Horsetail (Equisetum arvense) is an herbal remedy that dates back to ancient Roman and Greek times. It was used traditionally to stop bleeding, heal ulcers and wounds, and treat tuberculosis and kidney problems. Horsetail contains silicon, which helps strengthen bone. For that reason, some practitioners recommend horsetail as a treatment for osteoporosis. It is also used as a diuretic, and as an ingredient in some cosmetics. However, few studies have actually investigated horsetail's effect in humans. It also contains traces of nicotine and is therefore not recommended for children.
The global herbal products market has grown in recent years, making regulation of these products paramount for public healthcare. For instance, the common horsetail (Equisetum arvense L.) is used in numerous herbal products, but it can be adulterated with closely related species, especially E. palustre L. that can produce toxic alkaloids. As morphology-based identification is often difficult or impossible, the identification of processed material can be aided by molecular techniques.
Researchers from Denmark have therefore explored two molecular identification techniques as methods of testing the purity of these products: a Thin Layer Chromatography approach (TLC-test) included in the European Pharmacopoeia and DNA Barcoding:
We found that each method has advantages and disadvantages, but the TLC-test is the most efficient way of confirming that material in herbal products is indeed E. arvense. On the other hand, the DNA barcoding can be used as a complementary test to determine the identity of adulterant species, particularly E. palustre.
Future work can focus on systematically studying which Equisetum species produce toxic alkaloids, which will assist the quality control of E. arvense herbal products. Further, a chemical method that directly tests for the presence of alkaloids in herbal products can circumvent problems in species identification, directly testing for the quality and appropriateness for human consumption of herbal products. Additionally, the steadily dropping price of next generation sequencing techniques – which massively amplify short DNA fragments – may considerably enhance the success rates of DNA barcoding in degraded or processed material. Finally, given the presence of several putative hybrids between E. arvense and other Equisetum species, further techniques can be applied to investigate the presence of hybrid material in herbal products.