Benzo(a)pyrene-induced morphologic and developmental abnormalities in rainbow trout

In vitro and in silico AHR assays for assessing the risk of heavy oil-derived polycyclic aromatic hydrocarbons in fish

In the aftermath of the Great East Japan Earthquake of March 11, 2011, marine fish in Kesennuma Bay, Japan, have been contaminated with heavy oil containing polycyclic aromatic hydrocarbons (PAHs). To estimate the risk of six PAHs (benzo[α]pyrene, dibenzothiophene, phenanthrene, 2,3,5-trimethylnaphthalene, acenaphthene, and 1-methylphenanthrene), which have been detected at high levels in the tissues of fish from Kesennuma Bay, we attempted to evaluate the effects of these PAHs on the fish aryl hydrocarbon receptor (AHR) signaling pathway. We initially measured PAH concentrations and cytochrome P4501A catalytic activities (EROD: ethoxyresorufin-O-deethylase and MROD: methoxyresorufin-O-demethylase) as markers of AHR activation in greenlings (Hexagrammos otakii) collected from Kesennuma Bay in 2014. The results showed that alkylated PAH concentrations and EROD/MROD activities were higher in sites close to the oil-spilled sites than in the control site, suggesting AHR activation by spilled alkylated PAHs. We then investigated AHR-mediated responses to these PAHs in the in vitro reporter gene assay system where red seabream (Pagrus major) AHR1 (rsAHR1) or rsAHR2 expression plasmids were transiently transfected into COS-7 cells. The in vitro assay showed rsAHR isoform-, PAH-, and dose-dependent transactivation potencies. The relative effective concentrations of benzo[α]pyrene, dibenzothiophene, phenanthrene, 2,3,5-trimethylnaphthalene, acenaphthene, and 1-methylphenanthrene that induce 20% of the maximum benzo[α]pyrene response (REC_20-BaP) for rsAHR1 activation were 0.052, 38, 79, 88, 270 nM, and no response, respectively, and those for rsAHR2 activation were 0.0049, 32, 53, 88, 60 nM, and no response, respectively. The results showed that the REC_20-BaP values of benzo[α]pyrene for both the rsAHR1 and rsAHR2 isoforms were lower than the concentrations (0.041-0.20 nM) detected in the muscle tissue of fish from Kesennuma Bay, while the REC_20-BaP values of other PAHs were higher than their tissue concentrations. In silico rsAHR homology modeling and subsequent ligand docking simulation analyses indicated that the rsAHR activation potencies of PAHs could be predicted from a rsAHR2 model. This study shows that in vitro and in silico rsAHR analyses may be a useful tool for assessing the risks to fish contaminated with PAHs.

Fish as a model to assess chemical toxicity in bone

Environmental toxicology has been expanding as growing concerns on the impact of produced and released chemical compounds over the environment and human health are being demonstrated. Among the toxic effects observed in organisms exposed to pollutants, those affecting skeletal tissues (osteotoxicity) have been somehow overlooked in comparison to hepato-, immune-, neuro- and/or reproductive toxicities. Nevertheless, sub-lethal effects of toxicants on skeletal development and/or bone maintenance may result in impaired growth, reduced survival rate, increased disease susceptibility and diminished welfare. Osteotoxicity may occur by acute or chronic exposure to different environmental insults. Because of biologically and technically advantagous features - easy to breed and inexpensive to maintain, external and rapid rate of development, translucent larvae and the availability of molecular and genetic tools - the zebrafish (Danio rerio) has emerged in the last decade as a vertebrate model system of choice to evaluate osteotoxicity. Different experimental approaches in fish species and analytical tools have been applied, from in vitro to in vivo systems, from specific to high throughput methodologies. Current knowledge on osteotoxicity and underlying mechanisms gained using fish, with a special emphasis on zebrafish systems, is reviewed here. Osteotoxicants have been classified into four categories according to the pathway involved in the transduction of the osteotoxic effects: activation/inhibition of membrane and/or nuclear receptors, alteration of redox condition, mimicking of bone constituents and unknown pathways. Knowledge on these pathways is also reported here as it may provide critical insights into the development, production and release of future chemical compounds with none or low osteotoxicity, thus promoting the green/environmental friendly chemistry.

Rainbow trout exposed to benzo[a]pyrene yields conserved microRNA binding sites in DNA methyltransferases across 500 million years of evolution

The objective of this study was to examine the regulation of DNA methylation following acute (24 h) and prolonged (14 d) exposure to low (1 ng/L) and high (10 ng/L) benzo[a]pyrene. However, with the recent release of the rainbow trout genome, we were able to conduct a more detailed analysis regarding the regulation of the enzymes involved in DNA methylation; DNA methyltransferases (DNMTs). Bioinformatic approaches were used to identify candidate microRNA (miRNA) that potentially bind to the DNMT1 and DNMT3a 3′UTR. Results indicated a significant decrease in global methylation in both liver and muscle, with an associated decrease in DNA methyltransferase activity and DNMT3a transcript abundance. There was a significant increase in one specific candidate miRNA (miR29a) that was predicted to bind to DNMT3a. Taking a comparative genomics approach, the binding sites of miR29a to the DNMT3a 3′UTR was compared across species, spanning fish to mammals, and revealed a highly conserved binding motif that has been maintained since the vertebrate ancestor, approximately 500 million years ago. This research establishes that miRNA act as an essential mediator between the environment and DNA methylation patterns via DNMTs, which is further confirmed by a genomic regulatory mechanism that has been deeply conserved throughout evolution.

Assessing Aromatic-Hydrocarbon Toxicity to Fish Early Life Stages Using Passive-Dosing Methods and Target-Lipid and Chemical-Activity Models

Aromatic hydrocarbons (AH) are known to impair fish early life stages (ELS). However, poorly defined exposures often confound ELS-test interpretation. Passive dosing (PD) overcomes these challenges by delivering consistent, controlled exposures. The objectives of this study were to apply PD to obtain 5 d acute embryo lethality and developmental data and 30 d chronic embryo-larval survival and growth-effects data using zebrafish with different AHs; to analyze study and literature toxicity data using target-lipid (TLM) and chemical-activity (CA) models; and to extend PD to a mixture and test the assumption of AH additivity. PD maintained targeted exposures over a concentration range of 6 orders of magnitude. AH toxicity increased with log Kow up to pyrene (5.2). Pericardial edema was the most sensitive sublethal effect that often preceded embryo mortality, although some AHs did not produce developmental effects at concentrations causing mortality. Cumulative embryo-larval mortality was more sensitive than larval growth, with acute-to-chronic ratios of <10. More-hydrophobic AHs did not exhibit toxicity at aqueous saturation. The relationship and utility of the TLM-CA models for characterizing fish ELS toxicity is discussed. Application of these models indicated that concentration addition provided a conservative basis for predicting ELS effects for the mixture investigated.

Indoor air pollution and the risk of orofacial clefts in a rural population in Shanxi province, China

BACKGROUND

Shanxi Province is a region in China with a high incidence of orofacial clefts (OFCs). Our objective is to investigate the effect of maternal exposure to indoor air pollution (IAP) from coal combustion and tobacco smoke on the risk of an infant being born with orofacial clefts.

METHODS

Data were derived from an ongoing population-based case-control study of major external structural birth defects in Shanxi Province. Subjects included 213 cases with OFCs and 1319 healthy babies born between November 2002 and December 2014 in four rural counties. Exposure information was collected by face-to-face interview with mothers within 1 week of delivery or pregnancy termination. The authors derived an exposure index by integrating a series of IAP-related characteristics concerning dwelling and lifestyle.

RESULTS

Increased odds of OFC were associated with IAP exposure from heating (adjusted odds ratio [aOR] = 2.4; 95% confidence interval [CI], 1.2-4.5) and from smoking (aOR = 1.8; 95% CI: 1.3, 2.5), but not with exposure from cooking (aOR = 0.9; 95% CI, 0.6-1.4). Compared with women without IAP exposure, the aORs of OFC for children of women with exposure indices of 1, 2, 3 and ≥ 4 were 1.1 (95% CI, 0.6-1.8), 1.4 (95% CI, 0.8-2.4), 1.8 (95% CI, 1.0-3.2), and 3.4 (95% CI, 1.6-7.4), respectively, demonstrating a clear dose-response trend (p < 0.001).

CONCLUSION

Periconceptional exposure to IAP from coal combustion and tobacco smoking may increase the risk of OFCs in offsprings of women in Shanxi Province. Birth Defects Research (Part A) 106:708-715, 2016. © 2016 Wiley Periodicals, Inc.

Genotoxicity of oxy-PAHs to Japanese medaka (Oryzias latipes) embryos assessed using the comet assay

Polycyclic aromatic hydrocarbons (PAHs) have long been recognized as important environmental toxicants. Despite a plethora of information on the fate and effects of parent PAHs, relatively little is known about the environmental fate and toxicity of ketone- and quinone-substituted PAH oxidation products (termed oxy-PAHs), particularly in the aquatic environment. This study begins to fill that gap using embryos of the Japanese medaka (Oryzias latipes) as a model species. The genotoxic potential of two environmentally relevant oxy-PAHs, acenaphthenequinone and 7,12-benz[a]anthracenquinone, was assessed using the comet assay. We found that both oxy-PAHs could cause significant increases in DNA damage after only 48 h of exposure at the lowest concentrations tested (5 μg/L). Comparisons of the genotoxic potential between these oxy-PAHs and their corresponding parent PAHs (acenaphthene and benz[a]anthracene) and a well-known mutagenic PAH, benzo[a]pyrene, indicated similar potencies among all five of these compounds, particularly after longer (7 day) exposures. This study demonstrates the mutagenic potential of oxy-PAHs to an in vivo fish embryo model and points out the need for further study of their environmental occurrence and biologic effects.

In utero exposure to benzo(a)pyrene predisposes offspring to cardiovascular dysfunction in later-life

In utero exposure of the fetus to benzo(a)pyrene [B(a)P], a polycyclic aromatic hydrocarbon, is thought to dysregulate cardiovascular development. To investigate the effects of in utero B(a)P exposure on cardiovascular development, timed-pregnant Long Evans Hooded (LEH) rats were exposed to diluent or B(a)P (150, 300, 600 and 1200 μg/kg/BW) by oral gavage on embryonic (E) days E14 (the metamorphosing embryo stage) through E17 (the 1st fetal stage). There were no significant effects of in utero exposure to B(a)P on the number of pups born per litter or in pre-weaning growth curves. Pre-weaning profiles for B(a)P metabolite generation from cardiovascular tissue were shown to be dose-dependent and elimination of these metabolites was shown to be time-dependent in exposed offspring. Systolic blood pressure on postnatal day P53 in the middle and high exposure groups of offspring were significantly elevated as compared to controls. Microarray and quantitative real-time PCR results were directly relevant to a biological process pathway in animal models for "regulation of blood pressure". Microarray and quantitative real-time PCR analysis revealed upregulation of mRNA expression for angiotensin (AngII), angiotensinogen (AGT) and endothelial nitric oxide synthase (eNOS) in exposed offspring. Biological network analysis and gene set enrichment analysis subsequently identified potential signaling mechanisms and molecular pathways that might explain the elevated systolic blood pressures observed in B(a)P-exposed offspring. Our findings suggest that in utero exposure to B(a)P predispose offspring to functional deficits in cardiovascular development that may contribute to cardiovascular dysfunction in later life.

Biochemical response of anthracene and benzo [a] pyrene in milkfish Chanos chanos

Polycyclic aromatic hydrocarbons (PAHs) are common toxic pollutants found in the aquatic environment, and the assessment of their impact on biota is of considerable concern. The aim of the present research was to study the acute toxicity, bioaccumulation and biochemical response of milkfish Chanos chanos (Forsskal) to two selected PAHs: anthracene and benzo [a] pyrene. Acute toxicity test results were evaluated by the Probit analysis method and 96h LC(50) values for C. chanos exposed to anthracene was 0.030mgl(-1) and 0.014mgl(-1) for benzo [a] pyrene. Bioaccumulation concentration of anthracene was high when compared to benzo [a] pyrene. Biomarkers indicative of neurotoxicity (acetylcholinesterase, AchE), oxidative stress (lipid peroxidation, LPO and catalase, CAT) and phase II biotransformation of xenobiotics (glutathione S transferase, GST and reduced glutathione, GSH) were measured to assess effects of selected PAHs. Anthracene and benzo [a] pyrene increase LPO and CAT level of C. chanos suggesting that these PAHs may induce oxidative stress. Both the PAHs inhibited AchE indicating that they have at least one mechanism of neurotoxicity in common: the disruption of cholinergic transmission by inhibition of AChE. An induction of C. chanos glutathione S-transferase (GST) activity was found in fish exposed to benzo [a] pyrene, while an inhibition was observed after exposure to anthracene. These results suggest that GST is involved in the detoxification of benzo [a] pyrene, but not of anthracene.

Indoor air pollution from coal combustion and the risk of neural tube defects in a rural population in Shanxi Province, China

The authors evaluated indoor air pollution from coal combustion (IAPCC) as a potential risk factor for neural tube defects (NTDs) in a rural population in Shanxi Province, China. The studied rural population has both high IAPCC exposure and a high prevalence of NTDs. A population-based case-control study was used to identify 610 NTD cases and 837 normal controls between November 2002 and December 2007. Information was collected within 1 week following delivery or pregnancy termination due to prenatal NTD diagnosis. The authors derived an exposure index by integrating a series of IAPCC-related characteristics concerning dwelling and lifestyle. Compared with women with no IAPCC exposure, women with any exposure at all had a 60% increased risk of having a child with an NTD (adjusted odds ratio (OR) = 1.6, 95% confidence interval (CI): 1.1, 2.1). An increased NTD risk was linked to both residential heating (adjusted OR = 1.7, 95% CI: 1.1, 2.4) and cooking (adjusted OR = 1.5, 95% CI: 1.1, 2.1). The risk increased with increases in the exposure index, showing a dose-response trend (P < 0.001). This is the first known study to link IAPCC to NTDs. Additional studies are needed to confirm the link between IAPCC and NTDs.

Acute effects of Benzo[a]pyrene, anthracene and a fuel oil on biomarkers of the common goby Pomatoschistus microps (Teleostei, Gobiidae)

The objective of this study was to investigate the effects of two different PAHs and a complex petrochemical mixture on the common goby, Pomatoschistus microps, using selected biomarkers as effect criteria. Benzo[a]pyrene (BaP) and anthracene were used as reference substances, while the water accommodated fraction of #4 fuel-oil (#4 WAF) was used as an example of a petrochemical mixture. P. microps was used since it is both a suitable bioindicator and a good test organism. Groups of fish were exposed to different concentrations of each of the test substances for 96 h and the activities of several enzymes commonly used as biomarkers were determined at the end of the bioassays. All the substances inhibited P. microps acetylcholinesterase (AChE) indicating that they have at least one mechanism of neurotoxicity in common: the disruption of cholinergic transmission by inhibition of AChE. An induction of lactate dehydrogenase (LDH) activity was found in fish exposed to BaP or to anthracene, suggesting an increase of the anaerobic pathway of energy production. On the contrary, inhibition of LDH was found in fish exposed to #4 WAF, suggesting a distinct effect of the mixture. An induction of P. microps glutathione S-transferase (GST) activity was found in fish exposed to BaP or to #4 WAF, while an inhibition was observed after exposure to anthracene. These results suggest that GST is involved in the detoxification of BaP and #4 WAF, but not of anthracene. All the substances increased catalase activity and isolated PAHs also increased superoxide dismutase, glutathione reductase and glutathione peroxidase activities, while #4 WAF did not cause significant alterations on these enzymes. These results suggest that all the substances may induce oxidative stress on P. microps, with BaP and anthracene apparently having more oxidative stress potential than #4 WAF.

Effects of oil sands process-affected waters and naphthenic acids on yellow perch (Perca flavescens) and Japanese medaka (Orizias latipes) embryonic development

Syncrude Canada Ltd. is currently developing environmentally acceptable oil sands process-affected water management methods as part of their land reclamation strategy. Surface waters of the "wet landscape" reclamation option characteristically have elevated concentrations of sodium sulphate and naphthenic acids (NAs), with low levels of PAHs. The following experiment compared early-life stage responses of yellow perch (Perca flavescens) to those of Japanese medaka (Oryzias latipes) when exposed to Mildred Lake settling basin (MLSB) surface water and a commercial sodium naphthenate (Na-NA) standard. Perch eggs were fertilized and incubated in: 100%, 50%, 20%, 4%, 0.8%, and 0.16% dilutions of MLSB water, as well as 20, 10, 5, 2.5, and 1.25 mg/l solutions of the commercial standard. Medaka embryos were exposed to the same treatments, post-fertilization. Both species demonstrated an increase in the incidence of deformity, and a decrease in length at hatch as NA concentrations increased. MLSB surface water contained higher levels of NAs than the commercial standard, however, showed consistently higher NA threshold effect concentrations for both species. Significant differences between the MLSB water and the Na-NA standard suggest that they contain NA congeners with different toxicity, or other compounds such as PAHs. Species differences in thresholds could be explained by the difference in developmental stage in which the exposures were initiated.

Correlation of 2,3,7,8-tetrachlorodibenzo-p-dioxin induction of cytochrome P4501A in vascular endothelium with toxicity in early life stages of lake trout

Edema and cardiovascular dysfunction occur in vertebrates exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during early development. This study examined cytochrome P4501A (CYP1A) induction in endothelium and its possible association with mortality due to the edema and vascular effects of TCDD in lake trout early life stages. Lake trout (Salvelinus namaycush) eggs were injected at 24-50 hr postfertilization with 0.2 microl of 50 mM phosphatidylcholine liposomes or liposomes containing TCDD to give seven doses ranging from 11 to 176 pg TCDD/g egg. Doses of TCDD greater than 44 pg/g egg elicited hemorrhages; yolk sac, pericardial, and meningial edema; craniofacial malformations; regional ischemia; growth retardation; and mortality at the sac fry stage of development. Expression of CYP1A was assessed at four developmental stages, by immunohistochemical analysis of serial sections of individual fish with monoclonal antibody 1-12-3 to teleost CYP1A. CYP1A staining occurred in endothelial cells of many organs of TCDD-exposed but not vehicle-exposed embryos at 1 week prehatch and sac fry at 2 weeks posthatch. Earlier developmental stages examined were negative for CYP1A expression at any dose of TCDD. The strongest response occurred in sac fry at TCDD doses greater than 88 pg TCDD/g egg but was detected at doses as low as 22 pg TCDD/g egg. CYP1A staining in endothelium appeared at lower doses and was stronger than that in other cell types, in both prehatch embryos and posthatch sac fry. Thus, the vascular system is a major initial site affected by TCDD in lake trout early life stages, and the vascular endothelium is a cell type uniquely sensitive to induction of CYP1A in these developing animals. Based on an index of immunohistochemical staining of CYP1A, endothelial CYP1A induction in sac fry by TCDD occurred with an ED50 of 64-69 pg TCDD/g egg, similar to the dose-response for mortality occurring during the sac fry stage of development (LD50 = 47 pg TCDD/g egg). The correlations seen here suggest that CYP1A or aryl hydrocarbon receptor (AhR) in the endothelium may be linked to early lesions that result in TCDD-induced vascular derangements leading to yolk sac, pericardial, and meningial edema that is associated with lake trout sac fry mortality, but the precise mechanism remains to be determined.

Toxicity of weathered coal tar for shortnose sturgeon (Acipenser brevirostrum) embryos and larvae

Weathered coal tar collected from the Connecticut River near Holyoke, Massachusetts, was toxic to shortnose sturgeon embryos and larvae in whole sediment flow-through and elutriate static-renewal laboratory exposures. Sterile laboratory sand and clean Connecticut River sand, collected upstream from the coal tar deposits, produced no significant difference in toxicity to sturgeon embryos-larvae, while coal tar-contaminated sediment produced over 95% embryo-larval mortality. Hydrocarbon transfer and subsequent toxicity appeared to be via direct contact of the embryos with contaminated sediment, rather than via exposure to soluble hydrocarbons. This conclusion was supported by exposure of embryos and larvae to elutriates (e.g., water soluble extract) of coal-tar sediments, that resulted in embryo and larval mortality at low molecular weight PAH concentrations-0.47 mg/L, higher than would occur naturally. No decrease in petroleum hydrocarbon concentration was observed in sediments exposed to flowing water for 14 d, supporting the contention that soluble hydrocarbons were not responsible for the observed toxicity in whole sediment exposures under the conditions employed in this study.

Potential uses of sea urchin embryos for identifying toxic chemicals: description of a bioassay incorporating cytologic, cytogenetic and embryologic endpoints

A method for evaluating pollutant genotoxicity, embryotoxicity and teratogenicity using sea urchin embryos has been developed and was tested using benzo(a)pyrene (BP). Initial results suggested that the bioassay may be a sensitive indicator of pollutant toxicity and mutagenicity since several endpoints can be simultaneously assessed. The bioassay is rapid, inexpensive and appears applicable to a variety of toxicants and delivery methods. The test is based upon the standard 48 h sea urchin development assay and incorporates cytologic-cytogenetic analysis of embryos. Following toxic exposure of gametes, fertilization success is assessed. Embryos then develop for 48 h at which time survival and teratogenesis are evaluated. A subsample of embryos is stained and dissociated into monolayers and mitotic configurations are examined using light microscopy. Embryo mitotic rates are used as an indicator of overall embryonic health. Cytotoxic effects are concomitantly evaluated. Genotoxicity is measured using two methods: (1) anaphase aberration analysis, a technique which assesses abnormalities in the chromosome configurations (such as bridges and fragments) as the groups of chromosomes move to opposite poles and (2) micronucleus formation, a procedure examining the incidence of smaller, secondary nuclei composed of whole chromosomes or chromatid fragments. These two measurements preclude the need to examine individual chromosomes for deletions and exchanges, a laborious process in most aquatic organisms which possess numerous relatively small chromosomes. This genotoxicity-teratogenicity test appears promising for laboratory evaluations of individual substances or of complex chemical mixtures as well as for environmental monitoring of nearshore areas. The standard development assay has been used to screen pharmaceuticals and environmental contaminants and some recent investigations have included mitotic aberration analysis. Experiments in our laboratory suggest that the genotoxicity-teratogenicity test may be a feasible approach to field monitoring. Mutagen loads of spawning adult urchins could be assessed by conducting cytologic-cytogenetic analysis of resulting embryos although initial studies suggest that this method is less sensitive than direct embryo exposures.

Oxygen consumption rates of grunion (Leuresthes tenuis) embryos exposed to the petroleum hydrocarbon, benzo[a]pyrene

Bioconcentration of [14C]benzo[a]pyrene and effects of unlabeled benzo[a]pyrene (BaP) accumulation on the routine oxygen consumption of embryonic grunion (Leuresthes tenuis) were studied. At Day 15, bioconcentration factors over dissolved BaP levels ranged from 249 to 466. Weight-specific respiration rates at Days 14-15 were significantly increased (P less than or equal to 0.05) at a mean BaP body burden of 0.51 ppm wet wt. Oxygen consumption rates of embryos containing 0.70 to 12.80 ppm BaP were not significantly different from control rates. Because in a previous study embryos containing 0.51 ppm BaP exhibited hatching and developmental rates similar to those of controls, their metabolic response to low-level hydrocarbon exposure may be an example of hormesis, an overcompensating metabolic regulation to inhibitory challenges.