Herbal interactions involving cytochrome p450 enzymes: a mini review

Activation of CAR and PXR by Dietary, Environmental and Occupational Chemicals Alters Drug Metabolism, Intermediary Metabolism, and Cell Proliferation

The constitutive androstane receptor (CAR) and the pregnane × receptor (PXR) are activated by a variety of endogenous and exogenous ligands, such as steroid hormones, bile acids, pharmaceuticals, and environmental, dietary, and occupational chemicals. In turn, they induce phase I-III detoxification enzymes and transporters that help eliminate these chemicals. Because many of the chemicals that activate CAR and PXR are environmentally-relevant (dietary and anthropogenic), studies need to address whether these chemicals or mixtures of these chemicals may increase the susceptibility to adverse drug interactions. In addition, CAR and PXR are involved in hepatic proliferation, intermediary metabolism, and protection from cholestasis. Therefore, activation of CAR and PXR may have a wide variety of implications for personalized medicine through physiological effects on metabolism and cell proliferation; some beneficial and others adverse. Identifying the chemicals that activate these promiscuous nuclear receptors and understanding how these chemicals may act in concert will help us predict adverse drug reactions (ADRs), predict cholestasis and steatosis, and regulate intermediary metabolism. This review summarizes the available data on CAR and PXR, including the environmental chemicals that activate these receptors, the genes they control, and the physiological processes that are perturbed or depend on CAR and PXR action. This knowledge contributes to a foundation that will be necessary to discern interindividual differences in the downstream biological pathways regulated by these key nuclear receptors.

Bufalin inhibits CYP3A4 activity in vitro and in vivo

AIM

To investigate the inhibitory interactions of bufalin and CYP3A4.

METHODS

Recombinant human CYP3A4 was incubated with bufalin in vitro. Bufalin was administered ig and iv to Wistar rats to further estimate its impact on CYP3A4, and midazolam was given to index the activity of CYP3A4.

RESULTS

The IC(50) of bufalin was 14.52 micromol/L. Bufalin affected CYP3A4 activity with increases in AUC(0-t) and t(1/2), and decreases in CL and the formation of 1-hydroxy-midazolam after ig or iv administration of midazolam (P<0.05). An increase in C(max) after ig bufalin administration (P<0.05) was observed.

CONCLUSION

Bufalin showed a modest but significant inhibition of CYP3A4 both in vitro and in vivo. The likelihood of an interaction between bufalin and the CYP3A4-metabolized drugs in human might not be negated.

Aged garlic extract stimulates p-glycoprotein and multidrug resistance associated protein 2 mediated effluxes

The growing concomitant consumption of drugs and herbal preparations such as garlic, and the numerous reports about the influence of herbal preparations on intestinal transport, led us to evaluate the influence of aged garlic extract on the transport function and electrophysiological parameters of the small intestinal mucosa. Aged garlic extract induced increase of the absolute value of the transepithelial potential difference and of the short-circuit current in both permeability models tested (rat jejunum, Caco-2 cell monolayers) without affecting transepithelial electrical resistance. It also caused a significant increase of the P-glycoprotein and multidrug resistance associated protein 2 mediated effluxes through rat jejunum of marker substrates Rhodamine 123 and 2,4-dinitrophenyl-S-glutathione, respectively. Rhodamine 123 efflux through the Caco-2 cell monolayers was not altered by aged garlic extract, whereas the efflux of 2,4-dinitrophenyl-S-glutathione increased significantly. So altered activity of the important transport proteins could significantly change the pharmacokinetic properties of conventional medicines taken concomitantly with aged garlic extract.

Botanicals and herbs: a traditional approach to treating epilepsy

Botanicals and herbs have a centuries-old tradition of use by persons with epilepsy, in many cultures around the world. At present, herbal therapies are tried by patients in developing as well as developed countries for control of seizures or adverse effects from antiepileptic drugs (AEDs), or for general health maintenance, usually without the knowledge of physicians who prescribe their AEDs. Well-designed clinical trials of herbal therapies in patients with epilepsy are scarce, and methodological issues prevent any conclusions of their efficacy or safety in this population. Furthermore, some botanicals and herbs may be proconvulsant or may alter AED metabolism. In spite of these limitations, further preclinical evaluation of botanicals and herbs and their constituent compounds using validated scientific methods is warranted based on numerous anecdotal observations of clinical benefit in patients with epilepsy and published reports showing mechanisms of action relevant to epilepsy or anticonvulsant effects in animal models of epilepsy. This review highlights the use of herbal therapies for epilepsy, outlines the role of the U.S. Food and Drug Administration in regulating herbal products, and presents the author's approach to the scientific assessment of herbal therapies as potential therapies for patients with epilepsy.

Causality assessment in hepatotoxicity by drugs and dietary supplements

Structured causality assessment of hepatotoxicity by drugs and dietary supplements (DDS) is a major clinical challenge, since temporal associations as the sole criteria for a valid evaluation are not acceptable. Initially, a clear intuition for an ad hoc evaluation is necessary, but only provisional, and must be followed by a diagnostic algorithm using a pretest, main test and post test. The evaluation is based on a variety of items such as latency period, course of alanine aminotransferase and alkaline phosphatase after DDS discontinuation, risk factors, co-medication, previous information on hepatotoxicity of the DDS, response to rechallenge, and exclusion of other diseases. It is essential that practising and hospital physicians as well as other key health professionals, such as pharmacists, gather all information required for a sound causality assessment, obviating major discussions by expert panels, manufacturers and health agencies in face of scanty and fragmentary data. Because pharmacogenetic alterations may trigger metabolic hepatotoxicity by a few DDS, levels in plasma and urine should be measured and may be helpful for diagnosis. Concomitant genotyping of cytochrome P450 and other enzymes may also be useful in future to minimize the risk of unwanted side-effects, including toxic liver disease elicited by DDS.

Influence of fruit juices on drug disposition: discrepancies between in vitro and clinical studies

BACKGROUND

Grapefruit juice is known to alter the pharmacokinetics of over 30 prescription drugs by increasing their bioavailabilities. After the discovery of this interaction almost 20 years ago, there have been many reports investigating the effects of fruit juices on drug disposition.

OBJECTIVE

This article reviews the literature on fruit juice-prescription drug interaction studies to determine which juices are likely to cause clinically significant interactions.

METHODS

We examined the results from in vitro and clinical studies regarding the interactions between prescription drugs and over ten fruit beverages.

RESULTS/CONCLUSIONS

Grapefruit juice and Seville orange juice caused several clinically significant interactions with cytochrome P4503A (CYP3A). The OATP drug transporter was inhibited by grapefruit juice, orange juice, and apple juice. Other fruit juices also interacted with drug metabolizing enzymes and transporters in vitro, but more studies are needed to determine whether these interactions are clinically significant.

Clinical assessment of CYP2D6-mediated herb-drug interactions in humans: effects of milk thistle, black cohosh, goldenseal, kava kava, St. John's wort, and Echinacea

Cytochrome P450 2D6 (CYP2D6), an important CYP isoform with regard to drug-drug interactions, accounts for the metabolism of approximately 30% of all medications. To date, few studies have assessed the effects of botanical supplementation on human CYP2D6 activity in vivo. Six botanical extracts were evaluated in three separate studies (two extracts per study), each incorporating 16 healthy volunteers (eight females). Subjects were randomized to receive a standardized botanical extract for 14 days on separate occasions. A 30-day washout period was interposed between each supplementation phase. In study 1, subjects received milk thistle (Silybum marianum) and black cohosh (Cimicifuga racemosa). In study 2, kava kava (Piper methysticum) and goldenseal (Hydrastis canadensis) extracts were administered, and in study 3 subjects received St. John's wort (Hypericum perforatum) and Echinacea (Echinacea purpurea). The CYP2D6 substrate, debrisoquine (5 mg), was administered before and at the end of supplementation. Pre- and post-supplementation phenotypic trait measurements were determined for CYP2D6 using 8-h debrisoquine urinary recovery ratios (DURR). Comparisons of pre- and post-supplementation DURR revealed significant inhibition (approximately 50%) of CYP2D6 activity for goldenseal, but not for the other extracts. Accordingly, adverse herb-drug interactions may result with concomitant ingestion of goldenseal supplements and drugs that are CYP2D6 substrates.

Screening of active ingredients of herbal medicine for interaction with CYP450 3A4

A two-step algorithm is adopted in the screening of herbal species which possess significant inhibitory effects on cytochrome P450 3A4 (CYP450 3A4). The algorithm comprises an initial stage of high throughput screening with Herbochip for the identification of herbal fractions that exhibit interactions with CYP450 3A4. Fifty commonly used TCM species were screened with seven showing a positive signal reflecting interaction. In the inhibition assays that followed, six of the seven species gave a signal. Sophora flavescens stood out as it gave the highest number of wells with a response, the highest maximum index was 0.96, and the median index was 0.55. The selection of TCM species with inhibitory effects on CYP450 carries the potential role of its use to boost the effects of known therapeutic agents, a mechanism that has been exploited in the design of regimens for the treatment of HIV infection.

Personalizing protein-drug interactions

The development of new drugs today is a hugely expensive process, with estimated costs of up to $1 billion to take a drug through to market. However, despite this seemingly massive expenditure, statistics show that the great majority of prescription drugs on the market today are only effective for around 40 % of the patients to whom they are administered. Worse still, recently there have been a series of high-profile instances where potentially block-busting FDA-approved drugs have subsequently been withdrawn due to unanticipated side effects that were only revealed when the drug entered use in the general population. A variety of factors are at play in underpinning such statistics, but at the heart of the problem is the fact that, despite the extensive knowledge being generated in the postgenomic era about the genetic differences between individuals, Western medicine still today largely ignores such differences. The hope therefore is that by gaining a greater understanding of the individual nature of disease progression and of drug response, we might move toward a new era of personalized medicine in which the right drug is prescribed at the right dose to treat the precise disease afflicting the specific patient. As a step along this road, this review will discuss new approaches in the pharmacogenomics field to understanding in a quantitative manner the molecular consequence of polymorphic variation and mutation, both on encoded protein function and on protein-drug interactions.

CYP201A2, a cytochrome P450 from Rhodopseudomonas palustris, plays a key role in the biodegradation of tributyl phosphate

Tributyl phosphate (TBP) is a toxic organophosphorous compound widely used in nuclear fuel processing and chemical industries. Rhodopseudomonas palustris, one of the most metabolically versatile photosynthetic bacteria, is shown here to degrade TBP efficiently under photosynthetic conditions. This study shows that this O(2)- and NADPH/FMNH(2)-dependent process was also catalyzed when TBP was incubated with membrane-associated proteins extracted from this strain. The effects of several regulators of cytochrome P450 activity on the TBP consumption suggest a key role for a cytochrome P450 in this process. Disruption of the rpa0241 gene encoding a putative cytochrome P450 led to a 60% decrease of the TBP catabolism, whereas reintroducing the gene in the mutant restored the wild-type phenotype. The rpa0241 gene was expressed and purified in Escherichia coli. Characterization by UV-visible spectroscopy of the purified recombinant membrane-bound protein (CYP201A2) encoded by the rpa0241 gene revealed typical spectral characteristics of cytochrome P450 with a large spin state change of the heme iron associated with binding of TBP (K (d) approximately 65 microM). It is proposed that CYP201A2 catalyzes the initial step of the biodegradation process of TBP.

Strong synergistic induction of CYP1A1 expression by andrographolide plus typical CYP1A inducers in mouse hepatocytes

The effects of andrographolide, the major diterpenoid constituent of Andrographis paniculata, on the expression of cytochrome P450 superfamily 1 members, including CYP1A1, CYP1A2, and CYP1B1, as well as on aryl hydrocarbon receptor (AhR) expression in primary cultures of mouse hepatocytes were investigated in comparison with the effects of typical CYP1A inducers, including benz[a]anthracene, beta-naphthoflavone, and 2,3,7,8-tetrachlorodibenzo-p-dioxin. Andrographolide significantly induced the expression of CYP1A1 and CYP1A2 mRNAs in a concentration-dependent manner, as did the typical CYP1A inducers, but did not induce that of CYP1B1 or AhR. Interestingly, andrographolide plus the typical CYP1A inducers synergistically induced CYP1A1 expression, and the synergism was blocked by an AhR antagonist, resveratrol. The CYP1A1 enzyme activity showed a similar pattern of induction. This is the first report that shows that andrographolide has a potency to induce CYP1A1 enzyme and indicates that andrographolide could be a very useful compound for investigating the regulatory mechanism of the CYP1A1 induction pathway. In addition, our findings suggest preparing advice for rational administration of A. paniculata, according to its ability to induce CYP1A1 expression.

Supplementation With Goldenseal (Hydrastis canadensis), but not Kava Kava (Piper methysticum), Inhibits Human CYP3A Activity In Vivo

The effects of goldenseal (Hydrastis canadensis) and kava kava (Piper methysticum) supplementation on human CYP3A activity were evaluated using midazolam (MDZ) as a phenotypic probe. Sixteen healthy volunteers were randomly assigned to receive either goldenseal or kava kava for 14 days. Each supplementation phase was followed by a 30-day washout period. MDZ (8 mg, per os) was administered before and after each phase, and pharmacokinetic parameters were determined using standard non-compartmental methods. Comparisons of pre- and post-supplementation MDZ pharmacokinetic parameters revealed significant inhibition of CYP3A by goldenseal (AUC(0-infinity), 107.9+/-43.3 vs 175.3+/-74.8 ng x h/ml; Cl/F/kg, 1.26+/-0.59 vs 0.81+/-0.45 l/h/kg; T(1/2), 2.01+/-0.42 vs 3.15+/-1.12 h; Cmax, 50.6+/-26.9 vs 71.2+/-50.5 ng/ml). MDZ disposition was not affected by kava kava supplementation. These findings suggest that significant herb-drug interactions may result from the concomitant ingestion of goldenseal and CYP3A substrates.

The in vitro drug interaction potential of dietary supplements containing multiple herbal components

Herbal-based remedies are widely used as alternative treatments for a number of ailments. In addition, the use of products that contain both single and multiple herbal constituents is becoming increasingly common. The work described in this report examined the in vitro drug interaction potential for a commonly used herbal cold remedy reported to contain a mixture of eight herbal components. Experiments conducted in human liver microsomes exhibited significant inhibition (<10% of control activity remaining) of multiple cytochrome P450 (P450) isoforms, including CYP2B6, CYP2C9, and CYP2D6, by the herbal mixture. In an attempt to explain the observed P450 inhibition by the herbal mixture, individual active components were obtained and tested for inhibitory potency. Inhibition of multiple P450 activities by a single constituent, luteolin, was observed. Conversely, inhibition of a single isoform by several herbal components was noted for CYP2B6. Based on the data presented, it is concluded that mixtures of herbal components may exhibit multiple modes of P450 inhibition, indicating the potential for complex herbal-drug interaction scenarios to occur.

Primer on integrative oncology

At the present time, there is no obvious answer for many of these design difficulties. This problem will continue to constrain ability to determine the efficacy of integrative medical techniques for patients who have cancer. Patients, however, will continue to gravitate toward alternative treatments, especially when standard cancer treatments fail. Therefore oncologists must be aware of alternative medical agents and techniques, and be able to guide their patients, rather than simply being dismissive.

Complementary and alternative therapies for the management of dyslipidemia

OBJECTIVE

To review the literature on select alternative therapies for the management of dyslipidemia.

DATA SOURCES

Searches of MEDLINE and PubMed (1965-March 2006) were conducted using the key terms omega-3-fatty acids, policosanol, plant stanols and sterols, flaxseed, red yeast rice, guggulipid, garlic, fiber, almonds, and cholesterol and/or lipids.

STUDY SELECTION AND DATA EXTRACTION

Meta-analyses, published in English and involving adults, that incorporated randomized, controlled trials on alternative therapies for dyslipidemia were reviewed. Additionally, trials published subsequent to the meta-analyses were reviewed. Articles deemed relevant were included in this review.

DATA SYNTHESIS

Of the aforementioned alternative therapies, randomized controlled trials were found for omega-3-fatty acids, policosanol, plant stanols and sterols, flaxseed, red yeast rice, guggulipid, garlic, fiber, almonds, and soy. Studies for each of these agents report varying degrees of lipid reduction. Based on published data, effective therapeutic options for lipid-lowering include intake of fiber, intake of plant stanols/sterols, replacement of animal protein with soy protein, and substitution of foods high in saturated fat with those with monounsaturated fatty acids (eg, dry roasted almonds). Adding omega-3-fatty acids is effective for reducing triglycerides in patients with hypertriglyceridemia. Well-designed studies with long-term outcome data are necessary to further define the role for guggul, red yeast rice, policosanol, garlic, and flaxseed in the management of dyslipidemia.

CONCLUSIONS

Alternative therapeutic approaches with complementary therapies are becoming increasingly popular among patients. It is important for healthcare providers to be familiar with the safety and efficacy of these agents to facilitate optimal outcomes for patients with dyslipidemia.

Herb‐Drug Interactions in Oncology: Focus on Mechanisms of Induction

An increasing number of cancer patients are using complementary and alternative medicines (CAM) in combination with their conventional chemotherapeutic treatment. Considering the narrow therapeutic window of oncolytic drugs, this CAM use increases the risk of clinically relevant herb-anticancer drug interactions. Such a relevant interaction is that of St. John's wort with the anticancer drugs irinotecan and imatinib. It is, however, estimated that CAM-anticancer drug interactions are responsible for substantially more unexpected toxicities of chemotherapeutic drugs and possible undertreatment seen in cancer patients. Induction of drug-metabolizing enzymes and ATP-binding cassette drug transporters can be one of the mechanisms behind CAM-anticancer drug interactions. Induction will often lead to therapeutic failure because of lower plasma levels of the anticancer drugs, and will easily go unrecognized in cancer treatment, where therapeutic failure is common. Recently identified nuclear receptors, such as the pregnane X receptor, the constitutive androstane receptor, and the vitamin D-binding receptor, play an important role in the induction of metabolizing enzymes and drug transporters. This knowledge has already been an aid in the identification of some CAM probably capable of causing interactions with anticancer drugs: kava-kava, vitamin E, quercetin, ginseng, garlic, beta-carotene, and echinacea. Evidently, more research is necessary to prevent therapeutic failure and toxicity in cancer patients and to establish guidelines for CAM use.

Drug transporters in pharmacokinetics

This review deals with the drug transporters allowing drugs to enter and leave cells by carrier-mediated pathways. Emphasis is put on liver transporters but systems in gut, kidney, and blood-brain barrier are mentioned as well. Drug-drug interactions on carriers may provoke significant modification in pharmacokinetics as do carrier gene polymorphisms yielding functional carrier protein mutations. An integrated phase concept should reflect the interplay between drug metabolism and drug transport.