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Soluble complement receptor type 1 inhibits the complement pathway and prevents contractile failure in the
S M Shandelya1, P Kuppusamy, A Herskowitz
1Department of Medicine, Johns Hopkins Medical-Institutions, Francis Scott Key Medical Center, Baltimore, MD 21224.
Insights
Soluble complement receptor 1 (sCR1) effectively prevents postischemic myocardial dysfunction by inhibiting complement-mediated neutrophil activation and free radical generation. This study highlights sCR1 as a promising therapeutic for preventing heart reperfusion injury.
Area of Science:
- Cardiovascular Research
- Immunology
- Biochemistry
Background:
- Complement-mediated neutrophil activation is a key factor in reperfusion injury.
- Soluble complement receptor 1 (sCR1) inhibits complement pathways and may prevent neutrophil activation in postischemic myocardium.
- sCR1's potential to inhibit free radical generation and contractile failure warrants investigation.
Purpose of the Study:
- To determine the effects of sCR1 on postischemic heart contractile function.
- To assess sCR1's impact on polymorphonuclear leukocyte (PMN) adhesion and complement deposition.
- To evaluate sCR1's role in preventing PMN-derived free radical generation in the postischemic heart.
Main Methods:
- Isolated rat hearts were subjected to global ischemia and reperfusion.
- Hearts were perfused with plasma and PMNs in the presence or absence of sCR1.
- Contractile function, coronary flow, and free radical generation were measured using Langendorff perfusion and electron paramagnetic resonance spectroscopy.
Main Results:
- sCR1 significantly improved recovery of postischemic contractile function and coronary flow.
- sCR1 blocked complement-mediated free radical generation from PMNs.
- sCR1 prevented complement deposition in myocardial tissue but did not affect PMN adhesion.
Conclusions:
- sCR1 effectively prevents postischemic myocardial dysfunction and enhances coronary flow recovery.
- Complement activation in postischemic myocardium is essential for neutrophil oxidative burst and free radical generation.
- sCR1 is a potent agent for preventing complement-mediated PMN activation and reperfusion injury.
Background:
Complement-mediated neutrophil activation has been hypothesized to be an important mechanism of reperfusion injury. It has been proposed that soluble complement receptor 1 (sCR1), a potent inhibitor of both classical and alternative complement pathways, may prevent the complement-dependent activation of polymorphonuclear leukocytes (PMNs) that occurs within postischemic myocardium and thereby inhibit PMN-derived free radical generation and prevent postischemic contractile failure. Therefore, we performed studies to determine the effects of sCR1 on contractile function, PMN adhesion, complement deposition, and PMN-derived free radical generation in the postischemic heart.
Methods And Results:
Studies were performed in an isolated rat heart model in which the isolated effects of given cellular or humoral factors could be determined. Plasma and PMNs were present to study the effects of sCR1 on contractile function, coronary flow, leukocyte adhesion, complement deposition, and PMN-derived free radical generation. Isolated rat hearts were perfused by the method of Langendorff (n = 10 in each group) and subjected to 20 minutes of global ischemia and reperfusion with PMNs and plasma in the presence or absence of sCR1. Left ventricular developed pressure (LVDP), coronary flow (CF), left ventricular end-diastolic pressure (LVEDP), and rate-pressure product (RPP) were measured during the preischemic period, during 1-minute control infusion of PMNs and plasma, and on reflow following 20 minutes of global ischemia. During the preischemic control infusion, no significant alterations in the physiologic parameters were observed, and there was no measurable free radical generation. Reperfusion with sCR1 markedly improved the recovery of postischemic contractile function. LVDP after 45 minutes of reperfusion was 76 +/- 9.8% compared with 32 +/- 6.2% (P < .001). In addition, significant improvements in LVEDP, RPP, and CF were observed in hearts treated with sCR1. Additional experiments were also performed to determine the effect of sCR1 on complement-mediated PMN activation. Measurements of PMN-derived free radical generation were performed in both isolated PMNs and the coronary effluent of hearts using electron paramagnetic resonance spectroscopy (EPR) with the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). EPR measurements in both isolated PMNs and coronary effluent demonstrated that sCR1 blocked complement-mediated free radical generation from the PMNs. Increased accumulation of PMNs was observed both in hearts treated with sCR1 and in those not treated with sCR1. Immunohistochemical staining of the postischemic myocardial tissue demonstrated marked complement deposition on the endothelial surface of small arterioles and capillaries, which was prevented by sCR1 treatment. Thus, sCR1 did not prevent PMN adhesion but did prevent complement deposition with activation of the PMN oxidative burst.
Conclusions:
The potent complement inhibitor sCR1 was found to be effective at preventing postischemic myocardial contractile dysfunction and enhancing the recovery of coronary flow. This study demonstrated that complement activation occurs in postischemic myocardium and is necessary for activation of the neutrophil oxidative burst with the generation of reactive oxygen free radicals. The process of neutrophil adhesion, however, was not affected by sCR1 and was independent of complement factors. These findings demonstrate the sCR1 is a highly potent agent at preventing complement-mediated PMN activation and secondary free radical generation in the postischemic heart. This genetically engineered protein appears to be a promising therapeutic agent in the prevention of myocardial reperfusion injury.