High-molecular weight hyaluronic acid protects against colitis by remodeling microbiota and restoring barrier function.

Hyaluronic acid (HA) is a promising therapeutic candidate for ulcerative colitis (UC), yet how its molecular weight (Mw) governs efficacy and the associated microbiota-linked mechanisms remain insufficiently defined. Here, we systematically evaluated biotechnologically produced HA with distinct Mws (LHA, 2 kDa; MHA, 300 kDa; HHA, 3000 kDa) in a dextran sulfate sodium (DSS)-induced murine colitis model. A Mw-associated protective trend was observed, with HHA showing the most consistent beneficial profile in alleviating clinical manifestations, preserving colonic architecture, and restoring epithelial barrier integrity (Occludin, ZO-1, and mucin). Mechanistically, HHA attenuated systemic inflammation (TNF-α, IL-1β, and LPS) and was associated with modulation of the NF-κB/PPARγ signaling axis. Integrated 16S rRNA sequencing and untargeted metabolomics further revealed that HHA reshaped the gut ecosystem by enriching beneficial genera, including Bifidobacterium and Lactobacillus, and promoted metabolic homeostasis, characterized by increased vitamin B6-related metabolites (pyridoxal) and fatty acids, together with reduced purine metabolism. Molecular dynamics simulations suggested a putative interaction in which microbiota-associated pyridoxal may bind TNF-α, providing a structural hypothesis for the observed attenuation of inflammatory signaling. Moreover, fecal microbiota transplantation (FMT) demonstrated that the HHA-conditioned microbiota was sufficient to confer protection against DSS colitis. Collectively, these findings identify HHA as a bioactive polymer that ameliorates colitis via a coordinated microbiota-metabolism-immunity axis.