The Divergent Immunomodulatory Effects of Short Chain Fatty Acids and Medium Chain Fatty Acids

Fatty acids are derived from diet and fermentative processes by the intestinal flora. Two to five carbon chain fatty acids, termed short chain fatty acids (SCFA) are increasingly recognized to play a role in intestinal homeostasis. However, the characteristics of slightly longer 6 to 10 carbon, medium chain fatty acids (MCFA), derived primarily from diet, are less understood. Here, we demonstrated that SCFA and MCFA have divergent immunomodulatory propensities. SCFA down-attenuated host pro-inflammatory IL-1β, IL-6, and TNFα response predominantly through the TLR4 pathway, whereas MCFA augmented inflammation through TLR2. Butyric (C4) and decanoic (C10) acid displayed most potent modulatory effects within the SCFA and MCFA, respectively. Reduction in TRAF3, IRF3 and TRAF6 expression were observed with butyric acid. Decanoic acid induced up-regulation of GPR84 and PPARγ and altered HIF-1α/HIF-2α ratio. These variant immune characteristics of the fatty acids which differ by just several carbon atoms may be attributable to their origins, with SCFA being primarily endogenous and playing a physiological role, and MCFA exogenously from the diet.     

Gut Microbiota and Short Chain Fatty Acids: Implications in Glucose Homeostasis

Gut microbiota encompasses a wide variety of commensal microorganisms consisting of trillions of bacteria, fungi, and viruses. This microbial population coexists in symbiosis with the host, and related metabolites have profound effects on human health. In this respect, gut microbiota plays a pivotal role in the regulation of metabolic, endocrine, and immune functions. Bacterial metabolites include the short chain fatty acids (SCFAs) acetate (C2), propionate (C3), and butyrate (C4), which are the most abundant SCFAs in the human body and the most abundant anions in the colon. SCFAs are made from fermentation of dietary fiber and resistant starch in the gut. They modulate several metabolic pathways and are involved in obesity, insulin resistance, and type 2 diabetes. Thus, diet might influence gut microbiota composition and activity, SCFAs production, and metabolic effects. In this narrative review, we discuss the relevant research focusing on the relationship between gut microbiota, SCFAs, and glucose metabolism.     

Role of Short Chain Fatty Acids and Apolipoproteins in the Regulation of Eosinophilia-Associated Diseases

Eosinophils are key components of our host defense and potent effectors in allergic and inflammatory diseases. Once recruited to the inflammatory site, eosinophils release their cytotoxic granule proteins as well as cytokines and lipid mediators, contributing to parasite clearance but also to exacerbation of inflammation and tissue damage. However, eosinophils have recently been shown to play an important homeostatic role in different tissues under steady state. Despite the tremendous progress in the treatment of eosinophilic disorders with the implementation of biologics, there is an unmet need for novel therapies that specifically target the cytotoxic effector functions of eosinophils without completely depleting this multifunctional immune cell type. Recent studies have uncovered several endogenous molecules that decrease eosinophil migration and activation. These include short chain fatty acids (SCFAs) such as butyrate, which are produced in large quantities in the gastrointestinal tract by commensal bacteria and enter the systemic circulation. In addition, high-density lipoprotein-associated anti-inflammatory apolipoproteins have recently been shown to attenuate eosinophil migration and activation. Here, we focus on the anti-pathogenic properties of SCFAs and apolipoproteins on eosinophil effector function and provide insights into the potential use of SCFAs and apolipoproteins (and their mimetics) as effective agents to combat eosinophilic inflammation.     

Dietary Monounsaturated Fatty Acids but not Saturated Fatty Acids Preserve the Insulin Signaling Pathway via IRS-1/PI3K in Rat Skeletal Muscle

Saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) show different effects on the development of insulin resistance. In this study, we compared the effect of dietary SFA and MUFA on the insulin signaling pathway in the skeletal muscle of a type 2 diabetic animal model. Twenty-nine-week-old male Otsuka Long-Evans Tokushima fatty (OLETF) rats were randomly divided into three groups and fed one of the following diets for 3 weeks; a normal chow diet, an SFA (lard oil) enriched or a MUFA (olive oil) enriched high-fat diet. The vastus lateralis muscle was used for analyses. Insulin tolerance test showed improved insulin sensitivity in rats fed the MUFA diet, as compared to those fed the SFA diet (p < 0.001). The SFA diet reduced IRS-1 expression and phosphorylated PI3K levels in skeletal muscle, as compared with a chow diet (p < 0.001, respectively). On the contrary, muscle IRS-2 expression and phosphorylated ERK1/2 was significantly increased in rats fed the SFA diet (p < 0.001, respectively). Membrane translocation of glucose transporter type 4 decreased in the skeletal muscle of rats fed the SFA diet, as compared to those fed a chow diet (p < 0.001). These changes in insulin signaling pathway in skeletal muscle were not observed in rats fed the MUFA diet. In conclusion, the beneficial effect of dietary MUFA on insulin sensitivity is associated with a conserved IRS-1/PI3K insulin signaling pathway which was altered by dietary SFA.     

Effects of Chain Length of Saturated Fatty Acids on Plasma Total,LDL- and HDL-Cholesterol Levels

We conducted two clinical studies to examine the effects of diets high in stearic acid and lauric + myristic acid on plasma lipids and lipoproteins of healthy young men. In the first study subjects (n = 15) were fed whole food diets high in cocoa butter, butter, olive oil and soybean oil. In the second study, subjects were fed diets very high in saturated fatty acids (> 20% of calories) that were high in either stearic acid (from cocoa butter or milk chocolate) or lauric + myristic acid (from butter). In the first study, cocoa butter elicited a neutral cholesterolemic effect, whereas the butter diet was hypercholesterolemic and the olive oil and soybean oil diets were hypocholesterolemic. In the second study, the diets high in stearic acid did not raise plasma total and LDL-cholesterol levels, whereas, as in the first study, butter was markedly hypercholesterolemic. Regression analyses performed on the individual data from these two clinical studies were conducted to establish the cholesterolemic effects of individual fatty acids. The bestfitting linear regression equations relating ΔTC (change in plasma total cholesterol) was: ΔTC = 2.3 ΔC_14:0 + 3.0 ΔC_16:0-0.8 ΔC_18:0-1.0 ΔPUFA, where Δ fatty acid = change in intake expressed as percent of calories. This predictive equation separates stearic acid from the other long-chain saturated fatty acids and suggests that it has an independent cholesterol-lowering effect. In conclusion, stearic acid is a unique long-chain saturated fatty acid.     

Cistus ladanifer L. Shrub is Rich in Saturated and Branched Chain Fatty Acids and their Concentration Increases in the Mediterranean Dry Season

The Cistus ladanifer L. shrub is a widespread species of the Mediterranean region that is available as a feed source for ruminants all the year round, constituting a source of energy and nutrients when most of the vegetation is dry. However, there is no trustworthy information about the fatty acid composition of C. ladanifer, as well as no information about the seasonal and age related changes in their fatty acid composition. Thus, we collected the aerial parts of C. ladanifer plants of two age groups [young vs. older ones (2–6 years old)] during four consecutive seasons to characterize their fatty acid composition. The fatty acid composition of C. ladanifer is dominated by saturated fatty acids including the occurrence of two methyl branched chain fatty acids (BCFA), the iso‐19:0 and iso‐21:0, which as far as we know were detected for the first time in shrubs. Also, we demonstrated that several labdane type compounds might interfere with the fatty acid analysis of C. ladanifer. Marked seasonal changes in BCFA and polyunsaturated fatty acids (PUFA) were found, suggesting that BCFA can replace PUFA in plant lipids at high environmental temperatures.     

Detection of Small Quantities of Higher Saturated Fatty Acids in Mixed Fatty Acids of Oils by Lead Salt Separation and Thin-Layer Chromatography

A combination of Twitchell's lead salt separation procedure and reverse phase thin-layer chromatography on Plaster of Paris plates has enabled easy separation and identification of C₂₀-C₂₄ minor saturated acids in mustard seed oils. This has further demonstrated the inapplicability of Bellier's turbidity point test for mustard oils by showing the quantitative variation in the proportion of C₂₀-C₂₄ acids naturally present in these oils. Expected augmentation of minor acid spots in chromatograms could be shown by adulteration with groundnut oil. The method can be adapted for the detection of adulteration of fats and oils.     

Mild and Direct Multiple Deuterium‐Labeling of Saturated Fatty Acids

We have established a mild and direct platinum on carbon (Pt/C)‐catalyzed multi‐deuterium labeling of various saturated fatty acids including bioactive compounds with high deuterium efficiencies in a mixed solvent of isopropyl alcohol and deuterium oxide (i‐PrOH)/D₂O under neutral conditions at 120 °C without the external addition of deuterium or hydrogen gas.

     

A Concise Review of Liquid Chromatography-Mass Spectrometry-Based Quantification Methods for Short Chain Fatty Acids as Endogenous Biomarkers

Fatty acids are widespread naturally occurring compounds, and essential constituents for living organisms. Short chain fatty acids (SCFAs) appeared as physiologically relevant metabolites for their involvement with gut microbiota, immunology, obesity, and other pathophysiological functions. This has raised the demand for reliable analytical detection methods in a variety of biological matrices. Here, we describe an updated overview of sample pretreatment techniques and liquid chromatography-mass spectrometry (LC-MS)-based methods for quantitative analysis of SCFAs in blood, plasma, serum, urine, feces and bacterial cultures. The present review incorporates various procedures and their applications to help researchers in choosing crucial parameters, such as pretreatment for complex biological matrices, and variables for chromatographic separation and detection, to establish a simple, sensitive, and robust quantitative method to advance our understanding of the role of SCFAs in human health and disease as potential biomarkers.     

Parenteral Lipid Emulsions in Guinea Pigs Differentially Influence Plasma and Tissue Levels of Fatty Acids,Squalene, Cholesterol,and Phytosterols

Lipid emulsions are made by mixing vegetable and/or fish oils with egg yolk and contain different types and amounts of fatty acids and sterols. This study assessed the effects of oral diet, soybean oil (SO)-, fish oil (FO)-, a mixture of olive and soybean oil (OOSO)-, and a mixture of fish, olive, coconut, and soybean oil (FOCS)-based emulsions on plasma triacylglycerols and plasma and tissue fatty acid and sterol content following acute and chronic intravenous administration in the guinea pig. Upon acute administration, peak triacylglycerols were highest with SO and lowest with OOSO. Upon chronic administration, the plasma triglyceride levels did not increase in any group over that of the controls. Fatty acid levels varied greatly between organs of animals on the control diets and organs of animals following acute or chronic lipid administration. Squalene levels increased in plasma following acute administration of OOSO, but plasma squalene levels were similar to control in all emulsion groups following chronic administration. Total plasma phytosterol levels were increased in the SO, OOSO, and FOCS groups following both acute and chronic infusions, whereas phytosterols were not increased following FO infusion. Total phytosterol levels were higher in liver, lung, kidney and adipose tissue following SO and OOSO. Levels were not increased in tissues after FO and FOCS infusion. These results indicate that fatty acid and sterol contents vary greatly among organs and that no one tissue reflects the fatty acid or sterol composition of other tissues, suggesting that different organs regulate these compounds differently.     

Biocatalytic Heterogeneous Processes of the Esterification of Saturated Fatty Acids with Aliphatic Alcohols

Heterogeneous biocatalysts prepared by immobilizing a recombinant lipase from Thermomyces lanuginosus on mesoporous inorganic supports—silica (SiO₂), alumina (Al₂O₃), and titania (TiO₂)—are comparatively studied in the esterification of fatty acids with aliphatic alcohols. It is found that the T. lanuginosus lipase adsorbed on silica has the highest esterifying activity, while the lipase adsorbed on titania is completely inactivated. SiO₂-based catalysts have high activity and stability in the esterification of saturated fatty acids containing 4–18 carbon atoms (C4–C18) with aliphatic alcohols (C5–C16) in organic solvents (hexane and diethyl ether). The catalysts operate in this reaction for several tens of reaction cycles (>40) without loss of activity. The recombinant rPichia/lip lipase immobilized on silica exhibits the most pronounced specificity for its first substrate, a fatty acid. For instance, the rate of synthesis for esters of low molecular weight acids (С4–С6) is three to four times slower than for the esters of acids with more than seven carbon atoms. The catalyst has a relatively broad specificity for the second substrate, an aliphatic alcohol. It is found that the ester of enanthic acid (C7:0) and butanol (C4) is synthesized at the maximum rate.     

The Role of Cholesterol and Fatty Acids in the Etiology and Diagnosis of Autism Spectrum Disorders

Autism spectrum disorders (ASDs) are a group of neurodevelopmental disorders whose pathogenesis seems to be related to an imbalance of excitatory and inhibitory synapses, which leads to disrupted connectivity during brain development. Among the various biomarkers that have been evaluated in the last years, metabolic factors represent a bridge between genetic vulnerability and environmental aspects. In particular, cholesterol homeostasis and circulating fatty acids seem to be involved in the pathogenesis of ASDs, both through the contribute in the stabilization of cell membranes and the modulation of inflammatory factors. The purpose of the present review is to summarize the available data about the role of cholesterol and fatty acids, mainly long-chain ones, in the onset of ASDs. A bibliographic research on the main databases was performed and 36 studies were included in our review. Most of the studies document a correlation between ASDs and hypocholesterolemia, while the results concerning circulating fatty acids are less univocal. Even though further studies are necessary to confirm the available data, the metabolic biomarkers open to new treatment options such as the modulation of the lipid pattern through the diet.     

Polyunsaturated Fatty Acids and Modulation of Cholesterol Homeostasis in THP-1 Macrophage-Derived Foam Cells

Transformation of macrophages to foam cells is determined by the rates of cholesterol uptake and efflux. This study uses a real time RT-PCR technique to investigate the role of conjugated linoleic acid (CLA), α-linolenic acid (ALA) and eicosapentaenoic acid (EPA) in the regulation of the ATP-binding cassette A1 (ABCA1) and liver X receptor α (LXR) genes, which are involved in cholesterol homeostasis. Accordingly, these fatty acids significantly reduced the total, free and esterified cholesterols within the foam cells. While the expression of the ABCA1 and LXRα genes was increased in the presence of the pharmacological LXRα ligand, T0901317, their mRNA expression was not significantly affected by CLA, ALA and EPA. These results suggest that although polyunsaturated fatty acids have an effect on cholesterol homeostasis, they cannot change the expression of the ABCA1 and LXRα genes. Alternatively, several other genes and proteins may be involved.     

Temporal Changes of Phospholipids Fatty Acids and Cholesterol in Breast Milk and Relationship with Diet

Phospholipids (PLs) and cholesterol in human milk (HM) are affected by lactation, and differential lipids are closely related to maternal diet. The contents of PLs and cholesterol in Chinese HM are quantified by gas chromatography and high performance liquid chromatography, respectively, and the relationship between differential lipids and the maternal diet is obtained by Pearson. The result shows that SFA, MUFA, and polyunsaturated fatty acid (PUFA) are not affected by lactation and geography for total fatty acids, but almost all sn‐2 fatty acids are influenced by geography and remain unchanged during lactation. Most SFAs show absolute sn‐2 selectivity and the majority of MUFAs and PUFAs are esterified at the sn‐1 position. Cholesterol (13.8–22.6 mg per 100 g milk) and 25‐hydroxycholesterol (0.45–1.01 mg per 100 g milk) increase significantly and remain constant during lactation, respectively, and they are affected by regions. In addition, the differential lipids (22:1n‐9, C9:0, trans‐PUFA, 22:4n‐6, etc.) of PLs are closely related to the maternal diet. PLs and cholesterol content differ from western research and infant formula, which will help to design an infant formula that is more suitable for Chinese babies in the future. Practical Application: Compared with PLs and cholesterol in western countries and infant formula, the specificity of Chinese HM can more accurately target the development of formulas suitable for the growth of Chinese infants. At the same time, according to the influence of the mother?s diet on the composition of HM, it is more reasonable to guide the diet of the mother.     

Statistical Analysis of the Collaborative Study in Support of the Official Method AOCS Ce 1i-07: Determination of Saturated, cis-Monounsaturated and cis-Polyunsaturated Fatty Acids in Marine and Other Oils Containing Long Chain Polyunsaturated Fatty Acids by Capillary GLC

Analysis was done of the statistical results obtained by following recommended AOCS Collaborative Study Procedure M-86 to evaluate the performance of Official Method AOCS Ce 1i-07, which provides a gas–liquid chromatography (GLC) procedure for the determination of the fatty acid composition of oils containing long chain polyunsaturated fatty acids (PUFAs). The method obtains relative between-lab reproducibility (%RSDR) values on the order of 5% or less for most fatty acids that are present above ~0.5% w/w; however, the reproducibility worsens dramatically for analytes below this threshold. Apparently, several participating labs had problems identifying small peaks in the sample chromatograms. They also had problems correctly identifying certain larger peaks that occurred in a congested area of the sample chromatograms, including the 9c-16:1, 9c-11c-22:1, and 6c,9c,12c,15c-16:4 fatty acids. Finally, several analytes with chain lengths between 16 and 18 and between 21 and 22 carbons that were present at moderate concentrations had worse than expected reproducibilities due to severe overlap of these analytes’ peaks. A detailed inspection of the contributed data shows that the relatively poor between-lab reproducibility for analytes in this region is due to differences in the labs’ chromatographic efficiencies and perhaps in their methods of quantifying highly overlapped peaks.     

Distinct Influence of Saturated Fatty Acids on Malignant and Nonmalignant Human Lung Epithelial Cells

The impact of saturated fatty acids (FA) on viability and properties of malignant and nonmalignant cells has not been studied in detail so far. The present study was aimed at evaluation of the influence of saturated FA (10:0–18:0) on malignant (A459) and nonmalignant (BEAS-2B) human lung epithelial cells. FA strongly affected A549 cells, but not BEAS-2B cells. Viability of A549 cells incubated with 14:0–18:0 was decreased by 53–91% as compared to untreated cells. Cell membrane stiffness in those cells as measured by atomic force microscopy was also reduced. Median value of apparent Young's modulus of untreated A549 cell membrane was 16.9 kPa and it decreased to 8.9 kPa for cells incubated with 14:0. Viability and mechanical properties of BEAS-2B cells were not altered by presence of FA. Those surprising discrepancies can be related to the differences in FA uptake rate. A549 cells were found to incorporate higher amount of FA and this corresponded to decrease in cell membrane stiffness and reduced cell viability. The performed studies showed that saturated FA have distinct influence on various types of cells, which may be exploited in development of the advanced lipid drug delivery systems.     

Biosynthesis of Long Chain Polyunsaturated Fatty Acids in the Marine Ichthyosporean Sphaeroforma arctica

Sphaeroforma arctica is a unique, recently discovered marine protist belonging to a group falling close to the yeast/animal border. S. arctica is found in cold environments, and accordingly has a fatty acid composition containing a high proportion of very long chain polyunsaturated fatty acids, including the ω3 polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA). Two elongases and five desaturases, representing the complete set of enzymes necessary for the synthesis of DHA from oleic acid, were isolated from this species and characterized in yeast. One elongase showed high conversion rates on a wide range of 18 and 20 carbon substrates, and was capable of sequential elongation reactions. The second elongase had a strong preference for the 20-carbon fatty acids EPA and arachidonic acid, with over 80 % of EPA converted to docosapentaenoic acid (DPA) in the heterologous yeast host. The isolation of a Δ8-desaturase, along with the detection of eicosadienoic acid in S. arctica cultures indicated that this species uses the alternate Δ8-pathway for the synthesis of long-chain polyunsaturated fatty acids. S. arctica also carried a Δ4-desaturase that proved to be very active in the production of DHA from DPA. Finally, a long chain acyl-CoA synthetase from S. arctica improved DHA uptake in the heterologous yeast host and led to an improvement in desaturation and elongation efficiencies.     

Changes within Liver Accounts for Fatty Acids Decrease in the Blood of Rats with Adjuvant-Induced Arthritis

This study characterizes rheumatoid arthritis-related free fatty acids (FFAs) changes using adjuvant-induced arthritis (AIA) model. Blood FFAs of healthy and AIA rats are periodically determined. During acute inflammation, FFAs levels are analyzed under both fasting and non-fasting conditions. Oral intake capacities are compared by everted intestinal sac experiment. Tissue distribution of FFAs in the rats fed with/without linolenic acid is also investigated. AIA decreases FFAs in rats. Saturated FFAs are gradually recovered, but unsaturated FFAs are further reduced till the secondary inflammation. FFAs level gap remains unchanged regardless of feeding/fasting, and intestinal intake capacities of the rats are similar. FFAs levels in liver fluctuate in accordance with blood levels. Increased carnitine palmitoyltransferase 1 (CPT-1) reveals the accelerated FFAs utilization in AIA rats, resulting in the accumulation of acetoacetic acid and 2-hydroxybutyrate. Hepatocytes incubated with AIA serum take in more FFAs than normal controls when supply is sufficient. To the opposite, intracellular FFAs are reduced after AIA serum stimulus without additional supply. Besides, AIA serum-challenged cells produce more CPT-1. Hence, the reduced circulating FFAs in AIA rats should be attributed to the accelerated utilization in liver. Practical Applications: This study provides additional possible therapeutic approaches for the treatment of RA by focusing on the changes of blood FFAs. Obtained clues demonstrate that liver will be a key in the elucidation of RA-related lipid paradox, and diet supplement of the unsaturated FFAs will be beneficial in treating RA.