Effects of remote ischemic postconditioning on the pro-inflammatory neutrophils of peripheral blood in acute cerebral infarction

Background: Neutrophils play crucial roles in the inflammatory response after acute cerebral infarction (ACI). Previous studies revealed neutrophils are non-homogeneous and can be divided into at least two subtypes, pro-inflammatory and anti-inflammatory, correlated with patients' prognosis.Objective: We aimed to explore the correlation between disease severity and peripheral blood neutrophils in patients with ACI and determine whether remote ischemic postconditioning (RIPostC) exerts neuroprotective effects by regulating neutrophils. Methods: Patients (n = 38) with acute anterior circulation cerebral infarction were assigned to conventional treatment (n = 24; included aspirin, statins, neuro nutrition drugs, and circulation improvement drugs) or RIPostC (n = 14; 7-day ischemia adaptation [complete ischemia of both upper extremities for 5 minutes followed by remission for 5 minutes, 5 repeated cycles, twice a day, started from the morning of the second day of admission] based on conventional treatment) groups, based on their preference. General clinical data and peripheral blood samples were taken three times, in the morning before and 3 and 7 days after treatment. Fifteen adults with non-acute cerebral infarction matched for sex, age, and risk factors were recruited as controls; peripheral blood samples were only collected on the recruitment day. We used flow cytometry to detect the percentage of neutrophils and Real-Time PCR to detect the gene expression of interleukin (IL)-18 in the peripheral blood samples. Results: The percentage of neutrophils, pro-inflammatory neutrophils (IL-18 high expression in flow cytometry), and IL-18 mRNA expression increased after ACI (P = 0.01, P = 0.001, P < 0.001). The National Institutes of Health Stroke Scale (NIHSS) score of patients with ACI within one day of onset was positively correlated with the percentage of pro-inflammatory neutrophils (R = 0.618, P = 0.043). Pro-inflammatory neutrophils in the RIPostC group decreased compared with those in the conventional treatment group, with the most significant difference observed on Day 7 (P = 0.01). However, the percentage of neutrophils was not statistically different. IL-18 mRNA expression decreased, with the most significant difference on Day 3 (P = 0.004). The NIHSS and Modified Rankin Scale scores for RIPostC decreased more significantly than for conventional treatment (P = 0.002, P = 0.019).Conclusion: More severe cerebral infarction was associated with a higher percentage of pro-inflammatory neutrophils. The neuroprotective effect of RIPostC may partly be exerted through gene regulation to reduce pro-inflammatory neutrophils.