Conjugation of Di-n-butyl Phthalate Metabolites in Arabidopsis thaliana and Potential Deconjugation in Human Microsomes

Abstract

Plasticizers, due to the widespread use of plastics, occur ubiquitously in the environment. The reuse of waste resources (e.g., treated wastewater, biosolids, animal waste) and other practices (e.g., plastic mulching) introduce phthalates into agroecosystems. As a detoxification mechanism, plants are known to convert phthalates to polar monophthalates after uptake, which are followed by further transformations, including conjugation with endogenous biomolecules. The objective of this study was 2-fold: to obtain a complete metabolic picture of the widely used di-n-butyl phthalate (DnBP) by using a suite of complementary techniques, including stable isotope labeling, 14C tracing, and high-resolution mass spectrometry, and to determine if conjugates are deconjugated in human microsomes to release bioactive metabolites. In Arabidopsis thaliana cells, the primary initial metabolite of DnBP was mono-n-butyl phthalate (MnBP), and MnBP was rapidly metabolized via hydroxylation, carboxylation, glycosylation, and malonylation to seven transformation products. One of the conjugates, MnBP-acyl-β-d-glucoside (MnBP-Glu), was incubated in human liver (HLM) and intestinal (HIM) microsomes and was found to undergo rapid transformations. Approximately 15% and 10% of MnBP-Glu were deconjugated to the free form MnBP in HIM and HLM, respectively. These findings highlight that phthalates, as diesters, are susceptible to hydrolysis to form monoesters that can be readily conjugated via a phase II metabolism in plants. Conjugates may be deconjugated to release bioactive compounds after human ingestion. Therefore, an accurate assessment of the dietary exposure of phthalates and other contaminants must consider plant metabolites, especially including conjugates, to better predict their potential environmental and human health risks.

White Rot Fungi Produce Novel Tire Wear Compound Metabolites and Reveal Underappreciated Amino Acid Conjugation Pathways

“…Amino acid conjugates such as jasmonoyl isoleucine can have key roles in stress response, plant defense, and plant growth . Plants also form amino acid conjugates with xenobiotics, as evidenced by amino acid conjugation with the anticorrosive benzotriazole, the tire rubber vulcanizer 2-mercaptobenzothiazole, and the plasticizer di- n -butyl phthalate in Arabidopsis . − Some of these conjugates are structurally analogous to natural plant compounds such as indoles, which have critical functions in hormone storage. More work is necessary to determine the function of the amino acid-conjugated product discovered in this study.…”

Global Tracking of Transformation Products of Environmental Contaminants by 2H-Labeled Stable Isotope-Assisted Metabolomics

“…For data from UPLC-ESI-HRMS, the algorithm tracked 52 potential isotopologue pairs, and 13 isotopologue pairs were annotated as potential TPs (Figure , Table S3, and Figures S6–S10), which accounts for highly to 25% of the total extracted features. Two previous studies found seven and six isotopologue pairs as potential TPs of contaminants by MetExtract II or X13CMS, respectively. , By our proposed pipeline, 13 TPs of pyrene were annotated, proving its higher performance with cost-effective properties.…”

“…Two previous studies found seven and six isotopologue pairs as potential TPs of contaminants by MetExtract II or X13CMS, respectively. 38,39 By our proposed pipeline, 13 TPs of pyrene were annotated, proving its higher performance with cost-effective properties. Four isotopologue pairs detected from UPLC-ESI-HRMS data (e.g., M 221 , [M + H] + , Table S3) were further tracked by GC-EI-HRMS (e.g., M 220 , [M] + , Table S4).…”

Biotic and Abiotic Transformation Pathways of a Short-Chain Chlorinated Paraffin Congener, 1,2,5,6,9,10-C10H16Cl6, in a Rice Seedling Hydroponic Exposure System

“…Phase II reactions, amino acid conjugation, sulfation, glycosylation, and more are always considered as detoxification pathways for plants. Compared with the parent CPs, the conjugation metabolites were less toxic, more soluble for excretion, or easier to be sequestrated or incorporated into the cell walls (Phase III) to reduce damage to plants. ,, However, several works reported that when these conjugation metabolites in plants were taken by humans and other living organisms, they were deconjugated by enzymes, such as glucuronidase and sulfotransferases, to release the active compounds derived to conjugates. − In addition, as shown in previous works, toxicity effects of some metabolites, especially the hydroxylation metabolites of pollutants, were higher than their parent compound. ,− The abiotic and biotic transformations in the exposure system led to diversity of hydroxylation products for CP-4. Hence, the potential effects of the verified transformation products in agricultural plants should be seriously concerning.…”