Association of metals (mercury, cadmium and zinc) with metallothionein-like proteins in storage organs of stranded dolphins from the Mediterranean sea (Southern Italy)

Abstract

Selected toxic and essential metals (mercury, Hg; cadmium, Cd; and zinc, Zn) were determined in the liver and in the kidney collected from 13 dolphins (Stenella coeruleoalba and Tursiops truncatus) stranded along the southern coasts of Italy from 1991 to 1999. Liver samples were also analysed for their methyl mercury (MeHg) and selenium (Se) contents. For subcellular fractionation, liver and kidney samples were homogenized in Tris-HCl buffer; after centrifugation, the supernatant (cytosol) was separated from pellets (insoluble fraction), heated at 80 degrees C for 10 min and centrifuged in order to separate the precipitate containing the thermolabile high molecular weight proteins. The cytosol heat-stable fraction, including metallothionein-like proteins (MTLPs), was then purified by gel filtration chromatography on Sephadex G-75 column. The three subcellular fractions collected (insoluble fraction, thermolabile fraction and purified heat-stable fraction) were analysed for their Hg, Cd and Zn contents. The analytical results confirm previous similar studies on toothed whales in showing that: (1) in the liver, as well as in the kidney, Hg was mainly found in the insoluble fraction, therefore, metallothioneins seem to have no role in the Hg detoxification; (2) in the liver, the molar ratio between Se and inorganic Hg was very close to 1; this suggests that the final compound of MeHg detoxification could be HgSe (tiemannite); (3) in almost all the samples, Cd and Zn were detected in the purified heat-stable fraction (including MTLPs). The mechanism of Cd detoxification and Zn homeostasis is also discussed.

Establishment of a primary hepatocyte culture from the small Indian mongoose (Herpestes auropunctatus) and distribution of mercury in liver tissue

“…This shows that demethylation of methyl Hg is promoted in the body, particularly in the liver (Caurant et al 1996;Meador et al 1999;Cardellichio et al 2000;Cardellicchio et al 2002). In addition, a positive correlation between Se and T-Hg was found in marine mammals with high T-Hg in the liver (Caurant et al 1996;Wagemann et al 1998;Meador et al 1999;Fant et al 2001;Woshner et al 2001;Cardellicchio et al 2002;Endo et al 2002;Decataldo et al 2004). It is generally accepted that the Hg toxicity is reduced by being bonded with selenium (Wagemann et al 1998;Cardellichio et al 2000;Endo et al 2002;Arai et al 2004).…”

Tissue-specific response of metallothionein and superoxide dismutase in the clam Mactra veneriformis under sublethal mercury exposure

“…MT is a type of cysteine-rich, low-molecular-weight protein with high affinity for metals such as Hg, cadmium (Cd) and copper. MT occurs mainly in the cytosol but also in the nucleus and lysosomes (Decataldo et al 2004). It is thought to play an important role in metal metabolism and detoxification of heavy metals (Davis and Cousins 2000).…”

Bioaccumulation of trace elements in pelagic fish from the Western Indian Ocean

“…Hg by Se in the liver of many marine mammals, as well as certain birds and fish (Koeman et al, 1973;Mackay et al, 1975;Martoja and Berry, 1980;Nigro et al, 2002;Decataldo et al, 2004;Ikemoto et al, 2004). Among the four species considered here, the correlation between Hg and Se in liver increased with the Hg impregnation of the given species: Common Dolfinfish (r 2 = 0.007 ; p > 0.05), Skipjacks (r 2 = 0.063 ; p > 0.05), Yellowfin Tunas (r 2 = 0.226 ; p = 0.001) and Swordfish (r 2 = 0.747 ; p < 0.001).…”