These studies showed that oxymatrine from Sophora flavescens down-regulated the expression of cathepsin D, inhibiting high mobility group protein 1/toll-like receptor 4/nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) signaling pathway, resulting in the suppression of microglia-mediated neuroinflammation in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-stimulated mouse model of Parkinson’s disease [125]. Here, CTSD is linked to Parkinson disease.