Vascular network expansion, integrity of blood-brain interfaces, and cerebrospinal fluid cytokine concentration during postnatal development in the normal and jaundiced rat

Molecular events in brain bilirubin toxicity revisited

The mechanisms involved in bilirubin neurotoxicity are still far from being fully elucidated. Several different events concur to damage mainly the neurons among which inflammation and alteration of the redox state play a major role. An imbalance of cellular calcium homeostasis has been recently described to be associated with toxic concentrations of bilirubin, and this disequilibrium may in turn elicit an inflammatory reaction. The different and age-dependent sensitivity to bilirubin damage must also be considered in describing the dramatic clinical picture of bilirubin-induced neurological damage (BIND) formerly known as kernicterus spectrum disorder (KSD). This review aims to critically address what is known and what is not in the molecular events of bilirubin neurotoxicity to provide hints for a better diagnosis and more successful treatments. Part of these concepts have been presented at the 38th Annual Audrey K. Brown Kernicterus Symposium of Pediatric American Society, Washington DC, May 1, 2023.

Neonatal IL-4 Over-Exposure is Accompanied by Macrophage Accumulation in Dura Mater After Instant Anti-inflammatory Cytokine Response in CSF

Multiple studies have shown that clinical events resulting into neonatal IL-4 over-exposure, such as asthma in early life and food allergy, were associated with brain damage and that the neuroinflammation induced by them might lead to cognitive impairments, anxiety-/depressive-like behaviors. IL-4 is the most major elevated cytokine in periphery when these clinical events occur and peripheral IL-4 level positively correlates with the severity of those events. Our previous studies have verified that neonatal IL-4 over-exposure induced a delayed neuroinflammatory damage in rodents, which might have adverse implications for brain development and cognition. Neuroinflammation in brain parenchyma is often accompanied by changes in CSF cytokines levels. However, whether the cytokines levels in CSF change after neonatal IL-4 over-exposure is unknown. Here, we found a delayed pro-inflammatory cytokines response (higher IL-6, IL-1β and, TNF levels) in both hippocampus and CSF after an instant anti-inflammatory cytokine response in IL-4 over-exposed rats. Moreover, the pro-inflammatory cytokines response appeared earlier in CSF than in hippocampus. The level of each of the pro-inflammatory cytokines in CSF positively correlated with that in hippocampus at the age of postnatal day 42. More microglia numbers/activation and higher M-CSF level in the hippocampus in IL-4 over-exposed rats were also observed. Furthermore, there were more macrophages with inflammatory activation in dural mater of IL-4 over-exposed rats. In sum, neonatal IL-4 over-exposure in rats induces delayed inflammation in CSF, suggesting CSF examination may serve as a potential method in predicting delayed neuroinflammation in brain following neonatal IL-4 over-exposure.

More than a small adult brain: Lessons from chemotherapy-induced cognitive impairment for modelling paediatric brain disorders

Childhood is recognised as a period of immense physical and emotional development, and this, in part, is driven by underlying neurophysiological transformations. These neurodevelopmental processes are unique to the paediatric brain and are facilitated by augmented rates of neuroplasticity and expanded neural stem cell populations within neurogenic niches. However, given the immaturity of the developing central nervous system, innate protective mechanisms such as neuroimmune and antioxidant responses are functionally naïve which results in periods of heightened sensitivity to neurotoxic insult. This is highly relevant in the context of paediatric cancer, and in particular, the neurocognitive symptoms associated with treatment, such as surgery, radio- and chemotherapy. The vulnerability of the developing brain may increase susceptibility to damage and persistent symptomology, aligning with reports of more severe neurocognitive dysfunction in children compared to adults. It is therefore surprising, given this intensified neurocognitive burden, that most of the pre-clinical, mechanistic research focuses exclusively on adult populations and extrapolates findings to paediatric cohorts. Given this dearth of age-specific research, throughout this review we will draw comparisons with neurodevelopmental disorders which share comparable pathways to cancer treatment related side-effects. Furthermore, we will examine the unique nuances of the paediatric brain along with the somatic systems which influence neurological function. In doing so, we will highlight the importance of developing in vitro and in vivo paediatric disease models to produce age-specific discovery and clinically translatable research.

Correlation between hyperbilirubinemia risk and immune cell mitochondria parameters in neonates with jaundice

Purpose

To explore the correlation between mitochondria parameters of immune cells and hyperbilirubinemia risk in hospitalized neonates with jaundice.

Methods

This retrospective study included jaundiced neonates born between September 2020 and March 2022 at Shaoxing Keqiao Women & Children's Hospital. The neonates were divided into low, intermediate-low, intermediate-high, and high-risk groups according to the hyperbilirubinemia risk. The purpose parameters including percentage, absolute count, mitochondrial mass (MM), and single-cell MM (SCMM) of peripheral blood T lymphocytes detected by flow cytometry were collected.

Results

Finally, 162 neonates with jaundice (47, 41, 39, and 35 with low, intermediate-low, intermediate-high, and high-risk) were included. CD3⁺ SCMM was significantly higher in the high-risk group compared with the low and intermediate-low-risk groups (both P < 0.0083), CD4⁺ SCMM was significantly higher in the high-risk group compared with the three other groups (all P < 0.0083), and CD8⁺ SCMM was significantly higher in the intermediate-low and high-risk groups compared with the low-risk group (both P < 0.0083). CD3⁺ (r = 0.34, P < 0.001) and CD4⁺ (r = 0.20, P = 0.010) SCMM positively correlated with bilirubin levels.

Conclusions

The mitochondrial SCMM parameters differed significantly among jaundiced neonates with different hyperbilirubinemia risks. CD3⁺ and CD4⁺ T cell SCMM values were positively correlated with the serum bilirubin levels, and might correlated with hyperbilirubinemia risk.

Relationship between blood-brain barrier changes and drug metabolism under high-altitude hypoxia: obstacle or opportunity for drug transport?

The blood-brain barrier is essential for maintaining the stability of the central nervous system and is also crucial for regulating drug metabolism, changes of blood-brain barrier's structure and function can influence how drugs are delivered to the brain. In high-altitude hypoxia, the central nervous system's function is drastically altered, which can cause disease and modify the metabolism of drugs in vivo. Changes in the structure and function of the blood-brain barrier and the transport of the drug across the blood-brain barrier under high-altitude hypoxia, are regulated by changes in brain microvascular endothelial cells, astrocytes, and pericytes, either regulated by drug metabolism factors such as drug transporters and drug-metabolizing enzymes. This article aims to review the effects of high-altitude hypoxia on the structure and function of the blood-brain barrier as well as the effects of changes in the blood-brain barrier on drug metabolism. We also hypothesized and explore the regulation and potential mechanisms of the blood-brain barrier and associated pathways, such as transcription factors, inflammatory factors, and nuclear receptors, in regulating drug transport under high-altitude hypoxia.

Age dependent contribution of entry via the CSF to the overall brain entry of small and large hydrophilic markers

Background

Apparent permeability of the blood brain barrier to hydrophilic markers has been shown to be higher in the developing brain. Apart from synthesis in situ, any substance detected in the brain parenchyma can originate from two sources: directly through blood vessels of brain vasculature and/or indirectly by entry from the cerebrospinal fluid (CSF) after transfer across the choroid plexuses. The relative quantitative contribution of these two routes to the overall brain entry remains unclear.

Methods

In rats at embryonic day 16, 19 and postnatal day 4 and young adults, a small (sucrose, mw. 342 Da) or a large (dextran, mw. 70 kDa) radiolabelled hydrophilic marker was injected intravenously for very short periods of time (30 s to 5 min) before collection of plasma, cerebrospinal fluid (CSF) and brain samples. Results are presented as concentration ratios between radioactivity measured in CSF or brain and that in plasma (%).

Results

The dextran brain/plasma ratio five minutes post injection was similar (2–4%) from E16 to adulthood whereas the sucrose brain/plasma ratio was significantly higher in fetal brains, but was comparable to dextran values in the adult. Sucrose CSF/plasma ratios were also significantly higher in fetal animals and decreased with age. In very short experiments involving fetal animals, entry of sucrose into the CSF after only 30 s was similar to that of dextran and both markers showed similar brain/plasma ratios.

Conclusions

In the developing brain the apparent higher brain entry of a small hydrophilic marker such as sucrose can be attributed to its higher entry into the CSF and subsequent diffusion into the brain. By contrast, movement of a larger marker like 70 kDa dextran is restricted firstly by choroid plexus epithelial tight junctions and secondly by specialised junctions in the neuroependymal interface between the CSF and brain. Brain/plasma ratios of 70 kDa dextran were similar in fetal and adult rats. Therefore 70 kDa dextran should be considered an appropriate marker if brain residual vascular space is to be measured, especially in younger animals.

Models of bilirubin neurological damage: lessons learned and new challenges

OBJECTIVE

Jaundice (icterus) is the visible manifestation of the accumulation of bilirubin in the tissue and is indicative of potential toxicity to the brain. Since its very first description more than 2000 years ago, many efforts have been undertaken to understand the molecular determinants of bilirubin toxicity to neuronal cells to reduce the risk of neurological sequelae through the use of available chemicals and in vitro, ex vivo, in vivo, and clinical models. Although several studies have been performed, important questions remain unanswered, such as the reasons for regional sensitivity and the interplay with brain development. The number of new molecular effects identified has increased further, which has added even more complexity to the understanding of the condition. As new research challenges emerged, so does the need to establish solid models of prematurity.

METHODS

This review critically summarizes the key mechanisms of severe neonatal hyperbilirubinemia and the use of the available models and technologies for translational research.

IMPACT

We critically review the conceptual dogmas and models used for studying bilirubin-induced neurotoxicity. We point out the pitfalls and translational gaps, and suggest new clinical research challenges. We hope to inform researchers on the pro and cons of the models used, and to help direct their experimental focus in a most translational research.