Preparation And Evaluation Of Chrysin Loaded Metabolism-inhibitory Nanoemulsions

Objective: Chrysin is a naturally occurring flavonoid that demonstrates various types of health-promoting effects such as anti-cancer,antioxidant and anti-diabetic activities.However,the therapeutic applications of chrysin are significantly limited by its exceedingly low oral bioavailability/absorption.One of the main causes of poor bioavailability refers to the first-pass glucuronidation in the liver and intestine.Therefore,inhibiting the UGT metabolism can be an effictive approach to overcome the poor bioavailabilty of chrysin.Here we aimed to identify UGT-inhibitory pharmaceutical excipients(PEs),and develope a metabolism-inhibitory nanoemulsion to enhance the oral bioavailability of chrysin.Methods:1.The modulatory effects of 21 commly used PEs on chrysin glucuronidation were determined using tissue(liver/intestine)microsomes and expressed UGT1A1 enzyme.Inhibition kinetics were performed to elucidate the mechanism of UGT-inhibitory PEs2.Effects of PEs on chrysin glucuronidation was assessed at a cellular level using UGT1A1-overexpressing He La cells(He La1A1 cells).MTT assays were executed to evaluate the cytotoxicity of PEs on He La1A1 cells.3.Chrysin-loaded nanoemulsions were prepared using a modified emulsification technique.The sodium oleate-based nanoemulsions(SO-NE)was regarded as the UGT-inhibitory preparation,and the Tween80-based nanoemulsions(T80-NE)was regarded as the reference preparation.These two preparations were subsequently characterized by particle size,? potential,morphology,and in vitro drug release.Cellular uptake mechanisms of chrysin-loaded nanoemulsions(i.e.,SO-NE and T80-NE)were determined using endocytosis inhibitors.4.Rats were orally administered with chrysin-suspensions,SO-NE,T80-NE and physical mixture.Plasma concentrations of chrysin and its glucuronides were determined by UPLC-QTOF/MS analysis.The effect of UGT-inhibitory preparation(SO-NE)on pharmacokinetic properties of chrysin was evaluated by compareing the PK parameters in each group.Results:1.Of 21 PEs,five PEs(i.e.,Brij 35,Brij 58,labrasol,sodium oleate,and Tween 20)significantly inhibited chrysin glucuronidation,and the inhibitory effects was concentration-dependent.Of note,sodium oleate was the most potent inhibitor of chrysin glucuronidation(> 80%).Inhibition kinetics showed that sodium oleate was a mixed-type inhibitor of chrysin glucuronidation.2.The UGT-inhibitory PEs(i.e.,Brij 35,Brij 58,labrasol,sodium oleate,and Tween 20)were all efficient in inhibiting celluar glucuronidation of chrysin to different degrees.Sodium oleate led to the most significante reduction in glucuronide excretion and total glucuronidation of chrysin in He La1A1 cells compared to other PEs.3.Both SO-NE and T80-NE were near-spherical.SO-NE were 83.2 nm around in particle size with ? potential of-43.7 m V and entrapment efficiency of 89.5%,and T80-NE were 82.5 nm around in particle size with ? potential of-45.9 m V and entrapment efficiency of 90.3%.Drug release from SO-NE and T80-NE was all controlled by diffusion and erosion.Cellular uptake of both preparations was controlled by specific clathrin-dependent and specific caveolae-dependent endocytosis.4.UGT-inhibitory preparation(SO-NE)was able to greatly enhance oral bioavailability of chrysin.Comepared to chrysin suspentions,SO-NE led to a 4.3-fold increase in systemic exposure of chrysin and a 3.5-fold increase in Cmax value.Meanwhile,SO-NE caused significant reductions in UGT metabolism of chrysin(Inhibition rate was 42.5%).By contrast,T80-NE and physical mixture did not alter the pharmacokinetics properties of chrysin and C G.Conclusion:We have successfully prepared a chrysin loaded metabolism-inhibitory nanoemulsions.It can greatly enhance the oral absorption of chrysin through inhibition of UGT-mediated metabolism.This thesis has provided a feasible strategy for efficient delivery of flavonoid drugs.