What's in your herbal remedy? Using DNA barcoding and DNA-based biological reference material library to test herbal products
Previous studies led by Prof. Newmaster and colleagues in 2013 have estimated high levels of adulteration in North American herbal products resulting in investigations into some of the largest herbal supplements manufacturers in the nation. His lab continues to be a leading expert in this area of research and his students are highly sought after for their expertise in this field.
Dr. Newmaster’s most recent publications strives to do the same in India, a mega-biodiversity hotspot. There are approximately 8000 species of plants with known medicinal uses in India that have been used in indigenous medicine systems for over 1000 years.
The increase in demand for herbal products have led to an over-exploitation of natural resources and loss of habitats and consequently, adulteration has become more common in Indian herbal products.
Currently, analytical chemistry has been used as a commercial tool to validate herbal authenticity but there are serious limitations to these methods thus, the research team set out to solve this important problem in a recently published paper by (1) creating a Biological Reference Material (BRM) herbal DNA library and (2) assessing herbal product adulteration in the Indian marketplace using the BRM library.
The BRM herbal DNA library was assembled from 187 herbal species that have been identified by taxonomists. The researchers used a tiered approach to barcode these plant species, using two barcode regions, rbcL and ITS2.
The species identified in the herbal products were categorized as: authentic, contamination, substitution (i.e. contaminated product without the main ingredient that was listed) or filler (i.e. known filler species such as rice, soybean and wheat.
Using the BRM herbal DNA library, they discovered that 60% of the products were adulterated – product contamination was in 50% of the products, 10% were substituted and 6% contained fillers. None of the herbal products contained pure herbs.
Interestingly, product contamination was usually with legal substitutes of plant species with similar morphological and pharmacological activity but usually of a lesser value or those found in great abundance. This suggested intentional fraudulent product substitution.
These high-resolution tools also detected species that have never been recorded as adulterants such as some tree species that were likely accidental, sticky pieces that adhered to the desired species.
This study showed that there is a clear need for regulated industry standards and a curated BRM library for herbal products.
One example of the use of the DNA-based BRM library is shown in another recently published paper co-authored by Dr. Newmaster and other colleagues.
They assessed adulteration in the trade of Saraca asoca (Roxb.) Willd (Caesalpiniaceae) in India. This herb, commonly known as “Asoka” or Ashoka”, is an important medicinal plant used to alleviate uterine and menstrual disorders since the 11th century AD.
The demand for S. asoca has tripled in the last 10 years and this demand is likely met by adulteration with other plant materials. The researchers analysed market samples of S. asoka from 25 different shops using DNA barcodes for two chloroplastic regions (rbcL and psbA-trnH) because of their high discriminatory power for the BRM, and NMR spectroscopy to validate.
Their results showed that only 3 of the 25 markets samples matched the authentic S. asoca samples. Specifically, 14 out of the 17 market samples analysed for rbcL did not match those of S. asoca and 10 out of 11 samples analysed for psbA-trnH did not match. The majority of these market samples came from other species belonging to 7 other families.
While this type of research is usually published in traditional biology journals, this work on S. asoca adulteration was published in the International Journal of Legal Medicine. This makes the research accessible to lawyers and policy makers who will in turn have an impact on imposing regulations on the trade of raw herbal products.