Preclinical and clinical research on inflammation after intracerebral hemorrhage

Abstract

Intracerebral hemorrhage (ICH) is one of the most lethal stroke subtypes. Despite the high morbidity and mortality associated with ICH, its pathophysiology has not been investigated as well as that of ischemic stroke. Available evidence from preclinical and clinical studies suggests that inflammatory mechanisms are involved in the progression of ICH-induced secondary brain injury. For example, in preclinical ICH models, microglial activation has been shown to occur within 1h, much earlier than neutrophil infiltration. Recent advances in our understanding of neuroinflammatory pathways have revealed several new molecular targets, and related therapeutic strategies have been tested in preclinical ICH models. This review summarizes recent progress made in preclinical models of ICH, surveys preclinical and clinical studies of inflammatory cells (leukocytes, macrophages, microglia, and astrocytes) and inflammatory mediators (matrix metalloproteinases, nuclear factor erythroid 2-related factor 2, heme oxygenase, and iron), and highlights the emerging areas of therapeutic promise.

Conflict of interest statement

The author reports no conflicts of interest.

Copyright © 2010 Elsevier Ltd. All rights reserved.

Figures

Fig. 1

Effect of HO-1 on leukocyte infiltration after ICH. Infiltrating neutrophils (myeloperoxidase-positive cells) were apparent in the injury site 5 h post-ICH in WT mice (A), but not in HO-1−/− mice (B). At 24 h post-ICH, many more infiltrating neutrophils were present in and around the injury site in WT mice (C, E) than in HO-1−/− mice (D, F). The images in E and F represent higher magnification of the boxed area in C and D. (G) Quantification analysis indicated that HO-1−/− mice had significantly fewer infiltrating neutrophils than did WT mice at 24 h post-ICH (n = 5/group, **p < 0.01). Scale bar, A, B, E, F, 20 µm; (C, D) 300 µm. From Wang and Doré (2007a).

Fig. 2

Effect of HO-1 on microglial/macrophage activation after ICH. The distribution and morphology of microglia/macrophages (Iba1-positive) are shown in coronal sections collected at different time-points in WT (A, B, E, F, I,J, M, N) and HO-1−/− (C, D, G, H,K, L, O, P) mice. (A–D) Images shown at 0 h are from sham-operated mice. The images in B, F, J, N, D, H, L, P (scale bar: 20 µm) represent higher magnification of the boxed areas in A, E, I, M, C, G, K, and O (scale bar: 200 µm), respectively. In sham-operated WT (A, B) and HO-1−/− (C, D) mice, resting microglial cells were sparsely distributed. Insets in B and D (scale bar: 5 µm) illustrate Iba1-positive resting microglial cells at higher magnification. Microglial activation appeared as early as 1 h after ICH in WT (E, F) and HO-1 −/− (G, H) mice, but more intensely stained, activated cells (with large cell bodies and short processes) were observed in and around the ICH region in WT mice. This tendency persisted at 5 h (I–L) and up to 24 h (M–P) after ICH. (J) In a WT section 5 h post-ICH, two typical activated microglia/macrophages (elongated, rod cells) are indicated by arrows. (Q) Quantification of activated microglia/macrophages around the border region of injury. HO-1−/− mice had significantly fewer activated microglia/macrophages than did WT mice at 5 and 24 h post-ICH (n = 5/group, **p < 0.01). Values represent means ± SD. From Wang and Doré (2007a).

Fig. 3

Deletion of HO2 increases neuroinflammation in mice subjected to intracerebral hemorrhage (ICH). (A) Infiltrating neutrophils (myeloperoxidase-positive cells), (B) activated microglia/macrophages (Iba1-immunoreactive cells), and (C) reactive astrocytes (GFAP-positive cells) were apparent in or around the injury site in WT and HO2−/− mice 72 h post-ICH. (D) Three sections per mouse with similar brain injury size were chosen from six WT and six HO2−/− mice. Positive cells were counted randomly from 12 locations per animal (4 fields per section × 3 sections per animal) and the numbers were averaged and expressed as positive cells/field. Cell count analysis indicated that HO2−/− mice had significantly more infiltrating neutrophils, activated microglia/macrophages and astrocytes than did WT mice at 72 h post-ICH (all n = 6/group, *p < 0.05, **p < 0.01). Scale bar = 30 µm for A, B, C; IR, immunoreactive. Values are means ± SD. From Wang and Dore (2008).

Fig. 4

Increased in situ gelatinolytic activity after ICH on day 1 in control, wild-type (wt) and tPA knockout (−/−) mice. (A) Gelatinolytic activity-positive cells are present in the injury area in all animals. Column a, c: 100 × magnification; Column b, d: 400 × magnification. Scale bar, 20 µm. (B) Quantification of gelatinolytic activity-positive cells on day 1 in wt and tPA−/− mice. No significant difference was observed between the two genotypes of mice (n = 5). Values shown are means ± SD. Modified from Wang et al. (2003).

Fig. 5

Deletion of Nrf2 increases brain injury volume and neurologic deficits in mice subjected to intracerebral hemorrhage (ICH). Age- and weight-matched Nrf2 knockout (Nrf2−/−) and wild-type (WT) mice were subjected to ICH, and brains were sectioned and stained with Luxol fast blue/Cresyl Violet. (A) Representative sections from Nrf2−/− and WT mice 24 h after collagenase injection showing different areas of injury as represented by lack of staining. Scale bar =100 µm. (B) Quantification shows significantly larger brain injury volume in Nrf2−/− mice (n = 7) compared with WT mice (n = 10) 24 h after collagenase injection. (C) An investigator blinded to genotype assessed the neurologic deficits of Nrf2−/− and WT mice with a 24-point neurologic scoring system 24 h after collagenase injection. Neurologic deficits were significantly more severe in Nrf2−/− mice (n = 7) than in WT mice (n = 10). Values are means ± SD. *p < 0.05. From Wang et al. (2007).

Fig. 6

Deferoxamine reduces reddish zone around hematoma at day 3 and day 7 in a pig ICH model. Values are means ± SD, n = 4, #p < 0.01 vs vehicle. From Gu et al. (2009).