Effects Of Chronic Arsenic Exposure On Learning And Memory In Mice Based On GC-MS Metabolomics

Objective: To observe the effect of chronic arsenic exposure on learning and memory abilities and metabolomics profile of serum,hippocampus and cortex of mice,and to explore the possible mechanism of neurotoxicity induced by chronic arsenic exposure.Methods: Eighty healthy 3-week-old male C57BL/6J mice were randomly divided into 4 groups(20 mice each): control group(tap water),low-dose group(0.5 mg/L sodium arsenite),middle-dose group(5 mg/L sodium arsenite)and high-dose group(50 mg/L sodium arsenite).During the experiment,the mice were chronically exposed to arsenic for 24 weeks by free access to arsenic contained drinking water.Morris water maze test was conducted to assess the learning and memory abilities of mice at the 12 th and 24 th weeks,respectively.When exposure completed,blood and brain samples of mice were stored immediately after anesthesia,and hydride generation atomic fluorescence spectrometry was performed to determine the concentrations of arsenic,monomethylarsonic acid(MMA)The study was supported by the Natural Science Foundation Project of CQ CSTC(cstc2012jjA10070)and dimethylarsinic acid(DMA)in brain tissue.Effects of chronic arsenic exposure on metabolites of serum,cortex and hippocampus were measured by gas chromatography / mass spectrometry(GC/MS).Results: During arsenic exposure,the exposed groups showed restlessness,irritability and different degrees of hair shedding.Also,the exposed groups weighed slower,which were showed most obviously in the high-dose group,but none of the animals were found dead in all of the 4 groups.Organ coefficients of brain tissues of the exposed groups were lower than the control group,but had no statistical significance(P >0.05).Concentrations of inorganic arsenic in the brain tissues of each exposed group were higher than the control group,likewise,concentrations of DMA and MMA in the high-dose group were higher than the control group,and the difference was statistically significant(P <0.05).Morris water maze test showed that escape latency of the exposed group increased with the arsenic exposed dose,which had statistical significance(P <0.05)compared with the control group.In the probe trial,the number of platform crossings decreased with the arsenic exposed dose,and the difference between the 5 mg/L and the 50 mg/L group and the control group was statistically significant(P <0.05).Metabolomics results showed: compared with the control group,concentration of proline,glycine,glutamic acid,pyroglutamic acid,aspartic acid and serine increased,while α-ketoglutarate decreased in serum;in hippocampus,tyrosine and asparagine increased while aspartic acid and 2-hydroxy butyric acid decreased;in cerebral cortex,carbamic acid and itaconic acid increased,and phenylalanine,tyrosine,histidine,lysine and citric acid decreased.PCA analysis revealed statistical significances in metabolic characteristics between the exposed group and the control group(P <0.05).Conclusion: After arsenic exposure via drinking water,arsenic entered into blood circulation through the blood-brain barrier,accumulated in the brain tissue,and impaired the abilities of spatial learning and memory.Intriguingly,metabolites changes seduced by chronic arsenic exposure varied from tissue to tissue.Results of the study suggested that disorders of amino acids and energy metabolism may be one of the potential mechanisms of how chronic arsenic exposure impaired learning and memory abilities.