DNA fingerprints, chromatographic patterns and bioactivities of “Rang Chuet”

Thunbergia laurifolia Lindl., a member of the Acanthaceae family, is commonly known in Thai as “Rang Chuet”. The “Rang Chuet” herbal drugs have been widely used in Thai traditional medicine for the treatment of poisoning caused by toxic substances such as insecticides, ethyl alcohol, and metals. However, the confusion of the herbal drugs has arisen from the homonymity and close appearances of materials with different botanical origins. T. laurifolia, the most known species, has been substituted with other plant materials including Curcuma sp., Rinorea sp., and Crotalaria spectabilis. Therefore, authentication of specific “Rang Chuet” herbal drugs is necessary to ensure the authenticity and efficacy. TLC chemical characterization combined with molecular techniques including RAPD and PCR-RFLP offers highly reliable identification procedures. T. laurifolia was successfully differentiated from its related species based on the characteristic flavonoids and phenolic compounds. Variation sites in the matK gene of the species can be recognized by the restriction enzymes, DdeI and HaeIII. Two other species of herbaceous Thunbergia, T. grandiflora and T. erecta, were also included in the RAPD analysis. Out of 80 screened RAPD primers, nine primers gave clear and reproducible patterns with a total 70 polymorphic bands. Additionally, an HPLC system was developed for the determination of rosmarinic acid, a potent antioxidant, which represents a suitable biochemical marker for T. laurifolia. The established method has potential application at the commercial level for assessing the quality of T. laurifolia. Since “Rang Chuet” herbal drugs from different plant origins differ in their antioxidant activities, the use of “Rang Chuet” herbs should be done with care.