| Dityrosine(Dityr)is a marker product of protein oxidation caused by overprocessing of food,and its structure and chemical properties are stable.In recent years,the health hazards caused by peroxidation of food have attracted wide attention.Dityr is one of the key factors,but its digestive behavior in the gastrointestinal tract is still unclear.There are few studies on the effects of Dityr on the body with metabolic syndrome.Therefore,the contents of this study include:(1)To investigate the production of Dityr in cow milk and beef under different processing conditions;(2)The digestive law of Dityr in gastrointestinal digestive system was revealed by static simulation of gastrointestinal digestive environment;(3)A mouse model was established to explore the effects of Dityr on glucose and lipid metabolism in normal model mice and insulin resistance model mice induced by high fat diet(HFD).(4)The effects of Dityr on intestinal flora of normal and obese mice were investigated by simulated fermentation in vitro.The results show that:(1)According to the structural characteristics of protein oxidation products with fluorescence characteristic peaks,the fluorescence characteristic peaks of Dityr at 410 nm were detected by fluorescence spectrophotometer,and the fluorescence detection method of Dityr was applied to processed milk and beef.The results showed that the content of Dityr in UHT milk(290.67 ± 29.12 μg/mg prot)was significantly higher than that in fresh milk(34.02 ± 8.52μg/mg prot).Dityr content in spray-dried milk powder(388.53 ± 22.48 μg/mg prot)was significantly higher than that in UHT milk milk(290.67 ± 29.12 μg/mg prot)and fresh milk milk(34.02 ± 8.52 μg/mg prot).The concentration of Dityr increased with the increase of spray drying outlet temperature.The content of Dityr in boiled beef(314.28 ± 16.97 μg/mg prot)was significantly higher than that in raw beef(10.75 ± 0.54 μg/mg prot),and the concentration of Dityr increased with the increase of boiling temperature and cooking time.This indicates that the degree of food processing is closely related to the degree of protein oxidation.The deeper the degree of food processing,the higher the degree of protein oxidation and the more Dityr content.(2)The static simulated gastrointestinal digestion experiment of Dityr and processed milk showed that the digestibility of Dityr after gastrointestinal digestion for6 h was-37.99%,that of fresh milk after gastrointestinal digestion was-71.18%,and that of UHT milk was-79.05%.The digestibility of milk powder after spray drying was-100.09%.This indicates that Dityr tends to increase during intestinal digestion.It can be seen that after simulated digestion,the oxidation degree of protein was deepened and the digestibility of Dityr was reduced.These results indicate that Dityr is not only structurally stable in the external environment,but also difficult to be reduced to tyrosine in the complex digestive environment of the body.(3)The effects of Dityr on insulin resistance induced by HFD were investigated by establishing an insulin resistance model of high-fat feeding mice and 13 weeks after exposure to Dityr.After 13 weeks of Dityr administration,the body weight of mice in HFD + Dityr group was significantly higher than that in HFD group,and the intervention of Dityr aggravated epididymal fat and perirenal fat accumulation in HFD mice.Fasting blood glucose,plasma insulin,HOMA-IR and area under curve(AUC)of mice in HFD + Dityr group were significantly higher than those in HFD group.Dityr reduced the m RNA expression of glucose metabolism-related genes in the liver of HFD mice,indicating that Dityr intervention aggravated glucose metabolism disorder and insulin resistance of mice induced by HFD.Compared with HFD group,the contents of triglyceride(TG)and total cholesterol(T-CHO)in plasma and liver of mice in HFD+ Dityr group were significantly increased,the contents of low density lipoproteincholesterol(LDL-C)were significantly increased,and the contents of high density lipoprotein-cholesterol(HDL-C)were significantly decreased.Dityr reduced the m RNA expression of liver lipid metabolism related genes and increased the vacuoles in liver adipocyte of mice in HFD + dityr group.Liver fat accumulation was caused,and Dityr exposure exacerbated HFD-induced lipid metabolism abnormalities in mice.Compared with HFD group,the total antioxidant capacity(T-AOC)in plasma and liver of mice in HFD + Dityr group was significantly decreased,the activity of antioxidase was significantly weakened,the level of lipid oxidation was significantly increased,and the m RNA expression of genes related to antioxidant was significantly decreased.These results indicated that Dityr intervention could decrease antioxidant capacity in HFD mice and increase the oxidative stress level in HFD mice.Compared with HFD group,the pro-inflammatory cytokines and anti-inflammatory cytokines in mice in HFD + Dityr group were significantly increased,and the levels of lipopolysaccharide(LPS)and lipopolysaccharide binding protein(LBP)were significantly increased,indicating that the intervention of Dityr can aggravate the inflammation level of mice induced by HFD.The level of adenosine triphosphate(ATP)and the activity of adenosine triphosphate enzyme(ATPase)in the liver of mice in HFD + Dityr group were significantly lower than those in HFD group.The intervention of Dityr can aggravate the function defect of mitochondrial ATP synthesis in the liver of HFD mice,and aggravate the abnormal energy metabolism of insulin resistance mice.(4)By 16 S r DNA sequencing and short-chain fatty acid(SCFAs)determination of intestinal flora of HFD mice,the effect of Dityr on intestinal microorganisms of HFD mice was explored.Dityr intervention can significantly reduce the richness and diversity of intestinal flora in HFD mice,and aggravate the intestinal flora structure disorder induced by HFD.According to the analysis of intestinal flora at the phylum level,comparing with HFD + Dityr group,Dityr significantly increased the level of Firmicutes in HFD mice,significantly decreased the level of Bacteroidetes,and increased the ratio of Firmicutes to Bacteroidetes(F/B).Promote the absorption of heat by intestinal flora of HFD mice.The abundance of Verrucomicrobia in the intestinal microflora of HFD mice was significantly increased.The relative abundance of Proteobacteria and Actinobacteriota in intestinal flora of mice in HFD + Dityr group is significantly higher than that in HFD group.The intervention of Dityr can aggravate intestinal inflammation and reduce insulin sensitivity of HFD mice.Dityr significantly reduced the content of intestinal flora metabolites in HFD mice.Therefore,Dityr can reduce the total SCFAs content in intestinal tract of HFD mice.Exacerbates HFDinduced intestinal dysfunction.(5)The effects of Dityr on intestinal flora of insulin resistance mice were further explored by simulated fermentation of the feces of db/db deficient mice in vitro.By comparing db/m + Dityr group(Dityr low,middle and high levels of different doses)with db/m group,and db/db + Dityr group(Dityr low,middle and high levels of different doses)with db/db group,Dityr could significantly reduce the richness and diversity of intestinal flora in db/db mice.The F/B value in intestinal flora of db/db mice was significantly increased,the abundance of Proteobacteria was significantly increased,the level of metabolites of intestinal flora of db/db mice was decreased,and the intestinal microbial dysfunction of db/db mice was aggravated.In conclusion,with the deepening of processing,the content of Dityr increased,and it was difficult to be reduced to tyrosine during gastrointestinal digestion.Dityr can aggravate the glucose and lipid metabolism disorder,oxidative stress and inflammatory response induced by HFD,aggravate the intestinal flora disorder of insulin resistant mice,and make the pathological characteristics of metabolic syndrome more obvious.Dityr may affect insulin sensitivity through an inflammatory response induced by intestinal flora. |
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