Role of Neutrophils in Exacerbation of Brain Injury After Focal Cerebral Ischemia in Hyperlipidemic Mice

Abstract

Background and Purpose Inflammation-related co-morbidities contribute to stroke-induced immune responses and brain damage. We previously showed that hyperlipidemia exacerbates ischemic brain injury, which is associated with elevated peripheral and cerebral granulocyte numbers. Herein, we evaluate the contribution of neutrophils to the exacerbation of ischemic brain injury. Methods Wildtype mice fed with a normal chow and ApoE knockout mice fed with a high cholesterol diet were exposed to middle cerebral artery occlusion (MCAO). CXCR2 was blocked using the selective antagonist SB225002 (2 mg/kg) or neutralizing CXCR2 antiserum. Neutrophils were depleted using an anti-Ly6G antibody. At 72 hours post-ischemia immunohistochemistry, flow cytometry and real-time PCR was performed to determine cerebral tissue injury and immunological changes in the blood, bone marrow and brain. Functional outcome was assessed by accelerated rota rod and tight rope tests at 4, 7 and 14 days post-ischemia. Results CXCR2 antagonization reduced neurological deficits and infarct volumes that were exacerbated in hyperlipidemic ApoE−/− mice. This effect was mimicked by neutrophil depletion. Cerebral neutrophil infiltration and peripheral neutrophilia, which were increased upon ischemia in hyperlipidemia, were attenuated by CXCR2 antagonization. This downscaling of neutrophil responses was associated with increased neutrophil apoptosis and reduced levels of CXCR2, iNOS and NOX2 expression on bone marrow neutrophils. Conclusion Our data demonstrate a role of neutrophils in the exacerbation of ischemic brain injury induced by hyperlipidemia. Accordingly, CXCR2 blockade, which prevents neutrophil recruitment into the brain, might be an effective option for stroke treatment in patients suffering from hyperlipidemia.

Genetic neutrophil deficiency ameliorates cerebral ischemia-reperfusion injury

“…Although previous studies have shown CXCR2 pepducin can effectively suppress neutrophil chemotaxis, the milieu of chemotactic molecules during stroke is likely to be dramatically different and may be more profound. A previous report using the CXCR2 antagonist SB225002 found that pharmacological inhibition was only protective in hyperlipidemic mice (Herz et al, 2015). Our data suggest that a greater decrease in neutrophil infiltration is necessary to prevent the detrimental effects of neutrophils, and complete inhibition of neutrophil chemotaxis may not be achievable through inhibition of a single chemokine signaling pathway in our model.…”

Neutrophil-Lymphocyte Ratio Predicts Functional and Safety Outcomes after Endovascular Treatment for Acute Ischemic Stroke

“…When ischemic stroke occurs, neutrophils were recruited to the ischemic area in the early stages of inflammatory response [7]; they promoted the damage of blood-brain barrier by releasing inflammatory mediators [8, 9]. On the contrary, lymphocytes play an important role in the healing and repair of inflammation [10], and the lower lymphocyte count was associated with increased infarct volume and neurological deterioration [11, 12].…”

Neutrophil to Lymphocyte Ratio Predicts Short-Term Functional Outcome in Acute Ischemic Stroke

“…The inflammatory process in AIS involves cytokines and chemokines released from ischemic tissues, promoting the accumulation of leukocytes to the ischemic areas [5,6]. Among circulating leukocytes, neutrophils have been regarded as crucial mediators of ischemic injury [6][7][8]. Accumulated neutrophils release free oxygen radicals, various inflammatory cytokines, and neurotoxic substances, all of which cause cellular necrosis and apoptosis in ischemic tissues [9].…”