8 - Syn3 attenuates hypoxic-ischemic brain injury in neonatal rats

Poster Number: 8
Publication Number: 8.433

Brynn Kroke, Brown University, Providence, RI, United States; Mark Appleman, Brown University, Providence, RI, United States; Tuong Tran, Brown University, Providence, RI, United States; Xiaodi F. Chen, Women & Infants Hospital of Rhode Island, Providence, RI, United States; Barbara Stonestreet, Women & Infants Hospital of Rhode Island, Providence, RI, United States; John Marshall, The Warren Alpert Medical School of Brown University, Providence, RI, United States

Background: Hypoxic ischemic (HI) brain injury is a major cause of neurological abnormalities originating in the perinatal period. The only approved treatment for HI encephalopathy (E) is therapeutic hypothermia. This therapy is only approved for use in full-term infants, is only partially protective, and has a narrow therapeutic time window. Effective safe pharmacological agents are not available to treat HIE. Neuroinflammation is an important component of HI brain injury. Microglia are key mediators of neuroinflammation. Microglia-induced brain-derived neurotrophic factor (BDNF) has anti-inflammatory effects. A novel peptidomimetic therapeutic, Syn3 induces BDNF signaling by binding to the postsynaptic scaffold PSD-95. However, the efficacy of Syn3 to treat HI-related brain injury has not been examined in newborns.

Objective: To examine the effects of treatment with Syn3 on brain infarct volume loss and the number of microglia per counting area after exposure to HI insults in neonatal rats.

Design/Methods: Postnatal (P) day 7 rats were randomly assigned to 3 groups; Sham (n=3-6), placebo (HI-PL n=4-12), and HI-Syn3 (n=5-13). The rats were exposed to unilateral ligation of the carotid artery followed by 8% oxygen for 90 min. HI animals received PL (phosphate buffered saline) or Syn3 (1 mg/kg) intraperitoneally (i.p.) at 0, 24, and 48 h after HI. Sham received PL i.p. without HI exposure. 72 h after HI, brains were perfused, fixed, and prepared for analysis. 20-μm coronal cryosections were stained with cresyl violet. The images of hemispheric infarct areas were analyzed with Image J (NIH). Infarct fraction was calculated as the percentage of the ratio of the damaged area to the area of the total hemisphere with correction for hemispheric swelling due to edema. Corresponding volumes were calculated for the total set of slices. Immunohistochemistry was performed by staining sections with Iba-1 (microglia marker). Quantification was performed by unbiased stereological analyses (StereoInvestigator 10.0, Fractionator probe) without knowledge of group assignment.

Results: Treatment with Syn3 significantly attenuated (P< 0.05, Fig.1) brain volume loss in neonatal rats after exposure to 90 min of HI injury. Quantification of Iba1-stained cells revealed that Syn3 reduced the total microglia/counting area (P< 0.05) and amoeboid microglia/counting area (P< 0.001) in the hemisphere (P< 0.05, Fig.2) of the neonatal rats.

Conclusion(s): Treatment with Syn3 attenuates brain volume loss in the HI hemisphere of neonatal rats in part by its anti-inflammatory effects on microglia.
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