Discovery of potent small-molecule inhibitors of lipoprotein(a) formation.

Lipoprotein(a) (Lp(a)), an independent, causal cardiovascular risk factor, is a lipoprotein particle that is formed by the interaction of a low-density lipoprotein (LDL) particle and apolipoprotein(a) (apo(a))1,2. Apo(a) first binds to lysine residues of apolipoprotein B-100 (apoB-100) on LDL through the Kringle IV (KIV) 7 and 8 domains, before a disulfide bond forms between apo(a) and apoB-100 to create Lp(a) (refs. 3-7). Here we show that the first step of Lp(a) formation can be inhibited through small-molecule interactions with apo(a) KIV7-8. We identify compounds that bind to apo(a) KIV7-8, and, through chemical optimization and further application of multivalency, we create compounds with subnanomolar potency that inhibit the formation of Lp(a). Oral doses of prototype compounds and a potent, multivalent disruptor, LY3473329 (muvalaplin), reduced the levels of Lp(a) in transgenic mice and in cynomolgus monkeys. Although multivalent molecules bind to the Kringle domains of rat plasminogen and reduce plasmin activity, species-selective differences in plasminogen sequences suggest that inhibitor molecules will reduce the levels of Lp(a), but not those of plasminogen, in humans. These data support the clinical development of LY3473329-which is already in phase 2 studies-as a potent and specific orally administered agent for reducing the levels of Lp(a).

Carcinogenicity assessment of baricitinib in Tg.rasH2 mice and Sprague-Dawley (Crl:CD) rats.

Baricitinib is a potent and selective Janus kinase (JAK)1 and JAK2 inhibitor, and is approved for the treatment of moderately to severely active RA in adults in Europe, Japan, and other countries. This study evaluated the carcinogenic potential of baricitinib in Tg. rasH2 mice and Sprague-Dawley (Crl:CD) rats. Baricitinib was administered daily by oral gavage to Crl:CD rats for up to 94 weeks (dose levels of 0, 1, 3, or 8 mg/kg for males and 0, 3, 8, or 25 mg/kg for females) and to Tg. rasH2 mice for 26 weeks (dose levels of 0, 15, 40, or 300 mg/kg for males and 0, 10, 30, or 150 mg/kg for females). Baricitinib was well tolerated with no incidence of compound-related neoplasms at any dose levels in rats and mice. In mice, non-neoplastic events observed were bone marrow hypocellularity and increased adipocytes. In rats, baricitinib administration was associated with a dose-dependent increase in survival, with a decreased incidence of neoplasm (hematopoietic and mammary), potentially secondary to drug-related decreased weight gain. The incidence of proliferative changes such as neoplastic and hyperplastic lesions in the mammary glands of females and in the livers of males and females also decreased. In conclusion, baricitinib is not considered to be carcinogenic.

Prediction of Transporter-Mediated Drug-Drug Interactions for Baricitinib.

Baricitinib, an oral selective Janus kinase 1 and 2 inhibitor, undergoes active renal tubular secretion. Baricitinib was not predicted to inhibit hepatic and renal uptake and efflux drug transporters, based on the ratio of the unbound maximum eliminating-organ inlet concentration and the in vitro half-maximal inhibitory concentrations (IC50 ). In vitro, baricitinib was a substrate for organic anion transporter (OAT)3, multidrug and toxin extrusion protein (MATE)2-K, P-glycoprotein (P-gp), and breast cancer resistance protein (BCRP). Probenecid, a strong OAT3 inhibitor, increased the area under the concentration-time curve from time zero to infinity (AUC[0-∞] ) of baricitinib by twofold and decreased renal clearance to 69% of control in healthy subjects. Physiologically based pharmacokinetic (PBPK) modeling reproduced the renal clearance of baricitinib and the inhibitory effect of probenecid using the in vitro IC50 value of 4.4 µM. Using ibuprofen and diclofenac in vitro IC50 values of 4.4 and 3.8 µM toward OAT3, 1.2 and 1.0 AUC(0-∞) ratios of baricitinib were predicted. These predictions suggest clinically relevant drug-drug interactions (DDIs) with ibuprofen and diclofenac are unlikely.

Fertility and Embryo-Fetal Development Assessment in Rats and Rabbits with Evacetrapib: A Cholesteryl Ester Transfer Protein Inhibitor.

BACKGROUND: The purpose of these studies was to evaluate the effects of evacetrapib on male and female fertility and on embryo-fetal development (EFD). METHODS: Evacetrapib, a potent and selective inhibitor of cholesteryl ester transfer protein (CETP), was administered daily by oral gavage starting 2 weeks (for female) or 4 weeks (for male) before mating, during cohabitation, and until necropsy in the male rat fertility study or through gestation day (GD) 17 in the female rat combined fertility/EFD study. For rabbit EFD studies, animals were dosed from GDs 7 to 19 or from 1 week before mating through GD 19. Dose levels of evacetrapib ranged from 60 to 600 mg/kg for rats and from 1 to 100 mg/kg/day for rabbits. RESULTS: Parental findings in rats included decreased body weight and food consumption and moribund euthanasia in animals given 600 mg/kg/day and decreased food consumption at 300 mg/kg/day. There were no adverse effects on estrus cycling, fertility indices, sperm parameters, maternal reproductive parameters, male reproductive tissue, or fetal viability, growth, or external/visceral morphology. An increase in the incidence of 14th rudimentary ribs, a minor, transient variation considered nonadverse, was the only significant developmental finding in rats given 600 mg/kg/day. Slight decreases in body weight and food consumption at 100 mg/kg/day were the only maternal effects observed in rabbits with no adverse developmental effects noted. CONCLUSION: No adverse effects on fertility or EFD were observed in rats at doses up to 600 mg/kg/day and no adverse effects on EFD were noted in rabbits at doses up to 100 mg/kg/day. Birth Defects Research 109:513-527, 2017. © 2017 Wiley Periodicals, Inc.

Prenatal and Postnatal Assessment in Rabbits with Evacetrapib: A Cholesteryl Ester Transfer Protein Inhibitor.

BACKGROUND: Evacetrapib, a potent and selective inhibitor of cholesteryl ester transfer protein (CETP), was under development for the treatment of cardiovascular (CV) disease. The purpose of this pre-postnatal study in rabbits was to evaluate the effects of evacetrapib on pregnancy, parturition, and lactation of the maternal animals and on the growth, viability, development, and reproductive performance of the first filial (F1) offspring. The rabbit is considered a relevant species for toxicity testing with evacetrapib as it demonstrates significant CETP expression, whereas mice and rats do not express significant levels of CETP. METHODS: Evacetrapib was administered daily by oral gavage from gestation day (GD) 7 through lactation day (LD) 41 at dose levels of 0, 10, 30, and 100 mg/kg/day. RESULTS: There were no adverse effects on maternal survival, clinical signs, gestation length, parturition, and litter size. There were no effects on F1 clinical observations, body weight, sexual maturation, conditioned eye blink, functional observational battery, or pathology findings. Treatment-related decreases in F1 postnatal survival and equivocal reductions in F1 mating, fertility, and copulation/conception indices without changes in sperm parameters or pathology of reproductive organs were noted in F1 animals. CONCLUSIONS: The maternal no observed adverse effect level (NOAEL) after evacetrapib administration in female rabbits was 100 mg/kg/day. Based on the decreased F1 postnatal survival and equivocal changes in F1 fertility, the NOAEL for F1 neonatal developmental was 30 mg/kg/day. Birth Defects Research 109:486-496, 2017.© 2017 Wiley Periodicals, Inc.

The Discovery, Preclinical, and Early Clinical Development of Potent and Selective GPR40 Agonists for the Treatment of Type 2 Diabetes Mellitus (LY2881835, LY2922083, and LY2922470).

The G protein-coupled receptor 40 (GPR40) also known as free fatty acid receptor 1 (FFAR1) is highly expressed in pancreatic, islet ß-cells and responds to endogenous fatty acids, resulting in amplification of insulin secretion only in the presence of elevated glucose levels. Hypothesis driven structural modifications to endogenous FFAs, focused on breaking planarity and reducing lipophilicity, led to the identification of spiropiperidine and tetrahydroquinoline acid derivatives as GPR40 agonists with unique pharmacology, selectivity, and pharmacokinetic properties. Compounds 1 (LY2881835), 2 (LY2922083), and 3 (LY2922470) demonstrated potent, efficacious, and durable dose-dependent reductions in glucose levels along with significant increases in insulin and GLP-1 secretion during preclinical testing. A clinical study with 3 administered to subjects with T2DM provided proof of concept of 3 as a potential glucose-lowering therapy. This manuscript summarizes the scientific rationale, medicinal chemistry, preclinical, and early development data of this new class of GPR40 agonists.

Impact of Increased Gastric pH on the Pharmacokinetics of Evacetrapib in Healthy Subjects.

STUDY OBJECTIVE: To examine the effect of increased gastric pH on exposure to evacetrapib, a cholesteryl ester transfer protein inhibitor evaluated for the treatment of atherosclerotic heart disease. DESIGN: Open-label, two-treatment, two-period, fixed-sequence crossover study. SETTING: Clinical research unit. SUBJECTS: Thirty-four healthy subjects. INTERVENTION: In period 1, subjects received a single oral dose of evacetrapib 130 mg on day 1, followed by 7 days of analysis for evacetrapib plasma concentrations. In period 2, subjects received a once/day oral dose of omeprazole 40 mg on days 8-20, with a single oral dose of evacetrapib 130 mg administered 2 hours after the omeprazole dose on day 14, followed by 7 days of pharmacokinetic sampling. Subjects were discharged on day 21 and returned for a follow-up visit at least 14 days after the last dose of evacetrapib in period 2. Gastric pH was measured before subjects received each evacetrapib dose. MEASUREMENTS AND MAIN RESULTS: Noncompartmental pharmacokinetic parameters were estimated from plasma concentration-time data and compared between periods 1 and 2. Geometric mean ratios with 90% confidence intervals (CIs) were reported. Safety and tolerability were also assessed. The mean age of the 34 subjects was 40.9 years; mean body mass index was 27.2 kg/m(2) . Omeprazole treatment increased mean gastric pH across all subjects by 2.80 and increased evacetrapib area under the concentration versus time curve from time zero extrapolated to infinity (AUC0-∞ ) and maximum observed drug concentration (Cmax ) by 15% (90% CI -2 to 35) and 30% (90% CI 3-63), respectively. For both parameters, the upper bound of the 90% CI of the ratio of geometric least-squares means exceeded 1.25 but was less than 2, indicating a weak interaction. To assess the effect of gastric pH on subjects who responded best to omeprazole treatment, the analyses were repeated to include only the 22 subjects whose predose gastric pH was 3.0 or lower in period 1 and 4.0 or higher in period 2. In this subpopulation, mean gastric pH increased by 4.15 during omeprazole treatment, and evacetrapib AUC0-∞ and Cmax increased by 22% (90% CI 4-42) and 35% (90% CI 1-80), respectively. Despite the small mathematical differences between the analyses, the overall effect in both was a minimal increase in evacetrapib exposure. Of 35 adverse events reported during the study, 4 (11.4%) were considered to be treatment-related, and most were mild in severity. CONCLUSION: The impact of increased gastric pH on evacetrapib pharmacokinetics would not be expected to be clinically relevant. The magnitude of change in pH did not affect the degree of the interaction.

Effect of hepatic or renal impairment on the pharmacokinetics of evacetrapib.

PURPOSE: The aim of this study is to investigate the effect of hepatic or renal impairment on the pharmacokinetics of a single 130-mg evacetrapib dose. METHODS: Two open-label, parallel-design studies in males and females with normal hepatic function or Child-Pugh mild, moderate, or severe hepatic impairment, or with normal renal function or severe renal impairment. Non-compartmental pharmacokinetic parameters were estimated from plasma concentration-time data. Evacetrapib safety and tolerability were assessed. RESULTS: Pharmacokinetic parameter estimates were comparable between controls and mildly hepatically impaired subjects. Geometric mean area under the concentration-time curve (AUC) was greater, half-life (t1/2) was longer, and maximum concentration (Cmax) was lower in subjects with moderate and severe hepatic impairment than in controls. Apparent clearance (CL/F) did not differ between controls and those with mild hepatic impairment, but CL/F decreased for moderate and severe impairment. Spearman correlation coefficient showed no relationship between CL/F and Child-Pugh score. In the renal study, AUC and t1/2 were similar between groups, while Cmax was 15 % lower in subjects with severe impairment. CL/F in severely renally impaired subjects differed by <6 % from that in controls. Spearman correlation coefficient showed no apparent relationship between CL/F and estimated creatinine clearance or glomerular filtration rate. Neither study noted changes in clinical laboratory parameters or clinically significant findings. Adverse event incidence was low, and all were mild or moderate in severity. CONCLUSION: Evacetrapib exposure did not differ between mild hepatic impairment and normal hepatic function, but increased along the progression from mild to moderate to severe hepatic impairment. Severe renal impairment did not affect evacetrapib exposure.

Absolute bioavailability of evacetrapib in healthy subjects determined by simultaneous administration of oral evacetrapib and intravenous [(13) C8 ]-evacetrapib as a tracer.

This open-label, single-period study in healthy subjects estimated evacetrapib absolute bioavailability following simultaneous administration of a 130-mg evacetrapib oral dose and 4-h intravenous (IV) infusion of 175 µg [(13) C8 ]-evacetrapib as a tracer. Plasma samples collected through 168 h were analyzed for evacetrapib and [(13) C8 ]-evacetrapib using high-performance liquid chromatography/tandem mass spectrometry. Pharmacokinetic parameter estimates following oral and IV doses, including area under the concentration-time curve (AUC) from zero to infinity (AUC[0-∞]) and to the last measureable concentration (AUC[0-tlast ]), were calculated. Bioavailability was calculated as the ratio of least-squares geometric mean of dose-normalized AUC (oral : IV) and corresponding 90% confidence interval (CI). Bioavailability of evacetrapib was 44.8% (90% CI: 42.2-47.6%) for AUC(0-∞) and 44.3% (90% CI: 41.8-46.9%) for AUC(0-tlast ). Evacetrapib was well tolerated with no reports of clinically significant safety assessment findings. This is among the first studies to estimate absolute bioavailability using simultaneous administration of an unlabeled oral dose with a (13) C-labeled IV microdose tracer at about 1/1000(th) the oral dose, with measurement in the pg/mL range. This approach is beneficial for poorly soluble drugs, does not require additional toxicology studies, does not change oral dose pharmacokinetics, and ultimately gives researchers another tool to evaluate absolute bioavailability.

Discovery of 6-(4-{[5-Cyclopropyl-3-(2,6-dichlorophenyl)isoxazol-4-yl]methoxy}piperidin-1-yl)-1-methyl-1H-indole-3-carboxylic Acid: A Novel FXR Agonist for the Treatment of Dyslipidemia.

The farnesoid X receptor (FXR) is a member of the "metabolic" subfamily of nuclear receptors. Several FXR agonists have been reported in the literature to have profound effects on plasma lipids in animal models. To discover novel and effective therapies for dyslipidemia and atherosclerosis, we have developed a series of potent FXR agonists that robustly lower plasma LDL and vLDL in LDLr-/- mice. To this end the novel piperidinylisoxazole system LY2562175 was discovered. This molecule is a potent and selective FXR agonist in vitro and has robust lipid modulating properties, lowering LDL and triglycerides while raising HDL in preclinical species. The preclinical ADME properties of LY2562175 were consistent with enabling once daily dosing in humans, and it was ultimately advanced to the clinic for evaluation in humans. The synthesis and biological profile of this molecule is discussed.

Evacetrapib: in vitro and clinical disposition, metabolism, excretion, and assessment of drug interaction potential with strong CYP3A and CYP2C8 inhibitors.

Evacetrapib is an investigational cholesteryl ester transfer protein inhibitor (CETPi) for reduction of risk of major adverse cardiovascular events in patients with high-risk vascular disease. Understanding evacetrapib disposition, metabolism, and the potential for drug-drug interactions (DDI) may help guide prescribing recommendations. In vitro, evacetrapib metabolism was investigated with a panel of human recombinant cytochromes P450 (CYP). The disposition, metabolism, and excretion of evacetrapib following a single 100-mg oral dose of (14)C-evacetrapib were determined in healthy subjects, and the pharmacokinetics of evacetrapib were evaluated in the presence of strong CYP3A or CYP2C8 inhibitors. In vitro, CYP3A was responsible for about 90% of evacetrapib's CYP-associated clearance, while CYP2C8 accounted for about 10%. In the clinical disposition study, only evacetrapib and two minor metabolites circulated in plasma. Evacetrapib metabolism was extensive. A mean of 93.1% and 2.30% of the dose was excreted in feces and urine, respectively. In clinical DDI studies, the ratios of geometric least squares means for evacetrapib with/without the CYP3A inhibitor ketoconazole were 2.37 for area under the curve (AUC)(0-∞) and 1.94 for C max. There was no significant difference in evacetrapib AUC(0-τ) or C max with/without the CYP2C8 inhibitor gemfibrozil, with ratios of 0.996 and 1.02, respectively. Although in vitro results indicated that both CYP3A and CYP2C8 metabolized evacetrapib, clinical studies confirmed that evacetrapib is primarily metabolized by CYP3A. However, given the modest increase in evacetrapib exposure and robust clinical safety profile to date, there is a low likelihood of clinically relevant DDI with concomitant use of strong CYP3A or CYP2C8 inhibitors.

CYP-mediated drug-drug interactions with evacetrapib, an investigational CETP inhibitor: in vitro prediction and clinical outcome.

AIMS: Evacetrapib is a cholesteryl ester transfer protein (CETP) inhibitor under development for reducing cardiovascular events in patients with high risk vascular disease. CETP inhibitors are likely to be utilized as 'add-on' therapy to statins in patients receiving concomitant medications, so the potential for evacetrapib to cause clinically important drug-drug interactions (DDIs) with cytochromes P450 (CYP) was evaluated. METHODS: The DDI potential of evacetrapib was investigated in vitro, followed by predictions to determine clinical relevance. Potential DDIs with possible clinical implications were then investigated in the clinic. RESULTS: In vitro, evacetrapib inhibited all of the major CYPs, with inhibition constants (K(i)) ranging from 0.57 µM (CYP2C9) to 7.6 µM (CYP2C19). Evacetrapib was a time-dependent inhibitor and inducer of CYP3A. The effects of evacetrapib on CYP3A and CYP2C9 were assessed in a phase 1 study using midazolam and tolbutamide as probe substrates, respectively. After 14 days of daily dosing with evacetrapib (100 or 300 mg), midazolam exposures (AUC) changed by factors (95% CI) of 1.19 (1.06, 1.33) and 1.44 (1.28, 1.62), respectively. Tolbutamide exposures (AUC) changed by factors of 0.85 (0.77, 0.94) and 1.06 (0.95, 1.18), respectively. In a phase 2 study, evacetrapib 100 mg had minimal impact on AUC of co-administered simvastatin vs. simvastatin alone with a ratio of 1.25 (1.03, 1.53) at steady-state, with no differences in reported hepatic or muscular adverse events. CONCLUSIONS: Taken together, the extent of CYP-mediated DDI with the potential clinical dose of evacetrapib is weak and clinically important DDIs are not expected to occur in patients taking concomitant medications.

A Multidose Study to Examine the Effect of Food on Evacetrapib Exposure at Steady State.

PURPOSE: To determine the effect of a high-fat meal on evacetrapib exposure at steady state in healthy participants. METHODS: This was a randomized, 2-period, 2-sequence, open-label, crossover study. Patients were randomly assigned to 1 of the 2 treatment sequences in which they received evacetrapib 130 mg/d for 10 days following a 10-hour fast each day or following a high-fat breakfast each day. Plasma samples collected through 24 hours were analyzed for evacetrapib concentrations and pharmacokinetic parameter estimates including area under the concentration-time curve during a dosing interval (AUCτ), maximum observed concentration (Cmax), and time of Cmax (tmax) were calculated. Pharmacodynamic parameters, including cholesteryl ester transfer protein (CETP) activity, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total cholesterol, and triglycerides, were also assessed. RESULTS: A total of 34 males and 6 females, mean age 41.5 years and mean body mass index 26.6 kg/m(2), were enrolled. Statistical analysis showed AUCτ was 44% higher (90% confidence interval [CI]: 29%-62%) and Cmax was 51% higher (90% CI: 28%-79%) in the fed state than in the fasted state, indicating an effect of food. Consistent with higher evacetrapib exposure, changes in HDL-C, LDL-C, and CETP activity appeared to be greater in the fed state than in the fasted state. There were no notable changes in total cholesterol or triglycerides following administration in the fed and fasted states. The 130-mg doses of evacetrapib were well tolerated with and without food. CONCLUSION: A high-fat meal increased evacetrapib mean exposure at steady state by 44% in healthy participants.

Effects of the cholesteryl ester transfer protein inhibitor evacetrapib on lipoproteins, apolipoproteins and 24-h ambulatory blood pressure in healthy adults.

OBJECTIVES: We investigated the safety, tolerability, pharmacokinetics and pharmacodynamics of evacetrapib. METHODS: Healthy volunteers received multiple daily doses of evacetrapib (10-600 mg) administered for up to 15 days in a placebo-controlled study. KEY FINDINGS: Mean peak plasma concentrations of evacetrapib occurred at 4-6 h and terminal half-life ranged 24-44 h. Steady state was achieved at approximately 10 days; all subjects had undetectable levels of evacetrapib 3 weeks after their last dose. The trough inhibition of cholesteryl ester transfer protein (CETP) activity was 65 and 84% at 100 and 300 mg, respectively. At the highest dose (600 mg), evacetrapib significantly inhibited CETP activity (91%), increased HDL-C (87%) and apo AI (42%), and decreased LDL-C (29%) and apo B (26%) relative to placebo. For the highest dose tested, levels of evacetrapib, CETP activity, CETP mass, HDL-C and LDL-C returned to levels at or near baseline after a 2-week washout period. Evacetrapib at the highest dose tested did not produce any significant effect on 24-h ambulatory systolic or diastolic blood pressure. CONCLUSIONS: Multiple doses of evacetrapib potently inhibited CETP activity, leading to substantial elevations in HDL-C and lowering of LDL-C. Evacetrapib was devoid of clinically relevant effects on blood pressure and mineralocorticoid levels.

Design and synthesis of new tetrahydroquinolines derivatives as CETP inhibitors.

This letter describes the discovery and SAR optimization of tetrazoyl tetrahydroquinoline derivatives as potent CETP inhibitors. Compound 6m exhibited robust HDL-c increase in hCETP/hApoA1 double transgenic model and favorable pharmacokinetic properties.

Design, synthesis and structure-activity-relationship of 1,5-tetrahydronaphthyridines as CETP inhibitors.

This Letter describes the discovery and SAR optimization of 1,5-tetrahydronaphthyridines, a new class of potent CETP inhibitors. The effort led to the identification of 21b and 21d with in vitro human plasma CETP inhibitory activity in the nanomolar range (IC(50)=23 and 22nM, respectively). Both 21b and 21d exhibited robust HDL-c increase in hCETP/hApoA1 dual heterozygous mice model.

Evacetrapib is a novel, potent, and selective inhibitor of cholesteryl ester transfer protein that elevates HDL cholesterol without inducing aldosterone or increasing blood pressure.

Cholesteryl ester transfer protein (CETP) catalyses the exchange of cholesteryl ester and triglyceride between HDL and apoB containing lipoprotein particles. The role of CETP in modulating plasma HDL cholesterol levels in humans is well established and there have been significant efforts to develop CETP inhibitors to increase HDL cholesterol for the treatment of coronary artery disease. These efforts, however, have been hampered by the fact that most CETP inhibitors either have low potency or have undesirable side effects. In this study, we describe a novel benzazepine compound evacetrapib (LY2484595), which is a potent and selective inhibitor of CETP both in vitro and in vivo. Evacetrapib inhibited human recombinant CETP protein (5.5 nM IC(50)) and CETP activity in human plasma (36 nM IC(50)) in vitro. In double transgenic mice expressing human CETP and apoAI, evacetrapib exhibited an ex vivo CETP inhibition ED(50) of less than 5 mg/kg at 8 h post oral dose and significantly elevated HDL cholesterol. Importantly, no blood pressure elevation was observed in rats dosed with evacetrapib at high exposure multiples compared with the positive control, torcetrapib. In addition, in a human adrenal cortical carcinoma cell line (H295R cells), evacetrapib did not induce aldosterone or cortisol biosynthesis whereas torcetrapib dramatically induced aldosterone and cortisol biosynthesis. Our data indicate that evacetrapib is a potent and selective CETP inhibitor without torcetrapib-like off-target liabilities. Evacetrapib is currently in phase II clinical development.

Involvement of CYP 2E1 enzyme in ovotoxicity caused by 4-vinylcyclohexene and its metabolites.

4-Vinylcyclohexene (VCH) is bioactivated by hepatic CYP 2A and 2B to a monoepoxide (VCM) and subsequently to an ovotoxic diepoxide metabolite (VCD). Studies suggest that the ovary can directly bioactivate VCH via CYP 2E1. The current study was designed to evaluate the role of ovarian CYP 2E1 in VCM-induced ovotoxicity. Postnatal day 4 B6C3F(1) and CYP 2E1 wild-type (+/+) and null (-/-) mouse ovaries were cultured (15 days) with VCD (30 microM), 1,2-VCM (125-1000 microM), or vehicle. Twenty-eight days female CYP 2E1 +/+ and -/- mice were dosed daily (15 days; ip) with VCH, 1,2-VCM, VCD or vehicle. Following culture or in vivo dosing, ovaries were histologically evaluated. In culture, VCD decreased (p<0.05) primordial and primary follicles in ovaries from all three groups of mice. 1,2-VCM decreased (p<0.05) primordial follicles in B6C3F(1) and CYP 2E1 +/+ ovaries, but not in CYP 2E1 -/- ovaries in culture. 1,2-VCM did not affect primary follicles in any group of mouse ovaries. Conversely, following in vivo dosing, primordial and primary follicles were reduced (p<0.05) by VCD and VCM in CYP2E1 +/+ and -/-, and by VCH in +/+ mice. The data demonstrate that, whereas in vitro ovarian bioactivation of VCM requires CYP 2E1 enzyme, in vivo CYP 2E1 plays a minimal role. Thus, the findings support that hepatic metabolism dominates the contribution made by the ovary in bioactivation of VCM to its ovotoxic metabolite, VCD. This study also demonstrates the use of a novel ovarian culture system to evaluate ovary-specific metabolism of xenobiotics.

Expression and activity of cytochromes P450 2E1, 2A, and 2B in the mouse ovary: the effect of 4-vinylcyclohexene and its diepoxide metabolite.

4-Vinylcyclohexene (VCH), an occupational chemical, causes destruction of small preantral follicles (F1) in mice. Previous studies suggested that VCH is bioactivated via cytochromes P450 (CYP450) to the ovotoxic, diepoxide metabolite, VCD. Whereas hepatic CYP450 isoforms 2E1, 2A, and 2B can metabolize VCH, the role of ovarian metabolism is unknown. This study investigated expression of these isoforms in isolated ovarian fractions (F1, 25-100 microm; F2, 100-250 microm; F3, >250 microm; interstitial cells, Int) from B6C3F1 mice dosed daily (15 days; ip) with vehicle, VCH (7.4 mmol/kg/day) or VCD (0.57 mmol/kg/day). Ovaries were removed and either isolated into specific ovarian compartments for mRNA analysis, fixed for immunohistochemistry, or prepared for enzymatic assays. mRNA and protein for all isoforms were expressed/distributed in all ovarian fractions from vehicle-treated mice. In the targeted F1 follicles, VCH or VCD dosing increased (p < 0.05) mRNA encoding CYP2E1 (645 +/- 14% VCH; 582 +/- 16% VCD), CYP2A (689 +/- 8% VCH; 730 +/- 22% VCD), and CYP2B (246 +/- 7% VCH) above control. VCH dosing altered (p < 0.05) mRNA encoding CYP2E1 in nontargeted F3 follicles (168 +/- 7%) and CYP2A in Int (207 +/- 19%) above control. Immunohistochemical analysis revealed the greatest staining intensity for all CYP isoforms in the Int. VCH dosing altered (p < 0.05) staining intensity in Int for CYP2E1 (19 +/- 2.4% below control) and CYP2A (39 +/- 5% above control). Staining intensity for CYP2B was increased (p < 0.05) above control in granulosa cells of small preantral (187 +/- 42%) and antral (63 +/- 8%) follicles. Catalytic assays in ovarian homogenates revealed that CYP2E1 and CYP2B were functional. Only CYP2E1 activity was increased (149 +/- 12% above control; p < 0.05) by VCH dosing. The results demonstrate that mRNA and protein for CYP isoforms known to bioactivate VCH are expressed in the mouse ovary and are modulated by in vivo exposure to VCH and VCD. Interestingly, there is high expression of these isoforms in the Int. Thus, the ovary may contribute to ovotoxicity by promoting bioactivation of VCH to the toxic metabolite, VCD.

Expression and activity of microsomal epoxide hydrolase in follicles isolated from mouse ovaries.

Microsomal epoxide hydrolase (mEH) is involved in the detoxification of xenobiotics that are or can form epoxide metabolites, including the ovotoxicant, 4-vinylcyclohexene (VCH). This industrial chemical is bioactivated by hepatic CYP450 to the diepoxide metabolite, VCD, which destroys mouse small preantral follicles (F1). Since ovarian mEH may play a role in VCD detoxification, these studies investigated the expression and activity of mEH in isolated ovarian fractions. Mice were given 1 or 15 daily doses (ip) of VCH (7.4 mmol/kg/day) or VCD (0.57 mmol/kg/day); 4 h following the final dose, ovaries were removed, distinct populations of intact follicles (F1, 25-100 microm; F2, 100-250 microm; F3, > 250 microm) and interstitial cells (Int) were isolated, and total RNA and protein were extracted. Real-time polymerase chain reaction and the substrate cis-stilbene oxide (CSO; 12.5 microM) were used to evaluate expression and specific activity of mEH, respectively. Confocal microscopy evaluated ovarian distribution of mEH protein. Expression of mRNA encoding mEH was increased in F1 (410 +/- 5% VCH; 292 +/- 5% VCD) and F2 (1379 +/- 4% VCH; 381 +/- 11% VCD) follicles following repeated dosing with VCH or VCD. Catalytic activity of mEH increased in F1 follicles following repeated dosing with VCH/VCD (381 +/- 11% VCH; 384 +/- 27% VCD). Visualized by confocal microscopy, mEH protein was distributed throughout the ovary with the greatest staining intensity in the interstitial cells and staining in the theca cells that was increased by dosing (56 +/- 0.8% VCH; 29 +/- 0.9% VCD). We conclude that mEH is expressed and is functional in mouse ovarian follicles. Additionally,in vivo dosing with VCH and VCD affects these parameters.