Study On Self-microemulsifying Drug Delivery Systems Of Rhizoma Corydalis Decumbentis Alkaloids Extracts

Rhizoma corydalis decumbentis,with its Chinese name Xiatianwu,have become a widely used herbal remedy for centuries and been accepted in Chinese Pharmacopeia since 1990.It contains a variety of alkaloids as its active ingredients,in which Protopine（Pro） is the quality control index.The Xiatianwu alkaloids（XA） have extensive biological activities such as anti-hypertension,anti-arrhythmia,cerebral circulation and inferior extremity circulation, spasmolysis,analgesia,anti-inflammatory,anticoagulation,anti-dementia,hepar-protecting, etc,and have been used for apoplexia,hemiplegia,sequelae of infantile paralysis in clinical.It was found that Self-emulsifying drug delivery systems（SEDDS） could efficiently improve oral absorption of the sparingly soluble drugs by rapid self-emulsification and subsequently dispersion in the absorption sites.So the main objective of our study is to prepare SEDDS for increasing the dissolubility and adsorption,and improving its bio-availability.Firstly,the TLC was improved to discriminate the raw material,and the content of total alkaloids were determined by acid dye colorimetry,also the HPLC-UV analytic methods were established to detect the content and dissolution of active ingredients.The physical and chemical properties of Pro and THP were investigated in our study.The solubility of active components in solution increases with respect to the decrease of pH value because they are tertiary amine alkaloids.The logP increases with pH value of the water phase,the logP in pH 5.8,pH 6.8,pH 7,pH 7.4 were 0.734,1.808,2.276,2.338 for Pro,and 1.196,1.317,1.507, 1.557 for THP,respectively.The Xaitianwu alkaloids were extracted and purified by 732 cation exchange resin and CO₂ super-critical fluid extraction using total alkaloids and active ingredients as inspection targets.The result demonstrate that after purified by cation exchange resin,the content of total alkaloids,Pro,and THP were about 76.3%,17.1%,and 20.3%,respectively.After extracted by super-critical extraction technology,the content of total alkaloids,Pro,and THP were about 62.27%,16.75%,and 10.18%,respectively.In the pre-formulation study,the saturated solubility of Pro and THP in different oil phase,surfactant,and cosurfactant were examined.The solubility in cosurfactant（Transcutol P） was better than other excipients.Pseudo-ternary phase diagrams were conducted.The optical SMEDDS were obtained by comparing the self-microemulsifying domain and by the evaluation of the resultant of emulsion’s appearance.According to the assays,the optical SMEDDS were composed of Ethyl Oleate,Solutol,and Transcutol P.The temperature,flow shape,pH and volume of media on the self-emulsifying efficiency were investigated in details, and finally,the conditions of 37℃,low blending speed and diluting with 500-fold volume of the distilled water were utilized for evaluating the efficiency of self-microemulsifying.XA did not affect the self-microemulsifying region,but prolonged self-microemulsifying time and increased the droplet size comparing with the blank vehicles.The optical formulation for dissolution and bioavailability assessment consisted of 40%Ethyl Oleate,45%Solutol and 12%Transcutol.When the surfactant content increased from 35%to 70%,the self-microemulsifying time decreased firstly and then increased.The minimal self-microemulsifying time was found at the formulation that has 40%surfactant.When the cosurfactant content increased from zero to 60%,the self-microemulsifying time and the emulsifying ability decreased together.The droplet size distribution of the formulation and blank vehicle were determined.The dissolution rates of Pro and THP from optical SMEDDS were faster than those of the market tablets.The dissolution of SMEDDS at 20 min was about 80%,and the dissolution of tablet at 20 min was about 20%.The stability of XA SMEDDS was fine in cold-hot cycling and high humidity.The content of Pro and THP decreased obviously in high temperature and strong light.The intestinal transport of Pro and THP were performed by applying everted intestinal sacs method.The adsorption of active ingredients in ileum was much higher.As the concentration of Pro increased,absorption of Pro across intestinal membrane was increased in the rat duodenum,jejunum,and ileum,but they exhibited a concentration restrain of Pro itself, which might demonstrated exist of initiative transport process.When the pH value decreased, the adsorption across intestinal reduced,which revealed that pH values could affect intestinal absorption of alkaloids.The SMEDDS formulation could increase the intestinal absorption of Pro,but decrease the absorption of THP.A sensitive and selective HPLC-ESI-MS method was developed for simultaneous quantification of Pro and THP in rat plasma.The lower limit of quantification（LLOQ） of the method was 1.0 ng·mL^-1 for all analytes.The fully validated method was successfully applied to a pharmacokinetic study.The plasma profiles of Pro,THP and Pal in rats following oral administration of self-microemulsifying formulation of XA and tablets at a single dose were investigated. Comparing to the conventional tablets,the short T_max values of Pro in SMEDDS showed the fairly rapid absorption.The remarkable differences were also observed for the C_max for Pro. The AUC_0-t of Pro and THP were relevantly increased.The relative bioavailability of Pro and THP was 209.7%and 133.2%.These data clearly show the utility of SMEDDS could improve the rate and extent of oral absorption of XA.The analysis of main pharmacokinetic parameters showed that the absorptions of Pro and THP for SMEDDS and tablets were not bioequivalence.The protective effect of XA and the preparation on CCl₄-induced,ACAP-induced,and TAA-induced acute liver injury were studied,and the mechanism of actions was preliminary investigated.The effect of XA on bile secretion was also investigated in this paper.The data showed the content of AST and ALT in serum were significantly decrease in CCl₄-induced, ACAP-induced,and TAA-induced acute liver injury mice pretreated with different dosages of XA SMEDDS.The content of MDA in liver tissue of CCl₄-induced and ACAP-induced acute liver injury mice pretreated with XA SMEDDS were markedly decreased.Pretreated XA SMEDDS could also increase the activity of SOD and prevented the decrease of GSH induced by CCl₄ and ACAP,increase the activity of Ca²⁺-ATPase of CCl₄-induced acute liver injury mice.The XA has no obvious effect on bile secretion.These preliminary experimental studies revealed that XA has definite hepar-protecting effects.The mechanism might involve in inhibiting lipid peroxidation reaction,reducing the production of oxygen free radicals, protecting membrane of hepatic cell,and so on.