Multi-Malonylation Enhances the Neuroprotection of Cyanidin-3-<i>O</i>-Glucoside by Promoting Gut-Derived 5-Hydroxytryptophan Production via <i>Limosilactobacillus reuteri</i> through the Gut-Brain Axis

This study synthesized and structurally characterized malonylated derivatives of cyanidin-3-<i>O</i>-glucoside (C3G), namely cyanidin-3-<i>O</i>-(6-<i>O</i>-malonyl-β-d-glucoside) (C3GM) and cyanidin-3-<i>O</i>-(3,6-<i>O</i>-dimalonyl-β-d-glucoside) (C3GdM), and evaluated their neuroprotective effects in a high-fructose diet (HFrD)-induced neuroinflammation mouse. Malonylation enhanced C3G's neuroprotective bioactivity in a dose-dependent manner, with C3GdM showing superior efficacy in improving cognitive impairment, suppressing neuroinflammatory responses, restoring gut barrier integrity, and reshaping gut microbiota composition, notably enriching <i>Lactobacillus</i>. The key strain <i>Limosilactobacillus reuteri</i> LJJ 240337 was isolated and shown to synergize with C3GdM metabolism to produce gut-derived 5-hydroxytryptophan (5-HTP), a pivotal metabolite mediating neuroprotection against inflammation, validated in germ-free mice. Transcriptomic analysis further confirmed its conversion to 5-hydroxytryptamine (5-HT) in the brain, activating the cAMP/PKA/CREB signaling pathway, thereby contributing to the neuroprotective effects. These findings establish a potential structure-activity relationship between malonylation degree and neuroprotective efficacy. They also underscore the therapeutic potential of multiacylated anthocyanins in modulating the gut-brain axis and mitigating metabolic neuroinflammation.