Biochemical characterization of cholinesterases in Enchytraeus albidus and assessment of in vivo and in vitro effects of different soil properties, copper and phenmedipham

Abstract

Enchytraeus albidus are important organisms of the soil biocenosis, used as standard test species in environmental risk assessment. The inhibition of cholinesterases (ChE) activity of several species has been widely used to assess the exposure and effects of anti-cholinesterase environmental contaminants. Several studies have shown the association between ChE activity inhibition and adverse effects on behaviour and survival. Extensive studies addressing survival and behavioural endpoints, as well as other biomarkers, have been done in E. albidus with different types of soil contaminants. The main objectives of this study were: (1) to characterize biochemically the ChE present in the soluble post-mitochondrial fraction of E. albidus whole body homogenates, using different substrates and selective inhibitors; (2) to assess the in vivo effects of copper, phenmedipham and different soil properties (pH, organic matter, clay) on the ChE activity; (3) to assess the in vitro effects of copper and phenmedipham on the ChE activity. The results suggest the presence of one ChE in the soluble post-mitochondrial fraction of E. albidus whole body homogenates, which displays properties of both acetylcholinesterase and pseudocholinesterase considering the typical mammalian enzymes. It is also shown that ChE activity is not inhibited by exposure to different soil properties and that copper and phenmedipham inhibited ChE activity both in in vivo and in in vitro conditions and therefore ChE inhibition seems to be a robust biomarker for this herbicide and this heavy metal. This study showed that ChE activity in E. albidus might be correlated to previously determined higher level effects like survival and reproduction, as well as avoidance behaviour.

Effects of Organic Pesticides on Enchytraeids (Oligochaeta) in Agroecosystems: Laboratory and Higher-Tier Tests

“…It has been shown that dimethoate caused ChE inhibition in E. albidus, indicating an impairment of the neuronal function, but further work is surely needed before such endpoints can be used in regulatory testing . Similarly, Howcroft et al (2011) showed that a commercial formulation of phenmedipham inhibited ChE activity of E. albidus after 3 weeks of exposure, showing that ChE inhibition was a relevant biomarker for the studied pesticide.…”

“…They investigated enchytraeid molecular and biochemical mechanisms in response to pesticide exposure using differential gene expression, as well as defense and cell injury biomarker activities (e.g., Howcroft et al, 2011;Novais et al, 2012c.…”

“…When neurotoxic pesticides are used, the transmission of the nervous influx can be disrupted (Howcroft et al, 2011). Cholinesterases (ChE) are a family of enzymes that catalyze the breakdown of some choline esters that act as neurotransmitters.…”

“…For instance, when acetylcholinesterase (AChE) activity is inhibited, the cholinergic receptors are overstimulated because of large amounts of acetylcholine accumulate in the synaptic junction. This can lead to behavioral changes and potentially to death (Howcroft et al, 2011). Similarly, gamma-aminobutyric acid (GABA) is the major inhibitory transmitter at neuromuscular synapses and synapses in the central nervous system, being also a biomarker of neurotoxic effects .…”

Differential gene expression analysis in Enchytraeus albidus exposed to natural and chemical stressors at different exposure periods

“…Although these types of effect assessments are important to screen polluted soils for toxicity, they are time consuming and may underestimate effects occurring at the physiological and molecular levels. Recently, oxidative stress biomarkers and characterization of cholinesterase activity have been performed to further unravel the effects of soil properties, metals, phenmedipham and nanoparticles on E. albidus (Howcroft et al 2009(Howcroft et al , 2011Novais et al 2011;Gomes et al 2011). Nevertheless, the molecular pathways of toxicity of these stressors on these organisms are still uncertain.…”