Antenatal events causing neonatal brain injury in premature infants

Imaging of Premature Infants

According to the World Health Organization (WHO), 15 million babies are born preterm each year. Preterm infants are those born at less than 37 weeks, while extremely and very preterm neonates include those born at 22 to less than 32 weeks gestational age. Infants that fail to make it to term are missing a key part in neurodevelopment, as weeks 24 to 40 are a critical period of brain development. Neonatal brain injury is a crucial predictor for mortality and morbidity in premature and low birth weight (<1500 g) infants. Although the complications associated with preterm birth continue to be the number one cause of death in children under 5, the survival rates are increasing (Volpe, 2019). Despite this, the incidence of comorbidities, such as learning disabilities and visual and hearing problems, is still high. The functional deficits seen in these infants can be contributed to the white matter abnormalities (WMA) that have been found in 50% to 80% of extremely and very preterm neonates. While numerous, the etiology of the neonatal brain injury is essential for determining the mortality and morbidities of the infant, as there is an increased risk for both intraventricular hemorrhage (IVH) and periventricular leukomalacia (PVL), which can be attributed to their lack of cerebrovascular autoregulation and hypoxic events. Neuroimaging plays a key role in detecting and assessing these neurologic injuries that preterm infants are at risk for. It is essential to diagnose these events early on to assess neurologic damage, minimize disease progression, and provide supportive care. Brain MRI and cranial ultrasound (CUS) are both extensively used neuroimaging techniques to assess WMA, and it has become ever more important to determine the best imaging techniques and modalities with the increasing survival rates and high incidence of comorbidities among these infants.

Glial cell responses in a murine multifactorial perinatal brain injury model

The impact of traumatic brain injury during the perinatal period, which coincides with glial cell (astrocyte and oligodendrocyte) maturation was assessed to determine whether a second insult, e.g., increased inflammation due to remote bacterial exposure, exacerbates the initial injury's effects, possibly eliciting longer-term brain damage. Thus, a murine multifactorial injury model incorporating both mechanisms consisting of perinatal penetrating traumatic brain injury, with or without intraperitoneal injection of lipopolysaccharide (LPS), an analog of remote pathogen exposure has been developed. Four days after injury, gene expression changes for different cell markers were assessed using mRNA in situ hybridization (ISH) and qPCR. Astrocytic marker mRNA levels increased in the stab-alone and stab-plus-LPS treated animals indicating reactive gliosis. Activated microglial/macrophage marker levels, increased in the ipsilateral sides of stab and stab-plus LPS animals by P10, but the differences resolved by P15. Ectopic expression of glial precursor and neural stem cell markers within the cortical injury site was observed by ISH, suggesting that existing precursors and neural stem cells migrate into the injured areas to replace the cells lost in the injury process. Furthermore, single exposure to LPS concomitant with acute stab injury affected the oligodendrocyte population in both the injured and contralateral uninjured side, indicating that after compromise of the blood-brain barrier integrity, oligodendrocytes become even more susceptible to inflammatory injury. This multifactorial approach should lead to a better understanding of the pathogenic sequelae observed as a consequence of perinatal brain insult/injury, caused by combinations of trauma, intrauterine infection, hypoxia and/or ischemia in humans.

Angiogenesis induced by prenatal ischemia predisposes to periventricular hemorrhage during postnatal mechanical ventilation

BACKGROUND

Three risk factors are associated with hemorrhagic forms of encephalopathy of prematurity (EP): (i) prematurity, (ii) in utero ischemia (IUI) or perinatal ischemia, and (iii) mechanical ventilation. We hypothesized that IUI would induce an angiogenic response marked by activation of vascular endothelial growth factor (VEGF) and matrix metalloproteinase-9 (MMP-9), the latter degrading vascular basement membrane and increasing vulnerability to raised intravenous pressure during positive pressure mechanical ventilation.

METHODS

We studied a rat model of hemorrhagic-EP characterized by periventricular hemorrhages in which a 20-min episode of IUI is induced at E19, pups are born naturally at E21-22, and on P0, are subjected to a 20-min episode of positive pressure mechanical ventilation. Tissues were studied by H&E staining, immunolabeling, immunoblot, and zymography.

RESULTS

Mechanical ventilation of rat pups 2-3 d after 20-min IUI caused widespread hemorrhages in periventricular tissues. IUI resulted in upregulation of VEGF and MMP-9. Zymography confirmed significantly elevated gelatinase activity. MMP-9 activation was accompanied by severe loss of MMP-9 substrates, collagen IV and laminin, in microvessels in periventricular areas.

CONCLUSION

Our findings are consistent with the hypothesis that positive pressure mechanical ventilation of the newborn in the context of recent prenatal ischemia/hypoxia can predispose to periventricular hemorrhages.

The potential for cell-based therapy in perinatal brain injuries

Perinatal brain injuries are a leading cause of cerebral palsy worldwide. The potential of stem cell therapy to prevent or reduce these impairments has been widely discussed within the medical and scientific communities and an increasing amount of research is being conducted in this field. Animal studies support the idea that a number of stem cells types, including cord blood and mesenchymal stem cells have a neuroprotective effect in neonatal hypoxia-ischemia. Both these cell types are readily available in a clinical setting. The mechanisms of action appear to be diverse, including immunomodulation, activation of endogenous stem cells, release of growth factors, and anti-apoptotic effects. Here, we review the different types of stem cells and progenitor cells that are potential candidates for therapeutic strategies in perinatal brain injuries, and summarize recent preclinical and clinical studies.

The protective effect of glibenclamide in a model of hemorrhagic encephalopathy of prematurity

We studied a model of hemorrhagic encephalopathy of prematurity (EP) that closely recapitulates findings in humans with hemorrhagic EP. This model involves tandem insults of 20 min intrauterine ischemia (IUI) plus an episode of elevated venous pressure induced by intraperitoneal glycerol on post-natal day (P) 0. We examined Sur1 expression, which is upregulated after focal ischemia but has not been studied after brief global ischemia including IUI. We found that 20 min IUI resulted in robust upregulation of Sur1 in periventricular microvessels and tissues. We studied tandem insult pups from untreated or vehicle-treated dams (TI-CTR), and tandem insult pups from dams administered a low-dose, non-hypoglycemogenic infusion of the Sur1 blocker, glibenclamide, for 1 week after IUI (TI-GLIB). Compared to pups from the TI-CTR group, pups from the TI-GLIB group had significantly fewer and less severe hemorrhages on P1, performed significantly better on the beam walk and accelerating Rotarod on P35 and in tests of thigmotaxis and rapid learning on P35–49, and had significantly greater body and brain weights at P52. We conclude that low-dose glibenclamide administered to the mother at the end of pregnancy protects pups subjected to IUI from post-natal events of elevated venous pressure and its consequences.

Neutral head positioning in premature infants for intraventricular hemorrhage prevention: an evidence-based review

With the advancement of neonatal medicine during the past several decades, premature and critically ill infants are living past the neonatal period and surviving. The survival of these infants at smaller birth weights and younger gestational ages puts them at an increased risk for intraventricular hemorrhages (IVHs). Although shifts in cerebral perfusion have been linked to the development of these brain bleeds, many seemingly benign care activities have been linked to changes in cerebral blood flow patterns, possibly contributing to IVHs. The purpose of this article is to evaluate the current evidence to determine if the practice of midline positioning for infants born less than 32 weeks gestation for possible IVH prevention is supported by the literature. Many of the researchers involved in these studies attributed the consequential venule leakage of blood to occlusion of the jugular venous drainage system following a turn in the position of the head. Additionally, the articles that examined the connection between the effects of head tilting on brain hemodynamics attributed changes on the infants' potential inability to autoregulate cerebral blood flow adequately. Both of these findings were linked to the development of IVHs. Based on physiologic data and expert opinion, the authors found support in the literature and recommend implementing a plan of care that includes midline head positioning for premature infants.