Bioaccumulation and effects of metals on oxidative stress and neurotoxicity parameters in the frogs from the Pelophylax esculentus complex

Ecotoxicological effects of the emerging contaminant ivermectin on Rhinella arenarum: A comparative study of active ingredient and commercial formulation

Ivermectin (IVM) is a broad-spectrum veterinary antiparasitic used worldwide in cattle breeding. The aim of this study was to evaluate the lethal effects of the active ingredient and a commercial formulation of IVM (1 % active ingredient) in the embryonic stage (S. 4-6) and larval stage (S. 25) of the South American amphibian Rhinella arenarum through chronic standardized bioassays. Also, behavior analysis and oxidative stress and cholinergic effects biomarkers were analyzed at 1, 10 and 100 μg IVM/L concentrations. For the embryonic stage, the active ingredient (96 h- LC50: 15900 μg/L) was more toxic than the commercial formulation (96 h-LC50: 51230 μg/L) during the acute period, while at chronic exposure the commercial formulation was more toxic (504 h-LC50: 10.25 μg/L), compared to the active ingredient (504 h-LC50: 312.80 μg/L). For the larval stage, in acute exposure, the active ingredient (96 h-LC50: 800 μg/L) was more toxic than the commercial formulation (96 h-LC50: 1550 μg/L). In the chronic exposure, the commercial formulation (504 h-LC50: 77.33 μg/L) was more toxic than the active ingredient (504 h-LC50: 195.25 μg/L). Overall, larvae exhibited greater sensitivity to both the active ingredient and the commercial formulation. However, during chronic exposure, embryos were more sensitive to the commercial formulation than larvae. The commercial formulation primarily induced oxidative stress, and both forms of the compound affected behavior and cholinergic effect biomarkers, even at low environmentally relevant concentrations (1 μg/L). These results highlight the potential impact of IVM on aquatic ecosystems.

Evidence for a metal disease refuge: The amphibian-killing fungus (Batrachochytrium dendrobatidis) is inhibited by environmentally-relevant concentrations of metals tolerated by amphibians

The amphibian-killing fungus Batrachochytrium dendrobatidis (Bd) has caused substantial declines in Bd-susceptible amphibian species worldwide. However, some populations of Bd-susceptible frogs have managed to survive at existing metal-polluted sites, giving rise to the hypothesis that frogs might persist in the presence of Bd if Bd is inhibited by metals at concentrations that frogs can tolerate. We tested this hypothesis by measuring the survival of Bd zoospores, the life stage that infects amphibians, and calculated the LC50 after exposure to environmentally-relevant elevated concentrations of copper (Cu), zinc (Zn), and their combination (Cu + Zn) in two repeated 4-day acute exposure runs. We also measured the chronic sensitivity of Bd to these metals over three generations by measuring the number of colonies and live zoospores and calculating EC50 concentrations after 42 days of exposure. We then compared acute and chronic sensitivity of Bd with amphibian sensitivities by constructing species sensitivity distributions (SSDs) using LC50 and EC50 data obtained from the literature. Acute sensitivity data showed that Bd zoospore survival decreased with increasing metal concentrations and exposure durations relative to the control, with the highest LC50 values for Cu and Zn being 2.5 μg/L and 250 μg/L, respectively. Chronic exposures to metals resulted in decreased numbers of Bd colonies and live zoospores after 42 days, with EC50 values of 0.75 μg/L and 1.19 μg/L for Cu and Zn, respectively. Bd zoospore survival was 10 and 8 times more sensitive to Cu and Zn, respectively in acute, and 2 and 5 times more sensitive to Cu and Zn in chronic exposure experiments than the most sensitive amphibian species recorded. Our findings are consistent with the hypothesis that metals in existing metal-polluted sites may have a greater impact on Bd relative to amphibians' performance, potentially enabling Bd-susceptible amphibians to persist with Bd at these sites.

Glutathione-Mediated Metal Tolerance in an Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis)

The spread of the amphibian chytrid fungus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis, has resulted in amphibian declines and extinctions worldwide. Some susceptible amphibian species can persist in contaminated habitats, prompting the hypothesis that B. dendrobatidis might be sensitive to heavy metals. We tested a panel of 12 metals to rank their toxicity to B. dendrobatidis zoospores and zoosporangia during a 6-h exposure. To better understand the mechanism for metal detoxification, we also evaluated whether glutathione is required for metal tolerance by depleting cellular glutathione before metal exposure. In addition, we investigated whether prior exposure to low metal concentrations impacted tolerance of subsequent exposure, as well as identifying metal combinations that may act synergistically. Silver (Ag), cadmium (Cd), and copper (Cu) were particularly toxic to B. dendrobatidis, with zoospore minimum lethal concentration values of 0.01 mM (Ag), 0.025 mM (Cd), and 0.5 mM (Cu). These three metals along with zinc (Zn) were also inhibitory to zoosporangia, with minimum inhibitory concentration values of 0.005 mM (Ag), 0.04 mM (Cd), 0.075 mM (Cu), and 0.04 mM (Zn). The fungicidal effects of several metals was reduced when assays were conducted in nutrient medium compared with synthetic pond water, highlighting the need for careful in vitro assay design and interpretation. Glutathione depletion strongly influenced tolerance of Cd and Ag (85% and 75% less growth, respectively) and moderately influenced tolerance of Cu, Zn, and lead (37%, 18%, and 14% less growth, respectively), indicating the importance of glutathione for metal detoxification. In general, the minimum metal concentrations that inhibited growth of B. dendrobatidis far exceeded values detected in contaminated amphibian habitats in Australia, suggesting that metal contamination alone may not have a strong protective effect against chytridiomycosis. We discuss future research directions to futher understand the potential for dissolved metals to create chytrid refuges. Environ Toxicol Chem 2024;43:1583-1591. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Oxidative stress and neurotoxicity induced by exposure to settleable atmospheric particulate matter in bullfrog tadpoles, Aquarana catesbeiana, (Shaw, 1802)

Bullfrog tadpoles, Aquarana catesbeiana, were exposed to settleable particulate matter (SePM), (1 g L-1, 96 h) and their organs were collected for analysis of metal/metalloid, oxidative stress and neurotoxicity in liver, muscle, kidney and brain. The SePM water of the exposed groups contained 18 of the 28 metals/metalloids detected in ambient particulate matter (APM). Fe56 and Al were those that presented the highest concentrations, Cr, Mn, Pb and Cu increased from 10 to 20 times and Ti, V, Sr, Rb, Cd, Sn and Ni increased from 1 to 3 times compared to the control. Bioaccumulation of metals/metalloids in the exposure water varied significantly between organs, with the muscle and liver showing the highest concentrations of metals, followed by the brain. Lipoperoxidation and malondialdehyde increased only in muscle, while carbonyl proteins increased only in the liver and brain. Regarding nitric oxide synthase, there was an increase in the liver and brain in the group exposed to SePM. Catalase activity decreased in the liver and muscle, while the activity of glutathione peroxidase, increased in the liver and kidney and decreased in muscle. Glutathione S-transferase, which is mainly responsible for detoxification, increased in the liver and decreased in muscle and the kidney. Cholinesterase activity increased only in the muscle. The results indicate oxidative stress, due to oxidation catalyzed by metals, components of SePM. Thus, the results contribute to the understanding that SePM has a deleterious effect on the aquatic environment, negatively affecting bullfrog tadpoles, in different ways and levels in relation to the analyzed organs.

Microplastic prevalence in anatolian water frogs (Pelophylax spp.)

Frogs are on the verge of extinction due to various biotic and abiotic stressors. Rivers, lakes, ponds, wetlands, and ditches that make up their habitats are exposed to different anthropogenic pollutants. Today, plastics stand out among these pollutants due to their widespread use; however, the information on microplastic (MP) accumulation in frogs is insufficient. In the present study, adult frog samples were collected from 19 different stations in Türkiye, including marsh frogs (Pelophylax ridibundus) from 18 stations and levantine frogs (Pelophylax bedriagae) from 1 station. MP was found in 147 (82.4%) of the 176 frogs that were analyzed. MP abundance in frogs varied between 0.20 and 18.93 MP individual^-1. The characterization of MPs was determined predominantly as follows; PET (70.1%) in polymer type, fiber (92.2%) in shape, navy blue/blue (76.1%) in color, and >90% were smaller than 300 μm. No significant relationship with frog's weight (correlation coefficient = 0.01, P = 0.812) or length (correlation coefficient = 0.06, P = 0.473) and MP abundance was detected. The outcomes of this survey might be a baseline to assess the ecological risks posed by MPs and to guide future experimental research.

Stress Response, Immunity, and Organ Mass in Toads (Rhinella diptycha) Living in Metal-Contaminated Areas

Mining is one of the main activities that drive the economy of Brazil. Mining activity is associated with risk of contamination of environment and local fauna by metals. Amphibians have a life cycle that requires a transition between aquatic and terrestrial environments, increasing their vulnerability to metal contamination in the water and substrate. Metals are ubiquitous, with high bioaccumulative and biomagnifying potential, and may lead to immune and endocrine disruption. In this study, we analyzed two different components of the innate immune response, bacterial killing ability (BKA) and phytohemagglutinin edema (PHA), and two stress biomarkers, corticosterone plasma levels (CORT) and the neutrophil to lymphocyte ratio (N:L), of toads (Rhinella diptycha) living in places contaminated by metals. Blood samples were collected pre- and post-restraint (1h), followed by an immune challenge with PHA and tissue collection (liver, spleen, and kidneys). Toads liver metal bioaccumulation did not correlate with the immune response or stress biomarkers. Post-restraint, animals had increased CORT and reduced BKA, independently of the collection site, and these variables were not correlated with liver metal bioaccumulation. Interestingly, toads with the larger spleen (immune organ) showed increased N:L post-restraint and greater edema after the PHA challenge. Our results indicate that toads living in metal-contaminated environments responded to acute stressor, activating the hypothalamic-pituitary-interrenal axis and the immune response. Keep tracking the physiological variables of these animals and the presence of metals in the environment and tissues should provide valuable health status indicators for the population, which is vital for proposing amphibian conservation strategies in these areas.

Ecotoxicological evaluation of water from the Sorocaba River using an integrated analysis of biochemical and morphological biomarkers in bullfrog tadpoles, Lithobates catesbeianus ()

Lithobates catesbeianus tadpoles were exposed for 96 h to water from two sites of the Sorocaba River (summer and winter), Ibiúna (PI) and Itupararanga reservoir (PIR) that contained metals. In the liver, in PI, the glutathione peroxidase (GPx) decreased, and the glutathione S-transferase (GST) and carbonyl proteins (PCO) increased. In PIR, the glutathione reduced (GSH) increased, while there was a decrease in catalase (CAT), GPx, GST, PCO, and superoxide dismutase (SOD). In winter, GPx and GST increased in both points. Regarding the kidneys, lipoperoxidation (LPO) levels and GST decreased, while GSH increased in the summer. In the winter, LPO increased in PI. In the muscle, in the summer, there was an increase in GSH and GST and change in PCO. In the winter, the levels of PCO increased and CAT decreased in PIR. The area and volume of the hepatocyte and nucleus area increased in the summer and decreased in the winter. Hepatic melanin decreased in the summer after exposure to PIR water. There were the systemic effects of Sorocaba River water exposure at different times of the year with alterations in biomarkers at different levels, in which kidney shows highest Integrated Response of Biomarkers (IBR) value followed by liver and muscle. Biochemical biomarkers were more sensitive than morphological ones. The more sensitive biochemical markers were MT, PCO, GST and LPO. These effects confirm the hypothesis of metabolic alteration in bullfrog tadpoles by the Sorocaba River water.

Assessment of antioxidant system, cholinesterase activity and histopathology in Lithobates catesbeianus tadpoles exposed to water from an urban stream

Anthropogenic activities promote changes in community structure and decrease the species abundance of amphibians. The aim of this study was to assess potential alterations in the antioxidant system and cholinesterase activity, histopathological and oxidative damage in Lithobates catesbeianus tadpoles exposed to water from the Cascavel River, in Southern Brazil. Water samples (140 L each) were collected from the headwater, urban and rural areas of the river. Tadpoles were acclimated for seven days. After acclimatization tadpoles were reared in water from the river, except for the control aquarium. After seven days, a portion of the liver was removed and prepared for cholinesterase (ChE), superoxide dismutase (SOD), catalase (CAT) and lipid peroxidation (LPO) analysis; another part of the tissue was prepared for histological examination. An elevation of CAT activity was observed for water from both urban and rural environments. A decrease in LPO reaction was detected, mainly among the tadpoles exposed to water from the rural area. These alternations can cause delay the metamorphosis and lead to metabolic dysfunction, interfering in survival capacity and diminishing, not only individual fitness, but that of the whole population.

Antioxidative Defense and Fertility Rate in the Assessment of Reprotoxicity Risk Posed by Global Warming

The objective of this review is to briefly summarize the recent progress in studies done on the assessment of reprotoxicity risk posed by global warming for the foundation of strategic tool in ecosystem-based adaptation. The selected animal data analysis that was used in this paper focuses on antioxidative markers and fertility rate estimated over the period 2000-2019. We followed a phylogenetic methodology in order to report data on a panel of selected organisms that show dangerous effects. The oxidative damage studies related to temperature fluctuation occurring in biosentinels of different invertebrate and vertebrate classes show a consistently maintained physiological defense. Furthermore, the results from homeothermic and poikilothermic species in our study highlight the influence of temperature rise on reprotoxicity.

Toxicity of wine effluents and assessment of a depuration system for their control: assay with tadpoles of Rhinella arenarum (BUFONIDAE)

We evaluated the toxicity of the winery effluent and the efficiency of a symbiotic depuration system by means an experiment with Rhinella arenarum tadpoles. The studied effluent was taken from warehouses during the cleaning season. These effluents subsequently subjected to the purification treatment under evaluation. The effluent samples differentiated into two treatment levels: "raw" where the effluent was evaluated with field conditions and "treated" where the effluent was previously filtered with the symbiotic depuration system. The results of the bioassays compared with the physicochemical parameters determined in the effluent samples. The lethal response had a clear-cut correspondence with the effluent quality assessed utilizing physicochemical parameters. In all cases, dilution of the samples resulted in a significant reduction of their toxicity. It concluded that (a) winery effluents could be harmful to tadpoles of R. arenarum, (b) the symbiotic purification system used to treat wine effluents it would produce a significant reduction in the contaminant levels of the effluent. However, this reduction in contaminant levels does not provide sufficient safety for the release of the effluents into the environment.

Cu2−xSe nanoparticles (Cu2−xSe NPs) mediated neurotoxicityviaoxidative stress damage in PC-12 cells and BALB/c mice

Cu_2−xSe nanoparticles (Cu_2−xSe NPs) are widely used for optical diagnostic imaging and photothermal therapy due to their strong near-infrared (NIR) optical absorption. With the continuous expansion of applications using Cu_2−xSe NPs, their biosafety has received increasing attention in recent years. Cu_2−xSe NPs can enter the brain by crossing the blood–brain barrier, but the neurotoxicity of NPs remains unclear. The present investigation provides direct evidence that the toxicity of Cu_2−xSe NPs can be specifically exploited to kill rat pheochromocytoma PC-12 cells (a cell line used as an in vitro model for brain neuron research) in dose- and time-dependent manners. These cytotoxicity events were accompanied by mitochondrial damage, adenosine triphosphate (ATP) depletion, production of oxidizing species (including reactive oxygen species (ROS), malondialdehyde (MDA) and hydrogen peroxide (H₂O₂)), as well as reductions in antioxidant defense systems (glutathione (GSH) and superoxide dismutase (SOD)). Moreover, our in vivo study also confirmed that Cu_2−xSe NPs markedly induced neurotoxicity and oxidative stress damage in the striatum and hippocampal tissues of BALB/c mice. These findings suggest that Cu_2−xSe NPs induce neurotoxicity in PC-12 cells and BALB/c mice via oxidative stress damage, which provides useful information for understanding the neurotoxicity of Cu_2−xSe NPs.

Cu_2−xSe nanoparticles (Cu_2−xSe NPs) are widely used for optical diagnostic imaging and photothermal therapy due to their strong near-infrared (NIR) optical absorption.

Electron Spin Resonance (ESR) for the study of Reactive Oxygen Species (ROS) on the isolated frog skin (Pelophylax bergeri): A non-invasive method for environmental monitoring

BACKGROUND

Reactive oxygen species (ROS) in biological tissues of elected biosentinels represent an optimal biomarker for eco-monitoring of polluted areas. Electron spin resonance (ESR) is the most definitive method for detecting, quantifying and possibly identifying radicals in complex systems.

OBJECTIVE

A non-invasive method for monitoring polluted areas by the quantitative determination of ROS in frog skin biopsy is presented.

METHODS

We assessed by ESR spectroscopy the ROS level in adult male of Pelophylax bergeri, specie not a risk of extinction, collected from the polluted Sarno River (SA, Italy) basin. The spin-trap ESR method was validated by immunohistochemical analysis of the well-assessed pollution biomarkers cytochrome P450 aromatase 1A (CYP1A) and glutathione S-transferase (GST), and by determining the poly(ADPribose) polymerase (PARP) and GST enzymatic activity.

RESULTS

ROS concentration in skin samples from frogs collected in the polluted area is significantly higher than that determined for the unpolluted reference area. Immunohistochemical analysis of CYP1A and GST supported the reliability of our approach, even in the absence of evident morphological and ultrastructural differences. PARP activity assay, connected to possible oxidative DNA damage, and the detoxification index by GST enzymatic assay give statistically significant evidence that higher levels of ROS are associated to alterations of the different biomarkers.

CONCLUSIONS

ROS concentration, measured by ESR on isolated frog skin, through the presented non-lethal method, is a reliable biomarker for toxicity screening and represents a useful basic datum for future modelling studies on environmental monitoring and biodiversity loss prevention.

Oxidative stress parameters in two Pelophylax esculentus complex frogs during pre- and post-hibernation: Arousal vs heavy metals

In spring, frogs from temperate regions are faced with arousal-induced oxidative stress and exposure to various xenobiotics from the environment. The question is whether pollutants can significantly modify the antioxidative defense system (AOS) response of hibernators during recovery from hibernation. If this assumption is true, we would then expect different patterns of seasonal variations in the AOS between individuals exposed to different levels of pollution. To examine this assumption, we determined the relationship between seasonal variations of accumulated metals and AOS parameters in the skin and muscle of two frog species from the Pelophylax esculentus complex (P. ridibundus and P. esculentus) inhabiting two localities (the Danube-Tisza-Danube canal and the Ponjavica River) with different levels of pollution during pre- and post-hibernation periods, respectively autumn and spring. Our results showed that even though there were differences in the concentrations of accumulated metals and AOS parameters between localities and species, the frogs displayed almost the same patterns of AOS variations during seasons, with a higher AOS response observed in spring. The parameters SH groups, GSH, GR and SOD had been contributed most rather than others. Our findings indicate that oxidative stress during the post-hibernation period was mainly caused by the organisms' recovery from hibernation, as the result of natural selection acting on the AOS, and that the accumulated metals did not significantly modify the AOS response. The present study provides new insight into the biological and physiological cellular responses of frogs to arousal stress.