Stearic acid modifies very low density lipoprotein lipid composition and particle size differently from shorter-chain saturated fatty acids in cultured rat hepatocytes

A high fat diet with a high C18:0/C16:0 ratio induced worse metabolic and transcriptomic profiles in C57BL/6 mice

BACKGROUND

Differential effects of individual saturated fatty acids (SFAs), particularly stearic acid (C18:0), relative to the shorter-chain SFAs have drawn interest for more accurate nutritional guidelines. However, specific biologic and pathologic functions that can be assigned to particular SFAs are very limited. The present study was designed to compare changes in metabolic and transcriptomic profiles in mice caused by a high C18:0 diet and high palmitic acid (C16:0) diet.

METHODS

Male C57BL/6 mice were assigned to a normal fat diet (NFD), a high fat diet with high C18:0/C16:0 ratio (HSF) or an isocaloric high fat diet with a low C18:0/C16:0 ratio (LSF) for 10 weeks. An oral glucose tolerance test, 72-h energy expenditure measurement and CT scan of body fat were done before sacrifice. Fasting glucose and lipids were determined by an autobiochemical analyzer. Blood insulin, tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) levels were measured by enzyme-linked immunosorbent assay methods. Free fatty acids (FFAs) profiles in blood and liver were determined by using gas chromatography-mass spectrometry. Microarray analysis was applied to investigate changes in transcriptomic profiles in the liver. Pathway analysis and gene ontology analysis were applied to describe the roles of differentially expressed mRNAs.

RESULTS

Compared with the NFD group, body weight, body fat ratio, fasting blood glucose, insulin, homeostasis model assessment of insulin resistance (HOMA-IR), triglyceride, IL-6, serum and liver FFAs including total FFAs, C16:0 and C18:0 were increased in both high fat diet groups and were much higher in the HSF group than those in the LSF group. Both HSF and LSF mice exhibited distinguishable long non-coding RNA (lncRNA), microRNA and mRNA expression profiles when compared with those of NFD mice. Additionally, more differentially expressed lncRNAs and mRNAs were observed in the HSF group than in the LSF group. Some biological functions and pathways, other than energy metabolism regulation, were identified as differentially expressed mRNAs between the HSF group and the LSF group.

CONCLUSION

The high fat diet with a high C18:0/C16:0 ratio induced more severe glucose and lipid metabolic disorders and inflammation and affected expression of more lncRNAs and mRNAs than an isocaloric low C18:0/C16:0 ratio diet in mice. These results provide new insights into the differences in biological functions and related mechanisms, other than glucose and lipid metabolism, between C16:0 and C18:0.

Effects of low-stearate palm oil and high-stearate lard high-fat diets on rat liver lipid metabolism and glucose tolerance

Background

Excess consumption of energy-dense, high-fat Western diets contributes to the development of obesity and obesity-related disorders, such as fatty liver disease. However, not only the quantity but also the composition of dietary fat may play a role in the development of liver steatosis. The aim of this study was to determine the effects of low-stearate palm oil and high-stearate lard high-fat diets on in vivo liver lipid metabolism.

Methods

Wistar rats were fed with either normal chow (CON), a high-fat diet based on palm oil (HFP), or a high-fat diet based on lard (HFL). After 10 weeks of diet, magnetic resonance spectroscopy was applied for the in vivo determination of intrahepatocellular lipid content and the uptake and turnover of dietary fat after oral administration of ¹³C-labeled lipids. Derangements in liver lipid metabolism were further assessed by measuring hepatic very-low density lipoprotein (VLDL) secretion and ex vivo respiratory capacity of liver mitochondria using fat-derived substrates. In addition, whole-body and hepatic glucose tolerance were determined with an intraperitoneal glucose tolerance test.

Results

Both high-fat diets induced liver lipid accumulation (p < 0.001), which was accompanied by a delayed uptake and/or slower turnover of dietary fat in the liver (p < 0.01), but without any change in VLDL secretion rates. Surprisingly, liver lipid content was higher in HFP than in HFL (p < 0.05), despite the increased fatty acid oxidative capacity in isolated liver mitochondria of HFP animals (p < 0.05). In contrast, while both high-fat diets induced whole-body glucose intolerance, only HFL impaired hepatic glucose tolerance.

Conclusion

High-fat diets based on palm oil and lard similarly impair the handling of dietary lipids in the liver, but only the high-fat lard diet induces hepatic glucose intolerance.

Paradoxical effect of a pequi oil-rich diet on the development of atherosclerosis: balance between antioxidant and hyperlipidemic properties

Pequi is the fruit of Caryocar brasiliense and its oil has a high concentration of monounsaturated and saturated fatty acids, which are anti- and pro-atherogenic agents, respectively, and of carotenoids, which give it antioxidant properties. Our objective was to study the effect of the intake of a cholesterol-rich diet supplemented with pequi oil, compared to the same diet containing soybean oil, on atherosclerosis development, and oxidative stress in atherosclerosis-susceptible LDL receptor-deficient mice (LDLr^−/−, C57BL/6-background). Female mice were fed a cholesterol-rich diet containing 7% soybean oil (Soybean group, N = 12) or 7% pequi oil (Pequi group, N = 12) for 6 weeks. The Pequi group presented a more atherogenic lipid profile and more advanced atherosclerotic lesions in the aortic root compared to the Soybean group. However, the Pequi group presented a less advanced lesion in the aorta than the Soybean group and showed lower lipid peroxidation (Soybean group: 50.2 ± 7.1; Pequi group: 30.0 ± 4.8 µmol MDA/mg protein) and anti-oxidized LDL autoantibodies (Soybean group: 35.7 ± 9.4; Pequi group: 15.6 ± 3.7 arbitrary units). Peritoneal macrophages from the Pequi group stimulated with zymosan showed a reduction in the release of reactive oxygen species compared to the Soybean group. Our data suggest that a pequi oil-rich diet slows atherogenesis in the initial stages, possibly due to its antioxidant activity. However, the increase of serum cholesterol induces a more prominent LDL migration toward the intimae of arteries, increasing the advanced atherosclerotic plaque. In conclusion, pequi oil associated with an atherogenic diet worsens the lipid profile and accelerates the formation of advanced atherosclerotic lesions despite its antioxidant action.

High levels of dietary stearate promote adiposity and deteriorate hepatic insulin sensitivity

BACKGROUND

Relatively little is known about the role of specific saturated fatty acids in the development of high fat diet induced obesity and insulin resistance. Here, we have studied the effect of stearate in high fat diets (45% energy as fat) on whole body energy metabolism and tissue specific insulin sensitivity.

METHODS

C57Bl/6 mice were fed a low stearate diet based on palm oil or one of two stearate rich diets, one diet based on lard and one diet based on palm oil supplemented with tristearin (to the stearate level of the lard based diet), for a period of 5 weeks. Ad libitum fed Oxidative metabolism was assessed by indirect calorimetry at week 5. Changes in body mass and composition was assessed by DEXA scan analysis. Tissue specific insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp analysis and Western blot at the end of week 5.

RESULTS

Indirect calorimetry analysis revealed that high levels of dietary stearate resulted in lower caloric energy expenditure characterized by lower oxidation of fatty acids. In agreement with this metabolic phenotype, mice on the stearate rich diets gained more adipose tissue mass. Whole body and tissue specific insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp and analysis of insulin induced PKBser473 phosphorylation. Whole body insulin sensitivity was decreased by all high fat diets. However, while insulin-stimulated glucose uptake by peripheral tissues was impaired by all high fat diets, hepatic insulin sensitivity was affected only by the stearate rich diets. This tissue-specific pattern of reduced insulin sensitivity was confirmed by similar impairment in insulin-induced phosphorylation of PKBser473 in both liver and skeletal muscle.

CONCLUSION

In C57Bl/6 mice, 5 weeks of a high fat diet rich in stearate induces a metabolic state favoring low oxidative metabolism, increased adiposity and whole body insulin resistance characterized by severe hepatic insulin resistance. These results indicate that dietary fatty acid composition per sé rather than dietary fat content determines insulin sensitivity in liver of high fat fed C57Bl/6 mice.

Enrichment of amaranth oil with ethyl palmitate at the sn-2 position by chemical and enzymatic synthesis

Amaranth oil is rich in linoleic, oleic, and palmitic acids. Structured lipids (SLs) with specific functional and nutritional characteristics can be prepared through chemical or enzymatic interesterification. The aim of this study was to increase the palmitic acid content at the sn-2 position in amaranth oil triacylglycerols (TAG) for possible use in infant formula. Chemical and enzymatic interesterification techniques were assessed before selecting the latter for further optimization modeling. Enzymatic interesterification of ethyl palmitate and amaranth oil significantly increased the total content of palmitic acid, reduced linoleic acid content, and increased the amount of palmitic acid at the sn-2 position of the SL product. Even though amaranth oil content of palmitic acid (18.3%) was originally similar to that in breast milk (18.3-25.9%), the structural changes induced through enzymatic modification resulted in a SL closely resembling breast milk fat and hence its possible application as a fat substitute for infant nutrition. A second-order polynomial model was developed to predict the amount of total palmitic acid incorporated when reaction time and substrate level were manipulated, and to optimize the combination of parameters to achieve specific palmitic acid contents in amaranth oil. The resulting model is useful to develop an SL from amaranth oil enriched with palmitic acid specifically at the sn-2 position for possible application in infant formulas.

Detrimental Impact of Trans Fats on Human Health: Stearic Acid-Rich Fats as Possible Substitutes

  Strong evidence demonstrated the negative effect of trans fatty acid (TFA) intake on cardiovascular diseases (CVD), diabetes, systemic inflammation, and hemostasis. As a consequence, different regulatory actions have been developed around the world, aiming to reduce human consumption of TFA. Replacement for TFA functionality requires incorporation of plastic and stable saturated fats; the present options are palm or fully hydrogenated oils. Palm oil has been described as responsible for negative biological effects on serum cholesterol levels and CVD risk. Different epidemiological and clinical studies recommend reduction of saturated fatty acid (SFA) intake, mainly myristic and palmitic acids. Experimental evidence strongly suggests that stearic acid is a wholesome substitute for TFAs and other SFAs in food manufacturing. In this article, biological effects of stearic acid on human health are reviewed in comparison to TFAs, SFAs, and unsaturated fatty acids. Current revised understanding on dietary intake, digestion, and absorption is also covered.

The fate and intermediary metabolism of stearic acid

Coming from the Greek for "hard fat," stearic acid represents one of the most abundant FA in the Western diet. Otherwise known as n-octadecanoic acid (18:0), stearate is either obtained in the diet or synthesized by the elongation of palmitate, the principal product of the FA synthase system in animal cells. Stearic acid has been shown to be a very poor substrate for TG synthesis, even as compared with other saturated fats such as myristate and palmitate, and in human studies stearic acid has been shown to generate a lower lipemic response than medium-chain saturated FA. Although it has been proposed that this may be due to less efficient absorption of stearic acid in the gut, such findings have not been consistent. Along with palmitate, stearate is the major substrate for the enzyme stearoyl-CoA desaturase, which catalyzes the conversion of stearate to oleate, the preferred substrate for the synthesis of TG and other complex lipids. In mice, targeted disruption of the stearoyl-CoA desaturase-1 (SCD1) gene results in the generation of a lean mouse that is resistant to diet-induced obesity and insulin resistance. SCD1 also has been shown to be a key target of the anorexigenic hormone leptin, thus underscoring the importance of this enzyme, and consequently the cellular stearate-to-oleate ratio, in lipid metabolism and potentially in the treatment of obesity and related disorders.

Structured Lipids-Novel Fats with Medical, Nutraceutical, and Food Applications

Generally, structured lipids (SLs) are triacylglycerols (TAGs) that have been modified to change the fatty acid composition and/or their positional distribution in glycerol backbone by chemically and/or enzymatically catalyzed reactions and/or genetic engineering. More specifically, SLs are modified TAGs with improved nutritional or functional properties. SLs provide an effective means for producing tailor-made lipids with desired physical characteristics, chemical properties, and/or nutritional benefits. The production, commercialization outlook, medical, and food applications of SLs are reviewed here. Physical property measurements for SL in food systems and future research needs for increased industrial acceptance are also included in this review.

Octanoate inhibits very low-density lipoprotein secretion in primary cultures of chicken hepatocytes

The effects of octanoate, a medium-chain fatty acid, on very low-density lipoprotein (VLDL) secretion in primary cultures of chicken hepatocytes were compared with those of palmitate. Palmitate added to the incubation media at concentrations up to 0.36 mM increased intracellular triacylglycerol (TG) accumulation and VLDL-TG secretion in a concentration-dependent manner, whereas the addition of octanoate alone (0.21-0.6 mM) did not change these parameters. VLDL-TG secretion from hepatocytes cultured in media to which 0.6 or 1.0 mM octanoate had been added in the presence of 0.21 mM palmitate was significantly lower than that obtained under control incubation conditions (0.21 mM palmitate only). The addition of 1.0 mM octanoate to the incubation media with or without 0.21 mM palmitate decreased VLDL apolipoprotein B (apoB) secretion. These results demonstrate that the addition of octanoate to primary cultures of chicken hepatocytes reduces VLDL secretion in respect of both TG and apoB secretion. It is suggested that medium-chain fatty acids are a factor modulating VLDL secretion, which plays a key role in fat deposition in chickens.