Toxicokinetics of Polar Chemicals in Zebrafish Embryo (Danio rerio): Influence of Physicochemical Properties and of Biological Processes

Abstract

The time-resolved uptake of 17 nonionic and ionic polar compounds (logD ≤ 2) with a diversity of functional groups into zebrafish embryos (ZFE) was studied over 96 h of exposure. Among them were pharmaceuticals, pesticides and plant active ingredients. Uptake rates for the diffusion controlled passive uptake through the ZFE membrane ranged from 0.02 to 24 h(-1) for the nonionic compounds and were slower for ionic compounds (<0.008-0.08 h(-1)). The study compounds did not enrich much in the ZFE (median bioconcentration factor of 1, max. 7). Biotransformation significantly influenced the internal concentration of some of the test compounds over time (benzocaine, phenacetin, metribuzin, phenytoin, thiacloprid, valproic acid). For benzocaine, valproic acid and phenacetin several transformation products (TPs) were observed by LC-MS already at early life-stages (before 28 hpf); for benzocaine the TPs comprised >90% of the initial amount taken up into the ZFE. For six compounds internal concentrations remained very low (rel. int. conc. < 0.2). Besides biotransformation (sulfamethoxazole), poor membrane permeability (cimetidine, colchicine) and also affinity to efflux transporters (atropine and chloramphenicol) are the likely reasons for these low internal concentrations. This study outlines that the uptake of polar compounds into ZFE is influenced by their physicochemical properties. However, biological processes, biotransformation and, likely, efflux can strongly affect the internal concentrations already in early developmental stages of the ZFE. This should be considered in future toxicokinetic modeling. The evaluation of the toxicity of chemicals by ZFE requires toxicokinetic studies of the test compounds and their TPs to increase comparability to effects in fish.

Advancing the Zebrafish embryo test for endocrine disruptor screening using micro‐injection: Ethinyl estradiol as a case study

“…At 72 hpf, in vitro activity of some cytochrome P450s was also observed in zebrafish embryos Verbueken et al 2017). A similar decreasing pattern of internal doses, after a maximum of approximately 24 hpf, was also observed after aquatic exposure to benzocaine, phenacetin, metribuzin (Brox et al 2016), and benz[a]anthracene (Kuhnert et al 2013). In both studies, metabolites of the respective parent compounds were also detected, which supports the hypothesis of biotransformation.…”

Differential uptake of and sensitivity to diphenhydramine in embryonic and larval zebrafish

“…Uptake of select pharmaceuticals [27,40], perfluorooctanesulfonic acid [41], and polycyclic aromatic hydrocarbons (PAHs) [34,42] has been examined in embryonic stages of zebrafish. For example, there are fewer than 10 previous studies on the uptake of chemicals across embryo-larval stages of fish, and of these, the majority of work has been conducted with either eleutheroembryo or larval stages.…”

“…Although some mammalian homologs have been identified, functional conservation has not yet been established for most CYPs [53] across common fish models. For example, investigations of clofibric acid biotransformation [55], and a suite of other polar compounds [40], by developing zebrafish identified the presence of transformation products. For example, investigations of clofibric acid biotransformation [55], and a suite of other polar compounds [40], by developing zebrafish identified the presence of transformation products.…”

“…For example, there are fewer than 10 previous studies on the uptake of chemicals across embryo-larval stages of fish, and of these, the majority of work has been conducted with either eleutheroembryo or larval stages. Uptake of select pharmaceuticals [27,40], perfluorooctanesulfonic acid [41], and polycyclic aromatic hydrocarbons (PAHs) [34,42] has been examined in embryonic stages of zebrafish. Although each of the studied substances bioconcentrated in embryos, biotransformation and elimination capacities varied among chemicals.…”

Comparison of the In Vivo Biotransformation of Two Emerging Estrogenic Contaminants, BP2 and BPS, in Zebrafish Embryos and Adults

“…Using an in vitro approach based on the use of sub-cellular microsomal fractions and of specific probe substrates, Verbueken et al [25] concluded that the capacity of intrinsic biotransformation in zebrafish embryos appears to be lacking during a major part of organogenesis, at least concerning key phase I activities. Notwithstanding, recent in vivo studies demonstrated that biotransformation of some compounds can start very early, indicating that some phase I and phase II enzymes are already functional at early life-stages [26,27]. We previously demonstrated that the metabolic capacities expressed in zebrafish hepatic cellular models are close to that of metabolically competent hepatic human cell lines (HepaRG), at least for BPS and BP2 [8].…”