Investigating Pathways of Ventilation Induced Brain Injury on Cerebral White Matter Inflammation and Injury After 24 h in Preterm Lambs

The synergistic effects of mechanical ventilation and intrauterine inflammation on cerebral inflammation in preterm fetal sheep

Background

Intrauterine inflammation and the requirement for mechanical ventilation independently increase the risk of perinatal brain injury and adverse neurodevelopmental outcomes. We aimed to investigate the effects of mechanical ventilation for 24 h, with and without prior exposure to intrauterine inflammation, on markers of brain inflammation and injury in the preterm sheep brain.

Methods

Chronically instrumented fetal sheep at ~115 days of gestation were randomly allocated to receive a single intratracheal dose of 1 mg lipopolysaccharide (LPS) or isovolumetric saline, then further randomly allocated 1 h after to receive mechanical ventilation with room air or no mechanical ventilation (unventilated control + saline [UVC, n = 7]; in utero mechanical ventilation + saline [VENT, n = 8], unventilated control + intratracheal LPS [UVC + LPS, n = 7]; in utero ventilation + intratracheal LPS [VENT + LPS, n = 7]). Serial fetal blood and plasma samples were collected throughout the experimental protocol for assessment of blood biochemistry and plasma interleukin (IL)-6 levels. After 24 h of mechanical ventilation, fetal brains were collected for RT-qPCR and immunohistochemical analyses.

Results

LPS exposure increased numbers of microglia and upregulated pro-inflammatory related genes within the cortical gray matter (GM) and subcortical white matter (SCWM) (pLPS  < 0.05). Mechanical ventilation alone increased astrocytic cell density in the periventricular white matter (PVWM) (pVENT  = 0.03) but had no effect on pro-inflammatory gene expression. The combination of ventilation and LPS increased plasma IL-6 levels (p < 0.02 vs. UVC and VENT groups), and exacerbated expression of pro-inflammatory-related genes (IL1β, TLR4, PTGS2, CXCL10) and microglial density (p < 0.05 vs. VENT).

Conclusion

This study demonstrates that 24 h of mechanical ventilation after exposure to intrauterine inflammation increased markers of systemic and brain inflammation and led to the upregulation of pro-inflammatory genes in the white matter. We conclude that 24 h of mechanical ventilation following intrauterine inflammation may precondition the preterm brain toward being more susceptible to inflammation-induced injury.

The performance of the practices associated with the occurrence of severe intraventricular hemorrhage in the very premature infants: data analysis from the Chinese neonatal network

BACKGROUND

The occurrence of severe intraventricular hemorrhage (sIVH) was high in the very preterm infants (VPIs) in China. The management strategies significantly contributed to the occurrence of sIVH in VPIs. However, the status of the perinatal strategies associated with sIVH for VPIs was rarely described across the multiple neonatal intensive care units (NICUs) in China. We aim to investigate the characteristics of the perinatal strategies associated with sIVH for VPIs across the multiple NICUs in China.

METHODS

This was a retrospective analysis of data from a prospective cohort of Chinese Neonatal Network (CHNN) dataset, enrolling infants born at 24+0-31+6 from 2019 to 2021. Eleven perinatal practices performed within the first 3 days of life were investigated including antenatal corticosteroids use, antenatal magnesium sulphate therapy, intubation at birth, placental transfusion, need for advanced resuscitation, initial inhaled gas of 100% FiO2 in delivery room, initial invasive respiratory support, surfactant and caffeine administration, early enteral feeding, and inotropes use. The performances of these practices across the multiple NICUs were investigated using the standard deviations of differences between expected probabilities and observations. The occurrence of sIVH were compared among the NICUs.

RESULTS

A total of 24,226 infants from 55 NICUs with a mean (SD) gestational age of 29.5 (1.76) and mean (SD) birthweight of 1.31(0.32) were included. sIVH was detected in 5.1% of VPIs. The rate of the antenatal corticosteroids, MgSO4 therapy, and caffeine was 80.0%, 56.4%, and 31.5%, respectively. We observed significant relationships between sIVH and intubation at birth (AOR 1.52, 95% CI 1.13 to 1.75) and initial invasive respiratory support (AOR 2.47, 95% CI 2.15 to 2.83). The lower occurrence of sIVH (4.8%) was observed corresponding with the highest utility of standard antenatal care, the lowest utility of invasive practices, and early enteral feeding administration.

CONCLUSIONS

The current evidence-based practices were not performed in each VPI as expected among the studied Chinese NICUs. The higher utility of the invasive practices could be related to the occurrence of sIVH.

Early administration of umbilical cord blood cells following brief high tidal volume ventilation in preterm sheep: a cautionary tale

BACKGROUND

Umbilical cord blood (UCB) cells are a promising treatment for preterm brain injury. Access to allogeneic sources of UCB cells offer the potential for early administration to optimise their therapeutic capacities. As preterm infants often require ventilatory support, which can contribute to preterm brain injury, we investigated the efficacy of early UCB cell administration following ventilation to reduce white matter inflammation and injury.

METHODS

Preterm fetal sheep (0.85 gestation) were randomly allocated to no ventilation (SHAM; n = 5) or 15 min ex utero high tidal volume ventilation. One hour following ventilation, fetuses were randomly allocated to i.v. administration of saline (VENT; n = 7) or allogeneic term-derived UCB cells (24.5 ± 5.0 million cells/kg; VENT + UCB; n = 7). Twenty-four hours after ventilation, lambs were delivered for magnetic resonance imaging and post-mortem brain tissue collected. Arterial plasma was collected throughout the experiment for cytokine analyses. To further investigate the results from the in vivo study, mononuclear cells (MNCs) isolated from human UCB were subjected to in vitro cytokine-spiked culture medium (TNFα and/or IFNγ; 10 ng/mL; n = 3/group) for 16 h then supernatant and cells collected for protein and mRNA assessments respectively.

RESULTS

In VENT + UCB lambs, systemic IFNγ levels increased and by 24 h, there was white matter neuroglial activation, vascular damage, reduced oligodendrocytes, and increased average, radial and mean diffusivity compared to VENT and SHAM. No evidence of white matter inflammation or injury was present in VENT lambs, except for mRNA downregulation of OCLN and CLDN1 compared to SHAM. In vitro, MNCs subjected to TNFα and/or IFNγ displayed both pro- and anti-inflammatory characteristics indicated by changes in cytokine (IL-18 & IL-10) and growth factor (BDNF & VEGF) gene and protein expression compared to controls.

CONCLUSIONS

UCB cells administered early after brief high tidal volume ventilation in preterm fetal sheep causes white matter injury, and the mechanisms underlying these changes are likely dysregulated responses of the UCB cells to the degree of injury/inflammation already present. If immunomodulatory therapies such as UCB cells are to become a therapeutic strategy for preterm brain injury, especially after ventilation, our study suggests that the inflammatory state of the preterm infant should be considered when timing UCB cells administration.

Risk factors for brain injury in premature infants with twin-to-twin transfusion syndrome: a retrospective cohort study

Background

Brain injury (BI) is prevalent in premature infants with twin-to-twin transfusion syndrome (TTTS), while risk factors of BI in these patients remains unknown. Our study aims to discern potential risk factors that contribute to BI in premature infants with TTTS.

Methods

We conducted a retrospective cohort and analyzed clinical data of premature infants diagnosed with TTTS at the Northwest Women's and Children's Hospital between January 1, 2015 and January 1, 2020. Data included the infants' perinatal information, key postnatal examinations, laboratory tests, and treatments.

Results

Of the 84 patients enrolled in the study, 22 (26.2%) were categorized in the BI group and 62 (73.8%) in the non-BI group, based on cranial imaging. No significant differences were found at baseline between the groups in relation to the proportion of males (40.9% vs. 35.5%, P=0.845), median gestational age (weeks) [31.9 (31.5, 33.4) vs. 34.2 (31.6, 35.4), P=0.061], average weight (g) (1,676.4±567.5 vs. 1,845.2±511.7, P=0.200), maternal age (years) [29.5 (26.0, 31.0) vs. 28.5 (27.8, 31.0), P=0.656], the proportion of in-vitro fertilization (9.1% vs. 16.1%, P=0.648), cesarean sections (86.4% vs. 93.5%, P=0.549) or TTTS donor infants (50.0% vs. 51.6%, P=0.897). Multivariate logistic regression analysis indicated that invasive mechanical ventilation [invasive mechanical ventilation (IMV); odds ratio (OR) =4.365; 95% confidence interval (CI): 1.066-17.870; P=0.040], [necrotizing enterocolitis (NEC); OR =8.632; 95% CI: 1.542-48.318; P=0.014], [single intrauterine fetal demise (sIUFD); OR =14.067; 95% CI: 1.298-224.421; P=0.031], and a 5-minute Apgar score <9 (OR =4.663; 95% CI: 1.015-21.419; P=0.048) were strongly associated with BI in TTTS premature infants.

Conclusions

Our study identifies IMV, NEC, sIUFD, and a 5-minute Apgar score <9 as independent risk factors for BI in premature infants with TTTS.

Mechanical ventilation induces brainstem inflammation in preterm fetal sheep

Background

Preterm infants have immature respiratory drive and often require prolonged periods of mechanical ventilation. Prolonged mechanical ventilation induces systemic inflammation resulting in ventilation-induced brain injury, however its effect on brainstem respiratory centers is unknown. We aimed to determine the effects of 24 h of mechanical ventilation on inflammation and injury in brainstem respiratory centres of preterm fetal sheep.

Methods

Preterm fetal sheep at 110 ± 1 days (d) gestation were instrumented to provide mechanical ventilation in utero. At 112 ± 1 d gestation, fetuses received either mechanical ventilation (VENT; n = 7; 3 ml/kg) for 24 h, or no ventilation (CONT; n = 6). At post-mortem, fetal brainstems were collected for assessment of mRNA and histological markers of inflammation and injury.

Results

In utero ventilation (IUV) did not alter any blood-gas parameters. IUV significantly increased systemic IL-6 and IL-8 concentrations over the 24 h period compared to CONT. The number of ameboid microglia within the nucleus tractus solitarius and the raphe nucleus increased in VENT fetuses (p < 0.05 for both vs. control). The % area fraction of GFAP + staining was not significantly higher within the preBötzinger complex (p = 0.067) and retrotrapezoid nucleus and parafacial respiratory group (p = 0.057) in VENT fetuses compared to CONT. Numbers of caspase-3 and TUNEL-positive cells were similar between groups. Gene expression (mRNA) levels of inflammation, injury, cell death and prostaglandin synthesis within the brainstem were similar between groups.

Conclusion

Mechanical ventilation induces a systemic inflammatory response with only moderate inflammatory effects within the brainstem respiratory centres of preterm fetal sheep.