The biliary and urinary metabolites of [3H]17 alpha-ethynylestradiol in women

17α-ethynylestradiol and its two main conjugates in seven municipal wastewater treatment plants: Analytical method, their occurrence, removal and risk evaluation

This work shows the existence of both 17-ethinylestradiol-3-sulfate (EE2-3S) and 17-ethinylestradiol-3-glucuronide (EE2-3G) in seven municipal WWTPs with substantial concentrations (n.d-50.10 ng/L). The calculated removal efficiencies of 17-ethinylestradiol (EE2) in the seven municipal WWTPs ranged from 40.8%-100% with an average removal efficiency of 83.3%. However, upon the inclusion of EE2 concentration transformed from EE2-3S and EE2-3G, the corresponding removal efficiencies were increased to 91.4%-100% with an average removal efficiency of 97.3%. This work is the first to clearly illustrate that EE2 conjugates in raw wastewater could greatly underestimate the removal effectiveness of municipal WWTPs on EE2, indicating the importance of the EE2 conjugates in municipal wastewater having been hardly paid with attention. The EE2-derived estrogen equivalence (EEQ) values in the effluents of seven WWTPs ranged from 0 to 0.98 ng E2/L having an average level of 0.45 ng E2/L, which were relatively low. However, upon the inclusion of EE2 transformable from EE2-3S and EE2-3G in effluents, the EE2-derived EEQ values in effluents would be increased to 0.77-4.85 ng E2/L having an average level of 2.71 ng E2/L, which clearly suggested that ignorance of EE2 conjugates in effluent would largely underestimate EE2's environmental risk to receiving water bodies.

Drug-Drug Interaction Studies With Oral Contraceptives: Pharmacokinetic/Pharmacodynamic and Study Design Considerations

Oral contraceptives (OCs) are the most widely used form of birth control among women of childbearing potential. Knowledge of potential drug-drug interactions (DDIs) with OCs becomes imperative to provide information on the medication to women of childbearing potential and enable their inclusion in clinical trials, especially if the new molecular entity is a teratogen. Although a number of DDI guidance documents are available, they do not provide recommendations for the design and conduct of OC DDI studies. The evaluation of DDI potential of a new molecular entity and OCs is particularly challenging because of the availability of a wide variety of combinations of hormonal contraceptives, different doses of the ethinyl estradiol, and different metabolic profiles of the progestin component. The aim of this review is to comprehensively discuss factors to be considered such as pharmacokinetics (PK), pharmacodynamics (PD), choice of OC, and study population for the conduct of in vivo OC DDI studies. In this context, metabolic pathways of OCs, the effect of enzyme inhibitors and inducers, the role of sex hormone-binding globulin in the PK of progestins, current evidence on OC DDIs, and the interpretation of PD end points are reviewed. With the emergence of new tools like physiologically based PK modeling, the decision to conduct an in vivo study can be made with much more confidence. This review provides a comprehensive overview of various factors that need to be considered in designing OC DDI studies and recommends PK-based DDI studies with PK end points as adequate measures to establish clinical drug interaction and measurement of PD end points when there is basis for PD interaction.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

Analysis of steroid hormones and their conjugated forms in water and urine by on-line solid-phase extraction coupled to liquid chromatography tandem mass spectrometry

Background

In recent years, endocrine disrupting compounds (EDCs) have been found in rivers that receive significant inputs of wastewater. Among EDCs, natural and synthetic steroid hormones are recognized for their potential to mimic or interfere with normal hormonal functions (development, growth and reproduction), even at ultratrace levels (ng L⁻¹). Although conjugated hormones are less active than free hormones, they can be cleaved and release the unconjugated estrogens through microbial processes before or during the treatment of wastewater. Due to the need to identify and quantify these compounds, a new fully automated method was developed for the simultaneous determination of the two forms of several steroid hormones (free and conjugated) in different water matrixes and in urine.

Results

The method is based on online solid phase extraction coupled with liquid chromatography and tandem mass spectrometry (SPE–LC–MS/MS). Several parameters were assessed in order to optimize the efficiency of the method, such as the type and flow rate of the mobile phase, the various SPE columns, chromatography as well as different sources and ionization modes for MS. The method demonstrated good linearity (R² > 0.993) and precision with a coefficient of variance of less than 10 %. The quantification limits vary from a minimum of 3–15 ng L⁻¹ for an injection volume of 1 and 5 mL, respectively, with the recovery values of the compounds varying from 72 to 117 %.

Conclusion

The suggested method has been validated and successfully applied for the simultaneous analysis of several steroid hormones in different water matrixes and in urine.

Electronic supplementary material

The online version of this article (doi:10.1186/s13065-016-0174-z) contains supplementary material, which is available to authorized users.

Renal transport of organic anions and cations

Organic anions and cations (OAs and OCs, respectively) comprise an extraordinarily diverse array of compounds of physiological, pharmacological, and toxicological importance. The kidney, primarily the renal proximal tubule, plays a critical role in regulating the plasma concentrations of these organic electrolytes and in clearing the body of potentially toxic xenobiotics agents, a process that involves active, transepithelial secretion. This transepithelial transport involves separate entry and exit steps at the basolateral and luminal aspects of renal tubular cells. Basolateral and luminal OA and OC transport reflects the concerted activity of a suite of separate proteins arranged in parallel in each pole of proximal tubule cells. The cloning of multiple members of several distinct transport families, the subsequent characterization of their activity, and their subcellular localization within distinct regions of the kidney, now allows the development of models describing the molecular basis of the renal secretion of OAs and OCs. New information on naturally occurring genetic variation of many of these processes provides insight into the basis of observed variability of drug efficacy and unwanted drug-drug interactions in human populations. The present review examines recent work on these issues.

Occurrence and fate of steroid estrogens in the largest wastewater treatment plant in Beijing, China

Concern over steroid estrogens has increased rapidly in recent years due to their adverse health effects. Effluent discharge from wastewater treatment plants (WWTPs) is the main pollutant source for environmental water. To understand the pollutant level and fate of steroid estrogens in WWTPs, the occurrence of estrone (E1), 17-β-estradiol (E2), estriol (E3), and 17-β-ethinylestradiol (EE2) was investigated in the Gaobeidian WWTP in Beijing, China. Water samples from influent as well as effluent from second sedimentation tanks and advanced treatment processes were taken monthly during 2006 to 2007. In influent, steroid estrogen concentrations varied from 11.6 to 1.1 × 10(2) ng/l, 3.7 to 1.4 × 10(2) ng/l, no detection (nd) to 7.6×10(2) ng/l and nd to 3.3 × 10(2) ng/l for E1, E2, E3, and EE2, respectively. Compared with documented values, the higher steroid estrogen concentrations in the WWTP influent may be due to higher population density, higher birthrate, less dilution, and different sampling time. Results revealed that a municipal WWTP with an activated sludge system incorporating anaerobic, anoxic, and aerobic processes could eliminate natural and synthetic estrogens effectively. The mean elimination efficiencies were 83.2%, 96.4%, 98.8%, and 93.0% for E1, E2, E3, and EE2, respectively. The major removal mechanism for natural estrogens and synthetic estrogen EE2 were biodegradation and sorption on the basis of mass balance in water, suspension particles, and sludge. In the WWTP effluent, however, the highest concentrations of E1, E2, E3, and EE2 attained were 74.2, 3.9, 5.1, and 4.6 ng/l, respectively. This is concerning as residual steroid estrogens in WWTP effluent could lead to pollution of the receiving water. Advanced flocculation treatment was applied in the WWTP and transformed the residual estrogen conjugates to free species, which were reduced further by filtration with removal shifting from 32% to 57% for natural estrogen, although no EE2 was removed.

Occurrences of six steroid estrogens from different effluents in Beijing, China

Concentration levels of six natural and anthropogenic origin steroid estrogens, namely, diethylstilbestrol (DES), estrone (E1), estradiol (E2), estriol (E3), ethinylestradiol (EE2), and estradiol-17-valerate (Ev), from different effluents in Beijing were assessed. Sampling sites include two wastewater treatment plants (WWTPs), a chemical plant, a hospital, a pharmaceutical factory, a hennery, and a fish pool. In general, concentrations of estrogens in the effluents varied from no detection (nd) to 11.1 ng/l, 0.7 to 1.2 × 10(3) ng/l, nd to 67.4 ng/l, nd to 4.1 × 10(3) ng/l, nd to 1.2 × 10(3) ng/l, and nd to 11.2 ng/l for DES, E1, E2, EE2, E3, and Ev, respectively. The concentration levels of steroid estrogens from different effluents decreased in the order of pharmaceutical factory and WWTP inlets > hospital > hennery > chemical factory > fish pool. This study indicated that natural estrogens E1, E2, and E3 and synthetic estrogen EE2 are the dominant steroid estrogens found in the different Beijing effluents. For source identification, an indicator (hE = E3/(E1 + E2 + E3)) was used to trace human estrogen excretion. Accordingly, hE in effluents from the hospital and WWTP inlets exceeded 0.4, while much smaller values were obtained for the other effluents. Human excretions were the major contributor of natural estrogens in municipal wastewater. Estimation results demonstrated that direct discharge was the major contributor of steroid estrogen pollution in receiving waters.

Molecular cloning of vitellogenin gene and mRNA expression by 17alpha-ethinylestradiol from slender bitterling

Indigenous aquatic population such as fish could be used as a successful test species for evaluating the ecological effects in aquatic environment. In the present study, vitellogenin (Vtg) from slender bitterling (Acheilognathus yamatsutae), an indigenous aquatic species in Korea, was cloned and sequenced to determine if the Vtg gene possesses an important characteristic so as to act as a sensitive biomarker for estrogenic endocrine disrupting chemicals (EEDCs). The sbVtg cDNA is 5010 bp in length, containing a 4653 bp open reading frame, which encodes 1550 amino acid residues. The sbVtg cDNA was divided into lipovitellin heavy chain (LvH), phosvitin (Pv), lipovitellin light chain (LvL) as well as a beta'-component (beta'-c) domain, and belongs to VtgAo2. SbVtg has conserved important sequences for Vtg functions such as signal peptide, VtgR-binding region, and disulfide bond formation, all of which are consistent with those of other teleosts. In addition, the male slender bitterling aqueous exposed to 17 alpha-ethinylestradiol (EE2, 12.5, 25, and 50 ng/L) produced a statistically significant and concentration-dependent increase in hepatic Vtg mRNA expression, which showed a similar pattern to biliary estrogenic activity, measured by ERE-reporter gene assay. Thus, this study clearly indicates that the induction of Vtg in slender bitterling might be a suitable biomarker in toxicological research of EEDCs.

A novel and sensitive method for ethinylestradiol quantification in human plasma by high-performance liquid chromatography coupled to atmospheric pressure photoionization (APPI) tandem mass spectrometry: application to a comparative pharmacokinetics study

In the present study, a novel, fast, sensitive and robust method to quantify ethinylestradiol in human plasma using 17alpha-ethinylestradiol-d4 as the internal standard (IS) is described. The analyte and the IS were extracted from acidified plasma by liquid-liquid extraction (LLE) using diethyl ether-hexane followed by online solid phase extraction (SPE) using online C18 cartridges. Extracted samples were analyzed by high-performance liquid chromatography coupled to atmospheric pressure photoionization tandem mass spectrometry (HPLC-APPI-MS/MS). Chromatography was performed isocratically on a C18, 5 microm analytical column. The method had a chromatographic run time of 2.50 min and a linear calibration curve over the range 5-500 pg ml(-1) (r(2)>0.9992). The lowest concentration quantified was 5 pg ml(-1), demonstrating acceptable accuracy and precision. The intra-assay precisions ranged from 2.1 to 14.6%, while inter-assay precisions ranged from 4.4 to 11.4%. The intra-assay accuracies ranged from 94.6 to 103.8%, while the inter-assay accuracies ranged from 98.9 to 101.6%. The recovery of ethinylestradiol was determined as part of the assay validation process and was 73.1 and 79.0% for the concentrations 15 and 375 pg ml(-1), respectively. Short-term stability showed that ethinylestradiol was stable in plasma for at least 19 h at room temperature or for at least 385 days when stored at -20 degrees C. In the study of bioequivalence conducted in Brazil, healthy volunteers received two ethinylestradiol 0.035 mg tablet formulations using an open, randomized, two-period crossover design with a 2-week washout interval. Since the 90% confidence interval for C(max) and area under the curve ratios were all inside the 80-125% interval proposed by the US Food and Drug Administration, it was concluded that the two ethinylestradiol formulations are bioequivalent with respect to both the rate and the extent of absorption.

Interplay of conjugating enzymes with OATP uptake transporters and ABCC/MRP efflux pumps in the elimination of drugs

BACKGROUND

Biliary excretion is a major elimination route of many drugs and their metabolites. Hepatobiliary elimination is a vectorial process involving uptake transporters in the basolateral hepatocyte membrane, possibly Phase I and Phase II metabolizing enzymes, and ATP-dependent efflux pumps in the apical hepatocyte membrane.

OBJECTIVES

Because many drugs and their metabolites are anions, this review focuses on transporters involved in their hepatocellular uptake (members of the organic anion transporting polypeptide (OATP) family) and biliary elimination (apical conjugate efflux pump ABCC2/MRP2).

METHODS

The molecular and functional characteristics of the human OATP and ABCC/MRP transporters are presented, including a detailed overview of endogenous and drug substrates. Examples illustrate the interplay of transporters with Phase II conjugating enzymes. Model systems to study the vectorial transport of organic anions are also discussed.

RESULTS/CONCLUSIONS

OATP uptake transporters, conjugating enzymes, and ABCC2/MRP2 work in concert to enable the hepatobiliary elimination of anionic drugs and their metabolites. It is increasingly important to understand how genetic variants of these transporters and enzymes influence the interindividual variability of drug elimination.

Formation of estrogenic brominated ethinylestradiol in drinking water: implications for aquatic toxicity testing

17alpha-Ethinylestradiol (EE2) is a synthetic estrogen which is thought to contribute the feminisation of fish exposed to wastewater effluents. During laboratory exposure studies of fish to EE2, it was observed that the estrogen in the aquarium water was rapidly transformed (within 10 min) to mono- and di-brominated A-ring products. Exposure of roach (Rutilis rutilus) to 30 ng L(-1) EE2 resulted in accumulation of dibrominated EE2 in ovaries (apparent bioconcentration factor, BCF 130) and liver (apparent BCF 7894) at concentrations which were 18-67-fold greater than the test EE2 compound. The estrogenic activities of brominated EE2 compounds were tested in an in vitro yeast recombinant estrogen receptor transcription screen (YES). All the brominated products of EE2 were estrogenic, however monobrominated isomers of EE2 were 18-105-fold less estrogenic, and dibrominated EE2 2058-fold less active in the YES than EE2 itself. This study reveals the importance of using chemical methods to verify exposure concentrations of waterborne test chemicals and suggests that bromination of estrogens may occur during water treatment, potentially resulting in the formation of bioavailable estrogenic environmental contaminants.

Prediction of human pharmacokinetics-biliary and intestinal clearance and enterohepatic circulation

The main objective was to evaluate and propose methods for predicting biliary clearance (CL(bile)) and enterohepatic circulation (EHC) of intact drugs in man. Another aim was to evaluate to role of intestinal drug secretion and propose a method for prediction of intestinal secretion CL (CL(i)). Animal data poorly predict the CL and CL(bile) of biliary excreted drugs, and the suggested molecular weight threshold for bile excretion as the dominant elimination route does not seem to hold. Active transport, low metabolic intrinsic CL (CL(int)) and, as an approximation, permeability (P(e)) less than that of metoprolol is required for substantial CL(bile) to occur. The typical EHC plasma concentration vs time profile (multiple peaks) is demonstrated for many low metabolic CL(int)-compounds with efflux and moderate to high intestinal P(e) and fraction absorbed. Physiologically-based in-vitro to in-vivo (PB-IVIV) methodology with in-vitro intrinsic CL(bile)-data obtained with sandwich-cultured human hepatocytes has generated 2- and 5-fold underpredictions for two compounds with intermediate to high CL(bile). This is despite not considering the unbound fraction. Possible explanations include low transporter activity and diffusion limitations in the in-vitro experiments. Intestinal reabsorption and EHC were also neglected in these predictions and in-vivo CL(bile) estimations. The sandwich model and these reference data are still very useful. Consideration of an empirical scaling factor and a newly developed approach that accounts for intestinal reabsorption and EHC could potentially lead to improved PB-IVIV predictions of CL(bile). Apparently, no attempts have been made to predict CL(i). Elimination via the intestinal route does not appear to be of great importance for the few compounds with available data, but could be equally as important as bile excretion. Net secretion in-vitro P(e) and newly estimated in-vivo intrinsic CL(i) data for digoxin and rosuvastatin could be useful for approximation of CL(i) of other compounds.

Pharmacokinetic Drug Interactions Involving 17??-Ethinylestradiol

17alpha-Ethinylestradiol (EE) is widely used as the estrogenic component of oral contraceptives (OC). In vitro and in vivo metabolism studies indicate that EE is extensively metabolised, primarily via intestinal sulfation and hepatic oxidation, glucuronidation and sulfation. Cytochrome P450 (CYP)3A4-mediated EE 2-hydroxylation is the major pathway of oxidative metabolism of EE. For some time it has been known that inducers of drug-metabolising enzymes (such as the CYP3A4 inducer rifampicin [rifampin]) can lead to breakthrough bleeding and contraceptive failure. Conversely, inhibitors of drug-metabolising enzymes can give rise to elevated EE plasma concentrations and increased risks of vascular disease and hypertension. In vitro studies have also shown that EE inhibits a number of human CYP enzymes, such as CYP2C19, CYP3A4 and CYP2B6. Consequently, there are numerous reports in the literature describing EE-containing OC formulations as perpetrators of pharmacokinetic drug interactions. Because EE may participate in multiple pharmacokinetic drug interactions as either a victim or perpetrator, pharmaceutical companies routinely conduct clinical drug interaction studies with EE-containing OCs when evaluating new chemical entities in development. It is therefore critical to understand the mechanisms underlying these drug interactions. Such an understanding can enable the interpretation of clinical data and lead to a greater appreciation of the profile of the drug by physicians, clinicians and regulators. This article summarises what is known of the drug-metabolising enzymes and transporters governing the metabolism, disposition and excretion of EE. An effort is made to relate this information to known clinical drug-drug interactions. The inhibition and induction of drug-metabolising enzymes by EE is also reviewed.

Use of Immortalized Human Hepatocytes to Predict the Magnitude of Clinical Drug-Drug Interactions Caused by CYP3A4 Induction

Cytochrome P4503A4 (CYP3A4) is the principal drug-metabolizing enzyme in human liver. Drug-drug interactions (DDIs) caused by induction of CYP3A4 can result in decreased exposure to coadministered drugs, with potential loss of efficacy. Immortalized hepatocytes (Fa2N-4 cells) have been proposed as a tool to identify CYP3A4 inducers. The purpose of the current studies was to characterize the effect of known inducers on CYP3A4 in Fa2N-4 cells, and to determine whether these in vitro data could reliably project the magnitude of DDIs caused by induction. Twenty-four compounds were chosen for these studies, based on previously published data using primary human hepatocytes. Eighteen compounds had been shown to be positive for induction, and six compounds had been shown to be negative for induction. In Fa2N-4 cells, all 18 positive controls produced greater than 2-fold maximal CYP3A4 induction, and all 6 negative controls produced less than 1.5-fold maximal CYP3A4 induction. Subsequent studies were conducted to determine the relationship between in vitro induction data and in vivo induction response. The approach was to relate in vitro induction data (E(max) and EC(50) values) with efficacious free plasma concentrations to calculate a relative induction score. This score was then correlated with decreases in area under the plasma concentration versus time curve values for coadministered CYP3A4 object drugs (midazolam or ethinylestradiol) from previously published clinical DDI studies. Excellent correlations (r(2) values >0.92) were obtained, suggesting that Fa2N-4 cells can be used for identification of inducers as well as prediction of the magnitude of clinical DDIs.

Treatment of model soils contaminated with phenolic endocrine-disrupting chemicals with laccase from Trametes sp. in a rotating reactor

An enzymatic treatment system for the remediation of sand contaminated with endocrine-disrupting chemicals (EDCs) was studied. Laccase from Trametes sp. (Laccase Daiwa) decreased the amounts of nonylphenol, octylphenol, bisphenol A and ethynylestradiol (synthetic estrogen) adsorbed on sea sand (2 micromol g(-1)) in a test tube with shaking. The phenolic endocrine-disrupting chemicals might have polymerized via enzymatic conversion to their phenoxy radicals. The optimum pH for the enzymatic treatment was approximately 5. A rotating reactor was used for scaling up the enzymatic treatment. The reaction rate increased by rotating the reactor. The optimum speed of revolution was 10-15 rpm for the treatment of nonylphenol. The amounts of octylphenol, bisphenol A, and ethynylestradiol also decreased enzymatically in the reactor. Our enzymatic treatment system with a rotating reactor will be useful for the treatment of soil highly polluted with phenolic EDCs.

Biodegradation of natural and synthetic estrogens by nitrifying activated sludge and ammonia-oxidizing bacterium Nitrosomonas europaea

This report describes the uses of nitrifying activated sludge (NAS) and ammonia-oxidizing bacterium Nitrosomonas europaea to significantly degrade estrone (E1), 17beta-estradiol (E2), estriol (E3), and 17alpha-ethynylestradiol (EE2). Using NAS, the degradation of estrogens obeyed first-order reaction kinetics with degradation rate constants of 0.056 h(-1) for E1, 1.3 h(-1) for E2, 0.030 h(-1) for E3, and 0.035 h(-1) for EE2, indicating that E2 was most easily degraded. Then, we confirmed that E2 was degraded via E1 by NAS. With/without the ammonia oxidation inhibitor, it was observed that ammonia-oxidizing bacteria in conjunction with other microorganisms in NAS degraded estrogens. Using N. europaea, the degradation of estrogens reasonably obeyed zero-order reaction kinetics, and no remarkable difference is present among the four estrogens degradation rates and it was found that E1 was not detected during E2 degradation period. We suggested that E2 was degraded to E1 in NAS could be caused by other heterotrophic bacteria, not by ammonia-oxidizing bacteria.

Transport of ethinylestradiol glucuronide and ethinylestradiol sulfate by the multidrug resistance proteins MRP1, MRP2, and MRP3

Ethinylestradiol (EE) is one of the key constituents of oral contraceptives. Major metabolites of EE in humans are the glucuronide and sulfate conjugates, EE-3-O-glucuronide (EE-G) and EE-3-O-sulfate (EE-S). In the present study, transport of EE-G and EE-S by the human multidrug resistance proteins MRP1, MRP2, and MRP3 was investigated using inside-out membrane vesicles, isolated from Sf9 cells expressing human MRP1, MRP2, or MRP3. Vesicular uptake studies showed that EE-G was not a substrate for MRP1, whereas an ATP-dependent and saturable transport of [(3)H]EE-G was observed in MRP2 (K(m) of 35.1 +/- 3.5 microM) and MRP3 (K(m) of 9.2 +/- 2.3 microM) containing vesicles. EE-S was not transported by either MRP1, MRP2, or MRP3. However, low concentrations of EE-S stimulated MRP2-mediated uptake of ethacrynic acid glutathione. EE-S also stimulated MRP2 and MRP3-mediated uptake of 17beta-estradiol-17beta-D-glucuronide. Interestingly, EE-S stimulated strongly MRP2- and MRP3-mediated uptake of EE-G by increasing its apparent transport affinity, whereas no reciprocal stimulation of EE-S uptake by EE-G was observed. These data indicate that EE-S allosterically stimulates MRP2- and MRP3-mediated transport of EE-G and is not cotransported with EE-G. Our studies demonstrate specific active transport of a pharmacologically relevant drug conjugate by human MRP2 and MRP3, involving complex interactions with other organic anions. We also suggest that caution needs to be taken when using only competition studies as screening tools to identify substrates or inhibitors of MRP-mediated transport.

Interspecies scaling of biliary excreted drugs

The objective of this study is to predict clearance of drugs in humans from animals which are excreted in the bile. Clearance (CL) of eight drugs known to be excreted in the bile were randomly selected from the literature. Scaling of CL was performed using at least three animal species. Using simple allometry, CL x mean life-span potential (MLP) or CL x brain weight, CLs of studied drugs were predicted in humans. The choice of one of the methods depended on the 'rule of exponents' as described by Mahmood and Balian. A 'correction factor' was calculated by adjusting bile flow rate based on the species body weight (bile flow = mL/day/kg body weight) or liver weight (bile flow = mL/day/kg liver weight). Using the 'rule of exponents' and combining it with the 'correction factor', the CLs of biliary excreted drugs were predicted in humans. Predicted CLs in humans from animals using simple allometry were several times higher for all eight drugs (% error [range] = 46-1703). Using the 'rule of exponents' and combining it with a 'correction factor' as described in this report provided a substantial improvement (% error [range] = 5-91) in the prediction of CL for biliary excreted drugs. The results of this study indicate that the CL of a biliary excreted drug may be overpredicted in humans and by applying the 'correction factor' employed here, the predictability of drug CL in humans from animal data may be significantly improved.

In vitro analysis of human drug glucuronidation and prediction of in vivo metabolic clearance

The glucuronidation of a number of commonly used hepatic uridine diphosphate glucuronosyltransferase drug substrates has been studied in human tissue microsomes. Prediction of in vivo hepatic drug glucuronidation from liver microsomal data yielded a consistent 10-fold under-prediction. Consideration of protein binding was observed to be pivotal when predicting in vivo glucuronidation for acid substrates. Studies using human intestinal microsomes demonstrated the majority of drugs to be extensively glucuronidated such that the intrinsic clearance (CL(int)) of ethinylestradiol (CL(int) = 1.3 microl/min/mg) was twice that obtained using human liver microsomes (CL(int) = 0.7 microl/min/mg). The potential extrahepatic in vivo glucuronidation was calculated for a range of drug substrates from human microsomal data. These results indicate the contribution of intestinal drug glucuronidation to systemic drug clearance to be much less than either hepatic or renal glucuronidation. Therefore, data obtained with intestinal microsomes may be misleading in the assessment of the contribution of this organ to systemic glucuronidation. The use of hepatocytes to assess metabolic stability for drugs predominantly metabolized by glucuronidation was also investigated. Metabolic clearances for a range of drugs obtained using fresh preparations of human hepatocytes predicted accurately hepatic clearance reported in vivo. The use of cryopreserved hepatocytes as an in vitro tool to predict in vivo metabolism was also assessed with an excellent correlation obtained for a number of extensively glucuronidated drugs (R(2) = 0.80, p < 0.001).

Effects of cytochrome P450 inducers on 17alpha-ethinyloestradiol (EE2) conjugation by primary human hepatocytes

AIMS

Our objective was to elucidate further the underlying mechanism responsible for therapeutic failures observed with concomitant administration of the oral contraceptive 17alpha-ethinyloestradiol (EE2 ) and rifampicin.

METHODS

We investigated both oxidative and direct conjugative [3H]-EE2 metabolism by human liver S9 fraction and the effect of known enzyme-inducing drugs using a human hepatocyte induction model in vitro.

RESULTS

Cofactor dependent [3H]-EE2 metabolism by human liver S9 fraction produced 2-hydroxy-[3H]-EE2, 2-methoxy-[3H]-EE2, and direct [3H]-EE2 sulphate and glucuronide conjugates. Only two detectable metabolites of [3H]-EE2 were produced by the S9 fraction in the presence of all cofactors: [3H]-EE2-3-sulphate (75.7+/-7.6% s. d.) and 2-methoxy-3H-EE2 (2.6%+/-0.5% s.d.). Human hepatocytes extensively metabolized [3H]-EE2 to its glucuronide and sulphate conjugates. Small amounts of a 2-methoxy-[3H]-EE2 3-conjugate, < or = 10%, was observed but no. 2-hydroxy-[3H]-EE2 was detected. An unexpected finding in our study was increased [3H]-EE2-3-sulphate production (1.5-3.3 fold, n=3 donor livers) by hepatocytes pretreated with rifampicin compared to control hepatocytes. No statistically significant increase in [3H]-EE2-3-sulphation was observed in hepatocytes pretreated with 3-methylcholanthrene, phenobarbitone, dexamethasone, or omeprazole over nontreated hepatocytes. To our knowledge, this is the first observation of sulphotransferase induction by rifampicin in human hepatocytes in vitro resulting in increased [3H]-EE2 sulphation.

CONCLUSIONS

Our data indicate that the major EE2 metabolic products formed by human hepatocytes in vitro are direct EE2 conjugates with EE2 oxidation representing minor pathways. Further studies are required to establish the mechanism of sulphotransferase induction and the clinical relevance of our findings.

Transformation of a non-oestrogenic steroid metabolite to an oestrogenically active substance by minimal bacterial activity

The majority of oestrogenic material excreted from humans and wildlife, and therefore released into sewers, is in a conjugated form. However, the finding of "free" oestrogens in sewage effluent suggests that these metabolites are somehow converted back into an active form, before or during passage through a sewage treatment process. When male fathead minnows (Pimephales promelas) were continuously exposed to oestradiol-3-glucuronide, in a continuous-flow system, it demonstrated no inherent oestrogenic activity. However, when fish were exposed to effluent generated from laboratory simulations of sewage treatment processes, to which had been added oestradiol-3-glucuronide, oestrogenic activity was observed, suggesting microbial activity was capable of degrading the steroid metabolite into a more potent oestrogen. Oestrogenic potency was determined by measuring changes in plasma vitellogenin (egg yolk precursor) concentrations and gonadosomatic index. The results suggest that inactive metabolites of steroids are very readily biotransformed into biologically active oestrogens.

Pharmaceuticals in the environment--a human risk?

Pharmaceuticals in the environment and their potential toxic effects are emerging research areas, which is also reflected in the drug approval regulation. This far, focus has mainly been directed toward potential effects on nature and wildlife. In this paper, human risk as a consequence of exposure via the environment has been addressed and assessed. The synthetic estrogen 17alpha-ethinylestradiol (EE2), the antibiotic phenoxymethylpenicillin (Pen V), and the antineoplastic drug cyclophosphamide (CP) were chosen as modeling substances based on criteria of receptor specificity, elevated risk for human population groups for which the pharmaceuticals are not therapeutically intended, different modes of action, and prescription frequency. Attention has been focused on emissions from the use phase and subsequent diffuse release via the sewer systems. A reasonable worst-case environmental fate and human exposure were estimated using the software EUSES on worst-case emission quantities. The results indicate a negligible human risk connected to the environmental exposure for these substances. Danish conditions have been used as the modeling area, but the results are assumed to be valid for regions with similar drug consumption profiles.

Pig hepatocytes as an in vitro model to study the regulation of human CYP3A4: prediction of drug-drug interactions with 17 alpha-ethynylestradiol

The objective of this study was to provide evidence of the validity of pig hepatocytes as a model to study the regulation of human CYP3A4 with special emphasis on drug-drug interactions. Thirteen different drugs were incubated with primary monolayer cultures of pig hepatocytes (n = 4). The study included both drugs reported to cause drug interactions in the clinic with 17 alpha-ethynylestradiol (EE2), other drugs metabolized by CYP3A4, and drugs not reported to cause any problems. Effect of the drug exposure to pig hepatocytes was determined by immunodetection using a monoclonal human CYP3A4 antibody and measurement of 6 beta-hydroxylation of testosterone and 2-hydroxylation of 17 alpha-ethynylestradiol (EE2), both reactions known to be catalyzed by CYP3A4 in humans. Data were compared to data from human hepatocytes and to reported observations of drug-drug interactions in the clinic. The drugs known to be inducers of CYP3A4 in humans significantly increased a CYP isoform in pigs catalyzing 6 beta-hydroxylation of testosterone and 2-hydroxylation of EE2, whereas drugs not reported to have clinical interactions with EE2 had no or only marginal effect. Induction by the drugs known to be inducers of CYP3A4 increased with drug exposure time and the CYP3A4 activity, represented by testosterone 6 beta-hydroxylation, was highest at 72 h for the investigated induction periods (24, 48 and 72 h), except for dexamethasone where the effect peaked after 24 h. Induction of the 2-hydroxylation of EE2 correlated well with the increase in 6 beta-hydroxylation of testosterone (except for sulphinpyranzone) and the increase in the protein level of CYP3A detected by a monoclonal human CYP3A4 antibody, thus confirming the 2-hydroxylation of EE2 in pigs as being biotransformed by a CYP isoform presumably belonging to the CYP3A subfamily as in humans. In conclusion, these results indicate that pig hepatocytes may be a valuable model to mimic the regulation of human CYP3A4.

The role of cytochrome P450 enzymes in hepatic and extrahepatic human drug toxicity

The human cytochrome P450 enzyme system metabolises a wide array of xenobiotics to pharmacologically inactive metabolites, and occasionally, to toxicologically active metabolites. Impairment of cytochrome P450 activity, which may be either genetic or environmental, may lead to toxicity caused by the parent compound itself. In practise, this usually only applies to drugs that have a narrow therapeutic index and when their clearance is critically dependent upon the fraction normally metabolised by that pathway. P450 enzymes may also convert the drug to a chemically reactive metabolite, which, if not detoxified, may lead to various forms of hepatic and extrahepatic toxicity, including cellular necrosis, hypersensitivity, teratogenicity, and carcinogenicity, depending on the site of formation and the relative stability of the metabolite, and the cellular macromolecule with which it reacts. Variation in the regulation and expression of the drug metabolising enzymes may play a key role in both interindividual variation in sensitivity to drug toxicity and tissue-specific damage. Avoidance of toxicity may be possible in rare instances by prediction of individual susceptibility or by designing new chemical entities that are metabolised by a range of enzymes (both cytochromes P450 and others) and do not undergo bioactivation.

Structure-metabolism relationships of ring-A halogenated analogues of 17 alpha-ethynyloestradiol

The metabolic fates of 2-chloro-, 2-bromo-, 4-bromo- and 2-iodo-17 alpha-ethynyloestradiol (EE2) in rats were determined. 6,7-3H-labelled analogues (0.1-2.0 mumol/kg) were administered i.v. to anaesthetized animals. The metabolites of all four compounds were rapidly and extensively excreted in bile (79-93% of the dose over 6 h). Unlike EE2 and 2-fluoro-EE2 (2-FEE2), neither 2-chloro(Cl)-(2.0 mumol/kg),2-bromo(Br)-(0.1 mumol/kg), nor 2-iodo(I)-EE2-(0.1 mumol/kg) underwent C-2 hydroxylation in female rats; 2-BrEE2 was similarly refractory in male rats; females, was subject to approx. 2-fold greater C-2 hydroxylation than 2-FEE2 but this equalled only approx. 60% of that undergone by EE2. All three of the C-2 halogenated derivatives were substantially excreted unchanged except for conjugation. 2-ClEE2 alone was C-4 hydroxylated to an appreciable extent. The oxidative metabolism of 2- and 4-BrEE2 in rats was sexually differentiated: 2-BrEE2 yielded an alkyl hydroxylated metabolite and a two-component dihydroxylated fraction in the ratio 1:0.09 and 1:0.76 in males and females, respectively; 4-BrEE2 underwent C-2 and alicyclic (C-15) hydroxylation in the ratio 1:4.8 and 1:0.07 in males and females, respectively. 2-ClEE2 formed much less alkyl monohydroxylated metabolite (C-16 hydroxylated for 2-Cl- and 2-IEE2) than did either 2-BrEE2 or 2-IEE2. The observed structure-metabolism relationships are discussed.

Common food additives are potent inhibitors of human liver 17 alpha-ethinyloestradiol and dopamine sulphotransferases

Interactions between dietary xenobiotics, drugs and biologically active endogenous compounds are a potential source of idiosyncratic adverse pathology. We have examined the inhibition of the sulphation of a number of xenobiotics and endobiotics in human liver cytosol by 15 food additives and constituents. Sulphation of dehydroepiandrosterone was resistant to inhibition by all compounds tested; however, dopamine sulphotransferase (ST) activity was inhibited strongly by (+/-)-catechin, (+)-catechin, octyl gallate, tartrazine and vanillin. Sulphation of the xenobiotic steroid 17 alpha-ethinyloestradiol (EE2) was inhibited by vanillin, erythrosin B and octyl gallate. Of these compounds, only vanillin was found to be sulphated to a significant extent by both human liver and platelets, and vanillin was determined to be a substrate for the monoamine-sulphating isoenzyme of phenolsulphotransferase. Vanillin was found to inhibit 50% of liver EE2 ST activity (IC50) at a concentration of approximately 1.3 microM and the mode of inhibition was non-competitive. The implications of these results for the adverse side effects associated with food additives and oral contraceptives are discussed.

Metabolism of the oral contraceptive steroids ethynylestradiol, norgestimate and 3-ketodesogestrel by a human endometrial cancer cell line (HEC-1A) and endometrial tissue in vitro

Human endometrial cancer cells and human endometrial tissue have been extensively used to study steroid hormone action and metabolism. The natural estrogens estradial (E2) and estrone (E1) are known to be metabolized by both cells and tissue with the interconversion of the two steroids and the formation of sulphate conjugates. The aim of the present work was to see if the commonly used oral contraceptive steroids ethynylestradiol (EE2), norgestimate (Ngmate) and 3-ketodesogestrel (3-KDG) were metabolized by a human endometrial cancer cell line (HEC-1A) and human endometrial tissue in vitro. Metabolites were analysed by on-line radiometric HPLC. Endometrial tissue was obtained from women undergoing dilation and curettage or hysterectomy operations. In preliminary studies with endogenous estrogens, HEC-1A cells were able to interconvert E1 and E2; the equilibrium favouring the formation of E2. Normal endometrial tissue extensively converted E2 to E1, tumour tissue appeared to catalyse this reaction much less avidly. In addition sulphate conjugates were formed by normal tissue from some patients. Cell line and endometrial tissue was able to hydrolyse estrone 3-sulphate. With EE2 as substrate there was no evidence of phase I metabolism by cell line or tissue. However, conversion to the presumed 3-sulphate conjugate was observed following incubation with normal tissue from some women. Deacetylation of the progestogen Ngmate to norgestrel oxime (NgOx) was complete within 24 h. There was also some loss of the oxime moiety to give norgestrel (Ng) following incubation with HEC-1A cells. Metabolism of Ngmate was also complete within 24 h following incubation with endometrial tissue. There were both qualitative and quantitative differences in metabolite formation between tissue obtained from different women. In contrast, 3-KDG was relatively resistant to metabolism by cell line and tissue. The major metabolite formed by HEC-1A cells accounted for only 3.3 +/- 0.4% of total added radiolabelled steroid and co-chromatographed with 3 alpha-hydroxydesogestrel. Smaller amounts of other radiometabolites were formed. No phase I metabolites of 3-KDG were formed by normal endometrial tissue, however small amounts of radiometabolites appeared to be formed by malignant tissue. These studies have provided evidence to suggest that the oral contraceptives EE2, Ngmate and 3-KDG are metabolized in the human endometrium. Knowledge of the metabolism of these in target tissues such as the endometrium may be pertinent considering the possibility that metabolites may exert specific effects.

Oxidative dehalogenation of 2-fluoro-17 alpha-ethynyloestradiol in vivo. A distal structure-metabolism relationship of 17 alpha-ethynylation

Metabolic activation to catechols and their oxidation products is variously considered to contribute to the genotoxic, cytotoxic, transforming and tumour-promoting activities of exogenous steroidal oestrogens. 2-Fluoro-17 alpha-ethynyloestradiol (2-FEE2) was synthesized as a prototype of pharmacologically active derivatives of 17 beta-oestradiol which are resistant to metabolic activation in vivo. It possessed high affinity for the rat uterine oestrogen receptor and was oestrogenic in rats. Biliary metabolites of [6,7-3H]2-FEE2 (0.73 mumol/kg, 157 micrograms/kg, i.v.) in female rats were characterized: 87% of the radiolabel was excreted, principally as 2-FEE2 glucuronide, over 6 hr. Although 2-fluoro-17 beta-oestradiol is not metabolized to C-2 oxygenated products in vivo, 2-FEE2 underwent rapid and appreciable oxidative defluorination. 2-Hydroxy-17 alpha-ethynyloestradiol and 2-methoxy-17 alpha-ethynyloestradiol represented, respectively, 8% and 13% of the dose. Fluorination nevertheless restricted C-2 oxygenation to ca. 28% of that which 17 alpha-ethynyloestradiol undergoes in female rats. C-4 oxygenation of 2-FEE2, resulting in catechol formation, occurred but to a lesser extent (ca. 12% of dose). None of the major and identified minor biliary metabolites was a product of metabolic activation at the ethynyl function. A mechanistic rationalization of the long range enhancement by 17 alpha-ethynylation of oxidative defluorination at C-2 is presented.

The metabolism of 2- and 4-fluoro-17 beta-oestradiol in the rat and its implications for oestrogen carcinogenesis

2-Fluoro-[6,7-3H]17 beta-oestradiol([3H]2-FE2) and 4-fluoro-[6,7-3H]17 beta-oestradiol([3H]4-FE2) were synthesized by the fluorination and reduction of [3H]oestrone and purified by HPLC. [3H]2-FE2 and [3H]4-FE2 (72.5 micrograms/kg; 0.25 mumol/kg) were administered i.v. to anaesthetized female and male Wistar rats (N = 4) with biliary cannulae. Bile was collected for 6 hr. Female rats administered [3H]2-FE2 excreted 85% of the dose into bile over 6 hr whilst male rats excreted 77%. After the administration of [3H]4-FE2, female and male rats excreted 72 and 83% of dose into bile over 6 hr, respectively. The biliary metabolites were glucuronides in all cases. The principal metabolite of [3H]2-FE2 liberated from biliary conjugates by beta-glucuronidase was 2-fluoroestrone in both female rats (64% of dose) and male rats (57%). No 2-hydroxylated, i.e. oxidatively defluorinated, metabolites were detected in either sex. In contrast, 2-hydroxylation of [3H]4-FE2 did occur, but only in female rats: 2-hydroxy-4-fluoro-oestrone (22%) and 2-methoxy-4-fluoroestrone (17%) were identified as biliary aglycones. However, the major metabolite was 4-fluoroestrone (4FE1; 38%). In male rats, 4-FE1 and 4-fluoro D-ring-oxygenated products were the principal biliary aglycones. The differences in metabolism between the two fluoro analogues and oestradiol are discussed with particular reference to the possible involvement of 2- and 4-hydroxy (catechol) oestrogens in oestrogen toxicity.

Oral contraceptive steroids--pharmacological issues of interest to the prescribing physician

Oral contraceptive steroids (OCS) are well absorbed from the gastrointestinal tract in humans. However, while the progestogens are almost completely bioavailable, ethinylestradiol (EE2) is subject to extensive first pass metabolism consisting chiefly of conjugation with sulfate in the gut wall. Both EE2 and progestogens are well absorbed in patients with an ileostomy or with diseases such as cystic fibrosis or Crohn's disease. However in patients with celiac disease (gluten-sensitive enteropathy) the gut wall is less able to conjugate EE2 and thus its bioavailability is increased. The bioavailability returns to control values as the disease is improved following gluten withdrawal. Other drugs that are conjugated with sulfate, such as vitamin C and paracetamol, compete for available sulfate when coadministered with OCS leading to high plasma levels of EE2. Enzyme-inducing agents such as rifampicin, phenobarbitone, phenytoin and carbamazepine reduce blood levels of the OCS leading to contraceptive failure. In the case of anticonvulsants (but not rifampicin) this can be easily overcome by increasing the dose of OCS used. Broad-spectrum antibiotics are reported to cause failure of contraception by interfering with the enterohepatic circulation of EE2 but limited systematic studies show no evidence of such an interaction. Nevertheless practitioners are advised to recommend the use of alternative contraceptive precautions for women receiving broad-spectrum antibiotics concurrently with their OCS preparation.

Metabolism of the oral contraceptive steroids ethynylestradiol and norgestimate by normal (Huma 7) and malignant (MCF-7 and ZR-75-1) human breast cells in culture

Human breast cancer cells are used extensively for the study of steroid hormone action. It is known that in both receptor positive and receptor negative cell lines there is considerable metabolism of the natural estrogens, estradiol (E2) and estrone (E1) with interconversion of the two steroids and formation of sulphate and glucuronide conjugates. The aim of the present work was to see if the commonly used oral contraceptive steroids (OCS) ethynylestradiol (EE2) and norgestimate (Ngmate) were metabolized in human breast cancer cell lines (MCF-7 and ZR-75-1) and a normal breast cell line (Huma 7). MCF-7, ZR-75-1 and Huma 7 cells were maintained in Dulbeccos Modified Eagles Medium (DMEM) containing foetal calf serum (FCS) insulin and hydrocortisone. In addition, ZR-75-1 cells required epidermal growth factor (EGF) and E2 while MCF-7 cells required only EGF. On reaching confluence cells were transferred to DMEM containing charcoal-stripped FCS, insulin and hydrocortisone. 48 h later this medium was renewed, radiolabelled steroid ([3H]E1; [3H]E2; [3H]EE2, [3H]Ngmate; [3H]E1-SO4; 1 nM; 0.2 microCi) was added and incubation was for 24 or 48 h. Following incubation, the medium was removed and radioactive steroid extracted with ether. Metabolites were analysed by on-line radiometric HPLC. All the cell lines were able to interconvert E1 and E2; the equilibrium favouring the formation of E2 in MCF-7 and ZR-75-1 and E1 in Huma 7 cells. E1 and E2 also underwent phase II metabolism to form their respective estrogen sulphates, this activity being most marked in the Huma 7 cell line. In addition to sulphotransferase activity, the study with E1 sulphate demonstrated sulphatase activity in both normal and cancer cells. There appeared to be no difference in extent of hydrolysis, with both E1 and E2 formed. With EE2 as substrate there was no evidence of phase I metabolism in any of the cell lines but there was conversion to the presumed 3-sulphate conjugate. The percentage formation of this metabolite was very much greater in Human 7 cells (64.1 +/- 9.6% after 24 h) than in MCF-7 and ZR-75-1 cells (7.4 +/- 5.3% and 10.6 +/- 4.1%, respectively after 24 h). In all the cell lines deacetylation of the progestogen Ngmate to norgestrel oxime was complete within 24 h. In addition there was evidence of loss of the oxime moiety to give norgestrel.(ABSTRACT TRUNCATED AT 400 WORDS)

Interindividual variability in the glucuronidation and sulphation of ethinyloestradiol in human liver

1. Glucuronidation and sulphation of ethinyloestradiol (EE2) was studied in human liver. Microsomal glucuronyltransferase activity was measured in 110 livers whose donors were 71 women and 39 men. Enzyme activity ranged between 12.6 and 242 pmol min-1 mg-1 protein, i.e. over a 19-fold range and the mean (+/- s.d.) glucuronyltransferase activity was 96.8 +/- 47.9 pmol min-1 mg-1 protein. 2. Cytosolic sulphotransferase activity was measured in 138 livers whose donors were 90 women and 48 men. Enzyme activity ranged between 14.4 and 98.2 pmol min-1 mg-1 protein, i.e. over a 7-fold range, and the mean (+/- s.d.) sulphotransferase activity was 43.7 +/- 18.6 pmol min-1 mg-1 protein. 3. Human liver glucuronyltransferase and sulphotransferase activities showed a unimodal distribution pattern. Enzyme activities were neither sex-related nor age-dependent. Sulphotransferase activity did not correlate with glucuronyltransferase activity (n = 80) suggesting that the two enzymes are independently regulated. The ratio of specific glucuronyltransferase to sulphotransferase activity ranged between 0.15 and 8.0 (mean +/- s.d., 2.44 +/- 1.51) and was unimodally distributed.

Effect of the progestogens, gestodene, 3-keto desogestrel, levonorgestrel, norethisterone and norgestimate on the oxidation of ethinyloestradiol and other substrates by human liver microsomes

A number of different progestogens, levonorgestrel (LNG), norethisterone (NET), gestodene (GSD), desogestrel (DG) and norgestimate (NORG) are used in combination with the oestrogen ethinyloestradiol (EE2) in oral contraceptive steroid preparations. All the progestogens are acetylenic steroids and previous studies have indicated the potential of acetylenic steroids to cause mechanism-based or "suicide" inactivation of cytochrome P-450. We have compared the effects of the different progestogens on EE2 2-hydroxylation (a reaction catalyzed by enzymes from the P-450IIC, P-450IIIA and P-450IIE gene families) and also the oxidative metabolism of other drug substrates (cyclosporin, diazepam, tolbutamide) by human liver microsomes. On coincubation with EE2 as substrate, GSD, 3-keto desogestrel (3-KD, the active metabolite of desogestrel) and LNG produced some concentration-dependent inhibition of EE2 2-hydroxylation (maximum 32% inhibition at 100 microM 3-keto desogestrel). Ki values determined for GSD and 3-KD were 98.5 +/- 12.3 and 93.2 +/- 10.3 microM (mean +/- SD; n = 4), respectively. Preincubation of progestogens in a small volume (50 microliters) incubation for 30 min in the presence of an NADPH-generating system enhanced the inhibitory potential of all the steroids (at 100 microM, inhibition was for GSD 39%, 3-KD 46%, LNG 46%, NET 51% and NORG 43%). Inhibitory effects were therefore comparable and also similar to the macrolide antibiotic troleandomycin. The most marked inhibition seen was of diazepam N-demethylation and hydroxylation by GSD (71 and 57%, respectively) and 3-KD (62 and 50%, respectively). In preincubation studies involving cyclosporin as the substrate, the order of inhibitory potency was GSD greater than 3-KD greater than NET greater than LNG for production of both metabolite M17 and M21. The results of the study indicate that all the progestogens in common use have the propensity to inhibit a number of oxidative pathways but there is little evidence for one progestogen being more markedly inhibitory than others.

Factors affecting the enterohepatic circulation of oral contraceptive steroids

Oral contraceptive steroids may undergo enterohepatic circulation, but it is relevant for only estrogens, because these compounds can be directly conjugated in the liver. Animal studies show convincing evidence of the importance of the enterohepatic circulation, but studies in humans are much less convincing. The importance of the route and the rate of metabolism of ethinyl estradiol are reviewed. Some antibiotics have been reported anecdotally to reduce the efficacy of oral contraceptive steroids, but controlled studies have not confirmed this observation. Although gut flora are altered by oral antibiotics, the blood levels of ethinyl estradiol are not reduced, and one antibiotic at least (cotrimoxazole) enhances the activity of ethinyl estradiol.

Pharmacokinetic drug interactions with oral contraceptives

Oral contraceptive steroids are used by an estimated 60 to 70 million women world-wide. Over the past 20 years there have been both case reports and clinical studies on the topic of drug interactions with these agents. Some of the interactions are of definite therapeutic relevance, whereas others can be discounted as being of no clinical significance. Pharmacological interactions between oral contraceptive steroids and other compounds may be of 2 kinds: (a) drugs may impair the efficacy of oral contraceptive steroids, leading to breakthrough bleeding and pregnancy (in a few cases, the activity of the contraceptive is enhanced); (b) oral contraceptive steroids may interfere with the metabolism of other drugs. A number of anticonvulsants (phenobarbital, phenytoin, carbamazepine) are enzyme-inducing agents and thereby increase the clearance of the oral contraceptive steroids. Valproic acid has no enzyme-inducing properties, and thus women on this anticonvulsant can rely on their low dose oral contraceptive steroids for contraceptive protection. Researchers are now beginning to unravel the molecular basis of this interaction, with evidence of specific forms of cytochrome P450 (P450IIC and IIIA gene families) being induced by phenobarbital. Rifampicin, the antituberculous drug, also induces a cytochrome P450 which is a product of the P450IIIA gene subfamily. This isozyme is one of the major forms involved in 2-hydroxylation of ethinylestradiol. Broad spectrum antibiotics have been implicated in causing pill failure; case reports document the interaction, and general practitioners are convinced that it is real. The problem remains that there is still no firm clinical pharmacokinetic evidence which indicates that blood concentrations of oral contraceptive steroids are altered by antibiotics. However, perhaps this should not be a surprise, given that the incidence of the interaction may be very low. It is suggested that an individual at risk will have a low bioavailability of ethinylestradiol, a large enterohepatic recirculation and gut flora particularly susceptible to the antibiotic being used. Two drugs, ascorbic acid (vitamin C) and paracetamol (acetaminophen), give rise to increased blood concentrations of ethinylestradiol due to competition for sulphation. The interactions could have some significance to women on oral contraceptive steroids who regularly take high doses of either drug. Although on theoretical grounds adsorbents (e.g. magnesium trisilicate, aLuminium hydroxide, activated charcoal and kaolin) could be expected to interfere with oral contraceptive efficacy, there is no firm evidence that this is the case. Similarly, there is no evidence that smoking alters the pharmacokinetics of oral contraceptive steroids. These agents are now well documented as being able to alter the pharmacokinetics of other concomitantly administered drugs.(ABSTRACT TRUNCATED AT 400 WORDS)

Differences in the cytochrome P-450 isoenzymes involved in the 2-hydroxylation of oestradiol and 17 alpha-ethinyloestradiol. Relative activities of rat and human liver enzymes

The metabolism of oestradiol and 17 alpha-ethinyloestradiol to their 2-hydroxy derivatives is an important determinant in their biological effects. In this work, we have investigated which rat or human cytochrome P-450 isoenzymes are involved in catalysing these reactions. Oestradiol 2-hydroxylation was catalysed by a wide variety of rat cytochrome P-450s from gene families P450IA, P450IIB, P450IIC and P450IIIA. Interestingly, 17 alpha-ethinyloestradiol, which only differs structurally from oestradiol at a position distant from the site of oxidation, was metabolized predominantly by members of the P450IIC gene subfamily. In order to establish which enzymes are responsible for the oxidation of these substrates in man, antibodies to rat liver cytochrome P-450 isoenzymes were used to inhibit these reactions in a panel of human liver microsomal fractions. Also, possible correlations between the proteins recognized by the antibodies and the 2-hydroxylation rate were determined. These experiments provide evidence that 2-hydroxylation of 17 alpha-ethinyloestradiol in man is catalysed by cytochromes from the P450IIC, P450IIE and P450IIIA gene families. In contrast, the major proteins involved in oestradiol metabolism are from the P450IA gene family, although members of the P450IIC and P450IIE gene families may also play a role. These data demonstrate that the differences in the capacity of rat P-450s to metabolize these substrates are also present in the comparable enzymes involved in man, and that a variety of factors will determine the rate of disposition of these compounds in man.

The metabolism of 2,4-dibromo-17 alpha-ethynyl[6,7-3H]oestradiol in the rat

1. The metabolism of 2,4-dibromoethynyloestradiol (2,4-DBEE2) in the rat was studied in order to determine the influence of ring-A substituents on the phase I biotransformations of oestrogens. 2. 2,4-Dibromo-17 alpha-ethynyl[6,7-3H]oestradiol was synthesized by the one-stage bromination of 17 alpha-ethynyl[6,7-3H]oestradiol (EE2) with N-bromoacetamide, and administered (30 micrograms/kg, i.v.) to anaesthetized male and female rats. 3. A single metabolite, identified as a glucuronide of 2,4-DBEE2, was rapidly and extensively eliminated in bile by male rats (83% of the dose over 6 h). Females excreted additional minor conjugated metabolites. Neither unchanged 2,4-DBEE2 nor EE2 was detected in bile. 4. The hepatic residues after 6 h (percentage of dose) were 2.7% and 3.4% in male and female rats, respectively, whilst less than 0.1% per organ(s) was found in kidneys, heart, spleen, lungs and brain. 5. 2,4-Dibromo substitution of EE2 effectively blocked all phase I biotransformations whilst not limiting glucuronylation in male rats, but did not entirely preclude phase I metabolism in females. The inertness of 2,4-DBEE2 to ring-A hydroxylation in male rats conforms with the insignificant debromination of 2,4-dibromoestradiol by hepatic microsomes.