Object. The mechanisms involved in brain edema formation following intracerebral hemorrhage (ICH) have not been fully elucidated. The authors have found that red blood cell lysis plays an important role in edema development after ICH. In the present study, they sought to determine whether degradation products of hemoglobin cause brain edema. Methods. Hemoglobin, hemin, bilirubin, or FeCl₂ were infused with stereotactic guidance into the right basal ganglia of Sprague—Dawley rats. The animals were killed 24 hours later to determine brain water and ion contents. Western blot analysis and immunohistochemistry were applied for heme oxygenase-1 (HO-1) measurement. The effects of an HO inhibitor, tin-protoporphyrin (SnPP), and the iron chelator deferoxamine, on hemoglobin-induced brain edema were also examined. Intracerebral infusion of hemoglobin, hemin, bilirubin, or FeCl₂ caused an increase in brain water content at 24 hours. The HO-1 was upregulated after hemoglobin infusion and HO inhibition by SnPP-attenuated hemoglobin-induced edema. Brain edema induced by hemoglobin was also attenuated by the intraperitoneal injection of 500 mg/kg deferoxamine. Conclusions. Hemoglobin causes brain edema, at least in part, through its degradation products. Limiting hemoglobin degradation coupled with the use of iron chelators may be a novel therapeutic approach to limit brain edema after ICH.

In the last two decades it has become apparent that thrombin has many extravascular effects that are mediated by a family of protease‐activated receptors (PARs). PAR‐1, ‐3 and ‐4 are activated via cleavage by thrombin. The importance of extravascular thrombin in modulating ischemic, hemorrhagic and traumatic injury in brain has recently become clear. Thus, in vitro, thrombin at low concentration protects neurons and astrocytes from cell death caused by a number of different insults. In vivo, pretreating the brain with a low dose of thrombin (thrombin preconditioning), attenuates the brain injury induced by a large dose of thrombin, an intracerebral hemorrhage or by focal cerebral ischemia. Thrombin may also be an important mediator of ischemic preconditioning. In contrast, high doses of thrombin kill neurons and astrocytes in vitro and cause disruption of the blood–brain barrier, brain edema and seizures in vivo. This review examines the role of thrombin in brain injury and the molecular mechanisms and signaling cascades involved.

Object. The mechanisms of brain edema formation following spontaneous intracerebral hemorrhage (ICH) are not well understood. In previous studies, no significant edema formation has been found 24 hours after infusion of packed red blood cells (RBCs) into the brain of a rat or pig; however, there is evidence that hemoglobin can be neurotoxic. In this study, the authors reexamined the role of RBCs and hemoglobin in edema formation after ICH. Methods. The experiments involved infusion of whole blood, packed RBCs, lysed RBCs, rat hemoglobin, or thrombin into the right basal ganglia of Sprague—Dawley rats. The animals were killed at different time points and brain water and ion contents were measured. The results showed that lysed autologous erythrocytes, but not packed erythrocytes, produced marked brain edema 24 hours after infusion and that this edema formation could be mimicked by hemoglobin infusion. Although infusion of packed RBCs did not produce dramatic brain edema during the first 2 days, it did induce a marked increase in brain water content 3 days postinfusion. Edema formation following thrombin infusion peaked at 24 to 48 hours. This is earlier than the peak in edema formation that follows ICH, suggesting that there is a delayed, nonthrombin-mediated, edemogenic component of ICH. Conclusions. These results demonstrate that RBCs play a potentially important role in delayed edema development after ICH and that RBC lysis and hemoglobin toxicity may be useful targets for therapeutic intervention.

Object. Previous studies undertaken by the authors have indicated that iron accumulation and oxidative stress in the brain contribute to secondary brain damage after intracerebral hemorrhage (ICH). In the present study the authors investigate whether deferoxamine, an iron chelator, can reduce ICH-induced brain injury. Methods. Male Sprague—Dawley rats each received an infusion of 100 µl of autologous whole blood into the right basal ganglia and were killed 1, 3, or 7 days later. Iron distribution was examined histochemically (enhanced Perls reaction). The effects of deferoxamine on ICH-induced brain injury were examined by measuring brain edema and neurological deficits. Immunohistochemical analysis was performed to investigate 8-hydroxyl-2′-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, and Western blot analysis was performed to measure the amount of apurinic/apyrimidinic endonuclease/redox effector factor—1 (APE/Ref-1), a repair mechanism for DNA oxidative damage. Iron accumulation was observed in the perihematomal zone from 1 day after ICH. Deferoxamine attenuated brain edema, neurological deficits, and ICH-induced changes in 8-OHdG and APE/Ref-1. Conclusions. Deferoxamine and other iron chelators may be potential therapeutic agents for ICH. They may act by reducing the oxidative stress caused by the release of iron from the hematoma.

This article reviews current knowledge of the mechanisms underlying the initial hemorrhage and secondary blood–brain barrier (BBB) dysfunction in primary spontaneous intracerebral hemorrhage (ICH) in adults. Multiple etiologies are associated with ICH, for example, hypertension, Alzheimer’s disease, vascular malformations and coagulopathies (genetic or drug-induced). After the initial bleed, there can be continued bleeding over the first 24 hours, so-called hematoma expansion, which is associated with adverse outcomes. A number of clinical trials are focused on trying to limit such expansion. Significant progress has been made on the causes of BBB dysfunction after ICH at the molecular and cell signaling level. Blood components (e.g. thrombin, hemoglobin, iron) and the inflammatory response to those components play a large role in ICH-induced BBB dysfunction. There are current clinical trials of minimally invasive hematoma removal and iron chelation which may limit such dysfunction. Understanding the mechanisms underlying the initial hemorrhage and secondary BBB dysfunction in ICH is vital for developing methods to prevent and treat this devastating form of stroke.