title: Inhibition of monoamine oxidase (MAO) by β-carbolines and their interactions in live neuronal (PC12) and liver (HuH-7 and MH1C1) cells.
abstract: Interactions among monoamine oxidase (MAO) inhibitors in drugs, botanicals, and dietary supplements may lead to unpredictable neurochemical dysfunction due to excessive inhibition or therapeutic invalidation. Often recombinant MAO or brain tissue homogenates have been used to evaluate MAO inhibitors such as the β-carboline alkaloids (harmane, harmine, harmaline, and harmalol). However, there is a lack of cellular systems for evaluation of MAO activity, which represents a more advanced in vitro model compared to recombinant enzymes or tissue lysates. Using kynuramine assays, intracellular MAO inhibition by β-carbolines was measured in PC12 (rat pheochromocytoma), MH1C1 (rat liver), and HuH-7 (human liver) cell lines, which were compared with human recombinant MAO and cell lysates. β-Carbolines (1 μM, 90 min incubations) inhibited MAO by 40-99% in live PC12 cells where MAO A was the active isoform, and <12% in HuH-7 and MH1C1 cells where MAO B was primarily active. The combination index (CI), which serves as a quantitative indicator of pharmacological interactions, was determined for harmaline/harmine (CI, 1.01-1.25) and methylene blue/harmine (CI, 0.74-1.07) in PC12 cells. Overall, this study illustrates applications of cell-based in vitro assay platforms to gain a comprehensive understanding of intracellular MAO inhibitors and their interactions.
authors.affiliation: Division of Toxicology, Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, 8301 Muirkirk Rd, Laurel, MD 20708, USA. Electronic address: michael.santillo@fda.hhs.gov.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Santillo
authors.affiliation: Division of Toxicology, Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, 8301 Muirkirk Rd, Laurel, MD 20708, USA.
authors.forename: Yitong
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Division of Public Health and Biostatistics, Office of Analytics and Outreach, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, 5100 Paint Branch Pkwy, College Park, MD 20740, USA.
authors.forename: Martine
authors.initials: M
authors.lastname: Ferguson
authors.affiliation: Division of Toxicology, Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, 8301 Muirkirk Rd, Laurel, MD 20708, USA.
authors.forename: Sanah N
authors.initials: SN
authors.lastname: Vohra
authors.affiliation: Division of Toxicology, Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, 8301 Muirkirk Rd, Laurel, MD 20708, USA.
authors.forename: Paddy L
authors.initials: PL
authors.lastname: Wiesenfeld
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002243:Carbolines / Q000494:pharmacology*; D002460:Cell Line; D045744:Cell Line, Tumor; D006801:Humans; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D008954:Models, Biological; D008995:Monoamine Oxidase / Q000187:drug effects* / Q000378:metabolism; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology*; D016716:PC12 Cells; D051381:Rats; D013045:Species Specificity
chemical_list: D000470:Alkaloids; D002243:Carbolines; D008996:Monoamine Oxidase Inhibitors; D008995:Monoamine Oxidase
keywords: Botanical; Cell assay; Combination index; Harmaline; Harmine; Methylene blue