HDAC inhibitors vorinostat, butyrate and tubastatin A showed promising therapeutic potential in the treatment of inflammatory diseases such as rheumatoid arthritis, asthma, contact hypersensitivity and inflammatory bowel diseases, due to their ability to regulate inflammatory cells and cytokines through several G protein–coupled receptors (GPCRs) (Ran and Zhou, 2019; Li et al., 2021; Ni et al., 2021). Here, HDAC9 is linked to rheumatoid arthritis.