Interplay of Large Neutral Amino Acids, Metabolic Syndrome, and Apolipoprotein E ε4 on Brain Integrity at Midlife

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Introduction: Large neutral amino acids (LNAAs) tryptophan and phenylalanine have been implicated in the pathogenesis of neurodegenerative diseases. Given limited research on the effects of LNAA on brain health across different life stages, vascular risk, and genetic backgrounds, our study aimed to explore the interaction of LNAA levels, metabolic syndrome (MetS), and the presence of the apolipoprotein E ε4 (ApoE ε4) allele brain integrity at midlife. Methods: Sixty-eight adults aged 40–61 underwent a health assessment to calculate the number of MetS components, quantify LNAA, measure white matter hyperintensity (WMH) volume, and genotype ApoE ε4. Multivariate linear regression analyses were performed to test the joint effect of LNAA, MetS, and ApoE ε4 on WMH while adjusting for sex, age, and education. Results: Significant 3-way interactions were observed between serum tryptophan (β = 0.042, SE = 0.018, p < 0.05) and phenylalanine (β = 0.044, SE = 0.013, p < 0.01) levels, number of MetS components, and ApoE ε4 alleles status on WMH volume. Neither individual LNAA levels nor MetS components alone predicted WMH volume. Conclusions: The study highlights significant 3-way interactions between LNAA, MetS, and genetic risk factors in the pathology of WMH, particularly in individuals genetically predisposed to Alzheimer’s disease. These interactions suggest differential impacts of LNAA on WMH volume dependent on both genetic and metabolic factors. Results emphasize the need for personalized metabolic and genetic profile assessments in neurodegenerative disease management.