Formulation Optimization And The Absorption Mechanisms Of Nanoemulsion In Improving Baicalin Oral Exposure

Baicalin?BA,5,6-dihydroxyflavone-7-O-D-glucuronic?,is a flavonoid component extracted from the dried rhizomes of Scutellaria baicalensis Georgi.BA has been reported to possess a wide range of pharmacological and biological effects including antiviral,antibacterial,anti-inflammatory,anti-oxidation,and immune regulation and other pharmacological effects.However,the molecular structure of BA can form intramolecular hydrogen bonds between flavonoid and glucuronides,resulting in poor solubility in water and oil.It also has slow dissolution rate in water,and its oral bioavailability is only 2.2%,which limits its clinical application.Therefore,it is very important to solve the problem of insoluble and hardly soluble BA in water,increasing the absorption of drugs,and thus improving its oral bioavailability.Nanoemulsion is a transparent or translucent,stable,low-viscosity,isotropic,and thermodynamically stable dispersion system spontaneously formed of surfactant,cosurfactant,oil,and aqueous phase in proper proportions.Nanoemulsion as an effective drug delivery system could improve the solubility of insoluble drugs,increase the membrane permeability,and thus increase its oral bioavailability.Based on the previous research work,a stable O/W type BA nanoemulsion was prepared to increase the oral bioavailability of drug,and providing an ideal oral preparation for the clinical use of BA.Single-pass intestinal perfusion model was used to investigate the uptake of BA nanoemulsion in the intestine.A chylomicron-blocked rat model was utilized to assess the extent of the lymphatic transport.Therefore,the oral absorption mechanism of BA nanoemulsion was initially elucidated,which provides a theoretical basis for the optimization and application of the nanoemulsion prescription.Objective:A O/W type oral BA nanoemulsion was prepared to improve oral absorption in rats,and observed the absorption and transport pathways of BA nanoemulsion in different intestinal segments of the small intestine,preliminarily clarified the reasons forimproving the oral administration of BA nanoemulsion,so as to provide references for the formulation optimization of nanoemulsion.Method:Through the solubility experiments and pseudo-ternary phase diagrams,the nanoemulsion area was used as an index to select the optimal nanoemulsion formulation;the shape of the nanoemulsion droplet was observed by transmission electron microscopy,the particle size and Zeta potential were measured by using a nanoparticle size potential analyzer,and the appearance of nanoemulsion was observed under the condition of normal temperature for three months.Rats were given intragastric administration of baicalin suspension and baicalin nanoemulsion.Blood samples were taken at different time points after administration.Plasma concentration was measured by HPLC method,and pharmacokinetic parameters were fitted by DASS 2.0 software.The absorption of BA nanoemulsion and BA suspension in different intestinal segments of rats were investigated by using single-pass intestinal perfusion model.The absorption rate constant?K_a?and apparent permeability coefficient(P_app)of nanoemulsion and suspension in different intestinal segments were calculated.The chylomicron flow blocking model was used to investigate the BA nanoemulsion transport in vivo in rats.After blockade group and unblocked group rats were given BA nanoemulsion by orally administration,blood was taken from the eyelids at different time points to determine the blood drug concentration,fitting pharmacokinetic parameters,calculating the proportion by lymphatic pathway in vivo.Results:1.The preparation and quality evaluation of O/W type baicalin nanomulsionThe optimal formulation of BA nanoemulsion was:EL35:28.3%,PEG400:28.3%,IPM:4.7%,H₂O:37.8%,drug loading:9.8 mg/mL;BA nanoemulsion was spherical and uniform.Particle size of BA nanoemulsion was 58.43�2.1 nm,Zeta potential of BA nanoemulsion was-8.12�1.2 mV.BA nanoemulsions stored for 90 days,stable in nature,no stratification at room temperature in the dark.2.Pharmacokinetic study in rats of O/W type baicalin nanomulsionThe pharmacokinetic results showed that the C_maxax value of BA nanoemulsion and BA suspension were 6.756�0.42 mg/L and 1.990�0.21 mg/L.The AUC_?0-t?value of BA nanoemulsion and BA suspension were 125.241�4.47 mg/L*h and 8.602�1.41mg/L*h.The T_maxax value of BA nanoemulsion and BA suspension were 6 h and 2 h.The MRT_?0-t?value of BA nanoemulsion and BA suspension were 18.166�0.69 h and 5.237�0.56 h.The CL_z/F/F value of BA nanoemulsion and BA suspension were 0.913�0.04L/h/kg and 19.327�1.32 L/h/kg.3.Single-pass intestinal perfusion study of O/W type baicalin nanomulsionThe results of single-pass intestinal perfusion study showed that the K_a and P_apppp values of BA nanoemulsion in different intestine segments of rats were significantly increased compared with BA suspension?P<0.01?.Compared with BA suspension,the K_a(or P_app)values of BA nanoemulsion were remarkably improved by 10.75-fold?or11.98-fold?,8.19-fold?or 7.78-fold?,3.94-fold?or 3.55-fold?,and 1.66-fold?or1.69-fold?in duodenum,jejunum,ileum,and colon,respectively.4.Lymphatic transport of in rats of O/W type baicalin nanomulsionThe results of transport pathway showed that the AUC_?0-t?in BA non-lymphatic blocking group and lymphatic blocking group were 49.561�2.68?g/mL*h and 36.264�1.85?g/mL*h,C_maxax were 6.693�0.53?g/mL and 4.972�0.35?g/mL,respectively.The in vivo proportion of BA nanoemulsion from the lymphatic pathway was 26.8%.Conclusion:In this study,a stable O/W BA oral nanoemulsion was successfully prepared,which could significantly improve the absorption of BA in rats.Nanoemulsion could promote the absorption rate and extent of BA in rat intestinal segments,and increase the proportion of BA transported by the lymphatic pathway in vivo,which may be the main reason for the BA nanoemulsion system to increase BA uptake.