Mitigating the Impact of Admixtures in Thai Herbal Products

Development of an allele-specific PCR (AS-PCR) method for identifying high-methyl eugenol-containing purple Tulsi (Ocimum tenuiflorum L.) in market samples

BACKGROUND

Ocimum tenuiflorum L. is a highly traded medicinal with several therapeutic values. Green Tulsi and purple Tulsi are two subtypes in O. tenuiflorum and both have the same medicinal properties. Recent reports have revealed that purple Tulsi contains higher quantities of methyl eugenol (ME), which is moderately toxic and potentially carcinogenic. Therefore, we developed an allele-specific PCR (AS-PCR) method to distinguish the green and purple Tulsi.

METHODS AND RESULT

Using the green Tulsi as a reference, 12 single nucleotide polymorphisms (SNPs) and 10 insertions/deletions (InDels) were identified in the chloroplast genome of the purple Tulsi. The C > T SNP at the 1,26,029 position in the ycf1 gene was selected for the development of the AS-PCR method. The primers were designed to amplify 521 bp and 291 bp fragments specific to green and purple Tulsi, respectively. This AS-PCR method was validated in 10 accessions from each subtype and subsequently verified using Sanger sequencing. Subsequently, 30 Tulsi powder samples collected from the market were subjected to molecular identification by AS-PCR. The results showed that 80% of the samples were purple Tulsi, and only 3.5% were green Tulsi. About 10% of the samples were a mixture of both green and purple Tulsi. Two samples (6.5%) did not contain O. tenuiflorum and were identified as O. gratissimum.

CONCLUSION

The market samples of Tulsi were predominantly derived from purple Tulsi. The AS-PCR method will be helpful for quality control and market surveillance of Tulsi herbal powders.

HPLC and DNA barcoding profiles for identification of the selected twelve Mucuna species and its application for detecting prohibited aphrodisiac Mucuna products

Aphrodisiac herbal products originated from various plants including Mucuna species. In Thai folklore, Mucuna macrocarpa Wall. and M. pruriens (L.) DC. have long been consumed and utilized for their aphrodisiac properties. Consumption of these plants can lead to serious adverse effects caused by l-dopa. The plants have been legally banned for use as foods, dietary supplements, or nutraceuticals by the FDA of several countries. To protect consumers, methods for the identification of illicit plants or herbal products are needed. This study aimed to identify the selected twelve Mucuna species and examine the aphrodisiac herbal products containing M. macrocarpa and M. pruriens by using HPLC analysis of l-dopa coupled with DNA barcoding profiles of ITS, matK, rbcL, and trnH-psbA. The results showed that l-dopa could be found not only in the seeds of M. macrocarpa and M. pruriens but also in associated allied Mucuna species. Then, a DNA barcode was introduced to support in HPLC profiling to identify the plants. DNA barcodes of twelve Mucuna species found in Thailand were established and used to reconstruct a phylogenetic tree. In this study, ITS2 sequences showed the highest interspecific variability and could be used to differentiate all Mucuna species. The results of ITS2 sequence coupled with HPLC analysis revealed that all the purchased aphrodisiac products originated from M. pruriens only. Therefore, the integration of HPLC analysis and DNA barcoding profile was an efficient method for the identification of prohibited Mucuna species for safety monitoring of herbal supplements and protecting customer safety. Regulatory agencies should raise awareness and restrain the use of these commercial products.

Evaluating the in Vitro Efficacy of Quassinoids from Eurycoma longifolia and Eurycoma harmandiana against Common Cold Human Coronavirus OC43 and SARS-CoV-2 Using In-Cell Enzyme-Linked Immunosorbent Assay

Coronavirus disease-2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, has become a pandemic and public health crisis. SARS-CoV-2 and the seasonal common cold coronavirus (HCoV-OC43) belong to the beta genus of human coronaviruses (HCoVs). In-cell ELISA assays were performed using HCoV-OC43 and SARS-CoV-2 and evaluated the antiviral activity of herbal plants. Eurycoma longifolia (EL) and Eurycoma harmandiana (EH) roots (antipyretic properties) and their constituent quassinoids, especially chaparrinone and eurycomalactone, showed potent anti-HCoV-OC43 and SARS-CoV-2 activities, and the low IC₅₀ values of the mentioned constituents were observed in the range of 0.32-0.51 μM. Eurycomanone and 13β,21-dihydroeurycomanone may contribute to the antiviral activity of EL, whereas chaparrinone is the major and active antiviral constituent of EH root. The content of quassinoids, β-carboline, and canthin-6-one alkaloids and the cytotoxicity profile of EL and EH extracts were varied regarding extraction solvents. The boiled water and 50% EtOH extractions of both plants were less toxic than those with 95% EtOH as the extraction solvent. Our research suggests that quassinoids, which come from EL and EH roots and are anti-coronavirus compounds, are potential treatment candidates for COVID-19 and merit further in vivo investigations.

Development of a DNA barcode library of plants in the Thai Herbal Pharmacopoeia and Monographs for authentication of herbal products

Traditional herbal medicine has long been practiced as a method of health care in many countries worldwide. The usage of herbal products has been increasing and is expected to continue to do so in the future. However, admixture and adulteration are concerns regarding the quality of herbal medicine, including its safety and efficacy. We aimed to develop a reference DNA barcode library of plants listed in the Thai Herbal Pharmacopoeia (THP) and Monographs of Selected Thai Materia Medica (TMM) (n = 101 plant species) using four core barcode regions, namely, the ITS2, matK, rbcL and trnH-psbA intergenic spacer regions, for authentication of the plant origin of raw materials and herbal products. Checking sequences from samples obtained from local markets and the Thai Food and Drug Administration (Thai FDA) against our digital reference DNA barcode system revealed the authenticity of eighteen out of twenty tested samples as claimed on their labels. Two samples, no. 3 and 13, were not Cyanthillium cinereum (L.) H.Rob. and Pueraria candollei Wall. ex Benth. as claimed, respectively. They were recognized as Emilia sonchifolia (L.) DC. and Butea superba (Roxb.), respectively. Hence, it is important for the Thai FDA or regulatory agencies to immediately initiate strict enforcement for the development of pharmacopoeial standards as well as revisions or modifications of available regulatory guidelines and to implement close monitoring for the quality control of herbal products in terms of authentication before they enter the herbal market. The centralized digital reference DNA barcode database developed here could play a very important role in monitoring or checking the authenticity of medicinal plants.

Conventional and molecular pharmacognostic characters integrated with chemical profiles of five Piper plants in the Thai herbal pharmacopoeia and their admixture/adulteration/substitution situations in Thailand

The morphological and microscopy were combined with DNA-barcoding, together with rapid TLC for the characterization of Piper betle (PB), P. nigrum (PN), P. retrofractum (PR), P. sarmentosum (PS), and P. wallichii (PW), five medicinal Piper plants announced in the Thai Herbal Pharmacopoeia (THP). The authentic plants collected from various locations and voucher Piper products bought from commercial sites in Thailand were studied. The reproductive parts of authentic plants were subjected to ensure their morphological characters. Using sequencing analysis and genetic divergence for analyzing discriminatory performance, ITS2 was selected from eight candidate DNA markers to authenticate the origin of Piper crude drugs together with microscopic and TLC profiles for examining their characters, admixtures, adulterants, and substituents. PB and PR exhibited unique characters of the species, with no admixture, adulteration, and substitution. PN showed no variable characters of morphology and genetics. However, the microscopy could illustrate some commercial products of PN sold in Thailand have been adulterated with rice starch and roasted rice. In the herbal trade, PS has been sold in the form of mixed leaf, root, and stem more than the isolated part, but there is no variable character of the species. PW has shown more than one character of species explained by microscopic, chemical components, and genetic data. In conclusion, the conventional and molecular pharmacognostic data combined with chemical profile of authentic five Piper plants could be applied to indicate the plant origin and clarify the situations of admixture, adulteration, and substitution of the commercial Piper products launched in Thailand.

Anti-dermatophyte activity of the aqueous extracts of Thai medicinal plants

Medicinal plants have long been prescribed in Thailand for centuries. Different constituents of extracts have been used for treating of various infectious diseases. However, there is even less information available regarding the use in fungal skin infection. In order to assess traditional Thai claims about the therapeutic potential, this study is focused on exploring the anti-dermatophyte property of the plants that are currently used as traditional medicines. The potential of four different plant species were selected for investigate in vitro anti-dermatophyte activity. Ethanolic extracts of Chromolaena odorata (L.), Ageratina adenophora (Spreng.), Eclipta prostrate (Linn.), and Acorus calamus (L.). were analysed for their total phenolic content as well as total flavonoid content and were then subjected to test of their anti-dermatophyte properties using agar well diffusion method. Qualitative flavonoids and phenolics analysis of the extracts showed their biologically active constituents. Among the species examined, the result indicated that most of the extracts demonstrated anti-dermatophyte activity. In particular, A. calamus showed the highest efficacy against test organisms. The experiment confirmed the chemical constituents and efficacy of some selected plants and provides a scientific confirmation of the use of Thai plants in traditional medicine for fungal skin infections.

Differentiation of Mitragyna speciosa, a narcotic plant, from allied Mitragyna species using DNA barcoding-high-resolution melting (Bar-HRM) analysis

Mitragyna speciosa (Korth.) Havil. [MS], or “kratom” in Thai, is the only narcotic species among the four species of Mitragyna in Thailand, which also include Mitragyna diversifolia (Wall. ex G. Don) Havil. [MD], Mitragyna hirsuta Havil. [MH], and Mitragyna rotundifolia (Roxb.) O. Kuntze [MR]. M. speciosa is a tropical tree belonging to the Rubiaceae family and has been prohibited by law in Thailand. However, it has been extensively covered in national and international news, as its abuse has become more popular. M. speciosa is a narcotic plant and has been used as an opium substitute and traditionally used for the treatment of chronic pain and various illnesses. Due to morphological disparities in the genus, the identification of plants in various forms, including fresh leaves, dried leaf powder, and finished products, is difficult. In this study, DNA barcoding combined with high-resolution melting (Bar-HRM) analysis was performed to differentiate M. speciosa from allied Mitragyna and to assess the capability of Bar-HRM assays to identify M. speciosa in suspected kratom or M. speciosa-containing samples. Bar-HRM analysis of PCR amplicons was based on the ITS2, rbcL, trnH-psbA, and matK DNA barcode regions. The melting profiles of ITS2 amplicons were clearly distinct, which enabled the authentication and differentiation of Mitragyna species from allied species. This study reveals that DNA barcoding coupled with HRM is an efficient tool with which to identify M. speciosa and M. speciosa-containing samples and ensure the safety and quality of traditional Thai herbal medicines.

DNA metabarcoding to unravel plant species composition in selected herbal medicines on the National List of Essential Medicines (NLEM) of Thailand

Traditional medicines are widely traded across the globe and have received considerable attention in the recent past, with expectations of heightened demand in the future. However, there are increasing global concerns over admixture, which can affect the quality, safety, and efficacy of herbal medicinal products. In this study, we aimed to use DNA metabarcoding to identify 39 Thai herbal products on the Thai National List of Essential Medicines (NLEM) and assess species composition and admixture. Among the products, 24 samples were in-house-prepared formulations, and 15 samples were registered formulations. In our study, DNA metabarcoding analysis using ITS2 and rbcL barcode regions were employed to identify herbal ingredients mentioned in the products. The nuclear region, ITS2, was able to identify herbal ingredients in the products at the genus- and family-levels in 55% and 63% of cases, respectively. The chloroplast gene, rbcL, enabled genus- and family-level identifications in 58% and 73% of cases, respectively. In addition, plant species were detected in larger numbers (Family identified, absolute %) in registered herbal products than in in-house-prepared formulations. The level of fidelity increases concerns about the reliability of the products. This study highlights that DNA metabarcoding is a useful analytical tool when combined with advanced chemical techniques for the identification of plant species in highly processed, multi-ingredient herbal products.