Damjan Osredkar¹ ², Hemmen Sabir¹ ³, Mari Falck¹, Thomas Wood¹, Elke Maes¹, Torun Flatebø¹, Maja Puchades¹, Marianne Thoresen¹ ⁴
¹Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, Norway
²Department of Pediatric Neurology, University Children's Hospital Ljubljana, University Medical Centre, Slovenia
³Department of General Pediatrics, Neonatology and Pediatric Cardiology, University Children's Hospital, Düsseldorf, Germany
⁴School of Clinical Sciences, University of Bristol, St Michael’s Hospital, Bristol, United Kingdom
Bacterial lipopolysaccharide (LPS) injection prior to hypoxia-ischemia (HI) significantly increases HI brain injury in 7 day-old (P7) rats. In addition, therapeutic hypothermia (HT) is not neuroprotective in this setting. This study was designed to investigate the underlying cellular mechanisms in this double hit model of infection-sensitised HI brain injury.
P7 rat pups were injected with either vehicle or LPS, and after a 4 h delay were exposed to left carotid ligation followed by global hypoxia inducing a unilateral stroke-like HI injury. Pups were randomised to the following treatments: (1) vehicle treated pups receiving normothermia treatment (NT) (Veh-NT; n = 40); 2) LPS treated pups receiving NT treatment (LPS-NT; n = 40); 3) vehicle treated pups receiving hypothermia (HT) treatment (Veh-HT; n = 38); or 4) LPS treated pups receiving HT treatment (LPS-HT; n = 35). On postnatal day 8 or 14, western blot analysis or immunohistochemistry was performed to examine neuronal death, apoptosis, astrogliosis and microglial activation.
LPS sensitisation prior to HI significantly exacerbated apoptotic neuronal loss. NeuN was significantly reduced in the LPS-NT and LPS–HT groups (p = 0.008). Caspase-3 activation was significantly increased in the LPS sensitised groups (p < 0.001). A significant increase in astrogliosis (GFAP expression, p < 0.001) was seen, as well as a trend towards increased microglial activation (Iba 1 expression, p = 0.051) in LPS sensitised animals. Treatment with HT did not counteract these changes.
LPS-sensitised HI brain injury in newborn rats is mediated through neuronal death, apoptosis, astrogliosis and microglial activation. In this model, treatment with HT does not ameliorate these changes.
Keywords: hypoxia-Ischemia, hypothermia, infection, lipopolysaccharide, neuroprotection