oa Editorial [Hot Topic: Absorption, Disposition, and Pharmacokinetics of Herbal Medicines: What and How? (Guest Editor: Chuan Li)]

Botanical products are gaining growing popularity and increasing use worldwide, but they are very diverse with regard to product nature. Some products are identical to medicines, while others come close to food. When a botanical product at a defined dosage can be proven to have a clear medicinal effect for a defined medicinal purpose and presented with a medicinal claim, the product should be regarded and registered as an herbal medicine [1]. Such medicinal botanical products are expected to meet comparable standards for synthetic drugs with respect to efficacy, safety, and pharmaceutical quality. For the herbal medicine, an important scientific question from pharmaceutical scientists deals with the absorption, disposition (including distribution, metabolism, and excretion), and pharmacokinetics (ADME/PK) of their bioactive constituents after dosing, which is critically important in identifying the medicinal principles responsible for the medicine’s therapeutic effects and in establishing the risk-benefit relationship [2-4]. The ADME/PK information is also crucial to establishment of a therapeutic regimen providing optimal efficacy with minimal toxicity for an herbal medicine. In this issue, we hope to illustrate the current state of ADME/PK science relating to herbal medicines and the associated phytochemicals. Unlike synthetic drugs, herbal medicines are complex chemical mixtures. The effect of an herbal therapy is not necessarily the result of a single mechanism induced by a single ingredient, but a range of activities of multiple compounds working together to produce a medicinal benefit. Accordingly, the ADME/PK study of an herbal medicine should involve elucidating the systemic exposure to the multiple herbal compounds from the administered medicine and understanding their fates in the body. The aim of study is to bridge the gap between the complex chemical composition of the herbal medicine and its medicinal effects. Recently, a methodology has been established to implement multi-compound ADME/PK studies of herbal medicines [5,6], which is referred to as “ADME/PK-bridged pharmacology-to-chemistry” methodology. The study is performed to identify, from a certain group of pharmacologically active constituents present in an herbal medicine, the compounds that have favorable PK properties and substantial, medicine dose-dependent systemic exposure levels after administration of the medicine. In this issue, Li et al. describes another methodology for performing multi-compound ADME/PK studies of herbal medicines [7], which is designated as “ADME/PK-bridged chemistry-to-pharmacology” methodology. These authors identified, from a broad range of chemical constituents present in a standardized extract of Ginkgo biloba leaves (GBE50 extract; including 72 terpene lactones, flavonoids, and carboxylic acids), the ginkgo compounds that could traverse the enterohepatic barrier after p.o. administration of the extract to rats, as well as the chemical forms in which the ginkgo compounds entered considerably the systemic circulation. In addition, they also revealed the relevant mechanisms governing the intestinal absorption and presystemic elimination for the tested ginkgo compounds. With such research information, pharmacological and toxicological scientists can be aware which herbal compounds are worth their testing. These multicompound studies provide guidance for further systematic investigation into chemical basis responsible for the in vivo biological effects produced by herbal medicines....