Clinical blood sampling for oxylipin analysis - effect of storage and pneumatic tube transport of blood on free and total oxylipin profile in human plasma and serum

Oxylipin profiling for clinical research: Current status and future perspectives

Oxylipins are potent lipid mediators with increasing interest in clinical research. They are usually measured in systemic circulation and can provide a wealth of information regarding key biological processes such as inflammation, vascular tone, or blood coagulation. Although procedures still require harmonization to generate comparable oxylipin datasets, performing comprehensive profiling of circulating oxylipins in large studies is feasible and no longer restricted by technical barriers. However, it is essential to improve and facilitate the biological interpretation of complex oxylipin profiles to truly leverage their potential in clinical research. This requires regular updating of our knowledge about the metabolism and the mode of action of oxylipins, and consideration of all factors that may influence circulating oxylipin profiles independently of the studied disease or condition. This review aims to provide the readers with updated and necessary information regarding oxylipin metabolism, their different forms in systemic circulation, the current limitations in deducing oxylipin cellular effects from in vitro bioactivity studies, the biological and technical confounding factors needed to consider for a proper interpretation of oxylipin profiles.

A comprehensive UHPLC-MS/MS method for metabolomics profiling of signaling lipids: Markers of oxidative stress, immunity and inflammation

Signaling lipids (SLs) play a crucial role in various signaling pathways, featuring diverse lipid backbone structures. Emerging evidence showing the biological significance and biomedical values of SLs has strongly spurred the advancement of analytical approaches aimed at profiling SLs. Nevertheless, the dramatic differences in endogenous abundances across lipid classes as well as multiple isomers within the same lipid class makes the development of a generic analytical method challenging. A better analytical method that combines comprehensive coverage and high sensitivity is needed to enable us to gain a deeper understanding of the biochemistry of these molecules in health and disease. In this study, we developed a fast and comprehensive targeted ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for profiling SLs. The platform enables analyses of 260 metabolites covering oxylipins (isoprostanes, prostaglandins and other oxidized lipids), free fatty acids, lysophospholipids, sphingoid bases (C16, C18), platelet activating factors (C16, C18), endocannabinoids and bile acids. Various validation parameters including linearity, limit of detection, limit of quantification, extraction recovery, matrix effect, intra-day and inter-day precision were used to characterize this method. Metabolite quantitation was successfully achieved in both NIST Standard Reference Material for human plasma (NIST SRM 1950) and pooled human plasma, with 109 and 144 metabolites quantitated. The quantitation results in NIST SRM 1950 plasma demonstrated good correlations with certified or previously reported values in published literature. This study introduced quantitative data for 37 SLs for the first time. Metabolite concentrations measured in NIST SRM 1950 will serve as essential reference data for facilitating interlaboratory comparisons. The methodology established here will be the cornerstone for in-depth profiling of signaling lipids across diverse biological samples and contexts.

Predictors of upstream inflammation and oxidative stress pathways during early pregnancy

BACKGROUND

Inflammation and oxidative stress are critical to pregnancy, but most human study has focused on downstream, non-causal indicators. Oxylipins are lipid mediators of inflammation and oxidative stress that act through many biological pathways. Our aim was to characterize predictors of circulating oxylipin concentrations based on maternal characteristics.

METHODS

Our study was conducted among 901 singleton pregnancies in the LIFECODES Fetal Growth Study, a nested case-cohort with recruitment from 2007 to 2018. We measured a targeted panel of oxylipins in early pregnancy plasma and urine samples from several biosynthetic pathways, defined by the polyunsaturated fatty acid (PUFA) precursor and enzyme group. We evaluated levels across predictors, including characteristics of participants' pregnancy, socioeconomic determinants, and obstetric and medical history.

RESULTS

Current pregnancy and sociodemographic characteristics were the most important predictors of circulating oxylipins concentrations. Plasma oxylipins were lower and urinary oxylipins higher for participants with a later gestational age at sampling (13-23 weeks), higher prepregnancy BMI (obesity class I, II, or III), Black or Hispanic race and ethnicity, and lower socioeconomic status (younger age, lower education, and uninsured). For example, compared to those with normal or underweight prepregnancy BMI, participants with class III prepregnancy obesity had 45-46% lower plasma epoxy-eicosatrienoic acids, the anti-inflammatory oxylipins produced from arachidonic acid (AA) by cytochrome P450, and had 81% higher urinary 15-series F2-isoprostanes, an indicator of oxidative stress produced from non-enzymatic AA oxidation. Similarly, in urine, Black participants had 92% higher prostaglandin E2 metabolite, a pro-inflammatory oxylipin, and 41% higher 5-series F2-isoprostane, an oxidative stress indicator.

CONCLUSIONS

In this large pregnancy study, we found that circulating levels of oxylipins were different for participants of lower socioeconomic status or of a systematically marginalized racial and ethnic groups. Given associations differed along biosynthetic pathways, results provide insight into etiologic links between maternal predictors and inflammation and oxidative stress.

Oxylipin profiling by LC-ESI-MS/MS in canine serum and plasma to investigate ovulation-specific changes

New biomarkers that are directly associated with canine ovulation would be of value to ensure mating on optimal days of heat. In this study, canine plasma and serum were analyzed with liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) to quantify a broad range of oxylipins for the purpose of developing a method for biomarker discovery studies in canine reproduction. A majority of the 67 oxylipins probed for were detected at comparable levels in both sample types, but more oxylipins at higher concentrations were detected in serum than in plasma. Nine of the oxylipins were detected in a pilot study of serum at levels that significantly differed (p ≤ 0.1) between time-points before (n = 10), during (n = 10) and after (n = 10) ovulation, and might serve as putative biomarkers for canine ovulation. One oxylipin (20-HETE) was significantly altered after adjusting for multiple comparisons. In conclusion, the results showed that the LC-ESI-MS/MS method was suitable for quantification of canine oxylipins, revealing important similarities and differences between plasma and serum profiles as well as preliminary ovulation-specific changes in a subset of the investigated oxylipins.

Development of a quantitative proteomics approach for cyclooxygenases and lipoxygenases in parallel to quantitative oxylipin analysis allowing the comprehensive investigation of the arachidonic acid cascade

Oxylipins derived from the cyclooxygenase (COX) and lipoxygenase (LOX) pathways of the arachidonic acid (ARA) cascade are essential for the regulation of the inflammatory response and many other physiological functions. Comprehensive analytical methods comprised of oxylipin and protein abundance analysis are required to fully understand mechanisms leading to changes within these pathways. Here, we describe the development of a quantitative multi-omics approach combining liquid chromatography tandem mass spectrometry-based targeted oxylipin metabolomics and proteomics. As the first targeted proteomics method to cover these pathways, it enables the quantitative analysis of all human COX (COX-1 and COX-2) and relevant LOX pathway enzymes (5-LOX, 12-LOX, 15-LOX, 15-LOX-2, and FLAP) in parallel to the analysis of 239 oxylipins with our targeted oxylipin metabolomics method from a single sample. The detailed comparison between MRM3 and classical MRM-based detection in proteomics showed increased selectivity for MRM3, while MRM performed better in terms of sensitivity (LLOQ, 16-122 pM vs. 75-840 pM for the same peptides), linear range (up to 1.5-7.4 μM vs. 4-368 nM), and multiplexing capacities. Thus, the MRM mode was more favorable for this pathway analysis. With this sensitive multi-omics approach, we comprehensively characterized oxylipin and protein patterns in the human monocytic cell line THP-1 and differently polarized primary macrophages. Finally, the quantification of changes in protein and oxylipin levels induced by lipopolysaccharide stimulation and pharmaceutical treatment demonstrates its usefulness to study molecular modes of action involved in the modulation of the ARA cascade.

Inflammation and oxidative stress as mediators of the impacts of environmental exposures on human pregnancy: Evidence from oxylipins

Inflammation and oxidative stress play major roles in healthy and pathological pregnancy. Environmental exposure to chemical pollutants may adversely affect maternal and fetal health in pregnancy by dysregulating these critical underlying processes of inflammation and oxidative stress. Oxylipins are bioactive lipids that play a major role in regulating inflammation and increasing lines of evidence point towards an importance in pregnancy. The biosynthetic production of oxylipins requires oxygenation of polyunsaturated fatty acids, which can occur through several well-characterized enzymatic and nonenzymatic pathways. This review describes the state of the science of epidemiologic evidence on oxylipin production in pregnancy and its association with 1) key pregnancy outcomes and 2) environmental exposures. We searched PubMed for studies of pregnancy that measured one or more oxylipin analytes during pregnancy or delivery. We evaluated oxylipin associations with three categories of adverse pregnancy outcomes, including preeclampsia, preterm birth, and fetal growth restriction, along with several categories of environmental pollutants. The majority of studies evaluated one to two oxylipins, most of which focused on oxylipins produced from nonenzymatic processes of oxidative stress. However, an increasing number of recent studies have leveraged technological advancements to profile a large number of oxylipins produced from distinct biosynthetic pathways. Although the literature indicated robust evidence that oxylipins produced via nonenzymatic pathways are associated with pregnancy outcomes and environmental exposures, evidence for enzymatically produced oxylipins showed that associations may differ between biosynthetic pathways. Along with summarizing this evidence, we review promising therapeutic options to regulate oxylipin production and provide a set of recommendations for future epidemiologic studies in these research areas. Further evidence is needed to improve our understanding of how oxylipins may act as key biological mediators for the adverse effects of environmental pollutants on pregnancy outcomes.

Esterified Oxylipins: Do They Matter?

Oxylipins are oxygenated metabolites of fatty acids that share several similar biochemical characteristics and functions to fatty acids including transport and trafficking. Oxylipins are most commonly measured in the non-esterified form which can be found in plasma, free or bound to albumin. The non-esterified form, however, reflects only one of the possible pools of oxylipins and is by far the least abundant circulating form of oxylipins. Further, this fraction cannot reliably be extrapolated to the other, more abundant, esterified pool. In cells too, esterified oxylipins are the most abundant form, but are seldom measured and their potential roles in signaling are not well established. In this review, we examine the current literature on experimental oxylipin measurements to describe the lack in reporting the esterified oxylipin pool. We outline the metabolic and experimental importance of esterified oxylipins using well established roles of fatty acid trafficking in non-esterified fatty acids and in esterified form as components of circulating lipoproteins. Finally, we use mathematical modeling to simulate how exchange between cellular esterified and unesterified pools would affect intracellular signaling.. The explicit inclusion of esterified oxylipins along with the non-esterified pool has the potential to convey a more complete assessment of the metabolic consequences of oxylipin trafficking.

Influence of Trimethylamine N-Oxide on Platelet Activation

Microbiome-derived trimethylamine N-oxide (TMAO) has been associated with platelet hyperreactivity and subsequent atherogenesis. Whether physiological TMAO-levels influence platelet-derived lipid mediators remains unknown. Little is known about pre-analytic factors potentially influencing TMAO concentrations. We aimed at developing a quantitative LC-MS/MS method to investigate in-vivo and in-vitro pre-analytical factors in TMAO analysis to properly assess the proposed activating effect of TMAO on platelets. TMAO, betaine, carnitine, and choline were analyzed by HILIC-ESI-MS/MS within 6 min total run time. Method validation included investigation of reproducibility, recovery, sensitivity, and in-vitro pre-analytical factors. A 24-h monitoring experiment was performed, evaluating in-vivo pre-analytical factors like daytime or diet. Finally, the effects of different TMAO concentrations on platelet activation and corresponding alterations of platelet-derived eicosanoid release were analyzed. The method showed high reproducibility (CVs ≤ 5.3%), good recovery rates (96–98%), and negligible in-vitro pre-analytical effects. The influence of in-vivo pre-analytical factors on TMAO levels was not observable within the applied experimental conditions. We did not find any correlation between TMAO levels and platelet activation at physiological TMAO concentrations, whereas platelet-derived eicosanoids presented activation of the cyclooxygenase and lipoxygenase pathways. In contrast to previously published results, we did not find any indications regarding diet dependency or circadian rhythmicity of TMAO levels. Our results do not support the hypothesis that TMAO increases platelet responsiveness via the release of lipid-mediators.

Metabolite Ratios as Quality Indicators for Pre-Analytical Variation in Serum and EDTA Plasma

In clinical diagnostics and research, blood samples are one of the most frequently used materials. Nevertheless, exploring the chemical composition of human plasma and serum is challenging due to the highly dynamic influence of pre-analytical variation. A prominent example is the variability in pre-centrifugation delay (time-to-centrifugation; TTC). Quality indicators (QI) reflecting sample TTC are of utmost importance in assessing sample history and resulting sample quality, which is essential for accurate diagnostics and conclusive, reproducible research. In the present study, we subjected human blood to varying TTCs at room temperature prior to processing for plasma or serum preparation. Potential sample QIs were identified by Ultra high pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) based metabolite profiling in samples from healthy volunteers (n = 10). Selected QIs were validated by a targeted MS/MS approach in two independent sets of samples from patients (n = 40 and n = 70). In serum, the hypoxanthine/guanosine (HG) and hypoxanthine/inosine (HI) ratios demonstrated high diagnostic performance (Sensitivity/Specificity > 80%) for the discrimination of samples with a TTC > 1 h. We identified several eicosanoids, such as 12-HETE, 15-(S)-HETE, 8-(S)-HETE, 12-oxo-HETE, (±)13-HODE and 12-(S)-HEPE as QIs for a pre-centrifugation delay > 2 h. 12-HETE, 12-oxo-HETE, 8-(S)-HETE, and 12-(S)-HEPE, and the HI- and HG-ratios could be validated in patient samples.

Fatty acid and oxylipin concentration differ markedly between different fetal bovine serums: A cautionary note

Fetal bovine serum (FBS) has been used as a universal supplement in cell culture for more than six decades. This includes the investigation of lipid and lipid mediator formation and biology. Little is known about the (polyunsaturated) fatty acid composition and their oxidation products in FBS. Therefore, we analyzed six different FBS purchased from three different companies regarding their fatty acid and oxylipin concentrations. We found pronounced differences in the fatty acid concentrations. Even two batches of "standardized" FBS batches from one company showed drastic differences (e.g., for eicosapentaenoic acid 5 ± 1 μM vs. 11 ± 1 μM). Oxylipin concentrations also markedly differ between the FBS lots. The highest differences were found for 12-lipoxygenase products (e.g., 12-hydroxyeicosatetraenoic acid free 21-87 nM and total 58-108 nM), probably due to inconsistent serum generation procedures. Our results indicate that for cell culture studies dealing with lipid metabolism, researchers should carefully characterize their used FBS to ensure reliability and reproducibility of study outcomes.

Identifying oxidized lipid mediators as prognostic biomarkers of chronic posttraumatic headache

Chronic posttraumatic headache (PTH) is among the most common and disabling sequelae of traumatic brain injury (TBI). Current PTH treatments are often only partially effective and have problematic side effects. We previously showed in a small randomized trial of patients with chronic nontraumatic headaches that manipulation of dietary fatty acids decreased headache frequency, severity, and pain medication use. Pain reduction was associated with alterations in oxylipins derived from n-3 and n-6 fatty acids, suggesting that oxylipins could potentially mediate clinical pain reduction. The objective of this study was to investigate whether circulating oxylipins measured in the acute setting after TBI could serve as prognostic biomarkers for developing chronic PTH. Participants enrolled in the Traumatic Head Injury Neuroimaging Classification Protocol provided serum within 3 days of TBI and were followed up at 90 days postinjury with a neurobehavioral symptom inventory (NSI) and satisfaction with life survey. Liquid chromatography-tandem mass spectrometry methods profiled 39 oxylipins derived from n-3 docosahexaenoic acid (DHA), and n-6 arachidonic acid and linoleic acid. Statistical analyses assessed the association of oxylipins with headache severity (primary outcome, measured by headache question on NSI) as well as associations between oxylipins and total NSI or satisfaction with life survey scores. Among oxylipins, 4-hydroxy-DHA and 19,20-epoxy-docosapentaenoate (DHA derivatives) were inversely associated with headache severity, and 11-hydroxy-9-epoxy-octadecenoate (a linoleic acid derivative) was positively associated with headache severity. These findings support a potential for DHA-derived oxylipins as prognostic biomarkers for development of chronic PTH.

Plasma oxylipin levels associated with preterm birth in preterm labor✰

INTRODUCTION

Preterm labor is a common clinical problem in obstetrics. Since the majority of women with preterm labor eventually deliver at full term, biomarkers are needed to more accurately predict who will deliver preterm. Oxylipins, given their importance in inflammation regulation, are highly interesting in this respect since labor is an inflammatory process.

METHODS

Eighty women with preterm labor before 34 weeks of gestation were enrolled in a prospective observational multi-center cohort study. Oxylipin levels of 67 analytes in plasma samples were analyzed by liquid chromatography coupled to tandem mass spectrometry.

RESULTS

Twenty-one (26%) of the women delivered before 34 weeks of gestation, and of those women, fourteen delivered within 48 h of admission. Logistic multivariate regression showed that lower levels of 9,10-DiHODE were associated with delivery before 34 weeks of gestation (aOR 0.12 (0.024-0.62)) and within 48 h ((aOR 0.13 (0.019-0.93)). Furthermore, higher levels of 11,12-DiHETrE were associated with delivery before 34 weeks of gestation ((aOR 6.19 (1.17-32.7)) and higher levels of 8-HETE were associated with delivery within 48 h ((aOR 5.01 (1.13-22.14)).

CONCLUSIONS

The oxylipin 9,10-DiHODE may be protective in preterm labor, both for delivery after 34 weeks of gestation and for delivery later than 48 h of admission, whereas 11,12-DiHETrE and 8-HETE display the opposite effect. Larger studies are needed to validate these mediators as biomarkers for prediction of preterm birth following preterm labor.

Collection and Storage of Human Plasma for Measurement of Oxylipins

Oxylipins derived from omega-3 and -6 fatty acids are actively involved in inflammatory and immune processes and play important roles in human disease. However, as the interest in oxylipins increases, questions remain regarding which molecules are detectable in plasma, the best methods of collecting samples, and if molecules are stable during collection and storage. We thereby built upon existing studies by examining the stability of an expanded panel of 90 oxylipins, including specialized pro-resolving lipid mediators (SPMs), in human plasma (n = 5 subjects) during sample collection, processing, and storage at −80 °C. Oxylipins were quantified using liquid chromatography-tandem mass spectrometry (LC/MS/MS). Blood samples collected in ethylenediaminetetraacetic acid (EDTA) or heparin followed by up to 2 h at room temperature prior to processing showed no significant differences in oxylipin concentrations compared to immediately processed samples, including the SPMs lipoxin A4 and resolvin D1. The majority of molecules, including SPMs, remained stable following storage for up to 1 year. However, in support of previous findings, changes were seen in a small subset of oxylipins including 12-HETE, TXB₂, 14-HDHA, and 18-HEPE. Overall, this study showed that accurate measurements of most oxylipins can be obtained from stored EDTA or heparin plasma samples using LC/MS/MS.

Plasma and serum oxylipin, endocannabinoid, bile acid, steroid, fatty acid and nonsteroidal anti-inflammatory drug quantification in a 96-well plate format

The goal of this research was to develop a high-throughput, cost-effective method for metabolic profiling of lipid mediators and hormones involved in the regulation of inflammation and energy metabolism, along with polyunsaturated fatty acids and common over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs). We describe a 96-well plate protein precipitation and filtration procedure for 50 μL of plasma or serum in the presence of 37 deuterated analogs and 2 instrument internal standards. Data is acquired in two back-to-back UPLC-MS/MS analyses using electrospray ionization with positive/negative switching and scheduled multiple reaction monitoring for the determination of 145 compounds, including oxylipins, endocannabinoids and like compounds, bile acids, glucocorticoids, sex steroids, polyunsaturated fatty acids, and 3 NSAIDs. Intra- and inter-batch variability was <25% for >70% of metabolites above the LOQ in both matrices, but higher inter-batch variability was observed for serum oxylipins and some bile acids. Results for NIST Standard Reference Material 1950, compared favorably with the 20 certified metabolite values covered by this assay, and we provide new data for oxylipins, N-acylethanolamides, glucocorticoids, and 17-hydroxy-progesterone in this material. Application to two independent cohorts of elderly men and women showed the routine detection of 86 metabolites, identified fasting state influences on essential fatty acid-derived oxylipins, N-acylethanolamides and conjugated bile acids, identified rare presence of high and low testosterone levels and the presence of NSAIDs in ∼10% of these populations. The described method appears valuable for investigations in large cohort studies to provide insight into metabolic cross-talk between the array of mediators assessed here.