Antioxidant Mechanism Of Rice Protein Via Nrf2 Pahtway And Regulatory Effect Of Methionine

Rice protein(RP)is a high-quality plant protein,which is rich in sulfurcontaining amino acids(SAAs)and has hypolipidemic effect and antioxidant function.However,so far,the in-depth study on how rice protein activates the endogenous antioxidant reactions and how rice protein initiates the endogenous antioxidant mechanisms is still lacking.Nuclear factor-erythroid 2-related factor 2(Nrf2)is an important regulatory factor that activates and initiates the endogenous antioxidant mechanisms.In this paper,we chose rice protein as the research object,and adopted in vivo and in vitro experimental models.Under the dietary conditions of different cholesterol level(cholesterol-free,cholesterol-enriched)and different methionine(Met)level,we studied the antioxidant effect of rice protein,the endogenous enzymes/non-enzymes antioxidant mechanism of rice protein via Nrf2 pathway,and the regulatory effect of Met in male Wistar rats of different ages(growing and adult period).The main experimental findings are as follows:The growing and adult rats were used as the experimental objects.After 2 weeks' cholesterol-free or cholesterol-enriched diets,the results showed that rice protein could significantly reduce hepatic ROS and MDA level,while enhancing hepatic GCL and endogenous antioxidant enzymes(SOD,CAT,etc.)activity,and improving hepatic T-AOC and GSH content in growing and adult rats.These results indicated that rice protein had endogenous antioxidant effects,which were not affected and restricted by age and cholesterol level.After 2 weeks' cholesterol-free or cholesterol-enriched diets,the experimental results showed that rice protein could inhibit hepatic gene and protein expression of Keap1 and Cul3,while activating Nrf2,and promoting hepatic gene and protein expression of GCLC,GCLM,GS,GR,GST,GPx,CAT,SOD,HO-1 and NQO1 via Nrf2 pathway in growing and adult rats.These results indicated that activating Nrf2 and initiating Nrf2-regulated endogenous enzymes/non-enzymatic antioxidant reactions were the main antioxidant mechanisms of rice protein,which were not affected and restricted by age and cholesterol level.Using pepsin-pancreatin digestion model in vitro,after 1-2 h pepsin digestion and 1-4 h pancreatin digestion,the results showed that Met supplementation could enhance the in vitro antioxidant activity of rice protein,such as reducing power and scavenging free radicals(ABTS,superoxide and NO radicals).However,Met had no significant effect on the Fe2+.chelating ability of rice protein.After 2 weeks' feeding of Met supplemented rice protein,and under the condition of cholesterol-free diet,the experimental results showed that Met supplementation could enhance the antioxidant effects of rice protein through inhibiting hepatic ROS and MDA accumulation,increasing hepatic GCL,SOD and CAT activity,and improving hepatic T-AOC and GSH content in growing and adult rats.These results indicated that Met supplementation could enhance the endogenous antioxidant effects of rice protein,which were not affected and restricted by age.Using rice protein and Met supplemented rice protein as the main dietary protein sources,after 2 weeks' cholesterol-free diet,the experimental results showed that the addition of Met could enhance the effects of rice protein on inhibiting Keap1 and Cul3 expression,activating Nrf2,and promoting the initiation of endogenous enzymes/non-enzymatic antioxidant system via Nrf2 pathway in the liver of growing and adult rats.Meanwhile,these effects of rice protein were positively correlated with Met level.Additionally,Met supplementation could enhance the regulatory effects of rice protein on increasing hepatic gene and protein expression of Met sulfur transfer metabolic regulators(MAT1A,SAHH,CBS and CTH),thus promoting the endogenous synthesis of GSH.These results showed that Met had synergistic enhancement effect on the antioxidant mechanism of rice protein via Nrf2 pathway,and this regulatory effect was not affected and restricted by age.This paper illustrates that the activation of Nrf2 and the initiation of Nrf2-regulated endogenous enzymes/non-enzymatic antioxidant system are the main antioxidant mechanisms of rice protein.Meanwhile,this paper also reveals the synergistic regulation of Met on the endogenous antioxidant mechanism via Nrf2 pathway and in vitro antioxidant activity of rice protein.These provides theoretical basis and new research ideas for comprehensively analyzing the disease-prevention and health-care functions of rice protein,such as hypolipidemic effect.