Effects of environmental pollution on the liver parenchymal cells and Kupffer-melanomacrophagic cells of the frog Rana esculenta

Estrogen contamination increases vulnerability of amphibians to the deadly chytrid fungus

Aquatic contaminants and infectious diseases are among the major drivers of global amphibian declines. However, the interaction of these factors is poorly explored and could better explain the amphibian crisis. We exposed males and females of the Brazilian Cururu Toad, Rhinella icterica, to an environmentally relevant concentration of the estrogen 17-alpha-ethinylestradiol (an emerging contaminant) and to the chytrid infection (Batrachochytrium dendrobatidis), in their combined and isolated forms, and the ecotoxicity was determined by multiple biomarkers: cutaneous, hematological, cardiac, hepatic, and gonadal analysis. Our results showed that Cururu toads had many physiological alterations in response to the chytrid infection, including the appearance of cutaneous Langerhans's cells, increased blood leukocytes, increased heart contraction force and tachycardia, increased hepatic melanomacrophage cells, which in turn led to gonadal atrophy. The estrogen, in turn, increased the susceptibility of the toads to the chytrid infection (higher Bd loads) and maximized the deleterious effects of the pathogen: reducing leukocytes, decreasing the contraction force, and causing greater tachycardia, increasing hepatic melanomacrophage cells, and leading to greater gonadal atrophy, which were more extreme in females. The exposure to estrogen also revealed important toxicodynamic pathways of this toxicant, as shown by the immunosuppression of exposed animals, and the induction of the first stages of feminization in males, which corroborates that the synthetic estrogen acts as an endocrine disruptor. Such an intricate relationship is unprecedented and reinforces the importance of studying the serious consequences that multiple environmental stressors can cause to aquatic populations.

Prednisone and prednisolone effects on development, blood, biochemical and histopathological markers of Aquarana catesbeianus tadpoles

Synthetic glucocorticoids are often found in surface waters and can cause harmful effects to aquatic organisms such as amphibians. In this work we evaluated the effects of the drugs prednisone (PD) and prednisolone (PL) on developmental, molecular, blood, biochemical and histological markers. Aquarana catesbeianus tadpoles were exposed for 16 days to environmentally relevant concentrations of 0, 0.1, 1 and 10 µg/L of both drugs. PD increased the transcript levels of the enzyme deiodinase III (Dio3), the hormones cortisol and T4 and delayed development. Changes in the thyroid gland occurred after tadpoles were exposed to both drugs, with a reduction in the diameter and number of follicles and an increase/or decrease in area. Also, both drugs caused a decrease in lymphocytes (L) and an increase in neutrophils (N), thrombocytes, the N:L ratio and lobed and notched erythrocytes. Increased activity of the enzymes superoxide dismutase, glutathione S-transferase and glucose 6-phosphate dehydrogenase was observed after exposure to PD. Furthermore, both drugs caused an increase in the activity of the enzymes catalase and glutathione peroxidase. However, only PD caused oxidative stress in exposed tadpoles, evidenced by increased levels of malondialdehyde and carbonyl proteins. Both drugs caused an increase in inflammatory infiltrates, blood cells and melanomacrophages in the liver. Our results indicate that PD was more toxic than PL, affecting development and causing oxidative stress.

The Use of Multiple Biomarkers to Assess the Health of Anuran Amphibians in the Brazilian Cerrado Savanna: An Ecotoxicological Approach

Changes in the natural landscape and the indiscriminate use of pesticides can have a major impact on aquatic environments and have contributed to the worldwide decline of amphibian populations. In the present study, we sampled tadpoles of three anuran amphibians (Boana albopunctata, Physalaemus cuvieri, and Dendropsophus minutus) from ponds in six different agricultural landscapes of the Brazilian Cerrado savanna and evaluated whether and to what extent genotoxic and mutagenic damage was related to land use (the amount of forest and agricultural remnants, and related physicochemical factors) and the presence of pesticides in the water of the study ponds. We also evaluated the hepatotoxicity in P. cuvieri, which was the most abundant species at five of the six sampling points. Clomazone and atrazine were the most common pesticides found in the ponds. The B. albopunctata and P. cuvieri tadpoles presented similar patterns of DNA damage among the sampling points. The least DNA damage was found in the D. minutus tadpoles, although this species was present in only one of the study ponds. More binucleated and anucleated cells were observed in B. albopunctata, but there was no significant variation among species in terms of the number of micronuclei or other erythrocytic nuclear abnormalities. Land use and physicochemical factors did not explain the variation in the DNA damage observed in the three anurans. The hepatotoxicity analyses of P. cuvieri revealed the presence of a series of alterations, including the enlargement of the sinusoids, vacuolization of the hepatocytes, the infiltration of inflammatory cells, hepatic steatosis, and dilation of the blood vessels. The interaction between physicochemical factors and the biomarkers analyzed in the present study is complex. In particular, it will be important to better elucidate which factors are contributing, either directly or indirectly, to the decline of anuran amphibian populations, especially in threatened biomes, such as the Brazilian Cerrado. In this case, we would encourage further in situ studies that assess the ecotoxicology of the landscape, together with the systematic monitoring of aquatic environments, to guarantee the long-term integrity of amphibian populations, and those of other organisms that play an essential functional role in the ecosystem. Environ Toxicol Chem 2023;42:2422-2439. © 2023 SETAC.

Adverse effects and potential mechanisms of fluxapyroxad in Xenopus laevis on carbohydrate and lipid metabolism

Fungicides are one of significant contributing factors to the rapid decline of amphibian species worldwide. Fluxapyroxad (FLX), an effective and broad-spectrum succinate dehydrogenase inhibitor fungicide, has attracted major concerns due to its long-lasting in the environment. However, the potential toxicity of FLX in the development of amphibians remains mostly unknown. In this research, the potential toxic effects and mechanisms of FLX on Xenopus laevis were investigated. In the acute toxicity test, the 96 h median lethal concentration (LC₅₀) of FLX to X. laevis tadpoles was 1.645 mg/L. Based on the acute toxicity result, tadpoles at the stage 51 were exposed to 0, 0.00822, 0.0822, and 0.822 mg/L FLX during 21 days. Results demonstrated that FLX exposure led to an apparent delay in the growth and development of tadpoles and associated with severe liver injury. Additionally, FLX induced glycogen depletion and lipid accumulation in the liver of X. laevis. The biochemical analysis of plasma and liver indicated that FLX exposure could perturb liver glucose and lipid homeostasis by altering enzyme activity related to glycolysis, gluconeogenesis, fatty acid synthesis, and oxidation. Consistent with the biochemical result, FLX exposure altered the liver transcriptome profile, and the enrichment analysis of differential expression genes highlighted the adverse effects of FLX exposure on steroid biosynthesis, PPAR signaling pathway, glycolysis/gluconeogenesis, and fatty acid metabolism in the tadpole liver. Overall, our study was the first to reveal that sub-lethal concentrations of FLX could induce liver damage and produce obvious interference effects on carbohydrate and lipid metabolism of Xenopus, providing new insight into the potential chronic hazards of FLX for amphibians.

Exposure to ionizing radiation and liver histopathology in the tree frogs of Chornobyl (Ukraine)

Ionizing radiation has the potential to damage organic molecules and decrease the health and survival of wildlife. The accident at the Chornobyl Nuclear Plant (Ukraine, 1986) led to the largest release of radioactive material to the environment. Among the different organs of a vertebrate, the liver plays a crucial role in detoxification processes, and has been used as a biomarker to investigate cellular damage in ecotoxicological research. Here, we examined the impact of the exposure to the current levels of ionizing radiation present in the Chornobyl Exclusion Zone on the liver of Eastern tree frogs (Hyla orientalis). We quantified the area of melanomacrophage cells and morphological variables of hepatocytes, two cell types often used to estimate damage caused by pollutants in vertebrates. First, we investigated whether these hepatic parameters were indicative of frog (individual) condition. Then, we analyzed the effect of individual absorbed dose rates and ambient radiation levels on frog livers. Most of the studied parameters were correlated with individual body condition (a good predictor of amphibian fitness and survival). We did not detect marked morphological lesions in the liver of frogs captured in medium-high radiation environments. The area occupied by melanomacrophages and the morphology of hepatocytes did not change across a gradient of radiocontamination covering two orders of magnitude. Once accounting for body condition and sampling locality, the area of melanomacrophages was lower in areas with high radiation levels. Finally, the area occupied by melanomacrophages was not linked to dorsal skin coloration. Our results indicate that current levels of radiation experienced by tree frogs in Chornobyl do not cause histopathological damage in their liver. These results agree with previous physiological work in the species in the Chornobyl area, and encourage further molecular and physiological research to fully disentangle the current impact of the Chornobyl accident on wildlife.

Short-term effects of α-melanocyte-stimulating hormone in three distinct melanin-pigmented cell types of Anura

Ectothermic animals present melanin-containing cells in their integument and viscera. Besides cutaneous melanophores, amphibians have melanomacrophages in the hepatic parenchyma and melanocytes in the viscera, which are also present in their testicular stroma. The native melanocyte stimulating hormone (α-MSH) is the main hormone that modulates the color change in melanophores. However, we still know too little about how the α-MSH acts in vivo on visceral melanin-containing cells. In this study, we collected 30 adult males of Physalaemus nattereri (Anura, Leptodactylidae) to evaluate the short-term effects of α-MSH on melanophores, melanocytes and melanomacrophages under light microscopy. For this, we injected 0.05 ml of a single intraperitoneal dose containing 2.5x10-7 mmol/10g of α-MSH, diluted in ringer solution, in five experimental groups with five individuals each one. The different groups were analyzed after 1, 3, 6, 12 and 24h. The control group with five other individuals received only 0.05 ml of ringer solution. The skin pigmentation increased quickly after animals received the hormone α-MSH with the consequent darkening of the body (body darkness). Melanophores, melanocytes and melanomacrophages responded similarly to the test, with an increase in the area containing melanin. However, melanophores and melanomacrophages reached their darkest pigmentation in a shorter period of time in comparison to the testicular melanocytes, probably due to specific metabolic characteristics of each organ. Thus, we verified that the three types of cells, although present in different organs, are responsive to the native hormone α-MSH, which enables us to treat them as a pigmentary system.

Ultrastructural evidence of four types of lipofuscins in the melanomacrophagic centers in hepatocytes of zebrafish (Denio rerio)

Melanomacrophagic centers (MMCs) were studied in the hepatocytes of zebrafish using transmission electron microscope (TEM). The MMCs with irregular or amoeboid nucleus were located in the hepatocytes adjacent to the bile canaliculi. Several engulfed structures were present in the cytoplasm of MMCs. The most frequent observation was the presence of mitochondria, ranging in size from small to giant, with distorted shape and inconspicuous cristae. Occasionally the fragments of erythrocytes were found. The rough endoplasmic reticulum (rER) showed whirling around the mitochondria and lipid droplets, forming membrane-like structures. The damaged mitochondria were invaded by the lysosomes, and this was covered by a membrane led to the formation of lipofuscin. Four different types of lipofuscins were observed; namely, (1) granular with/without vacuoles of high electron-density, (2) homogenous surrounded by indistinct limiting membrane, (3) lamellated structures similar to inner matrix and cristae of mitochondria, and, (4) compound structure made by the combinations of first 3 types, (granular and homogenous, granular and lamellated, homogenous and lamellated). The present evidence suggests that MMCs in the hepatocytes of zebrafish perform continuous functions of removal of the damaged cellular organelles. The lipofuscin formation work in coordination with the cellular players of immune system and remove pathogens and maintain the internal homeostasis of cells.

Hepatic and blood alterations in Lithobates catesbeianus tadpoles exposed to sulfamethoxazole and oxytetracycline

In this study the effects of environmentally realistic concentrations of the antibiotics sulfamethoxazole (SMX) and oxytetracyclyne (OTC) on Lithobates catesbeianus tadpoles were evaluated, through the analyzes of the frequencies of micronucleus and nuclear abnormalities in erythrocytes, alterations in leucocytes, liver histopathology, and changes in hepatic esterase activities and oxidative stress biomarkers. The animals were exposed for 16 days at concentrations of 0 (control), 20, 90 and 460 ng L^-1. No significant difference was found in the frequencies of micronucleus and nuclear abnormalities. The two highest concentrations of SMX and all concentrations of OTC caused a significant increase in the number of lymphocytes. A significant decrease in the number of neutrophils compared to the control group was observed for all concentrations tested of both antibiotics. Also, decrease in the activity of glutathione S-transferase and high histopathological severity scores, indicating liver damage, were found in tadpoles exposed to the two highest concentrations of SMX and all concentrations of OTC. The main changes in the liver histopathology were the presence of inflammatory infiltrate, melanomacrophages, vascular congestion, blood cells and eosinophils. Esterase activities were unchanged. Indeed, the two highest concentrations of OTC caused a reduction in the activities of superoxide dismutase and glucose 6-phosphate dehydrogenase, while the highest concentration inhibited the activity of glutathione peroxidase and increased protein carbonyl levels. These results evidences that environmentally realistic concentrations of SMX and OTC in aquatic environments are capable to significantly disrupt tadpoles' physiology, possibly affecting negatively their survival rate in natural environments.

The effect of nonylphenol exposure on the stimulation of melanomacrophage centers, estrogen and testosterone level, and ERα gene expression in goldfish

The present study tried to measure the formation of melanomacrophage centers (MMCs) in various organs of male and female goldfish exposed to nonylphenol (NP) and aimed to assess its relationship with the main sexual hormones, estrogen receptor expression, and the pigment content of the MMCs. Immature goldfish were exposed to 10^-6 and 10^-7 M NP for 25 days. After obtaining blood for measuring testosterone and estrogen (E2) levels, tissue samples were collected from various organs for histological studies, quantifying pigments using ImageJ software and chemical analysis, and measuring ERα gene expression. Results showed that the order of forming MMCs in various organs exposed to NP was liver > spleen > kidney, and the order of ERα gene expression was liver > testes > spleen > kidney in the male, and liver > spleen > kidney > ovaries in the female. Among the three pigments present in MMCs after exposure to the two doses of NP, melanin was more obvious (especially in the liver) and increased mostly in a dose-dependent manner in both sexes (especially in the male). Chemical analyses confirmed these results. Measurement of testosterone and E2 level in male and female goldfish showed that NP had more effect on the concentration of these hormones in male fish, indicating more endocrine-disrupting potential of NP against the male fish. Generally, the increase of melanin content of melanomacrophage centers coincided with the increase of ERα gene expression and decrease of testosterone level in goldfish after exposure to NP.

Response of hepatic biomarkers in Physalaemus nattereri (Anura) to different benzo(α)pyrene exposure routes

For over 40 years, anurans have been used as a study model to assess the adverse effects of benzo(α)pyrene (BαP), which include genotoxic, hepatotoxic, and immunotoxic effects. In these studies, BαP is administered cutaneously or by injection, with no comparison between two or more routes. The purpose of this study is to assess whether the effect of BαP is influenced by its route of administration, using the response of hepatic biomarkers of Physalaemus nattereri. Specimens (n = 108) were collected and divided into three experimental treatments (cutaneous, injection, and oral) and three experimental times (one, three, and seven days). Specimens received 0.02 ml of pure mineral oil (control) or mineral oil containing 2 mg/kg of BαP. The BαP causes changes in morphological (melanin, hemosiderin, lipofuscin, and mast cells) and biochemical (superoxide dismutase and glutathione S-transferase) hepatic biomarkers. Compared to biochemical, morphological biomarkers underwent a greater number of significant changes due to the treatment with BαP. The route of exposure alters the effects of BαP, mainly seen in morphological biomarkers, especially the pigments melanin, hemosiderin, and lipofuscin. In these pigments, the effect of the exposure pathway changes according to the analyzed biomarker, and the exposure time modulates the exposure pathway effect. These results are unprecedented for anurans and contribute to the field of herpetology and ecotoxicology.

Effect of induced sublethal intoxication with neonicotinoid insecticides on Egyptian toads (Sclerophrys regularis)

The toxicity role of insecticides affecting nontarget vertebrate of wildlife population has become essential subject to focus on. In this vein, the current study aimed to illustrate some biochemical and histopathological alterations induced by two neonicotinoids in Egyptian toads. Forty-five toads were collected and divided equally into three groups (15 toads/group): control group, thiamethoxam group, and acetamiprid group. Both treatment groups received thiamethoxam and acetamiprid (30 and 40 mg/L, respectively) four times within 12 days for induction of sublethal toxicity. Blood and liver tissue samples were collected. Both insecticides cause the same changes, but acetamiprid group exhibited a pronounced significant (P ≥ 0.001) effect than thiamethoxam group on increasing serum lipid profile, ALT, and AST. Moreover, acetamiprid showed a significant (P ≥ 0.001) decrease in hepatic total protein, GSH, and SOD and increase in MDA levels in comparison with thiamethoxam and control groups, respectively. The histopathological hepatic examination showed markable alterations in hepatic architecture in treatment groups that was distinct in acetamiprid group. Finally, our findings illustrate the indirect effect of neonicotinoids on toads and may realize their life-threatening factors. Graphical Abstract.

Evaluation of the genotoxic, mutagenic, and histopathological hepatic effects of polyoxyethylene amine (POEA) and glyphosate on Dendropsophus minutus tadpoles

Herbicides improve the productivity of a monoculture by eliminating weeds, although they may also be toxic and have negative effects on non-target organisms, such as amphibians. The present study evaluated the genotoxic, mutagenic, and histopathological hepatic responses of Dendropsophus minutus tadpoles to acute exposure (96 h) to the herbicide glyphosate (GLY, 65, 130, 260 and 520 μg/L) and the surfactant polyoxyethylene amine (POEA, 1.25, 2.5, 5 and 10 μg/L). On average, 174 % more genomic damage was observed in the tadpoles exposed to all concentrations of POEA in comparison with the control, while up to seven times more micronuclei were recorded, on average, at a concentration of 5 μg/L of POEA. All the individuals exposed to 10 μg/L of POEA died. The tadpoles exposed to GLY presented 165 % more DNA damage than the control, on average, at the highest concentrations (260 and 520 μg/L), and up to six times more micronuclei at 520 μg/L. The Erythrocyte Nuclear Abnormality test (ENA) detected a relatively high frequency of cells with lobed nuclei in the tadpoles expose to POEA at 5 μg/L and binucleated cells in those exposed to GLY at 520 μg/L. The hepatic histopathological observations revealed several types of lesions in the tadpoles exposed to both GLY and POEA. Overall, then, the results of the study indicate that both GLY and POEA have potential genotoxic, mutagenic, and hepatotoxic effects in D. minutus tadpoles. We emphasize the need for further studies to monitor the amphibian populations, such as those of D. minutus, which breed in aquatic environments associated with agricultural areas. The release of pollutants into natural habitats may have significant long-term impacts on the survival of anuran tadpoles.

Nonylphenol and cyproterone acetate effects in the liver and gonads of Lithobates catesbeianus (Anura) tadpoles and juveniles

Environmental pollution plays an important role in amphibian population decline. Contamination with endocrine disrupting chemicals (EDCs) is particularly worrying due to their capacity to adversely affect organisms at low doses. We hypothesized that exposure to EDCs such as 4-nonylphenol (NP) and cyproterone acetate (CPA) could trigger responses in the liver and gonads, due to toxic and endocrine disrupting effects. Growth rate may also be impaired by contamination. We investigated sublethal effects of a 28-day exposure to three different concentrations of NP and CPA on liver pigmentation, gonadal morphology, body mass, and length of tadpoles and juveniles Lithobates catesbeianus. Liver pigmentation and the gonadal morphologies of treated tadpoles did not differ from control, but growth rate was impaired by both pollutants. Juveniles treated with 10 μg/L NP and 0.025 and 0.25 ng/L CPA displayed increased liver melanin pigmentation, but gonadal morphologies, sex ratios, and body mass were not affected after treatments. The increase in liver pigmentation may be related to defensive, cytoprotective role of melanomacrophages. The decreased growth rate in tadpoles indicates toxic effects of NP and CPA. Thus, contamination with NP and CPA remains a concern and sublethal effects of different dosages of the compounds on native species should be determined.

Multiple Level Effects of Imazethapyr on Leptodactylus latinasus (Anura) Adult Frogs

Imazethapyr is an herbicide that is used in a variety of crops worldwide, including soybean and corn. The aim of the present study was to evaluate the biomarkers responses of adult Leptodactylus latinasus exposed to the formulation Pivot^® H (10.59% imazethapyr) in the laboratory at concentrations and under conditions that simulate two potential field exposure scenarios: an immersion in field runoff (Scenario 1: 10 mg/L) and a direct exposure to the droplets emitted by spray noozles (Scenario 2: 1000 mg/L). In both scenarios, the experimental procedure involved completely immersing the frogs over a period of 15 s. Different endpoints were evaluated at several ecotoxicological levels 48 and 96 h after the herbicide exposure. These included individual (biometric indices and behavior alterations), histological (liver pigments and lesions), biochemical (catalase, glutathione system and cholinesterase activities) and genotoxic effects (micronuclei induction and nuclear abnormalities). Forty-eight hours after imazethapyr exposure, frogs submitted to Scenario 1 presented an inhibition of liver glutathione-S-transferase activity, whereas histological alterations and increased hepatic cholinesterase levels were observed in frogs exposed under Scenario 2. Ninety-six hours after exposure to the imazethapyr formulation, frogs from the Scenario 1 treatment presented a decrease in liver melanin and hemosiderin, increased hepatic catalase activity and micronuclei induction. For their part, frogs exposed to Scenario 2 presented a decrease in the hepatosomatic index, an increase in liver alterations, melanin reduction and micronuclei induction. The multivariate analysis enables correlations to be made between biomarkers of different organizational level in exposed anurans. Our result indicates that real exposure to imazethapyr formulations under field conditions may pose a risk to Leptodactylus latinasus populations living in the agroecosystems.

Enzymatic, morphological, and genotoxic effects of benzo[a]pyrene in rainbow trout (Oncorhynchus mykiss)

Fish have defense systems that are capable of repairing damages caused by xenobiotics like benzo[a]pyrene (BaP), so the aims of this study were to identify BaP toxicity in melanomacrophages (MMs) cytoskeleton, evaluate the melanin area in MMs, and analyze genotoxicity. Rainbow trout juveniles (n = 24) were split in 48h and 7d treatments that received 2 mg/kg of BaP. After the experiment, blood samples were collected and liver was removed, to proceed with the analysis: EROD activity, MMs melanin area quantification, melanosomes movements, and a genotoxicity test. The results revealed increased in EROD activity after 48-h and 7-day BaP exposure. The group 7d displayed a reduction in MMs pigmented area, melanosomes aggregation, in addition to an increased frequency of micronucleus. By means of the EROD assay, it was possible to confirm the activation of BaP biotransformation system. The impairment of the melanosomes' movements possibly by an inactivation of the protein responsible for the pigment dispersion consequently affects the melanin area and thus might negatively impact the MMs detoxification capacity. In addition to this cytotoxicity, the increased frequency of micronucleus might also indicate the genotoxicity of BaP in this important fish species.

Exposure of Physalaemus cuvieri (Anura) to benzo[a]pyrene and α-naphthoflavone: Morphofunctional effects on hepatic melanomacrophages and erythrocytes abnormalities

Benzo[a]pyrene (BaP) is a high-risk contaminant of elevated toxicity. Its biotransformation process occurs as the expression of CYP1A1 increases and produces toxic metabolites. In turn, α-naphthoflavone (aNF) represents an inhibitor of CYP1A1, preventing BaP metabolism. Toxicological studies in anurans show alterations in the melanomacrophage (MM) detoxification cell after exposure to xenobiotics. In this study, the production of melanin by MMs was evaluated, as were morphological alterations in the cytoskeleton, phagocytosis and the genotoxicity effects after exposure of an anuran species to BaP and aNF. Physalaemus cuvieri received subcutaneous injections of 2 mg/kg and/or 20 mg/kg aNF. For phagocytosis analyses, animals received an intraperitoneal injection with 0.4% trypan blue. The results revealed that melanin synthesis increased by 503.2% in animals exposed to BaP after 48 h, which was related to the antioxidant action of melanin, whereas the decreased in synthesis of 25.6% with the BaP + aNF interaction resulted in high toxicity to MMs and cell degeneration. The phagocytic activity reduced to 37.6% in animals exposed to BaP, characterizing a functional impairment; however, the BaP + aNF interaction led to the restoration of phagocytosis, reaching 419.23%. The decreased rate or absence of abnormalities may be explained by the fact that only the less damaged erythrocytes remained in the bloodstream, whereas the most damaged cells died. In conclusion, BaP and aNF are toxic to P. cuvieri, bringing risks to herpetofauna.

Synchrotron-Based Imaging Reveals the Fate of Selenium in Striped Marsh Frog Tadpoles

Synchrotron-based X-ray fluorescence microscopy (XFM) coupled with X-ray absorption near-edge structure (XANES) imaging was used to study selenium (Se) biodistribution and speciation in Limnodynastes peronii tadpoles. Tadpoles were exposed to dissolved Se (30 μg/L) as selenite (Se^IV) or selenate (Se^VI) for 7 days followed by 3 days of depuration. High-resolution elemental maps revealed that Se partitioned primarily in the eyes (specifically the eye lens, iris, and retinal pigmented epithelium), digestive and excretory organs of Se^IV-exposed tadpoles. Speciation analysis confirmed that the majority of accumulated Se was converted to organo-Se. Multielement analyses provided new information on Se colocalization and its impact on trace element homeostasis. New insights into the fate of Se on a whole organism scale contribute to our understanding of the mechanisms and risks associated with Se pollution.

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.

Influence of temperature on biomarker responses and histology of the liver of American bullfrog tadpoles (Lithobates catesbeianus, Shaw, 1802) exposed to the herbicide Tebuthiuron

Tebuthiuron (TBU) is a phenylurea herbicide that is extensively used in sugarcane fields. Owing to the low degradation rate, high water solubility, and leaching potential, TBU is believed to have harmful effects on aquatic organisms, such as anuran tadpoles. Contaminant effects can be influenced by temperature since increases in temperature are often associated with increased metabolic reactions. In this study, we evaluated the influence of temperature on the negative effects of TBU in bullfrog tadpoles (Lithobates catesbeianus) through a multi-biomarker approach. Tadpoles were exposed to 0 (control) 10, 50, and 200 ng L^-1 of TBU for 16 days at 25 and 32 °C. TBU increased the transcript levels of genes involved in biotransformation (glutathione S-transferase, GST, and sulfotransferase, SULT) and antioxidant (superoxide dismutase, SOD, and catalase, CAT) enzymes. TBU exposure also increased CAT and glutathione peroxidase (GPx) activities, whereas SOD and carboxylesterase activities were decreased. The highest temperature caused a decrease in the activities of ethoxyresorufin-O-deethylase and SOD but increased the activities of GST, GPx, glucose 6-phosphate dehydrogenase, and acetylcholinesterase. No effects of temperature or TBU exposure were observed in genotoxic markers (frequencies of micronucleous and nuclear abnormalities) or in lipid peroxidation levels. Tadpoles exposed to TBU at all tested concentrations presented a higher index of biomarker responses than that of the control groups. Higher values of severity scores from histological analyses were found in the liver of tadpoles exposed to 50 and 200 ng L^-1 of TBU at 32 °C compared with those of the control group at the same temperature. These results indicate that TBU and temperature increases are able to disturb the metabolic homeostasis of L. catesbeianus tadpoles after 16 days of exposure, causing substantial alterations in biomarker responses and liver morphology.

Hepatotoxicity of the anionic surfactant linear alkylbenzene sulphonate (LAS) in bullfrog tadpoles

The liver of anurans play an important role in metabolism, including detoxification, the biotransformation of molecules, and the storage of metabolites. Surfactants are part of domestic and industrial effluents. The effects of linear alkylbenzene sulfonate (LAS) on anuran liver remain unknown, however, some studies have evaluated the effects of LAS on the skin, gills, heart, testes, and liver of fishes. Here, we tested the hypothesis that LAS is hepatotoxic, promoting morphometric alterations in hepatocytes along with inflammation in the tissue, altering hepatic catabolism. We evaluated the effects of a LAS concentration that is considered environmentally safe in Brazilian inland waters on the liver of Lithobates catesbeianus tadpoles, including studies on morphology, morphometry, immunology, and metabolism. LAS exposure promoted enlargement of liver sinusoids and vacuolization of hepatocytes. Exposure to LAS also increased the area of mast cells and melanomacrophages (MMs). Additionally, LAS exposure increased hemosiderin inside MMs, suggesting alterations in the catabolism and storage of iron. Hepatocyte size increased after exposure to LAS, suggesting cytotoxic effects. Integrative analyses (i.e., morphometric, metabolic, and immunological) demonstrated hepatotoxic effects of LAS. These types of studies are key to understanding the negative effects of these substances on tadpole health, as these liver alterations impair anuran homeostasis.

Metabolic, immunologic, and histopathologic responses on premetamorphic American bullfrog (Lithobates catesbeianus) following exposure to lithium and selenium

The presence of chemicals and the destruction of freshwater habitats have been addressed as one of the reasons for the decline in the amphibians' populations worldwide. Considering the threat that these animals have been suffering in tropical regions, the present study tested if the Brazilian legislation, concerning the permissive levels of lithium and selenium in water bodies and effluents, warrants the protection of aquatic life. To do so, we assessed the metabolic, immunologic, and histopathologic alterations in liver samples of American bullfrog (Lithobates catesbeianus), at the premetamorphic stage, through biomarkers indicative of general energetic status, i.e., glucose, lipid, and protein metabolism using biochemical and histochemical approaches. The immunologic responses were assessed by the quantification of melanomacrophage centres (MMCs); the histopathologic evaluation of the liver sections was also performed. The assay was carried out over 21 days with two periods of sampling (after 7 and 21 days) to assess the effects of exposure over time. The animals were exposed to the considered safe levels of lithium (2.5 mg L^-1) and selenium (10 μg L^-1), both, isolated and mixed. The exposed animals showed alterations in glucose and lipid metabolism throughout the experiment. The intense presence of MMCs and histopathological responses are compatible with hepatotoxicity. The toxicity expressed by the employed animal model indicates that the Brazilian environmental legislation for the protection of aquatic life needs to be updated. With this study, we intend to provide data for better environmental policies and bring attention to sublethal effects triggered by the presence of contaminants in the aquatic environment.

Lowland tapir exposure to pesticides and metals in the Brazilian Cerrado

Abstract ContextThe Cerrado is a Global Biodiversity Hotspot as well as Brazil’s main frontier for large-scale agriculture and livestock production, making it one of the most threatened biomes in the country. Brazil is one of the biggest consumers of pesticides in the world and allows the use of chemicals that are banned in many other countries due to their adverse health effects in a wide range of species, including humans. AimsThis study aimed to assess pesticide and metal exposure of the lowland tapir – a threatened, large herbivorous mammal – to support future studies of the role of these chemicals in tapir health, survivorship, and population viability. MethodsFoot pad, proboscis, stomach contents, liver, bone, and nail samples were obtained from tapir carcasses found along highways (n=87). (i) Atomic absorption spectrophotometry (AAS) was used to detect metals in bone, nail and liver tissue; (ii) gas chromatography – nitrogen phosphorous detector (GC-NPD) to detect organophosphates in liver and skin; and (iii) high performance liquid chromatography – ultraviolet (HPLC-UV) to detect pyrethroids and carbamates in stomach contents. Key resultsTwo carbamates (aldicarb and carbaryl), three organophosphates (diazinon, malathion, and mevinphos), two pyrethroids (deltamethrin and permethrin), and two toxic metals (cadmium and lead) were detected in different tapir tissue samples, some at concentrations high enough to cause adverse health effects. In 90% of roadkill tapirs that were subjected to a full post-mortem examination (n=25), macroscopic alterations of liver and/or kidney tissue were observed. ConclusionsThis study provides the first report to date of the detection of pesticides and metals in lowland tapirs. ImplicationsSome of the reported pesticide concentrations exceed environmental safety thresholds. Consequently, results from this study raise concerns over potential adverse health effects in tapirs that could lead to population level impacts, thus requiring further investigation.

Differential liver histopathological responses to amphibian chytrid infection

Amphibians have been facing a pandemic caused by the deadly fungus Batrachochytrium dendrobatidis (Bd). Although studies have elucidated cutaneous and homeostatic disturbances, it is still unknown if the hepatic function can be affected or if hepatic effects differ among host species. Thus, we evaluated the effects of an experimental Bd infection on the liver (histopathology and the hepatosomatic index) of 2 anuran species (Xenopus laevis and Physalaemus albonotatus) with different susceptibilities to Bd infection and compared them to uninfected controls. Bd infection increased the melanomacrophage cell area and induced leukocyte infiltration in both species. The effects were more pronounced in the sensitive species, P. albonotatus, which showed severe reduction in glycogen stores and liver atrophy, due to energetic imbalance. Hepatocytes of P. albonotatus also showed ballooning degeneration (vacuolization), which could lead to cell death and liver failure. Our results provide evidence that although the sensitive species showed more severe effects, the tolerant species also had hepatic responses to the infection. These findings indicate that hepatic function can play an important role in detoxification and in immune responses to chytridiomycosis, and that it may be used as a new biomarker of health status in chytrid infections.

Idiosyncratic liver pigment alterations of five frog species in response to contrasting land use patterns in the Brazilian Cerrado

BACKGROUND

Changes in land use trigger environmental changes that can lead to decreased biodiversity and species loss. The liver is an essential detoxification organ that reflects systemic physiological responses to environmental changes. Here, we tested whether contrasting land use patterns influence the amount of substances from the hepatic cellular catabolism and melanomacrophages (MMs) of five anuran species in the Brazilian Cerrado.

METHODS

We collected the same five species of pond-dwelling frogs in one protected area and in an area with intense agricultural activity. We used routine histological and histochemical techniques to quantify the area occupied by lipofuscin, melanin, and hemosiderin in the liver of two frogs Leptodactylus fuscus, Physalaemus cuvieri, and three tree-frogs Dendropsophus minutus, Scinax fuscomarginatus, and Boana albopunctata. We classified land use types in a buffer around each pond based on satellite images. We then used a double-constrained Correspondence Analysis, a recently developed ecological method to relate functional traits to environmental variables, to test the effect of each land use type on the area of each liver pigment.

RESULTS

There was an increase in the amount of melanin in environments with high proportion of agriculture, as well as variation in the amount of lipofuscin and hemosiderin. Liver pigments of P. cuvieri and B. albopunctata varied more strongly in response to land use types, suggesting they could be good indicator species. Therefore, the area of MMs in the liver and the metabolic products in their cytoplasm can be used as biomarkers of environmental changes in regions with intense agricultural activities. Our results add a new perspective to the influence of land use patterns on environmental health by highlighting the effect of environmental changes on internal morphological aspects of animals.

The effects of chronic cadmium exposure on Bufo gargarizans larvae: Histopathological impairment, gene expression alteration and fatty acid metabolism disorder in the liver

Cadmium (Cd) a highly toxic metal to human and wildlife health and it is hazardous to both terrestrial and aquatic life. In this study, we used RNA sequencing analysis to examine the effects of chronic cadmium exposure on liver lipid metabolism of Bufo gargarizans larvae. Tadpoles were exposed to cadmium concentrations at 0, 5, 10, 50, 100 and 200 μg L^-1 from Gosner stage 26-42 of metamorphic climax. The results showed high dose cadmium (50, 100 and 200 μg L^-1) caused obvious histological changes characterized by hepatocytes deformation, nuclear pyknosis, increasing melanomacrophage centers (MMCs) and aggregated lipid droplets. Moreover, transcriptome analysis showed that liver function was seriously affected by cadmium exposure. Furthermore, high dose cadmium significantly upregulated the mRNA expression of elongation of very-long-chain fatty acids 1 (ELOVL1), Mitochondrial trans-2-enoyl-CoA reductase (MECR), Trans-2, 3-enoyl-CoA reductase (TER) and Hydroxysteroid (17β) dehydrogenase type 12 (HSD17B12) which are related with fatty acid synthesis. Meanwhile, mRNA levels of genes related with fat acid oxidation such as acetyl-CoA acyltransferase 2 (ACAA2) and enoyl-coenzyme A (CoA) hydratase short chain 1 (ECHS1) were significantly upregulated while the expression of Acyl-coA thioesterase 1 (ACOT1), 3-hydroxyacyl-CoA dehydrogenase (HADH), Palmitoyl-protein thioesterase 1(PPT1) and Acetyl-CoA acyltransferase 1(ACAA1) was significantly downregulated by high dose cadmium exposure. Furthermore, the mRNA level of ATP-binding cassette subfamily B member 11 (ABCB11) related with bile secretion was significantly decreased exposed to high dose cadmium. Our results suggested cadmium can cause liver dysfunction by inducing histopathological damages, genetic expression alterations and fatty acid metabolism disorder.

Ultrastructural Evidence of Melanomacrophagic Centers and Lipofuscin in the Liver of Zebrafish (Denio rerio)

Melanomacrophagic centers (MMCs) were studied in the liver of zebrafish using transmission electron microscope (TEM). The MMCs were located in the space of Disse (SD), and their pseudopodia protruded into the lumen of sinusoids. The degree of extension of body structure of MMCs in the SD was determined by the size of the phagocytosed content. An irregular or amoeboid nucleus was present. Vacuoles were occasionally present, both, in endothelium and MMCs. The cytoplasm of MMCs showed several engulfed structures. The most common structure was the presence of mitochondria of small to giant size and distorted shape with inconspicuous cristae. The product of mitochondrial degeneration accompanied by lysosomes contributed to the formation of lipofuscins. Besides, changes were also observed in rough endoplasmic reticulum (rER), the Golgi complex, and lysosomes. Occasionally, small to large fragments of the erythrocytes were found in the cytoplasm of MMCs. The rER encompassed the mitochondria and lipid droplets forming a membrane-like structure. Golgi complex were dilated. Lysosomes fused with such membrane-bound structures contributed to the formation of the lipofuscin. The results provide evidence of the role of liver-resident MMCs of zebrafish in phagocytosis of damaged organelles, clearance of the worn-out erythrocytes, and lipofuscin formation.

Probing the effects of hexavalent chromium exposure on histology and fatty acid metabolism in liver of Bufo gargarizans tadpoles

Hexavalent chromium is one of the major detrimental heavy metal pollutants. B. gargarizans tadpoles were treated with different concentrations of Cr⁶⁺ (0, 13, 52, 104, 208, and 416 μg Cr⁶⁺ L^-1) from Gs 2 to Gs 42. The effect of Cr⁶⁺ on histopathological alterations and transcript levels of fatty acid metabolism-related genes as well as fatty acids composition and content in liver were examined. Histopathological changes were observed in liver at 52, 104, 208, and 416 μg Cr⁶⁺ L^-1. Moreover, RT-qPCR analyses showed the downregulated mRNA levels of the genes related to fatty acid synthesis (SCD, MECR, TECR and ELOVL1) and fatty acid β-oxidation (ACOT1, PPT1, HADH and ACAA2) at 416 μg Cr⁶⁺ L^-1. However, the mRNA expression of fatty acid β-oxidation-related genes (ECHS1, HADHA and ACAA1) were significantly upregulated at 13, 52, 104, 208 and 416 μg Cr⁶⁺ L^-1. In situ hybridization revealed BSEP was expressed in hepatocyte nucleus and plasma membrane, and HSD17B12 was abundantly expressed in the plasma membrane. The HSD17B12 mRNA levels were significantly upregulated in tadpoles exposed to all Cr⁶⁺ treatment groups, while the BSEP mRNA levels were downregulated at 104, 208 and 416 μg Cr⁶⁺ L^-1 groups compared to control. In addition, an increase in polyunsaturated fatty acids and a decrease in monounsaturated fatty acids were found in 52, 104 and 416 μg Cr⁶⁺ L^-1 groups. Overall, chronic exposure to Cr⁶⁺ may suppress fatty acid synthesis, disturb fatty acid β-oxidation, aggravate disorders of hepatic function and induce hepatic impairment in B. gargarizans tadpoles.

Effect of triadimefon and its metabolite on adult amphibians Xenopus laevis

The decrease in the population of amphibians all over the world has raised concerns. Adult X. laevis frogs were exposed to 0, 1 and 10 mg/L triadimefon and triadimenol. After 14 or 28 days exposure, we collected male and female specimens to study swimming activity, lactic dehydrogenase (LDH) and antioxidant enzyme activity in blood samples, histopathology of liver and thyroid tissue, thyroid hormone levels and thyroid hormone-related gene expression levels in brains. Our results showed that triadimefon and triadimenol could affect the swimming activity of frogs and that this was distinct at different levels of triadimenol. Moreover, triadimefon and triadimenol exposure produced a greater effect on superoxide dismutase (SOD) in females than in males, which was reverse to the finding for glutathione S-transferase (GST) and catalase (CAT). After 28 days exposure, triadimefon produced more toxic effects on the liver than observed for triadimenol. Besides this, triadimefon and triadimenol exposure exerted a greater effect on liver histology and thyroid hormone levels in male frogs than in the females. Our results also found that the expression of genes related to thyroid hormone in brains depended on the exposure level and time, as well as the sex of the treated individual. This study shed light on the relationships between the toxicity of metabolite products and their parent compounds and provided further understanding of the risk of pesticide use on amphibians.

Xenopus laevis as a Bioindicator of Endocrine Disruptors in the Region of Central Chile

One of the direct causes of biodiversity loss is environmental pollution resulting from the use of chemicals. Different kinds of chemicals, such as persistent organic pollutants and some heavy metals, can be endocrine disruptors, which act at low doses over a long period of time and have a negative effect on the reproductive and thyroid system in vertebrates worldwide. Research on the effects of endocrine disruptors and the use of bioindicators in neotropical ecosystems where pressure on biodiversity is high is scarce. In Chile, although endocrine disruptors have been detected at different concentrations in the environments of some ecosystems, few studies have been performed on their biological effects in the field. In this work, Xenopus laevis (African clawed frog), an introduced species, is used as a bioindicator for the presence of endocrine disruptors in aquatic systems with different degrees of contamination in a Mediterranean zone in central Chile. For the first time for Chile, alterations are described that can be linked to exposure to endocrine disruptors, such as vitellogenin induction, decreased testosterone in male frogs, and histological changes in gonads. Dioxin-like and oestrogenic activity was detected in sediments at locations where it seem to be related to alterations found in the frogs. In addition, an analysis of land use/cover use revealed that urban soil was the best model to explain the variations in frog health indicators. This study points to the usefulness of an invasive species as a bioindicator for the presence of endocrine-disruptive chemicals.

Induction of hyperpigmentation and heat shock protein 70 response to the toxicity of methomyl insecticide during the organ development of the Arabian toad, Bufo arabicus (Heyden,1827)

Methomyl (MET) is a carbamate insecticide which is used as a substitute for organophosphorus compounds to protect crops against insects. The present study aims to evaluate the cytoprotection response of pigment cells and heat shock protein 70 (HSP70) after exposure to MET during the tadpole developmental stages of the Arabian toad, Bufo arabicus. Three developmental larval stages of the toad were selected and divided into two groups; Control and MET-exposed (MET-EX) tadpoles (10ppm). MET-EX tadpoles showed an increased number of pigment cells in the liver, kidney, anterior eye chamber, and skin tissues as compared to the control. The glycogen content in the developing liver and muscles (myotomes) of MET-EX tadpoles was decreased as compared to the control. In the MET-EX tadpoles, immunohistochemical staining showed an increase of HSP70 expression in the liver hepatocytes, the nucleated red blood cells (nRBC) in kidney glomeruli, the iridocorneal angle of anterior eye chamber, and the skin as compared to the control. The current study concluded that pigment cells and HSP70 represented a cytoprotecting response against MET insecticide during the organ development of B. arabicas tadpoles. Therefore, MET use should be regularly monitored in the environment to protect animals and human from exposure to this insecticide.

Exposure of liver cell culture from the orange-spotted grouper, Epinephelus coioides, to benzo[a]pyrene and light results in oxidative damage as measured by antioxidant enzymes

Among the various toxicants discharged into aquatic environments, benzo (a) pyrene (BaP) has been shown to effect on the antioxidant system of fish and the evaluation of its impact on biota is of considerable concern. The aim of the present study was to use the primary hepatocyte culture obtained from the orange-spotted grouper, Epinephelus coioides, to evaluate the adverse effects of benzo (a) pyrene (BaP) on cell viability and liver antioxidant system. BaP was selected for its high ability to produce reactive oxygen species (ROS) and oxidative stress. The liver was minced by a scalpel and digested in the PBS solution with 0.1% collagenase IV at room temperature for 20 min. Then, the cell suspension was transferred to a plate contained an equal amount of Leibovitz's L-15 medium with 20% fetal bovine serum (FBS), 100 IU mL^-1 of penicillin and 100 μg mL^-1 streptomycin. 5 mL of cell suspension were plated into sterile 25 cm² tissue culture flasks at the density of 1.5 × 10⁶ cell/ml L-15 and incubated at 30 °C for two weeks. The medium was renewed after 24-48 h. The number of the liver cells was adjusted to 4 × 10⁶ after two weeks. 10^-4 mol l^-1 was verified by MTT assay as the IC50 of BaP. Then, hepatocytes were exposed to three concentrations of BaP (10^-5, 2 × 10^-5, 3 × 10^-5 mol L^-1) and incubated for 24 h. Samples were collected after 6, 12 and 24 h and the amounts of SOD, CAT, GPx, LPO, LDH, AST, ALT, ALP and total protein were analyzed. The results showed that, 10^-5 mol L^-1 of BaP was not significantly toxic to cultivated hepatocytes, however, the sensitivity of cells to BaP increased in a dose-related pattern. The activity of the antioxidant enzymes (SOD, CAT and GPx) and liver enzymes (ALT, AST, ALP, LDH) significantly increased, though the amount of LPO, total antioxidant power and total protein decreased dose-dependently in BaP-exposed cells. In conclusion, according to the finding of the present study, BaP has a high potential to induce the oxidative stress in primary liver cell culture of E. coioides.

Biomarkers at different levels of organisation after atrazine formulation (SIPTRAN 500SC®) exposure in Rhinella schineideri (Anura: Bufonidae) Neotropical tadpoles

Brazil is an important consumer of herbicides. In sugarcane cultivation-the country's most extensive agricultural crop-atrazine-based formulations are the principal form of weed control. Several studies have investigated adverse effects of atrazine or their formulations on anurans, but not specifically on Brazilian species. Our aim was therefore to investigate the lethal and sublethal effects of an atrazine-based herbicide in Rhinella schneideri tadpoles and, in particular, effects on the pigmentation system as a new endpoint in ecotoxicological studies. Rhinella schneideri tadpoles at the Gosner-30 stage were exposed to the atrazine-based herbicide formulation, SIPTRAN 500 SC^®, in acute bioassays at concentrations of 1.5-25 mg/L. The lethal and sublethal effects induced were analysed at different ecotoxicological levels: organismal level (alterations in behaviour, growth, development, and body mass; morphologic abnormalities), histological level (liver histopathology), the pigmentation system (melanomacrophages and dermal-melanophores), and cellular level (erythrocyte micronucleus formation and other nuclear-abnormalities). This herbicide induced sublethal effects at the organismal level with alterations in swimming and growth and morphologic abnormalities. These results demonstrated that, in anuran tadpoles, the atrazine-based agrochemical increased the frequency of micronucleus formation and other nuclear-abnormalities in erythrocytes and caused liver damage. In addition, we demonstrated for the first time effects of an atrazine-based formulation on the pigmentation system of anuran tadpoles, specifically an increase in the number of melanomacrophages and dermal melanophores. This study is the first to use several widely differing endpoints at different ecotoxicological levels in a comprehensive manner for assessment of the effects of environmental stressors in order to determine the health status of Neotropical anuran species. In doing so, this study establishes a foundation for future ecological assessments.

Chronic effects of mercury on Bufo gargarizans larvae: Thyroid disruption, liver damage, oxidative stress and lipid metabolism disorder

Mercury is severely detrimental to organisms and is ubiquitous in both terrestrial and aquatic ecosystems. In the present study, we examined the effects of chronic mercury (Hg) exposure on metamorphosis, body size, thyroid microstructures, liver microstructural and ultrastructural features, and transcript levels of genes associated with lipid metabolism, oxidative stress and thyroid hormones signaling pathways of Chinese toad (Bufo gargarizans) tadpoles. Tadpoles were exposed to mercury concentrations at 0, 6, 12, 18, 24 and 30 µg/L from Gosner stage 26-42 of metamorphic climax. The present results showed that high dose mercury (24 and 30 µg/L) decelerated metamorphosis rate and inhibited body size of B. gargarizans larvae. Histological examinations have clearly exhibited that high mercury concentrations caused thyroid gland and liver damages. Moreover, degeneration and disintegration of hepatocytes, mitochondrial vacuolation, and endoplasmic reticulum breakdown were visible in the ultrastructure of liver after high dose mercury treatment. Furthermore, the larvae exposed to high dose mercury demonstrated a significant decrease in type II iodothyronine deiodinase (Dio2) and thyroid hormone receptor α and β (TRα and TRβ) mRNA levels. Transcript level of superoxide dismutase (SOD) and heat shock protein (HSP) were significantly up regulated in larvae exposed to high dose mercury, while transcript level of phospholipid hydroperoxide glutathione peroxidase (PHGPx) was significantly down regulated. Moreover, exposure to high dose mercury significantly down regulated mRNA expression of carnitine palmitoyltransferase (CPT), sterol carrier protein (SCP), acyl-CoA oxidase (ACOX) and peroxisome proliferator-activated receptor α (PPAPα), but significantly up regulated mRNA expression of fatty acid elongase (FAE), fatty acid synthetase (FAS) and Acetyl CoA Carboxylase (ACC). Therefore, we conclude that high dose mercury induced thyroid function disruption, liver oxidative stress and lipid metabolism disorder by damaging thyroid and liver cell structures and altering the expression levels of relevant genes.

Mutagenic and histopathological effects of hexavalent chromium in tadpoles of Lithobates catesbeianus (Shaw, 1802) (Anura, Ranidae)

The potential mutagenic and histopathological effects of the hexavalent chromium were investigated in Lithobates catesbeianus tadpoles. These larvae (GS 25-31) were exposed to three nominal concentrations of potassium dichromate (4, 12, and 36 mg L^-1) and 5 mg L^-1 of Cyclophosphamide as a positive control (PC), for 24 h. A negative control (NC) was also added to the experiment. Our results showed that, in general, the micronuclei (MN) were less frequent than the erythrocyte nuclear abnormalities (ENA); there was a significant difference in the frequency of MN between the NC and all treated groups (p < 0.05) in a concentration-dependent curve, in addition the PC did not differ from the chromium treatments. Also, only PC and the group treated with potassium dichromate at 36 mg L^-1 showed significantly higher frequencies of ENA than NC (p < 0.05). Chromium treatments promoted cell retention in the Sub-G1 phase and a decrease of cells in the S and G2/M phases indicating inhibition of the cell cycle. All treatments with chromium led to liver and kidney histopathological lesions, especially with 36 mg L^-1 (greater number of lesions). In conclusion, hexavalent chromium was mutagenic to L. catesbeianus tadpoles and its toxic effects also resulted in anti-mitotic activity, besides inducing histopathological alterations in liver and kidney. Amphibians have been proven to be useful bioindicators, and we suggest that tadpoles of different species can be used to represent the environmental impacts in aquatic ecosystems.

Effects of glyphosate and its commercial formulation, Roundup® Ultramax, on liver histology of tadpoles of the neotropical frog, Leptodactylus latrans (amphibia: Anura)

In the last years, the agricultural expansion has led to an increased use of pesticides, with glyphosate as the most widely used worldwide. This is also the situation in Argentina, where glyphosate formulations are the most commercialized herbicides. It is known that glyphosate formulations are much more toxic than the active ingredient, and this difference in toxicity can be attributed to the adjuvants present in the formula. In this context, the aim of the present study was to evaluate and compare sub-lethal histological effects of the glyphosate formulation Roundup Ultramax and glyphosate active ingredient on Leptodactylus latrans tadpoles at Gosner-stage 36. Semi-static bioassays were performed using 96 h of exposure with Roundup Ultramax formulation (RU; 0.37-5.25 mg a.e./L), glyphosate (GLY; 3-300 mg/L), and a control group. RU exposure showed an increment in the melanomacrophagic cells (MMc) and melanomacrophagic centers (MMCs) from 0.37 mg a.e./L. GLY exposure showed a significant increment in the number of MMc from 15 mg/L, and of MMCs from 3 mg/L. Also, histopathological lesions were observed in the liver of tadpoles exposed to both, GLY and RU. These lesions included: lipidosis and hepatic congestion, but only RU showed significant differences respect to control, with a LOEC value of 2.22 mg a.e./L for both effects. In sum, this study represents the first evidence of adverse effects of glyphosate and RU formulation on the liver of anuran larvae at concentrations frequently found in the environment.

The morphological changes and molecular biomarker responses in the liver of fluoride-exposed Bufo gargarizans larvae

The goal of the current study was to evaluate the negative influences of fluoride on liver of Bufo gargarizans larvae. B. gargarizans larvae were treated with 42.4mgF^-/L for 0, 24, 48 and 72h at Gosner stage 37. The morphological changes and responses of molecular biomarkers involved in lipid metabolism, oxidative stress and apoptosis were examined in liver. Disappearance of cell boundaries, degeneration of hepatic parenchyma cells and significant increase in the number of melanomacrophage centres and the quantity of lipid droplets were found in the liver treated with 42.4mgF^-/L for 72h. In addition, in the relative expression of acetyl CoA carboxylase 1 (ACC-1), fatty acid elongase 1 (FAE-1), sterol carrier protein 2 (SCP-2), and carnitine palmitoyltransferase-1 (CPT-1), decrease was observed after 24, 48 and 72h of 42.4mgF^-/L exposure. Furthermore, the transcript levels of superoxide dismutase (SOD) and glutathione peroxidase (GPx) were downregulated in tadpoles exposed for 24, 48 and 72h to 42.4mgF^-/L, while the transcript level of heat shock protein 90 (HSP90) was upregulated at 42.4mgF^-/L for 72h. Also, mRNA expression of Bcl-2-associated transcription factor 1(BCLAF1) and thyroid hormone receptors (TRα and TRβ) was significantly upregulated in tadpoles treated with 42.4mgF^-/L for 72h. Therefore, our results suggested that the liver injury induced by fluoride might result from disruption of lipid metabolism, oxidative damage and apoptosis.

The Influence of Six Pesticides on Physiological Indices of Pelophylax Ridibundus (Pallas, 1771)

The objective of the study is to screen for morphological, biochemical and histological changes induced by six widely used pesticides (Reldan 40EC, Actara 25WG, Tilt 250EC, Champion 50WG, Fusilade Forte, Dual Gold 960EC) in the amphibian species Pelophylax ridibundus (Pallas, 1771). Highly degenerative changes were observed in animals cultured at 22-24°C, compared to those cultured at 4-6°C. The hepatosomatic index increased upon exposure to almost all of the pesticides, the erythrocyte number decreased upon exposure to all pesticides except Reldan 40EC, while leucopenia was observed only for Reldan 40EC and Actara 25WG. Hyperglycemia was observed upon administration of pesticides (except Champion 50WG and Fusilade Forte, for which hypoglycemia is registered), while a decrease in cholesterol levels was induced by nearly all pesticides. Triglycerides varied only slightly. The results suggest that chronic pesticides exposure can lead to alteration of various indices, as well as to hepatic lesions in amphibians.

Melanomacrophage functions in the liver of the caecilian Siphonops annulatus

Melanomacrophages are phagocytes that synthesize melanin. They are found in the liver and spleen of ectothermic vertebrates, and in the kidney of fish. In agnathan and elasmobranch fish, melanomacrophages are seen as isolated cells, and forming clusters in all the other vertebrates. The natural phagocytic activity of melanomacrophages is poorly characterized, as most of the research works have focused on induced phagocytic activity only. Furthermore, little is known about amphibian melanomacrophages, mainly about those in caecilians - wormlike amphibians in the order of Gymnophiona, which is the least known group of terrestrial vertebrates. The present research work aimed at the structure and function of hepatic melanomacrophages of Siphonops annulatus, a species largely found in South America. We identified the role of these cells in the control of circulating basophils (pro-melanogenic cells), in the turnover of liver collagen stroma and in the hemocatheresis, interrelated physiological mechanisms.

Heavy metal-induced toxicity in the Indian green frog: Biochemical and histopathological alterations

Heavy metal contamination may have adverse effects on wetland biota, particularly on amphibians. Severe immunotoxic effects elicited in Euphlyctis hexadactylus (Indian green frog) because of metal exposure (Cd, Cr, Cu, Pb, and Zn) in the Bellanwila-Attidiya Sanctuary, a polluted urban wetland in Sri Lanka, provided the rationale for the present study. We evaluated the biochemical and histopathological effects of this metal contamination with a reference E. hexadactylus population and a laboratory exposure group that was subjected to 28 d of exposure to a mixture of Cd, Cr, Cu, Pb, and Zn (5 ppm in each mixture). A histopathological scoring for the semiquantification of tissue damage was established. Results of the biochemical and histopathological markers were remarkably consistent between the 2 exposure scenarios, providing validation for the heavy metal exposure hypothesis. Damage to liver, kidney, lung, and skin of metal-exposed E. hexadactylus quantified multiple impairments absent in the reference frogs. Liver injuries complemented significantly elevated aspartate transaminase (AST), alanine transaminase (ALT), γ-glutamyl transferase (γ-GT), and alkaline phosphatases in frog liver homogenate, indicating hepatocellular leakage and loss of functional and structural integrity of the hepatocyte membrane in both field- and laboratory-exposed frogs. Significant elevation of Kupffer cell hypertrophy, pigmentation, inflammatory cell infiltrates and hepatic inflammation, extramedullary hematopoiesis, karyocytomegaly of hepatocytes (p < 0.05) of the liver, and degeneration of epithelia and necrosis of the lung, manifested as impairments in both metal exposure scenarios. Significantly reduced serum total protein and albumin and significantly elevated urea and creatinine in metal-exposed frogs were indicative of hepatic and renal dysfunction, respectively. The present study affirms histopathology-related biochemical alterations as potential biomarkers for heavy metal toxicity in amphibians. Environ Toxicol Chem 2017;36:2855-2867. © 2017 SETAC.

Using a liver cell culture from Epinephelus coioides as a model to evaluate the nonylphenol-induced oxidative stress

The present study aimed to use primary liver cell culture derived from the orange-spotted grouper, Epinephelus coioides, to assess the toxic effects of nonylphenol (NP) on the hepatocyte viability and the liver antioxidant system. E. coioides was selected due to its commercial importance. NP was used in this study because of its high potential of producing oxidative stress due to increased reactive oxygen species (ROS). A liver of E. coioides was digested with PBS containing 0.1% collagenase IV. The digested cells were moved to Leibovitz L-15 culture medium with 20% fetal bovine serum (FBS), 100IUmL^-1 penicillin, 100μgmL^-1 streptomycin. Aliquots of cell suspension were seeded as a monolayer into sterile 25cm² tissue culture flasks and incubated at 30°C for 14days. The medium, containing non-attached cells, was removed after 24 to 48h and a new medium was added. The IC50 of 10^-4molL^-1 was determined for nonylphenol using MTT assay. Cells were then incubated with L-15 medium containing 10^-5, 2×10^-5, 3×10^-5molL^-1 of NP and samples were taken after 6, 12 and 24h of incubation for analysis of LPO, SOD, CAT, GPx, LDH, AST, ALT, and ALP. Based on the results, the lowest concentration of NP was not markedly cytotoxic to primary hepatocytes and the cell sensitivity to NP increased dose-dependently. The activities of SOD, CAT and GPx decreased significantly, while activities of LPO, LDH, AST, ALT and ALP, increased significantly in a dose-related pattern in NP-treated cells. In conclusion, this study revealed that NP could induce the oxidative stress in cultivated hepatocytes of E. coioides during a short-term exposure. NP toxicity is mainly due to the induction of the reactive oxygen species (ROS), which lead to cell membrane disruption, damage of cellular metabolism, and interference with cellular macromolecules.

Histopathological changes and lipid metabolism in the liver of Bufo gargarizans tadpoles exposed to Triclosan

In the current study, the adverse effects of TCS on liver health of B. gargarizans tadpoles were assessed. B. gargarizans larvae were exposed to TCS at 0, 10, 30, 60, and 150 μg L^-1 from Gosner stage 3 until metamorphic climax. The hepatosomatic index (HSI), hepatic histological and ultrastructural features, and transcript levels of genes associated with detoxification and oxidative stress as well as lipid metabolism in the livers were determined. Exposure to 150 μg L^-1 TCS resulted in increased HSI of tadpoles at metamorphic climax. Histological changes characterized by an increase in the number of melanomacrophage, nucleus pyknosis, and deposition of collagen fibers were observed in liver at 60 and 150 μg L^-1 TCS. Moreover, marked ultrastructural alterations including high electron dense in mitochondrial matrix and lipid accumulation were also observed. In addition, abundances of transcripts of Cu/Zn superoxide dismutase (SOD), phospholipid hydroperoxide glutathione peroxidase (PHGPx), and heat shock protein 90 (HSP₉₀) were decreased in larvae exposed to 60 and 150 μg L^-1 TCS, while transcript level of HSP₉₀ was increased at 30 μg L^-1 TCS. Also, abundances of transcripts of acetyl-CoA carboxylase (ACC), carnitine palmitoyltransferase 2 (CPT2), peroxisome proliferator-activated receptor alpha (PPARa), fatty acid elongase 1 (FAE), sterol carrier protein 2 (SCP) were significantly lesser in larvae exposed to 60 and 150 μg L^-1 TCS. Overall, TCS at high levels induced histopathological changes in the liver of B. gargarizans tadpoles. This might have been due to the alteration of oxidative stress-related genes and lipid metabolism-related genes expression levels.

Adipose tissue macrophages develop from bone marrow-independent progenitors in Xenopus laevis and mouse

ATMs have a metabolic impact in mammals as they contribute to metabolically harmful AT inflammation. The control of the ATM number may have therapeutic potential; however, information on ATM ontogeny is scarce. Whereas it is thought that ATMs develop from circulating monocytes, various tissue-resident Mϕs are capable of self-renewal and develop from BM-independent progenitors without a monocyte intermediate. Here, we show that amphibian AT contains self-renewing ATMs that populate the AT before the establishment of BM hematopoiesis. Xenopus ATMs develop from progenitors of aVBI. In the mouse, a significant amount of ATM develops from the yolk sac, the mammalian equivalent of aVBI. In summary, this study provides evidence for a prenatal origin of ATMs and shows that the study of amphibian ATMs can enhance the understanding of the role of the prenatal environment in ATM development.

Effects of heavy metal pollution on pigmented macrophages in kidney of Vardar chub (Squalius vardarensis Karaman)

Pollution with heavy metals may influence the immune system of fish, leading to impairment of their health or even increase their mortality. The fish kidney is one of the first fish organs to be affected by water contamination. Amounts of kidney macrophages (MACs), which are involved in fish immune response, as well as the qualitative and quantitative changes in the pigmented MACs in fish kidney, are used as biomarkers of pollution. Therefore, in this study, we have evaluated relative and total volumes of trunk kidney pigmented MACs, and analyzed the pigments accumulated within them. Fish were sampled from two mining impacted rivers, Kriva and Zletovska, highly contaminated with heavy metals, and from one reference river, Bregalnica, in spring and autumn of 2012. We have observed that main pigments found in kidney MACs of Vardar chub were melanin and lipofuscin/ceroid, as well as that relative volumes of MACs ranged from 0.56 to 1.68%. Moreover, the results showed that relative volumes of pigmented MACs were higher in metal contaminated rivers, especially in autumn season in the Zletovska River, concurrently with extremely high metal exposure. In addition, condition factors and kidney somatic indices were found significantly lower in the Zletovska River in both seasons, autumn and spring, possibly also as a consequence of high water pollution. Our data confirm that increase in relative volumes of pigmented MACs may serve as warning sign of potential heavy metal pollution in aquatic environment.

Flutamide effects on morphology of reproductive organs and liver of Neotropical Anura, Rhinella schneideri

Water contamination is one of the factors influencing the decline of amphibians. Flutamide is an antiandrogenic medicine that occurs as water contaminant. This compound especially affects the reproductive organs, but it can also show hepatotoxic effects. The Bufonidae family has a peculiar organ named Bidder's organ, considered by some authors as a rudimentary ovary, but capable to respond to some external stimuli. This study investigated flutamide effects on testes and Bidder's organ germ cells, liver pigmentation, and sexual hormones levels in Rhinella schneideri males. We randomly divided 15 males in three groups (N=5): two groups were injected with flutamide, at 1 and 5mg/kg, while the control group received only mineral oil, for 7days. After euthanasia, blood samples were collected and the organs were sent to histological routine. In the testes, both treatments caused an increase in spermatogonia and spermatocytes, and a decrease in spermatozoa and locular area. In the Bidder's organ, the final diplotene oocytes increased, but the initial diplotene, degrading and atresic oocytes reduced in both treatments. The lipofuscin in the Bidder's organ was not affected. In the liver, melanin and lipofuscin increased only for the 1mg/kg flutamide treatment. The 5mg/kg treatment did not affect the liver. Serum testosterone and estradiol levels did not vary compared with the control group. This compound has antiandrogenic activity, which can affect the spermatogenetic process. The decrease in degrading and atresic Bidderian oocytes indicated that flutamide could stimulate the organ, retarding the degradation processes. The increase in liver melanin, which has protective role, and lipofuscin, a sign of degradation, indicates that flutamide cause hepatotoxic effects. So we conclude that flutamide negatively affects the testes, especially by reducing the sperm area, and the liver, inducing cell degradation and producing protective responses. Furthermore, the compound encourages lower degradation rates of the Bidder's organ germ cells.

Effects of glyphosate on hepatic tissue evaluating melanomacrophages and erythrocytes responses in neotropical anuran Leptodactylus latinasus

Glyphosate (GLY) is the most used herbicide worldwide and its effects on anurans are well known. Pollutants can cause physiological and morphological effects. Therefore, this study evaluated the effects of GLY on hepatic melanomacrophages as a response to environmental stressors. Three treatments were exposed to different concentrations of pure GLY (100, 1000, and 10,000 μg g(-1), respectively), and there was also a control group. After the experimental time, liver and blood were analyzed. Melanomacrophages (MMCs) were located between the hepatocyte cordons, close to sinusoids. GLY increased the melanin area in MMCs of Leptodactylus latinasus exposed since lowest concentration until highest concentration. GLY also changed the occurrence of hepatic catabolism pigments into melanomacrophages and erythrocyte nuclear abnormalities; therefore, it can interfere with the hepatic metabolism. In conclusion, GLY promotes alterations in the hepatic tissue and erythrocyte nuclear abnormalities. Furthermore, MMCs may be useful as morphological responses of GLY effects.