Effects of diets enriched in linoleic acid and its peroxidation products on brain fatty acids, oxylipins, and aldehydes in mice

ALDH2 polymorphism and myocardial infarction: From alcohol metabolism to redox regulation

Acute myocardial infarction (AMI) remains a leading cause of death worldwide. Increased formation of reactive oxygen species (ROS) during the early reperfusion phase is thought to trigger lipid peroxidation and disrupt redox homeostasis, leading to myocardial injury. Whilst the mitochondrial enzyme aldehyde dehydrogenase 2 (ALDH2) is chiefly recognised for its central role in ethanol metabolism, substantial experimental evidence suggests an additional cardioprotective role for ALDH2 independent of alcohol intake, which mitigates myocardial injury by detoxifying breakdown products of lipid peroxidation including the reactive aldehydes, malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE). Epidemiological evidence suggests that an ALDH2 mutant variant with reduced activity that is highly prevalent in the East Asian population increases AMI risk. Additional studies have uncovered a strong association between coronary heart disease and this ALDH2 mutant variant. It appears this enzyme polymorphism (in particular, in ALDH2*2/2 carriers) has the potential to have wide-ranging effects on thiol reactivity, redox tone and therefore numerous redox-related signaling processes, resilience of the heart to cope with lifestyle-related and environmental stressors, and the ability of the whole body to achieve redox balance. In this review, we summarize the journey of ALDH2 from a mitochondrial reductase linked to alcohol metabolism, via pre-clinical studies aimed at stimulating ALDH2 activity to reduce myocardial injury to clinical evidence for its protective role in the heart.

Characterization of oxylipins in Antarctic krill oil (Euphausia superba) during storage based on RPLC-MS/MS analysis

Antarctic krill oil (AKO) is rich in polyunsaturated fatty acids (PUFAs), but is prone to oxidative degradation, resulting in the formation of oxylipins, which compromise AKO quality. Herein, we used reversed-phase-high performance liquid chromatography-tandem mass spectrometry (RPLC-MS/MS) to perform qualitative and semi-quantitative analyses of oxylipins in AKO during storage. A total of 27 oxylipins were identified. A notable decrease in epoxy oxylipins (from 41.8 % to 26.9 % of the total oxylipins) was observed, whereas the content of dihydro oxylipins initially increased and then decreased with 48 h, as a pivotal point for AKO quality decline during storage. We suspected that the ratio of dihydroxyl and epoxy oxylipins could be a novel oxidative index to evaluate the oxidation of AKO. Statistical analysis allowed the identification of five oxylipins which showed unique correlations with various indexes. The findings discussed herein provide important new insights into mechanisms of oxidation occurring in AKO during storage.

Excessive linoleic acid induces muscle oxidative stress through 5-lipoxygenase-dependent peroxidation

Oxidative stress in muscles is closely related to the occurrence of insulin resistance, muscle weakness and atrophy, age-related sarcopenia, and cancer. Aldehydes, a primary oxidation intermediate of polyunsaturated fatty acids, have been proven to be an important trigger for oxidative stress. However, the potential role of linoleic acid (LA) as a donor for volatile aldehydes to trigger oxidative stress has not been reported. Here, we reported that excessive dietary LA caused muscle redox imbalance and volatile aldehydes containing hexanal, 2-hexenal, and nonanal were the main metabolites leading to oxidative stress. Importantly, we identified 5-lipoxygenase (5-LOX) as a key enzyme mediating LA peroxidation in crustaceans for the first time. The inhibition of 5-LOX significantly suppressed the content of aldehydes produced by excessive LA. Mechanistically, the activation of the cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) pathway facilitated the translocation of 5-LOX from the nucleus to the cytoplasm, where 5-LOX oxidized LA, leading to oxidative stress through the generation of aldehydes. This study suggests that 5-LOX is a potential target to prevent the production of harmful aldehydes.

Intraperitoneally injected d11-11(12)-epoxyeicosatrienoic acid is rapidly incorporated and esterified within rat plasma and peripheral tissues but not the brain

Epoxyeicosatrienoic acids (EpETrEs) are bioactive lipid mediators of arachidonic acid cytochrome P450 oxidation. In vivo, the free (unbound) form of EpETrEs regulate multiple processes including blood flow, angiogenesis and inflammation resolution. Free EpETrEs are thought to rapidly degrade via soluble epoxide hydrolase (sEH); yet, in many tissues, the majority of EpETrEs are esterified to complex lipids (e.g. phospholipids) suggesting that esterification may play a major role in regulating free, bioactive EpETrE levels. This hypothesis was tested by quantifying the metabolism of intraperitoneally injected free d11-11(12)-Epoxyeicosatrienoic acid (d11-11(12)-EpETrE) in male and female rats. Plasma and tissues (liver, adipose and brain) were obtained 3 to 4 min later and assayed for d11-11(12)-EpETrE and its sEH metabolite, d11-11,12-dihydroxyeicosatrienoic acid (d11-11,12-diHETrE) in both the free and esterified lipid fractions. In both males and females, the majority of injected tracer was recovered in liver followed by plasma and adipose. No tracer was detected in the brain, indicating that brain levels are maintained by endogenous synthesis from precursor fatty acids. In plasma, liver, and adipose, the majority (>54 %) of d11-11(12)-EpETrE was found esterified to phospholipids or neutral lipids (triglycerides and cholesteryl esters). sEH-derived d11-11,12-diHETrE was not detected in plasma or tissues, suggesting negligible conversion within the 3-4 min period post tracer injection. This study shows that esterification is the main pathway regulating free 11(12)-EpETrE levels in vivo.

Ability of high fat diet to induce liver pathology correlates with the level of linoleic acid and Vitamin E in the diet

Increased uptake of fat, such as through the ingestion of high fat diet (HFD), can lead to fatty liver diseases and metabolic syndrome. It is not clear whether certain fatty acids may be more pathogenic than others to the liver. Linoleic acid (LA) is the most abundant polyunsaturated fatty acid in the Western diet and its excessive consumption can lead to increased lipid peroxidation. We hypothesized that a high level of LA in HFD will contribute significantly to the hepatic steatosis and injury, whereas vitamin E (VIT-E) may reverse the effects from LA by inhibiting lipid peroxidation. To test this hypothesis, we fed mice with the following diets for 20 weeks: a standard low-fat diet (CHOW), HFD with a low level of LA (LOW-LA, 1% of energy from LA), HFD with a high level of LA (HI-LA, 8% of energy from LA), or HI-LA diet with VIT-E supplement (HI-LA + VIT-E). We found that the HI-LA diet resulted in more body weight gain, larger adipocyte area, and higher serum levels of triglycerides (TG) and free fatty acids (FFA) relative to the CHOW and LOW-LA diets. In mice fed with the HI-LA diet, severer hepatic steatosis was seen with higher levels of hepatic TG and FFA. Expression of genes related to lipid metabolism was altered in the liver by HI-LA diet, including fibroblast growth factor 21 (Fgf21), cluster of differentiation 36 (Cd36), stearoyl-CoA desaturase 1 (Scd1), and acyl-CoA oxidase 1 (Acox1). Liver injury, inflammation and fibrotic response were all enhanced in mice fed with the HI-LA diet when compared with the LOW-LA diet. Notably, addition of VIT-E supplement, which restores the proper VIT-E/PUFA ratio, significantly reduced the detrimental effects of the high level of LA. Taken together, our results suggest that a high level of LA and a low ratio of VIT-E/PUFA in HFD can contribute significantly to metabolic abnormalities and hepatic injury.

A high sucrose diet modifies brain oxylipins in a sex-dependent manner

BACKGROUND

Oxylipins have been implicated in many biological processes and diseases. Dysregulation of cerebral lipid homeostasis and altered lipid metabolites have been associated with the onset and progression of dementia. Although most dietary interventions have focused on modulation of dietary fats, the impact of a high sucrose diet on the brain oxylipin profile is unknown.

METHODS

Male and female C57BL/6J mice were fed a high sucrose diet (HSD, 34%) in comparison to a control low sucrose diet (LSD, 12%) for 12 weeks beginning at 20 weeks of age. The profile of 53 free oxylipins was then measured in brain by ultra-high performance liquid chromatography tandem mass spectrometry. Serum glucose and insulin were measured enzymatically. We first assessed whether there were any effects of the diet on the brain oxylipin profile, then assessed for sex differences.

RESULTS

There were no differences in fasting serum glucose between the sexes for mice fed a HSD or in fasting serum insulin levels for mice on either diet. The HSD altered the brain oxylipin profile in both sexes in distinctly different patterns: there was a reduction in three oxylipins (by 47-61%) and an increase in one oxylipin (16%) all downstream of lipoxygenase enzymes in males and a reduction in eight oxylipins (by 14-94%) mostly downstream of cyclooxygenase activity in females. 9-oxo-ODE and 6-trans-LTB4 were most influential in the separation of the oxylipin profiles by diet in male mice, whereas 5-HEPE and 12-HEPE were most influential in the separation by diet in female mice. Oxylipins 9‑hydroxy-eicosatetraenoic acid (HETE), 11-HETE, and 15-HETE were higher in the brains of females, regardless of diet.

CONCLUSION

A HSD substantially changes brain oxylipins in a distinctly sexually dimorphic manner. Results are discussed in terms of potential mechanisms and links to metabolic disease. Sex and diet effects on brain oxylipin composition may provide future targets for the management of neuroinflammatory diseases, such as dementia.

A Review of Oxylipins in Alzheimer's Disease and Related Dementias (ADRD): Potential Therapeutic Targets for the Modulation of Vascular Tone and Inflammation

There is now a convincing body of evidence from observational studies that the majority of modifiable Alzheimer's disease and related dementia (ADRD) risk factors are vascular in nature. In addition, the co-existence of cerebrovascular disease with AD is more common than AD alone, and conditions resulting in brain ischemia likely promote detrimental effects of AD pathology. Oxylipins are a class of bioactive lipid mediators derived from the oxidation of long-chain polyunsaturated fatty acids (PUFAs) which act as modulators of both vascular tone and inflammation. In vascular cognitive impairment (VCI), there is emerging evidence that oxylipins may have both protective and detrimental effects on brain structure, cognitive performance, and disease progression. In this review, we focus on oxylipin relationships with vascular and inflammatory risk factors in human studies and animal models pertinent to ADRD. In addition, we discuss future research directions with the potential to impact the trajectory of ADRD risk and disease progression.

Maternal and Neonatal Polyunsaturated Fatty Acid Intake and Risk of Neurodevelopmental Impairment in Premature Infants

The N3 and N6 long chain polyunsaturated fatty acids (LCPUFA) docosahexaenoic acid (DHA) and arachidonic acid (AA) are essential for proper neurodevelopment in early life. These fatty acids are passed from mother to infant via the placenta, accreting into fetal tissues such as brain and adipose tissue. Placental transfer of LCPUFA is highest in the final trimester, but this transfer is abruptly severed with premature birth. As such, efforts have been made to supplement the post-natal feed of premature infants with LCPUFA to improve neurodevelopmental outcomes. This narrative review analyzes the current body of evidence pertinent to neurodevelopmental outcomes after LCPUFA supplementation in prematurely born infants, which was identified via the reference lists of systematic and narrative reviews and PubMed search engine results. This review finds that, while the evidence is weakened by heterogeneity, it may be seen that feed comprising 0.3% DHA and 0.6% AA is associated with more positive neurodevelopmental outcomes than LCPUFA-deplete feed. While no new RCTs have been performed since the most recent Cochrane meta-analysis in 2016, this narrative review provides a wider commentary; the wider effects of LCPUFA supplementation in prematurely born infants, the physiology of LCPUFA accretion into preterm tissues, and the physiological effects of LCPUFA that affect neurodevelopment. We also discuss the roles of maternal LCPUFA status as a modifiable factor affecting the risk of preterm birth and infant neurodevelopmental outcomes. To better understand the role of LCPUFAs in infant neurodevelopment, future study designs must consider absolute and relative availabilities of all LCPUFA species and incorporate the LCPUFA status of both mother and infant in pre- and postnatal periods.

Why Have the Benefits of DHA Not Been Borne Out in the Treatment and Prevention of Alzheimer's Disease? A Narrative Review Focused on DHA Metabolism and Adipose Tissue

Docosahexaenoic acid (DHA), an omega-3 fatty acid rich in seafood, is linked to Alzheimer's Disease via strong epidemiological and pre-clinical evidence, yet fish oil or other DHA supplementation has not consistently shown benefit to the prevention or treatment of Alzheimer's Disease. Furthermore, autopsy studies of Alzheimer's Disease brain show variable DHA status, demonstrating that the relationship between DHA and neurodegeneration is complex and not fully understood. Recently, it has been suggested that the forms of DHA in the diet and plasma have specific metabolic fates that may affect brain uptake; however, the effect of DHA form on brain uptake is less pronounced in studies of longer duration. One major confounder of studies relating dietary DHA and Alzheimer's Disease may be that adipose tissue acts as a long-term depot of DHA for the brain, but this is poorly understood in the context of neurodegeneration. Future work is required to develop biomarkers of brain DHA and better understand DHA-based therapies in the setting of altered brain DHA uptake to help determine whether brain DHA should remain an important target in the prevention of Alzheimer's Disease.

Sex-Specific Differences in Lysine, 3-Hydroxybutyric Acid and Acetic Acid in Offspring Exposed to Maternal and Postnatal High Linoleic Acid Diet, Independent of Diet

BACKGROUND

Linoleic acid (LA) is an essential polyunsaturated fatty acid (PUFA) that is required for foetal growth and development. Excess intake of LA can be detrimental for metabolic health due to its pro-inflammatory properties; however, the effect of a diet high in LA on offspring metabolites is unknown. In this study, we aimed to determine the role of maternal or postnatal high linoleic acid (HLA) diet on plasma metabolites in adult offspring.

METHODS

Female Wistar Kyoto (WKY) rats were fed with either low LA (LLA) or HLA diet for 10 weeks prior to conception and during gestation/lactation. Offspring were weaned at postnatal day 25 (PN25), treated with either LLA or HLA diets and sacrificed at PN180. Metabolite analysis was performed in plasma samples using Nuclear Magnetic Resonance.

RESULTS

Maternal and postnatal HLA diet did not alter plasma metabolites in male and female adult offspring. There was no specific clustering among different treatment groups as demonstrated by principal component analysis. Interestingly, there was clustering among male and female offspring independent of maternal and postnatal dietary intervention. Lysine was higher in female offspring, while 3-hydroxybutyric acid and acetic acid were significantly higher in male offspring.

CONCLUSION

In summary, maternal or postnatal HLA diet did not alter the plasma metabolites in the adult rat offspring; however, differences in metabolites between male and female offspring occurred independently of dietary intervention.

Feeding mice a diet high in oxidized linoleic acid metabolites does not alter liver oxylipin concentrations

The oxidation of dietary linoleic acid (LA) produces oxidized LA metabolites (OXLAMs) known to regulate multiple signaling pathways in vivo. Recently, we reported that feeding OXLAMs to mice resulted in liver inflammation and apoptosis. However, it is not known whether this is due to a direct effect of OXLAMs accumulating in the liver, or to their degradation into bioactive shorter chain molecules (e.g. aldehydes) that can provoke inflammation and related cascades. To address this question, mice were fed a low or high LA diet low in OXLAMs, or a low LA diet supplemented with OXLAMs from heated corn oil (high OXLAM diet). Unesterified oxidized fatty acids (i.e. oxylipins), including OXLAMs, were measured in liver after 8 weeks of dietary intervention using ultra-high pressure liquid chromatography coupled to tandem mass-spectrometry. The high OXLAM diet did not alter liver oxylipin concentrations compared to the low LA diet low in OXLAMs. Significant increases in several omega-6 derived oxylipins and reductions in omega-3 derived oxylipins were observed in the high LA dietary group compared to the low LA group. Our findings suggest that dietary OXLAMs do not accumulate in liver, and likely exert pro-inflammatory and pro-apoptotic effects via downstream secondary metabolites.

Dietary alteration of n-3 and n-6 fatty acids for headache reduction in adults with migraine: randomized controlled trial

OBJECTIVE

To determine whether dietary interventions that increase n-3 fatty acids with and without reduction in n-6 linoleic acid can alter circulating lipid mediators implicated in headache pathogenesis, and decrease headache in adults with migraine.

DESIGN

Three arm, parallel group, randomized, modified double blind, controlled trial.

SETTING

Ambulatory, academic medical center in the United States over 16 weeks.

PARTICIPANTS

182 participants (88% women, mean age 38 years) with migraines on 5-20 days per month (67% met criteria for chronic migraine).

INTERVENTIONS

Three diets designed with eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and linoleic acid altered as controlled variables: H3 diet (n=61)-increase EPA+DHA to 1.5 g/day and maintain linoleic acid at around 7% of energy; H3-L6 diet (n=61)-increase n-3 EPA+DHA to 1.5 g/day and decrease linoleic acid to ≤1.8% of energy; control diet (n=60)-maintain EPA+DHA at <150 mg/day and linoleic acid at around 7% of energy. All participants received foods accounting for two thirds of daily food energy and continued usual care.

MAIN OUTCOME MEASURES

The primary endpoints (week 16) were the antinociceptive mediator 17-hydroxydocosahexaenoic acid (17-HDHA) in blood and the headache impact test (HIT-6), a six item questionnaire assessing headache impact on quality of life. Headache frequency was assessed daily with an electronic diary.

RESULTS

In intention-to-treat analyses (n=182), the H3-L6 and H3 diets increased circulating 17-HDHA (log ng/mL) compared with the control diet (baseline-adjusted mean difference 0.6, 95% confidence interval 0.2 to 0.9; 0.7, 0.4 to 1.1, respectively). The observed improvement in HIT-6 scores in the H3-L6 and H3 groups was not statistically significant (-1.6, -4.2 to 1.0, and -1.5, -4.2 to 1.2, respectively). Compared with the control diet, the H3-L6 and H3 diets decreased total headache hours per day (-1.7, -2.5 to -0.9, and -1.3, -2.1 to -0.5, respectively), moderate to severe headache hours per day (-0.8, -1.2 to -0.4, and -0.7, -1.1 to -0.3, respectively), and headache days per month (-4.0, -5.2 to -2.7, and -2.0, -3.3 to -0.7, respectively). The H3-L6 diet decreased headache days per month more than the H3 diet (-2.0, -3.2 to -0.8), suggesting additional benefit from lowering dietary linoleic acid. The H3-L6 and H3 diets altered n-3 and n-6 fatty acids and several of their nociceptive oxylipin derivatives in plasma, serum, erythrocytes or immune cells, but did not alter classic headache mediators calcitonin gene related peptide and prostaglandin E2.

CONCLUSIONS

The H3-L6 and H3 interventions altered bioactive mediators implicated in headache pathogenesis and decreased frequency and severity of headaches, but did not significantly improve quality of life.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02012790.

Magnesium-L-threonate alleviate colonic inflammation and memory impairment in chronic-plus-binge alcohol feeding mice

Magnesium-l-threonate (MgT) is considered a food supplement. Alcohol-mediated diseases (AMD) are accompanied by inflammation and memory impairment. The purpose of this study is to investigate the function of MgT in AMD. Hence, chronic-plus-binge alcohol feeding mice model and multiply bioinformatics analysis were performed. Consequently, the expression of inflammatory cytokines downregulated, while the activities of antioxidases decreased in serum, colon, and brain. Interestingly, MgT relieved gut barrier dysfunction and reshaped microbiota. The relative abundance of Akkermansia, Odoribacter, and Blautia were increased, while that of Alloprevotella and Clostridium were decreased. Metabolic analysis elucidated amino acids and glutamate metabolism were enhanced in MgT-treated mice. Furthermore, morris water maze test confirmed memory ability was enhanced. Inflammation cytokines were negatively correlated with Blautia, and Akkermansia. Collectively, MgT relieved inflammation in gut-brain axis of mice, reshaped gut microbiota, and enhanced the amino acids and glutamate metabolism. MgT may be used as a food supplement to prevent inflammation and memory impairment induced by alcohol abuse.

Exposure to oxidized soybean oil induces mammary mitochondrial injury in lactating rats and alters the intestinal barrier function of progeny

Similar to other food contaminants, dietary oxidized soybean oil (OSO) is also a toxic xenobiotic for animal and human nutrition. This research evaluated the effects of maternal OSO exposure during lactation on mammary mitochondrial injury and intestinal barrier of sucking progeny. Twenty-four female adult SD rats were fed a fresh soybean oil (FSO) homozygous diet (7%) or an OSO homozygous diet (7%) during lactation. On day 21 of lactation, upregulated mRNA expression of Sirt3 and PRDX3 and downregulated mRNA expression of Mfn2 were observed in mammary tissues in the OSO group compared to the control group (P < 0.05). Maternal OSO consumption increased the FasL transcriptional level in the mammary glands of rat dams (P < 0.05), while the mRNA expression of Bax, Bcl-2, Caspase3, and Fas was not different from that in the control group (P > 0.05). OSO enhanced the Nrf2 transcriptional level and decreased the expression of Keap1 and PPARα in mammary tissues (P < 0.05). In addition, the contents of CAT, MDA, SOD were not affected by dietary OSO (P > 0.05), while the concentration of H2O2 was significantly decreased in the OSO-treated mammary glands of rat dams (P < 0.05). Maternal OSO exposure during lactation did not affect the organ coefficients of pups (P > 0.05). However, maternal OSO consumption influenced the intestinal tight junction protein expression of progeny (P < 0.05). In summary, the present study demonstrated that dietary OSO may aggravate mammary injury and mitochondria dysfunction, but the OSO-induced damage was self-alleviating via the promotion of Sirt3 and PRDX3 expression and further scavenging of oxidative products.

Method optimization of oxylipin hydrolysis in nonprocessed bovine milk indicates that the majority of oxylipins are esterified

The oxidation of polyunsaturated fatty acids produces bioactive primary oxidation products known as oxylipins. In many biological matrices, the majority of oxylipins are bound (i.e. esterified), and a relatively small proportion (<10%) exists in the free form. The present study tested whether this extends to bovine milk following method evaluation of various extraction and base hydrolysis protocols for measuring bound oxylipins. Free (unbound) oxylipins were also measured. Folch extraction followed by sodium carbonate hydrolysis in the presence of methanol containing 0.1% of acetic acid and 0.1% of butylated hydroxytoluene resulted in greater oxylipin concentrations and better surrogate standard recoveries compared to other methods that did not involve Folch extraction or the addition of methanol with hydrolysis base. Sodium hydroxide was better than sodium carbonate in hydrolyzing bound oxylipins under the same conditions. Milk analysis of oxylipins with mass-spectrometry following Folch extraction and sodium hydroxide hydrolysis revealed that 95% of oxylipins in bovine milk were esterified. Most of the detected oxylipins were derived from linoleic acid, which accounted for 92 and 88% of oxylipins in the free and esterified pools, respectively. These results demonstrate that the majority of bovine milk oxylipins are bound, and that linoleic-acid derived metabolites are the most abundant oxylipin species in free and bound lipid pools. Additional studies are needed to understand the role of different oxylipin pools in both calf and human nutrition. PRACTICAL APPLICATION: A method involving Folch lipid extraction and sodium hydroxide hydrolysis was validated for esterified oxylipin measurements in bovine milk. Application of the method revealed that the majority (∼95%) of oxylipins in bovine milk were bound. Linoleic-acid derived oxylipins were the most abundant species in both bound and free milk fractions (88-92%). The results highlight the presence of a new pool of oxidized lipids in milk, potentially involved in modifying its sensory and nutritional properties.

Linoleic acid-derived 13-hydroxyoctadecadienoic acid is absorbed and incorporated into rat tissues

Linoleic acid (LNA)-derived 13-hydroxyoctadecadienoic acid (13-HODE) is a bioactive lipid mediator that regulates multiple signaling processes in vivo. 13-HODE is also produced when LNA is oxidized during food processing. However, the absorption and incorporation kinetics of dietary 13-HODE into tissues is not known. The present study measured unesterified d4-13-HODE plasma bioavailability and incorporation into rat liver, adipose, heart and brain following gavage or intravenous (IV) injection (n = 3 per group). Mass spectrometry analysis revealed that d4-13-HODE was absorbed within 20 min of gavage, and continued to incorporate into plasma esterified lipid fractions throughout the 90 min monitoring period (incorporation half-life of 71 min). Following IV injection, unesterified d4-13-HODE was rapidly eliminated from plasma with a half-life of 1 min. Analysis of tracer incorporation kinetics into rat tissues following IV injection or gavage revealed that the esterified tracer preferentially incorporated into liver, adipose and heart compared to unesterified d4-13-HODE. No tracer was detected in the brain. This study demonstrates that dietary 13-HODE is absorbed, and incorporated into peripheral tissues from esterified plasma lipid pools. Understanding the chronic effects of dietary 13-HODE exposure on peripheral tissue physiology and metabolism merits future investigation.

Sample Preparation Methods for Lipidomics Approaches Used in Studies of Obesity

Obesity is associated with alterations in the composition and amounts of lipids. Lipids have over 1.7 million representatives. Most lipid groups differ in composition, properties and chemical structure. These small molecules control various metabolic pathways, determine the metabolism of other compounds and are substrates for the syntheses of different derivatives. Recently, lipidomics has become an important branch of medical/clinical sciences similar to proteomics and genomics. Due to the much higher lipid accumulation in obese patients and many alterations in the compositions of various groups of lipids, the methods used for sample preparations for lipidomic studies of samples from obese subjects sometimes have to be modified. Appropriate sample preparation methods allow for the identification of a wide range of analytes by advanced analytical methods, including mass spectrometry. This is especially the case in studies with obese subjects, as the amounts of some lipids are much higher, others are present in trace amounts, and obese subjects have some specific alterations of the lipid profile. As a result, it is best to use a method previously tested on samples from obese subjects. However, most of these methods can be also used in healthy, nonobese subjects or patients with other dyslipidemias. This review is an overview of sample preparation methods for analysis as one of the major critical steps in the overall analytical procedure.

Influence of Lipoxygenase Inhibition on Glioblastoma Cell Biology

BACKGROUND

The relationship between glioblastoma (GBM) and fatty acid metabolism could be the key to elucidate more effective therapeutic targets. 15-lipoxygenase-1 (15-LOX), a linolenic acid and arachidonic acid metabolizing enzyme, induces both pro- and antitumorigenic effects in different cancer types. Its role in glioma activity has not yet been clearly described. The objective of this study was to identify the influence of 15-LOX and its metabolites on glioblastoma cell activity.

METHODS

GBM cell lines were examined using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to identify 15-LOX metabolites. GBM cells treated with 15-LOX metabolites, 13-hydroxyoctadecadeinoic acid (HODE) and 9-HODE, and two 15-LOX inhibitors (luteolin and nordihydroguaiaretic acid) were also examined. Dose response/viability curves, RT-PCRs, flow cytometry, migration assays, and zymograms were performed to analyze GBM growth, migration, and invasion.

RESULTS

Higher quantities of 13-HODE were observed in five GBM cell lines compared to other lipids analyzed. Both 13-HODE and 9-HODE increased cell count in U87MG. 15-LOX inhibition decreased migration and increased cell cycle arrest in the G2/M phase.

CONCLUSION

15-LOX and its linoleic acid (LA)-derived metabolites exercise a protumorigenic influence on GBM cells in vitro. Elevated endogenous levels of 13-HODE called attention to the relationship between linoleic acid metabolism and GBM cell activity.

Importance of the Role of ω-3 and ω-6 Polyunsaturated Fatty Acids in the Progression of Brain Cancer

Brain cancer is one of the most malignant types of cancer in both children and adults. Brain cancer patients tend to have a poor prognosis and a high rate of mortality. Additionally, 20-40% of all other types of cancer can develop brain metastasis. Numerous pieces of evidence suggest that omega-3-polyunsaturated fatty acids (ω-PUFAs) could potentially be used in the prevention and therapy of several types of cancer. PUFAs and oxylipins are fundamental in preserving physiological events in the nervous system; it is, therefore, necessary to maintain a certain ratio of ω-3 to ω-6 for normal nervous system function. Alterations in PUFAs signaling are involved in the development of various pathologies of the nervous system, including cancer. It is well established that an omega-6-polyunsaturated fatty acid (ω-6 PUFA)-rich diet has a pro-tumoral effect, whereas the consumption of an ω-3 rich diet has an anti-tumoral effect. This review aims to offer a better understanding of brain cancer and PUFAs and to discuss the role and impact of PUFAs on the development of different types of brain cancer. Considering the difficulty of antitumor drugs in crossing the blood-brain barrier, the therapeutic role of ω-3/ω-6 PUFAs against brain cancer would be a good alternative to consider. We highlight our current understanding of the role of PUFAs and its metabolites (oxylipins) in different brain tumors, proliferation, apoptosis, invasion, angiogenesis, and immunosuppression by focusing on recent research in vitro and in vivo.

A single meal has the potential to alter brain oxylipin content

Our objective was to determine whether consumption of a single meal has the potential to alter brain oxylipin content. We examined the cerebrum of mice fed a single high-fat/high-sucrose Western meal or a low-fat/low-sucrose control meal, as well as fasted mice. We found no changes in fatty acid composition of cerebrum across the groups. The cerebral oxylipin profile of mice fed a Western meal is distinct from the profile of mice fed a low-fat/low-sucrose meal. Cerebral gene expression of cyclooxygenase 1, cyclooxygenase 2, and epoxide hydrolase 1 were elevated in Western meal-fed mice compared to low-fat/low-sucrose meal-fed mice. Mice that consumed either meal had lower gene expression of cytochrome P450, family 2, subfamily j, polypeptide 12 than fasted mice. Our data in this hypothesis-generating study indicates that the composition of a single meal has the potential to alter brain oxylipins and the gene expression of the enzymes responsible for their production.

Plasma oxylipins and unesterified precursor fatty acids are altered by DHA supplementation in pregnancy: Can they help predict risk of preterm birth?

Oxidized lipids derived from omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids, collectively known as oxylipins, are bioactive signaling molecules that play diverse roles in human health and disease. Supplementation with n-3 docosahexaenoic acid (DHA) during pregnancy has been reported to decrease the risk of preterm birth in singleton pregnancies, which may be due to effects of DHA supplementation on oxylipins or their precursor n-6 and n-3 fatty acids. There is only limited understanding of the levels and trajectory of changes in plasma oxylipins during pregnancy, effects of DHA supplementation on oxylipins and unesterified fatty acids, and whether and how oxylipins and their unesterified precursor fatty acids influence preterm birth. In the present study we used liquid chromatography-tandem mass spectrometry to profile oxylipins and their precursor fatty acids in the unesterified pool using plasma samples collected from a subset of pregnant Australian women who participated in the ORIP (Omega-3 fats to Reduce the Incidence of Prematurity) study. ORIP is a large randomized controlled trial testing whether daily supplementation with n-3 DHA can reduce the incidence of early preterm birth compared to control. Plasma was collected at study entry (≈pregnancy week 14) and again at ≈week 24, in a subgroup of 48 ORIP participants-12 cases with spontaneous preterm (<37 weeks) birth and 36 matched controls with spontaneous term (≥40 weeks) birth. In the combined preterm and term pregnancies, we observed that in the control group without DHA supplementation unesterified AA and AA-derived oxylipins 12-HETE, 15-HETE and TXB2 declined between weeks 14-24 of pregnancy. Compared to control, DHA supplementation increased unesterified DHA, EPA, and AA, DHA-derived 4-HDHA, 10-HDHA and 19,20-EpDPA, and AA-derived 12-HETE at 24 weeks. In exploratory analysis independent of DHA supplementation, participants with concentrations above the median for 5-lipoxygenase derivatives of AA (5-HETE, Odds Ratio (OR) 8.2; p = 0.014) or DHA (4-HDHA, OR 8.0; p = 0.015) at 14 weeks, or unesterified AA (OR 5.1; p = 0.038) at 24 weeks had higher risk of spontaneous preterm birth. The hypothesis that 5-lipoxygenase-derived oxylipins and unesterified AA could serve as mechanism-based biomarkers predicting spontaneous preterm birth should be evaluated in larger, adequately powered studies.

α-Linolenic acid-enriched butter attenuated high fat diet-induced insulin resistance and inflammation by promoting bioconversion of n-3 PUFA and subsequent oxylipin formation

α-Linolenic acid (ALA) is an essential fatty acid and the precursor for long-chain n-3 PUFA. However, biosynthesis of n-3 PUFA is limited in a Western diet likely due to an overabundance of n-6 PUFA. We hypothesized that dietary reduction of n-6/n-3 PUFA ratio is sufficient to promote the biosynthesis of long-chain n-3 PUFA, leading to an attenuation of high fat (HF) diet-induced obesity and inflammation. C57BL/6 J mice were fed a HF diet from ALA-enriched butter (n3Bu, n-6/n-3=1) in comparison with isocaloric HF diets from either conventional butter lacking both ALA and LA (Bu, n-6/n-3=6), or margarine containing a similar amount of ALA and abundant LA (Ma, n-6/n-3=6). Targeted lipidomic analyses revealed that n3Bu feeding promoted the bioconversion of long-chain n-3 PUFA and their oxygenated metabolites (oxylipins) derived from ALA and EPA. The n3Bu supplementation attenuated hepatic TG accumulation and adipose tissue inflammation, resulting in improved insulin sensitivity. Decreased inflammation by n3Bu feeding was attributed to the suppression of NF-κB activation and M1 macrophage polarization. Collectively, our work suggests that dietary reduction of the n-6/n-3 PUFA ratio, as well as total n-3 PUFA consumed, is a crucial determinant that facilitates n-3 PUFA biosynthesis and subsequent lipidomic modifications, thereby conferring metabolic benefits against obesity-induced inflammation and insulin resistance.

Linoleic acid-good or bad for the brain?

Increased intake of omega-6 rich plant oils such as soybean and corn oil over the past few decades has inadvertently tripled the amount of n-6 linoleic acid (LA, 18:2n-6) in the diet. Although LA is nutritionally “essential”, very little is known about how it affects the brain when present in excess. This review provides an overview on the metabolism of LA by the brain and the effects of excess dietary LA intake on brain function. Pre-clinical evidence suggests that excess dietary LA increases the brain’s vulnerability to inflammation and likely acts via its oxidized metabolites. In humans, excess maternal LA intake has been linked to atypical neurodevelopment, but underlying mechanisms are unknown. It is concluded that excess dietary LA may adversely affect the brain. The potential neuroprotective role of reducing dietary LA merits clinical evaluation in future studies.

Linoleic acid-derived metabolites constitute the majority of oxylipins in the rat pup brain and stimulate axonal growth in primary rat cortical neuron-glia co-cultures in a sex-dependent manner

In adult rats, omega-6 linoleic acid (LA, 18:2n-6) serves as a precursor to oxidized LA metabolites (OXLAMs) known to regulate multiple signaling processes in the brain. However, little is known regarding the levels or role(s) of LA and its metabolites during brain development. To address this gap, fatty acids within various brain lipid pools, and their oxidized metabolites (oxylipins) were quantified in brains from 1-day-old male and female pups using gas chromatography and liquid chromatography coupled to tandem mass spectrometry, respectively. Primary neuron-glia co-cultures derived from postnatal day 0-1 male and female rat neocortex were exposed to vehicle (0.1% ethanol), LA, the OXLAM 13-hydroxyoctadecadienoic acid (13-HODE), or prostaglandin E2 at 10-1000 nM for 48 h to test their effects on neuronal morphology. In both male and female pups, LA accounted for 1-3% of fatty acids detected in brain phospholipids and cholesteryl esters. It was not detected in triacylglycerols, and free fatty acids. Unesterified OXLAMs constituted 47-53% of measured unesterified oxylipins in males and females (vs. ~5-7% reported in adult rat brain). Of these, 13-HODE was the most abundant, accounting for 30-33% of measured OXLAMs. Brain fatty acid and OXLAM concentrations did not differ between sexes. LA and 13-HODE significantly increased axonal outgrowth. Separate analyses of cultures derived from male versus female pups revealed that LA at 1, 50, and 1000 nM, significantly increased axonal outgrowth in female but not male cortical neurons, whereas 13-HODE at 100 nM significantly increased axonal outgrowth in male but not female cortical neurons. prostaglandin E2 did not alter neuronal outgrowth in either sex. This study demonstrates that OXLAMs constitute the majority of unesterified oxylipins in the developing rat brain despite low relative abundance of their LA precursor, and highlights a novel role of LA and 13-HODE in differentially influencing neuronal morphogenesis in the developing male and female brain.

Epoxy Fatty Acids Are Promising Targets for Treatment of Pain, Cardiovascular Disease and Other Indications Characterized by Mitochondrial Dysfunction, Endoplasmic Stress and Inflammation

Bioactive lipid mediators resulting from the metabolism of polyunsaturated fatty acids (PUFA) are controlled by many pathways that regulate the levels of these mediators and maintain homeostasis to prevent disease. PUFA metabolism is driven primarily through three pathways. Two pathways, the cyclooxygenase (COX) and lipoxygenase (LO) enzymatic pathways, form metabolites that are mostly inflammatory, while the third route of metabolism results from the oxidation by the cytochrome P450 enzymes to form hydroxylated PUFA and epoxide metabolites. These epoxygenated fatty acids (EpFA) demonstrate largely anti-inflammatory and beneficial properties, in contrast to the other metabolites formed from the degradation of PUFA. Dysregulation of these systems often leads to chronic disease. Pharmaceutical targets of disease focus on preventing the formation of inflammatory metabolites from the COX and LO pathways, while maintaining the EpFA and increasing their concentration in the body is seen as beneficial to treating and preventing disease. The soluble epoxide hydrolase (sEH) is the major route of metabolism of EpFA. Inhibiting its activity increases concentrations of beneficial EpFA, and often disease states correlate to mutations in the sEH enzyme that increase its activity and decrease the concentrations of EpFA in the body. Recent approaches to increasing EpFA include synthetic mimics that replicate biological activity of EpFA while preventing their metabolism, while other approaches focus on developing small molecule inhibitors to the sEH. Increasing EpFA concentrations in the body has demonstrated multiple beneficial effects in treating many diseases, including inflammatory and painful conditions, cardiovascular disease, neurological and disease of the central nervous system. Demonstration of efficacy in so many disease states can be explained by the fundamental mechanism that EpFA have of maintaining healthy microvasculature and preventing mitochondrial and endoplasmic reticulum stress. While there are no FDA approved methods that target the sEH or other enzymes responsible for metabolizing EpFA, current clinical efforts to test for efficacy by increasing EpFA that include inhibiting the sEH or administration of EpFA mimics that block metabolism are in progress.

The effects of n-6 polyunsaturated fatty acid deprivation on the inflammatory gene response to lipopolysaccharide in the mouse hippocampus

Background

Neuroinflammation is thought to contribute to psychiatric and neurological disorders such as major depression and Alzheimer’s disease (AD). N-6 polyunsaturated fatty acids (PUFA) and molecules derived from them, including linoleic acid- and arachidonic acid-derived lipid mediators, are known to have pro-inflammatory properties in the periphery; however, this has yet to be tested in the brain. Lowering the consumption of n-6 PUFA is associated with a decreased risk of depression and AD in human observational studies. The purpose of this study was to investigate the inflammation-modulating effects of lowering dietary n-6 PUFA in the mouse hippocampus.

Methods

C57BL/6 male mice were fed either an n-6 PUFA deprived (2% of total fatty acids) or an n-6 PUFA adequate (23% of total fatty acids) diet from weaning to 12 weeks of age. Animals then underwent intracerebroventricular surgery, in which lipopolysaccharide (LPS) was injected into the left lateral ventricle of the brain. Hippocampi were collected at baseline and following LPS administration (1, 3, 7, and 14 days). A microarray (n = 3 per group) was used to identify candidate genes and results were validated by real-time PCR in a separate cohort of animals (n = 5–8 per group).

Results

Mice administered with LPS had significantly increased Gene Ontology categories associated with inflammation and immune responses. These effects were independent of changes in gene expression in any diet group. Results were validated for the effect of LPS treatment on astrocyte, cytokine, and chemokine markers, as well as some results of the diets on Ifrd2 and Mfsd2a expression.

Conclusions

LPS administration increases pro-inflammatory and lipid-metabolizing gene expression in the mouse hippocampus. An n-6 PUFA deprived diet modulated inflammatory gene expression by both increasing and decreasing inflammatory gene expression, without impairing the resolution of neuroinflammation following LPS administration.