SciCombinator

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Concept: Lipids

136

Effects of major dietary macronutrients on glucose-insulin homeostasis remain controversial and may vary by the clinical measures examined. We aimed to assess how saturated fat (SFA), monounsaturated fat (MUFA), polyunsaturated fat (PUFA), and carbohydrate affect key metrics of glucose-insulin homeostasis.

Concepts: Nutrition, Fatty acids, Saturated fat, Lipids, Trans fat, Unsaturated fat, Polyunsaturated fat, Diet and heart disease

114

Cardiovascular disease (CVD) is the leading global cause of death, accounting for 17.3 million deaths per year. Preventive treatment that reduces CVD by even a small percentage can substantially reduce, nationally and globally, the number of people who develop CVD and the costs of caring for them. This American Heart Association presidential advisory on dietary fats and CVD reviews and discusses the scientific evidence, including the most recent studies, on the effects of dietary saturated fat intake and its replacement by other types of fats and carbohydrates on CVD. In summary, randomized controlled trials that lowered intake of dietary saturated fat and replaced it with polyunsaturated vegetable oil reduced CVD by ≈30%, similar to the reduction achieved by statin treatment. Prospective observational studies in many populations showed that lower intake of saturated fat coupled with higher intake of polyunsaturated and monounsaturated fat is associated with lower rates of CVD and of other major causes of death and all-cause mortality. In contrast, replacement of saturated fat with mostly refined carbohydrates and sugars is not associated with lower rates of CVD and did not reduce CVD in clinical trials. Replacement of saturated with unsaturated fats lowers low-density lipoprotein cholesterol, a cause of atherosclerosis, linking biological evidence with incidence of CVD in populations and in clinical trials. Taking into consideration the totality of the scientific evidence, satisfying rigorous criteria for causality, we conclude strongly that lowering intake of saturated fat and replacing it with unsaturated fats, especially polyunsaturated fats, will lower the incidence of CVD. This recommended shift from saturated to unsaturated fats should occur simultaneously in an overall healthful dietary pattern such as DASH (Dietary Approaches to Stop Hypertension) or the Mediterranean diet as emphasized by the 2013 American Heart Association/American College of Cardiology lifestyle guidelines and the 2015 to 2020 Dietary Guidelines for Americans.

Concepts: Nutrition, Atherosclerosis, Fat, Saturated fat, Lipids, Trans fat, Unsaturated fat, Polyunsaturated fat

80

Saturated fat (SFA), ω-6 (n-6) polyunsaturated fat (PUFA), and trans fat (TFA) influence risk of coronary heart disease (CHD), but attributable CHD mortalities by country, age, sex, and time are unclear.

Concepts: Nutrition, Fatty acids, Essential fatty acid, Saturated fat, Lipids, Trans fat, Unsaturated fat, Polyunsaturated fat

53

Cardiovascular diseases and cancers are leading causes of morbidity and mortality. Reducing dietary saturated fat and replacing it with polyunsaturated fat is still the main dietary strategy to prevent cardiovascular diseases, although major flaws have been reported in the analyses supporting this approach. Recent studies introducing the concept of myocardial preconditioning have opened new avenues to understand the complex interplay between the various lipids and the risk of cardiovascular diseases. The optimal dietary fat profile includes a low intake of both saturated and omega-6 fatty acids and a moderate intake of omega-3 fatty acids. This profile is quite similar to the Mediterranean diet. On the other hand, recent studies have found a positive association between omega-6 and breast cancer risk. In contrast, omega-3 fatty acids do have anticancer properties. It has been shown that certain (Mediterranean) polyphenols significantly increase the endogenous synthesis of omega-3 whereas high intake of omega-6 decreases it. Finally, epidemiological studies suggest that a high omega-3 to omega-6 ratio may be the optimal strategy to decrease breast cancer risk. Thus, the present high intake of omega-6 in many countries is definitely not the optimal strategy to prevent cardiovascular disease and cancers. A moderate intake of plant and marine omega-3 in the context of the traditional Mediterranean diet (low in saturated and omega-6 fatty acids but high in plant monounsaturated fat) appears to be the best approach to reduce the risk of both cardiovascular diseases and cancers, in particular breast cancer.

Concepts: Nutrition, Fatty acid, Fatty acids, Essential fatty acid, Fat, Saturated fat, Lipids, Unsaturated fat

28

Thylakoid membranes, the universal structure where photosynthesis takes place in all oxygenic photosynthetic organisms from cyanobacteria to higher plants, have a unique lipid composition. They contain a high fraction of 2 uncharged glycolipids, the galactoglycerolipids mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), and an anionic sulfolipid, sulfoquinovosediacylglycerol (SQDG). A remarkable feature of the evolution from cyanobacteria to higher plants is the conservation of MGDG, DGDG, SQDG, and phosphatidylglycerol (PG), the major phospholipid of thylakoids. Using neutron diffraction on reconstituted thylakoid lipid extracts, we observed that the thylakoid lipid mixture self-organizes as a regular stack of bilayers. This natural lipid mixture was shown to switch from hexagonal II toward lamellar phase on hydration. This transition and the observed phase coexistence are modulated by the fine-tuning of the lipid profile, in particular the MGDG/DGDG ratio, and by the hydration. Our analysis highlights the critical role of DGDG as a contributing component to the membrane stacking via hydrogen bonds between polar heads of adjacent bilayers. DGDG interactions balance the repulsive electrostatic contribution of the charged lipids PG and SQDG and allow the persistence of regularly stacked membranes at high hydration. In developmental contexts or in response to environmental variations, these properties can contribute to the highly dynamic flexibility of plastid structure.-Demé, B., Cataye, C., Block, M. A., Maréchal, E., Jouhet, J. Contribution of galactoglycerolipids to the 3-dimensional architecture of thylakoids.

Concepts: Cyanobacteria, Photosynthesis, Chloroplast, Plant, Lipids, Thylakoid, Light-dependent reactions, ATP synthase

27

Apolipoprotein M (apoM) is a plasma apolipoprotein that mainly associates with high-density lipoproteins. Hence, most studies on apoM so far have investigated its effect on and association with lipid metabolism and atherosclerosis. The insight into apoM biology recently took a major turn. ApoM was identified as a carrier of the bioactive lipid sphingosine-1-phosphate (S1P). S1P activates five different G-protein-coupled receptors, known as the S1P-receptors 1-5 and, hence, affects a wide range of biological processes, such as lymphocyte trafficking, angiogenesis, wound repair and even virus suppression and cancer. The ability of apoM to bind S1P is due to a lipophilic binding pocket within the lipocalin structure of the apoM molecule. Mice overexpressing apoM have increased plasma S1P concentrations, whereas apoM-deficient mice have decreased S1P levels. ApoM-S1P is able to activate the S1P-receptor-1, affecting the function of endothelial cells, and apoM-deficient mice display impaired endothelial permeability in the lung. This review will focus on the putative biological roles of the new apoM-S1P axis in relation to lipoprotein metabolism, lipid disorders and atherosclerosis.

Concepts: Cholesterol, Atherosclerosis, Angiogenesis, Blood vessel, Lipoprotein, Endothelium, Lipid, Lipids

27

Human meibomian gland secretions (meibum) are the major lipid component of the human preocular tear film. The predominant lipid classes found in meibum include waxes (WE), cholesteryl esters (CE), and varying amounts of cholesterol (Chl). The classical sulfo-phospho-vanillin assay (SPVA), adapted for a microplate reader, was used to quantitate lipids in meibum. To account for varying reactivities of different lipids in SPVA, a model meibomian lipid mixture (MMx) that approximated the WE/CE/Chl composition of meibum was developed and used to quantitate meibomian lipids. The overall SPV responses of MMx and meibum were found to be close, with similar intermediate and final reaction products for both. Saturated WE that had not been expected to be reactive were found to be SPV-positive. A reaction mechanism for these compounds in SPVA which involves the formation of alkenyl ethers is proposed and discussed. Tested proteins were non-reactive in SPVA. Thus, by comparing the results of gravimetric analyses of meibum samples with the results of a properly calibrated SPVA, it was estimated that the SPV-reactive lipid content of dry meibum in tested samples was about 78 % (w/w). The SPV method can also be adopted for analyzing other types of complex lipids secretions, such as sebum, as well as whole lipid extracts from other lipid-enriched organs and tissues, if proper standards are chosen.

Concepts: Protein, Fat, Lipid, Biochemistry, Wax, Lipids, Gland, Meibomian gland

27

The lipid characteristics of microalgae are known to differ between species and change with growth conditions. This work provides a methodology for lipid characterization that enables selection of the optimal strain, cultivation conditions and processing pathway for commercial biodiesel production from microalgae. Two different microalgal species, Nannochloropsis sp. and Chlorella sp., were cultivated under both nitrogen replete and nitrogen depleted conditions. Lipids were extracted and fractionated into three major classes and quantified gravimetrically. The fatty acid profile of each fraction was analyzed using GC-MS. The resulting quantitative lipid data for each of the cultures is discussed in the context of biodiesel and omega-3 production. This approach illustrates how the growth conditions greatly affect the distribution of fatty acid present in the major lipid classes and therefore the suitability of the lipid extracts for biodiesel and other secondary products. Biotechnol. Bioeng. © 2013 Wiley Periodicals, Inc.

Concepts: Algae, Fatty acid, Triglyceride, Fat, Lipid, Lipids, Eicosapentaenoic acid, Glycerol

26

We hypothesized that brains from vitamin E-deficient (E-) zebrafish (Danio rerio) would undergo increased lipid peroxidation because they contain highly polyunsaturated fatty acids, thus susceptible lipids could be identified. Brains from zebrafish fed for 9 months defined diets without (E-) or with added vitamin E (E+, 500 mg RRR-α-tocopheryl acetate/kg diet) were studied. Using an untargeted approach, 1-hexadecanoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (DHA-PC 38:6, PC 16:0/22:6) was the lipid that showed the most significant and greatest fold-differences between groups. DHA-PC concentrations were approximately 1/3 lower in E- (4.3 ± 0.6) compared with E+ brains (6.5 ± 0.9 mg/g, mean ± SEM, n=10/group, P=0.04). Using lipidomics, 155 lipids in brain extracts were identified. Only four PL were different (P<0.05) between groups; they were lower in E- brains and contained DHA with DHA-PC 38:6 at the highest abundances. Moreover, hydroxy-DHA-PC 38:6 was increased in E- brains (P=0.0341) supporting the hypothesis of DHA peroxidation. More striking was the depletion in E- brains of nearly 60% of 19 different lysoPL (combined P=0.0003), which are critical for membrane PL remodeling. Thus, E- brains contained less DHA-PL, more hydroxy-DHA-PC and fewer lyso-PLs, suggesting that lipid peroxidation depletes membrane DHA-PC and homeostatic mechanisms to repair the damage result in lyso-PL depletion.

Concepts: Metabolism, Nutrition, Fatty acids, Antioxidant, Essential fatty acid, Fat, Lipid, Lipids

24

Marine fishes are important to health due to their high content of polyunsaturated fatty acids particularly those of the omega-3 family. These fatty acids play an important role in various physiological processes and as a consequence they may modulate and even prevent some human diseases. The aim of the present study was to investigate and compare the effect of fish oils of different origins (Sardinella longiceps, Rastrelliger kanagurta and Clarias batrachus) on lipid metabolism and membrane fluidity in diabetes. Alloxan was injected in repetitive doses for 1 month (100 mg/kg body weight every 5th day) to induce diabetes in Swiss albino mice. 10 % S. longiceps, R. kanagurta or C. batrachus fish oil was freshly blended with pellet feed which was provided to diabetic mice for 1 month. The serum lipid profile (serum total cholesterol, triglyceride, HDL, VLDL and LDL) along with liver, kidney and heart tissue lipid profile (i.e. triglyceride, total cholesterol, glycolipid and phospholipid) was analysed. Besides, the enzymatic activity of HMG-CoA reductase, HMG-CoA synthase and glucose-6-phosphate-dehydrogenase along with the membrane fluidity of these tissues was evaluated. Altered tissue lipid composition, enzyme activities and membrane fluidity due to diabetes were returned towards normal with the supplementation of 10 % fish oils. Fish oil from S. longiceps brought maximum changes in level of neutral lipid composition in heart, and increased the concentration of phospholipid and decreased the activity of HMG-CoA reductase in comparison with the fish oil from R. kanagurta and C. batrachus.

Concepts: Cholesterol, Nutrition, Fatty acid, Triglyceride, Omega-3 fatty acid, Fat, Lipid, Lipids