Claire N. Lieske

Studies of the amplification of carbaryl toxicity by various oximes

The administration of 2-pyridine aldoxime methyl chloride (2-PAM Cl) is a standard part of the regimen for treatment of human overexposure to many organophosphorus pesticides and nerve agents. However, some literature references indicate that poisoning by carbaryl (1-naphthyl N-methyl carbamate), an insecticide in everyday use, is aggravated by the administration of 2-PAM Cl. This effect has been reported in the mouse, rat, dog and man. We have found that the inhibition of both eel acetylcholinesterase (eel AChE, EC 3.1.1.7) and human serum cholinesterase (human BuChE, EC 3.1.1.8) by carbaryl was enhanced by several oximes. Based on 95% confidence limits the rank order of potentiation with eel AChE was TMB-4 = Toxogonin > HS-6 = HI-6 > 2-PAM Cl. By the same criterion, the rank order of potentiation with human BuChE was TMB-4 > Toxogonin > HS-6 = 2-PAM Cl. Carbaryl-challenged mice also reflected a potentiation since TMB-4 exacerbated the toxicity more than 2-PAM Cl. Our hypothesis is that certain oximes act as allosteric effectors of cholinesterases in carbaryl poisoning, resulting in enhanced inhibition rates and potentiation of carbaryl toxicity.

Spontaneous and induced reactivation of eel acetylcholinesterase inhibited by three organophosphinates

Abstract This paper constitutes the first report on the spontaneous reactivation of a cholinesterase following inhibition by an organophosphinate. The spontaneous reactivation of eel acetylcholinesterase following inhibition by p -nitrophenyl diphenylphosphinate (DPP), p -nitrophenyl methyl(phenyl)phosphinate (MPP), and p -nitrophenyl dimethylphosphinate (DMP) at 25.0°C in 0.10 M 3-( N -morpholino)propanesulfonic acid buffer of pH 7.60 reflected the following order of activity: MPP > DPP > DMP. Hydrolysis studies of the phosphinate esters under these conditions exhibited the same order of reactivity. Kinetic studies on the spontaneous reactivation of methyl(phenyl)phosphinylated eel acetylcholinesterase at pH 7.60 and pH 9.10 showed a 100% recovery of enzymatic activity, thus demonstrating the absence of aging. The absence of aging was further supported by oxime-induced reactivation studies.

Inhibition of two acetylcholinesterases by the 4-nitrophenyl esters of methyl-, ethyl-, and isopropyl(phenyl)phosphinic acid☆

Abstract The inhibition of eel acetylcholinesterase and bovine erythrocyte acetylcholinesterase by the 4-nitrophenyl esters of methyl-, ethyl-, and isopropyl(phenyl)phosphinic acid (MPP, EPP, and IPP, respectively) was investigated at pH 6.90 in 0.067 M phosphate buffer (25.0°C) using stopped-flow instrumentation and automated data processing. Our evaluation of the dissociation constant, K d , the unimolecular bonding rate constant, k 2 , and the bimolecular reaction constant, k i , are the first reported values for these constants for a homologous series of this class of organophosphorus compounds. The largest k 1 value (29,428 M −1 sec −1 ) was observed for the reaction of eel acetylcholinesterase with 4-nitrophenyl methyl(phenyl)phosphinate. The smallest k i value (9.6 M −1 sec −1 ) was observed for the reaction of bovine erythrocyte acetylcholinesterase with 4-nitrophenyl isopropyl(phenyl)phosphinate.

Eel acetylcholinesterase inhibition studies with heteroarylphosphinates

Abstract The inhibition of eel acetylcholinesterase by the 4-nitrophenyl esters of 2-furyl(methyl)-, methyl(2-thienyl)-, di-2-furyl-, and di-2-thienylphosphinic acid (I, II, III, and IV, respectively) was investigated at pH 6.90 in 0.067 M phosphate buffer (25.0°C) using stopped-flow instrumentation and automated data processing. Our evaluation of the dissociation constant, Kd, the unimolecular bonding rate constant, k2, and the bimolecular reaction constant, ki, are the first reported values for these constants for alkyl/heteroaryl and diheteroaryl esters of phosphinic acids. The largest ki value (19,330 M−1 sec−1) was observed for the reaction of I with the enzyme. The order for the remaining three is II > IV > III. There is no direct relationship between the hydrolysis rates of the esters and their anticholinesterase activities on eel acetylcholinesterase. Likewise, there is no direct relationship between their anticholinesterase activities and the LD50 values in rats.

Temperature Effects in Cyanolysis Using Elemental Sulfur

As part of our studies directed at new treatments for cyanide poisoning we examined the effect of temperature on both the non‐catalyzed and the albumin‐catalyzed reactions of cyanide with a colloidal suspension of elemental sulfur (CSES). Using saturated sulfur solutions prepared in two solvents, pyridine (PY) and methyl cellosolve (MC), the reactions were studied at 15.0, 25.0, 30.0 and 37.5°C. For all the cyanolysis reactions (non‐catalyzed and albumin‐catalyzed) there is an enhancement of reaction rate when the organic solvent for the sulfur is MC. Irrespective of the solvent for the CSES, the non‐catalyzed reactions gave linear Arrhenius plots (PY, correlation coefficient = 0.998; MC, correlation coefficient = 0.997). In each case the entropy of activation was positive (14.1 cal K−1 mol−1 for PY and 56.4 cal K−1 mol−1 for MC). In contrast with these results the albumin‐catalyzed reactions generated non‐linear Arrhenius plots and negative entropies of activation. Non‐linear plots were observed with the three albumins studied: human serum albumin, heat‐shock bovine serum albumin and fatty acid‐free bovine serum albumin. The non‐linear plots are the result of a more complex reaction sequence than a simple cyanolysis reaction.

Eel acetylcholinesterase studies with the 4-nitrophenyl esters of monochloro-, dichloro-, and trichloromethyl(phenyl)phosphinic acid

Abstract The inhibition of eel acetylcholinesterase by the 4-nitrophenyl esters of monochloromethyl(phenyl)-, dichloromethyl(phenyl)-, and phenyl(trichloromethyl)phosphinic acid (I, II, and III, respectively) was investigated at pH 6.90 in 0.067 M phosphate buffer (25.0°C) using stopped-flow instrumentation and automated data processing. The largest k i value (156,700 M −1 sec −1 ) was observed for the reaction of I with the enzyme. There is no direct relationship between the hydrolysis rates of the esters and their anticholinesterase activities on eel acetylcholinesterase. Spontaneous reactivation of the phosphinylated enzymes at pH 7.60 showed the following order of activity: I > III > II. The absence of aging is supported by oxime-induced reactivation studies.

Application of a new radiometric high-performance liquid chromatographic assay to define physostigmine pharmacokinetics in guinea pigs.

A sensitive high-performance liquid chromatographic method was developed to determine pharmacokinetic parameters of [3H]physostigmine from serial plasma samples from guinea pigs. Physostigmine was totally resolved from its metabolite, eseroline. The limit of sensitivity was 0.05 ng/ml from 0.2 ml plasma. Extraction efficiency was 99.6%. Within-run and among-run coefficients of variation (n = 6) for 0.2, 0.75, 1.5 and 2.5 ng/ml [3H]physostigmine ranged from 0.7 to 20% and 16 to 32%, respectively. Physostigmine (5 micrograms/kg) intramuscularly administered to the guinea pig (n = 6) reached maximum serum concentration (1.5 ng/ml) in 26 min. The apparent volume of distribution and systemic clearance were 1.4 l/kg and 26 ml/min/kg, respectively. This method was successful in defining physostigmine pharmacokinetic parameters in guinea pigs and can be employed for other small animal pharmacokinetic studies.