Simultaneous analysis of low plasma levels of deuterium-labeled saturated and unsaturated fatty acids as t-butyldimethylsilyl esters

Fatty acids in blood and intestine following docosahexaenoic acid supplementation in adults with cystic fibrosis

The objective of this study was to investigate the effect of docosahexaenoic acid (DHA) supplementation on blood and intestinal DHA levels and lung function in mild/moderately affected adult CF patients with the DeltaF508 genotype.

BACKGROUND

Cystic Fibrosis (CF) patients often present with plasma fatty acid levels indicating low levels of linoleic (18:2n-6) and docosahexaenoic (22:6n-3) acids and an increased level of arachidonic acid (20:4n-6). Improved dietary fat intake or reducing fat malabsorption with pancreatic enzymes has failed to normalize this biochemical deficiency of DHA.

METHODS

Five CF patients, aged 18-43, received 70 mg of DHA/kg body weight/d for six weeks. At baseline and at six weeks a physical exam, lung function, 3-day dietary intake, duodenal mucosal biopsy and blood sample were assessed. The blood was analyzed for plasma vitamin A, D and E levels, liver function tests, clinical chemistry (CBC, differential and electrolytes). Plasma and red blood cell fatty acid levels were also analyzed. At three weeks, assessment included a physical exam, lung function test and fasting blood sample (vitamin levels, liver function and clinical chemistry only).

RESULTS

Pre- and post-measurements were compared for the four subjects who completed the study. An increase in DHA content (% w/w) was observed in all phospholipid fractions of plasma, red blood cell and mucosal samples. No significant differences in vitamin levels, liver function or lung function were observed.

CONCLUSIONS

The study proves the concept that an increase in tissue DHA levels in CF patients can be achieved by supplementing for six weeks with 70 mg/kg/d DHA.

An enriched mixture of trans-10,cis-12-CLA inhibits linoleic acid metabolism and PGE2 synthesis in MDA-MB-231 cells

Conjugated linoleic acid (CLA) isomers are potent inhibitors of mammary tumor cell growth. Evidence suggests that CLA modulates essential fatty acid (EFA) metabolism; however, it is not clear which parts of this pathway are important regulatory points modulated by CLA. Enriched mixtures of D9-cis,11-trans (D9c,11t)- and D10-trans,12-cis (D10t,12c)-18:2 were used to assess outcome measures of EFA metabolism pertaining to membrane phospholipid incorporation, tumor cell growth, and prostaglandin E2 (PGE2) synthesis in the MDA-MB-231 mammary tumor cell line. Tumor cells were treated with linoleic acid (LA), an equal mixture (Mix), or enriched preparations of D9c,11t- or D10t,12c-18:2. Treatment with Mix or the enriched mixture of D10t,12c-18:2 significantly inhibited the synthesis of arachidonic acid (AA) from LA, resulting in increased levels of LA and decreased levels of AA in membrane phosphatidylcholine and phosphatidylethanolamine (P < 0.05). LA and AA levels were not altered in cells treated with enriched D9c,11t-18:2 and were similar to those in LA control treated cells. All CLA treatments reduced [3H]thymidine uptake, an indicator of tumor cell growth, by more than one-half relative to LA controls. MDA-MB-231 cells challenged with AA in the presence of all CLA mixtures resulted in significantly reduced PGE2 synthesis relative to controls treated with LA (P < 0.05). It is evident that individual isomers exert inhibitory effects at specific steps of EFA metabolism, which correspondingly leads to a reduction in PGE2 synthesis and, ultimately, tumor growth.

New hydrolysis method for extremely small amount of lipids and capillary gas chromatographic analysis as n(O)-tert.-butyldimethylsilyl fatty acid derivatives compared with methyl ester derivatives

The organic basic solution, 1 M tetramethylammonium hydroxide (TMAH) in methanol, was employed for the hydrolysis of extremely small amounts of lipids compared to the classical inorganic basic solution, 1 M KOH in ethanol. The hydrolysed fatty acids were derivatized as N(O)-tert.-butyldimethylsilyl (tBDMSi) esters with N-methyl-N-(tert.-butyldimethylsilyl) trifluoroacetamide (MTBSTFA) and compared with the classical derivatives, the methyl esters, made by the BF3-methanol method. Recoveries of fatty acids determined on the standard fatty acids and soybean oil hydrolysed with TMAH were high: about 1.1-2.1- and 2.0-5.4-times, respectively, in all fatty acids compared with the hydrolysis by KOH regardless of derivatization method. The relative standard deviations (RSDs) on the recoveries of standard fatty acids were less than 5% when hydrolysed with TMAH, regardless of derivatives, but when hydrolysed with KOH, RSDs were more than 5% for most fatty acids, especially for long-chain fatty acids. The RSDs on the recoveries of fatty acids on the soybean oil were also very high in the KOH hydrolysis. Fatty acid compositions of soybean oil were similar in the main fatty acids regardless of hydrolysis methods, but showed slightly different values, depending on the methods of derivatization. RSDs were also very high in the KOH hydrolysis. In view of these results, precision of analysis by KOH hydrolysis was very poor, so we could not rely on the data. On the other hand, the reliability of data by TMAH hydrolysis method was very high, so it is a useful new hydrolysis method for extremely small amounts of lipid samples. Both derivatives of 35 standard fatty acids were successfully separated on a HP-1 nonpolar capillary column. tBDMSi derivatives were completely resolved in 70 min by 295 degrees C. In the methyl ester derivatives it took about 80 min to get satisfying resolution, but these derivatives were completely resolved by 250 degrees C. The sensitivity of tBDMSi derivatives was about 1.5-6.3-times higher than that with methyl ester derivatives. The stability of tBDMSi derivatives was constant for about 144 h except arachidic, docosahexanoic, behenic and heneicosanoic acids, which were stable for only 86 h.

Analysis of tert.-butyldimethylsilyl [1-13C]palmitic acid in stool samples by gas chromatography-mass spectrometry with electron impact ionisation: comparison with combustion isotope-ratio mass spectrometry

The use of 13C-labelled compounds to study lipid metabolism is increasing. Typically less than 40% of the orally administered label is recovered in breath CO2. The remainder must be either absorbed and not oxidised or not absorbed and remain in the faeces. Two methods of determining how much tracer passes through the body, and is present in the stool, were compared. Compound specific analysis of tert.-butyldimethylsilyl [13C]hexadecanoic acid by gas chromatography-mass spectrometry (GC-MS) with electron impact ionisation was compared with bulk analysis of whole stool and lipid extract by continuous flow isotope ratio mass spectrometry (CF-IRMS) with a combustion interface. The mean difference between the IRMS and GC-MS methods was -0.02 mmol 13C d(-1) with a mean excretion of 14.2 mmol 13C d(-1). Combustion IRMS is both simpler and cheaper, when the objective is to determine how much administered dose appears in stool, and information about the form of the label is not required.

Mass spectrometric evaluation of the tert.-butyldimethylsilyl derivatives of monohydroxyeicosatetraenoic acids and leukotrienes

The tert.-butyldimethylsilyl (t-BDMS) derivatives of the hydroxyl and the carboxyl groups on the monohydroxyeicosatetraenoic acids (HETEs) 5-, 12- and 15-hydroxyeicosatetraenoic acid (5-HETE, 12-HETE and 15-HETE, respectively) as well as leukotriene B4 (LTB4), 20-carboxy-LTB4 (20-COOH-LTB4) and 20-hydroxy-LTB4 (20-OH-LTB4) have been prepared. The derivatization reagents N-methyl-N-tert.-butyldimethylsilyltrifluoroacetamide (MTBSTFA) and tert.-butyldimethylsilylimidazole (t-BDMSIM) were utilized and the derivatization yields evaluated by gas chromatographic analysis. While the derivatization of 12-HETE and 15-HETE was achieved with good yield using MTBSTFA, the 5-hydroxylated compounds could only be derivatized satisfactorily with t-BDMSIM. The t-BDMS ester derivatives of monohydroxy fatty acids and 20-COOH-LTB4 were found quite susceptible to hydrolysis upon attempted isolation. The mass spectrometric fragmentation patterns of the HETEs, LTB4, 20-COOH-LTB4 and 20-OH-LTB4 and their reduced analogues as the t-BDMS ester and ether derivatives were examined. The fragmentation of the unsaturated compounds was mainly influenced by the double bonds while, on the contrary, the saturated compounds showed intense high-mass ions derived from elimination of a tert.-butyl radical. Furthermore, it was observed that the t-BDMS ester moiety of the unsaturated compounds exerted certain influence upon the fragmentation pattern. With regard to earlier results obtained with the methyl ester t-BDMS ether derivative, it was demonstrated that the use of the t-BDMS ester derivative resulted in decreased intensities of high-mass ions with a few exceptions. Taking into account the mass spectrometric fragmentation and the poor hydrolytic stability of the t-BDMS ester derivatives of some of the studied compounds, the use of these derivatives was not found to constitute a major advantage over the use of the methyl ester derivative. However, a favourable fragmentation pattern with a very intense high-mass ion was obtained for 15-HETE and the levels of this compound were determined in human lung tissue samples.