Gut–Brain Metabolic Remodeling Mediates the Neuroprotective Effects of Combined Shrimp and Corn Peptides in Scopolamine-Induced Cognitive Impairment

(1) Background: Bioactive peptides from marine and plant sources show neuroprotective potential, yet how their combination ratios affect memory regulation via the gut-brain axis remains unclear. This study investigated the effects of different ratios of marine peptide QMDDQ (Glutamine-Methionine-Aspartate-Aspartate-Glutamine) and plant peptide AGLPM (Alanine-Glycine-Leucine-Proline-Methionine) on scopolamine-induced memory impairment in mice. (2) Methods: Cognitive function was assessed using the Morris water maze and novel object recognition tests. Nissl staining, microplate-based assays for acetylcholine (ACh) content and acetylcholinesterase (AChE) activity, Western blotting for neurotrophic factors, LC-MS/MS-based intestinal peptide profiling, and HPLC-based brain amino acid analysis were performed. (3) Results: The 1:1 ratio most effectively restored learning and memory, regulated hippocampal cholinergic function, mitigated neuronal damage, and elevated BDNF, NGF, and NTF-3 expression. In the gut, peptides were hydrolyzed into glutamate- and proline-rich fragments, which influenced brain amino acid balance by elevating glutamate and proline levels while reducing NH₃-related signaling. (4) Conclusions: These results highlight the ratio-dependent efficacy of QMDDQ-AGLPM combinations and provide evidence for a gut peptide remodeling-brain metabolic link relevant to cognitive impairment.