Monday, September 10, 2012

Dangerous herbs

DNA Barcoding and traditional Chinese medicine

Chinese herbs have been used as medicine for over 2000 years. There are some 13,000 natural medicinals used in China with over 100,000 recipes recorded in the ancient literature. More and more these traditional drugs are used outside of China and some producers of Chinese herbal medicines are pursuing FDA clinical trials to market their products as drugs in U.S. and European markets. Therefore, the authentication of the ingredients is becoming a critical, international issue because mistakes can cause illness and even death. Plant elements and extracts are by far the most common elements used and there is confusion and substitution happening. Not a surprise given the large number of potential ingredients for these products.

A couple of years ago a 60 year-old man from Hong-Kong was diagnosed with kidney failure and cancer of the urinary tract. He had been taking an herbal prescription and the case was investigated by the local Department of Health. The investigations revealed that the patient was mistakenly given a product called Herba Aristolochiae Mollissimae (made from Aristolochia mollissima) instead of Herba Solani Lyrati (made from Solanum lyratum). Herba Aristolochiae Mollissimae is known to contain the poisonous aristolochic acid which indeed can cause kidney failure and is known to be cancerogen when taken over a longer period of time.

Aristolochia mollissima
Solanum lyratum
In the wild both plants can be distinguished rather easily (see pictures) but some characteristics may vary with growing stages, environmental properties, physical forms, and post-harvest processing of the herbs. Confusion is further facilitated by the fact that both herbs share the same Chinese common name Bai Mao Teng (meaning  ‘white hair-bearing vine’).

Now a group of researchers from Hong Kong tested if DNA barcoding and chemical fingerprinting are useful alternatives to the use of microscopy and elaborate chemical analysis. Indeed they are. The chemical profiling was able to detect the harmful component aristolochic acid. However, the chemical composition of a herb can vary between different life stages and can be altered during processing. In contrast, DNA barcoding  is not affected by these factors and usually a small amount of sample is sufficient for DNA extraction. The study also showed that the smallest DNA fragment amplified was about 50 bp long which demonstrates that even partially degraded DNA could be retrieved. The researchers tested a variety of markers (the standards matK and rbcL, as well as ITS, trnH-psbA and trnL-trnF) which provides us with an arsenal of possible tests that will help to avoid such fatal confusions.

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