Melatonin affects conjugation of 4-hydroxynonenal with glutathione in liver of pacu, a hypoxia-tolerant fish.

In cytosol from liver of pacu, Piaractus mesopotamicus, a hypoxia-tolerant fish that dwells in Pantanal, we found an enzyme activity capable of modulating the alkenal 4-hydroxy-2-nonenal (HNE) by conjugating it with glutathione (GST-HNE activity). HNE is a downstream metabolite from the oxidation of polyunsaturated fatty acids by reactive oxygen species arisen from mitochondria of animal cells. HNE production may increase more intensively under oxidative stress. Harmful effects to cell survival may occur when HNE increases over 10(-4) M. Pacus submitted to hypoxia in July (cold season in Pantanal) showed 40% less of this GST-HNE conjugating activity in their liver cytosol. Injecting pacus subjected to hypoxia during the cold season with a summer physiological dose of melatonin caused their liver cytosolic GST-HNE activity to increase up to the levels found in the warm season. From October to March (warm season in Pantanal), pacus are prone to oxidative stress particularly during potamodromous active oxygen-demanding swimming, when they migrate up rivers to spawn. Thus, our findings point out that the higher levels of melatonin in circulation during the summer are important to avoid the increase of 4-HNE inside liver cells of this fish species.

Enzymatic GST levels and overall health of mullets from contaminated Brazilian Lagoons.

Glutathione S-transferase (GST) assays in non-mammalian organisms are usually conducted inappropriately, since no previous standardization of the optimal concentrations of proteins and substrates and adequate pH is conducted. Standardization is a key task to adjust enzyme assays at their kinetically correct maximal initial velocities, if one wants these velocities to indicate the amount of enzyme in a sample. In this paper GST assays were standardized in liver cytosol to compare seasonal GST levels in liver of mullet from two contaminated lagoons in the Rio de Janeiro to those from a reference bay. GST potential as a biomarker of sublethal intoxication in this species was also evaluated. Mullet liver GST levels assayed with substrates that corresponded to three different GST isoenzymes varied throughout the year. The differences indicated that mullets are suffering from sublethal intoxication from contaminants in these lagoons. Seasonal variations of activity were relevant, since these could indicate differences in xenobiotic input into the areas. An analysis of overall mullet health condition using a morphological index (the Fulton Condition Factor) and macroscopic abnormalities corroborated the differences in GST levels, with fish from one of the sites in worse overall health condition showing lower and significantly different FCF when compared to the reference site. Therefore, GST standardized activity levels are useful biomarkers of environmental contamination for mullet.