Exploring the endocrine disrupting potential of a complex mixture of PAHs in the estrogen pathway in Oreochromis niloticus hepatocytes.

This study aimed to investigate the toxicity and endocrine disrupting potential of a complex mixture of polycyclic aromatic hydrocarbons (PAHs) in the estrogen pathway using hepatocytes of Nile tilapia Oreochromis niloticus, the hepatocytes were exposed to various concentrations of the PAH mixture, and multiple endpoints were evaluated to assess their effects on cell viability, gene expression, oxidative stress markers, and efflux activity. The results revealed that the PAH mixture had limited effects on hepatocyte metabolism and cell adhesion, as indicated by the non-significant changes observed in MTT metabolism, neutral red retention, and crystal violet staining. However, significant alterations were observed in the expression of genes related to the estrogen pathway. Specifically, vitellogenin (vtg) exhibited a substantial increase of approximately 120% compared to the control group. Similarly, estrogen receptor 2 (esr2) showed a significant upregulation of approximately 90%. In contrast, no significant differences were observed in the expression of estrogen receptor 1 (esr1) and the G protein-coupled estrogen receptor 1 (gper1). Furthermore, the PAH mixture elicited complex responses in oxidative stress markers. While reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels remained unchanged, the activity of catalase (Cat) was significantly reduced, whereas superoxide dismutase (Sod) activity, glutathione S-transferase (Gst) activity, and non-protein thiols levels were significantly elevated. In addition, the PAH mixture significantly influenced efflux activity, as evidenced by the increased efflux of rhodamine and calcein, indicating alterations in multixenobiotic resistance (MXR)-associated proteins. Overall, these findings, associated with bioinformatic analysis, highlight the potential of the PAH mixture to modulate the estrogen pathway and induce oxidative stress in O. niloticus hepatocytes. Understanding the mechanisms underlying these effects is crucial for assessing the ecological risks of PAH exposure and developing appropriate strategies to mitigate their adverse impacts on aquatic organisms.

Multispecies and multibiomarker assessment of fish health from Iguaçu River reservoir, Southern Brazil.

This study investigated the impact of micropollutants on fish health from Segredo hydroelectric reservoir (HRS) along the Iguaçu River, Southern Brazil, contaminated by urban, industrial, and agricultural activities. This is the first comprehensive study assessment in the river after the severe drought in the 2020s in three fish species from different trophic levels Astyanax spp. (water column depth/omnivorous), Hypostomus commersoni (demersal/herbivorous), and Pimelodus maculatus (demersal/omnivorous). Animals, water, and sediment samples were collected from three distinct sites within the reservoir: Floresta (upstream), Iratim (middle), and Station (downstream). The chemical analysis revealed elevated concentrations of metals (Al, Cu, Fe) and the metalloid As in water, or Cu, Zn, and As in sediment, surpassing Brazilian regulatory limits, while the organic pollutants as DDT, PAHs, PCBs, and PBDEs were found under the Brazilian regulatory limits. The metal bioaccumulation was higher in gills with no significant differences among sites. The species Astyanax spp. and H. commersoni displayed variations in hepatosomatic index (HSI) and P. maculatus in the condition factor index (K) between sites, while adverse effects due to micropollutants bioaccumulation were observed by biochemical, genotoxic, and histopathological biomarkers. The principal component analysis and integrated biomarker response highlighted the upstream site Floresta as particularly inhospitable for biota, with distinctions based on trophic level. Consequently, this multifaceted approach, encompassing both fish biomarkers and chemical analyses, furnishes valuable insights into the potential toxic repercussions of micropollutant exposure. These findings offer crucial data for guiding management and conservation endeavors in the Iguaçu River.

Pollutant bioaccumulation in sentinel fish chronically exposed in Iguaçu river reservoirs (Southern Brazil) and human health risk of fish consumption.

Bioaccumulation studies in fish mark the initial phase of assessing the risk of chemical exposure to biota and human populations. The Iguaçu River boasting a diverse endemic ichthyofauna, is grappling with the repercussions of human activities. This study delved into the bioaccumulation of micropollutants, the early-warning effects on Rhamdia quelen and Oreochomis niloticus in the Segredo Reservoir (HRS) and the potential risk of human exposure. Two groups of caged fish in three sites of the reservoir were exposed during the autumn-winter and spring-summer, while a third group (O. niloticus) underwent a twelve-month exposure, and inorganic and organic chemicals analysis in water, sediment, and biota. Additionally, metallothionein expression and genotoxicity were employed as biomarkers. PAHs, PCBs, Al, Cu, Fe, and As in water and DDTs, Cu, Zn, and As in sediment surpassed the thresholds set by Brazilian regulations, where DDT exhibited bioaccumulation in muscle, alongside metals in liver, kidney, gills, and muscle tissues. R. quelen showed metallothionein expression whereas DNA damage and NMA frequencies were elevated in target organs and in brain and erythrocytes of O. niloticus during summer. In this species the DNA damage in liver was remarkable after twelve months. Target Hazard Quotients and Cancer Risk values shedding light on the vulnerability of both children and adults. The reservoir's conditions led to heightened sensitivity to micropollutants for R. quelen species. The data presented herein provides decision-makers with pertinent insights to facilitate effective management and conservation initiatives within the Iguaçu Basin.

Physicochemical and bioinformatic characterization of Oreochromis niloticus vitellogenin as an endocrine disruption biomarker.

Aquatic biota is increasingly being exposed to chemical pollutants due to human activities and the relationship between the level of environmental pollution and fish reproduction is a continuously ongoing issue. The vitellogenin (Vtg) protein synthesis can be induced in the liver of juvenile and male fish after stimulation of the estrogen receptor and therefore, Vtg has been used as a biomarker of xenoestrogen exposure in several fish species. The current study reported the first physicochemical characterization of Vtg from Oreochromis niloticus. Adult male fish were exposed to 17α-ethinylestradiol for Vtg induction. Purified vitellogenin from plasma showed low stability at 25 and 4 °C in saline conditions, and good stability in acidic (low pH) or in heated conditions. The 3D modeling provided useful information on the structure of O. niloticus Vtg showing conserved structural features. According to bioinformatics and experimental results, there are important structural differences between the two chemical forms of Vtg (VtgAb and VtgC) in a phylogenetic context. The present results add information about the development of ecotoxicological immunoassays to study the endocrine disruption in O. niloticus improving the Vtg performance as a biomarker of reproduction in fish.

Synthetic fish metallothionein design as a potential tool for monitoring toxic metals in water.

The diversity of aquatic ecosystems impacted by toxic metals is widely distributed throughout the world. The application of metallothionein (MT) as an early warning sign of metal exposure in freshwater fish is important in biomonitoring, but a more accessible, sensitive, safe, and efficient new methodological strategy is necessary. On this way, a fish MT synthetic gene from Oreochromis aureos was expressed in Escherichia coli to produce polyclonal antibodies against the protein. In the validation assays, these antibodies were able to detect hepatic MT from freshwater fishes Oreochromis niloticus, Pimelodus maculatus, Prochilodus lineatus, and Salminus brasiliensis showing a potential tool for toxic metals biomarker in biomonitoring of aquatic ecosystems. The current results showed the applicability of this molecule in quantitative immunoassays as a sensor for monitoring aquatic environments impacted by toxic metals. Due to the lack of methods focusing on metal pollution diagnostics in aquatic ecosystems, the current proposal revealed a promising tool to applications in biomonitoring programs of water resources, mainly in Brazil where the mining activity is very developed.