The complement cascade as a therapeutic target in intracerebral hemorrhage

Abstract

Intracerebral hemorrhage (ICH) is the second most common and deadliest form of stroke. Currently, no pharmacologic treatment strategies exist for this devastating disease. Following the initial mechanical injury suffered at hemorrhage onset, secondary brain injury proceeds through both direct cellular injury and inflammatory cascades, which trigger infiltration of granulocytes and monocytes, activation of microglia, and disruption of the blood-brain barrier with resulting cerebral edema. The complement cascade has been shown to play a central role in the pathogenesis of secondary injury following ICH, although the specific mechanisms responsible for the proximal activation of complement remain incompletely understood. Cerebral injury following cleavage of complement component 3 (C3) proceeds through parallel but interrelated pathways of anaphylatoxin-mediated inflammation and direct toxicity secondary to membrane attack complex-driven erythrocyte lysis. Complement activation also likely plays an important physiologic role in recovery following ICH. As such, a detailed understanding of the variation in functional effects of complement activation over time is critical to exploiting this target as an exciting translational strategy for intracerebral hemorrhage.

Fig. 1

Schematic depicting the three proximal pathways of complement activation converging on the central component C3, with subsequent production of the anaphylatoxins C3a and C5a as well as the more distal assembly of the membrane attack complex (MAC).

Fig. 2

The complement system plays a crucial role in the pathophysiology of cerebral injury following intracerebral hemorrhage.