Comparative Analysis of Neurotoxicity of Six Phthalates in Zebrafish Embryos

Abstract

The effects and underlying mechanisms of phthalates on neurotoxicity remain unclear as compared with the potentials of these substances as endocrine disruptors. The locomotor activities of zebrafish embryos were investigated upon exposure to six phthalates: dimethyl phthalate (DMP), diethyl phthalate (DEP), benzyl butyl phthalate (BBzP), di-2-ethylhexyl phthalate (DEHP), di-n-octyl phthalate (DnOP), and diisononyl phthalate (DiNP). Moreover, changes in fluorescence intensity in the green fluorescent protein (GFP) transgenic (Tg) lines Tg(HuC:eGFP), Tg(sox10:eGFP), and Tg(mbp:GFP) were measured after exposure to six phthalates, and changes in the expression profiles of genes involved in the cholinergic (ache) and dopaminergic systems (dat, th, and drd1b) were assessed. Exposure to BBzP, DEHP, and DiNP affected larval behaviors, whereas exposure to DMP, DEP, and DnOP revealed no alterations. A reduced expression of Tg(HuC:eGFP) was observed upon exposure to BBzP, DEHP, and DiNP. The expression of Tg(sox10:eGFP) and Tg(mbp:GFP) was reduced only in response to BBzP and DiNP, respectively. Further, exposure to DiNP upregulated ache and drd1b. The upregulation of ache and downregulation of drd1b was observed in DEHP-exposed groups. Exposure to BBzP suppressed th expression. These observations indicate that exposure to phthalates impaired embryogenesis of the neurological system and neurochemicals in zebrafish embryos, although the detailed mechanisms varied among the individual phthalates. Further mechanistic studies are needed to better understand the causality between phthalate exposure and neurotoxicity.

Review on Toxic Effects of Di(2-ethylhexyl) Phthalate on Zebrafish Embryos

“…In a separate study, a hatching rate 62.4% was reported in the DEHP-treated group at 72 hpf, with the concentration as low as 0.5 µg/L [ 39 ]. On the other hand, body length reduction was reported in DEHP-exposed zebrafish embryos [ 44 , 45 , 46 , 47 ]. Tran et al reported that the body lengths of 120 hpf zebrafish embryos were decreased upon DEHP exposures to the highest tested concentration (100 mg/L), which were however not significantly different after DEHP exposures to lower concentrations (0.5 µg/L–10 mg/L) [ 46 ].…”

“…On the other hand, body length reduction was reported in DEHP-exposed zebrafish embryos [ 44 , 45 , 46 , 47 ]. Tran et al reported that the body lengths of 120 hpf zebrafish embryos were decreased upon DEHP exposures to the highest tested concentration (100 mg/L), which were however not significantly different after DEHP exposures to lower concentrations (0.5 µg/L–10 mg/L) [ 46 ]. Kinch et al demonstrated that DEHP exposures induced a more serious effect on the morphology at earlier time points (3–24 hpf and 3–48 hpf) than at later time points (3–72 hpf) [ 45 ].…”

“…Exposures to DEHP have exerted behavioral toxicities on zebrafish embryos [ 37 , 42 , 46 , 53 ]. Spontaneous movement inhibition has been reported in zebrafish embryos upon DEHP exposures [ 37 , 53 ].…”

“…Locomotor activity was another marker to assess the behavioral ability in zebrafish embryos. DEHP exposure was confirmed to alter locomotor activities in zebrafish embryos [ 42 , 46 ]. In a related study, zebrafish embryos were exposed to four concentrations of DEHP (0, 10, 25, 50 µM) at 4 hpf, and after the 96 h exposure time point, the swimming activities were recorded using the Zebralab Video-Track system (ViewPoint Life Science, France) [ 42 ].…”

“…The results indicated that an exposure to 50 µM DEHP could significantly inhibit the locomotor activity compared to the control [ 42 ]. In a separate study, the locomotor activities under alternating light–dark conditions of DEHP-treated zebrafish embryos at 120 hpf were evaluated via the ZebraBox tracking system (ViewPoint Life Science, France) [ 46 ]. Suppression of locomotor activities was reported in DEHP-exposed embryos under the dark condition, while stimulation of locomotor activities was found under the light condition [ 46 ].…”