Interface potential-induced natural antioxidant mimic system for the treatment of Alzheimer’s disease

Alzheimer’s disease (AD) is a multifactorial, progressive neurodegenerative disorder and the leading cause of dementia-related disability and death, affecting ~50 million people worldwide. While the exact pathogenesis remains unclear, oxidative stress from mitochondrial dysfunction and neuroinflammation, together with synaptic dysfunction, are recognized as central pathological features. Antioxidant therapy is therefore a key therapeutic approach. However, current antioxidant strategies are limited: antioxidant enzymes have high catalytic efficiency but narrow substrate scope, while small-molecule antioxidants have broader effects but low efficiency, limited bioavailability, and poor blood–brain barrier penetration. Because the endogenous antioxidant defense comprises synergistic enzymatic (e.g., SOD, catalase, GSH-Px) and non-enzymatic systems (e.g., vitamin C, glutathione, tocopherols, flavonoids, carotenoids), a combined strategy may be superior to single agents. Motivated by this, the authors designed a synergistic antioxidant system by synthesizing a zinc-based MOF (ZnBTC) with SOD-like activity and loading curcumin (a non-enzymatic antioxidant and anti-inflammatory agent) via an interface electrostatic potential-driven interaction. The goal was to exploit complementary surface electrostatic potentials to enable spontaneous complexation, improved antioxidant activity, and efficient β-amyloid (Aβ) plaque scavenging, thereby ameliorating AD-related dysfunction in mice.

The paper frames oxidative stress as a core driver of AD pathology and reviews the roles of enzymatic antioxidants (SOD, catalase, GSH-Px) and non-enzymatic antioxidants (hydrophilic scavengers such as vitamin C and glutathione; lipophilic scavengers such as tocopherols, flavonoids, carotenoids). Existing antioxidant therapies are constrained by single mechanisms of action, insufficient bioavailability, and poor blood–brain barrier penetration. A synergistic approach that integrates both enzymatic and non-enzymatic antioxidant mechanisms is posited to better restore redox homeostasis and address multifactorial AD pathology.

• Synthesis of ZnBTC MOF: Hydrothermal synthesis by reacting 1,3,5-benzenetricarboxylic acid (H3BTC) with zinc nitrate hexahydrate (Zn(NO3)2·6H2O) in anhydrous ethanol at 120 °C. Resulting ZnBTC exhibited rod-like morphology (SEM/TEM).
• Curcumin loading (CUR@ZnBTC): Curcumin was incorporated into ZnBTC via solvent adsorption in anhydrous ethanol, driven by complementary surface electrostatic potentials between ZnBTC and curcumin.
• Structural/physicochemical characterization:
  • Morphology: SEM and TEM showed rod-like particles; curcumin loading did not significantly alter particle size or morphology.
  • XRD: ZnBTC displayed characteristic peaks at 10.1°, 17.8°, and 24.6°. CUR@ZnBTC retained ZnBTC peaks; curcumin peaks were not evident, indicating CUR encapsulation. UV–vis spectroscopy further confirmed CUR presence.
  • Stability: FTIR and XRD after exposure to saline and bovine serum albumin indicated good stability in salts and serum proteins.
  • Porosity (N2 adsorption–desorption at 77 K): ZnBTC BET surface area 943.421 m² g⁻¹, total pore volume 0.34 cm³ g⁻¹, average pore size 1.356 nm. CUR@ZnBTC BET surface area 468.93 m² g⁻¹, average pore size 0.58 nm.
  • Thermal analysis (TGA, N2, 25–800 °C): H3BTC crystal transition ~320 °C; ZnBTC showed reduced total weight loss (~57%) vs H3BTC (~100%), supporting framework formation. CUR@ZnBTC exhibited an additional ~20% weight loss between 240–400 °C attributable to curcumin; decomposition was slower than native curcumin, indicating enhanced stability upon encapsulation.
• Drug loading and interaction analysis:
  • Loading content: Post-loading supernatant UV–vis quantification indicated 47.3% curcumin loading (uploading reached 47.3%).
  • Computational analysis: Geometry optimization and frequency calculations indicated strong adsorption affinity of ZnBTC for curcumin.
• Drug release studies:
  • pH-dependent release assessed at pH 5.5, 6.5, 7.4, 9.0, and 10.0. Acidic conditions increased CUR release rate and amount; at pH 7.4, cumulative release was ~61% with a sustained-release profile.
  • Release also examined in DMEM and a simulated electrolyte environment (DMEM + 1 mg ml⁻¹ bovine serum albumin + 1 mg ml⁻¹ acid-hydrolyzed casein).
• Antioxidant assays:
  • Free radical scavenging: ABTS and DPPH assays evaluated antioxidant activity.
  • SOD-like activity: Assessed via inhibition of pyrogallol autoxidation by ZnBTC; kinetic profiling and Lineweaver–Burk plots were generated. Comparative assessment across different metals was performed.
• Biocompatibility and safety:
  • Hemolysis assay indicated no red blood cell damage.
  • Stability and biocompatibility supported by ZnBTC’s material properties and slow Zn²⁺ release profile.
• In vivo AD efficacy (5xFAD mouse model):
  • Animals: Male 5xFAD mice, 6–8 months. Ethical approvals and standard housing conditions reported.
  • Formulation processing: Ultrasonic crushing prior to gavage yielded nanoparticle sizes of 166.6 nm (ZnBTC) and 171.7 nm (CUR@ZnBTC).
  • Administration: Oral gavage (dose not specified). Body weight monitored daily.
  • Behavioral testing: Grip strength test; suspended self-exploration/hanging tail-related test; swing/transfer test to evaluate sensory, cognitive, and motor coordination.
  • Histology: Immunohistochemical staining of hippocampal sections for Aβ plaques; major organs stained for toxicity assessment.
  • Statistics: Data as mean ± SD; one-way ANOVA; significance denoted as p < 0.05, p < 0.01, p < 0.001.

• Successful synthesis of ZnBTC MOF with rod-like morphology and high crystallinity; CUR@ZnBTC retained structural integrity after curcumin loading.
• Porosity and loading: ZnBTC exhibited high BET surface area (943.421 m² g⁻¹) and suitable pore size (1.356 nm) for curcumin incorporation; CUR@ZnBTC surface area decreased to 468.93 m² g⁻¹, consistent with pore occupancy. Curcumin loading reached 47.3% based on supernatant quantification.
• Stability and thermal behavior: ZnBTC displayed improved thermal stability relative to H3BTC. CUR encapsulation in ZnBTC slowed curcumin decomposition, indicating enhanced stability and activity preservation.
• pH-responsive and sustained release: Acidic pH increased CUR release, while at physiological pH 7.4 cumulative release was ~61%, supporting sustained delivery under neutral conditions. Release behavior was characterized in DMEM and protein-containing simulated electrolyte media.
• Antioxidant performance: CUR@ZnBTC demonstrated strong free radical scavenging in ABTS and DPPH assays. ZnBTC exhibited SOD-like activity, inhibiting pyrogallol autoxidation with measurable enzyme-mimetic kinetics.
• In vivo efficacy in 5xFAD mice: CUR@ZnBTC significantly improved behavioral outcomes (grip strength, motor coordination, and exploratory behaviors) compared to untreated AD mice. Immunohistochemistry showed substantial reductions in hippocampal Aβ plaque burden after treatment, with CUR@ZnBTC outperforming ZnBTC or curcumin alone. Body weight remained stable across groups, hemolysis testing was negative, and major organ histology indicated no observable toxicity. Statistical significance was reported as p < 0.05, p < 0.01, and p < 0.001 for treatment effects.

The study addresses the limitations of single-mechanism antioxidant therapies in AD by combining enzymatic and non-enzymatic antioxidant capabilities in a single nanoplatform. Complementary surface electrostatic potentials between ZnBTC and curcumin promote spontaneous complexation, efficient loading, and a sustained-release profile that preserves curcumin activity at physiological pH. ZnBTC provides SOD-like catalytic activity and beneficial Zn²⁺-associated anti-inflammatory effects, while curcumin contributes potent radical scavenging and anti-inflammatory actions. Together, CUR@ZnBTC reduces ROS and oxidative stress, leading to inhibition of Aβ deposition and enhanced clearance of existing plaques. In 5xFAD mice, this synergy translates into improved behavioral performance and a marked reduction in hippocampal Aβ plaques, with no evident systemic toxicity. These findings support the concept that integrating enzymatic and non-enzymatic antioxidant mechanisms via interface potential-driven assembly can yield superior therapeutic outcomes in AD relative to monotherapies, and suggests a viable path for developing more effective, safe AD treatments.

In conclusion, in this work, we proposed a strategy to construct endogenous and exogenous antioxidant systems by designing on the interface potential effects for the treatment of AD, and successfully prepared CUR@ZnBTC composite nanoparticles. ZnBTC MOF exerted robust activity and then depending on the interface potential effect, curcumin (non-enzyme antioxidant agent) was loaded into ZnBTC to construct a synergistic antioxidant AD treatment system, which was reflected in the improved scavenging ability of Aβ. More importantly, due to the complementary surface electrostatic potential between MOF and curcumin, they can spontaneously form complexes and exhibit excellent synergistic antioxidant effects. The experimental results showed that CUR@ZnBTC could preserve CUR under an AD neutral environment, and effectively scavenge ROS, alleviate oxidative stress, and inhibit the deposition of Aβ and new plaque formation. In addition, it has a strong scavenging effect on already formed plaques, which even reverses the neurological damage caused by Aβ deposition, thus improving learning and cognitive impairment in 5xFAD mice. In addition, histological analyses reveal that CUR@ZnBTC does not have any toxicity to the major organs of mice. These results provide strong evidence that CUR@ZnBTC had both good antioxidant activity and efficient Aβ plaque scavenging ability, which slowed down the cognitive function in the brain of AD mice. It is expected that this combination drug can provide a feasible strategy for the treatment of AD and provide a scientific basis for the development of more effective and safe AD therapeutics.