By: T.V. Padma
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[NEW DELHI] Trees growing in a biodiversity hotspot in western India could yield a key substance needed to make the bird flu drug Tamiflu.
A team of scientists in Bangalore reported in Current Science last week (25 March) that they have identified several tree species that contain shikimic acid, a crucial component in the production of Tamiflu, the only drug used against bird flu caused by the H5N1 virus.
The fruits of the Chinese star anise tree, Illicium verum, contain 2–7 per cent shikimic acid and are an important source of the chemical. But the tree is difficult to grow, forms its first batch of fruits only in its sixth year and is unlikely to meet the global market demand, the scientists say.
Plants meet two-thirds of the requirements for shikimic acid and the remaining one-third is met by engineering the bacterium Escherichia coli to produce the chemical — which is not cost-effective.
The researchers screened 210 tree species in the Western Ghats region for shikimic acid content and shortlisted seven trees that contain 1–5 per cent shikimic acid by dry weight.
The acid is mostly present in the leaves of these trees. This is an advantage, the scientists report, as the sheer volume of leaves present on trees — compared with fruits — will make extraction cheaper.
"Leaves are abundant and present throughout the year," Ramanan Uma Shaanker, a researcher at the University of Agricultural Sciences in Bangalore, and one of the authors of the paper, told SciDev.Net.
The scientists are optimistic about the extraction of shikimic acid from the trees.
"Industries have existing technologies for isolation of shikimic acid from Illicium vernum [the Chinese plant]. The same could be applied to these [Western Ghats] plants as well with minor modifications," says Uma Shaanker. The process is relatively simple as shikimic acid is highly water soluble, he says.
Besides isolation, commercialisation would require bulk extraction on a large scale and validation of the shikimic acid content.
Shaanker’s laboratory now plans to demonstrate the feasibility of bulk extraction — in tens of kilograms compared to milligrams in the laboratory — in the two species, Araucaria excelsa and Calophyllum apetalum, with the highest shikimic acid content.
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