From plants to drugs – CPS lecture 4

By Penny Carmichael, on 8 November 2012

-Article by Abigail Mountain


In the West we often take our pharmaceuticals for granted and forget that a lot of the World still relies on traditional remedies to alleviate ailments. China, for one, has over 100,000 herbal products that people regularly use and will frequently take over “Western” medicines.  Furthermore, GSK are currently setting up R&D in China, in order to try to capture the chemistry behind some of these drugs. However, we don’t know the mechanisms behind a vast amount of traditional remedies. For example, out of the 150 commonly used species used here in the UK for the past centuries we only know how half of them work. As traditional treatments have been working for so long it’s not unreasonable for us to take them as a starting point for “new” drugs, and really get to the bottom of the chemistry.

Monique Simmonds from Kew Gardens gave a fascinating lecture on some of the work that her team has been doing over the past years. They set up a centre in South Africa to help a community cultivate plants commonly used as medicine. Over 80% of the people in this area rely on plants to get better and so it’s imperative that the quality should be as high as possible, and that the source is sustainable. What was interesting was that the procedure of blessing the land by the local healers involved planting the new shoots with soil from the old plot. The group experimented with the effect of old/new soil on the potency of the produce, finding that crops grown in brand new compost did not have the same medicinal effect. So the healers’ blessing requirement did in fact have a scientific explanation. Realising  technicalities such as these are just as important as understanding a plant’s chemistry. After the centre’s goal was reached the model taken to Namibia and Zimbawe, where good quality plants are being produced for similar communities.

Another focus of the lecture was antimalarial drugs from natural products. Most of us are aware of quinine, isolated from the shrub Cinchona, but malaria is becoming increasingly resistant to it. We must therefore find a replacement drug, and where better to look than places where the disease has been a threat for years. Plectranthus, a purple flowering plant, was found to be taken in Ghana and by an isolated tribe in South America. It is assumed that it was taken across the Atlantic on Portuguese slave ships, showing just how long this remedy has been an effective treatment. The fascinating part of this story is that in both instances the Plectranthus was only active when taken with at least one other plant, indicating that some interesting and complex chemistry is involved in its antimalarial mechanism. This if often the case with herbal drugs, making it extremely difficult to understand exactly how they work.

I can’t even begin to imagine how hard it is to analyse the action of plants as drugs. With so many compounds found in one leaf or petal, it must be like trying to find a chemical needle in a chemical haystack. Identifying the correct species of plant or natural product is also crucial. Star anise is a popular spice used in Chinese cooking, but it’s almost identical Japanese cousin is poisonous… Better examine those in the cupboard pretty carefully before making a curry!

Don’t forget that although lectures are off for the next week, CPS will still be delivering the goods! Tuesday evening sees Dr John Shaw tell us about Detecting fire, Smoke but not just smoke…