Herbal Science Research - cytochrome p450

Metabolic activation of herbal and dietary constituents and its clinical and toxicological implications: an update.

Site Editor — Thu, 04 Oct 2007 06:07:49 -0700

Metabolic activation of herbal and dietary constituents and its clinical and toxicological implications: an update.: Curr Drug Metab. 2007 Aug;8(6):526-53 Authors: Zhou SF, Xue CC, Yu XQ, Wang G

In recent years, there has been a globally increasing application of herbal medicines and dietary supplements to treat various chronic diseases and to promote health. However, there are increasing clinical reports on the organ toxicities associated with consumption of herbal medicines. This review updates the knowledge on metabolic activation of herbal components and its clinical and toxicological implications. Like many synthetic drugs undergoing metabolic activation to form reactive metabolites which are often associated with drug toxicity, it is recognized that some herbal components may also be converted to toxic, or even mutagenetic and carcinogenic metabolites by cytochrome P450s (CYPs) and less frequently by Phase II conjugating enzymes. This is exemplified by aristolochic acids (AAs) in Aristolochia spp, which undergo reduction of the nitro group by hepatic CYP1A1/2 or peroxidases in extrahepatic tissues to generate highly reactive cyclic nitrenium ions. The latter can react with macromolecules (DNA and protein), resulting in activation of H-ras oncogene and gene mutation in renal cells and finally carcinogenesis of the kidneys. Some naturally occurring flavonoids (e.g. quercetin) and alkenylbenzenes (e.g. safrole, methyleugenol and estragole) can undergo metabolic activation by sequential 1-hydroxylation and sulfation, resulting in reactive intermediates capable of forming DNA adducts and finally genotoxicity. Additional examples are pulegone present in essential oils from many mint species; and teucrin A, a diterpenoid found in germander (Teuchrium chamaedrys) used as an adjuvant to slimming dietary supplements but caused severe hepatotoxicity. Extensive pulegone metabolism generated p-cresol that was a glutathione depletory, whereas the furan ring of the diterpenoids in germander was oxidized by CYP3A4 to reactive epoxide which can inactivate hepatic CYP3A and epoxide hydrolase through covalent binding. The hepatotoxic and carcinogenic species of plant pyrrolizidine alkaloids (e.g. echimidine and jacobine), namely pyrrole-type metabolites, are generated by hepatic CYP2B6 and CYP3A4. Potential mechanisms underlying the hepatotoxicity of kava have been related to intracellular glutathione depletion and/or quinone formation. Some herbal constituents (e.g. capsaicin from chili peppers, glabridin from licorice root, oleuropein in olive oil, dially sulfone in garlic, and resveratrol found in red wine) behave as mechanism-based inhibitors of various CYPs. This may provide an explanation for some reported herb-drug interactions. In addition, the inhibition of CYPs by herbal constituents may decrease the formation of toxic metabolites and thus inhibit carcinogenesis, as CYPs play an important role in procarcinogen activation. Due to the wide use and easy availability of herbal medicines, further research should be conducted to ensure the safety and quality of herbal medicine.

PMID: 17691916 [PubMed - indexed for MEDLINE]

Effects of herbal products and their constituents on human cytochrome P450(2E1) activity.

Site Editor — Sat, 22 Sep 2007 17:46:51 -0700

Effects of herbal products and their constituents on human cytochrome P450(2E1) activity.: Food Chem Toxicol. 2007 Jun 15;
Raner GM, Cornelious S, Moulick K, Wang Y, Mortenson A, Cech NB

Ethanolic extracts from fresh Echinacea purpurea and Spilanthes acmella and dried Hydrastis canadensis were examined with regard to their ability to inhibit cytochrome P450(2E1) mediated oxidation of p-nitrophenol in vitro. In addition, individual constituents of these extracts, including alkylamides from E. purpurea and S. acmella, caffeic acid derivatives from E. purpurea, and several of the major alkaloids from H. canadensis, were tested for inhibition using the same assay. H. canadensis (goldenseal) was a strong inhibitor of the P450(2E1), and the inhibition appeared to be related to the presence of the alkaloids berberine, hydrastine and canadine in the extract. These compounds inhibited 2E1 with K(I) values ranging from 2.8muM for hydrastine to 18muM for berberine. The alkylamides present in E. purpurea and S. acmella also showed significant inhibition at concentrations as low as 25muM, whereas the caffeic acid derivatives had no effect. Commercial green tea preparations, along with four of the individual tea catechins, were also examined and were found to have no effect on the activity of P450(2E1).

The Role of Alkamides as an Active Principle of Echinacea.

Site Editor — Wed, 06 Jun 2007 00:22:32 -0700

The Role of Alkamides as an Active Principle of Echinacea.: Planta Med. 2007 May 31; Authors: Woelkart K, Bauer R

Alkamides are the major lipophilic constituents of ECHINACEA preparations, which are widely used in some European countries and in North America for common colds. In earlier investigations they have been shown to possess stimulatory effects on phagocytosis. Recent experiments have demonstrated that alkamides are detectable in human blood in relevant concentrations after oral administration of ECHINACEA preparations. Alkamides show structural similarity with anandamide, an endogenous ligand of cannabinoid receptors. Consequently, it was found that alkamides bind significantly to CB (2) receptors, which is now considered as a possible molecular mode of action of ECHINACEA alkamides as immunomodulatory agents. It was also demonstrated recently in several studies that alkamide-containing ECHINACEA preparations trigger effects on the pro-inflammatory cytokines. They were therefore suggested as a new class of cannabinomimetics. However, the therapeutic relevance of these findings is still not clear as clinical studies on the common cold show contradictory results. Among the many pharmacological properties reported, investigations concerning herb-drug interactions have been neglected for a long time. Latest research concludes that prolonged use of ECHINACEA poses a minimal risk for co-medications metabolized by the P450 enzymes.

[Effects of the flavonoids on cytochrome P-450 CYP1, 2E1, 3A4 and 19]

Site Editor — Wed, 30 May 2007 01:01:34 -0700

[Effects of the flavonoids on cytochrome P-450 CYP1, 2E1, 3A4 and 19]: Yao Xue Xue Bao. 2007 Jan;42(1):8-12 Authors: Zheng J, Zhou HH

Flavonoids are present in fruits, vegetables and beverages derived from plants, and in many dietary supplements or herbal remedies. A number of naturally occurring flavonoids have been shown to modulate the CYP450 system, including the induction or inhibition of these enzymes. This review focuses on the flavonoid effects on cytochrome P450 (CYP) enzyme CYP1, 2E1, 3A4 and 19. Flavonoids alter CYPs by various mechanisms, including the stimulation of gene expression via specific receptors and/or CYP protein, or mRNA stabilization and so on. But in vivo and in vitro, the effects of flavonoids are not always coincident as a result of concentrations of flavonoids, genetic and environmental factors. As well, flavonoids may interact with drugs through the induction or inhibition of their metabolism. Much attention should be paid to the metabolism interaction of the flavonoids when coadministered with other drugs.

The extent of induction of CYP3A by St. John's wort varies among products and is linked to hyperforin dose.

Site Editor — Sat, 20 Jan 2007 00:23:18 -0800

The extent of induction of CYP3A by St. John's wort varies among products and is linked to hyperforin dose.: Eur J Clin Pharmacol. 2006 Jan;62(1):29-36 Authors: Mueller SC, Majcher-Peszynska J, Uehleke B, Klammt S, Mundkowski RG, Miekisch W, Sievers H, Bauer S, Frank B, Kundt G, Drewelow B

OBJECTIVE: Induction of CYP3A by St. John's wort (SJW) extracts with high hyperforin (HYF) content is well described. Since SJW products vary in the amount of HYF and other main constituents, the aim of the study was to evaluate the effect on CYP3A function of SJW preparations with a range from very low to high HYF content. METHODS: Forty-two male, healthy volunteers were randomized into six parallel SJW medication groups with varying composition especially with regard to HYF content. Midazolam plasma concentration profiles were characterized after a single oral dose of 7.5 mg midazolam on the day before and on the 14th day of SJW medication. RESULTS: All SJW preparations tested resulted in a decrease in midazolam AUC, although the extent of the effect differed. The extract LI 160 (HYF 41 mg/day) decreased midazolam AUC0-12h by 79.4% (95% CI -88.6; -70.1), which was significantly greater than the effect by any other medication (p<0.05). SJW powder tablets 2.7 g/day (HYF 12 mg/day) resulted in a midazolam AUC0-12h decrease of 47.9% (95% CI -59.7;-36.2), while 2.7 g/day SJW powder tablets that were almost devoid of HYF (0.13 mg/day) reduced midazolam AUC0-12h by only 21.1% (95% CI -33.9; -8.3). Considering all six SJW medications tested, the extent of midazolam AUC decrease correlated significantly with increasing HYF dose (r=-0.765, p<0.001), but not with hypericin dose (r=-0.067; p=0.673). CONCLUSION: The extent of induction of CYP3A varies among St. John's wort products and depends on hyperforin dose.

Phytoestrogen Exposure, Polymorphisms in COMT, CYP19, ESR1, and SHBG Genes, and Their Associations With Prostate Cancer Risk.

Site Editor — Wed, 03 Jan 2007 19:04:33 -0800

Phytoestrogen Exposure, Polymorphisms in COMT, CYP19, ESR1, and SHBG Genes, and Their Associations With Prostate Cancer Risk.: Nutr Cancer. 2006;56(1):31-9 Authors: Low YL, Taylor JI, Grace PB, Mulligan AA, Welch AA, Scollen S, Dunning AM, Luben RN, Khaw KT, Day NE, Wareham NJ, Bingham SA

Abstract: Prospective phytoestrogen exposure was assessed using both biomarkers and estimates of intake in 89 British men recruited into the Norfolk arm of the European Prospective Investigation into Cancer and Nutrition study, men who subsequently developed prostate cancer. Results were compared with those from 178 healthy men matched by age and date of recruitment. Levels of seven phytoestrogens (daidzein, genistein, glycitein, O-desmethylangolensin, equol, enterodiol, and enterolactone) were measured in spot urine and serum samples. Five single-nucleotide polymorphisms in COMT, CYP19, ESR1, and SHBG genes were genotyped. Urinary levels of all phytoestrogens correlated strongly with serum levels. Correlation coefficients ranged from 0.63 (glycitein) to 0.88 (daidzein) (P < 0.001). Urinary and serum levels correlated significantly with isoflavone intake assessed from food diaries (R = 0.15-0.20; P < 0.05) but not with that from a food-frequency questionnaire. Odds ratios for phytoestrogen exposure, as assessed using the four methods, were not significantly associated with prostate cancer risk (P = 0.15-0.94). Men with the CC genotype for the ESRI PvuII polymorphism had significantly higher risk for prostate cancer compared with men with the TT genotype [adjusted odds ratio = 4.65 (1.60-13.49); P = 0.005]. Our results utilizing a combined prospective exposure provide no evidence that phytoestrogens alter prostate cancer risk in British men, whereas the C allele for the PvuII polymorphism may be associated with increased risk.

Does a kampo medicine containing schisandra fruit affect pharmacokinetics of nifedipine like grapefruit juice?

Site Editor — Wed, 04 Oct 2006 19:05:57 -0700

Does a kampo medicine containing schisandra fruit affect pharmacokinetics of nifedipine like grapefruit juice?: Biol Pharm Bull. 2006 Oct;29(10):2065-9 Authors: Makino T, Mizuno F, Mizukami H

Herb-drug interaction has attracted attention as medicinal topics recently. However, the drug information is sometimes confusing. Previous in vitro studies revealed that schisandra fruit had strong inhibitory effect on CYP3A4 and claimed the possibilities of its herb-drug interaction. In the present study, we evaluated the inhibitory effects of schisandra fruit and shoseiryuto, an herbal formula in Japanese traditional kampo medicine containing eight herbal medicines including schisandra fruit, on rat CYP3A activity in vitro, and the effect of shoseiryuto on pharmacokinetics of nifedipine in rats, in comparison with those of grapefruit juice, a well-characterized natural CYP3A inhibitor. Shoseiryuto and its herbal constituents, schisandra fruit, ephedra herb and cinnamon bark exhibited in vitro inhibitory effect of CYP3A. Although shoseiryuto inhibited rat CYP3A activity in vitro with a degree comparable to grapefruit juice, shoseiryuto did not significantly affect a plasma concentration profile of nifedipine in rats as grapefruit juice did. These results indicate that in vivo experiments using the extract of herbal medicine prepared with the same dosage form as patients take are necessary to provide proper information about herb-drug interaction.

Influence of Garlic (Allium sativum) on the Pharmacokinetics of Docetaxel.

Site Editor — Wed, 04 Oct 2006 18:20:56 -0700

Influence of Garlic (Allium sativum) on the Pharmacokinetics of Docetaxel.: Clin Cancer Res. 2006 Aug 1; 12(15): 4636-40
Cox MC, Low J, Lee J, Walshe J, Denduluri N, Berman A, Permenter MG, Petros WP, Price DK, Figg WD, Sparreboom A, Swain SM

PURPOSE: The herbal supplement garlic (Allium sativum) is commonly used by cancer patients. Preclinical studies have shown that allicin, a major component of garlic, may affect cytochrome P450 3A4 (CYP3A4) activity. This study examines the influence of garlic supplementation on the pharmacokinetics of docetaxel, a CYP3A4 substrate. EXPERIMENTAL DESIGN: Women with metastatic breast cancer were treated with docetaxel (30 mg/m(2)) given weekly for 3 of 4 weeks. Three days after the initial dose of docetaxel, patients received 600 mg of garlic twice daily for 12 consecutive days. Docetaxel pharmacokinetics were assessed during the first three administrations. RESULTS: In 10 evaluable patients, the mean baseline clearance of docetaxel was 30.8 L/h/m(2) [95% confidence intervals (95% CI), 16.7-44.9]. Coadministration of garlic reduced mean clearance of docetaxel to 23.7 L/h/m(2) (95% CI, 15.5-31.8) and 20.0 L/h/m(2) (95% CI, 13.3-26.7) on days 8 and 15, respectively (P = 0.17). Additional pharmacokinetic variables of docetaxel, including peak concentration (P = 0.79), area under the curve (P = 0.36), volume of distribution (P = 0.84), and half-life (P = 0.36), were also not statistically significantly different. The mean area under the curve ratio between day 15 and day 1 was 3.74 in three individuals with the CYP3A5*1A/*1A genotype (all African American) compared with 1.02 in six individuals with the CYP3A5*3C/*3C genotype (all Caucasian). CONCLUSIONS: This study indicates that garlic does not significantly affect the disposition of docetaxel. However, it cannot be excluded that garlic decreases the clearance of docetaxel in patients carrying a CYP3A5*1A allele.

Hyperforin in St. John's wort drug interactions.

Site Editor — Fri, 09 Jun 2006 07:23:48 -0700

Hyperforin in St. John's wort drug interactions.: Eur J Clin Pharmacol. 2006 Feb 14;:1-9 Authors: Madabushi R, Frank B, Drewelow B, Derendorf H, Butterweck V

Recently, interactions of herbal medicines with synthetic drugs came into focus of particular interest. In the past 3 years, more than 50 papers were published regarding interactions between St. John's wort (Hypericum perforatum L.; SJW) and prescription drugs. Co-medication with SJW resulted in decreased plasma concentrations of a number of drugs including amitriptyline, cyclosporine, digoxin, indinavir, irinotecan, warfarin, phenprocoumon, alprazolam, dextrometorphane, simvastatin, and oral contraceptives. Sufficient evidence from interaction studies and case reports indicate that SJW is a potent inducer of cytochrome P450 enzymes (particularly CYP3A4) and/or P-glycoprotein. Recent studies could show that the degree of enzyme induction by SJW correlates strongly with the amount of hyperforin found in the product. Products that do not contain substantial amounts of hyperforin (<1%) have not been shown to produce clinically relevant enzyme induction. On the other hand, some evidence suggests that hyperforin may also contribute to the antidepressant activity of SJW. However, clinical studies using SJW preparations with a low hyperforin amount (<1%) clearly demonstrated the superiority of this plant extract over placebo and its equivalence to imipramine and fluoxetine in the treatment of mild to moderate forms of depression. In the present paper clinical significant SJW interactions are critically evaluated against the background of hyperforin.

MDR- and CYP3A4-mediated drug-herbal interactions.

Site Editor — Fri, 09 Jun 2006 04:35:48 -0700

MDR- and CYP3A4-mediated drug-herbal interactions.: Life Sci. 2006 Jan 24; Authors: Pal D, Mitra AK

According to recent epidemiological reports, almost 40% of American population use complimentary and alternative medicine (CAM) during their lifetime. Patients detected with HIV or cancer often consume herbal products especially St. John's wort (SJW) for antidepressants in combination with prescription medicines. Such self-administered herbal products along with prescribed medicines raise concerns of therapeutic activity due to possible drug-herbal interactions. P-glycoprotein (P-gp) and cytochrome P450 3A4 (CYP3A4) together constitute a highly efficient barrier for many orally absorbed drugs. Available literature, clinical reports and in vitro studies from our laboratory indicate that many drugs and herbal active constituents are substrates for both P-gp and CYP3A4. Results from clinical studies and case reports indicate that self-administered SJW reduce steady state plasma concentrations of amitriptyline, cyclosporine, digoxin, fexofenadine, amprenavir, indonavir, lopinavir, ritonavir, saquinavir, benzodiazepines, theophyline, irinotecan, midazolan and warfarin. This herbal agent has been also reported to cause bleeding and unwanted pregnancies when concomitantly administered with oral contraceptives. Most of these medicinal agents and SJW are substrates for P-gp and/or CYP3A4. In vitro studies from our laboratory suggest that short-term exposure with pure herbal agents such as hypericin, kaempferol and quercetin or extract of SJW resulted in higher uptake or influx of ritonavir and erythromycin. Hypericin, kaempferol and quercetin also caused a remarkable inhibition of cortisol metabolism with the percent intact cortisol values of 64.58%, 89.6% and 90.1%, respectively, during short-term in vitro experiments. Conversely, long-term exposure of herbal agents (hyperforin, kaempferol and quercetin) showed enhanced expression of CYP3A4 mRNA in Caco-2 cells. In another study, we observed that long-term exposure of hypericin, kaempferol, quercetin and silibinin resulted in higher MDR-1 mRNA expression in Caco-2 cells. Therefore, herbs can pharmacokinetically act as inhibitors or inducers. Medicinal agents that are substrates P-gp-mediated efflux and/or CYP-mediated metabolism are likely to be potential candidates for drug-herbal interactions. The duration of exposure of cells/healthy volunteers/animals to herbals appears to be critical for drug-herbal interaction. An increase in plasma drug concentration is possible during concomitant administration of SJW and prescribed drugs. In contrast, prolonged intake of herbal supplement followed by drug administration may result in subtherapeutic concentrations. Therefore, clinical implications of such drug herbal interactions depend on a variety of factors such as dose, frequency and timing of herbal intake, dosing regimen, route of drug administration and therapeutic range. In vitro screening techniques will play a major role in identifying possible herb-drug interactions and thus create a platform for clinical studies to emerge. Mechanisms of drug-herbal interaction have been discussed in this review article.

Ginkgo biloba: Evaluation of CYP2C9 Drug Interactions In Vitro and In Vivo.

Site Editor — Fri, 09 Jun 2006 04:24:59 -0700

Ginkgo biloba: Evaluation of CYP2C9 Drug Interactions In Vitro and In Vivo.: Am J Ther. 2006 Jan-Feb;13(1):24-31 Authors: Mohutsky MA, Anderson GD, Miller JW, Elmer GW

Ginkgo biloba extract is one of the most widely used herbal products in the United States. However, bleeding episodes in patients taking Ginkgo biloba and warfarin have been documented. Therefore, in vitro and in vivo inhibition studies were done to ascertain the influence of ginkgo on CYP2C9, the P-450 isozyme responsible for the metabolism of the most potent warfarin enantiomer, (S)-warfarin. Ginkgo extract inhibited human liver microsomal CYP2C9 with an apparent Ki =14.8 mug/mL, and the inhibition was increased by acid hydrolysis (apparent Ki = 9.1 mug/mL). Two open-label, crossover pharmacokinetic studies in healthy subjects were performed using tolbutamide and diclofenac as probe CYP2C9 substrates. In contrast to the in vitro inhibition of CYP2C9, no interactions between Ginkgo biloba extract and CYP2C9 probe substrates were observed in vivo as evidenced by the lack of effect on the steady-state pharmacokinetics of diclofenac or on the urinary metabolic ratio of tolbutamide.

Cytochrome P450 2D6 (CYP2D6) inhibitory constituents of Catharanthus roseus.

Site Editor — Fri, 09 Jun 2006 04:21:50 -0700

Cytochrome P450 2D6 (CYP2D6) inhibitory constituents of Catharanthus roseus.: Biol Pharm Bull. 2005 Jun;28(6):1021-4 Authors: Usia T, Watabe T, Kadota S, Tezuka Y

The MeOH-soluble fraction of the water extract of Catharanthus roseus from Indonesia, having shown potent inhibitory activity on the metabolism mediated by CYP2D6, was subjected to activity-guided isolation to yield two triterpenes, ursolic acid (1) and oleanolic acid (2), and three alkaloids, vindoline (3), ajmalicine (4), and serpentine (5). The isolated compounds were tested for their inhibitory activity on the metabolism mediated by CYP3A4 or CYP2D6 using [N-methyl-14C]erythromycin or [O-methyl-14C]dextromethorphan as a substrate, respectively. Ajmalicine (4) and serpentine (5) showed very potent inhibitory activity against CYP2D6 with IC50 values of 0.0023 and 3.51 microM, respectively. All isolated compounds showed weak or no inhibition against CYP3A4. On time-, concentration-, and NADPH-dependent assay, serpentine (5) appear to be the mechanism-based inhibitor for CYP2D6 enzyme in which the inhibition was irreversible and driven by catalytic process. K(I) and k(inact) values for serpentine (5) were 0.148 microM and 0.090 min-1, respectively. On the other hand, ajmalicine (4) showed no time-dependent inhibition or reversible inhibition, and thus appear to be not mechanism-based inhibitor.

Fatal seizures due to potential herb-drug interactions with Ginkgo biloba.

Site Editor — Fri, 09 Jun 2006 04:21:25 -0700

Fatal seizures due to potential herb-drug interactions with Ginkgo biloba.: J Anal Toxicol. 2005 Oct;29(7):755-8 Authors: Kupiec T, Raj V

Alternative therapy including herbal drugs and complementary medicine is becoming increasingly popular. However, the rise in the incidence of herb-drug interactions is causing concern, especially in the absence of warning labels addressing potential adverse effects. We present the case of a 55-year-old male who suffered a fatal breakthrough seizure, with no evidence of non-compliance with his anticonvulsant medications. The autopsy report revealed subtherapeutic serum levels for both anticonvulsants Depakote and Dilantin. Concomitant with his prescribed medications, the decedent was also self-medicating with a cornucopia of herbal supplements and nutraceuticals, prominent among which was Ginkgo biloba. Ginkgo, an herbal extract from the leaves of the Ginkgo biloba tree, has been used medicinally for centuries and has been touted as a cure for a variety of medical conditions. The induction of Cytochrome P450 enzymes by components of herbal drugs has been known to affect the metabolism of various drugs. Dilantin is primarily metabolized by CYP2C9, and secondarily metabolized by CYP2C19. Valproate metabolism is also modulated in part by CYP2C9 and CYP2C19. A recent study revealed significant inductive effect of ginkgo on CYP2C19 activity. CYP2C19 induction by ginkgo could be a plausible explanation for the subtherapeutic levels of Dilantin and Depakote. Additionally, ginkgo nuts contain a potent neurotoxin, which is known to induce seizure activity. Evidence of other herbal drugs diminishing the efficacy of anticonvulsant medication does exist; however, there has been only one other documented instance of ginkgo potentiating seizure activity in the presence of anticonvulsant therapy. Highlighting the potential adverse effects and drug interactions of ginkgo on the packaging of the drug may help prevent inadvertent use in vulnerable individuals.

[Effect of intestinal cytochrome P450 3A on phytochemical presystemic metabolism.]

Site Editor — Fri, 09 Jun 2006 04:21:09 -0700

[Effect of intestinal cytochrome P450 3A on phytochemical presystemic metabolism.]: Chin J Integr Med. 2005 Sep;11(3):232-6 Authors: Xia F, Chen XY

Phytochemicals, orally administered substances, are found to undergo presystemic metabolism mainly in the intestine. Although early researches confirmed the role of intestinal bacteria in phytochemical presystemic metabolism, along with the development of molecular biology in investigating intestinal metabolism, a breakthrough has been won in research into metabolizing enzymes and transporters in intestine, which demands more attention and further studies. Recently, Cytochrome P450 3A has been found to be the most effective enzyme in mediating both oxidative (PhaseI) and conjugative (PhaseII) metabolism in the intestine. The present review summarizes the current findings correlated with the effect of intestinal cytochrome P450 3A on phytochemical presystemic metabolism, which provides a good basis for further research on phytochemical pharmacokinetics.

Mechanism-based inhibition of CYP3A4 and CYP2D6 by Indonesian medicinal plants.

Site Editor — Fri, 09 Jun 2006 04:17:19 -0700

Mechanism-based inhibition of CYP3A4 and CYP2D6 by Indonesian medicinal plants.: J Ethnopharmacol. 2006 Jan 12; Authors: Subehan , Usia T, Iwata H, Kadota S, Tezuka Y

Thirty samples of Indonesian medicinal plants were tested for their mechanism-based inhibition on cytochrome P450 3A4 (CYP3A4) and CYP2D6 via erythromycin N-demethylation and dextromethorphan O-demethylation activities in human liver microsomes. From screening with 0 and 20min preincubation at 0.5mg/ml of methanol extracts, five plants (Cinnamomum burmani bark, Foeniculum vulgare seed, Strychnos ligustrina wood, Tinospora crispa stem, and Zingiber cassumunar rhizome) showed more than 30% increase of CYP3A4 inhibition, while three (Alpinia galanga rhizome, Melaleuca leucadendron leaf, and Piper nigrum fruit) showed more than 30% increase of CYP2D6 inhibition. In these eight plants, Foeniculum vulgare seed, Cinnamomum burmani bark, and Strychnos ligustrina wood showed time-dependent inhibition on CYP3A4 and Piper nigrum fruit and Melaleuca leucadendron leaf on CYP2D6. Among these, four plants other than Melaleuca leucadendron revealed NADPH-dependent inhibition. Thus, Foeniculum vulgare, Cinnamomum burmani, and Strychnos ligustrina should contain mechanism-based inhibitors on CYP3A4 and Piper nigrum contain that on CYP2D6.

Lack of significant effect of grapefruit juice on the pharmacokinetics of lansoprazole and its metabolites...

Site Editor — Fri, 09 Jun 2006 04:09:45 -0700

Lack of significant effect of grapefruit juice on the pharmacokinetics of lansoprazole and its metabolites in subjects with different CYP2C19 genotypes.: J Clin Pharmacol. 2005 Jun;45(6):690-4 Authors: Uno T, Yasui-Furukori N, Takahata T, Sugawara K, Tateishi T

Analysis of frankincense from various Boswellia species with inhibitory activity on human drug metabolising cytochrome P450....

Site Editor — Fri, 09 Jun 2006 03:54:02 -0700

Analysis of frankincense from various Boswellia species with inhibitory activity on human drug metabolising cytochrome P450 enzymes using liquid chromatography mass spectrometry after automated on-line extraction.: J Chromatogr A. 2005 Dec 16; Frank A, Unger M

In our search for herbal remedies with inhibitory activity on cytochrome P450 (CYP) enzymes, we identified extracts of the gum-resin of Boswellia carteri, Boswellia frereana, Boswellia sacra and Boswellia serrata as equally potent, non-selective inhibitors of the major drug metabolising CYP enzymes 1A2/2C8/2C9/2C19/2D6 and 3A4. LC/LC/ESI-MS fingerprint analyses of the boswellic acids 11-keto-beta-boswellic acid, alpha-boswellic acid, beta-boswellic acid and their 3-O-acylated derivatives were used for the authentication of the commercially obtained frankincense samples. Although the boswellic acids could be identified as moderate to potent inhibitors of the applied CYP enzymes, they are not the major CYP inhibitory principle of frankincense.

Effects of St John's wort (Hypericum perforatum L.) extract on plasma androgen concentrations in healthy men and women...

Site Editor — Fri, 09 Jun 2006 03:46:46 -0700

Effects of St John's wort (Hypericum perforatum L.) extract on plasma androgen concentrations in healthy men and women: a pilot study.: Phytother Res. 2005 Oct;19(10):901-6 Authors: Donovan JL, DeVane CL, Lewis JG, Wang JS, Ruan Y, Chavin KD, Markowitz JS

St John's wort extract (SJW; Hypericum perforatum L.) is taken extensively as a putative herbal antidepressant. It has been shown to induce the activity of cytochrome P-450 3A4 (CYP3A4) and to increase the clearance of numerous drugs and steroids such as cortisol and ethinyl estradiol. This study was conducted to determine if SJW exposure also alters the concentrations of circulating androgenic steroid hormones. The study was conducted using healthy volunteers (6M, 6F) studied before and after a 14-day treatment period with a SJW preparation previously demonstrated to induce the activity of CYP3A4. Plasma concentrations of testosterone, dihydrotestosterone (DHT), dehydroepiandrosterone sulfate (DHEAS), sex hormone-binding globulin (SHBG) and the combined concentrations of androsterone sulfate (AoS) and epiandrosterone sulfate (epiAoS) were measured by immunoassay methods. The results of analysis demonstrated that SJW did not significantly alter the majority of the androgens studied (p > 0.05) although the combined concentrations of the 5alpha-reduced steroids, AoS and epiAoS, significantly declined following treatment in all subjects (p = 0.02), and in males (p = 0.04). Furthermore, the testosterone to DHT ratio was increased in both men and women. Although the latter increase did not reach statistical significance, it is also consistent with the possible inhibition of 5alpha-reductase by SJW. It is concluded that despite significant induction of CYP3A4, short term administration of SJW does not significantly alter the concentrations of most circulating androgens in men and women but may produce a dimunition in some of the circulating 5alpha-reduced androgens.

Dietary flavonoids: Effects on xenobiotic and carcinogen metabolism.

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Dietary flavonoids: Effects on xenobiotic and carcinogen metabolism. - Toxicol In Vitro. 2005 Nov 10; Authors: Moon YJ, Wang X, Morris ME

Flavonoids are present in fruits, vegetables and beverages derived from plants (tea, red wine), and in many dietary supplements or herbal remedies including Ginkgo Biloba, Soy Isoflavones, and Milk Thistle. Flavonoids have been described as health-promoting, disease-preventing dietary supplements, and have activity as cancer preventive agents. Additionally, they are extremely safe and associated with low toxicity, making them excellent candidates for chemopreventive agents. The cancer protective effects of flavonoids have been attributed to a wide variety of mechanisms, including modulating enzyme activities resulting in the decreased carcinogenicity of xenobiotics. This review focuses on the flavonoid effects on cytochrome P450 (CYP) enzymes involved in the activation of procarcinogens and phase II enzymes, largely responsible for the detoxification of carcinogens. A number of naturally occurring flavonoids have been shown to modulate the CYP450 system, including the induction of specific CYP isozymes, and the activation or inhibition of these enzymes. Some flavonoids alter CYPs through binding to the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, acting as either AhR agonists or antagonists. Inhibition of CYP enzymes, including CYP 1A1, 1A2, 2E1 and 3A4 by competitive or mechanism-based mechanisms also occurs. Flavones (chrysin, baicalein, and galangin), flavanones (naringenin) and isoflavones (genistein, biochanin A) inhibit the activity of aromatase (CYP19), thus decreasing estrogen biosynthesis and producing antiestrogenic effects, important in breast and prostate cancers. Activation of phase II detoxifying enzymes, such as UDP-glucuronyl transferase, glutathione S-transferase, and quinone reductase by flavonoids results in the detoxification of carcinogens and represents one mechanism of their anticarcinogenic effects. A number of flavonoids including fisetin, galangin, quercetin, kaempferol, and genistein represent potent non-competitive inhibitors of sulfotransferase 1A1 (or P-PST); this may represent an important mechanism for the chemoprevention of sulfation-induced carcinogenesis. Importantly, the effects of flavonoids on enzymes are generally dependent on the concentrations of flavonoids present, and the different flavonoids ingested. Due to the low oral bioavailability of many flavonoids, the concentrations achieved in vivo following dietary administration tend to be low, and may not reflect the concentrations tested under in vitro conditions; however, this may not be true following the ingestion of herbal preparations when much higher plasma concentrations may be obtained. Effects will also vary with the tissue distribution of enzymes, and with the species used in testing since differences between species in enzyme activities also can be substantial. Additionally, in humans, marked interindividual variability in drug-metabolizing enzymes occurs as a result of genetic and environmental factors. This variability in xenobiotic metabolizing enzymes and the effect of flavonoid ingestion on enzyme expression and activity can contribute to the varying susceptibility different individuals have to diseases such as cancer. As well, flavonoids may also interact with chemotherapeutic drugs used in cancer treatment through the induction or inhibition of their metabolism.