Analyses of lysophosphatidic acids by gas chromatography mass spectrometry without hydrolytic pretreatment

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.

Detection of the Ovarian Cancer Biomarker Lysophosphatidic Acid in Serum

Lysophosphatidic acid (LPA) is present during the medical condition of ovarian cancer at all stages of the disease, and, therefore possesses considerable potential as a biomarker for screening its presence in female patients. Unfortunately, there is currently no clinically employable assay for this biomarker. In the present work, we introduce a test based on the duel protein system of actin and gelsolin that could allow the quantitative measurement of LPA in serum samples in a biosensing format. In order to evaluate this possibility, actin protein was dye-modified and complexed with gelsolin protein, followed by surface deposition onto silica nanoparticles. This solid-phase system was exposed to serum samples containing various concentrations of LPA and analyzed by fluorescence microscopy. Measurements conducted for the LPA-containing serum samples were higher after exposure to the developed test than samples without LPA. Early results suggest a limit of detection of 5 μM LPA in serum. The eventual goal is to employ the chemistry described here in a biosensor configuration for the large population-scale, rapid screening of women for the potential occurrence of ovarian cancer.

Methods for quantifying lysophosphatidic acid in body fluids: a review

Lysophosphatidic acid (LPA) is a bioactive lipid involved in cellular signal transduction. LPA plays a role in both physiological and pathological processes. Elevated levels of LPA are observed in the plasma of patients with epithelial ovarian cancer, indicating its potential as a diagnostic marker. Quantification of total LPA can be performed by radioenzymatic, fluorometric, colorimetric, or immunoezymatic assay. Determination of individual LPA molecular species requires the use of capillary electrophoresis, gas chromatography, thin layer chromatography, liquid chromatography, or a matrix-assisted laser desorption/ionization time-of-flight method connected to an appropriate detection system.

Quantitative analysis of lysophosphatidic acid by time-of-flight mass spectrometry using a phosphate-capture molecule

Lysophosphatidic acid (LPA) is a lipid mediator that may play an important role in wound healing, embryonic development, and progression of cancer. Here, we report a procedure for the quantification of LPA by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The method is based on a characteristic mass shift with total charge change (from -2 to +1) of the phosphate species due to 1:1 complexation of LPA(2-) with a dinuclear zinc (II) complex [1,3-bis[bis(pyridin-2-ylmethyl)amino]propan-2-olato dizinc(II) complex; Zn(2)L(3+)] at physiological pH. The monocationic complex [LPA(2-)-Zn(2)L(3+)](+) was detected in the positive mode, in which no other signal of cation adducts of LPA(2-) was observed. The detection limit of 18:1 LPA by this method was 0.1 pmol on a sample plate. The intensity ratio of [LPA(2-)-Zn(2)L(3+)](+) against an internal standard [17:0 LPA(2-)-Zn(2)L(3+)](+) increased linearly with their molar ratio. Based on the relative intensities of complex ions, we determined the amounts of LPA homologs in an egg white by this method; the results obtained were in good agreement with those by gas liquid chromatography. This sensitive and convenient procedure for LPA-specific detection is useful for the quantification of LPA homologs occurring in biological materials.

Lysophosphatidic acid, a growth factor-like lipid, in the saliva

Lysophosphatidic acid is a multifunctional phospholipid mediator and elicits a variety of biological responses in vitro and in vivo. Evidence is accumulating that lysophosphatidic acid plays important physiological roles in diverse mammalian tissues and cells. In the present study, we first examined whether lysophosphatidic acid is present in human saliva. We found that a significant amount of lysophosphatidic acid is present in the saliva (0.785 nmol/ml). The predominant fatty acyl moiety of lysophosphatidic acid was 18:1n-9 + n-7 followed by 18:0 and 16:0. A small amount of lysoplasmanic acid, an alkyl ether-linked analog of lysophosphatidic acid, was also detected in the saliva (0.104 nmol/ml). We found that physiologically relevant concentrations of lysophosphatidic acid induced accelerated growth of cells of mouth, pharynx, and esophagus origin in vitro. Lysophosphatidic acid also induced rapid increases in the intracellular free Ca2+ concentrations in these cells. We obtained evidence that lysophosphatidic acid receptor mRNAs are actually present in these cells. These results strongly suggest that lysophosphatidic acid is involved in wound healing in the upper digestive organs such as the mouth, pharynx, and esophagus.

Human platelets respond differentially to lysophosphatidic acids having a highly unsaturated fatty acyl group and alkyl ether-linked lysophosphatidic acids

Lysophosphatidic acid (LPA) is a physiological agonist that is produced by lysophospholipase D, phospholipase A(1) and phospholipase A(2) in the blood of animals. It exerts diverse biological actions on a broad range of animal cells. Specific receptors for this important agonist have been characterized. In this investigation, for the first time we prepared LPAs having a highly unsaturated fatty acyl group, such as the eicosapentaenoyl or docosahexaenoyl residue, and their acetylated derivatives. Human platelets aggregated more potently in response to the highly unsaturated acyl-LPAs than to LPAs with a C(18) fatty acyl group, such as an oleoyl group, while alkyl ether-linked LPAs (alkyl-LPA) had much stronger aggregating activity. Two positional isomers of LPAs with an arachidonoyl, eicosapentaenoyl or docosahexaenoyl group had equipotent aggregatory activity as well as the positional isomers of their acetylated analogues, indicating that putative LPA receptors could not distinguish the difference between the positional isomers. We found that platelet preparations from two individuals showed no aggregatory response to alkyl-LPAs, although they contained mRNAs for known LPA receptors in the following order of expression level: endothelial differentiation gene (Edg)-4>Edg-7>Edg-2. We also obtained evidence that 2-(p-amylcinnamoyl)amino-4-chlorobenzoic acid (ONO-RS-082), a phospholipase A(2) inhibitor, potentiated alkyl-LPA-induced platelet aggregation, but inhibited highly unsaturated acyl-LPA-induced platelet aggregation. These results indicated that human platelets express acyl-LPA-selective and alkyl-LPA-selective receptors on their plasma membrane.

Hen egg yolk and white contain high amounts of lysophosphatidic acids, growth factor-like lipids: distinct molecular species compositions

Hen egg yolk and white were found to contain high amounts of lysophosphatidic acid (acyl LPA) in addition to small amounts of lysoplasmanic acid (alkyl LPA). The levels of acyl LPA in hen egg yolk (44.23 nmol/g tissue) and white (8.81 nmol/g tissue) were on the same order as or higher than the levels of acyl LPA known to be required to elicit biological responses in various animal tissues. Noticeably, there is a marked difference between the fatty acid composition of egg yolk acyl LPA and of egg white acyl LPA; egg yolk acyl LPA predominantly contains saturated fatty acids as the acyl moiety, whereas egg white acyl LPA primarily contains polyunsaturated fatty acids. We found that the level of acyl LPA, especially polyunsaturated fatty acid-containing acyl LPA, in egg white was augmented markedly during the incubation at 37 degrees C, while there was no change in egg yolk. We confirmed that egg white contains both the substrate, i.e., polyunsaturated fatty acid-containing lysophosphatidylcholine (LPC), and the enzyme activity catalyzing the hydrolysis of polyunsaturated fatty acid-containing LPC to the corresponding acyl LPA. Egg yolk LPA and egg white LPA may play separate physiological roles in the development, differentiation, and growth of embryos.

Occurrence of lysophosphatidic acid and its alkyl ether-linked analog in rat brain and comparison of their biological activities toward cultured neural cells

Rat brain was found to contain substantial amounts of potent bioactive lipids lysophosphatidic acid (acyl LPA) (3.73 nmol/g tissue) and lysoplasmanic acid (alkyl LPA) (0.44 nmol/g tissue). The presence of alkyl LPA was confirmed by mild alkaline hydrolysis analysis and by gas chromatography/mass spectrometry analysis of the trimethylsilyl derivative. This is the first clear evidence of the occurrence of an alkyl LPA in nature. The predominant molecular species of acyl LPA are 18:1-, 18:0- and 16:0-containing species (46. 9, 22.5 and 18.8%, respectively). A significant amount of a 20:4-containing species (7.2%) was also detected in the acyl LPA fraction. We also confirmed that rat brain alkyl LPA consists of 16:0-, 18:0- and 18:1-containing species. Noticeably, either acyl or alkyl LPA is capable of stimulating neuroblastomaxglioma hybrid NG108-15 cells to elicit a Ca(2+) transient, the potencies being almost the same. Both acyl and alkyl LPAs also induce cell rounding upon addition to the cells. These results suggest that acyl and alkyl LPAs play important physiological roles as intercellular signaling molecules as well as the roles as metabolic intermediates in the nervous system.

Substrate specificity of lysophospholipase D which produces bioactive lysophosphatidic acids in rat plasma

Previously we reported that lysophospholipase D in rat plasma hydrolyzes endogenous unsaturated lysophosphatidylcholines (LPCs) preferentially to saturated LPCs to lysophosphatidic acids with growth factor-like and hormone-like activities. In this study, we examined the possibility that association of LPCs with different proteins in rat plasma has an effect on the preference of lysophospholipase D for unsaturated LPCs. Large portions of various LPCs were found to be recovered in the lipoprotein-poor bottom fraction. Furthermore, the percentages of LPCs associated with albumin isolated from rat plasma were shown not to be consistent with their percentage conversions to lysophosphatidic acids by lysophospholipase D on incubation of rat plasma at 37 degrees C. These results indicate that distinct distributions of LPCs in the plasma protein fractions are not critical factors for the substrate specificity of lysophospholipase D. Experiments with Nagase analbuminemic rats suggested that albumin-LPC complexes are not necessarily required for the hydrolysis by lysophospholipase D; lipoprotein-associate LPCs appeared to be good substrates for the phospholipase. We found that both saturated and unsaturated LPCs are present mainly as 1-acyl isomers in rat plasma. This result indicates that the preference of lysophospholipase D for unsaturated LPCs is not attributable to a difference in position of the acyl group attached to the glycerol backbone of LPC. In addition, lysophospholipase D was also found to attack choline phospholipids with a long chain group and a short chain alkyl group, although their percentage hydrolyses were low. Taken altogether, these results suggest that lysophospholipase D shows higher affinities for free forms of unsaturated acyl type LPCs equilibrated with albumin-bound and lipoprotein-associated forms, than for free forms of saturated acyl type LPCs and analogs of platelet-activating factor.