Analysis of eicosanoid formation in humans by mass spectrometry

Effects of polyunsaturated fatty acids on calcium response and degranulation from RBL-2H3 cells

To investigate the biological activity of various polyunsaturated fatty acids (PUFAs) on the allergic reaction, we examined the effects of six PUFAs and two saturated fatty acids on calcium response and degranulation from rat basophilic leukemia (RBL-2H3) cells. Between 20 and 40 microM of six PUFAs (omega-6 series: arachidonic acid [AA, C20:4], gamma-linolenic acid [gamma-LN, C18:3] and linoleic acid [LA, C18:2]; omega-3 series: alpha-linolenic acids [alpha-LN, C18:3] and eicosapentaenoic acid [EPA, C20:5]; and omega-9 series: oleic acid [OLE, C18:1]), or two saturated fatty acids (stearic acid [STA, C18:0] and arachidic acid [AD, C20:0]) were used to examine the effects on calcium response and degranulation from RBL-2H3 cells. Calcium response was monitored using the fluorescent calcium indicator fura-2, while degranulation was monitored by measuring histamine release from the cells. Three omega-6 PUFAs (AA, alpha-LN and LA) dose-dependently increased the cytosolic free-calcium concentration and histamine release from RBL-2H3 cells. This phenomenon was specific to the omega-6 PUFAs, the omega-3 PUFAs (alpha-LA and EPA), omega-9 PUFA (OLE) and the saturated fatty acids (STA and AD) had no effect. The increase in the cytosolic free-calcium concentration caused by the omega-6 PUFAs depended on the existence of external calcium, cell viability and the cellular IP(3) levels remained unchanged throughout the experiment. These results suggest that omega-6 PUFAs work as direct mediators of calcium signaling pathways in RBL-2H3 cells.

Opposite effects of nicotinic acid and pyridoxine on systemic prostacyclin, thromboxane and leukotriene production in man

The effects of nicotinic acid (2500 mg orally during 12 hr) and pyridoxine (300 mg orally twice daily for seven days) on the excretion of urinary 2,3-dinor-6-ketoprostaglandin F1alpha, 11-dehydrothromboxane B2 and leukotriene E4, the markers of systemic prostacyclin, thromboxane A2 and cysteinyl leukotriene production, respectively, were investigated in healthy male volunteers (n=6-8). Nicotinic acid increased 11-dehydrothromboxane B2 and leukotriene E4 excretions to 2.6- and 2.0 times the initial values (P<0.05), respectively. In the volunteers treated with pyridoxine, 11-dehydrothromboxane B2 and leukotriene E4 excretions were decreased to 70% (P<0.05) and 65% (P<0.01) of the initial values, respectively, but the excretion of 2,3-dinor-6-ketoprostaglandin F1alpha was increased 1.7 times (P<0.01). The results suggest that nicotinic acid increases thromboxane and leukotriene synthesis which may not be beneficial for patients with cardiovascular diseases or asthma. In contrast, the increase in prostacyclin production and the inhibition in thromboxane and leukotriene synthesis by pyridoxine might be beneficial in disorders where the production of prostacyclin is decreased and the formation of thromboxane and cysteinyl leukotrienes is enhanced.

Tandem mass spectrometric quantification of 8-iso-prostaglandin F2alpha and its metabolite 2,3-dinor-5,6-dihydro-8-iso-prostaglandin F2alpha in human urine

Whole body synthesis of F2-isoprostanes, a family of cyclooxygenase-independent eicosanoids formed by free-radical catalysed peroxidation, should be best assessed by quantifying their urinary metabolites. Two methods for the quantitative determination of F2-isoprostane metabolites in human urine performing either thin-layer chromatography (TLC) (method A) or high-performance liquid chromatography (HPLC) (method B) prior to GC-tandem MS are described. Method A allows for simultaneous quantification of 8-iso-PGF2alpha, one prominent member of the F2-isoprostane family, and its major urinary metabolite, 2,3-dinor-5,6-dihydro-8-iso-PGF2alpha. Mean excretion was found to be 223 and 506 pg/mg creatinine of 8-iso-PGF2alpha and 2,3-dinor-5,6-dihydro-8-iso-PGF2alpha, respectively (n=14). A tight correlation existed between the urinary excretion of these two isoprostanes (r=0.86). Method B enables quantification of dinor-dihydro metabolites of various F2-isoprostanes including 8-iso-PGF2alpha. 2,3-Dinor-5,6-dihydro-8-iso-PGF2alpha was found to be an abundant dinor-dihydro F2-isoprostane metabolite. Validity of method A was proven by a combination of HPLC with TLC prior to GC-tandem MS analysis. A correlation was observed between the urinary concentrations of 2,3-dinor-5,6-dihydro-8-iso-PGF2alpha measured by GC-MS and GC-tandem MS (r=0.84).

Application of gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry to assess in vivo synthesis of prostaglandins, thromboxane, leukotrienes, isoprostanes and related compounds in humans

Prostaglandins, thromboxane, leukotrienes, isoprostanes and other arachidonic acid metabolites are structurally closely related, potent, biologically active compounds. One of the most challenging tasks in eicosanoids research has been to define the role of the various eicosanoids in human health and disease, and to monitor the effects of drugs on the in vivo synthesis of these lipid mediators in man. Great advances in instrumentation and ionization techniques, in particular the development of tandem mass spectrometry and negative-ion chemical ionization (NICI), in gas chromatography and also advances in methodologies for solid-phase extraction and sample purification by thin-layer chromatography and high-performance liquid chromatography have been made. Now gas chromatography-mass spectrometry (GC-MS) and GC-tandem MS in the NICI mode are currently indispensable analytical tools for reliable routine quantitation of eicosanoid formation in vivo in humans. In this article analytical methods for eicosanoids based on GC-MS and GC-tandem MS are reviewed emphasizing the quantitative measurement of specific index metabolites in human urine and its importance in clinical studies in man. Aspects of method validation and quality control are also discussed.

n-3 fatty acids reduce in vitro thromboxane production while having little effect on in vitro prostacyclin production in the rat

Male Sprague-Dawley rats were fed diets with 50% of the energy from fat over a 20-day period. The fats used were hydrogenated beef-fat (HBF), or HBF supplemented with ethyl arachidonate A, safflower oil (SO), or a mixture of SO and linseed oil (LO). For comparative purposes, another group of animals was fed a diet providing 50% of the energy as butter-fat. In vitro aortic prostacyclin (PGI2) and serum thromboxane (TXA2) levels (from clotting blood) were determined by radioimmunoassay of 6-keto PGF1 alpha and TXB2, respectively. The HBF diet had similar AA levels relative to the butter-fed rats but significantly reduced tissue levels of eicosapentaenoic acid (EPA) and this was associated with an increased production of serum TXB2. Supplementing the HBF diet with AA increased tissue levels of AA while maintaining low levels of n-3 fatty acids. These changes were accompanied by significant increases of both TXB2 and 6-keto-PGF1 alpha. LO supplementation to the HBF diet (with constant SO) led to elevated levels of EPA and relatively constant AA levels and this was associated with reduced production of TXB2. These results highlight the responsiveness of TXA2 to n-3 fatty acids in contrast to PGI2 which was more influenced by the level of AA in the tissue phospholipids in the rat.