The Effect of Nitecapone, a New Antioxidant, on Myocardial Function After Aortic Cross-clamping in Experimental Heart Ischemia

A Novel Porcine Model of Ischemia-Reperfusion Injury After Cross-Clamping the Thoracic Aorta Revealed Substantial Cardiopulmonary, Thromboinflammatory and Biochemical Changes Without Effect of C1-Inhibitor Treatment

Ischemic injury worsens upon return of blood and innate immunity including the complement system play a central role in ischemia-reperfusion injury (IRI) as in thoracic aortic surgery. Complement component1 inhibitor (C1-INH) has been shown to reduce IRI and is a broad-acting plasma cascade inhibitor. We established a new porcine model of IRI by cross-clamping the thoracic aorta and evaluated the global changes occurring in organ function, systemic inflammatory response and organ damage with or without treatment with C1-INH-concentrate. Twenty-four piglets (8.8-11.1 kg) underwent 45 minutes clamping of the thoracic aorta at the Th8 level. Upfront 12 piglets received human saline and 12 received C1-INH (250 IU/kg) intravenously. Three sham animals received thoracic opening without clamping. Reperfusion lasted 5 hours. We studied ten cardiorespiratory markers, three hematologic markers, eleven inflammatory markers, and twelve organ damage markers over the whole experimental period. Postmortem tissue homogenates from seven organs were examined for inflammatory markers and analysed by two-way repeated-measures ANOVA, area under the curve or unpaired t-tests. By excluding sham and combining treated and untreated animals, the markers reflected a uniform, broad and severe organ dysfunction. The mean and range fold change from before cross-clamp onset to maximum change for the different groups of markers were: cardiorespiratory 1.4 (0.2-3.7), hematologic 1.9 (1.2-2.7), plasma inflammatory 19.5 (1.4-176) and plasma organ damage 2.9 (1.1-8.6). Treatment with C1-INH had only a marginal effect on the IRI-induced changes, reaching statistical significance only for the plasma complement activation product TCC (p=0.0083) and IL-4 (p=0.022) and INF-α (p=0.016) in the colon tissue. In conclusion, the present novel model of porcine global IRI is forceful with regards to central markers and could generally be applicable for pathophysiological studies. C1-INH treatment had no significant effect, but the model allows for future testing of other drugs attenuating IRI globally.

Antithrombin reduces pulmonary hypertension during reperfusion after cardiopulmonary bypass in a pig

BACKGROUND

Antithrombin (AT) may alleviate many cardiopulmonary bypass (CPB) and ischemia-reperfusion (I/R)-related adverse effects. Using a porcine model of clinical cardiac surgery on CPB, we tested the effects of supplementary AT on myocardial and lung I/R injury.

METHODS

Twenty pigs undergoing 60-min aortic clamping and 75-min normothermic perfusion were randomized in a blinded setting to receive an intravenous (i.v.) bolus of AT (250 IU/kg) (AT group, n = 10) or placebo (n = 10) 15 min before aortic declamping. An additional group of five animals received 500 IU/kg AT in an open-label setting (AT+). Thrombin-antithrombin complexes (TAT), activated clotting times (ACT), AT and myeloperoxidase (MPO) activities, troponin T, and several hemodynamic parameters were measured before CPB and after weaning from CPB up to 120 min after aortic declamping. After 120 min of reperfusion, myocardial and lung biopsies were taken for histological examination.

RESULTS

AT effectively inhibited coagulation as assessed by ACT. In the AT and AT+ groups only, cardiac output (CO) and stroke volume (SV) showed a trend of post-ischemic recovery during the first 15 min after CPB. AT-attenuated reperfusion induced an increase in pulmonary arterial diastolic pressure (PAPD) but did not have significant effects on systemic or pulmonary vascular resistance. The effects of AT on SV, CO, and PAPD were fortified in the AT+ group. AT did not show effects on inflammatory changes in either myocardial or pulmonary tissue specimens. AT did not reduce post-ischemic troponin T release.

CONCLUSION

Supplementary AT, in doses with significant anticoagulant effect, did not alleviate myocardial I/R injury in terms of histological inflammatory changes or post-ischemic troponin T release. Instead, however, AT-attenuated reperfusion induced an increase in pulmonary pressure after CPB. Mechanisms and clinical implications of these effects remain to be explored.

Nitecapone as an additive to crystalloid cardioplegia in patients who had coronary artery bypass grafting

BACKGROUND

Nitecapone has been shown to have a protective effect against ischemia-reperfusion injury in experimental heart transplantation and in Langendorff preparations. This prospective, randomized study assessed the effects of nitecapone in patients who had coronary artery bypass grafting.

METHODS

Thirty patients with normal myocardial function were randomly divided into control patients (n = 15), who received crystalloid (Plegisol) cardioplegia, and nitecapone patients, who received nitecapone in a 50 microM solution (n = 15) in Plegisol. Cardioplegia was administered as an initial dose of 15 mL/kg of body mass after cross-clamping and 2 mL/kg every 15 minutes. Simultaneous coronary sinus and aortic blood samples, and myocardial biopsies were taken at 1, 5, and 10 minutes after unclamping. Hemodynamics were measured invasively for 24 hours and with transesophageal echocardiography for 3 hours after cardiopulmonary bypass.

RESULTS

There were no adverse effects. The incidence of ventricular arrhythmias was significantly lower in the treatment group during the recovery period (p = 0.02). Cardiac output and stroke volume did not differ significantly between the groups. The conjugated dienes gradient between the aorta and the coronary sinus increased significantly during the first minute of reperfusion in the control group (p = 0.02) compared with the nitecapone group. Myeloperoxidase activity in myocardial biopsies was higher in the control group (2.3 times higher at 5 minutes and 3.2 times higher at 10 minutes) than in the nitecapone group (p = 0.13).

CONCLUSIONS

Nitecapone did not exert any significant hemodynamic effects in patients with normal ejection fraction.