Fumio Matsumura

Evidence for similarities between cyclodiene type insecticides and picrotoxinin in their action mechanisms

Evidence has been obtained to indicate that cyclodiene-type insecticides, e.g., heptachlor epoxide and gamma-BHC, mimic the action of picrotoxinin. These insecticides inhibit the GABA (gamma-aminobutyric acid)-stimulated chloride uptake in the coxal muscle of the American cockroach, and directly compete against [3H]a-dihydropicrotoxinin for binding in the rat brain synaptosomes. Moreover, several cyclodiene-resistant insect strains are also resistant to picrotoxinin. This cross-resistance is specific to picrotoxinin and does not extend to other neuroexcitants. These insecticides, like picrotoxinin, cause central nerve excitation by stimulating transmitter release. Similarity in molecular structures also has been pointed out. These results indicate that some of the nerve excitation symptoms that insecticides cause are likely due to their interaction with picrotoxinin receptor.

Glutathione S-transferase 1 and 2 in susceptible and insecticide resistant Aedes aegypti

Abstract Glutathione S -transferase enzymes (GST) were characterized in permethrin and in DDT resistant and susceptible strains of Aedes aegypti . The predominant GST, designated GST-1, was purified from susceptible and resistant larvae using S -hexyl-glutathione affinity chromatography and anion-exchange chromatography. Rabbit antiserum directed against the 26.8-kDa GST-1 subunit purified from the susceptible strain was specific for a 26.8-kDa subunit in the resistant strain. There was no significant difference in enzyme kinetic constants ( K m and V max ) between GST-1 from susceptible and resistant strains. GST-1 enzyme activity varied during larval development in both resistant and susceptible strains, but was approximately 1.7 times greater in resistant larvae and pupae throughout development. The GST-1 amount (measured using a radioimmunoassay) also varied during development, and was generally higher in resistant larvae and pupae. GST-1 enzyme activity measured each day during the 6 days of larval development was significantly correlated with GST-1 protein amount on each of the previous days, suggesting that an inactive enzyme form is converted to the active form approximately 24 hr after it is synthesized. Another GST enzyme, GST-2, was also found in resistant and susceptible A. aegypti larvea. GST-2 was partially purified from resistant larvae using S -2,4-dinitrophenylglutathione affinity chromatography and anion-exchange chromatography. GST-2 has a molecular mass of 28 kDa, and an isoelectric point of less than 5.0. GST-2 was not cross-reactive with GST-1 antiserum. GST-2 enzyme activity varied during the development of both susceptible and resistant larvae, but the pattern was different than that for GST-1. Throughout development, GST-2 enzyme activity was substantially higher (approximately eight-fold) in resistant strains of A. aegypti compared to susceptible strains.

Induction of Proinflammatory Cytokines and C-Reactive Protein in Human Macrophage Cell Line U937 Exposed to Air Pollution Particulates

Exposure to particulate matter air pollution causes inflammatory responses and is associated with the progression of atherosclerosis and increased cardiovascular mortality. Macrophages play a key role in atherogenesis by releasing proinflammatory cytokines and forming foam cells in subendothelial lesions. The present study quantified the inflammatory response in a human macrophage cell line (U937) after exposure to an ambient particulate sample from urban dust (UDP) and a diesel exhaust particulate (DEP). The effect of native UDP and DEP was compared with their corresponding organic extracts (OE-UDP/OE-DEP) and stripped particles (sUDP/sDEP) to clarify their respective roles. Exposure to OE-UDP, OE-DEP, UDP, DEP, and 2,3,7,8-tetrachlorodibenzo-p-dioxin led to a greater increase of interleukin (IL)-8, tumor necrosis factor-α, and cyclooxygenase-2 mRNA expression than did the stripped particles, whereas sUDP, sDEP, UDP, and DEP led to a greater production of C-reactive protein and IL-6 mRNA. The particles and the organic extract-induced expression of cyclooxygenase-2 and cytochrome P450 (CYP)1a1 was significantly suppressed by co-treatment with an aryl hydrocarbon receptor (AhR) antagonist, indicating that these effects are mainly mediated by the organic components, which can activate the AhR and CYP1a1. In contrast, the induction of C-reactive protein and IL-6 seems to be a particle-related effect that is AhR independent. The inflammatory response induced by particulate matter was associated with a subsequent increase of cholesterol accumulation, a hallmark of foam cells. Together, these data illustrate the interaction between particulate matter and the inflammatory response as well as the formation of cholesterol-accumulating foam cells, which are early markers of cardiovascular disease.

TCDD (2,3,7,8-tetrachlorodibenzo-P-dioxin) causes increases in protein kinases particularly protein kinase C in the hepatic plasma membrane of the rat and the guinea pig

To study the cause of TCDD-evoked changes in the functions of plasma membrane constituents TCDDs effects on protein kinase activities in the liver of rats and guinea pigs were investigated. TCDD was found to cause a sharp increase in both c-AMP independent and dependent protein kinase activities in plasma membrane preparations from rat liver within 48 hours from the time of administration. Such effects reached maxima around day 20, and were quite noticeable even 40 days after a single administration of TCDD. As a result of SDS-polyacrylamide gel-electrophoresis (SDS-PAGE) analysis several substrate proteins for these increased protein kinases were observed. Among them are 170 K - 150 K bands, representing EGF receptor protein. TCDD was found to particularly stimulate protein kinase C which is known to influence many enzyme and receptor functions through protein phosphorylation. The possible significance of such an action of TCDD is discussed.

Difference in the picrotoxinin receptor between the cyclodiene-resistant and susceptible strains of the german cockroach

Abstract As a result of toxicity tests, it was established that all cyclodiene-resistant strains of the German cockroach are also resistant to picrotoxinin, a plant-origin neurotoxicant. Two of the cockroach strains which exhibit a distinct cross-resistance pattern to picrotoxinin (i.e., LPP and FRP) are the ones that have been purified genetically by backcrossing against the susceptible (CSMA) strain. This cross-resistance pattern appears to be specific to picrotoxinin and does not extend to other neuroexcitants such as bicuculline, beta-bungarotoxin, and DDT. The nervous system of the resistant cockroach was found to be less sensitive to picrotoxinin. Furthermore, it was determined that nerve components from the resistant cockroaches have significantly lower binding capacity to [ 3 H]α-dihydropicrotoxinin. The most likely explanation for the above phenomenon is that these cockroaches have developed the cyclodiene resistance by altering the nerve receptor for picrotoxinin.

Evidence for two types of toxic actions of pyrethroids on susceptible and DDT-resistant german cockroaches

Abstract The mode of action of six pyrethroid insecticides was investigated using Periplaneta americana and susceptible (CSMA) and resistant (VPIDLS) strains of Blattella germanica . We confirmed that the mechanism of DDT resistance in the VPIDLS strain, a strain which has not been exposed to any pyrethroid insecticide selection, was a kdr type. This kdr factor extends its cross-resistance to allethrin, pyrethrin, permethrin, and fenvalerate, but not to deltamethrin and only marginally to cypermethrin. Based upon the above data, electrophysiological data, and observations of the effect of temperature on toxicity, it was concluded that there are two distinct types of pyrethroid actions. Allethrin appears to possess mainly Type I action, while deltamethrin exhibits strong Type II action. The DDT-induced kdr resistance factor extended its cross-resistance only to compounds possessing predominantly Type I action. There were at least two compounds (permethrin and fenvalerate) which exhibited both types of actions. It was found that occurrence of repetitive discharges, a typical Type I action, could be suppressed by cypermethrin, indicating that these two types of actions interact.

Picrotoxinin receptor in the central nervous system of the American cockroach: Its role in the action of cyclodiene-type insecticides

Abstract The nature of the picrotoxinin receptor was studied using the central nervous system (CNS) of the American cockroach. It first was confirmed by using an electrophysiological technique that the abdominal nerve cord of the American cockroach was sensitive to picrotoxinin. By using a [ 3 H]α-dihydropicrotoxinin binding test it was determined that the picrotoxinin receptor in CNS of this insect had a higher affinity toward picrotoxinin and heptachlor epoxide than the corresponding receptor in the rat brain. Also, the cockroach brain preparation had a higher percentage of specific binding in the total binding, making this material suitable for receptor studies. By using a sucrose density centrifugation technique, it was determined that the fraction sedimented at the interphase of 1.0 to 1.2 M sucrose at 100,000 g contained the highest level of specific binding site. The receptor showed a sensitivity to all insecticidal cyclodienes tested, namely photodieldrin, oxychlordane, endrin, heptachlor epoxide, γ-chlordane, dieldrin, aldrin, heptachlor, and isodrin (expressed in the order of potency). Among four BHC isomers, the γ-isomer showed the highest potency to bind with this receptor.

Cytotoxic, mutagenic, and cell-cell communication inhibitory properties of DDT, lindane, and chlordane on Chinese hamster cellsin vitro

The cytotoxicity, mutagenicity, andin vitro inhibition of metabolic cooperation of DDT, lindane, and chlordane were studied with Chinese hamster V79 cells. The results showed differential cytotoxicity of these three pesticides (lindane < DDT < chlordane). There was no detectable mutagenic activity of any of these pesticides, using two genetic markers (6-thioguanine and diphtheria toxin resistance). DDT and lindane, however, were shown to have properties similar to 12-O-tetradecanoylphobol-13-acetate (a powerful mouse skin tumor promoter). Above what appeared to be a threshold level, there was a clear dose response of DDT and lindane in thein vitro cell-cell communication assay. Chlordane, which was the most cytotoxic pesticide tested, did not inhibit metabolic cooperation as significantly as did DDT or lindane. The role of these pesticides in carcinogenesis was speculated as being their tumor promoting properties, either at non-cytotoxic levels by mimicing TPA-like membrane alterations or at cytotoxic levels by mimicing partial hepatectomy.

Two different types of inhibitory effects of pyrethroids on nerve Ca- and Ca + Mg-ATPase activity in the squid, Loligo pealei

Abstract The biochemical process by which various pyrethroid insecticides affect membrane-bound ATPase activities of the squid nervous system was examined. Of the five ATP-hydrolyzing systems tested, only Ca2+-stimulated ATPase activities are seen to be clearly affected by pyrethroids. It was found that the “natural type” pyrethroids (e.g., pyrethrin and allethrin) primarily inhibit Ca-ATPase activity whereas the “highly modified type” pyrethroids (e.g., cypermethrin and decamethrin) mainly inhibit Ca + Mg-ATPase. permethrin, which is considered to possess structural similarities to both the natural type and the highly modified type pyrethroids, was found to have an intermediate property in terms of its inhibitory potency to both Ca- and Ca + Mg-ATPase activities. The level of inhibition of Ca2+-stimulated ATPase activities was generally high in the retinal axons and optic lobe synaptosomes but lowest in the axoplasmic preparations.

Inhibition of gamma-aminobutyric acid (GABA)-induced chloride uptake by gamma-BHC and heptachlor epoxide

Abstract 1. 1. A bioassay system was established using the coaxal muscle of the American cockroach to measure the stimulatory effect of γ-aminobutyric acid (GABA) on 36 Cl − permeability and the antagonistic effect of picrotoxinin. In this system half maximum stimulation by GABA is achieved at 80 μM. 2. 2. This stimulatory action by GABA was found to be antagonized by two cyclodiene-type insecticides, heptachlor epoxide and γ-BHC. Other insecticidal analogs, which do not posses cyclodiene-type neuro-excitant property, failed to show this phenomenon. 3. 3. These results clearly demonstrate that heptachlor and γ-BHC have picrotoxinin-type action.