Surgical stress induces acute coronary release of tissue-type plasminogen activator in the pig

Histone deacetylase inhibitor treatment increases coronary t-PA release in a porcine ischemia model

Background

The expression of the tissue plasminogen activator gene can be affected by histone deacetylation inhibition and thus appears to be under epigenetic control.

Objectives

The study aimed to test if in vivo pharmacological intervention by valproic acid treatment would lead to increase in tissue plasminogen activator release capacity.

Methods

In an anaesthetized pig model, a controlled transient coronary occlusion was used to stimulate coronary tissue plasminogen activator release in a valproic acid treated (one week) and a non-treated group. Coronary venous blood samples from the ischemic region were collected, great cardiac vein thermodilution flow measurements were performed, and trans-coronary tissue plasminogen activator fluxes were calculated. Plasminogen activator inhibitor-1 was also measured.

Results

Adequate sampling from the affected area after the 10 minute ischemic period was confirmed by lactate measurements. Fluxes for tissue plasminogen activator at minutes 1, 3, 5, 7 and 10 were measured and then used to present cumulative net tissue plasminogen activator release for the whole measurement period for both groups. Area under the curve was higher for the valproic acid treated group at 10 minutes; 932±173 nanograms (n = 12) compared to the non-treated group, 451±78 nanograms (n = 10, p = 0.023). There was no difference in levels of plasminogen activator inhibitor-1 between groups.

Conclusions

These findings support a proof of concept for histone deacetylation inhibition positive effect on tissue plasminogen activator expression in an in vivo setting. Further studies are needed to find an optimal way to implement histone deacetylation inhibition to achieve desired clinical changes in tissue plasminogen activator expression.

Impaired myocardial t-PA release in patients with coronary artery disease

AIMS

Myocardial ischemia remains a significant perioperative complication in coronary artery disease (CAD) patients. We hypothesized that noxious stimuli during major surgery are associated with an acute release of tissue-type plasminogen activator (t-PA) into the coronary circulation, and that this response is reduced by CAD.

METHODS AND RESULTS

Two patient groups, with (n=14) and without (n=8) CAD, were studied during the initial phase of heart surgery. After retrograde great cardiac vein catheterizations during closed-chest conditions, coronary arterial-venous concentration gradients of t-PA and plasminogen activator inhibitor type-1 (PAI-1) were measured together with coronary blood flow measurements, allowing derivation of coronary net release rates. Pre-surgery atrial pacing, performed to evaluate the influence of increases in heart rate (+ 40 beats/min) and coronary blood flow (+ 80 ml/min), did not significantly alter coronary net release of t-PA or PAI-1 in either patient group. Sternotomy induced a prominent increase in coronary net release of both total and active t-PA in the non-CAD group. This response was considerably reduced in the CAD group.

CONCLUSIONS

This study provides the first analysis of coronary t-PA release during major surgery and demonstrates a deficient local endothelial t-PA release in patients with CAD. This suggests a reduced local fibrinolytic capacity in CAD patients, which may explain the increased risk for coronary thrombosis in this patient group.

Procedure-induced Inflammation and Endothelial Cell Activation in an Artificially Ventilated and Circulated Porcine Double-Lung Model

Systemic inflammation is induced during extracorporeal circulation, resulting in an increased bleeding tendency and endothelial cell activation. Lungs from seven piglets were perfused by autologous blood in an extracorporeal circuit, where the lungs and the left atrium were attached to polyvinyl chloride (PVC) tubings and the blood circulated by a roller pump. The trachea was intubated and attached to a ventilator. The lungs maintained good gas exchange, despite a slight increase in lactate levels. Plasma tPA increased slightly over time, suggesting endothelial cell activation. Activation of inflammatory systems was reflected in increased levels of plasma interleukin (IL)-6 and IL-10. A model for the study of lung endothelial activation during extracorporeal circulation has been shown to be reproducible. The lung tissue was shown to be capable of gas exchange and activation of endothelial cells and procedure-induced inflammation were noted.

Cardiac fibrinolytic capacity is markedly increased after brief periods of local myocardial ischemia, but declines following successive periods in anesthetized pigs

BACKGROUND

Fibrinolysis in blood is mainly reflected by the activities of tissue plasminogen activator (tPA) and of plasminogen activator inhibitor-1 (PAI-1). The effect of myocardial ischemia on their activities in the coronary circulation is, however, not established.

OBJECTIVES

With an improved experimental model, we therefore examined the effect of a brief period of myocardial ischemia on their activities. Furthermore, the consequences of repeated periods of ischemia, mimicking the situations in patients with unstable angina, were investigated.

METHODS

In six anesthetized pigs, we occluded the distal left anterior descending coronary artery (LAD) four times for 10 min with 40 min intervals and determined the activities of tPA and PAI-1 in arterial and coronary venous blood. By simultaneously recording LAD flow, we could estimate cardiac release of these factors at baseline conditions and during reperfusion.

RESULTS

Neither net cardiac release of PAI-1 nor alterations in plasma PAI-1 levels were demonstrated during the experiment. However, a significant net release of tPA activity of 10.4 +/- 3.2 IU mL(-1) (P < 0.005) was recorded during baseline conditions. During reperfusion following the first period of ischemia, the cardiac release of tPA activity increased to a peak of 103 +/- 30-fold baseline release, but declined progressively after repeated periods of ischemia. After the fourth period, tPA release did not exceed an estimated baseline accumulation during ischemia and early reperfusion.

CONCLUSIONS

In this porcine model, a substantial local increase in fibrinolytic capacity was observed after brief periods of ischemia, but declined subsequently by repeated periods of ischemia.

Myocardial ischemia induces coronary t-PA release in the pig

BACKGROUND

Tissue-type plasminogen activator (t-PA) is the key factor in initiating endogenous fibrinolysis in the vascular compartment. Regulated release of t-PA from endothelial stores is rapidly induced by several humoral factors as well as coagulation activation products. The aim of the present study was to test the hypothesis that regional myocardial ischemia induces regulated release of t-PA in the coronary vasculature in vivo.

METHODS

Healthy anesthetized (pentobarbital) pigs (n=8) were studied before and after a 10-min left anterior descending region coronary artery occlusion (LAD). Coronary fluxes of lactate, total t-PA antigen (ELISA, detecting both complex bound and free fraction) and active t-PA (functional assay detecting biological free fraction) were determined at 1, 3, 5 and 10 min of reflow.

RESULTS

Coronary occlusion induced myocardial lactate production in all animals. Net coronary release of total t-PA, which was 21 ng/min during control, increased rapidly during reflow with a peak after only 1 min (136 ng/min), and returned to baseline within 3 min. Net release of active t-PA mirrored the overall net release response, but fell short of statistical significance.

CONCLUSION

Data indicate a local myocardial profibrinolytic response following regional ischemia, which may serve as a prompt defence against coronary thromboembolic events.