Studies On Oleanolic Acid Self-Microemulsion Drug Delivery System

Oleanolic acid is a triterpenoid compound possessing many pharmacological activities,such as hepatoprotective,anti-inflammatory,anti-virus,anti-tumor, antidiabetogenic activities,and so on.Oleanolic acid is commonly used in the therapy of hepatitis in clinic and remarkably improve the symptom,physical sign and hepatic function of hepatopath.Now there are only oral tablet and capsule of oleanolic acid in market and because of its poorly solubility in water,the oral administration of oleanolic acid often results in low bioavailability and the oral bioavailability in rat is 0.7%,which limits its therapeutic application.Self-microemulsion drug delivery system(SMEDDS)is a kind of new drug delivery system,which could increase solubility of poorly soluble drugs,protect drugs against enzymolysis in gastrointestinal tract,strengthen stabilities and promote absorption and bioavailability. So it is really a meaningful thing to study the oral oleanolic acid SMEDDS which not only provide new evidence for the clinical application of oleanolic acid,but also offer a new thinking for modernization of traditional Chinese medicine.The main research work was as follows:1.Foumula and preparation of oleanolic SMEDDS:(1)The basic components of the formulation were determined as Cremophor EL-alcohol-ethyl oleate by investigating the saturated solubility of oleanolic acid in various medium,the interaction between surfactants and oils,the area of microemulsion in the pseudo-ternary phase diagram of different cosurfactants;(2)The quality fraction of oil was determined as 15%by drawing the ternary phase diagram of SMEDDS.The solubility of oleanolic acid and the average particle were selected as the response variables to optimize the SMEDDS formulation and the final formulation(containing Cremophor EL 50%,alcohol 35%,ethyl oleate 15%,with content 1%of drug)had been found;(3)The processing factors that affect the self-microemulsifying ability of SMEDDS had been studied.The final process was stirred with a magnetic stirrer at the speed of 400 r·min^-1for 20 minutes at 37℃.2.Quality evaluation and release of oleanolic acid SMEDDS in vitro:(1)The preliminary quality assessment of oleanilic acid SMEDDS was evaluated by observation of the appearance,the physico-chemical property parameter(such as the viscosity,the refractive index,the conductivity,the Zeta-pontential),the morphology, the particle size and the content;(2)In vitro release studies,the dialysis bag diffusion technique was applied and the release curve of oleanolic acid SMEDDS and crude drug fit well with Weibull equation;(3)The influences of different temperature, disperse medium,dilution ratio on the self-microemulsifying efficiency were also examined;(4)The test of influencing factors and primary stability indicated that the oleanolic acid SMEDDS had a good stability.3.Absorption kinetics of oleanolic acid SMEDDS in rat stomach and intestine:(1) The intestinal absorption kineticses of oleanolic microemulsion and micelle were investigated and the two absorption processes were both first-process.The absorption kinetics equation of oleanolic microemulsion was lnX_{剩余}=lnX₀-0.090×t,and The absorption kinetics equation of oleanolic micelle was lnX_{剩余}=lnX₀-0.049×t.Ka and t_1/2of oleanolic microemulsion and micelle were significantly different;(2)The intestinal absorption kineticses of oleanolic microemulsion with low,middle,high concentrantion were investigated and the Ka were 0.100h^-1,0.090 h^-1å’Œ0.103 h^-1, respectively.So the principal mechanism of oleanolic acid in intestinal absorption conformed to passive diffusion;(3)The gastro in situ was investigated and the absorption percent of oleanolic acid ME was 10.92±1.28%after 2 hours.So oleanolic acid was absorbed poor in the stomach;(4)The test of main segment indicated that the oleanolic acid could be absorbed by all the segments of the intestine, and the absorption percentages of duodenum,jejunum,ileum and colonic were 27.52±1.90%,16.81±1.37%,18.83±1.18%,9.69±1.42%.The oleanolic acid ME was absorbed mainly in duodenum and leastly in colon.4.Investigation of pharmacokinetic behavior of oleanolic acid SMEDDS in rat in vivo:(1)HPLC-MS method was established to determine the concentration of oleanolic acid in plasma;(2)The pharmacokinetics behavior of oleanolic acid SMEDDS in rats was studied compared with commercial oleanolic acid conventional tablet and the results were treated with DAS ver2.0 procedure.T_maxof SMEDDS and reference tablet were 2.0±1.0 and 2.75±0.50 h,C_maxwere 209.8±47.19 and 77.6±16.79 ug·L^-1respectively.The relative bioavailability Fr was 507.03%by AUC_0.8.Therefore oleanolic acid SMEDDS could promote the absorption of oleanolic acid and improve the oral bioavailability.