New Research Presented at the American Society of Pharmacognosy Meeting

Genetic and Chemical Distinction of Three Licorice Species

Reviewed: Simmler C, Gauthier L, Anderson JR, et al. The combination of DNA barcoding and metabolomics for the multi-constituents characterization of licorice botanicals. Poster presentation PG3 at: American Society of Pharmacognosy Annual Meeting; July 25, 2015; Copper Mountain, CO.

The authors from the College of Pharmacy at the University of Illinois at Chicago have presented their extensive analytical work for the assignment of the correct species name to licorice. According to the definitions of the United States Pharmacopeia (USP), Japanese Pharmacopoeia, Korean Pharmacopoeia, and the monographs of the World Health Organization (WHO), licorice consists of the roots, rhizomes, and stolons of Glycyrrhiza glabra L. (Fabaceae) or Glycyrrhiza uralensis Fisch. ex DC. The European Pharmacopoeia, the Chinese Pharmacopoeia, and the Vietnamese Pharmacopoeia also include the roots and stolons of Glycyrrhiza inflata Bat. in their licorice definition.

Fifty-one samples were authenticated using the nuclear ribosomal internal transcribed spacer (ITS) DNA sequence based on criteria from previous work by Kondo et al.,¹ where the three official species were further classified into four G. uralensis genotypes, two G. glabra genotypes, and three G. inflata genotypes. The 51 samples were also classified by chemical analysis using non-targeted (NMR) and targeted (HPLC-UV) methods, followed by statistical evaluation with principal component analysis (PCA). The results showed that 37 samples (72%) consisted of a single species, eight samples (16%) were mixtures of multiple species, and six samples (12%) were hybrids. Eleven samples (21%), including the six hybrid samples, were found to be mislabeled. The results of this poster were published in more comprehensive form in August 2015.²

Comment: This poster presents substantial work on one of the most widely used herbal ingredients worldwide. The three licorice species can be distinguished morphologically based on differences in the leaf and seed anatomy, although the occurrence of intermediate species has been reported, making the botanical authentication more challenging.³ The methods will allow a distinction among the three official licorice species, although both DNA sequencing and NMR metabolomics are not commonly used in the herbal industry. Useful is the presentation of glabridin, licochalcone A, and glycycoumarin as species-specific markers for G. glabra, G. inflata, and G. uralensis, respectively, in the paper. Since the researchers are mainly interested in the lipophilic compounds of these materials as therapeutic agents, a distinction of the three species may be necessary in order to obtain the desired chemical profile.

However, it is a matter of debate just how important such a distinction is for the use of licorice as a phytotherapeutic agent, where crude plant material, dried extracts, or liquid extracts made most commonly with water are used as an expectorant or to treat gastrointestinal symptoms.⁴ Roy Upton, executive director of the American Herbal Pharmacopoeia, commented, “I appreciate the desire to separate the species, but for all intents and purposes, there is no need, as most pharmacopoeias worldwide do accept these three species as Radix glycyrrhizae and traditionally they are used interchangeably” (e-mail communication, August 7, 2015). Herb industry expert Steven Foster wrote, “Licorice root is a relatively inexpensive, very common item in the botanical trade. Nobody is going to go to these lengths, nor should be expected to go to the extraordinary expense, to authenticate the identity of licorice root, as outlined in the study” (e-mail communication, August 7, 2015).

References

1.     Kondo K, Shiba M, Yamaji H, et al. Species identification of licorice using nrDNA and cpDNA genetic markers. Biol Pharm Bull. 2007;30(8):1497-1502.

2.     Simmler C, Anderson JR, Gauthier L, et al. Metabolite profiling and classification of DNA-authenticated licorice botanicals. J Nat Prod. 2015;78(8):2007-2022.

3.     Hayashi H, Hattori S, Inoue K, Sarsenbaev K, Ito M, Honda G. Field survey of Glycyrrhiza plants in Central Asia (1). Characterization of G. uralensis, G. glabra and the putative intermediate collected in Kazakhstan. Biol Pharm Bull. 2003;26(6):867-871.

4.     Blumenthal M, Goldberg A, Brinckmann J, eds. Herbal Medicine: Expanded Commission E Monographs. Austin, TX: American Botanical Council; Newton, MA: Integrative Medicine Communications; 2000:233-239.