Juggling cadmium detoxification and zinc homeostasis: A division of labour between the two C. elegans metallothioneins.

The chemical properties of toxic cadmium and essential zinc are very similar, and organisms require intricate mechanisms that drive selective handling of metals. Previously regarded as unspecific "metal sponges", metallothioneins (MTLs) are emerging as metal selectivity filters. By utilizing C. elegans mtl-1 and mtl-2 knockout strains, metal accumulation in single worms, single copy fluorescent-tagged transgenes, isoform specific qPCR and lifespan studies it was possible to demonstrate that the handling of cadmium and zinc by the two C. elegans metallothioneins differs fundamentally: the MTL-2 protein can handle both zinc and cadmium, but when it becomes unavailable, either via a knockout or by elevated cadmium exposure, MTL-1 takes over zinc handling, leaving MTL-2 to sequester cadmium. This division of labour is reflected in the folding behaviour of the proteins: MTL-1 folded well in presence of zinc but not cadmium, the reverse was the case for MTL-2. These differences are in part mediated by a zinc-specific mononuclear His3Cys site in the C-terminal insertion of MTL-1; its removal affected the entire C-terminal domain and may shift its metal selectivity towards zinc. Overall, we uncover how metallothionein isoform-specific responses and protein properties allow C. elegans to differentiate between toxic cadmium and essential zinc.

Impact of GSM-EMW exposure on the markers of oxidative stress in fetal rat liver.

The current study investigated the effects of 24 h/day prenatal exposure to global system for mobile communication electromagnetic fields (GSM-EMFs), 900 MHZ-induced electromagnetic radiation (EMR), on oxidative stress (OS) status, apoptotic, and inflammatory changes in liver of rats during their fetal development period. Fifty-two Sprague-Dawley pregnant rats were equally divided into control and exposed groups. Whole embryos were removed at 7.5 dpc (days post coitus), while liver tissues were extracted from embryos at 11.5, 15.5, and 19.5 dpc. For exposed animals, results showed an increased OS reflected by high levels of malondialdehyde (MDA), a decrease in cytosolic superoxide dismutase (cytoSOD) activity, in mitochondrial superoxide dismutase (mitoSOD) levels and catalase (CAT) mRNA expression but also in hepatic nuclear factor erythroïd 2-related Factor 2 (Nrf-2), protein kinase B (Akt1), and intercellular adhesion molecule-1 (ICAM-1) mRNA expression at 15.5 dpc. Moreover, GSM-EMR exposure was shown to significantly decrease mitoSOD and CAT activities at almost all studied ages. Thus, rat embryos may be protected by their mothers from OS, apoptotic, and pro-inflammatory responses till a sensitive developmental stage, during a continuous prenatal EMR exposure. This protection could be then created from the embryos themselves.

Effects of continuous prenatal and postnatal global system for mobile communications electromagnetic waves (GSM-EMW) exposure on the oxidative stress biomarkers in female rat liver.

In light of the increased use of communication technologies, the harm caused by continuous exposure to emitted radiation on pregnancy and developing newborns is among the public concerns. Using Sprague-Dawley rats, our study investigates the effects of 24 h/day prenatal and postnatal 900 MHz radiofrequency electromagnetic radiation (RF-EMR) exposure of female rats on liver oxidative stress (OS) and other hepatic parameters at postnatal days (PND) 1, 9, and 21. Our results showed that RF-EMR exposure led to an increase in oxidative stress status as indicated by a significant elevation in MDA level at PND9 and PND21, a decrease in catalase (CAT) activity at all ages, a reduction (PND1 and PND9) in catalase amounts and mRNA expression, in addition to a decrease in GPx activity at PND21 in the exposed group. Current findings also showed a significant increase in cytoSOD at PND9 and 21 and a reduction in mitoSOD at PND21 in the exposed groups compared to the control groups. However, significant increases in glutathione peroxidase (GPx) level and mitoSOD activity were observed at all studied ages. Furthermore, cytoSOD activity showed a significant reduction in PND1, whereas in PND9 the value of this parameter increased compared to the non-exposed group. Moreover, while SOD1 mRNA expression increased at PND1, it decreased at PND9 and 21. However, GPx1 expression was shown to be always decreased in the exposed group. In addition, at PND1 and 9, exposed rats showed a similar response on Akt1, nuclear factor erythroïd 2-related factor 2 (Nrf-2), and intercellular adhesion molecule-1 (ICAM-1) expression. Therefore, an increased oxidative stress status produced from a continuous (24 h/day) GSM-modulated 900 MHz radiofrequency electromagnetic radiation (RF-EMR) exposure during the prenatal and postnatal periods may result in adverse health effects during future life stages.

C. elegans metallothioneins: response to and defence against ROS toxicity.

The genome of the nematode Caenorhabditis elegans encodes for two multifunctional metal binding metallothioneins (MTs), CeMT-1 and CeMT-2. Here we applied qPCR to identify a transcriptional up-regulation following the exposure to free radical generators (ROS) paraquat or hydrogen peroxide, a trend that was confirmed with Pmtl::GFP expressing alleles. The deletion of the MT loci resulted in an elevation of in vivo levels of hydrogen peroxide and exposure to ROS caused a reduction in total egg production, growth and life span in wild type nematodes, effects that were particularly pronounced in the CeMT-2 and double knockout. Moreover, in vitro incubation of recombinant MTs with hydrogen peroxide demonstrated the presence of direct oxidation of the CeMTs, with zinc released from both isoforms and concomitant formation of intra-molecular disulfides. Finally, metabolic profiling (metabolomic) analysis of wild type and MT knockouts in the presence/absence of oxidative stressors, confirmed the overall trend described by the other experiments, and identified 2-aminoadipate as a potential novel small-molecule marker of oxidative stress. In summary, this study highlights that C. elegans metallothioneins scavenge and protect against reactive oxygen species and potentially against oxidative stress, with CeMT-2 being more effective than CeMT-1.

Tools for metal ion sorting: in vitro evidence for partitioning of zinc and cadmium in C. elegans metallothionein isoforms.

In vitro evidence for the isoform-specific partitioning of cadmium and zinc ions between the two C. elegans metallothioneins is presented. This observation is discussed in terms of isoform-specific affinities towards zinc and cadmium and the implications of our study on the in vivo roles of C. elegans metallothioneins.

The two Caenorhabditis elegans metallothioneins (CeMT-1 and CeMT-2) discriminate between essential zinc and toxic cadmium.

The nematode Caenorhabditis elegans expresses two metallothioneins (MTs), CeMT-1 and CeMT-2, that are believed to be key players in the protection against metal toxicity. In this study, both isoforms were expressed in vitro in the presence of either Zn(II) or Cd(II). Metal binding stoichiometries and affinities were determined by ESI-MS and NMR, respectively. Both isoforms had equal zinc binding ability, but differed in their cadmium binding behaviour, with higher affinity found for CeMT-2. In addition, wild-type C. elegans, single MT knockouts and a double MT knockout allele were exposed to zinc (340 microm) or cadmium (25 microm) to investigate effects in vivo. Zinc levels were significantly increased in all knockout strains, but were most pronounced in the CeMT-1 knockout, mtl-1 (tm1770), while cadmium accumulation was highest in the CeMT-2 knockout, mtl-2 (gk125) and the double knockout mtl-1;mtl-2 (zs1). In addition, metal speciation was assessed by X-ray absorption fine-structure spectroscopy. This showed that O-donating, probably phosphate-rich, ligands play a dominant role in maintaining the physiological concentration of zinc, independently of metallothionein status. In contrast, cadmium was shown to coordinate with thiol groups, and the cadmium speciation of the wild-type and the CeMT-2 knockout strain was distinctly different to the CeMT-1 and double knockouts. Taken together, and supported by a simple model calculation, these findings show for the first time that the two MT isoforms have differential affinities towards Cd(II) and Zn(II) at a cellular level, and this is reflected at the protein level. This suggests that the two MT isoforms have distinct in vivo roles.