Neuroprotective effects of human recombinant interleukin-1 receptor antagonist in focal cerebral ischaemia in the rat.

Recombinant human interleukin-1 receptor antagonist (rhIL-1ra) markedly protects against focal cerebral ischaemia in the rat, implicating endogenous IL-1 in the events leading to cerebral infarction. The present experiments investigated the effect of intracerebroventricular (i.c.v.) administration of IL-1 beta or rhIL-1ra on ischaemia damage and physiological parameters after permanent middle cerebral artery occlusion in the rat. IL-1 beta (5 ng. i.c.v.) markedly (92%) enhanced infarct volume and caused a significant rise in body temperature, but rhIL-1ra (10 micrograms, i.c.v.) significantly reduced infarct volume and did not significantly affect heart rate, blood pressure, or body temperature, rhIL-1ra administered 30 min before, or at the time of ischaemia significantly reduced infarct volume in cortex (55 and 60%, respectively) and striatum (52 and 41%, respectively). rhIL-1ra administered 30 min after ischaemia significantly reduced total and cortical infarct volume (26 and 29%, respectively), but did not significantly protect striatal tissue. The effects of rhIL-1ra were still evident in both cortex and striatum 7 days after ischaemia. These results support the role of IL-1 in ischaemic brain damage, revealing potent, sustained, neuroprotective effects of rhIL-1ra in the cortex and striatum, which cannot be attributed directly to changes in physiological parameters.

Cerebral interleukin-6 is neuroprotective during permanent focal cerebral ischemia in the rat.

Interleukin-6 (IL-6) is a neurotrophic cytokine expressed in both neurons and glia. The present study shows that cerebral ischemia produced by permanent occlusion of the middle cerebral artery (MCAO) produces a dramatic increase in IL-6 bioactivity in the ischemic hemisphere within 2 hours of MCAO (167 +/- 55 IU versus sham: 50 +/- 35 IU), with further increases at 8 hours (3,456 +/- 1,162 IU) and 24 hours (6,088 +/- 1,772 IU). In a separate series of experiments, intracerebroventricular injection of recombinant IL-6 (3,100 or 31,000 IU) significantly reduced ischemic brain damage after MCAO (to 52% and 65% of controls, respectively). The large increase in endogenous IL-6 bioactivity in response to ischemia, together with the marked neuroprotection produced by exogenous IL-6 suggest that this cytokine is an important endogenous inhibitor of neuronal death during cerebral ischemia.

The progression and topographic distribution of interleukin-1beta expression after permanent middle cerebral artery occlusion in the rat.

The cytokine interleukin-1 (IL-1) has been implicated in the exacerbation of ischemic damage in the brains of rodents. This study has ascertained the cellular localization and chronologic and topographic distribution of pro/mature interleukin-1beta (IL-1beta) protein 0.5, 1, 2, 6, 24, and 48 hours after ischemia by subjecting rats to permanent unilateral occlusion of the middle cerebral artery. Interleukin-1beta was localized immunocytochemically in vibratome sections of perfusion-fixed brains. The cells that expressed IL-1beta had the morphologic features of microglia and macrophages. Interleukin-1beta was first detected 1 hour after occlusion in ipsilateral meningeal macrophage-like cells. By 6 hours, pro/mature IL-1beta-immunoreactive (IL-1(beta)ir) putative microglia were present in the ischemic cerebral cortex, corpus callosum, caudoputamen, and surrounding tissue. By 24 and 48 hours after ischemia, the number and spread of IL-1(beta)ir cells increased greatly, including those resembling activated microglia and macrophages, as the core of the infarct became infiltrated. Interleukin-1(beta)ir cells also were present in apparently undamaged tissue, adjacent to the lesion ipsilaterally, and contralaterally in the cerebral cortex, dorsal corpus callosum, dorsal caudoputamen, and hippocampus. These results support the functional role of IL-1 in ischemic brain damage and reveal a distinct temporal and spatial expression of IL-1beta protein in cells believed to be microglia and macrophages.

Neuroprotective effects of the CRF1 antagonist R121920 after permanent focal ischemia in the rat.

The neuroprotective effects of a systemically active, highly selective, corticotropin-releasing factor-1 (CRF1) receptor antagonist, R121920 ((7-(dipropylamino)-2,5-dimethyl-3- [2-(dimethylamino)-5-pyridyl] pyrazolo [1,5-a] pyrimidine), was assessed in two rat models of permanent focal cerebral ischemia, where the middle cerebral artery (MCA) was occluded either through the subtemporal approach or using the intraluminal suture technique. R121920 rapidly crossed the blood-brain barrier after intravenous (IV) bolus administration (10 mg/kg), with peak brain concentrations at 5 minutes (2.26 +/- 0.40 microg/mL), which were approximately 2-fold greater than those in plasma (0.98 +/- 0.24 microg/mL). Treatment with R121920 (10 mg/kg IV followed by 5 mg/kg subcutaneously at hourly intervals for 4 hours) significantly (P < 0.001) reduced total (by 40%) and cortical (by 37%) infarct volume at 24 hours after subtemporal MCA occlusion (MCAO). In the intraluminal suture MCAO model, IV administration of R121920 (10 mg/kg) at the time of ischemia onset (and at multiple times thereafter) reduced both hemispheric infarct volume (by 34%, P < 0.001) and brain swelling (by 50%, P < 0.001) when assessed at 24 hours. In this model of focal ischemia, significant reduction (P < 0.05) in both outcome measures was obtained when R121920 administration was delayed up to 1 hour after MCAO. These results further define the antiischemic properties of selective CRF 1 antagonists in two experimental models of permanent focal cerebral ischemia.

An ICE inhibitor, z-VAD-DCB attenuates ischaemic brain damage in the rat.

Interleukin-1 beta (IL-1 beta) converting enzyme (ICE) cleaves pro-IL-1 beta to produce mature IL-beta, and is a member of a family of proteases implicated in apoptosis. Intracerebroventricular (i.c.v.) administration of an irreversible ICE inhibitor, z-VAD-DCB (1 pmol, 30 min before and 15 min, 2, 4, 6 and 8 h after surgery) markedly reduced (50 +/- 4%, p < 0.001) infarct volume measured 24 h after focal cerebral ischaemia (middle cerebral artery occlusion, MCAo) in the rat. Inhibition of damage was observed in the cortex (51 +/- 5% reduction) and striatum (42 +/- 6% reduction). These data implicate ICE in ischaemic neuronal death in vivo. Inhibition of ICE could reduce ischaemic damage either by preventing IL-1 beta synthesis or by inhibiting apoptosis or by both of these processes, and may provide a useful therapeutic approach to the inhibition of ischaemic brain damage.

Focal cerebral ischemia induces CRH mRNA in rat cerebral cortex and amygdala.

Corticotropin-releasing hormone (CRH) antagonism has neuroprotective effects in models of ischemia. We examined CRH mRNA by in situ hybridization in a well-established rat model of focal cerebral ischemia caused by permanent middle cerebral artery occlusion (MCAo). In ischemic cortex CRH mRNA levels were elevated 2.6-fold 60 min after MCAo, compared with sham operated animals. CRH mRNA was also induced in the amygdala, 60 min following ischemia, in a pattern which was qualitatively different from that of sham operated animals. This rapid and profound increase in CRH mRNA levels during focal cerebral ischemia is likely to be associated with neurotoxicity, as CRH antagonism has been reported to cause a significant reduction in neuronal loss during ischemia.

An integrated analysis of the progression of cell responses induced by permanent focal middle cerebral artery occlusion in the rat.

Defining the chronology and severity of cell damage in an evolving lesion after ischemia is important for understanding the underlying mechanisms in the development of therapeutic intervention. In the present study, we used a combination of histological and immunocytochemical methods to evaluate cell responses from 30 min to 48 h after permanent occlusion of the middle cerebral artery (MCAO) in the rat. Specific immunocytochemical markers clearly revealed acute early responses in neurons (neurofilament protein 200), astrocytes (glial fibrillary acidic protein), and microglia/macrophages (OX-42 and ED-1) such as enlarged, convoluted neuronal processes, and disintegration of glia. Progressive topographic changes in the developing lesion, pinpointed by immunolabeling, indicated the severity and extension of the cell damage. Proliferation and hypertrophy of astrocytes and microglia around the infarct, and contralaterally, occurred 24-48 h after MCAO and coincided with mass necrosis and infiltration of neutrophils and macrophages into the core. These observations corroborate the suggestion that the inflammatory process is involved in the progression of the infarct.

Endogenous interleukin-1 receptor antagonist is neuroprotective.

Interleukin-1 (IL-1) has been implicated in chronic and acute cerebral neuropathologies. IL-1 receptor antagonist (IL-1ra), a naturally occurring protein that binds to IL-1 receptors without inducing signal transduction, blocks several actions of IL-1. IL-1ra acts at the local level and it also circulates in the bloodstream. We now report evidence for a biological function of IL-1ra in the brain as an endogenous neuroprotective molecule. Cerebral expression of IL-1ra mRNA is induced rapidly by focal cerebral ischemia in rats, and inhibition of the action of IL-1ra, by passive immuno-neutralization, markedly enhances ischemic damage. To our knowledge this is the first report of an action of endogenous IL-1ra in the brain. Control of IL-1ra expression or action may therefore provide a useful therapeutic strategy to limit acute neurodegeneration.

Displacement of insulin-like growth factors from their binding proteins as a potential treatment for stroke.

Insulin-like growth factors I and II (IGF-I and IGF-II) play an important role in normal growth and brain development and protect brain cells from several forms of injury. The effects of IGFs are mediated by type-I and type-II receptors and modulated by potentially six specific binding proteins that form high-affinity complexes with IGFs in blood and cerebrospinal fluid (CSF) and under most circumstances inactivate them. Because brain injury is commonly associated with increases in IGFs and their associated binding proteins, we hypothesized that displacement of this large "pool" of endogenous IGF from the binding proteins would elevate "free" IGF levels to elicit neuroprotective effects comparable to those produced by administration of exogenous IGF. A human IGF-I analog [(Leu24, 59, 60, Ala31)hIGF-I] with high affinity to IGF-binding proteins (Ki = 0.3-3.9 nM) and no biological activity at the IGF receptors (Ki = >10,000 nM) increased the levels of "free, bioavailable" IGF-I in the CSF. Intracerebroventricular administration of this analog up to 1h after an ischemic insult to the rat brain had a potent neuroprotective action comparable to IGF-I. This novel strategy for increasing "free" IGF levels in the brain may be useful for the treatment of stroke and other neurodegenerative diseases.