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Metabolism of Sulfamethoxazole by the Model Plant Arabidopsis thaliana

Huynh, Khang, Reinhold, Dawn
Environmental science & technology 2019 v.53 no.9 pp. 4901-4911
Arabidopsis thaliana, antibiotic resistance, antibiotics, culture media, excretion, glycosylation, humans, metabolites, models, plant tissues, screening, sulfamethoxazole
Phytometabolism of antibiotics is a potentially significant route of human exposure to trace concentrations of antibiotics, prompting concerns about antibiotic resistance. The present study evaluated the metabolism of sulfamethoxazole (SMX), a commonly used sulfonamide antibiotic, by Arabidopsis thaliana. SMX was intensively metabolized by A. thaliana, with only 1.1% of SMX in plant tissues present as the parent compound after 10 days of exposure. Untargeted screening of extractable metabolites revealed that N-glycosylation was the main transformation pathway of SMX in A. thaliana plants, with N⁴-glycosyl-SMX accounting for more than 80% of the extractable metabolites. Additionally, N⁴-glycosyl-glycoside SMX accounted for up to 4.4% of the extractable metabolites, indicating glycosylation of N⁴-glycosyl-SMX. The majority of minor extractable SMX metabolites were also conjugates of the parent compound, such as pterin–SMX and methyl salicylate–SMX conjugates. In ¹⁴C-SMX trials, ¹⁴C-radioactivity was detected in both extractable and bound residues in plant tissues. Extractable residues, which included ¹⁴C-SMX and its soluble metabolites, accounted for 35.8–43.6% of the uptaken ¹⁴C-radioactivity, while bound residues were 56.4–64.2%. Approximately 27.0% of the initially applied ¹⁴C-radioactivity remained in the culture media at the conclusion of the experiments, composed of both ¹⁴C-SMX and its metabolites, likely due to plant excretion.