Unravelling the mechanisms of mercury hepatotoxicity in wild fish (Liza aurata) through a triad approach: bioaccumulation, metabolomic profiles and oxidative stress

Abstract

Clarification of the mechanisms of mercury (Hg) toxicity in fish remains challenging. An innovative approach to this clarification is the combined assessment of metabolomic shifts, alterations in the antioxidant system and the risk of oxidative damage, and Hg bioaccumulation. This strategy was applied to the livers of golden grey mullet (Liza aurata) inhabiting an Hg-contaminated system in Aveiro Lagoon, Portugal. Marked changes in both the metabolic profile and the response to antioxidants were observed in fish exposed to Hg in the environment, indicating their compromised state of health. The metabolomics analysis showed a clear differentiation between the contaminated and uncontaminated areas, revealing that Hg has multiple levels of impact, including membrane stabilization/degradation/repair processes, osmoregulation, energy metabolism, gene expression and antioxidant protection. Research on oxidative stress biomarkers showed that Hg triggered adaptive responses in the antioxidant system as seen by an increase in the activities of glutathione-S-transferase and catalase, as well as the total glutathione content, which compensated for a decrease in glutathione peroxidase activity. The integration of metabolomics and oxidative stress endpoints allowed the identification of reduced glutathione as a first line of defence against Hg and evidenced oxidative insults in cell membranes, recognized through the increase in phosphatidylcholine degradation products (phosphocholine and glycerophosphocholine). Despite these effects, the induction of lipid peroxidation was efficiently prevented. The triad approach used here was demonstrated to be sensitive and effective towards a mechanistically based assessment of Hg hepatotoxicity in fish.

Integrated spatial health assessment of yellow perch (Perca flavescens) populations from the St. Lawrence River (QC, Canada), part B: cellular and transcriptomic effects

“…However, in a recent study, antioxidant enzyme activities of glutathione-Stransferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH) were found to be significantly induced in yellow perch exposed in vivo to Cu and Cd (Defo et al 2015). Similar results were also observed in golden grey mullets (Liza aurata) exposed to Hg, with an increased activity of antioxidant enzymes, which resulted in the prevention of lipid peroxidation (Brandao et al 2015). Inconsistent relationship between transcriptional and the related biochemical responses have often been reported for antioxidant enzymes in aquatic organisms.…”

Insights into neurosensory toxicity of mercury in fish eyes stemming from tissue burdens, oxidative stress and synaptic transmission profiles

“…In agreement, current data revealed an increment of ocular GSHt (summer) in fish exposed to Hg, probably as a manifestation of a protective and adaptive response. Though only total glutathione was determined in the current work, the hypothesis that it can reflect an increase of GSH pool is very plausible based on the direct relation already found between total and reduced glutathione in liver of L. aurata exposed to Hg [Brandão et al, 2015]. In summer, no LPO occurred despite the accumulation of iHg and MeHg in eye wall.…”

Shannon Entropy in a European Seabass (Dicentrarchus labrax) System during the Initial Recovery Period after a Short-Term Exposure to Methylmercury

“…Optimally, the behavior of each species should be tested. Furthermore, it must be considered that inorganic Hg is also a relevant environmental contaminant, and, while its physiological effects have been studied in different species and tissues [24][25][26], its effect on the SE of the fish system should also be mapped in future works.…”