Properties of cod metallothionein, its presence in different tissues and effects of Cd and Zn treatment

Blood cadmium and metallothionein concentrations in females of two sympatric pinnipeds species

Otaria flavescens (SASL) and Arctocephalus australis (SAFS) are endemic of South America. The aims were to assess Cd concentrations in red blood cells (RBC) and plasma from free living females of both species; and to establish metallothioneins (MT) levels in blood fractions and the possible relationship between MTs and Cd. Blood of fifteen SASL and eight SAFS females from Isla de Lobos were analyzed (years 2010-2011). All animals showed Cd levels above the detection limit. Cd concentrations on SAFS were higher than those of SASL, however, no significant differences were observed on metal concentrations between cell fractions by species. Metal levels were associated with a natural presence and ecological-trophic habits of the prey items. On SASL the MT concentrations between fractions were similar; whereas, SAFS plasma concentrations were higher than RBC. The results reported constitute the first information on Cd and MT blood levels in these species.

Metallothioneins pattern during ontogeny of coastal dolphin, Pontoporia blainvillei, from Argentina

Metallothioneins are signals of metal exposure and widely used in biomonitoring. Franciscana dolphin is an endemic cetacean from the Southwestern Atlantic Ocean, classified as Vulnerable A3d by the IUCN. Metallothionein, copper and zinc in Franciscana were assessed in two geographic groups; one inhabits La Plata River estuary, anthropogenically impacted, and the other inhabits marine coastal ecosystems, with negligible pollution. Despite the environment, hepatic and renal MT concentrations were similar, but there was a declining trend from early to later developmental stages. Metallothionein K/L, Cu and Zn levels corresponded to normal reported ranges. MT was not related with Cd. Fetal concentrations were higher than its mother. These results and the health status of dolphins are suggesting that MT correspond to physiological ranges for the species, and they are closely to homeostasis of Zn and Cu, according to its ontogenetic changes. The information constitutes the first MT information on Franciscana dolphin and can be considered as baseline for the species conservation.

Review on methods for determination of metallothioneins in aquatic organisms

One aspect of environmental degradation in coastal areas is pollution from toxic metals, which are persistent and are bioaccumulated by marine organisms, with serious public health implications. A conventional monitoring system of environmental metal pollution includes measuring the level of selected metals in the whole organism or in respective organs. However, measuring only the metal content in particular organs does not give information about its effect at the subcellular level. Therefore, the evaluation of biochemical biomarker metallothionein may be useful in assessing metal exposure and the prediction of potential detrimental effects induced by metal contamination. There are some methods for the determination of metallothioneins including spectrophotometric method, electrochemical methods, chromatography, saturation-based methods, immunological methods, electrophoresis, and RT-PCR. In this paper, different methods are discussed briefly and the comparison between them will be presented.

Heavy metal accumulation and metallothionein concentration in the frog Rana ridibunda after exposure to chromium or a mixture of chromium and cadmium

The accumulation of two heavy metals (chromium (Cr) and cadmium (Cd)) in the liver, kidney and gut of Rana ridibunda exposed to Cr or to a mixture of Cr and Cd was investigated. The concentration of metallothioneins (MTs) in the same tissues was also studied. Both metals accumulated mainly in the kidney. Cr accumulation in the liver and gut was not affected by the presence of Cd. Furthermore, Cr concentration in the kidney was doubled when Cd was present. MT concentration did not increase after Cr treatment but it increased two- to six-fold over control values in mixture-exposed frogs, the highest value being observed in the gut. MTs in the gut could act as a barrier preventing ingested heavy metals from entering the blood stream. MT concentration correlated positively with Cd concentrations in both the liver and the gut of mixture-exposed animals.

Application of biomarkers for assessing the biological impact of dredged materials in the Mediterranean: the relationship between antioxidant responses and susceptibility to oxidative stress in the red mullet (Mullus barbatus)

In the period 1997-2000, approximately 1,800,000 m3 of material dredged from the Port of Leghorn was discharged into a sea dumping site located 14 miles from the coast. The red mullet (Mullus barbatus) was used as a bioindicator species for monitoring the biological impact of these discharges on a geographical and temporal scale. Organisms were sampled over three years (1998-2000) at different stations and several biomarkers, both of exposure and effect, were analyzed. Bioavailability of specific classes of pollutants was evaluated by analyzing levels of metallothioneins, the activity of cytochrome P450 1A (CYPIA) and of glutathione S-transferases. Among biomarkers of effect, special attention was paid to the balance between prooxidant challenge and antioxidant defenses, and to the appearance of damage caused by oxidative stress. The analyses of the main components of the antioxidant system included superoxide dismutase, catalase, glutathione peroxidases, glutathione reductase, glyoxalase I and II, and total glutathione. These data were integrated with the measurement of total oxyradical scavenging capacity (TOSC) as an indication of the overall biological resistance to toxicity of different forms of oxyradicals (peroxyl radicals, hydroxyl radicals and peroxynitrite). Results indicated a biological impact in organisms sampled near the disposal site; the impact was particularly evident during 1999 and mainly related to organic chemicals such as PAH. Exposure to these pollutants also caused variations in the levels and activity of several antioxidants. The analysis of TOSC, however, revealed that the overall capacity of specific tissues of organisms to absorb various oxidants was not seriously compromised when challenged with increased prooxidant pressures. Variations of single antioxidants were useful in revealing early warning "biological responses", while integration with TOSC analyses indicated if such changes also reflect a more integrated and functional "biological effect" with possible consequences at the organisms level. The red mullet appears to be a useful sentinel species for a biomarker approach to monitoring impact caused by dredged materials.

Bioavailability and toxicity of dietborne copper and zinc to fish

To date, most researchers have used dietborne metal concentrations rather than daily doses to define metal exposure and this has resulted in contradictory data within and between fish species. It has also resulted in the impression that high concentrations of dietborne Cu and Zn (e.g. > 900 mg kg(-1) dry diet) are relatively non-toxic to fish. We re-analyzed existing data using rations and dietborne metal concentrations and used daily dose, species and life stage to define the toxicity of dietborne Cu and Zn to fish. Partly because of insufficient information we were unable to find consistent relationships between metal toxicity in laboratory-prepared diets and any other factor including, supplemented metal compound (e.g. CuSO(4) or CuCl(2)), duration of metal exposure, diet type (i.e. practical, purified or live diets), or water quality (flow rates, temperature, hardness, pH, alkalinity). For laboratory-prepared diets, dietborne Cu toxicity occurred at daily doses of > 1 mg kg(-1) body weight d(-1) for channel catfish (Ictalurus punctatus), 1-15 mg kg(-1) body weight d(-1) (depending on life stage) for Atlantic salmon (Salmo salar) and 35-45 mg kg(-1) body weight d(-1) for rainbow trout (Oncorhynchus mykiss). We found that dietborne Zn toxicity has not yet been demonstrated in rainbow trout or turbot (Scophthalmus maximus) probably because these species have been exposed to relatively low doses of metal ( < 90 mg kg(-1) body weight d(-1)) and effects on growth and reproduction have not been analyzed. However, daily doses of 9-12 mg Zn kg(-1) body weight d(-1) in laboratory-prepared diets were toxic to three other species, carp Cyprinus carpio, Nile tilapia Oreochromis niloticus, and guppy Poecilia reticulata. Limited research indicates that biological incorporation of Cu or Zn into a natural diet can either increase or decrease metal bioavailability, and the relationship between bioavailability and toxicity remains unclear. We have resolved the contradictory data surrounding the effect of organic chelation on metal bioavailability. Increased bioavailability of dietborne Cu and Zn is detectable when the metal is both organically chelated and provided in very low daily doses. We have summarized the information available on the effect of phosphates, phytate and calcium on dietborne Zn bioavailability. We also explored a rationale to understand the relative importance of exposure to waterborne or dietborne Cu and Zn with a view to finding an approach useful to regulatory agencies. Contrary to popular belief, the relative efficiency of Cu uptake from water and diet is very similar when daily doses are compared rather than Cu concentrations in each media. The ratio of dietborne dose:waterborne dose is a good discriminator of the relative importance of exposure to dietborne or waterborne Zn. We discuss gaps in existing data, suggest improvements for experimental design, and indicate directions for future research.

A modified mercury saturation assay for measuring metallothionein

A thorough re-evaluation of assay procedures for a mercury displacement analytical method for metallothionein (MT) described in 1993, was conducted using an analytical standard of rabbit liver MT-II and MT determinations, in liver, kidney, gill and intestine from lake trout (Salvelinus namaycush). These studies indicated that: (1) loss of MT by adherence to polypropylene material occurs with the dilution series; (2) use of a calibration curve using a rabbit liver MT-II analytical standard, is superior to the dilution series for determining unknown MT concentrations; (3) Hg incubation time requirements are less in 20% TCA than in 10% TCA; and (4) employing both 20% TCA and heat at 95 degrees C for 5 min to denature non MT proteins results in the most accurate MT spike recoveries, or recoveries that did not differ significantly from those closest to 100%, in liver, kidney, gill and intestine. Calibration curves with an average r(2) of 0.9998 for 69 trials over different days, while passing through the origin, provided evidence of negligible non-specific binding of mercury. Use of water or saline for preparing tissue homogenates, produced slight, but significant, differences in MT estimates in the intestine and kidney. Comparisons between the original and the modified methods were made on liver, kidney and gill from control, sham-injected and Cd-treated lake trout. Differences in MT estimates obtained between the two methods depended upon the tissue. MT estimates in liver by the modified method were 9, 13, and 10% higher in control, sham-injected and Cd-treated groups, respectively, than those resulting from the original assay. MT estimates in gill by the modified method, were 3.2-fold, 4.0-fold and 69% higher in control, sham-injected, and Cd-treated groups, respectively. Corresponding values for kidney were 37, 75, and 57% higher. Because percent recoveries of MT-II spikes were virtually 100%, in all four tissues, using the modified method, MT estimates obtained using these modifications were more accurate than those obtained using the procedures of the original assay. Application of the modified assay to fish tissues in a Canadian biomonitoring program for metal mining, demonstrated that in 1 week an experienced technologist can complete 90 MT analyses of liver and kidney and 75 analyses of gill and intestine.

Increase of metallothionein-immunopositive chloride cells in the gills of brown trout and rainbow trout after exposure to sewage treatment plant effluents

Metallothionein, a biomarker of exposure and toxicity of heavy metals, has been detected in the gills of brown trout (Salmo trutta fario L.) and rainbow trout (Oncorhynchus mykiss Richardson) by means of immunohistochemistry. A very prominent labelling of chloride cells was found after exposure to diluted sewage plant effluents. No significant increase was observed in either the number of labelled cells or their labelling intensity after exposure to water of a polluted river compared to fish kept in tap water. These results do not correlate with findings of a histopathological study, suggesting that the metal levels at the sewage treatment plant were too low to produce gross histopathology. A comparison between the species indicated that the rainbow trout showed a generally higher metallothionein expression than the brown trout.

Kinetics of cadmium accumulation and elimination in carp Cyprinus carpio tissues

Carp (Cyprinus carpio) were tested for cadmium accumulation and elimination during and after a simulated pollution exposure. Fish were distributed in two 1000-l indoor concrete aquaria supplied with a continuous flow (8 l min(-1)) of well water. The cadmium concentration was maintained at 53 microg l(-1) in one aquarium and 443 microg l(-1) in the other aquarium for 127 days. The exposure phase was followed by a 43-day depuration period. The cadmium accumulation in liver, kidney and muscle was measured by means of ICP-MS. The data showed that cadmium exposure produces significant cadmium uptake in tissues. Cadmium concentrations increased sharply in kidney and liver, whereas the pollutant level in muscle was only significant after 106 days. After 127 days of Cd exposure (53 microg l(-1)), the cadmium concentration in kidney was 4-fold higher than in liver and 50-fold higher than in muscle for a toxic level of 53 microg l(-1). At a Cd of 443 microg l(-1), kidney cadmium content was 2-fold higher than in liver and 100-fold higher than in muscle. In kidney and liver, the toxic concentration increased as the concentration of pollutant in water increased. During the 43 depuration days, the loss of accumulated cadmium was rapid and immediate in muscle. Conversely, no loss of cadmium was observed in kidney and liver.