Current trends in the role of neuroinflammation & α-synuclein in alcohol use disorder: A systematic quantitative literature review

The neurodegenerative effects alcohol use disorder (AUD) have been well characterized and are likely due to the long-term effects of alcohol on the brain. The molecular events that underlie regional neuronal loss are a focus of current research. Chronic inflammation in the central nervous system, termed neuroinflammation, contributes to the progressive loss of neurons in the brain. Using data from genome-wide association studies and genetic and gene expression data, α-synuclein was identified as a gene of interest for AUD almost 10 years ago. Despite this and the well-recognized role of α-synuclein in mediating neuroinflammation in other neurodegenerative diseases, its role in alcohol-induced brain damage and AUD is yet to be elucidated. This systematic literature review quantifies and analyzes relationships between AUD, α-synuclein, and neuroinflammation. The review identified fewer studies focused on the role in AUD of α-synuclein (30) than on neuroinflammation (177), with published studies heavily centered on the myeloid differentiation primary response 88 (MyD88)-dependent toll-like receptor 4 (TLR4) pathway. The systematic review revealed that no original literature investigates the roles of α-synuclein and neuroinflammation in AUD and that there are significantly fewer published articles on the role of α-synuclein in AUD than in other neuroinflammatory conditions. Studies of the role of neuroinflammation in AUD are largely centered on the TLR4 signaling cascade, followed by TLR2 and TLR3, and soluble cytokines such as IL-10, IL-1β, and TNF-α. Key research themes identified in other neurodegenerative disorders provide new insights for further investigation in AUD.