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Updated: Aug 19, 2026
Sub-acute Cerebral Microhemorrhages Induced by Lipopolysaccharide Injection in Rats
Published on: October 17, 2018
Accelerated cerebral ischemic injury by activated macrophages/microglia after lipopolysaccharide microinjection into
Jae-Chul Lee1, Geum-Sil Cho, Hye Jin Kim
1Department of Pharmacology, College of Medicine, Laboratory of Neurodegenerative Diseases, Ewha Institute of Neuroscience, Seoul, Republic of Korea.
Abstract:
In cerebral ischemic insults, activated inflammatory cells such as microglia and macrophages may be implicated in the pattern and degree of ischemic injury by producing various bioactive mediators. In the present study, we provide the evidence that activated microglia/macrophages accelerate cerebral ischemic injury by overexpression of inducible nitric oxide synthase (iNOS). To activate microglia/macrophages, a potent inflammation inducer lipopolysaccharide (LPS, 5 microg/5 microl) was microinjected into rat corpus callosum. Isolectin B4-positive microglia/macrophages were abundantly observed in ipsilateral hemisphere at 1 day after LPS injection. RT-PCR showed that LPS injection induced iNOS mRNA expression mostly in microglia/macrophages, peaking in intensity at 15 h after LPS injection. While ischemic injury was little evoked in control rats by 2-h middle cerebral artery occlusion (MCAO) followed by 3-h reperfusion, it was markedly increased in rats pre-injected with LPS 1 day before MCAO. However, no significant difference between control and LPS-pretreated groups was observed after 24-h reperfusion. The increased ischemic injury in LPS-treated rats was well correlated with iNOS level expressed over 3 orders of magnitude than in LPS-untreated rats. Immunohistochemical studies showed that iNOS- and nitrotyrosine (a peroxynitrite marker)-positive cells were prominent throughout the infarct area. NOS inhibitors aminoguanidine or N(G)-nitro-L-arginine, simultaneously injected with LPS, reduced the iNOS immunoreactivity and infarct volume, especially in penumbra regions. Total glutathione levels in ischemic regions were decreased more in LPS pre-injected rats than in control ones. Further defining the role of NO in cerebral ischemic insults would provide the rationale for new therapeutic strategies based on modulation of microglial and macrophageal NO production in the brain.
Insights
Activated microglia and macrophages accelerate brain injury after stroke by overexpressing inducible nitric oxide synthase (iNOS). Inhibiting iNOS reduces damage, suggesting new therapeutic targets for stroke.
Area of Science:
- Neuroscience
- Immunology
- Pathology
Background:
- Activated microglia and macrophages contribute to ischemic injury through bioactive mediators.
- Inducible nitric oxide synthase (iNOS) is implicated in inflammatory responses.
- Understanding the role of iNOS in cerebral ischemia is crucial for therapeutic development.
Purpose of the Study:
- To investigate the role of activated microglia/macrophages and iNOS in accelerating cerebral ischemic injury.
- To determine the effect of iNOS inhibition on ischemic damage.
Main Methods:
- Lipopolysaccharide (LPS) was used to activate microglia/macrophages in rat brains.
- Middle cerebral artery occlusion (MCAO) was performed to induce ischemic injury.
- RT-PCR, immunohistochemistry, and biochemical assays were used to assess iNOS expression, injury, and oxidative stress.
Main Results:
- LPS injection led to abundant microglia/macrophages and induced iNOS mRNA expression.
- Pre-treatment with LPS significantly increased ischemic injury 3 hours post-reperfusion, correlating with iNOS levels.
- iNOS and nitrotyrosine positive cells were prominent in infarct areas.
- NOS inhibitors reduced iNOS immunoreactivity and infarct volume.
Conclusions:
- Activated microglia/macrophages accelerate cerebral ischemic injury via iNOS overexpression.
- Modulating microglial and macrophageal NO production offers potential therapeutic strategies for stroke.
