Effects of chlorpyrifos on the catalytic efficiency and expression level of acetylcholinesterases in the bivalve mollusk Scapharca inaequivalvis

Abstract

Three acetylcholinesterase (AChE) forms were detected and recovered from foot or gill tissues of the benthonic bivalve mollusk Scapharca inaequivalvis. A study was performed to investigate changes in catalytic and hydrodynamic features of these enzymes, as well as in their expression levels, after a 4-d or a 15-d exposure to a sublethal concentration (0.1 microl/L) of the pesticide chlorpyrifos (CPF). Both considered organs hold, in either CPF-exposed or untreated animals, two nonamphiphilic AChE forms, G2 and G4, which copurified on a procainamide-containing affinity gel and were separated by density gradient centrifugation. A third AChE form, an amphiphilic membrane-anchored G2, was also purified on the same affinity matrix from both organs. All enzymatic forms are true AChEs and are poorly inhibited by CPE They show different increases in the maximum velocity (Vmax) and in the Michaelis constant (Km) values after CPF exposure. Consequently, catalytic efficiency of AChEs, as defined by the ratio Vmax:Km, rises in the gills and drops in the foot. This would produce an overexpression of AChE-specific mRNAs. The effect was longer lasting in the foot. The combined results indicate that overexpression of enzymes in the presence of organophosphate (OP) may be a consequence of OP resistance itself. Again, the resistance of the organism to CPF seem to depend mainly on the resulting increase in AChE content.

Cholinesterase activities as potential biomarkers: Characterization in two freshwater snails, Potamopyrgus antipodarum (Mollusca, Hydrobiidae, Smith 1889) and Valvata piscinalis (Mollusca, Valvatidae, Müller 1774)

“…However, On the contrary, this OP increased AChE activity in S. inaequivalvis after 15 days of exposure 346 to 0.3 nM (Romani et al, 2005), which comforts our results on V. piscinalis; however, the 347 biological explanation remains unknown. IC 50 of chlorpyrifos for AChE was 9.71 nM in P. 348 antipodarum at 96 h, which was ten times higher that for G. pulex in the same experimental 349 conditions (Xuereb et al, 2007 control.…”

“…The World Health Organization (Paris) recognizes AChE biomonitoring as a 66 preventive measure against OP overexposure in nontarget species (Romani et al, 2005). Its 67 use as a specific biomarker to assess the exposure of aquatic organisms to these compounds is 68 5 using different substrates (acetylthiocholine (ASCh), propionylthiocholine (PSCh) and 94 butyrylthiocholine (BSCh)) and specific inhibitors (eserine for ChE, BW284c51 …”

Acetylcholinesterase in the sea urchin Lytechinus variegatus: Characterization and developmental expression in larvae

“…To determine whether this plasticity confers an adaptive advantage or physiological consequence would require further culture and evaluation of the individuals. Besides the levels of AChE reflecting the physiological and environmental conditions, the assembly and distribution of the various molecular forms could also be modulated, as seen in other organisms (Witzemann and Boustead, 1982;Atkins and Pezzementi, 1993;Anselmet et al, 1994;Bertrand et al, 2001;Talesa et al, 2001;Falugi et al, 2002;Romani et al, 2005), which could be another focus of future studies with L. variegatus. Such additional research will help resolve whether the AChE of L. variegatus could be used as an invertebrate biomarker of environmental, nutritional, and toxicological conditions.…”

Pollutant mixtures as stressors of selected enzyme activities of the aquatic snail Helisoma duryi

“…Reports found in literature differ on how metals affect esterases of different organisms. Romani et al (2005) observed activation of acetylcholinesterase activity after chronic exposures to sublethal concentrations of copper. Metin et al (2006) reported enhanced esterase activity in Geobacillus sp.…”