Reversible effects on female rat fertility with abrocitinib, a Janus kinase 1 inhibitor.

BACKGROUND: Abrocitinib is a Janus kinase (JAK) 1 selective inhibitor approved for the treatment of atopic dermatitis. Female reproductive tissues were unaffected in general toxicity studies, but an initial female rat fertility study resulted in adverse effects at all doses evaluated. A second rat fertility study was conducted to evaluate lower doses and potential for recovery. METHODS: This second study had 4 groups of 20 females each administered abrocitinib (0, 3, 10, or 70 mg/kg/day) 2 weeks prior to cohabitation through gestation day (GD) 7. In addition, 2 groups of 20 rats (0 or 70 mg/kg/day) were dosed for 3 weeks followed by a 4-week recovery period before mating. All mated females were evaluated on GD 14. RESULTS: No effects were observed at ≤10 mg/kg/day. At 70 mg/kg/day (29x human exposure), decreased pregnancy rate, implantation sites, and viable embryos were observed. All these effects reversed 4 weeks after the last dose. CONCLUSIONS: Based on these data and literature on the potential role of JAK signaling in implantation, we hypothesize that these effects may be related to JAK1 inhibition and, generally, that peri-implantation effects such as these, in the absence of cycling or microscopic changes in nonpregnant female reproductive tissues, are anticipated to be reversible.

Discovery of the Potent and Selective MC4R Antagonist PF-07258669 for the Potential Treatment of Appetite Loss.

The melanocortin-4 receptor (MC4R) is a centrally expressed, class A GPCR that plays a key role in the regulation of appetite and food intake. Deficiencies in MC4R signaling result in hyperphagia and increased body mass in humans. Antagonism of MC4R signaling has the potential to mitigate decreased appetite and body weight loss in the setting of anorexia or cachexia due to underlying disease. Herein, we report on the identification of a series of orally bioavailable, small-molecule MC4R antagonists using a focused hit identification effort and the optimization of these antagonists to provide clinical candidate 23. Introduction of a spirocyclic conformational constraint allowed for simultaneous optimization of MC4R potency and ADME attributes while avoiding the production of hERG active metabolites observed in early series leads. Compound 23 is a potent and selective MC4R antagonist with robust efficacy in an aged rat model of cachexia and has progressed into clinical trials.

Juvenile toxicity study of PF-07256472/recifercept, a recombinant human soluble fibroblast growth factor receptor 3, in 2-3-month-old cynomolgus monkeys.

Achondroplasia is an autosomal disorder caused by point mutation in the gene encoding fibroblast growth factor receptor 3 (FGFR3) and resulting in gain of function. Recifercept is a potential disease modifying treatment for achondroplasia and functions as a decoy protein that competes for ligands of the mutated FGFR3. Recifercept is intended to restore normal bone growth by preventing the mutated FGFR3 from negative inhibitory signaling in pediatric patients with achondroplasia. Here we evaluated the potential effects of twice weekly administration of recifercept to juvenile cynomolgus monkeys (approximately 3-months of age at the initiation of dosing) for 6-months. No adverse effects were noted in this study, identifying the high dose as the no-observed-adverse-effect-level and supporting the use of recifercept in pediatric patients from birth. Considering that juvenile toxicity studies in nonhuman primates are not frequently conducted, and when they are conducted they typically utilize animals ≥9 months of age, this study demonstrates the feasibility of executing a juvenile toxicity study in very young monkeys prior to weaning.

The Postnatal Resolution of Developmental Toxicity Induced by Pharmacological Diacylglycerol Acyltransferase 2 (DGAT2) Inhibition During Gestation in Rats.

Ervogastat (PF-06865571) is a small molecule diacylglycerol acyltransferase 2 (DGAT2) inhibitor being developed for the oral treatment of nonalcoholic steatohepatitis (NASH) with liver fibrosis. DGAT2 is a key enzyme in triglyceride synthesis in tissues and in regulating energy metabolism. Fertility and developmental toxicity studies with ervogastat were conducted in female rats and rabbits. There were no effects on female rat fertility or rabbit embryo-fetal development. Administration of ervogastat to pregnant rats during organogenesis reduced fetal weight and caused higher incidences of bent bones in fetuses that were shown to resolve by postnatal day 28 and were therefore considered to be transient variations secondary to developmental delay. Extended dosing in rats through the end of gestation and lactation (pre- and post-natal development study) caused impaired skin development, reduced offspring viability, and growth retardation. The spectrum of developmental effects in rats is consistent with the intended pharmacology (altered triglyceride metabolism) and the transient nature of the skeletal findings, along with the late gestational window of sensitivity for the effects on skin barrier development, reduce the concern for potential adverse developmental effects following unintended early gestational exposure to ervogastat in humans where treatment can be discontinued once pregnancy is determined.

Lack of effects on female fertility and prenatal and postnatal offspring development in rats with BNT162b2, a mRNA-based COVID-19 vaccine.

BNT162b2 is a vaccine developed to prevent coronavirus disease 2019 (COVID-19). BNT162b2 is a lipid nanoparticle formulated nucleoside-modified messenger RNA (mRNA) encoding the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein locked in its prefusion conformation. A developmental and reproductive toxicity study was conducted in rats according to international regulatory guidelines. The full human BNT162b2 dose of 30 µg mRNA/dose (>300 times the human dose on a mg/kg basis) was administered intramuscularly to 44 female rats 21 and 14 days prior to mating and on gestation days 9 and 20. Half of the rats were subject to cesarean section and full fetal examination at the end of gestation, and the other half were allowed to deliver and were monitored to the end of lactation. A robust neutralizing antibody response was confirmed prior to mating and at the end of gestation and lactation. The presence of neutralizing antibodies was also confirmed in fetuses and offspring. Nonadverse effects, related to the local injection site reaction, were noted in dams as expected from other animal studies and consistent with observations in humans. There were no effects of BNT162b2 on female mating performance, fertility, or any ovarian or uterine parameters nor on embryo-fetal or postnatal survival, growth, physical development or neurofunctional development in the offspring through the end of lactation. Together with the safety profile in nonpregnant people, this ICH-compliant nonclinical safety data supports study of BNT162b2 in women of childbearing potential and pregnant and lactating women.

Knockout mouse models are predictive of malformations or embryo-fetal death in drug safety evaluations.

Traditionally, understanding potential developmental toxicity from pharmaceutical exposures has been based on the results of ICH guideline studies in two species. However, support is growing for the use of weight of evidence approaches when communicating the risk of developmental toxicity, where the intended pharmacologic mode of action affects fundamental pathways in developmental biology or phenotypic data from genetically modified animals may increasingly be included in the overall assessment. Since some concern surrounds the use of data from knockout (KO) mice to accurately predict the risk for pharmaceutical modulation of a target, a deeper understanding of the relevance and predictivity of adverse developmental effects in KO mice for pharmacological target modulation is needed. To this end, we compared the results of embryo-fetal development (EFD) studies for 86 drugs approved by the FDA from 2017 to 2019 that also had KO mouse data available in the public domain. These comparisons demonstrate that data from KO mouse models are overall highly predictive of malformations or embryo-fetal lethality (MEFL) from EFD studies, but less so of a negative outcome in EFD studies. This information supports the use of embryo-fetal toxicity data in KO models as part of weight of evidence approaches in the communication of developmental toxicity risk of pharmaceutical compounds.

Inhibition of Acetyl-CoA Carboxylase Causes Malformations in Rats and Rabbits: Comparison of Mammalian Findings and Alternative Assays.

Acetyl-CoA carboxylase (ACC) is an enzyme within the de novo lipogenesis (DNL) pathway and plays a role in regulating lipid metabolism. Pharmacologic ACC inhibition has been an area of interest for multiple potential indications including oncology, acne vulgaris, metabolic diseases such as type 2 diabetes mellitus, and nonalcoholic fatty liver disease/nonalcoholic steatohepatitis. A critical role for ACC in de novo synthesis of long-chain fatty acids during fetal development has been demonstrated in studies in mice lacking Acc1, where the absence of Acc1 results in early embryonic lethality. Following positive predictions of developmental toxicity in the alternative in vitro assays (positive in murine embryonic stem cell [mESC] assay and rat whole embryo culture, but negative in zebrafish), developmental toxicity (growth retardation and dysmorphogenesis associated with disrupted midline fusion) was observed with the oral administration of the dual ACC1 and 2 inhibitors, PF-05175157, in Sprague Dawley rats and New Zealand White rabbits. The results of these studies are presented here to make comparisons across the assays, as well as mechanistic insights from the mESC assay demonstrating high ACC expression in the mESC and that ACC-induced developmental toxicity can be rescued with palmitic acid providing supportive evidence for DNL pathway inhibition as the underlying mechanism. Ultimately, while the battery of alternative approaches and weight-of-evidence case were useful for hazard identification, the embryo-fetal development studies were necessary to inform the risk assessment on the adverse fetal response, as malformations and/or embryo-fetal lethality were limited to doses that caused near-complete inhibition of DNL.

Knockout mouse models are predictive of malformations or embryo-fetal death in drug safety evaluations.

Traditionally, understanding potential developmental toxicity from pharmaceutical exposures has been based on the results of ICH guideline studies in two species. However, support is growing for the use of weight of evidence approaches when communicating the risk of developmental toxicity, where the intended pharmacologic mode of action affects fundamental pathways in developmental biology or phenotypic data from genetically modified animals may increasingly be included in the overall assessment. Since some concern surrounds the use of data from knockout (KO) mice to accurately predict the risk for pharmaceutical modulation of a target, a deeper understanding of the relevance and predictivity of adverse developmental effects in KO mice for pharmacological target modulation is needed. To this end, we compared the results of embryo-fetal development (EFD) studies for 86 drugs approved by the FDA from 2017 to 2019 that also had KO mouse data available in the public domain. These comparisons demonstrate that data from KO mouse models are overall highly predictive of malformations or embryo-fetal lethality (MEFL) from EFD studies, but less so of a negative outcome in EFD studies. This information supports the use of embryo-fetal toxicity data in KO models as part of weight of evidence approaches in the communication of developmental toxicity risk of pharmaceutical compounds.

Decreased maternal and fetal cholesterol following maternal bococizumab (anti-PCSK9 monoclonal antibody) administration does not affect rat embryo-fetal development.

Bococizumab is a humanized monoclonal IgG2Δa antibody against proprotein convertase subtilisin/kexin type 9 (PCSK9) for the treatment of hyperlipidemia. The evaluation of potential effects on embryo-fetal development was conducted in the rat. In a pharmacokinetic/pharmacodynamic study bococizumab was administered intravenously to pregnant Sprague-Dawley (SD) rats (n = 8/group) at 0, 10, 30, and 100 mg/kg during organogenesis. Maternal and fetal bococizumab, total cholesterol and HDL concentrations were determined. Bococizumab was well tolerated and there were no effects on ovarian or uterine parameters. Maternal and fetal bococizumab exposure increased with increasing dose, with a corresponding dose-dependent decrease in fetal cholesterol levels. Maternal cholesterol levels were decreased significantly, with reductions that were of a similar magnitude regardless of dose. In the definitive embryo-fetal development study bococizumab was administered to pregnant SD rats (n = 20/group) at 0, 10, 30, and 100 mg/kg and no adverse maternal or developmental effects were observed up to 100 mg/kg. These studies have provided an appropriate and relevant safety assessment of bococizumab in pregnant rats to inform human risk assessment, demonstrating no adverse effects on embryo-fetal development at magnitudes greater than anticipated clinical exposure and in the presence of maximal reductions in maternal cholesterol and dose-dependent reductions in fetal cholesterol.

Altered regulation of hepatic efflux transporters disrupts acetaminophen disposition in pediatric nonalcoholic steatohepatitis.

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, representing a spectrum of liver pathologies that include simple hepatic steatosis and the more advanced nonalcoholic steatohepatitis (NASH). The current study was conducted to determine whether pediatric NASH also results in altered disposition of acetaminophen (APAP) and its two primary metabolites, APAP-sulfate and APAP-glucuronide. Pediatric patients with hepatic steatosis (n = 9) or NASH (n = 3) and healthy patients (n = 12) were recruited in a small pilot study design. All patients received a single 1000-mg dose of APAP. Blood and urine samples were collected at 1, 2, and 4 hours postdose, and APAP and APAP metabolites were determined by high-performance liquid chromatography. Moreover, human liver tissues from patients diagnosed with various stages of NAFLD were acquired from the Liver Tissue Cell Distribution System to investigate the regulation of the membrane transporters, multidrug resistance-associated protein 2 and 3 (MRP2 and MRP3, respectively). Patients with the more severe disease (i.e., NASH) had increased serum and urinary levels of APAP-glucuronide along with decreased serum levels of APAP-sulfate. Moreover, an induction of hepatic MRP3 and altered canalicular localization of the biliary efflux transporter, MRP2, describes the likely mechanism for the observed increase in plasma retention of APAP-glucuronide, whereas altered regulation of sulfur activation genes may explain decreased sulfonation activity in NASH. APAP-glucuronide and APAP-sulfate disposition is altered in NASH and is likely due to hepatic membrane transporter dysregulation as well as altered intracellular sulfur activation.

Age-related testicular toxicity of mGluR5 negative allosteric modulators appears to be unrelated to testis drug transporter maturity.

Testicular degeneration was observed in exploratory toxicity studies in Wistar rats treated with several mGluR5 negative allosteric modulators. To determine if these testis effects were influenced by animal age, these compounds were administered to male Wistar rats of different ages (8, 10, and 12 weeks old) for 2 weeks followed by evaluation of male reproductive organ weights, testis histopathology, and inhibin B levels. Overall, seminiferous tubule degeneration was observed in 2/15, 5/15, and 0/15 compound treated rats from the 8, 10, and 12 week old cohorts and inhibin B was decreased in 8 and 10 week old animals, but not in 12 week old rats, suggesting that there is an age-related component to this testis toxicity. The gene expression profiles of drug transporters in the testis of rats aged PND 38 through PND 91 were very similar, indicating that immaturity of these transporters is an unlikely factor contributing to the age-related toxicity.

Differential Fmo3 gene expression in various liver injury models involving hepatic oxidative stress in mice.

Flavin-containing monooxygenase-3 (FMO3) catalyzes metabolic reactions similar to cytochrome P450 monooxygenase, however, most metabolites of FMO3 are considered non-toxic. Recent findings in our laboratory demonstrated Fmo3 gene induction following toxic acetaminophen (APAP) treatment in mice. The goal of this study was to evaluate Fmo3 gene expression in other diverse mouse models of hepatic oxidative stress and injury. Fmo3 gene regulation by Nrf2 was also investigated using Nrf2 knockout (Nrf2 KO) mice. In our studies, male C57BL/6J mice were treated with toxic doses of hepatotoxicants or underwent bile duct ligation (BDL, 10 days). Hepatotoxicants included APAP (400 mg/kg, 24-72 h), alpha-naphthyl isothiocyanate (ANIT; 50 mg/kg, 2-48 h), carbon tetrachloride (CCl4; 10 or 30 µL/kg, 24 and 48 h) and allyl alcohol (AlOH; 30 or 60 mg/kg, 6 and 24 h). Because oxidative stress activates nuclear factor (erythroid-derived 2)-like 2 (Nrf2), additional studies investigated Fmo3 gene regulation by Nrf2 using Nrf2 knockout (Nrf2 KO) mice. At appropriate time-points, blood and liver samples were collected for assessment of plasma alanine aminotransferase (ALT) activity, plasma and hepatic bile acid levels, as well as liver Fmo3 mRNA and protein expression. Fmo3 mRNA expression increased significantly by 43-fold at 12 h after ANIT treatment, and this increase translates to a 4-fold change in protein levels. BDL also increased Fmo3 mRNA expression by 1899-fold, but with no change in protein levels. Treatment of mice with CCl4 decreased liver Fmo3 gene expression, while no change in expression was detected with AlOH treatment. Nrf2 KO mice are more susceptible to APAP (400mg/kg, 72 h) treatment compared to their wild-type (WT) counterparts, which is evidenced by greater plasma ALT activity. The Fmo3 mRNA and protein expression increased in Nrf2 KO mice after APAP treatment. Collectively, not all hepatotoxicants that produce oxidative stress alter Fmo3 gene expression. Along with APAP, toxic ANIT treatment in mice markedly increased Fmo3 gene expression. While BDL increased the Fmo3 mRNA expression, the protein level did not change. The discrepancy with Fmo3 induction in cholestatic models, ANIT and BDL, is not entirely clear. Results from Nrf2 KO mice with APAP suggest that the transcriptional regulation of Fmo3 during liver injury may not involve Nrf2.

Primary cell cultures for understanding rat epididymal inflammation.

Treatment-induced epididymal inflammation and granuloma formation is only an occasional problem in preclinical drug development, but it can effectively terminate the development of that candidate molecule. Screening for backup molecules without that toxicity must be performed in animals (generally rats) that requires at least 2 to 3 weeks of in vivo exposure, a great deal of specially synthesized candidate compound, and histologic examination of the target tissues. We instead hypothesized that these treatments induced proinflammatory gene expression, and so used mixed-cell cultures from the rat epididymal tubule to monitor the induction of proinflammatory cytokines. Cells were exposed for 24 hr and then cytotoxicity was evaluated with the MTS assay and mRNA levels of Interleukin-6 (IL-6) and growth-related oncogene (GRO) were measured. We found that compounds that were more toxic in vivo stimulated a greater induction of IL-6 and GRO mRNA levels in vitro. By relating effective concentrations in vitro with the predicted C(eff), we could rank compounds by their propensity to induce inflammation in rats in vivo. This method allowed the identification of several compounds with very low inflammatory induction in vitro. When tested in rats, the compounds produced small degrees of inflammation at an acceptable margin (approximately 20×), and have progressed into further development.

Analysis of changes in hepatic gene expression in a murine model of tolerance to acetaminophen hepatotoxicity (autoprotection).

Pretreatment of mice with a low hepatotoxic dose of acetaminophen (APAP) results in resistance to a subsequent, higher dose of APAP. This mouse model, termed APAP autoprotection was used here to identify differentially expressed genes and cellular pathways that could contribute to this development of resistance to hepatotoxicity. Male C57BL/6J mice were pretreated with APAP (400mg/kg) and then challenged 48h later with 600mg APAP/kg. Livers were obtained 4 or 24h later and total hepatic RNA was isolated and hybridized to Affymetrix Mouse Genome MU430_2 GeneChip. Statistically significant genes were determined and gene expression changes were also interrogated using the Causal Reasoning Engine (CRE). Extensive literature review narrowed our focus to methionine adenosyl transferase-1 alpha (MAT1A), nuclear factor (erythroid-derived 2)-like 2 (Nrf2), flavin-containing monooxygenase 3 (Fmo3) and galectin-3 (Lgals3). Down-regulation of MAT1A could lead to decreases in S-adenosylmethionine (SAMe), which is known to protect against APAP toxicity. Nrf2 activation is expected to play a role in protective adaptation. Up-regulation of Lgals3, one of the genes supporting the Nrf2 hypothesis, can lead to suppression of apoptosis and reduced mitochondrial dysfunction. Fmo3 induction suggests the involvement of an enzyme not known to metabolize APAP in the development of tolerance to APAP toxicity. Subsequent quantitative RT-PCR and immunochemical analysis confirmed the differential expression of some of these genes in the APAP autoprotection model. In conclusion, our genomics strategy identified cellular pathways that might further explain the molecular basis for APAP autoprotection.

Comparative assessment of the timing of sexual maturation in male Wistar Han and Sprague-Dawley rats.

Given the increasing use of Wistar Han (WH) rats in regulatory toxicology studies, these studies were performed to characterize the onset of sexual maturation in maturing WH rats as compared to Sprague-Dawley (SD) rats. Beginning on postnatal day (PND) 38 through PND 91 groups (n=8) of untreated WH rats were evaluated for maturation of the male reproductive system. Testicular spermatid head counts increased beginning on PND 42 until PND 70. Sperm were detected in the caput, corpus, and cauda epididymis on PND 45, 49, and 49, respectively, and counts increased through PND 91. Sperm motility was at adult levels by PND 63. The morphology of the testis/epididymis of all animals at day 70 or older was consistent with qualitative sexual maturity. Based on these endpoints, WH rats were determined to be sexually mature at PND 70, and many of these endpoints evaluated in SD rats exhibited nearly identical trends.

Sensitive windows of skeletal development in rabbits determined by hydroxyurea exposure at different times throughout gestation.

The critical periods of axial skeletal development in rats and mice have been well characterized, however the timing of skeletal development in rabbits is not as well known. It is important to have a more precise understanding of this timing of axial skeletal development in rabbits due to the common use of this species in standard nonclinical studies to assess embryo-fetal developmental toxicity. Hydroxyurea, a teratogen known to induce a variety of fetal skeletal malformations, was administered to New Zealand White rabbits as a single dose (500 mg/kg) on individual days during gestation (gestation day, GD 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 19) and fetal external, visceral, and skeletal morphology was examined following cesarean sections on GD 29. A wide range of fetal skeletal effects was observed following hydroxyurea treatment, with a progression of malformations from anterior to posterior structures over time, as well as from proximal to distal structures over time. The sensitive window of axial skeletal development was determined to be GD 8 to 13, while disruption of appendicular and cranio-facial skeletal development occurred primarily from GD 11 to 16 and GD 11 to 12, respectively. The results of this study provide a better understanding of the critical developmental window for different segments of the rabbit skeleton, which will aid in the design of window studies to investigate teratogenicity in rabbits.

Developmental toxicity of lersivirine in rabbits when administered throughout organogenesis and when limited to sensitive windows of axial skeletal development.

BACKGROUND: Lersivirine is a second-generation nonnucleoside reverse transcriptase inhibitor undergoing clinical development for the treatment of human immunodeficiency virus-1. An embryo-fetal development study was performed to evaluate the potential for maternal and developmental toxicity of lersivirine. METHODS: Pregnant New Zealand White rabbits were administered 0, 100, 250, and 500 mg/kg lersivirine by oral gavage once daily on gestation days (GDs) 7 to 19, followed by cesarean section on GD 29 and fetal evaluation. RESULTS: Maternal toxicity was noted at all dose levels (decreased food consumption and body weight gain), with fetal toxicity at 500 mg/kg (decreased fetal weights, increased postimplantation loss). Equivocal findings for axial skeletal malformations were observed in three fetuses at 500 mg/kg. To better understand if these malformations were related to treatment with lersivirine, a follow-up rabbit embryo-fetal development study was performed with 1000 mg/kg/day lersivirine (500 mg/kg BID, 12-hr interdose interval) for two different 3-day windows, GDs 8 to 10 or GDs 11 to 13, which represent the sensitive windows of axial skeletal development in rabbits. Control rabbits were administered vehicle following the same dosing regimen from GDs 8 to 13. Cesarean sections were performed on GD 29, and fetal skeletons were examined for the potential of lersivirine to cause skeletal malformations in rabbits. At maternal exposure levels higher than the initial study, lersivirine did not induce fetal skeletal malformations when administered in the sensitive windows of axial skeletal development. CONCLUSION: The results of these studies indicate that lersivirine did not exhibit any evidence of teratogenicity in rabbits.

Molecular alterations underlying the enhanced disruption of spermatogenesis by 2,5-hexanedione and carbendazim co-exposure.

The current study investigated the co-exposure effects of 2,5-hexanedione (HD) and carbendazim (CBZ) on gene expression underlying the enhanced pathology previously observed. Adult male rats were exposed to HD (0.33 or 1%) followed by CBZ (67 or 200 mg/kg), and testis samples were collected after 3 and 24 h. Microarray analysis at 3 h revealed that CBZ and HD interact in an agonistic, or synergistic, way at the gene level. Further analysis of candidate genes by qRT-PCR at both 3 and 24 h after co-exposure, revealed that Loxl1 and Clca2/Clca4l were both decreased in expression. Immunohistochemical analysis of Loxl1 at 24 h revealed that Loxl1 is localized to the seminiferous tubules, with the most intense staining in the basement membrane, blood vessels, and acrosomes, with the relative intensity reflecting the gene level changes at 3 h. These findings provide candidate genes for further investigation of the testicular response to damage.

Developmental toxicity study of lersivirine in mice.

Lersivirine is a second-generation nonnucleoside reverse transcriptase inhibitor undergoing clinical development for the treatment of HIV-1. An embryo-fetal developmental toxicity study was performed to evaluate the maternal and developmental toxicity of lersivirine in pregnant mice. Mated Crl:CD1(ICR) mice were administered 0, 150, 350, and 500 mg/kg lersivirine once daily by oral gavage on gestation days 6 to 17, followed by cesarean section on gestation day 18. The first 2 days of dosing for the high-dose group were done at 250 mg/kg to allow induction of hepatic metabolizing enzymes, after which the dose was increased to 500 mg/kg/day. This dosing paradigm allowed for maintenance of exposure in the high-dose group despite the considerable autoinduction that occurs in rodents following lersivirine treatment. Lersivirine did not cause an increase in external, visceral, or skeletal malformations. Intrauterine growth retardation, demonstrated by reduced fetal body weights and increased variations associated with delayed skeletal ossification, was noted at 350 and 500 mg/kg/day. The results of these studies indicate that lersivirine is not teratogenic in mice.

Isoflurane reduces motile sperm counts in the Sprague-Dawley rat.

Animal and care use practices are constantly evolving. These can have unexpected consequences on the data collected from such procedures. One example is the recent change in our animal facility, based on recommendations from the Newcastle Consensus Meeting on Carbon Dioxide Euthanasia of Laboratory Animals, from CO(2) to isoflurane for anesthesia. The current study was conducted to determine the effects of isoflurane on sperm motility, as compared to two different CO(2) euthanasia procedures. Sperm motility was evaluated after euthanasia by a standard 5-minute CO(2) euthanasia procedure, an extended 10-minute CO(2) euthanasia procedure, or by isoflurane anesthesia followed by exsanguination (iso/exsanguination). The 5-minute CO(2) procedure produced sperm motility of 94.3 ± 1.7% motile sperm with 65.6 ± 16.8 sperm/field. By comparison, iso/exsanguination reduced that count to 3.3 ± 2.3 sperm/field and only 60.7 ± 32.0% motile sperm. The reduction in sperm motility after iso/exsanguination appeared to have been due primarily to the reduction in the number of sperm expelled from the vas deferens (3.3), compared to that after 5-minute CO(2) (65.6). This reduction in number of sperm available for evaluation, in the presence of a constant level of background debris, which was counted by the computer optics system as nonmotile sperm, resulted in an apparent reduction in motility. Using the extended 10-minute CO(2) procedure produced sperm data in between the other two extremes: 77.6 ± 36.1% motile sperm with 34.6 ± 28.3 sperm/field. The results of this study support the hypothesis that isoflurane inhibits contraction of the smooth muscle of the vas deferens, resulting in a decreased number of expelled sperm. Given these findings, it is important that careful consideration be taken to select an appropriate anesthesia/euthanasia method.