Methodological and biological aspects to be considered in acetylcholinesterase reactivation assays using 2-PAM

In vitro studies on the pharmacological potential, anti-tumor, antimicrobial, and acetylcholinesterase inhibitory activity of marine-derived Bacillus velezensis AG6 exopolysaccharide

In the current study, Bacillus velezensis AG6 was isolated from sediment samples in the Red Sea, identified by traditional microbiological techniques and phylogenetic 16S rRNA sequences. Among eight isolates screened for exopolysaccharide (EPS) production, the R6 isolate was the highest producer with a significant fraction of EPS (EPSF6, 5.79 g L-1). The EPSF6 molecule was found to have a molecular weight (Mw) of 2.7 × 104 g mol-1 and a number average (Mn) of 2.6 × 104 g mol-1 when it was analyzed using GPC. The FTIR spectrum indicated no sulfate but uronic acid (43.8%). According to HPLC, the EPSF6 fraction's monosaccharides were xylose, galactose, and galacturonic acid in a molar ratio of 2.0 : 0.5 : 2.0. DPPH, H2O2, and ABTS tests assessed EPSF6's antioxidant capabilities at 100, 300, 500, 1000, and 1500 μg mL-1 for 15, 60, 45, and 60 minutes. The overall antioxidant activities were dose- and time-dependently increased, and improved by increasing concentrations from 100 to 1500 μg mL-1 after 60 minutes and found to be 91.34 ± 1.1%, 80.20 ± 1.4% and 75.28 ± 1.1% respectively. Next, EPSF6 displayed considerable inhibitory activity toward the proliferation of six cancerous cell lines. Anti-inflammatory tests were performed using lipoxygenase (5-LOX) and cyclooxygenase (COX-2). An MTP turbidity assay method was applied to show the ability of EPSF6 to inhibit Gram-positive bacteria, Gram-negative bacteria, and antibiofilm formation. Together, this study sheds light on the potential pharmacological applications of a secondary metabolite produced by marine Bacillus velezensis AG6. Its expected impact on human health will increase as more research and studies are conducted globally.

Brain cholinesterase reactivation as a marker of exposure to anticholinesterase pesticides: a case study in a population of yellow-legged gull Larus michahellis (Naumann, 1840) along the northern coast of Portugal

Between late 2010 to early 2011, an increased mortality in gulls was observed along the northern coast of Portugal, with individuals exhibiting neurologic disorders consistent with an eventual anticholinesterase pesticide poisoning event. To clarify if this mortality was related to organophosphate (OP) and/or carbamate (CB) poisoning, chemical and spontaneous cholinesterase (ChE) reactivation was tested in the brain of the yellow-legged gull (Larus michahellis). Initial brain ChE activity in L. michahellis was 40.92 ± 5.23 U/mg of protein (average ± SE). Following chemical and spontaneous reactivation, ChE activity increased in average 70.38 ± 48.59% and 131.95 ± 92.64%, respectively. ChE reactivation was found to decrease at increasing concentrations of the oxime pyridine-2-aldoxime methochloride and dilution factor, underscoring the importance of first optimizing the assay conditions prior to its use on bird species. These results suggest that birds analysed could have been exposed to OP and CB pesticide compounds and that in most cases CB exposure appeared to be the main cause of birds poisoning. These results are an important contribution to environmental monitoring as it demonstrates the suitability of L. michaellis as sentinel species of OP and CB pesticides within an urban environment.

Plasma esterases in the tegu lizard Tupinambis merianae (Reptilia, Teiidae): impact of developmental stage, sex, and organophosphorus in vitro exposure

PURPOSE

In this study, we determined normal serum butyrylcholinesterase (BChE) and carboxylesterase (CbE) activities in Tupinambis merianae in order to obtain reference values for organophosphorus pesticide monitoring.

METHODS

Forty-two T. merianae individuals were grouped by sex and size to identify potential differences in their enzyme levels to allow for proper representation of normal values for females, males, juveniles, and hatchlings. Mean CbE was determined using two model substrates: alpha-naphtylacetate (α-NA) and p-nitrophenyl valerate (4-NPV). BChE and CbE sensitivity to malaoxon (Mx) was also evaluated as well as the possibility of BChE reactivation with pyridine-2-aldoxime methochloride (2-PAM).

RESULTS

Mean adult females' BChE was significantly higher than adult males, juveniles, and hatchlings. No significant differences were found between groups regarding CbE. CbE (4-NPV) activity showed slightly negative correlation with lizard snout-vent length, while BChE and CbE (α-NA) showed no correlation with body size. Apparent IC(50) values for BChE and CbE (α-NA) suggested different sensitivities among groups. CbE (4-NPV) could not be inhibited. All Mx-inhibited groups treated with 2-PAM in a final concentration of 2.8 mM showed clear signs of reactivation.

CONCLUSIONS

In conclusion, the results demonstrate that (1) plasma esterase activity did not vary with age and sex, except for BChE activity, and (2) because biological and environmental variables could be confounding factors in the response of plasma cholinesterases, complementary biomarkers like CbE inhibition and oxime-induced reactivation of esterases are strongly recommended.

Inhibition, recovery and oxime-induced reactivation of muscle esterases following chlorpyrifos exposure in the earthworm Lumbricus terrestris

Assessment of wildlife exposure to organophosphorus (OP) pesticides generally involves the measurement of cholinesterase (ChE) inhibition, and complementary biomarkers (or related endpoints) are rarely included. Herein, we investigated the time course inhibition and recovery of ChE and carboxylesterase (CE) activities in the earthworm Lumbricus terrestris exposed to chlorpyrifos, and the ability of oximes to reactivate the phosphorylated ChE activity. Results indicated that these esterase activities are a suitable multibiomarker scheme for monitoring OP exposure due to their high sensitivity to OP inhibition and slow recovery to full activity levels following pesticide exposure. Moreover, oximes reactivated the inhibited ChE activity of the earthworms exposed to 12 and 48 mg kg(-1) chlorpyrifos during the first week following pesticide exposure. This methodology is useful for providing evidence for OP-mediated ChE inhibition in individuals with a short history of OP exposure (< or = 1 week); resulting a valuable approach for assessing multiple OP exposure episodes in the field.

B-type esterases in the snail Xeropicta derbentina: an enzymological analysis to evaluate their use as biomarkers of pesticide exposure

The study was prompted to characterize the B-type esterase activities in the terrestrial snail Xeropicta derbentina and to evaluate its sensitivity to organophosphorus and carbamate pesticides. Specific cholinesterase and carboxylesterase activities were mainly obtained with acetylthiocholine (K(m)=77.2 mM; V(max)=38.2 mU/mg protein) and 1-naphthyl acetate (K(m)=222 mM, V(max)=1095 mU/mg protein) substrates, respectively. Acetylcholinesterase activity was concentration-dependently inhibited by chlorpyrifos-oxon, dichlorvos, carbaryl and carbofuran (IC50=1.35x10(-5)-3.80x10(-8) M). The organophosphate-inhibited acetylcholinesterase activity was reactivated in the presence of pyridine-2-aldoxime methochloride. Carboxylesterase activity was inhibited by organophosphorus insecticides (IC50=1.20x10(-5)-2.98x10(-8) M) but not by carbamates. B-esterase-specific differences in the inhibition by organophosphates and carbamates are discussed with respect to the buffering capacity of the carboxylesterase to reduce pesticide toxicity. These results suggest that B-type esterases in X. derbentina are suitable biomarkers of pesticide exposure and that this snail could be used as sentinel species in field monitoring of Mediterranean climate regions.

Brain cholinesterase response in the snakehead fish (Channa striata) after field exposure to diazinon

The snakehead Channa striata is an economically important air-breathing fish species in the Mekong delta of Vietnam. Rice paddies, which are disturbed by the frequent application of agro-chemicals, are among the preferred habitats for this species during the rainy season. Diazinon is one of most commonly used chemicals in rice paddies. In the present study, exposure of adult snakehead fish to a single diazinon application in cages within a rice field resulted in long-term brain cholinesterase inhibition, while the water concentration of this insecticide fell below the detection limit within 3 days. In addition, incubation of brain homogenates with 2-PAM caused reactivation of the cholinesterase diazinon complex to within 80% of the control level. These experiments also showed that chemical ageing of the diazinon cholinesterase binding occurred, which may explain the long-term effects of this pesticide.

Pollution biomarkers in estuarine animals: critical review and new perspectives

In this review, recent developments in monitoring toxicological responses in estuarine animals are analyzed, considering the biomarker responses to different classes of pollutants. The estuarine environment imposes stressful conditions to the organisms that inhabit it, and this situation can alter their sensitivity to many pollutants. The specificity of some biomarkers like metallothionein tissue concentration is discussed in virtue of its dependence on salinity, which is highly variable in estuaries. Examples of cholinesterase activity measurements are also provided and criteria to select sensitive enzymes to detect pesticides and toxins are discussed. Regarding non-specific biomarkers, toxic responses in terms of antioxidant defenses and/or oxidative damage are also considered in this review, focusing on invertebrate species. In addition, the presence of an antioxidant gradient along the body of the estuarine polychaete Laeonereis acuta (Nereididae) and its relationship to different strategies, which deal with the generation of oxidative stress, is reviewed. Also, unusual antioxidant defenses against environmental pro-oxidants are discussed, including the mucus secreted by L. acuta. Disruption of osmoregulation by pollutants is of paramount importance in several estuarine species. In some cases such as in the estuarine crab Chasmagnathus granulatus, there is a trade off between bioavailability of toxicants (e.g. metals) and their interaction with key enzymes such as Na(+)-K(+)-ATPase and carbonic anhydrase. Thus, the metal effect on osmoregulation is also discussed in the present review. Finally, field case studies with fish species like the croaker Micropogonias furnieri (Scianidae) are used to illustrate the application of DNA damage and immunosuppressive responses as potential biomarkers of complex mixture of pollutants.

Effects of methyl parathion on Chasmagnathus granulatus hepatopancreas: protective role of sesamol

The protective role of sesamol, an inhibitor of the mixed function oxygenase (MFO) system, against histopathological effects of methyl parathion in the hepatopancreas of the estuarine crab, Chasmagnathus granulatus, was studied. Exposure (72 h) to a sublethal dose (0.05 mg/kg/day; 10% of 72 h-LD50) of injected methyl parathion increased the percentage of damaged hepatopancreatic tubules. Presence of melanin-like deposits in the connective tissue between hepatopancreatic tubules was also observed. Antioxidant enzyme activities (catalase and glutathione S-transferase) and lipid peroxidation (LPO) levels were also increased in hepatopancreas of crabs injected with methyl parathion. Pretreatment with sesamol (0.85 mg/kg/day) significantly protected against all these effects. These findings suggest that the hepatopancreatic damages induced by methyl parathion are due to LPO of hepatopancreatocytes membranes, as a consequence of the oxidative stress generated after methyl parathion oxidative biotransformation mediated by the MFO system.

Inhibition of plasma butyrylcholinesterase activity in the lizard Gallotia galloti palmae by pesticides: a field study

A field study was performed to evaluate the effect of exposure to organophosphorus (OP) and carbamate (CB) pesticides on the lizard Gallotia galloti palmae. Butyrylcholinesterase (BChE) activity was measured in the plasma of 420 lizards collected from agricultural and reference areas on the Island of La Palma (Canary Islands, Spain) in two sampling periods. Exposure to cholinesterase-inhibiting pesticides was evaluated by a statistical criterion based on a threshold value (two standard deviations below the mean enzyme activity) calculated for the reference group, and a chemical criterion based on the in vitro reactivation of BChE activity using pyridine-2-aldoxime methochloride (2-PAM) or after water dilution of the sample. Mean (+/- SD) BChE activity for lizards from agricultural areas was significantly lower (Fuencaliente site = 2.00 +/- 0.98 micromol min(-1) ml(-1), Tazacorte site = 2.88 +/- 1.08) than that for lizards from the reference areas (Los Llanos site = 3.06 +/- 1.17 micromol min(-1) ml(-1), Tigalate site = 3.96 +/- 1.62). According to the statistical criterion, the number of lizards with BChE depressed was higher at Fuencaliente (22% of males and 25.4% of females) than that sampled at Tazacorte (7.8% of males and 6.2% of females). According to the chemical criterion, Fuencaliente also yielded a higher number of individuals (112 males and 47 females) with BChE activity inhibited by both OP and CB pesticides. CBs appeared to be the pesticides most responsible for BChE inhibition because most of the samples showed reactivation of BChE activity after water treatment (63.3% from Fuencaliente and 29% from Tazacorte). We concluded that the use of reactivation techniques on plasma BChE activity is a better and more accurate method for assessing field exposure to OP/CB pesticides in this lizard species than making direct comparisons of enzyme activity levels between sampling areas.

Kinetic and toxicological characteristics of acetylcholinesterase from the gills of oysters (Crassostrea rhizophorae) and other aquatic species

The aim of this work was to characterize the cholinesterases from gills of Crassostrea rhizophorae in order to use them as biomarkers. Gills were homogenized and then centrifuged (9,000 x g, 4 degrees C, 30 min). S9 and Triton X-100 S9 treated (TX S9) fractions were employed as enzyme source. Km(ap) and Vmax were estimated, using acetylthiocholine iodide as substrate. Inhibition assays were performed with iso-OMPA and eserine. The Km(ap) for S9 and TX S9 fractions were 0.05 and 0.06 mM, whereas the Vmax were 1.92 and 5.84 nmol/min/mg protein. respectively. No inhibition was detected when the samples were incubated with iso-OMPA, suggesting the presence of acetylcholinesterases (AChE) in oyster gill homogenates. Sensitivity to eserine inhibition of AChE in the gills of oysters is intermediate when compared with other aquatic species.