Cholesterol Binding to Simple Micelles in Aqueous Bile-Salt–Cholesterol Solutions

The true thermodynamic activity (A_T) of cholesterol (Ch) in aqueous solutions containing taurocholate (TC)–Ch was determined by employing a direct assay of a 1 × 2-cm silicone polymer film with 0.025 cm thickness. Using theA_Tdata, information on the nature of micellar species present in the TC–Ch system, and employing a binding-site model previously developed for tauroursodeoxycholate (TUDC)–Ch and taurochenodeoxycholate (TCDC)–Ch systems, it appeared that the Ch-binding affinity for simple bile-salt micelles corresponds precisely with the order of hydrophobicity, TUDC < TC < TCDC. Further, although simple TC micelles and simple TCDC micelles have similar binding capacities, the first Ch binding to a simple TC micelle may not significantly facilitate the second Ch binding, as occurs in simple TCDC micelles. For TUDC–Ch, TC–Ch, and TCDC–Ch systems, the concentration of bound simple micelles increased with increasingA_Tvalues, whereas the unbound simple micelle concentration decreased proportionally. These results provide insights into the possible influence of bile-salt species on Ch-binding to simple micelles in bile-salt–Ch solutions.     

Enzyme Electrode with Collagen-Immobilized Cholesterol Oxidase for the Microdetermination of Free Cholesterol

Abstract

Cholesterol oxidase has been immobililzed on collagen films associated to an electrochemical sensor to form a “cholesterol electrode”. The electrode poised at a potential of + 650 my vs Ag/AgCl detects the hydrogen peroxide produced in the enzymatic reaction. This device presents a very high sensitivity and a wide range of linearity (10^?7 M - 0.8.10^?4 M). The use of a non enzymatic electrode associated with the enzymatic one allowed the detection and correction of electrochemical interferences when applied to human sera for free cholesterol determination.     

Membrane Cholesterol and the Formation of Cholesterol Domains in the Pathogenesis of Cardiovascular Disease

At least three types of cholesterol-rich membrane domains have been described in biological membranes including cholesterol rafts, membrane caveolae and crystalline cholesterol domains,. While clear biological functions have been ascribed to both rafts and caveolae, little attention has been directed to the biological consequences of cholesterol enrichment of cell membranes and the formation of cholesterol domains. Elevated blood cholesterol levels have been shown to result in the enrichment of the cell plasma membrane with cholesterol in arterial smooth muscle cells (SMC), endothelial cells (EC) and cardiac myocytes. In the early period of cholesterol feeding (within days), the cell membrane enriches with cholesterol and membrane viscosity and membrane bilayer width increase. This latter effect severely alters membrane protein function, and recent data indicates that this induces the modulation of vascular cells (SMC and EC) to the atherosclerotic phenotype. In cardiac myocytes these membrane modifications appear to induce alterations in gene expression patterns that lead to the development of a heart failure phenotype. In addition, as the cholesterol content increases, phase separation of cholesterol occurs resulting in the formation of immiscible cholesterol domains within the membrane. These domains likely initiate nucleation of cholesterol crystals which would explain the origin of “cholesterol clefts” in atherosclerotic lesions. Taken together, these membrane alterations secondary to cholesterol enrichment constitute a “membrane lesion” which contribute to the very early pathogenic events underlying major human diseases including coronary artery disease, stroke and heart failure.     

鸡蛋,胆固醇与动脉硬化

论述了鸡蛋的营养作用及其与动脉硬化的关系,包括:(1)“鸡蛋胆固醇升高血液胆固醇”的说法没有可靠证据;(2)鸡蛋———全面而平衡的天然营养品;(3)卵磷脂———胆固醇的最重要抑制剂;(4)高密度脂蛋白———防止动脉硬化的“好胆固醇”;(5)维生素———血管的扩张剂和抗凝血剂;(6)微量元素———代谢调控的总调度师。证明鸡蛋非但对心血管无害,还可担当心脏保护者的角色。主张国人,特别是青少年,应多吃新鲜鸡蛋。2图25表25参考文献。     

Poly(Neutral Red)/Cholesterol Oxidase Modified Carbon Film Electrode for Cholesterol Biosensing

New amperometric cholesterol oxidase (ChOx) based enzyme biosensors for cholesterol have been developed. The enzyme was immobilised with and without glutaraldehyde cross‐linking on top of carbon film electrodes modified with redox mediators. Mediators tested were: poly(neutral red) (PNR), Prussian blue and cobalt hexacyanoferrates. Amperometric detection of cholesterol showed that PNR/ChOx modified electrodes exhibited the best characteristics; under optimised conditions cholesterol was determined at ?0.4 V vs. SCE with a detection limit of 1.9 µM. The biosensors showed good reproducibility and stability and only a small influence from potential interferents in food. Analyses of cholesterol in egg yolk were successfully performed.     

Direct Electrochemistry of Cholesterol Oxidase Immobilized on a Conducting Polymer: Application for a Cholesterol Biosensor

Direct electrochemistry of cholesterol oxidase (ChOx) immobilized on the conductive poly‐3′,4′‐diamine‐2,2′,5′,2″‐terthiophene (PDATT) was achieved and used to create a cholesterol biosensor. A well‐defined redox peak was observed, corresponding to the direct electron transfer of the FAD/FADH₂ of ChOx, and the rate constant (k_s) was determined to be 0.75 s^?1. Glutathione (GSH) covalently bonded with PDATT was used as a matrix for conjugating AuNPs, ChOx, and MP, simultaneously. MP co‐immobilized with ChOx on the AuNPs‐GSH/PDATT exhibited an excellent amperometric response to cholesterol. The dynamic range was from 10 to 130 μM with a detection limit of 0.3±0.04 μM.     

Synthesis of New Water-Soluble Cholesterol Derivatives

L-Proline has been used as an organocatalyst for an efficient synthesis of 1,8-dioxo-octahydroxanthenes by treatment of aldehydes (aromatic, heteroaromatic, and aliphatic) with 5,5-dimethyl-1,3-cyclohexanedione. Three new compounds have been prepared.     

基于胆固醇的有机超分子智能凝胶

胆固醇分子具有特色的多环、多手性碳结构,因此可用于构筑有机超分子凝胶智能材料。该凝胶体系除了对温度有良好的感知响应性外,对其他的外界刺激,如光、pH、超声等也能够感知并响应。由于胆固醇分子是生命体中普遍存在的生物分子,基于胆固醇的有机超分子智能凝胶在生命现象模拟、药物输运等方面具有天然的优势。本文先根据胆固醇凝胶体系的不同种类,包括光响应型、氧化还原响应型、酸碱响应型、超声响应型,金属离子响应型以及触变响应型等,对该体系的结构与性能进行了介绍,然后介绍了对凝胶因子的修饰方法,最后结合目前的研究现状,探讨了胆固醇有机超分子凝胶的应用方向及前景。     

Cholesterol oxidation in meat-based baby foods

Cholesterol oxidation in commercial meat-based homogenized and freeze-dried baby foods was examined. The 7 major products of this reaction were determined by gas chromatography coupled with mass spectrometry (GC-MS). As far as single cholesterol oxidation products (COP) are concerned, 7-ketocholesterol was the major product of direct cholesterol oxidation in the 2 groups of analyzed samples, and this study confirmed that it is a useful marker of the whole cholesterol oxidation process. Nevertheless, the amounts of cholesterol-5beta,6beta-epoxide were often similar to and sometimes higher than the amounts of 7-ketocholesterol, thus showing a strong development of both direct and indirect cholesterol oxidation pathways. Total COP content was significantly higher in freeze-dried than in homogenized products. Moreover, in freeze-dried samples, the COP content per serving was quite variable and, in 2 samples, it was close to or even higher than 500 microg. The greater development of cholesterol oxidation in the freeze-dried samples was confirmed by their highest total COP/cholesterol percent ratios. A constant correlation between the fatty acid composition and the development of cholesterol oxidation was not found, although a positive correlation between unsaturated fatty acid content and total COP content occasionally exists in samples of the same brand.     

Cholesterol oxidation by microencapsulated cholesterol oxidase

Cholesterol oxidase fromBrevibacterium was microencapsulated using a phase-separation technique. The stability of the enzyme during storage and the activity of the microencapsulated enzyme were determined and compared with the soluble enzyme. The effects of various parameters during microencapsulation on enzyme activity are discussed.     

Voltammetric Sensor for Total Cholesterol Determination

We report on a voltammetric sensor for the detection of total cholesterol. The sensor was fabricated by co-immobilization of two enzymes: cholesterol oxidase (ChOx) and horseradish peroxidase (HRP) on porous graphite. The electrochemical behavior of the sensor was studied with the use of linear sweep voltammetry. It has been shown that the sensor has high stability and high sensitivity (16 μA mM⁻¹ cm⁻²). The biosensor exhibited a wide linear range up to 300 mol/dm³ in a condition close to physiological (pH=6.86). Besides, the interferences of some key analytes containing in the blood were studied. As a matter of fact, making a fabricated sensor is rather promising for using in clinical practice.     

聚吡咯固定胆固醇氧化酶/普鲁士蓝安培传感器的研制

利用电聚合吡咯的方法将胆固醇氧化酶固定在普鲁士蓝 (PB)修饰玻碳电极表面 ,制成了一种新型胆固醇安培传感器。PB膜修饰电极催化过氧化氢电还原 ,于 0V(vs.Ag ACl)产生灵敏还原峰 ,利用安培法可对胆固醇进行间接测定。胆固醇的测定范围为 0～ 2× 10 - 4mol L ,检出限为 6× 10 - 7mol L ,灵敏度较当前胆固醇传感器有明显的提高。同时该传感器对胆固醇的测定避免了常规电化学传感器测定中样品所含大量的易氧化物质带来的干扰     

壳聚糖固定双酶的丝网印刷胆固醇传感器的制备及应用

以亚甲基蓝为电子媒介,通过壳聚糖固定胆固醇氧化酶和辣根过氧化酶在丝网印刷电极表面,制成了一种新型胆固醇生物传感器,实现了低电位下对胆固醇的间接测定.循环伏安法和恒电位法用于研究修饰电极的电化学特性,在优化的试验条件下,安培法对胆固醇响应的线性范围为2.0×10-5～3.0×10-3mol·L-1,检出限(3S/N)为5.0×10-6mol·L-1.用同一支电极对6.0×10-4mol·L-1胆固醇溶液进行10次连续测定,测定值的相对标准偏差为4.6%,用3支电极做相同试验,测得相对标准偏差为6.2%.应用此传感器测定了血清样品中胆固醇含量,测定值的相对标准偏差(n=5)以及回收率试验结果依次在2.3%～6.1%之间及94.3%～105.2%之间.     

Cholesterol Dependent Activity of the Adenosine A2A Receptor Is Modulated via the Cholesterol Consensus Motif

Background: Membrane cholesterol dysregulation has been shown to alter the activity of the adenosine A_2A receptor (A_2AR), a G protein-coupled receptor, thereby implicating cholesterol levels in diseases such as Alzheimer’s and Parkinson’s. A limited number of A_2AR crystal structures show the receptor interacting with cholesterol, as such molecular simulations are often used to predict cholesterol interaction sites. Methods: Here, we use experimental methods to determine whether a specific interaction between amino acid side chains in the cholesterol consensus motif (CCM) of full length, wild-type human A_2AR, and cholesterol modulates activity of the receptor by testing the effects of mutational changes on functional consequences, including ligand binding, G protein coupling, and downstream activation of cyclic AMP. Results and conclusions: Our data, taken with previously published studies, support a model of receptor state-dependent binding between cholesterol and the CCM, whereby cholesterol facilitates both G protein coupling and downstream signaling of A_2AR.     

Rutin and Quercetin Decrease Cholesterol in HepG2 Cells but Not Plasma Cholesterol in Hamsters by Oral Administration

Rutin (R) and quercetin (Q) are two widespread dietary flavonoids. Previous studies regarding the plasma cholesterol-lowering activity of R and Q generated inconsistent results. The present study was therefore carried out to investigate the effects of R and Q on cholesterol metabolism in both HepG2 cells and hypercholesterolemia hamsters. Results from HepG2 cell experiments demonstrate that both R and Q decreased cholesterol at doses of 5 and 10 µM. R and Q up-regulated both the mRNA and protein expression of sterol regulatory element binding protein 2 (SREBP2), low-density lipoprotein receptor (LDLR), and liver X receptor alpha (LXRα). The immunofluorescence study revealed that R and Q increased the LDLR expression, while only Q improved LDL-C uptake in HepG2 cells. Results from hypercholesterolemia hamsters fed diets containing R (5.5 g/kg diet) and Q (2.5 g/kg diet) for 8 weeks demonstrate that both R and Q had no effect on plasma total cholesterol. In the liver, only Q reduced cholesterol significantly. The discrepancy between the in vitro and in vivo studies was probably due to a poor bioavailability of flavonoids in the intestine. It was therefore concluded that R and Q were effective in reducing cholesterol in HepG2 cells in vitro, whereas in vivo, the oral administration of the two flavonoids had little effect on plasma cholesterol in hamsters.     

溶胶-凝胶法固定胆固醇氧化酶偶联普鲁士蓝化学修饰电极的研究

用溶胶-凝胶法将胆固醇氧化酶固定在普鲁士蓝修饰的玻碳电极表面,制成了一种新型胆固醇传感器,实现了低电位下对胆固醇的间接测定,胆固醇的测定范围伏安法为5×10^-7～8×10^-5mol/L,安培法为5×10^-6～5×10^-4mol/L.伏安法检出限为1.2×10^-7mol/L,是目前所见灵敏度最高的胆固醇传感器之一,该传感器对胆固醇的测定可避免常规电化学传感器测定中由于样品中大量存在的易氧化物质所带来的干扰,该传感器的寿命长,使用次数在300次以上.     

An Overview on Electrochemical Determination of Cholesterol

Cholesterol detection is of great significance in biomedical applications because it is a crucial biomarker for some diseases. It is the precursor of different biological compounds such as vitamin D, hormones, and bile acid, etc. The cholesterol level in blood correlated to various diseases such as hypolipoproteinaemia, septicaemia, malnutrition hypertension, anaemia, brain thrombosis and arteriosclerosis for instance its levels in the blood of more than 200 mg/dL, increase the risk of heart disease. It is also found in foods from animal origin such as milk, meat, cheese, egg and seafood. With respect to dietary reference value for cholesterol intake, most of food safety authorities recommended maximum intake 300 mg per day for adults. Consequently, cholesterol is considered as a critical indicator of clinical biochemistry and so introducing new techniques for determination of it in biological samples and food is important. In this review, Principles, methods and recent developments in electrochemical cholesterol sensors are reviewed. Special attention is given to the discussion on some problems and bottlenecks in areas of enzymatic cholesterol sensing and new advances in non‐enzymatic sensors.