Drugs and Scaffold That Inhibit Cytochrome P450 27A1 In Vitro and In Vivo.

Cytochrome P450 27A1 (CYP27A1) is a ubiquitous enzyme that hydroxylates cholesterol and other sterols. Complete CYP27A1 deficiency owing to genetic mutations is detrimental to human health, whereas 50% of activity retention is not and does not affect the whole body cholesterol levels. CYP27A1 is considered a potential therapeutic target in breast cancer and age-related neurodegenerative diseases; however, CYP27A1 inhibition should be ≤50%. Herein, 131 pharmaceuticals were tested for their effect on CYP27A1-mediated cholesterol 27-hydroxylation by in vitro enzyme assay. Of them, 14 drugs inhibited CYP27A1 by ≥75% and were evaluated for in vitro binding to the enzyme active site and for inhibition constants. All drugs except one (dasatinib) elicited a spectral response in CYP27A1 and had Ki values for cholesterol 27-hydroxylation either in the submicromolar (clevidipine, delavirdine, etravirine, felodipine, nicardipine, nilotinib, and sorafenib) or low micromolar range (abiratone, candesartan, celecoxib, dasatinib, nilvadipine, nimodipine, and regorafenib). Clevidipine, felodipine, nicardipine, nilvadipine, and nimodipine have the same 1,4-dihydropyridine scaffold and are indicated for hypertension. We used two of these antihypertensives (felodipine and nilvadipine) for administration to mice at a 1-mg/kg of body weight dose, daily, for 7 days. Mouse 27-hydroxycholesterol levels in the plasma, brain, and liver were reduced, whereas tissue levels of total cholesterol were unchanged. Structure-activity relationships within the 1,4-dihydropyridine scaffold were investigated, and features important for CY27A1 inhibition were identified. We confirmed our previous finding that CYP27A1 is a druggable enzyme and found additional drugs as well as the scaffold with potential for partial CYP27A1 inhibition in humans.

Evaluation of peppermint oil and ascorbyl palmitate as inhibitors of cytochrome P4503A4 activity in vitro and in vivo.

OBJECTIVES: Our study was designed to determine the effect of peppermint oil and ascorbyl palmitate on cytochrome P4503A4 (CYP3A4) activity in vitro and oral bioavailability of felodipine in humans. METHODS: Reversible and mechanism-based inhibitions of nifedipine oxidation were studied in human liver microsomes. The oral pharmacokinetics of felodipine and its dehydrofelodipine metabolite were determined in 12 healthy volunteers after administration of felodipine, 10-mg extended-release tablet, with grapefruit juice (300 mL), peppermint oil (600 mg), ascorbyl palmitate (500 mg), or water in a randomized 4-way crossover study. RESULTS: Peppermint oil (inhibition constant [K(i)] = 35.9 +/- 3.3 microg/mL, mean +/- SEM) and 2 constituents, menthol (K(i) = 87.0 +/- 7.0 micromol/L), and menthyl acetate (K(i) = 124.0 +/- 7.0 micromol/L), produced reversible inhibition of nifedipine oxidation. Ascorbyl palmitate was more potent (K(i) = 12.3 +/- 0.5 micromol/L). None of these substances were mechanism-based inhibitors. Grapefruit juice and peppermint oil increased the area under the curve (AUC) values of felodipine to 173% (range, 94%-280%; P <.01) and 140% (range, 77%-262%; P <.05), respectively, of those with water. They augmented the peak plasma concentration (C(max)) of felodipine and the AUC and C(max) of dehydrofelodipine but did not alter the half-life (t(1/2)) of either substance. Grapefruit juice decreased the dehydrofelodipine/felodipine AUC ratio, but peppermint oil did not. Ascorbyl palmitate did not change the pharmacokinetics of felodipine or dehydrofelodipine compared with water. CONCLUSIONS: Peppermint oil, menthol, menthyl acetate, and ascorbyl palmitate were moderately potent reversible inhibitors of in vitro CYP3A4 activity. Grapefruit juice increased the oral bioavailability of felodipine by inhibition of CYP3A4-mediated presystemic drug metabolism. Peppermint oil may also have acted by this mechanism. However, this requires further investigation. Ascorbyl palmitate did not inhibit CYP3A4 activity in vivo.

Grapefruit-felodipine interaction: effect of unprocessed fruit and probable active ingredients.

OBJECTIVES: To determine whether unprocessed grapefruit can cause a drug interaction, whether the active ingredients are naturally occurring, and whether specific furanocoumarins or flavonoids are involved. METHODS: The oral pharmacokinetics of felodipine and its dehydrofelodipine metabolite were determined after administration of felodipine 10 mg extended-release tablet with 250 mL commercial grapefruit juice, homogenized grapefruit segments, or extract of segment-free parts equivalent to one unprocessed fruit or water in a randomized four-way crossover study. Inhibition of recombinant CYP3A4 by furanocoumarins (bergamottin, 6',7'-epoxybergamottin, 6',7'-dihydroxybergamottin) and flavonoids (naringenin optical isomers) was determined. Furanocoumarin and naringenin precursor (naringin) concentrations were measured in each grapefruit treatment. RESULTS: Felodipine AUC with commercial grapefruit juice, grapefruit segments, or grapefruit extract was on average 3-fold higher than that with water. Felodipine peak concentration was higher, but the half-life was unchanged. The dehydrofelodipine/felodipine AUC ratio was reduced. The furanocoumarins produced mechanism-based and competitive inhibition of CYP3A4. Bergamottin was the most potent mechanism-based inhibitor. Naringenin isomers produced only competitive inhibition. Bergamottin, 6',7'-dihydroxybergamottin, and naringin concentrations varied among grapefruit treatments but were sufficient to inhibit markedly in vitro CYP3A4 activity. CONCLUSIONS: Unprocessed grapefruit can cause a drug interaction with felodipine. The active ingredients are naturally occurring in the grapefruit. Bergamottin is likely important in drug interactions with commercial grapefruit juice. 6',7'-Dihydroxybergamottin and naringin may be more important in grapefruit segments because they are present in higher concentrations. Any therapeutic concern for a drug interaction with commercial grapefruit juice should now be extended to include whole fruit and possibly confectioneries made from grapefruit peel.

Grapefruit juice--felodipine interaction in the elderly.

BACKGROUND: Grapefruit juice can increase the oral bioavailability of a broad range of medications. This interaction has not been assessed in the elderly. METHODS: Twelve healthy elderly people (70 to 83 years of age) were administered 5 mg felodipine extended release with 250 mL grapefruit juice or water in a single-dose study. Subsequently, 6 of these people received 2.5 mg felodipine for 2 days, followed by 5 mg felodipine for 6 days with 250 mL grapefruit juice or water in a steady-state study. Plasma concentrations of felodipine and dehydrofelodipine metabolite, blood pressure, and heart rate were measured over 24 hours after single and final steady-state dose. RESULTS: Mean felodipine area under the curve and maximum concentration were 2.9-fold and 4.0-fold greater, respectively, with grapefruit juice in both studies. Interindividual variability in the extent of the interaction was high. Felodipine apparent elimination half-life was not altered. Dehydrofelodipine area under the curve and maximum concentration were increased and dehydrofelodipine/felodipine area under the curve ratio was reduced. Systolic and diastolic blood pressures were lower with grapefruit juice in the single-dose study, whereas they were not different between treatments in the steady-state study. Curvilinear relationships existed between plasma felodipine concentration and changes in systolic and diastolic blood pressures. Heart rates were higher with grapefruit juice in both studies; however, this effect was greater and more prolonged at steady state. CONCLUSIONS: A normal dietary amount of grapefruit juice produced a pronounced, unpredictable, and sustained pharmacokinetic interaction with felodipine by reducing its presystemic metabolism in the elderly. The different blood pressure results between the studies can be explained by felodipine concentration-blood pressure response relationships. The elderly should be particularly cautioned about concomitant grapefruit juice and felodipine ingestion.

The interaction effect of grapefruit juice is maximal after the first glass.

OBJECTIVE: To compare the acute effect of grapefruit juice intake on the pharmacokinetics and haemodynamic effects of felodipine ER tablets with the interaction after 14 days intake of drug with juice. METHODS: Twelve healthy male volunteers were included in this cross-over trial and randomly allocated to a daily intake of a 10-mg felodipine extended release tablet with water or grapefruit juice for 14 days. The two study periods were separated by at least 14 days. The pharmacokinetics of felodipine and dehydrofelodipine, as well as the haemodynamic effects of the drug, were studied during day 1 and 14 in each period. RESULTS: Similarly to previous single-dose studies, the treatment during the first day with grapefruit juice increased the AUC (+73%) and Cmax (+138%) of felodipine when compared with the control treatment. On day 14 a similar effect of grapefruit juice was observed, with an increased AUC24 (+57%) and Cmax (+114%) of felodipine compared with the control experiment. A significant accumulation of felodipine occurred during both the control (+37%) and grapefruit juice (+25%) period. The extent of accumulation was not significantly different in the two treatment periods. The pharmacokinetics of the metabolite dehydrofelodipine were affected to a similar extent by the juice on day 1 and day 14. The first dose of felodipine together with grapefruit juice was associated with a significant additional increase in heart rate when compared with the control therapy, whereas there was no additional effect on blood pressure when therapy included grapefruit juice. On day 14 the intake of drug with juice resulted in an additional increase in heart rate and reduction in diastolic blood pressure in comparison with the control experiment. Furthermore, the vascularly related adverse events were more frequent in the period including grapefruit juice. CONCLUSION: The interaction between grapefruit juice and felodipine appears to be already fully developed after the first glass of grapefruit juice, as the change in pharmacokinetics in comparison with the control experiment is similar on day 1 and on day 14. Concomitant intake of 10 mg felodipine ER and the juice is associated with increased haemodynamic effects in healthy subjects both after a single dose and following 14 days of concomitant intake.

Effects of grapefruit juice ingestion--pharmacokinetics and haemodynamics of intravenously and orally administered felodipine in healthy men.

OBJECTIVE: To examine the effect of grapefruit juice on the metabolism of felodipine following intravenous and oral administration. METHODS: The study had a randomised, four-way, crossover design in 12 healthy males. Single doses of felodipine were given as an intravenous infusion for 1 h (1.5 mg) or as an oral extended release (ER) tablet (10 mg). Grapefruit juice (150 ml) or water was ingested 15 min prior to drug intake. RESULTS: Intake of grapefruit juice did not significantly alter the intravenous pharmacokinetics of felodipine compared to control treatment, whereas after oral drug administration it did lead to an increase in the mean AUC and Cmax by 72% and 173%, respectively, and the mean absolute bioavailability was increased by 112%. The fraction of the oral felodipine dose reaching the portal system was increased from 45% to 80% when intake of drug was preceded by grapefruit juice ingestion. The pharmacokinetics of the primary metabolite, dehydrofelodipine, was affected by the intake of juice, resulting in a 46% increase in Cmax. Juice intake immediately before oral felodipine resulted in more pronounced haemodynamic effects of the drug as measured by diastolic blood pressure and heart rate. However, the haemodynamic effects of the intravenous administration were not altered by juice intake. Vascular-related adverse events were reported more frequently when oral drug administration was preceded by juice intake compared with control treatment. Taking grapefruit juice immediately prior to intravenous felodipine administration did not cause any alteration in the adverse event pattern. CONCLUSION: The main acute effect of the grapefruit juice on the plasma concentrations of felodipine is mediated by inhibition of gut wall metabolism.

Protection against hypoxic injury of rat proximal tubules by felodipine via a calcium-independent mechanism.

Most evidence for a key role of calcium entry in hypoxia-induced renal damage stems from studies with calcium channel blockers. In proximal tubules, a primary site of renal ischaemic injury, only phenyl-alkylamines, especially verapamil, have been studied. In the present study the effect of the dihydropyridine felodipine on hypoxic injury in isolated rat proximal tubules was investigated. To discriminate between the block of calcium entry and other effects, the enantiomers and a non-calcium blocking derivative of felodipine (H186/86) were included. Cell membrane injury was assessed by measuring the release of lactate dehydrogenase (LDH). At high concentrations (100 microM) felodipine, H186/86 and the two enantiomers all protected rat proximal tubules against hypoxia-induced injury to the same extent. Absence of extracellular calcium did not offer protection, but rather enhanced hypoxic injury. All dihydropyridines used increased the intracellular potassium concentration during normoxia. Felodipine attenuated the hypoxia-induced loss of cellular potassium. We have tried to mimic the effects of felodipine by using potassium channel blockers. The potassium channel blockers quinidine and glibenclamide afforded some protection against hypoxic injury, although their effects on cellular potassium were equivocal. We conclude that the dihydropyridine calcium channel blocker felodipine protects rat proximal tubules against hypoxic injury via a calcium-independent mechanism. We propose that high levels of intracellular potassium and attenuation of potassium loss during hypoxia are important in this protection.

Grapefruit juice-felodipine interaction: reproducibility and characterization with the extended release drug formulation.

1. Felodipine 10 mg extended release was administered with 250 ml regular-strength grapefruit juice or water in a randomized crossover manner followed by a second grapefruit juice treatment in 12 healthy men. The pharmacokinetics of felodipine and primary oxidative metabolite, dehydrofelodipine, were evaluated. 2. Initial grapefruit juice treatment increased felodipine AUC (mean +/- s.d.; 56.6 +/- 21.9 vs 28.1 +/- 11.5 ng ml-1 h; P < 0.001) and Cmax (8.1 +/- 2.5 vs 3.3 +/- 1.2 ng ml-1; P < 0.001) compared with water. Felodipine tmax (median; 2.8 vs 3.0 h) and t1/2 (7.3 +/- 3.7 vs 6.9 +/- 3.6 h) were not altered. 3. Readministration of felodipine with grapefruit juice produced mean felodipine AUC (61.5 +/- 32.2 ng ml-1 h) and Cmax (8.4 +/- 4.8 ng ml-1) which were similar to the initial grapefruit juice treatment 1-3 weeks previously. Felodipine AUC (r = 0.73, P < 0.01) and Cmax (r = 0.69, P < 0.02) correlated between grapefruit juice treatments among individuals. 4. The % increase in felodipine AUC with the initial grapefruit juice treatment compared with water correlated with the % increase in felodipine Cmax among individuals (r = 0.80, P < 0.01). Dehydrofelodipine AUC (74.7 +/- 28.7 vs 48.5 +/- 16.3 ng ml-1 h; P < 0.01) and Cmax (12.1 +/- 2.9 vs 7.9 +/- 2.6 ng ml-1; P < 0.01) were augmented with grapefruit juice compared with water.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between time of intake of grapefruit juice and its effect on pharmacokinetics and pharmacodynamics of felodipine in healthy subjects.

In this randomised, cross-over study, in nine healthy males given felodipine ER 10 mg PO 200 ml grapefruit juice was found to increase the plasma levels of felodipine even when the juice was taken 24 hours before the drug. Grapefruit juice drunk simultaneously with and 1, 4, 10 or 24 hours before the drug administration resulted in a 32-99% increase in mean Cmax values of felodipine, relative to concomitant water and felodipine intake. The effect on AUC was also significant when juice was taken up to 10 h before the drug. The effect of the interaction decreased with increasing time between juice and drug intake. All treatments produced a significant decrease in diastolic blood pressure and an increase in heart rate in comparison with morning basal values. The change in haemodynamic variables was approximately the same after all treatment combinations. Headache was reported more frequently after treatments including grapefruit juice.

In vivo reversal of multidrug resistance by two new dihydropyridine derivatives, S16317 and S16324.

Two new dihydropyridine derivatives with low calcium channel affinity, S16317 and S16324, were found to fully overcome multidrug resistance in vitro. These two compounds increased doxorubicin cytotoxicity on the human COLO 320DM cell line and completely reversed the vincristine resistance of murine P388/VCR cells. In vivo, S16324 administered p.o. (200 mg/kg on days 1 to 4) or i.p. (50 mg/kg on days 1, 5, 9) in combination with vincristine (i.p.) restored the antitumor activity of vincristine in P388/VCR-bearing mice. S16317 showed a reversing activity when administered p.o., i.v. (days 1 to 4) or i.p. (days 1, 5, 9) at the same dose (25 mg/kg), suggesting a remarkable bioavailability. Moreover, these two compounds potentiated the antitumor activity of vincristine in the sensitive P388 leukemia, increasing the number of long-term survivors. These results suggest that combination chemotherapy using S16317 or S16324 would be effective not only in circumventing multidrug resistance but also in preventing the emergency of a population of resistant tumor cells in sensitive tumors.

Grapefruit juice--felodipine interaction: mechanism, predictability, and effect of naringin.

Grapefruit juice produces a marked and variable increase in felodipine bioavailability. The pharmacokinetics of felodipine and its single primary oxidative metabolite, dehydrofelodipine, were studied after drug administration with 200 ml water, grapefruit juice, or naringin in water at the same concentration as the juice in a randomized crossover trial of nine healthy men. With grapefruit juice, mean +/- SEM felodipine area under the plasma concentration-time curve (AUC) and peak plasma concentration (Cmax) were 206% +/- 23% (range, 123% to 330%, p < 0.01) and 170% +/- 24% (range, 127% to 310%, p < 0.02), respectively, compared with water. Dehydrofelodipine/felodipine ratios for AUC (1.5 +/- 0.2 versus 2.2 +/- 0.2, p < 0.001) and felodipine Cmax (1.5 +/- 0.2 versus 2.2 +/- 0.2, p < 0.001) were reduced, consistent with inhibition of presystemic felodipine metabolism. Intersubject changes in felodipine and dehydrofelodipine AUC supported inhibition of both primary and secondary metabolic steps as a mechanism. The interaction could not be predicted from baseline pharmacokinetics with water and did not result in more consistent bioavailability among individuals. Naringin solution produced much less of an interaction, showing that other factors were important.

Felodipine pharmacokinetics and plasma concentration vs effect relationships.

UNLABELLED: Felodipine was completely absorbed from an oral solution (OS), as well as from the conventional (CT) and extended release (ER) tablets. The time to peak plasma concentration increased in the order OS < CT < ER. Peak plasma felodipine concentrations were significantly lower and trough concentrations higher when felodipine was administered in the ER-tablet compared with CT and oral solution. The variability in plasma felodipine concentration during the dose interval, expressed as the fluctuation index, increased in the order ER o.d. < CT b.i.d. < CT o.d. The distribution of the AUC of plasma felodipine concentrations vs time determined in 140 individuals was unimodal, indicating that genetic factors are unlikely to influence the metabolism of felodipine to any clinically significant extent. With increasing age the plasma concentrations and the terminal half-life of felodipine increased, whereas the plasma clearance and the ratio of the AUC of the primary pyridine metabolite to that of unchanged drug decreased. The time to maximum plasma felodipine concentration, the bioavailability and the volume of distribution were not consistently influenced by age. Body weight, body mass index and concomitant intake of beta-blockers had negligible influence on the pharmacokinetics of felodipine. The pharmacokinetics in the limited number females did not differ substantially from that of the males in our investigation. No consistent effect on blood pressure was seen in healthy subjects after administration of felodipine. In hypertensive patients, however, there was a good relationship between plasma felodipine concentration and antihypertensive effect. There was no hysteresis for the reduction in blood pressure. The relationship between plasma felodipine concentration and antihypertensive effect could, in most patients, be described by a modified Emax model. The average Emax value was estimated to be approximately 30 mmHg. Placebo correction decreased the magnitude of the blood pressure reduction. The Emax estimates increased with increasing initial blood pressures whereas age had a negligible effect. Patients with high and low plasma felodipine concentrations had similar Emax values. The EC50 values were not influenced by any of these factors. The Emax model used was less suitable for patients with low initial blood pressure levels. IN CONCLUSION: The plasma concentration vs time profile of felodipine is modified by using different pharmaceutical formulations, without loss of bioavailability. As a group, the elderly have higher total concentrations of unchanged felodipine in plasma compared with young individuals. The variation in plasma concentrations between individuals is, however, only partially explained by age. There is a good and direct relationship between felodipine plasma concentrations and antihypertensive effects in hypertensive patients.(ABSTRACT TRUNCATED AT 400 WORDS)