Characterization of brain acetylcholinesterase of bentonic fish Hoplosternum littorale: Perspectives of application in pesticides and metal ions biomonitoring

• Published in: Aquatic toxicology 2018-12, Vol.205, p.213-226
• Main Authors: Araújo, Marlyete Chagas, Assis, Caio Rodrigo Dias, Silva, Kaline Catiely Campos, Souza, Kelma Sirleide, Azevedo, Rafael Souto, Alves, Maria Helena Menezes Estevam, Silva, Luciano Clemente, Silva, Valdir Luna, Adam, Mônica Lúcia, Carvalho Junior, Luiz Bezerra, Souza Bezerra, Ranilson, Oliveira, Maria Betânia Melo
• Format: Article
• Language: English
• Subjects: Acetylcholinesterase - metabolism; Animals; Benzoylurea; Biomarker; Brain - drug effects; Brain - enzymology; Carbamate; Catfishes - physiology; Cholinesterase; Environmental Monitoring - methods; Enzyme Activation - drug effects; Hoplosternum littorale; Ions - analysis; Ions - toxicity; Metals, Heavy - analysis; Metals, Heavy - toxicity; Organophosphorus; Pesticides - analysis; Pesticides - toxicity; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - toxicity
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/j.aquatox.2018.10.017

•AChE from brain of H. littorale were physicochemical and kinetically characterized.•Selective inhibitors showed AChE as the main ChE in H. littorale brain.•The enzyme was exposed to carbamate, organophosphorus, benzoylurea and juvenile hormone analogue pesticides as well as ions.•The first report on the inhibition of brain AChE in the Siluriformes group by novaluron and pyriproxyfen.•Dichlorvos IC20 was below the concentrations allowed by current legislation whereas mercury was the strongest inhibitory ion. Acetylcholinesterase (AChE; EC 3.1.1.7) is a serine hydrolase, whose main function is to modulate neurotransmission at cholinergic synapses. It is, therefore, the primary target of some pesticides and heavy metals. Its inhibition in aquatic organisms has been used as an indicator of the presence of these pollutants in water bodies. The present study aimed to characterize physicochemical and kinetic parameters of brain AChE in the benthic fish Hoplosternum littorale and to analyze the in vitro effects of pesticides (dichlorvos, diazinon, chlorpyrifos, parathion-methyl, temephos, carbaryl, carbofuran, aldicarb, diflubenzuron, novaluron and pyriproxyfen) and metal ions (As3+, Cd2+, Cu2+, Fe2+, Mn2+, Mg2+, K+, Pb2+, Hg2+, Zn2+) investigating the potential of this enzyme as environmental biomarker based on current regulations. Specific substrates and inhibitors have indicated AChE to be the predominant cholinesterase (ChE) in the brain of H. littorale. Peak activity was observed at pH 8.0 and 30 °C. The enzymatic activity is otherwise moderately thermostable (≈ 50% activity at 45 °C). The enzyme can reduce the activation energy of acetylthiocholine hydrolysis reaction to 8.34 kcal mol−1 while reaching a rate enhancement of 106. Among the pesticides under study, dichlorvos presented an IC50 value below the maximum concentrations allowed by legislation. This study presents the first report on the inhibition of brain AChE activity from Siluriformes by the pesticides novaluron and pyriproxyfen. Mercury ion also exerted a strong inhibitory effect on its enzymatic activity. The H. littorale enzyme thus has the potential to function as an in vitro biomarker for the presence of the pesticide dichlorvos as well as mercury in areas of mining and industrial discharge.