In Vitro Cysteine Reactivates Organophosphate Insecticide Dichlorvos-Inhibited Human Cholinesterases

Abstract

Objectives: Organophosphate (OP) pesticides inhibit both red blood cell (RBC) and plasma cholinesterases (ChEs). Oximes, especially pralidoxime (2-PAM), are widely used as antidotes to treat OP poisoning. In addition, N-acetylcysteine (NAC) is sometimes used as an adjuvant antidote. The current study aimed to assess the feasibility of using NAC as a single therapeutic agent for OP poisoning in comparison to in vitro 2-PAM. Methods: This study was carried out at the Razi Drug Research Center of Iran University of Medical Sciences, Tehran, Iran, between April and September 2014. A total of 22 healthy human subjects were recruited and 8 mL citrated blood samples were drawn from each subject. Dichlorvos-inhibited blood samples were separately exposed to low and high doses (final concentrations of 300 and 600 μmol.L-1 , respectively) of 2-PAM, NAC and cysteine. Plasma and RBCs were then separated by centrifugation and their ChE activity was measured using spectrophotometry. Results: Although cysteine-and not NAC-increased the ChE activity of both plasma and RBCs over those of dichlorvos, it did not increase them over those of a high dose of 2-PAM. Conclusion: These results suggest that the direct reactions of 2-PAM and cysteine with dichlorvos and the reactivation of phosphorylated ChEs occurr via an associative stepwise addition-elimination process. High therapeutic blood concentrations of cysteine are needed for the elevation of ChE activity in plasma and RBCs; however, both this agent and NAC may still be effective in the reactivation of plasma and RBC ChEs.

Dual opposite actions of sodium bicarbonate in treatment of acute organophosphate poisoning

“…The IPCS working group on antidotes for organophosphorus pesticide poisoning of The World Health Organization has also highlighted the potential efficacy of sodium bicarbonate as an antidote for treatment of OP poisonings (Johnson et al, 2000[4]). Theoretically, sodium bicarbonate may exert its beneficial effect in treatment of OP poisoning by two mechanisms: the first is deactivation (dealkylation) of OPs by alkalinization of blood through a direct action and the second is reactivation of ChEs by breaking OP-ChE bond (Mohammadi et al, 2017[5]). The first pathway actually occurs because OP triesters are very sensitive to basic pH and are converted to di-substituted counterparts which are less reactive toward OPs.…”

“…The first pathway actually occurs because OP triesters are very sensitive to basic pH and are converted to di-substituted counterparts which are less reactive toward OPs. The second one does not actually occur as alkalinization of blood dealkylates OP moiety of OP-ChE complex which results in aging of ChEs and deterioration of poisoning (Shetab-Boushehri et al, 2012[8]; Mohammadi et al, 2017[5]). Moreover, the authors of the criticized paper showed no reactivation of inhibited ChEs by sodium bicarbonate (Balali-Mood et al, 2005[2]).…”

Ellman’s method is still an appropriate method for measurement of cholinesterases activities

“…Although above-mentioned problems have been stated about Ellman's method, each of them has its own logical solution. First, by simple appropriate dilution of sample, the thiol- and oxime-containing compounds in the sample are also diluted and hence the extent of reaction of DTNB with these substances is considerably reduced (Mohammadi et al, 2017[ 4 ]). Second, molar attenuation coefficients of indoxylacetate and TNB are 3900 M -1 .cm -1 (Pohanka et al, 2011[ 5 ]) and 13600 M -1 .cm -1 (Ellman et al, 1961[ 2 ]) respectively.…”

Erratum Notice of Formatting Correction: In Vitro Cysteine Reactivates Organophosphate Insecticide Dichlorvos-Inhibited Human Cholinesterases

“…The corresponding author, Seyed V. Shetab-Boushehri, contacted SQUMJ in October 2017 to inform the Editors of errors in the formatting of units of measurement throughout the article. The units of measurement had been erroneously formatted as "mg/kg- 1…”

“…For the reasons stated herein, the Editors of SQUMJ wish to notify readers that the formatting of the aforementioned units of measurement should therefore be interpreted as the following: "mg.kg -1 ", "μmol.L -1 ", "μg.mL -1 ", "μmol.L -1 ", "mg.mL -1 ", "mmol.L -1 ", "mol.L -1 ", "L.μmol -1 .cm -1 " and "U.L -1 ". 1 The Editors of SQUMJ take sole responsibility for this notice and would like to apologise to the authors and readers for this correction made after publication.…”