HDAC6 and Alzheimer disease: Another study found that protopine, a component of Corydalis, exhibited neuroprotective effects in P301S Tau and 3xTg-AD mouse models by inhibiting histone deacetylase 6 activity while enhancing the expression of molecular chaperones such as HSP70, HSP90, HSC70, and acetylated HSP90, thereby influencing the ubiquitin-proteasome pathway in AD (Sreenivasmurthy et al., 2022).