Effect of long-term exposure to bezafibrate on steroidogenesisand reproduction of Japanese medaka(Oryzias latipes)

Abstract

Fibrates are commonly used lipid regulator to control hypercholesterolemia in humans, and have been frequently detected in the freshwater environment. Bezafibrate is one of lipid regulators and has been detected in streams at up to 202.7 ng/L. While lipid regulation may lead to altered steroidogenesis, endocrine disruption potential of bezafibrate in aquatic non-target organisms has not been well documented. Present study aimed to understand ecological risks of this lipid regulator, and to identify potential endocrine disruption and related mechanisms. The PNEC is the concentration below which exposure to a chemical is not expected to cause an adverse effects. The MEC is the detecion levels found in environmental sample. The PNEC value of bezafibrate was calculated at 2.3 μg/L and hazard quotient (HQ) based on PNEC and MEC values was estimated at 0.09. Following long-term (135 day) exposure of Japanese medaka (Oryzias latipes) to bezafibrate (0.01, 0.1, 1, 10, or 100 mg/L), reproduction performance of the fish, e.g., number of eggs, hatchability, and hatching time, was affected. Such changes were accompanied by sex hormone alterations, i.e., significant E2 increase in female and decreasing T in male fish, at 165 days post-hatching (dph). Changes in sex hormone concentrations were supported by regulational changes of several steroidogenic genes. In gonads, steroidogenic genes such as star, 3β-hsd, cyp11b, and cyp19a showed up-regulation following the exposure. Bezafibrate appears to regulate lipid metabolism, as suggested by up-regulation of ppara1, ppara2 gene expression were observed in both male and female fish. However, plasma cholesterol levels were only reduced in male fish following the exposure. Increased steroidogenesis following long-term bezafibrate exposure in fish is different from the observations of the 30 day early life stage exposure and other previous reports. Our observations clearly show that long-term exposure to this lipid regulator can stimulate steroidogenesis among aquatic non-target species and increase estrogenicity that could lead to changes in reproduction.