Abstract 3216: The Serum of Pexelizumab-Treated ST-Segment Elevation MI Patients Reduces Complement Activation but not Cell Apoptosis
Objective: Complement (C) activation and apoptosis are involved in the pathophysiology of STEMI. Why C inhibition with Pexelizumab (PEX) in the APEX-AMI failed to reduce mortality in STEMI pts undergoing primary PCI is unclear. We therefore examined C activation and cell apoptosis in the serum of APEX pts in a model of human umbilical vein endothelial cells (HUVEC).
Methods: Batch analyses of pre-prepared frozen serum of 45 patients from a single center obtained before initiation of PEX and 24h later before drug discontinuation were performed. An amount of 500 μl serum was added to 2 ml endothelial basal medium in HUVEC culture for 72-hour at 37°C, 5% CO2 and 95% humidity. C4a, C3a, Bb, and MBL of proximal C, and C5a and sC5b-9, the soluble inactive form of C5b9 from the terminal C, were assessed in supernatants by CBA and ELISA assays. HUVEC-bound C5b-9, the membrane attack complex (MAC), was measured by flowcytometry. Apoptosis was quantified as % of HUVEC with DNA fragmentation after permeabilization and cells positive to annexinV and/or propidium iodide (PI). Analyses were performed blinded to treatment allocation.
Results(Table⇓): Basal levels of all parameters were similar in PEX (n=24) and placebo (n= 21) groups. Proximal C remained unchanged at 24 hours and unaffected by PEX. C5a, sC5b-9, and MAC all significantly increased at 24 hours in the placebo group, but were strikingly inhibited by PEX. MAC elevation correlated with C4a (r=0.322, p=0.004), C5a (0.468,< 0.0001), sC5b-9 (0.490,< 0.0001), and with apoptotic cell numbers by DNA fragmentation (0.449,<0.0001). Despite this, PEX had no detectable effects on apoptosis.
Conclusions: In this cell culture model, the serum of STEMI pts containing PEX almost completely inhibited terminal C while preserving proximal C. Why this did not translate into clinical benefit remains to be elucidated. The absence of effect on apoptosis suggests that C activation in PCI-reperfused STEMI is more a consequence than a cause of apoptosis.