Simultaneous determination of C2-C22 non-esterified fatty acids and other metabolically relevant carboxylic acids in biological material by gas chromatography of their benzyl esters

A straightforward LC-MS/MS analysis to study serum profile of short and medium chain fatty acids

Short and medium fatty acids derived from either dietary sources, gut microbiota, and liver production might play a role in the modulation of metabolism and inflammation. The outcome of different autoimmune or inflammatory diseases could be related to microbiota composition and consequently fatty acids production. Their analytical detection, historically completed by GC, was herein investigated using a sensitive approach of LC-MS/MS with straightforward chemical derivatization, using 3-NPH, to the respective acylhydrazines. An isopropanol protein precipitation coupled to LC-MS/MS analysis allowed to separate and quantify butyric, valeric, hexanoic acid and their branched forms. The serum physiological ranges of short and medium chain fatty acids were determined in a heterogeneous healthy population (n = 54) from 18 to 85 years finding a concentration of 935.6 ± 246.5 (butyric), 698.8 ± 204.7 (isobutyric), 62.9 ± 15.3 (valeric), 1155.0 ± 490.4 (isovaleric) and 468.7 ± 377.5 (hexanoic) ng/mL respectively (mean ± SD). As expected, the biological levels in human serum are reasonably wide-ranging depending on several factors such as body-weight, gut microbiome dysbiosis, gut permeability, cardiometabolic dysregulation, and diet.

Hybrid volatolomics and disease detection

This Review presents a concise, but not exhaustive, didactic overview of some of the main concepts and approaches related to "volatolomics"-an emerging frontier for fast, risk-free, and potentially inexpensive diagnostics. It attempts to review the source and characteristics of volatolomics through the so-called volatile organic compounds (VOCs) emanating from cells and their microenvironment. It also reviews the existence of VOCs in several bodily fluids, including the cellular environment, blood, breath, skin, feces, urine, and saliva. Finally, the usefulness of volatolomics for diagnosis from a single bodily fluid, as well as ways to improve these diagnostic aspects by "hybrid" approaches that combine VOC profiles collected from two or more bodily fluids, will be discussed. The perspectives of this approach in developing the field of diagnostics to a new level are highlighted.

A review of the volatiles from the healthy human body

A compendium of all the volatile organic compounds (VOCs) emanating from the human body (the volatolome) is for the first time reported. 1840 VOCs have been assigned from breath (872), saliva (359), blood (154), milk (256), skin secretions (532) urine (279), and faeces (381) in apparently healthy individuals. Compounds were assigned CAS registry numbers and named according to a common convention where possible. The compounds have been grouped into tables according to their chemical class or functionality to permit easy comparison. Some clear differences are observed, for instance, a lack of esters in urine with a high number in faeces. Careful use of the database is needed. The numbers may not be a true reflection of the actual VOCs present from each bodily excretion. The lack of a compound could be due to the techniques used or reflect the intensity of effort e.g. there are few publications on VOCs from blood compared to a large number on VOCs in breath. The large number of volatiles reported from skin is partly due to the methodologies used, e.g. collecting excretions on glass beads and then heating to desorb VOCs. All compounds have been included as reported (unless there was a clear discrepancy between name and chemical structure), but there may be some mistaken assignations arising from the original publications, particularly for isomers. It is the authors' intention that this database will not only be a useful database of VOCs listed in the literature, but will stimulate further study of VOCs from healthy individuals. Establishing a list of volatiles emanating from healthy individuals and increased understanding of VOC metabolic pathways is an important step for differentiating between diseases using VOCs.

Determination of short-chain fatty acids in serum by hollow fiber supported liquid membrane extraction coupled with gas chromatography

A method based on hollow fiber supported liquid membrane extraction coupled with a gas chromatograph equipped with flame ionization detector (GC-FID) was developed for the determination of six short-chain fatty acids including acetic acid, propionic acid, i-butyric acid, n-butyric acid, i-valeric acid and n-valeric acid in serum. Hollow fiber supported liquid membrane extraction was employed for preconcentration and clean-up of the samples. The fatty acids were extracted from the acidic donor (diluted serum) into a liquid membrane formed in the wall of the hollow fiber with 10% tri-n-octylphoshphine oxide (TOPO) in di-n-hexyl ether, and then extracted back into a basic acceptor solution filled in the lumen of the hollow fiber. After being acidified with HCl, the acceptor was directly analyzed by GC-FID. The acceptor concentration, donor pH, membrane liquid and extracting time were optimized giving an enrichment factor up to 155 times. The good linearity (r(2)>0.980), reasonable recovery (87.2-121%), and satisfactory intra-assay (8.2-11.5%) and inter-assay (6.1-11.6%) precision illustrated the good performance of the present method. Limits of detection (LOD) ranged from 0.04 to 0.24 microM and limits of quantification (LOQ) varied from 0.13 to 0.80 microM.

Metabolic acidosis: separation methods and biological relevance of organic acids and lactic acid enantiomers

Metabolic acidosis can result from accumulation of organic acids in the blood due to anaerobic metabolism or intestinal bacterial fermentation of undigested substrate under certain conditions. These conditions include short-bowel syndrome, grain overfeeding of ruminants and, as recently reported, severe gastroenteritis. Measuring fermentation products such as short-chain fatty acids (SCFAs) and lactic acid in various biological samples is integral to the diagnosis of bacterial overgrowth. Stereospecific measurement of D- and L-lactic acid is necessary for confirmation of the origin and nature of metabolic acidosis. In this paper, methods for the separation of SCFAs and lactic acid are reviewed. Analysis of the organic acids involved in carbohydrate metabolism has been achieved by enzymatic methods, gas chromatography, high-performance liquid chromatography and capillary electrophoresis. Sample preparation techniques developed for these analytes are also discussed.

Simultaneous micellar electrokinetic chromatographic determination of isomeric fatty acid hydroperoxides and corresponding hydroxy fatty acids

The high selectivity and efficiency of micellar electrokinetic chromatography with a borax-sodium dodecylsulfate (SDS) or meglumin-SDS buffer make possible the rapid separation of hydroperoxy and hydroxy fatty acids and the non-oxidised unsaturated fatty acids from which they are derived. Nearly all the isomers of the hydroperoxides and hydroxy fatty acids derived from oleic, linoleic, alpha- and gamma-linolenic and arachidonic acids can be determined both qualitatively and quantitatively within ca. 10 min. The system has as many as 1 x 10(6) theoretical plates, and the detection limits with UV diode array detection at 195 or 234 nm are in the micromolar range.

Determination of plasma non-esterified fatty acids and triglyceride fatty acids by gas chromatography of their methyl esters after isolation by column chromatography on silica gel

Non-esterified fatty acids (NEFA) and triglycerides were isolated from human plasma by column chromatography on silica gel. Eight principal fatty acids of each of these lipid classes were determined by gas chromatography of their methyl ester derivatives and quantified relative to multipoint standard curves. Within-day relative standard deviations for plasma non-esterified fatty acid and triglyceride fatty acid determinations were 2.4 and 3.2%, respectively. Day-to-day relative standard deviations for plasma non-esterified fatty acid and triglyceride fatty acid determinations were 1.4 and 1.1%, respectively. The total plasma concentration and the relative proportions of the eight non-esterified fatty acids determined by this method were significantly different from results obtained according to two generally accepted methods for direct plasma non-esterified fatty acid determination without a specific isolation step. These comparisons suggested that considerable fatty acid ester lipid hydrolysis occurred during these direct determination procedures, and that this hydrolysis resulted in 3-fold overestimation of plasma NEFA content by those methods. Measured levels of arachidonic acid are substantially overestimated by these direct determination methods in which non-esterified fatty acids are not isolated before derivatization.

Organic acid profiling by direct treatment of deproteinized plasma with ethyl chloroformate

Carboxylic acids in plasma or serum can be conveniently determined by capillary gas chromatography (GC) following treatment with ethyl chloroformate (ECF). The mixed organic solvent used for plasma deproteinization is also suitable as medium for the subsequent reaction step. Thus, isolation of the compounds of interest is not necessary. Before treatment of the supernatant with ECF, the neutral lipids and amino acids are removed easily by hexane extraction and cation-exchange chromatography. Ketocarboxylic acids do not require a preliminary oximation. Capillary columns with a length of 15 m and a polar silicone phase proved to be ideal for the separation of mixtures of derivatized keto-, hydroxy-, mono- and dicarboxylic acids. The run time is less than 30 min.

Method for isolation of non-esterified fatty acids and several other classes of plasma lipids by column chromatography on silica gel

A method is described for isolation from human plasma of non-esterified fatty acids, cholesteryl esters, triglycerides, cholesterol and diglycerides, monoglycerides, and some phospholipids by extraction and silica gel column chromatography. All of these lipid classes except diglycerides and cholesterol were separated cleanly in seven elution steps. Diglycerides and cholesterol were isolated together. Recovery of model compounds which represent the most significant classes of plasma lipids during the column chromatographic step was nearly complete. The overall recovery of added heptadecanoic acid from plasma specimens was 81% after both sample isolation steps. The overall recovery of added synthetic pentadecanoic acid and heptadecanoic acid ester lipid homologues from plasma was 80-91% after both sample preparation steps. About 6 h are required for extraction and isolation in duplicate of these lipid classes from twenty plasma specimens. Alternatively, non-esterified fatty acids can be isolated from twenty plasma specimens in duplicate within 4 h by a variation of the full procedure.

Compartmentation of acetyl CoA studied by analysis of tricarboxylic acid cycle acids and 3-hydroxybutyrate in bile of rats given [2,2,2-2H3]ethanol

Acetate, 3-hydroxybutyrate, pyruvate, lactate, citrate, 2-oxoglutarate, succinate, fumarate and malate were analysed in rat bile by gas chromatography and gas chromatography/mass spectrometry of their O-melthyloxime-t-butyldimethylsilyl derivatives. The concentration of acetate increased to about 1.8 mmol/l after administration of [2,2,2-2H3]ethanol. Acetate was formed from ethanol to an extent of about 82% and retained all of the 2H at C-2, whereas 15% of the 2H had been lost in the tricarboxylic acid cycle intermediates and 24% in 3-hydroxybutyrate. Thus the exchange of 2H for 1H takes place after formation of acetyl CoA. For citrate and 3-hydroxybutyrate, 41% and 11% respectively was formed from [2,2,2-2H3]ethanol. These results indicate that different pools of acetyl CoA are used for the synthesis of ketone bodies and citrate, with the latter being derived from ethanol to a much larger extent. Smaller fractions of 2-oxoglutarate (16%) and succinate (5%) were derived from [2,2,2--2H3]ethanol, indicating significant contributions from amino acids.