Degradation of norgestrel by bacteria from activated sludge: comparison to progesterone.

Natural and synthetic progestagens in the environment have become a concern due to their adverse effects on aquatic organisms. Laboratory studies were performed to investigate aerobic biodegradation of norgestrel by bacteria from activated sludge in comparison with progesterone, and to identify their degradation products and biotransformation pathways. The degradation of norgestrel followed first order reaction kinetics (T1/2 = 12.5 d), while progesterone followed zero order reaction kinetics (T1/2 = 4.3 h). Four and eight degradation products were identified for norgestrel and progesterone, respectively. Six norgestrel-degrading bacterial strains (Enterobacter ludwigii, Aeromonas hydrophila subsp. dhakensis, Pseudomonas monteilii, Comamonas testosteroni, Exiguobacterium acetylicum, and Chryseobacterium indologenes) and one progesterone-degrading bacterial strain (Comamonas testosteroni) were successfully isolated from the enrichment culture inoculated with aerobic activated sludge. To our best knowledge, this is the first report on the biodegradation products and degrading bacteria for norgestrel under aerobic conditions.

[In vitro metabolic interaction between diphenytriazol and steroid hormone drugs].

AIM: To observe the metabolic interaction between diphenytriazol and steroid hormone drugs, and provide some useful information for clinical medication. METHODS: The steroid hormone drugs which may be co-administrated with diphenytriazol were selected, such as mifepriston, estradiol, medroxyprogesterone acetate, progesterone, norethisterone and so on. Diphenytriazol was incubated with each drug in rat liver microsome. The residual concentration of diphenytriazol or steroid hormone drugs in the microsomal incubates was determined by reversed-phase high-performance liquid chromatography, separately. The inhibition constants (K(i)) for each of them were calculated. RESULTS: The inhibition constant K(is) of diphenytriazol for the metabolism of mifepristone, estradiol, medroxyprogesterone acetate, progesterone and norethisterone were (201.3 +/- 1.0), (94 +/- 4), (128.7 +/- 2.2), (64 +/- 5) and (80 +/- 4) micromol x L(-1), respectively. The inhibition constants K(i) of steroid hormone drugs for the metabolism of diphenytriazol was (66.9 +/- 2.2) micromol x L(-1) for estradiol, (60.0 +/- 2.3) micromol x L(-1) for medroxyprogesterone acetate, (163 +/- 10) micromol x L(-1) for progesterone and (88 +/- 5) micromol x L(-1) for norethisterone, respectively. CONCLUSION: Diphenytriazol shows metabolism interaction with steroid hormone drugs such as estradiol, medroxyprogesterone acetate, progesterone and norethisterone.

The oestrogenic effects of gestodene, a potent contraceptive progestin, are mediated by its A-ring reduced metabolites.

Gestodene (17 alpha-ethynyl-13 beta-ethyl-17 beta-hydroxy-4, 15-gonadien-3-one) is the most potent synthetic progestin currently available and it is widely used as a fertility regulating agent in a number of contraceptive formulations because of its high effectiveness, safety and acceptability. The observation that contraceptive synthetic progestins exert hormone-like effects other than their progestational activities, prompted us to investigate whether gestodene (GSD) administration may induce oestrogenic effects, even though the GSD molecule does not interact with intracellular oestrogen receptors (ER). To assess whether GSD may exert oestrogenic effects through some of its neutral metabolites, a series of experimental studies were undertaken using GSD and three of its A-ring reduced metabolites. Receptor binding studies by displacement analysis confirmed that indeed GSD does not bind to the ER, whereas its 3 beta,5 alpha-tetrahydro reduced derivative (3 beta GSD) interacts with a relative high affinity with the ER. The 3 alpha,5 alpha GSD isomer (3 alpha GSD) also binds to the ER, though to a lesser extent. The ability of the A-ring reduced GSD derivatives to induce oestrogenic actions was evaluated by the use of two different molecular bioassays: (a) transactivation of a yeast system co-transfected with the human ER alpha (hER alpha) gene and oestrogen responsive elements fused to the beta-galactosidase reporter vector and (b) transactivation of the hER alpha-mediated transcription of the chloramphenicol acetyl transferase (CAT) reporter gene in a HeLa cells expression system. The oestrogenic potency of 3 beta GSD was also assessed by its capability to induce oestrogen-dependent progestin receptors (PR) in the anterior pituitary of castrated female rats. The results demonstrated that 3 beta GSD and 3 alpha GSD were able to activate, in a dose-dependent manner, the hER alpha-mediated transcription of both the beta-galactosidase and the CAT reporter genes in the yeast and HeLa cells expression systems respectively. In both assays the 3 beta derivative of GSD exhibited a significantly greater oestrogenic effect than its 3 alpha isomer, while unchanged GSD and 5 alpha GSD were completely ineffective. Neither 3 beta GSD nor 3 alpha GSD exhibited oestrogen synergistic actions. Interestingly, the pure steroidal anti-oestrogen ICI-182,780 diminished the transactivation induced by 3 beta GSD and 3 alpha GSD in the yeast expression system. Furthermore, administration of 3 beta GSD resulted in a significant increase of oestrogen-dependent PR in the anterior pituitaries of castrated rats in comparison with vehicle-treated animals. The characteristics of the 3 beta GSD-induced PR were identical to those induced by oestradio benzoate. The overall results demonstrate that 3 beta GSD and its 3 alpha isomeric alcohol specifically bind to the ER and possess a weak intrinsic oestrogenic activity, whereas unmodified GSD does not. The data contribute to a better understanding of the GSD mechanism of action and allow the hypothesis to be advanced that the slight oestrogenlike effects attributable to GSD are mediated by its non-phenolic, tetrahydro reduced metabolites.

Occlusive vascular diseases in oral contraceptive users. Epidemiology, pathology and mechanisms.

Despite being an unprecedented departure from normal physiology, the combined oral contraceptive is not only highly effective, but it also has a remarkably good safety record. Concerns over safety persist, though, particularly with regard to venous thromboembolism (VTE), stroke and myocardial infarction (MI). Epidemiological studies consistently show an increase in risk of VTE, but the results are more contentious with regard to arterial diseases. Despite 40 years of research, the mechanisms behind these adverse effects are not understood. In this review, we integrate information from published studies of the epidemiology and pathology of the occlusive vascular diseases and their risk factors to identify likely explanations for pathogenesis in oral contraceptive users. Oral contraceptives induce both prothrombotic and fibrinolytic changes in haemostatic factors and an imbalance in haemostasis is likely to be important in oral contraceptive-induced VTE. The complexity of the changes involved and the difficulty of ascribing clinical significance has meant that uncertainty persists. A seriously under-researched area concerns vascular changes in oral contraceptive users. Histologically, endothelial and intimal proliferation have been identified in women exposed to high plasma estrogen concentrations and these lesions are associated with thrombotic occlusion. Other structural changes may result in increased vascular permeability, loss of vascular tone and venous stasis. With regard to arterial disease risk, epidemiological information relating to dose effects and joint effects with other risk factors, and studies of pathology and changes in risk factors, suggests that oral contraceptive use per se does not cause arterial disease. It can, nevertheless, synergise very powerfully with subclinical endothelial damage to promote arterial occlusion. Accordingly, the prothrombotic effects of the oral contraceptive estrogen intervene in a cycle of endothelial damage and repair which would otherwise remain clinically silent or would ultimately progress - in, for example, the presence of cigarette smoking or hypertension - to atherosclerosis. Future work in this area should focus on modification of the effects of established risk factors by oral contraceptive use rather than modification of the supposed risk of oral contraceptive use by established risk factors. Attempts to understand vascular occlusion in oral contraceptive users in terms of the general features of VTE or with reference to atherosclerosis may be limiting, and future work needs to acknowledge that such occlusions may have unique features. Unequivocal identification of the mechanisms involved would contribute considerably to the alleviation of fears over vascular disease and to the development of even safer formulations.

Characterization of immunoglobulins and cytokines in human cervical mucus: influence of exogenous and endogenous hormones.

Mucosal immunity in the female reproductive tract is influenced by immunoglobulins (Igs), cytokines, and reproductive hormones. Previous studies of reproductive-aged women demonstrated that IgA and IgG increases in cervical mucus corresponded to elevated levels of IL-1beta which occurred 1 day before the peak of endogenous estradiol production prior to ovulation. We sought to determine the effect of exogenous hormones on reproductive tract immunity in women on oral contraceptive pills (OCPs) and to compare the results with respect to naturally cycling women. Twelve women of reproductive age who had negative cervical cultures, a normal pap smear, and agreed to abstain from sexual intercourse during the study initiated OCPs. Cervical mucus and vaginal washes were collected at six intervals (2-3 days apart) throughout the treatment cycle. Fifteen naturally cycling women had similar samples collected prior to, during, and subsequent to ovulation. Cervical mucus samples were assayed for IgA, IgG, IL-1beta, IL-6, and IL-10 by enzyme-linked immunosorbent assay (ELISA). IgA, IgG and IL-1beta levels in women on OCPs paralleled increasing levels of norethindrone. Mean values of IgA increased from a low of 14.4+/-3.1 to 41.1+/-9.4 mg/dl and decreased significantly after the cessation of the pills (P < 0.001). In naturally cycling women, the largest quantities of Igs were detected prior to ovulation. By comparison, mean values of IgA in the cervical mucus of women on OCPs (24.4 mg/dl) exceeded peak levels of IgA in the cervical mucus of naturally cycling women (14.6 mg/dl). IgA was the predominant Ig detected in cervical mucus of women on OCPs. Both immunoglobulins in each group exhibited changes relative to their hormonal status. The increased levels of IgA in the cervical mucus of women on OCPs may explain the clinical observation of a lower incidence of sexually transmitted diseases.

Influence of nutritional status on pharmacokinetics of contraceptive progestogens.

PIP: In response to recent studies from India suggesting that malnutrition, as assessed by anthropometric indexes, affects metabolism of oral progestogens, this study administered a mini-pill containing .35 mg of norethindrone (NET) and combination pills containing 250 or 150 mcg of d-norgestrel (d-NG) and either 50 or 30 mcg ethinyl estradiol as a single dose for fasting women of high and low income. Blood samples were collected for up to 24 hours for NET and 80 hours for the combination pills. Pharmacokinetics were evaluated by a least-squares method. Anthropometric measurements were also made. Peak NET levels occurred within 1-2 hours; half-life of plasma NET was shorter among low income, malnourished women compared with high income, well-nourished women. A direct correlation between weight/height and half-life of the drug suggests that malnutrition enhanation rate and reduces NET's half-life. Peak levels for d-NG also were reached between 1 and 2 hours after dosing. In well-nourished women, the decline in plasma d-NG was tri-exponential; malnourished women showed a biphasic curve with a neglible alpha-phase. Therefore, the lower the nutrition status, the faster the plasma clearance of these 2 orally administered compounds. Studies inn rabbits designed to elucidate this connection showed a significant elevation in specific activities of liver microsomal glucuronyl transferase and cytochrome-p450 in undernourished compared with control animals. There was also an increase in the amount (but not affinity) of uterine progesterone receptors in undernourished animals. Another study of a small group of Thai and Indian women showed positive correlation between anthropometric indexes and post peak plasma NET levels; however, an obesity study of Thai women found no such correlation.^ieng

RU 486 (mifepristone). A short overview of its mechanisms of action and clinical uses at the end of 1996.

RU 486 (mifepristone) has proved to be a remarkably active antiprogesterone and antiglucocorticosteroid agent in humans. The mechanism of action of RU 486 involves the intracellular receptors of the antagonized hormones progesterone and glucocorticosteroids. At the molecular level, the most important features are high binding affinity to the receptor, interaction of the phenyl-aminodimethyl group in the 11 beta-position with a specific region of the receptor binding pocket, and RU 486-induced transconformation in the ligand binding domain. These properties have consequences at different steps of the receptor function as compared with agonists. However, this cannot be limited to the RU 486-receptor interaction; for instance, a switch from an antagonistic property to an agonist activity is possible, depending on the intervention of other signaling pathways. Derivatives with only one of the two antagonistic properties (antiprogestin, antiglucocorticosteroid) would be desirable in spite of similarities between the steroid structures, receptors involved, and responsive machineries in target cells. Clinically, the RU 486 plus prostaglandin method is ready to be used on a large scale, and is close to being as practical and safe as any medical method of abortion may be. The early use of RU 486, as a contragestive--that is, for use by a woman as soon as she fears a pregnancy she does not want--will help to defuse the abortion issue. Research should now be conducted to define an efficient and convenient contraceptive method with RU 486 or other antiprogestins. The usefulness of RU 486 for obstetrical indications, including facilitation of difficult delivery, has to be assessed rapidly. Gynecological trials, particularly in leiomyomata, should also be systematically continued. The very preliminary results obtained with tumors, including breast cancers, do indicate that further studies are necessary.

In vitro metabolism of gestodene in target organs: formation of A-ring reduced derivatives with oestrogenic activity.

Gestodene (13beta-ethyl-17alpha-ethynyl-17beta-hydroxy-4,5-gonadien-3-one), the most potent progestin ever synthesized, stimulates breast cancer cell growth through an oestrogen receptor-mediated mechanism, and its use in hormonal contraception has been associated with side effects attributable to oestrogenic actions. These observations have remained controversial, since gestodene does not bind to the oestrogen receptor or exert oestrogen-like activities. Recently, we have demonstrated that non-phenolic gestodene derivatives interact with oestrogen receptors and induce oestrogenic effects in cell expression systems. To assess whether gestodene is biotransformed to metabolites with intrinsic oestrogenic potency, [3H]- and [14C]-labelled gestodene were incubated in vitro with rat anterior pituitary, hypothalamus and ventral prostate homogenates under different experimental conditions. The most remarkable finding was the isolation and identification of 3beta,5alpha-tetrahydrogestodene and 3alpha,5alpha-tetrahydrogestodene as metabolic conversion products of gestodene, presumably with 5alpha-dihydrogestodene as intermediate. The overall results seem to indicate that the weak oestrogenic effects attributable to gestodene could be mediated by its tetrahydro metabolites.

Contraceptive steroid binding to the human uterine progesterone-receptor.

Using an equilibrium dialysis method, the competition was investigated between tritated-progesterone and a range of synthetic steroids for binding to 20,000 g. supernatants of human uterine endometrium and myometrium. Both types of uterine tissue showed similar patterns of progestogen binding and probably contain similar, or even identical, progesterone receptors. The gonane progestogen norgestrel binds strongly to the uterine receptors, but only the d-isomer is active. All three pregnane progestogens used in this study (chlormadinone acetate, medroxprogesterone acetate, megestrol acetate) also showed significant binding to receptors, but for the estrane progestogens, norethisterone was the only compound to show a high binding capacity. Other estranes (ethynodiol diacetate, lynestrenol, norethisterone acetate, norethynodrel) showed insignificant binding to the receptors and probably require prior metabolic activation to norethisterone before they can induce progestogenic effects.

Interaction of A-nor, A, 19-dinor, and A-homo-5 alpha-androstane derivatives with the androgen receptor and the epididymal androgen-binding protein.

The equilibrium affinity constant for rat prostate androgen receptor and epididymal androgen binding protein (ABP) has been determined for thirty-four potential progestogens. Three A-nor-, four A,19-dinor-, and one A-homo-5 alpha-androstane derivative bind to the androgen receptor (KD less than 0.5 muM). Five of these compounds also bind to ABP with an affinity of the same order of magnitude. "Anordrin" (compound 24) and "Dinordrins" (compounds 10, 14, 15, 16, 17), which are potential female contraceptives, do not bind with high affinity to the androgen receptor or to ABP. The following modifications in A-nor derivatives favour binding to the receptor as compared to ABP: 19-nor substitution (compound 1), C-18 methyl homologation (compound 5), 2 alpha-ethinylation (compound 22). One 2 alpha-allenyl A-nor derivative (compound 25) and one A-homo derivative (compound 34) bind almost exclusively to ABP. The interaction with either binding protein is decreased by oxidation or esterification of the hydroxyl group at C-17, and by addition of a 17 alpha-ethinyl group. The latter modifications are likely to increase the specificity of androstane derivatives for receptors other than androgen binding proteins, such as the progesterone receptor.

Norethisterone concentration in breast milk and infant and maternal plasma during ethynodiol diacetate administration.

Twelve women with established lactation of 4-8 weeks duration were given a low-dose progestogen-only contraceptive, ethynodiol diacetate 0.5 mg (Femulen) daily. On the seventh and eight day of the study, prior to the mother's taking the pill, a blood sample was taken from her and from the infant. Further blood samples were collected from the mother 4 and 12 hours later. Breast milk samples were collected at every feed on day 7 and day 8. Ethynodiol diacetate is rapidly metabolised in humans, changing into the metabolite norethisterone which is found in both blood and milk. Hence, norethisterone concentrations were estimated. On day 7 and day 8, four hours after ingestion of the pill, the median norethisterone maternal plasma concentration was 1.60 ng/ml and it fell to a median level of 0.30 ng/ml prior to the next dose of the pill. At this time the median infant concentration was 0.10 ng/ml but the maximum observed level was 0.50 ng/ml. In the breast milk the norethisterone concentration appears to peak at around 4-8 hours following the ingestion of the pill. The maximum observed concentration in breast milk was 0.84 ng/ml. The amount of norethisterone ingested by the infant averaged 0.02% (6.65 micrograms) of the dose of ethynodiol diacetate ingested by the mother. The maximum observed on any one day was 0.07% (27.52 micrograms). The above results indicate that the amount of progestogen ingested by the infant from its mother's milk is small and is unlikely to pose a risk to the infant.

A novel approach to human fertility control: contragestion by the anti-progesterone RU 486.

PIP: The introductory presentation for a session on antiprogestins summarizes the action of RU 486 relating to its use as a contragestive agent. RU 486, or mifepristone (Roussel-Uclaf), is a progestin analogue resembling norethindrone with a longer 17-alpha side chain and a 11-beta phenyl group that confers the progesterone antagonist activity. It binds the progesterone receptor with a half-life of about 20 hours. Since progesterone receptors are only located in a few tissues, notably the decidualized endometrium and the corpus luteum, its action can be targeted. RU 486 interrupts the cycle regardless of whether fertilization occurred. A single 600 mg dose arrests over 80% of pregnancies up to 41 days, then a decreasing proportion, down to 60% at 10 weeks, due to a greater chance of incomplete evacuation. There have been no recorded side effects in 4000 trails. The effect of prostaglandins is magnified when progesterone action is suppressed. 400 trials have confirmed that over 98% successful termination of pregnancy can be obtained if 600 mg RU 486 is followed by 1 mg synthetic prostaglandin 36 hours later. RU 486 has also tested successfully for delivery of dead fetuses, cervical dilation, a postcoital contraceptive, and as an antiglucocorticoid agent. It has been submitted to the French Ministry of Health, and will probably be approved for marketing in 1988. Clinical trials are underway in 15 countries. This drug is a useful contragestive agent, active in the beginning of the continuum of pregnancy, and may defuse the abortion issue.^ieng

Metabolic effects of depot-medroxyprogesterone acetate in long-term users: a cross-sectional study.

Oral glucose tolerance test and determination of insulin, cholesterol, triglycerides, total bilirubin, serum glutamic oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), alkaline phosphatase and cortisol in blood were performed on 57 Thai women who had used depot-medroxyprogesterone acetate (DMPA) for 5 years or more and 24 healthy non-DMPA users. Plasma insulin, alkaline phosphatase and morning cortisol levels were significantly higher in the DMPA users than in the non-users. There were no significant differences for other laboratory tests. The findings suggest some effects of DMPA on carbohydrate metabolism and liver function in long-term users.

Treatment of epilepsy in women of childbearing age.

PIP: This article updates the literature on the treatment of epilepsy in women of reproductive age. Specific areas discussed include the effect of menstruation on seizure frequency, use of oral contraceptives (OCs), the effect of pregnancy on epilepsy, the effect of seizures on pregnancy and the fetus, the impact of antiepileptic drugs on the fetus, medical termination of pregnancy, breast feeding, and the risk of epilepsy in offspring. Exacerbtion of seizure activity is often seen in premenstrual and menstrual phases, and cyclic use of acetazolamide and/or progesterone (which exerts a protective effect against seizures) is recommended. OCs appear to have only a minor impact on epilepsy and the metabolism of antiepileptic drugs. On the other hand, these drugs can influence the metabolism and effectiveness of OCs. Concomitant use of OCs and antiepileptics can result in a higher incidence of acne and hirsutism, increased intermenstrual bleeding, and failure of contraception. The incidence of contraceptive failure is higher with low-dose estrogen OCs. In general, pregnancy appears to have an unfavorable effect on cerebral dysrrhythmia in epileptics. Possible causes for the increase in seizure frequency during pregnancy include psychological, hormonal, metabolic, and pharmacokinetic factors. The effect of epilepsy and antiepileptics on offspring is unclear. There appears to be an increased risk of spontaneous abortion and stillbirths in women taking antiepileptic drugs. In addition, a 3-fold increase in the incidence of congenital malformations has been noted in these women. The risks of birth defects are greater when there is a family history of birth defects, when the father is also epileptic, when a previous pregnancy resulted in a malformed child, when seizures during pregnancy are poorly controlled, and when multipel antiepileptic drugs are used in high doses. Although offspring may inherit the epileptic trait, they do not always manifest the disease.^ieng

Human metabolism and steroid contraceptives. Part 2.

Biochemical studies on large groups of apparently healthy women taking oral contraceptives are intended to find which organs and tissues are most stressed, in the hope than an indication of clinical side effects will result. If contraceptive steroid dose is reduced, the incidence of systemic side effects decreases and this correlates well with the decreased abnormality of many metabolic and biochemical parameters. Reduction of dosage has an equivocal effect on gynaecological side affects-some increase, some decrease. An account is given of the possible relationship between clinical side effects of oral contraceptives, and dose-related changes in plasma proteins, vitamin status and tissue enzymes.

Human metabolism and steroid contraceptives. Part 1.

Metabolic activation of mestranol and certain progestagens is necessary before combination with their specific receptors. This process is subject to inhibition by other drugs. It is suggested that it is preferable to use agents not requiring metabolic activation. Widespread variation of human metabolic parameters is induced by oral contraceptives. A dose related effect of synthetic oestrogens on the synthesis and release of liver-derived plasma proteins is a major cause of this variation. The changes induced may be modified by norgestrel but not by other available progestagens. Changes in various specific plasma proteins, carrier proteins, enzymes and coagulation factors are discussed.

Metabolism of the synthetic progestogen norethynodrel by human ketosteroid reductases of the aldo-keto reductase superfamily.

Human ketosteroid reductases of the aldo-keto reductase (AKR) superfamily, i.e. AKR1C1-4, are implicated in the biotransformation of synthetic steroid hormones. Norethynodrel (NOR, 17α-ethynyl-17ß-hydroxy-estra-5(10)-en-3-one), the progestin component of the first marketed oral contraceptive, is known to undergo rapid and extensive metabolism to 3α- and 3ß-hydroxymetabolites. The ability of the four human AKR1C enzymes to catalyze the metabolism of NOR has now been characterized. AKR1C1 and AKR1C2 almost exclusively converted NOR to 3ß-hydroxy NOR, while AKR1C3 gave 3ß-hydroxy NOR as the main product and AKR1C4 predominantly formed 3α-hydroxy NOR. Individual AKR1C enzymes also displayed distinct kinetic properties in the reaction of NOR. In contrast, norethindrone (NET), the Δ(4)-isomer of NOR and the most commonly used synthetic progestogen, was not a substrate for the AKR1C enzymes. NOR is also structurally identical to the hormone replacement therapeutic tibolone (TIB), except TIB has a methyl group at the 7α-position. Product profiles and kinetic parameters for the reduction of NOR catalyzed by each individual AKR1C isoform were identical to those for the reduction of TIB catalyzed by the respective isoform. These data suggest that the presence of the 7α-methyl group has a minimal effect on the stereochemical outcome of the reaction and kinetic behavior of each enzyme. Results indicate a role of AKR1C in the hepatic and peripheral metabolism of NOR to 3α- and 3ß-hydroxy NOR and provide insights into the differential pharmacological properties of NOR, NET and TIB.

Occurrence, fate and removal of synthetic oral contraceptives (SOCs) in the natural environment: a review.

Synthetic oral contraceptives (SOCs) are a group of compounds with progestagenic and/or androgenic activities, with some also possessing estrogenic activities. Recent research has documented that some of these emerging contaminants have adverse effects on aquatic organisms at very low concentrations. To facilitate the evaluation of their latent risks, published works on their occurrence and fate in the environment are reviewed. Androgenic/progestagenic relative potencies or relative binding affinity of these SOCs as well as their physicochemical properties and toxicity are summarized. Appropriate analytical methods are outlined for various environmental sample types, including methods of sample preparation and limit of detection/quantification (LOD/LOQ). Finally results on their occurrence and fate in wastewater treatment plants (WWTPs) and other environments are critically examined.

The influence of gill and liver metabolism on the predicted bioconcentration of three pharmaceuticals in fish.

The potential for xenobiotic compounds to bioconcentrate is typically expressed through the bioconcentration factor (BCF), which has gained increased regulatory significance over the past decade. Due to the expense of in vivo bioconcentration studies and the growing regulatory need to assess bioconcentration potential, BCF is often calculated via single-compartment models, using K(OW) as the primary input. Recent efforts to refine BCF models have focused on physiological factors, including the ability of the organism to eliminate the compound through metabolic transformation. This study looks at the ability of in vitro biotransformation assays using S9 fractions to provide an indication of metabolic potential. Given the importance of the fish gill and liver in metabolic transformation, the metabolic loss of ibuprofen, norethindrone and propranolol was measured using rainbow trout (Oncorhynchus mykiss) and channel catfish (Ictalurus punctatus) gill and liver S9 fractions. Metabolic transformation rates (k(M)) were calculated and integrated into a refined BCF model. A significant difference was noted between BCF solely based on K(OW) and BCF including k(M). These studies indicate that the inclusion of k(M) in BCF models can bring predicted bioconcentration estimates closer to in vivo values.