Association of heavy metals with metallothionein and other proteins in hepatic cytosol of marine mammals and seabirds

Abstract

Distribution of Cu, Zn, Cd, Ag, Hg, and Se were determined in hepatocytosol of northern fur seals (Callorhinus ursinus), black-footed albatrosses (Diomedea nigripes), and Dall's porpoises (Phocoenoides dalli). Copper, Zn, and Cd were accumulated preferentially in metallothionein (MT) fraction and their contents in MT fraction increased with the amounts in the hepatocytosol. Silver was bound to both high-molecular-weight substances (HMWS) and MT in the hepatocytosol for all three species, whereas the distribution of Ag in the cytosol was different among the three species. In northern fur seals, Ag mainly was bound to MT, whereas it mainly was associated with HMWS in Dall's porpoises. In contrast, Ag was distributed almost equally in both HMWS and MT for black-footed albatrosses. Mercury content in HMWS and Se content in HMWS and low-molecular-weight substances (LMWS) increased with their contents in hepatocytosol for all the three species. A significant positive correlation was found between Se and Hg contents in high-molecular weight (HMW) fraction in cytosol. The molar ratio of Hg and Se was close to unity in HMW fraction of the specimens with high Hg concentration in cytosol, implying that the Hg-Se complex was bound to the HMWS. Analysis of metals in the hepatocytosol by high-performance liquid chromatography/inductively coupled plasma-mass spectrometry (HPLC/ICP-MS) suggests that multiple isoforms of MT are present in hepatocytosol of the three species and that the metal profiles in hepatocytosols are different among the species. To our knowledge, this is the first report on the association of Ag with HMWS and MT in hepatocytosol of marine mammals and seabirds. Also, distribution and interaction of Hg and Se were investigated for the first time in hepatocytosol of the higher trophic marine animals.

Organotin accumulation in an estuarine food chain: Comparing field measurements with model estimations

“…In the second approach, it is assumed that dissociation or ligand exchange does occur in biota and that elimination of the organotin cation is similar to metal elimination kinetics as metals bind to proteins as well. An important metalbinding protein in animals is metallothionein (Ikemoto et al, 2004). This binding to proteins is incorporated in OMEGA as a generic dry tissue-water distribution coefficient (K tw ), which results in a lower elimination rate compared to hydrophobic organic substances.…”

Biomagnification Profiles of Trace Elements through the Food Web of an Integrated Shrimp Mangrove Farm in Ba Ria Vung Tau, South Vietnam

“…It has been shown that various vertebrates are able to detoxify Hg by a specific chemical mechanism involving Se, suggesting that Se has an antagonistic effect on Hg metabolism (Elia et al, 2003;Ikemoto et al, 2004;Kunito et al, 2004). This relation has also been documented in marine ecosystem (Dietz et al, 2000;Campbell et al, 2005;Kehrig et al, 2009b).…”

“…In several studies, the ratio between Hg and Se molar concentrations was close to equimolarity in marine mammals and birds, but a large excess of Se in relation to Hg was observed in fishes and crustaceans (Andersen and Depledge, 1997;Dietz et al, 2000;Ikemoto et al, 2004;Kunito et al, 2004;Campbell et al, 2005;Kehrig et al, 2009b). It has been shown that various vertebrates are able to detoxify Hg by a specific chemical mechanism involving Se, suggesting that Se has an antagonistic effect on Hg metabolism (Elia et al, 2003;Ikemoto et al, 2004;Kunito et al, 2004).…”

The role of metallothioneins, selenium and transfer to offspring in mercury detoxification in Franciscana dolphins ( Pontoporia blainvillei )

“…In terrestrial mammals, such as rats and mice, binding of Hg to MT has been demonstrated and induction of these proteins after Hg exposure (Morcillo and Santamaria, 1993;García-Sevillano et al, 2015;Orct et al, 2015). However, the role of MT in the detoxification of Hg is controversial; studies in marine mammals have indicated that a small percentage of Hg is bound to MT in liver and kidney (Decataldo et al, 2004;Ikemoto et al, 2004aIkemoto et al, , 2004b. All specimens analyzed here had Hg concentrations below the tolerance limit for cetaceans (100-400 mg·kg −1 w.w. liver, Wagemann and Muir, 1984), and therefore, the Hg concentrations were likely not high enough to induce the synthesis of MT.…”