Benzo[a]pyrene exposure disrupts the organelle distribution and function of mouse oocytes

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon compound that is generated during combustion processes, and is present in various substances such as foods, tobacco smoke, and burning emissions. BaP is extensively acknowledged as a highly carcinogenic substance to induce multiple forms of cancer, such as lung cancer, skin cancer, and stomach cancer. Recently it is shown to adversely affect the reproductive system. Nevertheless, the potential toxicity of BaP on oocyte quality remains unclear. In this study, we established a BaP exposure model via mouse oral gavage and found that BaP exposure resulted in a notable decrease in the ovarian weight, number of GV oocytes in ovarian, and oocyte maturation competence. BaP exposure caused ribosomal dysfunction, characterized by a decrease in the expression of RPS3 and HPG in oocytes. BaP exposure also caused abnormal distribution of the endoplasmic reticulum (ER) and induced ER stress, as indicated by increased expression of GRP78. Besides, the Golgi apparatus exhibited an abnormal localization pattern, which was confirmed by the GM130 localization. Disruption of vesicle transport processes was observed by the abnormal expression and localization of Rab10. Additionally, an enhanced lysosome and LC3 fluorescence intensity indicated the occurrence of protein degradation in oocytes. In summary, our results suggested that BaP exposure disrupted the distribution and functioning of organelles, consequently affecting the developmental competence of mouse oocytes.

Disease burden and health risk to rural communities of northeastern India from indoor cooking-related exposure to parent, oxygenated and alkylated PAHs

Exposure to a total of 51 targeted and non-targeted polycyclic aromatic hydrocarbons (PAHs) and their oxygenated and alkylated derivatives associated with size-segregated aerosol was investigated in rural kitchens using liquefied petroleum gas (LPG), mixed biomass (MB) and firewood (FW) fuels in northeastern India. The averaged PM10-associated parent-, alkylated-, and oxygenated-PAHs concentrations increased notably from LPG (257, 54, and 116 ng m-3) to MB (838, 119, and 272 ng m-3) to FW-using kitchens (2762, 225, and 554 ng m-3), respectively. PAHs were preferentially associated with the PM1 fraction with contributions increasing from 80 % in LPG to 86 % in MB and 90 % in FW-using kitchens, which in turn was dominated by <0.25 μm particles (54-75 % of the total). A clear profile of enrichment of low-molecular weight PAHs in cleaner fuels (LPG) and a contrasting enrichment of high-molecular weight PAHs in biomass-based fuels was noted. The averaged internal dose of Benzo[a]pyrene equivalent was the lowest in the case of LPG (19 ng m-3), followed by MB (161 ng m-3) and the highest in FW users (782 ng m-3). Estimation of incremental lifetime cancer risk (ILCR) from PAH exposure revealed extremely high cancer risk in biomass users (factors of 8-40) compared to LPG. The potential years of life lost (PYLL) and PYLL rate averaged across kitchen categories was higher for lung cancer (PYLL: 10.55 ± 1.04 years; PYLL rate: 204 ± 426) compared to upper respiratory tract cancer (PYLL: 10.02 ± 0.05 years; PYLL rate: 4 ± 7), and the PYLL rates for biomass users were higher by factors of 9-56 as compared to LPG users. These findings stress the need for accelerated governmental intervention to ensure a quick transition from traditional biomass-based fuels to cleaner alternatives for the rural population of northeastern India.

Prenatal benzo[a]pyrene exposure impairs hippocampal synaptic plasticity and cognitive function in SD rat offspring during adolescence and adulthood via HDAC2-mediated histone deacetylation

Benzo[a]pyrene (B[a]P) is a widespread carcinogenic pollutant in the environment. Although previous studies have demonstrated the neurodevelopmental toxicity of B[a]P, the precise mechanisms underlying the neurotoxic effects induced by prenatal B[a]P exposure remain largely unknown. In the present study, pregnant Sprague-Dawley (SD) rats were injected intraperitoneally with 0, 10, 20, or 40 mg/kg-bw of B[a]P for three consecutive days on embryonic days 17-19. The learning and memory abilities of offspring were determined by Morris Water Maze (MWM) test, while the number of dendritic branches and the density of dendritic spines in hippocampal CA1 and DG regions were evaluated by Golgi-Cox staining at PND 45 and PND 75. The mRNA expression of BDNF, PSD-95, and SYP in offspring hippocampus were detected by qRT-PCR, and the protein expression of BDNF, PSD-95, SYP, HDAC2, acH3K9, and acH3K14 were measured by Western blotting or immunohistochemistry. CHIP-PCR was performed to further detect the levels of acH3K9 and acH3K14 in the promoter regions of BDNF and PSD-95 genes. Our results showed that rats prenatally exposed to B[a]P exhibited impaired spatial learning and memory abilities and the number of dendritic branches and the density of dendritic spines in the hippocampal CA1 and DG regions were significantly reduced during adolescence and adulthood. The expression of HDAC2 protein was significantly upregulated, while acH3K9, acH3K14, BDNF, PSD-95, and SYP protein levels were significantly downregulated in the hippocampus of B[a]P- exposed rats. In addition, CHIP results showed that prenatal B[a]P exposure markedly decreased the level of acH3K9 and acH3K14 in the promoter region of BDNF and PSD-95 gene in the hippocampus of PND 45 and PND 75 offspring. All of the results suggest that prenatal B[a]P exposure impairs cognitive function and hippocampal synaptic plasticity of offspring in adolescence and adulthood, and HDAC2-mediated histone deacetylation plays a crucial role in these deficits.

Prenatal exposure of bonny light crude oil induces embryotoxicity, impaired cognitive functions and cortico-hippocampal neurodegeneration on fetal outcomes of pregnant sprague-dawley rats

The low Sulfur level, heavy metals and easy production rate of Bonny Light Crude Oil (BLCO) makes it one of Nigeria's most explored oil. This study investigated the memory impairments, embryotoxicity and cortico-hippocampal neurodegeneration induced by prenatal exposure to BLCO of pregnant Sprague-Dawley (S-D) rats. Twenty pregnant rats were divided into 4 groups (A-D) of 5 rats each. Group A received normal saline as placebo. Group B-D received oral doses of BLCO at 0.73 ml/kg, 2 ml/kg and 3.8 ml/kg on pregnancy day 8-12.5 respectively. The pregnant rats were allowed to litter and nurse their pups. At 6 weeks postnatal life, twelve (12) selected young rats (n = 12) were accessed for behavioral study (Y-maze) and then sacrificed for biochemical and histological analysis. The results showed spontaneous abortion, still births and significantly reduced number of live births in the high dose group of BLCO compared to control. Length of gestation was significantly increased in the high dose group when compared to the control. CAT levels reduced significantly with concomitant increase in 8-OHdG among BLCO treated groups compared to control. Spontaneous alteration and number of arm entries decreased in the BLCO groups in comparison to control. Histological observation showed reduced cellular size, chromatolysis and presence of extracellular senile plaques in the prefrontal cortex and mild histological changes in the hippocampus architecture in the BLCO treated groups compared to the control. BLCO is capable of inducing embryotoxicity, impair cognition and cortico-hippocampal neurodegeneration.

Benzo[a]pyrene injures BMP2-induced osteogenic differentiation of mesenchymal stem cells through AhR reducing BMPRII

Benzo[a]pyrene(BaP), a polycyclic aromatic hydrocarbons (PAH) of environmental pollutants, is one of the main ingredients in cigarettes and an agonist of the aryl hydrocarbon receptor (AhR). Mesenchymal stem cells (MSCs) including C3H10T1/2 and MEF cells, adult multipotent stem cells, can be differentiated toward osteoblasts during the induction of osteogenic induction factor-bone morphogenetic protein 2(BMP2). Accumulating evidence suggests that BaP decreases bone development in mammals, but the further mechanisms of BaP on BMP2-induced bone formation involved are unknown. Here, we researched the role of BaP on BMP2-induced osteoblast differentiation and bone formation. We showed that BaP significantly suppressed early and late osteogenic differentiation, and downregulated the runt-related transcription factor 2(Runx2), osteocalcin(OCN) and osteopontin (OPN) during the induction of BMP2 in MSCs. Consistent with in vitro results, administration of BaP inhibited BMP2-induced subcutaneous ectopic osteogenesis in vivo. Interestingly, blocking AhR reversed the inhibition of BaP on BMP2-induced osteogenic differentiation, which suggested that AhR played an important role in this process. Moreover, BaP significantly decreased BMP2-induced Smad1/5/8 phosphorylation. Furthermore, BaP significantly reduced bone morphogenetic protein receptor 2(BMPRII) expression and excessively activated Hey1. Thus, our data demonstrate the role of BaP in BMP2-induced bone formation and suggest that impaired BMP/Smad pathways through AhR regulating BMPRII and Hey1 may be an underlying mechanism for BaP inhibiting BMP2-induced osteogenic differentiation.

Integrated Epigenetics, Transcriptomics, and Metabolomics to Analyze the Mechanisms of Benzo[a]pyrene Neurotoxicity in the Hippocampus

Benzo[a]pyrene (B[a]P) is a common environmental pollutant that is neurotoxic to mammals, which can cause changes to hippocampal function and result in cognitive disorders. The mechanisms of B[a]P-induced impairments are complex .To date there have been no studies on the association of epigenetic, transcriptomic, and metabolomic changes with neurotoxicity after B[a]P exposure. In the present study, we investigated the global effect of B[a]P on DNA methylation patterns, noncoding RNAs (ncRNAs) expression, coding RNAs expression, and metabolites in the rat hippocampus. Male Sprague Dawley rats (SD rats) received daily gavage of B[a]P (2.0 mg/kg body weight [BW]) or corn oil for 7 weeks. Learning and memory ability was analyzed using the Morris water maze (MWM) test and change to cellular ultrastructure in the hippocampus was analyzed using electron microscope observation. Integrated analysis of epigenetics, transcriptomics, and metabolomics was conducted to investigate the effect of B[a]P exposure on the signaling and metabolic pathways. Our results suggest that B[a]P could lead to learning and memory deficits, likely as a result of epigenetic and transcriptomic changes that further affected the expression of CACNA1C, Tpo, etc. The changes in expression ultimately affecting LTP, tyrosine metabolism, and other important metabolic pathways.

[Changes of cerebral cortical metabolomics in rats following benzo[a]pyrene exposure]

OBJECTIVE

To analyze the changes in endogenous small molecule metabolites after benzo[a]pyrene (B[a]P) exposure in rat cerebral cortex and explore the mechanism of B[a]P neurotoxicity.

METHODS

Five-day-old SD rats were subjected to gavage administration of 2 mg/kg B[a]P for 7 consecutive weeks. After the exposure, the rats were assessed for spatial learning ability using Morris water maze test, ultrastructural changes of the cortical neurons under electron microscope, and metabolite profiles of the cortex using GC/MS. The differential metabolites between the exposed and control rats were identified with partial least squares discriminant analysis (PLS-DA) and the metabolic pathways related with the differential metabolites were analyzed using Cytoscape software.

RESULTS

Compared with the control group, the rats exposed to B[a]P showed significantly increased escape latency (P<0.05) and decreased time spent in the target area (P<0.05). The exposed rats exhibited widened synaptic cleft, thickened endplate membrane and swollen cytoplasm compared with the control rats. Eighteen differential metabolites (VIP>1, P<0.05) in the cortex were identified between the two groups, and 9 pathways associated with B[a]P neurotoxicity were identified involving amino acid metabolism, tricarboxylic acid cycle and Vitamin B3 (niacin and nicotinamide) metabolism.

CONCLUSION

B[a]P can cause disturbance in normal metabolisms and its neurotoxicity is possibly related with disorders in amino acid metabolism, tricarboxylic acid cycle and vitamin metabolism.

Neonatal Benzo[a]pyrene Exposure Induces Oxidative Stress and DNA Damage Causing Neurobehavioural Changes during the Early Adolescence Period in Rats

Humans are exposed to polycyclic aromatic hydrocarbons (PAHs) by ingestion of contaminated food and water. Prenatal exposure to benzo[a]pyrene (B[a]P) like PAHs through the placental barrier and neonatal exposure by breast milk and the environment may affect early brain development. In the present study, single intracisternal administration of B[a]P (0.2 and 2.0 µg/kg body weight) to male Wistar rat pups at postnatal day 5 (PND5) was carried out to study its specific effect on neonatal brain development and its consequences at PND30. B[a]P administration showed a significant increase in exploratory and anxiolytic-like behaviour with elevated hippocampal lipid peroxidation and protein oxidation at PND30. Further, DNA damage was estimated in vitro (Neuro2a and C6 cell lines) by the comet assay, and oxidative DNA damage of hippocampal sections was measured in vivo following exposure to B[a]P. DNA strand breaks (single and double) significantly increased due to B[a]P at PND30 in hippocampal neurons and increased the nuclear tail moment in Neuro2a cells. Hippocampal 8-oxo-2′-deoxyguanosine production was significantly elevated showing expression of more TUNEL-positive cells in both doses of B[a]P. Histological studies also revealed a significant reduction in mean area and perimeter of hippocampal neurons in rats treated with B[a]P 2.0 μg/kg, when compared to naïve and control rats. B[a]P significantly increased anxiolytic-like behaviour and oxidative DNA damage in the hippocampus causing apoptosis that may lead to neurodegeneration in adolescence. The findings of the present study address the potential role of B[a]P in inducing oxidative stress-mediated neurodegeneration in the hippocampus through oxidative DNA damage in the early adolescence period of rats.

Impact of prenatal polycyclic aromatic hydrocarbon exposure on behavior, cortical gene expression and DNA methylation of the Bdnf gene

Prenatal exposure to polycyclic aromatic hydrocarbons (PAH) has been associated with sustained effects on the brain and behavior in offspring. However, the mechanisms have yet to be determined. We hypothesized that prenatal exposure to ambient PAH in mice would be associated with impaired neurocognition, increased anxiety, altered cortical expression of Bdnf and Grin2b, and greater DNA methylation of Bdnf. Our results indicated that during open-field testing, prenatal PAH exposed offspring spent more time immobile and less time exploring. Females produced more fecal boli. Offspring prenatally exposed to PAH displayed modest reductions in overall exploration of objects. Further, prenatal PAH exposure was associated with lower cortical expression of Grin2b and Bdnf in males, and greater Bdnf IV promoter methylation. Epigenetic differences within the Bdnf IV promoter correlated with Bdnf gene expression, but not with the observed behavioral outcomes, suggesting that additional targets may account for these PAH-associated effects.

Subchronic oral administration of Benzo[a]pyrene impairs motor and cognitive behavior and modulates S100B levels and MAPKs in rats

Benzo[a]pyrene (BaP) is an environmental contaminant produced during incomplete combustion of organic material that is well known as a mutagenic and carcinogenic toxin. There are few studies addressing the molecular and cellular basis of behavioural alterations related to BaP exposure. The aim of this study was to evaluate the effect of subchronic oral administration of BaP on behavioral and neurochemical parameters. Wistar male rats received BaP (2 mg/kg) or corn oil (control), once a day for 28 days (n = 12/group). Spontaneous locomotor activity and short- and long-term memories were evaluated. Glial fibrillary acid protein and S100B content in the hippocampus, serum and CSF were measured using ELISA and total and phosphorylated forms of mitogen activated protein kinases (MAPKs) named extracellular signal-regulated kinases 1 and 2, p38(MAPK) and c-Jun amino-terminal kinases 1 and 2, in the hippocampus, were evaluated by western blotting. BaP induced a significant increase on locomotor activity and a decrease in short-term memory. S100B content was increased significantly in cerebrospinal fluid. BaP induced a decrease on ERK2 phosphorylation in the hippocampus. Thus, BaP subchronic treatment induces an astroglial response and impairs both motor and cognitive behavior, with parallel inhibition of ERK2, a signaling enzyme involved in the hippocampal neuroplasticity. All these effects suggest that BaP neurotoxicity is a concern for environmental pollution.

Modulation of benzo[a]pyrene induced neurotoxicity in female mice actively immunized with a B[a]P-diphtheria toxoid conjugate

Benzo[a]pyrene (B[a]P) is a small molecular weight carcinogen and the prototype of polycyclic aromatic hydrocarbons (PAHs). While these compounds are primarily known for their carcinogenicity, B[a]P and its metabolites are also neurotoxic for mammalian species. To develop a prophylactic immune strategy against detrimental effects of B[a]P, female Balb/c mice immunized with a B[a]P-diphtheria toxoid (B[a]P-DT) conjugate vaccine were sub-acutely exposed to 2mg/kg B[a]P and behavioral performances were monitored in tests related to learning and memory, anxiety and motor coordination. mRNA expression of the NMDA receptor (NR1, 2A and 2B subunits) involved in the above behavioral functions was measured in 5 brain regions. B[a]P induced NMDA1 expression in three (hippocampus, amygdala and cerebellum) of five brain regions investigated, and modulated NMDA2 in two of the five brain regions (frontal cortex and cerebellum). Each one of these B[a]P-effects was reversed in mice that were immunized against this PAH, with measurable consequences on behavior such as anxiety, short term learning and memory. Thus active immunization against B[a]P with a B[a]P-DT conjugate vaccine had a protective effect and attenuated the pharmacological and neurotoxic effects even of high concentrations of B[a]P.

Silymarin prevents benzo(a)pyrene-induced toxicity in Wistar rats by modulating xenobiotic-metabolizing enzymes

Benzo(a)pyrene (B(a)P), which is commonly used as an indicator species for polycyclic aromatic hydrocarbon (PAH) contamination, has a large number of hazardous consequences on human health. In the presence of the enzyme cytochrome-P-450 1A1 (CYP1A1), it undergoes metabolic activation to form reactive intermediates that are capable of inducing mutagenic, cytotoxic, teratogenic and carcinogenic effects in various species and tissues. Research within the last few years has shown that flavonoids exhibit chemopreventive effect against these toxins. In the present study, the protective effect of silymarin (a flavonoid) against B(a)P-induced toxicity was monitored in Wistar rats by evaluating the levels of hepatic phase I (CYP1A1), phase II enzymes (glutathione-S-transferase, epoxide hydroxylases, uridinediphosphate glucuronosyltransferases, NAD(P)H: quinone oxidoreductase 1, sulfotransferases), cellular antioxidant enzyme heme oxygenase and total glutathione. The results reveal that silymarin possesses substantial protective effect against B(a)P-induced damages by inhibiting phase I detoxification enzyme CYP1A1 and modulating phase II conjugating enzymes, which were confirmed by histopathological analysis. Overall, the inhibition of CYP1A1 and the modulation of phase II enzymes may provide, in part, the molecular basis for the effect of silymarin against B(a)P.

Spatial learning and memory deficit of low level polybrominated diphenyl ethers-47 in male adult rat is modulated by intracellular glutamate receptors

Polybrominated diphenyl ethers (PBDEs), a class of widely used flame retardants, are extensively diffused in the environment. Of particular concern are the reported highly sensitivity of PBDEs in children or developmental animals, however, almost no information is available on their potential effects on adults and the mechanisms are still unknown. In the present study, we investigated the neurotoxic effects of sub-chronic PBDE-47 exposure on adult male Sprague-Dawley rats. Thus, PBDE-47, 0.1, 0.5 and 1 mg/kg per day was administered to rats by gavage for 30 days. The learning and memory function was tested by Morris water maze. Further, in order to explore the potential mechanism, the expression of NMDA-receptors was evaluated by using both immunohistochemistry (IHC) and RT-PCR. Our results showed that sub-chronic exposure to PBDE-47 produced learning and memory deficits in male adult rats. Also, significant decrease in the CA1, CA3 and dentate gyrus areas of hippocampus affected by all three doses of PBDE-47 on the expression of NR(1), NR(2)B and Glu were found by IHC. In addition, the evaluation of expression of the NR(1), NR(2)B and NR(2)C showed statistically significant decrease in mRNA expression in rats exposed to PBDE-47. These findings showed that sub-chronic exposure to PBDE-47 could also induce behavioral alterations and the neurotoxic effects might due to the down-regulation expression of NMDA receptors. Our data indicated that the possibility of exposure of adults to PBDE-47 warranted further studies to characterize their potential neurotoxicity.

Early postnatal benzo(a)pyrene exposure in Sprague-Dawley rats causes persistent neurobehavioral impairments that emerge postnatally and continue into adolescence and adulthood

Previous studies have demonstrated that benzo(a)pyrene (BaP) may disrupt the development of key biological systems, thus leaving children more vulnerable to functional impairments in adulthood. The current study was conducted to determine whether neurotoxic effects of postnatal BaP exposure on behavioral performance persist in juvenile and young adult stages. Therefore, neonate Sprague-Dawley pups were given oral doses of BaP (0.02, 0.2, and 2 mg/kg/day) continuing through a period of rapid brain development (on postnatal days [PNDs] 5-11). Further, developmental milestones and behavioral endpoints assessing sensory and motor maturation were examined. Also, in this study, Morris water maze and elevated plus maze were used for evaluating the cognitive function and anxiety-like behavior. Our results showed that there was altered ontogeny in a few measures of neuromotor development; however, other developmental milestones and sensory responses were not altered significantly. Moreover, the locomotor activity deficit in BaP-treated pups was evident at PND 36 and was most pronounced in the PND 69. Also, exposure to BaP during early postnatal development had an adverse effect on adult rats (PND 70) in the elevated plus maze, and the swim maze suggests that low doses of BaP impair spatial learning functions at adult test period. In contrast, BaP exposure had no evident effect on behaviors in these two mazes for adolescent animals. These data clearly indicate that behavioral impairments resulting from postnatal BaP exposure are potentially long-lasting and may not be apparent in juveniles, but are present in young adulthood.