Tryptophan in the diet ameliorates motor deficits in a rotenone‐induced rat Parkinson's disease model via activating the aromatic hydrocarbon receptor pathway

Abstract Background and purpose Parkinson's disease (PD), a common neurodegenerative disorder with motor and nonmotor symptoms, does not have effective treatments. Dietary tryptophan (Trp) supplementation has potential benefits for the treatment of multiple disorders. However, whether additional Trp in the diet could be beneficial for PD remains to beinvestigated. In the present study, the neuroprotective role of dietary Trp on a rotenone‐induced rat model of PD was determined. Methods The rotenone was injected to build the PD model, and then the rats were treated with Trp in the diet. And then, an open field test, western blot analysis, and enzyme linked immunosorbent assay (ELISA) were performed. Results We observed that dietary Trp significantly ameliorated impaired motor function, upregulated tyrosine hydroxylase expression, inhibited the nuclear transport of Nuclear factor‐kappa B (NF‐κB) in substantia nigra (SN), and downregulated the protein levels of IL‐1β, IL‐6, and TNF‐α in serum in rotenone‐treated rats. However, these patterns were reversed in response to treatment with ampicillin, an agent that can clean intestinal Trp metabolism flora. Moreover, after using CH223191, an inhibitor of the aromatic hydrocarbon receptor (AhR) pathway, dietary Trp could not exert neuroprotective roles in the rotenone‐induced rat model of PD. Conclusion These results suggest that Trp in the diet can protect against rotenone‐induced neurotoxicity to ameliorate motor deficits, which may be mediated through activating AhR pathway.