An inflammatory pulmonary insult post-traumatic brain injury worsens subsequent spatial learning and neurological outcomes

Extracranial Effects of Traumatic Brain Injury: A Narrative Review

BACKGROUND

Traumatic brain injury (TBI) is often associated with other injuries and comorbidities. However, even isolated TBI directly leads to dysfunction in multiple body systems outside the central nervous system. These extracranial effects of TBI target systems including the autonomic nervous, cardiovascular, renal, pulmonary, immune, gastrointestinal, and hemostasis systems, as well as causing significant alteration to systemic metabolism.

AIM

This review is intended to outline the effects of TBI on other body systems, and place these in context with treatment considerations for these patients.

SIGNIFICANCE

Systemic effects of TBI have implications for acute and critical care management of patients with TBI, including pharmacologic treatment. They also affect treatment decisions in chronic TBI care, as well as TBI-unrelated routine medical care for patients with chronic TBI. In addition, extracranial effects of TBI should be considered in research settings.

CONCLUSIONS

It is important for clinicians and researchers to be aware of these extracranial effects, and consider their effects on pathology, treatment decisions, and interpretation of research findings.

Aminophylline targets miR-128-3p/Slc7a11 axis to attenuate neuronal ferroptosis after traumatic brain injury

Traumatic brain injury (TBI) is a significant global health issue, characterized by high rates of morbidity and mortality, along with substantial economic strains on healthcare systems. This study explores the potential of Aminophylline (AMP), a medication traditionally used for cardiovascular conditions and bronchiectasis, to enhance TBI outcomes by protecting against neuronal damage. Our findings indicate that AMP treatment significantly reduces neuronal ferroptosis in the cortex, leading to less tissue damage and notable improvements in cognitive and motor functions in mice subjected to controlled cortical impact (CCI). Additionally, we found that TBI resulted in decreased expression of miR-128-3p, a reduction that was further strengthened by AMP treatment. Gain-of-function experiments showed that overexpressing miR-128-3p increases neuronal ferroptosis by targeting Slc7a11, indicating how AMP mitigates cognitive and motor impairments in CCI mice. This study highlights the potential of AMP in treating TBI through the miR-128-3p/Slc7a11 pathway, marking the first report of its protective effects against ferroptosis in TBI.

Genes Involved by Dexamethasone in Prevention of Long-Term Memory Impairment Caused by Lipopolysaccharide-Induced Neuroinflammation

Inflammatory activation within the brain is linked to a decrease in cognitive abilities; however, the molecular mechanisms implicated in the development of inflammatory-related cognitive dysfunction and its prevention are poorly understood. This study compared the responses of hippocampal transcriptomes 3 months after the striatal infusion of lipopolysaccharide (LPS; 30 µg), resulting in memory loss, or with dexamethasone (DEX; 5 mg/kg intraperitoneal) pretreatment, which abolished the long-term LPS-induced memory impairment. After LPS treatment, a significant elevation in the expression of immunity/inflammatory-linked genes, including chemokines (Cxcl13), cytokines (Il1b and Tnfsf13b), and major histocompatibility complex (MHC) class II members (Cd74, RT1-Ba, RT1-Bb, RT1-Da, and RT1-Db1) was observed. DEX pretreatment did not change the expression of these genes, but significantly affected the expression of genes encoding ion channels, primarily calcium and potassium channels, regulators of glutamate (Slc1a2, Grm5, Grin2a), and GABA (Gabrr2, Gabrb2) neurotransmission, which enriched in such GO biological processes as "Regulation of transmembrane transport", "Cognition", "Learning", "Neurogenesis", and "Nervous system development". Taken together, these data suggest that (1) pretreatment with DEX did not markedly affect LPS-induced prolonged inflammatory response; (2) DEX pretreatment can affect processes associated with glutamatergic signaling and nervous system development, possibly involved in the recovery of memory impairment induced by LPS.

Beta blockade in TBI: Dose-dependent reductions in BBB leukocyte mobilization and permeability in vivo

BACKGROUND

Traumatic brain injury (TBI) is accompanied by a hyperadrenergic catecholamine state that can cause penumbral neuroinflammation. Prospective human studies demonstrate improved TBI survival with beta blockade (bb), although mechanisms remain unclear. We hypothesized that deranged post-TBI penumbral blood brain barrier (BBB) leukocyte mobilization and permeability are improved by bb.

METHODS

CD1 male mice (n = 64) were randomly assigned to severe TBI-controlled cortical impact: 6 m/s velocity, 1 mm depth, 3 mm diameter-or sham craniotomy, and IP injection of either saline or propranolol (1, 2, or 4 mg/kg) every 12 hours for 2 days. At 48 hours, in vivo pial intravital microscopy visualized live endothelial-leukocyte (LEU) interactions and BBB microvascular leakage. Twice daily clinical recovery was assessed by regaining of lost body weight and the Garcia Neurological Test (motor, sensory, reflex, balance assessments). Brain edema was determined by hemispheric wet-to-dry ratios.

RESULTS

Propranolol after TBI reduced both in vivo LEU rolling and BBB permeability in a dose-dependent fashion compared with no treatment (p < 0.001). Propranolol reduced cerebral edema (p < 0.001) and hastened recovery of lost body weight at 48 hours (p < 0.01). Compared with no treatment (14.9 ± 0.2), 24-hour Garcia Neurologic Test scores were improved with 2 (15.8 ± 0.2, p = 0.02) and 4 (16.1 ± 0.1, p = 0.001) but not with 1 mg/kg propranolol.

CONCLUSION

Propranolol administration reduces post-TBI LEU mobilization and microvascular permeability in the murine penumbral neurovasculature and leads to reduced cerebral edema. This is associated with hastened recovery of post-TBI weight loss and neurologic function with bb treatment. Dose-dependent effects frame a mechanistic relationship between bb and improved human outcomes after TBI.

Pulmonary infection in traumatic brain injury patients undergoing tracheostomy: predicators and nursing care

Background

Pulmonary infection is common yet serious complication in patients with severe traumatic brain injury (STBI). We aimed to evaluate the predicators of pulmonary infection in STBI patients undergoing tracheostomy, to provide evidence for the clinical nursing care of STBI patients.

Methods

This study was a retrospective cohort design. STBI patients undergoing tracheostomy treatment from January 1, 2019 to August 31, 2021 in our hospital were included. The characteristics of pulmonary infection and no pulmonary infection patients were analyzed.

Results

A total 216 STBI patients undergoing tracheostomy were included, the incidence of pulmonary infection was 26.85%. Diabetes (r = 0.782), hypoproteinemia (r = 0.804), duration of coma(r = 0.672), duration of mechanical ventilation(r = 0.724) and length of hospital stay (r = 0.655), length of hospital stay post tracheostomy (r = 0.554), mortality (r = 0.598) were all correlated with pulmonary infection (all p < 0.05). Klebsiella pneumoniae (33.87%) and Staphylococcus aureus (29.03%) were the most commonly seen pathogens in the pulmonary infection of TBI patients. Logistic regression analyses indicated that diabetes (OR 2.232, 95% CI 1.215–3.904), hypoproteinemia with plasma total protein < 60 g/L (OR 1.922, 95% CI 1.083–3.031), duration of coma ≥ 22 h (OR 2.864, 95% CI 1.344–5.012), duration of mechanical ventilation ≥ 5 days (OR 3.602, 95% CI 1.297–5.626), length of hospital stay ≥ 21 days (OR 2.048, 95% CI 1.022–3.859) were the risk factors of pulmonary infection in TBI patients undergoing tracheostomy (all p < 0.05).

Conclusions

Further investigations on the early preventions and treatments targeted on those risk factors are needed to reduce the pulmonary infection in clinical practice.

Pediatric traumatic brain injury and a subsequent transient immune challenge independently influenced chronic outcomes in male mice

Traumatic brain injury (TBI) is a major contributor to death and disability worldwide. Children are at particularly high risk of both sustaining a TBI and experiencing serious long-term consequences, such as cognitive deficits, mental health problems and post-traumatic epilepsy. Severe TBI patients are highly susceptible to nosocomial infections, which are mostly acquired within the first week of hospitalization post-TBI. Yet the potential chronic impact of such acute infections following pediatric TBI remains unclear. In this study, we hypothesized that a peripheral immune challenge, such as lipopolysaccharide (LPS)-mimicking a hospital-acquired infection-would worsen inflammatory, neurobehavioral, and seizure outcomes after experimental pediatric TBI. To test this, three-week old male C57Bl/6J mice received a moderate controlled cortical impact or sham surgery, followed by 1 mg/kg i.p. LPS (or 0.9% saline vehicle) at 4 days TBI. Mice were randomized to four groups; sham-saline, sham-LPS, TBI-saline or TBI-LPS (n = 15/group). Reduced general activity and increased anxiety-like behavior were observed within 24 h in LPS-treated mice, indicating a transient sickness response. LPS-treated mice also exhibited a reduction in body weights, which persisted chronically. From 2 months post-injury, mice underwent a battery of tests for sensorimotor, cognitive, and psychosocial behaviors. TBI resulted in hyperactivity and spatial memory deficits, independent of LPS; whereas LPS resulted in subtle deficits in spatial memory retention. At 5 months post-injury, video-electroencephalographic recordings were obtained to evaluate both spontaneous seizure activity as well as the evoked seizure response to pentylenetetrazol (PTZ). TBI increased susceptibility to PTZ-evoked seizures; whereas LPS appeared to increase the incidence of spontaneous seizures. Post-mortem analyses found that TBI, but not LPS, resulted in robust glial reactivity and loss of cortical volume. A TBI × LPS interaction in hippocampal volume suggested that TBI-LPS mice had a subtle increase in ipsilateral hippocampus tissue loss; however, this was not reflected in neuronal cell counts. Both TBI and LPS independently had modest effects on chronic hippocampal gene expression. Together, contrary to our hypothesis, we observed minimal synergy between TBI and LPS. Instead, pediatric TBI and a subsequent transient immune challenge independently influenced chronic outcomes. These findings have implications for future preclinical modeling as well as acute post-injury patient management.

Post-traumatic brain injury antithrombin III recovers Morris water maze cognitive performance, improving cued and spatial learning

BACKGROUND

Neuroinflammation and cerebral edema development following severe traumatic brain injury (TBI) affect subsequent cognitive recovery. Independent of its anticoagulant effects, antithrombin III (AT-III) has been shown to block neurovascular inflammation after severe TBI, reduce cerebral endothelial-leukocyte interactions, and decrease blood-brain barrier permeability. We hypothesized that AT-III administration after TBI would improve post-TBI cognitive recovery, specifically enhancing learning, and memory.

METHODS

Fifteen CD1 male mice were randomized to undergo severe TBI (controlled cortical impact [CCI]: velocity, 6 m/s; depth, 1 mm; diameter, 3 mm) or sham craniotomy and received either intravenous AT-III (250 IU/kg) or vehicle (VEH/saline) 15 minutes and 24 hours post-TBI. Animals underwent Morris water maze testing from 6 to 14 days postinjury consisting of cued learning trials (platform visible), spatial learning trials (platform invisible, spatial cues present), and probe (memory) trials (platform removed, spatial cues present). Intergroup differences were assessed by the Kruskal-Wallis test (p < 0.05).

RESULTS

Morris water maze testing demonstrated that cumulative cued learning (overall mean time in seconds to reach the platform on days 6-8) was worst in CCI-VEH animals (26.1 ± 2.4 seconds) compared with CCI-AT-III counterparts (20.3 ± 2.1 seconds, p < 0.01). Cumulative noncued spatial learning was also worst in the CCI-VEH group (23.4 ± 1.8 seconds) but improved with AT-III (17.6 ± 1.5 seconds, p < 0.01). In probe trials, AT-III failed to significantly improve memory ability. Animals that underwent sham craniotomy demonstrated preserved learning and memory compared with all CCI counterparts (p < 0.05).

CONCLUSION

Antithrombin III improves neurocognitive recovery weeks after TBI. This improvement is particularly related to improvement in learning but not memory function. Pharmacologic support of enhanced learning may support new skill acquisition or relearning to improve outcomes after TBI.

LEVEL OF EVIDENCE

Therapeutic/care management, level II.

Bidirectional Brain-Systemic Interactions and Outcomes After TBI

Traumatic brain injury (TBI) is a debilitating disorder associated with chronic progressive neurodegeneration and long-term neurological decline. Importantly, there is now substantial and increasing evidence that TBI can negatively impact systemic organs, including the pulmonary, gastrointestinal (GI), cardiovascular, renal, and immune system. Less well appreciated, until recently, is that such functional changes can affect both the response to subsequent insults or diseases, as well as contribute to chronic neurodegenerative processes and long-term neurological outcomes. In this review, we summarize evidence showing bidirectional interactions between the brain and systemic organs following TBI and critically assess potential underlying mechanisms.