Fingerprints give the right prescription
Hepeng Jia/Beijing, China
Each ingredient has a fingerprint
A large research effort ensures that TCM prescriptions are of high quality. In the 1990s, the fingerprint approach - which uses chromatography and spectroscopy to measure the relative proportions of several well-known compounds - was adopted to bring quality control to TCM prescriptions.
'The fingerprint method tests the existence and contents of certain marker compounds to ensure that TCM herbs are consistent with the recognised criteria,' says Lei Yan, chief of the research section at the China Academy of Chinese Medical Sciences. These marker compounds might not be the most pharmaceutically active molecules, but their existence has proved to be constant in high-quality herbs.
Supporters say that the fingerprint approach offers quality control without destroying the synergistic effects of the TCM compounds. The 2005 China Pharmacopoeia lists the fingerprint criteria for several hundred herbs and TCM prescriptions and contains analysis results, including those from high performance liquid chromatography (HPLC) and mass spectrometry (MS).
Shi Yanping, a natural product chemist at the Lanzhou Institute of Chemical Physics, explains that scientists only need to compare marker compounds with the pharmacopoeia criteria and not worry about the minor compounds. 'For those who want to extract the most pharmaceutically active molecules, the fingerprint can also offer a good reference,' Shi told Chemistry World .
But HPLC and MS are too expensive for many labs and can only be afforded by some key research institutes, says Shi. The established criteria also need updating, he adds. Often, HPLC test results do not match pharmacopoeia criteria, yet this does not necessarily mean that the herbs tested are of poor quality. 'It is necessary to update the pharmacopoeia criteria for TCM fingerprints. Developing widely accepted databases of fingerprint information is also very important,' Shi says.
TCM prescriptions generally combine several herbs and contain hundreds of chemically different constituents. Often only one or two of the compounds are responsible for a prescription's effects.
Chemists have long been trying to extract the most active molecules from TCM prescriptions, often with a view to making modern pharmaceutical versions. Success has so far been limited and most of TCM's modes of action are unknown. TCM advocates often complain that the modern extraction approach misses the benefits of the synergistic effects of groups of compounds.