Complement Component C3 Mediates Inflammatory Injury Following Focal Cerebral Ischemia

Abstract

Abstract-The complement cascade has been implicated in ischemia/reperfusion injury, and recent studies have shown that complement inhibition is a promising treatment option for acute stroke. The development of clinically useful therapies has been hindered, however, by insufficient understanding of which complement subcomponents contribute to post-ischemic injury. To address this issue, we subjected mice deficient in selected complement proteins (C1q, C3, C5) to transient focal cerebral ischemia. Of the strains investigated, only C3 Ϫ/Ϫ mice were protected, as demonstrated by 34% reductions in both infarct volume (PϽ0.01) and neurological deficit score (PϽ0.05). C3-deficient mice also manifested decreased granulocyte infiltration (PϽ0.02) and reduced oxidative stress (PϽ0.05). Finally, administration of a C3a-receptor antagonist resulted in commensurate neurological improvement and stroke volume reduction (PϽ0.05). Together, these results establish C3 activation as the key constituent in complement-related inflammatory tissue injury following stroke and suggest a C3a anaphylatoxin-mediated mechanism. (Circ Res. 2006;99:209-217.)

C3a Receptor Modulation of Granulocyte Infiltration after Murine Focal Cerebral Ischemia is Reperfusion Dependent

“…They were housed in certified barrier facilities in microisolator cages with free access to food and water on a 12-h-light/12-h-dark cycle. C3a receptor antagonist (SB290157) purchased from Calbiochem (Darmstadt, Germany), or an equal volume of vehicle (10% ethanol in water), was administered via intraperitoneal injection (1 mg/kg) in a masked fashion 45 mins before, or 1 h after, ischemic onset; we used a dosing strategy similar to those used in earlier studies (Ames et al, 2001;Mocco et al, 2006;Proctor et al, 2004).…”

“…The number of C3aR-positive granulocytes was assessed using semiquantitative immunohistochemistry as previously described (Mocco et al, 2006). C3a receptor antagonist-treated (n = 3) and vehicle-treated mice (n = 3) were subjected to transient MCAO as described above and were euthanized after 24 h. Tissue sections were prepared as detailed above using anti-Ly-6G/C and anti-C3aR primary antibodies.…”

“…However, the lack of specificity of these agents left it unclear as to which complement components are most relevant in the pathogenesis of cerebral ischemia/reperfusion injury. Our group recently investigated the specific contribution of C1q, C3, and C5 to stroke pathology using genetic knockout strategies and showed that only C3 deficiency affords neuroprotection in mice (Mocco et al, 2006). This study suggested that C3 is the critical effector of complement-mediated ischemic neurotoxicity and showed a neuroprotective effect for the small-molecule inhibitor of C3a receptor (C3aR), SB 290157, also known as C3a receptor antagonist (C3aRA).…”

Complement Receptors in Inflammation

“…C3-deficient mice also exhibit diminished granulocyte infiltration and oxidative stress. The administration of a C3aR antagonist reduces stroke volume leading to neurological improvement (Mocco et al, 2006), implicating the involvement of C3a and C3aR in acute stroke. Studies with genetic knockouts of C5 in stroke have yielded conflicting data.…”

“…Studies with genetic knockouts of C5 in stroke have yielded conflicting data. C5-deficient animals show increased vulnerability to intracerebral hemorrhage (ICH) (Nakamura et al, 2004) and ischemic stroke (Mocco et al, 2006). In contrast, C5-deficient mice subjected to brain I/R injury exhibits improved functional outcome and less brain damage (Arumugam et al, 2007).…”