Mechanisms of Neonatal Brain Injury in a Rat Pup Hypoxic-Ischemic Model

<p>Perinatal hypoxic-ischemic (HI) brain injury is a major cause of acute morbidity and chronic nemological mortality in infants and children, with a reported incidence of 2- 9 per 1000 births. The pathophyiological mechanisms leading to immature brain damage after HI are complex and relate to the developmental stage of the brain. The objective of our study is to understand the neonatal hypoxic-ischemic brain injury and to aid in the development of pharmacological treatments.</p> <p>Hypoxic inducible factor 1 (HIF-1) is a transcription factor which is stabilized and activated by hypoxia. It is the most important factor involved in the cellular response to hypoxia. However, the role of HIF-1 in the central nervous system is unclear, which has been considered as a regulator of both prosurvival and prodeath pathways after brain injury. Here we tested the hypothesis that acute HIF-1 inhibition early after neonatal HI injiuy provides neuroprotection in the developing brain by preserving blood-brain barrier (BBB), ameliorating brain edema, and reducing infarct volume via VEGF-dependent pathway. We also investigated if matrix metalloproteinases (MMPs), one of HIF-1 downstream factors, are involved in the process of neonatal HI brain injury. We hypothesized that broad-spectrum MMPs inhibition confers neuroprotection by reducing tight junction proteins (TJPs) degradation and preserve BBB integrity. Moreover, acute MMPs inhibition provides long term neuroprotection and neurological function recovery against neonatal HI brain injury.</p> <p>Rice-Vannucci model of neonatal HI brain injury was used in seven-day-old rat pups, by subjecting unilateral carotid artery ligation followed by 2 h of hypoxia (8% O2 at 37°C). Following insult, brain infarction, neuronal cell death, brain edema, elevation of HIF-1 and MMP-2/-9 activity, elevation of VEGF and TIMP-1/-2 expression, degradation of TJPs, along with severe brain atrophy was observed in the ipsilateral hemisphere, which led to significant neurological deficits. HIF-1 a activity was inhibited by 2-methoxyestradiol (2ME2,1.5, 15 or 150 mg/kg) or enhanced by dimethyloxalylglycine (DMOG, 250 mg/kg). 2ME2 treatment exhibited dose-dependent neuroprotection by decreasing infarct volume and reducing brain edema at 48 h post HI. The neuroprotection was lost when 2ME2 was administered 3 h post HI. HIF-1 a upregulation by DMOG increased the permeability of the BBB and brain edema compared with HI group. 2ME2 (15 mg/kg) attenuated the elevation of HIF-1 a and VEGF at 24 h after HI. 2ME2 (15 mg/kg) also had a long-term effect of protecting against the loss of brain tissue. To investigate the role of MMPs, GM6001 (50 mg/kg or 100 mg/kg) or doxycycline (10 mg/kg or 30 mg/kg), a broad spectrum MMPs inhibitor, was injected intraperitoneally at 2 h and 24 h after HI injury. Either GM6001 (100 mg/kg) or doxycycline (30 mg/kg) treatment attenuated brain edema and BBB disruption. GM6001 (100 gm/kg) treatment also attenuated MMP-9/-2 activities, preserved the degradation of tight junction proteins (TJPs), protected BBB, and provided a long term neuroprotection morphologically and functionally. </p> <p>These results suggest that the early inhibition of HIF-1 acutely after injury provided neuroprotection after neonatal hypoxia-ischemia which was associated with preservation of BBB integrity, attenuation of brain edema, and neuronal death. Meanwhile, MMPs are also involved in the neonatal HI brain injury. Early MMPs inhibition affords both acute and long-term neuroprotection. Thus, we propose that either early HIF-1 inhibition or a short duration of MMPs inhibition in the early stage after neonatal HI injury may offer a promising therapeutic strategy for the prevention of the brain injury in the children who suffered a hypoxic-ischemic insult.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Pharmacology

Year

2009

Author dc:creator

• Chen, Wanqiu

Contributors dc:contributor

• John H. Zhang
• Richard Hartman
• Andre Obenaus
• Jiping Tang
• Lubo Zhang

• Pharmacology
• Brain Injuries Infant; Newborn Brain Edema -- physiopathology; Hypoxia-Ischemia; Brain -- physiopathology; Blood-Brain Barrier; Central Nervous System -- drug effects; Matrix Metalloproteinases -- antagonists and inhibitors; Neuroprotective Agents -- pharmacology; Models; Animal Rats; Sprague-Dawley; Survival Analysis; Cross-Sectional Studies

Statement dc:rights

• This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Language dc:language

English

Repository record dc:identifier

https://scholarsrepository.llu.edu/etd/1201

OAI identifier oai:identifier

oai:scholarsrepository.llu.edu:etd-2700