Polystyrene microplastics induced disturbances in neuronal arborization and dendritic spine density in mice prefrontal cortex.

An increasing use of plastics in daily life leads to the accumulation of microplastics (MPs) in the environment, posing a serious threat to the ecosystem, including humans. It has been reported that MPs cause neurotoxicity, but the deleterious effect of polystyrene (PS) MPs on neuronal cytoarchitectural morphology in the prefrontal cortex (PFC) region of mice brain remains to be established. In the present study, Swiss albino male mice were orally exposed to 0.1, 1, and 10 ppm PS-MPs for 28 days. After exposure, we found a significant accumulation of PS-MPs with a decreased number of Nissl bodies in the PFC region of the entire treated group compared to the control. Morphometric analysis in the PFC neurons using Golgi-Cox staining accompanied by Sholl analysis showed a significant reduction in basal dendritic length, dendritic intersections, nodes, and number of intersections at seventh branch order in PFC neurons of 1 ppm treated PS-MPs. In neurons of 0.1 ppm treated mice, we found only decrease in the number of intersections at the seventh branch order. While 10 ppm treated neurons decreased in basal dendritic length, dendritic intersections, followed by the number of intersections at the third and seventh branch order were observed. As well, spine density on the apical secondary branches along with mRNA level of BDNF was significantly reduced in all the PS-MPs treated PFC neurons, mainly at 1 ppm versus control. These results suggest that PS-MPs exposure affects overall basal neuronal arborization, with the highest levels at 1 and 10 ppm, followed by 0.1 ppm treated neurons, which may be related to the down-regulation of BDNF expression in PFC.

PFOS-induced dyslipidemia and impaired cholinergic neurotransmission in developing zebrafish: Insight into its mechanisms.

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant that has been widely detected in the environment and is known to accumulate in organisms, including humans. The study investigated dose-dependent mortality, hatching rates, malformations, lipid accumulation, lipid metabolism alterations, and impacts on cholinergic neurotransmission. Increasing PFOS concentration led to higher mortality, hindered hatching, and caused concentration-dependent malformations, indicating severe abnormalities in developing zebrafish. The results also demonstrated that PFOS exposure led to a significant increase in total lipids, triglycerides, total cholesterol, and LDL in a concentration-dependent manner, while HDL cholesterol levels were significantly decreased. Additionally, PFOS exposure led to a significant decrease in glucose levels. The study identified TGs, TCHO, and glucose as the most sensitive biomarkers in assessing lipid metabolism alterations. The study also revealed altered expression of genes involved in lipid metabolism, including upregulation of fasn, acaca, and hmgcr and downregulation of ldlr, pparα, and abca1, as well as decreased lipoprotein lipase (LPL) and increased fatty acid synthase (FAS) activity,suggesting an impact on fatty acid synthesis, cholesterol uptake, and lipid transport. Additionally, PFOS exposure led to impaired cholinergic neurotransmission, evidenced by a concentration-dependent inhibition of acetylcholinesterase activity, altered gene expressions related to neural development and function, and reduced Na+/K+-ATPase activity. STRING network analysis highlighted two distinct gene clusters related to lipid metabolism and cholinergic neurotransmission, with potential interactions through the pparα-creb1 pathway. Overall, this study provide important insights into the potential health risks associated with PFOS exposure, including dyslipidemia, cardiovascular disease, impaired glucose metabolism, and neurotoxicity. Further research is needed to fully elucidate the underlying mechanisms and potential long-term effects of PFOS exposure.

Polystyrene microplastics disrupt female reproductive health and fertility via sirt1 modulation in zebrafish (Danio rerio).

Microplastics (MPs) pollution poses an emerging threat to aquatic biota, which could hinder their physiological processes. Recently various evidence has demonstrated the toxic impacts of MPs on cellular and organismal levels, but still, the underlying molecular mechanism behind their toxicity remains ambiguous. The hypothalamic-pituitary-gonadal (HPG) axis regulates the synthesis and release of sex steroid hormones, and SIRT1 plays a vital role in this process. The current study aimed to elucidate the harmful effects of MPs on female reproduction via SIRT1 modulation. Healthy female zebrafish were exposed to different concentrations (50 and 500 µg/L) of polystyrene microplastics (PS-MPs). The results revealed a significant change in the gonadosomatic index (GSI) after exposure to PS-MPs. In addition, the decreased fecundity rate displayed an evident dosage effect, indicating that exposure to PS-MPs causes deleterious effects on fertilization. Furthermore, significantly enhanced levels of reactive oxygen species (ROS) and apoptotic signals through the TUNEL assay were evaluated in different treated groups. Moreover, morphological alterations in the gonads of zebrafish exposed to MPs were also observed through H&E staining. The subsequent change in plasma steroid hormone levels (E2/T ratio) showed an imbalance in hormonal homeostasis. Meanwhile, to follow PS-MPs' effects on the HPG axis via SIRT1 modulation and gene expression related to steroidogenesis, SIRT1/p53 pathway was evaluated through qPCR. The altered transcription levels of genes indicated the plausible interference of PS-MPs on the HPG axis function. Our in-silico molecular docking study proves that PS-MPs efficiently bind and inhibit endocrine receptors and SIRT1. Thus, these findings add to our understanding of the probable molecular mechanisms of reproductive impairment caused by PS-MPs in zebrafish.

Polystyrene microplastics modulated bdnf expression triggering neurotoxicity via apoptotic pathway in zebrafish embryos.

A ubiquitous presence of microplastics and nanoplastics created a new toxicological research area arising concept of "plastic rivers". But, the precise molecular mechanisms by which its exposure affects developmental neurotoxicity are poorly understood. Hence, in the present investigation, healthy zebrafish embryos were exposed to different concentrations of 500 nm polystyrene microplastics (0.1 ppm, 1 ppm and 10 ppm) to assess the neurotoxicity and the underlying biomolecular mechanism. On the last day of exposure, behaviour, accumulation, embryotoxicity, acridine orange staining, antioxidant enzyme assay, acetylcholinesterase assay, nitric oxide (NO) estimation, along with neurotransmitter (serotonin, dopamine) quantification and gene expression using qRT-PCR (bdnf, p53, bcl-2, caspase-3, caspase-9) were performed. As a result, we found that zebrafish embryos ingest and bioaccumulate microplastic without causing any morphological changes and lethality. The survival and hatching rates of the embryos were also unaffected but the swimming behaviour patterns were found to be altered. Further, acridine orange staining exhibited more apoptosis in treated groups with increased p53, caspase-3, caspase-9 and decreased bcl-2 gene expression. Moreover, polystyrene microplastics exposure resulted in reduced acetylcholinesterase activity leading to elevated NO concentration along with altered serotonin and dopamine levels and subsequently leading to down-regulated bdnf gene expression and modulated downstream apoptotic signalling, confirming the neurotoxicity potential of microplastics causing neuronal dysfunction. This study also compared the binding affinities between styrene and human proteins (Bdnf, p53 and Bcl-2) using bioinformatics methods, and docking results showed negative binding energy resulting in high binding affinities of Bcl-2 then p53 and Bdnf with styrene.

Unraveling the mechanisms of perfluorooctanesulfonic acid-induced dopaminergic neurotoxicity and microglial activation in developing zebrafish.

Perfluorooctanesulfonic acid (PFOS) is a prevalent, persistent organic pollutant in environmental matrices, yet its precise mechanism of neurotoxicity remains unclear. This study investigated the developmental and neurobehavioral effects of PFOS exposure (0, 100, 500, and 1000 µg/L) on zebrafish. The findings indicated that PFOS exposure caused various developmental abnormalities, including increased mortality, delayed hatching, shortened body length, bent spine, and edema in the pericardial and yolk sac regions. Subsequently, larvae exhibited a significant decrease in spontaneous movement frequency, altered touch-evoked response, and locomotor behavior. In fact, aberrant cellular responses in the brain and cardiac regions were observed. Microglial activation is a critical component of the inflammatory immune responses related to neurotoxicity. Likewise, our findings indicated that PFOS-induced microglial activation might be responsible for neuronal inflammation and apoptosis. Furthermore, AChE activity and dopamine content at the neurotransmitter level were also disrupted after PFOS exposure. The gene expression of dopamine signaling pathways and neuroinflammation were also altered. Collectively, our findings highlight that PFOS exposure can induce dopaminergic neurotoxicity and neuroinflammation through microglial activation, thus ultimately affecting behavior. Taken together, this study will provide mechanistic effects underlying the pathophysiology of neurological disorders.