Inflammatory cytokine receptor blockade in a rodent model of mild traumatic brain injury

IL-1R1 signaling in TBI: assessing chronic impacts and neuroinflammatory dynamics in a mouse model of mild closed-head injury

Neuroinflammation contributes to secondary injury cascades following traumatic brain injury (TBI), with alternating waves of inflammation and resolution. Interleukin-1 (IL-1), a critical neuroinflammatory mediator originating from brain endothelial cells, microglia, astrocytes, and peripheral immune cells, is acutely overexpressed after TBI, propagating secondary injury and tissue damage. IL-1 affects blood-brain barrier permeability, immune cell activation, and neural plasticity. Despite the complexity of cytokine signaling post-TBI, we hypothesize that IL-1 signaling specifically regulates neuroinflammatory response components. Using a closed-head injury (CHI) TBI model, we investigated IL-1's role in the neuroinflammatory cascade with a new global knock-out (gKO) mouse model of the IL-1 receptor (IL-1R1), which efficiently eliminates all IL-1 signaling. We found that IL-1R1 gKO attenuated behavioral impairments 14 weeks post-injury and reduced reactive microglia and astrocyte staining in the neocortex, corpus callosum, and hippocampus. We then examined whether IL-1R1 loss altered acute neuroinflammatory dynamics, measuring gene expression changes in the neocortex at 3, 9, 24, and 72 h post-CHI using the NanoString Neuroinflammatory panel. Of 757 analyzed genes, IL-1R1 signaling showed temporal specificity in neuroinflammatory gene regulation, with major effects at 9 h post-CHI. IL-1R1 signaling specifically affected astrocyte-related genes, selectively upregulating chemokines like Ccl2, Ccl3, and Ccl4, while having limited impact on cytokine regulation, such as Tnfα. This study provides further insight into IL-1R1 function in amplifying the neuroinflammatory cascade following CHI in mice and demonstrates that suppression of IL-1R1 signaling offers long-term protective effects on brain health.

The Single-Dose Application of Interleukin-4 Ameliorates Secondary Brain Damage in the Early Phase after Moderate Experimental Traumatic Brain Injury in Mice

Activation of the interleukin-4 (IL-4) pathway ameliorates secondary injury mechanisms after experimental traumatic brain injury (TBI); therefore, we assessed the effect of a therapeutic IL-4 administration on secondary brain damage after experimental TBI. We subjected 100 C57/Bl6 wildtype mice to controlled cortical impact (CCI) and administered IL-4 or a placebo control subcutaneously 15 min thereafter. Contusion volume (Nissl staining), neurological function (hole board, video open field, and CatWalkXT®), and the immune response (immunofluorescent staining) were analyzed up to 28 days post injury (dpi). Contusion volumes were significantly reduced after IL-4 treatment up to 14 dpi (e.g., 6.47 ± 0.41 mm3 vs. 3.80 ± 0.85 mm3, p = 0.011 3 dpi). Macrophage invasion and microglial response were significantly attenuated in the IL-4 group in the acute phase after CCI (e.g., 1.79 ± 0.15 Iba-1+/CD86+ cells/sROI vs. 1.06 ± 0.21 Iba-1/CD86+ cells/sROI, p = 0.030 in the penumbra 3 dpi), whereas we observed an increased neuroinflammation thereafter (e.g., mean GFAP intensity of 3296.04 ± 354.21 U vs. 6408.65 ± 999.54 U, p = 0.026 in the ipsilateral hippocampus 7 dpi). In terms of functional outcome, several gait parameters were improved in the acute phase following IL-4 treatment (e.g., a difference in max intensity of -7.58 ± 2.00 U vs. -2.71 ± 2.44 U, p = 0.041 3 dpi). In conclusion, the early single-dose administration of IL-4 significantly reduces secondary brain damage in the acute phase after experimental TBI in mice, which seems to be mediated by attenuation of macrophage and microglial invasion.

Inhibition of P2X4 and P2X7 receptors improves histological and behavioral outcomes after experimental traumatic brain injury in rats

Release of large amounts of adenosine triphosphate (ATP), a gliotransmitter, into the extracellular space by traumatic brain injury (TBI) is considered to activate the microglia followed by release of inflammatory cytokines resulting in excessive inflammatory response that induces secondary brain injury. The present study investigated whether antagonists of ATP receptors (P2X4 and/or P2X7) on microglia are beneficial for reducing the post-injury inflammatory response that leads to secondary injury, a prognostic aggravation factor of TBI. Adult male Sprague-Dawley rats were subjected to cortical contusion injury (CCI) and randomly assigned to injury and drug treatment conditions, as follows: i) No surgical intervention (naïve group); ii) dimethyl sulfoxide treatment after CCI (CCI-control group); iii) 5-BDBD (antagonist of P2X4 receptor) treatment after CCI (CCI-5-BDBD group); iv) CCI-AZ11645373 (antagonist of P2X7 receptor) treatment after CCI (CCI-AZ11645373 group); v) or 5-BDBD and AZ11645373 treatment after CCI (CCI-5-BDBD + AZ11645373 group). In the CCI-5-BDBD, CCI-AZ11645373, and CCI-5-BDBD + AZ11645373 groups, expression of activated microglia was suppressed in the ipsilateral cortex and hippocampus 3 days after the CCI. Western blotting with ionized calcium-binding adaptor molecule 1 antibody revealed that administration of CCI-5-BDBD and/or CCI-AZ11645373 suppressed expression of microglia and reduced expression of inflammatory cytokine mRNA 3 days after the CCI. Furthermore, the plus maze test, which reflects the spatial memory function and involves the hippocampal function, showed improvement 28 days after secondary injury to the hippocampus. These findings confirmed that blocking the P2X4 and P2X7 receptors, which are ATP receptors central in gliotransmission, suppresses microglial activation and subsequent cytokine expression after brain injury, and demonstrates the potential as an effective treatment for reducing secondary brain injury.

Orally Administered Brain Protein Combined With Probiotics Increases Treg Differentiation to Reduce Secondary Inflammatory Damage Following Craniocerebral Trauma

Craniocerebral trauma is caused by external forces that can have detrimental effects on the vasculature and adjacent nerve cells at the site. After the mechanical and structural primary injury, a complex series of secondary cascades of injury exacerbates brain damage and cognitive dysfunction following mechanical and structural primary injury. Disruption of the blood-brain barrier and exposure of brain proteins following craniocerebral trauma, recognition by the immune system triggering autoimmune attack, and excessive secondary inflammatory responses causing malignant brain swelling, cerebral edema, and subsequent brain cell apoptosis provide a new direction for the suppression of brain inflammatory responses in the treatment of craniocerebral trauma. We observed that CD4⁺T/CD8⁺T in peripheral blood T cells of craniocerebral trauma rats were significantly higher than those of normal rats, and the ratio of CD4⁺CD25⁺Foxp3 (Foxp3)⁺Regulatory T cell (Treg) was significantly lower than that of normal rats and caused increased secondary inflammation. We constructed a rat model of post-surgical brain injury and orally administered brain protein combined with probiotics, which was observed to significantly reduce CD4⁺T/CD8⁺T and induce T-cell differentiation into CD4⁺CD25⁺Foxp3⁺Treg, thus, reducing secondary inflammatory responses following craniocerebral trauma. However, collecting intestinal stool and small intestinal tissues for broad target metabolomics, 16s rRNA bacteriomics, and the combined analysis of intestinal tissue proteomics revealed that oral administration of brain protein combined with probiotics activates glycerophospholipid and vitamin B6 metabolic pathways to promote the production of CD4⁺CD25⁺Foxp3⁺Treg. Therefore, we propose the novel idea that oral administration of brain protein combined with probiotics can induce immune tolerance by increasing Treg differentiation, thus, reducing secondary inflammatory injury following craniocerebral trauma.

Inflammatory Regulation of CNS Barriers After Traumatic Brain Injury: A Tale Directed by Interleukin-1

Several barriers separate the central nervous system (CNS) from the rest of the body. These barriers are essential for regulating the movement of fluid, ions, molecules, and immune cells into and out of the brain parenchyma. Each CNS barrier is unique and highly dynamic. Endothelial cells, epithelial cells, pericytes, astrocytes, and other cellular constituents each have intricate functions that are essential to sustain the brain's health. Along with damaging neurons, a traumatic brain injury (TBI) also directly insults the CNS barrier-forming cells. Disruption to the barriers first occurs by physical damage to the cells, called the primary injury. Subsequently, during the secondary injury cascade, a further array of molecular and biochemical changes occurs at the barriers. These changes are focused on rebuilding and remodeling, as well as movement of immune cells and waste into and out of the brain. Secondary injury cascades further damage the CNS barriers. Inflammation is central to healthy remodeling of CNS barriers. However, inflammation, as a secondary pathology, also plays a role in the chronic disruption of the barriers' functions after TBI. The goal of this paper is to review the different barriers of the brain, including (1) the blood-brain barrier, (2) the blood-cerebrospinal fluid barrier, (3) the meningeal barrier, (4) the blood-retina barrier, and (5) the brain-lesion border. We then detail the changes at these barriers due to both primary and secondary injury following TBI and indicate areas open for future research and discoveries. Finally, we describe the unique function of the pro-inflammatory cytokine interleukin-1 as a central actor in the inflammatory regulation of CNS barrier function and dysfunction after a TBI.

3,6'-dithiopomalidomide reduces neural loss, inflammation, behavioral deficits in brain injury and microglial activation

Traumatic brain injury (TBI) causes mortality and disability worldwide. It can initiate acute cell death followed by secondary injury induced by microglial activation, oxidative stress, inflammation and autophagy in brain tissue, resulting in cognitive and behavioral deficits. We evaluated a new pomalidomide (Pom) analog, 3,6'-dithioPom (DP), and Pom as immunomodulatory agents to mitigate TBI-induced cell death, neuroinflammation, astrogliosis and behavioral impairments in rats challenged with controlled cortical impact TBI. Both agents significantly reduced the injury contusion volume and degenerating neuron number evaluated histochemically and by MRI at 24 hr and 7 days, with a therapeutic window of 5 hr post-injury. TBI-induced upregulated markers of microglial activation, astrogliosis and the expression of pro-inflammatory cytokines, iNOS, COX-2, and autophagy-associated proteins were suppressed, leading to an amelioration of behavioral deficits with DP providing greater efficacy. Complementary animal and cellular studies demonstrated DP and Pom mediated reductions in markers of neuroinflammation and α-synuclein-induced toxicity.

The anti-inflammation effect of Baige capsule and its principal components mixture in MCAO rats

BACKGROUND

Baige (BG) is a compound Chinese herbal preparation, constituted of different position extracts (ethanol extracts from Pueraria lobate and SFE-CO₂ extracts from Radix Angelicae dahuricae) of P. lobata and A. dahurica to treat the brain injury in patients.

AIM

The goal of this study was to identify the neuroprotective properties of BG and its principal component mixture (PCM) and verify whether the material basis for BG is its PCM.

METHODS

Middle cerebral artery occlusion (MCAO) was operated on male Sprague-Dawley rat for 2 h, different doses of BG or PCM or vehicle were gavaged after 3 h of MCAO. Rats were sacrificed after 30 days treatment. Blood serum inflammation factors and NGF were detected by ELISA.

RESULTS

After 30 days of treatment, both BG and PCM interventions reduced the infarct volume, modified neurological severity score (mNSS) in rats, declined IL-1β and IL-6 levels in the serum, increased NGF level in the serum and recovered the number of Nissl body in injured brain.

CONCLUSIONS

Both BG and PCM exert equivalent levels of recovery effect in MCAO on rats; and PCM is the material foundation of BG. This recovery effect is associated with inflammatory inhibition and NGF production.

Evaluation of Touchscreen Chambers To Assess Cognition in Adult Mice: Effect of Training and Mild Traumatic Brain Injury

Cognitive impairments are often experienced after a mild traumatic brain injury (mTBI). In the clinical arena, neuropsychological assessments are used frequently to detect cognitive deficits. Animal models of mTBI, however, rely on an assortment of behavioral tasks to assess cognitive outcome. Computer-based touchscreen systems have been developed for rodents and are hypothesized to offer a translational approach to evaluate cognitive function because of the similarities of tasks performed in rodents to those implemented in humans. While these touchscreen systems have been used in pre-clinical models of neurodegenerative diseases and psychiatric disorders, their use in assessing cognitive impairment after mTBI has not been investigated. We hypothesized that mTBI would result in impaired cognitive performance on touchscreen tasks, particularly those with hippocampal-based learning components, including the paired associate learning (PAL) task and the location discrimination (LD) task. Adult male, C57BL/6 mice received a single impact-acceleration mTBI. We found that training mice before injury to perform to criteria is arduous and that performance is sensitive to many environmental variables. Despite extensive optimization and training, mice failed to perform better than chance in the PAL paradigm. Alternatively, mice demonstrated some capacity to learn in the LD paradigm, but only with the easier stages of the task. The mTBI did not affect performance in the LD paradigm, however. Thus, we concluded that under the conditions presented here, the PAL and LD touchscreen tasks are not robust outcome measures for the evaluation of cognitive performance in C57BL/6 mice after a single impact-acceleration mTBI.

Hyperthermia and Mild Traumatic Brain Injury: Effects on Inflammation and the Cerebral Vasculature

Mild traumatic brain injury (mTBI) or concussion represents the majority of brain trauma in the United States. The pathophysiology of mTBI is complex and may include both focal and diffuse injury patterns. In addition to altered circuit dysfunction and traumatic axonal injury (TAI), chronic neuroinflammation has also been implicated in the pathophysiology of mTBI. Recently, our laboratory has reported the detrimental effects of mild hyperthermic mTBI in terms of worsening histopathological and behavioral outcomes. To clarify the role of temperature-sensitive neuroinflammatory processes on these consequences, we evaluated the effects of elevated brain temperature (39°C) on altered microglia/macrophage phenotype patterns after mTBI, changes in leukocyte recruitment, and TAI. Sprague-Dawley male rats underwent mild parasagittal fluid-percussion injury under normothermic (37°C) or hyperthermic (39°C) conditions. Cortical and hippocampal regions were analyzed using several cellular and molecular outcome measures. At 24 h, the ratio of iNOS-positive (M1 type phenotype) to arginase-positive (M2 type phenotype) cells after hyperthermic mTBI showed an increase compared with normothermia by flow cytometry. Inflammatory response gene arrays also demonstrated a significant increase in several classes of pro-inflammatory genes with hyperthermia treatment over normothermia. The injury-induced expression of chemokine ligand 2 (Ccl2) and alpha-2-macroglobulin were also increased with hyperthermic mTBI. With western blot analysis, an increase in CD18 and intercellular cell adhesion molecule-1 (ICAM-1) with hyperthermia and a significant increase in Iba1 reactive microglia are reported in the cerebral cortex. Together, these results demonstrate significant differences in the cellular and molecular consequences of raised brain temperature at the time of mTBI. The observed polarization toward a M1-phenotype with mild hyperthermia would be expected to augment chronic inflammatory cascades, sustained functional deficits, and increased vulnerability to secondary insults. Mild elevations in brain temperature may contribute to the more severe and longer lasting consequences of mTBI or concussion reported in some patients.

Perispinal Delivery of CNS Drugs

Perispinal injection is a novel emerging method of drug delivery to the central nervous system (CNS). Physiological barriers prevent macromolecules from efficiently penetrating into the CNS after systemic administration. Perispinal injection is designed to use the cerebrospinal venous system (CSVS) to enhance delivery of drugs to the CNS. It delivers a substance into the anatomic area posterior to the ligamentum flavum, an anatomic region drained by the external vertebral venous plexus (EVVP), a division of the CSVS. Blood within the EVVP communicates with the deeper venous plexuses of the CSVS. The anatomical basis for this method originates in the detailed studies of the CSVS published in 1819 by the French anatomist Gilbert Breschet. By the turn of the century, Breschet's findings were nearly forgotten, until rediscovered by American anatomist Oscar Batson in 1940. Batson confirmed the unique, linear, bidirectional and retrograde flow of blood between the spinal and cerebral divisions of the CSVS, made possible by the absence of venous valves. Recently, additional supporting evidence was discovered in the publications of American neurologist Corning. Analysis suggests that Corning's famous first use of cocaine for spinal anesthesia in 1885 was in fact based on Breschet's anatomical findings, and accomplished by perispinal injection. The therapeutic potential of perispinal injection for CNS disorders is highlighted by the rapid neurological improvement in patients with otherwise intractable neuroinflammatory disorders that may ensue following perispinal etanercept administration. Perispinal delivery merits intense investigation as a new method of enhanced delivery of macromolecules to the CNS and related structures.