Selenium Stimulates Cadmium Detoxification in Caenorhabditis elegans through Thiols-Mediated Nanoparticles Formation and Secretion

Abstract

Antagonism between heavy metal and selenium (Se) could significantly affect their biotoxicity, but little is known about the mechanisms underlying such microbial-mediated antagonistic processes as well as the formed products. In this work, we examined the cadmium (Cd)–Se interactions and their fates in Caenorhabditis elegans through in vivo and in vitro analysis and elucidated the machinery of Se-stimulated Cd detoxification. Although the Se introduction induced up to 3-fold higher bioaccumulation of Cd in C. elegans than the Cd-only group, the nematode viability remained at a similar level to the Cd-only group. The relatively lower level of reactive oxygen species in the Se & Cd group confirms a significantly enhanced Cd detoxification by Se. The Cd–Se interaction, mediated by multiple thiols, including glutathione and phytochelatin, resulted in the formation of less toxic cadmium selenide (CdSe)/cadmium sulfide (CdS) nanoparticles. The CdSe/CdS nanoparticles were mainly distributed in the pharynx and intestine of the nematodes, and continuously excreted from the body, which also benefitted the C. elegans survival. Our findings shed new light on the microbial-mediated Cd–Se interactions and may facilitate an improved understanding and control of Cd biotoxicity in complicated coexposure environments.

Mechanical Insights into Thiol-Mediated Synergetic Biotransformation of Cadmium and Selenium in Nematodes

“…Our previous work showed that Se can induce serial biotransformation of Cd in C. elegans distinct from that under Cd-alone condition, which ultimately leads to the formation of CdSe NPs. 17 Here, in situ Se K-edge (12658 eV) XANES spectrometry was performed on C. elegans to further unveil the compositional and structural changes of the Se and Cd species in vivo. The normalized XANES spectrum showed a distinct peak similar to that of CdSe (12659.5 eV) (Figure 1), indicating that the ingested Se IV (i.e., selenite) has been fully transformed into organoselenium and Se -II (i.e., CdSe).…”

“…Our previous study has demonstrated an obvious correlation between the genetic expression of these peptides and the Se and Cd exposure. 17 However, direct evidence regarding their specific roles and contributions to the NPs formation is still lacking. To clarify this issue, here we selectively silence specific genes using RNAi techniques.…”

“…To minimize the influence of bacteria on the CdSe NP formation, 24 the OP50 cells were added once every two days so that a low bacterial density (OD600 value of 0.20−0.25) was maintained. 17 The flasks were placed in a 20 °C incubator under continuous shaking (180 rpm). After cultivation for three days in the dark, 200 μM Na 2 SeO 3 was added to the culture medium.…”

“…In addition, to minimize the interferences of bacteria and the new generation of nematode larvae on the NP formation, the collected biosamples were floated on a cold 30% (w/v) sucrose cushion for nematode separation and washed three times with the K medium prior to the analysis. 17 Purification of Bioassembled CdSe NPs. To reveal the detailed microstructure and morphologic information of the bioassembled NPs, the NPs were extracted and purified following a reported method.…”

“…To reveal the detailed microstructure and morphologic information of the bioassembled NPs, the NPs were extracted and purified following a reported method. 17 Specifically, the nematodes were placed in water slution containing 215−300 μm glass beads, and crushed with a FastPrep TM-24 homogenizer (MP Biomedicals Inc.) at a stirring rate of 6.5 m/s. After 30 s homogenization treatment, the samples were ice-cooled for 1 min.…”