Crowdsourcing
to Support High School Project on DNA Authentication of 32 Herbal Dietary
Supplements
Reviewed: Molina J, Sherpa C, Ng J, Sonam T, Stuhr N. DNA barcoding of online herbal supplements:
crowd-sourcing pharmacovigilance in high school. Open Life
Sci. 2018;13:48-55.
Keywords: Adulteration, Astragalus membranaceus, Astragalus propinquus,
DNA barcoding, Dysphania ambrosidoides, Panax ginseng, Phyllanthus niruri,
Sanger sequencing
As part of the Urban Barcode Research Program (UBRP), a
science education initiative within high schools in New York City, three students from Brooklyn Technical High
School (Brooklyn, NY) collaborated with scientists from Long Island University
(Brooklyn, NY) to determine the identity of ingredients in 32 herbal dietary
supplements. The supplements, which were purchased from a major online
retailer, had to be single-ingredient and contain crude powdered plant material
(no extracts) from species that are non-native to the United States. Information
on the delivery form was not provided.
Dietary supplement contents were extracted using the
Qiagen (Germantown, MD) DNeasy Plant Mini Kit or the Phire Plant Direct PCR kit
(Thermo Fisher, Waltham, MA), and amplified using primers for the ITS2 and matK genomic regions. After assembling the sequences by
Sanger’s method, the data were compared to sequences in the NCBI GenBank
database.
The amplification success was limited, resulting in 17
ITS2 and 6 matK sequences from 20 of the 32 (62.5%)
dietary supplements. According to the authors, samples made from roots and barks
were more likely to yield no sequence data. While 16 of these 20 samples (80%)
were correctly labeled, barcodes for four of the supplements where
amplification was successful did not correspond to the plant species listed on
the label, i.e., Astragalus propinquus (a synonym
of A. membranaceus, Fabaceae), Dysphania ambrosioides (syn. Chenopodium
ambrosidoides, Chenopodiaceae), Panax ginseng
(Araliaceae), and Phyllanthus niruri (Euphorbiaceae).
Instead, the researchers found DNA from Plantago spp.
(Plantaginaceae), Artemisia absinthium
(Asteraceae), Astragalus propinquus, and Desmodium canandense (Fabaceae), respectively.
The authors concede that a combination of sequencing and
chemical authentication would be preferable and more appropriate for
authenticating herbal dietary supplements, but explain that “these [methods] can
only be afforded by big labs, such as government or well-funded academic labs,”
and “these results are not readily accessible to the general public because of
the technical jargon, with the actual brand names also not disclosed to avoid
legal consequences. Thus, these studies will not be able to help consumers.
However, for single-ingredient unprocessed HMPs consumers themselves take, they
may test for the taxonomic accuracy of these products given the accessibility
and low cost of Sanger-based DNA barcoding.”
Comment: While this research project may have been a good
learning experience for high school students, the results also point to some of
the limitations surrounding DNA barcoding on herbal dietary supplements,
especially when using Sanger’s method to sequence the DNA, which provides only
one plant species per sample and is known to be at risk for amplification bias.1,2
This increases the chance of getting false positive results. Despite the fact
that the researchers chose supplements containing solely powdered plant
materials, the amplification success was low, with ITS2 and matK sequences obtained for only 53% and 19% of the samples,
respectively, suggesting that many common herbal ingredients are not suitable
for identification by means of this approach.
As previously reported, herbal dietary supplements
usually contain DNA from non-listed plant species, such as common weed species,
or particles from other medicinal plant particles that became airborne during agricultural
collection and/or a previous manufacturing process.1 This raises the
question if some of the results for adulterated samples could be due to the
fact that an incidental contaminant could have been preferentially amplified
instead of the labeled species. In absence of any laboratory contamination
check, it cannot be excluded that some of the findings were related to plants
that were previously analyzed in the laboratory.1 A particular
coincidence is the finding of Astragalus propinquus
as an adulterant of Panax ginseng,
while the A. propinquus supplement in turn was
reportedly adulterated with a plantain (Plantago spp.).
No explanation for this peculiar result was provided by the authors.
As DNA identification technologies become more affordable
and easy to use, such tests are likely more and more often put into the hands
of laypeople. As an example, efforts are under way to develop test kits for
consumers that are linked to software applications to authenticate food items
(such as dietary supplements) in handheld devices such as cell phones. One of
the challenges is how to avoid erroneous results with these devices, and how
the baseline pass-or-fail criteria will be established with transparency. As
long as there is no solution to improving the accuracy of DNA tests, genetic
identification methods will always have to be combined with macroscopic,
microscopic, and/or chemical methods to assure the accuracy of the findings.
References
- Ivanova NV, Kuzmina ML, Braukmann TW, Borisenko
AV, Zakharov EV. Authentication of
herbal supplements using next-generation
sequencing. PLoS One. 2016;11(5):e0156426. doi: 10.1371/journal.pone.0156426.
- Parveen
I, Gafner S, Techen N, Murch SJ, Khan IA. DNA Barcoding for the identification
of botanicals in herbal medicine and dietary supplements: strengths and limitations.
Planta Med. 2016;82(14):1225-1235.
