Long-term exposure to environmentally relevant concentrations of tri-m-cresyl phosphate induces fecundity decline and gonadal dysplasia by disrupting reproductive endocrine homeostasis

Tricresyl phosphate (TCP) isomer mixtures are novel aryl-organophosphate esters that have been detected in aquatic environments, with concentrations ranging from not detected (ND) to 8100 ng/L. Among these isomers, Tri-m-cresyl phosphate (TmCP) has been identified as a predominant isomer. It has been demonstrated to exert toxic effects on fish. However, the reproductive toxicity of environmentally relevant concentrations of TmCP on zebrafish remain unclear. In the present study, one month-old zebrafish were exposed to 0, 0.2, 2, and 20 μg/L TmCP for 100 d. The results demonstrated that TmCP exposure disrupted fecundity of zebrafish, which was manifested by the decreases of cumulative number of eggs in females, sperm density and sperm motility in males, as well as yolk diameter and body length in F1 generation. Further research found that TmCP exposure reduced the proportion of late vitellogenic oocytes (LV) and spermatozoa (SZ) in ovaries and testes of zebrafish, respectively, and reduced the levels of sex steroid hormones in plasma, including 4-androstene-3,17-dione (AE), estrone (E1), and testosterone (T). In addition, expression of genes involved in hypothalamic-pituitary-gonadal (HPG) axis and molecular docking analysis were performed to explore toxic mechanisms of TmCP. The results showed that TmCP significantly inhibited the expressions of sex steroid hormones synthesis genes (hsd3b, cyp17, hsd17b, and hsd11b) in gonads and could bind to the active pocket sites of their upstream proteins. These results confirmed that TmCP could affect gonadal development and hormone homeostasis in zebrafish by interfering with steroid hormone synthesis pathway, thereby reducing fecundity of female and male zebrafish. The results of this study contribute to expanding the understanding of the reproductive toxicity of TmCP and provide new insights into its potential health risks.