Artemisinin: an endoperoxidic antimalarial from Artemisia annua L

Screening for hemostatic activities of popular Chinese medicinal herbs in vitro

AIMS

This study aimed to identify new hemostyptics by assessing the coagulation enhancing activity of 114 Chinese herbal extracts in vitro.

METHODS

Herbs were boiled in water for 30 min, filtered and then lyophilized filtrates (10 mg/mL) were dissolved in water. Coagulation was assayed as prothrombin time (PT). Plasma diluted in saline was incubated with each extract for 5 min and then PT reagent was added, followed by CaCl2 solution and the time taken to form clots was measured. Extracts that decreased coagulation time were regarded as containing active compounds. The abilities of extracts to activate Factor XII were assessed and the activated form of factor XII (XIIa) was resolved by SDS-PAGE and visualized by silver staining.

RESULTS

Coagulation time was obviously shortened by extracts of Alpinia Rhizome, Areca, Artemisia Leaf, Cassia Bark, Danshen Root, Ephedra Herb, Epimedium Herb, Forsythia Fruit, Great Burdock Achene, Moutan Bark, Perilla Herb, Red Paeony Root, Schizonepeta Spike, Senticosus Rhizome, Sweet Annie, Uncaria Thorn and Zanthoxylum Peel. Factor XII was obviously activated by extracts of Artemisia Leaf and Great Burdock Achene, and slightly by Perilla herb.

CONCLUSION

Some popular Chinese medicinal herbs have potential as hemostatic agents and could thus be develope as new strategies for the treatment and prevention of bleeding.

Carrier-mediated partitioning of artemisinin into Plasmodium falciparum-infected erythrocytes

The purpose of the present study was to characterize the partitioning of artemisinin into both uninfected and Plasmodium falciparum-infected red blood cells (RBCs). The partitioning of [(14)C](+)-artemisinin into RBCs was studied at four different hematocrit levels and eight time periods. At the optimum time of 2 h, the partitioning process was investigated with eight different drug concentrations ranging from 0.88 to 3.52 microM at 37 and 4 degrees C. The effect of the presence of unlabeled artemisinin on the partitioning of the same concentration of [(14)C]artemisinin was studied. About 35 to 40% of the drug was seen to partition into uninfected RBCs at a hematocrit of 33%, irrespective of the incubation period or the drug concentration used. In contrast, infected RBCs showed an increase in partitioning of the drug with time until saturation was achieved at 1 h. While the partitioning of artemisinin into parasitized RBCs at 37 degrees C was found to be significantly higher than that in nonparasitized RBCs, at 4 degrees C both parasitized and nonparasitized RBCs showed identical partitioning of the drug. The partitioning of [(14)C]artemisinin into parasitized RBCs was completely inhibited in the presence of the same concentration of unlabeled artemisinin. However, no such effect was observed in nonparasitized cells, and no evidence suggesting that binding of the drug in parasitized RBCs is reversible was found. The partitioning of artemisinin into parasitized RBCs was found to be rapid, saturable, temperature dependent, irreversible, and subject to competitive inhibition with unlabeled artemisinin. The results obtained suggest the involvement of carrier mediation in the partitioning of artemisinin across the parasitized RBC membrane. In contrast, simple passive diffusion of artemisinin was seen in nonparasitized RBCs.

Orally active, hydrolytically stable, semisynthetic, antimalarial trioxanes in the artemisinin family

In only three chemical operations, natural trioxane lactone artemisinin (1) was converted into a series of C-10 carbon-substituted 10-deoxoartemisinin compounds 4-9. The three steps involved lactone reduction, replacement of the anomeric lactol OH by F using diethylaminosulfur trifluoride, and finally boron trifluoride-promoted substitution of F by aryl, heteroaryl, and acetylide nucleophiles. All of these C-10 nonacetal, chemically robust, enantiomerically pure compounds 4-9 have high antimalarial potencies in vitro against Plasmodium falciparum malaria parasites, and furans 5a and 5b and pyrrole 7a are antimalarially potent also in vivo even when administered to rodents orally.