Benzo(a)pyrene exposure in early life suppresses spermatogenesis in adult male zebrafish and association with the methylation of germ cell-specific genes

Designing and applying a methodology to assess sperm cell viability and DNA damage in a model amphipod

Sperm quality is defined as the sperm cell ability to successfully fertilize eggs and allow normal embryo development⁠. Few studies explore sperm quality using aquatic invertebrates. Parhyale hawaiensis is a marine amphipod with a circumtropical distribution and considered a model for evolution, development, and ecotoxicological studies. We aimed to develop a methodology to collect sperm cells of P. hawaiensis and evaluate their viability and DNA damage (comet assay). We directly exposed the sperm cells to different mutagenic agents to optimize/develop the protocols. Then, as a proof of concept, we exposed the males to mutagenic compounds (EMS, benzo[a]pyrene (BaP), azo and anthraquinone dyes) at non-lethal concentrations verified by the proposed viability test and analyzed their sperm cells for DNA damage (comet assay). Organisms exposed to EMS presented a clear concentration response in the DNA damage response. We also showed that BaP was able to induce a statistically significant increase in DNA damage of the sperm cells. For the two dyes, although DNA damage increased, statistically differences were not observed. We believe we successfully developed a test to detect genotoxicity of chemicals in sperm cells using an invertebrate model. The protocol for sperm cell viability needs to be further explored with different chemicals to verify its utility as a toxicity endpoint. The developed genotoxicity test has the advantages to employ organisms that are easily cultivated in reduced space, use simple laboratory resources and reduced amount of material and reagents. Positive responses with this model could be used to disclose new germ cell mutagen candidates which could be further confirmed in vertebrates' systems.

Prenatal exposure to environmentally relevant levels of PAHs inhibits spermatogenesis in adult mice and the mechanism involved

Polycyclic aromatic hydrocarbons (PAHs) are a class of contaminants that cannot be banned. Exposure to PAHs has been reported to alter spermatogenesis in mammals, but little is known about prenatal exposure to a mixture of PAHs on the reproductive toxicity of adult offspring. In this study, we investigated the associations between prenatal exposure to environmentally relevant levels of PAHs in mice and testicular dysfunction, including impaired spermatogenesis and steroid hormone dysfunction in male offspring on postnatal day 180. The percentage of testicular apoptotic cells was significantly increased, which was further verified by the up-regulated BAX protein. The expression of Ar and the Leydig cell marker Cyp11a1 was down-regulated, suggesting an impairment in the synthesis of steroid hormones. DNA hypermethylation of the Tnp1 and Sohlh2 promoters suppresses transcriptional expression, consequently altering the sperm production process. This study shows that prenatal exposure to PAHs may induce long-term reproductive toxicity.

Long-term effects of an early-life exposure of fathead minnows to sediments containing bitumen. Part II: Behaviour, reproduction, and gonad histopathology

The oil sands area of northern Alberta has river sediments that contain natural bitumen. Eggs and fish in these rivers may be exposed to bitumen-related chemicals early in life. This paper assesses a short embryo-larval fish exposure to oil sands sediment and follows the fish behaviour as they mature in clean water and examines their breeding success as adults (5 months afterwards). The three different oil sands river sediments tested were: a sediment collected outside of the bitumen deposit (tested at 3 g/L, Reference sediment from upstream Steepbank River site), and two sediments collected within the deposit (each tested at low (1 g/L) and high (3 g/L) concentrations). The sediments within the bitumen deposit were from the Ells and Steepbank (Stp) Rivers, and both contained significant total PAHs (>170 ng/g wet weight sediment) and alkylated PAHs (>4480 ng/g). Fish were exposed to these sediments for 21 days (as eggs and larval fish), and then transferred permanently to clean water to mature and breed. There was a significant decrease in the number of egg clutches produced by fish exposed early in life to Stp downstream high sediment (compared to Reference sediment). There was also a decrease in overall cumulative egg production, with fish from Stp downstream high sediment producing just over 1000 eggs in total while fish exposed to Ref sediment produced nearly 6900 eggs. The fish with reduced egg production were also less social than expected as they matured, and they had a lower % of early vitellogenic eggs in their ovaries. Overall, the exposure shows that a single, brief exposure during early life stages to natural bitumen can affect fish in adulthood. Naturally occurring bitumen-derived PAHs can reduce fish reproductive output by complex mechanisms, measurable as lower ovary maturity and changes in social behaviour.

A systematic toxicologic study of polycyclic aromatic hydrocarbons on aquatic organisms via food-web bioaccumulation

Pollution-induced declines in fishery resources restrict the sustainable development of fishery. As a kind of typical environmental pollutant, the mechanism of polycyclic aromatic hydrocarbons (PAHs) facilitating fishery resources declines needs to be fully illustrated. To determine how PAHs have led to declines in fishery resources, a systematic toxicologic analysis of the effects of PAHs on aquatic organisms via food-web bioaccumulation was performed in the Pearl River and its estuary. Overall, PAH bioaccumulation in aquatic organisms was correlated with the trophic levels along food-web, exhibiting as significant positive correlations were observed between PAHs concentration and the trophic levels of fishes in the Pearl River Estuary. Additionally, waterborne PAHs exerted significant direct effects on dietary organisms (P < 0.05), and diet-borne PAHs subsequently exhibited significant direct effects on fish (P < 0.05). However, an apparent block effect was found in dietary organisms (e.g., zooplankton) where 33.49 % of the total system throughput (TST) was retained at trophic level II, exhibiting as the highest PAHs concentration, bioaccumulation factor (BAF), and biomagnification factor (BMF) of ∑15PAHs in zooplankton were at least eight-fold greater than those in fishes in both the Pearl River and its estuary, thereby waterborne PAHs exerted either direct or indirect effects on fishes that ultimately led to food-web simplification. Regardless of the block effect of dietary organisms, a general toxic effect of PAHs on aquatic organisms was observed, e.g., Phe and BaP exerted lethal effects on phytoplankton Chlorella pyrenoidosa and zooplankton Daphnia magna, and decreased reproduction in fishes Danio rerio and Megalobrama hoffmanni via activating the NOD-like receptors (NLRs) signaling pathway. Consequently, an assembled aggregate exposure pathway for PAHs revealed that increases in waterborne PAHs led to bioaccumulation of PAHs in aquatic organisms along food-web, and this in turn decreased the reproductive ability of fishes, thus causing decline in fishery resources.

Embryonic Exposure to the Benzotriazole Ultraviolet Stabilizer 2-(2H-benzotriazol-2-yl)-4-methylphenol Decreases Fertility of Adult Zebrafish (Danio rerio)

Benzotriazole ultraviolet stabilizers (BUVSs) are emerging contaminants of concern. They are added to a variety of products, including building materials, personal care products, paints, and plastics, to prevent degradation caused by ultraviolet (UV) light. Despite widespread occurrence in aquatic environments, little is known regarding the effects of BUVSs on aquatic organisms. The aim of the present study was to characterize the effects of exposure to 2-(2H-benzotriazol-2-yl)-4-methylphenol (UV-P) on the reproductive success of zebrafish (Danio rerio) following embryonic exposure. Embryos were exposed, by use of microinjection, to UV-P at <1.5 (control), 2.77, and 24.25 ng/g egg, and reared until sexual maturity, when reproductive performance was assessed, following which molecular and biochemical endpoints were analyzed. Exposure to UV-P did not have a significant effect on fecundity. However, there was a significant effect on fertilization success. Using UV-P-exposed males and females, fertility was decreased by 8.75% in the low treatment group and by 15.02% in the high treatment group relative to control. In a reproduction assay with UV-P-exposed males and control females, fertility was decreased by 11.47% in the high treatment group relative to the control. Embryonic exposure to UV-P might have perturbed male sex steroid synthesis as indicated by small changes in blood plasma concentrations of 17β-estradiol and 11-ketotestosterone, and small statistically nonsignificant decreases in mRNA abundances of cyp19a1a, cyp11c1, and hsd17b3. In addition, decreased transcript abundances of genes involved in spermatogenesis, such as nanos2 and dazl, were observed. Decreases in later stages of sperm development were observed, suggesting that embryonic exposure to UV-P impaired spematogenesis, resulting in decreased sperm quantity. The present study is the first to demonstrate latent effects of BUVSs, specifically on fish reproduction. Environ Toxicol Chem 2024;43:385-397. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.