Accelerated cerebral ischemic injury by activated macrophages/microglia after lipopolysaccharide microinjection into rat corpus callosum

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.

A3 Adenosine Receptor Agonist Reduces Brain Ischemic Injury and Inhibits Inflammatory Cell Migration in Rats

“…1, 45 We also found that LPS-activated microglia and monocytes accelerated and aggravated cerebral ischemic injury, 34 and that depletion of peripheral leukocytes by ␥-irradiation before ischemia reduced the cerebral infarction caused by MCAO/R (unpublished data). In the present study, LJ529 was found to inhibit the infiltration/migration of microglia/monocytes induced by MCAO/ R or injection of LPS into the corpus callosum ( Figure 1).…”

Modulation of the Purinergic P2X7Receptor Attenuates Lipopolysaccharide-Mediated Microglial Activation and Neuronal Damage in Inflamed Brain

“…Because nitrogen species contribute to responses in inflamed brain (Brown and Bal-Price, 2003;Lee et al, 2005), we examined levels of inducible enzyme iNOS and 3-NT. Marked upregulation of iNOS was evident in LPS-injected striatum (at 24 h) with colocalization to microglia (Fig.…”

Peripheral Inflammation Exacerbates Damage After Global Ischemia Independently of Temperature and Acute Brain Inflammation

“…26 These cells are a source of cytokines and other inflammatory mediators 34 and, when activated after a cerebral ischemia, accelerate injury via an overexpression of inducible nitric oxide synthase and production of cytotoxic nitric oxide. 27 In accordance with the similar levels of hippocampal cytokines between the groups, we also saw similar levels of activated microglia.…”