The systematic separation strategy has long and widely been applied in the research and development of herbal medicines. However, the pharmacological effects of many bioactive constituents are much weaker than those of the corresponding herbal extracts. Thus, there is a consensus that purer herbal extracts are sometimes less effective. Pharmacological loss of purified constituents is closely associated with their significantly reduced intestinal absorption after oral administration. In this review, pharmacokinetic synergies among constituents in herbal extracts during intestinal absorption were systematically summarized to broaden the general understanding of the pharmaceutical nature of herbal medicines. Briefly, some coexisting constituents including plant-produced primary and secondary metabolites, promote the intestinal absorption of active constituents by improving solubility, inhibiting first-pass elimination mediated by drug-metabolizing enzymes or drug transporters, increasing the membrane permeability of enterocytes, and reversibly opening the paracellular tight junction between enterocytes. Moreover, some coexisting constituents change the forms of bioactive constituents via mechanisms including the formation of natural nanoparticles. This review will focus on explaining this new synergistic mechanism. Thus, herbal extracts can be considered mixtures of bioactive compounds and pharmacokinetic synergists. This review may provide ideas and strategies for further research and development of herbal medicines.

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Jatrorrhizine, a protoberberine alkaloid derived from Coptis chinensis, is currently under investigation as a natural gastric prokinetic drug candidate. In vitro and in vivo studies were conducted to characterize its pharmacokinetics and metabolism. After intravenous administration, the plasma concentration kinetics and major metabolites in rats were investigated. The metabolic kinetics, key cytochrome P450 enzymes and UDP-glucuronosyltransferase isoforms (UGTs) of jatrorrhizine were studied in rat liver microsomes (RLMs). After intravenous administration, plasma jatrorrhizine concentrations showed a biphasic decline, dose-independent clearance and half-life of terminal elimination phase, and a relatively large distribution volume. The metabolic pathway for the conversion of jatrorrhizine was important for its elimination. In addition, the demethylated and glucuronidated products were found to be the major metabolites in rats. The enzyme kinetics for both demethylation and glucuronidation were fitted to the hyperbolic Michaelis-Menten equation in RLMs. CYP3A1/2 and CYP2D2 were mainly responsible for demethylation, and UGT 1A1 and 1A3 were responsible for glucuronidation in RLMs. The metabolic properties of jatrorrhizine suggest multiple metabolic pathways. These results will contribute to promote further research and development of jatrorrhizine.

Traditional Chinese medicine (TCM) has a long history of medical use in China and is still used worldwide. Unexpected herb-drug interactions (HDIs) may lead to adverse drug reactions or loss of therapeutic efficacy of the victim drug. Here, based on searches of Medline, EBSCO, Science Direct and Web of Science using various keywords, we summarize the TCM-derived pharmacokinetic HDIs that were reported from 1990 to 2015 and discuss the underlying mechanisms. In general, many pre-clinical and clinical pharmacokinetic HDIs have been reported. Our searches show that TCMs cause pharmacokinetic interactions with therapeutic drugs mainly by inhibiting or inducing drug-metabolizing enzymes and transporters. However, most of the interactions result from a small number of prescription medications and the actual potential for harm is low. Moreover, such HDIs can be avoided by discontinuing the TCMs. Despite the extensive number of reports on TCM-derived HDIs, the findings are frequently conflicting and can be confusing. The causes of the conflicts vary, but we classified them into three basic categories as follows: (1) complicated nature and poor quality control of TCMs, (2) different responses of various test systems to TCM exposure and (3) diverse study designs. Accordingly, we propose rational study designs for future HDI research. We also propose that a specific authoritative guide be established that provides recommendations for HDI studies. This review provides insights into the progress and challenges in TCM-derived pharmacokinetic HDI research.

Pharmacological activities of some natural products diminish and even disappear after purification. In this study, we explored the mechanisms underlying the decrease of acute oral toxicity of Coptidis Rhizoma extract after purification. The water solubility, in vitro absorption, and plasma exposure of berberine (the major active compound) in the Coptidis Rhizoma extract were much better than those of pure berberine. Scanning electron microscopy, laser scanning confocal microscopy (LSCM), and dynamic light scattering experiments confirmed that nanoparticles attached to very fine precipitates existed in the aqueous extract solution. The LSCM experiment showed that the precipitates were absorbed with the particles by the mouse intestine. High-speed centrifugation of the extract could not remove the nanoparticles and did not influence plasma exposure or acute oral toxicity. However, after extract dilution, the attached precipitates vanished, although the nanoparticles were preserved, and there were no differences in the acute oral toxicity and plasma exposure between the extract and pure berberine. The nanoparticles were then purified and identified as proteinaceous. Furthermore, they could absorb co-dissolved berberine. Our results indicate that naturally occurring proteinaceous nanoparticles in Coptidis Rhizoma extract act as concentration-dependent carriers that facilitate berberine absorption. These findings should inspire related studies in other natural products.