Supporting joint health through the gut-immune axis: squalene-based multiple emulsions enhance oral delivery of undenatured collagen type II for immune tolerance.

Undenatured collagen type II (UC-II), a dietary supplement, has shown potential to support joint health by alleviating discomfort and suppressing inflammation. However, its efficacy is often limited by poor water solubility, gastrointestinal degradation, and low bioavailability. To address these challenges, water-soluble UC-II was extracted from chicken sternal cartilage via enzymatic hydrolysis and encapsulated in food-grade water-in-oil-in-water (W/O/W) multiple emulsions using natural squalene as the oil phase. These emulsions effectively protected UC-II from acid and enzymatic degradation in the digestive tract, facilitated its uptake by Peyer's patches in gut-associated lymphoid tissue, and elicited robust mucosal immune responses. In a collagen-induced arthritis (CIA) mouse model, prophylactic administration of UC-II-loaded multiple emulsions significantly delayed arthritis progression by modulating immune responses. Oral administration of UC-II multiple emulsions not only alleviated systemic inflammation by suppressing Th1-mediated immune responses, but also promoted immune tolerance to autoantigens by inhibiting collagen type II (CII)-specific IgG antibody production, increasing regulatory T-cell proportion, and suppressing CII-specific T-cell proliferation in the spleen. These findings indicate that multiple emulsions significantly enhance the oral efficacy of UC-II and promote joint health via the gut-immune axis. This study highlights the potential of multiple emulsions for developing innovative functional foods or dietary supplements aimed at modulating immune function.