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

This study synthesized and structurally characterized malonylated derivatives of cyanidin-3-O-glucoside (C3G), namely cyanidin-3-O-(6-O-malonyl-β-d-glucoside) (C3GM) and cyanidin-3-O-(3,6-O-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 Lactobacillus. The key strain Limosilactobacillus reuteri 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.