Peripheral inflammatory biomarkers in Alzheimer's disease and mild cognitive impairment: a systematic review and meta‐analysis

BACKGROUND: In the past few decades, it has been demonstrated with animal models and clinical studies that a chronic inflammatory process significantly contributes to Alzheimer's disease (AD) pathogenesis. METHODS: We systematically searched on PubMed and Web of Science for studies associated with peripheral inflammatory biomarkers in AD and mild cognitive impairment (MCI) before July 2018. Meta-analysis was conducted to summarise results of studies relative to peripheral cytokines and chemokines in AD and MCI. RESULTS: Mean (± SD) concentrations of peripheral inflammatory biomarkers for AD, MCI and healthy controls were extracted from these studies. Our meta-analysis revealed consistently elevated concentrations of inflammatory biomarkers such as C-reactive protein, interleukin-1β (IL-1β), IL-2, IL-6, IL-12, IL-18, monocyte chemotactic protein-1 (MCP-1), MCP-3, IL-8 and interferon-γ-inducible protein 10 in AD patients, whereas no consistent results were obtained for elevated concentrations of cytokines or chemokines except MCP-1 in MCI patients. CONCLUSIONS: In conclusion, these results provided evidence to support that systematic inflammation might be a biomarker for AD diagnosis, whereas it might be a later event during AD disease progression.