Methylparaben protects 6-hydroxydopamine-induced neurotoxicity in SH-SY5Y cells and improved behavioral impairments in mouse model of Parkinson's disease

The association of bisphenol A and paraben exposure with sensorineural hearing loss in children

Bisphenol A (BPA) and parabens (PBs) are chemicals that are extensively used in personal care products (PCPs). In early childhood development, hearing is critical to speech and language development, communication, and learning. In vitro and in vivo, BPA/PBs exhibited neurotoxicity through elevated levels of oxidative stress. BPA also has the potential to be an ototoxicant. Therefore, this study aimed to determine the association of exposure to BPA/PBs with sensorineural hearing loss in children. A cross-sectional study based on hearing tests was conducted. This study enrolled 320 children aged 6-12 years from elementary school. Urinary BPA and PB concentrations were analyzed by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Logistic regression models were employed to determine the association of BPA/PB exposure with sensorineural hearing loss. Children with sensorineural hearing loss had higher BPA concentrations than normal-hearing children (0.22 ng/ml vs. 0.10 ng/ml, p = 0.05). After adjustment for covariates, the risk of hearing loss at middle frequencies reached 1.83-fold (95% CI: 1.12-2.99) when BPA concentrations increased by 1 log10. The risk of slight hearing loss reached 2.24-fold (95% CI: 1.05-4.78) when children had a tenfold increase in ethyl paraben (EP) concentration. This study clarifies the role of exposure to BPA/PBs in hearing loss in children. Future research needs to be expanded to include cohort designs and nationwide studies to identify causality.

The SH-SY5Y human neuroblastoma cell line, a relevant in vitro cell model for investigating neurotoxicology in human: focus on organic pollutants

Investigation of the toxicity triggered by chemicals on the human brain has traditionally relied on approaches using rodent in vivo models and in vitro cell models including primary neuronal cultures and cell lines from rodents. The issues of species differences between humans and rodents, the animal ethical concerns and the time and cost required for neurotoxicity studies on in vivo animal models, do limit the use of animal-based models in neurotoxicology. In this context, human cell models appear relevant in elucidating cellular and molecular impacts of neurotoxicants and facilitating prioritization of in vivo testing. The SH-SY5Y human neuroblastoma cell line (ATCC® CRL-2266^TM) is one of the most used cell lines in neurosciences, either undifferentiated or differentiated into neuron-like cells. This review presents the characteristics of the SH-SY5Y cell line and proposes the results of a systematic review of literature on the use of this in vitro cell model for neurotoxicity research by focusing on organic environmental pollutants including pesticides, 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD), flame retardants, PFASs, parabens, bisphenols, phthalates, and PAHs. Organic environmental pollutants are widely present in the environment and increasingly known to cause clinical neurotoxic effects during fetal & child development and adulthood. Their effects on cultured SH-SY5Y cells include autophagy, cell death (apoptosis, pyroptosis, necroptosis, or necrosis), increased oxidative stress, mitochondrial dysfunction, disruption of neurotransmitter homeostasis, and alteration of neuritic length. Finally, the inherent advantages and limitations of the SH-SY5Y cell model are discussed in the context of chemical testing.

Propylparaben Reduces the Long-Term Consequences in Hippocampus Induced by Traumatic Brain Injury in Rats: Its Implications as Therapeutic Strategy to Prevent Neurodegenerative Diseases

BACKGROUND

Severe traumatic brain injury (TBI), an important risk factor for Alzheimer's disease, induces long-term hippocampal damage and hyperexcitability. On the other hand, studies support that propylparaben (PPB) induces hippocampal neuroprotection in neurodegenerative diseases.

OBJECTIVE

Experiments were designed to evaluate the effects of subchronic treatment with PPB on TBI-induced changes in the hippocampus of rats.

METHODS

Severe TBI was induced using the lateral fluid percussion model. Subsequently, rats received subchronic administration with PPB (178 mg/kg, TBI+PPB) or vehicle (TBI+PEG) daily for 5 days. The following changes were examined during the experimental procedure: sensorimotor dysfunction, changes in hippocampal excitability, as well as neuronal damage and volume.

RESULTS

TBI+PEG group showed sensorimotor dysfunction (p < 0.001), hyperexcitability (64.2%, p < 0.001), and low neuronal preservation ipsi- and contralateral to the trauma. Magnetic resonance imaging (MRI) analysis revealed lower volume (17.2%; p < 0.01) and great damage to the ipsilateral hippocampus. TBI+PPB group showed sensorimotor dysfunction that was partially reversed 30 days after trauma. This group showed hippocampal excitability and neuronal preservation similar to the control group. However, MRI analysis revealed lower hippocampal volume (p < 0.05) when compared with the control group.

CONCLUSION

The present study confirms that post-TBI subchronic administration with PPB reduces the long-term consequences of trauma in the hippocampus. Implications of PPB as a neuroprotective strategy to prevent the development of Alzheimer's disease as consequence of TBI are discussed.

Seaweeds' neuroprotective potential set in vitro on a human cellular stress model

Neurodegenerative diseases, such as Parkinson's disease, represent a biggest challenge for medicine, imposing high social and economic impacts. As a result, it is of utmost importance to develop new therapeutic strategies. The present work evaluated the neuroprotective potential of seaweeds extracts on an in vitro dopamine (DA)-induced neurotoxicity cellular model. The neuroprotective effects on SH-SY5Y cells' viability were estimated by the MTT assay. Changes in mitochondrial membrane potential (MMP), caspase-3 activity, and hydrogen peroxide (H2O2) production were determined. DA (30-3000 µM; 24 h) treatment decreased SH-SY5Y cells' viability in concentration and time-dependent manner, increasing the H2O2 production, MMP depolarization, and caspase-3 activity. On the other hand, DA (1000 µM; 24 h) toxicity was reduced (10-15%) with Sargassum muticum and Codium tomentosum extracts (1000 µg/mL; 24 h). The highest neuroprotective activity was exhibited by a methanolic extract obtained from Saccorhiza polyschides, which completely blunted DA effects. Results show that the marine seaweed S. polyschides contain substances with high neuroprotective potential against the toxicity induced by DA, exhibiting anti-apoptotic effects associated with both mitochondrial protection and caspase-3 inhibition. S. polyschides reveals, therefore, to be an excellent source of bioactive molecules, for new drugs development aiming PD therapeutics.

7,8,4'-Trihydroxyisoflavone, a Metabolized Product of Daidzein, Attenuates 6-Hydroxydopamine-Induced Neurotoxicity in SH-SY5Y Cells

Daidzein isolated from soybean (Glycine max) has been widely studied for its antioxidant and anti-inflammatory activities. However, the protective effects of 7,8,4'-trihydroxyisoflavone (THIF), a major metabolite of daidzein, on 6-hydroxydopamine (OHDA)-induced neurotoxicity are not well understood. In the current study, 7,8,4'-THIF significantly inhibited neuronal cell death and lactate dehydrogenase (LDH) release induced by 6-OHDA in SH-SY5Y cells, which were used as an in vitro model of Parkinson' disease (PD). Moreover, pretreatment with 7,8,4'-THIF significantly increased the levels of superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) and decreased malondialdehyde (MDA) activity in 6-OHDA-induced SH-SY5Y cells. In addition, 7,8,4'-THIF significantly recovered 6-OHDA-induced cleaved caspase-3, cleaved caspase-9, cleaved poly-ADP-ribose polymerase (PARP), increased Bax, and decreased Bcl-2 levels. Additionally, 7,8,4'-THIF significantly restored the expression levels of phosphorylated c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase 1/2 (ERK 1/2), phosphatidylinositol 3-kinases (PI3K)/Akt, and glycogen synthase kinase-3 beta (GSK-3β) in 6-OHDA-induced SH-SY5Y cells. Further, 7,8,4'-THIF significantly increased the reduced tyrosine hydroxylase (TH) level induced by 6-OHDA in SH-SY5Y cells. Collectively, these results suggest that 7,8,4'-THIF protects against 6-OHDA-induced neuronal cell death in cellular PD models. Also, these effects are mediated partly by inhibiting activation of the MAPK and PI3K/Akt/GSK-3β pathways.

The sex-specific association between maternal paraben exposure and size at birth

Parabens are a group of esters of parahydroxybenzoic acid and are utilized as antimicrobial preservatives in the majority of personal care products (PCPs). Epidemiological studies regarding the adverse effects of parabens on fetuses are still limited. The aim of this study was to determine the association between maternal paraben exposure and birth outcomes. One hundred and ninety-nine pregnant women were enrolled, and maternal urine was collected in the third trimester. The urine concentrations of four parabens (methyl (MP), ethyl (EP), propyl (PP), and butyl (BP)) were determined by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry. Generalized additive model-penalized regression splines and a multivariable regression model were employed to determine the association between paraben exposure levels and birth outcomes. A causal mediation analysis was conducted to determine the mediation effect of oxidative stress on birth outcomes. The geometric means of urinary MP, EP, PP, and BP were 51.79, 1.26, 4.21, and 1.25 μg/g cre., respectively. In the penalized regression splines, sex-specific associations between maternal MP levels and birth outcomes were observed; a downward curvature was observed between the MP level and birth weight, length, head circumference, and thoracic circumference among female newborns. Pregnant women in the group with MP levels above the third quartile had neonates with significantly lower body weight (β = -215.98 g, p value = 0.02) compared to those in the group with MP levels lower than the third quartile. No significant mediation of oxidative stress was observed between maternal MP exposure and female birth weight. The estimated proportion mediated ranged from -6% to 15%. The negative association between maternal paraben exposure and female birth outcomes in relation to child development should be carefully considered.

Neuroprotective effects of seaweeds against 6-hydroxidopamine-induced cell death on an in vitro human neuroblastoma model

BACKGROUND

Parkinson's disease (PD) is a progressive neurodegenerative disorder of the central nervous system. Although the causes of PD pathogenesis remain incomplete, some evidences has suggested that oxidative stress is an important mediator in its pathogenesis. The aim of this study was to evaluate the protective effects of seaweeds with high antioxidant activity on 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in the human neuroblastoma cell line SH-SY5Y, as well as the associated intracellular signaling pathways.

METHODS

Cell viability studies were assessed by 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium (MTT) bromide assay and the intracellular signaling pathways analyzed were: hydrogen peroxide (H2O2) production, changes in the mitochondrial membrane potential and Caspase-3 activity.

RESULTS

Exposure of SH-SY5Y cells to 6-OHDA (10-1000 μM) reduced cell's viability in a concentration and time-dependent manner. The data suggest that the cell death induced by 6-OHDA was mediated by an increase of H2O2 production, the depolarization of mitochondrial membrane potential and the increase of Caspase-3 activity. Extracts from S. polyshides, P. pavonica, S. muticum, C. tomentosum and U. compressa revealed to efficiently protect cell's viability in the presence of 6-OHDA (100 μM; 24 h). These effects appear to be associated with the reduction of H2O2 cell's production, the protection of mitochondrial membrane's potential and the reduction of Caspase-3 activity.

CONCLUSIONS

These results suggest that seaweeds can be a promising source of new compounds with neuroprotective potential.

Effect of Oleracein E, a Neuroprotective Tetrahydroisoquinoline, on Rotenone-Induced Parkinson's Disease Cell and Animal Models

Oleracein E (OE), a tetrahydroisoquinoline possessing potent antioxidant activity, was first isolated from a traditional Chinese medicine, Portulaca oleraea L., and is hypothesized to be a neuroprotectant. In the present study, we evaluated the effects of racemic OE on rotenone-induced toxicity in Parkinson's disease (PD) cell and animal models. Pretreatment with OE (10 μM, 2 h) decreased lactic acid dehydrogenase (LDH) release and the apoptosis rate in rotenone (5 μM, 24 h)-treated SH-SY5Y human neuroblastoma cells. Further mechanistic study indicated that OE reduced reactive oxygen species (ROS) levels, inhibited extracellular signal-regulated kinase (ERK) 1/2 phosphorylation, reduced rotenone-induced up-regulation of the proapoptotic protein Bax, and prevented cytochrome C release and caspase-3 activation. In a rotenone-treated (intragastric 30 mg/(kg·d), 56 d) C57BL-6J mouse model, OE (intragastric 15 mg/(kg·d), 56 d) improved motor function, as indicated by an increased moving distance in the spontaneous activity test and sustained time on the rota-rod test. OE also elevated superoxide dismutase (SOD) activity, decreased malonaldehyde content, and reduced ERK1/2 phosphorylation in the midbrain and striatum of mice treated with rotenone. Furthermore, OE preserved tyrosine hydroxylase-positive neurons and maintained the density of dopaminergic (DAergic) fibers in the substantia nigra pars compacta (SNpc). Some of the effects of OE on PD models were similar to those of the positive control selegiline hydrochloride. Our results demonstrated that OE protects DAergic neurons against rotenone toxicity through reducing oxidative stress and down-regulating stress-related molecules. OE is worth exploring further for its neuroprotectant properties in the prevention and treatment of PD.

Stimulus-dependent neuronal cell responses in SH-SY5Y neuroblastoma cells

The aim of the present study was to elucidate the intracellular mechanisms that cause neuronal cell death following exposure to excitatory neurotransmitter‑induced neurotoxicity, neurotoxins and oxidative stress. Human SH‑SY5Y neuroblastoma cells were exposed to various stimuli, including glutamate, 6‑hydroxydopamine (6‑OHDA), and glucose oxidase, and cell viability was determined by MTT assay. Early apoptosis and necrosis were examined by Annexin V/propidium iodide double staining and flow cytometric analysis. Intracellular calcium ion concentration and mitochondrial membrane potential were assessed by Fluo‑3a and JC‑1 staining, respectively. In addition, protein expression of receptor‑interacting protein (RIP) kinase 1 and RIP kinase 3 were evaluated by western blotting. Glutamate, 6‑OHDA and glucose oxidase treatment decreased cell viability. Glutamate induced apoptosis and necrosis, whereas, 6‑OHDA induced cell necrosis and glucose oxidase induced apoptosis. Furthermore, glutamate, 6‑OHDA or glucose oxidase treatment significantly increased intracellular calcium concentrations (P<0.05). The effect of glutamate on mitochondrial membrane potential varied with high and low concentrations, whereas 6‑OHDA and glucose oxidase significantly increased the mitochondrial membrane potential in the SH‑SY5Y cells (P<0.05). Glutamate significantly upregulated expression levels of RIP kinase 1 (P<0.05), but not RIP kinase 3. These findings demonstrate that the response of SH‑SY5Y cells varies with the stimuli. Furthermore, RIP kinase 1 may specifically regulate programmed necrosis in glutamate‑mediated excitatory toxicity, but not in cell damage induced by either 6-OHDA or glucose oxidase.

Neuroprotection by 6-(methylsulfinyl)hexyl isothiocyanate in a 6-hydroxydopamine mouse model of Parkinson׳s disease

A number of pathogenic factors have been implicated in the progression of Parkinson׳s disease (PD), including oxidative stress, mitochondrial dysfunction, inflammation, excitotoxicity, and signals mediating apoptosis cascade. 6-(methylsulfinyl)hexyl isothiocyanate (6-MSITC) is a major component in wasabi, a very popular spice in Japan and a member of the Brassica family of vegetables. This study was designed to investigate the neuroprotective effects of 6-MSITC in a PD mouse model. Mice were treated with 6-MSITC (5mg/kg twice a week) for four weeks after the unilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA). On the 28th day, 6-OHDA-injected mice showed behavioral impairments, a significant decrease in tyrosine hydroxylase (TH) and an increase in apoptosis. In addition, lesioned mice showed reduced glutathione levels and glutathione-S-transferase and glutathione reductase activities. Notably, 6-MSITC demonstrated neuroprotective effects in our experimental model strongly related to the preservation of functional nigral dopaminergic neurons, which contributed to the reduction of motor dysfunction induced by 6-OHDA. Furthermore, this study provides evidence that the beneficial effects of 6-MSITC could be attributed to the decrease of apoptotic cell death and to the activation of glutathione-dependent antioxidant systems. These findings may render 6-MSITC as a promising molecule for further pharmacological studies on the investigation for disease-modifying treatment in PD.

Downregulation of thioredoxin reductase 1 expression in the substantia nigra pars compacta of Parkinson's disease mice

Because neurons are susceptible to oxidative damage and thioredoxin reductase 1 is extensively distributed in the central nervous system and has antioxidant properties, we speculated that the enzyme may be involved in the pathogenesis of Parkinson's disease. A Parkinson's disease model was produced by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine into C57BL/6 mice. Real-time reverse transcription-PCR, western blot analysis and colorimetric assay showed that the levels of thioredoxin reductase 1 mRNA and protein were decreased, along with a significant reduction in thioredoxin reductase activity, in the midbrain of Parkinson's disease mice compared with normal mice. Immunohistochemical staining revealed that the number of thioredoxin reductase 1-positive neurons in the substantia nigra pars compacta of Parkinson's disease mice was significantly decreased compared with normal mice. These experimental findings suggest that the expression of thioredoxin reductase 1 in the substantia nigra pars compacta of Parkinson's disease mice is significantly decreased, and that the enzyme may be associated with disease onset.