Inhibition of extension outgrowth in differentiating rat C6 glioma cells by chlorpyrifos and chlorpyrifos oxon: effects on microtubule proteins

The aim of this work was to assess the toxic effects of the phosphorothionate insecticide chlorpyrifos (CPF) and its major in vivo metabolite chlorpyrifos oxon (CPO) on differentiating rat C6 glioma cells. At sublethal concentrations (1-10 microM), both compounds were able to inhibit the development of extensions from C6 cells induced to differentiate by sodium butyrate. Western blot analysis of C6 cell lysates revealed that 4 h exposure to CPF was associated with decreased levels of the cytoskeletal protein MAP1B compared to controls, whereas the levels of the cytoskeletal proteins tubulin and MAP2c were not significantly affected. Western blot analysis of extracts of cells treated with CPO showed a significant, concentration-dependent decrease in the levels of tubulin after 24 h. MAP-1B levels were also significantly decreased. The above changes were not temporally related to acetylcholinesterase (AChE) inhibition. These results suggest that both CPF and CPO can exert toxic effects directly on glial cell differentiation and that the latter compound has a potent effect on the microtubule network.

The effects of diazinon and cypermethrin on the differentiation of neuronal and glial cell lines

Diazinon and cypermethrin are pesticides extensively used in sheep dipping. Diazinon is a known anti-cholinesterase, but there is limited information regarding its molecular mechanism of action. This paper describes the effects of diazinon and cypermethrin at a morphological and molecular level on differentiating mouse N2a neuroblastoma and rat C6 glioma cell lines. Concentrations up to 10 microM of both compounds and their mixture had no effect on the viability of either cell line, as determined by methyl blue tetrazolium reduction and total protein assays. Microscopic analysis revealed that 1 microM and 10 microM diazinon but not cypermethrin inhibited the outgrowth of axon-like processes in N2a cells after a 24-h exposure but neither compound affected process outgrowth by differentiating C6 cells at these concentrations. Under these conditions, 10 microM diazinon inhibited AChE slightly compared to the control after a 4-h exposure but not after 24 h. Western blotting analysis showed that morphological changes were associated with reduced cross-reactivity with antibodies that recognize the neurofilament heavy chain (NFH), microtubule associated protein MAP 1B and HSP-70 compared to control cell extracts, whereas reactivity with anti-alpha-tubulin antibodies was unchanged. Aggregation of NFH was observed in cell bodies of diazinon-treated N2a cells, as determined by indirect immunofluorescence staining. These data demonstrate that diazinon specifically targets neurite outgrowth in neuronal cells and that this effect is associated with disruption of axonal cytoskeleton proteins, whereas cypermethrin has no effect on the same parameters.

Inhibition of neurite outgrowth in N2a cells by leptophos and carbaryl: effects on neurofilament heavy chain, GAP-43 and HSP-70

The neurodegenerative properties of the organophosphate ester leptophos (LEP) and the carbamate ester carbaryl (CB), both of which can cause neuropathic effects in animals, were investigated in differentiating mouse N2a neuroblastoma cells. At a sublethal concentration of 3 microM, both LEP and CB were able to inhibit the outgrowth of axon-like processes from N2a cells after only 4 h of exposure. Extracts of cells exposed to LEP showed decreased cross-reactivities with monoclonal antibodies that recognise the neurofilament heavy chain (NFH) and the growth-associated protein GAP-43. However, they exhibited increased cross-reactivity with a monoclonal antibody that recognises the heat shock protein HSP-70. In contrast, no changes were noted in the levels of antibody binding in blots of extracts of cells exposed to CB. It is concluded that, although both LEP and CB inhibit the formation of axons in vitro, the early biochemical changes underlying the neurodegenerative effects of the two compounds are different.

Inhibition of rat platelet 5-hydroxytryptamine uptake by chlorpyrifos and carbaryl

The organophosphate insecticide chlorpyrifos and the carbamate insecticide carbaryl were investigated in adult male rats in terms of their effects on the activity of brain monoamine oxidase-A (MAO-A) activity and on the platelet uptake of 5-hydroxytryptamine (5-HT). The activities of brain acetylcholinesterase (AChE) and plasma butyrylcholinesterase (BuChE) were also determined. For each compound two different dosage regimens were employed. In the acute study, chlorpyrifos or carbaryl was administered at a single intraperitoneal dose of 100 mg/kg or 50 mg/kg, respectively In the subacute study, chlorpyrifos was injected at a daily dose of 20 mg/kg for 7 days, while carbaryl was given at a daily dose of 10 mg/kg for 14 days. Acute chlorpyrifos administration produced a 85.01% inhibition of AChE and a 43.4% inhibition of BuChE but had no effect on MAO-A activity and 5-HT uptake. In contrast, subacute chlorpyrifos exposure caused a 94.96% inhibition of AChE and a 85.8% inhibition of BuChE and, also, elicited a significant (35.02%) reduction in the platelet uptake of 5-HT. MAO-A activity was not affected. Acute carbaryl administration produced a 56.38% AChE inhibition and a 55.95% BuChE inhibition and also caused a significant (26.36%) decrease in 5-HT uptake but no change in MAO-A. Subacute carbaryl exposure failed to affect significantly any of the biochemical parameters determined. Interference with the 5-HT system by chlorpyrifos and carbaryl could contribute to the toxicity of these pesticides.

The toxicity of chlorpyrifos towards differentiating mouse N2a neuroblastoma cells

The aim of this work was to study the effects of chlorpyrifos (CPF) on the outgrowth of axons by differentiating mouse N2a neuroblastoma cells. This was achieved by morphological, Western blotting and enzymatic analyses of cells induced to differentiate in the presence and absence of CPF added either at the same time (co-differentiation) or 16 h after (post-differentiation) the induction of cell differentiation. The outgrowth of axon-like processes was impaired following 4 or 8 h exposure to CPF in both co- and post-differentiation experiments. Western blotting analysis revealed reduced levels of neurofilament heavy chain (NF-H) following 8 h of exposure but no significant effect at 4 h under both co- and post-differentiation conditions. By contrast, levels of the heat shock protein HSP-70 were raised at both time points, but only in co-differentiation experiments. Neuropathy target esterase (NTE) activity was lower than controls following 4 or 8 h of exposure under co-differentiation conditions, but not under any post-differentiation conditions. The results suggest that the inhibition of axon production and maintenance by CPF in differentiating N2a cells may involve multiple targets, which are different under co- and post-differentiation conditions.

Effects of neuropathic and non-neuropathic isomers of tricresyl phosphate and their microsomal activation on the production of axon-like processes by differentiating mouse N2a neuroblastoma cells

The aim of this work was to investigate the sublethal neuropathic effects of tricresyl phosphate (TCP: mixed isomers), triorthocresyl phosphate (TO:CP) and triparacresyl phosphate (TP:CP) on differentiating mouse N2a neuroblastoma cells. This was achieved by a combination of measurements of cell viability, axon outgrowth and the levels of cytoskeletal proteins detectable on western blots of extracts from cells induced to differentiate in the presence and absence of the compounds. In a time-course experiment TCP inhibited the outgrowth of axon-like processes following exposure times of 24 h or longer. Dose-response experiments indicated that TCP and TO:CP exhibited similar sustained levels of toxicity following both 24 and 48 h exposure, with no significant difference between their respective IC(50) values. By contrast, TP:CP demonstrated a transient effect on the outgrowth of axon-like processes, which was detectable after 24 but not 48 h of exposure. Isomer-specific patterns of toxicity were also evident at earlier time-points, with only the ortho isomer showing significant levels of inhibition of axon outgrowth following 4-8 h exposure. Probing of western blots with antibodies against cytoskeletal proteins indicated that the inhibition of axon outgrowth by these compounds was associated with a sustained reduction in the levels of phosphorylated neurofilament heavy chain. The inhibitory effect on axon outgrowth of TO:CP but not TP:CP was enhanced in the presence of a microsomal activation system. Since TO:CP is the most neuropathic of the isomers of TCP in vivo, differentiating N2a cells provide a useful cellular system for mechanistic studies of the neurodegenerative effects of this organophosphate.

The effects of carbaryl and trichlorphon on differentiating mouse N2a neuroblastoma cells

The ability of the carbamate pesticide carbaryl (CB) and the organophosphate pesticide trichlorphon (TCL) to inhibit the outgrowth of axon-like processes was studied using mouse N2a neuroblastoma cells induced to differentiate by serum withdrawal. At concentrations of 1 and 2 microg/ml (4.97 and 9.94 microM), CB did not cause cell death but inhibited the outgrowth of axon-like processes from N2a cells. This effect was noted as early as 24 h after exposure of the cells to CB. A similar effect was observed with TCL at concentrations of 1 and 2 microg/ml (3.89 and 7.78 microM). Western blot analysis of cell extracts treated with the pesticides showed decreased cross reactivities with the monoclonal antibody RMd09 compared to control extracts. The results indicate that CB and TCL are both able to inhibit axon development and that this effect is associated with reduced levels of the neurofilament high molecular weight protein subunit (NFH).

Tricresyl phosphate inhibits the formation of axon-like processes and disrupts neurofilaments in cultured mouse N2a and rat PC12 cells

Tricresyl phosphate (1 microg/ml) inhibited the outgrowth of axon-like processes in mouse N2a neuroblastoma and rat PC12 pheochromocytoma cell lines induced to differentiate by serum withdrawal and nerve growth factor addition, respectively. By contrast, it had no effect on the outgrowth of processes by rat C6 glioma cells induced to differentiate with sodium butyrate. The effect on axon outgrowth in the two neuronal cell lines correlated with altered distribution of neurofilament proteins, as determined by indirect immunofluorescence with monoclonal antibody RMd09. Western blots of neuronal cell extracts probed with the same antibody revealed decreased cross-reactivity after exposure to tricresyl phosphate. The results suggest that tricresyl phosphate has a selective effect on neuronal cell differentiation, which involves impaired axon outgrowth, reduced levels of the neurofilament heavy chain and disruption of the neurofilament network.

The influence of Datura ferox alkaloids on egg-laying hens

Seeds of the weed Datura ferox are frequent contaminants of raw materials used for animal feed. In this study a mixture of scopolamine and hyoscyamine (98:2), the 2 main alkaloids of Datura ferox seeds, was incorporated at 4 total alkaloid levels (1.5, 15, 75 or 150 mg/kg feed) into a control diet fed to 100 egg-laying hens for 3 mo. Alkaloid doses of 150 mg/kg feed reduced egg production for the first 5-6 w of feeding, whereas lower doses had no effect. Egg weight, eggshell thickness and body weight of hens were unaffected at all doses. Doses of 150 mg/kg feed produced significant increases in the cardiac rate of hens after 5 w. Breathing frequency at all doses was unaffected. Determination of plasma aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase and leucine aminopeptidase activities, as well as autopsy and histological examinations, revealed no obvious alkaloid-related toxic effects. It was concluded that a total alkaloid dose as high as 75 mg/kg feed can be safely administered to egg-laying hens.

The disruption of brain microtubules in vitro by the phospholipase inhibitor p-bromophenacyl bromide

The influence of p-bromophenacyl bromide (pBPAB) and structural analogues on the assembly and Ca2+ sensitivity of porcine brain microtubules (MTs) was studied by spectrophotometric measurements in vitro. MT assembly was inhibited by 36 microM pBPAB but not by the structural analogues p-chlorophenacyl chloride or acetophenone. In the presence of pBPAB, but not structural analogues, the addition of 10 mM Ca2+ induced aggregation of polymerized MT protein, whereas a decrease in turbidity (due to MT disassembly) was observed in controls. The effects of pBPAB on both MT assembly and Ca2+ sensitivity were blocked by glutathione, but not by N-acetyl L-cysteine, N-acetyl L-lysine nor L-tyrosine, indicating that a highly reduced sulphydryl group(s) may be involved. Western blotting analyses of drug-treated MTs revealed a form of tubulin with altered electrophoretic characteristics, probably caused by a covalent interaction with pBPAB. MT preparations polymerized in the presence of the drug contained fewer MTs than control samples, the predominant structures being identified as amorphous aggregates of MT proteins. The fact that pBPAB affects MT integrity at an effective anti-inflammatory dose in vitro may reflect the involvement of MT disruption in some of the pharmacological effects of this drug. pBPAB is not therefore a suitable tool for studying the specific involvement of phospholipase A2 in cellular events.

The toxicity of organophosphate compounds towards cultured PC12 cells

The effects of three representative organophosphates (OPs), tricresyl phosphate (TCP), triphenyl phosphite (TPP) and paraoxon (POX) on the proliferation and viability of rat PC12 pheochromocytoma cells were studied. With respect to its IC50, TCP was at least an order of magnitude more potent in its antiproliferative activity than both TPP and POX. All test OPs were cytotoxic at concentrations inhibiting cell proliferation. No compound inhibited cell growth below 10 micrograms/ml. For TCP and TPP the estimated IC50 values from proliferation assays were lower than published LD50 values in vivo, whereas paraoxon was much less toxic in vitro than in vivo. Subcytotoxic levels of TCP (1 micrograms/ml) were found to inhibit the maintenance of neurites on cells grown in the presence of nerve growth factor.

Toxicity study of the main alkaloids of Datura ferox in broilers

Seeds of the weed Datura ferox are frequent contaminants of raw materials used for animal feed. These seeds produce various toxic effects and contain mainly the alkaloids scopolamine and hyoscyamine. In this 3-month toxicity study, a mixture of scopolamine and hyoscyamine (98:2) was incorporated at four total alkaloid levels (1.5, 15, 75 or 150 mg/kg feed) into a control diet fed to 100 broilers. Alkaloid feeding caused significant reductions in the body weight gain of birds, especially of those fed a dose of 150 mg alkaloid/kg feed. Growth-retarding effects, however, were transient, as no changes in body weight gain were noted after 52 days of alkaloid feeding. Alkaloid-treated broilers showed no significant differences from controls with respect to the cardiac rate and breathing frequency nor in relation to plasma aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase activities. In contrast, plasma leucine aminopeptidase activity was significantly reduced after 3 months in all alkaloid-fed birds. Autopsy and histological examination of tissues by light and electron microscopy revealed no pathological changes associated with alkaloid feeding. Broilers appeared generally healthy and behaved normally throughout. These data should be considered in the formulation of new, improved regulations defining the maximum allowable alkaloid content of D. ferox seeds contaminating raw materials destined for use as broiler feed.

Platelet monoamine oxidase activity and 5-hydroxytryptamine uptake in agoraphobic patients

Platelet MAO activity and platelet serotonin uptake were determined in 20 agoraphobic and 16 neurotic depressive out-patients, and 19 healthy volunteers. Agoraphobic patients were characterised by significantly higher mean values of platelet MAO activity compared with the other two groups, while neurotic depressive patients exhibited significantly higher maximum platelet serotonin uptake velocity. These findings are compatible with an abnormality in the uptake and metabolism of serotonin.