Barcoding Medicinal Plants

A plant which has been used for medical purposes at one time or another, and which, although not necessarily a product or available for marketing, is the original material of herbal medicines.

Definition of the term "Medicinal Plants", WHO

The global market of products derived from plants is estimated at $83 billion US and continues to grow. Furthermore, it is estimated that approximately 25% of modern drugs are derived from plant products. According to the WHO, between 65% and 80% of the populations of developing countries use medicinal plants as remedies and this number is also steadily growing. 

More and more medicinal plant products are produced for the global market and companies seek clinical trials to market their products e.g. as drugs in U.S. and European markets. Therefore, the authentication of the ingredients is becoming a critical, international issue. Mis-identification and adulteration of herbal remedies needs to be monitored and addressed. In a guest post in this blog a colleague from Nigeria provided a local example of the problems agencies are facing worldwide.

A new study published in PLoSONE shows another piece of this truly global puzzle. A group of researchers from Brazil used DNA barcoding (matK, rbcL and ITS2 regions) as well as qualitative and quantitative chemical analyses to confirm the identity of selected products. The colleagues studied eight species approved by the WHO for the production of medicinal herbs and sold in Brazilian markets:

Hamamelis (Hamamelis virginiana)

Chamomile (Matricaria recutita)

Espinheira Santa (Maytenus ilicifolia)

Guaco (Mikania glomerata)

Asian Ginseng (Panax ginseng)

Passion flower (Passiflora incarnata)

Boldo-do-Chile (Peumus boldus)

Valerian (Valeriana officinalis)

The results of the study are interesting but also a bit alarming as the level of substitutions may be as high as 71%. Using qualitative and quantitative chemical analyses, this study identified situations in which the correct species was being sold, but the chemical compounds were not present. Even more troubling, some samples identified as substitutions using DNA barcoding contained the chemical compounds from the correct species at the minimum required concentration. This last situation may lead to the use of unknown species or species whose safety for human consumption remains unknown.

This shows the true power of this combined approach showing that it is possible for a sample to pass quality control tests even if it does not belong to the correct species and at the same time that there are correctly identified products that don't contain sufficient amounts of chemically active compounds. The authors conclude:

The present study showed a great number of species substitutions and mislabeling, demonstrating that the current surveillance methods are not being efficient to control he herbal medicine market. Also, we showed that the traditional methodologies of species identification using chemical analysis are, in the majority of cases, not adequate to correctly identify a plant species. Thus, we propose the use of DNA barcode as a powerful first screening step. Applying the DNA barcode technique to the quality control of herbal medicine production will make the process safer, more reliable, and cheaper because substitutions will be promptly discarded without requiring more expensive chemical analyses that are otherwise necessary.