Highlights► Risk factors for stroke include atherosclerosis, obesity, diabetes and hypertension. ► Stroke risk factors are associated with peripheral inflammation. ► Corpulent rats and atherogenic mice show increased inflammation in the brain. ► Pilot data show that patients at risk of stroke may also develop brain inflammation. ► Chronic peripheral inflammation can drive inflammatory changes in the brain.

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.

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) Iba. IL-1 and platelet-mediated signals converge on microglia, as both IL-1Ra and GPIba blockade reversed the production of IL-1a 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.

BackgroundSystemic inflammation contributes to brain pathology in cerebrovascular disease through mechanisms that are poorly understood.Methods and ResultsHere 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.ConclusionsThese 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.)

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.

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