Sex Differences in Embryonic Gonad Transcriptomes and Benzo[a]pyrene Metabolite Levels After Transplacental Exposure

Developmental exposure to polycyclic aromatic hydrocarbons (PAHs): Focus on benzo[a]pyrene neurotoxicity

Polycyclic Aromatic Hydrocarbons (PAHs) are a class of ubiquitous organic compounds produced during the incomplete combustion or pyrolysis of organic material. Dietary source is the main route for PAH human exposure by environmental contamination, food industrial processing or domestic cooking methods. The most studied PAH is benzo[a]pyrene (B[a]P), due to its harmful and multiple effects on human health: in addition to its well-known carcinogenic effects, emerging evidence indicates that B[a]P also induces neurotoxicity earlier and at lower doses than B[a]P-induced carcinogenicity making B[a]P neurotoxicity relevant to human health risk assessment. Developmental neurotoxicity of B[a]P has indeed received increasing attention: both human and experimental studies provide evidence of detrimental effects of prenatal or early postnatal B[a]P exposure, even at low doses. Indeed, in some of the multi-dose animal studies, maximal adverse effects were observed at lower B[a]P doses, according to a non-monotonic dose-response curve typical of endocrine-disrupting compounds. In substantial agreement with epidemiological studies, both rodents and zebrafish developmentally exposed to B[a]P exhibit long-term changes in multiple behavioural domains, in the absence of overt toxicological effects at birth (e.g. body weight and morphologic abnormalities). Notably, most targeted behavioural responses converge on locomotor activity and emotional profile, often, but not always, leading to a disinhibitory/hyperactive profile.

Effects of polycyclic aromatic hydrocarbons (PAHs) on pregnancy, placenta, and placental trophoblasts

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic pollutants that are carcinogenic, mutagenic, endocrine-toxic, and immunotoxic. PAHs can be found in maternal and fetal blood and in the placenta during pregnancy. They may thus affect placental and fetal development. Therefore, the exposure levels and toxic effects of PAHs in the placenta deserve further study and discussion. This review aims to summarize current knowledge on the effects of PAHs and their metabolites on pregnancy and birth outcomes and on placental trophoblast cells. A growing number of epidemiological studies detected PAH-DNA adducts as well as the 16 high-priority PAHs in the human placenta and showed that placental PAH exposure is associated with adverse fetal outcomes. Trophoblasts are important cells in the placenta and are involved in placental development and function. In vitro studies have shown that exposure to either PAH mixtures, benzo(a)pyrene (BaP) or BaP metabolite benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE) affected trophoblast cell viability, differentiation, migration, and invasion through various signaling pathways. Furthermore, similar effects of BPDE on trophoblast cells could also be observed in BaP-treated mouse models and were related to miscarriage. Although the current data show that PAHs may affect placental trophoblast cells and pregnancy outcomes, further studies (population studies, in vitro studies, and animal studies) are necessary to show the specific effects of different PAHs on placental trophoblasts and pregnancy outcomes.

Prenatal exposure to benzo[a]pyrene depletes ovarian reserve and masculinizes embryonic ovarian germ cell transcriptome transgenerationally

People are widely exposed to polycyclic aromatic hydrocarbons, like benzo[a]pyrene (BaP). Prior studies showed that prenatal exposure to BaP depletes germ cells in ovaries, causing earlier onset of ovarian senescence post-natally; developing testes were affected at higher doses than ovaries. Our primary objective was to determine if prenatal BaP exposure results in transgenerational effects on ovaries and testes. We orally dosed pregnant germ cell-specific EGFP-expressing mice (F0) with 0.033, 0.2, or 2 mg/kg-day BaP or vehicle from embryonic day (E) 6.5-11.5 (F1 offspring) or E6.5-15.5 (F2 and F3). Ovarian germ cells at E13.5 and follicle numbers at postnatal day 21 were significantly decreased in F3 females at all doses of BaP; testicular germ cell numbers were not affected. E13.5 germ cell RNA-sequencing revealed significantly increased expression of male-specific genes in female germ cells across generations and BaP doses. Next, we compared the ovarian effects of 2 mg/kg-day BaP dosing to wild type C57BL/6J F0 dams from E6.5-11.5 or E12.5-17.5. We observed no effects on F3 ovarian follicle numbers with either of the shorter dosing windows. Our results demonstrate that F0 BaP exposure from E6.5-15.5 decreased the number of and partially disrupted transcriptomic sexual identity of female germ cells transgenerationally.

Adolescent exposure to low-dose Δ9-tetrahydrocannabinol depletes the ovarian reserve in female mice

Cannabis use by adolescents is widespread, but its effects on the ovaries remain largely unknown. Δ9-tetrahydrocannabinol (THC) exerts its pharmacological effects by activating, and in some conditions hijacking, cannabinoid receptors (CBRs). We hypothesized that adolescent exposure to THC affects ovarian function in adulthood. Peripubertal female C57BL/6N mice were given THC (5 mg/kg) or its vehicle, once daily by intraperitoneal injection. Some mice received THC from postnatal day (PND) 30-33 and their ovaries were harvested PND34; other mice received THC from PND30-43, and their ovaries were harvested PND70. Adolescent treatment with THC depleted ovarian primordial follicle numbers by 50% at PND70, 4 weeks after the last dose. The treatment produced primordial follicle activation, which persisted until PND70. THC administration also caused DNA damage in primary follicles and increased PUMA protein expression in oocytes of primordial and primary follicles. Both CB1R and CB2R were expressed in oocytes and theca cells of ovarian follicles. Enzymes involved in the formation (N-acylphosphatidylethanolamine phospholipase D) or deactivation (fatty acid amide hydrolase) of the endocannabinoid anandamide were expressed in granulosa cells of ovarian follicles and interstitial cells. Levels of mRNA for CBR1 were significantly increased in ovaries after adolescent THC exposure, and upregulation persisted for at least 4 weeks. Our results support that adolescent exposure to THC may cause aberrant activation of the ovarian endocannabinoid system in female mice, resulting in substantial loss of ovarian reserve in adulthood. Relevance of these findings to women who frequently used cannabis during adolescence warrants investigation.

Gestational Benzo[a]pyrene Exposure Destroys F1 Ovarian Germ Cells Through Mitochondrial Apoptosis Pathway and Diminishes Surviving Oocyte Quality

Polycyclic aromatic hydrocarbons, including benzo[a]pyrene (BaP), are products of incomplete combustion. In female mouse embryos primordial germ cells proliferate before and after arriving at the gonadal ridge around embryonic (E) 10 and begin entering meiosis at E13.5. Now oocytes, they arrest in the first meiotic prophase beginning at E17.5. We previously reported dose-dependent depletion of ovarian follicles in female mice exposed to 2 or 10 mg/kg-day BaP E6.5-15.5. We hypothesized that embryonic ovaries are more sensitive to gestational BaP exposure during the mitotic developmental window, and that this exposure results in persistent oxidative stress in ovaries and oocytes of exposed F1 female offspring. We orally dosed timed-pregnant female mice with 0 or 2 mg/kg-day BaP in oil from E6.5-11.5 (mitotic window) or E12.5-17.5 (meiotic window). Cultured E13.5 ovaries were utilized to investigate the mechanism of BaP-induced germ cell death. We observed statistically significant follicle depletion and increased ovarian lipid peroxidation in F1 pubertal ovaries following BaP exposure during either prenatal window. Culture of E13.5 ovaries with BaP induced germ cell DNA damage and release of cytochrome c from the mitochondria in oocytes, confirming that BaP exposure induced apoptosis via the mitochondrial pathway. Mitochondrial membrane potential, oocyte lipid droplet (LD) volume, and mitochondrial-LD colocalization were decreased and mitochondrial superoxide levels were increased in the MII oocytes of F1 females exposed gestationally to BaP. Results demonstrate similar sensitivity to germ cell depletion and persistent oxidative stress in F1 ovaries and oocytes following gestational BaP exposure during mitotic or meiotic windows.

Benzo[a]pyrene—Environmental Occurrence, Human Exposure, and Mechanisms of Toxicity

Benzo[a]pyrene (B[a]P) is the main representative of polycyclic aromatic hydrocarbons (PAHs), and has been repeatedly found in the air, surface water, soil, and sediments. It is present in cigarette smoke as well as in food products, especially when smoked and grilled. Human exposure to B[a]P is therefore common. Research shows growing evidence concerning toxic effects induced by this substance. This xenobiotic is metabolized by cytochrome P450 (CYP P450) to carcinogenic metabolite: 7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE), which creates DNA adducts, causing mutations and malignant transformations. Moreover, B[a]P is epigenotoxic, neurotoxic, and teratogenic, and exhibits pro-oxidative potential and causes impairment of animals’ fertility. CYP P450 is strongly involved in B[a]P metabolism, and it is simultaneously expressed as a result of the association of B[a]P with aromatic hydrocarbon receptor (AhR), playing an essential role in the cancerogenic potential of various xenobiotics. In turn, polymorphism of CYP P450 genes determines the sensitivity of the organism to B[a]P. It was also observed that B[a]P facilitates the multiplication of viruses, which may be an additional problem with the widespread COVID-19 pandemic. Based on publications mainly from 2017 to 2022, this paper presents the occurrence of B[a]P in various environmental compartments and human surroundings, shows the exposure of humans to this substance, and describes the mechanisms of its toxicity.

The effects of polycyclic aromatic compounds (PACs) on mammalian ovarian function

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Toxicity of polycyclic aromatic compounds (PACs) is limited to a subset of PACs.

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Exposure to these compounds impact major processes necessary for ovarian function.

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PAC exposure causes follicle loss and aberrant steroid production and angiogenesis.

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PAC exposure may increase the risk for impaired fertility and ovarian pathologies.

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The study of PACs as ovarian toxicants should include additional compounds.

Polycyclic aromatic compounds (PACs) are a broad class of contaminants ubiquitously present in the environment due to natural and anthropogenic activities. With increasing industrialization and reliance on petroleum worldwide, PACs are increasingly being detected in different environmental compartments. Previous studies have shown that PACs possess endocrine disruptive properties as these compounds often interfere with hormone signaling and function. In females, the ovary is largely responsible for regulating reproductive and endocrine function and thus, serves as a primary target for PAC-mediated toxicity. Perturbations in the signaling pathways that mediate ovarian folliculogenesis, steroidogenesis and angiogenesis can lead to adverse reproductive outcomes including polycystic ovary syndrome, premature ovarian insufficiency, and infertility. To date, the impact of PACs on ovarian function has focused predominantly on polycyclic aromatic hydrocarbons like benzo(a)pyrene, 3-methylcholanthrene and 7,12-dimethylbenz[a]anthracene. However, investigation into the impact of substituted PACs including halogenated, heterocyclic, and alkylated PACs on mammalian reproduction has been largely overlooked despite the fact that these compounds are found in higher abundance in free-ranging wildlife. This review aims to discuss current literature on the effects of PACs on the ovary in mammals, with a particular focus on folliculogenesis, steroidogenesis and angiogenesis, which are key processes necessary for proper ovarian functions.