E. Wood

Partial purification and characterization of Triatoma infestans head acetylcholinesterase

Abstract A cholinesterase (ChE) from the heads of Triatoma infestans was purified partially by sodium deoxycholate solubilization and by ammonium sulphate and acetone fractionation. The enzyme was purified 14 fold with a yield of 78%. The purified ChE was considered to be an acetylcholinesterase (AChE) based on its substrate specificity, its response to selective inhibitors, the pH sensitivity of its hydrolysis of acetylcholine (ACh) and its inhibition by excess substrate. The purified fraction was shown to be free of butyrylcholinesterase and eserine-resistant esterases which were present in crude homogenates. Disc electrophoresis revealed three interconvertible forms of AChE in the purified enzyme. AChE from T. infestans hydrolyses ACh and its thio-analogue (ATC) at higher rates than other choline esters tested. Maximal velocity for the hydrolysis of ACh by this enzyme was shown at pH 3.3 and pH 7.2. With ATC a K m of 3.3 × 10 −5 M was obtained. The organophosphates were shown to be potent inhibitors of the purified AChE.

Evaluación de la b -cipermetrina para el control de Triatoma infestans

En este estudio se evaluo en el laboratorio y en el campo el efecto insecticida sobre Triatoma infestans, vector de la enfermedad de Chagas, del nuevo piretroide s-cipermetrina, y se comparo con el de la deltametrina. La comparacion de las dosis letales 50 (DL50) de ambos piretroides indico que la s-cipermetrina es mas efectiva en ninfas y la deltametrina, en adultos. La evaluacion de la concentracion letal 50 (CL50) de las dos formulaciones floables de ambos insecticidas depositados sobre distintos soportes mostro que su efectividad en vidrio es similar. En ceramica, la deltametrina es ligeramente mas efectiva. Los dos insecticidas floables se evaluaron en 100 viviendas infestadas de la provincia de Santiago del Estero, Argentina. La deltametrina floable se aplico a una concentracion superficial de 25 mg/m² y la s-cipermetrina, de 50 mg/m². Las concentraciones superficiales reales de ambos productos se analizaron por medio de papeles de filtro colocados en paredes y techos. El analisis por cromatografia de gases mostro buena coincidencia con las concentraciones previstas. Asimismo, se realizaron evaluaciones entomologicas 60, 90, 180 y 365 dias despues de los tratamientos. Solo en la ultima evaluacion se encontro 10% de infestacion en peridomicilios de viviendas tratadas con s-cipermetrina y 7% en las viviendas tratadas con deltametrina (6% en el peridomicilio y 1% en el domicilio). Los resultados indican que la efectividad de la s-cipermetrina para controlar a T. infestans cuando se aplica a una concentracion de 50 mg/m² es similar a la de la deltametrina cuando esta se administra a una concentracion de 25 mg/m².

Insecticidal Activity of Pyrethroids Against Triatoma infestans

The insecticide activity of synthetic pyrethroids to Triatoma infestans was tested by topical application. Deltamethrin, fenpropathrin, bioresmethrin, permethrin, Cypermethrin, d-phenothrin and cyphenothrin showed the highest activity.The susceptibility to poisoning of adult insects by these pyrethroids (except bioresmethrin) was increased by cotreatment with profenofos or with piperonyl butoxide (PBO). Assayed pyrethroids synergized by PBO showed similar general structure.The vinyl cyano pyrethroids showed a knockdown effect with a delayed recovery. During 15 days after intoxication with deltamethrin, insect recovery was observed. Recovery blockage by PBO was observed in cyphenothrin and deltamethrin poisoning at low doses.RésuméL’activité insecticide de pyréthrinoides de synthèse a été essayée par application topique sur Triatoma infestans.Deltaméthrine, fénpropathrine, biorésméthrine, permethrine, cyperméthrine, d-phénothrine et cyphénothrine ont montrée la meilleure activité.La susceptibilité à l’intoxication par ces pyréthrinoides des insectes adultes (avec l’exception de biorésmethrine) a été améliorée en ajoutant le profenofos ou le butoxide de pipéronyl (PBO) dans les traitements. Les pyréthrinoides synergisées par PBO ont montrée une structure chimique similaire. Les vinyl cyano piréthrinoides ont montrée l’effect choc accompagné d’une récupération retardée. Pendant 15 jours aprés l’intoxication avec la deltaméthrine, la récupération des insectes a été obtenue.

Evaluation of the flushing out activity of pyrethroids on Triatoma infestans

Tetramethrin, deltamethrin and Cypermethrin formulated as fumigant tablets or spray(ing) solutions showed flushing out activity on Triatoma infestans. Fumes arising from the tablets were analysed by gas chromatography. The proportion of pyrethroid liberated was between 10 and 20% of the original amount formulated. The flushing out activity shown was dependent on the pyrethroid compound, insect stage and sex. In general deltamethrin proved the most active flushing out agent and Cypermethrin the least active. Maximal activity was shown in the combination of nymphs and tetramethrin. Nymphs of Rhodnius prolixus were only flushed out by deltamethrin. In all cases, deltamethrin and Cypermethrin yielded 100% mortality 7 days after exposure to the pyrethroid fumes, while tetramethrin was not a killing agent.RésuméLa tetraméthrine, la deltaméthrine et la cyperméthrine sont des pyréthrinoides que, formulées soit comme tablette fumigène ou comme solutions (spray), ont expurgé des insectes vecteurs de la maladie de Chagas cachés dans des refuges standards. La concentration des pyréthrinoides libérés des tablettes fumigènes, détecté par la Chromatographie gazeuse, a été 10 à 20% l’original. En plus, il a été observé que l’activité d’expurger les insectes (flushing out) produite par les tablettes fumigènes dépend de: type de pyréthrinoide, espèce d’insecte, stade de développement larvaire et sexe. Les résultats observés indiqueraient que la deltaméthrine a l’effet maximal de “flushing out” tandis que l’activité de la cyperméthrine a démontré être sensiblement inférieur. La tetraméthrine a été la plus active sur le 5 éme stade de Triatoma infestans. D’ail leurs, le 5 éme stade de Rhodnius prolixus a été seulement expurgé par la deltaméthrine. Dans tout les cas, la deltaméthrine et la cyperméthrine ont démontré produire un 100% de mortalité sept jours après l’exposition aux pyréthrinoides, autant que la tetraméthrine a été incapable de produire une sensible mortalité.

Neurogenesis and occurrence of cholinesterase in eggs of Triatoma infestans

Abstract 1. Eggs of T. infestans incubated at 30°C and 50% r.h. hatched in 15 days. 2. The neurogenesis of T. infestans embryo was studied. The neuroblasts appeared on the third day and the nerve cells on the fourth day. 3. The ontogenesis of cholinesterases was investigated. Activity was first detected on the fourth day coincidentally with the nerve cells appearance. 4. The cholinesterases were characterized as butyrylcholinesterase and acetylcholinesterase. 5. The oxygen analogs of several phosphorothionates insecticides were found to be potent inhibitors of the embryonic acetylcholinesterase.

Cholinesterases and eserine-resistant esterases in the developing embryo of Triatoma infestans and its role as targets for inhibition in the ovicide action of parathion

Abstract 1. Activity of eserine-resistant esterases was found during all the embryonic development of Triatomainfestans. 2. The ontogenesis of esterases and cholinesterases was established by disc gel electrophoresis. Bands were classified as corresponding to aryl plus acetylesterases, carboxyesterases, acetylcholinesterases and butyrylcholinesterases according to the specificity to substrate and its inhibition by paraoxon. 3. Biochemical measurement of esterases after treatment of eggs with parathion showed partial inhibition of eserine-resistant esterases and cholinesterases. Disc gel electrophoresis revealed complete inhibition of bands corresponding to acetylcholinesterases and carboxyesterases and partial inhibition of butyrylcholinesterases. In vitro incubation with 10−5 M paraoxon caused similar inhibition of the esteratic bands. 4. Eggs of T. infestans rolled on 3.2 μg/cm2 of parathion (2 × LC50) developed fully but failed to hatch. A later acetylcholinesterase whose electrophoretic band was strongly visible at the hatching time was suggested as a possible critical target of the delayed ovicide action.

Role of a microsomal carboxylesterase in reducing the action of malathion in eggs of Triatoma infestans

Abstract A microsomal malathion carboxylesterase present in Triatoma infestans eggs was active from the first day of embryonic development. This microsomal egg malathionase (MEM) showed a unique band in polyacrilamide gel electrophoresis (PAGE) when malathion was used as substrate. In vivo metabolism of [ 14 C]malathion during all embryonic development showed a 10% degradation due to carboxylesterases. The in vitro evaluation of the same metabolic pathway catalyzed by the microsomal fraction of T. infestans eggs showed partial inhibition by paraoxon. α- and β-malathion monoacids were identified as the main metabolites of the in vivo and in vitro metabolic pathways. The carboxylesterase band that appeared in PAGE (MEM) from the first day of embryonic development could be the main cause of malathion tolerance in T. infestans eggs.

Fenitrothion toxicity in Triatoma infestans synergized by quercetin or thymol blue

Quercetin and thymol blue were shown to synergize the toxicity of fenitrothion to Triatoma infestans with synergistic ratios of 1.89 and 2.65 respectively. These synergistic ratios were statistically significant at P < 0.05. Both compounds inhibited glutathione S-transferases (GST) in vitro, with pI 50 values of 6.1 and 5.1 respectively. Quercetin or thymol blue caused in-vivo GST inhibition without affecting non-specific esterase (NSE) or acetylcholinesterase (AChE) activity. Incubation of [ 14 C]fenitrothion with T. infestans or rabbit liver GST produced desmethylfenitrothion as the major metabolite, which was specifically diminished in the presence of 0.3 mM quercetin. [ 14 C]Fenitrothion toxicokinetics study showed a significant decrease (P < 0.05) in radioactivity due to polar metabolites when insects were pre-treated with quercetin. These facts suggest that both assayed chemicals may be active in synergizing fenitrothion toxicity due to their ability to prevent the detoxification of organophosphorus insecticides by GSH conjugation.

Mode of action of N-ethylmaleimide as a parathion synergist in Triatoma infestans

Abstract N -Ethylmaleimide (NEM) injected in sublethal doses enhanced the triatomicide effect of parathion. The study of the possible causes responsible for this synergistic effect in Triatoma infestans showed (1) a depletion of SH groups in the hemolymph and the central nervous system (CNS) caused by NEM; (2) protein and lipid covalent binding of [ 14 C]NEM in the CNS; (3) partial inhibition by NEM of the glutathione S -transferase detoxifying pathway; (4) enhanced penetration of parathion and paraoxon into the insect CNS pretreated with NEM; (5) significant change in the electrophoretic and histochemical pattern of acetylcholinesterase inhibition in NEM-pretreated insects. The results obtained suggest that NEM synergizes parathion in adult T. infestans by inhibiting glutathione-dependent detoxification and enhancing penetration into the CNS.

An insect acetylcholinesterase inhibitor from compound eyes of Triatoma infestans (Hemiptera).

The presence of an acetylcholinesterase inhibitor in the compound eyes of adultTriatoma infestans was demonstrated. The inhibitory activity was localized in the ocular pigments separated by disc gel electrophoresis. The inhibitor was selective against insect acetylcholinesterase, reversible, noncompetitive and heat stable.