Bradykinin B2 Receptor Antagonism With LF 18-1505T Reduces Brain Edema and Improves Neurological Outcome After Closed Head Trauma in Rats

Bradykinin 2 Receptors Mediate Long-Term Neurocognitive Deficits After Experimental Traumatic Brain Injury

The kallikrein-kinin system is one of the first inflammatory pathways to be activated following traumatic brain injury (TBI) and has been shown to exacerbate brain edema formation in the acute phase through activation of bradykinin 2 receptors (B2R). However, the influence of B2R on chronic post-traumatic damage and outcome is unclear. In the current study, we assessed long-term effects of B2R-knockout (KO) after experimental TBI. B2R KO mice (heterozygous, homozygous) and wild-type (WT) littermates (n = 10/group) were subjected to controlled cortical impact (CCI) TBI. Lesion size was evaluated by magnetic resonance imaging up to 90 days after CCI. Motor and memory function were regularly assessed by Neurological Severity Score, Beam Walk, and Barnes maze test. Ninety days after TBI, brains were harvested for immunohistochemical analysis. There was no difference in cortical lesion size between B2R-deficient and WT animals 3 months after injury; however, hippocampal damage was reduced in B2R KO mice (p = 0.03). Protection of hippocampal tissue was accompanied by a significant improvement of learning and memory function 3 months after TBI (p = 0.02 WT vs. KO), whereas motor function was not influenced. Scar formation and astrogliosis were unaffected, but B2R deficiency led to a gene-dose-dependent attenuation of microglial activation and a reduction of CD45+ cells 3 months after TBI in cortex (p = 0.0003) and hippocampus (p < 0.0001). These results suggest that chronic hippocampal neurodegeneration and subsequent cognitive impairment are mediated by prolonged neuroinflammation and B2R. Inhibition of B2R may therefore represent a novel strategy to reduce long-term neurocognitive deficits after TBI.

Recent advances in the discovery and development of drugs targeting the kallikrein-kinin system

BACKGROUND

The kallikrein-kinin system is a key regulatory cascade involved in blood pressure maintenance, hemostasis, inflammation and renal function. Currently, approved drugs remain limited to the rare disease hereditary angioedema. However, growing interest in this system is indicated by an increasing number of promising drug candidates for further indications.

METHODS

To provide an overview of current drug development, a two-stage literature search was conducted between March and December 2023 to identify drug candidates with targets in the kallikrein-kinin system. First, drug candidates were identified using PubMed and Clinicaltrials.gov. Second, the latest publications/results for these compounds were searched in PubMed, Clinicaltrials.gov and Google Scholar. The findings were categorized by target, stage of development, and intended indication.

RESULTS

The search identified 68 drugs, of which 10 are approved, 25 are in clinical development, and 33 in preclinical development. The three most studied indications included diabetic retinopathy, thromboprophylaxis and hereditary angioedema. The latter is still an indication for most of the drug candidates close to regulatory approval (3 out of 4). For the emerging indications, promising new drug candidates in clinical development are ixodes ricinus-contact phase inhibitor for thromboprophylaxis and RZ402 and THR-149 for the treatment of diabetic macular edema (all phase 2).

CONCLUSION

The therapeutic impact of targeting the kallikrein-kinin system is no longer limited to the treatment of hereditary angioedema. Ongoing research on other diseases demonstrates the potential of therapeutic interventions targeting the kallikrein-kinin system and will provide further treatment options for patients in the future.

Colloidal therapeutics in the management of traumatic brain injury: Portray of biomarkers and drug-targets, preclinical and clinical pieces of evidence and future prospects

Complexity associated with the aberrant physiology of traumatic brain injury (TBI) makes its therapeutic targeting vulnerable. The underlying mechanisms of pathophysiology of TBI are yet to be completely illustrated. Primary injury in TBI is associated with contusions and axonal shearing whereas excitotoxicity, mitochondrial dysfunction, free radicals generation, and neuroinflammation are considered under secondary injury. MicroRNAs, proinflammatory cytokines, and Glial fibrillary acidic protein (GFAP) recently emerged as biomarkers in TBI. In addition, several approved therapeutic entities have been explored to target existing and newly identified drug-targets in TBI. However, drug delivery in TBI is hampered due to disruption of blood-brain barrier (BBB) in secondary TBI, as well as inadequate drug-targeting and retention effect. Colloidal therapeutics appeared helpful in providing enhanced drug availability to the brain owing to definite targeting strategies. Moreover, immense efforts have been put together to achieve increased bioavailability of therapeutics to TBI by devising effective targeting strategies. The potential of colloidal therapeutics to efficiently deliver drugs at the site of injury and down-regulate the mediators of TBI are serving as novel policies in the management of TBI. Therefore, in present manuscript, we have illuminated a myriad of molecular-targets currently identified and recognized in TBI. Moreover, particular emphasis is given to frame armamentarium of repurpose drugs which could be utilized to block molecular targets in TBI in addition to drug delivery barriers. The critical role of colloidal therapeutics such as liposomes, nanoparticles, dendrimers, and exosomes in drug delivery to TBI through invasive and non-invasive routes has also been highlighted.

Association of Angiotensin-Converting Enzyme Inhibitors with Increased Mortality Among Patients with Isolated Severe Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) is associated with one-third of all deaths from trauma. Preinjury exposure to cardiovascular drugs may affect TBI outcomes. Angiotensin-converting enzyme inhibitors (ACEIs) exacerbate brain cell damage and worsen functional outcomes in the laboratory setting. β-blockers (BBs), however, appear to be associated with reduced mortality among patients with isolated TBI.

OBJECTIVE

Examine the association between preinjury ACEI and BB use and clinical outcome among patients with isolated TBI.

METHODS

A retrospective cohort study of patients age ≥ 40 years admitted to an academic level 1 trauma center with isolated TBI between January 2010 and December 2014 was performed. Isolated TBI was defined as a head Abbreviated Injury Scale (AIS) score ≥ 3, with chest, abdomen, and extremity AIS scores ≤ 2. Preinjury medication use was determined through chart review. All patients with concurrent BB use were initially excluded. In-hospital mortality was the primary measured outcome.

RESULTS

Over the 5-year study period, 600 patients were identified with isolated TBI who were naive to BB use. There was significantly higher mortality (P = .04) among patients who received ACEI before injury (10 of 96; 10%) than among those who did not (25 of 504; 5%). A multivariate stepwise logistic regression analysis revealed a threefold increased risk of mortality in the ACEI cohort (P < .001), which was even greater than the twofold increased risk of mortality associated with an Injury Severity Score ≥ 16. A second analysis that included patients who received preinjury BBs (n = 98) demonstrated slightly reduced mortality in the ACEI cohort with only a twofold increased risk in multivariate analysis (P = .05).

CONCLUSIONS

Preinjury exposure to ACEIs is associated with an increase in mortality among patients with isolated TBI. This effect is ameliorated in patients who receive BBs, which provides evidence that this class of medications may provide a protective benefit.

A Systematic Review of Closed Head Injury Models of Mild Traumatic Brain Injury in Mice and Rats

Mild TBI (mTBI) is a significant health concern. Animal models of mTBI are essential for understanding mechanisms, and pathological outcomes, as well as to test therapeutic interventions. A variety of closed head models of mTBI that incorporate different aspects (i.e., biomechanics) of the mTBI have been reported. The aim of the current review was to compile a comprehensive list of the closed head mTBI rodent models, along with the common data elements, and outcomes, with the goal to summarize the current state of the field. Publications were identified from a search of PubMed and Web of Science and screened for eligibility following PRISMA guidelines. Articles were included that were closed head injuries in which the authors classified the injury as mild in rats or mice. Injury model and animal-specific common data elements, as well as behavioral and histological outcomes, were collected and compiled from a total of 402 articles. Our results outline the wide variety of methods used to model mTBI. We also discovered that female rodents and both young and aged animals are under-represented in experimental mTBI studies. Our findings will aid in providing context comparing the injury models and provide a starting point for the selection of the most appropriate model of mTBI to address a specific hypothesis. We believe this review will be a useful starting place for determining what has been done and what knowledge is missing in the field to reduce the burden of mTBI.

Implication of the Kallikrein-Kinin system in neurological disorders: Quest for potential biomarkers and mechanisms

Neurological disorders represent major health concerns in terms of comorbidity and mortality worldwide. Despite a tremendous increase in our understanding of the pathophysiological processes involved in disease progression and prevention, the accumulated knowledge so far resulted in relatively moderate translational benefits in terms of therapeutic interventions and enhanced clinical outcomes. Aiming at specific neural molecular pathways, different strategies have been geared to target the development and progression of such disorders. The kallikrein-kinin system (KKS) is among the most delineated candidate systems due to its ubiquitous roles mediating several of the pathophysiological features of these neurological disorders as well as being implicated in regulating various brain functions. Several experimental KKS models revealed that the inhibition or stimulation of the two receptors of the KKS system (B1R and B2R) can exhibit neuroprotective and/or adverse pathological outcomes. This updated review provides background details of the KKS components and their functions in different neurological disorders including temporal lobe epilepsy, traumatic brain injury, stroke, spinal cord injury, Alzheimer's disease, multiple sclerosis and glioma. Finally, this work will highlight the putative roles of the KKS components as potential neurotherapeutic targets and provide future perspectives on the possibility of translating these findings into potential clinical biomarkers in neurological disease.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

The blood-brain barrier as a target in traumatic brain injury treatment

Traumatic brain injury (TBI) is one of the most frequent causes of death in the young population. Several clinical trials have unsuccessfully focused on direct neuroprotective therapies. Recently immunotherapeutic strategies shifted into focus of translational research in acute CNS diseases. Cross-talk between activated microglia and blood-brain barrier (BBB) could initiate opening of the BBB and subsequent recruitment of systemic immune cells and mediators into the brain. Stabilization of the BBB after TBI could be a promising strategy to limit neuronal inflammation, secondary brain damage and acute neurodegeneration. This review provides an overview on the pathophysiology of TBI and brain edema formation including definitions and classification of TBI, current clinical treatment strategies, as well as current understanding on the underlying cellular processes. A summary of in vivo and in vitro models to study different aspects of TBI is presented. Three mechanisms proposed for stabilization of the BBB, myosin light chain kinases, glucocorticoid receptors and peroxisome proliferator-activated receptors are reviewed for their influence on barrier-integrity and outcome after TBI. In conclusion, the BBB is recommended as a promising target for the treatment of traumatic brain injury, and it is suggested that a combination of BBB stabilization and neuroprotectants may improve therapeutic success.

Role of the kallikrein-kinin system in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of mortality and morbidity worldwide. Despite improvements in acute intensive care, there are currently no specific therapies to ameliorate the effects of TBI. Successful therapeutic strategies for TBI should target multiple pathophysiologic mechanisms that occur at different stages of brain injury. The kallikrein-kinin system is a promising therapeutic target for TBI as it mediates key pathologic events of traumatic brain damage, such as edema formation, inflammation, and thrombosis. Selective and specific kinin receptor antagonists and inhibitors of plasma kallikrein and coagulation factor XII have been developed, and have already shown therapeutic efficacy in animal models of stroke and TBI. However, conflicting preclinical evaluation, as well as limited and inconclusive data from clinical trials in TBI, suggests that caution should be taken before transferring observations made in animals to humans. This review summarizes current evidence on the pathologic significance of the kallikrein-kinin system during TBI in animal models and, where available, the experimental findings are compared with human data.

HOE-140, an antagonist of B2 receptor, protects against memory deficits and brain damage induced by moderate lateral fluid percussion injury in mice

RATIONALE

There are evidences indicating the role of kinins in pathophysiology of traumatic brain injury, but little is known about their action on memory deficits.

OBJECTIVES

Our aim was to establish the role of bradykinin receptors B₁ (B₁R) and B₂ (B₂R) on the behavioral, biochemical, and histologic features elicited by moderate lateral fluid percussion injury (mLFPI) in mice.

METHODS

The role of kinin B₁ and B₂ receptors in brain damage, neuromotor, and cognitive deficits induced by mLFPI, was evaluated by means of subcutaneous injection of B₂R antagonist (HOE-140; 1 or 10 nmol/kg) or B₁R antagonist (des-Arg9-[Leu8]-bradykinin (DAL-Bk; 1 or 10 nmol/kg) 30 min and 24 h after brain injury. Brain damage was evaluated in the cortex, being considered as lesion volume, inflammatory, and oxidative damage. The open field and elevated plus maze tests were performed to exclude the nonspecific effects on object recognition memory test.

RESULTS

Our data revealed that HOE-140 (10 nmol/kg) protected against memory impairment. This treatment attenuated the brain edema, interleukin-1β, tumor necrosis factor-α, and nitric oxide metabolites content elicited by mLFPI. Accordingly, HOE-140 administration protected against the increase of nicotinamide adenine dinucleotide phosphate oxidase activity, thiobarbituric-acid-reactive species, protein carbonylation generation, and Na⁺ K⁺ ATPase inhibition induced by trauma. Histologic analysis showed that HOE-140 reduced lesion volume when analyzed 7 days after brain injury.

CONCLUSIONS

This study suggests the involvement of the B₂ receptor in memory deficits and brain damage caused by mLFPI in mice.

Taurine improves functional and histological outcomes and reduces inflammation in traumatic brain injury

We investigated the effect of taurine on inflammatory cytokine expression, on astrocyte activity and cerebral edema and functional outcomes, following traumatic brain injury (TBI) in rats. 72 rats were randomly divided into sham, TBI and Taurine groups. Rats subjected to moderate lateral fluid percussion injury were injected intravenously with taurine (200mg/kg) or saline immediately after injury or daily for 7days. Functional outcome was evaluated using Modified Neurological Severity Score (mNSS). Glial fibrillary acidic protein (GFAP) of the brain was measured using immunofluorescence. Concentration of 23 cytokines and chemokines in the injured cortex at 1 and 7days after TBI was assessed by Luminex xMAP technology. The results showed that taurine significantly improved functional recovery except 1day, reduced accumulation of GFAP and water content in the penumbral region at 7days after TBI. Compared with the TBI group, taurine significantly suppressed growth-related oncogene (GRO/KC) and interleukin (IL)-1β levels while elevating the levels of regulated on activation, normal T cell expressed and secreted (RANTES) at 1day. And taurine markedly decreased the level of 17 cytokine: eotaxin, Granulocyte colony-stimulating factor (G-CSF), Granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon-gamma (IFN-γ), IL-1α, IL-1β, IL-4, IL-5, IL-6, IL-10, IL-12p70, IL-13, IL-17, leptin, monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-α), vascular endothelial growth factor (VEGF), and only increased the level of MIP-1α in a week. The results suggest that taurine effectively mitigates the severity of brain damage in TBI by attenuating the increase of astrocyte activity and edema as well as pro-inflammatory cytokines.

Ischemic stroke and traumatic brain injury: the role of the kallikrein-kinin system

Acute ischemic stroke and traumatic brain injury are a major cause of mortality and morbidity. Due to the paucity of therapies, there is a pressing clinical demand for new treatment options. Successful therapeutic strategies for these conditions must target multiple pathophysiological mechanisms occurring at different stages of brain injury. In this respect, the kallikrein-kinin system is an ideal target linking key pathological hallmarks of ischemic and traumatic brain damage such as edema formation, inflammation, and thrombosis. In particular, the kinin receptors, plasma kallikrein, and coagulation factor XIIa are highly attractive candidates for pharmacological development, as kinin receptor antagonists or inhibitors of plasma kallikrein and coagulation factor XIIa are neuroprotective in animal models of stroke and traumatic brain injury. Nevertheless, conflicting preclinical evaluation as well as limited and inconclusive data from clinical trials suggest caution when transferring observations made in animals into the human situation. This review summarizes current evidence on the pathological significance of the kallikrein-kinin system during ischemic and traumatic brain damage, with a particular focus on experimental data derived from animal models. Experimental findings are also compared with human data if available, and potential therapeutic implications are discussed.

Anatomical location of arterial and venous lines significantly affects motor performance in rats

Several motor-function scales have been developed to assess neurological function in animal models of stroke, subarachnoid hemorrhage and closed head injury. We hypothesize that the location of arterial and venous catheters, even in the absence of brain injury, may impact rats' motor performance. Our study examined the effect of catheter location, rate of infection and the time required for catheter placement. We further describe an original technique of tail artery cannulation without exposure of the artery. Sixty-one rats were anesthetized and randomly assigned to one of seven groups, including no catheter, tail artery or artery + vein catheters, or femoral artery or artery + vein catheters. A neurological severity score (NSS) was determined at 1 h, 24 h and 48 h after surgical preparation or catheter placement. NSS at 1 h after placement of unilateral and bilateral femoral catheters was higher than the NSS observed at 1 h after placement of tail arterial and venous catheters (P < 0.01). The NSS also was higher at 24 h in the bilateral femoral catheter groups as compared with the tail catheter groups (P < 0.05). There were no differences in the NSS observed between the groups that had tail catheters and the sham group at 1 h, 24 h or 48 h. Infection rate at the site of catheter placement and the time required for catheter placement was also higher in the femoral catheter groups (P < 0.001). Thus, we propose that the line location may bias a study's results and lead to deceptive interpretations of neurological assessment following rat head injury. Compared to femoral vessels, tail blood vessels are preferable locations for lines placement.

Exercise pre-conditioning reduces brain inflammation and protects against toxicity induced by traumatic brain injury: behavioral and neurochemical approach

Although the favorable effects of physical exercise in neurorehabilitation after traumatic brain injury (TBI) are well known, detailed pathologic and functional alterations exerted by previous physical exercise on post-traumatic cerebral inflammation have been limited. In the present study, it is showed that fluid percussion brain injury (FPI) induced motor function impairment, followed by increased plasma fluorescein extravasation and cerebral inflammation characterized by interleukin-1β, tumor necrosis factor-α (TNF-α) increase, and decreased IL-10. In addition, myeloperoxidase (MPO) increase and Na⁺,K⁺-ATPase activity inhibition after FPI suggest that the opening of blood-brain barrier (BBB) followed by neurtrophils infiltration and cerebral inflammation may contribute to the failure of selected targets leading to secondary damage. In fact, Pearson's correlation analysis revealed strong correlation of MPO activity increase with Na⁺,K⁺-ATPase activity inhibition in sedentary rats. Statistical analysis also revealed that previous running exercise (4 weeks) protected against FPI-induced motor function impairment and fluorescein extravasation. Previous physical training also induced IL-10 increase per se and protected against cerebral IL-1β, and TNF-α increase and IL-10 decrease induced by FPI. This protocol of physical training was effective against MPO activity increase and Na⁺,K⁺-ATPase activity inhibition after FPI. The present protection correlated with MPO activity decrease suggests that the alteration of cerebral inflammatory status profile elicited by previous physical training reduces initial damage and limits long-term secondary degeneration after TBI. This prophylactic effect may facilitate functional recovery in patients suffering from brain injury induced by TBI.

Blood-brain barrier breakdown as a therapeutic target in traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death in young adults and children. The treatment of TBI in the acute phase has improved substantially; however, the prevention and management of long-term complications remain a challenge. Blood-brain barrier (BBB) breakdown has often been documented in patients with TBI, but the role of such vascular pathology in neurological dysfunction has only recently been explored. Animal studies have demonstrated that BBB breakdown is involved in the initiation of transcriptional changes in the neurovascular network that ultimately lead to delayed neuronal dysfunction and degeneration. Brain imaging data have confirmed the high incidence of BBB breakdown in patients with TBI and suggest that such pathology could be used as a biomarker in the clinic and in drug trials. Here, we review the neurological consequences of TBI, focusing on the long-term complications of such injuries. We present the clinical evidence for involvement of BBB breakdown in TBI and examine the primary and secondary mechanisms that underlie such pathology. We go on to consider the consequences of BBB injury, before analyzing potential mechanisms linking vascular pathology to neuronal dysfunction and degeneration, and exploring possible targets for treatment. Finally, we highlight areas for future basic research and clinical studies into TBI.

Novel small molecule bradykinin B2 receptor antagonists

Blockade of the bradykinin B(2) receptor provides therapeutic benefit in hereditary angioedema (HAE) and potentially in many other diseases. Herein, we describe the development of highly potent B(2) receptor antagonists with a molecular weight of approximately 500 g/mol. First, known quinoline-based B(2) receptor antagonists were stripped down to their shared core motif 53, which turned out to be the minimum pharmacophore. Targeted modifications of 53 resulted in the highly water-soluble lead compound 8a. Extensive exploration of its structure-activity relationship resulted in a series of highly potent B(2) receptor antagonists, featuring a hydrogen bond accepting functionality, which presumably interacts with the side chain of Asn-107 of the B(2) receptor. Optimization of the microsomal stability and cytochrome P450 inhibition eventually led to the discovery of the highly potent and orally available B(2) receptor antagonist 52e (JSM10292), which showed the best overall properties.

Beta-2 receptor antagonists for traumatic brain injury: a systematic review of controlled trials in animal models

A systematic review and meta-analysis of controlled trials was undertaken to assess the effects of beta-2 receptor antagonists in animal models of traumatic brain injury (TBI). Database and reference list searches were performed to identify eligible studies. Outcome data were extracted on functional status, as measured by the grip test or neurological severity score (NSS), and cerebral edema, as measured by brain water content (BWC). Data were pooled using the random-effects model. Seventeen controlled trials involving 817 animals were identified. Overall methodological quality was poor. Results from the grip test suggest that the treatment group maintained grip for a longer period than the control group; pooled weighted mean difference (WMD) = 8.28 (95% CI 5.78-10.78). The treatment group was found to have a lower NSS (i.e., better neurological function); pooled WMD =-3.28 (95% CI -4.72 to -1.85). Analysis of the cerebral edema data showed that the treatment group had a lower BWC than the control; pooled WMD =-0.42 (95% CI -0.59 to -0.26). There was evidence of statistical heterogeneity between comparisons for all outcomes. Evidence for small study effects was found for the grip test and BWC outcomes. The evidence from animal models of TBI suggests that beta-2 receptor antagonists can improve functional outcome and lessen cerebral edema. However, the poor methodological quality of the included studies and presence of small study effects may have influenced these findings.

Beta-2 receptor antagonists for acute traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Cerebral oedema, the accumulation of fluid within the brain, is believed to be an important contributor to the secondary brain damage that occurs following injury. The release of kinins is thought to be an important factor in the development of cerebral vasogenic oedema and the use of beta-2 receptor antagonists, which prevent the release of these kinins, have been proposed as a potential therapeutic intervention.

OBJECTIVES

The objective was to assess the safety and effectiveness of beta-2 receptor antagonists for TBI.

SEARCH STRATEGY

We searched the Cochrane Injuries Group's specialised register, CENTRAL, MEDLINE, EMBASE, National Research Register, LILACs, Zetoc, Web of Knowledge and Current Controlled Trials. We also searched the internet and checked the reference lists of relevant papers to identify any further studies. The searches were conducted in March 2007.

SELECTION CRITERIA

Randomised controlled trials of beta-2 receptor antagonists versus placebo for TBI.

DATA COLLECTION AND ANALYSIS

Two authors independently screened search results and assessed the full texts of potentially relevant studies for inclusion. Data were extracted and methodological quality was examined. Relative risks (RR) and 95% confidence intervals (CIs) were calculated and data were pooled using a fixed effect model.

MAIN RESULTS

Three studies were included, involving 178 participants. All three studies reported the effects of beta-2 receptor antagonists on mortality. The pooled RR for mortality was 0.63 (95% CI 0.36 to 1.10). Two studies measured disability, the RR of death or severe disability with beta-2 receptor antagonists was 0.81 (95% CI 0.59 to 1.09). Two studies measured the effect on intracranial pressure (ICP), although in only one did this finding reach statistical significance. There was no evidence for the presence of heterogeneity.

AUTHORS' CONCLUSIONS

There is no reliable evidence that beta-2 receptor antagonists are effective in reducing mortality or disability after TBI. Further well conducted randomised controlled trials are required.