| Phenylethanoid glycosides(PhGs)are natural phenolic compounds and characterized by cinnamic acid and hydroxyphenylethyl moieties that are attached to aβ-glucopyranose via a glycosidic bond,including acteoside,salidroside,echinacoside etc.PhGs exhibite anti-tumor activity,anti-inflammatory activity,antioxidant activity,neuroprotective effect and whitening activity,which are widely used in medicine,food and cosmetics industry.However,the bioavailability of PhGs is relatively low,and the oral bioavailability of acteoside is only 0.12%in rats.To improve the bioavailability and extend the application of PhGs,it is very important to explore the factors affecting the bioavailability and to enhance the bioavailability of PhGs.In this thesis,total phenylethanoid glycosides(TPG)in Osmanthus fragrans Lour.flowers extract(OFE),salidroside and acteoside were investigated by using the methods of chromatography,mass spectrometry,in vitro digestion model and Caco-2 cell model.The aim of this study is to clarify the influences of stability and in vivo digestion/absorption on the bioavailability of PhGs,and to construct nano-delivery system of PhGs by using natural food derived P-glycoprotein(P-gp)inhibitors and nanotechnology to improve the stability and bioavailability of PhGs.The main contents and results of this research are summarized as follows:1.The effects of temperature,light and pH on the stability of TPG,salidroside and acteoside were investigated in simulation conditions.Then the degradation kinetics model of PhGs was established.The degradation products and degradation pathways of salidroside and acteoside were studied in this research.The results showed that the degradation of TPG,salidroside and acteoside followed the first-order kinetics.High temperature,light exposure and high pH accelerated the degradation of acteoside.Salidroside was mainly hydrolyzed to tyrosol during storage.At high temperature(≥50 ℃),acteoside was hydrolyzed,isomerized and oxidized to verbasoside,isoacteoside,β-oxoacteoside,campneoside Ⅱ,etc.At alkaline condition(pH 9.0),acteoside was hydrolyzed,isomerized,oxidized and cyclized to cistanoside F,isoacteoside,β-oxoacteoside,campneoside Ⅱ,oraposide,etc.In other conditions,acteoside was hydrolyzed and isomerized to verbasoside,caffeic acid and isoacteoside.2.The digestive stability,absorption and transport mechanism of TPG,salidroside and acteoside were studied using simulated digestion/Caco-2 intestinal cell models.The in vitro digestion model revealed that the retention rates of TPG in OFE,salidroside and acteoside were 82.31%,99.77%and 51.46%,respectively,indicating that acteoside was instable during digestion.The absorption percentages of TPG,salidroside and acteoside were 1.42～1.54%,2.10～2.68%and 0.46～0.70%in the Caco-2 model,respectively.It revealed that acteoside was poorly absorbed.The permeation mechanism of acteoside and TPG was passive diffusion with active efflux mediated by P-gp.Salidroside permeated Caco-2 cell monolayers through passive diffusion.3.The natural food derived P-gp inhibitors were selected to promote the absorption of acteoside in Caco-2 cell monolayers.And the effect of inhibitors on the stability and pharmacokinetics of acteoside was studied.The results showed that quercetin and EGCG could improve the absorption of acteoside in Caco-2 cell monolayers,but could not enhance the storage and digestive stability of acteoside.The oral bioavailability of acteoside increased by 1.43 times by EGCG.4.Liposomes(Ac-Lip,AE-Lip),chitosan-coated liposome(CS-Ac-Lip,CS-AE-Lip)and chitosan-coated liposome tripolyphosphate particles(CS-Ac-Lip-TPP,CS-AE-Lip-TPP)were prepared and charactered.Acteoside(Ac)or acteoside/EGCG(AE)was encapsulated in the liposome,chitosan modified onto the surface of liposomes by electrostatic action to form chitosan-coated liposomes.Further crosslinking with TPP,chitosan-coated liposome tripolyphosphate particles were prepared.The nanoparticles were spherical,and the diameter was 69.62～169.73 nm.Ac-Lip and AE-Lip showed negative potential,and other nanoparticles showed positive potential.The entrapment efficiency(except AE-Lip)was above 80%.5.The in vitro release,storage stability,digestive stability,pharmackinetices and tissue distribution of acteoside in nanoparticles were evaluated.The nanoparticles slow the release of acteoside,and the release fits to Korsmeyer-Peppas model.The nanoparticles enhanced the storage and digestive stability of acteoside.CS-Ac-Lip-TPP and CS-AE-Lip-TPP showed better protection.The nanoparticles improved the bioavailability and tissue distribution of acteoside.CS-AE-Lip-TPP enhanced the bioavailability of acteoside to 5.32 times,and increased acteoside contents in different tissues in rats(especially in brain).In summary,the degradation during storage and digestion,low absorption and efflux during absorption lead to low bioavailability of acteoside.The stability and bioavailability of acteoside were improved by adding P-gp inhibitor and constructing nano-delivery system. |
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