title: Diclofenac in Arabidopsis cells: Rapid formation of conjugates.
abstract: Pharmaceutical and personal care products (PPCPs) are continuously introduced into the soil-plant system, through practices such as agronomic use of reclaimed water and biosolids containing these trace contaminants. Plants may accumulate PPCPs from soil, serving as a conduit for human exposure. Metabolism likely controls the final accumulation of PPCPs in plants, but is in general poorly understood for emerging contaminants. In this study, we used diclofenac as a model compound, and employed14C tracing, and time-of-flight (TOF) and triple quadruple (QqQ) mass spectrometers to unravel its metabolism pathways in Arabidopsis thaliana cells. We further validated the primary metabolites in Arabidopsis seedlings. Diclofenac was quickly taken up into A. thaliana cells. Phase I metabolism involved hydroxylation and successive oxidation and cyclization reactions. However, Phase I metabolites did not accumulate appreciably; they were instead rapidly conjugated with sulfate, glucose, and glutamic acid through Phase II metabolism. In particular, diclofenac parent was directly conjugated with glutamic acid, with acyl-glutamatyl-diclofenac accounting for >70% of the extractable metabolites after 120-h incubation. In addition, at the end of incubation, >40% of the spiked diclofenac was in the non-extractable form, suggesting extensive sequestration into cell matter. The rapid formation of non-extractable residue and dominance of diclofenac-glutamate conjugate uncover previously unknown metabolism pathways for diclofenac. In particular, the rapid conjugation of parent highlights the need to consider conjugates of emerging contaminants in higher plants, and their biological activity and human health implications.
authors.affiliation: Department of Environmental Sciences, University of California, Riverside, CA 92521, United States; Institute of Nuclear Agricultural Sciences, Zhejiang University, Hangzhou 310029, China. Electronic address: fuqiuguo@zju.edu.cn.
authors.forename: Qiuguo
authors.initials: Q
authors.lastname: Fu
authors.affiliation: Institute of Nuclear Agricultural Sciences, Zhejiang University, Hangzhou 310029, China.
authors.forename: Qingfu
authors.initials: Q
authors.lastname: Ye
authors.affiliation: Department of Health Sciences and Technology, ETH Zürich, Schmelzbergstrasse 9, 8092 Zürich, Switzerland.
authors.forename: Jianbo
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Environmental Sciences, University of California, Riverside, CA 92521, United States.
authors.forename: Jaben
authors.initials: J
authors.lastname: Richards
authors.affiliation: Chemistry Department, University of California, Riverside, CA 92521, United States.
authors.forename: Dan
authors.initials: D
authors.lastname: Borchardt
authors.affiliation: Department of Environmental Sciences, University of California, Riverside, CA 92521, United States.
authors.forename: Jay
authors.initials: J
authors.lastname: Gan
mesh_terms: D017360:Arabidopsis / Q000166:cytology* / Q000378:metabolism*; D004008:Diclofenac / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D004350:Drug Residues / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D050216:Metabolic Detoxication, Phase I; D050217:Metabolic Detoxication, Phase II; D059828:Plant Cells / Q000378:metabolism*; D036226:Seedlings / Q000378:metabolism
chemical_list: D004008:Diclofenac
keywords: Arabidopsis thaliana; Diclofenac; Non-extractable residue; PPCPs; Plant metabolism