Short-term cadmium exposure induces stress responses in frog (Pelophylax bergeri) skin organ culture

Cadmium bioaccumulation dynamics during amphibian development and metamorphosis

Cadmium pollution poses a significant threat to aquatic ecosystems due to its propensity to bioaccumulate and cause toxicity. This study assessed the complex dynamics of cadmium uptake, accumulation and distribution across anuran development to provide new insights into the fate of cadmium burdens during metamorphosis and compare the susceptibility of different life stages to cadmium accumulation. Tadpoles of various developmental stages were exposed to dissolved 109-cadmium and depurated in clean water in a series of experiments. Temporal changes in whole-body and tissue concentrations were analysed using gamma spectroscopy, and anatomical distributions were visualised using autoradiography. Results showed that animals exposed at the onset of metamorphic climax (forelimb emergence) retained significantly less cadmium than animals exposed through larval stages. After exposure, cadmium partitioned predominantly in the skin, gills and remains of metamorphs, whereas larvae accumulated cadmium predominately through their gut. This shows a shift in the primary route of uptake at the onset of climax, which relates to the structural and functional changes of uptake sites through metamorphosis. During climax, some cadmium was redistributed in tissues developing de novo, such as the forelimbs, and concentrated in the regressing tail. Our findings highlight the need for stage-specific considerations in assessing exposure risks.

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.

Effects of cadmium and diethylhexyl phthalate on skin microbiota of Rana chinensis tadpoles

Skin microbiotas play a crucial role in the health, homeostasis, and immune function of amphibians. The contaminants in water could affect the structure and composition of microbial communities. The effects of coexisting pollutants on frogs cannot be adequately explained by a single exposure due to the coexistence of Cd and DEHP in the environment. Following exposure to Cd and/or DEHP, we examined the histological characteristics of Rana chensinensis tadpoles. We also used the 16S rRNA gene sequencing technique to assess the relative abundance of skin microbial communities among tadpoles from each treatment group. Our findings indicate that R. chensinensis' skin experienced some degree of injury due to exposure to Cd and DEHP, which led to the imbalance of their skin microbial community homeostasis and thus interfered with the normal trial status of the host. That may eventually lead to the decline of the amphibian population.

Short-term continuous and pulse Pb exposure causes negative effects on skin histomorphological structure and bacterial composition of adult Pelophylax nigromaculatus

Lead (Pb) is a toxic heavy metal often present in the environment as a pulse in water. Traditional toxicity tests are usually carried out under conditions of continuous concentration, without considering the impact of pulse exposure on aquatic organisms. This study aimed to evaluate the effects of short-term continuous and pulse Pb exposures on the skin bacteria and histomorphological structure of Pelophylax nigromaculatus. Results showed that compared to the control (CON) and Pb continuous exposure group (CEPb), the Pb pulse exposure group (PEPb) showed the smallest size of granular glands, which would interfere with the permeability and secretory function of skin, making the individual more sensitive to external pollution. Lead exposure significantly changed the composition and diversity of skin bacteria. Compared to the CON and CEPb groups, the PEPb group showed a significant increase in the abundance of harmful bacteria (e.g., Bacteroidetes and Chryseobacterium) and a decrease in the abundance of beneficial bacteria (e.g., Pseudomonas). PICRUSt software showed that there were differences in the metabolic pathway of skin bacteria among the three groups (CON, CEPb, and PEPb). Overall, this study indicates that Pb pulse exposure can aggravate the toxicity of Pb for frog skin, providing a new framework for simulating short-term heavy metal exposure in the context of frog health.

In situ assessment of genetic and epigenetic alterations in frog Rana plancyi and Rana limnocharis inhabiting aquatic ecosystems associated with Pb/Zn/Cu mining

Exploration for metallic minerals leads to severe trace metal contamination, thus the ecological risk to aquatic organisms near mining regions has attracted widespread attention. In this study, two species of frog Rana plancyi and Rana limnocharis were collected as amphibian models to explore the genetic and epigenetic effects of trace metals in Dexing mining region. The results indicated that the surface water was heavily contaminated with trace metals and the two species of frog have high bioconcentration of trace metals in the liver. Trace metals disrupted the redox balance and increased reactive oxygen species levels. DNA strand breaks and increased 8-hydroxy-2'-deoxyguanosine levels were observed in the genomic DNA of frogs. Global DNA hypomethylation was found in the liver, which indicated adverse epigenetic effects on frogs. Overall, the study demonstrated that there was significant genotoxicity and epigenotoxicity of aquatic organisms living around the mining region. DNA damage and global DNA methylation are promising biomarkers for assessment of the ecological risk of trace metal pollution in aquatic amphibian frogs.

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.

Frog Skin Innate Immune Defences: Sensing and Surviving Pathogens

Amphibian skin is a mucosal surface in direct and continuous contact with a microbially diverse and laden aquatic and/or terrestrial environment. As such, frog skin is an important innate immune organ and first line of defence against pathogens in the environment. Critical to the innate immune functions of frog skin are the maintenance of physical, chemical, cellular, and microbiological barriers and the complex network of interactions that occur across all the barriers. Despite the global decline in amphibian populations, largely as a result of emerging infectious diseases, we understand little regarding the cellular and molecular mechanisms that underlie the innate immune function of amphibian skin and defence against pathogens. In this review, we discuss the structure, cell composition and cellular junctions that contribute to the skin physical barrier, the antimicrobial peptide arsenal that, in part, comprises the chemical barrier, the pattern recognition receptors involved in recognizing pathogens and initiating innate immune responses in the skin, and the contribution of commensal microbes on the skin to pathogen defence. We briefly discuss the influence of environmental abiotic factors (natural and anthropogenic) and pathogens on the immunocompetency of frog skin defences. Although some aspects of frog innate immunity, such as antimicrobial peptides are well-studied; other components and how they contribute to the skin innate immune barrier, are lacking. Elucidating the complex network of interactions occurring at the interface of the frog's external and internal environments will yield insight into the crucial role amphibian skin plays in host defence and the environmental factors leading to compromised barrier integrity, disease, and host mortality.

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.

Impact of cadmium exposure on swine enterocytes

We tested cadmium (Cd2+) effects on porcine IPEC-J2 cells, which represent an in vitro model of the interaction between intestinal cells and both infectious and non-infectious stressors. Accordingly, we investigated the effects of low (2 μM) to moderate (20 μM) concentrations of Cd2+, in terms of pro-inflammatory gene expression and protein release, as well as of infectivity in a Salmonella typhimurium penetration model. Our data showed a significant (P < .001) increase of intracellular Cd2+ after 3, 6 and 24 h of exposure with respect to levels at 1 h. These data showed the ability of IPEC-J2 to absorb Cd2+ as a function of both time and concentration. Also, the absorption of this heavy metal was related to a significant modulation of important pro-inflammatory messengers. In particular, down-regulation of IL-8 was associated with a significant decrease of Salmonella typhimurium ability to penetrate into IPEC-J2 cells, in agreement with a previous study in which an anti-IL 8 antibody could significantly inhibit Salmonella penetration into the same cells (Razzuoli et al., 2017). This finding demonstrates the ability of Cd2+ to affect the outcome of an important host-pathogen relationship. In conclusion, our study highlighted the ability of an environmental pollutant like Cd2+ to modulate innate immune responses in terms of chemokine release and gene expression, and susceptibility to microbial infections.

Oxidative stress, endocrine disruption, and malformation of Bufo gargarizans embryo exposed to sub-lethal cadmium concentrations

Thyroid hormone (TH) is critical for vertebrate postembryonic development as well as embryonic development. Chinese toad (Bufo gargarizans) embryos were exposed to different concentrations of cadmium (5, 50, 100, 200 and 500μg Cd L-1) for 7days. Malformations were monitored daily, and growth and development of embryos were measured at day 4 and 7, and type 2 and 3 iodothyronine deiodinase (Dio2 and Dio3), thyroid hormone receptors (TRα and TRβ) mRNA levels were also measured to assess disruption of TH synthesis. In addition, superoxide dismutase (SOD), glutathione peroxidase (GPx) and heat shock proteins (HSPs) mRNA expression were examined to evaluate the ability of scavenging ROS. Our results demonstrated a bimodal inhibitory effect of Cd on the embryo growth and development of Bufo gargarizans. Reduced mean stage, total length and weight were observed at 5, 50, 200 and 500, but not at 100μg Cd L-1. Embryos malformation occurred in all cadmium treatments. Morphological abnormalities of embryos are characterized by axial flexures, abdominal edema, stunted growth and fin flexure. Real-time PCR results show that exposure to cadmium down-regulated TRα and Dio3 mRNA expression and up-regulated Dio2 mRNA level. SOD and GPx mRNA expression was significantly up-regulated after cadmium exposure. We concluded that cadmium could change mRNA expression of TRα, Dio2 and Dio3 leading the inhibition of growth and development of B. gargarizans embryo, which suggests that cadmium might have the endocrine-disrupting effect in embryos. Moreover, the reduced ability of scavenging ROS induced by cadmium might be responsible for the teratogenic effects of cadmium.

Characterization of cadmium chloride-induced BiP accumulation in Xenopus laevis A6 kidney epithelial cells

Endoplasmic reticulum (ER) stress can result in the accumulation of unfolded/misfolded protein in the ER lumen, which can trigger the unfolded protein response (UPR) resulting in the activation of various genes including immunoglobulin-binding protein (BiP; also known as glucose-regulated protein 78 or HSPA5). BiP, an ER heat shock protein 70 (HSP70) family member, binds to unfolded protein, inhibits their aggregation and re-folds them in an ATP-dependent manner. While cadmium, an environmental contaminant, was shown to induce the accumulation of HSP70 in vertebrate cells, less information is available regarding the effect of this metal on BiP accumulation or function. In this study, cadmium chloride treatment of Xenopus laevis A6 kidney epithelial cells induced a dose- and time-dependent increase in BiP, HSP70 and heme oxygenase-1 (HO-1) accumulation. Exposure of cells to a relatively low cadmium concentration at a mild heat shock temperature of 30°C greatly enhanced BiP and HSP70 accumulation compared to cadmium at 22°C. Treatment of cells with the glutathione synthesis inhibitor, buthionine sulfoximine, enhanced cadmium-induced BiP and HSP70 accumulation. Immunocytochemistry revealed that cadmium-induced BiP accumulation occurred in a punctate pattern in the perinuclear region. In some cells treated with cadmium chloride or the proteasomal inhibitor, MG132, large BiP complexes were observed that co-localized with aggregated protein or aggresome-like structures. These BiP/aggresome-like structures were also observed in cells treated simultaneously with cadmium at 30°C or in the presence of buthionine sulfoximine. In amphibians, the association of BiP with unfolded protein and its possible role in aggresome function may be vital in the maintenance of cellular proteostasis.

The influence of low-dose cadmium on the laryngeal microstructure and ultrastructure of Pelophylax nigromaculata

Cadmium (Cd) is one of the common heavy metals dispersed throughout the modern environment that disrupts the development of aquatic organisms. Amphibians appear to be particularly vulnerable to this heavy metal contaminant since their eggs and aquatic larvae live in aquatic habitats and have permeable skin. During this critical sensitive period, amphibians live primarily in the water and are thus susceptible to the effects of environmental pollutants in water. Pelophylax nigromaculata completes their laryngeal development from Gosner stage 19 (GS 19, embryonic stage) to GS 46 (metamorphosis stage). To study whether long-term (from GS 19 to GS 46) exposure to low Cd concentrations (0, 4, 8, 16, 32, 64, and 128 μg/L) affects the development of the larynx in P. nigromaculata, a comparative study of microstructures and ultrastructures of female and male P. nigromaculata larynges was carried out. In histological structure, the larynx was composed of epithelial tissue, skeletal muscle, and hyaline cartilage, and there were no differences between male and female frogs except that males had a larger cross-section area than females. In contrast to controls, 64 and 128 μg/L Cd treatments caused a significant decrease in cross-sectional area, while other treatments showed no significant differences. Under the scanning electron microscope, the surface of the larynx could be seen to be attached to developed and evenly distributed cilia, with no significant differences between young male and female frogs, even among the Cd treatments. Under transmission electron microscopy, developed laryngeal epithelial cells could be observed, with obvious cross striations of skeletal muscle cells and mitochondria distributed around the muscle and skeletal muscle satellite cells. Compared with the control group, mitochondria around the skeletal muscle grew in size and decreased in number in the high-concentration treatment.