Small, Thin Graphene Oxide Is Anti-inflammatory Activating Nuclear Factor Erythroid 2-Related Factor 2 via Metabolic Reprogramming

Graphene oxide (GO), an oxidized form of graphene, has potential applications in biomedical research. However, how GO interacts with biological systems, including the innate immune system, is poorly understood. Here, we elucidate the effects of GO sheets on macrophages, identifying distinctive effects of GO on the inflammatory phenotype. Small, thin (s)-GO dose-dependently inhibited release of interleukin (IL)-1β and IL-6 but not tumor necrosis factor α. NLRP3 inflammasome and caspase-1 activation was not affected. The effect of s-GO was pretranslational, as s-GO blocked Toll-like receptor 4-dependent expression of Il1b and Il6 but not Nlrp3 or Tnf mRNA transcripts. s-GO was internalized by immortalized bone-marrow-derived macrophages, suggesting a potential intracellular action. Uptake of polystyrene beads with similar lateral dimensions and surface charge did not phenocopy the effects of s-GO, suggesting that s-GO-mediated inhibition of interleukin expression was not simply due to particle phagocytosis. RNA-Seq analysis established that s-GO had profound effects on the immunometabolism of the cells, leading to activation of the transcription factor nuclear factor erythroid 2-related factor 2, which inhibited expression of cytokines such as IL-1β and IL-6. Thus, we have identified immunometabolic effects of GO that reveal another dimension to its effects on cells. These findings suggest that s-GO may be used as a valuable tool to generate further insights into inflammatory mechanisms and indicate its potential applications in biomedicine.

SCIL-STROKE (Subcutaneous Interleukin-1 Receptor Antagonist in Ischemic Stroke): A Randomized Controlled Phase 2 Trial

BACKGROUND AND PURPOSE

The proinflammatory cytokine IL-1 (interleukin-1) has a deleterious role in cerebral ischemia, which is attenuated by IL-1 receptor antagonist (IL-1Ra). IL-1 induces peripheral inflammatory mediators, such as interleukin-6, which are associated with worse prognosis after ischemic stroke. We investigated whether subcutaneous IL-1Ra reduces the peripheral inflammatory response in acute ischemic stroke.

METHODS

SCIL-STROKE (Subcutaneous Interleukin-1 Receptor Antagonist in Ischemic Stroke) was a single-center, double-blind, randomized, placebo-controlled phase 2 trial of subcutaneous IL-1Ra (100 mg administered twice daily for 3 days) in patients presenting within 5 hours of ischemic stroke onset. Randomization was stratified for baseline National Institutes of Health Stroke Scale score and thrombolysis. Measurement of plasma interleukin-6 and other peripheral inflammatory markers was undertaken at 5 time points. The primary outcome was difference in concentration of log(interleukin-6) as area under the curve to day 3. Secondary outcomes included exploratory effect of IL-1Ra on 3-month outcome with the modified Rankin Scale.

RESULTS

We recruited 80 patients (mean age, 72 years; median National Institutes of Health Stroke Scale, 12) of whom 73% received intravenous thrombolysis with alteplase. IL-1Ra significantly reduced plasma interleukin-6 (P<0.001) and plasma C-reactive protein (P<0.001). IL-1Ra was well tolerated with no safety concerns. Allocation to IL-1Ra was not associated with a favorable outcome on modified Rankin Scale: odds ratio (95% confidence interval)=0.67 (0.29-1.52), P=0.34. Exploratory mediation analysis suggested that IL-1Ra improved clinical outcome by reducing inflammation, but there was a statistically significant, alternative mechanism countering this benefit.

CONCLUSIONS

IL-1Ra reduced plasma inflammatory markers which are known to be associated with worse clinical outcome in ischemic stroke. Subcutaneous IL-1Ra is safe and well tolerated. Further experimental studies are required to investigate efficacy and possible interactions of IL-1Ra with thrombolysis.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: ISRCTN74236229.

Interleukin-1 primes human mesenchymal stem cells towards an anti-inflammatory and pro-trophic phenotype in vitro

Background

Inflammation is a key contributor to central nervous system (CNS) injury such as stroke, and is a major target for therapeutic intervention. Effective treatments for CNS injuries are limited and applicable to only a minority of patients. Stem cell-based therapies are increasingly considered for the treatment of CNS disease, because they can be used as in-situ regulators of inflammation, and improve tissue repair and recovery. One promising option is the use of bone marrow-derived mesenchymal stem cells (MSCs), which can secrete anti-inflammatory and trophic factors, can migrate towards inflamed and injured sites or can be implanted locally. Here we tested the hypothesis that pre-treatment with inflammatory cytokines can prime MSCs towards an anti-inflammatory and pro-trophic phenotype in vitro.

Methods

Human MSCs from three different donors were cultured in vitro and treated with inflammatory mediators as follows: interleukin (IL)-1α, IL-1β, tumour necrosis factor alpha (TNF-α) or interferon-γ. After 24 h of treatment, cell supernatants were analysed by ELISA for expression of granulocyte-colony stimulating factor (G-CSF), IL-10, brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), IL-1 receptor antagonist (IL-1Ra) and vascular endothelial growth factor (VEGF). To confirm the anti-inflammatory potential of MSCs, immortalised mouse microglial BV2 cells were treated with bacterial lipopolysaccharide (LPS) and exposed to conditioned media (CM) of naïve or IL-1-primed MSCs, and levels of secreted microglial-derived inflammatory mediators including TNF-α, IL-10, G-CSF and IL-6 were measured by ELISA.

Results

Unstimulated MSCs constitutively expressed anti-inflammatory cytokines and trophic factors (IL-10, VEGF, BDNF, G-CSF, NGF and IL-1Ra). MSCs primed with IL-1α or IL-1β showed increased secretion of G-CSF, which was blocked by IL-1Ra. Furthermore, LPS-treated BV2 cells secreted less inflammatory and apoptotic markers, and showed increased secretion of the anti-inflammatory IL-10 in response to treatment with CM of IL-1-primed MSCs compared with CM of unprimed MSCs.

Conclusions

Our results demonstrate that priming MSCs with IL-1 increases expression of trophic factor G-CSF through an IL-1 receptor type 1 (IL-1R1) mechanism, and induces a reduction in the secretion of inflammatory mediators in LPS-activated microglial cells. The results therefore support the potential use of preconditioning treatments of stem cells in future therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0531-4) contains supplementary material, which is available to authorized users.

REVIEW ■ : Interleukin-1 and Neurodegeneration

The cytokine interleukin-1 (IL-1) has been implicated in many forms of neurodegeneration. Expression of IL-1 is increased in the brain (mainly by microglia) of animals and humans in response to acute insults (e.g., stroke and brain injury) and in chronic neurodegenerative conditions. Although IL-1 does not kill otherwise healthy neurons, small quantities of the cytokine dramatically enhance ischemic, traumatic, or excitotoxic damage in animals. Inhibition of the synthesis, release, or action of IL-1 (e.g., by administration of IL-1 receptor antagonist) markedly reduces all of these forms of experimental neurodegeneration, indicating that approaches to block or inhibit IL-1 activity may be of benefit in clinical neurodegenerative disease. NEURO SCIENTIST 4:195-201, 1998

Characterization of a conditional interleukin-1 receptor 1 mouse mutant using the Cre/LoxP system

IL-1 is a key cytokine known to drive chronic inflammation and to regulate many physiological, immunological, and neuroimmunological responses via actions on diverse cell types of the body. To determine the mechanisms of IL-1 actions as part of the inflammatory response in vivo, we generated a conditional IL-1 receptor 1 (IL-1R1) mouse mutant using the Cre/LoxP system (IL-1R1(fl/fl) ). In the mutant generated, exon 5, which encodes part of the extracellular-binding region of the receptor, is flanked by LoxP sites, thereby inactivating the two previously described functional IL-1R1 gene transcripts after Cre-mediated recombination. Using keratin 14-Cre driver mice, new IL-1R1 deficient (-/-) mice were subsequently generated, in which all signaling IL-1 receptor isoforms are deleted ubiquitously. Furthermore, using vav-iCre driver mice, we deleted IL-1 receptor isoforms in the hematopoietic system. In these mice, we show that both the IL-17 and IL-22 cytokine response is reduced, when mice are challenged by the helminth Trichuris muris. We are currently crossing IL-1R1(fl/fl) mice with different Cre-expressing mice in order to study mechanisms of acute and chronic inflammatory diseases.

Efficacy of Alteplase in a Mouse Model of Acute Ischemic Stroke: A Retrospective Pooled Analysis

BACKGROUND AND PURPOSE

The debate over the fact that experimental drugs proposed for the treatment of stroke fail in the translation to the clinical situation has attracted considerable attention in the literature. In this context, we present a retrospective pooled analysis of a large data set from preclinical studies, to examine the effects of early versus late administration of intravenous recombinant tissue-type plasminogen activator.

METHODS

We collected data from 26 individual studies from 9 international centers (13 researchers; 716 animals) that compared recombinant tissue-type plasminogen activator with controls, in a unique mouse model of thromboembolic stroke induced by an in situ injection of thrombin into the middle cerebral artery. Studies were classified into early (<3 hours) versus late (≥3 hours) drug administration. Final infarct volumes, assessed by histology or magnetic resonance imaging, were compared in each study, and the absolute differences were pooled in a random-effect meta-analysis. The influence of time of administration was tested.

RESULTS

When compared with saline controls, early recombinant tissue-type plasminogen activator administration was associated with a significant benefit (absolute difference, -6.63 mm(3); 95% confidence interval, -9.08 to -4.17; I(2)=76%), whereas late recombinant tissue-type plasminogen activator treatment showed a deleterious effect (+5.06 mm(3); 95% confidence interval, +2.78 to +7.34; I(2)=42%; Pint<0.00001). Results remained unchanged after subgroup analyses.

CONCLUSIONS

Our results provide the basis needed for the design of future preclinical studies on recanalization therapies using this model of thromboembolic stroke in mice. The power analysis reveals that a multicenter trial would require 123 animals per group instead of 40 for a single-center trial.

A cross-laboratory preclinical study on the effectiveness of interleukin-1 receptor antagonist in stroke

Stroke represents a global challenge and is a leading cause of permanent disability worldwide. Despite much effort, translation of research findings to clinical benefit has not yet been successful. Failure of neuroprotection trials is considered, in part, due to the low quality of preclinical studies, low level of reproducibility across different laboratories and that stroke co-morbidities have not been fully considered in experimental models. More rigorous testing of new drug candidates in different experimental models of stroke and initiation of preclinical cross-laboratory studies have been suggested as ways to improve translation. However, to our knowledge, no drugs currently in clinical stroke trials have been investigated in preclinical cross-laboratory studies. The cytokine interleukin 1 is a key mediator of neuronal injury, and the naturally occurring interleukin 1 receptor antagonist has been reported as beneficial in experimental studies of stroke. In the present paper, we report on a preclinical cross-laboratory stroke trial designed to investigate the efficacy of interleukin 1 receptor antagonist in different research laboratories across Europe. Our results strongly support the therapeutic potential of interleukin 1 receptor antagonist in experimental stroke and provide further evidence that interleukin 1 receptor antagonist should be evaluated in more extensive clinical stroke trials.

Interleukin-1 as a pharmacological target in acute brain injury

NEW FINDINGS

What is the topic of this review? This review discusses the latest findings on the contribution of inflammation to brain injury, how inflammation is a therapeutic target, and details of recent and forthcoming clinical studies. What advances does it highlight? Here we highlight recent advances on the role and regulation of inflammasomes, and the latest clinical progress in targeting inflammation. Acute brain injury is one of the leading causes of mortality and disability worldwide. Despite this, treatments for acute brain injuries are limited, and there remains a massive unmet clinical need. Inflammation has emerged as a major contributor to non-communicable diseases, and there is now substantial and growing evidence that inflammation, driven by the cytokine interleukin-1 (IL-1), worsens acute brain injury. Interleukin-1 is regulated by large, multimolecular complexes called inflammasomes. Here, we discuss the latest research on the regulation of inflammasomes and IL-1 in the brain, preclinical efforts to establish the IL-1 system as a therapeutic target, and the promise of recent and future clinical studies on blocking the action of IL-1 for the treatment of brain injury.

Requirement for interleukin-1 to drive brain inflammation reveals tissue-specific mechanisms of innate immunity

The immune system is implicated in a wide range of disorders affecting the brain and is, therefore, an attractive target for therapy. Interleukin-1 (IL-1) is a potent regulator of the innate immune system important for host defense but is also associated with injury and disease in the brain. Here, we show that IL-1 is a key mediator driving an innate immune response to inflammatory challenge in the mouse brain but is dispensable in extracerebral tissues including the lung and peritoneum. We also demonstrate that IL-1α is an important ligand contributing to the CNS dependence on IL-1 and that IL-1 derived from the CNS compartment (most likely microglia) is the major source driving this effect. These data reveal previously unknown tissue-specific requirements for IL-1 in driving innate immunity and suggest that IL-1-mediated inflammation in the brain could be selectively targeted without compromising systemic innate immune responses that are important for resistance to infection. This property could be exploited to mitigate injury- and disease-associated inflammation in the brain without increasing susceptibility to systemic infection, an important complication in several neurological disorders.

Long-term functional recovery and compensation after cerebral ischemia in rats

Cerebral ischemia is one of the most common causes of disabilities in adults and leads to long-term motor and cognitive impairments with limited therapeutic possibilities. Treatment options have proven efficient in preclinical models of cerebral ischemia but have failed in the clinical setting. This limited translation may be due to the suitability of models used and outcomes measured as most studies have focused on the early period after injury with gross motor scales, which have limited correlation to the clinical situation. The aim of this study was to determine long-term functional outcomes after cerebral ischemia in rats, focusing on fine motor function, social and depressive behavior as clinically relevant measures. A secondary objective was to evaluate the effects of an anti-inflammatory treatment (interleukin-1 receptor antagonist (IL-1Ra)) on functional recovery and compensation. Infarct volume was correlated with long-term (25 days) impairments in fine motor skills, but not with emotional components of behavior. Motor impairments could not be detected using conventional neurological tests and only detailed analysis allowed differentiation between recovery and compensation. Acute systemic administration of IL-1Ra (at reperfusion) led to a faster and more complete recovery, but delayed (24h) IL-1Ra treatment had no effect. In summary functional assessment after brain injury requires detailed motor tests in order to address long-term impairments and compensation processes that are mediated by intact tissues. Functional deficits in skilled movement after brain injury represent ideal predictors of long-term outcomes and should become standard measures in the assessment of preclinical animal models.

Release of interleukin-1α or interleukin-1β depends on mechanism of cell death

The cytokine interleukin-1 (IL-1) has two main pro-inflammatory forms, IL-1α and IL-1β, which are central to host responses to infection and to damaging sterile inflammation. Processing of IL-1 precursor proteins to active cytokines commonly occurs through activation of proteases, notably caspases and calpains. These proteases are instrumental in cell death, and inflammation and cell death are closely associated, hence we sought to determine the impact of cell death pathways on IL-1 processing and release. We discovered that apoptotic regulation of caspase-8 specifically induced the processing and release of IL-1β. Conversely, necroptosis caused the processing and release of IL-1α, and this was independent of IL-1β processing and release. These data suggest that the mechanism through which an IL-1-expressing cell dies dictates the nature of the inflammatory mechanism that follows. These insights may allow modification of inflammation through the selective targeting of cell death mechanisms during disease.

Streptococcus pneumoniae worsens cerebral ischemia via interleukin 1 and platelet glycoprotein Ibα

OBJECTIVE

Bacterial infection contributes to diverse noninfectious diseases and worsens outcome after stroke. Streptococcus pneumoniae, the most common infection in patients at risk of stroke, is a major cause of prolonged hospitalization and death of stroke patients, but how infection impacts clinical outcome is not known.

METHODS

We induced sustained pulmonary infection by a human S. pneumoniae isolate in naive and comorbid rodents to investigate the effect of infection on vascular and inflammatory responses prior to and after cerebral ischemia.

RESULTS

S. pneumoniae infection triggered atherogenesis, led to systemic induction of interleukin (IL) 1, and profoundly exacerbated (50-90%) ischemic brain injury in rats and mice, a response that was more severe in combination with old age and atherosclerosis. Systemic blockade of IL-1 with IL-1 receptor antagonist (IL-1Ra) fully reversed infection-induced exacerbation of brain injury and functional impairment caused by cerebral ischemia. We show that infection-induced systemic inflammation mediates its effects via increasing platelet activation and microvascular coagulation in the brain after cerebral ischemia, as confirmed by reduced brain injury in response to blockade of platelet glycoprotein (GP) Ibα. IL-1 and platelet-mediated signals converge on microglia, as both IL-1Ra and GPIbα blockade reversed the production of IL-1α by microglia in response to cerebral ischemia in infected animals.

INTERPRETATION

S. pneumoniae infection augments atherosclerosis and exacerbates ischemic brain injury via IL-1 and platelet-mediated systemic inflammation. These mechanisms may contribute to diverse cardio- and cerebrovascular pathologies in humans.

The acute-phase protein PTX3 is an essential mediator of glial scar formation and resolution of brain edema after ischemic injury

Acute-phase proteins (APPs) are key effectors of the immune response and are routinely used as biomarkers in cerebrovascular diseases, but their role during brain inflammation remains largely unknown. Elevated circulating levels of the acute-phase protein pentraxin-3 (PTX3) are associated with worse outcome in stroke patients. Here we show that PTX3 is expressed in neurons and glia in response to cerebral ischemia, and that the proinflammatory cytokine interleukin-1 (IL-1) is a key driver of PTX3 expression in the brain after experimental stroke. Gene deletion of PTX3 had no significant effects on acute ischemic brain injury. In contrast, the absence of PTX3 strongly compromised blood-brain barrier integrity and resolution of brain edema during recovery after ischemic injury. Compromised resolution of brain edema in PTX3-deficient mice was associated with impaired glial scar formation and alterations in scar-associated extracellular matrix production. Our results suggest that PTX3 expression induced by proinflammatory signals after ischemic brain injury is a critical effector of edema resolution and glial scar formation. This highlights the potential role for inflammatory molecules in brain recovery after injury and identifies APPs, in particular PTX3, as important targets in ischemic stroke and possibly other brain inflammatory disorders.

Surgical manipulation compromises leukocyte mobilization responses and inflammation after experimental cerebral ischemia in mice

Acute brain injury results in peripheral inflammatory changes, although the impact of these processes on neuronal death and neuroinflammation is currently unclear. To facilitate the translation of experimental studies to clinical benefit, it is vital to characterize the mechanisms by which acute brain injury induces peripheral inflammatory changes, and how these are affected by surgical manipulation in experimental models. Here we show that in mice, even mild surgical manipulation of extracranial tissues induced marked granulocyte mobilization (300%) and systemic induction of cytokines. However, intracranial changes induced by craniotomy, or subsequent induction of focal cerebral ischemia were required to induce egress of CXCR2-positive granulocytes from the bone marrow. CXCR2 blockade resulted in reduced mobilization of granulocytes from the bone marrow, caused an unexpected increase in circulating granulocytes, but failed to affect brain injury induced by cerebral ischemia. We also demonstrate that isoflurane anaesthesia interferes with circulating leukocyte responses, which could contribute to the reported vascular and neuroprotective effects of isoflurane. In addition, no immunosuppression develops in the bone marrow after experimental stroke. Thus, experimental models of cerebral ischemia are compromised by surgery and anaesthesia in proportion to the severity of surgical intervention and overall tissue injury. Understanding the inherent confounding effects of surgical manipulation and development of new models of cerebral ischemia with minimal surgical intervention could facilitate better understanding of interactions between inflammation and brain injury.

The effect of intravenous interleukin-1 receptor antagonist on inflammatory mediators in cerebrospinal fluid after subarachnoid haemorrhage: a phase II randomised controlled trial

Background

Interleukin-1 (IL-1) is a key mediator of ischaemic brain injury induced by stroke and subarachnoid haemorrhage (SAH). IL-1 receptor antagonist (IL-1Ra) limits brain injury in experimental stroke and reduces plasma inflammatory mediators associated with poor outcome in ischaemic stroke patients. Intravenous (IV) IL-1Ra crosses the blood–brain barrier (BBB) in patients with SAH, to achieve cerebrospinal fluid (CSF) concentrations that are neuroprotective in rats.

Methods

A small phase II, double-blind, randomised controlled study was carried out across two UK neurosurgical centres with the aim of recruiting 32 patients. Adult patients with aneurysmal SAH, requiring external ventricular drainage (EVD) within 72 hours of ictus, were eligible. Patients were randomised to receive IL-1Ra (500 mg bolus, then a 10 mg/kg/hr infusion for 24 hours) or placebo. Serial samples of CSF and plasma were taken and analysed for inflammatory mediators, with change in CSF IL-6 between 6 and 24 hours as the primary outcome measure.

Results

Six patients received IL-1Ra and seven received placebo. Concentrations of IL-6 in CSF and plasma were reduced by one standard deviation in the IL-1Ra group compared to the placebo group, between 6 and 24 hours, as predicted by the power calculation. This did not reach statistical significance (P = 0.08 and P = 0.06, respectively), since recruitment did not reach the target figure of 32. No adverse or serious adverse events reported were attributable to IL-1Ra.

Conclusions

IL-1Ra appears safe in SAH patients. The concentration of IL-6 was lowered to the degree expected, in both CSF and plasma for patients treated with IL-1Ra.

Microglia and macrophages differentially modulate cell death after brain injury caused by oxygen-glucose deprivation in organotypic brain slices

Macrophage can adopt several phenotypes, process call polarization, which is crucial for shaping inflammatory responses to injury. It is not known if microglia, a resident brain macrophage population, polarizes in a similar way, and whether specific microglial phenotypes modulate cell death in response to brain injury. In this study, we show that both BV2-microglia and mouse bone marrow derived macrophages (BMDMs) were able to adopt different phenotypes after LPS (M1) or IL-4 (M2) treatment in vitro, but regulated cell death differently when added to mouse organotypic hippocampal brain slices. BMDMs induced cell death when added to control slices and exacerbated damage when combined with oxygen-glucose deprivation (OGD), independently of their phenotype. In contrast, vehicle- and M2-BV2-microglia were protective against OGD-induced death. Direct treatment of brain slices with IL-4 (without cell addition) was protective against OGD and induced an M2 phenotype in the slice. In vivo, intracerebral injection of LPS or IL-4 in mice induced microglial phenotypes similar to the phenotypes observed in brain slices and in cultured cells. After injury induced by middle cerebral artery occlusion, microglial cells did not adopt classical M1/M2 phenotypes, suggesting that another subtype of regulatory phenotype was induced. This study highlights functional differences between macrophages and microglia, in response to brain injury with fundamentally different outcomes, even if both populations were able to adopt M1 or M2 phenotypes. These data suggest that macrophages infiltrating the brain from the periphery after an injury may be cytotoxic, independently of their phenotype, while microglia may be protective.

Central and haematopoietic interleukin-1 both contribute to ischaemic brain injury in mice

Interleukin-1 (IL-1) is a key regulator of inflammation and ischaemic brain injury, but the contribution of central and peripheral sources of IL-1 to brain injury is not well understood. Here we show that haematopoietic-derived IL-1 is a key driver of ischaemic brain injury. Wild type (WT) mice transplanted with IL-1αβ-deficient bone marrow displayed a significant (40%) reduction in brain injury induced by focal cerebral ischaemia compared with WT mice transplanted with WT bone marrow. This was paralleled by improved neurological outcome and the almost complete absence of splenic-derived, but not liver-derived, IL-1α after stroke in WT mice lacking haematopoietic-derived IL-1. IL-1αβ knockout (KO) mice transplanted with IL-1αβ-deficient bone marrow showed a 60% reduction in brain injury compared with WT mice receiving WT bone marrow. Transplantation of WT bone marrow in IL-1αβ KO mice resulted in a similar level of blood-brain-barrier injury to that observed in WT mice receiving IL-1αβ-deficient bone marrow. Cerebral oedema after brain injury was reduced in IL-1αβ KO recipients irrespective of donor-derived IL-1, but a lack of haematopoetic IL-1 has also been associated with smaller brain oedema independently of recipient status. Thus, both central and haematopoietic-derived IL-1 are important contributors to brain injury after cerebral ischaemia. Identification of the cellular sources of IL-1 in the periphery could allow targeted interventions at these sites.

[18F]DPA-714: direct comparison with [11C]PK11195 in a model of cerebral ischemia in rats

Purpose

Neuroinflammation is involved in several brain disorders and can be monitored through expression of the translocator protein 18 kDa (TSPO) on activated microglia. In recent years, several new PET radioligands for TSPO have been evaluated in disease models. [¹⁸F]DPA-714 is a TSPO radiotracer with great promise; however results vary between different experimental models of neuroinflammation. To further examine the potential of [¹⁸F]DPA-714, it was compared directly to [¹¹C]PK11195 in experimental cerebral ischaemia in rats.

Methods

Under anaesthesia, the middle cerebral artery of adult rats was occluded for 60 min using the filament model. Rats were allowed recovery for 5 to 7 days before one hour dynamic PET scans with [¹¹C]PK11195 and/or [¹⁸F]DPA-714 under anaesthesia.

Results

Uptake of [¹¹C]PK11195 vs [¹⁸F]DPA-714 in the ischemic lesion was similar (core/contralateral ratio: 2.84±0.67 vs 2.28±0.34 respectively), but severity of the brain ischemia and hence ligand uptake in the lesion appeared to vary greatly between animals scanned with [¹¹C]PK11195 or with [¹⁸F]DPA-714. To solve this issue of inter-individual variability, we performed a direct comparison of [¹¹C]PK11195 and [¹⁸F]DPA-714 by scanning the same animals sequentially with both tracers within 24 h. In this direct comparison, the core/contralateral ratio (3.35±1.21 vs 4.66±2.50 for [¹¹C]PK11195 vs [¹⁸F]DPA-714 respectively) showed a significantly better signal-to-noise ratio (1.6 (1.3–1.9, 95%CI) fold by linear regression) for [¹⁸F]DPA-714.

Conclusions

In a clinically relevant model of neuroinflammation, uptake for both radiotracers appeared to be similar at first, but a high variability was observed in our model. Therefore, to truly compare tracers in such models, we performed scans with both tracers in the same animals. By doing so, our result demonstrated that [¹⁸F]DPA-714 displayed a higher signal-to-noise ratio than [¹¹C]PK11195. Our results suggest that, with the longer half-life of [¹⁸F] which facilitates distribution of the tracer across PET centre, [¹⁸F]DPA-714 is a good alternative for TSPO imaging.

Cerebrospinal fluid and plasma cytokines after subarachnoid haemorrhage: CSF interleukin-6 may be an early marker of infection

BACKGROUND

Cytokines and cytokine receptor concentrations increase in plasma and cerebrospinal fluid (CSF) of patients following subarachnoid haemorrhage (SAH). The relationship between plasma and CSF cytokines, and factors affecting this, are not clear.

METHODS

To help define the relationship, paired plasma and cerebrospinal fluid (CSF) samples were collected from patients subject to ventriculostomy. Concentrations of key inflammatory cytokines, interleukin (IL)-1ß, IL-1 receptor antagonist (IL-1Ra), IL-1 receptor 2, IL-6, IL-8, IL-10, tumour necrosis factor (TNF)-α, and TNF receptors (TNF-R) 1 and 2 were determined by immunoassay of CSF and plasma from 21 patients, where samples were available at three or more time points.

RESULTS

Plasma concentrations of IL-1ß, IL-1Ra, IL-10, TNF-α and TNF-R1 were similar to those in CSF. Plasma TNF-R2 and IL-1R2 concentrations were higher than in CSF. Concentrations of IL-8 and IL-6 in CSF were approximately10 to 1,000-fold higher than in plasma. There was a weak correlation between CSF and plasma IL-8 concentrations (r = 0.26), but no correlation for IL-6. Differences between the central and peripheral pattern of IL-6 were associated with episodes of ventriculostomy-related infection (VRI). A VRI was associated with CSF IL-6 >10,000 pg/mL (P = 0.0002), although peripheral infection was not significantly associated with plasma IL-6.

CONCLUSIONS

These data suggest that plasma cytokine concentrations cannot be used to identify relative changes in the CSF, but that measurement of CSF IL-6 could provide a useful marker of VRI.

Interleukin-1 receptor antagonist is beneficial after subarachnoid haemorrhage in rat by blocking haem-driven inflammatory pathology

Subarachnoid haemorrhage (SAH) is a major contributor to the burden of stroke on society. Treatment options are limited and animal models of SAH do not always mimic key pathophysiological hallmarks of the disease, thus hindering development of new therapeutics. Inflammation is strongly associated with brain injury after SAH in animals and patients, and inhibition of the pro-inflammatory cytokine interleukin-1 (IL-1) represents a possible therapeutic target. Here we report that a rupture of the middle cerebral artery in the rat produces heterogeneous infarct patterns similar to those observed in human SAH. Administration of the IL-1 receptor antagonist (IL-1Ra) reduced blood-brain barrier breakdown, and the extent of breakdown correlated with brain injury. After SAH, haem oxygenase-1 (HO-1) was strongly expressed around the bleed site and in the cortex and striatum, indicating the presence of free haem, a breakdown product of haemoglobin. HO-1 expression was also found in the same regions as microglial/macrophage expression of IL-1α. The direct effect of haem on IL-1α expression was confirmed in vitro using organotypic slice culture (OSC). Haem-induced cell death was dependent on IL-1 signalling, with IL-1Ra completely blocking cellular injury. Furthermore, stimulation of mouse primary mixed glial cells with haem induced the release of IL-1α, but not IL-1β. Thus, we suggest that haem, released from lysed red blood cells (RBCs) in the subarachnoid space, acts as a danger-associated molecular pattern (DAMP) driving IL-1-dependent inflammation. These data provide new insights into inflammation after SAH-induced brain injury and suggest IL-1Ra as a candidate therapeutic for the disease.

Neuronal Toll-like receptor 4 signaling induces brain endothelial activation and neutrophil transmigration in vitro

BACKGROUND

The innate immune response in the brain is initiated by pathogen-associated molecular patterns (PAMPS) or danger-associated molecular patterns (DAMPS) produced in response to central nervous system (CNS) infection or injury. These molecules activate members of the Toll-like receptor (TLR) family, of which TLR4 is the receptor for bacterial lipopolysaccharide (LPS). Although neurons have been reported to express TLR4, the function of TLR4 activation in neurons remains unknown.

METHODS

TLR4 mRNA expression in primary mouse glial and neuronal cultures was assessed by RT-PCR. Mouse mixed glial, neuronal or endothelial cell cultures were treated with LPS in the absence or the presence of a TLR4 specific antagonist (VIPER) or a specific JNK inhibitor (SP600125). Expression of inflammatory mediators was assayed by cytometric bead array (CBA) and ELISA. Activation of extracellular-signal regulated kinase 1/2 (ERK1/2), p38, c-Jun-N-terminal kinase (JNK) and c-Jun was assessed by Western blot. The effect of conditioned media of untreated- versus LPS-treated glial or neuronal cultures on endothelial activation was assessed by neutrophil transmigration assay, and immunocytochemistry and ELISA were used to measure expression of intercellular cell adhesion molecule (ICAM-1) and vascular cell adhesion molecule (VCAM-1).

RESULTS

LPS induces strong release of the chemokines RANTES and CXCL1 (KC), tumor necrosis factor-α (TNFα) and IL-6 in primary mouse neuronal cultures. In contrast, LPS induced release of IL-1α, IL-1β and granulocyte-colony stimulating factor (G-CSF) in mixed glial, but not in neuronal cultures. LPS-induced neuronal KC expression and release were completely blocked by VIPER. In glial cultures, LPS induced activation of ERK1/2, p38 and JNK. In contrast, in neuronal cultures, LPS activated JNK but not ERK1/2 or p38, and the specific JNK inhibitor SP600125 significantly blocked LPS-induced KC expression and release. Finally, conditioned medium of LPS-treated neuronal cultures induced strong expression of ICAM-1 and VCAM-1 on endothelial cells, and induced infiltration of neutrophils across the endothelial monolayer, which was inhibited by VIPER.

CONCLUSION

These data demonstrate for the first time that neurons can play a role as key sensors of infection to initiate CNS inflammation.

Effect of dietary fish oil supplementation on fever and cytokine production in human volunteers

The effect of dietary fish oil supplementation on acute phase responses to intramuscular injection of typhoid vaccine, and in vitro cytokine production, was investigated in human volunteers. Half of the subjects supplemented their normal diet with 4.5 g/day of fish oil for 6-8 weeks. Injection of typhoid vaccine in unsupplemented subjects caused an increase in white cell count, resting heart rate, metabolic rate, oxygen consumption, and oral temperature. Fish oil supplementation inhibited the tachycardia and attenuated the maximal increases in oral temperature and metabolic rate following typhoid vaccine. However, interpretation of these latter results were complicated by similarly attenuated responses in saline-injected subjects. The in vitro production of interleukin-1 and interleukin-6 from whole blood was suppressed by fish oil supplementation, however, production of tumor necrosis factor alpha was not significantly altered. Fish oil supplementation may therefore provide a non-pharmacological approach of attenuating several of the responses associated with injury and infection and this may be related to reduced cytokine (IL-1 and IL-6) production.

Inflammation as a predictor for delayed cerebral ischemia after aneurysmal subarachnoid haemorrhage

BACKGROUND

The mechanism of development of delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (SAH) is poorly understood. Inflammatory processes are implicated in the development of ischemic stroke and may also predispose to the development of DCI following SAH. The objective of this study was to test whether concentrations of circulating inflammatory markers (C-reactive protein (CRP), interleukin-6 (IL-6) and interleukin 1 receptor antagonist (IL-1Ra)) were predictive for DCI following SAH. Secondary analyses considered white cell count (WCC) and erythrocyte sedimentation rate (ESR).

METHODS

This was a single-center case-control study nested within a prospective cohort. Plasma inflammatory markers were measured in patients up to 15 days after SAH (initial, peak, average, final and rate of change to final). Cases were defined as those developing DCI. Inflammatory markers were compared between cases and randomly selected matched controls.

RESULTS

Among the 179 participants there were 46 cases of DCI (26%). In primary analyses the rate of change of IL-6 was associated with DCI (OR 2.3 (95% CI 1.1 to 5.0); p=0.03). The final value and rate of change of WCC were associated with DCI (OR 1.2 (95% CI 1.0 to 1.3) and OR 1.3 (95% CI 1.0 to 1.6), respectively). High values of ESR were associated with DCI (OR 2.4 (95% CI 1.3 to 4.6) initial; OR 2.3 (95% CI 1.3 to 4.2) average; OR 2.1 (95% CI 1.1 to 3.9) peak; and OR 2.0 (95% CI 1.2 to 3.3) final value).

CONCLUSIONS

Leucocytosis and change in IL-6 prior to DCI reflect impending cerebral ischemia. The time-independent association of ESR with DCI after SAH may identify this as a risk factor. These data suggest that systemic inflammatory mechanisms may increase the susceptibility to the development of DCI after SAH.

Delayed administration of interleukin-1 receptor antagonist reduces ischemic brain damage and inflammation in comorbid rats

Many neuroprotective agents have been effective in experimental stroke, yet few have translated into clinical application. One reason for this may be failure to consider clinical comorbidities/risk factors in experimental models. We have shown that a naturally occurring interleukin-1 receptor antagonist (IL-1Ra) is protective against ischemic brain damage in healthy animals. However, protective effects of IL-1Ra have not been determined in comorbid animals. Thus, we tested whether IL-1Ra protects against brain injury induced by experimental ischemia in aged JCR-LA (corpulent) rats, which have clinically relevant risk factors. Male, aged, lean, and corpulent rats exposed to transient (90 minutes) occlusion of the middle cerebral artery (tMCAO) were administered two doses of IL-1Ra (25 mg/kg, subcutaneously) during reperfusion. Brain injury and neuroinflammatory changes were assessed 24 hours after tMCAO. Our results show that IL-1Ra administered at reperfusion significantly reduced infarct volume measured by magnetic resonance imaging (50%, primary outcome) and blood-brain barrier disruption in these comorbid animals. Interleukin-1Ra also reduced microglial activation, neutrophil infiltration, and cytokines levels in the brain. These data are the first to indicate that IL-1Ra protects against ischemic brain injury when administered via a clinically relevant route and time window in animals with multiple risk factors for stroke.

An immortalised astrocyte cell line maintains the in vivo phenotype of a primary porcine in vitro blood-brain barrier model

Whilst it is well documented that all components of the neurovascular unit contribute to the restrictive nature of the blood-brain barrier (BBB), astrocytes have been identified as the cellular component most likely to play an essential role in maintaining the barrier properties. The aim of this study was to examine the impact of the rat astrocyte cell line, CTX-TNA2, on the structural and functional characteristics of an in vitro BBB and determine the capacity of this astrocyte cell line to maintain the BBB phenotype. Co-culture of the CTX-TNA2 cells with primary porcine brain endothelial cells produced an in vitro BBB model which retains key features of the in vivo BBB. High transendothelial electrical resistances, comparable to those reported in vivo, were obtained. Ultrastructural analysis revealed distinct intercellular tight junction protein complexes and immunocytochemistry confirmed expression of the tight junction proteins ZO-1 and occludin. Western blotting and fluorescent tracer assays confirmed expression and functional activity of P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) efflux transporters. Studies employing Alexa-fluor 555-conjugated human transferrin revealed temperature-sensitive internalisation indicating the BBB model retains functional receptor-mediated transferrin uptake. The findings of this study indicate that a robust BBB model has been produced and this is the first report of the inductive capacity of the CTX-TNA2 cell line. Since this in vitro BBB model possesses many key characteristics of the BBB in vivo it has the potential to be a valuable tool for the study of biochemical and physiological processes associated with the BBB.

Neutrophil cerebrovascular transmigration triggers rapid neurotoxicity through release of proteases associated with decondensed DNA

Cerebrovascular inflammation contributes to diverse CNS disorders through mechanisms that are incompletely understood. The recruitment of neutrophils to the brain can contribute to neurotoxicity, particularly during acute brain injuries, such as cerebral ischemia, trauma, and seizures. However, the regulatory and effector mechanisms that underlie neutrophil-mediated neurotoxicity are poorly understood. In this study, we show that mouse neutrophils are not inherently toxic to neurons but that transendothelial migration across IL-1-stimulated brain endothelium triggers neutrophils to acquire a neurotoxic phenotype that causes the rapid death of cultured neurons. Neurotoxicity was induced by the addition of transmigrated neutrophils or conditioned medium, taken from transmigrated neutrophils, to neurons and was partially mediated by excitotoxic mechanisms and soluble proteins. Transmigrated neutrophils also released decondensed DNA associated with proteases, which are known as neutrophil extracellular traps. The blockade of histone-DNA complexes attenuated transmigrated neutrophil-induced neuronal death, whereas the inhibition of key neutrophil proteases in the presence of transmigrated neutrophils rescued neuronal viability. We also show that neutrophil recruitment in the brain is IL-1 dependent, and release of proteases and decondensed DNA from recruited neutrophils in the brain occurs in several in vivo experimental models of neuroinflammation. These data reveal new regulatory and effector mechanisms of neutrophil-mediated neurotoxicity (i.e., the release of proteases and decondensed DNA triggered by phenotypic transformation during cerebrovascular transmigration). Such mechanisms have important implications for neuroinflammatory disorders, notably in the development of antileukocyte therapies.

Interleukin-1 mediates neuroinflammatory changes associated with diet-induced atherosclerosis

BACKGROUND

Systemic inflammation contributes to brain pathology in cerebrovascular disease through mechanisms that are poorly understood.

METHODS AND RESULTS

Here we show that atherosclerosis, a major systemic inflammatory disease, is associated with severe cerebrovascular inflammation in mice and that this effect is mediated by the proinflammatory cytokine interleukin-1 (IL-1). Apolipoprotein E-deficient mice fed Paigen or Western diets develop vascular inflammation, microglial activation, and leukocyte recruitment in the brain, which are absent in apolipoprotein E-deficient mice crossed with IL-1 type 1 receptor-deficient mice. Systemic neutralization of IL-1β with an anti-IL-1β antibody reversed aortic plaque formation (by 34% after a Paigen and 45% after a Western diet) and reduced inflammatory cytokine expression in peripheral organs. Central, lipid accumulation-associated leukocyte infiltration into the choroid plexus was reversed by IL-1β antibody administration. Animals fed a Western diet showed 57% lower vascular inflammation in the brain than that of mice fed a Paigen diet, and this was reduced further by 24% after IL-1β antibody administration.

CONCLUSIONS

These results indicate that IL-1 is a key driver of systemically mediated cerebrovascular inflammation and that interventions against IL-1β could be therapeutically useful in atherosclerosis, dementia, or stroke. (J Am Heart Assoc. 2012;1:e002006 doi: 10.1161/JAHA.112.002006.).

Interleukin-1 receptor antagonist reverses stroke-associated peripheral immune suppression

INTRODUCTION

Infections are common following stroke and adversely affect outcome. Cellular immune suppression associated with acute stroke may increase susceptibility to infection. Cytokines are important contributors to both stroke pathology and the response to infection. Since interleukin (IL)-1 blockade is a candidate treatment for cerebral ischemia, we examined whether administration of interleukin-1 receptor antagonist (IL-1Ra) to patients with acute stroke affected innate cellular immune responses in a phase II placebo-controlled trial.

METHODS

Venous blood samples were taken prior to treatment initiation, at 24h and 5 to 7d. Blood was also drawn from stroke-free controls. Lipopolysaccharide (LPS) stimulation of whole-blood cultures assessed the potential of leukocytes to produce cytokines.

RESULTS

Induction of tumor necrosis factor (TNF)-α, IL-1β, IL-6, IL-8 and IL-10 by LPS was significantly reduced in patients at admission, compared to controls. At 24h, cytokine induction remained suppressed in the placebo group. In contrast, for patients treated with IL-1Ra, induction of TNF-α, IL-6 and IL-10 was similar to controls and IL-1β induction was significantly greater than in the placebo group. At 5 to 7d, TNF-α and IL-1β induction remained suppressed only in the placebo group (p<0.05). Plasma cortisol concentrations, elevated at admission in patients compared to controls, were substantially reduced at 24h in the patients receiving IL-1Ra (p<0.05) and inversely correlated (p<0.001) with either TNF-α (r=-0.71) or IL-1β induction (r=-0.67) at admission.

CONCLUSION

Treatment with IL-1Ra reverses peripheral innate immune suppression in the acute phase of stroke, which is associated with attenuated cortisol production. The mechanisms underlying these observations, including the potential impact of IL-1Ra on stroke severity and the clinical significance of immune suppression, require further evaluation in larger studies.

Interleukin-1 and stroke: biomarker, harbinger of damage, and therapeutic target

Inflammation is established as a contributor to cerebrovascular disease. Risk factors for stroke include many conditions associated with chronic or acute inflammation, and inflammatory changes in the brain after cerebrovascular events contribute to outcome in experimental studies, with growing evidence from clinical research. The brain is extremely susceptible to inflammatory challenge, but resident glia, endothelial cells and neurones can all mount a pronounced inflammatory response to infection or injury. Recent discoveries highlight the importance of peripherally-derived immune cells and inflammatory molecules in various central nervous system disorders, including stroke. The inflammatory cytokine, interleukin-1 (IL-1), plays a pivotal role in both local and systemic inflammation, and is a key driver of peripheral and central immune responses to infection or injury. Inhibition of IL-1 has beneficial effects in a variety of experimental paradigms of acute brain injury and is a promising clinical target in stroke. We propose that blockade of IL-1 could be therapeutically useful in several diseases which are risk factors for stroke, and there is already considerable pre-clinical and clinical evidence that inhibition of IL-1 by IL-1 receptor antagonist may be valuable in the management of acute stroke.

Efficient discovery of anti-inflammatory small-molecule combinations using evolutionary computing

The control of biochemical fluxes is distributed and to perturb complex intracellular networks effectively it is often necessary to modulate several steps simultaneously. However, the number of possible permutations leads to a combinatorial explosion in the number of experiments that would have to be performed in a complete analysis. We used a multi-objective evolutionary algorithm (EA) to optimize reagent combinations from a dynamic chemical library of 33 compounds with established or predicted targets in the regulatory network controlling IL-1β expression. The EA converged on excellent solutions within 11 generations during which we studied just 550 combinations out of the potential search space of ~ 9 billion. The top five reagents with the greatest contribution to combinatorial effects throughout the EA were then optimized pairwise. A p38 MAPK inhibitor with either an inhibitor of IκB kinase or a chelator of poorly liganded iron yielded synergistic inhibition of macrophage IL-1β expression. Evolutionary searches provide a powerful and general approach to the discovery of novel combinations of pharmacological agents with potentially greater therapeutic indices than those of single drugs.

Brain inflammation is induced by co-morbidities and risk factors for stroke

Chronic systemic inflammatory conditions, such as atherosclerosis, diabetes and obesity are associated with increased risk of stroke, which suggests that systemic inflammation may contribute to the development of stroke in humans. The hypothesis that systemic inflammation may induce brain pathology can be tested in animals, and this was the key objective of the present study. First, we assessed inflammatory changes in the brain in rodent models of chronic, systemic inflammation. PET imaging revealed increased microglia activation in the brain of JCR-LA (corpulent) rats, which develop atherosclerosis and obesity, compared to the control lean strain. Immunostaining against Iba1 confirmed reactive microgliosis in these animals. An atherogenic diet in apolipoprotein E knock-out (ApoE(-/-)) mice induced microglial activation in the brain parenchyma within 8 weeks and increased expression of vascular adhesion molecules. Focal lipid deposition and neuroinflammation in periventricular and cortical areas and profound recruitment of activated myeloid phagocytes, T cells and granulocytes into the choroid plexus were also observed. In a small, preliminary study, patients at risk of stroke (multiple risk factors for stroke, with chronically elevated C-reactive protein, but negative MRI for brain pathology) exhibited increased inflammation in the brain, as indicated by PET imaging. These findings show that brain inflammation occurs in animals, and tentatively in humans, harbouring risk factors for stroke associated with elevated systemic inflammation. Thus a "primed" inflammatory environment in the brain may exist in individuals at risk of stroke and this can be adequately recapitulated in appropriate co-morbid animal models.

Translational pharmacokinetics: challenges of an emerging approach to drug development in stroke

INTRODUCTION

There is increasing recognition of the importance of translational pharmacokinetics in stroke research, lack of which has been cited as one of the main contributing factors to failure of Phase III trials.

AREAS COVERED

The article reviews the translational issues in administration, distribution and sampling in the pharmacokinetics of putative therapeutic drugs in stroke. In addition, the role of translational pharmacometrics in drug development is discussed. The review uses the anti-inflammatory agent, IL-1 receptor antagonist, as an example. The reader will gain an insight into the pitfalls that are commonplace in translating pharmacokinetics from the preclinical to the clinical scenario. The reader will also gain an understanding of the complexities of blood-central nervous system (CNS) barriers in relation to brain pharmacokinetics and the increasing use of translational pharmacometrics in stroke research.

EXPERT OPINION

The translation of preclinical to clinical pharmacokinetics is a discipline that is traditionally overlooked and is likely to be a key factor responsible for failure of clinical trials. With a clear comprehensive insight into the benefits and limitations of translational pharmacokinetics in stroke, translational pharmacokinetics can be safely used to enhance the efficacy of clinical trials in stroke and their likelihood of success.

Does Inflammation Predispose to Recurrent Vascular Events after Recent Transient Ischaemic Attack and Minor Stroke? the North West of England Transient Ischaemic Attack and Minor Stroke (NORTHSTAR) Study

Background and hypothesis

Inflammation is implicated in the pathogenesis and outcome of ischaemic injury. Poststroke inflammation is associated with outcome but it remains unclear whether such inflammation precedes or results from ischaemic injury. We hypothesised that inflammatory markers are associated with an increased risk of recurrent vascular events soon after transient ischaemic attack and minor stroke.

Methods

This was a multicentre, prospective, nested case–control study. Plasma concentrations of C-reactive protein, interleukin-6, interleukin-1-receptor antagonist and fibrinogen, leucocyte counts, erythrocyte sedimentation rate and inflammatory gene allele frequencies were analysed in 711 patients with recent transient ischaemic attack or minor stroke. Cases were defined by the incidence of one or more recurrent vascular events during the three-month follow-up. Association of inflammatory markers with case-status was determined using conditional logistic regression.

Results

Plasma concentrations of C-reactive protein, interleukin-1-receptor antagonist and interleukin-6 were not associated with case-status. In secondary analyses, only erythrocyte sedimentation rate was significantly associated with case-status (odds ratio 1·39, 95% confidence interval 1·03–1·85; P=0·03), but this effect did not persist after adjustment for smoking and past history of transient ischaemic attack or stroke. Single nucleotide polymorphisms in four inflammatory genes (interleukin-6, fibrinogen, P-selectin and vascular cell adhesion molecule-1) were nominally associated with case-status.

Conclusions

Circulating inflammatory markers were not associated with recurrent vascular events. Nominally significant associations between genetic markers and case-status will require replication. These data provide little evidence for an inflammatory state predisposing to stroke and other vascular events in a susceptible population.

Inflammation and brain injury: acute cerebral ischaemia, peripheral and central inflammation

Inflammation is a classical host defence response to infection and injury that has many beneficial effects. However, inappropriate (in time, place and magnitude) inflammation is increasingly implicated in diverse disease states, now including cancer, diabetes, obesity, atherosclerosis, heart disease and, most relevant here, CNS disease. A growing literature shows strong correlations between inflammatory status and the risk of cerebral ischaemia (CI, most commonly stroke), as well as with outcome from an ischaemic event. Intervention studies to demonstrate a causal link between inflammation and CI (or its consequences) are limited but are beginning to emerge, while experimental studies of CI have provided direct evidence that key inflammatory mediators (cytokines, chemokines and inflammatory cells) contribute directly to ischaemic brain injury. However, it remains to be determined what the relative importance of systemic (largely peripheral) versus CNS inflammation is in CI. Animal models in which CI is driven by a CNS intervention may not accurately reflect the clinical condition; stroke being typically induced by atherosclerosis or cardiac dysfunction, and hence current experimental paradigms may underestimate the contribution of peripheral inflammation. Experimental studies have already identified a number of potential anti-inflammatory therapeutic interventions that may limit ischaemic brain damage, some of which have been tested in early clinical trials with potentially promising results. However, a greater understanding of the contribution of inflammation to CI is still required, and this review highlights some of the key mechanism that may offer future therapeutic targets.

Rapid brain penetration of interleukin-1 receptor antagonist in rat cerebral ischaemia: pharmacokinetics, distribution, protection

BACKGROUND AND PURPOSE

Limited data on the brain penetration of potential stroke treatments have been cited as a major weakness contributing to numerous failed clinical trials. Thus, we tested whether interleukin-1 receptor antagonist (IL-1RA), established as a potent inhibitor of brain injury in animals and currently in clinical development, reaches the brain via a clinically relevant administration route, in experimental stroke.

EXPERIMENTAL APPROACH

Male, Sprague-Dawley rats [either naïve or exposed to middle cerebral artery occlusion (MCAo)] were given a single s.c. dose of IL-1RA (100 mg*kg(-1)). The pharmacokinetic profile of IL-1RA was assessed in plasma and CSF up to 24 h post-administration. Brain tissue distribution of administered IL-1RA was assessed using immunohistochemistry. In a separate experiment, the neuroprotective effect of the single s.c. dose of IL-1RA in MCAo was assessed versus a placebo control group.

KEY RESULTS

A single s.c. dose of IL-1RA reduced damage caused by MCAo by 33%. This dose resulted in sustained, high concentrations in plasma and CSF, penetrated brain tissue exclusively in areas of blood-brain barrier breakdown and co-localized with morphologically viable neurones. CSF concentrations did not reflect massive parenchymal infiltration of IL-1RA in MCAo animals compared to naïve.

CONCLUSIONS AND IMPLICATIONS

These data are the first to show that a potential treatment for stroke, IL-1RA, rapidly reaches salvageable brain tissue via an administration route that is clinically relevant. This allows confidence that IL-1RA, as a candidate for further clinical development, is able to confer its protective actions both peripherally and centrally.

Dual functionality of interleukin-1 family cytokines: implications for anti-interleukin-1 therapy

Dysregulated inflammation contributes to disease pathogenesis in both the periphery and the brain. Cytokines are coordinators of inflammation and were originally defined as secreted mediators, released from expressing cells to activate plasma membrane receptors on responsive cells. However, a group of cytokines is now recognized as having dual functionality. In addition to their extracellular effects, these cytokines act inside the nuclei of cytokine-expressing or cytokine-responsive cells. Interleukin-1 (IL-1) family cytokines are key pro-inflammatory mediators, and blockade of the IL-1 system in inflammatory diseases is an attractive therapeutic goal. All current therapies target IL-1 extracellular actions. Here we review evidence that suggests IL-1 family members have dual functionality. Several IL-1 family members have been detected inside the nuclei of IL-1-expressing or IL-1-responsive cells, and intranuclear IL-1 is reported to regulate gene transcription and mRNA splicing. However, further work is required to determine the impact of IL-1 intranuclear actions on disease pathogenesis. The intranuclear actions of IL-1 family members represent a new and potentially important area of IL-1 biology and may have implications for the future development of anti-IL-1 therapies.

Transport of interleukin-1 across cerebromicrovascular endothelial cells

BACKGROUND AND PURPOSE

The inflammatory cytokine interleukin-1 (IL-1) has profound actions in the brain, causing neuronal cell death and exacerbating brain damage. While circulating levels are normally low, IL-1 can be produced on the vascular side of the brain endothelium, and within the brain. The naturally occurring IL-1 receptor antagonist has been administered peripherally in a Phase II trial in acute stroke patients; understanding how IL-1 and IL-1 receptor antagonist penetrate the brain is, therefore, of considerable importance.

EXPERIMENTAL APPROACH

An in vitro blood-brain barrier model was generated by co-culture of porcine brain microvascular endothelial cells with astrocytes. The mechanisms of transcellular transport of IL-1beta and IL-1 receptor antagonist were characterized in this model, using endocytosis inhibitors and IL-1 receptor-blocking antibodies.

KEY RESULTS

Transcellular IL-1beta and IL-1 receptor antagonist transport was temperature-dependent and IL-1beta was transported with higher affinity than IL-1 receptor antagonist. IL-1beta inhibited IL-1 receptor antagonist transport more potently than IL-1 receptor antagonist inhibited IL-1beta transport. Transport of IL-1beta and IL-1 receptor antagonist was not via adsorptive-mediated endocytosis, although inhibition of microtubule assembly significantly attenuated transport of both cytokines. An antibody directed to the type II IL-1 receptor significantly reduced IL-1beta transport.

CONCLUSIONS AND IMPLICATIONS

These results are consistent with IL-1 and IL-1 receptor antagonist being transported across cultured cerebromicrovascular endothelial cells and suggest that IL-1beta transport may occur via a type II IL-1 receptor-dependent mechanism. Understanding IL-1 transport into the brain may have benefits, particularly in enhancing penetration of IL-1 receptor antagonist into the brain.

Pannexin-1-dependent caspase-1 activation and secretion of IL-1beta is regulated by zinc

Inflammatory processes induced by IL-1β are critical for host defence responses, but are also implicated in disease. Zinc deficiency is a common consequence of, or contributor to, human inflammatory disease. However, the molecular mechanisms through which zinc contributes to inflammatory disease remain largely unknown. We report here that zinc metabolism regulates caspase-1 activation and IL-1β secretion. One of the endogenous mediators of IL-1β secretion is adenosine triphosphate, acting via the P2X7-receptor and caspase-1 activation in cells primed with an inflammatory stimulus such as LPS. We show that this process is selectively abolished by a brief pre-treatment with the zinc chelator N,N,N′,N′-tetrakis-(2-pyridylmethyl) ethylene diamine (TPEN). These effects on IL-1β secretion were independent of rapid changes in free zinc within the cell, not a direct effect on caspase-1 activity, and upstream of caspase-1 activation. TPEN did however inhibit the activity of pannexin-1, a hemi-channel critical for adenosine triphosphate and nigericin-induced IL-1β release. These data provide new insights into the mechanisms of caspase-1 activation and how zinc metabolism contributes to inflammatory mechanisms.

The dynamics and mechanisms of interleukin-1alpha and beta nuclear import

Pro-inflammatory members of the interleukin-1 (IL-1) family of cytokines (IL-1α and β) are important mediators of host defense responses to infection but can also exacerbate the damaging inflammation that contributes to major human diseases. IL-1α and β are produced by cells of the innate immune system, such as macrophages, and act largely after their secretion by binding to the type I IL-1 receptor on responsive cells. There is evidence that IL-1α is also a nuclear protein that can act intracellularly. In this study, we report that both IL-1α and IL-1β produced by microglia (central nervous system macrophages) in response to an inflammatory challenge are distributed between the cytosol and the nucleus. Using IL-1-β-galactosidase and IL-1-green fluorescent protein chimeras (analyzed by fluorescence recovery after photobleaching), we demonstrate that nuclear import of IL-1α is exclusively active, requiring a nuclear localization sequence and Ran, while IL-1β nuclear import is entirely passive. These data provide valuable insights into the dynamic regulation of intracellular cytokine trafficking.

Systemic infection, inflammation and acute ischemic stroke

Extensive evidence implicates inflammation in multiple phases of stroke etiology and pathology. In particular, there is growing awareness that inflammatory events outside the brain have an important impact on stroke susceptibility and outcome. Numerous conditions, including infection and chronic non-infectious diseases, that are established risk factors for stroke are associated with an elevated systemic inflammatory profile. Recent clinical and pre-clinical studies support the concept that the systemic inflammatory status prior to and at the time of stroke is a key determinant of acute outcome and long-term prognosis. Here, we provide an overview of the impact of systemic inflammation on stroke susceptibility and outcome. We discuss potential mechanisms underlying the impact on ischemic brain injury and highlight the implications for stroke prevention, therapy and modeling.

Differential effects of interleukin-1 alpha and beta on interleukin-6 and chemokine synthesis in neurones

Interleukin (IL)-1 is a key mediator of neuroinflammation via actions of two agonists IL-1alpha and beta that bind to the IL-1 type I receptor (IL-1RI), and are thought to trigger identical responses. However, evidence suggests that IL-1alpha and beta may have differential actions in the central nervous system (CNS). The objective of this study was to test the hypothesis that IL-1alpha and beta differentially regulate the expression of IL-6 and chemokines KC, IP-10 and MCP-1 in primary neurones. Here we demonstrate that, whilst IL-1beta induced significant synthesis of IL-6 in neurones, IL-1alpha had no effect. In contrast, IL-1alpha and beta induced strong synthesis and constitutive release of chemokines KC, IP-10 and MCP-1 from neurones, and these responses were IL-1RI-dependent. Whilst IL-1beta-induced IL-6 synthesis was dependent on the nSMase/Src kinase signalling cascade, specific inhibitors of nSMase (3-OMS) and Src kinase (PP2) failed to inhibit IL-1alpha- and IL-1beta-induced chemokines synthesis, suggesting the existence of alternative signalling pathway(s) in neurones.

Interleukin-1 receptor antagonist penetrates human brain at experimentally therapeutic concentrations

The proinflammatory cytokine interleukin (IL)-1 mediates several forms of experimentally induced acute brain injury and has been implicated in chronic neurodegenerative disorders. The IL-1 receptor antagonist, IL-1RA, protects rodents against ischaemic brain injury, but its molecular mass (17 kDa) potentially limits the brain penetration of peripherally administered IL-1RA. We therefore sought to identify whether therapeutically effective concentrations of IL-1RA in the rat were also achieved in brain of patients with subarachnoid haemorrhage (SAH), using a peripheral administration regime that had proved to be safe and reduce peripheral inflammation in patients after stroke. An intravenous bolus of IL-1RA, followed by infusion, was administered to rats after induction of focal cerebral ischaemia. The effects of IL-1RA on brain ischaemia and the concentrations achieved in cerebrospinal fluid (CSF), were determined. Interleukin-1 receptor antagonist was similarly administered to patients with SAH, and CSF was sampled via external ventricular drains. In rats, IL-1RA significantly reduced brain injury induced by focal cerebral ischaemia. The plasma IL-1RA concentrations reached 12+/-2 microg/mL by 30 mins, and CSF concentrations were maintained between 91 and 232 ng/mL between 1 and 24 h of infusion. In patients with SAH, IL-1RA reached a steady-state plasma concentration of 22+/-4 microg/mL by 15 mins, and CSF concentrations were maintained at 78 to 558 ng/mL between 1 and 24 h. Intravenous delivery of IL-1RA leads to CSF concentrations in patients comparable to those that are neuroprotective in rats, and might therefore be of therapeutic benefit.

Inflammation in human brain injury: intracerebral concentrations of IL-1alpha, IL-1beta, and their endogenous inhibitor IL-1ra

Following traumatic brain injury (TBI), cascades of inflammatory processes occur. Laboratory studies implicate the cytokines interleukin-1alpha (IL-1alpha) and IL-1beta in the pathophysiology of TBI and cerebral ischemia, whilst exogenous and endogenous interleukin-1 receptor antagonist (IL-1ra) is neuroprotective. We analyzed IL-1alpha, IL-1beta, and IL-1ra in brain microdialysates (100-kDa membrane) in 15 TBI patients. We also analyzed energy-related molecules (glucose, lactate, pyruvate, glutamate, and the lactate/pyruvate ratio) in these brain microdialysates. Mean of mean (+/-SD) in vitro microdialysis percentage recoveries (extraction efficiencies) were IL-1alpha 19.7+/-7.6%, IL-1beta 23.9+/-10.5%, and IL-1ra 20.9+/-6.3%. In the patients' brain microdialysates, mean of mean cytokine concentrations (not corrected for percentage recovery) were IL-1alpha 5.6+/-14.8 pg/mL, IL-1beta 10.4+/-14.7 pg/mL, and IL-1ra 2796+/-2918 pg/mL. IL-1ra was consistently much higher than IL-1alpha and IL-1beta. There were no significant relationships between IL-1 family cytokines and energy-related molecules. There was a significant correlation between increasing IL-1beta and increasing IL-1ra (Spearman r=0.59, p=0.028). There was also a significant relationship between increasing IL-1ra and decreasing intracranial pressure (Spearman r=-0.57, p=0.041). High concentrations of IL-1ra, and also high IL-1ra/IL-1beta ratio, were associated with better outcome (Mann Whitney, p=0.018 and p=0.0201, respectively), within these 15 patients. It is unclear whether these IL-1ra concentrations are sufficient to antagonize the effects of IL-1beta in vivo. This study demonstrates feasibility of our microdialysis methodology in recovering IL-1 family cytokines for assessing their inter-relationships in the injured human brain, and suggests a neuroprotective role for IL-1ra. It remains to be seen whether exogenous IL-1ra or other agents can be used to manipulate cytokine levels in the brain, for potential therapeutic effect.

A selective, non-peptide caspase-1 inhibitor, VRT-018858, markedly reduces brain damage induced by transient ischemia in the rat

Numerous preclinical studies have reported neuroprotective effects of new agents in animal studies. None of these agents has yet translated into a successful clinical trial and therefore to a new therapy. There are many possible reasons for this failure, including poor design of clinical trials, mismatch between preclinical and clinical protocols, and insufficient preclinical data. The enzyme caspase-1 has been implicated in neuronal death. Deletion of the caspase-1 gene, or administration of partially selective inhibitors, reduces neuronal injury induced by cerebral ischemia in rodents. We report here, for the first time, that VRT-018858, the non-peptide, active metabolite of the selective caspase-1 inhibitor pro-drug, pralnacasan, markedly reduced ischemic injury in rats. VRT-018858 was neuroprotective when delivered at 1 and 3h (42% and 58% neuroprotection, respectively) but not 6h after injury, and protection was sustained 7 days after the induction of ischemia (66% neuroprotection). These data confirm caspase-1 as an important target for intervention in acute CNS injury, and propose a new class of caspase-1 inhibitors as highly effective neuroprotective agents.

Pharmacokinetic modelling of interleukin-1 receptor antagonist in plasma and cerebrospinal fluid of patients following subarachnoid haemorrhage

What is already known about this subject? The naturally occurring interlukin-1 receptor antagonist (IL-1RA) markedly protects rodents against ischaemic, excitotoxic and traumatic brain injury, suggesting it may be of therapeutic value. When administered intravenously to patients soon after stroke, IL-1RA is safe and reduces the peripheral inflammatory response. However, IL-1RA is a large protein (17 kDa), which may limit brain penetration, thereby limiting its potential utility in brain injury. What this study adds. The purpose of these experiments was to determine the pharmacokinetics of IL-1RA in cerebrospinal fluid (CSF) of patients, to allow modelling that would aid development of therapeutic regimens. Peripherally administered IL-1RA crosses slowly into and out of the CSF of patients with subarachnoid haemorrhage and, at steady state, CSF IL-1RA concentration (range 115-886 ng ml(-1)) was similar to that found to be neuroprotective in rats (range 91-232 ng ml(-1)), although there was considerable variability among patients. However, there is a large concentration gradient of IL-1RA between plasma and CSF. These CSF:plasma data are consistent with very low permeation of IL-1RA into the CSF and elimination kinetics from it controlled by the volumetric turnover of CSF.

AIM

The naturally occurring interlukin-1 receptor antagonist (IL-1RA) markedly protects rodents against ischaemic, excitotoxic and traumatic brain injury, suggesting it may be of therapeutic value. The aim was to determine the pharmacokinetics of IL-1RA in cerebrospinal fluid (CSF) of patients, to allow modelling that would aid development of therapeutic regimens.

METHODS

When administered intravenously to patients soon after stroke, IL-1RA is safe and reduces the peripheral inflammatory response. However, IL-1RA is a large protein (17 kDa), which may limit brain penetration, thereby limiting its potential utility in brain injury. In seven patients with subarchnoid haemorrhage (SAH), IL-1RA was administered by intravenous bolus, then infusion for 24 h, and both blood and CSF, via external ventricular drains, were sampled during and after stopping the infusion.

RESULTS

Plasma steady-state concentrations were rapidly attained and maintained throughout the infusion, whereas CSF concentrations rose slowly towards a plateau during the 24-h infusion, reaching at best only 4% of that in plasma. Plasma kinetic parameters were within the literature range. Modelling of the combined data yielded rate constants entering and leaving the CSF of 0.0019 h(-1)[relative standard error (RSE) = 19%] and 0.1 h(-1) (RSE = 19%), respectively.

CONCLUSIONS

Peripherally administered IL-1RA crosses slowly into and out of the CSF of patients with SAH. However, there is a large concentration gradient of IL-1RA between plasma and CSF. These CSF:plasma data are consistent with very low permeation of IL-1RA into the CSF and elimination kinetics from it controlled by the volumetric turnover of CSF.

Matrix metalloproteinase-9 and urokinase plasminogen activator mediate interleukin-1-induced neurotoxicity

Matrix metalloproteinases (MMPs) are endopeptidases known to mediate acute neuronal injury, but it is unclear whether these proteases are induced by the primary insult or by inflammation associated with injury. We have reported recently that interleukin-1 (IL-1) induces neurotoxicity by an astrocyte-dependent mechanism. The aim of the present study was to test the hypothesis that MMPs mediate IL-1 neurotoxicity in rat, glial-neuronal cocultures. IL-1beta induced the release of astrocytic MMP-9 in cocultures, whilst an antagonist of MMP-9 inhibited IL-1beta-induced neuronal death. Urokinase plasminogen activator (uPA) was constitutively expressed on neuronal membrane fractions, and amiloride (an antagonist of uPA) or plasminogen activator inhibitor (PAI)-1 significantly reduced IL-1beta-induced neurotoxicity. Thus, neuronal uPA contributes to IL-1 neurotoxicity, and may be responsible for activating MMP-9 released from IL-1-primed astrocytes. In summary, IL-1-induced neurotoxicity is dependent on extracellular protease activity, and these mechanisms may contribute to neuronal cell death in CNS diseases.