Determination of cholesterol and triglycerides in serum lipoproteins using flow field-flow fractionation coupled to gas chromatography-mass spectrometry

Asymmetric flow field flow fractionation (AsFlFFF) was combined with pyrolysis-gas chromatography mass spectrometry for a sized based fractionation and a detailed compositional study of the triglycerides and cholesterol associated with the various lipoprotein subclasses present in human serum. Serum samples were injected in the AsFlFFF instrument and fractionated with a time-delayed exponential decay cross flow program. The fractions collected after AsFlFFF elution were injected into a programmable temperature vaporizer (PTV) GC-injector, containing a fritted liner. A temperature and split-flow program for the PTV injector was optimized for the thermally assisted hydrolysis and methylation of the compounds of interest. The resulting fatty acid and cholesterol methyl esters were separated by GC and characteristic fragment ions were detected by MS. The system was optimized and calibrated with triglyceride and cholesterol standards for quantitative analysis. The possible interference by phospholipids with the quantitative results was investigated and found to be of minor importance.The concentrations and lipoprotein profiles of triglycerides and cholesterol were determined in a pooled serum sample of healthy volunteers and a serum sample of a sepsis patient. The results obtained with the GC–MS approach were compared with those of a previously developed method based on AsFlFFF with a dual enzymatic reaction detection system. A good agreement of the profiles was found, for cholesterol as well as for the triglycerides, even when the GC–MS method quantifies the fatty acids while with the enzymatic reaction method the glycerol concentrations are determined. Total cholesterol and triglyceride concentration values for the serum samples showed good agreement with the results of the standard enzymatic method as used in practice in the university hospital.     

Characterization of internal lipids from wool

The internal lipids of wool were isolated after solubilizing the wool keratin with a mixture of papain and dithioerythritol 1.4. Thin layer chromatography of the internal lipids was applied to classify the extracted components. The internal wool lipids gave 11 spots of which some were identified as cholesterol and free fatty acids, C-16 and C-18 being predominant. A very small amount of triglycerides and cholesterol esters were also found. A characteristic difference between internal wool lipids and wool wax appears to be the limited number of well defined components of which free cholesterol and fatty acids constitute the main bulk. Furthermore another feature of keratin membrane lipids is the extremely reduced phospholipid: cholesterol ratio of 0.3. The internal lipids originate mainly from the cell membrane complex of the fiber. The existence of a chemically modified bilayer membrane structure without the essential phospholipids must be taken into consideration.     

Separation of acidic and neutral lipids by aminopropyl-bonded silica gel column chromatography.

The separation of acidic and neutral lipids by aminopropyl-bonded silica gel column chromatography is presented. Total lipid extracts from Escherichia coli and human spermatozoa were loaded onto pre-packed aminopropyl-bonded silica gel columns and the lipids separated into four fractions. Non-polar lipids including cholesterol esters, triglycerides, diglycerides, monoglycerides and cholesterol, were eluted with 4 ml of isopropanol-chloroform (1:2, v/v) (fraction 1); free fatty acids were eluted with 4 ml of 2% acetic acid in diethyl ether (fraction 2); neutral polar lipids, including phosphophatidylethanolamine, phosphatidylcholine, sphingomyelin and neutral glycolipids, were eluted with 4 ml of methanol (fraction 3); and, finally, polar acidic lipids, including phosphatidylglycerol, cardiolipin, phosphatidylinositol, phosphatidylserine, seminolipid lipid A and acidic glycosphingolipids, were eluted with 4 ml of chloroform-methanol-0.8 M sodium acetate (60:30:4.5, v/V/V) (fraction 4). The recoveries for the different lipids ranged between 89 and 98% and the intra-assay variation, expressed as the standard deviation, was less than 5%.     

N.m.r. determination of wax esters in marine lipids

The proton n.m.r. spectra of lipids containing triglycerides and wax esters dissolved in CDCl₃ are characterized by seven sets of signals. The areas of the signals of terminal methyl group and of methylene protons of both wax ester and triglyceride were integrated. These were used to calculate the content of wax esters in lipids or oils. The rapid n.m.r. procedure is directly usable for natural lipids containing as low as 3 mg of wax esters in 50-mg samples with an error of about 7%. The method described compares favorably with t.l.c. determination.     

Automated quantitative gas-liquid chromatography of intact lipis. II. Accuracy, precision and reproducibility of results

The effect of various factors on the precision and accuracy of the gas chromatographic determination of neutral lipids was studied in the concentration range where the correction factors are dependent on the amount analyzed. The mutual effect of individual components of the neutral lipid spectrum on the recovery was examined. A method is described which provides the stable recovery of the components present at low concentrations, using the addition of high-molecular-weight triglyceride (triarachidin) which does not interfere in the determination of the usual triglycerides. The validity of the correction factors measured with pure compounds was verified by hydrogenation of biological samples of various compositions. Hydrogenation of the sample also solves the problem of the determination of the triglyceride fraction of carbon number 46, which interferes under normal conditions with the determination of the cholesteryl ester fraction of carbon number 47. A method for the standardization of the gas chromatographic determination of neutral lipids is given using pure compounds instead of lyophilized biological samples. Long-term quality control was carried out using synthetic control samples. The results show sufficiently low values of the variation coefficients over the whole period. The values of the variation coefficients measured over an interval of 25 weeks are about 4% for the main components of the neutral lipid spectrum and 6.3% for the components present at concentrations up to 5%. Thw within-day variation for the most neutral lipid fractions and for lipid classes attains a value of 40-75% of the day-to-day variation. The most satisfactory values are obtained for the variation within a single series which amount to less than 2% for all substances except for triglyceride fractions 48 and 54. The correlation of the determination of total cholesterol and triglycerides by gas chromatography and by enzymatic methods shows a very good agreement between the results obtained by the two methods. Using quality control, it is possible to follow the accuracy of the calibration and to demonstrate objectively the necessity for system recalibration.     

Supercritical fluid chromatography of fish,shark and seal oils

Summary Various natural and treated fish, shark liver and seal oils have been analyzed by supercritical fluid chromatography (SFC) using a non-polar capillary column. The lipids are separated according to molecular mass. The lipid groups found included free fatty acids, cholesterol, squalene, vitamins, wax esters, cholesterol esters, diglycerides, triglycerides and ether lipids. Methods for the analysis of the marine oils depend on components present in the oil. When co-eluting lipid groups were present, modifications such as hydrogenation or TLC fractionation of the oils had to be made. In this paper applications of SFC on fish, seal and shark liver oils are presented.     

Thujone corrects cholesterol and triglyceride profiles in diabetic rat model

Thujone, which is the major constituent in Salvia sp. (Lamiaceae), was found to correct the lipid profile (cholesterol and triglycerides) in diabetic rats. Oral treatment with thujone (5 mg kg?1 body weight dose) significantly adjusted cholesterol and triglyceride levels in diabetic rats (p ≤ 0.05) to normal levels compared to diabetic untreated rats. This provides a premise in the field of finding new agents to treat diabetic complications.     

Liquid chromatographic analysis of sebum lipids and other lipids of medical interest

A technique is described for the high-pressure liquid chromatographic (HPLC) analysis of sebum lipid classes. The lipid present in sebum are separated by gradient elution HPLC from a microparticulate silica column and detected using a moving-wire detector. The system described can be linked to a computer. Quantitation can be carried out by comparing peak areas obtained with those of an internal standard. Peak trapping for further investigations of the separated components, for example by gas chromatography-mass spectrometry, is very easy. Sebum lipids are separated into the following lipid classes: hydrocarbons and squalene, cholesterol esters and wax esters, fatty acids as their methyl esters, triglycerides, 1,3-diglycerides, 1,2-diglycerides, free cholesterol, monoglycerides and other polar materials. Besides to sebum, the method has been successfully applied to other lipid mixtures, such as serum lipids. Examples of other applications are shown.     

Lipidomic-based investigation into the therapeutic effects of polyene phosphatidylcholine and Babao Dan on rats with non-alcoholic fatty liver disease

In recent years, with the improvement of people’s living standards, non-alcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease in the world. In this paper, the metabolic disorders in Sprague Dawley (SD) rats were induced by a choline-deficient, l -amino acid–defined (CDAA) diet. The therapeutic effects of polyene phosphatidylcholine (PPC) and Babao Dan (BBD) on NAFLD were observed. Lipidomic analysis was performed using ultra-high-performance liquid chromatography-Orbitrap MS, and data analysis and lipid identification were performed using the software LipidSearch. Both PPC and BBD can reduce lipid accumulation in the liver and improve abnormal biochemical indicators in rats, including reduction of triglycerides, total cholesterol, alanine transaminase and aspartate transaminase in serum. In addition, lipids in rat serum were systematically analyzed by lipidomics. The lipidomic results showed that the most obvious lipids with abnormal metabolism in CDAA diet–induced rats were glycerides (triglycerides and diacylglycerols), phospholipids and cholesterol esters. Both BBD and PPC partly reversed the disturbance to lipids induced by the CDAA diet. PPC may be more effective than BBD in alleviating NAFLD because it has a better effect on inhibiting the abnormal accumulation of lipids and reducing the inflammatory reaction in the body.     

Enzymatic determination of the major serum lipids with a common indicator reaction

Enzymatic, colorimetric assays for serum cholesterol, choline-containing phospholipids, and triglycerides were developed with the intent of being able to specifically determine these individual lipids after isolation of serum lipoproteins by a technology such as ultracentrifugation that is already developed, electrophoresis that is already available for cholesterol and awaits the other lipid stains, or chemical fractionation. Once the relative amounts of the lipids in each lipoprotein fraction are known, the absolute amounts in each separated fraction can then be calculated using the total serum concentrations. As a secondary purpose, the measurement and arithmetic summation of serum cholesterol, choline-containing phospholipids, and triglycerides concentrations appears to provide a close estimate of the major serum total lipids. This summation technique results in apparent lower serum total lipids values than are obtained by a conventional turbidimetric method. This bias appears to be due to a combination of overestimation by the turbidimetric method and underestimation by the summation technique. However, this summation technique appears to be able to provide more information for specific lipid measurements on chemical, ultracentrifugal, or electrophoretic separation of lipoproteins by revealing which lipid class(es) is/are present in an abnormal concentration. It could also prove useful in providing major total lipid information for nonspecific staining of electrophoretic zones where fat-soluble stains such as Sudan black B are presently used. In the latter case, cholesterol and triglycerides are already determined and only the choline-containing phospholipid assay is additional.     

Fractionation of human serum lipoproteins and simultaneous enzymatic determination of cholesterol and triglycerides

A method based on Asymmetric Flow Field-Flow Fractionation (AF4) was developed to separate different types of lipoproteins from human serum. The emphasis in the method optimization was on the possibilities to characterize the largest lipoprotein fractions (LDL and VLDL), which is usually not possible with the size-exclusion chromatography methods applied in routine analysis. Different channel geometries and flow programs were tested and compared. The use of a short fractionation channel was shown to give less sample dilution at the same fractionation power compared to a conventional, long channel. Different size selectivities were obtained with an exponential decay and a linear cross flow program. The ratio of the UV absorption signal to the light scattering signal was used to validate the relation between retention time and size of the fractionated particles.An experimental setup was developed for the simultaneous determination of the cholesterol and triglycerides distribution over the lipoprotein fractions, based on enzymatic reactions followed by UV detection at 500 nm. Coiled and knitted PTFE tubing reactors were compared. An improved peak sharpness and sensitivity were observed with the knitted tubing reactor. After optimization of the experimental conditions a satisfactory linearity and precision (2-3% rsd for cholesterol and 5-6% rsd for triglycerides) were obtained. Finally, serum samples, a pooled sample from healthy volunteers and samples of sepsis patients, were analyzed with the method developed. Lipoprotein fractionation and cholesterol and triglyceride distributions could be correlated with the clinical background of the samples.     

Development and application of an analytical method for the determination of storage lipids, fatty acids and fatty alcohols in Calanus finmarchicus

A method was developed for the determination of the major storage lipids, wax ester and triglycerides, in the copepod Calanus finmarchicus. A variation of the Folch method was used to extract the lipid. The method was scaled down to enable the extraction of either pooled (-1 mg) or individual (approximately 200 microg) copepods. The major lipid classes were identified using TLC and quantified using HPLC coupled with evaporative light scattering detection. Analysis of laboratory reference materials indicated that this method underestimated the minor triglyceride component, but gave a good estimate of the major wax ester component. The fatty acid and fatty alcohol composition of the C. finmarchicus were determined following trans-esterification of the lipid extract in methanol. Fatty acids and fatty alcohols were initially identified by comparison with authentic standard and by mass spectroscopy. Using GC with flame ionisation detection the normalised area percentage of the fatty alcohols and fatty acid methyl esters was determined simultaneously in one run for either pooled or individual copepod samples. These methods were applied to C. finmarchicus collected from the Irminger Sea, North Atlantic in 2001 and 2002.     

A Universal Standard for Direct Injection Hydrogen Enthalpimetry of Some Common Unsaturated Lipids

Abstract

The method of hydrogen enthalpimetry as previously applied to unsaturated and polyunsaturated lipids has employed an authentic sample of each lipid analyte for construction of the enthalpimetric calibration curve. This study shows that individual lipid standards are not necessary for several common naturally-occurring fatty acids, methyl esters and simple triglycerides, each of which can be expressed as equivalent mg of methyl oleate. Data are given for six lipids having from one to nine moles of double bonds per mole of analyte, i. e., from oleic acid to trilinolenin.     

Calculations of phase equilibria for mixtures of triglycerides,fatty acids,and their esters in lower alcohols

The objects of study were mixtures containing triglycerides and lower alcohols and also the products of the transesterification of triglycerides, glycerol and fatty acid esters. The Redlich-Kwong-Soave equation of state was used as a thermodynamic model for the phase state of the selected mixtures over wide temperature, pressure, and composition ranges. Group methods were applied to determine the critical parameters of pure substances and their acentric factors. The parameters obtained were used to calculate the phase diagrams and critical parameters of mixtures containing triglycerides and lower alcohols and the products of the transesterification of triglycerides, glycerol and fatty acid esters, at various alcohol/oil ratios. The conditions of triglyceride transesterification in various lower alcohols providing the supercritical state of reaction mixtures were selected.     

Imaging of lipids in atherosclerotic lesion in aorta from ApoE/LDLR-/- mice by FT-IR spectroscopy and Hierarchical Cluster Analysis

Spectroscopy-based approaches can provide an insight into the biochemical composition of a tissue sample. In the present work Fourier transform infrared (FT-IR) spectroscopy was used to develop a reliable methodology to study the content of free fatty acids, triglycerides, cholesteryl esters as well as cholesterol in aorta from mice with atherosclerosis (ApoE/LDLR(-/-) mice). In particular, distribution and concentration of palmitic, oleic and linoleic acid derivatives were analyzed. Spectral analysis of pure compounds allowed for clear discrimination between free fatty acids and other similar moieties based on the carbonyl band position (1699-1710 cm(-1) range). In order to distinguish cholesteryl esters from triglycerides a ratio of carbonyl band to signal at 1010 cm(-1) was used. Imaging of lipids in atherosclerotic aortic lesions in ApoE/LDLR(-/-) mice was followed by Hierarchical Cluster Analysis (HCA). The aorta from C57Bl/6J control mice (fed with chow diet) was used for comparison. The measurements were completed with an FT-IR spectrometer equipped with a 128 × 128 FPA detector. In cross-section of aorta from ApoE/LDLR(-/-) mice a region of atherosclerotic plaque was clearly identified by HCA, which was later divided into 2 sub-regions, one characterized by the higher content of cholesterol, while the other by higher contents of cholesteryl esters. HCA of tissues deposited on normal microscopic glass, hence limited to the 2200-3800 cm(-1) spectral range, also identified a region of atherosclerotic plaque. Importantly, this region correlates with the area stained by standard histological staining for atherosclerotic plaque (Oil Red O). In conclusion, the use of FT-IR and HCA may provide a novel tool for qualitative and quantitative analysis of contents and distribution of lipids in atherosclerotic plaque.     

Composition of the neutral lipids of Chlorella vulgaris

Summary The qualitative and quantitative compositions of the neutral lipids and the fatty-acid composition of the individual classes of neutral lipids isolated from fresh, freeze-dried, and air-dry cells of the algaChlorella vulgaris have been investigated.The presence of natural fatty acid methyl esters in the lipid extract of the fresh and air-dry chlorella cells has been established.It has been shown that the fatty acid methyl ester fraction is enriched with palmitic acid as compared with the triglyceride and free fatty acid fractions.The main unsaturated acids of the chlorella lipids contain the first double bond in the ⁹ position.Division of Microbiology of the Academy of Sciences of the Uzbek SSR, Tashkent. Institute of the Chemistry of Plant Substances, Academy of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 49–53, January–February, 1978.     

A system for identification of triglycerides in reversed phase HPLC chromatograms based on equivalent carbon numbers

A graphical system for tentative identification and prediction of peaks in reversed phase HPLC chromatograms of triglycerides is presented. Straight, parallel lines were found for different homologous series of triglycerides when plotting carbon numbers (CN) against equivalent chain numbers (ECN). ECN, defined as the carbon number of the hypothetical saturated triglyceride, which elutes at the same retention time as the unsaturated triglyceride being studied, are given for common triglycerides in vegetable oils for HPLC systems with propionitrile and acetonitrile/acetone (64/36) as mobile phases. The method is presumably also applicable to homologous series of other compounds such as wax esters.     

Decreased water: increased solids: distorted serum concentrations

Serum, in which there is a pathological ratio between its percentage of water and total solids concentration is a relatively frequent occurrence in a clinical chemistry laboratory. These two factors bear an inverse relationship to each other because as the solids increase, the water decreases in fixed volumes of serum. These solid classes are comprised of proteins, lipids and crystalloids, the latter being the smaller dissolved molecules distinguished in part by their ability to go from vascular sites to the tissues as with posture changes unlike serum proteins which remain in their vascular environment during such positional changes. Of the three solids classes, only the proteins and lipids can cause significant alterations in the distribution ratios where the lipids, especially the triglycerides appear to be the major offenders among these classes of compounds. When proteins or triglycerides are markedly elevated, some sera are obviously different in appearance as elevated triglycerides result in hazy to milky sera whereas elevated proteins are a more insidious presence in that serum retains the same yellowish color and clarity much as is seen in the normal circumstances. Mathematical corrective information is available for both excessive protein and triglyceride concentrations but they appear to be infrequently used. Similarly, clearing mechanisms due to triglyceride excesses are available, but except for kits where somewhat helpful detergent action is incorporated, most disturbed results rejected by automated instrumentation may either be rejected through instrument calibration or reported incorrectly if for some reason they are not asterisked by the instrumentation. The purpose of the present report is to describe the difficulties in obtaining accurate determinations of analyte concentrations in which there are creations of pseudo-hypo-findings along with the corrective actions that can be taken including a novel clearing mechanism when excess triglycerides create a problem such as a spectrophotometric perturbation. The rationale for terms such as water dilution or electrolyte exclusion with excess protein concentrations and plasma dilution with excess triglyceride concentrations will be suggested.     

Cholesterol and its fatty acid esters in native DNA preparations: lipid analysis,computer simulation of their interaction with DNA and cholesterol binding to immobilized oligodeoxyribonucleotides

Supramolecular DNA complexes were isolated from rat normal cells and murine tumors. The content of DNA-bound lipids (cholesterol and its esters) was determined. The content of cholesterol esters is higher than that of free cholesterol; the lipid content in tumor cells is higher than in normal cells. Using the molecular mechanics approach, it is demonstrated for the first time that cholesterol and its esters with stearic, oleic, linoleic, and linolenic acids bind to the DNA minor groove more strongly than with the major groove. The calculated DNA binding energies of cholesterol and its esters depend on both the number of double bonds in the fatty acid residue and on the DNA nucleotide composition. The formation of stable complexes between cholesterol molecules and d(AT)-rich oligonucleotides was demonstrated using biological microchip containing immobilized octadeoxyribonucleotides. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2138–2144, September, 2005.