Time-Dependent Induction of Hepatic Cytochrome P450 Enzyme Activity and mRNA Expression by Bilobalide in Rats

Application to Butterbur Products of a Suggested Daily Intake-Based Safety Evaluation of Individual Herbal Supplements with Cytochrome P450 Expression as a Major Index

The present paper first proposes a method for ensuring the safety of commercial herbal supplements, termed the suggested daily intake-based safety evaluation (SDI-based safety evaluation). This new method was inspired as a backward analog of the acceptable daily intake (ADI) derivation from the no observed adverse effect level (NOAEL), the basis of food additive risk analysis; namely, rats are dosed with individual herbal supplement products at the SDI for human use multiplied by 100 (the usual uncertainty factor value) per body weight for 8 d. The primary endpoint is the sign of adverse effects on liver, especially gene expression of cytochrome P450 (CYP) isoforms. The proposed method was then applied to three butterbur (Petasites hybridus) products without pyrrolizidine alkaloids but lacking clear safety information. Results showed that two oily products markedly enhanced the mRNA expression of CYP2B (>10-fold) and moderately enhanced that of CYP3A1 (<4-fold) with liver enlargement. These products also caused the renal accumulation of alpha 2-microglobulin. One powdery product showed no significant effect on liver and kidney. The large difference in effects of products was due to the difference in chemical composition revealed by liquid chromatography-mass spectroscopy. The oily and the powdery products required attention in terms of safety and effectiveness, respectively. Finally, the results from the SDI-based safety evaluation of butterbur and other herbal supplement products were grouped into four categories and cautionary notes were discussed. The SDI-based safety evaluation of their products by herbal supplement operators would contribute to safe and secure use by consumers.

Critical evaluation of causality assessment of herb-drug interactions in patients

The aim of this review was to assess the severity of adverse drug reactions (ADRs) due to herb-drug interactions (HDI) in patients taking herbs and prescribed medications based on published evidence. Electronic databases of PubMed, the Cochrane Library, Medline and Scopus were searched for randomized or nonrandomized clinical studies, case-control and case reports of HDI. The data were extracted and the causal relationship of ADRs as consequences of HDI assessed using Horn's drug interaction probability scale or Roussel Uclaf Causality Assessment Method scoring systems. The mechanism of interaction was ascertained using Stockley's herbal medicine interaction companion. Forty-nine case reports and two observational studies with 15 cases of ADRs were recorded. The majority of the patients were diagnosed with cardiovascular diseases (30.60%), cancer (22.45%) and renal transplants (16.32%) receiving mostly warfarin, alkylating agents and cyclosporine, respectively. HDI occurred in patients resulting in clinical ADRs with different severity. Patients may poorly respond to therapeutic agents or develop toxicity due to severe HDI, which in either scenario may increase the cost of treatment and/or lead to or prolong patient hospitalization. It is warranted to increase patient awareness of the potential interaction between herbs and prescribed medicines and their consequences to curb HDI as a potential health problem.

Induction of CYP3A by morroniside in rats

Morroniside is one of the most important iridoid glycosides in the herbal drug Cornus officinalis Sieb. et Zucc. The current study was designed to investigate the ex vivo and in vivo effects of morroniside on CYP3A activity in rats after treatment with morroniside for 7 days (at 10, 30, 90 mg/kg, i.g.). Morroniside was found to induce CYP3A. According to the ex vivo experiment, the activity of CYP3A was measured by the quantification of 1-hydroxymidazolam, which was the metabolite from CYP3A probe substrate, midazolam. The concentration of 1-hydroxymidazolam was determined by using a validated liquid chromatography coupled with tandem mass spectrometry detection (LC-MS/MS) method. The levels of messenger RNA (mRNA) and protein of CYP3A were determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting analysis, respectively. The pharmacokinetics of midazolam in rats after treatment with morroniside for 7 days (at 10, 30, 90 mg/kg, i.g.) were investigated in vivo. After treatment with morroniside, the activity, mRNA and protein expression of CYP3A were significantly induced and the absorbance and bioavailability of midazolam in rats were reduced. The results indicated that morroniside could induce the activity of CYP3A.

Induction of fatty liver by Coleus forskohlii extract through enhancement of de novo triglyceride synthesis in mice

Coleus forskohlii extract (CFE), an herbal ingredient, is used for weight-loss products. CFE's alleged efficacy is attributed to forskolin. However, CFE has been shown to induce fatty liver in mice, with components other than forskolin playing a part in this effect. The present study addressed the underlying mechanism of CFE-induced fatty liver by analyzing changes in CFE-treated mice of lipid concentrations and of the levels of mRNAs encoding enzymes and transcription factors known to be related to fatty liver. Mice were fed a diet containing 0, 0.3 and 1% CFE for 2 weeks. CFE at 1% clearly induced fatty liver, as demonstrated by histological examination and confirmed by increases in triglyceride concentrations in liver. However, treated mice did not exhibit elevation in plasma levels of non-esterified fatty acids. Comprehensive analysis of liver mRNA levels revealed accumulation of multiple transcripts, including mRNAs encoding enzymes acetyl-CoA carboxylase and long-chain elongase; transcription factor peroxisome proliferator-activated receptor gamma (PPARγ); and lipid-droplet-associated fat-specific protein 27 (Fsp27). These findings suggest that the de novo synthesis and accumulation of triglyceride in the liver, through the enhanced expression of specific lipogenic mRNAs, is a major underlying mechanism of fatty liver induction by CFE.

A potential drug-herbal interaction between Ginkgo biloba and efavirenz

Efavirenz (EFV) is primarily metabolized by cytochrome P450 (CYP) 2B6 and to a lesser extent by CYP3A4. Drugs that significantly inhibit or induce these enzymes would then be expected to increase or lower the levels of EFV potentially resulting in toxicity or therapeutic failure, respectively. The constituents of Ginkgo biloba extract have been demonstrated to induce gene expression of the CYP450 enzymes. We report a case in which a potential drug-herb interaction may have led to virological breakthrough in a patient that was maintained on the same regimen for 10 years. Therefore, a drug-herbal interaction may be expected when these agents are taken concurrently, and we advise clinicians to avoid this combination when possible.

Ginkgo biloba extract attenuates warfarin-mediated anticoagulation through induction of hepatic cytochrome P450 enzymes by bilobalide in mice

Ginkgo biloba extract (GBE) is a popular herbal ingredient used worldwide, but it is reported to induce bleeding as a serious adverse event. In this study we examined whether GBE induced spontaneous bleeding or accelerated warfarin anticoagulation via herb-drug interaction. Mice were given GBE or various active components of GBE orally for 5 days and blood coagulation parameters and hepatic cytochrome P450 enzymes (CYPs) were measured. Mice also received warfarin (racemate, (S)- or (R)-enantiomer) for the last 3 days of the 5-day regimen to examine GBE-warfarin interactions. Neither GBE (up to 1000 mg/kg) nor ginkgolide B (up to 140 mg/kg), a platelet-activating factor antagonist, influenced blood coagulation parameters. In contrast, GBE attenuated the anticoagulant action of warfarin. Bilobalide, a component of GBE that markedly induced hepatic CYPs including (S)-warfarin hydroxylase, showed similar effects. For (S)-warfarin, the anticoagulation action and the interaction with GBE was clear, while the influence on metabolism was greater for (R)-warfarin than for (S)-warfarin, which corresponded to the CYP types induced by GBE. These results suggest that GBE and ginkgolide B have no influence on blood coagulation in vivo, and that GBE attenuates the anticoagulation action of warfarin via induction of hepatic CYPs by bilobalide.

Coleus forskohlii extract induces hepatic cytochrome P450 enzymes in mice

Coleus forskohlii root extract (CFE) is popular for use as a weight loss dietary supplement. In this study, the influence of standardized CFE containing 10% active component forskolin on the hepatic drug metabolizing system was investigated to evaluate the safety through its drug interaction potential. Male ICR mice were fed AIN93G-based diets containing 0-5% CFE or 0.05% pure forskolin for 2-3 weeks. Intake of two different sources of 0.5% CFE significantly increased the relative liver weight, total content of hepatic cytochrome P450 (CYP) and induced CYPs (especially 2B, 2C, 3A types) and glutathione S-transferase (GST) activities. CFE significantly increased mRNA expression of CYPs and GST with dose related responses. However, unlike the CFE, intake of 0.05% pure forskolin was found to be associated with only weak induction in CYP3A and GST activities with no significant increases in relative liver weight, total hepatic content or other CYPs activities. The inductions of CYPs and GST by CFE were observed at 1 week of feeding and rapidly recovered by discontinuation of CFE. These results indicated the induction potential of CFE on CYPs, and that this effect was predominantly due to other, as yet unidentified constituents, and not forskolin contained in CFE.

Species-dependent and receptor-selective action of bilobalide on the function of constitutive androstane receptor and pregnane X receptor

Bilobalide is a naturally occurring sesquiterpene trilactone with therapeutic potential in the management of ischemia and neurodegenerative diseases such as Alzheimer's disease. In the present study, we investigated the effect of bilobalide on the activity of rat constitutive androstane receptor (rCAR) and rat pregnane X receptor (rPXR) and compared that with human CAR (hCAR) and human PXR (hPXR). Bilobalide activated rCAR in a luciferase reporter gene assay and increased rCAR target gene expression in cultured rat hepatocytes, as determined by the CYP2B1 mRNA and CYP2B enzyme activity (benzyloxyresorufin O-dealkylation) assays. This increase in hepatocyte CYP2B1 expression by bilobalide was not accompanied by a corresponding increase in rCAR mRNA level. In contrast to the activation of rCAR, the activity of rPXR, hCAR, and hPXR was not influenced by this chemical in cell-based reporter gene assays. Consistent with these results, bilobalide did not alter rPXR, hCAR, or hPXR target gene expression in rat or human hepatocytes, as evaluated by the CYP3A23, CYP2B6, CYP3A4 mRNA assays and the CYP3A (testosterone 6β-hydroxylation) and CYP2B6 (bupropion hydroxylation) enzyme activity assays. Bilobalide was not an antagonist of rPXR, hCAR, or hPXR, as suggested by the finding that it did not attenuate rPXR activation by pregnenolone 16α-carbonitrile, hCAR activation by 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime, or hPXR activation by rifampicin in reporter gene assays. In conclusion, bilobalide is an activator of rCAR, whereas it is not a ligand of rPXR, hCAR, or hPXR. Likewise, it is an inducer of rat CYP2B1, but not of rat CYP3A23, human CYP2B6, or human CYP3A4.