The impact of subchronic low-dose exposure to nonylphenol on depression-like behaviors in high-sucrose and high-fat diet induced rats

Nonylphenol induces depressive behavior in rats and affects gut microbiota: A dose-dependent effect

Nonylphenol (NP), an endocrine disruptor absorbed through food intake, was investigated in this study for its potential dose-response relationship with the manifestation of depression-like behavior in rats. Based on this, the mechanisms of NP-induced depressive behavior, encompassing neurotransmitters, gut barrier function, inflammatory response, gut microbiota composition and metabolites were further explored. At medium and high NP doses, both mRNA and protein levels of zonula occludens protein-1 and claudin-1 were considerably downregulated, concomitant with an elevation in tumor necrosis factor-α and interleukin-1β expression in a dose-dependent effect, resulting in damage to the gut mucosa. Despite a minimal impact on behavior and gut barriers at low NP doses, alterations in gut microbiota composition were observed. During NP exposure, dose-dependent changes in the gut microbiota revealed a decline in microbial diversity linked to the synthesis of short-chain fatty acids. NP not only adversely affected the gut microbiota structure but also exacerbated central nervous system damage through the gut-brain axis. The accumulation of NP may cause neurotransmitter disturbances and inflammatory responses in the hippocampus, which also exacerbate depressed behavior in rats. Therefore, NP could exacerbate the inflammatory response in the hippocampus and colon by compromising intestinal barrier integrity, facilitating the proliferation of pathogenic bacteria, impairing butyrate metabolism, and perturbing neurotransmitter homeostasis, thus aggravating the depressive behavior of rats. It is noteworthy that the changes in these indicators were related to the NP exposure dose.

Role and mechanism of MiR-542-3p in regulating TLR4 in nonylphenol-induced neuronal cell pyroptosis

BACKGROUND

This study aimed to investigate the spatial learning/memory and motor abilities of rats and the alteration of miR-542-3p and pyroptosis in the midbrain nigrostriatal area in vivo after nonylphenol (NP) gavage and to explore the mechanism of miR-542-3p regulation of Toll-like receptor 4 (TLR4) in NP-induced pyroptosis in BV2 microglia in vitro.

METHODS

In vivo: Thirty-six specific-pathogen-free-grade Sprague-Dawley rats were divided into three equal groups: blank control group (treated with pure corn oil), NP group (treated with NP, 80 mg/kg body weight per day for 90 days), and positive control group [treated with lipopolysaccharide (LPS), 2 mg/kg body weight for 7 days]. In vitro: The first part of the experiment was divided into blank group (control, saline), LPS group [1 µg/ml + 1 mM adenosine triphosphate (ATP)], and NP group (40 µmol/L). The second part was divided into mimics NC (negative control) group, miR-542-3p mimics group, mimics NC + NP group, and miR-542-3p mimics + NP group.

RESULTS

In vivo: Behaviorally, the spatial learning/memory and motor abilities of rats after NP exposure declined, as detected via Y-maze, open field, and rotarod tests. Some microglia in the substantia nigra of the NP-treated rats were activated. The downregulation of miR-542-3p was observed in rat brain tissue after NP exposure. The mRNA/protein expression of pyroptosis-related indicators (TLR4), NOD-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein (ASC), gasdermin-D (GSDMD), cysteinyl aspartate-specific proteinase-1 (caspase-1), and interleukin-1β (IL-1β) in the substantia nigra of the midbrain increased after NP exposure. In vitro: ASC fluorescence intensity increased in BV2 cells after NP exposure. The mRNA and/or protein expression of pyroptosis-related indicators (TLR4, NLRP3, GSDMD, caspase-1, and IL-1β) in BV2 cells was upregulated after NP exposure. The transfection of miR-542-3p mimics inhibited NP-induced ASC expression in BV2 cells. The overexpression of miR-542-3p, followed by NP exposure, significantly reduced TLR4, NLRP3, ASC, caspase-1, and IL-1β gene and/or protein expression.

CONCLUSIONS

This study suggested that NP exposure caused a decline in spatial learning memory and whole-body motor ability in rats. Our study was novel in reporting that the upregulation of miR-542-3p targeting and regulating TLR4 could inhibit NLRP3 inflammatory activation and alleviate NP-induced microglia pyroptosis.

Exposure to nonylphenol in early life causes behavioural deficits related with autism spectrum disorders in rats

Early-life exposure to environmental endocrine disruptors (EDCs) is a potential risk factor for autism spectrum disorder (ASD). Exposure to nonylphenol (NP), a typical EDC, is known to cause some long-term behavioural abnormalities. Moreover, these abnormal behaviours are the most frequent psychiatric co-morbidities in ASD. However, the direct evidence for the link between NP exposure in early life and ASD-like behavioural phenotypes is still missing. In the present study, typical ASD-like behaviours induced by valproic acid treatment were considered as a positive behavioural control. We investigated impacts on social behaviours following early-life exposure to NP, and explored effects of this exposure on neuronal dendritic spines, mitochondria function, oxidative stress, and endoplasmic reticulum (ER) stress. Furthermore, primary cultured rat neurons were employed as in vitro model to evaluate changes in dendritic spine caused by exposure to NP, and oxidative stress and ER stress were specifically modulated to further explore their roles in these changes. Our results indicated rats exposed to NP in early life showed mild ASD-like behaviours. Moreover, we also found the activation of ER stress triggered by oxidative stress may contribute to dendritic spine decrease and synaptic dysfunction, which may underlie neurobehavioural abnormalities induced by early-life exposure to NP.

Role of miR-219a-5p in regulating NMDAR in nonylphenol-induced synaptic plasticity damage

Nonylphenol (NP) is a typical environmental endocrine disruptor with estrogenic effects. It serves as an emulsifier and as the main ingredient of detergents and has become an increasingly common pollutant in both fresh and salt water, vegetables, and fruits. This study aimed to clarify whether NP exposure could lead to cognitive dysfunction and synaptic plasticity impairment, and also explore the mechanism of microRNA (miR)- 219a-5p regulation of N-methyl-D-aspartate receptor (NMDAR) in NP-induced synaptic plasticity impairment in vivo and in vitro. In vivo, 30 male Sprague-Dawley rats were randomly divided into 2 groups: blank control group (pure corn oil) and NP-exposed group [NP 80 mg/(kg·d)], with 15 rats in each group. In vitro, the extracted hippocampal neurons were divided into 6 groups: blank control group, mimics NC group, miR-219 mimics group, NP group (70 μmol/L NP), NP + mimics NC group, and NP + miR-219 mimics group. In vivo, the content of NP in hippocampal tissues after 90 days of NP exposure was significantly higher in the NP-stained group than in the blank control group. NP exposure could lead to a decrease in the ability to learn and memory, ability to remember, and space spatial memory ability in rats. The dendrites in the NP-stained group were disordered, with few dendritic spines and significantly decreased dendritic spine density. The postsynaptic densities were loosely arranged, the thickness and length of the postsynaptic densities shortened, and the length and width of the synaptic gap increased. Glutamine (Glu) and γ-aminobutyric acid (GABA) contents in hippocampal tissues decreased in the NP-stained group. The expression of miR-219a-5p mRNA decreased in the NP-stained group after 3 months of NP exposure. The expression of NMDAR1, NMDAR2A, NMDAR2B, nerve growth-associated protein (GAP-43), and Ca/calmodulin-dependent kinase II (CaMKII) mRNA/proteins decreased in the NP-stained group. In vitro, NMDAR protein expression decreased, while GAP-43 and CaMKII protein expression increased in the miR-219 mimics group compared with the control group. The expression levels of NMDAR and GAP-43 and CaMKII proteins were higher in the NP + miR-219 mimics group compared with the NP group. The levels of neurotransmitters Glu and GABA decreased in the NP and NP + mimics NC groups compared with the blank group. Shortened synaptic active band length, decreased thickness of postsynaptic densities, and shortened length of postsynaptic densities were observed in the NP, NP + mimics NC, and NP + miR-219 mimics groups compared with the blank control group. In vivo, NP exposure reduced learning memory capacity and neurotransmitter content in rats and caused a decrease in dendritic spine density and synaptic number density and a decrease in miR-219a-5p expression. In vitro, high expression of miR-219a-5p inhibited the expression of NMDAR, thus reducing the effect of NP on synaptic plasticity impairment in hippocampal neurons. Our study provided a scientific basis for the prevention of cognitive impairment owing to NP exposure and the development of targeted drug treatment strategies.

The mechanisms of learning and memory impairment caused by nonylphenol: a narrative review based on in vivo and in vitro studies

Learning and memory play a fundamental role on brain cognitive functions which are crucial for human life. Nonylphenol (NP), a serious environmental pollutant over the world, is proven to be harmful for learning and memory mainly via diet exposure. Currently, besides the administrative restrictions for the use of NP, there are rarely other effective approaches against learning and memory impairment caused by NP. This review summarized the mechanisms underlying NP-induced learning and memory impairment according to in vivo and in vitro experiments. Based on the studies involved in behavior tests, these mechanisms were classified as oxidative stress, neurotransmitter disorder, synaptic plasticity impairment, and neuron injury. In addition, according to the studies which did not conduct behavior tests, the possible mechanisms underlying NP-induced learning and memory impairment were proposed as chronic inflammation and gut permeability increment. Furthermore, this review also revealed the demanding questions for the mechanism investigations and therapeutic methods. Notably, the summarized mechanisms might accelerate the prevention and remediation of NP-induced learning and memory impairment.

Biology of cyclooxygenase-2: An application in depression therapeutics

Depressive Disorder is a common mood disorder or affective disorder that is dominated by depressed mood. It is characterized by a high incidence and recurrence. The onset of depression is related to genetic, biological and psychosocial factors. However, the pathogenesis is still unclear. In recent years, there has been an increasing amount of research on the inflammatory hypothesis of depression, in which cyclo-oxygen-ase 2 (COX-2), a pro-inflammatory cytokine, is closely associated with depression. A variety of chemical drugs and natural products have been found to exert therapeutic effects by modulating COX-2 levels. This paper summarizes the relationship between COX-2 and depression in terms of neuroinflammation, intestinal flora, neurotransmitters, HPA axis, mitochondrial dysfunction and hippocampal neuronal damage, which can provide a reference for further preventive control, clinical treatment and scientific research on depression.

Subchronic nonylphenol exposure induced anxiety-like behavior and decreased expressions of regulators of synaptic plasticity in rats

Studies have shown that there were associations between endocrine disrupting chemicals (EDCs) and anxiety. Nonylphenol (NP) is an EDC with weak estrogen activity. This study aimed to clarify whether subchronic exposure of NP at environmental concentrations induces anxiety-like behavior, and effects of NP on the regulators (NMDAR2B, PSD-95, Synapsin1) expressions of synaptic plasticity in vivo and in vitro experiments. In vivo, 40 male SD rats were randomly divided into 4 groups (each with 10 rats): low dose (0.4 mg/kg/day, L-NP), middle-dose (4 mg/kg/day, M - NP), high-dose (40 mg/kg/day, H-NP) and corn oil (Control) groups. In vitro, HT22 cells were divided into a control group (Control), NP group (NP, 20 μM), glutamine acid receptor inhibitor group (MK-801, 10 μM) and MK-801 + NP group. The concentration of NP in the hippocampus rised with the increase of NP exposure concentration in the treatment groups (F = 7.542, P = 0.001). Compared with the control group, the residence time in the dark box after NP exposure had extended (F = 117.927, P < 0.01). The duration (F = 112.054, P < 0.01) and the number of times (F = 13.514, P < 0.01) to enter the closed arm in the NP exposure group significantly increased. There were more neurons degeneration and nuclear shrinkage in the M - and H- NP groups, while the average number of shrinked neurons increased with the increasing dose of NP exposure. The protein expressions of PSD-95 (F = 97.723, P < 0.01), Synapsin1 (F = 41.797, P < 0.01) and NMDAR2B (F = 3.440, P = 0.036) in the NP group were lower than those of the control. Simultaneously, the expressions of PSD-95, Synapsin1 and NMDAR2B in the hippocampus were down-regulated; the mRNA expression of PSD-95 (F = 19.950, P < 0.01), Synapsin1 (F = 3.498, P = 0.035) and NMDAR2B (F = 9.293, P < 0.01) genes in the hippocampus decreased in the M - and H-NP groups. In vitro, the trend of the fluorescence intensity expressed by PSD-95 (F = 2.606, P = 0.124) and Synapsin1 (F = 20.573, P < 0.01) among the groups was: MK-801 + NP group < MK-801 < NP group. The protein expressions of PSD-95 (F = 5.699, P = 0.022), Synapsin1 (F = 10.820, P = 0.003) and NMDAR2B (F = 6.041, P = 0.019) were down-regulated. These results suggested that subchronic exposure to environmental concentrations of NP induced anxiety, and reduced the protein and/or mRNA expressions of regulators of synaptic plasticity (PSD-95, Synapsin1, NMDAR2B).

Behavioral disorders caused by nonylphenol and strategies for protection

Nonylphenol (NP) is widely used in daily production and life due to its good emulsification. In this review, we discuss toxicology studies that examined behavioral disorders caused by NP, the corresponding toxicological mechanisms in the central nervous system (CNS), and strategies for protection. Available in vitro and in vivo evidence suggests that exposure to NP during adulthood or early childhood is associated with cognitive dysfunction, including depression-like behaviors, anxiety-like behaviors, and impaired learning and memory. The main mechanisms underlying NP-related cognitive disorders include inflammation, destruction of synaptic plasticity, and destruction of important signaling pathways that affect the synthesis and secretion of neurotransmitters. The effects and mechanisms of NP exposure on CNS-mediated reproductive function, including interference with the expression of hormones, proteins, and enzymes, are discussed. Other abnormal behaviors such as locomotor activity and swimming behavior are also described. Several measures to prevent NP neurotoxicity are summarized. These measures are based on the toxicological mechanisms underlying NP exposure and include external protection and internal self-regulation of the nervous system. Finally, a new treatment idea is proposed based on the gut-brain axis. Characterizing the behavioral changes and underlying toxicity mechanisms associated with NP exposure and investigating the possible methods of treatment will help to expand the understanding of these mechanisms and could lead to more effective treatments.

Hospital-based case control study and animal study on the relationship between nonylphenol exposure and depression

Objectives

The aim of this work is to explore the association between chronic exposure to nonylphenol (NP), a representative environmental endocrine disruptor (EED), and the risk of depression and its potential mechanism.

Methods

A hospital-based case control study was conducted from August to December 2018. Forty-one patients with confirmed depression and 47 healthy volunteers were recruited. In vitro, 20 rats were randomly divided into the control group (corn oil) and NP exposure group (n=10 per group), which were gavaged at a dose of 4 mg/kg w/day for 180 days.

Results

The depressed patient group had higher Zung Self-Rating Depression Scale (SDS) (P<0.001) and Self-Rating Anxiety Scale (SAS) (P<0.001) scores than the healthy group. The serum NP level (P=0.009) in the depressed group was higher than that in the healthy group, and the BDNF level (P=0.001) was lower. The serum levels of monoamine neurotransmitters dopamine (DA) (P=0.070), epinephrine (E) (P=0.001), and noradrenaline (NE) (P=0.000) were lower than those in the healthy group. In the sucrose preference test, the sucrose preference time for the exposure group of rats was lower than that of the control group (P<0.001). In the forced swim test, a longer resting time was measured for the exposure group of rats as compared to the control group (P<0.05). The level of NP (P<0.001) in the brain tissue of the NP exposure group was higher than that in the control group, and the serum level of brain-derived neurotrophic factor (BDNF) (P=0.004) was lower. Histopathological examination of the brain biopsies illustrated that the neuronal cells and nuclei in the hippocampus of the exposed group exhibited slight shrinkage.

Conclusion

Chronic exposure to NP at environmental doses will result in the accumulation of NP in the brain and blood, and induction of depression, which might be associated with the alterations in the expression levels of BDNF and monoamine neurotransmitters.

Dietary and metabolic risk of neuropsychiatric disorders: insights from animal models

Neuropsychiatric disorders are major causes of the global burden of diseases, frequently co-occurring with multiple co-morbidities, especially obesity, type 2 diabetes mellitus, non-alcoholic fatty liver disease and its various risk factors in the metabolic syndrome. While the determining factors of neuropsychiatric disorders are complex, recent studies have shown that there is a strong link between diet, metabolic state and neuropsychiatric disorders, including anxiety and depression. There is no doubt that rodent models are of great value for preclinical research. Therefore, this article focuses on a rodent model of chronic consumption of high-fat diet (HFD), and/or the addition of a certain amount of cholesterol or sugar, meanwhile, summarising the pattern of diet that induces anxiety/depressive-like behaviour and the underlying mechanism. We highlight how dietary and metabolic risk influence neuropsychiatric behaviour in animals. Changes in dietary patterns, especially HFD, can induce anxiety- or depression-like behaviours, which may vary by diet exposure period, sex, age, species and genetic background of the animals used. Furthermore, dietary patterns significantly aggravate anxiety/depression-like behaviour in animal models of neuropsychiatric disorders. The mechanisms by which diet induces anxiety/depressive-like behaviour may involve neuroinflammation, neurotransmitters/neuromodulators, neurotrophins and the gut-brain axis. Future research should be focused on elucidating the mechanism and identifying the contribution of diet and diet-induced metabolic risk to neuropsychiatric disorders, which can form the basis for future clinical dietary intervention strategies for neuropsychiatric disorders.

Dynamic monitoring of depressive behavior induced by nonylphenol and its effect on synaptic plasticity in rats

The etiology of depression is not known, it is thought that endocrine-disrupting chemicals (EDCs) contribute to the disease. Results of our previous research have shown that nonylphenol (NP), a well-known EDC, has neurotoxic effects, however, whether NP can induce depressive behavior by affecting synaptic plasticity has not yet been clearly elucidated. The depressive behavior induced by subchronic exposure to NP and its effect on the neuronal synaptic plasticity in rats are dynamically observed. Thirty Sprague-Dawley rats were randomly divided into 3 groups: control group (C, corn oil), NP group (NP, 4 mg/kg), and depression model group (D, corticosterone 20 mg/kg). There were 8 rats in each group. The depressive behavior of rats was tested by sucrose preference test, open-field test, and forced swimming test once a month for 3 months. The serum levels of brain-derived neurotrophic factor (BDNF) and corticosterone were detected by ELISA assay, and cellular morphological changes were observed by hematoxylin-eosin (HE) staining. The number of nerve cells, the length of dendrites, and the density of dendritic spines were observed by Golgi staining, and the synaptic cleft width, the postsynaptic density (PSD) thickness, and the synaptic interface curvature were observed by transmission electron microscope. Compared with the control group, the consumption of sucrose solution decreased in the NP group at the 2nd and 3rd month compared to the 1st month (F = 9.887, P = 0.002). The number of central square entries, the central square duration, and the total distance of movement were all decreased, and the decreasing degrees at the 3rd month were greater than those at the 1st month (F = 21.191, P < 0.001; F = 9.836, P = 0.002). The time of immobility for the NP group at the 1st month was higher than that in the control group (F = 6.912, P = 0.002). The expression of BDNF in the NP-treated group was higher than the control, while the expression of corticosterone in the NP-treated group was lower than the control. In the NP group, the cytoplasm of nerve cells contracted and appeared disordered. The neuron arrangement was disordered, and the number of cells, the length of the apex, the length of the basal dendrites, and the dendritic spine density were all lower in the NP group than those in the control group. The PSD thickness, the synaptic cleft width, and synaptic interface curvatures were all decreased in the NP group when compared to the control group. Subchronic exposure to 4 mg/kg NP led to depressive behavior in rats, and the depressive behavior and alterations in synaptic plasticity were more obvious with longer exposure time.