On December 10, 2025, a research team led by Xin Zhou from the College of Chemistry and Environmental Science at Guangdong Ocean University published an article in the journal Marine Drugs titled "Trimethyl Chitosan-Engineered Cod Skin Peptide Nanosystems Alleviate Behavioral and Cognitive Deficits in D-Galactose-Induced Alzheimer's Disease Model Mice." By engineering trimethyl chitosan (TMC), a quaternized derivative of the Marine Polysaccharide chitosan, the researchers successfully encapsulated cod skin collagen peptides (CSCPs) into a stable nanosystem. Their findings demonstrate that this marine glycobiological intervention significantly reverses cognitive decline, repairs hippocampal damage, and mitigates oxidative stress in Alzheimer's disease (AD) mouse models, marking a pivotal step forward in the application of marine glycans for brain health.

Research Background

The global burden of Alzheimer's disease is escalating, yet the development of effective, non-toxic therapeutics remains one of the greatest challenges in modern medicine. Conventional Drug Delivery to the brain is notoriously difficult due to the blood-brain barrier (BBB), which excludes over 98% of small-molecule drugs and nearly all large biopharmaceuticals. This is where the intersection of marine biology and glycobiology offers a unique solution.

Marine organisms are a treasure trove of bioactive compounds, and cod skin collagen, often a byproduct of the fishing industry, contains specific sequences of amino acids that possess neuroprotective, antioxidant, and anti-inflammatory properties. However, these peptides are often degraded by digestive enzymes or fail to reach the brain in sufficient concentrations when administered orally or systemically.

Chitosan is one of the most versatile biopolymers in nature. Its biocompatibility and mucoadhesive properties are well-documented, but its poor solubility at physiological pH has historically limited its use. By chemically modifying it into TMC, the researchers have created a "smart" glycan. TMC carries a permanent positive charge, which not only improves solubility but also enhances its interaction with the negatively charged sialic acid residues on cell membranes and the BBB. This study builds upon the burgeoning field of "glyco-nanomedicine," using the natural recognition and transport properties of sugars to deliver life-saving marine bioactives to the central nervous system.

Research Results

The research journey described in this paper is a masterclass in marine glycotechnology, moving from precise molecular engineering to complex in vivo behavioral analysis. The study is broadly categorized into three fundamental phases: the architecture of the glycan nanocarrier, the evaluation of cognitive restoration, and the deep-tissue histopathological validation.

• Glycan Engineering and the Assembly of TMC-CSCPs Nanosystems

The team performed a controlled quaternization of medium-molecular-weight chitosan using dimethyl sulfate under alkaline conditions. This process yielded TMC with a precisely characterized quaternization degree of 57.3%, as confirmed by 1H-NMR spectroscopy. The innovation here is the transformation of a standard marine polysaccharide into a high-performance delivery vehicle. TMC possesses superior solubility and a strong positive surface charge compared to native chitosan, which is essential for interacting with negatively charged biological membranes. Through a process of electrostatic self-assembly, the TMC was complexed with CSCPs at an optimized mass ratio. The resulting nanoparticles (CSCPs-NPs) exhibited a spherical morphology with a narrow hydrodynamic diameter of approximately 93.25 nm.

From a glycobiology perspective, the stability of this nanosystem is remarkable. The nanoparticles achieved an encapsulation efficiency of 61.17% and demonstrated a sustained-release profile. Unlike many delivery systems that suffer from a "burst effect," these Marine Glyco-nanoparticles released their therapeutic cargo gradually—reaching 73.05% over 24 hours in physiological conditions. This sustained release is critical for maintaining therapeutic concentrations of marine peptides in the systemic circulation, potentially facilitating better transport across the blood-brain barrier.

Fig.1 Preparation and characterization of CSCPs-NPs. (Kong, et al., 2025)

• Reversing Cognitive Decline: Behavioral Recovery in AD Models

Following the successful synthesis of the nanosystem, the researchers transitioned to functional testing using a D-galactose-induced AD mouse model. D-Galactose is a reducing sugar that, when administered in excess, leads to the accumulation of advanced glycation end-products (AGEs) and oxidative stress, mimicking the natural aging process and AD-like pathology. The team utilized the Morris water maze (MWM) to evaluate the efficacy of the CSCPs-NPs. While the AD-model mice showed significant impairment, characterized by increased escape latency (the time taken to find a submerged platform) and disorganized swimming paths, the mice treated with the TMC-engineered nanosystem showed a rapid recovery of spatial orientation. By the fifth day of training, the escape latency in the nanoparticle-treated group was significantly reduced, comparable to healthy control levels.

Fig.2 CSCPs-NPs attenuate hippocampal atrophy and neuronal damage in D-galactose-induced AD mice. (Kong, et al., 2025)

Furthermore, in the probe trial, where the platform is removed to test memory retention, the CSCPs-NP group spent significantly more time in the target quadrant and exhibited a higher frequency of platform crossings. The researchers also employed a balance beam test to evaluate motor coordination, a facet of neurodegeneration often overlooked. The mice treated with the marine nanosystem showed fewer foot slips and faster traversal times, indicating that the glycan-peptide complex effectively protects both cognitive and motor functions.

Fig.3 CSCPs-NPs improve cognitive and motor functions in AD mice. (Kong, et al., 2025)

• Histopathological Preservation and Neuroprotective Mechanisms

The researchers focused on the hippocampus and the cerebral cortex, regions most severely impacted by AD. Using hematoxylin and eosin (HE) staining and Nissl staining, the team visualized the cellular architecture of the brain. In the untreated AD model mice, the histology revealed classic hallmarks of neurodegeneration: significant neuronal loss, nuclear pyknosis (shrunken, dark-staining nuclei), and widespread edema. These pathological changes are indicative of severe oxidative damage and apoptosis triggered by the D-galactose sugar overload.

However, the administration of CSCPs-NPs drastically altered this trajectory. The hippocampal neurons in the treated mice remained densely packed, with clear, prominent nucleoli and minimal signs of edema. Nissl staining confirmed an abundance of Nissl bodies, which are essential for protein synthesis and signify healthy, active neurons. The researchers concluded that the TMC-engineered nanosystem does not merely mask symptoms but provides a robust physical and biochemical shield for neurons. This protection is attributed to the synergistic effect of the marine peptides' antioxidant properties and the TMC's ability to enhance the bioavailability of these bioactive molecules within the neuro-environment.

Fig.4 CSCPs-NPs restore apoptotic balance in the hippocampus of AD mice. (Kong, et al., 2025)

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Conclusion

By successfully engineering a TMC-CSCPs, the researchers have demonstrated a viable pathway for utilizing marine waste—specifically cod skin and crustacean shells—to create high-value medical interventions. The innovation lies in two key areas:

• The molecular refinement of marine glycans to overcome solubility and delivery barriers.
• The synergistic formulation of glycan carriers and marine peptides effectively mitigates the cognitive and physical symptoms of AD.

This research highlights the transformative potential of marine-derived nanosystems in the treatment of neurodegenerative disorders. The application of these TMC-engineered particles could be expanded to deliver a wide array of neuroprotective agents, potentially revolutionizing how we approach brain aging and cognitive health. This work underscores the philosophy that the ocean's vast glycobiodiversity holds the keys to solving some of our most complex medical challenges, providing a sustainable and highly effective roadmap for future Drug Development.