Preterm brain injury is a major cause of disability in later life, and may result in motor, cognitive and behavioural impairment for which no treatment is currently available. The aetiology is considered as multifactorial, and one underlying key player is inflammation leading to white and grey matter injury. Extracellular vesicles secreted by mesenchymal stem/stromal cells (MSC-EVs) have shown therapeutic potential in regenerative medicine. Here, we investigated the effects of MSC-EV treatment on brain microstructure and maturation, inflammatory processes and long-time outcome in a rodent model of inflammation-induced brain injury. 3-Day-old Wistar rats (P3) were intraperitoneally injected with 0.25mg/kg lipopolysaccharide or saline and treated with two repetitive doses of 1×108 cell equivalents of MSC-EVs per kg bodyweight. Cellular degeneration and reactive gliosis at P5 and myelination at P11 were evaluated by immunohistochemistry and western blot. Long-term cognitive and motor function was assessed by behavioural testing. Diffusion tensor imaging at P125 evaluated long-term microstructural white matter alterations. MSC-EV treatment significantly ameliorated inflammation-induced neuronal cellular degeneration reduced microgliosis and prevented reactive astrogliosis. Short-term myelination deficits and long-term microstructural abnormalities of the white matter were restored by MSC-EV administration. Morphological effects of MSC-EV treatment resulted in improved long-lasting cognitive functions INTERPRETATION: MSC-EVs ameliorate inflammation-induced cellular damage in a rat model of preterm brain injury. MSC-EVs may serve as a novel therapeutic option by prevention of neuronal cell death, restoration of white matter microstructure, reduction of gliosis and long-term functional improvement.

Despite major advances in obstetrics and neonatal intensive care, preterm infants frequently suffer from neurological impairments in later life. Preterm and also full-term neonates are generally susceptible to injury caused by reactive oxygen species due to the immaturity of endogenous radical scavenging systems. It is well known that high oxygen levels experienced during the critical phase of maturation can profoundly influence developmental processes. Supraphysiological oxygen concentrations used for resuscitation or in the care of critically ill infants are known to have deleterious effects on the developing lung and retina, contributing to the pathophysiology of neonatal diseases like bronchopulmonary dysplasia and retinopathy of prematurity. Moreover, experimental work from the last decade suggests that hyperoxia also leads to neuronal and glial cell death, contributing to the injury of white and grey matter observed in preterm infants. During the critical phase of brain maturation, hyperoxia can alter developmental processes, resulting in the disruption of neural plasticity and myelination. However, oxygen therapy can often not be avoided in neonatal intensive care. Therefore, in situations requiring oxygen supplementation, in addition to the development of appropriate monitoring systems, protective and/or regenerative strategies are highly warranted. Here, we summarise the clinical and experimental evidence as well as potential therapeutic strategies, providing an overview of the pathophysiology of oxygen exposure on the developing central nervous system and its impact on neonatal brain injury.

Background: Untreated exposure to pain in preterm neonates might damage the vulnerable premature brain and alter development. Pain treatment is limited because analgesic agents may also have adverse neurodevelopmental consequences in newborns. Objective: To study the effects of neonatal pain and morphine treatment on the developing brain in a neonatal rat model. Methods: Newborn rats were randomly assigned to: treatment with formalin injections (group 1), saline injections (group 2) and controls receiving no injections (group 3). Treatment was given on postnatal days 1–3 (model A), 1–5 (model B) and 10–12 (model C). Brains were studied histologically and protein expression was evaluated (protein kinase C epsilon and doublecortin). Effects of preemptive morphine treatment were studied in the same models (models A+M and B+M). Results: Formalin injections resulted in increased apoptotic scores in models A and B. Saline injections increased the number of degenerative cells only in model B. Morphine showed protective effects in formalin-treated animals of model A+M and saline-treated animals of model B+M only. In model C, no neurodegenerative effects were detected. The protein expression of doublecortin showed a pain-related upregulation in the thalamus region, whereas protein kinase C epsilon expression was upregulated in the cortex. Conclusions: Severe inflammatory pain and pain caused by repetitive injections in neonatal rats may cause major changes in the developing brain during the first week of life. Morphine may only protect the newborn brain against these changes in specific situations.

Cerebral white matter injury is a leading cause of adverse neurodevelopmental outcome in prematurely born infants involving cognitive deficits in later life. Despite increasing knowledge about the pathophysiology of perinatal brain injury, therapeutic options are limited. In the adult demyelinating disease multiple sclerosis the sphingosine-1-phosphate (S1P) receptor modulating substance fingolimod (FTY720) has beneficial effects. Herein, we evaluated the neuroprotective potential of FTY720 in a neonatal model of oxygen-toxicity, which is associated with hypomyelination and impaired neuro-cognitive outcome. A single dose of FTY720 (1mg/kg) at the onset of neonatal hyperoxia (24h 80% oxygen on postnatal day 6) resulted in improvement of neuro-cognitive development persisting into adulthood. This was associated with reduced microstructural white matter abnormalities 4 months after the insult. In search of the underlying mechanisms potential non-classical (i.e. lymphocyte-independent) pathways were analysed shortly after the insult, comprising modulation of oxidative stress and local inflammatory responses as well as myelination, oligodendrocyte degeneration and maturation. Treatment with FTY720 reduced hyperoxia-induced oxidative stress, microglia activation and associated pro-inflammatory cytokine expression. In vivo and in vitro analyses further revealed that oxygen-induced hypomyelination is restored to control levels, which was accompanied by reduced oligodendrocyte degeneration and enhanced maturation. Furthermore, hyperoxia-induced elevation of S1P receptor 1 (S1P1) protein expression on in vitro cultured oligodendrocyte precursor cells was reduced by activated FTY720 and protection from degeneration is abrogated after selective S1P1 blockade. Finally, FTY720s' classical mode of action (i.e. retention of immune cells within peripheral lymphoid organs) was analysed demonstrating that FTY720 diminished circulating lymphocyte counts independent from hyperoxia. Cerebral immune cell counts remained unchanged by hyperoxia and by FTY720 treatment. Taken together, these results suggest that beneficial effects of FTY720 in neonatal oxygen-induced brain injury may be rather attributed to its anti-oxidative and anti-inflammatory capacity acting in concert with a direct protection of developing oligodendrocytes than to a modulation of peripheral lymphocyte trafficking. Thus, FTY720 might be a potential new therapeutic option for the treatment of neonatal brain injury through reduction of white matter damage.