The Influence of St. John's Wort on CYP2C19 Activity with Respect to Genotype

Hypericum perforatum: a comprehensive review on pharmacognosy, preclinical studies, putative molecular mechanism, and clinical studies in neurodegenerative diseases

The herb Hypericum perforatum, also referred to as St. John's wort, has drawn a lot of interest because of its potential therapeutic benefits in treating neurodegenerative illnesses. Due to the absence of effective therapies, illnesses like Alzheimer's and Parkinson's disease pose an increasing worldwide health concern. Because of its wide variety of phytochemicals, especially hyperforin, and hypericin, Hypericum perforatum is well known for its neuroprotective properties. These substances have proven to be able to affect different cellular processes linked to neurodegeneration. They can act as anti-inflammatory, antioxidant, and neurotransmitter system regulators, which may help halt neurodegenerative illnesses' progression. The use of Hypericum perforatum extracts and its contents has shown encouraging results in research on animal models of neurodegenerative disorders. These advantages include higher nerve cell survival, lowered oxidative stress, and higher cognitive performance. Underscoring its versatile potential to combat neurodegeneration, Hypericum perforatum has neuroprotective mechanisms that modulate neuroinflammation and prevent apoptotic pathways. In conclusion, Hypericum perforatum shows tremendous promise as a potential treatment for neurological illnesses due to its wide variety of phytochemicals. To completely comprehend its specific mechanisms of action and turn these discoveries into efficient clinical therapies, additional research is needed. Investigating Hypericum perforatum's function in neurodegenerative disorders may present new opportunities for the advancement of ground-breaking therapeutic strategies.

Inhibition and induction of CYP enzymes in humans: an update

The cytochrome P450 (CYP) enzyme family is the most important enzyme system catalyzing the phase 1 metabolism of pharmaceuticals and other xenobiotics such as herbal remedies and toxic compounds in the environment. The inhibition and induction of CYPs are major mechanisms causing pharmacokinetic drug–drug interactions. This review presents a comprehensive update on the inhibitors and inducers of the specific CYP enzymes in humans. The focus is on the more recent human in vitro and in vivo findings since the publication of our previous review on this topic in 2008. In addition to the general presentation of inhibitory drugs and inducers of human CYP enzymes by drugs, herbal remedies, and toxic compounds, an in-depth view on tyrosine-kinase inhibitors and antiretroviral HIV medications as victims and perpetrators of drug–drug interactions is provided as examples of the current trends in the field. Also, a concise overview of the mechanisms of CYP induction is presented to aid the understanding of the induction phenomena.

Pharmacokinetic Interactions between Herbal Medicines and Drugs: Their Mechanisms and Clinical Relevance

The therapeutic efficacy of a drug or its unexpected unwanted side effects may depend on the concurrent use of a medicinal plant. In particular, constituents in the medicinal plant extracts may influence drug bioavailability, metabolism and half-life, leading to drug toxicity or failure to obtain a therapeutic response. This narrative review focuses on clinical studies improving knowledge on the ability of selected herbal medicines to influence the pharmacokinetics of co-administered drugs. Moreover, in vitro studies are useful to anticipate potential herbal medicine-drug interactions. In particular, they help to elucidate the cellular target (metabolic or transporter protein) and the mechanism (induction or inhibition) by which a single constituent of the herbal medicine acts. The authors highlight the difficulties in predicting herbal–drug interactions from in vitro data where high concentrations of extracts or their constituents are used and pharmacokinetics are missed. Moreover, the difficulty to compare results from human studies where different kinds of herbal extracts are used is discussed. The herbal medicines discussed are among the best sellers and they are reported in the “Herbal Medicines for Human Use” section of the European Medicinal Agency (EMA).

Upregulation of cGMP-dependent Protein Kinase (PRKG1) in the Development of Adolescent Idiopathic Scoliosis

Objective

To explore the molecular regulatory mechanisms underlying fibroblast differentiation and dysfunction in the development of adolescent idiopathic scoliosis (AIS) in an effort to identify candidate therapeutic targets for AIS.

Methods

The GSE110359 dataset, obtained from the bone marrow stromal cells of 12 AIS patients and five healthy controls, was retrieved from the GEO database. The data were preprocessed and differentially expressed genes (DEGs) were identified. KEGG pathway and Gene Ontology (GO)‐Biological Process (BP) enrichment analyses were performed to identify the function of the DEGs. A protein–protein interaction (PPI) and a microRNA‐transcription factor (TF)‐target co‐regulatory network were constructed to identify hub genes in the development of AIS. In addition, hub DEGs were evaluated by quantitative PCR (qPCR) and immunohistochemical staining.

Results

A total of 188 DEGs including 100 up‐regulated and 88 down‐regulated genes were obtained. The up‐regulated DEGs were related to “p53 signaling pathway”, “FoxO signaling pathway”, and “cGMP‐PKG signaling pathway” terms, while the down‐regulated DEGs were significantly enriched in seven terms including “protein processing in endoplasmic reticulum”. The key up‐regulated genes, PRKG1, CCNG2, and KAT2B, and the key down‐regulated genes, MAP2K1 and DUSP6, were identified by the PPI and miRNA‐TF‐Target regulatory network analyses. mRNA expression patterns for PRKG1, DUSP6, and KAT2B were successfully verified by qPCR. In addition, PRKG1 protein levels were found to be elevated during the immunohistochemical analysis.

Conclusion

Increased expression of PRKG1 in AIS patients might be an attractive therapeutic target for AIS. However, further gain or loss‐of‐function studies should be conducted.

No Clinically Relevant Interactions of St. John's Wort Extract Ze 117 Low in Hyperforin With Cytochrome P450 Enzymes and P-glycoprotein

Hypericum perforatum L. (St. John's wort) is used to treat mild-to-moderate depression. Its potential safety risks are pharmacokinetic drug interactions via cytochrome P450 (CYP) enzymes and P-glycoprotein, presumably caused by hyperforin. In a phase I, open-label, nonrandomized, single-sequence study, the low-hyperforin Hypericum extract Ze 117 was investigated using a drug cocktail in 20 healthy volunteers. No pharmacokinetic interactions of Ze 117 were observed for CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP3A4, and P-glycoprotein. Area under the curve (AUC) and peak plasma concentration (C_max ) of the used probe drugs showed 90% confidence intervals (CIs) of the geometric mean ratios of the drugs taken together with Ze 117 vs. probe drug alone, well within the predefined bioequivalence range of 80-125%. Though Ze 117 did not induce dextromethorphan metabolism by CYP2D6, it weakly increased dextromethorphan AUC ratio (mean 147.99, 95% CI 126.32-173.39) but not the corresponding metabolic ratio. Ze 117 does not show clinically relevant pharmacokinetic interactions with important CYPs and P-glycoprotein.

A regulatory science viewpoint on botanical-drug interactions

There is a continued predisposition of concurrent use of drugs and botanical products. Consumers often self-administer botanical products without informing their health care providers. The perceived safety of botanical products with lack of knowledge of the interaction potential poses a challenge for providers and both efficacy and safety concerns for patients. Botanical–drug combinations can produce untoward effects when botanical constituents modulate drug metabolizing enzymes and/or transporters impacting the systemic or tissue exposure of concomitant drugs. Examples of pertinent scientific literature evaluating the interaction potential of commonly used botanicals in the US are discussed. Current methodologies that can be applied to advance our efforts in predicting drug interaction liability is presented. This review also highlights the regulatory science viewpoint on botanical–drug interactions and labeling implications.

Understanding drug interactions with St John's wort (Hypericum perforatum L.): impact of hyperforin content

Objective

The aim of this study was to review herb–drug interaction studies with St John's wort (Hypericum perforatum L.) with a focus on the hyperforin content of the extracts used in these studies.

Methods

PUBMED was systematically searched to identify studies describing pharmacokinetic interactions involving St John's wort. Data on study design and the St John's wort extract or product were gathered to extract hyperforin content and daily dose used in interaction studies.

Key findings

This analysis demonstrates that significant herb–drug interactions (resulting in a substantial change in systemic exposure) with St John's wort products were associated with hyperforin daily dosage. Products that had a daily dose of <1 mg hyperforin were less likely to be associated with major interaction for drugs that were CYP3A4 or p-glycoprotein substrates. Although a risk of interactions cannot be excluded even for low-dose hyperforin St. John's wort extracts, the use of products that result in a dose of not more than 1 mg hyperforin per day is recommended to minimise the risk of interactions.

Conclusions

This review highlights that the significance of herb–drug interactions with St John's wort is influenced by the nature of the herbal medicines product, particularly the hyperforin content.

Hepatotoxicity of Herbal Supplements Mediated by Modulation of Cytochrome P450

Herbal supplements are a significant source of drug-drug interactions (DDIs), herb-drug interactions, and hepatotoxicity. Cytochrome P450 (CYP450) enzymes metabolize a large number of FDA-approved pharmaceuticals and herbal supplements. This metabolism of pharmaceuticals and supplements can be augmented by concomitant use of either pharmaceuticals or supplements. The xenobiotic receptors constitutive androstane receptor (CAR) and the pregnane X receptor (PXR) can respond to xenobiotics by increasing the expression of a large number of genes that are involved in the metabolism of xenobiotics, including CYP450s. Conversely, but not exclusively, many xenobiotics can inhibit the activity of CYP450s. Induction of the expression or inhibition of the activity of CYP450s can result in DDIs and toxicity. Currently, the United States (US) Food and Drug Administration does not require the investigation of the interactions of herbal supplements and CYP450s. This review provides a summary of herbal supplements that inhibit CYP450s, induce the expression of CYP450s, and/or whose toxicity is mediated by CYP450s.

Adverse Effects of Nutraceuticals and Dietary Supplements

Over 70% of Americans take some form of dietary supplement every day, and the supplement industry is currently big business, with a gross of over $28 billion. However, unlike either foods or drugs, supplements do not need to be registered or approved by the US Food and Drug Administration (FDA) prior to production or sales. Under the Dietary Supplement Health and Education Act of 1994, the FDA is restricted to adverse report monitoring postmarketing. Despite widespread consumption, there is limited evidence of health benefits related to nutraceutical or supplement use in well-nourished adults. In contrast, a small number of these products have the potential to produce significant toxicity. In addition, patients often do not disclose supplement use to their physicians. Therefore, the risk of adverse drug-supplement interactions is significant. An overview of the major supplement and nutraceutical classes is presented here, together with known toxic effects and the potential for drug interactions.

Therapeutic Risk and Benefits of Concomitantly Using Herbal Medicines and Conventional Medicines: From the Perspectives of Evidence Based on Randomized Controlled Trials and Clinical Risk Management

Despite increased awareness of the potential of herb-drug interactions (HDIs), the lack of rigorous clinical evidence regarding the significance provides a challenge for clinicians and consumers to make rational decisions about the safe combination of herbal and conventional medicines. This review addressed HDIs based on evidence from randomized controlled trials (RCTs). Literature was identified by performing a PubMed search till January 2017. Risk description and clinical risk management were described. Among 74 finally included RCTs, 17 RCTs (22.97%) simply addressed pharmacodynamic HDIs. Fifty-seven RCTs (77.03%) investigated pharmacokinetic HDIs and twenty-eight of them showed potential or actual clinical relevance. The extent of an HDI may be associated with the factors such as pharmacogenomics, dose of active ingredients in herbs, time course of interaction, characteristics of the object drugs (e.g., administration routes and pharmacokinetic profiles), modification of herbal prescription compositions, and coexistence of inducers and inhibitors. Clinical professionals should enhance risk management on HDIs such as increasing awareness of potential changes in therapeutic risk and benefits, inquiring patients about all currently used conventional medicines and herbal medicines and supplements, automatically detecting highly substantial significant HDI by computerized reminder system, selecting the alternatives, adjusting dose, reviewing the appropriateness of physician orders, educating patients to monitor for drug-interaction symptoms, and paying attention to follow-up visit and consultation.

Hypericum perforatum (St John's wort) beyond depression: A therapeutic perspective for pain conditions

ETHNOPHARMACOLOGICAL RELEVANCE

Hypericum perforatum L. (Hypericaceae), popularly called St. John's wort (SJW), has a rich historical background being one of the oldest used and most extensively investigated medicinal herbs. Many bioactivities and applications of SJW are listed in popular and in scientific literature, including antibacterial, antiviral, anti-inflammatory. In the last three decades many studies focused on the antidepressant activity of SJW extracts. However, several studies in recent years also described the antinociceptive and analgesic properties of SJW that validate the traditional uses of the plant in pain conditions.

AIM OF THE REVIEW

This review provides up-to-date information on the traditional uses, pre-clinical and clinical evidence on the pain relieving activity of SJW and its active ingredients, and focuses on the possible exploitation of this plant for the management of pain.

MATERIALS AND METHODS

Historical ethnobotanical publications from 1597 were reviewed for finding local and traditional uses. The relevant data on the preclinical and clinical effects of SJW were searched using various databases such as PubMed, Science Direct, Scopus, and Google Scholar. Plant taxonomy was validated by the database Plantlist.org.

RESULTS

Preclinical animal studies demonstrated the ability of low doses of SJW dry extracts (0.3% hypericins; 3-5% hyperforins) to induce antinociception, to relieve from acute and chronic hyperalgesic states and to augment opioid analgesia. Clinical studies (homeopathic remedies, dry extracts) highlighted dental pain conditions as a promising SJW application. In vivo and in vitro studies showed that the main components responsible for the pain relieving activity are hyperforin and hypericin. SJW analgesia appears at low doses (5-100mg/kg), minimizing the risk of herbal-drug interactions produced by hyperforin, a potent inducer of CYP enzymes.

CONCLUSION

Preclinical studies indicate a potential use of SJW in medical pain management. However, clinical research in this field is still scarce and the few studies available on chronic pain produced negative results. Prospective randomized controlled clinical trials performed at low doses are needed to validate its potential efficacy in humans.

Neuroprotective Activity of Hypericum perforatum and Its Major Components

Hypericum perforatum is a perennial plant, with worldwide distribution, commonly known as St. John's wort. It has been used for centuries in traditional medicine for the treatment of several disorders, such as minor burns, anxiety, and mild to moderate depression. In the past years, its antidepressant properties have been extensively studied. Despite that, other H. perforatum biological activities, as its neuroprotective properties have also been evaluated. The present review aims to provide a comprehensive summary of the main biologically active compounds of H. perforatum, as for its chemistry, pharmacological activities, drug interactions and adverse reactions and gather scattered information about its neuroprotective abilities. As for this, it has been demonstrated that H. perforatum extracts and several of its major molecular components have the ability to protect against toxic insults, either directly, through neuroprotective mechanisms, or indirectly, through is antioxidant properties. H. perforatum has therefore the potential to become an effective neuroprotective therapeutic agent, despite further studies that need to be carried out.

Effects of Hypericum perforatum extract and its main bioactive compounds on the cytotoxicity and expression of CYP1A2 and CYP2D6 in hepatic cells

AIMS

Hypericum perforatum (H. perforatum) is one of the most used medicinal plants. However, it has been associated with relevant interactions with several drugs. This situation is probably mediated by cytochrome P450 enzymes (CYP450), namely the 1A2 (CYP1A2) and 2D6 (CYP2D6) isoforms This study aims to assess the cytotoxic and CYP1A2 and CYP2D6 inductive and/or inhibitory effects of a H. perforatum extract and its main bioactive components in hepatic cell lines.

MAIN METHODS

A MTT proliferation assay was performed in WRL-68, HepG2 and HepaRG cells after exposition to different concentrations of H. perforatum extract, hypericin and hyperforin for 24 and 72 h. Then, a real-time PCR analysis was accomplished after incubating the cells with these products evaluating the relative CYP1A2 and CYP2D6 expression.

KEY FINDINGS

These products have relevant cytotoxicity at a 10 μM concentration and it was also demonstrated for the first time that H. perforatum can lead to a significant CYP1A2 and CYP2D6 induction in all cell lines. Moreover, hypericin seems to induce CYP1A2 in HepG2 cells and to inhibit its expression in HepaRG cells while hyperforin induced CYP1A2 in HepG2 and in WRL-68 cells. Additionally, hypericin and hyperforin induce CYP2D6 in HepG2 cells but inhibits its expression in HepaRG and in WRL-68 cells.

SIGNIFICANCE

This study not only evidenced that H. perforatum extract and two of its bioactive components can have toxic effects in hepatic cell lines but also emphasized the potential risk of the consumption of H. perforatum with CYP1A2- and CYP2D6-metabolized drugs.

Medicinal herbs and therapeutic drugs interactions

People mistakenly think that all herbs are safe, because of the fact that they are natural, and the use of herbal medication is growing. Aspects of the efficacy, safety, and quality of herbal or natural products are the subjects of on-going debates. Concurrent administration of herbs may interfere with the effect of drugs. Lack of knowledge of the interaction potential together with an underreporting of herbal use poses a challenge for health care providers and a safety concern for patients. A good understanding of the mechanisms of herb-drug interactions is also essential for assessing and minimizing clinical risks. Examples of herbal medicine-pharmaceutical drug interactions of commonly used herbs are presented. The potential pharmacokinetic and pharmacodynamic basis of such interactions is discussed, as well as the challenges associated with the identification and prediction of herb-drug interactions.

Pharmacogenomics and herb-drug interactions: merge of future and tradition

The worldwide using of herb products and the increasing potential herb-drug interaction issue has raised enthusiasm on discovering the underlying mechanisms. Previous review indicated that the interactions may be mediated by metabolism enzymes and transporters in pharmacokinetic pathways. On the other hand, an increasing number of studies found that genetic variations showed some influence on herb-drug interaction effects whereas these genetic factors did not draw much attention in history. We highlight that pharmacogenomics may involve the pharmacokinetic or pharmacodynamic pathways to affect herb-drug interaction. We are here to make an updated review focused on some common herb-drug interactions in association with genetic variations, with the aim to help safe use of herbal medicines in different individuals in the clinic.

In Vitro Evaluation of Reversible and Time-Dependent Inhibitory Effects of Kalanchoe crenata on CYP2C19 and CYP3A4 Activities

Kalanchoe crenata popularly known as "dog's liver" is used in most African countries for the treatment of chronic diseases such as diabetes, asthma and HIV/AIDS related infections. The evaluation of K. crenata for herb-drug interactions has not been reported. This study therefore aims to evaluate the risk of K. crenata for herb-drug interaction in vitro. Crude methanol and fractions of K. crenata were incubated and preincubated with recombinant human CYP2C19 and CYP3A4. Comparative studies were conducted in both human liver microsomes and recombinant human CYP to ascertain the inhibition profile of the crude extract and the various fractions. The cocktail approach of recombinant human CYPs was conducted to confirm the inhibition potential of the fractions in the presence of other CYPs. The results showed significant time-dependent inhibition of tested samples on CYP3A4 with crude methanol (39KC), fractions 45A, 45B and 45D given IC50 fold decrease of 3.29, 2.26, 1.91 and 1.49, respective. Time dependent kinetic assessment of 39KC and 45D showed KI and kinact values for 39KC as 1.77 µg/mL and 0.091 min(-1) while that of 45D were 6.45 µg/mL and 0.024 min(-1), respectively. Determination of kinact based on IC50 calculations yielded 0.015 and 0.04 min(-1) for 39KC and 45D, respectively. Cocktail approach exhibited fold decreases in IC50 for all test fractions on CYP3A4 within the ranges of 2.10 - 4.10. At least one phytoconstituent in the crude methanol extract of Kalanchoe crenata is a reversible and time-dependent inhibitor of CYP3A4.

A randomized controlled trial of adjunctive Bunchang Naoxintong Capsule (步长脑心通胶囊) versus maintenance dose clopidogrel in patients with CYP2C19*2 polymorphism

OBJECTIVE

To determine the impact of adjunctive Buchang Naoxintong Capsule (, NXT) on dual antiplatelet therapy in patients with cytochrome P450 2C19*2 (CYP2C19*2) polymorphism undergoing percutaneous coronary intervention (PCI).

METHODS

Ninety patients with CYP2C19*2 polymorphism were enrolled, and their genotypes were confirmed by polymerase chain reaction (PCR). The patients were randomly assigned to receive either adjunctive NXT (triple group, 45 cases) or dual antiplatelet therapy (dual group, 45 cases) using a computer-generated randomization sequence and sealed envelopes. Platelet function was assessed at baseline and 7 days after treatment with conventional aggregometry. Subsequent major adverse cardiovascular events (MACE, including sudden cardiac arrest and acute coronary syndrome) were recorded during a 12-month follow-up.

RESULTS

Baseline platelet function measurements were similar in both groups. After 7 days, percent inhibitions of maximum platelet aggregation and late platelet aggregation were significantly greater in the triple versus dual group (42.3%±16.0% vs. 20.8%±15.2%, P<0.01, and 54.7%±18.3% vs. 21.5%±29.2%, P<0.01, respectively). During the 12-month follow-up, the rate of subsequent MACE (6/45) was significantly lower in the triple group compared with the dual group (14/45; P<0.05).

CONCLUSION

Adjunctive NXT to maintenance dose clopidogrel (75 g) could enhance the antiplatelet effect and decrease subsequent MACE in patients with the CYP2C19*2 polymorphism undergoing PCI.

The effect of induction of CYP3A4 by St John's wort on ambrisentan plasma pharmacokinetics in volunteers of known CYP2C19 genotype

To evaluate the impact of CYP2C19 polymorphisms on ambrisentan exposure and to assess its modification by St. John's wort (SJW), 20 healthy volunteers (10 CYP2C19 extensive, four poor and six ultrarapid metabolizers) received therapeutic doses of ambrisentan (5 mg qd po) for 20 days and concomitantly SJW (300 mg tid po) for the last 10 days. To quantify changes of CYP3A4 activity, midazolam (3 mg po) as a probe drug was used. Ambrisentan pharmacokinetics was assessed on days 1, 10 and 20, and midazolam pharmacokinetics before and on days 1, 10, 17 and 20. At steady state, ambrisentan exposure was similar in extensive and ultrarapid metabolizers but 43% larger in poor metabolizers (p < 0.01). In all volunteers, SJW reduced ambrisentan exposure and the relative change (17-26%) was similar in all genotype groups. The extent of this interaction did not correlate with the changes in CYP3A activity (midazolam clearance) (rs = 0.23, p = 0.34). Ambrisentan had no effect on midazolam pharmacokinetics. In conclusion, SJW significantly reduced exposure with ambrisentan irrespective of the CYP2C19 genotype. The extent of this interaction was small and thus likely without clinical relevance.

Hypericum perforatum: pharmacokinetic, mechanism of action, tolerability, and clinical drug-drug interactions

Hypericum perforatum (HP) belongs to the Hypericaceae family and is one of the oldest used and most extensively investigated medicinal herbs. The medicinal form comprises the leaves and flowering tops of which the primary ingredients of interest are naphthodianthrones, xanthones, flavonoids, phloroglucinols (e.g. hyperforin), and hypericin. Although several constituents elicit pharmacological effects that are consistent with HP's antidepressant activity, no single mechanism of action underlying these effects has thus far been found. Various clinical trials have shown that HP has a comparable antidepressant efficacy as some currently used antidepressant drugs in the treatment of mild/moderate depression. Interestingly, low-hyperforin-content preparations are effective in the treatment of depression. Moreover, HP is also used to treat certain forms of anxiety. However, HP can induce various cytochrome P450s isozymes and/or P-glycoprotein, of which many drugs are substrates and which are the main origin of HP-drug interactions. Here, we analyse the existing evidence describing the clinical consequence of HP-drug interactions. Although some of the reported interactions are based on findings from in vitro studies, the clinical importance of which remain to be demonstrated, others are based on case reports where causality can, in some cases, be determined to reveal clinically significant interactions that suggest caution, consideration, and disclosure of potential interactions prior to informed use of HP.

Efavirenz-mediated induction of omeprazole metabolism is CYP2C19 genotype dependent

Efavirenz increases CYP2C19- and CYP3A-mediated omeprazole metabolism. We hypothesized that CYP2C19 and CYP2B6 genetic polymorphisms influence the extent of induction of omeprazole metabolism by efavirenz. Healthy subjects (n=57) were administered a single 20mg oral dose of omeprazole with a single dose (600mg) or after multiple doses (600mg/day for 17 days) of efavirenz. DNA was genotyped for CYP2C19*2, *3 and *17 alleles and CYP2B6*6, *4 and *9 alleles using Taqman assays. Omeprazole, its enantiomers and metabolites were measured by LC/MS/MS. Our results showed that efavirenz increased omeprazole clearances in all CYP2C19 genotypes in non-stereoselective manner, but the magnitude of induction was genotype-dependent. Metabolic ratios of 5-hydroxylation of omeprazole were reduced in extensive and intermediate metabolizers of CYP2C19 (p<0.05). No significant associations were observed between CYP2B6 genotypes and induction by efavirenz on omeprazole metabolism. Our data indicate how interplays between drug interactions and CYP2C19 genetic variations may influence systemic exposure of CYP2C19 substrates.

Interactions between herbs and conventional drugs: overview of the clinical data

This article provides an overview of the clinical evidence of interactions between herbal and conventional medicines. Herbs involved in drug interactions--or that have been evaluated in pharmacokinetic trials--are discussed in this review. While many of the interactions reported are of limited clinical significance and many herbal products (e.g. black cohosh, saw palmetto, echinacea, hawthorn and valerian) seem to expose patients to minor risk under conventional pharmacotherapy, a few herbs, notably St. John's wort, may provoke adverse events sufficiently serious to endanger the patients' health. Healthcare professionals should remain vigilant for potential interactions between herbal medicines and prescribed drugs, especially when drugs with a narrow therapeutic index are used.

Antiepileptic drug interactions - principles and clinical implications

Antiepileptic drugs (AEDs) are widely used as long-term adjunctive therapy or as monotherapy in epilepsy and other indications and consist of a group of drugs that are highly susceptible to drug interactions. The purpose of the present review is to focus upon clinically relevant interactions where AEDs are involved and especially on pharmacokinetic interactions. The older AEDs are susceptible to cause induction (carbamazepine, phenobarbital, phenytoin, primidone) or inhibition (valproic acid), resulting in a decrease or increase, respectively, in the serum concentration of other AEDs, as well as other drug classes (anticoagulants, oral contraceptives, antidepressants, antipsychotics, antimicrobal drugs, antineoplastic drugs, and immunosupressants). Conversely, the serum concentrations of AEDs may be increased by enzyme inhibitors among antidepressants and antipsychotics, antimicrobal drugs (as macrolides or isoniazid) and decreased by other mechanisms as induction, reduced absorption or excretion (as oral contraceptives, cimetidine, probenicid and antacides). Pharmacokinetic interactions involving newer AEDs include the enzyme inhibitors felbamate, rufinamide, and stiripentol and the inducers oxcarbazepine and topiramate. Lamotrigine is affected by these drugs, older AEDs and other drug classes as oral contraceptives. Individual AED interactions may be divided into three levels depending on the clinical consequences of alterations in serum concentrations. This approach may point to interactions of specific importance, although it should be implemented with caution, as it is not meant to oversimplify fact matters. Level 1 involves serious clinical consequences, and the combination should be avoided. Level 2 usually implies cautiousness and possible dosage adjustments, as the combination may not be possible to avoid. Level 3 refers to interactions where dosage adjustments are usually not necessary. Updated knowledge regarding drug interactions is important to predict the potential for harmful or lacking effects involving AEDs.

Drug interaction between St John's wort and zolpidem in healthy subjects

WHAT IS KNOWN AND OBJECTIVE

St John's wort (SJW, Hypericum perforatum) is one of the most commonly used herbal antidepressants for treatment of mild to moderate depression. SJW enhances CYP3A4 activity and alters the pharmacokinetics of CYP3A4 substrates. This study investigated the effect of SJW on the pharmacokinetics of zolpidem in healthy subjects.

METHODS

A controlled, open-label, non-randomized, fixed-dose schedule design was used. Fourteen healthy male subjects received a single 10 mg oral dose of zolpidem followed by SJW administration (300 mg orally, three times a day) for 14 days; the last dose of SJW was coadministered with a single dose of zolpidem. Blood samples were obtained over a 24-h period after zolpidem administration. Pharmacokinetic data for zolpidem alone and in combination with SJW were analysed by high-performance liquid chromatography.

RESULTS

After repeated administration of SJW, the mean values of AUC and C(max) for zolpidem significantly decreased (380.3 ± 181.4 vs. 265.4 ± 134.2 ng h/mL, P = 0.001; 83.1 ± 30.1 vs. 55.1 ± 24.8 ng/mL, P = 0.000 respectively) and the mean value of CL/F for zolpidem significantly increased (38.4 ± 31.5 vs. 56.9 ± 57.2 mL/min, P = 0.040). However, in three subjects, the AUC showed a small increase after SJW treatment.

WHAT IS NEW AND CONCLUSION

The effect of SJW on the pharmacokinetics of zolpidem has not previously been reported. Repeated administration of SJW decreases the plasma concentration of zolpidem, probably by enhancing CYP3A4 activity. Given the wide inter-subject variability observed, for personalized medicine, advice on the use of the combination should be individualized, based on the circumstances of the patient.

Drug-botanical interactions: a review of the laboratory, animal, and human data for 8 common botanicals

Many Americans use complementary and alternative medicine (CAM) to prevent or alleviate common illnesses, and these medicines are commonly used by individuals with cancer.These medicines or botanicals share the same metabolic and transport proteins, including cytochrome P450 enzymes (CYP), glucuronosyltransferases (UGTs), and P-glycoprotein (Pgp), with over-the-counter and prescription medicines increasing the likelihood of drug-botanical interactions.This review provides a brief description of the different proteins, such as CYPs, UGTs, and Pgp.The potential effects of drug-botanical interactions on the pharmacokinetics and pharmacodynamics of the drug or botanical and a summary of the more common models used to study drug metabolism are described.The remaining portion of this review summarizes the data extracted from several laboratory, animal, and clinical studies that describe the metabolism, transport, and potential interactions of 8 selected botanicals. The 8 botanicals include black cohosh, Echinacea, garlic, Gingko biloba, green tea, kava, milk thistle, and St John's wort; these botanicals are among some of the more common botanicals taken by individuals with cancer.These examples are included to demonstrate how to interpret the different studies and how to use these data to predict the likelihood of a clinically significant drug-botanical interaction.

Herb-drug interactions with St John's wort (Hypericum perforatum): an update on clinical observations

St John's wort (SJW) extracts, prepared from the aerial parts of Hypericum perforatum, contain numerous pharmacologically active ingredients, including naphthodianthrones (e.g., hypericin and its derivatives), phloroglucinols derivatives (e.g., hyperforin, which inhibits the reuptake of a number of neurotransmitters, including serotonin), and flavonoids. Such extracts are widely used for the treatment of mild-to-moderate depression. As a monotherapy, SJW has an encouraging safety profile. However, relevant and, in some case, life-threatening interactions have been reported, particularly with drugs which are substrate of cytochrome P450 and/or P-glycoprotein. Well-documented SJW interactions include (1) reduced blood cyclosporin concentration, as suggested by multiple case reports as well as by clinical trials, (2) serotonin syndrome or lethargy when SJW was given with serotonin reuptake inhibitors, (3) unwanted pregnancies in women while using oral contraceptives and SJW, and (4) reduced plasma drug concentration of antiretroviral (e.g., indinavir, nevirapine) and anticancer (i.e., irinotecan, imatinib) drugs. Hyperforin, which is believed to contribute to the antidepressant action of St John's wort, is also strongly suspected to be responsible of most of the described interactions.

The transcriptional regulation of the human CYP2C genes

In humans, four members of the CYP2C subfamily (CYP2C8, CYP2C9, CYP2C18, and CYP2C19) metabolize more than 20% of all therapeutic drugs as well as a number of endogenous compounds. The CYP2C enzymes are found predominantly in the liver, where they comprise approximately 20% of the total cytochrome P450. A variety of xenobiotics such as phenobarbital, rifampicin, and hyperforin have been shown to induce the transcriptional expression of CYP2C genes in primary human hepatocytes and to increase the metabolism of CYP2C substrates in vivo in man. This induction can result in drug-drug interactions, drug tolerance, and therapeutic failure. Several drug-activated nuclear receptors including CAR, PXR, VDR, and GR recognize drug responsive elements within the 5' flanking promoter region of CYP2C genes to mediate the transcriptional upregulation of these genes in response to xenobiotics and steroids. Other nuclear receptors and transcriptional factors including HNF4alpha, HNF3gamma, C/EBPalpha and more recently RORs, have been reported to regulate the constitutive expression of CYP2C genes in liver. The maximum transcriptional induction of CYP2C genes appears to be achieved through a coordinative cross-talk between drug responsive nuclear receptors, hepatic factors, and coactivators. The transcriptional regulatory mechanisms of the expression of CYP2C genes in extrahepatic tissues has received less study, but these may be altered by perturbations from pathological conditions such as ischemia as well as some of the receptors mentioned above.

Trade herbal products and induction of CYP2C19 and CYP2E1 in cultured human hepatocytes

The aim of this study was to evaluate in vitro the dose-dependent induction potential of six commonly used trade herbal products on CYP2C19 and CYP2E1 metabolic activities in cultured human hepatocytes. S-mephenytoin and chlorzoxazone were used as specific CYP substrates, respectively, and rifampicin was used as a positive induction control for both enzymes. The hepatocytes were exposed to herbal extracts in increasing and biological relevant concentrations for 72 hrs and CYP substrate metabolites were quantified by validated HPLC methodologies. The major findings were that St John's wort was the most potent CYP-modulating herb, showing a dose-dependent induction/inhibition of both CYP2C19 and CYP2E1, with induction at low dosages and inhibition at higher. Ginkgo biloba showed an induction/inhibition profile towards CYP2C19 which was similar but weaker than that observed for St John's wort. If cooperative mechanisms are involved is still an open question. Common sage induced CYP2C19 in a log-linear dose-dependent manner with increasing concentrations. Common valerian was a weak inducer of CYP2C19, while horse chestnut and cone flower were characterized as non-inducers of CYP2C19. Only St John's wort showed an inductive effect towards CYP2E1. In addition to St John's wort, Gingko biloba and common sage should be considered as possible candidates for clinically relevant drug-herb interactions with selected CYP2C19 substrates.

The CYP2C19 ultra-rapid metabolizer genotype influences the pharmacokinetics of voriconazole in healthy male volunteers

AIM

To study the pharmacokinetic characteristics of voriconazole in healthy Chinese male volunteers in relation to cytochrome P450 (CYP) 2C19 genotype status, including ultra-rapid metabolizers (URMs), homozygous extensive metabolizers (EMs), and poor metabolizers (PMs).

METHOD

Twenty healthy Chinese male volunteers were recruited for the study. Of these, four were CYP2C19 heterozygous URMs (*1/*17), eight were CYP2C19 homozygous EMs (*1/*1), and eight were CYP2C19 PMs (*2/*2). After a single oral dose of 200 mg voriconazole, plasma concentrations of voriconazole were determined for a 24-h period by liquid chromatography-mass spectrometry/mass spectrometry.

RESULT

In Chinese male subjects, the allele frequencies of the CYP2C19*17 and CYP2C19*2 alleles were 0.64 and 35.6%, respectively, and both alleles were in Hardy-Weinberg equilibrium. The area under the concentration-time curve (AUC) from predose to 24 h (AUC(0-24)) and from predose to infinity (AUC(0-infinity)), and apparent oral clearance (CL/F) of voriconazole were statistically different among all three genotypic groups (P < 0.001, respectively). The maximum plasma concentration (C(max)) value of URMs also showed statistically significant differences from those of EMs and PMs (P = 0.036 and P = 0.035, respectively). The elimination half-life (t(1/2)) in URMs was 87% (P = 0.58) of that in EMs and 51% (P= 0.002) of that in PMs.

CONCLUSION

Our data indicate that the presence of the CYP2C19*17 allele results in ultra-rapid metabolism of voriconazole after a single oral dose.

Inhibition and induction of human cytochrome P450 enzymes: current status

Variability of drug metabolism, especially that of the most important phase I enzymes or cytochrome P450 (CYP) enzymes, is an important complicating factor in many areas of pharmacology and toxicology, in drug development, preclinical toxicity studies, clinical trials, drug therapy, environmental exposures and risk assessment. These frequently enormous consequences in mind, predictive and pre-emptying measures have been a top priority in both pharmacology and toxicology. This means the development of predictive in vitro approaches. The sound prediction is always based on the firm background of basic research on the phenomena of inhibition and induction and their underlying mechanisms; consequently the description of these aspects is the purpose of this review. We cover both inhibition and induction of CYP enzymes, always keeping in mind the basic mechanisms on which to build predictive and preventive in vitro approaches. Just because validation is an essential part of any in vitro-in vivo extrapolation scenario, we cover also necessary in vivo research and findings in order to provide a proper view to justify in vitro approaches and observations.

A composite screening tool for medication reviews of outpatients: general issues with specific examples

Regular performance of medication reviews is prominent among methods that have been advocated to reduce the extent and seriousness of drug-related problems, such as adverse drug reactions, drug-disease interactions, drug-drug interactions, drug ineffectiveness and cost ineffectiveness. Several screening tools have been developed to guide practising healthcare professionals and researchers in reviewing the medication patterns of elderly patients; however, each of these tools has its own limitations. This review discusses a wide range of general prescription-, treatment- and patient-related issues that should be taken into account when reviewing medication patterns by implicit screening. These include generic and therapeutic substitution; potentially superfluous or inappropriate medications; potentially inappropriate dosages or duration of treatment; drug-disease and drug-drug interactions; under-treatment; making use of laboratory test results; patient adherence, experiences and habits; appropriate dosage forms and packaging. A broad selection of specific examples and references that can be used as a basis for explicit screening of medication patterns in outpatients is also offered.

Induction of cytochrome P450: assessment in an immortalized human hepatocyte cell line (Fa2N4) using a novel higher throughput cocktail assay

Over recent years the application of cocktail studies to measure biological markers has become increasingly popular. The current study investigated a novel approach in assessing cytochrome P450 (P450) enzyme induction in an immortalized cell line using a cocktail of five P450 substrate probes compared with the traditional single-probe approach. The findings reported herein support use of a cocktail approach to assess the induction of the major P450s, namely, CYP3A4, CYP1A2, and CYP2C9. CYP2C19 and CYP2D6 could also be followed as part of the cocktail approach reported. Response to prototypical inducers did not differ to those observed in the presence of the specific probes alone. Consequently, this approach requires significantly fewer sample numbers if screening the induction potential of more than one P450. Moreover, these studies highlight the utility of the immortalized cell line Fa2N4 as a robust model system for induction studies. In conclusion, the current experimental setup is an improvement on current approaches used to assess P450 induction, significantly increasing sample throughput.

Evidence-based drug–herbal interactions

Due to the growing use of herbals and other dietary supplements healthcare providers and consumers need to know whether problems might arise from using these preparations in combination with conventional drugs. However, the evidence of interactions between natural products and drugs is based on known or suspected pharmacologic activity, data derived from in vitro or animal studies, or isolated case reports that frequently lack pertinent information. The usefulness of such information is questionable. More recently an increasing number of documented case reports, in vivo studies, and clinical trials have evaluated herbal-drug interactions. Results have sometimes been contradictory and more research is needed. Since there is a lack of rigorous studies that can establish the clinical significance of herb-drug interactions, an evidence-based evaluation of the current literature concerning commonly used herbal-drug interactions, as well as other dietary supplements, was conducted.

Effect of the St. John's wort constituent hyperforin on docetaxel metabolism by human hepatocyte cultures

BACKGROUND AND PURPOSE

St. John's wort is a commonly used herbal medication that increases cytochrome P450 3A (CYP3A) activity. Because docetaxel is inactivated by CYP3A, we studied the effects of the St. John's wort constituent hyperforin on docetaxel metabolism in a human hepatocyte model.

EXPERIMENTAL DESIGN

Hepatocytes, isolated from three donor livers, were exposed to hyperforin (0.1, 0.5, or 1.5 micromol/L) or rifampin (10 micromol/L) for 48 hours. After 48 hours, hyperforin- or rifampin-containing medium was replaced with medium containing 100 micromol/L docetaxel. After 1 hour, docetaxel metabolism was characterized by liquid chromatography-tandem mass spectrometry. Subsequent incubations characterized the specific cytochrome P450s that produced the docetaxel metabolites observed in hepatocyte incubations.

RESULTS

Rifampin induced docetaxel metabolism 6.8- to 32-fold above docetaxel metabolism in control cultures. Hyperforin induced docetaxel metabolism in all three hepatocyte preparations. Hyperforin induction was dose-dependent and, at maximum, was 2.6- to 7-fold greater than that in controls. Docetaxel metabolites identified in rifampin- and hyperforin-treated hepatocyte preparations included the previously described tert-butyl-hydroxylated metabolite and two previously unidentified metabolites involving hydroxylation on the baccatin ring. CYP3A4 produced the tert-butyl-hydroxylated metabolite and the two ring-hydroxylated metabolites. CYP2C8 produced one of the newly described ring-hydroxylated metabolites.

CONCLUSIONS

Exposure to the St. John's wort constituent hyperforin induces docetaxel metabolism in vitro. This implies that subtherapeutic docetaxel concentrations may result when docetaxel is administered to patients using St. John's wort on a chronic basis. The results also show induction of previously undescribed metabolic pathways for docetaxel, one of which may be analogous to the known 6-alpha-hydroxylation of paclitaxel by CYP2C8.

Molecular mechanisms of toxicity of important food-borne phytotoxins

At present, there is an increasing interest for plant ingredients and their use in drugs, for teas, or in food supplements. The present review describes the nature and mechanism of action of the phytochemicals presently receiving increased attention in the field of food toxicology. This relates to compounds including aristolochic acids, pyrrolizidine alkaloids, beta-carotene, coumarin, the alkenylbenzenes safrole, methyleugenol and estragole, ephedrine alkaloids and synephrine, kavalactones, anisatin, St. John's wort ingredients, cyanogenic glycosides, solanine and chaconine, thujone, and glycyrrhizinic acid. It can be concluded that several of these phytotoxins cause concern, because of their bioactivation to reactive alkylating intermediates that are able to react with cellular macromolecules causing cellular toxicity, and, upon their reaction with DNA, genotoxicity resulting in tumors. Another group of the phytotoxins presented is active without the requirement for bioactivation and, in most cases, these compounds appear to act as neurotoxins interacting with one of the neurotransmitter systems. Altogether, the examples presented illustrate that natural does not equal safe and that in modern society adverse health effects, upon either acute or chronic exposure to phytochemicals, can occur as a result of use of plant- or herb-based foods, teas, or other extracts.

Safety and Potential of Drug Interactions of Caspofungin and Voriconazole in Multimorbid Patients

Due to their broad antimycotic spectrum and the relatively low rate of side effects, the two antifungals caspofungin and voriconazole are considered as attractive therapeutic alternatives to amphotericin B. However, treatment of severe mycotic infections in patients taking co-medication is associated with the risk of severe adverse drug interactions. The risk of such interactions is increased if voriconazole and, much less pronounced caspofungin, are co-administered with drugs which have an inducing or inhibiting effect on the CYP 450 system, primarily on the isoenzymes CYP2C19, CYP2C9 and CYP3A4. This review provides a comprehensive overview on the potential drug interactions of caspofungin and voriconazole in multimorbid patients.