Activating toll-like receptor 4 after traumatic brain injury inhibits neuroinflammation and the accelerated development of seizures in rats

Dexmedetomidine directly binds to and inhibits Toll-like receptor 4

BACKGROUND

While a number of anesthetics has been shown potentially associated with neurotoxicity in the developing brain, dexmedetomidine, a drug that was rather recently introduced into the perioperative setting, is considered beneficial from neurological wellbeing. However, the underlying mechanism of how dexmedetomidine affects brain health remains to be determined. Based on our recent study, we hypothesized that dexmedetomidine would directly bind to and inhibit Toll-like receptor 4 (TLR4), a critical receptor largely expressed in microglia and responsible for neurological insult.

METHODS

We used TLR4 reporter assays to test if dexmedetomidine attenuates TLR4 activation. Furthermore, a direct binding of dexmedetomidine on TLR4 was tested using photoactivatable medetomidine. Lastly, the effect of dexmedetomidine on ketamine (anesthetic)-induced neurotoxicity was tested in rat pups (P7).

RESULTS

We showed that dexmedetomidine attenuated TLR4 activation using reporter assay (IC50 = 5.8 µg/mL). Photoactivatable dexmedetomidine delineated its direct binding sites on TLR4. We also showed that dexmedetomidine attenuated microglia activation both in vitro and in vivo.

DISCUSSION

We proposed a novel mechanism of dexmedetomidine-mediated neuroprotection.

Toll-Like Receptor 1/2 Postconditioning by the Ligand Pam3cys Tempers Posttraumatic Hyperexcitability, Neuroinflammation, and Microglial Response: A Potential Candidate for Posttraumatic Epilepsy

Toll-like receptors (TLRs) are activated by endogenous molecules released from damaged cells and contribute to neuroinflammation following traumatic brain injury (TBI) and epilepsy. TLR1/2 agonist tri-palmitoyl-S-glyceryl-cysteine (Pam3cys) is a vaccine adjuvant with confirmed safety in humans. We assessed impact of TLR1/2 postconditioning by Pam3cys on epileptogenesis and neuroinflammation in male rats, 6, 24, and 48 h after mild-to-moderate TBI. Pam3cys was injected into cerebral ventricles 30 min after controlled cortical impact (CCI) injury. After 24 h, rats underwent chemical kindling by once every other day injections of pentylenetetrazole (PTZ) 35 mg/kg until development of generalized seizures. Number of intact neurons, brain expression of proinflammatory cytokine TNF-α, anti-inflammatory cytokine IL-10, and marker of anti-inflammatory microglia arginase1 (Arg1) were determined by immunoblotting. Astrocytes and macrophage/microglia activation/polarization at the contused area was assessed by double immunostaining with Iba1/Arg1, Iba1/iNOS and GFAP/iNOS, specific antibodies. The CCI-injured rats became kindled by less number of PTZ injections than sham-operated rats (9 versus 14 injections, p < 0.0001). Pam3cys treatment returned the accelerated rate of epileptogenesis in TBI state to the sham level. Pam3cys decreased neural death 48 h after TBI. It decreased TNF-α (6 h post-TBI, p < 0.01), and up-regulated IL-10 (p < 0.01) and Arg1 (p < 0.05) 48 h after TBI. The iNOS-positive cells decreased (p < 0.001) whereas Iba1/Arg1-positive cells enhanced (p < 0.01) after Pam3cys treatment. Pam3cys inhibits TBI-accelerated acquisition of seizures. Pam3cys reprograms microglia and up-regulates anti-inflammatory cytokines during the first few days after TBI. This capacity along with the clinical safety, makes Pam3cys a potential candidate for development of effective medications against posttraumatic epilepsy.

Primary microglia cell cultures in translational research: Strengths and limitations

Microglia are the resident macrophages in the central nervous system, accounting for 10-15% of the cell mass in the brain. Next to their physiological role in development, monitoring neuronal function and the maintenance of homeostasis, microglia are crucial in the brain's immune defense. Brain injury and chronic neurological disorders are associated with neuroinflammation, in which microglia activation is a central element. Microglia acquire a wide spectrum of activation states in the diseased or injured brain, some of which are neurotoxic. The investigation of microglia (patho)physiology and therapeutic interventions targeting neuroinflammation is a substantial challenge. In addition to in vivo approaches, the application of in vitro model systems has gained significant ground and is essential to complement in vivo work. Primary microglia cultures have proved to be a useful tool. Microglia cultures have offered the opportunity to explore the mechanistic, molecular elements of microglia activation, the microglia secretome, and the efficacy of therapeutic treatments against neuroinflammation. As all model systems, primary microglia cultures have distinct strengths and limitations to be weighed when experiments are designed and when data are interpreted. Here, we set out to provide a succinct overview of the advantages and pitfalls of the use of microglia cultures, which instructs the refinement and further development of this technique to remain useful in the toolbox of microglia researchers. Since there is no conclusive therapy to combat neurotoxicity linked to neuroinflammation in acute brain injury or neurodegenerative disorders, these research tools remain essential to explore therapeutic opportunities.

Chitosan revokes controlled-cortical impact generated neurological aberrations in circadian disrupted mice via TLR4-NLRP3 axis

The severity of inevitable neurological deficits and long-term psychiatric disorders in the aftermath of traumatic brain injury is influenced by pre-injury biological factors. Herein, we investigated the therapeutic effect of chitosan lactate on neurological and psychiatric aberrations inflicted by circadian disruption (CD) and controlled-cortical impact (CCI) injury in mice. Firstly, CD was developed in mice by altering sporadic day-night cycles for 2 weeks. Then, CCI surgery was performed using a stereotaxic ImpactOne device. Mice subjected to CCI displayed a significant disruption of motor coordination at 1-, 3- and 5-days post-injury (DPI) in the rotarod test. These animals showed anxiety- and depression-like behaviors in the elevated plus maze and forced-swim test at 14 and 15 DPI, respectively. Notably, mice subjected to CD + CCI exhibited severe cognitive impairment in Y-maze and novel object recognition tasks. The compromised neurological, psychiatric, and cognitive functions were mitigated in chitosan-treated mice (1 and 3 mg/mL). Immunohistochemistry and real-time PCR assay results revealed the magnified responses of prima facie biomarkers like glial-fibrillary acidic protein and ionized calcium-binding adaptor molecule 1 in the pericontusional brain region of the CD + CCI group, indicating aggravated inflammation. We also noted the depleted levels of brain-derived neurotrophic factor and augmented expression of toll-like receptor 4 (TLR4)-leucine-rich-containing family pyrin domain-containing 3 (NLRP3) signaling [apoptosis-associated-speck-like protein (ASC), caspase-1, and interleukin 1-β] in the pericontusional area of CD + CCI group. CCI-induced changes in the astrocyte-glia and aggravated immune responses were ameliorated in chitosan-treated mice. These results suggest that the neuroprotective effect of chitosan in CCI-induced brain injury may be mediated by inhibition of the TLR4-NLRP3 axis.

Curcumin Lowers the Accelerated Speed of Epileptogenesis by Traumatic Brain Injury

Background

Traumatic brain injury or TBI can underlie epilepsy. Prevention of PTE has been of great interest to scientists. Given the antiepileptic, antioxidant and anti-inflammatory activities of curcumin, we examined whether this compound can affect epileptogenesis in rats after TBI.

Methods

Curcumin was injected once a day for two weeks. TBI was induced in the temporal cortex of anesthetized rats using a controlled cortical impact device. One day after TBI, pentylenetetrazole (PTZ), 35 mg/kg, was injected i.p. every other day until manifestation of generalized seizures. The number of PTZ injections was then recorded. Moreover, the extent of cortical and hippocampal IL-1β and glial fibrillary acidic protein (GFAP) expression in the epileptic rats were measured by Western blot analysis.

Results

Curcumin 50 and 150 mg/kg prevented the development of kindling, whereas TBI accelerated the rate of kindling. Curcumin 20 mg/kg prohibited kindling facilitation by TBI, and reduced the expression of IL-1β and GFAP induced by TBI.

Conclusion

Curcumin can stop the acceleration of epileptogenesis after TBI in rats. Inhibiting hippocampal and cortical overexpression of IL-1β and GFAP seems to be involved in this activity.

Intranasal Monophosphoryl Lipid a Administration Ameliorates depression-like Behavior in Chronically Stressed Mice Through Stimulation of Microglia

We and others have reported that systematic stimulation of the central innate immune system by a low dose of lipopolysaccharide (LPS) can improve depression-like behavior in chronically stressed animals. However, it is unclear whether similar stimulation by intranasal administration could improve depression-like behavior in animals. We investigated this question using monophosphoryl lipid A (MPL), a derivative of LPS that lacks the adverse effects of LPS but is still immuno-stimulatory. We found that a single intranasal administration of MPL at a dose of 10 or 20 µg/mouse, but not at a dose of 5 µg/mouse, ameliorated chronic unpredictable stress (CUS)-induced depression-like behavior in mice, as evidenced by the decrease in immobility time in tail suspension test and forced swimming test and the increase in sucrose intake in sucrose preference test. In the time-dependent analysis, the antidepressant-like effect of a single intranasal MPL administration (20 µg/mouse) was observed 5 and 8 h but not 3 h after drug administration and persisted for at least 7 days. Fourteen days after the first intranasal MPL administration, a second intranasal MPL administration (20 µg/mouse) still showed an antidepressant-like effect. The innate immune response mediated by microglia might mediate the antidepressant-like effect of intranasal MPL administration, because both inhibition of microglial activation by pretreatment with minocycline and depletion of microglia by pretreatment with PLX3397 prevented the antidepressant-like effect of intranasal MPL administration. These results suggest that intranasal administration of MPL can produce significant antidepressant-like effects in animals under chronic stress conditions via stimulation of microglia.

Fecal microbiota transplantation inhibited neuroinflammation of traumatic brain injury in mice via regulating the gut-brain axis

Introduction

Recent studies have highlighted the vital role of gut microbiota in traumatic brain injury (TBI). Fecal microbiota transplantation (FMT) is an effective means of regulating the microbiota-gut-brain axis, while the beneficial effect and potential mechanisms of FMT against TBI remain unclear. Here, we elucidated the anti-neuroinflammatory effect and possible mechanism of FMT against TBI in mice via regulating the microbiota-gut-brain axis.

Methods

The TBI mouse model was established by heavy object falling impact and then treated with FMT. The neurological deficits, neuropathological change, synaptic damage, microglia activation, and neuroinflammatory cytokine production were assessed, and the intestinal pathological change and gut microbiota composition were also evaluated. Moreover, the population of Treg cells in the spleen was measured.

Results

Our results showed that FMT treatment significantly alleviated neurological deficits and neuropathological changes and improved synaptic damage by increasing the levels of the synaptic plasticity-related protein such as postsynaptic density protein 95 (PSD-95) and synapsin I in the TBI mice model. Moreover, FMT could inhibit the activation of microglia and reduce the production of the inflammatory cytokine TNF-α, alleviating the inflammatory response of TBI mice. Meanwhile, FMT treatment could attenuate intestinal histopathologic changes and gut microbiota dysbiosis and increase the Treg cell population in TBI mice.

Conclusion

These findings elucidated that FMT treatment effectively suppressed the TBI-induced neuroinflammation via regulating the gut microbiota-gut-brain axis, and its mechanism was involved in the regulation of peripheral immune cells, which implied a novel strategy against TBI.

Microglia in epilepsy

Epilepsy is one of most common chronic neurological disorders, and the antiseizure medications developed by targeting neurocentric mechanisms have not effectively reduced the proportion of patients with drug-resistant epilepsy. Further exploration of the cellular or molecular mechanism of epilepsy is expected to provide new options for treatment. Recently, more and more researches focus on brain network components other than neurons, among which microglia have attracted much attention for their diverse biological functions. As the resident immune cells of the central nervous system, microglia have highly plastic transcription, morphology and functional characteristics, which can change dynamically in a context-dependent manner during the progression of epilepsy. In the pathogenesis of epilepsy, highly reactive microglia interact with other components in the epileptogenic network by performing crucial functions such as secretion of soluble factors and phagocytosis, thus continuously reshaping the landscape of the epileptic brain microenvironment. Indeed, microglia appear to be both pro-epileptic and anti-epileptic under the different spatiotemporal contexts of disease, rendering interventions targeting microglia biologically complex and challenging. This comprehensive review critically summarizes the pathophysiological role of microglia in epileptic brain homeostasis alterations and explores potential therapeutic or modulatory targets for epilepsy targeting microglia.

Pre-existing Toxoplasma gondii infection increases susceptibility to pentylenetetrazol-induced seizures independent of traumatic brain injury in mice

Introduction

Post-traumatic epilepsy (PTE) is a debilitating chronic outcome of traumatic brain injury (TBI), and neuroinflammation is implicated in increased seizure susceptibility and epileptogenesis. However, how common clinical factors, such as infection, may modify neuroinflammation and PTE development has been understudied. The neurotropic parasite, Toxoplasma gondii (T. gondii) incurably infects one-third of the world's population. Thus, many TBI patients have a pre-existing T. gondii infection at the time of injury. T. gondii infection results in chronic low-grade inflammation and altered signaling pathways within the brain, and preliminary clinical evidence suggest that it may be a risk factor for epilepsy. Despite this, no studies have considered how a pre-existing T. gondii infection may alter the development of PTE.

Methods

This study aimed to provide insight into this knowledge gap by assessing how a pre-existing T. gondii infection alters susceptibility to, and severity of, pentylenetetrazol (PTZ)-induced seizures (i.e., a surrogate marker of epileptogenesis/PTE) at a chronic stage of TBI recovery. We hypothesized that T. gondii will increase the likelihood and severity of seizures following PTZ administration, and that this would occur in the presence of intensified neuroinflammation. To test this, 6-week old male and female C57BL/6 Jax mice were intraperitoneally injected with 50,000 T. gondii tachyzoites or with the PBS vehicle only. At 12-weeks old, mice either received a severe TBI via controlled cortical impact or sham injury. At 18-weeks post-injury, mice were administered 40 mg/kg PTZ and video-recorded for evaluation of seizure susceptibility. Fresh cortical tissue was then collected for gene expression analyses.

Results

Although no synergistic effects were evident between infection and TBI, chronic T. gondii infection alone had robust effects on the PTZ-seizure response and gene expression of markers related to inflammatory, oxidative stress, and glutamatergic pathways. In addition to this, females were more susceptible to PTZ-induced seizures than males. While TBI did not impact PTZ responses, injury effects were evident at the molecular level.

Discussion

Our data suggests that a pre-existing T. gondii infection is an important modifier of seizure susceptibility independent of brain injury, and considerable attention should be directed toward delineating the mechanisms underlying this pro-epileptogenic factor.

Pickering emulsion technology based on the concept of “the combination of medicine and adjuvant” to enhance the oxidation stability of volatile oils in solid preparations—taking Lingzhu Pulvis as an example

The antioxidant properties of the volatile oil of Acorus calamus in Lingzhu Pulvis may be enhanced by the introduction of Pickering emulsion technology based on the concept of “the combination of medicine and adjuvant”. The characterization of each drinking tablet of Lingzhu Pulvis was conducted to determine the stabilizer. The optimal stabilizer concentration, oil–water ratio and preparation method of the Pickering emulsion were then determined and analyzed using NIR. The contents of malondialdehyde and peroxide in the volatile oils of each group were compared at different AIBA concentrations. The trends of the components were then analyzed by GC-MS. The pearl powder was screened as the stabilizer of the Pickering emulsion; the pearl powder concentration of 0.065 g mL⁻¹ and the oil–water ratio of 9 : 11 were found to be the optimal emulsion formation conditions, and the high-pressure homogenization method was the optimal preparation method. The NIR analysis showed that the volatile oil was wrapped by the pearl powder and no new chemical structure formed in the Pickering emulsion. The Pickering emulsions had lower oxidation levels than the crude oil groups at AIBA concentrations of 5, 10, and 15 mg mL⁻¹. The results of the GC-MS analysis showed that the antioxidant properties of the volatile components were significantly higher in the Pickering emulsion group compared to the crude oil group. Pickering emulsions can be used to enhance the antioxidant properties of volatile components in oil-containing solid formulations based on the concept of “the combination of medicine and adjuvant”.

The antioxidant properties of the volatile oil of Acorus calamus in Lingzhu Pulvis may be enhanced by the introduction of Pickering emulsion technology based on the concept of “the combination of medicine and adjuvant”.