Effects of diets of homogeneous saturated triglycerides on cholesterol balance in rats

Metabolomic profiling relates tianeptine effectiveness with hippocampal GABA, myo-inositol, cholesterol, and fatty acid metabolism restoration in socially isolated rats

RATIONALE

Discovering biomarkers of major depressive disorder (MDD) can give a deeper understanding of this mood disorder and improve the ability to screen for, diagnose, and treat MDD.

OBJECTIVES

In this study, metabolomics was used in unraveling metabolite fluctuations of MDD and drug outcome by creating specific metabolomic fingerprints. We report metabolomic patterns of change of the hippocampus of adult male Wistar rats following chronic social isolation (CSIS) (6 weeks), an animal model of depression, and/or chronic tianeptine (Tian) treatment (10 mg kg^-1 per day) (lasting 3 weeks of 6-week CSIS), monitored by using comprehensive GC × GC-MS.

RESULTS

The comparative metabolomic analysis highlighted the role of gamma aminobutyric acid (GABA), iso-allocholate, and unsaturated fatty acid metabolism alterations following the CSIS, which was corroborated with moderate to strong negative Pearson's correlation of GABA, docosahexaenoic, 9-hexadecenoic acid, 5,8,11,14-eicosatetraynoic, and arachidonic acids with immobility behavior in the forced swim test. The antidepressant effect of Tian restored GABA levels, which was absent in Tian resilient rats. Tian decreased myo-inositol and increased TCA cycle intermediates, amino acids, and cholesterol and its metabolite. As key molecules of divergence between Tian effectiveness and resilience, metabolomics revealed myo-inositol, GABA, cholesterol, and its metabolite. A significant moderate positive correlation between myo-inositol and immobility was revealed. Tian probably acted by upregulating NMDAR's and α₂ adrenergic receptors (AR) or norepinephrine transporter in both control and stressed animals.

CONCLUSION

Metabolomics revealed several dysregulations underlying CSIS-induced depressive-like behavior and responsiveness to Tian, predominantly converging into NMDAR-mediated glutamate and myo-inositol signalization and GABA inhibitory pathways.

Resveratrol Modulates Desaturase Expression and Fatty Acid Composition of Cultured Hepatocytes

This study aimed to evaluate whether resveratrol (RSV) and its microbial metabolites dihydro-resveratrol (DHR) and lunularin (LUN) affected fatty acid metabolism and omega-3 polyunsaturated fatty acid (n3-PUFA) synthesis in cultured hepatocytes. To this end, cultured human HepG2 hepatocytes were treated with non-toxic concentrations of these polyphenols (40 μM) and Δ5- and Δ6-desaturase (FADS1 and FADS2, respectively) expression was measured. Resveratrol induced both genes but DHR and LUN showed no effect. Co-incubation of RSV with α-linolenic acid (ALA) also induced FADS1 and FADS2 expression. Moreover, transcription of carnitine palmitoyltransferase 1A and fatty acid synthase expression was increased, indicating induction of β-oxidation and fatty acid synthesis, respectively. Using gas chromatography to measure fatty acid levels, we observed the impact of RSV with and without ALA treatment on fatty acid composition. However, RSV reduced unsaturated while increasing saturated fatty acid levels. We found lower amounts of monounsaturated fatty acids (16:1n-7c, 18:1n-9c, 18:1n7c, and 20:1n-9) and n3-PUFA docosahexaenoic acid whereas unsaturated fatty acid levels, especially of stearic acid, were elevated. Of interest, once we co-incubated the cells with RSV together with bovine serum albumin, we found no differences in gene expression compared to cells without RSV treatment. Although we found no positive effect of RSV on n3-PUFA synthesis, the stilbene could possibly prevent cellular stress by decreasing unsaturated fatty acid levels.

Food Ingredients That Inhibit Cholesterol Absorption

Cholesterol is a vital component of the human body. It stabilizes cell membranes and is the precursor of bile acids, vitamin D and steroid hormones. However, cholesterol accumulation in the bloodstream (hypercholesterolemia) can cause atherosclerotic plaques within artery walls, leading to heart attacks and strokes. The efficiency of cholesterol absorption in the small intestine is of great interest because human and animal studies have linked cholesterol absorption with plasma concentration of total and low density lipoprotein cholesterol. Cholesterol absorption is highly regulated and influenced by particular compounds in the food supply. Therefore, it is desirable to learn more about natural food components that inhibit cholesterol absorption so that food ingredients and dietary supplements can be developed for consumers who wish to manage their plasma cholesterol levels by non-pharmacological means. Food components thus far identified as inhibitors of cholesterol absorption include phytosterols, soluble fibers, phospholipids, and stearic acid.

Reduction in intestinal cholesterol absorption by various food components: mechanisms and implications

A number of different food components are known to reduce plasma and LDL-cholesterol levels by affecting intestinal cholesterol absorption. They include: soluble fibers, phytosterols, saponins, phospholipids, soy protein and stearic acid. These compounds inhibit cholesterol absorption by affecting cholesterol solubilization in the intestinal lumen, interfering with diffusion of luminal cholesterol to the gut epithelium and/or inhibiting molecular mechanisms responsible for cholesterol uptake by the enterocyte. Cholesterol content of intestinal chylomicrons is subsequently reduced, less cholesterol is transported to the liver within chylomicron remnants, hepatic LDL-receptor activity is increased and plasma levels of LDL-cholesterol are decreased. Reduced hepatic VLDL production and less conversion of VLDL to LDL also contribute to lower LDL levels. Certain food components may also affect intestinal bile acid metabolism. Further investigation of the way in which these functional ingredients affect intestinal lipid metabolism will facilitate their use and application as cardiovascular nutraceuticals.

Effects of stereospecific positioning of fatty acids in triacylglycerol structures in native and randomized fats: a review of their nutritional implications

Most studies on lipid lowering diets have focused on the total content of saturated, polyunsaturated and monounsaturated fatty acids. However, the distribution of these fatty acids on the triacylglycerol (TAG) molecule and the molecular TAG species generated by this stereospecificity are characteristic for various native dietary TAGs. Fat randomization or interesterification is a process involving the positional redistribution of fatty acids, which leads to the generation of new TAG molecular species. A comparison between native and randomized TAGs is the subject of this review with regards to the role of stereospecificity of fatty acids in metabolic processing and effects on fasting lipids and postprandial lipemia. The positioning of unsaturated versus saturated fatty acids in the sn-2 position of TAGs indicate differences in early metabolic processing and postprandial clearance, which may explain modulatory effects on atherogenecity and thrombogenecity. Both human and animal studies are discussed with implications for human health.

Reduction in cholesterol absorption is enhanced by stearate-enriched plant sterol esters in hamsters

Consumption of plant sterol esters reduces plasma LDL cholesterol concentration by inhibiting intestinal cholesterol absorption. Commercially available plant sterol esters are prepared by esterifying free sterols to fatty acids from edible plant oils such as canola, soybean, and sunflower. To determine the influence of the fatty acid moiety on cholesterol metabolism, plant sterol esters were made with fatty acids from soybean oil (SO), beef tallow (BT), or purified stearic acid (SA) and fed to male hamsters for 4 wk. A control group fed no plant sterol esters was also included. Hamsters fed BT and SA had significantly lower cholesterol absorption and decreased concentrations of plasma non-HDL cholesterol and liver esterified cholesterol, and significantly greater fecal sterol excretion than SO and control hamsters. Cholesterol absorption was lowest in hamsters fed SA (7.5%), whereas it was 72.9% in control hamsters. Cholesterol absorption was correlated with fecal sterol excretion (r = -0.72, P < 0.001), liver cholesterol concentration (r = 0.88, P < 0.001), and plasma non-HDL cholesterol concentration (r = 0.85, P < 0.001). A multiple regression model that included each sterol ester type vs. cholesterol absorption indicated that intake of steryl stearate was the only dietary component that contributed significantly to the model (R2 = -0.75, P < 0.001). Therefore, our results demonstrate that BT and SA are more effective than SO in reducing cholesterol absorption, liver cholesterol, and plasma non-HDL cholesterol concentration, suggesting that cardioprotective benefits can be achieved by consuming stearate-enriched plant sterol esters.

Dietary stearic acid alters gallbladder bile acid composition in hamsters fed cereal-based diets

Dietary stearic acid (18:0) lowers plasma and liver cholesterol concentration by reducing intestinal cholesterol absorption. We tested the hypothesis that dietary 18:0 reduces cholesterol absorption by altering hepatic bile acid synthesis and gallbladder bile acid composition. Male Syrian hamsters were fed modified NIH-07 open formula diets, enriched (5 g/100 g diet) in one of the following fatty acids: 18:0, palmitic acid (16:0), trans fatty acids (18:1t), oleic acid (18:1c) or linoleic acid (18:2). After 18 wk, gallbladders were removed and bile acid composition determined by HPLC. The distribution of primary bile acids (mol/100 mol) was unaffected by treatment. In contrast, dietary 18:0 significantly reduced the proportion of hydrophobic secondary bile acids, resulting in a lower hydrophobicity index of the bile. These data suggest that reduced cholesterol absorption by dietary 18:0 is due, at least in part, to reduced cholesterol solubility. The data further suggest that 18:0 may have altered the microflora populations that synthesize secondary bile acids. Although cholesterol 7alpha-hydroxylase (CYP7A1) activity was significantly higher in hamsters fed 18:0 compared with 16:0, this finding is most likely due to increased fecal bile acid output in the 18:0 group rather than transcriptional regulation of CYP7A1 by 18:0 or specific bile acids.

Dietary stearic acid reduces cholesterol absorption and increases endogenous cholesterol excretion in hamsters fed cereal-based diets

The observation that dietary stearic acid does not raise plasma cholesterol concentration is well documented, although the regulating mechanisms are not completely understood. Therefore, we examined the effect of dietary stearic acid on cholesterol absorption and sterol balance using male Syrian hamsters fed modified NIH-07 cereal-based diets selectively enriched in palmitic acid (16:0), stearic acid (18:0), trans fatty acid (18:1t), cis oleic acid (18:1c) or linoleic acid (18:2). All diets contained 17 g/100 g total fat and 0.05 g/100 g cholesterol; the five fat blends were enriched 30% with the fatty acid of interest above a constant fatty acid background. Cholesterol absorption efficiency was 50-55% in all treatment groups except for the 18:0 group, in which cholesterol absorption was significantly reduced to 21%. Plasma total cholesterol concentration was significantly lower in the 18:0 group compared to the 16:0 group. Fecal neutral steroid excretion was significantly greater in hamsters fed the high 18:0 diet compared to the other treatment groups. After accounting for unabsorbed dietary cholesterol, endogenous cholesterol excretion was about 100% higher in the 18:0 group. Consequently, the calculated rate of whole body cholesterol synthesis was significantly increased by dietary 18:0. Bile acid excretion accounted for only 12-20% of total sterol output by the hamsters in this study. Thus, the data suggest that reduced plasma cholesterol concentration in hamsters fed high 18:0 diets may be influenced by reduced cholesterol absorption and increased excretion of endogenous cholesterol.

Plasma clearance and hepatic utilization of stearic, myristic and linoleic acids introduced via chylomicrons in rats

The primary objective of the present study was to compare the rates of plasma clearance and hepatic utilization of stearic (18:0), myristic (14:0) and linoleic (18:2) acids, as introduced via chylomicrons. Lymph chylomicrons were specifically labeled in vivo with [14C]stearic and (SA), [14C]myristic acid (MA), or [14C]linoleic acid (LA) by infusing donor rats intraduodenally with the labeled fatty acids in a lipid emulsion. Following intravenous injection of recipient rats with the labeled chylomicrons, the rates of plasma clearance and incorporation of the label in triglycerides (TG), phospholipids (PL) and other lipids in the liver were compared at 5, 15 and 30 min. [14C]SA was cleared at a slightly faster rate (t1/2 = 7.0 min) than [14C]MA (t1/2 = 8.1 min) and [14C]LA (t1/2 = 8.0 min) (P < 0.05). [14C]SA was accumulated in the liver at a significantly faster rate than [14C]MA and [14C]LA. At the peak (15 min) of hepatic uptake, 30.3% of [14C]SA, 26.2% of [14C]LA and 21.9% of [14C]MA were recovered in the liver. At 30 min, 33.5% of [14C]SA was taken up by the liver, whereas 27.8% of [14]LA and only 15.2% of [14C]MA were removed. In the liver, the percentage of [14C]SA incorporated into PL steadily increased with time, whereas the percent-age incorporated into TG decreased. [14C]SA was preferentially incorporated into PL at all time intervals, as compared with [14C]MA and [14C]LA. At 30 min, 38.6% of [14C]SA was found in PL, and only 5.2% of [14C]MA and 12.0% of [14C]LA were present in PL.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the effects of feeding linoleic acid-rich lecithin or corn oil on cholesterol absorption and metabolism in the rat

Either purified soya phosphatidylcholine (lecithin) or triacylglycerol (corn oil) were fed to rats on a diet containing 0.5% cholesterol. The diets contained similar amounts of linoleic acid. The effects of the two preparations on (a) serum cholesterol concentrations, (b) fatty acid profiles, (c) HMG-CoA reductase activity, (d) cholesterol absorption, and (e) faecal excretion of neutral sterols are compared. Some comparisons are also made with diets containing saturated triacylglycerol (lard) and no additional fats other than cholesterol. Serum cholesterol levels were less markedly raised on the lecithin diet, compared with the corn oil or lard diets. Evidence is presented that lecithin reduces the absorption of dietary cholesterol and also increases the excretion of neutral sterols. Our results suggest that soya lecithin is a more potent hypocholesterolaemic agent than corn oil.