Influence of the terminal complement-complex on reperfusion injury, no-reflow and arrhythmias: a comparison between C6-competent and C6-deficient rabbits.

OBJECTIVE: The complement system has been suggested to play a role in reperfusion injury which may result from an enhanced destruction of myocardial tissue or from an impairment of reflow. We investigated the influence of the C5b-9 complement complex on infarct size, reflow and arrhythmogenesis. METHODS: Twenty-eight C6-competent rabbits and 18 rabbits with congenital C6 deficiency were subjected to either 30 min or 2 h of coronary artery occlusion followed by reperfusion. C6 deficiency was confirmed by the complement titration test and immunohistology. The triphenyl tetrazolium chloride method was used to delineate infarct size. Reflow into infarcted areas was evaluated histologically after an in vivo injection of propidium iodide which served as an early fluorescence microscopic marker of damaged myocardium subjected to reflow. Continuous ECG monitoring allowed the recording of arrhythmias. RESULTS: After 30 min of coronary artery occlusion infarct size was significantly smaller in C6-deficient rabbits (5.0 +/- 2% of the risk region) as compared to C6-competent rabbits (28.4 +/- 8.5%, P = 0.0371). The extent of reflow into damaged myocardium was nearly the same in both animal groups at this time (38 +/- 9 vs. 39 +/- 7% of the risk region). After 2 h of coronary artery occlusion, infarct size was not different between both animal groups, but the extent of reflow into damaged myocardium was significantly smaller in C6-competent rabbits than in C6-deficient rabbits (25 +/- 4 vs. 40 +/- 4%; P = 0.0185). Two of the 18 C6-deficient rabbits had ventricular arrhythmias (Lown II-IV), none of which was fatal. Eleven of the 28 C6-competent animals had major ventricular arrhythmias which were fatal in 6 rabbits. CONCLUSIONS: These results suggest that the lytic C5b-9 complement complex leads to reperfusion injury in the early phase (30 min) of ischaemia, resulting in a larger infarct. After 2 h of ischaemia, complement activation enhances the no-reflow phenomenon but does not affect infarct size. Finally, the C6 status seems to influence the susceptibility to ventricular arrhythmias after coronary artery occlusion, independent of reperfusion.

Early accumulation of the terminal complement-complex in the ischaemic myocardium after reperfusion.

The terminal, membrane-damaging complement complex C5b-9 accumulates in the infarcted myocardium. In experimental myocardial infarction, we investigated the time course of C5b-9 deposition and the influence of reperfusion. In a group of 17 rabbits (group 1), the circumflex coronary artery was occluded for different time periods ranging from 0.5 to 29 h without subsequent reperfusion. A second group of 23 rabbits (group 2) underwent coronary artery occlusion for periods ranging from 0.5 to 6 h followed by reperfusion. C5b-9 was determined in transmural myocardial biopsies by immunohistochemistry and by ELISA. In group 1, C5b-9 accumulation in the ischaemic myocardium was found only after 5 to 6 h of coronary artery occlusion. In group 2 (ischaemia and reperfusion), significant C5b-9 deposition was already observed after 30 min of myocardial ischaemia. We conclude that in the absence of reperfusion C5b-9 accumulation occurs as a late event when most of the jeopardized myocardium has probably already become necrotic. In the presence of reperfusion, however, the complement system is activated rapidly and this could play a role in the pathogenesis of reperfusion injury.

Quantitative measurement of SC5b-9 and C5b-9(m) in infarcted areas of human myocardium.

Previous immunohistochemical work has indicated that terminal C5b-9 complement complexes are selectively deposited in infarcted areas of human myocardium. In the present study, we sought to quantify C5b-9 levels in myocardial tissue, and to differentiate between the membrane-bound C5b-9 (m) and the cytolytically inactive SC5b-9 complex. Paired tissue specimens from infarcted and non-infarcted myocardium were obtained from 36 autopsies. The homogenized and washed tissues were extracted with n-octyl-beta-D-glucopyranoside (octylglucoside) detergent, and the concentrations of C5b-9 in the extracts were determined by ELISA. Membrane-derived C5b-9 (m) and SC5b-9 were differentiated from each other on the basis of their characteristic sedimentation behaviour in sucrose density gradients. It was found that infarcted myocardial tissue contained on average an approximately three-fold higher concentration of C5b-9, compared with non-infarcted tissue. This increase was due in part to an increase in levels of C5b-9 (m). The results corroborate previous immunohistochemical data and show that complement activation occurs to completion with the generation of potentially cytotoxic C5b-9 complexes in infarcted myocardial tissues.