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Annarita Meneguz

Publications and source records attributed to Annarita Meneguz.

10 recordsLinked to original sources
PubMed2005

Organophosphorothionate pesticides inhibit the bioactivation of imipramine by human hepatic cytochrome P450s.

The drug-toxicant interaction between the antidepressant imipramine (IMI) and three organophosphorothionate pesticides (OPTs), to which humans may be chronically and simultaneously exposed, has been investigated in vitro. Concentrations of IMI (2-400 microM) and OPTs (< or =10 microM) representative of actual human exposure have been tested with recombinant human CYPs and human liver microsomes (HLM). The different CYPs involved in IMI demethylation to the pharmacologically active metabolite desipramine (DES) were CYP2C19 > CYP1A2 > CYP3A4. The OPTs significantly inhibited (up to >80%) IMI bioactivation catalyzed by the recombinant CYPs tested, except CYP2D6, and by HLM; the inhibition was dose-dependent and started at low pesticide concentrations (0.25-2.5 microM). The OPTs, having lower K(m) values, efficiently competed with IMI for the enzyme active site, as in the case of CYP2C19. However, with CYP1A2 and CYP3A4, a time- and NADPH-dependent mechanism-based inactivation also occurred, consistently with irreversible inhibition due to the release of the sulfur atom, binding to the active CYP during OPT desulfuration. At low IMI and OPT concentrations, lower IC50 values have been obtained with recombinant CYP1A2 (0.7-1.1 microM) or with HLM rich in 1A2-related activity (2-10.8 microM). The K(i) values (2-14 microM), independent on substrate concentrations, were quite low and similar for the three pesticides. Exposure to OPTs during IMI therapeutic treatments may lead to decreased DES formation, resulting in high plasma levels of the parent drug, eventual impairment of its pharmacological action and possible onset of adverse drug reactions (ADRs).

Biotransformation↗
PubMed2005

In vitro inhibitory effect of aflatoxin B1 on acetylcholinesterase activity in mouse brain.

Growing concern on the problem of mycotoxins in the alimentary chain underlines the need to investigate the mechanisms explaining the cholinergic effects of aflatoxin B(1) (AFB(1)). We examined the effect of AFB(1), a mycotoxin produced by Aspergillus flavus, on mouse brain acetylcholinesterase (AChE) and specifically on its molecular isoforms (G(1) and G(4)) after in vitro exposure. AFB(1) (from 10(-9) to 10(-4)M), inhibited mouse brain AChE activity (IC(50) = 31.6 x 10(-6)M) and its G(1) and G(4) molecular isoforms in a dose-dependent manner. Michaelis-Menten parameters indicate that the K(m) value increased from 55.2 to 232.2% whereas V(max) decreased by 46.2-75.1%. The direct, the Lineweaver-Burk and the secondary plots indicated a non-competitive-mixed type antagonism, induced when the inhibitor binds to the free enzyme and to the enzyme-substrate complex. AFB(1)-inhibited AChE was partially reactivated by pyridine 2-aldoxime (2-PAM) (10(-4)M) but the AChE-inhibiting time courses of AFB(1) (10(-4)M) and diisopropylfluorophosphate (DFP) (2 x 10(-7)M) differed. Overall these data suggest that AFB(1) non-competitively inhibits mouse brain AChE by blocking access of the substrate to the active site or by inducing a defective conformational change in the enzyme through non-covalent binding interacting with the AChE peripheral binding site, or through both mechanisms.

Acetylcholinesterase↗
PubMed2005

Acute toxicity.

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Animal Testing Alternatives↗
PubMed2004

Malathion bioactivation in the human liver: the contribution of different cytochrome p450 isoforms.

Among organophosphorothioate (OPT) pesticides, malathion is considered relatively safe for use in mammals. Its rapid degradation by carboxylesterases competes with the cytochrome P450 (P450)-catalyzed formation of malaoxon, the toxic metabolite. However, impurities in commercial formulations are potent inhibitors of carboxylesterase, allowing a dramatic increase in malaoxon formation. Malathion desulfuration has been characterized in human liver microsomes (HLMs) with a method based on acetylcholinesterase inhibition that is able to detect nanomolar levels of oxon. The active P450 isoforms have been identified by means of a multifaceted strategy, including the use of cDNA-expressed human P450s and correlation, immunoinhibition, and chemical inhibition studies in a panel of phenotyped HLMs. HLMs catalyzed malaoxon formation with a high level of variability (>200-fold). One or two components (K(mapp1) = 53-67 microM; K(mapp2) = 427-1721 microM) were evidenced, depending on the relative specific P450 content. Results from different approaches indicated that, at low malathion concentration, malaoxon formation is catalyzed by CYP1A2 and, to a lesser extent, 2B6, whereas the role of 3A4 is relevant only at high malathion levels. These results are in line with those found with chlorpyrifos, diazinon, azynphos-methyl, and parathion, characterized by the presence of an aromatic ring in the molecule. Since malathion has linear chains as substituents at the thioether sulfur, it can be hypothesized that, independently from the chemical structure, OPTs are bioactivated by the same P450s. These results also suggest that CYP1A2 and 2B6 can be considered as possible metabolic biomarkers of susceptibility to OPT-induced toxic effects at actual human exposure levels.

Animals↗
PubMed2003

Developmental exposure to chlorpyrifos alters reactivity to environmental and social cues in adolescent mice.

Neonatal mice were treated daily on postnatal days (pnds) 1 through 4 or 11 through 14 with the organophosphate pesticide chlorpyrifos (CPF), at doses (1 or 3 mg/kg) that do not evoke systemic toxicity. Brain acetylcholinesterase (AChE) activity was evaluated within 24 h from termination of treatments. Pups treated on pnds 1-4 underwent ultrasonic vocalization tests (pnds 5, 8, and 11) and a homing test (orientation to home nest material, pnd 10). Pups in both treatment schedules were then assessed for locomotor activity (pnd 25), novelty-seeking response (pnd 35), social interactions with an unfamiliar conspecific (pnd 45), and passive avoidance learning (pnd 60). AChE activity was reduced by 25% after CPF 1-4 but not after CPF 11-14 treatment. CPF selectively affected only the G(4) (tetramer) molecular isoform of AChE. Behavioral analysis showed that early CPF treatment failed to affect neonatal behaviors. Locomotor activity on pnd 25 was increased in 11-14 CPF-treated mice at both doses, and CPF-treated animals in both treatment schedules were more active when exposed to environmental novelty in the novelty-seeking test. All CPF-treated mice displayed more agonistic responses, and such effect was more marked in male mice exposed to the low CPF dose on pnds 11-14. Passive avoidance learning was not affected by CPF. These data indicate that developmental exposure to CPF induces long-term behavioral alterations in the mouse species and support the involvement of neural systems in addition to the cholinergic system in the delayed behavioral toxicity of CPF.

Acetylcholinesterase↗
PubMed2003

CYP-specific bioactivation of four organophosphorothioate pesticides by human liver microsomes.

The bioactivation of azinphos-methyl (AZIN), chlorpyrifos (CPF), diazinon (DIA), and parathion (PAR), four widely used organophosphorothioate (OPT) pesticides has been investigated in human liver microsomes (HLM). In addition, the role of human cytochrome P450 (CYPs) in OPT desulfuration at pesticide levels representative of human exposure have been defined by means of correlation and immunoinhibition studies. CYP-mediated oxon formation from the four OPTs is efficiently catalyzed by HLM, although showing a high variability (>40-fold) among samples. Two distinct phases were involved in the desulfuration of AZIN, DIA, and PAR, characterized by different affinity constants (K(mapp1) = 0.13-9 microM and K(mapp2) = 5- 269 microM). Within the range of CPF concentrations tested, only the high-affinity component was evidenced (K(mapp1) = 0.27-0.94 microM). Oxon formation in phenotyped individual HLM showed a significant correlation with CYP1A2-, 3A4-, and 2B6-related activities, at different levels depending on the OPT concentration. Anti-human CYP1A2, 2B6, and 3A4 antibodies significantly inhibited oxon formation, showing the same OPT concentration dependence. Our data indicated that CYP1A2 is mainly involved in OPT desulfuration at low pesticide concentrations, while the role of CYP3A4 is more significant to the low-affinity component of OPT bioactivation. The contribution of CYP2B6 to total hepatic oxon formation was relevant in a wide range of pesticide concentrations, being a very efficient catalyst of both the high- and low-affinity phase. These results suggest CYP1A2 and 2B6 as possible metabolic biomarkers of susceptibility to OPT toxic effect at the actual human exposure levels.

Acetylcholinesterase↗
PubMed2002

Synthesis and cholinesterase activity of phenylcarbamates related to Rivastigmine, a therapeutic agent for Alzheimer's disease.

In order to develop new cholinesterase agents effective against Alzheimer's disease (AD) we synthesized some phenylcarbamates structurally related to Rivastigmine and evaluated their in vitro and in vivo biological activity. Among the compounds which displayed the most significant in vitro activity, 1-[1-(3-dimethylcarbamoyloxyphenyl)ethyl]piperidine (31b), in addition to a simple and cheaper synthesis, showed lower toxicity and very similar therapeutic index in comparison with Rivastigmine.

Acetylcholinesterase↗