Slow rewarming after hypothermia does not ameliorate white matter injury after hypoxia-ischemia in near-term fetal sheep.

BACKGROUND: The optimal rate to rewarm infants after therapeutic hypothermia is unclear. In this study we examined whether slow rewarming after 72 h of hypothermia would attenuate white matter injury. METHODS: Near-term fetal sheep received sham occlusion (n = 8) or cerebral ischemia for 30 min, followed by normothermia (n = 7) or hypothermia from 3-72 h, with either spontaneous fast rewarming (n = 8) within 1 h, or slow rewarming at ~0.5 °C/h (n = 8) over 10 h. Fetuses were euthanized 7 days later. RESULTS: Ischemia was associated with loss of total and mature oligodendrocytes, reduced expression of myelin proteins and induction of microglia and astrocytes, compared with sham controls (P < 0.05). Both hypothermia protocols were associated with a significant increase in numbers of total and mature oligodendrocytes, area fraction of myelin proteins and reduced numbers of microglia and astrocytes, compared with ischemia-normothermia (P < 0.05). There was no difference in the number of oligodendrocytes, microglia or astrocytes or expression of myelin proteins between fast and slow rewarming after hypothermia. CONCLUSION: The rate of rewarming after a clinically relevant duration of hypothermia had no apparent effect on white matter protection by hypothermia after cerebral ischemia in near-term fetal sheep. IMPACT: Persistent white matter injury is a major contributor to long-term disability after neonatal encephalopathy despite treatment with therapeutic hypothermia. The optimal rate to rewarm infants after therapeutic hypothermia is unclear; current protocols were developed on a precautionary basis. We now show that slow rewarming at 0.5 °C/h did not improve histological white matter injury compared with rapid spontaneous rewarming after a clinically established duration of hypothermia in near-term fetal sheep.

Persistent cortical and white matter inflammation after therapeutic hypothermia for ischemia in near-term fetal sheep.

BACKGROUND: Therapeutic hypothermia significantly improves outcomes after moderate-severe hypoxic-ischemic encephalopathy (HIE), but it is partially effective. Although hypothermia is consistently associated with reduced microgliosis, it is still unclear whether it normalizes microglial morphology and phenotype. METHODS: Near-term fetal sheep (n = 24) were randomized to sham control, ischemia-normothermia, or ischemia-hypothermia. Brain sections were immunohistochemically labeled to assess neurons, microglia and their interactions with neurons, astrocytes, myelination, and gitter cells (microglia with cytoplasmic lipid granules) 7 days after cerebral ischemia. Lesions were defined as areas with complete loss of cells. RNAscope® was used to assess microglial phenotype markers CD86 and CD206. RESULTS: Ischemia-normothermia was associated with severe loss of neurons and myelin (p < 0.05), with extensive lesions, astrogliosis and microgliosis with a high proportion of gitter cells (p < 0.05). Microglial wrapping of neurons was present in both the ischemia groups. Hypothermia improved neuronal survival, suppressed lesions, gitter cells and gliosis (p < 0.05), and attenuated the reduction of myelin area fraction. The "M1" marker CD86 and "M2" marker CD206 were upregulated after ischemia. Hypothermia partially suppressed CD86 in the cortex only (p < 0.05), but did not affect CD206. CONCLUSIONS: Hypothermia prevented lesions after cerebral ischemia, but only partially suppressed microglial wrapping and M1 marker expression. These data support the hypothesis that persistent upregulation of injurious microglial activity may contribute to partial neuroprotection after hypothermia, and that immunomodulation after rewarming may be an important therapeutic target.

Treating Seizures after Hypoxic-Ischemic Encephalopathy-Current Controversies and Future Directions.

Seizures are common in newborn infants with hypoxic-ischemic encephalopathy and are highly associated with adverse neurodevelopmental outcomes. The impact of seizure activity on the developing brain and the most effective way to manage these seizures remain surprisingly poorly understood, particularly in the era of therapeutic hypothermia. Critically, the extent to which seizures exacerbate brain injury or merely reflect the underlying evolution of injury is unclear. Current anticonvulsants, such as phenobarbital and phenytoin have poor efficacy and preclinical studies suggest that most anticonvulsants are associated with adverse effects on the developing brain. Levetiracetam seems to have less potential neurotoxic effects than other anticonvulsants but may not be more effective. Given that therapeutic hypothermia itself has significant anticonvulsant effects, randomized controlled trials of anticonvulsants combined with therapeutic hypothermia, are required to properly determine the safety and efficacy of these drugs. Small clinical studies suggest that prophylactic phenobarbital administration may improve neurodevelopmental outcomes compared to delayed administration; however, larger high-quality studies are required to confirm this. In conclusion, there is a distinct lack of high-quality evidence for whether and to what extent neonatal seizures exacerbate brain damage after hypoxia-ischemia and how best to manage them in the era of therapeutic hypothermia.

Dysmaturation of sleep state and electroencephalographic activity after hypoxia-ischaemia in preterm fetal sheep.

Antenatal hypoxia-ischaemia (HI) in preterm fetal sheep can trigger delayed evolution of severe, cystic white matter injury (WMI), in a similar timecourse to WMI in preterm infants. We therefore examined how severe hypoxia-ischaemia affects recovery of electroencephalographic (EEG) activity. Chronically instrumented preterm fetal sheep (0.7 gestation) received 25 min of complete umbilical cord occlusion (UCO, n = 9) or sham occlusion (controls, n = 9), and recovered for 21 days. HI was associated with a shift to lower frequency EEG activity for the first 5 days with persisting loss of EEG power in the delta and theta bands, and initial loss of power in the alpha and beta bands in the first 14 days of recovery. In the final 3 days of recovery, there was a marked rhythmic shift towards higher frequency EEG activity after UCO. The UCO group spent less time in high-voltage sleep, and in the early evening (7:02 pm ± 47 min) abruptly stopped cycling between sleep states, with a shift to a high frequency state for 2 h 48 min ± 40 min, with tonic electromyographic activity. These findings demonstrate persisting EEG and sleep state dysmaturation after severe hypoxia-ischaemia. Loss of fetal or neonatal sleep state cycling in the early evening may be a useful biomarker for evolving cystic WMI.

Blockade of connexin hemichannels with tonabersat protects against mild hypoxic ischemic brain injury in neonatal rats.

BACKGROUND AND PURPOSE: There is growing evidence that infants with mild hypoxic-ischemic (HI) encephalopathy have increased risk of brain injury and adverse neurodevelopmental outcomes. Currently, there is no approved treatment for these infants. It was previously shown that blocking connexin 43 hemichannels is neuroprotective in models of moderate to severe HI injury. However, it is yet to be established whether these channels play a role in the evolution of mild HI brain injury, and whether blocking these channels after mild HI is neuroprotective. METHODS: HI was induced in postnatal day 10 rats of both sexes by right carotid artery ligation followed by 80 min of hypoxia in 8% oxygen. Pups receiving HI were randomised to receive intraperitoneal injections of either saline, vehicle (2-hydroxypropyl-beta-cyclodextrin polyethylene glycol-400), or tonabersat (2 mg/kg), at 60 min, 24 h, and 48 h after hypoxia. Seven days after HI, brains were harvested for measurement of volume loss and histological analysis. RESULTS: HI resulted in a significant reduction in hemispheric, hippocampal, and white matter volumes, which were significantly attenuated after treatment with tonabersat. HI was also associated with a significant reduction in numbers of neurons in the CA1 and CA3 hippocampal regions, a reduction in the numbers of oligodendrocytes in the corpus callosum, and an increase in the number of astrocytes in both regions, which were significantly attenuated by tonabersat treatment. There were no differences in rectal temperatures between tonabersat- and vehicle-treated rat pups. CONCLUSIONS: Blockade of connexin hemichannels with tonabersat significantly reduced mild HI injury in the hippocampus and white matter, without causing hypothermia.

Connexins, Pannexins and Gap Junctions in Perinatal Brain Injury.

Perinatal brain injury secondary to hypoxia-ischemia and/or infection/inflammation remains a major cause of disability. Therapeutic hypothermia significantly improves outcomes, but in randomized controlled trials nearly half of infants still died or survived with disability, showing that additional interventions are needed. There is growing evidence that brain injury spreads over time from injured to previously uninjured regions of the brain. At least in part, this spread is related to opening of connexin hemichannels and pannexin channels, both of which are large conductance membrane channels found in many brain cells. Opening of these membrane channels releases adenosine triphosphate (ATP), and other neuroactive molecules, into the extracellular space. ATP has an important role in normal signaling, but pathologically can trigger the assembly of the multi-protein inflammasome complex. The inflammasome complex promotes activation of inflammatory caspases, and release of inflammatory cytokines. Overall, the connexin hemichannel appears to play a primary role in propagation of injury and chronic disease, and connexin hemichannel blockade has been shown to be neuroprotective in multiple animal models. Thus, there is potential for some blockers of connexin or pannexin channels to be developed into targeted interventions that could be used in conjunction with or separate to therapeutic hypothermia.

Challenges in developing therapeutic strategies for mild neonatal encephalopathy.

There is increasing evidence that infants with mild neonatal encephalopathy (NE) have significant risks of mortality, brain injury and adverse neurodevelopmental outcomes. In the era of therapeutic hypothermia, infants need to be diagnosed within 6 hours of birth, corresponding with the window of opportunity for treatment of moderate to severe NE, compared to the retrospective grading over 2 to 3 days, typically with imaging and formal electroencephalographic assessment in the pre-hypothermia era. This shift in diagnosis may have increased the apparent prevalence of brain damage and poor neurological outcomes seen in infants with mild NE in the era of hypothermia. Abnormal short term outcomes observed in infants with mild NE include seizures, abnormal neurologic examination at discharge, abnormal brain magnetic resonance imaging and difficulty feeding. At 2 to 3 years of age, mild NE has been associated with an increased risk of autism, language and cognitive deficits. There are no approved treatment strategies for these infants as they were not included in the initial randomized controlled trials for therapeutic hypothermia. However, there is already therapeutic creep, with many centers treating infants with mild NE despite the limited evidence for its safety and efficacy. The optimal duration of treatment and therapeutic window of opportunity for effective treatment need to be specifically established for mild NE as the evolution of injury is likely to be slower, based on preclinical data. Randomized controlled trials of therapeutic hypothermia for infants with mild NE are urgently required to establish the safety and efficacy of treatment. This review will examine the evidence for adverse outcomes after mild NE and dissect some of the challenges in developing therapeutic strategies for mild NE, before analyzing the evidence for therapeutic hypothermia and other strategies for treatment of these infants.

Electrophysiological Characterization of Novel Effects of the Uptake-2 Blocker Decynium-22 (D-22) on Dopaminergic Neurons in the Substantia Nigra Pars Compacta.

Extracellular levels of dopamine (DA) and other monoamines in the brain depend not only on the classic transporters encoded by SLC6A gene family such as DAT, NET and SERT, but also a more recently identified group of low-affinity/high-capacity 'Uptake-2' transporters, mainly OCT3 and PMAT. The most frequently used pharmacological tool in functional studies of Uptake-2 is decynium-22 (D-22) known to block these transporters. However, the effectiveness of this drug in enhancing extracellular DA remains uncertain. Our aim was to test the hypothesis that D-22 increases extracellular levels of DA released from the somatodendritic region of dopaminergic neurons in the substantia nigra pars compacta (SNc) by reducing the OCT3/PMAT-dependent component of DA uptake. Extracellular DA was assessed indirectly, by evoking D2-IPSCs in SNc neurons following stimulated release of this neurotransmitter in midbrain slices obtained from mice. Recordings were conducted after partial inhibition of DAT with nomifensine, and after application of L-DOPA which increased the releasable DA pool. Contrary to our expectations, D-22 reduced, rather than increased, the amplitude of D2-IPSCs. Other effects included inhibition of GABAB-IPSCs and Ih current, and a reduction in firing frequency of nigral neurons. These results show that in addition to the previously known non-specific inhibitory action on α1 adrenoceptors, D-22 exerts additional off-target effects by inhibiting dopaminergic and GABAergic synaptic transmission in the SNc and the spontaneous (pacemaker) activity of nigral neurons. It remains to be established if these novel effects contribute to a reduction in spontaneous locomotor activity reported in previous studies after systemic drug administration.

Type 2 Biomarkers and Prediction of Future Exacerbations and Lung Function Decline in Adult Asthma.

BACKGROUND: Type 2 biomarkers that predict both likelihood of future severe exacerbations and response to mAb therapy in asthma would be useful clinically in identifying patients both at greater risk of hospitalization and most likely to benefit from mAb therapy. OBJECTIVE: To describe the association between type 2 biomarkers, blood eosinophils, fractional exhaled nitric oxide (Feno), serum periostin, and serum IgE, and time to severe exacerbation in a broad asthma population. METHODS: Participants from 2 adult asthma cohorts with baseline measurements of blood eosinophils, Feno, serum periostin, and serum IgE were reviewed after at least 12 months to obtain an exacerbation history, corroborated with general practitioner and hospital medical records. The association between baseline type 2 biomarkers and time to exacerbation was described by Cox proportional hazard ratios (HRs) using multivariate models. RESULTS: A total of 212 participants were followed for a median (range) 3.8 (1.1-5.3) years; 67 of 212 (32%) had at least 1 severe exacerbation. The HRs (95% CI) of baseline type 2 biomarkers and time to exacerbation were as follows: blood eosinophils per 0.1 × 109/L increase, 0.89 (0.76-1.05), P = .17; log Feno per 0.693 increase, 0.65 (0.52-0.81), P < .001; log serum periostin per 0.693 increase, 0.62 (0.35-1.09), P = .10; log serum IgE per 0.693 increase, 0.89 (0.80-1.00), P = .05. CONCLUSIONS: The positive association between type 2 biomarkers and risk of severe exacerbations in populations with severe refractory asthma does not extend to mild and moderate asthma. Non-type 2 asthma may represent a phenotype associated with an increased risk of severe exacerbations in a broad asthma population.

Pilot study of feasibility of a randomised controlled trial of asthma risk with paracetamol versus ibuprofen use in infancy.

AIM: To undertake a randomised controlled trial (RCT) of paracetamol versus ibuprofen use during infancy to determine if paracetamol is associated with an increased risk of developing asthma, the preferred method of recruitment needs to be determined. We assessed three different recruitment domains to determine the likely enrolment rates of newborn infants into a three-year or six-year RCT of paracetamol versus ibuprofen and the development of asthma symptoms. The proposed RCT would require 1,806 participants. METHODS: A questionnaire was administered to a convenience sample of Auckland and Wellington based parents/guardians within three different recruitment domains: antenatal classes, postnatal wards and six-week well-child visits at primary healthcare centres. RESULTS: Over a twelve-week period 19/586 (3.2%), 196/861 (22.8%), and 0/110 (0%) questionnaires were completed by parents/guardians of newborn infants in antenatal, postnatal and primary healthcare domains. In the postnatal recruitment domain, the likelihood of newborn infants being enrolled in the proposed RCT was rated 'very likely', 'likely' and 'neutral' by 15 (8%, CI 4-12%), 65 (33%, CI 26-40%) and 64 (33%, CI 25-39%) of respondents for a RCT of three years duration; and by 5 (3%, CI 1-5%), 37 (19%, CI 14-25%) and 59 (30%, CI 24-36%) of respondents respectively for a RCT of six years duration. CONCLUSIONS: Postnatal wards are expected to be the most successful recruitment domain for the proposed RCT, likely a reflection of the face-to-face direct recruitment by researchers. It appears feasible to recruit into the proposed RCT using three large New Zealand tertiary hospitals.