Previous studies have demonstrated that the activation of
delta opioid receptors is neuroprotective against neonatal
hypoxia-
ischemia (HI)
brain injury. The aim of this study was to investigate the
neuroprotective effects of
biphalin, a dimeric
opioid peptide, in a mouse model of neonatal HI and the underlying mechanisms. On postnatal day 10, mouse pups were subjected to unilateral carotid artery
ligation followed by 1 h of
hypoxia (10 % O2 in N2). For treatment,
biphalin (5 mg/kg, 10 mg/kg, 20 mg/kg) was administered intraperitoneally immediately after HI. The
opioid antagonist naloxone or phosphatidylinositol-3-kinase inhibitor
Ly294002 was administered to determine the underlying mechanisms.
Infarct volume,
brain edema, phosphorylated Akt and apoptosis-related
proteins levels were evaluated by using a combination of
2,3,5-triphenyltetrazolium chloride staining, brain water content and Western blotting at 24 h after HI. The long-term effects of
biphalin were evaluated by brain
atrophy measurement, Nissl staining and neurobehavioral tests at 3 weeks post-HI.
Biphalin (10 mg/kg) significantly reduced the
infarct volume and ameliorated
brain edema.
Biphalin also had long-term protective effects against the loss of ipsilateral brain tissue and resulted in improvements in neurobehavioral outcomes. However,
naloxone or
Ly294002 abrogated the
neuroprotective effects of
biphalin. Furthermore,
biphalin treatment significantly preserved phosphorylated Akt expression, increased Bcl-2 levels, and decreased Bax and cleaved
caspase 3 levels after HI. These effects were also reversed by
naloxone and
Ly294002 respectively. In conclusion,
biphalin protects against HI
brain injury in neonatal mice, which might be through activation of the
opioid receptor/
phosphatidylinositol-3-kinase/Akt signaling pathway.