Entacapone

UK5099, CHC, zaprinast, lonidamine, mitoglitazone, pioglitazone, rosiglitazone, valproic acid, silibinin, entacapone and nitrofurantoin were purchased from Sigma Aldrich (Merck, Gillingham, UK). UK5099-based novel compounds (i.e., compounds 1–13) were obtained from the Chembridge chemical store Hit2Lead (ChemBridge Corporation, CA, USA). All compounds were dissolved at a 100 mM stock concentration in DMSO.

³H-serotonin (80 Ci/mmol), ³H-norepinephrine (20 Ci/mmol), and ³H-dopamine (60 Ci/mmol) were purchased from M.G.P. (Zlín, Czech Republic). Forskolin was obtained from Scintila, s.r.o. (Jihlava, CZ). Paroxetine hydrochloride, citalopram hydrobromide, sertraline hydrochloride, fluoxetine hydrochloride, fluvoxamine maleate, venlafaxine hydrochloride, phenelzine sulfate salt, entacapone, GBR 12935 dihydrochloride, nisoxetine hydrochloride, hydrocortisone, and decynium-22 were purchased from Sigma-Aldrich (St. Louis, USA). Pierce™ BCA Protein Assay Kit was purchased from Thermo Fisher Scientific (Waltham, United States). All other chemicals were of analytical grade.

Twenty natural pentacyclic triterpenes, quercetin and epicatechin were purchased from Chengdu Desite Biotechnology Co., Ltd. (Chengdu, China), and their purities more than 98%. Dithiothreitol (DTT, ≥99%), S-adenosyl-L-methionine (SAM, ≥80%), magnesium chloride hexahydrate (MgCl₂^.6H₂O, ≥99%), entacapone (C₁₄H₁₅N₃O₅, ≥98%) and tolcapone (C₁₄H₁₁NO₅, ≥98%) were supplied by Sigma-Aldrich Co. LLC. (Shanghai, China). 3-(Benzo[d]thiazol-2-yl)-7,8-dihydroxy-2H-chromen-2-one (3-BTD, ≥99%), 3-(Benzo[d]thiazol-2-yl)-7-dihydroxy-8-methoxy-2H-chromen-2-one (3-BTMD, ≥99%) and recombinant human S-COMT were made in our laboratory [22]. Phosphate buffer saline (50 mM, pH 7.4), Dulbecco's modified eagle medium (DMEM, with high glucose, pyruvate and L-glutamine), penicillin/streptomycin (PS, sterile), cell counting kit-8 (CCK-8), Hoechst 33342 and JC-10 dye were obtained from Dalian Meilun Biotechnology Co., Ltd. (Dalian, China). Foetal bovine serum (FBS, Gbico^®) was purchase from Thermo Fisher Scientific Co., Ltd. (Shanghai, China). Acetonitrile (ACN, ≥99.9%), dimethyl sulfoxide (DMSO, ≥99.7%) and formic acid (CH₃COOH, ≥98%) were of HPLC grade and purchased from Sigma-Aldrich Co. LLC. (Shanghai, China). Ultrapure water (18.2 MΩ cm) was produced using a Millipore water purification system (Milford, MA, U.S.A.).