Pharmacological Preventions of Brain Injury Following Experimental Germinal Matrix Hemorrhage: an Up-to-Date Review

Pharmacological Strategies and Surgical Management of Posthemorrhagic Hydrocephalus Following Germinal Matrix-Intraventricular Hemorrhage in Preterm Infants

Germinal matrix-intraventricular hemorrhage (GM-IVH) is a detrimental neurological complication that occurs in preterm infants, especially in babies born before 32 weeks of gestation and in those with a very low birth weight. GM-IVH is defined as a rupture of the immature and fragile capillaries located in the subependymal germinal matrix zone of the preterm infant brain, and it can lead to detrimental neurological sequelae such as posthemorrhagic hydrocephalus (PHH), cerebral palsy, and other cognitive impairments. PHH following GM-IVH is difficult to treat in the clinic, and no levelone strategies have been recommended to pediatric neurosurgeons. Several cellular and molecular mechanisms of PHH following GM-IVH have been studied in animal models, but no effective pharmacological strategies have been used in the clinic. Thus, a comprehensive understanding of molecular mechanisms, potential pharmacological strategies, and surgical management of PHH is urgently needed. The present review presents a synopsis of the pathogenesis, diagnosis, and cellular and molecular mechanisms of PHH following GM-IVH and explores pharmacological strategies and surgical management.

Intraventricular haemorrhage in premature infants: the role of immature neuronal salt and water transport

Intraventricular haemorrhage is a common complication of premature birth. Survivors are often left with cerebral palsy, intellectual disability and/or hydrocephalus. Animal models suggest that brain tissue shrinkage, with subsequent vascular stretch and tear, is an important step in the pathophysiology, but the cause of this shrinkage is unknown. Clinical risk factors for intraventricular haemorrhage are biomarkers of hypoxic-ischaemic stress, which causes mature neurons to swell. However, immature neuronal volume might shift in the opposite direction in these conditions. This is because immature neurons express the chloride, salt and water transporter NKCC1, which subserves regulatory volume increases in non-neural cells, whereas mature neurons express KCC2, which subserves regulatory volume decreases. When hypoxic-ischaemic conditions reduce active ion transport and increase the cytoplasmic membrane permeability, the effects of these transporters are diminished. Consequentially, mature neurons swell (cytotoxic oedema), whereas immature neurons might shrink. After hypoxic-ischaemic stress, in vivo and in vitro multi-photon imaging of perinatal transgenic mice demonstrated shrinkage of viable immature neurons, bulk tissue shrinkage and blood vessel displacement. Neuronal shrinkage was correlated with age-dependent membrane salt and water transporter expression using immunohistochemistry. Shrinkage of immature neurons was prevented by prior genetic or pharmacological inhibition of NKCC1 transport. These findings open new avenues of investigation for the detection of acute brain injury by neuroimaging, in addition to prevention of neuronal shrinkage and the ensuing intraventricular haemorrhage, in premature infants.

Adiponectin Ameliorates GMH-Induced Brain Injury by Regulating Microglia M1/M2 Polarization Via AdipoR1/APPL1/AMPK/PPARγ Signaling Pathway in Neonatal Rats

Adiponectin (APN), a fat-derived plasma hormone, is a classic anti-inflammatory agent. Multiple studies have demonstrated the beneficial role of APN in acute brain injury, but the effect of APN in germinal matrix hemorrhage (GMH) is unclear, and the underlying molecular mechanisms remain largely undefined. In the current study, we used a GMH rat model with rh-APN treatment, and we observed that APN demonstrated a protective effect on neurological function and an inhibitory effect on neuroinflammation after GMH. To further explore the underlying mechanisms of these effects, we found that the expression of Adiponectin receptor 1 (AdipoR1) primarily colocalized with microglia and neurons in the brain. Moreover, AdiopR1, but not AdipoR2, was largely increased in GMH rats. Meanwhile, further investigation showed that APN treatment promoted AdipoR1/APPL1-mediated AMPK phosphorylation, further increased peroxisome proliferator-activated receptor gamma (PPARγ) expression, and induced microglial M2 polarization to reduce the neuroinflammation and enhance hematoma resolution in GMH rats. Importantly, either knockdown of AdipoR1, APPL1, or LKB1, or specific inhibition of AMPK/PPARγ signaling in microglia abrogated the protective effect of APN after GMH in rats. In all, we propose that APN works as a potential therapeutic agent to ameliorate the inflammatory response following GMH by enhancing the M2 polarization of microglia via AdipoR1/APPL1/AMPK/PPARγ signaling pathway, ultimately attenuating inflammatory brain injury induced by hemorrhage.

Activation of GPR40 attenuates neuroinflammation and improves neurological function via PAK4/CREB/KDM6B pathway in an experimental GMH rat model

BACKGROUND

Germinal matrix hemorrhage (GMH) is defined by the rupture of immature blood vessels in the germinal matrix, where subsequent hemorrhage enters the subependymal zone and the cerebral lateral ventricles. The consequent blood clot has been identified as the causative factor of secondary brain injury, which triggers a series of complex parallel and sequential harmful mechanisms, including neuroinflammation. The orphan G-protein-coupled receptor 40 (GPR40), a free fatty acid (FFA) receptor 1, has been shown to exert anti-inflammatory effects when activated and improved outcomes in animal models of stroke. We aimed to investigate the anti-inflammatory effects of GPR40 and its underlying mechanisms after GMH.

METHODS

GMH model was induced in 7-day-old rat pups by an intraparenchymal injection of bacterial collagenase. GPR40 agonist, GW9508, was administered intranasally 1 h, 25 h, and 49 h after GMH induction. CRISPR targeting GPR40, PAK4, and KDM6B were administered through intracerebroventricular injection 48 h before GMH induction. Neurologic scores, microglia polarization, and brain morphology were evaluated by negative geotaxis, right reflex, rotarod test, foot fault test, Morris water maze, immunofluorescence staining, Western blots, and nissl staining respectfully.

RESULTS

The results demonstrated that GW9508 improved neurological and morphological outcomes after GMH in the short (24 h, 48 h, 72h) and long-term (days 21-27). However, the neuroprotective effects of treatment were abolished by GW1100, a selective GPR40 antagonist. GW9508 treatment increased populations of M2 microglia and decreased M1 microglia in periventricular areas 24 h after GMH induction. GW9508 upregulated the phosphorylation of PAK4, CREB, and protein level of KDM6B, CD206, IL-10, which was also met with the downregulation of inflammatory markers IL-1β and TNF-α. The mechanism study demonstrated that the knockdown of GPR40, PAK4, and KDM6B reversed the neuroprotective effects brought on by GW9508. This evidence suggests that GPR40/PAK4/CREB/KDM6B signaling pathway in microglia plays a role in the attenuation of neuroinflammation after GMH.

CONCLUSIONS

In conclusion, the present study demonstrates that the activation of GPR40 attenuated GMH-induced neuroinflammation through the activation of the PAK4/CREB/KDM6B signaling pathway, and M2 microglia may be a major mediator of this effect. Thus, GPR40 may serve as a potential target in the reduction of the inflammatory response following GMH, thereby improving neurological outcomes in the short- and long-term.

Therapeutic Attributes of Endocannabinoid System against Neuro-Inflammatory Autoimmune Disorders

In humans, various sites like cannabinoid receptors (CBR) having a binding affinity with cannabinoids are distributed on the surface of different cell types, where endocannabinoids (ECs) and derivatives of fatty acid can bind. The binding of these substance(s) triggers the activation of specific receptors required for various physiological functions, including pain sensation, memory, and appetite. The ECs and CBR perform multiple functions via the cannabinoid receptor 1 (CB1); cannabinoid receptor 2 (CB2), having a key effect in restraining neurotransmitters and the arrangement of cytokines. The role of cannabinoids in the immune system is illustrated because of their immunosuppressive characteristics. These characteristics include inhibition of leucocyte proliferation, T cells apoptosis, and induction of macrophages along with reduced pro-inflammatory cytokines secretion. The review seeks to discuss the functional relationship between the endocannabinoid system (ECS) and anti-tumor characteristics of cannabinoids in various cancers. The therapeutic potential of cannabinoids for cancer-both in vivo and in vitro clinical trials-has also been highlighted and reported to be effective in mice models in arthritis for the inflammation reduction, neuropathic pain, positive effect in multiple sclerosis and type-1 diabetes mellitus, and found beneficial for treating in various cancers. In human models, such studies are limited; thereby, further research is indispensable in this field to get a conclusive outcome. Therefore, in autoimmune disorders, therapeutic cannabinoids can serve as promising immunosuppressive and anti-fibrotic agents.

Posthemorrhagic hydrocephalus development after germinal matrix hemorrhage: Established mechanisms and proposed pathways

In addition to being the leading cause of morbidity and mortality in premature infants, germinal matrix hemorrhage (GMH) is also the leading cause of acquired infantile hydrocephalus. The pathophysiology of posthemorrhagic hydrocephalus (PHH) development after GMH is complex and vaguely understood, although evidence suggests fibrosis and gliosis in the periventricular and subarachnoid spaces disrupts normal cerebrospinal fluid (CSF) dynamics. Theories explaining general hydrocephalus etiology have substantially evolved from the original bulk flow theory developed by Dr. Dandy over a century ago. Current clinical and experimental evidence supports a new hydrodynamic theory for hydrocephalus development involving redistribution of vascular pulsations and disruption of Starling forces in the brain microcirculation. In this review, we discuss CSF flow dynamics, history and development of theoretical hydrocephalus pathophysiology, and GMH epidemiology and etiology as it relates to PHH development. We highlight known mechanisms and propose new avenues that will further elucidate GMH pathophysiology, specifically related to hydrocephalus.

Astrogliosis inhibition attenuates hydrocephalus by increasing cerebrospinal fluid reabsorption through the glymphatic system after germinal matrix hemorrhage

Germinal matrix hemorrhage (GMH) results from the rupture of the immature thin-walled blood vessels and consequent bleeding into the subependymal germinal matrix and possible lateral ventricles. The purpose of this study is to investigate how astrogliosis impacts the glymphatic-meningeal lymphatic system in cerebrospinal fluid (CSF) reabsorption after GMH and how the anti-scarring agent olomoucine attenuates post-hemorrhagic hydrocephalus. GMH was induced by stereotaxic collagenase infusion into P7 Sprague-Dawley rats of both sexes. Western blot and immunofluorescence were used to assess astrogliosis and how astrogliosis affects glymphatic function by measuring Aquaporin-4 expression. Intracisternal injection of fluorescence tracer was used to measure CSF diffusion throughout the brain, its dispersion in the paravascular area and CSF drainage into the deep cervical lymph nodes at 28 days after GMH. Both short-term and long-term behavioral tests were used to assess the neurological outcomes. Nissl staining was used to assess the morphological changes at 28 days after hemorrhage. GMH elicited astrogliotic scarring and reduced the exchange between CSF and interstitial fluid, as well as CSF reabsorption through the meningeal lymphatic vessels. This might be associated with redistribution of Aquaporin-4. Olomoucine ameliorated scar tissue formation and attenuated post-hemorrhagic hydrocephalus. These findings of this study suggested that the glymphatic system might play a role in CSF reabsorption in neonates following GMH. Scar tissue formation impairs this CSF clearance route, and therefore astrogliosis inhibition might be a potential therapeutic strategy for neonatal post-hemorrhagic hydrocephalus.

Secukinumab attenuates reactive astrogliosis via IL-17RA/(C/EBPβ)/SIRT1 pathway in a rat model of germinal matrix hemorrhage

Aims

Reactive astrogliosis plays a critical role in neurological deficits after germinal matrix hemorrhage (GMH). It has been reported that interleukin‐17A and IL‐17A receptor IL‐17RA/(C/EBPβ)/SIRT1 signaling pathway enhances reactive astrogliosis after brain injuries. We evaluated the effects of secukinumab on reactive astrogliosis in a rat pup model of GMH.

Methods

A total of 146 Sprague Dawley P7 rat pups were used. GMH was induced by intraparenchymal injection of collagenase. Secukinumab was administered intranasally 1 hour post‐GMH. C/EBPβ CRISPR or SIRT1 antagonist EX527 was administrated intracerebroventricularly (icv) 48 hours and 1 hour before GMH induction, respectively. Neurobehavior, Western blot, histology, and immunohistochemistry were used to assess treatment regiments in the short term and long term.

Results

The endogenous IL‐17A, IL‐17RA, C/EBPβ, and GFAP and proliferation marker CyclinD1 were increased, while SIRT1 expression was decreased after GMH. Secukinumab treatment improved neurological deficits, reduced ventriculomegaly, and increased cortical thickness. Additionally, treatment increased SIRT1 expression and lowered proliferation proteins PCNA and CyclinD1 as well as GFAP expression. C/EBPβ CRISPR activation plasmid and EX527 reversed the antireactive astrogliosis effects of secukinumab.

Conclusion

Secukinumab attenuated reactive astrogliosis and reduced neurological deficits after GMH, partly by regulating IL‐17RA/(C/EBPβ)/SIRT1 pathways. Secukinumab may provide a promising therapeutic strategy for GMH patients.

A comprehensive review of therapeutic targets that induce microglia/macrophage-mediated hematoma resolution after germinal matrix hemorrhage

Currently, there is no effective treatment for germinal matrix hemorrhage and intraventricular hemorrhage (GMH-IVH), a common and often fatal stroke subtype in premature infants. Secondary brain injury after GMH-IVH is known to involve blood clots that contribute to inflammation and neurological deficits. Furthermore, the subsequent blood clots disrupt normal cerebrospinal fluid circulation and absorption after GMH-IVH, contributing to posthemorrhagic hydrocephalus (PHH). Clinically, GMH-IVH severity is graded on a I to IV scale: Grade I is confined to the germinal matrix, grade II includes intraventricular hemorrhage, grade III includes intraventricular hemorrhage with extension into dilated ventricles, and grade IV includes intraventricular hemorrhage with extension into dilated ventricles as well as parenchymal hemorrhaging. GMH-IVH hematoma volume is the best prognostic indicator, where patients with higher grades have worsened outcomes. Various preclinical studies have shown that rapid hematoma resolution quickly ameliorates inflammation and improves neurological outcomes. Current experimental evidence identifies alternatively activated microglia as playing a pivotal role in hematoma clearance. In this review, we discuss the pathophysiology of GMH-IVH in the development of PHH, microglia/macrophage's role in the neonatal CNS, and established/potential therapeutic targets that enhance M2 microglia/macrophage phagocytosis of blood clots after GMH-IVH.

Neuroprotection provided by isoflurane pre-conditioning and post-conditioning

Isoflurane, a volatile and inhalational anesthetic, has been extensively used in perioperative period for several decades. A large amount of experimental studies have indicated that isoflurane exhibits neuroprotective properties when it is administrated before or after (pre-conditioning and post-conditioning) neurodegenerative diseases (e.g., hypoxic ischemia, stroke and trauma). Multiple mechanisms are involved in isoflurane induced neuroprotection, including activation of glycine and γ-aminobutyric acid receptors, antagonism of ionic channels and alteration of the function and activity of other cellular proteins. Although neuroprotection provided by isoflurane is observed in many animal studies, convincing evidence is lacking in human trials. Therefore, there is still a long way to go before translating its neuroprotective properties into clinical practice.

Simvastatin Promotes Hematoma Absorption and Reduces Hydrocephalus Following Intraventricular Hemorrhage in Part by Upregulating CD36

We previously found that hematoma worsens hydrocephalus after intraventricular hemorrhage (IVH) via increasing iron deposition and aggravating ependymal cilia injury; therefore, promoting hematoma absorption may be a promising strategy for IVH. Recently, some investigations imply that simvastatin has the ability of accelerating hematoma absorption. Thus, this study was designed to examine the efficacy of simvastatin for IVH in rats. Intracerebral hemorrhage with ventricular extension was induced in adult male Sprague-Dawley rats after autologous blood injection. Simvastatin or vehicle was administered orally at 1 day after IVH and then daily for 1 week. MRI studies were performed to measure the volumes of intracranial hematoma and lateral ventricle at days 1, 3, 7, 14, and 28 after IVH. Motor and neurocognitive functions were assessed at days 1 to 7 and 23 to 28, respectively. Iron deposition, iron-related protein expression, ependymal damage, and histology were detected at day 28. Expression of CD36 scavenger receptor (facilitating phagocytosis) was examined at day 3 after IVH using western blotting and immunofluorescence. Simvastatin significantly increased hematoma absorption ratio, reduced ventricular volume, and attenuated neurological dysfunction post-IVH. In addition, less iron accumulation and more cilia survival was observed in the simvastatin group when compared with the control. What's more, higher expression of CD36 was detected around the hematoma after simvastatin administration. Simvastatin significantly enhanced brain hematoma absorption, alleviated hydrocephalus, and improved neurological recovery after experimental IVH, which may in part by upregulating CD36 expression. Our data suggest that early simvastatin use may be a novel therapy for IVH patients.

Role of Glibenclamide in Brain Injury After Intracerebral Hemorrhage

Brain edema following intracerebral hemorrhage (ICH) causes severe secondary brain injury, and no efficient pharmacological preventions are available. The present study was designed to demonstrate the neuroprotective effects of glibenclamide on brain edema and key factors of the blood-brain barrier (BBB). The study was divided into two parts. First, we utilized an autoblood-induced rat model to investigate the expression of sulfonylurea receptor 1 (Sur1). Second, rats were randomized into sham, vehicle, and glibenclamide groups. Neurological scores, brain water content, Evans blue extravasation, Morris water maze test, western blots, and immunofluorescence were used to study the effects of glibenclamide. The expression of the Sur1-Trpm4 channel but not the Sur1-KATP channel was increased in the perihematomal tissue following ICH. Glibenclamide administration significantly decreased the brain water content, restored the BBB, and reduced the expression of MMPs. In addition, glibenclamide improved long-term cognitive deficits following ICH. Glibenclamide protected BBB integrity and improved neurological outcomes after ICH by inhibiting the Sur1-Trpm4 channel, which reduces the expression of MMPs and thereby increases BBB tight-junction protein levels. Glibenclamide may have potential to protect the BBB after ICH.

Cannabinoid receptor-2 stimulation suppresses neuroinflammation by regulating microglial M1/M2 polarization through the cAMP/PKA pathway in an experimental GMH rat model

Excessive inflammatory responses are involved in secondary brain injury during germinal matrix hemorrhage (GMH). The process of microglial polarization to the pro-inflammatory M1 or anti-inflammatory M2 phenotypes is considered to occur in a major immunomodulatory manner during brain inflammation. We previously found that cannabinoid receptor-2 (CB2R) stimulation attenuated microglial accumulation and brain injury following experimental GMH. However, whether CB2R has effects on microglial polarization after GMH remains unclear. Herein, we investigated the effects of CB2R stimulation on neuroinflammation after experimental GMH and the potential mechanisms that mediate M1/M2 microglial phenotype regulation. The results indicated that during the GMH acute phase, microglia primarily polarized to the M1 phenotype and induced an overwhelming release of pro-inflammatory cytokines. However, JWH133, a selective CB2R agonist, significantly prevented the pro-inflammatory cytokine release while promoting an M1 to M2 phenotype transformation in microglia, resulting in an increased anti-inflammatory cytokine release. Moreover, in thrombin-induced rat primary microglial cells, JWH133 reduced the pro-inflammatory cytokine levels and M1 phenotype by enhancing the acquisition of the M2 phenotype. Additionally, JWH133 facilitated synthesis of cyclic AMP (cAMP) and its downstream effectors, phosphorylated cAMP-dependent protein kinase (p-PKA) and exchange protein activated by cyclic-AMP 1 (Epac1). The promoting effects of JWH133 on M2 polarization were attenuated with a specific PKA inhibitor but not with an Epac inhibitor, indicating that the cAMP/PKA signaling pathway was involved in the JWH133 effects. This is the first study to propose that promotion of microglial M2 polarization through the cAMP/PKA pathway participates in the CB2R-mediated anti-inflammatory effects after GMH induction. The results will help to further understand the mechanisms that underlie neuroprotection by CB2R in GMH and promote clinical translational research for CB2R agonists.