Oral Bioavailability and Stability Investigation of Salvianolic Acids

摘要

The aim of this study was to determine the oral bioavailability of salvianolic acids (SAs), an acitive part of Radix Salviae Miltiorrhizae and to investigate the stability of SAs in gastro-intestinal tract, one of the major factors on the oral bioavailability. Firstly, a precise and reproducible HPLC method has been developed and validated for simultaneous quantification of the five SAs (salvianolic acid B (SalB), rosmarinic acid (RA) and lithospermic acid (LA), protocatechuic aldehyde (Pal) and Danshensu (DS)) in dog plasma with naringin as internal standard. Liquid-liquid extraction was adopted for the plasma sample preparation. Separation was accomplished on a C18 column with a linear gradient elution consisting of acetoniltrile and aqueous phosphoric acid. Ultraniolet detection was at 286 nm. The oral absolute bioavailability of SalB and the fate of other phenolic acids were investigated after SAs (9mg·kg-1, i.v.; 180mg·kg-1, p.o.) adminitration in beagle dogs. Furthermore, SAs were incubated in various pH (pH1.0~8.0) buffer solutions and gastro-intestinal contents and mucosal homogenates of rats at 37℃ and the contents change of the five SAs and total salvianolic acids (TSA) were simultaneously determined for the stability investigation. Results showed that the other four phenolic acids except Pal were detected in beagle dogs' plasma after intravenous and oral administration of SAs. However, the plasma concentrations of DS, RA and LA were so low and disappeared so rapidly that their pharmacokinetics parameters could not be estimated. The oral absolute bioavailability of SalB in beagle dogs was calculated be 1.23±0.63%. The SalB plasma concentration-time curve had found double peaks, which indicates that SalB could undergo enterohepatic circulation in dogs. SalB was relatively stable in the pH=1 to 6.0 buffer solution and gastric environment but unstable in where the pH value is higher than 6.5 and intestinal contents and mucosal homogenates and he optimal stability range was at pH 2.5~5.0. TSA decreased as well as SalB in high pH and intestinal environment, however, the degradation rate of TSA was less than that of SalB. Meanwhile, DS, Pal, RA and LA increased while SalB decreased and they should probably be the degradation middle products of SalB. The degradation of SalB in intestinal environment was more markedly than that in the same value of pH buffer solutions. Therefore, not only high pH but also the other substances in the intestinal tract should be responsible for the stability of SAs in intestinal environment and the unstable property of SAs in intestinal environment was one of important factors of the extremely low oral bioavailability of SalB. The influence of the other factors on the bioavailability of SalB goesneed further study.