HCAR2 and Parkinson disease: β-Hydroxybutyric acid (BHBA) acts on microglia to suppress LPS-induced inflammation through GPR109A to inhibit pro-inflammatory enzyme (iNOS and COX-2) and pro-inflammatory cytokine (TNF-α, IL-1β, and IL-6) production via the NF-κB signaling pathway in PD model rats [66].