| The physiological functions of procyanidins have been widely researched and verified,but the low bioavailability prevents the bioactivity and utilization of procyanidins.Although scientists commit to improving the bioavailability of procyanidins from different ways,the effect is still poor.On the basis of the positive effect of interaction between polysaccharides and polyphenols,we selected recognized good dietary fiber oat ?-glucan as the enhancer to investigate its effect on the bioavailability and the lipid metabolism regulation of litchi pericarp procyanidins(LPPC)in high-fat-diet rats.The underlying mechanisms were also explored.In the current study,oat P-glucan significantly improved the bioavailability and bioefficiency of LPPC in both normal and high-fat rats,and the underlying mechanisms were analyzed through gut microbiota and the expression of phase ? enzyme.Animal experiments revealed that administration with LPPC and oat ?-glucan for 8 weeks could significantly reversed the hyperlipemia induced by high-fat diet and promoted the antioxidant activity of serum and liver and and gut immunity through gut microbiota and AMPK pathway.The present study innovatively pointed out and verified that oat ?-glucan can be used as an outer dietary source to promote the bioavailability of procyanidins,and efficiently connected bioavailability with gut microbiota,which provided a new way to overcome the low bioavailability and bioefficiency of procyanidins.At the same time,the study offered the theoretical basis and experiment support for improving hyperlipemia and other metabolic diseases of combination procyanidins and dietary fiber.The main results are as follows:1 Preparation and characterization of the complex of LPPC and oat P-glucan and its antioxidant and lipid-absorption activityThe complex of LPPC and oat P-glucan was prepared by the method of dialysis,and the content of LPPC in the complex of TP with oat was 42.55 mg/g when dialysis reaching equilibrium.Then the complex of LPPC and oat P-glucan was characterized by ultraviolet visible spectrometry,Fourier transform infrared spectrometry and differential scanning calorimetry.The results showed there was no free LPPC in the the complex of LPPC and oat P-glucan,indicating the interaction between LPPC and oat ?-glucan.The complex of LPPC and oat ?-glucan exhibited synergistic effect and was better than(P<0.05)the physical mixture of LPPC and oat ?-glucan in DPPH radical scavenging and total antioxidant activity at certain concentration.Both the complex and physical mixture of LPPC and oat ?-glucan exhibited synergistic effect in OH radical scavenging at certain concentration,but the physical mixture showed higer activity(P<0.05).There was no synergistic effect of the complex and physical mixture of LPPC and oat ?-glucan in O2-radical scavenging,but the activity was significantly higher than single LPPC and oat?-glucan(P<0.05).Although there was no significant difference between LPPC and the complex and physical mixture of LPPC and oat ?-glucan on the absorption activity for cholesterol,the complex and physical mixture of LPPC and oat ?-glucan improved the absorption activity for fats and bile salt(P<0.05).It was pointed out that the physical mixture and complex of LPPC and oat ?-glucan could promote the bioefficiency of LPPC.2 The improving effect and mechanism of oat ?-glucan on the bioavailability of LPPCOn the basis of the improving effect of oat ?-glucan on the bioefficiency of LPPC in vitro,we studied the effect of oat P-glucan on the bioavailability of LPPC in normal rats.The Pharmacokinetic experiment showed that oat P-glucan promoted the absorption of LPPC in gastrointestinal tract of rats,and the content of(-)-epicatechin from 1 h to 8 h and the maximum absorption in serum were also significantly increased(P<0.05).In addition,the time of maximum absorption was also found to be prolonged as compared to the single LPPC.When LPPC and combined LPPC and oat ?-glucan was given to rats for 8 week at the dose of 100 mg/kg bw and 100 mg/kg·bw+50 mg/kg bw,respectively,the metabolism of procyanidins indicated the absorption of(-)-epicatechin in serum was obviously promoted(P<0.05),improving 20.00%as compared to the single LPPC,and the excretion of(-)-epicatechin and A-type dimers in urine were reduced 47.62%and 22.22%,respectively.Accordingly,the contents of phenolic acid metabolites significantly increased by the addition of oat ?-glucan(P<0.05),such as 3-hydroxybenzoic acid,vanillic acid,caffeic acid,3-hydroxyphenylpropionic acid,p-coumaric acid,shikimic acid,4-hydroxyphenylpropionic acid and m-coumaric acid.The metabolism of procyanidins indicated oat ?-glucan promoted the absorption and the conversion to phenolic acids of LPPC.The results of immunohistochemistry and real time PCR showed that the positive expression of UGT1A and SULT1A as well as mRNA in rat liver and small intestine was significantly enhanced by administration with LPPC and combined LPPC and oat?-glucan.Furthermore,the result of high-throughput sequencing indicated that the structure of gut microbiota was also improved by LPPC and combined LPPC and oat P-glucan intake,including the relative abundance of lactate-producers,butyrate-producers and mucin-degrading microflora increasing and other SCFA-producers decreasing.And the phase ? enzyme and gut microbiota improving effect of combined LPPC and oat?-glucan was better than LPPC.The above results indicated oat ?-glucan promoted the bioavailability of LPPC by promoting the absorption of LPPC in gastrointestinal tract,increasing the positive expression of phase ? enzyme and improving the relative abundance of lactate-producers.3 The improving effect and mechanism of oat ?-glucan on the lipid metabolism regulation of LPPC in high-fat-diet ratsOn the basis of the improving effect of oat ?-glucan on the bioavailability of LPPC in normal rats,we studied the effect of oat ?-glucan on the bioavailability and lipid metabolism regulation of LPPC in high-fat diet rats,which were fed a high-fat diet for 8 weeks inducing hyperlipemia.The results showed both LPPC and combined LPPC and oat P-glucan significantly inhibited the fat accumulation,the lipids level of serum and liver,and liver damage(P<0.05).In addition,the results of hepatic cell morphology showed that LPPC and combined LPPC and oat ?-glucan could improve hepatic steatosis and inflammatory cell infiltration in rats fed a high-fat diet.Although both LPPC and combined LPPC and oat ?-glucan exhibited notable effect of regulation lipid metabolism,in the aspect of decreasing perirenal fat and liver index,AST activity,TG and TC level of serum and liver,LPPC and oat ?-glucan combination exhibited better effect than single LPPC and oat ?-glucan(P<0.05).Oat ?-glucan also promoted the absorption of LPPC in high-fat diet rats,with the increasing 24.00%of(-)-epicatechin absorption in serum.Administration with LPPC significantly increased the antioxidant activity of serum and liver,and the high-fat diet rats intake with LPPC and oat ?-glucan combination exhibited better antioxidant activity than single LPPC and oat ?-glucan(P<0.05).The results of Western blot and real time PCR indicated LPPC and combined LPPC and oat ?-glucan regulated liver lipid metabolism through increasing AMPK phosphorylation level,down-regulating expression of FAS and HMG-CoAR as well as SREBP1C and genes involved in lipogenesis(P<0.05),up-regulating expression of CPT as well as genes involved in fatty acid oxidation(P<0.05),inducing the decrease of lipogenesis and increase of fatty acid oxidation.The sequencing results of gut microbiota indicated LPPC and combined LPPC and oat ?-glucan declined the ratio of Firmicutes/Bacteroidete,and promoted the relative abundance of lactate-producers Lactobacillus and Ruminococcus,butyrate-producers Subdoligranulum and Faecalibacterium and mucin-degrading microflora Akkermansia and Prevotella,and the relative abundance of Desulfovibrio and other SCFA-producers Bacteroides and Alistipes was decreased(P<0.05).The oat P-glucan only notably increased the relative abundance of Ruminococcus and Prevotella,while LPPC and oat ?-glucan combination owned the stronger activity in promoting the relative abundance of mucin-degrading microflora Akkermansia and Prevotella in contrast to single LPPC.The improvement of gut microbiota made the increasing of SIgA level and decreasing of TNF-? and IL-1? level in the gut.LPPC and oat ?-glucan combination showed the stronger hypolipidemic activity than single LPPC and oat?-glucan,which was related to the AMPK pathway improvement,and significant promoting mucin-degrading microflora Akkermansia and Prevotella level and gut immunity.4 The conversion of LPPC during chilling storageLPPC was always stored at-18 ? to inhibit the its own oxidation,in order to study the conversion ways of LPPC except bioconversion,the present study analysed the changes of LPPC during chilling storage.The polyphenol and procyanidins content of LPPC was decreased 6.79%and 15.31%during chilling storage for 3 years at-18?,respectively,while the content of flavonoids was increased 33.06%.The analysis of LPPC composition by HPLC-MS indicated the decrease of prcyanidins content and increase of flavonoids content were due to the conversion of(-)-epicatechin to quercetin during chilling storage.Simultaneously,the isomerization of procyanidin A2 to an unkown A-type dimer was also found at the storage condition.Toyopearl HW-40S column was used to separation and prepare oligomeric procyanidins in LPPC.The purity of(-)-epicatechin,unknown A-type dimer,A2 and A-type trimer from LPPC was more than 95%,and the yields were 19.74%,5.42%,8.71%and 5.03%,respectively,indicating this method was a useful way to obtain pure A-type oligomeric procyanidins.The unkown A-type dimer was identified as procyanidin A1(epicatechin-(4?-8,2?-O-7)-catechin)by 1H and 13C NMR and two-dimensional correlation spectra,and the Al was characterized for the first time in litchi pericarp.Therefore,the isomerization process of procyanidin A2 during chilling storage was the conversion from A2 to Al. |
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