Phthalic acid esters inhibit arachidonate metabolism by rat peritoneal leucocytes

Phthalic acid esters concentration-dependently inhibited the formation of both cyclo-oxygenase and lipoxygenase arachidonate products by rat peritoneal leucocytes. Phthalates are extracted by human transfusion blood stored in pvc bags, and might similarly affect the blood cells when administered to patients.     

Finding cholinesterase in endotheliocytes: cholinesterase inhibition by organophosphorus compounds leads to endotheliocyte deformation

Toxic action of some organophosphorus cholinesterase inhibitors (including phosphacol) on the state of microvessels was studied in rats. Cholinesterase was found in endotheliocytes and it was established that phosphacol inhibited this enzyme. This was one of the factors responsible for deformation of the luminal relief of the vessels and for violation of the blood microcirculation. The expression of these effects was different for various organophosphorus compounds.     

Inhibitory effect of various organophosphorus esters on rat liver malathion carboxylesterase in vitro: role of mixed-function oxidases

6 Structurally related trialkyl phosphorothioates were assessed for their inhibitory effects on rat liver malathion carboxylesterase in vitro. IC50 values indicate that all these compounds, except compound III, a phosphorodithioate, inhibited the activity of the enzyme progressively with increasing incubation time of the compounds with the enzyme preparation. Compounds with an ethyl substitution were more potent than the corresponding methyl-substituted inhibitors. There was cytochrome P-450-mediated oxidative deactivation of all compounds tested, this was especially profound with inhibitors containing an ethyl thiolate moiety.     

Hydrolysis by plasma cholinesterase of complex adamantyl-containing esters

The kinetics of cholinesterase enzymatic hydrolysis of carboxylic acid adamantyl derivatives was studied in vitro. The maximal rate of enzymatic hydrolysis in the series of bis-esters was shown to increase on elongation of the distance between ester groups. The maximal hydrolysis rate in the series of bis- and mono-esters decreases on elongation of the distance between ester group and quaternary nitrogen atom. The addition of adamantyl radical to the alcohol part of the molecule of bis- and mono-esters prevents the hydrolysis. The addition of lipophilic radicals to the cationic group of derivatives of mono- and dicarboxylic acids exerts a greater effect on the maximal hydrolysis rate in monoesters than in bis-esters.     

Esterase metabolism of cholinesterase inhibitors using rat liver in vitro

A variety of chemicals, such as organophosphate (OP) and carbamate pesticides, nerve agents, and industrial chemicals, inhibit acetylcholinesterase (AChE) leading to overstimulation of the cholinergic nervous system. The resultant neurotoxicity is similar across mammalian species; however, the relative potencies of the chemicals across and within species depend in part on chemical-specific metabolic and detoxification processes. Carboxylesterases and A-esterases (paraoxonases, PON) are two enzymatic detoxification pathways that have been widely studied. We used an in vitro system to measure esterase-dependent detoxification of 15 AChE inhibitors. The target enzyme AChE served as a bioassay of inhibitor concentration following incubation with detoxifying tissue. Concentration-inhibition curves were determined for the inhibitor in the presence of buffer (no liver), rat liver plus calcium (to stimulate PONs and thereby measure both PON and carboxylesterase), and rat liver plus EGTA (to inhibit calcium-dependent PONs, measuring carboxylesterase activity). Point estimates (concentrations calculated to produce 20, 50, and 80% inhibition) were compared across conditions and served as a measure of esterase-mediated detoxification. Results with well-known inhibitors (chlorpyrifos oxon, paraoxon, methyl paraoxon, malaoxon) were in agreement with the literature, serving to support the use of this assay. Only a few other inhibitors showed slight or a trend towards detoxification via carboxylesterases or PONs (mevinphos, aldicarb, oxamyl). There was no apparent PON- or carboxylesterase-mediated detoxification of the remaining inhibitors (carbofuran, chlorfenvinphos, dicrotophos, fenamiphos, methamidophos, methomyl, monocrotophos, phosphamidon), suggesting that the influence of esterases on these chemicals is minimal. Thus, generalizations regarding these metabolic pathways may not be appropriate. As with other aspects of AChE inhibitors, their metabolic patterns appear to be chemical-specific.     

Development of a model cell culture system in which to study early effects of neuropathy-inducing organophosphorus esters.

Certain organophosphorus (OP) compounds produce a delayed neuropathy in man and susceptible animal species after early inhibition and aging of the enzyme, neurotoxic esterase (NTE). In this study, the human neuroblastoma cell line, SY-5Y, was used to examine the time course of inhibition and aging of NTE after toxicant treatment. The time course and extent of detrimental effects on this enzyme were similar in the SY-5Y cells to those observed in homogenized chicken brain tissue after the same treatments. The results indicate that the SY-5Y model system shows promise for use in the determination of initial mechanisms contributing to the development of organophosphorus-induced delayed neuropathy.     

Delayed neuropathy in adult Peking ducks induced by some organophosphorus esters

Trio-o-cresyl phosphate (TOCP), leptophos [O-methyl O-(4-bromo-2,5,-dichlorophenyl) phenylphosphonothioate] and cyanofenphos [O-ethyl O-(4-cyanophenyl) phenyl-phosphonothioate] were used to determine whether adult peking ducks would exhibit neurotoxicity after exposure to such chemicals. Clinical, histopathological, and specific biochemical tests were used to detect the neurologic dysfunctions that were induced by these neurotoxic agents. Ducks were orally treated with TOCP or leptophos at 100 or 10 mg/kg X d for 30 d, respectively. Another group of ducks received cyanofenphos at 4 mg/kg X d for 10 d. All the TOCP- and leptophos-treated ducks developed clinical signs of delayed neuropathy, as manifested by ataxia and paralysis. Two of the cyanofenphos-treated ducks died from cholinergic effect during the course of dosing. Surviving ducks of this group completely recovered from the cholinergic effect 2 or 3 d after finishing the dosing regimen. However, they developed signs of delayed neurotoxicity 10-17 d later. Surviving ducks of all groups were sacrificed for biochemical and/or histopathologic tests 1 d after the last treatment or when they became paralyzed. Histopathologic examinations indicated that degenerative lesions of axons consistent with the type occurring in delayed neurotoxicity were seen in all TOCP-, leptophos-, or cyanofenphos-treated ducks and were specially evident in sections of spinal cord. Biochemically, it was found that duck brain neurotoxic esterase (NTE) activity was inhibited in vivo to less than 15% of control levels as measured 24 h after the last treatment with TOCP, leptophos, or cyanofenphos. These results indicate that adult peking ducks could be used to screen organophosphorus compounds for delayed toxic neuropathy.     

Degradation of organophosphorus neurotoxicity in SY5Y neuroblastoma cells by organophosphorus hydrolase (OPH)

Numerous approaches have been studied to degrade organophosphorus (OP) compounds and ameliorate their toxicity. In the current study, the potential of genetically engineered organophosphorus hydrolase (OPH) enzymes to functionally biotransform OP neurotoxicants was examined by assessing effects of OPH-hydrolyzed OPs on acute and delayed indicators of neurotoxicity. SY5Y human neuroblastoma cells were used as a model test system, as these cells respond distinctly to mipafox, which produces OP-induced delayed neuropathy, and paraoxon, which does not. Short-term effects of four OPH-treated OPs on acetylcholinesterase (AChE) and neuropathy target esterase (NTE) activities were measured in retinoic acid-differentiated or undifferentiated cells, and delayed effects of OPH-treated paraoxon or mipafox on levels of neuronal cytoskeletal proteins in nerve growth factor (NGF)-differentiated cells. The anti-AChE activity of paraoxon (maximum 3 muM) and anti-NTE activity of mipafox (250 muM) in SY5Y cells were prevented by biodegradation with OPH. Anti-AChE activities of mipafox, methyl parathion, and demeton-S were partially ameliorated, depending on OP concentration. Intracellular amounts of the 200-kD neurofilament protein NF200 were unchanged after treatment with OPH-treated or buffer-treated paraoxon, as expected, as this endpoint is insensitive to paraoxon. However, NF200 levels rose in cells treated during late differentiation with OPH-treated mipafox. This finding suggests the existence of a threshold concentration of mipafox below which SY5Y cells can maintain their viability for compensating cellular damage due to mipafox in neurite elongation. These results indicate that OPH may be used to biodegrade OPs and remediate their neurotoxic effects in vitro and that AChE and NTE are suitable detectors for OPH amelioration.     

In vitro and in vivo studies of the ability of tetraethyl lead to inhibit cholinesterase activity

In vitro experiments show that tetraethyl lead does not affect cholinesterase activity. Transient biologically insignificant depression of plasma cholinesterase was observed in rhesus monkeys after intravenous administration of 12 mg tetraethyl lead/kg body weight. Doses greater than 19 mg/kg given intravenously were rapidly fatal, with signs of gastrointestinal disturbance, nervousness and incoordination. However, depression of circulating and brain cholinesterase could not be correlated with the onset of symptoms and death. These results do not support the use of 2-pyridine-aldoxime as an antidote for tetraethyl lead poisoning.     

Effects of cholinesterase inhibitors on the spasmogenic action of acetate esters on rat uterus

Acetate esters, such as phenyl acetate and aspirin, induced atropine-sensitive contractions of isolated uterus only when choline was present. These contractions were selectively and reversibly inhibited by carbamate-type cholinesterase inhibitors, such as neostigmine and eserine, and quaternary ammonium compounds, such as tetraethylammonium and decamethonium. After treatment with organophosphorus cholinesterase inhibitors, such as di-isopropyl fluorophosphate and tetraethyl pyrophosphate, the uterus failed to respond to the acetate esters, even when high concentrations of choline were present. The inhibition of the response of the uterus by organophosphates was effectively removed by pyridine-2-aldoxime methiodide. Pretreatment of the uterus with neostigmine or simultaneous addition of high concentrations of quaternary ammonium compounds prevented the inhibition by organophosphates. The inhibition produced by neostigmine was also reduced by simultaneous addition of quaternary ammonium compounds. These findings suggest that some esterase having an anionic site and an esteratic site, probably cholinesterase, may mediate in the uterine contractions induced by acetate esters in the presence of choline, and that inhibition by organophosphates, carbamates and quaternary ammonium compounds of cholinesterase activity in the preparation may impede the initiation of contractions by the acetate esters in the presence of choline.     

Effects of azamethiphos, an organophosphorus insecticide, on serum cholinesterase activity and isoenzymes in the rat.

The inhibitory effect of azamethiphos (Az), an organophosphorus insecticide, was detected in both the serum cholinesterase (ChE) activity and the ChE isoenzyme concentration in male Wistar rats. In our highest Az dosage group (270 mg/kg), following a single po administration, the serum ChE activity was significantly inhibited at 6 and 24 h post-Az administration. Five days after Az treatment, the ChE activity was still inhibited, but the observed difference was not statistically significant. The ChE activity increased to levels comparable to the control group by day 10. For the other Az-dosed groups, the ChE activities were inhibited only 6 h following administration. The serum ChE isoenzymes for all Az-dosed and control groups had 6 bands, indicating that Az did not effect the number of isoenzyme bands, indicating that Az did not effect the number of isoenzyme bands. However, Az had a significant effect on the ratios of the concentrations of these isoenzyme bands. The ratio of the main ChE isoenzyme bands (bands 5 and 6) was band 6 greater than band 5 for the young control group. As our control group aged, this ratio was reversed, with band 5 greater than band 6. For the highest Az dosage group (270 mg/kg), the ChE isoenzyme band ratio was band 5 greater than band 6 6 h after Az dosing. This proportion of band 6 decreased in parallel with an increase in band 5 during our 30-d experimental period. A correlation between the total ChE activity and ChE isoenzyme band 6 was found.     

Inhibition of cholinesterase and acetylcholinesterase in vitro by butyrophenone neuroleptics

The inhibitory effect of six butyrophenone neuroleptics: haloperidol, triperidol, moperone, floropipamide, benperidol and droperidol on the activity of partially purified aspecific horse serum ChE and on purified Electrophorus electricus specific AChE was studied with AThCh as substrate using Ellman's spectrophotometric method.All butyrophenones were found to be inhibitors of ChE, the K_i being in the range 10^?5 M and all followed a fully competitive type of inhibition. There were small differences in K_i-values among various butyrophenones, while there were great differences in K_i-values between the butyrophenones, the two phenothiazines and imipramine, the last three drugs being far more potent competitive ChE inhibitors (K_i 10^?6–10^?7 M) than the butyrophenones.All the butyrophenones were also found to inhibit AChE, the overall inhibitor constants being in the range 10^?4 to 10^?5 M and all showed a mixed type of inhibition. The most potent of the butyrophenones are droperidol and benperidol, the benzimidazolone derivatives. There are no great differences in the K_i-values for the butyrophenones, the two phenothiazines and imipramine for inhibition of AChE.