| Abstract: |
The gut mucosa, composed mainly of mucin proteins, serves as a critical interface between the host and the microbiome. Mucin proteins possess sulfur-based functional groups that dynamically transition between thiol (–SH, reduced, "open" state) and disulfide (–S–S, oxidized, "closed" state) forms, modulating their structural properties. These thiol groups act as molecular switches, responding to the oxidative environment in the gut, influenced by reactive oxygen species (oxidants) and antioxidants (reductants). The redox state of mucins, regulated by both host and microbial factors, significantly impacts the mucus layer's barrier function and physiological role. Despite its importance, there is a lack of effective models to study the redox dynamics of the gut mucosa and the factors that influence it, leaving the interplay between host, microbiota, and external agents largely unexplored.
To address this gap, we developed a novel bioelectronic system to control and monitor the thiol-based redox state of mucins electrochemically. This model employs a mucus-like structure formed by electrodepositing mucin-2 proteins encapsulated in a calcium alginate porous hydrogel onto gold electrodes. A redox conduit comprising oxidative and reductive species facilitates electron transfer between the electrode and the sulfur groups within mucin proteins, enabling real-time monitoring and precise redox control. Oxidative species with high standard reduction potentials promote disulfide bond formation by accepting electrons from thiol groups, transferring the electrons to the electrode, and generating an oxidative charge. Conversely, reductive species with low reduction potentials donate electrons to disulfide bonds, converting them back to thiols and altering the mucin's structural state.
To validate this approach, we prepared electrodes coated with mucin-2 proteins (0.05 mg/ml in alginate) and performed cyclic voltammetry using 200 µM of the oxidative agent iridate (potential range: 0.1V to 0.8V vs. Ag/AgCl; scan rate: 0.1 V/s; 30 cycles). After every 10 cycles, the electrodes were treated with 50 µM Tris(2-carboxyethyl) phosphine hydrochloride (TCEP), a reductive agent, to reduce disulfide bonds. Initial voltammograms showed a decrease in oxidative charge over the first 10 cycles, indicating progressive thiol oxidation. However, upon TCEP treatment, a significant increase in oxidative charge was observed, reflecting the reduction of disulfide bonds back to thiols. This behavior was repeatable across subsequent cycles, demonstrating the model's reliability and controllability in regulating mucin redox states. These findings confirm that mucin biostructures can be electrochemically manipulated to monitor and control their redox states. This innovative gut model provides a robust platform to study how diet, inflammation, and disease influence the oxidative state of the mucus layer, paving the way for novel insights into gut physiology and redox-dependent processes in health and disease.
[1] J. Li et al., *Free Radic. Biol. Med.*, vol. 105, pp. 110–131, Apr. 2017. |