Steroid biosynthetic enzyme activities in leachate-exposed female perch (Perca fluviatilis) as biomarkers for endocrine disruption

Neuroendocrine effects of endocrine disruptors in teleost fish

Because a large proportion of potential endocrine disruptors (EDC) end up in surface waters, aquatic species are particularly vulnerable to their potential adverse effects. Recent studies identified a number of brain targets for EDC commonly present in environmentally relevant concentrations in surface waters. Among those neuronal systems disrupted by EDC are the gonadotropin-releasing hormone (GnRH) neurons, the dopaminergic and serotoninergic circuits, and more recently the Kiss/GPR54 system, which regulates gonadotropin release. However, one of the most striking effects of EDC, notably estrogen mimics, is their impact on the cyp19a1b gene that encodes the brain aromatase isoform in fish. Moreover, this is the only example in which the molecular basis of endocrine disruption is fully understood. The aims of this review were to (1) synthesize the most recent discoveries concerning the EDC effects upon neuroendocrine systems of fish and (2) provide, when possible, the underlying molecular basis of disruption for each system concerned. The potential adverse effects of EDC on neurogenesis, puberty, and brain sexualization are also described. It is important to point out the future environmental, social, and economical issues arising from endocrine disruption studies in the context of risk assessment.

Seasonal testosterone UDP-glucuronosyltransferase activity and biliary steroids in Eurasian perch: response to leachate exposure

In previous studies there was evidence of endocrine disruption in fish in waterways contaminated with leachate from a Swedish landfill. Symptoms included fewer sexually mature (SM) female perch (Perca fluviatilis), distinct sores, reduced gonadosomatic index, and decreased plasma androgen levels. Based on previous findings it was hypothesized that the decrease in plasma androgen concentrations could have been caused by increased steroid excretion. Therefore, testosterone UDP-glucuronosyl transferase (UDPGT) activity and biliary steroids were measured in SM and sexually immature (SIM) female perch during one reproductive cycle. UDPGT activity in exposed fish did not differ from reference fish and was similar in both SM and SIM female perch. Since androgen levels in SIM fish usually are much lower than in SM fish, this indicates expression of testosterone UDPGT irrespective of substrate availability. There was no general increase in biliary steroids in exposed female perch. Biliary steroid levels correlated with corresponding plasma steroid levels. In conclusion, the reduced androgen levels in exposed female perch are most likely not caused by increased steroid excretion.

Sex steroids in the female zebrafish (Danio rerio). Effects of cyproterone acetate and leachate-contaminated sediment extract

In Molnbyggen, a leachate-contaminated lake in Sweden, effects on the reproductive system of perch included a decreased frequency of sexually mature female perch, reduced gonadosomatic index and decreased plasma levels of androstenedione and testosterone, but the contaminants responsible for these effects have not yet been identified. A biomarker-directed fractionation approach could be used to narrow the search for the compound(s) responsible for the adverse effects in Molnbyggen female perch. Thus, it is important to develop and test a suitable biomarker, which can be used in this type of approach. We evaluated if decreased concentrations of sex steroids could work as an in vivo end-point in female zebrafish fed an organic extract of bottom sediments from Molnbyggen. The responsiveness of zebrafish to endocrine alteration was evaluated using a positive control substance, cyproterone acetate (CA), which is known to inhibit steroid biosynthesis. After the 21-day exposure period the concentrations of testosterone (T) and estradiol (E2) were successfully determined by HRGC/HRMS in whole-body homogenates of individual fish. Median T concentrations were 1.7pmol/g fish in controls and were decreased after exposure both to CA (0.55pmol/g fish) and Molnbyggen sediment extract (1.2-1.3pmol/g fish). Median E2 concentrations were 5.3pmol/g fish in controls and were decreased after CA exposure (2.3pmol/g fish) and after exposure to Molnbyggen sediment extract (4.0-4.5pmol/g fish). This suggests that sex steroid concentrations in zebrafish are responsive to endocrine alteration and indicates that compounds with endocrine altering potency are present in Molnbyggen sediments.