Study on the Identity of Commercial Crude Medicinal Plant Samples from Markets in China Finds a 4.2% Adulteration Rate

Reviewed: Han J, Pang X, Liao B, Yao H, Song J, Chen S. An authenticity survey of herbal medicines from markets in China using DNA barcoding. Sci Rep. 2016;6:18723. doi: 10.1038/srep18723.

Publications on the authentication of crude plant materials used in traditional Chinese medicine (TCM) by DNA barcoding are published on a regular basis, but the work by Han et al. is one of the largest studies available on the topic. The authors, from the Chinese Academy of Medical Sciences in Beijing, China, have analyzed 1436 crude herbal materials, representing 295 plant species from markets in seven Chinese provinces. Based on previous work, a combination of two genetic loci, psbA-trnH and ITS2, on which their TCM barcode database is built, was used to distinguish the various species and to detect the presence of adulterants.

In 176 (12.3%) samples, no DNA sequence was obtained; amplification proved more challenging with samples of barks, fungi, and roots, where 22.6%, 21.7%, and 15.0% of the samples, respectively, could not be sequenced. Samples from the stem or the leaf had much higher success rates, with failure rates of only 3.1% and 5.1%, respectively. Overall, only 4.2% of the 1260 samples where DNA barcodes were obtained were incorrectly labelled and thus considered adulterated. Adulteration was observed in 26 plant species, e.g., in 6/6 (100%) samples of Dalbergia odorifera (Fabaceae), 3/3 (100%) of Eleutherococcus nodiflorus (Araliaceae), 4/6 (67%) of Inula japonica (Asteraceae), 5/8 (63%) of Albizia julibrissin (Fabaceae), 10/19 (53%) of Rubus parvifolius (Rosaceae), 4/8 (50%) of Acorus calamus var. angustatus (Acoraceae), 4/9 (44%) of Bupleurum chinense (Apiaceae), 2/6 (33%) of Eleutherococcus senticosus (Araliaceae), and 3/15 (20%) of Panax ginseng (Araliaceae). The adulterating species of these botanicals are detailed in Table 1 below.

Table 1. Adulterants found in selected crude raw materials from seven Chinese markets

Species	Plant part	Adulterants (number of adulterated samples in brackets)
Acorus calamus var. angustatus (syn. Acorus tatarinowii)	Root and rhizome	Acorus calamus [2], Acorus spp. [2]
Albizia julibrissin	Bark	Albizia kalkora [5]
Bupleurum chinense	Root and rhizome	Bupleurum spp. [4]
Dalbergia odorifera	Stems	Caesalpinia sappan [6]
Eleutherococcus nodiflorus (syn. Acanthopanax gracilistylus)	Bark	Eleutherococcus giraldii [1], Periploca sepium [2]
Eleutherococcus senticosus (syn. Acanthopanax senticosus)	Root and rhizome	Alangium chinense [1], Aralia spp.
Inula japonica	Flower	Inula linariifolia [4]
Panax ginseng	Root and rhizome	Panax quinquefolius [3]
Rubus parvifolius	Root and rhizome	Cirsium japonicum [4], Rosa chinensis [4], Rubus alceifolius [2]

The DNA sequences were compared with those listed in the TCM barcode database, which contains the ITS2 and psbA-trnH barcodes for over 23,000 medicinal plants. The authors suggest that DNA barcoding is a suitable technique to authenticate a majority of crude botanical drugs, but concede that the technique is not suitable for heavily processed samples. As such, the widespread use of sulfur fumigation in China to prevent insect infestations of crude herbal raw materials may affect the DNA barcoding results. In addition, the authors’ state that DNA barcoding does not provide information on the concentrations of the active compounds; therefore, it cannot guarantee the quality of the material, and the authors suggest that a number of analytical techniques should be used to characterize crude herbal materials.

Comment: The introduction to this paper describes some of the cases where adulteration has led to serious adverse events, including death, e.g., the substitution of Stephania tetrandra (Menispermaceae) with the toxic species Aristolochia fangchi (Aristolochiaceae). The results of this study suggest that adulteration of crude raw herbs in China is a problem, but that in most cases, the adulterants are closely related to the labeled medicinal species and do not represent highly toxic species. In some instances, e.g., Dalbergia odorifera and Caesalpinia sappan (Fabaceae), the plants are used for the same conditions. In other cases, the common names may be similar enough to lead to confusion of two species, e.g., Periploca sepium (Apocynaceae) is known under the scientific name of gang liu,¹ but local merchants refer to it as bei wu jia pi, which can be confused with Eleutherococcus nodiflorus (with the scientific name xi zhu wu jia),¹ known as wu jia pi among traders.²

The publication shows that DNA barcoding can be a valuable tool to detect adulteration and provide information about the genus or species of the adulterating material, especially if the researchers are aware of the technique’s limitations. At the same time, the interpretation of some of the data has to be questioned. For example, in Table 1 above, Acorus calamus is defined as an adulterant of Acorus calamus var. angustatus and an unknown Bupleurum spp. is considered an adulterant of Bupleurum chinense. To consider these closely related species as adulterants would require data demonstrating a functional difference between the species based on accurate species identification. Moreover, if DNA was not recovered or amplified to a degree that allows for species identification, as was done with the Acorus spp., it may be incorrect to label the unknown species as an adulterant.

References

1.   Flora of China. eFloras.org website. Available at: http://www.efloras.org. Accessed May 11, 2016.

2.   Hu SY. The role of botany in Chinese medicinal material research: the case of eleuthero. In: Chang HM, Yeung HW, Tso W-W, Koo A, eds. Advances in Chinese Medicinal Materials Research. Singapore, Singapore: World Scientific Publishing; 1985:28-33.