Branched-chain amino acids ameliorate CD4⁺ T-cell-associated gut immune inflammation in Parkinson's disease

Previous studies have shown that alterations in the gut microbiota and its derived metabolites, branched-chain amino acids (BCAAs), are correlated with T-cell-associated immune imbalance and Parkinson's disease (PD). However, the associations among BCAAs, gastrointestinal dysfunction and T-cell-related gut inflammation remain unclear. This study showed that the constipation symptoms in the PD mice persisted after chronic MPTP treatment. An imbalance in the CD4⁺ T-cell subtypes was observed in the colonic lamina propria (cLP), mesenteric lymph nodes (mLNs), and spleen. Metagenomic and metabolomic analyses showed that microbial dysbiosis promoted BCAA degradation rather than biosynthesis, and reduced BCAA levels were confirmed in the serum. BCAA supplementation alleviated constipation symptoms and increased Th1 and Th17 cell infiltration in the cLP, mLNs and spleen were significantly attenuated after BCAA treatment. This study highlights the therapeutic value of BCAAs in mitigating gut immune inflammation-associated constipation symptoms in PD.