The role of metallothionein (MT) in the scavenging of superoxide radicals (˙O2–) generated by macrophages has been examined. The present work has focused on the effects of added cadmium, a known ...inducer of MT biosynthesis, on determined amounts of superoxide radicals produced by in vitro cultured rat peritoneal macrophages on their stimulation with phorbol‐12‐myristate‐13‐acetate (PMA). The levels of superoxide radicals (˙O2–) have been found to decrease when cadmium was added to cells exposed to PMA. However, substantially lower levels of MT have been determined in this case compared to cells untreated with PMA. This effect could be reversed by incubation of the PMA and cadmium‐treated cells with a reducing agent, 2‐mercaptoethanol (2‐ME). Results suggest that ˙O2– caused thiolate oxidation and subsequent metal loss, thus reducing the cellular MT content as quantified by the silver saturation method. This conclusion is supported by cell‐free experiments in which the oxidation of rabbit MT‐I by a xanthine/xanthine–oxidase system could be reversed by its subsequent reduction with 2‐ME. The data presented provide direct evidence of the involvement of MT in scavenging superoxide radicals in living cells.
Biochemical characterization of cholinesterase activity (ChE) was carried out on the Antarctic scallop Adamussium colbecki collected in winter 2000 from Campo Icaro (Ross Sea, Antarctica) in order to ...increase its suitability as a sentinel organism for monitoring the Antarctic environment. The digestive gland, gills and adductor muscle were investigated for substrate specificity and inhibitors sensitivity using acetylthiocholine iodide (ASCh) and butyrylthiocholine iodide (BSCh) as substrates and tetra (monoisopropyl)pyrophosphor-tetramide (Iso-OMPA), 1,5-bis(4-allyldimethylammoniumphenyl)-penthan-3-one dibromide (BW284c51) and the insecticide chlorpyrifos as inhibitors. Effect of in vivo exposure to ZnCl(2) was also investigated. All the tissues expressed ChE activity (gill > adductor muscle > digestive gland) and low substrates specificity throughout the hydrolysis of both ASCh and BSCh substrates. Partial (25-29%) and total inhibition (100%) of ChE activity in gills was demonstrated following in vitro incubation with Iso-OMPA and BW284c51 (3 mM), respectively. Concentration-dependent inhibition was also evident with chlorpyrifos in the range 10(-4)-10(-10) M (IC(50) 10(-6)) while in vivo exposure to ZnCl(2) did not seem to affect ChE activity in the scallop. The potential use of ChE in the A. colbecki as biomarker for monitoring water contamination in the marine Antarctic environment is discussed.
The aim of the present work was to determine the activities of selected antioxidant enzymes (SOD, Se-GPX, CAT) in two species of bivalves,
Scapharca inaequivalvis and
Tapes philippinarum, from two ...sites of the lagoon of Venice that are characterized by different pO
2 (Marghera and Chioggia). The specimens were collected at four times during a 1-year period.
In the two species studied, enzyme activities were found to be present in both digestive glands and gills, but with some species-specific differences that may also represent a different adaptation to seasonal variations. The presence of high SOD activities in the gills of both species may be related to their physiological role in respiration.
Scapharca inaequivalvis is less sensitive than
T. philippinarum to environmental changes, perhaps due to the presence of hemoglobins in this species. Moreover, in the digestive gland of
T. philippinarum we found a significant negative correlation between the activities of SOD and GPX that may indicate the presence of oxidative stress.
Some correlations between temperature/dissolved oxygen and antioxidant enzyme activity were present in specimens sampled in Marghera. Only GPX adequately responded to changes in dissolved oxygen and temperature, while the decrease in the activity of SOD and CAT in winter may be directly responsible for an enhanced susceptibility of mussels to oxidative stress during this period.
We can conclude that the observed differences between Chioggia and Marghera are due to different concentrations of dissolved oxygen. Marghera is an appropriate location to study seasonal variations in water temperature. In fact, in this site, the differences between hot and cold months are quite evident.
Cd-dependent regulation of MT expression in
Tetrahymena pigmentosa and
T. pyriformis was investigated by measuring MT-mRNA and MT accumulation in response to chronic exposure to subtoxic doses of the ...metal. MT synthesis occurs very soon and MT content increases progressively with Cd accumulation in both species. The induction of MT-mRNA in response to Cd is very rapid, with no observable lag period. At the beginning of exposure, very small amounts of intracellular Cd are sufficient to induce a strong response. Maximum levels of MT-mRNA induction, more than 40-fold, occurred within 30 min of metal treatment in
T. pigmentosa. This maximum induction was then followed by down-regulation to 20-fold above the original basal level over the next 30 min. In
T. pyriformis, the MT-mRNA maximum level was reached after 60 min, followed by a slow decrease to about 25-fold the basal level within 24 h. This transient fluctuation of mRNA levels is similar to those in other organisms. The data emphasise the importance of an efficient detoxification pathway by complex Cd regulation of MT transcription, which enables
Tetrahymena to survive in the continued elevated presence of toxic ions in the environment.
Physiological responses of
Mytilus galloprovincialis against environmental dissolved oxygen partial pressure (
pO
2) variation were studied in terms of the modulated induction of the main antioxidant ...enzymes: superoxide dismutase (SOD), catalase (CAT) and selenium-dependent glutathione peroxidase (GPX). Field in vivo studies were performed at two sites of the Lagoon of Venice, characterized by different aquatic environmental conditions implying different
pO
2. SOD and GPX are more active in gills, and their complementary role is discussed. CAT is more active in the digestive gland, where the enzyme dismutates H
2O
2 derived from divalent reduction of O
2 performed by various oxidases in peroxisomes. Antioxidant enzyme activities are correlated with water dissolved oxygen (DO), especially in the gills. This tissue, because of its anatomical localization and its physiological role, responds to DO variations modulating the induction of the antioxidant enzymes as a protection mechanism against potential toxicity due to increases in ROS formation.
The aims of the work presented here were to determine the effect of long term treatment with zinc (Zn) on both total metallothionine (MT) and, in particular, oxidized MT (MTox) concentrations in ...Long-Evans Cinnamon (LEC) rat liver. We also evaluated semi-quantitatively the cell death index using TUNEL assay as it is a useful method to localize the nuclear fragmentation occurring in oxidative stress conditions. The results demonstrate there were no statistically different MT concentrations between Zn-treated and untreated rats, whereas the Zn treatment was very effective in reducing the percentage of oxidized MT (MTox). MTox is not able to bind metals, so it does not perform its "scavenger" action against copper (Cu) accumulation in LEC rats. The intensity and quantity of fluorescent staining observed in untreated rat sections decreased compared to the treated ones. These findings suggest that in LEC rats one of zinc's roles is to protect from oxidative stress, however, its mode of action remains partially unknown: a hypothesis is competition for Cu binding sites. A new insight is that Zn induced MT can protect efficiently against DNA damage by free radicals.
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