Minocycline-Suppression of Early Peripheral Inflammation Reduces Hypoxia-Induced Neonatal Brain Injury.

Yingjun Min,Rong Mei,Kaiyu Xu,Qian Wang,Hongchun Li,Yilong Huang,Ling Yang,Ting Yang,Min Zhao,Jie Xiao,Hong Jiang,Weizhou Wang,Longjun Li,Lixuan Huang,Fan Li,Hairong Hua

doi:10.3389/fnins.2017.00511

Abstract

While extensive studies report that neonatal hypoxia-ischemia (HI) induces long-term cognitive impairment via inflammatory responses in the brain, little is known about the role of early peripheral inflammation response in HI injury. Here we used a neonatal hypoxia rodent model by subjecting postnatal day 0 (P0d) rat pups to systemic hypoxia (3.5 h), a condition that is commonly seen in clinic neonates, Then, an initial dose of minocycline (45 mg/kg) was injected intraperitoneally (i.p.) 2 h after the hypoxia exposure ended, followed by half dosage (22.5 mg/kg) minocycline treatment for next 6 consecutive days daily. Saline was injected as vehicle control. To examine how early peripheral inflammation responded to hypoxia and whether this peripheral inflammation response was associated to cognitive deficits. We found that neonatal hypoxia significantly increased leukocytes not only in blood, but also increased the monocytes in central nervous system (CNS), indicated by presence of C-C chemokine receptor type 2 (CCR2+)/CD11b+CD45+ positive cells and CCR2 protein expression level. The early onset of peripheral inflammation response was followed by a late onset of brain inflammation that was demonstrated by level of cytokine IL-1β and ionized calcium binding adapter molecule 1(Iba-1; activated microglial cell marker). Interrupted blood-brain barrier (BBB), hypomyelination and learning and memory deficits were seen after hypoxia. Interestingly, the cognitive function was highly correlated with hypoxia-induced leukocyte response. Notably, administration of minocycline even after the onset of hypoxia significantly suppressed leukocyte-mediated inflammation as well as brain inflammation, demonstrating neuroprotection in systemic hypoxia-induced brain damage. Our data provided new insights that systemic hypoxia induces cognitive dysfunction, which involves the leukocyte-mediated peripheral inflammation response.

Highlights

Neonatal encephalopathy due to perinatal asphyxia or hypoxiaischemia (HI) is an important cause of mortality in the neonatal period and is associated with high morbidity, mainly characterized by neurological deficits such as, cognitive dysfunctions
We found that hypoxia-exposed rats (Hy) had longer swimming distance (Figure 2B; p < 0.01 and p < 0.001 vs. normal control group (NG) group; p < 0.05 vs. hypoxia-exposed group (Hy) group) and longer latency to find the hidden platform compared to NG group (Figure 2C; p
Administration of minocycline after the onset of hypoxia for 7 days significantly increase the time spent in the target quadrant and the number of crossings in the platform region (Figures 2D,E; p < 0.05 Hy M vs. Hy)

Summary

Introduction

Neonatal encephalopathy due to perinatal asphyxia or hypoxiaischemia (HI) is an important cause of mortality in the neonatal period and is associated with high morbidity, mainly characterized by neurological deficits such as, cognitive dysfunctions. There are a number of studies demonstrating elevated microglia activation and IL-1β cytokine expression and release in the brain after hypoxia at the neonatal stage (Herrera-Marschitz et al, 2014; Kaur et al, 2014), and this brain endogenous inflammatory response is closely associated with brain damage and cognitive deficits (Fatemi et al, 2011; Alexandre et al, 2013) in HIE models. Considerable research revealed that peripheral immune cells such as, monocyte, macrophage, and neutrophil subtype of leukocytes infiltrated into CNS parenchyma in several adult rodent models including focal ischemia and experimental autoimmune encephalomyelitis, which contributed to inflammation/hypomyelination and neuronal injury (Morkos et al, 2007; Prinz and Priller, 2010; Herrera-Marschitz et al, 2014; Kichev et al, 2014). Given that the uncompleted development of the brain-blood-barrier (BBB) and the possible BBB broken down in response to hypoxia in neonates (Prinz and Priller, 2010), the peripheral leukocytes may invade into brain parenchyma and play a critical role in inflammation/hypomyelination and cognitive dysfunction

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