Plasma 6ß-hydroxycortisol to cortisol ratio as a less invasive cytochrome P450 3A phenotyping method.

AIM: A less invasive evaluation method of cytochrome P450 3A (CYP3A) activity provides an important tool for personalized medicine. We aimed to clarify the usefulness of the plasma 6ß-hydroxycortisol to cortisol concentration (6ß-OHF/F) ratio as a minimally invasive CYP3A phenotyping method. METHODS: Plasma 6ß-OHF and cortisol concentrations were measured via liquid chromatography/tandem mass spectrometry. The plasma 6ß-OHF/F ratio was compared with 6ß-hydroxylation clearance of endogenous cortisol (CLm(6ß); which we previously developed as an index of CYP3A activity) before, during and after oral contraceptive administration in 3 healthy women. The plasma 6ß-OHF/F ratio was observed during oral clarithromycin administration. The plasma 6ß-OHF/F ratio was also measured in 39 healthy participants. RESULTS: The plasma 6ß-OHF/F ratio in 3 healthy women on Day 21 of starting oral contraceptive administration decreased by 39, 49 and 61% compared with Day 0. These values were similar to CLm(6ß) values (43, 54 and 59%, respectively). Plasma 6ß-OHF/F ratio and CLm(6ß) exhibited a good correlation (r = .9053). The 6ß-OHF/F ratio decreased from 0.00921 to 0.00577 only 3 h following clarithromycin administration. The plasma 6ß-OHF/F ratio ranged 0.00565-0.01556 in 39 healthy participants. CONCLUSION: Based on its close relationship with CLm(6ß) and its decrease upon inhibition by clarithromycin, the plasma 6ß-OHF/F ratio serves as an index of CYP3A activity. Using this minimally invasive index, we can identify patients with extremely low CYP3A activity before treatment initiation and optimize the initial drug dose, thereby mitigating the risk of severe adverse reactions.

Potential Effects of Ibuprofen, Remdesivir and Omeprazole on Dexamethasone Metabolism in Control Sprague Dawley Male Rat Liver Microsomes (Drugs Often Used Together Alongside COVID-19 Treatment).

The role of individual cytochrome P450 (CYPs) responsible for the drug metabolism can be determined through their chemical inhibition. During the pandemic, dexamethasone and remdesivir with omeprazole were used for the treatment of COVID-19, while Ibuprofen was taken to treat the symptoms of fever and headache. This study aimed to examine the potency of ibuprofen remdesivir, and omeprazole as inhibitors of cytochrome P450s using rat liver microsomes in vitro. Dexamethasone a corticosteroid, sometimes used to reduce the body's immune response in the treatment of COVID-19, was used as a probe substrate and the three inhibitors were added to the incubation system at different concentrations and analysed by a validated High Performance Liquid Chromatography (HPLC) method. The CYP3A2 isoenzyme is responsible for dexamethasone metabolism in vitro. The results showed that ibuprofen acts as a non-competitive inhibitor for CYP3A2 activity with Ki = 224.981 ± 1.854 µM and IC50 = 230.552 ± 2.020 µM, although remdesivir showed a mixed inhibition pattern with a Ki = 22.504 ± 0.008 µM and IC50 = 45.007 ± 0.016 µM. Additionally, omeprazole uncompetitively inhibits dexamethasone metabolism by the CYP3A2 enzyme activity with a Ki = 39.175 ± 0.230 µM and IC50 = 78.351 ± 0.460 µM. These results suggest that the tested inhibitors would not exert a significant effect on the CYP3A2 isoenzyme responsible for the co-administered dexamethasone drug's metabolism in vivo.

Development and Validation of a Novel HPLC Method to Analyse Metabolic Reaction Products Catalysed by the CYP3A2 Isoform: In Vitro Inhibition of CYP3A2 Enzyme Activity by Aspirin (Drugs Often Used Together in COVID-19 Treatment).

Aspirin (also known as acetylsalicylic acid) is a drug intended to treat fever, pain, or inflammation. Treatment of moderate to severe cases of COVID-19 using aspirin along with dexamethasone has gained major attention globally in recent times. Thus, the purpose of this study was to use High-Performance Liquid Chromatography (HPLC) to evaluate the in vitro inhibition of CYP3A2 enzyme activity using aspirin in rat liver microsomes (RLMs). In this study, an efficient and sensitive HPLC method was developed using a reversed phase C18 column (X Bridge 4.6 mm × 150 mm, 3.5 µm) at 243 nm using acetonitrile and water (70:30 v/v). The linearity (r2 > 0.999), precision (<15%), accuracy and recovery (80-120%), limit of detection (5.60 µM and 0.06 µM), limit of quantification (16.98 µM and 0.19 µM), and stability of the newly developed method were validated for dexamethasone and 6ß-hydroxydexamethasone, respectively, following International Conference on Harmonization (ICH) guidelines. This method was applied in vitro to measure CYP3A2 activity. The results showed that aspirin competitively inhibits 6ß-hydroxylation (CYP3A2 activity) with an inhibition constant (Ki) = 95.46 µM and the concentration of the inhibitor causing 50% inhibition of original enzyme activity (IC50) = 190.92 µM. This indicated that there is a minimal risk of toxicity when dexamethasone and aspirin are co-administrated and a very low risk of toxicity and drug interaction with drugs that are a substrate for CYP3A2 in healthcare settings.

Erlotinib treatment induces cytochrome P450 3A activity in non-small cell lung cancer patients.

AIMS: Erlotinib is a tyrosine kinase inhibitor used in the treatment of non-small cell lung cancer highly metabolized by the cytochrome P450 (CYP) 3A. Hence, CYP3A4 activity might be a useful predictor of erlotinib pharmacokinetics in personalized medicine. The effect of erlotinib on CYP3A activity was therefore studied in non-small cell lung cancer patients. METHODS: The study included 32 patients scheduled for erlotinib monotherapy. CYP3A activity was assessed using quinine as a probe before and during erlotinib treatment. Plasma from blood samples drawn 16 hours post quinine administration were analysed using HPLC with fluorescence detection to determine the quinine/3-OH-quinine ratio. RESULTS: Matched samples, available from 13 patients, showed an induction of CYP3A activity (P = 0.003, Wilcoxon's signed rank test) after 2 months of treatment. The quinine/3-OH-quinine ratio decreased from 20.2 (± 13.4) at baseline to 11.0 (± 4.34). Single-point samples, available from 19 patients, supported the decrease in ratio (P = 0.007, Mann-Whitney U-test). Generally, females had a higher CYP3A activity both at baseline and after two months of treatment. Statistical analysis by gender also showed significant increase in CYP3A activity (males, n = 10, P = 0.001, and females, n = 22, P = 0.001). CONCLUSIONS: An induction of CYP3A activity was observed after 2 months of erlotinib treatment which was also seen when subdividing based on gender. It could be important to take this into consideration for patients co-administering other CYP3A-metabolizing drugs during erlotinib treatment and also makes it difficult to use baseline CYP3A activity to predict erlotinib pharmacokinetics.

A non-destructive BFCOD assay for in vivo measurement of cytochrome P450 3A (CYP3A) enzyme activity in fish embryos and larvae.

There is increasing interest in quantifying the exposure and effects of anthropogenic contaminants in fish. Determination of exposures in wild fish is routinely performed, but methods to investigate potential effects are less established. One of the most relevant approaches would be the use of in vivo assays, but existing assays are often limited to in vitro determination of enzyme activity. Many pharmaceuticals and some persistent pollutants activate, and are metabolized by cytochrome P4503A (CYP3A), which make it a relevant and desirable target for biomarker research. We altered the established 7-benzyloxy-4-trifluoromethylcoumarin-O-debenzylation (BFCOD) in vitro protocol for CYP3A activity determination, developing a rapid and inexpensive method to measure in vivo (and in ovo) CYP3A activity in two fish systems: Gulf killifish (Fundulus grandis) and zebrafish (Danio rerio) early life stages. Even with very low concentrations of 7-benzyloxy-4-trifluoromethyl coumarin (BFC, 0.06 µM or 20 µg/L), we were able to detect significant induction in CYP3A activity in embryos of F. grandis, as well as in larvae of D. rerio in response to benzo[a]pyrene (BaP) and fluoranthene (FL) exposures. Because of concerns regarding the possible contribution of CYP1A to BFCOD activity from previous research, we have used a CYP1A post-translational inhibitor (FL) in order to calculate the contribution of CYP1A to the BFCOD assay. We also dosed with benzo[k]fluoranthene (BkF) and showed significant induction of CYP1A activity, with no concurrent increase in CYP3A activity. In this paper, we have taken an established in vitro CYP3A activity assay, and utilized the reaction in a novel way to allow for the non-destructive determination of CYP3A. In summary, we describe a sensitive, cheap, fast and easy modified BFCOD assay for in ovo and in vivo determination of CYP3A activity for use in moderate throughput early-life-stage fish experiments.

4ß-hydroxycholesterol as an endogenous CYP3A marker in cancer patients treated with taxanes.

AIM: Taxanes are anti-cancer agents used to treat several types of solid tumours. They are metabolized by cytochrome P450 (CYP) 3A, displaying a large pharmacokinetic (PK) variability. In this study, we evaluated the endogenous CYP3A4 marker 4ß-hydroxycholesterol (4ß-OHC) as a potential individual taxane PK predictor. METHODS: Serum 4ß-OHC and cholesterol concentrations were determined in 291 paclitaxel and 151 docetaxel-treated patients, and were subsequently correlated with taxane clearance. RESULTS: In the patients treated with paclitaxel, no clinically relevant correlations between the 4ß-OHC or 4ß-OHC : cholesterol ratio and paclitaxel clearance were found. In the patients treated with docetaxel, 4ß-OHC concentration was weakly correlated with docetaxel clearance in males (r = 0.35 P = 0.01, 95% CI 0.08, 0.58). Of the 10% patients with taxane outlier clearance values, 4ß-OHC did correlate with docetaxel clearance in males (r = 0.76, P = 0.03, 95% CI 0.12, 0.95). CONCLUSION: There was no clinical correlation between paclitaxel clearance and the CYP3A4 activity markers 4ß-OHC or the 4ß-OHC : cholesterol ratio. A weak correlation was observed between 4ß-OHC and docetaxel clearance, but only in males. This endogenous CYP3A4 marker has limited predictive value for taxane clearance in patients.

CYP3A5 polymorphism affects the increase in CYP3A activity after living kidney transplantation in patients with end stage renal disease.

AIMS: It has been reported that cytochrome P450 (CYP)3A activity increases significantly in patients with end stage renal disease (ESRD) after kidney transplantation, with wide interindividual variability in the degree of increase. The aim of this study was to evaluate the influence of CYP3A5 polymorphism on the increase in CYP3A activity after living kidney transplantation, by measuring the plasma concentration of 4ß-hydroxycholesterol. METHODS: This prospective study recruited 22 patients with ESRD who underwent a first living kidney allograft transplantation, comprising 12 patients with CYP3A5*1 allele (CYP3A5*1/*1 or *1/*3) and 10 patients without CYP3A5*1 allele (CYP3A5*3/*3). RESULTS: No significant difference in estimated glomerular filtration rate over time was observed between patients with the CYP3A5*1 allele and patients without the CYP3A5*1 allele, suggesting that the degrees of recovery in renal function after living kidney transplantation were similar in the two groups. However, plasma concentrations of 4ß-hydroxycholesterol on days 90 (57.1 ± 13.4 vs. 39.5 ± 10.8 ng ml(-1)) and 180 (55.0 ± 14.5 vs. 42.4 ± 12.6 ng ml(-1)) after living kidney transplantation were significantly higher in the presence of the CYP3A5*1 allele than in the absence of the CYP3A5*1 allele [P = 0.0034 (95% confidence interval of difference 6.55, 28.6) and P = 0.043 (95% confidence interval of difference 0.47, 24.8), respectively], suggesting that CYP3A activity may increase markedly associated with recovery of renal function in patients with the CYP3A5*1 allele. CONCLUSIONS: These findings suggest that the presence of the CYP3A5*1 allele contributes to marked elevation of CYP3A activity associated with recovery of renal function after kidney transplantation.

Significant increase in plasma 4ß-hydroxycholesterol concentration in patients after kidney transplantation.

Several previous studies have shown that renal failure decreases not only renal elimination but also metabolic clearance of drugs, particularly those metabolized by CYP3A. However, whether recovery of renal function results in recovery of hepatic CYP3A activity remains unknown. In this study, we evaluated the effect of renal function on CYP3A activity after kidney transplantation in patients with end-stage renal disease (ESRD) by measuring the change in CYP3A activity using plasma concentration of 4ß-hydroxycholesterol as a biomarker. The study enrolled 13 patients with ESRD who underwent the first kidney allograft transplantation. Morning blood samples were collected before and 3, 7, 10, 14, 21, 30, 60, 90, 120, 150 and 180 days after kidney transplantation. Plasma concentration of 4ß-hydroxycholesterol was measured using GC-MS. Compared with before kidney transplantation, creatinine clearance increased significantly from day 3 after kidney transplantation and stabilized thereafter. Plasma concentration of 4ß-hydroxycholesterol was elevated significantly on days 90 and 180 after kidney transplantation. In conclusion, this study suggests the recovery of CYP3A activity with improvement in renal function after kidney transplantation in patients with ESRD.

Induction of CYP3A activity by dexamethasone may not be strong, even at high doses: insights from a case of tacrolimus co-administration.

BACKGROUND: Dexamethasone (DEX) induces CYP3A activity in a concentration-dependent manner. However, no study has examined changes in the blood concentration of CYP3A substrate drugs when DEX is administered at high doses. Herein, we present a case in which tacrolimus (TAC), a typical CYP3A substrate drug, was co-administered with a chemotherapy regimen that included high-dose DEX. CASE PRESENTATION: A 71-year-old woman underwent liver transplantation for hepatocellular carcinoma 18 years prior to her inclusion in this case study. She was receiving TAC orally at 2 mg/day and had a stable trough blood concentration of approximately 4 ng/mL and a trough blood concentration/dose (C/D) ratio of approximately 2. The patient was diagnosed with post-transplant lymphoproliferative disease (histological type: Burkitt's lymphoma) after admission. Thereafter, the patient received cyclophosphamide-prednisolone (CP), followed by two courses of R-HyperCVAD (rituximab, cyclophosphamide, doxorubicin, vincristine, and DEX) and R-MA (rituximab, methotrexate, and cytarabine) replacement therapy. DEX (33 mg/day) was administered intravenously on days 1-4 and days 11-14 of R-HyperCVAD treatment, and aprepitant (APR) was administered on days 1-5 in both courses. The TAC C/D ratio decreased to approximately 1 on day 11 during both courses, and then increased. Furthermore, a decreasing trend in the TAC C/D ratio was observed after R-MA therapy. The decrease in the TAC C/D ratio was attributed to APR administration rather than to DEX. CONCLUSION: The induction of CYP3A activity by a high dose of DEX may not be strong. The pharmacokinetic information on DEX and in vitro enzyme activity induction studies also suggested that CYP3A activity induction is not prominent under high-dose DEX treatment.

LPS-Induced Inflammation Affects Midazolam Clearance in Juvenile Mice in an Age-Dependent Manner.

PURPOSE: Inflammation has a significant impact on CYP3A activity. We hypothesized that this effect might be age dependent. Our objective was to conduct a population pharmacokinetic study of midazolam in mice at different developmental stages with varying degrees of inflammation to verify our hypothesis. METHODS: Different doses (2 and 5 mg/kg) of lipopolysaccharide (LPS) were used to induce different degrees of systemic inflammation in Swiss mice (postnatal age 9-42 days, n = 220). The CYP3A substrate midazolam was selected as the pharmacological probe to study CYP3A activity. Postnatal age, current body weight, serum amyloid A protein 1 (SAA1) levels and LPS doses were collected as covariates to perform a population pharmacokinetic analysis using NONMEM 7.2. RESULTS: A population pharmacokinetic model of midazolam in juvenile and adult mice was established. Postnatal age and current body weight were the most significant and positive covariates for clearance and volume of distribution. LPS dosage was the most significant and negative covariate for clearance. LPS dosage can significantly reduce the clearance of midazolam by 21.8% and 38.7% with 2 mg/kg and 5 mg/kg, respectively. Moreover, the magnitude of the reduction was higher in mice with advancing postnatal age. CONCLUSION: Both inflammation and ontogeny have an essential role in CYP3A activity in mice. The effect of LPS-induced systemic inflammation on midazolam clearance in mice is dependent on postnatal age.

Studies on CYP3A activity during the menstrual cycle as measured by urinary 6ß-hydroxycortisol/cortisol.

The 6ß-OH-cortisol/cortisol ratio (6ß-OHC/C) in urine is an endogenous marker of drug-metabolizing enzyme cytochrome P450 3A (CYP3A). The primary aim of this single center, prospective, non-interventional cohort study, was to investigate the variability of 6ß-OHC/C during the menstrual cycle. In addition, possible associations between the CYP3A activity and sex hormones, gut microbiota metabolite trimethylamine-N-Oxide (TMAO) and microRNA-27b, respectively, were investigated. Serum and urinary samples from healthy, regularly menstruating women followed for two menstrual cycles were analyzed. Twenty-six complete menstrual cycles including follicular, ovulatory, and luteal phase were defined based on hormone analyses in serum. 6ß-OHC/C were analyzed in urine and sex hormones, TMAO and miRNA-27b were analyzed in serum at the same time points. 6ß-OHC/C did not vary between the follicular, ovulatory, or luteal phases. There was a difference in the relative miRNA-27b expression between the follicular and ovulatory phase (p = .03). A significant association was found between 6ß-OHC/C and progesterone during the follicular (p = .005) and ovulatory (p = .01) phases (n = 26 for each phase). In addition, a significant association was found between the ratio and TMAO during the ovulatory (p = .02) and luteal (p = .002) phases. 6ß-OHC/C and gut microbiota TMAO were significantly associated (p = .003) when evaluating all values, for all phases (n = 78). Interestingly, the finding of an association between 6ß-OHC/C in urine and levels of TMAO in serum suggest that gut microbiota may affect CYP3A activity.

Urinary metabolic markers reflect on hepatic, not intestinal, CYP3A activity in healthy subjects.

Intestinal cytochrome P450 3A (CYP3A) plays an important role in oral drug metabolism, but only endogenous metabolic markers for measuring hepatic CYP3A activity were identified. Our study evaluated whether hepatic CYP3A markers reflected intestinal CYP3A activity. An open-label, three-period, six-treatment, one-sequence clinical trial was performed in 16 healthy Korean males. In the control phase, all subjects received a single dose of intravenous (IV) and oral midazolam (1 mg and 5 mg, respectively). Clarithromycin (500 mg) was administered twice daily for 4 days to inhibit hepatic and intestinal CYP3A, and 500 mL of grapefruit juice was given to inhibit intestinal CYP3A. Clarithromycin significantly inhibited total CYP3A activity, and the clearance of IV and apparent clearance of oral midazolam decreased by 0.15- and 0.32-fold, respectively. Grapefruit juice only reduced the apparent clearance of oral midazolam by 0.84-fold, which indicates a slight inhibition of intestinal CYP3A activity. Urinary markers, including 6ß-OH-cortisol/cortisol and 6ß-OH-cortisone/cortisone, were significantly decreased 0.5-fold after clarithromycin administration but not after grapefruit juice. The fold changes in 6ß-OH-cortisol/cortisol and 6ß-OH-cortisone/cortisone did not correlate to changes in intestinal availability but did correlate to hepatic availability. In conclusion, endogenous metabolic markers are only useful to measure hepatic, but not intestinal, CYP3A activity.

CYP3A Activity in End-of-Life Cancer Patients Measured by 4ß-Hydroxycholesterol/cholesterol Ratio, in Men and Women.

More than 50% of all drugs are metabolized by the cytochrome P450 3A enzyme (CYP3A). The aim of this study was to investigate if the CYP3A activity, measured by the endogenous marker 4ß-hydroxycholesterol/cholesterol ratio (4ß-OHC/C), is changed during the last weeks and days of life in men and women. To this end, serum samples from 137 deceased patients (median age 70 years) collected at a single time point 1-60 days before death, were analyzed and compared to 280 young (median 27 years), and 30 elderly (median age 70 years) non-cancer controls. There were no significant differences in the 4ß-OHC/C ratio between men and women in end-of-life patients (p < 0.25). The median 4ß-OHC/C was significantly higher in end-of-life male patients compared to both young (p < 0.0001) and elderly (p < 0.05) male controls. In a similar manner, 4ß-OHC/C in end-of-life female patients was significantly higher compared to young and elderly female controls, p < 0.0001 and p < 0.001, respectively. There was no significant correlation between 4ß-OHC/C and survival time. The results from this study suggest maintained CYP3A activity to the very last days of life and even a capacity of induction of the enzyme in end-of-life cancer patients.

Decreased Cytochrome P450 3A activity in palliative patients with haematological diseases: Potential impact on supportive drug therapies.

Cytochrome P450 3A (CYP3A) is the most relevant drug-metabolizing enzyme in human beings involved in the elimination of about 50% of the marketed drugs. Comprehensive in vivo data of CYP3A activity in palliative patients with haematological diseases are missing. Therefore, CYP3A activity was determined under real-life clinical conditions in patients to gain knowledge about dose adjustments for supportive therapies and symptom management in haematology. The single-arm, prospective trial obtained a 4-hours pharmacokinetic profile of midazolam after oral administration of a microdose as marker substance from each enrolled patient. Plasma concentrations of midazolam and its primary metabolite 1'-hydroxy-midazolam were quantified by mass spectrometry techniques. CYP3A activity was calculated as partial metabolic clearance from an established limited sampling area under the curve. All other drugs taken by the participating patients were considered as well as recent laboratory test results and the patients' diagnoses. Partial metabolic clearance of midazolam in patients with haematological diseases was highly variable (36.9 ± 52.7 L/h). In comparison with the CYP3A activity of healthy individuals, this was a highly significant 30% reduction of activity (P < 0.0001). Dosing of major CYP3A substrate drugs needs to be reduced in palliative patients with haematological diseases, otherwise escalation of debilitating symptoms due to drug interactions might occur.

In Vivo CYP3A Activity in Palliative Care Patients: Study Protocol for a Single Arm Prospective Trial.

BACKGROUND: Drug interactions are a common cause for escalation of debilitating symptoms in palliative care patients. CYP3A is the most relevant CYP enzyme in humans involved in metabolism of about half of all available pharmaceuticals. OBJECTIVE: To increase knowledge about the CYP3A enzyme and the impact of drug interactions on its activity to improve dosing in palliative care patients. DESIGN: The prospective clinical trial uses a secure method of analyzing CYP3A activity in humans: Administration of a marker substance followed by the determination of its blood concentrations as well as the concentrations of its metabolite at certain points of time and corresponding metabolic clearance calculations. SETTING: The ongoing trial is carried out at a palliative care unit under real-life clinical conditions. MEASUREMENTS: A four-hour pharmacokinetic profile after oral administration of the marker substance (microdose of midazolam) will be obtained from each enrolled patient. Plasma concentrations of midazolam and its primary metabolite will be quantified by mass spectrometry techniques. CYP3A activity will be calculated as partial metabolic clearance from a limited sampling area under the curve. All other drugs taken by the participating patients will be considered as well as recent blood test results and the patients' diagnoses. CONCLUSIONS: This is the first prospective study dealing with drug metabolism in patients on a palliative care unit. The trial is based on reliable and established methods aiming to provide improved dosing regimens and thus optimize pharmacological therapies in this specialty.

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 (PPAR α) 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 4ß-hydroxycholesterol. In addition, the correlation between miR-27b and CYP3A activity, measured by dextromethorphan N-demethylation and 6ß-hydroxylation of testosterone and the gene expression of CYP3A4, VDR and PPAR α were assessed in 20 human liver samples. A significant association between circulatory miR-27b levels and 4ß-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 PPAR α. There was a significant association between serum 25-hydroxyvitamin D levels and 4ß-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.

Use of endogenous cortisol 6ß-hydroxylation clearance for phenotyping in vivo CYP3A activity in women after sequential administration of an oral contraceptive (OC) containing ethinylestradiol and levonorgestrel as weak CYP3A inhibitors.

The present study was undertaken to evaluate the time courses of in vivo cytochrome P450 3A (CYP3A) inhibition in four healthy women after sequential administration of an oral contraceptive (OC) containing ethinylestradiol and levonorgestrel, using 6ß-hydroxylation clearance of endogenous cortisol (CLm(6ß)) as a new index for CYP3A phenotyping. The 6ß-hydroxylation clearance (CLm(6ß)) was followed every 2h from 9:00 or 11:00 to 17:00 on days 0 (baseline), 1, 2, 21, and 28 during a single menstrual cycle. The serum concentrations of endogenous estradiol and progesterone were also measured. The time course data of CLm(6ß) clearly demonstrated 43-64% inhibition of CYP3A activity in women taking a low daily dose of the OC for 21days. The average CLm(6ß) levels that were suppressed by the OC in four women were extremely low (0.60-1.23mL/min) compared with the normal CLm(6ß) range (1.5-3.5mL/min) that was obtained from 49 healthy subjects in our previous study. The in vivo inhibitory potencies (43-64%) obtained in this study were stronger than expected from reported in vitro studies (∼20%). Furthermore, it would take at least seven days to return to the baseline activity of CYP3A after discontinuation of the OC. The results presented here should provide important information on the inhibitory effect of OC on the CYP3A activities in women, which are involved in the metabolism of a number of drugs with a narrow therapeutic range.