Informatics securely separates snow lotus species

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  • Published: Oct 1, 2017
  • Author: Ryan De Vooght-Johnson
  • Channels: Laboratory Informatics / Chemometrics & Informatics
thumbnail image: Informatics securely separates snow lotus species

Three snow lotus species commonly confused

The snow lotus plant is used in a dried form in traditional Chinese medicine to treat inflammatory diseases, such as arthritis, and also as a painkiller. However, the name ‘snow lotus’ can refer to any one of three related species: Saussurea laniceps (the cotton-headed snow lotus), Saussurea medusa and Saussurea involucrata (Tianshan snow lotus). Modern research suggests that the former species is the most active. There has often been confusion between the three species, not only in the commercial world, but even in some academic studies. In addition, overharvesting of Saussurea laniceps has led to other species being substituted for it. Accurate methods are needed to distinguish between the dried plant material from the three different species.

The researchers from Hong Kong and Sichuan decided to differentiate between the three species on the basis of their chemical composition and to relate this to their efficacy. They employed ultra-high pressure liquid chromatography (UHPLC) in combination with quadrupole time-of-flight mass spectrometry (QTOF MS) to identify the particular metabolites in 49 plant samples identified by qualified botanists.

Composition of snow lotus species distinguished by GC and QTOF MS

Ground plant samples were extracted under sonication with 70% methanol, and the extracts were then filtered to remove solids. UHPLC-MS was carried out using an Agilent 6540 UHD (ultra-high definition) QTOF LC/MS system, with a Waters BEH C18 column and a VanGuard HSS C18 pre-column. The two gradient eluents were acetonitrile and water, both containing 0.1% formic acid. The proportion of acetonitrile was increased from 2% to 55% in a series of gradients. The mass spectrometry employed electrospray ionisation (ESI) in negative ionisation mode, which was shown to give more ion information than positive mode.

Peaks corresponding to 25 compounds were noted; the majority of these were identified unambiguously by comparison with authentic compounds. 12 compounds were selected as markers to be quantified. Taking into account all 49 plant samples, the average concentrations of these 12 compounds in the extracts from the three different species were calculated. Three coumarin compounds, umbelliferone, skimmin (a glucoside of umbelliferone) and scopoletin, were only found in Saussurea laniceps. The Saussurea medusa samples contained relatively high levels of the flavonoid isoquercetin compared to the other compounds present, while Saussurea involucrata samples contained much higher levels of the flavonoid rutin than the other two species. The authors noted that umbelliferone and scopoletin are believed to be responsible for the greater medicinal activity of Saussurea laniceps compared to the other two species.

PCA was carried out on the 49 samples using an IBM SPSS Statistics 20 package. A four-component model accounted for 84% of the variance. In the PCA plot, the points for Saussurea medusa samples clustered tightly together, as did those for Saussurea involucrata. The points for Saussurea lancipeps samples were more spread out across the plot, but still clearly separated from the other two species.

HCA was carried out using a Cluster 3.0 package, the results being presented as a dendrogram. Two main clusters were noted, one containing the Saussurea laniceps samples and another comprising the Saussurea medusa and Saussurea involucrata samples.

Snow lotus species can be identified by informatics methods

The use of PCA and HCA clearly distinguished the samples from the three species of snow lotus. It would be interesting to apply these methods to further samples to check that they held up. Such techniques could usefully be applied to other species where confusion exists. However, in the case of the snow lotus, the most potent species, Saussurea laniceps, suffers from over-picking in the wild, so substitution by other species is likely to remain a problem unless economical cultivation methods are developed.

Related Links

Drug Testing and Analysis, 2017, 9, 1105-1115. Chen et al. Comparative evaluation of chemical profiles of three representative 'snow lotus' herbs by UPLC-DAD-QTOF-MS combined with principal component and hierarchical cluster analyses.

Wikipedia, Hierarchical Clustering

Wikipedia, Principal Component Analysis

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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