The Deleterious or Beneficial Effects of Different Agents in
Intracerebral Hemorrhage
Think Big, Think Small, or Is Hematoma Size Important?
Richard F. Keep, PhD; Guohua Xi, MD; Ya Hua, MD; Julian T. Hoff, MD
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Background and Purpose—Thrombin, heme oxygenase, complement, microglia activation, and leukocyte infiltration are
all actively upregulated in intracerebral hemorrhage (ICH). Experimental evidence suggests that all these factors are
involved in ICH-induced brain injury. This suggests a scenario whereby ICH actively (through gene and protein
upregulation) induces pathways that result in brain injury.
Summary of Review—In this comment, we suggest a potential answer to this conundrum. The upregulation of these factors
may have been an evolutionary adaptation to limit brain injury during small hematomas (microbleeds). There is evidence
that low levels of thrombin and heme oxygenase limit brain injury. In contrast, the excessive upregulation of these same
factors may have a harmful effect after a large hematoma.
Conclusion—The mechanisms upregulated to limit brain injury after microbleeds may also induce injury after large
hematomas. The effect of hematoma size on the mechanisms involved in ICH-induced brain injury and the implications
of any such effect on clinical therapies merit further investigation. (Stroke. 2005;36:1594-1596.)
Key Words: inflammation 䡲 iron 䡲 thrombin
D
uring the past decade, animal experimentation has identified a number of pathways involved in intracerebral
hemorrhage (ICH)-induced brain injury. Thus, evidence indicates that thrombin, produced during clot formation, is
involved in ICH-induced brain edema and neurological deficits.1 Iron released from hemoglobin via the action of heme
oxygenase (HO) is also involved in inducing brain injury,2 as
is an influx of neutrophils,3 microglia activation,4 and complement activation.5,6 We have also recently found that
another iron-containing component of the hematoma, holotransferrin, in combination with thrombin can induce injury at
concentrations, whereas neither alone causes injury.7
It is interesting to note that many of the pathways that are
implicated in ICH-induced brain injury are actively enhanced
during ICH. Thus, whereas thrombin is actively generated
during clot formation, there is also a very marked induction of
HO-1 after ICH.2 There is also an influx of neutrophils and
other white blood cells into the brain after ICH.4 The
movement of such cells from blood to brain after brain injury
involves the upregulation of a variety of molecules involved
in the adhesion of white blood cells to the cerebral endothelium, their transmigration, and their direction to the site of
injury.8 Elements of the complement system are upregulated
in the perihematomal region,5 whereas there is extensive
microglia activation, with an upregulation of a number of cell
surface proteins, especially in aged animals.4,9 In the case of
the interaction between thrombin and holo-transferrin, it
appears that thrombin facilitates the intracellular uptake of
iron from holo-transferrin7 by upregulating levels of the
transferrin receptor in parenchymal cells.10
In all, these data suggest a scenario whereby ICH actively
(in terms of protein upregulation) induces pathways that
result in brain injury. This raises the question as to why this
should be the case. In this article, we hypothesize that
whereas activation of these pathways is deleterious after a
large ICH, activation of the same pathways may actually be
protective in the setting of small hematomas.
Thus, whereas extensive experimental data has been produced to support these pathways in ICH-induced brain injury,
there are also much data indicating that these same pathways
can be protective under certain circumstances. Many studies
indicate that although high concentrations of thrombin produce deleterious effects on the brain including edema, cytotoxicity, inflammation, and blood– brain barrier breakdown,
exposure of the brain to low concentrations can induce
protective effects.11 Pretreatment with low doses of thrombin
reduces brain injury in models of ICH, cerebral ischemia, and
Parkinson disease.11,12 Thrombin can upregulate the level of
iron-handling proteins and heat shock proteins that might
limit ICH-induced brain injury.10,13 Thrombin is also, of
course, involved in limiting the size of the ICH through its
role in coagulation. Similarly, although there is evidence that
Received January 17, 2005; final revision received April 15, 2005; accepted May 2, 2005.
From the Departments of Neurosurgery (R.F.K., G.X. Y.H., J.T.H.) and Physiology (R.F.K.), University of Michigan, Ann Arbor, Mich.
Correspondence to Richard F. Keep, PhD, Department of Neurosurgery, University of Michigan, 5550 Kresge I, Ann Arbor, MI 48109-0532. E-mail
[email protected]
© 2005 American Heart Association, Inc.
Stroke is available at http://www.strokeaha.org
DOI: 10.1161/01.STR.0000170701.41507.e1
1594
Keep et al
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HO inhibitors protect in both porcine and rat models of
ICH,14 –16 there is abundant evidence that HO-1 has protective
functions.17 This enzyme is involved in the breakdown of
potentially neurotoxic hemoglobin found in the hematoma
and represents an important step in the sequestration of the
iron found in hemoglobin.2 Evidence suggests that the effects
HO-1 depend on the levels of activity of the enzyme. Thus,
Suttner and Dennery, using hamster fibroblasts, found that
increasing HO-1 expression ⬍5-fold was protective against
oxidative stress, whereas increasing HO-1 expression ⬎15fold was detrimental.17 Similarly, although the influx of
neutrophils, activation of microglia, and activation of the
complement system appear to be involved in ICH-induced
injury, they are also important elements in hematoma resolution. All of these processes contribute to degradation of the
hematoma and the damaged perihematomal tissue. This
apparent dichotomy between the potential detrimental and
beneficial effects of the inflammatory systems has been noted
for other forms of brain injury.18
We hypothesize that whether these pathways are protective
or deleterious depends on hematoma size. Thus, for example,
in a small ICH, thrombin-induced upregulation of the transferrin receptor on parenchymal cells may serve to remove
potentially toxic iron from the extracellular space into the
intracellular compartment where it can be complexed to
molecules such as ferritin (which is also upregulated by
thrombin10). However, in a large ICH, thrombin induced iron
uptake may exceed the iron-handling capacity of the parenchymal cells and result in brain injury. Similarly, ironhandling proteins in the brain might be sufficient to handle
the iron generated by HO in the setting of a small but not a
large ICH.
Evolution may have resulted in the development of mechanisms to reduce the limited amount of brain injury that
occurs after small hemorrhages. In contrast, there may have
been little impact of evolution on generating defense mechanisms against large hemorrhages that would cause death or
debilitating injury. The injury from such a large hematoma
would still exclude the subject from future procreation or
enhancing the survival of previous progeny.
If our hypothesis is correct and the effect of the ICHinduced activation of certain pathways is size-dependent, a
major question is at what point(s) do these pathways cease to
be protective and start to become deleterious? Another
unanswered question is whether the size cutoff between
protection and harm will be species dependent? Certainly, the
effects of the same volume of ICH will differ between
species. A 400-␮L hematoma in a rat results in herniation and
death but it would have little effect on a human. We suggest,
therefore, that it is likely that the hematoma size cutoff
between where these pathways are protective and where they
are deleterious will be species-dependent, although it is
possible that mechanisms are designed to protect only against
microbleeds in all species.
Although this essay has focused on intracerebral hemorrhage, it should be noted that there is evidence for an
involvement of thrombin, HO, iron, neutrophils, complement,
and microglia in ischemic brain damage. Is it possible that
certain pathways are activated during small ischemic events
Hematoma Size and Brain Injury Mechanisms
1595
to limit brain damage, but that activation of those same
pathways during a large ischemic stroke will induce brain
damage? In relation to this point, the role of vascular
endothelial growth factor (VEGF) in ischemic stroke is
intriguing. VEGF is upregulated after ischemic stroke and
may limit ischemic brain damage by inducing new blood
vessel growth and by direct neuroprotective effects. However, it may also have adverse effects on neuronal survival,
blood– brain barrier disruption, and edema formation.19 Thus,
interestingly, the protective effects of exogenous VEGF are
very dose-dependent, with protection at low doses but not at
high doses.19 It is tempting to postulate that with a small
vessel blockage, VEGF may be beneficial by promoting
limited new vessel growth and by enhancing neuronal survival. However, a large artery stroke with high levels of
VEGF may cause too much angiogenesis with vascular
leakage and edema formation.
Though the hypotheses outlined may seem somewhat
esoteric, they raise an important issue. If certain ICH-induced
pathways result in injury or protection dependent on the size
of the hematoma, this would suggest that therapeutic strategies targeting those pathways should only be used for
hemorrhages of certain (as yet undefined) size ranges.
Is it possible to test the hypotheses outlined? Much of ICH
research has been performed in rodents (rats and, recently,
mice). In a rat autologous blood injection model, typically 50
or 100 ␮L of blood have been infused and thrombin antagonists protect against both hematoma sizes.20,21 Thus, at least
in terms of thrombin-induced pathways, the hypothesized
crossover point between protection and injury would have to
occur at hematoma sizes of less (and probably much less)
than 50 ␮L. It is likely that the current methods for assessing
ICH-induced injury will have difficulties in assessing damage
from such small hematomas (even when protective pathways
are inhibited). If we are correct and the hematoma size at
which crossover between protection and injury occurs is
species-dependent (and possibly dependent on the location of
the hematoma), it may be easier to detect protective effects in
larger species (such as pig or primate).14,22
In summary, there is evidence that multiple pathways
activated during ICH can have both protective and deleterious
effects. We hypothesize that these pathways may be protective in the setting of “small” hematomas but have a deleterious effect in the setting of “large” hematomas. The crossover
point between protection and injury may be speciesdependent. If this hypothesis is correct, it would impact
current preclinical experimental design by suggesting that
therapeutic agents should be assayed against more than one
size of hematoma. It would also suggest that clinical trials
might need to focus on a well-defined range of hematoma
sizes.
Acknowledgments
This work was supported by grants NS-17760 (J.T.H.), NS-39866,
NS-47245 (G.X.), and NS-34709 (R.F.K.) from the National Institutes of Health.
References
1. Xi G, Fewel ME, Hua Y, Thompson BG, Hoff JT, Keep RF. Intracerebral
hemorrhage: pathophysiology and therapy. Neurocrit Care. 2004;1:5–18.
1596
Stroke
July 2005
Downloaded from http://stroke.ahajournals.org/ by guest on July 28, 2017
2. Wagner KR, Sharp FR, Ardizzone TD, Lu A, Clark JF. Heme and iron
metabolism: role in cerebral hemorrhage. J Cereb Blood Flow Metab.
2003;23:629 – 652.
3. Gong C, Hoff JT, Keep RF. Acute inflammatory reaction following
experimental intracerebral hemorrhage. Brain Res. 2000;871:57– 65.
4. Wang J, Rogove AD, Tsirka AE, Tsirka SE. Protective role of tuftsin
fragment 1–3 in an animal model of intracerebral hemorrhage. Ann
Neurol. 2003;54:655– 664.
5. Hua Y, Xi G, Keep RF, Hoff JT. Complement activation in the brain after
experimental intracerebral hemorrhage. J Neurosurg. 2000;92:
1016 –1022.
6. Xi G, Hua Y, Keep RF, Younger JG, Hoff JT. Systemic complement
depletion diminishes perihematomal brain edema. Stroke. 2001;32:
162–167.
7. Nakamura T, Xi G, Park J-W, Hua Y, Hoff JT, Keep RF. Holo-transferrin
and thrombin can interact to cause brain injury. Stroke. 2005;36:348 –352.
8. Kato H, Oikawa T. Invasion of ischemic brain by immune cells. In: Walz
W, ed. The Neuronal Environment. Totowa, NJ: Humana Press; 2002:
401– 417.
9. Gong Y, Hua Y, Keep RF, Hoff JT, Xi G. Intracerebral hemorrhage
Effects of Aging on brain edema and neurological deficits. Stroke. 2004;
35:2571–2575.
10. Hua Y, Keep RF, Hoff JT, Xi G. Thrombin preconditioning attenuates
brain edema induced by erythrocytes and iron. J Cereb Blood Flow
Metab. 2003;23:1448 –1454.
11. Xi G, Reiser G, Keep RF. The role of thrombin and thrombin receptors
in ischemic, hemorrhagic and traumatic brain injury: deleterious or protective? J Neurochem. 2003;84:3–9.
12. Cannon J, Keep RF, Hua Y, Richardson RJ, Schallert T, Xi G. Thrombin
preconditioning provides protection in a 6-hydroxydopamine Parkinson’s
disease model. Neurosci Lett. 2005;373:189 –194.
13. Xi G, Keep RF, Hua Y, Xiang J, Hoff JT. Attenuation of thrombininduced brain edema by cerebral thrombin preconditioning. Stroke. 1999;
30:1247–1255.
14. Wagner KR, Hua Y, de Courten-Myers GM, Broderick JP, Nishimura
RN, Lu SY, Dwyer BE. Tin-mesoporphyrin, a potent heme oxygenase
inhibitor, for treatment of intracerebral hemorrhage: in vivo and in vitro
studies. Cell Mol Biol. 2000;46:597– 608.
15. Huang FP, Xi G, Hua Y, Keep RF, Nemoianu A, Hoff JT. Brain edema
after experimental intracerebral hemorrhage: Role of hemoglobin
breakdown products. J Neurosurg. 2002;96:287–293.
16. Koeppen AH, Dickson AC, Smith J. Hemeoxygenase in experimental
intracerebral hemorrhage: the benefit of tin-mesoporphyrin. J Neuropath
Exp Neurol. 2004;63:587–597.
17. Suttner DM, Dennery PA. Reversal of HO-1 related cytoprotection with
increased expression is due to reactive iron. FASEB J. 1999;13:
1800 –1809.
18. Stoll G, Jande S, Schroeter M. Detrimental and beneficial effects of
injury-induced inflammation and cytokine expression in the nervous
system. Adv Exp Med Biol. 2002;513:87–113.
19. Manoonkitiwongsa PS, Schultz RL, McCreery DB, Whitter EF, Lyden
PD. Neuroprotection of ischemic brain by vascular endothelial growth
factor is critically dependent on proper dosage and may be compromised
by angiogenesis. J Cereb Blood Flow Metab. 2004;24:693–702.
20. Lee KR, Colon GP, Betz AL, Keep RF, Kim S, Hoff JT. Edema from
intracerebral hemorrhage: the role of thrombin. J Neurosurg. 1996;84:
91–96.
21. Kitaoka T, Hua Y, Xi G, Hoff JT, Keep RF. Delayed argatroban treatment
reduces edema in a rat model of intracerebral hemorrhage. Stroke. 2002;
33:3012–3018.
22. Thiex R, Kuker W, Muller HD, Rohde I, Schroder JM, Gilsbach JM,
Rohde V. The long-term effect of recombinant tissue-plasminogen-activator (rt-PA) on edema formation in a large-animal model of intracerebal
hemorrhage. Neurological Res. 2003;25:254 –262.
The Deleterious or Beneficial Effects of Different Agents in Intracerebral Hemorrhage:
Think Big, Think Small, or Is Hematoma Size Important?
Richard F. Keep, Guohua Xi, Ya Hua and Julian T. Hoff
Downloaded from http://stroke.ahajournals.org/ by guest on July 28, 2017
Stroke. 2005;36:1594-1596; originally published online June 2, 2005;
doi: 10.1161/01.STR.0000170701.41507.e1
Stroke is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 2005 American Heart Association, Inc. All rights reserved.
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