High-performance liquid chromatographic determination of free fatty acids and esterified fatty acids in biological materials as their 2-nitrophenylhydrazides

Effect of Free Long-Chain Fatty Acids on Anagen Induction: Metabolic or Inflammatory Aspect?

Hair growth is a highly complex process regulated at multiple levels, including molecular pathways, stem cell behavior, metabolic processes, and immune responses. The hair follicle exhibits metabolic compartmentalization, with some cells relying on glycolysis and others on oxidative phosphorylation. Interestingly, in mice, the onset of the anagen phase can be stimulated by locally suppressing oxidative phosphorylation in the skin. This study showed that topical application of palmitate or oleate accelerated the onset of anagen in mice, while lactate, the end product of glycolysis, delayed it. We also investigated the effects of fatty acids on cytokine production in various human cell cultures. Fatty acids did not induce a cytokine response in fibroblasts or keratinocytes but significantly affected monocytes. Specifically, palmitic acid induced the production of TNF-α, IL-8, and CCL2. Oleic acid, however, elicited almost no response. By comparing the "metabolic" and "inflammatory" hypotheses of anagen stimulation, the results of our study suggest that metabolic regulation holds significant promise for influencing hair growth.

Quantifying Gut Microbial Short-Chain Fatty Acids and Their Isotopomers in Mechanistic Studies Using a Rapid, Readily Expandable LC-MS Platform

Short-chain fatty acids (SCFAs) comprise the largest group of gut microbial fermentation products. While absorption of most nutrients occurs in the small intestine, indigestible dietary components, such as fiber, reach the colon and are processed by the gut microbiome to produce a wide array of metabolites that influence host physiology. Numerous studies have implicated SCFAs as key modulators of host health, such as in regulating irritable bowel syndrome (IBS). However, robust methods are still required for their detection and quantitation to meet the demands of biological studies probing the complex interplay of the gut-host-health paradigm. In this study, a sensitive, rapid-throughput, and readily expandible UHPLC-QqQ-MS platform using 2-PA derivatization was developed for the quantitation of gut-microbially derived SCFAs, related metabolites, and isotopically labeled homologues. The utility of this platform was then demonstrated by investigating the production of SCFAs in cecal contents from mice feeding studies, human fecal bioreactors, and fecal/bacterial fermentations of isotopically labeled dietary carbohydrates. Overall, the workflow proposed in this study serves as an invaluable tool for the rapidly expanding gut-microbiome and precision nutrition research field.

Mass Spectrometry Based on Chemical Derivatization Has Brought Novel Discoveries to Lipidomics: A Comprehensive Review

Lipids, as one of the most important organic compounds in organisms, are important components of cells and participate in energy storage and signal transduction of living organisms. As a rapidly rising field, lipidomics research involves the identification and quantification of multiple classes of lipid molecules, as well as the structure, function, dynamics, and interactions of lipids in living organisms. Due to its inherent high selectivity and high sensitivity, mass spectrometry (MS) is the "gold standard" analysis technique for small molecules in biological samples. The combination chemical derivatization with MS detection is a unique strategy that could improve MS ionization efficiency, facilitate structure identification and quantitative analysis. Herein, this review discusses derivatization-based MS strategies for lipidomic analysis over the past decade and focuses on all the reported lipid categories, including fatty acids and modified fatty acids, glycerolipids, glycerophospholipids, sterols and saccharolipids. The functional groups of lipids mainly involved in chemical derivatization include the C=C group, carboxyl group, hydroxyl group, amino group, carbonyl group. Furthermore, representative applications of these derivatization-based lipid profiling methods were summarized. Finally, challenges and countermeasures of lipid derivatization are mentioned and highlighted to guide future studies of derivatization-based MS strategy in lipidomics.

Facile Titrimetric Assay of Lysophosphatidic Acid in Human Serum and Plasma for Ovarian Cancer Detection

Herein, an instrument free facile acid-base titrimetric methodology is reported for lysophosphatidic acid (LPA) measurement in serum and plasma samples for ovarian cancer detection. The concept is based on the titrimetric method in which alkaline solution was titrated with free fatty acid. Free fatty acid is generated due to action of the lysophospholipase to LPA. A phospholipid derivative known as LPA can function as a signaling molecule. A glycerol backbone serves as the foundation for phosphatidic acid, which also has bonds to an unsaturated fatty acid at carbon-1, a hydroxyl group at carbon-2, and a phosphate molecule at carbon-3. Free fatty acid and glycerol-3-phosphate are formed when LPA reacts with lysophospholipase. The formation of free fatty acid depends on the concentration of LPA. The standard graph of known concentrations of LPA, LPA spiked serum and LPA spiked plasma was plotted. The concentration of LPA in unknown serum and plasma were calculated from the standard graph. The limit of detection of LPA in spiked serum and plasma samples via titrimetric assay was calculated as 0.156 μmol/L. A patient's chance of survival may be outweighed by an early diagnosis of ovarian cancer.

Development of a simultaneous quantitation for short-, medium-, long-, and very long-chain fatty acids in human plasma by 2-nitrophenylhydrazine-derivatization and liquid chromatography-tandem mass spectrometry

Fatty acids (FA) have been important in clinical diagnosis for long, which makes the increasing need for a fast, reliable, and economic approach to determine FA of short-, medium-, long-, and very long-chain by widely available equipment and with high-throughput capacity. In the present work, 2‑nitrophenylhydrazine derivatization coupling with LC-MS/MS detection was utilized to simultaneously quantitate 18 FAs ranging from C4 to C26 in human plasma. The sample preparation protocol was optimized and extracting with diethyl ether‑potassium phosphate buffer twice was found as the highest efficiency along with economic feasibility. Under the optimized conditions, all the FA showed excellent linearity (R² > 0.999 for each), sufficient sensitivity (LOD 0.2-330 fmol and LOQ 2.3-660 fmol for all), favorable accuracy (recovery ranged from 98.1 ± 3.6% to 104.9 ± 5.5% with coefficient of variation no >8.6% for all), and negligible matrix effect. In the clinical application on 30 healthy subjects, compared with the previous HPLC-UV method, the developed method showed high reliability, as well as reduced time and reagent costs. The established method showed the potential to apply to not only diagnostic practice, but also nutritional and epidemiological studies.

Impairment of Intestinal Monocarboxylate Transporter 6 Function and Expression in Diabetic Rats Induced by Combination of High-Fat Diet and Low Dose of Streptozocin: Involvement of Butyrate-Peroxisome Proliferator-Activated Receptor-γ Activation

Generally, diabetes remarkably alters the expression and function of intestinal drug transporters. Nateglinide and bumetanide are substrates of monocarboxylate transporter 6 (MCT6). We investigated whether diabetes down-regulated the function and expression of intestinal MCT6 and the possible mechanism in diabetic rats induced by a combination of high-fat diet and low-dose streptozocin. Our results indicated that diabetes significantly decreased the oral plasma exposure of nateglinide. The plasma peak concentration and area under curve in diabetic rats were 16.9% and 28.2% of control rats, respectively. Diabetes significantly decreased the protein and mRNA expressions of intestinal MCT6 and oligopeptide transporter 1 (PEPT1) but up-regulated peroxisome proliferator-activated receptor γ (PPARγ) protein level. Single-pass intestinal perfusion demonstrated that diabetes prominently decreased the absorption of nateglinide and bumetanide. The MCT6 inhibitor bumetanide, but not PEPT1 inhibitor glycylsarcosine, significantly inhibited intestinal absorption of nateglinide in rats. Coadministration with bumetanide remarkably decreased the oral plasma exposure of nateglinide in rats. High concentrations of butyrate were detected in the intestine of diabetic rats. In Caco-2 cells (a human colorectal adenocarcinoma cell line), bumetanide and MCT6 knockdown remarkably inhibited the uptake of nateglinide. Butyrate down-regulated the function and expression of MCT6 in a concentration-dependent manner but increased PPARγ expression. The decreased expressions of MCT6 by PPARγ agonist troglitazone or butyrate were reversed by both PPARγ knockdown and PPARγ antagonist 2-chloro-5-nitro-N-phenylbenzamide (GW9662). Four weeks of butyrate treatment significantly decreased the oral plasma concentrations of nateglinide in rats, accompanied by significantly higher intestinal PPARγ and lower MCT6 protein levels. In conclusion, diabetes impaired the expression and function of intestinal MCT6 partly via butyrate-mediated PPARγ activation, decreasing the oral plasma exposure of nateglinide.

Determination of total, free and esterified short-chain fatty acid in human serum by liquid chromatography-mass spectrometry

Background

Short-chain fatty acids are primarily absorbed through the portal vein during lipid digestion, which is utilized as the energy source, as well as prevent type 2 diabetes and some cancers. However, reports on the determination of these short-chain fatty acids in human serum are limited.

Methods

Blood samples from human subjects ( n = 547, male/female = 246/301, age 58.85 ± 12.57) were collected. Saponification was applied to obtain total fatty acid. After derivatization by 2-nitrophenylhydrazine, fatty acid 4:0 and fatty acid 6:0 were measured by liquid chromatography-mass spectrometry.

Results

The developed method exhibited good linearity (R2 = 0.9996 for both). All the coefficients of variation of reproducibility and accuracy for fatty acid 4:0 and fatty acid 6:0 ranged 3.0%−6.1%, with the average recoveries of 87.8%−102.4% and 92.2%−98.2%, respectively. In all the samples, the concentration of fatty acid 4:0 (162.4 ± 76.4 μmol/L) was significantly higher than fatty acid 6:0 (2.0 ± 2.5 μmol/L, P < 0.001). Furthermore, the esterified form was predominant in both fatty acid 4:0 and fatty acid 6:0 (98.2% and 82.4% of total fatty acids, respectively). Besides, short-chain fatty acids showed no significant differences with regard to sex or age differences.

Conclusion

This developed liquid chromatography-mass spectrometry method is convenient and reliable, which might be useful for monitoring the variations of short-chain fatty acids in blood.

Metabolic adaptation to the aqueous leaf extract of Moringa oleifera Lam.-supplemented diet is related to the modulation of gut microbiota in mice

The aqueous leaf extract of Moringa oleifera Lam. (LM-A) is reported to have many health beneficial bioactivities and no obvious toxicity, but have mild adverse effects. Little is known about the mechanism of these reported adverse effects. Notably, there has been no report about the influence of LM-A on intestinal microecology. In this study, animal experiments were performed to explore the relationships between metabolic adaptation to an LM-A-supplemented diet and gut microbiota changes. After 8-week feeding with normal chow diet, the body weight of mice entered a stable period, and one of the group received daily doses of 750-mg/kg body weight LM-A by gavage for 4 weeks (assigned as LM); the other group received the vehicle (assigned as NCD). The liver weight to body weight ratio was enhanced, and the ceca were enlarged in the LM group compared with the NCD group. LM-A-supplemented-diet mice elicited a uniform metabolic adaptation, including slightly influenced fasting glucose and blood lipid profiles, significantly reduced liver triglycerides content, enhanced serum lipopolysaccharide level, activated inflammatory responses in the intestine and liver, compromised gut barrier function, and broken intestinal homeostasis. Many metabolic changes in mice were significantly correlated with altered specific gut bacteria. Changes in Firmicutes, Eubacterium rectale/Clostridium coccoides group, Faecalibacterium prausnitzii, Akkermansia muciniphila, segmented filamentous bacteria, Enterococcus spp., and Sutterella spp. may play an important role in the process of host metabolic adaptation to LM-A administration. Our research provides an explanation of the adverse effects of LM-A administration on normal adult individuals in the perspective of microecology.

The antiviral effect of mollusk mucus on measles virus

Measles is a viral disease highly contagious spread by respiratory transmission. Although infection can be controlled by vaccination, numerous cases of measles have been registered in many areas of the world, highlighting the need for additional interventions. Terrestrial gastropods exude mucus on their body surface when traveling, to protect the body from mechanical injury, desiccation or contact with harmful substances. The mucus of mollusks has been studied as a source of new natural compounds with diverse biological activities. In this study, the antiviral activity of the mucus of the land slug P. boraceiensis was demonstrated in vitro using Vero cells infected with measles virus. The crude sample and four fractions were tested in cultures infected with measles virus and the antiviral activity was assessed by the cytopathic effect in infected cell cultures as well as by immunofluorescence and qPCR. Fractions 39 and 50 of the mucus from P. boraceiensis were analyzed by HPLC-DAD-ESI-MS/MS and infrared spectroscopy. A mixture of polyunsaturated fatty acids was found in the two fractions. A reduction in the growth of the measles virus was observed, measured by qPCR, with a protection index of 80% in Vero cells infected with measles and treated with fraction 39. Fraction 39 exhibited the best antiviral action in vitro and high contents of hydroxy-tritriacontapentaenoic acid and hydroxy-pentatriacontapentaenoic acid were found in this fraction.

Excess of free fatty acids as a cause of metabolic dysfunction in skeletal muscle

Obesity is often associated with metabolic impairments in peripheral tissues. Evidence suggests an excess of free fatty acids (FFA) as one factor linking obesity and related pathological conditions and the impact of FFA overload on skeletal muscle metabolism is described herein. Obesity is associated with dysfunctional adipose tissue unable to buffer the flux of dietary lipids. Resulting increased levels and fluxes of plasma FFA lead to ectopic lipid deposition and lipotoxicity. FFA accumulated in skeletal muscle are associated with insulin resistance and overall cellular dysfunction. Mechanisms supposed to be involved in these conditions include the Randle cycle, intracellular accumulation of lipid metabolites, inflammation and mitochondrial dysfunction or mitochondrial stress. These mechanisms are described and discussed in the view of current experimental evidence with an emphasis on conflicting theories of decreased vs. increased mitochondrial fat oxidation associated with lipid overload. Since different types of FFA may induce diverse metabolic responses in skeletal muscle cells, this review also focuses on cellular mechanisms underlying the different action of saturated and unsaturated FFA.

Plasma capric acid concentrations in healthy subjects determined by high-performance liquid chromatography

BACKGROUND

Capric acid (FA10:0, decanoic acid) is a medium-chain fatty acid abundant in tropical oils such as coconut oil, whereas small amounts are present in milk of goat, cow, and human. Orally ingested FA10:0 is transported to the liver and quickly burnt within it. Only few reports are available for FA10:0 concentrations in human plasma.

METHODS

Fasting (n = 5, male/female = 3/2, age 31 ± 9.3 years old) and non-fasting (n = 106, male/female = 44/62, age 21.9 ± 3.2 years old) blood samples were collected from apparently healthy Japanese volunteers. The total FA10:0 in the plasma were measured by high-performance liquid chromatography after derivatization with 2-nitrophenylhydrazine followed by UV detection.

RESULTS

Inter and intra-assay coefficient of variation of FA10:0 assay at three different concentrations ranged in 1.7-3.9 and 1.3-5.4%, respectively, with an analytical recovery of 95.2-104.0%. FA10:0 concentration was below detection limit (0.1 µmol/L) in each fasting human plasma. FA10:0 was not detected in 50 (47.2%) of 106 non-fasting blood samples, while 29 (27.4%) plasma samples contained FA10:0 less than or equal to 0.5 µmol/L (0.4 ± 0.1), and 27 (25.5%) contained it at more than 0.5 µmol/L (0.9 ± 0.3).

CONCLUSION

A half of the non-fasting plasma samples contained detectable FA10:0. This simple, precise, and accurate high-performance liquid chromatography method might be useful for monitoring plasma FA10:0 during medium-chain triglycerides therapy.

An isotope-labeled chemical derivatization method for the quantitation of short-chain fatty acids in human feces by liquid chromatography-tandem mass spectrometry

Short-chain fatty acids (SCFAs) are produced by anaerobic gut microbiota in the large bowel. Qualitative and quantitative measurements of SCFAs in the intestinal tract and the fecal samples are important to understand the complex interplay between diet, gut microbiota and host metabolism homeostasis. To develop a new LC-MS/MS method for sensitive and reliable analysis of SCFAs in human fecal samples, 3-nitrophenylhydrazine (3NPH) was employed for pre-analytical derivatization to convert ten C2-C6 SCFAs to their 3-nitrophenylhydrazones under a single set of optimized reaction conditions and without the need of reaction quenching. The derivatives showed excellent in-solution chemical stability. They were separated on a reversed-phase C18 column and quantitated by negative-ion electrospray ionization - multiple-reaction monitoring (MRM)/MS. To achieve accurate quantitation, the stable isotope-labeled versions of the derivatives were synthesized in a single reaction vessel from (13)C6-3NPH, and were used as internal standard to compensate for the matrix effects in ESI. Method validation showed on-column limits of detection and quantitation over the range from low to high femtomoles for the ten SCFAs, and the intra-day and inter-day precision for determination of nine of the ten SCFAs in human fecal samples was ≤8.8% (n=6). The quantitation accuracy ranged from 93.1% to 108.4% (CVs≤4.6%, n=6). This method was used to determine the SCFA concentrations and compositions in six human fecal samples. One of the six samples, which was collected from a clinically diagnosed type 2 diabetes patient showed a significantly high molar ratio of branch-chain SCFAs to straight-chain SCFAs than the others. In summary, this work provides a new LC-MS/MS method for precise and accurate quantitation of SCFAs in human feces.

Association of GLP-1 secretion with anti-hyperlipidemic effect of ginsenosides in high-fat diet fed rats

OBJECTIVE

Ginsenosides, major bioactive constituents in Panax ginseng, have been shown to exert anti-hyperlipidemia effects. However, the underlying mechanism was not well-elucidated due to the low bioavailability of ginsenosides. Glucagon-like peptide-1 (GLP-1) was considered to be a critical regulator of energy homeostasis. Our previous studies have showed that ginseng total saponins (GTS) exhibited antidiabetic effects partly via modulating GLP-1 release. The aim of this study was to investigate the potential role of GLP-1 in anti-hyperlipidemia effect of GTS in rats fed with high-fat diet.

MATERIAL AND METHODS

Male Sprague-Dawley rats were fed with normal diet (CON) or high-fat diet (HFD) for 4 weeks. Then, the HFD rats orally received vehicle (HFD), 150 mg/kg/day (HFD-GL) and 300 mg/kg/day of GTS (HFD-GH) for another 4 weeks, respectively.

RESULTS

Four-week GTS treatment significantly ameliorated hyperlipidemia, decreased body fat, liver weight and improved insulin resistance. It was found that high-dose GTS treatment increased portal GLP-1 level induced by glucose loading, accompanied by increased intestinal GLP-1 content, L-cell number and prohormone convertase 3 mRNA expression. Data from NCI-H716 cells showed that both GTS and ginsenoside Rb1 significantly increased GLP-1 secretion as well as proglucagon mRNA level in NCI-H716 cells supplemented with 10% HFD-rat serum.

CONCLUSIONS

Hyperlipidemia and insulin resistance were attenuated effectively in response to GTS treatment. These improvements may be associated with the increased secretion of GLP-1.

Unsaturated fatty acids promote bioaccessibility and basolateral secretion of carotenoids and α-tocopherol by Caco-2 cells

Bioavailability of carotenoids and tocopherols from foods is determined by the efficiency of transfer from food/meal to mixed micelles during digestion, incorporation into chylomicrons for trans-epithelial transport to lymphatic/blood system, and distribution to target tissues.

Tissue distribution and identification of radioactivity components at elimination phase after oral administration of [¹⁴C]CS-1036, an α-amylase inhibitor, to rats

(2R,3R,4R)-4-hydroxy-2-(hydroxymethyl)pyrrolidin-3-yl 4-O-(6-deoxy-β-D-glucopyranosyl)-α-D-glucopyranoside (CS-1036) is a potent inhibitor of pancreatic and salivary α-amylase. After oral administration of [¹⁴C]CS-1036 to rats, the radioactivity was still detectable up to 7-14 days after administration in various tissues, and its terminal phase in plasma could be explained neither by the exposure of CS-1036 nor its major metabolite M1. The slow elimination of radioactivity in various tissues was hypothesized to be caused by covalent binding to macromolecules or use for biogenic components. To assess the use for biogenic components, amino acid analysis of plasma proteins and lipid analysis of adipose tissue were conducted after repeated oral administration of [¹⁴C]CS-1036 by high-performance liquid chromatography and accelerated mass spectrometry and by thin layer chromatography and liquid chromatography/mass spectrometry, respectively. In amino acid analysis, glutamic acid, aspartic acid, alanine, and proline were identified as major radioactive amino acids, and radioactive nonessential amino acids occupied 76.0% of the radioactivity. In lipid analysis, a part of the radioactive lipids were identified as the fatty acids constituting the neutral lipids by lipase-hydrolysis. The radioactive fatty acids from neutral lipids were identified as palmitic acid, oleic acid, and 8,11,14-eicosatrienoic acid. Intestinal flora were involved in CS-1036 metabolism and are indicated to be involved in the production of small molecule metabolites, which are the sources for amino acids and fatty acids, from [¹⁴C]CS-1036. In conclusion, radioactivity derived from [¹⁴C]CS-1036 was incorporated as the constituents of amino acids of plasma proteins and fatty acids of neutral lipids.

Recent trends in the advanced analysis of bioactive fatty acids

The consumption of dietary fats have been long associated to chronic diseases such as obesity, diabetes, cancer, arthritis, asthma, and cardiovascular disease; although some controversy still exists in the role of dietary fats in human health, certain fats have demonstrated their positive effect in the modulation of abnormal fatty acid and eicosanoid metabolism, both of them associated to chronic diseases. Among the different fats, some fatty acids can be used as functional ingredients such as alpha-linolenic acid (ALA), arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), gamma-linolenic acid (GLA), stearidonic acid (STA) and conjugated linoleic acid (CLA), among others. The present review is focused on recent developments in FAs analysis, covering sample preparation methods such as extraction, fractionation and derivatization as well as new advances in chromatographic methods such as GC and HPLC. Special attention is paid to trans fatty acids due its increasing interest for the food industry.

Quantification of 13C pyruvate and 13C lactate in dog blood by reversed-phase liquid chromatography–electrospray ionization mass spectrometry after derivatization with 3-nitrophenylhydrazine

Injection of hyperpolarized (13)C-labelled pyruvate ((13)C pyruvate) is under evaluation as an agent for medical metabolic imaging by measuring formation of (13)C lactate using magnetic resonance spectroscopy of the (13)C nuclei. A quantitative method for analysis of these (13)C-labelled substances in dog blood was needed as part of the development of this agent and we here describe a liquid chromatography-mass spectrometry method for that purpose. Immediately after blood collection, the blood proteins were precipitated using methanol added internal standard ([U-(13)C]pyruvate and [U-(13)C]lactate). Prior to analysis, the compounds were derivatized using 3-nitrophenylhydrazine. Following separation on a Supelco Discovery HS C18 column, (13)C pyruvate and (13)C lactate were detected using negative electrospray ionization mass spectrometry. Calibration standards (4.5-4500 microM (13)C pyruvate and 9-9000 microM (13)C lactate) and added internal standard were used to make the calibration curves, which were fitted to a non-linear equation y=a+bx+cx(2) and weighted with a weighting factor of 1/y(2). The analytical lower limit of quantification of (13)C pyruvate and (13)C lactate was 4.5 and 9 microM, respectively. The total precision of the method was below 9.2% for (13)C pyruvate and below 5.8% for (13)C lactate. The accuracy of the method showed a relative error less than 2.4% for (13)C pyruvate and less than 6.3% for (13)C lactate. The recoveries were in the range 93-115% for (13)C pyruvate and 70-111% for (13)C lactate. Both substances were stable in protein-free supernatant when stored for up to 3 weeks in a -20 degrees C freezer, during three freeze/thaw cycles, and when stored in an autosampler for at least 30 h.

Sulfonium and phosphonium, new ion-pairing agents with unique selectivity towards polarizable anions

Ion-pair chromatography (IPC) almost universally relies upon ammonium-based ion-pairing agents (IPAs) for anion separations. This work compares tetrabutylammonium (TBA) with tetrabutylphosphonium (TBP) and tributylsulfonium (TBS). To best understand the retention behavior analytes used for characterization of the IPAs spanned the Hofmeister series; from kosmotropic monoanions (iodate, chloride, nitrite) and intermediate anions (nitrate, bromide) to chaotropic ions (perchlorate, thiocyanate, iodide). The studies demonstrate that tetrabutylphosphonium is the most chaotropic IPA, followed by tetrabutylammonium and finally tributylsulfonium is the least chaotropic. In the case of the chaotropic anions, the retention of perchlorate was least with tributylsulfonium, and greatest for tetrabutylphosphonium, with tetrabutylammonium being intermediate. The multivalent kosmotropic anions (sulfate, chromate, thiosulfate) demonstrated unique selectivity changes depending on the kosmotropic/chaotropic nature of the IPA. Demonstrating increases in retention with increasing IPA concentration only with tributylsulfonium, whereas the more chaotropic IPAs universally decreased the retention of the multivalent anions.

Use of reversed phase HP liquid chromatography to assay conversion of N-acylglycines to primary fatty acid amides by peptidylglycine-alpha-amidating monooxygenase

Primary fatty acid amides (R-CO-NH2) and N-acylglycines (R-CO-NH-CH2-COOH) are classes of compounds that have only recently been isolated and characterized from biological sources. Key questions remain regarding how these lipid amides are produced and degraded in biological systems. Relative to the fatty acids, little has been done to develop methods to separate and quantify the fatty acid amides and N-acylglycines. We describe reversed phase HPLC methods for the separation of C2-C12 primary fatty acid amides and N-acylglycines and also C12-C22 fatty acid amides. Separation within each class occurs primarily on the basis of simple interactions between the acyl chain and the chromatographic stationary phase, but the polar headgroups on these and related fatty acids and N-acylethanolamides modulate the absolute retention in reversed phase mode. We use these methods to measure the enzyme-mediated, two-step conversion of N-octanoylglycine to octanoamide.

Determination of aldehydes and ketones using derivatization with 2,4-dinitrophenylhydrazine and liquid chromatography–atmospheric pressure photoionization-mass spectrometry

Atmospheric pressure photoionization-mass spectrometry (APPI-MS) is used for the analysis of aldehydes and ketones after derivatization with 2,4-dinitrophenylhydrazine (DNPH) and liquid chromatographic separation. In the negative ion mode, the [M - H]- pseudomolecular ions are most abundant for the carbonyls. Compared with the established atmospheric pressure chemical ionization (APCI)-MS, limits of detection are typically lower using similar conditions. Automobile exhaust and cigarette exhaust samples were analyzed with APPI-MS and APCI-MS in combination with an ion trap mass analyzer. Due to improved limits of detection, more of the less abundant long-chain carbonyls are detected with APPI-MS in real samples. While 2,4-dinitrophenylazide, a known reaction product of DNPH with nitrogen dioxide, is detected in APCI-MS due to dissociative electron capture, it is not observed at all in APPI-MS.

On-line determination of carboxylic acids, aldehydes and ketones by high-performance liquid chromatography-diode array detection-atmospheric pressure chemical ionisation mass spectrometry after derivatization with 2-nitrophenylhydrazine

2-Nitrophenylhydrazine (2-NPH) is widely used for the derivatization of carboxylic acids, aldehydes and ketones, in industrial and biological samples. These compounds react with 2-NPH to form derivatives, which are separated by high-performance liquid chromatography (HPLC) and detected with diode array detection (DAD). The UV spectra give information about the functionality of the compounds: carboxylic acid or ketone/aldehyde. Most of the eluting compounds in "known" samples are well characterised by the retention time (comparison with those of standards) of the 2-NPH derivative and their UV spectrum. The identification of different unknown 2-NPH derivatives of carboxylic acids, ketones and/or aldehydes, in industrial or biological samples, based on retention time and/or UV spectrum is not sufficient. These unknown 2-NPH compounds can be identified with on-line atmospheric pressure chemical ionisation mass spectrometry (APCI-MS) based on the molecular mass or/and the fragmentation of the derivative. A novel and specific on-line HPLC-DAD-APCI(-)-MS method is described for the determination of carboxylic acids, ketones and aldehydes, after on-line pre-column derivatization with 2-NHP. The fragmentation of different 2-NPH derivatives were investigated and the possibilities of APCI(-)-MS detection were demonstrated by the on-line identification of an unknown derivative, which turned out to be a side product between 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 2-NPH in the presence of high concentrations of a cyclic amide in the sample solution.