Effects of propranolol and clonidine on brain edema, blood-brain barrier permeability, and endothelial glycocalyx disruption after fluid percussion brain injury in the rat

Preclinical Studies on Mechanisms Underlying the Protective Effects of Propranolol in Traumatic Brain Injury: A Systematic Review

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity amongst trauma patients. Its treatment is focused on minimizing progression to secondary injury. Administration of propranolol for TBI maydecrease mortality and improve functional outcomes. However, it is our sense that its use has not been universally adopted due to low certainty evidence. The literature was reviewed to explore the mechanism of propranolol as a therapeutic intervention in TBI to guide future clinical investigations. Medline, Embase, and Scopus were searched for studies that investigated the effect of propranolol on TBI in animal models from inception until June 6, 2023. All routes of administration for propranolol were included and the following outcomes were evaluated: cognitive functions, physiological and immunological responses. Screening and data extraction were done independently and in duplicate. The risk of bias for each individual study was assessed using the SYCLE's risk of bias tool for animal studies. Three hundred twenty-three citations were identified and 14 studies met our eligibility criteria. The data suggests that propranolol may improve post-TBI cognitive and motor function by increasing cerebral perfusion, reducing neural injury, cell death, leukocyte mobilization and p-tau accumulation in animal models. Propranolol may also attenuate TBI-induced immunodeficiency and provide cardioprotective effects by mitigating damage to the myocardium caused by oxidative stress. This systematic review demonstrates that propranolol may be therapeutic in TBI by improving cognitive and motor function while regulating T lymphocyte response and levels of myocardial reactive oxygen species. Oral or intravenous injection of propranolol following TBI is associated with improved cerebral perfusion, reduced neuroinflammation, reduced immunodeficiency, and cardio-neuroprotection in preclinical studies.

THE NEUROENDOTHELIAL AXIS IN TRAUMATIC BRAIN INJURY: MECHANISMS OF MULTIORGAN DYSFUNCTION, NOVEL THERAPIES, AND FUTURE DIRECTIONS

ABSTRACT

Severe traumatic brain injury (TBI) often initiates a systemic inflammatory response syndrome, which can potentially culminate into multiorgan dysfunction. A central player in this cascade is endotheliopathy, caused by perturbations in homeostatic mechanisms governed by endothelial cells due to injury-induced coagulopathy, heightened sympathoadrenal response, complement activation, and proinflammatory cytokine release. Unique to TBI is the potential disruption of the blood-brain barrier, which may expose neuronal antigens to the peripheral immune system and permit neuroinflammatory mediators to enter systemic circulation, propagating endotheliopathy systemically. This review aims to provide comprehensive insights into the "neuroendothelial axis" underlying endothelial dysfunction after TBI, identify potential diagnostic and prognostic biomarkers, and explore therapeutic strategies targeting these interactions, with the ultimate goal of improving patient outcomes after severe TBI.

Blood-brain barrier dysfunction in intensive care unit

The central nervous system is characterized by a peculiar vascularization termed blood-brain barrier (BBB), which regulates the exchange of cells and molecules between the cerebral tissue and the whole body. BBB dysfunction is a life-threatening condition since its presence corresponds to a marker of severity in most diseases encountered in the intensive care unit (ICU). During critical illness, inflammatory response, cytokine release, and other phenomena activating the brain endothelium contribute to alterations in the BBB and increase its permeability to solutes, cells, nutrients, and xenobiotics. Moreover, patients in the ICU are often old, with underlying acute or chronic diseases, and overly medicated due to their critical condition; these factors could also contribute to the development of BBB dysfunction. An accurate diagnostic approach is critical for the identification of the mechanisms underlying BBB alterations, which should be rapidly managed by intensivists. Several methods were developed to investigate the BBB and assess its permeability. Nevertheless, in humans, exploration of the BBB requires the use of indirect methods. Imaging and biochemical methods can be used to study the abnormal passage of molecules through the BBB. In this review, we describe the structural and functional characteristics of the BBB, present tools and methods for probing this interface, and provide examples of the main diseases managed in the ICU that are related to BBB dysfunction.

Clonidine safety and effectiveness in the management of suspected paroxysmal sympathetic hyperactivity post-traumatic brain injury: A retrospective cohort study

INTRODUCTION

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity worldwide. In addition, TBI may cause paroxysmal sympathetic hyperactivity (PSH), which is associated with poor clinical outcomes. This study aimed to evaluate the safety and effectiveness of clonidine in patients with TBI and suspected PSH.

METHODS

A retrospective cohort study for critically ill patients with TBI with suspected PSH admitted to intensive care units (ICUs) from 1 May 2016 to 31 January 2020 at a tertiary academic medical center. Eligible patients were categorized based on clonidine use during their ICU stay (Clonidine group vs. Control group). The primary outcome was the improvement in functional outcomes during ICU stay, defined by a delta Glasgow Coma Score (GCS). Secondary outcomes included ICU and hospital length of stay, heart rate variation, and 90-day mortality.

RESULTS

A total of 2915 patients were screened, of which 169 were included. Based on multiple regression analysis, patients who received clonidine showed better improvement in functional outcomes by a higher mean delta GCS than patients who did not (Beta Coeff. 0.41; CI: 0.07 - 0.74; P = 0.02). In addition, the patient's GCS upon ICU discharge and IV opioids requirement on day three were higher in the clonidine group than control (beta coefficient (95% CI): 0.18 (0.03, 0.32); p = 0.02 and beta coefficient (95% CI): 1.38 (0.24, 2.52); p = 0.02, respectively). No statistical differences were observed in any of the other secondary outcomes after adjusting for confounders.

CONCLUSION

This study found that patients who received clonidine had better functional outcomes during their ICU stay, as shown by their delta GCS than those who did not. Other outcomes were similar between the groups. More data are needed to explore the role of clonidine in patients with TBI with suspected PSH.

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.

Endothelial glycocalyx in traumatic brain injury associated coagulopathy: potential mechanisms and impact

Traumatic brain injury (TBI) remains one of the leading causes of death and disability worldwide; more than 10 million people are hospitalized for TBI every year around the globe. While the primary injury remains unavoidable and not accessible to treatment, the secondary injury which includes oxidative stress, inflammation, excitotoxicity, but also complicating coagulation abnormalities, is potentially avoidable and profoundly affects the therapeutic process and prognosis of TBI patients. The endothelial glycocalyx, the first line of defense against endothelial injury, plays a vital role in maintaining the delicate balance between blood coagulation and anticoagulation. However, this component is highly vulnerable to damage and also difficult to examine. Recent advances in analytical techniques have enabled biochemical, visual, and computational investigation of this vascular component. In this review, we summarize the current knowledge on (i) structure and function of the endothelial glycocalyx, (ii) its potential role in the development of TBI associated coagulopathy, and (iii) the options available at present for detecting and protecting the endothelial glycocalyx.

β-Blockers for traumatic brain injury: A systematic review and meta-analysis

BACKGROUND

Paroxysmal sympathetic hyperactivity (PSH) and catecholamine surge, which are associated with poor outcome, may be triggered by traumatic brain injury (TBI).β Adrenergic receptor blockers (β-blockers), as potential therapeutic agents to prevent paroxysmal sympathetic hyperactivity and catecholamine surge, have been shown to improve survival after TBI. The principal aim of this study was to investigate the effect of β-blockers on outcomes in patients with TBI.

METHODS

For this systematic review and meta-analysis, we searched MEDLINE, EMBASE, and Cochrane Library databases from inception to September 25, 2020, for randomized controlled trials, nonrandomized controlled trials, and observational studies reporting the effect of β-blockers on the following outcomes after TBI: mortality, functional measures, and cardiopulmonary adverse effects of β-blockers (e.g., hypotension, bradycardia, and bronchospasm). With use of random-effects model, we calculated pooled estimates, confidence intervals (CIs), and odds ratios (ORs) of all outcomes.

RESULTS

Fifteen studies with 12,721 patients were included. Exposure to β-blockers after TBI was associated with a significant reduction in adjusted in-hospital mortality (OR, 0.39; 95% CI, 0.30-0.51; I2 = 66.3%; p < 0.001). β-Blockers significantly improved the long-term (≥6 months) functional outcome (OR, 1.75; 95% CI, 1.09-2.80; I2 = 0%; p = 0.02). Statistically significant difference was not seen for cardiopulmonary adverse events (OR, 0.91; 95% CI, 0.55-1.50; I2 = 25.9%; p = 0.702).

CONCLUSION

This meta-analysis demonstrated that administration of β-blockers after TBI was safe and effective. Administration of β-blockers may therefore be suggested in the TBI care. However, more high-quality trials are needed to investigate the use of β-blockers in the management of TBI.

LEVEL OF EVIDENCE

Systematic review and meta-analysis, level III.

Propranolol attenuates cognitive, learning, and memory deficits in a murine model of traumatic brain injury

BACKGROUND

β-blockers have been shown to improve survival after traumatic brain injury (TBI); however, the impact of continuous dosage of β-blockers on cognitive function has not been elucidated. We hypothesized that a daily dose of propranolol can improve memory, learning, and cognitive function following TBI.

STUDY DESIGN

Twenty male C57BL mice were subjected to a cortical-controlled moderate TBI. Two hours after TBI, animals were randomly allocated to either the β-blocker group (n = 10) or the placebo group (n = 10). Mice in the β-blocker group received intraperitoneal 4 mg/kg propranolol every 24 hours for 7 days while the placebo group received 4 mg/kg normal saline. Baseline novel object recognition and classic maze tests were done prior to TBI and then daily from Day 1 through 7 after TBI. Animals were sacrificed on Day 7. Serum biomarkers were measured using ELISA and brain sections were analyzed using western blot and hematoxylin and eosin staining.

RESULTS

Both the β-blocker and placebo groups had lower recognition index scores compared with the baseline following TBI. β-blocker mice had significantly higher novel object recognition scores compared with placebo mice 2 days after TBI. The β-blocker group required less time to complete the maze-test compared to placebo group after Day 4. There was no difference regarding the serum levels of IL-1β, IL-6, and TNF-α. The β-blocker group had lower levels of UCHL-1 and higher levels of Hsp-70 in brain lysate. Hematoxylin and eosin staining revealed that more neurons in the hippocampal-CA1 area underwent apoptosis in the placebo group compared with the β-blocker group.

CONCLUSION

Postinjury propranolol administration results in improved memory, learning and cognitive functions in a murine model of moderate TBI. Propranolol increases the expression of antiapoptotic protein (Hsp-70) and decreases cell death in the hippocampal-CA1 area compared with the placebo.

Effects and mechanism of the etanercept on pancreatic encephalopathy

Pancreatic encephalopathy (PE) is a common fatal complication of acute pancreatitis (AP). Proinflammatory cytokines such as tumor necrosis factor (TNF)‑α and interleukin (IL)‑6 are generated during AP, and act synergistically to promote PE and multisystem failure. Caerulein‑induced AP provides a convenient model to explore the role of proinflammatory cytokines in PE. The aim of the present study was to examine the effect of the TNF‑α inhibitor etanercept in PE models and elucidate the regulatory mechanisms. To model PE in vitro, rat hippocampal H19‑7/IGF‑IR neuronal cells were treated with 10 nmol/ml caerulein alone or in combination with etanercept (1, 10 or 100 µmol/ml). To model PE in vivo, rats were injected with 50 µg/kg caerulein alone or combined with 10 mg/kg etanercept. At 6 h after administration, it was noted that etanercept downregulated expression of TNF‑α, IL‑1β and IL‑6 by negatively regulating NF‑κB (a master regulator of cytokine expression) signaling, and prevented the accumulation of reactive oxygen species. Conversely, etanercept promoted the expression of the neurotrophic and anti‑inflammatory hypoxia‑inducible factor 1 α (HIF‑1α). In rat hippocampus, etanercept also reduced the levels of TNF‑α, IL‑1β and IL‑6, upregulated HIF‑1α expression and inhibited the inflammatory response to reduce edema and neural necrosis. Together, these data suggested that etanercept could attenuate caerulein‑induced PE, at least in part via suppression of NF‑κB signaling and alleviation of oxidative stress.

Nonselective alpha-/beta- AR antagonists can inhibit pericyte proliferation, migration, and secretion in vitro

It has been reported that the beta-adrenergic receptor blocker (propranolol) and the a-adrenergic receptor (AR) blocker (phentolamine) both can inhibit human endothelial cell (EC) angiogenesis in vitro. However, it is unknown whether this inhibition also acts on pericytes. The present study aimed to determine how pericytes react to treatment with an a-/β- AR blocker. In the study, cell proliferation assays and scratch assay were performed to assess the effect of phentolamine or propranolol on cell proliferation and migration. Western blot and ELISA were employed to determine changes in VEGF-A and Ang-1 expression levels. The results indicated that the nonselective a-/β- AR blocker inhibited the proliferation, migration, and secretion of pericytes. The use of the nonselective a-/β- AR blocker might have an impact on vascularization and vascular maturation. Our research suggests the rational use of nonselective a-/β- AR blockers to treat angiogenesis-dependent diseases.

Propranolol protects cerebral autoregulation and reduces hippocampal neuronal cell death through inhibition of interleukin-6 upregulation after traumatic brain injury in pigs

BACKGROUND

Traumatic brain injury (TBI) is associated with reduced cerebral blood flow and impaired autoregulation after TBI, which may lead to poor outcome. Clinical evidence has implicated neurological injuries and associated neuroinflammation as causes of cardiac dysfunction. Studies on newborn pigs show an association of elevated catecholamines with a sex-dependent impairment of cerebral autoregulation after TBI. One strategy to decrease sympathetic hyperactivity is pharmacological intervention with beta blockade. We tested the hypothesis that propranolol would prevent the impairment of cerebral autoregulation and tissue changes after TBI via inhibition of interleukin-6 (IL-6) upregulation.

METHODS

Using newborn pigs of both sexes equipped with a closed cranial window, TBI was induced via lateral fluid percussion injury. Propranolol was administered at 1 h post-TBI. Analyses included cerebral autoregulation (pial artery reactivity) before and 4 h post-TBI, CSF IL-6 analysed (enzyme-linked immunosorbent assay), and histopathology at 4 h post-TBI.

RESULTS

Propranolol administration prevented impairment of hypotensive dilation in both male and female newborn pigs after fluid percussion injury, which was paralleled by reduced upregulation of IL-6 in the CSF. Moreover, propranolol prevented neuronal cell death in cornu amonis (CA)1 and CA3 hippocampus equivalently in male and female pigs after TBI. Papaverine-induced dilation was unchanged by TBI and propranolol.

CONCLUSIONS

These data indicate that sympathetic hyperactivity noted after TBI can be limited by propranolol administration to result in improved brain outcome post-injury via block of IL-6 upregulation, and this effect is irrespective of sex.