Comparative lipoprotein metabolism of myristate, palmitate, and stearate in normolipidemic men

Antimicrobial potential of myristic acid against Listeria monocytogenes in milk

Listeria monocytogenes (L. monocytogenes), an important food-borne pathogenic microorganism, has resistance immune function to many commonly used drugs. Myristic acid is a traditional Chinese herbal medicine, but it has been rarely used as a food additive, limiting the development of natural food preservatives. In this study, the antibacterial activity and mechanism of myristic acid against L. monocytogenes were studied. The minimum inhibitory concentration (MIC) of myristic acid against 13 L. monocytogenes strains ranged from 64 to 256 μg ml^-1. The time-kill assay demonstrated that when myristic acid was added to dairy products, flow cytometry confirmed that myristic acid influenced cell death and inhibited the growth of L. monocytogenes. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and NPN uptake studies illustrated that myristic acid changed the bacterial morphology and membrane structure of L. monocytogenes, which led to rapid cell death. Myristic acid could bind to DNA and lead to changes in DNA conformation and structure, as identified by fluorescence spectroscopy. Our studies provide additional evidence to support myristic acid being used as a natural antibacterial agent and also further fundamental understanding of the modes of antibacterial action.

The relation of saturated fatty acids with low-grade inflammation and cardiovascular disease

The mantra that dietary (saturated) fat must be minimized to reduce cardiovascular disease (CVD) risk has dominated nutritional guidelines for decades. Parallel to decreasing intakes of fat and saturated fatty acids (SFA), there have been increases in carbohydrate and sugar intakes, overweight, obesity and type 2 diabetes mellitus. The "lipid hypothesis" coined the concept that fat, especially SFA, raises blood low-density lipoprotein-cholesterol and thereby CVD risk. In view of current controversies regarding their adequate intakes and effects, this review aims to summarize research regarding this heterogenic group of fatty acids and the mechanisms relating them to (chronic) systemic low-grade inflammation, insulin resistance, metabolic syndrome and notably CVD. The intimate relationship between inflammation and metabolism, including glucose, fat and cholesterol metabolism, revealed that the dyslipidemia in Western societies, notably increased triglycerides, "small dense" low-density lipoprotein and "dysfunctional" high-density lipoprotein, is influenced by many unfavorable lifestyle factors. Dietary SFA is only one of these, not necessarily the most important, in healthy, insulin-sensitive people. The environment provides us not only with many other proinflammatory stimuli than SFA but also with many antiinflammatory counterparts. Resolution of the conflict between our self-designed environment and ancient genome may rather rely on returning to the proinflammatory/antiinflammatory balance of the Paleolithic era in consonance with the 21st century culture. Accordingly, dietary guidelines might reconsider recommendations for SFA replacement and investigate diet in a broader context, together with nondietary lifestyle factors. This should be a clear priority, opposed to the reductionist approach of studying the effects of single nutrients, such as SFA.

ISSFAL 2014 Debate: It Is Time to Update Saturated Fat Recommendations

This paper summarizes a debate on whether to update recommendations for the consumption of saturated fatty acids (SFA); this debate was held at the 11th congress of the International Society for the Study of Fatty Acids and Lipids in Stockholm, Sweden, June 28-July 2, 2014. Recommendations to reduce SFA intakes are based largely on the premise that high intakes of SFA raise low-density lipoprotein (LDL)-cholesterol levels, which in turn increase the risk of coronary heart disease (CHD). Several systematic reviews question whether reducing SFA intakes lowers CHD risk. Arguing to revise SFA recommendations, Philippe Legrand noted that SFA are heterogeneous in structure and function, are synthesized de novo by humans and only certain SFA in excess have been linked to CHD risk. We cannot consider all SFA as a block. The effects of reducing SFA intakes depend on which nutrients replace them and on which biomarkers or endpoints are assessed, Ronald Mensink observed. The effects of reducing SFA on CHD risk vary with the nutrient of comparison, whether carbohydrates, monounsaturated or polyunsaturated fatty acids. Substitution of SFA with polyunsaturated fatty acids was associated with a lower incidence of cardiovascular disease, while the effects of substitution with monounsaturated fatty acids or high-glycemic index carbohydrates are less clear.

Consuming a balanced high fat diet for 16 weeks improves body composition, inflammation and vascular function parameters in obese premenopausal women

OBJECTIVE

Inflammation, insulin resistance and vascular dysfunction characterize obesity and predict development of cardiovascular disease (CVD). Although women experience CVD events at an older age, vascular dysfunction is evident 10years prior to coronary artery disease. Questions remain whether replacing SFA entirely with MUFA or PUFA is the optimal approach for cardiometabolic benefits. This study tested the hypotheses that: a) body composition, inflammation and vascular function would improve with a high fat diet (HFD) when type of fat is balanced as 1/3 SFA, 1/3 MUFA and 1/3 PUFA; and b) body composition, inflammation and vascular function would improve more when balanced HFD is supplemented with 18C fatty acids, in proportion to the degree of 18C unsaturation.

METHODS

Obese premenopausal women were stabilized on balanced HFD and randomized to consume 9g/d of encapsulated stearate (18:0), oleate (18:1), linoleate (18:2) or placebo.

RESULTS

Significant improvements occurred in fat oxidation rate (↑6%), body composition (%fat: ↓2.5±2.1%; %lean: ↑2.5±2.1%), inflammation (↓ IL-1α, IL-1β, 1L-12, Il-17, IFNγ, TNFα, TNFβ) and vascular function (↓BP, ↓PAI-1, ↑tPA activity). When compared to HFD+placebo, HFD+stearate had the greatest effect on reducing IFNγ (↓74%) and HFD+linoleate had the greatest effect on reducing PAI-1 (↓31%).

CONCLUSIONS

Balancing the type of dietary fat consumed (SFA/MUFA/PUFA) is a feasible strategy to positively affect markers of CVD risk. Moreover, reductions in inflammatory molecules involved in vascular function might be enhanced when intake of certain 18C fatty acids is supplemented. Long term effects need to be determined for this approach.

In rat hepatocytes, myristic acid occurs through lipogenesis, palmitic acid shortening and lauric acid elongation

The origin of myristic acid in mammalian cells and the regulation of its endogenous cellular low concentration are not known. Another intriguing question is the potential metabolic properties of endogenous myristic acid as compared with exogenous myristic acid. In the present paper, we hypothesised and demonstrated that, in liver cells, in addition to the usual fatty acid synthase (FAS) pathway that produces predominantly palmitic acid and minor amounts of myristic acid, part of endogenous cellular myristic acid also comes from a shortening of palmitic acid, likely by peroxisomal β-oxidation and from lauric acid by elongation. From a nutritional point of view, C16:0 is universally found in natural fats and its shortening to myristic acid could contribute to a non-negligible source of this fatty acid (FA) in the organism. Then, we measured the distribution of endogenously synthesised myristic acid in lipid species and compared it with that of exogenous myristic acid. Our results do not support the hypothesis of different metabolic fates of endogenous and exogenous myristic acid and suggest that whatever the origin of myristic acid, its cellular concentration and lipid distribution are highly regulated.

Postprandial metabolism of meal triglyceride in humans

The intake of dietary fat above energy needs has contributed to the growing rates of obesity worldwide. The concept of disease development occurring in the fed state now has much support and dysregulation of substrate flux may occur due to poor handling of dietary fat in the immediate postprandial period. The present paper will review recent observations implicating cephalic phase events in the control of enterocyte lipid transport, the impact of varying the composition of meals on subsequent fat metabolism, and the means by which dietary lipid carried in chylomicrons can lead to elevated postprandial non-esterified fatty acid concentrations. This discussion is followed by an evaluation of the data on quantitative meal fat oxidation at the whole body level and an examination of dietary fat clearance to peripheral tissues - with particular attention paid to skeletal muscle and liver given the role of ectopic lipid deposition in insulin resistance. Estimates derived from data of dietary-TG clearance show good agreement with clearance to the liver equaling 8-12% of meal fat in lean subjects and this number appears higher (10-16%) in subjects with diabetes and fatty liver disease. Finally, we discuss new methods with which to study dietary fatty acid partitioning in vivo. Future research is needed to include a more comprehensive understanding of 1) the potential for differential oxidation of saturated versus unsaturated fatty acids which might lead to meaningful energy deficit and whether this parameter varies based on insulin sensitivity, 2) whether compartmentalization exists for diet-derived fatty acids within tissues vs. intracellular pools, and 3) the role of reduced peripheral fatty acid clearance in the development of fatty liver disease. Further advancements in the quantitation of dietary fat absorption and disposal will be central to the development of therapies designed to treat diet-induced obesity. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.

The complex and important cellular and metabolic functions of saturated fatty acids

This review summarizes recent findings on the metabolism and biological functions of saturated fatty acids (SFA). Some of these findings show that SFA may have important and specific roles in the cells. Elucidated biochemical mechanisms like protein acylation (N-myristoylation, S-palmitoylation) and regulation of gene transcription are presented. In terms of physiology, SFA are involved for instance in lipogenesis, fat deposition, polyunsaturated fatty acids bioavailability and apoptosis. The variety of their functions demonstrates that SFA should no longer be considered as a single group.

Regulation of mammalian desaturases by myristic acid: N-terminal myristoylation and other modulations

Myristic acid, the 14-carbon saturated fatty acid (C14:0), usually accounts for small amounts (0.5%-1% weight of total fatty acids) in animal tissues. Since it is a relatively rare molecule in the cells, the specific properties and functional roles of myristic acid have not been fully studied and described. Like other dietary saturated fatty acids (palmitic acid, lauric acid), this fatty acid is usually associated with negative consequences for human health. Indeed, in industrialized countries, its excessive consumption correlates with an increase in plasma cholesterol and mortality due to cardiovascular diseases. Nevertheless, one feature of myristoyl-CoA is its ability to be covalently linked to the N-terminal glycine residue of eukaryotic and viral proteins. This reaction is called N-terminal myristoylation. Through the myristoylation of hundreds of substrate proteins, myristic acid can activate many physiological pathways. This review deals with these potentially activated pathways. It focuses on the following emerging findings on the biological ability of myristic acid to regulate the activity of mammalian desaturases: (i) recent findings have described it as a regulator of the Δ4-desaturation of dihydroceramide to ceramide; (ii) studies have demonstrated that it is an activator of the Δ6-desaturation of polyunsaturated fatty acids; and (iii) myristic acid itself is a substrate of some fatty acid desaturases. This article discusses several topics, such as the myristoylation of the dihydroceramide Δ4-desaturase, the myristoylation of the NADH-cytochrome b5 reductase which is part of the whole desaturase complex, and other putative mechanisms.

Saturated fatty acids: simple molecular structures with complex cellular functions

PURPOSE OF REVIEW

This review summarizes recent findings on the biological functions of saturated fatty acids. Some of these findings suggest that saturated fatty acids may have important and specific regulatory roles in the cells. Until now these roles have largely been outweighed by the negative impact of dietary saturated fatty acids on atherosclerosis biomarkers. Elucidated biochemical mechanisms like protein acylation (N-myristoylation, S-palmitoylation) and putative physiological roles are described.

RECENT FINDINGS

The review will focus on the following topics: new aspects on the metabolism of saturated fatty acids; recent reports on the biochemical functions of saturated fatty acids; current investigations on the physiological roles (elucidated and putative) of saturated fatty acids; and a discussion of the nutritional dietary recommendations (amounts and types) of saturated fatty acids.

SUMMARY

Dietary saturated fatty acids are usually associated with negative consequences for human health. Experimental results on the relationship between doses, physiological effects, specificities and functions of individual saturated fatty acids are, however, conflicting. In this context, this review describes emerging recent evidence that some saturated fatty acids have important and specific biological roles. Such data are needed to allow a balanced view in terms of potential nutritional benefits of saturated fatty acids, and, if necessary, reassessment of the current nutritional dietary recommendations.

Variations in daily intakes of myristic and alpha-linolenic acids in sn-2 position modify lipid profile and red blood cell membrane fluidity

The present study evaluated the effects of moderate intakes of myristic acid (MA), at 1.2% and 1.8% of total energy (TE), associated with a 0.9% TE intake of alpha-linolenic acid (ALA) on lipid and fatty acid profiles and red blood cell membrane fluidity. Twenty-nine monks without dyslipidaemia were enrolled in a 1-year nutritional study in which two experimental diets were tested for 3 months each: diet 1, MA 1.2 % and ALA 0.9%; diet 2, MA 1.8% and ALA 0.9%. A control diet (MA 1.2%, ALA 0.4%) was given 3 months before diets 1 and 2. Thus, two different levels of MA (1.2%, 1.8%) and ALA (0.4%, 0.9%) were tested. Intakes of other fatty acids were at recommended levels. Samples were obtained on completion of all three diets. For fluidity analysis, the red blood cells were labelled with 16-doxylstearate and the probe incorporated the membrane where relaxation-correlation time was calculated. Diet 1 was associated with a decrease in total cholesterol, in LDL-cholesterol, in triacylglycerols and in the ratio of total to HDL-cholesterol; ALA and EPA levels were increased in both phospholipids and cholesterol esters. Diet 2 was associated with a decrease in triacylglycerols and in the ratios of total to HDL-cholesterol and of triacylglycerols to HDL-cholesterol, and with an increase in HDL-cholesterol; EPA levels were decreased in phospholipids and cholesterol esters. Red blood cell membrane fluidity was increased in both diets (P<0.0001), but the higher increase was obtained with diet 1, mainly in the oldest subjects. Intakes of myristic acid (1.2%TE) and ALA (0.9%TE), both mainly in the sn-2 position, were associated with favourable lipid and n-3 long-chain fatty acid profiles. These beneficial effects coexisted with particularly high membrane fluidity, especially among the oldest subjects.

Cis-9, trans-11 conjugated linoleic acid is synthesized from vaccenic acid in lactating women

We studied the incorporation of the trans-11 vaccenic-1-(13)C acid ((13)C-VA) into milk and endogenous synthesis of cis-9, trans-11 conjugated linoleic acid (CLA) in lactating women. Subjects (n = 4) were 247 +/- 30 d postpartum, weighed 70.8 +/- 3.7 kg, breast-fed at least 6 times/d and consumed self-selected diets. After an overnight fast, they consumed the (13)C-VA (2.5 mg/kg body wt). Milk samples were obtained by complete breast expression at 0, 2, 4, 8, 12, 18, 24, and 48 h post-(13)C-VA ingestion. Lipid was extracted using chloroform:methanol. Fatty acids were methylated and converted to dimethyl disulfide and Diels-Alder derivatives before analysis by gas chromatography mass spectrometry. The mean (13)C-enrichment of milk VA was 3.1% at 8 h and reached maximal enrichment of 7.6% at 18 h. The (13)C enrichment of milk cis-9, trans-11 CLA reached a maximum of 0.4% at 18 h, confirming its conversion of VA to the Delta9-desaturase enzyme product. In the subjects examined, a portion (<10%) of the cis-9, trans-11 CLA present in milk was endogenously synthesized from VA.

Hydropyrolysis as a preparative method for the compound-specific carbon isotope analysis of fatty acids

Compound-specific stable carbon isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry is an effective and risk-free means of investigating fatty acid metabolism. Straightforward analysis, however, leads to poor chromatographic resolution, while derivatization adds carbon thereby corrupting the starting stable isotopic composition. Hydropyrolysis is a new approach which defunctionalizes fatty acids to yield the corresponding n-alkanes thus retaining the carbon skeleton intact and improving chromatography, allowing the faithful measurement of carbon isotope ratios.

Varying incorporation of fatty acids into phospholipids from muscle, adipose and pancreatic exocrine tissues and thymocytes in adult rats fed with diets rich in different fatty acids

Despite numerous studies, the importance which the tissue or the composition of the diet may have in the biological distribution of each fatty acid is not well known. To determine the importance of tissue origin and dietary fatty acids in the fatty acid composition of cell phospholipids, 54 male adult rats were fed isocaloric diets for one month varying only in their fatty acid compositions. The fat component of the six experimental groups was derived from olive oil, sunflower oil, fish oil, soybean oil, palmitic acid, or 82% palmitic acid plus 18% soybean oil, supplying the essential fatty acid. The fatty acid composition of phospholipids from thymocytes, pancreatic exocrine, muscle and adipose tissues was studied by gas-chromatography. The tissue of origin was a more important source of variation than diet in the fatty acid content of the cell phospholipids except for palmitic acid (16:0), eicosapentaenoic acid (20:5 n-3), and docosahexaenoic acid (22:6 n-3). This study points out the complexity of the interrelations between different families of fatty acids and of the specificity of each tissue to changes in the composition of dietary fatty acids, as well as the inconvenience of speaking from the dietary point of view of groups of fatty acid families based on the position of the double bond, since their individual behaviour, including saturated fatty acids, is very different in the face of dietary manipulation. The study also highlights the different behaviour of each of the fatty acids in relation to the others in the diet in each of the tissues, a circumstance which should be taken into account when evaluating the biological effects in both epidemiological and experimental studies.

Myristic acid, unlike palmitic acid, is rapidly metabolized in cultured rat hepatocytes

This study was designed to examine and compare the metabolism of myristic and palmitic acids in cultured rat hepatocytes. [1-(14)C]-Labeled fatty acids were solubilized with albumin at 0.1 mmol/L in culture medium. Incubation with 24-hr cultured hepatocytes was carried out for 12 hr. Myristic acid was more rapidly (P < 0.05) taken up by the cells than was palmitic acid (86.9 +/- 0.9% and 68.3 +/- 5.7%, respectively, of the initial radioactivity was cleared from the medium after 4 hr incubation). Incorporation into cellular lipids, however, was similar after the same time (33.4 +/- 2.8% and 34.9 +/- 9.3%, respectively, of initial radioactivity). In the early phase of the incubation (30 min), myristic acid was more rapidly incorporated into cellular triglycerides than was palmitic acid (7.4 +/- 0.9% and 3.6 +/- 1.9%, respectively, of initial radioactivity). However, after 12 hr incubation, the radioactivity of cellular triglycerides, cellular phospholipids, and secreted triglycerides was significantly higher with palmitic acid as precursor. Myristic acid oxidation was significantly higher than that of palmitic acid (14.9 +/- 2.2% and 2.3 +/- 0.6%, respectively, of the initial radioactivity was incorporated into the beta-oxidation products after 4 hr). Myristic acid was also more strongly elongated to radiolabeled palmitic acid (12.2 +/- 0.8% of initial radioactivity after 12 hr) than palmitic acid was to stearic acid (5.1 +/- 1.3% of initial radioactivity after 12 hr). The combination of elongation and beta-oxidation results in the rapid disappearance of C14:0 in hepatocytes whereas C16:0 is esterified to form glycerolipids. This study provides evidence that myristic acid is more rapidly metabolized in cultured hepatocytes than is palmitic acid.

Identification of components of Prunus africana extract that inhibit lipid peroxidation

Extractive and chromatographic separations were performed on V-1326, a chloroform extract from the bark of Prunus africana (also referred to as Pygeum africanum), which is used to treat the symptoms associated with benign prostate hyperplasia (BPH). The relative amounts of eleven identified constituents in crude V-1326 and in separated fractions were determined using gas chromatographic analysis. The ability of V-1326 and its separated fractions to inhibit ferrous ion-induced stimulation of lipid peroxidation in microsomal preparations from rabbit livers was evaluated. The extract, V-1326, and fractions containing high levels of myristic acid potently inhibited lipid peroxidation.