Consequences of Aroclor 1254 ingestion on the menstrual cycle of rhesus (Macaca mulatta) monkeys

Development of binary classification models for grouping hydroxylated polychlorinated biphenyls into active and inactive thyroid hormone receptor agonists

Some adverse effects of hydroxylated polychlorinated biphenyls (OH-PCBs) in humans are presumed to be initiated via thyroid hormone receptor (TR) binding. Due to the trial-and-error approach adopted for OH-PCB selection in previous studies, experiments designed to test the TR binding hypothesis mostly utilized inactive OH-PCBs, leading to considerable waste of time, effort and other material resources. In this paper, linear discriminant analysis (LDA) and binary logistic regression (LR) were used to develop classification models to group OH-PCBs into active and inactive TR agonists using radial distribution function (RDF) descriptors as predictor variables. The classifications made by both LDA and LR models on the training set compounds resulted in an accuracy of 84.3%, sensitivity of 72.2% and specificity of 90.9%. The areas under the ROC curves, constructed with the training set data, were found to be 0.872 and 0.880 for LDA and LR models, respectively. External validation of the models revealed that 76.5% of the test set compounds were correctly classified by both LDA and LR models. These findings suggest that the two models reported in this paper are good and reliable for classifying OH-PCB congeners into active and inactive TR agonists.

A computational insight into endocrine disruption by polychlorinated biphenyls via non-covalent interactions with human nuclear receptors

Production of polychlorinated biphenyls (PCBs) was banned a long time ago because of their harmful health effects but humans continue to be exposed to residual PCBs in the environment. In this study, the susceptibility of human nuclear receptors to binding by PCBs was investigated using molecular docking simulation. Findings revealed that PCBs belonging to ortho-substituted, mono-ortho-substituted and non-ortho-substituted congeners could bind to agonistic conformations of androgen (AR), estrogen (ER α and ER β), glucocorticoid (GR) and thyroid hormone (TR α and TR β) receptors as well as antagonistic conformation of androgen receptor (AR an) but only ortho-substituted and mono-ortho-substituted PCBs could bind to estrogen receptors in their antagonistic conformations (ER α an and ER β an). Further molecular docking analyses showed that PCBs mimic the modes of interaction observed for the co-crystallized ligands in the crystal structures of the affected receptors, utilizing 81%, 83%, 78%, 60%, 75%, 60%, 86%, 100% and 75% of the amino acid residues utilized by the co-crystallized ligands for binding in AR, AR an, ER α, ER α an, ER β, ER β an, GR, TR α and TR β respectively. This computational study suggests that PCBs may cause endocrine disruption via formation of non-covalent interactions with androgen, estrogen, glucocorticoid and thyroid hormone receptors.

Persistent organochlorine pollutants and menstrual cycle characteristics

An evolving body of evidence suggests an adverse relation between persistent organochlorine pollutants (POPs) and menstruation, though prospective longitudinal measurement of menses is limited and served as the impetus for study. We prospectively assessed the relation between a mixture of persistent organochlorine compounds and menstrual cycle length and duration of bleeding in a cohort of women attempting to become pregnant. Eighty-three (83%) women contributing 447 cycles for analysis provided a blood specimen for the quantification of 76 polychlorinated biphenyls and seven organochlorine pesticides, and completed daily diaries on menstruation until a human chorionic gonadotropin confirmed pregnancy or 12 menstrual cycles without conception. Gas chromatography with electron capture detection was used to quantify concentrations (ng g(-1)serum); enzymatic methods were used to quantify serum lipids (mg dL(-1)). A linear regression model with a mixture distribution was used to identify chemicals grouped by purported biologic activity that significantly affected menstrual cycle length and duration of bleeding adjusting for age at menarche and enrollment, body mass index, and cigarette smoking. A significant 3-d increase in cycle length was observed for women in the highest tertile of estrogenic PCB congeners relative to the lowest tertile (β=3.20; 95% CI 0.36, 6.04). A significant reduction in bleeding (<1 d) was observed among women in the highest versus lowest tertile of aromatic fungicide exposure (γ=-0.15; 95% CI -0.29, -0.00). Select POPs were associated with changes in menstruation underscoring the importance of assessing chemical mixtures for female fecundity.

Menstrual function among women exposed to polybrominated biphenyls: a follow-up prevalence study

BACKGROUND

Alteration in menstrual cycle function is suggested among rhesus monkeys and humans exposed to polybrominated biphenyls (PBBs) and structurally similar polychlorinated biphenyls (PCBs). The feedback system for menstrual cycle function potentially allows multiple pathways for disruption directly through the hypothalamic-pituitary-ovarian axis and indirectly through alternative neuroendocrine axes.

METHODS

The Michigan Female Health Study was conducted during 1997-1998 among women in a cohort exposed to PBBs in 1973. This study included 337 women with self-reported menstrual cycles of 20-35 days (age range: 24-56 years). Current PBB levels were estimated by exponential decay modeling of serum PBB levels collected from 1976-1987 during enrollment in the Michigan PBB cohort. Linear regression models for menstrual cycle length and the logarithm of bleed length used estimated current PBB exposure or enrollment PBB exposure categorized in tertiles, and for the upper decile. All models were adjusted for serum PCB levels, age, body mass index, history of at least 10% weight loss in the past year, physical activity, smoking, education, and household income.

RESULTS

Higher levels of physical activity were associated with shorter bleed length, and increasing age was associated with shorter cycle length. Although no overall association was found between PBB exposure and menstrual cycle characteristics, a significant interaction between PBB exposures with past year weight loss was found. Longer bleed length and shorter cycle length were associated with higher PBB exposure among women with past year weight loss.

CONCLUSION

This study suggests that PBB exposure may impact ovarian function as indicated by menstrual cycle length and bleed length. However, these associations were found among the small number of women with recent weight loss suggesting either a chance finding or that mobilization of PBBs from lipid stores may be important. These results should be replicated with larger numbers of women exposed to similar lipophilic compounds.

Polychlorinated biphenyls and menstrual cycle characteristics

BACKGROUND

Experimental studies in nonhuman primates provide evidence that low-level exposure to persistent organochlorine pollutants such as polychlorinated biphenyls (PCBs) may affect aspects of their menstrual cycle, including cycle length, regularity, and bleeding duration. Few studies have examined these associations in humans.

METHODS

We used data from 2314 pregnant women who participated in the Collaborative Perinatal Project, a cohort study that enrolled pregnant women in the 1960s in 12 centers in the United States. Information about usual (prepregnancy) menstrual cycle length, regularity, bleeding duration, and dysmenorrhea was collected at enrollment, and 11 PCBs and p,p'-DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) were measured in stored blood samples collected during the third trimester of pregnancy. We used multivariate linear and logistic regression to examine the association between organochlorine levels and menstrual cycles, adjusting for demographic factors, cholesterol, and triglycerides.

RESULTS

Total PCBs were positively associated with increasing menstrual cycle length (adjusted difference across 5 categories of PCB exposure = 0.7 days, trend-test P value = 0.02). Irregular cycles were slightly more frequent among those in the 2 highest categories of PCB exposure (odds ratio for highest category = 1.5; 95% confidence interval = 0.70-3.3), and there also was some evidence of an association with DDE. The strengths of these associations increased with various exclusions made to decrease potential misclassification of the outcome and the exposures. There was little evidence for associations between DDE or PCBs and bleeding duration, heavy bleeding, or dysmenorrhea.

CONCLUSIONS

This study supports experimental studies in monkeys showing an effect of low-dose PCB exposure on menstrual function.

Environmental pollutant Aroclor 1242 (PCB) disrupts reproduction in adult male rhesus monkeys (Macaca mulatta)

Adult male rhesus monkeys (Macaca mulatta) were given oral treatment of either Aroclor 1242 or vehicle (corn oil and glycerol) at a dose of 200 microg/kg body wt/day for 6 months to investigate the effects of the pollutant on plasma testosterone and the morphology of testes and accessory glands. Aroclor 1242 treatment significantly decreased testicular size and testosterone levels in plasma and adversely affected spermatogenic activity by disrupting epithelial organization. All components of the germinal epithelium were greatly reduced. The spermatogonia were either hypertrophied or had shrunken vesiculated cytoplasm with distorted mitochondria and nuclear pyknosis. Changes were milder in the Sertoli cells, where nuclear infoldings were reduced. Characteristic features of treated Leydig cells were the presence of electron-dense and electron-opaque zones, appearing as plaques, cell membrane abnormalities, and high variability in nuclear shape and heterochromatin distribution. All the Aroclor 1242-treated accessory glands contained more connective tissue than their vehicle-treated counterparts. The epithelium contained many layers of irregularly shaped necrotic cells possessing stereocilia in the epididymides, either hypochromic and hypertrophied or hyperchromic and hypotrophied cells in the prostate and shrunken cuboidal cells with elongated nuclei in the seminal vesicles. In conclusion, Aroclor 1242 treatment causes severe structural alterations on gonads and accessory organs in adult male rhesus monkeys, and these effects could be mediated through both estrogen and Ah receptors.

Effects elicited by toxaphene in the cynomolgus monkey (Macaca fascicularis): a pilot study

Toxaphene, which was added to glycerol/corn oil, was administered at a level of 1 mg/kg body weight/day in gelatin capsules to four healthy young adult cynomolgus (Macaca fascicularis) monkeys for 52 weeks. Four control monkeys ingested capsules containing only glycerol/corn oil. Each group had two males and two females. On a daily basis, each monkey's feed and water consumption was determined, its health was monitored and the females were swabbed to evaluate menstrual status. On a weekly basis, each monkey's body weight was determined and a detailed clinical evaluation was performed. At 4-week intervals, blood samples were taken for serum biochemistry, haematology and toxaphene analysis. Also, a local anaesthetic was administered to the nuchal fat pad area of each monkey, and adipose samples were obtained for toxaphene analysis. 1 day prior to the biopsies, a 24-h urine and faecal collection was obtained for toxaphene analysis. After 34 weeks of treatment, the immune system of the monkeys was evaluated. After 52 weeks of dosing, all treated and two control animals were necropsied. Liver samples were obtained and microsomal fractions were prepared immediately. A portion of liver and kidney was taken for toxaphene analysis. All of the major internal organs were weighed and bone marrow evaluations were conducted. Organ and tissue samples were fixed in 10% formalin and processed for light microscopy. There was no effect of treatment on body weight gain, feed consumption, water consumption or haematological parameters. Two major clinical findings were inflammation and/or enlargement of the tarsal gland and impacted diverticulae in the upper and lower eye lids. At necropsy, the relative spleen and thymus weights were greater for the treated monkeys than the controls. Toxaphene administration produced an increase in metabolism of aminopyrene, methoxyresorufin and ethoxyresorufin, three substrates that are altered specifically by cytochrome P450-based hepatic monooxygenase enzymes. Histopathological examination of tissues was unremarkable by light microscopy. Tissue analysis for toxaphene and immunology findings have been published elsewhere.

Toxicological consequences of toxaphene ingestion by cynomolgus (Macaca fascicularis) monkeys. Part 1: pre-mating phase

A total of 40 menstruating cynomolgus monkeys (Macaca fascicularis) with an average age of 7.25 +/- 1.06 years (standard deviation), five male cynomolgus monkeys with an average age of 12.6 +/- 0.66 years, and five male cynomolgus males with an average age of 6.2 +/- 0.23 years were obtained from the Health Canada breeding laboratory. The females were initially randomized to the four test groups in accordance with their previous reproductive success and body weight. They were then randomly allocated between two similar environmentally-controlled rooms (20 females/room). The males were randomly assigned to one of the test rooms (six or four males/room). The female test groups self-ingested capsules containing doses of 0, 0.1, 0.4 or 0.8 mg (Groups A, B, C, D) of technical grade toxaphene/kg body weight/day (i.e. five females/dose group/room). The older males (Group E) were proven breeders and were used exclusively for mating and their capsules contained no toxaphene. The younger males (Group F) ingested capsules containing 0.8 mg of technical grade toxaphene/kg body weight/day. After 20 weeks of daily dosing, it was assumed, based on the results of a pilot study [Andrews P., Headrick K., Pilon J.-C., Bryce F., Iverson F. (1996) Capillary GC-ECD and ECNI GCMS characterization of toxaphene residues in primate tissues during a feed study. Chemosphere 32, 1043-1053], that the treated monkeys had attained a qualitative pharmacokinetic steady state regarding the concentration of toxaphene in their adipose tissue and blood. On a daily basis, each monkey's feed and water consumption as well as its health were monitored. In addition, the females were swabbed daily to determine menstrual status. On a weekly basis, each monkey's body weight was determined and its dose of toxaphene adjusted. Detailed clinical examinations were conducted at intervals of 4 weeks or less. Periodically, starting prior to the initiation of dosing, blood samples were taken for serum biochemistry, haematology and toxaphene analysis. In addition, specimens from the nuchal fat pad were also obtained for toxaphene analysis. Statistical analysis did not reveal any effect of treatment on body weight gain, feed consumption, water consumption or haematological parameters during the 75-week pre-mating phase. The only serum biochemistry parameter which was consistently affected by treatment was cholesterol, the level of which decreased in a linear fashion as a consequence of dose, and this effect increased with time on test (P = 0.037). No other biological effects of toxaphene ingestion were found during the premating phase of this toxicological-reproduction study.