Significance of Garlic and Its Constituents in Cancerand Cardiovascular Disease

In Vitro Interactions of Water-Soluble Garlic Components with HumanCytochromes P4501–3

David J. Greenblatt,4 Richard A. Leigh-Pemberton, and Lisa L. von Moltke

Department of Pharmacology and Experimental Therapeutics, Tufts University School ofMedicine and Tufts-New England Medical Center, Boston, MA

ABSTRACT Eight water-soluble components of aged garlic extract were evaluated to assess their potential to in-hibit the activity of human cytochrome-P450 (CYP) enzymes. The in vitro model consisted of human liver microsomeswith index reactions chosen to profile the activity of the following six CYP isoforms: CYP1A2, 2B6, 2C9, 2C19, 2D6,and 3A. With only 2 exceptions, none of the 8 garlic components produced.50% inhibition even at high concentrations(100 mmol/L). S-methyl-L-cysteine and S-allyl-L-cysteine at 100 mmol/L produced modest inhibition of CYP3A, reduc-ing activity to 20–40% of control. However available clinical evidence does not indicate CYP3A inhibition in vivo.The findings suggest that drug interactions involving inhibition of CYP3A enzymes by aged garlic extract are veryunlikely. J. Nutr. 136: 806S–809S, 2006.

KEY WORDS: � aged garlic extract � Cytochromes P450 � in vitro metabolism � drug interaction

The increasingly extensive utilization of complementary oralternative medical therapies over the last decade is now welldocumented (1–7). This incorporates the use of botanicalmedicines either alone or in combination with prescriptionmedications. With the increased prevalence of botanical usecomes the need for clinical and scientific data on the phar-macologic properties, mechanisms of action, drug interactions,

and adverse effects of these agents such that consumers andhealth care providers will have the information available tomaximize therapeutic benefits of botanicals while minimizing thelikelihood of unwanted effects.

Commercial promotion of botanicals usually emphasizes thatthey are ‘‘safe,’’ ‘‘natural,’’ and contain ‘‘no chemicals.’’ In fact,plant systems have their own metabolic processes, and humanevolution has created processes to biotransform and eliminateingested plants. As such, plants can induce, inhibit, or be toxicto human metabolic systems, and seemingly safe and naturalplant products may have predictable influences on human drugmetabolism. Of particular concern are the increasing numbersof clinical and scientific reports of drug interactions involvingbotanical products (8–19). Some of these interactions, forexample, those involving St. John’s wort, are of major clinicalimportance. Mechanisms investigated to date include thepossibility that botanical medicines may induce or inhibit theactivity of human Cytochrome P450 enzymes or the activity oftransport proteins such as P-glycoprotein (20). Because thenumber of botanical medicines in clinical use is very large, it issimply not feasible to conduct clinical studies for all possibledrug interactions that need to be studied and understood.Accordingly, there are now large gaps in knowledge, and rec-ommendations regarding which drug combinations with bo-tanicals are safe or unsafe are often based on incomplete data.

An extensive literature supports the existence of the ther-apeutically beneficial effects of garlic preparations in the preven-tion of atherogenesis and neoplastic disease (21–31). A numberof components in garlic are postulated to act synergistically toprovide these health benefits (32–39). Due to the complexchemistry of garlic, variations in processing yield quite differentpreparations. Highly unstable thiosulfinates, such as allicin,

1 Published in a supplement to The Journal of Nutrition. Presented at thesymposium ‘‘Significance of Garlic and Its Constituents in Cancer and Cardiovas-cular Disease’’ held April 9–11, 2005 at Georgetown University, Washington, DC.The symposium was sponsored by Strang Cancer Prevention Center, affiliatedwith Weill Medical College of Cornell University, and Harbor-UCLA Medical Center,and co-sponsored by American Botanical Council, American Institute for CancerResearch, American Society for Nutrition, Life Extension Foundation, GeneralNutrition Centers, National Nutritional Foods Association, Society of Atheroscle-rosis Imaging, Susan Samueli Center for Integrative Medicine at the University ofCalifornia, Irvine. The symposium was supported by Alan James Group, LLC,Agencias Motta, S.A., Antistress AG, Armal, Birger Ledin AB, Ecolandia Inter-nacional, Essential Sterolin Products (PTY) Ltd., Grand Quality LLC, IC Vietnam,Intervec Ltd., Jenn Health, Kernpharm BV, Laboratori Mizar SAS, Magna Trade,Manavita B.V.B.A., MaxiPharm A/S, Nature’s Farm, Naturkost S. Rui a.s., NicheaCompany Limited, Nutra-Life Health & Fitness Ltd., Oy Valioravinto Ab, Panax, PT.Nutriprima Jayasakti, Purity Life Health Products Limited, Quest Vitamins, Ltd.,Sabinco S.A., The AIM Companies, Valosun Ltd., Wakunaga of America Co. Ltd.,and Wakunaga Pharmaceutical Co., Ltd. Guest editors for the supplementpublication were Richard Rivlin, Matthew Budoff, and Harunobu Amagase. GuestEditor Disclosure: R. Rivlin has been awarded research grants from Wakunagaof America, Ltd. and received an honorarium for serving as co-chair of theconference; M. Budoff has been awarded research grants from Wakunaga ofAmerica, Ltd. and received an honorarium for serving as co-chair of theconference; and Harunobu Amagase is employed by Wakunaga of America, Ltd.

2 Author disclosure: No relationships to disclose.3 This work was supported in part by grants AT-01381, AI-55412, MH-58435,

DA-13209, DK/AI-58496, DA-13834, AG-17880, AI-58784, and RR-00054 from theU.S. Department of Health and Human Services.

4 To whom correspondence should be addressed: E-mail: dj.greenblatt@tufts.edu.

0022-3166/06 $8.00 � 2006 American Society for Nutrition.

806S

by on October 19, 2010

jn.nutrition.orgD

ownloaded from

disappear during processing and are quickly and extensivelytransformed (34). Efficacy and safety are also contingent uponprocessing methods. The process of extraction has been assumedto increase the potency and bioavailability of various crude herbsand eliminate their harsh and toxic characteristics. Theirritating, acidic, and oxidizing compounds in raw garlic can beeliminated and modified through the extraction process. In fact,in some cultures, garlic is soaked or extracted with alcohol, wine,milk, or vinegar before being used as a therapeutic agent. Manyadverse reactions to garlic ingestion can be attributed to the oil-soluble constituents derived from allicin. The lipid-loweringeffect attributed to oil-soluble sulfur compounds in hepatocytesmay be due to cytotoxicity, as revealed by increased lactatedehydrogenase from cells exposed to various oil-soluble compo-nents. Acetone has been detected in the breath of subjectsconsuming allicin-derived oil-soluble compounds, further sug-gesting the cytotoxicity of such compounds. On the other hand,water-soluble sulfur compounds, though effective at reducingcholesterol, are not cytotoxic. Aged garlic extract contains anumber of the water-soluble constituents, such as S-allyl-cysteine, that significantly reduce its toxicity, as confirmed byvarious toxicological studies together with (32).

Clinical studies evaluating drug interactions with garlicpreparations are limited (40–42). This is not surprising, sincedesign and execution of pharmacokinetic drug interactionstudies in humans are costly and time consuming. Recently, invitro systems, using human liver microsomal preparations, havebeen increasingly utilized as approaches to screening for druginteractions that may be probable, possible, or unlikely (43–47).Data from these in vitro models can be utilized as a guide fortargeting of clinical resources such that the most importantresearch priorities are addressed.

The present study utilized the in vitro model to screen forpotential inhibitory metabolic effects of a number of compo-nents of aged garlic extract.

METHODS

Liver samples from individual human donors with no knownliver disease were provided by the International Institute for theAdvancement of Medicine (Exton, PA) or the Liver TissueProcurement and Distribution System (University of Minnesota,Minneapolis). All samples were of the CYP2D6 and CYP2C19 normalmetabolizer phenotype based on in vitro phenotyping studies.

Microsomes were prepared by ultracentrifugation; microsomalpellets were suspended in 0.1 mmol/L potassium phosphate buffercontaining 20% glycerol and stored at �808C until use.

Incubation mixtures contained 50 mmol/L phosphate buffer, 5mmol/L Mg11, 0.5 mmol/L NADP1, and an isocitrate/isocitricdehydrogenase regenerating system. Appropriate substrates (Table 1),with and without an inhibitor in methanol solution, were added to aseries of incubation tubes. The solvent was evaporated to dryness at408C under conditions of mild vacuum. Reactions were initiated byaddition of microsomal protein. After an appropriate incubationduration at 378C, reactions were stopped by cooling on ice andaddition of 100 mL of acetonitrile. Internal standard was added, theincubation mixture centrifuged, and the supernatant transferred to anautosampling vial for HPLC analysis.

The activity of 6 human CYP isoforms were evaluated using indexreactions and methods as follows (43,46,48–57) (see Table 1): CYP-1A2, phenacetin (100 mmol/L) to acetaminophen; CYP-2B6, bupropion(250 mmol/L) to hydroxybupropion; CYP-2C9, flurbiprofen (5 mmol/L)to OH-flurbiprofen; CYP-2C19, S-mephenytoin (25 mmol/L) to49-OH-mephenytoin; CYP-2D6, dextromethorphan (25 mmol/L) todextrorphan; CYP-3A, triazolam (250 mmol/L) to a-OH-triazolam and4-OH-triazolam.

TABLE 1

Experimental conditions for inhibition studies

CYP isoformSubstrate (concentration,

mmol/L) Product(s)Mobile phase

composition*, %Detectionmode, nm

1A2 Phenacetin (100) Acetaminophen CH3CN:buffer 15:85 U.V. 2542B6 Bupropion (250) OH-bupropion CH3CN:buffer 21:79 U.V. 2142C9 Flurbiprofen (5) 4-OH-flurbiprofen CH3CN:Na acetate (10 mM) 30:70 U.V. 2302C19 S-mephenytoin (25) 49-OH-mephenytoin CH3CN:buffer 42:58 Fluorescence: excit. 260 emis. 3202D6 Dextromethorphan (25) Dextrorphan CH3CN:buffer 30:70 Fluorescence: excit. 250 emis. 3103A Triazolam (250) a-OH-triazolam, 4-OH-triazolam CH3CN:CH3OH:buffer 22.5:10:67.5 U.V. 220

* Aqueous buffer is 50 mmol/L KH2PO4.

TABLE 2

Effect of aged garlic extract components on activity of human

Cytochrome P450 isoforms in vitro

Inhibitory effect vs. Cytochrome P450 isoforms

Garlic component* CYP3A CYP2C9 CYP2C19 CYP2D6 CYP1A2 CYP2B6

Alliin — — — — — —Cycloalliin — — — — — —Methylin — — — — — —S-Methyl-L-cysteine 1 — — — — —SAC 1 — — — — —N-Acetyl-SAC — — — — — —S-Allomercapto-L-cysteine — — — — — —Gamma-glutamyl-SAC — — — — — —

* All components were tested at a concentration of 100 mmol/L. SAC, S-allyl-L-cysteine.

807SWATER-SOLUBLE GARLIC AND HUMAN CYTOCHROMES P450

by on October 19, 2010

jn.nutrition.orgD

ownloaded from

Pure samples of water-soluble components of aged garlic extract(Table 2) were donated by Dr. Harunobu Amagase of Wakunaga ofAmerica. Solutions were prepared in methanol. Inhibitory effects of100 mmol/L concentrations of each component were evaluated in eachof the in vitro systems. For studies of CYP3A activity using triazolam asthe substrate, incubations were performed both without and withpreincubation of inhibitor with triazolam. This is done to evaluate thepossibility of irreversible or ‘‘mechanism-based’’ inhibition (58–60).

RESULTS

The outcome of in vitro studies is shown in Table 2. A minussign (�) indicates ,50% inhibition of the index reactionvelocity; a plus sign (1) indicates .50% inhibition. The con-centrations of garlic components in the incubation mixtures(100 mmol/L) are very high, probably exceeding by an order ofmagnitude or more the in vivo exposure that would beanticipated. Therefore the anticipated levels of clinical expo-sure confer a very low risk of pharmacokinetic drug interactionsincluding metabolic inhibition of any of the indicated CYPisoforms.

In only 2 instances, inhibition of CYP3A exceeded 50%.S-allyl-L-cysteine, an important component in terms of biologiceffects of aged garlic extract, reduced CYP3A activity to 40%of the control (Fig. 1). An evaluation of the concentrationdependence of the inhibitory action did not demonstrate clearevidence of classical concentration effect. Furthermore, inhi-bition of the 2 parallel pathways of triazolam hydroxylation(a-OH- and 4-OH-triazolam formation) revealed differentialinhibition of the 2 pathways (Fig. 2). There was no evidencethat the character of inhibition was ‘‘mechanism based.’’

DISCUSSION

Benefits and limitations of in vitro systems have beenextensively discussed (43–47). Of importance is that human

microsomal systems can be used to evaluate inhibition, notinduction. Furthermore, quantitative measures of the inhibi-tory potency of foods and natural products derived from in vitrostudies are notoriously difficult to interpret in terms of thepredictability of clinical drug interactions. This is because pro-cesses such as glycone removal and glucuronide conjugationmay occur before natural substances reach hepatic enzymes orthe systemic circulation (61–63). As an example, certain com-ponents of Ginkgo biloba (such as amentoflavone) are potent invitro inhibitors of human cytochrome P450 2C9 (64), but thereis no evidence to indicate that administration of ginkgo tohumans alters CYP2C9 activity in vivo (65,66).

The present study indicates that water-soluble garlic com-ponents are highly unlikely to inhibit activity of the 6 humancytochrome P450 isoforms responsible for the majority of drugmetabolism reactions. The in vitro screen did reveal the pos-sibility of modest inhibition of CYP3A by S-methyl-L-cysteineand S-allyl-L-cysteine. Although available data (41) providesno evidence that garlic inhibits CYP3A in vivo, the possibil-ity could be confirmed or ruled out through a straightfor-ward clinical drug-interaction study involving a suitable CYP3Asubstrate such as midazolam (67).

LITERATURE CITED

1. Goldman P. Herbal medicines today and the roots of modern pharmacol-ogy. Ann Intern Med. 2001;135:594–600.

2. Eisenberg DM, Davis RB, Ettner SL, Appel S, Wilkey S, Van Rompay M,Kessler RC. Trends in alternative medicine use in the United States, 1990–1997:results of a follow-up national survey. JAMA. 1998;280:1569–75.

3. Astin JA, Marie A, Pelletier KR, Hansen E, Haskell WL. A review of theincorporation of complementary and alternative medicine by mainstream physi-cians. Arch Intern Med. 1998;158:2303–10.

4. Astin JA. Why patients use alternative medicine: results of a nationalstudy. JAMA. 1998;279:1548–53.

5. Winslow LC, Kroll DJ. Herbs as medicines. Arch Intern Med. 1998;158:2192–9.

6. Bent S, Ko R. Commonly used herbal medicines in the United States: areview. Am J Med. 2004;116:478–85.

7. De Smet PA. Herbal remedies. N Engl J Med. 2002;347:2046–56.8. Boullata JI, Nace AM. Safety issues with herbal medicine. Pharmaco-

therapy. 2000;20:257–69.9. Greenblatt DJ and von Moltke LLInteraction of warfarin with drugs, natural

substances, and foods. J Clin Pharmacol. 2005;45:127–32.10. Izzo AA, Ernst E. Interactions between herbal medicines and prescribed

drugs: a systematic review. Drugs. 2001;61:2163–75.

FIGURE 2 Mean (6SE) rates of formation of triazolam metabolitesfrom triazolam (250 mM), the index substrate representing activity ofCYP3A, in relation to concentration of S-allyl-L-cysteine. Reaction veloci-ties are expressed as a percentage ratio of the control velocity with noinhibitor present.

FIGURE 1 Effect of coaddition of S-allyl-L-cysteine (100 mM) on thein vitro activity of human Cytochromes P450 3A, 2C9, 2C19, and IA2,based on the human liver microsomal model described in the text, usingindex reactions delineated in Table 1. Bars represent mean (6SE)reaction velocity with coaddition of 100 mM S-allyl-L-cysteine expressedas a percentage ratio of the reaction velocity in the control conditionwithout inhibitor.

808S SUPPLEMENT

by on October 19, 2010

jn.nutrition.orgD

ownloaded from

11. Fugh-Berman A, Ernst E. Herb-drug interactions: review and assessmentof report reliability. Br J Clin Pharmacol. 2001;52:587–95.

12. Scott GN, Elmer GW. Update on natural product–drug interactions. Am JHealth Syst Pharm. 2002;59:339–47.

13. Valli G, Giardina EG. Benefits, adverse effects and drug interactions ofherbal therapies with cardiovascular effects. J Am Coll Cardiol. 2002;39:1083–95.

14. Ernst E. The risk-benefit profile of commonly used herbal therapies:Ginkgo, St. John’s Wort, Ginseng, Echinacea, Saw Palmetto, and Kava. Ann InternMed. 2002;136:42–53.

15. Ioannides C. Pharmacokinetic interactions between herbal remedies andmedicinal drugs. Xenobiotica. 2002;32:451–78.

16. De Smet PA. Health risks of herbal remedies: an update. Clin PharmacolTher. 2004;76:1–17.

17. Sparreboom A, Cox MC, Acharya MR, Figg WD. Herbal remedies in theUnited States: potential adverse interactions with anticancer agents. J Clin Oncol.2004;22:2489–503.

18. Coxeter PD, McLachlan AJ, Duke CC, Roufogalis BD. Herb-drug inter-actions: an evidence based approach. Curr Med Chem. 2004;11:1513–25.

19. Foster BC, Arnason JT, Briggs CJ. Natural health products and drugdisposition. Annu Rev Pharmacol Toxicol. 2005;45:203–26.

20. Zhou S, Gao Y, Jiang W, Huang M, Xu A, Paxton JW. Interactions ofherbs with cytochrome P450. Drug Metab Rev. 2003;35:35–98.

21. Caron MF, White CM. Evaluation of the antihyperlipidemic properties ofdietary supplements. Pharmacotherapy. 2001;21:481–7.

22. Dorant E, van den Brandt PA, Goldbohm RA, Hermus RJ, Sturmans F.Garlic and its significance for the prevention of cancer in humans: a critical view.Br J Cancer. 1993;67:424–9.

23. Wang HX, Ng TB. Natural products with hypoglycemic, hypotensive,hypocholesterolemic, antiatherosclerotic and antithrombotic activities. Life Sci.1999;65:2663–77.

24. Spigelski D, Jones PJ. Efficacy of garlic supplementation in loweringserum cholesterol levels. Nutr Rev. 2001;59:236–41.

25. Stevinson C, Pittler MH, Ernst E. Garlic for treating hypercholesterolemia.A meta-analysis of randomized clinical trials. Ann Intern Med. 2000;133:420–9.

26. Fleischauer AT, Poole C, Arab L. Garlic consumption and cancerprevention: meta-analyses of colorectal and stomach cancers. Am J Clin Nutr.2000;72:1047–52.

27. Ackermann RT, Mulrow CD, Ramirez G, Gardner CD, Morbidoni L,Lawrence VA. Garlic shows promise for improving some cardiovascular riskfactors. Arch Intern Med. 2001;161:813–24.

28. Bianchini F, Vainio H. Allium vegetables and organosulfur compounds: dothey help prevent cancer? Environ Health Perspect. 2001;109:893–902.

29. Agarwal KC. Therapeutic actions of garlic constituents. Med Res Rev.1996;16:111–24.

30. Milner JA. A historical perspective on garlic and cancer. J Nutr. 2001;131:1027S–31S.

31. Fleischauer AT, Arab L. Garlic and cancer: a critical review of the epide-miologic literature. J Nutr. 2001;131:1032S–40S.

32. Amagase H, Petesch BL, Matsuura H, Kasuga S, Itakura Y. Intake ofgarlic and its bioactive components. J Nutr. 2001;131:955S–62S.

33. Lancaster JE, Shaw ML. g Glutamyl peptides in the biosynthesis of Salk(en)yl L cysteine sulfoxides (flavor precursors) in Allium. Phytochemistry. 1989;28:455–60.

34. Freeman F, Kodera Y. Garlic chemistry: stability of s-(2-propenyl)-2-propene-1-sulfinothioate (allicin) in blood, solvents, and simulated physiologicalfluids. J Agric Food Chem. 1995;43:2332–8.

35. Lawson LD, Hughes BG. Characterization of the formation of allicin andother thiosulfinates from garlic. Planta Med. 1992;58:345–50.

36. Iberl B, Winkler G, Muller B, Knobloch K. Quantitative determination ofallicin and alliin from garlic by HPLC. Planta Med. 1990;56:320–6.

37. Weinberg DS, Manier ML, Richardson MD, Haibach FG. Identification andquantification of organosulfur compliance markers in garlic extract. J Agric FoodChem. 1993;41:37–41.

38. Nagae S, Ushijima M, Hatono S, Imai J, Kasuga S, Matsuura H, Itakura Y,Higashi Y. Pharmacokinetics of the garlic compound S-allylcysteine. Planta Med.1994;60:214–7.

39. Borek C. Antioxidant health effects of aged garlic extract. J Nutr. 2001;131:1010S–5S.

40. Piscitelli SC, Burstein AH, Welden N, Gallicano KD, Falloon J. The effectof garlic supplements on the pharmacokinetics of saquinavir. Clin Infect Dis.2002;34:234–8.

41. Markowitz JS, Devane CL, Chavin KD, Taylor RM, Ruan Y, Donovan JL.Effects of garlic (Allium sativum L.) supplementation on cytochrome P450 2D6 and3A4 activity in healthy volunteers. Clin Pharmacol Ther. 2003;74:170–7.

42. Gallicano K, Foster B, Choudhri S. Effect of short-term administration ofgarlic supplements on single-dose ritonavir pharmacokinetics in healthy volun-teers. Br J Clin Pharmacol. 2003;55:199–202.

43. Venkatakrishnan K, von Moltke LL, Greenblatt DJ. Human drug metab-olism and the cytochromes P450: application and relevance of in vitro models.J Clin Pharmacol. 2001;41:1149–79.

44. Bertz RJ, Granneman GR. Use of in vitro and in vivo data to estimate thelikelihood of metabolic pharmacokinetic interactions. Clin Pharmacokinet. 1997;32:210–58.

45. von Moltke LL, Greenblatt DJ, Schmider J, Wright CE, Harmatz JS,Shader RI. In vitro approaches to predicting drug interactions in vivo. BiochemPharmacol. 1998;55:113–22.

46. Venkatakrishnan K, von Moltke LL, Obach RS, Greenblatt DJ. Drugmetabolism and drug interactions: application and clinical value of in vitro models.Curr Drug Metab. 2003;4:423–59.

47. Bjornsson TD, Callaghan JT, Einolf HJ, Fischer V, Gan L, Grimm S, Kao J,King SP, Miwa G, et al. The conduct of in vitro and in vivo drug-drug interactionstudies: a PhRMA perspective. J Clin Pharmacol. 2003;43:443–69.

48. von Moltke LL, Greenblatt DJ, Duan SX, Schmider J, Kudchadker L,Fogelman SM, Harmatz JS, Shader RI. Phenacetin O-deethylation by human livermicrosomes in vitro: inhibition by chemical probes, SSRI antidepressants,nefazodone, and venlafaxine. Psychopharmacology (Berl). 1996;128:398–407.

49. von Moltke LL, Greenblatt DJ, Harmatz JS, Duan SX, Harrel LM, Cotreau-Bibbo MM, Pritchard GA, Wright CE, Shader RI. Triazolam biotransformation byhuman liver microsomes in vitro: effects of metabolic inhibitors, and clinicalconfirmation of a predicted interaction with ketoconazole. J Pharmacol Exp Ther.1996;276:370–9.

50. von Moltke LL, Greenblatt DJ, Duan SX, Harmatz JS, Shader RI. Inhibitionof triazolam hydroxylation by ketoconazole, itraconazole, hydroxyitraconazole andfluconazole in vitro. Pharm Pharmacol Commun. 1998;4:443–5.

51. Perloff MD, von Moltke LL, Court MH, Kotegawa T, Shader RI, GreenblattDJ. Midazolam and triazolam biotransformation in mouse and human livermicrosomes: relative contribution of CYP3A and CYP2C9 isoforms. J PharmacolExp Ther. 2000;292:618–28.

52. Giancarlo GM, Venkatakrishnan K, Granda BW, von Moltke LL, GreenblattDJ. Relative contributions of CYP2C9 and 2C19 to phenytoin 4-hydroxylation in vitro:inhibition by sulfaphenazole, omeprazole and ticlopidine. Eur J Clin Pharmacol.2001;57:31–6.

53. von Moltke LL, Greenblatt DJ, Grassi JM, Granda BW, VenkatakrishnanK, Schmider J, Harmatz JS, Shader RI. Multiple human cytochromes contribute tobiotransformation of dextromethorphan in vitro: role of CYP2C9, CYP2C19,CYP2D6, and CYP3A. J Pharm Pharmacol. 1998;50:997–1004.

54. Schmider J, Greenblatt DJ, Fogelman SM, von Moltke LL, Shader RI.Metabolism of dextromethorphan in vitro: involvement of cytochromes P450 2D6,3A3/4, with a possible role of 2E1. Biopharm Drug Dispos. 1997;18:227–40.

55. Venkatakrishnan K, von Moltke LL, Greenblatt DJ. Human cytochromesP450 mediating phenacetin O-deethylation in vitro: validation of the high affinitycomponent as an index of CYP1A2 activity. J Pharm Sci. 1998;87:1502–7.

56. Venkatakrishnan K, von Moltke LL, Greenblatt DJ. Relative quantities ofcatalytically active CYP 2C9 and 2C19 in human liver microsomes: application ofthe relative activity factor approach. J Pharm Sci. 1998;87:845–53.

57. Hesse LM, Venkatakrishnan K, Court MH, von Moltke LL, Duan SX, ShaderRI, Greenblatt DJ. CYP2B6 mediates the in vitro hydroxylation of bupropion: poten-tial drug interactions with other antidepressants. Drug Metab Dispos. 2000;28:1176–83.

58. Zhou S, Chan E, Lim LY, Boelsterli UA, Li SC, Wang J, Zhang Q, HuangM, Xu A. Therapeutic drugs that behave as mechanism-based inhibitors ofcytochrome P450 3A4. Curr Drug Metab. 2004;5:415–42.

59. Perloff ES, Duan SX, Skolnik PR, Greenblatt DJ, von Moltke LL.Atazanavir: effects on P-glycoprotein transport and CYP3A metabolism in vitro.Drug Metab Dispos. 2005;33:764–70.

60. Bertelsen KM, Venkatakrishnan K, von Moltke LL, Obach RS, GreenblattDJ. Apparent mechanism-based inhibition of human CYP2D6 in vitro by par-oxetine: comparison with fluoxetine and quinidine. Drug Metab Dispos. 2003;31:289–93.

61. Erlund I, Meririnne E, Alfthan G, Aro A. Plasma kinetics and urinaryexcretion of the flavanones naringenin and hesperetin in humans after ingestion oforange juice and grapefruit juice. J Nutr. 2001;131:235–41.

62. Manach C, Donovan JL. Pharmacokinetics and metabolism of dietaryflavonoids in humans. Free Radic Res. 2004;38:771–85.

63. Manach C, Scalbert A, Morand C, Remesy C, Jimenez L. Polyphenols:food sources and bioavailability. Am J Clin Nutr. 2004;79:727–47.

64. von Moltke LL, Weemhoff JL, Bedir E, Khan IA, Harmatz JS, Goldman P,Greenblatt DJ. Inhibition of human cytochromes P450 by components of Ginkgobiloba. J Pharm Pharmacol. 2004;56:1039–44.

65. Jiang X, Williams KM, Liauw WS, Ammit AJ, Roufogalis BD, Duke CC,Day RO, McLachlan AJ. Effect of ginkgo and ginger on the pharmacokinetics andpharmacodynamics of warfarin in healthy subjects. Br J Clin Pharmacol. 2005;59:425–32.

66. Greenblatt DJ, von Moltke LL, Luo Y, Perloff ES, Horan KA, Bruce A,Reynolds RC, Harmatz JS, Avula B, et al. Ginkgo biloba does not alter clearance offlurbiprofen, a Cytochrome P450–2C9 substrate. J Clin Pharmacol. 2006;46:214–221.

67. Tsunoda SM, Velez RL, von Moltke LL, Greenblatt DJ. Differentiation ofintestinal and hepatic cytochrome P450 3A activity with use of midazolam as an invivo probe: effect of ketoconazole. Clin Pharmacol Ther. 1999;66:461–71.

809SWATER-SOLUBLE GARLIC AND HUMAN CYTOCHROMES P450

by on October 19, 2010

jn.nutrition.orgD

ownloaded from