In Vitro Cysteine Reactivates Organophosphate Insecticide Dichlorvos-Inhibited Human Cholinesterases.

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.

Efficacy of fresh packed red blood transfusion in organophosphate poisoning.

The mortality rate caused by organophosphate (OP) poisoning is still high, even the standard treatment such as atropine and oxime improves a lot. To search for alternative therapies, this study was aimed to investigate the effects of packed red blood cell (RBC) transfusion in acute OP poisoning, and compare the therapeutic effects of RBCs at different storage times.Patients diagnosed with OP poisoning were included in this prospective study. Fresh RBCs (packed RBCs stored less than 10 days) and longer-storage RBCs (stored more than 10 days but less than 35 days) were randomly transfused or not into OP poisoning patients. Cholinesterase (ChE) levels in blood, atropine usage and durations, pralidoxime durations were measured.We found that both fresh and longer-storage RBCs (200-400 mL) significantly increased blood ChE levels 6 hours after transfusion, shortened the duration for ChE recovery and length of hospital stay, and reduced the usage of atropine and pralidoxime. In addition, fresh RBCs demonstrated stronger therapeutic effects than longer-storage RBCs.Packed RBCs might be an alternative approach in patients with OP poisoning, especially during early stages.

Can anisodamine be a potential substitute for high-dose atropine in cases of organophosphate poisoning?

A case of organophosphate (OP) poisoning was admitted to the emergency room. The patient accepted treatment with pralidoxime (PAM), atropine, and supporting therapy. It was observed that even after 22 h after treatment, 960 mg of atropine was not enough for the patient to be atropinized. However, a 160-mg follow-up treatment of anisodamine was quite enough for atropinization after 4 h. As a case report, more studies are required before any definite conclusion can be reached regarding the use of anisodamine as a potential substitute for high-dose atropine in cases of OP poisoning.

Protective drugs in acute large-dose exposure to organophosphates: a comparison of metoclopramide and tiapride with pralidoxime in rats.

Weak and reversible inhibitors of cholinesterase(s), when coadministered in excess with a more potent inhibitor such as organophosphates, can act in a protective manner. The benzamide compound, metoclopramide, confers some protection (putatively via this mechanism) for cholinesterases against inhibition by paraoxon both in vitro and in vivo, after chronic small-dose exposure. Tiapride is a related benzamide. In this study, we compared the protection by metoclopramide and tiapride in rats acutely exposed to large doses of paraoxon with the therapeutic "gold standard," pralidoxime. Group 1 received 1 micromol paraoxon (approximately 75% lethal dose), Group 2 received 50 micromol metoclopramide, Group 3 received 50 micromol tiapride, Group 4 received 50 micromol pralidoxime, Group 5 received 1 micromol paraoxon + 50 micromol metoclopramide, Group 6 1 micromol paraoxon + 50 micromol tiapride, and Group 7 1 micromol paraoxon + 50 micromol pralidoxime. All substances were administered intraperitoneally. The animals were monitored for 48 h and mortality was recorded at 30 min, 1, 2, 3, 4, 24, and 48 h. Blood was taken for red blood cell acetylcholinesterase measurements at baseline, 30 min, 24, and 48 h. With the exception of Group 7, in which some late mortality was observed, mortality occurred mainly in the first 30 min after paraoxon administration with minimal changes occurring thereafter. Mortality at 30 min was 0% in the metoclopramide, tiapride, and pralidoxime groups and 73 +/- 20 (paraoxon), 65 +/- 15 (paraoxon + metoclopramide), 38 +/- 14 (paraoxon + tiapride), and 13 +/- 19 (paraoxon + pralidoxime). Mortality at 48 h was 75 +/- 18 (paraoxon), 67 +/- 17 (paraoxon + metoclopramide), 42 +/- 16 (paraoxon + tiapride), and 27 +/- 24 (paraoxon + pralidoxime). Metoclopramide does not significantly influence mortality after acute large-dose paraoxon exposure. Both tiapride and pralidoxime significantly decreased mortality in our model. The protection conferred by tiapride was significantly less than that conferred by pralidoxime at 30 min, but was not significantly different at 24 and 48 h.

Reappraisal of indications and limitations of oxime therapy in organophosphate poisoning.

1 In vitro studies with human erythrocyte acetylcholinesterase (AChE) and the mouse diaphragm model were performed to unravel the various microscopic reaction parameters that contribute to the dynamic equilibrium of AChE inhibition, ageing and reactivation. These data may help to define more precisely the indications and limitations of oxime therapy in organophosphate (OP) poisoning. 2 Diethylphosphoryl-AChE resulting from intoxications with parathion, chlorpyrifos, chlorfenvinphos, diazinon and other OPs is characterized by slow spontaneous reactivation and low propensity for ageing. This kind of phosphorylated enzyme is particularly susceptible to reactivation by oximes. 3 None of the oximes tested (pralidoxime, obidoxime, HI 6 and HLö 7) can be regarded as a universally suitable reactivator. Obidoxime turned out to be the most potent and most efficacious oxime in reactivating AChE inhibited by various classes of OP insecticides and tabun. Obidoxime, however, was inferior to HI 6 against soman, sarin, cyclosarin and VX. Pralidoxime was generally less potent. 4 The kinetic data of reactivation established for diethylphosphoryl-AChE of human red cells indicate that the usually recommended dosage to attain a plasma concentration of 4 micrograms/ml does not permit exploitation of the full therapeutic potential of the oximes, in particular of pralidoxime. However, in suicidal mega-dose poisoning, oximes, even at optimal plasma concentrations, may be unable to cope with the fast re-inhibition of reactivated AChE in the first days following intoxication. 5 It is suggested that oximes be administered by continuous infusion following an initial bolus dose as long as reactivation can be expected and until permanent clinical improvement is achieved.

Improvement of motor function in multiple sclerosis by use of protopam chloride.

PAM, a cholinesterase reactivator, was administered orally and parenterally to 37 patients with multiple sclerosis and a control group of 24 patients with other neurological diseases and pain syndromes. The effects of the administration of this compound in these patients with and without electrical stimulation of the spinal cord were studied. The clinical response to the drug follows a known time course and is dose related. Administration of large doses orally or intravenously aggravates existing neurological dysfunction. With a dose of 1,000 mg intravenously, a characteristic response is the temporary appearance of new ophthalmological abnormalities, followed by significant improvement in motor control and behavior, which gradually subsides. Parenteral administration is superior to oral. Tolerance to the drug is observed. The presence of electrical stimulation of the spinal cord complements the action of the drug. When electrical stimulation is withdrawn, the effect of the drug reproduces the effect of the electrical stimulation. It is suggested there is a defect in cholinesterase in multiple sclerosis patients, and its reactivation may have a significant relationship to signs and symptoms.

[Experimental studies on the efficacy of PAM against sumithion poisoning].

The efficacy of 2-Pyridine aldoximide methiodide (PAM) for lethal acute poisoning by fenitrothion (FNT) was investigated in mice and dogs. Sumithion (FNT 51.7%, emulsifiers 12.5% and xylol 35.8%) was used as fenitrothion. 1. FNT at 1500 mg/kg was administered orally to mice. After ten minutes 50 mg/kg of PAM was injected once iv, and plasma, erythrocyte, brain, liver and kidney ChE activities were investigated 30 and 60 min later. Recovery in ChE activity was found in every organ but the brain at 30 min, but no efficacy of PAM was observed at 60 min. 2. After administering 1500 mg/kg of FNT orally to mice, the life-saving effect was studied from the changes in mortality due to variation of PAM route, dosage and number of administrations. With oral administration of 1500 mg/kg of FNT, 75 to 85% of the animals died. The mortality ranged from 80 to 95% when the animals received a single intravenous injection of 50 mg/kg of PAM between zero and 60 min following the FNT administration. Thus, a single intravenous administration of PAM at 50 mg/kg showed no life-saving effect on the animals given FNT. However, the mortality was reduced to 45% when the animals received repeated subcutaneous injections of 20 mg/kg of PAM at a 3-hr interval from just after administration of FNT over 24-hr. In other repeated subcutaneous injection experiments, the mortality ranged from about 55 to 65%. In any PAM-treated group, the survival time was prolonged. This life-prolonging effect was more marked in the case of repeated subcutaneous injections of PAM by 12-hr and even more by 24-hr, than in the case of a single intravenous injection. FNT treatment caused marked salivation and watery diarrhea, and PAM clearly inhibited these signs of the muscarinic action of FNT. There was a high relationship between this inhibitory effect of PAM on the muscarinic action and its life-prolonging or life-saving effect. 3. PAM (150 mg/animal/shot, iv) was given 12 or 13 times during 7 hr from 10 min (4 animals), 3 hr (1 animal) and 6 hr (2 animals) after administration of FNT at 150 mg/kg. The effects of PAM on survival, plasma ChE activity, plasma protein (TP) and hematocrit (Ht) values were examined. The 3 dogs given FNT alone all died within 53 hr of administration, whereas 6 out of 7 animals treated with PAM survived.(ABSTRACT TRUNCATED AT 400 WORDS)