A simple and high-throughput screening method for the analysis of 136 pesticides in avocado ( Persea americana ) by LC-(+)-ESI-MS/MS and GC-MS/MS is presented. A modified QuEChERS sample preparation method was developed to improve the extraction recovery of highly lipophilic pesticides. Extracts from minced avocados after acetonitrile (MeCN) extraction were directly injected to LC-MS/MS, whereas other GC-amenable compounds were treated with the modified QuEChERS procedure for GC-MS/MS analysis. The average recoveries for 79 pesticides quantified by LC-MS/MS at 10, 50, and 200 ng/g fortifying levels were 86.1% or better (with maximum RSD at 9.2%), whereas GC-MS/MS analysis demonstrated 70.2% or better (RSD < 18%) for average recovery from 57 compounds at the same spike levels. The application of LC- and GC-MS/MS combined with the improved extraction procedures led to the current method, which can quantitate these pesticides even if they are present in avocados below the targeted action level by FDA. This method demonstrated the improved recovery of several challenging lipophilic pesticides in highly fat-rich avocados.
The routine use of tobacco products may modify key metabolizing systems, which will further impact the metabolism of environmental contaminants. The objective of this study was to quantify the effect of repeated in vivo exposures to nicotine, a major pharmacologically active component of cigarette smoke, on in vitro metabolism of chlorpyrifos (CPF). CPF is an organophosphorus (OP) insecticide that is metabolized by cytochrome P-450 (CYP450) to its major metabolites, chlorpyrifos-oxon (CPF-oxon) and 3,5,6-trichloro-2-pyridinol (TCP). Male Sprague-Dawley rats were dosed subcutaneously with 1 mg nicotine/kg for 1, 7, or 10 d. Rats were sacrificed 4 or 24 h after the last nicotine treatment, and liver microsomes were prepared. The microsomes were incubated with varying concentrations of CPF and the production of the metabolites CPF-oxon and TCP were measured. The metabolism of CPF to the active oxon metabolite did not show significant changes following repeated nicotine treatments, evidenced by the unchanged pseudo first-order clearance rate of V(max)/K(mapp). The V(max) describing the metabolism of CPF to the inactive metabolite, TCP was increased in 24-h postdosing groups, after both single and repeated treatments of nicotine. In contrast, the metabolism to TCP was unchanged in groups evaluated at 4 h (single or repeated) post nicotine dosing. Some basic marker substrate activities were also investigated to ensure that nicotine exerted effects on CYP450 activities. Total P450 reduced spectra were not altered by nicotine treatment, but marker substrate activities for CYP1A and CYP2E1 were increased at 24 h after the single treatment, and marker substrate activity for CYP2B was decreased 4 h after 7 d of treatment. Results of this in vitro study suggest that repeated nicotine exposure may result in altered metabolism of CPF. Future in vivo experiments based on these results need to be conducted to ascertain the impact of in vivo nicotine exposures on CPF metabolism in rats.
[reaction: see text] L-2'-Fluoro-4'-thio-2',3'-unsaturated cytidine 11 was synthesized from (R)-2-fluorobutenolide 2, which was prepared from 2,3-O-isopropylidene-L-glyceraldehyde 1. The synthesized compound 11 shows potent antiviral activity against HIV-1.
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