The interaction of gamma radiation with drugs used in cholinergic medications.

Purpose: Pharmacological medications can reduce the radiation damage in the organism when applied in the stage before or after exposure to radiation. Cholinergic drugs are a category of pharmaceutical agents acting on the neurotransmitter acetylcholine, the primary neurotransmitter in the parasympathetic nervous system. In this investigation, some gamma radiation interaction parameters namely mass attenuation coefficients (µρ), effective atomic number (Zeff) and electron densities (Nel) of 12 cholinergic system drugs have been calculated in the energy range 1 KeV-100 GeV. In addition, gamma-ray energy absorption (EABF) and exposure (EBF) of buildup factors have been computed using the five-parameter geometric progression (G-P) fitting formula for investigated drugs in the energy range 0.015-15 MeV, and for penetration depths up to 40 mean free path (mfp).Materials and methods: In order to perform these calculations, data obtained from WinXCom computer program were used. The computed µρ values were then used to calculate the effective atomic numbers and electron density of the investigated drugs. To compute the buildup factors, the G-P fitting parameters were determined by the method of interpolation from the equivalent atomic number, 'Zeq'Results and Conclusions: It has been concluded that effective atomic number and electron density of malathion is bigger than the other drugs and the variations in values of Zeff and Nel for all drugs depend on chemical compositions and photon energy where the K-absorption edge of elements may affect the energy dependence of Zeff and Nel. It should also be noted that the buildup of photons is less in malathion and carbachol and is more in tabun and parathion compared with other drugs. Photon interaction parameters evaluated in the present study may be beneficial in radiation dosimetry and therapy.

Analysis of Ran related to pesticide resistance in Drosophila Kc cells.

Pesticides have been used extensively for pest control, resulting in serious pesticide resistance. It is extremely valuable to identify the resistance genes related to pest control. In our previous studies, we reported that Ran is the deltamethrin (DM) resistance-associated gene. To clarify whether Ran is also related to the resistance of other pesticides, we selected four kinds of pesticides, including parathion, DDT, carbaryl and pleocidin, for further study. The results showed that Ran could be up-regulated by all pesticides. We further verified the relationship between Ran and resistance to the 4 pesticides by Ran RNAi, Ran overexpression and cell apoptosis. We found that the dsRNA of Ran induced more cell apoptosis than the control. Ran overexpression can significantly improve cell tolerance to various pesticides. These results demonstrate that Ran is associated with the resistance to and tolerance of multiple pesticides. Our evidence suggests the Ran is a potential molecular target gene of resistance control.

ER chaperone GRP78 regulates autophagy by modulation of p53 localization.

GRP78 (glucose regulated protein 78) is a major Endoplasmic Reticulum (ER) chaperone that plays a pivotal role in normal ER functioning. Its increased expression also works as an indicator of ER stress. Its anti-apoptotic and pro-autophagic activity makes it an intriguing target to study the relationship between GRP78 and p53, which is also a major regulator of apoptosis and autophagy. Here, we studied the effect of Rotenone and Parathion on human lung cancer cells (A549 cell line) specifically with respect to ER stress and its association with different cell death pathways. In our study, we observed that both compounds increase reactive oxygen species (ROS) generation, down regulate mitochondrial membrane potential (MMP) and affect DNA integrity. Our results indicate that Parathion causes ER stress, up regulates the expression of GRP78, leads to nuclear localization of p53 and induces autophagy while Rotenone down regulates GRP78, causes cytoplasmic localization of p53 and inhibits autophagy. Therefore, it may be concluded that GRP78 affects p53 localization which in turn regulates autophagy.

In vitro characterization of pralidoxime transport and acetylcholinesterase reactivation across MDCK cells and stem cell-derived human brain microvascular endothelial cells (BC1-hBMECs).

BACKGROUND: Current therapies for organophosphate poisoning involve administration of oximes, such as pralidoxime (2-PAM), that reactivate the enzyme acetylcholinesterase. Studies in animal models have shown a low concentration in the brain following systemic injection. METHODS: To assess 2-PAM transport, we studied transwell permeability in three Madin-Darby canine kidney (MDCKII) cell lines and stem cell-derived human brain microvascular endothelial cells (BC1-hBMECs). To determine whether 2-PAM is a substrate for common brain efflux pumps, experiments were performed in the MDCKII-MDR1 cell line, transfected to overexpress the P-gp efflux pump, and the MDCKII-FLuc-ABCG2 cell line, transfected to overexpress the BCRP efflux pump. To determine how transcellular transport influences enzyme reactivation, we developed a modified transwell assay where the inhibited acetylcholinesterase enzyme, substrate, and reporter are introduced into the basolateral chamber. Enzymatic activity was inhibited using paraoxon and parathion. RESULTS: The permeability of 2-PAM is about 2 × 10(-6) cm s(-1) in MDCK cells and about 1 × 10(-6) cm s(-1) in BC1-hBMECs. Permeability is not influenced by pre-treatment with atropine. In addition, 2-PAM is not a substrate for the P-gp or BCRP efflux pumps. CONCLUSIONS: The low permeability explains poor brain penetration of 2-PAM and therefore the slow enzyme reactivation. This elucidates one of the reasons for the necessity of sustained intravascular (IV) infusion in response to organophosphate poisoning.

Comparative effects of parathion and chlorpyrifos on endocannabinoid and endocannabinoid-like lipid metabolites in rat striatum.

Parathion and chlorpyrifos are organophosphorus insecticides (OPs) that elicit acute toxicity by inhibiting acetylcholinesterase (AChE). The endocannabinoids (eCBs, N-arachidonoylethanolamine, AEA; 2-arachidonoylglycerol, 2AG) are endogenous neuromodulators that regulate presynaptic neurotransmitter release in neurons throughout the central and peripheral nervous systems. While substantial information is known about the eCBs, less is known about a number of endocannabinoid-like metabolites (eCBLs, e.g., N-palmitoylethanolamine, PEA; N-oleoylethanolamine, OEA). We report the comparative effects of parathion and chlorpyrifos on AChE and enzymes responsible for inactivation of the eCBs, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), and changes in the eCBs AEA and 2AG and eCBLs PEA and OEA, in rat striatum. Adult, male rats were treated with vehicle (peanut oil, 2 ml/kg, sc), parathion (27 mg/kg) or chlorpyrifos (280 mg/kg) 6-7 days after surgical implantation of microdialysis cannulae into the right striatum, followed by microdialysis two or four days later. Additional rats were similarly treated and sacrificed for evaluation of tissue levels of eCBs and eCBLs. Dialysates and tissue extracts were analyzed by LC-MS/MS. AChE and FAAH were extensively inhibited at both time-points (85-96%), while MAGL activity was significantly but lesser affected (37-62% inhibition) by parathion and chlorpyrifos. Signs of toxicity were noted only in parathion-treated rats. In general, chlorpyrifos increased eCB levels while parathion had no or lesser effects. Early changes in extracellular AEA, 2AG and PEA levels were significantly different between parathion and chlorpyrifos exposures. Differential changes in extracellular and/or tissue levels of eCBs and eCBLs could potentially influence a number of signaling pathways and contribute to selective neurological changes following acute OP intoxications.

Over-transcription of genes in a parathion-resistant strain of mosquito Culex pipiens quinquefasciatus.

Insecticide resistance is an evolutionary adaptation that develops quite quickly in mosquitoes because of the high selection pressure of chemical insecticides, rapid generation time and large population size. Identification of genes associated with insecticide resistance is fundamental to understand the complex processes responsible for resistance. We compared the gene transcriptional profiles of parathion-resistant and -susceptible Culex pipiens quinquefasciatus using a combination of suppression subtractive hybridization and complementary DNA (cDNA) microarray techniques. A total of 278 colonies were selected from the resistant-susceptible mosquito subtractive library, 38 of which showed more than two fold stronger immunoblotting signals in the resistant strain than in the susceptible strain using cDNA microarray selection. The sequencing results showed that the 38 colonies can be matched to 12 genes of C. p. quinquefasciatus. Eight genes were confirmed to be overexpressed by more than two fold in the resistant strain. These genes encode chymotrypsin-1, theta glutathione S-transferase, lipase 3, larval serum protein 1 ß chain, cytochrome b, mitochondrial ribosomal large subunit, 28S rRNA, and a protein with unknown function. This study serves as a preliminary attempt to identify new genes associated with organophosphate resistance in this mosquito species and provides insights into the complicated physiological phenomenon of insecticide resistance.

Effect of ionising radiation on polyphenolic content and antioxidant potential of parathion-treated sage (Salvia officinalis) leaves.

The γ-irradiation effects on polyphenolic content and antioxidant capacity of parathion-pretreated leaves of Salvia officinalis plant were investigated. The analysis of phenolic extracts of sage without parathion showed that irradiation decreased polyphenolic content significantly (p<0.05) by 30% and 45% at 2 and 4kGy, respectively, compared to non-irradiated samples. The same trend was observed for the Trolox equivalent antioxidant capacity (TEAC), as assessed by the anionic DPPH and cationic ABTS radical-scavenging assays. The antioxidant potential decreased significantly (p<0.01) at 2 and 4kGy, by 11-20% and 40-44%, respectively. The results obtained with a pure chlorogenic acid solution confirmed the degradation of phenols; however, its TEAC was significantly (p<0.01) increased following irradiation. Degradation products of parathion formed by irradiation seem to protect against a decline of antioxidant capacity and reduce polyphenolic loss. Ionising radiation was found to be useful in breaking down pesticide residues without inducing significant losses in polyphenols.

Purification and characterization of carboxylesterase from the seeds of Jatropha curcas.

Carboxylesterases are hydrolases which catalyze the hydrolysis of various types of esters. Carboxylesterase from the seeds of Jatropha curcas has been purified to homogeneity using ammonium sulfate fractionation, CM-cellulose chromatography, Sephadex G-100 chromatography and preparative polyacrylamide gel electrophoresis (PAGE). The homogeneity of the purified enzyme was confirmed by PAGE, iso-electrofocusing and SDS-PAGE. The molecular weight of the purified enzyme was determined by both gel-permeation chromatography on Sephadex G-150 and SDS-PAGE. The molecular weight determined by Sephadex G-150 chromatography and SDS-PAGE both in the presence and absence of 2-mercaptoethanol was 31 kDa. The isoelectric point of the purified enzyme was found to be 8.9. JCSE-I (J. curcas seed esterase-I) was classified as carboxylesterase on the basis of substrate and inhibitor specificity. The K(m) of JCSE-I with 1-naphthyl acetate, 1-naphthyl propionate, 1-naphthyl butyrate and 2-naphthyl acetate as substrates were found to be 0.0,794, 0.0,658, 0.0,567 and 0.1 mM, respectively. The enzyme exhibited an optimum temperature of 45 °C and an optimum pH of 6.5. The enzyme was stable up to 15 min at 65 °C. The enzyme was resistant towards carbamates (carbaryl and eserine sulfate) and sulphydryl inhibitors (p-chloromercuricbenzoate, PCMB) and inhibited by organophosphates (dichlorvos, parathion and phosphamidon).

Prior exposure to immunosuppressive organophosphorus or organochlorine compounds aggravates the T(H)1- and T(H)2-type allergy caused by topical sensitization to 2,4-dinitrochlorobenzene and trimellitic anhydride.

Immunosuppressive environmental chemicals may increase the potency of allergens and thereby play a role in the development of allergic diseases. This study's primary objective was to examine the mechanisms behind the relationship between allergic diseases and the immunosuppression induced by some environmental chemicals. We focused on the modulation of allergic potential in vitro and in mice by the organophosphorus pesticide O,O-diethyl-O-4-nitrophenyl-thiophosphate (parathion) and the organochlorine pesticide 1,1,1-trichloro-2,2-bis(4-methoxy-phenyl)ethane (methoxychlor), with respect to the T(H)1-type allergen 2,4-dinitrochlorobenzene (DNCB) and the T(H)2-type allergen trimellitic anhydride (TMA). Mice (4-week-old) were orally administered parathion or methoxychlor. Four weeks after the final dosing, the mice were sensitized to DNCB or TMA, and T-lymphocyte proliferation measured in their (using a local lymph node assay [LLNA]). In addition, we analyzed T-lymphocytes via surface antigen expression and local cytokine production in auricular lymph nodes after treatment with 0.1% DNCB or 0.3% TMA. The estimated concentration of DNCB and TMA to yield a stimulation index (SI) of cell proliferation of three decreased markedly in parathion- and methoxychlor-pre-treated mice. Pesticide pre-treatment induced marked increases in the number of helper and cytotoxic T-cells, levels of T(H)1 and T(H)2 cytokines, and gene expression in lymph node cells. According to our results, T(H)1- and T(H)2-type allergies are aggravated by prior exposure to immunosuppressive environmental chemicals.

Neonatal exposure to parathion alters lipid metabolism in adulthood: Interactions with dietary fat intake and implications for neurodevelopmental deficits.

Organophosphates are developmental neurotoxicants but recent evidence also points to metabolic dysfunction. We determined whether neonatal parathion exposure in rats has long-term effects on regulation of adipokines and lipid peroxidation. We also assessed the interaction of these effects with increased fat intake. Rats were given parathion on postnatal days 1-4 using doses (0.1 or 0.2mg/kg/day) that straddle the threshold for barely detectable cholinesterase inhibition and the first signs of systemic toxicity. In adulthood, animals were either maintained on standard chow or switched to a high-fat diet for 7 weeks. We assessed serum leptin and adiponectin, tumor necrosis factor-alpha (TNFalpha) in adipose tissues, and thiobarbituric acid reactive species (TBARS) in peripheral tissues and brain regions. Neonatal parathion exposure uncoupled serum leptin levels from their dependence on body weight, suppressed adiponectin and elevated TNFalpha in white adipose tissue. Some of the effects were offset by a high-fat diet. Parathion reduced TBARS in the adipose tissues, skeletal muscle and temporal/occipital cortex but not in heart, liver, kidney or frontal/parietal cortex; it elevated TBARS in the cerebellum; the high-fat diet again reversed many of the effects. Neonatal parathion exposure disrupts the regulation of adipokines that communicate metabolic status between adipose tissues and the brain, while also evoking an inflammatory adipose response. Our results are consistent with impaired fat utilization and prediabetes, as well as exposing a potential relationship between effects on fat metabolism and on synaptic function in the brain.

Exposure of neonatal rats to parathion elicits sex-selective reprogramming of metabolism and alters the response to a high-fat diet in adulthood.

BACKGROUND: Developmental exposures to organophosphate pesticides are virtually ubiquitous. These agents are neurotoxicants, but recent evidence also points to lasting effects on metabolism. OBJECTIVES: We administered parathion to neonatal rats. In adulthood, we assessed the impact on weight gain, food consumption, and glucose and lipid homeostasis, as well as the interaction with the effects of a high-fat diet. METHODS: Neonatal rats were given parathion on postnatal days 1-4 using doses (0.1 or 0.2 mg/kg/day) that straddle the threshold for barely detectable cholinesterase inhibition and the first signs of systemic toxicity. In adulthood, animals were either maintained on standard lab chow or switched to a high-fat diet for 7 weeks. RESULTS: In male rats on a normal diet, the low-dose parathion exposure caused increased weight gain but also evoked signs of a prediabetic state, with elevated fasting serum glucose and impaired fat metabolism. The higher dose of parathion reversed the weight gain and caused further metabolic defects. Females showed greater sensitivity to metabolic disruption, with weight loss at either parathion dose, and greater imbalances in glucose and lipid metabolism. At 0.1 mg/kg/day parathion, females showed enhanced weight gain on the high-fat diet; This effect was reversed in the 0.2-mg/kg/day parathion group, and was accompanied by even greater deficits in glucose and fat metabolism. CONCLUSIONS: Neonatal low-dose parathion exposure disrupts glucose and fat homeostasis in a persistent and sex-selective manner. Early-life toxicant exposure to organophosphates or other environmental chemicals may play a role in the increased incidence of obesity and diabetes.

Human drug metabolism genes in parathion-and estrogen-treated breast cells.

Environmental chemicals may be involved in the etiology of breast cancer. Among them, organophosphorous compounds are the most widely used pesticides because of their extensive use in agriculture, medicine and industry. The risk of breast cancer is associated with prolonged exposure to female hormones and is attributed to estrogen since prolonged stimulation by steroid hormones may increase cell division. The aim of the present study was to identify the differentially expressed genes encoding enzymes that are important to drug transport and metabolism in parathion- and estrogen-treated human breast epithelial cell lines using cDNA microarrays. MCF-l0F, an immortalized human breast epithelial cell line was treated with parathion and estrogen, either alone or in combination, and malignant cells were developed through a series of sequential steps. Differential expression from the drug metabolism gene array showed that 17 genes were found to be altered either by parathion or estrogen alone, or the combination of both. Among the genes altered by parathion in comparison to the control were CHST5, CHST6 and CHST7 (sulfotransferases); CYP2F1, CYP3A7 and CYP4F3 (CYPs); GSTP1, GSTT2 and MGST1 (GSTs); MT1X (metallothionein); TPMT (methyltransferase); UGT1A1 and UGT2B (UDP glycosyltransferases). The same genes were down-regulated in estrogen alone including several metallothioneins (MT1A, MT1E, MT1H, MT1L and MT2A). The combination of parathion and estrogen induced down-regulation of three sulfotransferases, CYP2F1 and CYP4F3, MGST1, all metallothioneins and TPMT genes. There was no change in CYP3A7, GSTP1, GSTT2, UGT1A1 and UGT2B genes in the presence of both substances. It can be concluded from this study that organophosphorous pesticides such as parathion in the presence of estradiol induced changes in human drug metabolism gene expression in breast cells.

Gene and protein expressions induced by 17beta-estradiol and parathion in cultured breast epithelial cells.

Cancer of the breast is the most common form of malignant disease occurring among women of the western world and environmental substances seem to be involved in the etiology of this disease. Many studies have found an association between human cancer and exposure to agricultural pesticides and among them parathion, the organophosphorous pesticide used in agriculture to control mosquito plagues. The association between breast cancer and prolonged exposure to estrogens suggests that this hormone also may have a role in such process. However, the causative factors for breast carcinogenesis remain an enigma. The objective of this study was to determine the effects of 17beta-estradiol (E2) and parathion on cell transformation of human breast epithelial cells in vitro. The results of this study showed that parathion alone and in combination with E2 induced malignant transformation of an immortalized human breast epithelial cell line, MCF-10F, and the malignant feature was confirmed by anchorage independency and invasive capabilities. Parathion alone efficiently elevated the expression of EGFR, c-Kit, Trio, Rac 3, Rho-A, and mutant p53 proteins. Analysis of gene expression using commercially available human cell cycle array revealed transcriptional alterations in 22 out of a total of 96 genes. Among them, nine genes involved in the regulation of cell cycle were altered. These included cyclins (A1, A2, C, G1, G2, and H), cyclin-dependent kinases (CDKs), and minichromosome maintenance deficient (MCM). Results suggest that parathion has the potency to cause malignant transformation of breast epithelial cells through modulation of expression of cell cycle regulated genes.

Gene expression signature of parathion-transformed human breast epithelial cells.

Environmental substances seem to be involved in the etiology of breast cancers. Many studies have found an association between human cancer and exposure to agricultural pesticides such as the organophosphorous pesticides. Parathion is a cholinesterase inhibitor that induces the hydrolysis of body choline esters, including acetylcholine at cholinergic synapses. The primary target of action in insects is the nervous system whereby pesticides inhibit the release of the enzyme acetylcholinesterase at the synaptic junction. Atropine is a parasympatholytic alkaloid used as an antidote to acetylcholinesterase inhibitors. The aim of this study was to determine the effect of parathion and atropine on cell transformation of human breast epithelial cells in vitro. These studies showed that parathion alone was able to induce malignant transformation of an immortalized human breast epithelial cell line, MCF-10F as indicated by increased cell proliferation, anchorage independency and invasive capabilities. There was also an increase in c-kit, Trio, Rho-A, Rac-3, EGFR, Notch-4, Dvl-2, Ezrin, beta catenin and mutant p53 protein expression in the parathion-treated cells. However, atropine significantly inhibited this increase. In a human cell cycle array of 96 genes, 13 of them were altered by parathion treatment. Among the genes affected were the cyclins, such as cyclin D3, the cyclin-dependent kinases (CDKs) such as CDK41 and the minichromosome maintenance deficient (MCM) MCM2 and MCM3. It is suggested that parathion influences human breast epithelial cell transformation and is an initiator factor in the transformation process in breast cancer.

Effects of paraoxon and ethylparathion on choline oxidase from Alcaligenes species: inhibition and denaturation.

The kinetics and thermodynamics of the effects of paraoxon (POX) and ethylparathion (EPA) on choline oxidase (ChOx) were studied. Lineweaver-Burk plots of initial velocity data showed a parallel pattern indicating uncompetitive inhibition versus choline. The inhibition constant (K(I)) obtained from the secondary plots for POX and EPA were 0.14+/-0.01 and 0.48+/-0.05 mM, respectively, suggesting that POX is a more potent inhibitor of ChOx than EPA. UV absorption was used to monitor the denaturation of ChOx by POX and EPA. A decrease in FAD fluorescence associated with the interaction of POX and EPA with ChOx suggested a tertiary structural change. Interaction of the enzyme molecule with POX or EPA resulted in inhibition and subsequently denaturation of the enzyme. The results indicate that inhibition and denaturation of the enzyme by POX and EPA are linked, but not parallel events, with inhibition occurring at lower concentrations with respect to denaturation. This suggests that the loss of initial velocity of the enzyme is an active site specific effect and not due to global conformational changes induced by the inhibitors.

Comparative inhibition of inducible and constitutive CYPs in rat hepatic microsomes by parathion.

1. In microsomal fractions, the phosphorothioate pesticide parathion inhibits cytochrome P450 (CYP) enzymes by reversible and irreversible mechanisms resulting in the long-term suppression of drug oxidation. The present study evaluated the relative susceptibilities of constitutive and inducible CYP2 and CYP3 steroid hydroxylases to inhibition by the pesticide. 2. Enzyme kinetic analysis indicated that constitutive and dexamethasone (DEX)-induced androst-4-ene-3,17-dione (AD) 6beta-hydroxylations were similarly susceptible to inhibition by parathion (Km/Ki ratios 1.5-1.6). However, preincubation of parathion with NADPH-fortified microsomes intensified the extent of inhibition of CYP3A-dependent 6beta-hydroxylation. Comparison of Km/Ki ratios indicated that 6beta-hydroxylation activity in fractions from DEX-pretreated rats was about twice as susceptible as the control activity to inactivation by parathion metabolites (Km/Ki ratio of 8.0 versus 4.0). 3. The time-dependent loss of AD 6beta-hydroxylation by parathion occurred more efficiently in fractions from DEX-induced liver than in control. Thus, half-times of 1.3 and 6.1 min, respectively, were determined for the inactivation of DEX-inducible and constitutive activities. Parathion concentrations required for half-maximal inactivation were 32 and 67 microM in microsomes from DEX-induced and control rats. 4. In phenobarbital (PB)-induced fractions CYP2B1-mediated AD 16beta-hydroxylation was inhibited potently in a reversible fashion by parathion (Ki = 0.37 microM; Km/Ki ratio about 73). Inhibition was not enhanced at parathion concentrations near the Ki by a preincubation step with NADPH. 5. In control microsomes parathion elicited a type I binding interaction with oxidized CYP (Ks=7.7 microM, deltaAmax=2.2 x 10(-2) a.u.nmol CYP-1; deltaAmax/Ks 2.86 x 10(3) a.u. nmol CYP(-1)/mM). Ligand binding was 13- and 1.6-fold more efficient in PB and DEX microsomes, respectively. 6. These findings indicate that pretreatment of rats with enzyme-inducing drugs like DEX and PB alters the profile of CYPs and their susceptibility to inhibition by parathion. Potent reversible inhibition of CYP2B1 occurred in PB-induced fractions and DEX-inducible CYPs 3A were more susceptible to mechanism-based inactivation than the corresponding constitutive CYPs from the same subfamily.

Cardiac responses of Pacific oyster Crassostrea gigas to agents modulating cholinergic function.

To examine the functional effects of cholinergic modulation compounds in oyster hearts and to explore their possible use in monitoring intoxication with acetylcholine-esterase (AChE) inhibitors such as organophosphates, tests were performed with in situ oyster heart preparations. The endogenous cholinergic agonist acetylcholine (ACh), AChE-resistant synthetic agonist carbachol, and the reversible carbamate type of AChE inhibitor physostigmine, all potently depressed spontaneous cardiac contractility. The depression was reversed by extensive washout, or prevented by muscarinic cholinergic antagonist atropine. The irreversible organophosphate type AChE inhibitor parathion or its active metabolite paraoxon at concentrations up to 100 microM failed to depress cardiac contractility. While other reversible AChE inhibitors such neostigmine and pyridostigmine also depressed the contractility, organophosphate AChE inhibitors malathion, diazinon, or phenthoate did not. Despite the differential effect in depressing cardiac function between the reversible and irreversible inhibitors, both of these inhibitors effectively inhibited cardiac AChE activity. The results suggest that the activation of muscarinic cholinergic receptors is coupled to inhibitory cardiac modulation, and organophosphate AChE inhibitors may inhibit only an AChE isozyme located at sites that are not important for control of cardiac activity in oysters.

Parathion induces mouse germ cells apoptosis.

Germ cell loss occurs in normal spermatogenesis at defined stages of the seminiferous epithelial cycle. The process has been known for over a century but only recently it was analyzed under the concept of apoptosis. This is a programmed cell death that occurs during development and also in the adult. It is believed to play a key role as quality control in sperm formation, avoiding the passage of genetic defects to future generations. Chemical toxicants may increase apoptosis, disturbing tissue homeostasis. The effect of the agropesticide parathion upon apoptosis in mouse seminiferous tubules was analyzed in young mice (onset of spermatogenesis) and in adult animals (full spermatogenesis). In both young and adult mice, the pesticide increases the rate of apoptosis, which takes place at stages where spermatogonial proliferation occurs, affects spermatocytes at the beginning of the meiotic process and spermatids at the elongating period. Basal apoptotic rates are greater in young mice. In adults, commercial parathion is more toxic than the pure organophosphoric compound. From these observations plus in vitro effects of parathion reported previously, it can be concluded that the pesticide affects DNA (and RNA and protein) synthesis. The effect is reversible with moderate doses of the chemical after acute intoxication.

Effects of subchronic parathion exposure on cyclosporine pharmacokinetics in rats.

Parathion undergoes enzymatic oxidation by hepatic cytochrome P-450 (CYP450) enzymes to the active metabolite paraoxon. Consequently, alterations in CYP450-dependent oxidation may affect the pharmacokinetics and pharmacodynamics of drugs that are metabolized in the liver. The CYP3A family is known to be responsible for the majority of cyclosporine metabolism. The aim of the present study was to assess the disposition kinetics of cyclosporine during subchronic parathion exposure. Male Wistar rats were administered either water or two different doses of parathion (1/100 LD50, 1/25 LD50; LD50 = 14 mg/kg) by gavage for 6 wk. Subsequently, rats in each experimental group received a single oral dose of cyclosporine (10 mg/kg), and serial blood samples were drawn from the carotid artery over a period of 48 h. Pharmacokinetic analysis showed that parathion increased the blood cyclosporine concentration twofold as evidenced by AUC (area under the curve), half life (t 1/2) and peak plasma concentration (Cmax). This may be due to inhibition of cyclosporine metabolism, an interaction that may be of clinical relevance in immunosuppression therapy.

Chronic intracerebroventricular exposure to beta-amyloid(1-40) impairs object recognition but does not affect spontaneous locomotor activity or sensorimotor gating in the rat.

This study examined the cognitive effects of chronic in vivo exposure to beta-amyloid(1-40) via the intracerebroventricular route on two distinct paradigms. The first test evaluated a form of early attentional control referred to as sensorimotor gating in which an antecedent weak prepulse stimulus modulates the reactivity to a subsequent startle-eliciting stimulus. The second test utilized the spontaneous preference for a novel object over that of a familiar one in rats as a measure of object recognition memory. We found that beta-amyloid exposure leads to a severe deficit in the object memory test but spares sensorimotor gating. Moreover, unlike the water maze deficit induced by beta-amyloid (Nag et al., in preparation), the deficit on object recognition was resistant to amelioration by systemic physostigmine treatment at a dose of 0.06 mg/kg per day intraperitoneally. The present results add to previous reports that beta-amyloid exposure can lead to deficits on hippocampal lesion sensitive tasks, suggesting that dysfunction of the rhinal cortices in addition to that of the septohippocampal system is implicated in beta-amyloid-induced behavioral impairments. It therefore lends support to the hypothesis that beta-amyloid exposure can lead to severe impairment across multiple memory systems.