The intrathecal CD163-haptoglobin-hemoglobin scavenging system in subarachnoid hemorrhage

Delayed cerebral ischemia resulting from extracellular hemoglobin is an important determinant of outcome in subarachnoid hemorrhage. Hemoglobin is scavenged by the CD163-haptoglobin system in the circulation, but little is known about this scavenging pathway in the human CNS. The components of this system were analyzed in normal cerebrospinal fluid and after subarachnoid hemorrhage. The intrathecal presence of the CD163-haptoglobin-hemoglobin scavenging system was unequivocally demonstrated. The resting capacity of the CD163-haptoglobin-hemoglobin system in the normal CNS was 50 000-fold lower than that of the circulation. After subarachnoid hemorrhage, the intrathecal CD163-haptoglobin-hemoglobin system was saturated, as shown by the presence of extracellular hemoglobin despite detectable haptoglobin. Hemoglobin efflux from the CNS was evident, enabling rescue hemoglobin scavenging by the systemic circulation. Therefore, the CNS is not capable of dealing with significant intrathecal hemolysis. Potential therapeutic options to prevent delayed cerebral ischemia ought to concentrate on augmenting the capacity of the intrathecal CD163-haptoglobin-hemoglobin scavenging system and strategies to encourage hemoglobin efflux from the brain. This study was performed to examine the CD163-haptoglobin-hemoglobin system in the healthy human CNS and after subarachnoid hemorrhage. Compared with the circulation, the healthy human CNS has a very limited hemoglobin-scavenging capacity, which is clearly overwhelmed in subarachnoid hemorrhage. Results identify two potential therapeutic strategies to prevent delayed cerebral ischemia: inhibition of CD163 shedding and augmentation of Hb efflux from the brain. © 2011 The Authors.