Expression of enzymatically active CYP3A4 by Caco-2 cells grown on extracellular matrix-coated permeable supports in the presence of 1alpha,25-dihydroxyvitamin D3

miRNA-27b levels are associated with CYP3A activity in vitro and in vivo

Previous in vitro studies have shown that microRNA‐27b (miR‐27b) may regulate mRNA levels of CYP3A4, vitamin D receptor (VDR), and Peroxisome proliferator‐activated receptor α (PPARα) as well as CYP3A4 protein expression and activity. In vitro studies have also shown that vitamin D may affect the expression of CYP3A4. The primary aim of this pilot study was to investigate the association between miR‐27b and CYP3A expression and activity. The secondary aim was to investigate the association between 25‐hydroxy vitamin D in serum and CYP3A activity. Mi‐RNA‐27b was quantified using real‐time PCR in serum samples (n = 28) and 25‐hydroxyvitamin D was measured and correlated with the levels of the endogenous CYP3A activity marker 4β‐hydroxycholesterol. In addition, the correlation between miR‐27b and CYP3A activity, measured by dextromethorphan N‐demethylation and 6β‐hydroxylation of testosterone and the gene expression of CYP3A4, VDR and PPARα were assessed in 20 human liver samples. A significant association between circulatory miR‐27b levels and 4β‐hydroxycholesterol ratio was found; P = 0.04, and between hepatic miR‐27b levels and CYP3A activity, measured by dextromethorphan N‐demethylation in human liver (P = 0.04). There was no association between hepatic miR‐27b and mRNA levels of CYP3A4, VDR or PPARα. There was a significant association between serum 25‐hydroxyvitamin D levels and 4β‐hydroxycholesterol ratio, P = 0.002. In conclusion, this pilot‐study supports the hypothesis that miR‐27b levels as well as 25‐hydroxyvitamin D may affect CYP3A activity in vivo. The results indicate that miR‐27b exerts its inhibitory effect on a translational level rather than affecting mRNA levels.

No impact of vitamin D on the CYP3A biomarker 4β-hydroxycholesterol in patients with abnormal glucose regulation

Purpose

To investigate the effect of vitamin D3 on hepatic Cytochrome P450 enzyme (CYP) 3A4 in patients with abnormal glucose regulation using the endogenous marker 4β-hydroxycholesterol (4β-OHC):cholesterol ratio.

Methods

The present study took advantage of a trial primarily aiming to investigate the effect of vitamin D3 on beta cell function and insulin sensitivity in patients with abnormal glucose regulation. 44 subjects were randomized to receive vitamin D3, 30000 IU given orally once weekly or placebo for 8 weeks. The two sample t-test was used to test the means of the intra-individual differences of 4β-OHC:cholesterol ratio between the two groups.

Results

Mean (SD) 4β-OHC in the whole group of patients before and after the intervention was 26 (11) ng/ml and 26 (12). Mean (SD) 4β-OHC:cholesterol ratio in the whole group of patients before and after the intervention was 0.12 (0.046) and 0.13 (0.047). In the Vitamin D group mean (SD) serum 25-OH-vitamin D3 increased from 46 (16) to 85nM (13) during the corresponding time period. To investigate the impact of vitamin D3 on hepatic CYP3A4 we calculated the mean intra-individual differences in 4β-OHC:cholesterol ratio (delta 4β-OHC:cholesterol ratio) before versus after the intervention in the two treatment groups. The difference (95% CI) between delta 4β-OHC:cholesterol ratio in the control group and intervention group was -0.0010 (-0.0093, 0.0072), a difference being not statistically significant (p = 0.80).

Conclusions

We provide further evidence that vitamin D3 may not substantially affect hepatic CYP3A4. This does not exclude the possibility of an impact of intestinal first-pass metabolism of orally administered drugs which should be investigated.

Trial Registration

ClinicalTrials.gov NCT01497132

Effect of brivaracetam on CYP3A activity, measured by oral midazolam

Brivaracetam is a synaptic vesicle protein 2A ligand in phase III development for epilepsy. A phase I, open-label, randomized study was conducted in 42 healthy male participants to assess the effect of brivaracetam on CYP3A activity using midazolam as a probe. Participants were randomized to oral brivaracetam 5, 50, or 150 mg/day from Day 8 to Day 14. A single oral dose (7.5 mg) of midazolam was administered on Days 1, 13, and 20, and full pharmacokinetic profiles were obtained. For all brivaracetam doses, the areas under the plasma concentration-time curves from 0 to infinity (AUCinf ) for midazolam and 1'-hydroxymidazolam were similar on Days 13 and 20 compared with Day 1. Following brivaracetam 150 mg/day, the Day 13/Day 1 AUCinf ratio (90% confidence interval) was 1.09 (0.97, 1.21) and 1.04 (0.93, 1.17) for midazolam and 1'-hydroxymidazolam, respectively. For the Day 20/Day 1 comparison, the corresponding AUCinf ratios were 1.10 (0.98, 1.23) and 1.07 (0.97, 1.18). Maximum midazolam plasma concentration was increased on both Day 13 and Day 20 vs. Day 1 but the relevance of this finding was unclear. This study indicates that brivaracetam up to 150 mg/day has no significant inducing or inhibiting effect on CYP3A activity.

In situ perfusion in rodents to explore intestinal drug absorption: challenges and opportunities

The in situ intestinal perfusion technique in rodents is a very important absorption model, not only because of its predictive value, but it is also very suitable to unravel the mechanisms underlying intestinal drug absorption. This literature overview covers a number of specific applications for which the in situ intestinal perfusion set-up can be applied in favor of established in vitro absorption tools, such as the Caco-2 cell model. Qualities including the expression of drug transporters and metabolizing enzymes relevant for human intestinal absorption and compatibility with complex solvent systems render the in situ technique the most designated absorption model to perform transporter-metabolism studies or to evaluate the intestinal absorption from biorelevant media. Over the years, the in situ intestinal perfusion model has exhibited an exceptional ability to adapt to the latest challenges in drug absorption profiling. For instance, the introduction of the mesenteric vein cannulation allows determining the appearance of compounds in the blood and is of great use, especially when evaluating the absorption of compounds undergoing intestinal metabolism. Moreover, the use of the closed loop intestinal perfusion set-up is interesting when compounds or perfusion media are scarce. Compatibility with emerging trends in pharmaceutical profiling, such as the use of knockout or transgenic animals, generates unparalleled possibilities to gain mechanistic insight into specific absorption processes. Notwithstanding the fact that the in situ experiments are technically challenging and relatively time-consuming, the model offers great opportunities to gain insight into the processes determining intestinal drug absorption.

Vitamin D receptor activation induces P-glycoprotein and increases brain efflux of quinidine: an intracerebral microdialysis study in conscious rats

PURPOSE

Since the vitamin D receptor (VDR) was found to up-regulate cerebral P-glycoprotein expression in vitro and in mice, we extend our findings to rats by assessing the effect of rat Vdr activation on brain efflux of quinidine, a P-gp substrate that is eliminated primarily by cytochrome P450 3a.

METHODS

We treated rats with vehicle or the active VDR ligand, 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3] (4.8 or 6.4 nmol/kg i.p. every 2nd day × 4) and examined P-gp expression and cerebral quinidine disposition via microdialysis in control and treatment studies conducted longitudinally in the same rat.

RESULTS

The 6.4 nmol/kg 1,25(OH)2D3 dose increased cerebral P-gp expression 1.75-fold whereas hepatic Cyp3a remained unchanged. Although there was no change in systemic clearance elicited by 1,25(OH)2D3, brain extracellular fluid quinidine concentrations were lower in treated rats. We noted that insertion of indwelling catheters increased plasma protein binding of quinidine and serial sampling decreased the blood:plasma concentration ratio, factors that alter distribution ratios in microdialysis studies. After appropriate correction, KECF/P,uu and KECF/B,uu, or ratios of quinidine unbound concentrations in brain extracellular fluid to plasma or blood at steady-state, were more than halved.

CONCLUSION

We demonstrate that VDR activation increases cerebral P-gp expression and delimits brain penetration of P-gp substrates.

Modulation of cytochrome P450 metabolism and transport across intestinal epithelial barrier by ginger biophenolics

Natural and complementary therapies in conjunction with mainstream cancer care are steadily gaining popularity. Ginger extract (GE) confers significant health-promoting benefits owing to complex additive and/or synergistic interactions between its bioactive constituents. Recently, we showed that preservation of natural "milieu" confers superior anticancer activity on GE over its constituent phytochemicals, 6-gingerol (6G), 8-gingerol (8 G), 10-gingerol (10 G) and 6-shogaol (6S), through enterohepatic recirculation. Here we further evaluate and compare the effects of GE and its major bioactive constituents on cytochrome P450 (CYP) enzyme activity in human liver microsomes by monitoring metabolites of CYP-specific substrates using LC/MS/MS detection methods. Our data demonstrate that individual gingerols are potent inhibitors of CYP isozymes, whereas GE exhibits a much higher half-maximal inhibition value, indicating no possible herb-drug interactions. However, GE's inhibition of CYP1A2 and CYP2C8 reflects additive interactions among the constituents. In addition, studies performed to evaluate transporter-mediated intestinal efflux using Caco-2 cells revealed that GE and its phenolics are not substrates of P-glycoprotein (Pgp). Intriguingly, however, 10 G and 6S were not detected in the receiver compartment, indicating possible biotransformation across the Caco-2 monolayer. These data strengthen the notion that an interplay of complex interactions among ginger phytochemicals when fed as whole extract dictates its bioactivity highlighting the importance of consuming whole foods over single agents. Our study substantiates the need for an in-depth analysis of hepatic biotransformation events and distribution profiles of GE and its active phenolics for the design of safe regimens.

Human small intestinal epithelial cells differentiated from adult intestinal stem cells as a novel system for predicting oral drug absorption in humans

Adult intestinal stem cells (ISCs) possess both a long-term proliferation ability and differentiation capability into enterocytes. As a novel in vitro system for the evaluation of drug absorption, we characterized a human small intestinal epithelial cell (HIEC) monolayer that differentiated from adult ISCs. Continuous proliferation/differentiation from ISCs consistently conferred the capability of maturation of enterocytes to HIECs over 25 passages. The morphologically matured HIEC monolayer consisted of polarized columnar epithelia with dense microvilli, tight junctions, and desmosomes 8 days after seeding onto culture inserts. Transepithelial electrical resistance across the monolayer was 9-fold lower in HIECs (98.9 Ω × cm(2)) than in Caco-2 cells (900 Ω × cm(2)), which indicated that the looseness of the tight junctions in the HIEC monolayer was similar to that in the human small intestine (approximately 40 Ω × cm(2)). No significant differences were observed in the overall gene expression patterns of the major drug-metabolizing enzymes and transporters between the HIEC and Caco-2 cell monolayers. Furthermore, the functions of P-glycoprotein and breast cancer resistance protein in the HIEC monolayer were confirmed by the vectorial transport of marker substrates and their disappearance in the presence of specific inhibitors. The apparent drug permeability values of paracellularly transported compounds (fluorescein isothiocyanate-dextran 4000, atenolol, and terbutaline) and nucleoside transporter substrates (didanosine, ribavirin, and doxifluridine) in the HIEC monolayer were markedly higher than those of Caco-2 cells, whereas transcellularly transported drugs (pindolol and midazolam) were equally well permeated. In conclusion, the HIEC monolayer can serve as a novel and superior alternative to the conventional Caco-2 cell monolayer for predicting oral absorption in humans.

Plasma levels of 25-hydroxyvitamin D3 and in vivo markers of cytochrome P450 3A activity in Swedes and Koreans: effects of a genetic polymorphism and oral contraceptives

In vitro studies have shown that vitamin D may induce several cytochrome P450 (CYP) enzymes in general and CYP3A4 in particular. The primary aim of this study was to investigate the relationship between plasma levels of 25-hydroxyvitamin D3 and suggested in vivo markers of CYP3A activity in healthy volunteers from Sweden and Korea. Plasma concentrations of 25-hydroxyvitamin D3 were analysed in samples from three previously performed studies, and the correlation between these levels and suggested in vivo markers of CYP3A activity was investigated by means of nonparametric correlation. In addition, we studied the modulating effects of three vitamin D receptor promoter polymorphisms on the association between 25-hydroxyvitamin D3 and CYP3A enzyme activity in Swedish subjects. The plasma levels of 25-hydroxyvitamin D3 were not significantly associated with CYP3A phenotypes in any of the three studies, but after accounting for the vitamin D receptor polymorphism rs4516035, there was a significant positive association between 25-hydroxyvitamin D3 and CYP3A activity (p = 0.004). Swedes (n = 65) had significantly higher 25-hydroxyvitamin D3 levels than Koreans (n = 67), 75 nM compared with 31 nM (p < 0.001). Swedish women taking oral contraceptives (OC) (n = 19) had somewhat higher plasma levels of 25-hydroxyvitamin D3 compared with Swedish women not taking oral contraceptives (n = 21), 89 and 72 nM, respectively (p = 0.02). In conclusion, our results suggest that the overall influence on the CYP3A activity by 25-hydroxyvitamin D3 is of marginal importance.

Contribution of baicalin on the plasma protein binding displacement and CYP3A activity inhibition to the pharmacokinetic changes of nifedipine in rats in vivo and in vitro

Baicalin purified from the root of Radix scutellariae is widely used in clinical practices. This study aimed to evaluate the effect of baicalin on the pharmacokinetics of nifedipine, a CYP3A probe substrate, in rats in vivo and in vitro. In a randomised, three-period crossover study, significant changes in the pharmacokinetics of nifedipine (2 mg/kg) were observed after treatment with a low (0.225 g/kg) or high (0.45 g/kg) dose of baicalin in rats. In the low- and high-dose groups of baicalin-treated rats, C max of total nifedipine decreased by 40%±14% (P<0.01) and 65%±14% (P<0.01), AUC0-∞ decreased by 41%±8% (P<0.01) and 63%±7% (P<0.01), Vd increased by 85%±43% (P<0.01) and 224%±231% (P<0.01), and CL increased by 97%±78% (P<0.01) and 242%±135% (P<0.01), respectively. Plasma protein binding experiments in vivo showed that C max of unbound nifedipine significantly increased by 25%±19% (P<0.01) and 44%±29% (P<0.01), respectively, and there was a good correlation between the unbound nifedipine (%) and baicalin concentrations (P<0.01). Furthermore, in vitro results revealed that baicalin was a competitive displacer of nifedipine from plasma proteins. In vitro incubation experiments demonstrated that baicalin could also competitively inhibit CYP3A activity in rat liver microsomes in a concentration-dependent manner. In conclusion, the pharmacokinetic changes of nifedipine may be modulated by the inhibitory effects of baicalin on plasma protein binding and CYP3A-mediated metabolism.

Investigating permeability related hurdles in oral delivery of 11-keto-β-boswellic acid

11-Keto-β-boswellic acid (KBA) is an important and potent boswellic acids responsible for anti-inflammatory action of Boswellia extract. However, its pharmaceutical development has been severely limited by its poor oral bioavailability. The present work aims to investigate the permeability related hurdles in oral delivery of KBA. Gastrointestinal stability, gastrointestinal metabolism, adsorption-desorption kinetics and Caco-2 permeability studies have been carried out. KBA was found poorly permeable with Papp value of 2.85 ± 0.14 × 10(-6)cm/s. Higher absorptive transport indicated role of carrier mediated transport. Moreover, KBA transport across monolayer showed saturation kinetics at higher concentrations. KBA exposed to 1α,25-(OH)2 vitamin D3 treated cell monolayer showed the lowest Papp value of 2.01×10(-6) ± 0.02 × 10(-6)cm/s indicating role of CYP3A4 mediated metabolism during KBA transport. Metabolic stability experiments in jejunum S9 fractions further confirmed this. KBA was found unstable in simulated gastrointestinal fluids and also got accumulated in the enterocytes. Sorption and desorption kinetic studies using Caco-2 cells further confirmed accumulation of KBA inside the enterocytes. KBA also showed pH dependent permeability with higher flux at gradient pH condition of pH 6.5 at apical and 7.4 at basolateral. Taken as whole, the major permeability related hurdles that hampered oral bioavailability of KBA included its gastrointestinal instability, CYP3A4 mediated intestinal metabolism, accumulation within the enterocytes and saturable kinetics. The present investigation may help in designing novel drug delivery system for KBA.

In vitro inhibition of metabolism but not transport of gliclazide and repaglinide by Cree medicinal plant extracts

ETHNOPHARMACOLOGICAL RELEVANCE

Interactions between conventional drug and traditional medicine therapies may potentially affect drug efficacy and increase the potential for adverse reactions. Cree traditional healing is holistic and patients may use medicinal plants simultaneously with the conventional drugs. However, there is limited information that these medicinal plants may interact with drugs and additional mechanistic information is required. In this study, extracts from traditionally used Cree botanicals were assessed for their potential interaction that could alter the disposition of two blood glucose lowering drugs, gliclazide (Diamicron) and repaglinide (Gluconorm) though inhibition of either metabolism or transport across cell membranes.

MATERIALS AND METHODS

The effect of 17 extracts on metabolism was examined in a human liver microsome assay by HPLC and individual cytochrome P450s 2C9, 2C19, 2C8 and 3A4 in a microplate fluorometric assay. Gliclazide, rhaponticin and its aglycone derivative, rhapontigenin were also examined in the fluorometric assay. The effect on transport was examined with 11 extracts using the intestinal epithelial Caco-2 differentiated cell monolayer model at times up to 180 min.

RESULTS

Both blood glucose lowering medications, gliclazide and repaglinide traversed the Caco-2 monolayer in a time-dependent manner that was not affected by the Cree plant extracts. Incubation of the Cree plant extracts inhibited CYP2C9, 2C19, 2C8 and 3A4-mediated metabolism, and the formation of four repaglinide metabolites: M4, m/z 451-A, m/z 451-B and the glucuronide of repaglinide in the human liver microsome assay. Gliclazide caused no significant inhibition. Likewise, rhaponticin had little effect on the enzymes causing changes of less than 10% with an exception of 17% inhibition of CYP2C19. By contrast, the aglycone rhapontigenin showed the greatest effects on all CYP-mediated metabolism. Its inhibition ranged from a mean of 58% CYP3A4 inhibition to 89% inhibition of CYP2C9. While rhaponticin and the aglycone did not show significant effects on repaglinide metabolism, they demonstrated inhibition of gliclazide metabolism. The aglycone significantly affected levels of gliclazide and its metabolites.

CONCLUSION

These studies demonstrate that the Cree plant extracts examined have the potential in vitro to cause drug interactions through effects on key metabolic enzymes.

Nuclear receptors in regulation of biotransformation enzymes and drug transporters in the placental barrier

Over the past 20 years, the toxicological and protective roles of the placental barrier with respect to drug detoxification and transporter-controlled protection of the fetus have been intensively examined. Several cytochrome P450 enzymes are expressed in placental trophoblast at different stages of pregnancy, though only a few of these have functional activity to metabolize xenobiotics. Drug transporters such as P-glycoprotein/MDR1 or breast cancer resistance protein (BCRP) are highly expressed in the placenta, and their functional activities have been demonstrated in the placenta both in vitro and in vivo. In addition, several studies have reported on ligand-activated transcription factors and nuclear receptors referred to as "xenosensors" in the placenta. The xenosensors control transcriptional regulation of both xenobiotic-metabolizing enzymes and drug transporters in different organs. Their ligands include toxic compounds and environmental pollutants, drugs, as well as herbal, dietary or vitamin supplements. Nevertheless, it remains debatable whether the placental barrier adapts to toxic injuries coming either from maternal medication or environmental contamination and whether the placenta contains a mechanism to respond dynamically in protecting the developing fetus. In the present paper, we summarize current knowledge about the activity and expression of major ligand-activated transcriptional mechanisms involved in biotransformation enzymes and transporters regulation in human placenta. In particular, we highlight the emerging roles of aryl hydrocarbon (AHR), vitamin D (VDR), glucocorticoid (GR) and pregnane X (PXR) receptors in that regulation. We show that the placenta constitute a unique metabolizing organ with significant overlap of exogenous and endogenous compounds metabolism controlled by nuclear receptors.

Baicalin pharmacokinetic profile of absorption process using novel in-vitro model: cytochrome P450 3A4-induced Caco-2 cell monolayers combined with rat intestinal rinse fluids

Objectives

This study was designed to investigate baicalin (BG) pharmacokinetic profile in absorption process using a new model and evaluate the potentiality as a new model.

Methods

The effects of BG on intestinal cytochrome P450 3A4 (CYP3A) protein/mRNA expression, activity and permeability glycoprotein (P-gp) were evaluated in CYP3A4-induced Caco-2 cell monolayers or rats. Intestinal rinse fluids (IF) were obtained from rat were added to modified Caco-2 monolayers.

Key findings

Orally administered BG (7 days pretreatment) inhibited intestinal CYP3A activity and protein expression. Baicalein (B) converted from BG by IF was detected in the upper jejunum in a portion-dependent manner. Subsequently, most BG were converted to B in the caecum. In modified Caco-2 monolayers, BG exhibited no effect on CYP3A4 activity or mRNA, whereas B and BG treated with IF inhibited CYP3A4 transcription and activity.

Conclusions

Intestinal CYP3A was inhibited following oral administration of BG to rat. Correspondingly, BG-mediated CYP3A inhibition was shown in vitro using modified Caco-2 monolayers treated with IF. Hence, in-vivo intestinal absorption pharmacokinetic was reproduced in vitro. IF is a key determinant of intestinal absorption, and it facilitated inhibition of CYP3A by B, not BG.

Nuclear-receptor-mediated regulation of drug- and bile-acid-transporter proteins in gut and liver

Adverse drug events (ADEs) are a common cause of patient morbidity and mortality and are classically thought to result, in part, from variation in expression and activity of hepatic enzymes of drug metabolism. It is now known that alterations in the expression of genes that encode drug- and bile-acid-transporter proteins in both the gut and liver play a previously unrecognized role in determining patient drug response and eventual clinical outcome. Four nuclear receptor (NR) superfamily members, including pregnane X receptor (PXR, NR1I2), constitutive androstane receptor (NR1I3), farnesoid X receptor (NR1H4), and vitamin D receptor (NR1I1), play pivotal roles in drug- and bile-acid-activated programs of gene expression to coordinately regulate drug- and bile-acid transport activity in the intestine and liver. This review focuses on the NR-mediated gene activation of drug and bile-acid transporters in these tissues as well as the possible underlying molecular mechanisms.

Interplay between vitamin D and the drug metabolizing enzyme CYP3A4

Cytochrome P450 3A4 (CYP3A4) is a multifunctional enzyme involved in both xenobiotic and endobiotic metabolism. This review focuses on two aspects: regulation of CYP3A4 expression by vitamin D and metabolism of vitamin D by CYP3A4. Enterohepatic circulation of vitamin D metabolites and their conjugates will be also discussed. The interplay between vitamin D and CYP3A4 provides new insights into our understanding of how enzyme induction can contribute to vitamin D deficiency. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Toxic effects of dietary exposure to T-2 toxin on intestinal and hepatic biotransformation enzymes and drug transporter systems in broiler chickens

The effects of the mycotoxin T-2 on hepatic and intestinal drug-metabolizing enzymes (cytochrome P450) and drug transporter systems (MDR1 and MRP2) in poultry were investigated during this study. Broiler chickens received either uncontaminated feed, feed contaminated with 68μg/kg or 752μg/kg T-2 toxin. After 3weeks, the animals were euthanized and MDR1, MRP2, CYP1A4, CYP1A5 and CYP3A37 mRNA expression were analyzed using qRT-PCR. Along the entire length of the small intestine no significant differences were observed. In the liver, genes coding for CYP1A4, CYP1A5 and CYP3A37 were significantly down-regulated in the group exposed to 752μg/kg T-2. For CYP1A4, even a contamination level of 68μg/kg T-2 caused a significant decrease in mRNA expression. Expression of MDR1 was not significantly decreased in the liver. In contrast, hepatic MRP2 expression was significantly down-regulated after exposure to 752μg/kg T-2. Hepatic and intestinal microsomes were prepared to test the enzymatic activity of CYP3A. In the ileum and liver CYP3A activity was significantly increased in the group receiving 752μg/kg T-2 compared to the control group. The results of this study show that drug metabolizing enzymes and drug transporter mechanisms can be influenced due to prolonged exposure to relevant doses of T-2.

Vitamin D and drug-metabolising enzymes

Experimental studies on the molecular regulation of human drug metabolism have revealed that vitamin D up-regulates transcription of several key enzymes, such as CYP3A4, through the vitamin D receptor pathway in intestinal and hepatic cells. Recent data suggest that this results in seasonal changes with higher clearance of orally administered drugs during periods with high UV-B radiation and vitamin D levels. Taken together, vitamin D status might contribute to inter- and intraindividual differences in drug metabolism, but the therapeutic impact of these findings remains to be established.

CYP3A4 and seasonal variation in vitamin D status in addition to CYP2D6 contribute to therapeutic endoxifen level during tamoxifen therapy

Tamoxifen is a widely utilized adjuvant anti-estrogen agent for hormone receptor-positive breast cancer, known to undergo CYP2D6-mediated bioactivation to endoxifen. However, little is known regarding additional genetic and non-genetic determinants of optimal endoxifen plasma concentration. Therefore, 196 breast cancer patients on tamoxifen were enrolled in this prospective study over a 24-month period. Blood samples were collected for pharmacogenetic and drug-level analysis of tamoxifen and metabolites. Regression analysis indicated that besides CYP2D6, the recently described CYP3A4*22 genotype, seasonal variation, and concomitant use of CYP2D6-inhibiting antidepressants were significant predictors of endoxifen concentration. Of note, genetic variation explained 33 % of the variability while non-genetic variables accounted for 13 %. Given the proposed notion of a sub-therapeutic endoxifen concentration for predicting breast cancer recurrence, we set the therapeutic threshold at 18 nM, the 20th percentile for endoxifen level among enrolled patients in this cohort. Nearly 70 % of CYP2D6 poor metabolizers as well as extensive metabolizers on potent CYP2D6-inhibiting antidepressants exhibited endoxifen levels below 18 nM, while carriers of CYP3A4*22 were twofold less likely to be in sub-therapeutic range. Unexpectedly, endoxifen levels were 20 % lower during winter months than mean levels across seasons, which was also associated with lower vitamin D levels. CYP3A4*22 genotype along with sunshine exposure and vitamin D status may be unappreciated contributors of tamoxifen efficacy. The identified covariates along with demographic variables were integrated to create an endoxifen concentration prediction algorithm to pre-emptively evaluate the likelihood of individual patients falling below the optimal endoxifen concentration.

Serum levels of 25-hydroxyvitamin D and the CYP3A biomarker 4β-hydroxycholesterol in a high-dose vitamin D supplementation study

The primary aim was to study the relationship between individual serum levels of 25-hydroxyvitamin D and 4β-hydroxycholesterol, which is an endogenous biomarker of the drug-metabolizing CYP3A enzymes. In addition, the relationship between this biomarker and inflammation, measured as C-reactive protein (CRP), was investigated. Serum samples were used from a recently performed clinical trial in patients with antibody deficiency or increased susceptibility to respiratory tract infections that were randomized to either placebo or high-dose (4000 IU/day) vitamin D for 12 months. One hundred sixteen patients were included in the final analyses, and serum samples collected 6 months after study start were analyzed. At this time point, 25-hydroxyvitamin D levels were found to range between 10 and 284 nM. Individual levels of 25-hydroxyvitamin D as well as CRP were compared with 4β-hydroxycholesterol levels. In addition, all participants were genotyped for two polymorphisms (Taq1 and Foq1) in the vitamin D receptor gene. There was no significant correlation between individual serum levels of 25-hydroxyvitamin D and 4β-hydroxycholesterol. However, a moderate, but statistically significant, negative correlation between CRP and 4β-hydroxycholesterol levels was observed. This study in patients with highly variable serum levels of 25-hydroxyvitamin D could not reveal any relationship between vitamin D and 4β-hydroxycholesterol, an endogenous biomarker of CYP3A activity. However, the negative correlation between CRP and 4β-hydroxycholesterol supports earlier experimental results that inflammation may suppress hepatic CYP3A activity, a finding of potentially high clinical relevance that warrants further exploration.

1α,25-Dihydroxyvitamin D3-liganded vitamin D receptor increases expression and transport activity of P-glycoprotein in isolated rat brain capillaries and human and rat brain microvessel endothelial cells

Induction of the multidrug resistance protein 1 (MDR1)/P-glycoprotein (P-gp) by the vitamin D receptor (VDR) was investigated in isolated rat brain capillaries and rat (RBE4) and human (hCMEC/D3) brain microvessel endothelial cell lines. Incubation of isolated rat brain capillaries with 10 nM of the VDR ligand, 1α,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] for 4 h increased P-gp protein expression fourfold. Incubation with 1,25(OH)(2)D(3) for 4 or 24 h increased P-gp transport activity (specific luminal accumulation of NBD-CSA, the fluorescent P-gp substrate) by 25-30%. In RBE4 cells, Mdr1b mRNA was induced in a concentration-dependent manner by exposure to 1,25(OH)(2)D(3). Concomitantly, P-gp protein expression increased 2.5-fold and was accompanied by a 20-35% reduction in cellular accumulation of the P-gp substrates, rhodamine 6G (R6G), and HiLyte Fluor 488-labeled human amyloid beta 1-42 (hAβ(42)). In hCMEC/D3 cells, a 3 day exposure to 100 nM 1,25(OH)(2)D(3) increased MDR1 mRNA expression (40%) and P-gp protein (threefold); cellular accumulation of R6G and hAβ(42) was reduced by 30%. Thus, VDR activation up-regulates Mdr1/MDR1 and P-gp protein in isolated rat brain capillaries and rodent and human brain microvascular endothelia, implicating a role for VDR in increasing the brain clearance of P-gp substrates, including hAβ(42), a plaque-forming precursor in Alzheimer's disease.

A Semi-Mechanistic Metabolism Model of CYP3A Substrates in Pregnancy: Predicting Changes in Midazolam and Nifedipine Pharmacokinetics

Physiological changes in pregnancy, including changes in body composition and metabolic enzyme activity, can alter drug pharmacokinetics. A semi-mechanistic metabolism model was developed to describe the pharmacokinetics of two cytochrome P450 3A (CYP3A) substrates, midazolam and nifedipine, in obstetrics patients. The model parameters were optimized to fit the data of oral midazolam pharmacokinetics in pregnant women, by increasing CYP3A-induced hepatic metabolism 1.6-fold in the model with no change in gut wall metabolism. Fetal metabolism had a negligible effect on maternal plasma drug concentrations. Validation of the model was performed by applying changes in volume of distribution and metabolism, consistent with those observed for midazolam, to the pharmacokinetics parameters of immediate-release nifedipine in healthy volunteers. The predicted steady-state areas under the concentration–time curve (AUCs) for nifedipine were within 15% of the data observed in pregnant women undergoing treatment for preterm labor. This model predicts the pharmacokinetics of two CYP3A substrates in pregnancy, and may be applicable to other CYP3A substrates as well.

Cyclamen Trochopteranthum: Cytotoxic activity and possible adverse interactions including drugs and carcinogens

OBJECTIVE: To examine the effect of water extracts of cyclamen tubers on the expression of main cytochrome P450 (CYP450s) including CYP1A1, CYP1A2 CYP2E1, CYP2B6, CYP2C9 and CYP3A4 that participate in the metabolism of both drugs and carcinogens and cytotoxic activity in human cancer cell lines, namely HepG2 and Caco-2. METHODS: Cyclamen trochopteranthum tubers were extracted with dH(2)O and then lyophilized under vacuum. Infrared spectral study was made for extracts by Fourier transform infrared spectroscopy (FT-IR). Cytotoxic activity of cyclamen was determined by crystal violet staining in HepG2 and Caco-2 cells. CYP expression was determined by reverse transcription polymerase chain reaction (RT-PCR). RESULTS: Cyclamen water extract had moderate cytotoxic activity. It was found that lethal concentration (LC50) value of the cyclamen extract was 50 and 125 μg/mL in HepG2 and Caco-2 cell lines, respectively. Moreover, it caused induction and suppression of CYP450s mRNA levels in HepG2 and Caco-2 cells. CONCLUSION: Cyclamen may have a potential not only inhibition and/or induction of the metabolism of certain co-administered drugs but also development of toxicity, mutagenesis and malignant transformation due to induction or suppression of the CYP450s dependent drug metabolizing enzymes.

A co-culture system of human intestinal Caco-2 cells and lymphoblastoid TK6 cells for investigating the genotoxicity of oral compounds

Here, we assessed a co-culture system of intestinal Caco-2 cells and lymphoblastoid TK6 cells for modelling the role of intestinal first-pass effects, i.e. absorption and metabolism, in the genotoxicity of oral drugs and food contaminants. Caco-2 cells were seeded onto semipermeable culture inserts for 21 days until differentiation, and then TK6 cells were added to the basal compartment. After apical loading with mutagenic compounds [methylmethanesulfonate (MMS), benzo[a]-pyrene (BaP) and aflatoxin B1 (AFB1)], comet and micronucleus assays were performed on both cell lines. MMS (10 µg/ml) showed positive results in the micronucleus assays in both cell lines, even though DNA damage was only detected in the Caco-2 cells with the comet assay. At concentrations of 0.5-50 µM, BaP induced dose-dependent comet and micronucleus formation at 24h in Caco-2 cells, but no DNA damage was observed in TK6 cells. Although AFB1 failed to induce comet formation, it resulted in a high level of micronuclei in both cell lines. Treatment of Caco-2 cells with the CYP3A4 inhibitor, ketoconazole, inhibited the AFB1-induced cytotoxicity and micronucleus formation in TK6 cells, suggesting that intestinal metabolism is involved in the AFB1 genotoxic response in TK6 cells. Our results suggest that the Caco-2/TK6 co-culture model is suitable for modelling the role of intestinal biotransformation and transport processes in the genotoxic potential of oral drugs and food contaminants in target blood cells.

The effects of intralaboratory modifications to media composition and cell source on the expression of pharmaceutically relevant transporters and metabolizing genes in the Caco-2 cell line

Expression and function of drug transporters and drug-metabolizing enzymes (DMEs) in the gastrointestinal tract are critical attributes of intestinal physiology that influence the absorption of orally administered compounds. The purpose of this study was to examine the effects of media composition and cell source on mRNA expression and function of pharmaceutically relevant drug transporters and DMEs from two different sources of Caco-2 cells. Briefly, cells were cultured in either minimum essential medium alpha or Dulbecco's modified Eagle's medium. Total RNA was isolated from each experimental group, and mRNA expression was evaluated using quantitative reverse-transcriptase polymerase chain reaction arrays. Principal component analysis was used to analyze results, which indicated variable transporter and metabolic expression attributable to differences in media composition and cell source. In addition, transport properties of paracellular markers and proton-dependent oligopeptide transporter-mediated substrates across Caco-2 cell monolayers were assessed. Transport experiments demonstrated significant differences in both paracellular and transcellular permeation resultant from differences in media composition and cell source. These studies support previous findings that media composition and cell source may significantly impact expressional and functional characteristics of Caco-2 cells. Standardization of culture-related methodology may reduce variability associated with Caco-2 cells, enabling more meaningful intralaboratory and interlaboratory data comparisons.

Rate of onset of inhibition of gut-wall and hepatic CYP3A by clarithromycin

AIMS

To determine the extent and time-course of hepatic and intestinal cytochrome P450 3A (CYP3A) inactivation due to the mechanism-based inhibitor clarithromycin.

METHODS

Intestinal and hepatic CYP3A inhibition was examined in 12 healthy volunteers following the administration of single and multiple doses of oral clarithromycin (500 mg). Intestinal biopsies were obtained under intravenous midazolam sedation at baseline and after the first dose, on days 2-4, and on days 6-8 of the clarithromycin treatment. The formation of 1'-hydroxymidazolam in biopsy tissue and the serum 1'-hydroxymidazolam:midazolam ratio were indicators of intestinal and hepatic CYP3A activity, respectively.

RESULTS

Intestinal CYP3A activity decreased by 64 % (p = 0.0029) following the first dose of clarithromycin, but hepatic CYP3A activity did not significantly decrease. Repeated dosing of clarithromycin caused a significant decrease in hepatic CYP3A activity (p = 0.005), while intestinal activity showed little further decline. The CYP3A5 or CYP3A4*1B genotype were unable to account for inter-individual variability in CYP3A activity.

CONCLUSIONS

Following the administration of clarithromycin, the onset of hepatic CYP3A inactivation is delayed compared to that of intestinal CYP3A. The time-course of drug-drug interactions due to clarithromycin will vary with the relative contribution of intestinal and hepatic CYP3A to the clearance and bioavailability of a victim substrate.

Andrographolide inhibits the expression and metabolic activity of cytochrome P450 3A4 in the modified Caco-2 cells

AIM OF THE STUDY

The aim of this study is to examine the effects of andrographolide on intestinal enzyme cytochrome P450 3A4 (CYP3A4) and predict whether oral administration of andrographolide-containing remedy leads to herb-drug interaction.

MATERIALS AND METHODS

Caco-2 cells are treated with 1α, 25-dihydroxyvitamin D3 for 3 wks to induce the expression of CYP3A4, and then andrographolide (1, 10, 100 μM) is added and treated for 72 h. Upon the further 4-h testosterone (250 μM) or nifedipine (200 μM) treatment, the basolateral medium samples and the Caco-2 monolayers are collected for analyses.

RESULTS

Andrographolide (1, 10, 100 μM) significantly down-regulates the mRNA level and protein level of CYP3A4, and inhibits nifedipine oxidation and testosterone 6β-hydroxylation.

CONCLUSION

Oral administration of andrographolide likely leads to reduction of the metabolic activity of intestinal CYP3A4, therefore herb preparations containing andrographolide may result to herb-drug interactions in combination therapy.

Intestinal CYP3A4 and midazolam disposition in vivo associate with VDR polymorphisms and show seasonal variation

Vitamin D, whose levels vary seasonally with sunlight, is activated to 1α,25-dihydroxyvitamin D(3) that binds the vitamin D receptor (VDR) and transcriptionally regulates intestinal CYP3A4 expression. We genotyped VDR polymorphisms and determined their associations with intestinal CYP3A4 and with midazolam pharmacokinetics, and whether intestinal CYP3A4 levels/activity varied seasonally. The VDR BsmIG > A (rs1544410) polymorphism was significantly associated with CYP3A4 jejunal expression/activity, with CYP3A4 duodenal mRNA, and with midazolam area under the curve (AUC). Intestinal CYP3A4 expression/activity was significantly higher in biopsies with the VDR promoter polymorphisms Cdx2-3731G > A and GATA-1012A > G that increase VDR activation of target genes. Duodenal CYP3A4 mRNA was significantly higher between April and September than between October and March. Midazolam p.o. AUC and oral bioavailability trended higher October through March compared to April through September. These data suggest VDR polymorphisms are predictors of intestinal CYP3A4, and that CYP3A4 intestinal expression varies seasonally--likely related to annual changes in UV sunlight and vitamin D levels.

Estimating intestinal mucosal permeation of compounds using Caco-2 cell monolayers

Step-by-step protocols are provided in this unit for the measurement of apparent permeability coefficients of compounds using Caco-2 cell monolayers as an in vitro model of the intestinal mucosa. Procedures for culturing the cells and transmonolayer transport studies are also included. Critical issues for successfully estimating intestinal mucosal permeation of drugs are discussed. Step-by-step protocols are provided in this unit for the measurement of apparent permeability coefficients of compounds using.

Potential of an in vitro toolbox combined with exposure data as a first step for the risk assessment of dietary chemical contaminants

In vitro risk assessment of dietary contaminants has become a priority in human food safety. This paper proposes an in vitro approach associating different complementary tools in an original toolbox and aims to improve the assessment of the toxicological impact of dietary contaminants at realistic human exposure levels, with a special focus on the intestinal compartment. The system is based on the use of four complementary cellular tools, namely stress gene induction in transgenic strains of Escherichia coli, modulation of the activity of key biotransformation enzymes (cytochrome P-450 (CYP) 1A1 and 3A4) in a human intestinal cell line, and activation of aryl hydrocarbon receptor (AhR) and oestrogenic receptor (ER)-dependent genes in agonistic and antagonistic assays with luciferase reporter cells. It was applied to four chosen model molecules: ochratoxin A (OTA) and deoxynivalenol (DON), two common food-borne mycotoxins, and imazalil (IMA) and benomyl (BEN), two fungicides widely occurring in foodstuffs. All these assays were performed at or around a realistic intestinal concentration, determined through a deterministic approach based on the calculation of a theoretical maximum daily intake (TMDI). Using the four model molecules, it is clearly highlighted that induction of CYP1A1 activity and inhibition of CYP3A4 activity occurred in Caco-2 cells at a realistic intestinal concentration of IMA. Furthermore, some bacterial stress genes were induced in a range of realistic concentrations, following exposure to DON and IMA. In addition, BEN clearly provoked an ER agonistic activity in a human oestrogen sensitive reporter cell line. All these results are in accordance with the literature, suggesting that the in vitro toolbox constitutes an interesting approach in order to obtain a first 'fingerprint' of dietary contaminants at realistic human exposure for further risk assessment.

Cell growing density affects the structural and functional properties of Caco-2 differentiated monolayer

The human intestinal Caco-2 cell line has been extensively used as a model of the intestinal barrier. However, it is widely reported in literature that culture-related conditions, as well as the different Caco-2 cell lines utilized in different laboratories, often lead to problems of reproducibility making difficult to compare results. We developed a new cell-maintenance protocol in which Caco-2 cells were subcultured at 50% of confluence instead of 80% of confluence, as usually suggested. Using this new protocol, Caco-2 cells retained a higher proliferation potential resulting in a cell population, which, on reaching confluence, was able to differentiate almost synchronously, forming a more homogeneous and polarized cell monolayer, as compared to that obtained using a high cell growing density. This comparison has been done by analyzing the gene expression and the structural characteristics of the 21-days differentiated monolayers by microarrays hybridization and by confocal microscopy. We then investigated if these differences could also modify the effects of toxicants on 21-days-differentiated cells. We analyzed the 2 h-acute toxicity of CuCl(2) in terms of actin depolymerization and metallothionein 2A (MT2A) and heat shock protein 70 (HSPA1A) genes induction. Copper treatment resulted in different levels of actin depolymerization and gene expression induction in relationship with culture protocol, the low-density growing cells showing a more homogeneous and stronger response. Our results suggest that cell growing density could influence a number of morphological and physiological properties of differentiated Caco-2 cells and these effects must be taken in account when these cells are used as intestinal model.

Curdione Plays an Important Role in the Inhibitory Effect of Curcuma aromatica on CYP3A4 in Caco-2 Cells

Curcuma aromatica is a plant belonging to genus Curcuma of family Zingiberaceae and is widely used as supplements in Japan. Rhizomes of C. aromatica have curcumin as a major yellow pigment and curdione as a main ingredient of essential oils. In this study, we investigated the affect of C. aromatica on CYP3A4 using 1α,25-(OH)₂-D₃-treated Caco-2 clone cells. Caco-2 cells were treated with methanol extract (0.1 mg ml⁻¹), its hexane soluble fraction (0.1 mg ml⁻¹), curcumin (4 μM) and curdione (20 μM) for 72 hours. Nifedipine was used as a substrate of CYP3A4. Methanol extract, hexane fraction and curdione inhibited the formation of oxidized nifedipine by 50–70%, and curcumin showed no effect. The IC50s of methanol extract, hexane fraction and curdione to oxidized nifedipine formation were 21, 14 and 3.9 μg ml⁻¹ (16.9 μM), respectively. The content of curdione in methanol extract was 11.4%. Moreover, all of methanol extract, hexane fraction and curdione decreased CYP3A4 protein expression but had no affect on CYP3A4 mRNA expression. Our results showed that these drugs further decreased the CYP3A4 protein expression level after the protein synthesis was inhibited by cychroheximide. These findings suggest that curdione plays an important role in the CYP3A4 inhibitory activity of C. aromatica and curdione might inhibit the activity by accelerating the degradation of CYP3A4.

Molecular mechanisms of drug transporter regulation

Interindividual differences in drug transporter expression can result in variability in drug response. This variation in gene expression is determined, in part, by the actions of nuclear hormone receptors that act as xenobiotic- and endobiotic-sensing transcription factors. Among the ligand-activated nuclear receptors, signaling through the pregnane X receptor (PXR), constitutive androstane receptor (CAR), farnesoid X receptor (FXR), and vitamin D receptor (VDR) constitute major pathways regulating drug transporter expression in tissues. Hence, these endobiotic- and xenobiotic-sensing nuclear receptors are intrinsically involved in environmental influences of drug response. Moreover, because nuclear receptor genes are polymorphic, these transcription factors are also thought to contribute to heritability of variable drug action. In this chapter, the molecular aspects of drug transporter gene regulation by ligand-activated nuclear receptors will be reviewed including their clinical relevance.

Seasonal variation in blood drug concentrations and a potential relationship to vitamin D

The most important enzyme in hepatic drug metabolism is cytochrome P450 3A4. Published in vitro data indicate that vitamin D may up-regulate the expression of the CYP3A4 gene. Individual vitamin D levels are highly dependent on sunlight exposure and show great seasonal variability in northern countries. The aim of the present study was to investigate whether plasma concentrations of CYP3A4 drug substrates exhibit seasonal changes compatible with a stimulatory effect of vitamin D on drug metabolism. Three immunosuppressants (tacrolimus, sirolimus, and cyclosporine) were analyzed, because these CYP3A4 drug substrates are subject to long-term use and repeated concentration determinations. In addition, mycophenolic acid was included in the analysis as a control drug independent of CYP3A4 metabolism. Concentration-to-dose ratios were extracted from the Karolinska Therapeutic Drug Monitoring database and compared between the 3-month periods of lowest and highest vitamin D levels. Sirolimus and tacrolimus levels showed seasonal variability that was highly consistent with changes in vitamin D; for example, significantly lower drug concentrations in July to September than in January to March. As expected, no significant difference was evident for mycophenolic acid, but this result was also the case with cyclosporine, possibly due to cross-reactivity of CYP3A4-mediated metabolites with the immunoassay used for quantification. In conclusion, there is cyclic variation in blood levels of important immunosuppressants throughout the year that correlates with UV light-dependent changes in vitamin D levels. Even though a causal relationship remains to be established, it is suggested that individual differences in vitamin D may contribute to variability in drug metabolism and disposition.

Identification of permeability-related hurdles in oral delivery of curcumin using the Caco-2 cell model

Curcumin a poly-phenolic compound possesses diverse pharmacologic activities; however, its development as a drug has been severely impeded by extremely poor oral bioavailability. Poor aqueous solubility and extensive metabolism have been implicated for this but the role of membrane permeability has not been investigated. In the present study, permeability of curcumin was assessed using the Caco-2 cell line. Curcumin was poorly permeable with a P(app) (A → B) value of 2.93 ± 0.94 × 10(-6)cm/s. P(app) value in (B → A) study was found out to be 2.55 ± 0.02 × 10(-6)cm/s, thus ruling out the role of efflux pathways in poor oral bioavailability of curcumin. Studies using verapamil, a P-gp inhibitor, further confirmed this finding. Detailed mass balance studies showed loss of curcumin during transport. Further experiments using lysed cells revealed that 11.78% of curcumin was metabolized during transport. Studies using itraconazole, a CYP3A4 inhibitor, established its role in curcumin metabolism. Curcumin was also found to accumulate in cells as revealed by CLSM studies. Sorption and desorption kinetic studies further confirmed accumulation of curcumin inside the cells. Amount accumulated was quantitated by HPLC and found to be >20%. Thus, intestinal first-pass metabolism and intracellular accumulation played a role in poor permeability of curcumin. Based on its poor aqueous solubility and intestinal permeability, curcumin can be classified as a BCS Class IV molecule. This information can facilitate designing of drug delivery systems for enhancement of oral bioavailability of curcumin.

Chemical and physical modifications to poly(dimethylsiloxane) surfaces affect adhesion of Caco-2 cells

Polydimethylsiloxane (PDMS) silicone elastomer is extensively used in soft lithography processes to fabricate microscale or nano scale systems for microfluidic or cell culture applications. Though PDMS is biocompatible, it is not an ideal material for cell culture due to its poor cell adhesion properties. In this study, PDMS surfaces were modified to promote intestinal cell adhesion, in the interest of testing feasibility of using microfabricated PDMS systems for high throughput drug screening. Modification techniques included changing chemical composition of PDMS (i.e., varying curing to mixing agent ratio, and oxidization of PDMS surface by oxygen plasma), surface treatment of PDMS by coating with charged molecules (i.e., poly-D-lysine, L-alpha-phosphatidylcholine, and a layer bylayer coating), and deposition of extracellular matrix (ECM) proteins (i.e., laminin, fibronectin, and collagen). The influence of these modifications on PDMS properties, including elastic modulus and surface properties (wettability, chemical composition, topography, and protein adsorption) were characterized. Modification techniques were all found to change PDMS properties and influence the attachment and proliferation of Caco-2 cells over three days of culture to varying degrees. Generally, Caco-2 cells preferred to attach on collagen-coated, fibronectin-coated, and fibronectin-coated oxygen-plasma treated PDMS. The results highlight the importance of considering multiple physical and chemical factors that may be influenced by biomaterial modification and result in altered cell attachment to microfabricated systems, including surface hydrophobicity, chemical composition, stiffness, and topography. This study provides a foundation for further miniaturization, utilizing soft lithography techniques, of Caco-2 cell-based system for high-throughput screening of drug intestinal absorption during lead optimization in drug discovery. The understanding of different surface modifications on adjusting cell adhesion on PDMS allows systemic design of Biomicroelectromechanical Systems (BioMEMS) with tunable cell adhesion properties.

Regulation of human pregnane X receptor and its target gene cytochrome P450 3A4 by Chinese herbal compounds and a molecular docking study

The pregnane X receptor (PXR) plays a critical role in the regulation of human cytochrome P450 3A4 (CYP3A4) gene. In this study, we investigated the effect of an array of compounds isolated from Chinese herbal medicines on the activity of PXR using a luciferase reporter gene assay in transiently transfected HepG2 and Huh7 cells and on the expression of PXR and CYP3A4 in LS174T cells. Furthermore, molecular docking was performed to investigate the binding modes of herbal compounds with PXR. Praeruptorin A and C, salvianolic acid B, sodium danshensu, protocatechuic aldehyde, cryptotanshinone, emodin, morin, and tanshinone IIA significantly transactivated the CYP3A4 reporter gene construct in either HepG2 or Huh7 cells. The PXR mRNA expression in LS174T cells was significantly induced by physcion, protocatechuic aldehyde, salvianolic acid B, and sodium danshensu. However, epifriedelanol, morin, praeruptorin D, mulberroside A, tanshinone I, and tanshinone IIA significantly down-regulated the expression of PXR mRNA in LS174T cells. All the herbal compounds tested can be readily docked into the ligand-binding cavity of PXR mainly through hydrogen bond and aromatic interactions with Ser247, Gln285, His407, and Arg401. These findings suggest that herbal medicines can significantly regulate PXR and CYP3A4 and this has important implication in herb-drug interactions.

Comparative effects of doxercalciferol (1α-hydroxyvitamin D₂) versus calcitriol (1α,25-dihydroxyvitamin D₃) on the expression of transporters and enzymes in the rat in vivo

Effects of 1.28 nmol/kg doxercalciferol [1α(OH)D₂], a synthetic vitamin D₂ analog that undergoes metabolic activation to 1α,25-dihydroxyvitamin D₂, the naturally occurring, biologically active form of vitamin D₂, on rat transporters and enzymes were compared with those of 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃, active form of vitamin D₃; 4.8 and 6.4 nmol/kg] given on alternate days intraperitoneally for 8 days. Changes were mostly confined to the intestine and kidney where the vitamin D receptor (VDR) was highly expressed: increased intestinal Cyp24 and Cyp3a1 messenger RNA (mRNA) and a modest elevation of apical sodium-dependent bile salt transporter (Asbt) and P-glycoprotein (P-gp) protein; increased renal VDR, Cyp24, Cyp3a9, Mdr1a, and Asbt mRNA, as well as Asbt and P-gp protein expression; and decreased renal PepT1 and Oat1 mRNA expression. In comparison, 1α(OH)D₂ treatment exerted a greater effect than 1,25(OH)₂D₃ on Cyp3a and Cyp24 mRNA. However, the farnesoid X receptor -related repressive effects on liver Cyp7a1 were absent because intestinal Asbt, FGF15 and portal bile acid concentrations were unchanged. Rats on the alternate day regimen showed milder changes and lessened signs of hypercalcemia and weight loss compared with rats receiving daily injections (similar or greater amounts of 0.64-2.56 nmol/kg daily ×4) described in previous reports, showing that the protracted pretreatment regimen was associated with milder inductive and lesser toxic effects in vivo.

Induction of CYP3A4 by vinblastine: Role of the nuclear receptor NR1I2

BACKGROUND

Several microtubule targeting agents are capable of inducing CYP3A4 via activation of the pregnane X receptor (PXR; NR1I2).

OBJECTIVE

To evaluate the CYP3A4 induction potential of vinblastine both clinically and in vitro and determine the involvement of the nuclear receptors NR1I2 and the constitutive androstane receptor (NR1I3).

METHODS

Midazolam pharmacokinetics were evaluated in 6 patients who were enrolled in a Phase 1/2 study of infusional vinblastine given in combination with the ABCB1 (P-glycoprotein) antagonist valspodar (PSC 833) and received the CYP3A4 phenotyping probe midazolam on more than 1 occasion. Genotyping was conducted in CYP3A4, CYP3A5, and ABCB1 to rule out potential pharmacogenetic influences. Clinical data were followed-up by Western blotting and reporter assays in HepG2 and NIH3T3 cells treated with vinblastine over a dose range of 150-4800 ng/mL for 48 hours.

RESULTS

In 6 patients with cancer, vinblastine increased the median (95% CI) clearance of the CYP3A4 phenotyping probe midazolam from 21.7 L/h (12.6 to 28.1) to 32.3 L/h (17.3 to 53.9) (p = 0.0156, Wilcoxon signed-rank test). No obvious effect of polymorphisms in CYP3A4, CYP3A5, and ABCB1 on midazolam clearance was observed. In vitro, vinblastine induced CYP3A4 protein. Furthermore, cell-based reporter gene assays using transiently transfected HepG2 and NIH3T3 cells indicated that vinblastine (150-4800 ng/mL) weakly activated human and mouse full-length NR1I2, but had no influence on NR1I3.

CONCLUSIONS

Collectively, these findings suggest that vinblastine is able to induce CYP3A4, at least in part, via an NR1I2-dependent mechanism, and thus has the potential to facilitate its own elimination and cause interactions with other CYP3A4 substrates.

The role of lithocholic acid in the regulation of bile acid detoxication, synthesis, and transport proteins in rat and human intestine and liver slices

The effects of the secondary bile acid, lithocholic acid (LCA), a VDR, FXR and PXR ligand, on the regulation of bile acid metabolism (CYP3A isozymes), synthesis (CYP7A1), and transporter proteins (MRP3, MRP2, BSEP, NTCP) as well as nuclear receptors (FXR, PXR, LXRα, HNF1α, HNF4α and SHP) were studied in rat and human precision-cut intestine and liver slices at the mRNA level. Changes due to 5 to 10 μM of LCA were compared to those of other prototype ligands for VDR, FXR, PXR and GR. LCA induced rCYP3A1 and rCYP3A9 in the rat jejunum, ileum and colon, rCYP3A2 only in the ileum, rCYP3A9 expression in the liver, and CYP3A4 in the human ileum but not in liver. LCA induced the expression of rMRP2 in the colon but not in the jejunum and ileum but did not affect rMRP3 expression along the length of the rat intestine. In human ileum slices, LCA induced hMRP3 and hMRP2 expression. In rat liver slices, LCA decreased rCYP7A1, rLXRα and rHNF4α expression, induced rSHP expression, but did not affect rBSEP or rNTCP expression; whereas in the human liver, a small but significant decrease was found for hHNF1α expression. These data suggests profound species differences in the effects of LCA on bile acid transport, synthesis and detoxification. An examination of the effects of prototype VDR, PXR, GR and FXR ligands showed that these pathways are all intact in precision cut slices and that LCA exerted VDR, PXR and FXR effects. The LCA-induced altered enzymes and transporter expressions in the intestine and liver would affect the disposition of drugs.

Effects of 1alpha,25-dihydroxyvitamin D3 on transporters and enzymes of the rat intestine and kidney in vivo

1alpha,25-Dihydroxyvitamin D3 (1,25(OH)2D3), the natural ligand of the vitamin D receptor (VDR), was found to regulate bile acid related transporters and enzymes directly and indirectly in the rat intestine and liver in vivo. The kidney is another VDR-rich target organ in which VDR regulation on xenobiotic transporters and enzymes is ill-defined. Hence, changes in protein and mRNA expression of nuclear receptors, transporters and enzymes of the rat intestine and kidney in response to 1,25(OH)2D3 treatment (0 to 2.56 nmol/kg/day intraperitoneally in corn oil for 4 days) were studied. In the intestine, protein and not mRNA levels of Mrp2, Mrp3, Mrp4 and PepT1 in the duodenum and proximal jejunum were induced, whereas Oat1 and Oat3 mRNA were decreased in the ileum after 1,25(OH)2D3 treatment. In the kidney, VDR, Cyp24, Asbt and Mdr1a mRNA and protein expression increased significantly (2- to 20-fold) in 1,25(OH)2D3-treated rats, and a 28-fold increase of Cyp3a9 mRNA but not of total Cy3a protein nor Cyp3a1 and Cyp3a2 mRNA was observed, implicating that VDR played a significant, renal-specific role in Cyp3a9 induction. Additionally, renal mRNA levels of PepT1, Oat1, Oat3, Ostalpha, and Mrp4, and protein levels of PepT1 and Oat1 were decreased in a dose-dependent manner, and the approximately 50% concomitant reduction in FXR, SHP, HNF-1alpha and HNF-4alpha mRNA expression suggests the possibility of cross-talk among the nuclear receptors. It is concluded that the effects of 1,25(OH)2D3 changes are tissue-specific, differing between the intestine and kidney which are VDR-rich organs.

The missing linkage: what pharmacogenetic associations are left to find in CYP3A?

IMPORTANCE OF THE FIELD

An enormous amount of drugs and endogenous substrates are metabolized by the enzymes encoded in the CYP3A gene cluster, making variation at this locus of utmost importance in the field of pharmacogenetics. However, the identification of genetic variation that contributes to the wide phenotypic variability at this locus has been elusive. While dozens of studies have investigated the effects of coding variants, none have found the definitive answer to what variant or variants explain the distribution of enzyme activity and clinical effects seen with the drug metabolized by these genes.

AREAS COVERED IN THIS REVIEW

This review highlights the recent pharmacogenetic work at the CYP3A locus, in particular studies on known functional variants in CYP3A4 and CYP3A5. In addition, common pharmacogenetic strategies as well as considerations specific to the CYP3A locus are discussed.

WHAT THE READER WILL GAIN

The reader will gain a greater understanding of the complexities involved in studying the CYP3A locus, population differences that may affect pharmacogenetic studies at this locus and the importance of variation that affect gene regulation.

TAKE HOME MESSAGE

More innovative and comprehensive methods to assay this region are needed, with particular attention paid to the role of gene regulation and non-coding sequence.