Ecotoxicity of nanomaterials in amphibians: A critical review

Influence of polystyrene nanoplastics on the toxicity of haloperidol to amphibians: An in vivo and in vitro approach

Chemical pollution is a major driver for the current worldwide crisis of amphibian decline. The present study aimed to assess the influence of polystyrene nanoplastics (PS-NPLs) on the toxicity of haloperidol to aquatic life stages of amphibians, by using in vivo (tadpoles of Xenopus laevis and Pelophylax perezi) and in vitro (A6 and XTC-2 cell lines of X. laevis) biological models. Tadpoles of both species were exposed, for 96 h, to haloperidol: 0.404 to 2.05 mg l-1 (X. laevis) or 0.404 to 3.07 mg L-1 (P. perezi). The most sensitive species to haloperidol (X. laevis) was exposed to haloperidol's LC50,96h combined with two PS-NPLs concentrations (0.01 mg L-1 or 10 mg L-1); the following endpoints were monitored: mortality, malformations, body lengths and weight. In vitro cytotoxicity was assessed by exposing the two cell lines, for 72 h, to: haloperidol (0.195 to 100 mg L-1) alone and combined with 0.01 mg L-1 or 10 mg L-1 of PS-NPLs. Xenopus laevis tadpoles revealed a higher lethal and sublethal sensitivity to haloperidol than those of P. perezi, with LC50,96h of 1.45 and 2.20 mg L-1. In vitro assays revealed that A6 cell line is more sensitive haloperidol than XTC-2: LC50,72h of 13.2 mg L-1 and 5.92 mg L-1, respectively. Results also suggested a higher sensitivity of in vivo models when compared to in vitro biological. Overall, PS-NPLs did not influence haloperidol's toxicity for in vivo and in vitro biological models, except for a reduction on the incidence of malformations while increasing the lethal toxicity (at the lowest concentration) in tadpoles. These opposite interaction patterns highlight the need for a deeper comprehension of NPLs and pharmaceuticals interactions. Results suggest a low risk of haloperidol for anuran tadpoles, though in the presence of PS-NPLs the risk may be increased.

A multi-approach analysis of the toxicity of a commercial formulation of monensin on Rhinella arenarum embryos and larvae

Monensin, an antibacterial commonly used in animal fattening, can enter aquatic ecosystems and harm non-target organisms. Since there are no previous studies about the effects of monensin on amphibians, the aim of the present study was to evaluate the lethal and sublethal toxicity of a commercial formulation of monensin (CFM) through standardized bioassays with embryos and larvae of the amphibian Rhinella arenarum. Oxidative stress (catalase and glutathione S-transferase activities, and reduced glutathione and lipid peroxidation levels), cholinesterasic effect (acetylcholinesterase and butyrylcholinesterase activities) and mutagenicity (micronuclei frequency) biomarkers were evaluated. The CFM produced teratogenic effects, with a teratogenic index of 6.21. Embryos (504 h-LC50: 273.33 µg/L) were more sensitive than larvae, as no significant mortality was observed on larvae exposed up to 3000 µg/L for 504 h. However, oxidative stress, cholinesterasic effect and mutagenicity biomarkers were altered on larvae exposed for 96 h to environmentally relevant concentrations (4, 12 and 20 µg/L of monensin active ingredient). The CFM caused adverse effects on the exposed organisms, primarily on embryos, leading to lethal and sublethal effects, which could impact the wildlife when it reaches aquatic ecosystems.

Metal nanoparticle-induced effects on green toads (Amphibia, Anura) under climate change: conservation implications

The toxicity of aluminum oxide (Al2O3), copper oxide (CuO), iron oxide (Fe3O4), nickel oxide (NiO), zinc oxide (ZnO), and titanium dioxide (TiO2) nanoparticles (NPs) on amphibians and their interaction with high temperatures, remain unknown. In this study, we investigated the survival, developmental, behavioral, and histological reactions of Bufotes viridis embryos and larvae exposed to different NPs for a duration of 10 days, using lethal concentrations (LC25%, LC50%, and LC75% mg/L) under both ambient (AT: 18 °C) and high (HT: 21 °C) temperatures. Based on LC, NiONPs > ZnONPs > CuONPs > Al2O3NPs > TiO2NPs > Fe3O4NPs showed the highest mortality at AT. A similar pattern was observed at HT, although mortality occurred at lower concentrations and Fe3O4NPs were more toxic than TiO2NPs. The results indicated that increasing concentrations of NPs significantly reduced hatching rates, except for TiO2NPs. Survival rates decreased, abnormality rates increased, and developmental processes slowed down, particularly for NiONPs and ZnONPs, under HT conditions. However, exposure to low concentrations of Fe3O4NPs for up to 7 days, CuONPs for up to 72 h, and NiO, ZnONPs, and TiO2NPs for up to 96 h did not have a negative impact on survival compared with the control group under AT. In behavioral tests with larvae, NPs generally induced hypoactivity at AT and hyperactivity at HT. Histological findings revealed liver and internal gill tissue lesions, and an increase in the number of melanomacrophage centers at HT. These results suggest that global warming may exacerbate the toxicity of metal oxide NPs to amphibians, emphasizing the need for further research and conservation efforts in this context.

Microplastics and TiO2 nanoparticles mixture as an emerging threat to amphibians: A case study on bullfrog embryos

Emerging contaminants can act as contributing factors to the decline of amphibian populations worldwide. Recently, scientists have drawn attention to the potential ecotoxicity of microplastics and nanomaterials in amphibians, however, their possible effects on embryonic developmental stages are still absent. Thus, the present study analyzed the developmental toxicity of environmentally relevant concentrations of polyethylene microplastics (PE MPs; 60 mg/L) and titanium dioxide nanoparticles (TiO2 NPs; 10 μg/L), isolated or in combination (Mix group) on bullfrog embryos, Aquarana catesbeiana, adapting the Frog Embryo Teratogenesis Assay (FETAX, 96h). Allied to the FETAX protocol, we also analyzed the heart rate and morphometric data. The exposure reduced the survival and hatching rates in groups exposed to TiO2 NPs, and to a lesser extent, also affected the Mix group. TiO2 NPs possibly interacted with the hatching enzymes of the embryos, preventing hatching, and reducing their survival. The reduced effects in the Mix group are due to the agglomeration of both toxicants, making the NPs less available for the embryos. PE MPs got attached to the gelatinous capsule of the chorion (confirmed by fluorescence microscopy), which protected the embryos from eventual direct effects of the microplastics on the hatching and survival rates. Although there were no cardiotoxic effects nor morphometric alterations, there was a significant increase in abdominal edemas in the hatched embryos of the PE MPs group, which indicates that osmoregulation might have been affected by the attachment of the microplastics on the embryos' gelatinous capsule. This study presents the first evidence of developmental toxicity of environmental mixtures of microplastics and nanoparticles on amphibians and reinforces the need for more studies with other amphibian species, especially neotropical specimens that could present bigger sensibility. Our study also highlighted several features of the FETAX protocol as useful tools to evaluate the embryotoxicity of several pollutants on amphibians.

Investigating the toxic mechanism of iron oxide nanoparticles-induced oxidative stress in tadpole (Duttaphrynus melanostictus): A combined biochemical and molecular study

Metal oxide nanomaterials have toxicity towards aquatic organisms, especially microbes and invertebrates, but little is known about their impact on amphibians. We conducted a study on Duttaphrynus melanostictus (D. melanostictus) tadpoles to explore the chronic toxicity effects of iron oxide nanoparticles (IONPs) and the underlying mechanisms of IONPs-induced oxidative stress. IONPs exposure led to increased iron accumulation in the blood, liver, and kidneys of tadpoles, significantly affecting blood parameters and morphology. Higher IONPs concentrations (10 and 50 mg L-1) triggered reactive oxygen species generation, resulting in lipid peroxidation, oxidative stress, and pronounced toxicity in tadpoles. The activity levels of antioxidant enzymes/proteins (SOD, CAT, albumin, and lysozyme) decreased after IONPs exposure, and immunological measures in the blood serum were significantly reduced compared to the control group. Molecular docking analysis revealed that IONPs primarily attached to the surface of SOD/CAT/albumin/lysozyme through hydrogen bonding and hydrophobic forces. Overall, this study emphasizes the ability of IONPs to induce oxidative damage by decreasing immunological profiles such as ACH50 (34.58 ± 2.74 U mL-1), lysozyme (6.94 ± 0.82 U mL-1), total Ig (5.00 ± 0.35 g dL-1), total protein (1.20 ± 0.17 g dL-1), albumin (0.52 ± 0.01 g dL-1) and globulin (0.96 ± 0.01 g dL-1) and sheds light on their potential toxic effects on tadpoles.

Carbon nitride dots do not impair the growth, development, and telomere length of tadpoles

Carbon nanoparticles, or carbon dots, can have many beneficial uses. However, we must consider whether they may have any potential negative side effects on wildlife or the ecosystem when these particles end up in wastewater. Early development stages of amphibians are particularly sensitive to contaminants, and exposure to carbon dots could disrupt their development and cause morbidity or death. Past studies have investigated short-term exposure to certain types of nanoparticles, but if these particles get into wastewater exposure may not be short term. Therefore, we tested whether chronic exposure to different concentrations of carbon dots affects the growth, metamorphosis, and telomere length of Cuban tree frog (Osteopilus septentrionalis) tadpoles. We exposed 12 groups of five tadpoles each to different concentrations of carbon dots and a control for three months and tracked survival, growth and metamorphosis. We used carbon nitride dots approximately 2 nm in size at concentrations of 0.01 mg/ml and 0.02 mg/ml, known to interrupt development in zebrafish embryos. After three months, we measured telomere length from tissue samples. We found no difference in tadpole survivorship, growth, development rate, or telomere length among any of the groups, suggesting that carbon dots at these concentrations do not disrupt tadpole development.

Carbon nanotubes and nanofibers seen as emerging threat to fish: Historical review and trends

Since the discovery of the third allotropic carbon form, carbon-based one-dimensional nanomaterials (1D-CNMs) became an attractive and new technology with different applications that range from electronics to biomedical and environmental technologies. Despite their broad application, data on environmental risks remain limited. Fish are widely used in ecotoxicological studies and biomonitoring programs. Thus, the aim of the current study was to summarize and critically analyze the literature focused on investigating the bioaccumulation and ecotoxicological impacts of 1D-CNMs (carbon nanotubes and nanofibers) on different fish species. In total, 93 articles were summarized and analyzed by taking into consideration the following aspects: bioaccumulation, trophic transfer, genotoxicity, mutagenicity, organ-specific toxicity, oxidative stress, neurotoxicity and behavioral changes. Results have evidenced that the analyzed studies were mainly carried out with multi-walled carbon nanotubes, which were followed by single-walled nanotubes and nanofibers. Zebrafish (Danio rerio) was the main fish species used as model system. CNMs' ecotoxicity in fish depends on their physicochemical features, functionalization, experimental design (e.g. exposure time, concentration, exposure type), as well as on fish species and developmental stage. CNMs' action mechanism and toxicity in fish are associated with oxidative stress, genotoxicity, hepatotoxicity and cardiotoxicity. Overall, fish are a suitable model system to assess the ecotoxicity of, and the environmental risk posed by, CNMs.

Assessment of toxicity, genotoxicity and oxidative stress in Fejervarya limnocharis exposed to tributyltin

Tributyltin (TBT) is widely used in various commercial applications due to its biocidal properties. Toxicological and genotoxicological data on TBT exposure to amphibians is insufficient. Our study aimed to determine the acute toxicity and genotoxic potential of TBT in Fejervarya limnocharis tadpoles. Furthermore, oxidative stress was also investigated in TBT-treated tadpoles. Tadpoles of Gosner stage (26-30) were screened and subjected to increasing concentrations of TBT (0, 3, 7, 11, 15, 19, 23 µg/L) for determining the LC50 values for 24 h, 48 h, 72 h, and 96 h. LC50 values of TBT for 24 h, 48 h, 72 h, and 96 h were found to be 19.45, 15.07, 13.12, and 11.84 μg/L respectively. Based on the 96 h LC50 value (11.84 µg/L), tadpoles were exposed to different sub-lethal concentrations of TBT for the evaluation of its genotoxic potential and effects on oxidative balance. The role of TBT on survivability, growth, and time to metamorphosis was also assessed. TBT exposure significantly altered the life history traits measured, increased mortality, and delayed the time taken to metamorphosis. Results indicated significant induction of micronucleus (MN, p < 0.001) and other erythrocytic nuclear aberrations (ENA, p < 0.01) in the TBT-treated groups. Significant alterations in comet parameters and oxidative balance were also observed in the treated groups. The present study findings might add to the cause of the gradual population decline seen in the amphibians. This study also demonstrates the alteration of the life-history traits, oxidative balance, and DNA damage upon TBT exposure which can have long-term consequences for the anuran amphibian F. limnocharis.

Toxic, genotoxic, mutagenic, and bioaccumulative effects of metal mixture from settleable particulate matter on American bullfrog tadpoles (Lithobates catesbeianus)

Amphibians are more susceptible to environmental stressors than other vertebrates due to their semipermeable skin and physiological adaptations to living in very specific microhabitats. Therefore, the aim of the present study was to investigate the effects of a metal mixture from settleable particulate matter (SePM) released from metallurgical industries on Lithobates catesbeianus tadpoles. Endpoints analyzed included metal bioconcentration, morphological (biometrical indices), hematological parameters (hemoglobin and blood cell count), and erythrocyte DNA damage (genotoxicity and mutagenicity). American bullfrog tadpoles (Gosner's stage 25) were kept under control condition (no contaminant addition) or exposed to a sub-lethal and environmentally relevant concentration (1 g.L-1) of SePM for 96 h. Tadpoles exposed to SePM exhibited elevated whole blood levels of Fe56, AL, Sn, Pb, Zn, Cr, Cu, Ti, Rb, V, Ce, La, Ag, As. SePM-exposed tadpoles showed a significant decrease in condition factor (12%) and increases in hepatosomatic index (25%), hemoglobin concentration (17%), and total leukocytes (82%), thrombocytes (90%), and monocytes (78%) abundance. In addition, exposed tadpoles showed higher MN and ENAs (340 and 140%, respectively) frequencies, and erythrocyte DNA damage with approximately 1.2- to 1.8-fold increases in comet parameters. Taken together, these results suggest that the multimetal mixture found in SePM is potentially genotoxic and mutagenic to L. catesbeianus tadpoles, induces stress associated with hematological changes, and negatively affects growth. Although such contamination occurs at sublethal levels, regulatory standards are needed to control the emission of SePM and protect amphibian populations.

Subacute toxicity and endocrine-disrupting effects of Fe2O3, ZnO, and CeO2 nanoparticles on amphibian metamorphosis

This study evaluated the potential toxic and endocrine-disrupting effects of sublethal concentrations of Fe2O3, CeO2 and ZnO nanoparticles (NPs) on amphibian metamorphosis. Tadpoles were exposed to several NPs concentrations, reaching a maximum of 1000 µg/L, for up to 21 days according to the amphibian metamorphosis assay (AMA). Some standard morphological parameters, such as developmental stage (DS), hind limb length (HLL), snout-to-vent length (SVL), wet body weight (WBW), and as well as post-exposure lethality were recorded in exposed organisms on days 7 and 21 of the bioassay. Furthermore, triiodothyronine (T3), thyroxine (T4) and malondialdehyde (MDA) levels and the activities of glutathione S-transferases (GST), glutathione reductase (GR), catalase (CAT), carboxylesterase (CaE), and acetylcholinesterase (AChE) were determined in exposed tadpoles as biomarkers. The results indicate that short-term exposure to Fe2O3 NPs leads to toxic effects, both exposure periods cause toxic effects and growth inhibition for ZnO NPs, while short-term exposure to CeO2 NPs results in toxic effects and long-term exposure causes endocrine-disrupting effects. The responses observed after exposure to the tested NPs during amphibian metamorphosis suggest that they may have ecotoxicological effects and their effects should be monitored through field studies.

The amphibian's spleen as a source of biomarkers for ecotoxicity assessment: Historical review and trends

Amphibians are very sensitive to many environmental changes, so these animals are considered good bioindicator models for ecotoxicology. Given the importance of the amphibian spleen for hematopoietic and immune responses, this can be a key organ for the evaluation of biomarkers to monitor the health of individuals in nature or in captivity. In this systematic review, we searched databases and summarized the main findings concerning the amphibian spleen as a source of possible biomarkers applied in different scientific fields. The searches resulted in 83 articles published from 1923 to 2022, which applied the use of splenic samples to evaluate the effects of distinct stressors on amphibians. Articles were distributed in more than twenty countries, with USA, Europe, and Brazil, standing out among them. Publications focused mainly on anatomical and histomorphological characterization of the spleen, its physiology, and development. Recently, the use of splenic biomarkers in pathology and ecotoxicology began to grow but many gaps still need to be addressed in herpetological research. About 85 % of the splenic biomarkers showed responses to various stressors, which indicates that the spleen can provide numerous biomarkers to be used in many study fields. The limited amount of information on morphological description and splenic anatomy in amphibians may be a contributing factor to the underestimated use of splenic biomarkers in herpetological research around the world. We hope that this unprecedented review can instigate researchers to refine herpetological experimentation, using the spleen as a versatile and alternative source for biomarkers in ecotoxicology.

Subchronic toxicity of iron-selenium nanoparticles on oxidative stress response, histopathological, and nuclear damage in amphibian larvae Rana saharica

In this work, we evaluated the subchronic toxicity of FeSe nanoparticles (NPs) in tadpoles of Rana saharica. Tadpoles were exposed for 1-3 weeks to FeSe NPs at 5 mg/L and 100 mg/L rates. Parameters of oxidative stress were measured in whole larvae, and the micronucleus test was performed on circulating blood erythrocytes. We noted a disturbance of the detoxification systems. Enzymatic and non-enzymatic data showed that exposure to FeSe NPs involved a highly significant depletion of GSH, a significant increase in GST activity, and a lipid peroxidation associated with a highly significant increase in MDA. We also noted a neurotoxic effect characterized by a significant inhibition of AChE activity. A micronucleus test showed concentration-dependent DNA damage. This research reveals that these trace elements, in their nanoform, can cause significant neurotoxicity, histopathologic degeneration, cellular and metabolic activity, and genotoxic consequences in Rana larvae.

Potential ecotoxicity of substrate-enriched zinc oxide nanoparticles to Physalaemus cuvieri tadpoles

Although the ecotoxicological effects of ZnO nanoparticles (ZnO NPs) have already been reported in different taxa, little is known about their impacts on amphibians. Thus, we aimed to evaluate the potential effects of exposure of Physalaemus cuvieri tadpoles to substrates enriched with ZnO NPs (and with its ionic counterpart, Zn+2, ZnCl2 - both at 100 mg/kg) previously used in the cultivation of Panicum maximum (Guinea grass). We showed that although exposure for 21 days did not impact the survival, growth, and development of tadpoles, we noted an increase in the frequency of erythrocyte nuclear abnormalities in the "ZnCl2" and "ZnONP" groups, which was associated with suppression of antioxidant activity in the animals (inferred by SOD and CAT activity and DPPH free radical scavenging capacity). In the tadpoles of the "ZnONP" group, we also noticed a reduction in creatinine and bilirubin levels, alpha-amylase activity, and an increase in alkaline phosphatase activity. But the treatments did not alter the activity of the enzymes lactate dehydrogenase and gamma-glutamyl-transferase and total protein and carbohydrate levels. On the other hand, we report a cholinesterase and hypotriglyceridemic effect in the "ZnCl2" and "ZnONP" groups. Zn bioaccumulation in animals, from ZnO NPs, from Zn+2 released from them, or both, has been associated with causing these changes. Finally, principal component analysis (PCA) and the values of the "Integrated Biomarker Response" index revealed that the exposure of animals to substrates enriched with ZnO NPs caused more pronounced effects than those attributed to its ionic counterpart. Therefore, our study reinforces the need to consider the environmental risks of using these nanomaterials for agricultural purposes for amphibians.

Ecotoxicity risk assessment of copper oxide nanoparticles in Duttaphrynus melanostictus tadpoles

In recent years, copper oxide nanoparticles (CONPs) have gained considerable importance in ecotoxicology studies. CONP ecotoxicity studies on amphibians are limited, particularly on Duttaphrynus melanostictus (D. melanostictus) tadpoles, and most CONP ecotoxicity studies have shown developmental effects on amphibians. Therefore, the present study aimed to determine the ecotoxicity of CONPs in D. melanostictus tadpoles by assessing multi-biomarkers including bioaccumulation, antioxidants, biochemical, haematological, immunological and oxidative stress biomarkers. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to characterize the morphology and physicochemical properties of CONPs. After 30 d of the experiment, blood and organs were collected to measure the levels of multiple biomarkers. The dissolution rate of copper ions in exposed media was observed in all studied groups. According to the results, significant (p < 0.05) increase in copper ion bioaccumulation (blood, liver and kidney), oxidative stress and biochemical biomarkers in the blood serum of CONPs exposed tadpoles compared to control tadpoles, which was accompanied by significant variations in morphological and haematological parameters. In contrast to the untreated tadpoles, the CONPs-exposed tadpoles showed statistically significant (p < 0.05) decreases in antioxidants and immunological indices of blood serum. Based on our results, we concluded that the ecotoxicity of CONPs is due to the production of reactive oxygen species (ROS), which can cause oxidative stress in tadpoles, resulting in impairments. According to our knowledge, the present study was the first to use a multi-biomarker ecotoxicity approach on D. melanostictus tadpoles that could be used as an ecological bioindicator to assess aquatic toxicity.

Assessment of multiple biomarkers in Lithobates catesbeianus (Anura: Ranidae) tadpoles exposed to zinc oxide nanoparticles and zinc chloride: integrating morphological and behavioral approaches to ecotoxicology

The ecotoxicological risk to vertebrates posed by zinc oxide nanoparticles (ZnO NPs) is still poorly understood, especially in animals with a biphasic life cycle, which have aquatic and terrestrial phases, such as amphibians. In the present study, we investigated whether acute exposure (7 days) to ZnO NPs and zinc chloride (ZnCl₂) at three environmentally relevant concentrations (0.1, 1.0, and 10 mg L^-1) induces changes in the morphology, chondrocranium, and behavior of the tadpoles of Lithobates catesbeianus (Anura: Ranidae). Tadpoles exposed to both forms of Zn did not undergo any morphological or behavioral changes at the lowest concentrations (0.1 and 1.0 mg L^-1). However, the animals exposed to the highest concentration (10 mg L^-1) lacked oral disc structures, were smaller in size, had a longer tail, and presented changes in the position and coiling of the intestine and malformations of the chondrocranium in comparison with the control group. This indicates that ZnO NPs and ZnCl₂ altered the development of the tadpoles, causing delays in their metamorphosis and even reducing individual fitness. The tadpoles exposed to both forms of Zn at 10 mg L^-1 also had reduced mobility, especially in the presence of conspecifics. Based on these findings, we emphasize the importance of studying morphological, skeletal, and behavioral biomarkers to evaluate the toxic effects of metal-based nanoparticles in amphibians.

Ecotoxicological perspectives of microplastic pollution in amphibians

Microplastics (MPs) are contaminants widely distributed in the environment and biota. Previously, most studies focused on identifying and characterizing microplastics in the marine environment, while their impact on freshwater ecosystems remains to be determined. This review summarizes recent findings regarding MPs physiological, immunological, and genetic effects on amphibians based upon the biological relevance of this species as indicators of freshwater pollution. Data demonstrated that MPs contamination may potentially alter various physiological processes in aquatic animals, mainly in the embryonic stages. It is worthwhile noting that adverse effects might be enhanced in synergy with other pollutants. However, amphibians might counteract the effect of MPs and other pollutants through microbiota present both in the intestine and on the skin. In addition, amphibian microbial composition might also be altered by MPs themselves in a manner that leads to unpredicted health consequences in amphibians.

Titanium dioxide nanoparticles as a risk factor for the health of Neotropical tadpoles: a case study of Dendropsophus minutus (Anura: Hylidae)

The production and use of titanium dioxide (TiO₂) nanoparticles are increasing worldwide. The release of this substance into the environment can induce toxic effects in aquatic invertebrates and vertebrates, although the exact nature of its impacts on Neotropical amphibians is still poorly understood. In this context, the present study evaluated the toxicity of TiO₂ nanoparticles and their counterpart-dissolved titanium dioxide (TiO₂)-in the tadpoles of Dendropsophus minutus. The biometric parameters, DNA damage, and behavioral changes were verified in tadpoles exposed to three different concentrations (0.1 mg·L^-1, 1.0 mg·L^-1, and 10 mg·L^-1) of TiO₂ nanoparticles and dissolved TiO₂ for 7 days. We verified significant DNA damage in the D. minutus tadpoles exposed to both forms of Ti, in comparison with the control group. We also identified a reduction in total size, body length, and width, and the height of the musculature of the tail of the tadpoles exposed to all concentrations of both substances in comparison with the control. In the behavioral test, the tadpoles exposed to nanoparticles and dissolved TiO₂ presented reduced mobility and a tendency to be less aggregated than normal. Here, the simultaneous use of multiple biomarkers was fundamental for the reliable assessment of the adverse effects of nanomaterials on anuran amphibians and the establishment of a systematic approach to the biomonitoring of aquatic ecosystems. The present study expands our understanding of the genotoxic, morphological, and behavioral effects of TiO₂ nanoparticles and dissolved TiO₂ on anuran amphibians, and contributes to the establishment of further research for the more systematic assessment of the environmental risk of nanomaterials.

Single and Mixture Toxicity of Boron and Vanadium Nanoparticles in the Soil Annelid Enchytraeus crypticus: A Multi-Biomarker Approach

The increased use and production of new materials has contributed to Anthropocene biodiversity decrease. Therefore, a careful and effective toxicity evaluation of these new materials is crucial. However, environmental risk assessment is facing new challenges due to the specific characteristics of nanomaterials (NMs). Most of the available ecotoxicity studies target the aquatic ecosystems and single exposures of NMs. The present study evaluated Enchytraeus crypticus survival and reproduction (28 days) and biochemical responses (14 days) when exposed to nanoparticles of vanadium (VNPs) and boron (BNPs) (single and mixture; tested concentrations: 10 and 50 mg/kg). Although at the organism level the combined exposures (VNPs + BNPs) did not induce a different toxicity from the single exposures, the biochemical analysis revealed a more complex picture. VNPs presented a higher toxicity than BNPs. VNPs (50 mg/kg), independently of the presence of BNPs (additive or independent effects), caused a decrease in survival and reproduction. However, acetylcholinesterase, glutathione S-transferase, catalase, glutathione reductase activities, and lipid peroxidation levels revealed alterations in neurotoxicity, detoxification and antioxidant responses, depending on the time and type of exposure (single or mixture). The results from this study highlight different responses of the organisms to contaminants in single versus mixture exposures, mainly at the biochemical level.

Assessment of toxicity in the freshwater tadpole Polypedates maculatus exposed to silver and zinc oxide nanoparticles: A multi-biomarker approach

Nanoparticles (NPs), especially silver nanoparticles (Ag NPs) and zinc oxide nanoparticles (ZnO NPs), are widely used in various industrial applications and are released into the surrounding environment through industrial and household wastewater. They have enormous toxic effects on aquatic animals and amphibians. In the current study, a multi-biomarker approach was used to assess toxicity on Polypedates maculatus (P. maculatus) tadpoles collected from a freshwater pond and exposed to sub-lethal concentrations of Ag-NPs (1, 5 and 10 mg L^-1) and ZnO-NPs (1, 10 and 50 mg L^-1). A significant bioaccumulation of silver (Ag) and Zinc (Zn) was observed in the blood, liver, kidney and bones in comparison to control tadpoles. Blood parameters (Red blood cells (RBC), Hematocrit (Htc), White blood cells (WBC), monocytes, lymphocytes and neutrophils), immunological markers (ACH50, lysozyme, total Ig, total protein, albumin, and globulin), biochemical markers (glucose, cortisol, cholesterol, triglycerides, alanine transaminase (ALT), asparatate transaminase (AST), alkaline phosphatase (ALP), urea and creatinine) and the oxidative stress marker (LPO) of serum were increased significantly (p < 0.05) in Ag/ZnO-NPs exposed groups when compared to the control groups. The levels of mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), mean corpuscular volume (MCV) and haemoglobin (Hb) in the ZnO NP-exposed groups were significantly different from those in the control group. Antioxidant (SOD and CAT) levels were significantly declined in the treatment groups. Based on the results, Ag/ZnO-NPs are toxic to aquatic organisms and amphibians at sub-lethal concentrations. The species P. maculatus can be used as a bioindicator for the nanomaterial (NM) contamination of freshwater systems.

Influence of nano and bulk copper on agile frog development

Nanotechnology, as one of the fastest-growing industries, offers many benefits in various fields. However, properties that contribute to its positive effects, in other context, can cause adverse effects to various organisms, such as amphibians. Identifying possible negative effects on its survival is crucial since amphibians are the most threatened group of vertebrates. In that context, we investigated the influence of both nano and bulk copper on embryonic development of agile frog, Rana dalmatina. The embryos were exposed to various concentrations (0.01 mg/L, 0.075 mg/L, 0.15 mg/L or 0.3 mg/L) of either nano (CuO, declared size 40-80 nm) or bulk form (CuSO₄·5H₂O) for 16 days. Upon the experiment, tadpoles were measured and weighted, then homogenized and their protein, lipid, and carbohydrates content determined, as well as the activity of LDH. Our results suggest stronger negative influence of nano copper to size and weight of tadpoles, and bulk copper on lipid content, while both had strong negative effect on carbohydrates content, and LDH activity. In addition, our results suggest agile frog to be more susceptible to negative influence of both, nano and bulk copper, than commonly used Xenopus laevis.

Emerging trends in nanoparticle toxicity and the significance of using Daphnia as a model organism

Nanoparticle production is on the rise due to its many uses in the burgeoning nanotechnology industry. Although nanoparticles have growing applications, there is great concern over their environmental impact due to their inevitable release into the environment. With uncertainty of environmental concentration and risk to aquatic organisms, the microcrustacean Daphnia spp. has emerged as an important freshwater model organism for risk assessment of nanoparticles because of its biological properties, including parthenogenetic reproduction; small size and short generation time; wide range of endpoints for ecotoxicological studies; known genome, useful for providing mechanistic information; and high sensitivity to environmental contaminants and other stressors. In this review, we (1) highlight the advantages of using Daphnia as an experimental model organism for nanotoxicity studies, (2) summarize the impacts of nanoparticle physicochemical characteristics on toxicity in relation to Daphnia, and (3) summarize the effects of nanoparticles (including nanoplastics) on Daphnia as well as mechanisms of toxicity, and (4) highlight research uncertainties and recommend future directions necessary to develop a deeper understanding of the fate and toxicity of nanoparticles and for the development of safer and more sustainable nanotechnology.

Nanomaterials-induced toxicity on cardiac myocytes and tissues, and emerging toxicity assessment techniques

The extensive production and use of nanomaterials have resulted in the continuous release of nano-sized particles into the environment, and the health risks caused by exposure to these nanomaterials in the occupational population and the general population cannot be ignored. Studies have found that particle exposure is closely related to cardiovascular disease. In addition, there have been many reports that nanomaterials can enter the heart tissue, accumulate and then cause damage. Therefore, in the present article, literature related to nanomaterials-induced cardiotoxicity in recent years was collected from the PubMed database, and then organized and summarized to form a review. This article mainly discusses heart damage caused by nanomaterials from the following three aspects: Firstly, we summarize the research 8 carbon nanotubes, etc. Secondly, we discuss in depth the possible underlying mechanism of the damage to the heart caused by nanoparticles. Oxidative stress damage, mitochondrial damage, inflammation and apoptosis have been found to be key factors. Finally, we summarize the current research models used to evaluate the cardiotoxicity of nanomaterials, highlight reliable emerging technologies and in vitro models that have been used for toxicity evaluation of environmental pollutants in recent years, and indicate their application prospects.

Recent advances in Shrimp aquaculture wastewater management

Aquaculture has been celebrated globally and believed to usher in a viable alternative to capture fisheries. It is most welcomed especially now that the world population explosion has pushed the demand on fisheries products to worrisome limits. Shrimp farming is an area of aquaculture that has witnessed significant growth in recent years, contributing substantially to the global aquaculture production. However, intensification of shrimp aquaculture has come with unintended consequences such as wastewater management and other problems emanating from environmental impact of the wastewater. This study identified excess feed and fertilizer application, metabolite wastes, shrimp mortalities, oil spillage from farm machines, drug and chemical abuse as some of the activities contributing to wastewater generation in shrimp aquaculture farming. The impact of shrimp effluent water discharged has been observed to be socio-economic with both positive and negative dimensions. In attempt to overcome the overwhelming problems associated with shrimp effluent water and bring reassurances to its sustainability, a good number of new technological approaches have been identified including caviation, high-rate algal pond system, use of nanomaterials, biofloc technology, nanoadsorbent and polymeric nanoadsorbents. Although all have been proven to be useful, none could boast of a complete and integrated approach that considers all the technological, legal, social, environmental, public health and institutional concerns.

Toxicity of Titanium Dioxide Nanoparticles to Tadpoles of Asian Common Toad (Duttaphrynus melanostictus) Following Short Term and Chronic Exposures

Nanotoxicity data for amphibians are limited compared to other taxonomic groups. The present study assessed toxicity of titanium dioxide nanoparticles (nanoTiO₂, anatase form, particle size < 25 nm) on tadpoles of Duttaphrynus melanostictus after short term and chronic exposures. Exposure to nanoTiO₂ (≤ 100 mg/L) for 96 h had no significant effect on survival but upon transfer to nanoTiO₂ free water for another 21 days, survival of the tadpoles pre-exposed to nanoTiO₂ was greatly reduced and their development was delayed. Chronic exposure to nanoTiO₂ (0.1 to 10 mg/L) for 14 days had no significant effects on acetylcholinesterase activities but induced mortalities (up to 40%) and histological alterations in the intestine and liver tissues. The results indicate that release of nanoTiO₂ to aquatic ecosystems could pose negative impacts to amphibian populations.

Micro(nano)plastics as an emerging risk factor to the health of amphibian: A scientometric and systematic review

Although the toxicity of microplastics (MPs) and nanoplastics (NPs) is recognized at different trophic levels, our know-how about their effects on amphibians is limited. Thus, we present and discuss the current state on studies involving amphibians and plastic particles, based on a broad approach to studies published in the last 5 years. To search for the articles, the ISI Web of Science, ScienceDirect, and Scopus databases were consulted, using different descriptors related to the topic of study. After the systematic search, we identified 848 publications. Of these, 12 studies addressed the relationship "plastic particles and amphibians" (7 studies developed in the laboratory and 5 field studies). The scientometric analysis points to geographic concentration of studies in Brazil and China; low investment in research in the area, and limited participation of international authors in the studies carried out. In the systematic approach, we confirm the scarcity of available data on the toxicity of plastic particles in amphibians; we observed a concentration of studies in the Anura order, only one study explored the toxicological effects of NPs and polystyrene and polyethylene are the most studied plastic types. Moreover, the laboratory tested concentrations are distant from those of the environmentally relevant; and little is known about the mechanisms of action of NPs/MPs involved in the identified (eco)toxicological effects. Thus, we strongly recommend more investments in this area, given the ubiquitous nature of NPs/MPs in aquatic environments and their possible consequences on the dynamics, reproduction, and survival of species in the natural environment.

Cytotoxicity and mutagenicity of the waters of the Marrecas River (Paraná, Brazil) to bullfrogs (Lithobates catesbeianus)

Animals have a long history of assessing ecosystem responses to environmental disturbances, and amphibians stand out for presenting themselves as good animal model and bioindicators of environmental quality. The main purpose of the present work was to investigate the cellular effects of contamination of waters of the Marrecas River, located in the southwest of the state of Paraná, Brazil. Therefore, the objective of the present study was to investigate and monitor the cytotoxic and mutagenic effect, with bullfrog tadpoles, and to discuss these effects with land use along this hydrographic basin. Mutagenic effects were determined by micronucleus assay, and cytotoxicity by other nuclear changes, such as segmented cells, binucleated cells, cells with buds and reniform cells. Water samples were obtained at nine sites along the Marrecas River, covering areas with rural and urban hydrological contribution. For each site, four samples were collected, along the years 2017 and 2018, encompassing the four seasons (summer, autumn, winter, and spring). The results showed mutagenic and cytotoxic effect in four sampling sites, and only cytotoxic effect in other four sites. These effects may be due, possibly, to the use of different agrochemicals across the hydrographic basin region, which have predominant hydrological contributions from crops. Data of this study indicate the presence of cytotoxic and mutagenic contaminants in the waters of the Marrecas River, which can generate environmental problems on the river fauna/flora, and can also affect the local population health.

Environmental risk of nanomaterials and nanoparticles and EPR technique as an effective tool to study them-a review

Nanotechnologies and different types of nanomaterials belong in present day to intensively studied materials due to their unique properties and diverse potential applications in, e.g., electronics, medicine, or display technologies. Together with the investigation of their desired beneficial properties, a need to investigate and evaluate their influence on the environment and possible harmful effects towards living organisms is growing. This review summarizes possible toxic effects of nanomaterials on environment and living organisms, focusing on the possible bioaccumulation in organisms, toxicity, and its mechanisms. The main goal of this review is to refer to potential environmental risks rising from the use of nanomaterials and the necessity to deal with the possible toxic effects considering the growing interest in the wide-scale utilization of these materials. Electron paramagnetic resonance spectroscopy as the only analytical technique capable of detecting radical species enables detection, quantification, and monitoring of the generation of short-lived radicals often coupled with toxic effects of nanomaterials, which makes it an important method in the process of nanotoxicity mechanism determination.

Commentary: Revisiting nanoparticle-assay interference: There's plenty of room at the bottom for misinterpretation

Engineered nanomaterials (ENMs) are a diverse class of materials whose distinct properties make them desirable in a multitude of applications. The proliferation of nanotoxicology research has improved our understanding of ENM toxicity, but an under appreciation for their potential to interfere with biochemical assays has hampered progress in the field. The physicochemical properties of ENMs can promote their interaction with membranes or biomacromolecules (e.g. proteins, genomic material). This can influence the activity of enzymes used as biomarkers or as reagents in biochemical assay protocols, bind indicator dyes in cytotoxicity tests, and/or interfere with the cellular mechanisms controlling the uptake of such dyes. The spectral characteristics of some ENMs can cause interference with common assay chromophores, fluorophores, and radioisotope scintillation cocktails. Finally, the inherent chemical reactivity of some ENMs can short circuit assay mechanisms by directly oxidizing or reducing indicator dyes. These processes affect data quality and may lead to significant misinterpretations regarding ENM safety. We provide an overview of some ENM properties that facilitate assay interference, examples of interference and the erroneous conclusions that may result from it, and a number of general and specific recommendations for validating cellular and biochemical assay protocols in nanotoxicology studies.

Xenopus in revealing developmental toxicity and modeling human diseases

The Xenopus model offers many advantages for investigation of the molecular, cellular, and behavioral mechanisms underlying embryo development. Moreover, Xenopus oocytes and embryos have been extensively used to study developmental toxicity and human diseases in response to various environmental chemicals. This review first summarizes recent advances in using Xenopus as a vertebrate model to study distinct types of tissue/organ development following exposure to environmental toxicants, chemical reagents, and pharmaceutical drugs. Then, the successful use of Xenopus as a model for diseases, including fetal alcohol spectrum disorders, autism, epilepsy, and cardiovascular disease, is reviewed. The potential application of Xenopus in genetic and chemical screening to protect against embryo deficits induced by chemical toxicants and related diseases is also discussed.

An integrated approach to assess the sublethal effects of colloidal gold nanorods in tadpoles of Xenopus laevis

Gold nanorods (AuNR) have been explored for many applications, including innovative nanomedicines, which also might contribute to its increase in the environment, namely due to inadequate disposable of wastes into aquatic environments. Early-life stages of amphibians are usually aquatic and sensitive to chemical contamination. Accordingly, this study aimed to determine the sublethal effects of CTAB functionalized AuNR on Xenopus laevis tadpoles. As such, tadpoles were exposed to serial concentrations of AuNR for 72 h. A reduction in the rate of feeding (EC₅₀ = 4 μg.L^-1), snout to vent growth (EC₅₀ = 5 μg.L^-1) and weight gain (EC₅₀ = 6 μg.L^-1), was observed for AuNR-exposed tadpoles. Also, tadpoles actively avoided concentrations ≥ 4 μg.L^-1 of AuNR, after 12 h of exposure. At the biochemical level, AuNR caused impairments in antioxidant and nervous system related enzymes. Exposure to CTAB alone caused a high mortality. Results indicated that CTAB functionalized AuNR may induce several sublethal effects that may compromise the organism's fitness. Avoidance behavior (which corresponds to the disappearance of organisms, thus, similar to their death), observed at concentrations matching those inducing sublethal effects, suggest that it should be considered in the risk assessment for amphibians.

Toxicity of engineered nanomaterials to aquatic and land snails: A scientometric and systematic review

The emerging growth of nanotechnology has attracted great attention due to its application in the parasite and intermediate host control. However, the knowledge concerning the mechanism of action (MoA) and toxicity of nanomaterials (NMs) to snails remain unclear. In this context, the present study revised the historical use of snails as experimental models in nanotoxicological studies and summarized the MoA and toxicity of NMs in aquatic and land snails. The data concerning the bioaccumulation, reproductive and transgenerational toxicity, embryotoxicity, genotoxicity and potential molluscicidal activity of NMs were revised. Furthermore, the data about the experimental conditions, such as exposure time, concentrations, cell and tissue-specific responses, snail species and nanoparticle types are discussed. Revised data showed that the toxic effects of NMs were reported for 21 snail species with medical, veterinary and ecological importance. The NM toxicity to snails is dependent on the physical and chemical properties of NMs, as well as their environmental transformation and experimental design. The NM bioaccumulation on snails was related to several toxic effects, such as reactive oxygen species (ROS) production, oxidative stress, following by oxidative damage to DNA, lipids and proteins. The NM metabolism in snails remains unknown. Results showed the potential use of NMs in the snail control program. Also, significant research gaps and recommendations for future researches are indicated. The present study confirms that snails are suitable invertebrate model system to assess the nanotoxicity.

Oxidative stress and genotoxicity in Rhinella arenarum (Anura: Bufonidae) tadpoles after acute exposure to Ni-Al nanoceramics

The employ of nanomaterials (NMs) has exponentially grown due to the large number of technological advances in industrial, pharmaceutical and medical areas. That is the case of alumina (Al) nanoparticles which are extensively employed as support in heterogeneous catalysis processes. However, these NMs can cause great toxicity because of their ubiquitous properties, such as extremely small size and high specific surface area. So, it is required to assess the potential deleterious effects of these NMs on living organisms. In the present study, we analyze the oxidative stress and genotoxic potential of a nanoceramic catalyst Ni/<gamma>-Al₂O₃ (NC) and the NMs involved in their synthesis, <gamma>-Al₂O₃ support (SPC) and NiO/<gamma>-Al₂O₃ precursor (PC) on Rhinella arenarum larvae. Biomarkers of oxidative stress and genotoxic damage were measured in tadpoles exposed to 5 and 25 mg/L of each NMs for 96 h. The results indicated an inhibition of catalase activity in tadpoles exposed to both concentrations of PC and to 25 mg/L of SPC and NC. Moreover, both exposure concentrations of PC and NC significantly inhibited superoxide dismutase activity. Exposure to the three NMs caused inhibition of glutathione S-transferase activity, but there were no significant variations in reduced glutathione levels. Oxidative stress damage (lipid peroxidation) was observed in tadpoles treated with 25 mg/L PC, while the other treatments did not produce alterations. The MNs frequency significantly increased in larvae exposed to 25 mg/L PC indicating irreversible genotoxic damage. The results show that these NMs exert genotoxic effects and antioxidant defense system disruption in R. arenarum larvae.

Accumulation and toxicity of multi-walled carbon nanotubes in Xenopus tropicalis tadpoles

Multi-walled carbon nanotubes (MWCNTs), a common nanomaterial widely used and discharged in environment, might exert toxic effects on aquatic animals. In this paper, filter-feeding tadpole of Xenopus tropicalis was selected as bioindicator to study the exposure effects of MWCNTs suspensions of 0.5, 1, 2, 4 and 8 mg/L for 72 h. The results showed that the tadpoles could remain high survival rate of over 96.7% after 24 h's exposure to MWCNTs, but then decrease considerably, showing a significant time-dependent relationship. The LC₅₀ was 2.53 mg/L for tadpoles exposed to MWCNTs for 72 h, when MWCNTs accumulated in their gills and digestive tracts. Moreover, the enrichment degree of MWCNTs in tadpole was related to exposure density than time. When MWCNTs suspension concentration was not over 1 mg/L, the heart rates increased significantly and then decreased continuously. The survivors from the toxicity test were transferred to fresh filtered water for recovery, but MWCNTs accumulated in the tadpoles' body didn't decrease obviously after 4 days. Although the maximum tadpoles survival rate of 80% was recorded in the exposure group of 0.5 mg/L MWCNTs, only 43.3% of the survivors could recover. Therefore, the final survival rate was negative related to the exposure densities of MWCNTs but positive related to the accumulating degree in tadpoles' body. The results demonstrated that MWCNTs exposure posed potential health risks to filter-feeding organisms by intake and accumulation in organs, which could provide useful information for the reasonable evaluation and scientific management of nanomaterials.

New Relevant Descriptor of Linear QNAR Models for Toxicity Assessment of Silver Nanoparticles

The use of silver nanoparticles (NPs) in medical, industrial and agricultural fields is becoming more widespread every year. This leads to an increasing number of experimental toxicological and microbiological studies of silver NPs aimed at establishing the risk-benefit ratio for their application. The following key parameters affecting the biological activity of silver dispersions are traditionally taken into consideration: mean diameter of NPs, surface potential of NPs and equilibrium concentration of Ag+. These characteristics are mainly predetermined by the chemical nature of the capping agent used for stabilization. However, the extent to which they influence the biological activity and the toxicity of silver NPs varies greatly. In this work, dispersions of silver NPs stabilized with a wide array of substances of different chemical nature were used for quantitative evaluation of whether the various measurable properties of silver NPs fit as descriptors of linear QNAR (quantitative nanostructure-activity relationship) models for silver NP toxicity evaluation with respect to a model eukaryotic microorganism-Saccharomyces cerevisiae yeast cells. It was shown that among the factors that determine silver NP toxicity, the charge of particles, their colloidal stability and the ability to generate Ag+ ions carry more importance than the descriptors related to the particle size. A significant synergistic effect between the ζ-potential and the colloidal stability of silver NPs on their toxicity was also discovered. Following this, a new descriptor has been proposed for the integral characterization of the silver dispersion colloidal stability. According to the obtained data, it can be considered applicable for building QNAR models of higher efficacy. The validity testing of the proposed model for theoretical prediction of silver NP toxicity using a wide range of living organisms has shown that this new descriptor correlates with toxicity much better compared to most traditionally used descriptors. Consequently, it seems promising in terms of being used not only in situations involving the rather narrow array of the objects tested, but also for the construction of silver NP toxicity models with respect to other living organisms.

Metabolic responses in bullfrog, Lithobates catesbeianus after exposure to zinc, copper and cadmium

This study investigated the activity of lactated dehydrogenase (LDH), malate dehydrogenase (MDH) enzymes and the levels of glucose, protein and triglyceride in bullfrog tadpoles after exposure to 1 μg L^-1 of zinc (Zn), copper (Cu) and cadmium (Cd) isolated and combined for 2 and 16 days. Zn, Cu + Cd and Zn + Cu + Cd increased the activity of the LDH (2 and 16 days) and MDH (2 days) enzymes in the liver; and MDH increased in the kidney after 16 days in all co-exposed groups compared to the control. Glucose increased in the liver in the Zn and Cu groups at 2 and 16 days of exposure and decreased in the kidney (groups Cd, Zn + Cd and Cu + Cd) and muscle (Cd) at 2 days of exposure. After 2 days of exposure, the protein increased in the liver (Zn), in the kidney in all groups exposed to metals except in the groups exposed to Cd and Zn + Cu + Cd, which did not change and decreased in muscle in all the groups exposed to isolated metals. Regarding triglycerides, the kidney and muscle were the most affected, leading to a decrease in the Zn, Cu and Cd groups and in the Zn + Cu (16 days) and Zn + Cu + Cd groups (2 days). The anaerobiosis and aerobiosis were activated in the liver and kidney after short-term exposure (2 days) and in the kidney, the aerobic metabolism was activated after chronic exposure (16 days). The metals caused toxicity and were higher in co-exposure to metals with a potential to cause metabolism damage in L. catesbeianus.

Recent Advances in Metal Decorated Nanomaterials and Their Various Biological Applications: A Review

Nanoparticles (nanoparticles) have received much attention in biological application because of their unique physicochemical properties. The metal- and metal oxide-supported nanomaterials have shown significant therapeutic effect in medical science. The mechanisms related to the interaction of nanoparticles with animal and plant cells can be used to establish its significant role and to improve their activity in health and medical applications. Various attempts have been made to discuss the antibiotic resistance and antimicrobial activity of metal-supported nanoparticles. Despite all these developments, there is still a need to investigate their performance to overcome modern challenges. In this regard, the present review examines the role of various types of metal-supported nanomaterials in different areas such as antibacterial, antifungal, anticancer, and so on. Based on the significant ongoing research and applications, it is expected that metal-supported nanomaterials play an outstanding role not only in medical but also in other important areas.

Proteasomal and lysosomal degradation for specific and durable suppression of immunotherapeutic targets

Cancer immunotherapy harness the body’s immune system to eliminate cancer, by using a broad panel of soluble and membrane proteins as therapeutic targets. Immunosuppression signaling mediated by ligand-receptor interaction may be blocked by monoclonal antibodies, but because of repopulation of the membrane via intracellular organelles, targets must be eliminated in whole cells. Targeted protein degradation, as exemplified in proteolysis targeting chimera (PROTAC) studies, is a promising strategy for selective inhibition of target proteins. The recently reported use of lysosomal targeting molecules to eliminate immune checkpoint proteins has paved the way for targeted degradation of membrane proteins as crucial anti-cancer targets. Further studies on these molecules’ modes of action, target-binding “warheads”, lysosomal sorting signals, and linker design should facilitate their rational design. Modifications and derivatives may improve their cell-penetrating ability and the in vivo stability of these pro-drugs. These studies suggest the promise of alternative strategies for cancer immunotherapy, with the aim of achieving more potent and durable suppression of tumor growth. Here, the successes and limitations of antibody inhibitors in cancer immunotherapy, as well as research progress on PROTAC- and lysosomal-dependent degradation of target proteins, are reviewed.

Current Applications of Biopolymer-based Scaffolds and Nanofibers as Drug Delivery Systems

BACKGROUND

The high surface-to-volume ratio of polymeric nanofibers makes them an effective vehicle for the release of bioactive molecules and compounds such as growth factors, drugs, herbal extracts and gene sequences. Synthetic polymers are commonly used as sensors, reinforcements and energy storage, whereas natural polymers are more prone to mimicking an extracellular matrix. Natural polymers are a renewable resource and classified as an environmentally friendly material, which might be used in different techniques to produce nanofibers for biomedical applications such as tissue engineering, implantable medical devices, antimicrobial barriers and wound dressings, among others. This review sheds some light on the advantages of natural over synthetic polymeric materials for nanofiber production. Also, the most important techniques employed to produce natural nanofibers are presented. Moreover, some pieces of evidence regarding toxicology and cell-interactions using natural nanofibers are discussed. Clearly, the potential extrapolation of such laboratory results into human health application should be addressed cautiously.