Highly sensitive analysis of cholesterol and sitosterol in foods and human biosamples by liquid chromatography with fluorescence detection

High Performance Liquid Chromatography (HPLC) with Fluorescence Detection for Quantification of Steroids in Clinical, Pharmaceutical, and Environmental Samples: A Review

Steroids are compounds widely available in nature and synthesized for therapeutic and medical purposes. Although several analytical techniques are available for the quantification of steroids, their analysis is challenging due to their low levels and complex matrices of the samples. The efficiency and quick separation of the HPLC combined with the sensitivity, selectivity, simplicity, and cost-efficiency of fluorescence, make HPLC coupled to fluorescence detection (HPLC-FLD) an ideal tool for routine measurement and detection of steroids. In this review, we covered HPLC-FLD methods reported in the literature for the steroids quantification in clinical, pharmaceutical, and environmental applications, focusing on the various approaches of fluorescent derivatization. The aspects related to analytical methodology including sample preparation, derivatization reagents, and chromatographic conditions will be discussed.

Determination of Cholesterol Content in Butter by HPLC: Up-to-Date Optimization, and In-House Validation Using Reference Materials

This work deals with up-to-date optimization of cholesterol content determination when saponification and extraction procedures as well as HPLC conditions were studied. As found, optimal conditions for saponification process were identified by 15 min heating in the presence of 0.015 L of methanolic KOH solution with a concentration 1 mol/L with subsequent 0.015 L n-hexane–chloroform binary mixture (1:1, v/v) double extraction. HPLC separation consisted of isocratic elution with flow rate of 0.5 mL/min mobile phase composed of acetonitrile/methanol 60:40 (v/v) and stationary phase Zorbax Eclipse Plus C18 column 2.1 × 100 mm, 3.5 μm particle size diameters with detector wavelength 205 nm. The method passed through in-house validation criteria and its suitability was verified by analysis of butter reference materials. In final, the average content of cholesterol content in butter was determined at 2271.0 mg/kg. Thus, the method is suitable for the determination of cholesterol content in butter and probably also in other dairy products.

Reagent-Free Colorimetric Cholesterol Test Strip Based on Self Color-Changing Property of Nanoceria

Paper-based test strip consisting of cerium oxide nanoparticles (nanoceria) as hydrogen peroxide (H₂O₂)-dependent color-changing nanozymes and cholesterol oxidase (ChOx) has been developed for convenient colorimetric determination of cholesterol without the need for chromogenic substrate. The construction of the cholesterol strip begins with physical adsorption of nanoceria on the paper surface, followed by covalent immobilization of ChOx via silanization, chitosan-mediated activation, and glutaraldehyde treatment of the nanoceria-embedded paper matrices. In the presence of cholesterol, ChOx catalyzes its oxidation to produce H₂O₂, which forms peroxide complex on the nanoceria surface and induces visual color change of the nanoceria-embedded paper from white/light yellow into intense yellow/orange, which was conveniently quantified with an image acquired by a conventional smartphone with the ImageJ software. Using this strategy, target cholesterol was specifically determined down to 40 μM with a dynamic linear concentration range of 0.1–1.5 mM under neutral pH condition, which is suitable to measure the serum cholesterol, with excellent stability during 20 days and reusability by recovering its original color-changing activity for 4 consecutive cycles. Furthermore, the practical utility of this strategy was successfully demonstrated by reliably determining cholesterol in human blood serum samples. This study demonstrates the potential of self color-changing nanozymes for developing colorimetric paper strip sensor, which is particularly useful in instrumentation-free point-of-care environments.

Suitability of stationary phase for LC analysis of biomolecules

Biologically active compounds such as carotenoids/isoprenoids, vitamins, steroids, saponins, sugars, long chain fatty acids, and amino acids play a very important role in coordinating functions in living organisms. Determination of those substances is indispensable in advanced biological sciences. Engineered stationary phase in LC for the analysis of biomolecules has become easier with the development of chromatographic science. In general, C₁₈ column is being used for routine analysis but specific columns are being used for specific molecule. Monolithic columns are found to have higher efficiency than normal column. Among recent introduction, triacontyl stationary phases, designed for the separation of carotenoid isomers, are widely used for the estimation of carotenoids. In comparison to conventional C₁₈ phases, C₃₀ phases exhibited superior shape selectivity for the separation of isomers of carotenoids. It is also found useful for better elution and analysis of tocopherols, vitamin K, sterols, and fatty acids. Vitamin K, E, and their isomers are also successfully resoluted and analyzed by using C₃₀ column. Amino bonded phase column is specifically used for better elution of sugars, whereas phenyl columns are suitable for the separation and analysis of curcuminoids and taxol. Like triacontyl stationary phase, pentafluorophenyl columns are also used for the separation and analysis of carotenoids. Similarly, HILIC column are best suited for sugar analysis. All the stationary phases are made possible to resolute and analyze the target biomolecules better, which are the future of liquid chromatography. The present article focuses on the differential interaction between stationary phase and target biomolecules. The applicability of these stationary phases are reported in different matrices.

Development of colorimetric cholesterol detection kit using TPU nanofibre/cellulose acetate membrane

In this study, the authors report a simple fabrication of thermoplastic polyurethane (TPU) nanofibres-based kit for cholesterol detection. TPU is a polymer that is highly elastic, resistant to microorganisms, abrasion and compatible with blood; thus, making it a natural selection as an immobilisation matrix for cholesterol oxidase (ChOx) enzyme. The nanofibre was fabricated by electrospinning process and was characterised using scanning electron microscopy and Fourier transform-infrared spectroscopy. ChOx was covalently immobilised on TPU nanofibre and cholesterol level/concentration was visually found using 4-aminoantipyrine, a dye that reacts with H₂O₂ produced from the oxidation of cholesterol by ChOx and changes colour from yellow to red. The efficacy of the nanofibre to act as a detecting substrate was compared with cellulose acetate (CA) membrane, a well-documented enzyme immobilisation matrix. The optimisation of enzyme concentration and dye quantity were performed using standard ChOx spectrophotometric assay and the same was used in CA membrane and TPU nanofibre. The ChOx immobilised nanofibre showed good linear range from 2 to 10 mM with a lower detection limit of 2 mM and was highly stable compared to that of CA membrane. The enzyme immobilised nanofibre was further validated in serum samples.

A novel chemiluminescence sensor for sensitive detection of cholesterol based on the peroxidase-like activity of copper nanoclusters

A sensitive and selective chemiluminescence (CL) sensor based on the peroxidase-like activity of copper nanoclusters was established for the detection of cholesterol. Copper nanoclusters catalyse the CL reaction between luminol and H₂O₂. Because H₂O₂ is the oxidative product of cholesterol in the presence of cholesterol oxidase, the oxidation of cholesterol can be quantitatively converted to a CL response by combining the two reactions. The proposed method is simple and can be completed in a few minutes with high sensitivity. Under the optimal conditions, the CL intensity was proportional to the concentration of cholesterol over a wide range of 0.05-10 mM, with a detection limit of 1.5 μM. Furthermore, the method was successfully applied to determine cholesterol in milk powder and human serum with satisfactory accuracy and precision. This method expands the applications of nano-mimic enzymes in the field of CL-based sensors.

Cholesterol determination in foods: Comparison between high performance and ultra-high performance liquid chromatography

Analytical methods for cholesterol evaluation in foods are crucial since this compound was closely related with cardiovascular disease. In the present study, two chromatographic methods were implemented and validated, in order to achieve the ideal analytical method for the quantification of cholesterol in food matrices. The developed methods were applied to different foodstuffs, sour cream, egg, egg yolk and chicken nuggets. Both HPLC and UHPLC methods are rapid, specific, sensitive, precise (RSD<2.5%) and accurate. The achieved LOD and LOQ for UHPLC were 0.7 and 2.4μg/mL, respectively, while for HPLC were 3 and 11μg/mL. UHPLC method allowed reduction of the organic solvents consumption (8 times lower) and decreased analysis time in 4min, being more eco-friendly, than conventional HPLC methods. Moreover, it will be very useful for the quality control of cholesterol content in food matrices and can be easily adopted by analytical laboratories.

Chemiluminescent cholesterol sensor based on peroxidase-like activity of cupric oxide nanoparticles

A chemiluminescent cholesterol sensor with good selectivity and enhanced sensitivity was constructed based upon the peroxidase-like activity of cupric oxide nanoparticles. Cupric oxide nanoparticles can catalyze the oxidation of luminol by H2O2, which was produced by the reaction of cholesterol and oxygen that was catalyzed by cholesterol oxidase. Therefore, the oxidation of cholesterol could be transduced into the chemiluminescence of luminol by combining these two reactions. Under the optimum conditions, the CL intensity was proportional to the concentration of cholesterol over the range of 0.625-12.5μM and a detection limit was 0.17μM. The applicability of proposed method has been validated by determination of cholesterol in milk powder and human serum samples with satisfactory results.

Colorimetric detection of cholesterol with G-quadruplex-based DNAzymes and ABTS2-

A novel colorimetric method for detection of cholesterol was developed with hemin-G-quadruplex DNAzyme by transducing oxidation of cholesterol into the color change of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS(2-)). Oligonucleotide 5'-GTGGGTAGGGCGGGTTGG-3' (Oligo-1) formed G-quadruplex structure in the presence of K(+), it acted as a horseradish peroxidase (HRP) mimicking DNAzyme when binding hemin and catalyzed the oxidation of colorless ABTS(2-) to green ABTS(·-) by H(2)O(2), which was produced by the reaction of cholesterol and oxygen that catalyzed by cholesterol oxidase. Therefore, the oxidation of cholesterol could be transduced into the color change of ABTS(2-) by combining these two reactions. Under the optimum conditions, the absorbance was proportional to the concentration of cholesterol over the range of 1.0-30 μM, with a linear regression equation of A=0.362+0.0256C (C: μM, R=0.998) and a detection limit of 0.10 μM (3σ/slope). Moreover, the practicability of the assay in the detection of cholesterol in human serum was studied as well.

An ultra performance liquid chromatographic method for determining phytosterol uptake by Caco-2 cells

A simple method for the determination of cellular uptake of phytosterols by Caco-2 cells has been developed by ultra performance liquid chromatography with ultraviolet detection (UPLC-UV). UPLC-UV was established using an ODS column, acetonitrile/H(2)O (9:1, v/v) as a mobile phase, and a detection wavelength at 210 nm. As analytes, β-sitosterol, campesterol, stigmasterol, and brassicasterol were selected based on the abundance in foods and the similarity of their structures. A linear relation was observed between the peak area and the amount of sterol injected from 50 to 2000 pmol (r>0.999) with a relative standard deviation (RSD) of less than 2.5% (n=6). This method was applied to the determination of cellular uptake of phytosterols by Caco-2 cells. Recovery tests showed that phytosterols were extracted from the cell lysates by chloroform and determined by UPLC-UV with a recovery rate of more than 80.2% and an RSD of less than 11.3% (n=3). When Caco-2 cells were incubated with phytosterols at 37°C, their uptake was increased with time in a concentration-dependent manner. This method will be useful for the simultaneous determination of cellular phytosterols in an in vitro intestine model.

When cholesterol is not cholesterol: a note on the enzymatic determination of its concentration in model systems containing vegetable extracts

BACKGROUND

Experimental evidences demonstrate that vegetable derived extracts inhibit cholesterol absorption in the gastrointestinal tract. To further explore the mechanisms behind, we modeled duodenal contents with several vegetable extracts.

RESULTS

By employing a widely used cholesterol quantification method based on a cholesterol oxidase-peroxidase coupled reaction we analyzed the effects on cholesterol partition. Evidenced interferences were analyzed by studying specific and unspecific inhibitors of cholesterol oxidase-peroxidase coupled reaction. Cholesterol was also quantified by LC/MS. We found a significant interference of diverse (cocoa and tea-derived) extracts over this method. The interference was strongly dependent on model matrix: while as in phosphate buffered saline, the development of unspecific fluorescence was inhibitable by catalase (but not by heat denaturation), suggesting vegetable extract derived H(2)O(2) production, in bile-containing model systems, this interference also comprised cholesterol-oxidase inhibition. Several strategies, such as cholesterol standard addition and use of suitable blanks containing vegetable extracts were tested. When those failed, the use of a mass-spectrometry based chromatographic assay allowed quantification of cholesterol in models of duodenal contents in the presence of vegetable extracts.

CONCLUSIONS

We propose that the use of cholesterol-oxidase and/or peroxidase based systems for cholesterol analyses in foodstuffs should be accurately monitored, as important interferences in all the components of the enzymatic chain were evident. The use of adequate controls, standard addition and finally, chromatographic analyses solve these issues.

Rapid method for cholesterol analysis in bovine milk and options for applications

The adaptation of a colorimetric technique for the analysis of cholesterol in raw milk is presented. Performance quality was satisfying (mean intra-assay coefficient of variation (CV) 4·8, inter-assay CV 9·1%, linearity between 0 and 7 mm, recovery of spiked cholesterol into raw milk 98·1 and 106·3%). However, the milk fat extraction must be carried out within the 48 hours following milk sampling. When performing sampling, the significant variation of milk cholesterol composition during the milking process has to be taken into account.