A study in mice showed that a plant extract called Tripterygium wilfordii multi‑glycoside (GTW) can lessen arthritis‑like symptoms and inflammation by improving gut barrier health and boosting good gut bacteria, but it does not involve the peptide palmitoyl‑dipeptide‑6 and offers no direct guidance for using that peptide.

Ankylosing spondylitis (AS) is a chronic autoimmune inflammatory disorder characterized by severe inflammation in the axial skeleton. Tripterygium wilfordii multi-glycoside (GTW) is widely used in clinical practice for AS and related immune diseases, yet its precise mechanism of action remains unclear. Explore the therapeutic effects of GTW on AS and its potential mechanisms, with a focus on its impact on the gut microbiota and associated metabolites. An AS mouse model was established via intraperitoneal injection of proteoglycan and Freund's complete adjuvant. The therapeutic effects and underlying mechanisms of GTW were explored through phenotypic analysis, 16S rRNA sequencing, and metabolomic profiling. GTW significantly reduced arthritis index, gait score, paw thickness, and pro-inflammatory cytokines in AS mice. Additionally, it modulated mRNA and protein expression related to osteoclast and osteoblast differentiation while restoring intestinal barrier integrity. Notably, GTW reversed the AS-induced depletion of Bifidobacterium and Akkermansia. Correlation analysis between gut microbiota, fecal metabolites, and AS-related phenotypes suggested that GTW-enriched bacteria were positively associated with beneficial metabolites, including 3-methylxanthine, 5'-methylthioadenosine, cinnamic acid, kaempferol, and palmitoyl glucuronide. Both of those gut bacteria and metabolites were strongly negatively correlated with AS severity markers (IL-6, IL-17, IL-23, Th17 cell percentage, arthritis index, gait score, paw thickness, and Rankl expression) and positively associated with protective factors (Zo-1, Occludin, Claudin-1, Ocn, and Alp gene expression). This study implies that GTW treatment is associated with amelioration of AS-related symptoms in mice, suggesting a potential role of the gut microbiota-metabolite axis in GTW-associated AS improvement, though causal relationships require further validation.