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  • The purpose of the present study is to characterize


    The purpose of the present study is (1) to characterize AChE from the monogonont B. koreanus and to analyze the modulation of the AChE activity and its transcription level after exposure to six pharmaceuticals, (2) to evaluate the usefulness of AChE as a molecular biomarker upon pharmaceutical exposure in this species, and (3) to unveil the mode of action of the pharmaceutical effect in B. koreanus.
    Materials and methods
    Discussion Due to the target-specific action and the persistence of pharmaceuticals in the body, these compounds have a potential ecotoxicological effect on aquatic organisms (Fent et al., 2006). Several pharmaceuticals have been detected in aquatic ecosystems due to their high solubility. Regarding the environmental levels of pharmaceuticals used in this study, their concentrations in the aquatic environment definitely vary depending on their usage and exposure route. Park (2005) reviewed that these pharmaceuticals have been detected in aquatic environment of US, Canada, EU, and other countries including Korea from ng/L up to μg/L levels. Moreover, some of them are active at low concentration, but the effects of pharmaceutical accumulation or their metabolites on aquatic animals are not yet known. Although several studies have documented the harmful effect of pharmaceuticals on the growth, development, and reproduction of aquatic organisms (Flaherty and Dodson, 2005; Lürling et al., 2006; Rhee et al., 2012), the ecotoxicological modes of the actions of these compounds still remain unclear. AChE activity has been used as a biomarker for rapid detection to predict early signals of toxicity of environmental pollutants, particularly pesticides (Dutta and Arends, 2003). AChE is involved in the hydrolysis of SB 204990 synthesis into choline and acetate, and plays a key role in neurotransmission at the cholinergic synapses (Kwong, 2002). Thus, inhibition of AChE activity causes the neurotransmitter to accumulate acetylcholine, leading to disruption of the nervous system. This has a deleterious effect resulting in death (Fukuto, 1990; Koelle, 1994). In aquatic organisms, it has been reported that AChE activity is inhibited by contaminants such as heavy metals, insecticides, and a some pharmaceuticals as well as pesticides (Banni et al., 2005; Kavitha and Rao, 2008; Anquiano et al., 2009; Solé et al., 2010; Ezemonye and Ikpesu, 2011; Richetti et al., 2011; Li et al., 2012). Although diverse environmental toxicants have been considered as potential modulators of the disruption of the nervous system via AChE inhibition, there is little evidence of the impact of pharmaceutical-mediated detrimental effects for the neurophysiology of aquatic invertebrates. Previously, Nogrady and Alai (1983) reported the presence of AChE using acetylcholine-specific histochemical staining in twelve species of rotifers. However, AChE gene information and its activity measurement in any research area has not been reported for the rotifer species. Therefore, our findings are helpful to obtain knowledge of the potential of using transcript/activity measurement of rotifer AChE for risk assessment of pharmaceutical pollution. Our results should therefore be useful to obtain a better understanding of the mode of action of pharmaceuticals on the nervous system of rotifers. In the present study, we investigated AChE activity and its transcriptional modulation in the monogonont rotifer B. koreanus exposed to six pharmaceuticals. To confirm whether the rotifer preserves the general function of AChE, we measured the changes in the transcript/activity of Bk-AChE in response to chlorpyrifos treatment as a strong inhibitor of AChE activity. With mosquitofish, Gambusia affinis exposed to 297μg/L (LC50 value for 96h) of chlorpyrifos (Kavitha and Rao, 2008), the freshwater mussel Lamellidens marginalis exposed to sub-lethal concentrations of chlorpyrifos (5ppm for 30days) showed a reduction of AChE activity in the hepatopancreas (Amanullah et al., 2010). As shown in other studies, Bk-AChE activity and its mRNA expression in our study were significantly decreased in a time- and concentration-dependent manner (Fig. 1) after exposure to chlorpyrifos for 12h and 24h. These results are also in accord with those reported by Xing et al. (2010) where the AChE mRNA level was significantly decreased in the common carp, Cyprinus carpio L. exposed to sub-lethal concentrations (1.16–11.6μg/L for 20days) of chlorpyrifos. They suggested that inhibition of the AChE activity by exposure to chlorpyrifos may be directly related to a decrease in the AChE gene expression. Taken together, our findings demonstrate that the polypeptide of Bk-AChE is likely to be a functional AChE and is sensitive to chlorpyrifos treatment. Even though several rotifer species including B. plicatilis have been employed for gene mining, there has been no report of the sequence information or the biochemical result of AChE as yet. Based on the in silico similarity and transcript/activity measurement, we assume that Bk-AChE has a cholinergic role in the AChE-mediated cascade in the rotifer neurotransmission system.