Metabolomics Solutions for Medicinal Plants

The metabolome monitors chemical changes in living cells by qualitative and quantitative analysis of all low molecular weight metabolites in a given organism or cell.

Metabolomics Solutions for the Study of Medicinal Plants

Sample preparation and pre-treatment

Sample preparation and pretreatment need to take into account various factors such as time, region, site and developmental stage of medicinal plant collection to reduce the impact of sample variation on the results of metabolomics analysis. Biological inactivation of medicinal plants, such as snap freezing in liquid nitrogen, is required after sample collection to reduce redox reactions and degradation of the samples to be tested by various hydrolytic enzymes.

The process of preparing samples is based on the nature of the object of study and the chosen research method to pre-treat the samples. For example, solvents of different polarity are applied to separate the water-soluble components of medicinal plants, which are more polar, from the lipid-soluble components, which are less polar. In addition, most of the primary secondary metabolites are not volatile, so after sample extraction, derivatization of the sample, such as esterification, acylation, ionization, alkylation, etc., is required to obtain more samples available for analysis.

Isolation and identification of metabolites

The separation techniques of metabolites usually include gas chromatogram (GC), liquid chromatogram (LC) and capillary electrophoresis (CE). The detection and identification techniques include IR spectrum, UV spectrum, nuclear magnetic resonance (NMR) and mass spectrometry (MS).

Data conversion and analysis

After the metabolites are separated and identified, the raw chromatographic data are obtained. These data are voluminous and need to be converted into digital matrix data in order to clarify the statistical relationships between compounds and their biological significance. The methods of converting these numbers include eliminating noise interference, correcting the baseline, and segmenting the data to exclude the interference of environmental factors during the measurement.

After processing the raw data, the data needs to be analyzed. Commonly used data analysis can be divided into two types of identification models, supervised classification and unsupervised classification. The difference between the two models is that unsupervised classification uses known mathematical models to predict samples, while supervised classification classifies and filters metabolite assays from the original assay profiles. Supervised classification includes principal components analysis (PCA), hierarchical clustering analysis (HCA), and self-organizing map (SOM). Unsupervised classification mainly includes partial least squares-discriminant analysis (PLS-DA) and orthogonal partial least squares-discriminant analysis (OPLS-DA).

Figure 1. Various phytochemical techniques used in the field of medicinal plant research (Mukherjee et al., 2016).

Application of Metabolome in Medicinal Plants

Fingerprinting technology can effectively provide comprehensive quality control of medicinal plants and ensure safe and stable effects of their use.

The changes of metabolites in medicinal plants under different treatment conditions such as external physical, chemical or biological stimuli are monitored. The differences in metabolites of medicinal plants before and after stimulation will be compared and comprehensively analyzed to lay the foundation for finding and determining the key steps and laws of plant metabolism.

To study the gene functions of medicinal plants. The analysis of metabolites reveals changes in the expression levels of relevant genes, and the influence of genes on metabolic flow can be inferred.

To assist in the cultivation and harvesting of medicinal plants. The chemical composition of medicinal plants changes according to the growth period and environment, and the accumulation of metabolites in different periods and environments can effectively ensure the quality and yield of medicinal herbs and provide a scientific basis for the rational and effective utilization of medicinal herbs.

Reference

1. Mukherjee, P. K., Harwansh, R. K., et al. (2016). Metabolomics of medicinal plants–a versatile tool for standardization of herbal products and quality evaluation of ayurvedic formulations. Current Science, 1624-1630.