The Neurotoxicity Of Endocrine Disrupter Nonylphenol And Its Molecular Mechanism

Nonylphenol (NP) is an organic compound of the broad family of alkylphenols. It is widely used in industrial and agricultural production and the production of consumer goods, and was released into the natural world, causing environmental pollution. As an endocrine disruptor, the exposure of NP could disturb the function of reproductive systems and immune system. However, few in vivo studies have assessed whether chronically administering of NP produces neurotoxic effects. The present study was performed to investigate the molecular mechanism of the neurotoxicity of NP on the view of ROS related apoptosis and inflammatory pathway for the first time, which laid the theoretical foundation for the following in-depth study and control of the alkylphenols neurotoxicity. And these results provide a theoretical basis for the development of relevant environmental standards.The NP exposed sub-chronic toxicological experimental model was established by oral gavages. Young male mice were randomly divided into four groups, and nine mice per group. After acclimatization to the laboratory conditions for one week, the treated groups were given NP (dissolved in corn oil) daily by oral gavages at 50, 100, 200 mg/kg per day, respectively. Mice in the control group were given the vehicle (corn oil) alone. After treating for 90 days, the mice were sacrificed for analysis. To detect the antioxidant defense system in central nervous system (CNS) by biochemical studies, we found that NP could induce lipid peroxidation and oxidative stress by refraining Superoxide Dismutase (SOD) activity, catalase (CAT) activity, total antioxidative capacity, and the scavenging activity on hydroxyl free radical.The expressions of the key genes on the apoptosis pathway were detected by in situ hybridization, RT-PCR, immunohistochemistry and immunoblotting assays, and the apoptosis in the brain was examine by TUNEL assay. The probes for in situ hybridization were generated by gene clone and in vitro transcription. In our present study, NP could significantly down-regulate the transcription of the anti-apoptosis gene bcl-2 and up-regulation of active caspase-3 in hippocampus and cortex, which is in accord with the results of terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) (p<0.05). However the expression of pro-apoptosis gene, bax mRNA, in the intrinsic apoptotic pathway and the expression of the key protein, Fas and Fas-L, in the extrinsic pathway were not affected in NP treated mice. These results indicated that NP induced apoptosis in the mice brain via suppression the transcription of the anti-apoptosis gene bcl-2 and up-regulation of active caspase-3.Western Blot and immunohistochemistry assays were used to detect the quantity and distribution of the key protein on the inflammatory signaling pathways. NP could up-regulate the nuclear transcription factor-κB (NF-κB) activation, and induce the expression of its downstream inflammatory mediators iNOS and COX-2 in hippocampus and cortex. The results of biochemical studies also suggested that nitric oxide synthase (NOS) activity and nitric oxide (NO) level were significantly higher in NP treated mice brain. These findings demonstrated that NP may have the potential to induce the chronic inflammatory and cause neurotoxicity in the mouse brain.Open-field test, step-through test and Morris-maze test were used to detect the effect of NP on the behaviors (learning and memory, excitability, adaptability, exploration and tensity) in the new environment. High dose of NP could significantly impair spatial learning and memory. NP could also make the mice easier to tension, weaken the adaptability, and reduce the exploration in the new environment. These results give more evidences that NP could induce neurotoxicity in CNS on the view of learning and memory behavior.All of these findings indicated that chronic exposure to NP could induce neurotoxicity and damage in the CNS of male mice. The neurotoxicity of NP was probably via activation of mitochondrial apoptosis pathway and NF-κB mediated inflammatory signaling pathway, which influence the expression of apoptosis genes and inflammatory mediators.