A new method to characterize the kinetics of cholinesterases inhibited by carbamates

Design, Synthesis and Biological Evaluation of Biscarbamates as Potential Selective Butyrylcholinesterase Inhibitors for the Treatment of Alzheimer's Disease

As butyrylcholinesterase (BChE) plays a role in the progression of symptoms and pathophysiology of Alzheimer's disease (AD), selective inhibition of BChE over acetylcholinesterase (AChE) can represent a promising pathway in treating AD. The carbamate group was chosen as a pharmacophore because the carbamates currently or previously in use for the treatment of AD displayed significant positive effects on cognitive symptoms. Eighteen biscarbamates with different substituents at the carbamoyl and hydroxyaminoethyl chain were synthesized, and their inhibitory potential toward both cholinesterases and inhibition selectivity were determined. The ability of carbamates to cross the blood-brain barrier (BBB) by passive transport, their cytotoxic profile and their ability to chelate biometals were also evaluated. All biscarbamates displayed a time-dependent inhibition with inhibition rate constants within 10^-3-10^-6 M^-1 min^-1 range for both cholinesterases, with generally higher preference to BChE. For two biscarbamates, it was determined that they should be able to pass the BBB by passive transport, while for five biscarbamates, this ability was slightly limited. Fourteen biscarbamates did not exhibit a cytotoxic effect toward liver, kidney and neuronal cells. In conclusion, considering their high BChE selectivity, non-toxicity, ability to chelate biometals and pass the BBB, compounds 2 and 16 were pointed out as the most promising compounds for the treatment of middle and late stages of AD.

Microbial elimination of carbamate pesticides: specific strains and promising enzymes

Carbamate pesticides are widely used in the environment, and compared with other pesticides in nature, they are easier to decompose and have less durability. However, due to the improper use of carbamate pesticides, some nontarget organisms still may be harmed. To this end, it is necessary to investigate effective removal or elimination methods for carbamate pesticides. Current effective elimination methods could be divided into four categories: physical removal, chemical reaction, biological degradation, and enzymatic degradation. Physical removal primarily includes elution, adsorption, and supercritical fluid extraction. The chemical reaction includes Fenton oxidation, photo-radiation, and net electron reduction. Biological degradation is an environmental-friendly manner, which achieves degradation by the metabolism of microorganisms. Enzymatic degradation is more promising due to its high substrate specificity and catalytic efficacy. All in all, this review primarily summarizes the property of carbamate pesticides and the traditional degradation methods as well as the promising biological elimination. KEY POINTS: • The occurrence and toxicity of carbamate pesticides were shown. • Biological degradation strains against carbamate pesticides were presented. • Promising enzymes responsible for the degradation of carbamates were discussed.

Cholinesterase characterization and effects of the environmental contaminants chlorpyrifos and carbofuran on two species of marine crabs, Carcinus maenas and Pachygrapsus marmoratus

Among the most frequent targets for toxic effects of modern pesticides, namely organophosphates and carbamates, one may find cholinesterases (ChEs). ChEs exist in a wide variety of animals and have been used actively to discriminate among the environmental effects of different pollutant groups, including the aforementioned pesticides. This study had three purposes, namely (i) identifying the ChE forms present in tissues (eyes and walking legs muscle) of two crab species, Carcinus maenas and Pachygrapsus marmoratus; to (ii) determine the in vitro toxicological effects, and (iii) compare the sensitivity of such enzymatic forms towards commonly used anti-ChE pesticides, namely the organophosphate chlorpyrifos and the carbamate carbofuran. Our results showed that there was not a clear preference for any of the tested substrates in any of the tissues from both species. Furthermore, the ChE activity was almost completely suppressed following incubation with eserine and with the specific inhibitor BW284C51 in all tissues from both species. In vitro exposure to chlorpyrifos promoted a significant decrease in ChE activity in both species. Furthermore, the ChE activity was completely suppressed following incubation with carbofuran and chlorpyrifos. These results suggest that the major ChE forms present in tissues of both crab species show intermediate structural properties and activity patterns, halfway between classic acetylcholinesterase and pseudocholinesterases. However, the sensitivity of the found forms towards ChE inhibitors was established, and the responsiveness of such forms towards common anti-ChE chemicals was established. Both tested species seem to be promising test organisms to be used in marine and coastal scenarios of putative contaminations by anti-ChE chemicals, considering the here reported patterns of response.

Cholinesterases characterization of three tropical fish species, and their sensitivity towards specific contaminants

Cholinesterases are frequent targets for toxic effects, namely by insecticides derived from phosphoric and carbamic acids. This effects allows the use of cholinesterase inhibition as a biomarker for contamination of aquatic environments by these specific chemical agents. However, cholinesterases are differently responsive to environmental contaminants, according to their different forms and locations. In addition, cholinesterases seem also to be inhibited by metals, so their use as an environmental criterion requires the prior characterization of their specific forms in each species and tissues, and the study of their sensitivity. The objective of this study was to characterize the cholinesterase isoenzymes present in the brain and dorsal muscle of three tropical fish species, namely Phalloceros harpagos (Lucinda, 2008), Pterygoplichthys pardalis (Castelnau, 1855) and Astyanax altiparanae (Garutti and Britski, 2000). In vitro assays were conducted to quantify the effect of pesticides (dimethoate and carbaryl) and metals (lead and copper) on cholinesterases activity. Although acetylcholinesterase seems to be the most prevalent and abundant form, as commonly described in vertebrates, the here-obtained results showed that three cholinesterase isoenzymes occur in tissues of the three fish species. In addition, the pesticide carbaryl caused a stronger inhibition than dimethoate. Copper caused a significantly higher cholinesterasic inhibition than lead, which is also in line with most results concerning the anticholinesterasic effects by these metals. The here obtained results allowed to conclude that acetylcholinesterase is the predominant form in all tissues from the three analyzed species. In addition, cholinesterases of these three fish were responsive to common environmental contaminants, namely metals and pesticides, similarly to what was already described for fish of temperate areas. This allows using the here proposed fish species in environmental studies for the assessment of the presence of neurotoxicants under neotropical conditions.

Kinetically-controlled mechanism-based isolation of metabolic serine hydrolases in active form from complex proteomes: butyrylcholinesterase as a case study

In this work an activity-based probe containing a carbamate group was designed to isolate human butyrylcholinesterase (hBChE), a metabolic serine hydrolase (mSH), from complex proteomes. The method took advantage of the native interaction mechanism of mSHs with carbamate pseudo-substrates for temporarily capturing the enzyme on a resin functionalized with the carbamate probe and releasing the enzyme in active form after removal of the contaminating proteins. The isolation relied on the possibility of manipulating the carbamylation and decarbamylation kinetics favoring the former during the capture and wash steps and the latter in the release step. The designed probe captured and released all the active hBChE isoenzymes present in plasma with high selectivity (up to ∼2000-fold purification) and reasonable yields (17% to 36%). The parameters affecting the performance were the incubation time used in the load and elution steps, the plasma to resin volumetric ratio, the elution temperature and the nature and concentration of the eluting agent. The carbamate resin could be prepared either by coupling a fully synthesized probe with an activated resin or by building the probe onto the resin by a step-by-step procedure, without major differences in performance between the two routes. The prepared resins allowed to process up to about 8.5 mL of plasma per g of resin with constant performance. Since the method was based on the general catalytic cycle of mSHs, we expect this approach to be applicable to other enzymes of the family, by selecting a suitable target-selective feature to link to the carbamate group.

The modulation of the equilibrium between carbamylation and decarbamylation kinetics is used to isolate a model metabolic serine hydrolase.