Dietary cholesterol and plant sterols differentially modulate cholesterol kinetics and circulating cholesterol. Understanding how healthy individuals with their inherent variabilities in cholesterol trafficking respond to such dietary sterols will aid in improving strategies for effective cholesterol lowering and alleviation of CVD risk. The objectives of this study were to assess plasma lipid responsiveness to dietary cholesterol v. plant sterol consumption, and to determine the response in rates of cholesterol absorption and synthesis to each sterol using stable isotope approaches in healthy individuals. A randomised, double-blinded, crossover, placebo-controlled clinical trial (n 49) with three treatment phases of 4-week duration were conducted in a Manitoba Hutterite population. During each phase, participants consumed one of the three treatments as a milkshake containing 600 mg/d dietary cholesterol, 2 g/d plant sterols or a control after breakfast meal. Plasma lipid profile was determined and cholesterol absorption and synthesis were measured by oral administration of [3, 4-13C] cholesterol and 2H-labelled water, respectively. Dietary cholesterol consumption increased total (0·16 (sem 0·06) mmol/l, P=0·0179) and HDL-cholesterol (0·08 (sem 0·03) mmol/l, P=0·0216) concentrations with no changes in cholesterol absorption or synthesis. Plant sterol consumption failed to reduce LDL-cholesterol concentrations despite showing a reduction (6 %, P=0·0004) in cholesterol absorption. An over-compensatory reciprocal increase in cholesterol synthesis (36 %, P=0·0026) corresponding to a small reduction in absorption was observed with plant sterol consumption, possibly resulting in reduced LDL-cholesterol lowering efficacy of plant sterols. These data suggest that inter-individual variability in cholesterol trafficking mechanisms may profoundly impact plasma lipid responses to dietary sterols in healthy individuals.

To assess the effect of lupin protein on concentrations of lipids in plasma lipoproteins and liver and hepatic mRNA concentrations of genes involved in lipid metabolism, adult rats were fed egg albumin-based diets containing either lupin protein from Lupinus albus or casein (50 g/kg) supplemented (hypercholesterolaemic) or not (normolipaemic) with a cholesterol–cholate mixture for 20 d. Lupin protein compared with casein lowered the concentrations of TAG in liver (P < 0·01) and circulating VLDL + chylomicrons (P < 0·05) of hypercholesterolaemic rats, but not of normolipaemic rats. Hepatic mRNA concentrations of genes involved in fatty acid synthesis such as sterol regulatory element-binding protein-1c, glucose-6-phosphate dehydrogenase, fatty acid synthase, stearoyl-CoA desaturase-1 and acyl-CoA:glycerol-3-phosphate acyltransferase were lower and mRNA concentrations of lipoprotein lipase, hepatic lipase and apoA5 involved in TAG hydrolysis were higher in rats fed lupin protein than in rats fed casein. These effects were stronger in hypercholesterolaemic rats than in normolipaemic rats. Hypercholesterolaemic rats fed the lupin protein had higher liver cholesterol concentrations (P < 0·01) and lower levels of LDL-cholesterol (P < 0·05) than rats fed casein. No effect of lupin protein was observed on cholesterol concentration in VLDL + chylomicrons and HDL and hepatic mRNA concentrations of genes involved in cholesterol and bile acid metabolism. In conclusion, the present study shows that lupin protein has hypotriacylglycerolaemic action possibly via down regulation of fatty acid synthesis genes and up regulation of genes involved in TAG hydrolysis. Alterations in cholesterol metabolism could not be explained on the basis of mRNA data.

Nutrigenetics and nutrigenomics are promising multidisciplinary fields that focus on studying the interactions between nutritional factors, genetic factors and health outcomes. Their goal is to achieve more efficient individual dietary intervention strategies aimed at preventing disease, improving quality of life and achieving healthy aging. Our studies, and those of many other investigators, using population-based and intervention studies have found evidence for interactions between dietary factors, genetic variants and biochemical markers of CVD. Now, the characterization of individuals who may respond better to one type of dietary recommendation than another can be begun. Thus, a low-fat low-cholesterol strategy may be particularly efficacious in lowering the plasma cholesterol levels of those subjects carrying the apoE4 allele at the APOE gene. HDL-cholesterol (HDL-C) levels are also modulated by dietary, behavioural and genetic factors. It has been reported that the effect of PUFA intake on HDL-C concentrations is modulated by an APOA1 genetic polymorphism. Thus, subjects carrying the A allele at the –75 G/A polymorphism show an increase in HDL-C with increased intakes of PUFA, whereas those homozygotes for the more common G allele have the expected lowering of HDL-C levels with increased intake of PUFA. Variability at the hepatic lipase gene is also associated with interactions between intake of fat and HDL-C concentrations that could shed some light on the different abilities of certain ethnic groups to adapt to new nutritional environments. This knowledge should lead to successful dietary recommendations partly based on genetic factors that may help to reduce cardiovascular risk more efficiently than the current universal recommendations.

In the present study the effects of some C18 fatty acids on hepatic fatty acid metabolism have been compared. Male rats were fed cholesterol-free diets containing either C18:0, C18:1cis or C18:1trans isomers as the variables. In accordance with previous work, oleic acid in the diet caused an increase in cholesterol concentration in the liver and in the lipoprotein fraction of density (d; kg/l)<1·006. Oleic acid also reduced the triacylglycerol:cholesterol value in this fraction. Surprisingly, the C18:1trans isomers diet induced a decrease in the amount of cholesterol in total plasma as well as in the 1·019<d<1·063 lipoprotein fraction. Both oleic acid and C18:1trans isomers increased the concentration of triacylglycerols in the liver. The two C18:1 fatty acids differently influenced the hepatic activities of carnitine palmitoyltransferase-I and 3-hydroxy-acyl-CoA dehydrogenase; both enzymes were inhibited by C18:1trans isomers, while no change was induced by oleic acid. The activity of the citrate carrier was lower in the oleic acid- and C18:1trans isomers-fed rats, when compared with the rats fed stearic acid. No diet effects were seen for the activities of acetyl-CoA carboxylase, fatty acid synthase, diacylglycerol acyltransferase, citrate synthase and phosphofructokinase. The results are interpreted in that oleic acid raised liver triacylglycerol by reducing the secretion of it with the d<1·006 lipoprotein fraction whereas the C18:1trans isomers enhanced liver triacylglycerol by lowering the hepatic oxidation of fatty acids.

To test, at the level of individual amino acids, the conformation of an exchangeable apolipoprotein in aqueous solution and in the presence of an osmolyte trimethylamine-N-oxide (TMAO), six synthetic peptide analogues of human apolipoprotein C-1 (apoC-1, 57 residues) containing point mutations in the predicted α-helical regions were analyzed by circular dichroism (CD). The CD spectra and the melting curves of the monomeric wild-type and plasma apoC-1 in neutral low-salt solutions superimpose, indicating 31 ± 4% α-helical structure at 22 °C that melts reversibly with Tm,WT = 50 ± 2 °C and van't Hoff enthalpy ΔHv,WT(Tm) = 18 ± 2 kcal/mol. G15A substitution leads to an increased α-helical content of 42 ± 4% and an increased Tm,G15A = 57 ± 2 °C, which corresponds to stabilization by δΔGapp = +0.4 ± 1.5 kcal/mol. G15P mutant has ∼20% α-helical content at 22 °C and unfolds with low cooperativity upon heating to 90 °C. R23P and T45P mutants are fully unfolded at 0–90 °C. In contrast, Q31P mutation leads to no destabilization or unfolding. Consequently, the R23 and T45 locations are essential for the stability of the cooperative α-helical unit in apoC-1 monomer, G15 is peripheral to it, and Q31 is located in a nonhelical linker region. Our results suggest that Pro mutagenesis coupled with CD provides a tool for assigning the secondary structure to protein groups, which should be useful for other self-associating proteins that are not amenable to NMR structural analysis in aqueous solution. TMAO induces a reversible cooperative coil-to-helix transition in apoC-1, with the maximal α-helical content reaching 74%. Comparison with the maximal α-helical content of 73% observed in lipid-bound apoC-1 suggests that the TMAO-stabilized secondary structure resembles the functional lipid-bound apolipoprotein conformation.

We have compared the effects on lipoproteins and haemostatic variables of two hard margarines with similar functional properties, one traditional margarine containing partially hydrogenated fish oil (PHFO), and one experimental margarine based on vegetable oil (VO). Both were all-purpose cooking margarines with nearly identical functional properties. Trans fatty acids from PHFO in the traditional margarine were replaced mostly by saturated, monounsaturated and trans fatty acids of vegetable origin in the new formulation. Both test margarines contained approximately the same amount of cis polyunsaturated fatty acids. Sixteen female normolipidaemic students consumed each diet with the two test margarines for 14 d in random order (crossover design). The amount of fat was 31 % energy in the PHFO diet and 32 % energy in the VO diet. The test margarines provided approximately 26% energy in both diets. In the PHFO diet 7.8 % of the energy was derived from trans fatty acids and 9.2 % from saturated fatty acids (12:0, 14:0 and 16:0) while in the VO diet, 1.1 % energy was derived from trans fatty acids and 13.3% from saturated fatty acids (12:0, 14:0 and 16:0). The natural content of cholesterol in PHFO was deliberately not balanced by addition of cholesterol to the VO diet, thus the PHFO diet contained 215 mg and the VO diet 86 mg cholesterol per 8.5 MJ. LDL-cholesterol concentration was 19 % higher in subjects on the PHFO diet compared with the VO diet (P < 0.01). The ratio LDL-cholesterol:HDL-cholesterol was 12.6 % higher in subjects on the PHFO diet compared with the VO diet (P < 0.01). The level of apolipoprotein (apo)A-I was 6 % lower in subjects on the PHFO diet compared with the VO diet (P < 0.01). The ratio apoB:apoA-I was 10.4 % higher in subjects on the PHFO diet than on the VO diet (P < 0.01). There were no significant differences in total cholesterol, HDL-cholesterol, triacylglycerols, apoB, lipoprotein(a) and haemostatic variables between the diets. Our results demonstrate that PHFO, with its unfavourable effects on plasma lipids, can be replaced by vegetable oils in margarine without appreciable loss of functional properties but with significant improvement in the effects on plasma lipoproteins.