L-Alliin Modulates Brain Region-Specific Neuroinflammatory Responses to Lipopolysaccharide in Diet-Induced Obese Mice

Background/Objectives: A high-fat diet disrupts metabolic and neuroimmune balance in the brain, making neural tissue more reactive to inflammatory challenges. However, it is not well understood how this vulnerability varies across brain regions or how natural anti-inflammatory compounds influence it. Methods: In this study, we examined how the garlic-derived molecule L-alliin modulates the inflammatory response triggered by lipopolysaccharide in the frontal cortex, hippocampus, and hypothalamus of mice fed either a standard or high-fat diet. Results: Measurements of cytokine gene expression showed that the high-fat diet greatly increased the inflammatory response in the frontal cortex and hypothalamus, with the hypothalamus displaying the strongest overall activation. Treatment with L-alliin significantly reduced elevated cytokine levels in both regions, with the reductions most pronounced in animals on the high-fat diet. In contrast, the hippocampus showed a distinct pattern: expression of TNF-α and IL-1β changed very little across diets or treatments, whereas IL-6 and CCL2 were selectively altered by L-alliin, depending on the animals’ metabolic state. Conclusions: These findings demonstrate that diet-induced obesity does not affect the entire brain uniformly. Instead, inflammatory pathways are altered region-specifically, and L-alliin modulates these pathways with sensitivity to both brain region and metabolic condition. This work emphasizes the importance of accounting for neuroanatomical differences when developing strategies to reduce inflammation in obesity-associated conditions.