Elemental imaging (LA-ICP-MS) of zebrafish embryos to study the toxicokinetics of the acetylcholinesterase inhibitor naled

Abstract

The zebrafish embryo is an important model in ecotoxicology but the spatial distribution of chemicals and the relation to observed effects is not well understood. Quantitative imaging can help to gain insights into the distribution of chemicals in the zebrafish embryo. Laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) is used to quantify the uptake and the uptake kinetics of the bromine (Br) containing organophosphate naled (Dibrom®, dimethyl-1,2-dibromo-2,2-dichloroethylphosphate) and its distribution in zebrafish embryos using Br as the marker element. During exposure, the Br amounts increase in the embryos parallel to the irreversible inhibition of the acetylcholinesterase (AChE). The final amount of Br in the embryo (545 pmol/embryo) corresponds to a 280-fold enrichment of naled from the exposure solution. However, LC-MS/MS analyses showed that the internal concentration of naled remained below the LOD (7.8 fmol/embryo); also the concentration of its known transformation product dichlorvos remained low (0.85 to 2.8 pmol/embryo). These findings indicate the high reactivity and high transformation rate of naled to other products than dichlorvos. 12C normalized intensity distributions of Br in the zebrafish embryo showed an enrichment of Br in its head region. Kernel density estimates of the LA-ICP-MS data were calculated and outline the high reproducibility between replicated and the shift in the Br distribution during exposure. The Br enrichment indicates a preferential debromination or direct covalent reaction of naled with AChE in this region. Graphical abstractᅟ Electronic supplementary materialThe online version of this article (10.1007/s00216-018-1471-2) contains supplementary material, which is available to authorized users.

Effective processing and evaluation of chemical imaging data with respect to morphological features of the zebrafish embryo

“…2a and 3a ). This confirms that the 12 C signal may be used to reflect best the varying tissue densities of the ablated material as the yolk is a lipid- and protein-rich body compartment [ 27 , 37 ]. The potassium channels are expressed mainly in the brain and trunk, which could be why the different distribution patterns of 39 K and 12 C were observed [ 38 ].…”

“…The two compounds contain characteristic elements suited for their determination by LA-ICP-MS: the bromine-containing compound naled and 4-iodophenol. Naled was shown to be an acetylcholinesterase inhibitor, and 4-iodophenol is presumably a baseline toxic compound that accumulates in the yolk of the ZFE [ 27 , 40 ]. By applying the k-means algorithm, the baseline-corrected bromine or iodine intensities together with the carbon signal (as a thickness measure since whole ZFEs are ablated [ 27 ]) and the spatial information were partitioned into 5 clusters for both exposures, respectively (selected based on the elbow method).…”

“…Provided that the LA-ICP-MS system is adequately calibrated [ 27 , 31 ], the amount of an analyte in the respective ROI can be quantified (Table 3 and Fig. 4 ).…”

Soft X-ray laser ablation for nano-scale chemical mapping microanalysis

“…For instance, Halbach et al 43 discussed critical aspects of protein labeling with heteroatoms (i.e. any elements except C and H) for performing laser ablation ICP-MS hyperspectral microanalysis.…”

“…A further critical aspect is the obtainment of (absolute) quantitative information, for which the authors discuss a decalogue of requirements. Halbach et al 43 used LA-ICP-MS for studying the analyte distribution, following Br-labeled organophosphate uptake, in the zebrash embryo, which is an important model in ecotoxicology.…”