Interleukins and cerebral ischaemia

The Traditional Chinese Medicine MLC901 inhibits inflammation processes after focal cerebral ischemia

Inflammation is considered as a major contributor to brain injury following cerebral ischemia. The therapeutic potential of both MLC601/MLC901, which are herbal extract preparations derived from Chinese Medicine, has been reported both in advanced stroke clinical trials and also in animal and cellular models. The aim of this study was to investigate the effects of MLC901 on the different steps of post-ischemic inflammation in focal ischemia in mice. In vivo injury was induced by 60 minutes of middle cerebral artery occlusion (MCAO) followed by reperfusion. MLC901 was administered in post-treatment 90 min after the onset of ischemia and once a day during reperfusion. MLC901 treatment resulted in a reduction in infarct volume, a decrease of Blood Brain Barrier leakage and brain swelling, an improvement in neurological scores and a reduction of mortality rate at 24 hours after MCAO. These beneficial effects of MLC901 were accompanied by an inhibition of astrocytes and microglia/macrophage activation, a drastically decreased neutrophil invasion into the ischemic brain as well as by a negative regulation of pro-inflammatory mediator expression (cytokines, chemokines, matrix metalloproteinases). MLC901 significantly inhibited the expression of Prx6 as well as the transcriptional activity of NFκB and the activation of Toll-like receptor 4 (TLR4) signaling, an important pathway in the immune response in the ischemic brain. MLC901 effects on the neuroinflammation cascade induced by cerebral ischemia probably contribute, in a very significant way, in its potential therapeutic value.

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

Role of SH levels and markers of immune response in the stroke

Background. Sulfhydryl groups (SH) are considered a key factor in redox sensitive reaction of plasma, and their modification could be considered an expression of abnormal generation of oxygen free radicals. Methods. Fifty consecutive patients with acute brain stroke were enclosed in this study. The plasma concentrations of SH groups were correlated to cytokines (IL-1b, IL-6, IL-8, TNF-α), plasma chitotriosidase (Chit), metalloprotease (MMP2–9), intercellular adhesion molecule-1 (ICAM-1). Results. The results demonstrated a significant reduction of SH groups within 24 hours from the onset of an acute ischemic stroke, a reduction of plasma IL-1b, IL-6, and IL-8, and an increase of Chit and TNF-α in relation to the stroke severity. Conclusion. The observation of an intense microenvironment activation that follows the stroke and the correlation between SH levels and markers of immune response suggest that, especially in stroke, is necessary to maintain the redox function to prevent the brain damage. The reduced SH levels represent an attempt to neutralize the abnormal generation of free radicals. Since the reperfusion of brain after ischemic event represents a severe oxidative stress, which must be corrected by regeneration of redox sensitive function, pharmacological intervention could be beneficial in this setting.

Proinflammatory cytokines in the prefrontal cortex of teenage suicide victims

Teenage suicide is a major public health concern, but its neurobiology is not well understood. Proinflammatory cytokines play an important role in stress and in the pathophysiology of depression-two major risk factors for suicide. Cytokines are increased in the serum of patients with depression and suicidal behavior; however, it is not clear if similar abnormality in cytokines occurs in brains of suicide victims. We therefore measured the gene and protein expression levels of proinflammatory cytokines interleukin (IL)-1β, IL-6, and tissue necrosis factor (TNF)-α in the prefrontal cortex (PFC) of 24 teenage suicide victims and 24 matched normal control subjects. Our results show that the mRNA and protein expression levels of IL-1β, IL-6, and TNF-α were significantly increased in Brodmann area 10 (BA-10) of suicide victims compared with normal control subjects. These results suggest an important role for IL-1β, IL-6, and TNF-α in the pathophysiology of suicidal behavior and that proinflammatory cytokines may be an appropriate target for developing therapeutic agents.

Cornel iridoid glycoside inhibits inflammation and apoptosis in brains of rats with focal cerebral ischemia

The capacity of cornel iridoid glycoside (CIG) to suppress the manifestations of ischemic stroke was investigated. CIG was administered to rats by the intragastric route once daily for 7 days. Focal cerebral ischemia was induced by 2 h of middle cerebral artery occlusion followed by 24 h of reperfusion. In non-treated rats large infarct areas were observed within 24 h of reperfusion. Examination of the ischemic cerebral cortex revealed microglia and astrocyte activation, increased interleukin-1beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) concentrations, increased DNA fragmentation in the ischemia penumbra, elevated Bax expression, increased caspase-3 cleavage, and decreased Bcl-2 expression. Pretreatment with CIG decreased the infarct area, DNA fragmentation, IL-1beta and TNF-alpha concentrations, microglia and astrocyte activation, Bax expression, and caspase-3 cleavage while increasing Bcl-2 expression. CIG exerts anti-neuroinflammatory and anti-apoptotic effects which should prove beneficial for prevention or treatment of stroke.

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.

Serum and CSF levels of cytokines in acute encephalopathy following prolonged febrile seizures

It is well known that an acute encephalopathy occasionally follows prolonged febrile seizures. We measured the concentrations of interferon-gamma, tumor necrosis factor-alpha (TNF-alpha), interleukin-2 (IL-2), IL-4, IL-6, IL-10, and soluble TNF receptor 1 (sTNFR1) in serum and CSF during the acute stage in 13 children with acute encephalopathy following prolonged febrile seizures (AEPFS) and 23 with prolonged febrile seizures without encephalopathy (PFS) to investigate the pathogenesis of AEPFS. Serum IL-6, IL-10, sTNFR1, and CSF IL-6 levels were significantly higher in AEPFS and PFS compared with control subjects. CSF IL-6 levels in AEPFS were significantly higher than those in PFS, but not serum IL-6, IL-10, or sTNFR1. The CSF IL-6 levels were significantly higher than the serum levels in AEPFS, but not PFS. The serum levels of sTNFR1 and IL-10 were significantly higher than those in the CSF in AEPFS and PFS. The serum IL-10 and sTNFR1 levels in patients who did not experience a second seizure were significantly higher than those in patients who experienced a second seizure, which was characterized by clusters of complex partial seizures several days after the initial prolonged febrile seizure. Our results suggest that serum IL-6, IL-10, TNF-alpha, and CSF IL-6 are part of the regulatory system of cytokines in AEPFS.

Immunological aspects of acute stroke: therapeutic implications

Recent studies strongly suggest that cerebral ischaemia initiates a focal inflammatory response that results in significant secondary injury to brain tissue,thereby extending the ultimate size of a stroke. Factors involved in this cascade include the release of cytokines that cause a pro-inflammatory and prothrombotic state on cerebral vessel endothelium, the expression of leucocyte adhesion molecules, and the release of chemotactic factors allowing the migration of leucocytes into the area of injured brain tissue causing further damage. Animal studies have clearly demonstrated the detrimental effects of these inflammatory mediators in stroke models and additionally have shown dramatic reduction in infarct size using leucocyte adhesion modification and cytokine receptor blockade. The approach of modifying the effects of inflammatory cytokines and/or limiting leucocyte adhesion and migration into the region of injury holds great promise for identifying agents that will give significant neuronal protection following a stroke.

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.

Inflammatory biomarkers in blood of patients with acute brain ischemia

Although many failed surrogate markers are provided in the literature, inflammation may contribute to the outcome of ischemic stroke. In 50 consecutive patients with acute ischemic stroke, in the absence of symptoms and signs of concomitant infection, we evaluated a panel of biomarkers reported to be variably associated with brain ischemia, and correlate their serum level with the brain lesion volume and clinical outcome. Infarct size was calculated on computed tomography (CT) scans by means of the Cavalieri's method. Neurological impairment was scored by using the Glasgow Coma Scale, Glasgow Outcome Scale and National Institutes of Health (NIH) scales at stroke onset and 3-month follow-up. Some markers showed a direct significant correlation with both initial and final NIH scale and with infarct size, particularly tumor necrosis factor alpha (TNF-alpha) (P=0.002), intercellular adhesion molecule-1 (P<0.01) and matrix metalloproteinase-2/9 (P=0.001). In contrast to previous reports, interleukin-6 (IL-6) serum level showed a significant inverse correlation with both final neurological impairment and infarct size (P<0.001). This novel finding allows us suggesting that IL-6, in the context of a complex pro-inflammatory network occurring during stroke, is associated with neuroprotection rather than neurotoxicity in patients with ischemic brain injury.

Modulatory effect of interleukin-1β on rat isolated basilar artery contraction

An increased level of cytokine interleukin-1 (IL-1) has been detected around the site of stroke. However, the effect of IL-1beta on the basilar artery has received little attention. We evaluated the effects of IL-1beta on the contractile response of rat isolated basilar artery by measuring isometric tension change. IL-1beta (10 ng/ml) and phenylephrine (0.1 nM) markedly enhanced U46619 (30 and 100 nM)-induced basilar artery contraction. The IL-1beta-mediated potentiation was partly suppressed by zinc protoporphyrin (3 microM) and was abolished by tetrodotoxin (TTX, 100 nM), (-)-perillic acid (1 microM), PD98059 (0.3 microM), SB203580 (1 microM) and prazosin (1 microM). Our data suggest that IL-1beta (10 ng/ml) causes an enhancement of U46619-mediated basilar artery contraction that probably involves TTX-sensitive neuronal release of an alpha1-adrenoceptor agonist and activation of p42/p44 and p38 mitogen-activated protein kinases/p21(ras) pathways.

Chitotriosidase in patients with acute ischemic stroke

BACKGROUND

Following an acute brain ischemia, local endothelia allow monocyte chemoattraction into the lesion site which contributes to brain damage through a group of neurotoxic factors. A relationship exists between the extent of brain damage and the plasma level of monocyte products, including chitotriosidase, though usually strictly related to preexisting infectious-inflammatory diseases.

PURPOSE

Since chitotriosidase activity is also elevated in pathogen-free conditions, we tested whether chitotriosidase upregulation might be specifically related to stroke and unrelated to clinically relevant infectious diseases.

METHODS

We studied the plasma level of chitotriosidase activity, TNF-alpha and IL-6 in 44 consecutive patients with acute brain ischemia without concomitant symptoms or signs of inflammatory-infectious diseases. Results were compared with stroke severity and outcome as detected by brain CT and NIH scale. Blood samples were collected, on average, 11 h after stroke onset.

RESULTS

Chitotriosidase activity positively correlates with stroke severity, as measured by NIH scale (r = 0.69, p < 0.01), to the extent of brain damage as documented by CT (r = 0.75, p < or = 0.001) and the TNF-alpha level (r = 0.76, p < 0.001); it also inversely correlates with the IL-6 level (r = -0.43, p < or = 0.05).

CONCLUSION

Our results indicate that chitotriosidase is a specific marker of macrophage activation occurring in stroke which directly correlates with stroke severity independently of preexisting inflammatory or infectious conditions.

Interleukin-1β exacerbates and interleukin-1 receptor antagonist attenuates neuronal injury and microglial activation after excitotoxic damage in organotypic hippocampal slice cultures

The effects of interleukin (IL)-1beta and IL-1 receptor antagonist (IL-1ra) on neurons and microglial cells were investigated in organotypic hippocampal slice cultures (OHSCs). OHSCs obtained from rats were excitotoxically lesioned after 6 days in vitro by application of N-methyl-D-aspartate (NMDA) and treated with IL-1beta (6 ng/mL) or IL-1ra (40, 100 or 500 ng/mL) for up to 10 days. OHSCs were then analysed by bright field microscopy after hematoxylin staining and confocal laser scanning microscopy after labeling of damaged neurons with propidium iodide (PI) and fluorescent staining of microglial cells. The specificity of PI labeling of damaged neurons was validated by triple staining with neuronal and glial markers and it was observed that PI accumulated in damaged neurons only but not in microglial cells or astrocytes. Treatment of unlesioned OHSCs with IL-1beta did not induce neuronal damage but caused an increase in the number of microglial cells. NMDA lesioning alone resulted in a massive increase in the number of microglial cells and degenerating neurons. Treatment of NMDA-lesioned OHSCs with IL-1beta exacerbated neuronal cell death and further enhanced microglial cell numbers. Treatment of NMDA-lesioned cultures with IL-1ra significantly attenuated NMDA-induced neuronal damage and reduced the number of microglial cells, whereas application of IL-1ra in unlesioned OHSCs did not induce significant changes in either cell population. Our findings indicate that: (i) IL-1beta directly affects the central nervous system and acts independently of infiltrating hematogenous cells; (ii) IL-1beta induces microglial activation but is not neurotoxic per se; (iii) IL-1beta enhances excitotoxic neuronal damage and microglial activation and (iv) IL-1ra, even when applied for only 4 h, reduces neuronal cell death and the number of microglial cells after excitotoxic damage.

Antenatal risk factors associated with unfavorable neurologic status in newborns and at 2 years of age

The aim of this prospective cohort study was to evaluate the influence of different antenatal factors on neurologic signs in the first days of life and neurodevelopmental outcome at 2 years of age. The study group consisted of 390 children drawn from a cohort of 828 consecutive live births. The data about potential antenatal risk factors, birth complications, and neonatal course were abstracted from pregnancy and delivery records and the hospital register. Odds ratio estimates with 95% confidence intervals were used to measure the associations between antenatal factors and neurologic status in newborns and at 2 years of age. Significance level was set at P < .05. At the mean age of 2 years, 49 of 390 children exhibited adverse neurodevelopmental outcome (cerebral palsy and other developmental disorders). The development of 341 children was normal. Comparative analysis of risk factors was conducted. The strongest correlation with development of hypoxic-ischemic encephalopathy during the first days of life was found in trichomoniasis during pregnancy (odds ratio 4.34; 95% confidence interval 1.32-14.23) and acute respiratory disease (temperature > or = 38 degrees C) in the second half of pregnancy (odds ratio 2.86; 95% confidence interval 1.08-7.58). Of various antenatal factors, bacterial vaginosis combined with impending abortion in the first half of pregnancy (odds ratio 4.96; 95% confidence interval 1.35-18.26) had a significant association with adverse outcome at 2 years of age. The presence of at least one complication at delivery placed the child at risk of adverse neurologic outcome (odds ratio 2.44; 95% confidence interval 1.32-4.54). The study provides supportive evidence that antenatal factors associated with maternal infections can influence the development of hypoxic-ischemic encephalopathy and later neurodevelopmental outcome. These children should be assigned to risk groups for early intervention.

The role of inflammatory processes in the pathophysiology and treatment of brain and spinal cord trauma

Traumatic injury to the brain and spinal cord results in an early inflammatory response that is initiated by the release of proinflammatory cytokines followed by the infiltration and accumulation of polymorphonuclear leukocytes (PMNLs). The role of the inflammatory cascade on traumatic outcome remains controversial. Pleiotropic cytokines appear to function both protectively and destructively. The induction of cytokines can lead to the expression of the inducible form of nitric oxide synthase (iNOS), which in turn provokes the release of excessive amounts of nitric oxide (NO) that may participate in the pathogenesis of tissue injury. Hypothermia has been reported by various groups to be neuroprotective in brain and spinal cord trauma. We studied the effect of therapeutic hypothermia on cerebral IL-1beta concentrations, PMNL accumulation and iNOS activity after traumatic brain injury (TBI) and spinal cord injury (SCI). Based on current data therapeutic hypothermia may protect in models of traumatic injury by modulating deleterious inflammatory processes.

The pathophysiological role of cytokines

Cytokines are important hormonal mediators, produced in tissues undergoing defence, growth and repair processes. Infection and inflammation in particular result in a cascade of cytokine induction that acts to maintain tissue homeostasis. Most cytokines act within the injured tissues, although some have an endocrine action, recruiting distant tissues in defence of the tissue producing the cytokine and many are important for regulating acquired immunity in secondary lymphoid tissues. Induction of interleukin-1 (IL-1), tumour necrosis factor (TNF) and IL-6 highlight the way in which local tissue cytokine responses are induced and act. Since most cytokines act locally, cytokine measurement presents several difficulties. Only where cytokines (such as IL-6) have a systemic action are plasma cytokine concentrations really meaningful. The presence of cytokine antagonists and soluble cytokine receptors, often released in concert with their respective cytokine agonists, presents additional complexity to interpretation. Measurement and manipulation of cytokines can contribute towards an understanding of their pathophysiological role in both experimental and clinical settings. This includes measurement of plasma IL-6, which has striking relationships to tissue inflammation. Its value is exemplified by some recent studies of stroke patients, where IL-6 reflects not only the initial response but also clinical outcome and survival.

Chemically induced neuronal damage and gliosis: enhanced expression of the proinflammatory chemokine, monocyte chemoattractant protein (MCP)-1, without a corresponding increase in proinflammatory cytokines(1)

Enhanced expression of proinflammatory cytokines and chemokines has long been linked to neuronal and glial responses to brain injury. Indeed, inflammation in the brain has been associated with damage that stems from conditions as diverse as infection, multiple sclerosis, trauma, and excitotoxicity. In many of these brain injuries, disruption of the blood-brain barrier (BBB) may allow entry of blood-borne factors that contribute to, or serve as the basis of, brain inflammatory responses. Administration of trimethyltin (TMT) to the rat results in loss of hippocampal neurons and an ensuing gliosis without BBB compromise. We used the TMT damage model to discover the proinflammatory cytokines and chemokines that are expressed in response to neuronal injury. TMT caused pyramidal cell damage within 3 days and a substantial loss of these neurons by 21 days post dosing. Marked microglial activation and astrogliosis were evident over the same time period. The BBB remained intact despite the presence of multiple indicators of TMT-induced neuropathology. TMT caused large increases in whole hippocampal-derived monocyte chemoattractant protein (MCP)-1 mRNA (1,000%) by day 3 and in MCP-1 (300%) by day 7. The mRNA levels for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-6, cytokines normally expressed during the earliest stage of inflammation, were not increased up to 21 days post dosing. Lipopolysaccharide, used as a positive control, caused large inductions of cytokine mRNA in liver, as well as an increase in IL-1beta in hippocampus, but it did not result in the induction of astrogliosis. The data suggest that enhanced expression of the proinflammatory cytokines, TNF-alpha, IL-1beta and IL-6, is not required for neuronal and glial responses to injury and that MCP-1 may serve a signaling function in the damaged CNS that is distinct from its role in proinflammatory events.

Plasma cytokines in acute stroke

GOALS

The aim of this study was to test the relations between plasma cytokines and the clinical characteristics, course, and risk factors in acute stroke.

PATIENTS AND METHODS

The analysis was based on 179 patients with acute stroke included within 24 hours of stroke onset. On inclusion and 3 months later plasma levels of interleukin 1 beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), interleukin-1 receptor antagonist (IL-1RA), interleukin 6 (IL-6), interleukin 10 (IL-10), soluble tumor necrosis factor receptor 1 (sTNF-R1), and soluble tumor necrosis factor receptor 2 (sTNF-R2) were measured by enzyme-linked immunoassay (ELISA).

FINDINGS

The levels of most cytokines were significantly different in acute stroke from the levels 3 months later; but only IL-10 was positively associated with stroke severity. C-reactive protein and white blood cell count were positively associated with the cytokine response.

CONCLUSIONS

We found a substantial overall cytokine reaction that reflected the stroke incident. However, these results do not, at present, suggest a potential for clinical use, as they do not seem to add to the information obtained from the clinical workup of the individual patient.

Astrogliosis in the adult and developing CNS: is there a role for proinflammatory cytokines?

Astrogliosis, characterized by the enhanced expression of GFAP, represents a remarkably homotypic response of astrocytes to all types of injuries of the CNS, including injuries of the developing CNS. As such, astrocytes serve as microsensors of the injured microenvironment regardless of their location in the CNS. The diversity of insults that engender astrogliosis and the brain-wide nature of the astrocytic response suggest that common injury factors serve as the trigger of this cellular reaction. One prominent theme that has emerged in recent years is that proinflammatory cytokines and chemokines serve as a stimulus for induction of astrogliosis. Here we present a brief critique of this hypothesis based on a review of literature and some of our own recentfindings. Studies of astrocytes, in vitro, clearly indicate that these cell types are responsive to a variety of growth factors, including cytokines and chemokines. A somewhat different picture, however, can be seen from data obtained in vivo. It is true that trauma and diseases of the nervous system, as well as some exposures to neurotoxic chemicals, can be associated with the expression in brain of large varieties of cytokines and chemokines. That these same conditions result in astrogliosis has fostered the circumstantial link between cytokine/chemokine expression and the induction of astrogliosis. Several lines of evidence argue against this view, including (a) suppression of cytokine expression does not suppress gliosis, (b) gliosis can occur in the absence of enhanced expression of cytokines, (c) elevations in brain cytokines can occur in the absence of gliosis and (d) the patterns of cytokine expression in the adult and developing CNS are more consistent with a trophic role for these chemical messengers rather than a role in the induction of inflammation. Enhanced expression of cytokines and chemokines after brain injury appear to be signal transduction events unrelated to the induction of astrogliosis.

IL-1 receptor antagonist prevents apoptosis and caspase-3 activation after spinal cord injury

One of the consequences of cytokine-orchestrated inflammation after CNS trauma is apoptosis. Our hypothesis is that cell death in the spinal cord after injury results in part from increased synthesis and release of IL-1beta. Using a ribonuclease protection assay, we demonstrated that there is increased transient expression of IL-1beta mRNA and, by using IL-1beta protein ELISA assay, that there are increased IL-1beta protein levels in the contused rat spinal cord, initially localized to the impact region of the spinal cord (segment T8). Using an ELISA cell death assay, we showed that there is apoptosis in the spinal cord 72 h after injury, a finding that was confirmed by measuring caspase-3 activity, which also significantly increased at the site of injury 72 h after trauma. Treatment of the contused spinal cord at the site of injury with the IL-1 receptor antagonist (rmIL-lra, 750 ng/mL) for 72 h using an osmotic minipump completely abolished the increases in contusion-induced apoptosis and caspase-3 activity.

Cortical interleukin-1 beta elevation after traumatic brain injury in the rat: no effect of two selective antagonists on motor recovery

Interleukin-1 is an inflammatory cytokine implicated in secondary responses to traumatic brain injury. We utilized a specific IL-beta enzyme-linked immunoadsorbant assay to examine the expression of IL-beta after lateral fluid percussion brain injury in the rat. IL-beta was significantly elevated in the ipsilateral injured cortex at 4 h after injury. Increased levels of IL-beta were also observed at 12, 24 and 72 h after injury, although such changes did not reach statistical significance. To determine whether injury-induced IL-beta expression may contribute to subsequent neurological impairment, we treated rats with either of two structurally different, selective IL-1 antagonists and monitored neurological recovery 1, 7 and 14 days later. Intracerebroventricular treatment with either the endogenous interleukin-1 receptor antagonist (10 microg) at 15 min, 2, 4, 6, and 8 h after injury or soluble IL-1 receptors (10 microg) at 15 min, 4 and 8 h after injury did not significantly alter outcome in a series of motor tasks. These data suggest that cortical elevations of IL-beta follow traumatic brain injury, but they may not contribute to subsequent neurological impairment.

A tetracycline derivative, minocycline, reduces inflammation and protects against focal cerebral ischemia with a wide therapeutic window

The only treatment of patients with acute ischemic stroke is thrombolytic therapy, which benefits only a fraction of stroke patients. Both human and experimental studies indicate that ischemic stroke involves secondary inflammation that significantly contributes to the outcome after ischemic insult. Minocycline is a semisynthetic second-generation tetracycline that exerts antiinflammatory effects that are completely separate from its antimicrobial action. Because tetracycline treatment is clinically well tolerated, we investigated whether minocycline protects against focal brain ischemia with a wide therapeutic window. Using a rat model of transient middle cerebral artery occlusion, we show that daily treatment with minocycline reduces cortical infarction volume by 76 +/- 22% when the treatment is started 12 h before ischemia and by 63 +/- 35% when started even 4 h after the onset of ischemia. The treatment inhibits morphological activation of microglia in the area adjacent to the infarction, inhibits induction of IL-1beta-converting enzyme, and reduces cyclooxygenase-2 expression and prostaglandin E(2) production. Minocycline had no effect on astrogliosis or spreading depression, a wave of ionic transients thought to contribute to enlargement of cortical infarction. Treatment with minocycline may act directly on brain cells, because cultured primary neurons were also salvaged from glutamate toxicity. Minocycline may represent a prototype of an antiinflammatory compound that provides protection against ischemic stroke and has a clinically relevant therapeutic window.

T cell receptor BV gene rearrangements in the spinal cords and cerebrospinal fluid of patients with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal disorder whose etiology and pathogenesis remain unknown. Recent studies, however, have demonstrated the presence of inflammatory infiltrates within ALS spinal cord and suggested the possibility of an immune-mediated process in motor neuron degeneration. We have analyzed the diversity of T-cells in the spinal cord in ALS. Reverse transcriptase polymerase chain reaction (RT-PCR) with variable (V) region sequence specific oligonucleotide primers was used to amplify T-cell receptor (TCR)BV transcripts from spinal cords obtained at autopsy from patients with ALS, patients who died without inflammatory disease of the central nervous system, brains from patients with ALS, and brains from patients who died with inflammatory CNS disease. Sequencing was then performed on the amplified transcripts. An overall increase in the level of TCRBV 2 transcripts was detected in ALS specimens when compared to controls. This result was independent of the HLA genotype of the individual. Furthermore, enrichment of TCRBV2-positive T cells could be demonstrated in cerebrospinal fluid derived from patients with ALS, using PCR analysis and a T cell stimulation assay with toxic shock syndrome toxin-1 (TSST-1), a Vbeta2-specific superantigen. Our results suggest that an immunological process involving the specific expansion of Vbeta2 TCR-positive T-cells may be important in the pathogenesis of ALS.

Recent advances on neuronal caspases in development and neurodegeneration

In view of a large and growing literature, this overview emphasizes recent advances in neuronal caspases and their role in cell death. To provide historical perspective, morphology and methods are surveyed with emphasis on early studies on interleukin converting enzyme (ICE) as a prototype for identifying zymogen subunits. The unexpected homology of ICE (caspase-1) to Caenorhabditis elegans death gene CED-3 provided early clues linking caspases to programmed cell death, and led later to discovery of bcl-2 proteins (CED-9 homologs) and 'apoptosis associated factors' (Apafs). Availability of substrates, inhibitors, and cDNAs led to identification of up to 16 caspases as a new superfamily of unique cysteine proteinases targeting Asp groups. Those acting as putative death effectors dismantle neurons by catabolism of proteins essential for survival. Caspases degrade amyloid precursor protein (APP), presenilins (PS1, PS2), tau, and huntingtin, raising questions on their role in neurodegeneration. Brain contains 'inhibitors of apoptosis proteins' (IAPs) survivin and NAIP associated also with some neuronal disorders. Apoptotic stress in neurons initiates a chain of events leading to activation of distal caspases by pathways that remain to be fully mapped. Neuronal caspases play multiple roles for initiation and execution of cell death, for morphogenesis, and in non-mitotic neurons for homeostasis. Recent studies focus on cytochrome c as pivotal in mediating conversion of procaspase-9 as a major initiator for apoptosis. Identifying signaling pathways and related events paves the way to design useful therapeutic remedies to prevent neuronal loss in disease or aging.

Annual review prize lecture cytokines - killers in the brain?

Given at the Meeting of the Physiological Society held at the University of Southampton on 10 September 1998

Expression and localization of p80 and p68 interleukin-1 receptor proteins in the brain of adult mice

The biological effects of interleukin-1 (IL-1) are mediated by two distinct receptors, the p80 type I IL-1 and p68 type II IL-1 receptor proteins (IL-1RI and IL-1RII, respectively), both of which have been recently co-localized to the growth hormone synthesizing cells of the adenohypophysis. Previous studies have shown that IL-1 can bind to specific structures in the central nervous system, but the distribution of IL-1RI and IL-1RII proteins in the adult mouse brain has not been reported. Here we have used immunohistochemistry to study the expression, distribution and cellular localization of both isoforms of the IL-1 receptor proteins in the adult mouse brain. Using a combination of processing techniques (AMeX fixation and cryosectioning), we have immunolabeled brain sections for each isoform of the IL-1R. Both isoforms are expressed in the CNS, particularly in neuronal soma of the granular layer of the dentate gyrus and pyramidal cells of fields CA1-CA4 of Ammon's horn of the hippocampus, in epithelial cells of the choroid plexus and ependymal layer, and in neuronal soma of Purkinje cells of the cerebellum. The IL-1RII isoform, but not IL-1RI, is expressed in specific neuronal soma and proximal cell processes of neurons of the paraventricular gray matter of the hypothalamus. These immunohistochemical data directly demonstrate the neuronal expression of both IL-1R proteins in situ. The distribution and cellular localization of IL-1R proteins in the CNS provide a molecular basis for understanding reciprocal interactions between the immune system and the brain.