Effects Of Oxidized Casein On Redox Status And Gene Expression In Mice

In recent years, it has been widely reported that food protein is easy to be oxidized during foodprocessing which will impact food quality. However, there are few reports about whether intake ofoxidized protein will have effects on redox state, metabolism process and body health. The mainobjective of this paper is to study the impacts of oxidized protein and oxidation protein products onthe redox status and lipid metabolism of mice, the mechanism was also be discussed.Methods: Casein was modified by H₂O₂, H₂O₂combined with Cu （Ⅱ）（H₂O₂-Cu）, HClO, heatingand malonaldehyde （MDA）. Contents of thiol, carbonyl, dityrosine （Dtyr）, dvanced oxidationprotein products （AOPPs） and the in vitro digestibility of casein were determined. After that, thefree radical scavenging ability of digestion products was evaluated. Casein samples were given tomice through oral administration. Changes of blood reduced oxygen species （ROS） level of micewithin2.5hours after gavage was detected and levels of ROS, MDA and T-AOC in mice liver,pancreas, duodenum and jejunum were measured2hours after gavage. Then, rats wereadministrated by the same gastric perfusion of casein as mice.2hours later, peptide composition ofrats’ chyme, hepatic portal vein blood and peripheral blood was analyzed by HPLC-MS method.Furthermore, mice were treated with origin and oxidized casein diet for10weeks. Then, the growthrate and organ index, as well as oxidative damage indicators of mice blood and digestive organswere detected. Finally, genes expression in mice liver and kidney tissues were determined by Real-time PCR.The main results are as fallows:（1） After oxidation, contents of advanced oxidation proteinproducts （AOPPs）, dityrosine （Dtyr） and carbonyl in oxidized casein increased, while thiol contentdecreased （P<0.05）.（2） Protein digestibility and free radical scavenging capacity of proteindigestive juice all decreased （P<0.05） in oxidized casein teams.（3） Blood ROS of mice aftershort-term gavage showed higher levels in mice perfused with oxidized casein than the control.2hours after stomach perfusion, ROS and MDA in mice organs increased significantly while totalantioxidant capacity （T-AOC） content decreased significantly （P<0.05）, oxidative stress biomarkersin mice blood showed strong correlations to those in casein samples.（4） HPLC-MS results showedthat fragments of oxidized protein, such as peptide with carbonyl, Dtyr and cross-linked proteinappeared more in chyme, hepatic portal vein blood and peripheral blood of mice fed with oxidizedcasein.（5） After10weeks feeding with oxidized casein diet, the growth rate of mice dropped, whileorgan index （liver, jejunum, kidney） increased significantly. Redox state imbalance ofmice digestive organs was identified by the decrease of GSH-Px, CAT, T-AOC. Oxidative damagewas confirmed by the performance of ROS, Carbonyl, MDA, Dtyr and AOPP.（6） Real-time PCRresults showed that in mice fed with oxidized casein diet, the expression of peroxidase（Prdx-1）, acyl-CoA thioesterases4（Acot4）, acyl-CoA oxidase1（Acox1）, transforming growthfactor （TGF-β） and endothelin （ET-1）, was up-regulate in both mice liver and kidney. However, thegene expression of Cyp7a1in liver, nephrin and podocin in kidney was down-regulate.（7） Theexpression of Prdx-1, TGF-β, ET-1, Acot4, Acox1in mice liver, and the expression of Prdx-1,TGF-β, ET-1in mice kidney were positively correlated with levels of ROS, MDA, and oxidizedprotein products respectively. Cyp7a1expression in mice liver and nephrin and podocin expressionin mice kidney were negatively correlated with ROS, MDA, and oxidized protein products.Conclusion: The above results show that after oxidation, contents of protein oxidation products, such as Dtyr and AOPPs, will increase, protein digestibility and free radical scavenging capacity ofprotein digestive juice will decrease. The products of oxidized protein can be absorbed into bloodand lead to the accumulation of protein oxidation products in mice blood and organs, which willcause the imbalance of redox state and oxidized damage to mice. Further more, long-term intake ofoxidized casein will further influence fat metabolism process and may affect the process of the liverand renal fibrosis.