Hypoxic-ischemic neonatal encephalopathy: animal experiments for neuroprotective therapies

Differential Effects of Pentoxifylline on Learning and Memory Impairment Induced by Hypoxic-ischemic Brain Injury in Rats

Objective

Hypoxic-ischemic (HI) brain injury in the human perinatal period often leads to significant long-term neurobehavioral dysfunction in the cognitive and sensory-motor domains. Using a neonatal HI injury model (unilateral carotid ligation followed by hypoxia) in postnatal day seven rats, the present study investigated the long-term effects of HI and potential behavioral protective effect of pentoxifylline.

Methods

Seven-day-old rats underwent right carotid ligation, followed by hypoxia (F_iO₂ = 0.08). Rats received pentoxifylline immediately after and again 2 hours after hypoxia (two doses, 60‒100 mg/kg/dose), or serum physiologic. Another set of seven-day-old rats was included to sham group exposed to surgical stress but not ligated. These rats were tested for spatial learning and memory on the simple place task in the Morris water maze from postnatal days 77 to 85.

Results

HI rats displayed significant tissue loss in the right hippocampus, as well as severe spatial memory deficits. Low-dose treatment with pentoxifylline resulted in significant protection against both HI-induced hippocampus tissue losses and spatial memory impairments. Beneficial effects are, however, negated if pentoxifylline is administered at high dose.

Conclusion

These findings indicate that unilateral HI brain injury in a neonatal rodent model is associated with cognitive deficits, and that low dose pentoxifylline treatment is protective against spatial memory impairment.

Ischemic Conditioning and neonatal hypoxic ischemic encephalopathy: a literature review

Hypoxic Ischemic Encephalopathy (HIE) is the result of severe anoxic brain injury during the neonatal period and causes life-long morbidity and premature mortality. Currently, therapeutic hypothermia immediately after birth is the standard of care for clinically relevant HIE. However, therapeutic hypothermia alone does not provide complete neuroprotection and there is an urgent need for adjunctive therapies. Ischemic conditioning is an adaptive process of endogenous protection in which small doses of sub-lethal ischemia can provide a protection against a lethal ischemic event. Remote Ischemic Post-conditioning (RIPC), a form of ischemic conditioning, is highly translatable for HIE diagnosed immediately after birth as the conditioned ischemic stimulus is applied at the limb after the lethal ischemic episode. A number of studies in neonatal rats have demonstrated that RIPC is effective at reducing injury in focal cerebral ischemia models and improves neurological outcomes. In this review, we focus on the available data on HIE and its current treatment, models in HIE studies, ischemic conditioning/RIPC and its mechanism. We discuss in particular the effect of RIPC on neonatal brain with HIE. We postulate that combining RIPC with standard therapeutic hypothermia can be an attractive therapeutic approach for HIE.

Knockdown of IL-1β improves hypoxia-ischemia brain associated with IL-6 up-regulation in cell and animal models

A study was conducted to investigate the effect of interleukin-1β (IL-1β) on hypoxia ischemia (HI) of cultured astrocyte and neonatal rat models and to explore the underlying molecular regulation mechanism. Primary rat astrocyte was exposed to hypoxia (2 % O2, 98 % N2) and cultured in serum-free medium for 6, 12, and 18 h to establish cell model of HI. Morphologic changes of astrocyte were monitored and gene expression change of IL-1β evaluated by real-time polymerase chain reaction (PCR). To establish the HI animal model, 3 days old postnatal Sprague-Dawley (SD) rats were treated with the right carotid artery ligation and were exposed to 8 % oxygen for 8, 16 and 24 h, respectively. Longa score scale, hematoxylin and eosin (HE) staining and water content were examined to assess neurologic function and morphology changes. IL-1β siRNA lentivirus (IL-1β-RNAi-LV) was injected into cerebral cortex motor area 2 days before HI and the interference efficiency examined by real-time PCR and Western blotting, respectively. Immunofluorescence staining of GFAP and IL-1β was performed to identify the location and interference effect of IL-1β, respectively. To further explore the potential mechanisms, the expression of inflammatory factors, including IL-6, IL-10 and tumor necrosis factor-alpha (TNF-α), was examined following IL-1β down-regulation. The size of soma astrocyte was increased greatly after 12 and 18 h of HI with IL-1β up-regulation. IL-1β knockdown by siRNA in vitro or by lentivirus in vivo can reverse cell swelling, brain edema and neurologic function deficiencies induced by HI. Lastly, interference of IL-1β remarkably increased IL-6 expression but not IL-10 and TNF-α. Therefore, down-regulation of IL-1β improves the deficiencies of neurologic function and morphology induced by HI, maybe closely associating with IL-6 regulation.