Conjugated linoleic acid isomers reduce blood cholesterol levels but not aortic cholesterol accumulation in hypercholesterolemic hamsters

The aim of the present study was to characterize plasma lipids and lipoprotein cholesterol and glucose concentrations in hamsters fed either cis-9, trans-11 CLA (9c, 11t CLA); trans-10, cis-12 CLA (10t, 12c CLA); or linoleic acid (LA) on the accumulation of aortic cholesterol in hypercholesterolemic hamsters. One hundred male F₁B strain Syrian Golden Hamsters (Mesocricetus auratus) (BioBreeders Inc., Watertown, MA) approximately 9 wk of age were housed in individual stainless stel hanging cages at room temperature with a 12-h light/dark cycle. Hamsters were given food and water ad libitum. Following a 1-wk period of acclimation, the hamsters were fed a chow-based (nonpurified) hypercholesterolemic diet (HCD) contaning 10% coconut oil (92% saturated fat) and 0.1% cholesterol for 2 wk. After an overnight fast, the hamsters were bled and plasma cholesterol concentrations were measured. The hamsters were then divided into 4 groups of 25 based on similar mean plasma VLDL and LDL cholesterol (non HDL-C) concentrations. Group 1 remained on the HCD (control). Group 2 was fed the HCD plus 0.5% 9c, 11t CLA isomer. Group 3 was fed the HCD plus 0.5% 10t, 12c CLA isomer. Group 4 was fed the HCD plus 0.5% LA. Compared with the control, both CLA isomers and LA had significantly lower plasma total cholesterol and HDL cholesterol concentrations (P<0.001) after 12 but not 8 wk of treatment and were not significantly different from each other. Also, both CLA isomers had significantly lower plasma non HDL-C concentrations (P<0.01) compared with the control after 12 but not 8 wk of treatment and were not significantly different from each other or the LA-fed hamsters. Plasma TG concentrations were significantly higher (P<0.004) with the 10t, 12c CLA isomer compared with the other treatments at 8 but not at 12 wk of treatment. Plasma TG concentrations were also significantly lower (P<0.03) with the 9c, 11t CLA isomer compared with the control at 12 wk of treatment. Also, the 10t, 12c CLA isomer and LA had significantly higher plasma glucose concentrations compared with the control and 9c, 11t CLA isomer (P<0.008) at 12 wk of treatment whereas at 8 wk, only the LA treatment had significantly higher plasma glucose concentrations (P<0.001) compared with the 9c, 11t CLA isomer. Although liver weights were significantly higher in 10t, 12c CLA isomer-fed hamsters, liver total cholesterol, free cholesterol, cholesterol ester, and TG concentrations were significantly lower in these hamsters compared with hamsters fed the control, 9c, 11t CLA isomer, and LA diets (P<0.05). The 9c, 11t CLA isomer and LA diets tended to reduce cholesterol accumulation in the aortic arch, whereas the 10t, 12c CLA isomer diet tended to raise cholesterol accumulation compared with the control diet; however, neither was significant. In summary, no differences were observed between the CLA isomers for changes in plasma lipids or lipoprotein cholesterol concentrations. However, the 9c, 11t CLA isomer did appear to lower plasma TG and glucose concentrations compared with the 10t, 12c CLA isomer. Such differences may increase the risk of insulin resistance and type 2 diabetes in humans when the 10t, 12c CLA isomer is fed separately.     

Effects of dietary phenolic compounds on tocopherol, cholesterol, and fatty acids in rats

The effects of the phenolic compounds butylated hydroxytoluene (BHT), sesamin (S), curcumin (CU), and ferulic acid (FA) on plasma, liver, and lung concentrations of α- and γ-tocopherols (T), on plasma and liver cholesterol, and on the fatty acid composition of liver lipids were studied in male Sprague-Dawley rats. Test compounds were given to rats ad libitum for 4 wk at 4 g/kg diet, in a diet low but adequate in vitamin E (36 mg/kg of γ-T and 25 mg/kg of α-T) and containing 2 g/kg of cholesterol. BHT significantly reduced feed intake (P<0.05) and body weight and increased feed conversion ratio; S and BHT caused a significant enlargement of the liver (P<0.001), whereas CU and FA did not affect any of these parameters. The amount of liver lipids was significantly lowered by BHT (P<0.01) while the other substances reduced liver lipid concentrations but not significantly. Regarding effects on tocopherol levels, (i) feeding of BHT resulted in a significant elevation (P<0.001) of α-T in plasma, liver, and lung, while γ-T values remained unchanged; (ii) rats provided with the S diet had substantially higher γ-T levels (P<0.001) in plasma, liver, and lung, whereas α-T levels were not affected; (iii) administration of CU raised the concentration of α-T in the lung (P<0.01) but did not affect the plasma or liver values of any of the tocopherols; and (iv) FA had no effect on the levels of either homolog in the plasma, liver, or lung. The level of an unknown substance in the liver was significantly reduced by dietary BHT (P<0.001). BHT was the only compound that tended to increase total cholesterol (TC) in plasma, due to an elevation of cholesterol in the very low density lipoprotein + low density lipoprotein (VLDL+LDL) fraction. S and FA tended to lower plasma total and VLDL+LDL cholesterol concentrations, but the effect for CU was statistically significant (P<0.05). FA increased plasma high density lipoprotein cholesterol while the other compounds reduced it numerially, but not significantly. BHT, CU, and S reduced cholesterol levels in the liver TC (P<0.001) and percentages of TC in liver lipids (P<0.05). With regard to the fatty acid composition of liver lipids, S increased the n-6/n-3 and the 18∶3/20∶5 polyunsaturated fatty acids (PUFA) ratios, and BHT lowered total monounsaturated fatty acids and increased total PUFA (n−6+n−3). The effects of CU and FA on fatty acids were not highly significant. These results suggest some in vivo interactions between these phenolic compounds and tocopherols that may increase the bioavailability of vitamin E and decrease cholesterol in rats.     

Fasting and postprandial lipid response to the consumption of modified milk fats by guinea pigs

The objective of the present study was to investigate the effect of three modified milk fats with different melting profiles on fasting and postprandial lipid responses and on fecal fat content in guinea pigs. We hypothesized that the consumption of modified milk fat with a high m.p. results in reduced fasting and postprandial lipid responses compared with that of modified milk fat fractions with lower m.p. To test this hypothesis, male Hartley guinea pigs were fed isoenergetic diets containing 110 g of fat/kg, either from one of the three modified milk fats with high (HMF), medium (MMF), or low melting profiles (LMF), or from one of the two reference fats as whole mil fat (MF) or a fat blend similar to that of nonhydrogenated soft margarine (MA) for 28 d. Food intake (P<0.05) and body weight gain (P<0.05) were reduced in the animals fed the HMF diet compared with the other groups. In the fasting state, plasma LDL cholesterol was highest in animals fed the LMF diet, intermediary in those fed the MMF and MF diets, and lowest in those fed the HMF and MA diets (P<0.05). Postprandially, the areas under the 0- to 3-h curves for the changes in plasma TG were lower in the HMF group than in the MA- and LMF-fed guinea pigs (P<0.05). The fecal fat content was higher (P<0.05) in the HMF group compared to the other milk fat groups. The present results suggest that modified milk fats can impact food intake, body weight gain, fasting cholesterolemia, and postprandial triglyceridemia, and these changes may be attributed to an altered fat absorption.     

Gender and dietary fat affect α-tocopherol status in F344/N rats

For four weeks, groups of eight male and eight female F344/N rats were fed diets containing 15.5, 20, 30 or 40% of energy (en%) as fat. The fat was composed of corn oil and beef tallow with 9 en% from linoleate in all diets. Females had greater mean hepatic α-tocopherol levels, whereas males had greater plasma α-tocopherol and cholesterol concentrations. In males, the plasma ratio of α-tocopherol/cholesterol was significantly greater than in females (P<0.05). Plasma α-tocopherol increased with increasing en% fat (r=0.51,P<0.001) in both sexes, but dietary fat did not alter hepatic α-tocopherol levels. These results suggest that plasma α-tocopherol may serve as a biomarker of total dietary fat intake and that in F344/N rats gender differences affect α-tocopherol and cholesterol status.     

Water-soluble organosulfur compounds of garlic inhibit fatty acid and triglyceride syntheses in cultured rat hepatocytes

The putative hypolipidemic effect of garlic remains controversial. To gain further insight into the effect of garlic on lipid metabolism, the present study determined the inhibitory effects of water-soluble organosulfur compounds present in garlic on triglyceride (TG) and fatty acid synthesis in cultured rat hepatocytes. When incubated at 0.05 to 4.0 mmol/L with cultured hepatocytes, S-allyl cysteine (SAC) and S-propyl cysteine (SPC) decreased [2-¹⁴C]acetate incorporation into triglyceride in a concentration-dependent fashion achieving a maximal inhibition at 4.0 mmol/L of 43 and 51%, respectively. The rate of [2-¹⁴C]acetate incorporation into phosphlipids was depressed to a similar extent by SAC and SPC. SPC, SAC, S-ethyl cysteine (SEC), and γ-glutamyl-S-methyl cysteine decreased [2-¹⁴C]acetate incorporation into fatty acid synthesis by 81, 59, 35, and 40%, respectively, at 2.0–4.0 mmol/L concentrations. Alliin, γ-glutamyl-S-allyl cysteine, γ-glutamyl-S-propyl cysteine S-allyl-N-acetyl cysteine, S-allylsulfonyl alanine, and S-methyl cysteine had no effect on fatty acid synthesis. The activities of lipogenic enzymes, fatty acid synthase (FAS), and glucose-6-phosphate dehydrogenase (G6PDH) were measured in cultured hepatocytes treated with the inhibitors. The activity of FAS in cells treated with 4.0 mmol/L SAC and SPC, respectively, was 32 and 27% lower than that of non-treated cells. Neither SAC nor SPC affected G6PDH activity. The results indicate that SAC, SEC, and SPC inhibit lipid biosynthesis in cultured rat hepatocytes, and further suggest that these S-alk(en)yl cysteines of garlic impair triglyceride synthesis in part due to decreased de novo fatty acid synthesis resulting from inhibition on FAS. Whether tissue concentrations of active garlic components can achieve levels required to inhibit TG synthesis in vivo warrants further investigation.     

Dietary CLA alters yolk and tissue FA composition and hepatic histopathology of laying hens

The effect of dietary CLA along with n-3 PUFA on yolk FA profile and hepatic lipid accumulation was investigated. Laying hens (n=40) were randomly assigned to four experimental diets containing 0, 0.5, 1.0, or 2.0% CLA. Menhaden oil was used as the source of n-3 PUFA. Dietary CLA did not affect the total lipid content of egg yolk (P>0.05). The amounts of CLA isomers (cis-9 trans-11, trans-10 cis-12) in the egg yolk were proportional to the levels of CLA in the diet (P<0.05). The total CLA content in the egg yolk was 0, 0.97, 2.4, and 5.3 wt%, respectively (P<0.05). Addition of CLA resulted in an increase in saturated FA (P<0.05) with a concomitant reduction in monounsaturated FA (P<0.05) in the yolk, liver, abdominal fat, breast, and thigh muscle. No difference in saturated and monounsaturated FA content in heart and spleen tissue was noted. Dietary CLA at all concentrations resulted in an increase (P<0.05) in the total number of fat vacuoles and lipid infiltration in hepatocytes. The number of cells with 75% or higher lipid vacuolation in the cytoplasm was also increased (P<0.05) by 2.0% CLA. Dietary CLA at 0.5% levels resulted in an increase (P<0.05) in the total lipid content of hepatic tissue. The total lipid content in leg muscle was lower (P<0.05) in CLA-fed birds. However, no effect of CLA on lipid content of breast muscle, heart, spleen and adipose tissue was observed (P>0.05). The current study used CLA in a FFA form. The effects of using CLA in other form such as TG on avian hepatic tissue need to be investigated.     

Dietary fats and energy levels differently affect tissue lipogenic enzyme activity in finishing pigs

The aim of the present study was to determine the relationship between high and low digestible energy levels (9.5 vs. 15.4 MJ ME/kg) and either tallow or soy oil supplementation (5%rpar; on lipogenic activities and fatty acid profile of the backfat tissue outer layer and liver tissue in finishing pigs. Twenty Large White pigs averaging 30 (initial) to 106 kg (final) live weight were allocated into four dietary groups and fed the diets ad libitum. The lipid content and fatty acid composition of the tissues were determined and glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (ME), and fatty acid synthase (FAS) activity were measured. Growth performance and carcass measurements were affected by the dietary energy levels but not by the fat sources. Lipid deposition rate of animals fed the low energy diets was lowered regardless whether tallow or soy oil was supplemented. Unlike lipid deposition, fatty acid profile was influenced by both dietary factors. Pigs fed the low energy diet supplemented with soy oil exhibited the lowest level of saturated (P<0.001), monounsaturated (P<0.001), and the highest level of polyenic fatty acids in the backfat, the opposite was the case for the pigs fed the high energy diet supplemented with beef tallow. The fatty acid profile of the adipose tissue of animals fed the other two diets were intermediate, but clear distinction of the profile due to diets was visible. Independent of dietary treatments, lipogenic activities were up to 10 times higher in the backfat than in the liver. G6PDH activity was higher (P<0.05) due to high energy diet, whereas the activities of ME and FAS were not affected. Animals fed the high energy diet either supplemented with tallow or soy oil exhibited higher ME activity lpar;P<0.05) in the backfat, without any effects on G6PDH activity. In contrast, dietary fat sources affected the FAS activity, with lower activity lpar;P<0.05) exhibited in the backfat of animals fed the soy oil diets. The present results indicate that dietary manipulation, which change the flux through the pathway of lipogenesis and pentose-phosphate must affect differently the activities of the involved enzymes. The effect of the dietary energy level was stronger and overwhelmed the inducing effect of the PUFA on the activities of the collateral enzymes. In contrast the immediately involved lipogenic enzyme FAS responded more to dietary PUFA stimulation than to the energy supply.     

Ground Beef High in Total Fat and Saturated Fatty Acids Decreases X Receptor Signaling Targets in Peripheral Blood Mononuclear Cells of Men and Women

We hypothesized that consumption of saturated fatty acids in the form of high‐fat ground beef for 5 weeks would depress liver X receptor signaling targets in peripheral blood mononuclear cells (PBMC) and that changes in gene expression would be associated with the corresponding changes in lipoprotein cholesterol (C) concentrations. Older men (n = 5, age 68.0 ± 4.6 years) and postmenopausal women (n = 7, age 60.9 ± 3.1 years) were assigned randomly to consume ground‐beef containing 18% total fat (18F) or 25% total fat (25F), five patties per week for 5 weeks with an intervening 4‐week washout period. The 25F and 18F ground‐beef increased (p < 0.05) the intake of saturated fat, monounsaturated fat, palmitic acid, and stearic acid, but the 25F ground‐beef increased only the intake of oleic acid (p < 0.05). The ground‐beefs 18F and 25F increased the plasma concentration of palmitic acid (p < 0.05) and decreased the plasma concentrations of arachidonic, eicosapentaenoic, and docosahexaenic acids (p < 0.05). The interventions of 18F and 25F ground‐beef decreased very low‐density lipoprotein C concentrations and increased particle diameters and low‐density lipoprotein (LDL)‐I‐C and LDL‐II‐C concentrations (p < 0.05). The ground‐beef 25F decreased PBMC mRNA levels for the adenosine triphosphate (ATP) binding cassette A, ATP binding cassette G1, sterol regulatory element binding protein‐1, and LDL receptor (LDLR) (p < 0.05). The ground‐beef 18F increased mRNA levels for stearoyl‐CoA desaturase‐1 (p < 0.05). We conclude that the increased LDL particle size and LDL‐I‐C and LDL‐II‐C concentrations following the 25F ground‐beef intervention may have been caused by decreased hepatic LDLR gene expression.     

Response of plasma lipids to dietary cholesterol and wine polyphenols in rats fed polyunsaturated fat diets

This experiment was designed to evaluate the effects of dietary red wine phenolic compounds (WP) and cholesterol on lipid oxidation and transport in rats. For 5 wk, weanling rats were fed polyunsaturated fat diets (n−6/n−3=6.4) supplemented or not supplemented with either 3 g/kg diet of cholesterol, 5 g/kg diet of WP, or both. The concentrations of triacylglycerols (TAG, P<0.01) and cholesterol (P<0.0002) were reduced in fasting plasma of rats fed cholesterol despite the cholesterol enrichment of very low density lipoprotein + low density lipoprotein (VLDL+LDL). The response was due to the much lower plasma concentration of high density lipoprotein (HDL) (−35%, P<0.0001). In contrast, TAG and cholesteryl ester (CE) accumulated in liver (+120 and +450%, respectively, P<0.0001). However, the cholesterol content of liver microsomes was not affected. Dietary cholesterol altered the distribution of fatty acids mainly by reducing the ratio of arachidonic acid to linoleic acid (P<0.0001) in plasma VLDL+LDL (−35%) and HDL (−42%) and in liver TAG (−42%), CE (−78%), and phospholipids (−28%). Dietary WP had little or no effect on these variables. On the other hand, dietary cholesterol lowered the α-tocopherol concentration in VLDL+LDL (−40%, P<0.003) and in microsomes (−60%, P<0.0001). In contrast, dietary WP increased the concentration in microsomes (+21%, P<0.0001), but had no effect on the concentration in VLDL+LDL. Cholesterol feeding decreased (P<0.006) whereas WP feeding increased (P<0.0001) the resistance of VLDL+LDL to copper-induced oxidation. The production of conjugated dienes after 25 h of oxidation ranged between 650 (WP without cholesterol) and 2,560 (cholesterol without WP) μmol/g VLDL+LDL protein. These findings show that dietary WP were absorbed at sufficient levels to contribute to the protection of polyunsaturated fatty acids in plasma and membranes. They could also reduce the consumption of α-tocopherol and endogenous antioxidants. The responses suggest that, in humans, these substances may be beneficial by reducing the deleterious effects of a dietary overload of cholesterol.     

Maternal dietary conjugated linoleic acid alters hepatic triacylglycerol and tissue fatty acids in hatched chicks

The effects of feeding CLA to hens on newly hatched chick hepatic and carcass lipid content, liver TAG accumulation, and FA incorporation in chick tissues such as liver, heart, brain, and adipose were studied. These tissues were selected owing to their respective roles in lipid assimilation (liver), as a major oxidation site (heart), as a site enriched with long-chain polyunsaturates for function (brain), and as a storage depot (adipose). Eggs with no, low, or high levels of CLA were produced by feeding hens a corn-soybean meal-basal diet containing 3% (w/w) corn oil (Control), 2.5% corn oil +0.5% CLA oil (CLA1), or 2% corn oil +1.0% CLA oil (CLA2). The egg yolk content of total CLA was 0.0, 1.0, and 2.6% for Control, CLA1, and CLA2, respectively (P<0.05). Maternal dietary CLA resulted in a decrease in chick carcass total fat (P<0.05). Liver tissue of CLA2 chicks had the lowest fat content (P<0.05). The liver TAG content was 8.2, 5.8, and 5.1 mg/g for Control, CLA1, and CLA2 chicks, respectively (P<0.05). The chicks hatched from CLA1 and CLA2 incorporated higher levels of cis-9,trans-11 CLA in the liver, plasma, adipose, and brain than Control (P<0.05). The content of 18∶0 was higher in the liver, plasma adipose, and brain of CLA1 and CLA2 than Control (P<0.05), but no difference was observed in the 18∶0 content of heart tissue. A significant reduction in 18∶1 was observed in the liver, plasma, adipose, heart, and brain of CLA1 and CLA2 chicks (P<0.05). DHA (22∶6n−3) was reduced in the heart and brain of CLA1 and CLA2 chicks (P<0.05). No difference was observed in carcass weight, dry matter, or ash content of chicks (P>0.05). The hatchabilities of fertile eggs were 78, 34, and 38% for Control, CLA1, and CLA2, respectively (P<0.05). The early dead chicks were higher in CLA1 and CLA2 than Control (18 and 32% compared with 9% for Control), and alive but not hatched chicks were 15 and 19% for CLA1 and CLA2, compared with 8% for Control (P<0.05). Maternal supplementation with CLA leads to a reduction in hatchability, liver TAG, and carcass total fat in newly hatched chicks.     

Effect of modified dairy fat on postprandial and fasting plasma lipids and lipoproteins in healthy young men

Fatty acid profile of milk fat can be modified by cow feeding strategies. Our aim was postprandially and after 4 wk to compare the effect of a modified milk fat (M diet) [with 16% of the cholesterolemic saturated fatty acid (C12–16) replaced by mainly oleic and stearic acids] with the effect of D diet, including a conventional Danish milk fat on plasma lipids and lipoproteins. A side effect of the cow feeding regime was a 5% (w/w) increase in trans fatty acid in M diet. Eighteen subjects were fed for two periods of 4 wk strictly controlled isoenergetic test diets with 40% of energy from total fat and the same content of dietary cholesterol in a randomized study with cross-over design. Contrary to expectations, fasting low density lipoprotein (LDL) cholesterol concentration did not differ after the experimental periods. However, M diet resulted in a higher fasting total triacylglycerol concentration compared to D diet (P=0.009). Postprandial samples were taken at two different occasions (i) at day 21, after breakfast and lunch and (ii) on the last day of the study 2, 4, 6, and 8 h after a fat load. Postprandial plasma triacylglycerol and chylomicron triacylglycerol showed higher peak values after D diet than M diet (interaction effect, diet × times P<0.05). In conclusion, M diet did not lower LDL cholesterol compared to D diet. Thus any cholesterol-lowering effect of oleic and stearic acids may have been obscured by the high content of cholesterol-raising saturated fatty acids in milk fat. A higher content of the trans fatty acids in M diet might have counteracted the cholesterol neutral/decreasing effect and increased plasma triacylglycerol.     

Potato and soy peptides alter caecal fermentation and reduce serum non‐HDL cholesterol in rats fed cholesterol

We examined the effect of potato peptides (PPC) in rats fed a cholesterol‐enriched diet, in comparison with two cholesterol‐enriched diets containing soy peptides (SPC) or casein (CNC), and a cholesterol‐free diet containing casein (CN) for 4 weeks. The serum non‐high‐density lipoprotein (HDL) cholesterol level was lower in the PPC‐ (–18.39%) and SPC‐fed (–32.76%) groups (p <0.05) than in the CNC‐fed group at the end of the feeding period. The low‐density lipoprotein receptor mRNA level in the PPC‐fed group, and cholesterol 7α‐hydroxylase and scavenger receptor class B type 1 mRNA levels in the SPC‐fed group, were higher (p <0.05) than in the CN‐ and CNC‐fed groups. Faecal neutral sterol and caecal short‐chain fatty acid concentrations in the PPC‐ and SPC‐fed groups were higher (p <0.05) than in the CN‐ and CNC‐fed groups. The faecal total acidic sterol concentration was higher in the SPC‐fed group than in the CN‐ and PPC‐fed groups. Caecal anaerobe and Bifidobacterium populations were higher (p <0.05) in the PPC‐ and SPC‐fed groups than in the CN‐fed group. This study suggests that potato peptides, as soy peptides, alter caecal fermentation and steroid absorption and reduce the serum non‐HDL cholesterol level in rats fed cholesterol.     

Dietary conjugated linolenic acid in relation to CLA differently modifies body fat mass and serum and liver lipid levels in rats

The present study compared the effect of dietary conjugated linolenic acid (CLNA) on body fat and serum and liver lipid levels with that of CLA in rats. FFA rich in linoleic acid, α-linolenic acid, CLA, or CLNA were used as experimental fats. Male Sprague-Dawley rats (4 wk old) were fed purified diets containing 1% of one of these experimental fats. After 4 wk of feeding, adipose tissue weights, serum and liver lipid concentrations, serum tumor necrosis factor (TNF)-α and leptin levels, and hepatic β-oxidation activities were measured. Compared with linoleic acid, CLA and, more potently, CLNA were found to reduce perirenal adipose tissue weight. The same trend was observed in the weight of epididymal adipose tissue. CLNA, but not CLA, was found to significantly increase serum and liver IG concentrations. Serum FFA concentration was also increased in the CLNA group more than in the other groups. The activity of β-oxidation in liver mitochondria and peroxisomes was significantly higher in the CLNA group than in the other groups. Thus, the amount of liver TG exceeded the ability of hepatic β-oxidation. Significant positive correlation was found between the adipose tissue weights and serum leptin levels in all animals (vs. perirenal: r=0.557, P<0.001; vs. epididymal: r=0.405, P<0.05). A less significant correlation was found between adipose tissue weights and serum TNF-α level (vs. perirenal: r=0.069, P<0.1; vs. epididymal: r=0.382, P<0.05). Although the mechanism for the specific effect of CLNA is not clear at present, these findings indicate that in rats CLNA modulated the body fat and TG metabolism differently from CLA.     

Oryzanol decreases cholesterol absorption and aortic fatty streaks in hamsters

Oryzanol is a class of nonsaponifiable lipids of rice bran oil (RBO). More specifically, oryzanol is a group of ferulic acid esters of triterpene alcohol and plant sterols. In experiment 1, the mechanisms of the cholesterol-lowering action of oryzanol were investigated in 32 hamsters made hypercholesterolemic by feeding chow-based diets containing 5% coconut oil and 0.1% cholesterol with or without 1% oryzanol for 7 wk. Relative to the control animals, oryzanol treatment resulted in a significant reduction in plasma total cholesterol (TC) (28%, P<0.01) and the sum of IDL-C, LDL-C, and VLDL-C (NON-HDL-C) (34%, P<0.01). In addition, the oryzanol-treated animals also exhibited a 25% reduction in percent cholesterol absorption vs. control animals. Endogenous cholesterol synthesis, as measured by the liver and intestinal HMG-CoA reductase activities, showed no difference between the two groups. To determine whether a lower dose of oryzanol was also efficacious and to measure aortic fatty streaks, 19 hamsters in experiment 2 were divided into two groups and fed for 10 wk chow-based diets containing 0.05% cholesterol and 10% coconut oil (w/w) (control) and the control diet plus 0.5% oryzanol (oryzanol). Relative to the control, oryzanol-treated hamsters had reduced plasma TC (44%, P<0.001), NON-HDL-C (57%, P<0.01), and triglyceride (TG) (46%, P<0.05) concentrations. Despite a 12% decrease in high density lipoprotein cholesterol (HDL-C) (P<0.01), the oryzanol-treated animals maintained a more optimum NON-HDL-C/HDL-C profile (1.1±0.4) than the contorl (2.5±1.4; P<0.0075). Aortic fatty streak formation, so defined by the degree of accumulation of Oil Red O-stained macrophage-derived foam cells, was reduced 67% (P<0.01) in the oryzanol-treated animals. From these studies, it is concluded that a constituent of the nonsaponifiable lipids of RBO, oryzanol, is at least partially responsible for the cholesterol-lowering action of RBO. In addition, the cholesterol-lowering action of oryzanol was associated with significant reductions in aortic fatty streak formation.     

Alterations of high density lipoprotein subclasses in obese subjects

The object of this study was to investigate the characteristics of lipid metabolism in obese subjects, with particular emphasis on the alteration of HDL subclass contents and distributions. A population of 581 Chinese individuals was divided into four groups (25 underweight subjects, 288 of desirable weight, 187 overweight, and 45 obese) according to body mass index (BMI). Apoprotein A-I (apoA-I) contents of plasma HDL subclasses were determined by 2-D gel electrophoresis associated with an immunodetection method. The concentrations of TG and the apoA-I content of pre-α₁-HDL were significantly higher (P<0.01 and P<0.01, respectively), but the levels of HDL cholesterol, and the apoA-I contents of HDL_2a and HDL_2b were significantly lower (P<0.01, P<0.05, and P<0.01, respectively) in obese subjects than in subjects having a desirable weight. Moreover, with the elevation of BMI, small-sized pre-α₁-HDL increased gradually and significantly, whereas large-sized HDL_2b decreased gradually and significantly. Meanwhile, the variations in HDL subclass distribution were more obvious with the elevation of TG levels in obese as well as overweight subjects. In addition, Pearson correlation analysis revealed that BMI and TG levels were positively correlated with pre-α₁-HDL but negatively correlated with HDL_2b. Multiple regression analysis also showed that TG concentrations were associated independently and positively with high pre-α₁-HDL and independently and negatively with low HDL_2b in obese and overweight subjects. The HDL particle size was smaller in obese and overweight subjects. The shift to smaller size was more obvious with the elevation of BMI and TG, especially TG levels. These observations, in turn, indicated that HDL maturation might be abnormal, and reverse cholesterol transport might be impaired. The first two authors contributed equally to this study.     

Short-term effects of 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor on cholesterol and bile acid synthesis in humans

Competitive inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase improve hypercholesterolemia. However, reports about the effects of these agents on bile acid synthesis, the metabolic pathway of cholesterol, are conflicting. We studied the short-term effect of one of these agents, pravastatin, on bile acid synthesis. Six male volunteers were given 40 mg of pravastatin. Plasma mevalonate level (which reflects cholesterol synthesis) and 7α-hydroxy-4-cholesten-3-one level 9which reflects bile acid synthesis) were measured every 2 h for 8 h. These plasma levels were compared to those of the same volunteers without pravastatin. Plasma mevalonate level after 2 h was lower than control (3.0 ± 1.1 ng/ml vs. 6.7 ± 2.5, mean ±SD; P<0.05). This decrease continued for 8 h (2.5 ± 0.8 vs. 5.2 ± 1.5; P<0.05). On the other hand, plasma 7α-hydroxy-4-cholesten-3-one level did not change until after 6 h; then at 8 h it was lower than control (15.7 ± 11.8 ng/mL vs. 24.7 ± 16.9; P <0.05). According to three-way layout analysis of variance, mevalonate level was influenced by both pravastatin treatment (P<0.01) and time-course (P<0.01). On the other hand, the 7α-hydroxy-4-cholesten-3-one level was affected by both individual difference (P<0.01) and time course (P<0.01), but pravastatin treatment did not influence this compound. This indicates that bile acid synthesis was not influenced by pravastatin, although cholesterol synthesis was inhibited. The shortterm inhibition of cholesterol synthesis did not affect bile acid synthesis.     

Enzyme-resistant fractions of beans lowered serum cholesterol and increased sterol excretions and hepatic mRNA levels in rats

Feeding rats beans with resistant starch reduces their serum cholesterol concentration; however, the mechanism by which this occurs is not fully understood. We examined the effects of enzyme-resistant fractions of adzuki (Vigna angularis) and tebou (Phaseolus vulgaris, var.) beans on serum cholesterol and hepatic mRNA in rats. Rats were fed a cholesterol-free diet with 50 g of cellulose powder (CP)/kg, 50 g of an enzyme-resistant fraction of adzuki starch (AS)/kg, or 50 g of an enzyme-resistant fraction of tebou starch (TS)/kg diet for 4 wk. There were no significant differences in body weight, liver weight, and cecum contents among the groups, nor was there a significant difference in food intake among the groups. The levels of serum total cholesterol, VLDL + intermediate density lipoprotein + LDL-cholesterol, and HDL cholesterol in the AS and TS groups were significantly (P<0.05) lower than in the CP group throughout the feeding period. Total hepatic cholesterol in the CP group was significantly (P<0.05) lower than in the AS and TS groups, fecal cholesterol excretion in the TS group was significantly (P<0.05) greater than in the CP and AS groups, and the fecal total bile acid concentrations in the AS and TS groups were significantly (P<0.05) higher than in the CP group. Cecal acetate, propionate, and n-butyrate concentrations in the AS and TS groups were significantly (P<0.05) higher than in the CP group. The level of hepatic scavenger receptor class B1 (SR-B1) mRNA in the TS group was significantly (P<0.05) higher than in the CP group, and the levels of hepatic cholesterol 7α-hydroxylase mRNA in the AS and TS groups were significantly (P<0.05) higher than in the CP group. These results suggest that AS and TS have a serum cholesterol-lowering function due to the enhanced levels of hepatic SR-B1 and cholesterol 7α-hydroxylase mRNA.     

Effect of dietary cholesterol on low density lipoprotein-receptor, 3-hydroxy-3-methylglutaryl-CoA reductase, and low density lipoprotein receptor-related protein mRNA expression in healthy humans

We investigated the possibility that dietary cholesterol downregulates the expression of low density lipoprotein (LDL) receptor and 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase genes of circulating mononuclear cells in vivo in healthy humans. We also studied the variations of the LDL receptor-related protein (LRP) gene in the same conditions. Dieters (n=5) were submitted to a 4-d fat restriction (mean cholesterol intake: 6±4 mg/d), followed by a 7-d cholesterol (a mean of 791±150 mg/d) supplementation. Controls (n=3) did not change their diet. During fat restriction, serum total and LDL cholesterol decreased significantly (P<0.05), and LDL receptor and HMG-CoA reductase mRNA copy numbers in mononuclear cells increased by 57 and 147%, respectively (P<0.05). After reintroducing cholesterol, serum cholesterol was stable whereas LDL receptor and HMG-CoA reductase mRNA decreased by 46 and 72% (P<0.05) and LRP mRNA increased by 59% (P<0.005). The changes in LDL receptor and HMG-CoA reductase mRNA abundance were correlated (r=+0.79, P=0.02) during cholesterol reintroduction as were LDL receptor and LRP mRNA levels, but negatively (r=−0.70, P=0.05). Also, 70% of the variability in LRP mRNA (P<0.005) was explained by dietary cholesterol. Thus, the basic mechanisms regulating cellular cholesterol content, the coordinate feedback repression of genes governing the synthesis and uptake of cholesterol, are operating in vivo in humans. However, serum cholesterol did not increase in response to dietary cholesterol, suggesting that these mechanisms may not play as predominant a role as previously believed in the short-term control of serum cholesterol in vivo in humans. A new finding is that LRP gene is also sensitive to dietary cholesterol, suggesting that it may participate in the control of serum cholesterol. Further in vivo studies in humans are warranted to explore the molecular mechanisms of the physiological response to dietary cholesterol in humans.     

8302A/C and (TTA)n polymorphisms in the HMG-CoA reductase gene may be associated with some plasma lipid metabolic phenotypes in patients with coronary heart disease

HMG-CoA reductase (HMGCR) is a rate-limiting enzyme that participates in cholesterol metabolism. Here we analyzed the 8302A/C and the (TTA)n polymorphisms in the HMGCR gene in 169 Chinese patients with coronary heart disease (CHD) and 161 age-matched controls. Results indicated that the levels of plasma VLDL and TG in patients with the AA genotype of the 8302A/C locus were significantly higher than in patients with other genotypes (P<0.05). In addition, the frequency of allele A4 of the (TTA)n locus was higher (P<0.05) and the frequency of allele A5 was lower (P=0.002) in CHD patients than in the controls. This suggests that both polymorphisms in the HMGCR gene may be associated with lipid and lipoprotein abnormalities in CHD in the Chinese.     

Long-chain polyunsaturated fatty acids in plasma lipids of obese children

Fatty acid composition of plasma phospholipids (PL), triglycerides (TG), and sterol esters (STE) was determined by high-resolution capillary gas-liquid chromatography in 22 obese children (age: 13.7±1.4 y, body weight relative to normal weight for height: 170±24%, mean ±SD) and compared with data obtained in 25 age-matched healthy controls. There were no differences in the levels of linoleic acid (LA, C_18∶2n-6) in any of the plasma fractions from the obese children and the controls. Obese children exhibited significantly higher values of arachidonic acid (AA, C_20∶4n-6) than controls both in PL (12.6 [2.4] vs. 8.3 [1.4], % wt/wt, [median (interquartile range)],P<0.001) and STE (7.3 [1.8] vs. 6.0 [1.1],P<0.05). Similarly, obese children showed higher values than controls for dihomo-γ-linolenic acid (DHGLA, C_20∶3n-6) in PL (4.0 [0.5] vs. 3.0 [0.6],P<0.001), TG (0.4 [0.1] vs. 0.2 [0.1],P<0.001), and STE (0.9 [0.1] vs. 0.7 [0.1],P<0.01), and for γ-linolenic acid (C_18∶3n-6) in STE (1.1 [0.2] vs. 0.8 [0.2],P<0.001). The AA/LA ratios were higher in obese children than in controls in PL (0.68 [0.16] vs. 0.42 [0.09],P<0.0005) and STE (0.16 [0.04] vs. 0.12 [0.02],P<0.05), whereas the AA/DHGLA ratios were lower in TG of obese children than in controls (3.40 [0.64] vs. 5.10 [1.75],P<0.005). Plasma glucose concentrations were inversely related to AA in TG (r=0.53,P<0.05), and plasma TG concentrations were inversely related to AA in PL and STE (r=−0.49,P<0.05 andr=−0.48,P<0.05) and to the AA/DHGLA ratios in PL (r=−0.57,P<0.01),TG (r=−0.56,P<0.01) and STE (r=−0.56,P<0.01). We conclude that the significantly higher values of n-6 long-chain polyunsaturated fatty acids (LCP) in plasma lipids of obese children than in age-matched controls may be caused by an enhanced activity of Δ6-desaturation, and we speculate that elevated fasting immunoreactive insulin seen in obese children (19.4±8.0 μU/mL) may stimulate synthesis of n-6 LCP fatty acids.