Chronic Effects of Realistic Concentrations of Non-essential and Essential Metals (Lead and Zinc) on Oxidative Stress Biomarkers of the Mosquitofish, Gambusia holbrooki

Abstract

Metallic contamination is widespread, particularly in areas impacted by human activities. Human activities result in high loads of metals being discarded into the aquatic compartment, reinforcing the need to evaluate their toxic effects especially on exposed fish. The purpose of this study was to determine the toxic response (namely, antioxidant levels and lipoperoxidative damage) in both liver and gills of the freshwater fish species Gambusia holbrooki, exposed to lead and zinc. Fish were exposed for 28 days (chronic exposure) to ecologically relevant concentrations of the selected compounds. The following oxidative stress/damage biomarkers were evaluated: glutathione-S-transferases (GSTs), glutathione reductase (GR), and thiobarbituric acid reactive substances (TBARS). The results indicate that lead caused a significant oxidative response, with significant increase of the enzymatic antioxidant defense (GSTs activity in hepatic tissue, and GR activity in branchial tissue) of exposed organisms. On the other hand, zinc caused a significant inhibition of G. holbrooki hepatic GR, a biological response that may be related to the antioxidant activity exhibited by this metal. The obtained results are of high importance, especially if one considers that the obtained toxic responses occurred at low, albeit ecologically relevant, levels of exposure.

Pollution effects on biochemical pathways determined in the polychaete Hediste diversicolor collected in three Portuguese estuaries

“…Several other aquatic organisms (namely sh, including Anguilla anguilla and Gambusia holbrooki) have already been shown to be highly responsive to metals, favoring a biological response with the involvement of specic antioxidant enzymes such as those quantied in our study. [54][55][56] Similar results were also published by Ferreira et al, 57 showing the responsiveness of the sh Diplodus sargus to metallic contamination. The overexpression of GSTs, which are a phase II group of enzymes, can be likely related to an increase of metabolic capacity, namely by conjugation with intracellular cofactors, including glutathione.…”

“…26 These metals are also well known for their effects on the enhancement of GSTs activity in several sh species, such as Anguilla anguilla, 54 and Gambusia holbrooki. 55,56 As a consequence, it is not surprising that organisms collected in the vicinity of this sampling site exhibit higher levels of GST activity. Similarly, the study by Gravato et al 24 evidenced the relationship between metal exposure and the need for increased conjugation capacity; higher activity of GST isoenzymes was reported in eels (A. anguilla) collected in the Douro River Estuary, when compared with organisms from the reference site, Minho River.…”