Effects Of Oxidized Pork Protein Product Dityrosine On Learning And Memory In Growing Mice

Proteins and amino acids in food can cause oxidation during processing and storage.Ingestion of oxidized tyrosine products(OTPs)may adversely affect the health of the body.There are no reports on the effects of food-borne OTPs on learning and memory.In this study,pork protein oxidation was taken as an example to explore the effects and mechanism of dityrosine(DT),the major product of OTPs on learning and memory in growing mice.The study is divided into two parts.The first part is the oxidized pork diet test.Forty-eight healthy male SPF 3-week-old C57BL/6J mice were randomly divided into control group(CON),low-oxidation pork group(LO),high-oxidation pork group(HO),low-oxidation pork + dityrosine group(LO+DT).After feeding for 12 weeks,tail-flick test,open field test,novel object recognition test,elevated plus-maze test,and Morris water maze test were performed.The results showed that with the increase of the degree of dietary oxidation,the other three groups besides the control group showed varying degrees of thermal stimulation response delay,anxiety-like behavior,spatial and non-spatial learning,and memory impairment.Subsequent tests found that feeding highoxidized oxidized pork diets can cause an imbalance of redox status in plasma and brain tissues,increase deposition of protein oxidation products,and up-regulate the expression of genes related to oxidative defense in the hippocampus,Nrf2,and Prdx-1.Inflammatory factor-related indicators in hippocampal tissues found that feeding high-oxidized pork diets will increase IL-6,IL-1β,TNF-α levels,decrease IL-10 levels,and expressions of inflammatory genes P38 and NF-κB up-regulate.The detection of hippocampal learning memory and expression of apoptosis-related genes revealed that the expression of NMDAR and CaMKⅡ related learning and memory genes was downregulated,Bcl-2 expression was down-regulated,and Bax gene expression was up-regulated with the increase oxidation of diets.These results indicated that feeding different degrees of oxidized pork diets can lead to the imbalance of redox status in mice,and then cause problems such as learning and memory disorders.Moreover,DT in pork oxidation products may play a more important role in inducing learning and memory disorders.To further explored the mechanism by which the OTPs and its major product DT affected the learning and memory of growing mice,we performed an OTPs intragastric administration test.Thirty freshly weaned male and female SPF C57BL/6J mice were randomly divided into six groups according to body weight,with 10 mice in each group.Among them:(1)control group(CON♂ and CON♀,daily intragastric administration Tyr 420 μg/kg·bw/d);(2)oxidized tyrosine product group(OTPs♂ and OTPs♀,daily intragastric administration OTPs 1909 μg/kg·bw/d);(3)dityrosine group(DT♂ and DT♀,daily intragastric administration DT 420 μg/kg·bw/d).After 5 weeks of intragastric administration,the same behavioral test was performed,and the results showed that both the DT group and the OTPs group showed thermal stimulation response delay,anxiety-like behavior,spatial and non-spatial learning and memory disorders.We found that the plasma and cerebral cortex ROS level and MDA level increased,and the levels of T-AOC,SOD,GSH/GSSG decreased in the DT group and the OTPs group.The hippocampus protein oxidation products DT,3-NT,AOPPs,and Aβ40 deposits in the DT group and the OTPs group were significantly increased,and the expressions of redox defense-related genes Nrf2 and Prdx-1 in the hippocampus were up-regulated.The results of hippocampal inflammatory factors showed that IL-6,IL-1β,TNF-α levels increased,IL-10 levels decreased,and the expressions of inflammatory genes P38 and NF-κB were up-regulated in the DT group and the OTPs group.Monoamine neurotransmitters results showed that 5-HT,DA,NE levels decreased,and MAO levels increased in the cerebral cortex.The DT and DA binding dopamine D2 receptors test found that transdityrosine may compete with DA combine dopamine D2 receptors.These may be the important cause of anxiety-like behavior in growing mice.The results of the hippocampal gene and protein determinations revealed that pure DT and OTPs administration can lead to down-regulation of learning and memory LTP pathway expression and up-regulation of mitochondrial apoptotic pathway gene expression.In this part of the test,we also found that female growing mice are slightly more resistant to oxidative stress caused by DT and OTPs than males.Moreover,DT plays an important role in OTPs.In conclusion,oxidized pork protein product DT may cause learning and memory impairment in individuals during the growing period.The specific mechanism may be that DT continues to induce oxidative stress in the body after deposition,which leads to redox in the body.Then the body and brain tissues protein oxidative deposition increased,inflammatory factors levels increased,monoamine neurotransmitter disorders,downregulation of LTP learning and memory pathway expression,and upregulation of mitochondrial pro-apoptotic pathway in hippocampal.