Optimization of Ultrafast Proteomics Using an LC-Quadrupole-Orbitrap Mass Spectrometer with Data-Independent Acquisition.

Proteomics has become an increasingly important tool in medical and medicinal applications. It is necessary to improve the analytical throughput for these applications, particularly in large-scale drug screening to enable measurement of a large number of samples. In this study, we aimed to establish an ultrafast proteomic method based on 5-min gradient LC and quadrupole-Orbitrap mass spectrometer (Q-Orbitrap MS). We precisely optimized data-independent acquisition (DIA) parameters for 5-min gradient LC and reached a depth of >5000 and 4200 proteins from 1000 and 31.25 ng of HEK293T cell digest in a single-shot run, respectively. The throughput of our method enabled the measurement of approximately 80 samples/day, including sample loading, column equilibration, and wash running time. We demonstrated that our method is applicable for the screening of chemical responsivity via a cell stimulation assay. These data show that our method enables the capture of biological alterations in proteomic profiles with high sensitivity, suggesting the possibility of large-scale screening of chemical responsivity.

Saturated fatty acid is a principal cause of anxiety-like behavior in diet-induced obese rats in relation to serum lysophosphatidyl choline level.

BACKGROUND: Obesity is considered to be a risk factor for neurodegenerative- and psychiatric- diseases including Alzheimer's disease, schizophrenia, and depression. A high-lard diet is widely used to induce obesity in model animal experiments, which also leads to anxiety-like and depression-like behaviors. However, the contribution of dietary fat source to these abnormal behaviors in obesity is largely unknown. METHODS: Sprague-Dawley rats were treated with different types of high-fat (lard and olive oil) diet with high sucrose for more than 8 weeks. Anxiety-like behavior (open-field and social interaction tests) and cognitive function (Y-maze test) after the treatment were analyzed. The expression of mRNA related to neurotransmitter and nutrient transporters in the prefrontal cortex were determined using real-time PCR. Serum lipid species were determined using liquid chromatography with tandem mass spectrometry. RESULTS: Both high-fat/high-sucrose diets increased body weight (BW), adipose tissue, and serum leptin level. However, the high-lard/high-sucrose (HL/HS), but not high-olive oil/HS, diet induced anxiety-like behavior in open field and social interaction tests. BW and endocrine hormones such as leptin and insulin were not correlated to anxiety-like behavior. HL/HS diet induced an increase in glutamate transporter and a decrease of glutamate receptor mRNA expressions in the prefrontal cortex. Further, serum lysophosphatidyl choline conjugated with several fatty acids was decreased by HL/HS diet. LPC conjugated with eicosapentaenoic acid (EPA) was strongly correlated with anxiety-like behavior. CONCLUSIONS: These results suggest that lipid composition, rather than obesity per se, is a major cause of anxiety-like behavior in high-fat diet-induced obesity. Decreased levels of peripheral LPC conjugated with EPA and altered glutamate system in the prefrontal cortex might be involve in the pathophysiology of the behavioral change.

Evaluation of the pharmacokinetics of 2-carba-cyclic phosphatidic acid by liquid chromatography-triple quadrupole mass spectrometry.

Cyclic phosphatidic acid (cPA) is a lysophospholipid mediator that suppresses cancer metastasis and osteoarthritis. It also has neuroprotective roles in diseases such as multiple sclerosis and delayed neuronal death following transient ischemia. In order to take advantage of the properties of cPA for the development of new therapeutic strategies, we have synthesized several cPA derivatives and discovered 2-carba-cPA (2ccPA) as a promising candidate. To develop 2ccPA as a therapeutic agent, we investigated the pharmacokinetic profile of 2ccPA by liquid chromatography-triple quadrupole mass spectrometry in this study. When 2ccPA was administered intraperitoneally to mice at a dose of 1.6 mg/kg, the half-life of 2ccPA in plasma was 16 min. The 2ccPA, dosed intraperitoneally to mice at 16 mg/kg, distributed to each organ including brain at 20 min after dosing. It was found that 2ccPA was stable in neutral or alkaline conditions (e.g., intestine) but unstable in acidic conditions (e.g., stomach). When 2ccPA was orally administrated to rats as a gastro-resistant form using an enterosoluble capsule, plasma 2ccPA levels peaked at 2 h, slowly declined thereafter and persistently detected even at 10 h after administration. Here, we present the findings on the effect of the continuous release of 2ccPA from the capsule to reduce the lysophospholipase D activity and also decrease plasma levels of lysophosphatidic acid in rat. These findings will be useful in further studies for evaluating the application of 2ccPA in several disorders.

Two-carba cyclic phosphatidic acid treatment promotes phenotypic switch from M1 to M2 microglia and prevents behavioral abnormalities in a mouse model of neuropsychiatric systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is an autoimmune disease associated with the production of double-stranded DNA (dsDNA) antibodies and other antibodies that predominantly affects women with a wide range of lesions. Although neuropsychiatric lupus erythematosus (NPSLE), characterized by neuropsychiatric symptoms related to cerebrovascular diseases or depression, ranks high in severity, no specific treatment has been defined. Two-carba cyclic phosphatidic acid (2ccPA), a derivative of cyclic phosphatidic acid, was isolated from the true slime mold Physarum polycephalum in 1992. 2ccPA treatment suppresses neuroinflammation and promotes tissue repair in mouse multiple sclerosis and traumatic brain injury models. In this study, we performed behavioral tests on MRL/lpr mice as an NPSLE model. MRL/lpr mice showed increased depression-like behaviors compared with control mice, which were significantly suppressed by 2ccPA treatment. The expression of CD68, an M1 phenotypic marker of microglia, was significantly elevated in the prefrontal cortex and hippocampus of MRL/lpr mice, which was significantly suppressed by 2ccPA treatment. In contrast, the expression of Arginase1, an M2 phenotypic marker of microglia, was significantly increased by 2ccPA treatment. Compared to control mice, MRL/lpr mice showed higher plasma levels of anti-dsDNA antibodies, which are mainly involved in SLE pathogenesis. 2ccPA treatment decreased these levels in the MRL/lpr mice. These results suggest that 2ccPA treatment suppresses behavioral abnormalities by promoting a microglial phenotypic switch from M1 to M2 in MRL/lpr mice.

2-Carba-lysophosphatidic acid is a novel ß-lysophosphatidic acid analogue with high potential for lysophosphatidic acid receptor activation and autotaxin inhibition.

Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator that, along with its chemically stabilized analogue 2-carba-cyclic phosphatidic acid (2ccPA), induces various biological activities in vitro and in vivo. Although cPA is similar to lysophosphatidic acid (LPA) in structure and synthetic pathway, some of cPA biological functions apparently differ from those reported for LPA. We previously investigated the pharmacokinetic profile of 2ccPA, which was found to be rapidly degraded, especially in acidic conditions, yielding an unidentified compound. Thus, not only cPA but also its degradation compound may contribute to the biological activity of cPA, at least for 2ccPA. In this study, we determined the structure and examined the biological activities of 2-carba-lysophosphatidic acid (2carbaLPA) as a 2ccPA degradation compound, which is a type of ß-LPA analogue. Similar to LPA and cPA, 2carbaLPA induced the phosphorylation of the extracellular signal-regulated kinase and showed potent agonism for all known LPA receptors (LPA1-6) in the transforming growth factor-α (TGFα) shedding assay, in particular for LPA3 and LPA4. 2carbaLPA inhibited the lysophospholipase D activity of autotaxin (ATX) in vitro similar to other cPA analogues, such as 2ccPA, 3-carba-cPA, and 3-carba-LPA (α-LPA analogue). Our study shows that 2carbaLPA is a novel ß-LPA analogue with high potential for the activation of some LPA receptors and ATX inhibition.

Oleic acid is a potent inducer for lipid droplet accumulation through its esterification to glycerol by diacylglycerol acyltransferase in primary cortical astrocytes.

Astrocytes exhibit an important role in neural lipid metabolism for the regulation of energy balance to supply fatty acids (FAs) and ketone bodies to other neural cells. Lipid droplets (LDs) consisting of neutral- and phospho-lipids increase in the brains of patients with neurodegenerative diseases, such as Alzheimer's disease and multiple sclerosis. However, the role of LDs and its lipid source remains largely unexplored. Here, we found that oleic acid (OA) was a potent inducer of astrocytic LD accumulation among various FAs. Lipidomic analysis using liquid chromatography equipped with tandem mass spectrometry revealed that the cellular triacylglycerol and phospholipid compositions in astrocytes during LD accumulation reflected the condition of extracellular FAs. Furthermore, the inhibition of diacylglycerol acyltransferase blocked OA-induced LD accumulation and caused lipotoxicity-induced cell death in astrocytes. The present study demonstrated that the formation of LDs, caused due to the increased extracellular OA, facilitated survival against lipotoxic condition.

Qualitative and quantitative comparison of cyclic phosphatidic acid and its related lipid species in rat serum using hydrophilic interaction liquid chromatography with tandem-mass spectrometry.

Cyclic phosphatidic acid (cPA) is a simple lipid containing a fatty acid attached at the sn-1 position and a cyclic phosphate ring structure at the sn-2 and sn-3 positions of the glycerol backbone. The pharmacological effects of cPA have been demonstrated in several diseases such as cancer and neuropathic pain; however, the composition of the molecular species of cPA in relative to other lipid species in biological samples is still unclear. Recently, hydrophilic interaction liquid chromatography (HILIC) has demonstrated the ability to perform lipidomic analyses of biological samples. In the present study, we developed the quantitative measurement of cPA and its related lipid species, such as lysophosphatidic acid (LPA) and lysophosphatidylcholine (LPC), in rat serum using HILIC equipped with tandem-mass spectrometry (MS/MS). The lipid analysis using HILIC-MS/MS system demonstrated high linearity and reproducibility. The modified Bligh and Dyer method using citric acid was showed high efficiency on the extraction of cPA and LPA without contamination of artificial products. In rat serum, cPA and LPC contained more saturated fatty acids such as palmitic acid and stearic acid than unsaturated fatty acids, whereas LPA and phosphatidylcholine more contained unsaturated fatty acids than saturated fatty acids. The analytical methods for measuring cPA and its related lipid species in the present study will aid the analysis of their metabolism.

2-O-Carba-oleoyl cyclic phosphatidic acid induces glial proliferation through the activation of lysophosphatidic acid receptor.

Lysophosphatidic acid (LPA) and cyclic phosphatidic acid (cPA) are one of the lipid mediators regulating cell proliferation and differentiation through the activation of LPA receptors. An LPA receptor-mediated signal is important for the development of the central nervous system, while it has been demonstrated that LPA caused microglial activation and astroglial dysfunction. Previously, we have reported that cPA and carba analog of cPA, 2-O-carba-cPA (2ccPA), protected neural damage caused by transient ischemia. However, little is known about the target cell of cPA/2ccPA in the central nervous systems. Here, we examined the effect of 2ccPA on glial proliferation and differentiation using the primary astrocytes and oligodendrocyte precursor cells (OPCs) cultures. 2ccPA increased the DNA synthesis of astrocytes and OPCs, but it did not reduce the formazan production in the mitochondria. Further, 2ccPA increased the cell number and cell survival against oxidative stress. The inhibition of LPA receptors by ki16425 abolished 2ccPA-induced DNA synthesis. Extracellular signal-regulated kinase (ERK) was activated by 2ccPA, which contributed to the astroglial DNA synthesis. These results suggest that 2ccPA is a beneficial regulator of glial population through the activation of LPA receptor without reduction of mitochondrial activity.

Quantitative determination of cyclic phosphatidic acid and its carba analog in mouse organs and plasma using LC-MS/MS.

Cyclic phosphatidic acid (cPA), an analog of lysophosphatidic acid, is involved in the regulation of many cellular processes. A sensitive and specific method to quantify the molecular species of cPA is important for studying the physiological and pathophysiological roles of cPA. Here, we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based quantification method for the simultaneous detection of cPA species having various fatty acids (16:0, 18:0, 18:1, and 18:2) as well as 2-carba-cPA, a chemically synthesized analog of cPA. Chromatography was performed using a reversed-phase C18 column. cPA species were detected using a triple quadrupole mass spectrometer. cPA 17:0 was used as an internal standard. Intra- and interday precision values (CV%) were within 10%. The linear range of detection for each cPA species was 0.01 µg/mL to 5 µg/mL, with correlation coefficients of 0.998 or higher. The developed method was applied to the quantification of cPA species in mouse plasma and organs. The concentrations of cPA 16:0, 18:0, and 18:1 were revealed to be significantly reduced in the brains of cuprizone-treated mice, a model of multiple sclerosis, compared with control mice. These findings could be important for understanding the roles of cPA in the neurodegenerative processes associated with multiple sclerosis.