Two Typical Glycosylated Metabolites of Tetrabromobisphenol A Formed in Plants: Excretion and Deglycosylation in Plant Root Zones

Abstract

The glycosylation process was investigated for the common brominated flame retardant tetrabromobisphenol A (TBBPA) in hydroponic exposure systems with pumpkin seedlings. Two typical glycosylation metabolites of TBBPA formed in pumpkin seedlings, TBBPA mono-β-d-glucopyranoside (TBBPA MG) and TBBPA di-β-d-glucopyranoside (TBBPA DG), increasing their mass early in the exposure (reaching maximum masses of 608 ± 53 and 3806 ± 1570 pmol at 12 h, respectively) and then falling throughout exposure. These two metabolites were released from roots to rhizosphere solutions, where they also exhibited initial increases followed by decreasing trends (reaching maximum masses of 595 ± 272 pmol at 3 h and 77.1 ± 36.0 pmol at 6 h, respectively). However, a (pseudo)­zero-order deglycosylation of TBBPA MG and TBBPA DG (during the first 1.5 h) back to TBBPA was unexpectedly detected in the hydroponic solutions containing pumpkin exudates and microorganisms. The function of microorganisms in the solutions was further investigated, revealing that the microorganisms were main contributors to deglycosylation. Plant detoxification through glycosylation and excretion, followed by deglycosylation of metabolites back to the toxic parent compound (TBBPA) in hydroponic solutions, provides new insight into the uptake, transformation, and environmental fate of TBBPA and its glycosylated metabolites in plant/microbial systems.

Deglycosylation of Two Typical Plant-Generated Glycoconjugates of Tetrabromobisphenol A through In Vitro Digestion Processes

“…Generally, glycosylation of exogenous pollutants is considered as an important detoxification process for plants (sometimes as the dominant process). , A large amount of TBBPA (86%) was found to be transformed to TBBPA glycoconjugates . As a consequence, the exposure levels of TBBPA glycoconjugates to human and animals may be more than TBBPA.…”

“…In addition, plants are the beginning of the food chain, and the transformation products of organic pollutants occurring in plants can be delivered through the food chain and directly by crop and vegetable intake, finally entering the human body. In previous reports, TBBPA and other phenolic compounds, including 2,4-dibromophenol, 2,4,6-tribromophenol, and triclosan, were all transformed to glycosylation conjugates, malonyl glycosylation conjugates, and other conjugates in exposed pumpkin, carrot, and rice seedlings. ,− The glycosylation of TBBPA was even the predominant transformation process in pumpkin which showed high accumulation and transformation abilities to various persistent organic pollutants (POPs). − The conjugates of phenolic compounds contain larger and more complex structures, but their core structures are still their parent compounds. Those studies all mentioned that the conjugates may regenerate their more toxic parent compounds, especially in the human digestive system.…”

Rapid plant uptake of isothiazolinone biocides and formation of metabolites by hydroponic Arabidopsis

“…29,31 Nevertheless, recent evidence demonstrates that some xenobiotic compounds do not follow all the phases of classical plant metabolism. For example, recent evidence indicates that conjugated metabolites can subsequently deconjugate 33,34 and/ or be excreted from the plant, [25][26][27]32,[35][36][37] presenting previously unknown exposure routes. Additionally, amino-acid conjugated xenobiotics may closely resemble natural plant compounds and be incorporated into those biosynthesis pathways rather than simply being sequestered.…”

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

“…The "green liver model" proposed that Phase I is the first excitation step for xenobiotic pollutants without active functional groups, such as CPs, and Phase II metabolisms happen following Phase I metabolisms. 49 Only the xenobiotic pollutants containing active functional groups (e.g., −OH), like tetrabromobisphenol A, 52 could perform Phase II reactions directly. Our work verified that the reactions of Phase I and Phase II were interlaced, and the Phase II metabolites could also undergo Phase I reactions, which caused more complicated metabolic networks in plants.…”