High-level semi-synthetic production of the potent antimalarial artemisinin.

In 2010 there were more than 200 million cases of malaria, and at least 655,000 deaths. The World Health Organization has recommended artemisinin-based combination therapies (ACTs) for the treatment of uncomplicated malaria caused by the parasite Plasmodium falciparum. Artemisinin is a sesquiterpene endoperoxide with potent antimalarial properties, produced by the plant Artemisia annua. However, the supply of plant-derived artemisinin is unstable, resulting in shortages and price fluctuations, complicating production planning by ACT manufacturers. A stable source of affordable artemisinin is required. Here we use synthetic biology to develop strains of Saccharomyces cerevisiae (baker's yeast) for high-yielding biological production of artemisinic acid, a precursor of artemisinin. Previous attempts to produce commercially relevant concentrations of artemisinic acid were unsuccessful, allowing production of only 1.6 grams per litre of artemisinic acid. Here we demonstrate the complete biosynthetic pathway, including the discovery of a plant dehydrogenase and a second cytochrome that provide an efficient biosynthetic route to artemisinic acid, with fermentation titres of 25 grams per litre of artemisinic acid. Furthermore, we have developed a practical, efficient and scalable chemical process for the conversion of artemisinic acid to artemisinin using a chemical source of singlet oxygen, thus avoiding the need for specialized photochemical equipment. The strains and processes described here form the basis of a viable industrial process for the production of semi-synthetic artemisinin to stabilize the supply of artemisinin for derivatization into active pharmaceutical ingredients (for example, artesunate) for incorporation into ACTs. Because all intellectual property rights have been provided free of charge, this technology has the potential to increase provision of first-line antimalarial treatments to the developing world at a reduced average annual price.

A comparison of three different root canal sealers when used to obturate a moisture-contaminated root canal system.

Sealing ability of three classes of endodontic sealers, in moisture-contaminated canals, was evaluated. A total of 120 single-rooted extracted teeth were divided into three groups. The groups were obturated with either Procosol, Sealapex, or Ketac-Endo using saline as a moisture contaminant in all cases. Half (20 teeth) of each group was placed in a saline storage medium for 9 months. The remainder of the samples were placed in India ink, under a vacuum, cleared, and the amount of dye penetration measured under magnification. The stored samples were similarly treated after the 9-month storage period. In a moisture-contaminated canal, Procosol exhibited the least amount of apical leakage, followed by Sealapex, then Ketac-Endo. There was no significant difference in the amount of dye penetration after 9 months of storage over that found initially, which indicates that the deleterious effects of moisture contamination occur during the initial placement and setting reaction.