lowering oxygen tension to about 25 mm Hg. The study was terminated in five piglets at the end of hypoxemia, whereas 15 others were reoxygenated at an oxygen tension about 400 mm Hg or about 100 mm Hg for 60 minutes. Oxygen delivery was maintained during hypoxemia by increasing cardiopulmonary bypass flow and hematocrit level to avoid metabolic acidosis and lactate production. Myocardial function after cardiopulmonary bypass was evaluated from end-systolic elastance (conductance catheter) and Starling curve analysis. Myocardial conjugated diene production and creatine kinase leakage were assessed as biochemical markers of injury, and antioxidant reserve capacity was determined by measuring malondialdehyde after cardiopulmonary bypass in myocardium incubated in the oxidant, t-butylhydroperoxide. Cardiopulmonary bypass without hypoxemia caused no oxidant or functional damage. Conversely, reoxygenation at an oxygen tension about 400 mm Hg raised myocardial conjugated diene level and creatine kinase production (CD: 3.5 +/- 0.7 A233 nm/min/100 g, creatine kinase: 8.5 +/- 1.5 U/min/100 g, p < 0.05 vs cardiopulmonary bypass control), reduced antioxidant reserve capacity (malondialdehyde: 1115 +/- 60 nmol/g protein at 4.0 mmol t-butylhydroperoxide, p < 0.05 vs control), and produced severe postbypass dysfunction (end-systolic elastance recovered only 39% +/- 7%, p < 0.05 vs cardiopulmonary bypass control). Lowering oxygen tension to about 100 mm Hg during reoxygenation avoided conjugated diene production and creatine kinase release, retained normal antioxidant reserve, and improved functional recovery (80% +/- 11%, p < 0.05 vs oxygen tension about 400 mm Hg). These findings show that conventional hyperoxemic cardiopulmonary bypass causes unintended reoxygenation injury in hypoxemic immature hearts that may contribute to myocardial dysfunction after cardiopulmonary bypass and that normoxemic management may be used to surgical advantage.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. III. Comparison of the magnitude of damage by hypoxemia/reoxygenation versus ischemia/reperfusion

The immature heart is more tolerant to ischemia than the adult heart, yet infants with cyanosis show myocardial damage after surgical correction of congenital cardiac defects causing hypoxemia. This study tested the hypothesis that the hypoxemic developing heart is susceptible to oxygen-mediated damage when it is reoxygenated during cardiopulmonary bypass and that this hypoxemic/reoxygenation injury is more severe than ischemic/reperfusion stress. Fifteen Duroc-Yorkshire piglets (2 to 3 weeks old, 3 to 5 kg) underwent 60 minutes of 37 degrees C cardiopulmonary bypass. Five piglets (control) were not made ischemic or hypoxemic. Five underwent 30 minutes of normothermic ischemia (aortic clamping) and 25 minutes of reperfusion before cardiopulmonary bypass was discontinued. Five others underwent 30 minutes of hypoxemia (bypass circuit primed with blood with oxygen tension 20 to 30 mm Hg) and 30 minutes of reoxygenation during cardiopulmonary bypass. Functional (left-ventricular contractility) and biochemical (levels of plasma and tissue conjugated dienes and antioxidant reserve capacity) measurements were made before ischemia/hypoxemia and after reperfusion/reoxygenation. Cardiopulmonary bypass (no ischemia or hypoxemia) caused no changes in left-ventricular function or coronary sinus levels of conjugated dienes. The tolerance to normothermic ischemia was confirmed, inasmuch as left-ventricular function returned to 108% of control values and coronary sinus levels of conjugated dienes did not rise after reperfusion. Conversely, reoxygenation raised plasma levels of conjugated dienes in coronary sinus blood in the hypoxic group 57% compared with end-hypoxic levels (p < 0.05 versus end-hypoxic levels and versus ischemia, by analysis of variance). Antioxidant reserve capacity showed the lowest levels (highest production of malondialdehyde) in the hypoxemic group (51% higher than control values; p < 0.05 by analysis of variance). These biochemical changes were associated with a 62% depression of left-ventricular function after bypass because end-systolic elastance recovered only 38% of control levels (p < 0.05 by analysis of variance). These data confirm the tolerance of the immature heart to ischemia and reperfusion and document a hypoxemic/reoxygenation injury that occurs in immature hearts reoxygenated during bypass. Hypoxemia seems to render the developing heart susceptible to reoxygenation damage that depresses postbypass function and is associated with lipid peroxidation. These findings suggest that starting bypass in cyanotic immature subjects causes an unintended reoxygenation injury that may potentially be counteracted by adding antioxidants to the prime of the extracorporeal circuit.

Studies of hypoxemic/reoxygenation injury: with aortic clamping. XIII. Interaction between oxygen tension and cardioplegic composition in limiting nitric oxide production and oxidant damage

This study tests the interaction between oxygen tension and cardioplegic composition on nitric oxide production and oxidant damage during reoxygenation of previously cyanotic hearts. Of 35 Duroc-Yorkshire piglets (2 to 3 weeks, 3 to 5 kg), six underwent 30 minutes of blood cardioplegic arrest with hyperoxemic (oxygen tension about 400 mm Hg), hypocalcemic, alkalotic, glutamate/aspartate blood cardioplegic solution during 1 hour of cardiopulmonary bypass without hypoxemia (control). Twenty-nine others were subjected to up to 120 minutes of ventilator hypoxemia (oxygen tension about 25 mm Hg) before reoxygenation on CPB. To simulate routine clinical management, nine piglets underwent uncontrolled cardiac reoxygenation, whereby cardiopulmonary bypass was started at oxygen tension of about 400 mm Hg followed by the aforementioned blood cardioplegic protocol 5 minutes later. All 20 other piglets underwent controlled cardiac reoxygenation, whereby cardiopulmonary bypass was started at the ambient oxygen tension (about 25 mm Hg), and reoxygenation was delayed until blood cardioplegia was given. The blood cardioplegia solution was kept normoxemic (oxygen tension about 100 mm Hg) in 10 piglets and made hyperoxemic (oxygen tension about 400 mm Hg) in 10 others. The cardioplegic composition was also varied so that the cardioplegic solution in each subgroup contained either KCl only (30 mEq/L) or components that theoretically inhibit nitric oxide synthase by including hypocalcemia, alkalosis, and glutamate/aspartate. Function (end-systolic elastance) and myocardial nitric oxide production, conjugated diene production, and antioxidant reserve capacity were measured. Blood cardioplegic arrest without hypoxemia did not cause myocardial nitric oxide or conjugated diene production, reduce antioxidant reserve capacity, or change left ventricular functional recovery. In contrast, uncontrolled cardiac reoxygenation raised nitric oxide and conjugated diene production 19- and 13-fold, respectively (p < 0.05 vs control), reduced antioxidant reserve capacity 40%, and contractility recovered only 21% of control levels. After controlled cardiac reoxygenation at oxygen tension about 400 mm Hg with cardioplegic solution containing KCl only, nitric oxide and conjugated diene production rose 16- and 12-fold, respectively (p < 0.05 vs control), and contractility recovered only 43% +/- 5%. Normoxemic (oxygen tension of about 100 mm Hg) controlled cardiac reoxygenation with the same solution reduced nitric oxide and conjugated diene production 85% and 71%, and contractile recovery rose to 55% +/- 7% (p < 0.05 vs uncontrolled reoxygenation). In comparison, controlled cardiac reoxygenation with an oxygen tension of about 400 mm Hg hypocalcemic, alkalotic, glutamate/aspartate blood cardioplegic solution reduced nitric oxide and conjugated diene production 85% and 62%, respectively, and contractility recovered 63% +/- 4% (p < 0.05 vs KCl only).(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of hypoxemic/reoxygenation injury with aortic clamping: XI. Cardiac advantages of normoxemic versus hyperoxemic management during qardiopulmonary bypass

The conventional way to start cardiopulmonary bypass is to prime the cardiopulmonary bypass circuit with hyperoxemic blood (oxygen tension about 400 mm Hg) and deliver cardioplegic solutions at similar oxygen tension levels. This study tests the hypothesis that an initial normoxemic oxygen tension strategy to decrease the oxygen tension-dependent rate of oxygen free radical production will, in concert with normoxemic blood cardioplegia, limit reoxygenation damage and make subsequent hyperoxemia (oxygen tension about 400 mm Hg) safer. Thirty-five immature (3 to 5 kg, 2 to 3 week old) piglets underwent 60 minutes of cardiopulmonary bypass. Eleven control studies at conventional hyperoxemic oxygen tension (about 400 mm Hg) included six piglets that also underwent 30 minutes of blood cardioplegic arrest. Of 25 studies in which piglets were subjected to up to 120 minutes of ventilator hypoxemia (reducing fraction of inspired oxygen to 5% to 7%; oxygen tension about 25 mm Hg), 11 underwent either abrupt (oxygen tension about 400 mm Hg, n = 6) or gradual (increasing oxygen tension from 100 to 400 mm Hg over a 1-hour period, n = 5) reoxygenation without blood cardioplegia. Fourteen others underwent 30 minutes of blood cardioplegic arrest during cardiopulmonary bypass. Of these, nine were reoxygenated at oxygen tension about 400 mm Hg, and five others underwent normoxemic cardiopulmonary bypass and blood cardioplegia (oxygen tension about 100 mm Hg) with systemic oxygen tension raised to 400 mm Hg after aortic unclamping. Measurements of lipid peroxidation (conjugated dienes and antioxidant reserve capacity) and contractile function (pressure-volume loops, conductance catheter, end-systolic elastance) were made before and during hypoxemia and 30 minutes after reoxygenation. Hyperoxemic cardiopulmonary bypass did not produce oxidant damage or reduce functional recovery after cardiopulmonary bypass in nonhypoxemic controls. In contrast, abrupt and gradual reoxygenation without blood cardioplegia produced significant lipid peroxidation (84% increase in conjungated dienes), lowered antioxidant reserve capacity 68% +/- 5%, 44% +/- 8%, respectively, and decreased functional recovery 75% +/- 6% (p < 0.05), 66% +/- 4% (p < 0.05). Similar impairment followed abrupt reoxygenation before blood cardioplegic myocardial management, because conjungated diene production increased 13-fold, antioxidant reserve capacity fell 40%, and contractility recovered only 21% +/- 2% (p < 0.05). Conversely, normoxemic induction of cardiopulmonary bypass and blood cardioplegic myocardial management reduced conjungated diene production 73%, avoided impairment of antioxidant reserve capacity, and resulted in 58% +/- 11% recovery of contractile function.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of hypoxemic/reoxygenation injury: without aortic clamping. IV. Role of the iron-catalyzed pathway: deferoxamine

This study tests the hypothesis that an iron chelator, deferoxamine, can reduce oxygen-mediated myocardial injury and avoid myocardial dysfunction after cardiopulmonary bypass by its action on the iron-catalyzed Haber-Weiss pathway. Twenty-one immature 2- to 3-week-old piglets were placed on cardiopulmonary bypass for 120 minutes, and five piglets served as biochemical controls without cardiopulmonary bypass. Five piglets underwent cardiopulmonary bypass without hypoxemia (cardiopulmonary bypass control). Sixteen others became hypoxemic while undergoing cardiopulmonary bypass for 60 minutes by lowering oxygen tension to about 25 mm Hg, followed by reoxygenation at oxygen tension about 400 mm Hg for 60 minutes. Oxygen delivery was maintained during hypoxemia by increasing cardiopulmonary bypass flow and hematocrit level. In seven piglets deferoxamine (50 mg/kg total dose) was given both intravenously just before reoxygenation and by a bolus injection (5 mg/kg) into the cardiopulmonary bypass circuit; nine others were not treated (no therapy). Myocardial function after cardiopulmonary bypass was evaluated form end-systolic elastance (conductance catheter) and Starling curve analysis. Myocardial conjugated diene production and creatine kinase leakage were assessed as biochemical markers of injury, and antioxidant reserve capacity was determined by measuring malondialdehyde in postcardiopulmonary bypass myocardium incubated in the oxidant, t-butylhydroperoxide. Cardiopulmonary bypass without hypoxemia caused no oxidant or functional damage. Conversely, reoxygenation (no therapy) raised myocardial conjugated diene levels and creatine kinase production (conjugated diene: 3.5 +/- 0.7 absorbance 233 nm/min/100 g, creatine kinase: 8.5 +/- 1.5 U/min/100 g; p < 0.05 versus cardiopulmonary bypass control), reduced antioxidant reserve capacity (malondialdehyde: 1115 +/- 60 nmol/g protein at 4 mmol/L t-butylhydroperoxide; p < 0.05 versus control), and produced severe post-bypass dysfunction (end-systolic elastance recovered only 39% +/- 7%, p < 0.05 versus cardiopulmonary bypass control). Deferoxamine avoided conjugated diene production and creatine kinase release and retained normal antioxidant reserve, and functional recovery was complete (95% +/- 11%, p < 0.05 versus no treatment). These findings show that iron-catalyzed oxidants may contribute to a reoxygenation injury and imply that deferoxamine may be used to surgical advantage.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. VII. Counteraction of oxidant damage by exogenous antioxidants: coenzyme Q10

Coenzyme Q10 (CoQ10) is a natural mitochondrial respiratory chain constituent with antioxidant properties. This study tests the hypothesis that CoQ10 administered before the onset of reoxygenation on cardiopulmonary bypass, can reduce oxygen-mediated myocardial injury and avoid myocardial dysfunction after cardiopulmonary bypass. The antioxidant properties of CoQ10 were confirmed by an in vitro study in which normal myocardial homogenates were incubated with the oxidant, t-butylhydroperoxide. Fifteen immature piglets (< 3 weeks old) were placed on 60 minutes of cardiopulmonary bypass. Five piglets underwent cardiopulmonary bypass without hypoxemia (oxygen tension about 400 mm Hg). Ten others became hypoxemic on cardiopulmonary bypass for 30 minutes by lowering oxygen tension to approximately 25 mm Hg, followed by reoxygenation at oxygen tension about 400 mm Hg for 30 minutes. In five piglets, CoQ10 (45 mg/kg) was added to the cardiopulmonary bypass circuit 15 minutes before reoxygenation, and five others were not treated (no treatment). Myocardial function after cardiopulmonary bypass was evaluated from end-systolic elastance (conductance catheter), oxidant damage (lipid peroxidation) was assessed by measuring conjugated diene levels in coronary sinus blood, and antioxidant reserve capacity was determined by measuring malondialdehyde in myocardium after cardiopulmonary bypass incubated in the oxidant, t-butylhydroperoxide. Cardiopulmonary bypass without hypoxemia caused no oxidant damage and allowed complete functional recovery. Reoxygenated hearts (no treatment) showed a progressive increase in conjugated diene levels in coronary sinus blood after reoxygenation (2.3 +/- 0.6 A233 nm/0.5 ml plasma at 30 minutes after reoxygenation) and reduced antioxidant reserve capacity (malondialdehyde: 1219 +/- 157 nmol/g protein at 4.0 mmol/L t-butylhydroperoxide), resulting in severe postbypass dysfunction (percent end-systolic elastance = 38 +/- 6). Conversely, CoQ10 treatment avoided the increase in conjugated diene levels (2.1 +/- 0.6 vs 1.1 +/- 0.3, p < 0.05 vs no treatment), retained normal antioxidant reserve (896 +/- 76 nmol/g protein, p < 0.05 vs no treatment), and allowed nearly complete recovery of function (94% +/- 7%, p < 0.05 vs no treatment). We conclude that reoxygenation of the hypoxemic immature heart on cardiopulmonary bypass causes oxygen-mediated myocardial injury, which can be limited by CoQ10 treatment before reoxygenation. These findings imply that coenzyme Q10 can be used to surgical advantage in cyanotic patients, because therapeutic blood levels can be achieved by preoperative oral administration of this approved drug.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. II. Evidence for reoxygenation damage

This study tested the hypothesis that the developing heart is susceptible to oxygen-mediated damage after reintroduction of molecular oxygen and that this "unintended" reoxygenation injury causes lipid peroxidation and functional depression that may contribute to perioperative cardiac dysfunction. Among 49 Duroc-Yorkshire piglets (2 to 3 weeks old, 3 to 5 kg) 15 control studies were done without hypoxemia to test the effects of the surgical preparation (n = 10) and 60 minutes of cardiopulmonary bypass (n = 5). Twenty-nine piglets underwent up to 2 hours of ventilator hypoxemia (with inspired oxygen fraction reduced to 6% to 7%) to lower arterial oxygen tension to approximately 25 mm Hg. Five piglets did not undergo reoxygenation to determine alterations caused by hypoxemia alone. Twenty-four others received reoxygenation by either raising ventilator inspired oxygen fraction to 1.0 (n = 12) or instituting cardiopulmonary bypass at oxygen tension 400 mm Hg (n = 12). Ventilator hypoxemia produced sufficient hemodynamic compromise and metabolic acidosis that 18 piglets required premature reoxygenation (78 +/- 12 minutes). To avoid the influence of acidosis and hemodynamic deterioration during ventilator hypoxemia, five others underwent 30 minutes of hypoxemia during cardiopulmonary bypass (circuit primed with blood at oxygen tension 25 mm Hg) and 30 minutes of reoxygenation (oxygen tension 400 mm Hg) during cardiopulmonary bypass. Biochemical markers of oxidant damage included measurement of coronary sinus and myocardial conjugated dienes to determine lipid peroxidation and antioxidant reserve capacity assessed by incubating myocardial tissue in the oxidant t-butylhydroperoxide. Functional recovery was determined by inscribing pressure volume loops to determine end-systolic elastance and Starling curves by volume infusion. No biochemical or functional changes occurred in control piglets. Hypoxemia without reoxygenation did not change plasma levels of conjugated dienes, but lowered antioxidant reserve capacity 24%. Reoxygenation by ventilator caused refractory ventricular arrhythmias in two piglets (17% mortality), raised levels of conjugated dienes 45%, and reduced antioxidant reserve capacity 40% with recovery of 39% of mechanical function in the survivors. Comparable biochemical and functional changes occurred in piglets undergoing ventilator hypoxemia and/or cardiopulmonary bypass hypoxemia and reoxygenation on cardiopulmonary bypass. We conclude that hypoxemia increases vulnerability to reoxygenation damage by reducing antioxidant reserve capacity and that reoxygenation by either ventilator or cardiopulmonary bypass produces oxidant damage with resultant functional depression that is not a result of cardiopulmonary bypass. These findings suggest that initiation of cardiopulmonary bypass in cyanotic immature subjects causes an unintended reoxygenation injury, which may increase vulnerability to subsequent ischemia during surgical repair.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. V. Role of the L-arginine-nitric oxide pathway: the nitric oxide paradox

This study tests the hypothesis that nitric oxide, which is endothelial-derived relaxing factor, produces reoxygenation injury via the L-arginine-nitric oxide pathway in hypoxemic immature hearts when they are placed on cardiopulmonary bypass. Twenty 3-week-old piglets undergoing 2 hours of hypoxemia (oxygen tension about 25 mm Hg) on a ventilator were reoxygenated by initiating cardiopulmonary bypass (oxygen tension about 400 mm Hg). Five animals were not treated, whereas the pump circuit was primed with the nitric oxide-synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 4 mg/kg) in five piglets. L-Arginine, the substrate for nitric oxide, was administered in a fivefold excess (20 mg/kg), together with L-NAME in five piglets (L-NAME and L-arginine), and given alone in five other piglets (L-arginine). Five normoxemic, instrumented piglets served as a control group, and five others underwent 30 minutes of cardiopulmonary bypass without preceding hypoxemia. Left ventricular contractility was determined as end-systolic elastance by pressure-dimension loops. Myocardial conjugated dienes were measured as a marker of lipid peroxidation, and the antioxidant reserve capacity (malondialdehyde production in tissue incubated with t-butylhydroperoxide) was measured. Nitric oxide level was determined in coronary sinus plasma as its spontaneous oxidation product, nitrite. Cardiopulmonary bypass per se did not alter left ventricular contractility, cause lipid peroxidation, or lower antioxidant capacity. Reoxygenation without treatment depressed cardiac contractility (end-systolic elastance 38% +/- 12% of control*), raised nitric oxide (127% above hypoxemic values), increased conjugated dienes (1.3 +/- 0.2 vs 0.7 +/- 0.1, control*), and reduced antioxidant reserve capacity (910 +/- 59 vs 471 +/- 30, control*). Inhibition of nitric oxide production by L-NAME improved end-systolic elastance to 84% +/- 12%,** limited conjugated diene elution (0.8 +/- 0.1 vs 1.3 +/- 0.2, no treatment**), and improved antioxidant reserve capacity (679 +/- 69 vs 910 +/- 59, no treatment**). Conversely, L-arginine counteracted these beneficial effects of L-NAME, because left ventricular function recovered only 24% +/- 6%,* conjugated dienes were 1.2 +/- 0.1,* and antioxidant reserve capacity was 826 +/- 70.* L-Arginine alone caused the same deleterious biochemical changes as L-NAME/L-arginine and resulted in 60% mortality. The close relationship between postbypass left ventricular dysfunction (percent end-systolic elastance) and myocardial conjugated diene production (r = 0.752) provides in vivo evidence that lipid peroxidation contributes to myocardial dysfunction after reoxygenation.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of hypoxemic/reoxygenation injury: without aortic clamping. VIII. Counteraction of oxidant damage by exogenous glutamate and aspartate

Previous studies show that (1) hypoxemia depletes immature myocardium of amino acid substrates and their replenishment improves ischemic tolerance, (2) reoxygenation on cardiopulmonary bypass causes oxygen-mediated damage without added ischemia, and (3) this damage may be related to the nitric oxide-L-arginine pathway that is affected by amino acid metabolism. This study tests the hypothesis that priming the cardiopulmonary bypass circuit with glutamate and aspartate limits reoxygenation damage. Of 22 immature Duroc-Yorkshire piglets (< 3 weeks old), five were observed over a 5-hour period (control), and five others underwent 30 minutes of CPB without hypoxemia (cardiopulmonary bypass control). Twelve others became hypoxemic by reducing ventilator inspired oxygen fraction to 6% to 7% (oxygen tension about 25 mm Hg) before reoxygenation on cardiopulmonary bypass for 30 minutes. Of these five were untreated (no treatment), and the cardiopulmonary bypass circuit was primed with 5 mmol/L glutamate and aspartate in seven others (treatment). Left ventricular function before and after bypass was measured by inscribing pressure-volume loops (end-systolic elastance). Myocardial conjugated diene levels were measured to detect lipid peroxidation, and antioxidant reserve capacity was tested by incubating cardiac muscle with the oxidant t-butylhydroperoxide to determine the susceptibility to subsequent oxidant injury. CPB (no hypoxemia) allowed complete functional recovery without changing conjugated dienes and antioxidant reserve capacity, whereas reoxygenation injury developed in untreated hearts. This was characterized by reduced contractility (elastance end-systolic recovered only 37% +/- 8%*), increased conjugated diene levels (1.3 +/- 0.1 vs 0.7 +/- 0.1*), and decreased antioxidant reserve capacity (910 +/- 59 vs 471 +/- 30 malondialdehyde nmol/g protein at 2 mmol/L t-butylhydroperoxide*). In contrast, priming the cardiopulmonary bypass circuit with glutamate and aspartate resulted in significantly better left ventricular functional recovery (75% +/- 8% vs 37% +/- 8%*), minimal conjugated diene production (0.8 +/- 0.1 vs 1.3 +/- 0.1*), and improved antioxidant reserve capacity (726 +/- 27 vs 910 +/- 59 malondialdehyde nmol/g protein*) (*p < 0.05 vs cardiopulmonary bypass control). We conclude that reoxygenation of immature hypoxemic piglets by the initiation of cardiopulmonary bypass causes myocardial dysfunction, lipid peroxidation, and reduced tolerance to oxidant stress, which may increase vulnerability to subsequent ischemia (i.e., aortic crossclamping). These data suggest that supplementing the prime of cardiopulmonary bypass circuit with glutamate and aspartate may reduce these deleterious consequences of reoxygenation.

Studies of hypoxemic/reoxygenation injury: with aortic clamping. X. Exogenous antioxidants to avoid nullification of the cardioprotective effects of blood cardioplegia

This study tests the hypothesis that reoxygenation of cyanotic immature hearts when starting cardiopulmonary bypass produces an "unintended" reoxygenation injury that (1) nullifies the cardioprotective effects of blood cardioplegia and (2) is avoidable by adding antioxidants N-(2-mercaptopropionyl)-glycine plus catalase to the cardiopulmonary bypass prime. Twenty immature piglets (2 to 3 weeks) underwent 30 minutes of aortic clamping with a blood cardioplegic solution that was hypocalcemic, alkalotic, hyperosmolar, and enriched with glutamate and aspartate during 1 hour of cardiopulmonary bypass. Of these, six piglets did not undergo hypoxemia (blood cardioplegic control) and 14 others remained hypoxemic (oxygen tension about 25 mm Hg) for up to 2 hours by lowering ventilator fraction of inspired oxygen before reoxygenation on cardiopulmonary bypass. The primary solution of the cardiopulmonary bypass circuit was unchanged in eight piglets (no treatment) and supplemented with the antioxidants N-(2-mercaptopropionyl)-glycine (80 mg/kg) and catalase (5 mg/kg) in six others (N-(2-mercaptopropionyl)-glycine and catalase). Myocardial function (end-systolic elastance), lipid peroxidation (myocardial conjugated diene production), and antioxidant reserve capacity were evaluated. Blood cardioplegic arrest produced no biochemical or functional changes in nonhypoxemic control piglets. Reoxygenation caused an approximate 10-fold increase in conjugated production that persisted throughout cardiopulmonary bypass, lowered antioxidant reserve capacity 86% +/- 12%, and produced profound myocardial dysfunction, because end-systolic elastance recovered only 21% +/- 2%. Supplementation of the cardiopulmonary bypass prime with N-(2-mercaptopropionyl)-glycine and catalase reduced lipid peroxidation, restored antioxidant reserve capacity, and allowed near complete functional recovery (80% +/- 8%).** Lipid peroxidation (conjugated diene) production was lower during warm blood cardioplegic reperfusion than during induction in all reoxygenated hearts, which suggests that blood cardioplegia did not injure reoxygenated myocardium. We conclude that reoxygenation of the hypoxemic immature heart causes cardiac functional and antioxidant damage that nullifies the cardioprotective effects of blood cardioplegia that can be avoided by supplementation of the cardiopulmonary bypass prime with antioxidants (*p < 0.05 vs blood cardioplegic control; **p < 0.05 vs reoxygenation).

Studies of hypoxemic/reoxygenation injury: with aortic clamping. XII. Delay of cardiac reoxygenation damage in the presence of cyanosis: a new concept of controlled cardiac reoxygenation

Twenty-one immature piglets (< 3 weeks old) underwent 30 minutes of aortic clamping with hypocalcemic glutamate/aspartate blood cardioplegia. Six piglets underwent hyperoxemic cardiopulmonary bypass and blood cardioplegia without preceding hypoxemia (control). Fifteen piglets became hypoxemic (oxygen tension about 25 mm Hg) for up to 2 hours by decreasing ventilator fraction of inspired oxygen to 6% to 7% before cardiopulmonary bypass. Of these, six piglets underwent 5 minutes of abrupt hyperoxemic uncontrolled reoxygenation by starting cardiopulmonary bypass at oxygen tension of about 400 mm Hg before they received oxygen tension of about 400 mm Hg blood cardioplegia. Nine others underwent controlled cardiac reoxygenation by starting cardiopulmonary bypass at ambient oxygen tension (about 25 mm Hg) followed 5 minutes later by 30 minutes of cardiopulmonary bypass at normoxemic oxygen tension (about 100 mm Hg) before raising oxygen tension to about 400 mm Hg. Myocardial function after cardiopulmonary bypass was evaluated from end-systolic elastance by conductance catheter, oxidant damage was estimated by measuring transcoronary conjugated diene levels to detect lipid peroxidation, and antioxidant reserve capacity was determined by measuring malondialdehyde produced from myocardium incubated with the oxidant t-butylhydroperoxide. Hyperoxemic cardiopulmonary bypass and blood cardioplegia preserved myocardial function and produced no oxidant damage in nonhypoxemic piglets. In contrast, uncontrolled reoxygenation at oxygen tension about 400 mm Hg, followed by blood cardioplegia, resulted in marked conjugated dienes production (42 +/- 4* vs 3 +/- 1) A233 nm/min/100 g during blood cardioplegic induction, reduced antioxidant reserve capacity malondialdehyde at 4 mmol/L t-butylhydroperoxide; 1342 +/- 59* vs 958 +/- 50 nmol/g protein) and caused profound myocardial dysfunction; end-systolic elastance recovered only 21% +/- 2%* despite a blood cardioplegic regimen that was cardioprotective in nonhypoxemic piglets. Conversely, controlled cardiac reoxygenation reduced lipid peroxidation (conjugated dienes production was 2 +/- 1**), restored antioxidant reserve capacity (malondialdehyde at 4 mmol/L t-butylhydroperoxide; 982 +/- 88**), and allowed near-complete (83 +/- 8%**) functional recovery. We conclude that reoxygenation of the hypoxemic immature heart by initiating conventional hyperoxemic cardiopulmonary bypass causes oxidant damage characterized by lipid peroxidation, reduced antioxidant reserve capacity, and results in functional depression that nullifies the cardioprotective effects of blood cardioplegia. These changes can be reduced by starting cardiopulmonary bypass at the ambient oxygen tension of the hypoxemic subject and delaying subsequent reoxygenation until blood cardioplegic induction by controlled cardiac reoxygenation (*p < 0.05 vs control; **p < 0.05 vs uncontrol reoxygenation) and analysis of variance.

Marked reduction in myocardial infarct size due to prolonged infusion of an antioxidant during reperfusion

BACKGROUND

There has been controversy about whether early reperfusion of myocardial infarcts causes further necrosis mediated by reactive oxygen species or other mechanisms. Unequivocal evidence that therapeutic agents given only during reperfusion can prevent, rather than delay or modify, injury has been sparse. Failure to account for variables, such as collateral blood flow, that influence infarct size independently and attempts to measure infarct size too early in reperfusion may have limited the sensitivity and specificity of some previous studies.

METHODS AND RESULTS

After 90 minutes of coronary occlusion and 48 hours of reperfusion in a canine model, we examined the effect on infarct size of intravenous infusion of N-(2-mercaptopropionyl)-glycine (MPG), a diffusible antioxidant. Infarct size and region at risk were measured by post-mortem dual perfusion with triphenyl tetrazolium chloride and Evans blue dyes, and regional myocardial blood flow was measured with radioactive microspheres. Infusion of MPG 100 mg.kg-1.h-1, beginning either 15 minutes before the onset of reperfusion or 30 minutes after the onset of reperfusion and continued until 4 hours of reperfusion and followed by an intramuscular dose, reduced infarct size, normalized for both region at risk and the level of collateral blood flow, by 60% and 45%, respectively. When infusion of MPG was limited to the last 15 minutes of ischemia and the first hour of reperfusion only, the normalized infarct size was reduced by 26%. Heart rate, blood pressure, and their product did not differ among the four groups studied. The plasma half-time of MPG was < 10 minutes. In in vitro experiments MPG was a scavenger of hydrogen peroxide but not of superoxide radical.

CONCLUSIONS

After 90 minutes of coronary ligation, infusion of the diffusible hydrogen peroxide scavenger, MPG, for several hours, beginning as late as 30 minutes after the onset of reperfusion, substantially reduced infarct size measured 48 hours later. In this model, necrosis caused by processes during reperfusion may be more extensive than necrosis caused by ischemia alone. Since infusion of this agent for only the first hour of reperfusion was considerably less effective, it appears that most of the oxidant injury leading to necrosis occurred after the first 60 minutes but within the first 4 hours of reperfusion.

The safety of simultaneous arterial and coronary sinus perfusion: experimental background and initial clinical results

Concern over myocardial damage from simultaneous arterial (antegrade) and coronary sinus (retrograde) perfusion has led to alternating between these delivery routes to maximize their individual benefits. Based upon predominant retrograde drainage via Thebesian veins, this study: (1) confirms experimentally the safety of simultaneous arterial and coronary sinus perfusion; and (2) reports initial clinical application of this combined strategy in 155 consecutive patients.

EXPERIMENTAL

Five mini-pigs (25 to 30 kg) underwent 1 hour of aortic clamping with simultaneous aortic and coronary sinus perfusion at 200 mL/min with normal blood (37 degrees C) before and after 30 minutes of perfusion with either warm (37 degrees C) or cold (4 degrees C) blood cardioplegia. Coronary sinus pressure was always less than 30 mmHg. There was no right or left ventricular edema, lactate production, or lipid peroxidation as transmyocardial and myocardial conjugated dienes were unaltered, and postbypass recovered left ventricular end-systolic elastance (conductance catheter) and preload recruitable stroke work index 101% +/- 3% and 109% +/- 90%, respectively. CLINICAL: Simultaneous arterial/coronary sinus perfusion was used in 155 consecutive high risk patients (New York Heart Association Class III to IV) undergoing isolated coronary artery bypass grafting (CABG) (n = 109) and CABG+valve replacement/repair or aneurysm (n = 46). Included were 16 patients in cardiogenic shock and 24 undergoing reoperation. Mean aortic clamping time averaged 90 +/- 4 minutes (range 30 to 207), with 3.5 +/- 0.1 grafts per patient; all anastomoses were performed with the aorta clamped. Cold intermittent blood cardioplegia was used for distal anastomoses and valve implantation/repair in 123 patients, and warm continuous blood cardioplegia was used in 32 patients. Following a warm cardioplegic reperfusate, all patients received warm noncardioplegic blood perfusion simultaneously via grafts and coronary sinus. Coronary sinus pressure was always less than 40 mmHg. Of 18 patients requiring postoperative mechanical circulatory support (IABP), 16 had IABP placed preoperatively for cardiogenic shock. There were three postoperative myocardial infarctions (2%), and six patients died (3.9% mortality).

CONCLUSION

These experimental and clinical findings overcome perceived concerns about myocardial damage from simultaneous arterial and coronary sinus perfusion, and suggest this approach may add to the armamentarium of cardioprotective strategies.

Trolox C, a lipid-soluble membrane protective agent, attenuates myocardial injury from ischemia and reperfusion

The lipophilic antioxidant Trolox C, a vitamin E analog, was administered to isolated, buffer-perfused rabbit hearts subjected to 25 min of global stop-flow ischemia and 30 min of reperfusion. In six hearts, Trolox C (200 microM) was infused for 15 min immediately prior to ischemia and for the first 15 min of reperfusion. Six control hearts received only vehicle. Gas chromatography analysis confirmed that effective myocardial levels of Trolox were attained. At 30 min reperfusion, the recovery of left ventricular developed pressure was 56 +/- 3% of baseline in control hearts versus 70 +/- 4% in Trolox-treated hearts (p < .01). There was also significant improvement in recovery of Trolox-treated hearts in diastolic pressure and both maximum and minimum values of the first derivative of left ventricular pressure (dP/dt). Creatine phosphokinase release into the coronary effluent at 30 min of reperfusion was 16.5 +/- 8.4 IU/min in untreated and 6.3 +/- 1.0 IU/min (p < .05) in Trolox-treated hearts. Thus Trolox C, a lipophilic antioxidant, attenuated myocardial injury during stop-flow ischemia and reperfusion.

Reduction of infarct size by cell-permeable oxygen metabolite scavengers

The timely restoration of blood flow to severely ischemic myocardium limits myocardial infarct size. However, experimental studies demonstrate that the myocardial salvage achieved is suboptimal because of additional injury that occurs during reperfusion, due in part to the generation of reactive oxygen metabolites. Initially, superoxide (O2-) was considered to be the central mediator of reperfusion injury. While there are several potential pathways of O2- generation in reperfused myocardium, O2- is poorly reactive toward tissue biomolecules. However, O2-, in the presence of redox-active metals such as iron, generates .OH or hydroxyl-like species that are highly reactive with cell constituents. Thus, while O2- may initiate reaction sequences leading to myocardial injury, it may not be the actual injurious agent. In vitro studies suggest that oxygen metabolite injury occurs at intracellular sites and involves iron-catalyzed processes. Consistent with this mechanism, extracellular oxygen metabolite scavengers have not convincingly reduced infarct size. However, treatment around the time of reperfusion, after ischemia is well established, with cell-permeable scavengers of .OH reduce infarct size. Results with these cell-permeable agents suggest that in the intact animal during regional ischemia and reperfusion, oxygen metabolite injury also occurs at intracellular sites. Cell-permeable scavenger agents are a promising class of drugs for potential clinical use, though further experimental and toxicologic studies are required.

Reduction of canine myocardial infarct size by a diffusible reactive oxygen metabolite scavenger. Efficacy of dimethylthiourea given at the onset of reperfusion

A number of scavengers of reactive oxygen metabolites reduce myocardial injury when given before ischemia and reperfusion, but few, if any, have proven to be effective when given near the onset of reperfusion. This is particularly true when infarct size is measured after at least 48 hours of reperfusion, when the full extent of myocardial damage has become apparent. Dimethylthiourea (DMTU) is an extremely diffusible, potent scavenger of hydroxyl radical, hydrogen peroxide, and hypochlorous acid, with a long half-life of 43 hours. Sixteen chloralose-anesthetized dogs underwent 90 minutes of left anterior descending coronary artery (LAD) occlusion followed by 48 hours of reperfusion. Collateral flow was measured by radioactive microspheres. Infarct size and risk area were measured by a postmortem dual-perfusion technique using triphenyl tetrazolium chloride and Evan's blue dye. In eight dogs, therapy with DMTU (500 mg/kg i.v.) was given during the last 15 minutes of ischemia and the first 15 minutes of reperfusion. In eight control dogs, the same volume of 0.9% saline was given during the last 15 minutes of ischemia through the first 15 minutes of reperfusion. Infarct size as a percent of risk area was reduced in the DMTU-treated group compared with the saline-treated controls (DMTU = 42 +/- 4% versus saline = 59 +/- 4%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial sulfhydryl pool alterations occur during reperfusion after brief and prolonged myocardial ischemia in vivo

Myocardial sulfhydryl (SH)-containing compounds, including reduced glutathione (GSH), are both defenses against and potential markers of reactive oxygen metabolite injury during ischemia and reperfusion. We examined the alterations in GSH and other myocardial SH pools during reperfusion in anesthetized dogs exposed to brief (15 minutes, n = 7) or prolonged (90 minutes, n = 6) regional ischemia caused by occlusion of the left anterior descending artery. Ninety minutes of ischemia followed by 5 hours of reperfusion, which resulted in myocardial necrosis of 43.9 +/- 4.0% of the area at risk, caused a 22% reduction in total myocardial SH groups (p less than 0.01), a 57% decrease in nonprotein myocardial SH groups (p less than 0.01), a 56% decrease in GSH (p less than 0.01), and a 62% decrease in non-GSH, nonprotein SH groups (p less than 0.02). However, protein SH groups were not significantly reduced (12% decrease, p = NS). Also, myocardial release of GSH and oxidized glutathione (GSSG) into the coronary venous effluent occurred during early reperfusion. In contrast, 15 minutes of ischemia, followed by 30 minutes of reperfusion, did not alter myocardial total SH groups, protein SH groups, or GSH (9% decrease, p = NS); nor was there reperfusion release of GSH or GSSG. However, even with brief ischemia, nonprotein SH groups decreased 23% (p less than 0.05), due mainly to a 59% decrease in the non-GSH, nonprotein SH pool (p less than 0.05). These changes after brief ischemia occurred without alterations in myocardial GSSG or the GSH/GSSG ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of dopaminergic drugs for the chronic treatment of congestive heart failure

1. The search of orally active dopaminergic drugs for the chronic treatment of congestive heart failure has followed two different approaches. 2. On the one hand, a selective DA-1 receptor agonist, such as fenoldopam, has been investigated as an agent developed for the stimulation of vascular and tubular DA-1 receptors in the kidney. On the other hand, orally active prodrugs were synthetized with the aim of mimicking the full pattern of dopaminergic and adrenergic actions of intravenous dopamine. 3. Ibopamine, the diisobutyric ester of N-methyldopamine, has shown effects comparable to those of dopamine in various animal models and in clinical investigations. Furthermore, patients suffering from mild or severe congestive heart failure were shown to benefit from ibopamine treatment in a number of therapeutic trials. 4. Limited experience is currently available on other prodrugs, such as docarpamine and Sim 2055, i.e. the 4-0-phosphate ester of N-methyldopamine. The latter is an analogue of ibopamine designed for a preferential delivery of N-methyldopamine in the kidney. 5. Based upon some additional studies with levodopa, the results suggest that a combination of DA-1 and DA-2 agonistic activity is a desirable feature of a new drug, since it appears suitable to provide vasodilation while counteracting the neurohumoral abnormality of congestive heart failure.

Coronary endothelial dysfunction from ischemia and reperfusion: effect of reactive oxygen metabolite scavengers

Using anesthetized mongrel dogs exposed to 60 min of ligation of the left anterior descending coronary artery followed by 60 min of reperfusion, we examined the effect of superoxide dismutase (SOD) and dimethylthiourea (DMTU) on evidence of endothelial injury in coronary rings studied in vitro. In 13 dogs treated with saline rings from the normal left circumflex coronary artery (LCF) relaxed by 98 +/- 4% when exposed to 10(-5) M acetylcholine whereas rings from the left anterior descending coronary artery (LAD) relaxed by 79 +/- 7% (p less than 0.05). In the same rings maximum relaxation with the ionophore A23187 was 107 +/- 5% versus 87 +/- 8% (p less than 0.05) for the LCF and the LAD, respectively. Comparisons of concentration-response curves through a range of doses of both acetylcholine and A23187 revealed significant differences for both vasodilators between the LCF and the LAD (p less than 0.01 for each). Nine dogs were treated with bovine SOD infused in the left atrium the last 20 min of ligation and throughout reperfusion (140 units/kg/min) and six other dogs were treated with DMTU 500 mg/kg i.v. given the last 30 min of the ligation period. Neither SOD nor DMTU prevented endothelial injury in the LAD. Despite pretreatment with these agents, there were significant reductions in maximum relaxation and in total concentration-response curves in the LAD as compared with the results in rings from the LCF with both acetylcholine and A23187. There were normal responses to nitroprusside in both the LCF and LAD in all three experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)