| Parabens (PBs) are esters of p-hydroxybenzoic acid (PHBA), including methylparaben (MP), ethylparaben (EP), propylparaben (PP), isopropylparaben (iPP), butylparaben (BP), isobutylparaben (iBP) and benzylparaben (BeP). The features, including broad spectrum of activity against yeasts, chemical stability and low costs of production, determining parabens are widely used as preservatives in food, pharmaceuticals and cosmetics. A number of recent studies suggested that parabens pose estrogenic effects, endocrine disrupting potential and the possible link with breast cancer.Experiments were carried out in the wild type Drosophila melanogaster Canton-S strain. We tested the effects of a direct administration of of ethylparaben on pre-adult growth and development in Drosophila. One-hour embryo collections were transferred to standard medium containing either no EP (control),0.03%,0.07%, or 0.10% EP and continuing through eclosion. In physiological level, we test the effects of different concentrations of EP on the time of egg-pupa and pupa-adult, the number of pupation and eclosion, sex ratio and fertility through direct administration in food. In molecular level, the effects of EP on the expression of five genes related to metamorphosis (Met、 Gce、EcR、Kr-h1、Br) were assayed by quantitative real-time PCR after the larvae were treated by EP for 2,3 and 4 days. The juvenile hormone and ecdysone concentration was quantified using ELISA beginning at 2 d and continuing through eclosion. The results show:1. Larvae exposed to the lowest concentration treatment (0.03%) show a decrease in development time, but there was no significant difference. While the development time of the two higher treatment groups (0.07% and 0.10%) were found to be significantly increased. There was no significant difference in the percentage of pupation and eclosion among the control and EP-treated groups.2. We tested the effects of EP on the growth of Drosophila by imaging the larvae after exposure 2,3,4 and 5 days, then determined the area using ImageJ software. Pupal area was also analyzed. Larvae exposed to the higher concentration treatment groups (0.07%and 0.10%) were found to be significantly smaller in mean area than the non-treated control group. The lowest concentration treatment group,0.03%, found to be larger in area than control group, but there was no significant difference.3. There was no significant difference in the number of male and female adult flies emergence from the EP treatment groups. In all the EP exposed groups the mean offspring numbers were significantly less than that of the control groups (p< 0.05). The results reflect a monotonic dose-response and suggest that EP exposure can affected the reproduction of Drosophila melanogaster.4. The quantitative real-time PCR results showed EP treated resulted in a significant increase in the expression of EcR. While the expression of other four genes reflected a fluctuation. During the exposure time, the expression of Met and Gce began to down after rise then down again. Kr-hl expression increased at 2 d and 3 d and decreased at 4 d. The expression of Br did not tested at 2 d, but at 3 d, the expression of Br in 0.03%of EP were increased while 0.07% and 0.10% EP groups were decreased. At 4 d, the Br expression in 0.03% and 0.07% were increased but in 0.10% EP group it was decreased.5. We measured the juvenile hormone(JH) and ecdysone concentration of larval and pupal beginning at 2 d and continuing through eclosion, and found that EP treated larvae and pupal had significantly reduced JH and ecdysone levels. The time of ecdysone peak were also prolonged.Collectively, EP can affect development time, growth rate, fecundity, gene expression level and JH and ecdysone levels. Since these processes in Drosophila are controlled through the complex interaction of a lot of hormone signaling pathways, our findings suggest that EP exerts its effects through disruption of endocrine signaling in Drosophila.This study will provide toxicology data for the effects of parabens on invertebrate and the safety evalution of parabens. |
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