Harmaline and harmine are β-carboline alkaloids with effective pharmacological effects. Harmaline can be transformed into harmine after oral administration. However, enzymes involved in the metabolic pathway remain unclear. In this study, harmaline was incubated with rat liver microsomes (RLM), rat brain microsomes (RBM), blood, plasma, broken blood cells, and heme peroxidases including horseradish peroxidase (HRP), lactoperoxidase (LPO), and myeloperoxidase (MPO). The production of harmine was determined by a validated UPLC-ESI-MS/MS method. Results showed that heme peroxidases catalyzed the oxidative dehydrogenation of harmaline. All the reactions were in accordance with the Hill equation. The reaction was inhibited by ascorbic acid and excess H₂O₂. The transformation of harmaline to harmine was confirmed after incubation with blood, plasma, and broken blood cells, rather than RLM and RBM. Harmaline was incubated with blood, plasma, and broken cells liquid for 3 h, and the formation of harmine became stable. Results indicated an integrated metabolic pathway of harmaline, which will lay foundation for the oxidation reaction of dihydro-β-carboline. Moreover, the metabolic stability of harmaline in blood should not be ignored when the pharmacokinetics study of harmaline is carried out.
Animals ; Harmaline/metabolism* ; Harmine/metabolism* ; Heme ; Hydrogen Peroxide ; Rats ; Tandem Mass Spectrometry

The indole alkaloid harmaline has been to cause tremor and ataxia, and produce cerebellar neurotoxicity in rat. Degeneration of Purkinje cell alligned in narrow parasagittal bands result from excitation of inferior olivary nucleus in harmaline-treated rats. The objective of this study was to investigate the hypothesis that excitation of climbing fiberinduced by harmaline mediates Purkinje cell injury or degeneration. For this purpose, the inferior olive of rats was chemically ablated by using 3-acetyl pyridine, a neurotoxic chemical, and cerebellar damage followed by administration of harmaline was analyzed using immunohistochemical markers for neurons, glial cells. The results demonstrated that a subset of Purkinje cell in the vermis and paravermis degenerated after harmaline treatment, but harmaline produced little or no Purkinje cell degeneration after inferior olivary ablation. These results suggested that harmalineinduced activation of inferior olivary neurons may lead to release of glutamate from climbing fiber synaptic terminal distributed over the Purkinje cells, and may lead to cytotoxic degeneration of Purkinje cells.
Animals ; Ataxia ; Cerebellum ; Glutamic Acid ; Harmaline* ; Neuroglia ; Neurons ; Olea ; Olivary Nucleus ; Presynaptic Terminals ; Purkinje Cells* ; Rats ; Tremor