Sorption of ochratoxin A from aqueous solutions using β-cyclodextrin-polyurethane polymer

The ability of a cyclodextrin-polyurethane polymer to remove ochratoxin A from aqueous solutions was examined by batch rebinding assays. The results from the aqueous binding studies were fit to two parameter models to gain insight into the interaction of ochratoxin A with the nanosponge material. The ochratoxin A sorption data fit well to the heterogeneous Freundlich isotherm model. The polymer was less effective at binding ochratoxin A in high pH buffer (9.5) under conditions where ochratoxin A exists predominantly in the dianionic state. Batch rebinding assays in red wine indicate the polymer is able to remove significant levels of ochratoxin A from spiked solutions between 1-10 μg·L(-1). These results suggest cyclodextrin nanosponge materials are suitable to reduce levels of ochratoxin A from spiked aqueous solutions and red wine samples.     

Impact of pH on the Stability and the Cross-Reactivity of Ochratoxin A and Citrinin

Mycotoxins are secondary metabolites produced by several fungi contaminating crops. In several countries, the maximum permitted levels of mycotoxins are found in foodstuffs and feedstuffs. The common strategy of mycotoxin analysis involves extraction, clean-up and quantification by chromatography. In this paper, we analyzed the reasons of underestimation of ochratoxin A (OTA) content in wine, and overestimation of OTA in wheat, depending on the pH of the clean-up step and the simultaneous presence of citrinin (CIT). We demonstrated that the increase of pH by adding polyethylene glycol (PEG) to wine led to an underestimation of OTA by conversion of OTA into open ring ochratoxin A OP-OA. In comparing three methods of extraction and clean-up for the determination of OTA and CIT in wheat—(i) an inter-laboratory validated method for OTA in cereals using immunoaffinity column clean-up (IAC) and extraction by acetonitrile/water; (ii) a validated method using IAC and extraction with 1% bicarbonate Na; and (iii) an in-house validated method based on acid liquid/liquid extraction—we observed an overestimation of OTA after immunoaffinity clean-up when CIT is also present in the sample, whereas an underestimation was observed when OTA was alone. Under neutral and alkaline conditions, CIT was partially recognized by OTA antibodies.     

分子印记搅拌棒的研究及应用

搅拌棒吸附萃取技术(SBSE)是从20世纪90年代逐渐发展起来的新型的样品预处理技术,基于固相萃取(SPE)原理,常与高效液相色谱、气相色谱等分析仪器相结合使用,建立的分析方法具有较高的灵敏度以及较好的重现性,应用十分广泛.分子印记技术(MIT)是一项发展迅速的分子识别新技术,制得的分子印记聚合物(MIPs)具有预定性、识别性和广泛的使用性,对模板分子空间结构的"记忆"效应和作用位点的"识别"作用,能够高选择性的分离富集复杂体系中的微量成分.将分子印记技术与搅拌棒吸附萃取技术相结合,弥补了SPE选择性有限的缺点,在复杂样品预处理领域得到了广泛应用.     

Molecularly imprinted polymers as drug delivery systems for the sustained release of glycyrrhizic acid

Objectives The aim was to synthesize molecularly imprinted polymers (MIPs) with high recognition properties towards glycyrrhizic acid and to evaluate the performance of these materials to act as base excipients in glycyrrhizic acid sustained release in gastrointestinal simulating fluids. Methods MIPs were synthesized using methacrylic acid (MAA) as acidic, 2‐(dimethylamino)ethyl methacrylate (DMAEMA) as basic, and 2‐hydroxyethylmethacrylate (HEMA) as neutral functional monomers, while ethylene glycol dimethacrylate (EGDMA) was chosen as a crosslinking agent. The imprinting effect was evaluated by binding experiments using glycyrrhizic acid and glycyrrhetic acid (analogue molecule) solutions and in‐vitro release studies were performed in gastrointestinal simulating fluids. Key findings Good recognition and selectivity properties were found in all the synthesized materials in both ethanol and ethanol–water mixture. The release from non‐imprinted polymers was indeed higher at acidic pH, while a slower release was observed in MIPs' case, because of the presence of imprinted cavities in the polymeric structure. The stronger capacity of MAA to interact by hydrogen bonds with the template makes MAA‐containing MIPs the most effective materials in both rebinding and release experiments. Conclusions The release tests confirm the applicability of imprinted polymer for glycyrrhizic acid sustained release in gastrointestinal simulating fluids.     

High performance liquid chromatography of mycotoxin metabolites in human urine

Because mycotoxins occur worldwide in grain and grain products, evaluating their effects on the health of the population has become important. The development of a high performance liquid chromatographic (HPLC) procedure was investigated for the analysis of aflatoxin B1, citrinin, and ochratoxin A, from hydrolyzed human urine. Solid-phase extraction (SPE) was used for sample clean-up and concentration. Reversed-phase liquid chromatography (RPLC) was used with fluorescence detection for sample analysis. The presence of aflatoxin B1 was confirmed by converting it to the hemiacetal. With 10 mL of urine, the detection limit for aflatoxin B1 and ochratoxin A was in the high parts per trillion (ppt) and that for citrinin was about 10 ppb.     

Screening for ochratoxin A in blood by flow injection analysis

A micromethod for ochratoxin A detection in human sera by flow injection technique is described. The method requires 50 microliter of sera, and it is designed to distinguish samples containing less than 10 ng ochratoxin A per ml. The method is based on fluorescence measurement following a simple extraction procedure for which very small amounts of chemicals are needed. Since the method is not confirmatory, all samples showing fluorescence above a certain intensity have to be reanalysed with some other method where a confirmation step in included. Because of the small amount of serum needed and the rapid procedure (less than 15 min), a large number of samples can be analysed very quickly. The method may therefore be applicable for large screening campaigns conducted to determine the presence of ochratoxin A in blood. This conclusion is based on 1675 samples and 147 standards analysed concurrently by the flow injection technique and an earlier published enzymic method. The method is also suitable for monitoring ochratoxin A levels in the blood of experimental animals.     

Optimization, evaluation, and characterization of molecularly imprinted polymers

The underlying mechanisms for molecular recognition exhibited by the imprinting effect can be attributed to two processes. The pre-organization of complementary functional groups in the polymer by the template and the formation of a shape-selective cavity that is complementary to the template. However, measurements of binding and selectivity combine all effects contributing to molecular recognition in MIPs into one figure of merit. If the two molecules being compared are not enantiomers, then there are other factors which contribute to differential binding such as size or different partitioning effects due to differences in polarity, hydrophobicity, ionization state or shape and/or conformational effects. The best probe for the imprinting effect is therefore an enantiomeric pair. Therefore, the first section of this article discusses enantioselective optimization of polymerization, the second section will review methods employed for evaluation of MIPs and the last section will cover materials science methods used to characterize the physical properties of MIP materials.     

Syntheses of 14C-Ochratoxin A and 14C-Ochratoxin B and a Comparative Study of their Distribution in Rats Using Whole Body Autoradiography

Abstract: Methods for preparation of labelled ochratoxin A and B are described. The method for preparation of labelled ochratoxin B involves the synthesis of the azide of ochratoxin β via the mixed anhydride and subsequent conjugation to labelled phenylalanine to yield ¹⁴C-ochratoxin B. The labelled ochratoxins were injected into male Wistar rats and after different survival times they were sacrificed and subjected to whole body autoradiography. The distribution pattern of ochratoxin A in the rat did not differ from that earlier registered for mouse. The previously known, high susceptibility of rats (and not mice) to ochratoxin A-induced cancer could thus not be explained by an accumulation of the toxin in specific cells or organs. The distribution patterns of ochratoxin A and B were almost congruent – the only apparent difference being a much longer retention of the labelled ochratoxin A in the blood compared to ochratoxin B, which was much faster excreted. When analyzing tissue extracts for labelled metabolites only the extracts from the rats injected with ochratoxin B were found to contain easily detectable concentrations, while no metabolites of ochratoxin A were seen.     

Synthesis of 14C-ochratoxin A and 14C-ochratoxin B and a comparative study of their distribution in rats using whole body autoradiography.

Methods for preparation of labelled ochratoxin A and B are described. The method for preparation of labelled ochratoxin B involves the synthesis of the azide of ochratoxin beta via the mixed anhydride and subsequent conjugation to labelled phenylalanine to yield 14C-ochratoxin B. The labelled ochratoxins were injected into male Wistar rats and after different survival times they were sacrificed and subjected to whole body autoradiography. The distribution pattern of ochratoxin A in the rat did not differ from that earlier registered for mouse. The previously known, high susceptibility of rats (and not mice) to ochratoxin A-induced cancer could thus not be explained by an accumulation of the toxin in specific cells or organs. The distribution patterns of ochratoxin A and B were almost congruent--the only apparent difference being a much longer retention of the labelled ochratoxin A in the blood compared to ochratoxin B, which was much faster excreted. When analyzing tissue extracts for labelled metabolites only the extracts from the rats injected with ochratoxin B were found to contain easily detectable concentrations, while no metabolites of ochratoxin A were seen.     

Levels of ochratoxin A in serum from urban and rural Portuguese populations and estimation of exposure degree.

Urban and rural population exposure to ochratoxin A (OTA) in central zone of Portugal was investigated in three places: Coimbra, Verride and Ereira. The analytical method proposed for the determination of ochratoxin A involved extraction with chloroform-orthophosphoric acid, cleanup through an immunoaffinity column (IAC), high performance liquid chromatography (HPLC) with spectrofluorimetric detection (FD) for separation and identification of ochratoxin A, and confirmation with HPLC-FD after OTA methylation in serum. The limit of quantification of the proposed method was 0.1 microg/L for serum and 0.05 microg/L for blood. OTA recoveries in serum ranged from 70.3% to 115.3% for levels at 0.25 microg/L and 0.5 microg/L, respectively, with a within-day RSD between 8.0% and 16.2%. Ochratoxin A serum levels were evaluated in an hundred and four donors from Coimbra city, Verride, and Ereira. The study revealed a frequency of detection of 100%. The ratio of ochratoxin A level in serum to whole blood was 2.0+/-0.7. The overall concentrations range from 0.25 to 2.49 microg/L, 0.14 to 1.91 microg/L, and 0.19 to 0.96 microg/L, for samples of Verride, Ereira, and Coimbra, respectively. The mean concentration and standard deviation were 0.78+/-0.53 microg/L, 0.44+/-0.31 microg/L, and 0.42+/-0.18 microg/L for the same samples. A significant difference was found in Verride population (P-value=0.000). Levels of OTA are clearly higher in males from rural areas than in females. For all samples, a significant difference was found in Verride male population (P-value=0.014).     

Saccharomyces Cerevisiae Cell Wall Components as Tools for Ochratoxin A Decontamination

The aim of this study was to evaluate the usefulness of Saccharomyces cerevisiae cell wall preparations in the adsorption of ochratoxin A (OTA). The study involved the use of a brewer’s yeast cell wall devoid of protein substances, glucans obtained by water and alkaline extraction, a glucan commercially available as a dietary supplement for animals and, additionally, dried brewer’s yeast for comparison. Fourier Transform Infrared (FTIR) analysis of the obtained preparations showed bands characteristic for glucans in the resulting spectra. The yeast cell wall preparation, water-extracted glucan and the commercial glucan bound the highest amount of ochratoxin A, above 55% of the initial concentration, and the alkaline-extracted glucan adsorbed the lowest amount of this toxin. It has been shown that adsorption is most effective at a close-to-neutral pH, while being considerably limited in alkaline conditions.     

Molecularly imprinted polymers in the drug discovery process

Since molecularly imprinted polymers (MIPs) are designed to have a memory for their molecular templates it is easy to draw parallels with the affinity between biological receptors and their substrates. Could MIPs take the place of natural receptors in the selection of potential drug molecules from synthetic compound libraries? To answer that question this review discusses the results of MIP studies which attempt to emulate natural receptors. In addition the possible use of MIPs to guide a compound library synthesis towards a desired biological activity is highlighted.     

Wavelength-Dependent Degradation of Ochratoxin and Citrinin by Light in Vitro and in Vivo and Its Implications on Penicillium

It has previously been shown that the biosynthesis of the mycotoxins ochratoxin A and B and of citrinin by Penicillium is regulated by light. However, not only the biosynthesis of these mycotoxins, but also the molecules themselves are strongly affected by light of certain wavelengths. The white light and blue light of 470 and 455 nm are especially able to degrade ochratoxin A, ochratoxin B and citrinin after exposure for a certain time. After the same treatment of the secondary metabolites with red (627 nm), yellow (590 nm) or green (530 nm) light or in the dark, almost no degradation occurred during that time indicating the blue light as the responsible part of the spectrum. The two derivatives of ochratoxin (A and B) are degraded to certain definitive degradation products which were characterized by HPLC-FLD-FTMS. The degradation products of ochratoxin A and B did no longer contain phenylalanine however were still chlorinated in the case of ochratoxin A. Citrinin is completely degraded by blue light. A fluorescent band was no longer visible after detection by TLC suggesting a higher sensitivity and apparently greater absorbance of energy by citrinin. The fact that especially blue light degrades the three secondary metabolites is apparently attributed to the absorption spectra of the metabolites which all have an optimum in the short wave length range. The absorption range of citrinin is, in particular, broader and includes the wave length of blue light. In wheat, which was contaminated with an ochratoxin A producing culture of Penicillium verrucosum and treated with blue light after a pre-incubation by the fungus, the concentration of the preformed ochratoxin A reduced by roughly 50% compared to the control and differed by > 90% compared to the sample incubated further in the dark. This indicates that the light degrading effect is also exerted in vivo, e.g., on food surfaces. The biological consequences of the light instability of the toxins are discussed.     

Pharmaceutical development of the novel arsenical based cancer therapeutic GSAO for Phase I clinical trial

The aim of the present study was to prepare nanoparticles of molecular imprinted polymers (MIPs) with high loading capacity for naltrexone as template drug. To achieve this goal, a computational protocol was employed to select the most appropriate monomer for MIP preparation. Density functional theory (DFT) method at the B3LYP level of theory in conjugate with the 6-31+G(d) basis set was used to evaluate the extent of interaction between naltrexone and a small library of frequently used vinylic monomers. The results revealed that acrylic acid (AA) and methacrylic acid (MAA) can be considered as suitable monomers. To select the best monomer, two MIPs with AA and MAA monomer were synthesized and their loading capacity, selectivity and release profile were evaluated. The experimental results showed that the MIPs synthesized using AA (MIP-AA) exhibited a surprisingly high loading capacity to naltrexone (75mg of drug/g of MIP) compared to MIP-MAA (34mg of drug/g of MIP). In vitro release dynamics of the drug from MIPs was also investigated and modeled. It was found that non-Fickian-type diffusion mechanism was responsible for drug release. The results can lead to the conclusion that MIPs designed by computational approach can be considered as promising candidates for drug delivery systems.     

How to find effective functional monomers for effective molecularly imprinted polymers?

Molecularly imprinted polymers (MIPs) are materials mimicking biological receptors in their specific recognition of analytes. Although molecular imprinting has been around for over 30 years, recently this technology has made rapid developments. However, recent investigations have led mainly to the synthesis of new polymers imprinted for a wider range of compounds without real and better understanding of the mechanisms occurring during the polymerisation and the recognition process. This review covers work developed in understanding these mechanisms and presents different strategies utilised in optimising MIP design.     

Ochratoxins in Wines: A Review of Their Occurrence in the Last Decade,Toxicity, and Exposure Risk in Humans

Ochratoxins (OTs) are mycotoxins frequently found in wines, and their contamination can occur during any stage of the winemaking process. Ochratoxin A (OTA) has been the most widely reported and the only one whose concentrations are legislated in this beverage. However, ochratoxin B, ochratoxin A methyl ester, ochratoxin B methyl ester, ochratoxin A ethyl ester, ochratoxin B ethyl ester, ochratoxin α, ochratoxin β, OTα methyl ester, OTA ethyl amide, and OTA glucose ester have also been reported in wines. Thus, detecting only OTA would lead to the underestimation of ochratoxin levels, which is a risk to human health. Considering the threat represented by the presence of ochratoxins in wines and the long-term health problems that they can cause in wine drinkers, this paper aims to review reports of the last 10 years regarding the presence of different ochratoxins in wines and how the winemaking process influences the degree of contamination, mainly by OTA. Additionally, toxicity from human exposure due to the consumption of contaminated wines is addressed.     

Direct enantioseparation of adrenergic drugs via thin-layer chromatography using molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) of (-)-pseudoephedrine and (-)-norephedrine were prepared to use as chiral stationary phases (CSPs) in thin layer chromatography (TLC). The resolution of the enantiomers of adrenergic drugs, including pseudoephedrine, ephedrine, norephedrine, and epinephrine were investigated on these CSPs. In preparation of MIPs, two monomers: (1) methacrylic acid and (2) itaconic acid were employed as functional monomers. Mobile phase system of either methanol or acetonitrile was used and the effects of acetic acid content of the mobile phases were also investigated. The best resolution was achieved for enantioseparation of norephedrine on plates based on MIP of (-)-norephedrine using itaconic acid as functional monomer (alpha = 5.1) in mobile phase 1% acetic acid in methanol. Moreover, these MIPs were able to resolve the racemates of compounds whose structures corresponded to print molecule. The results obtained showed that TLC based on MIPs could succeed the direct separation of enantiomers of adrenergic drugs as a method of separation. The method offers a rapid, sensitive and reliable method for quality control of optically active compounds.     

甲基莲心碱分子印迹聚合物的制备

目的研究甲基莲心碱分子印迹聚合物的制备。方法采用均匀设计,以甲基莲心碱为模板分子,a-甲基丙烯酸（-αMAA）为功能单体,乙二醇二甲基丙烯酸酯（EDMA）为交联剂,偶氮二异丁腈（AIBN）为引发剂,通过热引发聚合,优化甲基莲心碱分子印迹聚合物的制备条件,并通过固相萃取法检验该聚合物对甲基莲心碱的吸附性能。结果当甲基莲心碱用量为0.1 mmol时,最优制备条件为a-甲基丙烯酸和乙二醇二甲基丙烯酸酯用量分别为0.8 mmol和2.5 mmol,反应温度为50℃。结论用该工艺制备的分子印迹聚合物对甲基莲心碱具有较好的选择性和吸附性。     

Renal enzyme activities in experimental ochratoxin A-induced porcine nephropathy: diagnostic potential of phosphoenolpyruvate carboxykinase and gamma-glutamyl transpeptidase activity

Enzyme activities have been measured in needle biopsies from kidneys of pigs fed 1 ppm or 0.2 ppm of ochratoxin A for 1-5 wks. After feeding 1 ppm toxin for 1 wk, the activity of cytosolic phosphoenolpyruvate carboxykinase (PEPCK) was decreased by 40% and remained inhibited until the termination of the experiment (5 wk). The activity of gamma-glutamyl transpeptidase, a brush-border enzyme found in the proximal tubules, was reduced to a similar degree and remained inhibited. The activities of hexokinase, a cytosolic enzyme of general distribution in the nephron, and phosphate-dependent glutaminase, a distal tubule enzyme, were not affected. The biopsy results were confirmed by measurements in renal slices taken at the termination of the experiment, except that biopsy samples showed more variation in enzyme activity and a lower PEPCK activity. A guinea pig antibody against the cytosolic form of PEPCK was used to demonstrate that the mitochondrial form of the enzyme, which accounts for a considerable part of the total cellular activity, was not affected by ochratoxin A. When mitochondrial PEPCK activity present in the cytosolic fraction was accounted for, ochratoxin A was found to reduce PEPCK activity by 70-80%. The increase of ochratoxin A exposure from zero through 0.2 ppm to 1 ppm, which resulted in dose-dependent activity decrease of PEPCK and gamma-glutamyl transpeptidase, was accompanied by dose-dependent decrease of renal function, as measured by a reduction of maximal tubular excretion of para-aminohippurate per clearance of inulin (TmPAH/CIn) and an increase in glucose excretion. This suggest that these enzymes are sensitive indicators of ochratoxin A-induced porcine nephropathy. Assuming that porcine nephropathy represents a valid model of endemic (Balkan) nephropathy in humans, the measurement of cytosolic PEPCK and gamma-glutamyl transpeptidase activity in the kidney could be a sensitive test for ochratoxin A-induced disease in humans.     

Perturbation of liver microsomal calcium homeostasis by ochratoxin A

The effect of ochratoxin A on hepatic microsomal calcium sequestration was studied both in vivo and in vitro. The rate of ATP-dependent calcium uptake was inhibited by 42-45% in ochratoxin A intoxicated rats as compared to controls. In the presence of NADPH, addition of ochratoxin A (2.5 to 100 microM) caused a concentration-dependent inhibition of calcium uptake (28-94%) by untreated rat liver microsomes. The rate of NADPH-dependent lipid peroxidation, measured as malondialdehyde formed, was also greatly enhanced by ochratoxin A. Various agents that inhibited ochratoxin A enhanced lipid peroxidation were also able to block the destruction of calcium uptake activity. Lipid peroxidation enhanced by ochratoxin A was also accompanied by leakage of calcium from calcium-loaded microsomes. These results suggest that ochratoxin A disrupts microsomal calcium homeostasis by an impairment of the endoplasmic reticulum membrane probably via enhanced lipid peroxidation.