Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 12, 2007
Publication Date: March 20, 2008
Citation: Myung, K., Manthey, J.A., Narciso, J.A. 2007. A Preliminary investigation of furanocoumarin metabolism by Aspergillus niger. Proceedings of Florida State Horticultural Society. 120:229-303. Interpretive Summary: There are compounds called furanocoumarins in grapefruit juice that cause the grapefruit/drug interactions in humans. Metabolism of the grapefruit furanocoumarins by organisms has not been studied. In this study, we carried out fermentation experiments using several fungi. Among them, Aspergillus niger showed a capability of metabolizing these grapefruit furanocoumarins. As a result, new metabolites were found along with a detection of the presence of novel enzymatic activities in the fungus. This will contribute to an understanding of furanocoumarin metabolism by the fungus, leading to a possibility of identifying other novel compounds and related enzymes in the metabolic pathways. This work would also be important in biotechnology applications in the future, ie metabolic engineerring.
Technical Abstract: Fungi metabolize polycyclic aromatic hydrocarbons by a number of detoxification processes. Prevalent fungal detoxification pathways for aromatic compounds include the formation of sulfated and glycosidated conjugates. Such fungal metabolism has been extensively studied as models of mammalian metabolism. Furanocoumarins, a class of aromatic compounds, are important due to their biological activities and clinical applications. The 6',7'-dihydroxybergamottin (DHB), 6',7'-epoxybergamottin (EB), and bergamottin (BM) are three major furanocoumarins in grapefruit and their metabolism in humans is involved in the "grapefruit/drug interactions". Thus far, the metabolism by fungi of these furanocoumarins has received little attention. In our study, the metabolism by Aspergillus niger of DHB, EB, and BM has been investigated. A. niger was observed to metabolize EB, DHB, and BM into a water-soluble sulfate conjugate possibly using etherase-like and sulfotransferase-like enzyme activities. In addition, A. niger showed a specificity in metabolizing furanocoumarins, in which the fungus metabolized bergaptol and xanthotoxol into sulfate conjugates but did not metabolize 5-methoxypsoralen and 8-methoxypsoralen. These sulfate conjugates, i.e. bergaptoyl sulfate and xanthotoxoyl sulfate, were characterized by UV spectra, mass spectrometry, and acid hydrolysis.