Effect of fish oil on levels of R- and S-enantiomers of 5-, 12-, and 15-hydroxyeicosatetraenoic acids in mouse colonic mucosa

Sex- and enantiospecific differences in the formation rate of hydroxyeicosatetraenoic acids in rat organs

Hydroxyeicosatetraenoic acids (HETEs) are hydroxylated arachidonic acid (AA) metabolites that are classified into midchain, subterminal, and terminal HETEs. Hydroxylation results in the formation of R and S enantiomers for each HETE, except for 20-HETE. HETEs have multiple physiological and pathological effects. Several studies have demonstrated sex-specific differences in AA metabolism in different organs. In this study, microsomes from the heart, liver, kidney, lung, intestine, and brain of adult male and female Sprague-Dawley rats were isolated and incubated with AA. Thereafter, the enantiomers of all HETEs were analyzed by liquid chromatography-tandem mass spectrometry. We found significant sex- and enantiospecific differences in the formation levels of different HETEs in all organs. The majority of HETEs, especially midchain HETEs and 20-HETE, showed significantly higher formation rates in male organs. In the liver, the R enantiomer of several HETEs showed a higher formation rate than the corresponding S enantiomer (e.g., 8-, 9-, and 16-HETE). On the other hand, the brain and small intestine demonstrated a higher abundance of the S enantiomer. 19(S)-HETE was more abundant than 19(R)-HETE in all organs except the kidney. Elucidating sex-specific differences in HETE levels provides interesting insights into their physiological and pathophysiological roles and their possible implications for different diseases.

The enantioselective separation and quantitation of the hydroxy-metabolites of arachidonic acid by liquid chromatography - tandem mass spectrometry

Arachidonic acid (AA) is a polyunsaturated fatty acid with a structure of 20:4(ω-6). Cytochrome P450s (CYPs) metabolize AA to several regioisomers and enantiomers of hydroxyeicosatetraenoic acids (HETEs). The hydroxy-metabolites (HETEs) exist as enantiomers in the biological system. The chiral assays developed for HETEs are so far limited to a few assays reported for midchain HETEs. The developed method is capable of quantitative analysis for midchain, subterminal HETE enantiomers, and terminal HETEs in microsomes. The peak area or height ratios were linear over concentrations ranging (0.01 -0.6 µg/ml) with r2 > 0.99. The intra-run percent error and coefficient of variation (CV) were ≤ ± 12 %. The inter-run percent error and coefficient of variation (CV)were ≤ ± 13 %, and ≤ 15 %, respectively. The matrix effect for the assay was also within the acceptable limit (≤ ± 15 %). The recovery of HETE metabolites ranged from 70 % to 115 %. The method showed a reliable and robust performance for chiral analysis of cytochrome P450-mediated HETE metabolites.

The Quantitative Profiling of Oxylipins from Arachidonic Acid by LC-MS/MS in Feces at Birth 3 Days and 21 Days of Piglets

Oxylipins (also called eicosanoids) are enzymatically or nonenzymatically generated by oxidation of arachidonic acid (ARA) and are major mediators of ARA effects in the body. Previous studies demonstrated the importance of ARA in infant growth, brain development, immune response, and health. With the developments in lipidomic methodologies, it is important for exploring more ARA-deprived oxylipins to better understand the physiological functions of ARA. The concentrations of oxylipins in feces were determined from days 3 to 21 postnatally of suckling piglets in vivo. Feces were collected at two critical time points of the suckling piglets (3d and 21d after birth) and about 48 oxylipins were analyzed by using a target metabolomics approach based on Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). Here, 21 oxylipins were derived from ARA, and 11 differential oxylipins (Log2|fold change| ≥ 1.0) at birth 3d and 21d were identified. Particularly, 12-HETE was more abundant in feces at birth 3 days rather than 21 days. Considering that 12-HETE was a racemic mixture of stereoisomers containing the S and R enantiomers, we further detected the concentrations of 12(S)-HETE and 12(R)-HETE between the two time points by chiral LC-MS/MS analysis. There was no significant difference in the concentrations of 12(S)-HETE and 12(R)-HETE. It was showed that ARA - derived oxylipins might be related to the physiological changes of piglets during growing. Our results provided new information for describing the physiological changes of the piglets over the suckling period.

Enantioselective metabolomics by liquid chromatography-mass spectrometry

Metabolomics strives to capture the entirety of the metabolites in a biological system by comprehensive analysis, often by liquid chromatography hyphenated to mass spectrometry. A particular challenge thereby is the differentiation of structural isomers. Common achiral targeted and untargeted assays do not distinguish between enantiomers. This may lead to information loss. An increasing number of publications demonstrate that the enantiomeric ratio of certain metabolites can be meaningful biomarkers of certain diseases emphasizing the importance of introducing enantioselective analytical procedures in metabolomics. In this work, the state-of-the-art in the field of LC-MS based metabolomics is summarized with focus on developments in the recent decade. Methodologies, tagging strategies, workflows and general concepts are outlined. Selected biological applications in which enantioselective metabolomics has documented its usefulness are briefly discussed. In general, targeted enantioselective metabolomics assays are often based on a direct approach using chiral stationary phases (CSP) with polysaccharide derivatives, macrocyclic antibiotics, chiral crown ethers, chiral ion exchangers, donor-acceptor phases as chiral selectors. Rarely, these targeted assays focus on more than 20 analytes and usually are restricted to a certain metabolite class. In a variety of cases, pre-column derivatization of metabolites has been performed, especially for amino acids, to improve separation and detection sensitivity. Triple quadrupole instruments are the detection methods of first choice in targeted assays. Here, issues like matrix effect, absence of blank matrix impair accuracy of results. In selected applications, multiple heart cutting 2D-LC (RP followed by chiral separation) has been pursued to overcome this problem and alleviate bias due to interferences. Non-targeted assays, on the other hand, are based on indirect approach involving tagging with a chiral derivatizing agent (CDA). Besides classical CDAs numerous innovative reagents and workflows have been proposed and are discussed. Thereby, a critical issue for the accuracy is often neglected, viz. the validation of the enantiomeric impurity in the CDA. The majority of applications focus on amino acids, hydroxy acids, oxidized fatty acids and oxylipins. Some potential clinical applications are highlighted.

Methods of the Analysis of Oxylipins in Biological Samples

Oxylipins are derivatives of polyunsaturated fatty acids and due to their important and diverse functions in the body, they have become a popular subject of studies. The main challenge for researchers is their low stability and often very low concentration in samples. Therefore, in recent years there have been developments in the extraction and analysis methods of oxylipins. New approaches in extraction methods were described in our previous review. In turn, the old analysis methods have been replaced by new approaches based on mass spectrometry (MS) coupled with liquid chromatography (LC) and gas chromatography (GC), and the best of these methods allow hundreds of oxylipins to be quantitatively identified. This review presents comparative and comprehensive information on the progress of various methods used by various authors to achieve the best results in the analysis of oxylipins in biological samples.

Increases in Colonic Bacterial Diversity after ω-3 Fatty Acid Supplementation Predict Decreased Colonic Prostaglandin E2 Concentrations in Healthy Adults

BACKGROUND

The intestinal microbiome is an important determinant of inflammatory balance in the colon that may affect response to dietary agents.

OBJECTIVE

This is a secondary analysis of a clinical trial, the Fish Oil Study, to determine whether interindividual differences in colonic bacteria are associated with variability in the reduction of colonic prostaglandin E2 (PGE2) concentrations after personalized supplementation with ω-3 (n-3) fatty acids.

METHODS

Forty-seven healthy adults (17 men, 30 women, ages 26-75 y) provided biopsy samples of colonic mucosa and luminal stool brushings before and after personalized ω-3 fatty acid supplementation that was based on blood fatty acid responses. Samples were analyzed using 16S ribosomal RNA sequencing. The data analyses focused on changes in bacterial community diversity. Linear regression was used to evaluate factors that predict a reduction in colonic PGE2.

RESULTS

At baseline, increased bacterial diversity, as measured by the Shannon and Inverse Simpson indexes in both biopsy and luminal brushing samples, was positively correlated with dietary fiber intakes and negatively correlated with fat intakes. Dietary supplementation with ω-3 fatty acids increased the Yue and Clayton community dis-similarity index between the microbiome in luminal brushings and colon biopsy samples post-supplementation (P = 0.015). In addition, there was a small group of individuals with relatively high Prevotella abundance who were resistant to the anti-inflammatory effects of ω-3 fatty acid supplementation. In linear regression analyses, increases in diversity of the bacteria in the luminal brushing samples, but not in the biopsy samples, were significant predictors of lower colonic PGE2 concentrations post-supplementation in models that included baseline PGE2, baseline body mass index, and changes in colonic eicosapentaenoic acid-to-arachidonic acid ratios. The changes in bacterial diversity contributed to 6-8% of the interindividual variance in change in colonic PGE2 (P = 0.001).

CONCLUSIONS

Dietary supplementation with ω-3 fatty acids had little effect on intestinal bacteria in healthy humans; however, an increase in diversity in the luminal brushings significantly predicted reductions in colonic PGE2. This trial was registered at www.clinicaltrials.gov as NCT01860352.

Higher baseline expression of the PTGS2 gene and greater decreases in total colonic fatty acid content predict greater decreases in colonic prostaglandin-E2 concentrations after dietary supplementation with ω-3 fatty acids

This study evaluated whether mRNA expression of major genes regulating formation of prostaglandin (PG)E2 in the colon and colonic fatty acid concentrations are associated with the reduction in colonic mucosal PGE2 after dietary supplementation with omega-3 (ω-3) fatty acids. Supplementation with ω-3 fatty acids was done for 12 weeks using personalized dosing that was expected to reduce colonic PGE2 by 50%. In stepwise linear regression models, the ω-3 fatty acid dose and baseline BMI explained 16.1% of the inter-individual variability in the fold change of colonic PGE2 post-supplementation. Increases in mRNA gene expression after supplementation were, however, modest and were not associated with changes in PGE2. When baseline expression of PTGS1, PTGS2 and HPGD genes was included in the linear regression model containing dose and BMI, only PTGS2, the gene coding for the inducible form cyclooxygenase, was a significant predictor. Higher relative expression of PTGS2 predicted greater decreases in colonic PGE2, accounting for an additional 13.6% of the inter-individual variance. In the final step of the regression model, greater decreases in total colonic fatty acid concentrations predicted greater decreases in colonic PGE2, contributing to an additional 18.7% of the variance. Overall, baseline BMI, baseline expression of PTGS2 and changes in colonic total fatty acids together accounted for 48% of the inter-individual variability in the change in colonic PGE2. This is consistent with biochemical data showing that fatty acids which are not substrates for cyclooxygenases can activate cyclooxygenase-2 allosterically. Further clinical trials are needed to elucidate the factors that regulate the fatty acid milieu of the human colon and how this interacts with key lipid metabolizing enzymes. Given the central role of PGE2 in colon carcinogenesis, these pathways may also impact on colon cancer prevention by other dietary and pharmacological approaches.

The Anti-inflammatory Effect of Personalized Omega-3 Fatty Acid Dosing for Reducing Prostaglandin E2 in the Colonic Mucosa Is Attenuated in Obesity

This clinical trial developed a personalized dosing model for reducing prostaglandin E₂ (PGE₂) in colonic mucosa using ω-3 fatty acid supplementation. The model utilized serum eicosapentaenoic acid (EPA, ω-3):arachidonic acid (AA, ω-6) ratios as biomarkers of colonic mucosal PGE₂ concentration. Normal human volunteers were given low and high ω-3 fatty acid test doses for 2 weeks. This established a slope and intercept of the line for dose versus serum EPA:AA ratio in each individual. The slope and intercept was utilized to calculate a personalized target dose that was given for 12 weeks. This target dose was calculated on the basis of a model, initially derived from lean rodents, showing a log-linear relationship between serum EPA:AA ratios and colonic mucosal PGE₂ reduction. Bayesian methods allowed addition of human data to the rodent model as the trial progressed. The dosing model aimed to achieve a serum EPA:AA ratio that is associated with a 50% reduction in colonic PGE₂ Mean colonic mucosal PGE₂ concentrations were 6.55 ng/mg protein (SD, 5.78) before any supplementation and 3.59 ng/mg protein (SD, 3.29) after 12 weeks of target dosing. In secondary analyses, the decreases in PGE₂ were significantly attenuated in overweight and obese participants. This occurred despite a higher target dose for the obese versus normal weight participants, as generated by the pharmacodynamic predictive model. Large decreases also were observed in 12-hydroxyicosatetraenoic acids, and PGE₃ increased substantially. Future biomarker-driven dosing models for cancer prevention therefore should consider energy balance as well as overall eicosanoid homeostasis in normal tissue. Cancer Prev Res; 10(12); 729-37. ©2017 AACR.

Effects of fish oil supplementation on prostaglandins in normal and tumor colon tissue: modulation by the lipogenic phenotype of colon tumors

Dietary fish oils have potential for prevention of colon cancer, and yet the mechanisms of action in normal and tumor colon tissues are not well defined. Here we evaluated the impact of the colonic fatty acid milieu on the formation of prostaglandins and other eicosanoids. Distal tumors in rats were chemically induced to model inflammatory colonic carcinogenesis. After 21 weeks of feeding with either a fish oil diet containing an eicosapentaenoic acid/ω-6 fatty acid ratio of 0.4 or a Western fat diet, the relationships between colon fatty acids and prostaglandin E₂ (PGE₂) concentrations were evaluated. PGE₂ is a key proinflammatory mediator in the colon tightly linked with the initiation and progression of colon cancer. The fish oil vs. the Western fat diet resulted in reduced total fatty acid concentrations in serum but not in colon. In the colon, the effects of the fish oil on fatty acids differed in normal and tumor tissue. There were distinct lipodomic patterns consistent with a lipogenic phenotype in tumors. In tumor tissue, the eicosapentaenoic acid/arachidonic acid ratio, cyclooxygenase-2 expression and the mole percent of saturated fatty acids were significant predictors of inter-animal variability in colon PGE₂ after accounting for diet. In normal tissues from either control rats or carcinogen-treated rats, only diet was a significant predictor of colon PGE₂. These results show that the fatty acid milieu can modulate the efficacy of dietary fish oils for colon cancer prevention, and this could extend to other preventive agents that function by reducing inflammatory stress.

Gas chromatography-mass spectrometry analysis of effects of dietary fish oil on total fatty acid composition in mouse skin

Altering the fatty acid (FA) composition in the skin by dietary fish oil could provide therapeutic benefits. Although it has been shown that fish oil supplementation enhances EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) abundance in the skin, comprehensive skin FA profiling is needed. We established a gas chromatography-mass spectrometry method, which allows precise quantification of FA profile using small (<24 mm² for mice and <12 mm² for humans) skin specimens that can be readily obtained from live mice and humans. We determined mouse skin FA composition after 2, 4 and 8 weeks of consuming a control diet or a diet supplemented with fish oil. Fish oil markedly enhanced EPA and DHA in mouse skin within 2 weeks, and this increase plateaued after 4 weeks. The FA composition in mouse skin was different from that of serum, indicating that skin has homeostatic control of FA metabolism. Mice fed the control diet designed to simulate Western human diet displayed similar skin FA composition as that of humans. The present study presents a validated method for FA quantification that is needed to investigate the mechanisms of actions of dietary treatments in both mouse and human skin.

Biomarkers for personalizing omega-3 fatty acid dosing

Prostaglandin E2 (PGE2) has been linked to a higher risk of colorectal cancer. PGE2 in colon tissue can be reduced by increasing dietary eicosapentaenoic acid (EPA). The dose-dependent relationships between dietary EPA, serum EPA:arachidonate (AA) ratio, urinary PGE2 metabolites, and colonic eicosanoids were evaluated to develop biomarkers for prediction of colonic PGE2. Male rats were fed diets containing EPA:ω6 fatty acid ratios of 0, 0.1, 0.2, 0.4, or 0.6 for 5 weeks. Increasing the dietary EPA:ω6 fatty acid ratio increased EPA:AA ratios in serum and in the proximal, transverse, and distal colon (P < 0.001). The urinary PGE2 metabolite was reduced (P = 0.006). EPA-rich diets reduced colonic tissue PGE2 concentrations by 58% to 66% and increased PGE3 by 19- to 28-fold. Other AA-derived eicosanoids were reduced by 35% to 83%. The changes were not linear, with the largest changes in eicosanoids observed with the lower doses. A mathematical model predicts colonic tissue eicosanoids from the EPA:AA ratio in serum and the EPA dose. Every 10% increase in serum EPA:AA was associated with a 2% decrease in the (geometric) mean of PGE2 in the distal colon. These mathematical relationships can now be applied to individualized EPA dosing in clinical trials.

Liquid chromatography-tandem mass spectrometry analysis of eicosanoids and related compounds in cell models

Enzyme- and free radical-catalyzed oxidation of polyunsaturated fatty acids (PUFAs) produces the eicosanoids, docosanoids and octadecanoids. This large family of potent bioactive lipids is involved in many biochemical and signaling pathways which are implicated in physiological and pathophysiological processes and can be viable therapeutic targets. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) offers selectivity, sensitivity, robustness and high resolution and is able to analyze a large number of eicosanoids in biological samples in a short time. The present article reviews and discusses reported LC-MS/MS methods and the results obtained from their application in cell models. Reliable analytical outcomes are critically important for understanding physiological and pathophysiological cellular processes, such as inflammation, diseases with inflammatory components (e.g., cardiovascular disease, diabetes, metabolic syndrome), as well as cancer. Reported findings obtained by using the LC-MS/MS methodology in cell systems may have important predictive as well as nutritional and pharmacological implications. We conclude that the LC-MS/MS methodology is a versatile and reliable analytical tool for the simultaneous analysis of multiple PUFA-derived metabolites including the eicosanoids in cell culture samples at concentrations on the pM/nM threshold, i.e. at baseline and after stimulation.

Liquid chromatography-tandem mass spectrometry for the analysis of eicosanoids and related lipids in human biological matrices: a review

Today, there is an increasing number of liquid chromatography tandem-mass spectrometric (LC-MS/MS) methods for the analysis of eicosanoids and related lipids in biological matrices. An overview of currently applied LC-MS/MS methods is given with attention to sample preparation strategies, chromatographic separation including ultra high performance liquid chromatography (UHPLC) and chiral separation, as well as to mass spectrometric detection using multiple reacting monitoring (MRM). Further, the application in recent clinical research is reviewed with focus on preanalytical aspects prior to LC-MS/MS analysis as well as applications in major diseases of Western civilization including respiratory diseases, diabetes, cancer, liver diseases, atherosclerosis, and neurovascular diseases.

Dietary linoleic acid and α-linolenic acid differentially affect renal oxylipins and phospholipid fatty acids in diet-induced obese rats

Analysis of oxylipins derived from fatty acids may provide insight into the biological effects of dietary lipids beyond their effects on tissue fatty acid profiles. We have previously observed that diets with higher amounts of α-linolenic acid (ALA; 18:3n3) are associated with reduced obesity-related glomerulopathy (ORG). Therefore, to examine the renal oxylipin profile, the effects of dietary linoleic acid (LA; 18:2n6) and ALA on oxylipins and renal phospholipid fatty acid composition, and the relationship between oxylipins and ORG, diet-induced obese rats displaying ORG were fed 8 different diets for 8 wk as follows (oil/oil = combination of two oils) [shown as ALA/LA (in g) per 100 g oil]: canola/flax (20/18), canola (8/18), soy (9/53), high-oleic canola/canola (5/16), high-oleic canola (2/15), lard/soy (1/8), and safflower (0.2/73). Targeted lipidomic analysis by HPLC-tandem mass spectrometry revealed that LA and ALA oxylipins comprised 60% of the total renal oxylipin profile examined. Of the >60 oxylipins screened, only those derived either directly or indirectly from ALA were associated with less glomerulomegaly, indicative of reduced ORG progression. Both the amount and ratio of dietary LA and ALA influenced renal polyunsaturated fatty acids (PUFAs); in contrast, only fatty acid amount altered oxylipins derived from these fatty acids, but there was no apparent competition by LA or ALA on their formation. Dietary LA incorporation into renal phospholipids was higher than for ALA, but ALA oxylipin:ALA ratios were higher than the analogous LA ratios for select lipoxygenase reactions. This indicates that the effect of dietary ALA on renal oxylipins exceeded what was reflected in renal PUFA composition. In conclusion, dietary LA and ALA have differential effects on renal oxylipins and PUFAs, and ALA-derived oxylipins are associated with renoprotection in this model of ORG.

Quantitative metabolic profiling of lipid mediators

Lipids are heterogeneous biological molecules that possess multiple physiological roles including cell structure, homeostasis, and restoration of tissue functionality during and after inflammation. Lipid metabolism constitutes a network of pathways that are related at multiple biosynthetic hubs. Disregulation of lipid metabolism can lead to pathophysiological effects and multiple lipid mediators have been described to be involved in physiological processes, (e.g. inflammation). Accordingly, a thorough description of these pathways may shed light on putative relations in multiple complex diseases, including chronic obstructive pulmonary disease, asthma, Alzheimer's disease, multiple sclerosis, obesity, and cancer. Due to the structural complexity of lipids and the low abundance of many lipid mediators, mass spectrometry is the most commonly employed method for analysis. However, multiple challenges remain in the efforts to analyze every lipid subfamily. In this review, the biological role of sphingolipids, glycerolipids, oxylipins (e.g. eicosanoids), endocannabinoids, and N-acylethanolamines in relation to health and disease and the state-of-the-art analyses are summarized. The characterization and understanding of these pathways will increase our ability to examine for interrelations among lipid pathways and improve the knowledge of biological mechanisms in health and disease.

Differential contribution of lipoxygenase isozymes to nigrostriatal vulnerability

The 5- and 12/15-lipoxygenase (LOX) isozymes have been implicated to contribute to disease development in CNS disorders such as Alzheimer's disease. These LOX isozymes are distinct in function, with differential effects on neuroinflammation, and the impact of the distinct isozymes in the pathogenesis of Parkinson's disease has not as yet been evaluated. To determine whether the isozymes contribute differently to nigrostriatal vulnerability, the effects of 5- and 12/15-LOX deficiency on dopaminergic tone under naïve and toxicant-challenged conditions were tested. In naïve mice deficient in 5-LOX expression, a modest but significant reduction (18.0% reduction vs. wildtype (WT)) in striatal dopamine (DA) was detected (n=6-8 per genotype). A concomitant decline in striatal tyrosine hydroxylase (TH) enzyme was also revealed in null 5-LOX vs. WT mice (26.2%); however, no changes in levels of DA or TH immunoreactivity were observed in null 12/15-LOX vs. WT mice. When challenged with the selective dopaminergic toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), WT mice showed a marked reduction in DA (31.9%) and robust astrocytic and microglial activation as compared to saline-treated animals. In contrast, null 5-LOX littermates demonstrated no significant striatal DA depletion or astrogliosis (as noted by Western blot analyses for glial acidic fibrillary protein (GFAP) immunoreactivity). In naïve null 12/15-LOX mice, no significant change in striatal DA values was observed compared to WT, and following MPTP treatment, the transgenics revealed striatal DA reduction similar to the challenged WT mice. Taken together, these data provide the first evidence that: (i) LOX isozymes are involved in the maintenance of normal dopaminergic function in the striatum and (ii) the 5- and 12/15-LOX isozymes contribute differentially to striatal vulnerability in response to neurotoxicant challenge.