The physiological role and toxicological significance of the non-metal-selective cadmium/copper-metallothionein isoform differ between embryonic and adult helicid snails

In vivo assessment of oxidative stress, neurotoxicity and histological alterations induction in the marine gastropod Stramonita haemastoma exposed to Cr2O3 and Al2O3 nanoparticles

The increased use of nanoparticles (NPs) is expected to raise their presence in the marine ecosystem, which is considered as the final destination of released NPs. This study investigated the toxicity of Cr2O3 (42 nm) and Al2O3 (38 nm) NPs (1, 2.5, and 5 mg/L) on the digestive glands of Stramonita haemastoma for 7, 14, and 28 days by oxidative stress biomarkers, neurotoxicity indicator assessment, and histological study. Results revealed an imbalance in antioxidants at all periods. Following 7 days, both NPs caused GSH depletion with marked impacts from Al2O3. GPx, CAT, and AChE were also decreased with the highest changes induced by Cr2O3. Both NPs inducted GSH and GST levels on days 14 and 28, with more effects from Cr2O3 exposure. GPx, AChE, and MDA induction were observed on day 28, while MT varied through NPs and time, with imbalanced levels at all periods noticed, SOD was mostly not affected. Histology revealed alterations including necrosis and interstitial deteriorations; quantitative analysis through the histological condition index revealed dose-dependent impacts, with the highest values attributed to Cr2O3 exposure. While PCA revealed the co-response of GSH, GST, GPx, CAT, and AchE with separated MT responses. This study reported oxidative stress induction through a multi-biomarkers investigation, neurotoxicity, and histological damages in the digestive gland of S. haemastoma following Cr2O3 and Al2O3 NPs exposure.

Study on metal binding capacity of the freshwater crab Sinopotamon henanense's recombinant copper specific binding metallothionein expressed in Escherichia coli

The copper specific binding metallothionein (CuMT) is a type of cysteine-rich, metal-binding, small protein which plays an important role in Cu²⁺ metabolism in vertebrates. In this study, we investigated the metal tolerance and removing ability of recombinant strains harboring CuMT obtained in vivo from the freshwater crab Sinopotamon henanense (ShCuMT) in order to study its physiological functions and metal binding capacity. We performed a 3D modeling of ShCuMT and created its structural and functional models using the I-TASSER program. The shCumt gene was inserted into a pGEX-4t-1 vector and recombinant soluble ShCuMT was expressed in Escherichia coli. In addition, in order to characterize the tolerance and removing ability of heavy metals in E. coli with ShCuMT expression, the recombinant strains harboring ShCuMT were exposed to various concentrations of Cd²⁺, Cu²⁺ and Zn²⁺, respectively. The results showed that ShCuMT contains transition metal binding sites. In addition, E. coli cells expressing ShCuMT exhibited enhanced metal tolerance and higher removing ability of metal ions than control cells. However, compared with Cd²⁺ and Zn²⁺, E. coli cells expressing ShCuMT have stronger tolerance and higher removing ability of Cu²⁺. In general, ShCuMT contains multiple transition metal binding sites, and it could enhance tolerance and removing ability of metal ions. Therefore, ShCuMT can provide potential candidates for heavy metal bioremediation. This research on the metal binding properties of ShCuMT provides a scientific basis for bioremediation of heavy metal pollution by the recombinant strains.

Seasonal variation of biomarker responses in Cantareus aspersus and physic-chemical properties of soils from Northeast Algeria

This study belongs to the biomonitoring program of soil qualities using a land snail, Cantareus aspersus, as bioindicator. The metal-soil contamination in some sites (National Park of El Kala (NPK), El Bouni, Sidi Amar, Nechmaya, and Guelma) located in Northeast Algeria were determined during two seasons (winter and spring 2015, 2016). Glutathione (GSH) content and acetylcholinesterase (AChE) activity were significantly decreased in snails collected during spring as compared with those noticed during winter under bioclimate change. In addition, a significant difference between various sites was observed, depending on the proximity to pollution sources. The significant variation of biomarker levels is a function of the physic-chemical properties of soils when they positively correlated with EC, H, and OM, and negatively correlated with all metallic elements. Moreover, Fe and Al₂O₃ are the most abundant in all the sites, and the most polluted site was found as that of El Bouni, followed by Sidi Amar, Nechmaya, and Guelma, since NPK is the less polluted site and considered a reference site. The tested biomarkers are sensitive oxidative parameters in snails exposed to pollution correlated significantly with the soil physic-chemical properties and metallic element contents in soil. Indeed, C. aspersus could be used as sentinel species in field monitoring of Mediterranean climate regions.

Cadmium Uptake, MT Gene Activation and Structure of Large-Sized Multi-Domain Metallothioneins in the Terrestrial Door Snail Alinda biplicata (Gastropoda, Clausiliidae)

Terrestrial snails (Gastropoda) possess Cd-selective metallothioneins (CdMTs) that inactivate Cd²⁺ with high affinity. Most of these MTs are small Cysteine-rich proteins that bind 6 Cd²⁺ equivalents within two distinct metal-binding domains, with a binding stoichiometry of 3 Cd²⁺ ions per domain. Recently, unusually large, so-called multi-domain MTs (md-MTs) were discovered in the terrestrial door snail Alinda biplicata (A.b.). The aim of this study is to evaluate the ability of A.b. to cope with Cd stress and the potential involvement of md-MTs in its detoxification. Snails were exposed to increasing Cd concentrations, and Cd-tissue concentrations were quantified. The gene structure of two md-MTs (9md-MT and 10md-MT) was characterized, and the impact of Cd exposure on MT gene transcription was quantified via qRT PCR. A.b. efficiently accumulates Cd at moderately elevated concentrations in the feed, but avoids food uptake at excessively high Cd levels. The structure and expression of the long md-MT genes of A.b. were characterized. Although both genes are intronless, they are still transcribed, being significantly upregulated upon Cd exposure. Overall, our results contribute new knowledge regarding the metal handling of Alinda biplicata in particular, and the potential role of md-MTs in Cd detoxification of terrestrial snails, in general.

Cadmium Pathways in Snails Follow a Complementary Strategy between Metallothionein Detoxification and Auxiliary Inactivation by Phytochelatins

Metal detoxification is crucial for animals to cope with environmental exposure. In snails, a pivotal role in protection against cadmium (Cd) is attributed to metallothioneins (MTs). Some gastropod species express, in a lineage-specific manner, Cd-selective MTs devoted exclusively to the binding and detoxification of this single metal, whereas other species of snails possess non-selective MTs, but still show a high tolerance against Cd. An explanation for this may be that invertebrates and in particular snails may also synthetize phytochelatins (PCs), originally known to be produced by plants, to provide protection against metal or metalloid toxicity. Here we demonstrate that despite the fact that similar mechanisms for Cd inactivation exist in snail species through binding of the metal to MTs, the actual detoxification pathways for this metal may follow different traits in a species-specific manner. In particular, this depends on the detoxification capacity of MTs due to their Cd-selective or non-specific binding features. In the terrestrial slug Arion vulgaris, for example, Cd is solely detoxified by a Cd-selective MT isoform (AvMT1). In contrast, the freshwater snail Biomphalaria glabrata activates an additional pathway for metal inactivation by synthesizing phytochelatins, which compensate for the insufficient capacity of its non-selective MT system to detoxify Cd. We hypothesize that in other snails and invertebrate species, too, an alternative inactivation of the metal by PCs may occur, if their MT system is not Cd-selective enough, or its Cd loading capacity is exhausted.

Extreme metal adapted, knockout and knockdown strains reveal a coordinated gene expression among different Tetrahymena thermophila metallothionein isoforms

Metallothioneins (MT) constitute a superfamily of small cytosolic proteins that are able to bind metal cations through numerous cysteine (Cys) residues. Like other organisms the ciliate Tetrahymena thermophila presents several MT isoforms, which have been classified into two subfamilies (Cd- and Cu-metallothioneins). The main aim of this study was to examine the specific functions and transcriptional regulation of the five MT isoforms present in T. thermophila, by using several strains of this ciliate. After a laboratory evolution experiment over more than two years, three different T. thermophila strains adapted to extreme metal stress (Cd²⁺, Cu²⁺ or Pb²⁺) were obtained. In addition, three knockout and/or knockdown strains for different metallothionein (MT) genes were generated. These strains were then analyzed for expression of the individual MT isoforms. Our results provide a strong basis for assigning differential roles to the set of MT isoforms. MTT1 appears to have a key role in adaptation to Cd. In contrast, MTT2/4 are crucial for Cu-adaptation and MTT5 appears to be important for Pb-adaptation and might be considered as an “alarm” MT gene for responding to metal stress. Moreover, results indicate that likely a coordinated transcriptional regulation exists between the MT genes, particularly among MTT1, MTT5 and MTT2/4. MTT5 appears to be an essential gene, a first such report in any organism of an essential MT gene.

Unravelling the Role of Metallothionein on Development, Reproduction and Detoxification in the Wall Lizard Podarcis sicula

Metallothioneins (MTs) are an evolutionary conserved multigene family of proteins whose role was initially identified in binding essential metals. The physiological role of MT, however, has been revealed to be more complex than expected, since not only are MTs able to bind to toxic heavy metals, but many isoforms have shown specialized and alternative functions. Within this uncertainty, the information available on MTs in non-mammalian vertebrates, particularly in neglected tetrapods such as the reptiles, is even more scant. In this review, we provide a summary of the current understanding on metallothionein presence and function in the oviparous lizard Podarcis sicula, highlighting the results obtained by studying MT gene expression in most representative adult and embryonic tissues. The results demonstrate that in adults, cadmium induces MT transcription in a dose- and tissue-specific manner. Thus, the MT mRNAs appear, at least in some cases, to be an unsuitable tool for detecting environmental ion contamination. In early embryos, maternal RNAs sustain developmental needs for MT protein until organogenesis is well on its way. At this time, transcription starts, but again in a tissue- and organ-specific manner, suggesting an involvement in alternative roles. In conclusion, the spatiotemporal distribution of transcripts in adults and embryos definitively confirms that MT has deserved the title of elusive protein.