Effects of diazinon on the activity and gene expression of mitochondrial glutamate dehydrogenase from rat pancreatic Langerhans islets

The main propose of the present study was to determine the effects of diazinon on the activity and gene expression of glutamate dehydrogenase (GDH) as the key enzyme of Langerhans islet for secretion of insulin. Diazinon was administered intraperitoneally at doses of 15, 30, and 60 mg/kg. Langerhans islets were isolated from the pancreas of rats by a standard collagenase digestion, separation by centrifugation, and hand-picking technique. The activity and gene expression of the mitochondrial GDH was determined in the islets homogenates. Glutamate, C-peptide, and insulin were determined in plasma.Diazinon at all tested doses (15, 30, and 60 mg/kg) significantly (p < 0.01) decreased plasma insulin after 1 h while the values did not differ from control when examined after 18 h. Diazinon at all tested doses (15, 30, and 60 mg/kg) significantly (p < 0.01) increased concentration of C-peptide both 1 and 18 h post-administration. Diazinon at all tested doses (15, 30, and 60 mg/kg) significantly (p < 0.05) increased production of glutamate while the values did not differ from control when tested after 18 h. Administration of diazinon at doses of 30 and 60 mg/kg significantly (p < 0.001) increased activity of GDH after 1 h while all doses of diazinon increased GDH activity when measured after 18 h. Diazinon at dose of 60 mg/kg significantly (p < 0.01) decreased expression of GDH gene 18 h post-administration.It is concluded that GDH is a component of diazinon-induced changes in release of improper insulin.     

Induction of insulin resistance by malathion: Evidence for disrupted islets cells metabolism and mitochondrial dysfunction

Hyperglycemia is observed with exposure to organophosphorus (OP) pesticides. The aim of this study was to investigate the effects of malathion on secretion of insulin from rat pancreatic islets in vitro and in vivo. Malathion was administered through food for 4 weeks at concentrations of 100, 200, and 400 ppm. For in vivo experiment, at the end of treatment, blood sample was obtained and plasma was separated. For in vitro experiment, the treated rats were anesthetized and underwent a laparatomy. The common bile duct was cannulated and the pancreas distended by injecting of cold collagenase V using peristaltic infusion pump. Islets were then hand picked under a stereomicroscope and cultured in the presence of various doses of glucose and KCl. Malathion at doses of 200 and 400 ppm increased plasma glucose and insulin concentrations and lowered activity of erythrocyte acetylcholinesterase. The isolated islets from pretreated animals with malathion 200 and 400 ppm showed lower glucose-stimulated insulin secretion while no change was observed in the presence of KCl. Light microscopic examination revealed that malathion causes patchy degenerative changes in pancreatic islets. Combination of in vivo and in vitro findings suggests that malathion induces a kind of insulin resistance that cannot overwhelm hyperglycemia. This action of malathion is mediated through disruption of islets mitochondrial function.     

Protection by cAMP and cGMP phosphodiesterase inhibitors of diazinon-induced hyperglycemia and oxidative/nitrosative stress in rat Langerhans islets cells: Molecular evidence for involvement of non-cholinergic mechanisms

The objective of this study was to study the effects of acute administration of diazinon alone or in combination with two phosphodiesterase (PDE) inhibitors with selectivity to cAMP and cGMP (theophylline and sildenafil, respectively) on oxidative/nitrosative stress biomarkers, including nitric oxide (NO), lipid peroxides (TBARS), total antioxidant power (TAP), and concentration of tumor necrosis factor (TNF-α) in isolated Langerhans islets, plasma glucose and insulin levels, and the activity of plasma cholinesterase (ChE). Examination by different doses of diazinon (15, 30, and 60 mg/kg) in single administration lead us to choose diazinon (30 mg/kg) in combination therapies. Theophylline and sildenafil were used at doses of 25 and 5 mg/kg, respectively. In all diazinon-treated groups, plasma ChE activity and plasma insulin level were significantly decreased and plasma glucose concentration and Langerhans islets TNF-α, TBARS, and NO levels were significantly increased in comparison to controls. The TAP did not change in comparison to control. In combination therapy, both theophylline and sildenafil restored diazinon-induced changes in plasma glucose concentration, Langerhans islets TNF-α, NO, and TBARS concentrations but Langerhans islets TAP, plasma insulin, and ChE levels. It is concluded that diazinon stimulates oxidative/nitrosative stress in Langerhans islets that results in hyperglycemia due to insufficiency of insulin. Altered glucagons/insulin ratio, activated hepatic glucose production/release, and insulin resistance are possible mechanisms. The protective effects of cAMP and cGMP PDE inhibitors in restoration of diazinon-induced oxidative/nitrosative stress and hyperglycemia stress back to their antioxidant potentials that seem to be independent of ChE inhibition.     

Effect of short-time malathion administration on glucose homeostasis in Wistar rat

The main objective of this study is to investigate the 24 h kinetic effect of acute administration of malathion, an organophosphorus insecticide, on glucose homeostasis in adult rats. A single dose of malathion (400 mg/kg, 1/5 of LD₅₀) was administered orally to rats, blood glucose was measured, liver and pancreas were removed to determine the level of hepatic glycogen, the activity of pancreatic acetylcholinesterase and butyrylcholinesterase, as well as the level of TBARs. Blood glucose increased in rats treated with a single dose of malathion. This effect was observed in the first hours of treatment, reached a 2.2 fold peak after 2 h, and then decreased after 4 h, followed by a decrease in the level of hepatic glycogen. The storage of glycogen starts from 6 to 12 h of administration. A decrease in cholinesterase activities was noted. The level of TBARs increased considerably in liver and pancreas. Results of this study can be explain by a stimulation of glycogenolysis and gluconeogenesis by liver, with a temporarily loss of endocrine functions of pancreas leading to hyperglycemia.     

Impact of malathion stress on lipid metabolism in Limnonectus limnocharis

Despite mounting concerns about amphibian population declines, information on impact of pesticides on physiological changes is meager. The present study deals the influence of an organophosphate pesticide—malathion on the lipid metabolism of Limnonectus limnocharis under laboratory conditions. Changes in the lipid metabolism were analyzed in the liver, muscle, ovary, and testis of frogs exposed to lethal (10.67 mg L⁻¹ for 1, 2, 3, and 4 days) and sub-lethal (2.13 mg L⁻¹ for 1, 5, 10, 15, 20, and 25 days) concentrations of malathion. Upon lethal concentration treatment, against the increase of fatty acids, glycerol, and lipase activities in all tested tissues, there was decrease in the total lipids content over different durations. On the other hand, exposure to sub-lethal concentration, the amount of total lipids content, free fatty acids, glycerol and lipase activity increased. Changes in the lipid metabolism due to lethal concentration of malathion exposure could depict the negative impact on the reproductive success, which would result in decline of amphibian population.     

Biochemical evidence on positive effects of rolipram a phosphodiesterase-4 inhibitor in malathion-induced toxic stress in rat blood and brain mitochondria

Malathion is an organophosphate (OP) pesticide that has been shown to induce oxidative stress in brain through the generation of free radicals and alteration of the cellular antioxidant defense system independent of its anticholinesterase effects. The aim of this study was to investigate the possible protective role of rolipram as a selective phosphodiesterase (PDE) type 4 inhibitor, on toxicity of malathion, by measuring the activities of brain mitochondrial and plasma peroxynitrite (ONOO⁻), glutathione peroxidase (GPx), superoxide dismutase (SOD), Mn-SOD, catalase (CAT), and lipid peroxidation (LPO) in rats. Effective doses of malathion (200 mg/kg/day) and rolipram (200 μg/kg/day) were administered alone or in combination for 7 days by intraperitoneal injection. At the end of the experiment, the brain mitochondria and plasma of the animals were separated. In the brain cells mitochondria and blood plasma, the LPO, ONOO⁻, and GPx were higher in the malathion group as compared with controls. Rolipram ameliorated all of malathion-induced changes. Plasma CAT decreased in malathion-treated animals while it increased in brain mitochondria comparing with controls. Co-administration of rolipram with malathion improved CAT in both brain mitochondria and plasma. Malathion and rolipram did not alter total SOD or Mn-SOD in the plasma while both caused a significant elevation in brain mitochondria. In conclusion, this model of study that we employed, in a large extent, characterized the relationships among malathion-induced neurotoxicity, mitochondrial dysfunction, and significant increase in systemic and local oxidative/nitrosative stress in plasma and brain, respectively. Intracellular cAMP-elevating agents like rolipram, may be considered beneficial for the protection or recovery of malathion-induced toxic damage in brain mitochondria and blood.     

Influence of organophosphorus pesticides on peroxidase and chlorination activity of human myeloperoxidase

Inhibitory effects of five organophosphorus pesticides (diazinon, malathion, chlorpyrifos, azinphos-methyl and phorate) and their oxo-analogs on human myeloperoxidase (MPO) activity were investigated. While inspecting separately peroxidase and chlorination activity, it was observed that investigated OPs affect peroxidase activity, but not chlorination activity. Among investigated pesticides, malathion and malaoxon have showed the highest power to inhibit MPO peroxidase activity with IC₅₀ values of the order of 3 × 10⁻⁷ and 5 × 10⁻⁹ M, respectively. It was proposed that inhibition trend is rendered by molecular structure which invokes steric hindrance for OPs interaction with MPO active center responsible for peroxidase activity. In addition, it was concluded that physiological function of MPO is not affected by any of the investigated OPs.     

Improvement by Satureja khuzestanica essential oil of malathion-induced red blood cells acetylcholinesterase inhibition and altered hepatic mitochondrial glycogen phosphorylase and phosphoenolpyruvate carboxykinase activities

The aim of this study was to examine whether Satureja khuzestanica (Lamiaceae) essential oil (SKEO) might have protective effects on toxicity of malathion, a commonly used organophosphorus (OP), by measuring the activities of hepatic cells mitochondrial glycogen phosphorylase (GP) and phosphoenolpyruvate carboxykinase (PEPCK) activities and blood levels of glucose and acetylcholinesterase (AChE) in rats. Malathion (20 mg/kg/day) and SKEO (225 mg/kg/day) were administered alone or in combination by intragastric intubation for 28 days. Treatment by malathion increased blood glucose as measured at days 18 and 28 of treatment. Malathion inhibited erythrocyte AChE and increased hepatic cells GP and PEPCK activities. Coadministration SKEO resulted in restoration of malathion-induced changes in hepatic cells GP and PEPCK activities and levels of blood AChE and glucose. It is concluded that SKEO interferes with malathion-induced stimulation of hepatic cells glycogenolysis and gluconeogenesis through its antioxidant potential and increasing AChE activity.     

Comparison of the effect of Roundup Ultra 360 SL pesticide and its active compound glyphosate on human erythrocytes

The effects of exposure of human erythrocytes to different concentrations of Roundup Ultra 360 SL and its active compound glyphosate were studied. We studied hemolysis after 1, 5, and 24 h incubation; lipid peroxidation, hemoglobin oxidation, the level of reduced glutathione, and the activity of catalase after 1 h. Human erythrocytes were incubated with 100-1500 ppm (100 μg/ml erythrocytes at 5% hematocrite) Roundup Ultra 360 SL and glyphosate. We have found that after 1 h of incubation only Roundup Ultra 360 SL increased the level of methemoglobin, products of lipid peroxidation at 500 ppm and hemolysis at 1500 ppm [Curr. Top. Biophys. 26 (2002) 245], while its active compound glyphosate increased the level of methemoglobin and the level of lipid peroxidation at much higher dose—1000 ppm. At the same time hemolysis was observed to only at the highest dose of glyphosate (1500 ppm) and the longest time of incubation (24 h). Both Roundup Ultra 360 SL and glyphosate did not cause statistically significant changes in the level of GSH, but increased the activity of catalase. Roundup Ultra 360 SL provokes more changes in the function of erythrocytes than its active substance glyphosate, which is probably a result of the properties of additives. Taking into account the limited accumulation of Roundup Ultra 360 SL and glyphosate in the organism as well as the fact that the threshold doses which caused changes in erythrocytes for Roundup Ultra 360 SL were only 500 and 1000 ppm for glyphosate, one may conclude that this pesticide is safe towards human erythrocytes.     

Effects of trichlorfon and sodium dodecyl sulphate on antioxidant defense system and acetylcholinesterase of Tilapia nilotica in vitro

The effects of organophosphorus insecticide trichlorfon, surfactant sodium dodecyl sulphate (SDS), and the mixture of trichlorfon and SDS on the antioxidant defense system and acetylcholinesterase (AChE) in Tilapia nilotica were assessed in vitro. Various concentrations of trichlorfon (0, 0.0001, 0.001, 0.01, 0.1 and 1 g/L) and SDS (0, 0.0625, 0.125, 0.25, 0.5, 1 g/L) were incubated with homogenate of liver and muscle, respectively, at 25 °C for 0, 30, 60 and 90 min. Two concentrations of mixture of trichlorfon and SDS (0.0001 g/L trichlorfon + 0.5 g/L SDS, 0.1 g/L trichlorfon + 0.5 g/L SDS) and 0.0001 g/L trichlorfon, 0.1 g/L trichlorfon, 0.5 g/L SDS and control, were incubated simultaneously with homogenate of liver and muscle, respectively, at 25 °C for 60 min. After incubation, the content of reduced-glutathione (GSH) and the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) in homogenate of liver were determined, and the activities of AChE in homogenate of muscle were also measured.Treatment with trichlorfon caused a significant concentration-dependent and time-related inhibition of AChE activity at all treatment concentrations and times since trichlorfon is a cholinesterase inhibitor. For the same trichlorfon treatment, an apparent decrease in GSH content was found in concentration of 0.01, 0.1, 1 g/L, whereas no significant alteration in antioxidant enzyme activity were found at all experiment concentrations and times, which might indicate that antioxidant enzymes have not involved in the metabolism of trichlorfon. The depletion of GSH might indicate that ROS could be involved in the toxic effects of trichlorfon. Exposure of SDS can inhibit activities of AChE, GST and CAT at concentrations of 0.5 and/or 1 g/L, which could be due to the denaturing process of SDS to the enzymes. For the mixture exposure of trichlorfon and SDS, the effect of the mixture of 0.0001 g/L trichlorfon and 0.5 g/L SDS on inhibition of AChE shows synergistic other than simple additive of trichlorfon and SDS. The combined effects of chemicals and detergents deserve to be particularly noted. It should be noted that the toxicity experiments were made in tissue homogenates instead of whole organisms. The responses against the toxic compounds will not be the same in both systems.     

In ovo embryotoxicity of α-endosulfan adversely influences liver and brain metabolism and the immune system in chickens

There is a lack of laboratory-based embryonic chicken toxicity studies with the ecologically relevant low dose/s of endosulfan that utilizes a more practical approach such as the chorioallontoic membrane (CAM) injection. In this investigation, 2μg AR grade α-endosulfan/egg (40% of LD₅₀ for embryos) was injected through the CAM in 12-day-old chicken embryos and the activities of glucose-6-phosphatase (G6Pase, EC 3.1.3.9), fructose 1,6-diphosphatase (FDPase, EC 3.1.3.11), adenosine triphosphatase (ATPase, EC 3.6.1.3) and succinic dehydrogenase (SDH, EC 1.3.99.1) and DNA and RNA content in liver and brain tissues and acetyl cholinesterase (AChE, EC 3.1.1.7) in the latter were determined at 24, 48, and 72 h post-exposure. The wet weight of the embryos did not differ between groups. Following endosulfan exposure, except increase in the hepatic ATPase activity (P < 0.01), there was a significant decrease in the following parameters: G6Pase activity in both the liver and brain (P < 0.01), SDH activity in the brain (P < 0.01), brain overall DNA and RNA concentration (P < 0.05), brain AChE activity (P < 0.01). Exposure of 18-day-old embryos to 2-μg endosulfan for 24 h caused decrease (P < 0.01) in the lymphocyte count and IgG content. Histopathology of thymus and bursa of Fabricius revealed a reduction in the population of thymic follicles, smaller thymocytes with the clear vacuoles in cytoplasm and fewer bursocytes accompanied by infiltration of erythrocytes in lymphoid follicles of the endosulfan-treated embryos. It was inferred that in ovo injection of 0.041 μg/g egg weight of α-endosulfan suppress gluconeogenesis (main energy source in embryonic life), nerve transmission, and immunity.     

Endocrine disruption and metabolic changes following exposure of Cyprinus carpio to diethyl phthalate

Diethyl phthalate (DEP) enter into aquatic environment from industries manufacturing cosmetics, plastic and many commercial products and can pose potential fish and human health hazard. This experiment evaluated effects of DEP in adult male (89 g) common carp (Cyprinus carpio) by exposing them to fractions of LC₅₀ (1/500-1/2.5) doses with every change of water for 28 days. Vitellogenin induction metabolic enzymes, somatic indices and bioaccumulation were studied on 7th, 14th, 21st and 28th day. The 96th hour LC₅₀ of DEP in fingerlings was found to be 48 mg/L. Compared to control, except increase (P < 0.01) in alkaline phosphatase activity (EC 3.1.3.1) and liver size, there was decrease (P < 0.01) in activity of acid phosphatase (EC 3.1.3.2), aspartate aminotransferase (EC 2.6.1.1), alanine aminotransferase (EC 2.6.1.2) and testiculosomatic index following exposure to 1, 5 and 20 ppm DEP. Significant (P < 0.01) dose dependant vitellogenin induction was observed with exposure of fish to 0.1, 1 and 5 ppm DEP. The bioaccumulation of DEP in testis, liver, brain, gills and more importantly in muscle tissues of fish increased significantly (P < 0.01) with increase of dose from 1 to 5 ppm. Significant interaction (P < 0.01) of dose and duration of exposure indicated that exposure period of a week to two was sufficient to bring about changes in quantifiable parameters studied. Fish exposed to 20 ppm DEP became lethargic and discolored during onset of the 4th week. This is the first report describing metabolic changes and vitellogenin induction following exposure of C. carpio to DEP dose that is as low as 1/500th fraction of LC₅₀.     

Hormone profile of an edible, freshwater teleost, Sarotherodon mossambicus (Peters) under endosulfan toxicity

The hormone profile of Sarotherodon mossambicus (Peters) under endosulfan (an organochlorine pesticide) toxicity was investigated by estimating the serum levels of T₃ (triiodothyronine), T₄ (thyroxine), cortisol, prolactin and insulin in control and sub-lethal (0.001 mg L⁻¹) endosulfan-exposed fish for 1, 6, 12, 24 h and 5 days. Exposure of fish to sub-lethal concentration of endosulfan caused varying changes in the levels of serum hormones studied. Based on the results obtained, it was concluded that (i) the fish registered an increased metabolic activity during the initial period followed by an adaptive lowering of metabolic rate as indicated by changes in the serum T₃ and T₄ levels, (ii) the fish showed an adaptive stress response as indicated by the reduced cortisol level which could be probably due to severe interrenal exhaustion, (iii) the increased serum prolactin levels in the fish under endosulfan exposure is indicative of a possible action of prolactin on gills and kidney towards hydromineral regulation in the fish body under pesticide stress, (iv) the fish adaptively increases its serum insulin level thereby registering a possible adaptive hypoglycemic role of the hormone to favour the transport of glucose to different tissues besides a possible lipogenic activity of the higher insulin level in fish tissue under pesticide toxicity and (v) the fish appears to exhibit a possible adaptive recovery response in its hormone profile following prolonged exposure for 24 h and 5 days.     

Oxidation of diazinon and malathion by myeloperoxidase

The aim of the work was to investigate the in vitro oxidation of diazinon and malathion, organophosphorous pesticides (OPs) containing phosphorthioate group, catalyzed by enzyme myeloperoxidase (MPO). The oxidation was performed in the presence of hydrogen peroxide. The products were identified as oxon derivatives (phosphates), where the sulfur atom from thioate group was substituted by an oxygen atom. No hydrolysis products were detected after enzyme - induced oxidation. The oxidation efficiency was controlled using acethylcholinesterase (AChE) bioassay for determination of oxon derivatives concentration. The influence of OPs concentration, incubation time of OPs with MPO, as well as MPO concentration on the yield of oxo forms was investigated. Kinetic constants of MPO in oxidation of malathion and diazinon were estimated. The maximum concentration of oxo forms was achieved after 10 min incubation of OPs in 50 mM phosphate buffer (pH 6.0) with 100 nM MPO.     

Changes in renal clearance and renal tubular function in albino mice under the influence of Dichlorvos

It is known that organophosphate pesticides and their metabolites are generally eliminated through urine and are likely to affect nephrons. Despite the widespread application of Dichlorvos only limited studies appear to have been done on its toxicity to kidney. Intraperitoneal administration of 400 μg/kg Dichlorvos in mice exhibited maximum reduction in total protein concentration of kidney after exposure to 120 h (52-fold decrease, t-test, P < 0.001). Variations in renal clearance and percent reabsorption of acid phosphatase, alkaline phosphatase and nonspecific esterase enzymes were significant at P < 0.01 and at P < 0.001 (2-way ANOVA), respectively. Maximum significant increase in renal contents of Na⁺ and Ca⁺⁺ was induced by 200 μg/kg dose after 120 and 240 h exposure (P < 0.001), while significantly highest retention of K⁺ and Cl⁻ ions was caused by 400 μg/kg dose after 24 and 72 h exposure (P < 0.01). Histopathological changes in glomeruli, PCTs, DCTs and CTs along with altered renal tubular function and renal clearance of enzymes and various ions indicate the development of acute renal disturbances under the influence of Dichlorvos.     

Oxygen consumption and ammonia excretion of the freshwater crab Trichodactylus borellianus exposed to chlorpyrifos and endosulfan insecticides

The effects of lethal and sublethal concentrations of chlorpyrifos and endosulfan on oxygen consumption and ammonia excretion rate of the crab Trichodactylus borellianus were evaluated. Oxygen consumption and energy expenditure had significant effect in relation to exposure times. Regarding endosulfan, a significant difference in consumption among times of exposure was registered in 625 μg L⁻¹. Moreover, at the highest concentration, energy expenditure rate was observed stabilized during 1-3 h. A significant increase in ammonia excretion was evidenced in 150 and 300 μg L⁻¹ of chlorpyrifos. The O:N ratio showed a decrease in chlorpyrifos and in 2500 μg L⁻¹ of endosulfan. This indicated a shift towards protein primary metabolism. An increment in the O:N ratio was observed in the lower endosulfan solutions. The relation oxygen:nitrogen showed a shift towards lipid and carbohydrate primary metabolism. This work indicated the complexity of the metabolism in the freshwater crab affected by xenobiotic elements.     

Influences of sub-acute exposure to paraquat on cytochrome P450 3A2 expression in rat liver and lungs

This study was designed to investigate the possible effects of paraquat sub-acute poisoning on cytochrome P450 3A2 expression in the liver and lungs. Twenty adult male rats (150-200 g) were exposed either against saline normal as control group or various doses of paraquat (3.5, 7 and 10 mg/kg, s.c.) as test groups for 7 consecutive days. Paraquat-exposed animals showed loss of body weight and elevation in serum levels of alkaline phosphates and alanine aminotransferase in a dose-dependent fashion. Moreover, animals in the test groups demonstrated a significant (P < 0.05) increase of malondialdehyde content in both the liver and lung tissues. Ultimately, by using RT-PCR method it became clear that 7 days exposure to paraquat resulted in a total suppression of cytochrome P450 3A2 at the mRNA level in the lungs. By contrast, a considerable up regulation of the same gene occurred in the liver. This data suggest that paraquat not only affect the lungs as a main target tissue but also up regulates the predominant cytochrome P450 gene in the liver which may induce detoxification processes.     

Evaluation of aspect of some oxidative stress parameters using vitamin E, proanthocyanidin and N-acetylcysteine against exposure to cyfluthrin in mice

A hundred and sixty female white mice, each weighing 35-40 g, were used in this study. The animals were assigned into eight groups as one control group and 7 experimental groups. Groups 2, 3 and 4 were administered N-acetylcysteine (NAC), proanthocyanidin and vitamin E alone, at doses of 100 mg/kg/body weight/day by intra-peritoneal, oral route and, intramuscular, respectively. Group 5 was administered a single dose of cyfluthrin (100 mg g/kg/body weight ∼1/3LD₅₀) by oral, whereas Groups 6, 7 and 8 were given cyfluthrin+NAC, cyfluthrin+proanthocyanidin and cyfluthrin+vitamin E, at the same dose, respectively. The administration of the drugs was initiated following the administration of cyfluthrin, and continued until the end of the seventh day of the study. Blood samples were collected from each group, 24 h, and 3, 7 and 9 days after the administration of cyfluthrin for the assessment of blood malondialdehyde (MDA) levels and superoxide dismutase (SOD) and catalase (CAT) activities. According to the data obtained, compared to the control group, increase in the plasma MDA level of the group administered cyfluthrin alone, and decrease in erythrocyte SOD activities in some periods and CAT activities in all periods were determined. On the other hand, especially, MDA levels and CAT activities were observed to move closer to values of the control group, in the groups that were administered NAC, proanthocyanidin and vitamin E in addition to cyfluthrin. In other words, in most periods, decrease in plasma MDA levels, and increase in erythrocyte CAT and SOD activities were observed in comparison to the group administered cyfluthrin alone. Statistical analyses demonstrated significant differences to exist between the groups on the third, seventh and ninth days with respect to plasma MDA levels, and the third and ninth days with respect to erythrocyte SOD and CAT activities (P < 0.05). However no significant difference was demonstrated in any of the periods in the groups that were administered NAC, proanthocyanidin and vitamin E alone in comparison to the control group (P > 0.05). In view of the parameters examined, animals were concluded to be affected by cyfluthrin and the administration of the three compounds at the indicated doses and for the indicated periods were considered to alleviate the adverse effects of cyfluthrin partly throughout the study period.     

Cytochrome P450 monooxygenase-mediated permethrin resistance confers limited and larval specific cross-resistance in the southern house mosquito, Culex pipiens quinquefasciatus

The cytochrome P450-dependent monooxygenases (P450s) are an important enzymatic system that metabolizes xenobiotics (e.g., pesticides), as well as endogenous compounds (e.g., hormones). P450-mediated metabolism can result in detoxification of insecticides such as pyrethroids, or can be involved in the bioactivation and detoxification of insecticides such as organophosphates. We isolated (from the JPAL strain) a permethrin resistant strain (ISOP450) of Culex pipiens quinquefasciatus, having 1300-fold permethrin resistance using standard backcrossing procedures. ISOP450 is highly related to the susceptible lab strain (SLAB) and the high resistance to permethrin is due solely to P450-mediated detoxification. This is the first time in mosquitoes that P450 monooxygenase involvement in pyrethroid resistance has been isolated and studied without the confounding effects of kdr. Resistance in ISOP450 is incompletely dominant (D = +0.3), autosomally linked, and monofactorally inherited. It is expressed in the larvae, but not in adults. Cross-resistance to pyrethroids lacking a 3-phenoxybenzyl moiety (tetramethrin, fenfluthrin, bioallethrin, and bifenthrin) ranged from 1.5- to 12-fold. ISOP450 had only limited (6.6- and 11-fold) cross-resistance to 3-phenoxybenzyl pyrethroids with an α-cyano group (cypermethrin and deltamethrin, respectively). Examination of cross-resistance patterns to organophosphate insecticides in ISOP450 showed an 8-fold resistance to fenitrothion, while low, but significant, levels of negative cross-resistance were found for malathion (RR = 0.84), temephos (RR = 0.73), and methyl-parathion (RR = 0.55). The importance and uniqueness of this P450 mechanism in insecticide resistance is discussed.     

Insecticide resistance in the tropical bedbug Cimex hemipterus

Insecticide resistance in the bedbug Cimex hemipterus was investigated using 4211 bedbugs collected from three districts of Sri Lanka. Insecticide bioassays were carried out with discriminating dosages of deltamethrin, permethrin, DDT, malathion, and propoxur. Activity levels of insecticide metabolizing enzymes and the insecticide target site acetylcholinesterase were monitored using biochemical assays. Percentage survivals after DDT, malathion, and propoxur exposure were 41-88%, 18-64%, and 11-41%, respectively. For deltamethrin and permethrin, KT₅₀/KT₉₀ (time to knock-down 50%/90% of the population) values were 0.5-24/1.0-58 and 1.3-10/2.5-47 h, respectively. Both elevated esterase and malathion carboxylesterase mechanisms were present in bedbug populations. Monooxygenase levels were heterogeneous. Organophosphate and carbamate target site acetylcholinesterase, was insensitive in 29-44% of the populations. High DDT resistance was probably due to glutathione S-transferases. Malathion carboxylesterases are mainly responsible for high malathion resistance. High tolerance to both DDT and pyrethroids suggests the presence of ‘kdr’ type resistance mechanism in one population.