Isoform‐specific quantification of metallothionein in the terrestrial gastropod Helix pomatia. II. A differential biomarker approach under laboratory and field conditions

Abstract

The two function-specific metallothionein (MT) isoforms characterized from the midgut gland and mantle tissue of Helix pomatia differ substantially in their metal-binding preferences, as well as molecular and biochemical features. These differences make them potential candidates for biomarker studies based on a differential, isoform-specific approach. To prove this hypothesis, induction experiments with two metals (Cd and Cu) that are normally bound by the two isoforms were compared with a range of organic chemicals and physical stressors under laboratory conditions to test the responsiveness of the two isoforms to the stressors applied. In addition, field studies were conducted with Roman snails and substrate samples collected from different metal-contaminated sites in Austria to test the suitability of the two isoforms as biomarkers under field conditions. The results of these combined laboratory and field studies confirmed the validity of the biomarker approach with the two metal- and tissue-specific isoforms. It is demonstrated that the Cd-binding MT specifically and exclusively responds to Cd exposure by increasing concentrations, whereas the Cu-binding MT isoform decreases in its concentration upon exposure to physical stress (X-ray irradiation and cold). This suggests researchers should adopt, under certain preconditions, a dual biomarker approach by combining the simultaneous quantification of Cd-MT concentrations in the midgut gland as a biomarker for Cd pollution and of Cu-MT concentration in the mantle as a biomarker for the impairment of snails by additional physical stressors.

Copper inHelix pomatia(Gastropoda) is regulated by one single cell type: differently responsive metal pools in rhogocytes

“…In terrestrial pulmonates, for example, Cu tissue levels of individuals from nonpolluted soil habitats are in the range from 10 Ϫ4 to 10 Ϫ3 mol/kg dry mass, whereas the respective concentrations in animals from polluted areas range from about 10 Ϫ3 to 10 Ϫ2 mol/kg dry mass (2,19,20,27). This means that in tissues of individuals from polluted sites, Cu is biologically concentrated about 10 times with respect to the tissue levels of animals from nonpolluted habitats.…”

“…These data are consistent with the concept that H. pomatia and some of its helicid relatives are able to maintain Cu concentrations in their organs within a moderate range (16), even under conditions of increased Cu availability in the environment. In contrast, pulmonate snails from metal-contaminated sites accumulate the nonessential Cd about 100 -1,000 times above Cd levels detected in animals from nonpolluted areas (2,19,20,47). Irrespective of environmental exposure, an important fraction of Cu in snail tissues is always bound to a Cu-specific MT isoform (3).…”

“…They need elevated amounts of Cu specifically as a constituent of hemocyanin, their oxygen-carrying respiratory protein (33). On the other hand, terrestrial snails may suffer from elevated Cu concentrations in their environment due to environmental pollution (19). Cu-sulfate, for example, is often used as a snail poison against certain pulmonate species that are considered pest organisms in horticulture (26).…”

Cd Accumulation and Cd?Metallothionein as a Biomarker in Cepaea hortensis (Helicidae, Pulmonata) from Laboratory Exposure and Metal-polluted Habitats

“…Third and as mentioned above, the biomarker concept in the present and in related studies (see Kammenga et al, 2000) implies that Cd-MT induction in pulmonate snails is only one among several other biomarkers to be applied in parallel in these animals. And, fourth, the peculiar function and handling of organ-and metalspecific MT isoforms in terrestrial pulmonates (Dallinger et al, 1997) offers the possibility of adopting an MT isoform-specific biomarker approach (Kammenga et al, 2000) where alternating concentrations of different isoforms stand for responses to different kinds of stress (Dallinger et al, 2004). Figure 6.…”

Trace Metal Exposure and Effects on Soil‐Dwelling Species and Their Communities

“…Metallothionein-like proteins, for example, have been found to be upregulated in metal-exposed earthworms [123,124], enchytraeids [125], molluscs [126,127], and springtails [128]. High metallothionein expression phenotypes have been found in springtail populations collected from metalcontaminated sites, indicating a likely role of these proteins in inherited metal tolerance [129].…”