bergamottin and 6--7--dihydroxybergamottin

Our objective was to determine whether Seville orange juice produces a grapefruit juice-like interaction with felodipine and whether bergamottin, 6',7'-dihydroxybergamottin, or other furocoumarins are involved.. In a randomized three-way crossover design, 10 volunteers received a felodipine 10-mg extended-release tablet with 240 mL of Seville orange juice, dilute grapefruit juice (that contained equivalent total molar concentrations of bergamottin plus 6',7'-dihydroxybergamottin), or common orange juice (negative control). The pharmacokinetics of felodipine and its dehydrofelodipine metabolite were determined. Juice concentrations of furocoumarins were measured. CYP3A4 inhibitory activity of newly identified furocoumarins was assessed.. The felodipine area under the plasma concentration-time curve was increased by 76% and 93% after Seville orange juice and grapefruit juice ingestion, respectively, compared with common orange juice. The effects of Seville orange juice and grapefruit juice were similar in that the felodipine maximum concentration was augmented while the terminal elimination half-life was unchanged and the dehydrofelodipine area under the plasma concentration time-curve was increased, but the dehydrofelodipine-felodipine area under the plasma concentration-time curve ratio was reduced. Bergamottin and 6',7'-dihydroxybergamottin concentrations were 5 and 36 micromol/L, respectively, in Seville orange juice and were 16 and 23 micromol/L, respectively, in dilute grapefruit juice. A newly identified furocoumarin, bergapten, was detected only in Seville orange juice (31 micromol/L), and it was found to be a mechanism-based inhibitor of recombinant CYP3A4. Relative to the control, 6',7'-dihydroxybergamottin (10 micromol/L) inhibited CYP3A4 activity in cultured intestinal epithelial cells by 93%, whereas bergapten (10 micromol/L) inhibited the activity by only 34%.. Seville orange juice and grapefruit juice interact with felodipine by a common mechanism, which is probably inactivation of intestinal CYP3A4. Bergamottin and 6',7'-dihydroxybergamottin may be "marker substances" in foods for this interaction. The lack of interaction between Seville orange juice and cyclosporine (INN, ciclosporin) suggests that grapefruit juice may also inhibit intestinal P-glycoprotein, whereas Seville orange juice may selectively "knock out" intestinal CYP3A4.

Topics: 5-Methoxypsoralen; Administration, Oral; Adult; Antihypertensive Agents; Beverages; Biological Availability; Caco-2 Cells; Citrus; Cross-Over Studies; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; DNA, Complementary; Enzyme Activation; Enzyme Inhibitors; Felodipine; Female; Food-Drug Interactions; Furocoumarins; Humans; Male; Methoxsalen; Mixed Function Oxygenases

Grapefruit is a moderate to strong inactivator of CYP3A4, which metabolizes up to 50% of marketed drugs. The inhibitory effect is mainly attributed to furanocoumarins present in the fruit, irreversibly inhibiting preferably intestinal CYP3A4 as suicide inhibitors. Effects on CYP3A4 victim drugs can still be measured up to 24 hours after grapefruit juice (GFJ) consumption. The current study aimed to establish a physiologically-based pharmacokinetic (PBPK) grapefruit-drug interaction model by modeling the relevant CYP3A4 inhibiting ingredients of the fruit to simulate and predict the effect of GFJ consumption on plasma concentration-time profiles of various CYP3A4 victim drugs. The grapefruit model was developed in PK-Sim and coupled with previously developed PBPK models of CYP3A4 substrates that were publicly available and already evaluated for CYP3A4-mediated drug-drug interactions. Overall, 43 clinical studies were used for model development. Models of bergamottin (BGT) and 6,7-dihydroxybergamottin (DHB) as relevant active ingredients in GFJ were established. Both models include: (i) CYP3A4 inactivation informed by in vitro parameters, (ii) a CYP3A4 mediated clearance estimated during model development, as well as (iii) passive glomerular filtration. The final model successfully describes interactions of GFJ ingredients with 10 different CYP3A4 victim drugs, simulating the effect of the CYP3A4 inactivation on the victims' pharmacokinetics as well as their main metabolites. Furthermore, the model sufficiently captures the time-dependent effect of CYP3A4 inactivation as well as the effect of grapefruit ingestion on intestinal and hepatic CYP3A4 concentrations.

Topics: Citrus paradisi; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme Inhibitors; Drug Interactions; Food-Drug Interactions; Furocoumarins

Natural products, including botanical dietary supplements and exotic drinks, represent an ever-increasing share of the health-care market. The parallel ever-increasing popularity of self-medicating with natural products increases the likelihood of co-consumption with conventional drugs, raising concerns for unwanted natural product-drug interactions. Assessing the drug interaction liability of natural products is challenging due to the complex and variable chemical composition inherent to these products, necessitating a streamlined preclinical testing approach to prioritize precipitant individual constituents for further investigation. Such an approach was evaluated in the current work to prioritize constituents in the model natural product, grapefruit juice, as inhibitors of intestinal organic anion-transporting peptide (OATP)-mediated uptake. Using OATP2B1-expressing MDCKII cells (Madin-Darby canine kidney type II) and the probe substrate estrone 3-sulfate, IC

Topics: Animals; Cells, Cultured; Citrus paradisi; Computer Simulation; Dogs; Estrone; Flavanones; Flavones; Food-Drug Interactions; Fruit and Vegetable Juices; Furocoumarins; Hesperidin; Humans; Inhibitory Concentration 50; Models, Biological; Organic Anion Transporters

Due to the furanocoumarin compounds in the fruit, the production and consumption of grapefruit have been affected in the past decades since the 'grapefruit juice effect' was declared. To provide elite germplasm and obtain knowledge for future citrus breeding programs, the contents of 4 furanocoumarin monomers (FCMs) in the juice sacs from 73 citrus germplasms were evaluated using ultra-performance liquid chromatography. 6',7'-Dihydroxybergamottin and bergamottin were dominant in all the tested grapefruits, while there were some pomelos with dominant epoxybergamottin, and some with dominant 6',7'-dihydroxybergamottin and bergamottin. The contents of FCMs were low or below detection in sweet oranges, mandarins, lemons and trifoliate oranges. The results also show that the dominant patterns of FCMs are genotype-related, and crossing and selection are effective approaches to alter FCM profiles in citrus breeding. Furthermore, the contribution of pomelo as a parent to grapefruit regarding their FCM profiles was discussed.

Topics: Chromatography, High Pressure Liquid; Citrus; Citrus paradisi; Fruit and Vegetable Juices; Furocoumarins

Dietary supplements are a multi-billion dollar business, with yearly profit increases. Allegedly safe, these supplements are marketed to a variety of niches, encompassing claims from immune support to weight loss. Six sports nutrition supplements were acquired that were labeled to contain the furanocoumarin(s) bergamottin and/or 6',7'-dihydroxybergamottin (DHB), both of which are potent irreversible inhibitors of the prominent drug metabolizing enzyme cytochrome P450 3A (CYP3A). Both furanocoumarins are typically present in grapefruit juice, which has been shown to inhibit intestinal CYP3A, perpetrating an increase in the systemic exposure of certain concomitant 'victim' drugs. The acquired supplements were analyzed using ultra-performance liquid chromatography coupled to both a photodiode array (PDA) detector and a triple quadrupole mass spectrometer (MS). Contrary to the product labeling, four of the supplements contained no detectable quantities of either furanocoumarin (LOD 0.060μg/capsule), while two of the supplements contained minimal amounts (one contained 12.13 (±0.23) μg bergamottin and 65.51 (±0.64) μg DHB per capsule; the other contained 2.705 (±0.069) μg bergamottin per capsule and no detectable quantities of DHB). A CYP3A inhibition bioassay was used to assess whether the actual content of the furanocoumarins correlated with CYP3A inhibitory activity. Despite the low amounts of bergamottin and DHB, CYP3A inhibition by the supplements was greater than could be accounted for by the two furanocoumarins. The additional activity suggests the presence of other potent or highly abundant CYP3A inhibitors.

Topics: Beverages; Chromatography, High Pressure Liquid; Citrus; Citrus paradisi; Cytochrome P-450 CYP3A Inhibitors; Dietary Supplements; Furocoumarins; Mass Spectrometry

Grapefruits (Citrus paradisi Macfad) contain several phytochemicals known to have health maintaining properties. Due to the consumer's interest in obtaining high levels of these phytochemicals, it is important to understand the changes in their levels by common household processing techniques. Therefore, mature Texas "Rio Red" grapefruits were processed by some of the common household processing practices such as blending, juicing, and hand squeezing techniques and analyzed for their phytochemical content by high performance liquid chromatography (HPLC). Results suggest that grapefruit juice processed by blending had significantly (P < 0.05) higher levels of flavonoids (narirutin, naringin, hesperidin, neohesperidin, didymin, and poncirin) and limonin compared to juicing and hand squeezing. No significant variation in their content was noticed in the juice processed by juicing and hand squeezing. Ascorbic acid and citric acid were significantly (P < 0.05) higher in juice processed by juicing and blending, respectively. Furthermore, hand squeezed fruit juice had significantly higher contents of dihydroxybergamottin (DHB) than juice processed by juicing and blending. Bergamottin and 5-methoxy-7 gernoxycoumarin (5-M-7-GC) were significantly higher in blended juice compared to juicing and hand squeezing. Therefore, consuming grapefruit juice processed by blending may provide higher levels of health beneficial phytochemicals such as naringin, narirutin, and poncirin. In contrast, juice processed by hand squeezing and juicing provides lower levels of limonin, bergamottin, and 5-M-7-GC. These results suggest that, processing techniques significantly influence the levels of phytochemicals and blending is a better technique for obtaining higher levels of health beneficial phytochemicals from grapefruits. Practical Application:  Blending, squeezing, and juicing are common household processing techniques used for obtaining fresh grapefruit juice. Understanding the levels of health beneficial phytochemicals present in the juice processed by these techniques would enable the consumers to make a better choice to obtain high level of these compounds.

Topics: Ascorbic Acid; Beverages; Chromatography, High Pressure Liquid; Citric Acid; Citrus paradisi; Disaccharides; Flavanones; Flavonoids; Food Handling; Furocoumarins; Glycosides; Hesperidin; Limonins; Plant Extracts

Grapefruit juice (GFJ) is known to affect the pharmacokinetics of a variety of drugs administered concomitantly and this is due to inhibition of intestinal CYP3A, a barrier protein for drug absorption. Some compounds such as furanocoumarin derivatives have been reported as inhibitors of the enzyme. On the other hand, inhibitory potentials of GFJ on CYP3A-oxidation activities differ widely between brands of juices. Information on the percentage contributed by ingredients in GFJ is also limited. Therefore, construction of prediction models for the CYP3A inhibitory potentials of GFJ brands was attempted by using concentrations of ingredients in GFJ. Concentrations of bergaptol, bergamottin, 6', 7'-dihydroxybergamottin, naringin, and naringenin in 23 kinds of GFJ were determined with high-performance liquid chromatography (HPLC). Furthermore, inhibitory effects on CYP3A activity were measured based on the initial rate for testosterone 6beta-hydroxylation in the presence of each GFJ. Results of multi-regression analyses between the ingredients and the enzymatic inhibitory effects revealed that concentrations of bergamottin, 6',7'-dihydroxybergamottin, and naringin were significant variables for CYP3A inhibition of GFJ. According to the standard partial regression coefficient for each explanatory variable, bergamottin and 6',7'-dihydroxybergamottin are the most important factors for inhibition. The multiple correlation coefficient (R) and the multiple correlation coefficient with leave-one-out cross validation (Q) of the model equation were 0.94 and 0.91, respectively. These results suggest that the concentrations of ingredients can explain most variances of inhibitory effects among brands. This model may be a useful method for the prediction of the GFJ interaction potential.

Topics: Antioxidants; Beverages; Citrus paradisi; Cytochrome P-450 CYP3A Inhibitors; Enzyme Inhibitors; Female; Flavanones; Food-Drug Interactions; Forecasting; Furocoumarins; Humans; In Vitro Techniques; Linear Models; Microsomes, Liver; Models, Statistical; Oxidation-Reduction; Testosterone

Furocoumarins are phototoxic and photogenotoxic natural plant constituents occurring in cosmetics, food and drugs. Grapefruit juice is considered as a major dietary source of furocoumarins although few is known about the variability of furocoumarins in grapefruit juice. We analyzed the major furocoumarins in eight commercial grapefruit juices and in freshly prepared juices made from pink grapefruit obtained from German retailers. Bergaptol was the major furocoumarin in commercial juices, followed by bergamottin and 6',7'-dihydroxy-bergamottin (DHB), whereas an inverse picture (DHB>bergamottin>bergaptol) was obtained in freshly prepared juices. Results from different batches of a single brand of commercial juice, purchased over a period of 7 months, revealed a variability of about 50% for the individual furocoumarins and the sum. In a study with healthy volunteers, consumption of 900 ml commercial grapefruit juice (containing 12.5mg bergaptol, 6.9 mg bergamottin, and 0.6 mg DHB) resulted in an average urinary excretion of 0.36 mg free plus 13.23 mg conjugated bergaptol within 6h. Other furocoumarins were not found in urine. Thus, other grapefruit furocoumarins were obviously converted in the human body, at least in part, into bergaptol excreted in urine, since the excreted amount of bergaptol exceeded the consumed one.

Topics: Adult; Beverages; Citrus paradisi; Female; Furocoumarins; Humans; Limit of Detection; Male; Young Adult

Since the early 1990's, grapefruit juice has been implicated in drug interaction with various furanocoumarins (FCs) now associated with the effect. Although FCs are present in various fruits and vegetables, it is their presence in grapefruit that has attracted the most attention. Studies have shown that FCs in grapefruit juice can vary significantly and from multiple causes. Most of all, FCs are stress-induced molecules, their levels affected by many factors ranging from UV exposure to insect infestation. There are also varietal and seasonal factors. In this study, juice processing and storage parameters were investigated. Prolonged fruit storage prior to processing and most steps involved in juice processing had little influence on the levels of 6',7'-dihydroxybergamottin (DHB), paradisin C, or bergamottin. However, products that were hot filled or stored at room temperature had lower amounts of DHB and paradisin C and higher amounts of bergaptol compared to juices that were not hot filled and stored at refrigerated temperatures. Both DHB and paradisin C are potent CYP3A4 inhibitors, while bergaptol is a very weak inhibitor. Bergamottin amounts decreased to a lesser extent. Therefore, grapefruit juice products that were hot filled or have been stored at room temperature for an extended period of time will have a reduced drug interaction potential.

Topics: Beverages; Citrus paradisi; Food Storage; Food-Drug Interactions; Fruit; Furocoumarins; Linear Models

Fungi metabolize polycyclic aromatic hydrocarbons by a number of detoxification processes, including the formation of sulfated and glycosidated conjugates. A class of aromatic compounds in grapefruit is the furanocoumarins (FCs), and their metabolism in humans is centrally involved in the "grapefruit/drug interactions." Thus far, the metabolism by fungi of the major FCs in grapefruit, including 6', 7'-epoxybergamottin (EB), 6', 7'-dihydroxybergamottin (DHB), and bergamottin (BM), has received little attention. In this study, Aspergillus niger was observed to convert EB into DHB and a novel water-soluble metabolite (WSM). Bergaptol (BT) and BM were also metabolized by A. niger to the WSM, which was identified as BT-5-sulfate using mass spectrometry, UV spectroscopy, chemical hydrolysis, and (1)H and (13)C nuclear magnetic resonance spectroscopy. Similarly, the fungus had a capability of metabolizing xanthotoxol (XT), a structural isomer of BT, to a sulfated analog of BT-5-sulfate, presumably XT-8-sulfate. A possible enzyme-catalyzed pathway for the grapefruit FC metabolism involving the cleavage of the geranyl group and the addition of a sulfate group is proposed.

Topics: Aspergillus niger; Citrus paradisi; Furocoumarins; Magnetic Resonance Spectroscopy; Mass Spectrometry; Spectrum Analysis

To investigate the potential interaction between selected ingredients of grapefruit juice and, the transport of talinolol, a P-gp substrate, across Caco-2 cells monolayers was determined in the absence and presence of distinct concentrations of grapefruit juice, bergamottin, 6',7'-dihydroxybergamottin, 6',7'-epoxybergamottin, naringin, and naringenin. Talinolol permeability was selectively inhibited by grapefruit juice and its components. The furano coumarin, 6',7'-epoxybergamottin, was the most potent inhibitor (IC(50) = 0.7 microM), followed by 6',7'-dihydroxybergamottin (IC(50) = 34 microM) and bergamottin that did not show any inhibition at concentrations up to 10 microM. The flavonoid aglycone naringenin was around 10-fold more potent than its glycoside naringin with IC(50) values of 236 and 2409 microM, respectively. The flavonoids and furanocoumarins tested in this study are in the same range of concentration they are present in the juice contributing, therefore, for the overall inhibitory effect of GFJ on P-gp activity. The in vitro data suggest that compounds present in grapefruit juice are able to inhibit the P-gp activity modifying the disposition of drugs that are P-gp substrates such as talinolol.

Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; Beverages; Caco-2 Cells; Citrus paradisi; Dose-Response Relationship, Drug; Flavanones; Food-Drug Interactions; Furocoumarins; Humans; Intestinal Absorption; Intestinal Mucosa; Membrane Transport Modulators; Permeability; Propanolamines

Grapefruit juice (GFJ) has been found to interact with several medications, increasing their oral bioavailability and the risk of toxicity. Inhibition of CYP3A4 in the small intestine by flavonoids (such as naringin and naringenin) and furanocoumarins (including bergamottin and 6',7'-dihydroxybergamottin) present in GFJ seems to be the predominant mechanism, although P-glycoprotein and influx transporters in the small intestine are also involved. The quantity of interactive compounds ingested may affect the magnitude and mechanism of the food-drug interaction. Therefore, these four compounds were quantified by HPLC analysis in commercially available and fresh-squeezed GFJ and in grapefruit tissues. Considerable variability in naringin (174-1492 micromol/L), bergamottin (1.0-36.6 micromol/L), and 6',7'-dihydroxybergamottin (0.22-52.5 micromol/L) was observed, whereas naringenin could not be detected. White grapefruit showed higher concentrations of naringin and furanocoumarins located in the albedo and flavedo compared with red varieties. Findings from this study suggest considering concentrations of components with a potential for drug interactions in GFJ-drug interaction studies. The concentration of potentially contributing compounds may crucially influence the magnitude of observed interaction and impair direct comparison of studies in which different juices have been used.

Topics: Beverages; Chromatography, High Pressure Liquid; Citrus paradisi; Flavanones; Flavonoids; Furocoumarins

Grapefruit juice (GJ) contains components that may increase the bioavailability of drugs; however, approaches to the removal of these components have been little investigated. It is known that furanocoumarin derivatives (FCs), such as bergamottin (BG) and 6',7'-dihydroxybergamottin (DHB) in GJ, induce such drug interactions. In the present study, it was found that the heat treatment of grapefruit juice decreases concentrations of BG and DHB as well as their interactions both in vitro and in vivo. We incubated GJ for 10, 20, 30, 40, 50, and 60 min at 37, 62, 72, and 95 degrees C; FCs in each sample were then measured, using high-performance liquid chromatography (HPLC). The concentrations of BG and DHB were decreased in a time- and temperature-dependent manner, by 82.5 and 97.9% respectively, after incubation for 1 h at 95 degrees C. In contrast, the concentration of bergaptrol (BT) increased in a time- and temperature-dependent manner (27.7% after 60 min at 95 degrees C). In addition, the effect of each GJ sample on testosterone 6beta-oxidation in human liver microsomes was observed. The inhibitory effects of GJ heated to 95 degrees C were decreased in a time-dependent manner, as in the case of BG and DHB concentrations. Furthermore, 2 ml of GJ treated for 60 min at 95 degrees C was administered into the rat duodenum. After 30 min, nifedipine (NFP) was administered intraduodenally at a dose of 3 mg/kg body weight. The concentrations of NFP in the plasma samples were determined by HPLC. No significant increase in the AUC of NFP was observed in the rats given heat-treated GJ. These results suggest that the heat treatment of GJ reduces the concentrations of FCs, thus eliminating the potential for drug interactions.

Topics: Animals; Area Under Curve; Beverages; Calcium Channel Blockers; Chromatography, High Pressure Liquid; Citrus paradisi; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inhibitors; Duodenum; Food-Drug Interactions; Furocoumarins; Hot Temperature; Hydroxytestosterones; Intubation, Gastrointestinal; Male; Microsomes, Liver; Molecular Structure; Nifedipine; Rats; Rats, Wistar; Time Factors

Grapefruit juice elevates blood levels of some drugs taken orally, primarily by inhibiting intestinal CYP3A4-mediated first-pass metabolism. Two prominent furanocoumarins in the juice, 6',7'-dihydroxybergamottin (DHB) and bergamottin (BG), have been demonstrated as important contributors to grapefruit juice-drug interactions. Using CYP3A4-expressing Caco-2 cells and representative probes from distinct CYP3A4 substrate subgroups (midazolam, testosterone), we compared the time-dependent inhibitory properties of DHB and BG. DHB rapidly inhibited CYP3A4 activity in a substrate-independent fashion with maximal inhibition (>/=85%) generally occurring within 30 min. In contrast, BG had a slower onset and exhibited substrate-dependent inhibition. Whereas testosterone 6beta-hydroxylation was inhibited by >50% with all exposure times (0.5-3 h), midazolam 1'-hydroxylation was unaffected, or even activated, with short exposure times (<1 h). After a 3-h exposure, however, BG had begun to "catch up" with DHB, causing >/=70% inhibition, independent of substrate. Likewise, loss of CYP3A4 protein, believed to reflect rapid intracellular degradation of the enzyme following mechanism-based inactivation, was comparable between the furanocoumarins (40-50%). The time course of BG-mediated inhibition was similar after just a 30-min exposure, indicating that the short exposure presumed to occur after juice ingestion is sufficient to initiate the events required to cause substantial inhibition (>/=50%). These results suggest that after ingestion of a glass of grapefruit juice, CYP3A4 is maximally inhibited by DHB before BG has the opportunity to act. However, foods containing BG but not DHB (e.g., lime juice) could produce a substrate-dependent interaction with drugs consumed concomitantly, but a substrate-independent interaction with drugs taken several hours after food consumption.

Topics: Caco-2 Cells; Catalysis; Citrus paradisi; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Dose-Response Relationship, Drug; Enzyme Inhibitors; Furocoumarins; Humans; Time Factors

It has been reported that grapefruit juice (GJ) causes a pharmacokinetic interaction with many drugs after co-ingestion. It is postulated that the substances in GJ may inhibit the first-pass metabolism during the intestinal absorption process. In recent years, several furanocoumarin derivatives that inhibit P450 activity in intestinal microsomes were isolated from GJ. In this study, we report the effects of the furanocoumarin derivatives in GJ on the nifedipine (NFP) pharmacokinetics in rats.. Three furanocoumarin derivatives (bergaptol [BT], bergamottin [BG], and 6',7'-dihydroxybergamottin [DHB]) found in GJ were used in this study. Each furanocoumarin was reconstituted in orange juice at the same concentration as in the GJ. Two milliliters of each sample was administered into the rat duodenum. After 30 min, NFP was intraduodenally administered at a dose of 3 mg/kg body weight. The NFP concentrations in the plasma samples were determined by HPLC.. A significant increase in the AUC of NFP was observed only in the rats administered BG; 1.5 times that of the control group. The result was quite identical with that of the group that was administered GJ. BT and DHB had no significant effects on the NFP pharmacokinetics.. The results strongly suggested that BG in GJ might be the substance that elevates the NFP plasma concentrations.

Topics: Animals; Area Under Curve; Calcium Channel Blockers; Citrus; Dose-Response Relationship, Drug; Drug Interactions; Food-Drug Interactions; Furocoumarins; Male; Nifedipine; Rats; Rats, Wistar

1. The presence of inhibitors of drug efflux transporters, such as P-glycoprotein (P-gp), in grapefruit juice (GFJ) was confirmed based on the uptake of [(3)H]-vinblastine (VBL) by Caco-2 cells. 2. The uptake of [(3)H]-VBL by Caco-2 cells was significantly increased by the ethyl acetate extract of GFJ as well as by cyclosporin A. The extract was separated on a Cosmosil column and the eluate with 60% methanol increased [(3)H]-VBL uptake, while the activity to inhibit CYP3A4 was greatest in the 70 and 80% eluates. 3. These results show that the major inhibitor of efflux transport of VBL is different from that of CYP3A4. 4. Further separation of the 60% methanol eluate afforded dihydroxybergamottin (DHBG). Both ethyl acetate extract of GFJ and DHBG increased steady-state [(3)H]-VBL uptake by LLC-GA5-COL300 cells. Besides DHBG, other furanocoumarins contained in GFJ, such as bergamottin, FC726, bergaptol and bergapten, increased the steady-state uptake of [(3)H]-VBL by Caco-2 cells. 5. The order of inhibitory potency of these compounds was FC726>DHBG>bergamottin>bergapten>bergaptol . While, the IC(50) values for inhibition of CYP3A4 were 0.075, 0.45, 1.0, 1.0 and >20 microM, respectively. Bergaptol specifically inhibited VBL efflux. 6. DHBG was thus identified as a candidate for inhibitors of VBL transport, together with other furanocoumarins. Moreover, partly involvement of the P-gp inhibition was suggested. 7. Therefore, the inhibition of efflux transport of drugs as well as of drug metabolism by CYP3A4 could be an important cause of drug-GFJ interaction.

Topics: 3-O-Methylglucose; 5-Methoxypsoralen; Acetates; Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; Caco-2 Cells; Carbon Radioisotopes; Cell Line; Cell Line, Transformed; Citrus; Coumarins; Cyclosporine; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Dose-Response Relationship, Drug; Furocoumarins; Humans; Hydroxylation; Magnetic Resonance Spectroscopy; Methoxsalen; Microsomes, Liver; Mixed Function Oxygenases; Phenylalanine; Plant Extracts; Recombinant Proteins; Testosterone; Tritium; Vinblastine

Five compounds including furanocoumarin monomers (bergamottin, 6', 7'-dihydroxybergamottin (DHB)), furanocoumarin dimers (4-¿¿6-hydroxy-71-¿(1-hydroxy-1-methyl)ethyl-4-methyl-6-(7-oxo-7H- furo¿3,2-g1benzopyran-4-yl)-4-hexenyl]oxy]-3,7-dimethyl- 2-octenyl]oxy]-7H-furo[3,2-g]¿1benzopyran-7-one (GF-I-1) and 4-¿¿6-hydroxy-7¿¿4-methyl-1-(1-methylethenyl)-6-(7-oxo-7H-furo¿3, 2-g1benzopyran-4-yl)-4-hexenylŏxy-3, 7-dimethyl-2-octenylŏxy-7H-furo¿3,2-g1benzopyran-7-one (GF-I-4)), and a sesquiterpene nootkatone have been isolated from grapefruit juice and screened for their inhibitory effects toward human cytochrome P450 (P450) forms using selective substrate probes. Addition of ethyl acetate extract of grapefruit juice into an incubation mixture resulted in decreased activities of CYP3A4, CYP1A2, CYP2C9, and CYP2D6. All four furanocoumarins clearly inhibited CYP3A4-catalyzed nifedipine oxidation in concentration- and time-dependent manners, suggesting that these compounds are mechanism-based inhibitors of CYP3A4. Of the furanocoumarins investigated, furanocoumarin dimers, GF-I-1 and GF-I-4, were the most potent inhibitors of CYP3A4. Inhibitor concentration required for half-maximal rate of inactivation (K(I)) values for bergamottin, DHB, GF-I-1, and GF-I-4 were calculated, respectively, as 40.00, 5. 56, 0.31, and 0.13 microM, whereas similar values were observed on their inactivation rate constant at infinite concentration of inhibitor (k(inact), 0.05-0.08 min(-1)). Apparent selectivity toward CYP3A4 does occur with the furanocoumarin dimers. In contrast, bergamottin showed rather stronger inhibitory effect on CYP1A2, CYP2C9, CYP2C19, and CYP2D6 than on CYP3A4. DHB inhibited CYP3A4 and CYP1A2 activities at nearly equivalent potencies. Among P450 forms investigated, CYP2E1 was the least sensitive to the inhibitory effect of furanocoumarin components. A sesquiterpene nootkatone has no significant effect on P450 activities investigated except for CYP2A6 and CYP2C19 (K(i) = 0.8 and 0.5 microM, respectively).

Topics: Aryl Hydrocarbon Hydroxylases; Beverages; Chromatography, High Pressure Liquid; Citrus; Coumarins; Cytochrome P-450 CYP2A6; Cytochrome P-450 CYP2C19; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Dose-Response Relationship, Drug; Enzyme Inhibitors; Furocoumarins; Humans; Inhibitory Concentration 50; Kinetics; Liver; Microsomes, Liver; Mixed Function Oxygenases; Polycyclic Sesquiterpenes; Sesquiterpenes; Substrate Specificity; Time Factors