Endocrine disruptor responses in African sharptooth catfish (Clarias gariepinus) exposed to di-(2-ethylhexyl)-phthalate

Abstract

In the present study, we have investigated the endocrine disruptive effects of waterborne di-(2-ethylhexyl) phthalate (DEHP: 0 (control), 10, 100, 200 and 400 μg/L) on juvenile Clarias gariepinus by analyzing transcript patterns for hepatic vitellogenin (vtg), estrogen receptor-α (er-α), aromatase (cyp19a1b) and peroxisome proliferator activated receptor-α (ppar-α) using quantitative real-time PCR after 3, 7 and 14 days exposure period. In addition, we analyzed CYP19 and PPAR protein levels using enzyme-linked immunosorbent assay (ELISA), while cellular testosterone (T) and 17β-estradiol (E2) levels were measured using enzyme immune assay (EIA). Tissue burden of DEHP was measured in the liver using gas chromatography-mass spectroscopy (GC–MS). We observed apparent concentration- and time-dependent increases of vtg, er-α, cyp19a1b transcripts, E2 and T levels after exposure to DEHP. A biphasic pattern of effect was observed for ppar-α, showing a concentration-dependent increase that peaked at 100 μg/L and thereafter, an apparent concentration-dependent decrease at 200 and 400 μg/L at all exposure days. Given that the post-differentiation changes of gonads in C. gariepinus corresponded with the 14-day sampling period, we separated the analyzed data into sexes after histological examination of the gonads, showing that females responded stronger, compared to males, to DEHP exposure at all exposure concentrations. Oocyte atresia, intersex (ovotestis) and karyoplasmic clumping were observed in females while male fish showed distortion and degeneration of seminiferous tubules and condensation of tubular cells in the 400 μg/L exposure group after 14 days. Corresponding canonical analysis (CCA) of all analyzed variables revealed a positive relationship between analyzed biological variables with increasing DEHP concentrations. Overall, molecular, biochemical and physiological responses presented in the present study indicate that exposure of C. gariepinus to waterborne DEHP produced endocrine disruptive responses with potential consequences for overt reproduction, development, physiology and general health of fish populations inhabiting phthalate contaminated aquatic environments. These responses represent valuable and effective biomarkers of exposure and effects, that can be adopted for screening the presence of EDCs in Nigeria and other developing countries.