Phytochemical analysis of Viburnum davidii Franch. and cholinesterase inhibitory activity of its dihydrochalcones.

One flavonoid (quercetin, 1) and three dihydrochalcones (6''-O-p-hydroxybenzoyl-davidioside, 2, 4'-O-methyl-davidioside, 3, and davidioside, 4) were isolated from the leaves and young branches of Viburnum davidii Franch. All the structures were identified by comparison of their spectroscopic data (NMR and MS) with those present in literature. In addition, compounds 2-4 were evaluated for their cholinesterase inhibitory (ChEI) activity, for the first time. Accordingly, compounds 2 and 4 showed significant inhibition of both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with IC50 values equal to 36.883 and 39.274 µM, respectively for the former and 39.504 and 43.101 µM, respectively for the latter.

Effects of maternal chlorpyrifos diet on social investigation and brain neuroendocrine markers in the offspring - a mouse study.

BACKGROUND: Chlorpyrifos (CPF) is one of the most widely used organophosphate pesticides worldwide. Epidemiological studies on pregnant women and their children suggest a link between in utero CPF exposure and delay in psychomotor and cognitive maturation. A large number of studies in animal models have shown adverse effects of CPF on developing brain and more recently on endocrine targets. Our aim was to determine if developmental exposure to CPF affects social responsiveness and associated molecular neuroendocrine markers at adulthood. METHOD: Pregnant CD1 outbred mice were fed from gestational day 15 to lactation day 14 with either a CPF-added (equivalent to 6 mg/kg/bw/day during pregnancy) or a standard diet. We then assessed in the offspring the long-term effects of CPF exposure on locomotion, social recognition performances and gene expression levels of selected neurondocrine markers in amygdala and hypothalamus. RESULTS: No sign of CPF systemic toxicity was detected. CPF induced behavioral alterations in adult offspring of both sexes: CPF-exposed males displayed enhanced investigative response to unfamiliar social stimuli, whereas CPF-exposed females showed a delayed onset of social investigation and lack of reaction to social novelty. In parallel, molecular effects of CPF were sex dimorphic: in males CPF increased expression of estrogen receptor beta in hypothalamus and decreased oxytocin expression in amygdala; CPF increased vasopressin 1a receptor expression in amygdala in both sexes. CONCLUSIONS: These data indicate that developmental CPF affects mouse social behavior and interferes with development of sex-dimorphic neuroendocrine pathways with potential disruptive effects on neuroendocrine axes homeostasis. The route of exposure selected in our study corresponds to relevant human exposure scenarios, our data thus supports the view that neuroendocrine effects, especially in susceptible time windows, should deserve more attention in risk assessment of OP insecticides.

New cholinesterase inhibiting bisbenzylisoquinoline alkaloids from Abuta grandifolia.

The phytochemical study of the stem bark and wood of Abuta grandifolia (Mart.) Sandwith led to the identification of four bisbenzylisoquinoline alkaloids (BBIQs), namely (R,S)-2 N-norberbamunine (1), (R,R)-isochondodendrine (2), (S-S)-O4″-methyl, Nb-nor-O6'-demethyl-(+)-curine (3), and (S-S)-O4″-methyl, O6'-demethyl-(+)-curine (4), together with the aporphine alkaloid R-nornuciferine (5), all obtained by countercurrent distribution separation (CCD) and identified on the basis of their spectroscopic data. Alkaloids 3 and 4 were new. All the isolated compounds were tested for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities. 1 was the most active against AChE, whereas 3 and 4 were the most potent against BChE. Interestingly, all tested alkaloids are more potent against BChE than against AChE. This selectivity of cholinesterase (ChE) inhibition could be important in order to speculate on their potential therapeutic relevance.

Cholinesterase inhibition and alterations of hepatic metabolism by oral acute and repeated chlorpyrifos administration to mice.

Chlorpyrifos (CPF) is a broad spectrum organophosphorus insecticide bioactivated in vivo to chlorpyrifos-oxon (CPFO), a very potent anticholinesterase. A great majority of available animal studies on CPF and CPFO toxicity are performed in rats. The use of mice in developmental neurobehavioural studies and the availability of transgenic mice warrant a better characterization of CPF-induced toxicity in this species. CD1 mice were exposed to a broad range of acute (12.5-100.0mg/kg) and subacute (1.56-25mg/kg/day from 5 to 30 days) CPF oral doses. Functional and biochemical parameters such as brain and serum cholinesterase (ChE) and liver xenobiotic metabolizing system, including the biotransformation of CPF itself, have been studied and the no observed effect levels (NOELs) identified. Mice seem to be more susceptible than rats at least to acute CPF treatment (oral LD(50) 4.5-fold lower). The species-related differences were not so evident after repeated exposures. In mice a good correlation was observed between brain ChE inhibition and classical cholinergic signs of toxicity. After CPF-repeated treatment, mice seemed to develop some tolerance to CPF-induced effects, which could not be attributed to an alteration of P450-mediated CPF hepatic metabolism. CPF-induced effects on hepatic microsomal carboxylesterase (CE) activity and reduced glutathione (GSH) levels observed at an early stage of treatment and then recovered after 30 days, suggest that the detoxifying mechanisms are actively involved in the protection of CPF-induced effects and possibly in the induction of tolerance in long term exposure. The mouse could be considered a suitable experimental model for future studies on the toxic action of organophosphorus pesticides focused on mechanisms, long term and age-related effects.

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.

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.

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.

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.

Kinetic parameters of OPT pesticide desulfuration by c-DNA expressed human CYPs.

The role of different cytochrome P450 isoforms (CYPs) in the desulfuration of four organophosphorothionate pesticides (OPTs), namely diazinon (DIA), azinphos-methyl (AZ), chlorpyrifos (CPF) and parathion (PARA), at OPT levels representative of actual human exposure has been investigated. For this purpose c-DNA expressed human CYPs and a method, based on acetylcholinesterase (AChE) inhibition, able to detect nM levels of oxon have been used. Our results indicate that the four tested OPTs at low concentration were mainly desulfurated by CYP2B6, 2C19 and 1A2, showing K(m) values in the range 0.8-5 µM and the highest efficiency (intrinsic clearance (ICL)) values. CYP3A4 was generally endowed with high K(m) and resulted linear up to 25-100 µM OPT, concentrations saturating the most efficient CYPs. The tentative extrapolation of the relative contribution of single CYPs, taking into account the average content of different isoforms in the human liver, indicate that CYP1A2 is the major responsible for oxon formation. Indeed this CYP catalyses the 50-90% of desulfuration reaction, depending on the OPT. As CYP3A4 activity is not completely saturated up to 100 µM OPT, and due to the high hepatic content, its contribution to oxon formation may result relevant in poisoning episodes, when individuals are exposed at high doses of OPTs.