Defu He

Microplastic particles cause intestinal damage and other adverse effects in zebrafish Danio rerio and nematode Caenorhabditis elegans

Microplastics have been frequently detected in aquatic environments, and there are increasing concerns about potential effects on biota. In this study, zebrafish Danio rerio and nematode Caenorhabditis elegans were used as model organisms for microplastic exposure in freshwater pelagic (i.e. water column) and benthic (i.e. sediment) environments. We investigated the toxic effects of five common types of microplastics: polyamides (PA), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and polystyrene (PS) particles. Results showed no or low lethality in D. rerio after exposure for 10d at 0.001-10.0mgL-1 microplastics. The PA, PE, PP and/or PVC microplastics with ~70μm size caused intestinal damage including cracking of villi and splitting of enterocytes. Exposure to 5.0mgm-2 microplastics for 2d significantly inhibited survival rates, body length and reproduction of C. elegans. Moreover, exposure to microplastics reduced calcium levels but increased expression of the glutathione S-transferase 4 enzyme in the intestine, which indicates intestinal damage and oxidative stress are major effects of microplastic exposure. Among 0.1, 1.0 and 5.0μm sizes of fluorescently labeled PS, 1.0μm particles caused the highest lethality, the maximum accumulation, the lowest Ca2+ level in the intestine and the highest expression of glutathione S-transferase 4 in nematodes. Taken together, these findings suggest that intestinal damage is a key effect of microplastics; and that the toxicity of microplastics is closely dependent on their size, rather than their composition.

Chronic Exposure to Perfluorooctane Sulfonate Induces Behavior Defects and Neurotoxicity through Oxidative Damages, In Vivo and In Vitro

Perfluorooctane sulfonate (PFOS) is an emerging persistent pollutant which shows multiple adverse health effects. However, the neurotoxicity of PFOS and its mechanisms have not been fully elucidated. Using a combination of in vivo and in vitro methods, the present study provides a detailed description of PFOS-induced neurotoxicity. Results showed that the median lethal concentration of PFOS was 2.03 mM in Caenorhabditis elegans for 48 h exposure. 20 µM PFOS caused decrease of locomotor behaviors including forward movement, body bend and head thrash. Additionally, PFOS exposure reduced chemotaxis index of C. elegans, which indicates the decline of chemotaxis learning ability. Using green fluorescent protein (GFP) labelled transgenic strains, we found that PFOS caused down-regulated expression of a chemoreceptor gene, gcy-5, in ASE chemosensory neurons, but did not affect cholinergic neurons and dopaminergic neurons. In SH-SY5Y cells, 48 h exposure to 25 µM and 50 µM PFOS induced cell damage, apoptosis and the reactive oxygen species (ROS) generation. PFOS caused significant increases of lipid peroxidation and superoxide dismutase activity, but an actual decrease of glutathione peroxidase activity. Furthermore, antioxidant N-acetylcysteine rescued cells from PFOS-induced apoptosis via blocking ROS. Our results demonstrate that chronic exposure to PFOS can cause obvious neurotoxicity and behavior defects. Oxidative damage and anti-oxidative deficit are crucial mechanisms in neurotoxicity of PFOS.

Acrylamide induces locomotor defects and degeneration of dopamine neurons in Caenorhabditis elegans

Acrylamide can form in foods during the cooking process and cause multiple adverse effects. However, the neurotoxicity and mechanisms of acrylamide have not been fully elucidated. In Caenorhabditis elegans, we showed that 48 h exposure to 10–625 mg l−1 acrylamide resulted in a significant decline in locomotor frequency of body bending, head thrashing and pharynx pumping. In addition, acrylamide exposure reduced crawling speeds and changed angles of body bending. It indicates that acrylamide induces locomotor defects, along with parkinsonian‐like movement impairment, including bradykinesia and hypokinesia. Acrylamide also affected chemotaxis plasticity and reduced learning ability. Using transgenic nematodes, we found that acrylamide induced downexpression of Pdat‐1 and led to the degeneration of dopaminergic neurons. Moreover, the enhanced expression of unc‐54, encoding a subunit of α‐synuclein was found. It illustrates that acrylamide is efficient in inducing crucial parkinsonian pathology, including dopaminergic damage and α‐synuclein aggregation. These findings suggest the acrylamide‐induced locomotor defects and neurotoxicity are associated with Parkinsons disease. Copyright

Strong lethality and teratogenicity of strobilurins on Xenopus tropicalis embryos: Basing on ten agricultural fungicides

Agricultural chemical inputs have been considered as a risk factor for the global declines in amphibian populations, yet the application of agricultural fungicides has increased dramatically in recent years. Currently little is known about the potential toxicity of fungicides on the embryos of amphibians. We studied the effects of ten commonly used fungicides (four strobilurins, two SDHIs, two triazoles, fludioxonil and folpet) on Xenopus tropicalis embryos. Lethal and teratogenic effects were respectively examined after 48 h exposure. The median lethal concentrations (LC50s) and the median teratogenic concentrations (TC50s) were determined in line with actual exposure concentrations. These fungicides except two triazoles showed obvious lethal effects on embryos; however LC50s of four strobilurins were the lowest and in the range of 6.81-196.59 μg/L. Strobilurins, SDHIs and fludioxonil induced severe malformations in embryos. Among the ten fungicides, the lowest TC50s were observed for four strobilurins in the range of 0.61-84.13 μg/L. The teratogenicity shared similar dose-effect relationship and consistent phenotypes mainly including microcephaly, hypopigmentation, somite segmentation and narrow fins. The findings indicate that the developmental toxicity of currently-used fungicides involved with ecologic risks on amphibians. Especially strobilurins are highly toxic to amphibian embryos at μg/L level, which is close to environmentally relevant concentrations.

Differential effects of activating D1 and D2 receptors on electrophysiology of neostriatal neurons in a rat model of Parkinson's disease induced by paraquat and maneb.

Neostriatum plays an important role in the pathophysiology of Parkinsons disease (PD). However, the changes of sensitivity of dopamine receptors of neostriatal neurons in PD have been less addressed in vivo. In the present study, systemic exposure to paraquat and maneb induced Parkinsonian symptoms and neuronal loss of substantia nigra pars compacta. Using single-unit recording methods, three types of neostriatal neurons were recorded including medium spiny-like neurons, large aspiny-like neurons and fast-spiking interneurons. In the exposed rats, increased firing activity of neostriatal neurons was revealed when compared to control rats. Following D1 receptor agonist, SKF38393 and D2 receptor agonist, LY171555 iontophoretically administrated respectively, effects of increase and decrease in firing activity were both observed in neostriatal neurons. However, stronger inhibitory effects of activating D1 receptors and weaker excitatory effects of activating D2 receptors were found in the exposed rats as compared to controls. It indicated that differential changes of sensitivity of D1 and D2 receptors in Parkinsons disease were related to the modulation of the imbalance between D1-receptor-dependent striatonigral direct pathway and D2-receptor-dependent striatopallidal indirect pathway. Our results illustrate the electrophysiological changes of in vivo neostriatal neurons in Parkinsons disease, thereby providing insight into the regulatory mechanisms of dopamine-mediated physiology.

Morpho‐Physiologic Characteristics of Dorsal Subicular Network in Mice after Pilocarpine‐Induced Status Epilepticus

The goal of this study was to examine the morpho‐physiologic changes in the dorsal subiculum network in the mouse model of temporal lobe epilepsy using extracellular recording, juxtacellular and immunofluorescence double labeling, and anterograde tracing methods. A significant loss of total dorsal subicular neurons, particularly calbindin, parvalbumin (PV) and immunopositive interneurons, was found at 2 months after pilocarpine‐induced status epilepticus (SE). However, the sprouting of axons from lateral entorhinal cortex (LEnt) was observed to contact with surviving subicular neurons. These neurons had two predominant discharge patterns: bursting and fast irregular discharges. The bursting neurons were mainly pyramidal cells, and their dendritic spine density and bursting discharge rates were increased significantly in SE mice compared with the control group. Fast irregular discharge neurons were PV‐immunopositive interneurons and had less dendritic spines in SE mice when compared with the control mice. When LEnt was stimulated, bursting and fast irregular discharge neurons had much shorter latency and stronger excitatory response in SE mice compared with the control group. Our results illustrate that morpho‐physiologic changes in the dorsal subiculum could be part of a multilevel pathologic network that occurs simultaneously in many brain areas to contribute to the generation of epileptiform activity.

Chronic exposure to graphene‐based nanomaterials induces behavioral deficits and neural damage in Caenorhabditis elegans

Nanomaterials of graphene and its derivatives have been widely applied in recent years, but whose impacts on the environment and health are still not well understood. In the present study, the potential adverse effects of graphite (G), graphite oxide nanoplatelets (GO) and graphene quantum dots (GQDs) on the motor nervous system were investigated using nematode Caenorhabditis elegans as the assay system. After being characterized using TEM, SEM, XPS and PLE, three nanomaterials were chronically exposed to C. elegans for 6 days. In total, 50–100 mg l−1 GO caused a significant reduction in the survival rate, but G and GDDs showed low lethality on nematodes. After chronic exposure of sub‐lethal dosages, three nanomaterials were observed to distribute primarily in the pharynx and intestine; but GQDs were widespread in nematode body. Three graphene‐based nanomaterials resulted in significant declines in locomotor frequency of body bending, head thrashing and pharynx pumping. In addition, mean speed, bending angle‐frequency and wavelength of the crawling movement were significantly reduced after exposure. Using transgenic nematodes, we found high concentrations of graphene‐based nanomaterials induced down‐expression of dat‐1::GFP and eat‐4::GFP, but no significant changes in unc‐47::GFP. This indicates that graphene‐based nanomaterials can lead to damages in the dopaminergic and glutamatergic neurons. The present data suggest that chronic exposure of graphene‐based nanomaterials may cause neurotoxicity risks of inducing behavioral deficits and neural damage. These findings provide useful information to understand the toxicity and safe application of graphene‐based nanomaterials. Copyright

Polystyrene (nano)microplastics cause size-dependent neurotoxicity, oxidative damage and other adverse effects in Caenorhabditis elegans

(Nano)microplastics (N/MPs) are emerging contaminants of increasing concern. However, little is known about the potential toxicity difference between nanoplastics and microplastics on organisms. In this study, we investigated the effects of polystyrene N/MPs with diameter sizes of 100 and 500 nm at the nanoscale and 1.0, 2.0 and 5.0 μm at the microscale on the survival, lifespan, motor behavior, movement-related neurons and oxidative stress in Caenorhabditis elegans. After 3 days of exposure to 1.0 mg L−1 polystyrene particles of the five sizes, the 1.0 μm group had the lowest survival rate, the largest decrease in body length and the shortest average lifespan in nematodes. We demonstrated that exposure to N/MPs accelerated the frequency of body bending and head thrashing, and increased crawling speed, which indicate that N/MPs can induce size-dependent excitatory toxicity on locomotor behavior. Of the five sizes of N/MPs, 1.0 μm particles significantly downregulated the expression of unc-17 and unc-47, and resulted in obvious damage to cholinergic and GABAergic neurons. We also found that polystyrene N/MPs significantly elevated the expression of gst-4, which encodes glutathione S-transferase-4, a key enzyme in oxidative stress. Additionally, N/MPs-induced oxidative damage was effectively attenuated by natural antioxidants, curcumin and oligometric proanthocyanidins. Taken together, these findings suggest that (nano)microplastics can exert size-dependent toxicity and have extensive impacts on organisms.

Single and mixture toxicity of strobilurin and SDHI fungicides to Xenopus tropicalis embryos

The decline in amphibian populations is a critical threat to global biodiversity, and pesticide pollution is considered as one of the major factors. Although effects of single pesticides on amphibians have been documented, toxicological interactions prevailing in mixtures of pesticides have not been well elucidated. Strobilurin and succinate dehydrogenase inhibitor (SDHI) fungicides are new types of commonly used pesticides. In this study, effects of three strobilurins (pyraclostrobin, trifloxystrobin and azoxystrobin), two SDHIs (isopyrazam and bixafen), and their mixtures on X. tropicalis embryos were fully investigated. Results showed that exposure to individual fungicides induced lethal and teratogenetic effects; and malformed embryos displayed similar phenotypes including microcephaly, hypopigmentation, somite segmentation and narrow fin. Exposure to two strobilurins or two SDHIs at equitoxic concentrations caused additive or synergetic effects at environmentally relevant concentrations. TU for mixtures of isopyrazam and bixafen was 0.53 and 0.30 for lethal and teratogenic toxicity, respectively. Finally, binary mixtures of strobilurins and SDHIs also exhibited additive or synergetic effects on amphibian embryos. Overall, these results reveal that the mixtures of multiple fungicides caused a higher incidence of lethality and teratogenicity of amphibian embryos, compared to a single fungicide at the corresponding doses. Our findings provide important data about the ecotoxicology of agricultural fungicides on non-target organisms, which is useful for guiding management practices for pesticides.

Microplastic pollution in rice-fish co-culture system: A report of three farmland stations in Shanghai, China

Microplastics are emerging contaminants of increasing concern. Despite the occurrence of microplastics in farmland soils, the knowledge on microplastics in rice-fish co-culture ecosystems is limited. In this study, we investigated the distribution of microplastics in three rice-fish culture stations in Shanghai. During non-rice and rice-planting periods, microplastics in water, soils and aquatic animals (eel, loach and crayfish) were systematically assayed using methods of NaCl density extraction, H2O2 digestion and micro-fourier transform infrared spectroscopy. Results showed that average microplastic abundances were 0.4 ± 0.1 items L-1, 10.3 ± 2.2 items kg-1, 1.7 ± 0.5 items individual-1 in water, soils and aquatic animal samples, respectively. We found an increasing trend in microplastic abundances in water, soil and animal samples from non-rice period to rice-planting period. Almost all of microplastics were found in digestive tracts of animals. Major microplastics were small (<1 mm) polyethylene and polypropylene fibers, with color of white and translucent. Size, shape, color and polymer type distributions of microplastics were similarly found in environmental and animal samples. Moreover, microplastic abundances in aquatic animals correlated to abundance in farmland soils. This study, for the first time, reveals the occurrence and characteristics of microplastic pollution in rice-fish culture ecosystem which suggests the potential ecological risks of microplastics in the agroecosystem.