Chronic Effects of Fluoride Exposure on Growth, Metamorphosis, and Skeleton Development in Bufo gargarizans Larvae

Decrypting the skeletal toxicity of vertebrates caused by environmental pollutants from an evolutionary perspective: From fish to mammals

The rapid development of modern society has led to an increasing severity in the generation of new pollutants and the significant emission of old pollutants, exerting considerable pressure on the ecological environment and posing a serious threat to both biological survival and human health. The skeletal system, as a vital supportive structure and functional unit in organisms, is pivotal in maintaining body shape, safeguarding internal organs, storing minerals, and facilitating blood cell production. Although previous studies have uncovered the toxic effects of pollutants on vertebrate skeletal systems, there is a lack of comprehensive literature reviews in this field. Hence, this paper systematically summarizes the toxic effects and mechanisms of environmental pollutants on the skeletons of vertebrates based on the evolutionary context from fish to mammals. Our findings reveal that current research mainly focuses on fish and mammals, and the identified impact mechanisms mainly involve the regulation of bone signaling pathways, oxidative stress response, endocrine system disorders, and immune system dysfunction. This study aims to provide a comprehensive and systematic understanding of research on skeletal toxicity, while also promoting further research and development in related fields.

Histo-anatomical mutilations of developing chick brain induced by in-ovo fluoride and bifenthrin exposure

Comparative developing brain histo-anatomical pathologies of Fluoride ions and Bifenthrin in-ovo exposures were explored in the golden black variety of domestic chick. Three exposure groups were -the Vehicle control group (Vg); Fluoride (F) group and the Bifenthrin (Bn) group each with forty fertilized eggs and received their respective group treatment at zero day of incubation. Embryos were extracted, dissected from head region and the embryonic whole brains were recovered after 14 days of incubation. The embryonic brains were preserved in bouin fixative for 24 h for further studies. The morphological results show the atrophied and hypertrophied embryonic brain in F and Bn groups respectively as compared to Vg group. The toxicological signs of encephalic anatomy and histology of F and Bn exposure were the enlarged third ventricles, optocoeles and arachnoid mater, encephalic spongiosis and decreased neuroglial density. The morphometric data showed significant decrease (p ≤ 0.05) in mean weight and density of whole brain in F and Bn groups compared Vg. The mean length and width of whole brain in F were significantly lower than that of the Bn and Vg. whereas, the mean breadth of third ventricle in Bn remained significantly lower than F and Vg groups. On the other hand, the mean breadth of optocoele and fourth ventricle in F and Bn groups remained significantly higher than Vg. Conversely the mean optic lobe wall thickness in F remained significantly lower than Bn and Vg. Additionally, the mean neuronal density in diencephalon, optic lobe and cerebellum in F group and Bn group remained significantly (p ≤ 0.05) lower than Vg. Results show that low dose in-ovo fluoride or bifenthrin exposure may cause neuro-developmental abnormalities in the developing chick embryos indicating that the Fluoride-ions and Bifenthrin harbor strong developmental neurotoxic capacity.

Double-edged sword: Fluoxetine and ibuprofen as development jeopardizers and apoptosis' inducers in common toad, Bufo bufo, tadpoles

Nowadays the presence of pharmaceuticals in the environment is a real problem. Ending up in aquatic environments they negatively affect non-target organisms. Considering the limited studies on the negative effects of pharmaceuticals in amphibians, a better understanding of the mechanisms underlying the sub-lethal effects of drug mixtures in wildlife is an urgent call. Representing particularly vulnerable organisms currently at risk of extinction, amphibians are perfect non-target organisms to explore the consequences of pharmaceuticals during sensitive life-stages. To address this existing research gap, the effects of two drugs, the antidepressant fluoxetine and the anti-inflammatory ibuprofen, as well as their combination has been studied. Tadpoles of Bufo bufo were exposed for seven days to two environmentally realistic concentrations of fluoxetine, ibuprofen and their mixture. The development, behavior and erythron profile were then evaluated as endpoints of exposure response. Both drugs negatively affected tadpoles' growth and development by significantly delayed their time to metamorphosis and reduced body weight. Behaviors were also impaired with a significant increase of unresponsiveness to different stimuli. Mutagenic analysis of blood revealed a significant increase in the frequency of cellular and nuclear abnormalities. Given the complexity of systems and functions affected, our work confirms the toxicological potential of fluoxetine and ibuprofen in B. bufo tadpoles by emphasizing their role as tadpole development delayers and erythrocyte apoptosis-inducers. To our knowledge, this is the first study trying to elucidate the potentially toxic effects of a mixture of an antidepressant with a non-steroidal anti-inflammatory drug using bullfrog tadpole as model organism. Both drugs interacted in impairing development and fitness in tadpoles, which might affect long-term species perpetuation and population dynamic. More in-depth research is needed to elucidate the nature of interaction and molecular mechanisms of mixed pharmaceutical compounds on non-targeted organisms.

Intestinal response characteristic and potential microbial dysbiosis in digestive tract of Bufo gargarizans after exposure to cadmium and lead, alone or combined

The gastrointestinal tract is the largest immune organ in the body and meanwhile, accommodates a large number of microorganisms. Heavy metals could disturb the intestinal homeostasis and change the gut microbial composition. However, the information regarding the links between dysbiosis of gut microbiota and imbalance of host intestinal homeostasis induced by the mixture of heavy metals is insufficient. The present study investigates the effects of Cd/Pb, both single and combination exposure, on the growth performance, intestinal histology, digestive enzymes activity, oxidative stress and immune parameters, and intestinal microbiota in Bufo gargarizans tadpoles. Our results revealed that co-exposure of Cd-Pb induced more severe impacts not only on the host, but the intestinal microbiota. On the one hand, co-exposure of Cd-Pb significantly induced growth retardation, intestinal histological injury, decreased activities of digestive enzymes. On the other hand, Cd and Pb exposure, especially in mixed form, changed the diversity and richness, structure of microbiota. Also, the intestinal microbial composition was altered by Cd/Pb exposure (alone and combination) both at the different levels. Proteobacteria, act as front-line responder, was significantly increased in tadpoles under the exposure of metals. Finally, the functional prediction revealed that the disorders of metabolism and immune responses of intestinal microbiota was increased in tadpoles exposed to Cd/Pb (especially the mixture of Cd and Pb). Our research complements the understanding of links between changes in host fitness loss and intestinal microbiota and will add a new dimension of knowledge to the ecological risks of mixed heavy metals in amphibian.

Response Patterns of Biomarkers as Tools to Identify Toxic Effects of Cadmium and Lead on Bufo gargarizans Embryo

Molecular biomarkers play an increasing crucial role in evaluating and predicting toxicity of metals. Expressions patterns of genes related to oxidative stress, apoptosis, immune and inflammation response in the Bufo gargarizans embryo exhibited a development dependent manner. The genes related to oxidative stress (HSP, GPx and SOD) are the first response in the development of embryo, followed by the apoptosis (Bax, BCLAF1 and TRAIL) and inflammation and immune response (SOCS3, IL-27 and IL-17D), respectively. Then, we have verified the HSP, Bax and SOCS3 IL-27 (expressed highest in their respective processes) exhibited the most significant changes in Cd-Pb mixed group compared with control. In addition, we found exposure of Cd-Pb mixed metals causes greater adverse effects than Cd, Pb alone on development and morphology of embryo. Overall, our results provide a useful tool to use the sensitive molecular biomarkers as indicators of developmental toxicity in amphibian embryo.

Effects of fluoride on the histology, lipid metabolism, and bile acid secretion in liver of Bufo gargarizans larvae

In our study, Bufo gargarizans (B. gargarizans) larvae were exposed to control, 0.5, 5, 10 and 50 mg/L of NaF from Gs 26 to 42. At Gs 42, we evaluated the changes of liver histology and the mRNA levels of target genes in liver. In addition, we also examined the composition and content of fatty acids. Histological analysis revealed that fluoride caused liver injury, such as the increase of number of melanomacrophage centres, atrophy of nucleus, dilation of bile canaliculus, and decrease of quantity, degradation and deposition of lipid droplets. The results of RT-qPCR indicated that exposure to 5, 10 and 50 mg/L of NaF significantly decreased the transcript levels of genes related to fatty acid synthesis (FASN, FAE, MECR, KAR and TECR) in liver. Besides, mRNA expression of genes involved in fatty acid β-oxidation (ECHS1, HADHA, SCP2, CPT2, ACAA1 and ACAA2) and oxidative stress (SOD, GPx, MICU1 and HSP90) was significantly downregulated in 0.5, 5, 10 and 50 mg/L of NaF treatment groups. Also, in the relative expression of genes associated with synthesis and secretion of bile acid, BSEP significantly increased at 0.5, 5 and 50 mg/L of NaF while HSD3B7 significantly reduced in 0.5, 5, 10 and 50 mg/L of NaF. Finally, the fatty acid extraction and GC-MS analysis showed that the content of saturated fatty acids (SFAs) was decreased and the content of polyunsaturated fatty acids (PUFAs) was increased in all fluoride treatment groups. Taken together, the present results indicated that fluoride-induced the histological alterations of liver might be linked to the disorder of lipid metabolism, oxidative damage.

Morphological abnormalities in natural populations of the common South American toad Rhinella arenarum inhabiting fluoride-rich environments

Morphological abnormalities in amphibians may be attributed to contaminants, ultraviolet radiation and trematode parasites, or a synergistic effect between them. In the present study, morphological abnormalities in Rhinella arenarum adults from natural and artificial fluoride-rich environments were identified and evaluated. Three sites were sampled in central Argentina: Los Vallecitos stream (LF-LV), Los Cerros Negros stream (MF-CN), and Decantation ponds (HF-DP), with low (0.33 mg/L), middle (2.03 mg/L) and high (14.0 mg/L) fluoride levels respectively; the latter site is associated with a fluoride mine. Abnormal individuals were photographed and then standard radiographs were taken. Abnormality frequencies and relative percentage of abnormal individuals were calculated for each site. In addition, skeletochronology was used to estimate toad's age. Five abnormality types were identified: syndactyly, ectrodactyly, polydactyly, microphthalmia and ectromelia. Percentages of abnormal individuals per site were: LF-LV = 4%, MF-CN = 21.2% and HF-DP = 6.4%. The MF-CN and HF-DP populations had morphological abnormality frequencies that exceeded the reference value (5%) reported in the literature. The average age did not differ between sites. The results of this study indicate that there is an association between frequency of morphological abnormalities and high fluoride levels.

Anuran tadpoles inhabiting a fluoride-rich stream: diets and morphological indicators

We in situ assessed the influence of natural fluoride concentrations in lotic freshwater ecosystems on diet and morphology of Boana cordobae tadpoles. Two streams were sampled in Argentina: Los Vallecitos stream (LF-LV) and Los Cerros Negros stream (HF-CN) with low and high fluoride levels, respectively. We captured tadpoles of B. cordobae in each stream using nets. Body weight (BW), total length (TL) and body condition (BC) of tadpoles was registered. Food items were identified to genus level and assigned to functional traits. Tadpoles showed significant differences in TL between streams, with smaller individuals in HF-CN, while did not show differences in BW and BC. The diet of tadpoles consisted mostly of microalgae. In tadpoles from HF-CN stream the proportion of cyanobacteria was lower than tadpoles from LF-LV. In relation to functional traits, small algae, high profile and colonial algae were more abundant in HF-CN. Algae attached by pads showed a higher proportion in HF-CN diets and stalked algae were more abundant in LF-LV. The differences in TL and diet of tadpoles can be attributed to differences in algal community composition, with genera that are affected by high concentrations of natural fluoride; for example cyanobacteria. The low algal richness registered in HF-CN stream does not affect the physiological state of the tadpoles, possibly because of a higher algal density in HF-CN diets. However, in further studies it would be important to evaluate the population status of B. cordobae from the HF-CN, because a small body length of tadpoles could have consequences at the population level.

Sub-lethal effects induced by a mixture of different pharmaceutical drugs in predicted environmentally relevant concentrations on Lithobates catesbeianus (Shaw, 1802) (Anura, ranidae) tadpoles

The increasing consumption of medications by humans has negative effects such as the increased disposal of these compounds in the environment. Little is known about how the disposal of a "drug mix" (DM) in aquatic ecosystems can affect their biota. Thus, we evaluated whether the exposure of Lithobates casteibeianus tadpoles to a DM composed of different medication classes (antibiotic, anti-inflammatory, antidepressant, anxiolytic, analgesic, and antacid drugs)-at environmentally relevant concentrations-may change their oral morphology, trigger behavioral disorders, and have mutagenic effects on erythrocyte cells. Based on our data, animals exposed to the DM showed changes in mandibular sheath pigmentation, dentition, and swimming activity, as well as atypical behavior in the social aggregation test [with co-specific and interspecific (Physalaemus cuvieri) individuals] and antipredatory defensive response deficit (chemical stimulus from Odonata larvae), after 15 exposure days. The mutagenic analysis revealed higher frequency of nuclear abnormalities in the erythrocytes of tadpoles exposed to the DM (e.g., multilobulated, blebbed, kidney-shaped, notched nucleus, binuclear, and micronucleated erythrocytes). Given the chemical complexity of the DM, we assumed that several organic functions may have been affected, either by the isolated, synergistic, antagonistic, or additive action of DM compounds. Finally, our study confirms the toxicological potential of DM in L. catesbeianus tadpoles, with emphasis to impacts that can affect the fitness of individuals and their natural populations. Thus, we suggest that more attention should be given to the disposal of medications in the environment and reinforce the need of improving water and sewage treatment systems.

Behavioral and mutagenic biomarkers in tadpoles exposed to different abamectin concentrations

It is known that pesticides such as abamectin (ABA) present cytotoxic effects on target organisms; however, the effects from ABA on non-target organisms such as amphibians are poorly understood. The aim of the current study is to investigate whether the exposure of Lithobates catesbeianus tadpoles to different abamectin concentrations [12.5, 25, and 50% of the median lethal concentration (LC₅₀)] leads to behavioral and morphological changes and/or generates possible cytotoxic effects. The aggregation test showed that tadpoles exposed to the highest ABA concentrations did not respond to the stimulus from non-familial and unrelated co-specific species. On the other hand, there was no difference in the total number of crossings in the central line of the herein adopted apparatus between groups; it suggests that ABA did not affect animal locomotion in the aforementioned test, although changes in the normal swimming pattern of tadpoles exposed to the pesticide were recorded in the swimming activity test. In addition, the herein exposed animals did not respond to the predatory stimulus in the antipredator response test; this result suggests defensive response deficit caused by the pesticide. With respect to their oral morphology, tadpoles exposed to ABA presented the lowest scores for mandibular pigmentation and structures, as well as for dentition condition. Finally, it was possible seeing that the exposure to ABA, even at the lowest concentration (12.5% of the LC₅₀), resulted in nuclear changes in the erythrocytes of the animals; these changes became evident in the increased number of micronuclei and in other nuclear abnormalities. Thus, besides confirming the cytotoxic potential of ABA in amphibians, the current study corroborates the hypothesis that the exposure to the herein investigated pesticide leads to behavioral and morphological changes in tadpoles, fact that may negatively reflect on the survival, as well as on natural populations of these individuals.

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.

Role of fluoride induced histone trimethylation in development of skeletal fluorosis

Chronic exposure to fluoride has been associated with the development of skeletal fluorosis. Limited reports are available on fluoride induced histone modification. However, the role of histone modification in the pathogenesis of skeletal fluorosis is not investigated. In the present study, we have investigated the role of fluoride induced histone modification on fluorosis development using human osteosarcoma (HOS) cell line. The expression of histone methyltransferases (EHMT1 and EHZ2) and level of global histone trimethylation (H3K9 and H3K27) have been assessed and observed to be increased significantly after fluoride exposure (8 mg/L). EpiTect chromatin immunoprecipitation (CHIP) qPCR Array (Human TGFβ/BMP signaling pathway) was performed to assess the H3K9 trimethylation at promoter regions of pathway-specific genes. H3K9 ChIP PCR array analysis identified hyper H3K9 trimethylation in promoter regions of TGFBR2 and SMAD3. qPCR and STRING analysis was carried out to determine the repressive epigenetic effect of H3K9 trimethylation on expression pattern and functional association of identified genes. Identified genes (TGFBR2 and SMAD3) showed down-regulation which confirms the repressive epigenetic effect of promoter H3K9 hyper trimethylation. Expression of two other vital genes COL1A1 and MMP13 involved in TGFBR2-SMAD signaling pathway was also found to be down-regulated with a decrease in expression of TGFBR2 and SMAD3. STRING analysis revealed functional association and involvement of identified genes TGFBR2, SMAD3, COL1A1 and MMP13 in the collagen and cartilage development/morphogenesis, connective tissue formation, bio-mineral tissue development, endochondral bone formation, bone and skeletal morphogenesis. In conclusion, present investigation is a first attempt to link fluoride induced hyper H3K9 tri-methylation mediated repression of TGFBR2 and SMAD3 with the development of skeletal fluorosis.

Responses of growth, malformation, and thyroid hormone-dependent genes expression in Bufo gargarizans embryos following chronic exposure to Pb2

The aim of this study was to examine the adverse effects of lead (Pb) exposure on Bufo gargarizans embryos. The 96 h-LC₅₀ of Pb²⁺ for B. gargarizans embryos was determined to be 26.6 mg L^-1 after an acute test. In the chronic test, B. gargarizans embryos at Gosner stage 3 were exposed to 10~2000 μg Pb²⁺ L^-1 during embryogenesis. Total length, weight, developmental stage, and malformation were monitored. In addition, the transcript levels of type II and type III iodothyronine deiodinase (Dio2 and Dio3) and thyroid hormone receptors (TRα and TRβ) were determined to assess the thyroid-disrupting effects of Pb²⁺. Slightly increased growth and development of B. gargarizans embryos were observed at low concentrations of Pb²⁺ (10, 50, and 100 μg L^-1), while retarded growth and development were found at high concentrations of Pb²⁺ (1000 and 2000 μg L^-1). In addition, Pb²⁺ exposure induced morphological abnormalities, which were characterized by edema at tail, wavy fin, abdominal edema, stunted growth, hyperplasia, and axial flexures in B. gargarizans embryos. Furthermore, our results showed that exposure to 2000 μg Pb²⁺ L^-1 decreased the transcript levels of Dio2, TRα, and TRβ, but it increased Dio3 mRNA level. In contrast, exposure to 50 μg Pb²⁺ L^-1 increased TRα mRNA level and decreased Dio3 mRNA level. These results suggested that Pb²⁺ might have thyroid-disrupting effects, leading to the disruption of growth and development in B. gargarizans embryos.