In vitro metabolism of cis- and trans-permethrin by rat liver microsomes, and its effect on estrogenic and anti-androgenic activities

Mediating role of host metabolites in strontium's effect on osteoporosis among older individuals: Findings from Wuhan, China

Strontium is receiving widespread attention due to its remarkable biological qualities in preventing bone resorption and fostering osteogenesis. However, the chemical processes behind strontium's dual activities on bone cells are not yet fully understood. This study used the metabolomic technique to identify and examine potential biomarkers between strontium exposure and osteoporosis (OP) risk. A total of 806 participants were recruited for the detection of plasma strontium content via inductively coupled plasma-mass spectrometry. Plasma metabolites were profiled in 254 participants through an untargeted metabolomics technique. Generalized linear models were primarily used to analyze associations among plasma strontium, metabolites, and OP. The mediating effects of metabolites on the strontium-OP association were further investigated. A total of 31 differential metabolites were observed, 10 of which were upregulated and 21 were downregulated in the OP group compared with the non-OP group. Five metabolites (3-phenoxybenzoic acid, Cer (t18:0/16:1), HexCer(t16:1/12:1(2OH)), HexCer(t14:2/18:1(2OH)), and TG(16:0-18:1-24:4)) were selected as potential mediators based on their significant association with OP risk and with femoral neck and lumbar spine bone mineral density (BMD). Moreover, all except TG(16:0-18:1-24:4) were involved in the OP discrimination model with excellent power combined with several traditional variables. 3-Phenoxybenzoic acid and Cer(t18:0/16:1) had significant indirect effects on the strontium-OP association. The five candidate metabolites mediated 83.79 % of the strontium-OP association. Plasma strontium level was associated with reduced OP risk in the Han population in Wuhan. Thus, plasma metabolite profiling revealed five BMD/OP-associated metabolites that acted as mediators in the strontium-OP association. Our findings provided evidence of the mediating role of host plasma metabolites in strontium's effect on OP pathology.

Exposure to non-persistent pesticides and sexual maturation of Spanish adolescent males

BACKGROUND

Several non-persistent pesticides are endocrine disrupting chemicals and may impact on sexual maturation.

OBJECTIVE

To examine the association between urinary biomarkers of non-persistent pesticides and sexual maturation in adolescent males in the Environment and Childhood (INMA) Project.

METHODS

The metabolites of several pesticides were measured in spot urine samples collected from 201 boys aged 14-17 years, including: 3,5,6-trichloro-2-pyridinol (TCPy), metabolite of chlorpyrifos; 2-isopropyl-4-methyl-6-hydroxypyrimidine (IMPy), metabolite of diazinon; malathion diacid (MDA), metabolite of malathion; diethyl thiophosphate (DETP) and diethyl dithiophosphate, non-specific metabolites of organophosphates; 3-phenoxybenzoic acid (3-PBA) and dimethyl cyclopropane carboxylic acid, metabolites of pyrethroids; 1-naphthol (1-NPL), metabolite of carbaryl; and ethylene thiourea (ETU), metabolite of dithiocarbamate fungicides. Sexual maturation was assessed using Tanner stages, self-reported Pubertal Development Scale, and testicular volume (TV). Multivariate logistic regression was employed to examine associations between urinary pesticide metabolites and the odds of being in Tanner stage 5 of genital development (G5) or pubic hair growth (PH5); stage ≥4 of overall pubertal development, gonadarche, and adrenarche; or having mature TV (≥25 mL).

RESULTS

DETP concentrations>75th percentile (P75) were associated with lower odds of being in stage G5 (OR = 0.27; 95% CI = 0.10-0.70), detectable TCPy with lower odds of gonadal stage≥4 (OR = 0.50; 95% CI = 0.26-0.96), and intermediate detectable MDA concentrations (<P75) with lower odds of adrenal stage≥4 (OR = 0.32; 95% CI = 0.11-0.94). Conversely, detectable concentrations of 1-NPL were associated with higher odds of adrenal stage≥4 (OR = 2.61; 95% CI = 1.30-5.24) but lower odds of mature TV (OR = 0.42; 95% CI = 0.19-0.90).

CONCLUSION

Exposure to certain pesticides may be associated with delayed sexual maturity in adolescent males.

Multiple-P450 Gene Co-Up-Regulation in the Development of Permethrin Resistance in the House Fly, Musca domestica

This paper reports a study conducted at the whole transcriptome level to characterize the P450 genes involved in the development of pyrethroid resistance, utilizing expression profile analyses of 86 cytochrome P450 genes in house fly strains with different levels of resistance to pyrethroids/permethrin. Interactions among the up-regulated P450 genes and possible regulatory factors in different autosomes were examined in house fly lines with different combinations of autosomes from a resistant house fly strain, ALHF. Eleven P450 genes that were significantly up-regulated, with levels > 2-fold those in the resistant ALHF house flies, were in CYP families 4 and 6 and located on autosomes 1, 3 and 5. The expression of these P450 genes was regulated by trans- and/or cis-acting factors, especially on autosomes 1 and 2. An in vivo functional study indicated that the up-regulated P450 genes also conferred permethrin resistance in Drosophila melanogaster transgenic lines. An in vitro functional study confirmed that the up-regulated P450 genes are able to metabolize not only cis- and trans-permethrin, but also two metabolites of permethrin, PBalc and PBald. In silico homology modeling and the molecular docking methodology further support the metabolic capacity of these P450s for permethrin and substrates. Taken together, the findings of this study highlight the important function of multi-up-regulated P450 genes in the development of insecticide resistance in house flies.

Androgen receptor signaling and pyrethroids: Potential male infertility consequences

Infertility is a global health concern inflicting a considerable burden on the global economy and a severe socio-psychological impact. Approximately 15% of couples suffer from infertility globally, with a male factor contribution of approximately 50%. However, male infertility remains largely unexplored, as the burden of infertility is mostly assigned to female people. Endocrine-disrupting chemicals (EDCs) have been proposed as one of the factors causing male infertility. Pyrethroids represent an important class of EDCs, and numerous studies have associated pyrethroid exposure with impaired male reproductive function and development. Therefore, the present study investigated the potentially toxic effects of two common pyrethroids, cypermethrin and deltamethrin, on androgen receptor (AR) signaling. The structural binding characterization of cypermethrin and deltamethrin against the AR ligand-binding pocket was performed using Schrodinger's induced fit docking (IFD) approach. Various parameters were estimated, such as binding interactions, binding energy, docking score, and IFD score. Furthermore, the AR native ligand, testosterone, was subjected to similar experiments against the AR ligand-binding pocket. The results revealed commonality in the amino acid-binding interactions and overlap in other structural parameters between the AR native ligand, testosterone, and the ligands, cypermethrin and deltamethrin. The estimated binding energy values of cypermethrin and deltamethrin were very high and close to those calculated for AR native ligand, testosterone. Taken together, the results of this study suggested potential disruption of AR signaling by cypermethrin and deltamethrin, which may result in androgen dysfunction and subsequent male infertility.

Association of urinary metabolites of non-persistent pesticides with serum sex hormones among the US females: NHANES 2013-2014

BACKGROUND

Evidence indicated the possibility of non-persistent pesticides disrupting the homeostasis of sex hormones. However, few studies have focused on this relationship in females. We aimed to explore the relationship between non-persistent pesticide exposure and sex hormones among the US females from the National Health and Nutrition Examination Survey 2013-2014.

METHODS

A total of 790 females, including girls (6-11 years), female adolescents (12-19 years), and adult females (>19 years), were enrolled in this study. Age stratified associations of individual non-persistent pesticide metabolites and their mixtures with sex hormones were analyzed by weighted multiple linear regression and Bayesian kernel machine regression (BKMR) using spot urinary non-persistent pesticide measurement, including 2,4-dichlorophenoxyacetic acid (2,4-D), 3,5,6-trichloropyridinol (TCPY), para-nitrophenol (PNP) and 3-phenoxybenzoic acid (3-PBA), and three serum sex hormones [total testosterone (TT), estradiol (E2) and sex hormone binding globulin (SHBG)].

RESULTS

In girls, weighted multivariate linear regression indicated that both 2,4-D and PNP were negatively associated with TT, and TCPY was inversely associated with SHBG. In female adolescents, TCPY was negatively associated with TT and E2, and 3-PBA was negatively associated with SHBG; positive associations were detected both in 2,4-D with SHBG, and in PNP with TT. In adult females, a higher concentration of 3-PBA was associated with higher levels of TT. The BKMR model showed that in female adolescents, the concentrations of pesticide metabolite mixtures at or above the 55th percentile were negatively related to the levels of E2 compared with their mixtures at 50th percentile, and an inverse U-shaped exposure-response function between PNP and E2 was found.

CONCLUSIONS

Associations between the four non-persistent pesticide metabolites and serum sex hormones were identified in the US females from NHANES 2013-2014 and these associations were age dependent, especially in adolescents. Large-scale cohort studies are needed to confirm these findings and elucidate the potential biological mechanisms.

The Central Role of Multiple P450 Genes and Their Co-factor CPR in the Development of Permethrin Resistance in the Mosquito Culex quinquefasciatus

Mosquitoes’ increasing resistance to insecticides is becoming a major threat for control efforts worldwide. Multiple P450 genes that are up-regulated in permethrin resistant strains of Culex quinquefasciatus have been linked to the development of resistance. In the current study, we characterized the function of six P450 genes, CYP6P14, CYP6BZ2, CYP9J33, CYP9J34, CYP9J40, and CYP9J45, that are overexpressed in the permethrin resistant Culex mosquitoes and showed their capability in metabolism of permethrin. These six P450 genes can convert 3-phenoxybenzoic alcohol (PBCHO) to a less toxic product, 3-phenoxybenzoic acid (PBCOOH), indicating that these P450s play an important role in permethrin degradation pathways. Although we know multiple P450 genes are over-expressed in permethrin resistant Culex mosquitoes, it remains to be seen whether cytochrome P450-reductase (CPR) gene that are co-overexpressed with P450 genes in permethrin resistant mosquitoes do indeed serve as a resistance mechanism. An in-depth investigation of the expression of CPR gene in resistant mosquitoes was conducted in permethrin resistant mosquitoes. The finding of CPR gene overexpression in permethrin resistant mosquitoes suggested the importance of co-overexpression of multiple P450 genes with their obligatory electron donor CPR in the complex detoxification system, boosting the metabolism of permethrin and hence the development of permethrin resistance in Cx. quinquefasciatus.

Construction and characterization of a class-specific single-chain variable fragment against pyrethroid metabolites

Pyrethroids are insecticides that are widely used in rural and urban areas worldwide. After entering the environment, pyrethroids are rapidly metabolized or degraded by various biological or abiotic methods. In this study, a single-chain variable fragment (scFv) which could simultaneously detect three pyrethroid metabolites was constructed based on a hybridoma raised against 3-phenoxybenzoic acid (3-PBA). By molecular docking, it showed that there were hydrogen bonds, hydrophobic interactions, CH-π interaction, and cation-π interaction between 3-PBA and its scFv. All the contact residues contributing to hydrogen bonds are located in VH-CDR2 or its neighboring region, and two of them were mutants of the closest germline sequence. Based on competitive ELISA, the half maximal inhibitory concentration (IC₅₀) of the scFv for 3-PBA, 3-phenoxybenzaldehyde (PBAld), and 3-phenoxybenzyl alcohol (PBAlc) were calculated to be 0.55, 0.59, and 0.63 μgmL^-1, respectively. The scFv also showed 23.91%, 13.41%, 1.15%, 1.00%, and 0.56% cross-reactivity with phenothrin, deltamethrin, fenvalerate, beta-cypermethrin, and fenpropathrin. The broad specificity of the scFv may be due to its hapten design. The scFv could be employed in class-specific immunoassays for pyrethroid metabolites with phenoxybenzyl (PB) group. It is also potentially used for characterizing degradation of pyrethroids or detecting PBAlc (PBAld) alone, and the detection results should be confirmed by other selective methods. KEY POINTS: • A scFv which can simultaneously detect 3-PBA, PBAlc, and PBAld was constructed. • Antibody informatics and binding mode of the scFv were obtained. • The reason for its broad specificity was discussed. • It could be used to monitor single or multi-pyrethroid metabolites with PB group.

Effects and mechanisms of pyrethroids on male reproductive system

Synthetic pyrethroids are used as insecticides in agriculture and a variety of household applications worldwide. Pyrethroids are widely distributed in all environmental compartments and the general populations are exposed to pyrethroids through various routes. Pyrethroids have been identified as endocrine-disrupting chemicals (EDCs) which are responsible for the male reproductive impairments. The data confirm pyrethroids cause male reproductive damages. The insecticides exert the toxic effects on male reproductive system through various complex mechanisms including antagonizing androgen receptor (AR), inhibiting steroid synthesis, affecting the hypothalamic-pituitary-gonadal (HPG) axis, acting as estrogen receptor (ER) modulators and inducing oxidative stress. The mechanisms of male reproductive toxicity of pyrethroids involve multiple targets and pathways. The review will provide further insight into pyrethroid-induced male reproductive toxicity and mechanisms, which is crucial to preserve male reproductive health.

Activation of PXR, CAR and PPARα by pyrethroid pesticides and the effect of metabolism by rat liver microsomes

In this study, we used reporter gene assays in COS-1 cells to examine the activation of rat pregnane X receptor (PXR), rat constitutive androstane receptor (CAR) and rat peroxisome-proliferator activated receptor (PPAR)α by pyrethroid pesticides, and to understand the effects of metabolic modification on their activities. All eight pyrethroids tested in this study showed rat PXR agonistic activity; deltamethrin was the most potent, followed by cis-permethrin and cypermethrin. However, when the pyrethroids were incubated with rat liver microsomes, their rat PXR activities were decreased to various extents. Cis- and trans-permethrin showed weak rat CAR agonistic activity, while the other pyrethroids were inactive. However, fenvalerate showed dose-dependent inverse agonistic activity toward rat CAR, and this activity was reduced after metabolism. None of the pyrethroids showed rat PPARα agonistic activity, but a metabolite of cis-/trans-permethrin and phenothrin, 3-phenoxybenzoic acid, activated rat PPARα. Since PXR, CAR and PPARα regulate various xenobiotic/endobiotic-metabolizing enzymes, activation of these receptors by pyrethroids may result in endocrine disruption due to changes of hormone-metabolizing activities.

The pyrethroid insecticides permethrin and esfenvalerate do not disrupt testicular steroidogenesis in the rat fetus

The present study investigated the effects of maternal exposure to the widely used pyrethroid insecticides, permethrin and esfenvalerate, on fetal testicular steroidogenesis. Pregnant Sprague-Dawley rats were administered permethrin at doses of 1, 10, 50, or 100 mg/kg/day, or esfenvalerate at 0.1, 1, 7.5 or 15 mg/kg/day, by gavage, from gestation day (GD) 13 to 19. Testicular testosterone production and the expression of several key genes necessary for cholesterol and androgen synthesis and transport were assessed in GD 19 male fetuses. Dams treated with 100 mg/kg/day of permethrin or 15 mg/kg/day of esfenvalerate showed clinical signs of neurotoxicity. The highest dose of esfenvalerate also resulted in reduced maternal body weight gain throughout the treatment period. In the fetal testes, mRNA expressions of HMG-CoA synthase and reductase, SR-B1, StAR, P450scc, 3βHSD, P450 17A1, and 17βHSD were not affected by exposure to either pyrethroid. No significant change was observed in ex vivo testosterone production. In conclusion, in utero exposure to permethrin or esfenvalerate has no effect on the testosterone biosynthesis pathway in the fetal rat testis up to maternal toxic doses.

[Effect of the Metabolic Modification of Environmental Chemicals on Endocrine-disrupting Activity]

　The endocrine-disrupting activities of various environmental chemicals are metabolically activated. For example, diphenyls, styrene oligomers, chalcones, trans-stilbene and 2-nitrofluorene are not estrogens, but after incubation with liver microsomes, their metabolites show estrogenic activities. Thus, these chemicals are estrogenically activated by the cytochrome P450 system. In contrast, the antiandrogenic activity of fenthion, an organophosphorus insecticide, is abolished after metabolism to sulfoxide and sulfone derivatives. Structural requirements of twenty bisphenol A related compounds, as well as various benzophenones, for estrogenic and antiandrogenic activities have been investigated. The estrogenic and antiandrogenic activities of Benzophenone 3, a representative UV absorbant, are activated by oxidative metabolism. Parabens (used as antimicrobial agents) exhibit estrogenic activity, and their potency shows a bell-shaped curve between C1 (methylparaben) and C12 (dodecylparaben) parabens. The AhR ligand activity of indirubin is decreased by metabolism. Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDE) are activated by hydroxylation to show estrogenic and thyroid hormone-disrupting activities. Halogen adjacent to a hydroxyl group is essential for thyroid hormone-disrupting activity. Tetrabromobisphenol A, tetrachlorobisphenol A and tetramethylbisphenol A also exhibit thyroid hormone-disrupting activity. Amphibian metamorphosis of tadpoles to frogs is affected by hydroxylated PCB, hydroxylated PBDE and bisphenol A derivatives. These chemicals suppress thyroid hormone-dependent metamorphosis, acting as antagonists of thyroid hormone. Thus, metabolic modification can have a dramatic impact on the endocrine-disrupting activities of environmental chemicals.

Prediction of Estrogenic Bioactivity of Environmental Chemical Metabolites

The US Environmental Protection Agency's (EPA) Endocrine Disruptor Screening Program (EDSP) is using in vitro data generated from ToxCast/Tox21 high-throughput screening assays to assess the endocrine activity of environmental chemicals. Considering that in vitro assays may have limited metabolic capacity, inactive chemicals that are biotransformed into metabolites with endocrine bioactivity may be missed for further screening and testing. Therefore, there is a value in developing novel approaches to account for metabolism and endocrine activity of both parent chemicals and their associated metabolites. We used commercially available software to predict metabolites of 50 parent compounds, out of which 38 chemicals are known to have estrogenic metabolites, and 12 compounds and their metabolites are negative for estrogenic activity. Three ER QSAR models were used to determine potential estrogen bioactivity of the parent compounds and predicted metabolites, the outputs of the models were averaged, and the chemicals were then ranked based on the total estrogenicity of the parent chemical and metabolites. The metabolite prediction software correctly identified known estrogenic metabolites for 26 out of 27 parent chemicals with associated metabolite data, and 39 out of 46 estrogenic metabolites were predicted as potential biotransformation products derived from the parent chemical. The QSAR models estimated stronger estrogenic activity for the majority of the known estrogenic metabolites compared to their parent chemicals. Finally, the three models identified a similar set of parent compounds as top ranked chemicals based on the estrogenicity of putative metabolites. This proposed in silico approach is an inexpensive and rapid strategy for the detection of chemicals with estrogenic metabolites and may reduce potential false negative results from in vitro assays.

Enantioselective Metabolism of Flufiprole in Rat and Human Liver Microsomes

The enantioselective metabolism of flufiprole in rat and human liver microsomes in vitro was investigated in this study. The separation and determination were performed using a liquid chromatography system equipped with a triple-quadrupole mass spectrometer and a Lux Cellulose-2 chiral column. The enantioselective metabolism of rac-flufiprole was dramatically different in rat and human liver microsomes in the presence of the β-nicotinamide adenine dinucleotide phosphate regenerating system. The half-lives (t1/2) of flufiprole in rat and human liver microsomes were 7.22 and 21.00 min, respectively, for R-(+)-flufiprole, whereas the values were 11.75 and 17.75 min, respectively, for S-(-)-flufiprole. In addition, the Vmax of R-(+)-flufiprole was about 3-fold that of S-(-)-flufiprole in rat liver microsomes, whereas its value in the case of S-(-)-flufiprole was about 2-fold that of R-(+)-flufiprole in human liver microsomes. The CLint of rac-flufiprole also showed opposite enantioselectivy in rat and human liver microsomes. The different compositions and contents of metabolizing enzyme in the two liver microsomes might be the reasons for the difference in the metabolic behavior of the two enantiomers.

Lambda-cyhalothrin disrupts the up-regulation effect of 17β-estradiol on post-synaptic density 95 protein expression via estrogen receptor α-dependent Akt pathway

Lambda-cyhalothrin (LCT), one of the type II pyrethroids, has been widely used throughout the world. The estrogenic effect of LCT to increase cell proliferation has been well established. However, whether the estrogenic effect of LCT will influence neurodevelopment has not been investigated. In addition, 17β-Estradiol (E2) plays a crucial role in neurodevelopment and induces an increase in synaptic proteins. The post-synaptic density 95 (PSD95) protein, which is involved in the development of the structure and function of new spines and localized with estrogen receptor α (ERα) at the post-synaptic density (PSD), was detected in our study by using hippocampal neuron cell line HT22. We found that LCT up-regulated PSD95 and ERα expression, estrogen receptor (ER) antagonist ICI182,780 and phosphatidylinositol-4; 5-bisphosphate 3-kinase (PI3K) inhibitor LY294,002 blocked this effect. In addition, LCT disrupted the promotion effect of E2 on PSD95. To investigate whether the observed changes are caused by ERα-dependent signaling activation, we next detected the effects of LCT on the ERα-mediated PI3K-Protein kinase B (PKB/Akt)-eukaryotic initiation factor (eIF) 4E-binding protein 1 (4E-BP1) pathway. There existed an activation of Akt and the downstream factor 4E-BP1 after LCT treatment. In addition, LCT could disrupt the activation effect of E2 on the Akt pathway. However, no changes in cAMP response element-binding protein (CREB) activation and PSD95 messenger ribonucleic acid (mRNA) were observed. Our findings demonstrated that LCT could increase the PSD95 protein level via the ERα-dependent Akt pathway, and LCT might disrupt the up-regulation effect of E2 on PSD95 protein expression via this signaling pathway.

Estrogenic endocrine disruptors: Molecular mechanisms of action

A comprehensive summary of more than 450 estrogenic chemicals including estrogenic endocrine disruptors is provided here to understand the complex and profound impact of estrogen action. First, estrogenic chemicals are categorized by structure as well as their applications, usage and effects. Second, estrogenic signaling is examined by the molecular mechanism based on the receptors, signaling pathways, crosstalk/bypassing and autocrine/paracrine/homeostatic networks involved in the signaling. Third, evaluation of estrogen action is discussed by focusing on the technologies and protocols of the assays for assessing estrogenicity. Understanding the molecular mechanisms of estrogen action is important to assess the action of endocrine disruptors and will be used for risk management based on pathway-based toxicity testing.

The role of P450 metabolism in the estrogenic activity of bifenthrin in fish

Bifenthrin, a pyrethroid pesticide, is estrogenic in vivo in fishes. However, bifenthrin is documented to be anti-estrogenic in vitro, in the ER-CALUX (estrogen receptor) cell line. We investigated whether metabolite formation is the reason for this incongruity. We exposed Menidia beryllina (inland silversides) to 10ng/l bifenthrin, 10ng/l 4-hydroxy bifenthrin, and 10ng/l bifenthrin with 25μg/l piperonyl butoxide (PBO) - a P450 inhibitor. Metabolite-exposed juveniles had significantly higher estrogen-mediated protein levels (choriogenin) than bifenthrin/PBO-exposed, while bifenthrin alone was intermediate (not significantly different from either). This suggests that metabolites are the main contributors to bifenthrin's in vivo estrogenicity.

Methodologies, bioindicators, and biomarkers for assessing gender-related differences in wildlife exposed to environmental chemicals

Male and female organisms may have significant differences in their exposure, toxicokinetics, and response to chemicals, but gender effects have received relatively little attention, often viewed as a confounder rather than of primary importance. In this paper, we examine some of the key issues and methodologies for incorporating gender in studies of the effects of chemicals on wildlife, and explore bioindicators and biomarkers of gender effects. Examining gender-related differences in response to chemicals is complicated in wildlife because of the vast array of species, and differences in niches, lifespans, reproductive cycles and modes, and population dynamics. Further, organisms are more at risk in some ecosystems than others, which may increase the magnitude of effects. Only by studying wild animals, especially native species, can we truly understand the potential impact of gender-specific effects of chemical exposure on populations. Several factors affect gender-related differences in responses to chemicals, including exposure, age, size, seasonality, and genetic and phenotypic variation. There are clear examples where gender-related differences have had significant effects on reproductive success and population stability, including destabilization of gamete release in invertebrates, and alterations of endocrine and neuroendocrine system functioning in vertebrates. A wide range of new technologies and methods are available for examining gender-related differences in responses to chemicals. We provide examples that show that there are gender-related differences in responses to chemicals that have significant biological effects, and these gender-related differences should be taken into account by scientists, regulators, and policy makers, as well as the public.