Lipopolysaccharide Preconditioning Reduces Neuroinflammation Against Hypoxic Ischemia and Provides Long-Term Outcome of Neuroprotection in Neonatal Rat

Abstract

Hypoxic ischemia (HI) in newborns causes long-term neurologic abnormalities. Systemic lipopolysaccharide (LPS) is neuroprotective in neonatal rats when injected 24 h before HI. However, the effect on HI-induced neuroinflammation and the long-term outcome of LPS preconditioning in neonatal rats have not been examined. In a rat-pup HI model, compared with normal saline (NS), 0.3 mg/kg of LPS injected 24 h before HI greatly increased microglial cell and macrophage activation and up-regulated TNF-alpha and inducible NOS expression 12-h postinjection and resulted in high mortality during HI. In contrast, 0.05 mg/kg of LPS elicited very little microglia and macrophage activation and TNF-alpha and inducible NOS expression and resulted in low mortality. Given 24 h before HI, low-dose (0.05 mg/kg) LPS greatly reduced microglia and macrophage activation, TNF-alpha expression, and reactive oxygen species production 24-h post-HI compared with NS-treated rats. Rats in the low-dose LPS group also showed significantly better learning and memory and less brain damage in adulthood. Learning and memory performance among the LPS-HI, LPS, and NS groups was not significantly different. We conclude that low-dose LPS preconditioning in neonatal rats greatly reduces HI-induced neuroinflammation and provides long-term neuroprotection against behavioral and pathologic abnormalities. T wenty percent of newborns with hypoxic ischemia (HI) die and an additional 25% have long-term neurodevelopmental handicaps (1). Although hypothermia has been used to treat newborns with HI encephalopathy, there is no effective pharmacological therapy. Sublethal lipopolysaccharide (LPS) stimulation, preconditioning, protects against subsequent lethal injury. Elucidating the neuroprotective mechanisms of LPS preconditioning may offer potential therapies against HI brain injury (2,3).Systemic LPS preconditioning (0.5 to 0.9 mg/kg) 48 to 72 h before ischemic insults protected adult rats against cerebral ischemia (4,5). LPS (0.3 or 1 mg/kg) sensitized neonatal Wistar rats and worsened HI brain injury when given 4, 6, or 72 h before HI (6). In contrast, 0.3 mg/kg of LPS 24 h before HI protected them (7,8). There are several neuroprotective preconditioning models for the neonatal brain (7,9 -13), but there are only few evaluations of long-term outcomes of LPS preconditioning at behavioral and pathologic levels.Inflammatory responses are important for developing neonatal HI brain injury (1). Up-regulated reactive oxygen species (ROS) production is also critical in inducing HI damage in the neonatal brain (1,14). One study (15) of adult rats showed that low-dose (0.05 mg/kg) LPS pretreatment 24 h before transient middle-cerebral-artery occlusion decreased ischemic infarct size despite increases of inflammatory cells in the ischemic hemisphere. In contrast, another study (16) suggested that LPS (0.2 mg/kg) preconditioning 48 h before transient middlecerebral-artery occlusion suppressed neuroinflammatory responses. Although up-regulating endogenous corticost...

Regulation of Lentivirus Neurovirulence by Lipopolysaccharide Conditioning: Suppression of CXCL10 in the Brain by IL-10

“…Alternatively, sequential activation of TLR4 initiates different outcomes depending on the model; repeated LPS exposures of mice carrying a mutant SOD1 accelerated the disease course leading to death (50). In contrast, LPS exposure before the induction of cerebral ischemia ameliorated the size of the ensuing lesion, although these effects might be related to age and the species used in the respective studies (51)(52)(53). LPS also shows diverse effects on the outcomes of experimental autoimmune encephalomyelitis, which might depend on the phenotype of the dendritic cells under different experimental conditions (15).…”

The Akt-Endothelial Nitric Oxide Synthase Pathway in Lipopolysaccharide Preconditioning-Induced Hypoxic-Ischemic Tolerance in the Neonatal Rat Brain

“…Postnatal (P) Day 6 Sprague-Dawley female rat pups (purchased from BioLASCO Taiwan Co, Ltd) were intraperitoneally injected with LPS (0.05 mg/kg; Escherichia coli 0111:B4; Sigma-Aldrich) or pyrogen-free normal saline (NS) 24 hours before HI on P7. 6 On P7, the rats were anesthetized (2.5% halothane), and then the right common carotid artery was permanently ligated. After they had been allowed to recover for 1 hour, the rats were placed in airtight 500-mL containers with humidified 8% oxygen flow rate of 3 L/min for 2 hours.…”

“…The percentage of hemispheric weight loss, measured as [(left hemisphere weightϪright hemisphere weight)/left hemisphere weight], was used as the measure of cerebral HI injury. 6,13 …”

“…Three visual fields in the cortex of the hemisphere per section and 2 sections per brain were analyzed and averaged. 6 …”

“…11 Our previous study showed that low-dose LPS (0.05 mg/kg) preconditioning provided longterm neuroprotection in neonatal rats. 6 Whether Akt-eNOS signaling is critical in LPS preconditioning-induced HI toler-ance in the neonatal brain remains undetermined. A shared signaling pathway may underlie preconditioning-induced protection in neurons and vascular endothelial cells.…”