Exhibition introduces DNA technologies for authentication of Chinese herbs
Traditional Chinese medicine has been in practise for centuries and is still widely used. However, substitutes and adulterants of medicinal materials are often introduced either intentionally or accidentally, which can seriously affect the therapeutic effects, or even lead to life-threatening poisoning. An accurate authentication of traditional Chinese Medicine is essential. With the advance in molecular technology, herb authentication based on Deoxyribonucleic acid (DNA)-based markers has become an objective and accurate approach.
The new Science News Corner exhibition -ˇ§DNA Technologies for Chinese Herbs Authenticationˇ¨ was opened today (April 28) at the Hong Kong Science Museum and will run until August 20. Focusing on a comprehensive DNA molecular technology developed by Professor of the Department of Biochemistry of the Chinese University of Hong Kong (CUHK), Professor Shaw Pang-chui and Professor of the Department of Biology of CUHK, Professor But Pui-hay, the exhibition employs DNA fingerprinting, DNA sequences and DNA chip for fast identification of expensive, endangered or toxic Chinese herbs, such as ginseng, American ginseng, Baiying, Dendrobium and crocodile.
DNA is a double-stranded macromolecule composed of two complementary chains of nucleotides. Each nucleotide bears one of the purine or pyrimidine bases: adenine, guanine, thymine and cytosine. The sequence of the nucleotides on the DNA serves as genetic codes. Different species would have different DNA sequences.
Two approaches are commonly used for molecular authentication of traditional Chinese medicine, both involve the use of Polymerase Chain Reaction to obtain DNA. DNA fingerprints, the first approach, is to obtain several regions in the genome and compare fingerprints of different samples. Another approach - DNA sequences - is to obtain DNA sequences of a particular region and they are aligned and compared using bioinformatics tools. The information can be used to build a DNA fingerprint or sequence database which provides useful information for authentication of traditional Chinese medicine.
When working on a kind of traditional Chinese medicine, samples of genuine and adulterant from various sources, including specimens from botanical or zoological gardens, medicinal materials and wild samples are first collected. Then molecular analysis on the samples collected, including DNA fingerprinting and sequencing, will be carried out. This data will be used as reference for identifying unknown samples.
DNA molecules offer a definitive means of authentication with advantages such as uniqueness for each taxon, and identical across different organs. Other advantages are that DNA molecules are not affected by age, growth conditions and physiological states, and that only a small amount of sample is required. The cost of DNA work keeps on reducing while steps can be automated.
Ginseng and American ginseng are important tonics and anti-ageing agents. It is found that some dishonest merchants sell ginseng as American ginseng. The Institute of Chinese Medicine of CUHK has found that Ginseng and American ginseng each has its unique DNA fragment which can be used for identification. These fragments can also be used to differentiate them from other adulterants. A United States patent was granted for this invention.
Findings from CUHK revealed that the two herbs, Baiying and Xungufeng, were erroneously swapped by the herbal industry in Hong Kong. By comparing the DNA sequences in the chloroplast genome, people were able to distinguish Baiying from Xungufeng.
Dendrobium is a beautiful orchid that is used in Chinese medicine to nourish ˇ§yinˇ¨ and removes ˇ§heatˇ¨. Market prices vary from $80 to $40,000 for one kilogram. It is frequently adulterated with other cheap orchids. The Institute of Chinese Medicine of CUHK established a DNA chip for identifying genuine Dendrobium species. The specific DNA probes are first devised based on species-specific DNA sequences obtained from each Dendrobium species. The probes are then spotted on DNA chips at specific sites. When performing a test, DNA from different kinds of genuine Dendrobium will hybridise with its corresponding probes at specific location on the DNA chip and emit signal. The identity of the specimen can then be determined through analysing the signals. This technique is also able to detect the presence of Herba Dendrobii in complex Chinese medicinal formulation.
Crocodile meat is often used for cough, bronchitis and asthma. After analysing four crocodile fried meat samples with DNA sequencing, it was found that only one of them was from crocodile, while the other three were from two endangered snake species.
With this comprehensive molecular technology, fast identification of different commonly-used, toxic, valuable and rare traditional Chinese medicine can be conducted to avoid misuse of herbal materials as well as to ensure public safety.
The Science Museum is located at 2 Science Museum Road, Tsim Sha Tsui East, Kowloon. It is open from 1pm to 9pm from Monday to Friday and from 10am to 9pm on Saturdays, Sundays and public holidays. It is closed on Thursdays (except public holidays). Admission is $25, with a half-price concession applicable to full-time students, people with disabilities and senior citizens aged 60 or above. Admission is free on Wednesdays.
For enquiries, call 2732 3232 or visit the Science Museum's website at http://hk.science.museum
for further information.
Ends/Friday, April 28, 2006