Investigating causal associations among inflammatory proteins, blood metabolites, and Alzheimer's disease risk

Alzheimer's disease (AD) is a prevalent degenerative neurological disorder with limited treatment options. Prior studies reported specific metabolites and inflammatory proteins to be related to AD risk. However, the intricate relationship between inflammatory proteins, blood metabolites, and AD risk in European population remains unclear. Genetic instruments for 1,091 metabolites and 736 inflammatory proteins were derived from two recent comprehensive genome-wide association studies. Univariable Mendelian Randomization was employed to assess potential causal effects of metabolites on AD risk, potential effects of inflammatory proteins on metabolites, and effects of inflammatory proteins on AD risk. Multivariable MR (MVMR) was further applied to disentangle direct effects of proteins and metabolites on AD. Twelve metabolites were identified to be associated with AD risk, and 226 inflammatory proteins demonstrated likely to be causal effects on these 12 metabolites. Further examining the associations between such inflammatory proteins and AD risk revealed 22 associations for which the effect directions from inflammatory proteins to metabolites, from metabolites to AD risk, and from inflammatory proteins to AD risk were aligned, suggesting inflammatory protein - metabolite - AD risk pathway. MVMR further highlighted four trios in which the effect directions were consistent with the UVMR results, supporting a metabolite‑mediated pattern. This large‑scale genetic analysis highlights specific metabolites as direct contributors to AD risk and suggests that certain inflammatory proteins may influence AD primarily through downstream metabolic pathways. Our findings offer potential novel therapeutic targets for AD intervention.