A Review on Environmental Contaminants-Related Fertility Threat in Male Fishes: Effects and Possible Mechanisms of Action Learned from Wildlife and Laboratory Studies

Impact of absolute food deprivation on the reproductive system in male goldfish exposed to sex steroids

There is a link between metabolism and reproduction as metabolic hormones affect hypothalamus-pituitary-testis (HPT) hormonal functions and vice versa. The aim of the present study was to investigate the effects of negative energy balance on the reproductive system in male goldfish exposed to testosterone (T) and 17β-estradiol (E2). Following 7 days of food deprivation (FD), ANOVA models showed significant FD × sex steroid interactions on sperm quality and circulating sex steroid levels. When FD effects were investigated, 11-ketotestosterone (11-KT) level and sperm motility and velocity decreased in food-deprived goldfish in the control group. In E2-exposed goldfish, FD decreased sperm production in addition to sperm motility and velocity that coincided with an elevation of circulating E2 level. However, FD did not significantly impact sex steroids and sperm quality in T-exposed goldfish. ANOVA models showed non-significant FD × sex steroid interactions for HSI, GSI, circulating luteinizing hormone (Lh) level, and metabolic (preproghrelin, goat and nucb2) and reproductive (kiss1, gpr54 and gnrh3) mRNAs. Furthermore, results showed that FD decreased HSI, and increased Lh levels and testicular preproghrelin and goat mRNAs, while sex steroids increased mid-brain nucb2, kiss1 and gpr54 mRNAs. Together, our results suggest that FD-induced inhibition of androgenesis resulted in diminished sperm quality associated with activation of the testicular ghrelinergic system, and negative feedback of 11-KT increased Lh level. The FD-induced testicular metabolic and hormonal system was impacted in goldfish exposed to sex steroids. However, the negative effects of FD on sperm quality were accelerated in E2-exposed goldfish due to estrogenic activity. This study provides novel information to better understand metabolic-associated reproductive disorders in fish.

Estradiol-17β and bisphenol A affect growth and mineralization in early life stages of seabass

Natural and synthetic estrogens are contaminants present in aquatic ecosystems. They can have significant consequences on the estrogen-sensitive functions of organisms, including skeletal development and growth of vertebrate larvae. Synthetic polyphenols represent a group of environmental xenoestrogens capable of binding the receptors for the natural hormone estradiol-17β (E2). To better understand how (xeno-)estrogens can affect the skeleton in fish species with high ecological and commercial interest, 16 days post-hatch larvae of the seabass were experimentally exposed for 7 days to E2 and Bisphenol A (BPA), both used at the regulatory concentration of surface water quality (E2: 0.4 ng.L-1, BPA: 1.6 μg.L-1) or at a concentration 100 times higher. Skeletal mineralization levels were evaluated using Alizarin red staining, and expression of several genes playing key roles in growth, skeletogenesis and estrogen signaling pathways was assessed by qPCR. Our results show that E2 exerts an overall negative effect on skeletal mineralization at the environmental concentration of 0.4 ng.L-1, correlated with an increase in the expression of genes associated only with osteoblast bone cells. Both BPA exposures inhibited mineralization with less severe effects and modified bone homeostasis by regulating the expression of gene encoding osteoblasts and osteoclasts markers. Our results demonstrate that environmental E2 exposure inhibits larval growth and has an additional inhibitory effect on skeleton mineralization while both BPA exposures have marginal inhibitory effect on skeletal mineralization. All exposures have significant effects on transcriptional levels of genes involved in the skeletal development of seabass larvae.

Tetrabromobisphenol A reduces male rats reproductive organ coefficients and disrupting sexual hormone by causing oxidative stress

Tetrabromobisphenol A (TBBPA) has become a topic of public attention due to its pervasive detection in the environment and organisms in recent decades. However, limited information is available regarding the toxicity of TBBPA on reproductive ability of male mammals. Herein, the reproductive toxicity of TBBPA was investigated in male rats to fill the knowledge gap. In this study, male rats were exposed to TBBPA (0, 10, 100, and 1000 mg/kg) for 6 weeks. Subsequently, body and organ indexes, histopathological evaluation of testis and epididymis, ultrastructural observation of sperm, testosterone and progesterone levels, and oxidative stress indicators were conducted to reveal corresponding mechanisms. Results obtained showed that compare to the control group, the body weight, testes weight, epididymis weight, seminal vesicle and coagulation glands weight of rats in the 1000 mg/kg group lost 8.30%, 16.84%, 20.16%, 19.72% and 26.42%, respectively. Intriguingly, exposure to TBBPA (10, 100, 100 mg/kg) resulted in substantial pathological damage in testis, epididymis and sperm. TBBPA exposure also increased malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents, as well as superoxide dismutase (T-SOD) and catalase (CAT) activities in testicular tissue. What's more, the testosterone and progesterone levels in male rat serum were significantly decreased after exposure to TBBPA for 6 weeks. Meanwhile, results of molecular docking showed that TBBPA has a strong affinity with estrogen receptors (ERs). These findings demonstrated that TBBPA exposure negatively impacts the reproductive ability of male rats, thus providing new insights for risk assessment for reproductive health under TBBPA exposure.

Ultrastructure of Javaen barb fish Systomus orphoides Valenciennes, 1842 spermatozoa (Cypriniformes: Cyprinidae) by electron microscopes

Javaen barb fish Systomus orphoides Valenciennes, 1842 (Cypriniformes: Cyprinidae) is a freshwater fish whose population is declining and threatened with extinction. In this study, the ultrastructure of spermatozoa of Javaen barb fish (S. orphoides) was studied using transmission and scanning electron microscopy. The spermatozoa of S. orphoides are relatively simple cells composed of a spherical head, a short midpiece, and a flagellum, as in most Cyprinidae. The ultrastructure is characterized by the absence of acrosome, the total length of spermatozoa is 27.16 ± 4.5 μm, and the head has spherical with a length of 1.84 ± 0.10 μm and width of 1.55 ± 0.15 μm containing a nucleus, midpiece region containing the proximal and distal centrioles and mitochondria. Two or three mitochondria surrounding the axoneme (with a 9 + 2 microtubular pattern). Ultrastructural analyses by SEM and TEM of Javaen barb fish spermatozoa cells are very consistent with those of Cyprinidae. This study provides the ultrastructure information of S. orphoides spermatozoa in the Cyprinidae family this research could be useful in increasing reproductive efficiency and further prevent the extinction of this species.

Declines in Reproductive Condition of Male Largemouth Bass (Micropterus salmoides) Following Seasonal Exposure to Estrogenic Endocrine-Disrupting Compounds

Reproductive abnormalities, that could lead to possible effects at the population level, have been observed in wild fish throughout the United States, with high prevalence in largemouth bass (LMB; Micropterus salmoides) and smallmouth bass (Micropterus dolomieu). Estrone (E1) and atrazine (ATR) are common environmental contaminants often associated with agricultural land use. 17alpha-ethinylestradiol (EE2) is a contaminant associated with wastewater treatment effluent, and a representative, well-studied estrogen commonly used for fish toxicity testing. Our objective was to assess whether early gonad recrudescence in adult fish was a period of sensitivity for alterations in reproductive condition and function. Adult male LMB were exposed from post-spawning to early gonad recrudescence to either a mixture of E1 (47.9 ng/L) + ATR (5.4 µg/L), or EE2 (2.4 ng/L) in outdoor experimental ponds. Gonad samples were collected from fish just prior to the start of exposure (July), at the end of the exposure period (December), the following spring just prior to spawning (April), and post spawning (May). Gonadosomatic index (GSI) was significantly reduced in E1 + ATR-exposed and EE2-exposed males compared to control at every post-exposure time point. Reduced sperm count and sperm motility were observed in the mixture treatment (E1 + ATR) compared to the control. Sperm motility was also reduced in the EE2 treatment. These data together indicate that estrogenic endocrine-disrupting compounds can lessen the reproductive condition of adult male LMB, and that effects of exposure during early gonad recrudescence can persist at least through the subsequent spawning cycle.

A chronic exposure to bisphenol A reduces sperm quality in goldfish associated with increases in kiss2, gpr54, and gnrh3 mRNA and circulatory LH levels at environmentally relevant concentrations

The bisphenol A (BPA)-disrupted reproductive functions have been demonstrated in male animals. In fish, it has been shown that environmentally relevant concentrations of BPA decrease sperm quality associated with inhibition of androgen biosynthesis. However, BPA effects on neuroendocrine regulation of reproduction to affect testicular functions are largely unknown. In the present study, reproductive functions of hypothalamus and pituitary were studied in mature male goldfish exposed to nominal 0.2, 2.0 and 20.0 μg/L BPA. At 90 d of exposure, sperm volume, velocity, and density and motility were decreased in goldfish exposed to 0.2, 2.0, and 20.0 μg/L BPA, respectively (p < 0.05). At 30 d of exposure, there were no significant changes in circulatory LH levels and mRNA transcripts of kiss1, Kiss2, gpr54, and gnrh3. At 90 d of exposure, circulatory LH levels showed trends toward increases in BPA exposed goldfish, which was significant in those exposed to 2.0 μg/L (P < 0.05). At this time, Kiss2, gpr54, and gnrh3 mRNA levels were increased in goldfish exposed to any concentrations of BPA (p < 0.05). This study shows that BPA-diminished sperm quality was accompanied by an increase in circulatory LH levels associated with increases in mRNA transcripts of upstream neuroendocrine regulators of reproduction in goldfish. Further, this is the first study to report circulatory levels of LH in fish exposed to BPA.