A comprehensive evaluation of the efficacy of leading oxime therapies in guinea pigs exposed to organophosphorus chemical warfare agents or pesticides.

The currently fielded pre-hospital therapeutic regimen for the treatment of organophosphorus (OP) poisoning in the United States (U.S.) is the administration of atropine in combination with an oxime antidote (2-PAM Cl) to reactivate inhibited acetylcholinesterase (AChE). Depending on clinical symptoms, an anticonvulsant, e.g., diazepam, may also be administered. Unfortunately, 2-PAM Cl does not offer sufficient protection across the range of OP threat agents, and there is some question as to whether it is the most effective oxime compound available. The objective of the present study is to identify an oxime antidote, under standardized and comparable conditions, that offers protection at the FDA approved human equivalent dose (HED) of 2-PAM Cl against tabun (GA), sarin (GB), soman (GD), cyclosarin (GF), and VX, and the pesticides paraoxon, chlorpyrifos oxon, and phorate oxon. Male Hartley guinea pigs were subcutaneously challenged with a lethal level of OP and treated at approximately 1 min post challenge with atropine followed by equimolar oxime therapy (2-PAM Cl, HI-6 DMS, obidoxime Cl2, TMB-4, MMB4-DMS, HLö-7 DMS, MINA, and RS194B) or therapeutic-index (TI) level therapy (HI-6 DMS, MMB4-DMS, MINA, and RS194B). Clinical signs of toxicity were observed for 24 h post challenge and blood cholinesterase [AChE and butyrylcholinesterase (BChE)] activity was analyzed utilizing a modified Ellman's method. When the oxime is standardized against the HED of 2-PAM Cl for guinea pigs, the evidence from clinical observations, lethality, quality of life (QOL) scores, and cholinesterase reactivation rates across all OPs indicated that MMB4 DMS and HLö-7 DMS were the two most consistently efficacious oximes.

Effect of some acetylcholinesterase reactivators on human platelet aggregation in vitro.

Acetylcholinesterase (AChE) reactivators are employed for the prophylaxis and treatment of intoxications with organophosphorus AChE inhibitors, including nerve agents and pesticides. For the recovery of inhibited enzyme, derivatives from the group of pyridinium or bispyridinium aldoximes (called oximes) are used. Adverse effects of these substances are not well elucidated, because of their narrow and one-shot usage. Owing to this fact, the study evaluated the influence of some currently applied oximes on human platelet aggregation in vitro. The antiplatelet activity of pralidoxime, obidoxime, HI-6, methoxime and HLö 7 was assayed in human platelet rich plasma (2.5 x 10(8) platelets.ml(-1)) at a concentration of 1.35 mM. Arachidonic acid (AA), adenosine diphosphate (ADP), collagen (COL) and thrombin (TR) were used as agonists of platelet aggregation. All tested substances, except pralidoxime and methoxime, caused a significant inhibition of the aggregation process induced by AA, ADP and COL. Of the oximes assayed, none was found to influence TR triggered aggregation. Since reduced platelet aggregation can play an important role as an adverse effect in reactivator administration, further evaluation is needed for the estimation of the real impact of active oximes to the aggregation process in humans.

Padronizaçäo da metodologia para avaliaçäo de colinesterase eritrocitária: otimizaçäo das técnicas para monitoramento da exposiçäo ocupacional a pesticidas organofosforados / Standardize methodology to avaliation of the cholinesterase erythrocyte: otimization of the techniques of occupational exposure assessment in organophosphorus pesticides compounds

Compostos organofosforados säo amplamente utilizados na agricultura para controlar pragas, o uso indiscriminado destas substâncias tem provocado inúmeros casos de intoxicaçäo aguda e crônica em trabalhadores rurais. A determinaçäo da atividade enzimática das colinesterases sanguíneas é utilizada em todo o mundo no monitoramento da exposiçäo a estas substâncias, principalmente a da colinesterase plasmática. Entretanto, a colinesterase eritrocitária reflete de forma mais acurada o real grau da inativaçäo desta enzima no sistema nevoso, alvo principal dos pesticidas organofosforados. O objetivo básico deste trabalho foi padronizar uma metodologia enzimática sensível para a determinaçäo da colinesterase eritrocitária. Tomando por base a metodologia de preparaçäo de membrana de eritrócitos desenvolvida por Oliveira-Silva (1994) e o método de determinaçäo da atividade de colinesterase de Ellman (1961), vários experimentos foram feitos no sentido de simplificar esta técnica. A metodologia proposta para a preparaçäo de membranas de eritrócitos é a seguinte: 1 ml de eritrócitos é lavado em 10 volumes de soluçäo salina (NaCL 0,9 por cento) e centrifugados a 2000xg/15 min; o sedimento é ressuspenso em 10 volumes de soluçäo lisante (fosfato de sódio 20 mM, pH, 7,2), congelado por 24 horas e lavado 3x com soluçäo lisante; o sedimento final é ressuspenso no volume inicial de eritrócitos em tampäo fosfato de sódio 120 mM, pH 7,2. Para a determinaçäo da exposiçäo ocupacional, esta preparaçäo pode ser guardada refrigerada por no máximo 24 horas sem perda significativa da sua atividade. Por se tratar de uma metodologia que possui várias etapas de diluiçäo, verificamos se a interaçäo enzima-pesticida poderia ser revertida, através de experimentos onde a enzima inibida por paraoxon passou por todas as etapas de processamento, chegando ao final com o mesmo percentual de inibiçäo inicial. Através da aplicaçäo desta metodologia em trabalhadores rurais expostos a pesticidas organofosforados, foram encontradas inibiçöes da colinesterase eritrocitária de até 50 por cento. A metodologia desenvolvida se mostrou sensível e reprodutível, podendo ser utilizada na determinaçäo da intoxicaçäo crônica por pesticidas organofosforados.