Elucidating the Differences in Metal Toxicity by Quantitative Adverse Outcome Pathways

Abstract

Numerous studies have reported that the toxicity differences among metals are widespread; however, little is known about the mechanism of differences in metal toxicity to aquatic organisms due to the lack of quantitative understanding of their adverse outcome pathway. Here, we investigated the effects of Cd and Cu on bioaccumulation, gene expression, physiological responses, and apical effects in zebrafish larvae. RNA sequencing was conducted to provide supplementary mechanistic information for the effects of Cd and Cu exposure. On this basis, we proposed a quantitative adverse outcome pathway (qAOP) suitable for metal risk assessment of aquatic organisms. Our work provides a mechanistic explanation for the differences in metal toxicity where the strong bioaccumulation of Cu enables the newly accumulated Cu to reach the threshold that causes different adverse effects faster than Cd in zebrafish larvae, resulting in a higher toxicity of Cu than that of Cd. Furthermore, we proposed a parameter C IT/BCF (the ratio of internal threshold concentration and bioaccumulation factor) that helps to understand the toxicity differences by combining the information of bioaccumulation and internal threshold of adverse effects. This work demonstrated that qAOP is an effective quantitative tool for understanding the toxicity mechanism and highlight the importance of toxicokinetics and toxicodynamics at different biological levels in determining the metal toxicity.

Predicting the Metal Mixture Toxicity with a Toxicokinetic–Toxicodynamic Model Considering the Time-Dependent Adverse Outcome Pathways

“…Among all DEGs, the interleukin 1, β ( il1b ) gene was selected as a candidate because it is one of the common DEGs (Figure H) and has high expression levels among all DEGs (Figure S6). In addition, il1b is one of the significant genes reported to be involved in many metals’ toxicity , and showed a good dose–response relationship with mortality in our previous study . Another advantage is that for complex mixtures exposed to natural environments, it might be easier to determine one or a set of genes than to determine the internal residues of each mixture component, especially with the development of high-throughput genetic detection technologies. , …”

“…Impact of Cd, Cu, and the Mixture on Different Toxic End Points. The functional analyses of common DEGs showed that several pathways were highly relevant to the known toxic mechanisms of Cd and Cu exposure, 40 and we further performed confirmatory assays accordingly (Figure 3). The time-dependent functional analysis of transcriptomic data is also used as the Supporting Information on the mode of action (Figure S3).…”

“…In addition, il1b is one of the significant genes reported to be involved in many metals' toxicity 65,66 and showed a good dose−response relationship with mortality in our previous study. 40 Another advantage is that for complex mixtures exposed to natural environments, it might be easier to determine one or a set of genes than to determine the internal residues of each mixture component, especially with the development of highthroughput genetic detection technologies. 67,68 Damage based on measured data can be used to fit the change in damage over time after metal exposure.…”

“…33 Fluorescence imaging of live larvae after exposure was performed using commercial kits to determine relative apoptosis. The detailed protocols can be found in previous publications 33,40 and are described in Text S3.…”

Near-Infrared-II In Vivo Visualization and Quantitative Tracking of Micro/Nanoplastics in Fish

“…Adult zebrafish (Danio rerio) were purchased from the Institute of Hydrobiology, Chinese Academy of Sciences (Wuhan, China) and cultured in the laboratory as described in previous work. 62 Zebrafish were maintained in a tank with carbonfiltered dechlorinated tap water for 2 weeks to acclimate to laboratory conditions. The temperature was set at 26 ± 1 °C and the photoperiod of 12 h/12 h light/dark was implemented.…”