Published: Dec 14, 2015
Author: Ryan De Vooght-Johnson
Channels: Laboratory Informatics
Not all plants are created equal
A simple method for chemical fingerprint analysis of traditional Chinese medicines, using high-performance liquid chromatography with diode array detection, is described in a new study.
With more and more people looking for a less interventionist style of medicine, traditional Chinese medicine is attracting worldwide attention. In place of prescription drugs, Chinese medicine relies on herbal medicines, often based on plant extracts.
Although many of these extracts have scientifically validated activity, the field remains in need of better quality control. The quality of traditional herbal medicines depends on where the plant was grown, when it was harvested and how it was processed.
As these are not currently standardised, there is great variation between extracts.
To enter the global market and compete with regulated, clinically tested Western medicine, traditional Chinese medicine needs to modernise, and this means thorough quality evaluation. Perhaps the best approach is chemical fingerprint analysis, which assesses the full profile of chemical components and their relative concentrations in a compound, and is an internationally accepted as a method of quality control.
In this study, Chinese researchers used HPLC to fingerprint Vitex negundo, better known as Chinese chastetree, an aromatic shrub distributed widely across South Asia. Its seeds have been used as a painkiller and treatment for arthritis. A number of studies have shown that chemicals isolated from the plant have anti-inflammatory and anti-bacterial properties.
The main bioactive components of the seeds are the lignans, which have promising clinical properties. Four lignans in particular (of the phenylnaphthalene type) have been reported to have anti-inflammatory, anti-oxidative and painkilling properties. As the major compounds responsible for the activity of the seeds, their rapid characterisation in plant extracts is essential for quality control, yet no such characterisation has so far been performed.
Chemical complexities
To provide the first characterisation, the researchers combined HPLC – the principal method for fingerprinting, owing to its simplicity, stability and durability – with quantitative analysis of the four major lignans. They developed a method to do both simultaneously, using HPLC with diode array detection (DAD) – a device that detects components of a mixture as it is eluted off the liquid chromatography column.
A total of 13 different seed samples were collected from different regions of China. The samples were dried and pulverised before extraction, followed by HPLC analysis under optimised conditions. The HPLC-DAD fingerprinting method showed good results and was validated according to the guidelines of the Chinese Food and Drug Administration.
Peaks found in the chromatograms of all tested samples were defined as ‘characteristic common peaks’. A total of 21 such peaks were found, which covered over 80% of the total area.
Foundation for quality control
The chromatograms, while similar, did show minor differences. To avoid overlooking these chemical complexities, the samples were compared using a computer programme designed to analyse traditional Chinese medicines. The program applied Hierarchical Cluster Analysis (HCA), a chemical pattern recognition method, to classify and evaluate the different samples. The program separated the samples into three groups, based on the relative peak areas of the 21 common peaks. Sorting was consistent with the chromatography results and may provide references for further quality studies of V. negundo seeds.
The four major lignans were successfully separated and quantified, revealing significant differences between the samples. The wide variation in lignin contents of seeds collected from different locations demonstrates the importance of quality control. Particularly large variation was found in VN-5 content, which could scarcely be detected in some samples. As VNL and VN-2 – the two major lignans identified – showed the least variation, and have scientifically proven biological activity, the researchers conclude that these two compounds should be used as indicators of quality.
The rapid and effective method described here will pave the way for the first quality control standards for this herbal medicine. The results also demonstrate the potential of HPLC fingerprinting for assessing the quality of traditional Chinese medicines and ensuring consistency between batches – something the discipline is currently lacking.
Related Links
J. Sep. Sci., 2015, Early View Article, Chemical Fingerprint and Quantitative Analysis for the Quality Evaluation of Vitex negundo Seeds by reversed-phase high-performance liquid chromatography coupled with Hierarchical Clustering Analysis.
Source: Separations Now
