Thursday, May 29, 2014

Medicinal plants in our own backyard

The discovery of plants with medicinal or health-promoting properties began with indigenous cultures around the world thousands of years ago.  The practice of herbal medicine is truly the "oldest profession," and even pre-dates humanity.  Chimpanzees are known to seek out certain plants in their native forests that can relieve illness or discomfort. One such plant comes from a shrub native to the forests of Africa called Aspilia (Asteraceae), which has been shown to kill bacteria, fungi and nematodes in the intestinal tract.  It may also serve as a stimulant - the morning coffee for chimps.  Each culture has discovered useful plants in their own backyards, and modern medicine is now slowly exploring that priceless knowledge and verifying what these people have known for a long time.

The prickly poppy, Argemone mexicana, was introduced into Africa in the
19th century and has been used as a medication against malaria almost
as long. Photo by B. Navez, posted in Wikipedia.
So it was a personal surprise to me - even though I teach a course in Medicinal Botany - that a plant frequently found in my own backyard has within it compounds that may cure malaria.  The plant is Argemone mexicana, the prickly poppy. The new information was featured in the recent issue (June 2014) of Scientific American, in the article "Seeds of a Cure," by Brendan Borrell.  The article describes the efforts by researchers working in the field in Africa, Mali to be specific, to document the effectiveness of the plant among people taking this natural medicine as an herbal tea.  The researchers documented a successful cure rate of about 89%, which compares quite favorably with the 95% rate of the much more expensive conventional treatments based on artemisin.

I went back to my classic textbook on medicinal botany by Lewis and Lewis, and found mention of prickly poppy as treatment for heart arrhythmias, but not malaria.  So I didn't feel so stupid then, but a still little bit ignorant compared with the native African healers who have been using this for over a century. The plant is native to tropical America, and was introduced into Africa sometime in the 19th century, which means the native healers there caught onto its medicinal properties fairly quickly!  We tend to think of traditional healers in general as following procedures cast in stone hundreds or thousands of years ago - a clearly unjustified stereotype.  In this instance at least, there were  intellectually flexible experimenters in the profession.

So what are the active principles in  prickly poppy tea? The Lewis text indicates a-allocrytopine obtained from the roots as the active principle in treatment of heart arrhythmia.  It also indicates that a more toxic mix of sanguinarine, berberine, protopine is present in the plants, and that prickly poppy occasionally contaminates grain.   This may be from the seeds of the prickly poppy, which have been implicated in poisoning events in India.  Sanguinarine is considered the primary culprit.

The leaves, however, have little sanguinarine, and the herbal tea, according to Borrell, is fairly non-toxic.  Isolated berberine has shown some anti-malarial effect, but much weaker than that of whole leaf infusions. So it is not known exactly what mix of compounds in the leaves is so potent against malaria.

Argemone mexicana might  turn out to be the tip of an iceberg.  There are 32 species in this genus, native mostly to tropical America, with one species in Hawaii.  Relationship among plants is highly predictive of similarity in secondary plant compounds.  These other species may have similar or even better combinations of compounds for treating malaria or other parasites.

This is not to mention the numerous other genera and species of the poppy family.  One must of course be very careful to steer away from the dangerous compounds found throughout this family, including the opiates in Papaver somniferum.  As I say on the first day of my medical botany course: "DO NOT TRY THIS AT HOME!"  Self-experimentation with natural plant compounds is exceedingly risky. If you can get a hold of the Lewis text, there is an excellent section on all the ways people inadvertently poison themselves.

The study of medicinal botany is both ancient and very new.  The new part is applying the modern scientific method to finding and verifying the curative or preventative properties of plant compounds.  The possibilities and opportunities in this field are endless.

References:

Borrell, Brendan.  2014.  Seeds of a Cure.  Scientific American 310 (#6): 64-69.

Lewis, W. H. and M. P. F. Elvin-Lewis. 2003.  Medical Botany, 2nd Ed., John Wiley and Sons.

2 comments:

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