Preventive effects of dexamethasone on hypoxic-ischemic brain damage in the neonatal rat

Corticosteroids and perinatal hypoxic-ischemic brain injury

Perinatal hypoxic-ischemic (HI) brain injury is the major cause of neonatal mortality and severe long-term neurological morbidity. Yet, the effective therapeutic interventions currently available are extremely limited. Corticosteroids act on both mineralocorticoid (MR) and glucocorticoid (GR) receptors and modulate inflammation and apoptosis in the brain. Neuroinflammatory response to acute cerebral HI is a major contributor to the pathophysiology of perinatal brain injury. Here, we give an overview of current knowledge of corticosteroid-mediated modulations of inflammation and apoptosis in the neonatal brain, focusing on key regulatory cells of the innate and adaptive immune response. In addition, we provide new insights into targets of MR and GR in potential therapeutic strategies that could be beneficial for the treatment of infants with HI brain injury.

Dexamethasone-induced neuroprotection in hypoxic-ischemic brain injury in newborn rats is partly mediated via Akt activation

Prior treatment with dexamethasone (Dex) provides neuroprotection against hypoxia ischemia (HI) in newborn rats. Recent studies have shown that the phosphatidylinositol-3-kinase/Akt (PI3K/Akt) pathway plays an important role in the neuroprotection. The objective of this study is to evaluate the role of the PI3K/Akt pathway in the Dex-induced neuroprotection against subsequent HI brain injury. Seven-day-old rat pups had the right carotid artery permanently ligated followed by 160min of hypoxia (8% oxygen). Rat pups received i.p. injection of either saline or Dex (0.25mg/kg) at 24 and 4h before HI exposure. To quantify the effects of a PI3K/Akt inhibitor, wortmannin (1μl of 1μg/μl) or vehicle was injected intracerebroventricularly in the right hemisphere on postnatal day 6 at 30min prior to the first dose of Dex or saline treatment. Dex pretreatment significantly reduced the brain injury following HI which was quantified by the decrease in cleaved caspase-3 protein as well as cleaved caspase-3 and TUNEL positive cells at 24h and percent loss of ipsilateral hemisphere weight at 22d after HI, while wortmannin partially reversed these effects. We conclude that Dex provides robust neuroprotection against subsequent HI in newborn rats in part via activation of PI3/Akt pathway.

Dexamethasone pre-treatment protects brain against hypoxic-ischemic injury partially through up-regulation of vascular endothelial growth factor A in neonatal rats

Dexamethasone (Dex) provides neuroprotection against subsequent hypoxia ischemia (HI) in newborn rats, but the mechanism of this neuroprotection is not well understood. It is known that vascular endothelial growth factor A (VEGF) has neuroprotective effects. The objective of this study was to evaluate the role of the VEGF signaling pathway in the Dex-induced neuroprotection in newborn rats. Seven-day-old rat pups had the right carotid artery permanently ligated followed by 140 or 160 min of hypoxia (8% oxygen). Rat pups received two i.p. injections of either saline or Dex (0.25 mg/kg) at 24 and 4 h before HI exposure. To quantify the effects of a glucocorticoid receptor (GR) blocker, on postnatal day (PD) 6 and 15 min prior to Dex treatment rat pups received s.c. vehicle or RU486 (GR blocker, 60 mg/kg). After 24 h at PD 7, all rat pups had HI as described earlier. To quantify the effects of a VEGFR 2 blocker, at 24 h after Dex/Veh treatment (PD7), SU5416, a VEGFR 2 inhibitor or vehicle was injected intracerebroventricularly in the right hemisphere at 30 min before and 2 h after HI. Dex pre-treatment reduced brain injury and enhanced the HI-induced brain VEGF protein while a GR blocker inhibited these effects. Treatment with VEGFR 2 blocker decreased Dex-induced neuroprotection also. Dex pre-treatment enhanced the HI-induced increase in mRNA expression of VEGF splice variants and decreased the HI-induced reduction of Akt phosphorylation. Additionally, it also decreased HI-induced increase of caspase-3 activity and DNA fragments in neonatal rat brain. We conclude that Dex provides robust neuroprotection against subsequent HI in newborn rats via GR likely with the partial involvement of VEGF signaling pathway.

Associations between serum cortisol, cardiovascular function and neurological outcome following acute global hypoxia in the newborn piglet

Perinatal asphyxia is a significant contributor to neonatal brain injury. However, there is significant variability in neurological outcome in neonates after global hypoxia-ischemia. The aims of this study were to identify which physiological response/s during global hypoxia-ischemia influence the severity of brain injury and to assess their relative importance. Hypoxia/hypercapnia was induced in 20 anaesthetized piglets by reducing the inspired oxygen fraction to 10% and the ventilation rate from 30 to 10 breaths per minute for 45 min. Neurological outcome was assessed using functional markers including cerebral function amplitude (via electroencephalography) and cerebral impedance, and the structural marker microtubule associated protein-2 by immunohistochemistry at 6 h post hypoxia. Significant variability in neurological outcome was observed following the constant hypoxia/hypercapnia insult. There was a high degree of variability in cardiovascular function (mean arterial blood pressure and heart rate) and serum cortisol concentrations in response to hypoxia. More effective maintenance of cardiovascular function and higher serum cortisol concentrations were associated with a better outcome. These two variables were strongly associated with neurological outcome, and together explained 68% of the variation in the severity of neurological outcome. The variability in the cardiovascular and cortisol responses to hypoxia may be a more important determinant of neurological outcome then previously recognized.

A new trial liposteroid (dexamethasone palmitate) therapy for intractable epileptic seizures in infancy

West syndrome (WS) is a severe age-dependent intractable epilepsy in infants that frequently results in mental retardation. ACTH or glucocorticoids are among several effective treatments in WS, but the relative advantages and disadvantages of these two therapies are still unknown. In a previous study, liposteroid (LS; dexamethasone palmitate) was used for the treatment of WS and compared with ACTH therapy in relation to therapeutic effect and adverse reactions. In this study, a new regimen of LS therapy was tried for WS and its related syndrome in an attempt to hasten the onset of the therapeutic effect and reduce the relapse rate. A single intravenous injection of LS (0.25mg/kg) was administered 12 times in 1 month (total dosage 3.0mg/kg) to four patients with WS and with post-WS aged 5-25 months, and one patient with Lennox-Gastaut syndrome (post-WS) aged 84 months. All five patients had daily seizures uncontrolled by conventional antiepileptic drugs, such as VPA, CZP or ZNS. Nodding spasm and hypsarrhythmia on EEG disappeared in one patient with WS within four doses. More than 50% decrease in seizures, and EEG improvement, were found in other two patients. No notable effects were seen in the other two patients. There were no clinically significant adverse reactions throughout the therapy. Efficacy can be determined in this new experimental LS therapy earlier than with conventional LS therapy. In this small study, a new protocol for LS therapy could be completed safely. This regimen may be useful for those susceptible to adverse reactions from conventional treatment or those unresponsive to other treatments.

Recruitment of the p160 coactivators by the glucocorticoid receptor: dependence on the promoter context and cell type but not hypoxic conditions

In the nervous system, glucocorticoids exert beneficial or noxious effects, depending on their concentration and time-exposure. They act via the glucocorticoid receptor (GR) which recruits the p160 coactivators (SRC-1, SRC-2 and SRC-3). It was often shown that the three SRCs are interchangeable. The aim of the present study was to evaluate if the GR-SRCs interactions are dependent on several parameters like the target promoter structure, cell type or exogenous stressful parameters like hypoxia. We investigated the GR-SRCs interactions in two glial cells: astrocytes for the central nervous system and Schwann cells for the peripheral nervous system. We have shown by performing functional studies (overexpression and siRNA knock-down) that the recruitment of the three p160 by the GR is promoter-dependent and cell-specific. Moreover, we have shown that hypoxia (5% of oxygen) enhanced GR transactivation in both glial cells. Although hypoxia enhanced GR transactivation, it did not alter the interactions between the GR and the three p160s. Finally, we have shown that the potentiation of GR transactivation by hypoxia is due to an increase of the GR transcripts in Schwann cells but not in astrocytes. Altogether, these results reveal that the p160s are not interchangeable and that their recruitment by the GR is a multiparametric event.

Perinatal glucocorticoid therapy and neurodevelopmental outcome: an epidemiologic perspective

A relatively brief course of antenatal glucocorticoids (ACS), given to reduce the severity of respiratory distress syndrome in preterm infants, improves survival and appears to protect against brain damage. In clinical trials as well as observational studies, ACS have been associated with a decreased risk of intraventricular haemorrhage and cerebral palsy. In observational studies a decreased risk of white-matter damage, identified with cranial ultrasound, has been observed. There is some evidence, from observational studies, that repeated courses of ACS (typically given at weekly intervals) can reduce the rate of fetal head growth, and experiments in animals provide further support for this possibility. In contrast to the effects of a brief course of ACS, postnatal glucocorticoids (PCS), given to preterm infants to reduce the severity of chronic lung disease have been associated with an increased risk of neurologic impairment. Available evidence suggests that PCS does not improve survival. Further study is needed of the neurodevelopmental consequences of both multiple courses of ACS, as well as PCS.

Antecedents of cerebral palsy in very low-birth weight infants

Research from the last two decades provides directions for efforts to prevent CP in VLBW infants. The pathogenesis of CP seems to involve factors operating both during pregnancy and in the neonatal period. The most important prenatal factor appears to be intrauterine infection. Perinatal infection and other risk factors, such as the death of a co-twin, placental abruption, and cerebral ischemia, could trigger a cytokine cascade resulting in damage to the developing brain. The low frequency of intrauterine infection in mothers with preeclampsia might explain the apparent protective effect of this disorder. If the brain damage attributed to intrauterine infection and other risk factors involves cytokines as intermediates, then blockade of the proinflammatory cascade or promotion of endogenous inhibitors might prevent CP. Other potentially preventive strategies include corticosteroids given to mothers (but not those given to neonates) and thyroid hormone.

Liposteroid (dexamethasone palmitate) therapy for West syndrome: a comparative study with ACTH therapy

Dexamethasone palmitate (liposteroid) was used for the treatment of West syndrome and compared with adrenocorticotropic hormone (ACTH) therapy. A single intravenous injection of liposteroid (0.25 mg/kg) was administered seven times in 3 months (total dosage = 1.75 mg/kg) to five symptomatic patients with West syndrome, aged 4-11 months. ACTH (0.025 mg/kg/day) was administered intramuscularly for 6 weeks according to the conventional therapy in Japan (total dosage = 0.625 mg/kg) to five symptomatic patients with West syndrome, aged 6-10 months. Nodding spasm and hypsarrhythmia on EEG disappeared in all patients in the liposteroid therapy group within four doses; however, partial seizures and focal spikes on EEG reappeared in three patients 2 months after the end of liposteroid therapy. In the ACTH therapy group, nodding spasm and hypsarrhythmia on EEG similarly disappeared during treatment in all patients, but nodding spasm reappeared 2 months after therapy in two patients and partial seizures reappeared in one patient 3 months after therapy. No notable adverse reactions occurred in the liposteroid group, but transient dysfunction of the thyroid and anterior pituitary gland and increased levels of serum cortisol were experienced in the ACTH group. These results suggest that glucocorticoid incorporated in a lipid emulsion is useful for the treatment of West syndrome.

Protection against hypoxic-ischemic damage with corticosterone and dexamethasone: inhibition of effect by a glucocorticoid antagonist RU38486

We investigated whether the neuroprotection provided by dexamethasone against neonatal hypoxic-ischemic damage can be inhibited by a glucocorticoid antagonist and whether corticosterone, the endogenous glucocorticoid in the rat, also provides protection. Rats (6 days old) were treated with either vehicle (0.1 ml/10 g), corticosterone (3.5-80 mg/kg, s.c.) or dexamethasone alone or in combination with RU38486 (20-80 mg/kg, s.c.) 15 min prior to dexamethasone (0.1 mg/kg, i.p.). At 7 days of age, cerebral hypoxia-ischemia was produced by right carotid artery ligation under anesthesia and subsequent exposure to 2 h of hypoxia. Damage was quantified from brains perfusion-fixed and processed 2 days later. The reduction in somatic growth, thymus weight and the relatively elevated blood glucose levels at the end of hypoxia-ischemia were inhibited by RU38486. The protective effect of dexamethasone was also prevented by RU38486 (P < 0.001). Similar to pre-treatment with dexamethasone, administration of corticosterone (40-80 mg/kg) markedly reduced the extent of infarction compared to vehicle-treated controls (P < 0.0001). Thus, the endogenous glucocorticoid in the rat also provides protection against hypoxic-ischemic damage. RU38486 inhibits the beneficial effects of dexamethasone demonstrating that the neuroprotection observed with dexamethasone is a glucocorticoid receptor-mediated effect.

Microglia-astrocyte interactions after cortisone treatment in a neonatal hypoxia-ischemia model

Microglial and astrocyte responses to glucocorticoid pretreatment in the neonate exposed to hypoxia-ischemia (HI) are largely unknown. The expression of microglial antigens and astrocytic proliferation was compared in neonatal rats exposed to HI with and without cortisone. HI was induced in 7 day old rats. One group of rats received cortisone within 24 h of birth. Immunocytochemical and immunoblot investigations were performed. Monoclonal antibodies (OX18 and OX42) were used for the detection of the major histocompatibility complex (MHC) class I antigens and complement receptor 3 (CR3) respectively. Antibodies directed against glial fibrillary acidic protein (GFAP) and microtubule associated protein II (MAP II) were used to evaluate the extent of brain damage. Cortisone treatment provoked a decline in the number of microglial cells but did not modify GFAP levels in control rats which were not exposed to HI. Neuronal damage was similar in control and cortisone treated rats exposed to HI. There were also similarities in the expression of CR3 antigens on microglia. However microglial cells expressing MHC class I antigens were less prevalent in rats exposed to HI only. Cortisone pretreatment enhanced the expression of MHC class I antigens. Astrocytic proliferation was intense in rats exposed to HI; however in rats treated with cortisone and exposed to HI there was a drastic reduction in astrocytic proliferation. In conclusion it is suggested that microglia which survive cortisone pretreatment become over-activated thereby preventing astrocytic proliferation.